Next Article in Journal
Comparative Issues of Cathode Materials for Li-Ion Batteries
Next Article in Special Issue
Half-Lantern Pt(II) and Pt(III) Complexes. New Cyclometalated Platinum Derivatives
Previous Article in Journal
Syntheses of Macromolecular Ruthenium Compounds: A New Approach for the Search of Anticancer Drugs
Article Menu

Export Article

Inorganics 2014, 2(1), 115-131; doi:10.3390/inorganics2010115

Diarylplatinum(II) Compounds as Versatile Metallating Agents in the Synthesis of Cyclometallated Platinum Compounds with N-Donor Ligands
Margarita Crespo
Departament de Química Inorgànica, Facultat de Química, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain; Tel.: +34-93-4039132; Fax: +34-93-4907725
Received: 14 February 2014; in revised form: 13 March 2014 / Accepted: 13 March 2014 / Published: 21 March 2014


: This review deals with the reactions of diarylplatinum(II) complexes with N-donor ligands to produce a variety of cycloplatinated compounds including endo-five-, endo-seven-, endo-six- or exo-five-membered platinacycles. The observed reactions result from a series of oxidative addition/reductive elimination processes taking place at platinum(II)/platinum(IV) species and involving C–X (X = H, Cl, Br) bond activation, arene elimination, and, in some cases, Caryl–Caryl bond formation.
platinum; cyclometallation; N-donor ligands; diarylplatinum(II) precursors; synthesis

1. Introduction

In recent years, research involving platinum complexes has focused on the study of their photophysical properties and their biological activities. Cyclometallated platinum compounds containing N-donor ligands have attracted a great deal of attention because of their potential interest in both areas [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. For this reason, the development of new methods for the preparation of cycloplatinated compounds containing N-donor ligands is a pursued goal. In contrast to cyclopalladation reactions for which Pd(OAc)2 is a very useful precursor leading to formation of a wide variety of palladacycles [18,19], an analogous “universal” starting material is unknown for cycloplatination reactions. Recent reports on cycloplatination reactions proved that cis-[PtCl2(dmso)2] is a reasonable metallating agent leading to higher yields and cleaner reactions than the more classical K2[PtCl4] starting material [20,21,22,23,24,25,26,27,28,29,30]. In these systems, the labile sulfoxide ligands are easily replaced for nitrogen atoms, thus affording the required initial coordination of the nitrogen-donor ligand, which is followed by ortho-metallation. On the other hand, the lower electrophilicity of platinum(II) compared to palladium(II) facilitates oxidative addition as an alternative pathway. Thus, for electron-rich platinum precursors such as [PtMe2(dmso)2] [31,32,33,34,35,36] or dimer [Pt2Me4(μ-SMe2)2] [37,38,39,40,41,42,43], the initial coordination of the ligand is followed by a cyclometallation step which, in this case, consists on oxidative addition followed by reductive elimination of methane. As shown in Scheme 1, in addition to formation of cyclometallated platinum(II) compounds, dimethylplatinum precursors allow formation of stable cyclometallated platinum(IV) compounds arising from intramolecular activation of C–X bonds (X = Cl, Br) [41,42,43] of adequately designed ligands. In recent years, several diarylplatinum(II) compounds containing labile ligands such as dimethylsulfoxide or dialkylsulfide have also been tested as metallating agents for N-donor ligands. The obtained results indicate that they may produce a variety of cycloplatinated compounds and these processes will be reviewed in the present article.

Scheme 1. Synthesis of cyclometallated platinum(II) and platinum(IV) compounds from a dimethylplatinum(II) precursor [41].
Scheme 1. Synthesis of cyclometallated platinum(II) and platinum(IV) compounds from a dimethylplatinum(II) precursor [41].
Inorganics 02 00115 g001 1024

2. Activation of C–H Bonds at Diarylplatinum(II) Precursors

Diphenylplatinum(II) compounds such as [PtPh2(dmso)2] [31,32,33,44,45] or [PtPh2(SMe2)2] [46,47,48,49] have been often used as metallation precursors analogous to those containing dimethylplatinum(II) moieties. In these reactions, the labile dimethylsulfoxide or dimethylsulfide ligands can be readily replaced by N-donor ligands, and the intramolecular C–H bond activation proceeds with elimination of benzene. Although, diphenylplatinum(II) derivatives are reported to be less prone to cyclometallation than the corresponding dimethyl derivatives, metallation of 2-phenylpyridines, benzo[h]quinoline or imines containing biphenyl, pyridyl or pyrimidine fragments has been achieved [44,45,46,47,48]. In addition, “rollover” cyclometallation of substituted bipyridines, including multiple C–H bond activation, and functionalized N-(2'-pyridyl)-7-azaindolyl ligands has been achieved using diarylplatinum precursors (see Scheme 2) [31,32,33,49,50].

Scheme 2. Examples of “rollover” and multiple C–H bond activation of substituted bipyridines [31].
Scheme 2. Examples of “rollover” and multiple C–H bond activation of substituted bipyridines [31].
Inorganics 02 00115 g002 1024

Other diarylplatinum(II) compounds such as [PtAr2(SMe2)2] (Ar = 4-MeC6H4; 4-MeOC6H4) have been shown to be efficient metallation agents in front of 2-phenylpyridine or benzo[h]quinoline ligands, and the assembly of the resulting cyclometallated organoplatinum complexes through bridging diphosphine ligands has been reported (see Scheme 3) [51,52].

In these systems, the cyclometallation process involves oxidative addition of the C–H bond to the platinum(II) center to produce a platinum(IV) hydride complex, and subsequent reductive elimination of arene. Complexes having more electron-donating substituents at the aryl group undergo faster cyclometallation, however, as shown in Scheme 4, compounds [Pt(Ar)(PhPy)(dmso)] containing a cyclometallated phenylpyridine could be obtained from compounds [PtAr2(dmso)] even when the aryl groups contain electronwithdrawing substituents such as Ar = 3,5-(CF3)2C6H3 [45].

Scheme 3. Synthesis and assembly of cyclometallated platinum compounds containing aryl ligands [51,52].
Scheme 3. Synthesis and assembly of cyclometallated platinum compounds containing aryl ligands [51,52].
Inorganics 02 00115 g003 1024
Scheme 4. Further examples of cyclometallation at diarylplatinum(II) compounds [45].
Scheme 4. Further examples of cyclometallation at diarylplatinum(II) compounds [45].
Inorganics 02 00115 g004 1024

Moreover, the perfluorinated compound cis-[Pt(C6F5)2(thf)2] (thf = tetrahydrofurane) has also been used as a metallation precursor in the reactions with N-donor ligands leading to cyclometallated platinum compounds containing a tridentate [C,N,(η2-phenyl)] [53] or a bidentate [C,N] [54] ligand as shown in Scheme 5.

Evidence from the fact that cis configuration of the platinum precursor is not required comes from the fact that double cyclometallation of 3,6-bis(2-thienyl)-1,2,4,5-tetrazine has been achieved from the precursor trans-[Pt(2,4,6-Me3C6H2)2(dmso)2] in a reaction leading to a dinuclear platinum(II) compound [55].

Scheme 5. Reactivity of compound cis-[Pt(C6F5)2(thf)2] (thf = tetrahydrofurane) with N-donor ligands [53,54].
Scheme 5. Reactivity of compound cis-[Pt(C6F5)2(thf)2] (thf = tetrahydrofurane) with N-donor ligands [53,54].
Inorganics 02 00115 g005 1024

3. Activation of C–X Bonds (X = Br, Cl or H) at Diarylplatinum(II) Precursors: Seven- versus Five-Membered Platinacycles

As shown in Scheme 6, the reactions involving intramolecular C–Br bond activation and subsequent reductive elimination of 4,4'-bitolyl have been reported as a convenient method for the synthesis of pincer-[N,C,N] cyclometallated platinum(II) compounds when [Pt(4-MeC6H4)2(μ-SEt2)]2 was used as platinum precursor [56,57,58,59].

Scheme 6. Synthesis of [N,C,N] cyclometallated compounds via C–Br bond activation followed by reductive elimination [56].
Scheme 6. Synthesis of [N,C,N] cyclometallated compounds via C–Br bond activation followed by reductive elimination [56].
Inorganics 02 00115 g006 1024

The reactions of potentially tridentate [C,N,N'] ligands RCH=NCH2CH2NMe2 (R = C6H5, 2-BrC6H4, 2,6-Cl2C6H3 and 2-ClC6H4) with [PtPh2(SMe2)2] have been studied [60] in order to compare the results with those obtained when [Pt2Me4(μ-SMe2)2] was used as precursor. These reactions gave, in addition to cyclometallated platinum(II) and platinum(IV) compounds analogous to those described for the dimethylplatinum precursor, a new type of platinum(II) compound with a seven-membered metallacycle when X = Cl (Scheme 7). In agreement with previous results for the chemistry of dimethylplatinum analogues [41,42,43], a concerted mechanism is suggested for intramolecular C–X bond activation [61]; for X = Br a platinum(IV) compound is obtained at room temperature, while for X = H a platinum(II) compound is formed along with reductive elimination of benzene after refluxing in toluene the corresponding coordination compounds. Unexpectedly, under the conditions required for intramolecular activation of the C–Cl bond, a seven-membered metallacycle including a biaryl linkage is formed.

Scheme 7. Synthesis of cyclometallated platinum(II) and platinum(IV) compounds from a diphenylplatinum(II) precursor [60].
Scheme 7. Synthesis of cyclometallated platinum(II) and platinum(IV) compounds from a diphenylplatinum(II) precursor [60].
Inorganics 02 00115 g007 1024

It is interesting to point out that despite the involvement of triarylplatinum(IV) species in these processes and the known susceptibility of such compounds to undergo reductive elimination of two aryl ligands to release a free biaryl [56], no evidence of such reductive elimination of biphenyl was observed.

In order to gain insight into the different processes that might take place when diarylplatinum compounds are used as metallating substrates, the study of the reactions of cis-[Pt(4-MeC6H4)2(μ-SEt2)]2 with imines of general formula RCH=NCH2CH2NMe2 in which the aryl group R may contain either Br, Cl, H or F in the ortho positions was undertaken [62]. Dinuclear compound cis-[Pt(4-MeC6H4)2(μ-SEt2)]2, previously used as metallating agent as stated above, was selected for this study since the presence of an electron-donor methyl substituent in the aryl ring could facilitate the activation of the ortho C–X bonds. In addition, the position of the methyl substituent in the final products is relevant in order to confirm the mechanism of the process. As shown in Scheme 8, the reactions proceed as expected, yielding as final products a cyclometallated platinum(IV) compound 3a (for X = Br), a cyclometallated platinum(II) compound 4c (for X = H) and a seven-membered platinum(II) compound 6b for X = Cl. In the latter case, it was possible to detect a platinum(IV) compound (3b) as a precursor of the seven membered platinacycle. In addition, the presence of the methyl substituent, initially para to platinum, in a meta position in compound 6b suggests that the Caryl–Caryl bond is formed in a reductive elimination reaction from the platinum(IV) compound. A subsequent cyclometallation process takes place through Caryl–H bond activation at the biaryl fragment and elimination of one molecule of toluene.

Scheme 8. Synthesis of cyclometallated platinum(II) and platinum(IV) compounds from cis-[Pt(4-MeC6H4)2(μ-SEt2)]2 [62,63].
Scheme 8. Synthesis of cyclometallated platinum(II) and platinum(IV) compounds from cis-[Pt(4-MeC6H4)2(μ-SEt2)]2 [62,63].
Inorganics 02 00115 g008 1024

An initial attempt to produce a seven-membered platinacycle from the more inert bromide platinum(IV) compound [PtBr(4-MeC6H4)2(C6H4CH=NCH2CH2NMe2)] was carried out in refluxing toluene and lead to a complex mixture of compounds in which the major component was surprisingly a five-membered platinacycle with an “exo Caryl–Caryl” bond (5a). To analyze the factors governing the selective formation of either five or seven-membered platinacycles from the corresponding cyclometallated platinum(IV) compounds, a kinetico-mechanistic study of these processes was carried out [63]. Based on these studies, the mechanism depicted in Scheme 9 is proposed. In all cases, a common reductive elimination reaction occurs to form a non-cyclometallated intermediate containing a dangling biaryl moiety, which leads to the selective formation of five or seven-membered platinacycles through a trans (X, NMe2)-cis (X, NMe2) isomers equilibrium. The trans form leads exclusively to the five-membered compound, as observed for X = Br. A fast trans to cis isomerization process takes place for X = Cl, and in the obtained cis isomer the steric hindrance forces a Z conformation of the imine, for which only formation of the seven-membered platinacycle is plausible. Along this work, using the reaction conditions extracted from the kinetic studies, both E-cis and E-trans intermediates could be detected and crystallographically characterized.

The reactions of diarylplatinum(II) substrates have been also tested with imine ligands containing a single nitrogen atom. Initial work was based on the reaction of [PtPh2(SMe2)2] with imine 2-BrC6H4CH=NCH2C6H5 [64,65] and further work was carried out using cis-[Pt(4-MeC6H4)2(μ-SEt2)]2 and imines 2-BrC6H4CH=NCH2(4-ClC6H4) and 2,6-Cl2C6H3CH=NCH2(4-ClC6H4) [62]. In these reactions, both intramolecular activation of C–Br or C–Cl bonds lead eventually to formation of seven-membered platinacycles.

Scheme 9. Proposed mechanism for the formation of five and seven-membered platinacycles [63].
Scheme 9. Proposed mechanism for the formation of five and seven-membered platinacycles [63].
Inorganics 02 00115 g009 1024

Although for these reactions the corresponding non-cyclometallated intermediates containing a dangling biaryl moiety were not detected, an analogous mechanism to that proposed for ligands containing two nitrogen donor atoms should operate. Accordingly, the cyclometallated platinum(IV) compound initially formed undergoes a process involving reductive elimination to form a biaryl that remains coordinated through the nitrogen atom to platinum(II), and this step is followed by Caryl–H bond activation and reductive elimination of arene (benzene or toluene) to yield a seven-membered platinum(II) metallacycle. Taking into account the results described above for ligands containing two nitrogen atoms, isomerization to the adequate isomer should be more facile for ligands containing one single nitrogen, thus allowing formation of seven-membered platinacycles even for the less prone bromo derivatives.

On the other hand, although intramolecular C–F bond activation has been achieved upon reaction of [Pt2Me4(μ-SMe2)2] with ligand C6F5CH=NCH2CH2NMe2 [41,42,43] such process has not been observed for precursors cis-[PtPh2(SMe2)2] or cis-[Pt(4-MeC6H4)2(μ-SEt2)]2. This result can be related with the strength of the C–F bond and the lower reactivity of the later substrates toward intramolecular activation of σ bonds. In order to achieve Caryl–Caryl coupling leading to a fluorinated biphenyl moiety, a new preparative strategy based on the reaction of cis-[Pt(C6F5)2(SEt2)2] with imine 2-BrC6H4CH=NCH2(4-ClC6H4) was tested. In this process, a five-membered metallacycle, in which the formed Caryl–Caryl is not included, was obtained. In this case, formation of a seven-membered platinacycle, which requires C–F bond activation, is not favored and indeed is not observed. The kinetico-mechanistic studies carried out for this system [66] indicate initial formation of platinum(IV) compound arising from the activation of the C–Br bond of the imine. This process is followed by a Caryl–Caryl reductive elimination and a final Caryl–H bond activation leading to a five-membered cyclometallated platinum(II) compound with elimination of pentafluorobenzene as shown in Scheme 10. In this case, 19F NMR monitoring of the process allows the detection of all proposed intermediates.

Scheme 10. An example of Caryl–Caryl reductive coupling leading to a fluorinated biphenyl moiety [66].
Scheme 10. An example of Caryl–Caryl reductive coupling leading to a fluorinated biphenyl moiety [66].
Inorganics 02 00115 g010 1024

4. Six- versus Five-Membered and endo- versus exo-Platinacycles

In all cases reported above, the Caryl–Caryl coupling processes leading to either seven- or five-membered platinacycles involve formation of stable endo-metallacycles. In order to analyze whether formation of a biaryl linkage is also possible for N-benzylidenebenzylamines for which formation of less stable exo-metallacycles is preferred, the reactions of cis-[Pt(4-MeC6H4)2(μ-SEt2)]2 with imines containing a C–Br bond at an ortho position of the more flexible benzyl ring have been studied and are summarized in Scheme 11 [67,68]. According to the obtained results, these reactions proceed through activation of the C–Br bond to produce a platinum(IV) compound with a five-membered exo-metallacycle, followed by Caryl–Caryl bond formation between the benzyl group of the imine ligand and one of the para-tolyl ligands leading to a biaryl linkage. The subsequent Caryl–H bond activation does not necessarily take place at the biaryl system; instead, a Caryl–H bond of the benzylidene group is activated to produce a five-membered endo-metallacycle with elimination of a toluene molecule (ligands 1d and 1e). For ligand 1f, the mesityl group was chosen in order to block the ortho positions of the benzylidene group and drive the reaction towards the benzyl group of the ligand. Instead, an aliphatic C–H bond of the mesityl group is activated to produce a six-membered endo-metallacycle. This result, analogous to those reported for cyclopalladation reactions [69,70] can be related to the higher stability of the endo versus exo-metallacycles (the so-called endo effect), which allows to overcome the low tendency to form six-membered rings and to activate a sp3 C–H bond [18]. For imine 2,6-F2C6H3CH=NCH2(2-BrC6H4), the fluoro substituents block cyclometallation at the benzylidene ring, and drive the reaction towards formation of a five-membered exo-metallacycle (2g). As a whole, the obtained results indicate that intramolecular C–X bond activation at the saturated arm of N-benzylidene-benzylamines may promote formation of a biaryl linkage between one of the tolyl ligands and the benzyl group of the imine ligand. However, the biaryl linkage is not necessarily involved in the subsequent metallation process which leads to either endo-five, endo-six or exo-five-membered platinacycles as shown in Scheme 11.

Scheme 11. Synthesis of cyclometallated platinum(II) compounds from N-benzylidenebenzylamines and cis-[Pt(4-MeC6H4)2(μ-SEt2)]2 [67,68].
Scheme 11. Synthesis of cyclometallated platinum(II) compounds from N-benzylidenebenzylamines and cis-[Pt(4-MeC6H4)2(μ-SEt2)]2 [67,68].
Inorganics 02 00115 g011 1024

Finally, it is interesting to point out that analogous processes from cyclometallated platinum(IV) complexes obtained from dimethylplatinum(II) precursors such as [PtMe2X{C6H4CH=NCH2R'}L] (X = Cl, Br; R' = aryl; L = SMe2, PPh3) have been recently reported [71,72]. In this case, Csp2–Csp3 reductive elimination involving the metallated ring and one methyl ligand takes place and is followed by formation of five or six-membered platinacycles.

5. Conclusions

As a whole, several diarylplatinum(II) compounds displaying monomeric or dimeric structures in which the square-planar coordination of the platinum is completed with labile ligands such as dimethylsulfoxide or dialkylsulfides have been shown to be useful in the synthesis of several classes of platinacycles containing N-donor ligands. The observed reactions result from a series of oxidative addition/reductive elimination processes involving platinum(II)/platinum(IV) species. The initial coordination of the ligand takes place easily by substitution of the labile ligands and/or cleavage of the dinuclear structure and is followed by intramolecular C–X (X = Br, Cl, H) bond activation leading to cyclometallated platinum(IV) compounds. When C–H bond activation is involved, straightforward reductive elimination of a molecule of arene leads to formation of a cyclometallated platinum(II) compound. However, cyclometallated platinum(IV) compounds are formed for X = Br or Cl and subsequent reductive elimination from these species leads to Caryl–Caryl bond formation. When the formed biaryl moiety remains coordinated to the platinum through one or two nitrogen atoms, as for ligands RCH=NCH2R' or RCH=NCH2CH2NMe2, a further step involving C–H bond activation at either the formed biaryl fragment, or at other available aromatic or aliphatic positions produces a cyclometallated platinum(II) compound with reductive elimination of one molecule of arene. In this process, in addition to the more prevalent endo-five-membered platinacycles, other metallacycles such as endo-seven, endo-six or exo-five-membered can be obtained. In summary, a careful choice of the aryl groups in both the platinum precursor and the employed ligands allows the synthesis of a great variety of cycloplatinated compounds.


This work was supported by the Spanish Ministery of Science and Technology (project CTQ2009-11501).

Conflicts of Interest

The authors declare no conflict of interest.


  1. Williams, J.A.G.; Develay, S.; Rochester, D.L.; Murphy, L. Optimising the luminescence of platinum(II) complexes and their application in organic light emitting devices (OLEDs). Coord. Chem. Rev. 2008, 252, 2596–2611. [Google Scholar] [CrossRef]
  2. Kalinowski, J.; Fattori, V.; Cocchi, M.; Williams, J.A.G. Light-emitting devices based on organometallic platinum complexes as emitters. Coord. Chem. Rev. 2011, 255, 2401–2425. [Google Scholar] [CrossRef]
  3. Murphy, L.; Brulatti, P.; Fattori, V.; Cocchi, M.; Williams, J.A.G. Blue-shifting of the monomer and excimer phosphorescence of tridentate cyclometallated platinum(II) complexes for optimal white-light OLEDs. Chem. Commun. 2012, 48, 5817–5819. [Google Scholar] [CrossRef]
  4. Kui, S.C.F.; Hung, F.-F.; Lai, S.-L.; Yuen, M.-Y.; Kwok, C.-C.; Low, K.-H.; Chui, S.S.-Y.; Che, C.-M. Luminescent organoplatinum(II) complexes with functionalized cyclometalated CNC ligands: Structures, photophysical properties, and material applications. Chem. Eur. J. 2012, 18, 96–109. [Google Scholar] [CrossRef]
  5. Zhang, L.-K.; Xing, L.-B.; Chen, B.; Yang, Q.-Z.; Tong, Q.-X.; Wu, L.-Z.; Tung, C.-H. A highly selective and sensitive luminescent chemosensor for Zn2+ ions based on cyclometalated platinum(II) complexes. Dalton Trans. 2013, 42, 4244–4247. [Google Scholar] [CrossRef]
  6. Li, Z.; Badaeva, E.; Ugrinov, A.; Kilina, S.; Sun, W. Platinum chloride complexes containing 6-[9,9-di(2-ethylhexyl)-7-R-9H-fluoren-2-yl]-2,2'-bipyridine ligand (R = NO2, CHO, benzothiazol-2-yl, n-Bu, carbazol-9-yl, NPh2): Tunable Photophysics and reverse saturable absorption. Inorg. Chem. 2013, 52, 7578–7592. [Google Scholar] [CrossRef]
  7. Turner, E.; Bakken, N.; Li, J. Cyclometalated platinum complexes with luminescent quantum yields approaching 100%. Inorg. Chem. 2013, 52, 7344–7351. [Google Scholar] [CrossRef]
  8. Li, Z.; Sun, W. Synthesis, photophysics, and reverse saturable absorption of platinum complexes bearing extended π-conjugated C^N^N ligands. Dalton Trans. 2013, 42, 14021–14029. [Google Scholar] [CrossRef]
  9. Samouei, H.; Rashidi, M.; Heinemann, F.W. A cyclometalated diplatinum complex containing 1,1'-bis(diphenylphosphino)ferrocene as spacer ligand: Antitumor study. J. Organomet. Chem. 2011, 696, 3764–3771. [Google Scholar] [CrossRef]
  10. Wang, P.; Leung, C.-H.; Ma, D.-L.; Sun, R.W.-Y.; Yan, S.-C.; Chen, Q.-S.; Che, C.-M. Specific blocking of CREB/DNA binding by cyclometalated platinum(II) complexes. Angew. Chem. Int. Ed. 2011, 50, 2554–2558. [Google Scholar] [CrossRef]
  11. Ruiz, J.; Vicente, C.; de Haro, C.; Espinosa, A. Synthesis and antiproliferative activity of a C,N-cycloplatinated(II) complex with a potentially intercalative anthraquinone pendant. Inorg. Chem. 2011, 50, 2151–2158. [Google Scholar] [CrossRef]
  12. Ruiz, J.; Rodríguez, V.; Cutillas, N.; Espinosa, A.; Hannon, M.J. Novel C,N-chelate platinum(II) antitumor complexes bearing a lipophilic ethisterone pendant. J. Inorg. Biochem. 2011, 105, 525–531. [Google Scholar] [CrossRef]
  13. Quirante, J.; Ruiz, D.; González, A.; López, C.; Cascante, M.; Cortés, R.; Messeguer, R.; Calvis, C.; Baldomà, L.; Pascual, A.; et al. Platinum(II) and palladium(II) complexes with (N,N′) and (C,N,N′) ligands derived from pyrazole as anticancer and antimalarial agents: Synthesis, characterization and in vitro activities. J. Inorg. Biochem. 2011, 105, 1720–1728. [Google Scholar] [CrossRef]
  14. Chellan, P.; Land, K.M.; Shokar, A.; Au, A.; An, S.H.; Clavel, C.M.; Dyson, P.J.; de Kock, C.; Smith, P.J.; Chibale, K.; et al. Exploring the versatility of cycloplatinated thiosemicarbazones as antitumor and antiparasitic agents. Organometallics 2012, 31, 5791–5799. [Google Scholar] [CrossRef]
  15. Cortés, R.; Crespo, M.; Davin, L.; Martín, R.; Quirante, J.; Ruiz, D.; Messeguer, R.; Calvis, C.; Baldomà, L.; Badia, J.; et al. Seven-membered cycloplatinated complexes as a new family of anticancer agents. X-ray characterization and preliminary biological studies. Eur. J. Med. Chem. 2012, 54, 557–566. [Google Scholar] [CrossRef]
  16. Talancón, D.; López, C.; Font-Bardia, M.; Calvet, T.; Quirante, J.; Calvis, C.; Messeguer, R.; Cortés, R.; Cascante, M.; Baldomà, L.; et al. Diastereomerically pure platinum(II) complexes as antitumoral agents. The influence of the mode of binding {(N), (N,O) or (C,N)} of (1S,2R)-[(η5-C5H5)Fe{(η5-C5H4)–CH=N–CH(Me)–CH(OH)–C6H5}] and the arrangement of the auxiliary ligands. J. Inorg. Biochem. 2013, 118, 1–12. [Google Scholar] [CrossRef]
  17. Albert, J.; Bosque, R.; Crespo, M.; Granell, J.; López, C.; Cortés, R.; González, A.; Quirante, J.; Calvis, C.; Messeguer, R.; et al. Pt(II) complexes with (N,N') or (C,N,E) (E = N, S) ligands: Cytotoxic studies, effect on DNA tertiary structure and structure-activity relationships. Bioorg. Med. Chem. 2013, 21, 4210–4217. [Google Scholar] [CrossRef]
  18. Albrecht, M. Cyclometalation using d-block transition metals: Fundamental aspects and recent trends. Chem. Rev. 2010, 110, 576–623. [Google Scholar] [CrossRef]
  19. Albrecht, M. C–H bond activation. In Palladacycles; Dupont, J., Pfeffer, M., Eds.; Wiley-VCH: Weinheim, Germany, 2008; Chapter 2; pp. 13–31. [Google Scholar]
  20. Ranatunge-Bandarage, P.R.R.; Robinson, B.H.; Simpson, J. Ferrocenylamine complexes of platinum(II) including cycloplatinated derivatives. Organometallics 1994, 13, 500–510. [Google Scholar] [CrossRef]
  21. Ranatunge-Bandarage, P.R.R.; Duffy, N.W.; Johnston, S.M.; Robinson, B.H.; Simpson, J. Synthesis and stereochemistry of bis(platinum) complexes of ferrocenylamines. Organometallics 1994, 13, 511–521. [Google Scholar] [CrossRef]
  22. Wu, Y.J.; Ding, L.; Wang, H.X.; Liu, Y.H.; Yuan, H.Z.; Mao, X.A. Synthesis, characterization and structure of ferrocenylketimine complexes of platinum(II). J. Organomet. Chem. 1997, 535, 49–58. [Google Scholar] [CrossRef]
  23. Ryabov, A.D.; Kazankov, G.M.; Panyashkina, I.M.; Grozovsky, O.V.; Dyachenko, O.G.; Polyakov, V.A.; Kuz’mina, L.G. Cycloplatination of aryl and ferrocenyl oximes by cis-[PtCl2(SOMe2)2] affording expected platinum(II) and unexpected platinum(IV) compounds. J. Dalton Trans. 1997, 4385–4391. [Google Scholar]
  24. Ding, L.; Zou, D.P.; Wu, Y.J. Cyclometallation reaction of 1,1'-bis[1-aryliminoethyl]ferrocenes with platinum(II). Polyhedron 1998, 17, 2511–2516. [Google Scholar] [CrossRef]
  25. Alexandrova, L.; D’yachenko, O.G.; Kazankov, G.M.; Polyakov, V.A.; Samuleev, P.V.; Sansores, E.; Ryabov, A.D. Mechanism of biologically relevant deoxygenation of dimethylsulfoxide coupled with Pt(II) to Pt(IV) oxidation of orthoplatinated oximes. Synthetic, kinetic, electrochemical, X-ray structural and density functional study. J. Am. Chem. Soc. 2000, 122, 5189–5200. [Google Scholar] [CrossRef]
  26. Meijer, M.D.; Kleij, A.W.; Lutz, M.; Spek, A.L.; van Koten, G. Synthesis and characterization of platinum(II)-terminated dendritic carbosilanes: X-ray crystal structure of the model species [PtCl(C6H3{CH2NMe2}-2-SiMe3–5)(PPh3)]. J. Organomet. Chem. 2001, 621, 190–196. [Google Scholar] [CrossRef]
  27. Ryabov, A.D.; Panyashkina, I.M.; Polyakov, V.A.; Fisher, A. Access to central carbon chirality through cycloplatination of 1-(2-pyridinylthio)propanone by cis-[PtCl2(S-SOMe(p-tolyl))]. Organometallics 2002, 21, 1633–1636. [Google Scholar] [CrossRef]
  28. Ryabov, A.D.; Otto, S.; Samuleev, P.V.; Polyakov, V.A.; Alexandrova, L.; Kazankov, G.M.; Shova, S.; Revenco, M.; Lipkowski, J.; Johansson, M. Structural and mechanistic look at the orthoplatination of aryl oximes by dichlorobis(sulfoxide or sulfide)platinum(II) complexes. Inorg. Chem. 2002, 41, 4286–4294. [Google Scholar] [CrossRef]
  29. Crespo, M.; Font-Bardia, M.; Granell, J.; Martínez, M.; Solans, X. Cyclometallation on platinum(II) complexes; the role of the solvent and added base donor capability on the reaction mechanisms. Dalton Trans. 2003, 3763–3769. [Google Scholar]
  30. Capapé, A.; Crespo, M.; Granell, J.; Font-Bardia, M.; Solans, X. A comparative study of the structures and reactivity of cyclometallated platinum compounds of N-benzylidenebenzylamines and cycloplatination of a primary amine. Dalton Trans. 2007, 2030–2039. [Google Scholar]
  31. Zucca, A.; Doppiu, A.; Cinellu, M.A.; Stoccoro, S.; Minghetti, G.; Manassero, M. Multiple C–H bond activation. Threefold-deprotonated 6-Phenyl-2,2'-bipyridine as a bridging ligand in dinuclear platinum(II) derivatives. Organometallics 2002, 21, 783–785. [Google Scholar] [CrossRef]
  32. Minghetti, G.; Stoccoro, S.; Cinellu, M.A.; Soro, B.; Zucca, A. Activation of a C-H bond in a pyridine ring. Reaction of 6-Substituted 2,2'-Bipyridines with methyl and phenyl platinum(II) derivatives: N',C(3)-“rollover” cyclometalation. Organometallics 2003, 22, 4770–4777. [Google Scholar] [CrossRef]
  33. Zucca, A.; Petretto, G.L.; Stoccoro, S.; Cinellu, M.A.; Minghetti, G.; Manassero, M.; Manassero, C.; Male, L.; Albinati, A. Dinuclear C,N,C cyclometalated platinum derivatives with bridging delocalized ligands. fourfold deprotonation of 6,6'-Diphenyl-2,2'-bipyridine, H4L, promoted by “Pt(R)2” fragments (R = Me, Ph). Crystal Structures of [Pt2(L)(3,5-Me2py)2] and {Pt2(L)(dppe)}2 (dppe = 1,2-bis(diphenylphosphino)ethane). X-ray powder diffraction of [Pt2(L)(CO)2]. Organometallics 2006, 25, 2253–2265. [Google Scholar] [CrossRef]
  34. Zucca, A.; Petretto, G.L.; Stoccoro, S.; Cinellu, M.A.; Manassero, M.; Manassero, C.; Minghetti, G. Cyclometalation of 2,2'-bipyridine. Mono- and dinuclear C,N platinum(II) derivatives. Organometallics 2009, 28, 2150–2159. [Google Scholar] [CrossRef]
  35. Zucca, A.; Cordeschi, D.; Stoccoro, S.; Cinellu, M.A.; Minghetti, G.; Chelucci, G.; Manassero, M. Platinum(II)-cyclometalated “roll-over” complexes with a chiral pinene-derived 2,2'-bipyridine. Organometallics 2011, 30, 3064–3074. [Google Scholar] [CrossRef]
  36. Maidich, L.; Zucca, A.; Clarkson, G.J.; Rourke, J.P. Oxidative addition to diplatinum(II) complexes: Stereoselectivity and cooperative effects. Organometallics 2013, 32, 3371–3375. [Google Scholar] [CrossRef]
  37. Baar, C.R.; Jenkins, H.A.; Vital, J.J.; Yap, G.P.A.; Puddephatt, R.J. Stereoselectivity in organometallic reactions: Oxidative addition of alkyl halides to platinum(II). Organometallics 1998, 17, 2805–2818. [Google Scholar] [CrossRef]
  38. Baar, C.R.; Carbray, L.P.; Jennings, M.C.; Puddephatt, R.J. Oxidative addition to diplatinum(II) complexes: Stereoselectivity and cooperative effects. Organometallics 2000, 19, 2482–2497. [Google Scholar] [CrossRef]
  39. Zhao, S.-B.; Wang, R.-Y.; Wang, S. Intramolecular C–H activation directed self-assembly of an organoplatinum(II) molecular square. J. Am. Chem. Soc. 2007, 129, 3092–3093. [Google Scholar] [CrossRef]
  40. Zhao, S.-B.; Wang, R.-Y.; Wang, S. Reactivity of SiMe3- and SnR3-functionalized bis(7-azaindol-1-yl)methane with [PtR2(μ-SMe2)]n (R = Me, Ph) and the resulting Pt(II) and Pt(IV) complexes. Organometallics 2009, 28, 2572–2582. [Google Scholar] [CrossRef]
  41. Anderson, C.M.; Puddephatt, R.J.; Ferguson, G.; Lough, A.J. Oxidative addition of aryl-halogen bonds to platinum(II) and the structure of a complex formed by aryl-fluoride oxidative addition. J. Chem. Commun. 1989, 1297–1298. [Google Scholar]
  42. Anderson, C.M.; Crespo, M.; Ferguson, G.; Lough, A.J.; Puddephatt, R.J. Activation of aromatic carbon-fluorine bonds by organoplatinum complexes. Organometallics 1992, 11, 1177–1181. [Google Scholar] [CrossRef]
  43. Anderson, C.M.; Crespo, M.; Jennings, M.C.; Lough, A.J.; Ferguson, G.; Puddephatt, R.J. Competition between intramolecular oxidative addition and ortho metalation in organoplatinum(II) compounds: Activation of aryl-halogen bonds. Organometallics 1991, 10, 2672–2679. [Google Scholar] [CrossRef]
  44. Rao, Y.-L.; Wang, S. Impact of constitutional isomers of (BMes2)phenylpyridine on structure, stability, phosphorescence, and Lewis acidity of mononuclear and dinuclear Pt(II) complexes. Inorg. Chem. 2009, 48, 7698–7713. [Google Scholar] [CrossRef]
  45. Yagyu, T.; Ohashi, J.; Maeda, M. Monoarylplatinum(II) complexes with a 2-phenylpyridyl ligand and coordinated solvent, [Pt(Ar)(Phpy)(solv)] (Phpy = 2-phenylpyridyl; solv = NCCH3, dmso). Preparation from [Pt(Ar)2(solv)2], structures, and chemical properties. Organometallics 2007, 26, 2383–2391. [Google Scholar] [CrossRef]
  46. Nabavizadeh, S.M.; Amini, H.; Shahsavari, H.R.; Namdar, M.; Rashidi, M.; Kia, R.; Hemmateenejad, B.; Nekoeinia, M.; Ariafard, A.; Hosseini, F.N.; et al. Assembly of cyclometalated platinum(II) complexes via 1,10-bis(diphenylphosphino)ferrocene ligand: Kinetics and mechanisms. Organometallics 2011, 30, 1466–1477. [Google Scholar] [CrossRef]
  47. Crespo, M.; Font-Bardia, M.; Solans, X. A comparative study of metallating agents in the synthesis of [C,N,N']-cycloplatinated compounds derived from biphenylimines. J. Organomet. Chem. 2006, 691, 1897–1906. [Google Scholar] [CrossRef]
  48. Crespo, M.; Anderson, C.M.; Tanski, J.M. Synthesis of platinum(II) cyclometallated compounds derived from imines containing pyridyl or pyrimidyl groups. Can. J. Chem. 2009, 87, 80–87. [Google Scholar] [CrossRef]
  49. Hudson, Z.M.; Zhao, S.-B.; Wang, R.-Y.; Wang, S. Switchable ambient temperature singlet-triplet dual emission in nonconjugated donor-acceptor triarylboron-Pt(II) complexes. Chem. Eur. J. 2009, 15, 6131–6137. [Google Scholar] [CrossRef]
  50. Skapski, A.C.; Sutcliffe, V.F.; Young, G.B. ‘Roll-over’ 3-metallation of co-ordinated 2,2'-bipyridyl in the thermal rearrangement of diaryl(bipyridyl)platinum(II) complexes: Molecular structure of (μ-bidyl)[PtPh(Butpy)]2. J. Chem. Soc. Chem. Commun. 1985, 609–611. [Google Scholar] [CrossRef]
  51. Nabavizadeh, S.M.; Haghighi, M.G.; Esmaeilbeig, A.R.; Raoof, F.; Mandegani, Z.; Jamali, S.; Rashidi, M.; Puddephatt, R.J. Assembly of symmetrical or unsymmetrical cyclometalated organoplatinum complexes through a bridging diphosphine ligand. Organometallics 2010, 29, 4893–4899. [Google Scholar] [CrossRef]
  52. Nabavizadeh, S.M.; Shahsavari, H.; Namdar, M.; Rashidi, M.; Puddephatt, R.J. Substitution reactions involving cyclometalated platinum(II) complexes: Kinetic investigations. J. Organomet. Chem. 2011, 696, 3564–3571. [Google Scholar] [CrossRef]
  53. Forniés, J.; Menjón, B.; Gómez, N.; Tomás, M. Reactivity of cis-Pt(C6F5)2(OC4H8)2 toward (C6H5)2CN2. Synthesis and molecular structure of Pt(C6F5)[(2-C6H4)C(C6H5)=N–N=(η2-C6H5)C(C6H5)], an ortho-metalated compound containing an unusual intramolecular η2-Arene-Pt interaction. Organometallics 1992, 11, 1187–1193. [Google Scholar] [CrossRef]
  54. Berenguer, J.R.; Lalinde, E.; Moreno, M.T.; Sánchez, S.; Torroba, J. Facile metalation of Hbzq by cis-[Pt(C6F5)2(thf)2]: A route to a pentafluorophenyl benzoquinolate solvate complex that easily coordinates terminal alkynes. Spectroscopic and optical properties. Inorg. Chem. 2012, 51, 11665–11669. [Google Scholar] [CrossRef]
  55. Sarkar, B.; Schurr, T.; Hartenbach, I.; Shleid, T.; Fiedler, J.; Kaim, W. Double cyclometallation of bridging 3,6-bis(2-thienyl)-1,2,4,5-tetrazine in a dinuclear mesityl(dimethylsulfoxide)platinum(II) complex: Structure and properties. J. Organomet. Chem. 2008, 693, 1703–1706. [Google Scholar] [CrossRef]
  56. Rodríguez, G.; Albrecht, M.; Schoenmaker, J.; Ford, A.; Lutz, M.; Spek, A.L.; van Koten, G. Bifunctional pincer-type organometallics as substrates for organic transformations and as novel building blocks for polymetallic materials. J. Am. Chem. Soc. 2002, 124, 5127–5138. [Google Scholar] [CrossRef]
  57. Albrecht, M.; Rodríguez, G.; Schoenmaker, J.; van Koten, G. New peptide labels containing covalently bonded platinum(II) centers as diagnostic biomarkers and biosensors. Org. Lett. 2000, 2, 3461–3464. [Google Scholar] [CrossRef]
  58. Canty, A.J.; Patel, J.; Skelton, B.W.; White, A.H. Facial and meridional [N–C–N] intramolecular coordination systems: Structure of fac-PtBrMe2{2,6-(pzCH2)2C6H3}·1/2C6H6 {[2,6-(pzCH2)2C6H3] = 2,6-(bis{(pyrazol-1-yl)methyl}phenyl)} and mer-PtBr{2,6-(3,5-Me2pzCH2)2C6H3}, and an alternative synthetic route to the platinum(II) [N–C–N] kernel. J. Organomet. Chem. 2000, 599, 195–199. [Google Scholar] [CrossRef]
  59. Slagt, M.Q.; Gebbink, R.J.M.K.; Lutz, M.; Spek, A.L.; van Koten, G. Synthetic strategies towards new para-functionalised NCN-pincer palladium(II) and platinum(II) complexes. Dalton Trans. 2002, 2591–2592. [Google Scholar]
  60. Crespo, M.; Font-Bardia, M.; Solans, X. Compound [PtPh2(SMe2)2] as a versatile metallating agent in the preparation of new types of [C,N,N'] cyclometallated platinum compounds. Organometallics 2004, 23, 1708–1713. [Google Scholar] [CrossRef]
  61. Calvet, T.; Crespo, M.; Font-Bardia, M.; Jansat, S.; Martinez, M. Kinetico-mechanistic studies on intramolecular C–X bond activation (X = Br, Cl) of amino-imino ligands on Pt(II) compounds. Prevalence of a concerted mechanism in nonpolar, polar and ionic liquid media. Organometallics 2012, 31, 4367–4373. [Google Scholar] [CrossRef]
  62. Martín, R.; Crespo, M.; Font-Bardia, M.; Calvet, T. Five- and seven-membered metallacycles in [C,N,N'] and [C,N] cycloplatinated compounds. Organometallics 2009, 28, 587–597. [Google Scholar] [CrossRef]
  63. Bernhardt, P.V.; Calvet, T.; Crespo, M.; Font-Bardia, M.; Jansat, S.; Martínez, M. New insights in the formation of five- versus seven- membered platinacycles: A kinetico-mechanistic study. Inorg. Chem. 2013, 52, 474–484. [Google Scholar] [CrossRef]
  64. Font-Bardia, M.; Gallego, C.; Martinez, M.; Solans, X. Unexpected formal aryl insertion in a cyclometalated diphenylplatinum(IV) Complex: The first seven-membered cyclometalated platinum compound structurally characterized. Organometallics 2002, 21, 3305–3307. [Google Scholar] [CrossRef]
  65. Gallego, C.; Martinez, M.; Safont, V.S. Mechanism of the competition between phenyl insertion and ligand reductive elimination on a hindered platinum(IV) cyclometalated complex. Organometallics 2007, 26, 527–537. [Google Scholar] [CrossRef]
  66. Calvet, T.; Crespo, M.; Font-Bardia, M.; Gómez, K.; González, G.; Martínez, M. Kinetico-mechanistic insight into the platinum-mediated C–C coupling of fluorinated arenes. Organometallics 2009, 28, 5096–5106. [Google Scholar] [CrossRef]
  67. Crespo, M.; Calvet, T.; Font-Bardia, M. Platinum mediated aryl-aryl bond formation and sp3 C–H bond activation. Dalton Trans. 2010, 39, 6936–6938. [Google Scholar] [CrossRef]
  68. Crespo, M.; Font-Bardia, M.; Calvet, T. Biaryl formation in the synthesis of endo- and exo-platinacycles. Dalton Trans. 2011, 40, 9431–9438. [Google Scholar] [CrossRef]
  69. Albert, J.; Granell, J.; Sales, J.; Solans, X.; Font-Altaba, M. Competitive metalation reactions between aliphatic and aromatic carbon atoms in N-benzylideneamines. X-ray molecular structure of [Pd{1-CH2-2-(HC=NC6H5)-3,5-(CH3)2C6H2)BrPPh3]. Organometallics 1986, 5, 2567–2568. [Google Scholar] [CrossRef]
  70. Albert, J.; Ceder, R.M.; Gomez, M.; Granell, J.; Sales, J. Cyclopalladation of N-mesitylbenzylideneamines. Aromatic versus aliphatic C–H activation. Organometallics 1992, 11, 1536–1541. [Google Scholar] [CrossRef]
  71. Crespo, M.; Anderson, C.M.; Kfoury, N.; Font-Bardia, M.; Calvet, T. Reductive elimination from cyclometalated platinum(IV) complexes to form Csp2–Csp3 bonds and subsequent competition between Csp2–H and Csp3–H bond activation. Organometallics 2012, 31, 4401–4404. [Google Scholar] [CrossRef]
  72. Anderson, C.M.; Crespo, M.; Kfoury, N.; Weinstein, M.A.; Tanski, J.M. Regioselective C–H activation preceded by Csp2–Csp3 reductive elimination from cyclometalated platinum(IV) complexes. Organometallics 2013, 32, 4199–4207. [Google Scholar] [CrossRef]
Inorganics EISSN 2304-6740 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top