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Article

Theoretical Study of the Photolysis Mechanisms of Methylpentaphenyldimetallanes (Ph3MM′Ph2Me; M, M′ = Si and Ge)

by
Shih-Hao Su
1 and
Ming-Der Su
1,2,*
1
Department of Applied Chemistry, National Chiayi University, Chiayi 60004, Taiwan
2
Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
*
Author to whom correspondence should be addressed.
Molecules 2018, 23(6), 1351; https://doi.org/10.3390/molecules23061351
Submission received: 12 May 2018 / Revised: 28 May 2018 / Accepted: 1 June 2018 / Published: 4 June 2018
(This article belongs to the Special Issue Theoretical Investigations of Reaction Mechanisms)
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Abstract

:
The mechanisms of the photolysis reactions are studied theoretically at the M06-2X/6-311G(d) level of theory, using the four types of group 14 molecules that have the general structure, Ph3M–M′Ph2Me (M and M′ = Si and Ge), as model systems. This study provides the first theoretical evidence for the mechanisms of these photorearrangements of compounds that contain a M–M′ single bond. The model investigations indicate that the preferred reaction route for the photolysis reactions is, as follows: reactant → Franck-Condon (FC) region → minimum (triplet) → transition state (triplet) → triplet/singlet intersystem crossing → photoproducts (both di-radicals and singlets). The theoretical findings demonstrate that the formation of radicals results from reactions of the triplet states of these reactants. This could be because both the atomic radius and the chemical properties of silicon and germanium are quite similar to each other and compared to other group 14 elements, their photolytic mechanisms are nearly the same. The results for the photolytic mechanisms that are studied in this work are consistent with the available experimental observations and allow for a number of predictions for other group 14 dimetallane analogues to be made.

The photochemistry of disilanes that have various substituents have attracted intense interest because they are used in the study of fundamental chemistry problems, as well as for their potential applications [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23]. It is established that the direct irradiation of aryldisilanes in solution results in the formation of transient silenes, which are formally derived from the disproportionation and recombination of the silyl free radicals that are developed in the homolysis of the Si–Si single bond (Scheme 1) [24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41]. Although there has been much experimental study of the photoreactions of aryldisilanes and their derivatives, to the authors’ best knowledge, no theoretical studies deal with the photochemical mechanisms of these silicon-based compounds.
These interesting experimental results for photochemical aryldisilane stimulate this study of the potential energy surfaces for these reactions, using density functional theory (DFT). A study of the photolysis reaction, Scheme 2, is thus detailed.
Scheme 2 is chosen as the model because there have been many experimental studies of methylpentaphenyldisilane photochemistry [24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41]. However, there have been no reported theoretical studies of these experimental results. In particular, there are no systematic theoretical computations that relate to the effect of the elements on the 1-methyl-1,1,2,2,2-pentaphenyldimetallane (1; Ph3M–M′Ph2Me; M and M′ = Si and Ge) systems.
In order to give a realistic representation of the photochemical reaction of Ph3M–M′Ph2Me, all of the DFT computations are accomplished using the GAUSSIAN 09 package of programs [42] at the M06-2X/6-311G(d) [43] level of theory. All of the optimized structures were confirmed by normal mode vibrational analysis. Time-dependent density functional theory (TD-DFT) computations [44,45] were also performed with the same DFT and 6-311G(d) basis sets. The minimum energy of the intersystem crossing points between the singlet and triplet potential energy surfaces are also calculated using the GAUSSIAN 09 package, together with the code that was developed by Harvey et al. [46,47].
According to the model (Scheme 2) that was studied in this work, the lowest singlet (S0) or triplet (T1) excitation for the Ph3Si–SiPh2Me (1-Si-Si) is the σSi–Si (HOMO) → σSi–Si* (LUMO) transition. It was experimentally reported that Ph3Si–SiPh2Me (1-Si-Si) was directly irradiated using 254-nm (=113 kcal/mol) lamps [24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41], which is in good agreement with the present computational data (117 kcal/mol). This inspires confidence that these model computations are trustworthy for these studies of the mechanisms of the photolysis reactions of Ph3Si–GePh2Me (1-Si-Ge), Ph3Ge–SiPh2Me (1-Ge-Si) and Ph3Ge–GePh2Me (1-Ge-Ge).
The TD-DFT computations [44,45] also demonstrate that the excited states (kcal/mol) increase in the order (Figure 1):
(a)
For 1-Si-Si: [1-Si-Si(T1)]* (95.2) < [1-Si-Si(T2)]* (106.3) < [1-Si-Si(S1)]* (108.6) < [1-Si-Si(T3)]* (117.2) < [1-Si-Si(S2)]* (120.6).
(b)
For 1-Si-Ge: [1-Si-Ge(T1)]* (99.7) < [1-Si-Ge(T2)]* (104.8) < [1-Si-Ge(S1)]* (107.3) < [1-Si-Ge(T3)]* (114.6) < [1-Si-Ge(S2)]* (121.9).
(c)
For 1-Ge-Si: [1-Ge-Si(T1)]* (100.8) < [1-Ge-Si(T2)]* (105.2) < [1-Ge-Si(S1)]* (110.6) < [1-Ge-Si(T3)]* (116.2) < [1-Ge-Si(S2)]* (120.0).
(d)
For 1-Ge-Ge: [1-Ge-Ge(T1)]* (98.4) < [1-Ge-Ge(S1)]* (108.3) < [1-Ge-Ge(T2)]* (117.2) < [1-Ge-Ge(T3)]* (123.5) < [1-Ge-Ge(S2)]* (124.4).
Namely, the theoretical evidences indicate that the lowest-lying excited state for these four molecules (1-Si-Si, 1-Si-Ge, 1-Ge-Si, and 1-Ge-Ge) is the first excited triplet state (T1). It is well known that spin-allowed absorption cross-sections are typically larger than those for spin-forbidden excitations. As a result, photo-excitation promotes these four molecules to a singlet excited electronic state (S1), and the molecule subsequently relaxes, branching between the T1 and S0 states, so considerations start on the triplet state energy surface. This computational data strongly suggest that the photolysis reactions of 1 must firstly progress on the triplet states and must only include the σ → σ* transition. As a result, the triplet state surfaces are the main focus of this study.
The essential characteristic of the photochemical mechanisms of 1 is the location of the intersystem crossing in the excited-triplet and the ground-singlet electronic states. In this study, since triphenylsilyl and methyldiphenylsilyl radicals are observed as photoproducts of 1-Si-Si (Scheme 1) [24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41], the Si–Si single bond in 1-Si-Si must be broken. Accordingly, a Si–Si σ bond cleavage mechanism is suggested for the conversion of 1-Si-Si to triphenylsilyl and methyldiphenylsilyl radicals, and this is shown in Figure 2(i) [48]. It is worthy of note that although the silicon-silicon σ bond cleavage does not require full optimization of 1-Si-Si, this at least shows that there is degeneracy between a HOMO (σ) and a LUMO (σ*) when the silicon-silicon single bond is lengthened. Increasing the M–M′ single bonds in 1-Si-Ge, 1-Ge-Si, and 1-Ge-Ge, can also lead to degeneracy of the S0 and T1 energy surfaces at about 4.0 Å, which are estimates, as shown in Figure 2(ii–iv), respectively. These results are used to explain the mechanisms for the photolysis reactions of 1-Si-Si, 1-Si-Ge, 1-Ge-Si and 1-Ge-Ge in the following study.
In order to understand the similarities and differences between the four types of photolysis reactions (Figure 2), the reaction profiles are shown in Figure 1, which also contains the relative energies for all of the critical points with respect to the energy of the corresponding reactants 1. The optimized geometrical structures are all collected in Figure 3 (Ph3Si–SiPh2Me), Figure 4 (Ph3Si–GePh2Me), Figure 5 (Ph3Ge–SiPh2Me), and Figure 6 (Ph3Ge–GePh2Me), respectively.
The potential energy surfaces for the photolytic mechanisms (Scheme 2) that are studied in this work are analogous to each other. That is to say, these theoretical computations suggest that the reaction mechanisms for all of the photolysis reactions for 1 proceed, as follows:
1(S0) + hν → (1-T1)* → 1-T1 − Min → 1-T1-TS → 1-T1/S0 → 2,3-S0 → 4,5-S0 and 6-S0.
In other words, the reactant (1) is initially excited to its lowest-lying triplet state (T1), which is denoted as (1-T1)*, by absorbing light. From this (1-T1)* point, the molecule relaxes to a local minimum (1-T1-Min) near to the S0 geometry. When the M–M′ bond distance is increased, the transition state (1-T1-TS) is obtained, which is still located on the triplet state surface. The experimental observations [24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41] show that the photolysis reaction for 1-Si-Si is non-adiabatic [49]. The reaction begins from the triplet surface and advances ultimately along the ground singlet state pathway. Therefore, the intersystem crossing point of the T1 and S0 surfaces must play a key role in the mechanistic photolysis reactions of 1. As illustrated in Figure 1, the spin crossover from the triplet state (T1) to the ground singlet state (S0) states occurs in the region of the T1/S0 intersection (1-T1/S0). The results given in Figure 1 show that relaxing through 1-T1/S0 may create the first photoproducts that have doublet radicals (i.e., 2,3-S0; Ph3M· and ·M′Ph2Me; path (I)). When the dispropotionation (path (II)) and the recombination (path (III)) processes are complete, the other singlet photoproducts are produced. These are 4,5-S0 (Ph3M–H and H2C=M′Ph2) and 6-S0.
The computational results outlined in Figure 1 allow for the following conclusions to be drawn:
(1)
The theoretical studies using the M06-2X/6-311G(d) level of theory show that after the direct irradiation of aryldisilanes, arylgermasilanes, and aryldigermanes of the general structure, Ph3M–M′Ph2Me (1), they occupy the lowest excited triplet state and then proceed to M–M′ bond homolysis via the intersystem crossing, to acquire two doublet radicals, 2 and 3 (overall singlet). After the subsequent dispropotionation and recombination procedures, they finally generate a mixture of singlet photoproducts (4–6). It should be emphasized that this is the first theoretical verification that radicals are formed as a result of reactions of the triplet states of Ph3M–M′Ph2Me (1).
(2)
Figure 1 clearly shows that the reactants 1 have an excess of energy, because of the vertical excitation to the Frank-Condon point at the triplet state (1-T1)*, which is larger than the subsequent activation barriers. That is to say, when Ph3M–M′Ph2Me (1) absorbs light, this molecule has sufficient internal energy to overcome the energy barriers to produce various types of photoproducts (2–6) without any difficulty. This theoretical finding for the 1-Si-Si molecule is in good agreement with the experimental evidence [24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41]. Since there are no pertinent experimental or theoretical reports on the photolysis reactions of the compounds, 1-Si-Ge, 1-Ge-Si, and 1-Ge-Ge, this result is a prediction.
(3)
The theoretical observations that are shown in Figure 1 indicate that the relative energies of two monoradical species (Ph3M·and·M′Ph2Me) are higher than those of the other singlet photoproducts (4–6). The quantum yields of the former are estimated to be lower than those of the latter. This prediction is again consistent with the available experimental observations for the 1-Si-Si molecule, in which it is reported that the formation of the corresponding silyl radicals (2 and 3), 1,1-diphenylsilene (5), and the silatriene (6) give respective yields of ca. 20%, 35%, and 42% [30]. Therefore, in the photolysis reactions for compounds 1-Si-Ge, 1-Ge-Si and 1-Ge-Ge, the quantum yields for their singlet photoproducts 4–6 should be larger than those of the other two doublet radicals, 2 and 3 [50]. Molecules 23 01351 i001
(4)
The theoretical conclusions shown in Figure 1 also apply to other group 14 dimetallane analogues, such as 1,1,1-trimethyl-2,2,2-triphenyldimetallanes (7; Ph3M–M′Me3; M and M′ = Si and Ge) and 1,1,1,2,2-pentamethyl-2-phenyldimetallanes (8; PhMe2M–M′Me3; M and M′ = Si and Ge). That is to say, the direct irradiation of these compounds produces the triplet species, which then mainly results in M–M′ bond homolysis to generate the formation of a radical and other singlet photoproducts (similar to 4–6), via radical disproportionation and recombination. Indeed, some earlier experimental studies of 7d by Mochida and Hayashi [51] and a related those for series of molecules (8b–8d), as reported by Mochida and Gaspar [52,53] and their co-workers, show similar results that are in reasonable agreement with these theoretical predictions.
In conclusion, this M06-2X/6-311G(d) study presents the first theoretical explanation for the photolytic mechanisms of group 14 dimetallanes that contain a M–M′ single bond. This work demonstrates that the spin crossover plays a central role in the photolysis reactions of these compounds, from the excited triplet state to singlet ground state. In principle, the theoretical evidence that is given by this study demonstrates that both the potential energy surfaces and the order of the photochemical reactivity are similar for these group 14 dimetallanes, regardless of whether silicon or germanium elements are concerned. This may be because silicon and germanium are quite analogous to each other, in terms of both their atomic radius (117 pm and 122 pm for silicon and germanium, respectively) and their chemical properties [54,55]. Therefore, their photolytic behavior should be analogous, as outlined in Figure 1.
It is hoped that this work will stimulate further study of the photolysis reactions of substituted group 14 dimetallanes that have a M–M′ σ bond.

Author Contributions

S.-H.S. performed the theoretical calculations; M.-D.S. wrote the paper.

Acknowledgments

The authors are grateful to the National Center for High-Performance Computing of Taiwan for generous amounts of computing time, and the Ministry of Science and Technology of Taiwan for the financial support. In particular, one of the authors (M.-D.S.) also wishes to thank Michael A. Robb, S. Wilsey, Michael J. Bearpark, (University of London, UK) and Massimo Olivucci (Universita degli Sstudi di Siena, Italy), for their encouragement and support during his stay in London. Special thanks are also due to reviewers 1, 2, and 3 for very helpful suggestions and comments.

Conflicts of Interest

The authors declare no conflict of interest.

References and Notes

  1. Steinmetz, M.G. Organosilane Photochemistry. Chem. Rev. 1995, 95, 1527–1588. [Google Scholar] [CrossRef]
  2. Brook, A.G.; Brook, M.A. The Chemistry of Silenes. Adv. Organomet. Chem. 1996, 39, 71–158. [Google Scholar]
  3. Brook, A.G. The Chemistry of Organic Silicon Compounds; Rappoport, Z., Apeloig, Y., Eds.; John Wiley and Sons: New York, NY, USA, 1998; pp. 1233–1310. [Google Scholar]
  4. Kira, M.; Miyazawa, T. The Chemistry of Organic Silicon Compounds; Rappoport, Z., Apeloig, Y., Eds.; John Wiley & Sons: New York, NY, USA, 1998; pp. 1311–1337. [Google Scholar]
  5. Ohshita, J.; Niwa, H.; Ishikawa, M. Silicon−Carbon Unsaturated Compounds. 59. Stereochemistry in Addition of Carbonyl Compounds to Silenes Generated Photochemically from meso- and rac-1,2-Diethyl-1,2-dimethyldiphenyldisilane. Organometallics 1996, 15, 4632–4638. [Google Scholar] [CrossRef]
  6. Ohshita, J.; Niwa, H.; Ishikawa, M.; Yamabe, T.; Yoshii, T.; Nakamura, K. Silicon−Carbon Unsaturated Compounds. 57. Photolysis of meso- and racemic-1,2-Diethyl-1,2-dimethyldiphenyldisilane, Direct Evidence for a Concerted 1,3-Silyl Shift to ortho-Carbon in the Phenyl Ring. J. Am. Chem. Soc. 1996, 118, 6853–6859. [Google Scholar] [CrossRef]
  7. Ishikawa, M.; Fuchikami, T.; Sugaya, T.; Kumada, M. Photolysis of Organopolysilanes. Novel Addition Reaction of Aryl Substituted Disilanes to Olefins. J. Am. Chem. Soc. 1975, 97, 5923–5924. [Google Scholar] [CrossRef]
  8. Ishikawa, M.; Fuchikami, T.; Kumada, M. Photochemically Generated Silicon-carbon Double-bonded Intermidiates: II. Photolysis of Aryldisilanes in the Presence of Dienes. J. Organomet. Chem. 1976, 118, 139–153. [Google Scholar] [CrossRef]
  9. Ishikawa, M.; Fuchikami, T.; Kumada, M. Photochemically Generated Silicon—Carbon Double-bonded Intermediates: V. Photolysis of Arylpentamethyldisilanes in the Presence of Carbonyl Compounds. J. Organomet. Chem. 1977, 133, 19–28. [Google Scholar] [CrossRef]
  10. Sluggett, G.W.; Leigh, W.J. Photochemistry of 1,2-Di-tert-butyl-1,1,2,2-tetraphenyldisilane, a Clean, Direct Source of Arylalkylsilyl Radicals. Organometallics 1992, 11, 3731–3736. [Google Scholar] [CrossRef]
  11. Miller, R.D.; Michl, J. Polysilane High Polymers. Chem. Rev. 1989, 89, 1359–1410. [Google Scholar] [CrossRef]
  12. West, R. The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; John Wiley & Sons: New York, NY, USA, 1989; pp. 1207–1240. [Google Scholar]
  13. Michl, J. Solution Photophysics and Electronic Structure of Polysilanes. Synthet. Met. 1992, 50, 367–386. [Google Scholar] [CrossRef]
  14. Mazieres, S.; Raymond, M.K.; Raabe, G.; Prodi, A.; Michl, J. [2]Staffane Rod as a Molecular Rack for Unraveling Conformer Properties: Proposed Singlet Excitation Localization Isomerism in anti,anti,anti-Hexasilanes. J. Am. Chem. Soc. 1997, 119, 6682–6683. [Google Scholar] [CrossRef]
  15. Kira, M.; Sakamoto, K.; Sakurai, H. Photochemistry of Dibenzo-1,1,2,2-tetramethyl-1,2-disilacyclohexa-3,5-diene and the Germanium Analog. Exclusive Extrusion of the Divalent Species. J. Am. Chem. Soc. 1983, 105, 7469–7470. [Google Scholar] [CrossRef]
  16. Leigh, W.J.; Sluggett, G.W. Aryldisilane Photochemistry. A Kinetic and Product Study of the Mechanism of Alcohol Additions to Transient Silenes. J. Am. Chem. Soc. 1994, 116, 10468–10476. [Google Scholar] [CrossRef]
  17. Toltl, N.P.; Leigh, W.J. Synthesis and isolation of stable 1,2-siloxetanes from reaction of transient silenes with acetone. Organometallics 1996, 15, 2554–2561. [Google Scholar] [CrossRef]
  18. Toltl, N.P.; Leigh, W.J. Direct Detection of 1,1-Diphenylgermene in Solution and Absolute Rate Constants for Germene Trapping Reactions. J. Am. Chem. Soc. 1998, 120, 1172–1178. [Google Scholar] [CrossRef]
  19. Leigh, W.J. Kinetics and Mechanisms of the Reactions of Si=C and Ge=C Double Bonds. Pure Appl. Chem. 1999, 71, 453–462. [Google Scholar] [CrossRef]
  20. Ishikawa, M.; Fuchikami, T.; Kumada, M. Photochemically Generated Silicon—Carbon Double-bonded Intermediates: III. The Reaction of p-Tolylpentamethyldisilane with Methanol and Methanol-d1. J. Organomet. Chem. 1976, 118, 155–160. [Google Scholar] [CrossRef]
  21. Shizuka, H.; Okazaki, K.; Tanaka, M.; Ishikawa, M.; Sumitani, M.; Yoshihara, K. Intramolecular 2pπ* → 3dπ Charge Transfer in the Excited State of Phenyldisilane Studied by Picosecond and Nanosecond Laser Spectroscopy. Chem. Phys. Lett. 1985, 113, 89–92. [Google Scholar] [CrossRef]
  22. Sakurai, H.; Nakadaira, Y.; Kira, M.; Sugiyama, H.; Yoshida, K.; Takiguchi, T. Chemistry of Organosilicon Compounds: CXXIX. Evidence for Formation of Free Silyl Radicals in the Photolysis of Aryldisilanes. J. Organomet. Chem. 1980, 184, C36–C40. [Google Scholar] [CrossRef]
  23. Boudjouk, P.; Roberts, J.R.; Golino, C.M.; Sommer, L.H. Photochemical Dehydrosilylation of Pentaphenylmethyldisilane. Generation and Trapping of an Unstable Intermediate Containing a Silicon-carbon Double Bond or Its Equivalent. J. Am. Chem. Soc. 1972, 94, 7926–7927. [Google Scholar] [CrossRef]
  24. Ishikawa, M. Photolysis of Organopolysilanes. Generation and Reactions of Silicon-carbon Double-Bonded Intermediates. Pure Appl. Chem. 1978, 50, 11–18. [Google Scholar] [CrossRef]
  25. Sakurai, H. Spectra and Some Reactions of Organopolysilanes. J. Organomet. Chem. 1980, 200, 261–286. [Google Scholar] [CrossRef]
  26. Ishikawa, M.; Kumada, M. Photochemistry of Organopolysilanes. Adv. Organomet. Chem. 1981, 19, 51–95. [Google Scholar]
  27. Shizuka, H.; Hiratsuka, H. Photochemistry and Photophysics of Organosilicon Compounds. Res. Chem. Intermed. 1992, 18, 131–182. [Google Scholar] [CrossRef]
  28. Kira, M.; Miyazawa, T.; Sugiyama, H.; Yamaguchi, M.; Sakurai, H. sp* Orthogonal Intramolecular Charge-transfer (OICT) Excited States and Photoreaction Mechanism of Trifluoromethyl-substituted Phenyldisilanes. J. Am. Chem. Soc. 1993, 115, 3116–3124. [Google Scholar] [CrossRef]
  29. Sluggett, G.W.; Leigh, W.J. Reactive Intermediates from the Photolysis of Methylpentaphenyl- and pentamethylphenyldisilane. J. Am. Chem. Soc. 1992, 114, 1195–1201. [Google Scholar] [CrossRef]
  30. Sluggett, G.W.; Leigh, W.J. Aryldisilane Photochemistry. The Role of Silyl Free Radicals in Silene Formation from Photolysis of Methylpentaphenyldisilane. Organometallics 1994, 13, 1005–1013. [Google Scholar] [CrossRef]
  31. Leigh, W.J.; Sluggett, G.W. Triplet-state Photoreactivity of Phenyldisilanes. J. Am. Chem. Soc. 1993, 115, 7531–7532. [Google Scholar] [CrossRef]
  32. Leigh, W.J.; Sluggett, G.W. Aryldisilane Photochemistry. Substituent and Solvent Effects on the Photochemistry of Aryldisilanes and the Reactivity of 1,3,5-(1-sila)Hexatrienes. Organometallics 1994, 13, 269–281. [Google Scholar] [CrossRef]
  33. Sakurai, H. Silicon Chemistry; Corey, J.Y., Corey, E.Y., Gaspar, P.P., Eds.; Ellis Horwood: Chichester, UK, 1988; pp. 163–172. [Google Scholar]
  34. Brook, A.G. The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York, NY, USA, 1989; pp. 965–1005. [Google Scholar]
  35. Braddock-Wilking, J.; Chiang, M.Y.; Gaspar, P.P. Photolysis of 1,3-Dimesitylhexamethyltrisilane and 1,2-Dimesityltetramethyldisilane. Organometallics 1993, 12, 197–209. [Google Scholar] [CrossRef]
  36. Ishikawa, M.; Kikuchi, M.; Kunai, A.; Takeuchi, T.; Tsukihara, T.; Kido, M. Silicon-carbon Unsaturated Compounds. 47. Dimerization of Silenes Generated from 1,4-bis(pentamethyldisilanyl)Benzene and 1-(pentamethyldisilanyl)-4-(trimethylsilyl)Benzene and the Molecular Structure of a Dimer. Organometallics 1993, 12, 3474–3479. [Google Scholar] [CrossRef]
  37. Ishikawa, M.; Oda, M.; Nishimura, K.; Kumada, M. Silicon–Carbon Unsaturated Compounds. XVI. Photorearrangement of an Adduct Derived from Reaction of a Silicon–Carbon Unsaturated Compound with t-Butyl Alcohol. Bull. Chem. Soc. Jpn. 1983, 56, 2795–2798. [Google Scholar] [CrossRef]
  38. Ishikawa, M.; Sakamoto, H. Silicon-carbon Unsaturated Compounds: XXXII. Photolysis of Tolyl- and xylylpentamethyldisilanes. J. Organomet. Chem. 1991, 414, 1–10. [Google Scholar] [CrossRef]
  39. Ishikawa, M.; Fuchikami, T.; Kumada, M. Photochemically Generated Silicon—Carbon Double-bonded Intermediates IV. Photolysis of 1-Alkenyldisilanes. J. Organomet. Chem. 1976, 117, C58–C62. [Google Scholar] [CrossRef]
  40. Ishikawa, M.; Fuchikami, T.; Kumada, M. Photochemically Generated Silicon-carbon Double-bonded Intermediates: VII. A New Route to Silaethene Derivatives from 1-Alkenyldisilanes. J. Organomet. Chem. 1978, 149, 37–48. [Google Scholar] [CrossRef]
  41. Leigh, W.J.; Toltl, N.P.; Apodaca, P.; Castruita, M.; Pannell, K.H. Photochemistry of Group 14 1,1,1-Trimethyl-2,2,2-triphenyldimetallanes (Ph3MM‘Me3; M, M′ = Si, Ge). Direct Detection and Characterization of Silene and Germene Reactive Intermediates. Organometallics 2000, 19, 3232–3241. [Google Scholar] [CrossRef]
  42. Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G.A.; et al. Gaussian 09, Revision A. 02; Gaussian, Inc.: Wallingford CT, USA, 2013. [Google Scholar]
  43. Zhao, Y.; Truhlar, D.G. Density Functionals with Broad Applicability in Chemistry. Acc. Chem. Res. 2008, 41, 157–167. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  44. Casida, M.E.; Jamorski, C.; Casida, K.C.; Salahub, D.R. Molecular Excitation Energies to High-lying Bound States from Time-dependent Density-functional Response Theory: Characterization and Correction of the Time-dependent Local Density Approximation Ionization Threshold. J. Chem. Phys. 1998, 108, 4439–4449. [Google Scholar] [CrossRef]
  45. Stramann, R.E.; Scuseria, G.E.; Frisch, M.J. An Efficient Implementation of Time-dependent Density-functional Theory for the Calculation of Excitation Energies of Large Molecules. J. Chem. Phys. 1998, 109, 8218–8224. [Google Scholar] [CrossRef]
  46. Harvey, J.N.; Aschi, M.; Schwarz, H.; Koch, W. The Singlet and Triplet States of Phenyl Cation. A Hybrid Approach for Locating Minimum Energy Crossing Points between Non-interacting Potential Energy Surfaces. Theor. Chem. Acc. 1998, 99, 95–99. [Google Scholar] [CrossRef]
  47. Harvey, J.N.; Aschi, M. Spin-forbidden Dehydrogenation of Methoxy Cation: A Statistical View. Phys. Chem. Chem. Phys. 1999, 1, 5555–5563. [Google Scholar] [CrossRef]
  48. The points in the graphs of Figure 2 were obtained using fixed potential energy surface scans.
  49. However, the absorption, fluorescence, and phosphorescence spectra in Reference 27 indicate S1 and T1 energies of ca. 105 and 78 kcal mol−1 for PhMe2Si SiMe3. UV absorption and fluorescence spectra are available for 1-Si-Si in Reference 29, and place its S1 (0-0) energy at ca. 95 kcal mol−1.
  50. However, it is believed that photolysis of 1-Si-Ge, 1-Ge-Si, and 1-Ge-Ge in more polar solvents can lead to high yields of the corresponding silyl and/or germyl radicals, rather than other singlet photoproducts.
  51. Mochida, K.; Wakasa, M.; Sakaguchi, Y.; Hayashi, H. Photochemical Reactions of Aryl-Substituted Digermanes through a Pair of Organogermyl Radicals. Bull. Chem. Soc. Jpn. 1991, 64, 1889–1895. [Google Scholar] [CrossRef]
  52. Mochida, K.; Kikkawa, H.; Nakadaira, Y. Photochemical Reactions of Aryl-substituted Catenates of Group 4B Elements, PhMe2E-E’Me3 (E, E’ = Si and Ge). Formation of a Radical Pair. J. Organomet. Chem. 1991, 412, 9–19. [Google Scholar] [CrossRef]
  53. Bobbitt, K.L.; Maloney, V.M.; Gaspar, P.P. New Photochemical Routes to Germylenes and Germenes and Kinetic Evidence Concerning the Germylene-diene Addition Mechanism. Organometallics 1991, 10, 2772–2777. [Google Scholar] [CrossRef]
  54. Zumdahl, S.S.; DeCoste, D.J. Chemical Principles; Mary Finch: New York, NY, USA, 2013; Chapter 18; pp. 893–903. [Google Scholar]
  55. It should be mentioned here that triplet/ground state singlet conversions are common in photoreactions that produce two non-coupled radical centers. See, for example: Mohamed, R.K.; Mondal, S.; Jorner, K.; Delgado, T.F.; Lobodin, V.V.; Ottosson, H.; Alabugin, I.V. The Missing C1–C5 Cycloaromatization Reaction: Triplet State Antiaromaticity Relief and Self-Terminating Photorelease of Formaldehyde for Synthesis of Fulvenes from Enynes. J. Am. Chem. Soc. 2015, 137, 15441–15450.
Sample Availability: Samples of the compounds are not available from the authors.
Molecules 23 01351 sch001 550
Scheme 1. The photochemical reactions of aryldisilane.
Scheme 1. The photochemical reactions of aryldisilane.
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Scheme 2. The experimental results. See the text.
Scheme 2. The experimental results. See the text.
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Molecules 23 01351 g001a 550Molecules 23 01351 g001b 550
Figure 1. The potential energy profiles for the photochemical isomerization models of Ph3M–M′Ph2Me (M and M′ = Si and Ge; (i–iv)). The star represents Frank–Condon. For more information see the text.
Figure 1. The potential energy profiles for the photochemical isomerization models of Ph3M–M′Ph2Me (M and M′ = Si and Ge; (i–iv)). The star represents Frank–Condon. For more information see the text.
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Figure 2. The minimum-energy pathway for a M–M′ bond cleavage in Ph3M–M′Ph2Me (M and M′ = Si and Ge) along the distance, r, optimized for the S0 and T1 states at the M06-2X/6-311G(d) level of theory.
Figure 2. The minimum-energy pathway for a M–M′ bond cleavage in Ph3M–M′Ph2Me (M and M′ = Si and Ge) along the distance, r, optimized for the S0 and T1 states at the M06-2X/6-311G(d) level of theory.
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Figure 3. The optimized structures for the photochemical isomerization model of Ph3Si–SiPh2Me at the M06-2X/6-311G(d) level of theory.
Figure 3. The optimized structures for the photochemical isomerization model of Ph3Si–SiPh2Me at the M06-2X/6-311G(d) level of theory.
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Molecules 23 01351 g004 550
Figure 4. The optimized structures for the photochemical isomerization model of Ph3Si–GePh2Me at the M06-2X/6-311G(d) level of theory.
Figure 4. The optimized structures for the photochemical isomerization model of Ph3Si–GePh2Me at the M06-2X/6-311G(d) level of theory.
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Molecules 23 01351 g005 550
Figure 5. The optimized structures for the photochemical isomerization model of Ph3Ge–SiPh2Me at the M06-2X/6-311G(d) level of theory.
Figure 5. The optimized structures for the photochemical isomerization model of Ph3Ge–SiPh2Me at the M06-2X/6-311G(d) level of theory.
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Molecules 23 01351 g006 550
Figure 6. The optimized structures for the photochemical isomerization model of Ph3Ge–GePh2Me at the M06-2X/6-311G(d) level of theory.
Figure 6. The optimized structures for the photochemical isomerization model of Ph3Ge–GePh2Me at the M06-2X/6-311G(d) level of theory.
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Su, S.-H.; Su, M.-D. Theoretical Study of the Photolysis Mechanisms of Methylpentaphenyldimetallanes (Ph3MM′Ph2Me; M, M′ = Si and Ge). Molecules 2018, 23, 1351. https://doi.org/10.3390/molecules23061351

AMA Style

Su S-H, Su M-D. Theoretical Study of the Photolysis Mechanisms of Methylpentaphenyldimetallanes (Ph3MM′Ph2Me; M, M′ = Si and Ge). Molecules. 2018; 23(6):1351. https://doi.org/10.3390/molecules23061351

Chicago/Turabian Style

Su, Shih-Hao, and Ming-Der Su. 2018. "Theoretical Study of the Photolysis Mechanisms of Methylpentaphenyldimetallanes (Ph3MM′Ph2Me; M, M′ = Si and Ge)" Molecules 23, no. 6: 1351. https://doi.org/10.3390/molecules23061351

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