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Molbank 2020, 2020(1), M1110; https://doi.org/10.3390/M1110

Communication
Half-Sandwich Arene-Osmium(II) Complexes with Phosphinite Ligands
1
Laboratorio de Compuestos Organometálicos y Catálisis (Unidad Asociada al CSIC), Centro de Innovación en Química Avanzada (ORFEO-CINQA), Departamento de Química Orgánica e Inorgánica, IUQOEM, Facultad de Química, Universidad de Oviedo, Julián Clavería 8, E-33006 Oviedo, Spain
2
Departamento de Química Física y Analítica, Facultad de Química, Universidad de Oviedo, Julián Clavería 8, E-33006 Oviedo, Spain
*
Authors to whom correspondence should be addressed.
Received: 17 December 2019 / Accepted: 15 January 2020 / Published: 17 January 2020

Abstract

:
The synthesis of a series of arene-osmium(II) complexes containing phosphinite-type ligands, namely, [OsCl2(η6-p-cymene){R2PO(CH2)nPh}] (R = Ph, n = 1 (4a), 2 (4b), 3 (4c); R = iPr, n = 1 (5a), 2 (5b), 3 (5c)) and [OsCl2(η6-benzene){iPr2PO(CH2)2Ph}] (7), is presented. All these compounds were characterized by elemental analysis and multinuclear NMR spectroscopy (31P{1H}, 1H and 13C{1H}), and the structure of [OsCl2(η6-p-cymene){Ph2PO(CH2)3Ph}] (4c) unequivocally confirmed through a single-crystal X-ray diffraction study. Attempts to generate the tethered species [OsCl2{η6:κ1(P)-C6H5(CH2)nOPR2}] by intramolecular exchange of the coordinated arene in 4-5a-c or 7, upon thermal or MW heating, failed.
Keywords:
organometallic compounds; osmium complexes; phosphinite ligands; half-sandwich complexes

1. Introduction

We recently described the preparation of the ruthenium(II) complexes [RuCl2{η6:κ1(P)-C6H5(CH2)nOPR2}] (R = Ph, iPr; n = 1, 2, 3; see Scheme 1) starting from the corresponding phosphinites R2PO(CH2)nPh and the chloride-bridged dimers [{RuCl(μ-Cl)(η6-arene)}2] (arene = p-cymene, benzene), along with their structural characterization by single-crystal X-ray diffraction [1].
These compounds are of interest as they represent rare examples of tethered arene-ruthenium(II) complexes incorporating pendant phosphinite donors [2,3,4], a field largely dominated by the use of arene ligands featuring classical phosphines as the pendant donor group [1,5]. Moreover, we also demonstrated their utility as catalysts for the cross dehydrogenative coupling of hydrosilanes with alcohols [1], a process of relevance since it allows a simple access to useful alkoxysilane reagents [6,7], and with potential application in the field of hydrogen storage and production [8]. As shown in Scheme 1, the synthesis of complexes [RuCl2{η6:κ1(P)-C6H5(CH2)nOPR2}] was accomplished in two steps involving the initial cleavage of the chloride bridges of [{RuCl(μ-Cl)(η6-arene)}2] by the phosphinites, to generate the corresponding mononuclear adducts [RuCl2(η6-arene){R2PO(CH2)nPh}], and a subsequent intramolecular exchange of the coordinated arene under thermal conditions (120 °C) [1].
On the other hand, tethered osmium complexes are uncommon, and most of the examples currently known involve η5-cyclopentadienyl-type ligands connected to P- [9,10], N- [10], C- [11], or Sn-donor [12] groups. In fact, the only tethered η6-arene-osmium(II) derivatives described to date in the literature are compounds B, synthesized by Xia and co-workers from the reactions of the hydride-alkenylcarbyne complex A with allenoates (Scheme 2) [13].
All these facts prompted us to study the reactivity of the osmium(II) dimers [{OsCl(μ-Cl)(η6-arene)}2] (arene = p-cymene, benzene) towards phosphinites R2PO(CH2)nPh as a potential entry to tethered species related to those previously described for ruthenium.

2. Results and Discussion

As the starting point of our investigation, we synthesized the mononuclear complexes [OsCl2(η6-p-cymene){R2PO(CH2)nPh}] (R = Ph, n = 1 (4a), 2 (4b), 3 (4c); R = iPr, n = 1 (5a), 2 (5b), 3 (5c)) by reacting the cymene-osmium dimer [{OsCl(μ-Cl)(η6-p-cymene)}2] (3) with the appropriate phosphinite ligand R2PO(CH2)nPh (1-2a-c). As shown in Scheme 3, the cleavage of the chloride bridges of 3 proceeded quickly and cleanly in tetrahydrofuran at room temperature, affording complexes 4-5a-c in good yields (67–85%).
Compounds [OsCl2(η6-p-cymene){R2PO(CH2)nPh}] (4-5a-c) were isolated as air-stable yellow solids and fully characterized by means of elemental analyses and multinuclear NMR spectroscopy (31P{1H}, 1H and 13C{1H}; copies of the spectra are included in the Supplementary Materials file), being the data obtained in complete accord with the proposed formulations. In particular, the 31P{1H} NMR spectra confirmed the coordination of the phosphinite ligands to the osmium center by the appearance of singlet resonances shielded 40–50 ppm with respect to those of the uncoordinated phosphinites 1-2a-c (see Table 1). Concerning the 1H and 13C{1H} NMR spectra, they showed the expected signals for the η6-coordinated p-cymene unit, as well as those of the respective P-donor ligand (details are given in the Materials and Methods section). For the former, only two signals for the aromatic CH proton and carbon atoms of the cymene ring were observed, which is in full accord with the presence of a symmetry plane in the complexes. Interestingly, while the POCH2 carbon in complexes 4a-c resonates as a singlet, a doublet signal was observed for 5a-c (2JPC = 10–12 Hz). This difference, previously observed in the analogous ruthenium complexes [1], is probably associated with the higher steric requirements of the iPr vs. Ph groups that would affect the corresponding P–O–C bond angle and consequently the P–C coupling.
Additionally, the structure of [OsCl2(η6-p-cymene){Ph2PO(CH2)3Ph}] (4c) was unequivocally confirmed by single-crystal X-ray diffraction. An ORTEP-type view of the molecule, along with selected bond distances and angles, is shown in Figure 1. The osmium atom features the expected pseudo-octahedral three-legged piano-stool geometry, with metrical parameters around the metallic core comparing well with those previously described for the related complexes [OsCl2(η6-p-cymene)(PPh3)] [14] and [OsCl2(η6-p-cymene)(PPh2OH)] [15]. The Os(1)-P(1) and P(1)-O(1) bond distances (2.318(2) and 1.611(4) Å, respectively) are also comparable to those found in the structure of [OsCl2(η6-p-cymene)(PPh2OH)] (Os-P = 2.321(1) Å and P-O = 1.603(4) Å) [15].
Once characterized, compounds 4-5a-c were next evaluated as potential precursors of the corresponding tethered species [OsCl2{η6:κ1(P)-C6H5(CH2)nOPR2}]. Against our wishes, heating solutions of 4-5a-c in 1,2-dichloethane (DCE) or toluene at 120 °C did not lead to the intramolecular exchange of the coordinated arene, even after long reaction periods (24 h). In all the cases, complexes 4-5a-c were recovered unchanged. Application of microwaves irradiation (MW), instead of conventional oil-bath thermal heating, was also unsuccessful. In view of this, we decided to explore the possibility of using related osmium(II) precursors containing benzene instead of p-cymene, as, in our previous work with ruthenium, the displacement of the η6-coordinated benzene ligand proceeded in general much faster than that of the p-cymene one (Scheme 1) [1]. To this end, complex [OsCl2(η6-benzene){iPr2PO(CH2)2Ph}] (7) was synthesized by reacting dimer [{OsCl(μ-Cl)(η6-benzene)}2] (6) with iPr2PO(CH2)2Ph (2b) (see Scheme 4). Due to the poor solubility of 6, the bridge-splitting reaction required in this case harsher conditions (refluxing in toluene for 24 h), and 7 could only be isolated in moderate yield (synthetic details and characterization data are included in the Materials and Methods section). Unfortunately, all attempts to generate [OsCl2{η6:κ1(P)-C6H5(CH2)2OPiPr2}] from 7, upon thermal or MW heating, also failed.
The marked differences in reactivity found between the osmium complexes herein synthesized, i.e., 4-5a-c and 7, and their ruthenium counterparts can be ascribed to the higher activation energies associated to ligand substitution processes in osmium vs. ruthenium complexes, a fact well documented in the literature [16,17,18].

3. Materials and Methods

All manipulations were carried out under an inert atmosphere of dry argon employing vacuum-line and Schlenk techniques. Solvents were dried and purified before use, according to standard procedures [19]. The phosphinite ligands 1-2a-c [20,21] and the osmium(II) dimers 3 [22] and 6 [23] were synthesized as described in the literature. A Bruker DPX-300 instrument (Billerica, MA, USA) was employed for NMR measurements (all the spectra were recorded at room temperature). For the 13C{1H} and 1H NMR chemical shifts, the residual signal of deuterated solvent was employed as reference, while for the 31P{1H} NMR ones 85% H3PO4 was used as external standard. DEPT experiments were carried out for all the compounds synthesized. Elemental analyses were provided by the Analytical Service of the Instituto de Investigaciones Químicas (IIQ-CSIC) of Seville using a LECO TruSpec CHN analyzer (St. Joseph, MI, USA).

3.1. General Procedure for the Preparation of Complexes [OsCl26-p-cymene){R2PO(CH2)nPh}] (R = Ph, n = 1 (4a), 2 (4b), 3 (4c); R = iPr, n = 1 (5a), 2 (5b), 3 (5c))

A suspension of dimer [{OsCl(μ-Cl)(η6-p-cymene)}2] (3; 0.184 g, 0.3 mmol) and the corresponding phosphinite ligand R2PO(CH2)nPh (1-2a-c; 0.8 mmol) in THF (20 mL) was stirred for 1 h at room temperature. The resulting solution was then evaporated to dryness, the oily residue formed dissolved in the minimum amount of CH2Cl2 (ca. 5 mL), and the product precipitated by adding 20 mL of a diethyl ether/hexane mixture (1:1 v/v). The same precipitation procedure was repeated twice and the yellow solid was finally washed with diethyl ether (5 mL) and dried in vacuo. Characterization data for the resulting complexes 4-5a-c are as follows.

3.1.1. [OsCl2(η6-p-cymene)(Ph2POCH2Ph)] (4a)

Yield: 0.351 g (85%). 31P{1H} NMR (121 MHz, CDCl3): δ = 64.2 (s) ppm. 1H NMR (300 MHz, CDCl3): δ = 8.00–7.93 (m, 4H, Ph), 7.43–7.28 (m, 11H, Ph), 5.41 and 5.35 (d, 2H each, 3JHH = 5.7 Hz, CH of p-cymene), 4.86 (d, 2H, 3JPH = 5.4 Hz, OCH2), 2.54 (sept, 1H, 3JHH = 6.9 Hz, CHMe2), 1.96 (s, 3H, Me), 1.10 (d, 6H, 3JHH = 6.9 Hz, CHMe2) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ = 137.8 (d, 3JPC = 3.5 Hz, Cipso of Ph), 136.2 (d, 1JPC = 57.0 Hz, Cipso of PPh), 132.6 (d, JPC = 11.0 Hz, CHortho or CHmeta of PPh), 130.9 (s, CHpara of PPh), 128.4 and 127.0 (s, CHortho and CHmeta of Ph), 127.8 (d, JPC = 15.5 Hz, CHortho or CHmeta of PPh), 127.7 (s, CHpara of Ph), 103.9 and 91.1 (s, C of p-cymene), 81.8 (d, 2JPC = 3.2 Hz, CH of p-cymene), 80.0 (d, 2JPC = 4.8 Hz, CH of p-cymene), 68.2 (s, OCH2), 29.8 (s, CHMe2), 22.1 (s, CHMe2), 17.4 (s, Me) ppm. Elemental analysis calcd. (%) for C29H31Cl2OPOs: C 50.65, H 4.54; found: C 50.78, H 4.63.

3.1.2. [OsCl2(η6-p-cymene)(Ph2POCH2CH2Ph)] (4b)

Yield: 0.299 g (71%). 31P{1H} NMR (121 MHz, CDCl3): δ = 63.1 (s) ppm. 1H NMR (300 MHz, CDCl3): δ = 7.85–7.78 (m, 4H, Ph), 7.41–7.25 (m, 11H, Ph), 5.33 and 5.21 (d, 2H each, 3JHH = 5.7 Hz, CH of p-cymene), 3.95 (td, 2H, 3JHH = 6.3 Hz, 3JPH = 5.1 Hz, OCH2), 2.93 (t, 2H, 3JHH = 6.3 Hz, CH2Ph), 2.40 (sept, 1H, 3JHH = 6.9 Hz, CHMe2), 1.87 (s, 3H, Me), 1.10 (d, 6H, 3JHH = 6.9 Hz, CHMe2) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ = 138.7 (s, Cipso of Ph), 136.3 (d, 1JPC = 56.2 Hz, Cipso of PPh), 132.5 (d, JPC = 9.7 Hz, CHortho or CHmeta of PPh), 130.7 (s, CHpara of PPh), 129.3 and 128.4 (s, CHortho and CHmeta of Ph), 127.7 (d, JPC = 8.8 Hz, CHortho or CHmeta of PPh), 126.5 (s, CHpara of Ph), 102.8 and 91.7 (s, C of p-cymene), 81.4 and 80.2 (s, CH of p-cymene), 67.6 (s, OCH2), 37.1 (s, CH2Ph), 29.9 (s, CHMe2), 21.9 (s, CHMe2), 17.1 (s, Me) ppm. Elemental analysis calcd. (%) for C30H33Cl2OPOs: C 51.35, H 4.74; found: C 51.26, H 4.97.

3.1.3. [OsCl2(η6-p-cymene)(Ph2POCH2CH2CH2Ph)] (4c)

Yield: 0.296 g (69%). 31P{1H} NMR (121 MHz, CD2Cl2): δ = 62.2 (s) ppm. 1H NMR (300 MHz, CD2Cl2): δ = 7.93–7.87 (m, 4H, Ph), 7.45–7.18 (m, 11H, Ph), 5.42 and 5.33 (d, 2H each, 3JHH = 5.6 Hz, CH of p-cymene), 3.82–3.76 (m, 2H, OCH2), 2.75 (t, 2H, 3JHH = 7.2 Hz, CH2Ph), 2.49 (sept, 1H, 3JHH = 6.9 Hz, CHMe2), 2.01–1.92 (m, 2H, CH2), 1.95 (s, 3H, Me), 1.13 (d, 6H, 3JHH = 6.9 Hz, CHMe2) ppm. 13C{1H} NMR (100 MHz, CD2Cl2): δ = 141.5 (s, Cipso of Ph), 136.5 (d, 1JPC = 56.7 Hz, Cipso of PPh), 132.5 (d, JPC = 10.8 Hz, CHortho or CHmeta of PPh), 130.7 (s, CHpara of PPh), 128.4 (s, CHortho and CHmeta of Ph), 127.7 (d, JPC = 10.2 Hz, CHortho or CHmeta of PPh), 125.9 (s, CHpara of Ph), 102.8 and 91.2 (s, C of p-cymene), 81.8 (s, CH of p-cymene), 80.1 (d, 2JPC = 5.4 Hz, CH of p-cymene), 66.3 (s, OCH2), 32.1 (d, 3JPC = 7.9 Hz, CH2), 32.0 (s, CH2Ph), 29.9 (s, CHMe2), 21.9 (s, CHMe2), 17.1 (s, Me) ppm. Elemental analysis calcd. (%) for C31H35Cl2OPOs: C 59.43, H 5.63; found: C 52.02, H 4.93.

3.1.4. [OsCl2(η6-p-cymene)(iPr2POCH2Ph)] (5a)

Yield: 0.249 g (67%). 31P{1H} NMR (121 MHz, CD2Cl2): δ = 103.5 (s) ppm. 1H NMR (300 MHz, CD2Cl2): δ = 7.45–7.38 (m, 5H, Ph), 5.62 and 5.55 (d, 2H each, 3JHH = 5.9 Hz, CH of p-cymene), 5.02 (d, 2H, 3JPH = 4.2 Hz, OCH2), 3.15–2.98 (m, 2H, PCHMe2), 2.74 (sept, 1H, 3JPH = 6.9 Hz, CHMe2), 2.17 (s, Me), 1.43 (dd, 6H, 3JPH = 13.8 Hz, 3JHH = 7.2 Hz, PCHMe2), 1.31 (dd, 6H, 3JPH = 15.3 Hz, 3JHH = 7.2 Hz, PCHMe2), 1.20 (d, 6H, 3JHH = 6.9 Hz, CHMe2) ppm. 13C{1H} NMR (100 MHz, CD2Cl2): δ = 137.7 (d, 3JPC = 6.4 Hz, Cipso of Ph), 128.6 and 127.5 (s, CHortho and CHmeta of Ph), 128.1 (s, CHpara of Ph), 98.8 and 91.1 (s, C of p-cymene), 80.5 (d, 2JPC = 3.8 Hz, CH of p-cymene), 80.3 (d, 2JPC = 3.6 Hz, CH of p-cymene), 69.4 (d, 2JPC = 10.2 Hz, OCH2), 29.8 (s, CHMe2), 28.5 (d, 1JPC = 27.0 Hz, PCHMe2), 22.1 (s, CHMe2), 17.5 and 17.1 (s, PCHMe2), 17.4 (s, Me) ppm. Elemental analysis calcd. (%) for C23H35Cl2OPOs: C 44.58, H 5.69; found: C 44.80, H 5.80.

3.1.5. [OsCl2(η6-p-cymene)(iPr2POCH2CH2Ph)] (5b)

Yield: 0.277 g (73%). 31P{1H} NMR (121 MHz, CD2Cl2): δ = 103.3 (s) ppm. 1H NMR (300 MHz, CD2Cl2): δ = 7.41–7.29 (m, 5H, Ph), 5.50 and 5.44 (d, 2H each, 3JHH = 5.8 Hz, CH of p-cymene), 4.24 (td, 2H, 3JHH = 6.3 Hz, 3JPH = 3.9 Hz, OCH2), 3.04 (t, 2H, 3JHH = 6.3 Hz, CH2Ph), 2.99–2.89 (m, 2H, PCHMe2), 2.74 (sept, 1H, 3JPH = 6.8 Hz, CHMe2), 2.14 (s, Me), 1.35 (dd, 6H, 3JPH = 13.8 Hz, 3JHH = 7.2 Hz, PCHMe2), 1.24–1.17 (m, 12H, PCHMe2 and PCHMe2) ppm. 13C{1H} NMR (100 MHz, CD2Cl2): δ = 138.1 (s, Cipso of Ph), 128.9 and 128.6 (s, CHortho and CHmeta of Ph), 126.7 (s, CHpara of Ph), 97.8 and 89.5 (s, C of p-cymene), 81.1 (d, 2JPC = 3.5 Hz, CH of p-cymene), 80.6 (d, 2JPC = 3.4 Hz, CH of p-cymene), 68.7 (d, 2JPC = 12.0 Hz, OCH2), 37.4 (d, 3JPC = 5.9 Hz, CH2Ph), 29.9 (s, CHMe2), 27.6 (d, 1JPC = 26.4 Hz, PCHMe2), 22.2 (s, CHMe2), 17.3 (s, PCHMe2), 16.7 (s, Me) ppm. Elemental analysis calcd. (%) for C24H37Cl2OPOs: C 45.49, H 5.89; found: C 45.65, H 5.96.

3.1.6. [OsCl2(η6-p-cymene)(iPr2POCH2CH2CH2Ph)] (5c)

Yield: 0.307 g (79%). 31P{1H} NMR (121 MHz, CDCl3): δ = 102.3 (s) ppm. 1H NMR (CDCl3): δ = 7.37–7.22 (m, 5H, Ph), 5.67 and 5.59 (d, 2H each, 3JHH = 5.8 Hz, CH of p-cymene), 4.01–3.96 (m, 2H, OCH2), 3.00–2.90 (m, 3H, CHMe2 and PCHMe2), 2.79 (t, 2H, 3JHH = 7.5 Hz, CH2Ph), 2.21 (s, Me), 2.09–2.03 (m, 2H, CH2), 1.38–1.23 (m, 18H, CHMe2 and PCHMe2) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ = 141.0 (s, Cipso of Ph), 128.6 and 128.2 (s, CHortho and CHmeta of Ph), 126.2 (s, CHpara of Ph), 99.1 and 90.0 (s, C of p-cymene), 80.7 (d, 2JPC = 4.0 Hz, CH of p-cymene), 80.3 (d, 2JPC = 3.9 Hz, CH of p-cymene), 66.9 (d, 2JPC = 11.0 Hz, OCH2), 32.8 (d, 3JPC = 6.0 Hz, CH2), 32.2 (s, CH2Ph), 29.9 (s, CHMe2), 27.9 (d, 1JPC = 26.8 Hz, PCHMe2), 22.5 (s, CHMe2), 17.7 (s, Me), 17.6 and 17.1 (s, PCHMe2), ppm. Elemental analysis calcd. (%) for C25H39Cl2OPOs: C 46.36, H 6.07; found: C 46.23, H 6.01.

3.2. Preparation of Complex [OsCl26-benzene){iPr2PO(CH2)2Ph}] (7)

A suspension of dimer [{OsCl(μ-Cl)(η6-benzene)}2] (6; 0.203 g, 0.3 mmol) and the phosphinite ligand iPr2PO(CH2)2Ph (2b; 0.191 g, 0.8 mmol) in toluene (20 mL) was heated under refluxing conditions for 24 h. The reaction mixture was then filtered over Kieselguhr and the filtrate evaporated to dryness. The resulting oily residue was then dissolved in the minimum amount of CH2Cl2 (~5 mL), and the product precipitated by adding 20 mL of hexane. The same precipitation procedure was repeated twice and the yellow solid was finally washed with hexane (5 mL) and dried in vacuo. Yield: 0.149 g (43%). 31P{1H} NMR (121 MHz, CD2Cl2): δ = 101.0 (s) ppm. 1H NMR (300 MHz, CD2Cl2): δ = 7.38–7.25 (m, 5H, Ph), 5.64 (s, 6H, C6H6), 4.44 (td, 2H, 3JHH = 6.3 Hz, 3JPH = 3.9 Hz, OCH2), 2.99 (t, 2H, 3JHH = 6.3 Hz, CH2Ph), 2.95–2.87 (m, 2H, PCHMe2), 1.30 (dd, 6H, 3JPH = 14.7 Hz, 3JHH = 7.2 Hz, PCHMe2), 1.20 (dd, 6H, 3JPH = 15.0 Hz, 3JHH = 7.2 Hz, PCHMe2) ppm. 13C{1H} NMR (100 MHz, CD2Cl2): δ = 138.6 (s, Cipso of Ph), 129.1 and 128.5 (s, CHortho and CHmeta of Ph), 126.6 (s, CHpara of Ph), 80.5 (s, C6H6), 68.2 (d, 2JPC = 8.6 Hz, OCH2), 37.2 (d, 3JPC = 6.8 Hz, CH2Ph), 28.8 (d, 1JPC = 29.9 Hz, PCHMe2), 17.4 (d, 2JPC = 4.8 Hz, PCHMe2) ppm. Elemental analysis calcd. (%) for C20H29Cl2OPOs: C 41.59, H 5.06; found: C 41.74, H 4.99.

3.3. X-ray Crystal Structure Determination of Compound 4c

Crystals of 4c suitable for X-ray diffraction analysis were obtained by slow diffusion of hexane into a saturated solution of the complex in dichloromethane. The most relevant crystal and refinement data are collected in Table 2. Diffraction data were recorded on an Oxford Diffraction Xcalibur Nova single-crystal diffractometer using Cu-Kα radiation (λ = 1.5418 Å). Images were collected at a fixed crystal-to-detector distance of 62 mm using the oscillation method with 1.10° oscillation and 1.25–2.5 s variable exposure time per image. Data collection strategy was calculated with the program CrysAlis Pro CCD [24]. Data reduction and cell refinement were performed with the program CrysAlis Pro RED [24], and an empirical absorption correction was applied by means of a SCALE3 ABSPACK algorithm as implemented in the program CrysAlis Pro RED [24]. The software package WINGX was used for space group determination, structure solution, and refinement [25]. The structure was solved by Paterson interpretation and phase expansion using DIRDIF2008 [26]. Isotropic least-squares refinement on F2 using SHELXL97 was performed [27].
During the final stages of the refinements, all the positional parameters and the anisotropic temperature factors of all non-H atoms were refined except C(8), C(9A), C(9B), C(10A), and C(10B), because the isopropyl group of the p-cymene ligand was found in two disordered positions (69% for the major position and 31% for the minor one). The distances from C(9A), C(9B), C(10A), and C(10B) to C(8) were fixed at 1.50 Å (by comparison with other structures previously described [14,15]). All H atoms were geometrically located and their coordinates were refined riding on their parent atoms. The function minimized was [Σw(Fo2Fc2)/Σw(Fo2)]1⁄3 where w = 1/[σ2(Fo2) + (0.0460P)2 + 6.2548P] with σ(Fo2) from counting statistics and P = (Max (Fo2,0) + 2Fc2)/3. Atomic scattering factors were taken from the International Tables for X-ray Crystallography [28]. Geometrical calculations related to the centroid C* were made with PARST [29]. CCDC-1972510 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44 1223 336033; E-mail: [email protected]).

4. Conclusions

In summary, different half-sandwich arene-Os(II) complexes bearing P-coordinated phosphinite ligands, namely, [OsCl2(η6-p-cymene){R2PO(CH2)nPh}] (R = Ph, n = 1 (4a), 2 (4b), 3 (4c); R = iPr, n = 1 (5a), 2 (5b), 3 (5c)) and [OsCl2(η6-benzene){iPr2PO(CH2)2Ph}] (7), have been synthesized and characterized. Unlike their ruthenium analogs, these compounds are completely inert and do not undergo intramolecular exchange of the η6-coordinated arene ligand under heating or MW-irradiation, thus preventing the access to tethered species featuring a η6:κ1(P)-coordination of the phosphinites.

Supplementary Materials

The following are available online, Figures S1–S21: NMR spectra of the osmium complexes 4-5a-c and 7.

Author Contributions

Conceptualization, V.C. and P.C.; Synthesis and spectroscopic characterization of the complexes, R.G.-F.; Crystal structure refinement, J.B.; All the authors contributed to the discussion of the experimental results as well as writing and editing of the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO project CTQ2016-75986-P) and the University of Oviedo (project PAPI-18-GR-2011-0032).

Acknowledgments

R.G.-F. thanks MECD of Spain for the award of a FPU fellowship.

Conflicts of Interest

The authors declare no conflicts of interest.

References

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Scheme 1. Route employed for the synthesis of complexes [RuCl2{η6:κ1(P)-C6H5(CH2)nOPR2}].
Scheme 1. Route employed for the synthesis of complexes [RuCl2{η6:κ1(P)-C6H5(CH2)nOPR2}].
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Scheme 2. Synthesis of the tethered arene-osmium(II) complexes B.
Scheme 2. Synthesis of the tethered arene-osmium(II) complexes B.
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Scheme 3. Synthesis of the osmium(II) complexes [OsCl2(η6-p-cymene){R2PO(CH2)nPh}] (4-5a-c).
Scheme 3. Synthesis of the osmium(II) complexes [OsCl2(η6-p-cymene){R2PO(CH2)nPh}] (4-5a-c).
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Figure 1. ORTEP-type view of the structure of complex 4c showing the crystallographic labeling scheme. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at the 20% probability level. Selected bond distances (Å) and angles (deg): Os(1)-C* = 1.1706(2); Os(1)-Cl(1) = 2.408(2); Os(1)-Cl(2) = 2.406(2); Os(1)-P(1) = 2.318(2); P(1)-O(1) = 1.611(4); P(1)-C(11) = 1.803(6); P(1)-C(17) = 1.823(6); Os(1)-C(23) = 1.448(7); C*-Os(1)-P(1) = 127.47(4); C*-Os(1)-Cl(1) = 125.55(5); C*-Os(1)-Cl(2) = 127.96(4); Cl(1)-Os(1)-Cl(2) = 86.83(7); Cl(1)-Os(1)-P(1) = 86.26(6); Cl(2)-Os(1)-P(1) = 89.31(6); Os(1)-P(1)-O(1) = 114.0(2); Os(1)-P(1)-C(11) = 111.6(2); Os(1)-P(1)-C(17) = 124.2(2); C(11)-P(1)-C(17) = 103.1(3); C(11)-P(1)-O(1) = 98.5(2); C(17)-P(1)-O(1) = 101.9(3); P(1)-O(1)-C(23) = 120.2(4); C* denotes the centroid of the p-cymene ring (C(2), C(3), C(4), C(5), C(6) and C(7)).
Figure 1. ORTEP-type view of the structure of complex 4c showing the crystallographic labeling scheme. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at the 20% probability level. Selected bond distances (Å) and angles (deg): Os(1)-C* = 1.1706(2); Os(1)-Cl(1) = 2.408(2); Os(1)-Cl(2) = 2.406(2); Os(1)-P(1) = 2.318(2); P(1)-O(1) = 1.611(4); P(1)-C(11) = 1.803(6); P(1)-C(17) = 1.823(6); Os(1)-C(23) = 1.448(7); C*-Os(1)-P(1) = 127.47(4); C*-Os(1)-Cl(1) = 125.55(5); C*-Os(1)-Cl(2) = 127.96(4); Cl(1)-Os(1)-Cl(2) = 86.83(7); Cl(1)-Os(1)-P(1) = 86.26(6); Cl(2)-Os(1)-P(1) = 89.31(6); Os(1)-P(1)-O(1) = 114.0(2); Os(1)-P(1)-C(11) = 111.6(2); Os(1)-P(1)-C(17) = 124.2(2); C(11)-P(1)-C(17) = 103.1(3); C(11)-P(1)-O(1) = 98.5(2); C(17)-P(1)-O(1) = 101.9(3); P(1)-O(1)-C(23) = 120.2(4); C* denotes the centroid of the p-cymene ring (C(2), C(3), C(4), C(5), C(6) and C(7)).
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Scheme 4. Synthesis of the osmium(II) complex [OsCl2(η6-benzene){iPr2PO(CH2)2Ph}] (7).
Scheme 4. Synthesis of the osmium(II) complex [OsCl2(η6-benzene){iPr2PO(CH2)2Ph}] (7).
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Table 1. 31P chemical shifts for the phosphinite ligands 1-2a-c and the osmium(II) complexes 4-5a-c 1.
Table 1. 31P chemical shifts for the phosphinite ligands 1-2a-c and the osmium(II) complexes 4-5a-c 1.
LigandδP (ppm)ComplexδP (ppm)
1a114.54a64.2
1b126.64b63.1
1c112.14c262.2
2a154.55a2103.5
2b152.35b2103.3
2c151.45c102.3
1 Unless otherwise stated, the spectra were recorded in CDCl3. 2 Spectra recorded in CD2Cl2.
Table 2. Crystal data and structure refinement details for compound 4c.
Table 2. Crystal data and structure refinement details for compound 4c.
Chemical FormulaC31H35Cl2OOsP
fw715.66
T (K)293(2)
cryst. syst.monoclinic
space groupP 21/c
cryst. size mm30.24 × 0.16 × 0.16
a, Å10.3465(2)
b, Å19.1010(3)
c, Å15.1007(3)
α, deg90
β, deg105.009(2)
γ, deg90
Z4
V, Å32882.5(1)
ρcalcd, g cm–31.649
μ, mm−110.751
F(000)1416
θ range, deg3.813 to 69.621
index ranges−12 ≤ h ≤ 12; −22 ≤ k ≤ 22; −18 ≤ l ≤ 13
completeness to θmax97.9%
no. of data collected14414
no. of unique data5321
no. of parameters/restrains319/4
refinement methodfull-matrix least-squares on F2
goodness of fit on F21.065
R1a [I > 2σ(I)] 0.0407
wR2a [I > 2σ(I)]0.0978
R1 (all data)0.0486
wR2 (all data)0.1033
largest diff. peak and hole, e Å−30.935 and −1.683
aR1 = ∑(|Fo| − |Fc|)/∑|Fo|; wR2 = {∑[w(Fo2Fc2)]/∑[w(Fo2)2]}½.
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