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Article

Si–H Bond Activation of a Primary Silane with a Pt(0) Complex: Synthesis and Structures of Mononuclear (Hydrido)(dihydrosilyl) Platinum(II) Complexes

by
Norio Nakata
*,
Nanami Kato
,
Noriko Sekizawa
and
Akihiko Ishii
*
Department of Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan
*
Authors to whom correspondence should be addressed.
Inorganics 2017, 5(4), 72; https://doi.org/10.3390/inorganics5040072
Submission received: 3 October 2017 / Revised: 23 October 2017 / Accepted: 24 October 2017 / Published: 25 October 2017
(This article belongs to the Special Issue Coordination Chemistry of Silicon)
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Versions Notes

Abstract

:
A hydrido platinum(II) complex with a dihydrosilyl ligand, [cis-PtH(SiH2Trip)(PPh3)2] (2) was prepared by oxidative addition of an overcrowded primary silane, TripSiH3 (1, Trip = 9-triptycyl) with [Pt(η2-C2H4)(PPh3)2] in toluene. The ligand-exchange reactions of complex 2 with free phosphine ligands resulted in the formation of a series of (hydrido)(dihydrosilyl) complexes (3–5). Thus, the replacement of two PPh3 ligands in 2 with a bidentate bis(phosphine) ligand such as DPPF [1,2-bis(diphenylphosphino)ferrocene] or DCPE [1,2-bis(dicyclohexylphosphino)ethane] gave the corresponding complexes [PtH(SiH2Trip)(L-L)] (3: L-L = dppf, 4: L-L = dcpe). In contrast, the ligand-exchange reaction of 2 with an excess amount of PMe3 in toluene quantitatively produced [PtH(SiH2Trip)(PMe3)(PPh3)] (5), where the PMe3 ligand is adopting trans to the hydrido ligand. The structures of complexes 2–5 were fully determined on the basis of their NMR and IR spectra, and elemental analyses. Moreover, the low-temperature X-ray crystallography of 2, 3, and 5 revealed that the platinum center has a distorted square planar environment, which is probably due to the steric requirement of the cis-coordinated phosphine ligands and the bulky 9-triptycyl group on the silicon atom.

Graphical Abstract

1. Introduction

The transition metal catalyzed synthesis of functionalized organosilicon compounds gained substantial momentum during the past few decades [1]. Among these catalytic conversions, the oxidative addition of hydrosilanes with platinum(0) complexes is an efficient method for the generation of the platinum(II) hydride species, which has been proposed as a key intermediate in platinum-catalyzed hydrosilylations [2,3,4,5,6] and bis-silylations [7,8], as well as the dehydrogenative couplings of hydrosilanes [9,10,11,12,13]. While a number of reactions of hydrosilanes with platinum(0) complexes affording mononuclear bis(silyl) [14,15,16,17,18] and silyl-bridged multinuclear complexes [19,20,21,22,23,24,25,26,27,28,29] have been described so far, the isolation of mononuclear hydrido(silyl) complexes has been less well studied due to the high reactivity of a Pt–H bond [30,31,32,33,34]. In particular, the synthesis of hydrido(dihydrosilyl) platinum(II) complexes, which are anticipated as the initial products in the Si–H bond activation reactions of primary silanes with platinum(0) complexes, is quite rare. Indeed, only two publications have previously reported the characterization of hydrido(dihydrosilyl) platinum(II) complexes. In 2000, Tessier et al. reported that the reaction of a primary silane with a bulky m-terphenyl group with [Pt(PPr)3] produced the first example of a stable hydrido(dihydrosilyl) complex [cis-PtH(SiH2Ar)(PPr3)2] (Ar = 2,6-MesC6H3) [35]. Quite recently, Lai et al. also described the synthesis of a bis(phosphine) hydrido(dihydrosilyl) complex [PtH(SiH2SitBu2Me)(dcpe)] (dcpe = 1,2-bis(dicyclohexylphosphino)ethane) containing a Si–Si bond [36]. Meanwhile, we succeeded in the first isolation of a series of hydrido(dihydrogermyl) platinum(II) complexes [PtH(GeH2Trip)(L)] (Trip = 9-triptycyl) using a bulky substituent, 9-triptycyl group [37]. In addition, we reported the first syntheses and structural characterizations of hydrido palladium(II) complexes with a dihydrosilyl- or dihydrogermyl ligand, [PdH(EH2Trip)(dcpe)] (E = Si, Ge) [38]. Very recently, we also found that hydride-abstraction reactions of [MH(EH2Trip)(dcpe)] (M = Pt, Pd, E = Si, Ge) with B(C6F5)3 led to the formations of new cationic dinuclear complexes with bridging hydrogermylene and hydrido ligands, [{M(dcpe)}2(μ-GeHTrip)(μ-H)]+ [39]. As an extension of our previous work and taking into account the interest devoted to hydrido platinum(II) complexes, we present here the synthesis and characterization of a series of mononuclear (hydrido)(dihydrosilyl) complexes [PtH(SiH2Trip)(L)2].

2. Results

2.1. Synthesis and Characterization of [cis-PtH(SiH2Trip)(PPh3)2] (2)

The reaction of TripSiH3 1 with [Pt(η2-C2H4)(PPh3)2] in toluene proceeded efficiently at room temperature under inert atmosphere to form the corresponding complex [cis-PtH(SiH2Trip)(PPh3)2] (2) in 91% yield as colorless crystals (Scheme 1). In the 1H NMR spectrum of 2, the characteristic signals of the platinum hydride were observed at δ = −2.15, which were split by 19 and 157 Hz of 31P–1H couplings accompanying 958 Hz of satellite signals from the 195Pt isotope. This chemical shift is comparable with those of the related (hydrido)(dihydrosilyl) complexes, [cis-PtH(SiH2Ar)(PPr3)2] (Ar = 2,6-MesC6H3) (δ = −3.40) [35] and [cis-PtH(SiH2SitBu2Me)(dcpe)] (δ = −0.89) [36]. The SiH2 resonance appeared as a multiplet at δ = 4.68 ppm. The 31P{1H} NMR spectrum of 2 exhibited two doublets (2JP–P = 15 Hz) at δ = 33.8 and 34.5 with 195Pt–31P coupling constants, 2183 and 1963 Hz, which were assigned to the phosphorus atoms lying trans to the hydrido and dihydrosilyl ligands, respectively, in agreement with the NMR data for reported germanium congener [cis-PtH(GeH2Trip)(PPh3)2] [δ = 31.2 (1JPt–P = 2317 Hz) and 31.6 (1JPt–P = 2252 Hz)] [37]. The silicon atom of 2 gave rise to a resonance around δ = −40.6 with splitting due to 31P–29Si couplings (2JP(trans)–Si = 161, 2JP(cis)–Si = 15 Hz) and 195Pt satellites (1JPt–Si = 1220 Hz) in the 29Si{1H} NMR spectrum. In the solid state IR spectrum for 2, Pt–H and Si–H stretching vibrations were observed at 2041 and 2080 cm−1, respectively. Complex 2 is thermally and air stable in the solid state (melting point: 123 °C (dec.)) or in solution, and no dimerization or dissociation of phosphine ligands was observed.
The molecular structure of 2 was determined unambiguously by X-ray crystallographic analysis, as depicted in Figure 1. The X-ray crystallographic analysis of 2 revealed that the platinum center attains a distorted square-planar environment, which was probably due to the steric requirement of the cis-coordinated PPh3 ligands and the bulky 9-triptycyl group on the silicon atom. The P1–Pt1–P2 angle of 101.63(3)° and P1–Pt1–Si1 angle of 96.17(3)° deviated considerably from the ideal 90° of square-planar geometry. The Pt–Si bond length is 2.3458(9) Å, which is comparable to those ranging from 2.321 to 2.406 Å observed in the related mononuclear platinum(II) complexes bearing silyl ligands [1]. The hydrogen atom on the platinum atom was located in the electron density map and has a Pt–H distance of 1.59(4) Å. The Pt1–P1 bond length [2.2945(8) Å] is slightly shorter than the Pt1–P2 bond length [2.3401(8) Å], which indicates the stronger trans influence of the silicon atom compared with that of the hydride in this complex. This result is consistent with the 195Pt–31P coupling constants (2183 and 1963 Hz) observed in the 31P{1H} NMR spectrum.

2.2. Ligand Exchange Reactions of 2 with Free Phosphine Ligands

We next examined the ligand-exchange reactions of complex 2 with free phosphine ligands. The replacement of two PPh3 ligands in 2 with a bidentate bis(phosphine) ligand such as DPPF (1,2-bis(diphenylphosphino)ferrocene) or DCPE gave the corresponding complexes [PtH(SiH2Trip)(L-L)] (3: L-L = dppf, 4: L-L = dcpe) in 87% and 80% yields, respectively (Scheme 2). In the 1H NMR spectra of 3 and 4, the hydride resonated as a doublet of doublets at δ = –1.62 (2JP–H = 20, 164, 1JPt–H = 995 Hz) for 3 and –0.46 (2JP–H = 13, 166, 1JPt–H = 1004 Hz) for 4. These chemical shifts are shifted downfield in comparison with that of the starting complex 2 (δ = −2.15), which is probably due to the stronger electron-donating ability of chelating phosphines compared with PPh3. The spectrum for 3 also displayed a multiplet signal centering at δ = 4.61 corresponding to the SiH2 protons, which is shifted upfield by 0.89 ppm in comparison with that of 4. The 31P{1H} NMR spectrum of 3 showed two doublets (2JP–P = 21 Hz) with 195Pt satellites at δ = 30.5 (1JPt–P = 2247 Hz) and 34.5 (1JPt–P = 1837 Hz), which are close to those of 2 [δ = 33.8 (1JPt–P = 2183 Hz) and 34.5 (1JPt–P = 1963 Hz)]. The observation of P–P coupling indicates a large deviation of the P–Pt–P angle from 90° of the ideal square planar geometry around the Pt(II) center (vide infra). In contrast, the 31P{1H} resonances for 4 were observed as two singlets at δ = 69.2 (1JPt–P = 1809 Hz) and 85.3 (1JPt–P = 1678 Hz), respectively, which are relatively shifted downfield relative to those of 2 and 3. The larger 1JPt–P values (2183 Hz for 3, 1809 Hz for 4) are assigned to the phosphorus atom trans to the hydrido ligand, as in the case of 2. Furthermore, the 29Si{1H} NMR spectra of 3 and 4 showed a doublet of doublets signals at δ = −39.0 (2JSi–P = 167, 12 Hz) for 3, and −44.6 (2JSi–P = 173, 11 Hz) for 4, which were accompanied by 195Pt satellites of 1207 Hz for 3 and 1253 Hz for 4, respectively.
The molecular structure of DPPF-derivative 3 in the crystalline state was confirmed by X-ray crystallography (Figure 2). The platinum atom lies in a distorted square-planar geometry; the sum of the bond angles around the platinum atom is 360.48°. The P1–Pt1–P2 angle is 102.29(9)°, and other angles around the platinum atom are less than 90°, except the P1–Pt1–Si1 angle [95.19(9)°]. The Pt–Si [2.331(3) Å] and two Pt–P bond lengths [2.286(2), 2.319(2) Å] are comparable to those of the corresponding DPPF-ligated hydrido complex [PtH(SiHPh2)(dppf)] [2.3366(4), 2.2830(4), and 2.3192(4) Å, respectively] [40].
It is well known that trimethylphosphine (PMe3) is a strong σ-donating ligand for a wide variety of transition-metal complexes. Therefore, one can reasonably expect the formation of [PtH(SiH2Trip)(PMe3)2] in a similar ligand-exchange reaction of 2 with PMe3. However, we found that the reaction of 2 with 2.2 equivalents of PMe3 in toluene at room temperature did not proceed completely, which resulted in the formation of [PtH(SiH2Trip)(PMe3)(PPh3)] (5), where the PPh3 ligand trans to hydrido in 2 is exchanged with a PMe3 ligand (Scheme 3). Complex 5 was isolated as colorless crystals in quantitative yield after workup. In the 1H NMR spectrum of 5 at 298 K, the characteristic broad doublet signal due to the platinum hydride was observed centering at δ = −1.91 with splitting by 31P–1H (2JP(trans)–H = 157 Hz) and 195Pt–1H (1JPt–H = 899 Hz) couplings. The SiH2 protons also appeared as a broad multiplet at δ = 5.95, which is shifted downfield relative to those of the above complexes 2–4 (δ = 4.68–5.50). The 31P{1H} NMR spectrum of 5 at 298 K exhibited two nonequivalent broad singlet signals at δ = −22.9 and 37.4, with two sets of 195Pt satellites of 2115 and 1833 Hz. The former signal was assigned to the PMe3 trans to the hydrido ligand using a non 1H-decoupled 31P NMR technique at 253 K. The 29Si{1H} NMR spectrum of 5 at 223 K featured one 29Si resonance as a broad doublet signal at δ = −43.9 (2JSi–P = 151 Hz). The broadening of NMR signals possibly implies the existence of the Si–H σ-complex intermediate 6 in the NMR time scale [38,41,42]. Unfortunately, attempts to probe further the fluxional behavior of 5 by VT (variable temperature)-NMR in solution revealed no appreciable changes in spectroscopic features by 1H and 31P NMR spectroscopy. The molecular structure of 5 is also determined by X-ray analysis, as shown in Figure 3. Distortions from square planar geometry at the platinum center were observed, similar to the cases of 2 and 4. The Pt–Si bond length of 5 [2.3414(13) Å] is almost equal to those of 2 [2.3458(9) Å] and 4 [2.331(3) Å]. As expected, the Pt1–P1 bond length for the PMe3 ligand of 5 [2.2978(12) Å] is shortened compared with the Pt1–P2 bond length for the PPh3 ligand of 5 [2.3203(11) Å] due to the different ligands in the trans positions of the phosphorus atoms. While only a few cationic platinum complexes containing different phosphine ligands have been reported [43,44,45], complex 5 is the first example of a neutral platinum complex bearing a weakly electron-donating PPh3 and strongly electron-donating PMe3.
A plausible formation mechanism for 5 is shown in Scheme 4. According to the stronger trans influence of the silyl ligand than that of the hydrido ligand, the ligand-exchange of a PPh3 trans to silyl ligand takes place to yield the intermediate 5′ in the first step, while 5 might be formed directly from the corresponding coordinatively unsaturated intermediate (3-coordinated 14-electron complexes) [46,47]. Then, the intramolecular interchange of coordination environments between the silyl and hydrido ligands through the Si–H σ-complex intermediate 6 would occur, probably due to the steric repulsion between the bulky 9-triptycyl group on the silicon atom and the cis-PPh3 ligand in 5′. Finally, the corresponding complex 5 was obtained as the thermodynamic product. As another pathway, it is likely that the direct formation of 5 is caused by an initial dissociation of the PPh3 ligand at the trans position of the hydrido ligand in 2 due to steric reason.

3. Materials and Methods

3.1. General Procedures

All of the experiments were performed under an argon atmosphere unless otherwise noted. Solvents were dried by standard methods and freshly distilled prior to use. 1H, 13C, and 31P NMR spectra were recorded on Bruker DPX-400 or DRX-400 (400, 101 and 162 MHz, respectively), Avance-500 (500, 126 and 202 MHz, respectively) (Karlsruhe, Germany) spectrometers using CDCl3 or C6D6 as the solvent at room temperature. 29Si NMR spectra were recorded on Bruker Avance-500 (Karlsruhe, Germany) or JEOL EX-400 (Tokyo, Japan) (99.4 and 79.3 MHz, respectively) spectrometers using CDCl3, CD2Cl2, C6D6, or THF-d8 as the solvent at room temperature, unless otherwise noted. IR spectra were obtained on a Perkin-Elmer System 2000 FT-IR spectrometer (Walham, MA, USA). Elemental analyses were carried out at the Molecular Analysis and Life Science Center of Saitama University. All of the melting points were determined on a Mel-Temp capillary tube apparatus (Stafford, UK) and are uncorrected. 9-Triptycylsilane (TripSiH3, 1) [48] and [Pt(η2-C2H4)(PPh3)2] [49] were prepared according to the reported procedures.

3.1.1. [cis-PtH(SiH2Trip)(PPh3)2] (2)

A solution of TripSiH3 1 (50.9 mg, 0.179 mmol) and [Pt(η2-C2H4)(PPh3)2] (149.3 mg, 0.199 mmol) in toluene (3 mL) was stirred at room temperature for 1 h to form a pale yellow solution. After the removal of the solvent in vacuo, the residual colorless solid was purified by washing with hexane to give [cis-PtH(SiH2Trip)(PPh3)2] (2) (164.3 mg, 91%) as colorless crystals.
1H NMR (400 MHz, CDCl3): δ = −2.15 (dd, 2JH–P(trans) = 157, 2JH–P(cis) = 19, 1JH–Pt = 958 Hz, 1H, PtH), 4.68 (m, 2H, SiH2), 5.28 (s, 1H, TripCH), 6.83–6.89 (m, 6H, Ar), 7.02–7.06 (m, 6H, Ar), 7.15–7.31 (m, 21H, Ar), 7.49 (t, J = 7 Hz, 6H, Ar), 7.81 (d, J = 7 Hz, 3H, Ar). 13C{1H} NMR (101 MHz, CDCl3): δ = 46.6 (TripC), 55.3 (TripCH), 122.7 (Ar(CH)), 123.7 (Ar(CH) × 2), 126.2 (Ar(CH)), 127.8 (Ar(CH)), 127.9 (Ar(CH)), 129.4 (Ar(CH)), 129.6 (Ar(CH)), 134.1 (Ar(CH)), 134.2 (Ar(CH)), 133.7–134.8 (m, Ar(C)), 135.5 (d, 1JC–P = 38 Hz, Ar(C)), 148.4 (Ar(C)), 149.5 (Ar(C)). 31P{1H} NMR (162.0 MHz, CDCl3): δ = 33.8 (d, 2JP–P = 15, 1JP–Pt = 2183 Hz), 34.5 (d, 2JP–P = 15, 1JP–Pt = 1963 Hz). 29Si{1H} NMR (79.3 MHz, CD2Cl2): δ = −40.6 (dd, 2JSi–P(trans) = 161, 2JSi–P(cis) = 15, 1JSi–Pt = 1220 Hz). IR (KBr, cm−1): ν = 2041 (Pt–H), 2080 (Si–H). Anal. Calcd. for C56H46P2PtSi: C, 66.99; H, 4.62. Found: C, 66.55; H, 4.61. Melting point: 123 °C (dec.).

3.1.2. [PtH(SiH2Trip)(dppf)] (3)

A solution of 2 (40.5 mg, 0.040 mmol) and DPPF (28.2 mg, 0.048 mmol) in toluene (3 mL) was stirred at room temperature for 5 h. After the removal of the solvent in vacuo, the residual colorless solid was purified by washing with Et2O and hexane to give [PtH(SiH2Trip)(dppf)] (3) (37.1 mg, 0.035 mmol, 87%) as yellow crystals.
1H NMR (400 MHz, CDCl3): δ = −1.62 (dd, 2JH–P(trans) = 164, 2JH–P(cis) = 20, 1JH–Pt = 995 Hz, 1H, PtH), 3.86 (s, 2H, Cp), 4.20 (s, 2H, Cp), 4.37 (s, 2H, Cp), 4.58–4.64 (m, 4H, Cp and SiH2), 5.30 (s, 1H, TripCH), 6.87–6.89 (m, 6H, Ar), 7.26 (m, 6H, Ar), 7.41 (br, 6 H, Ar), 7.66–7.81 (m, 14H, Ar). 13C{1H} NMR (101 Hz, CDCl3): δ = 46.5 (m, TripC), 55.2 (TripCH), 71.3 (d, 3JC–P = 5 Hz, Cp(CH)), 72.1 (d, 3JC–P = 6 Hz, Cp(CH)), 74.5 (d, 2JC–P = 7 Hz, Cp(CH)), 75.6 (d, 2JC–P = 8 Hz, Cp(CH)), 79.3 (dd, 1JC–P = 42, 3JC–P = 5 Hz, Cp(C)), 80.7 (dd, 1JC–P = 47, 3JC–P = 6 Hz, Cp(C)), 122.7 (Ar(CH)), 123.71 (Ar(CH)), 123.68 (Ar(CH)), 126.4 (Ar(CH)), 127.7 (d, 3JC–P = 11 Hz, Ar(CH)), 128.0 (d, 3JC–P = 10 Hz, Ar(CH)), 129.9 (Ar(CH)), 130.1 (Ar(CH)), 134.3 (d, 2JC–P = 13 Hz, Ar(CH)), 134.6 (d, 2JC–P = 14 Hz, Ar(CH)), 134.8–135.5 (m, Ar(C)), 136.2 (d, 1JC–P = 43 Hz, Ar(C)), 148.4 (Ar(C)), 149.7 (Ar(C)). 31P{1H} NMR (202 MHz, CDCl3): δ = 30.5 (d, 2JP–P = 21 Hz, 1JPt–P = 2247 Hz), 34.5 (d, 2JP–P = 21, 1JPt–P = 1837 Hz). 29Si{1H} NMR (79.3 MHz, CDCl3): δ = −39.0 (dd, 2JSi–P(trans) = 167, 2JSi–P(cis) = 12, 1JSi–Pt = 1207 Hz). IR (KBr, cm−1): ν = 2055 (Pt–H), 2081 (Si–H). Anal. Calcd. for C54H44FeP2PtSi: C, 62.73; H, 4.29. Found: C, 62.70; H, 4.27. Melting point: 183 °C (dec.).

3.1.3. [PtH(SiH2Trip)(dcpe)] (4)

A solution of 2 (35.6 mg, 0.035 mmol) and DCPE (18.8 mg, 0.044 mmol) in toluene (3 mL) was stirred at room temperature for 5 h. After the removal of the solvent in vacuo, the residual colorless solid was purified by washing with Et2O and hexane to give [PtH(SiH2Trip)(dcpe)] (4) (25.5 mg, 0.028 mmol, 80%) as colorless crystals.
1H NMR (500 MHz, CDCl3): δ = −0.45 (dd, 2JH–P(trans) = 165, 2JH–P(cis) = 13, 1JPt–H = 1004 Hz, 1H, PtH), 1.16–1.51 (m, 20H, Cy), 1.65–1.86 (m, 24H, Cy), 2.16–2.19 (m, 2H, Cy), 2.30–2.37 (m, 2H, Cy), 5.32 (s, 1H, TripCH), 5.50 (dd, 2JH–H = 15, 3JH–P(trans) = 6, 2JPt–H = 31 Hz, 2H, SiH2), 6.84–6.90 (m, 6H, Ar), 7.30–7.32 (d, J = 7 Hz, 3H, Ar), 7.94–7.96 (d, J = 7 Hz, 3H, Ar). 13C{1H} NMR (101 Hz, CDCl3): δ = 23.2 (dd, 3JC–P = 21, 16 Hz, PCH2), 26.2 (dd, 3JC–P = 23, 21 Hz, PCH2), 26.9 (d, 3JC–P = 14 Hz, PCy(CH2)), 26.4 (d, 3JC–P = 13 Hz, PCy(CH2)), 26.8 (d, 3JC–P = 10 Hz, PCy(CH2)), 27.0 (d, 3JC–P = 12 Hz, PCy(CH2)), 28.9 (m, PCy(CH2) × 2), 29.7 (m, PCy(CH2)), 35.3–35.8 (m, PCy(CH) × 2), 46.8 (TripC), 55.4 (TripCH), 122.7 (Ar(CH)), 123.6 (Ar(CH)), 126.9 (Ar(CH)), 148.6 (Ar(C)), 159.2 (Ar(C)). 31P{1H} NMR (162 Hz, CDCl3): δ = 69.2 (s, 1JPt–P = 1809 Hz), 85.3 (s, 1JPt–P = 1678 Hz). 29Si{1H} NMR (79.3 MHz, CD2Cl2): δ = −44.6 (dd, 2JSi–P(trans) = 173, 2JSi–P(cis) = 11, 1JSi–Pt = 1253 Hz). IR (KBr, cm−1): ν = 2057 (Pt–H), 2081 (Si–H). Anal. Calcd for C46H64P2PtSi: C, 61.24; H, 7.15. Found: C, 61.10; H, 7.10. Melting point: 134 °C (dec.).

3.1.4. [PtH(SiH2Trip)(PMe3)(PPh3)] (5)

A toluene solution of PMe3 (1.0 M, 0.2 mL, 0.200 mmol) was added to a solution of 2 (98.0 mg, 0.098 mmol) in toluene (3.5 mL) at room temperature. The reaction mixture was stirred at room temperature for 30 min. After the removal of the solvent in vacuo, the residual colorless solid was purified by washing with Et2O and hexane to give [PtH(SiH2Trip)(PMe3)(PPh3)] 5 (75.6 mg, 94%) as colorless crystals.
1H NMR (400 MHz, C6D6): δ = −1.91 (d, 2JH–P(trans) = 157, 1JH–Pt = 899 Hz, 1H, PtH), 1.03–1.11 (m, 9H, PMe), 5.34 (s, 1H, TripCH), 5.95–5.97 (m, 2H, SiH2), 6.82–6.97 (m, 15H, Ar), 7.31 (d, J = 7 Hz, 3H, Ar), 7.57 (br, 6H, Ar), 8.50 (d, J = 7 Hz, 3H, Ar). 13C{1H}-NMR (101 Hz, CDCl3): δ = 16.4–17.1 (m, PMe), 53.6 (TripC), 55.4 (TripCH), 123.0 (Ar(CH)), 123.9 (Ar(CH)), 124.1 (Ar(CH)), 126.5 (Ar(CH)), 128.5 (d, 3JC–P = 10 Hz, Ar(CH)), 130.0 (Ar(CH)), 134.4 (d, 2JC–P = 13 Hz, Ar(CH)), 135.6 (d, 1JC–P = 36 Hz, Ar(CH), 148.5 (Ar(C)), 149.7 (Ar(C)). 31P{1H}-NMR (162 Hz, C6D6): δ = −22.9 (s, 1JPt–P = 2115 Hz), 37.4 (br, 1JPt–P = 1833 Hz). 29Si{1H}-NMR (79.3 MHz, THF-d8, 223 K) δ −43.9 (d, 2JSi–P(trans) = 151 Hz). IR (KBr, cm−1) ν = 2029 (Pt–H), 2054 (Si–H). Anal. Calcd for C41H40P2PtSi: C, 60.21; H, 4.93. Found: C, 60.57; H, 5.00. Melting point: 115 °C (dec.).

3.2. X-ray Crystallographic Studies of 2, 3, and 5

Colorless single crystals of 2 were grown by the slow evaporation of its saturated toluene solution, and single crystals of 3 and 5 were grown by the slow evaporation of its saturated CH2Cl2 and hexane solution. The intensity data were collected at 103 K on a Bruker AXS SMART diffractometer (Karlsruhe, Germany) employing graphite-monochromatized Mo Kα radiation (λ = 0.71073 Å). The structures were solved by direct methods and refined by full-matrix least-squares procedures on F2 for all reflections (SHELX-97) [50]. Hydrogen atoms, except for the PtH and SiH hydrogens of 2, 3, and 5, were located by assuming ideal geometry, and were included in the structure calculations without further refinement of the parameters. Full details of the crystallographic analysis and accompanying cif files (see Supplementary Materials) may be obtained free of charge from the Cambridge Crystallographic Data Centre (CCDC numbers 1577277, 1577278, and 1577279) 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]).

3.2.1. [cis-PtH(SiH2Trip)(PPh3)2] (2)

C56H46P2PtSi, C7H8, MW = 1096.18, triclinic, space group P-1, a = 12.7971(6) Å, b = 13.4847(6) Å, c = 14.8861(7) Å, α = 99.2791(10)°, β = 99.2791(10)°, γ = 90.3020(10)°, V = 2472.4(2) Å3, Z = 2, Dcalc. = 1.472 g·cm−3, R1 (I > 2σI) = 0.0310, wR2 (all data) = 0.0718 for 11639 reflections and 617 parameters, GOF = 1.025.

3.2.2. [PtH(SiH2Trip)(dppf)] (3)

C54H44FeP2PtSi, CH2Cl2, MW = 1118.79, monoclinic, space group P21, a = 12.2585(6) Å, b = 15.5003(7) Å, c = 12.9367(6) Å, β = 110.8060(10)°, V = 2297.81(19) Å3, Z = 2, Dcalc = 1.617 g·cm−3, R1 (I > 2σI) = 0.0484, wR2 (all data) = 0.1171 for 8350 reflections, 571 parameters, and 2 restraints, GOF = 1.018.

3.2.3. [PtH(SiH2Trip)(PMe3)(PPh3)] (5)

C41H40P2PtSi, CH2Cl2, MW = 902.78, orthorhombic, space group Pbca, a = 15.9074(6) Å, b = 20.9224(8) Å, c = 22.6113(9) Å, V = 7525.5(5) Å3, Z = 8, Dcalc = 1.594 g·cm−3, R1 (I > 2σI) = 0.0325, wR2 (all data) = 0.0706 for 7011 reflections and 448 parameters, GOF = 1.026.

4. Conclusions

We have demonstrated that the oxidative addition of the sterically bulky primary silane, TripSiH3 1 with [Pt(η2-C2H4)(PPh3)2] in toluene, resulted in the formation of the mononuclear (hydrido)(dihydrosilyl) complex [cis-PtH(SiH2Trip)(PPh3)2] 2. The ligand-exchange reactions of 2 with free chelating bis(phosphine)s such as DPPF or DCPE resulted in the formations of a series of (hydrido)(dihydrosilyl) complexes [PtH(SiH2Trip)(L)] (3: L = dppf, 4: L = dcpe). In contrast, the reaction of 2 with an excess amount of PMe3 in toluene quantitatively produced [PtH(SiH2Trip)(PMe3)(PPh3)] 5. The latter is of particular interest, as it represents the first platinum complex having different simple phosphine ligands such as a weakly electron-donating PPh3 and a strongly electron-donating PMe3. Further investigations on the reactivity of these complexes are currently in progress.

Supplementary Materials

The following are available online at www.mdpi.com/2304-6740/5/4/72/s1, cif and cif-checked files.

Acknowledgments

This work was partially supported by JSPS KAKENHI Grant Number T17K05771 (to Norio Nakata). We are grateful to Kohtaro Osakada and Makoto Tanabe (Tokyo Institute of Technology, Japan) for their assistance in measurement of 29Si NMR spectroscopy.

Author Contributions

Norio Nakata, Nanami Kato, and Norio Sekizawa contributed to the synthesis and data analysis; Norio Nakata performed X-ray crystallography and wrote the manuscript; Norio Nakata and Akihiko Ishii proposed idea on the design of the experiment, reviewed and approved the final manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Inorganics 05 00072 sch001 550
Scheme 1. Synthesis of [cis-PtH(SiH2Trip)(PPh3)2] 2.
Scheme 1. Synthesis of [cis-PtH(SiH2Trip)(PPh3)2] 2.
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Figure 1. ORTEP of [cis-PtH(SiH2Trip)(PPh3)2] 2 (50% thermal ellipsoids, a solvation toluene molecule, and hydrogen atoms, except H1, H2, and H3 were omitted for clarity). Selected bond lengths (Å) and bond angles (°): Pt1–Si1 = 2.3458(9), Pt1–P1 = 2.2945(8), Pt1–P2 = 2.3401(8), Pt1–H1 = 1.59(4), Si1–C1 = 1.918(3), P1–Pt1–P2 = 101.63(3), Si1–Pt1–P1 = 96.17(3), Si1–Pt1–H1 = 79.7(16), P2–Pt1–H1 = 82.5(16), Si1–Pt1–P2 = 162.13(3), P1–Pt1–H1 = 175.8(16).
Figure 1. ORTEP of [cis-PtH(SiH2Trip)(PPh3)2] 2 (50% thermal ellipsoids, a solvation toluene molecule, and hydrogen atoms, except H1, H2, and H3 were omitted for clarity). Selected bond lengths (Å) and bond angles (°): Pt1–Si1 = 2.3458(9), Pt1–P1 = 2.2945(8), Pt1–P2 = 2.3401(8), Pt1–H1 = 1.59(4), Si1–C1 = 1.918(3), P1–Pt1–P2 = 101.63(3), Si1–Pt1–P1 = 96.17(3), Si1–Pt1–H1 = 79.7(16), P2–Pt1–H1 = 82.5(16), Si1–Pt1–P2 = 162.13(3), P1–Pt1–H1 = 175.8(16).
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Scheme 2. Ligand-exchange reaction of [cis-PtH(SiH2Trip)(PPh3)2] 2 with chelating bis(phosphine)s.
Scheme 2. Ligand-exchange reaction of [cis-PtH(SiH2Trip)(PPh3)2] 2 with chelating bis(phosphine)s.
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Figure 2. ORTEP of [PtH(SiH2Trip)(dppf)] 3 50% thermal ellipsoids, a solvation CH2Cl2 molecule, and hydrogen atoms, except H1, H2, and H3 were omitted for clarity. Selected bond lengths (Å) and bond angles (°): Pt1–Si1 = 2.331(3), Pt1–P1 = 2.286(2), Pt1–P2 = 2.319(2), Pt1–H1 = 1.687(10), Si1–C1 = 1.920(10), P1–Pt1–P2 = 102.29(9), Si1–Pt1–P1 = 95.19(9), Si1–Pt1–H1 = 76(5), P2–Pt1–H1 = 87(5), Si1–Pt1–P2 = 162.10(9), P1–Pt1–H1 = 171(5).
Figure 2. ORTEP of [PtH(SiH2Trip)(dppf)] 3 50% thermal ellipsoids, a solvation CH2Cl2 molecule, and hydrogen atoms, except H1, H2, and H3 were omitted for clarity. Selected bond lengths (Å) and bond angles (°): Pt1–Si1 = 2.331(3), Pt1–P1 = 2.286(2), Pt1–P2 = 2.319(2), Pt1–H1 = 1.687(10), Si1–C1 = 1.920(10), P1–Pt1–P2 = 102.29(9), Si1–Pt1–P1 = 95.19(9), Si1–Pt1–H1 = 76(5), P2–Pt1–H1 = 87(5), Si1–Pt1–P2 = 162.10(9), P1–Pt1–H1 = 171(5).
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Scheme 3. Ligand-exchange reaction of [cis-PtH(SiH2Trip)(PPh3)2] 2 with trimethylphosphine (PMe3).
Scheme 3. Ligand-exchange reaction of [cis-PtH(SiH2Trip)(PPh3)2] 2 with trimethylphosphine (PMe3).
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Figure 3. ORTEP of [PtH(SiH2Trip)(PMe3)(PPh3)] 5 50% thermal ellipsoids, a solvation CH2Cl2 molecule, and hydrogen atoms, except H1, H2, and H3 were omitted for clarity. Selected bond lengths (Å) and bond angles (°): Pt1–Si1 = 2.3414(13), Pt1–P1 = 2.2978(12), Pt1–P2 = 2.3203(11), Pt1–H1 = 1.44(6), Si1–C1 = 1.930(5), P1–Pt1–P2 = 103.47(4), Si1–Pt1–P1 = 92.34(4), Si1–Pt1–H1 = 75(2), P2–Pt1–H1 = 89(2), Si1–Pt1–P2 = 164.19(4), P1–Pt1–H1 = 167(2).
Figure 3. ORTEP of [PtH(SiH2Trip)(PMe3)(PPh3)] 5 50% thermal ellipsoids, a solvation CH2Cl2 molecule, and hydrogen atoms, except H1, H2, and H3 were omitted for clarity. Selected bond lengths (Å) and bond angles (°): Pt1–Si1 = 2.3414(13), Pt1–P1 = 2.2978(12), Pt1–P2 = 2.3203(11), Pt1–H1 = 1.44(6), Si1–C1 = 1.930(5), P1–Pt1–P2 = 103.47(4), Si1–Pt1–P1 = 92.34(4), Si1–Pt1–H1 = 75(2), P2–Pt1–H1 = 89(2), Si1–Pt1–P2 = 164.19(4), P1–Pt1–H1 = 167(2).
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Scheme 4. Plausible reaction pathway for the formation of [PtH(SiH2Trip)(PMe3)(PPh3)] 5.
Scheme 4. Plausible reaction pathway for the formation of [PtH(SiH2Trip)(PMe3)(PPh3)] 5.
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Nakata, N.; Kato, N.; Sekizawa, N.; Ishii, A. Si–H Bond Activation of a Primary Silane with a Pt(0) Complex: Synthesis and Structures of Mononuclear (Hydrido)(dihydrosilyl) Platinum(II) Complexes. Inorganics 2017, 5, 72. https://doi.org/10.3390/inorganics5040072

AMA Style

Nakata N, Kato N, Sekizawa N, Ishii A. Si–H Bond Activation of a Primary Silane with a Pt(0) Complex: Synthesis and Structures of Mononuclear (Hydrido)(dihydrosilyl) Platinum(II) Complexes. Inorganics. 2017; 5(4):72. https://doi.org/10.3390/inorganics5040072

Chicago/Turabian Style

Nakata, Norio, Nanami Kato, Noriko Sekizawa, and Akihiko Ishii. 2017. "Si–H Bond Activation of a Primary Silane with a Pt(0) Complex: Synthesis and Structures of Mononuclear (Hydrido)(dihydrosilyl) Platinum(II) Complexes" Inorganics 5, no. 4: 72. https://doi.org/10.3390/inorganics5040072

APA Style

Nakata, N., Kato, N., Sekizawa, N., & Ishii, A. (2017). Si–H Bond Activation of a Primary Silane with a Pt(0) Complex: Synthesis and Structures of Mononuclear (Hydrido)(dihydrosilyl) Platinum(II) Complexes. Inorganics, 5(4), 72. https://doi.org/10.3390/inorganics5040072

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