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

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Si–H Bond Activation of a Primary Silane with a Pt(0) Complex: Synthesis and Structures of Mononuclear (Hydrido)(Dihydrosilyl) Platinum(II) Complexes inorganics Article Si–H Bond Activation of a Primary Silane with a Pt(0) Complex: Synthesis and Structures of Mononuclear (Hydrido)(dihydrosilyl) Platinum(II) Complexes Norio Nakata * ID , 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; [email protected] (N.K.); [email protected] (N.S.) * Correspondence: [email protected] (N.N.); [email protected] (A.I.); Tel.: +81-48-858-3392 (N.N.); Fax: +81-48-858-3700 (N.N.) Received: 3 October 2017; Accepted: 24 October 2017; Published: 25 October 2017 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) 2 with [Pt(η -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. Keywords: platinum; primary silane; hydrido complex; oxidative addition; ligand-exchange reaction; X-ray crystallography 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 [2–6] and bis-silylations [7,8], as well as the dehydrogenative couplings of hydrosilanes [9–13]. While a number of reactions of hydrosilanes with platinum(0) complexes affording mononuclear bis(silyl) [14–18] and silyl-bridged multinuclear complexes [19–29] 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 [30–34]. 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 Inorganics 2017, 5, 72; doi:10.3390/inorganics5040072 www.mdpi.com/journal/inorganics Inorganics 2017, 5, 72 2 of 11 Inorganics 2017, 5, 72 2 of 11 t described the synthesis of a bis(phosphine) hydrido(dihydrosilyl) complex [PtH(SiH2Si Bu2Me)(dcpe)] of a bis(phosphine) hydrido(dihydrosilyl) complex [PtH(SiH2SitBu2Me)(dcpe)] (dcpe = 1,2- bis(dicyclohexylphos(dcpe = 1,2-bis(dicyclohexylphosphino)ethane)phino)ethane) containing containinga Si–Si bond a Si–Si [36]. bond Meanwhile, [36]. Meanwhile, we succeeded we succeeded in the in the first isolation of a series of hydrido(dihydrogermyl) platinum(II) complexes [PtH(GeH2Trip)(L)] first isolation of a series of hydrido(dihydrogermyl) platinum(II) complexes [PtH(GeH2Trip)(L)] (Trip =(Trip 9-triptycyl) = 9-triptycyl) using using a bulky a bulky substi substituent,tuent, 9-triptycyl 9-triptycyl group group [37]. [37 In]. Inaddition, addition, we we reported reported the the first first synthesessyntheses and and structural structural characterizations characterizations of of hydrido hydrido palladium(II) palladium(II) complexes complexes with with a a dihydrosilyl- dihydrosilyl- or dihydrogermyl ligand, [PdH(EH2Trip)(dcpe)] (E = Si, Ge) [38]. Very recently, we also found that or dihydrogermyl ligand, [PdH(EH2Trip)(dcpe)] (E = Si, Ge) [38]. Very recently, we also found that hydride-abstraction reactions of [MH(EH Trip)(dcpe)] (M = Pt, Pd, E = Si, Ge) with B(C F ) led to the hydride-abstraction reactions of [MH(EH22Trip)(dcpe)] (M = Pt, Pd, E = Si, Ge) with B(C66F5)33 led to the formationsformations of of new new cationic cationic dinuclear dinuclear complexes complexes with with bridging bridging hydrogermylene hydrogermylene and and hydrido hydrido ligands, ligands, [{M(dcpe)} (µ-GeHTrip)(µ-H)]+ [39]. As an extension of our previous work and taking into account the [{M(dcpe)}22(μ-GeHTrip)(μ-H)]+ [39]. As an extension of our previous work and taking into account theinterest interest devoted devoted to hydrido to hydrido platinum(II) platinum(II) complexes, complexes, we present we here present the synthesis here andthe characterizationsynthesis and of a series of mononuclear (hydrido)(dihydrosilyl) complexes [PtH(SiH Trip)(L) ]. characterization of a series of mononuclear (hydrido)(dihydrosilyl) complexes2 [PtH(SiH2 2Trip)(L)2]. 2. Results 2. Results 2.1. Synthesis and Characterization of [cis-PtH(SiH2Trip)(PPh3)2](2) 2.1. Synthesis and Characterization of [cis-PtH(SiH2Trip)(PPh3)2] (2) 2 The reaction of TripSiH3 1 with [Pt(η -C2H4)(PPh3)2] in toluene proceeded efficiently at room 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] temperature(2) in 91% yield under as inert colorless atmosphere crystals to (Scheme form the1). corresponding In the 1H NMR complex spectrum [cis-PtH(SiH of 2, the2 characteristicTrip)(PPh3)2] 1 (signals2) in 91% of yield the platinumas colorless hydride crystals were (Scheme observed 1). In the at δ H= NMR−2.15, spectrum which wereof 2, the split characteristic by 19 and 31 signals157 Hz of of the31 platinumP–1H couplings hydride accompanyingwere observed at 958 δ = Hz−2.15, of which satellite were signals split by from 19 and the 157195 PtHz isotope.of P– 1 195 ThisH couplings chemical accompanying shift is comparable 958 Hz of with satellite those signals of the from related the (hydrido)(dihydrosilyl)Pt isotope. This chemical complexes, shift is comparable with those of the related (hydrido)(dihydrosilyl) complexes, [cis-PtH(SiH2tAr)(PPr3)2] (Ar [cis-PtH(SiH2Ar)(PPr3)2](Ar = 2,6-MesC6H3) (δ = −3.40) [35] and [cis-PtH(SiH2Si Bu2Me)(dcpe)] = 2,6-MesC6H3) (δ = −3.40) [35] and [cis-PtH(SiH2SitBu2Me)(dcpe)] (δ = −0.89) [36]. The SiH31 2 resonance1 (δ = −0.89)[36]. The SiH2 resonance appeared as a multiplet at δ = 4.68 ppm. The P{ H} NMR appeared as a multiplet at δ = 4.68 ppm. 2The 31P{1H} NMR spectrum of 2 exhibited195 two doublets31 (2JP– spectrum of 2 exhibited two doublets ( JP–P = 15 Hz) at δ = 33.8 and 34.5 with Pt– P coupling 195 31 Pconstants, = 15 Hz) 2183at δ and= 33.8 1963 and Hz, 34.5 which with were Pt– assignedP coupling to the phosphorusconstants, 2183 atoms and lying 1963trans Hz,to which the hydrido were assignedand dihydrosilyl to the phosphorus ligands, respectively, atoms lying intrans agreement to the hydrido with the and NMR dihydrosilyl data for ligands, reported respectively, germanium in agreement with the NMR data for reported germanium1 congener [cis-PtH(GeH1 2Trip)(PPh3)2] [δ = congener [cis-PtH(GeH2Trip)(PPh3)2][δ = 31.2 ( JPt–P = 2317 Hz) and 31.6 ( JPt–P = 2252 Hz)] [37]. 1 1 31.2The ( siliconJPt–P = 2317 atom Hz) of and2 gave 31.6 rise ( JPt–P to = a 2252 resonance Hz)] [37]. around The siliconδ = −40.6 atom with of 2 splittinggave rise dueto a toresonance31P–29Si around δ = 2−40.6 with splitting2 due to 31P–29Si couplings195 (2JP(trans)–Si =1 161, 2JP(cis)–Si = 15 Hz) and29 1951Pt couplings ( JP(trans)–Si = 161, JP(cis)–Si = 15 Hz) and Pt satellites ( JPt–Si = 1220 Hz) in the Si{ H} 1 29 1 satellitesNMR spectrum. ( JPt–Si = 1220 In theHz) solid in the state Si{ IRH} spectrum NMR spectrum. for 2, Pt–H In the and solid Si–H state stretching IR spectrum vibrations for 2, Pt–H were −1 andobserved Si–H atstretching 2041 and vibrations 2080 cm−1 were, respectively. observed Complex at 2041 2andis thermally 2080 cm and, respectively. air stable in Complex the solid state2 is thermally(melting point: and air 123 stable◦C (dec.)) in theor insolid solution, state and(melting no dimerization point: 123 or°C dissociation (dec.)) or ofin phosphinesolution, and ligands no dimerizationwas observed. or dissociation of phosphine ligands was observed. Scheme 1. Synthesis of [cis-PtH(SiH2Trip)(PPh3)2] 2. Scheme 1. Synthesis of [cis-PtH(SiH2Trip)(PPh3)2] 2. The molecular structure of 2 was determined unambiguously by X-ray crystallographic analysis, as depictedThe molecular in Figure structure1. The of X-ray 2 was crystallographic determined unambiguously analysis of 2 byrevealed X-ray crystallographic that the platinum analysis, center asattains depicted a distorted in Figure square-planar 1. The X-ray environment, crystallographic which analysis was probably of 2 revealed due to that the stericthe platinum requirement center of attainsthe cis-coordinated a distorted square-planar PPh3 ligands environment, and the bulky whic 9-triptycylh was probably group on due the siliconto the steric atom.
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