Cationic Platinum(II) σ‐SiH Complexes in Carbon Dioxide Hydrosilation

Abstract

The low-electron-count cationic platinum complex [Pt(ItBu')(ItBu)][BAr ], 1, interacts with primary and secondary silanes to form the corresponding σ-SiH complexes. According to DFT calculations, the most stable coordination mode is the uncommon η -SiH. The reaction of 1 with Et SiH leads to the X-ray structurally characterized 14-electron Pt species [Pt(SiEt H)(ItBu) ][BAr ], 2, which is stabilized by an agostic interaction. Complexes 1, 2, and the hydride [Pt(H)(ItBu) ][BAr ], 3, catalyze the hydrosilation of CO , leading to the exclusive formation of the corresponding silyl formates at room temperature.

Homogeneous Catalytic Reduction of CO2 with Silicon‐Hydrides, State of the Art

“…The species [Pt(ItBu')(ItBu)][BAr F ] ( 9 ) (0.5 mol %) (BAr F =tetrakis(3,5‐trifluoromethyl)phenyl)borate) has demonstrated to be an effective catalyst for the hydrosilylation of CO 2 (5 bar) with H 3 SiBu in CH 2 Cl 2 at r.t. to afford the corresponding silylformate H 2 SiBu(OCOH) in 15 min (TOF=714 h −1 ) . The activity of this catalytic system depends on the silane.…”

“…Thus, using H 2 SiEt 2 the hydrosilylation reactions are slower than with H 3 SiBu. 1 H NMR studies of the reactions of complex 9 with H 3 SiBu evidenced the formation of the σ‐Si−H adduct [Pt(ItBu')(ItBu){η 1 ‐ (H 3 SiBu)}][BAr F ] ( 10 ), whose structure was proposed based on 1 H and 29 Si NMR spectroscopy in solution at 223 K (Scheme ) . In this regard, it is remarkable that Conejero and collaborators have recently reported the characterization by X‐ray diffraction methods of a cation platinum σ‐silane species, related to 10 , bearing the silane HSiEt 3 (or HSiPh 3 ) in η 1 ‐(Si−H) coordination mode .…”

Mechanistic Insights on the Reduction of CO2 to Silylformates Catalyzed by Ir‐NSiN Species

“…[3a] Therefore, the development of active and selectivec atalytic systemsf or the reduction of CO 2 with silanes is of great interest. Some examples of catalytic systems that allow the selective reduction of CO 2 with hydrosilanes or hydrosiloxanest og ive the corresponding silylformate, [4][5][6][7][8][9][10][11][12] bissilylacetal, [13] methoxysilane, [14] or methane [15] are known. Particularly,s ilylformates have attracted attention during the last recenty ears owing to their potentialu se as aC 1s ource in organic synthesis.…”

Enhancing the catalytic properties of well-defined electrophilic platinum complexes

“…96 According to DFT calculations carried out on the interaction of complex 49 with silanes, the most stable coordination mode is the unusual Z 1 -SiH. 97 Only very recently, we have succeeded in the isolation of closely related species of this type confirming the predicted Z 1 -SiH coordination. 98 It is likely that this mode of coordination of the silane to the cationic platinum centre enhances even more the reactivity of the silicon atom, since p-back donation from the metal to the s*-Si-H bond is expected to be low.…”

“…96 In fact, it is likely that this electrophilic character is also relevant in the selective catalytic hydrosilylation of carbon dioxide (Scheme 38) to the formic acid level by complex 49 and the related complexes 50 and 51, a reaction taking place at rt with catalyst loadings leading to TONs and TOFs up to 200 and 714 h À1 , respectively. 97 Nevertheless, according to DFT calculations all three complexes 49-51 lead to Z 1 -SiH complexes, but their catalytic performance is rather different, with complex 49 being the most active. Therefore, other parameters (electronic and steric) may be also important in the electrophilic activation of the silane.…”