Di- and Trinuclear Complexes of Pd(0) and Pt(0) with Bridging Silylene Ligands: Structures with a Coordinatively Unsaturated Metal Center and Their Reactions with Alkynes

• Published in: Organometallics Vol. 41; no. 22; pp. 3301 - 3312
• Main Authors: Tanabe, Makoto, Nakamura, Yu, Niwa, Taka-aki, Sakai, Masaru, Kaneko, Akira, Toi, Hiroyuki, Okuma, Kazuki, Tsuchido, Yoshitaka, Koizumi, Take-aki, Osakada, Kohtaro, Ide, Tomohito
• Format: Journal Article
• Language: English
• Published: American Chemical Society 28.11.2022
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.2c00286

Reactions of Et2NSiPh2B­(pin) with [Pd­(PCy3)2] and [Pt­(PCy3)2] produce dinuclear Pd(0) and Pt(0) complexes bearing a bridging diphenylsilylene ligand, [{M1(PCy3)}­{M2(PCy3)2}­(μ-SiPh2)] (1-Pd 2 , M1 = M2 = Pd; 1-PdPt, M1 = Pd, M2 = Pt; 1-Pt 2 , M1 = M2 = Pt), and a trinuclear Pd complex, [{Pd­(PCy3)}3(μ-SiPh2)­(μ3-SiPh2)] (2), depending on the conditions used. X-ray crystallographic studies of 1-Pd 2 , 1-PdPt, and 1-Pt 2 show that the molecules contain an almost linear P–M–M–P arrangement with P–M–M angles in the range of 157–168°. The distance between two metal centers decreased in the order of 1-Pd 2 > 1-PdPt > 1-Pt 2 . Complex 2 is composed of a bent Pd3 backbone with a Pd–Pd–Pd angle of 110°. All Pd atoms are bridged by a SiPh2 ligand, while two of them are bridged by another SiPh2 ligand. Complex 1-Pd 2 catalyzes the 1:2 cycloaddition of Et2NSiPh2B­(pin) with HCCPh to form 2,4- and 3,4-disubstituted siloles. A similar reaction with HCC t Bu afforded a mixture of the corresponding siloles and alkynyl­(alkenyl)­diphenylsilane, ( t BuCC)­( t BuCHCH)­SiPh2 (5c). The yields and selectivities of the products are lower than those obtained in the previously reported reactions catalyzed by the Pd–PPh3 catalytic system. The stoichiometric reactions of HCC t Bu and HCCSiMe3 with 1-Pt 2 trigger a C–H­(sp) bond activation process to occur to form complexes with the alkynyl ligand, [{PtH­(PCy3)}­{Pt­(PCy3)}­(μ-SiPh2)­(μ-η1,η2-CCR)] (6b, R = t Bu; 6c, R = SiMe3) at room temperature. Complex 6c reacts with alkynes at 70 °C to form complexes bearing the bridging alkenylsilyl ligand, [{Pt­(PCy3)}2{μ-η1,η2-SiPh2C­(SiMe3)CH2 }(μ-η1,η2-CCR)] (7b, R = t Bu; 7c, R = SiMe3). Complex 7c undergoes reductive elimination of alkynyl­(alkenyl)­diphenylsilane upon the addition of a diphosphine ligand. The reaction of dimethyl acetylenedicarboxylate with 1-Pt2 gives a diplatinum complex with a silaplatinacyclohexadiene structure, [{(Cy3P)Pt­(CZCZSiPh2CZCZ)Pt­(PCy3)}­(μ-η1,η2-CZCZ)] (8, Z = CO2Me). The mechanisms of the stoichiometric and catalytic reactions are discussed based on our experimental results.