Dinuclear Palladium and Platinum Complexes with Bridging Silylene Ligands. Preparation Using (Aminosilyl)boronic Ester as the Ligand Precursor and Their Reactions with Alkynes

Abstract

Equimolar reactions of (aminosilyl)boronic ester Et2NSiPh2BOCMe2CMe2O with zerovalent complexes of Pt and Pd, M(PMe3)4 (M = Pt, Pd), afforded the dinuclear complexes with bridging silylene ligands {M(PMe3)2}2(μ-SiPh2)2 (1: M = Pt, 2: M = Pd). X-ray crystallographic studies of 1 and 2 revealed a Si···Si interaction in the M2Si2 four-membered ring. Diplatinum complex 1 reacted with arylacetylenes HC≡CAr (Ar = C6H5, C6H4Me-4), yielding 3,5-disila-4-platinacyclopentene Pt(SiPh2CAr═CHSiPh2)(PMe3)2 (3a: Ar = C6H5, 3b: Ar = C6H4Me-4), although the reaction mixture also contained complexes with the alkyne or the alkynyl ligands. The reaction of PhC≡CPh with dipalladium complex 2 gave Pd(SiPh2CPh═CPhSiPh2)(PMe3)2 as well as alkyne complex Pd(η2-PhC≡CPh)(PMe3)2. The reactions of HC≡CAr (Ar = C6H5, C6H4Me-4) with Pt(SiHPh2)2(PMe3)2 also formed 3a and 3b accompanied by 6-sila-3-platina-1,4-cyclohexadienes Pt(CAr═CHSiPh2CH═CAr)(PMe3)2 as the byproduct. A similar reaction of HC≡CCOOMe with Pt(SiPh2H)2(PMe3)2 yielded the five-membered disilaplatinacycle Pt(SiPh2C(COOMe)═CHSiPh2)(PMe3)2 as the sole product. Both the dinuclear complexes of Pd and Pt with bridging silylene ligands and mononuclear Pt complexes with two silyl ligands were converted to the disilaplatinacyclopentene via independent pathways. Details of the mechanism are discussed.