Insertion of Alkynes into the Pt-Si Bond of Silylplatinum Complexes Leading to Formation of 4-Sila-3-platinacyclobutenes and 5-Sila-2-platina-1,4-cyclohexadienes
The reaction of dimethyl acetylenedicarboxylate (DMAD) with [Pt(SiHPh2)2(PMe3)2] produces cis-[Pt(CZCZSiHPh2)(SiHPh2)(PMe3)2] (cis-1, Z = COOMe) and [P[bar t(CZCZSi ]Ph2)(PMe3)2] (2) depending on the reaction conditions. cis-1 and 2 are equilibrated in solution at room temperature, and they are isolated by recrystallization of the mixtures. cis-1 is converted slowly in solution into trans-[Pt(CZCZSiHPh2)(SiHPh2)(PMe3)2] (trans-1) via intermediate 2 followed by reaction with H2SiPh2. DMAD also reacts with [Pt(SiHPh2)2(dmpe)] (dmpe = 1,2-bis(dimethylphosphino)ethane) to afford [Pt(CZCZSiHPh2)(SiHPh2)(dmpe)] (3). Conversion of 3 into 4-sila-3-platinacyclobutene [P[bar t(CZCZSi ]Ph2)(dmpe)] (4) takes place, accompanied by formation of H2SiPh2, to give an equilibrated mixture of the two complexes. Crystallographic and spectroscopic data of cis-1, trans-1, and 3 suggest the presence of an intramolecular interaction between the SiH group of the 3-sila-1-propenyl ligand and Pt via an SiHPt three-center-four-electron bond in the solid state and in solution. DMAD reacts with 2 to give 5-sila-2-platina-1,4-cyclohexadiene with -coordinated DMAD, [P[bar t(CZCZSiPh2CZC ]Z)(DMAD)(PMe3)2] (5), which is also obtained from the reaction of excess DMAD with [Pt(SiHPh2)2(PMe3)2]. Unsymmetrical six-membered silaplatinacycles without -coordinated alkyne, [P[bar t(CZCZSiPh2CHC ]X)(PMe3)2] (6: X = COOMe; 7: X = Ph), are prepared analogously from the respective reactions of phenyl acetylene and of methyl acetylene carboxylate with 2. Methyl 2-butynolate reacts with 2 at 50 ｰC to form a mixture of the regioisomers [P[bar t(CZCZSiPh2CMeC ]Z)(PMe3)2] (8) and [P[bar t(CZCZSiPh2CZC ]Me)(PMe3)2] (9).
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