Insertion of alkynes into the Pt-Si bond of silylplatinum complexes leading to the formation of 4-sila-3-platinacyclobutenes and 5-sila-2-platina-1,4-cyclohexadienes.

Abstract

The reaction of dimethyl acetylenedicarboxylate (DMAD) with [Pt(SiHPh(2))(2)(PMe(3))(2)] produces cis-[Pt(CZ=CZ-SiHPh(2))(SiHPh(2))(PMe(3))(2)] (cis-1, Z = COOMe) and [Pt(CZ=CZ-SiPh(2))(PMe(3))(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(CZ=CZ-SiHPh(2))(SiHPh(2))(PMe(3))(2)] (trans-1) via intermediate 2 followed by reaction with H(2)SiPh(2). DMAD also reacts with [Pt(SiHPh(2))(2)(dmpe)] (dmpe = 1,2-bis(dimethylphosphino)ethane) to afford [Pt(CZ=CZ-SiHPh(2))(SiHPh(2))(dmpe)] (3). Conversion of 3 into 4-sila-3-platinacyclobutene [Pt(CZ=CZ-SiPh(2))(dmpe)] (4) takes place, accompanied by formation of H(2)SiPh(2), 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 Si-H group of the 3-sila-1-propenyl ligand and Pt via an Si-H-Pt 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 pi-coordinated DMAD, [Pt(CZ=CZ-SiPh(2)-CZ=CZ)(DMAD)(PMe(3))(2)] (5), which is also obtained from the reaction of excess DMAD with [Pt(SiHPh(2))(2)(PMe(3))(2)]. Unsymmetrical six-membered silaplatinacycles without pi-coordinated alkyne, [Pt(CZ=CZ-SiPh(2)-CH=CX)(PMe(3))(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 degrees C to form a mixture of the regioisomers [Pt(CZ=CZ-SiPh(2)-CMe=CZ)(PMe(3))(2)] (8) and [Pt(CZ=CZ-SiPh(2)-CZ=CMe)(PMe(3))(2)] (9).