Ring Opening of Methylbenzothiophenes and Methyldibenzothiophenes by Tris(triethylphosphine)platinum(0)

Abstract

The reaction of [Pt(PEt3)3], 1, with 3-methylbenzothiophene and 2-methylbenzothiophene afforded the thiaplatinacycles [(Et3P)2Pt(C,S-C9H8S)], 3 and 4, respectively. In the formation of both complexes (Et3P)2Pt has inserted into the C−S bond to the vinylic carbon. Complex 4 rearranges in solution to a dimeric thiaplatinacycle, 5, in which the platinum has moved from lying between the vinylic C−S bond into the aromatic C−S bond. Reaction of 1 with 4-methyldibenzothiophene gave a mixture of isomeric thiaplatinacycles [(Et3P)2Pt(C,S-C13H10S)], 6 and 7. The reaction of 1 with 4,6-dimethyldibenzothiophene containing some 1,9-dimethyldibenzothiophene led to the isolation of complex 9, [(Et3P)2Pt(C,S-C14H12S)]. This is derived from 1,9-dimethyldibenzothiophene, which is a byproduct in the preparation of 4,6-dimethyldibenzothiophene by a metalation pathway. The reaction of 1 with highly pure 4,6-dimethyldibenzothiophene gave the hydride complex, 10, in which (Et3P)2Pt has inserted into the C−H bond at the 3-position. The thiaplatinacycle cis-[(Et3P)2Pt(η2-C,S-C14H12S)], 8, was obtained by reaction of highly pure 4,6-dimethyldibenzothiophene with cis-[PtCl2(PEt3)2] and metallic sodium under hydrogen. X-ray structures of complexes 3, 5, and 9 are reported.