Abstract
The reaction of the cycloneophylplatinum complex [Pt(CH(2)CMe(2)C(6)H(4))(NN)], 1, NN = 4,4'-di-t-butyl-2,2'-bipyridine (bubipy) or 2, NN = 3,4,7,8-tetramethyl-1,10-phenanthroline (phen*), with PhCHBr(2) gave the corresponding complex [PtBr(2)(CH(2)CMe(2)C(6)H(4)CHPh)(NN)], 3 or 4, which are formed by formal oxidative insertion of benzylidene, PhCH, into the arylplatinum bond of 1 or 2 respectively. By monitoring the reactions by (1)H NMR spectroscopy, intermediates were detected and shown to be products of oxidative addition [PtBr(CHBrPh)(CH(2)CMe(2)C(6)H(4)CHPh)(NN)], 5 and 6, along with a side product [PtBr(2)(CH(2)CMe(2)C(6)H(4))(NN)], formed by formal bromine addition to 1 or 2. Oxidative addition also occurs with complex [PtMe(2)(bubipy)] to give a single isomer of [PtBrMe(2)(CHBrPh)(bubipy)]. The formation of 3 and 4 gives the first examples of selective benzylidene insertion reactions into aryl-platinum bonds, and mechanistic studies show that the reactions are retarded in the presence of LiBr. DFT calculations predict that the insertion reaction occurs synchronously or immediately following cleavage of the C-Br bond of intermediate 5 or 6, perhaps involving a shortlived benzylidene complex of platinum(iv). The potential for applications in catalysis of related reactions involving benzylidene insertion step is discussed.