0277..5387191 $3.00+.00 Q 1991 Pergamon Press plc C-X AND C-H CLEAVAGE BY ELE~TRO~HEMICALLY GENERATED NON-LINEAR [PtLz] COMPLEXES JULIAN A. DAVIES? and RICHARD J. STAPLESS Dep~tments of Chemists and M~i~inal and Biological Chemistry, The University of Toledo, Toledo, OH 43606, U.S.A. Abstract-The electrochemical reduction of [PtX,L,] (X = halide, L, = bidentate diphos- phine: Ph2PCH2CH2PPh2, dppe; Cy,PCH2CH,PCy2, dcpe; Cy,P{CH2},PCy2, dcpp) has been used as a method of generating non-linear [PtL,] compounds whose reactivity with substrates Ar-X (X = CI, Br, CN, H, C=CPh) has been examined. Generation of [PtL,] (Lz = dppe or dcpe) in the presence of excess Ph-X (X = Cl, Br) produces [PtXPhL2] efficiently. Similarly, generation of [PtL,] (Lz = dppe or dcpe) in the presence of PhC=CPh results in trapping to form [PtL,(PhC=CPh)]. Generation of [PtL,] (IL, = dppe or dcpe) in the presence of PhCN or PhH results in indis~~minate reactions that do not produce tractable products. In contrast, reduction of ~PtCl*(d~pp)] in CH~C~~C~H~~Bu~NClO~ produces [PtHPh(dcpp)] with considerable selectivity via aromatic C-H activation by [Pt(dcpp)]. At room temperature the complex [PtHPh(dcpp)] undergoes exchange with C&, to generate [PtD(C,D,)(dcpp)]. In a recent series of papers Whitesides and co- workerslA3 have shown that Czv [PtL,] complexes can react with hydrocarbon substrates, including alkanes, by C-H oxidative addition. Thus, ther- molysis of the alkylhydride [PtH(CH&Me?) (Cy,PCH2CH,PCy,)] (Me = methyl, Cy = cyclo- hexyl) was shown to result in reductive elimination of neopentane and reaction of the resulting non- linear [PtLJ fragment with an organic substrate present in excess. We have demonstrated”7 that electrochemical reduction of cis-[PtCl,L,] com- plexes generates [PtL,3 equivalents and that in the case where L2 is a bidentate tertiary phosphine ligand’ the non-linear intermediate may be trapped by other bidentate ligands to produce [PtL2L2*]. Here we report on the reactions of non-linear [PtL,] equivalents, generated by electrochemical reduc- tion, with organic substrates including examples where C-X (X = halogen) and C-H oxidative additions are observed. 909 Initially we believed that the electrochemical generation of non-linear [PtL,] equivalents by reduction of [PtX,L,] might prove to be prob- 7 Author to whom correspondence should be addressed. $ Present address : Department of Chemistry, Texas A&M University, College Station, TX 77843, U.S.A. lematic since the electrochemical method requires the use of a relatively polar solvent and a back- ground electrolyte, both of which might participate in indiscriminate reactions with the Cae inter- mediate. However, work with bidentate ligands as trapping agents’ showed that unselective reactions with the solvent;ele~trolyte could largely be avoided provided a suitable trap was already present in solu- tion as the [PtLJ intermediate was generated. Thus, in order to probe the reactions of non-linear [PtL,] complexes with organic substrates we sought suit- able compounds to act as trapping agents. The requirements are quite stringent since the trapping agent must survive the very negative poten- tials required to reduce the [PtX,LJ precursors (typieally”7 zyxwvutsrqponmlkjihgfedcbaZYXWVUT ca - 1.50 to -2.40 V vs Ag/AgCl). Additionally, we sought trapping agents that would not react with the [PtX,L,] precursors, a problem that we had previously encountered in using biden- tate ligands as trapping agents.7 Based upon these requirements we examined compounds of the type Ph-X (where X = Cl, Br, CN, H, CzKPh) which could either be used as solvents for electrochemical reduction or added to a solvent/electrolyte system of acetonitrile/TBAP [TBAP = tetra(n-butyl)am- monium perchlorate]. In order to probe ligand effects on the reactivity of non-linear [PtLJ com-