Synthesis and electrochemical characterization of halide, isocyanide, and alkynyl synthons containing the encumbered...

Useful synthons containing the tribridged triangular unit {Pt(3)} = [Pt(3)(mu-P(t)Bu(2))(3)](+) were prepared starting from the known tricarbonyl derivative [{Pt(3)}(CO)(3)]Z, [(1(+))Z, Z = CF(3)SO(3)(-)]. This was easily converted into the monohalides {Pt(3)}(CO)(2)X [2, X = Cl; 3, X = Br; 4, X = I], by reaction with the appropriate halide salt. The coupling reaction between 2 and terminal alkynes in the presence of CuI afforded in good yields the sigma-alkynyl derivatives {Pt(3)}(CO)(2)(CC-R) [6, R = SiMe(3); 7, R = CC-SiMe(3); 8, R = C(6)H(5); 9, R = C(6)H(4)-4-Br; 10, R = C(6)H(4)-4-CCH; 11, R = 2-C(4)H(2)S-5-CCH; 12, R = 9-C(14)H(8)-10-CCH], while desilylation of 6 or 7 with TBAF/THF gave, respectively, the derivatives 13 (R = H) and 14 (R = CCH). The stepwise elongation of the arylalkynyl chain was obtained by the Sonogashira coupling of 10 with an excess of 1,4-diiodobenzene, which produced 15 (R = C(6)H(4)-4-CC-C(6)H(4)-4-I), and by coupling the latter with an excess of 1,4-diethynylbenzene, which formed 16 (R = [C(6)H(4)-4-CC](3)H). Branched synthons were obtained by substitution of the carbonyl ligands with functional isocyanides; the reaction of an excess of CN-C(6)H(4)-4-R (R = I, CCH) with {Pt(3)}(CO)(2)H, 5, or with complex (1(+))Z afforded, respectively, {Pt(3)}(CN-C(6)H(4)-4-I)(2)H, 17, or [{Pt(3)}(CN-C(6)H(4)-4-R)(3)]Z [(18(+))Z, R = I; (19(+))Z, R = CCH]. The crystal structures of complexes 2, 8, and 9 were established by X-ray diffraction studies. The electrochemical characterization of representative examples of the clusters prepared in this work shows that all clusters are characterized by the presence of two oxidations; an analysis of ligands' effects on the redox processes is also included.