Synthesis and structure of the diynyl complexes [Mo(Ctriple bond; length of mdashCCtriple bond; length of mdashCR)L2(η-C7H7)], L2 = chelate N- or P-donor ligand, R = SiMe3 or H: X-ray crystal structures of [Mo(Ctriple bond; length of mdashCCtriple bond; l

The reaction of LiCtriple bond; length of mdashCCtriple bond; length of mdashCSiMe3 with [MoBr(N –N )(η-C7H7)] in thf affords the diynyl complexes [Mo(Ctriple bond; length of mdashCCtriple bond; length of mdashCSiMe3)(N –N )(η-C7H7)], [1, N –N = 2,2′-bipyridine (bipy); 2, N –N =1,4-View the MathML sourceBu2t-1,3-diazabutadiene (But-dab)]; an analogous procedure yields [Mo(Ctriple bond; length of mdashCCtriple bond; length of mdashCSiMe3)(CO)(PPh3)(η-C7H7)], 3 starting from [MoBr(CO)(PPh3)(η-C7H7)]. Replacement of bipy in complex 1 with Ph2PCH2CH2PPh2 (dppe) in refluxing toluene gives [Mo(Ctriple bond; length of mdashCCtriple bond; length of mdashCSiMe3)(dppe)(η-C7H7)], 4. Proto-desilylation of 2 and 4 leads to formation of the unsubstituted diynyls [Mo(Ctriple bond; length of mdashCCtriple bond; length of mdashCH)L2(η-C7H7)] (5, L2 = But-dab; 6, L2 = dppe). Cyclic-voltammetric studies in CH2Cl2 reveal that each of complexes 1, 2 and 4–6 undergo reversible one-electron oxidation processes on the electrochemical time-scale. The X-ray crystal structures of complexes 1 and 6 are reported; the bipyridine complex 1, exhibits a π–π stacking interaction between the bipy ligands of adjacent molecules leading to a head-to-head interaction between diynyl ligands and a resultant substantial bending of the diynyl chain.