Synthesis and structure of the diynyl complexes [Mo(C [tbnd]CC [tbnd]CR)L 2(η-C 7H 7)], L 2 = chelate N- or P-donor ligand, R = SiMe 3 or H: X-ray crystal structures of [Mo(C [tbnd]CC [tbnd]CSiMe 3)(2,2′-bipyridine)(η-C 7H 7)] and [Mo(C [tbnd]CC [tbnd]CH)(Ph 2PCH 2CH 2PPh 2)(η-C 7H 7)

Abstract

The reaction of LiC CC CSiMe 3 with [MoBr( N– N)(η-C 7H 7)] in thf affords the diynyl complexes [Mo(C CC CSiMe 3)( N– N)(η-C 7H 7)], [ 1, N– N = 2,2′-bipyridine (bipy); 2, N– N=1,4- Bu 2 t -1,3-diazabutadiene (Bu t -dab)]; an analogous procedure yields [Mo(C CC CSiMe 3)(CO)(PPh 3)(η-C 7H 7)], 3 starting from [MoBr(CO)(PPh 3)(η-C 7H 7)]. Replacement of bipy in complex 1 with Ph 2PCH 2CH 2PPh 2 (dppe) in refluxing toluene gives [Mo(C CC CSiMe 3)(dppe)(η-C 7H 7)], 4. Proto-desilylation of 2 and 4 leads to formation of the unsubstituted diynyls [Mo(C CC CH)L 2(η-C 7H 7)] ( 5, L 2 = Bu t -dab; 6, L 2 = dppe). Cyclic-voltammetric studies in CH 2Cl 2 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.