SYNTHESIS OF MONONUCLEAR, DINUCLEAR AND OLIGOMERIC RIGID-ROD ACETYLIDE COMPLEXES OF RHODIUM, AND THE MOLECULAR-STRUCTURE OF [RH(PME3)4(CC-PARA-C6H4-CC)RH(PME3)4]

Reaction of two equivalents of [Rh(PMe3)4]Cl with HC = C-X-C = CH (X = none, p-C6H4, p-C6F4, p-C6H4-C6H4-p) yields the dinuclear acetylide bridged dications cis-cis-[Rh(PMe3)4(H) (C = C-X-C = C)Rh(PMe3)4(H) ]2+[Cl-]2, whereas reaction of [Rh(PMe3)4(Me)] with HC = C-X-C = CH (X = P-C6H4, P-C6H4-C6H4-p) yields neutral mononuclear, dinuclear or oligomeric rigid-rod complex mer-trans-[Rh(PMe3)3(H)(C = C-X-C = CH)2], [Rh(PMe3)4(CC = C-X-C = C)Rh(PMe3)4] or mer-trans-[-Rh(PMe3)3(H)-C = C-X-C = C]n, depending upon the stoichiometry employed (1:2, 2:1, or 1:1 respectively); the crystal and molecular structure of the dinuclear Rhl complex [Rh(PMe3)4(C = C-C6H4-C = C)Rh(PMe3)4] has been determined by X-ray diffraction, and soluble rigid-rod oligomers have been isolated from reactions employing the PBu(n)3 ligand.