An unprecedented bending of a bridging diynyl ligand in an unsymmetrical binuclear rhodium(I) complex

Article abstract of DOI:10.1021/om00004a035

The reaction of [Rh(η²-O₂CCH₃)(PiPr₃) ₂] (2) with 2 equiv of phenylbutadiyne leads, in the presence of Na₂CO₃, to the formation of the five-coordinate bis(diynyl)hydridorhodium(III) complex [RhH(C≡CC≡CPh)₂(PiPr₃)₂] (3). While 3 reacts with pyridine to give the stable octahedral compound [RhH(C≡CC≡CPh)₂(py)(PiPr₃)₂] (4), on treatment with carbon monoxide the square-planar complex trans-[Rh(C≡CC≡CPh)(CO)(PiPr₃)₂] (6) is formed via the spectroscopically characterized 1:1 adduct 5 as a labile intermediate. Compound 6, which has also been prepared from [Rh(η³-CH₂C₆H₅)(PiPr ₃)₂] (7), CO, and phenylbutadiyne, reacts with [RhCl(PiPr₃)₂]_n (1) to yield the binuclear complex [Rh(CO)(PiPr₃)₂(η¹,η ²-C≡CC≡CPh)-RhCl(PiPr₃)₂] (8). The X-ray structural analysis of 8 (triclinic space group P1 (No. 2) with a = 12.460(2) A?, b = 13.954(2) A?, c = 16.431(2) A?, α = 97.98(1)°, β = 91.47(1)°, γ = 109.61-(1)°, V = 2657(1) A?³, and Z = 2) reveals a square-planar coordination around each of the metal centers which are bridged by a strongly bent diynyl ligand. The reaction of 1 with phenylbutadiyne leads, via the isomeric diyne and diynyl hydrido species 9 and 10 as intermediates, to the alkynyl-substituted vinylidenerhodium(I) complex trans-[RhCl-(=C=CHC≡CPh)(PiPr₃)₂] (11). In the presence of pyridine the diynyl(hydrido)rhodium derivative [RhH(C≡CC≡CPh)Cl(py)(PiPr₃)₂] (12) is obtained.