Structural Systematics of Metal Acetylide Complexes: X-Ray Studies of Some 'Extended-Chain' Gold σ-Acetylide Complexes

Abstract

The structures of Au(4-C≡CC₆H₄XYC₆H₄-4′-NO₂)(PPh₃) (XY = (E )-CH=CH (1), (Z)-CH=CH (2), C≡C (3), N=CH (4)) have been determined by single-crystal X-ray diffraction analyses, refining by full-matrix least-squares analysis. For (1), crystals are triclinic, space group P^-1, with a8·847(1), b 17·870(4), c 19·705(3) Å, α116·25(1), β 93·33(1), γ 92·64(2)˚, Z 4, 6747 unique reflections (703 parameters), converging at R 0·025 and R_w 0·029. For (2), crystals are monoclinic, space group P 2₁/a, with a 10·718(6), b 19·398(5), c14·469(3) Å, β 108·96(2)˚, Z 4, 3295 unique reflections (352 parameters), converging atR 0·040 and R_w 0·034. For (3), crystals are triclinic, space group P^-1, with a 10·671(4), b 17·599(7), c 18·220(8) Å, α 116·31(3), β 105·00(4), γ 95·08(4)˚, Z 4, 4828 unique reflections (703 parameters), converging at R 0·043 and R_w 0·030. For (4), crystals are triclinic, space group P^-1, with a 8·8314(6), b 17·834(2), c 20·001(2) Å, α 115·249(7), β 90·930(7), γ 94·082(7)˚, Z 4, 4724 unique reflections (703 parameters), converging at R 0·035 and R_w 0·034. Despite the [ligated metal donor]-bridge-[nitro acceptor] composition of these complexes, Au–C and C≡C distances are normal and consistent with minimal allenylidene contribution to the ground-state geometry. Within the 3σ confidence limits, the structural data do not provide evidence for π*-back-bonding in these complexes