COMPARISON OF THE CLOSO TRIGONAL-BIPYRAMIDAL STRUCTURES OF MU-3-ETA-2-PERPENDICULAR-TO-ACETYLENE AND MU-3-ETA-2-PERPENDICULAR-TO-ACETYLIDE CLUSTERS - SYNTHESIS OF (ETA-5-C5H5)NIFE2(CO)6(MU-3-ETA-2-C=CPR(I) AND X-RAY STRUCTURES OF (ETA-C5H5)NIFE2(CO)5(L)(MU-3-ETA-2-C=CR) (R = PR(I), L = CO, R = BU(T), L = PPH3)

A comparison between the structures of closo trigonal-bipyramidal acetylene and acetylide clusters with M3C2 frameworks is made. The synthesis of (eta-5-C5H5)NiFe2(CO)6(mu-3-eta-2-C = CPr(i)) (1) from [(eta-5-C5H5)Ni(CO)]2, Ph2PC = CPr(i), and Fe2(CO)9 is described. X-ray structural analyses of (eta-5-C5H5)NiFe2(CO)5(L)(mu-3-eta-2-C = CR) (L = CO, R = Pr(i), 1; L = PPh3, R = Bu(t), 2) are described. Crystal data: 1, C16H12Fe2NiO6, M(r) = 470.67, triclinic space group P1BAR, a = 14.769 (7) angstrom, b = 14.824 (6), c = 8.708 (4), alpha = 91.77 (2)degrees, beta = 96.45 (2)degrees, gamma = 109.27 (2)degrees, V = 1784 (1) angstrom 3, Z = 4; 2, C35H29Fe2NiO5P.0.5C7H16, M(r) = 781.10, space group P2(1)/c, a = 10.058 (3) angstrom, b = 13.225 (6) angstrom, c = 26.906 (8) angstrom, beta = 96.08 (2)degrees, V = 3559 (2) angstrom 3, Z = 4. The structures of 1 and 2 were solved and refined on the basis of 5143 and 3289 observed intensities measured on Siemens AED and Syntex P2(1) diffractometers. Final R and R(w) values were 0.048 and 0.054 for 1 and 0.056 and 0.066 for 2. There are significant structural differences between the closo trigonal-bipyramidal M3C2 skeletons of the acetylide and acetylene clusters. In particular the M-C-alpha distances are much shorter in the acetylides, perhaps indicating substantial pi-character to the metal-sigma-acetylide bond. The intrapolyhedral M-C-alpha-C-beta angles are much larger in the acetylides than in the acetylenes. The C-alpha-R fragments in the mu-3-eta-2- perpendicular-to -acetylene clusters approximate more closely to an equatorial component of a trigonal bipyramid than the ''bare'' C-alpha in the mu-3-eta-2-acetylides. The acetylides show a closer structural resemblance to the M4 cluster carbides.