The Alkyne-Cluster Interaction: Structural, Theoretical and Spectroscopic Study on the Parallel m3- h2 Bonding Mode in Trinuclear Carbonyl Clusters of Ruthenium and Osmium

The parallel m-h-alkyne-cluster interaction in compounds of formula H2M3(C0)9(RC2R’)(M = Ru, Os) has been studied by means of X-ray diffraction, ‘H and I3C VT (variable temperature) NMR and UV-PES spectroscopy, and CNDO theoretical techniques. Crystals of H20s3(C0)9(CH3C2CH3) belong to the monoclinic space group P2 1 / n with unit cell dimensions of a = 14.538 (4) A, b = 13.004 (4) A, c = 9.817 (3) A, ,9 = 100.17 ( 5 ) O , and 2 = 4. Full-matrix least-squares refinement converged to R = 4.95% for 3223 unique reflections. Relevant interatomic distances (A): Os(l)-Os(2) = 3.016 (I), Os(l)-Os(3) = 2.763 = 2.364 (28), Os(3)-C(43) = 2.263 (27). The small differences observed between the Os(l)-C(42) and Os(2)-C(43) distances are thought to reflect the charge imbalance on the metal atoms. The lowest energy dynamic process observed in the ”C NMR spectra is consistent with an oscillatory motion of the alkyne and of the hydride bridging the Os(l)-0s(2) edge (Ha) coupled with the edge hopping of the second hydride (Hb). Subtle electronic changes induced by different substituents on the alkyne cause remarkable differences in the 2Jc,Hc oupling pattern between H, and CO ligands. The results of CNDO calculations have been used for the interpretation of the UV-PE spectra and for discussion of the bonding scheme of the studied molecules.