SYNTHESIS OF UNSATURATED OS3W2 AND METASTABLE OS4W OXO-ETHYLIDYNE CLUSTERS BY SOLID-STATE PYROLYSIS - DIRECT C-O BOND-CLEAVAGE OF A COORDINATED KETENYL LIGAND

Heterometallic ketenyl complex OS3(CO)10(mu-H)[C(O)CH2(W(CO)3CP)] (1a) possessing a pendant CPW(CO)3 substituent was prepared by condensation Of OS3(CO)10(NCMe)2 with the metal-aldehyde compleX CPW(CO)3CH2CHO. Pyrolysis of 1a in the solid state at 185-degrees-C afforded two heteropentametallic cluster compounds, CP2W2OS3(CO)12(mu-O)(mu3-CMe) (2) and CPWOS4-(CO)12(mu-O)(mu3-CMe) (3), demonstrating a unique example of C-0 bond scission of a ligated ketene fragment and a cluster aggregation process. Complex 2 crystallizes in orthorhombic space group Pnma with a = 18.913(4) angstrom, b = 16.229(3) angstrom, c = 9.129(2) angstrom, Z = 4, R = 0.054, and R(w) = 0.055 for 2551 observed reflections. The W2Os3 cluster that contains 72 cluster valence electrons has a distorted square-pyramidal array of metal atoms with one Os-H-Os hydride ligand, one bridging oxo ligand associated with a W-W double bond, and an ethylidyne ligand bridging a unique W2Os triangle. Crystals of 3 are monoclinic of space group P2(1)/n with a = 15.941(2) angstrom, b = 19.395(4) angstrom, c = 16.369(4) angstrom, beta = 94.72(2)-degrees, Z = 8, R = 0.050, and R(w) = 0.041 for 6568 observed reflections. This molecule possesses a WOS4 trigonal-bipyramidal skeleton with an oxo ligand bridging a W-Os edge and an ethylidyne ligand capping a WOS2 face, Isomerization of 3 occurred upon dissolution at room temperature to afford edge-bridging tetrahedral cluster CpWOS4(CO)12(mu3-0)(mu3-CMe) (4), in which the oxo ligand formally migrated from an edge-bridging to a face-bridging position. Pyrolysis of 4 in the solid state at 190-degrees-C regenerated 3 in h gh yield, suggesting the existence of a delicate equilibrium between these two cluster complexes. Crystal data for 4: space group P2(1)/n, a = 9.492(3) angstrom, b = 16.990(2) angstrom, c = 15.887(3) angstrom, beta = 98.79(2)-degrees, Z = 4. The structure was solved by direct methods and refined to R and R(w) values of 0.039 and 0.032 for 4455 observed reflections with I > 2sigma(I).