CARBON-CARBON BOND-CLEAVAGE BY OSMIUM CLUSTERS - RING-OPENING OF A CYCLOBUTENYL LIGAND BY A TRIOSMIUM CLUSTERS

The reaction of 1-iodo-2-methylcyclobutene with the triosmium cluster complex OS3(CO)(10)-(NCMe)(2) has yielded four new osmium cluster compounds: Os-2(CO)(6)(mu-I)[mu-CC(Me)CH2CH2], 1 (5% yield), Os-3(CO)(9)(mu-I)[mu(3)-CC(Me)CH2CH2], 2 (8% yield), Os-3(CO)(9)(mu-I)[mu(3)-CC(Me)CH2-CH2], 3 (16% yield), and Os-3(CO)(10)(mu-I)[mu-CC(Me)CH2CH2], 4 (33% yield). Compounds 1-3 were characterized by single-crystal X-ray diffraction analysis. Compounds 1 and 4 contain a sigma,pi-coordinated 2-methylcyclobutenyl ligand. Compounds 2 and 3 are isomers. Both contain open triosmium clusters with a metalated acyclic sigma,pi-coordinated bridging alkenylidene ligand formed by the cleavage of one of the carbon-carbon bonds of the cyclobutenyl ring. An iodo ligand bridges one of the two metal-metal bonds in 2 and the nonbonded Os-Os pair of metal atoms in 3. Compound 2 is an intermediate to 3 and is converted to 3 in 90% yield in solution at 25 degrees C in 48 h. From the structure of 2 it can be inferred that the C-C bond cleavage process involves a direct oxidative addition of the C-CH2 carbon-carbon sigma-bond of the sigma,pi-coordinated bridging cyclobutenyl ligand in 4 adjacent to the pi-coordinated C-C double bond and occurs at the same metal atom. Crystal data for 1: space group = P2(1)/n, a = 8.376(2) Angstrom, b = 13.925(2) Angstrom, c = 13.138(3) Angstrom, beta = 102.32(1)degrees, Z = 4, 1719 reflections, R = 0.033. For 2: space group = P $($) over bar$$ 1, a = 9.146(2) Angstrom, b = 14.618(3) Angstrom, c = 8.528(2) Angstrom, alpha = 94.49(2)degrees, beta = 116.38(1)degrees, gamma = 81.94(2)degrees, Z = 2, 2246 reflections, R = 0.025. For 3: space group = P $($) over bar$$ 1, a = 13.900(3) Angstrom, b = 18.022(6) Angstrom, c = 12.896(2) Angstrom, alpha = 94.82(2)degrees, beta = 109.44(1)degrees, gamma = 90.17(2)degrees, Z = 6, 3941 reflections, R = 0.045.