SEQUENTIAL SYNTHESIS OF SOME TETRAOSMIUM ARENE CLUSTERS

On activation with Me3NO the tetrahydrido-tetranuclear cluster [Os4(mu-H)4(CO)12] 1 underwent reaction with cyclohexa-1,3-diene in CH2Cl2 under ambient conditions to give, as the major products, the four organometallic clusters [Os4(mu-H)3(CO)11(eta3-C6H9)] 2, [Os4(mu-H)2(CO)12(eta2-C6H8)] 3, [Os4(mu-H)2(CO)11(eta4-C6H8)] 4 and [Os4(mu-H)2(CO)10(eta6-C6H6)] 5. On heating in hexane, 3 is converted into 4 and subsequently 4 into 5. Compound 5 underwent further reaction with Me3NO in CH2Cl2 in the presence of cyclohexa-1,3-diene to produce [Os4(CO)9(eta6-C6H6)(eta4-C6H8)] 6 and [Os4(mu-H)2(CO)8(eta6-C6H6)(eta4-C6H8)] 7. Structural analyses of 4 and 7 by single-crystal X-ray diffraction have shown that the C6H8 ligand is bonded through two alkene bonds and that the benzene ligand in 7 is co-ordinated in an eta6 fashion. In each case the ligands are bonded to single osmium atoms only. Compound 5 was also found to react with Me3NO in CH2Cl2 in the presence of benzene yielding [Os4(CO)8(eta6-C6H6)2] 8, whilst with either toluene or mesitylene it undergoes arene displacement to produce [Os4(mu-H)2(CO)10(eta6-C6H5Me)] 9 or [Os4(mu-H)2(CO)10(eta6-C6H4Me2-1,3)] 10 respectively.