SYNTHESIS, X-RAY STRUCTURAL AND SPECTROSCOPIC STUDY OF NEW SILYL-SUBSTITUTED TRIOSMIUM CLUSTERS

The 2-pyridyldimethylsilane, 2-(CH3)2SiHC5H4NLH reacts with [Os3(mu-H) 2(CO)10] to afford the novel cluster [Os3(mu-H)2(CO)10L2] 1 in which e ach of the ligands L has been shown from single crystal X-ray diffract ion study to bond to one osmium atom through the silicon atom only. In addition, several silyl-substituted triosmium clusters of general for mula [Os3(mu-H)(CO)11{2BrC6H4CH2Si(CH3)2-nHn}] (n = 0, 2A; 1, 2B; 2, 2 C), [Os3(mu-H)(CO)10(CH3CN){2-BrC6H4CH2Si(CH3)2-nHn}] (n = 0, 3A; 1, 3 B) have been synthesized from the reactions of the silane derivatives BrC6H4CH2Si(CH3)3-mHm [m = 1, I; 2, II; 3, III] with the activated clu sters [Os3(CO)11CH3CN] and [Os3(CO)10(CH3CN)2], respectively. The acet onitrile molecule in 3A is readily substituted by a triphenylphosphine molecule to yield [Os3(mu-H)(CO)10(Ph3P){2-BrC6H4CH2Si(CH3)2}] (4). R eaction of [Os3(mu-H)2(CO)10] with 2-BrC6H4Si(CH3)2H affords the clust er [Os3(mu-H)3(CO)9{2-BrC6H4CH2Si(CH3)2}](5). In the case of 3A the si lane moiety bonds to an osmium atom at a position equatorial to the Os 3 triangle while the acetonitrile molecule takes up an axial position. The molecular structure of 4 contains both the silane and the triphen ylphosphine moieties at the terminal, equatorial positions on two sepa rate osmium atoms. The behaviour under high performance liquid chromat ography of these clusters has been determined and correlated with the nature of the ligands and with the molecular weights and sizes of the clusters.