Coordination of Phosphine-Thioether Ligands to Low-valent Metal Centers

Abstract: The reactivity of the phosphine-thioether ligands bis(2-diphenylphosphino) ethylthio)ethane (PSSP), bis(2-(diphenylphosphino) ethyl)sulfane (PSP), PPh2CH2CH2SMe (PS), PPh2(o-C6H4SMe (PortoS), and PPh(o-C6H4SMe)2 (PSS) towards low-valent carbonyl clusters has been studied. In all structurally characterized clusters, the ligand donor atoms are terminally coordinated. The phosphine-thioether ligands primarily react with triosmium clusters as phosphines, but prior coordination of the phosphine groups enables the thioether moieties to be coordinated also. The clusters [Os3(CO)11(L)] and [Os3(CO)11(PSnP)] (n=1,2), formed by reaction of the ligand with [Os3(CO)11(NCMe)], are coordinated through (one of) the phosphine groups whereas the remaining parts of the ligands remain in a dangling mode. In the dimeric clusters [{Os3(CO)11}2(m-PSnP)], which are also formed by reaction of the ligand with [Os3(CO)11(NCMe)], the ligands link two cluster subunits, coordinating via their phosphine moieties. The mono-coordinated clusters show a similar stereochemical non-rigid behaviour as found for [Os3(CO)11(L)] (L=phosphine, phosphite) clusters. Treatment of [Os3(CO)10(NCMe)2] with PSnP (n=1,2) affords clusters of formula [Os3(CO)10(m-PSnP)], in which the phosphines of the PSnP ligand occupy equatorial sites on different osmium atoms with the phosphorus atoms coordinated in cis,cis (n=1) or cis,trans (n=2) modes to the bridged metal atoms. NMR-data of the latter compound indicate that a concerted cis/trans isomerism with respect to the phosphines operates in the cluster. In the clusters 1,2-[Os3(CO)10(L)] (L= PS, PortoS or [Os3(CO)10(m-PSP)]), prepared by reaction of the ligands with [Os3(CO)10(NCMe)2], the phosphine- and the thioether moieties coordinate to different metal atoms of the metal triangle at equatorial positions. The P,S bridged clusters/cluster units are unstable, leading to isomerization to form clusters in which the ligands chelate one osmium atom. The clusters bridged by the ligands PortoS and PSS are less stable than complexes bridged by the ligands PS, PSP and PSSP. Spectroscopic evidence indicate hemilabile coordination of the thioether moieties in P,S-coordinated clusters. Oxidative decarbonylation of 1,1-[Os3(CO)10(PSS)] with Me3NO yields the symmetrical cluster [Os3(CO)9(PSS)]. In the tetrasubstituted clusters [Os3(CO)10{1,1-L}{2,2-L’}] (L=PortoS, PSS), formed by refluxing [Os3(CO)10(NCMe)2] with excess of ligand in benzene, the ligands chelate {Os(CO)2}-fragments having the sulfur donor atoms at opposite sides of the triosmium plane.