Chemistry of low-valent osmium

by Grundy, Kevin Rodger

This study concerns the synthesis, structure and reactivity of complexes of d? and d? osmium. The reactivity of certain ligands coordinated to low-valent osmium has also been investigated.

Various hydride complexes of osmium(II) were prepared as potential precursors of osmium(O). OsH?(PPh?)? reacts with p-tolylisocyanide (TIC) and 4-ethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane (ETPO) to yield OsH?(L)(PPh?)? from which were derived OsH?(L’)(L)(PPh?)? (L, L’=CO, TIC, ETPO).

Attempts to eliminate hydrogen from the dihydrides failed. OsHCl(CO) (PPh?)? reacts with neutral ligands L (=TIC, ETPO, P(OMe)?, P(OPh)?, PPh?Me) to give OsHCl(CO)(L)(PPh?)? which, with silver perchlorate (L=TIC, ETPO only) afford OsH(OClO?)(CO)(L)(PPh?)?. The labile perchlorate ligand can be replaced by ligands L’ affording [OsH(CO)(L)(L’)(PPh?)?]ClO4 (L=TIC, L’=CO, TIC, PPh? L=ETPO, L’=CO, ETPO). OsHCl(CO)(PPh?)? reacts with silver perchlorate in acetonitrile to yield [OsH(CO)(CH N)?(PPh?)?]ClO4, which in turn reacts with neutral ligands to give [OsH(CO)(CH?N)(L)(PPh?)?]ClO? (L=CO, TIC, ETPO, PPh?). Cationic [OsH(CO)?(PPh?)?]+ and [OsH(TIC)?(PPh?)?]+ can be prepared from the action of PPh? on [OsH(CO)?(CH?N)(PPh?)?]+ and TIC on OsH(O?CCH?)(PPh?)? respectively. With base, [OsH(CO)(CH?N)(PPh?)?]ClO4 affords OsH(OH)(CO)(PPh?)? from which a series of hydroxide complexes OsH(OH)(CO)(L)(PPh?)? (L=CO, TIC ETPO) can be obtained. The hydroxide group in OsH(OH)(CO)(PPh?)? is cleaved by acids HX to yield OsHX(CO)(PPh?)? (X=F, Br, Cl, I, CH?, CF?, SC?H?, OClO?). Those members of the series with X=CN, N?, OCN, SCN were obtained from OsH(OClO?)(CO)(PPh?)? and the appropriate anion. From the values of vCO for this series can be gained some understanding of the bonding properties of the anionic ligands.