Trinuclear clusters of osmium containing monodentate, chelating and orthometallated forms of 2,2 '-bis(diphenylphosphino)-1,1 '-binaphthyl (BINAP)

The trinuclear cluster [Os-3(CO)(11){(R)-BINAP}] 1 containing monodentate ( R)-BINAP is formed by thermal treatment of [Os-3(CO)(12)] with 2,2'-bis(dip henylphosphino)-1,1'-binaphthyl, (R)-BINAP. This complex decarbonylates the rmally to give the cluster [Os-3(CO)(10){(R)-BINAP}] 2, which was shown spe ctroscopically to contain chelating BINAP. On further thermal decarbonylati on orthometallation at a phenyl group takes place to give [Os-3(mu-H)(CO)(8 ){mu(3)-(R)-BINAP - H}] 3. There is no evidence for restricted rotation abo ut the P-Ph bonds within the PPh2 groups as we have previously observed for [Ru-3(mu-OH)(2)(CO)(8){mu-(R)-BINAP}]. This restricted rotation is an effe ct of crowding and appears to be a distinct property of mu-coordination rat her than chelation of BINAP. However, both clusters 1 and 2 are fluxional, but as a result of different processes. Cluster 1 exists as two interconver ting isomers 1A and 1B (P-31 NMR evidence) which we believe have different conformations within the monodentate (R)-BINAP ligand. Our observations are consistent with restricted rotations about the Ph,P-naphthyl bonds. The de cacarbonyl cluster 2 has C-2 symmetry and shows C-13 NMR coalescences consi stent with a dynamic merry-go-round motion at the two Os(CO)(4) units but n ot at the Os(CO)(2)(BINAP) unit. Single-crystal structures of clusters I an d 3 confirm these two new modes of BINAP coordination.