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

Abstract

The trinuclear cluster [Os₃(CO)₁₁{(R)-BINAP}] 1 containing monodentate (R)-BINAP is formed by thermal treatment of [Os₃(CO)₁₂] with 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl, (R)-BINAP. This complex decarbonylates thermally to give the cluster [Os₃(CO)₁₀{(R)-BINAP}] 2, which was shown spectroscopically to contain chelating BINAP. On further thermal decarbonylation orthometallation at a phenyl group takes place to give [Os₃(µ-H)(CO)₈{µ₃-(R)-BINAP – H}] 3. There is no evidence for restricted rotation about the P–Ph bonds within the PPh₂ groups as we have previously observed for [Ru₃(µ-OH)₂(CO)₈{µ-(R)-BINAP}]. This restricted rotation is an effect of crowding and appears to be a distinct property of µ-coordination rather than chelation of BINAP. However, both clusters 1 and 2 are fluxional, but as a result of different processes. Cluster 1 exists as two interconverting isomers 1A and 1B (³¹P NMR evidence) which we believe have different conformations within the monodentate (R)-BINAP ligand. Our observations are consistent with restricted rotations about the Ph₂P–naphthyl bonds. The decacarbonyl cluster 2 has C₂ symmetry and shows ¹³C NMR coalescences consistent with a dynamic merry-go-round motion at the two Os(CO)₄ units but not at the Os(CO)₂(BINAP) unit. Single-crystal structures of clusters 1 and 3 confirm these two new modes of BINAP coordination.

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