Trinuclear Clusters of Ruthenium-Containing Bridging and Ortho-Metalated 2,2‘-Bis(diphenylphosphino)-1,1‘-binaphthyl (BINAP): X-ray Structures of (R)-BINAP and [Ru3(μ-OH)2(CO)8{μ-(R)-BINAP}

Abstract

The cluster [Ru3(CO)12] normally reacts readily with tertiary phosphines and diphosphines in the presence of Me3NO to give simple phosphine-substituted derivatives by a reaction involving nucleophilic attack of the amine oxide at CO leading to CO2 formation. However, the corresponding reaction of [Ru3(CO)12] with (R)-BINAP [2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl] in the presence of Me3NO does not give [Ru3(CO)10(BINAP)], as expected, but instead an 80% yield of the dihydroxy complex [Ru3(μ-OH)2(CO)8{μ-(R)-BINAP}] (1) as the first example of a μ-BINAP complex. NMR coalescence effects are observed in the 1H NMR spectra, but by using a 13CO-enriched sample, we were able to show that the fluxionality is not cluster-centered since the 13C{1H} NMR spectrum for the CO ligands is invariant over a wide temperature range. COSY spectra were used to show that there is restricted rotation about two of the four P−Ph bonds while the other two are rotating freely. From a single-crystal XRD study it can be seen that two Ph groups are unimpeded while the other two are closely aligned to the naphthyl rings in a graphitic manner and it is this that leads to the restricted rotation. This bridging ligand adopts quite a different conformation about the C−PPh2 bonds to that in free BINAP, the structure of which was also determined for comparison, and somewhat different from that in known chelating BINAP complexes. In contrast, the direct thermal reaction of (R)-BINAP with [Ru3(CO)12] in octane gives, in addition to traces of two uncharacterized species, a 38% yield of the cluster [Ru3(μ-H){μ-(R)-BINAP-H}(CO)9] (2), in which we believe that ortho metalation has occurred at one of the four Ph rings to form the first example of a cyclometalated BINAP ligand. We have been unable to obtain simple derivatives such as [Ru3(CO)11(BINAP)] or [Ru3(CO)10(BINAP)], although we have shown that the osmium analogues may be synthesized.