Platinum-rhodium carbonyl clusters: New structures and new types of dynamical activity

The reaction of Rh-4(CO)(12) with Pt(PBu3t)(2) in CH2Cl2 at room temperature yielded three new complexes: Rh-4(CO)(4)-(mu-CO)(4) (mu(4)-CO)(PBU3t)(2)[Pt(PBu3t)], 10, Rh-2(CO)(8)[Pt(PBU3t)](2)[Pt(CO)], 11, and Rh-2(CO)(8)[Pt(PBU3t)](3), 12. The reaction of Rh-4(CO)(12) with an excess of Pt(PBu3t)2 in hexane at 68 degrees C yielded the new hexarhodium-tetraplatinum compound, Rh-6(CO)(16)[Pt(PBU3t)](4), 13, in a low yield. All four compounds were characterized by P-31 NMR and single-crystal X-ray diffraction analyses. Compound 10 contains an unsymmetrical quadruply bridging carbonyl ligand in the fold of a butterfly tetrahedral cluster of four rhodium atoms with a Pt(PBu3t) group bridging the hinge of the butterfly tetrahedron. Compound 11 contains an unsaturated trigonal bipyramidal Rh2Pt3 cluster. Compound 12 is similar to 11 except the trigonal bipyramidal Rh2Pt3 Cluster opened by cleavage of one Pt-Rh bond due to steric interactions produced by the replacement of one of the carbonyl ligands in 11 with a tri-tert-butylphosphine ligand. Compound 12 undergoes facile dynamical rearrangements of the metal atoms in the cluster which average the three inequivalent phosphine ligands on the platinum atoms. Compound 13 contains an octahedral cluster of six rhodium atoms with four Pt(PBu3t) groups bridging edges of that octahedron.