Chemistry of multi-site bound unsaturated ligands on metal carbonyl clusters. Intramolecular reductive coupling in the conversion of [Ru3(µ-H)(CO)9(µ3,η2-CCBut)] to the butadienyl cluster [Ru3(CO)8{µ3,η4C(But)CC(H)C(Ph)(PPh2)}], and its crystal structure. An example of ligand isomerism on metal clusters

Abstract

The hydride [Ru₃(µ-H)(CO)₉(µ₃,η²-CCBu^t)](1) reacts with PPh₂CCPh, in the presence of Me₃NO, forming the monosubstituted cluster [Ru₃(µ-H)(CO)₈(PPh₂CCPh)(µ₃,η²-CCBu^t)](2), which has been characterized spectroscopically. Upon thermal treatment (2) gives the isomeric derivative [Ru₃(CO)₈{µ₃,η⁴-C(Bu^t)CC(H)C(Ph)(PPh₂)}](3), whose structure has been determined by X-ray diffraction methods. Crystals of (3) are triclinic, space group P, with Z= 2 in a unit cell of dimensions a= 12.351(5), b= 15.530(6), c= 10.558(5)Å, α= 91.27(2), β= 110.87(3), and γ= 106.94(3)°. The structure has been solved by direct and Fourier methods and refined by blocked-matrix least squares to R= 0.0472 for 4 109 observed reflections. The triangular cluster of Ru atoms is bound to eight carbonyl groups, of which seven are terminal and one is semibridging, and to a substituted butadienyl ligand, interacting with all three metal atoms, through a σ bond to Ru(3) and through extensive η bonding to Ru(1) and Ru(2). This organic ligand is obtained by tail-to-tail coupling of the cluster-bound C₂Bu^t of (2) with the phenylacetylide derived from the terminally bound phosphinoalkyne with shift of a phenyl group. A mechanism of formation of (3) from (2) is proposed and discussed.