Polycarbon Ligand Complexes: Synthesis, Molecular Structures, and Selected EHMO Studies of Ru4, Ru5, and Ru6 Clusters with Carbon Ligands Derived from Phosphinodiynes

Thermolysis of the monosubstituted cluster Ru 3 (CO) 11 (Ph 2 PC⋮C−C⋮CR) (R = Bu t, Ph, SiMe 3 ), obtained via CO substitution in Ru 3 (CO) 12, results in P−C and Ru−Ru bond cleavage. Recombination of the fragments yields a range of polyruthenium compounds containing −(C⋮C)− n ligands ( n = 2−4). The complexes Ru 4 (CO) 9 (μ-PPh 2 ) 2 {μ 4 -η 1,η 2,η 2,η 1 -C⋮C−C C(Bu t )−C⋮C−C⋮CBu t } ( 2 ), Ru 4 (CO) 10 (μ-CO)(μ 4 -PPh){μ 4 -η 1,η 1,η 2,η 2 -(Bu t C⋮C)C⋮CPh} ( 3 ), Ru 4 (CO) 10 (μ 4 -PPh)(μ 4 -η 1,η 1,η 3,η 3 -PhC⋮C−C⋮CBu t ) ( 4 ), Ru 5 (CO) 11 (μ-CO)(μ-PPh 2 ) 2 (μ 3 -η 1,η 1,η 1 -C⋮C−C⋮CBu t )(μ 4 -C)(μ 2 -η 1,η 1 -C−C⋮CBu t ) ( 5 ), Ru 6 (CO) 13 (μ-CO) 2 (μ-PPh 2 )(μ 5 -C)(μ 3 -η 1,η 1,η 1 -C−C⋮CR) ( 6a, R = Bu t; 6b, R = Ph), and {Ru 2 (CO) 6 (μ-PPh 2 } 2 (μ-η 1,η 2:μ-η 1,η 2 -C⋮C−C⋮C−) ( 7 ) have been fully characterized. The crystal structure of 2 revealed a polyunsaturated C 8 chain formed by the head−tail coupling of two diynyl units bound to the metal core in μ 4 -η 3 mode to produce a pendant penta-1-enediyne functionality. Clusters 3 and 4 feature square-planar arrangements of metal atoms capped on one side by a μ 4 -PPh ligand and on the other side by a −C⋮C−C⋮C− group. The hydrocarbyl units in 3 and 4 arise as a result of phenyl migration from a PPh 2 group to a terminal carbon of the diynyl fragment. On heating, 3 readily decarbonylates to generate 4 . The pentanuclear cluster 5 and hexanuclear cluster 6 both contain unusually coordinated C 4 chains which may be considered as being comprised of carbido- and alkynyl-substituted alkylidyne ligands. The alkylidyne carbide ligand is coordinated across the basal face of a pentagonal pyramid in 6 and across a distorted spiked square in 5 . The latter also features a second C 4 group which forms a rare μ 3 -η 1 -butadiynyl ligand. An EHMO analysis of the model compound Ru 6 (CO) 13 (μ-CO) 2 (μ-PH 2 )(μ 5 -C)(μ 3 -η 1,η 1,η 1 -C−C⋮CH) ( 6a ‘) suggests that the cluster is best described in terms of an Ru 4 C 2 octahedron bicapped by a phosphido-bridged Ru 2 unit, with the C−C−R (R = C⋮CH) radical contributing a total of seven electrons to the CVE count of the entire polyhedron.