Acetylide Participation in Ligand Substitution and P−C Bond Cleavage in the Reaction between HRu₃(CO)₉(μ₃,η²,η²,η¹-C⋮CPh) and 4,5-Bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd). Syntheses and X-ray Structures of HRu₃(CO)₇[μ₃,η²,η²,η¹,η¹,η¹-Ph₂PCCC(O)CH₂C(O)PPh₂CCPh] and Ru₃(CO)₇(μ,η²,η¹-PhCCHPh)[μ₂,η²,η¹- PPhCCC(O)CH₂C(O)PPh₂]

Abstract

The triruthenium cluster HRu 3 (CO) 9 (μ 3,η 2,η 2,η 1 -C⋮CPh) ( 1 ) reacts with the diphosphine ligand bpcd in the presence of Me 3 NO to afford the new cluster compounds HRu 3 (CO) 7 (bpcd)(μ 3,η 2,η 2,η 1 -C⋮CPh) ( 2 ) and ( 3 ). Cluster 2 is the sole product from the controlled thermolysis of 1 with bpcd. Both 2 and 3 have been isolated and characterized in solution by IR and NMR ( 1 H and 31 P) spectroscopies, and by X-ray crystallography in the case of the latter cluster. The bpcd ligand in 2 chelates to the ruthenium center that is σ bound by the acetylide ligand, and in the zwitterionic compound 3 one of the PPh 2 moieties of the bpcd ligand coordinates to a hydride-bridged ruthenium atom while the other PPh 2 group exists as a phosphonium center due to attack on the acetylide C α carbon. Whereas 3 slowly decomposes in solution at elevated temperatures, cluster 2 was found to undergo a clean conversion to the new cluster ( 4 ). The bridging alkenyl ligand in 4 results from the formal cleavage of one of the P−Ph bonds of the bpcd ligand, followed by the concomitant coupling of the phenyl and hydride groups with the acetylide ligand. Cluster 4 has been fully characterized in solution and the solid-state structure established by X-ray analysis. NMR data are presented from a labeling study employing HRu 3 (CO) 7 (bpcd)(μ 3,η 2,η 2,η 1 -C⋮Ctol- p ) that shows that the hydrogen in the μ,η 2,η 1 -RC CHR‘ moiety of is distributed between both the phenyl and tol- p groups. The scrambling of the alkenyl hydrogen between the phenyl- and tol- p -substituted carbon atoms in the μ,η 2,η 1 -RC CHR‘ moiety suggests that hydride transfer from the triruthenium frame occurs via a transient cluster compound that possesses a coordinated PhC⋮Ctol- p ligand.