Formation of Alkyne Bridged Multicobalt Carbonyl Complexes with Tris(2‐Thienyl)Phosphine or Bis(Trimethylsilylethynyl)Phenylphosphine Ligand

Treatment of Co 4 (CO) 12 with an excess of trimethylsilylacetylene (TMSA) in the presence of tri(2‐thienyl)phosphine in THF at 25 °C for 2 hours yielded six compounds. Two pseudo‐octahedral, alkyne‐bridged tetracobalt clusters, [Co 4 (μ 4 ‐η 2 ‐HC≡CSiMe 3 )(CO) 10 (μ‐CO) 2 ] ( 4 ) and [Co 4 (μ 4 ‐η 2 ‐HC≡CSiMe 3 )‐(CO) 9 (μ‐CO) 2 {P(C 4 H 4 S) 3 }] ( 6 ), along with an alkyne‐bridged dicobalt complex, [Co 2 (CO) 5 (μ‐HC≡CSiMe 3 )‐{P(C 4 H 4 S) 3 }] ( 5 ), were obtained as new compounds. The addition of the thienylphosphine ligand, in fact, facilitates the reaction rate. Reaction of an alkyne‐bridged dicobalt complex, [(η 2 ‐H‐C≡C‐SiMe 3 )Co 2 (CO) 6 ] ( 3 ), with a bi‐functional ligand, PPh(‐C≡C‐SiMe 3 ) 2 , yielded an unexpected six‐membered, cyclic compound, {(Ph)(Me 3 Si‐C≡C)P‐[(η 2 ‐C≡C‐SiMe 3 )Co 2 (CO) 5 ]} 2 ( 7 ). All of these new compounds were characterized by spectroscopic means; the solid‐state structures of ( 5 ), ( 6 ) and ( 7 ) have been established by X‐ray crystallography.