A catalytic cycle of reaction between [η5-1-(diphenylphosphino)-2,4-diphenylcyclopentadienyl]tricarbonylmetal iodides, [η5-1-Ph2P-2,4-Ph2C5H2]M(CO)3I (1a, M = Mo; 1b, M = W), with zerovalent palladium and tributyltin acetylides affords the final acetylide products [η5-1-Ph2P-2,4-Ph2C5H2]M(CO)3C⋮CPh (5a, M = Mo; 5b, M = W). This communication describes the main processes and intermediates involved in this palladium-catalyzed metal−carbon bond formation.

To investigate the reaction mechanism of the Pd-catalyzed metal-carbon bond formation, the model compounds [η 5 -1-Ph 2 P-2,4-Ph 2 C 5 H 2 ](CO) 3 MI (M ) Mo, 12; M ) W, 13) have been prepared and their reactions studied under coupling conditions. Treatment of 12 and 13 with stoichiometric amounts of zerovalent palladium yields the complexes [η 5 -1-Ph 2 P-2,4-Ph 2 C 5 H 2 ](CO) 3 MPd(PPh 3 )I (M ) Mo, 16; M ) W, 17) by oxidative addition of the M-I moieties on Pd 0 . Subsequent reaction of intermediates 16 and 17 with 4-nitro-1-[2-(tributylstannyl)ethynyl]benzene (Bu 3 SnCtC(C 6 H 4 )p-NO 2 , 18) leads to the formation of the transmetalation products [η 5 -1-Ph 2 P-2,4-Ph 2 C 5 H 2 ](CO) 3 MPd(PPh 3 )CtC(C 6 H 4 )p-NO 2 (M ) Mo, 19; W, 20), which have been isolated and characterized. Complexes 13 and 17 have been also characterized by X-ray analysis.