4902
J. Am. Chem. SOC.1993,115,49024903
Zirconium-Mediated Reactions of Carbon Monoxide and Alkynes. Insertion Chemistry of Cationic Zr(IV) acyl and Alkenyl Complexes
Scheme I
Q Cp,lr/-o p
Ani1 S.Guram, Zhaoyu Guo, and Richard F. Jordan'
3
5
Department of Chemistry The University of Iowa Iowa City, Iowa 52242 Received February 3, 1993 Reactions of carbon monoxide and alkynesmediated by middleand late-transition-metal complexes provide a general approach to unsaturated carbonyl compounds.Is2 In contrast, analogous reactions at early-transition-metal centers are unknown. We report here that Cp2Zr(R)(THF)+ complexesundergoalternating insertion of carbon monoxide and alkyne leading to a variety of useful organic products. As part of our program to develop synthetic applications of Cp2Zr(R)(L)+ complexe~,~ we reported that Cp2Zr(+NICpyridyl)(L)+ and related complexes derived via C-H activation4 regioselectively insert alkenes, alkynes, and other unsaturated substrates.5 This suggested that isolobal Cp2Zr(q2-0,C-acyl)(L)+ complexes, derived from CO insertion of Cp2Zr(R)(L)+,6 would exhibit similar insertion chemistry. Our results are summarized in Scheme I. The cationic complex Cp2Zr(CH3)(THF)+(1)' reacts rapidly (23 OC, 1-2 h) with 1-pentyneto afford the (6)-alkenyl complex 2 (Scheme No regioisomers, multiple insertion products, or pentyne C-H bond activation products are observed. The configuration of the alkenyl ligand in 2 is established by the lack of coupling between the vinyl-H and the vinyl-CH3 in the lH NMR spectrum, and the downfield Z r - C H = resonance (6 185, confirmed by a DEPT experiment) in the I3C NMR spectrum. Complexes 1and 2 react rapidly with carbon monoxide (
