Articles Reaction of the Ruthenium(II) Indenyl Complex [Ru(η 5 -C 9 H 7 ){K 3 (P,C,C)-PPh 2 (CH 2 CHdCH 2 )}(PPh 3 )][PF 6 ] with Terminal Alkynes. Mechanisms of 1-Alkyne to η 1 -Vinylidene Transformation and Kinetic Detection of Hemilability of the Allylphosphine Ligand Mauro Bassetti,* ,† Patricia Alvarez, ‡ Jose ´ Gimeno, ‡ and Elena Lastra ‡ Istituto CNR di Metodologie Chimiche, Sezione Meccanismi di Reazione, Dipartimento di Chimica, Universita ` La Sapienza, 00185 Roma, Italy, and Departamento de Quı ´mica Orga ´ nica e Inorga ´ nica, Instituto de Quı ´mica Organometa ´ lica “Enrique Moles” (Unidad Asociada al CSIC), Universidad de Oviedo, Oviedo, Principado de Asturias, Spain Received May 13, 2004 The reaction of the complex [Ru(η 5 -C 9 H 7 ){κ 3 (P,C,C)-PPh 2 (CH 2 CHdCH 2 )}(PPh 3 )][PF 6 ](1) with p-XC 6 H 4 CtCH (X ) H, Cl) yields the transient and observable vinylidene species [Ru(η 5 -C 9 H 7 ){κ 1 (P)-PPh 2 (CH 2 CHdCH 2 )}(PPh 3 )(dCdCH(p-XC 6 H 4 ))] + , which react further by an intramolecular [2 + 2] cycloaddition process, forming bicyclic alkylidene compounds. The formation of the vinylidene intermediates, associated with a change of the binding mode of the allylphosphine ligand from κ 3 (P,C,C) to monodentate κ 1 (P) coordination, has been investigated by kinetic measurements carried out in chloroform-d at 38 °C. Plots of first- order k obs values vs concentration of arylalkyne are linear with a positive intercept on the y axis. The reaction proceeds via two parallel pathways, one which is first order in complex 1 and first order in arylalkyne, second order overall, and one which is zero order in arylalkyne, overall first order. The second-order pathway implies rate-determining nucleophilic attack of the arylalkyne on complex 1, k 2 ) [5.5((0.4)] × 10 -4 (X ) H) and [2.8((0.3)] × 10 -4 M -1 s -1 (X ) Cl) being the corresponding rate constants, associated with displacement of the allylic double bond or a haptotropic shift of the indenyl ring. The first-order pathway involves rate-determining formation of a transient 16-electron intermediate arising from complex 1 by reversible decoordination of the allylic double bond and rapid reaction with the incoming arylalkyne. The rate of this route is independent of the concentration and nature of the alkyne (k 1 ) [9.5((2.5)] × 10 -5 s -1 for X ) H; [6.9((1.5)] × 10 -5 s -1 for X ) Cl) and corresponds to the rate of formation of the intermediate species [Ru(η 5 -C 9 H 7 ){κ 1 (P)- PPh 2 (CH 2 CHdCH 2 )}(PPh 3 )] + . The vinylidene complexes [Ru(η 5 -C 9 H 7 )(CdCdRR′){κ 1 (P)- PPh 2 (CH 2 CHdCH 2 )}(PPh 3 )][BF 4 ] (R′ ) H, R ) Ph (3a), p-MeC 6 H 4 (3b), p-ClC 6 H 4 (3c); R′ ) Me, R ) Ph (4a), p-MeC 6 H 4 (4b)) have been independently synthesized by electrophilic attack of HBF 4 or MeSO 3 CF 3 on the alkynyl derivatives [Ru(η 5 -C 9 H 7 )(CtCR){κ 1 (P)-PPh 2 (CH 2 - CHdCH 2 )}(PPh 3 )] (R ) Ph (2a), p-MeC 6 H 4 (2b), p-ClC 6 H 4 (2c)), obtained in turn from [Ru(η 5 -C 9 H 7 )Cl{κ 1 (P)-PPh 2 (CH 2 CHdCH 2 )}(PPh 3 )]. Introduction The transformation of terminal alkynes into ruthe- nium cumulenylidene derivatives represents a conve- nient method of alkyne functionalization, 1 as well as a direct access into metal-vinylidene species (eq 1). 2 These compounds are extremely useful for catalytic reactions 3 or for further synthetic elaboration of the organic fragment. 4 The interaction of the 1-alkyne with the metal com- plex involves first the formation of an η 2 adduct, which * To whom correspondence should be addressed. E-mail: mauro.bassetti@uniroma1.it. † Universita ` La Sapienza. ‡ Universidad de Oviedo. (1) Bruce, M. I. Chem. Rev. 1991, 91, 197-257; 1998, 98, 2797- 2858. (2) Cadierno, V.; Gamasa, M. P.; Gimeno, J. Eur. J. Inorg. Chem. 2001, 571-591. (3) (a) Bruneau, C.; Dixneuf, P. H. Acc. Chem. Res. 1999, 311-323. (b) Naota, T.; Takaya, H.; Murahashi, S.-I. Chem. Rev. 1998, 98, 2599- 2660. (4) (a) Wakatsuki, Y.; Yamazaki, H.; Kumegawa, N.; Satoh, T.; Satoh, J. Y. J. Am. Chem. Soc. 1991, 113, 9604-9610. (b) Bianchini, C.; Casares, J. A.; Peruzzini, M.; Romerosa, A.; Zanobini, F. J. Am. Chem. Soc. 1996, 118, 4585-4594. RCtCH + RuL n h Ru(dCdCHR)L n-1 + L (1) 5127 Organometallics 2004, 23, 5127-5134 10.1021/om040068d CCC: $27.50 © 2004 American Chemical Society Publication on Web 09/30/2004