Synthesis and Characterization of Palladium(II) π-Allyl Complexes with Chiral Phosphinocarbene Ligands. Kinetics and Mechanism of Allylic Amination Fabiano Visentin* ,† and Antonio Togni § Dipartimento di Chimica, UniVersita ` Ca’ Foscari Venezia, Calle Larga S. Marta 2137, 30123, Venice, Italy, and Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, ETH Zu ¨rich, CH-8093, Zu ¨rich, Switzerland ReceiVed March 7, 2007 New palladium π-allyl complexes with chelating phosphinocarbene ligands (P-C) have been prepared and fully characterized. The adopted synthetic strategy is based on the reaction between the appropriate silver precursors and the labile [Pd(η 3 -allyl)OCOCF 3 ] 2 . These complexes react with amines in the presence of dimethyl fumarate, yielding the new palladium(0) complexes [Pd(η 2 -dmfu)(P-C)] and allylamine. Under pseudo-first-order conditions, the amination rates obey the simple law k obs ) k 2 [NHR 2 ], and this observation seems to rule out the possibility of a simultaneous amine attack at the central atom with displacement of the bidentate ancillary ligand (or of one of its donor groups). The k 2 values increase with increasing basicity of the amine, with decreasing steric hindrance at the allyl fragment, and with increasing bulkiness of the P-C heterocyclic nitrogen substituent. Moreover a remarkable decrease of the amination rate is observed for the phosphinocarbene complexes as compared to the “isostructural” phoshinopyrazole (P-N) derivatives, in agreement with the strong σ-donating and weak π-accepting character of the carbene ligands. The new posphinocarbene ligands are tested in the palladium-catalyzed amination of 1,3-diphenylallylethyl carbonate, and the resulting low enantioselectivity may support the view of the comparable trans influence of carbene and phosphine ligands, which renders the corresponding trans allyl carbons electronically equivalent. Introduction The discovery of stable N-heterocyclic carbenes by Arduengo and co-workers 1 led to a rapid development of the chemistry of these compounds. In particular, increasing attention has been focused on using them as ancillary ligands for a number of transition metal-mediated catalytic reactions. 2 The reasons for this success are the high stability of metal-heterocyclic-carbene complexes against heat, moisture, and oxygen, 3 the strong coordination to the metal, which reduces dissociation so that no excess of ligand is required in catalytic processes, and finally the low toxicity. In all these aspects they are not only competitive but often superior to usual phosphines. 2a,4 Additionally, the N-heterocyclic carbene moiety easily permits a fine-tuning of the ligand structure, through the introduction of appropriate substituents at the nitrogen atoms or at the five-membered-ring carbon atoms. In this respect considerable attention has been given to the incorporation of the carbene functionality into ligand systems containing other “classical” donor groups; in this way it is possible to obtain an electronic tuning of the metal coordination sphere. 5 Therefore, the syntheses of several chelating N- functionalized NHCs with various substituted pyridines, 6 imi- nes, 7 ethers, 8 arylphosphines, 8a,9 and arylsulfides 9 and of their complexes with platinum-group metals, mainly Pd, Ru, Ir, and Rh, have been recently reported. 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