635702-11-3Relevant articles and documents
Kinetic studies of the oxidative addition and transmetallation steps involved in the cross-coupling of alkynyl stannanes with aryl iodides catalysed by η2-(dimethyl fumarate)(iminophosphane)palladium(0) complexes
Crociani, Bruno,Antonaroli, Simonetta,Canovese, Luciano,Uguagliati, Paolo,Visentin, Fabiano
, p. 732 - 742 (2007/10/03)
The complexes [Pd(η2-dmfu)(P-N)] {dmfu = dimethyl fumarate; P-N = 2-(PPh2)C6H4-1-CH=NR, R = C 6H4OMe-4 (1a), CHMe2 (2a), C6H 3Me2-2,6 (3a), C6H3(CHMe 2)2-2,6 (4a)} undergo dynamic processes in solution which consist of a P-N ligand site exchange through initial rupture of the Pd-N bond at lower energy and an olefin dissociation-association at higher energy. According to equilibrium constant values for olefin replacement, the complex [Pd(η2-fn)(P-N)] (fn = fumaronitrile, 1b) has a greater thermodynamic stability than its dmfu analogue 1a. The kinetics of the oxidative addition of ArI (Ar = C6H4CF3-4) to 1a and 2a lead to the products [PdI(Ar)(P-N)] (1c, 2c) and obey the rate law, k obs = k1A k2A[ArI]. The k1A step involves oxidative addition to a reactive species [Pd(solvent)(P-N)] formed from dmfu dissociation. The k2A step is better interpreted in terms of oxidative addition to a species [Pd(η2-dmfu)(solvent) (κ1-P-N)] formed in a pre-equilibrium step from Pd-N bond breaking. The complexes 1c and 2c react with PhC≡CSnBu3 in the presence of an activated olefin (ol = dmfu, fn) to yield the palladium(0) derivatives [Pd(η2-ol)(P-N)] along with ISnBu3 and PhC≡CAr. The kinetics of the transmetallation step, which is rate-determining for the overall reaction, obey the rate law: kobs = k2T[PhC≡CSnBu3]. The k2T values are markedly enhanced in more polar solvents such as CH3CN and DMF. The solvent effect and the activation parameters suggest an associative S E2 mechanism with substantial charge separation in the transition state. The kinetic data of the above reactions in various solvents indicate that, for the cross-coupling of PhC≡CSnBu3 with ArI catalysed by 1a or 2a, the rate-determining step is represented by the oxidative addition and that CH3CN is the solvent in which the highest rates are observed. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
Kinetics and mechanism of regioselective amination of the 1-phenylallyl group in cationic palladium(II) complexes bearing bidentate ligands
Crociani, Bruno,Antonaroli, Simonetta,Canovese, Luciano,Visentin, Fabiano,Uguagliati, Paolo
, p. 172 - 182 (2008/10/08)
The complexes [Pd(η3-1-PhC3H4) (L-L′)]+ [L-L′ = 2-(PPh2)C6H4-1-CH = NR (R = Me (1a), i-Pr (1b), t-Bu (1c), (R)-bornyl (1d), C6H4OMe-4 (1e), C6H3Me2-2,6 (1f), C6H3(i-Pr)2-2,6 (1g)), 6-MeC5H3N-2-CH = NC6H4OMe-4 (2a), C5H4N-2-CH = N-t-Bu (2b) and C5H4N-2-CH2S-t-Bu (3a)] are generally present in solution as two geometrical isomers, the relative abundance of which depends essentially on the steric requirements of the L-L′ ligand. In the presence of fumaronitrile the cationic complexes undergo a regioselective amination by secondary amines HY at the CH2 allyl terminus, yielding [Pd(η2-fn)(L-L′)] and the allylamines (E)-PhCH = CHCH2Y. Under pseudo-first-order conditions the amination rates (kobs) are found to depend on the k2[HY] term for 2a and 3a, and on the sum k2[HY]+k3[HY]2 for the other complexes. The second-order term k2 is related to direct nucleophilic attack on the CH2 allyl terminus of the substrate whereas the third-order term k3 is ascribed to parallel attack by a further HY molecule on the intermediate [Pd(1-PhC3H4)(L-L′)(HY)]+. The k2 values depend on the steric and electronic properties of both the amine HY and the ligand L-L′. For complexes 1a-1g, the relatively higher k2 values and their increase with increasing steric crowding at the nitrogen-bonded carbon of substituent R are interpreted in terms of a greater reactivity of the isomer with the CH2 allyl terminus trans to phosphorus and cis to the NR group. The high amination rate of 2a, as compared with that of 2b, is related to substantial steric interaction of the CH2 allyl terminus with the 6-Me pyridine group in close proximity in the predominant isomer.
