Solution Behavior and X-ray Structure of Cationic Allylpalladium(II) Complexes with Iminophosphine Ligands. Kinetics and Mechanism of Allyl Amination by Secondary Amines
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- 作者：Bruno Crociani ; Simonetta Antonaroli ; Giuliano Bandoli ; Luciano Canovese ; Fabiano Visentin ; and Paolo Uguagliati
- 刊名：Organometallics
- 出版年：1999
- 出版时间：March 29, 1999
- 年：1999
- 卷：18
- 期：7
- 页码：1137 - 1147
- 全文大小：361K
- 年卷期：v.18,no.7(March 29, 1999)
- ISSN：1520-6041
文摘
The solution behavior of the cationic complexes [Pd(
3-allyl)(P-N)]+ (P-N = o-(PPh2)C6H4CH=NR (R = C6H4OMe-4, Me, CMe3, (R)-bornyl); allyl = propenyl (1a-4a) and 3-methyl-2-butenyl (1b-4b)) consists essentially of three dynamic processes: (i) a very fastconformational change of the P-N chelate ring, which moves above and below the P-Pd-Ncoordination plane, (ii) a relatively fast 3-1-3 interconversion which brings about a syn-anti exchange only for the allylic protons cis to phosphorus; (iii) a slower apparent rotationof the 3-allyl ligand around its bond axis. For 1b-3b, two geometrical isomers are observed,the predominant one having the allyl CMe2 group trans to phosphorus. The complexes 4aand 4b, containing the chiral (R)-bornyl group, are present in solution with two and fourdiastereomeric species, respectively. The X-ray structural analysis of 4b(ClO4) shows thepresence of two diastereomeric molecules in the unit cell, both having distorted-square-planar coordination geometries, characterized by rather elongated Pd-CMe2 bonds trans tophosphorus and by a marked distortion of the allyl ligand, which is rotated away from thePPh2 group. The complexes [Pd(3-allyl)(P-N)]+ react with secondary amines HY in thepresence of fumaronitrile, yielding [Pd(2-fn)(P-N)] and allylamines. Under pseudo-first-order conditions the amination rates obey the laws kobs = k2[HY] + k3[HY]2 for 1a-4a andkobs = k2[HY] for 1b, 3b, and 4b. The k2 term is related to direct bimolecular attack on aterminal allyl carbon of the substrate, whereas the k3 term is ascribed to parallel attack bya further amine molecule on the intermediate [Pd(allyl)(P-N)(HY)]+. The k2 values increasewith increasing basicity and decreasing steric hindrance of the amine, and with increasingelectron-withdrawing ability and increasing bulkiness of the P-N nitrogen substituent. Thehigher amination rates for [Pd(3-allyl)(P-N)]+, compared to [Pd(3-allyl)(
-diimine)]+, areessentially due to lack of displacement equilibria of the P-N ligand by amines.
3-allyl)(P-N)]+ (P-N = o-(PPh2)C6H4CH=NR (R = C6H4OMe-4, Me, CMe3, (R)-bornyl); allyl = propenyl (1a-4a) and 3-methyl-2-butenyl (1b-4b)) consists essentially of three dynamic processes: (i) a very fastconformational change of the P-N chelate ring, which moves above and below the P-Pd-Ncoordination plane, (ii) a relatively fast 3-1-3 interconversion which brings about a syn-anti exchange only for the allylic protons cis to phosphorus; (iii) a slower apparent rotationof the 3-allyl ligand around its bond axis. For 1b-3b, two geometrical isomers are observed,the predominant one having the allyl CMe2 group trans to phosphorus. The complexes 4aand 4b, containing the chiral (R)-bornyl group, are present in solution with two and fourdiastereomeric species, respectively. The X-ray structural analysis of 4b(ClO4) shows thepresence of two diastereomeric molecules in the unit cell, both having distorted-square-planar coordination geometries, characterized by rather elongated Pd-CMe2 bonds trans tophosphorus and by a marked distortion of the allyl ligand, which is rotated away from thePPh2 group. The complexes [Pd(3-allyl)(P-N)]+ react with secondary amines HY in thepresence of fumaronitrile, yielding [Pd(2-fn)(P-N)] and allylamines. Under pseudo-first-order conditions the amination rates obey the laws kobs = k2[HY] + k3[HY]2 for 1a-4a andkobs = k2[HY] for 1b, 3b, and 4b. The k2 term is related to direct bimolecular attack on aterminal allyl carbon of the substrate, whereas the k3 term is ascribed to parallel attack bya further amine molecule on the intermediate [Pd(allyl)(P-N)(HY)]+. The k2 values increasewith increasing basicity and decreasing steric hindrance of the amine, and with increasingelectron-withdrawing ability and increasing bulkiness of the P-N nitrogen substituent. Thehigher amination rates for [Pd(3-allyl)(P-N)]+, compared to [Pd(3-allyl)(-diimine)]+, areessentially due to lack of displacement equilibria of the P-N ligand by amines.