The marked influence of steric and electronic properties of ancillary pyridylthioether ligands on the rate of allene insertion into the palladium-carbon bond

被引:30
作者
Canovese, L
Visentin, F
Chessa, G
Santo, C
Uguagliati, P
Bandoli, G
机构
[1] Univ Venice, Dipartimento Chim, I-30123 Venice, Italy
[2] Univ Padua, Dipartimento Sci Farmaceut, Padua, Italy
关键词
allene; pyridylthioether; palladium-carbon bond; insertion mechanism;
D O I
10.1016/S0022-328X(02)01145-2
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
Neutral methyl- and acyl-palladium chloro complexes containing pyridylthioether ancillary ligands (R'N-SR) (R' = H, Me, Cl; R = Me. Et, i-Pr, t-Bu, Ph) have been synthesised and characterised by elemental analysis and spectroscopic methods. The reactivity of these complexes toward allene (allene = DMA = 1,1-dimethylpropadiene: TMA = 1,1,3,3-tetramethylpropadiene) insertion into the palladium-carbon bond has been studied by H-1-NMR and UV-vis techniques. The rate of reaction appears to be strongly influenced by the steric and electronic properties of the ancillary ligand. The distortion induced by the substituent R' in position 6 of the pyridine ring on the main coordination plane of the substrate (allowed by sulphur sp(3) hybridisation) renders the substrate itself more prone to nucleophilic attack by the allene. The rate of allene insertion can further be enhanced by lowering the basicity of the chelating atoms in the N-S moiety which results in an increase of electrophilicity of the palladium core, so that the rate constants measured in the case of the complexes containing the ligand 6-chloro-2-phenylthiomethylpyridine (ClN-SPh) are by far the greatest observed so far for similar reactions. Furthermore, on the basis of the indications emerging from the exhaustive study on the behaviour of all the related pyridylthioether methyl complexes. an associative asynchronous bond making mechanism for the rate determining nucleophilic attack by allene is proposed. (C) 2002 Elsevier Science B.V. All rights reserved.
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页码:43 / 56
页数:14
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