Issue 5, 2016

Palladium(ii) complexes featuring a mixed phosphine–pyridine–iminophosphorane pincer ligand: synthesis and reactivity

Abstract

An original mixed ligand (labelled L) of formula PPh2–CH2–Pyr–CH2–N[double bond, length as m-dash]PPh3, combining a pyridine core with phosphine and iminophosphorane, was synthesised. Its coordination with palladium(II) centers was studied. With [Pd(COD)Cl2], a cationic complex [LPdCl](Cl) 1, where L is coordinated in the pincer mode, was obtained. Chloride abstraction with silver salt in the presence of pyridine generated the dicationic complex [LPd(py)](BF4)2 (2). When reacting with a base such as potassium hexamethyldisilazane (KHMDS), 1 gave the neutral complex 3 [L*PdCl], wherein the benzylic position alpha to phosphine was selectively deprotonated, which induced dearomatisation of the pyridine ring. A similar complex [L*Pd(CH3)] (4) was obtained upon a reaction of [Pd(CH3)2(TMEDA)] and Lvia the departure of methane. Neutral complexes with the deprotonated ligand such as 3 yielded in the presence of deuterated methanol the corresponding deuterated complex, showing that the protonation is reversible with this ligand. Finally, upon attempting to dealkylate complex 4 using B(C6F5)3, an unexpected zwitterionic borated complex 5, resulting from the formation of a C–B bond in the benzylic position with restoration of the aromatic character of the pyridine, was isolated. Interestingly, when the metal was introduced after the ligand interacted with the borane reagent, another palladium complex formed, namely, [LPdMe][MeB(C6F5)3], originating from methyl abstraction.

Graphical abstract: Palladium(ii) complexes featuring a mixed phosphine–pyridine–iminophosphorane pincer ligand: synthesis and reactivity

Supplementary files

Article information

Article type
Paper
Submitted
22 jul 2015
Accepted
25 ago 2015
First published
26 ago 2015

Dalton Trans., 2016,45, 2069-2078

Author version available

Palladium(II) complexes featuring a mixed phosphine–pyridine–iminophosphorane pincer ligand: synthesis and reactivity

T. Cheisson and A. Auffrant, Dalton Trans., 2016, 45, 2069 DOI: 10.1039/C5DT02789F

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