β-Hydrogen Elimination Reactions of Nickel and Palladium Methoxides Stabilised by PCP Pincer Ligands

Journal Reference

Chemistry. 2015 Jun 26;21(27):9833-49. 

Martínez-Prieto LM¹, Ávila E¹, Palma P¹, Álvarez E¹, Cámpora J².

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1. Instituto de Investigaciones Químicas, CSIC, Universidad de Sevillac/Américo Vespucio, 49, 41092 Sevilla (Spain).
2. Instituto de Investigaciones Químicas, CSIC, Universidad de Sevillac/Américo Vespucio, 49, 41092 Sevilla (Spain). [email protected].

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Abstract

Nickel and palladium methoxides [((iPr)PCP)M-OMe], which contain the (iPr)PCP pincer ligand, decompose upon heating to give products of different kinds. The palladium derivative cleanly gives the dimeric Pd(0) complex [Pd(μ-(iPr)PCHP)]2 ((iPr)PCHP = 2,6-bis(diisopropylphosphinomethyl)phenyl) and formaldehyde. In contrast, decomposition of [((iPr)PCP)Ni-OMe] affords polynuclear carbonyl phosphine complexes. Both decomposition processes are initiated by β-hydrogen elimination (BHE), but the resulting [((iPr)PCP)M-H] hydrides undergo divergent reaction sequences that ultimately lead to the irreversible breakdown of the pincer units. Whereas the Pd hydride spontaneously experiences reductive C-H coupling, the decay of its Ni analogue is brought about by its reaction with formaldehyde released in the BHE step. Kinetic measurements showed that the BHE reaction is reversible and less favourable for Nickel  than for palladium for both kinetic and thermodynamic reasons. DFT calculations confirmed the main conclusions of the kinetic studies and provided further insight into the mechanisms of the decomposition reactions.

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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