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β‐Hydrogen Elimination Reactions of Nickel and Palladium Methoxides Stabilised by PCP Pincer Ligands
Author(s) -
MartínezPrieto Luis M.,
Ávila Elena,
Palma Pilar,
Álvarez Eleuterio,
Cámpora Juan
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201500652
Subject(s) - pincer movement , palladium , chemistry , phosphine , reductive elimination , nickel , hydride , formaldehyde , medicinal chemistry , ligand (biochemistry) , decomposition , hydrogen , pincer ligand , coupling reaction , derivative (finance) , inorganic chemistry , catalysis , photochemistry , combinatorial chemistry , organic chemistry , biochemistry , receptor , financial economics , economics
Nickel and palladium methoxides [( i Pr PCP)M‐OMe], which contain the i Pr PCP pincer ligand, decompose upon heating to give products of different kinds. The palladium derivative cleanly gives the dimeric Pd 0 complex [Pd(μ‐ i Pr PCHP)] 2 ( i Pr PCHP=2,6‐bis(diisopropylphosphinomethyl)phenyl) and formaldehyde. In contrast, decomposition of [( i Pr PCP)Ni‐OMe] affords polynuclear carbonyl phosphine complexes. Both decomposition processes are initiated by β‐hydrogen elimination (BHE), but the resulting [( i Pr 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 CH 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 Ni than for Pd 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.