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A Cation-Captured Palladium(0) Anion: Synthesis, Structure, and Bonding of [PdBr(PPh3)2] Ligated by an N-Heterocyclic Phosphenium Cation

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posted on 14.09.2009, 00:00 authored by Christine A. Caputo, Allison L. Brazeau, Zachery Hynes, Jacquelyn T. Price, Heikki M. Tuononen, Nathan D. Jones
Unsaturated N-heterocyclic phosphenium cations (uNHP) stabilize the [Pd0(PR3)2X] anion proposed over the past decade to be the crucial but elusive intermediate in palladium-catalyzed cross-coupling reactions (X = halide). Insertion of metal into the P−Br bond of the precursor mesityl-substituted bromophosphine gives the structurally characterized Pd(0)-phosphenium complex (uNHPMes)Pd(PPh3)2Br, which features a long Pd−Br bond (2.7240(9) Å) and the shortest known Pd−P bond (2.1166(17) Å). The reaction is proposed to proceed by an associative pathway involving a Pd-bromophosphine complex that undergoes P-to-Pd bromide transfer.