Preparation and reactions of palladium(0)-olefin complexes with iminophosphine ligands

The complexes [Pd(eta(2)-ol){o-(Ph2P)-C6H4-CH=NR}] [ol, dimethyl fumarate (dmf), 1,4-naphtoquinone (nq), fumaronitrile (fn); R = C6H4OMe-4, CMe3, Me, bornyl] can be prepared in good yields from the reaction of the allyl derivatives [Pd(eta(3)-C3H5)- {o-(Ph-2P)-C6H4-CH=NR}]BF4 with an excess of NHEt2 in the presence of the activated olefin ol. The complex [Pd(eta(2)-ma){o-(Ph2P)-C6H4-CH=NC6H4OMe-4}] (ma, maleic anhydride) is more conveniently obtained via olefin substitution from [Pd(eta(2)- dmf){o-(Ph2P)-C6H4-CH=NC6H4OMe-4}]. The alpha-diimine ligand of [Pd(eta(2)-fn)(py-2-CH=NC6H4OMe-4)] is quantitatively displaced by the appropriate iminophosphine to give [Pd(eta(2)-fn){o-(Ph2P)-C6H4-CH=NC6H4OMe-4}]. The new zerovalent complexes with P-N ligands are characterized by multinuclear NMR spectroscopy. In solution, olefin rotation or olefin exchange are generally slow. The compound [Pd(eta(2)-fn)(o-(Ph2P)-C6H4-CH=NC6H4OMe-4}] reacts with a second molecule of iminophosphine yielding [Pd(eta(2)-fn){o-(Ph2P)-C6H4-CH=NC6H4OMe-4)(2)] in which the iminophosphines act essentially as P-monodentate ligands. [Pd(eta(2)-dmf) {o-(Ph2P)-C6H4-CH=NC6H4OMe-4}] undergoes fast oxidative addition of allyl chloride to [Pd(eta(3)-C3H5){o-(Ph2P)-C6H4-CH=NC6H4OMe-4}](+). (C) 1998 Elsevier Science S.A. All rights reserved.