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

Abstract

The complexes [Pd( η 2- ol){ o-(Ph 2P)–C 6H 4–CHNR}] [ ol, dimethyl fumarate ( dmf), 1,4-naphtoquinone ( nq), fumaronitrile ( fn); R=C 6H 4OMe-4, CMe 3, Me, bornyl] can be prepared in good yields from the reaction of the allyl derivatives [Pd( η 3-C 3H 5) { o-(Ph 2P)–C 6H 4–CHNR}]BF 4 with an excess of NHEt 2 in the presence of the activated olefin ol. The complex [Pd( η 2- ma){ o-(Ph 2P)–C 6H 4-CHNC 6H 4OMe-4}] ( ma, maleic anhydride) is more conveniently obtained via olefin substitution from [Pd( η 2- dmf){ o-(Ph 2P)–C 6H 4–CHNC 6H 4OMe-4}]. The α-diimine ligand of [Pd( η 2- fn)(py-2-CHNC 6H 4OMe-4)] is quantitatively displaced by the appropriate iminophosphine to give [Pd( η 2- fn){ o-(Ph 2P)–C 6H 4–CHNC 6H 4OMe-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( η 2- fn){ o-(Ph 2P)–C 6H 4–CHNC 6H 4OMe-4}] reacts with a second molecule of iminophosphine yielding [Pd( η 2- fn){ o-(Ph 2P)–C 6H 4–CHNC 6H 4OMe-4} 2] in which the iminophosphines act essentially as P-monodentate ligands. [Pd( η 2- dmf) { o-(Ph 2P)–C 6H 4–CHNC 6H 4OMe-4}] undergoes fast oxidative addition of allyl chloride to [Pd( η 3-C 3H 5){ o-(Ph 2P)–C 6H 4–CHNC 6H 4OMe-4}] +.