Effects of phosphine substituents on CO and norbornene insertion rates into (P,N)–Pd–alkyl and –acyl bonds

Abstract

The synthesis is described of (P,N)–PdMe(X) (P,N=R 2P- o-C 6H 4CH 2NMe 2 ( L1), Me 2N- o-C 6H 4CH 2–PR 2 ( L2), 1-(dimethylamino)-8-(R 2phosphino)naphthalene ( L3) with R 2=Ph 2 ( a), Cy 2 ( b), Me,Ph ( c, for L1 only); X=Cl, OTf) and cationic (P,N)–PdMe(L) + (L, MeCN, CO; anion, −B[3,5-Ph–(CF 3) 2] 4). The complexes react with CO to give (P,N)–Pd{C(O)Me}(X/L +) derivatives. Carbonylation is faster in complexes with the more basic phosphines of type 1, but slower in ligand type 2 and 3. Norbornene inserts slowly into the (P,N)–Pd–acetyl bond of the cationic borate complexes with L1– 3, and for L2 with X=Cl, OTf. Cationic palladium complexes with phenyl substituted phosphine ligands are more reactive toward CO/norbornene mixtures than those with cyclohexyl and complexes of L2 and L1 react faster than that of L3. The observed reactivity is described in terms of differences in CO insertion rates and a rate determining isomerization or trapping by norbornene of the intermediates, trans-P (P,N)–Pd{C(O)Me} + complexes.