The synthesis and late transition metal chemistry of 7-aza-N-indolyl phosphines and the activity of their palladium complexes in CO-ethene co-polymerisation

The 7-aza-N-indolyl phosphine ligands PR2(N2C7H5) (L-1, R = Ph; L-2, R = NC4H4) were prepared in a two-step process involving treatment of 7-azaindole with BuLi, followed by reaction of the lithium salt with PCIR2. L-1 and L-2 react with [MCl2(cod)] (M = Pd, Pt) to give [PdCl2(L-kappa(2) P,N)] (1a, L = L-1; 1b, L = L-2) or [PtCl2(L-kappa(2) P,N)] (2a, L = L-1; 2b, L = L-2) and with [Rh(mu-Cl)(cod)](2) in the presence of CO to give [RhCl(CO)(L-kappa(2) P,N)] (3a, L = L-1; 3b, L = L-2). Crystal structures for 1a,b and 3a,b are reported, and structural and spectroscopic evidence confirm that L-2 is a poorer sigma-donor/better pi-acceptor than L-1. The complexes [PdClMe(L-kappa(2) P,N)] (4a, L = L-1; 4b, L = L-2), prepared from [PdClMe(cod)], react with AgOTf to yield [PdMe(OTf)(L-kappa(2) P,N)] (5a, L = L-1 5b, L = L-2). Complexes 5a,b are active catalysts for the co-polymerisation of CO and ethene, with activities similar to previously reported catalysts containing P,N-donor ligands. From the stepwise insertion reactions of CO and ethene with 5a,b, the acyl complexes [Pd{C(O)Me}(OTf)(L-kappa(2) P,N)] (7a, L = L-1; 7b, L = L-2) and alkyl complexes [Pd{CH2CH2C(O)-Me-kappa(2) C,O} (L-kappa(2) P,N)]OTf (8a, L = L-1; 8b, L = L-2) have been isolated and crystallographically characterised, and the acyl complexes [Pd{C(O)CH2CH2C(O)Me-kappa(2) C,O}(L-kappa(2) P,N)]OTf (9a, L = L-1; 9b, L = L-2) have been spectroscopically characterised. Reactions of 7a and 9a with MeOH gave methyl acetate and methyl 4-ketopentanoate respectively, with formation of palladium metal and conversion of the remaining palladium to [Pd(L-1-kappa(2) P,N)(2)](OTf)(2) 10 which has been crystallographically characterised.