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)(L1, R = Ph; L2, R = NC4H4) were prepared in a two-step process involving treatment of 7azaindole with BuLi, followed by reaction of the lithium salt with PClR2. L1 and L2 react with [MCl2(cod)](M = Pd, Pt) to give [PdCl2(L-(kappa) 2P,N)](1a, L =L1; 1b, L =L2) or [PtCl2(L-(kappa)2P,N)](2a, L =L1; 2b, L =L2) and with [Rh(µ-Cl)(cod)]2 in the presence of CO to give [RhCl(CO)(L(kappa)2P,N)](3a, L =L1; 3b, L =L2). Crystal structures for 1a,b and 3a,b are reported, and structural and spectroscopic evidence confirm that L2 is a poorer (sigma)-donor/better (pi)-acceptor than L1. The complexes [PdClMe(L-(kappa)^2P,N)](4a, L =L1; 4b, L =L2), prepared from [PdClMe (cod)], react with AgOTf to yield [PdMe(OTf)(L-(kapa)^2P,N)](5a, L =L1; 5b, L =L2). Complexes 5a,b are active catalysts for the copolymerisation 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)^2P,N)](7a, L =L1; 7b, L =L2) and alkyl complexes [Pd{CH2CH2C(O)Me-(kappa)^2C,O}(L-(kappa)^2P,N)]OTf (8a, L =L1; 8b, L =L2) have been isolated and crystallographically characterised, and the acyl complexes [Pd{C(O)CH2CH2C(O)Me-(kappa)^2C,O}(L-(kappa)^2P,N)]OTf (9a, L =L1; 9b, L =L2) 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(L1-(kappa)^2P,N)2](OTf)210 which has been crystallographically characterised