Comparing the reactivity of isomeric phosphinoferrocene nitrile and isocyanide in Pd(II) complexes: synthesis of simple coordination compounds vs. preparation of P-chelated insertion products and Fischer-type carbenes
Abstract
Isomeric phosphinoferrocene ligands, viz 1'-(diphenylphosphino)-1-cyanoferrocene (1) and 1'-(diphenylphosphino)-1-isocyanoferrocene (2), show markedly different coordination behaviours. For instance, the reactions of 1 with [PdCl2(MeCN)(2)] and [(L-NC)Pd(-Cl)](2) (L-NC = [2-(dimethylaino-kappa N)methyl]phenyl-C-1) produced the "phosphine" complexes [PdCl2(1-kappa P)(2)] (7) and [(L-NC)PdCl(1-kappa P)] (8), and the latter was converted into the coordination polymer [(L-NC)Pd((P,N)-1)][SbF6] (9).
Conversely, the reaction of 2 with [(L-NC)Pd(-Cl)](2) involved coordination of the phosphine moiety and simultaneous insertion of the isocyanide group into the Pd-C bond, giving rise to the P,eta(1)-imidoyl complex [PdCl(Ph(2)PfcN=CC6H4CH2NMe2-kappa C-3,N,P)] (10; fc = ferrocene-1,1'-diyl). Compound 10 was further transformed into the Fischer carbene [PdCl(Ph(2)PfcN(Me)CC(6)H(4)CH(2)NMe2-kappa P-3,C,N)][BF4] (11) by methylation with [Me(3)O][BF4].
The reactions of 2 with Pd-Me and Pd(eta(3)-allyl) precursors also led to imidoyl complexes [Pd(-Cl)(Ph(2)PfcN=CR-kappa C-2,P)](2) (R = Me: 12, R = allyl: 15), which were cleaved with PPh3 into the corresponding monopalladium complexes [PdCl(PPh3)(Ph(2)PfcN=CR-kappa C-2,P)] (R = Me: 13, R = allyl: 16). The treatment of 12 and 15 with thallium(I) acetylacetonate (acac) produced [Pd(acac-O,O')(Ph(2)PfcN=CR-kappa C-2,P)] (R = Me: 17, R = allyl: 18).
Through proton transfer, these complexes reacted with Ph(2)PCH(2)CO2H, ultimately producing bis-chelate coplexes [Pd(Ph2PCH2CO2-kappa O-2,P)(Ph(2)PfcN=CR)] (R = Me: 19, R = prop-1-enyl (sic!): 20). In addition, compound 13 was converted into the P-chelated carbene [PdCl(PPh3)(Ph(2)PfcN(Me)Ce-kappa C-2,P)][BF4] (14).
Compounds 10, 11, 13 and 14 were studied by cyclic voltammetry and by DFT computations.