Protonation of palladium(II)-allyl and palladium(0)-olefin complexes containing 2-pyridyldiphenylphosphine

The pendant nitrogen atom of the Ph2PPy ligand in the Pd(II)-allyl complexes [PdCl(eta(3)-2-CH3C3H4)( Ph2PPy)] (1) and [Pd(eta(3)-2-CH3-C3H4)(Ph2PPy)(2)]BF4 (3) has been protonated with methanesulfonic acid to afford the corresponding pyridinium salts [PdCl(eta(3)-2-CH3-C3H4)(Ph2PPyH)](CH3SO3) (1a) and [Pd(eta(3)-2-CH3-C3H4)(Ph2PPyH)(2)](CH3SO3)(2)(BF4) (3a). Protonation strongly influences the H-1 and C-13 NMR spectral parameters of the allyl moieties of 1a and 3a whose signals resonate at lower fields with respect to the parent species indicating that upon protonation Ph2PPy becomes a weaker sigma-donor and a stronger Pi-acceptor. The allyl moiety, which in 1 is static, becomes dynamic in 1a, the observed syn-syn and anti-anti exchange being due to deligation of the protonated phosphine from the metal centre. Treatment of complex 3 with diethylamine in the presence of fumaronitrile gives the new Pd(0)-olefin complex [Pd(eta(2)-fumaronitrile)(PPh2Py)(2)] (4) which has been characterized by elemental analysis and NMR spectroscopy. Low temperature protonation of 4 with methanesulfonic acid leads to the bis-protonated species [Pd(eta(2)-fumaronitrile)(Ph2PPyH)(2)](CH3SO3)(2) (4a) which is stable only at temperatures < 0 degrees C. (C) 2008 Elsevier B. V. All rights reserved.