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(η3-2-CH3-C3H4)(Ph2PPy)] (1) and [Pd(η3-2-CH3-C3H4)(Ph2PPy)2]BF4 (3) has been protonated with methanesulfonic acid to afford the corresponding pyridinium salts [PdCl(η3-2-CH3-C3H4)(Ph2PPyH)](CH3SO3) (1a) and [Pd(η3-2-CH3-C3H4)(Ph2PPyH)2](CH3SO3)2(BF4) (3a). Protonation strongly influences the 1H and 13C 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 σ-donor and a stronger Π-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(η2-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(η2-fumaronitrile)(Ph2PPyH)2](CH3SO3)2 (4a) which is stable only at temperatures <0 °C.