Synthesis and electrospray mass spectrometry of palladium(II) diphosphine complexes from oxidative addition of 2-bromopyridine to Pd0

Oxidative addition reactions of palladium(0) phosphine complexes with 2-bromopyridine gave rise to a series of structurally distinctive complexes, namely trans-(N,P)-[Pd2Br2(PPh3)(2)(mu-C5H4N-C-2,N)(2)] 1, [Pd-2(mu-C5H4N-C-2,N)(2)-(mu-dppm)(2)]Br-2 2, [Pd-2(eta(1)-dppp)(2)(mu-C5H4N-C-2, N)(2)(mu-dppp)]Br-2 3, trans-[{PdBr(eta(1)-C5H4N-C-2)(mu-dppb)}(n)] 4, trans-(N,P) -[Pd2Br2(mu-C5H4N-C-2,N)(2)(mu-dppb)] 5 and cis-[PdBr(eta(1)-C5H4NH-C-2)(eta(2)-dppf)]Br 6 [Ph2P(CH2)(n)PPh2, n = 1 (dppm), 3(dppp) or 4(dppb); dppf = Fe(Ph2PC5H4)(2)]. SimilarIy, trans-(N,P)-[Pd2Cl2(mu-C9H6N-C-2,N)(2)(mu-dppb)] 7 has been obtained from 2-chloroquinoline and [Pd(dppb)(2)]. An array of structural possibilities is envisaged based on the different co-ordination modes of the pyridine (C or/and N bonded; terminal or bridging; pyridyl, pyridine or pyridinium), phosphine (terminal, bridging or chelating) bromide (terminal or ionised) ligands. Complexes 2 and 3, but not the others, can be obtained from phosphine exchange reactions of 1. Complexes 5 and 6 were analysed by X-ray single-crystal crystallographic methods. The former reveals a dinuclear structure with a dppb ligand bridging diagonally two metals that are juxtaposed by two syn-bridging pyridyl groups. It represents an unusual dinuclear core stabilised by two types of bridging ligands of contrasting steric and geometric demands. The latter shows a cationic and mononuclear square planar palladium(II) complex containing a chelating dppf, terminal bromide and an unusual C-bonded pyridyl group with the N-site protonated. The fragmentation of these complexes was investigated by electrospray mass spectrometry under different cone voltages. Breakdown of the dinuclear framework is facilitated by addition of H-Br to the N-Pd bonds of the bridging pyridyl group.