Electrospray ionization mass spectrometry of palladium(II) quinolinylaminophosphonate complexes.

The mass spectrometric behavior of palladium(II) halide complexes of three types of quinolinylaminophosphonates, diethyl and dibutyl esters of [α-anilino-(quinolin-2-yl)methyl]phosphonic (L1, L2), [α-anilino-(quinolin-3-yl)methyl]phosphonic (L3, L4), and [α-(quinolin-3-ylamino)-N-benzyl]phosphonic acid (L5, L6), was investigated under positive ion electrospray ionization conditions. Each type of ligand forms complexes with different metal-ligand interactions. Mononuclear dihalide adducts cis-[Pd(L1/L2)X(2)] (1-4) and trans-[Pd(L3/L4)(2)X(2)] (5-8) as well as dinuclear tetrahalide complexes [Pd(2)(L5/L6)(3)X(4)] (9-12) (X=Cl, Br) are formed by metal bonding either through the quinoline or both the quinoline and amino nitrogen atoms. The sodiated molecule M + Na is observed in the mass spectra of all the complexes, and its abundance as well as the fragmentation pathway depend on the type of the complex. In the cis complexes (1-4) the initial decomposition goes under two fragmentation routes: those in which the sodium molecular adduct sequentially loses halides HX/NaX and those in which this loss is in the competition with the loss of dialkyl phosphite. The predominant pathways for decomposition of trans dihalide (5-8) and tetrahalide (9-12) complexes include three competitive reactions; the loss of halides, dialkyl phosphites and the intact phosphonate ligand molecule and its fragments formed by ester dissociation or complete loss of the phosphonate ester moiety. A series of acetonitrile adducts and cluster ions derived from dimolecular clusters 2M + Na were also detected. The most important fragmentation patterns are rationalized and supported by the MS(n) studies.