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 [alpha-anilino-(quinolin-2-yl)methyl]phosphonic (L1, L2), [alpha-anilino-(quinolin-3-yl)methyl]phosphonic (L3, L4), and [alpha-(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.