Formation and gas phase fragmentation reactions of ligand substitution products of platinum(II) complexes via electrospray ionization tandem mass spectrometry

Solution phase ligand substitution reactions of [Pt(dien)Cl](+) and [Pt(Me( 5)dien)Cl](+) (Me(5)dien=N,N,N',N ",N "-pentamethyldiethylenetriamine) have been monitored using electrospray ionization mass spectrometry. The [Pt(Me (5)dien)Cl](+) ion undergoes much slower ligand substitution than [Pt(dien) Cl](+), which is consistent with the crystal structure of [Pt(Me(5)dien)Cl] (+) determined, which suggests steric crowding (relative to the [Pt(dien)Cl ](+) structure) induced by the buttressing methyl groups. In addition, the gas phase collision induced dissociation reactions of [Pt(dien)X](n+) ions (n=1, X=bromide, iodide, thiocyanate, cyanate, azide or nitrite; n=2, X=pyr idine) formed via solution phase ligand substitution have been examined. In most cases the ligand is lost as HX, giving rise to the co-ordinatively un saturated [Pt(dien)-H](+) ion. Noteable exceptions include n=1, where X=N-3 (-) or NO2-, which instead exhibit ligand fragmentation via loss of N-2 and NO respectively to yield the novel platinum species [Pt(dien)N](+) and [Pt (dien)O](+). The structures of these ions have been examined using density functional calculations at the B3LYP/LAV1S level of theory.