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

Abstract

Solution phase ligand substitution reactions of [Pt(dien)Cl]⁺ and [Pt(Me₅dien)Cl]⁺ (Me₅dien = N,N,N′,N′′,N′′-pentamethyldiethylenetriamine) have been monitored using electrospray ionization mass spectrometry. The [Pt(Me₅dien)Cl]⁺ ion undergoes much slower ligand substitution than [Pt(dien)Cl]⁺, which is consistent with the crystal structure of [Pt(Me₅dien)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 = pyridine) formed via solution phase ligand substitution have been examined. In most cases the ligand is lost as HX, giving rise to the co-ordinatively unsaturated [Pt(dien) − H]⁺ ion. Noteable exceptions include n = 1, where X = N₃⁻ or NO₂⁻, which instead exhibit ligand fragmentation via loss of N₂ 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.