ESI/MSn in the structural characterisation of some nitrido-Re heterocomplexes

Six different nitride-containing rhenium heterocomplexes with a mixed coordination sphere comprising heterodiphosphines (PNP) and dithiocarbamates (DTC) or halides (X) have been studied by means of electrospray mass spectrometry and collisional experiments. Two compounds are neutral intermediates of the type [Re(N)Cl2(PNP)], and four are cationic species of general formula [Re(N)(DTC)(PNP)]+, obtained after treatment of the intermediate species with dithiocarbamate. Both Cl-containing intermediates do not show the formation of molecular ions, being the [M - Cl]+ and [M - 2Cl]+ ions the only species detected in the ESI spectra. This behaviour, already observed for some Cl-containing Pt complexes, has been explained by Re–Cl bond cleavage activated by the high positive charge density present on the ESI droplet surface. However, the four mixed heterocomplexes display only the molecular cation with no detectable fragmentation. Further MSn spectra of all compounds show instead specific fragmentation processes, mainly related to the different outer sphere substituents. Comparison with the fragmentation profiles of isostructural technetium complexes evidence similar primary cleavage followed by quite different decomposition pathways.