ORGANOMETALLIC CHEMISTRY OF MAIN-GROUP ELEMENTS IN THE GAS-PHASE - FORMATION AND REACTIONS OF GASEOUS [ASI2-CENTER-DOT-ARENE](+) COMPLEXES

The reactions of AsI3.+ in the gas phase with arenes or n-donor substrates efficiently yield the complexes [AsI2 . arene](+) (3) and [AsI2 . n-donor](+) (5), respectively, by substitution of one iodine atom. This reaction was studied by FT-ICR spectrometry preparing AsI3.+ by electron impact in an external ion source and reacting AsI3.+ with an excess of the neutral Ligand in the FT-ICR cell. The complexes 3 and 5 exchange the pi- or n-donor ligand by a ligand with a larger AsI2+ affinity, Delta G(ASI2), with reaction efficiencies > 50%. This fast ligand exchange is reversible, and measurements of the ligand exchange equilibrium were used to establish quantitatively the relative AsI2+ affinity, delta Delta G(AsI2), of pi- and n-donor ligands. For both types of ligands, delta Delta G(AsI2), is related to the ligand proton affinity by a single correlation line with a slope of 0.6, showing that the As-ligand bond is less sensitive to substituent effects. The bond dissociation energy (BDE) of the As-ligand bond in the benzene complex 3a and the acetone complex 5c was determined by energy-resolved collision-induced decomposition (CID), yielding BDE(3a) = 77 +/- 19 kJ/mol and BDE(5c) = 106 +/- 19 kJ/mol. The collisional activation (CA) mass spectra of the arene complexes 3 show back-dissociation into AsI2+ and the arene and hydride abstraction from methyl-substituted benzenes by the leaving AsI2+ as the main fragmentations indicating an intact AsI2 group in the complexes. The combined experimental results agree with a structure of the arene complexes 3 which corresponds to an AsI2+ fragment weakly bonded to the arene either in a sigma-complex (I) or an electrostatically bonded pi-complex (II), but not with structures III and IV which result from an insertion of the carbenic AsI2+ into C-C bonds of the arene.