Synthesis, Structure, and Haptotropic Interconversions of Tungsten Cycloheptatrienyl–Acetonitrile–Carbonyl Complexes

Tungsten cycloheptatrienyl complexes (η7-C7H7)W(CO)2I (I), [(η3-C7H7)W(CO)2(CH3CN)3]PF6 (II), and [(η7-C7H7)W(CO)2(CH3CN)]PF6 (III) (CIF files CCDC nos. 1875096 (I), 1875097 (II), 1875098 (III)), characterized earlier only by spectroscopic methods, were prepared and studied by X-ray diffraction. The tris(acetonitrile) complex II can lose two acetonitrile ligands in both coordinating and non-coordinating solvents with the η3 → η7 change in the hapticity of the cycloheptatrienyl ring to be converted to III. The reverse ligand attachment process with the η7 → η3 change in the hapticity of the cycloheptatrienyl ring takes place upon the dissolution of monoacetonitrile complex III in acetonitrile. The electron-compensating η3 ↔ η7 change in the hapticity of the tropylium ligand is reversible.