Synthesis and Characterization of Monohaloalkoxyarsoranes Bearing a Novel Tridentate Ligand Occupying One Apical and Two Equatorial Sites

A series of pentavalent organoarsenic monohalides (F, Cl, and Br) were synthesized using a rigid tridentate ligand with a 2,2,2-trifluoro-1,1-diphenylethanol skeleton. The chloro derivative (4) could not be isolated due to its sensitivity to air, whereas the fluoro (5) and bromo derivatives (6) were isolated as crystalline solids. The X-ray crystallography of 5 and 6 revealed that both compounds adopted a pentacoordination at the arsenic atom with a covalent arsenic-halogen bond rather than the tetracoordinated ionic form. The solid state structures around the arsenic atom of 5 and 6 were almost ideal trigonal bipyramidal (TBP) geometries. The NMR measurements implied that 4, 5, and 6 were in the pentacoordinated state even in solution.