PCl bond length depression upon coordination of a diazaphosphasiletidine to a group 13 element Lewis acid or a transition metal carbonyl fragment – Synthesis and structural characterization of diazaphosphasiletidine adducts with P-coordination

Abstract

Abstract Three P-chloro-substituted diazaphosphasiletidines, Me2Si(NtBu)2PCl (1) and Me2Si(NtBu)2P(E)Cl (E=BCl3 (2); W(CO)5 (3)), are presented for comparison. 1 was first prepared more than 30 years ago and studied by means of spectroscopic methods, however, no crystal structure has been reported until now. In the presence of the comparatively weak Lewis acid BCl3 and the labile metal carbonyl complex [W(CO)5(THF)], 1 can be easily converted into its corresponding adducts 2 and 3. All products were characterized by single-crystal X-ray diffraction studies. The structures of the new compounds 2 and 3 reveal a remarkable P–Cl bond contraction caused by the coordination of 1 to the Lewis acid or the Lewis acidic W(CO)5 fragment. Although the coordination number of the P atom is increased in 2 and 3, the P–Cl bond length is reduced dramatically, some kind of bond length paradoxon. A computational study suggests that these P–Cl bond shortenings result from a less effective donation of electron density from the lone pairs at the nitrogen atoms to the antibonding σ *(P–Cl) orbital in 2 and 3 as compared to 1.