Structural Characterization and Coordination Behavior of 1,2-Diphosphino and 1,2-Diarsino-Diborane(4) Compounds

Abstract

Reaction of either LiPPh₂ or LiAsMes₂ with the diborane(4) compound (Me₂N) BrBBBr (NMe₂) affords the compounds (Me₂N) (Ph₂P)BB(PPh₂) (NMe₂), 1, and (Me₂N) (Mes₂As)BB(AsMes₂)(NMe₂)·0.5 PhMe, 2·0.5PhMe (Mes = 2,4,6-Me₃C₆H₂-). Both 1 and 2 feature normal B–B single bond lengths; however, the empty boron p-orbitals display strong π-interactions with the dimethylamino substituents. The B–P and B–As distances and the pyramidal phosphorus and arsenic geometries are consistent with single bonding. Furthermore, the stereochemical activity of the phosphorus and arsenic lone pairs is demonstrated by the ready formation of the complex cis-[Cr(CO)₄(Me₂N) (Ph₂P)BB(PPh₂)(NMe₂)]·C₆H₆, 3·C₆H₆, by treatment of 1 with [Cr(CO)₄(2,5-norbornadiene)]. Compounds 1–3 were characterized by X-ray crystallography, ¹¹B and ³¹P NMR spectroscopy, and by IR spectroscopy in the case of 3.