Can One σ*-Antibonding Orbital Interact with Six Electrons of Lewis Bases? Analysis of a Multiply Interacting σ* Orbital

One empty orbital normally interacts with one lone pair of a Lewis base to form one dative bond, and we do not know any example where one antibonding orbital interacts with more than two lone pairs of Lewis bases. We wish to report here the first example which is beyond our aforementioned common knowledge of dative bonds. We synthesized heptacoordinate tris{( o -diphenylphosphino)phenyl}tin fluoride and found that three lone pairs of phosphine donors equivalently interact with the antibonding σ*(Sn–F) orbital of the Sn center. The nature of this “multiply interacting σ* orbital” was theoretically elucidated by DFT calculations.