P–Ge/Sn π Interactions Versus Arene···Ge/Sn Contacts for the Stabilization of Diphosphatetrylenes, (R 2 P) 2 E (E = Ge, Sn)

• Published in: Inorganic chemistry Vol. 59; no. 1; pp. 863 - 874
• Main Authors: Izod, Keith, Evans, Peter, Waddell, Paul G.
• Format: Journal Article
• Language: English
• Published: United States 06.01.2020
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.9b03109

The diphosphatetrylenes {(Dipp)(R')P} E [R' = Mes, E = Ge ( ), Sn ( ); R' = CH(SiMe ) , E = Sn ( )] have been isolated and characterized by multinuclear and variable temperature NMR spectroscopy and X-ray crystallography [Dipp = 2,6- Pr C H , Mes = 2,4,6-Me C H ]. All three compounds crystallize as discrete monomers with two pyramidal phosphorus centers. However, variable-temperature P{ H} NMR spectroscopy indicates that both and are subject to dynamic exchange between this form and a form containing one planar and one pyramidal phosphorus center in solution. In contrast, retains two pyramidal phosphorus centers in solution and exhibits no evidence for exchange with a form containing a planar phosphorus center. The related compound [{(Me Si) CH} P] Sn ( ) was isolated in very low yield and was shown by X-ray crystallography to possess one planar and one pyramidal phosphorus center in the solid state. DFT calculations reveal that the conformations of , , and observed in the solid state are significantly stabilized by the delocalization of electron density from the aromatic rings into the vacant p-orbital at the tetrel center. Thus, for diphosphatetrylenes possessing aromatic substituents at phosphorus, stabilization may be achieved by two competing mechanisms: (i) planarization of one phosphorus center and consequent delocalization of the phosphorus lone pair into the vacant tetrel p-orbital or (ii) pyramidalization of both phosphorus centers and delocalization of aromatic π-electron density into the tetrel p-orbital. For , which lacks aromatic groups, only the former stabilization mechanism is possible.