On the nature of M–CO(lone pair)⋯π(arene) interactions in the solid state of fluorinated oxaphosphirane complexes

Abstract

We have recently communicated [CrystEngComm, 2015, 17, 1769–1772] the synthesis and X-ray characterization of several oxaphosphirane tungsten(0) complexes especially designed to analyse the intramolecular W–CO(lone pair)⋯π(arene) interaction varying the degree of fluorination in the arene. Unexpectedly, the phenyl-substituted oxaphosphirane complex showed the shortest CO⋯π distance in the solid state which is very close to that observed for the pentafluorophenyl derivative. Other complexes with two or three fluorine substituents exhibited longer distances. We rationalized the affinity of the M–CO moiety for both electron-rich and electron-deficient rings by considering that the interaction can be also understood as a π–π interaction where the negative part of the CO is dominant in the π-acidic arene and the positive part of the CO is dominant in the π-basic arene. This explanation was supported by DFT calculations using orbital analysis and Bader's theory of “atoms-in-molecules”. Herein, we expand the previous study with new theoretical results of some model complexes to gain insight into the energetic and geometric features of the interaction. The experimental behaviour of the ³¹P-NMR chemical shifts of the title compounds agrees well with previous theoretical explanation of the physical nature of the interaction. Furthermore, we analyse the crystal packing of the four X-ray structures previously communicated in order to scrutinize other interactions in the solid state that may influence the W–CO⋯π interaction. Finally, stronger intermolecular interactions that influence the crystal packing are also analysed using DFT calculations.