Phosphorus As a Simultaneous Electron-Pair Acceptor in Intermolecular P center dot center dot center dot N Pnicogen Bonds and Electron-Pair Donor to Lewis Acids

摘要: Ab initio MP2/aug'-cc-pVTZ calculations have been performed to investigate the structures and energies of binary complexes LA: PH2F and LA: PH3 and of ternary complexes LA: H2FP: NFH2 and LA: H3P: NH3 in which the pnicogen-bonded P atom also acts as an electron-pair donor to a Lewis acid (LA), for LA= BH3, NCH, ClH, FH, FCl, and HLi. Hydrogen bonds, halogen bonds, and dative covalent bonds are found at P in some cases, depending on the nature of the Lewis acid. HLi forms a lithium bond with P only in the binary complex HLi: PH3. The binding energies of ternary complexes exhibit a classical synergistic effect, although the computed cooperativity may be overestimated due to neglect of the interaction of the Lewis acid with NH2F or NH3 in some cases. The hydrogen-bonding Lewis acids appear to have little effect on the strength of the P center dot center dot center dot N bond, while the remaining Lewis acids strengthen the pnicogen bond. P-31 absolute chemical shieldings increase in LA: H2FP: NFH2 complexes relative to the corresponding LA: PH2F complexes as the positive charge on P decreases, while chemical shieldings decrease in LA: H3P: NH3 relative to the corresponding LA: PH3 complexes as the positive charge increases. Absolute values of (1P) J (PN) spin-spin coupling constants in complexes LA: H2FP: NFH2 decrease as the PN distance decreases. It appears that this behavior is associated with the presence of a second intermolecular interaction, whether electron-donation by P or hydrogen bond formation at PF.