Phenylhydrides of the Groups 4B and 5B Elements and Their Monoanions

Abstract

<p>¹H, ¹³C and, where appropriate, ³¹P NHR spectra for the series of compounds (C₆H₅)nXH₃_n and (C₆H₅)nXH₂_nNa (n = 1, 2; X = N, P or As), have been recorded and assigned. The results are consistent with the existence of a pπ-pπ interaction between substituent and phenyl ring in all cases when the atom is nitrogen but only in the anions when the substituent atom is phosphorus or arsenic. ¹³C NMR spectra of the compounds (C₆H₅)nGeH₄_n and (C₆H₅)nGeH₃_nNa as well as (p-CH₃C₆H₄)₃GeM (M = H, Na) have also been recorded and assigned. Comparison of the chemical shifts demonstrated that the extent of delocalization of the negative charge is significantly less in the phenylgermyl anions than in the analogous group 5B species. This corroborates the observed differences in the effect of phenyl-substitution on the acidities of main group hydrides as rationalized in terms of hybridization at the anionic centre and subsequent degree of resonance delocalization.</p> <p>The distribution of π-electrons in the mono-substituted benzenes, whose substituents are anionic centres, appears to be the result of the balance between mesomeric and electric field effects. The latter effect produces a polarization of the phenyl ring dependent upon the extent to which the negative charge is localized on the substituent atom. The magnitudes of these effects depend somewhat on the extent and nature of solute-solvent interaction, ion-pairing and association in the solutions of these salts which, in turn, are a function of the polarity of the solvent.</p> <p>Adduct formation between cuprous iodide and both PH₃ and C₆H₅PH₂ was investigated. Comparison with literature results for complexes of (C₆H₅)₂PH, P(C₆H₅)₃ or other tertiary phosphines indicates that σ-donor strength alone, as opposed to π-acidity or steric bulk, is the dominant factor influencing the stability of the coordinative interactions of the smaller phosphines. The structure of the complex [CuI(C₆H₅PH₂)₂]₂ is reported. ¹²⁷I Mössbauer spectroscopy was found to be incapable of discriminating between different iodine environments in such complexes.</p>