A comparative study of chalcogenated phosphanylborohydrides [EPR2BH3](-) (R = ph, tBu) and triorganophosphane chalcogenides EPPh2CH3 (E = O, S, Se, Te)

摘要

Chalcogenation of the phosphanylborohydrides K(PPh2BH3) and K(PtBU2BH3) with N2O, S-8, Se-infinity, and Te-infinity leads to the corresponding species K(EPR2BH3) in excellent yield (E = O-Te; R = Ph, tBu). The parent systems as well as all the chalcogen derivatives have been structurally characterised as their 18-crown-6 adducts by X-ray crystallography. In the case of [K(18-c-6)][EPPh2BH3] the anionic ligand binds to the K+ ion through both its E atom and its BH3 substituent. Significantly larger K-B distances together with shorter K-E contacts are observed in the sterically more congested tert-butyl derivatives [K(18-c-6)][EPtBU2BH3]. Based on a comparison of characteristic NMR parameters (e.g. (1)J(P,B), (1)J(P,C)) of K(EPPh2BH3) and EPPh2CH3, we come to the conclusion that the formal replacement of CH3+ by BH3 leads to a significant increase in the p character of the E-P bond, which therefore indicates that [PPh2BH3](-) is better suited to direct electron density towards an acceptor atom than its triorganophosphane congener PPh2CH3. In line with this interpretation, displacement experiments between K(PPh2BH3) and EPPh2CH3 (E = S-Te) resulted in the quantitative formation of K(EPPh2BH3) and PPh2CH3. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)