P 8 O 12 ·2BH 3 − The Borane Adduct of a New Molecular Phosphorus Oxide

P 4 O 6 ·BH 3 , which readily forms from P 4 O 6 and Me 2 S·BH 3 in a stoichiometric reaction, dimerizes spontaneously at −30 °C in a concentrated toluene solution resulting in the crystallization of P 8 O 12 ·2BH 3 ( 1 ). The synthesis of 1 represents the first selective interconnection of molecular phosphorus chalcogenides leading to the formation of a new, flexible P 8 O 12 cage. The thermodynamic driving force for the dimerization reaction results from a gain of enthalpy due to enhanced P−O double‐bond contributions and a relief of angular strain. In terms of kinetics, the behavior of P 4 O 6 ·BH 3 , differing from that of other P 4 O 6 derivatives, is caused by the low π‐donor ability of BH 3 provoking a Michaelis−Arbuzov‐like reactivity at the adjacent phosphorus atom and thus inducing cage opening. 1 was characterized by means of X‐ray diffractometry (powder, single crystal), NMR spectroscopy (solution, solid), IR spectroscopy, Raman spectroscopy, and mass spectrometry. Mass spectrometric investigations suggest considerable BH 3 abstraction as well as an enhanced stability of P 8 O 12 ·BH 3 and P 8 O 12 , compared to 1 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)