Synthese und Struktur- und Konformationsanalyse von Triphenylphosphonium-bis(diphenylarsino)methylid

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Abstract
Triphenylphosphonium -diphenylarsinomethylide (1) and -bis-(diphenylarsino)methylide (2) are easily available through transylidation processes using Ph3P = CH2 and Ph2AsCl as the starting materials in the appropriate molar ratio. Analytical and spectroscopic data are presented for both ylides. The structure of 2 was studied in detail by single-crystal X-ray diffraction. The basic PCAs2 skeleton is found to deviate strongly from planarity. The Ph2As-substituents adopt a cis/trans conformation relative to the ylidic P = C bond with the directions of the lone pairs of electrons at the arsenic atoms in the heavy atom plane as expected for a maximum compensation of the electrostatic vectors. For 1, a cis-conformation of the lone pair of electrons and a large PCAs angle are predicted on the basis of NMR analogies with the phosphorus homologues. Single bond rotational barriers appear to be much lower for 1 and 2, however, than for the corresponding phosphino-substituted ylides.

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