Arsonium ylides complexes

The synthesis of arsonium ylides 384 from diazocyclopentadienes 383 and tri-phenylarsine has been reexamined with respect to the efficiency of various copper-containing catalysts Whereas copper bronze gave only ca. 55 % of ylide, yields over 80% were provided by the use of Ou(II) complexes of p-diketonates derived from acetylacetone, 3-methylacetylacetone, benzoylacetone or dibenzoylmethane, as well as by bis[4-(phenylimino)-2-pentanonato-N,0-]copper(II) and Cu(II) acetate, all used in boiling benzene. The sterically more demanding complex bis(dipivaloyl-methanato)copper(II) as well as dichlorodipyridinecopper(II) proved less efficient. CopperfTI) tartrate, the dibenzo-14-crown 6/copper complex and furthermore the acetylacetonate complexes of Co, Ni, Pt and Zn were totally ineffective. When 383a was decomposed by Cu(acac)2 in the presence of pyridine or thioanisole. 

Functions [R2Au] are also present in the large family of gold(i) complexes of phosphonium, arsonium, and sulfonium ylides . Section 2.05.6 is dedicated to this class of complexes, where dinuclear compounds with gold in the oxidation state +2 are also common. 

Methylene trimethylarsorane (the term trimethylarsonium methylide is equally correct) had already been formulated in 1953 by Wittig and Torssell (104) who studied the reaction of tetramethylarsonium salts with organolithium compounds. Although this method cannot be used for the preparation of the salt-free material due to the strong complexation by the lithium cations, it is clear from reactions of the product mixture that the ylide is present in solution. The formation of arsonium salts upon addition of alkyl halides is a typical example ... 

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