Interstitial phosphorus arsenic and antimony atoms

Transition metal phosphido clusters usually result from pyrolysis reactions in the presence of an external source of the phosphorus atom. PCI3, white phosphorus, PH3, and, more commonly, PPh3 have all been used in this respect, and it has been shown that the thermal decomposition of triphenylphosphine by successive loss of phenyl radicals can result in the formation of naked phosphorus atoms in interstitial cavities. This phosphorus metalation is thought to prevail in cluster chemistry because of the presence of several transition metal atoms neighboring the arylpho-sphine coordination site which aid the P-C bond cleavage process. 

The reaction of [Rh(acac)(CO)2] and PPh3 in the presence of cesium benzoate at high temperature and pressure results in the formation of [Rh9P(CO)2i] and [RhioP(CO)22] J the phosphorus atom being derived from triphenylphosphine. This reaction is difficult to follow and seems to proceed in a non-specific, non-stoichiometric manner, probably because the harsh conditions employed in the reaction do not allow for the isolation of intermediate species. The trigonal prismatic cluster [Os6P(CO)i8] has, however, been prepared in a far more systematic fashion and some key intermediates have been isolated these have helped elucidate the mechanism of interstitial phosphido atom formation.  

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