Transition metal complexes bearing a phosphenium ligand

Nakazawa, Hiroshi, Transition Metal Complexes Bearing a Phosphenium Ligand. 50 107... 

Transition Metal Complexes Bearing a Phosphenium Ligand... 

Transition metal complexes bearing a phosphenium ligand (cyclic phosphenium ions in the synthesis of A,.P-heterocycles) 04MI5. 

The chemistry of transition metal complexes bearing a cationic phosphenium ligand dates back to the synthesis and characterization of [(CO)4Fe P(NR2)2 ][PF6] by Parry in 1978.2 Since then, many cationic phosphenium complexes have been investigated because a phosphenium may serve as a a-donor (a Lewis base) and also as a 7i-acceptor (a Lewis acid) due to the lone pair electrons and a vacant p orbital, and a few review articles have appeared.3 7 [LraM(PR2)], being an electrically neutral transition metal complex, is sometimes treated as a phosphenium complex because it can be considered to consist of LraM and PR. 8 11 In this chapter, the focus is on electrically cationic transition metal complexes described as [LraM(PRR )]+ -... 

Alkoxide anion abstraction by a Lewis acid from phosphorus ligand on a transition metal is one of the most useful methods to prepare cationic phosphenium complexes. It has been reported that OR anion abstraction from an alkoxyalkyl ligand, C(OR)R2, on a transition metal complex leads to the formation of a cationic carbene complex.39-42 It is similarly expected that OR anion abstraction from an alkoxysilyl ligand, Si(OR)R2, would cause the formation of a cationic silylene complex. Therefore, increased attention has been focused on the reaction with a Lewis acid of transition metal complexes bearing both alkoxyalkyl and phosphite ligands and of complexes bearing both alkoxysilyl and phosphite ligands. 

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