Cationic Functionalisation by Phosphenium Ion Insertion

Abstract

The reaction of [Cp'''Ni(η³ -P₃ )] (1) with in situ generated phosphenium ions [RR'P]⁺ yields the unprecedented polyphosphorus cations of the type [Cp'''Ni(η³ -P₄ R₂ )][X] (R=Ph (2 a), Mes (2 b), Cy (2 c), 2,2'-biphen (2 d), Me (2 e); [X]^- =[OTf]^- , [SbF₆ ]^- , [GaCl₄ ]^- , [BAr^F ]^- , [TEF]^- ) and [Cp'''Ni(η³ -P₄ RCl)][TEF] (R=Ph (2 f), tBu (2 g)). In the reaction of 1 with [Br₂ P]⁺ , an analogous compound is observed only as an intermediate and the final product is an unexpected dinuclear complex [{Cp'''Ni}₂ (μ,η³ :η¹ :η¹ -P₄ Br₃ )][TEF] (3 a). A similar product [{Cp'''Ni}₂ (μ,η³ :η¹ :η¹ -P₄ (2,2'-biphen)Cl)][GaCl₄ ] (3 b) is obtained, when 2 d[GaCl₄ ] is kept in solution for prolonged times. Although the central structural motif of 2 a-g consists of a "butterfly-like" folded P₄ ring attached to a {Cp'''Ni} fragment, the structures of 3 a and 3 b exhibit a unique asymmetrically substituted and distorted P₄ chain stabilised by two {Cp'''Ni} fragments. Additional DFT calculations shed light on the reaction pathway for the formation of 2 a-2 g and the bonding situation in 3 a.

Keywords: nickel; phosphenium cations; phosphorus; polyphosphorus cations; ring expansion.