Formation of Cationic [RP₅Cl]⁺-Cages via Insertion of [RPCl]⁺-Cations into a P–P Bond of the P₄Tetrahedron

Abstract

Fluorobenzene solutions of RPCl2 and a Lewis acid such as ECl3 (E = Al, Ga) in a 1:1 ratio are used as reactive sources of chlorophosphenium cations [RPCl]+, which insert into P–P bonds of dissolved P4. This general protocol represents a powerful strategy for the synthesis of new cationic chloro-substituted organophosphorus [RP5Cl]+-cages as illustrated by the isolation of several monocations (21a-g +) in good to excellent yields. For singular reaction two possible reaction mechanisms are proposed on the basis of quantum chemical calculations. The intriguing NMR spectra and structures of the obtained cationic [RP5Cl]+-cages are discussed. Furthermore, the reactions of dichlorophosphanes and the Lewis acid GaCl3 in various stoichiometries are investigated to obtain a deeper understanding of the species involved in these reactions. The formation of intermediates such as RPCl2·GaCl3 (14) adducts, dichlorophosphanylchlorophosphonium cations [RPCl2–RPCl]+ (16 +) and [RPCl2–RPCl–GaCl3]+ (17 +) in reaction mixtures of RPCl2 and GaCl3 in fluorobenzene strongly depends on the basicity of the dichlorophosphane RPCl2 (R = tBu, Cy, iPr, Et, Me, Ph, C6F5) and the reaction stoichiometry.

Synthesis of Cationic R2P5+ Cages and Subsequent Chalcogenation Reactions

“…The formation of 13 and 14A C H T U N G T R E N N U N G [GaCl 4 ] is observed in solution [11] and in melts. [5] The different reactivities of alkyl-and aryl-substituted phosphanes in the syn-Scheme 1. Similar reactivity has previously been reported for related reactions.…”

“…[15] The resonances of the tetra-coordinated P atoms in alkyl-substituted R 2 P 5 + cages exhibit a gradual shift to higher field with increasing number of hydrogen atoms at the a-carbon atom of the substituent (1 a + : d(P X ) = 35.4 ppm, 1 c + : d(P X ) = 32.0 ppm, 1 d + : d(P M ) = 12.5 ppm). [5]. However, it constitutes a characteristic feature of phosphonium moieties and was termed the a-effect.…”

“…This observation is counterintuitive considering the inductive effects of the respective substituents. [5,17] Single crystals of compounds 1 a- GaCl 4 ] suitable for X-ray structure determination were obtained by slow diffusion of n-hexane into solutions of the respective compounds in CH 2 Cl 2 or C 6 H 4 F 2 . [16] The resonances of the P M atoms in aryl-substituted R 2 P 5 + cages are shifted to higher field compared to those of the corresponding P atoms in the alkyl-substituted cages.…”

“…[2] The first examples were the binary cationic P 5 X 2 + cages (X = Cl, Br, I), which were obtained by insertion of an in situ formed PX 2 + ion into a PÀP bond of the P 4 tetrahedron. [5] The preparation of cation Ph 2 P 5 + (1 e + ), however, required the reaction of Ph 2 PCl, GaCl 3 and P 4 in a solvent-free melt. [4] Chloro-and organo-substituted P 5 + -cage compounds, for example, were obtained from mixtures of dichlorophosphanes RPCl 2 , ECl 3 (E = Al, Ga) and P 4 in fluorobenzene.…”

Phosphine complexes of lone pair bearing Lewis acceptors

“…The potential for the phosphine centre in phosphinophosphonium cations to behave as a donor is demonstrated (Scheme 6a) by the isolation of [Me 2 ClPP(Me 2 )GaCl 3 ] 1+ , 56 spectroscopic characterization of related [RCl 2 PP(R)(Cl)GaCl 3 ] 1+ cations, 57 and isolation of transition metal complexes like the Scheme 4 Proposed mechanism for insertion of phosphenium cations into P-P bonds. tungsten complex of a cyclic phosphinophosphonium (Scheme 6b).…”