A versatile, high-yielding synthesis of NHC-stabilized [PCl(2)](+) and [PCl](2+) phosphorus synthons has been achieved by using an "onio-substituent transfer" reagent. Subsequent functionalization yields access to cationic cyano- and azido-substituted derivatives which represent first examples of a displacement reaction on NHC-stabilized phosphorus(III)-centered cations. The new salts have been fully characterized by NMR spectroscopy and X-ray crystallography.
A cationic phosphoranide featuring a normal and an abnormal imidazoliumyl substituent was prepared through the reaction of a P‐centered cation with an N‐heterocyclic carbene (NHC). The remarkable reactivity of this compound allows the formation of two‐ or three‐coordinate P‐centered cations, illustrating the ability of imidazoliumyl substituents to stabilize high‐ and low‐coordinated P atoms.
Reaction of tetraphosphine platinum(II) complexes with 2-azidoethyl isocyanide 3 in methanol leads to complexes with two trans-coordinated NH,NH-stabilized carbene ligands 6(X)(2). Complexes 6(X)(2) react with phenyldivinylphosphine under substitution of the remaining phosphine ligands followed by an intramolecular hydroamination reaction to produce complex 1(PF(6))(2) with a macrocyclic [16]ane-P(2)C(NHC)(2) ligand.
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.
Herein we report on reactions of "imidazoliumyl-transfer" reagents [L((R/R'))SiMe3][OTf] (4((R/R'))[OTf]); L = imidazolium-2-yl, R/R': Me/Me, (i)Pr/Me, Dipp/H, Dipp/Cl) with pnictogen trichlorides PnCl3 (Pn = P, As, Sb) in various stoichiometries. In the case of the 1:1 reaction of [L((R/R'))SiMe3][OTf] with PCl3 the corresponding cationic imidazoliumyl-substituted dichlorophosphanes [L((R/R'))PCl2](+) (1P((R/R')))(+) are obtained as triflate salts on a multigram scale. We found that the reactions using various stoichiometries of [L((R/R'))SiMe3][OTf] and PnCl3 are less selective in the case of the heavier congeners or by decreasing steric demand of the R-group attached to the N atoms of the heterocycle. An equilibrium between the monocation [L((Me/Me))PCl2](+) (1P((Me/Me)+)), the dication [L((Me/Me))2PCl](2+) (2P((Me/Me)2+)), and the trication [L((Me/Me))3P](3+) (5P((Me/Me)3+)) is observed in solution. Reactions of the monocationic derivatives [L((R/R'))PnCl2][OTf] (Pn = P, As) with Me3SiX (X = CN, N3) resulted in the exchange of the chloro groups for the respective pseudohalogen and yielded the dicyano [L((R/R'))Pn(CN)2][OTf] (6Pn((R/R'))[OTf]) and diazido-substituted pnictanes [L((R/R'))Pn(N3)2][OTf] (7Pn((R/R'))[OTf]), respectively. All new compounds are thoroughly characterized by multinuclear NMR, IR, and Raman spectroscopy. For most cases the molecular structure was confirmed by X-ray crystal structure analysis.
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