A convenient one-pot synthesis of chelating bis-N-heterocyclic carbene-ligated P(I) salts is described. The solid state structures of these remarkably stable phosphamethine cyanine dyes with various N-alkyl groups and counter-anions are reported, and initial reactivity results are discussed.

A safe, convenient, and P-atom-efficient synthesis of N-heterocyclic-carbene- (NHC-) stabilized phosphorus(I) bromide salts is reported that involves P(+) transfer from an easily prepared triphosphenium precursor. The resulting family of phosphamethine cyanine dyes featuring N,N'-dialkyl-substituted 4,5-dimethylimidazole-2-ylidenes ((R)NHC(Me)) and benzimidazole-2-ylidenes ((R)NHC(B)) (R = Me, Et, iPr) have been fully characterized. We found that increasing N-alkyl group size causes increased twisting of the carbene fragments from the C-P-C plane, which decreases the magnitude of hyperconjugation between the π-type lone pair on phosphorus and the carbene fragments. This decrease is manifested as changes in the (31)P NMR chemical shifts, magnitudes of the P-C coupling constants, and electronic spectra of the cations. The reactivities of these ions toward various oxidants are reported: Oxidation by sulfur generates dithiophosphinium salts, protonation or methylation gives dicationic phosphines, and coordination to 1 or 2 equiv of gold(I) chloride results in mono or bimetallic complexes, respectively.

Although salts of thiazolium cations are known, many readily prepared iodide salts have eluded spectroscopic and structural characterization; herein, data for a variety of such salts are reported. It has been demonstrated that thiazolium cations can be deprotonated to generate S,N-heterocyclic carbenes and their "electron rich olefin" dimers, but use of the former has been largely overshadowed by that of the more common N-heterocyclic carbenes. We report herein that the deprotonation of thiazolium iodides and their subsequent reaction with a conveniently prepared triphosphenium precursor grants phosphamethine cyanine cations with solid-state geometry and electronic structure unlike those of NHC-stabilized cations. Protection of the phosphorus atom in such ions with elemental sulfur provides an air- and moisture-stable dithiophosphinium salt.