Convenient Preparation and Detailed Analysis of a Series of NHC-Stabilized Phosphorus(I) Dyes and Their Derivatives

Abstract

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.

Assessing the Ligand Properties of NHC‐Stabilised Phosphorus(I) Cations

“…All other solvents were dried on a series of Grubbs’ type columns and were degassed prior to use . [L][BPh 4 ] was synthesised according to literature methods . NMR spectra were recorded at room temperature on Bruker Avance III 500 MHz, Bruker Avance Ultrashield 300 MHz or Bruker Avance DPX 300 MHz spectrometers.…”

Synthesis of Heavy Dicyanamide Homologues from Air‐Stable Precursors

“…Schmidpeter had observed early on that cyanide ions displace 1,2‐bis(diphenylphosphino)ethane (dppe) from a triphosphenium cation to form DCP anions in solution using 31 P NMR spectroscopy . Indeed, nucleophilic substitution of the phosphine ligands from triphosphenium cations has been used by our group as a conceptually simple and practical method for the generation of new or useful univalent phosphorus containing molecules and oligomers . Using these results as a basis, we investigated the reactions of [dppeP][Br] and commercial cyanide sources like [K][CN], [Na][CN] and [ n Bu 4 N][CN] in the hopes of finding a safe, straightforward method of synthesizing and isolating DCP salts.…”

“…[32] Indeed, nucleophilic substitution of the phosphinel igandsf rom triphosphenium cations hasb een used by our group as ac onceptually simple and practical method for the generation of new or useful univalent phosphorus containing molecules ando ligomers. [33][34][35][36][37][38] in the hopes of finding as afe, straightforward method of synthesizing and isolatingD CP salts. While in all cases the generation of DCP was confirmed by its distinctive singlet in the 31 PNMR spectrum (ca.…”

Recent Advances in Imidazoliumyl‐Substituted Phosphorus Compounds

“…The authors also isolated the corresponding Fe(CO) 4 complex and bimetallic Mn 2 (CO) 8 complex . Protonation and methylation of compound 49 [BPh 4 ] succeeds through the reaction with electrophiles HOTf and MeOTf, respectively …”

“…[40] Protonationa nd methylation of compound 49[BPh 4 ]s ucceeds through the reaction with electrophiles HOTf and MeOTf, respectively. [42] Robinson andc o-workerss tarted from PCl 3 and reacted it with one equivalent of the sterically encumbered NHC 8,a ffording phosphoranide derivative 54 a (please note that the same group also synthesized this compound with mesityl (Mes) groups at the imidazolium Na toms (54 b)). [43] The reduction of 54 a with three equivalents of KC 8 in THF gives neutral diphosphanediide 55 (Scheme 15).…”