(L)₂C₂P₂: Dicarbondiphosphide Stabilized by N‐Heterocyclic Carbenes or Cyclic Diamido Carbenes

Abstract

Carbon phosphides, C P , may have highly promising electronic, optical, and mechanical properties, but they are experimentally almost unexplored materials. Phosphaheteroallenes stabilized by N-heterocyclic carbenes undergo a one-electron reduction to yield compounds of the type (L) C P with diverse structures. The use of imidazolylidenes as ligands L give complexes with a central four-membered ring C P , while more electrophilic cyclic diamidocarbenes (DAC) give a compound with an acyclic π-conjugated CP-PC unit. Cyclic C P compounds are best described as non-Kekulé molecules that are stabilized by coordination to the NHC ligands NHC→(C P )←NHC. These species can be easily oxidized to give stable radical cations [(NHC) C P ] . The remarkably stable molecules with an acylic C P core are best described with electron-sharing bonds (DAC)=C=P-P=C=(DAC).

The Chemistry of the 2‐Phosphaethynolate Anion

“…[60] Primary products are zwitterionic compounds which could be isolated in some cases and which result from the nucleophilic attack of the carbenes on the carbon atom of the P=C=Ounit. [63] These are best described as non-KekulØ molecules with aromatic 6pelectron systems with as mall but significant contribution of as inglet biradical character. [62] The OP(NR) 2 (CR 1 ) 2 units are potential leaving groups and indeed upon reaction with KC 8 are cleanly removed as K + [OP(NR) 2 -(CR 1 ) 2 ] À to give the NHC-stabilized C 2 P 2 rings.…”

L3C3P3: Tricarbontriphosphide Tricyclic Radicals and Cations Stabilized by Cyclic (alkyl)(amino)carbenes

“…In the 13 CNMR spectra, doublet resonances in the range from d = 273.1 ppm (2a)tod = 282.8 ppm (2e)with 1 J P-C coupling constants of about 20 Hz are observed for the carbon nucleus bonded directly to CAACs which is in between that of structurally similar phosphaallenes stabilized with NHC (289.5 ppm) [7a] or DAC( 249.8 ppm). [8] This ordering of the resonance frequencies from high to low values reflects the p-electron acceptor strength of carbenes which increases in the order NHC < CAAC < DAC. [9] Thestructures of 2b and 2e were determined by single crystal X-ray diffraction analysis.A sa ne xample,t he structure of 2b is shown in Figure 1a (see the Supporting Information for further details on all of the structures reported herein).…”

“…the reactive centers of carbene-stabilized dicarbondiphosphides. [8] These additions cause the basal C 2 P 2 heterocycles to deviate from planarity as seen in L 2 C 2 P 2 and dihedral angles of 38.98 8 (averaged) are observed in 5a-c.…”

“…[8] Carbene-bound CP radicals L=C=PC 4 may be formed as first intermediates.W ereasoned that with sterically less demanding carbenes higher oligomers of these radicals may be obtained. Cyclic (alkyl)-(amino)carbenes,C AACs,c an be easily prepared on am ulti-gram scale and their steric demand can be facilely tuned.…”

“…Thes tructural parameters in 6e (C1=C2 1.32 ); C1=P1 1.63 ); P1ÀP1' (2.25 )a re comparable to the DAC stabilized acyclic C 2 P 2 core. [8] Thec yclic neutral and diamagnetic dicarbondiphosphides L 2 C 2 P 2 (L = NHC) are easily oxidized (E 1/2 = À0.451 V) to give stable cyclic radical cations [L 2 C 2 P 2 ]C + . [8] In contrast, cyclic voltammograms of the paramagnetic neutral radical cages 5a-c show no reversible redox waves but are chemically oxidized upon reaction with Fc + PF 6 À .…”