N‐Heterocyclic Vinylidene‐Stabilized Phosphorus Biradicaloid

Abstract

Four-membered biradicaloid compounds containing a N E (E=main group element) framework have been thoroughly investigated; however, the synthesis of stable analogues with a C P skeleton remains a challenge. Base-mediated double C-H functionalization of IPr=CH (1) (IPr=C[N(2,6-iPr -C H )CH] ) with PCl affords [{(IPr)CP} Cl]Cl (2) as a royal blue solid. Treatment of 2 with KC yields the stable phosphorus biradicaloid [(IPr)CP] (3) featuring a four-membered C P ring. Compound 3 is diamagnetic and shows sharp and temperature-independent NMR resonances, revealing its singlet biradicaloid nature. The stability of 3 is attributed to the σ- and π-electron-donating property of the N-heterocyclic vinylidene [(IPr)C] group.

A Modular Access to Divinyldiphosphenes with a Strikingly Small HOMO–LUMO Energy Gap

“…The solid‐state molecular structure of a typical compound 3 is shown in Figure . The C1−C4 bond length of 3 (1.420(2) Å) is considerably longer than that of the parent NHO but compares well to the NHV derivatives IV and V . In addition, the C4−P1 (1.728(2) Å) bond is considerably shorter than a C−P single bond (1.85 Å) but in line with those observed for phosphinines .…”

“…Each phosphorus atom is twofold coordinated with the P1−P1′ bond length of 2.062(1) ( 5 ) and 2.055(1) Å ( 6 ), which is in the typical range of diphosphenes (2.02–2.08 Å) . Although the C1−C4 bond length of 5 (1.387(2)) and 6 (1.375(2) Å) is shorter compared with the precursor 3 (1.420(2) Å), this is however comparable with related phosphorus compounds IV and V (Figure ) . This indicates some π‐electron‐density transfer from the NHC onto the phosphorus atom in 5 and 6 , which is nonetheless lower than that in 3 .…”

A Phosphorus Analogue of p‐Quinodimethane with a Planar P4 Ring: A Metal‐Free Diphosphorus Source

“…[12c, 13] In 2017, we also reported as table non-KekulØ diradicaloid [(IPrC)P] 2 (VI)s tabilized with an NHC (IPr = C{N(Ar)CH} 2 ;A r = 2,6-iPr 2 C 6 H 3 ). [14] These results prompted us to investigate the synthetic accessibility of the phosphorus analogueo fpQDM, which maye xist either as B or as C ( Figure 1).…”

“…[17] Remarkably,t his is also more stretched in comparison with those of 3 [av.1 .408 (3) ]. [14] In addition, C28ÀP1/P2 bond lengths of 2 [av.1 .759(1) ]a re shorter than those of 3 [1.816 (3) ]. This suggests that considerably more p-electron density was transferred from the NHC unit to the phosphorus atomsi n2 relative to 3.T his is most likely due to the presence of two electronegative chlorine atoms on each of the phosphorus atoms of 2.…”

“…The use of excess KC 8 should be avoided because it leads to furtherr eduction of 5 into VI (Figure 1). [14] Compound 5 is indefinitelys table in solution as well as in the solid state under an inert-gas atmosphere.T he 1 HNMR spectrum of 5 exhibits two sets of signals fort he NHC protons. The 31 PNMR spectrum of 5 shows as harp signala td = À87.9 ppm, which compares well to Niecke'sc ompound I (d = À87.6 ppm, Figure 1).…”