A Fragile Zwitterionic Phosphasilene as a Transfer Agent of the Elusive Parent Phosphinidene (:PH)

Abstract

The simplest parent phosphinidene, :PH (1), has been observed only in the gas phase or low temperature matrices and has escaped rigorous characterization because of its high reactivity. Its liberation and transfer to an unsaturated organic molecule in solution has now been accomplished by taking advantage of the facile homolytic bond cleavage of the fragile Si═P bond of the first zwitterionic phosphasilene LSi=PH (8) (L = CH[(C═CH2)CMe(NAr)2]; Ar = 2,6-(i)Pr2C6H3). The latter bears two highly localized lone pairs on the phosphorus atom due to the LSi═PH ↔ LSi(+)-PH(-) resonance structures. Strikingly, the dissociation of 8 in hydrocarbon solutions occurs even at room temperature, affording the N-heterocyclic silylene LSi: (9) and 1, which leads to oligomeric [PH]n clusters in the absence of a trapping agent. However, in the presence of an N-heterocyclic carbene as an unsaturated organic substrate, the fragile phosphasilene 8 acts as a :PH transfer reagent, resulting in the formation of silylene 9 and phosphaalkene 11 bearing a terminal PH moiety.

HPCO—A Phosphorus‐Containing Analogue of Isocyanic Acid

“…All other vibrations are considerably weaker. The P−H stretch vibration was found at 2306 cm −1 , which is in good agreement for ν P‐H vibrations in known R=PH species (R=Si{CH[(CCH 2 )CMe‐(NDipp) 2 ]} 2261,54 R=NHC 2291,50 2295, 2311 cm −1 ),51 while the corresponding ν PD in DPCO was found at 1620 cm −1 . Further assignment of vibrations of DPCO is severely hampered by the presence of HDO and D 2 O in the mixture, which prevent the unambiguous identification of DPCO vibrations.…”

A Persistent 1,2‐Dihydrophosphasilene Adduct

“…The 1 J(P,H) coupling constant is 12 Hz smaller than that of the Me 4 -NHC-stabilized form of II (NHC-II), [30] indicating lower 3s character of the PÀ Hbond. The 31 Psignal of 2 is shifted to higher field compared with the resonance of NHC-II (d( 31 P) = À259.8 ppm) and is even more shielded than signals of existing "half-parent" phosphasilenes.T he upfield-shifted 29 Si signal (d( 29 Si) = À25.6 ppm, 1 J(Si,P) = 120.7 Hz) is similar to the 29 Si resonance signal of III (d( 29 Si) = À21.1 ppm). [31] In the 1 HNMR spectrum the signal for the hydrogen nucleus at the phosScheme 1.…”

“…These species and related low-valent Group 14 compounds are stabilized either by taking advantage of steric congestion through the presence of bulky substituents and/or by pushpull electronic effects. Only recently,t he first isolable "half-parent" phosphasilenes I, [28] II, [29,30] and III [31] of the type R 2 Si = PH or R(H)Si = PR could be realized (Scheme 1). However,a1,2-dihydrophosphasilene IV with hydrogen atoms at silicon and phosphorus R(H)Si=PH, which are closer to the parent system, has not been reported to date.…”

“…dme (dme = 1,2-dimethoxyethane) at room temperature in THF afforded, after 18 h, the 1,2-dihydrophosphasilene 2,p resumably through tautomerization of its elusive phosphanylsilylene isomer (Scheme 2). The 31 PNMR spectrum of 2 shows adoublet of doublets with 29 Si satellites at d( 31 P) = À301.4 ppm ( 1 J(P,H) = 132.0 Hz, 2 J(P,H) = 11.3 Hz, 1 J(Si,P) = 120.7 Hz). The 1 J(P,H) coupling constant is 12 Hz smaller than that of the Me 4 -NHC-stabilized form of II (NHC-II), [30] indicating lower 3s character of the PÀ Hbond.…”

Triamidoamine–Uranium(IV)‐Stabilized Terminal Parent Phosphide and Phosphinidene Complexes

“…[4a, 9] Indeed, there is a paucity of well-defined compounds containing a terminal PH group and structurally elucidated examples are confined to the p-block, where the bonding descriptions are open to interpretation, for example, NHCphosphinidene vs. phosphaalkene. [10] Herein, we describe the straightforward synthesis and characterization of the first example of a metal-stabilized terminal parent phosphinidene complex. This is only the second actinide terminal phosphinidene complex, [11,12] and was prepared from the first example of an f-block parent terminal phosphide complex; terminal phosphide complexes are rare, as the sterically unencumbered PH 2 group often bridges metal centers.…”