Carbene insertion into a P–H bond: parent phosphinidene–carbene adducts from PH₃ and bis(phosphinidene)mercury complexes

Abstract

PH3 reacts with the in situ generated N-heterocyclic carbene DippNHC* (DippNHC* = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) to give the phosphanyl-imidazolidine [(Dipp)NHC*-H]-[PH2]. Upon treatment with an ortho-quinone, [(Dipp)NHC*-H]-[PH2] is dehydrogenated to give the parent phosphinidene-carbene adduct (Dipp)NHC*[double bond, length as m-dash]PH. Alternative routes to [(Dipp)NHC*-H]-[PH2] and (Dipp)NHC*[double bond, length as m-dash]PH employ NaPH2 and (TMS)3P7 (TMS = trimethylsilyl), respectively, as phosphorus sources. The adduct (Dipp)NHC*[double bond, length as m-dash]PH and the related adduct (Dipp)NHC[double bond, length as m-dash]PH ((Dipp)NHC = bis(2,6-diisopropylphenyl)imidazol-2-ylidene) possessing an unsaturated NHC backbone both react with HgCl2 to give the bis(carbene-phosphinidenyl) complexes [((Dipp)NHC*[double bond, length as m-dash]P)2Hg] and [((Dipp)NHC[double bond, length as m-dash]P)2Hg].

PH3 as a Phosphorus Source for Phosphinidene–Carbene Adducts and Phosphinidene–Transition Metal Complexes

“…The in situ generated carbene inserts into the P-H bond of PH 3 , giving rise to a phosphanyl-imidazolidine 2a, which can be subsequently dehydrogenated to the NHC=PH adduct 3a. [12] N is observed. Excess NHC=PH and M(CO) 6 were removed by washing with n-hexane, yielding the pentacarbonyl complexes as pale yellow powders in 65 to 82% yield.…”

“…A comparison of the structural properties of the adducts 1a and 3a and the mercury complexes 5a and 5b revealed that the different electronic properties of the unsaturated versus saturated NHCs are not reflected in the structures. [12] In addition to these findings, here we describe group 6 pentacarbonyl parent phosphinidene complexes of the structure [( Dipp NHC=PH)M(CO) 5 ] (6a-c, M = Cr, Mo, W), in which the NHC=PH unit acts as a two-electron ligand. These complexes are easily accessible from the metal hexacarbonyls and the adduct 1a (Scheme 5).…”

“…This can subsequently be dehydrogenated with an orthoquinone to the phosphinidene 3a. [12] This reaction is highly sensitive to the electronic properties of the NHC. Whereas the saturated Dipp NHC * reacts readily with PH 3 , the unsaturated analogue Dipp NHC does not show any reaction.…”

Iron‐ and Cobalt‐Catalyzed Synthesis of Carbene Phosphinidenes

“…Thecompounds 3-5 are new members of the family.Much of the intrigue in this type of phospha-alkene focuses on the "inversely polarized" nature of the phosphorus-carbon bond, [18] which has been considered to have three resonance forms,o ne with af ormal C=Pd ouble bond, az witterionic form with aC À Ps ingle bond, and at hird form with aC!P donor-acceptor interaction (Scheme 3). Thelatter two forms have been invoked to rationalize the fact that the 31 PNMR chemical shifts in carbene phosphinidenes occur much further upfield than in typical phospha-alkenes.I na greement with this trend, the 31 PNMR chemical shifts for 3-5 in [D 6 ]benzene are d = À59.1, À52.1, and À75.1 ppm, respectively.T he compounds 3 and 4 also fit the observed trend of long C-P distances in carbene phosphinidenes, [15,16] with the distances being 1.769(3) and 1.766(2) , respectively (see Figure S67 and Table S3;d iffraction-quality crystals of 5 could not be obtained).…”

“…Carbene phosphinidenes were first reported in 1997, [15] and recent studies have shown that these compounds, [16] and closely related systems, [17] are the subject of renewed interest. Thecompounds 3-5 are new members of the family.Much of the intrigue in this type of phospha-alkene focuses on the "inversely polarized" nature of the phosphorus-carbon bond, [18] which has been considered to have three resonance forms,o ne with af ormal C=Pd ouble bond, az witterionic form with aC À Ps ingle bond, and at hird form with aC!P donor-acceptor interaction (Scheme 3).…”