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

Abstract

The olefinic C−H bond functionalization of (NHC)CHPh (NHC=IPr=C{(NAr)CH}2 1; SIPr=C{(NAr)CH2}2 2; Ar=2,6‐iPr2C6H3), derived from classical N‐heterocyclic carbenes (NHCs), with PCl3 affords the dichlorovinylphosphanes {(NHC)C(Ph)}PCl2 (NHC=IPr 3, SIPr 4). Two‐electron reduction of 3 and 4 with magnesium leads to the formation of the divinyldiphosphenes [{(NHC)C(Ph)}P]2 (NHC=IPr 5, SIPr 6) as crystalline solids. Unlike literature‐known diphosphenes, which are mostly yellow or orange, 5 is a green whereas 6 is a purple solid. Although the P=P bond lengths of 5 (2.062(1)) and 6 (2.055(1) Å) are comparable to those of the known diphosphenes (2.02–2.08 Å), the C−P bond lengths of 5 (1.785(1)) and 6 (1.797(1) Å) are, however, considerably shorter than a Csp2 −P single bond length (1.85 Å), indicating a considerable π‐conjugation between C=C and P=P moieties. The HOMO–LUMO energy gap for 5 (4.15) and 6 (4.52 eV) is strikingly small and thus the narrowest among the diphosphenes (>4.93 eV) reported as yet. Consequently, 5 readily undergoes P=P bond cleavage at room temperature on treatment with sulfur to form the unique dithiophosphorane {(IPr)C(Ph)}P(S)2 7. Interestingly, reaction of 5 with selenium gives the selenadiphosphirane [{(IPr)C(Ph)}P]2Se 8 with an intact P−P bond.

Crystalline Divinyldiarsenes and Cleavage of the As=As Bond

“…Synthesis of NHC-based divinyldiarsenes by adopting as imilarm ethodology [15] seems challenging due to limited accessibility of appropriate arsaalkynes [16] as well as the weaker p-accepting property of NHCs than CAACs. Therefore, we decided to establish ad ifferent as well as modulars ynthetic route to divinyldiarsenes V. [17] Herein, we report the synthesis, characterization, and reactivity of the first divinyldiarsenes [{(IPr)C(Ph)}As] 2 3a and [{(SIPr)C(Ph)}As] 2 3b derived from N-heterocyclic olefins (NHOs) 1a and 1b,r espectively (Scheme 1).…”

“…We commencedo ur investigation with NHOs 1a and 1b, which are readily accessible in al arge scale upon reactions of air stable 1,3-imidazoli(ni)um salts and benzyl bromide with a base. [17,18] Treatmento faTHFs olution of 1a and 1b with AsCl 3 in the presenceo fD ABCO (1,4-diazabicyclo[2.2.2]octane) led to the formationo fd ichlorides 2a and 2b,r espectively (Scheme 1a).…”

“…[12] More recently,T amm and co-workers employed an anionic NHC to prepare variousd ipnictenes III. Therefore, we decided to establish ad ifferent as well as modulars ynthetic route to divinyldiarsenes V. [17] Herein, we report the synthesis, characterization, and reactivity of the first divinyldiarsenes [{(IPr)C(Ph)}As] 2 3a and [{(SIPr)C(Ph)}As] 2 3b derived from N-heterocyclic olefins (NHOs) 1a and 1b,r espectively (Scheme 1). [14] Very recently, Stephana nd co-workers reported the stabled ivinyldiphosphenes derived from aC AAC and ap hos-phaalkyneR C P( R = tBu or adamantyl).…”

“…[17,18] Treatmento faTHFs olution of 1a and 1b with AsCl 3 in the presenceo fD ABCO (1,4-diazabicyclo[2.2.2]octane) led to the formationo fd ichlorides 2a and 2b,r espectively (Scheme 1a). [17,18] Treatmento faTHFs olution of 1a and 1b with AsCl 3 in the presenceo fD ABCO (1,4-diazabicyclo[2.2.2]octane) led to the formationo fd ichlorides 2a and 2b,r espectively (Scheme 1a).…”

“…Theb ond energy (in kcal mol À1 )o fN 2 (226) is nearly twice that of P 2 (116) [22] and thrice that of As 2 (83), [23] thus suggesting ad iminished importance of p-p bonding among third and fourth-period elements. [15,17] Among pnictinidenes, an in situ generated Bi I compound supported by aN CN pincer-type ligand was shown to cleave the EÀEb ond of diphenydichalcogenides PhEEPh (E = S, Se, Te ), producing Bi III phenylchalcogenolate derivatives. [15,17] Among pnictinidenes, an in situ generated Bi I compound supported by aN CN pincer-type ligand was shown to cleave the EÀEb ond of diphenydichalcogenides PhEEPh (E = S, Se, Te ), producing Bi III phenylchalcogenolate derivatives.…”