A Phosphanyl‐Phosphagallene that Functions as a Frustrated Lewis Pair

Abstract

Phosphagallenes (1 a/1 b) featuring double bonds between phosphorus and gallium were synthesized by reaction of (phosphanyl)phosphaketenes with the gallium carbenoid Ga(Nacnac) (Nacnac=HC[C(Me)N(2,6‐i‐Pr2C6H3)]2). The stability of these species is dependent on the saturation of the phosphanyl moiety. 1 a, which bears an unsaturated phosphanyl ring, rearranges in solution to yield a spirocyclic compound (2) which contains a P=P bond. The saturated variant 1 b is stable even at elevated temperatures. 1 b behaves as a frustrated Lewis pair capable of activation of H2 and forms a 1:1 adduct with CO2.

NHC‐Stabilised Parent Tripentelyltrielanes

“…Goicoechea et al . showed the successful synthesis of (Nacnac)‐stabilised phosphanyl‐phosphagallene and demonstrated its reactivity as a frustrated Lewis pair by conversions with H 2 and CO 2 [12] . Furthermore, (Nacnac)EH Pn H 2 (E=Ga, Al, In; Pn =P, As, Sb) and (Nacnac)E( Pn H 2 ) 2 were reported by our own group as well as by the von Hänisch group [13,14] .…”

“…[11] Goicoechea et al showed the successful synthesis of (Nacnac)-stabilised phosphanyl-phosphagallene and demonstrated its reactivity as a frustrated Lewis pair by conversions with H 2 and CO 2 . [12] Furthermore, (Nacnac)EHPnH 2 (E = Ga, Al, In; Pn = P, As, Sb) and (Nacnac)E(PnH 2 ) 2 were reported by our own group as well as by the von Hänisch group. [13,14] Von Hänisch et al were also able to synthesise neutral 13/(15/14)/13 chain compounds by oxidative addition of (Nacnac)GaHPnH 2 or silyl(di)phosphanes with (Nacnac)Ga. [14,15] In view of tripentelyltrielanes E(PnH 2 ) 3 , however, only tris(dialkylphosphanyl)boranes B(PR 2 ) 3 are known so far, as the strong bonds between phosphorus and boron in combination with bulky organic residues keep the molecules together as monomers despite lacking external stabilisation.…”

Theoretical Investigation on Dialumenes toward Dihydrogen Activation: Mechanism and Ligand Effect

“…However, with respect to the predominately used d -block elements, main group elements have the advantages of being readily available, inexpensive, and less toxic. Consequently, a variety of the TM-free systems, including the main group multiply bonded compounds, − frustrated Lewis pairs (FLPs), − group 13 carbene analogues, − tetrylenes, , and pnictogen (Pn) compounds, have also been developed to activate dihydrogen, which exhibits TM-like reactivity.…”

On the Reactivity of Mes*P(PMe3) towards Aluminum(I) Compounds – Evidence for the Intermediate Formation of Phosphaalumenes

“…Phosphagallenes were synthesised by Goicoechea and Schulz using phosphanyl‐ or gallaphosphaketenes, respectively. Both groups utilized the readily available Ga(I) precursor ( Dip Nacnac)Ga ( Dip Nacnac=HC[C(Me)NDip] 2 ) in conjunction with the phosphaketenes [(S)P]−PCO ([(S)P]=(H n CNDip) 2 P; n=1, 2) or ( Dip Nacnac)Ga(Cl)−PCO facilitating CO cleavage and formation of [(S)P]−P=Ga( Dip Nacnac) ( G , Figure 1), [11] or ( Dip Nacnac)Ga=P−Ga(Cl)( Dip Nacnac) ( H , Figure 1), [12] respectively. Early attempts to generate monomeric phosphagallenes, revealed the formation of the trimeric species [(2,4,6‐Ph 3 ‐C 6 H 2 )GaP c Hex] 3 when (2,4,6‐Ph 3 ‐C 6 H 2 )GaCl 2 was treated with Li 2 P c Hex ( c Hex= cyclo ‐C 6 H 11 ) in a 1 : 1 molar ratio [13] .…”

“…Phosphaalumenes C and D were found to react with alkynes, alkenes and butadiene, to give P,Al‐heterocycles and P,Al‐barrelenes, after initial [2+2] cycloaddition reactions at the P−Al double bond. Phosphanylphosphagallenes ( G ), mainly show 1,3‐dipolar reactivity, akin to frustrated Lewis pairs (FLP), towards a range of protic substrates, with the anionic group being added to Ga, while the phosphanyl P atom is protonated [11,19] . H mainly reacts at the P−Ga double bond in 1,2‐additions, [20] and the reversible activation of carbodiimides and CO 2 was reported [21] .…”