Reaction of Singlet Dioxygen with Phosphine–Borane Derivatives: From Transient Phosphine Peroxides to Crystalline Peroxoboronates

Abstract

Singlet dioxygen is readily split by phosphine–boronates under mild conditions. The initially formed phosphine peroxides spontaneously rearrange by B→O migration. The resulting peroxoboronates have been structurally characterized, and their ability to undergo oxygen transfer reactions substantiated.

Design principles in frustrated Lewis pair catalysis for the functionalization of carbon dioxide and heterocycles

“…It was found, however, that phosphine-borane 1-Ph2P-2-Bcat-C6H4 (7) was also generated in the reaction conditions (Scheme 6). This family of phosphinoboranes is well known and several derivatives were previously reported by Bourissou and coworkers [39][40]. The independent synthesis of 7 did show that this species does not react with CO2 nor with catecholborane (Scheme 7).…”

Reduction of Dioxygen by Radical/B(p‐C6F4X)3 Pairs to Give Isolable Bis(borane)superoxide Compounds

“…[5] Ther eaction of triethylborane with triplet dioxygen is atypical example,which provides amethod of generating ethyl radicals. [6] Bourissou et al reported the addition/insertion reaction of singlet dioxygen to ap hosphane/ borane pair, [7] and there were several ways to form peroxy boron compounds that have been reported. [8] Agapie et al recently described the reduction of dioxygen by two molar equivalents of ferrocenes in the presence of the strong boron Lewis acid B(C 6 F 5 ) 3 to yield the bis(ferrocenium) bis(borane)peroxides 1a,b (Scheme 1).…”

Ring‐opening of Epoxides Mediated by Frustrated Lewis Pairs

“…Selectedbondlengths []a nd angles [8]for 2a:P1 ÀC221.8179(11), C22À C23 1.5400(15), C23ÀO1 1.4068(13), C23ÀC24 1.5220(15), O1ÀB1 1.4909 (14), B1ÀC1 1.7023(16), C1ÀP1 1.7934(11);P1-C1-B11 15.77 (7),P 1-C22-C23 110.36 (7), C22-C23-O1107.78(9), C23-O1-B11 15.06(8). 2b:P1 ÀC22 1.8228 (12), C22ÀC231 .5479 (15),C 23ÀO1 1.4040 (14), C23ÀC241.5223(16), O1ÀB1 1.4838(15), B1ÀC1 1.6924(17), C1ÀP1 1.7872 (12);P1-C1-B1 115.77(8), P1-C22-C23 113.34(8), C22-C23-O1 110.02(9), C23-O1-B1 117.07(9).…”

“…The molecular structure of 3a is unambiguously established by single-crystal X-ray diffraction analysis (Figure 3, bottom) [24] and shows that the ring-opened 2-methyloxirane gives rise to Scheme3.Relative wB97X-D/6-31G(d,p) Gibbs free energies (in kcal mol À1 )for the conversion of 1 into 2a-c (only the methyl-substituted species a are shown;hydrogen atoms are omitted for clarity). (17),C22ÀC23 1.538(2),C 23ÀO1 1.403(2), C23ÀC24 1.532(2), O1ÀB1 1.519(2), C1ÀP1 1.7956 (19);P1-C22-C23 118.56 (12), C22-C23-O1 107.67 (15), C23-O1-B1119.77 (14).…”

“…[1] Accordingly,t he combination of aL ewis acid andaLewis base, whicha re sterically prevented from forming ac lassical Lewis acid-base adduct, allows the activation of av ariety of small molecules, [2] including dihydrogen, [2,3] olefins, [4] alkynes, [5] CO 2 , [6] SO 2 , [7] NO, [8] CO, [9] N 2 O, [10] isocyanates, azides, [11] as well as singlet dioxygen. [12] Moreover,F LPs are also able to ring-open cyclic substrates. Stephan and co-workers showedt hat phosphine/borane [13] or amine/borane [14] combinations induce ring-opening of THF,w hile Ta mm's group dem-onstrated that N-heterocyclic carbenes (NHCs) as Lewis bases can cleave THF in the presence of the highlye lectron-deficient tris(pentafluorophenyl)borane (B(C 6 F 5 ) 3 )a ffording in all cases zwitterionic species of type A (Figure 1).…”