Acylation Reactions of Dibenzo‐7‐phosphanorbornadiene: DFT Mechanistic Insights

Abstract

Extensive DFT calculations provide deep mechanistic insights into the acylation reactions of tert‐butyl dibenzo‐7‐phosphanobornadiene with PhCOX (X=Cl, Br, I, OTf) in CH2Cl2 solution. Such reactions are initialized by the nucleophilic P⋅⋅⋅C attack to the carbonyl group to form the acylphosphonium intermediate A+ together with X− anion, followed either by nucleophilic X−⋅⋅⋅P attack (X=Cl, Br, and I) toward A+ to eliminate anthracene or by slow rearrangement or decomposition of A+ (X=OTf). In contrast to the first case (X=Cl) that is rate‐limited by the initial P⋅⋅⋅C attack, other reactions are rate‐limited by the second X−⋅⋅⋅P attack for X=Br and I and even thermodynamically prevented for X=OTf, leading to isolable phosphonium salts. The rearrangement of phosphonium A+ is initiated by a P‐C bond cleavage, followed either by sequential proton‐shifts to form anthracenyl acylphosphonium or by deprotonation with additional base Et3N to form neutral anthracenyl acylphosphine. Our DFT results strongly support the separated acylphosphonium A+ as the key reaction intermediate that may be useful for the transfer of acylphosphenium in general.

Organoiron- and Fluoride-Catalyzed Phosphinidene Transfer to Styrenic Olefins in a Stereoselective Synthesis of Unprotected Phosphiranes

“…The addition of a fluoride anion to [Fp(t-BuPA)]-[BF 4 ], resulting in compound 2, is conceptually related to the ability of chloride to promote anthracene loss from a phosphonium derived from an RPA compound that we reported recently 17 and was the subject of a more detailed computational study by Grimme and co-workers. 32 Next, addition of styrene to 2 furnishes intermediate [4] capable of rotation about the newly formed C−C single bond, which could plausibly go on to form [Fp(1-t-Bu)] + with the ejection of fluoride. Closure of the phosphirane ring in this sequence presumably dictates the trans stereochemistry found in the product.…”

Catalyst-free CO2 hydrogenation with BH3NH3 in water: DFT mechanistic insights

“…The reaction energies from both DFT functionals are in good mutual agreement with overall deviations of 1.1 ± 2.3 (average ± standard deviation) kcal mol −1 , with the meta-GGA TPSS-D3 functional tending to predict 4.4 ± 2.6 kcal mol −1 lower reaction barriers (see the ESI†), as also observed in our recent DFT studies. 33 In the discussion, the more reliable PW6B95-D3+COSMO-RS free energies (in kcal mol −1 , at 298.15 K and 1 mol L −1 standard state concentration) are used unless specified otherwise. The applied DFT methods in combination with the large AO basis sets provide usually accurate electronic energies with typical errors of 1–2 kcal mol −1 for chemical energies (including barriers), which have been tested thoroughly for the huge data base GMTKN55 34 that is the common standard in the field of DFT benchmarking.…”

The story of acyl phosphines: Synthesis, reactivity, and catalytic applications

“…[35] The comprehensive mechanism was probed by extensive DFT calculations at B3LYP/Def2-TZVP level of theory for acylation reactions of tert-butyl dibenzo-7λ 3 The treatment of 26 with AdC(O)Cl in THF at room temperature produced unsymmetrically substituted di (acyl) phosphines 27 as shown in Scheme 5. [35,36] Phosphinoboranes 28 are considered a good source of phosphides. Murphy et al reacted acid chlorides with various aliphatic and aromatic substituted phosphinoboranes 28 to obtain corresponding acyl phosphines 29 in good yields at room temperature (Scheme 6).…”

“…The treatment of 26 with AdC(O)Cl in THF at room temperature produced unsymmetrically substituted di (acyl) phosphines 27 as shown in Scheme 5. [ 35,36 ]…”