Metal-free dihydrogen activation chemistry: structural and dynamic features of intramolecular P/B pairs

Abstract

Hydroboration of allyl(dimesityl)phosphane with HB(C(6)F(5))(2) gives the intramolecular five-membered P-B Lewis pair 7, that was characterized by X-ray diffraction. Similarly, HB(C(6)F(5))(2) addition to the substrates (mesityl)(2)P-CR[double bond, length as m-dash]CH(2) (R = CH(3), Ph) yield the corresponding (mesityl)(2)P(micro-CHRCH(2))B(C(6)F(5))(2) products 9a (R = CH(3)) and 9b (R = Ph) that show a weak intramolecular P...B interaction. The activation energy of the (reversible) P...B cleavage of these substrates was determined by dynamic (19)F NMR spectroscopy (9a: Delta G(not equal)(inv) (280 K) = 11.7 +/- 0.4 kcal mol(-1)). Compounds 9b and 9c show similar values. Compound 9c was prepared by HB(C(6)F(5))(2) addition to (mesityl)(2)P-CH=CHSiMe(3). Compound 9a reacts rapidly with dihydrogen (2.5 bar) at room temperature in pentane to give the zwitterionic H(2)-activation product (mesityl)(2)PH(+)(micro-CHMeCH(2))BH(-)(C(6)F(5))(2) (11).

Reaction of Frustrated Lewis Pairs with Conjugated Ynones‐Selective Hydrogenation of the Carbon–Carbon Triple Bond

“…[8] The reaction of 1 a with the ynone 3 a takes a different course. At low temperature we observe the formation of the zwitterionic 1,4-addition product 7 a, which upon heating is converted into the isomer 4, the 1,2-addition product of the FLP 1 a to the carbon-carbon triple bond of 3 a (see Scheme 1)…”

Frustrierte Lewis‐Paare: metallfreie Wasserstoffaktivierung und mehr

“…In diesem besonderen Fall bildete sich einfach das klassische Lewis-Säure/BaseAddukt 20 (Schema 6, Abbildung 4). [15] Im Unterschied dazu gingen die verwandten Allyl-und Butenylphosphine 21 (21 a: R = Ph, 21 b: R = tBu) bzw. 23 (CH 2 = CHCH 2 CH 2 PPh 2 ) glatt die Hydroborierung mit HB(C 6 F 5 ) 2 zu den difunktionellen Phosphin-Boran-Produkten 22 (22 a: R = Ph, 22 b: R = tBu) bzw.…”

“…[15] Die Verbindungen mit Substituenten in alpha-(26 b: 19 F-NMR-Signale der p-F-Substituenten (Abbildung 9) der beiden C 6 F 5 -Substituenten von 26 b wurde die Gibbs-Aktivierungsenergie [23] für die reversible Ringöffnung zu DG°d is (280 K) % (11.7 AE 0. 4 [14a] hergestellt.…”

Reversible Metal‐Free Carbon Dioxide Binding by Frustrated Lewis Pairs

“…These systems offer latent Lewis acidity and basicity for reaction with small molecules. In this vein, we [13] and others [14] have exploited this notion for the heterolytic activation of dihydrogen and subsequent application of the resulting systems in metal-free catalytic hydrogenation and addition to olefins. [15,16] Herein, we demonstrate that the concept of frustrated Lewis pairs can be exploited to effect the reversible binding of carbon dioxide under mild conditions.…”

“…The 19 F NMR spectrum showed signals at d = À133.5, À160.4, and À166.0 ppm, typical of C 6 F 5 substituents on a four-coordinate boron center. The 13 C NMR spectrum of 1 showed resonances expected for the constituent phosphorus and boron fragments as well as a signal at d = 161.6 ppm, which exhibited a PÀC coupling of 93 Hz; the IR spectrum of 1 showed an absorption at 1695 cm À1 attributable to a C = O stretch. Collectively, these data support the formulation of 1 as tBu 3 P(CO 2 )B(C 6 F 5 ) 3 .…”