Reactions of an Intramolecular Frustrated Lewis Pair with Unsaturated Substrates: Evidence for a Concerted Olefin Addition Reaction

Abstract

The intramolecular frustrated Lewis pair (mesityl)(2)P-CH(2)-CH(2)-B(C(6)F(5))(2) was generated in situ by HB(C(6)F(5))(2) hydroboration of dimesitylvinylphosphine. The compound reacts with 1-pentyne by C-H bond cleavage. It undergoes a 1,2-addition to the carbonyl group of trans-cinnamic aldehyde to yield a zwitterionic six-membered heterocycle by B-O and P-C bond formation. The Lewis pair regioselectively adds to the electron-rich C=C double bond of ethyl vinyl ether, and it selectively undergoes an exo-cis-2,3-addition to norbornene. A combined experimental/theoretical study suggests that this reaction takes place in an asynchronous concerted fashion with the B-C bond being formed in slight preference to the P-C bond. The addition products were characterized by X-ray crystal structure analyses.

Frustrated Lewis Pair Chemistry: Development and Perspectives

“…[109] Similarly, the species t Bu 3 P(N 2 O)B(C 6 H 4 F) 3 (136) was prepared and used in Lewis acid exchange reactions to give a variety of analogues including the exchange of the weak Lewis acid for other more electrophilic boranes. [109] For example, treatment with a variety of boranes gave (140).…”

“…[11,136] An intramolecular version of this reaction was probed by bridged vinylphosphine/borane systems generated in situ by HB(C 6 F 5 ) 2 hydroboration of the aryldivinylphosphine bearing the bulky 2,4,6-tri-tert-butylphenyl ("supermesityl") substituent. Interestingly, the simple hydroboration product was not observed, rather the heterocyclic, intramolecular zwitterionic methylenephosphonium derivative 198 is obtained (Scheme 69).…”

The reaction mechanisms of boron amidinate and small molecules: a density function theory study

“…A number of experiments have demonstrated that the special nature exactly results in the activation of H 2 [3,4,[8][9][10][11][12] and other small molecules, such as THF [13,14], N 2 O [15], olefins [16,17], terminal alkynes [18,19], catechol boranes [20], dienes [21], amine [22,23], and so on [5,24,25], as well as applications in catalysis simultaneously.…”

“…Recently, another analogous sterically hindered N-heterocyclic carbene borane [9,27] has been synthesized and the literature reported that one FLP compound containing N-heterocyclic carbene was also capable of reacting with CO 2 , CO, olefin, phenylacetylene, etc. Although several papers have been published in order to consider the mechanisms of the reactions between phosphane and borane compounds and H 2 , or the other small molecules [17,24] by the method of quantum computation [23], nevertheless, little work has been carried out for the mechanisms of the analogous N-heterocyclic carbene borane towards them, especially the small molecules.…”

Phosphinoborane-induced fragmentation of the unsaturated hydride H2Re2(CO)8: X-ray structure of HRe(CO)4(κB,P-Ph2PCH2CH2BR2) (where BR2 = 9-borabicyclo[3.3.1]nonanyl) and DFT Evaluation of hydride versus CO coordination by the ancillary borane

“…Within the expanse of such compounds, phosphinoboranes are unique because they contain tethered nucleophilic phosphorus and electrophilic boron centers, typically in close proximity [4,5,6,7,8,9,10,11]. The ambiphilic ligand properties of phosphinoboranes have been exploited in CO reduction and the modeling of alkyl-abstraction schemes related to ZieglereNatta catalysis [12,13,14,15].…”