title: Reaction of a bridged frustrated Lewis pair with nitric oxide: a kinetics study.
abstract: Described is a kinetics and computational study of the reaction of NO with the intramolecular bridged P/B frustrated Lewis pair (FLP) endo-2-(dimesitylphosphino)-exo-3-bis(pentafluorophenyl)boryl-norbornane to give a persistent FLP-NO aminoxyl radical. This reaction follows a second-order rate law, first-order in [FLP] and first-order in [NO], and is markedly faster in toluene than in dichloromethane. By contrast, the NO oxidation of the phosphine base 2-(dimesitylphosphino)norbornene to the corresponding phosphine oxide follows a third-order rate law, first-order in [phosphine] and second-order in [NO]. Formation of the FLP-NO radical in toluene occurs with a ΔH(‡) of 13 kcal mol(-1), a feature that conflicts with the computation-based conclusion that NO addition to a properly oriented B/P pair should be nearly barrierless. Since the calculations show the B/P pair in the most stable solution structure of this FLP to have an unfavorable orientation for concerted reaction, the observed barrier is rationalized in terms of the reversible formation of a [B]-NO complex intermediate followed by a slower isomerization-ring closure step to the cyclic aminoxyl radical. This combined kinetics/theoretical study for the first time provides insight into mechanistic details for the activation of a diatomic molecule by a prototypical FLP.
authors: Department of Chemistry and Biochemistry, University of California at Santa Barbara , Santa Barbara, California 93106-9510, United States.
authors: José Clayston Melo
authors: JC
authors: Pereira
authors: Muhammad
authors: M
authors: Sajid
authors: Gerald
authors: G
authors: Kehr
authors: Ashley M
authors: AM
authors: Wright
authors: Birgitta
authors: B
authors: Schirmer
authors: Zheng-Wang
authors: ZW
authors: Qu
authors: Stefan
authors: S
authors: Grimme
authors: Gerhard
authors: G
authors: Erker
authors: Peter C
authors: PC
authors: Ford