Frustrated Lewis pairs incorporating the bifunctional Lewis acid 1,1′-fc{B(C₆F₅)₂}₂: reactivity towards small molecules

Abstract

Applications of the bifunctional ferrocenediyl Lewis acid 1,1'-fc{B(CF)} in frustrated Lewis pair (FLP) chemistry are described. The coordination (or otherwise) of a range of sterically encumbered C-, N- and P-centred Lewis bases has been investigated, with lutidine, tetramethylpiperidine, PPh, PBu and the expanded ring carbene 6Dipp being found to be sterically incapable of coordinate bond formation. The chemistry of a range of these FLPs in the presence of HO, NH, CO and cyclohexylisocyanate (CyNCO) has been investigated, with the patterns of reactivity identified including simple coordination chemistry, E-H bond cleavage and C-B insertion.

Linkage Isomerism Leading to Contrasting Carboboration Chemistry: Access to Three Constitutional Isomers of a Borylated Phosphaalkene

“…The carboboration of isocyanates, valencei soelectronic analogues of phosphaketenes, was recently found to give rise to 1,2-carboborated productsa cross the C=Ob ond, which insert as econd equivalent of isocyanate to yield six-membered heterocycles. [10,11] In contrast, related isoelectronic compounds, such as hydrazoic acid and organica zides reactw ith BCF via a 1,1-carboboration accompanied by loss of dinitrogen to afford aminoboranes. [23] The PÀCb ond length is again consistent with significant pcharacter (1.692(2) ).…”

“…It is worth noting that we have previously observed boryl group migration in reactions of both [B]OCP with nucleophiles, however that this is the first instance of such migration reactions occurring with its isomeric form [B]PCO. The carboboration of isocyanates, valence isoelectronic analogues of phosphaketenes, was recently found to give rise to 1,2‐carboborated products across the C=O bond, which insert a second equivalent of isocyanate to yield six‐membered heterocycles . In contrast, related isoelectronic compounds, such as hydrazoic acid and organic azides react with BCF via a 1,1‐carboboration accompanied by loss of dinitrogen to afford aminoboranes …”

“…All reactions and product manipulations were carried out under an inert atmosphere of argon or dinitrogen using standard Schlenk- [8]: B1ÀC1 1.566(2); C1ÀP1 1.692(2), C1À O1 1.393(2), O1ÀB2 1.341(2); B1-C1-P1122.52(9);B 1-C1-O1 112.59(10), P1-C1-O1 124.31(9); C1-O1-B21 30.72 (10). line or glovebox techniques (MBraun UNIlab glovebox maintained at < 0.1 ppm H 2 Oa nd < 0.1 ppm O 2 ).…”

“…[7,8] In the case of tris(pentafluorophenyl)borane, related reactions are only possible using more reactive substrates, such as allenyl ketones and isocyanates. [9][10][11][12] It is these latters tudies, as well as relatedw ork exploring the hydroboration of phosphaalkynes, [13][14][15] that prompted us to explore the reactivityo fB CF towardst wo isomericf orms of ab oryl-phosphaethynolate, [B]OCPa nd [B]PCO( where [B] = N,N'-bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-1,3,2-diazaboryl). [16,17] Interestingly,t hese reactions give rise to three different borylatedp hosphaalkenes with the same molecular formula.…”

Carboboration of isocyanates with tris(pentafluorophenyl)borane and evidence for dissociative FLP chemistry of an acid–base pair

“…13 Trapping of isocyanates with intramolecular FLPs has also been reported by Erker and co-workers, 14 while Martin has shown that isocyanates can insert into antiaromatic boroles. 15 It is worth noting that a six-membered carboboration product related to 1a-1c, resulting from the reaction of FcB(C6F5)2 [Fc = Fe(η 5 -C5H5)(η 5 -C5H4)] with cyclohexyl isocyanate, has been previously reported by Aldridge, 16 although the subsequent chemistry of this compound has not been investigated. To the best of our knowledge, in all of the aforementioned examples there is no evidence for the reversibility of such insertion reactions.…”