Accessing Frustrated Lewis Pair Chemistry from a Spectroscopically Stable and Classical Lewis Acid‐Base Adduct

Detailed mechanistic information is crucial to our understanding of reaction pathways and selectivity. Dynamic exchange NMR techniques, in particular 2D exchange spectroscopy (EXSY) and its modifications, provide indispensable intricate information on the mechanisms of organic and inorganic reactions and other phenomena, for example, the dynamics of interfacial processes. In this Review, key results from exchange NMR studies of small molecules over the last few decades are systemised and discussed. After a brief introduction to the theory, the key types of dynamic processes are identified and fundamental examples given of intra‐ and intermolecular reactions, which, in turn, could involve, or not, bond‐making and bond‐breaking events. Following that logic, internal molecular rotation, intramolecular stereomutation and molecular recognition will first be considered because they do not typically involve bond breaking. Then, rearrangements, substitution‐type reactions, cyclisations, additions and other processes affecting chemical bonds will be discussed. Finally, interfacial molecular dynamics and unexpected combinations of different types of fluxional processes will also be highlighted. How exchange NMR spectroscopy helps to identify conformational changes, coordination and molecular recognition processes as well as quantify reaction energy barriers and extract detailed mechanistic information by using reaction rate theory in conjunction with computational techniques will be shown.

Section: Nucleophile–electrophile Reactionsmentioning

confidence: 99%

Mechanisms and Beyond: Elucidation of Fluxional Dynamics by Exchange NMR Spectroscopy

Nikitin

O'Gara

2019

“…[50] 2 Ph :c olorless crystals, C 27 H 35 BN 3 P, M r = 443.36, crystal size 0.20 0.10 0.06 mm, orthorhombic, space group Pca2 1 (no.29), a = 20.3505(5), b = 18.8682(5), c = 12.8093(3) , V = 4918.5(2) 3 , Z = 8, 1 = 1.197 Mg m À1À3 , m(Cu-K a ) = 1.12 mm À1 , F(000) = 1904, 2q max = 144.08,3 6741 reflections, of which 9434 were independent (R int = 0.039), 578 parameters, 1r estraint, R1 = 0.034 (for 8901 I > 2s(I)), wR2 = 0.086 (all data), S = 1.03, largest diff. peak/hole = 0.30/ À0.22 e À3 , x = 0,452 (17). 3 t Bu :c olorless crystals, C 25 H 39 BN 3 P, M r = 423.37, crystal size 0.22 0.08 0.06 mm, monoclinic, space group P2 1 /n (no.14), a = 8.8381 (6), b = 14.9452(9), c = 19.3839 (12) , b = 102.622(2)8, V = 2498.5 (3) 3 , Z = 4, 1 = 1.126 Mg m À1À3 , m(Mo-K a ) = 0.13 mm À1 , F(000) = 920, 2q max = 55.28,4 9835 reflections, of which 5768 were independent (R int = 0.040), 272 parameters, R1 = 0.045 (for 4845 I > 2s(I)), wR2 = 0.113 (all data), S = 1.05, largest diff.…”

Section: X-ray Crystal Structure Determinationsmentioning

confidence: 99%

“…Phosphorus/boron-based FLPs have been shown to add to the a-nitrogen of the azide form-ing coordinationm ode D (Figure 1) [14] and, in one case, it was found that upon irradiation this speciesr earranges to a,b-nitrogen adduct E. [15] The a,g-nitrogen coordinationm ode F was found by treatingageminal FLP with mesityl azide. [16,17] In analogy to the reactivityo fN HCs (C;F igure 1), dinitrogen elimination occurs when TMS azide was reacted with aP /Al-based FLP affording heterocycle G, [18] yet in this case no follow-up chemistry has been investigated.…”

Section: Introductionmentioning

confidence: 99%

New Insights in Frustrated Lewis Pair Chemistry with Azides

Boom

Jupp

Nieger

et al. 2019

The geminal frustrated Lewis pair (FLP) tBu2PCH2BPh2 (1) reacts with phenyl‐, mesityl‐, and tert‐butyl azide affording, respectively, six, five, and four‐membered rings as isolable products. DFT calculations revealed that the formation of all products proceeds via the six‐membered ring structure, which is thermally stable with an N‐phenyl group, but rearranges when sterically more encumbered Mes−N3 and tBu−N3 are used. The reaction of 1 with Me3Si−N3 is believed to follow the same course, yet subsequent N2 elimination occurs to afford a four‐membered heterocycle (5), which can be considered as a formal FLP‐trimethylsilylnitrene adduct. Compound 5 reacts with hydrochloric acid or tetramethylammonium fluoride and showed frustrated Lewis pair reactivity towards phenylisocyanate.

“…Of growing interest is the development of FLPs in which transition-metals pecies appear as one of the components [8d,f, 9] with the aim of combining the powerful cooperative main-group FLP reactivity with the rich transition-metal chemistry.F or some FLP systems, the equilibrium between the dissociateda cid and base and the classical Lewis acid/base adduct was detected.I nterestingly,F LP reactivity has been observed even when the equilibrium wasa lmostc ompletely shiftedt oward the classical Lewis acid/base adduct, providedt hat the dissociated state was thermally accessible. [10] For this reactivity the concept of "thermally inducedf rustration" was introduced [11] and the terms "masked" [12] and" dormant" [13] have been used to describe the involved FLPs.…”

mentioning

confidence: 99%

Reversible Activation of Water by an Air‐ and Moisture‐Stable Frustrated Rhodium Nitrogen Lewis Pair

Carmona

Ferrer

Rodrı́guez

et al. 2019