Metal‐Free Catalytic Hydrogenation

Chase, Preston A.; Welch, Gregory C.; Jurca, Titel; Stephan, Douglas W.

doi:10.1002/anie.200702908

Cited by 585 publications

(362 citation statements)

References 27 publications

Supporting

Mentioning

343

Contrasting

Unclassified

Order By: Relevance

“…9 Since then, many different FLP systems have been developed 10 and reactivity with a variety of substrates has been observed, including B-H bonds, 11 CO2, 12,13 unsaturated bonds 10 and even catalytic, metal-free hydrogenation. [14][15][16][17][18] The silylene LSi (L = CH{(C=CH2)(CMe)(2,6-i Pr2C6H3N)2}) will oxidatively add ammonia to give four-coordinate LSi(H)NH2 19 and is the only reported main group molecule that has been successfully used in the activation of PH3, yielding LSi(H)PH2. 20 Phosphenium cations [R2P] + are a class of phosphorus-containing molecules that have a rich history of reactivity, including reactions with Lewis bases, 21-23 inorganic and organic unsaturated bonds, 24 and as ligands on transition metals.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, Reactivity, and Computational Analysis of Halophosphines Supported by Dianionic Guanidinate Ligands

et al. 2012

View full text Add to dashboard Cite

The reported chemistry and reactivity of guanidinate supported group 15 elements in the +3 oxidation state, particularly phosphorus, is limited when compared to their ubiquity in supporting metallic elements across the periodic table. We have synthesized a series of chlorophosphines utilizing homo-and heteroleptic (dianionic)guanidinates and have completed a comprehensive study of their reactivity. Most notable is the reluctancy of these four-membered rings to form the corresponding Nheterocyclic phosphenium cations, the tendency to chemically and thermally eliminate carbodiimide and the scarcely observed ring expansion by insertion of a chloro(imino)phosphine into a P-N bond of the P-N-C-N framework.Computational analysis has provided corroborating evidence for the unwillingness of the halide abstraction reaction by demonstrating the exceptional electron acceptor properties of the target phosphenium cations and the underscoring strength of the P-X bond.

show abstract

Section: Introductionmentioning

confidence: 99%

Synthesis, Reactivity, and Computational Analysis of Halophosphines Supported by Dianionic Guanidinate Ligands

et al. 2012

View full text Add to dashboard Cite

show abstract

“…24,25 Amine activation reactions have also been reported. 26,27 To our knowledge, however, no dehydrogenation reactions have been reported using these systems, 28 although calculations suggest such reactions should be possible.…”

mentioning

confidence: 98%

Dehydrogenation of amine–boranes with a frustrated Lewis pair

Miller

Bercaw

2010

Chem. Commun.

View full text Add to dashboard Cite

Bulky tertiary phosphine/borane Lewis pairs P t Bu 3 /B(C 6 F 5 ) 3 react with amine-boranes to afford dehydrocoupling products and phosphonium borohydride salts.Amine-boranes are the subject of intense interest due to their potential application in hydrogen storage schemes. 1,2 A number of fast and efficient transition metal dehydrocoupling catalysts have been discovered, 3-7 and various coordination compounds relevant to the catalytic pathways have been isolated. [8][9][10] Progress has also been made in the challenging area of regeneration of spent ammonia-borane fuel. [11][12][13] Theoretical studies 14,15 of one amine-borane dehydrocoupling system employing N-heterocyclic carbenes (NHCs) as ligands 3 suggested that the free NHC could heterolytically dehydrogenate NH 3 ÁBH 3 , yielding (NH 2 BH 2 ) n and NHC-H 2 , similar to the H 2 cleavage reactivity of Bertrand's carbenes. 16 Because the reactivity of these NHC species has been compared to that of bulky phosphine/borane ''frustrated Lewis pairs'' (FLPs), it occurred to us that FLPs might also be able to dehydrogenate amine-boranes.FLPs-combinations of particularly bulky Lewis acids and bases that are unable to form traditional Lewis acid/base pairs 17 -exhibit a number of unusual reactions, [18][19][20] in particular the heterolytic cleavage of H 2 , 21-23 which has been utilized for metal-free catalytic hydrogenation of bulky imines. 24,25 Amine activation reactions have also been reported. 26,27 To our knowledge, however, no dehydrogenation reactions have been reported using these systems, 28 although calculations suggest such reactions should be possible. 29 Herein we report that the simple frustrated Lewis pair P t Bu 3 /B(C 6 F 5 ) 3 rapidly and cleanly dehydrogenates amine-boranes at room temperature, with concomitant formation of the phosphonium borohydride salt [ t Bu 3 PH][HB(C 6 F 5 ) 3 ] (Scheme 1).Initial experiments were carried out with Me 2 NHÁBH 3 , a common model for NH 3 ÁBH 3 which has desirable solubility properties and generally releases only 1 equivalent of H 2 . The frustrated Lewis pair P t Bu 3 /B(C 6 F 5 ) 3 was formed according to literature procedures in C 6 D 5 Cl, 22 and no discernable reaction was observed by NMR. The pre-formed FLP was added to a C 6 D 5 Cl solution of Me 2 NHÁBH 3 at 25 1C, giving a clear colorless solution. 30 1 H, 31 P (Fig. 1), 19 F, and 11 B (Fig. 2) The order of reagent addition is important in the dehydrocoupling reaction. If B(C 6 F 5 ) 3 and Me 2 NHÁBH 3 are dissolved Scheme 1 Fig. 2 11 B NMR spectrum shortly after FLP-mediated dehydrocoupling of Me 2 NHÁBH 3 . The underlying broad feature arises from borosilicate glass in the probe construction.

show abstract

“…Although some previous observations already suggested that cooperativity between Lewis pairs could promote metal-free transformations, notably for hydrosilylation [7], it is the use of FLPs for molecular hydrogen activation that led to a surge in research in this field [8][9]. Since, FLPs have been shown to activate many small molecules in addition to being active catalysts in reductive transformations [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Design principles in frustrated Lewis pair catalysis for the functionalization of carbon dioxide and heterocycles

Fontaine

Courtemanche

Légaré

et al. 2017

Coordination Chemistry Reviews

View full text Add to dashboard Cite

This is the peer reviewed version of the following article: [Design Principles in Frustrated Lewis KeywordsFrustrated Lewis pairs, Ambiphilic molecules, Boron, Aluminum, Carbon dioxide, Methanol, C-H activation. Highlights 1.Phosphine-aluminum frustrated Lewis pairs (FLPs) can activate CO2 but show significant stability issues. 2.The Lewis acidity and basicity need to be fine-tuned to the desired reactivity for efficient FLP catalysis.3. FLP catalysts need to generate strong hydrides to reduce catalytically carbon dioxide. 4.Transition metal catalysis can serve as an inspiration for the design of metal-free catalysts for many transformations, including the borylation of heteroarenes. Graphical abstract AbstractThis account describes our work on the use of ambiphilic molecules as catalysts for the reduction of carbon dioxide. Starting with the discovery that aluminum ambiphilic species (Me2PCH2AlMe2)2 (1) and Al(C6H4-PPh3)3 (5) could coordinate CO2 but showed significant instability, we found that phosphinoborane Ph2P-2-Bcat-C6H4 (7) was an exceptional catalyst for the hydroboration of CO2 to methoxyboranes, a molecule that can be readily hydrolyzed to methanol. A mechanistic investigation allowed us to outline the similarities between the catalytic activity of frustrated Lewis pairs (FLPs) and that of transition metal complexes. We were able to extrapolate four important guidelines, described in this account, to synthesize efficient metal-free catalysts. We demonstrate that using these concepts it was possible to rationally design FLP catalysts for the C-H borylation of heteroarenes.

show abstract

Metal‐Free Catalytic Hydrogenation

Cited by 585 publications

References 27 publications

Synthesis, Reactivity, and Computational Analysis of Halophosphines Supported by Dianionic Guanidinate Ligands

Synthesis, Reactivity, and Computational Analysis of Halophosphines Supported by Dianionic Guanidinate Ligands

Dehydrogenation of amine–boranes with a frustrated Lewis pair

Design principles in frustrated Lewis pair catalysis for the functionalization of carbon dioxide and heterocycles

Contact Info

Product

Resources

About