331958-90-8Relevant articles and documents
Effect of Ligand Structure on the Electron Density and Activity of Iridium Catalysts for the Borylation of Alkanes
Hartwig, John F.,Larsen, Matthew A.,Oeschger, Raphael J.
, p. 3415 - 3424 (2020)
An in-depth study of iridium catalysts for the borylation of alkyl C-H bonds is reported. Although the borylation of aryl C-H bonds can be catalyzed by iridium complexes containing phen or bpy ligands at mild temperatures and with limiting arene, the borylation of alkyl C-H bonds remains underdeveloped. We prepared a library of phenanthrolines that contain varying substitution patterns. The corresponding phen-Ir trisboryl carbon monoxide complexes were synthesized to determine the electron-donating ability of these ligands, and the initial rates for the borylation of the C-H bonds in THF and diethoxyethane β to oxygen catalyzed by Ir complexes containing these ligands were measured. For some subsets of these ligands, the donor ability correlated positively with the rate of C-H borylation catalyzed by the complexes containing ligands within a given subset. However, across subsets, ligands possessing similar donor properties to one another form catalysts for the borylation of alkyl C-H bonds with widely varying activity. This phenomenon was investigated computationally, and it was discovered that the stabilizing interactions between the phenanthroline ligand and the boryl ligands attached to Ir in the transition state for C-H oxidative addition could account for the differences in the activity of the catalysts that possess similar electron densities at Ir. The effect of these interactions on the borylation of secondary alkyl C-H bonds is larger than it is on the borylation of primary alkyl C-H bonds.
Origin of the Difference in Reactivity between Ir Catalysts for the Borylation of C-H Bonds
Oeschger, Raphael J.,Larsen, Matthew A.,Bismuto, Alessandro,Hartwig, John F.
supporting information, p. 16479 - 16485 (2019/10/14)
A mechanistic study on the origin of the difference in reactivity between Ir catalysts for C-H borylation reactions is reported. Catalytic reactions of B2pin2 with a series of substrates that require high temperatures and long reaction times were conducted. These reactions catalyzed by the combination of [Ir(COD)(OMe)]2 and 3,4,7,8-tetramethylphenanthroline (tmphen) occur in yields that are substantially higher than those of reactions catalyzed by [Ir(COD)(OMe)]2 and 4,4′-di-tert-butylbipyridine (dtbpy). The electronic properties of Ir catalysts ligated by dtbpy or tmphen and their stoichiometric reactivity were investigated. It was found that a longer lifetime rather than higher reactivity of the catalyst leads to higher yields of reactions catalyzed by Ir-tmphen. The catalyst ligated by dtbpy decomposes principally by dissociation of the ligand and rapid borylation at the positions alpha to nitrogen. Thus, the greater stability of the catalyst containing tmphen results from its greater binding constant.
Iridium-catalysed borylation of sterically hindered C(sp3)-H bonds: Remarkable rate acceleration by a catalytic amount of potassium tert-butoxide
Ohmura, Toshimichi,Torigoe, Takeru,Suginome, Michinori
supporting information, p. 6333 - 6336 (2014/06/09)
The C(sp3)-H bonds located on the methyl groups of an isopropyl group participate in iridium-catalysed C-H borylation with bis(pinacolato) diboron via a significant rate acceleration caused by a catalytic amount of t-BuOK. the Partner Organisations 2014.
