Catalytic Hydroboration of Carbonyl Derivatives, Imines, and Carbon Dioxide

Abstract

Organoborane compounds present a class of versatile synthetic intermediate for myriad organic transformations. The direct addition of a B−H bond across unsaturated bondnamely, hydro-borationis a powerful tool for the preparation of organoborane derivatives. This review outlines recent advances in catalytic hydroboration of unsaturated organic compounds, specifically those involving C-X (X = N, O) bonds. We will discuss the chemical behavior of both transition metal catalysts and main group catalysts in hydroboration. Emphasis will also be placed on the reaction mechanism of these catalytic reactions. Furthermore, recent achievements in catalytic hydroboration of carbon dioxide CO 2 will be highlighted.

Interconverting Lanthanum Hydride and Borohydride Catalysts for C=O Reduction and C−O Bond Cleavage

“…[15] Further mechanistic insight was sought from in-situmonitored catalytic experiments.Second-order plots indicate that reaction rate is directly proportional to the concentration of HBpin and ester.T he pseudo-second-order rate constants (k obs )plotted vs. [1]reveal alinear relationship consistent with first-order dependence on catalyst concentration, giving the ternary-order rate constant k' obs = 1.95 AE 0.86 m À2 s À1 for the experimental rate law in Equation (1). Thus,t he lanthanum hydride species of 2 and 3 are reactive toward the C = Obond of ketones but not competent for reaction with esters.A si st he case for many catalytic species,isolation of 2 and 3 in pure form was not possible,and the related YH 3 species has been assigned on the basis of mass balance in reactions trimethylyttrium and H 2 AlMes.…”

“…[1] More reactive catalysts are needed for conversions of inert substrates,s uch as esters and ethers,a nd new mechanisms are needed to ameliorate the thermodynamic barriers associated with breaking strong M À Ob onds.O ne approach that could avoid M À Obond formation involves an activating interaction of the hydride source with the electrophilic catalytic center (Scheme 1B). [1] More reactive catalysts are needed for conversions of inert substrates,s uch as esters and ethers,a nd new mechanisms are needed to ameliorate the thermodynamic barriers associated with breaking strong M À Ob onds.O ne approach that could avoid M À Obond formation involves an activating interaction of the hydride source with the electrophilic catalytic center (Scheme 1B).…”

“…[1,2] Fore xample,h ydride species Cp* 2 LaH (Cp* = h 5 -C 5 Me 5 )a nd {HC(CMeNDipp) 2 }MgH (Dipp = 2,6-C 6 H 3 iPr 2 )a re proposed catalytic intermediates in ketone,aldehyde,imine,carbodiimide,nitrile,and pyridine hydroborations. [1,2] Fore xample,h ydride species Cp* 2 LaH (Cp* = h 5 -C 5 Me 5 )a nd {HC(CMeNDipp) 2 }MgH (Dipp = 2,6-C 6 H 3 iPr 2 )a re proposed catalytic intermediates in ketone,aldehyde,imine,carbodiimide,nitrile,and pyridine hydroborations.…”

Reaction Mechanisms of CO2 Reduction to Formaldehyde Catalyzed by Hourglass Ru, Fe, and Os Complexes: A Density Functional Theory Study

“…As mild reducing agents, boron-containing compounds have been widely used in carbon dioxide reduction [14,15]. Hazari and co-workers [16] reported the allene carboxylation with CO 2 using a PSiP pincer ligand supported palladium complex as the catalyst in the hydroboration of CO 2 .…”

Olefin Hydroborations with Diamidocarbene–BH3 Adducts at Room Temperature

“…Moreover, hydroboration chemistry has been extended to afford halogenated and other oxidized hydrocarbons as well as their reduced congeners [3][4][5]. Numerous transition metal-based hydroboration catalysts have been developed over the past several decades to improve chemo-, regio-and/or stereo-selectivities [5][6][7][8][9]. Efforts toward the development of organocatalyzed analogues have also been pursued, with particular attention focused on stable carbenes, including the cyclic (alkyl)(amino) carbenes (CAACs) and the N-heterocyclic carbenes (NHCs) [10][11][12][13][14].…”