A number of studies were conducted to demonstrate C-H activation for the construction of C-B bonds. Investigations revealed that the conversion of C-H bonds to C-B bonds was both thermodynamically and kinetically favorable. The reaction at a primary C-H bond of methane or a higher alkene B 2(OR)4 formed an alkylboronate ester R' -B(OR)2 and the accompanying borane H-B(OR2. The ester and the borane were formed on the basis of calculated bond energies for methylboronates and dioaborolanes. The rates of key steps along the reaction pathway for the conversion of a C-H bond in an alkane or arene to the C-B bond in an alkyl or arylboronate ester were favorable. These studies also highlighted the accessible barriers for C-H bond cleavage and B-C bond formation during the borylation of alkanes and arenes.

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C−H Activation for the Construction of C−B Bonds

Dehydrogenation as a substrate-activating strategy in homogeneous transition-metal catalysis.

Key green chemistry research areas—a perspective from pharmaceutical manufacturers

Conventional oxidations of organic compounds formally transfer hydrogen atoms from the substrate to an acceptor molecule such as oxygen, a metal oxide, or a sacrificial olefin. In acceptorless dehydrogenation (AD) reactions, catalytic scission of C-H, N-H, and/or O-H bonds liberates hydrogen gas with no need for a stoichiometric oxidant, thereby providing efficient, nonpolluting activation of substrates. In addition, the hydrogen gas is valuable in itself as a high-energy, clean fuel. Here, we review AD reactions selectively catalyzed by transition metal complexes, as well as related transformations that rely on intermediates derived from reversible dehydrogenation. We delineate the methodologies evolving from this recent concept and highlight the effect of these reactions on chemical synthesis.

http://science.sciencemag.org/content/sci/341/6143/1229712.full.pdf

Applications of acceptorless dehydrogenation and related transformations in chemical synthesis.

Hydrogen autotransfer in the N-alkylation of amines and related compounds using alcohols and amines as electrophiles.

N-Alkylation of amines with alcohols catalyzed by a Cp*Ir complex

A new effective catalytic system consisting of [Cp*IrCl2]2/K2CO3 (Cp*=pentamethylcyclopentadienyl) for the N-alkylation of primary amines with alcohols has been developed. As an example, the reaction of aniline with benzyl alcohol in the presence of [Cp*IrCl2]2 (5.0 mol%Ir) and K2CO3 (5.0 mol%) in toluene at 110°C for 17 h gave benzylaniline in an isolated yield of 88%.

Naohiro Ozeki

Papers

N-Alkylation of amines with alcohols catalyzed by a Cp*Ir complex

N-Alkylation of Amines with Alcohols Catalyzed by a Cp*Ir Complex.