A new catalytic system based on a Zn(II) NHC precursor has been developed for the cross-coupling reaction of alkyl halides with diboron reagents, which represents a novel use of a Group XII catalyst for CX borylation. This approach gives borylations of unactivated primary, secondary, and tertiary alkyl halides at room temperature to furnish alkyl boronates, with good functional-group compatibility, under mild conditions. Preliminary mechanistic investigations demonstrated that this borylation reaction seems to involve one-electron processes.
The latest development in the catalytic hydroboration of CO groups is summarized in this review. Access to borate ester intermediates provides a pathway to convert them into the corresponding valuable functionalized alcohols.
Organoboron reagents represent a unique class of compounds because of their utility in modern synthetic organic chemistry, often affording unprecedented reactivity. The transformation of the carbon−boron bond into a carbon−X (X = C, N, and O) bond in a stereocontrolled fashion has become invaluable in medicinal chemistry, agrochemistry, and natural products chemistry as well as materials science. Over the past decade, first-row dblock transition metals have become increasingly widely used as catalysts for the formation of a carbon−boron bond, a transformation traditionally catalyzed by expensive precious metals. This recent focus on alternative transition metals has enabled growth in fundamental methods in organoboron chemistry. This review surveys the current state-of-the-art in the use of first-row d-block element-based catalysts for the formation of carbon−boron bonds.
A zinc‐catalyzed combined CX and CH borylation of aryl halides using B2pin2 (pin=OCMe2CMe2O) to produce the corresponding 1,2‐diborylarenes under mild conditions was developed. Catalytic CH bond activation occurs ortho to the halide groups if such a site is available or meta to the halide if the ortho position is already substituted. This method thus represents a novel use of a group XII catalyst for CH borylation. This transformation does not proceed via a free aryne intermediate, but a radical process seems to be involved.
Reaction of [1,2-(Cp*RuH)(2)B(3)H(7)] (1; Cp*=η(5)-C(5)Me(5)) with [Mo(CO)(3)(CH(3)CN)(3)] yielded arachno-[(Cp*RuCO)(2)B(2)H(6)] (2), which exhibits a butterfly structure, reminiscent of 7 sep B(4)H(10). Compound 2 was found to be a very good precursor for the generation of bridged borylene species. Mild pyrolysis of 2 with [Fe(2)(CO)(9)] yielded a triply bridged heterotrinuclear borylene complex [(μ(3)-BH)(Cp*RuCO)(2)(μ-CO){Fe(CO)(3)}] (3) and bis-borylene complexes [{(μ(3)-BH)(Cp*Ru)(μ-CO)}(2)Fe(2)(CO)(5)] (4) and [{(μ(3)-BH)(Cp*Ru)Fe(CO)(3)}(2)(μ-CO)] (5). In a similar fashion, pyrolysis of 2 with [Mn(2)(CO)(10)] permits the isolation of μ(3)-borylene complex [(μ(3)-BH)(Cp*RuCO)(2)(μ-H)(μ-CO){Mn(CO)(3)}] (6). Both compounds 3 and 6 have a trigonal-pyramidal geometry with the μ(3)-BH ligand occupying the apical vertex, whereas 4 and 5 can be viewed as bicapped tetrahedra, with two μ(3)-borylene ligands occupying the capping position. The synthesis of tantalum borylene complex [(μ(3)-BH)(Cp*TaCO)(2)(μ-CO){Fe(CO)(3)}] (7) was achieved by the reaction of [(Cp*Ta)(2)B(4)H(9)(μ-BH(4))] [corrected] at ambient temperature with [Fe(2)(CO)(9)]. Compounds 2-7 have been isolated in modest yield as yellow to red crystalline solids. All the new compounds have been characterized in solution by mass spectrometry; IR spectroscopy; and (1)H, (11)B, and (13)C NMR spectroscopy and the structural types were unequivocally established by crystallographic analysis of 2-6.
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