C O M M U N I C A T I O N S
Scheme 1
Bridging diazaborolanyl complexes 8a and 8b cannot be exact
intermediates in the catalytic functionalization of alkanes by alkoxy-
substituted B2pin2, and no C-H bond functionalization has been
reported by any diazaboryl complex or aminoborane reagent.
Nevertheless, 8a and 8b were precatalysts for the functionalization
of alkanes with B2pin2 and 2 mol % of 8b after 48 h at 150 °C,
yielding 20% octylBpin.
Considering the higher reactivity of pinacolborane reagents than
of diaminoborane reagents, one would expect the pinacolboryl
analogues of 8a and 8b to be more reactive than the isolated
diazaboryl complexes, and possibly to be the species that react with
alkanes. Such a complex could react directly with alkanes, in line
with the reactions of alkanes with trinuclear ruthenium polyhy-
drides,5,18 or after cleavage to monomeric boryl complexes that
would be related to Cp*Rh-boryl intermediates in the Rh-catalyzed
borylation of alkanes.11 Studies to prepare the pinacolboryl
analogues of 8a and 8b are ongoing.
Chart 1. Products from Ru-Catalyzed Terminal Borylation of
Heteroatom-Containing Substratesa
In summary, we have shown that several ruthenium compounds
serve as precatalysts for the terminal borylation of alkanes, that
high yields can be obtained from reactions catalyzed by complexes
of this metal, that the catalyst is tolerant of heteroatoms, and that
these catalysts display an unusual trend of higher yields for reactions
of alkanes than for reactions of arenes. This work presents the
opportunity to develop catalysts with ligands and geometries distinct
from those of the existing rhodium catalysts for alkane function-
alization, and this work will be part of future studies.
b
a Conditions: neat, 150 °C, 24 h, yield determined by GC. Neat, 150
°C, 48 h, yield determined by GC.
Acknowledgment. We thank the NSF (CHE-03019071) for
support of this work. J.L. thanks the NIH (GM069172) for a
postdoctoral fellowship.
Supporting Information Available: Procedures for synthesis and
characterization of reaction products (PDF and CIF). This material is
Figure 1. ORTEP diagram of Cp*2Ru2H3[B(N,N-dimethylphenylenedi-
amine)] (8a).
complexes occurred with ethers (vide supra), fluoroalkanes, and
amines in yields that were comparable to those of the reactions of
alkanes (Chart 1). Moreover, these reactions were selective for
functionalization at the less hindered methyl group regardless of
the identity or presence of a heteroatom. The optimal ruthenium
catalyst for these reactions depended on substrate, but either 1 or
2 catalyzed these reactions in good to excellent yields.
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The solid-state structure of 8a, determined by X-ray crystal-
lography, is shown in Figure 1; the boryl ligand of 8b lies on a
crystallographic mirror plane and, therefore, symmetrically bridges
the two metal centers. The only other complexes with bridging boryl
groups include three with a semi-bridging structure16 and one with
an unsymmetrical heterodinuclear structure.17 The 1H NMR spectra
of 8a and 8b at room temperature exhibit only one hydride signal.
However, 1H NMR spectra at -40 °C contain two singlet
resonances in a 2:1 ratio of intensities.
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