ORGANIC
LETTERS
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Vol. XX, No. XX
000–000
Highly Selective Bis(imino)pyridine
Iron-Catalyzed Alkene Hydroboration
Jennifer V. Obligacion and Paul J. Chirik*
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
Received April 9, 2013
ABSTRACT
Bis(imino)pyridine iron dinitrogen complexes have been shown to promote the anti-Markovnikov catalytic hydroboration of terminal, internal, and
geminal alkenes with high activity and selectivity. The isolated iron dinitrogen compounds offer distinct advantages in substrate scope and overall
performance over known precious metal catalysts and previously reported in situ generated iron species.
Transition metal catalyzed hydroboration has emerged
as an atom-economical and selective route for the synthesis
of alkylboronic acids.1 Alkylboranes are valuable targets
due to their diverse range of applications in organic
synthesis,2 principally as the nucleophilic partner in me-
tal-catalyzed SuzukiꢀMiyaura cross-coupling reactions.3
Historically, precious metal catalysts, specifically organo-
metallic rhodium and iridium complexes,4,5 have been the
most commonly employed for homogeneous hydrobora-
tion. In certain instances, a broad alkene scope and high
selectivity have been reported.5
Because of the potential high cost, low terrestrial abun-
dance, and performance limitations associated with pre-
cious metal catalysts, there has been renewed interest in the
discovery of catalysts based on earth-abundant, first row
transition metals.6 Often times the unique electronic struc-
tures available to these metals in conjunction with smaller
atomic radii compared to heavier elements offer the pos-
sibility for distinct reactivity. Cu-catalyzed hydroboration
of trans-β-substituted styrenes and related arenes have
been reported by Yun et al.7 Using a Cu(I) source, chiral
bidentate phosphines, and NaOtBu, alkylboronic esters
were isolated in high yield and enantiopurity. This method
has recently been extended to the asymmetric synthesis of
1,1-diborylalkanes.7c
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10.1021/ol400990u
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