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Scheme 2 Hydrosilylation of 2-phenylquinoline.
It is noteworthy that analogous catalytic hydrosilylation22
of 2-phenyquinoline using Et3SiH gives exclusively the 1,4
N-SiEt3 product (7) (Scheme 2). The inability of the silyl-
group to migrate to regenerate an imine precludes further
reduction.
In conclusion, the N-heterocycles acridine and bulky
quinolines form weak adducts with B(C6F5)3 that exist in
equilibrium with the corresponding FLP. In the case of
phenanthroline, the isolated adduct exhibits a long N–B bond.
Nonetheless, all of these heterocycles are reduced in the
presence of a catalytic amount of borane B(C6F5)3 and H2
to dihydroacridine substituted 1,2,3,4-tetrahydroquinolines
and 1,2,3,4-tetrahydro-1,10-phenanthrolines, respectively.
These are the first such metal-free, atom economic reductions
of N-heterocycles. The utility of such reductions continues to
be the subject of study in our laboratories.
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Financial support from NSERC of Canada is gratefully
acknowledged. DWS is grateful for the award of a Killam
Research Fellowship and a Canada Research Chair. SJG is
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Notes and references
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space group triclinic, P1, a = 12.4522(10) A, b = 12.8361(10) A,
ꢀ
c = 16.6764(13) A, a = 79.106(4)1, b = 79.436(4)1, g = 85.941(4)1,
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ꢁc
This journal is The Royal Society of Chemistry 2010
4886 | Chem. Commun., 2010, 46, 4884–4886