Pleas Ce hd eo mni oc ta al dS j cu ise tn mc ea rgins
DOI: 10.1039/C6SC01037G
ARTICLE
Journal Name
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rate order from zero to first. However, no inhibition effect
was found in terms of reaction rate as evident that hydrosi-
lylations of 2a with Et SiH in the presence of significant
amount of 3a or cyclooctene showed the catalytic activity
similar to that obtained under standard conditions (see SI for
details).
1
3
2
2
2
4
5
15 A similar reactivity trend was observed in the La-catalyzed
1,2-hydroboration of substituted pyridines, in which the
turnover frequency (TOF) increased in the order 3-I > 3-Cl >
3-Br > 3-F ~ 3-H, while 3-halopyridines were more reactive
than the same type of 4-halopyridines (Ref. 6e).
16 Two types of hydride resonance at -12.5 and -12.8 ppm, as-
signable to Ir-(H) and Ir-(H) , respectively for both I/I’, were
3
2
1
clearly separated from each in H NMR over the range of -70
o
to 25 C without coalescence, suggesting that the hydrides at
o
2
007, 46, 5734; (f) H. Mizoguchi, H. Oikawa and H. Oguri, Nat.
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go cross-exchange between the two Ir centers at least at 25
C (see SI for this variable temperature experiments).
o
2
014, 53, 3877; (h) G. Zhao, U. C. Deo and B. Ganem, Org.
17 In order to observe resting state(s) of the present process,
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Et SiH under various conditions. It turned out that multiple
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Ir-hydride species were formed as the catalytic turnover in-
creased. This rendered resting species(s) difficult to charac-
terize. For such a reason, 3-methylpyridine that displayed
lower reactivity under catalytic conditions was chosen as a
model substrate.
1
37, 4916; (c) M. Arrowsmith, M. S. Hill, T. Hadlington, G. Ko-
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(
18 Each hydride signal at δ -13.01 and -13.20 remained sharp
o
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over the range of -70 to 60 C without broadening and/or co-
alescence (see SI for this variable temperature experiments).
This observation suggests that hydrides of 6a (or 6a’) do not
undergo scrambling between two bridged Ir centers. For rel-
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9
0 For our recent reports in the relevant reactions, see: (a) N.
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20 For selected reviews on transition metal-silane σ-complexes,
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1
1
1 T. P. Forrest, G. A. Dauphinee and S. A. Deraniyagala, Can. J.
Chem., 1985, 63, 412.
2 Although the quinolinium salt 3a-HCl slowly underwent re-
o
aromatization over time in DMSO-d at 25 C to return to
6
quinoline 2a, solid 3a-HCl was stable enough to be stored at -
o
3
0 C over 1 week without being rearomatized.
clear transition metal complexes with M−H−Si interactions in
2
1
3 Treatment of 4f with 1.1 equiv of Et SiH under otherwise
2 2
an
η
-mode, see: (h) M. J. Bennett and K. A. Simpson, J. Am.
conditions gave a mixture of isomeric mono-hydrosilylated
products, while the reaction of 4l led to a mixture of doubly
reduced product 5l and the remaining starting material 4l
Chem. Soc., 1971, 93, 7156; (i) M. Ciriano, M. Green, J. A. K.
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(
see SI for the crude NMR spectra).
4 Initially, we assumed the inhibition effect via coordination of
a and/or cyclooctene, which might lead to the alteration of
1
3
1
991, 10, 2537; (l) H. Suzuki, T. Takao, M. Tanaka, Y. Moro-
8
| J. Name., 2012, 00, 1-3
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