Addition of boranes to N-aryl-salicylaldimines: Intramolecular hydrogenation of imines

Article abstract of DOI:10.1039/c1dt10132c

Addition of boranes to N-aryl-salicylaldimines takes place initially at the reactive phenolic O-H bond to give an activated boron-containing imine and dihydrogen. In some cases a subsequent intramolecular hydrogenation step is observed and the CN imine bond is reduced to the corresponding amine. Reactions with dimesitylborane in THF are unique in that the reduced amine product is the major product observed in solution.

Full text of DOI:10.1039/c1dt10132c

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PAPER
Addition of boranes to N-aryl-salicylaldimines: Intramolecular hydrogenation
of imines†
Stephanie S. Barnes,a Christopher M. Vogels,a Andreas Deckenb and Stephen A. Westcott*a
Received 23rd January 2011, Accepted 15th February 2011
DOI: 10.1039/c1dt10132c
Addition of boranes to N-aryl-salicylaldimines takes place initially at the reactive phenolic O–H bond
to give an activated boron-containing imine and dihydrogen. In some cases a subsequent
intramolecular hydrogenation step is observed and the C N imine bond is reduced to the
corresponding amine. Reactions with dimesitylborane in THF are unique in that the reduced amine
product is the major product observed in solution.
to (E)-2-((phenylimino)methyl)phenol at room temperature to
Introduction
give the corresponding reduced amine adduct 1 (Scheme 1).4
Boron products of imines and related substrates have garnished
much attention recently1 as these compounds have a number of ap-
plications, including their use in bifunctional catalysis, molecular
recognition, fluorescent chemosensors, fungicidal additives, chiral
Compound 1 was characterized in the solid state by a single
crystal X-ray diffraction study but no solution data were reported.
Although we had originally suggested that the formation of 1
proceeded via initial hydroboration of the C N double bond,
sensors, electroluminescent devices, and non-linear optical studies.
followed by B–O bond formation and hydrogen transfer, recent
Indeed, Schiff bases derived from the addition of boron halides
work by Stephan and co-workers on their remarkable Frustrated
Lewis Pair chemistry5 persuaded us to re-investigate this reaction
in more detail, the results of which are presented herein.
to salicylaldimines have recently shown considerable luminescent
behaviour (Fig. 1, I).1g Farfa´n, Santilla´n, Barba and co-workers
have been investigating the imino Diels–Alder reactions with
imines (Fig. 1, II and III) and have discovered that related systems
are potential candidates for third order non-linear optical studies.2
These latter two compounds are prepared by the condensation
of the salicylaldimines with phenylboronic acid (PhB(OH)2) and
phenylborinic acid (Ph2BOH), respectively.
Although simple boranes (HBR2, R = H, alkyl groups) have
been used to reduce the C N bond in imines,3 we have previously
reported that catecholborane (HBcat, cat = 1,2-O2C6H4) adds
Scheme 1 Addition of catecholborane (HBcat) to (E)-2-((phenyli-
mino)methyl)phenol to give aminoborane 1.
aDepartment of Chemistry and Biochemistry, Mount Allison University,
Sackville, NB E4L 1G8, Canada. E-mail: swestcott@mta.ca
Results and discussion
bDepartment of Chemistry, University of New Brunswick, Fredericton, NB
E3B 5A3, Canada
In this study, we have found that addition of HBcat to N-aryl-
salicylaldimines a–d did indeed give a mixture of products, as
determined by multinuclear NMR spectroscopy, including both
† CCDC reference numbers 807112–807115. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1dt10132c
Fig. 1 Salicylaldimine derived boron compounds.
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Scheme 2 Addition of boranes to N-aryl-salicylaldimines.
the boronate imine, 2, as well as the saturated amine, 3 (Scheme
2). The formation of both these species in solution suggests that
the initial reaction occurs by addition of the borane to the phenolic
OH to generate the imine, 2, along with dihydrogen. This pathway
While other pathways are plausible, the liberated dihydrogen
may add to the imine in a mechanism similar to that reported for
the activation of small molecules using Frustrated Lewis Pairs.7
The disappearance of the methine proton followed by a peak
observed at around d 4.3 ppm indicates that the imine is being
reduced to the amine. Not surprisingly, reactions with the less
bulky para methoxy substituted salicylaldimine a gave significant
amounts of the amine product, 3a, although the imine products
were favoured with the sterically encumbered ortho substituted
salicylaldimines (b–d).
1
is supported by the observation of dihydrogen in the H NMR
spectra for these reactions with a peak at d 4.6 ppm in CD2Cl2.
As expected, the imine methine proton is observed at about d
8 ppm in the 1H NMR spectra and a resonance at 166 ppm
in the 13C NMR spectra corresponds to the N CH carbon.
A sharp peak at 8 ppm in the 11B NMR spectra indicates that
the boron atom lies in a four-coordinate environment.6 Imine 2b
has also been characterized by a single crystal X-ray diffraction
study, the structure of which is shown in Fig. 2a, along with
pertinent bond distances and angles. Crystallographic data are
shown in Table 1. While all bond distances and angles are well
within the range expected for similar complexes,1,2 the short N(1)–
Once again both products were observed in reactions
with either pinacolborane (HBpin, pin = 1,2-O2C2Me4) or 9-
borabicyclo[3.3.1]nonane (9-BBN) with salicylaldimine a. Re-
actions with the ortho-substituted N-aryl-salicylaldimines (b–
d) however, gave the corresponding imines 4b–d and 6b–d as
the formation of the reduced amines was minimal (Table 2).
These imines have been characterized by multinuclear NMR
spectroscopy and by elemental analyses. The 1H NMR spectra of
these species were quite diagnostic as the imine C(H) N proton
˚
C(7) bond distance of 1.2907(18) A confirms that the imine
double bond has not been reduced. In comparison, the adjacent
˚
N(1)–C(8) bond length is 1.4592(18) A, typical for a N–C single
1
bond.
can be clearly seen around d 7–8 ppm. Likewise, the 13C{ H} NMR
shows the resonance for the imine carbon at around d 165 ppm
while the 11B NMR data clearly demonstrates that the boron atom
is four coordinate with a peak at d 6 (4) and 8 ppm (6). Complex 6d
was also characterized by a single crystal X-ray diffraction study
and the molecular structure of this imine is shown in Fig. 2b. Once
˚
again, the short N(1)–C(7) bond distance of 1.296(2) A confirms
the presence of the imine functionality.
Although dicyclohexylborane has been used as a selective
hydroborating agent in organic synthesis,8 much like 9-BBN,9
reactions of [HBCy2]2 with salicylaldimines are unique in that only
the imine products 8 were generated, even with substrate a. The
formation of amine products was not detected to any extent using
NMR spectroscopy. While we initially thought this selectivity
arose from the increased steric bulk of [HBCy2]2, compared with
9-BBN, it is more likely a result of the combination of increased
sterics and reduced Lewis acidity (vide infra). Spectroscopic data
reveal the existence of the C N double bond while maintaining
a four coordinate boron atom as the 11B NMR peaks range
from d 6–8 ppm. Although attempts to generate crystals of these
imines proved unsuccessful, we have structurally characterized
the ether complex Cy2BOBCy2, which presumably results from
the addition of adventitious water to [HBCy2]2, along with the
formation of dihydrogen. The molecular structure of one of the
two crystallographically independent molecules of Cy2BOBCy2
is depicted in Fig. 3, along with pertinent bond distances and
angles. Of significance are the large B–O–B bond angles of
Fig.
2
(a) Molecular structure of 2b with ellipsoids drawn at
50% probability level. Hydrogen atoms omitted for clarity. Selected
bond distances (A) and angles (deg): B(1)–O(1) 1.445(2), B(1)–O(3)
˚
1.458(2), B(1)–O(2) 1.471(2), B(1)–N(1) 1.6074(19), N(1)–C(7) 1.2907(18),
N(1)–C(8) 1.4592(18), O(1)–B(1)–O(3) 112.17(13), O(1)–B(1)–O(2)
112.56(13), O(3)–B(1)–O(2) 106.22(13), O(1)–B(1)–N(1) 109.07(12),
O(3)–B(1)–N(1) 108.95(12), O(2)–B(1)–N(1) 107.71(12), C(7)–N(1)–C(8)
120.04(12): (b) Molecular structure of 6d with ellipsoids drawn at
50% probability level. Hydrogen atoms omitted for clarity. Selected
˚
bond distances (A) and angles (deg): B(1)–O(1) 1.510(2), B(1)–C(20)
1.606(2), B(1)–C(27) 1.619(2), B(1)–N(1) 1.651(2), N(1)–C(7) 1.296(2),
N(1)–C(8) 1.4596(19), O(1)–B(1)–C(20) 109.45(13), O(1)–B(1)–C(27)
110.07(13), C(20)–B(1)–C(27) 107.11(14), O(1)–B(1)–N(1) 102.22(12),
C(20)–B(1)–N(1) 116.14(13), C(27)–B(1)–N(1) 111.74(13), C(7)–N(1)–
C(8) 119.11(14).
4708 | Dalton Trans., 2011, 40, 4707–4714
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Table 1 Crystallographic Data Collection Parameters
Complex
2b
6d
12a
Cy2BOBCy2
Formula
C21H18BNO3
343.17
monoclinic
C27H36BNO
401.38
orthorhombic
C32H36BNO2
477.43
monoclinic
C44H22B2O
370.21
Molecular weight
Crystal system
Space group
triclinic
¯
P21/c
P212121
C2/c
P1
˚
a/A
16.124(6)
7.653(3)
14.192(5)
90
98.931(5)
90
1730.0(11)
4
1.318
8.9551(13)
15.564(2)
16.659(3)
90
90
90
2321.8(6)
4
1.148
0.55 ¥ 0.38 ¥ 0.33
173(1)
22.194(4)
7.8827(13)
32.456(6)
90
100.937(5))
90
5575.0(17)
8
1.138
10.170(4)
12.049(4)
19.696(7)
88.903(9)
78.163(7)
86.724(6)
2358.1(14)
4
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
r
calc./mg m-3
1.043
0.60 ¥ 0.23 ¥ 0.23
173(1)
Crystal size/mm3
Temp/K
0.55 ¥ 0.45 ¥ 0.08
173(1)
0.50 ¥ 0.15 ¥ 0.10
213(1)
Radiation
MoKa (l = 0.71073)
0.087
11 611
3860
307
1.28 to 27.50
0.196/-0.192
1.076
0.0380
0.1045
MoKa (l = 0.71073)
0.067
16 167
2990
415
1.79 to 27.49
0.245/-0.140
1.076
0.0322
0.0872
MoKa (l = 0.71073)
0.069
18 597
6208
332
1.28 to 27.50
0.331/-0.175
1.072
0.0625
0.1886
MoKa (l = 0.71073)
0.059
11 326
11 326
488
1.06 to 27.50
0.264/-0.179
0.976
0.0548
0.1560
m/mm-1
Total reflections
Total unique reflections
No. of variables
q Range/◦
-3
˚
Largest difference peak/hole/e A
S (GoF) on F2
a
R1 (I>2s(I))
b
wR2 (all data)
ꢀ
ꢀ
ꢀ
ꢀ
a R1 = ꢀFo| - |Fcꢀ/ |Fo|. b wR2 = ( [w(Fo - Fc2)2]/ [wFo4])1/2, where w = 1/[s (Fo2) + (0.0403 ¥ P)2 + (0.4779 ¥ P)] (2b), 1/[s (Fo2) + (0.0468 ¥
Fc2)/3.
2
2
2
P)2 + (0.3957 ¥ P)] (6d), 1/[s (Fo2) + (0.0729 ¥ P)2 + (4.3722 ¥ P)] (12a) and 1/[s (Fo2) + (0.0769 ¥ P)2] (Cy2BOBCy2), where P = (max(Fo2, 0) + 2 ¥
2
2
Table 2 Product ratios derived from the reaction of boranes with N-aryl salicylaldimines a–d in THF
a
b
c
d
Borane
imine
60
70
amine
40
30
imine
75
95
amine
25
5
imine
80
95
amine
20
5
imine
90
95
amine
10
5
HBcat
HBpin
9-BBN
60
100
1
40
0
99
100
100
100
10
0
0
90
90
100
100
25
0
0
75
90
100
100
30
0
0
70
80
[HBCy2]2
HB(C6F5)2
[HBMes2]2
0
10
10
20
Reaction conditions: 0.10 mmol of salicylaldimine, 0.10 mmol of borane in 2 mL of THF at RT for 18 h. The relative yields (%) were determined by
integration of 1H NMR data (using anisole as a standard) from duplicate reactions.
170.31(17)◦ and 178.8(2)◦ in the two independent molecules. There
are a number of similarly near-linear structures reported in the
literature, where the steric bulk of the aryl or alkyl groups on
boron are presumably responsible for the increase in the boron–
ether bond angles.10
complete, the Lewis acidic boron group then forms a bond with
the amine nitrogen as indicated by the 11B NMR data, with a peak
at d 1.9 ppm. Increasing the steric bulk on the imine nitrogen
group decreased the amount of hydrogenation and significant
amounts of the corresponding imines 9b–d were observed in
solution.
Interestingly, similar results were also observed in reactions with
the bulky dimesitylborane [HBMes2]2 (Scheme 3).11 Addition of
[HBMes2]2 to salicylaldimine a gave the corresponding amine, 12a,
as the only new product in solution. This result is remarkable in
that it may represent a rare example of a FLP hydrogenation
taking place using a borane derived from something other than
Piers’ borane. Stephan and co-workers have recently shown that
dihydrogen can be activated at elevated temperatures (100 ◦C) by
o-benzylphosphino- and o-a-methylbenzyl(N,N-dimethyl)amine-
boranes derived from both Piers’ borane and dimesitylborane.5s In
this study, it appears that the boron atom remains three coordinate
We then investigated the use of Lewis acidic Piers’ borane
for these reactions as Lewis base derivatives of this borane are
well known to display classical ‘Frustrated Lewis Pair (FLP)’
chemistry.5,7 Remarkably, we found that addition of HB(C6F5)2 to
salicylaldimine a gave the corresponding saturated hydrogenation
product 10a as the major boron-containing product, with only
1
an insignificant amount of the imine 9a detected by H NMR
spectroscopy (<2%). Once again we presume initial reactivity
occurs at the phenolic O–H bond to generate the borate O–
B(C6F5)2 species along with dihydrogen, the latter of which could
then react with the resulting intramolecular FLP and activate the
dihydrogen bond and allow for addition to the C N group. Once
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Fig. 4 Molecular structure of 12a with ellipsoids drawn at 50% proba-
bility level. Hydrogen atoms omitted for clarity. Selected bond distances
Fig. 3 The molecular structure of one of the two independent molecules
of Cy2BOBCy2, with ellipsoids drawn at 50% probability level. Hydrogen
atoms omitted for clarity. Selected bond distances (A) and angles
˚
(A) and angles (deg): B(1)–O(1) 1.378(3), B(1)–C(24) 1.576(4), B(1)–C(15)
˚
1.582(4), O(1)–C(1) 1.385(3), N(1)–C(8) 1.386(4), N(1)–C(7) 1.446(3),
O(1)–B(1)–C(24) 122.2(2), O(1)–B(1)–C(15) 111.2(2), C(24)–B(1)–C(15)
126.6(2), B(1)–O(1)–C(1) 127.7(2), C(8)–N(1)–C(7) 122.1(3).
(deg): Molecule A: B(1)–O(1) 1.348(3), B(1)–C(7) 1.568(3), B(1)–C(1)
1.584(3), B(2)–O(1) 1.350(3), B(2)–C(19) 1.577(3), B(2)–C(13) 1.578(3),
O(1)–B(1)–C(7) 119.77(17), O(1)–B(1)–C(1) 116.76(18), C(7)–B(1)–C(1)
123.44(18), O(1)–B(2)–C(19) 118.19(19), O(1)–B(2)–C(13) 118.29(19),
C(19)–B(2)–C(13) 123.44(18), B(1)–O(1)–B(2) 170.31(17); Molecule B:
B(3)–O(2) 1.343(3), B(3)–C(31) 1.574(3), B(3)–C(25) 1.577(3), B(4)–O(2)
1.336(3), B(4)–C(37) 1.577(3), B(4)–C(43) 1.588(3), O(2)–B(3)–C(31)
118.2(2), O(2)–B(3)–C(25) 118.5(2), C(31)–B(3)–C(25) 123.31(18),
O(2)–B(4)–C(37) 119.43(19), O(2)–B(4)–C(43) 118.2(2), C(37)–B(4)–C(43)
122.40(18), B(4)–O(2)–B(3) 178.8(2).
Conclusion
We have examined the addition of simple boranes to a group of
Schiff bases derived from salicylaldehyde and found that, contrary
to a previous report, reactions occur initially at the OH functional-
ity to generate an activated iminoborate and dihydrogen. In some
cases, a subsequent hydrogenation of the imine C N bond is
observed to give the corresponding amine. Indeed, the amine is the
major product formed in reactions with Piers’ borane HB(C6F5)2
and with [HBMes2]2. Reactions with dimesitylborane are quite
significant as they may represent a rare example of dihydrogen
activation by a FLP derived from a simple non-fluorinated borane.
We are in the process of investigating this mechanism further, as
well as expanding the use of dimesitylborane chemistry, and will
report our findings in due course.
as the peak at d 49.0 ppm in the 11B NMR spectra is almost
identical to that obtained by reacting [HBMes2]2 with PhOH
(d 49.9 ppm). It is likely that the increased steric bulk caused
by the mesityl groups inhibits coordination of the boron to the
neighbouring nitrogen atom. This observation was confirmed by
a single crystal X-ray diffraction study. The molecular structure of
12a is shown in Fig. 4 along with the pertinent bond distances
˚
and angles. The long N(1)–C(7) bond distance of 1.446(3) A
demonstrates that the imine bond has in fact been reduced and
the sum of the angles (R = 360.0(2)◦) around boron shows that
the atom is trigonal planar. Solvent seemed to have no significant
effect on this hydrogenation as complete conversion to the amine
was observed in all cases (Table 3). However, solvent played
a significant role in the analogous reactions with the bulkier
substrates and more of the amine was observed in reactions carried
out in THF and other coordinating solvents such as glyme and
dioxane. Conversely, reactions carried out in toluene gave the imine
product primarily.
Experimental
General procedures and materials
Reagents and solvents were purchased from Aldrich Chemicals
and used as received except for [HBCy2]212 and [HBMes2]211g which
were prepared according to literature procedures. NMR spectra
were recorded on a JEOL JNM-GSX270 FT NMR (1H: 270 MHz;
11B: 87 MHz; 13C: 68 MHz; 19F: 254 MHz) spectrometer. Chemical
shifts (d) are reported in ppm [relative to residual solvent peaks
Scheme 3 Addition of [HBMes2]2 to a–d.
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Table 3 Solvent effect upon the distribution of products derived from the reaction of [HBMes2]2 with salicylaldimines a–d
THF
Glyme
Dioxane
Diethyl Ether
CH2Cl2
Toluene
Substrate
11
12
11
12
11
12
11
12
11
12
11
12
a
b
c
0
100
90
90
0
5
10
30
100
95
90
0
100
65
50
0
100
30
15
5
0
100
15
5
0
100
2
2
10
10
20
35
50
65
70
85
95
85
95
98
98
98
100
d
80
70
35
2
0
Reaction conditions: 0.10 mmol of salicylaldimine, 0.05 mmol of [HBMes2]2 in 2 mL of solvent at RT for 18 h. The relative yields (%) were determined
by integration of 1H NMR data (using anisole as a standard) from duplicate reactions.
(1H and 13C) or external BF3·OEt2 (11B)] and coupling constants
(J) in Hz. Multiplicities are reported as singlet (s), doublet (d),
triplet (t), quartet (q), septet (sept), multiplet (m), broad (br), and
overlapping (ov). Melting points were determined using a Mel-
Temp apparatus and are uncorrected. Elemental analyses were
performed by Guelph Chemical Laboratories (Guelph, ON). All
reactions were performed under an atmosphere of dinitrogen.
(br). Anal. Calc. for C25H34BNO3·C4H8O (479.53): C, 72.36; H,
8.85; N, 2.92. Found: C, 72.63; H, 8.41; N, 2.99.
Imine 6b
Isolation method B. Yield: 87%. Mp 130–132 ◦C. 1H NMR (C6D6):
d 7.13–7.00 (ov m, 2H, Ar), 6.92–6.72 (ov m, 5H, Ar & C(H) N),
6.52 (ov ddd, J = 6.9, 6.9, 1.2 Hz, 1H, Ar), 2.66 (br s, 2H, BBN),
2.32–1.85 (ov m, 12H, BBN & CH3), 1.51 (br s, 4H, BBN), 1.34
General synthesis
1
(br s, 2H, BBN). 11B (C6D6): d 7.5 (sharp). 13C{ H} (C6D6):
d 165.5, 163.5, 145.8, 137.7, 131.7, 131.3, 128.7, 127.2, 120.5,
120.3, 118.1, 33.6, 31.2, 24.8, 23.3 (br, C–B), 18.8. Anal. Calc.
for C23H28BNO·0.5 C4H8O (381.39): C, 78.73; H, 8.47; N, 3.67.
Found: C, 78.47; H, 8.52; N, 3.88.
To a stirred solution of salicylaldimine was added a solution of
the appropriate borane. Reactions were stirred for 18 h at which
point the solvent was removed under vacuum and the residual
solid or oil dissolved in a minimum amount of (A) hot hexane or
(B) a 1 : 1 solution of THF and hexane and stored at -30 ◦C. The
resulting precipitate was collected by suction filtration and dried
under vacuum.
Imine 6c
Isolation method A. Yield: 85%. Mp 134–136 ◦C. 1H NMR
(C6D6): d 7.28 (s, 1H, C(H) N), 7.12–7.00 (ov m, 3H, Ar), 6.94–
6.91 (ov m, 2H, Ar), 6.75 (dd, J = 7.8, 1.6 Hz, 1H, Ar), 6.50
(ov ddd, J = 6.6, 6.6, 1.2 Hz, 1H, Ar), 2.63 (q, J = 7.4 Hz, 4H,
CH2CH3), 2.18–1.83 (br ov m, 8H, BBN), 1.46–1.37 (br ov m, 6H,
BBN), 0.92 (t, J = 7.4 Hz, 6H, CH2CH3). 11B (C6D6): d 7.9 (sharp).
Imine 4b
Isolation method A. Yield: 87%. Mp 162–165 ◦C. 1H NMR
(C6D6): d 7.05–6.88 (ov m, 6H, Ar & C(H) N), 6.71 (d, J =
7.8 Hz, 1H, Ar), 6.49 (m, 1H, Ar), 2.32 (s, 6H, CH3), 1.15 (br
1
13C{ H} (C6D6): d 165.3, 163.6, 144.4, 137.8, 137.6, 131.2, 127.9,
1
s, 12H, pin). 11B (C6D6): d 6.0 (sharp). 13C{ H} (C6D6): d 166.5,
126.8, 120.5, 120.1, 118.3, 33.6 (br), 31.1 (br), 24.9, 24.7, 23.3 (br,
C–B), 15.3. Anal. Calc. for C25H32BNO (373.39): C, 80.41; H, 8.66;
N, 3.75. Found: C, 79.90; H, 8.80; N, 3.95.
162.8, 143.8, 137.5, 134.4, 131.4, 128.0, 127.7, 120.1, 117.9, 115.8,
80.4, 25.9, 18.4. Anal. Calc. for C21H26BNO3 (351.29): C, 71.80;
H, 7.48; N, 3.99. Found: C, 71.57; H, 7.06; N, 3.82.
Imine 6d
Imine 4c
Isolation method A. Yield: 82%. Mp 174–176 ◦C. 1H NMR
(C6D6): d 7.72 (s, 1H, C(H) N), 7.12–6.99 (ov m, 5H, Ar), 6.78
(dd, J = 7.0, 1.6 Hz, 1H, Ar), 6.49 (ov ddd, J = 6.2, 6.2, 1.6 Hz, 1H,
Ar), 3.45 (sept, J = 7.0 Hz, 2H, CH(CH3)2), 2.68 (br s, 2H, BBN),
2.21–1.84 (ov br m, 6H, BBN), 1.52 (br s, 4H, BBN), 1.37 (br s, 2H,
BBN), 1.22 (d, J = 7.0 Hz, 6H, CH(CH3)2), 0.80 (d, J = 7.0 Hz, 6H,
Isolation method B. Yield: 85%. Mp 158–162 ◦C. 1H NMR (C6D6):
d 7.21 (s, 1H, C(H) N), 7.13–7.00 (ov m, 5H, Ar), 6.72 (d, J =
7.8 Hz, 1H, Ar), 6.47 (m, 1H, Ar), 2.84 (q, J = 7.4 Hz, 4H,
CH2CH3), 1.14 (br s, 12H, pin), 1.07 (t, J = 7.4 Hz, 6H, CH2CH3).
1
11B (C6D6): d 5.9 (sharp). 13C{ H} (C6D6): d 166.7, 162.9, 142.7,
1
CH(CH3)2). 11B (C6D6): d 7.8 (sharp). 13C{ H} (C6D6): d 165.2,
139.7, 137.6, 131.3, 128.1, 125.7, 120.1, 118.1, 115.6, 80.4, 26.0,
∑
24.1, 14.4. Anal. Calc. for C23H30BNO3 C4H8O (451.47): C, 71.83;
163.6, 143.2, 142.3, 137.7, 131.1, 128.5, 124.2, 120.6, 120.5, 118.5,
33.6 (br), 30.9 (br), 28.6, 26.3, 24.8, 22.8 (br, C–B), 22.1. Anal.
Calc. for C27H36BNO (401.45): C, 80.77; H, 9.06; N, 3.49. Found:
C, 80.01; H, 9.17; N, 3.64.
H, 8.50; N, 3.10. Found: C, 71.57; H, 7.90; N, 3.44.
Imine 4d
Isolation method B. Yield: 88%. Mp 148–151 ◦C. 1H NMR (C6D6):
d 7.74 (s, 1H, C(H) N), 7.19–7.03 (ov m, 5H, Ar), 6.68 (d,
J = 7.8 Hz, 1H, Ar), 6.44 (m, 1H, Ar), 3.55 (sept, J = 7.0 Hz,
Imine 8a
Isolation method A. Yield: 84%. Mp 100–103 ◦C. 1H NMR
(C6D6): d 7.12 (s, 1H, C(H) N), 7.02 (ov ddd, J = 7.0, 7.0, 1.7 Hz,
1H, Ar), 6.94 (d, J = 9.1 Hz, 2H, Ar), 6.91–6.86 (ov m, 2H, Ar),
6.58 (d, J = 9.1 Hz, 2H, Ar), 6.38 (app t, J = 7.0 Hz, 1H, Ar),
2H, CH(CH3)2), 1.22–1.16 (br ov m, 24H, CH(CH3)2 & pin). 11
B
1
(C6D6): d 5.6 (sharp). 13C{ H} (C6D6): d 166.4, 163.0, 144.4, 141.1,
137.8, 131.2, 128.6, 123.7, 120.1, 118.2, 115.4, 80.4, 28.0, 25.9, 24.4
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3.19 (s, 3H, OCH3), 2.20 (m, 2H, Cy), 1.97 (m, 2H, Cy), 1.84 (m,
for C26H14BF10NO2 (573.22): C, 54.47; H, 2.47; N, 2.44. Found: C,
54.36; H, 2.63; N, 2.35.
4H, Cy), 1.58–1.29 (ov m, 10H, Cy), 1.22–1.03 (ov m, 4H, Cy). 11
B
(C6D6): d 8.0 (br). 13C{ H} (C6D6): d 164.4, 164.2, 159.5, 139.7,
138.3, 132.0, 125.5, 119.2, 116.8, 116.6, 113.9, 54.7, 33.5 (br, C–B),
30.1, 29.4, 29.3, 29.2, 28.0. Anal. Calc. for C26H34BNO2 (403.42):
C, 77.40; H, 8.51; N, 3.47. Found: C, 77.13; H, 8.47; N, 3.32.
1
Imine 11b
Isolation method A. Yield: 82%. Mp 153–157 ◦C. 1H NMR
(C6D6): d 8.94 (s, 1H, C(H) N), 8.54 (dd, J = 7.4, 1.6 Hz, 1H,
Ar), 6.98–6.65 (ov m, 10H, Ar), 2.24 (s, 12H, CH3), 2.16 (s, 6H,
1
CH3), 2.07 (s, 6H, CH3). 11B (C6D6): d 48.7 (br). 13C{ H} (C6D6): d
Imine 8b
157.8, 155.1, 151.8, 141.3, 139.4, 136 (br, C–B), 131.6, 128.7, 128.4,
127.5, 127.0, 126.9, 123.8 (2C), 120.5, 22.5, 21.0, 18.3. Anal. Calc.
for C33H36BNO (473.46): C, 83.69; H, 8.41; N, 2.71. Found: C,
83.08; H, 8.35; N, 3.10.
Isolation method B. Yield: 89%. Mp 115–120 ◦C. 1H NMR (C6D6):
d 7.06 (ov ddd, J = 6.7, 6.7, 2.0 Hz, 1H, Ar), 7.00–6.87 (ov m, 2H,
Ar), 6.80–6.78 (ov m, 3H, Ar & C(H) N), 6.67 (dd, J = 7.7,
2.0 Hz, 1H, Ar), 6.46 (ov ddd, J = 6.7, 6.7, 1.2 Hz, 1H, Ar), 2.07
(s, 6H, CH3), 1.93–1.77 (br ov m, 8H, Cy), 1.40–1.22 (br ov m,
Imine 11c
1
12H, Cy), 0.77 (br m, 2H, Cy). 11B (C6D6): d 6.0 (br). 13C{ H}
Isolation method B. Yield: 84%. Mp 140–142 ◦C. 1H NMR (C6D6):
d 8.99 (s, 1H, C(H) N), 8.53 (dd, J = 7.8, 2.1 Hz, 1H, Ar), 7.01–
6.99 (ov m, 3H, Ar), 6.85–6.65 (ov m, 7H, Ar), 2.59 (q, J = 7.8 Hz,
4H, CH2CH3), 2.25 (s, 12H, CH3), 2.07 (s, 6H, CH3), 1.14 (t, J =
(C6D6): d 165.7, 164.6, 145.3, 137.8, 133.0, 131.2, 128.7, 127.5,
120.2, 119.7, 117.5, 34.2 (br, C–B), 30.6, 29.6, 28.0, 18.8. Anal.
Calc. for C27H36BNO·2 C4H8O (545.69): C, 77.03; H, 9.62; N,
2.57. Found: C, 76.42; H, 9.28; N, 3.22.
1
7.8 Hz, 6H, CH2CH3). 11B (C6D6): d 47.7 (br). 13C{ H} (C6D6):
d 157.4, 155.1, 151.0, 141.3, 139.4, 135.6 (br, C–B), 133.1, 131.6,
128.7, 128.1, 127.6, 126.7, 124.1, 123.8, 120.4, 25.0, 22.5, 21.0,
15.0. Anal. Calc. for C35H40BNO·C4H8O (573.69): C, 81.65; H,
8.45; N, 2.44. Found: C, 81.33; H, 8.44; N, 2.53.
Imine 8c
Isolation method B. Yield: 91%. Mp 145–148 ◦C. 1H NMR (C6D6):
d 7.18 (s, 1H, C(H) N), 7.07–6.90 (ov m, 5H, Ar), 6.65 (dd, J =
7.8, 1.6 Hz, 1H, Ar), 6.44 (ov ddd, J = 6.6, 6.6, 1.2 Hz, 1H, Ar),
2.55 (q, J = 7.4 Hz, 4H, CH2CH3), 2.01–1.77 (ov br m, 8H, Cy),
1.47–1.24 (br ov m, 12H, Cy), 1.01 (t, J = 7.4 Hz, 6H, CH2CH3),
Imine 11d
Isolation method A. Yield: 88%. Mp 190–192 ◦C. 1H NMR
(C6D6): d 9.00 (s, 1H, C(H) N), 8.54 (dd, J = 7.8, 1.6 Hz, 1H,
Ar), 7.13–7.05 (ov m, 3H, Ar), 6.85–6.66 (ov m, 7H, Ar), 3.26
(sept, J = 6.6 Hz, 2H, CH(CH3)2), 2.26 (s, 12H, CH3), 2.07 (s, 6H,
CH3), 1.18 (d, J = 6.6 Hz, 12H, CH(CH3)2). 11B (C6D6): d 48.2
1
0.79 (br m, 2H, Cy). 11B (C6D6): d 6.9 (br). 13C{ H} (C6D6): d
165.6, 164.6, 144.0, 138.8, 137.8, 131.2, 128.0, 126.4, 120.0, 119.8,
117.7, 33.8 (br, C–B), 30.7, 29.6, 28.0, 24.6, 15.1. Anal. Calc. for
C29H40BNO·2 C4H8O (573.75): C, 77.45; H, 9.85; N, 2.44. Found:
C, 77.23; H, 9.93; N, 3.21.
1
(br). 13C{ H} (C6D6): d 157.6, 155.1, 149.9, 141.3, 139.4, 137.6,
135.7 (br, C–B), 131.6, 128.7, 127.6, 127.0, 124.5, 123.9, 123.3,
120.4, 28.2, 23.6, 22.5, 21.0. Anal. Calc. for C37H44BNO (529.63):
C, 83.90; H, 8.39; N, 2.65. Found: C, 83.42; H, 8.83; N, 2.71.
Imine 8d
Isolation method B. Yield: 83%. Mp 128–130 ◦C. 1H NMR (C6D6):
d 7.60 (s, 1H, C(H) N), 7.13–6.95 (ov m, 5H, Ar), 6.61 (dd, J =
7.8, 1.2 Hz, 1H, Ar), 6.41 (ov ddd, J = 6.6, 6.6, 1.2 Hz, 1H, Ar), 3.20
(sept, J = 7.0 Hz, 2H, CH(CH3)2), 2.01–1.77 (ov br m, 8H, Cy),
1.46–1.23 (br ov m, 12H, Cy), 1.14–0.82 (ov m, 14H, CH(CH3)2
Amine 12a
Isolation method A. Yield: 87%. Mp 102–105 ◦C. 1H NMR
(C6D6): d 7.33 (d, J = 7.0 Hz, 1H, Ar), 6.76 (d, J = 8.6 Hz, 2H,
Ar), 6.76–6.66 (ov m, 7H, Ar), 6.46 (d, J = 8.6 Hz, 2H, Ar), 4.30
(d, J = 6.2 Hz, 2H, CH2), 3.39 (t, J = 6.2 Hz, 1H, NH), 3.36 (s, 3H,
OCH3), 2.30 (s, 12H, CH3), 2.11 (s, 6H, CH3). 11B (C6D6): d 49.0
1
& Cy). 11B (C6D6): d 7.2 (br). 13C{ H} (C6D6): d 165.2, 164.6,
143.7, 142.7, 137.9, 131.2, 128.5, 124.0, 119.8, 119.6, 117.8, 33.5
(br, C–B), 30.7 (br), 29.4, 28.4, 28.0, 25.0 (br). Anal. Calc. for
C31H44BNO·C4H8O (529.69): C, 79.36; H, 9.92; N, 2.64. Found:
C, 78.77; H, 9.68; N, 2.83.
1
(br). 13C{ H} (C6D6): d 152.6, 152.5, 142.7, 141.3, 139.1, 136.2 (br,
C–B), 130.2, 128.7, 128.6, 127.2, 123.5, 119.2, 115.0, 114.1, 55.0,
44.3, 22.4, 21.0. Anal. Calc. for C32H36BNO2 (477.50): C, 80.48;
H, 7.61; N, 2.93. Found: C, 80.39; H, 7.55; N, 2.79.
Amine 10a
Isolation method A. Yield: 93%. Mp 218–220 ◦C. 1H NMR
(C6D6): d 7.40 (d, J = 8.2 Hz, 1H, Ar), 7.09 (ov ddd, J = 7.4,
6.9, 1.5 Hz, 1H, Ar), 6.86 (d, J = 8.9 Hz, 2H, Ar), 6.68 (ov ddd, J =
8.2, 7.4, 1.5 Hz, 1H, Ar), 6.57 (br s, 1H, NH), 6.45 (d, J = 6.9 Hz,
1H, Ar), 6.16 (d, J = 8.9 Hz, 2H, Ar), 4.48 (dd, J = 15.8, 5.5 Hz,
1H, CHH), 3.40 (d, J = 15.8 Hz, 1H, CHH), 2.90 (s, 3H, OCH3).
Reaction of (E)-2-((2,6-diethylphenylimino)methyl)phenol and
HBcat
To a stirred C6D6 (0.5 mL) solution of (E)-2-((2,6-diethyl-
phenylimino)methyl)phenol (50 mg, 0.20 mmol) was added a C6D6
(0.5 mL) solution of catecholborane (26 mg, 0.26 mmol). The
reaction mixture was stirred for 18 h at which point spectroscopic
NMR data was collected in C6D6. 1H: d 7.94 (br s, C(H) N, 2c),
7.73 (d, J = 8.2 Hz, Ar), 7.12–6.68 (ov m, Ar), 6.61–6.32 (ov m, Ar),
4.31 (m, CH2NH, 3c), 4.12 (m, CH2NH, 3c), 2.79 (q, J = 7.6 Hz,
CH2CH3), 2.59 (q, J = 7.6 Hz, CH2CH3), 1.05 (t, J = 7.6 Hz,
1
11B (C6D6): d 1.9 (sharp). 13C{ H} (C6D6): d 159.4, 154.2, 147.7
(dm, JCF = 237 Hz), 140.3 (dm, JCF = 241 Hz), 137.3 (dm, JCF
=
246 Hz), 134.1, 130.1, 126.8, 123.6, 120.5, 115.5, 114.7 (2C), 54.5,
1
54.3. 19F{ H} (C6D6): d -134.6, -137.1, -154.8 (t, JF–F = 18.7 Hz),
-155.4 (t, JF–F = 18.7 Hz), -161.6 (m), -162.8 (br). Anal. Calc.
4712 | Dalton Trans., 2011, 40, 4707–4714
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CH2CH3), 0.94 (t, J = 7.6 Hz, CH2CH3). 11B: d 13.3 (sharp), 7.9
(sharp).
2.26 (s, CH3, 11d), 2.10 (s, CH3, 12d), 2.07 (s, CH3, 11d), 1.18 (d,
J = 6.6 Hz, CH(CH3)2, 11d), 1.13 (d, J = 6.6 Hz, CH(CH3)2, 12d).
11B: d 49.9 (br).
Reaction of (E)-2-((2,6-diethylphenylimino)methyl)phenol and
X-ray Crystallography
HBpin
Crystals of 2b were grown from a 1 : 2 THF : hexane solution while
6d and 12a were grown from saturated hexane solutions at -30 ◦C
and crystals of Cy2BOBCy2 were grown from slow evaporation
of C6D6 at RT. Single crystals were coated with Paratone-N
oil, mounted using a polyimide MicroMount and frozen in the
cold nitrogen stream of the goniometer. A hemisphere of data
was collected on a Bruker AXS P4/SMART 1000 diffractometer
using w and q scans with a scan width of 0.3◦ and 10 s, 20
s (Cy2BOBCy2), and 30 s (12a) exposure times. The detector
distances were 5 cm. All data collection was performed at 173
K with the exception of 12a which was carried out at 213 K
due to loss of crystallinity at lower temperatures. The data were
reduced (SAINT)13 and corrected for absorption (SADABS).14
For Cy2BOBCy2, the crystal was twinned and the orientation
matrixes for two components were determined (CELL_NOW).15
The data were reduced (SAINT) and corrected for absorption
(TWINABS).16 The structures were solved by direct methods
and refined by full-matrix least squares on F2 (SHELXTL).17 All
non-hydrogen atoms were refined using anisotropic displacement
parameters. Hydrogen atoms were included in calculated positions
and refined using a riding model. CCDC 807112–807115 contain
the supplementary crystallographic data for this and are available
free of charge at http://ccdc.cam.ac.uk/data_request/cif.†
To a stirred C6D6 (0.5 mL) solution of (E)-2-((2,6-diethyl-
phenylimino)methyl)phenol (50 mg, 0.20 mmol) was added a C6D6
(0.5 mL) solution of pinacolborane (33 mg, 0.26 mmol). The
reaction mixture was stirred for 18 h at which point spectroscopic
1
NMR data was collected in C6D6. H: d 7.21 (s, C(H) N, 4c),
7.21–7.00 (ov m, Ar, 4c & 5c), 6.72 (d, J = 7.8 Hz, Ar, 4c), 6.47
(m, Ar, 4c), 4.19 (d, J = 5.5 Hz, CH2NH, 5c), 3.47 (t, J = 5.5 Hz,
CH2NH, 5c), 2.84 (q, J = 7.4 Hz, CH2CH3, 4c), 2.70 (q, J = 7.8 Hz,
CH2CH3, 5c), 1.14 (br s, pin, 4c & 5c), 1.10–1.00 (ov m, CH2CH3,
4c & 5c). 11B: d 13.3 (sharp), 6.2 (sharp).
Reaction of (E)-2-((2,6-dimethylphenylimino)methyl)phenol and
[HBMes2]2
To a stirred Et2O (1 mL) solution of (E)-2-((2,6-dimethyl-
phenylimino)methyl)phenol (25 mg, 0.11 mmol) was added a Et2O
(1 mL) solution of dimesitylborane (30 mg, 0.06 mmol). The
reaction mixture was stirred for 18 h at which point the solvent
was removed and spectroscopic NMR data was collected in C6D6.
1H: d 8.94 (s, C(H) N, 11b), 8.54 (dd, J = 7.4, 1.6 Hz, Ar, 11b),
7.33 (d, J = 7.4 Hz, Ar, 12b), 6.98–6.65 (ov m, Ar, 11b & 12b), 4.18
(d, J = 7.9 Hz, CH2NH, 12b), 3.51 (t, J = 7.9 Hz, CH2NH, 12b),
2.27 (s, CH3, 12b), 2.24 (s, CH3, 11b), 2.16 (s, CH3, 11b), 2.15 (s,
CH3, 12b), 2.08 (s, CH3, 12b), 2.07 (s, CH3, 11b). 11B: d 49.9 (br).
Acknowledgements
Reaction of (E)-2-((2,6-diethylphenylimino)methyl)phenol and
[HBMes2]2
Thanks are gratefully extended to NSERC, the Canada Re-
search Chairs Program, the Canadian Foundation for Innovation-
Atlantic Innovation Fund, and Mount Allison University for
financial support. We also thank Roger Smith and Dan Durant for
expert technical assistance, Dr’s. Stephen J. Geier and Douglas W.
Stephan for helpful discussions and the generous gift of HB(C6F5)2
and anonymous reviewers for their very helpful comments.
To a stirred THF (0.5 mL) solution of (E)-2-((2,6-diethyl-
phenylimino)methyl)phenol (50 mg, 0.20 mmol) was added a THF
(0.5 mL) solution of dimesitylborane (49 mg, 0.10 mmol). The
reaction mixture was stirred for 18 h at which point the solvent
was removed and spectroscopic NMR data was collected in C6D6.
1H: d 8.99 (s, C(H) N, 11c), 8.53 (dd, J = 7.8, 2.1 Hz, Ar, 11c),
7.05–6.99 (ov m, Ar, 11c & 12c), 6.85–6.65 (ov m, Ar, 11c & 12c),
4.21 (d, J = 7.8 Hz, CH2NH, 12c), 3.58 (t, J = 7.8 Hz, CH2NH,
12c), 2.64 (q, J = 7.8 Hz, CH2CH3, 12c), 2.59 (q, J = 7.8 Hz,
CH2CH3, 11c), 2.28 (s, CH3, 12c), 2.25 (s, CH3, 11c), 2.10 (s, CH3,
12c), 2.07 (s, CH3, 11c), 1.14 (t, J = 7.8 Hz, CH2CH3, 11c), 1.09
(t, J = 7.8 Hz, CH2CH3, 12c). 11B: d 49.9 (br).
References
1 (a) S. Schlecht, W. Frank and M. Braun, Eur. J. Org. Chem., 2010, 3721–
3731; (b) I. Georgiou, G. Ilyashenko and A. Whiting, Acc. Chem. Res.,
2009, 42, 756–768; (c) L. Zhang, J. A. Kerszulis, R. J. Clark, T. Ye and
L. Zhu, Chem. Commun., 2009, 2151–2153; (d) S.-H. Li, F.-R. Chen,
Y.-F. Zhou, J.-N. Wang, H. Zhang and J.-G. Xu, Chem. Commun.,
2009, 4179–4181; (e) V. I. Grachek and A. N. Lukashik, Russ. J. Appl.
Chem., 2006, 79, 819–822; (f) B. E. Collins, S. Sorey, A. E. Hargrove,
S. H. Shabbir, V. M. Lynch and E. V. Anslyn, J. Org. Chem., 2009, 74,
4055–4060; (g) V. Christou, S. E. Watkins, R. McCann, C. Redshaw
and M. R. J. Elsegood, Inorg. Chim. Acta, 2010, 363, 1173–1178; (h) L.
Zhu, S. H. Shabbir, M. Gray, V. M. Lynch, S. Sorey and E. V. Anslyn,
J. Am. Chem. Soc., 2006, 128, 1222–1232; (i) G. Mirri, S. D. Bull, P. N.
Horton, T. D. James, L. Male and J. H. R. Tucker, J. Am. Chem. Soc.,
2010, 132, 8903–8905; (j) H. Ho¨pfl, J. Organomet. Chem., 1999, 581,
129–149; (k) J. Yoshino, N. Kano and T. Kawashima, Bull. Chem. Soc.
Jpn., 2010, 83, 1185–1187; (l) Q. Hou, L. Zhao, H. Zhang, Y. Wang and
S. Jiang, J. Lumin., 2007, 126, 447–451; (m) X. Liu, H. Xia, X. Fan, Q.
Su, W. Gao and Y. Mu, J. Phys. Chem. Solids, 2009, 70, 92–96.
Reaction of (E)-2-((2,6-diisopropylphenylimino)methyl)phenol and
[HBMes2]2
To a stirred THF (0.5 mL) solution of (E)-2-((2,6-diisopropyl-
phenylimino)methyl)phenol (30 mg, 0.11 mmol) was added a THF
(0.5 mL) solution of dimesitylborane (27 mg, 0.05 mmol). The
reaction mixture was stirred for 18 h at which point solvent was
removed and spectroscopic NMR data was collected in C6D6. 1H:
d 9.00 (s, C(H) N, 11d), 8.54 (dd, J = 7.8, 1.6 Hz, Ar, 11d), 7.42
(d, J = 7.4 Hz, Ar, 12d), 7.13–7.05 (ov m, Ar, 11d & 12d), 6.85–6.66
(ov m, Ar, 11d & 12d), 4.20 (d, J = 7.8 Hz, CH2NH, 12d), 3.66
(t, J = 7.8 Hz, CH2NH, 12d), 3.52 (sept, J = 6.6 Hz, CH(CH3)2,
12d), 3.26 (sept, J = 6.6 Hz, CH(CH3)2, 11d), 2.28 (s, CH3, 12d),
2 (a) H. Lo´pez-Ruiz, H. Brisen˜o-Ortega, S. Rojas-Lima, R. Santilla´n and
N. Farfa´n, Tetrahedron Lett., 2010, 51, 2633–2635; (b) M. Rodr´ıguez,
R. Castro-Beltra´n, G. Ramos-Ortiza, J. L. Maldonadoa, N. Farfa´n,
O. Dom´ınguez, J. Rodr´ıguez, R. Santilla´n, M. A. Meneses-Nava, O.
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 4707–4714 | 4713
©

View Article Online
Barbosa-Garc´ıa and J. Peon, Synth. Met., 2009, 159, 1281–1287; (c) M.
Rodr´ıguez, G. Ramos-Ort´ız, M. I. Alcala´-Salas, J. L. Maldonado, K.
A. Lo´pez-Varela, Y. Lo´pez, O. Dom´ınguez, M. A. Meneses-Nava, O.
Barbosa-Garc´ıa, R. Santilla´n and N. Farfa´n, Dyes Pigm., 2010, 87,
76–83; (d) V. Barba, R. Herna´ndez, H. Ho¨pfl, R. Santilla´n and N.
Farfa´n, J. Organomet. Chem., 2009, 694, 2127–2133; (e) B. M. Mun˜oz,
R. Santilla´n, M. Rodr´ıguez, J. M. Me´ndez, M. Romero, N. Farfa´n,
P. G. Lacroix, K. Nakatani, G. Ramos-Ort´ız and J. L. Maldonado, J.
Organomet. Chem., 2008, 693, 1321–1334; (f) H. Lo´pez-Ruiz, I. Mera-
Moreno, S. Rojas-Lima, R. Santilla´n and N. Farfa´n, Tetrahedron Lett.,
2008, 49, 1674–1677; (g) M. Rodr´ıguez, M. E. Ochoa, C. Rodr´ıguez,
R. Santilla´n, V. Barba and N. Farfa´n, J. Organomet. Chem., 2007, 692,
2425–2435; (h) H. Reyes, J. M. Rivera, N. Farfa´n, R. Santilla´n, P. G.
Lacroix, C. Lepetit and K. Nakatani, J. Organomet. Chem., 2005, 690,
3737–3745; (i) A. Abreu, S. J. Alas, H. I. Beltra´n, R. Santilla´n and N.
Farfa´n, J. Organomet. Chem., 2006, 691, 337–348; (j) M. Rodr´ıguez,
M. E. Ochoa, R. Santilla´n, N. Farfa´n and V. Barba, J. Organomet.
Chem., 2005, 690, 2975–2988; (k) V. Barba, H. Ho¨pfl, N. Farfa´n, R.
Santilla´n, H. I. Beltranc and L. S. Zamudio-Rivera, Chem. Commun.,
2004, 2834–2835; (l) V. Barba, D. Cuahutle, R. Santilla´n and N. Farfa´n,
Can. J. Chem., 2001, 79, 1229–1237.
3 (a) J. Tanaka, H. Mimaki and S. Kanemasa, Rep. Inst. Adv. Mat., 1994,
8, 71–78; (b) L. Koren-Selfridge, H. N. Londino, J. K. Vellucci, B. J.
Simmons, C. P. Casey and T. B. Clark, Organometallics, 2009, 28, 2085–
2090; (c) J. Yang and A. R. Barron, Chem. Commun., 2004, 2884–2885;
(d) H. Braunschweig, T. Herbst, K. Radacki, G. Frenking and M. Ali
Celik, Chem.–Eur. J., 2009, 15, 12099–12106; (e) I. Peuser, R. Fro¨hlich,
G. Kehr and G. Erker, Eur. J. Inorg. Chem., 2010, 849–853; (f) M.
Scheideman, P. Shapland and E. Vedejs, J. Am. Chem. Soc., 2003, 125,
10502–10503; (g) C. A. G. Carter, C. M. Vogels, D. J. Harrison, M. K. J.
Gagnon, D. W. Norman, R. F. Langler, R. T. Baker and S. A. Westcott,
Organometallics, 2001, 20, 2130–2132; (h) J. D. Webb, D. J. Harrison,
D. W. Norman, J. M. Blacquiere, C. M. Vogels, A. Decken, C. G. Bates,
D. Venkataraman, R. T. Baker and S. A. Westcott, J. Mol. Catal. A:
Chem., 2007, 275, 91–100; (i) M. J. Geier, C. M. Vogels, A. Decken
and S. A. Westcott, J. Organomet. Chem., 2009, 694, 3154–3159; (j) S.
A. Westcott and R. T. Baker, Modern Reduction Methods, Wiley-VCH
Verlag GmbH & Co KGaA, P. G. Anderson and I. J. Munslow, ed.,
Weinheim, 2008, 297–320.
F. Haddow, J. P. H. Orton and D. F. Wass, Dalton Trans., 2010, 39,
6184–6186; (e) A. Berkefeld, W. E. Piers and M. Parvez, J. Am. Chem.
Soc., 2010, 132, 10660–10661; (f) C. Fan, L. G. Mercier, W. E. Piers,
H. M. Tuononen and M. Parvez, J. Am. Chem. Soc., 2010, 132, 9604–
9606; (g) V. Sumerin, F. Schulz, M. Atsumi, C. Wang, M. Nieger, M.
Leskela¨, T. Repo, P. Pyykko¨ and B. Rieger, J. Am. Chem. Soc., 2008,
130, 14117–14119; (h) B. Ine´s, S. Holle, R. Goddard and M. Alcarazo,
Angew. Chem., Int. Ed., 2010, 49, 8389–8391; (i) G. R. Whittell, E.
I. Balmond, A. P. M. Robertson, S. K. Patra, M. F. Haddow and I.
Manners, Eur. J. Inorg. Chem., 2010, 3967–3975; (j) E. Theuergarten,
D. Schlu¨ns, J. Grunenberg, C. G. Daniliuc, P. G. Jones and M. Tamm,
Chem. Commun., 2010, 46, 8561–8563; (k) C. Chen, F. Eweiner, B.
Wibbeling, R. Fro¨hlich, S. Senda, Y. Ohki, K. Tatsumi, S. Grimme, G.
Kehr and G. Erker, Chem.–Asian J., 2010, 5, 2199–2208; (l) Y. Zhang,
G. M. Miyake and E. Y.-X. Chen, Angew. Chem., Int. Ed., 2010, 49,
10158–10162; (m) K. V. Axenov, C. M. Mo¨mming, G. Kehr, R. Fro¨hlich
and G. Erker, Chem.–Eur. J., 2010, 16, 14069–14073; (n) L. Roy, P. M.
Zimmerman and A. Paul, Chem.–Eur. J., 2011, 17, 435–439; (o) C.
Jiang, O. Blacque, T. Fox and H. Berke, Dalton Trans., 2011, 40, 1091–
1097; (p) C. M. Mo¨mming, G. Kehr, R. Fro¨hlich and G. Erker, Chem.
Commun., 2011, 47, 2006–2007; (q) T. Voss, J.-B. Sortais, R. Fro¨hlich,
G. Kehr and G. Erker, Organometallics, 2011, 30, 584–594; (r) G. Erker,
Organometallics, 2011, 30, 358–368; (s) J. D. Webb, V. S. Laberge, S. J.
Geier, D. W. Stephan and C. M. Crudden, Chem.–Eur. J., 2010, 16,
4895–4902.
8 (a) X. Ariza, J. Cornella`, Me. Font-Bardia, J. Garcia, J. Ortiz, C.
Sa´nchez and X. Solans, Angew. Chem., Int. Ed., 2009, 48, 4202–
4205; (b) M. M. Hussain, H. Li, N. Hussain, M. Uren˜a, P. J. Carroll
and P. J. Walsh, J. Am. Chem. Soc., 2009, 131, 6516–6524; (c) M.
H. Kerrigan, S.-J. Jeon, Y. K. Chen, L. Salvi, P. J. Carroll and P.
J. Walsh, J. Am. Chem. Soc., 2009, 131, 8434–8445; (d) Ah. Kamal,
P. V. Reddy, S. Prabhakar and P. Suresh, Tetrahedron: Asymmetry,
2009, 20, 1798–1801; (e) T. Shono and T. Harada, Org. Lett., 2010, 12,
5270–5273.
9 H. C. Brown, C. G. Scouten and R. Liotta, J. Am. Chem. Soc., 1979,
101, 96–99.
10 (a) C. J. Cardin, H. E. Parge and J. W. Wilson, J. Chem. Res., 1983,
93, 810–817; (b) T. Lange, U. Bo¨hme and G. Roewer, Inorg. Chem.
Commun., 2002, 5, 377–379; (c) I. Cynkier and N. Furmanova, Cryst.
Struct. Commun., 1980, 9, 307–308; (d) J.-H. Son and J. D. Hoefelmeyer,
Acta Crystallogr., Sect. E: Struct. Rep. Online, 2009, E65, o470.
11 (a) S. K. Murphy, C. Bail, J. Lu and S. Wang, Org. Lett., 2010, 12,
5266–5269; (b) J.-H. Son, M. A. Pudenz and J. D. Hoefelmeyer, Dalton
Trans., 2010, 39, 11081–11090; (c) C. D. Entwistle and T. B. Marder,
Chem. Mater., 2004, 16, 4574–4585; (d) J. C. Araujo, Da Silva, M. Birot,
J.-P. Pillot and M. Pe´traud, J. Organomet. Chem., 2002, 646, 179–190;
(e) X. Feng, M. M. Olmstead and P. P. Power, Inorg. Chem., 1986,
25, 4615–4616; (f) E. Sakuda, A. Funahashi and N. Kitamura, Inorg.
Chem., 2006, 45, 10670–10677; (g) J. Hooz, S. Akiyama, F. J. Cedar,
M. J. Bennett and R. M. Tuggle, J. Am. Chem. Soc., 1974, 96, 274–276;
(h) Y. Kim and F. Gabba¨ı, J. Am. Chem. Soc., 2009, 131, 3363–3369;
(i) T. C. Chung, G. Xu, Y. Lu and Y. Hu, Macromolecules, 2001, 34,
8040–8050; (j) D. J. Parks, W. E. Piers and G. P. A. Yap, Organometallics,
1998, 17, 5492–5503; (k) T. Kawashima, T. Kannabe, N. Tokitoh and
R. Okazaki, Organometallics, 1999, 18, 5180–5182; (l) C. D. Entwistle,
T. B. Marder, P. S. Smith, J. A. K. Howard, M. A. Fox and S. A. Mason,
J. Organomet. Chem., 2003, 680, 165–172; (m) N. Wang, Z. M. Hudson
and S. Wang, Organometallics, 2010, 29, 4007–4011; (n) Z. M. Hudson,
X.-Y. Liu and S. Wang, Org. Lett., 2011, 13, 300–303; (o) J. K. Day, C.
Bresner, N. D. Coombs, I. A. Fallis, L.-L. Ooi and S. Aldridge, Inorg.
Chem., 2008, 47, 793–804; (p) M. H. Lee and F. P. Gabba¨ı, Inorg. Chem.,
2007, 46, 8132–8138.
4 R. T. Baker, J. C. Calabrese and S. A. Westcott, J. Organomet. Chem.,
1995, 498, 109–117.
5 (a) D. W. Stephan, Dalton Trans., 2009, 3129–3136; (b) M. Ullrich, A.
J. Lough and D. W. Stephan, Organometallics, 2010, 29, 3647–3654;
(c) L. Cabrera, G. C. Welch, J. D. Masuda, P. Wei and D. W. Stephan,
Inorg. Chim. Acta, 2006, 359, 3066–3071; (d) G. C. Welch, J. D. Masuda
and D. W. Stephan, Inorg. Chem., 2006, 45, 478–480; (e) G. C. Welch,
L. Cabrera, P. A. Chase, E. Hollink, J. D. Masuda, P. Wei and D.
W. Stephan, Dalton Trans., 2007, 3407–3414; (f) G. C. Welch, R. R.
S. Juan, J. D. Masuda and D. W. Stephan, Science, 2006, 314, 1124–
1126; (g) G. C. Welch and D. W. Stephan, J. Am. Chem. Soc., 2007,
129, 1880–1881; (h) J. S. J. McCahill, G. C. Welch and D. W. Stephan,
Angew. Chem., Int. Ed., 2007, 46, 4968–4971; (i) P. A. Chase and D. W.
Stephan, Angew. Chem., Int. Ed., 2008, 47, 7433–7437; (j) M. Ullrich,
A. J. Lough and D. W. Stephan, J. Am. Chem. Soc., 2009, 131, 52–53;
(k) D. W. Stephan, Chem. Commun., 2010, 46, 8526–8533; (l) J. G. M.
Morton, M. A. Dureen and D. W. Stephan, Chem. Commun., 2010,
46, 8947–8949; (m) M. A. Dureen, C. C. Brown and D. W. Stephan,
Organometallics, 2010, 29, 6594–6607; (n) M. A. Dureen, C. C. Brown
and D. W. Stephan, Organometallics, 2010, 29, 6422–6432; (o) S. J.
Geier, T. M. Gilbert and D. W. Stephan, Inorg. Chem., 2011, 50, 336–
344; (p) R. C. Neu, E. Y. Ouyang, S. J. Geier, X. Zhao, A. Ramos and
D. W. Stephan, Dalton Trans., 2010, 39, 4285–4294; (q) P. A. Chase,
T. Jurca and D. W. Stephan, Chem. Commun., 2008, 1701–1703; (r) X.
Zhao and W. D. Stephan, Chem. Commun., 2011, 47, 1833–1835; (s) Z.
M. Heiden, M. Schedler and D. W. Stephan, Inorg. Chem., 2011, 50,
1470–1479.
12 K. Smith, In Organometallics in Synthesis: A Manual M. Schlosser,
Ed.; Wiley: New York, 2004; p 473.
13 SAINT 7.23A, 2006, Bruker AXS Inc. Madison, Wisconsin, USA.
14 SADABS 2008, George Sheldrick, 2008, Bruker AXS, Inc., Madison,
Wisconsin, USA.
6 H. No¨th, B. Wrackmeyer, In Nuclear Magnetic Resonance Spectroscopy
of Boron Compounds Springer-Verlag, Berlin, 1978.
7 (a) T. A. Rokob, A. Hamza and I. Pa´pai, J. Am. Chem. Soc., 2009,
131, 10701–10710; (b) C. M. Mo¨mming, G. Kehr, B. Wibbeling, R.
Fro¨hlich and G. Erker, Dalton Trans., 2010, 39, 7556–7564; (c) G. Ero¨s,
H. Mehdi, I. Pa´pai, T. A. Rokob, P. Kira´ly, G. Ta´rka´nyi and T. Soo´s,
Angew. Chem., Int. Ed., 2010, 49, 6559–6563; (d) A. M. Chapman, M.
15 CELL_NOW, V. 2008/2, George Sheldrick, Bruker AXS, Inc., Madi-
son, Wisconsin, USA.
16 TWINABS 1.05, George Sheldrick, 2004, Bruker Nonius, Inc., Madi-
son, Wisconsin, USA.
17 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
A64, 112–122.
4714 | Dalton Trans., 2011, 40, 4707–4714
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