Synthesis, characterization, and reactivity of rhodium(I) acetylacetonato complexes containing pyridinecarboxaldimine ligands

Article abstract of DOI:10.1021/ic800703n

Addition of o-C₆H₄NCH=NAr to Rh(coe) ₂(acac) (coe = cis-cyclooctene, acac = acetylacetonato) gave several new iminopyridine rhodium(I) complexes of the type Rh(acac)(κ²- o-C₆H₄NCH=NAr) (1a Ar = 4-C₆H₄-OMe; 1b Ar = 2,6-C₆H₃-Me₂; 1c Ar = 2,6-C ₆H₃-Et₂; 1d Ar = 2,6-C₆H ₃-i-Pr₂). All new rhodium complexes have been characterized by a number of physical methods, including multinuclear NMR spectroscopy and X-ray diffraction studies for 1b and 1c. Addition of CHCl ₃ to 1a afforded the corresponding rhodium(III) complex trans-Rh(κ²-o-C₆H₄NCH=NAr)(CHCl ₂)(Cl)(acac) (2). Addition of B₂cat₃ (cat = 1,2-O₂C₆H₄) to 1 gave zwitterionic Rh(η⁶-catBcat)(κ²-o-C₆H ₄NCH=NAr) (3). The molecular structure of 3b has been confirmed by a single crystal X-ray diffraction study and shows that the N₂Rh fragment is bound to the catBcat anion via one of the catecholato groups in a η⁶-fashion. These complexes have also been examined for their ability to catalyze the hydroboration of a series of vinylarenes. Reactions using catecholborane and pinacolborane seem to proceed largely through a dehydrogenative borylation mechanism to give a number of boronated products.

Full text of DOI:10.1021/ic800703n

Inorg. Chem. 2008, 47, 8727-8735
Synthesis, Characterization, and Reactivity of Rhodium(I) Acetylacetonato
Complexes Containing Pyridinecarboxaldimine Ligands
Diane A. Kanas,† Stephen J. Geier,‡ Christopher M. Vogels,‡ Andreas Decken,§
and Stephen A. Westcott*,‡
Department of Biochemistry and Chemistry, Mount Allison UniVersity, SackVille NB E4L 1G8,
Canada, and Department of Chemistry, UniVersity of New Brunswick,
Fredericton NB E3B 5A3, Canada
Received April 21, 2008
Addition of o-C6H4NCHdNAr to Rh(coe)2(acac) (coe ) cis-cyclooctene, acac ) acetylacetonato) gave several
new iminopyridine rhodium(I) complexes of the type Rh(acac)(κ2-o-C6H4NCHdNAr) (1a Ar ) 4-C6H4-OMe; 1b Ar
) 2,6-C6H3-Me2; 1c Ar ) 2,6-C6H3-Et2; 1d Ar ) 2,6-C6H3-i-Pr2). All new rhodium complexes have been characterized
by a number of physical methods, including multinuclear NMR spectroscopy and X-ray diffraction studies for 1b
and 1c. Addition of CHCl3 to 1a afforded the corresponding rhodium(III) complex trans-Rh(κ2-o-
6
C6H4NCHdNAr)(CHCl2)(Cl)(acac) (2). Addition of B2cat3 (cat ) 1,2-O2C6H4) to 1 gave zwitterionic Rh(η -catBcat)(κ2-
o-C6H4NCHdNAr) (3). The molecular structure of 3b has been confirmed by a single crystal X-ray diffraction study
6
and shows that the N2Rh fragment is bound to the catBcat anion via one of the catecholato groups in a η -fashion.
These complexes have also been examined for their ability to catalyze the hydroboration of a series of vinylarenes.
Reactions using catecholborane and pinacolborane seem to proceed largely through a dehydrogenative borylation
mechanism to give a number of boronated products.
Introduction
of B-H bonds to unsaturated organic moieties using
polyhedral boranes.5 Ma¨nnig and No¨th then demonstrated
that rhodium complexes could be used to catalyze the
hydroboration of alkenes with HBcat under mild conditions
and with selectivities differing from that of the uncatalyzed
reaction.6 Since this remarkable discovery, a considerable
amount of research has focused on investigating the mech-
anism and scope of the catalyzed hydroboration reaction.7
A number of transition metals have been found to catalyze
hydroborations with HBcat; however, reactions using rhod-
ium catalysts are usually the most effective for hydrobora-
tions of vinylarenes.8 The judicious choice of the rhodium
complex can be used to effectively generate either the
expected linear or the unusual branched hydroboration
product (Scheme 1). Unfortunately, these reactions often
suffer from poor selectivities or competing pathways (i.e.,
The discovery that boron-hydrogen bonds add to unsatur-
ated organic molecules to form a class of compounds known
as organoboranes has become a remarkably important
synthetic methodology in organic synthesis.1 Although
borane adds readily to alkenes at -80 °C,2 other hydrobo-
rating agents, such as diorganyloxyboranes, are slow to react
even at room temperature. For instance, addition of
H3B · THF to catechol affords catecholborane (HBcat, cat )
1,2-O2C6H4), a relatively stable hydroborating agent which
adds to alkenes and alkynes only at elevated temperatures
(ca. 100 and 70 °C, respectively).3,4
An interesting extension to this chemistry was discovered
when transition metals were found to accelerate the addition
* To whom correspondence should be addressed. E-mail: swestcott@
mta.ca.
†
Inorganic Chemistry Exchange Researcher.
Mount Allison University.
University of New Brunswick.
‡
§
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10.1021/ic800703n CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 19, 2008 8727
Published on Web 09/06/2008

Kanas et al.
Scheme 1. Postulated Mechanism for the RhCl(PPh3)3 Catalyzed Hydroboration of Alkenes Using Catecholborane (HBcat)
hydrogenation or dehydrogenative borylation9) and, as a
result, a significant amount of research has focused on
designing new catalyst systems.10 Recently, there has been
considerable interest in the use of rhodium complexes
containing P,N-bidentate ligands as catalysts for the hy-
droboration of vinylarenes.11 Although mixtures of “hy-
droboration” products were reported in these cases, we have
found that reactions using rhodium complexes containing a
bulky P,N ligand gave a number of boronated products
arising from a competing dehydrogenative borylation path-
way. To gain an understanding of the factors that influence
selectivities in these reactions we have prepared a series of
rhodium(I) complexes containing iminopyridine ligands and
examined their ability to catalyze the hydroboration of
vinylarenes with HBcat.
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8728 Inorganic Chemistry, Vol. 47, No. 19, 2008

Rhodium(I) Acetylacetonato Pyridinecarboxaldimine Complexes
Results and Discussion
Pyridinecarboxaldimine ligands have been used in con-
junction with a variety of metals for a wide range of
applications.12-15 For instance, metal oligonucleotides have
recently been prepared using ruthenium complexes contain-
ing 2′-iminomethylpyridyl-2′-deoxyuridine.12a Likewise, imi-
nopyridines have also been reported to be efficient ligands
in the palladium catalyzed cyclization of (Z)-4′-acetoxy-2′-
butenyl 2-alkynoates.14a These ligands were found to not only
inhibit ꢀ-hydride elimination but also stabilize a unique vinyl-
palladium intermediate. While rhodium complexes containing
these ligands are known,16 to the best of our knowledge,
acetylacetonato (acac) compounds have not yet been reported.
Figure 1. Iminopyridine rhodium(I) acetylacetonato complexes 1a-d.
Addition of pyridinecarboxaldimine ligands o-C6H4-
NCHdNAr to Rh(coe)2(acac) (coe ) cis-cyclooctene) gave
iminopyridine rhodium(I) complexes of the type Rh(κ2-o-
C6H4NCHdNAr)(acac) (1) (Figure 1). All new rhodium
complexes have been characterized by a number of physical
methods, including multinuclear NMR spectroscopy. A
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1
significant downfield shift in the H NMR is observed for
the imine sp2 proton upon coordination to the metal center.
For instance, the singlet at δ 8.61 ppm for the free ligand
4-methoxy-N-((pyridin-2-yl)methylene)benzenamine shifts to
8.78 ppm in complex 1a. This resonance is also observed as
a doublet with coupling to rhodium of J ) 3.2 Hz. Similar
trends are observed for the pyridine hydrogen R to the
nitrogen atom as the chemical shift changes from δ 8.69 ppm
to 10.84 ppm (d, J ) 5.9 Hz). Significant shifts are also
observed in the 13C{1H} NMR spectra, as the imine carbon
for the free ligand is observed at δ 158.6 pm while that for
1a is found at 150.2 ppm.
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Complexes 1b and 1c have also been characterized by
single crystal X-ray diffraction studies, the molecular
structures of which are shown in Figures 2 and 3, respec-
tively, and crystallographic data provided in Table 1. Bond
distances and angles for the acetylacetonato ligands are
similar to those reported previously in related rhodium
ethylene16a,b and mixed phosphine/CO systems.16c,d Like-
wise, the iminopyridine ligands are well within the expected
range for similar rhodium complexes.17 The metals assume
a slightly distorted square planar configuration with Rh-N
distances of 1.980(3) (pyridine, 1b), 1.985(2) (pyridine, 1c),
1.963(3) (imine, 1b), and 1.9698(19) (imine, 1c). As
observed previously, the plane of the N-aryl group also lies
approximately perpendicular to the metal coordination
plane.18 This conformation places the two ortho groups in
positions which will block approach of substrates to the
vacant axial sites, which may ultimately affect the regiose-
lectivity of the catalyzed hydroboration reaction.
As with the analogous diphosphine acetylacetonato
complexes,19a these novel iminopyridine compounds all
decompose in chlorinated solvents over time to give a
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Inorganic Chemistry, Vol. 47, No. 19, 2008 8729

Kanas et al.
distances and angles are within the range of related com-
plexes.19 The trans addition of alkyl halides to rhodium
complexes has been reported previously and is believed to
be favored when bulky ligands are coordinated to the metal
center.19aSuch addition reactions are believed to occur via
either direct oxidative addition, followed by isomerization,
or by a concerted nucleophilic displacement (SN2) pathway.19g
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plexes are active and selective catalysts for the hydroboration
of a wide range of alkenes using HBcat, the catalyst resting
state in these systems has been reported to be the zwitterionic
complexes Rh(η6-catBcat)(P2), arising from the redistribution
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Bacchi, A.; Pelizzi, C. Inorg. Chim. Acta 2003, 351, 235. (e) Chandra,
M.; Sahay, A. N.; Mobin, S. M.; Pandey, D. S. J. Organomet. Chem.
2002, 658, 43. (f) Hernan, P.; del Pino, C.; Ruiz-Hitzky, E. Chem.
Mater. 1992, 4, 49. (g) Crociani, B.; Di Bianca, F.; Paci, M.; Boschi,
T. Inorg. Chim. Acta 1988, 145 (2), 253. (h) Brunner, H.; Wachter,
J.; Schmidbauer, J.; Sheldrick, G. M.; Jones, P. G. Organometallics
1986, 11, 2212.
(18) (a) Tempel, D. J.; Johnson, L. K.; Huff, R. L.; White, P. S.; Brookhart,
M. J. Am. Chem. Soc. 2000, 122, 6686. (b) van Asselt, R.; Elsevier,
C. J.; Smeets, W. J. J.; Spek, A. L. Inorg. Chem. 1994, 33, 1521. (c)
Hill, G. S.; Yap, G. P. A.; Puddephatt, R. J. Organometallics 1999,
18, 1408. (d) Kokkes, M. W.; Stufkens, D. J.; Oskam, A. J. Chem.
Soc., Dalton Trans. 1983, 439.
Figure 2. Molecular structure of 1b with ellipsoids drawn at 50%
probability level. Hydrogen atoms omitted for clarity. Selected bond
distances (Å) and angles (deg): Rh-N(1) 1.963(3), Rh-N(2) 1.980(3),
Rh-O(1) 2.010(2), Rh-O(2) 2.010(2), N(1)-C(1) 1.298(4), N(2)-C(2)
1.368(4), O(1)-C(15) 1.273(4), O(2)-C(17) 1.280(4); N(1)-Rh-N(2)
79.78(12), N(1)-Rh-O(1) 94.55(11), N(2)-Rh-O(1) 173.60(10), N(1)-
Rh-O(2) 172.93(10), N(2)-Rh-O(2) 93.54(11), O(1)-Rh-O(2) 92.24(10),
C(1)-N(1)-C(7) 119.0(3), C(1)-N(1)-Rh 116.4(2), C(7)-N(1)-Rh
124.2(2), C(6)-N(2)-C(2) 118.1(3).
(19) (a) Fennis, P. J.; Budzelaar, P. H. M.; Frijns, J. H. G.; Orpen, A. G.
J. Organomet. Chem. 1990, 393, 287. (b) Ciriano, M. A.; Tena, M. A.;
Oro, L. A. J. Chem. Soc., Dalton Trans. 1992, 2123. (c) Germoni,
A.; Deschamps, B.; Ricard, L.; Mercier, F.; Mathey, F. J. Organomet.
Chem. 2005, 690, 1133. (d) Dorta, R.; Shimon, L. J. W.; Rozenberg,
H.; Milstein, D. Eur. J. Inorg. Chem. 2002, 1827. (e) Chan, K. T. K.;
Spencer, L. P.; Masuda, J. D.; McCahill, J. S. J.; Wei, P.; Stephan,
D. W. Organometallics 2004, 23, 381. (f) Tejel, C.; Ciriano, M. A.;
Lo´pez, Jime´nez, S.; Bordonaba, M.; Oro, L. A. Chem.sEur. J. 2007,
13, 2044. (g) de Jong, G. T.; Bickelhaupt, F. M. J. Chem. Theory
Comput. 2007, 3, 514. (h) Uchimara, H.; Ito, J.; Iwasa, S.; Nishiyama,
H. J. Organomet. Chem. 2007, 692, 481. (i) Burkill, H. A.; Vilar, R.;
White, A. J. P. Inorg. Chim. Acta 2006, 359, 3709. (j) Zeng, J. Y.;
Hsieh, M.-H.; Lee, H. M. J. Organomet. Chem. 2005, 690, 5662. (k)
Teuma, E.; Malbosc, F.; Etienne, M.; Daran, J.-C.; Kalck, P. J.
Organomet. Chem. 2004, 689, 1763. (l) Lobana, T. S.; Isobe, K.;
Kitayama, H.; Nishioka, T.; Doe, M.; Kinoshita, I. Organometallics
2004, 23, 5347. (m) Kawamoto, T. Inorg. Chim. Acta 2000, 300-302,
512. (n) Bradd, K. J.; Heaton, B. T.; Jacob, C.; Sampanthar, J. T.;
Steiner, A. J. Chem. Soc., Dalton Trans. 1999, 1109. (o) Haarman,
H. F.; Ernsting, J. M.; Kranenburg, M.; Kooijman, H.; Veldman, N.;
Spek, A. L.; van Leeuwen, P. W. N. M.; Vrieze, K. Organometallics
1997, 16, 887. (p) Adolfsson, H.; Cernerud, M.; Moberg, C. Inorg.
Chim. Acta 1997, 26 (2), 65. (q) Kashiwabara, K.; Morikawa, A.;
Suzuki, T.; Isobe, K.; Tatsumi, K. J. Chem. Soc., Dalton Trans. 1997,
1075. (r) Ziessel, R.; Toupet, L.; Chardon-Noblat, S.; Deronzier, A.;
Matt, D. J. Chem. Soc., Dalton Trans. 1997, 3777. (s) Ball, G. E.;
Cullen, W. R.; Fryzuk, M. D.; James, B. R.; Rettig, S. J. Organome-
tallics 1991, 10, 3767. (t) Nishiyama, H.; Horihata, M.; Hirai, T.;
Wakamatsu, S.; Itoh, K. Organometallics 1991, 10, 2706. (u) Marder,
T. B.; Fultz, W. C.; Calabrese, J. C.; Harlow, R. L.; Milstein, D.
J. Chem. Soc., Chem. Commun. 1987, 1543. (v) Burns, E. G.; Chu,
S. S. C.; de Meester, P.; Lattman, M. Organometallics 1986, 5, 2383.
(w) Yoshida, T.; Ueda, T.; Adachi, T.; Yamamoto, K.; Higuchi, T.
J. Chem. Soc., Chem. Commun. 1985, 1137.
Figure 3. Molecular structure of 1c with ellipsoids drawn at 50%
probability level. Hydrogen atoms omitted for clarity. Selected bond
distances (Å) and angles (deg): Rh-N(2) 1.9698(19), Rh-N(1) 1.985(2),
Rh-O(1) 2.0176(18), Rh-O(2) 2.0190(17), N(1)-C(2) 1.377(3), N(2)-C(1)
1.306(3), O(1)-C(17) 1.274(3), O(2)-C(19) 1.288(3); N(2)-Rh-N(1)
79.70(8), N(2)-Rh-O(1) 94.59(7), N(1)-Rh-O(1) 173.33(8), N(2)-
Rh-O(2) 172.15(8), N(1)-Rh-O(2) 93.92(7), O(1)-Rh-O(2) 92.05(7),
C(6)-N(1)-C(2) 117.3(2), C(6)-N(1)-Rh 127.38(17), C(2)-N(1)-Rh
115.27(16), C(1)-N(2)-C(7) 118.6(2).
mixture of products arising from the oxidative addition of
the C-Cl bond. For example, addition of CHCl3 to 1a
afforded the corresponding rhodium(III) complex trans-
Rh(κ2-o-C6H4NCHdNAr)(CHCl2)(Cl)(acac) (2) in 81% yield.
The ability of rhodium(I) complexes to oxidatively add
carbon chlorine bonds is well documented19 and many of
these complexes are active catalyst precursors for the
Kharasch reaction.20 Spectroscopic data for 2 are similar to
´
(20) (a) D´ıaz-Alvarez, A. E.; Crochet, P.; Zablocka, M.; Duhayon, C.;
Cadierno, V.; Majoral, J.-P. Eur. J. Inorg. Chem. 2008, 786; and
references therein. (b) Gossage, R. A.; van de Kuil, L. A.; van Koten,
G. Acc. Chem. Res. 1998, 31, 423. (c) Mun˜oz-Molina, J. M.; Caballero,
A.; D´ıaz-Requejo, M. M.; Trofimenko, S.; Balderra´ın, T. R.; Pe´rez,
P. J. Inorg. Chem. 2007, 46, 7428. (d) Pandarus, V.; Zargarian, D.
Organometallics 2007, 26, 4321. (e) Quebatte, L.; Thommes, K.;
Severin, K. J. Am. Chem. Soc. 2006, 128, 7440. (f) Lundgren, R. J.;
Rankin, M. A.; McDonald, R.; Stradiotto, M. Organometallics 2008,
27, 254.
1
those for 1a except a doublet is observed in the H NMR
spectrum for the CHCl2 group at δ 6.40 ppm with coupling
to rhodium at JHRh ) 2.7 Hz. Complex 2 has also been
characterized by an X-ray diffraction study (Figure 4),
showing a trans addition of the alkyl chloride. All bond
8730 Inorganic Chemistry, Vol. 47, No. 19, 2008

Rhodium(I) Acetylacetonato Pyridinecarboxaldimine Complexes
Table 1. Crystallographic Data Collection Parameters for 1b, 1c, 2, and 3b
complex
1b
1c
2
3b
chemical formula
formula mass
crystal dimensions (mm3)
crystal system
space group
Z
C19H21N2O2Rh
412.29
C21H25N2O2Rh
440.34
0.40 × 0.15 × 0.05
monoclinic
P2(1)/n
C23H28Cl3N2O4Rh
605.73
C26H22BN2O4Rh
540.18
0.20 × 0.20 × 0.05
monoclinic
P2(1)/c
0.45 × 0.125 × 0.05
0.28 × 0.05 × 0.03
monoclinic
monoclinic
P2(1)/n
4
P2(1)/n
4
4
4
a (Å)
b (Å)
c (Å)
9.442(6)
7.753(5)
24.080(16)
90
90.896(11)
90
1763(2)
1.554
10.8979(13)
11.1449(13)
16.4137(19)
90
106.008(2)
90
1916.2(4)
1.526
198(1)
13.268(8)
13.693(8)
14.352(9)
90
104.815(9)
90
2521(3)
1.596
173(1)
11.245(4)
15.187(6)
13.529(5)
90
94.561(6)
90
2303.0(15)
1.558
173(1)
R (deg)
ꢀ (deg)
γ (deg)
volume (Å3)
Dcalcd (mg m-3
T (K)
)
173(1)
radiation
Mo KR (λ ) 0.71073Å)
Mo KR (λ ) 0.71073Å)
Mo KR (λ ) 0.71073Å)
Mo KR (λ ) 0.71073Å)
µ (mm-1
)
0.982
0.908
1.028
0.778
total reflections collected
no. of variables
θ (deg)
10853
230
1.69-27.48
1.023
0.0426
0.1172
0.935, -0.932
2
12916
239
2.02-27.50
1.004
0.0284
0.0704
16705
301
1.87-27.50
1.074
0.0428
0.1101
15610
309
1.82-27.50
1.135
0.0378
0.1060
GoF on F2
a
R1 [I > 2σ(I)]
b
wR2 (all data)
largest diff peak and hole (Å)
0.490, -0.375
0.802, -0.544
1.315, -0.390
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) (∑[w(Fo2 - Fc )2]/∑[Fo ])1/2, where w ) 1/[σ2(Fo ) + (0.0643P)2] (1b), 1/[σ2(Fo ) + (0.032P)2] (1c), 1/[σ2(Fo ) +
4
2
2
2
2
2
2
(0.0342P)2 + (1.5989P)] (2), and 1/[σ2(Fo ) + (0.0388P)2 + (2.1165P)] (3b), where P ) (max (Fo , 0) + 2Fc )/3.
C6H4NCHdNAr) (3) in good yields (Scheme 2). The 11B
NMR spectra have a sharp peak at 14 ppm, consistent with
the boron atom being four coordinate.23 The molecular
structure of 3b has been confirmed by a single crystal X-ray
diffraction study (Figure 5) and shows that the N2Rh
fragment is bound to the catBcat anion via one of the
catecholato groups in a η6-fashion. As with related
systems,9f-i,24 there appears to be a noticeable slippage of
the N2Rh group with respect to the π-bound arene ring.
Interestingly, two bond distances are considerably short
(Rh(1)-C(18) 2.198(4), Rh(1)-C(17) 2.254(4) Å), two are
average (Rh(1)-C(15) 2.294(4), Rh(1)-C(16) 2.306(4) Å),
and the last two are considerably longer with Rh(1)-C(19)
and Rh(1)-C(20) bonds at 2.328(4) and 2.355(4) Å,
respectively. Although this suggests bonding of the type η2:
η2:η2, no such localization within the C-C bond distances
of the aromatic ring is observed. The potential surface for
such distortions is therefore likely quite shallow and further
studies are required to understand the nature of the bonding
in these metal aryl spiroboronate esters.
Figure 4. Molecular structure of 2·THF with ellipsoids drawn at 50%
probability level. Hydrogen atoms and the solvent molecule omitted for
clarity. Selected bond distances (Å) and angles (deg): Rh-O(1) 2.008(3),
Rh-O(2) 2.021(3), Rh-N(2) 2.023(4), Rh-N(1) 2.040(4), Rh-C(19)
2.049(4), Rh-Cl(1) 2.4820(18), C(1)-N(1) 1.296(6), C(1)-C(2) 1.454(6),
C(2)-N(2) 1.367(6); O(1)-Rh-O(2) 92.51(13), O(2)-Rh-N(2) 174.90(13),
O(1)-Rh-N(1) 171.20(14), N(2)-Rh-N(1) 80.34(15), O(1)-Rh-Cl(1)
88.86(9), O(2)-Rh-Cl(1) 89.94(10), N(2)-Rh-Cl(1) 92.61(11), N(1)-
Rh-Cl(1) 87.26(10), C(19)-Rh-Cl(1) 176.72(13), Cl(2)-C(19)-Cl(3)
107.1(2).
To compare complexes 1a-d against other rhodium
catalysts, we have examined their ability to catalyze the
hydroboration of a series of vinylarenes (i.e., 4-vinylanisole,
2-vinylnaphthalene, perfluorostyrene, etc.) using multinuclear
NMR spectroscopy.7c-e Reactions were conducted at room
of substituents on catecholborane (HBcat).7d In an elegant
study, Marder and co-workers have shown that addition of
B2cat3 to Rh(acac)(P2) led to the zwitterionic complexes
Rh(η6-catBcat)(P2) in high yields, along with concomitant
formation of acacBcat.21 The diboron species B2cat3 is
generated as a decomposition product in nucleophilic reac-
tions with HBcat or when HBcat is heated at elevated
temperatures.7c,22 In this study we have found that addition
of B2cat3 to 1a-d gave zwitterionic Rh(η6-catBcat)(κ2-o-
(23) No¨th, H.; Wrackmeyer, B. Nuclear Magnetic Resonance Spectroscopy
of Boron Compounds; Springer-Verlag: Berlin, 1978.
(24) (a) Vogels, C. M.; Decken, A.; Westcott, S. A. Can. J. Chem. 2006,
84, 146. (b) Norman, N. C.; Orpen, A. G.; Quayle, M. J.; Robins,
E. G. Acta Crystallogr., Sect C. Cryst. Struct. Commun. 2000, 56, 50.
(c) Clegg, W.; Elsegood, M. R. J.; Marder, T. B.; Dai, C.; Norman,
N. C.; Pickett, N. L.; Robins, E. G. Acta Crystallogr., Sect C. Cryst.
Struct. Commun. 1999, 55, 733. (d) He, X.; Hartwig, J. F. J. Am. Chem.
Soc. 1996, 118, 1696. (e) Downard, A.; Nieuwenhuyzen, M.; Seddon,
K. R.; van den Berg, J.-A.; Schmidt, M. A.; Vaughan, J. F. S.; Welz-
Biermann, U. Cryst. Growth Des. 2002, 2, 111. (f) Miyazaki, T.;
Sugawara, M.; Danjo, H.; Imamoto, T. Tetrahedron Lett. 2004, 45,
9341.
(21) (a) Coapes, R. B.; Souza, F. E. S.; Thomas, R. L.; Hill, J. J.; Marder,
T. B. Chem. Commun. 2003, 614. (b) Dai, C.; Robins, E. G.; Scott,
A. J.; Clegg, W.; Yufit, D. S.; Howard, J. A. K.; Marder, T. B. Chem.
Commun. 1998, 1983.
(22) Kanth, J. V. B.; Periasamy, M.; Brown, H. C. Org. Process Res. DeV.
2000, 4, 550.
Inorganic Chemistry, Vol. 47, No. 19, 2008 8731

Kanas et al.
Scheme 2. Synthesis of Rhodium(I) Arylspiroboronate Ester Complexes
Scheme 3. Rhodium Pyridinecarboxaldimine Catalyzed Hydroboration of 4-Vinylanisolea
a All reactions were conducted in C6D6 at RT (conversion 100%, TON ) 20) and product ratios were determined by 1H NMR spectroscopy and confirmed
by GC/MS.
temperature using 5 mol% of catalyst and a slight excess of
formation of trans-4-MeOC6H4CHdCHBcat (III). It is
possible that the traditional hydroboration product I may also
be generated by a rhodium catalyzed hydrogenation of the
vinyl boronate ester, as dihydrogen is liberated as a side
product in the dehydrogenative borylation reaction. The
bisborated product IV presumably arises from a subsequent
hydroboration of the vinyl boronate ester III. Similar product
distributions were observed in reactions using other viny-
larenes and in reactions run in other solvents, such as THF-
borane to ensure complete conversion of the starting viny-
larene. Unfortunately, reactions using HBcat with catalytic
amounts of complexes 1a-d all gave complex product
distributions arising from a competing dehydrogenative
borylation reaction. For instance, addition of HBcat to
4-vinylanisole (Scheme 3) using a catalytic amount of 1d
(5 mol%, TON ) 20) gave a mixture of hydroboration
products I and II, along with products derived from the initial
8732 Inorganic Chemistry, Vol. 47, No. 19, 2008

Rhodium(I) Acetylacetonato Pyridinecarboxaldimine Complexes
Figure 5. Molecular structure of 3b with ellipsoids drawn at 50% probability level. Hydrogen atoms omitted for clarity. Selected bond distances (Å) and
angles (deg): Rh(1)-N(1) 1.986(3), Rh(1)-N(2) 2.002(3), Rh(1)-C(18) 2.198(4), Rh(1)-C(17) 2.254(4), Rh(1)-C(15) 2.294(4), Rh(1)-C(16) 2.306(4),
Rh(1)-C(19) 2.328(4), Rh(1)-C(20) 2.355(4), O(1)-B(1) 1.505(5), O(2)-B(1) 1.507(5), O(3)-B(1) 1.478(5), O(4)-B(1) 1.463(5), N(1)-C(1) 1.317(5),
N(2)-C(2) 1.361(5), C(15)-C(16) 1.405(5), C(15)-C(20) 1.429(5), C(16)-C(17) 1.412(6), C(17)-C(18) 1.408(6), C(18)-C(19) 1.425(5), C(19)-C(20)
1.395(5); N(1)-Rh(1)-N(2) 78.39(13), O(4)-B(1)-O(3) 106.4(3), O(4)-B(1)-O(1) 113.8(3), O(3)-B(1)-O(1) 111.7(3), O(4)-B(1)-O(2) 110.0(3),
O(3)-B(1)-O(2) 111.5(3), O(1)-B(1)-O(2) 103.4(3).
d8. A small amount of borane degradation7d to give B2cat3
and H2 was also observed, further complicating product
distributions.
the catalyst precursors upon completion of these reactions
appears to be the zwitterionic complexes 3a-d, where the
coordinated imine fragment has not been reduced by either
the borane or the liberated dihydrogen. Unfortunately, all
attempts to improve selectivities by optimizing catalyst
conditions (lowering reaction temperatures, changing order
of substrate addition, rate of substrate addition, etc.) proved
unsuccessful.
In summary, we have prepared four novel rhodium(I)
acetylacetonato complexes containing bidentate o-C6H4NCHd
NAr ligands. These complexes react with B2cat3 to give the
corresponding zwitterions of the type Rh(η6-catBcat)(κ2-o-
C6H4NCHdNAr) (3) in moderate to good yields. Unlike the
bisphosphine analogs, hydroborations of vinylarenes using
complexes with nitrogen containing ligands give complex
product distributions arising from competing dehydrogenative
borylation reactions and borane degradation.
Reactions using pinacolborane (HBpin, pin ) 1,2-
O2C2Me4), another common reagent in metal catalyzed
hydroboration reactions,25 also gave complicated product
distributions. Although none of the internal hydroboration
product II was observed in reactions using HBpin, this is
not unusual as hydroborations using this less reactive borane
predominantly give the corresponding linear product. A
notable exception to this observed selectivity is when cationic
rhodium25s or iridium25c complexes are used to catalyze this
reaction. Likewise, changing the catalyst precursor to the
less bulky 1a did not improve selectivities. Reactions using
the zwitterionic species 3 gave product distributions similar
to those using the acetylacetonato precursors. The fate of
(25) (a) Pereira, S.; Srebnik, M. Tetrahedron Lett. 1996, 37, 3283. (b)
Moteki, S. A.; Wu, D.; Chandra, K. L.; Reddy, D. S.; Takacs, J. M.
Org. Lett. 2006, 8, 3097. (c) Yamamoto, Y.; Fujikawa, R.; Umemoto,
T.; Miyaura, N. Tetrahedron 2004, 60, 10695. (d) Hadebe, S. W.;
Robinson, R. S. Tetrahedron Lett. 2006, 47, 1299. (e) Hadebe, S. W.;
Robinson, R. S. Eur. J. Org. Chem. 2006, 4898. (f) Zheng, B.; Srebnik,
M. J. Org. Chem. 1995, 60, 486. (g) Wang, Y. D.; Kimball, G.;
Prashad, A. S.; Wang, Y. Tetrahedron Lett. 2005, 46, 8777. (h) Kinder,
R. E.; Widenhoefer, R. A. Org. Lett. 2006, 8, 1967. (i) Rubin, M.;
Gevorgyan, V. Synthesis 2004, 796. (j) Rubina, M.; Rubin, M.;
Gevorgyan, V. J. Am. Chem. Soc. 2003, 125, 7198. (k) Ohmura, T.;
Yamamoto, Y.; Miyaura, N. J. Am. Chem. Soc. 2000, 122, 4990. (l)
Hoffman, R. W.; Kru¨ger, J.; Bru¨ckner, D. New J. Chem. 2001, 25,
102. (m) Ramachandran, P. V.; Jennings, M. P.; Brown, H. C. Org.
Lett. 1999, 1, 1399. (n) Pereira, S.; Srebnik, M. Organometallics 1995,
14, 3127. (o) Ghebreyessus, K. Y.; Angelici, R. J. Organometallics
2006, 25, 3040. (p) Scurto, A. M.; Leitner, W. Chem. Commun. 2006,
3681. (q) Onodera, G.; Nishibayashi, Y.; Uemura, S. Organometallics
2006, 25, 35. (r) Lee, T.; Baik, C.; Jung, I.; Song, K. H.; Kim, S.;
Kim, D.; Kang, S. O.; Ko, J. Organometallics 2004, 23, 4569. (s)
Crudden, C. M.; Hleba, Y. B.; Chen, A. C. J. Am. Chem. Soc. 2004,
126, 9200. (t) Cipot, J.; Vogels, C. M.; McDonald, R.; Westcott, S. A.;
Stradiotto, M. Organometallics 2006, 25, 5965. (u) Aubin, S.; Le
Floch, F.; Carrie´, D.; Guegan, J. P.; Vaultier, M. ACS Symposium
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SYNLETT 2004, 2639.
Experimental Section
Reagents and solvents were purchased from Aldrich Chemicals
and used as received. Rh(acac)(coe)2,26 B2cat3,27 and iminopy-
ridines12 were synthesized as previously reported. NMR spectra
were recorded on a JEOL JNM-GSX270 FT NMR (1H 270 MHz;
11B 87 MHz;13C 68 MHz) spectrometer. Chemical shifts (δ) are
reported in ppm [relative to residual solvent peaks (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). Decomposition points were determined using a Mel-Temp
apparatus and are uncorrected. Elemental analyses were performed
(26) Bennett, M. A.; Mitchell, T. R. B. J. Organomet. Chem. 1985, 295,
223.
(27) Kanth, J. V. B.; Periasamy, M.; Brown, H. C. Org. Process Res. DeV.
2002, 4, 550.
(28) (a) GEMINI 1.0; Bruker AXS, Inc.: Madison, WI, 1999. (b) RLATT
2.72; Bruker AXS, Inc.: Madison, WI, 1999.
(29) (a) SAINT 6.45; Bruker AXS, Inc.: Madison, WI, 2003. (b) Sheldrick,
G. SADABS 2.10; Bruker AXS, Inc.: Madison, WI, 1997. (c) SHELXTL
6.14; Bruker AXS, Inc.: Madison, WI, 2000.
Inorganic Chemistry, Vol. 47, No. 19, 2008 8733

Kanas et al.
by Guelph Chemical Laboratories (Guelph, ON). All reactions were
performed under an atmosphere of dinitrogen.
was washed with hexane (2 × 3 mL) and 1d was collected as a
dark purple solid by suction filtration. Yield: 265 mg (80%), mp
261-263 °C (decomp.). NMR spectroscopic data (in C6D6): 1H δ:
10.81 (d, J ) 5.7 Hz, 1H, Ar), 8.76 (d, JHRh ) 4.2 Hz, 1H, C(H)N),
7.41 (2nd order ov dd, J ) 6.6, 6.6 Hz, 1H, Ar), 7.33 (2nd order
dd, J ) 6.6, 2.0 Hz, 2H, Ar), 7.15 (ov ddd, J ) 7.9, 7.9, 1.5 Hz,
1H, Ar), 7.05 (ddd, J ) 7.9, 5.7, 1.5 Hz, 1H, Ar), 6.64 (d, J ) 7.9
Hz, 1H, Ar), 4.93 (s, 1H, C(H)dC), 3.80 (sept, J ) 6.7 Hz, 2H,
CH(CH3)2), 1.92 (s, 3H, acac-CH3), 1.68 (s, 3H, acac-CH3), 1.44
(d, J ) 6.7 Hz, 6H, CH(CH3)2), 1.10 (d, J ) 6.7 Hz, 6H,
CH(CH3)2); 13C{1H} δ: 184.2 (C(O)), 182.5 (C(O)), 157.3 (d, JCRh
) 2.6 Hz), 153.2, 150.5, 149.7, 142.3, 130.2, 126.7, 125.6, 123.7,
122.7, 99.7 (C(H)dC), 27.9 (acac-CH3), 26.9 (CH(CH3)2), 26.8
(CH(CH3)2), 24.2 (CH(CH3)2), 23.9 (CH(CH3)2). Anal. Calcd for
C23H29N2O2Rh (468.44) (%): C 58.97, H 6.25, N 5.98; found: C
59.39, H 6.11, N 5.63.
Synthesis of 2. To a 3 mL toluene solution of Rh(acac)(coe)2
(200 mg, 0.47 mmol) was added a 1 mL toluene solution of
4-methoxy-N-((pyridin-2-yl)methylene)benzenamine (100 mg, 0.47
mmol). The reaction mixture was heated at reflux for 18 h then
allowed to cool to room temperature (RT). Dry CHCl3 (1 mL) was
added and the reaction allowed to proceed for 18 h. The resulting
orange precipitate was collected by suction filtration and recrystal-
lized from THF (10 mL) stored at -30 °C for 3 days. The resulting
orange precipitate was collected by suction filtration and dried under
vacuum. Yield: 205 mg (81%), mp 218-222 °C (decomp.). NMR
spectroscopic data (in CDCl3): 1H δ: 9.18 (d, J ) 5.2 Hz, 1H, Ar),
8.39 (d, JHRh ) 2.7 Hz, 1H, C(H)N), 8.01-7.92 (ov m, 2H, Ar),
7.67-7.62 (ov m, 3H, Ar), 6.91 (d, J ) 8.9 Hz, 2H, Ar), 6.40 (d,
JHRh ) 2.7 Hz, 1H, Rh-CHCl2), 5.47 (s, 1H, C(H)dC), 3.85 (s,
3H, OCH3), 2.18 (s, 3H, acac-CH3), 2.03 (s, 3H, acac-CH3); 13C{1H}
δ: 187.4 (C(O)), 186.6 (C(O)), 163.6, 160.8, 156.2, 150.1, 139.7,
138.3, 127.6, 126.7, 125.9, 113.7, 100.5 (C(H)dC), 72.5 (d, JCRh
) 37.4 Hz, Rh-CHCl2), 55.6 (OCH3), 27.2 (acac-CH3), 27.1 (acac-
CH3). Anal. Calcd for C19H20Cl3N2O3Rh·C4H8O (605.93) (%): C
45.59, H 4.67, N 4.62; found: C 46.18, H 4.63, N 4.66.
Synthesis of 1a. To a 5 mL tetrahydrofuran (THF) solution of
Rh(acac)(coe)2 (250 mg, 0.59 mmol) was added a 3 mL THF
solution of 4-methoxy-N-((pyridin-2-yl)methylene)benzenamine
(128 mg, 0.60 mmol). The reaction mixture was heated at reflux
for 18 h at which point solvent was removed under vacuum. The
resulting oily solid was washed with hexane (2 × 3 mL) and 1a
was collected as a dark purple solid by suction filtration. Yield:
225 mg (92%), mp 264-268 °C (decomp.). NMR spectroscopic
data (in C6D6): 1H δ: 10.84 (d, J ) 5.9 Hz, 1H, Ar), 8.78 (d, JHRh
) 3.2 Hz, 1H, C(H)N), 8.08 (d, J ) 8.7 Hz, 2H, Ar), 7.21 (ov
ddd, J ) 7.2, 7.2, 1.0 Hz, 1H, Ar), 7.05 (ddd, J ) 7.2, 5.9, 1.0 Hz,
1H, Ar), 6.92 (d, J ) 8.7 Hz, 2H, Ar), 6.67 (d, J ) 7.2 Hz, 1H,
Ar), 5.06 (s, 1H, C(H)dC), 3.39 (s, 3H, OCH3), 1.99 (s, 3H, acac-
CH3), 1.84 (s, 3H, acac-CH3); 13C{1H} δ: 184.0 (C(O)), 182.7
(C(O)), 159.5, 158.2 (d, JCRh ) 2.0 Hz), 151.1, 150.2, 147.2, 129.8,
126.3, 124.7, 124.1, 113.5, 99.7 (C(H)dC), 54.8 (OCH3), 27.1
(acac-CH3), 27.0 (acac-CH3). Anal. Calcd for C18H19N2O3Rh
(414.29) (%): C 52.18, H 4.63, N 6.76; found: C 51.88, H 4.61, N
6.56.
Synthesis of 1b. To a 5 mL toluene solution of Rh(acac)(coe)2
(300 mg, 0.71 mmol) was added a 3 mL toluene solution of 2,6-
dimethyl-N-((pyridin-2-yl)methylene)benzenamine (155 mg, 0.74
mmol). The reaction mixture was heated at reflux for 18 h at which
point solvent was removed under vacuum. The resulting oily solid
was washed with hexane (2 × 3 mL) and 1b was collected as a
dark purple solid by suction filtration. Yield: 200 mg (68%), mp
218-222 °C (decomp.). NMR spectroscopic data (in C6D6): 1H δ:
10.81 (d, J ) 5.7 Hz, 1H, Ar), 8.38 (d, JHRh ) 4.2 Hz, 1H, C(H)N),
7.29-7.16 (ov m, 4H, Ar), 7.06 (ddd, J ) 7.9, 5.7, 1.5 Hz, 1H,
Ar), 6.64 (d, J ) 7.9 Hz, 1H, Ar), 4.93 (s, 1H, C(H)dC), 2.42 (s,
6H, Ar-CH3), 1.95 (s, 3H, acac-CH3), 1.65 (s, 3H, acac-CH3);
13C{1H} δ: 184.6 (C(O)), 182.5 (C(O)), 157.7 (d, JCRh ) 4.1 Hz),
153.3, 152.8, 150.6, 131.9, 130.1, 127.8, 125.9, 125.4, 123.9, 99.6
(d, JCRh ) 2.7 Hz, C(H)dC), 27.0 (acac-CH3), 18.6 (Ar-CH3). Anal.
Calcd for C19H21N2O2Rh (412.32) (%): C 55.35, H 5.14, N 6.80;
found: C 54.92, H 4.99, N 6.40.
Synthesis of 1c. To a 5 mL toluene solution of Rh(acac)(coe)2
(300 mg, 0.71 mmol) was added a 3 mL toluene solution of 2,6-
diethyl-N-((pyridin-2-yl)methylene)benzenamine (177 mg, 0.74
mmol). The reaction mixture was heated at reflux for 18 h at which
point solvent was removed under vacuum. The resulting oily solid
was washed with hexane (2 × 3 mL) and 1c was collected as a
dark purple solid by suction filtration. Yield: 250 mg (80%), mp
208-210 °C (decomp.). NMR spectroscopic data (in C6D6): 1H δ:
10.81 (d, J ) 5.7 Hz, 1H, Ar), 8.54 (d, JHRh ) 4.2 Hz, 1H, C(H)N),
7.36 (2nd order ov dd, J ) 6.7, 6.7 Hz, 1H, Ar), 7.26-7.15 (ov m,
3H, Ar), 7.06 (ddd, J ) 7.9, 5.7, 1.5 Hz, 1H, Ar), 6.65 (d, J ) 7.9
Hz, 1H, Ar), 4.92 (s, 1H, C(H)dC), 3.04 (q, J ) 7.7 Hz, 1H,
CHHCH3), 2.98 (q, J ) 7.7 Hz, 1H, CHHCH3), 2.91 (q, J ) 7.7
Hz, 1H, CHHCH3), 2.85 (q, J ) 7.7 Hz, 1H, CHHCH3), 1.94 (s,
3H, acac-CH3), 1.65 (s, 3H, acac-CH3), 1.20 (t, J ) 7.7 Hz, 6H,
CH2CH3); 13C{1H} δ: 184.4 (C(O)), 182.5 (C(O)), 157.5 (d, JCRh
) 4.1 Hz), 153.8, 151.5, 150.6, 137.7, 130.2, 126.3, 125.8, 125.6,
123.9, 99.6 (d, JCRh) 2.3 Hz, C(H)dC), 27.0 (acac-CH3), 24.7
(CH2CH3), 15.0 (CH2CH3). Anal. Calcd for C21H25N2O2Rh (440.38)
(%): C 57.28, H 5.72, N 6.36; found: C 57.47, H 5.79, N 5.90.
Synthesis of 1d. To a 5 mL toluene solution of Rh(acac)(coe)2
(300 mg, 0.71 mmol) was added a 3 mL toluene solution of 2,6-
diisopropyl-N-((pyridin-2-yl)methylene)benzenamine (198 mg, 0.74
mmol). The reaction mixture was heated at reflux for 18 h at which
point solvent was removed under vacuum. The resulting oily solid
Synthesis of 3a. To a 5 mL toluene solution of 1a (150 mg,
0.36 mmol) was added a 5 mL toluene suspension of B2cat3 (125
mg, 0.36 mmol). The reaction was allowed to proceed for 18 h at
which point a dark precipitate was collected by suction filtration.
The solid was washed with THF (1 × 2 mL) and dried under
vacuum. Yield: 175 mg (92%), mp 192 °C (decomp.). NMR
spectroscopic data (in CDCl3): 1H δ: 9.37 (d, J ) 5.9 Hz, 1H, Ar),
7.81 (d, JHRh ) 4.9 Hz, 1H, C(H)N), 7.77 (d, J ) 7.2 Hz, 1H, Ar),
7.62 (ov dd, J ) 7.2, 7.2 Hz, 1H, Ar), 7.27-7.12 (ov m, 3H, Ar),
6.90 (d, J ) 8.9 Hz, 2H, Ar), 6.82-6.69 (ov m, 4H, catechol),
6.49 (ov m, 2H, catechol), 5.01 (dd, J ) 4.5, 2.7 Hz, 2H,
η6-C6H4O2), 3.84 (s, 3H, OCH3); 11B δ: 14.1 (sharp). Anal. Calcd
for C25H20N2BO5Rh·C4H8O (614.30) (%): C 57.06, H 3.84, N 5.33;
found: C 56.75, H 4.13, N 4.87.
Synthesis of 3b. To a 5 mL toluene solution of 1b (175 mg,
0.42 mmol) was added a 5 mL toluene suspension of B2cat3 (147
mg, 0.42 mmol). The reaction was allowed to proceed for 18 h at
which point a dark precipitate was collected by suction filtration.
Yield: 180 mg (79%), mp 266-269 °C (decomp.). NMR spectro-
1
scopic data (in CDCl3): H δ: 9.48 (d, J ) 6.2 Hz, 1H, Ar), 7.78
(2nd order d, J ) 7.4 Hz, 1H, Ar), 7.68 (ov ddd, J ) 7.4, 7.4, 1.5
Hz, 1H, Ar), 7.64 (d, JHRh ) 5.4 Hz, 1H, C(H)N), 7.28 (ddd, J )
7.4, 6.2, 1.5 Hz, 1H, Ar), 7.14-7.11 (ov m, 3H, Ar), 6.80-6.72
(m, 4H, catechol), 6.61 (2nd order ddd, J ) 4.2, 2.4, 1.2 Hz, 2H,
η6-C6H4O2), 4.54 (dd, J ) 4.2, 2.5 Hz, 2H, η6-C6H4O2), 2.17 (s,
6H, CH3); 11B δ: 13.9 (sharp); 13C{1H} δ: 152.9, 151.9, 151.0,
150.8, 148.3, 132.0, 131.5, 129.1, 128.5, 127.1, 126.5, 122.0, 118.9
8734 Inorganic Chemistry, Vol. 47, No. 19, 2008

Rhodium(I) Acetylacetonato Pyridinecarboxaldimine Complexes
(d, JCRh ) 13.3 Hz, η6-C6H4O2), 109.5 (d, JCRh ) 15.4 Hz, η6-
C6H4O2), 86.7 (C(H)dC), 81.8 (d, JCRh ) 7.2 Hz, η6-C6H4O2), 17.5
(CH3). Anal. Calcd for C26H22N2BO4Rh (540.21) (%): C 57.80, H
4.11, N 5.19; found: C 57.82, H 4.21, N 4.88.
6.34 (d, J ) 18.3 Hz, CHdCH(Bcat)); 4-MeOC6H4CH2CH(Bcat)2,
IV: 3.36 (d, J ) 8.2 Hz, CH2CH(Bcat)2), 2.11 (t, J ) 8.2 Hz,
CH2CH(Bcat)2); 4-MeOC6H4CH2CH3, V: 2.45 (q, J ) 7.7 Hz,
CH2CH3), 1.10 (t, J ) 7.7 Hz, CH2CH3).
Synthesis of 3c. To a 5 mL toluene solution of 1c (200 mg,
0.45 mmol) was added a 5 mL toluene suspension of B2cat3 (157
mg, 0.45 mmol). The reaction was allowed to proceed for 18 h at
which point a dark precipitate was collected by suction filtration.
Yield: 190 mg (74%), mp 243-245 °C (decomp.). NMR spectro-
Selected NMR spectroscopic data for 4-FC6H4CH2CH2(Bcat),
I: 2.64 (t, J ) 8.2 Hz, CH2CH2(Bcat)), 1.28 (t, J ) 8.2 Hz,
CH2CH2(Bcat)); 4-FC6H4CH(Bcat)CH3, II: 2.60 (q, J ) 7.7 Hz,
CH(Bcat)CH3), 1.36 (d, J ) 7.7 Hz, CH(Bcat)CH3); 4-FC6H4CHd
CH(Bcat), III: 7.62 (d, J ) 18.3 Hz, CH ) CH(Bcat)), 6.23 (d, J
) 18.3 Hz, CHdCH(Bcat)); 4-FC6H4CH2CH(Bcat)2, IV: 3.22 (d,
J ) 8.2 Hz, CH2CH(Bcat)2), 1.99 (t, J ) 8.2 Hz, CH2CH(Bcat)2);
4-FC6H4CH2CH3, V: 2.28 (q, J ) 7.7 Hz, CH2CH3), 0.97 (t, J )
7.7 Hz, CH2CH3).
1
scopic data (in CDCl3): H δ: 9.48 (d, J ) 5.9 Hz, 1H, Ar), 7.78
(2nd order d, J ) 7.9 Hz, 1H, Ar), 7.71-7.64 (ov m, 2H, Ar and
C(H)N), 7.31-7.23 (ov m, 2H, Ar), 7.18-7.15 (ov m, 2H, Ar),
6.83-6.70 (ov m, 4H, catechol), 6.58 (app t, J ) 2.7 Hz, 2H, η6-
C6H4O2), 4.51 (dd, J ) 4.2, 2.5 Hz, 2H, η6-C6H4O2), 2.57 (q, J )
Selected NMR spectroscopic data for 4-MeOC6H4CH2CH2-
(Bpin), I: 2.85 (t, J ) 7.9 Hz, CH2CH2(Bpin)), 1.10 (t, J ) 7.9 Hz,
CH2CH2(Bpin)); 4-MeOC6H4CHdCH(Bpin), III: 7.76 (d, J ) 18.3
Hz, CH ) CH(Bpin)), 6.35 (d, J ) 18.3 Hz, CHdCH(Bpin)).
Selected NMR spectroscopic data for 4-FC6H4CH2CH2(Bpin),
I: 2.69 (t, J ) 8.1 Hz, CH2CH2(Bpin)), 1.10 (t, J ) 8.1 Hz,
CH2CH2(Bpin)); 4-FC6H4CHdCH(Bpin), III: 7.90 (d, J ) 18.0
Hz, CH ) CH(Bpin)), 6.23 (d, J ) 18.0 Hz, CHdCH(Bpin)).
X-ray Crystallography. Crystals of 1b and 1c were grown from
saturated hexane solutions at -25 °C, 2 from THF, and 3b from
nitromethane at -25 °C. Single crystals were coated with Para-
tone-N oil, mounted using a glass fiber, and frozen in the cold
stream of the goniometer. A hemisphere of data were collected on
a Bruker AXS P4/SMART 1000 diffractometer using ω and θ scans
with a scan width of 0.3° and 20 s (1b) and 30 s (1c, 2, and 3b)
exposure times. The detector distance was 5 cm. Crystals of 1b
were twinned, and the orientation matrix for two components
determined (RLATT, GEMINI).28a The data were reduced (SAINT)
and corrected for absorption (SADABS).29a The structures were
solved by direct methods and refined by full-matrix least-squares
on F2(SHELXTL) (1c, 2, and 3a) or on all but partially overlapping
data (1b). All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were included in calculated positions and refined
using a riding model. CCDC 684246-684249 contain the supple-
mentary crystallographic data for this paper.
7.4 Hz, 4H, CH2CH3, 4H), 1.14 (t, J ) 7.4 Hz, 6H, CH2CH3); 11
B
δ: 13.8 (sharp); 13C{1H} δ: 151.8, 151.3, 151.0, 150.5 (d, JCRh
)
2.0 Hz), 148.8, 135.1, 132.1, 131.4, 127.5, 126.5, 126.4, 122.1,
119.0 (d, JCRh ) 11.8 Hz, η6-C6H4O2), 109.5 (d, JCRh ) 14.3 Hz,
η6-C6H4O2), 86.8 (d, JCRh ) 3.7 Hz, C(H)dC), 81.9 (d, JCRh ) 7.2
Hz, η6-C6H4O2), 23.6 (CH2CH3), 15.3 (CH2CH3). Anal. Calcd for
C28H26N2BO4Rh (568.27) (%): C 59.18, H 4.62, N 4.93; found: C
58.91, H 4.73, N 4.80.
Synthesis of 3d. To a 5 mL toluene solution of 1d (200 mg,
0.43 mmol) was added a 5 mL toluene suspension of B2cat3 (148
mg, 0.43 mmol). The reaction was allowed to proceed for 18 h at
which point a dark precipitate was collected by suction filtration.
Yield: 150 mg (59%), mp 251-254 °C (decomp.). NMR spectro-
1
scopic data (in CDCl3): H δ: 9.50 (d, J ) 6.2 Hz, 1H, Ar), 7.79
(2nd order d, J ) 7.4 Hz, 1H, Ar), 7.69 (ddd, J ) 7.4, 6.2, 1.2 Hz,
1H, Ar), 7.62 (d, J ) 5.2 Hz, 1H, C(H)N), 7.34-7.27 (ov m, 2H,
Ar), 7.2 (2nd order dd, J ) 6.9, 1.5 Hz, 2H, Ar), 6.84-6.78 (ov
m, 2H, catechol), 6.75-6.68 (ov m, 2H, catechol), 6.61 (ddd, J )
4.4, 2.4, 1.0 Hz, 2H, η6-C6H4O2), 4.60 (2nd order dd, J ) 4.2, 2.5
Hz, 2H, η6-C6H4O2), 3.11 (sept, J ) 6.9 Hz, 2H, CH(CH3)2), 1.30
(d, J ) 6.9 Hz, 6H, CH(CH3)2), 1.03 (d, J ) 6.9 Hz, 6H,
CH(CH3)2); 11B δ: 13.9 (sharp); 13C{1H} δ: 151.8, 151.0, 150.3
(d, JCRh ) 3 Hz), 149.8, 149.0, 140.2, 132.1, 131.6, 127.9, 126.5,
123.6, 122.2, 119.0 (d, JCRh ) 14.3 Hz, η6-C6H4O2), 109.5 (d, JCRh
) 17.4 Hz, η6-C6H4O2), 86.6 (d, JCRh ) 3.6 Hz, C(H)dC), 81.6
(d, JCRh ) 7.2 Hz, η6-C6H4O2), 27.5, 26.2, 22.9. Anal. Calcd for
C30H30N2BO4Rh (596.33) (%): C 60.42, H 5.08, N 4.70; found: C
60.50, H 5.24, N 4.68.
Acknowledgment. Thanks are gratefully extended to the
Canada Research Chairs Programme, Canadian Foundation
for Innovation-Atlantic Innovation Fund, Natural Science and
Engineering Research Council of Canada, and Mount Allison
University for financial support. We also thank Roger Smith
and Dan Durant for expert technical assistance and anony-
mous reviewers for helpful comments.
General Procedure for the Catalyzed Hydroboration of
Vinylarenes. The appropriate borane (1.2 equiv) in 0.5 mL of C6D6,
was added to a 0.5 mL C6D6 solution of 1 or 3 and the vinylarene.
Reactions were allowed to proceed for 18 h and then monitored
by multinuclear NMR spectroscopy.7c-e
Selected NMR spectroscopic data for 4-MeOC6H4CH2CH2(Bcat),
I: 2.79 (t, J ) 7.9 Hz, CH2CH2(Bcat)), 1.42 (t, J ) 7.9 Hz,
CH2CH2(Bcat)); 4-MeOC6H4CH(Bcat)CH3, II: 2.74 (q, J ) 7.7 Hz,
CH(Bcat)CH3), 1.48 (d, J ) 7.7 Hz, CH(Bcat)CH3); 4-MeOC6-
H4CHdCH(Bcat), III: 7.82 (d, J ) 18.3 Hz, CH ) CH(Bcat)),
Supporting Information Available: X-ray crystallographic files
in CIF format for complexes 1b, 1c, 2, and 3b. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC800703N
Inorganic Chemistry, Vol. 47, No. 19, 2008 8735