Iridium phosphane complexes containing arylspiroboronate esters for the hydroboration of alkenes

Article abstract of DOI:10.1002/ejic.201100057

Iridium phosphane arylspiroboronate esters have been prepared by addition of B₂cat₃ (cat = 1,2-O₂C₆H ₄) to the iridium precursors Ir(acac)(coe)₂/PR₃ (acac = acetylacetonato, coe

Full text of DOI:10.1002/ejic.201100057

FULL PAPER
DOI: 10.1002/ejic.201100057
Iridium Phosphane Complexes Containing Arylspiroboronate Esters for the
Hydroboration of Alkenes
Graham M. Lee,[a] Christopher M. Vogels,[a] Andreas Decken,[b] and Stephen A. Westcott*[a]
Keywords: Iridium / Boron / Hydroboration / Zwitterions
Iridium phosphane arylspiroboronate esters have been pre-
pared by addition of B2cat3 (cat = 1,2-O2C6H4) to the iridium
precursors Ir(acac)(coe)2/PR3 (acac = acetylacetonato, coe =
cis-cyclooctene) or Ir(acac)(coe)2/P-P (chelating bidentate li-
gands) at elevated temperatures. These novel complexes
have been characterized by a number of physical methods
including X-ray diffraction studies for the PCy3 (2) and dppp
(6, 1,3-diphenylphosphanopropane) derivatives. The arylspi-
roboronate esters, as seen with the more common rhodium
complexes, are bound to the metal centre via one of the
benzene catecholato rings. These organometallic complexes
can be used as precatalysts for the selective hydroboration of
vinylarene derivatives with HBpin (pin = 1,2-O2C2Me4) to
give the corresponding linear hydroboration products. Reac-
tions with methyl oleate proceed at elevated temperatures to
give the isomerised/hydroboration product selectively along
with equal amounts of hydrogenation product.
ably active catalyst precursors for the hydroboration of a
wide range of alkenes using HBcat, where catalyst resting
states in these systems are believed to be the zwitterionic
complexes of the type Rh(η6-catBcat)(P2), arising from the
redistribution of borane substituents. The unusual arylspi-
roboronate ester [Bcat2]– is bound to the rhodium fragment
via all six carbons of one of the catecholato rings.
Introduction
The addition of boranes to unsaturated organic mole-
cules has become a remarkably important synthetic meth-
odology in organic synthesis.[1] Although borane reagents
H3B·X (X = THF, SMe2) add readily to alkenes at –80 °C,[2]
other hydroboration reagents, such as diorganyloxyboranes,
are slow to react even at room temperature. For instance,
catecholborane (HBcat, cat = 1,2-O2C6H4) and pinacolbor-
ane (HBpin, pin = 1,2-O2C2Me4) add to alkenes and alk-
ynes only at elevated temperatures[3] or in the presence of a
transition metal catalyst.[4] A considerable amount of re-
search has therefore focused on investigating the mecha-
nism and scope of these catalysed hydroboration reac-
tions.[5] Although a number of transition metals have been
found to catalyse hydroborations with HBcat and HBpin,
rhodium complexes are usually the most effective for reac-
tions with alkenes. For instance, the judicious choice of a
rhodium precatalyst in hydroborations with HBcat can give
exclusive formation of either the linear or branched product
in the hydroboration of vinylarene derivatives (Scheme 1).[6]
Indeed, the unusual branched product can be obtained in
reactions employing either a catalytic amount of Wilkin-
son’s catalyst, RhCl(PPh3)3, or phosphane acetylacetonato
rhodium complexes of the type Rh(acac)(P2) (where acac
= acetylacetonato, P2 is a bidentate phosphane).[7] These
phosphane rhodium acetylacetonato complexes are remark-
Scheme 1. The rhodium-catalysed hydroboration of styrene using
catecholborane (HBcat).
More recently, there has been considerable interest in the
use of iridium complexes in an effort to expand the scope
of these catalysed hydroborations.[8] For instance, an ele-
gant study by Suzuki, Miyata and co-workers[8b] has used
the catalyst system of [IrCl(cod)]2/diphosphane and HBpin
as a key step in the synthesis of boron-containing histone
deacetylases inhibitors containing a α-amino acid group. In
light of this work, we decided to generate the zwitterionic
iridium complexes of the type Ir(η6-catBcat)(P2) and exam-
ine their potential to catalyse the borylation of various al-
kenes, our findings are presented herein.
[a] Department of Biochemistry and Chemistry,
Mount Allison University, Sackville, NB E4L 1G8, Canada
Fax: +1-506-364-2313
Results and Discussion
E-mail: swestcott@mta.ca
[b] Department of Chemistry, University of New Brunswick,
Fredericton, NB E3B 5A3, Canada
Marder and co-workers have found that addition of
B2cat3 to Rh(acac)(P2) led to the zwitterionic complexes
E-mail: adecken@unb.ca
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G. M. Lee, C. M. Vogels, A. Decken, S. A. Westcott
FULL PAPER
Rh(η6-catBcat)(P2) in high yields, along with concomitant though the mixed phosphane cyclooctene complex Ir(acac)-
formation of acacBcat.[7b] The diboron reagent B2cat3 can (coe)(PCy3) (1) has been characterized spectroscopically,[14]
be readily prepared by the addition of catechol to solutions the molecular structure for this mixed ligand complex has
of BH3·SMe2.[9] Although rhodium compounds containing not yet been reported. To confirm monosubstitution, we
arylspiroboronate esters are known,[7b,10] and a ruthenium have carried out a single-crystal X-ray diffraction study on
example has been characterized by multinuclear NMR 1 and the molecular structure of which is shown in Figure 1.
spectroscopy,[11] we have just begun to prepare a number Bond lengths and angles are well within the expected range
of iridium complexes containing these unusual ligands and for similar iridium acetylacetonate phospane complexes.[13]
examine their potential to act as precatalysts in the hydro- Crystallographic data are presented in Table 1.
boration of alkenes and alkynes.[12] We have previously gen-
We then used 1 to prepare the zwitterionic complex
erated the starting iridium precursors from addition of Ir(η2-coe)(PCy3)(η6-catBcat) (2, cat = 1,2-O2C6H4) in good
phosphane to Ir(acac)(coe)2 (coe = cis-cyclooctene).[13] Al- yield (79%) by the addition of B2cat3. The 11B{1H} NMR
spectrum shows a sharp singlet at δ = 13.8 ppm for the four
coordinate boron anion[15] and the 31P{1H} NMR peak
shifts from δ = 0.6 ppm in 1 to 7.6 ppm for complex 2.
1
More diagnostic, however, is the H NMR spectroscopic
data in [D8]THF, as the resonances for the hydrogens on
the Bcat group bound directly to iridium are observed at δ
= 6.10 and 5.75 ppm, while the uncoordinated catecholato
peaks remain downfield from δ = 6.46 to 6.52 ppm. In com-
parison, these catecholato proton peaks are observed at δ =
6.57 ppm for [NBu4][Bcat2].[16] The chemical shifts of the
bound protons are quite dependent upon solvent as they
move to δ = 5.93 and 5.55 ppm in CDCl3 and δ = 5.47
and 4.78 ppm in C6D6. Significant upfield shifts are also
observed in 2 by 13C{1H} NMR spectroscopy, where the
Figure 1. Molecular structure of 1 with atom labelling scheme,
carbon atoms of the Bcat group coordinated to the iridium
fragment are located at δ = 139.4, 85.9, and 79.0 ppm. For
comparison, the related carbon resonances in [NBu4][Bcat2]
are observed at δ = 151.8, 117.9, and 108.5 ppm.
Complex 2 has also been characterised by a single-crystal
X-ray diffraction study (Figure 2, Table 1), confirming that
thermal ellipsoids are drawn at the 50% probability level with hy-
drogen atoms omitted for clarity. Selected bond lengths [Å]: Ir(1)–
O(1) 2.065(3), Ir(1)–O(2) 2.093(4), Ir(1)–C(25) 2.106(5), Ir(1)–C(24)
2.118(5), Ir(1)–P(1) 2.2202(14); selected bond angles (°): O(1)–
Ir(1)–O(2) 87.09(15), O(1)–Ir(1)–C(25) 159.30(18), O(2)–Ir(1)–
C(25) 89.83(17), O(1)–Ir(1)–C(24) 160.60(18), O(2)–Ir(1)–C(24)
88.90(18), O(1)–Ir(1)–P(1) 88.39(11), O(2)–Ir(1)–P(1) 175.23(11).
Table 1. Crystallographic data collection parameters for 1, 2 and 6.
Complex
1
2
6
Formula
C31H54IrO2P
681.91
0.45ϫ0.40ϫ0.25
monoclinic
P21/n
C38H55BIrO4P
809.80
0.35ϫ0.15ϫ0.08
monoclinic
P21/n
C39H34BIrO4P2
831.61
0.60ϫ0.10ϫ0.05
monoclinic
P21/n
Formula mass
Dimensions [mm]
Crystal system
Space group
Z
4
4
4
a [Å]
b [Å]
c [Å]
α [°]
13.195(4)
18.870(6)
13.807(5)
90
16.071(3)
9.6251(17)
23.247(4)
90
11.2363(12)
20.635(2)
14.6540(17)
90
β [°]
γ [°]
115.595(4)
90
3100.6(17)
1.461
108.381(2)
90
3412.5(10)
1.576
106.329(2)
90
3260.6(6)
1.694
Volume [Å3]
Dcalcd. [mgm–3]
T [K]
173(1)
173(1)
213(1)
Radiation [Å]
μ [mm–1]
Total reflections
Number of variables
Θ [°]
Mo-Kα (λ = 0.71073)
4.382
20845
6912
1.78 to 27.50
1.051
Mo-Kα (λ = 0.71073)
3.999
7642
7642
1.36 to 27.50
1.127
Mo-Kα (λ = 0.71073)
4.236
22239
7188
1.75 to 27.50
1.084
GoF on F2
[a]
R1 [IϾ2σ(I)]
0.0514
0.1389
0.0375
0.0974
0.0256
0.0635
[b]
wR2 (all data)
Largest difference peak & hole [Å]
4.335 & –3.765
3.145 & –1.383
1.018 & –0.566
2 2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = {Σ[w(Fo2 – Fc ) ]/Σ[Fo]4}1/2, where w = 1/[σ2(Fo)2 + (0.0917P)2 + (3.0571P)] (for 1), 1/[σ2(Fo)2 +
(0.058P)2 + (1.8907P)] (for 2), 1/[σ2(Fo) + (0.0262P)2 + (0.1357P)] (for 6).
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Iridium Phosphane Complexess for the Hydroboration of Alkenes
the arylspiroboronate ester is bound to the iridium frag-
ment in a η6 fashion. Within the bound Bcat group, four
of the iridium carbon distances Ir(1)–C(30) 2.275(6), Ir(1)–
C(31) 2.296(6), Ir(1)–C(29) 2.330(6), and Ir(1)–C(32)
2.338(6), are noticeably shorter than the other two at
2.420(6) Ir(1)–C(27) and 2.434(6) Ir(1)–C(28) Å. This slipp-
age away from a true η6 bonding mode has been observed
in the rhodium analogues where the potential surface for
such distortions is reputably quite shallow. Bond lengths
and angles within the arylspiroboronate ester are similar to
those reported previously.[17] Also of significance is that
boron oxygen distances for the catecholato group bound to
the metal centre, B(1)–O(1) 1.491(9) and B(1)–O(2)
1.532(9) Å,[18] are somewhat longer than the analogous dis-
tances for the unbound group at B(1)–O(4) 1.449(8) and
B(1)–O(3) 1.463(8) Å. Not surprisingly, attempts to substi-
tute the second coe ligand with another bulky PCy3 group
did not prove successful.
Scheme 2. Synthesis of iridium arylspiroboronate esters using
B2cat3.
In this study, complexes 3–6 have been characterized by
a number of physical methods including multinuclear NMR
spectroscopy. The 11B NMR spectroscopic data for these
species is consistently between δ = 14.8–15.2 ppm, which is
only slightly different from the monophosphane PCy3 spe-
cies at δ = 13.9 ppm. Similar shifts for the 1H and 13C NMR
peaks are observed for the bisphosphane complexes 3–6 as
seen for 2. Most noticeable are the shifts for bound cate-
cholato hydrogens for 3, which appear at δ = 4.91 and
4.11 ppm in C6D6. Likewise, these peaks are observed at δ
= 4.60 and 4.44 ppm in C6D6 for complex 6. Complex 6
has been characterized by a single-crystal X-ray diffraction
study, the molecular structure of which is shown in Fig-
ure 3.
Figure 2. Molecular structure of 2 with atom labelling scheme,
thermal ellipsoids are drawn at the 50% probability level with hy-
drogen atoms omitted for clarity. Selected bond lengths [Å]: Ir(1)–
C(20) 2.104(5), Ir(1)–C(19) 2.128(6), Ir(1)–P(1) 2.2850(15), Ir(1)–
C(30) 2.275(6), Ir(1)–C(31) 2.296(6), Ir(1)–C(29) 2.330(6), Ir(1)–
C(32) 2.338(6), Ir(1)–C(27) 2.420(6), Ir(1)–C(28) 2.434(6), B(1)–
O(4) 1.449(8), B(1)–O(3) 1.463(8), B(1)–O(1) 1.491(9), B(1)–O(2)
1.532(9); selected bond angles (°): C(20)–Ir(1)–C(19) 40.0(2),
C(20)–Ir(1)–P(1) 93.18(17), C(19)–Ir(1)–P(1) 90.77(17), O(4)–B(1)–
O(3) 107.2(5), O(4)–B(1)–O(1) 114.7(5), O(3)–B(1)–O(1) 111.7(6),
O(4)–B(1)–O(2) 111.1(6), O(3)–B(1)–O(2) 109.4(5), O(1)–B(1)–O(2)
102.8(5).
Figure 3. Molecular structure of 6 with atom labelling scheme,
thermal ellipsoids are drawn at the 50% probability level with hy-
drogen atoms omitted for clarity. Selected bond lengths [Å]: Ir(1)–
P(1) 2.2144(9), Ir(1)–P(2) 2.2185(9), Ir(1)–C(31) 2.284(4), Ir(1)–
C(32) 2.293(4), Ir(1)–C(33) 2.304(3), Ir(1)–C(30) 2.306(3), Ir(1)–
C(28) 2.449(3), Ir(1)–C(29) 2.455(3); selected bond angles (°): P(1)–
Ir(1)–P(2) 92.67(3), P(1)–Ir(1)–C(31) 108.71(10), P(2)–Ir(1)–C(31)
142.30(10),
P(1)–Ir(1)–C(32)
139.69(11),
P(2)–Ir(1)–C(32)
110.81(10), O(3)–B(1)–O(4) 106.5(3), O(3)–B(1)–O(2) 111.9(3),
O(4)–B(1)–O(2) 111.0(3), O(3)–B(1)–O(1) 112.9(3), O(4)–B(1)–O(1)
111.5(3), O(2)–B(1)–O(1) 103.2(3).
Addition of B2cat3 to Ir(acac)(PPh3)2 at elevated tem-
peratures, however, lead to the bisphosphane complex
The structure once again confirms that the arylspiro-
Ir(PPh3)2(η6-catBcat) (3) in high yield. Similar reactivity boronate ester is bound to the iridium fragment in a η6
was observed with chelating bidentate systems Ir(acac)- fashion where the bound catecholato group has four rela-
(P-P)2 to give the corresponding species Ir(dppm)(η6- tively short carbon distances: Ir(1)–C(31) 2.284(4), Ir(1)–
catBcat) (dppm
=
1,1-diphenylphosphanomethane, 4), C(32) 2.293(4), Ir(1)–C(33) 2.304(3), and Ir(1)–C(30)
1,2-diphenylphosphano- 2.306(3) along with two longer bonds of Ir(1)–C(28)
Ir(dppe)(η6-catBcat) (dppe
=
ethane, 5) and Ir(dppp)(η6-catBcat) (dppp = 1,3-diphenyl- 2.449(3) and Ir(1)–C(29) 2.455(3) Å. By comparison, four
phosphanopropane, 6, Scheme 2). It should be noted that short bond lengths are also observed in the dppb derivative
the precursor Ir(acac)(dppe) had to be prepared using mi- [2.270(3), 2.297(3), 2.302(3), and 2.312(3) Å].[12] Further
crowave radiation[13] as conventional heating of Ir(acac)- studies are needed to see if this degree of slippage is a com-
(coe)2 with dppe lead to a mixture of products including mon trend observed in arylspiroboronate esters bound to
[Ir(dppe)2]+(acac)–.
transition metals.[19]
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G. M. Lee, C. M. Vogels, A. Decken, S. A. Westcott
FULL PAPER
We then decided to examine these iridium arylspiro- from the degradation of the borane into B2pin3 (δ = 23 ppm
boronate complexes for their potential to catalyse the ad- in the 11B NMR spectra) and H2.[5a,5b] The molecular struc-
dition of HBcat and HBpin to a number of vinylarenes (4- ture of B2pin3 has been reported by Marder, Norman and
R-C6H4CH=CH2, where R = MeO, F, Bpin). Contrary to co-workers.[22] The dihydrogen adds to the starting alkene
results using the highly active and selective rhodium ana- in the presence of an active catalyst system. Although the
logues, no significant reaction was observed with HBcat iridium complexes 2–6 could be used to effectively catalyse
using a catalytic amount of these species at room tempera- this isomerisation/hydroboration reaction, we will continue
ture after 16 h. Interestingly, however, reactions of HBpin to investigate this reaction using other metal systems in an
and the vinylarenes proceeded smoothly at room tempera- effort to reduce the amount of competing hydrogenation,
ture to the exclusive formation of the corresponding linear the results of which will be presented in due course.
hydroboration product (4-R-C6H4CH2CH2Bpin), along
1
with minor amounts (Ͻ2% by H NMR spectroscopy) of
the saturated hydrogenation product 4-R-C6H4CH2CH3
Conclusions
(Scheme 3). The nature of the para substituent R had negli-
gible effect on product selectivities. Unfortunately, attempts
to add either HBcat or HBpin to the more hindered sub-
strates α- and β-methylstyrene proceeded with no clear se-
lectivites and gave a complicated mixture of products.
Iridium phosphane arylspiroboronate ester complexes
have been prepared by addition of B2cat3 (cat = 1,2-
O2C6H4) to the iridium precursors Ir(acac)(coe)2/PR3 or Ir-
(acac)(coe)2/P-P (chelating bidentate ligands) at elevated
temperatures. These novel complexes have been prepared in
good to high yields and have been characterized by a
number of physical methods including X-ray diffraction
studies for the PCy3 (2) and dppp [6, 1,3-bis(diphenylphos-
phanyl)propane] derivatives. The work represents the first
iridium complexes containing these unusual arylspiro-
boronate ester ligands. Solid state and solution data show
that the arylspiroboronate ester is bound to the metal via
the six-membered ring of the catecholato group. The poten-
tial of these zwitterionic species to change in hapticity from
an η6 to an η4 or even an η2 to an η0 bonding mode, could
facilitate catalysis without loss of a ligand. Indeed, we have
found that these novel iridium species can be used for the
selective hydroboration of vinylarenes using pinacolborane
(HBpin) to give the corresponding terminal hydroboration
products. However, elevated temperatures are required for
these complexes to be used as catalyst precursors for the
isomerisation and subsequent hydroboration of methyl ole-
ate, an important feedstock in biomass research. We are
investigating the nature of the arylspiroboronate ester metal
bond but further work is needed, however, to design a more
effective catalyst for these reactions and the results of which
will be published in due course.
Scheme 3. The iridium arylspiroboronate ester catalysed hydrobor-
ation of vinyl arenes using pinacolborane (HBpin).
Recent interests into the catalytic functionalization of
methyl oleate [CH3(CH2)7CH=CH(CH2)7CO2CH3] are of
considerable interest in biomass research.[20] In a recent ele-
gant study by Ghebreyessus and Angelici,[21] it was shown
that [IrCl(coe)2]2/dppe can be used to isomerise and hydro-
borate methyl oleate with HBpin to give the organoboron-
ate ester pinBCH2(CH2)16CO2CH3 in 45% yield. This re-
markable reaction prompted us to investigate our new irid-
ium complexes for this possible transformation. Although
no reaction was observed with methyl oleate and HBpin
using 5 mol-% of catalyst precursors 2–6 at room tempera-
ture, we were able to affect this reaction at elevated tem-
peratures (Scheme 4). Indeed, complete conversion of
methyl oleate was observed in THF at reflux after 18 h
using three equivalents of HBpin. Complex 2 gave the best
yields (ca. 50%) of the desired hydroboration product
pinBCH2(CH2)16CO2CH3, but unfortunately, as was ob-
served by Ghebreyessus and Angelici, equal amounts of the
saturated hydrogenation product CH3(CH2)16CO2CH3 was
also observed. Competing hydrogenation reactions during
Experimental Section
General: Reagents and solvents were purchased from Aldrich
[13]
[9]
Chemicals and used as received. Ir(acac)(η2-coe)2
and B2cat3
were prepared by known procedures. Ir(acac)(PPh3)2, Ir(acac)-
(dppm), Ir(acac)(dppe), and Ir(acac)(dppp) were synthesized as
hydroborations are well documented, and believed to arise previously reported.[13] NMR spectra were recorded on a JEOL
Scheme 4. Isomerisation and hydroboration of methyl oleate with HBpin using iridium arylspiroboronate esters 2–6.
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Iridium Phosphane Complexess for the Hydroboration of Alkenes
JNM-GSX270 FT NMR (1H: 270 MHz; 11B: 87 MHz; 13C: m, 2 H, η6-C6H4O2), 3.99 (t, JH-P = 11.1 Hz, 2 H, P CH2) ppm.
68 MHz; 31P: 109 MHz) spectrometer. Chemical shifts (δ) are re-
ported in ppm [relative to residual solvent peaks (1H and 13C) or
external B(OH)3 (11B) and H3PO4 (31P)] and coupling constants (J)
in Hz. Multiplicities are reported as singlet (s), doublet (d), triplet
(t), multiplet (m), broad (br), and overlapping (ov). Melting or de-
composition 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.
11B NMR (C6D6): δ = 14.8 (sharp); 13C {1H} δ: 152.5, 152.4, 137.1,
136.2 (t, JC-P = 26.6 Hz), 132.0 (t, JC-P = 6.1 Hz), 130.3, 128.4 (t,
JC-P = 5.6 Hz), 125.4, 118.8, 118.6, 109.7, 108.8, 80.0, 77.2, 21 (br.
m, CH2-P) ppm. 31P{1H} NMR (C6D6): δ = –55.8 ppm. C37H30BI-
rO4P2 (803.70): calcd. C 55.29, H 3.77; found C 55.44, H 3.98.
Ir(dppe)(η6-catBcat) (5): To a toluene (5 mL) solution of Ir(acac)-
(dppe) (160 mg, 0.23 mmol) was added a toluene (5 mL) solution
of B2cat3 (80 mg, 0.23 mmol) and the reaction mixture was heated
at 100 °C for 18 h. Upon cooling to –30 °C, a solid precipitated
and was collected by suction filtration. The solid was dissolved in
toluene (5 mL) and Et2O (1 mL) and the solution stored at –30 °C.
A precipitate was collected by suction filtration to afford 5 as a
yellow solid; yield 75 mg (40%), m.p. 171–174 °C (decomp.). Spec-
troscopic NMR data: 1H NMR (C6D6): δ = 7.50 (m, 8 H, Ar),
7.19–7.01 (ov m, 14 H, Ar & C6H4O2), 6.97–6.84 (ov m, 2 H,
C6H4O2), 5.24 (2nd order m, 2 H, η6-C6H4O2), 4.42 (2nd order m,
2 H, η6-C6H4O2), 1.66 (d, JH-P = 17.3 Hz, 4 H, P-CH2) ppm. 11B
NMR (C6D6): δ = 14.8 (sharp) ppm. 13C{1H} NMR (C6D6): δ =
152.7, 152.5, 139.5, 136.9 (m, C-P), 132.7 (t, JC-P = 5.7 Hz), 130.2,
128.3 (t, JC-P = 5.7 Hz), 125.4, 118.9, 118.6, 109.7, 108.7, 83.0, 76.9,
30.2 (t, JC-P = 28.1 Hz) ppm. 31P{1H} NMR (C6D6): δ = 41.6 ppm.
C38H32BIrO4P2 (817.73): calcd. C 55.81, H 3.95; found C 56.12, H
4.09.
Ir(dppp)(η6-catBcat) (6): To a toluene (5 mL) solution of Ir(acac)-
(dppp) (200 mg, 0.28 mmol) was added a toluene (5 mL) solution
of B2cat3 (98 mg, 0.28 mmol). Following 18 h of stirring at room
temp. a precipitate was collected by suction filtration. The solid
was washed with toluene (3ϫ3 mL) to afford 6 as an orange solid;
yield 200 mg (86%), m.p. 172–174 °C (decomp.). Spectroscopic
NMR data: 1H NMR (C6D6): δ = 7.47 (m, 8 H, Ar), 7.29–7.10 (ov
m, 14 H, Ar & C6H4O2), 7.00–6.79 (ov m, 2 H, C6H4O2), 4.60 (2nd
order m, 2 H, η6-C6H4O2), 4.44 (2nd order m, 2 H, η6-C6H4O2),
2.08 (m, 4 H, P-CH2), 1.36 (br. m, 2 H, CH2CH2CH2); 11B δ: 15.2
(sharp) ppm. 13C{1H} NMR (C6D6): δ = 153.0, 152.9, 141.1, 136.9
Ir(acac)(η2-coe)(PCy3) (1): To a toluene (5 mL) solution of Ir-
(acac)(η2-coe)2 (300 mg, 0.59 mmol) was added a toluene (3 mL)
solution of tricyclohexylphosphane (164 mg, 0.59 mmol). The reac-
tion was allowed to proceed for 18 h at which point solvent was
removed under vacuum. The residual oil was dissolved in a mini-
mum amount of hexane and stored at –30 °C. The resulting yellow-
orange precipitate was collected by suction filtration and washed
with cold hexane (1 mL) to afford 1; yield 315 mg (79%), m.p. 145–
148 °C. Selected spectroscopic NMR data: 13C{1H} NMR (C6D6):
δ = 184.7, 180.6, 101.0, 43.9, 30.9, 30.6 (d, JCP = 28.7 Hz), 30.1,
28.2 (d, JCP = 10.7 Hz), 27.9, 27.3, 27.0, 26.4 ppm.
Ir(η2-coe)(PCy3)(η6-catBcat) (2): To a toluene (5 mL) solution of
Ir(acac)(η2-coe)(PCy3)(250 mg, 0.37 mmol) was added a toluene
(5 mL) solution of B2cat3 (128 mg, 0.37 mmol). The reaction was
allowed to proceed for 18 h at which point solvent was removed
under vacuum. The resulting yellow solid was washed with Et2O
(3ϫ15 mL) before being collected by suction filtration to afford 2
as a pale yellow solid; yield 237 mg (79%), m.p. 191–193 °C. Spec-
1
troscopic NMR data: H NMR ([D8]THF): δ = 6.52–6.46 (ov m,
4 H, catechol), 6.10 (m, 2 H, η6-C6H4O2), 5.74 (m, 2 H, η6-
C6H4O2), 2.30–2.21 (m, 3 H), 1.84–1.57 (ov m, 30 H), 1.41–1.27
(ov m, 12 H) . 11B ([D8]THF): δ = 13.9 (sharp) ppm. 13C{1H}
NMR ([D8]THF): δ = 150.0, 149.8, 138.0, 115.9, 115.7, 106.2, 84.9,
76.2, 39.1, 32.6 (d, JCP = 29.7 Hz), 30.9, 28.5, 28.0, 25.8, 25.6, 24.6
ppm. 31P{1H} ([D8]THF): δ = 7.5. C38H55BIrO4P (809.94): calcd.
C 56.35, H 6.86; found C 56.58, H 6.99.
(t, JC-P = 28.2 Hz), 132.8 (t, JC-P = 5.6 Hz), 130.0, 128.7 (t, JC-P
6.7 Hz), 125.4, 119.0, 118.7, 109.8, 108.7, 84.2, 77.8, 27.6 (t, JC-P
=
=
Ir(PPh3)2(η6-catBcat) (3): To a toluene (5 mL) solution of Ir(acac)-
(PPh3)2 (250 mg, 0.31 mmol) was added a toluene (5 mL) solution
of B2cat3 (106 mg, 0.31 mmol). The reaction was heated at 100 °C
for 18 h. Upon cooling to room temp. a precipitate formed and was
collected by suction filtration. The solid was washed with toluene
(3ϫ1 mL) to afford 3 as a brick-red solid; yield 262 mg (90%),
m.p. 192 °C (decomp.). Spectroscopic NMR data: 1H NMR
(C6D6): δ = 7.54 (m, 12 H, Ar), 7.34–7.10 (ov m, 4 H, C6H4O2),
6.96–6.85 (ov m, 18 H, Ar), 4.91 (m, 2 H, η6-C6H4O2), 4.11 (m, 2
H, η6-C6H4O2); 11B δ: 15.1 (sharp) ppm. 13C{1H} NMR (C6D6): δ
24.0 Hz), 19.1 ppm. 31P{1H} NMR (C6D6): δ = –10.1 ppm.
C39H34BIrO4P2 (831.74): calcd. C 56.31, H 4.13; found C 56.67, H
4.08.
General Procedure for the Hydroboration of Alkenes: To a stirred
C6D6 (0.5 mL) solution of alkene and the desired iridium catalyst
(2 mol-%) was added the appropriate borane (1 molar equiv.) in
C6D6 (0.5 mL). The reaction was allowed to proceed at room temp.
for 18 h at which point the reaction was analyzed by multinuclear
NMR spectroscopy and compared to known compounds.[5a]
= 152.8, 152.6, 141.6, 136.1 (t, JC-P = 28.6 Hz), 134.5 (t, JC-P
=
Isomerizing Hydroboration of Methyl Oleate: To a stirred THF
(1 mL) solution of methyl oleate (50 mg, 0.17 mmol) and Ir(η2-
coe)(PCy3)(η6-catBcat) (3 mg, 0.003 mmol) was added a THF
(1 mL) solution of pinacolborane (65 mg, 0.51 mmol). The reaction
was heated at reflux for 18 h at which point solvent was removed
under vacuum and the resultant oil analyzed by multinuclear NMR
spectroscopy in CDCl3. Selected spectroscopic 13C{1H} NMR
spectroscopic data: δ: 11.3 (br., C-B).
5.7 Hz), 129.6, 127.5 (t, JC-P = 4.7 Hz), 125.4, 119.1, 118.8, 109.9,
108.9, 85.1, 80.3 ppm. 31P{1H} NMR (C6D6): δ = 8.4 ppm.
C48H38BIrO4P2 (943.89): calcd. C 61.07, H 4.07; found C 61.33, H
4.15.
Ir(dppm)(η6-catBcat) (4): To a toluene (5 mL) solution of Ir(acac)-
(dppm) (163 mg, 0.24 mmol) was added a toluene (5 mL) solution
of B2cat3 (83 mg, 0.24 mmol). The reaction was heated at 100 °C
for 18 h. Upon cooling to –30 °C, a solid precipitated and was col-
lected by suction filtration. The solid was redissolved in hot toluene
(10 mL) and stored at –30 °C. After 3 days, a precipitate was col-
X-ray Crystallography: Crystals of 1, 2, and 6 were grown from
saturated THF solutions, at –30 °C. Single crystals were coated
with Paratone-N oil, mounted using a polyimide MicroMount and
lected by suction filtration and washed with Et2O (3ϫ1 mL) to frozen in the cold nitrogen stream of the goniometer. A hemisphere
afford 4 as an orange-yellow solid; yield 95 mg (49%), m.p. 158–
162 °C. Spectroscopic NMR data: H NMR (C6D6): δ = 7.56 (m,
of data was collected on a Bruker AXS P4/SMART 1000 dif-
fractometer using ω and θ scans with a scan width of 0.3° and 10 s
1
8 H, Ar), 7.13–6.97 (ov m, 14 H, Ar & C6H4O2), 6.87–6.80 (ov m, exposure times. The detector distances were 5 cm. All data collec-
2 H, C6H4O2), 5.84 (2nd order m, 2 H, η6-C6H4O2), 4.52 (2nd order
tion was performed at 173 K with the exception of 6 which was
Eur. J. Inorg. Chem. 2011, 2433–2438
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2437

G. M. Lee, C. M. Vogels, A. Decken, S. A. Westcott
FULL PAPER
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We thank National Sciences and Engineering Research Council of
Canada, the American Chemical Society-Petroleum Research Fund
(Grant Number 50093-UR3), the Canada Research Chair Pro-
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Shrubby Durant and Roger Smith are thanked for their valuable
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Received: January 18, 2011
Published Online: April 7, 2011
2438
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Eur. J. Inorg. Chem. 2011, 2433–2438