Rhodium(I) complexes of the conformationally rigid IBioxMe4 ligand: Preparation of mono-, bis-, and tris-ligated NHC complexes

Article abstract of DOI:10.1021/om500332n

The preparation and characterization of a series of mono-, bis-, and tris-ligated rhodium(I) complexes of Glorius' conformationally rigid bioxazoline-derived N-heterocyclic carbene ligand IBioxMe₄ are described. Through reaction of [Rh(COE)₂Cl]₂ (COE = cis-cyclooctene) with isolated IBioxMe₄, [Rh(IBioxMe ₄)(COE)Cl]₂ (1), trans-[Rh(IBioxMe₄) ₂(COE)Cl] (2), and [Rh(IBioxMe₄)₃Cl] (3) were each isolated by careful choice of the reaction conditions. Further substitution and salt metathesis reactions of 1-3 were investigated, and derivatives containing CO, norbornadiene, and cyclopentadienyl ancillary ligands were readily isolated. Notably, halide abstraction from 2 and 3 using Na[BAr ^F₄] (Ar^F = 3,5-C₆H ₃(CF₃)₂) resulted in the formation of low-coordinate T-shaped cis-[Rh(IBioxMe₄)₂(COE)][BAr ^F₄] (9) and [Rh(IBioxMe₄)₃][BAr ^F₄] (11). The solid-state structures of 2, 9, and 11 each feature IBioxMe₄ ligands that bind unusually with tilted coordination geometries.

Full text of DOI:10.1021/om500332n

Article
pubs.acs.org/Organometallics
Rhodium(I) Complexes of the Conformationally Rigid IBioxMe4
Ligand: Preparation of Mono‑, Bis‑, and Tris-ligated NHC Complexes
Adrian B. Chaplin*
Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, U.K.
*
S Supporting Information
ABSTRACT: The preparation and characterization of a series of mono-, bis-, and tris-ligated rhodium(I) complexes of Glorius’
conformationally rigid bioxazoline-derived N-heterocyclic carbene ligand IBioxMe4 are described. Through reaction of
[
Rh(COE) Cl] (COE = cis-cyclooctene) with isolated IBioxMe , [Rh(IBioxMe )(COE)Cl] (1), trans-[Rh(IBioxMe ) (COE)-
2 2 4 4 2 4 2
Cl] (2), and [Rh(IBioxMe ) Cl] (3) were each isolated by careful choice of the reaction conditions. Further substitution and salt
4
3
metathesis reactions of 1−3 were investigated, and derivatives containing CO, norbornadiene, and cyclopentadienyl ancillary
F
F
ligands were readily isolated. Notably, halide abstraction from 2 and 3 using Na[BAr ] (Ar = 3,5-C H (CF ) ) resulted in the
4
6
3
3 2
F
F
formation of low-coordinate T-shaped cis-[Rh(IBioxMe ) (COE)][BAr ] (9) and [Rh(IBioxMe ) ][BAr ] (11). The solid-
4
2
4
4 3
4
state structures of 2, 9, and 11 each feature IBioxMe ligands that bind unusually with tilted coordination geometries.
4
8
INTRODUCTION
even been shown to support double cyclometalation, and
subsequent reactivity of NHC-based metallocycles can lead to
■
With generally stronger σ-donating characteristics and
orthogonal steric profiles compared to phosphine ligands, N-
heterocyclic carbenes (NHCs) have quickly emerged as a
powerful class of carbon-based ligand in organometallic
6a,7,9
alkyl dehydrogenation.
However, although cyclometalation
10
reactions are of interest in their own right, they can represent
unwanted and potentially detrimental reactivity characteristics
of NHC-based metal complexes.
Recognizing that substituent flexibility, particularly rotation
about N-aryl/alkyl bonds, is a key prerequisite for cyclo-
metalation reactions of NHC ligands, conformationally rigid
analogues were targeted as a means to attenuate such reactivity,
while retaining the desirable electronic and steric properties of
the ligand class. With such features in mind, bioxazoline-derived
1
chemistry and catalysis. While in the majority of applications
3
spectator roles are intended, intramolecular C(sp )−H bond
activation reactions of coordinated NHC ligands are increas-
ingly being observed when partnered with reactive late
transition metal fragments. Examples include activation of
the N-aryl and alkyl substituents of common NHC ligands: 1,3-
diisopropyl-4,5-dimethylimidazol-2-ylidene (I Pr Me ), 1,3-bis-
tert-butylimidazol-2-ylidene (I Bu), 1,3-bis-mesitylimidazol-2-
ylidene (IMes), and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-
ylidene (IPr), among others (Chart 1). The IMes ligand has
2
i
2
2
t
NHC ligands (IBiox) developed by Glorius and co-workers
11,12
were identified from the literature.
IBiox ligands are
3
−7
particularly notable for their application in palladium-catalyzed
cross-coupling reactions, although their coordination chemistry
has not been widely explored. Given the structural similarity
Chart 1. Cyclometalated NHC Topologies
i
t
with I Pr Me and I Bu, the tetramethyl-substituted IBiox
2
2
ligand, IBioxMe , was chosen for investigation (Scheme 1).
4
With a view of contrasting the cyclometalation processes
t
3,4
observed by Nolan and others in rhodium complexes of I Bu,
the coordination chemistry of IBioxMe with rhodium was
4
targeted and a range of mono-, bis-, and tris-ligated derivatives
are reported herein. Some aspects of this chemistry were
Received: March 28, 2014
Published: June 2, 2014
©
2014 American Chemical Society
3069
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Organometallics
Article
Scheme 1. Hypothesized Reactivity Modulation
Isolated 1 is stable in solution, showing no apparent reaction
1
after 7 days in C D6 solution (293 K) by H NMR
6
spectroscopy. While A has also been reported to be stable in
3
t
benzene solution, in the presence of excess I Bu sequential
formation of monomeric cyclometalated derivatives C and D
occurs, where these complexes contain one and two cyclo-
t
t
metalated I Bu ligands (I Bu′), respectively (Chart 2). Addition
t
Chart 2. Cyclometalated Rhodium Complexes of I Bu
published as a communication (i.e., tris-NHC complexes 11
1
3
and 12).
RESULTS AND DISCUSSION
Synthesis of Free Carbene. The target imidazolium pro-
■
ligand IBioxMe ·HOTf was synthesized in four steps, from
4
commercially available 2-amino-2-methylpropanol and dieth-
of excess IBioxMe4 similarly resulted in fragmentation of
11
yloxalate, as previously described by Glorius and co-workers.
dimeric 1 in C D solution. However, instead of intramolecular
6
6
The corresponding free carbene ligand was readily formed by
reaction of the pro-ligand with the strong hindered base
activation of the NHC ligand, mixtures of the bis- and tris-
NHC complexes trans-[Rh(IBioxMe ) (COE)Cl] (2) and
13
4 2
K[N(SiMe ) ] in THF (Scheme 2). In this manner IBioxMe4
3
2
[
Rh(IBioxMe ) Cl] (3) were obtained, the latter almost
4 3
completely insoluble in benzene (Scheme 4). Following this
Scheme 2. Preparation of IBioxMe4
Scheme 4. Reaction of 1 with IBioxMe4
was isolated in 80% yield, following removal of volatiles in
vacuo and extraction with pentane, and stored under argon in a
glovebox. Satisfactory microanalyses were obtained, and the
free carbene was fully characterized in C D solution by NMR
6
6
spectroscopy. C2v symmetry is observed in solution with the
carbene resonance at 190.1 ppm, significantly downfield from
the pro-ligand (112.4 ppm) and consistent with other
1
2b,14
systems.
Reaction of IBioxMe with [Rh(COE) Cl] . Following the
4
2
2
3
procedure of Nolan and co-workers, reaction of IBioxMe with
4
the rhodium(I) precursor [Rh(COE) Cl] (COE = cis-
2
2
cyclooctene) in pentane resulted in the formation of dimeric
reaction in situ by NMR spectroscopy (C D , 293 K) revealed a
significant rate dependence on the concentration of the NHC
6
6
4
chloro-bridged rhodium(I) complex [Rh(IBioxMe )(COE)Cl]2
(
1), which was isolated in good yield following recrystallization
ligand. With 4 equiv of IBioxMe the initial rate for the
4
from benzene−heptane (66%, Scheme 3). Coordination of the
−6
−1 −1
disappearance of 1 was ca. 3.7 × 10 mol L s , which
increased to ca. 8.2 × 10− mol L
the ligand. After 90% consumption of 1, the resulting ratios of
:3 were 5.8 and 4.5, respectively. These data indicate
6
−1 −1
s
when using 8 equiv of
Scheme 3. Preparation of Dimeric 1
2
approximate first-order dependence on [IBioxMe ] and a faster
4
rate of formation for 2 relative to 3. Given that reaction
between 2 and IBioxMe to give 3 is 2 orders of magnitude
4
slower than the reaction of 1 with IBioxMe (vide infra), the
4
most plausible mechanism for this reaction involves bifurcated
(
associative) ligand substitution chemistry of 1 (Scheme 4). A
COE and carbene ligands was confirmed by the observation of
suggestion that invokes the presence of transient (unobserved)
bis-NHC complex cis-[Rh(IBioxMe ) (COE)Cl] or [Rh-
(IBioxMe ) Cl] in the formation of 3. Throughout these in
1
3
1
C doublet resonances at δ 60.4 ( J
= 17 Hz) and δ 158.3
RhC
4 2
(1
JRhC = 59 Hz), respectively, by NMR spectroscopy. Likewise,
4 2 2
coordinated alkene protons are observed at 2.97 ppm as an
situ reactions no evidence for ligand cyclometalation was
observed, supporting the hypothesized reactivity attenuation of
1
integral 2H multiplet in the H NMR spectrum. These data are
t
3
t
in good agreement with those of the I Bu analogue (A) and
related dimeric complexes [Rh(NHC)(H CCH )Cl]
the conformationally rigid ligand in comparison to I Bu. The
t
ability of I Bu to undergo cyclometalation is further
2
2
2
t
15
(
NHC = IMes, SIMes, IPr, SIPr, I Bu (B)) previously
substantiated using B, which has been reported to undergo
spontaneous intramolecular activation of the NHC ligand,
4
prepared by Crudden and co-workers.
3
070
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Organometallics
resulting in formation of the rhodium(III) dimer [Rh(I Bu′)-
Article
t
To establish if 2 is a kinetically relevant intermediate in the
formation of 3 from 1, in situ NMR experiments were carried
4
(
CH CH )Cl] , C, and metallic rhodium.
2 3 2
Complexes 2 and 3 are most conveniently prepared by direct
reaction between [Rh(COE) Cl] and excess IBioxMe (4.6
equiv) in benzene and were obtained in this way with isolated
yields of 47% and 24%, respectively; the insolubility of 3
enabled easy separation of the two complexes. The structures of
out involving reaction of 2 with excess IBioxMe (2 and 4
4
equiv) in C D6 (293 K). A slow reaction was observed,
2
2
4
6
involving substitution of the COE ligand independent of
[IBioxMe ], with an initial rate for the disappearance of 2 of ca.
4
7.0 × 10− mol L
8
−1 −1
s
and approximate half-life of 82 h. These
2
and 3 were determined by X-ray crystallography (Figure 1)
data suggest a dissociative mechanism for the substitution of
the COE ligand and clearly show the formation of 3 via 2 is not
a kinetically relevant pathway in the reaction of dimeric 1 with
IBioxMe . Consistent with this suggestion, isolated 2 slowly lost
4
COE in solution (ca. 15% decomposition after 24 h in C D at
6
6
2
93 K). Complex 3 is observed during the decomposition;
however, the other species involved have eluded identification
so far.
Coordination Chemistry of 1−3. Seeking to further
explore the coordination chemistry of these rhodium(I)
IBioxMe4 complexes, incorporation of other carbon-based
ancillary ligands was targeted. To this end, reactions of 1
with CO, norbornadiene (NBD), and Na[Cp] were inves-
tigated (Scheme 5). Under an atmosphere of CO, 1 was rapidly
Scheme 5. Preparation of 4−6
Figure 1. Solid-state structures of 2 (left) and 3 (right). Thermal
ellipsoids for selected atoms are drawn at the 50% probability level;
most hydrogen atoms are omitted for clarity; only one of the two
independent molecules is shown for each complex (Z′ = 2 for both 2
and 3). Selected bond lengths (Å) and angles(deg): 2, Rh1−Cl2,
2
2
.4231(5); Rh1−C3, 2.125(2); Rh1−C4, 2.117(2); Rh1−C11,
.100(2); Rh1−C26, 2.026(2); C3−C4, 1.411(3); Cl2−Rh1−Cnt-
(
1
1
C3,C4), 175.10(2); C11−Rh1−C26, 167.49(7); Θ (@C11),
NHC
56.50(14); Θ
(@C26), 172.98(13); ΘNHC(@C11A),
NHC
64.72(13); Θ (@C26A), 170.1(2); 3, Rh1−Cl2, 2.4224(14);
NHC
Rh1−C3, 2.046(5); Rh1−C18, 2.060(5); Rh1−C33, 2.016(5); Cl2−
Rh1−C33, 177.3(2); C3−Rh1−C18, 169.2(2); all Θ > 175.
NHC
and corroborated in solution by NMR spectroscopy. Both
complexes adopt the expected square planar geometries,
although for 2 (with two crystallographically independent,
but structurally similar complexes) there is a significant degree
of distortion: the C11−Rh1−C26 angle deviating from linearity
(<10 min) and quantitatively (by NMR spectroscopy)
converted to the bis-carbonyl complex cis-[Rh(IBioxMe )-
4
(CO) Cl] (4) (solid-state structure in Figure 2). Complexes of
2
the formulation cis-[M(NHC)(CO) Cl] (M = Rh, Ir) have
2
been widely used to probe the electronic and steric character-
22
(
167.49(7)°; 167.47(7)° for Rh1A equivalent). Interestingly,
istics of NHC ligands (Table 1). Notably, the Tolman
23
one of the IBioxMe4 ligands binds unusually, pitching
electronic parameter (TEP) for the NHC ligand can be
significantly out of plane as quantified by a nonlinear NHC
1
6
centroid−C
−Rh angle (ΘNHC)
of 156.50(14)°
164.72(13)° for Rh1A equivalent). Such large deviations
from planar coordination are rare in transition metal
NCN
(
1
7,18
complexes
and notably more pronounced in 2 in
comparison to related [Rh(SIMes)(PPh )(H CCH )Cl]
3
2
2
4
(
(
(
Θ
= 170.5°), trans-[Rh(SIMes) LCl] (L = N , O , CO
NHC 2 2 2
19
E); Θ
NHC
= 177.4−178.5°), and trans-[Ir(NHC) (COE)Cl]
NHC
2
20
Θ
= 169.6−178.4°). This tilting is attributed to steric
interactions between the NHC and the coordinated COE
ligands and borne out through the presence of close {COE}
CH ···H C{IBioxMe } contacts of ca. 3.6 Å (sum of van der
2
3
4
Figure 2. Solid-state structures of 4 (left) and 5 (right). Thermal
ellipsoids for selected atoms are drawn at the 50% probability level;
most hydrogen atoms are omitted for clarity. Selected bond lengths
Waals radii = 3.4 Å). Moreover in line with this reasoning,
essentially planar IBioxMe coordination is observed when
4
COE is replaced with a less bulky ancillary ligand (i.e., 7, vide
infra). Complex 3 is an NHC analogue of Wilkinson’s catalyst,
examples of which have been previously reported by Lappert et
(
Å) and angles (deg): 4, Rh1−Cl2, 2.3519(5); Rh1−C3, 1.830(2);
Rh1−C5, 1.897(2); Rh1−C7, 2.069(2); Θ (@C7), 178.97(13); 5,
Rh1−Cl2, 2.3642(15); Rh1−C3, 2.048(6); Rh1−C18, 2.197(6);
Rh1−C19, 2.182(6); Rh1−C21, 2.098(6); Rh1−C22, 2.105(6);
NHC
2
1
al. The IBioxMe ligands twist in a helical fashion, and all
4
ΘNHC are greater than 175° in the solid-state structure of 3.
Θ
(@C3), 177.2(4).
NHC
3
071
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Organometallics
Article
Table 1. Steric and Electronic Properties of NHC Ligands
substituted further with carbon monoxide in the presence of
F
F
Derived from cis-[M(NHC)(CO) Cl]
Na[BAr ] (Ar = 3,5-C H (CF ) ), as a halide-abstracting
4 6 3 3 2
2
agent, to give the bis-carbonyl complex trans-[Rh-
(IBioxMe ) (CO) ][BArF ] (8) (Scheme 6). The structures
a
ν(CO)
TEP [calcd]
−1
−1
b
M
NHC
[CH Cl ]/cm
(expt)/cm
%Vbur
ref
4 2
2
4
2
2
Rh
IBioxMe4
2081
2000
2053
32.0
this
work
11
a
Scheme 6. Reactions of Bis-IBioxMe Complexes
4
Ir
IBioxMe4
2066
2076
2065
2065
2066
1982
1996
1981
1980
1980
2052
i
c
Rh
Ir
I Pr Me
2051
28.0
28.1
37.6
33.8
28
2
d
2
29
ICy
2051 (2050)
2050
25
t
Ir
I Bu
25
2
9
Ir
IMes
2051 (2051)
25
a
Tolman electronic parameter calculated using established correlations
22 b
with average ν(CO) value.
Calculated using SambVca (sphere
radius = 3.5, distance from center of sphere = 2.0, mesh spacing = 0.5,
27 c
hydrogens omitted, bondi radii scaled by 1.17). Estimated from X-
i
30 d
ray structure of [Rh(I Pr Me )(COD)(OH)].
ICy = 1,3-bis-
2
2
cyclohexylimidazol-2-ylidene.
determined from the carbonyl stretching frequencies of cis-
[
M(NHC)(CO) Cl], avoiding the need to prepare toxic nickel
2
24,25
adducts.
Using this approach the calculated TEP for
−1
IBioxMe using 4 (2053 cm ) is in good agreement with that
4
determined using the previously reported iridium analogue cis-
−1
11
[
Ir(IBioxMe )(CO) Cl] (2052 cm ). Thus, in line with the
4 2
presence of the electronegative oxygen substituents, the TEP
a
F
−
[
BAr ] anions omitted for clarity
4
for IBioxMe appears to be marginally larger in magnitude than
4
i
−1
t
−1
those of I Pr Me (2051 cm ) and I Bu (2050 cm ). The
2
2
steric characteristics of IBioxMe have also been quantified
through measurement of the NHCs percentage buried volume
4
of both carbonyl complexes were established through a
combination of NMR and IR spectroscopy (C , 7; D , 8),
2v
2h
(
%V ) using the solid-state structure of 4 for the relevant
bur
alongside crystallographic characterization (Figure 3). A more
2
6,27
t
i
2 2
upfield 13C resonance for the NHC (141.0 vs 160.5 ppm),
calculation.
Steric bulk increases in the order I Pr Me <
1
IBioxMe < I Bu, with the %V of IBioxMe (32.0) similar to
4
bur
4
reduced carbonyl J
coupling constant (64 vs 82 Hz), and
RhC
−1
that of aryl-substituted IMes (33.8)
In comparison to the reaction with CO, the reaction between
and NBD to afford [Rh(IBioxMe )(NBD)Cl] (5) occurred
higher carbonyl stretching frequency (2024 vs 1942 cm ) are
observed for 8 in comparison to 7, fully consistent with the
more electron-deficient nature of the metal center. While there
are a number of examples of complexes of the formulation
[Rh(NHC) (CO)Cl] (e.g., E),
nonchelating precedent for 8 to the author’s knowledge.
1
4
significantly slower, with an approximate half-life of 3.6 h.
Indeed, 5 was more readily prepared by reaction of IBioxMe4
5
x,19,28,32
there is only one
2
33
with the dimeric rhodium(I) precursor [Rh(NBD)Cl] (88%
2
isolated yield). The solid-state structure of 5 (Figure 2)
resembles that of 4 and is otherwise unremarkable, as are NMR
data. Placing 5 under an atmosphere of CO quantitatively
afforded 4 (by NMR spectroscopy) alongside free NBD,
therefore offering an alternative synthetic route to the bis-
carbonyl compound (Scheme 5).
Targeting the preparation of a low-coordinate bis-NHC
complex derivative, 2 was reacted with the halide-abstracting
F
4
agent Na[BAr ] in difluorobenzene at reduced temperature
(
(
(
253 K). From this reaction, cationic cis-[Rh-
F
4
IBioxMe ) (COE)][BAr ] (9) was isolated in good yield
4
2
71%). Formation of 9, a formally 14 valence electron complex,
1
Cyclopentadienyl complex [Rh(IBioxMe )(Cp)(COE)] (6)
4
was readily apparent by H NMR spectroscopy (250 K) by a
resulted from salt metathesis of 1 in CH Cl using Na[Cp] and
2
2
2H coordinated alkene resonance centered at δ 3.97, which
13
was isolated in good yield (72%). Coordination of the
hydrocarbon ligands is apparent by the presence of 5H and
gave a strong HMQC cross-peak with a C signal at δ 76.3,
F
−
1
(
2H resonances for the [BAr ] anion, and two singlet signals
4
2
H signals at δ 5.11 and 2.11 together with characteristic
8H, 24H) for the IBioxMe ligands. The complex is thus
4
13
1
1
doublets in the1 C{ H} NMR spectrum at δ 86.2 ( J
= 3
RhC
highly fluxional in solution (500 MHz). On the basis of the low
stability of 9 (vide infra) and to reconcile the high time-
averaged symmetry implicated from the IBioxMe4 proton
resonances (D ), a mechanism involving COE ligand
−
Hz) and 53.1 ( J = 17 Hz) for the [Cp] and COE ligands,
RhC
respectively; the carbene signal was observed at δ 159.7 (d,
1
JRhC = 66 Hz). Surprisingly, few examples of nonchelating
2
h
NHC rhodium(I) cyclopentadienyl complexes are known,
dissociation is suggested. Cooling further to 200 K did not
halt this process, although the onset of decoalescence was
noted, particularly through resolution of inequivalent methyl-
ene signals for the NHC backbone (see SI).
Subsequent to the NMR characterization, a relatively low
quality solid-state structure of 9 was determined, containing
two crystallographically independent, but structurally similar
molecules (Z′ = 2), one of which is shown in Figure 3. The
refined structure unambiguously confirms coordination of the
[
[
Rh(IMes)(C R )(H CCH )] (R = H (F), Me) and
5
5
2
2
Rh(SIMe)(Cp)(CO)] (SIMe = 1,3-bis-methylimidazolin-2-
31
ylidene) being the only precedents. The NMR characteristics
of 6 are in agreement with those reported for F: δ
84.7 (d,
C5H5
1
1
J
= 4 Hz), δC2H4 24.3 (d, J
= 16 Hz), and δNCN 185.0
RhC
RhC
(
1J
= 70 Hz).
RhC
Reaction of bis-NHC 2 with carbon monoxide readily
afforded trans-[Rh(IBioxMe ) (CO)Cl] (7), which could be
4
2
3
072
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Organometallics
Article
Figure 3. Solid-state structures of 7−10 (left to right). Thermal ellipsoids for selected atoms are drawn at the 50% probability level; most hydrogen
atoms, minor disordered components, anions, and solvent molecules are omitted for clarity; only one of the two independent molecules is shown for
9
(Z′ = 2); symmetry operations −x, −y, −z (7) and 2−x, +y, 3/2−z (10) were used to generate the starred atoms. Selected bond lengths (Å) and
angles (deg): 7, Rh1−Cl2, 2.386(2); Rh1−C3*, 1.807(6); Rh1−C5, 2.050(2); C5−Rh1−C5* 180.00; Θ (@C5), 176.8(2); 8, Rh1−C2,
NHC
1
.910(3); Rh1−C4, 1.917(3); Rh1−C6, 2.063(2); Rh1−C21, 2.061(2); C6−Rh1−C21, 177.53(9); all Θ (NHC) > 175; 9, Rh1−C2, 2.196(14);
NHC
Rh1−C3, 2.123(14); Rh1−C4, 2.56(2); Rh1−C10, 2.099(14); Rh1−C25, 1.971(15); all other Rh1−C > 3.0; C10−Rh1−C25, 100.5(6); Θ (@
NHC
C10), 168(1); Θ (@C25), 178.5(12); Rh1A−C4A, 2.94(2); all other noncoordinated Rh1A−C > 3.0; Θ (@C10A), 168.4(11); ΘNHC(@
NHC
NHC
C25A), 177.8(13); 10, Rh1−C2, 2.163(2); Rh1−C4, 2.159(2); Rh1−C6, 2.121(2); C6−Rh1−C6*, 101.51(9); Θ (@C6), 173.05(12).
NHC
a
COE and IBioxMe ligands, with 9 adopting an overall T-
Scheme 7. Reactions of Tris-IBioxMe Complexes
4
4
shaped coordination geometry. The complex is stabilized by an
agostic interaction with the COE ligand, a feature that is much
more pronounced in one of the independent molecules (Rh1···
C4 = 2.56(2) Å) than the other (Rh1A···C4A = 2.94(2) Å).
Notably, the methyl substituents of the IBioxMe ligand remain
4
distant from the metal center, with the closest approaches
having Rh···C distances of 3.67(4) and 3.18(3) Å in the
independent molecules (containing Rh1 and Rh1A, respec-
i
t
+
34
tively). [Rh(P Bu )(P Bu CH CH CHCH )] (G) and
3
2
2
2
2
[
(
Rh{((2,6-Me C H )NMeC) CH}(L)] (L = norbornene
2 6 3 2
H), COE (I)) are closely related rhodium(I) alkene
3
5
complexes; G and H are stabilized by strong agostic
interactions (Rh···C = 2.41 and 2.53 Å, respectively), while I
is considered a genuinely low coordinate T-shaped complex
with Rh···C distances of 2.89 and 2.97 Å. Consistent with the
T-shaped formulation of 9, the NHC binding trans to the open
coordination site does so with a significantly shorter Rh−CNCN
bond distance (Rh1, 1.971(15) vs 2.099(14) Å; Rh1A,
a
F
−
[BAr ] anions omitted for clarity.
4
1
.921(17) vs 2.070(15) Å).
In both CD Cl and difluorobenzene solution at 298 K, 9
2
2
undergoes decomposition via loss of COE, although this
process is much faster in the former (t1/2 = 0.54 h vs 6.6 h),
presumably reflecting the differing coordinating ability of the
two solvents; the resulting mixtures have so far proven
intractable to further characterization in either solvent.
Complex 9 does, however, act as a source of the reactive
+
{
Rh(IBioxMe ) } fragment in solution, affording 8 and the
4
2
F
diene complex [Rh(IBioxMe ) (NBD)][BAr ] (10) quantita-
4
2
4
tively by NMR spectroscopy on addition of carbon monoxide
and NBD, respectively (Scheme 6). The formation of 10 was
further verified by independent synthesis from 5, IBioxMe , and
Figure 4. Solid-state structures of 11 (Z′ = 2). Thermal ellipsoids for
selected atoms are drawn at the 50% probability level; most hydrogen
atoms, minor disordered components, anions, and solvent molecule
are omitted for clarity. Selected distances (Å): Rh1−C13, 3.273(3);
4
F
Na[BAr ], and the solid-state structure is shown in Figure 3.
4
Encouraged by the formation of 9 from 2, reaction of tris-
F
NHC complex 3 with Na[BAr ] in CH Cl at room
4
2
2
Rh1−C29, 3.574(3); Rh1A−C13A, 3.421(3); Rh1A−C29A,
temperature led to the isolation of cationic formally 14 valence
13
3
.191(3).
F
electron Rh(I) complex [Rh(IBioxMe ) ][BAr ] 11 in 65%
4
3
4
yield (Scheme 7, Figure 4). Complex 11 can also be prepared as
previously described using a high-yielding one-pot procedure
3
073
dx.doi.org/10.1021/om500332n | Organometallics 2014, 33, 3069−3077

Organometallics
Article
involving reaction between [Rh(COE) Cl] and IBioxMe in
steric interactions between the ancillary chloride/carbonyl
2
2
4
F
difluorobenzene, using Na[BAr ] as a halide abstractor (83%
ligand and the cis IBioxMe ligands counteracting NHC tilting
4
4
1
3
isolated yield). In contrast to 9, the tris-NHC complex was
found to be completely stable in CD Cl and difluorobenzene
(CH ···Cl = 3.38−3.72 Å, cf. sum of van der Waals radii = 3.45
3
Å; CH ···OC = 3.35−3.76 Å, cf. sum of van der Waals radii =
2
2
3
13
solution at room temperature (over 48 h under argon). This
increased stability is readily accounted for by the stronger
3.40 Å). Likewise in the context of 9, only slight tilting is
observed in 10, containing cis IBioxMe ligands (Θ
=
4
NHC
donor characteristics of IBioxMe in comparison to COE and
173.05(12)°).
4
confirmed by rapid COE substitution by IBioxMe on addition
As reported earlier, complex 11 shows no reaction with
4
1
of the NHC to 9, forming 11 quantitatively by H NMR
excess IBioxMe , PCy , or NBD, but reacts rapidly with carbon
4
3
F
spectroscopy (Scheme 7).
monoxide to generate [Rh(IBioxMe ) (CO)][BAr ], 12
4 3 4
13
As noted by Reed reporting on the solid-state structure of
(Scheme 7). Notably, the static C2v structure observed for
+
[
Rh(PPh ) ] (J), the adoption of a T-shaped geometry is
12 in solution at room temperature (400 MHz) contrasts with
3
3
+
electronically favored over trigonal planar for three-coordinate
previously reported tris-NHC complexes [Rh(NHC) (CO)]
3
8
36
i
d metal centers to allow for diamagnetism (Figure 5).
[NHC = I Pr Me , ICy], which undergo restricted rotation of
2
2
the NHC ligands (about Rh−CNCN) at room temperature (500
43
MHz). This difference in behavior is presumably attributed to
the more imposing steric profile of IBioxMe compared to
4
i
I Pr Me and ICy, a feature quantified by %V values listed in
2
2
bur
Table 1 (ca. 32 vs 28).
SUMMARY AND OUTLOOK
■
A series of new rhodium(I) complexes of Glorius’ conforma-
tionally rigid bioxazoline-derived N-heterocyclic carbene ligand
t
IBioxMe have been prepared. In contrast to nonrigid I Bu,
4
complexes of IBioxMe4 appear to be more resistant to
cyclometalation reactions, allowing the coordination of up to
three NHC ligands to rhodium via the common (isolated)
dimeric intermediate [Rh(IBioxMe )(COE)Cl] (1), i.e.,
8
Figure 5. Frontier molecular orbitals for d metal centers in idealized
41
trigonal planar and T-shaped coordination geometries.
4
2
8
Moreover, T-shaped low-coordinate d metal fragments can be
stabilized through formation of agostic interactions with alkyl
ligand appendages, due to the presence of accessible frontier
isolation of trans-[Rh(IBioxMe ) (COE)Cl] (2) and [Rh-
4
2
(
IBioxMe ) Cl] (3). Substitution and salt metathesis reactions
4 3
of 1−3 were investigated, and derivatives containing CO,
norbornadiene, and cyclopentadienyl ancillary ligands were
readily isolated. In search of low-coordinate complexes of
IBioxMe , 2 and 3 were reacted with Na[BAr ] and led to the
isolation of T-shaped cis-[Rh(IBioxMe ) (COE)][BAr ] (9)
orbitals of suitable symmetry and energy (i.e., b and 2a ). This
facet is borne in the solid state for rhodium(I) phosphine
1
1
i
+
F
complexes G, H, and J (Rh···C = 2.62 Å), [Rh(P Pr ) ] (Rh···
3
3
4
4
3
7
t
t
t
2
F
C = 2.49 Å), and [Rh( Bu PCH P Bu )(CH Bu)] (Rh···C =
2
2
2
4 2 4
3
8
F
2
.49 Å), as well as platinum(II) NHC and phosphine
and [Rh(IBioxMe ) ][BAr ] (11). Although 9 exhibits low
4
3
4
+
6b
complexes [Pt(IPr)(IPr′)] (Pt···C = 2.89 Å) and [Pt-
solution stability, readily losing COE at room temperature, 11
shows excellent stability. Using these complexes as pertinent
i
+
39
(
P Pr ) (Me)] (Pt···C = 2.86 Å). As an additional interesting
3 2
example, phosphine-boryl-pincer complex [Rh-
examples, the rigid geometry of the IBioxMe ligand appears to
4
t
{
(P Bu CH ) (BN C H )}] adopts intermolecular σ-C−H
bond interactions between individual complexes in the absence
of accessible alkyl groups. In the case of 11, however, there is
no evidence for any significant agostic interactions between the
NHC ligands and the metal center in both solution (highly
fluxional at 298 K) and the solid state (Rh···C distances for the
2
2
2
2
6
4
preclude interaction of the metal center with the ligand’s alkyl
appendages as hypothesized. The large steric profile of
IBioxMe (%V = 32.0) also leads to interesting tilted NHC
40
4
bur
coordination geometries (2, 9, and 11). The electronic
structure and additional reactivity of these complexes is
currently being investigated together with that of iridium
analogues. These results will be reported in due course.
13
methyl substituents >3.1 Å). Thus, the rigid geometry of the
IBioxMe ligand appears to prohibit any significant interaction
4
of the methyl substituents in both 9 and 11.
EXPERIMENTAL SECTION
■
Inspection of the IBioxMe coordination geometries in 9 and
1 reveals tilted binding for those cis to open coordination
4
General Experimental Methods. All manipulations were
performed under an atmosphere of argon, using Schlenk and glovebox
techniques. Glassware was oven-dried at 130 °C overnight and flamed
under vacuum prior to use. Anhydrous C H , CH Cl , heptane, and
1
sites: Θ = 168(1)/168.4(11)° for 9 and 160.0(2)−
NHC
1
3
1
73.1(2)° for 11. Given that related distortions observed in
6
6
2
2
coordinatively saturated 2 can be confidently ascribed to steric
effects, and taking into account the bulky nature of IBioxMe4
pentane (<0.005% H O) were purchased from ACROS or Aldrich and
2
freeze−pump−thaw degassed three times before being placed under
and the absence any significant Rh···H C interactions (Rh···C
argon. C D , CD Cl , and 1,2-difluorobenzene (C H F ) were dried
6 6 2 2 6 4 2
3
42
over CaH and vacuum distilled, and the latter stored over thoroughly
≥
3.18 Å and Rh···H ≥ 2.44 Å), it seems reasonable to
2
vacuum-dried 3 Å molecular sieves. Norbornadiene was dried over Na,
vacuum distilled, and stored over thoroughly vacuum-dried 3 Å
similarly attribute the unusual NHC geometries in 9 and 11 to
steric effects. Related phenomena in main group bis-NHC
complexes of gallium and indium have been reported, with
11
44
molecular sieves. IBioxMe ·HOTf, [Rh(COE) Cl] , [Rh(NBD)-
4
2
2
45
46
F
47
Cl]2, Na[Cp], and Na[BAr ] were synthesized using literature
4
Θ
values ranging from 144.8° to 154.6° and attributed to π-
NHC
procedures. All other solvents and reagents are commercial products
and were used as received. NMR spectra were recorded on Bruker
DPX-400, AV-400, and DRX-500 spectrometers at 298 K unless
otherwise stated. Chemical shifts are quoted in ppm, and coupling
18a
bonding interactions [s(M) to p(CNCN)]. Contrasting with
1, all IBioxMe ligands in coordinatively saturated tris-NHC
1
4
complexes 3 and 12 (vide infra) bind with ΘNHC angles >175°;
3
074
dx.doi.org/10.1021/om500332n | Organometallics 2014, 33, 3069−3077

Organometallics
Article
−
1
constants in Hz. IR spectra were recorded on a PerkinElmer Spectrum
One FT-IR spectrometer. Microanalyses were performed by Stephan
Boyer at London Metropolitan University.
C H ClN O Rh (402.64 g mol ): C, 38.78; H, 4.01; N, 6.96.
13 16 2 4
Found: C, 38.83; H, 4.04; N, 6.88.
1.5. [Rh(IBioxMe )(NBD)Cl] (5). To a mixture of [Rh(NBD)Cl]
4
2
Synthesis of New Compounds.
(0.100 g, 0.22 mmol) and IBioxMe (0.100 g, 0.48 mmol) was added
4
1
.1. IBioxMe . Prepared from IBioxMe ·HOTf as described in an
benzene (5 mL). The resulting suspension was stirred at room
temperature for 2 h before the volatiles were removed in vacuo. The
residue was chromatographed on silica using 1:3 THF−CH Cl (in
4
4
13
earlier communication.
.2. [Rh(IBioxMe )(COE)Cl] (1). To a suspension of [Rh-
1
4
2
2
2
(
COE) Cl] (0.100 g, 0.14 mmol) in pentane (30 mL) was added a
air) and then recrystallized from CH Cl −hexane. Yield = 0.168 g
2
2
2
2
1
solution of IBioxMe4 (0.058 g, 0.28 mmol) in pentane (30 mL)
dropwise over 5 min. The resulting suspension was stirred at room
temperature for 1 h and then filtered. The filtrate was washed with
pentane (2 × 10 mL), and the residue recrystallized from benzene−
(88%, yellow microcrystalline solid). H NMR (CD Cl , 400 MHz): δ
2 2
2
4.69 (app q, J = 2, 2H, CHCH), 4.47 (d, J = 8.2, 2H, OCH2),
HH
2
4.42 (d, J = 8.2, 2H, OCH ), 3.78 (br, 2H, CH CH), 3.56 (app q, J
HH
2
2
= 2, 2H, CHCH), 1.98 (s, 6H, CH ), 1.89 (s, 6H, CH ), 1.37 (td,
= 8.2, J = 1, 1H, CH {NBD}), 1.30 (dt, J = 8.2, J = 1,
HH HH 2 HH HH
3
3
1
2
3
2
3
heptane. Yield = 0.085 g (66%, microcrystalline cream solid). H NMR
J
2
2
(
8
C D , 400 MHz): δ 3.76 (d, J = 8.1, 2H, OCH ), 3.71 (d, J
=
13
1
6
6
HH
2
HH
1H, CH {NBD}). C{ H} NMR (CD Cl , 101 MHz): δ 162.3 (d,
2
2
2
.1, 2H, OCH ), 2.89−3.05 (m, 2H, CH), 2.41−2.65 (m, 4H,
1
1
2
JRhC = 56.5, NCN), 126.1 (s, COCH ), 88.0 (OCH ), 76.9 (d, J
=
RhC
2
2
CHCH ), 2.02 (s, 6H, CH ), 1.80 (s, 6H, CH ), 1.68−1.88 (m, 4H,
3
2
3
3
6, CHCH), 63.9 (d, J
= 5, CH {NBD}), 61.9 (s, C(CH ) ),
1
3
1
RhC 2 3 2
CH {COE}), 1.44−1.65 (m, 4H, CH {COE}). C{ H} NMR (C D ,
1
2
2
6
6
5
(
1.3 (s, CH CH), 49.2 (d, J
= 12, CHCH), 27.1 (s, CH ), 26.0
1
2
RhH
3
1
01 MHz): δ 158.3 (d, J = 59, NCN), 126.4 (s, COCH ), 87.4 (s,
−1
RhC
2
s, CH ). Anal. Calcd for C H ClN O Rh (438.75 g mol ): C,
1
3
18 24
2
2
OCH ), 62.2 (s, C(CH ) ), 60.4 (d, JRhC = 17, CH), 31.2 (s,
2
3 2
4
9.27; H, 5.51; N, 6.38. Found: C, 49.29; H, 5.81; N, 6.22.
.6. [Rh(IBioxMe )(Cp)(COE)] (6). A suspension of 1 (0.060 g, 0.066
CH {COE}), 30.4 (s, CHCH ), 27.5 (s, CH ), 27.2 (s, CH {COE}),
2
2
3
2
1
4
2
9
4.9 (s, CH ). Anal. Calcd for C H N O Rh .0.66(C H ) ([913.62]
65.18 g mol ): C, 52.22; H, 6.68; N, 5.80. Found: C, 52.21; H, 6.91;
N, 5.95. Reproducible microanalyical data were unable to be obtained
between different batches of this product due the presence of variable
3 38 60 4 4 2 6 6
mmol) and Na[Cp] (0.012 g, 0.140 mmol) in CH Cl (2 mL) was
−1
2
2
stirred at room temperature for 3 h. The volatiles were removed in
vacuo, and the product was obtained by extraction of the residue with
1
heptane (2 × 5 mL). Yield = 0.052 g (72%, yellow powder). H NMR
1
13
1
benzene solvate (confirmed by dissolving in CD Cl ). H and C{ H}
2
2
2
(
C D , 400 MHz): δ 5.11 (s, 5H, Cp), 3.70 (d, J = 8.1, 2H,
6
6
HH
NMR spectra are provided in the SI.
.3. trans-[Rh(IBioxMe ) (COE)Cl] (2) and [Rh(IBioxMe ) Cl] (3).
2
OCH ), 3.67 (d, J = 8.1, 2H, OCH ), 2.48−2.58 (m, 2H, CHCH ),
2
HH
2
2
1
4
2
4 3
2
.06−2.15 (m, 2H, CH), 1.70−1.95 (m, 6H, CH {COE}), 1.75 (s,
2
To a solution of [Rh(COE) Cl] (0.150 g, 0.21 mmol) in benzene (10
mL) was added a solution of IBioxMe (0.200 g, 0.960 mmol) in
benzene (10 mL) dropwise (over ca. 1 min). The resulting solution
was stirred at room temperature for 24 h, during which time 3
crystallized. Complex 3 was isolated by filtration and washed with
benzene (2 × 2 mL), the washings being discarded. Yield = 0.080 g
24%/Rh, deep yellow crystalline solid). Addition of excess heptane to
the reaction filtrate afforded 2. Yield = 0.140 g (47%/Rh, yellow
microcrystalline solid). Higher yields of 3 can be achieved using a
larger excess of IBioxMe ; for example, repeating using 8 equiv of
ligand gave a 55% yield of 3 after 24 h.
2
2
6
H, CH ), 1.48−1.62 (m, 4H, CH {COE}), 1.32 (s, 6H, CH ).
3
2
3
4
13
1
1
C{ H} NMR (C D , 101 MHz): δ 159.7 (d, J = 66, NCN),
6
6
RhC
1
1
25.6 (s, COCH ), 87.2 (s, OCH ), 86.2 (d, J
= 3, Cp), 62.4 (s,
RhC
= 17, CH), 34.7 (s, CH {COE}), 33.9 (s,
2
2
1
C(CH ) ), 53.1 (d, J
3
2
RhC
2
CH {COE}), 27.3 (s, CH {COE}), 27.3 (s, CH ), 23.2 (s, CH ).
2
2
3
3
−1
Anal. Calcd for C H N O Rh (486.45 g mol ): C, 59.26; H, 7.25;
24
35
2
2
(
N, 5.76. Found: C, 59.40; H, 7.35; N, 5.83.
.7. trans-[Rh(IBioxMe ) (CO)Cl] (7). A solution of 2 (0.050 g,
1
4
2
0
.071 mmol) in benzene (2 mL) was placed under CO (1 atm) and
4
stirred at room temperature for 24 h. The volatiles were removed in
1
2
vacuo, and the crude product was recrystallized from CH Cl −heptane
2
2
Data for 2. H NMR (C D , 400 MHz): δ 3.93 (d, J = 7.9, 4H,
6
6
HH
2
at room temperature. Yield = 0. 035 g (85%, pale yellow
OCH ), 3.80 (d, J = 7.9, 4H, OCH ), 3.19−3.28 (m, 2H, CH),
2
HH
2
1
microcrystalline solid). H NMR (CD Cl , 400 MHz): δ 4.56 (d,
2
2
2
1
.50−2.61 (m, 2H, CHCH ), 2.13 (s, 12H, CH ), 1.77 (s, 12H, CH ),
2
3
3
2
2
JHH = 8.3, 4H, CH ), 4.52 (d, J = 8.3, 4H, CH ), 1.93 (s, 12H,
2
HH
1
2
.71−1.85 (obscured m, 4H, CH {COE}), 1.52−1.62 (m, 4H,
2
13
1
3
1
CH ), 1.91 (s, 12H, CH ). C{ H} NMR (CD Cl , 101 MHz): δ
CHCH + CH {COE}), 1.39−1.52 (m, 2H, CH {COE}). C{ H}
3 3 2 2
2
2
2
1
1
1
188.0 (d, J
= 82, CO), 160.5 (d, J
= 39, NCN), 125.5 (s,
RhC
NMR (C D , 101 MHz): δ 169.6 (d, J
= 42, NCN), 126.5 (s,
RhC
6
6
RhC
1
COCH ), 88.6 (s, CH ), 61.3 (s, C(CH ) ), 27.3 (s, CH ), 26.3 (s,
COCH ), 87.8 (s, OCH ), 62.5 (s, C(CH ) ), 57.7 (d, J
CH), 34.4 (s, CHCH ), 31.7 (s, CH {COE}), 27.2 (s, CH {COE}),
6.7 (s, CH ), 24.4 (s, CH ). Anal. Calcd for C H ClN O Rh·
.5(C H ) ([665.07] 704.13 g mol ): C, 56.29; H, 7.01; N, 7.96.
Found: C, 56.18; H, 7.07; N, 8.17. Benzene solvate is readily apparent
from the crystal structure and on dissolving in CD Cl (not stable).
Data for 3. H NMR (C D , 400 MHz): δ 4.00 (d, J = 7.4, 4H,
OCH ), 3.97 (d, J = 7.4, 4H, OCH ), 3.89 (d, J = 7.7, 4H,
OCH ), 3.82 (d, J = 7.7, 4H, OCH ), 3.74 (s, 4H, OCH ), 2.34 (s,
H, CH ), 2.33 (s, 6H, CH ), 2.27 (s, 6H, CH ), 2.18 (s, 6H, CH ),
.76 (s, 6H, CH ), 0.55 (s, 6H, CH ). C NMR (C D , 101 MHz):
concentration was too low to measure. Anal. Calcd for
= 16,
2 2 3 2 3
2
2
3
2
RhC
−
1
CH ). IR (CH Cl , cm ): ν(CO) 1942 (s). Anal. Calcd for
3
2
2
2
2
2
−1
C H ClN O Rh (582.88 g mol ): C, 47.39; H, 5.53; N, 9.61.
2
0
23 32
4
5
3
3
30 46
4
4
−
1
Found: C, 47.41; H, 6.04; N, 9.69.
.8. trans-[Rh(IBioxMe ) (CO) ][BAr ] (8). A suspension of 7
6
6
F
1
4 2
2
4
4
8
F
(
0.020 g, 0.034 mmol) and Na[BAr ] (0.034 g, 0.038 mmol) in
4
2
2
1
2
CH Cl2 was placed under CO (1 atm) and stirred at room
2
6
6
HH
2
2
temperature for 30 min. The reaction was placed under an argon
atmosphere, the solution filtered, and the filtrate layered with heptane
to afford a crystalline product upon diffusion. Yield = 0.034 g (70%,
2
HH
2
HH
2
2
HH
2
2
6
0
3
3
3
3
13
1
yellow crystals). H NMR (CD
Cl
, 400 MHz): δ 7.69−7.73 (m, 8H,
3
3
6
6
2
2
F
F
1
Ar ), 7.56 (br, 4H, Ar ), 4.63 (s, 8H, OCH
NMR (C , 500 MHz): δ 8.34 (br, 8H, Ar ), 7.70 (br, 4H, Ar ),
4.58 (s, 8H, OCH
MHz): δ 185.4 (d, JRhC = 64, CO), 162.3 (q, JBC = 50, Ar ), 141.0 (d,
JRhC = 37, NCN), 135.4 (s, Ar ), 129.4 (qq, JFC = 32, JBC = 3, Ar ),
), 1.80 (s, 24H, CH ). H
2
3
−1
F
F
C H ClN O Rh.0.25(C H ) ([763.13] 782.66 g mol ): C, 52.94;
H F
6 4 2
3
3
48
6
6
6
6
13
1
H, 6.37; N, 10.75. Found: C, 52.72; H, 6.38; N, 10.68. Benzene solvate
was confirmed by dissolving in CD Cl (not stable).
2
), 1.91 (s, 24H, CH
3
). C{ H} NMR (CD
Cl
2
, 101
2
1
1
F
2
2
1
F
2
3
F
1
.4. cis-[Rh(IBioxMe )(CO) Cl] (4). A solution of 1 (0.050 g, 0.055
4
2
1
F
3
mmol) in benzene (2 mL) was placed under CO (1 atm) and stirred at
room temperature for 10 min. The solution was placed under argon,
and the product crystallized by addition of excess heptane (ca. 40 mL)
and cooling to 5 °C. Yield = 0.040 g (90%, pale yellow microcrystalline
solid). H NMR (C D , 400 MHz): δ 3.66 (d, J = 8.3, 2H, CH2),
.61 (d, J = 8.3, 2H, CH ), 1.51 (s, 12H, CH ), 1.25 (s, 12H, CH ).
128.4 (s, COCH ), 125.2 (q, J = 272, Ar ), 118.0 (sept, J = 4,
2 FC FC
F
Ar ), 88.1 (OCH ), 61.9 (s, C(CH ) ), 26.8 (s, CH ). IR (CH Cl ,
cm ): ν(CO) 2024 (s). Anal. Calcd for C H BF N O Rh (1438.65
g mol ): C, 46.75; H, 3.08; N, 3.89. Found: C, 46.91; H, 2.96; N,
2
3
2
3
2
2
−
1
56
44
24
4
6
−
1
1
2
6
6
HH
4.08.
2
F
3
1.9. cis-[Rh(IBioxMe ) (COE)][BAr ] (9). In an inert atmosphere
HH
2
3
3
4 2
4
1
3
1
1
C{ H} NMR (C D , 101 MHz): δ 186.7 (d, J = 55, CO), 183.9
glovebox, cold C H F (1.5 mL, −20 °C) was added to a mixture of 2
6
6
RhC
6
4 2
1
1
F
(
d, J = 73, CO), 149.4 (d, J = 42, NCN), 126.2 (s, COCH2),
(0.060 g, 0.090 mmol) and Na[BAr ] (0.088 g, 0.099 mmol). The
RhC
RhC
4
8
7.3 (s, CH ), 61.3 (s, C(CH ) ), 26.7 (s, CH ), 25.2 (s, CH ). IR
resulting suspension was held at −20 °C for 10 min with periodic
shaking. The mixture was diluted with cold heptane (−20 °C) and
2
3
2
3
3
−1
(
CH Cl , cm ): ν(CO) 2081 (s), 2000 (s). Anal. Calcd for
2 2
3
075
dx.doi.org/10.1021/om500332n | Organometallics 2014, 33, 3069−3077

Organometallics
Article
rapidly filtered through Celite. Addition of excess cold heptane
resulted in the precipitation of the product, which was subsequently
washed with cold heptane (2 × 2 mL) and dried in vacuo. Yield =
AUTHOR INFORMATION
■
*
Corresponding Author
E-mail: a.b.chaplin@warwick.ac.uk.
0.095 g (71%, light red-brown solid). The sample for NMR analysis
was prepared by vacuum transfer of CD Cl into a J Young’s NMR
Notes
2
2
tube containing the solid product cooled to −196 °C. The complex
dissolved on warming the tube to −78 °C; the sample was then
transferred directly into the NMR spectrometer precooled to −23 °C
The author declares no competing financial interest.
1
ACKNOWLEDGMENTS
(
250 K). H NMR (CD Cl , 500 MHz, 250 K): δ 7.68−7.72 (m, 8H,
■
2
2
F
F
Ar ), 7.54 (br, 4H, Ar ), 4.44 (s, 8H, CH ), 3.93−4.01 (m, 2H, CH),
The author thanks the University of Warwick and the Royal
Society for financial support. Crystallographic data were
collected using a diffractometer purchased through support
from Advantage West Midlands and the European Regional
Development Fund.
2
2
.46−2.56 (m, 2H, CHCH ), 1.66 (s, 24H, CH ), 1.17−1.75 (m, 10H,
2
3
1
CH {COE}; δ 1.29, 2H, CHCH ′). H NMR (C H F , 500 MHz, 298
2
2
6
4 2
F
F
K): δ 8.34 (br, 8H, Ar ), 7.70 (br, 4H, Ar ), 4.45 (s, 8H, CH ), 4.24−
2
4
1
2
3
1
.31 (m, 2H, CH), 2.29−2.38 (m, 2H, CHCH ), 1.62 (s, 24H, CH ),
2
3
13 1
.26−1.85 (m, 10H, CH {COE}). C{ H} NMR (CD Cl , 126 MHz,
2
2
2
1
F
F
2
50 K): δ 161.9 (q, J = 50, Ar ), 134.9 (s, Ar ), 128.9 (qq, J
=
BC
FC
REFERENCES
(1) (a) Díez-Gonzal
3
F
1
F
2, J = 3, Ar ), 126.8 (br, COCH ), 124.7 (q, J = 272, Ar ),
17.7 (sept, J = 4, Ar ), 87.6 (s, CH ), 76.3 (very br, from HMQC,
■
BC
2
FC
3
F
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6.0 (s, CH {COE}), 25.6 (br, CH ). The NCN resonance was not
2
3
observed; presumably it is very broad. Anal. Calcd for
−1
(2) Crudden, C. M.; Allen, D. P. Coord. Chem. Rev. 2004, 248, 2247−
C H BF N O Rh (1492.83 g mol ): C, 49.88; H, 3.92; N, 3.75.
62
58
24
4
4
2
273.
Found: C, 49.74; H, 3.87; N, 3.90.
F
(3) (a) Scott, N. M.; Dorta, R.; Stevens, E. D.; Correa, A.; Cavallo, L.;
1
.10. [Rh(IBioxMe ) (NBD)][BAr ] (10). To a mixture of 5 (0.056 g,
4 2 4
F
Nolan, S. P. J. Am. Chem. Soc. 2005, 127, 3516−3526. (b) Dorta, R.;
0
0
.13 mmol), IBioxMe (0.030 g, 0.14 mmol), and Na[BAr ] (0.124 g,
4
4
Stevens, E. D.; Nolan, S. P. J. Am. Chem. Soc. 2004, 126, 5054−5055.
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6
4 2
(4) Zenkina, O. V.; Keske, E. C.; Wang, R.; Crudden, C. M.
stirred at room temperature for 90 min. The solution was filtered and
the product crystallized by addition of excess heptane. Yield = 0.150 g
Organometallics 2011, 30, 6423−6432.
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(
78%, yellow-orange microcrystalline solid). H NMR (CD Cl , 400
2
2
2
014, 50, 685−687. (b) Ouyang, Z.; Deng, L. Organometallics 2013,
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F
MHz): δ 7.70−7.74 (m, 8H, Ar ), 7.57 (br, 4H, Ar ), 4.60 (app q, J =
3
2, 7268−7271. (c) Day, B. M.; Pugh, T.; Hendriks, D.; Guerra, C. F.;
2
2
2
4
, 4H, CHCH), 4.44 (d, J = 8.3, 4H, OCH ), 4.40 (d, J = 8.3,
2 2 3
HH
2
HH
Evans, D. J.; Bickelhaupt, F. M.; Layfield, R. A. J. Am. Chem. Soc. 2013,
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H, OCH ), 3.92 (br, 2H, CH CH), 1.87 (s, 12H, CH ), 1.60 (s, 12H,
3
1
CH ), 1.49 (t, J = 1, 2H, CH {NBD}). H NMR (C H F , 500
3
HH
2
6
4 2
F
F
MHz): δ 8.34 (br, 8H, Ar ), 7.70 (br, 4H, Ar ), 4.73 (app q, J = 2, 4H,
2
2
CHCH), 4.43 (d, J = 8.4, 4H, OCH ), 4.39 (d, J = 8.4, 4H,
HH
2
HH
OCH ), 3.95 (br, 2H, CH CH), 1.94 (s, 12H, CH ), 1.70 (s, 12H,
2
2
3
3
13
1
CH ), 1.53 (t, J = 1, 2H, CH {NBD}). C{ H} NMR (CD Cl ,
2010, 50, 1359−1362. (g) Burling, S.; Mas-Marza,
V.; Mahon, M. F.; Whittlesey, M. K. Organometallics 2009, 28, 6676−
6686. (h) Haller, L. J. L.; Page, M. J.; Macgregor, S. A.; Mahon, M. F.;
́
E.; Valpuesta, J. E.
3
HH
2
2
2
1
F
1
1
1
1
6
01 MHz): δ 162.3 (q, J = 50, Ar ), 157.0 (d, J
35.4 (s, Ar ), 129.4 (qq, J = 32, J = 3, Ar ), 127.4 (s, COCH ),
25.2 (q, J = 272, Ar ), 118.0 (sept, J = 4, Ar ), 88.7 (OCH ),
= 57, NCN),
BC
RhC
F
2
3
F
̈
FC
BC
2
1
F
3
F
Whittlesey, M. K. J. Am. Chem. Soc. 2009, 131, 4604−4605. (i) Torres,
O.; Martín, M.; Sola, E. Organometallics 2009, 28, 863−870. (j) Ledger,
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Prior, T. J.; Pregosin, P. S.; Whittlesey, M. K.; Williams, J. M. J. J. Am.
FC
FC
2
1
3
7.9 (d, J = 8, CHCH), 66.9 (d, J = 4, CH {NBD}), 63.8 (s,
RhC
RhC
2
C(CH ) ), 52.6 (s, CH CH), 27.6 (s, CH ), 24.4 (s, CH ). Anal.
3
2
2
3
3
−
1
Calcd for C H BF N O Rh (1474.77 g mol ): C, 49.68; H, 3.55;
61
52
24
4
4
N, 3.80. Found: C, 49.87; H, 3.46; N, 3.90.
F
1
.11. [Rh(IBioxMe ) ][BAr ] (11). To a mixture of 3 (0.100 g, 0.131
4 3 4
F
mmol) and Na[BAr ] (0.128 g, 0.144 mmol) was added CH Cl (4
4
2
2
mL). The resulting dark purple solution was filtered and the filtrate
layered with heptane to afford a crystalline product upon diffusion.
Yield = 0.140 g (65%, purple crystals). Complex 11 can also be made
from [Rh(COE) Cl] and IBioxMe4 in difluorobenzene, using
́
Chem. Soc. 2007, 129, 1987−1995. (n) Corberan, R.; Sanau, M.; Peris,
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Y.; Fujita, K.-I.; Yamaguchi, R. Organometallics 2006, 25, 826−831.
2
2
(p) Scott, N. M.; Pons, V.; Stevens, E. D.; Heinekey, D. M.; Nolan, S.
F
4
Na[BAr ] as a halide abstractor (83% isolated yield). Details of this
alternative procedure and NMR data were reported earlier.
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1
3
́
F
1
.12. [Rh(IBioxMe ) (CO)][BAr ] (12). Prepared from 11 as
4 3 4
13
(
−1
described in an earlier communication. IR (CH Cl , cm ):
2
2
Williams, J. M. J. Organometallics 2004, 23, 4537−4539. (s) Abdur-
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2
004, 23, 86−94. (t) Chilvers, M. J.; Jazzar, R. F. R.; Mahon, M. F.;
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ASSOCIATED CONTENT
■
(
* Supporting Information
S
K. Angew. Chem., Int. Ed. 2004, 43, 5824−5827. (v) Trnka, T. M.;
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Experimental details for NMR-scale reactions, selected NMR
spectra of 1−10, crystallographic data, and the structure of
2
546−2558. (w) Jazzar, R. F. R.; Macgregor, S. A.; Mahon, M. F.;
[
Rh(IBioxMe ) Cl ]. This material is available free of charge via
4 2 2
Richards, S. P.; Whittlesey, M. K. J. Am. Chem. Soc. 2002, 124, 4944−
the Internet at http://pubs.acs.org. Full crystallographic details
are document in CIF format and have been deposited with the
Cambridge Crystallographic Data Centre under CCDC
4
1
(
945. (x) Huang, J.; Stevens, E. D.; Nolan, S. P. Organometallics 2000,
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́
6) (a) Rivada-Wheelaghan, O.; Ortuno, M. A.; Díez, J.; Lledos, A.;
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2
2
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dx.doi.org/10.1021/om500332n | Organometallics 2014, 33, 3069−3077