Bis(diethylphosphino)methane as a bridging ligand in complexes of Ir 2, Rh2, and IrRh: Geminal C-H activation of α-olefins

Article abstract of DOI:10.1021/om201214z

Bis(diethylphosphino)methane (depm, Et₂PCH₂PEt ₂) is used as a new bridging ligand for the syntheses of a series of diiridium, dirhodium, and iridium/rhodium complexes, starting from trans-[MM′Cl₂(CO)₂(depm)₂] (M = M′ = Ir (1); M = M′ = Rh (11); M = Ir, M′ = Rh (19)). The reduction of all three chloro compounds in aqueous KOH under an atmosphere of CO produces the neutral tricarbonyl complexes [MM′(CO)₃(depm)₂] (M = M′ = Ir (2); M = M′ = Rh (12); M = Ir, M′ = Rh (20)). Protonation of these tricarbonyl complexes by triflic acid (HOTf) or Brookhart's acid (HBAr^F₄) yields the hydride-bridged tricarbonyl complexes [MM′(CO)₃(μ-H)(depm)₂][X] (M = M′ = Ir (9); M = M′ = Rh (16); M = Ir, M′ = Rh (25); X = SO ₃CF₃ or B(3,5-(CF₃)₂C ₆H₃)₄). Reaction of 2 with methyl triflate yields the methylene/hydride product [Ir₂(H)(CO)₃(μ- CH₂)(depm)₂][OTf] (4), while the same reaction with the dirhodium analogue (12) produces the methyl complex [Rh₂(CH ₃)(CO)₃(depm)₂][OTf] (14) at below -20 °C, which upon warming to above -20 °C results in migratory insertion to yield an acetyl-bridged species, [Rh₂(CO)₂(μ-C(CH ₃)O)(depm)₂][OTf] (14a). The analogous Rh/Ir species(20) reacts with methyl triflate to give the methyl-tricarbonyl product [IrRh(CH ₃)(CO)₃(depm)₂][OTf] (22). Removal of a carbonyl from 4 and 22 yields [MIr(CH₃)(CO)₂(depm) ₂][OTf] (M = Ir (5); M = Rh (23)), which are highly susceptible to hydrolysis; however the dirhodium species 14 and 14a are not susceptible to CO loss under the conditions investigated. The reaction of [Ir₂(CO) ₃(μ-H)(depm)₂][BAr^F₄] (9) with a number of α-olefins results in double C-H bond activation of the geminal hydrogens to give the vinylidene-bridged trihydride products of the form [Ir₂(H)₂(CO)₂(μ-H)(μ-C=CRR′)(depm) ₂][BAr^F₄].

Full text of DOI:10.1021/om201214z

Article
pubs.acs.org/Organometallics
Bis(diethylphosphino)methane As a Bridging Ligand in Complexes
of Ir2, Rh2, and IrRh: Geminal C−H Activation of α-Olefins
Michael E. Slaney,† D. Jason Anderson,† Michael J. Ferguson,†,‡ Robert McDonald,†,‡
and Martin Cowie*,†
‡
†Department of Chemistry and X-ray Crystallography Laboratory, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
S
* Supporting Information
ABSTRACT: Bis(diethylphosphino)methane (depm,
Et2PCH2PEt2) is used as a new bridging ligand for the syntheses
of a series of diiridium, dirhodium, and iridium/rhodium com-
plexes, starting from trans-[MM′Cl2(CO)2(depm)2] (M = M′ =
Ir (1); M = M′ = Rh (11); M = Ir, M′ = Rh (19)). The re-
duction of all three chloro compounds in aqueous KOH under
an atmosphere of CO produces the neutral tricarbonyl com-
plexes [MM′(CO)3(depm)2] (M = M′ = Ir (2); M = M′ = Rh (12); M = Ir, M′ = Rh (20)). Protonation of these tricarbonyl
complexes by triflic acid (HOTf) or Brookhart’s acid (HBArF ) yields the hydride-bridged tricarbonyl complexes [MM′(CO)3
4
(μ-H)(depm)2][X] (M = M′ = Ir (9); M = M′ = Rh (16); M = Ir, M′ = Rh (25); X = SO3CF3 or B(3,5-(CF3)2C6H3)4). Reaction of
2 with methyl triflate yields the methylene/hydride product [Ir2(H)(CO)3(μ-CH2)(depm)2][OTf] (4), while the same reaction with
the dirhodium analogue (12) produces the methyl complex [Rh2(CH3)(CO)3(depm)2][OTf] (14) at below −20 °C, which upon
warming to above −20 °C results in migratory insertion to yield an acetyl-bridged species, [Rh2(CO)2(μ-C(CH3)O)(depm)2][OTf]
(14a). The analogous Rh/Ir species (20) reacts with methyl triflate to give the methyl-tricarbonyl product [IrRh(CH3)-
(CO)3(depm)2][OTf] (22). Removal of a carbonyl from 4 and 22 yields [MIr(CH3)(CO)2(depm)2][OTf] (M = Ir (5); M = Rh
(23)), which are highly susceptible to hydrolysis; however the dirhodium species 14 and 14a are not susceptible to CO loss under
the conditions investigated. The reaction of [Ir2(CO)3(μ-H)(depm)2][BArF ] (9) with a number of α-olefins results in double C−H
4
bond activation of the geminal hydrogens to give the vinylidene-bridged trihydride products of the form [Ir2(H)2(CO)2(μ-H)(μ-C
CRR′)(depm)2][BArF ].
4
only a few examples having been reported.41,56−63 Of these, all
INTRODUCTION
■
but one62 involve pairs of metals at some stage in the activation
process.
Interest in the reactivity of binuclear complexes1 containing
either pairs of identical metals2−18 or two metals that differ19−33
has primarily been driven by the idea that these metals may act
together in some way, either in a cooperative manner,18,26−36
whereby the pair of adjacent metals give rise to reactivity that
differs from that observed at single-metal sites, or in tandem,
whereby one metal performs one transformation, followed by
a second transformation at the other metal.37−40 A binuclear
compound studied by us, namely, [Ir2(CH3)(CO)2(dppm)2][X]
(dppm = μ-Ph2PCH2PPh2, X = anion), has demonstrated a
wealth of reactivity including C−H41,42 and C−F36,43,44 bond
activation, in which the pair of adjacent metals play a pivotal role.
In addition to the interesting reactivity displayed by this species,
its simplicity and the fact that each ligand present has one or
In a previous study we observed the unusual double activa-
tion of a pair of geminal C−H bonds in 1,3-butadiene by the
above diiridium complex and proposed the cooperative involve-
ment of the pair of metals in this transformation.41 However,
this reaction is extremely slow (48 h at 22 °C), and the binding
of the butadiene, in a presumed intermediate, is extremely weak
and only observed at temperatures below ca. −50 °C. Further-
more, this reactivity was limited to 1,3-butadiene, with no C−H
activation observed for other α-olefins investigated. Seeking to
improve the scope of double, geminal C−H activation, we
considered replacing the bridging dppm groups by smaller,
more basic alkyl diphosphines to allow better substrate access
to the metals and to increase metal basicity, respectively. The
obvious diphosphine of choice for this replacement was bis-
(dimethylphosphino)methane (dmpm), the smallest of the
fully alkyl-substituted diphosphines. Furthermore, the dmpm
analogue of the above methyl complex, namely, [Ir2(CH3)-
(CO)2(dmpm)2]+, had been reported.11 Unfortunately, our
attempts to duplicate the reported synthesis were unsuccessful,
more convenient NMR-active nuclei (31P, 13C, H) have often
1
allowed the stepwise transformations to be conveniently followed
by multinuclear and variable-temperature NMR studies, giving
us an appreciation of the roles of the adjacent metals in the
chemistry.
One transformation of interest to us, which could make use
of the cooperative involvement of pairs of metals, is the double
activation of pairs of geminal C−H bonds in α-olefins.
Although the activation of single olefinic C−H bonds is
common,45−55 double, geminal C−H activation is rare, with
Received: December 6, 2011
Published: March 7, 2012
© 2012 American Chemical Society
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Scheme 1
and in general we found that the dmpm chemistry deviated sig-
nificantly from that of dppm in rather unpredictable ways.64
The capricious nature of this dmpm chemistry (in our
hands) led us to instead investigate the closely related depm
(Et2PCH2PEt2) ligand, the chemistry of which, we find, paral-
lels that of dppm in a rational manner. Surprisingly, the use of
depm as a bridging ligand has received little attention, with the
majority of examples involving group 10 metals.65−69 In this
paper we report the synthesis and characterization of a series of
depm-bridged complexes of Ir2, Rh2, and RhIr and investigate
their reactivity toward a series of α-olefins. Although the Rh/Ir
and Rh2 analogues of [Ir2(CH3)(CO)2(dppm)2]+ were un-
reactive toward 1,3-butadiene, we were also interested in
determining whether these Rh-containing analogues, incorpo-
rating a pair of more basic depm groups, might display re-
activity toward olefin C−H activation, not previously observed
with the dppm system.
compound 2 has spectroscopic characteristics similar to those
of 1 and its dppm congener,7 displaying a singlet in the 31P{1H}
NMR spectrum at δ = −11.0 a quintet for the backbone-
1
methylene group (Et2PCH2PEt2) in the H NMR spectrum at
δ 2.67 and one carbonyl signal in the 13C{1H} NMR spectrum at
δ 185.6. However, upon cooling to −80 °C, the 31P{1H} NMR
spectrum displays two signals at δ −8.9 and −28.0, consistent with
the chemically inequivalent environments, and although there is
1
no noticeable change in the H NMR spectrum at this tem-
perature, three unique CO resonances are observed in the
13C{1H} NMR at δ 179.8, 189.3, and 193.8, indicating that a flux-
ional process is occurring at higher temperatures. This fluxion-
ality most likely involves a “merry-go-round” exchange of the
carbonyls, accompanied by the alternating exchange of cis-
to-trans phosphine arrangement at the different metals, as was
also proposed in both the dppm and dmpm analogues.7,12 The
similarities in the low-temperature NMR spectra of 2 compared to
those of [Rh2(CO)3(dppm)2],8 [RhIr(CO)3(dppm)2],22 and
[Ir2(CO)3(dppm)2]7 suggest similar structures, which were
established for the Rh-containing dppm species by X-ray struc-
ture determinations, in which they are shown to have a trans
arrangement of diphosphines at one metal and a cis arrangement
at the other.
RESULTS AND DISCUSSION
■
a. Synthesis of Ir2, Rh2, and IrRh Complexes.
Diiridium Complexes. The addition of [IrCl(COD)]2 to a
CH2Cl2 solution of bis(diethylphosphino)methane (depm)
followed by a slow CO purge results in the formation of trans-
[Ir2Cl2(CO)2(depm)2] (1) in modest yields (the structure of 1
is diagrammed in Scheme 1 and has been determined by an
X-ray study, which appears as Supporting Information). Com-
pound 1 displays a singlet in the 31P{1H} NMR spectrum at
δ 8.3, indicating the chemical equivalence of all four 31P nuclei,
In the presence of CO, compound 2 is converted to the tetra-
carbonyl complex [Ir2(CO)4(depm)2] (3) (Scheme 2), while
removal of the CO atmosphere causes compound 3 to revert to
2 within minutes in solution. Again at ambient temperature a
singlet is observed for 3 in the 31P{1H} NMR, while only a
1
and the H NMR spectrum also displays a single resonance at
Scheme 2
δ 2.52 for the backbone-methylene protons of depm, consistent
with “front/back” symmetry in the species; this signal appears
as a quintet owing to virtual coupling to all 31P nuclei. The
chemical equivalence of both carbonyls also gives rise to a
single resonance in the 13C{1H} spectrum at δ 168.3. In all
cases described herein, carbonyl resonances in the 13C NMR
spectra are obtained using 13CO-enriched compounds.
Compound 1 is the precursor for all other Ir2 compounds
reported in this paper and is readily reduced under an atmo-
sphere of CO in aqueous KOH to yield [Ir2(CO)3(depm)2]
(2). More conventional reduction methods such as the reaction
with sodium borohydride or zinc powder under carbon mono-
xide were also investigated; however, these methods resulted in
mixtures of products that were difficult to separate and con-
sequently gave substantially lower yields of 2, making aqueous
KOH/CO the preferred method. At ambient temperature,
single 13CO resonance is observed in the 13C{1H} NMR
spectrum. However, cooling a solution of 3 to −80 °C results in
similar behavior to that of compound 2, with two distinct
31P{1H} signals observed (δ −19.6 and −41.1), along with four
distinct carbonyl resonances in the 13C{1H} NMR at δ 181.2,
191.8, 194.2, and 195.2, again indicating fluxionality, presumably
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analogous to that of 2. Compound 3 is similar to the dmpm
analogue, the structure of which was reported by Reinking and
shown to have the unsymmetrical structure diagrammed below
for our species.70
depm groups. The bridging methylene group is unsymmetrically
bound, being slightly closer to the less crowded Ir(2) center
(Ir(2)−C(4) = 2.075(5) Å) than to Ir(1) (Ir(1)−C(4) =
2.163(5) Å). There is a 50/50 disorder of the ethyl groups on
P(4), with two different orientations forcing the neighboring
carbonyl (C(3) and O(3)) to also be disordered over two posi-
tions. Placing compound 4 under a CO atmosphere results in the
formation of two other compounds, identified as [Ir2(CH3)-
(CO)4(depm)2][OTf] (5) and [Ir2(CO)4(C(O)CH3)(depm)2]-
[OTf] (6), the result of sequential CO uptake (Scheme 3). Both
compounds are susceptible to CO loss upon CO removal, result-
In parallel with the analogous dppm-bridged diiridium
species,18 reaction of 2 with methyl trifluoromethanesulfonate
(MeOTf) results in the formation of [Ir2(H)(CO)3(μ-CH2)-
(depm)2][OTf] (4; Scheme 1), in which the methyl group has
undergone C−H bond activation to produce a methylene/hy-
dride species. For all cationic species the accompanying anion is
triflate, unless otherwise noted. The 31P{1H} NMR spec-
trum displays two broad resonances at δ −8.9 and −19.5, which
sharpen into pseudotriplets upon cooling to −80 °C. The
1H NMR spectrum at this temperature confirms the
methylene/hydride formulation with the metal-bridged meth-
ylene protons appearing at δ 3.95 and the hydride resonance at
δ −12.42. In the reaction of 2 with carbon-13-labeled MeOTf,
the resulting 13C{1H} resonance appears in the methylene
region at δ 44.2. Also observed in the 13C{1H} NMR spectrum
for the 13CO-labeled product is a single resonance at δ 177.2 for
the three carbonyls, and cooling to −80 °C results in its separa-
tion into three signals (δ 166.3, 178.7, and 180.2). A spin-
saturation transfer experiment on the methylene and hydride
protons at ambient temperature confirms that the fluxionality at
elevated temperatures involves the reversible transformation of
the methylene and hydride groups to a methyl ligand, much as
reported for the dppm analogue.18
1
ing in reversion to 4. In the H NMR spectrum of 5, a triplet
appears at δ 0.68 (3JHP = 5.4 Hz) for the Ir-bound methyl group,
while for 6 the methyl group appears as a singlet at δ 2.60, con-
sistent with migration of this group to a carbonyl. In the 13C{1H}
NMR spectrum two carbonyl signals (δ 187.4 and 191.1) appear
for 5 in a 2:2 ratio, while for 6 three resonances appear in a 2:2:1
ratio at δ 187.8, 195.0, and 221.2; the downfield signal is typical
of an Ir-bound acyl carbonyl.71 Additional coupling of the meth-
yl group to the acyl carbonyl (1JCC = 28.0 Hz; 13CH3/13CO-
enriched sample) also supports the migratory insertion product.
The similarities in the spectral parameters of 5 and 6 are con-
sistent with their similar geometries.
Reacting compound 4 with trimethylamine-N-oxide (TMNO)
at ambient temperature produces the dicarbonyl product
[Ir2(CH3)(CO)2(depm)2][OTf] (7), as shown earlier in Scheme 1.
Compound 7 displays a single broad resonance at ambient
temperature in the 31P{1H} NMR spectrum at δ 23.2, similar to
the methyl dicarbonyl analogues of dppm and dmpm.11,18 The
1H NMR spectrum displays a quintet at δ 0.57 (3JHP = 4.4 Hz)
for the methyl ligand, and the 13C{1H} NMR spectrum also dis-
plays a single carbonyl resonance at δ 174.2, suggesting a sym-
metric, methyl-bridged structure as reported for the dmpm
analogue.11 However, cooling to −80 °C gives rise to the separa-
tion of the 31P{1H} signal into two distinct resonances at δ 26.1 and
19.8 and the appearance of two carbonyl resonances, δ 179.9 and
168.3, in the 13C{1H} NMR spectrum, suggesting an unsym-
metrical structure, such as that shown in Scheme 1, and
analogous to that observed for the dppm analogues [IrRh-
(CH3)(CO)2(dppm)2]+ and [Ir2(CH3)(CO)2(dppm)2]+.18,25
The symmetrical structure suggested by the ambient temperature
spectra is presumably the result of migration of the methyl group
from metal to metal on one face of the Ir2P4 plane, in
conjunction with the two CO ligands migrating across the
opposite face of the metals. A merry-go-round migration of these
ligands is ruled out owing to the appearance of two 1H
resonances for the methylene linkers of the depm ligands,
indicating front/back asymmetry in the time-averaged structure.
Unfortunately, compound 7 is unstable in solution at ambient
temperature, transforming to [Ir2(CO)2(μ-OH)(depm)2][OTf]
(8; Scheme 1) within 5 min, owing to its reaction with adven-
titious water that results from either the earlier aqueous KOH/
CO reduction step or the use of trimethylamine-N-oxide, which
is difficult to obtain fully dried.72 In both cases, an azeotropic
distillation in benzene or dimethylformamide, respectively, was
performed in attempts to minimize residual water. However, the
transformation of 7 to 8 in solution could not be prevented by
these precautions, having still occurred after 45 min. Compound
8 displays spectral parameters similar to its dppm analogue7 and,
therefore, is not discussed here (refer to Experimental Section for
NMR data).
An X-ray structure determination of 4 confirms the ligand
orientation proposed by spectroscopy, as displayed in Figure 1.
Figure 1. Perspective view of the complex cation of [Ir2(H)(CO)3-
(μ-CH2)(depm)2][OTf] (4) showing the atom-labeling scheme.
Thermal parameters are shown at the 20% probability level. Hydrogen
atoms are shown with arbitrarily small thermal parameters for the
hydride, bridging methylene, and depm methylene groups, but are not
shown for the Et groups. Only one pair of disordered methyl
substituents of the ethyl groups on P(4), along with the disordered
carbonyl on Ir(2), are shown for clarity. Relevant bond distances (Å)
and angles (deg): Ir(1) − Ir(2) = 2.7887(3); Ir(1)−C(4) = 2.163(5);
Ir(2)−C(4) = 2.075(5); P(1)−P(2) = 3.049(2); P(3)−P(4) =
3.015(2); Ir(1)−C(4)−Ir(2) = 82.3(2).
The Ir(1)−Ir(2) separation of 2.7887(3) Å indicates the pre-
sence of a metal−metal bond, displaying significant compres-
sion compared to the nonbonded P(1)−P(2) and P(3)−P(4)
distances of 3.049(2) and 3.015(2) Å, respectively, within the
Reaction of compound 8 with CO generates the hydride-
bridged species [Ir2(CO)3(μ-H)(depm)2][OTf] (9-OTf), as
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Scheme 3
shown in Scheme 1, which was obtained more directly by
b. Dirhodium Complexes. Reacting [Rh2Cl2(COD)2] with
depm under a CO purge results in the formation of trans-
[Rh2Cl2(CO)2(depm)2] (11; Scheme 5) much as described for
the Ir2 analogue. The 31P{1H}, 1H, and 13C{1H} spectral
parameters are all as expected, including rhodium−phosphorus
protonation of 2. Compound 9, as either the triflate or BArF ¯
4
salt, displays a singlet in the 31P{1H} NMR spectrum, while
1
the H NMR spectrum displays a single, upfield resonance at
δ −10.40, appearing as a quintet with equal coupling to all four
phosphorus nuclei (2JHP = 9.8 Hz). At ambient temperature, the
13C{1H} NMR spectrum shows a single, broad resonance at
δ 183.7, which upon cooling to −80 °C resolves into two re-
sonances at δ 185.3 and 183.3, in a 1:2 intensity ratio, respec-
coupling observed in the 31P{1H} NMR spectrum (1JRhP
=
117.2 Hz) and rhodium−carbon coupling for the carbonyls in
the 13C{1H} NMR spectrum (1JRhC = 74.8 Hz). An X-ray struc-
ture determination of compound 11 reveals a near super-
imposable structure to that of the diiridium analogue (1) and is
given as Supporting Information.
1
tively; at low temperature the 31P{1H} and H NMR spectra
remain unchanged, appearing to rule out a fluxional process at
higher temperatures.
As described earlier for the Ir2 complex, compound 11 can
also be reduced under a CO atmosphere in the presence of
aqueous KOH, resulting in the formation of [Rh2(CO)3-
(depm)2] (12). Multinuclear NMR spectra show similarities to
compound 2 at ambient temperature, with the exception of
additional rhodium−phosphorus coupling (1JRhP = 137.7 Hz).
Cooling 12 to −110 °C shows separation of the single 31P{1H}
signal into two doublets of pseudotriplets at δ 22.5 and 8.5,
with rhodium−phosphorus couplings of 117.1 and 152.6 Hz,
respectively, along with mutual phosphorus−phosphorus
coupling of 69.7 Hz. At −110 °C, the broad carbonyl resonance
observed at ambient temperature resolves into three signals at
δ 209.1, 206.8, and 183.4 (1JRhC = 77.0 Hz, 71.2, and 67.9 Hz,
respectively). Selective 13C{31P} decoupling establishes that the
upfield carbonyl is coupled to one end of the diphosphines
(δ 22.5), while the two downfield signals are coupled to the
other end, consistent with the structure proposed in Scheme 5
and in agreement with the structures determined for the dppm
analogues, [Rh2(CO)3(dppm)2]2 and [IrRh(CO)3(dppm)2].22
As shown earlier in Scheme 2, compound 12 reacts under
an atmosphere of CO, producing [Rh2(CO)4(depm)2] (13),
which is highly susceptible to CO loss. Multinuclear NMR
Under a CO atmosphere, compound 9 generates [Ir2(H)-
(CO)4(depm)2]+ (10), in which the hydride ligand is now
terminally bound to one Ir center (Scheme 4), as shown by the
Scheme 4
triplet in the 1H NMR spectrum at δ −8.80, displaying coupling
to only one pair of 31P nuclei (2JHP = 14.4 Hz). The appearance
of only two equal-intensity carbonyl resonances in the carbon-
13 NMR spectrum, in conjunction with only one signal for the
backbone-methylene protons, suggests that compound 10 has a
similar geometry to those of compounds 5 and 6, with front/
back symmetry about the metal−phosphine plane.
Scheme 5
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spectroscopy displays broad resonances at ambient temper-
ature; however cooling the sample to −80 °C produces the
pattern expected for an AA′BB′XY spin system in the 31P{1H}
NMR spectrum and, in conjunction with two 13C{1H} re-
sonances at δ 214.3 and 204.1 in a 1:3 ratio, confirms the
presence of a fourth carbonyl (refer to Experimental Section for
full spectroscopic characterization). This intensity ratio is not
the 1:1:1:1 ratio expected and appears to indicate coincidental
overlap of three resonances masked by the breadth of the
resulting signal.
complex [Rh2(CO)3(μ-H)(depm)2][OTf] (16-OTf), which is
also obtained as either the OTf− or BArF − salt by protonation
4
of 12 by the appropriate acid, as shown in Scheme 5. Com-
pound 16 contains a symmetrically bridged hydride, as shown
1
by the complex multiplet in the H NMR at δ −10.34, dis-
playing couplings to both rhodium atoms (1JRhH = 24.3 Hz) and
all four phosphorus nuclei (2JHP = 12.2 Hz). The 13C{1H}
NMR spectrum displays three overlapped carbonyl signals at δ
194.3 and, upon cooling to −80 °C, shows slight separation of
the signal into two broad resonances at δ 195.1 and 194.0 in a
1:2 ratio; interestingly, the 13C{1H} chemical shifts for the
bridging and terminal CO ligands do not differ significantly,
much as observed earlier for the diiridium analogue.
The addition of MeOTf to compound 12 at −20 °C pro-
duces the tricarbonyl methyl species [Rh2(CH3)(CO)3-
(depm)2][OTf] (14), as shown in Scheme 5. Unlike the
diiridium analogue (4), the methyl moiety does not undergo
C−H activation to give a methylene/hydride isomer, but re-
An X-ray structure determination of 16-BArF confirms the
4
structure proposed, revealing a symmetrically bridged hydrido
ligand with two terminal carbonyls and one bridging on the face
opposite the hydride, as shown in Figure 2. The rhodium−
1
mains intact, as confirmed by both H and 13C{1H} NMR
spectroscopy at −80 °C, with the methyl protons appearing as a
broad multiplet at δ 0.63 and the methyl carbon appearing as a
broad, unresolved resonance at δ −0.7. The 13C{1H} NMR
spectrum also displays two carbonyl resonances at δ 214.3 (2C)
and 199.3 (1C), with the downfield signal suggesting two bridg-
ing carbonyls, while the upfield signal indicates one ter-
minal carbonyl. The 13C{1H, 31P} NMR spectrum shows the
downfield multiplet as a triplet due to coupling to rhodium
(32.7 Hz), while the upfield signal resolves to a doublet from
coupling to rhodium (74.9 Hz). Although the single low-field
resonance for the pair of carbonyls suggests two symmetrically
bridging groups, the static structure more likely resembles that
depicted in Scheme 5, with one bridging carbonyl and one
semibridging carbonyl, which are rapidly exchanging on the
NMR time scale, as seen in a similar Rh/Os system.73
Warming compound 14 to 0 °C results in its transformation
to [Rh2(CO)2(μ-C(CH3)O)(depm)2][OTf] (14a) by the
migratory insertion of the CH3 and a CO ligand, as outlined
1
in Scheme 5. The H NMR spectrum displays the methyl pro-
tons as a singlet with no observable coupling to phosphorus,
and the 13C{1H} NMR spectrum displays a broad, downfield
signal at δ 319.9, similar to its dppm counterpart,15 indicative of
a bridging acetyl moiety, as shown in Scheme 5. Unfortunately,
14a readily decomposes above 0 °C, with the major product
(ca. 50%), [Rh2(CO)2(μ-OH)(depm)2][OTf] (15), resulting
from reaction with adventitious H2O. Compound 15 can be
prepared in near quantitative yield by reacting 14 or 14a with
water, resulting in the elimination of methane. The spectral
parameters for 15 are as expected and are given in the
Experimental Section.
Attempts to produce the rhodium analogue of compound 7,
[Rh2(CH3)(CO)2(depm)2][OTf], proved unsuccessful, with
TMNO failing to react with compound 14 below −20 °C.
Increasing the temperature to near 0 °C yields only 14a, which
is unreactive to TMNO below this temperature, while at higher
temperatures the irreversible conversion to 15 and numerous
unidentified decomposition products was observed. Our failure
to remove a carbonyl is consistent with the lower lability of the
carbonyl ligands in the presence of the smaller, more basic
depm group. Also consistent with the more basic depm com-
pared to dppm is the observation of the methyl complex 14, the
dppm analogue of which was not observed; the more basic
depm groups disfavor migratory insertion owing to the result-
ing lower electrophilicity of the carbonyls, resulting from in-
creased π-back-donation.
Figure 2. Perspective view of the complex cation of [Rh2(CO)2-
(μ-H)(μ-CO)(depm)2][BArF ] (16-BArF ) showing the atom-labeling
4
4
scheme. Thermal parameters are as described in Figure 1. Relevant
bond distances (Å) and angles (deg): Rh(1)−Rh(2) = 2.7613(3);
P(1)−P(2) = 3.046(1); P(3)−P(4) = 3.051(1); Rh(1)−C(1) =
1.842(4); Rh(1)−C(3) = 2.143(3); Rh(2)−C(2) = 1.850(3); Rh(2)−
C(3) = 2.119(3); Rh(1)−C(3)−Rh(2) = 80.8(1); P(1)−Rh(1)−P(3) =
162.52(3); P(2)−Rh(2)−P(4) = 163.54(3).
rhodium separation (Rh(1)−Rh(2) = 2.7613(3) Å) is sig-
nificantly shorter than the nonbonding P−P distances within
the diphosphine backbones (P(1)−P(2) = 3.046(1), P(3)−
P(4) = 3.051(1) Å), indicating significant contraction along the
Rh−Rh vector, consistent with a strong metal−metal inter-
action. Other crystallographic parameters are as expected and
are in close agreement to those reported for the dppm analogue,
[Rh2(CO)3(μ-H)(dppm)2]+.2
Compound 16 reacts with additional acid, producing the
dicationic complex [Rh2(CO)3(depm)2]2+ (17), accompanied
by H2 evolution (Scheme 6), and this product takes up two
additional carbonyl ligands under a CO atmosphere to yield
[Rh2(CO)5(depm)2]2+ (18), which readily reverts to 17 in the
absence of CO. Both compounds 17 and 18 are fluxional at
ambient temperatures; however the nature of the fluxionality was
not investigated by low-temperature NMR. Compound 18 is
analogous to the diiridium complex [Ir2(CO)4(μ-CO)(dppm)2]2+,7
which was shown to have fluxional behavior similar to that ob-
served for 18 at ambient temperature.
As observed in the Ir2 analogue, the hydroxide-bridged Rh2
complex (15) reacts with CO to produce the hydride-bridged
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Scheme 6
The structure proposed for compound 18 has been con-
firmed crystallographically for the ditriflate salt and is shown in
the ORTEP representation of the cation in Figure 3. The struc-
ture shows a symmetrical arrangement of carbonyls with both
metals having nearly identical geometries. The carbonyls
oriented along the Rh−Rh bond have significantly shorter
Rh−C distances (1.904(3), 1.924(3) Å) than those that are
pseudo trans to the bridging carbonyl (1.992(3), 1.998(3) Å);
the bridging carbonyl displays Rh−C bond lengths that are
elongated relative to the terminal ligands and is unsymmetri-
cally bound (Rh(1)−C(3) = 2.195(3) Å; Rh(2)−C(3) =
2.025(3) Å), presumably a result of nonbonded contacts involv-
ing the depm ethyl groups, which are in different orientations at
each end of the depm ligands, as shown in Figure 3.
c. Iridium/Rhodium Complexes. The addition of depm to
Vaska’s complex, [IrCl(CO)(PPh3)2], followed by 0.5 equiv of
[Rh(Cl)(CO)2]2 produces a dark orange solution of trans-
[IrRhCl2(CO)2(depm)2] (19). As is the case with related dppm-
bridged mixed-metal Ir/Rh systems, the 31P{1H} NMR displays
two signals, corresponding to an AA′BB′X spin system, with
the downfield signal displaying rhodium coupling along with the
expected phosphorus coupling, while the upfield signal,
corresponding to the iridium-bound phosphines, shows only
phosphorus coupling. All other spectral parameters for compound
19 closely match those already discussed for compounds 1 and 11.
As with the homobimetallic analogues, compound 19 is readily
reduced (Scheme 7), producing a 1:1 mixture of the neutral tri-
carbonyl and tetracarbonyl compounds, [IrRh(CO)3(depm)2]
(20) and [IrRh(CO)4(depm)2] (21), upon the addition of aque-
ous KOH under a CO atmosphere. A CO purge converts 20 to
21 (Scheme 2), which reverts to 20 in the absence of a CO
atmosphere. At ambient temperature, the NMR spectra of
compound 20 differ from those of its homobimetallic congeners,
displaying two signals in the 31P{1H} NMR spectrum, while the
13C{1H} NMR spectrum shows two signals: broad singlet at δ
189.0 (2C) and a doublet at δ 185.7 (1C); the additional coupling
of the latter signal is due to rhodium. Interestingly, cooling to
−80 °C shows separation of the downfield signal in the
13C{1H} NMR spectrum into two broad singlets at δ 192.6
(1C) and 188.9 (1C), while the upfield signal remains un-
changed. Although there is no evidence of exchange of the Rh-
and Ir-bound carbonyls, the pair of Ir-bound carbonyls are ex-
changing, presumably accompanied by movement of the
Ir-bound ends of the diphosphines from above the plane of
the drawing in Scheme 7 to below.
At ambient temperature 21 displays broad resonances in the
1
31P{1H}, H, and 13C{1H} NMR spectra; however cooling
to −80 °C yields two sharp signals in the 31P{1H} spectrum
and four carbonyl resonances in the 13C{1H} spectrum, the two
downfield signals of which display additional coupling to
rhodium (1JCRh = 73.5 Hz, 72.4 Hz). We propose a structure for
21 similar to the homobimetallic analogues and much like that
of the dmpm-bridged diiridium species reported by Reinking.70
Addition of MeOTf to 20 yields [IrRh(CH3)(CO)3(depm)2]-
[OTf] (22), as shown in Scheme 7, resembling the dirhodium
analogue (14), in which the methyl group remains intact, and in
contrast to the Ir2 analogue, which undergoes intramolecular
C−H activation to give the methylene/hydride compound 4.
Unlike compound 14, which is proposed to contain a bridging
and a semibridging CO (see above), only one carbonyl shows
coupling to rhodium, suggesting that the other two carbonyls are
bound solely to iridium.
An X-ray structure confirms the proposed geometry for 22
(Figure 4), although the structure is disordered such that the
metals are found to have 60/40 occupancy across the two sites
(refer to the Experimental Section for an overlapped view of
disorder). The relatively long Rh(A)−C(2A) and Rh(A)−
C(3A) distances (2.70(1) and 2.71(1) Å) and the close-to-
linear Ir(A)−C(2A)−O(2A) and Ir(A)−C(3A)−O(3A) angles
(175(1)°, 170(4)°) indicate that any interaction with rhodium
is weak, consistent with the absence of Rh coupling in the
13C{1H} NMR spectrum.
Compound 22 reacts with TMNO to give the dicarbonyl
complex [IrRh(CH3)(CO)2(depm)2][OTf] (23; Scheme 7), in
which the methyl group remains terminally bound to iridium, as
demonstrated by 1H{31P} and 13C{1H} NMR experiments; in par-
ticular, the absence of rhodium coupling in the 13CH3 resonance
confirms its binding to Ir. Two equal-intensity carbonyl signals
are observed in the 13C{1H} NMR spectrum, with only the
Figure 3. Perspective view of the complex cation of [Rh2(CO)4-
(μ-CO)(depm)2][OTf]2 (18) showing the atom-labeling scheme. Thermal
parameters are as described in Figure 1. Relevant bond distances (Å)
and angles (deg): Rh(1)−Rh(2) = 2.8373(3); Rh(1)−C(1) = 1.992(3);
Rh(1)−C(2) = 1.904(3); Rh(1)−C(3) = 2.195(3); Rh(2)−C(3) =
2.025(3); Rh(2)−C(4) = 1.924(3); Rh(2)−C(5) = 1.998(3); C(1)−
Rh(1)−C(2) = 117.2(1); C(1)−Rh(1)−C(3) = 146.8(1); C(2)−
Rh(1)−C(3) = 96.0(1); C(3)−Rh(2)−C(4) = 111.1(1); C(3)−
Rh(2)−C(5) = 141.6(1); C(4)−Rh(2)−C(5) = 107.3(1).
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Scheme 7
2. Geminal C−H Activation of Olefins. Compound 9, as
either the OTf− or BArF − salt, reacts with a variety of α-olefins
4
(ethylene, vinylfluoride, propylene, 3,3,3-trifluoropropene, 1,3-
butadiene, and styrene) under a variety of conditions to give
the vinylidene-bridged trihydride products [Ir2(H)2(CO)2-
(μ-H)(μ-CCRR′)(depm)2][BArF ] (R = R′ = H (26); R =
4
H, R′ = F (27); R = H, R′ = CH3 (28); R = H, R′ = CF3 (29);
R = H, R′ = C(H)CH2 (30); R = H, R′ = C6H5 (31)), in which
a pair of geminal C−H bonds in the α-olefin have been cleaved.
Although most of the above reactions take place over the
course of several hours at ambient temperature, the reaction
with styrene required elevated temperatures (40 °C) for several
days, while the reaction with vinyl fluoride yielded 27 in only
5% yield (the major product resulting from geminal C−H and
C−F bond activation).69 However, all products (26−31) were
obtained in a fraction of the time (10−30 min) at ambient tem-
perature upon the addition of TMNO to solutions of 9 and the
olefin (Scheme 8). In addition, isobutylene, which was un-
reactive with 9, yielded the dimethylvinylidene-bridged product
[Ir2(H)2(CO)2(μ-H)(μ-CCMe2)(depm)2][BArF ] (32) in
4
30 min upon reaction with TMNO, and the fluorovinylidene-
bridged 27 was obtained as the sole product upon inclusion of
TMNO. The activation of a pair of geminal C−H bonds in
α-olefins has precedent, but is not common.41,56−63 In attempts
to obtain a difluorovinylidene analogue, compound 9 was exposed
to 1,1-difluoroethylene in the presence of TMNO; however
decomposition to numerous unidentified products occurred, with
no indication of geminal C−H activation occurring.
Figure 4. Perspective view of the complex cation of [RhIrMe-
(CO)3(depm)2][OTf] (22) showing the atom-labeling scheme. Only
the major orientation of the disordered “RhIr(CO)3(CH3)” fragment
(IrA, RhA, O1A, O2A, O3A, C1A, C2A, C3A, C4A) is shown. Thermal
parameters are as described in Figure 1, except that all hydrogen atoms
are shown, having arbitrarily small thermal parameters. Relevant bond
distances (Å) and angles (deg) for the major orientation: Ir(A)−Rh(A)
= 2.7282(7); Ir(A)−C(4A) = 2.10(2); Rh(A)−C(1A) = 1.93(2);
Ir(A)−C(2A) = 1.95(1); Ir(A)−C(3A) = 2.02(2), Rh(A)−C(2A) =
2.70(1); Rh(A) − C(3A) = 2.71(1); Ir(A)−Rh(A)−C(1A) = 173.3(9);
Rh(A)−Ir(A)−C(4A) = 177.6(9); Ir(A)−C(2A)−O(2A) = 175(1);
Ir(A)−C(3A)−O(3A) = 170(4).
Compounds 26 and 32 each display a singlet in their
31P{1H} NMR spectra due to the symmetrical nature of each
bridging vinylidene unit, while compounds 27−31, formed
from the unsymmetrical α-olefins (R ≠ R′), display two multi-
plets as a result of the unsymmetrical vinylidene group generat-
ing different chemical environments at the two metals. These
1
upfield signal displaying coupling to rhodium, suggesting two
terminal carbonyls with one on each metal. Unfortunately,
compound 23 is transient and, within 30 min, decomposes to
[IrRh(CO)2(μ-OH)(depm)2][OTf] (24), again due to adven-
titious water.
Compound 24 is readily converted to [IrRh(CO)3(μ-H)-
(depm)2][OTf] (25-OTf) upon the addition of a CO purge,
the latter of which can also be formed by protonation of 20
(refer to Scheme 7). As for the homobimetallic congeners, the
hydride ligand appears to be symmetrically bridging the two
metals, displaying coupling to all four phosphorus nuclei
(2JHP = 9.8 Hz) and to rhodium (1JHRh = 21.1 Hz).
symmetry differences are also evident in the H NMR spectra
with two hydride signals, in a 2:1 ratio for the two symmetric
products (26 and 32), while compounds 27−31 each show
three hydride signals (two relatively downfield signals for the
terminal hydrides and an upfield signal arising from the bridg-
ing hydride). Interestingly, no trans H−H coupling between
the bridging and terminal hydrides is observed in any of these
species; the analogous vinylvinylidene-bridged/dppm species,
which was crystallographically characterized,41 also did not
exhibit this coupling. However, the nonsymmetric compounds
(27−31) display long-range coupling between the two terminal
hydrides, typically on the order of 9.0 Hz. Compounds 26 and
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Scheme 8
32 display a single proton resonance for the vinylidene moiety:
a singlet for the vinylidene hydrogens at δ 6.57 for compound
26 and a singlet for the methyl protons at δ 1.40 for compound
32. The bridging fluorovinylidene unit (27) shows a doublet
The scrambling in the absence of TMNO is presumably the
result of reversible ethylene insertion into the Ir−D−Ir unit of
9-D, whereas in the presence of TMNO, carbonyl loss and
subsequent C−H bond activation are favored. The reaction of 9
with 1,1-dideuteroethylene (D2CCH2) in the absence of
TMNO again shows deuterium scrambling across all hydride
and vinylidene positions of 26, presumably a result of reversible
olefin insertion, while in the presence of TMNO no deuterium
incorporation into the bridging hydride position is observed,
although the terminal hydride and vinylidene sites are par-
tially deuterated, owing to competing C−H and C−D bond
activation.
Attempts to bring about geminal C−H activation of the
above α-olefins in reactions with [MM′(CO)3(depm)2] (M =
M′ = Ir (2), Rh (12); M = Rh, M′ = Ir (20)), formally M(0)/
M′(0) complexes, gave no reaction over a range of conditions,
even in the presence of TMNO. Similarly, neither of the
rhodium hydride species [RhIr(CO)3(μ-H)(depm)2]+ (25) or
[Rh2(CO)3(μ-H)(depm)2]+ (16) reacts with these olefins,
either in the presence or absence of TMNO. Furthermore,
attempts to react the dppm species [Ir2(CO)3(μ-H)(dppm)2]+
with the above α-olefins under identical conditions yielded only
starting materials.
1
(2JHF = 108.2 Hz) at δ 6.61 in the H NMR spectrum, with a
matching doublet found at δ −72.1 in the 19F NMR spectrum,
while the bridging trifluoromethylvinylidene moiety shows no
coupling between the proton and fluorines, each appearing as
1
singlets in their H and 19F NMR spectra. The vinylvinylidene
unit in 30, formed from the double C−H activation of 1,3-
butadiene, displays four proton resonances at δ 6.82, 6.28, 4.93,
and 4.82, all showing mutual couplings (3JHHvicinal = 9.9 Hz,
3JHHcis = 9.9 Hz, 3JHHtrans = 17.1 Hz) that are in close agreement
with the values reported for [Ir2(CH3)(H)(CO)2(μ-H)(μ-C
3
C(H)C(H)CH2)(dppm)2]+ (3JHHvicinal = 10.0 Hz, JHHcis
=
10.0 Hz, JHHtrans = 16.5 Hz).41 Finally, the 13C{1H} NMR
spectra display a single carbonyl resonance for the symmetric
complexes, while the nonsymmetric compounds each show two
signals. The addition of 13C2H4 to 9 produced two additional
signals in the 13C{1H} NMR spectrum: a doublet of triplets of
triplets at δ 190.1 and a doublet at δ 130.4. Each displays
mutual coupling of 64.9 Hz, while the downfield resonance,
corresponding to the α-carbon, also displays coupling to both
sets of chemically inequivalent 31P nuclei. Although we were
unsuccessful in obtaining X-ray structures of these vinylidene
species, their spectroscopy clearly defines their formulations; in
particular, the above 13C{1H} NMR data clearly identify the
bridging vinylidene fragment by the coupling of the α-carbon to
the four 31P nuclei and the absence of 31P coupling to the
β-carbon and rule out the acetylene-bridged isomer, for which
31P coupling to both carbons would be observed. The presence
of two unique resonances also supports the proposed bridging-
vinylidene moiety, with a bridging acetylene group expected to
have only a single resonance due to symmetry. Furthermore,
the spectroscopic parallels between compound 30 and the
crystallographically determined dppm analogue42 convincingly
support this proposed structure.
3
DISCUSSION
■
As noted in the Introduction of this paper, the advantage of
depm over dmpm in this chemistry is that although both bridg-
ing groups contain small alkyl substituents that result in greater
basicity over the more commonly used dppm ligand and better
substrate access to the metals, the depm chemistry is much
better behaved than that of dmpm, allowing rational modi-
fications to the well-studied dppm system. The parallels
between depm and dppm are clearly seen in the similarities
between the series of Ir2, Rh/Ir, and Rh2 complexes involving
both diphosphines, as described earlier. Nevertheless, substitut-
ing dppm by depm has had the targeted effect on the reactivity,
and the depm complexes are much more reactive than the
dppm analogues. One unfortunate consequence of this in-
creased reactivity is the extreme sensitivity of the methyl
dicarbonyl species [MM′(CH3)(CO)2(depm)2]+ (MM′ = Ir2
(7) and RhIr (23)) to adventitious water, resulting in hydro-
lysis of these species to hydroxide-bridged products accompa-
nied by methane elimination. Although none of the precautions
taken in this paper to minimize water were taken in previ-
ous studies with dppm,7,15,18,25 the analogous dppm complexes
showed no adverse affects of water; in fact the dppm complexes
were stable to the deliberate addition of water. In any future
attempts to study the methyl dicarbonyl complexes of depm,
other methods for reduction of the dihalide precursors, and the
use of scrupulously dried TMNO for carbonyl removal will
have to be employed, since the targeted methyl complexes are
intolerant of water. Otherwise, other routes to these targets will
have to be devised.
Labeling the bridging hydride position in the starting
material 9 with deuterium (9-D) proved to be challenging
due to its propensity for H/D exchange with adventitious water
remaining from earlier transformations. However, the addition
of D2O to 9 gave conversion to 9-D and 9 in a 4:1 ratio after
24 h. Repeating the experiment shown in Scheme 8 with either
1,3-butadiene or vinyl fluoride and this 9-D/9 mix of
isotopologues results in the original D/H ratio in the bridging
hydride position of the products, with no deuterium incorpora-
tion into the terminal hydride sites, whereas the reaction with
ethylene results in scrambling of deuterium across all three
hydride sites, along with deuterium incorporation into the
bridging vinylidene ligand. However, repeating the ethylene re-
action in the presence of TMNO produces 26, having the
original D/H ratio in the bridging hydride position and no
deuterium in the terminal sites or in the vinylidene positions.
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Chart 1
Addition of methyl triflate to the complexes [MM′(CO)3-
(depm)2] (MM′ = Ir2 (2), Rh2 (12), RhIr (20)) led to re-
activity that very much parallels that of the dppm analogues
with some minor variations. As a consequence, both depm and
dppm Ir2 systems give rise to C−H activation of the added
methyl group at the pair of adjacent Ir centers, consistent with
the greater tendency of the third-row metal for oxidative addi-
tion. In the Rh/Ir complexes involving either dppm or depm,
the methyl group binds to Ir, having the stronger metal−carbon
bond, and although we had considered the possibility of C−H
activation by Rh in the depm system, as a consequence of the
greater basicity of this ligand, this is not observed. Similarly in
the Rh2 systems, both depm and dppm systems yield the acetyl
product, the result of facile migratory insertion at this metal.
However, here the greater basicity of depm over dppm is
evident in two ways. First, although the methyl tricarbonyl pro-
duct was never observed in the dppm chemistry, this precursor
to migratory insertion is observed with depm, presumably
owing to the lower electrophilicity of the carbonyls in this more
electron-rich system, which inhibits migratory insertion. In
addition, although a carbonyl could be removed from the
acetyl-bridged dicarbonyl under reflux in the dppm system,15
we were unable to remove a carbonyl in the depm analogue,
consistent with the increased π-back-donation in this species
(of course in the depm complex its instability does not allow
refluxing, and only TMNO addition was attempted).
However, the most significant consequence of replacement
of dppm by depm is seen in the reactivity of [Ir2(CO)3-
(μ-H)(depm)2]+ with α-olefins. Although the analogous dppm
complex is inert to α-olefins under the conditions inves-
tigated, even in the presence of TMNO, the depm complex
reacts readily with a number of α-olefins to give the cor-
responding vinylidene-bridged trihydride products from
activation of the pair of geminal C−H bonds on the olefin.
Furthermore, in the presence of TMNO these activations are
extremely facile, requiring only minutes for completion at
ambient temperature. Few examples of this type of reactivity
were previously known,41,56−63 and this system represents (by
far) the most reactive system to date, reacting under very mild
conditions with a number of α-olefins.
B in Chart 1. In structure D of the resulting vinyl complex the
second metal can be involved in an agostic interaction with the
second olefinic C−H bond, leading to the second activation.
Although the involvement of the second metal in the second
activation step seems clear, initial coordination of the olefin at
one metal (structure A) preceding C−H activation at the
adjacent metal is more speculative.
We had hoped that the increased reactivity noted above in
the “Ir2(depm)2” system over that of “Ir2(dppm)2” might also
be reflected in the chemistry of the Rh-containing congeners,
either in allowing C−H activation at this metal or at least in
allowing the Rh-containing species to model key intermediates
in the double C−H activation observed for the Ir2 system. Even
in the event that the Rh center was unreactive toward C−H
activation, we anticipated that the mixed-metal species
[RhIr(CO)3(μ-H)(depm)2]+ (particularly in the presence of
TMNO) might still result in a single C−H activation at Ir,
allowing us to obtain information about the first C−H activa-
tion product. Furthermore, we anticipated that although un-
reactive to C−H bond cleavage, the Rh2 systems might yield an
olefin adduct, giving information about the adduct prior to
C−H activation. Unfortunately, none of this is observed with the
least encumbered olefin, ethylene. Although this is surprising and
disappointing, it does demonstrate the cooperative nature of
these activations, whereby the proximity of the unreactive Rh
also deactivates the Ir center to oxidative addition. This lack of
reactivity may in fact support the “prior coordination” model,
whereby C−H activation at Ir requires prior coordination at
Rh, which is apparently not effective enough in this role.
The steric differences between dppm and depm are evident
in the range of olefins activated by the depm system, in which
even the disubstituted isobutylene and the bulky styrene react
readily in the presence of TMNO. Finally, this study reaffirms
the pronounced synergic effect that two metal centers can have
in giving rise to reactivity that is not commonly observed in single-
metal complexes. This example of geminal C−H activa-
tion of olefins represents one of the few of its kind41,56−61,63,75,76
and appears to be the most reactive, requiring only TMNO
addition to initiate facile activation and being reactive for
a range of α-olefins, even those having reasonably bulky
substituents.
Although C−H bond activation in unsaturated substrates by
mononuclear species can proceed via prior π-coordination of
the substrate, Bergman et al. have demonstrated that this is not
always necessary.46,48 In binuclear complexes a third mecha-
nism that essentially combines these two mononuclear path-
ways is also possible, whereby π-coordination at one metal
positions the olefin for σ-complex formation with the adjacent
metal, leading to C−H bond cleavage,74 as shown in structure
EXPERIMENTAL SECTION
■
General Comments. All solvents were dried (using appropriate
drying agents), distilled before use, and stored under dinitrogen.
Deuterated solvents used for NMR experiments were freeze−pump−
thaw degassed (three cycles) and stored under nitrogen or argon over
molecular sieves. Reactions were carried out under argon using standard
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Schlenk techniques, and compounds that were obtained as solids were
purified by recrystallization. Prepurified argon and nitrogen were pur-
chased from Praxair, and carbon-13-enriched CO (99%) was supplied
by Isotec Inc. All purchased gases were used as received. Bis-
(diethylphosphino)methane,77,78 [IrCl(COD)]2,79 [IrCl(CO)-
and 1H NMR spectra showing the purity can be found in the
1
Supporting Information. H NMR (400 MHz, C6D6, 27 °C): δ 2.67
(quin., 4H, depm). 13C{1H} NMR (101 MHz, C6D6, 27 °C): δ 185.6
(s, 3C, Ir−CO). 31P{1H} NMR (162 MHz, C6D6, 27 °C): δ −11.0
(s, 4P). Low-temperature data: 13C{1H} NMR (101 MHz, CD2Cl2,
−80 °C): δ 193.8 (bs, 1C, Ir−CO), 189.3 (bs, 1C, Ir−CO), 179.8
(bs, 1C, Ir−CO). 31P{1H} NMR (162 MHz, CD2Cl2, −80 °C): δ −8.9
(b, 2P), −28.0 (b, 2P).
82
(PPh3)2],80 [RhCl(COD)]2,81 [RhCl(CO)2]2 and [H(Et2O)2][B-
(3,5-(CF3)2C6H3)4] (HBArF )83 were all prepared as previously
4
described. Trimethylamine-N-oxide dihydrate was dried by azeotropic
distillation as described in the literature.72 All other reagents were
obtained from Aldrich and were used as received (unless otherwise
stated).
c. [Ir2(CO)4(depm)2] (3). Compound 2 (50 mg, 0.058 mmol) was
dissolved in 10 mL of benzene and stirred under a dynamic atmo-
sphere of CO for 0.5 h, causing the color to change from orange to
bright yellow. The solvent was removed, giving an oily, dark yellow-
orange residue containing a mixture of 2 and 3 in variable proportions,
as gauged by NMR spectroscopy, revealing the susceptibility of 3 to
CO loss. The lability of this carbonyl has limited the characterization
Proton NMR spectra were recorded on Varian Unity 400 or 500
spectrometers or on a Bruker AM400 spectrometer. Carbon-13 NMR
spectra were recorded on Varian Unity 400 or 500 or Bruker AM300
spectrometers. Phosphorus-31 and fluorine-19 NMR spectra were
recorded on Varian Unity 400 or 500 or Bruker AM400 spectrometers.
1
to NMR spectroscopy. H NMR (400 MHz, CD2Cl2, 27 °C): δ 2.71
1
Two-dimensional NMR experiments (COSY, NOESY, and H−13C
(quin., 4H, depm). 13C{1H} NMR (101 MHz, CD2Cl2, 27 °C):
δ 189.8 (bs, 4C, Ir−CO). 31P{1H} NMR (162 MHz, CD2Cl2, 27 °C):
δ −31.4 (bs, 4P). Low-temperature data: 13C{1H} NMR (101 MHz,
CD2Cl2, −80 °C): δ 195.2 (bs, 1C, Ir−CO), 194.2 (bs, 1C, Ir−CO),
191.8 (bs, 1C, Ir−CO), 181.2 (bs, 1C, Ir−CO). 31P{1H} NMR
(162 MHz, CD2Cl2, −80 °C): δ −19.6 (bt, 2P, 2JPP = 53.7 Hz), −41.1
HMQC) were obtained on Varian Unity 400 or 500 spectrometers.
a. Preparation of Compounds. trans-[Ir2Cl2(CO)2(depm)2] (1).
To a solution of [Ir(Cl)(COD)]2 (200 mg, 0.30 mmol) in
25 mL of dichloromethane was quickly added, via cannula,
100 μL (0.60 mmol) of bis(diethylphosphino)methane (depm)
in 5 mL of dichloromethane, causing the solution to change
from orange-red to yellow-orange. The solution was stirred for
15 min and then placed under a slow CO purge for 5 min. The
CO was replaced by an argon purge, and the solution was set to
reflux for 0.5 h. Reducing the solution to dryness left an oily
orange residue, which was redissolved into 25 mL of THF. This
solution was set to reflux again for 1.5 h, with a continuing
argon purge, resulting in a color change to dark red-purple. The
solution was reduced to ∼5 mL, and Et2O (40 mL) was added
to precipitate a deep red-purple solid, which was isolated, wash-
ed twice with Et2O (2 × 10 mL), and dried to yield 150 mg
(60%) of 1. HRMS m/z calcd for Ir2P4O2C20H44Cl: 860.3804.
Found: 860.3805. 1H NMR (400 MHz, CD2Cl2, 27 °C): δ 2.52
(quin, 4H, depm). 13C{1H} NMR (101 MHz, CD2Cl2, 27 °C):
δ 168.3 (s, 2C, Ir−CO). 31P{1H} NMR (162 MHz, CD2Cl2,
27 °C): δ 8.3 (s, 4P). Anal. Calcd (%) for Ir2P4Cl2O2C20H44
(895.80): C 26.82, H 4.95. Found: C 26.87, H, 5.02.
2
(bt, 2P, JPP = 53.7 Hz).
d. [Ir2(H)(CO)3(μ-CH2)(depm)2][CF3SO3] (4). Neat methyl trifluor-
omethanesulphonate (MeOTf) (11 μL, 1.00 mmol) was slowly added
dropwise to a solution of 2 (75 mg, 0.088 mmol) in 15 mL of benzene.
The resulting turbid, dark orange mixture was stirred for 1 h, where-
upon it was reduced to ∼2 mL, followed by the dropwise addition of
pentane (10 mL) to precipitate a yellow-orange solid. This solid was
further washed with pentane (2 × 10 mL) and dried, giving 80 mg of a
pale orange powder (89% yield). HRMS m/z calcd for Ir2P4O3C22H47:
1
867.9729. Found: 867.9732. H NMR (400 MHz, CD2Cl2, 27 °C):
δ 3.95 (bs, 2H, Ir−CH2−Ir), 2.75 (m, 4H, depm), −12.42 (t, 1H, 2JHP
=
4.3 Hz). 13C{1H} NMR (101 MHz, CD2Cl2, 27 °C): δ 177.2 (s, 3C,
Ir−CO), 44.2 (m, 1C, Ir−CH2−Ir). 31P{1H} NMR (162 MHz,
CD2Cl2, 27 °C): δ −8.9 (bm, 2P), −19.5 (bm, 2P). Low-temperature
data: 13C{1H} NMR (101 MHz, CD2Cl2, −80 °C): δ 180.2 (bs, 1C,
Ir−CO), 178.7 (bs, 1C, Ir−CO), 166.3 (bs, 1C, Ir−CO), 45.3 (m, 1C,
Ir−CH22−Ir). 31P{1H} NMR (162 MHz, CD2Cl2, −80 °C): δ −8.9
2
b. [Ir2(CO)3(depm)2] (2). Method i. 1 (100 mg, 0.090 mmol) was
dissolved in 10 mL of THF, giving a turbid, deep scarlet-purple
solution. This was placed under an atmosphere of CO, resulting in a
series of color changes, through red, and finally to clear orange. The
addition of 2.5 mL of 1 M KOH/H2O yielded a dark orange solution,
which was stirred (closed under CO) at room temperature for 0.5 h.
The solution was stripped to dryness, extracted with 3 × 10 mL of
benzene, and filtered through Celite. A further 50 mL of benzene was
added, and the resulting solution was distilled for 2 h to remove
residual water by azeotropic distillation, after which time it could be
carried forward as such or stripped again to dryness to give a dark
brown-orange residue. (98%). Method ii. Compound 1 (54 mg,
0.049 mmol) was dissolved in 10 mL of acetone. Excess NaBH4
(0.200 mmol) was added directly to the solution, which was allowed to
stir for 1 h. The solvent was removed, and the product redissolved in
10 mL of benzene. Filtration through Celite gave a clear orange-brown
solution, which was purged with CO for 5 min followed by argon for
10 min. The solvent was reduced to dryness, affording the complex
as a viscous orange-brown oil. However, samples obtained via this
method were always less pure, spectroscopically, and were generally
obtained in poorer yields compared to the first method. Method iii.
Compound 1 (30 mg, 0.027 mmol) was dissolved in 20 mL of
acetonitrile. Excess zinc (0.500 mmol) was added directly to the
solution, producing a gray slurry, which was allowed to stir for 1 h
under a CO purge. The mixture was filtered through Celite, and the
clear orange solution was reduced to dryness under vacuum. The
residue was redissolved in CD2Cl2, and the purity of the product was
verified by NMR spectroscopy. This method also resulted in a product
that is less pure, spectroscopically, and generally in poorer yields com-
pared to the first method. Due to compound 2 not being isolated as a
solid, an elemental analysis could not be obtained; however 31P{1H}
(t, 2P, JPP = 32.4 Hz), −19.5 (t, 2P, JPP = 32.4 Hz). Anal. Calcd
(%) for Ir2SP4F3O6C23H47 (1017.00): C 27.16, H 4.66. Found: C
26.82, H, 4.55.
e. [Ir2(CH3)(CO)4(depm)2][CF3SO3] (5) and [Ir2(CO)4(C(O)CH3)-
(depm)2][CF3SO3] (6). Excess carbon monoxide (3 mL, 0.131 mmol)
was transferred via gastight syringe onto a solution of 50 mg
(0.037 mmol) of compound 3 in 0.7 mL of CD2Cl2. Under these con-
ditions both complexes were identified and characterized through
NMR spectroscopy. However, we were unable to isolate either
compound due to the regeneration of 3 upon the removal of the CO
1
atmosphere. Compound 5: H NMR (400 MHz, CD2Cl2, 27 °C):
3
δ 2.75 (quin., 4H, depm), 0.68 (t, JHP = 5.4 Hz, Ir−CH3). 13C{1H}
2
NMR (101 MHz, CD22Cl2, 27 °C): δ 191.1 (t, 2C, JCP = 11.2 Hz,
2
Ir−CO), 187.4 (t, 2C, JCP = 12.9 Hz, Ir−CO), −39.9 (t, 1C, JCP
=
5.8 Hz, Ir−CH3). 31P{1H} NMR (162 MHz, CD2Cl2, 27 °C): δ −14.9
(m, 2P), −18.6 (m, 2P). Compound 6: 1H NMR (400 MHz, CD2Cl2,
27 °C): δ 3.35 (quin., 4H, depm), 2.60 (s, 3H, Ir−C(O)CH3).
2
13C{1H} NMR (101 MHz, CD2Cl2, 27 °C): δ 221.2 (t, 1C, JCP
=
6.3 Hz, Ir−C(O)CH3), 195.0 (t, 2C, 2JCP = 10.3 Hz, Ir−CO), 187.8 (t,
2C, JCP = 12.9 Hz, Ir−CO), 53.2 (m, 1C, Ir−C(O)CH3). 31P{1H}
2
NMR (162 MHz, CD2Cl2, 27 °C): δ −15.7 (m, 2P), −20.9 (m, 2P).
f. [Ir2(CH3)(CO)2(depm)2][CF3SO3] (7). To a solution of compound 3
(55 mg, 0.63 mmol) in 0.5 mL of CD2Cl2 was added, dropwise,
trimethylamine-N-oxide (4 mg, 0.53 mmol) in 0.3 mL of CD2Cl2. The
resulting solution was mixed, and the reaction was monitored via NMR.
The product was found to be extremely moisture-sensitive and was sus-
ceptible to further reaction in solution, at ambient temperature, resulting in
the formation compound 8 after 30 min. Therefore, compound 7 was
characterized via solution spectroscopy, through comparison of its spectral
parameters to those of its dppm analogue [Ir2(CH3)(CO)2-
(dppm)2][CF3SO3].18 1H NMR (400 MHz, CD2Cl2, 27 °C): δ 2.80
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3
(m, 2H, depm), 2.30 (dm, 2H, depm), 0.57 (quin., 3H, JHP = 4.4 Hz,
Ir−CH3). 13C{1H} NMR (101 MHz, CD2Cl2, 27 °C): δ 174.2 (bs, 2C,
Ir−CO), 19.5 (bs, 1C, Ir−CH3). 31P{1H} NMR (162 MHz, CD2Cl2,
27 °C): δ 23.2 (s, 4P). Low-temperature data: 13C{1H} NMR (101 MHz,
CD2Cl2, −80 °C): δ 179.9 (bs, 1C, Ir−CO), 168.3 (bs, 1C, Ir−CO).
31P{1H} NMR (162 MHz, CD2Cl2, −80 °C): δ 26.1 (b, 2P), 19.8 (b, 2P).
g. [Ir2(CO)2(μ-OH)(depm)2][CF3SO3] (8). To a solution of com-
pound 7 (50 mg, 0.050 mmol), generated in situ at −20 °C in 5 mL of
dichloromethane, was added 5 μL (0.277 mmol) of water, and the
resultant mixture stirred while warming to room temperature over the
course of 0.5 h. The solvent was removed, and the product recrys-
tallized from dichloromethane and pentane, affording a bright yellow
powder (70% yield). 1H NMR (400 MHz, CD2Cl2, 27 °C): δ 3.60 (bs,
1H, Ir−OH−Ir), 2.85 (m, 4H, depm). 13C{1H} NMR (101 MHz,
CD2Cl2, 27 °C): δ 184.7 (s, 2C, Ir−CO). 31P{1H} NMR (162 MHz,
CD2Cl2, 27 °C): δ 16.5 (s, 4P). Anal. Calcd (%) for Ir2SP4F3O6C21H45
(990.97): C 25.45, H 4.58. Found: C 25.65, H, 4.59.
k. [Rh2(CO)3(depm)2] (12). Compound 11 (65 mg, 0.091 mmol)
was dissolved in 20 mL of THF and stirred under a static atmosphere
of CO. Two milliliters of aqueous 1 M KOH was transferred dropwise,
via a syringe, onto the stirred solution, and the resulting mixture left to
stir for 1.5 h. The solvent was removed to give an oily brown residue,
which was then extracted with benzene (3 × 10 mL). Filtration
through Celite gave a clear orange-brown solution, which was reduced
to dryness to afforded 55 mg of the spectroscopically pure 12 as a
1
viscous orange-brown oil (90% yield). H NMR (400 MHz, C6D6,
27 °C): δ 2.17 (quin., 4H, depm). 13C{1H} NMR (101 MHz, C6D6,
27 °C): δ 198.8 (bs, 3C, Rh−CO). 31P{1H} NMR (162 MHz, C6D6,
1
27 °C): δ 15.1 (d, 4P, JRhP = 137.7 Hz). Low-temperature data:
13C{1H} NMR (101 MHz, CD2Cl2, −110 °C): δ 209.1 (bd, 1C,
1
1JRhC = 77.0 Hz, Rh−CO), 206.8 (bd, 1C, JRhC = 71.2 Hz, Rh−CO),
1
183.4 (bd, 1C, JRhC = 67.9 Hz, Rh−CO). 31P{1H} NMR (162 MHz,
1
CD2Cl2, −110 °C): δ 22.5 (bd, 2P, JRhP = 117.1 Hz), 8.5 (bd,
1
2P, JRhP = 152.6 Hz).
h. [Ir2(CO)3(μ-H)(depm)2][X] (X = OTf (9-OTf), BArF (9-BArF )).
l. [Rh2(CO)4(depm)2] (13). Compound 12 (50 mg, 0.072 mmol)
was dissolved in 7 mL of CD2Cl2 and placed under an atmosphere of
CO, causing the color of the solution to change from orange to yellow.
The conversion of 12 to 13 was determined to be quantitative via
NMR spectroscopy. However, removal of the CO atmosphere resulted
in complete reversion back to 12. Therefore, 13 has only been char-
acterized in situ via NMR spectroscopy. 1H NMR (400 MHz, CD2Cl2,
27 °C): δ 2.60 (bm, 4H, depm). 13C{1H} NMR (101 MHz, CD2Cl2,
27 °C): δ 206.7 (bs, 4C, Rh−CO). 31P{1H} NMR (162 MHz, CD2Cl2,
4
4
9-OTf: Method i. To a solution of compound 2 (100 mg,
0.118 mmol) in 25 mL of CH2Cl2 was slowly added neat HOTf
(11 μL, 0.124 mmol) via microsyringe. The solution was stirred for
1 h, whereupon it was reduced to dryness. The solid was recrystallized
from THF and pentane to afford a dark brown solid (74% yield).
Method ii. To a solution of 8 was added a CO purge at a rate of
1 cm3/s. After 15 min, the CO purge was removed and an argon purge
was added for 15 min to remove excess carbon monoxide, resulting in
9-OTf. 9-BArF : To a solution of 2 (125 mg, 0.147 mmol) in 30 mL of
1
27 °C): δ 12.4 (bd, JRhP = 133.2 Hz, 4P). Low-temperature data:
4
13C{1H} NMR (101 MHz, CD2Cl2, −80 °C): δ 214.3 (dt, 1C, 1JRhP
=
CH2Cl2 was slowly added dropwise (170 mg, 0.170 mmol)
[H(Et2O)2][B(3,5-(CF3)2C6H3)4] in 10 mL of CH2Cl2. The resulting
mixture was stirred for 1 h, whereupon it was reduced to dryness. The
resulting residue was redissolved in ∼5 mL of diethyl ether, and 10 mL
of pentane was added to precipitate a dark red solid, which was
isolated, further washed with pentane (2 × 10 mL), and dried, giving
115 mg of 9 (78% yield). 1H NMR (400 MHz, CD2Cl2, 27 °C): δ 2.45
2
90.2 Hz, JCP = 29.7 Hz, Rh−CO), 204.1 (bs, 3C, Rh−CO). 31P{1H}
NMR (162 MHz, CD2Cl2, −80 °C): δ 24.3 (m, 2P), −1.3 (m, 2P).
m. [Rh2(CH3)(CO)3(depm)2][CF3SO3] (14) and [Rh2(CO)2(μ-κ1:κ1-
C(CH3)O)- (depm)2][CF3SO3] (14a). To a solution of 12 (35 mg, 0.052
mmol) in 0.8 mL of CD2Cl2, cooled in a dry ice/acetone ice bath to
−80 °C, was slowly added 6 μL (0.054 mmol) of neat methyl trifluoro-
methanesulphonate (MeOTf). The reaction was then monitored via
low-temperature NMR at −40 °C, showing the formation of com-
pound 14. Upon warming to −20 °C, 14 slowly converted to com-
pound 14a after 1 h. Warming to above 0 °C resulted in the decom-
position of 14 to 15, along with numerous unidentified products.
Compound 14: 1H NMR (400 MHz, C3D6O, −80 °C): δ 2.35 (quin.,
4H, depm), 0.63 (bm, 3H, Rh−CH3). 13C{1H} NMR (101 MHz,
2
(quin., 4H, depm), −10.40 (quin., 1H, JHP = 9.8 Hz, Ir−H−Ir).
13C{1H} NMR (101 MHz, CD2Cl2, 27 °C): δ 183.7 (s, 3C, Ir−CO).
31P{1H} NMR (162 MHz, CD2Cl2, 27 °C): δ 14.3 (s, 4P). Low-tem-
perature data: 1H NMR (400 MHz, CD2Cl2, −80 °C): δ 2.45 (b, 4H,
depm), −10.40 (b, 1H, Ir−H−Ir). 13C{1H} NMR (101 MHz, CD2Cl2,
−80 °C): δ 185.3 (b, 1C, Ir−CO), 183.3 (b, 2C, Ir−CO). 31P{1H}
NMR (162 MHz, CD2Cl2, −80 °C): δ 14.4 (b, 4P). Anal. Calcd (%)
for Ir2SP4F3O6C22H45 (9-OTf, 1002.98): C 26.35, H 4.52. Found:
C 26.45, H, 4.50.
1
C3D6O, −80 °C): δ 214.3 (bt, 2C, JCRh = 32.7 Hz, Rh−CO), 199.3
(bd, 1C, 1JCRh = 74.9 Hz, Rh−CO), −0.7 (bm, 1C, Rh−CH3). 31P{1H}
NMR (162 MHz, C3D6O, −80 °C): δ 35.6 (bm, 4P). Compound 14a:
1H NMR (400 MHz, C3D6O, −20 °C): δ 2.55 (quin., 4H, depm), 2.42
(s, 3H, Rh−C(CH3)O). 13C{1H} NMR (101 MHz, C3D6O, −20 °C):
δ 319.9 (bm, 1C, Rh−C(CH3)O), 199.8 (m, 1C, Rh−CO), 194.1
(d, 1C, 1JRhC = 76.3 Hz), 44.2 (s, 1C, Rh−C(CH3)O). 31P{1H} NMR
(162 MHz, C3D6O, −20 °C): δ 22.5 (bm, 2P), 17.2 (bm, 2P).
n. Addition of TMNO to 14. To a 0.5 mL solution of 14 (32 mg,
0.038 mmol) in CD2Cl2, cooled to −40 °C, was added trimethyl-
amine-N-oxide (3 mg, 0.040 mmol) dissolved in 0.3 mL of CD2Cl2.
The mixture was monitored by variable-temperature NMR. Below
−20 °C, no observable reaction was observed. Warming the solution
to −10 °C resulted in the formation of 14a as described above, but
there was no indication of reaction with TMNO. Warming the mix-
ture above 0 °C resulted in decomposition to compound 15 along
with various unidentified products.
i. [Ir2(H)(CO)4(depm)2][BArF ] (10). A solution of 9 dissolved in
4
0.7 mL of CD2Cl2 was placed under an atmosphere of CO, resulting in
the generation of 10, as determined spectroscopically. This species was
characterized only in solution, since removal of the CO atmosphere
resulted in quantitative conversion to 9. 1H NMR (400 MHz, CD2Cl2,
27 °C): δ 3.40 (m, 4H, depm), −8.80 (t, JHP = 14.4 Hz). 13C{1H}
2
2
NMR (101 MHz, CD2Cl2, 27 °C): δ 192.3 (t, 2C, JCP = 11.2 Hz,
Ir−CO), 186.9 (t, 2C, JCP = 12.9 Hz, Ir−CO). 31P{1H} NMR
2
2
(162 MHz, CD2Cl2, 27 °C): δ −9.5 (t, 2P, JPP = 29.8 Hz), −11.2
2
(t, 2P, JPP = 29.8 Hz).
j. trans-[Rh2Cl2(CO)2(depm)2] (11). A solution of [Rh2Cl2(COD)2]
(110 mg, 0.223 mmol) in 20 mL of acetone was placed under an
atmosphere of CO and stirred for 10 min. To this solution was added
dropwise, over a 5 min period, 100 μL (0.441 mmol) of depm in 10 mL
of acetone, causing the color to change from yellow to orange. The
solution was then refluxed for 0.5 h, whereupon it was cooled to room
temperature and reduced to dryness. The residue was redissolved into
5 mL of THF, and Et2O (20 mL) was added to precipitate an orange
solid, which was further washed with Et2O (2 × 5 mL) and dried,
yielding 85 mg (53% yield) of spectroscopically pure 11. HRMS m/z
o. [Rh2(CO)2(μ-OH)(depm)2][CF3SO3] (15). To a solution of 14
(34 mg, 0.041 mmol) in 0.8 mL of d6-acetone cooled to −20 °C was
added 5 μL (0.277 mmol) of water, causing the solution to lighten in
color. Maintaining this temperature for 0.5 h, while stirring, caused the
color to become bright yellow. The solvent was subsequently removed,
and the residue extracted three times into 5 mL of ether. The extrac-
tion solvent was removed, and the product was isolated as a yellow,
oily material. 1H NMR (400 MHz, CD2Cl2, 27 °C): δ 2.65 (quin., 4H,
depm). 13C{1H} NMR (101 MHz, CD2Cl2, 27 °C): δ 192.3 (dt, 2C,
1JRhC = 70.3 Hz, 2JCP = 15.8 Hz, Rh−CO). 31P{1H} NMR (162 MHz,
1
calcd for Rh2P4O2C20H44Cl: 681.0088. Found: 681.0090. H NMR
(400 MHz, CD2Cl2, 27 °C): δ 2.37 (quin., 4H, depm). 13C{1H} NMR
1
(101 MHz, CD2Cl2, 27 °C): δ 189.1 (d, 2C, JCRh = 74.8 Hz,
Rh−CO). 31P{1H} NMR (162 MHz, CD2Cl2, 27 °C): δ 17.9 (dm, 4P,
1JRhP = 117.2 Hz). Anal. Calcd (%) for Rh2P4Cl2O2C20H44 (717.17):
C 33.49, H 6.18. Found: C 33.22, H, 5.85.
1
CD2Cl2, 27 °C): δ 21.7 (dm, 4P, JRhP = 120.3 Hz).
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p. [Rh2(CO)3(μ-H)(depm)2][X] (X = OTf (16-OTf), BArF4 (16-BArF )).
was transferred dropwise, via syringe, to the stirred solution, and the
resulting mixture was stirred for 1.5 h. The solvent was removed under
vacuum, and the product extracted into 3 × 20 mL of benzene. Filtra-
tion through Celite gave a clear orange-brown solution, which was
purged with CO for 5 min followed by argon for 10 min. The solvent
was reduced to dryness, affording the complex as a spectroscopically
pure, viscous orange-brown oil. Method ii. Compound 19 (37 mg,
0.046 mmol) was dissolved in 10 mL of acetone. Excess NaBH4 (0.200
mmol) was added directly to the solution, which was stirred for 1 h.
The solvent was removed, and the product redissolved in 10 mL of
benzene or THF. Filtration through Celite gave a clear orange-brown
solution, which was purged with CO for 5 min followed by argon for
10 min. The solvent was reduced to dryness, affording the complex as
a viscous orange-brown oil. Samples obtained via this method were
always less pure, spectroscopically, and were generally obtained in
poorer yields compared to the first method (76% yield). HRMS m/z
calcd for IrRhP4O2C20H45 [M + H+ − CO]: 737.1054. Found:
4
16-OTf: Method i. To a solution of compound 12 (140 mg, 0.207
mmol) in 30 mL of CH2Cl2 was slowly added neat triflic acid (18 μL,
0.203 mmol) via microsyringe. The solution was stirred for 1 h,
whereupon it was reduced to dryness. The solid was recrystallized
from THF and pentane to afford a dark brown solid (81% yield).
Method ii. To a solution of 15 was added a CO purge at a rate of
1 cm3/s. After 15 min, the CO purge was replaced by a brief argon
purge to remove excess carbon monoxide. 16-BArF : To a solution of
4
12 (100 mg, 0.148 mmol) in 30 mL of CH2Cl2 was slowly added
dropwise 150 mg (0.150 mmol) of [H(Et2O)2][B(3,5-(CF3)2C6H3)4].
The resulting mixture was stirred for 1 h, whereupon it was reduced to
dryness and redissolved in ∼2 mL of ether. Pentane (10 mL) was
added to precipitate a dark orange-red solid, which was isolated and
further washed with pentane (2 × 10 mL), then dried, giving 155 mg
of spectroscopically pure 16 (75% yield). HRMS m/z calcd for
1
Rh2P4O2C20H45 [M+ − CO]: 647.0473. Found: 647.0475. H NMR
1
(400 MHz, CD2Cl2, 27 °C): δ 2.23 (quin., 4H, depm), −10.34
(m, 1H, 1JRhH = 24.3 Hz, 2JHP = 12.2 Hz, Rh−H−Rh). 13C{1H} NMR
(101 MHz, CD2Cl2, 27 °C): δ 194.3 (bm, 3C, Rh−CO). 31P{1H}
737.1049. H NMR (400 MHz, C6D6, 27 °C): δ 2.67 (quin., 4H,
depm). 13C{1H} NMR (101 MHz, C6D6, 27 °C): δ 189.0 (bs, 2C),
1
185.7 (d, 1C, JRhC = 70.1 Hz, Rh−CO). 31P{1H} NMR (162 MHz,
1
C6D6, 27 °C): δ 17.1 (dt, 2P, 1JRhP = 124.0 Hz, 2JPP = 64.3 Hz), −28.8
NMR (162 MHz, CD2Cl2, 27 °C): δ 35.2 (dm, 4P, JRhP = 97.4 Hz).
Low-temperature data: 1H NMR (400 MHz, CD2Cl2, −80 °C): δ 2.25
(b, 4H, depm), −10.39 (b, 1H, Rh−H−Rh). 13C{1H} NMR
(101 MHz, CD2Cl2, −80 °C): δ 195.1 (b, 1C, Rh−CO), 194.0
(b, 2C, Rh−CO). 31P{1H} NMR (162 MHz, CD2Cl2, 27 °C): δ 35.2
(b, 4P). Anal. Calcd (%) for Rh2P4F24O3C53H57B (1538.50): C 41.38,
H 3.73. Found: C 41.17, H, 3.95.
2
(t, 2P, JPP = 64.3 Hz).
u. [IrRh(CO)4(depm)2] (21). Compound 20 (275 mg, 0.341 mmol)
was dissolved in 20 mL of CH2Cl2 and stirred under a dynamic atmo-
sphere of CO for 1 h. NMR spectroscopy confirmed the formation of
21; however subsequent removal of the CO atmosphere resulted in
the loss of a CO, with quantitative reversion back to the starting com-
pound. Thus, the characterization of 21 has been limited to solution
q. [Rh2(CO)3(depm)2][CF3SO3]2 (17). To a solution of 12 (95 mg,
0.089 mmol), in 10 mL of acetone at 0 °C, was added a large excess of
neat triflic acid (85 μL, 0.960 mmol), and the solution stirred for 3 h
while warming to ambient temperature. The solvent was subsequently
removed, and the isolated orange solid was recrystallized from acetone
and pentane, affording a yellow residue. 1H NMR (400 MHz, C3D6O,
27 °C): δ 2.70 (quin., 4H, depm). 13C{1H} NMR (101 MHz, C3D6O,
27 °C): δ 188.6 (s, 3C, Rh−CO). 31P{1H} NMR (162 MHz, C3D6O,
1
1
31P{1H} and H NMR spectroscopy. H NMR (400 MHz, CD2Cl2,
27 °C): δ 2.79 (bs, 4H, depm). 13C{1H} NMR (101 MHz. CD2Cl2,
27 °C): δ 197.5 (b, 4C). 31P{1H} NMR (162 MHz, CD2Cl2, 27 °C): δ
1
−0.6 (b, 2P), −17.2 (b, 2P). Low-temperature data: H NMR (400
MHz, CD2Cl2, −80 °C): δ 3.15 (bs, 4H, depm). 13C{1H} NMR (101
MHz. CD2Cl2, −80 °C): δ 210.2 (dt, 1C, 1JCRh = 73.5 Hz, 2JCP = 48.6
1
2
Hz), 200.6 (dt, 1C, JCRh = 72.4 Hz, JCP = 10.5 Hz), 194.6 (m, 1C,
1
27 °C): δ 29.0 (bd, 4P, JRhP = 93.1 Hz).
2JCC = 10.5 Hz, 2JCP = 13.7 Hz), 192.7 (m, 1C, JCC = 10.5 Hz, 2JCP
=
2
r. [Rh2(CO)5(depm)2][CF3SO3]2 (18). To an NMR-scale solution
(50 mg, 0.037 mmol) of 17 in 0.7 mL of d6-acetone was added excess
CO, producing a clear yellow solution. The sample was subsequently
investigated via multinuclear NMR spectroscopy. X-ray quality crystals
of 18 were obtained by diffusion of diethyl ether into a CH2Cl2 solu-
tion of 18, under a CO atmosphere; however removal of the CO
atmosphere resulted in reversion to starting material. 1H NMR
(400 MHz, C3D6O, 27 °C): δ 3.00 (quin., 4H, depm). 13C{1H} NMR
(101 MHz, C3D6O, 27 °C): δ 191.7 (b, 5C, Rh−CO). 31P{1H} NMR
(162 MHz, C3D6O, 27 °C): δ 32.0 (bs, 4P).
11.1 Hz). 31P{1H} NMR (162 MHz, CD2Cl2, −80 °C): δ −2.4 (m, 2P,
1JPRh = 140.1 Hz, JPP = 57.5 Hz), −14.5 (t, 2P, JPP = 57.5 Hz).
v. [IrRh(CH3)(CO)3(depm)2][CF3SO3] (22). To a solution of 20
(75 mg, 0.098 mmol) in 10 mL of benzene was slowly added dropwise,
over a 5 min period, neat MeOTf (11 μL, 0.098 mmol). The resulting
mixture was stirred for 1 h, whereupon it was reduced to dryness and
redissolved in a minimum volume of THF (∼2 mL). Pentane (10 mL)
was added to precipitate a dark yellow-brown solid, which was isolated
and further washed with pentane (2 × 10 mL), then dried under
vacuum. 1H NMR (400 MHz, CD2Cl2, 27 °C): δ 3.00 (m, 4H, depm),
2
2
s. trans-[IrRhCl2(CO)2(depm)2] (19). To a solution of Vaska’s
complex, [Ir(Cl)(CO)(PPh3)2] (250 mg, 0.320 mmol), in 15 mL
of THF was added 150 μL (0.66 mmol) of bis(diethylphosphino)-
methane, which caused the solution to change from yellow to red-
purple. Leaving the solution to stir for 1 h resulted in a cloudy yellow
slurry, signifying the formation of [IrCl(CO)(depm)2]. The solvent
was removed, and the faint yellow solid was redissolved in 10 mL
of CH2Cl2, while in a separate flask, [Rh(Cl)(CO)2]2 (75 mg,
0.197 mmol) was dissolved in 7 mL of CH2Cl2. The [IrCl(CO)-
(depm)2] solution was then added to the [Rh(Cl)(CO)2]2 solution,
and the resulting orange mixture was stirred for 2 h. The solvent was
removed, and the residue redissolved in 7 mL of THF, followed by the
addition of pentane (30 mL) to precipitate a dark orange solid. The
solid was further washed with pentane (2 × 10 mL) and dried, giving
200 mg (67% yield). HRMS m/z calcd for IrRhP4O2C20H44Cl:
0.20 (t, JHP = 6.2 Hz, Ir−CH3). 13C{1H} NMR (101 MHz, CD2Cl2,
3
27 °C): δ 185.4 (s, 2C, Ir−CO), 184.2 (dt, 1JRhC = 71.1 Hz, 2JCP = 22.3
Hz, Rh−CO), −34.8 (s, 1C, Ir−CH3). 31P{1H} NMR (162 MHz,
1
2
CD2Cl2, 27 °C): δ 33.0 (dt, 2P, JRhP = 110.3 Hz, JPP = 41.8 Hz),
−11.0 (t, 2P, 2JPP = 39.5 Hz). Anal. Calcd (%) for IrRhSP4F3O6C23H47
(927.69): C 29.78, H 5.11. Found: C 29.64, H, 5.15.
w. [IrRh(CH3)(CO)2(depm)2][CF3SO3] (23). To a solution of 21
(45 mg, 0.049 mmol) in 0.8 mL of CD2Cl2 was slowly added 100 μL
of 0.5 M TMNO in CD2Cl2. The reaction was monitored by NMR,
which verified the formation of compound 23 after 10 min. Much like
its homobinuclear congeners, this product was unstable and extremely
moisture-sensitive; subsequent recrystallization attempts from various
dried solvents resulted only in decomposition or hydrolysis products;
thus 23 has been characterized via NMR spectroscopy. 1H NMR
(400 MHz, CD2Cl2, 27 °C): δ 2.70 (m, 2H, depm), 2.40 (m, 2H,
1
771.0659. Found: 771.0658. H NMR (400 MHz, CD2Cl2, 27 °C): δ
3
depm), 0.58 (t, 3H, JHP = 9.2 Hz, Ir−CH3). 13C{1H} NMR (101
2.42 (quin., 4H, depm). 13C{1H} NMR (101 MHz, CD2Cl2, 27 °C): δ
2
190.0 (bs, 1C, Rh−CO), 171.8 (s, 1C, Ir−CO). 31P{1H} NMR
MHz, CD2Cl2, 27 °C): δ 183.2 (t, 1C, JCP = 7.2 Hz, Ir−CO), 177.4
2
2
1
2
(dt, JRhC = 73.1 Hz, JCP = 16.7 Hz, Rh−CO), 9.9 (s, 1C, Ir−CH3).
(162 MHz, CD2Cl2, 27 °C): δ 18.0 (dt, 2P, JRhP = 118.3 Hz, JPP
=
31P{1H} NMR (162 MHz, CD2Cl2, 27 °C): δ 22.5 (dt, JRhP = 107.1
1
2
63.9 Hz), 9.6 (t, 2P, JPP = 63.9 Hz), Anal. Calcd (%) for
IrRhP4Cl2O2C20H44 (806.49): C 29.79, H 5.50. Found: C 29.72, H, 5.34.
t. [IrRh(CO)3(depm)2] (20). Method i. Compound 19 (275 mg,
0.341 mmol) was dissolved in 20 mL of THF and stirred under a
dynamic atmosphere of CO. Eight millilliters of aqueous 1 M KOH
2
2
Hz, JPP = 47.2 Hz, 2P), 19.8 (t, JPP = 47.2 Hz, 2P).
x. [IrRh(CO)2(μ-OH)(depm)2][CF3SO3] (24). To a solution of 23
(90 mg, 0.097 mmol), prepared in situ in 7 mL of CH2Cl2, was added
water (5 μL, 0.277 mmol). The solution was stirred at room tem-
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perature for 0.5 h, during which time the color lightened to a pale
orange. The solvent was removed, and the product recrystallized from
dichloromethane and pentane, affording an orange, oily material. H
bb. [Ir2(H)2(CO)2(μ-H)(μ-CC(H)CH3)(depm)2][BArF ] (28). Meth-
4
od i. In an NMR tube containing 9 (24 mg, 0.014 mmol) dissolved in
0.8 mL of CD2Cl2 was added 5 mL of propylene (0.0219 mmol) via a
gastight syringe. The solution was mixed, and the reaction was
monitored by multinuclear NMR. After 2.5 h, complete conversion to
28 was observed. Method ii. In an NMR tube containing 9 (33 mg,
0.019 mmol) dissolved in 0.6 mL of CD2Cl2 was added TMNO (1 mg,
0.014) dissolved in 0.2 mL of CD2Cl2, followed by the addition of
propylene (5 mL, 0.219 mmol). The reaction was mixed and moni-
tored by multinuclear NMR, which showed complete conversion after
15 min. Attempts to isolate the product as a solid for crystallization
were unsuccessful due to its solubility in both polar and nonpolar sol-
vents. HRMS m/z calcd for IrP4O2C23H51: 869.2092. Found:
869.2082. 1H NMR (498 MHz, CD2Cl2, 27 °C): δ 6.00 (m, 2H,
CC(H)CH3), 2.58 (m, 2H, depm), 1.88 (m, 3H, CC(H)CH3),
1
NMR (400 MHz, CD2Cl2, 27 °C): δ 3.33 (s, 1H, Ir−OH−Rh), 2.70
(m, 2H, depm), 2.05 (m, 2H, depm). 13C{1H} NMR (101 MHz,
CD2Cl2, 27 °C): δ 191.2 (dt, 1C, 1JRhC = 72.4 Hz, 2JCP = 16.6 Hz, Rh−
2
CO), 174.9 (t, JCP = 11.2 Hz, Ir−CO). 31P{1H} NMR (162 MHz,
CD2Cl2, 27 °C): δ 20.6 (dm, 2P, 1JRhP = 116.6 Hz), 17.2 (t, 2P, 2JPP
=
14.3 Hz).
y. [IrRh(CO)3(μ-H)(depm)2][X] (X = OTf (25-OTf), BArF (25-
4
BArF )). 25-OTf: Method i. To a solution of compound 20 (124 mg,
4
0.162 mmol) in 25 mL of CH2Cl2 was slowly added neat triflic acid
(15 μL, 0.169 mmol) via microsyringe. The solution was stirred for
1 h, whereupon it was reduced to dryness. The solid was recrystallized
from THF and pentane to afford a dark brown solid (71% yield).
Method ii. To a solution of 24 was added a CO purge at a rate of
1 cm3/s. After 15 min, the CO purge was replaced by a brief argon
4
1.63 (m, 2H, depm), −12.37 (m, 1H, JHH = 8.2 Hz, Ir−H), −12.63
4
(m, 1H, JHH = 8.2 Hz, Ir−H), −14.80 (m, 1H, Ir−H−Ir). 13C{1H}
purge to remove excess carbon monoxide. 25-BArF : To a solution of
NMR (125 MHz, CD2Cl2, 27 °C): δ 171.9 (m, 2C, Ir−CO). 31P{1H}
NMR (202 MHz, CD2Cl2, 27 °C): δ −6.2 (m, 2P), −7.5 (m, 2P).
4
compound 20 (100 mg, 0.131 mmol) in 30 mL of CH2Cl2 was slowly
added a solution of [H(Et2O)2][B(3,5-(CF3)2C6H3)4] (170 mg,
0.170 mmol) in 10 mL of CH2Cl2. The resulting mixture was stirred
for 1 h, whereupon it was reduced to dryness. The solid was recrys-
tallized from ether and pentane, affording a dark brown solid, which,
after isolation and further washing with pentane (2 × 10 mL), was
dried under vacuum (75% yield). HRMS m/z calcd for RhIrP4-
O3C21H45: 913.6678. Found: 913.6676. 1H NMR (400 MHz, CD2Cl2,
cc. [Ir2(H)2(CO)2(μ-H)(μ-CC(H)CF3)(depm)2][BArF ] (29). Method
4
i. In an NMR tube containing 9 (42 mg, 0.025 mmol) dissolved in 0.8 mL
of CD2Cl2 was added 5 mL of 3,3,3-trifluoropropylene (0.0219 mmol)
via a gastight syringe. The solution was mixed, and the reaction
was monitored by multinuclear NMR. After 2 h, complete conversion
to 29 was observed. Method ii. In an NMR tube containing 9 (39 mg,
0.024 mmol) dissolved in 0.6 mL of CD2Cl2 was added TMNO (2 mg,
0.027) dissolved in 0.2 mL of CD2Cl2, followed by the addition of
3,3,3-trifluoropropylene (5 mL, 0.219 mmol) to the headspace via a
gastight syringe. The reaction was mixed and monitored by multi-
nuclear NMR, which showed complete conversion after 15 min.
Attempts to isolate the product as a solid for crystallization were un-
successful due to its solubility in both polar and nonpolar solvents. 1H
NMR (498 MHz, CD2Cl2, 27 °C): δ 6.70 (s, 1H, CC(H)CF3), 2.08
(m, 2H, depm), 1.74 (m, 2H, depm), −12.33 (m, 1H, Ir−H), −12.61
(m, 1H, Ir−H), −14.84 (m, 1H, Ir−H−Ir). 13C{1H} NMR (125 MHz,
27 °C): δ 2.85 (quin., 4H, depm), −11.32 (m, 1JRhH = 21.1 Hz, 2JHP
=
9.8 Hz, Ir−H−Rh). 13C{1H} NMR (101 MHz, CD2Cl2, 27 °C):
1
2
δ 187.2 (dt, 1C, JCRh = 74.6 Hz, JCP =16.2 Hz, Rh−CO), 180.3 (t,
2C, JCP = 9.3 Hz, Ir−CO). 31P{1H} NMR (162 MHz, CD2Cl2,
2
27 °C): δ 27.7 (dt, 2P, 1JRhP = 106.9 Hz, 2JPP = 45.5 Hz), −5.5 (t, 2P,
2JPP = 45.5 Hz). Anal. Calcd (%) for IrRhSP4F3O6C22H45 (913.67): C
28.92, H 4.96. Found: C 29.14, H, 4.97.
z. [Ir2(H)2(CO)2(μ-H)(μ-CCH2)(depm)2][BArF ] (26). Method i. In
4
an NMR tube containing 9 (38 mg, 0.022 mmol) dissolved in 0.8 mL
of CD2Cl2 was added ethylene (5 mL, 0.219 mmol) via a gastight
syringe to the headspace. The solution was mixed, and the reaction
was monitored by multinuclear NMR. After 2 h, complete conversion
to 26 was observed. Method ii. In an NMR tube containing 9 (42 mg,
0.024 mmol) dissolved in 0.6 mL of CD2Cl2 was added TMNO (2 mg,
0.027) dissolved in 0.2 mL of CD2Cl2, followed by the addition of
ethylene (5 mL, 0.219 mmol) to the headspace. The reaction was
mixed and monitored by multinuclear NMR, which showed complete
conversion after 15 min. Attempts to isolate the product as a solid for
crystallization were unsuccessful due to its solubility in both polar and
nonpolar solvents. HRMS m/z calcd for IrP4O2C22H49: 855.1936.
Found: 855.1901. 1H NMR (498 MHz, CD2Cl2, 27 °C): δ 6.57 (s, 2H,
CCH2), 2.85 (m, 2H, depm), 1.75 (m, 2H, depm), −12.66 (m, 2H,
Ir−H), −14.69 (m, 1H, Ir−H−Ir). 13C{1H} NMR (125 MHz, CD2Cl2,
2
CD2Cl2, 27 °C): δ 172.3 (t, 1C, JCP = 8.7 Hz, Ir−CO), 171.7 (t, 1C,
2JCP = 8.2 Hz, Ir−CO). 19F NMR (469 MHz, CD2Cl2, 27 °C): δ −59.9
(s, 3F). 31P{1H} NMR (202 MHz, CD2Cl2, 27 °C): δ −8.6 (t, 2P,
2
2JPP = 28.4 Hz), −9.4 (t, 2P, JPP = 28.4 Hz).
dd. [Ir2(H)2(CO)2(μ-H)(μ-CC(H)C(H)CH2)(depm)2][BArF ] (30).
4
Method i. To the headspace above an NMR tube containing 9
(46 mg, 0.027 mmol) dissolved in 0.8 mL of CD2Cl2 was added 5 mL
of 1,3-butadiene (0.0219 mmol) via a gastight syringe. The solution
was mixed, and the reaction was monitored by multinuclear NMR.
After 5 h, complete conversion to 30 was observed. Method ii. In an
NMR tube containing 9 (51 mg, 0.030 mmol) dissolved in 0.6 mL of
CD2Cl2 was added TMNO (2 mg, 0.027) dissolved in 0.2 mL of
CD2Cl2, followed by the addition of 1,3-butadiene (5 mL,
0.219 mmol) via a gastight syringe to the headspace. The reaction
was mixed and monitored by multinuclear NMR, which showed com-
plete conversion after 15 min. Attempts to isolate the product as a
solid for crystallization were unsuccessful due to its solubility in both
polar and nonpolar solvents. HRMS m/z calcd for IrP4O2C24H51:
1
2
2
27 °C): δ 190.1 (dtt, 1C, JCC = 64.9 Hz, JCP = 10.0 Hz, JCP
=
=
1
10.0 Hz, μ-CCH2), 172.4 (m, 2C, Ir−CO), 130.4 (d, 1C, JCC
64.9 Hz, μ-CCH2). 31P{1H} NMR (202 MHz, CD2Cl2, 27 °C):
δ −6.9 (s, 4P).
aa. [Ir2(H)2(CO)2(μ-H)(μ-CCHF)(depm)2][BArF ] (27). In an NMR
1
881.2092. Found: 881.2084. H NMR (498 MHz, CD2Cl2, 27 °C):
4
3
tube containing 9 (43 mg, 0.025 mmol) dissolved in 0.5 mL of CD2Cl2
was added TMNO (2 mg, 0.027 mmol) in 0.3 mL of CD2Cl2, along
with 5 mL of vinylfluoride (0.0219 mmol) via a gastight syringe to the
headspace. The solution was mixed, and the reaction was monitored
by multinuclear NMR. After 30 min, complete conversion to 27 was
observed. Attempts to isolate the product as a solid for crystallization
were unsuccessful due to its solubility in both polar and nonpolar sol-
vents. Performing the same reaction in the absence of TMNO still
produced 27; however the yield was <10% based on NMR integration
δ 6.82 (d, 1H, JHH = 9.9 Hz, CC(H)C(H)C(H)H), 6.28 (ddd,
3
3
3
1H, JHH = 17.1 Hz, JHH = 9.9 Hz, JHH = 9.9 Hz, CC(H)C(H)
3
C(H)H), 4.93 (d, 1H, JHH = 17.1 Hz, CC(H)C(H)C(H)H),
3
4.82 (d, 1H, JHH = 9.9 Hz, CC(H)C(H)C(H)H), 2.57 (m, 2H,
depm), 1.65 (m, 2H, depm), −12.31 (m, 1H, Ir−H), −12.56 (m, 1H,
Ir−H), −14.70 (m, 1H, Ir−H−Ir). 13C{1H} NMR (125 MHz, CD2Cl2,
2
2
27 °C): δ 171.5 (t, 1C, JCP = 7.9 Hz, Ir−CO), 171.3 (t, 1C, JCP
=
7.8 Hz, Ir−CO). 31P{1H} NMR (202 MHz, CD2Cl2, 27 °C): δ −6.6
(m, 2P), −7.1 (m, 2P).
after 2 h. 1H NMR (498 MHz, CD2Cl2, 27 °C): δ 6.61 (d, 1H, 2JHF
=
ee. [Ir2(H)2(CO)2(μ-H)(μ-CC(H)Ph)(depm)2][BArF4] (31). Method i.
In a round-bottom flask containing 9 (89 mg, 0.052 mmol) dissolved
in 15 mL of CH2Cl2 was added neat styrene (200 μL, 1.746 mmol).
The solution was brought to reflux for 48 h, after which the solution
was cooled to ambient temperature. The solvent was removed, and the
yellow residue was dried under reduced pressure. Method ii. In an
NMR tube charged with 9 (44 mg, 0.025 mmol) dissolved in 0.6 mL
108.2 Hz, CCHF), 2.77 (m, 2H, depm), 1.67 (m, 2H, depm),
−12.54 (m, 1H, Ir−H), −13.09 (m, 1H, Ir−H), −15.48 (m, 1H, Ir−
H−Ir). 13C{1H} NMR (125 MHz, CD2Cl2, 27 °C): δ 171.1 (m, 2C,
Ir−CO). 19F NMR (469 MHz, CD2Cl2, 27 °C): δ −72.1 (d, 1F, 2JHF
=
108.2 Hz). 31P{1H} NMR (202 MHz, CD2Cl2, 27 °C): δ −7.1
(m, 2P), −9.1 (m, 2P).
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of CD2Cl2 was added neat styrene (100 μL, 0.873 mmol), followed
immediately by TMNO (2.5 mg, 0.033 mmol) dissolved in 0.2 mL of
CD2Cl2. The solution was mixed, and the reaction monitored by
NMR, after which quantitative conversion to 31 was observed after
10 min. Attempts to isolate the product as a solid for crystallization
were unsuccessful due to its solubility in both polar and nonpolar sol-
O(2B), O(3B), C(1B), C(2B), C(3B), C(4B)) were restrained to have
the same values as the corresponding ones for the major orientation, as
shown in Figure 5. In cases involving partial occupancy for atoms, the
occupancy factors were refined in initial refinements, but were fixed in
the final refinements.
1
3
vents. H NMR (498 MHz, CD2Cl2, 27 °C): δ 7.67 (d, 2H, JHH
=
7.9 Hz, -ortho), 7.66 (s, 1H, CC(H)Ph), 7.28 (t, 2H, 3JHH = 7.9 Hz,
3
-meta), 7.17 (t, 1H, JHH = 7.9 Hz, -para), 2.26 (m, 2H, depm), 1.65
(m, 2H, depm), −11.90 (dt, 1H, 2JHP = 15.7 Hz, 4JHH = 9.0 Hz, Ir−H),
−12.36 (dt, 1H, 2JHP = 14.9 Hz, 4JHH = 9.0 Hz, Ir−H), −14.64 (m, 1H,
Ir−H−Ir). 13C{1H} NMR (125 MHz, CD2Cl2, 27 °C): δ 171.2
(m, 2C, Ir−CO). 31P{1H} NMR (202 MHz, CD2Cl2, 27 °C): δ −8.7
(m, 2P), −9.2 (m, 2P).
ff. [Ir2(H)2(CO)2(μ-H)(μ-CC(CH3)2)(depm)2][BArF ] (32). In an
4
NMR tube containing 9 (52 mg, 0.030 mmol) dissolved in 0.8 mL of
CD2Cl2 and cooled to −80 °C was added TMNO (2.5 mg, 0.033 mmol)
followed by isobutylene (25 μL, 0.262 mmol), which had also been
cooled to −80 °C. The solution was mixed and slowly allowed to
warm to ambient temperature. Once ambient temperature was re-
ached, the reaction was monitored by multinuclear NMR. Attempts to
isolate the product as a solid for crystallization were unsuccessful
1
due to its solubility in both polar and nonpolar solvents. H NMR
Figure 5. Perspective view of the disordered “IrRhMe(CO)3” fragment
in the cation of compound 22. The depm atoms have been omitted for
clarity. The atoms of one disordered form are connected by solid
bonds, while the others are connected by dashed bonds.
(400 MHz, CD2Cl2, 27 °C): δ 2.42 (m, 2H, depm), 1.52 (m, 2H,
depm), 1.40 (s, 6H, CC(CH3)2), −13.73 (m, 3H, Ir−H), −15.88
(m, 1H, Ir−H−Ir). 13C{1H} NMR (101 MHz, CD2Cl2, 27 °C):
δ 167.6 (m, 2C, Ir−CO). 31P{1H} NMR (162 MHz, CD2Cl2, 27 °C):
δ −6.2 (m, 4P).
gg. Reaction of 25 with Ethylene. In an NMR tube containing 25-
OTf (36 mg, 0.039 mmol) dissolved in 0.8 mL of CD2Cl2 and cooled
to −80 °C was added TMNO (3 mg, 0.040 mmol) followed by
ethylene (5 mL, 0.219 mmol). The solution was mixed and slowly
allowed to warm to ambient temperature. Once ambient temperature
was reached, the reaction was monitored by multinuclear NMR. De-
composition of 25-OTf was observed, leading to multiple unidentified
products.
ASSOCIATED CONTENT
* Supporting Information
■
S
Tables of crystallographic experimental details for 1, 4, 11, 16,
18, and 22; ORTEP diagrams for the complex cations of 1 and
11, showing all non-hydrogen atoms of phenyl groups. Atomic
coordinates, interatomic distances and angles, anisotropic
thermal parameters, and hydrogen parameters for 1, 4, 11,
16, 18, and 22 in a CIF file. The 31P{1H} and 1H NMR spectra
are given for compound 2. This material is available free of
charge via the Internet at http://pubs.acs.org.
a. X-ray Structure Determinations. General. Crystals were
grown via slow diffusion using the following solvent com-
binations: CH2Cl2/Et2O (1, 18); THF/n-pentane (4); THF/
Et2O (11); Et2O/n-pentane (16); CH2Cl2/n-pentane (22). Data
were collected using a Bruker SMART 1000 CCD detector/
PLATFORM diffactometer with the crystals cooled to −80 °C
(1, 4, 11, 18, 22) or with a Bruker APEX II CCD detector/D8
diffractometer84 with the crystal cooled to −100 °C (16); all data
were collected using Mo Kα radiation (λ = 0.71073 Å). The data
were corrected for absorption via a multiscan method (1, 11, 18,
22) or through Gaussian integration from indexing of the crystal
faces (4, 16). Structures were solved using direct methods
(SHELXS-9785 for 1, 4, 11, 18, and 22) or Patterson search/
structure expansion (DIRDIF-200886 for 16). Refinements were
completed using the program SHELXL-97.85 Non-hydridic
hydrogen atoms were assigned positions based on the sp2 or
sp3 hybridization geometries of their attached carbon atoms and
were given isotropic displacement parameters 20% greater than
those of their parent atoms. See Supporting Information for a
listing of crystallographic experimental data.
b. Special Refinement Conditions. (i) 1: The chloro and carbonyl
ligands attached to iridium were disordered, thus refined as two sets of
positions (Cl(A), C(1A), O(1A) with an occupancy factor of 0.6 and
Cl(B), C(1B), O(1B) with an occupancy factor of 0.4). (ii) 4: The
Ir(2)−H(2) distance was restrained to be 1.65(1) Å. The C(25)−
C(26A) and C(25)−C(26B) distances (within a disordered phosphine
ethyl group) were restrained to be 1.53(1) Å. (iii) 11: The chloro and
carbonyl ligands attached to rhodium were disordered, thus refined as
two sets of positions ({Cl(A), C(1A), O(1A)} and {Cl(B), C(1B),
O(1B)}, each with an occupancy factor of 0.5). (iv) 16: The atomic
coordinates and isotropic displacement parameter for the bridging
hydrido ligand (H(1)) were allowed to refine without restraints. (v)
22: Bond distances and angles within the minor (40%) component of
the disordered “RhIr(CO)3(CH3)” fragment (Ir(B), Rh(B), O(1B),
AUTHOR INFORMATION
Corresponding Author
*E-mail: martin.cowie@ualberta.ca. Fax: 01 7804928231. Tel:
01 7804925581.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the Natural Sciences and Engineering Research
Council of Canada (NSERC) and the University of Alberta for
financial support for this research and NSERC for funding the
Bruker D8/APEX II CCD diffractometer. We thank the
Chemistry Department’s NMR Spectroscopy and Analytical
and Instrumentation Laboratories. Finally, we thank NSERC
and Alberta Innovates−Technology (formerly Alberta Ingen-
uity Fund) for scholarships to M.E.S.
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