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

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 (HBAr^F) 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 = SO₃CF₃or 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][BAr^F] (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][BAr^F].

4

only a few examples having been reported.^41,56−63Of these, all

INTRODUCTION

■

but one⁶²involve pairs of metals at some stage in the activation

process.

Interest in the reactivity of binuclear complexes¹containing

either pairs of identical metals²⁻¹⁸or 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.³⁷⁻⁴⁰A 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−H^41,42and C−F^36,43,44bond

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.⁴¹However,

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.¹¹Unfortunately, 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,⁴⁵⁻⁵⁵double, geminal C−H activation is rare, with

Received: December 6, 2011

Published: March 7, 2012

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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.⁶⁵⁻⁶⁹In 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 Rh₂analogues 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,⁷displaying 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.^7,12The

similarities in the low-temperature NMR spectra of 2 compared to

those of [Rh₂(CO)₃(dppm)₂],⁸[RhIr(CO)₃(dppm)₂],²²and

[Ir₂(CO)₃(dppm)₂]⁷suggest 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)]₂to a

CH₂Cl₂solution 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 Ir₂compounds

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,¹⁸reaction 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 (³J_HP= 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.⁷¹Additional coupling of the meth-

yl group to the acyl carbonyl (¹J_CC= 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.^11,18The

¹H NMR spectrum displays a quintet at δ 0.57 (³J_HP= 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.¹¹However, 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 Ir₂P₄plane, 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.⁷²In 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 analogue⁷and,

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 Ir₂analogue. 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 BAr^F¯

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 (²J_HP= 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 (¹J_RhP

=

117.2 Hz) and rhodium−carbon coupling for the carbonyls in

the ¹³C{¹H} NMR spectrum (¹J_RhC= 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 Ir₂complex, 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 (¹J_RhP= 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 (¹J_RhC= 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]²and [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 (²J_HP= 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 BAr^{F −}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 (¹J_RhH= 24.3 Hz) and

all four phosphorus nuclei (²J_HP= 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-BAr^Fconfirms 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 CH₃and 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,¹⁵indicative 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][BAr^F] (16-BAr^F) showing the atom-labeling

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 H₂evolution (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 Ir₂analogue, 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]₂produces 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 (¹J_CRh= 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 Ir₂analogue, 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 ¹³CH₃resonance

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 BAr^{F −}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][BAr^F] (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).⁶⁹However, 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][BAr^F] (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.^41,56−63In 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

(²J_HP= 9.8 Hz) and to rhodium (¹J_HRh= 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,⁴¹also 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

(²J_HF= 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 (³J_HHvicinal= 9.9 Hz,

³J_HHcis= 9.9 Hz, ³J_HHtrans= 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]⁺(³J_HHvicinal= 10.0 Hz, J_HHcis

=

10.0 Hz, J_HHtrans= 16.5 Hz).⁴¹Finally, 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 ¹³C₂H₄to 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 analogue⁴²convincingly

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 Rh₂complexes 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,^7,15,18,25the 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 Ir₂systems 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 Rh₂systems, 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,^41,56−63and 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 Ir₂system. 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 Rh₂systems 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 kind^{41,56−61,63,75,76}

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.^46,48In 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,⁷⁴as 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]₂and [H(Et₂O)₂][B-

(3,5-(CF₃)₂C₆H₃)₄] (HBAr^F)⁸³were all prepared as previously

4

described. Trimethylamine-N-oxide dihydrate was dried by azeotropic

distillation as described in the literature.⁷²All 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, ²J_PP= 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, J_PP= 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, ²J_HP

=

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, J_PP= 32.4 Hz), −19.5 (t, 2P, J_PP= 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, J_HP= 5.4 Hz, Ir−CH₃). ¹³C{¹H}

2

NMR (101 MHz, CD₂₂Cl₂, 27 °C): δ 191.1 (t, 2C, J_CP= 11.2 Hz,

2

Ir−CO), 187.4 (t, 2C, J_CP= 12.9 Hz, Ir−CO), −39.9 (t, 1C, J_CP

=

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, J_CP

=

6.3 Hz, Ir−C(O)CH₃), 195.0 (t, 2C, ²J_CP= 10.3 Hz, Ir−CO), 187.8 (t,

2C, J_CP= 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 CD₂Cl₂was 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].¹⁸¹H 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, J_HP= 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, J_RhP= 137.7 Hz). Low-temperature data:

¹³C{¹H} NMR (101 MHz, CD₂Cl₂, −110 °C): δ 209.1 (bd, 1C,

1

¹J_RhC= 77.0 Hz, Rh−CO), 206.8 (bd, 1C, J_RhC= 71.2 Hz, Rh−CO),

1

183.4 (bd, 1C, J_RhC= 67.9 Hz, Rh−CO). ³¹P{¹H} NMR (162 MHz,

1

CD₂Cl₂, −110 °C): δ 22.5 (bd, 2P, J_RhP= 117.1 Hz), 8.5 (bd,

1

2P, J_RhP= 152.6 Hz).

h. [Ir₂(CO)₃(μ-H)(depm)₂][X] (X = OTf (9-OTf), BAr^F(9-BAr^F)).

l. [Rh₂(CO)₄(depm)₂] (13). Compound 12 (50 mg, 0.072 mmol)

was dissolved in 7 mL of CD₂Cl₂and 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

9-OTf: Method i. To a solution of compound 2 (100 mg,

0.118 mmol) in 25 mL of CH₂Cl₂was 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-BAr^F: To a solution of 2 (125 mg, 0.147 mmol) in 30 mL of

1

27 °C): δ 12.4 (bd, J_RhP= 133.2 Hz, 4P). Low-temperature data:

4

¹³C{¹H} NMR (101 MHz, CD₂Cl₂, −80 °C): δ 214.3 (dt, 1C, ¹J_RhP

=

CH₂Cl₂was 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, J_CP= 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, J_HP= 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, J_CRh= 32.7 Hz, Rh−CO), 199.3

(bd, 1C, ¹J_CRh= 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, ¹J_RhC= 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][BAr^F] (10). A solution of 9 dissolved in

4

0.7 mL of CD₂Cl₂was 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, J_HP= 14.4 Hz). ¹³C{¹H}

2

NMR (101 MHz, CD₂Cl₂, 27 °C): δ 192.3 (t, 2C, J_CP= 11.2 Hz,

Ir−CO), 186.9 (t, 2C, J_CP= 12.9 Hz, Ir−CO). ³¹P{¹H} NMR

2

(162 MHz, CD₂Cl₂, 27 °C): δ −9.5 (t, 2P, J_PP= 29.8 Hz), −11.2

2

(t, 2P, J_PP= 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,

¹J_RhC= 70.3 Hz, ²J_CP= 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, J_CRh= 74.8 Hz,

Rh−CO). ³¹P{¹H} NMR (162 MHz, CD₂Cl₂, 27 °C): δ 17.9 (dm, 4P,

¹J_RhP= 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, J_RhP= 120.3 Hz).

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p. [Rh₂(CO)₃(μ-H)(depm)₂][X] (X = OTf (16-OTf), BAr^F₄(16-BAr^F)).

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 CH₂Cl₂was 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-BAr^F: To a solution of

4

12 (100 mg, 0.148 mmol) in 30 mL of CH₂Cl₂was 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, ¹J_RhH= 24.3 Hz, ²J_HP= 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, J_RhC= 70.1 Hz, Rh−CO). ³¹P{¹H} NMR (162 MHz,

1

C₆D₆, 27 °C): δ 17.1 (dt, 2P, ¹J_RhP= 124.0 Hz, ²J_PP= 64.3 Hz), −28.8

NMR (162 MHz, CD₂Cl₂, 27 °C): δ 35.2 (dm, 4P, J_RhP= 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, J_PP= 64.3 Hz).

u. [IrRh(CO)₄(depm)₂] (21). Compound 20 (275 mg, 0.341 mmol)

was dissolved in 20 mL of CH₂Cl₂and 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

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, ¹J_CRh= 73.5 Hz, ²J_CP= 48.6

1

2

Hz), 200.6 (dt, 1C, J_CRh= 72.4 Hz, J_CP= 10.5 Hz), 194.6 (m, 1C,

1

27 °C): δ 29.0 (bd, 4P, J_RhP= 93.1 Hz).

²J_CC= 10.5 Hz, ²J_CP= 13.7 Hz), 192.7 (m, 1C, J_CC= 10.5 Hz, ²J_CP

=

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 CH₂Cl₂solu-

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,

¹J_PRh= 140.1 Hz, J_PP= 57.5 Hz), −14.5 (t, 2P, J_PP= 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

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]₂solution,

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, J_HP= 6.2 Hz, Ir−CH₃). ¹³C{¹H} NMR (101 MHz, CD₂Cl₂,

3

27 °C): δ 185.4 (s, 2C, Ir−CO), 184.2 (dt, ¹J_RhC= 71.1 Hz, ²J_CP= 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, J_RhP= 110.3 Hz, J_PP= 41.8 Hz),

−11.0 (t, 2P, ²J_PP= 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 CD₂Cl₂was 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, J_HP= 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, J_CP= 7.2 Hz, Ir−CO), 177.4

2

1

2

(dt, J_RhC= 73.1 Hz, J_CP= 16.7 Hz, Rh−CO), 9.9 (s, 1C, Ir−CH₃).

(162 MHz, CD₂Cl₂, 27 °C): δ 18.0 (dt, 2P, J_RhP= 118.3 Hz, J_PP

=

³¹P{¹H} NMR (162 MHz, CD₂Cl₂, 27 °C): δ 22.5 (dt, J_RhP= 107.1

1

2

63.9 Hz), 9.6 (t, 2P, J_PP= 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

Hz, J_PP= 47.2 Hz, 2P), 19.8 (t, J_PP= 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][BAr^F] (28). Meth-

4

od i. In an NMR tube containing 9 (24 mg, 0.014 mmol) dissolved in

0.8 mL of CD₂Cl₂was 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 CD₂Cl₂was 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, ¹J_RhC= 72.4 Hz, ²J_CP= 16.6 Hz, Rh−

2

CO), 174.9 (t, J_CP= 11.2 Hz, Ir−CO). ³¹P{¹H} NMR (162 MHz,

CD₂Cl₂, 27 °C): δ 20.6 (dm, 2P, ¹J_RhP= 116.6 Hz), 17.2 (t, 2P, ²J_PP

=

14.3 Hz).

y. [IrRh(CO)₃(μ-H)(depm)₂][X] (X = OTf (25-OTf), BAr^F(25-

4

BAr^F)). 25-OTf: Method i. To a solution of compound 20 (124 mg,

4

0.162 mmol) in 25 mL of CH₂Cl₂was 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, J_HH= 8.2 Hz, Ir−H), −12.63

4

(m, 1H, J_HH= 8.2 Hz, Ir−H), −14.80 (m, 1H, Ir−H−Ir). ¹³C{¹H}

purge to remove excess carbon monoxide. 25-BAr^F: 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 CH₂Cl₂was 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][BAr^F] (29). Method

4

i. In an NMR tube containing 9 (42 mg, 0.025 mmol) dissolved in 0.8 mL

of CD₂Cl₂was 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 CD₂Cl₂was 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, ¹J_RhH= 21.1 Hz, ²J_HP

=

9.8 Hz, Ir−H−Rh). ¹³C{¹H} NMR (101 MHz, CD₂Cl₂, 27 °C):

1

2

δ 187.2 (dt, 1C, J_CRh= 74.6 Hz, J_CP=16.2 Hz, Rh−CO), 180.3 (t,

2C, J_CP= 9.3 Hz, Ir−CO). ³¹P{¹H} NMR (162 MHz, CD₂Cl₂,

2

27 °C): δ 27.7 (dt, 2P, ¹J_RhP= 106.9 Hz, ²J_PP= 45.5 Hz), −5.5 (t, 2P,

²J_PP= 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][BAr^F] (26). Method i. In

4

an NMR tube containing 9 (38 mg, 0.022 mmol) dissolved in 0.8 mL

of CD₂Cl₂was 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 CD₂Cl₂was 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, J_CP= 8.7 Hz, Ir−CO), 171.7 (t, 1C,

²J_CP= 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

²J_PP= 28.4 Hz), −9.4 (t, 2P, J_PP= 28.4 Hz).

dd. [Ir₂(H)₂(CO)₂(μ-H)(μ-CC(H)C(H)CH₂)(depm)₂][BAr^F] (30).

4

Method i. To the headspace above an NMR tube containing 9

(46 mg, 0.027 mmol) dissolved in 0.8 mL of CD₂Cl₂was 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

CD₂Cl₂was 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

27 °C): δ 190.1 (dtt, 1C, J_CC= 64.9 Hz, J_CP= 10.0 Hz, J_CP

=

1

10.0 Hz, μ-CCH₂), 172.4 (m, 2C, Ir−CO), 130.4 (d, 1C, J_CC

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][BAr^F] (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, J_HH= 9.9 Hz, CC(H)C(H)C(H)H), 6.28 (ddd,

3

1H, J_HH= 17.1 Hz, J_HH= 9.9 Hz, J_HH= 9.9 Hz, CC(H)C(H)

3

C(H)H), 4.93 (d, 1H, J_HH= 17.1 Hz, CC(H)C(H)C(H)H),

3

4.82 (d, 1H, J_HH= 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

27 °C): δ 171.5 (t, 1C, J_CP= 7.9 Hz, Ir−CO), 171.3 (t, 1C, J_CP

=

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, ²J_HF

=

ee. [Ir₂(H)₂(CO)₂(μ-H)(μ-CC(H)Ph)(depm)₂][BAr^F₄] (31). Method i.

In a round-bottom flask containing 9 (89 mg, 0.052 mmol) dissolved

in 15 mL of CH₂Cl₂was 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, ²J_HF

=

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 CD₂Cl₂was 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, J_HH

=

7.9 Hz, -ortho), 7.66 (s, 1H, CC(H)Ph), 7.28 (t, 2H, ³J_HH= 7.9 Hz,

3

-meta), 7.17 (t, 1H, J_HH= 7.9 Hz, -para), 2.26 (m, 2H, depm), 1.65

(m, 2H, depm), −11.90 (dt, 1H, ²J_HP= 15.7 Hz, ⁴J_HH= 9.0 Hz, Ir−H),

−12.36 (dt, 1H, ²J_HP= 14.9 Hz, ⁴J_HH= 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][BAr^F] (32). In an

4

NMR tube containing 9 (52 mg, 0.030 mmol) dissolved in 0.8 mL of

CD₂Cl₂and 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 CD₂Cl₂and 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

diffractometer⁸⁴with 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-97⁸⁵for 1, 4, 11, 18, and 22) or Patterson search/

structure expansion (DIRDIF-2008⁸⁶for 16). Refinements were

completed using the program SHELXL-97.⁸⁵Non-hydridic

hydrogen atoms were assigned positions based on the sp²or

sp³hybridization 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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Bis(diethylphosphino)methane as a bridging ligand in complexes of Ir 2, Rh2, and IrRh: Geminal C-H activation of α-olefins

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