Carbene-anchored/pendent-imidazolium species as precursors to di-N-heterocyclic carbene-bridged mixed-metal complexes

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N-Heterocyclic Carbenes

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Westfälische Wilhelms-Universität, Münster, Germany

Published in issue 35, 2009 of Dalton Transactions

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www.rsc.org/dalton | Dalton Transactions

Carbene-anchored/pendent-imidazolium species as precursors to

di-N-heterocyclic carbene-bridged mixed-metal complexes†

Matthew T. Zamora, Michael J. Ferguson,‡ Robert McDonald‡ and Martin Cowie*

Received 6th April 2009, Accepted 16th June 2009

First published as an Advance Article on the web 4th August 2009

DOI: 10.1039/b906884h

Reaction of a series of linked diimidazolium dibromide salts with one-half equivalent of

[Rh(m-OAc)(COD)]₂under reﬂux conditions generates a series of carbene-anchored/

1

pendent-imidazolium complexes, [RhBr(COD)(^RC(H)-h -C^eth)][Br] (^MeC(H)-h -C^eth

=

ethylene[(N-methyl)imidazolium][(N-methyl)imidazole-2-ylidene] and ^tBuC(H)-h -C^eth

=

1

ethylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imidazole-2-ylidene]) via deprotonation of one end

of the diimidazolium salt and coordination of the resulting carbene to Rh. Reaction of these complexes

1

with carbon monoxide or the appropriate diphosphine yields either [RhBr(CO)₂(^RC(H)-h -C^eth)][Br]

1

(R = Me, ^tBu) or [RhBr(P^«P)(^MeC(H)-h -C^eth)][Br] (P^«P = Ph₂PCH₂PPh₂, Ph₂PCH₂CH₂PPh₂,

Et₂PCH₂PEt₂), respectively. The resulting diphosphine complexes readily decompose in solution. A

1

series of palladium complexes [PdI_3-n(PR₃)_n(L)][I]_n(n = 1,2) and [PdI(P^«P)(L)][I]₂(L = ^tBuC(H)-h -C^meth

,

1

^tBuC(H)-h -C^eth

;

^tBuC(H)-h -C^meth= methylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imidazole-

2-ylidene]), containing the linked NHC-imidazolium moiety, have also been prepared by reacting the

triiodo complexes, [PdI₃(^tBuC(H)-h -C^meth)] and [PdI₃(^tBuC(H)-h -C^eth)] with several mono- and

diphosphines. Attempts to generate mixed Rh/Pd complexes using Pd(OAc)₂to deprotonate the

pendent arm of several of the above carbene-anchored/pendent-imidazolium complexes of Rh have

proven unsuccessful. However, a targeted di-NHC-bridged heterobimetallic complex

1

[PdI₂(PEt₃)(m-^tBuCC^meth)RhI(COD)] (^tBuCC^meth= 1,1¢-methylene-3,3¢-di-tert-butyldiimidazol-2,2¢-

diylidene) can be generated by deprotonation of the imidazolium group in [PdI₂(PEt₃)(^tBuC(H)-

h -C^meth)][I] using half an equivalent of [Rh(m-OAc)(COD)]₂. The X-ray structure determination of this

1

Pd/Rh complex conﬁrms the dicarbene-bridged formulation and shows a metal-metal separation of

˚

approximately 6.2 A. Reaction of this Rh/Pd complex with CO yields the corresponding dicarbonyl

product [PdI₂(PEt₃)(m-^tBuCC^meth)RhI(CO)₂] via replacement of the COD ligand. The related

dicarbene-bridged Ir/Rh complex [IrBr(COD)(m-^tBuCC^meth)RhBr(COD)] can be generated by reaction

1

of [IrBr(COD)(^tBuC(H)-h -C^meth)][Br] with [Rh(m-OAc)(COD)]₂, while the Pd/Ir complexes

[PdI₂(PR₃)(m-^tBuCC^meth)IrI(COD)] (PR₃= PPh₃, PMe₂Ph) can be generated by reaction of the

1

monometallic [PdI₂(PR₃)(^tBuC(H)-h -C^meth)][I] species with K[N(SiMe₃)₂] in the presence of

[Ir(m-Cl)(COD)]₂. The carbonyl analogues, [PdI₂(PR₃)(m-^tBuCC^meth)IrI(CO)₂], can be generated via a

gentle purge of CO gas. These di-NHC-bridged heterobimetallic species represent some of the ﬁrst

examples of this class and are the ﬁrst involving palladium.

NHC ligands having an unsaturated backbone are more planar,

having a slimmer, less sterically hindered axis perpendicular

to the carbene ring plane. This quasi two-dimensional shape

is evident in square-planar complexes of NHCs in which the

NHC plane is usually perpendicular to the metal coordination

plane.^21–28

Most reports on NHC complexes involve monocarbenes,^1–4

however there are a number of reports involving di-N-heterocyclic

carbenes (di-NHCs), in which pairs of NHC groups are linked

in a number of ways, as replacements for chelating^16,29–41or

bridging^{7,8,16,29–32,34–45}diphosphines. Our initial study on binuclear

di-NHC-bridged complexes concentrated on homobinuclear com-

plexes of rhodium.⁴⁶However our ongoing interest in mixed-metal

systems,^47–56and their use as mixed-metal catalysts^57–60led us to

extend our investigation to complexes in which di-NHC ligands

could be used as bridging groups connecting different pairs of

metals.

Introduction

N-heterocyclic carbenes (NHCs)^1–4have emerged as versatile

ligands in organometallic chemistry, and offer a useful alternative

to the ubiquitous phosphine ligands.^5–15Although these carbene

ligands are considered to have bonding properties similar to

those of trialkylphosphines^16–19their steric properties differ sig-

niﬁcantly; whereas phosphines are often described as conical,²⁰

Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada

T6G 2G2. E-mail: martin.cowie@ualberta.ca; Fax: 01 7804928231; Tel: 01

7804925581

† Electronic supplementary information (ESI) available: ¹H and ¹³C{ H}

1

NMR spectra of 2c, 8b, 10b and 23b; decoupled spectra for 9b; variable

temperature spectral data for 18b. CCDC reference numbers 726822–

726827. For ESI and crystallographic data in CIF or other electronic

format see DOI: 10.1039/b906884h

‡ X-Ray Crystallography Laboratory.

This journal is

The Royal Society of Chemistry 2009

Dalton Trans., 2009, 7269–7287 | 7269

©

For the rational generation of mixed-metal species it appeared

that stepwise incorporation of the different metals was the most

straightforward strategy. A series of carbene-anchored/pendent-

imidazolium salts of the type diagrammed in Chart 1,^{11,37,42,43,46,61–69}

appeared ideal for this purpose, through deprotonation of the

pendent imidazolium salt in the presence of the second metal. We

therefore set out togenerate amore extensive series of such pendent

species and to use them as synthons for a series of dicarbene-

bridged mixed-metal complexes. The results of this study, in which

the ﬁrst series of di-NHC-bridged heterobinuclear compounds⁶⁹

are characterized, are reported herein.

to the reported iodo analogue,¹¹while methylene[(N-tert-

butyl)imidazolium][(N-tert-butyl)imidazole-2-ylidene]triiodo-

palladium(II) was prepared as previously reported.⁶³The ¹H,

1

¹³C and ³¹P{ H} NMR spectra were recorded on a Varian

DirectDrive 500 MHz, iNova-500, or iNova-400 spectrometer

operating at 499.82, 498.12, or 399.79 MHz for ¹H; 125.68,

125.26, or 100.53 MHz for ¹³C; and 202.33, 201.64, or 161.8 MHz

for ³¹P, respectively; or on a Varian iNova-300 operating at

1

299.97 MHz for ¹H. The ¹H and ¹³C{ H} chemical shifts are

1

referenced to TMS; whereas the ³¹P{ H} chemical shifts are

referenced to 85% H₃PO₄. Elemental analyses were performed

by the microanalytical service within this department. Likewise,

mass spectrometric analyses were performed by the departmental

Mass Spectrometry Laboratory using positive ion electrospray

ionization on a Micromass ZabSpec Hybrid Sector-TOF or

an Agilent Technologies 6220 Accurate-mass TOF LC/MS.

Infrared spectra were obtained using a Nicolet Avatar 370DGTS

instrument. Carbonyl stretches reported are for non-isotopically

enriched samples. Conductivity measurements on compounds

Chart 1

10b and 15b as the iodide salts were carried out on 1 ¥ 10^-3

M

solutions in nitromethane using a Yellow Springs Instruments

Model 31 conductivity bridge. For these species the conductivities

obtained were K = 82.8 and 135.2 X^-1cm²mol^-1, respectively.

Experimental

General comments

Preparation of compounds

All solvents were dried (using appropriate drying agents),

distilled before use, and stored under a dinitrogen atmosphere.

Deuterated solvents used for NMR experiments were freeze-

pump-thaw degassed and stored under argon over appropriate

molecular sieves. Reactions were performed under an inert

argon atmosphere or the reactant gas using standard Schlenk

techniques. Unless otherwise speciﬁed, reactions were carried out

at ambient temperature. Ammonium carbonate, tert-butylamine,

1,5-cyclooctadiene, 1,2-dibromoethane, dibromomethane, bis(di-

phenylphosphino)methane (dppm), formaldehyde, glyoxal, 1-me-

thylimidazole, palladium(II) acetate, potassium bis(trimethyl-

isilyl)amide, triethylphosphine, triphenylphosphine and sodium

iodide were purchased from Aldrich; diammonium hexachloro-

iridate(IV), 1,2-bis(diphenylphosphino)ethane (dppe), dimethyl-

phenylphosphine, trimethylphosphine and rhodium(III) chloride

hydrate were purchased from Strem; potassium bromide was

purchased from BDH; and sodium acetate was purchased

from Fischer Scientiﬁc. All chemicals were used without

further puriﬁcation, with the exception of sodium acetate,

which was puriﬁed by repetitive melting under dynamic

vacuum before use. 1-tert-Butylimidazole was prepared using

a published procedure and puriﬁed by vacuum distillation.^70,71

The preparations of diimidazolium salts used in this paper have

been reported;^11,16,30,72however, a general synthetic approach has

been outlined below. Bis(diethylphosphino)methane (depm) was

prepared using published procedures and used without further

puriﬁcation,⁷³as was bis(cycloocta-1,5-diene)(m-dichloro)-

dirhodium ([Rh(m-Cl)(COD)]₂) and bis(cycloocta-1,5-diene)-

(m-dichloro)diiridium ([Ir(m-Cl)(COD)]₂).^74,75Bis(cycloocta-1,5-

(a) General synthetic route to diimidazolium salts (1a–d).

A

500 mL round-bottom ﬂask was charged with 100 mmol of

the dibromoalkane and dissolved in 200 mL of toluene. An

excess (250 mmol) of the 1-alkylimidazole was then added and

the solution reﬂuxed for 24 h. The resulting precipitate was

collected by vacuum ﬁltration and recrystallized from boiling

methanol by cooling to -25 ^◦C, whereupon colourless crystals

were obtained in yields ranging from 50 to 90%. The salts

were then dried in vacuo for several days to remove residual

solvent and stored in a desiccator before use. In this paper

we use the abbreviations originally suggested by Green and

coworkers,⁴²with compounds 1a–d as diprotonated versions

of the respective dicarbenes ^MeCC^meth(a), ^tBuCC^meth(b), ^MeCC^eth

(c), ^tBuCC^eth(d) as dibromide salts, namely 1,1¢-(methylene)-

3,3¢-dimethyldiimidazolium-2,2¢-diylidene dibromide 1a), 1,1¢-

(methylene)-3,3¢-di-tert-butyldiimidazolium-2,2¢-diylidene dibro-

mide (1b), 1,1¢-(1,2-ethylene)-3,3¢-dimethyldiimidazolium-2,2¢-

diylidene dibromide (1c) and 1,1¢-(1,2-ethylene)-3,3¢-di-tert-

butyldiimidazolium-2,2¢-diylidene dibromide (1d). As an adap-

tation of these abbreviations, the carbene-anchored/pendent-

1

imidazolium ligands are designated as ^MeC(H)-h -C^meth

,

^tBuC(H)-

1

h -C^meth

,

^MeC(H)-h -C^ethand ^tBuC(H)-h -C^eth

.

(b) Ethylene[(N-methyl)imidazolium][(N-methyl)imidazole-2-

ylidene)bromo(g²:g²-cyclooctadiene)rhodium(I)] bromide, [RhBr-

(COD)(^MeC(H)-g¹-C^eth)][Br] (2c). A 20 mL portion of CH₃CN

was added to a solid mixture containing 1c (422 mg, 1.17 mmol)

and [Rh(m-OAc)(COD)]₂(301 mg, 0.56 mmol). The resulting

slurry was stirred for 18 h under reﬂux conditions and cooled to

room temperature. The solvent was then removed under reduced

pressure and the crude product redissolved in 10 mL of CH₂Cl₂.

A 45 mL portion of diethyl ether was added to precipitate a

white solid and the solution ﬁltered via cannula. The solvent

was removed under reduced pressure, giving 261 mg (83%).

diene)(m-diacetato)dirhodium

([Rh(m-OAc)(COD)]₂)

was

prepared as previously reported and recrystallized from

ethyl acetate.⁷⁶The pendent complex methylene[(N-tert-butyl)-

2

imidazolium][(N-tert-butyl)imidazole-2-ylidene]bromo(h :h -1,5-

cyclooctadiene)iridium(I) bromide was prepared similarly

7270 | Dalton Trans., 2009, 7269–7287

This journal is

The Royal Society of Chemistry 2009

©

¹H NMR (399.79 MHz, CD₂Cl₂, 27.0 ^◦C): 10.18 (br dd, 1H,

product redissolved in 10 mL of CH₂Cl₂. A 30 mL portion of

diethyl ether was added to precipitate an oily pale yellow solid,

which was washed with 3 ¥ 25 mL portions of pentane before

4

3

⁴J_H-H= 1.9 Hz, J_H-H= 1.9 Hz, NCHN); 7.90 (dd, 1H, J_H-H

=

4

3

4

1.9 Hz, J_H-H= 1.9 Hz), 7.15 (dd, 1H, J_H-H= 1.9 Hz, J_H-H

1.9 Hz, NCH_imid-H); 4.03 (s, 3H, N_imid-HCH₃); 7.22 (d, 1H, ³J_H-H

1.9 Hz), 6.76 (d, 1H, J_H-H= 1.9 Hz, NCH_imid-Rh); 3.96 (s,

3H, N_imid-RhCH₃); 5.60 (m, 1H), 5.12 (m, 2H), 4.99 (m, 1H,

NCH₂CH₂N); 5.09 (m, 1H), 4.99 (m, 1H), 3.48 (m, 1H), 3.30

drying in vacuo, giving 157 mg (85%). H NMR (399.79 MHz,

1

CD₂Cl₂, 27.0 ^◦C): 10.11 (br dd, 1H, NCHN); 7.62 (br dd, 1H),

7.15 (br dd, 1H, NCH_imid-H); 3.98 (s, 3H, N_imid-HCH₃); 7.72 (d, 1H,

³J_H-H= 1.7 Hz), 6.96 (d, 1H, ³J_H-H= 1.7 Hz, NCH_imid-Rh); 3.86 (s,

3H, N_imid-RhCH₃); 5.56 (br m, 3H), 5.33 (br m, 1H, NCH₂CH₂N).

3

(m, 1H), 2.41 (m, 4H), 1.97 (m, 4H, COD). ¹³C{ H} NMR

1

◦

(125.68 MHz, CD₂Cl₂, 27.0 C): 182.8 (d, 1C, J_C-Rh= 50.1 Hz,

C_carbene); 124.1 (s, 1C, NCH_imid-Rh); 123.3 (s, 1C, NCH_imid-Rh); 36.9

(s, 1C, N_imid-RhCH₃); 135.8 (s, 1C, NCHN_imid-H); 122.4 (s, 1C,

NCH_imid-H); 122.3 (s, 1C, NCH_imid-H); 38.1 (s, 1C, N_imid-HCH₃);

50.0 (s, 1C), 49.6 (s, 1C, CH₂CH₂); 98.9 (d, 1C, ¹J_C-Rh= 7.0 Hz),

¹³C{ H} NMR (125.68 MHz, CD₂Cl₂, 27.0 ^◦C): 186.2 (d, 1C,

1

¹J_C-Rh= 53.6 Hz), 182.1 (d, 1C, J_C-Rh= 76.2 Hz, CO); 173.7

1

(d, 1C, J_C-Rh= 42.6 Hz, C_carbene); 138.1 (s, 1C, NCHN); 124.2

(s, 1C), 123.6 (s, 1C), 123.4 (s, 1C), 122.7 (s, 1C, NCH); 50.3 (s,

1C), 49.6 (s, 1C, CH₂CH₂); 38.8 (s, 1C), 37.0 (s, 1C, NCH₃). IR

(solution, cm^-1): 2083 (CO), 2007 (CO). HRMS m/z Calcd for

1

98.5 (d, 1C, J_C-Rh= 7.0 Hz), 71.0 (d, 1C, J_C-Rh= 15.0 Hz),

1

69.5 (d, 1C, J_C-Rh= 15.0 Hz), 33.5 (s, 1C), 32.3 (s, 1C), 30.0 (s,

C₁₂H₁₅BrN₄O₂Rh (M⁺- Br): 428.9428. Found: 428.9427 (M⁺

-

1C), 28.6 (s, 1C, COD). HRMS m/z Calcd for C₁₈H₂₇BrN₄Rr

(M⁺- Br): 481.0469. Found: 481.0470 (M⁺- Br). Anal. Calcd for

C₁₈H₂₇Br₂N₄Rh · 0.17 CH₂Cl₂: C, 37.85; H, 4.8; N, 9.7. Found: C,

37.6; H, 4.8; N, 9.9. The presence of 0.17 equivalents of CH₂Cl₂

was conﬁrmed by ¹H NMR spectroscopy in chloroform. The ¹H

Br). Compound 3c could only be isolated as an oil so satisfactory

elemental analyses could not be obtained.

(e)

zole-2-ylidene)bromo-dicarbonylrhodium(I)] bromide, [RhBr(CO)₂-

(

^tBuC(H)-g¹-C^eth)][Br] (3d). The desired complex was prepared

Ethylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imida-

and ¹³C{ H} NMR spectra of this compound are given in the

1

electronic supplementary information, ESI (Fig. S1).†

as described for 3c using 2d (152 mg, 0.235 mmol), and the crude

product puriﬁed using 10 mL of CH₂Cl₂and 25 mL of diethyl

ether, to precipitate an oily pale yellow solid, which was then

washed with 2 ¥ 25 mL portions of pentane before drying in va_◦cuo,

giving 104 mg (87%). ¹H NMR (299.97 MHz, CD₂Cl₂, 27.0 C):

10.01 (dd, 1H, ⁴J_H-H= 1.8 Hz, ⁴J_H-H= 1.8 Hz NCHN); 7.90 (dd,

1H, ³J_H-H= 1.8 Hz, ⁴J_H-H= 1.8 Hz), 7.51 (dd, 1H, ³J_H-H= 1.8 Hz,

⁴J_H-H= 1.8 Hz, NCH_imid-H); 1.94 (s, 9H, N_imid-HC(CH₃)₃); 7.60 (d,

(c)

Ethylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imida-

zole-2-ylidene)bromo-(g²:g²-cyclooctadiene)rhodium(I)] bromide,

[RhBr(COD)(^tBuC(H)-g¹-C^eth)][Br] (2d). The desired complex

was prepared as described for 2c, using 1d (818 mg, 1.875 mmol)

and [Rh(m-OAc)(COD)]₂(507 mg, 0.938 mmol) in 40 mL of

CH₃CN, heated at reﬂux for 75 h. The crude product was puriﬁed

as described for 2c, and isolated using 10 mL of CH₂Cl₂and

45 mL of diethyl ether, resulting in 835 mg (69%) of a yellow

3

1H, J_H-H= 2.0 Hz), 7.35 (d, 1H, J_H-H= 2.0 Hz, NCH_imid-Rh);

1.82 (s, 9H, N_imid-RhC(CH₃)₃); 5.70 (br m, 2H), 5.31 (br m, 2H,

solid. H NMR (399.79 MHz, CD₂Cl₂, 27.0 ^◦C): 9.93 (dd, 1H,

1

NCH₂CH₂N). ¹³C{ H} NMR (100.54 MHz, CD₂Cl₂, 27.0 ^◦C):

1

4

3

⁴J_H-H= 2.2 Hz, J_H-H= 2.2 Hz, NCHN); 7.98 (dd, 1H, J_H-H

=

1

186.2 (d, 1C, J_C-Rh= 54.2 Hz), 182.3 (d, J_C-Rh= 77.8 Hz, CO);

4

3

4

2.2 Hz, J_H-H= 2.2 Hz), 7.29 (dd, 1H, J_H-H= 2.2 Hz, J_H-H

=

1

171.5 (d, 1C, J_C-Rh= 42.1 Hz, C_carbene); 136.0 (s, 1C, NCHN);

2.2 Hz, NCH_imid-H); 1.94 (s, 3H, N_imid-HC(CH₃)₃); 7.16 (d, 1H,

124.7 (s, 1C), 122.9 (s, 1C), 120.7 (s, 1C), 118.8 (s, 1C, NCH);

59.3 (s, 1C), 30.0 (s, 3C, N_imid-RhC(CH₃)₃); 60.8 (s, 1C), 32.1

(s, 3C, N_imid-HC(CH₃)₃); 51.7 (s, 1C), 48.4 (s, 1C, CH₂CH₂). IR

(solution, cm^-1): 2081 (CO), 2005 (CO). HRMS m/z Calcd for

³J_H-H= 2.2 Hz), 6.96 (d, 1H, J_H-H= 2.2 Hz, NCH_imid-Rh); 1.66

3

(s, 3H, N_imid-RhC(CH₃)₃); 5.66 (m, 2H), 5.31 (m, 1H), 5.04 (m,

1H, NCH₂CH₂N); 5.07 (m, 1H), 4.94 (m, 1H), 3.42 (m, 1H),

3.30 (m, 1H), 2.39 (m, 4H), 1.89 (m, 2H), 1.65 (m, 2H, COD).

C₁₈H₂₇BrN₄O₂Rh (M⁺- Br): 513.0367. Found: 513.0366 (M⁺

-

¹³C{ H} NMR (100.54 MHz, CD₂Cl₂, 27.0 ^◦C): 180.5 (d, 1C,

1

Br). Compound 3d could only be isolated as an oil so satisfactory

elemental analyses could not be obtained.

¹J_C-Rh= 49.4 Hz, C_carbene); 120.0 (s, 1C, NCH_imid-Rh); 118.7 (s, 1C,

NCH_imid-Rh); 59.0 (s, 1C), 32.1 (s, 3C, N_imid-RhC(CH₃)₃); 135.8 (s, 1C,

NCHN_imid-H); 122.8 (s, 1C, NCH_imid-H); 124.0 (s, 1C, NCH_imid-H);

60.4, (s, 1C), 30.0 (s, 3C, N_imid-HC(CH₃)₃); 51.6 (s, 1C), 48.9 (s,

(f)

ylidene)bromo(g¹:g¹-bis(diphenylphosphino)methane)rhodium(I)]

bromide, [RhBr(dppm)(^MeC(H)-g¹-C^eth)][Br] (4c).

10 mL

Ethylene[(N-methyl)imidazolium][(N-methyl)imidazole-2-

1C, CH₂CH₂); 96.8 (d, 1C, ¹J_C-Rh= 7.5 Hz), 94.1 (d, 1C, ¹J_C-Rh

=

A

1

6.9 Hz), 71.9 (d, 1C, J_C-Rh= 15.4 Hz), 70.3 (d, 1C, J_C-Rh

=

portion of CH₂Cl₂was added to a solid mixture containing

2c (49 mg, 0.087 mmol) and dppm (39 mg, 0.101 mmol). The

resulting solution bleached to a paler yellow immediately. ¹H

NMR (299.97 MHz, CD₂Cl₂, 27.5 ^◦C): 10.15 (br s, 1H, NCHN);

7.21 (br s, 1H), 6.79 (br, 1H, NCH_imid-H); 3.95 (s, 3H, N_imid-HCH₃);

14.1 Hz), 32.8 (s, 1C), 31.4 (s, 1C), 29.5 (s, 1C), 29.0 (s, 1C, COD).

HRMS m/z Calcd for C₂₄H₃₉BrN₄Rh (M⁺- Br): 565.1408.

Found: 565.1410 (M⁺- Br). Anal. Calcd for C₂₄H₃₉Br₂N₄Rh: C,

44.6; H, 6.1; N, 8.7. Found: C, 44.95; H, 6.2; N, 8.6.

3

(d)

2-ylidene)bromo-dicarbonylrhodium(I)] bromide, [RhBr(CO)₂-

^MeC(H)-g¹-C^eth)][Br] [3c]. A 10 mL portion of CH₂Cl₂was

Ethylene[(N-methyl)imidazolium][(N-methyl)imidazole-

8.04 (d, 1H, J_H-H= 1.8 Hz), 6.79 (br s, 1H, NCH_imid-Rh); 3.91 (s,

3H, N_imid-RhCH₃); 4.44 (m, 2H), 4.09 (m, 2H, NCH₂CH₂N); 8.04

(

(m, 4H), 7.34 (m, 16H, Ph); 5.88 (ddd, 1H, ²J_H-H= 13.7 Hz, ²J_H-P

=

2

added to a ﬂask containing 2c (175 mg, 0.311 mmol). A 15 min

gentle purge of CO to a stirring solution yielded a more pale yellow

solution. The conversion to the respective dicarbonyl complex

3c was accompanied by the facile loss of 1,5-cyclooctadiene and

9.7 Hz, J_H-P= 6.5 Hz), 4.70 (ddd, 1H, J_H-H= 13.7 Hz, J_H-P

=

3.6 Hz, J_H-P= 3.6 Hz, PCH₂P).³¹P{ H} NMR (161.84 MHz,

2

1

CD₂Cl₂, 27.0 ^◦C): -13.6 (dd, 1P, J_P-Rh= 172.8 Hz, J_P-P

=

1

2

95.9 Hz), -36.0 (dd, 1P, ¹J_P-Rh= 103.9 Hz, ²J_P-P= 95.9 Hz, dppm).

1

was monitored to completion using H NMR spectroscopy. The

The transient nature of the product precluded the acquisition of

1

solvent was then removed under reduced pressure and the crude

¹³C{ H} NMR spectra and elemental analyses.

This journal is

The Royal Society of Chemistry 2009

Dalton Trans., 2009, 7269–7287 | 7271

©

(g) Ethylene[(N-methyl)imidazolium][(N-methyl)imidazole-2-

ylidene)bromo(g¹:g¹-bis(diphenylphosphino)ethane)rhodium(I)]

bromide, [RhBr(dppe)(^MeC(H)-g¹-C^eth)][Br] (5c). The desired

complex was prepared as described for 4c using 2c (87 mg,

0.155 mmol) and dppe (62 mg, 0.156 mmol). The resulting

solution bleached to a paler yellow immediately. ¹H NMR

(299.97 MHz, CD₂Cl₂, 27.5 ^◦C): 10.12 (br s, 1H, NCHN); 7.92

(br s, 1H), 7.07 (br s, 1H, NCH_imid-H); 3.92 (s, 3H, N_imid-HCH₃); 6.87

(br s, 1H), 6.65 (br s, 1H, NCH_imid-Rh); 3.72 (s, 3H, N_imid-RhCH₃);

7.98 (m, 4H, NCH₂CH₂N); 7.33 (m, 20H, Ph); 2.02 (m, 4H,

C₁₆H₂₇I₃N₄Pd: C, 25.2; H, 3.6; N, 7.35. Found: C, 25.4; H, 3.75; N,

7.5.

(j) Methylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imida-

zole-2-ylidene)]-diiodotrimethylphosphinopalladium(II)

iodide,

[PdI₂(PMe₃)(^tBuC(H)-g¹-C^meth)][I] (8b). A 10 mL portion of

CH₃CN was added to a ﬂask containing 7b (106 mg, 0.133 mmol).

The resulting slurry was stirred for 10 min, after which PMe₃

(14.7 mL, 0.143 mmol) was injected into the reaction vessel. The

slurry changed from dark red to a pale green solution almost

instantly, and was stirred for another 10 min. The solvent was

reduced to 5 mL under reduced pressure and passed through a

bed of Celite via cannula to remove small deposits of colloidal

Pd. The rest of the solvent was then removed under reduced

pressure and the crude product redissolved in 10 mL of CH₂Cl₂.

A 20 mL portion of diethyl ether was added to precipitate a

bright orange solid, which was then washed with 3 ¥ 7 mL

portions of diethylether and 3 ¥ 7 mL portions of pentane before

PCH₂CH₂P). ³¹P{ H} NMR (161.84 MHz, CD₂Cl₂, 27.0 ^◦C):

1

2

72.9 (dd, 1P, J_P-Rh= 197.6 Hz, J_P-P= 33.4 Hz), 57.4 (dd, 1P,

¹J_P-Rh= 125.3 Hz, ²J_P-P= 33.4 Hz, dppe). The transient nature of

1

the product precluded the acquisition of ¹³C{ H} NMR spectra

and elemental analyses.

(h) Ethylene[(N-methyl)imidazolium][(N-methyl)imidazole-2-

ylidene)bromo(g¹:g¹-bis(diethylphosphino)methane)rhodium(I)]

bromide, [RhBr(depm)(^MeC(H)-g¹-C^eth)][Br] (6c).

A

10 mL

drying in vacuo, giving 84 mg (72%). H NMR (399.80 MHz,

1

portion of CH₂Cl₂was added to a ﬂask containing 2c (50 mg,

0.089 mmol). The resulting solution was stirred for 10 min after

which depm (30.2 mL, 0.134 mmol) was injected into the reaction

vessel bleaching the solution to a paler yellow immediately.

¹H NMR (400.39 MHz, CD₂Cl₂, 27.0 ^◦C): 10.29 (br s, 1H,

NCHN); 7.90 (br s, 1H), 6.77 (br s, 1H, NCH_imid-H); 3.97 (s, 3H,

N_imid-HCH₃); 8.16 (br s, 1H), 7.03 (br s, 1H, NCH_imid-Rh); 3.91 (s,

3H, N_imid-RhCH₃); 5.10 (m, 4H, NCH₂CH₂N); 2.41 (m, 2H), 1.82

CD₃CN, 26.5 ^◦C): 9.11 (dd, 1H, NCHN, ⁴J_H-H= 1.7 Hz, ⁴J_H-H

=

3

4

1.7 Hz); 7.73 (dd, 1H, J_H-H= 1.7 Hz, J_H-H= 1.7 Hz), 7.61

3

4

(dd, 1H, J_H-H= 1.7 Hz, J_H-H= 1.7 Hz NCH_imid-H); 1.81 (s, 9H,

3

5

N_imid-HC(CH₃)₃); 7.72 (dd, 1H, J_H-H= 2.3 Hz, J_H-P= 1.4 Hz),

3

5

7.53 (dd, 1H, J_H-H= 2.3 Hz, J_H-P= 2.3 Hz NCH_imid-Pd); 1.63 (s,

2

9H, N_imid-PdC(CH₃)₃); 6.69 (s, 1H, NCH₂N); 1.76 (d, 9H, J_H-P

=

10.4 Hz P(CH₃)₃). ¹³C{ H} NMR (100.54 MHz, DMSO-d₆,

1

◦

2

26.5 C): 163.3 (d, 1C, J_C-P= 194.3 Hz, C_carbene); 136.6 (s, 1C,

NCHN); 122.6 (s, 1C), 122.8 (s, 1C, NCH_imid-H); 124.2 (d, 1C,

⁴J_C-P= 6.1 Hz), 123.5 (d, 1C, ⁴J_C-P= 6.5 Hz, NCH_imid-Pd); 60.6 (s,

1C, NCH₂N); 62.6 (s, 1C), 31.9 (s, 3C, N_imid-HC(CH₃)₃); 59.8 (s,

(m, 8H), 1.28 (m, 5H), 0.97 (m, 5H, PEt₂); 5.90 (ddd, 1H, ²J_H-H

=

14.2 Hz, ²J_H-P= 11.9 Hz, ²J_H-P= 6.9 Hz), 4.89 (ddd, 1H, ²J_H-H

=

1

14.2 Hz, ²J_H-P= 14.2 Hz, ²J_H-P= 4.1 Hz, PCH₂P). ³¹P{ H} NMR

(161.08 MHz, CD₂Cl₂, 27.0 ^◦C): -11.5 (dd, 1P, ¹J_P-Rh= 169.1 Hz,

1C), 29.5 (s, 3C, N_imid-PdC(CH₃)₃); 18.6 (d, 3C, J_C-P= 32.2 Hz,

1

²J_P-P= 102.7 Hz), -30.2 (dd, 1P, J_P-Rh= 102.7 Hz, J_P-P

=

P(CH₃)₃). ³¹P{ H} NMR (161.84 MHz, CD₃CN, 27.0 ^◦C):

1

2

1

102.7 Hz, depm). The transient nature of the product precluded

the acquisition of ¹³C{ H} NMR spectra, as well as and elemental

-25.2 (s, 1P, P(CH₃)₃). HRMS m/z Calcd for C₁₈H₃₄I₂N₄PPd

(M⁺- I): 696.9640. Found: 696.9644 (M⁺- I). Repeated

attempts to separate this compound from minor amounts of

1

analyses.

1

the double-substituted 12b failed (as observed in the H NMR

(i) Methylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imida-

zole-2-ylidene)]-triiodopalladium(II), [PdI₃(^tBuC(H)-g¹-C^eth)] (7d).

A 20 mL portion of DMSO was added to a solid mixture

containing 1d (664 mg, 1.522 mmol) and Pd(OAc)₂(343 mg,

1.526 mmol). The resulting solution was heated at 50 ^◦C for exactly

4 hours, during which time the solution bleached to a paler orange.

At this point an excess of KI (19.456 g, 117.203 mmol) was added

along with 8 mL DMSO. The resulting dark purple solution was

heated for another hour. DMSO was removed overnight in vacuo

at 50 ^◦C to give a dark purple solid, which was then dissolved in a

30 mL:30 mL acetonitrile/water mixture. The solution was heated

at 80 ^◦C for 10 min followed by the removal of the acetonitrile in

vacuo and ﬁltered to precipitate a dark brown solid which was

washed with CH₂Cl₂to give the product as a brick red solid

which was then recrystallized from acetonitrile_◦, giving 956 mg

(82%). ¹H NMR (399.80 MHz, DMSO-d₆, 26.5 C): 9.17 (br dd,

1H, NCHN); 7.95 (br s, 1H), 7.68 (br s, 1H), 7.66 (br s, 1H),

7.31 (br s, 1H, NCH); 1.84 (s, 9H), 1.53 (s, 9H, NC(CH₃)₃); 4.92

1

spectrum) so elemental analysis could not be obtained. The H

and ¹³C{ H} NMR spectra of this compound are given in the ESI

1

(Fig. S2).†

(k) Methylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imida-

zole-2-ylidene)]-diiodotriethylphosphinopalladium(II) iodide, [PdI₂-

(PEt₃)(^tBuC(H)-g¹-C^meth)][I] (9b). The desired complex was pre-

pared as described for 8b, using 7b (136 mg, 0.182 mmol) and

PEt₃(65.7 mL, 0.441 mmol). The slurry changed from dark red to

a pale green solution almost instantly, and was stirred for another

20 min. The crude product was puriﬁed as described for 8b, and

isolated using 10 mL of CH₂Cl₂, 20 mL of diethyl ether and 20 mL

of pentane to precipitate a bright yellow solid, which was then

washed with 3 ¥ 10 mL of pentane before drying in vacuo, giving

130 mg (82%). ¹H NMR (399.80 MHz, DMSO-d₆, 26.5 ^◦C): 9.24

4

(dd, 1H, NCHN, J_H-H= 1.8 Hz, J_H-H= 1.8 Hz); 8.12 (dd, 1H,

³J_H-H= 1.8 Hz, ⁴J_H-H= 1.8 Hz, ^tBuNCH_imid-H); 7.92 (dd, 1H, ³J_H-H

=

1.8 Hz, ⁴J_H-H= 1.8 Hz H₂CNCH_imid-H); 1.58 (s, 9H, N_imid-HC(CH₃)₃);

7.90 (dd, 1H, ³J_H-H= 1.9 Hz, ⁵J_H-P= 1.9 Hz, ^tBuNCH_imid-Pd); 7.84

1

(br s, 4H, NCH₂CH₂N). ¹³C{ H} NMR (125.27 MHz, DMSO-

d₆, 26.5 ^◦C): C_carbenenot visible; 135.3 (s, 1C, NCHN); 123.7 (s,

1C), 123.5 (s, 1C), 123.1 (s, 1C), 121.0 (s, 1C, NCH); 60.4 (s, 1C),

32.1 (s, 3C), 59.5 (s, 1C), 29.6 (s, 3C, NC(CH₃)₃); 52.4 (s, 1C),

47.4 (s, 1C, NCH₂CH₂N). HRMS m/z Calcd for C₁₆H₂₇I₂N₄Pd

(M⁺- I): 634.9355. Found: 634.9353 (M⁺- I). Anal Calcd for

(dd, 1H, J_H-H= 1.9 Hz, J_H-P= 1.3 Hz CH₂NCH_imid-Pd); 1.77 (s,

3

5

9H, N_imid-PdC(CH₃)₃); 6.67 (s, 1H, NCH₂N); 2.09 (dq, 6H, ²J_H-P

=

3

9.5 Hz, J_H-H= 7.5 Hz), 1.07 (dt, 9H, J_H-P= 16.2 Hz, J_H-H

7.5 Hz, P(CH₂CH₃)₃). ¹³C{ H} NMR (125.69 MHz, DMSO-d₆,

1

◦

2

26.1 C): 162.2 (d, 1C, J_C-P= 185.9 Hz, C_carbene); 136.2 (s, 1C,

7272 | Dalton Trans., 2009, 7269–7287

This journal is

The Royal Society of Chemistry 2009

©

NCHN); 121.9 (s, 1C, ^tBuNCH_imid-H); 122.6 (s, 1C, CH₂NCH_imid-H);

NMR (125.69 MHz, CD₃CN, 26.5 ^◦C): 157.5 (d, 1C, J_C-P

=

2

123.6 (d, 1C, ⁴J_C-P= 4.7 Hz, ^tBuNCH_imid-Pd); 124.0 (d, 1C, ⁴J_C-P

=

194.3 Hz, C_carbene); 135.0 (s, 1C, NCHN); 122.7 (s, 1C), 120.7 (s,

6.3 Hz, CH₂NCH_imid-Pd); 62.8 (s, 1C, NCH₂N); 60.7 (s, 1C), 29.4

1C, NCH_imid-H), 123.7 (d, 1C, ⁴J_C-P= 6.7 Hz), 123.2 (d, 1C, ⁴J_C-P

=

(s, 3C, N_imid-HC(CH₃)₃); 60.0 (s, 1C), 32.0 (s, 3C, N_imid-PdC(CH₃)₃);

4.9 Hz, NCH_imid-Pd); 63.5 (s, 1C, NCH₂N); 61.1 (s, 1C), 28.9 (s,

3C, N_imid-HC(CH₃)₃); 60.2 (s, 1C), 31.3 (s, 3C, N_imid-PdC(CH₃)₃);

1

18.8 (d, 3C, J_C-P= 30.2 Hz), 9.23 (s, 3C, P(CH₂CH₃)₃). ³¹P{ H}

NMR (161.84 MHz, CD₃CN, 27.0 ^◦C): 10.0 (s, 1P, P(CH₂CH₃)₃).

HRMS m/z Calcd for C₂₁H₄₀I₂N₄PPd (M⁺- I): 739.0115. Found:

739.0109 (M⁺- I). Anal Calcd for C₂₁H₄₀I₃N₄PPd: C, 29.1; H,

4.65; N, 6.5. Found: C, 28.9; H, 4.7; N, 6.3.

1

2

132.6 (d, 3C, J_C-P= 45.5 Hz), 128.4 (d, 6C, J_C-P= 10.1 Hz),

1

130.7 (d, 6C, ³J_C-P= 2.2 Hz), 134.9 (s, 3C, PPh₃). ³¹P{ H} NMR

◦

(202.33 MHz, CD₃CN, 27.0 C): 17.5 (s, 1P, PPh₃). HRMS m/z

Calcd for C₃₃H₄₀I₂N₄P₂Pd (M⁺- I): 883.0109. Found: 883.0116

(M⁺- I). Repeated attempts to obtain satisfactory elemental

analyses were always low in the carbon analysis. The ¹H and

(l)

Ethylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imida-

iodide,

zole-2-ylidene)]diiodo-triethylphosphinopalladium(II)

1

¹³C{ H} NMR spectra of this compound are given in the ESI

[PdI₂(PEt₃)(^tBuC(H)-g¹-C^eth)][I] (9d). The desired complex was

prepared as described for 8b, using 7d (151 mg, 0.198 mmol) and

PEt₃(58.3 mL, 0.396 mmol). The slurry changed from dark red to

a pale yellow solution almost instantly, and was stirred for another

30 min. The crude product was puriﬁed as described for 8b, and

isolated using 10 mL of CH₂Cl₂, 10 mL of diethyl ether and 30 mL

of pentane to precipitate a bright yellow solid, which was then

washed with 3 ¥ 10 mL of pentane before drying in vacuo, giving

215 mg (81%). ¹H NMR (399.80 MHz, DMSO-d₆, 26.5 ^◦C): 9.13

(Fig. S3).†

(n) Methylene[(N-tert-butyl)imidazolium]-[(N-tert-butyl)imi-

dazole-2-ylidene)]diiodo-dimethylphenylphosphinopalladium(II)

iodide, [PdI₂(PMe₂Ph)(^tBuC(H)-g¹-C^meth)][I] (11b). The desired

complex was prepared as described for 8b, using 7b (122 mg,

0.164 mmol) and PMe₂Ph (20.0 mL, 0.141 mmol). The slurry

changed from dark red to a pale green solution almost instantly,

and was stirred for another 10 min. The crude product was

puriﬁed as described for 8b, and isolated using 10 mL of CH₂Cl₂

and 20 mL of diethyl ether to precipitate a pale green solid, which

was then washed with 2 ¥ 5 mL portions of diethyl ether before

4

(dd, 1H, NCHN, J_H-H= 1.5 Hz, J_H-H= 1.5 Hz); 8.02 (dd, 1H,

4

3

³J_H-H= 1.5 Hz, J_H-H= 1.5 Hz); 7.61 (dd, 1H, J_H-H= 1.5 Hz,

⁴J_H-H= 1.5 Hz, NCH_imid-H); 1.77 (s, 9H, N_imid-HC(CH₃)₃); 7.75 (dd,

1H, ³J_H-H= 1.9 Hz, ⁵J_H-P= 1.9 Hz); 7.37 (dd, 1H, ³J_H-H= 1.9 Hz,

⁵J_H-P= 1.3 Hz, NCH_imid-Pd); 1.57 (s, 9H, N_imid-PdC(CH₃)₃); 4.88 (m,

1

drying in vacuo, giving 106 mg (85%). H NMR (399.80 MHz,

CD₃CN, 26.5 ^◦C): 9.21 (dd, 1H, NCHN, ⁴J_H-H= 1.6 Hz, ⁴J_H-H

=

2

3

4

2H), 4.80 (m, 2H, NCH₂CH₂N); 2.08 (dq, 6H, J_H-P= 9.4 Hz,

1.6 Hz); 7.76 (dd, 1H, J_H-H= 1.6 Hz, J_H-H= 1.6 Hz), 7.59

3

4

³J_H-H= 7.7 Hz), 1.07 (dt, 9H, J_H-P= 15.5 Hz, J_H-H= 7.5 Hz,

(dd, 1H, J_H-H= 1.6 Hz, J_H-H= 1.6 Hz NCH_imid-H); 1.59 (s, 9H,

3 5

◦

P(CH₂CH₃)₃). ¹³C{ H} NMR (100.54 MHz, DMSO-d₆, 26.5 C):

N_imid-HC(CH₃)₃); 7.87 (dd, 1H, J_H-H= 2.2 Hz, J_H-P= 1.4 Hz),

3 5

1

2

159.5 (d, 1C, J_C-P= 186.1 Hz, C_carbene); 135.2 (s, 1C, NCHN);

7.54 (dd, 1H, J_H-H= 2.2 Hz, J_H-P= 1.8 Hz NCH_imid-Pd); 1.78 (s,

4

123.5 (s, 1C), 121.2 (s, 1C, NCH_imid-H); 123.0 (d, 1C, J_C-P

=

9H, N_imid-PdC(CH₃)₃); 6.78 (s, 2H, NCH₂N); 7.73 (m, 2H), 7.47

2

1

5.8 Hz), 122.7 (d, 1C, ⁴J_C-P= 5.2 Hz, NCH_imid-Pd); 51.9 (s, 1C), 47.7

(m, 3H), 2.13 (d, 6H, J_H-P= 10.2 Hz, P(CH₃)₂Ph). ¹³C{ H}

◦

2

(s, 1C, NCH₂CH₂N); 60.4 (s, 1C), 29.6 (s, 3C, N_imid-HC(CH₃)₃);

NMR (125.69 MHz, DMSO-d₆, 26.1 C): 160.5 (d, 1C, J_C-P

=

1

59.3 (s, 1C), 32.1 (s, 3C, N_imid-PdC(CH₃)₃); 18.6 (d, 3C, J_C-P

=

197.8 Hz, C_carbene); 136.5 (s, 1C, NCHN); 122.6 (s, 1C), 121.8 (s,

28.3 Hz), 9.20 (s, 3C, P(CH₂CH₃)₃). ³¹P{ H} NMR (161.84 MHz,

CD₃CN, 27.0 ^◦C): 9.3 (s, 1P, P(CH₂CH₃)₃). HRMS m/z Calcd

for C₂₂H₄₂I₂N₄PPd (M⁺- I): 753.0266. Found: 753.0266 (M⁺- I).

Anal Calcd for C₂₂H₄₂I₃N₄PPd: C, 30.0; H, 4.8; N, 6.4. Found: C,

31.3; H, 4.9; N, 6.7.

1C, NCH_imid-H); 124.3 (d, 1C, ⁴J_C-P= 4.5 Hz), 123.8 (d, 1C, ⁴J_C-P

=

1

5.9 Hz, NCH_imid-Pd); 62.7 (s, 1C, NCH₂N); 60.6 (s, 1C), 29.5 (s, 3C,

N_imid-HC(CH₃)₃); 59.8 (s, 1C), 31.9 (s, 3C, N_imid-PdC(CH₃)₃); 136.3

(d, 1C, ¹J_C-P= 44.0 Hz), 131.8 (d, 2C, ²J_C-P= 10.5 Hz), 129.0 (d,

3

1

2C, J_C-P= 9.8 Hz), 130.7 (s, 1C), 18.7 (d, 2C, J_C-P= 32.9 Hz,

P(CH₃)₂Ph). ³¹P{ H} NMR (161.84 MHz, CD₃CN, 27.0 ^◦C):

1

(m)

Methylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imi-

-16.9 (s, 1P, P(CH₃)₂Ph). HRMS m/z Calcd for C₂₃H₃₆I₂N₄PPd

(M⁺- I): 758.9796. Found: 758.9799 (M⁺- I). Anal Calcd for

C₂₃H₃₆I₃N₄PPd: C, 31.2; H, 4.1; N, 6.3. Found: C, 31.2; H, 3.8; N,

6.4.

dazole-2-ylidene)]diiodo-triphenylphosphinopalladium(II) iodide,

[PdI₂(PPh₃)(^tBuC(H)-g¹-C^meth)][I] (10b). A 20 mL portion of

CH₃CN was added to a solid mixture of containing 7b (139 mg,

0.186 mmol) and PPh₃(49 mg, 0.153 mmol). The resulting slurry

was stirred for 10 min, gradually changing from dark red to

bright orange solution. The solvent was reduced to 5 mL under

reduced pressure and passed through a bed of Celite via cannula

to remove small deposits of colloidal Pd. The rest of the solvent

was then removed under reduced pressure and the crude product

redissolved in 10 mL of CH₂Cl₂. A 30 mL portion of diethyl ether

was added to precipitate a bright orange solid, which was then

washed with 3 ¥ 7 mL portions of diethylether before drying in

(o) Methylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imida-

zole-2-ylidene)]iodo-bis(trimethylphosphino)palladium(II) diiodide,

[PdI(PMe₃)₂(^tBuC(H)-g¹-C^meth)][I]₂(12b). The desired complex

1

was prepared as described for 8b, using [Pd(^tBuC(H)-h -C^meth)I₃]

(143 mg, 0.191 mmol) and PMe₃(47.5 mL, 0.461 mmol). The

slurry changed from dark red to a pale green solution almost

instantly, and was stirred for another 20 min. The crude product

was puriﬁed as described for 8b, and isolated using 7 mL of

CH₂Cl₂, 20 mL of diethyl ether and 20 mL of pentane to precipitate

a bright yellow solid, which was then washed with 3 ¥ 7 mL

portions of diethylether and 3 ¥ 7 mL portions of pentane before

1

vacuo, giving 151 mg (80%). H NMR (498.12 MHz, CD₃CN,

26.1 ^◦C): 8.83 (dd, 1H, ⁴J_H-H= 1.7 Hz, ⁴J_H-H= 1.7 Hz, NCHN);

7.63 (dd, 1H, ³J_H-H= 1.7 Hz, ⁴J_H-H= 1.7 Hz), 7.56 (dd, 1H, ³J_H-H

=

4

1

1.7 Hz, J_H-H= 1.7 Hz, NCH_imid-H); 1.56 (s, 9H, N_imid-HC(CH₃)₃);

drying in vacuo, giving 160 mg (93%). H NMR (498.12 MHz,

7.63 (dd, 1H, ³J_H-H= 1.7 Hz, ⁵J_H-P= 1.7 Hz), 7.60 (dd, 1H, ³J_H-H

=

CD₃CN, 26.1 ^◦C): 10.27 (dd, 1H, NCHN, ⁴J_H-H= 1.8 Hz, ⁴J_H-H

=

5

3

4

2.0 Hz, J_H-P= 1.7 Hz NCH_imid-Pd); 1.91 (s, 9H, N_imid-PdC(CH₃)₃);

1.8 Hz); 7.81 (dd, 1H, J_H-H= 1.8 Hz, J_H-H= 1.8 Hz), 7.65

1

3

4

6.71 (s, 2H, NCH₂N); 7.73 (m, 6H), 7.47 (m, 9H, PPh₃). ¹³C{ H}

(dd, 1H, J_H-H= 1.8 Hz, J_H-H= 1.8 Hz NCH_imid-H); 1.80 (s, 9H,

Dalton Trans., 2009, 7269–7287 | 7273

This journal is

The Royal Society of Chemistry 2009

©

N_imid-HC(CH₃)₃); 8.02 (dd, 1H, ³J_H-H= 2.2 Hz, ⁵J_H-P= 1.2 Hz), 7.73

changed from dark red to a bright orange, and was stirred for

another 20 min. The crude product was puriﬁed as described for

10b, and isolated using 10 mL of CH₂Cl₂and 30 mL of diethyl ether

to precipitate a bright orange solid, which was then washed with

3 ¥ 7 mL portions of pentane before drying in vacuo, giving 155 mg

(90%). ¹H NMR (399.79 MHz, DMSO-d₆, 26.5 ^◦C): 9.14 (dd, 1H,

3

5

(dd, 1H, J_H-H= 2.2 Hz, J_H-P= 2.2 Hz NCH_imid-Pd); 1.70 (s, 9H,

N_imid-PdC(CH₃)₃); 7.22 (d, 1H, ²J_H-H= 14.0 Hz), 6.78 (d, 1H, ²J_H-H

=

14.0 Hz, NCH₂N); 1.91 (dd, 9H, ²J_H-P= 10.4 Hz, ⁴J_H-P= 0.6 Hz),

1

1.60 (dd, 9H, ²J_H-P= 10.9 Hz, ⁴J_H-P= 0.7 Hz, P(CH₃)₃). ¹³C{ H}

◦

2

NMR (125.27 MHz, DMSO-d₆, 26.1 C): 165.3 (dd, 1C, J_C-P

=

2

4

3

158.7 Hz, J_C-P= 6.2 Hz C_carbene); 137.1 (s, 1C, NCHN); 122.7

⁴J_H-H= 1.6 Hz, J_H-H= 1.6 Hz NCHN); 8.09 (dd, 1H, J_H-H

=

4

3

4

(s, 1C), 121.9 (s, 1C, NCH_imid-H); 124.9 (d, 1C, J_C-P= 4.6 Hz),

1.6 Hz, J_H-H= 1.6 Hz), 7.84 (dd, 1H, J_H-H= 1.6 Hz, J_H-H

=

4

124.8 (d, 1C, J_C-P= 3.6 Hz, NCH_imid-Pd); 62.7 (s, 1C, NCH₂N);

1.6 Hz, NCH_imid-H); 1.40 (s, 9H, N_imid-HC(CH₃)₃); both NCH_imid-Pd

peaks disguised by phenyl multiplets; 1.51 (s, 9H, N_imid-PdC(CH₃)₃);

60.9 (s, 1C), 30.9 (s, 3C, N_imid-HC(CH₃)₃); 60.6 (s, 1C), 29.5 (s, 3C,

N_imid-PdC(CH₃)₃); 18.6 (d, 3C, ¹J_C-P= 32.3 Hz), 17.2 (dd, 3C, ¹J_C-P

=

6.76 (d, 1H, J_H-H= 13.8 Hz), 6.23 (d, 1H, J_H-H= 13.8 Hz

NCH₂N); 8.05 (m, 6H), 7.63 (m, 8H), 7.48 (m, 1H), 7.30 (m, 3H),

7.00 (m, 2H, PPh₂); 5.44 (dm, 1H, ²J_H-H= 16.7 Hz), 5.34 (dm, 1H,

2

33.1 Hz, J_C-P= 2.6 Hz, P(CH₃)₃). ³¹P{ H} NMR (201.64 MHz,

3

1

◦

2

CD₃CN, 27.0 C): -11.1 (d, 1P, J_P-P= 27.3 Hz), -19.4 (d, 1P,

²J_P-P= 27.3 Hz, P(CH₃)₃). HRMS m/z Calcd for C₁₈H₃₄I₂N₄PPd

(M²⁺- 2I): 323.0516. Found: 323.0514 (M²⁺- 2I). Anal Calcd for

C₂₁H₄₃I₃N₄P₂Pd: C, 28.0; H, 4.8; N, 6.2. Found: C, 27.6; H, 4.8;

N, 5.7.

²J_H-H= 16.7 Hz, PCH₂P). ¹³C{ H} NMR (100.54 MHz, DMSO-

1

d₆, 26.5 ^◦C): 164.1 (dd, 1C, ²J_C-P= 172.2 Hz, ²J_C-P= 2.8 Hz, C_carbene);

136.3 (s, 1C, NCHN); 122.5 (s, 1C), 122.2 (s, 1C, NCH_imid-H); 125.4

(d, 1C, ⁴J_C-P= 4.4 Hz), 125.1 (d, 1C, ⁴J_C-P= 2.9 Hz, NCH_imid-Pd);

62.2 (s, 1C, NCH₂N); 60.7 (s, 1C), 29.3 (s, 3C, N_imid-HC(CH₃)₃); 60.5

(s, 1C), 31.3 (s, 3C, N_imid-PdC(CH₃)₃); 137.0–121.8 (24C, PPh₂); 36.8

(p) Methylene[(N-tert-butyl)imidazolium]-[(N-tert-butyl)imida-

zole-2-ylidene)]iodo-bis(dimethylphenylphosphino)palladium(II) di-

iodide, [PdI(PMe₂Ph)₂(^tBuC(H)-g¹-C^meth)][I]₂(13b). The desired

complex was prepared as described for 8b, using 7b (142 mg,

0.190 mmol) and PMe₂Ph (81.5 mL, 0.570 mmol). The slurry

changed from dark red to a bright yellow solution almost instantly,

and was stirred for another 10 min. The crude product was puriﬁed

as described for 8b, and isolated using 10 mL of CH₂Cl₂, 20 mL

of diethyl ether and 20 mL of pentane to precipitate a pale

yellow solid, which was then washed with 3 ¥ 10 mL portions

of pentane before drying in vacuo, giving 126 mg (65%). ¹H NMR

(dd, J_C-P= 27.5 Hz, J_C-P= 27.5 Hz), PCH₂P). ³¹P{ H} NMR

1

◦

2

(162.08 MHz, DMSO-d₆, 27.0 C): -47.3 (d, J_P-P= 77.0 Hz,

1P), -55.7 (d, ²J_P-P= 77.0 Hz, 1P, dppm). HRMS m/z Calcd for

C₄₀H₄₇IN₄P₂Pd (M²⁺- 2I): 439.0672. Found: 439.0670 (M²⁺- 2I).

Anal Calcd for C₄₀H₄₇I₃N₄P₂Pd: C, 42.4; H, 4.2; N, 4.95. Found:

C, 42.0; H, 4.2; N, 5.0.

(r)

Ethylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imida-

zole-2-ylidene)iodo-(g¹:g¹-bis(diphenylphosphino)methane)pallad-

ium(II)] diiodide, [PdI(dppm)(^tBuC(H)-g¹-C^eth)][I]₂(14d). The

desired complex was prepared as described for 10b, using 7d

(275 mg, 0.361 mmol) and dppm (140 mg, 0.364 mmol). The

slurry changed from dark red to a bright orange, and was stirred

for another 20 min. The crude product was puriﬁed as described

for 10b, and isolated using 15 mL of CH₂Cl₂, 30 mL of diethyl

ether, and 25 mL of pentane to precipitate a bright yellow solid,

which was then washed with 3 ¥ 15 mL portions of pentane before

(498.12 MHz, CD₃CN, 26.1 ^◦C): 10.18 (dd, 1H, NCHN, ⁴J_H-H

=

4

3

4

2.0 Hz, J_H-H= 2.0 Hz); 7.90 (dd, 1H, J_H-H= 2.0 Hz, J_H-H

=

2.0 Hz), 7.69 (dd, 1H, ³J_H-H= 2.0 Hz, ⁴J_H-H= 2.0 Hz NCH_imid-H);

1.82 (s, 9H, N_imid-HC(CH₃)₃); 7.86 (dd, 1H, ³J_H-H= 2.4 Hz, ⁵J_H-P

=

1.1 Hz), 7.66 (dd, 1H, ³J_H-H= 2.4 Hz, ⁵J_H-P= 2.4 Hz NCH_imid-Pd);

1.70 (s, 9H, N_imid-PdC(CH₃)₃); 7.32 (d, 1H, ²J_H-H= 13.6 Hz), 6.78 (d,

1H, ²J_H-H= 13.6 Hz, NCH₂N); 2.15 (d, 3H, ²J_H-P= 10.2 Hz), 2.01

2

(d, 3H, J_H-P= 10.2 Hz), 1.70 (d, 3H, J_H-P= 10.6 Hz), 1.59 (d,

1

drying in vacuo, _◦giving 310 mg (75%). H NMR (399.80 MHz,

3H, J_H-P= 10.6 Hz, P(CH₃)₂Ph). ¹³C{ H} NMR (125.69 MHz,

2

1

4

DMSO-d₆, 26.5 C): 9.19 (br dd, 1H, J_H-H= 2.1 Hz, J_H-H

=

◦

2

DMSO-d₆, 26.1 C): 162.3 (dd, 1C, J_C-P= 161.1 Hz, J_C-P

=

2.1 Hz NCHN); 7.99 (dd, 1H, ³J_H-H= 2.1 Hz, ⁴J_H-H= 2.1 Hz), 7.45

(dd, 1H, ³J_H-H= 2.1 Hz, ⁴J_H-H= 2.1 Hz, NCH_imid-H); 1.48 (s, 9H,

N_imid-HC(CH₃)₃); 7.90 (br dd, 1H, ³J_H-H= 2.1 Hz, ⁵J_H-P= 2.1 Hz),

7.0 Hz, C_carbene); 137.1 (s, 1C, NCHN); 122.8 (s, 1C), 121.8 (s, 1C,

4

NCH_imid-H); 125.5 (d, 1C, J_C-P= 5.0 Hz), 124.5 (d, 1C, J_C-P

=

4.1 Hz, NCH_imid-Pd); 62.9 (s, 1C, NCH₂N); 61.0 (s, 1C), 29.5 (s,

3C, N_imid-HC(CH₃)₃); 60.7 (s, 1C), 31.1 (s, 3C, N_imid-PdC(CH₃)₃);

3

4

7.56 (br dd, 1H, J_H-H= 2.1 Hz, J_H-H= 2.1 Hz, NCH_imid-Pd);

1.55 (s, 9H, N_imid-PdC(CH₃)₃); 4.86 (m, 2H), 4.73 (m, 1H), 4.17

1

134.0 (d, 1C, J_C-P= 48.0 Hz), 132.7 (dd, 1C, J_C-P= 50.2 Hz,

(m, 1H, NCH₂CH₂N); 7.94 (m, 6H), 7.59 (m, 9H), 7.42 (m,

³J_C-P= 3.0 Hz), 131.6 (d, 2C, J_C-P= 11.4 Hz), 130.1 (d, 2C,

2

5H), 7.29 (m, 3H), 7.16 (m, 2H, PPh₂); 5.36 (ddd, 1H, J_H-H

=

²J_C-P= 10.7 Hz), 132.0 (d, 2C, J_C-P= 10.3 Hz), 129.3 (d, 2C,

3

16.1 Hz, ²J_H-P= 11.3 Hz, ²J_H-P= 10.6 Hz), 5.12 (ddd, 1H, ²J_H-H

=

³J_C-P= 10.3 Hz), 132.4 (d, 1C, J_C-P= 1.8 Hz), 131.3 (d, 1C,

4

16.1 Hz, J_H-P= 11.7 Hz, J_H-P= 10.1 Hz, PCH₂P). ¹³C{ H}

2

1

⁴J_C-P= 1.8 Hz), 18.6 (d, 1C, ¹J_C-P= 33.0 Hz), 16.8 (d, 1C, ¹J_C-P

=

◦

2

NMR (125.17 MHz, DMSO-d₆, 26.1 C): 162.2 (dd, 1C, J_C-P

=

32.2 Hz), 16.0 (d, 2C, ¹J_C-P= 31.3 Hz, P(CH₃)₂Ph). ³¹P{ H} NMR

1

2

173.7 Hz, J_C-P= 5.9 Hz, C_carbene); 135.4 (s, 1C, NCHN); 123.5

◦

2

(201.64 MHz, CD₃CN, 27.0 C): -5.0 (d, 1P, J_P-P= 25.6 Hz),

-11.7 (d, 1P, ²J_P-P= 25.6 Hz, P(CH₃)₂Ph). HRMS m/z Calcd for

C₃₁H₄₇IN₄P₂Pd (M²⁺- 2I): 385.0672. Found: 385.0675 (M²⁺- 2I).

Anal Calcd for C₃₁H₄₇I₃N₄P₂Pd: C, 36.3; H, 4.6; N, 5.5. Found: C,

36.2; H, 4.9; N, 5.3.

4

(s, 1C), 121.2 (s, 1C, NCH_imid-H); 133.2 (d, 1C, J_C-P= 5.2 Hz),

124.4 (d, 1C, ⁴J_C-P= 4.9 Hz, NCH_imid-Pd); 51.7 (s, 1C), 47.9 (s, 1C,

NCH₂CH₂N); 60.5 (s, 1C), 29.6 (s, 3C, N_imid-HC(CH₃)₃); 59.8 (s,

1C), 31.2 (s, 3C, N_imid-PdC(CH₃)₃); 134.2–126.5 (24C, PPh₂); 37.5

(dd, J_C-P= 26.7 Hz, J_C-P= 26.7 Hz), PCH₂P). ³¹P{ H} NMR

1

◦

2

(q) Methylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imida-

zole-2-ylidene)iodo-(g¹:g¹-bis(diphenylphosphino)methane)palla-

dium(II)] diiodide, [PdI(dppm)(^tBuC(H)-g¹-C^meth)][I]₂(14b). The

desired complex was prepared as described for 10b, using 7b

(114 mg, 0.152 mmol) and dppm (59 mg, 0.153 mmol). The slurry

(161.84 MHz, DMSO-d₆, 27.0 C): -45.3 (d, J_P-P= 79.6 Hz,

1P), -54.5 (d, ²J_P-P= 79.6 Hz, 1P, dppm). HRMS m/z Calcd for

C₄₁H₄₉IN₄P₂Pd (M²⁺- 2I): 446.0751. Found: 446.0750 (M²⁺- 2I).

Anal Calcd for C₄₁H₄₉I₃N₄P₂Pd: C, 42.9; H, 4.3; N, 4.9. Found:

C, 43.2; H, 4.45; N, 4.95.

7274 | Dalton Trans., 2009, 7269–7287

This journal is

The Royal Society of Chemistry 2009

©

(s) Methylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imida-

zole-2-ylidene)iodo-(g¹:g¹-bis(diphenylphosphino)ethane)palla-

dium(II)] diiodide, [PdI(dppe)(^tBuC(H)-g¹-C^meth)][I]₂(15b). The

desired complex was prepared as described for 10b, using 7b

(103 mg, 0.138 mmol) and dppe (51 mg, 0.128 mmol). The slurry

changed from dark red to a pale green, and was stirred for another

10 min. The crude product was puriﬁed as described for 10b, and

isolated using 20 mL of CH₂Cl₂and 20 mL of diethyl ether to

precipitate a pale green solid, which was then washed with 2 ¥

5 mL portions of pentane before drying in vacuo, giving 101 mg

(161.84 MHz, DMSO-d₆, 27.0 ^◦C): 57.6 (d, 1P, ²J_P-P= 11.8 Hz),

2

52.9 (d, 1P, J_P-P= 11.8 Hz, dppe). HRMS m/z Calcd for

C₄₂H₅₁IN₄P₂Pd (M²⁺- 2I): 453.0829. Found: 453.0833 (M²⁺- 2I).

Anal Calcd for C₄₂H₅₁I₃N₄P₂Pd: C, 43.45; H, 4.4; N, 4.8. Found:

C, 43.45; H, 4.5; N, 4.7.

(u) Methylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imida-

zole-2-ylidene)iodo-(g¹:g¹-bis(diethylphosphino)methane)palla-

dium(II)] diiodide, [PdI(depm)(^tBuC(H)-g¹-C^meth)][I]₂(16b). The

desired complex was prepared as described for 8b, using 7b

(109 mg, 0.146 mmol) and depm (32.8 mL, 0.145 mmol). The slurry

changed from dark red to a pale green solution almost instantly,

and was stirred for another 10 min. The crude product was puriﬁed

as described for 8b, and isolated using 10 mL of CH₂Cl₂, and 20 mL

of diethyl ether to precipitate a pale yellow solid, which was then

washed with 2 ¥ 5 mL portions of pentane before drying in va_◦cuo,

giving 125 mg (92%). ¹H NMR (399.80 MHz, CD₃CN, 26.5 C):

10.24 (dd, 1H, ³J_H-H= 1.7 Hz, ⁴J_H-H= 1.7 Hz NCHN); 7.78 (dd,

(69%). H NMR (498.12 MHz, DMSO-d₆, 26.1 ^◦C): 9.19 (dd,

1

1H, NCHN, ⁴J_H-H= 1.7 Hz, ⁴J_H-H= 1.7 Hz); 8.13 (dd, 1H, ³J_H-H

=

1.7 Hz, ⁴J_H-H= 1.7 Hz), 7.79 (dd, 1H, ³J_H-H= 1.7 Hz, ⁴J_H-H= 1.7 Hz

3

NCH_imid-H); 1.29 (s, 9H, N_imid-HC(CH₃)₃); 7.86 (dd, 1H, J_H-H

=

2.2 Hz, ⁵J_H-P= 2.2 Hz), 7.72 (dd, 1H, ³J_H-H= 2.2 Hz, ⁵J_H-P= 1.0 Hz,

2

NCH_imid-Pd); 1.55 (s, 9H, N_imid-PdC(CH₃)₃); 6.62 (d, 1H, J_H-H

=

2

14.1 Hz), 6.06 (d, 1H, J_H-H= 14.1 Hz, NCH₂N); 7.95 (m, 2H),

7.87 (m, 2H), 7.69 (m, 2H), 7.59 (m, 10H), 7.41 (m, 2H) 7.23 (m,

2H, PPh₂); 3.20 (m, 2H), 3.02 (m, 1H), 2.15 (m_◦, 1H, PCH₂CH₂P).

³J_H-H= 1.7 Hz, ³J_H-H= 1.7 Hz 1H), 7.63 (dd, ³J_H-H= 1.7 Hz, ³J_H-H

=

1.7 Hz 1H, NCH_imid-H); 1.66 (s, 9H, N_imid-HC(CH₃)₃); 8.00 (dd, 1H,

1

¹³C{ H} NMR (125.69 MHz, DMSO-d₆, 26.1 C): 163.8 (dd, 1C,

5

3

³J_H-H= 2.2 Hz, J_H-P= 1.1 Hz), 7.65 (dd, 1H, J_H-H= 1.1 Hz,

2

²J_C-P= 152.5 Hz, J_C-P= 5.0 Hz, C_carbene); 136.4 (s, 1C, NCHN);

⁵J_H-H= 1.1 Hz, NCH_imid-Pd); 1.77 (s, 9H, N_imid-PdC(CH₃)₃); 7.42 (d,

122.7 (s, 1C), 122.2 (s, 1C, NCH_imid-H); 126.0 (d, 1C, ⁴J_C-P= 4.2 Hz),

2

1H, J_H-H= 13.9 Hz), 6.68 (d, 1H, J_H-H= 13.9 Hz NCH₂N);

4

123.8 (d, 1C, J_C-P= 3.5 Hz, NCH_imid-Pd); 62.6 (s, 1C, NCH₂N);

2.89 (dm, 1H, ²J_H-P= 11.4 Hz), 2.67 (m, 2H), 2.46 (m, 1H), 2.11

61.1 (s, 1C), 29.4 (s, 3C, N_imid-HC(CH₃)₃); 60.0 (s, 1C), 30.7 (s, 3C,

3

(m, 2H), 1.65 (m, 2H), 1.27 (dt, 3H, J_H-P= 20.0 Hz, J_H-H

=

1

N_imid-PdC(CH₃)₃); 134.4–129.0 (24C, PPh₂); 31.3 (dd, 1C, J_C-P

=

7.4 Hz), 1.17 (dt, 3H, ³J_H-P= 18.7 Hz, J_H-H= 7.7 Hz), 1.03 (dt,

3H, ³J_H-P= 19.1 Hz, ³J_H-H= 7.4 Hz), 0.88 (dt, 3H, ³J_H-P= 20.0 Hz,

3

2

1

2

33.5 Hz, J_C-P= 13.2 Hz), 23.8 (dd, 1C, J_C-P= 31.8 Hz, J_C-P

=

12.4 Hz, PCH₂CH₂P). ³¹P{ H} NMR (162.08 MHz, DMSO-d₆,

27.0 ^◦C): 57.8 (d, 1P, ²J_P-P= 11.5 Hz), 53.7 (d, 1P, ²J_P-P= 11.5 Hz,

dppe). HRMS m/z Calcd for C₄₁H₄₉IN₄P₂Pd (M²⁺- 2I): 446.0751.

Found: 446.0749 (M²⁺- 2I). Anal Calcd for C₄₁H₄₉I₃N₄P₂Pd: C,

42.9; H, 4.3; N, 4.9. Found: C, 42.5; H, 4.5; N, 4.7.

1

³J_H-H= 7.4 Hz, PEt₂); 4.16 (ddd, 1H, J_H-H= 16.6 Hz, J_H-P

=

2

12.4 Hz, ²J_H-P= 12.4 Hz) 3.43 (ddd, 1H, ²J_H-H= 16.6 Hz, ²J_H-P

10.8 Hz, J_H-P= 9.7 Hz, PCH₂P). ¹³C{ H} NMR (125.69 MHz,

DMSO-d₆, 26.1 ^◦C): 169.6 (d, 1C, ²J_C-P= 158.5 Hz, C_carbene); 136.4

(s, 1C, NCHN); 122.5 (s, 1C), 122.1 (s, 1C, NCH_imid-H); 124.4 (d,

2

1

4

1C, J_C-P= 4.3 Hz), 124.1 (d, 1C, J_C-P= 3.4 Hz, NCH_imid-Pd);

(t)

Ethylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imida-

62.6 (s, 1C, NCH₂N); 60.9 (s, 1C), 29.4 (s, 3C, N_imid-HC(CH₃)₃);

zole-2-ylidene)iodo-(g¹:g¹-bis(diphenylphosphino)ethane)pallad-

ium(II)] diiodide, [PdI(dppe)(^tBuC(H)-g¹-C^eth)][I]₂(15d). The

desired complex was prepared as described for 10b, using 10d

(447 mg, 0.586 mmol) and dppe (234 mg, 0.587 mmol). The

slurry changed from dark red to a pale green, and was stirred for

another 10 min. The crude product was puriﬁed as described for

10b, and isolated using 10 mL of CH₂Cl₂, 20 mL of diethyl ether,

and 30 mL of pentane to precipitate a pale green solid, which

was then washed with 3 ¥ 10 mL portions of pentane before

1

61.0 (s, 1C), 31.1 (s, 3C, N_imid-PdC(CH₃)₃); 20.8 (dd, 1C, J_C-P

=

3

1

13.6 Hz, J_C-P= 13.6 Hz), 19.5 (d, 1C, J_C-P= 22.7 Hz), 18.0

1

3

(d, 1C, J_C-P= 23.4 Hz), 17.5 (dd, 1C, J_C-P= 19.5 Hz, J_C-P

=

19.5 Hz), 9.0 (s, 1C), 8.0 (d, 1C, ²J_C-P= 5.8 Hz), 6.8 (d, 1C, ²J_C-P

2

1

4.9 Hz), 6.4 (d, 1C, J_C-P= 5.3 Hz, PEt₂); 27.7 (dd, 1C, J_C-P

27.2 Hz, ¹J_C-P= 27.2 Hz, PCH₂P). ³¹P{ H} NMR (161.84 MHz,

1

◦

2

DMSO-d₆, 27.0 C): -46.6 (d, 1P, J_P-P= 81.1 Hz), -51.2 (d, 1P,

²J_P-P= 81.1 Hz, depm). HRMS m/z Calcd for C₂₄H₄₇IN₄P₂Pd

(M²⁺- 2I): 343.0672. Found: 343.0675 (M²⁺- 2I). Anal Calcd for

C₂₄H₄₇I₃N₄P₂Pd: C, 30.6; H, 5.0; N, 6.0. Found: C, 30.4; H, 5.0;

N, 6.0.

1

drying in vacuo, _◦giving 453 mg (67%). H NMR (399.80 MHz,

4

DMSO-d₆, 26.5 C): 9.41 (br dd, 1H, NCHN, J_H-H= 2.3 Hz,

3

4

⁴J_H-H= 2.3 Hz); 7.93 (dd, 1H, J_H-H= 2.3 Hz, J_H-H= 2.3 Hz),

7.50 (dd, 1H, ³J_H-H= 2.3 Hz, ⁴J_H-H= 2.3 Hz, NCH_imid-H); 1.15 (s,

9H, N_imid-HC(CH₃)₃); 7.67 (dd, 1H, ³J_H-H= 2.1 Hz, ⁵J_H-P= 2.1 Hz),

7.65 (dd, 1H, ³J_H-H= 2.1 Hz, ⁵J_H-P= 2.1 Hz, NCH_imid-Pd); 1.54 (s,

9H, N_imid-PdC(CH₃)₃); 4.83 (m, 3H), 4.11 (m, 1H, NCH₂CH₂N);

7.94 (m, 3H), 7.82 (m, 2H), 7.55 (m, 15H), 7.39 (m, 2H), 7.21

(v)

Diiodotriethylphosphinopalladium(II)-l-(1,1¢-methylene-

3,3¢-di-tert-butyldiimidazoline-2,2¢-diylidene)iodo(g²:g²-cyclo-

octadiene)rhodium(I), [PdI₂(PEt₃)(l-^tBuCC^meth)RhI(COD)] (17b).

A 10 mL portion of CH₃CN was added to a solid mixture

containing 9b (79 mg, 0.091 mmol) and [Rh(m-OAc)(COD)]₂

(25 mg, 0.046 mmol). The resulting slurry was stirred for 36 h

under reﬂux conditions and allowed to cool to room temperature.

After settling, the mother liquor was decanted to waste via

cannula and the resulting dark green product was dissolved in

10 mL of CH₂Cl₂. The green solution was passed through a

bed of Celite via cannula to remove small deposits of colloidal

Pd resulting in a bright yellow solution. The solvent was then

removed under reduced pressure resulting in a bright yellow

powder. The crude product washed with 3 ¥ 20 mL portions of

1

(m, 2H, PPh₂); 3.04 (m, 3H), 1.84 (m, 1H, PCH₂CH₂P). ¹³C{ H}

◦

2

NMR (100.54 MHz, DMSO-d₆, 26.5 C): 162.0 (dd, 1C, J_C-P

=

2

154.0 Hz, J_C-P= 4.6 Hz, C_carbene); 135.6 (s, 1C, NCHN); 123.9

4

(s, 1C), 120.9 (s, 1C, NCH_imid-H); 124.7 (d, 1C, J_C-P= 4.2 Hz),

4

123.1 (d, 1C, J_C-P= 4.2 Hz, NCH_imid-Pd); 55.6 (s, 1C), 52.4 (s,

1C, NCH₂CH₂N); 60.4 (s, 1C), 30.5 (s, 3C, N_imid-HC(CH₃)₃); 59.2

(s, 1C), 29.6 (s, 3C, N_imid-PdC(CH₃)₃); 135.0–128.6 (24C, PPh₂);

1

2

31.4 (dd, 1C, J_C-P= 33.5 Hz, J_C-P= 13.0 Hz), 25.7 (dd, 1C,

¹J_C-P= 33.5 Hz, J_C-P= 11.9 Hz, PCH₂CH₂P). ³¹P{ H} NMR

2

1

This journal is

The Royal Society of Chemistry 2009

Dalton Trans., 2009, 7269–7287 | 7275

©

1

acetone before drying in vacuo, giving 64 mg (65%). H NMR

then removed under reduced pressure and the crude product

redissolved in 10 mL of hot CH₂Cl₂and allowed to cool to room

temperature, precipitating a dark orange crystalline solid. After

settling, the mother liquor was decanted to waste via cannula

and the resulting product was dried in vacuo, giving 300 mg

(399.95 MHz, CD₂Cl₂, 26.5 ^◦C): 7.63 (d, 1H, ³J_H-H= 2.2 Hz), 7.12

3

(d, 1H, J_H-H= 2.2 Hz, NCH_imid-Rh); 1.95(s, 9H, N_imid-RhC(CH₃)₃);

3

5

7.77 (br dd, 1H), 7.21 (dd, 1H, J_H-H= 1.8 Hz, J_H-P= 1.8 Hz,

2

NCH_imid-Pd); 1.88(s, 9H, N_imid-PdC(CH₃)₃); 8.08 (d, 1H, J_H-H

=

13.2 Hz), 7.40 (d, 1H, J_H-H= 13.2 Hz NCH₂N); 5.26 (m, 1H),

(46%). H NMR (399.95 MHz, CD₂Cl₂, 27.0 ^◦C): 7.89 (d, 1H,

2

1

5.07 (m, 1H), 3.49 (m, 1H), 3.39 (m, 1H), 2.57 (m, 1H), 2.27

³J_H-H= 2.3 Hz), 7.73 (d, 1H, ³J_H-H= 2.3 Hz), 7.07 (d, 1H, ³J_H-H

=

2

3

(m, 3H), 1.88 (m, 4H, COD); 2.19 (dq, 6H, J_H-P= 9.5 Hz,

2.3 Hz), 7.06 (d, 1H, J_H-H= 2.3 Hz, NCH_imid); 8.24 (d, 1H,

³J_H-H= 7.6 Hz), 1.15 (dt, 9H, J_H-P= 16.3 Hz, J_H-H= 7.6 Hz,

²J_H-H= 11.5 Hz), 8.06 (d, 1H, J_H-H= 11.5 Hz, NCH₂N); 1.97

3

2

P(CH₂CH₃)₃). ¹³C{ H} NMR (125.69 MHz, CD₂Cl₂, 26.1 ^◦C):

(s, 9H), 1.89 (s, 9H, N_imidC(CH₃)₃); 5.03 (m, 2H), 3.38 (m, 2H),

4.61 (m, 1H), 4.52 (m, 1H), 3.03 (m, 1H), 2.99 (m, 1H), 2.63 (m,

1

2

180.9 (d, 1C, J_C-Rh= 49.3 Hz, C_carbene-Rh); 160.8 (d, 1C, J_C-P

=

1

187.7 Hz, C_carbene-Pd); 121.4 (s, 1C), 120.7 (s, 1C, NCH_imid-Rh); 121.8

4H), 2.48 (m, 4H), 1.78 (m, 4H), 1.64 (m, 4H, COD). ¹³C{ H}

(d, 1C, ⁴J_C-P= 4.1 Hz), 121.7 (d, 1C, ⁴J_C-P= 6.1 Hz, NCH_imid-Pd);

NMR(100.58 MHz, CD₂Cl₂, 27.0 ^◦C): 180.5 (d, 1C, J_C-Rh

=

1

66.9 (s, 1C, NCH₂N); 58.8 (s, 1C), 32.0 (s, 3C, N_imid-RhC(CH₃)₃);

50.1 Hz, C_carbene-Rh), 179.2 (s, 1C, C_carbene-Ir); 121.4 (s, 1C), 121.2

(s, 1C), 120.4 (s, 1C), 120.4 (s, 1C, NCH_imid); 68.0 (s, 1C, CH₂),

59.0 (s, 1C), 58.7 (s, 1C, N_imidC(CH₃)₃); 32.4 (s, 3C), 32.0 (s, 3C,

1

59.2 (s, 1C), 31.8 (s, 3C, N_imid-PdC(CH₃)₃); 18.7 (d, 3C, J_C-P

=

1

28.3 Hz), 8.8 (s, 3C, P(CH₂CH₃)₃); 95.9 (d, 1C, J_C-Rh= 7.8 Hz),

92.9 (d, 1C, ¹J_C-Rh= 7.1 Hz), 74.3 (d, 1C, ¹J_C-Rh= 15.7 Hz), 71.9 (d,

1C, ¹J_C-Rh= 14.2 Hz), 33.1 (s, 1C), 31.2 (s, 1C), 30.2 (s, 1C), 29.2 (s,

N_imidC(CH₃)₃); 96.7 (d, 1C, ¹J_C-Rh= 7.3 Hz), 94.8 (d, 1C, ¹J_C-Rh

=

1

7.0 Hz), 72.3 (d, 1C, J_C-Rh= 15.7 Hz), 68.6 (d, 1C, J_C-Rh

=

◦

1C, COD). ³¹P{ H} NMR (161.84 MHz, CD₂Cl₂, 27.0 C): 10.0

(s, 1P, P(CH₂CH₃)₃). HRMS m/z Calcd for C₂₉H₅₁I₂N₄PPdRh

(M⁺- I): 949.0025. Found: 949.0021 (M⁺- I). Anal Calcd for

C₂₉H₅₁I₃N₄PPdRh: C, 32.4; H, 4.8; N, 5.2. Found: C, 32.7; H, 4.9;

N, 5.1.

14.0 Hz), 82.3 (s, 1C), 80.7 (s, 1C), 55.4 (s, 1C), 52.4 (s, 1C), 32.3

(s, 1C), 30.3 (s, 1C), 29.5 (s, 1C), 28.5 (s, 1C), 34.3 (s, 1C), 34.1 (s,

1C), 30.1 (s, 1C), 25.8 (s, 1C, COD). HRMS m/z Calcd for C₃₁H₄₈

BrN₄IrRh (M⁺- Br): 851.1741. Found: 851.1741 (M⁺-Br).

1

(y) Diiodotriphenylphosphinopalladium(II)-l-(1,1¢-methylene-

3,3¢-di-tert-butyldiimidazoline-2,2¢-diylidene)iodo(g²:g²-cyclo-

octadiene)iridium(I), [PdI₂(PPh₃)(l-^tBuCC^meth)IrI(COD)] (20b).

A 5 mL portion of CH₃CN was added to 10b (70 mg, 0.069 mmol),

and the resulting orange solution was added slowly to a 10 mL

CH₃CN solution containing K[N(SiMe₃)₂] (34 mg, 0.170 mmol)

and [Ir(m-Cl)(COD)]₂(23 mg, 0.034 mmol). The solution was

stirred for 24 h, and the solvent removed under reduced pressure.

The resulting solid was dissolved in 15 mL of CH₂Cl₂and passed

through a bed of Celite via cannula to remove suspended white

salts. The solvent was removed under reduced pressure and

the product extracted with 40 mL of pentane. The solvent was

removed and the deep red solid dried in vacuo, giving 14 mg

(w)

3 , 3¢ - di - tert - butyldiimidazoline - 2 , 2¢ - diylidene ) iododicarbonyl-

rhodium(I), (18b). The

[PdI₂(PEt₃)(l-^tBuCC^meth)RhI(CO)₂]

Diiodotriethylphosphinopalladium(II)-l-(1,1¢-methylene-

desired complex was prepared as described for complexes 3

using 17b (238 mg, 0.221 mmol), and the crude product puriﬁed

using 4 mL of CH₂Cl₂and 40 mL of diethyl ether, to precipitate

a pale yellow solid at 4^◦C, which was then washed with 3 ¥

20 mL portions of pentane before drying in vacuo, giving 215 mg

(85%). H NMR (399.80 MHz, CD₂Cl₂, 50.0 ^◦C, see Fig. S6,

1

ESI†): 7.92 (d, ³J_H-H= 2.1 Hz, 1H), 7.30 (d, 1H, ³J_H-H= 2.1 Hz,

NCH_imid-Rh); 1.82 (s, 9H, N_imid-RhC(CH₃)₃); 7.49 (br dd, 1H, ³J_H-H

=

2.1 Hz), 7.22 (dd, 1H, ³J_H-H= 2.1 Hz, ⁵J_H-P= 2.1 Hz, NCH_imid-Pd);

◦

2

1

1.87 (s, 9H, N_imid-PdC(CH₃)₃); 7.12 (d, 1H, J_H-H= 13.2 Hz),

(15%). H NMR (498.12 MHz, CD₂Cl₂, 26.1 C): 7.74 (dd, 1H,

2

5

7.08 (d, 1H, J_H-H= 13.2 Hz NCH₂N); 2.17 (dq, 6H, J_H-P

=

³J_H-H= 2.4 Hz, J_H-P= 1.7 Hz, NCH_imid-Pd), other NCH_imid-Pd

3

9.4 Hz, J_H-H= 7.6 Hz), 1.14 (dt, 9H, J_H-P= 16.3 Hz, J_H-H

peak disguised by phenyl multiplets; 1.99 (s, 9H, N_imid-PdC(CH₃)₃);

NCH_imid-Irpeaks disguised by phenyl multiplets; 1.90 (s, 9H,

7.5 Hz, P(CH₂CH₃)₃). ¹³C{ H} NMR (125.69 MHz, CD₂Cl₂,

1

◦

1

2

26.1 C): 187.2 (d, 1C, J_C-Rh= 54.6 Hz), 181.6 (d, 1C, J_C-Rh

=

N_imid-IrC(CH₃)₃); 7.01 (d, 1H, J_H-H= 11.5 Hz), 6.96 (d, 1H,

1

76.3 Hz, CO); 171.0 (d, 1C, J_C-Rh= 42.3 Hz, C_carbene-Rh); 162.2

²J_H-H= 11.5 Hz NCH₂N); 5.58 (m, 2H), 4.85 (m, 2H), 3.11–0.06

◦

2

1

(d, 1C, J_C-P= 184.9 Hz, C_carbene-Pd); 122.0 (s, 1C), 121.8 (s, 1C,

(m, 8H, COD). ¹³C{ H} NMR (100.54 MHz, CD₂Cl₂, 26.5 C):

2

NCH_imid-Rh); 121.1 (br d, 1C), 122.0 (br d, 1C, NCH_imid-Pd); 66.4 (s,

1C, NCH₂N); 59.4 (s, 1C), 31.9 (s, 3C, N_imid-RhC(CH₃)₃); 59.5 (s,

176.6 (s, 1C, C_carbene-Ir); 164.4 (d, 1C, J_C-P= 217.1 Hz, C_carbene-Pd);

4

128.7 (s, 1C), 128.6 (s, 1C, NCH_imid-Ir); 128.1 (d, 1C, J_C-P

=

1

4

1C), 32.0 (s, 3C, N_imid-PdC(CH₃)₃); 18.7 (d, 3C, J_C-P= 30.3 Hz),

8.1 Hz), 128.0 (d, 1C, J_C-P= 7.1 Hz, NCH_imid-Pd); 75.3 (s, 1C,

NCH₂N); 69.6 (s, 1C), 22.5 (s, 3C, N_imid-IrC(CH₃)₃); 67.9 (s, 1C),

14.0 (s, 3C, N_imid-PdC(CH₃)₃); 131.0 (d, 3C, ¹J_C-P= 49.6 Hz), 132.1

8.8 (s, 3C, P(CH₂CH₃)₃). ³¹P{ H} NMR (161.84 MHz, CD₂Cl₂,

1

◦

27.0 C): 9.7 (s, 1P, P(CH₂CH₃)₃). IR (solution, cm^-1): 2076,

2

3

2004 (CO). HRMS m/z Calcd for C₂₂H₃₉I₂N₄O₂PPdRh (M⁺

-

(d, 6C, J_C-P= 9.6 Hz), 132.0 (d, 6C, J_C-P= 3.0 Hz), 135.4 (s,

CO, I): 868.9036. Found: 868.9035 (M⁺- CO, I). Anal Calcd for

C₂₃H₃₉I₃N₄O₂PPdRh: C, 27.0; H, 3.8; N, 5.5. Found: C, 27.3; H,

4.0; N, 5.6.

3C, PPh₃); 92.2 (s, 1C), 92.0 (s, 1C), 57.0 (s, 1C), 52.7 (s, 1C),

1

34.8 (s, 1C), 34.3 (s, 1C), 34.2 (s, 1C), 31.7 (s, 1C, COD). ³¹P{ H}

NMR (201.64 MHz, CD₂Cl₂, 27.0 ^◦C): 28.3 (s, 1P, PPh₃). HRMS

m/z Calcd for C₄₁H₅₁I₂N₄PPdIr (M⁺- I): 1183.0600. Found:

1183.0610 (M⁺- I). Anal Calcd for C₄₁H₅₁I₃IrN₄PPd: C, 37.6; H,

3.9; N, 4.3. Found: C, 37.9; H, 4.1; N, 4.2.

(x) Bromo(g²:g²-cyclooctadiene)iridium(I)-l-(1,1¢-methylene-

3,3¢-di-tert-butyldiimidazoline-2,2¢-diylidene)bromo(g²:g²-cyclo-

octadiene)rhodium(I), [IrBr(COD)(l-^tBuCC^meth)RhBr(COD)] (19b).

A 40 mL portion of THF was added to a solid mixture containing

(z) Diiododimethylphenylphosphinopalladium(II)-l-(1,1¢-methy-

lene-3,3¢-di-tert-butyldiimidazoline-2,2¢-diylidene)iodo(g²:g²-

cyclooctadiene)iridium(I), [PdI₂(PMe₂Ph)(l-^tBuCC^meth)IrI(COD)]

(21b). The desired complex was prepared as described for

1

Ir(COD)Br(^tBuC(H)-h -C^eth)][Br] (504 mg, 0.70 mmol) and

[Rh(m-OAc)(COD)]₂(187 mg, 0.35 mmol). The resulting slurry

was stirred for 2.5 h under reﬂux conditions. The solvent was

7276 | Dalton Trans., 2009, 7269–7287

This journal is

The Royal Society of Chemistry 2009

©

20b, using 11b (64 mg, 0.072 mmol), K[N(SiMe₃)₂] (36 mg,

0.180 mmol), and [Ir(m-Cl)(COD)]₂(24 mg, 0.036 mmol). The

crude product was puriﬁed as described for 20b, resulting in 17 mg

(20%) of a yellow solid. ¹H NMR (498.12 MHz, CD₂Cl₂, 26.1 ^◦C):

7.77 (d, 1H, ³J_H-H= 2.2 Hz), 7.14 (d, 1H, ³J_H-H= 2.2 Hz, NCH_imid-Ir);

(d, 1H, ²J_H-H= 13.2 Hz), 6.91 (d, 2H, ²J_H-H= 13.2 Hz, NCH₂N);

2

7.82–7.41 (m, 5H), 2.13 (d, 3H, J_H-P= 9.8 Hz), 2.13 (d, 3H,

1

²J_H-P= 9.8 Hz, PMe₂Ph).¹³C{ H} NMR (125.27 MHz, CD₃CN,

◦

26.1 C): 169.6 (s, 1C), 167.5 (s, 1C, CO); 180.6 (s, 1C, C_carbene-Ir);

2

159.6 (d, 1C, J_C-P= 194.1 Hz, C_carbene-Pd); 122.4 (s, 1C), 121.9 (s,

1.89(s, 9H, N_imid-IrC(CH₃)₃); 7.78 (dd, 1H, ³J_H-H= 1.9 Hz, ⁵J_H-P

=

1C, NCH_imid-Ir); 122.6 (d, 1C, ⁴J_C-P= 6.5 Hz), 121.5 (d, 1C, ⁴J_C-P

=

1.9 Hz), 7.23 (dd, 1H, ³J_H-H= 1.9 Hz, ⁵J_H-P= 1.9 Hz, NCH_imid-Pd);

1.87 (s, 9H, N_imid-PdC(CH₃)₃); both NCH₂N peaks disguised by

phenyl multiplets; 7.88–7.16 (m, 5H), 2.16 (d, 3H, ²J_H-P= 9.8 Hz),

2.15 (d, 3H, ²J_H-P= 9.8 Hz, PMe₂Ph); 4.87 (m, 1H), 4.65 (m, 1H),

5.2 Hz, NCH_imid-Pd); 66.6 (s, 1C, NCH₂N); 59.9 (s, 1C), 31.6 (s, 3C,

N_imid-IrC(CH₃)₃); 59.4 (s, 1C), 31.4 (s, 3C, N_imid-PdC(CH₃)₃); 136.3

(d, 1C, ¹J_C-P= 46.1 Hz), 131.5 (d, 2C, ²J_C-P= 10.9 Hz), 128.6 (d,

3

4

2C, J_C-P= 10.2 Hz), 130.2 (d, 1C, J_C-P= 2.5 Hz), 18.2 (d, 1C,

1

3.06 (m, 1H), 3.90 (m, 1H), 2.30–1.23 (m, 8H, COD).¹³C{ H}

¹J_C-P= 33.6 Hz), 17.9 (d, 1C, ¹J_C-P= 33.6 Hz, PMe₂Ph). ³¹P{ H}

NMR (125.26 MHz, CD₂Cl₂, 26.1 ^◦C): 179.2 (s, 1C, C_carbene-Ir);

NMR (161.84 MHz, CD₃CN, 26.5 ^◦C): -17.1 (s, 1P, PMe₂Ph).

IR (solution, cm^-1): 2065, 1986 (CO). HRMS m/z Calcd for

C₂₅H₃₅I₂IrN₄O₂PPd (M⁺–I): 1006.9246. Found: 1006.9234 (M⁺-

2

171.9 (d, 1C, J_C-P= 207.5 Hz, C_carbene-Pd); 121.7 (s, 1C), 120.3

4

(s, 1C, NCH_imid-Ir); 128.9 (d, 1C, J_C-P= 6.7 Hz), 121.6 (d, 1C,

⁴J_C-P= 6.6 Hz, NCH_imid-Pd); 66.7 (s, 1C, NCH₂N); 59.1 (s, 1C), 32.2

I). The ¹H and ¹³C{ H} NMR spectra of this compound are given

1

(s, 3C, N_imid-IrC(CH₃)₃); 57.3 (s, 1C), 32.0 (s, 3C, N_imid-PdC(CH₃)₃);

in the ESI (Fig. S4).†

1

2

136.3 (d, 1C, J_C-P= 44.7 Hz), 131.3 (d, 2C, J_C-P= 10.6 Hz),

3

1

128.4 (d, 2C, J_C-P= 10.0 Hz), 130.1 (s, 1C), 18.8 (d, 1C, J_C-P

=

X-Ray structure determinations

1

32.6 Hz), 18.7 (d, 1C, J_C-P= 33.0 Hz, PMe₂Ph); 82.0 (s, 1C),

79.3 (s, 1C), 59.1 (s, 1C), 55.5 (s, 1C), 33.4 (s, 1C), 31.8 (s, 1C),

(a) General considerations. Crystals were grown either from

concentrated CH₃CN solutions of the compound (11b, 13b), via

slow diffusion of ether and pentane into a CH₂Cl₂solution of the

compound (2c, 2d, 17b), or via slow diffusion of ether and pentane

into an acetone solution of compound (16b). Data were collected⁷⁷

using either a Bruker SMART 1000 CCD detector/PLATFORM

diffractometer with the crystals cooled to -80 ^◦C (2c, 2d) or using

a Bruker APEX II detector/D8 diffractometer with the crystals

cooled to -100 ^◦C (11b, 13b, 16b, 17b); in all cases Mo Ka

radiation was used. The data were corrected for absorption

through use of a multiscan model (SADABS) (2c, 2d, 11b, 13b)

or through use of Gaussian integration (using the indexed faces

and measured dimensions of the crystal (16b, 17b). Structures

were solved using direct methods (SHELXS-97⁷⁸(2c, 11b, 13b) or

SIR97⁷⁹(2d, 17b)) or through Patterson location of heavy atom

positions followed by structure expansion (DIRDIF-2008⁸⁰(16b)).

The program SHELXL-97⁷⁸was used for structure reﬁnements.

Hydrogen atoms (including those involved in hydrogen bonds)

were assigned positions on the basis of the geometries of their

attached carbon atoms and were given thermal parameters 120%

of their parent carbons. See Table 1 for a listing of crystallographic

experimental data.

30.6 (s, 1C), 30.1 (s, 1C, COD). ³¹P{ H} NMR (201.64 MHz,

1

CD₂Cl₂, 26.1 ^◦C): 17.0 (s, 1P, PMe₂Ph). HRMS m/z Calcd for

C₃₁H₄₇I₂IrN₄PPd (M⁺- I): 1059.0286. Found: 1059.0276 (M⁺- I).

Anal Calcd for C₃₁H₄₇I₃IrN₄PPd: C, 31.4; H, 4.0; N, 4.7. Found:

C, 31.7; H, 4.3; N, 4.9.

(za)

Diiododimethylphenylphosphinopalladium(II)-l-(1,1¢-

methylene-3,3¢-di-tert-butyldiimidazoline-2,2¢-diylidene)iodo-

dicarbonyliridium(I), [PdI₂(PPh₃)(l-^tBuCC^meth)IrI(CO)₂] (21b).

The desired complex was prepared as described for complexes

3 using 20b (10 mg, 0.008 mmol), 10 mL THF, and the crude

product puriﬁed by ﬁltration after washing with 1 mL of pentane

before drying in vacuo, giving 7 mg (80%). ¹H NMR (498.12 MHz,

CD₂Cl₂, 26.1 ^◦C): NCH_imid-Irpeaks disguised by phenyl multiplets;

1.87 (s, 9H, N_imid-IrC(CH₃)₃); NCH_imid-Pdpeaks disguised by phenyl

2

multiplets; 1.83 (s, 9H, N_imid-PdC(CH₃)₃); 7.26 (d, 1H, J_H-P

=

2

16.1 Hz), 6.98 (d, 1H, J_H-P= 16.1 Hz, NCH₂N); 7.77–7.31 (m,

15H, PPh₃). ¹³C{ H} NMR (125.26 MHz, CD₂Cl₂, 26.1 ^◦C):

1

169.7 (s, 1C), 167.1 (s, 1C, CO); 180.1 (s, 1C, C_carbene-Ir); 164.1

2

(d, 1C, J_C-P= 214.5 Hz, C_carbene-Pd); 128.7 (s, 1C), 128.7 (s, 1C,

4

NCH_imid-Ir); 129.8 (d, 1C, J_C-P= 9.1 Hz), 128.8 (d, 1C, J_C-P

=

10.3 Hz, NCH_imid-Pd); 75.3 (s, 1C, NCH₂N); 69.6 (s, 1C), 34.8 (s, 3C,

N_imid-IrC(CH₃)₃); 68.0 (s, 1C), 34.2 (s, 3C, N_imid-PdC(CH₃)₃); 131.5

(d, 3C, ¹J_C-P= 38.7 Hz), 132.2 (d, 6C, ²J_C-P= 9.7 Hz), 132.1 (d, 6C,

(b) Special reﬁnement conditions. (i) Despite crystallizing in

a chiral space group (P2₁), the crystal of 2d was found to be

racemically twinned. This was accommodated during reﬁnement

through use of the SHELXL-97⁷⁸TWIN instruction, and the

Flack parameter reﬁned to a value of 0.364(6). (ii) For 13b, a

half-occupancy molecule of solvent acetonitrile was found to be

disordered about the inversion center (1/2, 0, 1/2). Distances

within this molecule were constrained during reﬁnement to be

³J_C-P= 3.0 Hz), 133.6 (s, 3C, PPh₃). ³¹P{ H} NMR (201.64 MHz,

1

◦

CD₂Cl₂, 26.1 C): 28.4 (s, 1P, PPh₃). IR (solution, cm^-1): 2065,

1987 (CO). Anal Calcd for C₃₅H₃₉I₃IrN₄O₂PPd: C, 33.4; H, 3.1;

N, 4.45. Found: C, 33.5; H, 3.3; N, 4.6.

(zb)

Diiododimethylphenylphosphinopalladium(II)-l-(1,1¢-

methylene-3, 3¢-di-tert -butyldiimidazoline-2, 2¢-diylidene)iodo-

dicarbonyliridium(I), [PdI₂(PMe₂Ph)(l-^tBuCC^meth)IrI(CO)₂] (23b).

The desired complex was prepared as described for complexes 3

using 20b (15 mg, 0.013 mmol), and the crude product puriﬁed

by ﬁltration after washing with 1 mL of pentane before drying

˚

equal (within 0.01 A) to the corresponding distances within

the other (full-occupancy, non-disordered) cocrystallized solvent

CH₃CN molecule: d(N(1S)–C(1S)) = d(N(2S)–C(3S)); d(C(1S)–

C(2S)) = d(C(3S)–C(4S)); d(N(1S) ◊ ◊ ◊ C(2S)) = d(N(2S) ◊ ◊ ◊ C(4S)).

1

in vacuo, giving 12 mg (84%). H NMR (299.97 MHz, CD₃CN,

27.5 ^◦C): 7.73 (d, 1H, J_H-H= 2.2 Hz), 7.45 (d, 1H, J_H-H

=

3

Results and compound characterization

2.2 Hz, NCH_imid-Ir); 1.85 (s, 9H, N_imid-IrC(CH₃)₃); 7.42 (dd, 1H,

³J_H-H= 2.1 Hz, ⁵J_H-P= 1.4 Hz, NCH_imid-Pd), other NCH_imid-Pdpeak

disguised by phenyl multiplets; 1.81 (s, 9H, N_imid-PdC(CH₃)₃); 7.04

As noted earlier, it appeared that di-N-heterocyclic carbene-

bridged complexes involving two different metals could be

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7278 | Dalton Trans., 2009, 7269–7287

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©

Scheme 1

accessed via deprotonation of a carbene-anchored/pendent-

imidazolium complex, of the type shown earlier in Chart

1, in the presence of second metal. We had already

carbene-anchored complexes possible. Most often, single depro-

tonation of the diimidazolium salts is carried out using complexes

containing basic ligands such as acetate or methoxide groups,

which serve to deprotonate these salts. This is the method used

with some success in this report, and in previous reports by

us⁴⁶and others.^{18,31,46,81–84,86–88,90–93}In a previous study we had

shown that the acetate-bridged complex, [Rh(m-OAc)(COD)]₂,

was effective in the deprotonation of a number of diimidazolium

salts generating the corresponding series of di-NHC-bridged

dirhodium products.⁴⁶In one case the mononuclear carbene-

anchored/pendent-imidazolium complex [RhBr(COD)(^tBuC(H)-

a

shown that such a strategy could be employed to gener-

ate dicarbene-bridged Rh₂complexes via deprotonation of

1

the mononuclear species, [RhBr(COD)(^tBuC(H)-h -C^meth)][Br]

1

(

^tBuC(H)-h -C^meth

=

methylene[(N-tert-butyl)imidazolium][(N-

tert-butyl)imidazole-2-ylidene]), by [Rh(m-OAc)(COD)]₂. A num-

ber of carbene-anchored/pendent-imidazolium species of Rh,^18,31

Ir,^18,68,69,81Pd,^82–86Ni,^81,87,88Fe,⁸⁹and Ru,⁶⁷which seemed appropri-

ate for generation of binuclear species, were already known and in

this paper we sought to extend the number of these complexes of

Rh and Pd to serve as potential synthons for a range of dicarbene-

bridged mixed-metal complexes involving these metals.

1

h -C^meth)][Br] (2b, Scheme 1) was generated and found to be a

probable intermediate in the formation of the di-NHC-bridged

target. Although our initial attempts to prepare the other members

In this paper we use the abbreviations, ^RC(H)-h -C^alkfor the

of this series, namely, [RhBr(COD)L][Br] (L = ^MeC(H)-h -C^meth

,

1

monodentate pendent species and m-^RCC^alkfor bidentate dicarbene

systems, as originally suggested by Green, et al. and as shown

in Chart 2.⁴²In these abbreviations the substituent (R) on the

carbene or imidazolium rings appears ﬁrst, followed by the

^MeC(H)-h -C^eth

,

^tBuC(H)-h -C^eth), from the corresponding diimida-

1

zolium salts were unsuccessful, we have subsequently been able

to generate both the methyl- and tert-butyl-substituted ethylene-

linked systems (2c,d, Scheme 1) by using longer reaction times (see

Experimental section). Attempts to generate the fourth member of

1

pendent/anchored (C(H)-h -C) or dicarbene notation (CC) and

1

ﬁnally an abbreviation (alk = meth, eth) designating a methylene

or ethylene linker between the NHC/NHC or NHC/imidazolium

rings. We will additionally use the label a in the numbering scheme

to indicate the Me/meth combination, the label b to indicate

the series, [RhBr(COD)(^MeC(H)-h -C^meth)][Br] (2a), using a similar

procedure gave only a mixture of unidentiﬁed products, under a

variety of conditions.

1

The H NMR spectral parameters for the series of complexes

t

^tBu/meth, the label c to indicate Me/eth, and d for the Bu/eth

(2c and 2d) are closely comparable to those described for 2b⁴⁶and

also to those of previously reported pendent complexes involving

other metals.^{18,31,67,81–89}Complexes 2b-2d show typical resonances

for the coordinated COD ligands (between d 1.7 and d 5.7) as

given in the Experimental section. The acidic proton of the pendent

imidazolium group appears characteristically downﬁeld at ca. d 10

as a pseudotriplet, displaying approximately equal coupling to the

pair of inequivalent oleﬁnic protons, while these oleﬁnic protons

on the imidazolium group display mutual coupling (³J_H-Hª 2 Hz)

in addition to coupling (⁴J_H-Hª 2 Hz) to the acidic proton and

therefore also appear as pseudotriplets. The appearance of two

different resonances for the N-bound substituents (at ca. d 4.0 for

the methyl groups in 2c; and at ca. d 1.8 for the tert-butyl groups in

2b,d) is as expected for an unsymmetrical, carbene/imidazolium

system, and the four separate resonances for the oleﬁnic protons

within the NHC and imidazolium rings offer further support for

the pendent species. The AB quartet observed for the methylene

linker in 2b rather than a singlet suggests that the NHC unit adopts

the usual orientation in which it is bound perpendicular to the

square plane of the metal. In this orientation, the plane bisecting

the linking CH₂group is unsymmetrical on each side, having a

bromo ligand on one side and one half of the COD ligand on the

combination.

Chart 2

(a) Carbene-anchored/pendent-imidazolium complexes of Rh.

Although there are a few examples in which an external base

can be used to deprotonate only one end of a diimidazolium

salt to generate pendent-imidazolium species, they are usually

speciﬁc to diimidazolium salts terminated by bulky N-substituents

t

such as Bu and Mes^11,43,66,67and therefore limit the scope of

1

other. The ¹³C{ H} NMR data offer additional support for the

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©

1

Fig. 1 Three-dimensional representations of the complex cation of [RhBr(COD)(^MeC(H)-h -C^eth)][Br] (2c) and both the anion and cation of

1

[RhBr(COD)(^tBuC(H)-h -C^eth)][Br] (2d) showing the numbering schemes. Thermal ellipsoids are shown at the 20% probability level. Hydrogen atoms

are shown only on the linked carbene/imidazolium group. Relevant parameters for 2c (distances in A and angles in ^◦): Rh–Br(1) = 2.5054(4),

˚

Rh–C(1) = 2.205(3), Rh–C(2) = 2.226(3), Rh–C(5) = 2.102(3), Rh–C(6) = 2.123(3), Rh–C(10) = 2.022(3); Br(1)–Rh–C(10)–N(12) = 83.2(3)^◦,

◦

N(11)–C(13)–C(14)–N(13) = 61.7(4) . Relevant parameters for 2d (distances in A and angles in ^◦.): Rh–Br(1) = 2.5338(4), Rh–C(1) = 2.190(4),

Rh–C(2) = 2.229(3), Rh–C(5) = 2.101(3), Rh–C(6) = 2.127(3), Rh–C(10) = 2.053(3); Br(1)–Rh–C(10)–N(12) = 98.5(3)^◦, N(11)–C(13)–C(14)–N(13) =

-176.6(2)^◦.

˚

pendent structure, displaying two different signals for the N-bound

substituents on the carbene and imidazolium rings, and four

different oleﬁnic carbons. More signiﬁcantly, the carbene carbon

in these complexes appears at ca. d 181.7 with typical coupling to

Rh^{39,46,94–96}of approximately 50 Hz, while the protonated carbon

of the imidazolium group appears as a singlet at ca. d 122.0.

This imidazolium carbon resonance appears as a doublet in

Although replacement of the COD ligands by CO in com-

pounds 2c and 2d proceeds as expected to yield the analogous

1

dicarbonyl complexes [RhBr(CO)₂(^MeC(H)-h -C^eth)][Br] (3c) and

1

[RhBr(CO)₂(^tBuC(H)-h -C^eth)][Br] (3d), shown in Chart 3, CO addi-

tion to the C₁-linked complex 2b does not proceed as expected, but

instead yields a number of unidentiﬁed decomposition products.

This result parallels the previously observed differences with the

C₁- and C₂-linked dicarbene ligands ^RCC^methand ^RCC^eth(R = Me,

^tBu), respectively, in which the C₂-linked dicarbene-bridged com-

plexes [RhX(COD)]₂(m-^RCC^eth) underwent facile COD replace-

ment by CO to give the anticipated products, [RhX(CO)₂]₂(m-

^RCC^eth), while the related C₁-linked species [RhBr(COD)]₂(m-

^RCC^meth) did not undergo simple substitution, instead yielding

1

the proton-coupled ¹³C NMR spectrum having J_C-Hª 220 Hz

coupling to the acidic proton (as conﬁrmed by 2D Heteronuclear

Single Quantum Coherence (HSQC) and Heteronuclear Multiple

Quantum Coherence (HMQC) NMR experiments).

The proposed pendent structures for complexes 2c,d are con-

ﬁrmed by X-ray crystallography and their structures are shown in

Fig. 1. Consistent with the NMR data, the NHC plane lies close

to perpendicular to the metal coordination plane in both cases

(dihedral angles = 83.2(3)^◦and 98.5(3)^◦respectively); and the

Rh–C_carbenedistances are normal, suggesting a metal–carbon single

1

the unexpected mononuclear products [RhBr(CO)(h :h -^RCC^meth)]

together with [Rh(m-Br)(CO)₂]₂,⁴⁶through fragmentation of the

dicarbene-bridged precursors.

˚

bond. The Rh–C(1) and Rh–C(2) separations (2.205(3), 2.226(3) A

˚

in 2c; 2.190(4), 2.229(3) A in 2d) involving the oleﬁnic moiety of the

COD ligand trans to the NHC are longer than those of Rh–C(5)

˚

and Rh–C(6) to the other oleﬁn moiety (2.102(3), 2.123(3) A in

˚

2c; 2.101(3), 2.127(3) A in 2b). This difference can be rationalized

either on the basis of steric repulsions between half of the COD

ligand and the adjacent bromo ligand or the larger trans inﬂuence

of the carbene ligand.^16,31,34,39The weaker Rh–oleﬁn interaction

Chart 3

˚

Although single crystals of 3c,d suitable for an X-ray diffraction

is paralleled by a shorter C(1)–C(2) distance (1.382(4) A in 2c;

-

study could not be obtained (the Br^-, BF₄and OTf ^-salts could

˚

1.383(6) A in 2d) compared to C(5)–C(6) (1.404(5) A in 2c;

˚

only be obtained as oils), the spectral data leave little doubt about

their formulations. In addition to the downﬁeld pseudotriplet at

ca. d 10.1 in the ¹H NMR spectrum for the imidazolium proton,

a downﬁeld peak for the carbene carbon appears as a doublet

1.403(5) A in 2d), consistent with less p back-donation in this

case. The major difference between the two structures involves the

different torsion angles around the C₂H₄linker as shown in Fig. 1.

These differences are presumably a consequence of packing effects

and are unlikely to be of chemical signiﬁcance.

The close separation (2.67 A) between the acidic proton of the

imidazolium group and the bromide counterion in 2d, which is

signiﬁcantly shorter than the sum of their van der Waals radii

(3.05 A), indicates hydrogen bonding between the two whereas

for 2c the closest H–Br distance (3.12 A) is normal and does not

1

(¹J_C-Rhª 42 Hz) in the ¹³C{ H} NMR at ca. d 172.6 together

˚

with a singlet at ca. d 137.1, corresponding to the imidazolium

carbon. Furthermore, the carbonyl stretches of 3c,d appear at

ca. 2006 and 2082 cm^-1in the IR spectra, with these carbons

1

appearing at ca. d 186.2 and 182.2 in the ¹³C{ H} NMR spectra

97

˚

showing typical coupling to rhodium. The carbonyl trans to the

carbene displays approximately 54 Hz coupling to Rh while the

suggest such an interaction.

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Scheme 2

carbonyl group trans to the bromide shows approximately 77 Hz

1

coupling, as is seen in similar systems.³⁹The larger J_Rh-Cand

smaller n_COis consistent with this carbonyl, opposite the bromo

ligand, being more strongly bound—presumably a consequence

of both the lower trans inﬂuence of the bromo ligand compared

to the NHC group^16,31,34,39and its greater p donor ability.

Reaction of the COD complex (2c) with a series of diphos-

phine ligands generates the diphosphine-chelated products

1

[RhBr(P^«P)(^MeC(H)-h -C^eth)][Br] (4c-6c), as shown in Scheme 2.

1

The ³¹P{ H} NMR spectra of these products display two sets

of doublets of doublets; both resonances display coupling to Rh

(ranging from 102.7 to 197.6 Hz) and to the other ³¹P nucleus (33.4

to 102.7 Hz). Additionally, these peaks are located more upﬁeld

when methylene-linked diphosphines (4c, 6c) are used (both peaks

centred about d -25, -21, respectively) whereas a more downﬁeld

set of peaks is observed in the ethylene-linked case of 5c (centred

about d 65), consistent with the large deshielding reported for ﬁve-

membered diphosphine rings,⁹⁸conﬁrming the chelating formula-

tion above. As observed in the parent complex 2c, the acidic proton

of the pendent imidazolium group in these pendent species appears

Scheme 3

reacts with monophosphines in a stepwise manner yielding

ﬁrst the monophosphine products (8b-11b) which subsequently,

in the presence of additional PR₃, result in a second iodide

substitution to give the bis(phosphine) species 12b and 13b. With

a number of diphosphines, the diphosphine-substituted prod-

ucts (14b-16b) are produced. The analogous methyl-substituted

1

downﬁeld at ca. d 10.2 in the H NMR spectrum. The pendent

nature is also evident by the four different peaks for the oleﬁnic

protons, as well as two different peaks for the methyl substituents

1

in the H NMR spectra. Surprisingly perhaps, the other COD

precursors 2b,d fail to react with these diphosphines, even after

prolonged reﬂux. In addition, all complexes (2a-d) are inert to a

number of monophosphines, even under forcing conditions.

The resulting diphosphine complexes (4c-6c) are unstable and

decompose over the course of 1 h to form undesired complexes

species, [PdI₃(^MeC(H)-h -C^meth)] and [PdI₃(^MeC(H)-h -C^eth)], were

1

not investigated since Herrmann, et al. have reported that only

di-NHC-chelated dicarbene products [PdX₂(h :h -^MeCC^meth)] and

1

[PdX₂(h :h -^MeCC^eth)] were obtained.⁸³

1

lacking the acidic proton. On the basis of ¹H and ³¹P{ H} NMR

The spectral parameters for the carbene/imidazolium groups of

complexes 8b-16b are closely comparable to those in related pen-

dent species which have previously been reported,^{11,37,42,43,61–65,67–69,99}

and again conﬁrm the carbene-anchored/pendent-imidazolium

formulation. The methylene protons of the C₁-linker in the pendent

group show up as a singlet at ca. d 6.71 in the monophosphine

complexes, reﬂecting the symmetry on either side of the NHC

plane, whereas for the bis(phosphine) species (12b, 13b) and

the chelated diphosphine complexes (14b-16b) the protons of

the methylene linker appear as an AB quartet, (²J_H-Hª 14 Hz,

Dd ª 0.4–0.7 ppm) consistent with the lack of symmetry on either

side of the carbene plane for these products. As was observed

with 4c-6c, complexes 15 exhibit a similar downﬁeld shift in their

spectroscopy, the resulting species most likely contain chelating

diphosphine and dicarbene groups, and are themselves unstable,

decomposing to a mixture of unidentiﬁed products over the course

of 1–1.5 h, even in the presence of coordinating solvents such

as THF or CH₃CN. These transient intermediates were not of

interest, and were not characterized further.

(b) Carbene-anchored/pendent-imidazolium complexes of Pd.

An analogous series of carbene-anchored/pendent-imidazolium

complexes of palladium can be generated by substitution of

1

the iodo ligands in [PdI₃(^tBuC(H)-h -C^meth)] (7b),⁶³by a number

of mono- and diphosphine ligands as outlined in Scheme 3.

Unlike the previously described Rh species that were unreactive

to monophosphines, the triiodide C₁-linked Pd precursor (7b)

³¹P{ H} NMR resonances (centred at ca. d 56) compared to the

1

four-membered ring-containing analogues 14 and 16b (centred

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1

Fig. 2 Three-dimensional representations of [PdI₂(PMe₂Ph)(^tBuC(H)-h -C^meth)][I], 11b and the dication complex [PdI(PMe₂Ph)₂(^tBuC(H)-h -C^meth)][I]₂,

13b showing the numbering scheme. Thermal ellipsoids are as described in Fig. 1. Hydrogen atoms are shown only on the linked carbene/imidazolium

group. Relevant parameters for 11b (distances in A and angles in ^◦): Pd–C(11) = 2.049(4); N(12)–C(14)–N(13) = 110.6(3)^◦. Relevant parameters for 13b

˚

(distances in A and angles in ^◦): Pd–C(11) = 2.052(2); N(12)–C(14)–N(13) = 110.98(19)^◦.

˚

at ca. d -51 and d -49, respectively), consistent with the ring

contribution effect⁹⁸noted earlier. As an interesting contrast to this

chelating diphosphine phenomenon, the midpoint of the two dou-

blets in the bis(phosphine) complex 13b is located at about d -8.

All oleﬁnic protons, for the carbene and imidazolium moieties

appear as pseudotriplets; for the imidazolium groups these oleﬁnic

protons again display mutual coupling as well as coupling to the

acidic proton, whereas for the carbene groups the oleﬁnic protons

show essentially equal coupling to each other and to the ³¹P nucleus

in the position opposite the carbene ligand. These resonances are

readily differentiated by appropriate ¹H{ P} and H{ H} NMR

experiments (Fig. S5, ESI).† Identiﬁcation of individual ¹H and ¹³C

resonances is also aided by ¹H Nuclear Overhauser Effect (NOE),

HSQC, HMQC and Heteronuclear Multiple Bond Correlation

(HMBC) NMR experiments (assignments are outlined in the

Experimental section).

substitute a second iodide ion, even in the presence of a tenfold

excess of phosphine. The only phosphines to give the double-

substitution products were the two smallest studied.²⁰For the

three diphosphines studied, all have cone angles less than that

of PEt₃,²⁰and coordination of both ends of these diphosphines is

additionally favoured entropically by the chelate effect.

The X-ray structure determinations for compounds 11b and

13b, shown in Fig. 2, and of 16b, shown in Fig. 3 conﬁrm the

31

1

The carbene carbon in each case appears at ca. d 160.0 in

1

the ¹³C{ H} NMR spectrum. In the case of the monophosphine

complexes (8b-11b) this carbene resonance displays coupling (²J_C-P

ª 190 Hz) to the trans-phosphine; while in the bis(phosphine) (12b,

13b) or diphosphine (14b-16b) complexes, additional coupling to

the cis-phosphorus nucleus (²J_C-Pª 3–7 Hz) can also be observed

for some species. However, in the case of 16b only the large trans-

phosphine coupling is resolvable. Coupling of the pair of oleﬁnic

carbons in the carbene moiety to the trans-phosphine can also be

observed (⁴J_C-Pª 5 Hz). In the proton-coupled ¹³C NMR spectrum,

the resonance for the pendent protonated carbon appears as a

doublet displaying approximately 220 Hz coupling to the attached

acidic proton, as noted above for the Rh species 2.

Although all reactions involving monophosphines were carried

out with an excess of phosphine, only in the cases of PMe₃

and PMe₂Ph did I^-substitution by a second phosphine occur

(Scheme 3). This is presumably a result of steric repulsion

between the phosphine and the nearby tert-butyl group since the

somewhat larger, yet strongly basic triethylphosphine does not

Fig.

3

Three-dimensional representation of the cation complex

[PdI(depm)(^tBuC(H)-h -C^meth)][I]₂, 16b showing the numbering scheme.

Thermal ellipsoids are as described in Fig. 1. Hydrogen atoms are shown

only on the linked carbene/imidazolium group. Relevant parameters (dis-

1

tances in A and angles in ^◦): Pd–C(11) = 2.062(3); N(12)–C(14)–N(13) =

˚

111.5(2)^◦, P(1)–C(20)–P(2) = 94.71(15)^◦, P(2)–Pd–C(11) = 170.58(8)^◦,

I(1)–Pd–P(1) = 167.14(2)^◦.

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Scheme 4

structural assignments determined on the basis of spectral data. In

anchored/pendent-imidazolium precursor by deprotonating the

pendent acidic imidazolium hydrogen of 2b using one-half-

equivalent of [Rh(m-OAc)(COD)]₂yielding the dirhodium tar-

get. Attempts to extend this strategy to generate mixed-metal

complexes of rhodium using 2b-2d as precursors and using the

complexes [Ir(m-OAc)(COD)]₂, or [Pd(OAc)₂], containing the basic

acetate ligands, all failed. Although the ¹H NMR spectra indicate

that deprotonation of the acidic proton on the imidazolium

group has occurred (as evident from the absence of a downﬁeld

pseudotriplet), no evidence of a binuclear Rh/Ir or Rh/Pd product

could be detected by NMR or HRMS.

However, using the reverse strategy, starting with carbene-

anchored/pendent-imidazolium complexes of other metals and

using [Rh(m-OAc)(COD)]₂to perform the deprotonation, has

allowed us to successfully prepare dicarbene-bridged products

of both Pd/Rh and Ir/Rh. Additionally, a number of related

Pd/Ir systems can be generated by deprotonation of the pendent-

imidazolium group by an external base in the presence of [Ir(m-

Cl)(COD)]₂.

all three structures the geometry is typical of square-planar NHC

complexes in which the carbene plane lies essentially perpendicular

to the metal coordination plane, having a dihedral angle with

the plane deﬁned by I(1), Pd, C(11) and N(11) of -93.1(3)^◦

for 11b; 86.1(2)^◦for 13b; and -86.0(3)^◦for 16b. The Pd–C_carbene

distances are also typical of such systems, suggesting a metal–

carbon single bond. All three complexes display some degree of

hydrogen bonding involving the imidazolium proton and a nearby

˚

iodide ion, having H(15)–I contacts of 2.75 A, 2.95 A and 2.94 A

for 11b, 13b and 16b, respectively, which are less than the sum of

their van der Waals radii of 3.18 A.⁹⁷In the case of compounds 11b

˚

and 16b, this hydrogen bond involves an iodide counterion, while

for 13b this is an inner-sphere interaction with the coordinated

iodo ligand, forming an 8-membered pseudometallocycle (both

interactions are diagrammed in Fig. 2 and 3). For compound

˚

13b an additional hydrogen bond of 2.87 A appears between one

of the outer-sphere iodide ions (I(2)) and one of the methylene

hydrogens on the linker carbon C(14), while a similar interaction

˚

(I(3)–H(17) = 2.85 A) involves a oleﬁnic hydrogen of 16b.

Using the ﬁrst approach, the heterobimetallic Pd/Rh complex

[PdI₂(PEt₃)(m-^tBuCC^meth)RhI(COD)] (17b), can successfully be gen-

erated by reacting the carbene-anchored/pendent-imidazolium

complex 9b and half an equivalent of [Rh(m-OAc)(COD)]₂, as

shown in Scheme 4. Deprotonation of the imidazolium moiety

of 9b and concomitant incorporation of Rh, yielding 17b, is

obvious in the spectral data. The low-ﬁeld acidic proton of 9b

is conspicuously absent in the ¹H NMR spectrum and the oleﬁnic

protons remote from Pd no longer display coupling to this acidic

proton, and now appear as doublets, whereas the oleﬁnic protons

on the NHC ring bound to palladium still appear as pseudotriplets

due to coupling to the trans-phosphorus nucleus of the PEt₃

group. In addition, the loss of symmetry upon incorporation of

the “RhI(COD)” moiety transforms the singlet resonance for the

methylene protons of the linker in 9b into an AB quartet in 17b.

The rhodium-coordinated COD protons display similar NMR

properties to those of the pendent Rh complexes noted earlier,

displaying two resonance signals at ca. d 5.2, and another set of

multiplets at ca. d 3.4, representing the protons on the oleﬁnic

moiety trans to the carbene and the iodide, respectively. One

multiplet from each set of resonances displays a through-space

interaction (monitored via NOE experiments) with one of the ^tBu

signals, further conﬁrming the perpendicular arrangement of the

NHC ring to the Rh coordination plane.

The strain within complex 16b, resulting from diphosphine

chelation to a square-planar centre, is evident in the geometry

within the depm group as well as in the angles about Pd. Within

˚

the diphosphine the P(1)–P(2) separation (2.6907(11) A) is much

smaller than is usually observed in an unstrained depm moiety,

where values near 3.05 A are more typical,⁴⁶and is accompanied by

˚

an acute P(1)–C(20)–P(2) angle (94.71(15)^◦) which is signiﬁcantly

less than the idealized 109.5^◦. Accompanying this strain, the P(1)–

Pd–P(2) angle (72.29(3)^◦) is also compressed from the idealized

90^◦.

The C₂-linked analogue, [PdI₃(^tBuC(H)-h -C^eth)] (7d), in which

the carbene is connected to the imidazolium ring by a C₂H₄

linker was also successfully prepared using a similar procedure to

that used by Herrmann, et al. to generate [PdI₃(^tBuC(H)-h -C^meth)]

1

(7b),⁶³and a number of mono- (9d) and diphosphine (14d, 15d)

derivatives involving this C₂-linked carbene/imidazolium species

have also been generated as described for the C₁-linked products

(Scheme 3). These species display NMR spectra very similar to

those described for compounds 8b-11b and 14b-15b, respectively,

as documented in the Experimental section. Interestingly, the peak

corresponding to the carbene carbon in 7d could not be observed

in the ¹³C{ H} NMR spectrum, as also reported by Herrmann,

1

et al. for the C₁-linked system.⁶³

1

In the ¹³C{ H} NMR spectra, two carbene moieties can now

be observed; a doublet at d 160.8 (²J_C-P= 187.7 Hz) compares

closely to that of the precursor 9b (and other phosphine-

containing Pd-carbenes) and again shows strong coupling to the

(c) Mixed-metal, di-NHC-bridged heterobimetallic complexes.

In our initial study,⁴⁶we were able to prepare

a

binu-

clear dicarbene-bridged complex from a mononuclear, carbene-

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©

trans-phosphine while the other is signiﬁcantly downﬁeld at d 180.9

appearing in the region of other Rh-carbene species with typical

coupling to Rh (¹J_C-Rh= 49.3 Hz).^{39,46,94–96}The remaining peaks

display typical resonances for an unsymmetric di-NHC-bridging

backbone, a Pd-coordinated PEt₃ligand, and a Rh-coordinated

COD ligand.

The X-ray structure determination for compound 17b, shown

in Fig. 4 conﬁrms the above assignment in which the two different

metals are bridged by a di-NHC ligand. All parameters associated

with this structure are typical of such NHC complexes. At

each metal the NHC plane lies essentially perpendicular to the

metal coordination plane and the metal-carbene distances are

A gentle purge of carbon monoxide gas through a solution

of 17b readily results in substitution of COD and generation

of the less sterically hindered carbonyl analogue [PdI₂(PEt₃)(m-

^tBuCC^meth)RhI(CO)₂] (18b, Scheme 4), as seen by the appearance of

two carbonyl stretches at 2004 and 2076 cm^-1in the IR spectrum,

1

along with two carbonyl peaks in the ¹³C{ H} NMR spectrum

(d 187.2, d 181.6) alongside the carbenes. The carbonyl resonance

1

show coupling to rhodium (¹J_C-Rh= 54.6 Hz; J_C-Rh= 76.3 Hz),

representing the carbonyl ligands trans to the carbene and iodo

ligands respectively, much as described earlier for 3c and 3d.

Attempts to generate di-NHC-bridged Pd/Rh complexes via

deprotonation of the carbene-anchored/pendent-imidazolium Pd

species 8–16 using [Rh(m-OAc)(COD)]₂has only succeeded with

9b, as noted above; all other attempts failed. Even the other very

similar monophosphine complexes, 8b, 9d, 10b and 11b did not

generate the targeted Pd/Rh species using the conditions used to

generate 17b. In the reaction of compounds 14 and 15 (using both

the C₁- and C₂-linked dicarbenes) trace amounts of the mixed-

metal products could be detected by HRMS but these species

were not detectable by NMR techniques.

˚

consistent with single bonds (Pd–C(11) = 2.045(3) A, Rh–C(15) =

˚

2.037(3) A). The slightly larger Pd–C(11) distance may result

from the larger trans inﬂuence of the PEt₃group. Consistent

with such a proposal, this Pd–C(11) distance is very close to

those in the phosphine compounds 11b and 13b (vide infra)

and is substantially longer than the Pd-carbene distances in

1

7b⁶³and [PdI₂(OAc)(^tBuC(H)-h -C^meth)]⁶³(1.990(9) and 1.953(5) A,

˚

respectively) in which iodo and acetate ligands, having a low trans

inﬂuence, are opposite the carbene. As is also typical of binuclear

species bridged by only a di-NHC ligand, the dicarbene framework

is twisted in such a way to allow the metal coordination planes

to avoid each other. As a result the Pd–Rh separation is quite

Using an identical strategy, deprotonation of the pendent

1

imidazolium species, [IrBr(COD)(^tBuC(H)-h -C^meth)][Br] (the iodo

analogue of which is known)¹¹by [Rh(m-OAc)(COD)]₂success-

fully yielded the mixed Ir/Rh product, [IrBr(COD)(m-^tBuCC^meth)-

RhBr(COD)] (19b) as outlined in Scheme 5. The carbene carbons

˚

large, at 6.2054(5) A. This skewing about the dicarbene methylene

1

linker is shown clearly in Fig. 4 and is evident by the dihedral

angle of 71.43(12)^◦between the two NHC planes. Interestingly,

the close contacts between part of the COD ligand on Rh and the

PEt₃group on Pd, observed in the solid state, are also present in

solution as shown by the NOE experiment noted above.

of the di-NHC groups are surprisingly close in the ¹³C{ H}

NMR spectrum, at d 180.5 and 179.2, with the former being

readily identiﬁed as being Rh-bound by the 50.1 Hz coupling to

this metal.^{39,46,94–96}Additionally, the appearance of two different

resonances for the N-bound tert-butyl groups in the ¹H and

1

¹³C{ H} NMR spectra, combined with the absence of the low-

ﬁeld acidic proton in the ¹H NMR spectrum further support our

formulation. Interestingly, reaction of 19b with dppm or carbon

monoxide did not yield the desired substituted products, but rather

gave a mix of unidentiﬁed products. The instability of complex

19b towards CO substitution parallels that of the analogous

COD-substituted di-NHC-linked dirhodium complex mentioned

earlier.⁴⁶

Scheme 5

Although the conditions employed to generate complex 17b

failed when extended to other Pd pendent species, related

mixed-metal species involving Pd can be obtained using milder

conditions and an external base. In the presence of half an

equivalent of a suitable Ir precursor, such as [Ir(m-Cl)(COD)]₂,

the pendent-imidazolium arm of the monophosphine-containing

10b and 11b can be deprotonated using K[N(SiMe₃)₂], presumably

generating a transient Pd carbene-anchored/pendent-carbene

Fig.

4

Three-dimensional

representation

of

[PdI₂(PEt₃)(m-

^tBuCC^meth)RhI(COD)], 17b showing the numbering scheme. Thermal

ellipsoids are as described in Fig. 1. Hydrogen atoms are shown only

on the dicarbene backbone. Relevant parameters (distances in A and

˚

angles in ^◦): Pd–C(11) = 2.045(3), Rh–C(15) = 2.037(3), Rh–C(21) =

2.137(3), Rh–C(22) = 2.137(3), Rh–C(25) = 2.211(3), Rh–C(26) =

2.194(3); N(12)–C(14)–N(13) = 110.6(2)^◦, I(1)–Pd–I(2) = 170.078(12)^◦,

I(1)–Pd–C(11)–N(11) = 93.3(3)^◦, I(3)–Rh–C(15)–N(14) = -91.9(3)^◦.

7284 | Dalton Trans., 2009, 7269–7287

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Scheme 6

intermediate which subsequently attacks the Ir dimer, forming

syntheses of di-NHC-bridged complexes of dirhodium using the

basic acetate ligands of [Rh(m-OAc)(COD)]₂to deprotonate the

imidazolium salts, we had anticipated that this approach should

be quite general for the generation of mixed-metal analogues.

However, one problem with this method appears to be the

rather harsh conditions necessary for deprotonation of the imi-

dazolium group, requiring extended reﬂux in acetonitrile. Even

for the ﬁrst deprotonation, to give the carbene-anchored/pendent-

imidazolium precursors, conditions need to be carefully controlled

for imidazolium deprotonation and successful incorporation of

the metal. So although we have successfully generated three of four

members of a series of carbene-anchored/pendent-imidazolium

precursors of Rh, the fourth member, [RhBr(COD)(^MeC(H)-

the desired di-NHC-bridged mixed-metal species [PdI₂(PR₃)(m-

^tBuCC^meth)IrI(COD)] (PR₃= PPh₃(20b); PMe₂Ph (21b), Scheme 6).

Although the high solubility of both complexes in most solvents

did not allow us to obtain single crystals, the spectral data leave

little doubt about their formulations. The carbene carbons of

1

the di-NHC groups in the ¹³C{ H} NMR spectrum appear at

ca. d 177.9 and ca. 168.2, with the latter being readily identiﬁed

as Pd-bound by the ca. 212 Hz coupling to the trans phosphorus

nucleus. As was observed in the Pd/Rh and Ir/Rh complexes,

the appearance of two different resonances for the N-bound tert-

1

butyl groups in the ¹H and ¹³C{ H} NMR spectra combined

1

with the absence of the low-ﬁeld acidic proton in the H NMR

1

spectrum further support our formulation. Additionally, the AB

quartet observed for the protons of the C₁linker suggest the

plane bisecting the linking CH₂group is now unsymmetrical on

each side, conﬁrming the replacement of a pendent proton with

an “IrBr(COD)” moiety. As a result, the methyl protons of the

PMe₂Ph moiety in 21b have become atropisotopic which gives rise

to a set of two doublets in the ¹H NMR spectrum (²J_H-Pª 10 Hz),

h -C^meth)][Br] has remained elusive. It appears that successful

deprotonation of the pendent imidazolium group and incorpo-

ration of the second metal, using the same strategy, is equally

sensitive to reaction conditions, and is additionally plagued by

the tendency of the dicarbenes to chelate rather than bridge.

We are also investigating whether the acetic acid produced in

the deprotonation by acetate complexes is interfering with the

generation of the desired bimetallic species.

1

as well as a corresponding pair in the ¹³C{ H} NMR spectrum

(¹J_C-Pª 33 Hz).

The lack of success in generating the di-NHC-bridged Pd/Rh

1

A gentle purge of carbon monoxide gas through a CH₂Cl₂

solution of both 20b and 21b readily results in substitu-

tion of COD generating the carbonyl analogues [PdI₂(PPh₃)(m-

^tBuCC^meth)IrI(CO)₂] (22b) and [PdI₂(PMe₂Ph)(m-^tBuCC^meth)IrI(CO)₂]

(23b), respectively, as seen by the appearance of two carbonyl

stretches in the IR spectra (1987 and 2065 cm^-1(22b); 1986

and 2065 cm^-1(23b)) along with two carbonyl resonances in the

species utilizing the zwitterionic [PdI₃(^tBuC(H)-h -C^meth)] (7b) and

1

[PdI₃(^tBuC(H)-h -C^eth)] (7d) is probably not surprising, since depro-

tonation of the imidazolium group by the Rh-bound acetate group

leaves a three-coordinate Rh centre after carbene incorporation.

Although such a three-coordinate Rh centre should be stabilized

through binding of CH₃CN solvent, generation of binuclear

species using this stepwise strategy has only been successful when

replacement of the acetate group by a halide occurs. No free halide

is available in 7b and 7d, and the sharing of a Pd-bound iodo

ligand in a bridging arrangement may not be favourable. However,

the lack of success in the case of the monophosphine (8–13) and

diphosphine (14–16) complexes, in which iodo counterions are

available, remains puzzling. It was expected that upon generation

of the targeted Pd/Rh complex, using the diphosphine-chelated

Pd complexes 14–16, the diphosphine could easily unwind to

bridge the metals, thereby locking the metals into close proximity.

However, it appears that these systems are not well suited for the

harsh conditions required for deprotonation of the weakly acidic

imidazolium group. It is especially surprising that the monophos-

phine complexes 8, 9d, 10 and 11 did not yield di-NHC-bridged

1

¹³C{ H} NMR spectrum (d 169.7, 167.1 (22b); d 169.6, 167.5

(23b)) alongside the carbene peaks. The AB quartet resonances

representing the protons of the methylene linker, previously buried

under the multiplets of the aromatic region in 21b, shift upﬁeld

in 23b to ca. d 6.98 upon replacement of COD by two carbonyl

ligands, distancing themselves from the phenyl resonances.

Discussion

Our strategy of using carbene-anchored/pendent-imidazolium

complexes as precursors for di-NHC-bridged, mixed-metal com-

plexes via deprotonation of the pendent imidazolium salt through

an internal base route has succeeded in two cases, but has to date

been surprisingly unproductive with the majority of closely related

mononuclear precursors studied. On the basis of our successful

Pd/Rh complexes, while the closely analogous [PdI₂(PEt₃)-

1

(

^tBuC(H)-h -C^eth)][I] (9b) did yield the mixed-metal target.

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In spite of the convenience in using a metal-coordinated base

to effect the deprotonation of pendent imidazolium groups, we

sought to avoid the harsh conditions noted above by using an

external strong base to bring about this deprotonation under

milder conditions, in the presence of a complex containing

the second metal. Using this strategy, we have been able to

successfully prepare the ﬁrst examples of a di-NHC-bridged Pd/Ir

system using potassium bis(trimethylsilyl)amide as an external

base. Although this method generates a substantial number of

unwanted byproducts (including di-NHC-chelated species), the

desired products are indeed observable via NMR and can be

isolated from the crude mixture. Various Pd/Rh combinations

(not yet accessible using [Rh(m-OAc)(COD)]₂) also seem possible,

although not pursued in this report. The importance of choice

of base for deprotonating the imidazolium group in pendent

imidazolium complexes has previously been noted.⁶⁹

In any case, these strategies have been successful in generating

the ﬁrst unambiguously characterized examples of di-NHC-

bridged heterobinuclear complexes,⁶⁹and studies are underway

investigating the reactivity of these new species. Future work will

also focus on other ways of converting the pendent imidazolium

group to a metal-bound carbene, such as the use of Ag₂O in order

to generate dicarbene-bridged M/Ag species as carbene-transfer

agents for accessing other M/M¢ combinations, or through the

oxidative addition of the imidazolium C–H bond to a suitable

electron-rich metal precursor (ie, Ni(COD)₂, Pd(PPh₃)₄, etc.).¹⁰⁰

12 M. Poyatos, P. Uriz, J. A. Mata, C. Claver, E. Fernandez and E. Peris,

Organometallics, 2003, 22, 440–444.

13 M. Poyatos, E. Mas-Marza´, J. A. Mata, M. Sanau´ and E. Peris,

Eur. J. Inorg. Chem., 2003, 1215–1221.

14 G. D. Frey, J. Schutz, E. Herdtweck and W. A. Herrmann,

Organometallics, 2005, 24, 4416–4426.

15 M. Scholl, S. Ding, C. W. Lee and R. H. Grubbs, Org. Lett., 1999, 1,

953–956.

16 W. A. Herrmann, M. Elison, J. Fischer, C. Ko¨cher and G. R. J. Artus,

Chem. Eur. J., 1996, 2, 772–780.

17 J. C. Green, R. G. Scurr, P. L. Arnold and F. G. N. Cloke, Chem.

Commun., 1997, 1963–1964.

18 C. Ko¨cher and W. A. Herrmann, J. Organomet. Chem., 1997, 532,

261–265.

19 J. Huang, H.-J. Schanz, E. D. Stevens and S. P. Nolan, Organometallics,

1999, 18, 2370–2375.

20 C. A. Tolman, Chem. Rev., 1977, 77, 313–348.

21 J. M. Praetorius and C. M. Crudden, Dalton Trans., 2008, 4079–

4094.

22 M. Poyatos, W. McNamara, C. Incarvito, E. Clot, E. Peris and R. H.

Crabtree, Organometallics, 2008, 27, 2128–2136.

23 H. M. Peng, R. D. Webster and X. Li, Organometallics, 2008, 27,

4484–4493.

24 T. A. P. Paulose, J. A. Olson, J. W. Quail and S. R. Foley, J. Organomet.

Chem., 2008, 693, 3405–3410.

˙

¨

25 I. Ozdemir, H. Arslan, S. Demir, D. VanDerveer and B. C¸ etinkaya,

Inorg. Chem. Commun., 2008, 1462–1465.

26 I. Nieto, R. P. Bontchev and J. M. Smith, Eur. J. Inorg. Chem., 2008,

2476–2480.

27 A. Poater, F. Ragone, S. Giudice, C. Costabile, R. Dorta, S. P. Nolan

and L. Cavallo, Organometallics, 2008, 27, 2679–2681.

28 A. C. Hillier, W. J. Sommer, B. S. Yong, J. L. Petersen, L. Cavallo and

S. P. Nolan, Organometallics, 2003, 22, 4322.

29 W. A. Herrmann, J. Schwarz, M. G. Gardiner and M. Spegler,

J. Organomet. Chem., 1999, 575, 80–86.

30 R. E. Douthwaite, D. Hau¨ssinger, M. L. H. Green, P. J. Silcock, P. T.

Gomes, A. M. Martins and A. A. Danopoulos, Organometallics, 1999,

18, 4584–4590.

Acknowledgements

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

PLATFORM/SMART 1000 CCD diffractometer, the Bruker

D8/APEX II CCD diffractometer and the Nicolet Avator IR spec-

trometer. We thank the Department’s Mass Spectrometry Facility

and the NMR Spectroscopy and Analytical and Instrumentation

Laboratories. Michael Slaney is acknowledged for supplying the

sample of depm while Kyle Wells provided initial diimidazolium

salt samples. In addition, we acknowledge support from NSERC

and Alberta Ingenuity Fund (AIF) in the form of postgraduate

scholarships to M.T.Z.

31 M. Albrecht, R. H. Crabtree, J. Mata and E. Peris, Chem. Commun.,

2002, 32–33.

32 A. A. Danopoulos, S. Winston and W. B. Motherwell, Chem.

Commun., 2002, 1376–1377.

33 R. E. Douthwaite, M. L. H. Green, P. J. Silcock and P. T. Gomes,

Dalton Trans., 2002, 1386–1390.

34 M. Poyatos, J. A. Mata, E. Falomir, R. H. Crabtree and E. Peris,

Organometallics, 2003, 22, 1110–1114.

35 L. G. Bonnet, R. E. Douthwaite and R. Hodgson, Organometallics,

2003, 22, 4384–4386.

36 K. A. Kreisel, G. P. A. Yap and K. H. Theopold, Organometallics,

2006, 25, 4670–4679.

37 M. Viciano, M. Poyatos, M. Sanau´, E. Peris, A. Rossin, G. Ujaque

and A. Lledo´s, Organometallics, 2006, 25, 1120–1134.

38 M. Poyatos, M. Sanau´ and E. Peris, Inorg. Chem., 2003, 42, 2572–2576.

39 J. A. Mata, A. R. Chianese, J. R. Miecznikowski, M. Poyatos, E. Peris,

J. W. Faller and R. H. Crabtree, Organometallics, 2004, 23, 1253–1263.

40 C. A. Quezada, J. C. Garrison, M. J. Panzner, C. A. Tessier and W. J.

Youngs, Organometallics, 2004, 23, 4846–4848.

Notes and references

1 H.-W. Wanzlick and H.-J. Scho¨nherr, Angew. Chem. Int. Ed., 1968, 7,

41 C. H. Leung, C. D. Incarvito and R. H. Crabtree, Organometallics,

2006, 25, 6099–6107.

141–142.

¨

2 K. J. Ofele, J. Organomet. Chem., 1968, 12, P42–P43.

42 R. E. Douthwaite, M. L. H. Green, P. J. Silcock and P. T. Gomes,

J. Chem. Soc. Dalton Trans., 2002, 1386–1390.

3 A. J. Arduengo III, H. V. R. Dias, R. L. Harlow and M. Kline, J. Am.

Chem. Soc., 1992, 114, 5530–5534.

43 M. Vogt, V. Pons and D. M. Heinekey, Organometallics, 2005, 24,

4 A. J. Arduengo III, Acc. Chem. Res., 1999, 32, 913–921.

5 U. Frenzel, T. Weskamp, F. J. Kohl, W. C. Schattenmann, O. Nuyker

and W. A. Herrmann, J. Organomet. Chem., 1999, 586, 263–265.

6 D. Bourissou, O. Guerret, F. P. Gabai and G. Bertrand, Chem. Rev.,

2000, 100, 39–91.

7 A. Do¨hring, J. Go¨hre, P. W. Jolly, B. Kryger, J. Rust and G. P. J.

Verhovnik, Organometallics, 2000, 19, 388–402.

1832–1836.

44 J. C. Garrison, R. S. Simons, J. M. Talley, C. Wesdemiotis, C. A. Tessier

and W. J. Youngs, Organometallics, 2001, 20, 1276–1278.

45 D. M. Khramov, A. J. Boydston and C. W. Bielawski, Angew. Chem.

Int. Ed., 2006, 45, 6186–6189.

46 K. D. Wells, M. J. Ferguson, R. McDonald and M. Cowie,

Organometallics, 2008, 27, 691–703.

47 R. W. Hilts, R. A. Franchuk and M. Cowie, Organometallics, 1991,

10, 304–316.

48 B. T. Sterenberg, R. W. Hilts, G. Moro, R. McDonald and M. Cowie,

J. Am. Chem. Soc., 1995, 117, 245–258.

8 C. W. Bielawski and R. H. Grubbs, Angew. Chem. Int. Ed., 2000, 39,

2903–2906.

9 W. A. Herrmann, Angew. Chem. Int. Ed., 2002, 41, 1290–1309.

10 C. W. K. Gsto¨ttmayr, V. P. W. Bo¨hm, E. Herdweck, M. Grosche and

W. A. Herrmann, Angew. Chem. Int. Ed., 2002, 41, 1363–1365.

11 M. Albrecht, J. R. Miecznikowski, A. Samuel, J. W. Faller and R. H.

Crabtree, Organometallics, 2002, 21, 3596–3604.

49 B. T. Sterenberg, R. McDonald and M. Cowie, Organometallics, 1997,

16, 2297–2312.

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This journal is

The Royal Society of Chemistry 2009

©

50 B. D. Rowsell, S. J. Trepanier, R. Lam, R. McDonald and M. Cowie,

Organometallics, 2002, 21, 3228–3237.

51 S. J. Trepanier, R. McDonald and M. Cowie, Organometallics, 2003,

22, 2638–2651.

52 A. Chokshi, B. D. Rowsell, S. J. Trepanier, M. J. Ferguson and M.

Cowie, Organometallics, 2004, 23, 4759–4770.

53 S. J. Trepanier, J. N. L. Dennett, B. T. Sterenberg, R. McDonald and

M. Cowie, J. Am. Chem. Soc., 2004, 126, 8046–8058.

54 J. R. Wigginton, A. Chokshi, T. W. Graham, R. McDonald, M. J.

Ferguson and M. Cowie, Organometallics, 2005, 24, 6398–6410.

55 J. R. Wigginton, S. J. Trepanier, R. McDonald, M. J. Ferguson and

M. Cowie, Organometallics, 2005, 24, 6194–6211.

56 J. N. L. Dennett, M. Bierenstiel, M. J. Ferguson, R. McDonald and

M. Cowie, Inorg. Chem., 2006, 45, 3705–3717.

57 J. Sinfelt, Bimetallic Catalysts—Discoveries, Concepts, and Applica-

tions, Wiley, New York, USA, 1983.

58 M. Shenglof, G. Dmitri, B. Heymey, H. Schumann, G. A. Molander

and J. Blum, Synthesis (Stuttgart), 2003, 302–306.

59 H. R. Reinhoudt, E. Crezee, A. D. van Langeveld, P. J. Kooyman,

J. A. R. van Veen and J. A. Moulijn, J. Catal., 2000, 196, 315–329.

60 M. Shenglof, G. A. Molander and J. Blum, Synthesis (Stuttgart),

2006, 111–114.

61 M. Viciano, E. Mas-Marza´, M. Poyatos, M. Sanau´, R. H. Crabtree

and E. Peris, Angew. Chem. Int. Ed., 2005, 44, 444–447.

62 J. Wolf, A. Labande, J.-C. Daran and R. Poli, Eur. J. Inorg. Chem.,

2008, 3024–3030.

75 Y. Lin, K. Nomiya and R. G. Finke, Inorg. Chem., 1993, 32, 6040–

6045.

76 J. Chatt and L. M. Venanzi, J. Chem. Soc., 1957, 4735–4741.

77 Programs for the diffractometer operation, data collection, data

reduction and absorption correction were those supplied by Bruker.

78 G. M. Sheldrick, Acta Crystallogr.. Sect. A: Fundam. Crystallogr.,

2008, 64, 112–122.

79 A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C.

Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori and R.

Spagna, J. Appl. Cryst., 1999, 32, 115–119.

80 P. T. Beurskens, G. Beurskens, R. de Gelder, J. M. M. Smits, S. Garcia-

Granada and R. O. Gould, Crystallography Laboratory, Radboud

University Nijmegen, The Netherlands, 2008.

81 C. D. Abernethy, A. R. Cowley and R. A. Jones, J. Organomet. Chem.,

2000, 596, 3–5.

82 W. A. Herrmann, M. Elison, J. Fischer, C. Ko¨cher and G. R. J. Artus,

Angew. Chem. Int. Ed. Engl., 1995, 34, 2371–2374.

83 W. A. Herrmann, C.-P. Reisinger and M. Spiegler, J. Organomet.

Chem., 1998, 557, 93–96.

84 M. V. Baker, D. H. Brown, P. V. Simpson, B. W. Skelton, A. H. White

and C. C. Williams, J. Organomet. Chem., 2006, 691, 5845–5855.

85 M. Heckenroth, A. Neels, H. Stoeckli-Evans and M. Albrecht, Inorg.

Chim. Acta, 2006, 359, 1929–1938.

86 Y. Han, Y.-T. Hong and H. V. Huynh, J. Organomet. Chem., 2008,

693, 3159–3165.

87 R. A. Kelly III, N. M. Scott, S. D´ıez-Gonza´lez, E. D. Stevens and S. P.

Nolan, Organometallics, 2005, 24, 3442–3447.

88 V. Ritleng, C. Barth, E. Brenner, S. Milosevic and M. J. Chetcuti,

Organometallics, 2008, 27, 4223–4228.

89 Y. Ohki, T. Hatanaka and K. Tatsumi, J. Am. Chem. Soc., 2008, 130,

17174–17186.

90 J. M. Praetorius, M. W. Kotyk, J. D. Webb, R. Wang and C. M.

Crudden, Organometallics, 2007, 26, 1057–1061.

63 W. A. Herrmann, J. Schwarz and M. G. Gardiner, Organometallics,

1999, 18, 4082–4089.

64 D. V. Yandulov and N. T. Tran, J. Am. Chem. Soc., 2007, 129, 1342–

1358.

65 E. F. Penka, C. W. Schla¨pfer, M. Atanasov, M. Albrecht and C. Daul,

J. Organomet. Chem., 2007, 692, 5709–5716.

66 L.-C. Song, X. Luo, Y.-Z. Wang, B. Gai and Q.-M. Hu, J. Organomet.

Chem., 2008, 694, 103–112.

67 M. Poyatos, E. Mas-Marza´, M. Sanau´ and E. Peris, Inorg. Chem.,

2004, 43, 1793–1798.

68 M. Raynal, C. S. J. Cazin, C. Valle´e, H. Olivier-Bourbigou and P.

Braunstein, Organometallics, 2009, 28, 2460–2470.

69 One di-NHC-bridged, heterobinuclear complex has been brieﬂy

described. See:M. Raynal, C. S. J. Cazin, C. Valle´e, H. Olivier-

Bourbigou and P. Braunstein, Dalton Trans., 2009, 3824–3832.

70 J. Liu, J. Chen, J. Zhao, Y. Zhao, L. Li and H. Zhang, Synthesis

(Stuttgart), 2003, 2661–2666.

91 S. J. Na, B. Y. Lee, N.-N. Bui, S. Mho and H.-Y. Jang, J. Organomet.

Chem., 2007, 692, 5523–5527.

92 F. A. Cotton and J. P. Fackler Jr., J. Am. Chem. Soc., 1961, 83, 2818–

2825.

93 R. G. Charles and M. A. Pawlikowski, J. Phys. Chem., 1958, 62, 440–

444.

94 S. Wolf and H. Plenio, J. Organomet. Chem., 2009, 694, 1487–1492.

95 F. Ullah, M. K. Kindermann, P. G. Jones and J. Heinicke,

Organometallics, 2009, 28, 2441–2449.

96 H. Tu¨rkmen, T. Pape, F. E. Hahn and B. C¸ etinkaya, Eur. J. Inorg.

Chem., 2008, 5418–5423.

97 A. Bondi, J. Phys. Chem., 1964, 68, 441–451.

71 A. A. Gridnev and I. M. Mihaltseva, Synth. Commun., 1994, 24,

1547–1555.

72 R. M. Claramunt, J. Heterocycl. Chem., 1983, 20, 1245–1249.

73 A. A. Prishchenko, N. E. Nifantev, Z. S. Novikova and I. F. Lutsenko,

Zh. Obshch. Khim., 1980, 50, 1881–1882.

74 G. Giordano, R. H. Crabtree, R. M. Heintz, D. Forster and D. E.

Morris, Inorg. Synth., 1979, 19, 218–220.

98 P. E. Garrou, Inorg. Chem., 1975, 14, 1435–1439.

99 D. Enders, J. Han and A. Henseler, Chem. Commun., 2008, 3989–

3991.

100 S. Gru¨ndemann, M. Albrecht, A. Kovacevic, J. W. Faller and R. H.

Crabtree, J. Chem. Soc. Dalton Trans., 2002, 2163–2167.

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Article Doi

Carbene-anchored/pendent-imidazolium species as precursors to di-N-heterocyclic carbene-bridged mixed-metal complexes

DOI: 10.1039/b906884h

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