First examples of structurally imposing eight-membered-ring (Diazocanylidene) N-Heterocyclic carbenes: Salts, free carbenes, and metal complexes

Article abstract of DOI:10.1021/om200467x

Eight-membered-ring (diazocanylidene) N-heterocyclic carbenes (8-NHCs) are reported for the first time.The precursor salts, readily prepared by the amidine route, are converted to the free carbene by treatment with KHMDS; in general, the free NHCs can be isolated, and in one example the molecular structure was obtained. Silver complexes were prepared by direct reaction of Ag₂O with the diazocanylidinium salts, and Rh complexes were formed by treatment of in situ formed free carbene with the appropriate Rh precursor complex. The salts and complexes were fully characterized using spectroscopic methods, including in some cases by X-ray crystallography. Key features of these new ring-expanded heterocyclic carbenes (RE-NHCs) are the extreme steric strain they impose on the metal center (they are the most sterically imposing class of NHC reported to date) and their high donor capacity, being some of the most basic NHCs currently available.

Full text of DOI:10.1021/om200467x

ARTICLE
pubs.acs.org/Organometallics
First Examples of Structurally Imposing Eight-Membered-Ring
(Diazocanylidene) N-Heterocyclic Carbenes: Salts, Free Carbenes, and
Metal Complexes
Wei Y. Lu, Kingsley J. Cavell,* James S. Wixey, and Benson Kariuki
School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, U.K.
S Supporting Information
b
ABSTRACT: Eight-membered-ring (diazocanylidene) N-het-
erocyclic carbenes (8-NHCs) are reported for the first time.
The precursor salts, readily prepared by the amidine route, are
converted to the free carbene by treatment with KHMDS; in
general, the free NHCs can be isolated, and in one example the
molecular structure was obtained. Silver complexes were pre-
pared by direct reaction of Ag2O with the diazocanylidinium
salts, and Rh complexes were formed by treatment of in situ
formed free carbene with the appropriate Rh precursor com-
plex. The salts and complexes were fully characterized using spectroscopic methods, including in some cases by X-ray
crystallography. Key features of these new ring-expanded heterocyclic carbenes (RE-NHCs) are the extreme steric strain they
impose on the metal center (they are the most sterically imposing class of NHC reported to date) and their high donor capacity,
being some of the most basic NHCs currently available.
’ INTRODUCTION
the ring size increases further, and therefore what new chemistry
will result.
Ring-expanded N-heterocyclic carbenes (RE-NHCs) offer
markedly changed steric and electronic properties in comparison
to the more traditional five-membered NHCs. Following reports
of more rigid large-ring systems by Richeson,1 Stahl,2 and
Bertrand,3 we reported the first examples of flexible, seven-
membered-ring diazepanylidene NHCs (salts, free carbenes,
and complexes).4 There has been growing interest in these
large-ring NHC ligands, and a number of investigations into
their structural properties, rich chemistry, and catalytic applica-
tions are now appearing;5,6 their novel features and reaction
chemistry are manifest in comparison to those of the more
traditional five-membered-ring imidazolium base NHCs, re-
cently reviewed by Hahn and Jahnke.5f Nonoptimized catalyst
systems based on RE-NHCs have shown excellent activity in
hydrogenation,7 transfer hydrogenation,8 hydrosilylation,9a and
CꢀC coupling.9b Key features of these ligands are an increase in
basicity and a marked increase in steric “pressure” on the metal
center as the ring size increases from five through six to seven for
a set of related ligands and complexes5 leading to the unique
coordination chemistry and reactivity noted for these systems. In
particular, it appears that the substantial steric demands of the
flexible large rings provide unexpected opportunities in NHC
chemistry and are highly effective in stabilizing novel complexes
and in promoting unusual reactivity.7,8,10 For example, recent
studies by Whittlesey and co-workers demonstrated that large-
ring NHCs can generate either metalated Ni(II) or novel Ni(I)
complexes, depending on reaction conditions.6 It is important
to establish whether these trends in properties will continue as
We report here the first examples of saturated eight-mem-
bered-ring (diazocanylidene) NHCs. In this study several diazo-
can-1-ium salts have been prepared, free carbenes isolated, and
silver and rhodium complexes of 8-NHCs synthesized. The
structural features of each are discussed and compared with
those of smaller ring sizes.
’ RESULTS AND DISCUSSION
Synthesis of Diazocanylidene Salts and Free NHCs. Bro-
mide salts of the eight-membered 1,3-diazocane ring, with
mesityl (Mes), xylyl (Xyl), diisopropylphenyl (DIPP), and
o-tolyl (oTol) groups on the nitrogen atoms, were prepared via the
amidine route (Scheme 1).3,5a The reaction is slow, but yields are
generally good (g75%). Bromide salts were readily converted to
the tetrafluoroborate salts in high yield by treatment with NaBF4.
The salts were fully characterized by spectroscopic and analytical
methods, and crystal structures of several were obtained (crystal
structures are presented in the Supporting Information). In the
1H NMR spectra of the salts the characteristic CNHCꢀH proton
shifts occurred in the range 7.31ꢀ7.61 ppm, and in 13C NMR the
CNHCꢀH shifts were clustered in the range 156.8ꢀ158.0 ppm.5a
The molecular structures reveal that the eight-membered ring is
neatly folded back over the central NCHN carbon. The NCHN
Received: May 31, 2011
Published: October 14, 2011
r
2011 American Chemical Society
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Organometallics
ARTICLE
Scheme 1. Synthesis of Salts, Free NHCs, and Metal Complexes
free 8-Xyl NHC. The eight-membered ring is boat-shaped with
the backbone folded over the central NHC carbon, and the
NCNHCN angle (120.11(18)°) is large with the attendant
CNHCNCXyl angles (113.75(12)°) being very small, pushing
the xylyl substituent toward the CNHC (and the metal center
on coordination). The structure of the free NHC is completely
symmetrical, with both halves of the molecule having equivalent
bond lengths and angles. The structure of the free 8-Xyl NHC is
shown in Figure 1a. A comparison of selected bond lengths and
distances for free carbenes with seven- and eight-membered rings
is shown in Table 1. It is evident that as the ring size increases the
above structural features become more pronounced.
Figure 1. ORTEP ellipsoid plots of (a) free 8-Xyl NHC and (b) Ag(8-Xyl)-
Br at the 50% probability level.
Silver and Rhodium Complexes of Diazocanylidene NHCs.
Silver complexes of the 8-NHCs were prepared by stirring a
mixture of the diazocanylidene salts, Ag2O, and NaBr in DCM at
room temperature; the complexes were isolated and fully character-
ized. In 13C NMR the characteristic CNHC shifts for [Ag(8-Mes)Br]
and [Ag(8-Xyl)Br] were 217.2 ppm (1JAgC = 224/256 Hz) and
217.4 ppm (1JAgC = 223/255 Hz), respectively.5a The complexes
were crystallized from DCM/diethyl ether to obtain crystals
suitable for X-ray analysis. The structure of the Ag(8-Xyl)Br
complex is shownin Figure 1b, and the structure of [Ag(8-Mes)Br]
is provided in the Supporting Information. As shown in Figure 1b,
the coordinated ligands demonstrate structural features similar to
those observed for the salts and free ligands; the ring has a boat
structure with a large NCNHCN and small CNHCNCAr angle. A
comparison of the structures of silver-NHC complexes for five-,
six-, seven-, and eight-membered-ring NHCs (Table 2) shows
the impact of increasing ring size on the relevant angles and on
the AgꢀCNHC bond lengths. Although the halide and the NHC
vary between complexes, the structural trends are very clear; for
the large rings the aromatic substituents on the ring nitrogens
bend around and essentially enclose the Ag center, in effect
protecting the metal center against further reaction and prevent-
ing a second NHC from coordinating. The 8-DIPP NHC is so
sterically demanding we were unable to form a Ag complex,
despite several attempts. These large ligands favor complexes
with low coordination numbers.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
7-Mes and 8-Xyl
lengths (Å)
angles (deg)
7-Mes5a
C(1)ꢀN(2)
C(2)ꢀN(1)
C(5)ꢀN(2)
1.346(5)
1.483(5)
1.502(6)
N(1)ꢀC(1)ꢀN(2)
C(1)ꢀN(1)ꢀC(6)
C(1)ꢀN(2)ꢀC(15)
116.6(4)
115.5(3)
115.0(4)
8-Xyl
C(1)ꢀN(1/10)
1.3475(16) N(1)ꢀC(1)ꢀN(10)
120.11(18)
C(2/20)ꢀN(1/10) 1.4982(19) C(1)ꢀN(1/10)ꢀC(5/50) 113.75(12)
C(5/50)ꢀN(1/10) 1.443(2)
angles are extremely large and the CMesNCH angles correspond-
ingly small; for example, in the N-mesityl salt the angles are
131.3(4) and 115.8(3)°, respectively.
Treatment of the bromide salts containing Mes, DIPP, and Xyl
substituents with KHMDS in THF gave the free carbenes
1
(Scheme 1), which were isolated and characterized by H and
13C NMR spectroscopy, and the structure of 8-Xyl was deter-
mined by single-crystal X-ray crystallography. As noted for other
large-ring NHCs, the CNHC peak shows a significant downfield
shift in the 13C NMR with chemical shifts for the eight-
membered rings commonly between 250 and 260 ppm (a table
comparing 13C NMR data for five-, six-, seven-, and eight-
membered NHCs is provided in the Supporting Information).5a
Similar structural features noted for the salts are evident in the
Torsional angles (α) are defined by the CArꢀN NꢀCAr
3 3 3
atoms and are a measure of the spatial twist of the N coordination
planes and hence the relative position of the aromatic substituents,
which point directly into the coordination sphere of the metal.
Torsional angles were calculated for the silver complexes [Ag(8-
Mes)Br] and [Ag(8-Xyl)Br]; the angles are 1.85 and 0.96°,
respectively. Therefore, unlike the the case for [Ag(7-Mes)Br]
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Organometallics
ARTICLE
(α = 30.3°) and [Ag(7-Xyl)I] (α = 23.1°),5a the eight-membered
rings show little sign of spatial twisting of the aromatic
substituents.
rings are given in Table 5 and compared with those of [Rh-
(8-oTol)(CO)2Cl]. These data indicate that electron density
on the Rh center (an indication of ligand donor ability), as
indicated by carbonyl stretching frequencies, are very similar for
6- and 7-NHCs, but higher stretching frequencies for the
complex of the five-membered NHC is consistent with relatively
lower ligand basicity. Overall, it would appear that the 8-oTol
NHC is the most basic of all the NHC ligands compared.
However, these figures should be treated with some caution, as
other methods for determining ligand basicity may well give
somewhat different outcomes.16c
In summary, a straightforward route to the first 8-NHC
(diazocanylidinium) salts from readily accessible formamidines
and dihalopentanes has been developed. Free 8-NHCs have been
isolated, and one example has been structurally characterized.
The upfield shift of the NC(H)N proton in the salts and the large
downfield 13C shift of the free NHC (conjugate base) indicates
that these NHCs are very strong σ donors. The steric demands of
these 8-NHCs are so large as to impede the formation of metal
complexes in some cases. Such features impact on coordination
behavior (favoring complexes with low coordination numbers),
complex reactivity, and catalytic performance. Further novel
structures, novel reactivity, and catalytic behavior promoted by
these RE-NHCs will be reported in forthcoming papers. Exam-
ples of functionalized 8-NHC ligands and complexes will also be
the subject of a later report.
To further demonstrate the enhanced steric bulk of the RE-
14
NHCs, the percentage buried volumes (%Vbur
)
of the silver
complexes have also been determined; the results are presented
in Table 3. The buried volume increases considerably with NHC
ring size in going from five- to eight-membered NHCs; the values
reflect the high steric demand imposed by the RE-NHCs and are
consistent with X-ray and other data and with observed reactivity
behavior. The different halide ions are expected to have little
impact on the calculated buried volume for the complexes, which
adopt a linear geometry; thus, a comparison of %Vbur between
complexes in this context is valid.14,15
In situ formation of the free NHC, by treatment with
KHMDS, and reaction with appropriate Rh starting compounds
(e.g. [Rh(CO2)(acac)] and [Rh(COD)Cl]2) gives rise to
8-NHC-Rh complexes (Scheme 1). The extreme steric congestion
at the metal center presages novel structures and novel chemistry,
as previously noted for seven-membered-ring NHCs.5b Consis-
tent with this expectation, we have found that the 8-Mes ligand is
too large to coordinate to the [Rh(COD)Cl]2 dimer, and less
sterically demanding examples of the large ring (e.g., 8-oTol) were
necessary to yield a stable [(8-NHC)Rh(COD)Cl] complex.
However, the planar acac coligand is better able to accommodate
the large NHC ligands, and a full range of [(NHC)Rh(CO)-
(acac)] complexes could be prepared. Molecular structures of
[(8-oTol)Rh(COD)Cl] (Figure 2a) and [(8-oTol)Rh(CO)(acac)]
(Figure 2b) are provided, and a comparison of selected bond
lengths and angles for a range of [Rh(NHC)(COD)Cl] com-
plexes is provided in Table 4. The molecular structures of other
(8-NHC)Rh complexes are provided in the Supporting Informa-
tion. To accommodate the RE-NHCs, the tilt angle θ (defined as
the angle between the coordination plane and the NꢀCNHCꢀN
plane of the NHC) is very close to 90° (for 8-oTol it is 88.4°),
whereas tilt angles for complexes of five-membered-ring carbenes
are much smaller (59.0° for [Rh(5- Mes)(COD)Cl]). The
8-NHCs are even more effective in enclosing the metal center
than all previous ring sizes, and this steric congestion can be
expected to influence reactivity at the metal center.
’ EXPERIMENTAL SECTION
The preparation of free NHCs and Rh complexes were performed
using standard Schlenk techniques under an argon atmosphere, unless
otherwise specified. Air-sensitive compounds were stored and handled
in an MBraun UNIlab glovebox. Solvents of analytical grade were freshly
distilled using an MBraun SPS-800 solvent purification system. Deuter-
ated solvents for NMR measurements were distilled from the appro-
priate drying agents under N2 immediately prior to use, following
Table 3. %Vbur Values for NHCs in [Ag(NHC)X]
Complexesa
complex
%Vbur
The carbonyl stretching frequencies for complexes of the type
[M(NHC)(CO)2Cl] (M = Rh, Ir) are often used to compare
NHC ligand basicity/donor ability.16 Consequently, we prepared
the complex Rh(8-oTol)(CO)2Cl by treating a DCM solution of
[Rh(8-oTol)(COD)Cl] with carbon monoxide. Crystals suitable
for X-ray analysis were obtained by diffusion of hexane vapor into
dichloromethane. The molecular structure is included in the Suppor-
ting Information. Carbonyl stretching frequencies for [Rh(NHC)-
(CO)2Cl] complexes with five-, six-, and seven-membered
[Ag(5-IMes)Cl]15
[Ag(5-SIMes)Cl]15
[Ag(6-Mes)Cl]11
36.1
36.1
44.0
44.7
48.7
49.1
[Ag(7-Mes)Br]5a
[Ag(8-Mes)Br] (this work)
[Ag(8-Xyl)Br] (this work)
a NHC structures extracted from crystal structure CIF files (r = 3.5 Å, d =
2.0 Å, bond radii scaled by 1.17).
Table 2. Comparison of Structures for 5-, 6-, 7-, and 8-NHC Ag(NHC) Complexes
AgꢀCNHC (Å)
AgꢀX (Å)
N(1)ꢀCNHCꢀN(2) (deg)
CNHCꢀN(1)ꢀCAr, CNHCꢀN(2)ꢀCAr (deg)
[Ag(5-Mes)Cl]11,12
[Ag(5-SDIPP)Cl]13
[Ag(6-Mes)Cl]11,5a
[Ag(6-DIPP)Br]5a
[Ag(7-Mes)Br]5a
[Ag(7-Xyl)I]5a
2.056(7)
2.059(9)
2.095(3)
2.104(6)
2.097(6)
2.114(6)
2.132(4)
2.123(3)
2.314(2)
104.4(5)
107.8(8)
118.3(3)
118.8(5)
118.8(6)
121.2(5)
123.2(3)
123.3(3)
121.8(3)
2.306(2)
123.1(5)
2.3213(10)
2.4254(9)
2.3792(11)
2.5659(7)
2.4553(5)
2.4370(5)
119.4(2), 118.5(2)
118.7(5), 120.6(5)
117.0(5), 117.3(5)
116.8(5), 117.8(5)
115.3(3), 115.7(3)
115.1(3), 115.4(3)
[Ag(8-Mes)Br] (this work)
[Ag(8-Xyl)Br] (this work)
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Organometallics
ARTICLE
Figure 2. ORTEP ellipsoid plots of (a) [(8-oTol)Rh(COD)Cl] and (b) [(8-oTol)Rh(CO)(acac)] at the 50% probability level.
The resulting reaction mixture was refluxed for 10ꢀ14 days, after which
the resulting solution was filtered to remove solid impurities and the
solvent was removed in vacuo. The residue was dissolved in the minimum
amount of dichloromethane, to which diethyl ether was added, to afford
the diazocanylidium bromide salt as a white crystalline solid.
To convert the bromide salts to tetrafluoroborate salts, 1,3-diazocane
bromide (0.5 mmol) in acetone (30 mL) and sodium tetrafluoroborate
(0.07 g, 0.6 mmol) in water (10 mL) were stirred together at room
temperature for 20 min. The acetone was evaporated under reduced
pressure to afford a suspension of the tetrafluoroborate salt in water. The
solid material was collected via filtration, dissolved in dichloromethane
(20 mL), and subsequently dried over MgSO4. After filtration, the
solvent was concentrated to approximately 2 mL and ether was added to
the solution until the product precipitated as a white crystalline material,
which was collected by filtration.
Table 4. Bond Lengths (Å) and Angles (deg) for
[Rh(NHC)(COD)Cl] Complexes
5-Mes5b
6-Mes5b
7-Mes5b 7-oTol5b
8-oTol
RhꢀCNHC
RhꢀCl
2.0513(14) 2.078(4) 2.085(3) 2.030(3) 2.061(3)
2.3665(3) 2.3876(13) 2.3817(8) 2.4470(7) 2.4357(8)
CArꢀNꢀCNHC 127.62(13) 119.5(4) 119.1(2) 117.1(2) 117.3(2)
127.06(12) 119.1(4) 117.2(2) 120.5(3) 118.2(2)
NꢀCNHCꢀN 107.29(12) 117.0(4) 118.0(3) 117.2(3) 121.3(2)
CNHCꢀRhꢀCl 91.86(4) 86.75(13) 85.27(9) 86.59(8) 88.01(8)
tilt angle θa
59.0
83.5
87.8
81.1
88.4
a The tilt angle is defined as the angle between the coordination plane
and the NHC NꢀCNHCꢀN plane.
1,3-Bis(2,4,6-trimethylphenyl)-3,4,5,6,7,8-hexahydro-1,3-diazocin-
1-ium Bromide (8-Mes HBr). White solid. Yield: 75%. 1H NMR(CDCl3,
Table 5. Infrared ν(CO) for [Rh(NHC)(CO)2Cl]
Complexes
3
400 MHz, 298 K): δ7.33 (s, 1H, NCHN), 6.87 (s, 4H, m-CH), 4.79 (s, 4H,
NCH2), 2.36 (s, 12H, o-CH3), 2.21 (m, 4H, NCH2CH2), 2.20 (s, 6H, p-
CH3), 1.56 (s, 2H, NCH2CH2CH2). 13C NMR (CDCl3, 100 MHz,
298 K): δ 158.0 (s, NCHN), 141.8 (s, Ar-C), 140.1 (s, Ar-C), 133.5 (s, Ar-
C), 130.4 (s, Ar-m-CH), 53.8 (s, NCH2), 40.4 (s, NCH2CH2), 28.3 (s,
NCH2CH2CH2), 20.8 (s, Ar-p-CH3), 18.7 (s, o-CH3). HRMS (ES): m/z
349.2657 ([M ꢀ Br]+; C24H33N2 requires 349.2644). Anal. Calcd for
C24H33N2Br: C, 67.13; H, 7.75; N, 6.52. Found: C, 66.76; H, 7.73; N, 6.38.
1,3-Bis-(2,4,6-trimethylphenyl)-3,4,5,6,7,8-hexahydro-1,3-diazocin-
complex
νs,as (cmꢀ1
)
νav (cmꢀ1
)
[Rh(5-Mes)(CO)2Cl]17
[Rh(6-Mes)(CO)2Cl]18
[Rh(7-Mes)(CO)2Cl]5b
[Rh(7-Xyl)(CO)2Cl]5b
1995, 2080
1987, 2071
1987, 2069
1986, 2071
1981, 2068
2037.5 (2038)
2029 (2029)
2028
2028.5
[Rh(8-oTol)(CO)2Cl] (this work)
2024.5
1-ium Tetrafluoroborate (8-Mes HBF4). White crystalline solid. Yield:
3
92%. 1H NMR (CDCl3, 400 MHz, 298 K): δ 7.31 (s, 1H, NCHN), 6.90
(s, 4H, m-CH), 4.46 (s, 4H, NCH2), 2.33 (s, 12H, o-CH3), 2.22 (s, 6H,
standard literature methods. All other reagents were used as received. 1H
and 13C spectra were recorded using a Bruker Avance AMX 400 or 500
spectrometer. Chemical shifts δ were expressed in ppm downfield from
TMS using the residual proton as an internal standard. Coupling
constants J are given in hertz as positive values. The multiplicity of the
signals is indicated as “s”, “d”, “t”, and “m” for singlet, doublet, triplet, and
multiplet, respectively. Mass spectra and high-resolution mass spectra
were obtained in electrospray (ES) mode unless otherwise reported on a
Waters Q-T micromass spectrometer. Infrared spectra were recorded
using a JASCO FT/IR-660 Plus spectrometer.
General Procedure for the Synthesis of Diazocanylidium
Bromide and Tetrafluorophosphate Salts. The appropriate
formamidine (1 mmol) was dissolved in acetonitrile (50 mL), to which
potassium carbonate (0.14 g, 1 mmol) was added. The mixture was stirred
for 20 min prior to the addition of 1,5-dibromopentane (0.23 g, 1 mmol).
p-CH3), 2.10 (m, 4H, NCH2CH2), 1.62 (s, 2H, NCH2CH2CH2). 13
C
NMR (CDCl3, 100 MHz, 298 K): δ 158.02 (s, NCHN), 141.69 (s, Ar-C),
140.23 (s, Ar-C), 133.53 (s, Ar-C), 130.46 (s, Ar-m-CH), 52.93 (s,
NCH2), 40.51 (s, NCH2CH2), 28.35 (s, NCH2CH2CH2), 20.87 (s, Ar-
p-CH3), 18.34 (s, Ar-o-CH3). HRMS (ES): m/z 349.2651 ([M ꢀ BF4]+;
C24H33N2 requires 349.2644).
1,3-Bis(2,6-dimethylphenyl)- 3,4,5,6,7,8-hexahydro-1,3-diazocin-1-
ium Bromide (8-Xyl HBr). White crystalline solid. Yield: 79%. 1H
3
NMR (CDCl3, 400 MHz, 298 K): δ 7.37 (s, 1H, NCHN), 7.16 (t,
3
3JHH = 6.8 Hz, 2H, p-CH), 7.09 (d, JHH = 7.6 Hz, 4H, m-CH), 4.85
(m, 4H, NCH2), 2.42 (s, 12H, o-CH3), 2.52 (m, 4H, NCH2CH2), 2.10
(m, 2H, NCH2CH2CH2). 13C NMR (CDCl3, 100 MHz, 298 K): δ
157.8 (s, NCHN), 144.0 (s, CAr), 133.9 (s, CAr), 130.0 (s, CHAr), 129.9
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Organometallics
Table 6. Crystal Data and Structure Refinement Details for 8-Xyl, Ag(8-Xyl)Br, (8-oTol)Rh(COD)Cl, and (8-oTol)RhCO(acac)
ARTICLE
8-Xyl
Ag(8-Xyl)Br
(8-oTol)Rh(COD)Cl
(8-oTol)RhCO(acac)
empirical formula
fw
C
320.46
22H28N2
C22H28AgBrN2
508.24
C28H36ClN2Rh
538.95
C26H32N2O3Rh
523.45
cryst syst, space group
orthorhombic, Pnma
11.2458(3)
20.1481(7)
8.1507(3)
90
orthorhombic, Pbca
15.7187(3)
17.1912(3)
15.7875(4)
90
monoclinic, C2/c
35.3100(10)
9.1520(4)
16.3260(6)
90
triclinic, P1
8.6728(4)
10.6096(5)
14.6223(6)
79.733(2)
77.374(2)
72.399(3)
1242.34(10)
2, 1.399
a (Å)
b (Å)
c (Å)
α (deg)
β (deg)
90
90
108.3940(10)
90
γ (deg)
V (Å3)
Z, calcd density (Mg mꢀ3
90
90
1846.80(11)
4, 1.153
4266.15(15)
8, 1.583
5006.3(3)
8, 1.430
)
abs coeff (mmꢀ1
)
0.067
2.826
0.807
0.716
F(000)
696
2048
2240
542
cryst habit, color
cryst dimens/mm3
block, colorless
0.20 ꢁ 0.20 ꢁ 0.08
3.09ꢀ27.49
3921/2163
0.0517
block, colorless
0.30 ꢁ 0.30 ꢁ 0.10
2.99ꢀ27.52
25 592/4895
0.0748
block, colorless
0.18 ꢁ 0.16 ꢁ 0.10
2.63ꢀ29.05
13 464/6227
0.0588
block, colorless
0.10 ꢁ 0.10 ꢁ 0.08
2.62ꢀ27.53
8223/5549
0.0547
θ range (deg)
no. of rflns collected/unique
Rint
no. of data/restraints/params
final R indices (F2 < 2σ(F2)): R1, wR2
R indices (all data): R1, wR2
2163/0/115
0.0573, 0.1310
0.1007, 0.1501
4895/0/239
0.0446, 0.0978
0.0756, 0.1105
6227/0/292
0.0438, 0.0853
0.0621, 0.0920
0.1158, 0.3031
0.1677, 0.3420
(s, CHAr), 53.8 (s, NCH2), 28.3 (s, NCH2CH2), 20.9 (s, NCH2CH2CH2),
18.9 (s, o-CH3). HRMS (ES): m/z 321.2317 ([M ꢀ Br]+; C22H29N2
requires 321.2331. Anal. Calcd for C22H29N2Br: C, 65.83; H, 7.28; N, 6.98.
Found C, 65.58; H, 7.31; N, 6.81.
(s, NCH2CH2CH2). HRMS(ES):m/z433.3581 ([M ꢀ BF4]+;C30H45N2
requires 433.3583).
1,3-Bis(2-methylphenyl)-3,4,5,6,7,8-hexahydro-1,3-diazocin-1-ium
Bromide (8-oTol HBr). White semicrystalline solid. Yield: 77%. 1H NMR
3
1,3-Bis-(2,6-dimethylphenyl)-3,4,5,6,7,8-hexahydro-1,3-diazocin-1-
(CDCl3, 400 MHz, 298 K): δ 7.55 (s, 1H, NCHN), 7.46 (s, 2H, o-CH),
7.30ꢀ7.23 (m, 6H, m,p-CH), 4.04 (s, 4H, NCH2), 2.47 (s, 6H, CH3),
2.13 (s, 4H, NCH2CH2), 1.89 (m, 2H, NCH2CH2CH2). 13C NMR
(CDCl3, 100 MHz, 298 K): δ 156.8 (s, NCHN), 144.1 (s, ipso-C), 133.5
(s, CAr), 132.2 (s, CAr), 130.0 (s, CAr), 127.9 (s, CAr), 53.6 (s, NCH2),
27.7 (s, NCH2CH2), 20.9 (NCH2CH2CH2), 18.3 (s, CH3). HRMS
(ES): m/z 293.2013 ([M ꢀ Br]+; C20H25N2 requires 293.2018). Anal.
Calcd for C20H25N2Br: C, 64.34; H, 6.75; N, 7.50. Found: C, 64.06; H,
6.57; N, 7.35.
ium Tetrafluoroborate (8-Xyl HBF4). White crystalline solid. Yield: 91%.
3
1H NMR (CDCl3, 400 MHz, 298 K): δ 7.37 (s, 1H, NCHN), 7.15 (t, 2H,
p-CH), 7.10 (d, 3JHH = 7.6 Hz, 4H, m-CH), 4.48 (m, 4H, NCH2), 2.37
(s, 12H, o-CH3), 2.22 (m, 4H, NCH2CH2), 2.09 (m, 2H, NCH2CH2CH2).
13C NMR (CDCl3, 100 MHz, 298 K): δ 158.0 (s, NCHN), 143.9 (s, CAr),
133.9 (s, CAr), 130.1 (s, CHAr), 129.9 (s, CHAr), 52.9 (s, NCH2), 28.3
(s, NCH2CH2), 20.9 (s, NCH2CH2CH2), 18.4 (s, o-CH3). HRMS (ES):
m/z 321.2337 ([M ꢀ BF4]+; C22H29N2 requires 321.2331).
1,3-Bis(2-methylphenyl)-3,4,5,6,7,8-hexahydro-1,3-diazocin-1-ium
Tetrafluoroborate (8-oTol HBF4). White crystalline solid. Yield: 91%. 1H
1,3-Bis(2,6-diisopropylphenyl)-3,4,5,6,7,8-hexahydro-1,3-diazocin-
1
1-ium Bromide (8-DIPP HBr). Crystalline white solid. Yield: 44%. H
3
3
NMR (CDCl3, 400 MHz, 298 K): δ 7.44 (s, 1H, NCHN), 7.36 (t, 3JHH
=
NMR (CDCl3, 400 MHz, room temperature): δ 7.61 (s, 1H, NCHN),
7.44 (s, 1H, o-CH), 7.319ꢀ7.30 (m, 7H, m,p-CH), 4.06 (s, 4H, NCH2),
7.7 Hz, 2H, p-CH), 7.17 (d, 4H, m-CH), 4.64 (m, 4H, NCH2), 3.22
(sept, 3JHH = 6.7, 4H, o-CH(CH3)2), 2.23 (m, 4H, NCH2CH2), 2.04 (m,
2H, NCH2CH2CH2), 1.31 (d, 3JHH = 6.7 Hz, 12H, o-CH(CH3)2), 1.19
(d, 3JHH = 6.8 Hz, 12H, o-CH(CH3)2). 13C NMR (CDCl3, 100 MHz,
298 K): δ 157.0 (s, NCHN), 144.8 (s, CAr), 141.0 (s, CAr), 130.6 (s,
CHAr) 125.5 (s, CHAr), 55.1 (s, NCH2), 28.7 (s, CH(CH3)2), 27.6
(s, CH(CH3)2), 25.1 (s, CH(CH3)2), 24.9 (s, NCH2CH2), 21.4 (s,
NCH2CH2CH2). HRMS (ES): m/z 433.3578 ([M ꢀ Br]+; C30H45N2
requires 433.3583).
2.48 (s, 6H, CH3), 2.19 (s, 4H, NCH2CH2), 2.09 (NCH2CH2CH2). 13
C
NMR (CDCl3, 100 MHz, 298 K): δ 157.4 (NCHN), 144.2 (s, ipso-C),
132.6 (s, CAr), 130.5 (s, CAr), 128.4 (s, CAr), 127.2 (CAr), 53.0 (s, NCH2),
28.1 (s, NCH2CH2), 21.5 (s, NCH2CH2CH2), 18.1 (s, CH3). HRMS
(ES): m/z 293.2005 ([M ꢀ BF4]+; C20H25N2 requires 293.2018).
General Procedure for the Preparation of Free 8-NHCs. To
a suspension of 8-NHC HBr (0.47 mmol) in THF (30 mL) was added 2
3
equiv of KN(SiMe3)2 (0.19 g, 0.95 mmol). The resulting suspension was
stirred for 30 min, after which time the residue was filtered into a flame-
dried Schlenk flask. The solvent was then removed to yield the free NHC
as an orange-red solid.
1,3-Bis(2,6-diisopropylphenyl)-3,4,5,6,7,8-hexahydro-1,3-diazocin-
1-ium Tetrafluoroborate (8-DIPP HBF4). White crystalline solid. Yield:
3
89%. 1H NMR (CDCl3, 400 MHz, 298 K): δ 7.42 (s, 1H, NCHN), 7.30
(t, 3JHH = 7.7 Hz, 2H, p-CH), 7.14 (s, 4H, m-CH), 4.75 (m, 4H, NCH2),
3.21 (sept, 3JHH = 6.7 Hz, 4H, o-CH(CH3)2), 2.29 (m, 4H, NCH2CH2),
1,3-Dimesityl-1,3-diazocane-2-ylidene (8-Mes). Yield: 51%. 1H NMR
(C6D6, 500 MHz, 298 K): δ 6.85 (s, 4H, Ar-CH), 3.25 (br t, 4H, NCH2),
2.19 (s, 12H, o-Me’s), 2.10 (s, 6H, p-Me), 1.69 (br peak, 2H, NCH2-
CH2CH2), 1.13 (br db, 4H, NCH2CH2) ppm. 13C NMR (C6D6, 125
MHz, 298 K): δ 245.4 (s, NCN), 149 (s, CAr), 135.5 (s, CAr), 134 (s, CAr),
130.1 (s, CAr), 128.2 (s, CHAr), 51.0 (s, NCH2), 29.5 (s, NCH2CH2), 21.0
(s, p-Me), 19.2 (s, o-Me) ppm.
3
2.08 (m, 2H, NCH2CH2CH2), 1.30 (d, JHH = 6.4 Hz, 12H, o-CH-
(CH3)2), 1.18 (d, 3JHH = 6.8 Hz, 12H, o-CH(CH3)2). 13C NMR (CDCl3,
100 MHz, 298 K): δ 156.9 (s, NCHN), 144.7 (s, CAr), 140.8 (s, CAr),
130.8 (s, CHAr), 125.5 (s, CHAr), 54.3 (s, NCH2), 28.7 (s, CH(CH3)2),
27.6 (s, CH(CH3)2), 24.9 (s, CH(CH3)2), 24.8 (s, NCH2CH2), 21.5
5653
dx.doi.org/10.1021/om200467x |Organometallics 2011, 30, 5649–5655

Organometallics
ARTICLE
1,3-Bis(2-methylphenyl)-1,3-diazocane-2-ylidene (8-Xyl). Yield: 51%.
1H NMR (C6D6, 500 MHz, 298 K): δ 6.81ꢀ6.92 (m, 6H, CHAr), 3.19
(m, 4H, NCH2), 2.18 (s, 12H, o-CH3), 1.24 (m, 4H, NCH2CH2), 1.02
(m, 2H, NCH2CH2CH2). 13C NMR (CDCl3, 125 MHz, 298 K): δ 251.1
(s, NCN), 151.8 (s, CAr), 134.4 (CAr), 129.1 (s, CHAr), 126.0 (s, CHAr),
50.6 (s, NCH2), 29.6 (s, NCH2CH2), 20.2 (s, NCH2CH2CH2), 19.3 (s,
o-CH3). Crystals suitable for X-ray analysis (see Table 6) were obtained
by precipitation from a pentane solution at ꢀ34 °C in a glovebox.
1,3-Diisopropyl-1,3-diazocane-2-ylidene (8-DIPP). Yield: 31%. 1H
NMR (C6D6, 400 MHz, 298 K): δ 7.18 (t, 3JHH = 7.6 Hz, 2H, p-CH),
7.08 (d, 4H, m-CH), 3.50 (m, 4H, NCH2), 3.45 (m, 4H, o-CH(CH3)2),
o-CH3). HRMS (ES): m/z 591.2332 ([M ꢀ CO + CH3CN]+; C32H42-
N3O2Rh requires 591.2341). Anal. Calcd for C30H39N2O3Rh: C, 62.28; H,
6.79; N, 4.84. Found: C, 62.01; H, 6.71; N, 4.92.
[Rh(8-Xyl)(acac)CO]. Yield: 80%. 1H NMR (CDCl3, 400 MHz,
298 K): δ 7.03 (m, 4H, m-CH), 6.92 (m, 2H, p-CH), 5.00 (s, 1H, CHacac),
4.09 (m, 2H, NCH2), 3.92 (m, 2H, NCH2), 2.33 (s, 6H, o-CH3), 2.31
(s, 6H, o-CH3), 2.06 (m, 4H, NCH2CH2), 1.99 (m, 2H, NCH2CH2CH2),
1.72 (s, 3H, CH3 acac), 1.62 (s, 3H, CH3 acac). 13C NMR (CDCl3, 125 MHz,
1
1
298K): δ 210.7 (d, JRhC = 52.5 Hz, NCN), 190.3 (d, JRhC = 85 Hz,
CO), 185.7 (s, CCH3 acac), 181.7 (s, CCH3 acac), 147.6 (s, CAr), 134.4
(s, CAr), 133.6 (s, CAr), 128.9 (s, p-CHAr), 127.9 (s, m-CHAr), 127.6
(s, m-CHAr), 98.5 (s, CHacac), 53.2 (s, NCH2), 26.9 (s, NCH2CH2), 26.5
(s, CH3 acac), 25.5 (s, CH3 acac), 22.6 (s, NCH2CH2CH2), 18.5 (s, o-CH3).
HRMS (ES): m/z 563.2009 ([M ꢀ CO + CH3CN]+; C30H38N3O2Rh
requires 563.2019).
1.80 (m, 2H, NCH2CH2CH2), 1.49 (m, 4H, NCH2CH2), 1.19 (d, 3JHH
=
6.7 Hz, 12H, o-CH(CH3)2), 1.14 (d, 3JHH = 6.3 Hz, 12H, o-CH(CH3)2).
13C NMR (C6D6, 125 MHz, 298 K): δ 253.2 (s, NCN), 147.1 (s, CAr),
145.5 (s, CAr), 142.6 (s, CHAr), 140.6 (s, CHAr), 65.4 (s, NCH2), 30.1
(s, CH(CH3)2), 26.7 (s, CH(CH3)2), 25.9 (s, CH(CH3)2), 23.4 (s,
NCH2CH2CH2), 22.8 (NCH2CH2).
1
[Rh(8-oTol)(acac)CO]. Yield: 87%. H NMR (CDCl3, 400 MHz,
298 K): δ 7.16 (m, 3H, CHAr), 7.07 (t, 3H, CHAr), 6.99 (m, 2H, CHAr),
5.03 (s, 1H, CHacac), 4.84 (m, 2H, NCH2), 3.44 (m, 2H, NCH2), 2.25 (s,
6H, o-CH3), 1.87 (m, 4H, NCH2CH2), 1.70 (m, 2H, NCH2CH2CH2),
1.62 (s, 3H, CH3 acac), 1.54 (s, 3H, CH3 acac). 13C NMR (CDCl3, 75
MHz, 298 K): δ 211.8 (d, 1JRhC = 53 Hz, NCN), 191.7 (d, 1JRhC = 84 Hz,
CO), 186.8 (s, CCH3 acac), 182.8 (s, CCH3 acac), 148.7 (s, CAr), 135.6
(s, p-CHAr), 134.7 (s, p-CHAr), 129.0 (s, o-CAr), 128.7 (s, o-CHAr), 127.0
(s, m-CHAr), 126.9 (s, m-CHAr), 99.6 (s, CHacac), 54.3 (s, NCH2), 30.4
(s, NCH2CH2), 28.3 (s, CH3 acac), 28.0 (s, CH3 acac), 23.7 (s, NCH2-
CH2CH2), 19.6 (s, o-CH3), 19.5 (s, o-CH3). HRMS (ES): m/z 522.1406
([M]+; C26H31N2O3Rh requires 522.1390); 451.1079 [M ꢀ acac +
CO]+; 464.1422 ([M ꢀ acac + CH3CN]+). Anal. Calcd for C26H31N2-
O3Rh: C, 59.77; H, 5.98; N, 5.36. Found: C,59.01; H, 6.02; N, 5.48.
[Rh(8-oTol)(COD)Cl]. A flame-dried Schlenk was charged with
Synthesis of Silver Complexes. A mixture of 8-NHC HBr
3
(1.2 mmol), Ag2O (0.22 g, 0.96 mmol), and NaBr (0.6 g, 5.8 mmol)
in dichloromethane (50 mL) was stirred in the dark at room temperature
for 3 days. The resulting suspension was filtered and ether was added to
the solution until the white microcrystalline material precipitated. The
product was isolated by filtration, washed with diethyl ether and dried in
vacuo. Crystals suitable for X-ray diffraction (see Table 6) were obtained
by layering a DCM solution of the compound with diethyl ether.
[Ag(8-Mes)Br]. Yield: 25%. 1H NMR (CDCl3, 400 MHz, 298 K): δ
6.85 (s, 4H, m-CH), 4.03 (br t, 4H, NCH2), 2.27 (s, 12H, o-Me), 2.17
(s, 6H, p-Me), 2.08 (s, 2H, NCH2CH2CH2), 1.95 (br m, 4H,
NCH2CH2) ppm. 13C NMR (CDCl3, 125 MHz, 298 K): δ 217.2 (dd,
1JC107Ag = 224, 1JC109Ag = 256, NCN), 147.9 (s, CAr), 137.6 (s, CAr), 133.3
(s, CAr), 130.4 (s, CAr), 130.0 (s, CHAr), 51.7 (s, NCH2), 29.0 (s,
NCH2CH2), 21.6 (s, NCH2CH2CH2), 20.9 (s, p-Me), 18.8 (s, o-Me)
ppm. HRMS (ES): m/z 496.1891 ([M ꢀ Br + CH3CN]+; C26H35N3Ag
requires 496.1882). Anal. Calcd for C24H32N2BrAg: C, 53.75; H, 6.01;
N, 5.22. Found: C, 53.71; H, 5.98; N, 5.08.
8-oTol HBr (76 mg, 0.20 mmol) and KN(SiMe3)2 (45 mg, 0.23 mmol)
3
in THF (15 mL) and the mixture stirred for ca. 30 min at room tem-
perature. The solution was subsequently filtered via a cannula into a
separate flame-dried Schlenk charged with [Rh(COD)Cl]2 (50 mg,
0.10 mmol) in THF (10 mL) and stirred at room temperature for 2 h.
The solvent was removed in vacuo, yielding a yellow solid which was
washed with hexane (2 ꢁ 10 mL) and dried in vacuo (78 mg, 72%). 1H
NMR (CDCl3, 500 MHz, 298 K): δ 8.60 (d, 3JHH = 7.7 Hz, 2H, CHAr),
7.32 (m, 2H, CHAr), 7.21 (m, 4H, CHAr) 4.71 (m, 2H, NCH2), 4.28 (m,
2H, CHCOD), 3.24 (m, 2H, NCH2), 2.79 (m, 1H, NCH2CH2), 2.41 (d,
2H, NCHCOD), 2.20 (s, 6H, CH3), 2.14 (m, 2H, NCH2CH2), 1.70 (m,
1H, NCH2CH2), 1.60 (m, 2H, NCH2CH2CH2), 1.36 (m, 2H, CH2 COD),
1.10 (m, 4H, CH2 COD), 0.95 (m, 2H, CH2 COD). 13C NMR (CDCl3,
125 MHz, 298 K): δ 215.9 (d, 1JCRh = 45.0 Hz, CNHC), 147.6 (s, ipso-
CAr), 132.1 (s, CAr1), 131.5 (s, CAr), 129.2 (s, CAr), 126.1 (s, CAr), 125.1
1
[Ag(8-Xyl)Br]. Yield: 60%. H NMR (CDCl3, 400 MHz, 298 K): δ
7.00ꢀ7.04 (m, 6H, CHAr), 4.08 (m, 4H, NCH2), 2.32 (s, 12H, o-Me), 2.07
(m, 4H, NCH2CH2), 1.99 (m, 2H, NCH2CH2CH2). 13C NMR (CDCl3,
125 MHz, 298 K): δ 217.4 (dd, 1JC107Ag = 223, 1JC109Ag = 255, NCN), 150.4
(s, CAr), 134.0 (s, CAr), 130.2 (s, CHAr), 129.9 (s, CHAr), 128.4 (s, CHAr),
51.8 (s, NCH2), 29.3 (s, NCH2CH2), 21.8 (s, NCH2CH2CH2), 19.1 (s,
o-CH3). HRMS (ES): m/z 468.1581 ([M ꢀ Br + CH3CN]+; C24H31N3Ag
requires 468.1569). Anal. Calcd for C22H28N2BrAg: C, 51.99; H, 5.55; N,
5.51. Found: C, 51.76; H, 5.31; N, 5.32.
Synthesis of Rh Complexes. Synthesis of [Rh(8-NHC)(acac)CO]
Complexes. A solution of free carbene, prepared by in situ deprotonation
1
(s, CAr), 92.7 (d, JRhC = 7.5 Hz, CHCOD), 64.8 (d, JRhC = 15.0 Hz,
of 8-NHC HBr (0.33 mmol) with KHMDS (0.65 mmol) in 10 mL
CHCOD), 54.3 (s, NCH2), 30.4 (s, CH2 COD), 27.3 (s, CH2 COD), 26.2 (s,
NCH2CH2), 19.4 (s, NCH2CH2CH2), 17.4 (s, CH3). HRMS (ES): m/z
503.1942 ([M ꢀ Cl]+; C28H36N2Rh requires 503.1934). Anal. Calcd for
C28H36N2ClRh: C, 62.40; H, 6.73; N, 5.20. Found C, 62.56; H, 6.57;
N, 5.04.
3
of THF, was added dropwise to a stirred solution of Rh(CO)2(acac)
(0.38 mmol) in THF (10 mL). An immediate color change was observed
from yellow to orange to green. After the reaction mixture was stirred at
room temperature overnight, the insoluble impurities were filtered off and
the solvent removed in vacuo. The yellow solid was washed with pentane
(20 mL) and dried.
[Rh(8-o-Tol)(CO)2Cl]. A solution of [Rh(8-oTol)(COD)Cl] (50 mg,
0.93 mmol) in dichloromethane (20 mL) was treated with carbon
monoxide for 30 min, during which time a color change from dark to pale
yellow was observed. The volatiles were removed under reduced
pressure, furnishing a pale yellow solid, which was washed with cold
[Rh(8-Mes)(acac)CO]. Yield: 79%. 1H NMR (CDCl3, 400 MHz, 298
K): δ 6.84 (s, 2H, m-CH), 6.72 (s, 2H, m-CH), 5.03 (s, 1H, CHacac), 4.06
(m, 2H, NCH2), 3.86 (m, 2H, NCH2), 2.27 (s, 6H, o-CH3), 2.25 (s, 6H,
o-CH3), 2.18 (s, 6H, p-CH3), 2.04 (m, 2H, NCH2CH2), 1.95 (m, 4H,
NCH2CH2), 1.74 (s, 3H, CH3acac), 1.64 (s, 3H, CH3 acac). 13C NMR
(CDCl3, 125 MHz, 298 K): δ 210.8 (d, 1JRhC = 52.5 Hz, NCN), 190.4
(d, 1JRhC = 85 Hz, CO), 185.7 (s, CCH3 acac), 181.8 (s, CCH3 acac), 145.3
(s, CAr), 135.2 (s, p-CAr), 134.0 (s, o-CAr), 133.2 (s, o-CAr), 128.6 (s,
m-CHAr), 128.3 (s, m-CHAr), 98.5 (s, CHacac), 53.4 (s, NCH2), 30.5
(s, NCH2CH2), 27.4 (s, NCH2CH2CH2), 26.7 (s, CH3 acac), 25.6 (s,
CH3 acac), 22.8 (s, p-CH3), 21.6 (s, p-CH3), 19.9 (s, o-CH3), 18.3 (s,
1
hexane (2 ꢁ 30 mL) and dried in vacuo (38 mg, 84%). H NMR
(CDCl3, 400 MHz, 298 K): δ 7.67 (m, 2H, CHAr), 7.18 (m, 4H, CHAr),
7.03 (m, 2H, CHAr), 4.85 (m, 2H, NCH2), 3.38 (m, 2H, NCH2), 2.28
(s, 6H, o-CH3), 1.84 (m, 2H, NCH2CH2CH2), 1.74 (m, 4H, NCH2CH2).
13C NMR (CDCl3, 125 MHz, 298 K): δ 207.1 (d, 1JRhC = 36 Hz, CNHC),
1
1
185.4 (d, JRhC = 55 Hz, CO), 182.2 (d, JRhC = 78 Hz, CO), 146.5
(s, CAr), 132.3 (s, CAr), 130.8 (s, CAr), 129.9 (s, CAr), 127.6 (s, CAr), 125.5
(s, CAr), 53.0 (NCH2), 27.4 (NCH2CH2), 20.5 (NCH2CH2CH2), 16.5
5654
dx.doi.org/10.1021/om200467x |Organometallics 2011, 30, 5649–5655

Organometallics
ARTICLE
(s, o-CH3). IR: ν 2068, 1981 cmꢀ1 (CH2Cl2), ν(CO)av 2024.5 cmꢀ1
.
(14) Cavello, L.; Correa, A.; Costabile, C.; Jacobsen., H. J. Organomet.
Chem. 2005, 690, 5407.
HRMS (ES): m/z 464.1077 ([M + CH3CN]+; C22H24O2N2Rh requires
(15) Clavier, H.; Nolan., S. P. Chem. Commun. 2010, 46, 841.
(16) (a) Chianese, A. R.; Li, X.; Janzen, M. C.; Faller, J. W.; Crabtree,
R. H. Organometallics 2003, 22, 1663. (b) Mata, J. A.; Poyatos, M.; Peris,
E. Coord. Chem. Rev. 2007, 251, 841. (c) Droge, T.; Glorius, F. Angew.
Chem., Int. Ed. 2010, 49, 6940.
464.1097).
’ ASSOCIATED CONTENT
S
Supporting Information. CIF files giving crystallographic
b
(17) Denk, K.; Sirsch, P.; Herrmann, W. A. J. Organomet. Chem.
2002, 649, 219.
data for the compounds 8-Mes BF4, 8-Xyl BF4, 8-DIPP BF4,
3
3
3
8-Xyl, Ag(8-Mes)Br, Ag(8-Xyl)Br, Rh(8-Mes)(acac)CO, Rh(8-
Xyl)(acac)CO, Rh(8-oTol)(acac)CO, Rh(8-oTol)(COD)Cl, and
Rh(8-oTol)(CO)2Cl and ORTEP drawings of 8-Mes BF4, 8-Xyl
(18) (a) Alder, R. W.; Blake, M. E.; Bortolotti, C.; Bufali, S.; Butts,
C. P.; Linehan, E.; Oliva, J. M.; Orpen, A. G.; Quayle, M. J. Chem. Commun.
1999, 241. (b) Mayr, M.; Wurst, K.; Ongania, K.-H.; Buchmeiser, M. R.
Chem. Eur. J. 2004, 10, 1256. (c) Bortenschlager, M.; Mayr, M.; Nuyken,
O.; Buchmeiser, M. R. J. Mol. Catal. A 2005, 233, 67. (d) Yun, J.; Marinez,
E. R.; Grubbs, R. H. Organometallics 2004, 23, 4172. (e) Kremzow, D.;
Seidel, G.; Lehmann, C. W.; F€urstner, A. Chem. Eur. J. 2005, 11, 1833.
(f) Imlinger, N.; Mayr, M.; Wang, D.; Wurst, K.; Buchmeiser, M. R. Adv.
Synth. Catal. 2004, 346, 1836. (g) Wang, D.; Yang, L.; Decker, U.;
Findeisen, M.; Buchmeiser, M. R. Macromol. Rapid Commun. 2005,
26, 1757. (h) Jazzar, R.; Bourg, J.-B.; Dewhurst, R. D.; Donnadieu, B.;
Bertrand, G. J. Org. Chem. 2007, 72, 3492. (i) Bazinet, P.; Ong, T.-G.;
O’Brien, J. S.; Lavoie, N.; Bell, E.; Yap, G. P. A.; Korobkov, I.; Richeson,
3
3
BF4, 8-DIPP BF4, Ag(8-Mes)Br, Rh(8-Mes)(acac)CO, and Rh-
3
(8-oTol)(CO)2Cl. This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: CavellKJ@Cardiff.ac.uk.
€
D. S. Organometallics 2007, 26, 2885. (j) Ozdemir, I.; G€urbuz, N.; G€ok,
’ ACKNOWLEDGMENT
Y.; C-etinkaya, B. Heteroat. Chem. 2008, 19, 82.
We thank Johnson Matthey for the loan of precious metal salts
and EPSRC for studentship support for W.Y.L. We also acknowl-
edge Jay Dunsford for his help and advice on some aspects of
this work.
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