Tetrazolyl and tetrazolylidene complexes of gold: A synthetic and structural study

Article abstract of DOI:10.1039/b907022b

Lithiation of 1-benzyl-1H-tetrazole followed by transmetallation with [AuCl(PPh₃)], [Au(C₆F₅)(tht)] or [AuCl(tht)] (tht = tetrahydrothiophene) and subsequent alkylation afforded cationic 1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene(triphenylphosphine) gold(i), 1, neutral 1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5- ylidene(pentafluorophenyl)gold(i), 2, and a cationic biscarbene complex, bis(1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene)gold(i), 3. The first complex underwent a homoleptic rearrangement in solution to form 3. Reaction of [Au(N₃)PPh₃] with the three isocyanides (CH₃)₂C₆H₃NC, ^tBuNC and CyNC, respectively, yielded the corresponding neutral tetrazolyl(phosphine) complexes of gold, [1-(2,6-dimethylphenyl)-1H-tetrazol-5-yl](triphenylphosphine) gold(i), 4, [1-(tert-butyl)-1H-tetrazol-5-yl](triphenylphosphine)gold(i), 6, and [1-(cyclohexyl)-1H-tetrazol-5-yl](triphenylphosphine)gold(i), 7. Alkylation of 4 with methyl triflate on N⁴ allowed isolation of the crystalline carbene complex 1-(2,6-dimethylphenyl)-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol- 5-ylidene)(triphenylphosphine)gold(i), 5. Complex 7 was not isolable in pure form but converts by isocyanide substitution of triphenylphosphine into [1-cyclohexylisocyanide][1-(cyclohexyl)-1H-tetrazol-5-yl]gold(i), 8. From a product mixture of 7 and 8 the transformed molecules [(cyclohexylamino)(ethoxy) carbene](1-cyclohexyl-1H-tetrazol-5-yl)gold(i), 9, and [bis(cyclohexylamino) carbene](1-cyclohexyltetrazol-5-yl)gold(i), 10, co-crystallised spontaneously after a long time at -20 °C.

Full text of DOI:10.1039/b907022b

View Article Online / Journal Homepage / Table of Contents for this issue
New Journal of Chemistry
An international journal of the chemical sciences
Volume 33 | Number 11 | November 2009 | Pages 2185–2356
www.rsc.org/njc
ISSN 1144-0546
PAPER
Helgard G. Raubenheimer et al.
Tetrazolyl and tetrazolylidene
complexes of gold: a synthetic and
structural study
1144-0546(2009)33:11;1-#

PAPER
www.rsc.org/njc | New Journal of Chemistry
Tetrazolyl and tetrazolylidene complexes of gold: a synthetic
and structural studyw
William F. Gabrielli, Stefan D. Nogai, Jean M. McKenzie, Stephanie Cronje and
Helgard G. Raubenheimer*
Received (in Montpellier, France) 7th April 2009, Accepted 3rd June 2009
First published as an Advance Article on the web 7th July 2009
DOI: 10.1039/b907022b
Lithiation of 1-benzyl-1H-tetrazole followed by transmetallation with [AuCl(PPh3)],
[Au(C6F5)(tht)] or [AuCl(tht)] (tht = tetrahydrothiophene) and subsequent alkylation afforded
cationic 1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene(triphenylphosphine)gold(I), 1,
neutral 1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene(pentafluorophenyl)gold(I), 2,
and a cationic biscarbene complex, bis(1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-
ylidene)gold(I), 3. The first complex underwent a homoleptic rearrangement in solution to form 3.
t
Reaction of [Au(N3)PPh3] with the three isocyanides (CH3)2C6H3NC, BuNC and CyNC,
respectively, yielded the corresponding neutral tetrazolyl(phosphine) complexes of gold,
[1-(2,6-dimethylphenyl)-1H-tetrazol-5-yl](triphenylphosphine)gold(I), 4, [1-(tert-butyl)-1H-tetrazol-
5-yl](triphenylphosphine)gold(I), 6, and [1-(cyclohexyl)-1H-tetrazol-5-yl]-
(triphenylphosphine)gold(I), 7. Alkylation of 4 with methyl triflate on N4 allowed isolation of the
crystalline carbene complex 1-(2,6-dimethylphenyl)-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-
ylidene)(triphenylphosphine)gold(I), 5. Complex 7 was not isolable in pure form but converts by
isocyanide substitution of triphenylphosphine into [1-cyclohexylisocyanide][1-(cyclohexyl)-1H-
tetrazol-5-yl]gold(I), 8. From a product mixture of 7 and 8 the transformed molecules
[(cyclohexylamino)(ethoxy)carbene](1-cyclohexyl-1H-tetrazol-5-yl)gold(I), 9, and
[bis(cyclohexylamino)carbene](1-cyclohexyltetrazol-5-yl)gold(I), 10, co-crystallised spontaneously
after a long time at ꢀ20 1C.
followed by alkylation or protonation, has been developed in
Introduction
our laboratory and provides an access route to a variety of
this class of gold(I) carbene.6 Both mono and bis(carbene)
complexes of gold(I) derived from lithiated pyridine have, for
example, been prepared and structurally characterised.7
Furthermore, numerous thiazolyl, imidazolyl and triazolyl
gold(I) carbene complexes are obtainable from routes and
methods described in the literature.8 Glaring in their absence
from the range of well-characterised C-bonded or carbene-
bonded N-heterocyclic gold(I) complexes are those that
contain tetrazole rings. To the best of our knowledge, the
only reports of C-bonded tetrazolyl gold(I) complexes are of
the type (RNC)(RN4C)Au(I) (R = methyl, cyclohexyl, phenyl)
that have been prepared in the group of Beck and Fehlhammer.9
Although these complexes have been isolated as crystalline
solids, their rapid decomposition in the X-ray beam impedes
their structural characterisation. The preparation of a carbene
complex by protonation of the corresponding tetrazolyl
precursor is reported but the authors acknowledge that no
unambiguous proof exists to confirm that such a reaction had
indeed taken place. A search in the Cambridge Crystallo-
graphic Database shows a solitary entry of a tetrakis(tetrazol-
5-yl)gold(III) complex prepared by the same research group.10
The synthesis of tetrazole-derived NHC complexes of gold(I)
poses, from a structural point of view, certain challenges.
First, lithiated tetrazoles are innately unstable and readily
lose molecular nitrogen to form cyanamide by-products11
The study of N-heterocyclic carbene (NHC) complexes of
various metals remains a topical field of research in inorganic
chemistry. Since the first isolable NHC was characterised more
than a decade ago, dedicated efforts have been made to
develop transition metal derivatives of such compounds.1
The emerging interest in NHCs as surrogates for phosphines
in organometallic catalysis is testimony to the remarkable
stability and versatility observed for such transition metal
complexes.2 NHCs have also replaced phosphines recently
in chrysotherapy and in the pursuit of gold(I) compounds as
anti-tumour agents.3a,b Several synthetic approaches now exist
to prepare gold(I) NHC complexes.4 These include (i) homolytic
cleavage of electron rich olefins; (ii) transmetallation of
carbene ligands from group 6 carbonyl complexes and (iii)
transmetallation between Ag(I)–NHCs and Au(I) precursors.5
A further preparative route via the sequential lithiation
of an azole substrate, transmetallation to a gold(I) substrate,
Department of Chemistry and Polymer Science, University of
Stellenbosch, Private Bag X1, Matieland, 7602, South Africa.
E-mail: hgr@sun.ac.za; Fax: +27 21 808 3849;
Tel: +27 21 808 3850
w Electronic supplementary information (ESI) available: Crystal data,
data collection and structure refinement of 5. CCDC reference
numbers 734732 (3), 734733 (4), 734735 (5) and 734734 (9ꢁ10). For
ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/b907022b
ꢂc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
2208 | New J. Chem., 2009, 33, 2208–2218

and, second, although alkylation should be favoured on the
more nucleophilic adjacent a-nitrogen in (tetrazolyl)aurates,
electrophilic additions could also occur at one of two remote
nitrogens, b placed with regard to the coordinated carbon
owing to the delocalisation of electronic charge around the
ring. Herrmann and co-workers have recently reported on
the preparation of the first thermodynamically stable, trans-
(dicarbene)tetracarbonylchromium complex derived from the
corresponding tetrazolium salt.12 They further exploit the
weak s-donating ability of the tetrazolylidene ligand to effect
a single carbon monoxide substitution in preparing the
sym–mer configurated tricarbonyl–chromium complex.
The 1,3-dipolar cycloaddition of organic isocyanides to
metal azides (‘click chemistry’), in this regard, provides an
elegant alternative for the preparation of various C-coordinated
tetrazolyl gold(I) complexes. In contrast to the widely applied
and related cycloaddition reaction of nitriles and coordinated
azides which afford N-coordinated tetrazolate complexes, the
former reaction, yielding carbon–metal bonded complexes, is
limited to only a few reports.13–15 Ironically, the structural
motifs found in these complexes, i.e. metal-coordinated iso-
cyanides, are representatives of the first known gold(I) carbene
precursor functionalities. A well established methodology to
functionalise these ‘‘masked carbenes’’, i.e. by the nucleophilic
addition of alcohols and amines, to afford acyclic (diamino)-
and (alkoxy)(amino)carbene gold(I) complexes, exists.16,17 In
recent times such gold(I) carbene types have often been found
to display interesting photoluminescent properties both in the
solid state and in solution.18
Scheme 1 The synthetic route towards mono- and bis(tetrazolylidene)
ꢀ
gold(I) complexes;
X
=
CF3SO3
:
(i) n-butyllithium in thf;
(ii) [AuCl(PPh3)]; (iii) CF3SO3CH3; (iv) [Au(C6F5)(tht)]; (v) [AuCl(tht)].
(vide infra). A number of attempts to recrystallise 1 only
yielded crystals of the homoleptic by-products. Furthermore,
in the solid state complex 1 is highly hygroscopic which ruled
out an accurate elemental analysis.
The neutral mono(carbene)gold(I) complex 2 was prepared
by treatment of a thf solution containing lithiated 1-benzyl-
tetrazole, with [Au(C6F5)(tht)] (tht = tetrahydrothiophene).
The aurate salt was not isolated but directly alkylated with
CF3SO3CH3 at low temperature. The neutral complex was
extracted from the residual product with a diethyl ether–
n-pentane (1 : 1) mixture. The colourless microcrystalline
material of complex 2 is thermodynamically stable in air at
room temperature.
Herein, as a contribution to the rapidly expanding field of
(NHC)gold(I) chemistry,4 we report for the first time the
crystal and molecular structures of normal gold(I) carbene
complexes derived from tetrazoles. By adopting known classical
preparative routes with small variations, these interesting
nitrogen-rich heterocyclic azolylidenes could now be prepared
and isolated. En-route, interesting behaviour in solution of
these complexes was also observed and unexpected acyclic
carbene complexes were espied.
The cationic bis(carbene)gold(I) complex 3 was prepared in
very much a similar fashion as described for 1 and 2. The
addition of half a molar amount of [AuCl(tht)] to a solution of
1-benzyltetrazol-5-yllithium in thf at ꢀ98 1C afforded the
corresponding aurate complex, which was directly alkylated
with CF3SO3CH3 at a slightly elevated temperature (ꢀ68 1C)
to give complex 3 in high yield. An analytically pure sample of
3 could be obtained by recrystallisation from a dichloro-
methane solution layered with n-pentane at ꢀ20 1C. The
colourless needle-like crystals are thermodynamically stable
in air and in solution at room temperature. The formation of
trace amounts of an isomeric product to 3 was indicated by
15N NMR measurements (vide infra).
Results and discussion
NHC complexes derived from lithiated precursors
Scheme 1 illustrates the protocol used in the preparation of
various novel (tetrazolylidene)gold(I) complexes. The procedure
involves sequential lithiation of the CH-acidic tetrazole, trans-
metallation involving a gold(I) substrate, and finally alkylation
of the resultant azolyl complex which could be neutral or an
aurate.
Homoleptic rearrangement of complex 1
The spontaneous rearrangement of mixed carbene complexes of
gold(I) has been described on a few occasions in the literature.
Shaw and co-workers20 also found that for neutral gold(I)
complexes of the type [Au(CN)PR3], a ligand scrambling
reaction occurs to afford ionic mixtures of [Au(CN)2]ꢀ
and [Au(PR3)2]+. Similar reactions occur with anionic gold(I)
complexes of the type [Au(CN)SR]ꢀ to yield the dicyanate and
dithiolate gold(I) complexes.21 We have previously established
that (pentafluorophenyl)(isothiazol-5-ylidene)gold(I) rearranges
The cationic mono(carbene)gold(I) complex 1 was prepared
by lithiation of 1-benzyltetrazole in thf with n-butyllithium at
ꢀ98 1C (for related applications compare ref. 19a–d), followed
by the addition of [Au(Cl)(PPh3)] at ꢀ68 1C and direct
alkylation with CF3SO3CH3. Although complex 1 could
initially be isolated in microcrystalline form, it was unstable
in solution and underwent a gradual homoleptic rearrangement.
The rearrangement afforded the corresponding bis(carbene)-
gold(I) and bis(triphenylphosphine)gold(I) triflate complexes,
and their formation could be followed by 1H NMR measurements
1
slowly and the process can be followed by H NMR spectro-
scopy.22 This reaction occurs more rapidly for the precursor
complex, (pentafluorophenyl)(isothiazol-5-yl)gold(I), which has
ꢂc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 2208–2218 | 2209

¨
Ofele–Wanzlick-type carbene complexes can be prepared from
prompted an in situ carbene preparation by immediate
alkylation to avoid complicating reactions. In contrast,
(triphenylphosphine)(isothiazol-5-yl)gold(I) is very stable in
solution and could be isolated in pure form. Using the same
methodology as described above, i.e. circumvention of the
isolation of the (tetrazol-5-yl)(phosphine)gold(I) complex by
immediate alkylation of the reaction product at low temperature
(ꢀ78 1C), a white microcrystalline solid was obtained, after the
precipitation of the cationic product, 1, with diethyl ether.
The 31P NMR spectrum of the crystalline material dissolved
in CD2Cl2 revealed a broadened singlet signal at d 44.1, typical
of an exchanging phosphorus atom. In addition, crystallisation
from the NMR tube, by slow evaporation of the solvent,
afforded colourless crystals of [Au(PPh3)2][CF3SO3]. The
phosphorus resonance at d 31.8 assigned to this bis(phosphine)
complex is in close agreement with the signal for
[Au(PPh3)2]Cl at d 29.7.23 The 15N chemical shifts of the
nitrogen atoms in complex 1 were measured in a long range
1H-detected, 1H, 15N gHMQC experiment in which a specified
proton resonance could be used to locate coupling N atoms
that are removed by two to three bonds. The resulting
spectrum thus represents not only signals pertaining to
complex 1 but also to the homoleptically rearranged product,
3. Fig. 1 shows two sets of four closely related nitrogen
resonances, separated as shielded (alkyl substituted) and
deshielded (imine) nitrogen nuclei. The signals for compound 3
were also observed in the 15N NMR spectrum of 3 prepared
according to the procedure mentioned above.
precursors in which the nucleophilic heteroatom is located g to
the co-coordinated carbon atom and not in the conventional
a-position.24 The reaction of phenylpyrazol-5-yllithium,
and [Fe(Cp)(CO)2Cl], followed by protonation, yields the
amino(organo)carbene complex, dicarbonyl(Z5-cyclopentadienyl)-
(1-phenylpyrazol-5-ylidene)iron(I) triflate, representing carbene
complex formation mediated by a remote protonation on a
nitrogen atom more than one bond removed from the metal-
coordinated carbon atom. This procedure has later been
extended to include complexes in which the nucleophilic
heteroatom in the precursor substrate is located outside the
coordinated ring and separated from the coordinated carbon
by more than two bonds.25
During the preparation and structural characterisation of 3,
it was established that alkylation of the bis(1-benzyltetrazol-5-
yl)gold(I) precursor complex on the N atom in the 4-position
(a to the coordinated carbon) is favoured above alkylation of
the nitrogen atoms in the 2- and 3-positions. This result
elucidates the findings by Wehlan and co-workers,10 who
reported that the protonation of sodium tetrakis(tetrazol-5-yl)-
aurate(III) affords
a (supposedly normal) monocarbene
complex by alkylation on one of the four tetrazole rings. Their
finding has not been confirmed by either structural or spectro-
scopic analysis. 1H NMR analysis of the crude product
mixture of 3 revealed that trace amounts of secondary
products, which share common diagnostic resonances, i.e.
benzylic and NMe protons, with complex 3, were present.
Such by-products could arise from the alkylation of the
nitrogen atoms in the 2- or 3-positions, b to the coordinated
carbon. Future studies should concentrate on such possibilities
especially since 3-alkylation would afford an abnormal carbene
ligand.
In each case the nitrogen atoms can be related to the proton
two or three bonds removed. Two further resonances
(d ꢀ133.2, d ꢀ11.5) are also noted, and they have been
ascribed to the possible formation of a benzylmethylcyanamide
compound as a product of ring fragmentation. In this instance
the benzylic proton resonance (CH2) is correlated to the only
two remaining nitrogen atoms, after the loss of dinitrogen in
the cyanamide product.
NHC complexes derived from azide complex templates
The reaction of metal azides with isocyanides, first reported by
Beck and co-workers,9 represents a straightforward and
elegant route to a series of novel carbon-bonded metal tetra-
zolates. Under very mild conditions, the addition of a large
excess (25 fold) of isocyanide (methylisocyanide, cyclohexyliso-
cyanide and phenylisocyanide) to a dichloromethane solution
of azido(triphenylphosphine)gold(I) affords, after precipitation
by the addition of diethyl ether, the neutral but relatively
unstable isocyanide(tetrazol-5-yl)gold(I)complexes.
Carbene formation by remote alkylation
Members of our research group have shown that by using
the lithiation–transmetallation–protonation route atypical
Later Wehlan and co-workers10 report that the reactivity of
chosen isocyanides in such reactions increases with their
assumed nucleophilicity, i.e. 1-tert-butylisocyanide 4 1-cyclo-
hexylisocyanide B 2,6-dimethylphenylisocyanide.
After a further investigation of the 1,3-dipolar cycloaddition
reactions of isocyanides to metal azides, we now report
alternative phosphine-containing products that are obtained
when [Au(N3)(PPh3)] is reacted with a smaller excess of related
isocyanides (Scheme 2).
The reaction of 2,6-dimethylphenylisocyanide (10 fold
excess) with [Au(N3)(PPh3)] at ambient temperature (while
protected from light) affords after 17 h [1-(2,6-dimethyl-
phenyl)-1H-tetrazol-5-yl](triphenylphosphine)gold(I), 4, in good
yield. The colourless crystalline solid is stable in air at room
Fig. 1 1H, 15N gHMQC experiment of 1, collected over a 24 h period
in CD2Cl2 at ambient temperature; for 1 [d ꢀ119.9 (N1), d ꢀ11.2 (N2),
d ꢀ11.5 (N3), d ꢀ132.5 (N4)] and 3 [d ꢀ121.3 (N1), d ꢀ12.0 (N2),
d ꢀ10.9 (N3), d ꢀ132.8 (N4)].
ꢂc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
2210 | New J. Chem., 2009, 33, 2208–2218

Scheme 3 Postulated steps in the formation of complexes 9 and 10:
(i) CyNH2 (as hydrolysis product), ethanol.
Scheme
2
The synthesis of C-tetrazolyl gold(I) complexes;
owing to its extremely low solubility in most common organic
solvents. Numerous attempts to obtain suitable crystals for
X-ray structure determination were fruitless. However this
complex could be characterised by NMR spectroscopy (slight
solubility in d6-DMSO), and FAB-MS spectrometry (in an
m-nitrobenzylalcohol matrix).
X = CF3SO3ꢀ: (i) RNC = 2,6-Me2C6H3NC, tBuNC or CyNC;
(ii) CF3SO3CH3.
temperature and is readily soluble in polar solvents, and
insoluble in diethyl ether and pentane. Colourless prisms of
complex 4 were obtained from a dichloromethane solution
layered with diethyl ether overnight at ꢀ20 1C. Alkylation
of the carbeniate complex, 4, at ꢀ70 1C afforded the
mono(carbene)gold(I) complex, [1-(2,6-dimethylphenyl)-4-methyl-
4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene](triphenylphosphine)-
gold(I) triflate, 5, in almost quantitative yield. In striking
contrast to both the observations made during the preparation
of the tetrazolylidene complex 1, carbene complex 5 appeared,
according to this preparative procedure, as the exclusive
product. In complex 5, the steric bulk and/or an additional
electronic effect of the N1 substituent may play a role in
selectively directing alkylation on the N4 atom. The propensity
of NHC(phosphine)gold(I) complexes to convert to the homo-
leptic bis(carbene)gold(I) complexes has been mentioned
above and it could be a reason behind the limited number
of structurally characterised mono(carbene) complexes
described in the literature [{1,3-bis(5H-dibenzo[a,d]cyclo-
heptenyl)imidazol-2-ylidene}(triphenylphosphine)gold(I) chloride
and [1,3-di(tert-butyl)imidazol-2-ylidene](triphenylphosphine)-
The reaction of a larger (20 fold) excess of cyclohexyl-
isocyanide with [Au(N3)(PPh3)] afforded, after work-up, the
(1-cyclohexyl-1H-tetrazol-5-yl)(triphenylphosphine)gold(I)
complex, 7. However now a further substitution product,
(cyclohexylisocyanide)(1-cyclohexyl-1H-tetrazol-5-yl)gold(I),
8, appeared to be in equilibrium with the phosphine complex 7
(Scheme 3). In agreement with the findings of Beck and
co-workers9 the mixture of 7 and 8, upon exposure to air,
almost immediately exhibited a bright yellow luminescence.
Further evidence for the presence of 8 in solution is infrared
bands typical of the CRN moiety, as well as the spontaneous
formation of two acyclic carbene complexes derived from 8
(Scheme 3 and crystallography section). The presence of both
complexes 7 and 8 could be clearly identified by NMR
measurements in the resulting solution occurring in a 1 : 2
ratio but eventually a crystalline product was isolated that
contained co-crystallised 9 and 10. The formation of 10
required the formation of CyNH2 in the alcohol solution.
In an attempt to crystallise the non-isocyanide-containing
complex 7 from a mixture of 7 and 8 (the former the major
component) a mixed co-crystallised product (9ꢁ10) that
contained both of the two well documented Bonati–Minghetti-
type16 complexes 9 and 10 shown in Scheme 3 was isolated.
Ethanol (solvent with pentane) and cyclohexylamine addition
to the gold isocyanide has been invoked to explain the
formation of the complexes. The amine is most likely a
hydrolysis product of 7 or of free isocyanide. Schmidbaur
and co-workers28 have reported a similar example, where the
formation of (isocyanide)(diaminocarbene)gold(I) chloride
results from the addition of an alkylamine, present owing to
the hydrolysis of the free isocyanide, to bis(isocyanide)gold
chloride. Aliphatic and aromatic amines react readily in low
concentrations and under mild conditions, whereas alcohols
normally require prolonged reaction times at higher temperatures.
Such variance in nucleophilicity is illustrated in this reaction
(at ꢀ20 1C over 8 months) which only required a limited
amount of amine to form 10 despite the overwhelming excess
of alcohol present.
gold(I) hexafluorophosphate].3,26 Pyykko and co-workers27
¨
have concluded that the structural, NMR and solution
equilibrium data describing the homoleptic rearrangement of
neutral gold(I) complexes of the type LAuX (L = donor
ligand, X = anionic ligand) suggest that reactants and
products energetically do not differ much. However, it remains
tempting to ascribe the stability of 5 (towards homoleptic
rearrangement), in part to the sterically bulky substituent on N1.
Using the same methodology as for the preparation of
complex 5, the related carbeniate complex, [1-(tert-butyl)-
1H-tetrazol-5-yl](triphenylphosphine)gold(I), 6, could be
obtained from the metal azide and tert-butylisocyanide (10 fold
excess). However, whereas complex
4 was isolated by
precipitation from a dichloromethane solution after the addi-
tion of diethyl ether, 6 formed overnight as an insoluble
precipitate from the reaction mixture. The colourless micro-
crystalline solid is stable in air at room temperature. Subsequent
alkylation of this compound to afford the corresponding
mono(carbene)gold(I) complex was unsuccessful, probably
ꢂc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 2208–2218 | 2211

NMR spectroscopy
Many of the NMR signals are found in their normal positions
and are not discussed here in detail. In the 1H NMR spectra of
1 and 3 the singlet signals at d 4.26 and 4.36, which are
respectively assigned to the three and six NMe protons in
the cationic complexes, confirm the formation of mono- and
biscarbene complexes. The corresponding resonance in the
neutral complex 2 appears slightly upfield at d 3.85, in close
agreement with that of (1,3-dimethylimidazol-5-ylidene)-
(pentafluorophenyl)gold(I) (d 3.82).29 The 13C NMR spectra
reveal characteristic NMe resonances for 1 (d 38.7), 2 (d 38.4)
and 3 (d 39.9). The carbene carbon in 1 resonates as a singlet at
d 180.6, and the phenyl carbons appear as uncharacteristically
broad signals, devoid of distinguishing C–P coupling patterns.
This observation could be due to phosphine group exchange
during the homoleptic rearrangement of 1 in solution. Also in
agreement, the 31P NMR spectrum of this complex in solution
reveals a broad signal (d 44.0) and then a sharp singlet (d 31.1)
for the homoleptic cationic gold(I) product, bis(triphenyl-
phosphine)gold(I), indicative of an irreversible reaction.
Well-defined 13C NMR signals at d 186.6 and d 182.6 are
assigned to the carbene carbons in 2 and 3, respectively. These
resonances are again in close agreement with reported values
for the two-N-heterocycles in (1,3-dimethylimidazol-5-ylidene)-
(pentafluorophenyl)gold(I) (d 189.5) and bis(1,3-dimethyl-
imidazol-2-ylidene)gold(I) chloride (d 185.7).29 The complex
coupling patterns for the C6F5 ligand in 2 are well resolved,
and the presence of the ligand is also confirmed by three sets of
multiplets in the 19F NMR spectrum.
The 15N NMR signals of the nitrogen atoms of 1 and 3
could be determined in a long range 1H detected 1H, 15N
gHMQC experiment. The shielded nitrogens, sp3 hybridised
N1 and N4, appear at highest field for both complexes 1 and 3.
Large downfield changes in chemical shift are observed for N1
in 1 (Dd 21.7) and 3 (Dd 20.0) in relation to 1-benzyltetrazole.
Notable is the simultaneous pronounced upfield change in
chemical shift found for the N4 resonance in both 1 (Dd 81.8)
and 3 (Dd 83.2) confirming that N4 obtains more p character in
the process of carbene formation. In the 1H NMR spectra of 4
and 5 the signals at d 1.94 and d 2.05 are, respectively, assigned
to the CCH3 groups. The only other proton resonance at high
field is a sharp singlet resonance at d 4.51, representing the
three NMe protons in 5.
Fig. 2 Complexes 7 and 8 showing the numbering schemes.
carbon–phosphorus coupling via a gold(I) centre, observed
for (3,4-dimethylthiazol-2-ylidene)(triphenylphosphine)gold(I)
triflate (209.8, 2JC–P = 126 Hz).30 Because of the low solubility
of complex 6 the 1H, 13C and 31P{1H} NMR spectra could
only be measured in d6-DMSO where only broad signals were
observed. The broad signal at d 172.9 is assigned to the metal-
bonded carbon atom. The 31P{1H} NMR spectrum shows a
single resonance at d 26.7.
Owing to the fact that the attempted synthesis of 7 also
afforded the related complex 8, an unambiguous assignment of
1
signals in the H and 13C{1H} NMR spectra of the product
mixture was challenging (Fig. 2).
In their preparation of 8, Beck and co-workers9 reported the
proton resonances, which could now be subtracted in the
spectrum of the mixture of 7 and 8. Furthermore, using a
two-dimensional gHSQC experiment, 13C NMR resonances
could be assigned to carbon nuclei in 7. The combined
1H NMR spectra of 7 and 8 reveal two sets of proton
resonances which integrate in an approximately 1 : 2 ratio,
for the ipso-H signals of the Cy-groups. The well-resolved
multiplet at d 4.65 is assigned to the tetrazole H6 protons
occurring in both 7 and 8. The corresponding resonance H600 in
the Cy-group, attached to the coordinated isocyanide, appears
as a broad signal at d 3.71. The H7, H70, H8 and H80 resonances
of the tetrazole-bonded Cy-group can be distinguished from
the corresponding signals in the isocyanide Cy-group (H700
,
0 0 0
0 0 0
H7 , H800 and H8 ). However, the three sets of H4 protons
overlap and could not be assigned independently. In the 13C
NMR spectrum a singlet at d 59.4 is assigned to the ipso-C6
which occurs in both 7 and 8. The other carbon resonances of
the two inequivalent Cy-rings can be assigned by correlation
with the 1H NMR resonances. Four sets of doublet signals
are assigned to the phenyl carbons exhibiting characteristic
carbon–phosphorus coupling patterns. The coordinated iso-
cyanide carbon atom in 8 is not resolved and a weak signal at d
181.7 is assigned to the metal-bonded tetrazole carbon atoms.
The 31P{1H} NMR spectrum shows a single broadened signal
at d 38.3, assigned to the coordinated phosphine in 7.
The 13C NMR spectrum reveals a characteristic NMe
resonance for complex 5 at d 39.0, in addition to the single
carbon resonance (d 18.0) observed for the chemically equivalent
methyl phenyl carbons. The latter observation suggests a free
rotation of the 2,6-dimethylphenyl substituent about the
N1–C6 axis, a crucial impediment towards N2 alkylation.
For both complexes 4 and 5, the carbon signals of the
phosphine ligands are well resolved, showing distinctive
phosphorus coupling to all four chemically inequivalent
carbon atoms. This result is in contrast to the broad singlet
resonances, suggestive of a dynamic system, reported above
for complex 1. The diagnostic carbene resonance of 5 appears
as a strong doublet resonance at d 186.9 (d, 2JC–P = 121.6 Hz),
similar to the chemical shift of the signal for the same atom in
4 (d 186.6). This result is also in agreement with the carbene
Crystallography
The unprecedented molecular structure of a coordinated
tetrazolylidene in 3 (Fig. 3) embodies a two-coordinated,
cationic bis(carbene) complex with the angle about the Au(I)
centre approximately linear [C(21)–Au(1)–C(11) 177.3(3)1].
The tetrazole rings are only slightly twisted from planarity
[torsion angles N(11)–C(11)–C(21)–N(21) and N(14)–C(11)–
C(21)–N(21), respectively, ꢀ6.61 and 174.41] in agreement
ꢂc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
2212 | New J. Chem., 2009, 33, 2208–2218

Fig. 4 Unit cell and packing pattern along the c-axis in the crystal
lattice of 3, showing p–p interactions between the phenyl and tetrazole
rings.
Fig. 3 Molecular structure of 3 showing the numbering scheme;
phenyl hydrogen atoms omitted for clarity (thermal ellipsoids drawn
at 50% probability level). Selected bond lengths (A) and bond angles
(1): Au(1)–C(11) 2.035(7), Au(1)–C(21) 2.001(7), C(11)–N(11) 1.31(1),
C(11)–N(14) 1.36(1), C(21)–N(21) 1.35(1), C(21)–N(24), 1.34(1);
C(21)–Au(1)–C(11) 177.3(3), N(11)–C(11)–Au(1) 132.2(6), N(14)–
C(11)–Au(1) 124.6(6), N(21)–C(21)–Au(1) 129.9(6), N(24)–C(21)–
Au(1) 128.7(6).
Au(carbene)2 core allowing two chlorine ions to join the two
complex cations through four hydrogen bond bridges. The
organisation of the cations, however, is in agreement with the
monomeric structure of (1,3-dimethylimidazol-5-ylidene)-
(1-methylimidazol-5-ylidene)gold(I) triflate, which exhibits no
aurophilic interactions.32
The gold centre in compound 4 (Fig. 5) is coordinated
to a phosphorus atom of a PPh3 moiety and to an
azolyl carbon on the tetrazolyl ring. The coordination
about the metal is significantly distorted from linearity,
[C(1)–Au(1)–C(1) 172.60(3)1], in contrast to the essentially
linear (isothiazol-5-yl)(triphenylphosphine)gold(I) [177.1(2)1],22
and [1,3-di(tert-butyl)imidazol-2-ylidene](triphenylphosphine)-
gold(I) hexafluorophosphate [177.0(1)1],3a but comparable to
with the perfectly co-planar classical NHC complex, bis(1,3-
dimethylbenzimidazol-2-ylidene)gold(I) pentafluorophosphate8
but in contrast to the larger interplanar angles of the
dimeric bis(1-benzylimidazol-2-ylidene)gold(I) chloride [52.71
and 49.81]31 and bis(1,3-diethylbenzimidazol-2-ylidene)gold(I)
pentafluorophosphate [52.961].8
The Au(1)–C(11) and Au(1)–C(21) separations [2.035(7) A
and 2.001(7) A] are similar within 4s and correspond to
Au(I)–NHC bonds in related compounds, bis(1-benzylimidazol-
2-ylidene)gold(I) chloride [2.01(1) A, 2.02(1) A],31 (1,3-dimethyl-
imidazol-5-ylidene)(1-methylimidazol-5-ylidene gold(I) triflate
[1.99(1) A, 2.00(2) A],32 bis(1,3-dimethylbenzimidazol-2-ylidene)-
gold(I) pentafluorophosphate [2.05(1) A], bis(1,3-diethyl-
benzimidazol-2-ylidene)gold(I) pentafluorophosphate [2.02(1) A]
and bis(1-methylpyridin-2-ylidene)gold(I) chloride [2.03(2) A,
2.02(2) A].8 It is worth noting that the N–N bond lengths
within the tetrazole ring in 3 are consistent with those in
1-benzyltetrazole. The only notable difference occurs in the
N(14)–C(11) and N(24)–C(21) separations [1.36(1) A and
1.34(1) A, respectively], which are similar to the N–C distances
in other Au(I)–NHC but marginally longer than the related
1-benzyltetrazole [1.315(8) A].8,33 The organisation of the
molecules in the crystal lattice, along the c-axis, is shown in
Fig. 4, which illustrates the stacking of the phenyl and
5-membered rings of adjacent molecules (at 3.504 A and
3.639 A).
The lack of intermolecular Auꢁ ꢁ ꢁAu interactions can partly
be ascribed to the steric bulk of the N1-benzyl substituents,
which prevent a close approach of the metal centres. Bonati
and co-workers31 reported that bis(1-benzylimidazol-2-ylidene)-
gold(I) chloride aggregates as two independent molecules
with Auꢁ ꢁ ꢁAu interactions [3.2630(5) A]. In this instance, the
benzyl moieties are in a trans disposition with regard to the
Fig. 5 Molecular structure of 4 showing the numbering scheme; the
included dichloromethane is omitted for clarity (thermal ellipsoids
drawn at 50% probability level). Selected bond lengths (A) and bond
angles (1): Au(1)–C(1) 2.031(3), Au(1)–P(1) 2.2775(7), N(1)–C(1)
1.353(3), N(4)–C(1) 1.333(3); C(1)–Au(1)–P(1) 172.61(8), N(4)–C(1)–
Au(1) 132.6(2), N(1)–C(1)–Au(1) 121.2(2).
ꢂc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 2208–2218 | 2213

summarised in the ESIw for completeness. Due to the low
quality of the structure determination, only basic structural
features of 5 will be discussed.
From dichloromethane–diethyl ether 5 crystallises in the
monoclinic space group P21/c with Z = 8 formula units in the
unit cell. The asymmetric unit thus consists of 2 independent
formula units. Fig. 6 depicts the best structural model
obtained for the two independent cations of 5. In both cases
a PPh3Au+-fragment is bonded to the carbene carbon of a
tetrazolylidene ligand, giving rise to
a virtually linear
P–Au–carbene carbon unit. The steric bulk of the 2,6-di-
methylphenyl N1 substituent is clearly visible and no inter-
molecular Auꢁ ꢁ ꢁAu contacts are discernible. A selective
alkylation on the N4 atom is confirmed, similar to complex 3.
Colourless crystals that contain both carbene complexes,
[alkoxy(amino)carbene][tetrazol-5-yl]gold(I), 9, and (diamino-
carbene)(tetrazol-5-yl)gold(I), 10, were isolated. The bis(cyclo-
hexylamine)- and ethoxy(cyclohexylamine)-substituents are
coordinated to two (1-cyclohexyltetrazol-5-yl)gold(I) units
(Fig. 7). Coordination around the metal center is essentially
linear [C(4)–Au(2)–C(21) 178.1(4)1 and C(1)–Au(1)–C(11)
176.7(4)1]. Notably all four trigonally planar metal-bonded
carbon atoms have equal bond distances to gold: [C(1)–Au(1)
2.02(1) A, C(11)–Au(1) 2.01(1) A, C(4)–Au(2) 2.07(1) A and
C(21)–Au(2) 2.02(1) A]. These bond lengths are in good
agreement with related compounds, [{cis,cis-(p-MeC6H4NH)-
(EtO)C}2Au(I)][ClO4] [2.03(3) A and 1.93(3) A],34 [(ArNH)(EtO)-
CAuCl] [2.04(4) A and 1.98(3) A],34 [{(MeNH)(Me2N)-
C}2Au(I)][PF4] [2.050(3) A]18 and [{(MeNH)2C}2Au(I)][ClꢁH2O]
[2.039(4) A].35
Fig. 6 The molecular structure of 5 showing two independent, two-
coordinate molecules in the asymmetric unit. The hydrogen atoms and
two triflate counter anions are omitted for clarity.
{1,3-bis(5H-dibenzo[a,d]cycloheptenyl)imidazol-2-ylidene}-
(triphenylphosphine)gold(I) chloride (a bistropNHC gold
carbene complex) [173.8(2)1].26 The Au(1)–C(1) and
Au(1)–P(1) bond separations [2.031(3) A and 2.2777(7) A,
respectively] are normal. Unfortunately, due to the unsatisfactory
refinement of the parent carbene complex, 5 (Fig. 6), a critical
assessment cannot be made with regard to common structural
parameters found in complexes 4 and 5. However, compared
to the structures of the two known mixed phosphine, NHC
gold(I) complexes, the Au–P bonds appear not to change
significantly upon subsequent carbene complex formation,
i.e. {1,3-bis(5H-dibenzo[a,d]cycloheptenyl)imidazol-2-ylidene}-
(triphenylphosphine)gold(I) chloride [2.299(2) A]26 and [1,3-di-
(tert-butyl)imidazol-2-ylidene](triphenylphosphine)gold(I)
hexafluorophosphate [2.275(1) A].3a The Au–C single bond in
4 [2.031(3) A] differs somewhat from the corresponding bond
length found for the carbene complex, {1,3-bis(5H-dibenzo-
[a,d]cycloheptenyl)imidazol-2-ylidene}(triphenylphosphine)-
gold(I) chloride [2.111(7) A],26 but is essentially similar to the
Au–Ccarbene bond in [1,3-di(tert-butyl)imidazol-2-ylidene]-
(triphenylphosphine)gold(I) hexafluorophosphate [2.034(1) A].
Molecules of 4 pack in regular rows along the a-axis as
monomeric units and are interspersed with included dichloro-
methane. The latter molecule is disordered in two positions
with equal occupancy. No intermolecular aurophilic inter-
actions are present, presumably due to the overcrowding
around the metal centre as a result of the presence of the
triphenylphosphine and 2,6-dimethylphenyl moieties.
Despite repeated efforts under various conditions and from
various solvent systems, only poor quality crystals of 5 were
obtained by layering a dichloromethane solution of the
complex with diethyl ether. Multiple attempts to collect a
satisfactory crystallographic data set from these crystals were
fruitless. We mention this structure since only two examples of
NHC(phosphine)gold(I) complexes have been reported in the
CCD. However, the data obtained allowed us to at least
establish a basic connectivity of 5 which is corroborated by
Fig. 7 Molecular structure of 9ꢁ10 showing the two independent
molecules in the asymmetric unit and the numbering scheme (thermal
ellipsoids drawn at 50% probability level). Selected bond lengths (A)
and bond angles (1): Au(1)–C(11) 2.01(1), Au(1)–C(1) 2.02(1),
Au(2)–C(21) 2.02(1), Au(2)–C(4) 2.07(1), Au(1)–Au(2) 3.2880(9),
C(11)–N(15) 1.33(1), C(11)–N(12) 1.37(1), C(21)–N(25) 1.33(1),
C(21)–N(22) 1.37(1); C(11)–Au(1)–C(1) 176.8(4), C(11)–Au(1)–Au(2)
89.0(3), C(1)–Au(1)–Au(2) 93.9(3), C(21)–Au(2)–C(4) 178.1(4),
C(21)–Au(2)–Au(1) 91.4(3), C(4)–Au(2)–Au(1) 88.2(3), N(15)–C(11)–
Au(1) 129.1(8), N(4)–C(4)–Au(2) 119.0(8), N(25)–C(21)–Au(2)
126.4(8).
1
other analytical methods, such as elemental analysis, H, 13C
and 31P NMR spectroscopy and mass spectrometry. Details of
the data collection and structure determination of 5 are
ꢂc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
2214 | New J. Chem., 2009, 33, 2208–2218

A series of phosphine-containing (tetrazolyl)gold(I) complexes,
some different from the Beck and Fehlhammer examples, were
prepared. These isolable compounds are precursors to new
NHC compounds of gold(I), as illustrated by the successful
isolation of a mono(carbene) complex. Structural analysis of
this compound revealed that electrophilic addition is again
favoured on the N4 position. In our contribution to the
Bonati–Minghetti approach towards carbene complex formation,
a tetrazolyl(phosphine)gold(I) complex, 7, is converted in a
serendipitous finding to an amino(ethoxy)carbene complex of
gold, 9, and a di(amino)carbene complex, 10, which co-crystallise.
Experimental
General procedures and instruments
Fig. 8 Molecular structure of 9ꢁ10 with the modelled disorder in the
Reactions were carried out under argon using standard
Schlenk and vacuum-line techniques. Tetrahydrofuran (thf),
n-hexane, n-pentane and diethyl ether were distilled under N2
from sodium benzophenone, dichloromethane from CaH2,
ethanol and methanol from magnesium. 2,6-Dimethylphenyl-,
tert-butyl-, 1-cyclohexyl- and benzotriazol-1-ylmethyl-isocyanide,
1,2,4-triazol-3-ylamine, butyllithium (1.6 M solution n-hexane)
and CF3SO3Me were purchased from Aldrich. TMEDA was
purchased from Merck. Literature methods were used to
prepare 1-benzyltetrazole,36 [AuCl(tht)],37 [Au(C6F5)(tht)],38
[AuCl(PPh3)],39 [Au(NO3)(PPh3)]40 and [Au(N3)(PPh3)].41
Melting points were determined on a Stuart SMP3 apparatus
and are uncorrected. Mass spectra were recorded on an AMD
604 (EI, 70 eV), VG Quattro (ESI, 70 eV methanol, acetonitrile)
or VG 70 SEQ (FAB, 70 eV, (nitrophenyl)methanol matrices)
instrument. In the instance of EI and FAB MS the isotopic
distribution patterns were checked against the theoretical
distribution. All NMR spectra were recorded on a Varian
VXR 300 or Varian INOVA 400 or 600 MHz spectrometer
(1H NMR at 300/400/600 MHz, 13C{1H} NMR at 75/100/
150 MHz, 31P{1H} NMR at 121/162/243 MHz, 15N NMR at
60.8 MHz, 19F NMR at 284/376/564 MHz). Chemical shifts
(d) are reported relative to solvent resonance or external
reference of 85% H3PO4 (31P), NH3NO2 (15N) or CFCl3
(19F). Infrared spectra were recorded on a Thermo Nicolet
Avatar 330 FT-IR with a Smart OMNI ATR (attenuated total
reflectance) sampler. Elemental analyses were carried out at
the School of Chemistry, University of the Witwatersrand.
For elemental analysis, products were evacuated under high
vacuum for 10 h prior to analysis.
cyclohexyl rings.
Schmidbaur and co-workers28 reported the complex
[(CyNC){(CyNH)2C}Au(I)][Cl] with an identical ligand to
the one in complex 9, but which contains a 1-cyclohexyl-
isocyanide ligand instead of the 1-cyclohexyltetrazol-5-yl
present in 9. In [(CyNC){(CyNH)2C}Au(I)][Cl] and 9 the
metal–carbene bonds are similar [Au–Ccarbene 2.03(1) A and
Au(2)–C(4) 2.07(1) A]. The two molecules that co-crystallise
(in 9ꢁ10) illustrate that the relative trans influence of
ethoxy(amino)carbene and di(amino)carbene substituents are
very similar, based on the very consistent Au–C(tetrazolyl)
bond lengths [2.01(1) and 2.02(1) A]. In both complexes 9
and 10, the acyclic carbene ligands are rotated out of plane to
the plane occupied by the heterocyclic rings. Within the
crystalline lattice, the two carbene complex types aggregate
by relatively weak Au(I)ꢁ ꢁ ꢁAu(I) interactions [3.2880 (9) A].
The two molecules approach each other at an almost
perpendicular angle [torsion angles C(11)–Au(1)–Au(2)–
C(21), C(1)–Au(1)–Au(2)–C(21), at 109.6(4)1 and ꢀ69.1(4)1,
respectively] (Fig. 8). Three of the four cylohexyl rings
[N(3), N(5) and N(22)] are disordered in two positions, the
modelled disorder is shown in Fig. 8.
Conclusions
In the present study we reconfirmed that stable tetrazolyl and
tetrazolylidene complexes of gold(I), although rare, can be
prepared according to two classic procedures. First, by follow-
ing a lithiation–transmetallation–alkylation sequence, neutral
and cationic mono(carbene)gold(I) complexes can be obtained.
The first X-ray structure analysis performed on a C-bonded
tetrazole-derived carbene gold(I) complex, bis(1-benzyltetrazol-
5-ylidene)gold(I) triflate (3)—also obtained by homoleptic
rearrangement of 1—revealed that alkylation to afford
carbene complex formation occurs selectively on the nucleo-
philic N4 heteroatom. Secondly, by using the elegant ‘‘click
chemistry’’ of Beck and co-workers,9 we could show that
simultaneous 1,3-cycloaddition and ligand substitution reac-
tions to afford various neutral isocyanide(tetrazol-5-yl)gold(I)
complexes are strongly dependent on the reactivity and
concentration of isocyanide employed.
Syntheses
(1-Benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene)-
(triphenylphosphine)gold(I) triflate, 1. A solution of 1-benzyl-
tetrazole (0.24 g, 1.5 mmol) in thf (15 ml) was treated with
n-butyllithium in hexane (1.0 ml, 1.5 mmol) at ꢀ98 1C. After
30 min of stirring [AuCl(PPh3)] (0.74 g, 1.5 mmol) in thf
(10 ml) was added to the orange coloured solution. The
reaction mixture was stirred for a further 1.5 h between
ꢀ98 1C and ꢀ78 1C, during which time the solution became
colourless. The product was treated with CF3SO3CH3 (0.18 ml,
1.6 mmol) at ꢀ78 1C, reacted for 1 h, and slowly allowed to
reach room temperature. The solvent was removed in vacuo to
ꢂc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 2208–2218 | 2215

yield a colourless oily residue. The residue was extracted
sequentially with a diethyl ether–n-pentane mixture (1 : 1,
30 ml), and dichloromethane (30 ml) and the extracts were
filtered individually through MgSO4. The dichloromethane
extract was concentrated in vacuo to afford a colourless
microcrystalline solid, 1 (0.83 g, 71%); mp 61–63 1C. dH
[300 MHz, CD2Cl2] 7.51–7.67 (15H, m, PPh3), 7.16–7.42
(5H, m, CH2C6H5), 5.82 (2H, s, NCH2), 4.36 (3H, s, CH3).
dC [75 MHz, CD2Cl2] 180.6 (s, AuC), 134.7 (br s, o-PC6H5),
130.3 (br s, m-PC6H5), 129.7 (s, o/m-C6H5), 129.4 (br s,
i-PC6H5), 129.3 (br s, p-PC6H5), 129.3 (s, p-C6H5), 129.2
(s, m/o-C6H5), 128.9 (s, i-C6H5), 55.4 (s, NCH2), 38.70
(s, CH3). dN [61 MHz, CD2Cl2] ꢀ11.2 (s, N2), ꢀ11.5 (s, N3),
ꢀ119.9 (s, N1), ꢀ132.5 (s, N4). dP [121 MHz, CD2Cl2] 44.0 (s).
m/z (EI) 633 [2, (M ꢀ CF3SO3)+], 459 [15, (M ꢀ CF3SO3 ꢀ
C9H10N4)+], 371 [2, (M ꢀ CF3SO3 ꢀ PPh3)+].
dichloromethane (25 ml) was reacted with 2,6-dimethylphenyl-
isocyanide (0.91 g, 6.9 mmol) in dichloromethane (10 ml). The
reaction was protected from sunlight and left unstirred for
17 h, upon which the solution was concentrated to approximately
15 ml. The addition of diethyl ether to the solution produced a
colourless precipitate, which upon recrystallisation from a
dichloromethane solution layered with diethyl ether afforded
colourless prisms of 4 (0.20 g, 69%). Mp 97–98 1C. Found: C,
51.8; H, 3.6; N, 9.0%. C27H24AuN4P requires C, 51.3; H, 3.8;
N, 8.9%. dH [300 MHz, (CD2Cl2)] 7.34–7.56 (15H, m, PPh),
7.23 (2H, d, JHH 1.2, m-C6H5), 7.21 (1H, dd, JHH 1.3, JHH
1.4, p-C6H5), 1.94 (6H, br s, 2CH3). dC [75 MHz, CD2Cl2]
186.6 (s, AuC), 137.0 (s, i-C6H3[CH3]2), 136.7 (s,
o-C6H3[CH3]2), 134.7 (d, JCP 13.9, o-PC6H5), 132.3 (d, JCP
2.2, p-PC6H5), 129.9 (s, p-C6H3[CH3]2), 129.8 (d, JCP 11.4,
m-PC6H5), 129.8 (d, JCP 56.6, i-PC6H5), 128.7 (s, m-C6H3[CH3]2),
17.9 (s, 2CH3). dP [121 MHz, CD2Cl2] 41.3 (s). m/z (EI) 459
[9, AuPPh3+], 262 [19, PPh3+].
3
3
3
(1-Benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene)-
(pentafluorophenyl)gold(I), 2. Complex 2 was prepared as
described above using 1-benzyltetrazole (0.14 g, 0.87 mmol),
n-butyllithium in hexane (0.56 ml, 0.87 mmol), [Au(C6F5)(tht)]
(0.39 g, 0.87 mmol) and CF3SO3CH3 (0.10 ml, 0.87 mmol) to
afford a colourless microcrystalline solid, 2 (0.36 g, 77%); mp
136–139 1C. Found: C, 33.3; H, 2.0; N, 10.5%. C15H10AuF5N4
requires C, 33.5; H, 1.9; N, 10.4%. dH [300 MHz, (CD3)2CO]
7.28–7.52 (5H, m, CH2C6H5), 5.91 (2H, s, NCH2), 3.85 (3H, s,
CH3). dC [75 MHz, CD2Cl2] 186.6 (s, AuC), 150.6 (dm, JCF
227.6, o-C6F5), 139.7 (dm, JCF 230.8, p-C6F5), 138.1 (dm,
JCF 250.5, m-C6F5), 134.2 (tm, JCF 61.2, m-C6F5), 131.2
(s, i-C6H5), 131.2 (s, o/m-C6H5), 131.1 (s, m/o-C6H5), 129.9
(s, p-C6H5), 123.0 (q, JC–F 320.9, CF3SO3), 55.6 (s, NCH2),
38.4 (s, CH3). dF [376 MHz, CD2Cl2] ꢀ115.6 (m, o/m-C6F5),
ꢀ160.3 (m, p-C6F5), ꢀ163.5 (m, m/o-C6F5). m/z (EI)
538 [12, (M)+], 510 [7, (M ꢀ CF3SO3 ꢀ N2)+], 364
[2, (M ꢀ CF3SO3 ꢀ C9H10N4)+], 334 [15, (C12F10)+].
Crystals suitable for X-ray diffraction were grown from a
dichloromethane solution layered with diethyl ether.
[1-(2,6-Dimethylphenyl)-4-methyl-4,5-dihydro-1H-1,2,3,4-
tetrazol-5-ylidene](triphenylphosphine)gold(I) triflate, 5.
A
solution of 4 (0.14 g, 0.22 mmol) in dichloromethane (10 ml)
was cooled to ꢀ70 1C, treated with CF3SO3Me (0.03 ml,
0.2 mmol) and stirred for 30 min, whereafter the mixture
was allowed to reach room temperature. The solvent was
removed in vacuo to yield a dark brown residue. The residue
was extracted sequentially with diethyl ether (30 ml) and
dichloromethane (30 ml) and the extracts were filtered
individually through MgSO4. The ether extract was concen-
trated in vacuo to yield a colourless solid. Recrystallisation
from a dichloromethane solution layered with diethyl ether
afforded colourless needles of 5 (0.13 g, 91%). Mp 165–167 1C.
Found: C, 43.5; H, 3.3; N, 7.6%. C29H27AuF3N4O3PS
requires C, 43.7; H, 3.4; N, 7.0%. dH [300 MHz, (CD2Cl2)]
7.46–7.63 (15H, m, PPh), 7.33 (2H, m, m-C6H5), 7.31 (1H, m,
p-C6H5), 4.51 (3H, s, NCH3), 2.05 (6H, br s, 2CH3). dC
[75 MHz, CD2Cl2] 186.9 (d, JCP 121.6, AuC), 136.3
(s, o-C6H3[CH3]2), 134.7 (d, JCP 13.8, o-PC6H5), 134.1
(s, i-C6H3[CH3]2), 133.1 (d, JCP 2.6, p-PC6H5), 132.4
(d, p-C6H3[CH3]2), 130.2 (d, JCP 11.9, m-PC6H5), 129.7
(s, m-C6H3[CH3]2), 127.8 (d, JCP 60.8, i-PC6H5), 121.7 (q, JCF
322.5, CF3SO3), 39.0 (s, NCH3), 18.0 (s, 2CH3).dP [121 MHz,
CD2Cl2] 39.7 (s). m/z (ESI) 647 [49, (M ꢀ CF3SO3)+],
619 [91, (M ꢀ CF3SO3 ꢀ N2)+], 459 [7, AuPPh3+], 385
[2, (M ꢀ CF3SO3 ꢀ PPh3)+].
Bis(1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene)-
gold(I) triflate, 3. The same experimental procedure as
described for 1 was used to prepare 3 from 1-benzyltetrazole
(0.31 g, 1.9 mmol), n-butyllithium in hexane (1.3 ml,
1.9 mmol), [AuCl(tht)] (0.31 g, 0.98 mmol) and CF3SO3CH3
(0.22 ml, 1.9 mmol) to obtain a colourless solid, which was
recrystallised from a dichloromethane solution layered with
diethyl ether at ꢀ20 1C to yield colourless needles, 3 (0.47 g,
69%). Mp 118–120 1C (decomp.). Found: C, 32.6; H, 2.8; N,
16.3%. C19H20AuF3N8O3S requires C, 32.7; H, 2.9; N, 16.1%.
dH [300 MHz, (CD3)2CO] 7.41–7.56 (5H, m, CH2C6H5), 5.96
(2H, s, NCH2), 4.36 (3H, s, CH3). dC [75 MHz, (CD3)2CO]
182.6 (s, AuC), 131.4 (s, o/m-C6H5), 131.3 (s, p-C6H5), 131.0
(s, m/o-C6H5), 130.8 (s, i-C6H5), 123.6 (q, JC–F 322.8,
CF3SO3), 56.7 (s, NCH2), 39.9 (s, CH3). dN [61 MHz, CD2Cl2]
ꢀ12.7 (s, N3), ꢀ14.4 (s, N2), ꢀ123.0 (s, N1), ꢀ134.2 (s, N4).
m/z (EI) 545 [7, (M ꢀ CF3SO3)+], 517 [13, (M ꢀ CF3SO3 ꢀ
N2)+], 489 [9, (M ꢀ CF3SO3 ꢀ 2N2)+].
Crystals more suitable for X-ray diffraction studies were
grown from
diethyl ether.
a dichloromethane solution layered with
[1-(tert-Butyl)-1H-tetrazol-5-yl](triphenylphosphine)gold (I),
6. The same experimental procedure as for the preparation
of 4 was used to prepare 6 from [Au(N3)(PPh3)] (0.30 g,
0.60 mmol) and tert-butylisocyanide (0.50 g, 6.0 mmol) to
produce a colourless microcrystalline product, 6 (0.26 g, 74%);
mp 146 1C (decomp.). Found: C, 47.0; H, 4.6; N, 9.3%.
C23H24AuN4P requires C, 47.3; H, 4.1; N, 9.6%. dH
[300 MHz, (CD2Cl2)] 7.51–7.75 (15H, m, PPh), 1.75 (9H, br s,
Crystals suitable for X-ray diffraction were grown from a
dichloromethane solution layered with diethyl ether.
[1-(2,6-Dimethylphenyl)-1H-tetrazol-5-yl](triphenylphosphine)-
gold(I), 4. A solution of [Au(N3)(PPh3)] (0.23 g, 0.46 mmol) in
ꢂc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
2216 | New J. Chem., 2009, 33, 2208–2218

C[CH3]3). dC [75 MHz, CD2Cl2] 172.9 (s, AuC), 134.1 (d, JCP
13.7, o-PC6H5), 132.3 (d, JCP 2.8, p-PC6H5), 129.8 (d, JCP 11.9,
m-PC6H5), 129.3 (d, JCP 63.4, i-PC6H5), 31.1 (s, C[CH3]3), 28.7
(s, C[CH3]3). dP [121 MHz, CD2Cl2] 26.7 (s). m/z (FAB) 583
[13, M+], 555 [3, (M ꢀ N2)+], 501 [3, (M ꢀ C4H9N2)+], 486
[3, (AuPPh3CN)+].
[75 MHz, CD2Cl2] 181.7 (s, AuC), 59.4 (s, C6H11), 34.6
(s, C6H11), 32.5 (s, C6H11), 25.9 (s, C6H11), 25.5 (s, C6H11),
25.0 (s, C6H11), 23.0 (s, C6H11). m/z (ESI) 611 [10, M+],
459 [7, AuPPh3+]. nmax/cmꢀ1 3050s, 2861vs, 2251vs.
The formation of complexes, [1-cyclohexyl-1H-tetrazol-5-yl]-
[cyclohexylamine(ethoxy)ylidene]gold(I), 9, and [1-cyclohexyl-
1H-tetrazol-5-yl][bis(cyclohexylamine)ylidene]gold(I), 10. The
product mixture of 7 and 8 (containing some residual amounts
of 1-cyclohexylisocyanide) was dissolved in freshly distilled
ethanol layered with n-pentane and was stored in a narrow
Schlenk tube at ꢀ20 1C for 8 months. Apart from an
unidentified and insoluble bright yellow luminescent micro-
crystalline solid which formed towards the base of the gas-inlet
tap and cap, colourless needle-like crystals, a co-crystallate of
9 and 10, formed from the solution.
The formation of [1-(cyclohexyl)-1H-tetrazol-5-yl](triphenyl-
phosphine)gold(I), 7, and [1-cyclohexylisocyanide][1-(cyclohexyl)-
1H-tetrazol-5-yl]gold (I), 8. The same experimental procedure
as described for 4 was used to prepare the mixture of 7 and 8
from [Au(N3)(PPh3)] (0.50 g, 1.00 mmol) and 1-cyclohexyliso-
cyanide (2.18 g, 20.0 mmol) to form a colourless micro-
crystalline product, a mixture of complexes 7 and 8 (0.37 g).
7 dH [300 MHz, (CD2Cl2)] 7.47–7.62 (15H, m, PPh), 4.65
(1H, m, C6H11), 2.08 (4H, m, C6H11), 1.38 (4H, m, C6H11),
1.24 (2H, m, C6H11). dC [75 MHz, CD2Cl2] 181.7 (s, AuC),
134.7 (d, JCP 13.9, o-PC6H5), 132.4 (d, JCP 2.5, p-PC6H5),
129.9 (d, JCP 58.1, i-PC6H5), 129.8 (d, JCP 11.6, m-PC6H5),
59.4 (s, C6H11) 34.6, (s, C6H11), 25.9 (s, C6H11), 25.0
(s, C6H11).dP [121 MHz, CD2Cl2] 38.3 (br s). m/z (ESI) 611
[10, M+], 459 [7, AuPPh3+].
Crystal structure determination
Specimens of suitable quality and size of 3, 4, 5 and 9ꢁ10 were
mounted on the ends of glass fibres in inert oil and used for
intensity data collection on a Bruker SMART Apex CCD
diffractometer,42 employing graphite-monochromated Mo-Ka
radiation (l = 0.71073 A). Data reduction was carried out
using the SAINT43 suite of programs and multi-scan absorption
corrections were performed with SADABS.44,45 The structures
8 dH [300 MHz, (CD2Cl2)] 4.65 (1H, m, C6H11), 3.71 (1H,
br s, C6H11), 2.08 (4H, m, C6H11), 1.89 (4H, m, C6H11), 1.70
(4H, m, C6H11), 1.38 (4H, m, C6H11), 1.24 (4H, m, C6H11). dC
Table 1 Crystallographic and data collection parameters of 3, 4 and 9ꢁ10
Compound
3
4
9ꢁ10
C36H63Au2N11
1059.91
173(2)
0.71073
Triclinic
ꢀ
P1
10.569(3)
12.484(3)
16.827(5)
95.641(4)
98.979(4)
110.714(4)
2022.8(9)
2
Empirical formula
Mr
T/K
Wavelength/A
Crystal system
Space group
a/A
b/A
C19H20AuF3N8O3S
694.46
100(2)
C28H26AuCl2N4P
717.36
100(2)
0.71073
Monoclinic
P21/c
8.6440(8)
12.738(1)
24.885(2)
90
94.429(2)
90
2731.8(4)
O
0.71073
Orthorhombic
Pna21
11.812(2)
22.452(3)
8.892(1)
90
90
90
2358.1(5)
c/A
a/1
b/1
g/1
Volume/A3
Z
4
1.956
4
1.744
dcalcd/g cmꢀ3
1.740
7.287
Absorption coefficient, m/mmꢀ1
Absorption correction
F(000)
6.390
Semi-empirical from equivalents
1344
5.664
Semi-empirical from equivalents
1400
Semi-empirical from equivalents
1044
Crystal size/mm
y-Range for data collection/1
Index range
0.20 ꢃ 0.20 ꢃ 0.10
1.81 to 26.72
ꢀ10 r h r 14,
ꢀ25 r k r 28,
ꢀ11 r l r 11
12 896
4842 [Rint = 0.0356]
0.5280 and 0.3181
Full-matrix least-squares on F2
4842/1/318
0.037(11)
0.30 ꢃ 0.20 ꢃ 0.10
2.29 to 26.76
ꢀ10 r h r 10
ꢀ16 r k r 16
ꢀ29 r l r 31
20 718
5797 [Rint = 0.0239]
0.4182 and 0.6012
Full-matrix least-squares on F2
5797/0/355
0.20 ꢃ 0.10 ꢃ 0.10
1.77 to 25.35
ꢀ12 r h r 12
ꢀ15 r k r 15
ꢀ20 r l r 20
No. of reflections collected
No. independent reflections
Max. and min. transmission
Refinement method
19 845
7361 [Rint = 0.0635]
0.5294 and 0.3235
Full-matrix least-squares on F2
7361/258/599
Data/restraints/parameters
Flack parameter
Goof on F2
1.108
1.047
R1 = 0.0213
wR2 = 0.0487
R1 = 0.0241
wR2 = 0.0498
1.176 and ꢀ0.698
a = 0.0223, b = 2.9786
1.077
R1 = 0.0589
wR2 = 0.1180
R1 = 0.0874
wR2 = 0.1283
2.108 and ꢀ2.521
a = 0.0582, b = 0.2758
Final R-indices [I 4 2s 4(I)]a
R1 = 0.0407
wR2 = 0.0854
R1 = 0.0517
wR2 = 0.0890
2.900 and ꢀ1.222
a = 0.0355, b = 3.4720
R indices (all data)
Largest diff. peak and hole/e Aꢀ3
Weighting scheme
a
2
2
wR2 = {S[w(Fo ꢀ Fc2)2]/S[w(Fo2)2]}1/2; w = 1/[s2(Fo)2 + ap2 + bp] where p = (Fo + 2Fc2)/3.
ꢂc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 2208–2218 | 2217

were solved by a combination of direct methods (SHELXS-97)
and difference-Fourier syntheses and refined by full matrix
least-squares calculations on F2 (SHELXL-97)46 within the
X-Seed environment.47 Thermal motion was treated aniso-
tropically for all non-hydrogen atoms. All hydrogen atoms
were calculated in ideal positions and refined using a riding
model. The asymmetric unit of 3 contains one molecule
of dichloromethane which is disordered over two sites. A
split atom model was used to take this into account. Three
cyclohexyl groups in the structure of 9ꢁ10 are disordered over
two sites each. Similarity restraints were applied to obtain
similar geometries for each pair of corresponding cyclohexyl
positions. The nitrogen bound hydrogen atoms were placed on
maxima on a difference fourier map. For subsequent refinements
their coordinates had to be fixed to the positions of original
placement. Fixed isotropic displacement parameters were used
for the refinement of these three hydrogen atoms. Further
details regarding the data collection and structure refinement
for compounds 3, 4 and 9ꢁ10 are listed in Table 1, details for
compound 5 can be found in the ESIw.
14 Y.-J. Kim, Y.-S. Joo, J.-T. Han, W. S. Han and S.-W. Lee,
J. Chem. Soc., Dalton Trans., 2002, 3611.
15 J. Sarju, J. Arbour, J. Sayer, B. Rohrmoser, W. Scherer and
G. Wagner, Dalton Trans., 2008, 5302.
16 F. Bonati and G. Minghetti, Gazz. Chim. Ital., 1973, 103(3), 373.
´ ´
17 R. Uson, A. Laguna, J. Vicente, J. Garcıa and B. Bergareche,
J. Organomet. Chem., 1979, 173, 349.
18 R. L. White-Morris, M. M. Olmstead, F. Jiang, D. S. Tinti and
A. L. Balch, J. Am. Chem. Soc., 2002, 124, 2327.
19 (a) L. L. Garber and C. H. Brubaker, Jr., J. Am. Chem. Soc., 1968,
90, 309; (b) R. Raap, Can. J. Chem., 1971, 49, 2139; (c) J. C. Kauer
and W. A. Sheppard, J. Org. Chem., 1967, 32, 3580; (d) Y. Satoh
and N. Marcopulos, Tetrahedron Lett., 1995, 36, 1759.
20 A. L. Hormann, C. F. Shaw III, D. W. Benett and W. M. Reiff,
Inorg. Chem., 1986, 25, 3953.
21 G. Lewis and C. F. Shaw III, Inorg. Chem., 1986, 25, 58.
22 H. G. Raubenheimer, M. Desmet and G. J. Kruger, J. Chem. Soc.,
Dalton Trans., 1995, 2067.
23 G. H. Woehrle, L. O. Brown and J. E. Hutchison, J. Am. Chem.
Soc., 2005, 127, 2172.
24 H. G. Raubenheimer, M. Desmet, P. Olivier and G. J. Kruger,
J. Chem. Soc., Dalton Trans., 1996, 4431.
25 H. G. Raubenheimer and S. Cronje, Dalton Trans., 2008, 1265.
26 C. Bohler, D. Stein, N. Donati and H. Grutzmacher, New J.
Chem., 2002, 26, 1291.
¨
¨
27 P. Pyykko, W. Schneider, A. Bauer, A. Bayler and H. Schmidbaur,
¨
Chem. Commun., 1997, 1111.
28 H. Ehlich, A. Schier and H. Schmidbaur, Organometallics, 2002,
21, 2400.
Acknowledgements
29 H. G. Raubenheimer, L. Lindeque and S. Cronje, J. Organomet.
Chem., 1996, 511, 177.
30 H. G. Raubenheimer, F. Scott, G. J. Kruger, J. G. Toerien,
R. Otte, W. van Zyl, I. Taljaard, P. Olivier and L. Linford,
J. Chem. Soc., Dalton Trans., 1994, 2091.
All the authors thank Stellenbosch University, the NRF
(South Africa) and Harmony Gold for financial support.
SDN gratefully acknowledges the Alexander von Humboldt
Stiftung for a Feodor Lynen Scholarship.
31 F. Bonati, A. Burini and B. R. Pietroni, J. Organomet. Chem.,
1989, 375, 147.
32 G. J. Kruger, P. J. Olivier, L. Lindeque and H. G. Raubenheimer,
Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 1995, 51, 1814.
33 W. F. Gabrielli, PhD Thesis, University of Stellenbosch, 2006.
34 G. Banditelli, F. Bonati, S. Calogero, G. Valle, F. E. Wagner and
R. Wordel, Organometallics, 1986, 5, 1346.
35 R. L. White-Morris, M. M. Olmstead, F. Jiang and A. L. Balch,
Inorg. Chem., 2002, 41, 2313.
36 Y. Satoh and N. Marcopulos, Tetrahedron Lett., 1995, 36(11),
1759.
Notes and references
1 A. J. Arduengo III, R. L. Harlow and M. Kline, J. Am. Chem.
Soc., 1991, 113, 361.
2 N. Marion and S. P. Nolan, Chem. Soc. Rev., 2008, 37, 1776.
3 (a) M. W. Baker, P. J. Barnard, S. J. Berners-Price,
S. K. Brayshaw, J. L. Hickey, B. W. Skelton and A. H. White,
J. Organomet. Chem., 2005, 690, 5625; (b) J. L. Hickey,
R. A. Ruhayel, P. J. Barnard, M. W. Baker, S. J. Berners-Price
and A. Filipovska, J. Am. Chem. Soc., 2008, 130, 12570.
4 H. G. Raubenheimer and S. Cronje, Chem. Soc. Rev., 2008, 37,
1998.
37 R. Uson and A. Laguna, in Organometallic Synthesis, ed.
R. B. Lang and J. J. Eisch, Elsevier, Amsterdam, 1986, vol. 3,
p. 325.
5 I. J. B. Lin and C. S. Vasam, Can. J. Chem., 2005, 83, 812.
6 H. G. Raubenheimer and S. Cronje, J. Organomet. Chem., 2001,
617–618, 170.
38 R. Uson and A. Laguna, in Organometallic Synthesis, ed.
R. B. Lang and J. J. Eisch, Elsevier, Amsterdam, 1986, vol. 3,
p. 326.
7 H. G. Raubenheimer, J. G. Toerien, G. J. Kruger, R. Otte,
W. van Zyl and P. Olivier, J. Organomet. Chem., 1994, 466,
291.
8 H. M. J. Wang, C. S. Vasam, T. Y. R. Tsai, S. H. Chen, A. H.
H. Chang and I. J. B. Lin, Organometallics, 2005, 24, 486.
9 W. Beck, K. Burger and W. P. Fehlhammer, Chem. Ber., 1971, 104,
1816.
39 M. I. Bruce, B. K. Nicholson and O. Bin Shawkataly, Inorg.
Synth., 1989, 324.
40 L. Malatesta, L. Naldini, G. Simonetta and F. Cariati, Coord.
Chem. Rev., 1966, 1, 25.
41 G. Beuter and J. Strahle, J. Organomet. Chem., 1989, 372, 67.
¨
42 SMART Data Collection Software, Version 5.629, Bruker AXS
Inc., Madison, WI, 2003.
10 M. Wehlan, R. Thiel, J. Fuchs, W. Beck and W. P. Felhammer,
J. Organomet. Chem., 2000, 613, 159.
43 SAINT, Data Reduction Software, Version 6.45, Bruker AXS Inc.,
Madison, WI, 2003.
11 L. L. Garber and C. H. Brubaker, Jr., J. Am. Chem. Soc., 1966, 88,
4266.
44 R. H. Blessing, Acta Crystallogr., Sect. A: Fundam. Crystallogr.,
1995, 51, 33.
¨
12 G. D. Frey, K. Ofele, H. G. Krist, E. Herdtweck and
45 SADABS, Version 2.05, Bruker AXS Inc., Madison, WI, 2002.
46 G. M. Shelrick, SHELX-97. Program for Crystal Structure Analysis,
University of Gottingen, Germany, 1997.
¨
W. A. Herrmann, Inorg. Chim. Acta, 2006, 359, 2622.
13 Y.-J. Kim, Y.-S. Kwak, Y.-S. Joo and S.-W. Lee, J. Chem. Soc.,
Dalton Trans., 2002, 144.
47 L. J. Barbour, J. Supramol. Chem., 2001, 1, 189.
ꢂc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
2218 | New J. Chem., 2009, 33, 2208–2218