Preparation of a super bulky silver N-heterocyclic carbene complex

Article abstract of DOI:10.1039/b821368b

The preparation of a 1,3-bis(2,6-terphenyl)imidazolium salt and the first coordination complex containing a 1,3-bis(2,6-terphenyl)imidazol-2-ylidene NHC (IDitop) is reported; comparison of the steric parameters of IDitop with commonly used bulky NHCs such

Full text of DOI:10.1039/b821368b

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LETTER
www.rsc.org/njc | New Journal of Chemistry
Preparation of a super bulky silver N-heterocyclic carbene complexw
Sean G. Alexander,a Marcus L. Cole*b and Jonathan C. Morrisa
Received (in Montpellier, France) 28th November 2008, Accepted 22nd January 2009
First published as an Advance Article on the web 17th February 2009
DOI: 10.1039/b821368b
The preparation of a 1,3-bis(2,6-terphenyl)imidazolium salt and
the first coordination complex containing a 1,3-bis(2,6-terphenyl)-
imidazol-2-ylidene NHC (IDitop) is reported; comparison of the
steric parameters of IDitop with commonly used bulky NHCs
such as 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IDip)
indicates a significantly greater cone angle for the former,
and the molecular structures of [AgCl(IDitop)], the parent
diazabutadiene of IDitop and the 1,3-bis(2-phenylphenyl)imidazol-
2-ylidene (IBp) complex [AgCl(IBp)] are reported.
Of the aryl substituents employed, the 2,6-terphenyl based
Tripp, Dipp (2,6-bis(2,6-diisopropylphenyl)phenyl) and Dmp
(2,6-dimesitylphenyl, mesityl = 2,4,6-Me3C6H2) aryls, in
which the 2,6-aryls are positioned orthogonal to the primary
aryl plane, have been particularly effective due to their spatial
shielding of substituents at the ipso-carbon.1
Considering the wide application of 2,6-terphenyls1 it is
perhaps surprising that they have not yet been incorporated
into 1,3-disubstituted imidazol-2-ylidene N-heterocyclic
carbenes (NHCs) (Fig. 1), one of the most studied ligand
classes in modern organometallic chemistry.8 As recently
reviewed by Hahn and Jahnke,9 imidazol-2-ylidenes have
been successfully incorporated into dendrimer frameworks,10
solid-state scaffolds11 and even porphyrin based constructs;12
however, 1,3-substitution of these NHCs by 2,6-terphenyl
groups has not been accomplished. To our knowledge, only
3,5-terphenyls have been applied in this regard.13 The
most commonly utilised bulky NHC at this time is IDip
(1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) (Fig. 1),
first prepared by Nolan and co-workers.14 In view of the
unusual reaction of palladium N,N0-bis(3,5-terphenyl)imidazol-
2-ylidene complexes with carbon dioxide, which affords
carbonate under aerobic conditions,13 and the distinct hydro-
silylation selectivities reported for monovalent rhodium
catalysts supported by dendrimeric polyaryl NHCs (Scheme 1),10
it is our contention that N,N0-bis(2,6-terphenyl)imidazol-
2-ylidenes will generate metal complexes with unique reactivities
relative to less bulky counterparts. Herein we report the
preparation of the first N,N0-bis(2,6-terphenyl)imidazolium
salt, IDitopꢀHCl (Fig. 1), from its parent diazabutadiene,
and the preparation of its silver(I) chloride coordination
The use of super bulky aryl substituents to kinetically
stabilise unusual or unprecedented chemical functionalities
is
a common feature of contemporary organometallic
chemistry.1 Two landmark examples are Yoshifuji’s
preparation of a diphosphene in 19812 and Robinson’s report
of Na2[Ar*GaGaAr*] (Ar* = Tripp = 2,6-(iPr3C6H2)2C6H3,
see Fig. 1) in 1997 that was controversially described as
containing a ‘gallyne’ metal–metal triple bond.3 Compounds
such as these have inspired many research ensembles to
incorporate super bulk into a variety of ligand classes, such
as cyclopentadienyls,4 N,N0-disubstituted amidinates5 and
b-diketiminates,6 in order to quantitatively evaluate the
impact of ‘steric engineering’ on their chemistry.7
Fig. 1 Example main group species stabilised by aryl super bulk and
the underlying structural scaffold for 1,3-disubstituted imidazol-2-
ylidene NHCs.
a School of Chemistry and Physics, University of Adelaide, Adelaide,
SA 5005, Australia
b School of Chemistry, University of New South Wales, Sydney,
NSW 2052, Australia. E-mail: m.cole@unsw.edu.au;
Fax: +61 2 93856141; Tel: +61 2 93854678
w CCDC 717572–717574. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/b821368b
Scheme 1 Example hydrosilylation catalysts that highlight selectivities
based on the N-aryl bulk of the catalyst NHC ligand.10
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1.453(5) A) are comparable with those of the related
a-diimines Ar0NQC(Me)–C(Me)QN0Ar, where Ar0 is 3- or
4-trimethylsilylphenyl, which also exist as E-anti isomers in the
solid-state.17 The imine functionalities of both DmpDAB
and DitopDAB are evidenced by medium intensity CQN
absorptions at ca. 1610 cmꢂ1 in the IR spectra of both
a-dialdimines.
The preparation of 1,3-bis(2,6-terphenyl)imidazolium salts
from DitopDAB and DmpDAB was initially attempted using
paraformaldehyde in the presence of hydrochloric acid, as per
the method described by Nolan and co-workers for
IDipꢀHCl.14 This led to hydrolysis of the diazabutadiene to
regenerate the parent anilines as their hydrochloride salts.
Arduengo and co-workers have described an alternative
preparation of IMesꢀHCl and IDipꢀHCl (IMes = 1,3-bis-
(2,4,6-trimethylphenyl)imidazol-2-ylidene) involving treatment
Scheme 2 Preparation to the first N-2,6-terphenyl a-dialdimines.
complex. We also report the preparation of the N,N0-bis-
(2-phenylphenyl)imidazolium (IBpH+) and imidazol-2-
ylidene (IBp) congeners. The spatial bulk of IDitop and IBp
is discussed relative to existing bulky NHCs like IDip using the
molecular structure of their silver(I) chloride complexes as a
basis for calculation.
The bulky NHC precursors DmpDAB (DAB = N,N0-
disubstituted-1,4-diazabutadiene) and DitopDAB (Ditop =
2,6-bis(4-tolyl)phenyl) were prepared in moderate yield by
condensation of the respective anilines, DmpNH2 and
DitopNH2, with half an equivalent of glyoxal in acetonitrile
(Scheme 2).
of
a diazabutadiene with chloromethyl ethyl ether in
acetonitrile at ambient temperature.18 This method was
successfully applied to DitopDAB to give IDitopꢀHCl
(Scheme 3) but the analogous reaction of DmpDAB, even at
elevated temperatures, afforded only Dmp anilinium chloride.
As cyclisation of diazabutadienes to imidazolium salts
necessitates an E-syn isomer for formylation,16 it is likely
that the steric buttressing of DmpDAB prevents imidazolium
formation.
Although this preparation has previously been used to
access several N,N0-bis(2,6-terphenyl)-a-diketimines, which
have found utility in late transition metal catalysis,15 DitopDAB
and DmpDAB are the first a-dialdimines.
The imidazolium salt IDitopꢀHCl is a colourless deliquescent
thermally robust solid (dec. 188 1C without melting). As per
DitopDAB, its 1H NMR spectrum (d6-DMSO) exhibits a
single well-defined methyl singlet at 2.35 ppm that is indicative
of symmetrical Ditop chemical environments in solution.
Attempts to obtain crystalline samples of IDitopꢀHCl
suitable for single crystal X-ray structure determination have
not been successful to date.
Both a-dialdimines exhibit N-arylimine symmetrical
chemical environments in solution, as evidenced by H NMR
1
spectroscopy (C6D6). This suggests C2-symmetric E-anti
or -syn isomerism.16 The E-anti structure of DitopDAB
in the solid-state was determined by XRD methods
(Fig. 2, POV-RAY illustration, 10% van der Waals radii),
wherein DitopDAB crystallises in the monoclinic space group
P21/c with half a molecular unit in the asymmetric unit. The
bonding parameters of DitopDAB (CQN 1.279(3) A, C–C
NHC silver(I) coordination compounds are commonly
utilised precursors for transmetallation of NHCs onto
catalytically active group 8–10 metals.8,9 As a preliminary
foray into the coordination chemistry of IDitop, a silver(I)
chloride coordination complex, [AgCl(IDitop)] (1), was
prepared by reaction of IDitopꢀHCl with excess silver(I) oxide
in dichloromethane (Scheme 4).10,19 In order to assess the
contribution of both 2- and 6-aryl substituents on the principal
N-aryls of IDitop and its overall steric bulk, a silver(I) chloride
complex coordinated by N,N0-bis(2-phenylphenyl)imidazol-
2-ylidene (IBp), [AgCl(IBp)] (2), was also prepared using
analogous preparative procedures.
Fig. 2 Molecular structure of DitopDAB. All hydrogen atoms
omitted for clarity. Selected bond lengths (A) and angles (1):
C(1)–N(1) 1.279(3), C(1)–C(1)# 1.453(5), N(1)–C(2) 1.421(3),
C(1)–N(2)–C(2) 118.9(2), N(1)–C(1)–C(1)# 119.2(3). Symmetry
tranformation used to generate ‘#’ atoms: 2 ꢂ x, ꢂy, 1 ꢂ z.
Scheme 3 Preparation of IDitopꢀHCl by treatment of DitopDAB
with chloromethyl ethyl ether.
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such that their steric bulk is beyond the metal coordination
sphere. This effects minimal spatial influence at the metal.
Thus, to our knowledge, IDitop possesses the largest cone
angle of any NHC prepared to date.
The 2-phenyl placement of 2 (Fig. 3) has precedent in the
1,3-bis(2-phenylphenyl)imidazolin-2-ylidene NHC of Bellemin-
Laponnaz et al.,21 which differs to 2 in its saturation of the
4,5-heterocyclic C–C bond, and the recent chiral imidazolin-2-
ylidenes of Shi and Xu22 that utilise the asymmetric principles
of Grubbs, cf. asymmetric olefin metathesis catalysts
(chirality at 4- and 5-position of heterocycle, e.g. 4R,5R-
NC(H)PhC(H)PhN),23 to guide the 2-phenyl groups in order
to effect C2–NHC symmetry at a coordinated metal.
Scheme 4 Preparation of silver(I) chloride complexes from 1,3-bis-
(2,6-tolylphenyl)- and -(2-phenylphenyl)imidazolium chloride salts.
Compounds 1 and 2 are thermally robust complexes
(dec. 4 315 1C) that, even on prolonged exposure to sunlight,
do not reductively deposit silver. Both compounds are soluble
in dichloromethane and may be isolated in analytically pure
form simply by filtration of Ag2O–NHCꢀHCl reaction
mixtures and removal of volatiles under reduced pressure.
Single crystals of 1 and 2 suitable for single crystal X-ray
structure determination were grown from dichloromethane–
hexane solutions (Fig. 3, POV-RAY illustration, 10% van der
Waals radii). Compound 1 crystallises with half a molecule in
the asymmetric unit that lies about a two-fold axis with Ag(1),
Cl(1) and C(1) on the two-fold axis. Compound 2 crystallises
with one whole molecule in the asymmetric unit.
In summary, we have successfully prepared the first
N,N0-bis(2,6-terphenyl) substituted imidazol-2-ylidene, IDitop,
as its silver(I) transmetallation complex in readiness for
catalytic application as
a support ligand. Attempts to
undertake similar chemistry using the bulkier terphenyl Dmp
were unsuccessful. Molecular structure comparison of AgCl
coordinated IDitop with IBp indicates a significantly greater
‘cone angle’ for the former which surpasses that of the
presently favoured ‘bulky’ NHCꢀIDip.
The synthesis and application of IDitop, IBp and related
NHCs to homogeneous and organocatalysis are ongoing in
our laboratory.
The authors would like to thank Dr Craig M. Forsyth and
Dr Matthias Hilder (Monash University) for the collection of
single crystal X-ray diffraction data, the Australian Research
Council for financial support of this research (DP0558562),
and the Australian Commonwealth Government for an
Australian Postgraduate Award (SGA).
The molecular structures of 1 and 2 provide considerable
insight into the steric bulk of coordinated NHCs bearing
N-2,6-terphenyl and N-2-phenylphenyl substituents. Calculation
of ‘Tolman’ type cone angles20 for the NHCs of 1 and 2 using
the structural location of the Ag atoms calculated here indicate
angles of 184.01(20)1 and 131.07(5)1, respectively. The former
angle exceeds the 155.11 angle calculated for the Ag(IDip) unit
of [AgCl(IDip)],19 which exhibits Ag–Cl–C bonding
parameters consistent with those of 1 and 2 (Ag–Cl 2.316(17),
Ag–C 2.056(6) A).19 The impressive cone angles of 1,3-bis-
(Tmt)imidazol-2-ylidene (Tmt = 3,5-bis(2,4,6-trimethyl)phenyl)13
and 1,3-bis(4-(20,30,40,5-tetraphenylphenyl)phenyl)imidazol-
2-ylidene,10 which are both likely to exceed 1801, are calculated
Experimental
Diethyl ether and hexane were dried over sodium and freshly
distilled from sodium diphenylketyl before freeze-thaw
degassing prior to use. Toluene was dried over sodium and
freshly distilled from potassium before freeze-thaw degassing
prior to use. Dichloromethane was dried over calcium hydride
and freshly distilled prior to use. DmpNH2 and DitopNH2
were prepared using the procedure of Tilley and Gavenonis for
the preparation of DmpNH2.24 BpDAB was made using the
same procedure as that used for DitopDAB with ethanol
as solvent. All other chemicals were purchased from
Sigma-Aldrich and used as received. The preparations of
compounds 1 and 2 were performed using conventional
Schlenk techniques under an atmosphere of ultra high
purity argon.
Infrared spectra were recorded as Nujol mulls using sodium
chloride plates on a Nicolet Nexus FTIR spectrophotometer.
1H and 13C{1H} NMR spectra were recorded at 300.13 MHz
and 75.46 MHz, respectively, using a Varian Gemini 2000
spectrometer with chemical shifts referenced to the residual 1H
resonances of the deuterated solvents used. Melting points
were determined in glass capillaries. Mass spectrometric
analyses were conducted on a Finnegan LCQMS under
electronic ionisation conditions. All microanalyses were
conducted by the Campbell Microanalytical Laboratory,
Fig. 3 Molecular structures of compounds 1 and 2. All hydrogen
atoms omitted for clarity. Selected bond lengths (A) and angles (1)
(those of 2 listed in square parentheses after those of 1): Ag(1)–Cl(1)
2.345(2) [2.3440(11)], Ag(1)–C(1) 2.062(8) [2.079(2)], 4,5-C–C 1.326(11)
[1.343(3)], N(1)–C(1)–N(1)# 103.1(7) [103.79(18)], Tolman cone angle20
formed by NHC about Ag(1) 184.01(20) [131.07(5)]. Symmetry
transformation used to generate ‘#’ atoms of 1: ꢂx, y, 1/2 ꢂ z.
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Chemistry Department, University of Otago, P.O. Box 56,
Dunedin, New Zealand.
cmꢂ1: 1512 m, 1402 m, 1309 m, 1243 s, 1202 s, 1107 m,
1088 m, 1036 m, 1019 m, 954 w, 937 w, 924 w, 851 m,
841 m, 814 s, 790 s, 768 m, 749 m, 670 w, 616 w.
Syntheses
IBpꢀHCl. BpDAB (1.08 g, 3.0 mmol) and chloromethyl
ethyl ether (4.0 mL, 44 mmol) were stirred for 2 minutes
before adding acetonitrile (10 mL). The resultant brown
solution was stirred for 1 hour, after which the volatiles were
removed in vacuo to afford a brown solid. After washing with
diethyl ether (30 mL), the crude product was extracted into
water (30 mL) and dried under reduced pressure to give the
title compound as a brown solid that was washed with toluene
(5 mL) (0.78 g, 64%), mp 140–143 1C. As per IDitopꢀHCl,
microanalyses for IBpꢀHCl were repeatedly low in carbon.
Representative example: elemental analysis calculated (%) for
C27H21N2Cl: C 79.30, H 5.18, N 6.85; found: C 79.37, H 5.53,
DitopDAB. DitopNH2 (3.30 g, 12.07 mmol), 40% aqueous
glyoxal (0.86 g, 6.03 mmol), and acetonitrile (20 mL) were
stirred at 50 1C for three days, resulting in a colour change to
brown and the formation of DmpDAB as a yellow precipitate.
Filtration and washing with cold methanol afforded analytically
pure DmpDAB (1.81 g, 53%), mp 208 1C. Elemental analysis
calculated (%) for C42H36N2: C 88.69, H 6.38, N 4.93; found:
C 88.94, H 6.31, N 4.91; 1H NMR (C6D6): d 2.20 (s, 12H,
3
p-CH3), 6.98 (d, 8H, JHH 7.8 Hz, 2/3-Ar0CH), 7.00 (t, 2H,
3JHH 7.5 Hz, 4-ArCH), 7.14 (d, 8H, 3JHH 7.8 Hz, 2/3-Ar0CH),
3
7.23 (d, 4H, JHH 7.5 Hz, 3/5-ArCH), 7.62 (s, 2H, NQCH);
13C{1H} NMR (C6D6): d 21.6 (p-CH3), 125.9, 129.3, 130.6,
133.8 (ArCH), 129.5, 136.4, 137.7, 148.0 (ArC), 165.5 (NQC);
IR (Nujol), cmꢂ1: 1613 m, 1571 w, 1303 w, 1289 w, 1188 w,
1111 w, 1076 w, 1035 w, 1017 w, 948 w, 941 w, 846 w, 830 w,
812 m, 787 m, 764 m, 745 m, 660 w; EIMS (m/z) 568.3
(100% [M+]).
3
N 6.37; 1H NMR (d6-DMSO): d 7.20 (d, 4H, JHH 6.0 Hz,
2/6-Ar0CH), 7.42 (coincident dd and t, 6H, 3,4,5-Ar0CH), 7.62
(coincident d and s, 4H, 3-ArCH and 4,5-C2H2), 7.69 (dd, 2H,
3
3JHH 7.8 Hz, 7.8 Hz, 4-ArCH), 7.74 (dd, 2H, JHH 7.8 Hz,
3
7.8 Hz, 5-ArCH), 7.75 (d, 2H, JHH 7.8 Hz, 6-ArCH), 9.91
(s, 1H, 2-CH); 13C{1H} NMR (d6-DMSO): d 124.1 (4,5-C2),
127.2, 128.4, 128.6, 128.8, 129.1, 131.2, 131.5, 131.3, 136.1,
137.3 (ArC), 138.2 (2-C); IR (Nujol), cmꢂ1: 1662 w, 1596 w,
1538 m, 1338 m, 1266 m, 1224 m, 1159 m, 1118 m, 1069 m,
1009 w, 918 w, 763 s, 734 s, 702 s, 682 m, 654 m, 610 m.
DmpDAB. DmpNH2 (1.10 g, 3.90 mmol), 40% aqueous
glyoxal (0.4 mL, 1.95 mmol), and acetonitrile (10 mL) were
stirred for two days at 60 1C resulting in the precipitation of
DmpDAB as a yellow solid. The product was filtered, washed
with acetonitrile (10 mL) and recrystallised from ethyl acetate
to afford a microcrystalline powder (0.819 g, 72%), mp
252–253 1C. Elemental analysis calculated (%) for
C50H52N2: C 88.19, H 7.70, N 4.11; found: C 87.59, H 7.97,
N 4.16; 1H NMR (C6D6,): d 1.86 (s, 24H, o-CH3), 2.29 (s, 12H,
[AgCl(IDitop)] (1). IDitopꢀHCl (0.46 g, 0.74 mmol) and
Ag2O (0.18 g, 0.74 mmol) were stirred under vacuum for
30 minutes before addition of dichloromethane (50 mL). The
resulting slurry was stirred for 20 hours to afford a pale brown
solution. Filtration, followed by removal of volatiles under
reduced pressure, afforded the title compound as a pale brown
solid that was subsequently recrystallised from dichloromethane–
hexane as colourless plates (0.40 g, 73%), mp 4 315 1C.
Elemental analysis calculated (%) for C44H38AgCl3N2
(NB: +CH2Cl2): C 65.32, H 4.73, N 3.46; found: C 65.97, H
4.64, N 3.79; 1H NMR (CD2Cl2): d 2.35 (s, 12H, p-CH3), 6.33
(s, 2H, 4,5-C2H2), 6.92 (d, 8H, 3JHH 8.2 Hz, 2/3-Ar0CH), 7.19
3
p-CH3), 6.81 (s, 8H, 3/5-Ar0CH), 6.89 (d, 4H, JHH 6.0 Hz,
3
3/5-ArCH), 6.90 (t, 2H, JHH 6.0 Hz, 4-ArCH) 7.13
(s, 2H, NQCH); 13C{1H} NMR (C6D6): d 20.8 (o-CH3),
21.7 (p-CH3), 126.0, 130.0, 132.5, 136.2, 136.5, 136.6, 148.0,
(ArC), 161.4 (NQC); IR (Nujol), cmꢂ1: 1612 m; 1574 w, 1414
m, 1290 m, 1261 m, 1192 w, 1156 w, 1096 m, 1072 m, 1029 m,
932 w, 848 s, 825 m, 803 s, 799 w, 765 s, 741 m, 659 w, 604 s;
EIMS (m/z) 681.5 (25% [MH+]), 703.6 (100% [MNa+]).
3
3
(d, 8H, JHH 8.2 Hz, 2/3-Ar0CH), 7.33 (d, 4H, JHH 7.2 Hz,
3/5-ArCH), 7.48 (t, 2H, 3JHH 7.2 Hz, 4-ArCH); 13C{1H} NMR
(CD2Cl2): d 21.0 (p-CH3), 122.9 (4,5-C2), 128.8, 129.3, 131.7,
IDitopꢀHCl. DitopDAB (0.57 g, 1.0 mmol) and chloro-
methyl ethyl ether (2.0 mL, 22 mmol) were stirred for
5 minutes before adding acetonitrile (3 mL). The resultant
brown solution was stirred for 1 hour after which all volatiles
were removed in vacuo to afford a brown solid. The crude
product was extracted with water (10 mL), washed with
diethyl ether (10 mL) and recrystallised from acetone to
afford fine white needles (0.44 g, 70%), mp 288 1C (dec).
Microanalyses for IDitopꢀHCl were repeatedly low in carbon,
perhaps suggesting cocrystallisation with acetone or residual
moisture. Representative example: elemental analysis calcu-
lated (%) for C43H37N2Cl: C 83.68, H 6.04, N 4.54; found:
C 83.15, H 6.09, N 4.36; 1H NMR (d6-DMSO): d 2.35
137.5 (ArCH), 128.6, 130.0, 136.0, 139.2 (ArC); IR (Nujol), cmꢂ1
:
1944 w, 1890 m, 1831 w, 1781 w, 1736 w, 1642 w, 1609 w, 1566
w, 1512 s, 1470 s, 1449 s, 1402 s, 1309 m, 1243 s, 1206 s, 1203 s,
1197 m, 1107 m, 1088 m, 1036 m, 1019 w, 954 w, 937 w, 924 w,
851 m, 841 m, 815 s, 791 s, 768 m, 749 m, 670 w, 616 w; EIMS
(m/z) 581.4 (100% IDitopH+).
[AgCl(IBp)]ꢀCH2Cl2 (2). IBpꢀHCl (0.82 g, 2.0 mmol) and
Ag2O (0.46 g, 2.0 mmol) were reacted and worked up in an
identical fashion to 1. Recrystallisation from dichloromethane–
hexane afforded 2 as small colourless plates (0.64 g, 62%), mp
135–137 1C, dec. 4 315 1C. Elemental analysis calculated (%)
for C28H22AgCl3N2: C 55.98, H 3.69, N 4.66; found: C 55.41,
3
(s, 12H, p-CH3), 6.85 (d, 8H, JHH 8.2 Hz, 2/3-Ar0CH), 7.12
3
3
1
(d, 8H, JHH 8.2 Hz 2/3-Ar0CH), 7.41 (d, 4H, JHH 7.6 Hz,
H 3.70, N 4.69; H NMR (CD2Cl2): d 6.79 (s, 2H, 4,5-C2H2),
3
4-ArCH), 7.49 (s, 2H, 4,5-C2H2), 7.68 (s, 2H, JHH 7.6 Hz,
7.19 (br d, 4H, 2/6- or 3/5-Ar0CH), 7.36 (m, 6H, coincident
2/6- or 3/5-Ar0CH and ArCH), 7.46 (br d, 2H, 3- or 6-ArCH),
7.54 (m, 4H, coincident 3- or 6-ArCH and 4- or 5-ArCH), 7.59
(br t, 2H, 4- or 5-ArCH); 13C{1H} NMR (CD2Cl2): d 123.7
3/5-ArCH), 9.41 (s, 1H, 2-CH); 13C{1H} NMR (d6-DMSO):
20.8 (CH3), 124.8 (4,5-C2), 128.5, 129.2, 130.6, 131.5 (ArCH),
129.3, 133.6, 137.5, 138.8 (ArC), 139.1 (2-C); IR (Nujol),
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(4,5-C2), 128.1, 128.4, 129.3, 129.4, 129.6, 130.4, 132.1 (ArCH),
137.9, 138.4, 138.8 (s, ArC); IR (Nujol), cmꢂ1: 1978 w, 1958 w,
1938 w, 1922 w, 1893 w, 1815 w, 1769 w, 1746 w, 1731 w, 1704 w,
1698 w, 1681 w, 1660 w, 1651 w, 1633 w, 1606 w, 1583 w, 1564 w,
1557 w, 1538 w, 1503 m, 1407 m, 1352 m, 1339 m, 1279 m, 1264
s, 1224 w, 1185 w, 1166 w, 1152 w, 1115 w, 1090 w, 1073 w, 1049
w, 1031 w, 996 w, 979 w, 968 w, 945 m, 925 w, 892 w, 871 w, 831
w, 761 s, 749 m, 725 s, 702 s, 686 m, 661 w, 611 m; EIMS (m/z)
373.4 (100% IBpH+), 852.3 (24% Ag(IBp)2+).
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2 M. Yoshifuji, I. Shima, N. Inamoto, K. Hirotsu and T. Higuchi,
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3 J. Su, X.-W. Li, R. C. Crittendon and G. H. Robinson, J. Am.
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4 (a) G. B. Deacon, C. M. Forsyth, F. Jaroschik, P. C. Junk,
D. L. Kay, T. Maschmeyer, A. F. Masters, J. Wang and
L. D. Field, Organometallics, 2008, 27, 4772–4778; (b) C. Ruspic,
J. R. Moss, M. Schurmann and S. Harder, Angew. Chem., Int. Ed.,
¨
2008, 47, 2121–2126.
5 See for example: (a) J. A. R. Schmidt and J. Arnold, Chem.
Commun., 1999, 2149–2150; (b) S. P. Green, C. Jones,
P. C. Junk, K.-A. Lippert and A. Stasch, Chem. Commun., 2006,
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2003, 666, 55–62.
6 See for example: (a) H. Zhu, J. Chai, V. Chandrasekhar,
H. W. Roesky, J. Magull, D. Vidovic, H.-G. Schmidt,
M. Noltemeyer, P. P. Power and W. A. Merrill, J. Am. Chem.
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H. W. Roesky, W. H. Fink and P. P. Power, Angew. Chem., Int.
Ed., 2001, 40, 2172–2174.
Single crystal X-ray structure determination
All single crystal X-ray structure determinations were
undertaken using samples mounted on glass fibres in silicone
oil. Data were collected using graphite monochromated MoKa
X-ray radiation (l = 0.71073 A) at 123(2) K on a Bruker X8
Apex diffractometer. Structural solution and refinement were
carried out using the SHELX suite of programs.25
Crystal data for DitopDAB: C42H36N2, M = 568.764,
monoclinic, P2(1)/c (No. 14),
7 (a) M. L. Cole, G. B. Deacon, P. C. Junk and K. Konstas, Chem.
Commun., 2005, 1581–1583; (b) M. L. Cole, G. B. Deacon,
C. M. Forsyth, P. C. Junk, K. Konstas and J. Wang, Chem.–Eur.
J., 2007, 13, 8092–8110.
a = 14.4140(8), b =
16.8693(10), c = 6.3926(3) A, b = 90.377(3)1, V =
1554.35(15) A3, Z = 2, Dc = 1.215 g cmꢂ3, F000 = 604,
m = 0.070 mmꢂ1, 2ymax = 56.341, 13 663 reflections collected,
8 D. Bourissou, O. Guerret, F. P. Gabbaı and G. Bertrand, Chem.
Rev., 2000, 100, 39–91.
¨
3727 unique (Rint = 0.1345). Final GooF = 0.996, R1
=
9 F. E. Hahn and M. C. Jahnke, Angew. Chem., Int. Ed., 2008, 47,
3122–3172.
10 H. Sato, T. Fujihara, Y. Obora, M. Tokumaga, J. Kiyosu and
Y. Tsuji, Chem. Commun., 2007, 269–271.
11 M. Wang, P. Li and L. Wang, Eur. J. Org. Chem., 2008,
2255–2261.
0.0796, wR2 = 0.1660, R indices based on 1626 reflections
with I 4 2s(I) (refinement on F2), 201 parameters, 0 restraints.
Crystal data for 1: C43H36AgClN2, M = 724.06, orthorhombic,
Pbcn (no. 60), a = 15.701(2), b = 13.1938(16), c = 16.310(2) A,
V = 3378.8(8) A3, Z = 4, Dc = 1.423 g cmꢂ3, F000 = 1488,
m = 0.710 mmꢂ1, 2ymax = 55.881, 20 798 reflections collected,
3748 unique (Rint = 0.0636). Final GooF = 1.227, R1 = 0.0989,
wR2 = 0.1580, R indices based on 3244 reflections with I 4 2s(I)
(refinement on F2), 206 parameters, 0 restraints.
12 S. Richeter, A. Hadj-Aıssa, C. Taffin, A. van der Lee and
¨
D. Leclercq, Chem. Commun., 2007, 2418–2150.
13 M. Yamashita, K. Goto and T. Kawashima, J. Am. Chem. Soc.,
2005, 127, 7294–7295.
14 L. Jafarpour, E. D. Stevens and S. P. Nolan, J. Organomet. Chem.,
2000, 606, 49–54.
Crystal data for 2: C27H20AgClN2ꢀCH2Cl2, M = 600.70,
15 See for example: (a) D. H. Camacho and Z. Guan, Macromolecules,
2005, 38, 2544–2546; (b) C. S. Popeney, D. H. Camacho and
Z. Guan, J. Am. Chem. Soc., 2007, 129, 10062–10063.
16 Terminology based on principles described for imidates in: The
Chemistry of the Amidines and Imidates, ed. S. Patai,
Z. Rappoport, Wiley, Chichester, UK, 1991.
17 A. S. Ionkin and W. J. Marshall, J. Organomet. Chem., 2004, 689,
1057–1063.
18 A. J. Arduengo, R. Krafczyk, R. Schmutzler, H. A. Craig,
J. R. Goerlich, W. J. Marshall and M. Unverzagt, Tetrahedron,
1999, 55, 14523–14534.
ꢀ
triclinic, P1 (no. 2), a = 9.4785(19), b = 10.348(2), c =
14.088(3) A, a = 69.73(3), b = 76.14(3), g = 82.22(3)1,
V = 1256.4(4) A3, Z = 2, Dc = 1.588 g cmꢂ3, F000 = 604,
m = 1.141 mmꢂ1, 2ymax = 55.981, 21 644 reflections collected,
5938 unique (Rint = 0.0362). Final GooF = 1.038, R1 = 0.0310,
wR2 = 0.0791, R indices based on 5476 reflections with
I 4 2s(I) (refinement on F2), 307 parameters, 0 restraints.
Variata: The XRD data for compound 1 are of poor quality
but the gross connectivity of the structure has been established.
Two atoms could not be refined with satisfactory anisotropic
thermal parameters. Attempts to refine these atoms (C(5)
(meta carbon of primary Ditop aryl) and C(15) (methyl of one
tolyl group) using ISOR refinements were also unsatisfactory.
Both atoms have been refined with isotropic thermal parameters.
19 P. de Fremont, N. M. Scott, E. D. Stevens, T. Ramnial,
´
O. C. Lightbody, C. L. B. Macdonald, J. A. C. Clyburne,
C. D. Abernethy and S. P. Nolan, Organometallics, 2005, 24,
6301–6309.
20 C. A. Tolman, Chem. Rev., 1977, 77, 313–348.
21 C. Fliedel, A. Maisse-Franc¸ ois and S. Bellemin-Laponnaz, Inorg.
Chim. Acta, 2007, 360, 143–148.
22 L. Xu and Y. Shi, J. Org. Chem., 2008, 73, 749–751.
23 T. J. Seiders, D. W. Ward and R. H. Grubbs, Org. Lett., 2003, 3,
3225–3228.
24 J. Gavenonis and T. D. Tilley, Organometallics, 2002, 21,
5549–5563.
25 G. M. Sheldrick, SHELXL-97 and SHELXS-97, University of
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¨
ꢁc
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724 | New J. Chem., 2009, 33, 720–724