Annulated N-heterocyclic carbenes: 1,3-Ditolylphenanthreno[9,10-d]imidazol- 2-ylidene and transition metal complexes thereof

Article abstract of DOI:10.1021/om9000132

The N, N'-bis(tolylamino)phenanthrenes 1a and 1b were synthesized by reductive cyclization of benzil- bis(tolylimines) and cyclized with triethyl orthoformate in the presence of NH4PF6 to give the corresponding bis(tolyl)phenanthreno[9,10-d]imidazolium he

Full text of DOI:10.1021/om9000132

Organometallics 2009, 28, 2441–2449
2441
Annulated N-Heterocyclic Carbenes:
1,3-Ditolylphenanthreno[9,10-d]imidazol-2-ylidene and Transition
Metal Complexes Thereof
Farman Ullah,† Markus K. Kindermann,† Peter G. Jones,‡ and Joachim Heinicke*,†
Institut fu¨r Biochemie-Anorganische Chemie, UniVersita¨t Greifswald, Felix-Hausdorff-Strasse 4,
17487 Greifswald, Germany, and Institut fu¨r Anorganische and Analytische Chemie, Technische
UniVersita¨t Braunschweig, Hagenring 30, 38106 Braunschweig, Germany
ReceiVed January 7, 2009
The N,N′-bis(tolylamino)phenanthrenes 1a and 1b were synthesized by reductive cyclization of benzil-
bis(tolylimines) and cyclized with triethyl orthoformate in the presence of NH4PF6 to give the corresponding
bis(tolyl)phenanthreno[9,10-d]imidazolium hexafluorophosphates 2a,b. These were deprotonated with
excess KH in THF. Whereas the p-tolyl-substituted phenanthrene-annulated imidazol-2-ylidene (phenimy)
3a proved to be unstable and dimerized to 4a, the bulkier o-tolyl derivative is isolable as the monomer
carbene 3b. Cationic silver complexes were prepared by the method of Wang and Lin (6a, 6b) or directly
(6b), rhodium and palladium complexes 7b-9b by reaction of 3b and the respective metal precursors.
Detailed structural information is given by X-ray crystal structure analyses of 6a and 7b and by HH- and
CH-COSY NMR measurements of 1b, 2a, 2b, 3b, and 7b, representing the various compound types.
The phenimy ligands are distinguished from benzo- or linear naphtho-annulated imidazol-2-ylidene ligands
by higher basicity and free 3b by lower deshielding of the 13CII nuclei.
and, particularly for unsaturated NHC, also by annulation.6-18
The first stable annulated NHC was dineopentylbenzimidazol-
Introduction
The discovery of stable, highly nucleophilic N-heterocyclic
carbenes (NHCs) by Arduengo in 19911 has revitalized the
interest in these divalent carbon compounds. Their unique
electronic and steric ligand properties2 have inspired burgeoning
research activities and led to many applications in organome-
tallic3 and organic chemistry.4 The extensive stabilization of
transition metal fragments by NHC makes them ideal tools for
transition metal catalysis.5 Tuning of the electronic ligand
properties is possible by varying substituents and saturation2-5
(6) For example: (a) O’Brien, C. J.; Kantchev, E. A. B.; Chass, G. A.;
Hadei, N.; Hopkinson, A. C.; Organ, M. G.; Setiadi, D. H.; Tang, T.-H.;
Fang, D.-C. Tetrahedron 2005, 61, 9723–9735. (b) Hadei, N.; Kantchev,
E. A. B.; O’Brien, C. J.; Organ, M. G. Org. Lett. 2005, 7, 1991–1994. (c)
Saravanakumar, S. PhD thesis, Greifswald, 2006.
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J. 1999, 5, 1931–1935. (b) Boesveld, W. M.; Gehrhus, B.; Hitchcock, P. B.;
Lappert, M. F.; Schleyer, P. v. R. Chem. Commun. 1999, 755–756. (c)
Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F. J. Chem. Soc., Dalton Trans.
2000, 3094–3099. (d) Khramov, D. M.; Bielawski, C. W. J. Org. Chem.
2007, 72, 9407–9417 (Supporting Information). (e) Ku¨hl, O.; Saravanaku-
mar, S.; Ullah, F.; Kindermann, M. K.; Jones, P. G.; Ko¨ckerling, M.;
Heinicke, J. Polyhedron 2008, 27, 2825–2832.
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Commun. 2002, 2704–2705. (b) Lohre, C.; Froehlich, R.; Glorius, F.
Synthesis 2008, 2221–2228.
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Int. Ed. 2005, 44, 7240–7244. (b) Arduengo, A. J., III.; Tapu, D.; Marschall,
W. J. J. Am. Chem. Soc. 2005, 127, 16400–16401.
* To whom correspondence should be addressed. Tel: (+)49 3834
864318. Fax: (+)49 3834 864377. E-mail: heinicke@uni-greifswald.de.
† Universita¨t Greifswald.
‡ Technische Universita¨t Braunschweig.
(1) (a) Arduengo, A. J., III.; Harlow, R. L.; Kline, M. J. Am. Chem.
Soc. 1991, 113, 361–363. (b) Arduengo, A. J., III. Acc. Chem. Res. 1999,
32, 913–921.
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874–883. (b) Cavallo, L.; Correa, A.; Costabile, C.; Jacobsen, H. J.
Organomet. Chem. 2005, 690, 5407–5413.
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10.1021/om9000132 CCC: $40.75
2009 American Chemical Society
Publication on Web 04/02/2009

2442 Organometallics, Vol. 28, No. 8, 2009
Ullah et al.
2-ylidene,7 originally synthesized by thione reduction using
potassium-sodium alloy7a or KC8,7b,c later also by
deprotonation.7d,e Subsequently, functionally substituted benz-
imidazol-2-ylidenes6 and a variety of further annulated NHCs
were reported, including electron-rich oxazolino and thiazolo,8
metalloceno,9 benzimidazol-2-ylideno,10 N-heterocyclic pyrido,11,12
pyrimidino,13 quinolino,11a and quinoxalino14 as well as more
extended carbocyclic naphtho,15 naphthochinono,16 and very
recently also a phenanthreno17 annulated imidazol-2-ylidene.
A few six- and seven-membered annulated NHCs are also
known.18 One goal of our recent research was a comparison of
carbo- (benzo, naphtho) and heterocyclic (pyrido, quinoxalino)
annulated dineopentylimidazol-2-ylidenes7c,12,14,15 with homolo-
gous heterocyclic silylenes, germylenes, and stannylenes.19,20
To study the effect of more extended carbocyclic annulation,
we also investigated phenanthreno[9,10-d]imidazol-2-ylidenes21
and present here our results.
Scheme 1. Synthesis of N,N′-Ditolylphenanthreno[9,10-d]-
imidazolium Salts 2
Scheme 2. Deprotonation of 2a,b to Phenimy 3b and Dimer
4a, and Conversion of 3b to 5b
Results and Discussion
Synthesis of Precursors. In most of our earlier work on
annulated NHCs or their homologues we used N,N′-dineopentyl
substituents for comparability and estimation of annulation
effects. With few exceptions,14 these provide sufficient steric
bulk to obtain isolable compounds without hindering cyclization
reactions. However, attempts to condense phenanthrene quinone
with alkyl amines even under harsh conditions (200 °C, 10 bar)
failed in our hands to give defined diimines as starting materials
for phenanthrene-annulated imidazoliums salts. Whereas Tapu
et al. were able to obtain the latter by stepwise N,N′-dialkylation
of phenanthreno[9,10-d]imidazole,17 we had turned to N,N′-
diarylphenanthrene diimines, which can be obtained by reductive
cyclodehydrogenation of benzil-bis(arylimines), as reported so
far for N-phenyl22 and N-3,5-dimethylphenyl groups.23 To
provide a NMR probe and indicator of steric effects, we chose
p- and o-tolyl groups. The corresponding benzil-bis(tolylimines)
formed in high yields by condensation of benzil and p- or
o-toluidine in the presence of p-toluenesulfonic acid (2 day
reflux) or more efficiently with TiCl4 (2-3 days 20 °C) as acid
catalyst. The diimines were cycloreduced by 4-6 equiv of
lithium and hydrolytically worked up to give 9,10-bis(tolylami-
no)phenanthrenes 1a,b. Subsequent cyclocondensation with
triethyl orthoformate in the presence of ammonium hexafluo-
rophosphate provided the ditolylphenanthreno[9,10-d]imidazo-
lium salts 2a,b (Scheme 1). Attempts to extend the synthesis
to the more bulky and symmetric N-mesityl derivative failed at
the stage of the reductive cyclization. A similar observation was
made in an attempt to synthesize 9,10-bis(2,6-diisopropylphe-
nylimino)phenanthrene via reductive cyclization of the corre-
sponding benzildiimine and air oxidation of the intermediate
phenanthrene diamide.24 Attempts to introduce electron-donating
methoxy groups into the phenanthrene moiety starting from
bis(p-methoxy)benzil also failed.
Reactions of Phenanthreno[9,10-d]imidazolium Salts
and Carbene Characterization. The deprotonation of the p-
and o-tolyl-substituted phenanthreno[9,10-d]imidazolium salts
2a and 2b with potassium hydride in THF furnished different
results. The less bulky p-tolyl compound did not afford the
monomer “phenimy” 3a but instead the dimer 4a, whereas the
one o-methyl group per N-aryl group in 3b provides sufficient
steric bulk to allow isolation of the monomer as a viscous oil.
For monomer benzimidazol-2-ylidenes, stronger hindrance is
required to prevent dimerization or monomer-dimer equilib-
ria.25 3b can be stored at room temperature, at least for some
days, but is sensitive to air and moisture and cannot be purified
by chromatography on silica gel. In the mass spectrum the
molecular cation is the base peak if the sample is supplied under
inert conditions. The dimer 4a does not show a molecular cation
but undergoes fragmentation with the base peak at [M + 2]+
(M - monomer). Apart from mass and NMR spectra the carbene
3b was characterized by addition of selenium, yielding the
phenanthrenoimidazol-2-selone 5b (Scheme 2).
(18) (a) Bazinet, P.; Yap, G. P. A.; Richeson, D. S. J. Am. Chem. Soc.
2003, 125, 13314–13315. (b) Scarborough, C. S.; Grady, M. J. W.; Guzei,
I. A.; Gandhi, B. A.; Bunel, E. B.; Stahl, S. S. Angew. Chem., Int. Ed.
2005, 44, 5269–5272.
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Kindermann, M. K.; Bajor, G.; Veszpre´mi, T.; Heinicke, J. J. Organomet.
Chem. 2009, 694, 397–403. (c) Ku¨hl, O.; Lo¨nnecke, P.; Heinicke, J. New
J. Chem. 2002, 26, 1304–1307. (d) Ku¨hl, O.; Lo¨nnecke, P.; Heinicke, J.
Polyhedron 2001, 20, 2215–2222. (e) Heinicke, J.; Oprea, A.; Kindermann,
M. K.; Karpati, T.; Nyula´szi, L.; Veszpre´mi, T. Chem.-Eur. J. 1998, 4,
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Synthesis of Phenimy Transition Metal Complexes. In
contrast to free 3a, stable transition metal complexes thereof
(21) Ullah, F. Ph.D. thesis, University Greifswald, May 2008.
(22) (a) MacPherson, E. J.; Smith, J. G. Tetrahedron 1971, 27, 2645–
2649. (b) MacPherson, E. J.; Smith, J. G. Chem. Commun. 1970, 1552–
1553.
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10626–10627.

Annulated N-Heterocyclic Carbenes
Organometallics, Vol. 28, No. 8, 2009 2443
Scheme 3. Syntheses of Phenimy Transition Metal Complexes 6-9
are easily accessible using the method of Wang and Lin.26 An
example is the cationic silver complex 6a(PF6), obtained in high
yield by reaction of the phenimy precursor 2a with silver oxide
in methylene chloride and trapping of water by molecular sieves
A3. The related o-tolyl-substituted phenimy silver complex
6b(PF6) was obtained in the same way, whereas 6b(OTf) and
6b(SbF6) were synthesized directly from the respective silver
salt and carbene 3b, previously generated in THF, and separated
from KPF6 and excess KH by filtration. Chlororhodium(I)-
(phenimy)(COD) (7b), allylpalladium(II)(phenimy) chloride (8),
and palladium(0)(phenimy)(dvds) (9) were also prepared from
free 3b and the corresponding precursor complexes (Scheme
3).
To compare 3b with higher group 14 homologues, an attempt
was made to synthesize the corresponding germylene, which
should be easily accessible and stable as a monomer in contrast
to the more easily associating annulated N-heterocyclic
stannylenes.19f,27 The reaction of dilithium phenanthrene-9,10
diamide 1bLi with GeCl2 dioxane solvate in THF led indeed to
the germylene 10b, which, after removal of THF and extraction
with diethyl ether, forms an orange viscous oil, stable at room
temperature. The compound is however highly sensitive to any
trace of moisture and polar groups in silica gel, which easily
regenerates 1b and prevented further purification by column
chromatography.
deviations from the best plane are 0.05 and 0.04 Å for
6a(PF6) · 3CH2Cl2 (whereby the atoms C35 and C36 lie ca. 0.25
Å out of the plane and were omitted in its calculation) and 0.04
Å for 7b · CH2Cl2. The π-planes of the N-tolyl groups are
markedly rotated with respect to the π-planes of the annulated
imidazole rings, with interplanar angles between the phenimy
ring and the toluene rings of 59° to 85° (in 6a(PF6) · 3CH2Cl2)
and 78.5(1)° and 68.5(1)° (in 7b · CH2Cl2). In the crystals of
7b · CH2Cl2 both o-methyl groups point to the same side of the
phenimy plane, while in solution two forms were indicated,
suggesting rotamers with cis- and trans-orientation of the
o-methyl groups, whose signals do not average out within the
NMR time scale at 25 °C. The C(II)-Ag-C(II) angle of
6a(PF6) · 3CH2Cl2 deviates from a linear arrangement by only
about 10°, and the two phenimy planes around silver subtend
an interplanar angle of 62.1(1)°. Other structural features, bond
lengths, and angles are similar to those reported for other NHC
rhodium3c,17 and silver3d,e,17 complexes. The average value of
the Rh-(CdC) distances (2.2048(18) Å) trans to the CII atom
and thus the trans-influence of the NHC ligand are almost the
same as in (nBu2phenimy)Rh(COD)Cl (2.213(3)17 Å).
For solution NMR characterization HH- and CH-COSY
experiments were carried out with representatives of the new
Structure and Properties. All compounds were characterized
by conclusive 1H and 13C NMR data, complemented by HRMS
data or elemental analysis. Two of the phenanthrene-annulated
NHC complexes formed single crystals by slow diffusion of
hexane into the CH2Cl2 solution. 6a(PF6) · 3CH2Cl2 (Figure 1)
is monoclinic (P21/c); the cation displays no crystallographic
symmetry but approximates closely to 2-fold symmetry (rms
deviation 0.06 Å). The anion and all solvent molecules are well-
ordered. 7b · CH2Cl2 (Figure 2) is also monoclinic (P21/n). Like
for the related (di-n-butyl-phenimy)Rh(COD)Cl complex,17 the
annulated ring system is to a good approximation planar; rms
Figure 1. Molecular structure of the cation of 6a(PF6) · 3CH2Cl2
(ellipsoids with 50% probability). Selected bond lengths (Å) and
angles (deg): Ag-C(1) 2.0827(18), Ag-C(31) 2.0809(18),
C(1)-N(1) 1.356(2), C(1)-N(2) 1.353(2), N(1)-C(2) 1.399(2),
N(2)-C(3) 1.395(2), C(2)-C(3) 1.379(3), C(3)-C(4) 1.438(3),
C(9)-C(10) 1.461(3); C(31)-Ag-C(1) 169.57(7), N(2)-
C(1)-N(1)105.44(16),N(2)-C(1)-Ag124.83(13),N(1)-C(1)-Ag
128.99(14), C(1)-N(1)-C(2) 111.06(16), C(3)-C(2)-N(1)
106.02(16), C(1)-N(1)-C(16) 120.98(15), C(2)-N(1)-C(16)
127.42(15).
(26) Wang, H. M. J.; Lin, I. J. B. Organometallics 1998, 17, 972–975.
(27) Hahn, F. E.; Wittenbecher, L.; LeVan, D.; Zabula, A. V. Inorg.
Chem. 2007, 46, 7662–7667. (b) Braunschweig, H.; Gehrhus, B.; Hitchcock,
P. B.; Lappert, M. F. Z. Anorg. Allg. Chem. 1995, 621, 1922–1928.

2444 Organometallics, Vol. 28, No. 8, 2009
Ullah et al.
50.4, JAgC ) 185.1-188.2, 213.7-218.1 Hz).3c-e,17,28 The
bis(p-tolyl) phenimy complex 6a, which provides only one set
of well-resolved signals, shows additionally small coupling to
two further quarternary 13C carbon nuclei, assigned according
to increasing distance to Cq-4 (3JAgC ) 5.9 Hz) and Cq-5 (4JAgC
) 1.1 Hz). In the bis(o-tolyl)phenanthreno-imidazol-2-ylidene
complexes one of the two (7b-9b) or four (6b) rotamers, which
make the spectra more complex, is usually favored and displays
more intense signals than the others.
1
The most characteristic chemical shift values of NHCs and
their metal complexes are those of the 13CII signals. Whereas
increasing linear annulation causes downfield shift, for benzo-
to naphtho[b]-annulated N,N′-dineopentylimidazol-2-ylidenes at
δ ) 231.87 to δ ) 239.9,15 the Y-shaped phenanthrene-
annulated imidazolylidenes 3b (δ ) 224.5, 224.9) and
nBu2phenimy (δ ) 225.1)17 display the CII resonance more
upfield, between benzo- and nonannulated imidazol-2-ylidenes.
The coordination chemical shifts of the complexes depend on
the metal, its oxidation state, and slightly on the annulation (6b
∆δ ) -38, 8b and 9b ∆δ ) -33.6 and -13.6, cf. 29). For
(NHC)Rh(COD)Cl complexes a (small) response to annulation
is known rather for the downfield CdC-nuclei trans to CII of
the 1,5-COD ligand than for ∆δCII,15 and these resonate at δ
) 97.2, close to those of nonannulated R2imy-Rh(COD)Cl
complexes (e.g., R ) cHex δ ) 97.530). This indicates strong
donor properties of the phenanthrene-annulated imidazol-2-
ylidenes. For (nBu2phenimy)Rh(CO)2Cl17 this was detected also
via the influence on the CO stretching frequency. The high donor
strength and the unexpected relatively upfield 13CII resonance
may be due to partial electronic decoupling of the imidazol-2-
ylidene ring from the benzene rings in the Y-shaped π-system,
reflected in rather short C(2)-C(3), elongated C(3)-C(4)/
C(2)-C(15), and even longer C(9)-C(10) bonds, i.e., alternate
bond lengths in the central six-membered ring of 6a and 7b
(see above). This may be expressed by a high weight of a
resonance structure with strong 6π-delocalization within the two
outer benzene rings and the five-membered imidazole ring but
weak mutual coupling.
The different electronic structure of 1 and 2 is evident also
in the UV and emission spectra. The long-wavelength absorption
of 1 (333 nm), caused by the tolylamino group, is lacking in 2,
which displays only the strong band at 254 nm and shoulders
at 247, 277, 287, and 195 nm. The maxima of the o- and p-tolyl
compounds are very similar; only the extinctions are slightly
different. In the fluorescence spectra 2a and 2b display strong
emission bands (max. 355 nm, 6-8 times stronger than
phenanthrene) in the same region as phenanthrene,31 whereas
the emission is strongly red-shifted in 1b (460 nm). In the Pd0
complex 9b the emission (355 nm) is strongly reduced, ca. 20%
relative to phenanthrene, but less strongly than in the
nBu2phenimy Rh(COD)Cl complex of Tapu et al.17
Figure 2. Molecular structure of the formula unit of 7b · CH2Cl2
(ellipsoids with 50% probability). Selected bond lengths (Å) and
angles (deg): Rh-C(1) 2.0167(16), Rh-Cl(1) 2.4115(5),
C(1)-N(1) 1.364(2), C(1)-N(2) 1.361(2), N(1)-C(3) 1.400(2),
N(2)-C(2) 1.405(2), C(2)-C(3) 1.371(2), C(3)-C(4) 1.435(2),
C(9)-C(10) 1.464(2); C(1)-Ag-Cl(1) 86.61(5), N(2)-C(1)-N(1)
104.96(14), N(2)-C(1)-Rh 131.68(12), N(1)-C(1)-Rh
122.81(11), C(1)-N(1)-C(3) 111.16(13), N(1)-C(3)-C(2)
106.49(14), C(1)-N(1)-C(21) 119.99(13), C(3)-N(1)-C(21)
128.01(14).
phenanthrene diamines, phenanthrene-imidazolium salts, and
phenimy complexes (1b Figure 3, 3b Figure 4; 2a, 2b, and 7b
see Supporting Information) to allow conclusive assignment of
the proton and 13C NMR signals, which except for methyl
signals are all localized in the aryl region. For the phenanthrene
diamines 1a,b a strong downfield doublet is assigned to the H-4
protons in the o,o′-positions of the planarized biphenyl sub-
structure. H-1 (weak 5J cross-peak in the HH-COSY spectrum
of 1b) is also downfield shifted. The o-tolyl signals appear all
relatively upfield, indicating +M interactions with the lone
electron pair at the amino group, particularly for the H-6′
doublet. The assignment of the CH carbon nuclei is based on
the cross-peaks in the CH-COSY spectrum. The quaternary
carbon nuclei were assigned analogously to 6a and 6b, where
two of these nuclei couple with silver.
The spectra of the phenanthreno[9,10-d]imidazolium salts 2a
and 2b differ strongly from those of 1a,b by the cyclodelocalized
π-electron system, involving also the electron lone pairs at
nitrogen. Hence the tolyl group can no longer profit from the
+M effect of the amino group, and the proton and carbon signals
are downfield shifted, especially the o-protons (-I effect). The
fixation of the N-C(tolyl) bond in the NHC-ring plane and
hindrance of the tolyl rotation around the N-C axis exposes
H-6 to the anisotropy cone of the toluene π-system and causes
a strong upfield shift compared to this proton (H-1) in 1a,b.
The carbon signal (C-6 of 2a,b versus C-1 of 1a,b) is less upfield
shifted. The spectra of the o-tolyl compound are rendered more
complicated by hindrance of the N-tolyl rotation and occurrence
of two isomers with the o-methyl groups at the same or different
sides. This can be seen, for example, in the 2D NMR spectra
of 3b (Figure 4) (for others see Supporting Information). The
RhI(phenimy)(COD)Cl complex 7b displays only one of the
expected two rotamers, but the general features of the spectra
do not differ strongly from those of the salt 2b (the greatest
difference being a small downfield shift of H-6′ by δ ca. 0.5/
0.4 ppm). The one-bond couplings of CII with rhodium (7a)
and with silver (6a,b) display typical values (1J(103Rh13C) )
Conclusion
N,N′-Diaryl-substituted phenanthreno[9,10-d]imidazolium salts
are accessible by reductive cyclization of not too bulky benzil-
(28) Arduengo, A. J., III.; Dias, H. V. R.; Calabrese, J. C.; Davidson,
F. Organometallics 1993, 12, 3405–3409.
(29) (a) Mihai, S. V.; Germaneau, F. G.; Navarro-Fernandez, O.; Stevens,
E. D.; Nolan, S. P. Organometallics 2002, 21, 5470–5472. (b) Jackstell,
R.; Harkal, S.; Jiao, H.; Spannenberg, A.; Borgmann, C.; Ro¨ttger, D.;
Nierlich, F.; Cavell, K.; Nolan, S. P.; Beller, M. Chem.-Eur. J. 2004, 10,
3891–3900.
(30) Herrmann, W. A.; Ko¨cher, C.; Goossen, C. J.; Artus, G. R. J.
Chem.-Eur. J. 1996, 2, 1627–1636.
(31) Dawson, W. R.; Windsor, M. W. J. Phys. Chem. 1968, 72, 3251–
3259.

Annulated N-Heterocyclic Carbenes
Organometallics, Vol. 28, No. 8, 2009 2445
Figure 3. HH-COSY (left) and CH-COSY (right) spectra of 1b.
Figure 4. HH-COSY (left) and CH-COSY (right) spectra of 3b.
compounds were conducted under an argon atmosphere using
Schlenk techniques. Benzil bis(arylimines) were prepared by
variation of a known procedure32 from benzil (ca. 30 mmol) and
excess anilines in toluene at 0-20 °C (3 days) using TiCl4 (ca. 2
mL) as a catalyst and were purified after removal of toluene by
extraction with diethyl ether and precipitation with ethanol, yields
72-86%. Other chemicals were used as purchased. NMR spectra
were recorded on a multinuclear FT-NMR ARX300 or AVANCE
II 300 spectrometer (Bruker) at 300.1 (1H), 75.5 (13C), and 121.5
bis(arylimines) with 4-6 equiv of lithium in THF and subse-
quent cyclization with excess trialkyl orthoformate and an
ammonium salt. The route is limited to aryl groups with not
more than one o-substituent. Deprotonation with KH in THF
provides the free N,N′-diarylphenanthreno[9,10-d]imidazol-2-
ylidenes, which are stable in the presence of sterically stabilizing
o-substituents but dimerize in its absence to the corresponding
entetramine. The 13C NMR spectrum of the isolated carbene
shows a surprising upfield chemical shift of the CII resonance
relative to linear carbocyclic annulated imidazol-2-ylidenes. This
hints at partial decoupling of the cyclodelocalized five-
membered ring from the planar tetracyclic π-system, which
causes higher donor strengths than for linear carbocyclic
annulated imidazol-2-ylidenes. Transition metal complexes of
the isolable o-substituted N,N′-diarylphenanthreno[9,10-d]imi-
dazol-2-ylidenes can be obtained directly from the ligand and
the corresponding metal precursor, whereas the p-tolyl isomers
will be accessible by the known transmetalation route of the
silver complex, obtained in high yield by the method of Wang
and Lin.
1
(31P) MHz. Shift references are tetramethylsilane for H and 13C
and H3PO4 (85%) for 31P. Assignment numbers are given in Scheme
1. Coupling constants refer to JHH unless stated otherwise. Assign-
ments are based on HH- and CH-COSY NMR experiments and
DEPT 13C NMR spectra for selected compounds. HRMS measure-
ments were carried out in Go¨ttingen with a double-focusing sector-
field instrument MAT 95 (Finnigan) with EI (70 eV, PFK as
reference substances) or with ESI in MeCN, MeOH, or MeOH/
NH4OAc using a 7 T APEX IV Fourier transfrom ion cyclotron
resonance mass spectrometer (Bruker Daltonics) or in Bielefeld with
EI using an Autospec X VG sectorfield mass spectrometer. UV
spectra were measured with a UV/vis Lambda 800 (Perkin-Elmer)
spectrometer, and emission spectra with a Varioskan fluorescence
spectrometer (Thermo Electron), using λexc ) 256 nm for excitation.
Experimental Section
All solvents except methanol and ethanol were carefully dried
and distilled prior to use. Reactions with air- or moisture-sensitive
(32) Belzer, R. V.; Klein, R. A.; Smeets, W. J. J.; Spek, A. L.; Benedix,
R.; Elsevier, C. J. Recl. TraV. Chim. Pays-Bas. 1996, 115, 275–285.

2446 Organometallics, Vol. 28, No. 8, 2009
Ullah et al.
Fluorescence units of emission bands are given relative (FUrel
)
(CH-4), 124.96 (CH-1), 126.12 (CH-3), 126.79 (CH-2), 128.78 (Cq-
4′), 129.80 (CH-3′/5′), 129.83, 130.04, 131.08 (Cq-4a, Cq-8a, Cq-
9), 144.28 (Cq-1′). MS (EI, 70 eV, 250 °C): m/z (%) 389 (30) [M+
+ H], 388 (100), [M+], 373 (35), 283 (25), 282 (23), 281 (26), 91
(20), 57 (23). Anal. Calcd for C28H24N2 (388.50): C, 86.56; H, 6.23;
N, 7.21. Found: C, 86.67; H, 6.51; N, 6.92.
RFUλ/RFUphen360) to the RFU of the emission band of phenanthrene
at 360 nm (for 10-4 M solution in CH2Cl2). Melting points
(uncorrected) were determined with a Sanyo Gallenkamp melting
point apparatus, and elemental analysis was determined with a
CHNS-932 analyzer from LECO using standard conditions or a
combustion aid (V2O5 for 6a(PF6), 6b(PF6), 8b, 9b).
N,N′-Di-o-tolylphenanthrene-9,10-diamine (1b). Di(o-tolyl)-1,2-
diphenylethane-1,2-diimine (8.15 g, 21.0 mmol) was dissolved in
THF (150 mL) and reduced with Li (874 mg, 125.9 mmol, excess,
about 6 equiv) using the same procedure and workup as described
above for 1a, yielding 5.52 g (68%) of NMR-pure off-white solid
1b. UV (10-5 M in MeOH): λmax (ꢀ) sh 247 (31200), 251.5 (33 700),
333 (4700) nm. Emission (10-4 M in CH2Cl2): λmax (FUrel) 458 nm
(2.6), sh 485 (2.2). 1H (HH-COSY) NMR (CDCl3): δ 2.13 (s, 6 H,
Precursors for Phenanthrene-Annulated Imidazol-2-ylidenes.
N,N′-Di(p-tolyl)-1,2-diphenylethane-1,2-diimine. TiCl4 (about 2 mL,
used as catalyst) was added dropwise through a septum to a cooled
solution (0 °C) of benzil (10.0 g, 47.6 mmol) and excess o-toluidine
(30 mL, 6 equiv) in toluene (150 mL). The solution was stirred at
room temperature for 3 days. Diethyl ether (150 mL) was added,
and the solution was filtered to remove solid products. The solvent
was evaporated under vacuum to give an orange-red liquid crude
product, which was precipitated by addition of ethanol (50 mL).
The precipitate was collected by filtration, washed with ethanol,
and dried in vacuum to give 15.7 g (85%) of NMR pure product.
1H NMR (CDCl3): δ 2.24 (s, 6 H, Me-4′), 6.51 (dd, 3J ) 8.4, 4J )
1.8 Hz, 4 H, H-2′/6′), 6.87 (d, 3J ) 8.4 Hz, 4 H, H-3′/5′), 7.39 (m,
3
2 Me), 5.44 (br s, 2 H, NH), 6.27 (d br, J ) 7.8 Hz, 2 H, H-6′),
3
3
4
6.73 (ddd, J ) 7.4, J ) 7.3, J ) 0.9 Hz, 2 H, H-4′), 6.87 (ddd,
3J ) 7.7, J ) 7.6, J ) 1.2 Hz, 2 H, H-5′), 7.13 (d br, J ) 7.3
Hz, 2 H, H-3′), 7.51 (ddd, J ) 8.1, J ) 7.1, J ) 1.1 Hz, 2 H,
H-2), 7.63 (ddd, J ) 8.1, J ) 7.1, J ) 1.2 Hz, 2 H, H-3), 8.02
3
4
3
3
3
4
3
3
4
3
4
3
(dd, J ) 8.1, J ) 1.0 Hz, 2 H, H-1), 8.74 (d br, J ) 8.1 Hz, 2
H, H-4). 13C{1H} (CH-COSY) NMR (CDCl3): δ 17.40 (Me-2′),
113.32 (CH-6′), 119.15 (CH-4′), 122.90 (CH-4), 123.57 (Cq-2′),
124.62 (CH-1), 126.33 (CH-3), 126.92, 126.93 (CH-5′, CH-2),
130.43 (CH-3′), 129.87, 130.44 (sh), 131.16 (Cq-4a, Cq-8a, Cq-9),
144.57 (Cq-1′). MS (EI, 70 eV, 250 °C): m/z (%) 389 (35), 388
(100) [M+], 373 (13), 283 (38), 282 (33), 281 (31), 280 (30), 267
(16), 165 (22), 106 (15), 65 (16), 57 (15). Anal. Calcd for C28H24N2
(388.50): C, 86.56; H, 6.23; N, 7.21. Found: C, 86.77; H, 6.56; N,
7.19.
3
4
6 H, H-3/5, H-4), 7.86 (dd, J ) 8.0, J ) 1.6 Hz, 4 H, H-2/6).
13C{1H} NMR (CDCl3): δ 20.92 (Me-4′), 120.30 (C-2′/6′), 128.21
128.67,128.98 (CH-2/6, CH-3/5, CH-3′/5′), 130.90 (CH-4), 134.56
(Cq-4′), 137.54 (Cq-1), 146.76 (Cq-1′), 163.77 (CqdN). MS (EI, 70
eV, 345 °C): m/z (%) 389 (2), 388 (10) [M+], 373 (6), 195 (18),
194 (100), 106 (6), 105 (6), 90 (38), 66 (19), 57 (16). Anal. Calcd
for C28H24N2 (388.19): C, 86.56; H, 6.23; N, 7.21. Found: C, 85.72;
H, 6.24; N, 6.94.
N,N′-Di(o-tolyl)-1,2-diphenylethane-1,2-diimine. TiCl4 (2 mL)
was added at 0 °C to a solution of benzil (6.0 g, 28.5 mmol) and
excess o-toluidine (25 mL, ca. 8 equivalents) in toluene (100 mL).
Workup by using the procedure described above gave an orange-
red liquid crude product, which was precipitated by addition of
ethanol (50 mL). The precipitate was collected by filtration, washed
with ethanol, and dried under vacuum, yielding 9.5 g (86%) of
NMR-pure yellow solid di(o-tolyl)-1,2-diphenylethane-1,2-diimine.
Synthesis of Phenanthreno-Annulated Imidazolium Salts. 1,3-
Di-p-tolyl-1H-phenanthreno[9,10-d]imidazolium hexafluorophos-
phate (2a). Compound 1a (1.43 g, 3.68 mmol), NH4PF6 (628 mg,
3.85 mmol), and triethyl orthoformate (15 mL) were heated for
6 h at 140 °C in a rectification apparatus for removal of the ethanol
generated in the reaction. The solution was allowed to cool to room
temperature. The product precipitated was collected by filtration
and washed with diethyl ether and n-hexane (3 × 10 mL),
respectively, and then dried under vacuum to give 1.6 g (80%) of
pale brown solid 2a. UV (10-5 M in MeOH): λmax (ꢀ) sh 247
(45 400), 253.6 (60 200), sh 277 (11 600), sh 287 (9200), 195 (6000)
3
1H NMR (CDCl3): δ 1.34 (s, 6 H, 2 Me), 6.55 (d, J ) 7.7 Hz, 2
H, H-6′), 6.83 (td, 2 H, H-4′), 6.96 (m, 4 H, H-3′/5′), 7.42-7.51
(m, 6 H, H-3, H-4, H-5), 8.00 (dd, J ) 8.1, J ) 1.8 Hz 4 H, H-2,
H-6). 13C{1H} NMR (CDCl3): δ 16.59 (Me-2′), 116.70 (C-6′),
125.03, 125.51(C-4′, C-5′), 128.40, 128.75 (CH-2/6, CH-3/5),
129.89 (CH-3′), 130.92 (CH-4), 132.26 (Cq-2′), 138.30 (Cq-1),
147.85 (Cq-1′), 162.47 (CqdN). MS (EI, 70 eV, 345 °C): m/z (%)
389 (4), 388 (15) [M+], 348 (4), 319 (21), 195 (18), 194 (100),
105 (21), 91 (37), 77 (20), 66 (19), 57 (13). Anal. Calcd for
C28H24N2 (388.19): C, 86.56; H, 6.23; N, 7.21. Found: C, 86.20;
H, 6.19; N, 6.92.
1
nm. Emission (10-4 M in CH2Cl2): λmax (FUrel) 355 nm (8). H
NMR (HH-COSY) (DMSO-d6): δ 2.57 (s, 6 H, 2 Me), 7.36 (dd, 3J
) 7.8, 4J ) 0.6 Hz, 2 H, H-6), 7.61 (t, 3J ) 7.8, 7.5 Hz, 2 H, H-7),
3
3
7.68 (d, J ) 8.2 Hz, 4 H, H-m′), 7.83 (td superimposed, J ≈ 8,
4J ) 0.9 Hz, 2 H, H-8), 7.86 (d, 3J ) 8 Hz, 4 H, H-o’), 9.10 (d, 3J
) 8.4 Hz, 2 H, H-9), 10.26 (s, 1 H, H-2). 13C{1H} NMR (CH-
COSY) (DMSO-d6): δ 21.03 (Me-p’), 120.15 (Cq-10), 120.95 (CH-
6), 125.00 (CH-9), 125.96 (Cq-4), 127.15 (2 CH-3′,5′), 128.29,
128.37 (CH-7, 8), 129.63 (Cq-4′), 131.10 (2 CH-2′,6′), 132.46 (Cq-
5), 141.91 (Cq-1′), 142.55 (br, CH-2). 31P{1H} NMR (DMSO-d6):
δ -143.2 (hept, 1JPF ) 711 Hz). MS (EI, 70 eV, 345 °C): m/z (%)
400 (10), 399 (18) [M+ - PF6], 284 (10), 283 (60), 106 (23), 91
(13), 57 (18), 44 (100). Anal. Calcd for C29H23N2PF6 (544.47): C,
63.97; H, 4.26; N, 5.15. Found: C, 63.74, H, 4.60; N, 5.14.
N,N′-Di-p-tolylphenanthrene-9,10-diamine (1a). Di(p-tolyl)-1,2-
diphenylethane-1,2-diimine (4.1 g, 10.6 mmol) was dissolved in
THF (100 mL), and Li suspension (440 mg, 63.4 mmol, excess,
about 6 equiv) was added at room temperature. Reaction (dissolu-
tion) of Li was started by sonification and allowed to complete by
stirring at room temperature for 20 h. Excess lithium was removed
by filtration through glass wool. Methanol was added dropwise to
the filtrate with continued stirring until the evolution of hydrogen
ceased. Then water was added, and the product was extracted with
diethyl ether. After drying with MgSO4 and removal of ether a
yellow-orange viscous liquid was obtained. A small amount of
diethyl ether was added, and the resulting precipitate was separated
by filtration, washed with few milliliters of diethyl ether, and dried
under vacuum to give 2.75 g (67%) of NMR-pure off-white solid
1,3-Di-o-tolyl-1H-phenanthreno[9,10-d]imidazolium hexafluo-
rophosphate (2b). Compound 1b (1.5 g, 3.86 mmol), NH4PF6 (692
mg, 4.25 mmol), and triethyl orthoformate (15 mL) were heated
for 7 h at 140 °C in a rectification apparatus. Workup in the same
way as described for compound 2a gave 1.65 g (78%) of pale brown
solid 2b, forming a mixture of two axial isomers, E/Z-2b, with the
o-methyl groups on opposite or the same side. Signals with subscript
index a are slightly stronger (2′-Me proton intensity ratio 55:45%)
than those indexed b; no index indicates complete superimposition.
UV (10-5 M in MeOH): λmax (ꢀ) sh 246 (46 000), 253.5 (62 600),
sh 270 (14 800), sh 277 (12 300), sh 287 (10 600), 295 (6800) nm.
Emission (10-4 M in CH2Cl2): λmax (FUrel) 355 nm (6.9). 1H NMR
(HH-COSY) (DMSO-d6): δ 2.19, 2.23 (s, 6 H, 2 Me), 7.19, 7.21
1
1a. H NMR (CDCl3): δ 2.23 (s, 6 H, Me-4′), 5.74 (br s, 2 H,
3
3
NH), 6.55 (d, J ) 8.4 Hz, 4 H, H-2′/6′), 6.93 (d, J ) 8.1 Hz, 4
3
3
H, H-3′/5′), 7.50 (ddd, J ) 8.1, J ) 7.0, J ) 1.0 Hz, 2 H, H-2),
7.61 (ddd, 3J ) 8.2, 3J ) 7.0, 4J ) 1.2 Hz, 2 H, H-3), 8.01 (dd, 3J
) 8.2, 4J ) 1.1 Hz, 2 H, H-1), 8.72 (d br, 3J ) 8.1 Hz, 2 H, H-4).
13C{1H} NMR (CDCl3): δ 20.48 (Me-4′), 115.38 (CH-2′/6′), 122.85

Annulated N-Heterocyclic Carbenes
Organometallics, Vol. 28, No. 8, 2009 2447
7b · CH2Cl2
Table 1. Crystal Data and Structure Refinement
6a(PF6) · 3CH2Cl2
empirical formula
fw
C61H50AgCl6F6N4P
1304.59
C38H36Cl3N2Rh
729.95
temperature
wavelength
cryst syst
100(2) K
0.71073 Å
monoclinic
133(2) K
0.71073 Å
monoclinic
space group
unit cell dimens
P21/c
P21/n
a ) 13.0015(4) Å, R ) 90°
b ) 19.2789(8) Å, ꢀ ) 90.098(3)°
c ) 22.4380(11) Å, γ ) 90°
5624.2(4) Å3
a ) 14.0608(11) Å, R ) 90°
b ) 14.9417(11) Å, ꢀ ) 106.750(4)°
c ) 16.1758(12) Å, γ ) 90°
3254.2(4) Å3
volume
Z
4
4
density (calculated)
absorp coeff
1.541 Mg/m3
1.490 Mg/m3
0.737 mm-1
0.802 mm-1
F(000)
cryst size
θ range for data collection
index ranges
reflns collected
indep reflns
completeness to given θ
absorp corr
max. and min. transmn
refinement method
data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak and hole
2648
1496
0.27 × 0.15 × 0.15 mm3
0.30 × 0.25 × 0.20 mm3
1.39 to 32.06°
-19 e h e 18, -28 e k e 28, -33 e l e 33
161 379
19 460 [R(int) ) 0.0487]
99.2% to 31.5°
semiempirical from equivalents
0.8975 and 0.7723
full-matrix least-squares on F2
19 460/0/716
1.69 to 30.51°
-20 e h e 20, -21 e k e 21, -23 e l e 23
68 990
9919 [R(int) ) 0.0327]
99.9% to 30°
semiempirical from equivalents
0.8561 and 0.7331
full-matrix least-squares on F2
9919/6/415
1.050
1.057
R1 ) 0.0435, wR2 ) 0.1079
R1 ) 0.0627, wR2 ) 0.1219
2.300 and -1.812 e · Å-3
R1 ) 0.0290, wR2 ) 0.0689
R1 ) 0.0422, wR2 ) 0.0774
0.631 and -0.467 e · Å-3
(each dd, 3J ) 8.3, 4J ) 0.8 Hz, 2 H, H-6a,b), 7.62 (t br, 3J ) 7-8
Hz, 2 H, H-7a slightly upfield from H-7b), 7.65-7.88 (m, 8 H),
assigned by HH-COSY: 7.69 (t) H-4′b, 7.72 (t) H-4′a, 7.75 (d) H-3′b,
7.77 (d) H-3′a, 7.82 (t) H-5′b, 7.84 (t) H-5′a, 7.86 (t) H-8), 7.95,
137.22, 137.25 (Cq-5a,b), 143.22 (Cq-1′), 224.48, 224.92 (s, CIIa,b);
two superimposing sets of signals make assignment of Cq uncertain.
MS (EI, 70 eV, 300 °C): m/z (%) 399 (40) [M + 1+], 398 (100),
397 (52), 396 (60), 387 (51), 280 (35), 279 (62), 267(21), 164 (24);
additionally, M+ of the water adduct was detected. HRMS (EI):
calcd for C29H22N2 398.17776; found 398.17780.
3
4
3
8.07 (each dd, J ) 7.8, J ) 0.9 Hz, 2 H, H-6′a,b), 9.13 (d, J )
8.4 Hz, 2 H, H-9), 10.29, 10.33 (2 s, 1 H, H-2a,b). 13C{1H} NMR
(CH-COSY) (DMSO-d6): δ 16.80, 16.99 (2′-Mea,b), 120.02 (CH-
6), 120.18, 120.34 (Cq-10a,b), 125.06, 125.10 (CH-9b,a), 125.81,
125.97 (Cq-4a,b), 127.82, 128.32 (CH-6′a,b), 128.27, 128.49 (CH-
4′b,a), 128.72, 128.74 (CH-7, CH-8), 129.76, 129.81 (Cq-2′b,a),
132.05, 132.15 (CH-3′b,a), 132.25, 132.35 (CH-5′b,a), 134.01 (Cq-
5), 135.36, 135.56 (Cq-1′a,b), 141.46, 141.79 (CH-2b,a). 31P{1H}
2,2′-Bis(1,3-di-p-tolyl-1H-phenanthreno[9,10-d]imidazol-2-
ylidene) (4a). A suspension of 2a (500 mg, 0.92 mmol) in THF
was added at room temperature to a suspension of 30% KH in
mineral oil (74 mg, 1.8 mmol), washed before use with THF. The
mixture was stirred 2 h at room temperature. Hydrogen evolved,
and the color of the solution became red-brown after 30 min. After
filtration the solvent was removed under vacuum, and the residue
was extracted with benzene. Removal of solvent under vacuum gave
1
NMR (DMSO-d6): δ -143.2 (sept, JPF ) 711.4 Hz). MS (EI, 70
eV, 330 °C): m/z (%) 401 (19), 399 (87) [M+ - PF6], 388 (100),
397 (8), 384 (12), 309 (20), 308 (11), 282 (12), 281 (35), 279 (12),
107 (32), 91 (11), 65 (15). Anal. Calcd for C29H23N2PF6 (544.47):
C, 63.97; H, 4.26; N, 5.15. Found: C, 63.78, H, 4.20, N, 5.01.
Deprotonation of Phenanthrenoimidazolium Salts and Car-
bene Selenium Adduct. 1,3-Di-o-tolylphenanthreno[9,10-d]imida-
zol-2-ylidene (3b). A suspension of 2b (300 mg, 0.55 mmol) in
THF was added at room temperature to a suspension of 30% KH
in mineral oil (56 mg, 1.4 mmol, 2.5 equiv), washed before use
with THF. The mixture was stirred 2 h at room temperature.
Hydrogen evolved, and the color of the solution became red-brown
on stirring after 30 min. After filtration the solvent was removed
under vacuum, and the residue was extracted with benzene.
Evaporation of the solvent under vacuum gave 185 mg (84%) of a
red-brown viscous oil, stable at room temperature for a long time
under inert atmosphere. NMR spectra in C6D6 showed complete
conversion of the starting material to the carbene 3b containing
only traces of an impurity (<5%). 1H (HH- and CH-COSY) NMR
(C6D6): δ 2.07, 2.10 (2s, 6 H, 2 Mea,b, 60:40%), 7.09-7.27 (m, 8
H; 7.17 [t, H-7], 7.18 [t, H-4′], 7.19 [d, H-6′], 7.23 [t, H-5′]), 7.31
1
302 mg (82%) of a red-brown oil identified by NMR as 4a. H
3
NMR (C6D6): δ 1.97 (s, 6 H, 2 Me), 6.72 (d, J ) 8.4 Hz, 4 H,
3
H-2′,6′), 7.28 (sym m, 4 H, H-7,8), 7.49 (d, J ) 8.4 Hz, 4 H,
H-3′,5′), 7.71 (m, 2 H, H-6), 8.44 (m, 2 H, H-9). 13C{1H} NMR
(C6D6): δ 21.46 (CMe), 124.36 (CH-3′,5′, superimposed CH-6),
125.07, 125.64, 127.01 (CH-7, CH-8,9), 126.13 (Cq-10), 130.10
(Cq-4′), 130.25 (CH-2′,6′), 134.51, 134.75 (NCq-4,5), 138.97 (half-
intensity, N2Cq-2), 145.79 (NCq-1). MS (adduct of moisture at the
monomer after handling at air): calcd for C29H24N2O 416.2; found
(EI, 70 eV, 240 °C) m/z (%) 418 (8), 417 (23) [M + 1+], 416 (15),
415 (41) [M - 1+], 400 (100), 399 (70), 398 (53), 389 (52), 282
(25), 281 (29), 91 (20).
1,3-Di-o-tolyl-1,3-dihydrophenanthreno[9,10-d]imidazole-2-
selone (5b). Selenium powder (73 mg, 0.92 mmol) was added to a
THF solution of free carbene 3b generated from imidazolium salt
2b (500 mg, 0.92 mmol) as described above and stirred for 5 h at
room temperature. The mixture was filtered, and the solvent was
removed under vacuum. The residue was washed with hexane,
dissolved in CH2Cl2, and crystallized by overlayering with n-hexane
to give 377 mg (86%) of brown-red crystals of 5b. 1H NMR
3
3
(t, J ) 7.6 Hz, 2 H, H-8), 7.49 (d, J ) 7.5 Hz, H-3′), 7.55
3
3
4
(superimp. d, H-3′), 7.56, 7.58 (2d, J ≈ 7.5 Hz, 2 H, H-6), 8.54
(CDCl3): δ 2.07, 2.12 (2s, 6 H, E/Z 2′-Me), 7.03 (dt, J ) 8.4, J
3 4
(d, 3J ) 8.7 Hz, 2 H, H-9). 13C{1H} (CH-COSY) NMR (C6D6, ref
C6H6 δ ) 128.7): δ 18.55, 18.65 (2′-Mea,b), 122.01, 122.03 (CH-
6), 123.88, 123.92 (Cq-10a,b), 124.91 (CH-9), 126.22 (CH-8), 128.00
(CH-7), 128.08, 128.18 (CH-4′b,a), 129.11 (Cq-4), 129.69 (CH-5′),
129.71 (CH-3′a), 129.80 (Cq-2′), 129.89 (CH-3′b), 131.89 (CH-6′),
) 1.5 Hz, 2 H, H-6′), 7.23 (dt, J ) 7.2, J ) 1.2 Hz, 2 H, H-3′),
3
7.42-7.58 (m, 10 H), 8.70 (d, J ) 8.4 Hz, 2 H, H-9). 13C{1H}
NMR (CDCl3): δ 17.92, 18.04 (2 E/Z 2′-Me), 120.66 (CH-6),
120.85 (Cq-10), 123.77 (CH-9), 126.10 (CH-7), 126.34, 126.39 (Cq-
4), 127.52, 127.98 (CH-4′,8), 128.64, 128.78 (Cq-2′), 129.25, 129.34

2448 Organometallics, Vol. 28, No. 8, 2009
Ullah et al.
(CH-5′), 130.51 (CH-3′), 131.79, 131.81 (CH-6′), 136.73, 136.86
(Cq-5), 138.36, 138.42 (Cq-1′), 165.21, 165.43 (Cq-2). MS (EI, 70
eV, 200 °C): m/z (%) ) 481 (4) [M+], 480 (15) [M+ (82Se)],
479(21), 478 (51) [M+ (80Se)], 477 (11), 476 (32) [M+ (78Se)], 475
(14) [M+ (77Se)], 474 (12) [M+ (76Se)], 398 (32), 397 (100), 308
(12), 307 (40), 306 (19), 305 (20), 281 (18), 280 (55), 278 (19),
252 (11), 239 (16), 190 (16), 91 (16), 65 (15). HRMS (EI): calcd
for C29H22N2Se 478.09482 (80Se); found 478.09386 (100%) and
correct isotopic pattern.
tolyl nuclei Cq-2′ and CH-6′ and by Cq4 and are not listed. HRMS
(EI) for C59H44AgF3N4O3S: calcd for cation (C58H44N4Ag+)
903.26114; found 903.26097.
Bis(1,3-di-o-tolylphenanthreno[9,10-d]imidazol-2-ylidene)sil-
ver Hexafluoroantimonate (6b(SbF6)). Silver hexafluoroantimonate
(127 mg, 0.37 mmol) was added to a THF solution of free carbene
3b generated from 2b (400 mg, 0.74 mmol) as described above
and stirred for 10 h at room temperature. Workup as described for
6b(OTf) gave 280 mg (66%) of colorless solid 6b(SbF6). 1H NMR
and 13C NMR data are in accordance with those of 6b(OTf). HRMS
(EI) for C58H44N4SbF6Ag: calcd for cation (C58H44N4Ag+) 903.26114;
found 903.26079.
Synthesis of Phenanthreno-Annulated Imidazol-2-ylidene Tran-
sition Metal Complexes. Bis(1,3-di-p-tolylphenanthreno[9,10-d]imi-
dazol-2-ylidene)silver Hexafluorophosphate (6a(PF6)). Silver oxide
(171 mg, 0.74 mmol), freshly dried molecular sieves (4A), and
hexafluorophosphate 2a (400 mg, 0.74 mmol) were added to a
Schlenk tube, which was evacuated and flashed with argon before
addition of CH2Cl2 (15 mL). The resulting suspension was stirred
for 2 days at ambient temperature and filtered. The solvent was
partly removed under vacuum (to 5 mL), and hexane (10 mL) was
added. White crystals, in part single crystals, formed. Some single
crystals of 6a(PF6) · 3CH2Cl2 with mother liquor were retained for
X-ray diffraction study; the remaining sample was filtered, washed
with hexane, and dried under vacuum (5 min at 3 Torr, 20 °C) to
give 308 mg (69%) of colorless crystals of 6a(PF6) · 2CH2Cl2. For
crystal data see Table 1, for selected bond lengths and angles see
Figure 1. 1H NMR (CD2Cl2): δ 2.64 (s, 6 H, 2 Me), 7.29 (dd, 3J )
8.3, 4J ) 0.9 Hz, 2 H, H-6), 7.29 (d, 3J ) 8.2 Hz, 4 H, H-2′, H-6′),
7.41 (superimposed td, 3J ) 8, 7, 4J ) 0.9 Hz, 2 H, H-8), 7.45 (d,
3J ) 8.2 Hz, 4 H, H-3′, H-5′), 7.67 (td, 3J ) 8.4, 7.1, 4J ) 1.2 Hz,
(1,3-Di-o-tolylphenanthreno[9,10-d]imidazol-2-ylidene)(1,5-cy-
clooctadiene)rhodium(I) Chloride (7b). [RhCl(COD)]2 (228 mg,
0.46 mmol) was added to a THF solution of free carbene 3b (336
mg, 0.84 mmol) and stirred for 10 h. After filtration the solvent
was removed under vacuum. The residue was washed several times
with hexane, dissolved in CH2Cl2, and crystallized by overlayering
with n-hexane to give pale yellow crystals (303 mg, 56%) of
7b · CH2Cl2, after drying under vacuum. For crystal data see Table
1; for selected bond lengths and angles see Figure 3. 1H NMR (HH-
COSY) (CD2Cl2): δ 1.48 (m, 4 H, CH2 trans), 1.57, 1.73 (m, 4 H,
CH2cis), 1.88 (s, 6 H, 2 Me), 2.95 (unresolved dd, 2 H, CHtrans),
3
4
4.75 (dd, J ) 4.4, J ) 2.9 Hz, 2 H, CHcis), 7.34 (m, 4 H, H-6,
3
4
H-7), 7.46 (dd, J ) 7.2, J ) 1.0 Hz, 2 H, H-3′), 7.56 (m, 2 H,
3
4
3
H-8), 7.63 (td, J ) 7.5, J ) 1.5 Hz, 2 H, H-5′), 7.69 (td, J )
7.6, 7.4, 4J ) 1.5 Hz, 2 H, H-4′), 8.63 (dd, 3J ) 7.5, 4J ) 1.5 Hz,
3
2 H, H-7), 8.79 (d br, J ) 8.3, Hz, 2 H, H-9). 13C{1H} NMR
2 H, H-6′), 8.73 (d, J ) 8.5 Hz, 2 H, H-9). 13C{1H} NMR (CH-
3
(CD2Cl2): δ 21.64 (Me-p′), 121.39 (Cq-10), 122.21 (CH-6), 124.42
(CH-9), 127.29 (CH-7), 127.66, (CH-3′,5′), 127.73 (CH-8), 128.23
(d, JAgC ) 5.9 Hz, Cq-4), 129.88 (Cq-4′), 131.15 (CH-2′,6′), 137.65
(d, JAgC ) 1.1 Hz, Cq-5), 140.99 (Cq-1′), 187.82 (2 d, 1JAgC ) 188.2,
218.1 Hz, Cq-2). HRMS (ESI in CH3CN) of C58H44AgF6N4P: calcd
for cation (C58H44N4Ag+) 903.26114; found 903.26050. Anal. Calcd
for C58H44AgF6N4P · 2CH2Cl2 (1219.69): C, 59.08; H, 3.97; N, 4.59.
Found: C, 59.11, H, 3.93, N, 4.74.
COSY) (CDCl3): δ 17.79 (2′-Me), 28.08 (CH2, cis to Cl), 32.15
(CH2, trans), 66.72 (d, J ) 15.0 Hz, CHdCHtrans), 97.22 (d, J )
7.5 Hz, CHdCHcis), 120.47 (CH-6), 121.49 (Cq-10), 123.58 (CH-
9), 125.84 (CH-8), 127.30 (CH-4′), 127.48 (CH-7), 128.29, 128.44
(Cq-2′, NCq-4), 129.56 (CH-5′), 130.15 (CH-3′), 131.73 (CH-6′),
135.02 (Cq-5), 139.47 (NCq-1′), 192.29 (d, 1J(103Rh13C) ) 50.4 Hz,
Cq-2). MS (EI, 70 eV, 270 °C): m/z (%) ) 647 (3) [M + 1+], 646
(10) [M + 1+], 645 (9) [M+], 644 (23) [M+ (35Cl)], 498 (16), 496
(11), 494 (10), 401 (35), 400 (100), 41 (14). HRMS (EI): calcd for
C37H34N2ClRh 644.14656, found 644.14594. Anal. Calcd for
C37H34ClN2Rh (644.15): C, 68.69; H, 5.31. Found: C 68.84; H,
5.66.
Bis(1,3-di-o-tolylphenanthreno[9,10-d]imidazol-2-ylidene)sil-
ver Hexafluorophosphate (6b(PF6)). Compound 6b(PF6) was pre-
pared in analogy to 6a(PF6) · 2CH2Cl2 from 2b and excess silver
oxide in CH2Cl2 in the presence of freshly dried molecular sieves
1
(4A), Yield: 310 mg of off-white powder. H NMR data are in
accordance with those of 6b(OTf). Anal. Calcd for C58H44AgF6N4P
(1049.83): C, 66.36; H, 4.22; N, 5.43. Found: C, 66.55, H, 4.34,
N, 5.22.
(Allyl)(1,3-di-o-tolylphenanthreno[9,10-d]imidazol-2-ylidene)pal-
ladium(II) Chloride (8b). [Pd(allyl)Cl]2 (189 mg, 0.47 mmol) was
added to a THF solution of free carbene 3b (373 mg, 0.94 mmol),
generated from imidazolium salt 2b (600 mg, 1.10 mmol) as
described above, and stirred for 10 h at room temperature. After
filtration the solvent was removed under vacuum. The residue
was washed with hexane, redissolved in CH2Cl2, and crystallized
by overlayering with n-hexane to give 453 mg (74%) of brown
Bis(1,3-di-o-tolylphenanthreno[9,10-d]imidazol-2-ylidene)sil-
ver Triflate (6b(OTf)). Silver triflate (47 mg, 0.18 mmol) was added
to a THF solution of free carbene 3b generated from imidazolium
salt 2b (200 mg, 0.37 mmol) as reported above and stirred for 10 h
at room temperature. The solution was filtered, and the solvent was
removed under vacuum. The residue was washed several times with
hexane, dissolved in CH2Cl2, and crystallized by overlayering with
hexane to give 130 mg (67%) of colorless solid 6b(OTf). 1H NMR
(CD2Cl2): δ 1.76, 1.81, 1.82, 1.88 (6 H, 2′-Me), 7.04-7.12
1
crystals of 8b · THF. H NMR (CD2Cl2): δ 2.11, 2.16 (super-
3
imposed br s, d, 7 H, 2′-Me, allyl-Hanti-C), 2.69 (d, Janti ) 13.4
3
Hz, 1 H, allyl-Hanti-A), 3.32 (br d, Jsyn ) 13.4 Hz, 1 H, allyl-
3
Hsyn-C), 3.79 (d br, Jsyn) 7.4 Hz, 1 H, allyl-Hsyn-A), 4.79 (m, 1
3
(superimposed dd, J ) 8.3 Hz, 2 H, H-6′), 7.15-7.28 (superim-
3
H, allyl-HB), 7.15-7.27 (superimposed, 2 H, H-6′), 7.38 (t, J
posed dd, 2 H, H-6), 7.39 (tm, 2 H, H-8), 7.55 (m, 2 H, H-7), 7.55
3
) 7.2, J ) 8.1 Hz, 2 H, H-6), 7.46-7.54 (br m, 4 H, H-7,
3
(superimposed d, 2 H, H-3′), 7.67 (tm, J ) 7.5 Hz, 2 H, H-5′),
3
H-8), 7.60-7.78 (superimposed m, 6 H, aryl’), 8.78 (d J ) 8.5
3
4
3
7.70 (td, J ) 7.8, J ) 0.9 Hz, 2 H, H-4′), 8.80 (d, J ) 8.4 Hz,
2 H, H-9); assignment except H-6′ in analogy to Rh(COD)Cl
complex. 13C{1H} NMR (CD2Cl2, 25 °C): δ 17.44 (w), 17.48 (st),
17.54 (st), 17.57 (m), 17.62 (w), 17.68 (m) (2′-Me stereoisomers;
weak, medium, strong intensity), 121.08 (CH-6), 121.56 (Cq-10),
124.39 (CH-9), 127.49 (CH-7), 128.25, 128.27 (CH-4′, CH-8),
127.8-129.3 (isom., Cq-2′), 128.47 (Cq-4), 129.81 (CH-5′), 131.13
(CH-3′), 132.24 (and isom., CH-6′), 136.04 (and isom., Cq-5),
139.13 (Cq-1′), 186.75 (dd, 1J(107/109Ag13C) ) 185.1, 213.7 Hz, Cq-
2); isom.: smaller isomer peaks are shown particularly by the ortho-
Hz, 2 H, H-9). 13C{1H} (DEPT) NMR (CD2Cl2): δ 18.03 (br,
2′-Me), 49.57 (s br, CH2-C), 71.19 (br, CH2-A), 114.53 (br, CHB),
121.02 (br, CH-6), 121.97, 122.02 (Cq-10a,b), 124.19 (CH-9),
126.59 (CH-7), 127.53, 127.89 (CH-4′, CH-8), 128.65, 129.06
(Cq-2′, NCq-4), 130.42 (CH-5′), 131.06 (vbr, CH-3′, CH-6′;
131.54 (s), 137.45 (Cq-5), 139.6, 139.9 (Cq-1′), 191.1 (Cq-2).
MS (EI, 70 eV, 280 °C): m/z (%) 545 (0.2) [M+ - Cl], 505
(1.3) [M+ - Cl - C3H5], 440 (2.2), 413 (5), 398 (10), 91 (9),
42 (70), 41 (100). HRMS (ESI in CH3CN): calcd for

Annulated N-Heterocyclic Carbenes
Organometallics, Vol. 28, No. 8, 2009 2449
C32H27ClN2Pd 580.08921; found 580.08953. Anal. Calcd for
8b · THF C36H35ClN2OPd (653.55): C, 66.16; H, 5.40; N, 4.29.
Found: C (incomplete combustion); H, 5.44, N, 4.04.
for a further 6 h. THF was evaporated under vacuum, and the
product was extracted with diethyl ether to give 154 mg of a
strongly moisture-sensitive orange-red viscous oil, which according
to the HRMS and NMR spectra was impure 10b, contaminated by
1b (ca. 70:30 mol % by integration of 1H methyl signals). 1H NMR
(D8-THF/C6D6, ref C6H6 δ 7.16): δ 1.85, 1.87 (s, E/Z-Me),
1,3-Di-o-tolylphenanthreno[9,10-d]imidazol-2-ylidene-palladium(0)-
η2,η2-1,1,3,3-tetramethyl-1,3-divinyldisiloxane (9b). A Pd(0)(dvds)
solution (0.75 mL, 1.1 mmol) was added to a filtered solution of
free carbene 3b in THF, generated from 2b (300 mg, 0.55 mmol)
and KH (44 mg, 1.1 mmol) at room temperature. THF was
evaporated under vacuum, hexane was added and partially evapo-
rated, and the concentrated solution was stored at -20 °C for 3
days. The precipitated product was collected by filtration and
washed several times with hexane to give 181 mg (48%) of NMR-
pure pale yellow crystals of 9b. The complex consists of a mixture
of a major isomer (indicated by subscript a), where the vinyl and
the two different methyl groups of the dvds ligand each display
one set of signals, and a minor isomer (indicated by subscript b),
where the vinyl and one of the two methyl signals (probably outside
the coordination plane) of the dvds ligand are different in the
orientation toward and opposite the o-methyl group and each show
two sets of signals (indicated b,b′). UV (10-5 M in MeOH): λmax (ꢀ)
sh 247 (53 000), 253.5 (61 000), sh 278 (24 500), sh 287 (6600)
3
4
7.03-7.45 (m, aryl), 7.75 (dd, J ) 8.5, J ) 1.2 Hz, H-6), 7.81
3
4
3
(dd, J ) 8.5, J ) 1.2 Hz, H-9′), 8.53 (d br, J ) 8.3 Hz, H-9).
MS (EI, 70 eV, 345 °C): m/z (%) 462 (2.1), 461 (3.6), 460 (14)
[M+], 459 (5), 458 (10), 457 (1), 456 (6.4); 387 (100) [1b]. HRMS
(EI): calcd for C28H22N274Ge 460.0995; found 460.0994 (and correct
isotopic pattern).
Crystal Structure Analysis. Data Collection. Data were
recorded at low temperature using monochromated Mo KR radiation
on a Bruker APEX-2 diffractometer for 6a(PF6) and a Bruker
SMART diffractometer for 7b and corrected for absorption
(program SADABS).
Structure Refinement. The structures were refined anisotropi-
cally on F2 using the program SHELXL-97.33 Hydrogen atoms were
refined using rigid methyl groups or a riding model. Special features
and exceptions: Compound 6a(PF6) is monoclinic despite the
closeness of the ꢀ angle to 90°. No significant amount of
pseudomerohedral twinning could be detected. Hydrogen atoms at
the coordinated double bonds of 7b were refined freely with C-H
distance restraints. The crystallographic data of 6a(PF6) and 7b are
listed in Table 1.
1
nm. Emission (10-4 M in CH2Cl2): λmax (FUrel) 355 (0.2) nm. H
NMR (THF-d8, ref solv. δ 1.72): δ -0.86 (s, SiMeb), -0.69 (s,
SiMea), -0.50 (s, SiMeb’), 2.07, 2.11 (2s, 2′-Meba), 2.04 (dd, 3J )
15.1, 12.4 Hz, dCHb), 2.14 (dd, 3J ) 15.1, 12.2 Hz, dCHa), 2.19
(dd, 3J ) 15.1, 12.1 Hz, dCHb’), 2.43 (d, 3J ) 15.3, 2J ) 1.3 Hz,
dCH2trans b), 2.61 (d br, 3J ) 14 Hz, dCH2trans a), 2.64 (d, 3J ) 16
Hz, dCH2trans b′), 2.69 (dd, 3J ) 12.5, 2J ) 1.3 Hz, dCH2cis b), 2.88
Acknowledgment. F.U. is grateful to the DAAD for a
scholarship within the Sandwich Programme. We thank B.
Witt, W. Heiden, and M. Steinich for NMR and LR mass
spectra, Dr. R. Wardenga for emission spectra and Dr. H.
Frauendorf and G. Sommer-Udvarnoki (Georg-August-
Universita¨t Go¨ttingen, Institut fu¨r Organische and Biomole-
kulare Chemie) for HRMS. A gift of Pd(dvds) by Dr. Karch,
UMICORE, is gratefully acknowledged.
3
3
2
(d br, J ) 12.3 Hz, dCH2cis a), 3.07 (dd, J ) 12.1, J ) 1.1 Hz,
dCH2cis b′), 7.17-7.61 (m, 14 H, aryl), 8.87 (d, 3J ) 8.5 Hz, 2 H,
H-9). 13C{1H} NMR (THF-d8, ref solv. δ 25.2): δ -1.49, -1.08
(SiMebb′), -1.17 (SiMea), 1.52 (br, SiMeb), 17.98 (br, 2′-Meab),
56.60, 56.94, 57.08, (dCHbb′a), 58.89, 59.15, 59.47 (dCH2bb′a),
121.20, 121.30 (CH-6ba), 122.47, 122.53 (Cq-10ab), 124.77 (br, CH-
9ab), 126.46, 126.50 (CH-7ab), 127.96 (br, CH-4′, CH-8), 129.32,
129.37, 129.72 (br) (Cq-2′ or Cq-4), 129.90, 130.13 (CH-5′ab), 130.25
(br, CH-3′ab), 131.76, 131.83 (CH-6′ba), 136.89, 137.01 (Cq-5ba),
141.55, 141.63 (Cq-1′ab), 211.04, 211.24 (Cq-2ab). MS (EI, 70 eV,
250 °C): m/z (%) 507 (0.14) [L108Pd+], 505 (0.16) [L106Pd+], 504
(0.14) [L105Pd+]; 399 (0.7) [L+], 398 (0.7), 309 (1.3), 184 (1.5),
173 (86), 172 (11), 171 (62), 117 (100), 73 (60), 59 (71). HRMS
(EI): calcd for C37H40N2OPdSi2 690.17085; found 690.172249.
Anal. Calcd for C37H40N2OPdSi2 (690.32): C, 64.28; H, 5.83; N,
4.05. Found: C 64.52; H, 6.07; N, 4.04.
Supporting Information Available: Figures of HH- and CH-
COSY NMR spectra of 2a, 2b, and 7b; 13C NMR spectra of 3b,
4a, 5b, 6a(PF6), 6b(CF3SO3), 8b, and 9b; overview table with 13
C
NMR data of the phenanthrene diamines, phenanthreno-imidazolium
or -imidazol-2-ylidene compounds 1-9(a and/or b); Tables with
atomic coordinates and equivalent isotropic displacement parameters
and with bond lengths and angles of 6a and 7b; view of the packing
of 6a; Figures with UV and emission spectra of 1b, 2a, 2b, 9b,
phenanthrene as reference, all in CH2Cl2. This material is available
free of charge via the Internet at http://pubs.acs.org.
Bis(1,3-di-o-tolylphenanthreno[9,10-d]-1,3,2λ2-diazagermole (10b).
Compound 1b (150 mg, 0.38 mmol) was dissolved in dry THF
(10 mL) and dilithiated at -78 °C with nBuLi (2.5 M) in hexane
(0.34 mL, 0.84 mmol). After stirring for 2 h, solid GeCl2 dioxane
(98 mg, 0.42 mmol) was added in small portions to the cold
solution. The reaction is indicated by a color change from yellow
to orange-red. The mixture was allowed to warm to RT and stirred
OM9000132
(33) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.