Indenyl- and fluorenyl-functionalized N-heterocyclic carbene complexes of titanium and vanadium

Article abstract of DOI:10.1021/om051017z

The new N-heterocyclic carbene ligands functionalized with indenyl and fluorenyl groups, 1-[ind-(CH₂)₂]-NHC, (Ind-NHC) ^-, and 1-[fl-(CH₂)₂]-NHC, (Fl-NHC)^-, where ind = 1-indenyl, fl = 9-flu

Full text of DOI:10.1021/om051017z

Organometallics 2006, 25, 1337-1340
1337
Indenyl- and Fluorenyl-Functionalized N-Heterocyclic Carbene
Complexes of Titanium and Vanadium
Stephen P. Downing and Andreas A. Danopoulos*
Department of Chemistry, UniVersity of Southampton, Highfield, Southampton, U.K. SO17 1BJ
ReceiVed NoVember 25, 2005
Summary: The new N-heterocyclic carbene ligands functional-
ized with indenyl and fluorenyl groups, 1-[ind-(CH2)2]-NHC,
(Ind-NHC)-, and 1-[fl-(CH2)2]-NHC, (Fl-NHC)-, where ind
) 1-indenyl, fl ) 9-fluorenyl, NHC ) 3-DiPP-imidazol-2-
ylidene, DiPP ) 2,6-Pri2-C6H3, serVe as Versatile building
blocks of Ti(III) and V(III) complexes.
rise to active polymerization,6a-c oligomerization,6d,e C-H
activation,6f and hydroamination6g catalysts. The role of the
pendant group in these catalytic reactions is subtle and diverse.
For example, it can increase complex catalyst stability by chelate
formation, impose coordination rigidity by suppressing substitu-
tion or conproportionation reactions,7 promote hemilability,8
modify the sterics around the metal, and create chirality.
In this communication we wish to describe (i) the synthesis
of the first imidazolium salts with pendant indene or fluorene
groups, (ii) their deprotonation to the neutral indene- or fluorene-
NHC and the anionic indenyl- and fluorenyl-NHC species,
respectively, and (iii) the synthesis and structural characterization
of the first Ti and V complexes with the new bidentate chelate
ligands.
The use of N-heterocyclic carbenes (NHCs) in catalytic
transition metal systems has been an active area of research
over the last decade.1 The most successful applications are in
the metathesis (Ru catalyst) and C-C coupling (Pd catalyst)
reactions.2 Polydentate NHC ligands in which the NHC is linked
to a neutral or anionic donor by an organic spacer are being
developed, because they could offer fine-tuning of the coordina-
tion sphere of metals.3 However, cyclopentadienyl and the alkyl-
substituted or -annulated derivatives (indenyl, fluorenyl, etc.)
with pendant NHC groups are not known, even though “half-
sandwich” complexes of the type (Cp)M(NHC)(Ligand)n have
been prepared.4 Work on cyclopentadienyl-type ligands with
pendant neutral or anionic “classical” donor groups5 has given
The new imidazolium pro-ligands (Scheme 1) are obtained
in good yields by the quaternization of â-bromoethylindene9
or â-bromoethylfluorene10 with DiPP-imidazole.11,12 Attempts
to prepare analogous tetramethylcyclopentadienyl derivatives
(6) (a) Do¨rling, A.; Go¨hre, G.; Jolly, P. W.; Kryger, B.; Rust, J.;
Vehrovnik, G. P. J. Organometallics 2000, 19, 388. (b) Okuda, J. In
Metallocenes; Togni, A., Halterman R. L., Eds.; Wiley-VCH: Weinheim,
1998; p 415. (c) Zhang, H.; Ma, J.; Qian, Y.; Huang, J. Organometallics
2004, 23, 5861. (d) Huang, J.; Wu, T.; Qian, Y. Chem. Commun. 2003,
2816. (e) Deckers, P. J. W.; Hessen, B.; Teuben, J. H. Angew. Chem., Int.
Ed. 2001, 40, 2516. (f) Kohl, G.; Rudolph, R.; Pritzkow, H.; Enders, M.
Organometallics 2005, 24, 4774, and references therein. (g) Esteruelas, M.
A.; Lo´pez, A. M.; Mateo, A. C.; Onate, E. Organometallics 2005, 24, 5084,
and references therein.
* To whom correspondence should be addressed. Fax: +44(0)-
2380596805. E-mail: ad1@soton.ac.uk.
(1) Bourissou, D.; Guerret, O.; Gabbai, F. P.; Bertrand, G. Chem. ReV.
2000, 100, 39.
(2) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290.
(3) See for example: (a) Li, W.; Sun, H.; Chen, M.; Wang, Z.; Hu, D.;
Shen, Q.; Zang, Y. Organometallics 2005, 24, 5925. (b) Aihara, H.; Matsuo,
T.; Kawaguchi, H. Chem. Commun. 2003, 2204.
(7) Klei, S. R.; Tilley, T. D.; Bergman. R. G. Organometallics 2002,
21, 4905.
(4) For selected references see: (a) Abernethy, C. D.; Cowley, A. H.;
Jones, R. A.; Macdonald, C. L. B.; Shukla, P.; Thompson, L. K.
Organometallics 2001, 20, 3629 (Mn). (b) Arduengo, A. J.; Tamm, M.;
McLain S. J.; Calabrese, J. C.; Davidson, F.; Marshall, W. J. J. Am. Chem.
Soc. 1994, 116, 7927 (Sm, Eu, Y). (c) Schumann, H.; Glanz, M.; Winterfeld,
J.; Kuhn, N.; Krantz, T. Chem. Ber. 1994, 127, 2369 (Sm, Yb). (d) Simms,
R. W.; Drewitt, M. J.; Baird, M. C. Organometallics 2002, 21, 2958 (Co).
(e) Baratta, W.; Herdtweck, E.; Herrmann, W. A.; Rigo, P.; Schwartz, J.
Organometallics 2002, 21, 2101 (Ru). (f) Baudry-Barbier, D.; Andre, N.;
Dormond, A.; Pardes, C.; Richard, P.; Visseaux, M.; Zhu, C. J. Eur. J.
Inorg. Chem. 1998, 1721 (Sm). (g) Dioumaev, V. K.; Szalda, D. J.; Hanson,
J.; Franz, J. A.; Bullock, R. M. Chem. Commun. 2003, 1670 (Mo). (h)
Abernethy, C. D.; Cowley, A. H.; Jones, R. A. J. Organomet. Chem. 2000,
596, 3 (Ni). (i) Niehues, M.; Erker, G.; Kehr, G.; Schwab, P.; Fro¨hlich, R.;
Blacque, O.; Berke, H. Organometallics 2002, 21, 2905 (Ti, Zr). (j)
Buchgraber, P.; Toupet, L.; Guerchais, V. Organometallics 2003, 22, 5144
(Fe). (k) Vogt, M.; Pons, V.; Heinekey, M. D. Organometallics 2005, 24,
1832 (Ir). (l) Jensen, V. R.; Angermund, K.; Jolly, P. W. Organometallics
2000, 19, 403 (Cr). (m) Abernethy, C. D.; Jason, A. C. Clyburne, J. A. C.;
Cowley, A. H.; Jones, R. A. J. Am. Chem. Soc. 1999, 121, 2329 (Ni, Cr).
(n) Huang, J.; Jafarpour, L.; Hillier, A. C.; Stevens, E. D.; Nolan, S. P.
Organometallics 2001, 20, 2878 (Ru). (o) Roy A.; Kelly, R. A.; Scott, N.
M.; Diez-Gonzalez, S.; Edwin D.; Stevens, E. D.; Nolan, S. P. Organo-
metallics 2005, 24, 3442 (Ni). (p) Fooladi, E.; Dalhus, B.; Tilset, M. Dalton
Trans. 2005, 3909 (Co, Rh). (q) Hanasaka, F.; Fujita, K.; Yamaguchi, R.
Organometallics 2004, 23, 1490 (Ir). (r) Hanasaka, F.; Fujita, K.; Yamagu-
chi, R. Organometallics 2005, 24, 3422 (Ir).
(8) Sloane C. S.; Weinberger, D. A.; Mirkin, C. A. Prog. Inorg. Chem.
1999, 48, 233.
(9) Deppner, M.; Burger, R.; Alt, H. G. J. Organomet. Chem. 2004, 689,
1194.
(10) Kukral, J.; Lehmus, P.; Leskela, M.; Rieger, B. Eur. J. Inorg. Chem.
2002, 1349.
(11) Other alkyl- or aryl-imidazoles react similarly.
(12) (a) Spectroscopic data for (IndH-NHC-H)Br: NMR (CDCl3), 1H:
δ, 10.13 (1H, s, imidazolium-H); 8.01 (1H, s, indene aromatic), 7.43-7.36
(3H, m, indene aromatic); 7.23-7.11 (5H, m, indene and DiPP aromatic);
6.99 (1H, s, backbone imidazolium); 6.48 (1H, s, backbone imidazolium);
5.10 (2H, t, J ) 6.5 Hz, imid-CH2CH2-ind); 3.30 (2H, t, J ) 6.5 Hz, imid-
CH2CH2-ind); 3.21 (2H, s, indenyl-CH2); 2.02 (2H, sept, J ) 7 Hz,
(CH3)2CH); 1.06 (6H, d, J ) 7 Hz, (CH3)2CH)); 0.97 (6H, d, J ) 7 Hz,
(CH3)2CH)). 13C{1H}: δ, 144.3, 143.1, 137.8, 137.1, 130.8, 127.2, 125.4,
124.3, 124.2, 123.6, 123.0, 122.8, and 118.0 (all aromatic), 48.1 (imid-
CH2CH2-ind), 37.1 (imid-CH2CH2-ind), 27.6 (CH3)2CH); 27.6(CH2), 23.1
((CH3)2CH). (b) Spectroscopic data for (FlH-NHC-H)Br: NMR, (CDCl3);
1H: δ, 10.45 (1H, s, imid-H); 7.75 (2H, d, J ) 7.5 Hz, fluorene) 7.63 (2H,
d, J ) 8.0 Hz, fluorene); 7.46 (1H, t, J ) 8.5 Hz, DiPP); 7.37 (2H, t, J )
7.5 Hz, fluorene); 7.29 (2H, d, J ) 7.5 Hz, fluorene); 7.23 (2H, d, J ) 8.0
Hz, DiPP); 7.16 (1H, s, backbone imidazolium); 6.90 (1H, s, backbone
imidazolium); 4.46 (2H, m, imid-CH2CH2-fl), 4.19 (1H, t, J ) 5.0 Hz,
fluorenyl-H); 2.9 (2H, m, 2H, m, imid-CH2CH2-fl); 2.15 (2H, sept, J ) 6.5
Hz, CH(CH3)2); 1.19 (6H, d, J ) 6.5 Hz, CH(CH3)2); 1.19 (6H, d, J ) 6.5
Hz, CH(CH3)2). 13C{1H}: δ, 145.2 (aromatic), 145.1 (aromatic), 141.0
(aromatic), 138.1 (imidazolium-CH), 131.8 (backbone imidazolium), 130.1
(aromatic), 127.7 (backbone imidazolium), 127.5 (aromatic) 124.8 (aro-
matic), 124.5 (aromatic), 123.6 (aromatic), 123.2 (aromatic), 120.1 (aro-
matic), 47.6 (imid-CH2CH2-fl), 44.9 (fluorenyl-CH) 33.9 (imid-CH2CH2-
fl), 28.5 (CH(CH3)2, 24.4 (CH(CH3)2, 24.2 (CH(CH3)2)2.
(5) (a) Jutzi, P.; Redeker, T. Eur. J. Inorg. Chem. 1998, 663. (b)
Butenscho¨n, H. Chem. ReV. 2000, 100, 1527. (c) Siemeling, U. Chem. ReV.
2000, 100, 1495. (d) Qian, Y.; Huang, J.; Bala, M. D.; Lian, B.; Zhang, H.;
Zhang, H. Chem. ReV. 2003, 103, 2633. (e) Mu¨ller, C.; Vos, D.; Jutzi, P.
J. Organomet. Chem. 2000, 600, 127.
10.1021/om051017z CCC: $33.50 © 2006 American Chemical Society
Publication on Web 02/11/2006

1338 Organometallics, Vol. 25, No. 6, 2006
Scheme 1. Synthesis of the Functionalized Imidazolium and N-Heterocyclic Carbene Ligandsa
Communications
a Reagents and conditions: (i) 1 equiv of DiPP-imidazole, dioxane 100° C, 24 h (50-61%); (ii) 1 equiv of KN(SiMe3)2, benzene, 12 h (55-
80%); (iii) 1 equiv of KN(SiMe3)2, benzene (50%).
were hampered by the lack of synthetic methods leading to pure
work and solvent effects. Heating of IndH-NHC or FlH-NHC
(60 °C, THF-d8, 8 h) results in the formation of equilibrium
mixtures with the corresponding tautomers Ind-NHC-H and
non-geminal-substituted â-haloethyltetramethylcyclopentadienes.13
Deprotonation of the bifunctional pro-ligands takes place in
two steps. With 1 equiv of KN(SiMe3)2 in benzene, deproton-
ation leads to crude, hydrocarbon-soluble NHCs functionalized
with neutral indene (IndH-NHC) or fluorene (FlH-NHC)
moieties; these carbenes can be easily separated from insoluble
potassium halides by filtration. Further deprotonation of the
crude neutral NHCs with 1 equiv of KN(SiMe3)2 in benzene
affords sparingly soluble indenide, (Ind-NHC)-K+, and fluo-
renide, (Fl-NHC)-K+, species, respectively, in good yields.14
Minor amounts of the benzene-soluble spiro hydrocarbon spiro-
(cyclopropane-1,9′-fluorene) were isolated as side product from
the deprotonation of FlH-NHC. The observed order of depro-
tonation of the C-H acidic groups in the new imidazolium salts
is the opposite of that expected based on the basicity of NHCs,
indenyl, and fluorenyl anions in DMSO.15 This discrepancy may
be related to the kinetic nature of the products isolated in this
1
Fl-NHC-H (by H NMR, see Supporting Information).
The structure of (Fl-NHC)-K+ was determined crystallo-
graphically.16 It comprises polymeric “zigzag” chains with
potassium atoms and bridging fluorenyl units. Two types of
alternating repeat units featuring potassium atoms with different
coordination spheres are observed and depicted in Figure 1a
and 1b.
Assuming that the longest K-fluorene interaction can be
estimated by the sum of the ionic radius of potassium and the
van der Waals radius of the carbon neighbor, the coordination
sphere of K in Figure 1a comprises two η4-phenyl rings that
sandwich the metal, while in Figure 1b there is one η2- and
one η4-phenyl ring; in both types the K coordination sphere is
completed by the tethered NHC group. The K-C (carbene)
distances (2.896-2.911 Å) are much shorter than those observed
previously (3.048 Å).17 The crystallographic C12 carbon deviates
slightly from planarity (angle sum 355-356°), while the angle
between the CNC plane and the K-C vector is in the range
22-24°.
Reaction of the imidazolium salts with Ag2O in dichloro-
methane18 gives the corresponding silver carbene complexes in
quantitative yields. The identity of the new complexes was
established by analytical and spectroscopic (NMR and mass
spectrometric) methods.19 We have been unable to grow X-ray-
quality crystals of the Ag complexes.
(13) There are reports in the patent literature claiming the synthesis of
nongeminal â-haloethyltetramethylcyclopentadienes by the reaction of
tetramethylcyclopentadienyllithium with 2-chloroethyl-p-toluenesulfonate
or 1-bromo-2-chloroethane in THF or ether, respectively. The second
method, giving a mixture of nongeminal and geminal isomers (variable
ratio), has been recently used for the synthesis of 1,2,3,4-tetramethylbicyclo-
[2.4]hepta-1,3-diene. McConell, A. C.; Pogorzelec, P. J.; Slawin, A. M.
Z.; Williams G. L.; Elliott, P. I. P.; Haynes, A.; Marr, A. C.; Cole-Hamilton,
D. J. Dalton Trans. 2006, 91, and references therein.
(14) (Fl-NHC)-K+. NMR (THF-d8), 1H: δ, 8.02 (2H, d, J ) 8 Hz,
fluorene H), 7.51 (1H, s, carbene backbone), 7.26 (3H, m, overlap. 1H
carbene backbone and 2H from fluorene), 7.12 (2 H, d, J ) 7 Hz, fluorene),
6.97 (3H, m, overlap; 1H from DiPP and 2H from fluorene), 6.58 (2H, m,
arom. of DiPP), 4.52 (2H, m, NCH2CH2-Fl), 3.67 (2H, m, Fl-CH2CH2),
2.33 (2H, sept, J ) 7 Hz, CH(CH3)2), 1.10 (6H, d, J ) 7 Hz, CH(CH3)2),
0.81 (6H, d, J ) 7 Hz, CH(CH3)2). 13C{1H}: δ, 206.9 (carbene C); 144.3,
136.2, 132.5, 126.2, 121.0, 120.5, 118.2, 117.5, 117.5, 116.7, 111.7 and
106.5 (all aromatic); 88.4 (fluorenyl C); 51.3 (Fl-CH2CH2N); 26.7 (Fl-
CH2CH2-N ); 25.6 (CH(CH3)2); 22.0 (CH(CH3)2); 21.10 (CH(CH3)2). (Ind-
NHC)-K+. NMR (pyridine-d5): 1H, δ, 7.82 (1H, d, J ) 8 Hz, indenyl);
7.72 (1H, d, J ) 8 Hz, indenyl); 7.46-7.43 (1H, m, indenyl); 7.32-7.20
(4H, m, overlapping DiPP and 1H indenyl); 6.98 (2H, m, indenyl); 6.75
(1H, s, carbene backbone); 6.48 (1H, s, carbene backbone); 4.45 (2H, m,
NCH2CH2-ind); 3.59 (2H, m, NCH2CH2-ind); 2.93 (2H, sept, J ) 7 Hz,
CH(CH3)2); 1.19 (6H, d, J ) 7 Hz, CH(CH3)2); 1.14 (6H, d, J ) 7 Hz,
CH(CH3)2).13C{1H}: δ, 211.0 (C, carbene); 147.5 (Ar); 130.2 (Ar); 129.9
(ArH); 129.5 (Ar); 128.3 (Ar); 126.6 (Ar); 125.0 (Ar); 120.8 (ArH); 120.6
(ArH); 120.1 (ArH); 117.3 (ArH); 113.9 (ArH); 104.9 (indenyl); 93.4 (Ind-
CH2CH2N); 55.6 (Ind-CH2CH2N); 32.6 (CH(CH3)2); 29.32 CH(CH3)2).
(15) (a) Alder R. W.; Allen, P. R.; Williams, S. J. Chem. Commun. 1995,
1267. (b) Kim, Y.-J.; Streitwieser, A. J. Am. Chem. Soc. 2002, 124, 5757.
(c) Filipponi, S.; Jones, J. N.; Johnson, J. A.; Cowley, A. H.; Grepioni, F.;
Braga, D. Chem. Commun. 2003, 2716.
(16) Compound (Fl-NHC)-K+ crystallized from benzene in the mono-
clinic space group P21/n with a ) 20.531(7) Å, b )13.027(4) Å c )
23.378(8) Å, â ) 92.220(5)°. V ) 6248(4) Å3 and Dcalcd ) 1.141 Mg m-3
for Z ) 4. Data were collected at 120(2) K on a Bruker-Nonius KappaCCD
diffractometer. Least-squares refinement of the model based on 6715 unique
reflections (Rint ) 11.36%) converged to a final R1 ) 6.62% (I > 2(I)) and
2
Rw ) 15.2%.
(17) Arnold, P. L.; Rodden, M.; Wilson, C. Chem Commun. 2005, 13,
1743.
(18) (a) Wang, H. M. J.; Lin, I. J. B. Organometallics 1998, 17, 972.
(b) Tulloch, A. A. D.; Danopoulos, A. A.; Winston, S.; Kleinhenz, S.;
Eastham, G. J. Chem. Soc., Dalton Trans. 2000, 449.

Communications
Organometallics, Vol. 25, No. 6, 2006 1339
Scheme 2. Synthesis of Ti(III) and V(III) Complexes
The structure of the molecule was determined crystallo-
graphically (Figure 2) and comprises one tetrahedral Ti(III)
center coordinated by the chelate fluorenyl-NHC (binding
through the fluorenyl and the NHC), one dimethylamido group,
and one chloride.20 This is the first example of a complex of a
cyclopentadienyl-type derivative with a pendant NHC.
Figure 1. ORTEP representation of the coordination sphere of K
in the two repeat units of the chain structure of (Fl-NHC)-K+ with
50% probability ellipsoids. H atoms are omitted for clarity. Selected
bond lengths (Å) and angles (deg) with estimated standard
deviations: C(1)-K(1) 2.896(5); C(7)-K(1) 2.941(5); C(8)-K(1)
3.014(5); C(48)-K(1) 3.244(5); C(12)-K(2) 2.911(5); C(20)-K(2)
3.177(5); C(21)-K(2) 3.018(5); C(22)-K(2) 3.029(5); C(23)-K(2)
3.142(5); C(24)-K(2) 3.252(5); C(25)-K(2) 3.287(5); N(2)-
C(1)-K(1) 127.7(3); N(1)-C(1)-K(1) 125.1(3); N(2)-C(1)-N(1)
102.6(4); N(4)-C(12)-K(2) 123.7(3); N(3)-C(12)-K(2)
130.5(3).
Figure 2. ORTEP representation of complex (Fl-NHC)Ti(NMe2)-
Cl showing 50% probability ellipsoids. H atoms are omitted for
clarity. Selected bond lengths (Å) and angles (deg) with estimated
standard deviations: C(3)-Ti(1) 2.221(2); N(1)-Ti(1) 1.984(2);
C(3)-N(2) 1.372(3); C(3)-N(3) 1.365(3); N(3)-C(3)-Ti(1)
123.49(14); N(2)-C(3)-Ti(1) 133.84(14).
The use of the new ligands in transition metal chemistry is
demonstrated by the following two examples. The reaction of
(Fl-NHC)-K+ with Ti(NMe2)2Cl2 in benzene gave, after
filtration and crystallization, the yellow-brown, air-sensitive,
crystalline paramagnetic complex (Fl-NHC)Ti(NMe2)Cl in low
yields (Scheme 2).
The Ti-C(fluorene) bond distances (Ti-C8 to C12 in the
range 2.383-2.471 Å) support a symmetrically coordinated η5-
fluorenyl ring; comparable metrical data, albeit with some slip
distortion, have been reported for the only other Ti(III) fluorenyl
complex that has been structurally characterized.21 The Ti-C
(NHC) (2.221 Å) is in the range observed previously (2.192-
2.210 Å).22 The exact mechanism of the reduction of the metal
center is not clear at present. It is plausible that the ligand acts
as a reducing agent, which is supported by the isolation from
the supernatant solution by fractional crystallization and crystal-
lographic characterization of the spiro imidazolium salt shown
(19) Fl-NHC-Ag-Br. NMR (CDCl3): 1H, δ, 7.80 (2H, m, Ar); 7.61 (2H,
m, Ar); 7.40 (5H, m, Ar); 7.22 (2H, d, J ) 8 Hz, Ar); 6.76 (1H, m, carbene
backbone); 6.70 (1H, m, carbene backbone); 3.82 (2H, m, N-CH2CH2-Fl);
2.82 (2H, m, N-CH2CH2-Fl); 2.25 (2H, septet, J ) 7 Hz, CH(CH3)2); 1.21
(6H, d, J ) 7 Hz, CH(CH3)2), 1.08 (6H, d, J ) 7 Hz, CH(CH3)2)).13C-
{1H}: δ, 145.6, 145.0, 141.7, 130.5, 127.8, 124.3, 124.2, 123.3, 120.9,
120.2 (all aromatic), 48.2 (Fl-CH2CH2N) 45.1 (CH, fluorene) 34.7 (Fl-
CH2CH2-N); 28.2 CH(CH3)2), 24.5 CH(CH3)2), 24.34 CH(CH3)2). MS
ES+: 947 [AgL2]+. Anal. Calcd for C30H32N2AgBr (%): C, 59.23, H, 5.30,
N, 4.60. Found: C, 59.36, H, 5.39, N, 4.50. Ind-NHC-Ag-Br. NMR
(CDCl3): 1H: δ, 7.42-7.13 (7H, m, aromatic); 6.95 (1H, s, carbene
backbone); 6.79 (1H, s, carbene backbone); 6.24 (1H, bs, indenyl H); 4.53
(2H, t, J ) 7 Hz, bridge); 3.30 (2H, s, indenyl CH2); 3.13 (2H, t, J ) 7 Hz,
bridge); 2.15 (2H, septet, J ) 7 Hz, isopropyl CH); 1.95 (6H, d, J ) 7 Hz,
isopropyl CH3), 0.98 (6H, d, J ) 7 Hz, isopropyl CH3). 13C{1H}: δ, 145.6,
144.7, 144.2, 139.4, 131.5, 130.5, 126.4, 125.2, 124.2 (all aromatic), 51.1
(CH2, bridge); 38.0 (CH2, bridge); 29.9 (CH2, indenyl); 28.2 (CH, isopropyl);
24.4 (CH3, isopropyl). MS ES+ (m/z): 847 [AgL2]+. Anal. Calcd for
C26H30N2AgBr (%): C, 55.43, H, 5.42 N, 5.02. Found: C, 55.90, H, 5.34,
N, 4.95.
(20) Compound (Fl-NHC)Ti(NMe2)Cl was crystallized from benzene
in the triclinic space group P1h with a ) 8.3495(6) Å, b ) 10.7139(13) Å,
c ) 16.8282(19) Å, R ) 73.535(9)°, â ) 86.508(7)°, γ ) 71.966(7)°, V )
1372.1(2) Å3, and Dcalcd ) 1.324 Mg m-3 for Z ) 2. Data were collected
at 120(2) K on a Bruker-Nonius KappaCCD diffractometer. Least-squares
refinement of the model based on 6276 unique reflections (Rint ) 4.11%)
2
converged to a final R1 ) 4.84% (I > 2(I)) and Rw ) 10.81%.
(21) Putzer, M. A.; Lachicotte, R. J.; Bazan, G. C. Inorg. Chem. Commun.
1999, 2, 319.
(22) Pugh, D.; Wright, J. A.; Freeman, S.; Danopoulos, A. A. Dalton
Trans. 2006, 775.

1340 Organometallics, Vol. 25, No. 6, 2006
Communications
Scheme 3. Organic Side-Product Formed during the
Preparation of (Fl-NHC)Ti(NMe2)Cl
in Scheme 3. Attempts to further elucidate the reduction
mechanism are under way.
Aminolysis of V(NMe2)4 by (IndH-NHC-H)Br in toluene
is also accompanied by reduction to V(III) (Scheme 2). The
red-brown crystalline product (Ind-NHC)V(NMe2)Br, isolated
in moderate yields, was shown by X-ray diffraction to have the
structure shown in Figure 3.23
The geometry around the metal center is distorted tetrahedral;
the Ind-NHC ligand is chelating through the five-membered ring
of the indenyl and the NHC groups. The V-C(carbene) and
V-amido bond lengths are in the range reported in the
literature.22,24 Inspection of the V-C(indenyl) distances shows
a slip distortion toward C8, C9, and C10 (∆ ) 0.114 Å).25 The
bridgehead C atoms of the indenyl ring are strictly planar,
indicating absence of strain in the chelate.
In conclusion, we have prepared the first class of imidazolium
salt pro-ligands and the NHCs derived therefrom with pendant
neutral or anionic indenyl and fluorenyl groups. We have also
demonstrated the potential of the new ligands with some early
transition metals, where a preferred chelate coordination mode
is adopted. The wide scope for electronic and steric tuning, the
possibility of hemilabile dynamic behavior, especially in
catalytic systems, and the support of homo- or hetero-bimetallic
Figure 3. ORTEP representation of complex (Ind-NHC)V(NMe2)-
Br showing 50% probability ellipsoids. H atoms are omitted for
clarity. Selected bond lengths (Å) and angles (deg) with estimated
standard deviations: V(1)-N(1) 1.885(3); V(1)-C(3) 2.185(3);
N(3)-C(3)1.363(4); N(2)-C(3) 1.388(4); N(3)-C(3)-N(2) 103.5(3);
N(2)-C(3)-V(1) 132.0(2); N(3)-C(3)-N(2) 103.5(3).
complexes, when the ligands act as bridging, are some attractive
features that are now being explored in our group. Last, the
development of new water- and ionic-liquid-compatible com-
plexes or chiral designs is another future path of development.
Acknowledgment. We thank M. B. Hursthouse for the
provision of X-ray facilities, W. Clegg at the EPSRC single
crystal synchrotron service at Daresbury for data collection of
(Fl-NHC)-K+, and Dr. J. A. Wright for assistance in solving
the crystal structure of (Fl-NHC)-K+.
(23) Compound V(Ind-NHC)(NMe2)(Br) was crystallized from THF/
toluene in the triclinic space group P1h with a ) 8.208(4) Å, b ) 9.877(6)
Å, c ) 17.305(10) Å, R ) 100.63(8)°, â ) 97.83(4)°, γ ) 105.38(5)°, V
) 1303.8(13) Å3, and Dcalcd ) 1.387 Mg m-3 for Z ) 2. Data were collected
at 120(2) K on a Bruker-Nonius KappaCCD diffractometer. Least-squares
refinement of the model based on 5819 unique reflections (Rint ) 7.00%)
Supporting Information Available: Experimental methods for
the preparation and characterization of the new compounds. Full
details of the X-ray crystal structures, including complete tables of
crystal data, atomic coordinates, bond lengths and angles, and
positional and anisotropic thermal parameters. This material is
available free of charge via the Internet at http://pubs.acs.org.
2
converged to a final R1 ) 5.34% (I > 2(I)) and Rw ) 8.75%.
(24) Haaland, A.; Rypdal, K.; Volden, H. V.; Andersen, R. A. J. Chem.
Soc., Dalton Trans. 1992, 891.
(25) Faller, J. W.; Crabtree, R. H.; Habib, A. Organometallics 1985, 4,
929.
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