Synthesis of 1,2-cyclopentadienyl diimine anions and their zirconium complexes

Article abstract of DOI:10.1021/om980409l

1,2-disubstituted cyclopentadienyl diimine anions are examples of extended π-systems that bind metals through the nitrogen atoms. Reaction of Cp₂Mg with benzonitrile gives the product (1,2-C₅H₃(C(Ph)NH)₂)CpMg(NCPh) (1) in 98% yield. In an analogous manner, the related complexes (1,2-C₅H₃)(C(Ph)NH₂)CpMg(OEt₂) (2) and ((4-Me₃SiC₅H₂)(1,2-(C(Ph)NH) ₂)(Me₃-SiC₅H₄Mg(OEt₂) (3) were prepared in situ. Demetalation of these complexes 1-d yields fhe corresponding free diimine ligands of formulation H[(1,2-C₅H₃(C(Ph)NH)₂)] (4) and H[4-Me₃SiC₅H₂-1,2-(C(Ph)NH)₂] (5). Hydrolysis of compound 4 leads to the fulvene derivative 1-(C(OH)Ph)-2-(O=C(Ph))C₅H₃ (6). The zirconium complexes (C₅H₃-1,2(C(Ph)NH)₂)-ZrCl₃(THF) (7) and (C₅H₃-1,2-(C(Ph)NH)₂)₃ZrCl (8) were isolated from reactions of 4 with ZrCl₄(THF)₂ X-ray crystallographic studies of 1, 7, and 8 are reported. Evidence suggests that these new 1,2-disubstituted cyclopentadienyl diimine anions impart some charge delocalization, thus offering a new approach to electronic metal centers. This view is supported by EHMO calculations.

Full text of DOI:10.1021/om980409l

3656
Organometallics 1998, 17, 3656-3660
Syn th esis of 1,2-Cyclop en ta d ien yl Diim in e An ion s a n d
Th eir Zir con iu m Com p lexes
Nola Etkin,† Christopher M. Ong, and Douglas W. Stephan*
Department of Chemistry and Biochemistry, University of Windsor,
Windsor, Ontario, Canada N9B 3P4
Received May 21, 1998
1,2-disubstituted cyclopentadienyl diimine anions are examples of extended π-systems that
bind metals through the nitrogen atoms. Reaction of Cp2Mg with benzonitrile gives the
product (1,2-C5H3(C(Ph)NH)2)CpMg(NCPh) (1) in 98% yield. In an analogous manner, the
related complexes (1,2-C5H3(C(Ph)NH)2)CpMg(OEt2)(2)and ((4-Me3SiC5H2)(1,2-(C(Ph)NH)2)(Me3-
SiC5H4)Mg(OEt2) (3) were prepared in situ. Demetalation of these complexes 1-3 yields
the corresponding free diimine ligands of formulation H[(1,2-C5H3(C(Ph)NH)2)] (4) and H[4-
Me3SiC5H2-1,2-(C(Ph)NH)2] (5). Hydrolysis of compound 4 leads to the fulvene derivative
1-(C(OH)Ph)-2-(OdC(Ph))C5H3 (6). The zirconium complexes (C5H3-1,2-(C(Ph)NH)2)-
ZrCl3(THF) (7) and (C5H3-1,2-(C(Ph)NH)2)3ZrCl (8) were isolated from reactions of 4 with
ZrCl4(THF)2. X-ray crystallographic studies of 1, 7, and 8 are reported. Evidence suggests
that these new 1,2-disubstituted cyclopentadienyl diimine anions impart some charge
delocalization, thus offering a new approach to electrophilic metal centers. This view is
supported by EHMO calculations.
In tr od u ction
among those recently explored. In our own efforts to
develop new early-metal systems, we have uncovered a
convenient synthesis of 1,2-disubstituted cyclopentadi-
enyl derivatives, an elusive class of cyclopentadienyl
ligands.17-21 Specifically, the synthesis of 1,2-disubsti-
tuted cyclopentadienyl diimine ligands and the Zr com-
plexes thereof are described. These ligands, which bind
via the imine nitrogen atoms, are anionic analogues of
classic, chelating Schiff bases. Whereas related ligands
have a rich, well-established late-transition-metal chem-
istry, the use of such ligands in early-transition-metal
chemistry has only received limited attention.22
The chemical landscape of early-transition-metal
chemistry has undergone dramatic growth over the past
few years. Much effort has focused on metallocenes
and on the preparation of various related species. For
example, a large variety of substituted cyclopentadienyl
ligands have been utilized to mediate the steric or
electronic character of the resulting metal complexes.1,2
A second approach to controlling metal atom environ-
ments involves the development of systems incorporat-
ing alternative ancillary ligands. Early-metal systems
using ligands traditionally reserved for later transition
metals, such as bulky aryloxide,3 amide,4,5 or carbodi-
iminate ligands,6 porphyrins,7-14 or calixarenes,15,16 are
Exp er im en ta l Section
Gen er a l Da ta . All preparations were done under an
atmosphere of dry, O2-free N2 employing either Schlenk line
techniques or a Vacuum Atmospheres or Innovative Technolo-
gies inert-atmosphere glovebox. Solvents were reagent grade,
distilled from the appropriate drying agents under N2 and
degassed by the freeze-thaw method at least three times
prior to use. All organic reagents were purified by conven-
tional methods. 1H and 13C{1H} NMR spectra were recorded
on Bruker Avance 300 and 500 MHz spectrometers. Trace
amounts of protonated solvents were used as references, and
chemical shifts are reported relative to SiMe4. Combustion
analyses were performed by E+R Microanalytical Labor-
† Present address: Department of Chemistry, University of Prince
Edward Island, Charlottetown, PEI, Canada C1A 4P3.
(1) Okuda, J . Top. Curr. Chem. 1992, 160, 97.
(2) J aniak, C.; Schumann, H. Adv. Organomet. Chem. 1991, 33,
291.
(3) Firth, A. V.; Stephan, D. W. Organometallics 1997, 16, 2183.
(4) Tayebani, M.; Feghali, K.; Gambarotta, S.; Bensimon, C. Orga-
nometallics 1997, 16, 5084.
(5) Moore, M.; Gambarotta, S.; Bensimon, C. Organometallics 1997,
16, 1086.
(6) Dawson, D. Y.; Arnold, J . Organometallics 1997, 16, 1111.
(7) Arnold, J . J . Chem. Soc., Chem. Commun. 1990, 976.
(8) Berreau, L. M.; Hays, A.; Young, J . V. G.; Woo, L. K. Inorg. Chem.
1994, 33, 105.
(9) Berreau, L. M.; Young, J . V. G.; Woo, L. K. Inorg. Chem. 1995,
34, 527.
(10) Brand, H.; Arnold, J . Organometallics 1993, 12, 3655.
(11) Brand, H.; Capriotti, J . A.; Arnold, J . Organometallics 1994,
13, 4469.
(12) J acoby, D.; Isoz, S.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J .
Am. Chem. Soc. 1995, 117, 2793.
(13) J acoby, D. I. S.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J . Am.
Chem. Soc. 1995, 117, 2805.
(14) Woo, L. K.; Hays, J . A.; J acobson, R. A.; Day, C. L. Organome-
tallics 1991, 10, 2102.
(15) Giannini, L.; Caselli, A.; Solari, E.; Floriani, C.; Chiesi-Villa,
A.; Rizzoli, C.; Re, N.; Sgamellotti, A. J . Am. Chem. Soc. 1997, 119,
998.
(16) Giannini, L.; Caselli, A.; Solari, E.; Floriani, C.; Cheisi-Villa,
A.; Rizzoli, C.; Re, N.; Sgamellotti, A. J . Am. Chem. Soc. 1997, 119,
9709.
(17) Hughes, R. P.; Kowalski, A. S.; Lomprey, J . R. Organometallics
1994, 13, 2691.
(18) Hughes, R. P.; Lomprey, J . R.; Rheingold, A. L.; Yap, G. J .
Organomet. Chem. 1996, 517, 63.
(19) Hughes, R. P.; Lomprey, J . R.; Rheingold, A. L.; Haggerty, B.
S.; Yap, G. J . Organomet. Chem. 1996, 517, 89.
(20) Little, W., F.; Koestler, R. C. J . Chem. Soc. 1961, 3245.
(21) Lappert, M. F.; Liu, D. S. J . Organomet. Chem. 1995, 500, 203.
(22) Martin, A.; Uhrhammer, R.; Gardner, T. G.; J ordan, R. F.;
Rogers, R. D. Organometallics 1998, 17, 382.
S0276-7333(98)00409-9 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 07/21/1998

Zr Complexes of 1,2-Cyclopentadienyl Diimine Anions
Organometallics, Vol. 17, No. 17, 1998 3657
Ta ble 1. Cr ysta llogr a p h ic P a r a m eter s
1
4
7
8
formula
fw
cryst size
a (Å)
b (Å)
c (Å)
C
37H31MgN3
C19H16N2
272.34
C23H23Cl3ON2Zr
541.03
0.30 × 0.25 × 0.18
10.316(3)
13.812(2)
8.805(2)
97.29(2)
94.54(2)
97.02(2)
triclinic
P1h
C57H45ClN6Zr
940.66
541.96
0.50 × 0.30 × 0.30
8.0498(13)
13.014(3)
16.376(4)
111.81(2)
101.55(2)
91.15(2)
triclinic
P1h
1552.1(6)
1.16
2
0.860
6803
0.40 × 0.40 × 0.30
0.20 × 0.18 × 0.16
13.258 70(10)
16.1031(4)
12.3010(3)
23.9529(5)
16.8857(2)
R (deg)
â (deg)
γ (deg)
cryst syst
space group
V (Å3)
92.4690(10)
tetragonal
I41cd
2968.39(5)
1.22
monoclinic
P21/n
4740.3(2)
1.32
4
3.33
6970
5092
586
1229.4(5)
1.46
Dcalcd (g cm-1
Z
)
8
2
7.89
4700
2643
271
n/a
5.80
abs coeff, µ, cm-1
0.072
4847
763
96
n/a
no. of data collected
2
2
no. of data Fo > 3σ(Fo
)
5904
415
0.966-1.255
5.80
no. of variables
transmissn factors
R (%)
0.850-1.120
5.34
8.95
Rw (%)
goodness of fit
16.15
1.132
26.70
1.081
5.90
2.710
10.51
1,101
atory Inc., Corona, NY. Cp2Mg was prepared via literature
methods. All other reagents were purchased from the Aldrich
Chemical Co.
Syn th esis of 1-(C(OH)P h )-2-(OdC(P h ))C5H3) (6).20 To
a solution of compound 4 (0.126 g, 0.46 mmol) in THF (5 mL)
was added 5 mL of 10% aqueous HCl under nitrogen. The
solution was stirred for 1 h. Addition of THF was followed by
separation of the organic layer, which was dried over MgSO4
overnight. The mixture was filtered and the solvent removed,
giving 6 in 62% yield. Spectroscopic data were in agreement
with literature data. 1H NMR (C6D6, 25 °C): δ 7.70 (4H, d,
|J H-H| ) 4.6 Hz), 7.61 (4H, t, |J H-H| ) 4.4 Hz), 7.48 (2H, t,
|J H-H| ) 4.4 Hz), 6.89 (2H, d, |J H-H| ) 2.2 Hz), 6.27 (1H, t,
|J H-H| ) 2.2 Hz), 5.58 (1h, br s). 13C{1H} NMR (C6D6, 25 °C):
δ 171.5, 138.6, 135.9, 133.7, 131.9, 128.5, 121.1, 120.5.
Syn th esis of (1,2-C5H3(C(P h )NH)2)Cp Mg(NCP h ) (1). To
a solution of Cp2Mg (0.930 g, 0.60 mmol) in 4 mL of ether was
added benzonitrile (0.252 g, 2.45 mmol). The reaction mixture
was stirred for 10 h, and the solvent was removed under
vacuum. Recrystallization of the product from benzene af-
forded 1 as orange crystals (yield 98%). 1H NMR (C6D6, 25
°C): δ 7.47 (2H, s), 7.44 (4H, d, |J H-H| ) 1.7 Hz), 7.07-7.00
(6H, m), 6.74-6.68 (5H, m), 6.64 (2H, d, |J H-H| ) 3.8 Hz), 6.62
(5H, s), 6.35 (1H, t, |J H-H| ) 3.7 Hz). 13C{1H} NMR (C6D6, 25
°C): δ 178.1, 146.8, 133.5, 133.0, 129.3, 128.9, 128.6, 121.1,
Gen er a tion of (C5H3(1,2-C(P h )NH)2)Zr Cl3(THF ) (7) a n d
(1,2-C5H3(C(P h )NH)2)3Zr Cl (8). To solutions of varying
amounts of 4 in benzene (5 mL) was added sodamide, and the
mixture was stirred for 3 h. ZrCl4(THF)2 was added and
stirring continued for an additional 10 h. NMR data revealed
a mixture of species dependent on stoichiometry. Use of 4
(0.100 g, 0.367 mmol) and ZrCl4(THF)2 (0.198 g, 0.525 mmol)
gave predominantly 7 in solution, whereas use of 4 (0.050 g,
0.183 mmol) and ZrCl4(THF)2 (0.198 g, 0.525 mmol) gave
predominantly 8 in solution. Attempts to isolate material led
to an inseparable mixture of products; nonetheless, X-ray-
quality crystals of 7 and 8 were obtained from these mixtures.
7: 1H NMR (C6D6, 25 °C) δ 8.32 (2H,s), 7.37 (4H, d, |J H-H| )
4.5 Hz), 7.02-7.06 (4H, m), 6.95 (2H, t, |J H-H| ) 4.5 Hz), 6.69
(2H, d, |J H-H| ) 2.2 Hz), 6.28 (1H, t, |J H-H| ) 2.2 Hz), 3.86
(4H, br m), 0.76 (4H, br m); 13C{1H} NMR (C6D6, 25 °C) δ 175.9,
143.0, 140.0, 130.4, 129.6, 123.8, 119.6, 119.4, 69.2, 25.2. 8:
orange crystals, yield 76%; 1H NMR (C6D6, 25 °C) δ 9.58 (2H,
s), 7.30 (4H, d, |J H-H| ) 7.4 Hz), 6.85-7.00 (6H, m), 6.77 (2H,
d, |J H-H| ) 3.5 Hz), 6.39 (1H, t, |J H-H| ) 3.5 Hz); 13C{1H} NMR
(C6D6, 25 °C) δ 175.3, 144.1, 138.8, 130.0, 129.6, 122.9, 120.2,
119.6.
120.2, 118.8, 113.7, 109.8, 105.8. Anal. Calcd for C31H24
MgN3: C, 80.44; H, 5.23; N, 9.08. Found: C, 79.99; H, 5.69;
N, 8.78.
-
Syn th esis of (1,2-C5H3(C(P h )NH)2)CpMg(OEt2) (2). This
compound was prepared as for 1 using a benzonitrile:Cp2Mg
ratio of 2.5:1. Yield: 95%. 1H NMR (C6D6, 25 °C): δ 7.44-
7.41 (6H, m), 7.12-7.08 (6H, m), 6.61 (2H, d, |J H-H| ) 3.8 Hz),
6.38-6.34 (6H, m), 3.10 (4H, q, |J H-H| ) 7.02), 0.77 (6H, t,
|J H-H| ) 6.3). 13C{1H} NMR (C6D6, 25 °C): δ 77.8, 146.7, 134.1,
129.3, 128.8, 120.8, 119.5, 114.4, 105.5, 64.7, 14.1. Anal. Calcd
for C28H28MgON2: C, 77.70; H, 6.52; N, 6.47. Found: C, 77.14;
H, 6.74; N, 6.77.
Syn th esis of H[1,2-C5H3(C(P h )NH)2] (4). (i) Compound
1 (0.800 g, 0.17 mmol) was dissolved in benzene and chro-
matographed on an neutral alumina column with benzene
elution. This afforded 4 in 92% yield.
(ii) Compound 2 (0.40 g, 0.09 mmol) was dissolved in 5 mL
of ether, and methanol was added (0.17 g, 0.55 mmol). The
mixture was stirred for 1 h. Addition of ether, filtration, and
solvent removal afforded the white solid 4 in 89% yield. 1H
NMR (C6D6, 25 °C): δ 14.96 (1H, s), 7.30 (4H, d, |J H-H| ) 7.0
Hz), 7.01-7.07 (6H, m), 6.84 (2H, d, |J H-H| ) 3.7 Hz), 6.71
(2H, s), 6.47 (1H, t, |J H-H| ) 3.7 Hz). 13C{1H} NMR (C6D6, 25
°C): δ 69.8, 142.4, 135.1, 128.4, 128.1, 122.3, 120.1, 118.7.
Anal. Calcd for C19H15N2: C, 84.10; H, 5.57; N,10.32. Found:
C, 84.01; H, 5.96; N, 10.57.
Syn th esis of H[4-Me3SiC5H2-1,2-(C(P h )NH)2] (5). This
compound was prepared following methods used to prepare 4
with the use of (Me3SiC5H4)2Mg as the starting material. 1H
NMR (C6D6, 25 °C): δ 15.0 (1H, s), 7.75 (4H, d, |J H-H| ) 29.4
Hz), 7.42 (2H, s), 6.78-6.92 (6H, m), 6.56 (2H, s), 0.40 (9H, s).
13C{1H} NMR (C6D6, 25 °C): δ 173.6, 146.1, 138.8, 135.7, 133.5,
132.9, 126.0, 122.3, 5.2. Anal. Calcd for C22H23N2Si: C, 76.92;
H, 6.75; N, 8.15. Found: C, 76.89; H, 6.70; N, 8.11.
Molecu la r Or bita l Ca lcu la tion s. Extended Huckel cal-
culations were performed and visualized employing the Per-
sonal Cache Software Package operating on a Pentium 166
computer. Initial coordinates and geometric parameters were
derived from
geometry.
a molecular mechanics optimization of the
X-r a y Da ta Collection a n d Red u ction . X-ray-quality
crystals of 1, 4, 7, and 8 were obtained directly from the
preparation as described above. The crystals were manipu-
lated and mounted in capillaries in a glovebox, thus maintain-
ing a dry, O2-free environment for each crystal. Diffraction
experiments were performed on a Siemens SMART System
CCD diffractometer collecting a hemisphere of data in 1329

3658 Organometallics, Vol. 17, No. 17, 1998
Etkin et al.
Sch em e 1
frames with 10 s exposure times. Crystal data are sum-
marized in Table 1. The observed extinctions were consistent
with the space groups in each case. The data sets were
collected (4.5° < 2θ < 50.0°). A measure of decay was obtained
by recollecting the first 50 frames of each data set. The
intensities of reflections within these frames showed no
statistically significant change over the duration of the data
collections. The data were processed using the SAINT and
XPREP processing packages. An empirical absorption correc-
tion based on redundant data was applied to each data set.
Subsequent solution and refinement was performed using the
SHELXTL solution package operating on a SGI Indy computer.
The reflections with Fo2 > 3σFo2 were used in the refinements.
Str u ctu r e Solu tion a n d Refin em en t. Non-hydrogen
atomic scattering factors were taken from the literature
tabulations. The heavy-atom positions were determined using
direct methods, employing the SHELXTL direct methods
routines. The remaining non-hydrogen atoms were located
from successive difference Fourier map calculations. The
refinements were carried out by using full-matrix least-squares
techniques on F, minimizing the function w(|Fo| - |Fc|)2, where
the weight w is defined as 4Fo2/2σ(Fo2) and Fo and Fc are the
observed and calculated structure factor amplitudes. In the
final cycles of each refinement, all non-hydrogen atoms were
assigned anisotropic temperature factors. Carbon-bound hy-
drogen atom positions were calculated and allowed to ride on
the carbon to which they were bonded, assuming a C-H bond
length of 0.95 Å. Hydrogen atom temperature factors were
fixed at 1.10 times the isotropic temperature factor of the
carbon atom to which they were bonded. The hydrogen atom
contributions were calculated but not refined. The final values
of R, Rw, and the goodness of fit in the final cycles of the
refinements are given in Table 1. The locations of the largest
peaks in the final difference Fourier map calculation as well
as the magnitude of the residual electron densities in each case
were of no chemical significance. Positional parameters,
hydrogen atom parameters, thermal parameters, and bond
distances and angles have been deposited as Supporting
Information.
F igu r e 1. ORTEP drawing of 1; 30% thermal ellipsoids
are shown. Bond distances and angles are as follows: Mg-
N(1) ) 2.055(2) Å, Mg-N(2) ) 2.046(2) Å, Mg-N(3) )
2.152(2) Å, Mg-C(1) ) 2.384(2) Å, Mg-C(2) ) 2.433(2) Å,
Mg-C(3) ) 2.483(2) Å, Mg-C(4) ) 2.479(2) Å, Mg-C(5) )
2.423(2) Å, N(1)-C(6) ) 1.302(2) Å, N(2)-C(7) ) 1.306(2)
Å, N(3)-C(8) ) 1.133(3) Å; N(2)-Mg-N(1) ) 94.97(7)°,
N(2)-Mg-N(3) ) 97.07(8)°, N(1)-Mg-N(3) ) 96.25(8)°,
C(6)-N(1)-Mg ) 129.74(13)°, C(7)-N(2)-Mg ) 130.27-
(13)°, C(8)-N(3)-Mg ) 172.4(2)°.
group remains unaltered, while the other is 1,2-disub-
stituted. The 1H NMR resonance at 6.1 ppm infer
nitrile reduction to imino-NH groups. The formulation
of complex 1 was unambiguously determined to be (1,2-
C5H3(C(Ph)NH)2)CpMg(NCPh) via X-ray crystallogra-
phy (Figure 1). The pseudo-tetrahedral coordination
sphere about Mg in 1 is comprised of an η5-cyclopenta-
dienyl group, two nitrogen donors of the newly formed
monoanionic 1,2-cyclopentadienyl diimine ligand, and
a coordinated molecule of benzonitrile. Within the
diimine anionic ligand, the cyclopentadienyl ring and
the CN moieties are essentially planar. The extended
π-system is consistent with C-N distances of 1.304(2)
Å and C(Cp)-C(CN) distances of 1.436(2) Å. Some
degree of C-N bond order reduction, as well as steric
crowding, accounts for the pseudo-pyramidal geometry
about N. The phenyl groups on the imino carbon are
approximately orthogonal to the plane of the ligand,
presumably a further consequence of steric demands.
In an analogous manner, the related complex (1,2-
C5H3(C(Ph)NH)2)CpMg(OEt2) (2) is readily obtained via
reaction of Cp2Mg and 2 equiv of benzonitrile in diethyl
ether (Scheme 1). Demetalation of the complexes 1 and
2 and isolation of the corresponding free diimine ligands
is readily accomplished via chromatography on alumina
with benzene elution. Alternatively, treatment of 1 with
6 equiv of methanol in benzene solution affords 4. This
Resu lts a n d Discu ssion
1
Reaction of Cp2Mg with 4-5 equiv of benzonitrile
proceeds rapidly and easily in benzene to yield an
orange solution. Upon concentration of the solution and
standing, orange crystals of the product 1 were obtained
in 98% yield. NMR data for 1 were consistent with the
incorporation of 3 equiv of benzonitrile (Scheme 1).
Integration data suggested that one cyclopentadienyl
species exhibits H NMR resonances, including peaks
at 6.1 and 14.9 ppm, attributed to imino NH hydrogens.
The lower field resonance infers N-H-N hydrogen
bonding. This and the cyclopentadienyl proton reso-
nances suggest the zwitterionic formulation H[1,2-C5H3-
(C(Ph)NH)2] for 4. This notion was confirmed crystal-
lographically. The molecule 4 is planar and 2-fold

Zr Complexes of 1,2-Cyclopentadienyl Diimine Anions
Organometallics, Vol. 17, No. 17, 1998 3659
F igu r e 2. ORTEP drawing of 4; 30% thermal ellipsoids
are shown.
Ch a r t 1
F igu r e 4. ORTEP drawing of 8; 30% thermal ellipsoids
are shown. Bond distances and angles are as follows: Zr-
N(1) ) 2.257(3) Å, Zr-N(2) ) 2.218(3) Å, Zr-N(3) ) 2.237-
(3) Å, Zr-N(4) ) 2.225(3) Å, Zr-N(5) ) 2.218(3) Å, Zr-
N(6) ) 2.235(3) Å, Zr-Cl ) 2.6163(11) Å, N(1)-C(1) )
1.327(5) Å, N(2)-C(2) ) 1.325(5) Å, N(3)-C(3) ) 1.312(5)
Å, N(4)-C(4) ) 1.320(5) Å, N(5)-C(5) ) 1.338(5) Å, N(6)-
C(6) ) 1.317(5) Å; N(2)-Zr-N(5) ) 113.52(12)°, N(2)-Zr-
N(4) ) 118.01(12)°, N(5)-Zr-N(4) ) 108.48(12)°, N(2)-
Zr-N(6) ) 150.70(12)°, N(5)-Zr-N(6) ) 80.15(12)°, N(4)-
Zr-N(6) ) 78.16(12)°, N(2)-Zr-N(3) ) 78.27(12)°, N(5)-
Zr-N(3) ) 157.42(12)°, N(4)-Zr-N(3) ) 79.88(12)°, N(6)-
Zr-N(3) ) 81.22(12)°, N(2)-Zr-N(1) ) 78.81(12)°, N(5)-
Zr-N(1) ) 80.51(12)°, N(4)-Zr-N(1) ) 152.74(12)°, N(6)-
Zr-N(1) ) 78.20(12)°, N(3)-Zr-N(1) ) 83.28(12)°, N(2)-
Zr-Cl 74.14(9)°, N(5)-Zr-Cl ) 74.92(9)°, N(4)-Zr-Cl )
75.32(9)°, N(6)-Zr-Cl ) 135.15(9)°, N(3)-Zr-Cl ) 127.64-
(9)°, N(1)-Zr-Cl ) 131.74(9)°, C(1)-N(1)-Zr ) 140.8(3)°,
C(2)-N(2)-Zr ) 143.6(3)°, C(3)-N(3)-Zr ) 141.5(3)°,
C(4)-N(4)-Zr ) 142.3(3)°, C(5)-N(5)-Zr ) 143.9(3)°,
C(6)-N(6)-Zr ) 142.5(3)°.
magnesium with subsequent attack of the nitrile carbon
by a cyclopentadienyl ligand and H atom migration to
nitrogen. It is presumably the template effect of the
Mg center that mediates or encourages 1,2-substitution,
although the mechanistic details of these reactions have
not been investigated as yet.
Hydrolysis of compound 4 leads to the fulvene deriva-
tive 1-(C(OH)Ph)-2-(OdC(Ph))C5H3 (6)20 (Scheme 1).
This is achieved via addition of 10% aqueous HCl to a
THF solution of 4 or 5 followed by typical organic
extraction and drying over MgSO4, filtration, and
solvent removal. Compounds 4-6 represent rare ex-
amples of 1,2-disubstituted cyclopentadienyl derivatives.
Certainly, the ease of these preparations is unprec-
edented, as the syntheses of related 1,2-disubstituted
species are more arduous.17,20
Zirconium complexes of 4 were targeted in reactions
of the diimine with 3 equiv of sodamide and varying
stoichiometric amounts of ZrCl4(THF)2 in benzene.
Monitoring these reactions via NMR spectroscopy in-
ferred the presence of mixtures of products, presumably
arising from varying degrees of ligand substitution. In
the presence of 1.5 equiv of ZrCl4(THF)2, NMR data
showed the preponderance of a species characterized by
F igu r e 3. ORTEP drawing of 7; 30% thermal ellipsoids
are shown. Bond distances and angles are as follows:
Zr(1)-Cl(2) ) 2.425(3) Å, Zr(1)-Cl(3) ) 2.429(3) Å, Zr(1)-
Cl(5) ) 2.379(3) Å, Zr(1)-O(1) ) 2.237(7) Å, Zr(1)-N(1) )
2.198(9) Å, Zr(1)-N(2) ) 2.182(7) Å; Cl(2)-Zr(1)-Cl(3) )
99.8(1)°, Cl(2)-Zr(1)-Cl(5) ) 94.8(1)°, Cl(2)-Zr(1)-O(1) )
84.6(2)°, Cl(2)-Zr(1)-N(1) ) 87.0(2)°, Cl(2)-Zr(1)-N(2) )
164.3(2)°, Cl(3)-Zr(1)-Cl(5) ) 96.6(1)°, Cl(3)-Zr(1)-O(1)
) 87.7(2)°, Cl(3)-Zr(1)-N(1) ) 170.2(2)°, Cl(3)-Zr(1)-N(2)
) 90.4(2)°, Cl(5)-Zr(1)-O(1) ) 175.6(2)°, Cl(5)-Zr(1)-N(1)
) 89.8(2)°, Cl(5)-Zr(1)-N(2) ) 95.8(2)°, O(1)-Zr(1)-N(1)
) 85.9(3)°, O(1)-Zr(1)-N(2) ) 84.0(3)°, N(1)-Zr(1)-N(2)
) 81.6(3)°.
symmetric in the solid state, with one hydrogen atom
bridging the two nitrogen atoms (Figure 2). Metric
parameters within 4 are unexceptional.
The similar reaction of (Me3SiC5H4)2Mg with 2 equiv
of benzonitrile in diethyl ether generates ((4-Me3-
SiC5H2)(1,2-(C(Ph)NH)2)(Me3SiC5H4)Mg(OEt2) (3) in situ.
Subsequent methanolysis of 3 affords the species H[4-
Me3SiC5H2-1,2-(C(Ph)NH)2] (5) in 80% yield. Mecha-
nistically, the formation of these complexes 1-3 is
thought to be initiated via coordination of nitrile to

3660 Organometallics, Vol. 17, No. 17, 1998
Etkin et al.
8. Each of these diimine chelates in 8 offers one nitro-
gen donor that forms Cl-Zr-N angles of 74.14(9)-
75.32(9)° while the remaining nitrogen atoms give
rise to N-Zr-Cl angles of 127.64(9)-135.15(9)°. The
Zr-Cl distance of 2.6163(11) Å in 8 is dramatically
longer than the typical values seen in 7 (Zr-Cl ) 2.427-
(3) Å), also consistent with the steric congestion of the
seven-coordinate Zr center. It is noteworthy that efforts
to specifically prepare the L2ZrCl2 complex were unsuc-
cessful. Rather, mixtures of 7 and 8 were observed at
all intermediate stoichiometries of ligand to metal. It
may be that the lack of substitution on N facilitates
ligand redistribution. Related monoanions which present
a sterically encumbering coordination sphere are the
subject of current synthetic efforts.
The 1,2-disubstituted cyclopentadienyl diimine anions
are extended planar π-systems, which bind to a metal
center via the nitrogen atoms. Computation of the
frontier orbitals of the model (1,2-C5H3(C(H)NH)2)ZrCl3-
(THF) by extended Huckel methods reveal that the
HOMO is essentially π-orbitals centered on the cyclo-
pentadienyl group, while the LUMO is largely a vacant
metal-based d orbital (Figure 5). Thus, the bonding
mode provides an avenue for formal charge separation
and thus imparts electrophilic character to the zirco-
nium. Such Lewis acidity is further exemplified by the
seven-coordinate metal center in 8.
F igu r e 5. (a) HOMO and (b) LUMO of the model com-
pound (1,2-C5H3(C(H)NH)2)ZrCl3(THF).
a single 1H NMR resonance at 8.32 ppm attributable
to the imino NH protons, while the 1:1 integral ratio of
diimine ligand and coordinated THF were consistent
with the formulation of 7 as (1,2-C5H3(C(Ph)NH)2)ZrCl3-
(THF) (7) (Chart 1). X-ray-quality orange crystals of 7
were separated from the mixture of solid products.
Crystallographic data affirm that 7 is a pseudo-
octahedral complex in which the diimine ligand binds
to Zr through the N atoms (Figure 3). The chlorides
form a facial array, two of which are trans to the N
atoms. A coordinated molecule of THF completes the
Zr coordination sphere. The structural parameters
within the ligand are similar to those seen in 1.
A second Zr species was isolable in the presence of
greater than 3 equiv of the diimine ligand. Under these
conditions the product 8 was predominant in solution.
NMR data were characterized by a single 1H NMR
resonance at 9.57 ppm attributable to the imino NH
protons. An X-ray crystallographic study unambigu-
ously confirmed 8 to be (1,2-C5H3((Ph)CNH)2)3)ZrCl
(Chart 1, Figure 4). The interaction of the three anionic
diimine ligands with Zr is similar to that seen in 1 and
7, in that coordination occurs through nitrogen, forming
a chelate complex. The result is a seven-coordinate Zr
center in which the coordination sphere is comprised of
six nitrogen atoms of the diimine ligands and a single
chloride atom. The Zr-N distances in 8 range from
2.218(3) to 2.257(3) Å, slightly longer than the Zr-N
distances of 2.190(9) Å seen in 7. Also, the N-Zr-N
bite angles for the three chelating diimines in 8 average
79.68(12)°, which is slightly smaller than the N-Zr-N
angle of 81.6(3)° seen in 7. These metric differences are
presumably associated with the steric congestion within
Su m m a r y
The reactions of Cp2Mg with benzonitrile provide a
facile synthetic route to the otherwise illusive 1,2-
difunctionalized cyclopentadienyl ligands. Use of these
extended π-ligand systems imparts some formal charge
separation to the complex and thus offers a unique
approach to enhancing the electrophilic character of the
metal center. The ramification of such electrophilicity
on the resulting chemistry is the subject of current
investigations.
Ack n ow led gm en t . Financial support from the
NSERC of Canada is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
parameters, in CIF format, are available. Access information
is given on any current masthead page.
OM980409L