Mono- And bimetallic (Nacnac)Ni cyclopentadienyl complexes

Article abstract of DOI:10.1021/om060757k

Complexes of the form (Nacnac)Ni(η⁵-L) (L = Cp (3), indenyl (4)) are readily prepared and have been protonated to generate the corresponding cationic species [(HNacNac)Ni(η⁵-L)][B(C₆F ₅)₄] (L = Cp (5), indenyl (6)). While the symmetric compound 3 is paramagnetic, disruption of the symmetry in 4-6 results in diamagnetism. The species [((Nacnac)Ni)₂(μ-η⁵: η⁵-Cp)][B(C₆F₅)₄] (7) was prepared in an unusual fashion from the reaction of [(NacNac)Ni] ₂(η⁶:η⁶-C₆H₅Me) (2) with [Ph₃C][B(C₆F₅)₄] and Cp₂ZrMe₂, while compound 3 serves as a synthon to the neutral bimetallic Ni(II)/Ni(I) species [((Nacnac)Ni)₂(μ- η²:η²-Cp)] (8). Compounds 7 and 8 are readily interconverted electrochemically. Consideration of the molecular orbitals reveals that the unpaired electron in 8 prompts alteration of the nature of the bridging cyclopentadienyl ligand between the metal centers. Crystal structures of 3-5, 7, and 8 are reported.

Full text of DOI:10.1021/om060757k

5870
Organometallics 2006, 25, 5870-5878
Mono- and Bimetallic (NacNac)Ni Cyclopentadienyl Complexes†
Guangcai Bai, Pingrong Wei, Anjan Das, and Douglas W. Stephan*
Department of Chemistry & Biochemistry, UniVersity of Windsor, Windsor, Ontario, Canada N9B 3P4
ReceiVed August 21, 2006
Complexes of the form (Nacnac)Ni(η5-L) (L ) Cp (3), indenyl (4)) are readily prepared and have
been protonated to generate the corresponding cationic species [(HNacNac)Ni(η5-L)][B(C6F5)4] (L ) Cp
(5), indenyl (6)). While the symmetric compound 3 is paramagnetic, disruption of the symmetry in 4-6
results in diamagnetism. The species [((Nacnac)Ni)2(µ-η5:η5-Cp)][B(C6F5)4] (7) was prepared in an unusual
fashion from the reaction of [(NacNac)Ni]2(η6:η6-C6H5Me) (2) with [Ph3C][B(C6F5)4] and Cp2ZrMe2,
while compound 3 serves as a synthon to the neutral bimetallic Ni(II)/Ni(I) species [((Nacnac)Ni)2(µ-
η2:η2-Cp)] (8). Compounds 7 and 8 are readily interconverted electrochemically. Consideration of the
molecular orbitals reveals that the unpaired electron in 8 prompts alteration of the nature of the bridging
cyclopentadienyl ligand between the metal centers. Crystal structures of 3-5, 7, and 8 are reported.
plexes. In the case of Ni(I) synthons we described the complex
Introduction
[(Nacnac)Ni)2(µ-η3:η3-C6H5Me)] (Nacnac ) HC(C(Me)NC6H3i-
â-Diketiminate ligand complexes continue to draw consider-
ableattention.Main-groupcomplexes,1-8 aswellaslanthanide3,9-12
and transition-metal compounds,7,13-46 have been the focus of
numerous recent studies. Our interests in such species have
focused on Ni(I),47 Fe(I),48 and Ti(III)49 â-diketiminato com-
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† This paper is dedicated to Professor Gerhard Erker on the occasion of
his 60th birthday.
* To whom correspondence should be addressed. Fax: 519-973-7098.
E-mail: stephan@uwindsor.ca.
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10.1021/om060757k CCC: $33.50 © 2006 American Chemical Society
Publication on Web 10/24/2006

(NacNac)Ni Cyclopentadienyl Complexes
Chart 1. The (Nacnac)Ni fragment
Organometallics, Vol. 25, No. 25, 2006 5871
out under an atmosphere of N2 using a BAS potentiostat, with a
Ag/AgCl reference electrode, a Pt working electrode, 0.1 M [Bu4N]-
[PF6] as the supporting electrolyte, and a scan rate of 50 mV s-1
.
All electrochemical data were collected at 298 K and are uncor-
rected for junction potentials. Combustion analyses were performed
at the University of Windsor Chemical Laboratories employing a
Perkin-Elmer CHN analyzer. (Nacnac)Ni(µ-Br)2Li(THF)2 (1) and
[(NacNac)Ni]2(η6:η6-C6H5Me) (2) were prepared as previously
reported.47
Synthesis of (Nacnac)Ni(η5-Cp) (3). THF (40 mL) was added
to a mixture of 1 (6.30 g, 8.0 mmol) and LiCp (0.576 g, 8.0 mmol)
at 25 °C, and the mixture was stirred overnight. THF was removed
in vacuo, leaving a deep red solid, which was then dissolved in
toluene (20 mL) and the solution stirred for 20 min at 25 °C. After
filtration and subsequent concentration in vacuo, the deep red
solution was stored at -35 °C for 1 week to isolate dark red crystals
of 3 (3.05 g). Yield: 70%. Magnetic susceptibility: µ ) 2.05 µB.
IR (Nujol): 1940 (w), 1922 (w), 1865 (w), 1804 (w), 1729 (m),
1701 (w), 1655 (w), 1624 (m), 1548 (s), 1528 (s), 1464 (s), 1435
(s), 1400 (s), 1257 (s), 1229 (m), 1178 (s), 1102 (s), 1056 (m),
1026 (s), 935 (s), 885 (m), 854 (m), 796 (s), 779 (s), 763 (s), 717
Pr2)2; Chart 1), which proved to act as a synthon for â-diketimi-
nato Ni(I) complexes.47 The bridging nature of the toluene
fragment in this complex prompted us to consider (â-diketimi-
nato)Ni cyclopentadienyl complexes. While transition-metal
complexes containing cyclopentadienyl ligands have been
known since the genesis of organometallic chemistry in the
1950s, the vast majority of compounds containing Cp ligands
involve a metal-Cp interaction that is η5 in nature. In addition,
a number of examples of complexes containing bridging
cyclopentadienyl ligands have also been characterized. Such a
“triple-decker” complex, [(CpNi)2(µ-η5-Cp)][BF4],50,51 was first
reported in 1974. Since then, related symmetric homobimetallic
complexes, including [(CpFe)2(µ-η5-Cp)]PF6,52 [(η-C6Me6)Co-
(µ-η5-Cp)NiCp]PF6,53 and [(η-9-Me2S-7,8-C2B9H10Ni)2(µ-η5-
Cp)]X (X ) PF6, BF4),54 have also been described. In addition,
dissymmetric, cyclopentadienyl-bridged, heterobimetallic com-
plexes such as [Cp*M(µ-Cp)RuCp*]CF3SO3 (M ) Ru, Fe)55
and [(Cp*Ru(µ-η5-Cp*)Ru(η-9-Me2S-7,8-C2B9H10)]PF654 were
also reported. In this report we describe the synthesis and
characterization of both monometallic and bimetallic Ni-â-
diketiminato complexes that incorporate cyclopentadienyl ligands.
The nature of the Cp-metal interaction is probed with structural
and electronic perturbations.
1
(m), 629 (w), 599 (w), 530 (m), 458 (m) cm-1. H NMR (C6D6):
δ 15.54 (s, 4 H, Ar), 14.11 (br s, 4 H, CHMe2), 4.32 (br s, 12 H,
CHMe2), 2.69 (br s, 2 H, Ar), 2.08 (br s, 12 H, CHMe2), -24.75
(s, 6 H, CMe), -66.8 (s, 1 H, γ-CH), -105.40 (br s, 5 H, Cp). 13
C
NMR (C6D6): δ 237.3, 159.4, 127.0, 123.7, 85.0, 47.1, 44.2, 28.5,
-8.0, -154.4; Anal. Calcd for C34H46N2Ni (541.5): C, 75.4; H,
8.6; N, 5.2. Found: C, 75.5; H, 8.9; N, 5.2.
Synthesis of (Nacnac)Ni(η3-Ind) (4). LiBu (1.6 M in hexanes;
2.5 mL, 4.0 mmol) was added to a solution of indene (0.46 g, 4.0
mmol) in toluene (20 mL) at 25 °C, and the reaction mixture was
stirred overnight. 1 (3.14 g, 4.0 mmol) was subsequently added,
resulting in an intense red mixture which was stirred for an
additional 24 h. After filtration and subsequent concentration in
vacuo, the resulting deep red solution was kept at -35 °C for 2
days to isolate dark red crystals of 4 (2.2 g). Yield: 92%. IR
(Nujol): 1914 (w), 1859 (w), 1795 (w), 1718 (w), 1690 (w), 1657
(w), 1582 (w), 1527 (s), 1500 (m), 1463 (s), 1431 (s), 1403 (s),
1383 (s), 1337 (m), 1310 (s), 1252 (s), 1220 (m), 1176 (s), 1110
(m), 1059 (m), 1046 (s), 1024 (s), 936 (m), 919 (m), 892 (m), 859
(m), 794 (s), 758 (s), 735 (s), 644 (w), 601 (w), 522 (m), 457 (m),
Experimental Section
General Data. All preparations were performed under an
atmosphere of dry O2-free N2, employing either Schlenk-line
techniques or a Vacuum Atmospheres inert-atmosphere glovebox.
Solvents were purified by employing Grubbs-type column systems
manufactured by Innovative Technologies or were distilled from
1
3
431(m) cm-1. H NMR (C6D6): δ 7.92 (t, JHH ) 3 Hz, 1 H, Ind
H2), 7.21-7.06 (m, Ar), 6.61 (m, 3JHH ) 5 Hz, 4JHH ) 3 Hz, 2 H,
Ind H4,7), 6.24 (m, 3JHH ) 5 Hz, 4JHH ) 3 Hz, 2 H, Ind H5,6), 5.03
1
the appropriate drying agents under N2. H and 13C{1H} NMR
spectra were recorded on Bruker Avance 300 and 500 spectrometers
operating at 300 and 500 MHz, respectively. Deuterated benzene
and toluene were purchased from Cambridge Isotopes Laboratories,
freeze-pump-thaw-degassed (three times), and vacuum-distilled
from the appropriate drying agents. Trace amounts of protonated
solvents were used as references, and 1H and 13C{1H} NMR
chemical shifts are reported relative to SiMe4. 31P{1H}, 11B{1H},
and 19F NMR spectra were referenced to external 85% H3PO4, BF3·
Et2O, and CFCl3, respectively. Magnetic moments were determined
by employing the Evans method.56 Cyclic voltammetry was carried
3
(s, 1 H, γ-CH), 3.63 (sept, JHH ) 7 Hz, 4 H, CHMe2), 3.25 (d,
3JHH ) 3 Hz, 2 H, Ind H1,3), 1.57 (s, 6 H, CMe), 1.35 (d, JHH
)
3
7 Hz, 12 H, CHMe2), 1.15 (d, 3JHH ) 7 Hz, 12 H, CHMe2). 13C{1H}
NMR (C6D6): δ 160.5 (NC), 152.4, 141.7 (Ar), 141.3 (Ind C2),
125.3 (Ind C3a,7a), 125.2, 123.9 (Ar), 119.5 (Ind C4,7), 108.9 (Ind
C5,6), 100.3 (γ-C), 73.8 (Ind C1,3), 28.3 (CHMe2), 24.8, 24.4
(CHMe2), 23.0 (NCMe). Anal. Calcd for C38H48N2Ni (591.5): C,
77.1; H, 8.2; N, 4.7. Found: C, 77.3; H, 8.5; N, 4.6.
Synthesis of [(HNacNac)Ni(η5-L)][B(C6F5)4]‚C7H8 (L ) Cp
(5), Ind (6)). These compounds were prepared in a similar fashion,
and thus only one preparation is detailed. [PhMe2NH][B(C6F5)4]
(0.320 g, 0.4 mmol) was added to the solution of 3 (0.216 g, 0.4
mmol) in toluene (10 mL). The solution immediately turned orange,
and an orange precipitate was formed. After it was stirred for 2 h,
the solution was allowed to stand at 25 °C for 2 days. The orange
crystalline compound 5 (0.51 g) was isolated. Yield: 96%. IR
(Nujol): 1944 (w), 1877 (w), 1800 (w), 1732 (m), 1640 (s), 1559
(w), 1512 (s), 1461 (s), 1406 (m), 1376 (s), 1319 (m), 1271 (s),
1207 (m), 1162 (m), 1086 (s), 1055 (m), 1029 (m), 975 (s), 914
(m), 834 (m), 794 (s), 772 (m), 754 (m), 726 (s), 684 (m), 661 (s),
(48) Bai, G.; Wei, P.; Das, A. K.; Stephan, D. W. Dalton Trans. 2006,
1141-1146.
(49) Bai, G.; Wei, P.; Stephan, D. W. Organometallics 2006, 25, 2649-
2655.
(50) Dubler, E.; Textor, M.; Oswald, H. R.; Salzer, A. Angew. Chem.
1974, 86, 125.
(51) Dubler, E.; Textor, M.; Oswald, H. R.; Jameson, G. B. Acta
Crystallogr., Sect. B 1983, B39, 607-612.
(52) Kudinov, A. R.; Fil’chikov, A. A.; Petrovskii, P. V.; Rybinskaya,
M. I. Russ. Chem. Bull. 1999, 48, 1352-1355.
(53) Kudinov, A. R.; Muratov, D. V.; Petrovskii, P. V.; Rybinskaya, M.
I. Russ. Chem. Bull. 1999, 48, 794-795.
(54) Kudinov, A. R.; Petrovskii, P. V.; Meshcheryakov, V. I.; Rybin-
skaya, M. I. Russ. Chem. Bull. 1999, 48, 1356-1361.
(55) Herberich, G. E.; Englert, U.; Marken, F.; Hofmann, P. Organo-
metallics 1993, 12, 4039-4045.
1
607 (m), 573 (m), 466 (m) cm-1. H NMR (C6D5Br): δ 7.24-
7.10 (m, PhMe and Ar), 4.27 (s, 5 H, Cp), 3.90 (s, 2 H, γ-CH2),
3
(56) Loliger, J.; Scheffold, R. J. Chem. Educ. 1972, 49, 646-647.
3.13 (sept, JHH ) 7 Hz, 4 H, CHMe2), 2.26 (s, PhMe), 1.67 (s, 6

5872 Organometallics, Vol. 25, No. 25, 2006
Bai et al.
H, CMe), 1.30 (d, 3JHH ) 6 Hz, 12 H, CHMe2), 0.99 (d, 3JHH ) 6
Hz, 12 H, CHMe2). 13C{1H} NMR (C6D5Br): δ 179.0 (NC), 148.1
0.076 V). Anal. Calcd for C63H87N4Ni2 (1017.8): C, 74.3; H, 8.6;
N, 5.5. Found: C, 73.8; H, 8.9; N, 5.5.
(d(m), 1JCF ) 245 Hz, o-C(C6F5)), 146.8 (Ar), 138.3 (d(m), 1JCF
)
Molecular Orbital Computations. All DFT calculations were
performed using the Gaussian 03 suite of programs.57 The basis
set consisted of the LANL2DZ basis set on Ti in combination with
the 6-31G(d) basis set58-61 on the all other atom types. The
geometries for the computational models were based on the
crystallographic results presented herein.
1
247 Hz, p-C(C6F5)), 137.3 (Ar), 137.2 (PhMe), 136.4 (d(m), JCF
) 245 Hz, m-C(C6F5)), 128.9 (PhMe), 128.6 (Ar), 128.1 (PhMe),
125.2 (PhMe), 124.7 (Ar), 96.3 (Cp), 49.0 (γ-C), 28.1 (CHMe2),
26.5, 24.1 (CHMe2), 23.5 (NCMe), 21.3 (PhMe). 19F NMR
(C6D5Br): δ -54.1 (8F, o-F), -84.5 (s br, 4F, p-F), -88.3 (s br,
8F, m-F). 11B{1H} NMR (C6D5Br): δ -16.7 (s). Anal. Calcd for
C65H55BF20N2Ni (1313.67): C, 59.4; H, 4.2; N, 2.1. Found: C,
59.6; H, 4.2; N, 2.1. 6: Yield: 93%. IR (Nujol): 1945 (w), 1877
(w), 1807 (w), 1733 (m), 1641 (s), 1617 (m), 1513 (s), 1465 (s),
1377 (s), 1317 (m), 1278 (s), 1210 (m), 1164 (m), 1088 (s), 979
(s), 935 (m), 916 (m), 879 (w), 815 (m), 797 (m), 774 (m), 755
(m), 730 (m), 685 (m), 662 (m), 608 (m), 573 (m), 470 (m), 431
(w) cm-1. 1H NMR (C6D5Br): δ 7.17-6.94 (m, Ar, Ind H2), 6.65
X-ray Data Collection and Reduction. Crystals were manipu-
lated and mounted in capillaries in a glovebox, thus maintaining a
dry, O2-free environment for each crystal. Diffraction experiments
were performed on a Siemens SMART System CCD diffractometer.
The data (4.5° < 2θ < 45-50.0°) were collected in a hemisphere
of data in 1329 frames with 10 s exposure times. The observed
extinctions were consistent with the space groups in each case. A
measure of decay was obtained by re-collecting 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
SHELXTL processing packages. An empirical absorption correction
based on redundant data was applied to each data set. Subsequent
solution and refinement was performed using the SHELXTL
solution package.
(m, 3JHH ) 5.6 Hz,4JHH ) 3.1 Hz, 2 H, Ind H4,7), 5.75 (m, 3JHH
)
6 Hz, 4JHH ) 3 Hz, 2 H, Ind H5,6), 3.82 (d, 3JHH ) 3 Hz, 2 H, Ind
3
H1,3), 3.48, 3.46 (ds, 2 H, γ-CH2), 2.77 (sept, JHH ) 7 Hz, 2 H,
3
CHMe2), 2.28 (sept, JHH ) 7 Hz, 2 H, CHMe2), 2.17 (s, 1 H,
3
PhMe), 1.53 (s, 6 H, CMe), 1.18 (d, JHH ) 7 Hz, 6 H, CHMe2),
3
3
1.08 (d, JHH ) 7 Hz, 6 H, CHMe2), 0.90 (d, JHH ) 7 Hz, 6 H,
CHMe2), 0.70 (d, JHH ) 7 Hz, 6 H, CHMe2). 13C{1H} NMR
3
(C6D5Br): δ 177.7 (NC), 148.5 (d(m), 1JCF ) 243 Hz, o-C(C6F5)),
Structure Solution and Refinement. Non-hydrogen atomic
scattering factors were taken from the literature tabulations.62 The
heavy atom positions were determined using direct methods
employing the SHELXTL direct methods routine. 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
1
145.3 (Ar), 138.3 (d(m), JCF ) 245 Hz, p-C(C6F5)), 137.7 (Ar),
137.5 (PhMe), 137.3 (Ind, C2), 136.4 (d(m), JCF ) 248 Hz,
1
m-C(C6F5)), 133.3 (Ar), 128.9 (PhMe), 128.8, 128.2 (Ar), 128.0
(PhMe), 125.4 (Ind, C3a,7a), 125.2 (PhMe), 124.2, 123.9 (Ar), 119.8
(Ind, C4,7), 107.5 (Ind, C5,6), 78.5 (Ind, C1,3), 47.4 (γ-C), 29.0, 27.6
(CHMe2), 26.7, 24.4, 24.3, 23.5 (CHMe2), 23.5 (NCMe), 21.3
(PhMe). 11B{1H} NMR (C6D5Br): -16.7 (s). 19F NMR (C6D5Br):
δ -54.20 (s, 8F, o-F), -84.57 (t, 4F, 3JFF ) 21.1 Hz, p-F), -88.40
2
2
w(|Fo| - |Fc|)2, where the weight w is defined as 4Fo /2σ(Fo ) and
Fo and Fc are the observed and calculated structure factor
amplitudes, respectively. In the final cycles of each refinement, all
non-hydrogen atoms were assigned anisotropic temperature factors
in the absence of disorder or insufficient data. In the latter cases
atoms were treated isotropically. C-H atom positions were
calculated and allowed to ride on the carbon to which they are
bonded, assuming a C-H bond length of 0.95 Å. H atom
temperature factors were fixed at 1.10 times the isotropic temper-
ature factor of the C atom to which they are bonded. The H atom
contributions were calculated but not refined. 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. Additional details are provided
in the Supporting Information.
3
(t, 8F, JFF ) 17.3 Hz, m-F). Anal. Calcd for C69H57BF20N2Ni
(1363.73): C, 60.8; H, 4.2; N, 2.1. Found: C, 60.5; H, 4.4; N, 2.2.
Synthesis of [((Nacnac)Ni)2(µ-η5:η5-Cp)][B(C6F5)4]‚C6H6 (7).
[Ph3C][B(C6F5)4] (0.184 g, 0.20 mmol) was added to a solution of
Cp2ZrMe2 (0.050 g, 0.20 mmol) in toluene (10 mL) at room
temperature. Stirring was continued for 20 min, after which 2 (0.208
g, 0.20 mmol) was added to the resulting pale yellow solution at
25 °C. Stirring was continued for 12 h. After concentration (to 3
mL) in vacuo, the resulting brown solution was kept at -35 °C for
1 week to isolate orange crystals of 7 (0.15 g). Yield: 42%. X-ray
crystals were obtained from benzene solution. IR (Nujol): 1936
(w), 1872 (w), 1810 (w), 1733 (s), 1642 (s), 1584 (m), 1533 (s),
1513 (s), 1464 (s), 1374 (s), 1317 (s), 1277 (s), 1259 (s), 1193
(m), 1175 (m), 1089 (s), 1058 (m), 1026 (m), 979 (s), 936 (m),
906 (m), 843 (m), 797 (s), 771 (s), 761 (s), 731 (s), 701 (m), 684
Crystallographic data for 3, 4, 5‚C7H8, 7‚C6H6, and 8‚2C7H8 are
given in Table 1.
(m), 662 (m), 637 (m), 607 (m), 574 (m), 525 (m), 452 (m) cm-1
.
1H NMR (C6D5Br): δ 7.24-7.10 (m, PhMe and Ar), 4.56 (s, 2 H,
(57) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A.
D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi,
M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.;
Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick,
D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.;
Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi,
I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M.
W.; Johnson, B. G.; Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon,
M.; Replogle, E. S.; Pople, J. A. Gaussian 98; Gaussian, Inc.: Pittsburgh,
PA, 1998.
3
γ-CH), 3.21 (s, 5 H, Cp), 2.90 (sept, JHH ) 7 Hz, 8 H, CHMe2),
3
2.18 (s, PhMe), 1.46 (s, 12 H, CMe), 1.17 (d, JHH ) 6 Hz, 24 H,
3
CHMe2), 0.86 (d, JHH ) 6 Hz, 24 H, CHMe2). 19F NMR
(C6D5Br): δ -53.6 (s, 8F, o-F), -83.9 (s br, 4F, p-F), -87.7 (s
br, 8F, m-F). 11B{1H} NMR (C6D5Br): δ -16.0 (s). Anal. Calcd
for C94H95BF20N4Ni2 (1789.03): C, 63.1; H, 5.4; N, 3.1. Found:
C, 62.9; H, 5.6; N, 3.1.
Synthesis of [((Nacnac)Ni)2(µ-η2:η2-Cp)]‚2C7H8 (8). Toluene
(10 mL) was added to a mixture of 2 (0.208 g, 0.200 mmol) and
3 (0.216 g, 0.400 mmol) at 25 °C, and the mixture was stirred
overnight. The solution was concentrated in vacuo to give a deep
green solution, which was then kept at -35 °C overnight to isolate
dark green crystals of 8 (0.39 g). Yield: 95%. Magnetic susceptibil-
ity: µ ) 2.74 µB. IR (Nujol): 1918 (w), 1868 (w), 1843 (w), 1795
(w), 1774 (w), 1739 (m), 1684 (m), 1650 (m), 1530 (s), 1458 (s),
1408 (s), 1258 (s), 1176 (s), 1099 (s), 1026 (s), 933 (m), 859 (m),
796 (s), 758 (m), 719 (m), 669 (m), 524 (m) cm-1. EPR
(C6H5Me): 2.0638. Cyclic voltammetry: E1/2 ) 0.186 V (∆Ep )
(58) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971, 54,
724-728.
(59) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56,
2257-2261.
(60) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213-
222.
(61) Hariharan, P. C.; Pople, J. A. Mol. Phys. 1974, 27, 209-214.
(62) Cromer, D. T.; Waber, J. T. International Tables for X-Ray
Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. 4, pp 71-
147.

(NacNac)Ni Cyclopentadienyl Complexes
Organometallics, Vol. 25, No. 25, 2006 5873
Table 1. Crystallographic Data
3
4
5‚C7H8
7‚C6H6
8‚2C7H8
formula
formula wt
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C68H92N4Ni2
1082.88
C38H48N2Ni
591.49
monoclinic
P21/m
9.1721(10)
20.653(2)
9.4619(10)
C65H55BF20N2Ni
1313.63
triclinic
P1h
12.9531(6)
16.1270(8)
17.2826(9)
115.0140(10)
90.7370(10)
110.5410(10)
3007.8(3)
2
C93H93BF20N4Ni2
1774.94
monoclinic
P21/n
16.4974(5)
24.8888(8)
21.5075(7)
C77H103N4Ni2
1202.05
monoclinic
C2/c
26.558(3)
13.5604(14)
20.873(2)
monoclinic
P21/c
15.9906(8)
20.2397(10)
19.3992(10)
90.1420(10)
116.5660(10)
92.0440(10)
109.646(2)
6278.4(5)
4
1.146
0.641
24 198
7863
1603.1(3)
2
1.225
0.633
10 838
2335
8825.4(5)
4
7079.5(12)
4
1.128
0.575
16 955
5077
Z
d(calcd) (g cm-3
)
1.450
0.427
10 123
5812
1.336
0.516
31 748
10 366
1101
abs coeff, µ (cm-1
)
no. of data collected
no. of data Fo2 >3σ(Fo )
2
no. of variables
667
190
802
340
R
Rw
GOF
0.0401
0.0871
0.818
0.0469
0.1224
0.989
0.0428
0.1218
0.847
0.0393
0.0796
0.826
0.0844
0.2219
0.947
Scheme 1. Synthesis of (Nacnac)NiCp complexes 3-6
Figure 1. NMR spectra of (a) 3 and (b) 4.
Ni(II) complex containing Cp and Nacnac ligands. Indeed, an
X-ray crystallographic study confirmed the formulation of 3 as
(NacNac)Ni(η-Cp) (Figure 2). The Ni center in 3 is coordinated
to the Nacnac ligand as well as to the cyclopentadienyl ligand
in an π fashion. The Ni-N distances were found to be 1.937(3)
and 1.948(3) Å with a N-Ni-N angle of 94.19(11)°. The Ni-C
bond lengths were found to fall in two ranges: three Ni-C
bond lengths were between 2.185(5) and 2.189(5) Å, while the
remaining two were found to be 2.197(5) and 2.202(5) Å. The
plane of the cyclopentadienyl ligand is oriented at an angle of
90.8° with respect to the NiN2 plane. The Ni-C distances are
similar to those seen in η5-bound Ni(II)-cyclopentadienyl
complexes CpNi(L)Cl (L ) carbene, phosphine).63 How-
ever, it is noteworthy that the observation of two significantly
longer Ni-C bond lengths in 3 suggests a distortion toward an
η3-bonding mode.
Results and Discussion
Monometallic Species. Reaction of the previously reported
species (Nacnac)Ni(µ-Br)2Li(THF)2 (1) with LiCp proceeds in
THF to give the new red crystalline solid 3 in 70% yield after
1
workup (Scheme 1). The H NMR spectra (Figure 1a) show
paramagnetically shifted resonances at chemical shifts ranging
from 15.5 to -105 ppm. The resonances were assigned on the
basis of integrations. It is noteworthy that two resonances at
4.32 and 2.08 ppm, attributable to the isopropyl methyl groups,
were observed. In addition, resonances attributed to the aromatic
protons were observed at 15.54 and 2.69 ppm, while resonances
at 14.11 and -24.75 ppm were attributed to the isopropyl
methine and backbone methyl groups of the Nacnac ligand.
Resonances at -66.8 and -105.40 ppm were assigned to the
backbone methine protons of the Nacnac and Cp ligands,
respectively. Similarly, the 13C{1H} NMR spectrum of 3 gave
rise to corresponding resonances ranging from 237.3 to -154.4
ppm. These data suggest the formulation of 3 as a paramagnetic
(63) Kelly, R. A., III; Scott, N. M.; Diez-Gonzalez, S.; Stevens, E. D.;
Nolan, S. P. Organometallics 2005, 24, 3442-3447.

5874 Organometallics, Vol. 25, No. 25, 2006
Bai et al.
Figure 2. Grayscale POV-ray drawing of 3. Hydrogen atoms are
omitted for clarity. Selected distances (Å) and angles (deg): Ni-
(1)-N(1) ) 1.937(3), Ni(1)-N(2) ) 1.948(3), Ni(1)-C(34) )
2.185(5), Ni(1)-C(31) ) 2.189(5), Ni(1)-C(33) ) 2.188(5), Ni-
(1)-C(32) ) 2.197(5), Ni(1)-C(30) ) 2.202(5); N(1)-Ni(1)-
N(2) ) 94.19(11).
Figure 4. Grayscale POV-ray drawing of 4. Hydrogen atoms are
omitted for clarity. Selected distances (Å) and angles (deg): Ni(1)-
N(1) ) 1.919(2), Ni(1)-C(16) ) 2.007(5), Ni(1)-C(17) )
2.108(3); N(1)-Ni(1)-N(1)′ ) 95.33(3).
Figure 5. Grayscale POV-ray drawing of the cation of 5. Hydrogen
atoms, with the exception of those on the central methylene carbon
of the protonated Nacnac ligand, are omitted for clarity. Selected
distances (Å) and angles (deg): Ni(1)-N(1) ) 1.928(3), Ni(1)-
N(2) ) 1.942(3), Ni(1)-C(30) ) 2.069(4), Ni(1)-C(31) ) 2.154-
(5), Ni(1)-C(32) ) 2.155(4), Ni(1)-C(33) ) 2.092(4), Ni(1)-
C(34) ) 2.143(3), C(13)-C(15) ) 1.516(5), C(15)-C(16) )
1.487(5); N(1)-Ni(1)-N(2) ) 95.50(12).
Figure 3. Plots of δ vs T-1 for the 1H spectrum of 3: (a) Nacnac
ligand resonances; (b) Cp ligand resonance.
1
to 3, compound 4 exhibited H NMR resonances typical of a
diamagnetic species (Figure 4). Of particular interest are the
resonances at 7.92 and 3.25 ppm, which were attributed to the
protons on the C5 ring of the indenyl ligand. The backbone
methine proton of the Nacnac ligand was observed at 5.03 ppm,
while the methine protons of the isopropyl substituents gave
rise to a multiplet at 3.63 ppm. These data, together with the
13C{1H} NMR spectrum, were consistent with the formulation
of 4 as (Nacnac)Ni(η3-Ind). This was subsequently confirmed
by X-ray diffraction (Figure 4). The overall geometry of 4 is
similar to that seen for 3, as the Ni-N distance was found to
be 1.919(2) Å, with a chelate bite angle of 95.33(13)°. The
indenyl ligand adopts an η3 coordination mode with Ni-C
distances of 2.007(5) and 2.108 Å. The other two carbons of
the C5 ring reside 2.570 and 2.676 Å away from Ni. The closer
approach of three of the carbons of the C5 ring of the indenyl
ligand to Ni in 4 is also reflected in the angle of 79.7° between
the C5 plane and the NiN2 plane. The orientation of the indenyl
ring directs the 1,3-protons toward the center of the arene rings
of the Nacnac ligand at distances of 2.77 and 2.74 Å from the
The paramagnetic behavior of 3 was investigated via variable-
temperature 1H NMR experiments. Over the temperature range
from -90 to 80 °C, there were relatively small shifts in the
positions of the resonances associated with the Nacnac ligand,
while the Cp resonance shifted from -105 to -76 ppm (Figure
3). These data for 3 show a trend similar to that reported for
(Acac)NiCp*, although in this latter case decreasing temperature
results in a change in the chemical shift of the Cp* protons
from almost 90 ppm into the diamagnetic region, consistent with
a triplet to singlet high-spin to low-spin crossover.64 While the
smaller shift for 3 suggests that 3 may approach diagmagnetism
at very low temperature, it remains paramagnetic above -90
°C.
In a similar fashion the Ni synthon 1 was reacted with
indenyllithium (Scheme 1). This ultimately afforded the related
dark red crystalline complex 4 in 92% yield. In marked contrast
(64) Smith, M. E.; Andersen, R. A. J. Am. Chem. Soc. 1996, 118, 11119-
11128.

(NacNac)Ni Cyclopentadienyl Complexes
Organometallics, Vol. 25, No. 25, 2006 5875
Figure 6. Frontier orbitals of (Nacnac)MCl.26
Figure 8. Gaussview depictions of (a) the HOMO and (b) the
LUMO of 5.
Scheme 2. Synthesis of Bimetallic Complexes 7 and 8
Figure 7. Gaussview depictions of (a) the higher energy SOMO
and (b) the lower energy SOMO for the triplet state of 3.
The structural data confirm the η5-binding mode of the
cyclopentadienyl ligand and the puckered nature of the proto-
nated Nacnac ligand backbone. Such puckering has been
previously described for the species (HNacnac)NiBr2.65 Similar
to that seen in 3, the angle between the NiN2 and the C5 planes
in 5 is 90.5°. The Ni-N distances were found to be 1.928(3)
and 1.942(3) Å, slightly longer than those reported above for
3, consistent with the protonation of the Nacnac ligand and,
thus, poorer donor ability. Nonetheless, the N-Ni-N bite angle
in 5 is 95.50(12)°, similar to that seen in 3. Protonation of the
central carbon of the Nacnac ligand is further evidenced by the
increase in the C-C bond lengths of the ligand backbone, as
the C(13)-C(15) and C(15)-C(16) bond lengths were found
to be 1.516(5) and 1.487(5) Å, respectively. The Ni-C bond
lengths for the Ni-Cp fragment ranged from 2.069(4) to 2.155-
arene planes. It is this geometry that presumably accounts for
the upfield resonance described above and attributed to these
protons.
Compounds 3 and 4 were found to react rapidly with 1 equiv
of [PhMe2NH][B(C6F5)4], affording the orange crystalline
compounds 5 and 6 in 96% and 93% yield, respectively (Scheme
1). Both compounds displayed poor solubility in toluene
compared to their precursors; nonetheless, NMR data typical
of diamagnetic species were obtained for 5 and 6 in C6D5Br.
In the case of 5, resonances observed were as expected, with
the addition of a resonance at 3.90 ppm, attributable to a
methylene group derived from protonation of the central carbon
of the Nacnac ligand. Similarly, resonances at 3.48 and 3.46
ppm are attributable to the similar but inequivalent protons in
6. X-ray crystallographic data were obtained for 5 (Figure 5).
(65) Feldman, J.; McLain, S. J.; Parthasarathy, A.; Marshall, W. J.;
Calabrese, J. C.; Arthur, S. D. Organometallics 1997, 16, 1514-1516.

5876 Organometallics, Vol. 25, No. 25, 2006
Bai et al.
Figure 11. Grayscale POV-ray drawing of 8. Hydrogen atoms are
omitted for clarity. Selected distances (Å) and angles (deg): Ni(1)-
N(1) ) 1.936(7), Ni(1)-N(2) ) 1.930(7), Ni(1)-C(30) ) 2.050(11),
Ni(1)-C(33) ) 2.138(10), Ni(1)-C(31) ) 2.343(6); N(2)-Ni(1)-
N(1) ) 96.1(3).
Figure 9. Grayscale POV-ray drawing of the cation of 7. Hydrogen
atoms are omitted for clarity. Selected distances (Å) and angles
(deg): Ni(1)-N(1) ) 1.903(3), Ni(1)-N(2) ) 1.916(3), Ni(1)-
C(59) ) 2.246(4), Ni(1)-C(60) ) 2.229(4), Ni(1)-C(61) ) 2.212-
(4), Ni(1)-C(62) ) 2.240(4), Ni(1)-C(63) ) 2.252(4), Ni(2)-
N(4) ) 1.906(3), Ni(2)-N(3) ) 1.908(3), Ni(2)-C(61) ) 2.207(4),
Ni(2)-C(62) ) 2.214(4), Ni(2)-C(60) ) 2.240(4), Ni(2)-C(63)
) 2.260(4), Ni(2)-C(59) ) 2.271(4), N(1)-C(13) ) 1.335(4),
N(1)-C(1) ) 1.451(4), N(2)-C(16) ) 1.322(4), N(2)-C(18) )
1.451(4), N(3)-C(42) ) 1.335(4), N(3)-C(30) ) 1.449(4), N(4)-
C(45) ) 1.338(4), N(4)-C(47) ) 1.447(4); N(1)-Ni(1)-N(2) )
95.62(12), N(4)-Ni(2)-N(3) ) 96.43(11).
Figure 12. Cyclic voltammogram of 8.
energy. The singly occupied orbitals (SOMOs) in 3 (Figure 7)
have significant contributions from the π orbitals of Cp and
Nacnac ligands; the metal-based contributions are best described
as dxz and dyz in character, consistent with the MO analysis of
Holland, Cundari, and co-workers.26 Analogous calculations
performed for the singlet states of 4 and 5 showed the HOMOs
were comprised of a significant interaction between the metal
dxz orbital with π orbitals of the Cp ligand. The metal
contribution to the LUMOs is best described as being derived
from the Ni dyz orbital (Figure 8). The HOMO-LUMO gaps
in both cases were found to be greater than 300 kJ/mol,
consistent with the experimentally observed diamagnetism of
4 and 5. It appears that disruption of the symmetry of (Nacnac)-
NiL either by the nature of L or by protonation of the Nacnac
ligand results in the a stabilization of the MO involving the Ni
dxz orbital, thus prompting the observed diamagnetism.
Figure 10. EPR spectrum of 8.
(4) Å. These distances are considerably shorter than those
observed in 3, reflecting the cationic charge on the Ni center.
The frontier orbitals for a series of complexes of the form
(Nacnac)MCl have been described by Holland, Cundari, and
co-workers (Figure 6).26 In these cases, the computed orbitals
were found to be primarily (∼90%) metal in character, with
minor contributions from the diketiminate N ligand. To consider
the nature of the present complexes, single-point molecular
orbital calculations were performed using the Gaussian software
package employing DFT methods and geometries based on the
crystallographic structural data. Comparative computations of
the high- and low-spin states for 3 were consistent with the
experimental observation that the high-spin state is lower in
Bimetallic Systems. Reaction of 2 with a toluene solution
of [Ph3C][B(C6F5)4] and Cp2ZrMe2 afforded a brown solution
that gave orange crystals of 7 in 42% yield (Scheme 2).
Compound 7 proved to be sparingly soluble in most nonreactive
solvents; however, it persisted for a couple of hours in C6H5-
1
Br. H NMR data suggested a 2:1 ratio of the Nacnac and Cp

(NacNac)Ni Cyclopentadienyl Complexes
Organometallics, Vol. 25, No. 25, 2006 5877
Figure 13. Gaussview depictions of the HOMO of 7.
Figure 14. Gaussview depictions of (a) the LUMO of 7 and (b)
the SOMO of 8.
ligands, while the 19F and 11B{1H} NMR data were consistent
with the presence of the borate anion. The nature of 7 was
ultimately identified by X-ray crystallography to be [((Nacnac)-
Ni)2(µ-η5:η5-Cp)][B(C6F5)4]·C6H6 (Figure 9). The cation of 7
is comprised of two (Nacnac)Ni units bridged by a cyclopen-
tadienyl ligand. The Ni-N distances were found to range from
1.903(3) to 1.916(3) Å, with N-Ni-N bite angles of 95.62-
(12) and 96.43(11)°. The angle between the two NiN2 planes is
73.8°. The cyclopentadienyl ligand binds to the two Ni centers
in η5 fashions with Ni-C distances focused between 2.212(4)
and 2.271(4) Å, somewhat longer than the Ni-C distances for
the bridging Cp of 2.166(17) and 2.162(10) Å in [(CpNi)2(µ-
η5:η5-Cp)][BF4].50,51 The approximate 2-fold symmetry of this
interaction is also reflected in the angles of 88.1 and 93.1°
between the two NiN2 planes and the C5 plane.
In the above formation of 7, the reaction mechanism, as well
as the fate of the Zr fragment, is unknown. Nonetheless, it is
reasonable to speculate that exchange of the bridging toluene
in 2 for a bridging cyclopentadienyl-Zr fragment could initiate
the Cp ligand transfer from Zr to Ni. In an effort to probe related
reactions, the species 2 was reacted with 3. This gave a deep
green solution and ultimately dark green crystals of 8 in 95%
yield (Scheme 2). This paramagnetic compound gave a single
resonance in the EPR spectrum with g ) 2.0638 (Figure 10).
X-ray crystallographic analysis identified 8 as [((Nacnac)Ni)2-
(µ-η2:η2-Cp)]·2C7H8 (Figure 11), confirming the bimetallic
nature of 8. Although 8 is generally similar in structure to that
seen in the cation of 7, it is a neutral species consistent with a
formal mixed-valence Ni(II)/Ni(I) formulation. The Ni-N
distances to each Ni are 1.930(7) and 1.936(7) Å. The chelate
bite angle was 96.1(3)°, while the angle between the NiN2 planes
was 49.7°, significantly smaller than the corresponding angle
in the cation of 7. The bridging cyclopentadienyl ligand also
forms a dissymmetric bridge. The Ni(1)-C(30), Ni(1)-C(34),
and Ni(1)-C(31) distances were found to be 2.050(12),
2.138(10), and 2.343(6) Å. This affirms the best description of
the bridging ligand is as a bridging η2:η2-cyclopentadienyl
group.
The neutral species 8 exhibits a reversible oxidation at E1/2
) 0.186 V in a cyclic voltammetric experiment in CH2Cl2 using
[Bu4N][PF6] as the supporting electrolyte. The peak-to-peak
separation is 0.076 V, consistent with a one-electron process
(Figure 12). Moreover, this suggests the electrochemical genera-
tion of 7. This was unambiguously confirmed by an analogous
cyclic voltammetric study of 7, which showed the expected
reversible redox at the same potential. These data confirm the
facile electrochemical interconversion of 7 and 8 (Scheme 2).
Single-point molecular orbital calculations were performed
using the Gaussian software package employing DFT methods
and the basis sets based on the crystallographic structural data
for 7 and 8. The HOMO and HOMO-1 orbitals for 7 (Figure
13) are admixtures of metal d orbitals with the Cp and Nacnac
π systems. Conceptually, one can consider these the products
of the interactions of the SOMOs of 3 with the frontier orbitals
of a (Nacnac)Ni+ fragment. The LUMO of 7 is a similarly
symmetric admixture of d orbitals on both metal centers and
the Cp π system orbitals (Figure 14). The corresponding SOMO
of 8 shows an MO with similar character. Thus, the presence
of the additional electron in the SOMO of 8 is consistent with
the observed structural perturbation to the Ni-Cp interactions.
In summary, both monometallic and bimetallic cyclopenta-
dienyl and related derivatives of (Nacnac)NiII are readily
prepared. The magnetic properties of monometallic species
appear to be strongly linked to the symmetry of the molecule.

5878 Organometallics, Vol. 25, No. 25, 2006
Bai et al.
It is also clear that steric and electronic perturbations to
(Nacnac)Ni impact the nature and symmetry of bridging
cyclopentadienyl ligands of the bimetallic derivatives. The
reactivity of the Nacnac-metal complexes continues to be an
area of fruitful study in our laboratories. Further results will be
reported in due course.
correct solvate, C6H6, appears in Table 1. The correct solvate
now appears in the text. Also, space groups for 4 and 8 have
been altered to the centrosymmetric P21/m and C2/c, respec-
tively. In the case of 8 this results in slightly higher R factors
as a consequence of poor crystal quality. Details of the refine-
ments now appear in the Supporting Information in revised CIF
files.
Acknowledgment. Financial support from the NSERC of
Canada is gratefully acknowledged.
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
Note Added after ASAP Publication. In the version of this
paper published on the Web October 24, 2006, compound 7
was reported in the text with the wrong solvate, although the
OM060757K