A β-diketiminato-nickel(II) synthon for nickel(I) complexes

Article abstract of DOI:10.1021/om050544f

The compound (Nacnac)Ni(μ-Br)₂Li(THF)₂ (Nacnac = (HC(CMeNC₆H₃(i-Pr)₂)₂) was reduced by reaction with K/Na alloy in toluene. The resulting product [((Nacnac)Ni) ₂(μ-η³:η³-C₆H ₅-Me)] (1) was characterized and is best described as a Ni(II) species in which electron transfer from Ni to toluene has occurred. This compound reacts with a variety of donors to give Ni(I) complexes. For example, compound 1 reacts with phosphines, nitriles, acetylenes, olefins, and ketones to give the paramagnetic complexes (Nacnac)Ni(PCy₃) (2), (Nacnac)Ni(Ph₂PCH₂-PPh₂) (3), (Nacnac)Ni(NCPh) (4), (Nacnac)Ni(η²-PhCCPh) (5), (Nacnac)Ni(η²- Me₃SiCCSiMe₃)-(6), (Nacnac)Ni(η²-H ₂CCPh₂) (7), and (Nacnac)Ni(CCPh₂) (8). In the related reaction of 1 with dimethylfulvene, electron transfer from metal to ligand is evidenced by the formation of the dimetallic species [((Nacnac)Ni(η³:η³-C₅H ₄CMe₂))₂] (9). The crystal structures of 1-9 are reported, and the bonding and reactivity of these products are discussed.

Full text of DOI:10.1021/om050544f

Organometallics 2005, 24, 5901-5908
5901
Α â-Diketiminato-Nickel(II) Synthon for Nickel(I)
Complexes
Guangcai Bai, Pingrong Wei, and Douglas W. Stephan*
Department of Chemistry & Biochemistry, University of Windsor,
Windsor, Ontario, Canada N9B 3P4
Received June 29, 2005
The compound (Nacnac)Ni(µ-Br)2Li(THF)2 (Nacnac ) (HC(CMeNC6H3(i-Pr)2)2) was reduced
by reaction with K/Na alloy in toluene. The resulting product [((Nacnac)Ni)2(µ-η3:η3-C6H5-
Me)] (1) was characterized and is best described as a Ni(II) species in which electron transfer
from Ni to toluene has occurred. This compound reacts with a variety of donors to give Ni(I)
complexes. For example, compound 1 reacts with phosphines, nitriles, acetylenes, olefins,
and ketones to give the paramagnetic complexes (Nacnac)Ni(PCy3) (2), (Nacnac)Ni(Ph2PCH2-
PPh2) (3), (Nacnac)Ni(NCPh) (4), (Nacnac)Ni(η2-PhCCPh) (5), (Nacnac)Ni(η2-Me3SiCCSiMe3)-
(6), (Nacnac)Ni(η2-H2CCPh2) (7), and (Nacnac)Ni(OCPh2) (8). In the related reaction of 1
with dimethylfulvene, electron transfer from metal to ligand is evidenced by the formation
of the dimetallic species [((Nacnac)Ni(η3:η3-C5H4CMe2))2] (9). The crystal structures of 1-9
are reported, and the bonding and reactivity of these products are discussed.
Introduction
tion.46-48 More recent studies have focused on the steric
demands of these chelating ligands to access low-
coordinate â-diketiminato complexes.7,13-25,47,49,50 In one
such study, Puiu and Warren25 described three-coordi-
nate â-diketiminato-nickel nitrosyl complexes derived
from a Ni(I) precursor. In other work employing reduced
â-diketiminato complexes, Smith, Lachicotte, and Hol-
land41 described the cleavage of N-N double bonds by
a three-coordinate â-diketiminato-iron hydride com-
plex, while Warren and co-workers30 have also described
the reactivity of a â-diketiminato-Co(I) toluene complex
with O2, N3R, and RNO. Our interest in â-diketiminato
The study of complexes of â-diketiminate ligands
(Nacnac) is an area of inorganic and organometallic
chemistry that has enjoyed a resurgence in recent years.
While these ligands have been used in chemistry from
main-group1-8 to lanthanide3,9-12 compounds, a good
deal of effort has focused on late-transition-metal deriv-
atives,7,13-46 prompted in large part by the discovery of
the utility of Ni-diimine complexes in olefin polymeriza-
* To whom correspondence should be addressed. E-mail:
stephan@uwindsor.ca.
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10.1021/om050544f CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/19/2005

5902 Organometallics, Vol. 24, No. 24, 2005
Bai et al.
Typical measurement conditions were 20 mW microwave
power, 9.7 GHz microwave frequency, 3.830 G modulation
amplitude, and 4K data points covering a sweep range of 4000
G. IR spectra were recorded on a Bruker FTIR spectrometer.
Combustion analyses were done in-house, employing a Perkin-
Elmer CHN analyzer. In this paper, the abbreviation Nacnac
refers to the â-diketiminate ligand (HC(CMeNC6H3(i-Pr)2)2.
Synthesis of (Nacnac)Ni(µ-Br)2Li(THF)2. BuLi (2.5 M in
hexane; 12 mL, 30 mmol) was added dropwise to the solution
of (H2C(CMeNC6H3(i-Pr)2)2 (12.56 g, 30 mmol) in THF (50 mL)
at 25 °C. Stirring was continued overnight. NiBr2 (6.56 g, 30
mmol) was added to the above solution, and the resulting
mixture was refluxed for 48 h. After concentration in vacuo,
the deep green solution was kept at -35 °C for 2 days,
affording dark green crystals (17.8 g) which were isolated by
filtration. Yield: 17.8 g (75%). Anal. Calcd for C37H57Br2LiN2-
NiO2 (787.3): C, 56.5; H, 7.3; N, 3.6. Found: C, 56.5; H, 7.0;
N, 3.4.
Chart 1
complexes focuses on the synthesis and reactivity of low-
valent transition-metal complexes. Mindiola and co-
workers29 have described reductions of â-diketiminato-
Zr complexes that lead to C-N bond scission, resulting
in Zr-imido derivatives, whereas reduction of â-diketim-
inato-Ni(II) compounds affords the three-coordinate Ni-
(I) complexes (Nacnac)Ni(THF) and (Nacnac)Ni(luti-
dine).25 In this report, we describe the reduction of a
â-diketiminato-Ni(II) complex in toluene (Chart 1). The
resulting product has been characterized and its reac-
tivity examined, revealing that this compound is a
useful reagent for the generation of Ni(I) complexes and
intermediates.
Synthesis of ((Nacnac)Ni)2(µ-η3:η3-C6H5Me) (1). Method
A. (Nacnac)Ni(µ-Br)2Li(THF)2 (2.222 g, 2.13 mmol) and K/Na
alloy (0.066 g of K, 1.69 mmol; 0.022 g of Na, 0.96 mmol) were
added to toluene (15 mL) at 25 °C and stirred for 1 week. After
filtration and subsequent concentration (to 5 mL) in vacuo,
the resulting deep red solution was kept at -35 °C for 1 week
to isolate dark red crystals of 1 (0.53 g). After concentration
of the filtrate to 3 mL, the solution was kept at -35 °C for 3
days. An additional crop of 1 was formed, affording a total yield
of 0.74 g (67%).
Experimental Section
General Data. All preparations were done under an
atmosphere of dry, O2-free N2 by employing both Schlenk line
techniques and a Vacuum Atmospheres inert-atmosphere
glovebox. Solvents were purified employing a Grubbs type
solvent purification system manufactured by Innovative Tech-
nology. Deuterated solvents were purified using the appropri-
ate techniques. All organic reagents were purified by conven-
Method B. MeMgBr (3.0 M in ether, 0.3 mL, 0.9 mmol) was
added to the solution of (Nacnac)Ni(µ-Br)2Li(THF)2 (0.709 g,
0.90 mmol) in toluene (10 mL) at 25 °C, and the mixture was
stirred overnight. After filtration and concentration in vacuo,
the solution was stored at -35 °C, whereupon dark red crystals
of 2 were obtained. Yield: 0.32 g (64%). IR (Nujol, cm-1): 1905
(w), 1847 (w), 1789 (w), 1653 (w), 1623 (m), 1551 (s), 1517 (s),
1462 (s), 1433 (s), 1411 (s), 1318 (s), 1255 (s), 1224 (m), 1173
(s), 1098 (m), 1054 (m), 1033 (s), 930 (s), 887 (s), 842 (m), 791
(s), 759 (s), 722 (s), 631 (m), 559 (m), 543 (m), 500 (m), 436
(m). 1H NMR (δ): 7.15-6.86 (m, 17 H, PhMe and Ar), 4.70 (s,
1
tional methods. H and 13C{1H} NMR spectra were recorded
on Bruker Avance 300 and 500 spectrometers. All NMR
spectra were recorded in C6D6 at 25 °C. Trace amounts of
protonated solvents were used as references, and chemical
shifts are reported relative to SiMe4. EPR spectra were
recorded on a X-band Bruker ESP 300E spectrometer equipped
with an electromagnet capable of providing a magnetic field
from 50 G to 15 kG, a gaussmeter, and a microwave counter.
3
2 H, γ-CH), 3.91 (sept, JHH ) 7 Hz, 8 H, CHMe2), 2.11 (s, 3
3
H, PhMe), 1.47 (d, JHH ) 7 Hz, 24 H, CHMe2), 1.43 (s, 12 H,
3
CMe), 1.11 (d, JHH ) 7 Hz, 24 H, CHMe2). 13C{1H} NMR (δ):
159.9 (NC), 151.6, 141.1 (Ar), 138.1, 129.7, 128.7, 126.0 (PhMe),
125.2, 123.6 (Ar), 98.1 (γ-C), 28.6 (CHMe2), 25.2 (PhMe), 24.6
(CHMe2), 24.4 (NCMe). EPR (toluene, 25 °C): g ) 2.20 (broad,
weak signal). EPR (toluene, -78 °C): g ) 2.14, 2.17, 2.46. Anal.
Calcd for C65H90N4Ni2 (1044.8): C, 74.7; H, 8.7; N, 5.4.
Found: C, 74.3; H, 8.9; N, 5.4.
Synthesis of (Nacnac)Ni(PCy3) (2), (Nacnac)Ni(Ph2-
PCH2PPh2) (3), (Nacnac)Ni(NCPh) (4), (Nacnac)Ni(η2-
PhCCPh) (5), (Nacnac)Ni(η2-Me3SiCCSiMe3) (6), (Nac-
nac)Ni(η2-H2CCPh2) (7), and (Nacnac)Ni(OCPh2) (8). These
compounds were prepared in a similar fashion, and thus, only
one preparation is detailed. Toluene (8 mL) was added to a
mixture of 1 (0.208 g, 0.20 mmol) and PCy3 (0.112 g, 0.40
mmol) at 25 °C. The solution became pale yellow immediately.
Stirring was continued for 2 h. After removal of toluene in
vacuo and recrystallization in hexane at -35 °C, green-yellow
crystals of 2 (0.25 g) were isolated.
Data for 2 are as follows. Yield: 0.25 g (83%). Green-yellow
crystals. EPR (toluene, 25 °C): not observed. EPR (toluene,
-78 °C): g ) 2.03, 2.17, 2.54. IR (Nujol, cm-1): 1904 (w), 1848
(w), 1786 (w), 1623 (w), 1550 (s), 1519 (s), 1455 (s), 1412 (s),
1316 (s), 1261 (s), 1224 (m), 1171 (s), 1098 (m), 1027 (m), 926
(m), 888 (m), 848 (m), 792 (m), 759 (m), 722 (m), 628 (m), 557
(m), 502 (m), 435 (m). Anal. Calcd for C47H74N2NiP (756.8):
C, 74.6; H, 9.9; N, 3.7. Found: C, 74.9; H, 10.2; N, 4.1.
Data for 3 are as follows. Yield: 0.29 g (94%). Yellow
crystals. EPR (toluene, 25 °C): not observed. EPR (toluene,
-78 °C): 2.03, 2.16, 2.43. IR (Nujol, cm-1): 1800 (w), 1736
(w), 1620 (w), 1583 (m), 1547 (m), 1522 (s), 1461 (s), 1432 (s),
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A â-Diketiminato-Nickel(II) Synthon
Organometallics, Vol. 24, No. 24, 2005 5903
1407 (s), 1379 (s), 1357 (m), 1319 (s), 1264 (m), 1249 (m), 1225
(m), 1175 (s), 1151 (m), 1096 (s), 1055 (m), 1023 (m), 997 (m),
963 (w), 931 (m), 852 (m), 791 (m), 765 (m), 742 (s), 722 (m),
693 (s), 637 (m), 617 (w), 514 (m), 500 (m), 480 (m), 442 (m),
418 (m). Anal. Calcd for C54H63N2NiP2 (860.8): C, 75.4; H, 7.4;
N, 3.3. Found: C, 75.0; H, 7.6; N, 3.1.
Data for 4 are as follows. Yield: 0.22 g (96%) Red crystals.
EPR (toluene, 25 °C): g ) 2.19. IR (Nujol, cm-1): 2197 (s),
1913 (w), 1848 (w), 1793 (w), 1723 (w), 1621 (w), 1539 (s), 1523
(s), 1460, 1438 (s), 1408 (s), 1378 (s), 1321 (s), 1255 (m), 1229
(m), 1179 (s), 1102 (m), 1057 (m), 1026 (m), 934 (m), 795 (m),
756 (s), 720 (m), 685 (m), 653 (w), 520 (m), 443 (m). Anal. Calcd
for C36H46N3Ni (579.5): C, 74.6; H, 8.0; N, 7.3. Found: C, 74.1;
H, 8.5; N, 7.3.
Data for 5 are as follows. Yield: 0.25 g (83%). Green crystals.
Crystals were 5‚0.5PhCCPh. EPR (toluene, 25 °C): g ) 2.19.
IR (Nujol, cm-1): 1852 (m), 1731 (m), 1624 (m), 1591 (w), 1531
(s), 1462 (m), 1437 (s), 1376 (s), 1317 (s), 1258 (s), 1177 (m),
1103 (m), 1066 (m), 1026 (m), 936 (m), 908 (w), 859 (m), 797
(m), 756 (s), 692 (s), 629 (m), 553 (m), 529 (m), 447 (m). Anal.
Calcd for C50H56N2Ni (743.7): C, 80.8; H, 7.6; N, 3.8. Found:
C, 80.2; H, 8.0; N, 3.8.
Data for 6 are as follows. Yield: 0.24 g (93%). Green crystals.
EPR (toluene, 25 °C): g ) 2.20. IR (Nujol, cm-1): 1918 (w),
1859 (w), 1803 (s), 1626 (w), 1531 (s), 1459 (s), 1430 (s), 1393
(s), 1318 (s), 1250 (s), 1178 (s), 1107 (m), 1059 (w), 1024 (m),
932 (m), 846 (s), 795 (m), 755 (s), 701 (m), 640 (m), 520 (w),
437 (m). Anal. Calcd for C37H59N2NiSi2 (646.8): C, 68.7; H,
9.2; N, 4.3. Found: C, 68.3; H, 8.8; N, 4.4.
Data for 7 are as follows. Yield: 0.23 g (88%). Green crystals.
EPR (toluene, 25 °C): g ) 2.22. IR (Nujol, cm-1): 1945 (w),
1911 (w), 1890 (w), 1850 (w), 1791 (w), 1728 (m), 1622 (w),
1599 (w), 1587 (w), 1577 (w), 1527 (s), 1493 (m), 1461 (s), 1434
(s), 1404 (s), 1383 (s), 1341 (m), 1314 (s), 1276 (m), 1259 (s),
1227 (m), 1178 (s), 1157 (m), 1129 (m), 1098 (s), 1056 (m), 1025
(s), 981 (w), 956 (w), 935 (s), 912 (m), 897 (m), 869 (m), 853
(m), 791 (s), 757 (s), 716 (m), 695 (s), 628 (m), 609 (m), 589
(m), 568 (m), 551 (w), 522 (m), 458 (m). Anal. Calcd for
C43H53N2Ni (656.6): C, 78.7; H, 8.1; N, 4.3. Found: C, 78.4;
H, 8.2; N, 4.3.
Data for 8 are as follows. Yield: 0.25 g (96%). Green crystals.
EPR (toluene, 25 °C): g ) 2.23. IR (Nujol, cm-1): 1974 (w),
1913 (w), 1856 (w), 1817 (w), 1791 (w), 1727 (m), 1662 (m),
1646 (m), 1596 (m), 1577 (m), 1522 (s), 1463 (s), 1406 (vs), 1318
(s), 1282 (s), 1250 (s), 1227 (m), 1178 (s), 1157 (m), 1101 (s),
1075 (m), 1057 (m), 1023 (m), 934 (s), 857 (m), 844 (m), 792
(s), 761 (s), 740 (m), 695 (s), 660 (m), 634 (s), 595 (s), 531 (w),
493 (w), 439 (m). Anal. Calcd for C42H51N2NiO (658.6): C, 76.6;
H, 7.8; N, 4.3. Found: C, 76.5; H, 7.7; N, 4.1.
3JHH ) 7 Hz, 6 H, CHMe2), 0.94 (s, 6 H, CdCMeMe), 0.50 (s,
6 H, CdCMeMe). 13C{1H} NMR (δ): 160.4, 151.9 (NC), 125.5,
151.9, 142.9, 141.4, 141.1, 140.2, 124.8, 124.7, 123.9, 123.8,
123.8 (Ar), 123.7 (CdCMe2), 120.4 (CdCMe2), 99.3 (γ-C), 97.1,
77.0, 66.2, 47.7 (CH), 29.4, 28.4, 28.3, 27.7 (CHMe2), 25.7, 25.1,
24.9, 24.6, 24.4, 24.0, 24.0, 23.9 (CHMe2), 23.9, 22.7 (NCMe).
Anal. Calcd for C74H102N4Ni2 (1165.1): C, 76.3; H, 8.8; N, 4.8.
Found: C, 76.1; H, 9.0; N, 4.8.
X-ray Data Collection and Reduction. Crystals were
manipulated 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 were collected in a
hemisphere of data in 1448 frames with 10 s exposure times.
The observed extinctions were consistent with the space groups
in each case. The data sets were collected (4.5° < 2θ < 45-
50.0°). 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 absorp-
tion correction based on redundant data was applied to each
data set. Subsequent solution and refinement was performed
using the SHELXTL solution package.
Structure Solution and Refinement. Non-hydrogen
atomic scattering factors were taken from the literature
tabulations.51 The heavy-atom positions were determined using
direct methods employing the SHELXTL direct-methods rou-
tine. The remaining non-hydrogen atoms were located from
successive difference Fourier map calculations. The refine-
ments were carried out by using full-matrix least-squares
techniques on F, minimizing the function w(Fo - Fc)2, where
2
2
the weight w is defined as 4Fo /2σ(Fo ) 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 in the absence of
disorder or insufficient data. In the latter cases atoms were
treated isotropically. In the case of compound 1 the methyl
group of toluene was modeled by a 50:50 two-site disorder.
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 temperature 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.
Crystallographic data and structure solution and refinement
details are given in Table 1.
Synthesis of ((Nacnac)Ni(η3-C5H4CMe2))2 (9). Dimeth-
ylfulvene (0.042 g, 0.40 mmol) was added to a solution of 1
(0.208 g, 0.20 mmol) in toluene (8 mL) at 25 °C. The mixture
was stirred overnight. After concentration in vacuo, the
resulting deep brown solution was kept at -35 °C for 3 days
to isolate red crystals of 9‚3C7H8 (0.21 g, 72%). IR (Nujol, cm-1):
2119 (m), 1923 (w), 1860 (w), 1797 (w), 1661 (w), 1582 (w),
1525 (s), 1467 (s), 1456 (s), 1438 (s), 1385 (s), 1377 (s), 1318
(s), 1227 (s), 1180 (s), 1102 (s), 1055 (m), 1023 (s), 936 (m),
909 (m), 857 (m), 822 (m), 793 (s), 762 (s), 716 (m), 632 (m),
552 (m), 527 (m), 506 (m), 469 (m), 454 (m). 1H NMR (δ): 7.15-
6.95 (m, 27 H, PhMe, Ar), 6.87 (tr, 3JHH ) 8 Hz, 2 H, Ar), 6.70
(dd, 3JHH ) 8 Hz, 2 H, Ar), 6.38 (t, 3JHH ) 3 Hz, 2 H, CH), 4.79
Results and Discussion
The compound (Nacnac)Ni(µ-Br)2Li(THF)2 was re-
duced by reaction with K/Na alloy at 25 °C for 1 week
in toluene. After filtration, concentration, and storage
of the solution at -35 °C dark red crystals of 1 were
formed. Isolation of a second crop of product in a similar
manner afforded a total yield of 67%. In a similar
fashion treatment of (Nacnac)Ni(µ-Br)2Li(THF)2 with
MeMgBr in toluene resulted in reduction and the
1
3
formation of 1 in 64% yield. The H NMR spectrum of
(s, 2 H, γ-CH), 4.07 (sept, JHH ) 7 Hz, 2 H, CHMe2), 3.85
(sept, 3JHH ) 7 Hz, 2 H, CHMe2), 3.45 (br t, 3JHH ) 3 Hz, 1 H,
1 is composed of sharp resonances indicative of a
diamagnetic compound (Figure 1). The elemental analy-
ses were consistent with a â-diketiminato ligand-to-
toluene ratio of 2:1, while a single-crystal X-ray crys-
CH), 3.23 (sept, 3JHH ) 7 Hz, 2 H, CHMe2), 3.12 (sept, 3JHH
)
7 Hz, 2 H, CHMe2), 2.09 (s, 9 H, PhMe), 1.94 (brs, 2 H, CH),
3
1.84 (br t, JHH ) 3 Hz, 2 H, CH), 1.51 (s, 6 H, CMe), 1.47 (d,
3
3JHH ) 7 Hz, 6 H, CHMe2), 1.41 (s, 6 H, CMe), 1.40 (dd, JHH
3
) 7 and 7 Hz, 12 H, CHMe2), 1.19 (d, JHH ) 7 Hz, 6 H,
(51) Cromer, D. T.; Waber, J. T. International Tables of X-ray
Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. 4, pp
71-147.
CHMe2), 1.12 (d, 3JHH ) 7 Hz, 6 H, CHMe2), 1.11 (d, 3JHH ) 6
3
Hz, 6 H, CHMe2), 1.05 (d, JHH ) 7 Hz, 6 H, CHMe2), 0.96 (d,

5904 Organometallics, Vol. 24, No. 24, 2005
Bai et al.
Figure 1. 1H NMR spectrum of 1. Expansions of the
aromatic, methine, and methyl resonances are shown in
a-c, respectively.
Figure 2. ORTEP drawing of 1, with 30% thermal
ellipsoids. Hydrogen atoms are omitted for clarity. One
position of the disordered toluene methyl group is shown
in gray. Selected distances (Å) and angles (deg): Ni(1)-
N(1) ) 1.894(6), Ni(1)-N(2) ) 1.930(4), Ni(1)-C(31) )
1.980(5), Ni(1)-C(30) ) 2.185(6), Ni(1)-C(32) ) 2.209(5),
C(30)-C(31) ) 1.425(9), C(30)-C(32)′ ) 1.445(9), C(31)-
C(32) ) 1.412(8); N(1)-Ni(1)-N(2) ) 96.48(19).
tallographic study revealed the formulation of 1 as
((Nacnac)Ni)2(µ-η3:η3-C6H5Me) (Figure 2). The Ni is
coordinated to two N atoms at distances of 1.894(6) and
1.930(4) Å and interacts with the sides of the 2-fold
disordered toluene molecule in an η3:η3 manner. The
crystallographic symmetry constrains the two NiN2
planes to be parallel to each other and results in an
angle of 88° between NiN2 planes and the plane of the
toluene molecule. The Ni-C distances of 2.185(6), 1.980-
(5), and 2.209(5) Å are reminiscent of a Ni-allyl
fragment. The C-C (C30-C32′) distances between the
allyl fragments are 1.445(9) Å. This geometry, together
with the diamagnetic nature of 1, supports the notion
that electron transfer from Ni to toluene has occurred,
affording a compound containing two Ni(II) centers and
a bridging dianionic toluene fragment. Single-electron
transfer to toluene has been previously described by
Lappert and co-workers in the presentation of the
compound (18-crown-6)K(η6-C6H5Me).52
signal. The g values of 2.14, 2.17, and 2.46 were
determined via simulation. This compares with the
signals at 2.068, 2.133, and 2.435 reported for (HC-
(CMeNC6H3Me2)2)Ni(2,4-lutidine).50 While the solid-
state structure and NMR data support a Ni(II) formu-
lation, the observation of a weak EPR signal for 1
suggest that a Ni(I) species is accessible in solution. This
view is further supported by the reactivity of 1. For
example, compound 1 reacts with the phosphines PCy3
and Ph2PCH2PPh2 to give the paramagnetic complexes
(Nacnac)Ni(PCy3) (2) and (Nacnac)Ni(Ph2PCH2PPh2)
(3), respectively (Scheme 1). These products do not give
rise to an EPR signal at 25 °C in solution; however, in
frozen toluene solution at -78 °C these species gave
similar spectra (Figure 3). Spectral simulations were
used to determine the g values. This coupling is con-
sistent with a single Ni-P bond in both complexes.
Highly concentrated toluene solutions of compound
1 (18 mg in 0.2 mL) reveal a broad, weak, but discernible
EPR signal with g ) 2.20 at room temperature. At low
temperature, frozen solutions of 1 exhibit a weak axial
Table 1. Crystallographic Data
1
2
3
4
5.0.5PhCCPh
6
7
8
9.3(toluene)
formula
formula wt
cryst syst
space group
a (Å)
C65H90N4Ni2 C47H74N2NiP C54H64N2NiP2 C36H46N3Ni C50H56N2Ni C37H59N2NiSi2 C43H53N2Ni C42H51N2NiO C95H126N4Ni2
1044.82
756.76
861.72
579.47
743.68
646.75
656.58
658.56
1441.42
triclinic
P1h
monoclinic monoclinic
orthorhombic monoclinic triclinic
orthorhombic monoclinic monoclinic
P21/n
P21
P212121
P21/n
P1h
Pbcn
P21/n
C2/c
10.783(3)
19.725(6)
14.118(4)
11.2919(6)
17.6025(9)
11.7930(6)
13.4602(8)
18.2396(12)
19.8633(12)
8.722(3)
15.043(5)
25.743(8)
9.9381(19)
10.815(2)
20.289(4)
86.755(4)
82.996(4)
80.134(3)
10.7774(16)
17.672(3)
21.089(3)
11.995(5)
53.177(10)
13.3750(16)
14.8811(18)
24.154(3)
104.371(2)
93.535(2)
109.941(2)
4320.9(9)
2
b (Å)
22.680(11) 9.1830(17)
c (Å)
13.875(7)
40.478(8)
R (deg)
â (deg)
γ (deg)
V (Å3)
94.810(10)
108.8510(10)
95.613(7)
97.749(11) 130.063(2)
2992.2(14)
2218.3(2)
2
1.133
4876.6(5)
4
3361.5(19) 2130.9(7)
4
4016.5(10)
3740(3)
4
1.166
15128(5)
16
1.157
Z
2
2
4
d(calcd)
1.160
1.174
1.145
1.159
1.070
1.108
(g cm-3
)
abs coeff, µ
0.670
4276
0.505
0.500
0.603
0.490
4950
0.567
0.549
0.545
0.481
(mm-1
)
no. of data
collected
R(int)
no. of data,
Fo2 >3σ(Fo
no. of
variables
R
11 041
24 116
15 561
36 415
13 603
70 936
36 457
0.0162
2775
0.0197
6297
0.0490
7030
0.1190
4896
0.0259
3356
0.0461
3534
0.0804
5476
0.1954
13 294
0.0676
12 530
2
)
325
460
532
361
478
191
415
829
754
0.0727
0.1769
1.016
0.0325
0.0779
1.024
0.0392
0.0885
0.988
0.0808
0.1892
1.009
0.0737
0.2118
1.126
0.0522
0.1383
1.031
0.0605
0.1302
1.009
0.0821
0.1847
0.988
0.0837
0.2235
1.006
Rw
GOF

A â-Diketiminato-Nickel(II) Synthon
Organometallics, Vol. 24, No. 24, 2005 5905
Figure 3. Frozen toluene solution EPR spectrum of 2. g
values of 2.14, 2.17, and 2.45 were determined by spectral
simulation.
Figure 5. ORTEP drawing of 3, with 30% thermal
ellipsoids. Hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (deg): Ni(1)-N(1) ) 1.889(3),
Ni(1)-N(2) ) 1.935(3), Ni(1)-P(1) ) 2.2150(9); N(1)-
Ni(1)-N(2) ) 96.44(12), N(1)-Ni(1)-P(1) ) 142.96(9),
N(2)-Ni(1)-P(1) ) 120.56(9).
Figure 4. ORTEP drawing of 2, with 30% thermal
ellipsoids. Hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (deg): Ni(1)-N(1) ) 1.943(2),
Ni(1)-N(2) ) 1.957(2), Ni(1)-P(1) ) 2.2786(8); N(1)-
Ni(1)-N(2) ) 96.70(9), N(1)-Ni(1)-P(1) ) 135.43(6), N(2)-
Ni(1)-P(1) ) 127.25(7).
Scheme 1
Figure 6. ORTEP drawing of 4, with 30% thermal
ellipsoids. Hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (deg): Ni(1)-N(3) ) 1.811(6),
Ni(1)-N(1) ) 1.848(5), Ni(1)-N(2) ) 1.920(4), N(3)-C(30)
) 1.183(8); N(3)-Ni(1)-N(1) ) 158.8(2), N(3)-Ni(1)-N(2)
) 103.1(2), N(1)-Ni(1)-N(2) ) 97.88(18), C(30)-N(3)-
Ni(1) ) 172.8(6), N(3)-C(30)-C(31) ) 176.2(7).
and 3, respectively. The N-Ni-P angles are 135.43(6)
and 127.25(7)° in 2 and 142.96(9) and 120.56(9)° in 3.
The longer Ni-P bond in 2 results from that the greater
steric demands of PCy3, despite its greater basicity in
comparison to Ph2PCH2PPh2. Similarly, the distortion
of the geometry about Ni in 3 is consistent with a
sterically crowded coordination site and the dissym-
metric nature of the monodentate coordinating phos-
phine Ph2PCH2PPh2.
In a similar fashion, compound 1 reacts with PhCN
to give a Ni(I) coordination complex, formulated as
(Nacnac)Ni(NCPh) (4) (Scheme 1) on the basis of EPR
spectroscopy and confirmed by crystallography (Figure
6). The Ni-N bond lengths in 4 for the Nacnac ligand
were found to be 1.848(5) and 1.920(4) Å, while the
N-Ni-N chelate bite angle is 97.88(18)°. This geometry
is similar to those described above. The Ni-N bond
distance for the coordinated nitrile was found to be
1.811(6) Å, consistent with strong σ donation. However,
the geometry about Ni is not symmetric. The Nacnac
ligand N atoms form angles with the coordinated
These formulas were confirmed via crystallographic
studies (Figures 4 and 5). In these compounds, the Ni
atom is three-coordinate. In 2, the Ni-N distances are
1.943(2) and 1.957(2) Å and the Ni-P distance is 2.2786-
(8) Å, whereas in 3, the corresponding distances are
1.889(3), 1.935(3), and 2.2150(9) Å. The Ni(I) centers
reside in pseudo-trigonal-planar coordination spheres
with chelate bite angles of 96.70(9) and 96.44(12)° in 2
(52) Hitchcock, P. B.; Lappert, M. F.; Protchenko, A. V. J. Am. Chem.
Soc. 2001, 123, 189-190.

5906 Organometallics, Vol. 24, No. 24, 2005
Bai et al.
Figure 7. Frontier orbitals of (Nacnac)NiL.
Figure 9. ORTEP drawing of 6, with 30% thermal
ellipsoids. Hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (deg): Ni(1)-N(1) ) 1.944(2),
Ni(1)-C(16) ) 1.960(3), C(16)-C(16)′ ) 1.250(7); N(1)-
Ni(1)-N(1) ) 94.97(15), N(1)-Ni(1)-C(16) ) 121.32(13),
N(1)-Ni(1)-C(16) ) 139.56(14), N(1)-Ni(1)-C(16) )
139.56(14), N(1)-Ni(1)-C(16) ) 121.32(13), C(16)′-C(16)-
Si(1) ) 147.09(11), C(16)′-C(16)-Ni(1) ) 71.40(10), Si(1)-
C(16)-Ni(1) ) 141.5(2).
less, the geometries about Ni in both products are
neither square planar nor tetrahedral. The angles
between the NiN2 and NiC2 planes were found to be 37.9
and 59.1° for 5 and 6, respectively. These distorted
geometries reflect the steric congestion resulting from
interaction of the sterically demanding Nacnac ligand
and acetylene substituents. The Ni-N distances are
1.917(7) and 1.920(7) Å in 5 and 1.944(2) Å in 6, while
the ligand bite angles are 94.7(3) and 94.97(15)° in 5
and 6, respectively. These Ni-N bond lengths are
similar to those seen above for the Ni(I) products and
significantly longer than those seen in the Ni(III)-imido
compound (Nacnac)NidNAd (1.884(2), 1.874(2) Å).50 The
Ni-C distances were found to be 1.906(9) and 1.914(8)
Å in 5 and 1.960(3) Å in 6. The longer Ni-C distance
in 6 reflects the greater steric demands of the acetylene
substituents. Nonetheless, the geometries about the
acetylenic carbons in 5 and 6 are similar, as revealed
by Ni-C-CPh angles of 141.1(7) and 146.7(8)° and
C-C-CPh angles of 147.0(9) and 141.9(6)° in 5 and the
corresponding Ni-C-Si and C-C-Si angles of 141.5(2)
and 147.09(11)° respectively in 6. These “bend-back”
angles suggest the possibility of electron donation from
the Ni to the acetylenic π* orbitals. However, this is not
reflected in the acetylenic C-C bond distances of
1.266(14) and 1.250(7) Å in 5 and 6, respectively. These
metric data are consistent with the view that the
products are best viewed as Ni(I)-acetylene adducts
rather than Ni(III) metallacycles.
A closely related situation results in the product of
the reaction of 1 with the olefin Ph2CCH2. This reaction
gives the product (Nacnac)Ni(η2-H2CCPh2) (7) in 88%
isolated yield (Scheme 1). This species gives rise to a
broad EPR resonance in solution at g ) 2.22. A crystal-
lographic study (Figure 10) of 7 revealed that, similar
to 5 and 6, compound 7 is four-coordinate. However, the
geometry about Ni is best described as pseudo sqaure
planar, as the angle between the NiN2 and the NiC2
plane is only 13.1°. Despite the difference in geometry
at Ni, the Nacnac-Ni parameters in 7 are similar to
those in 5 and 6 (Ni-N ) 1.902(4), 1.943(4) Å, N-Ni-N
) 97.03(17)°). The Ni-C bond lengths were found to be
Figure 8. ORTEP drawing of 5, with 30% thermal
ellipsoids. Hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (deg): Ni(1)-C(4) ) 1.906(9),
Ni(1)-C(5) ) 1.914(8), Ni(1)-N(2) ) 1.917(7), Ni(1)-N(1)
) 1.920(7); C(5)-Ni(1)-N(2) ) 118.2(4), C(4)-Ni(1)-N(1)
) 114.8(4), C(5)-Ni(1)-N(1) ) 143.7(4), N(2)-Ni(1)-N(1)
) 94.7(3), C(5)-C(4)-Ni(1) ) 71.0(6), C(4)-C(5)-Ni(1) )
70.3(5).
benzonitrile N of 158.8(2) and 103.1(2)°. This geometry
about Ni is best described as a pseudo-T-shaped.
Nonetheless, the geometry of the nitrile is linear as
expected, with C-N-Ni and N-C-C angles of 172.8(6)
and 176.2(7)°, respectively. Similar geometries have
been described for (Nacnac)Ni(2,4-lutidine).50
The differing geometries of 2-4 can be understood
by consideration of the (Nacnac)NiX frontier orbitals
described by Holland and co-workers.17,19 Addition of an
electron to the Ni(II) frontier orbitals fills the b1 orbital
in the xz plane, leaving the HOMO as the singly
occupied b2 orbital in the yz plane. In the case of 4,
donation from the N of the nitrile to this SOMO is
consistent with the “T-shaped” coordination sphere
about Ni. The closer approach of the geometry of the
phosphine adducts 2 and 3 to trigonal-planar geometry
may result from the steric issues discussed above.
However, this geometry also provides for the π back-
donation from Ni to phosphorus (Figure 7).
Compound 1 also reacts with the acetylenes PhCCPh
and Me3SiCCSiMe3, resulting in the formation of the
crystalline products (Nacnac)Ni(η2-PhCCPh) (5) and
(Nacnac)Ni(η2-Me3SiCCSiMe3) (6) in yields of 83% and
93%, respectively (Scheme 1). Crystallographic studies
of 5‚0.5PhCCPh and 6 (Figures 8 and 9) confirmed these
formulations. In these compounds, the Ni centers are
four-coordinate with coordination of the Nacnac ligand
and the acetylene. In the case of 6, crystallographic site
symmetry imposes a C2 axis on the molecule. Nonethe-

A â-Diketiminato-Nickel(II) Synthon
Organometallics, Vol. 24, No. 24, 2005 5907
Figure 10. ORTEP drawing of 7, with 30% thermal
ellipsoids. Hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (deg): Ni(1)-N(2) ) 1.902(4),
Ni(1)-N(1) ) 1.943(4), Ni(1)-C(30) ) 1.982(5), Ni(1)-C(31)
) 2.088(5), C(30)-C(31) ) 1.391(6); N(2)-Ni(1)-N(1) )
97.03(17), N(2)-Ni(1)-C(30) ) 168.20(18), N(1)-Ni(1)-
C(30) ) 94.72(19), N(2)-Ni(1)-C(31) ) 128.45(19), N(1)-
Ni(1)-C(31) ) 133.16(19), C(31)-C(30)-Ni(1) ) 74.2(3),
C(30)-C(31)-Ni(1) ) 66.0(3).
Figure 12. ORTEP drawing of 9, with 30% thermal
ellipsoids. Hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (deg): Ni(1)-N(1) ) 1.917(5),
Ni(1)-N(2) ) 1.930(5), Ni(1)-C(30) ) 1.915(6), Ni(1)-C(31)
) 2.029(6), Ni(1)-C(34) ) 2.112(6), Ni(2)-N(3) ) 1.917(5),
Ni(2)-N(4) ) 1.918(5), Ni(2)-C(67) ) 1.925(6), Ni(2)-C(68)
) 2.112(6), Ni(2)-C(71) ) 2.005(6), C(30)-C(31) ) 1.404(8),
C(30)-C(34) ) 1.407(9), C(31)-C(32) ) 1.523(8), C(32)-
C(33) ) 1.519(8), C(32)-C(70) ) 1.573(8), C(33)-C(35) )
1.371(9), C(33)-C(34) ) 1.453(9), C(67)-C(71) ) 1.377(9),
C(67)-C(68) ) 1.425(9), C(68)-C(69) ) 1.455(9), C(69)-
C(72) ) 1.340(9), C(69)-C(70) ) 1.527(8), C(70)-C(71) )
1.517(9), C(72)-C(73) ) 1.506(10), C(72)-C(74) ) 1.521(12);
C(30)-Ni(1)-N(1) ) 127.0(3), C(30)-Ni(1)-N(2) ) 125.2-
(3), N(1)-Ni(1)-N(2) ) 96.0(2), N(3)-Ni(2)-N(4) ) 96.5-
(2).
distance of 1.825(5) Å. The bite angle for the Nacnac
ligand is similar to those above at 96.7(2)°, while the
N-Ni-O angles were found to be 138.2(2) and 125.0(2)°.
The geometry at O is approximately linear, with a Ni-
O-C angle of 172.0(5)°. The C-O bond distance is
1.239(7) Å. This orientation may reflect the steric
crowding within the coordination site as a result of
interactions of the ketonic aryl groups with the aryl
substituents on the Nacnac ligand. In addition, the
geometry at O allows for electron donation to the HOMO
(b2) on Ni and for π back-donation from the filled Ni b1
orbital to the π* orbital of the carbonyl fragment. The
degree of electron transfer from Ni to ligand is an
interesting aspect of this compound. If electron transfer
from the metal to the ligand occurred, then 8 could be
formulated as a Ni(II)-benzophenone radical anion.
However, the EPR signal for 8 gives rise to a resonance
at g ) 2.23. This is typical of the formally Ni(I) species
and distinct from carbon-based radicals, thus implying
that the unpaired electron resides in a metal-based
orbital and supporting a Ni(I)-benzophenone adduct
description.
Figure 11. ORTEP drawing of one of the two molecules
of 8 in the asymmetric unit, with 30% thermal ellipsoids.
Hydrogen atoms are omitted for clarity. Selected distances
(Å) and angles (deg): Ni(1)-O(1) ) 1.825(5), Ni(1)-N(2)
) 1.899(5), Ni(1)-N(1) ) 1.910(5), O(1)-C(30) ) 1.239(7);
O(1)-Ni(1)-N(2) ) 138.2(2), O(1)-Ni(1)-N(1) ) 125.0(2),
N(2)-Ni(1)-N(1) ) 96.7(2), C(30)-O(1)-Ni(1) ) 172.0(5).
1.982(5) and 2.088(5) Å, with the latter longer bond
resulting from the substituted carbon of the olefin.
These distances are significantly longer than the Ni-C
distances seen in the acetylene adducts 5 and 6,
consistent with the poorer donor ability of olefins as well
as the additional steric demands provided by the phenyl
substituents of Ph2CCH2. The olefinic C-C bond length
of 1.391(6) Å and the sum of the C-C-C angles about
the subsituted olefinic carbon of 357.5° indicate little
perturbation of the olefin upon coordination to Ni.
In the related reaction of 1 with Ph2CO, the para-
magnetic Ni(I) complex (Nacnac)Ni(OCPh2) (8) is formed
in 96% isolated yield (Scheme 1). While only weakly
diffracting crystals could be obtained, X-ray crystal-
lographic data (Figure 11) for this product did confirm
pseudo-trigonal-planar geometry about Ni with Ni-N
bond lengths of 1.899(5) and 1.910(5) Å and a Ni-O
The possibility of metal-to-ligand electron transfer
was demonstrated in the reaction of 1 with dimethyl-
fulvene. Stirring of the reaction mixture in toluene at
25 °C overnight resulted in a deep brown solution.
Following concentration of the solution and storage at

5908 Organometallics, Vol. 24, No. 24, 2005
Bai et al.
-35 °C of the solution red crystals of 9‚3C7H8 were
isolated in 72% yield. The 1H and 13C{1H} NMR spectra
of 9 confirmed the presence of the ligand and fulvene
fragments. The methyl groups of the dimethylfulvene
fragments were inequivalent, exhibiting 1H NMR reso-
nances at 0.50 and 0.94 ppm. These data together with
the observation of the 13C{1H} NMR resonance at 47.7
ppm corresponding to a methine carbon suggest dimer-
ization of via coupling of two dimethylfulvene units. A
crystallographic study confirmed that crystals of 9‚
3C7H8 formed in toluene were formulated as [(Nacnac)-
Ni)2(η3:η3-C5H4CMe2)2]‚3C7H8 (Scheme 1). In this com-
pound, two (Nacnac)Ni centers bind to linked fulvenide
fragments in η3 fashions (Figure 12). The two fulvenide
fragments are linked by a typical C-C single bond
(1.573(8) Å) between the carbons R to the dimethyl-
methylene substituents. This geometry about the Ni
centers in 9 is reminiscent of that seen in 1. The Ni-N
bond distances are 1.917(5), 1.930(5), 1.917(5), and
1.918(5) Å, and the chelate rings form N-Ni-N angles
of 96.0(2) and 96.5(2)°. The fulvenide fragments coor-
dinate to the metal in an η3 fashion with Ni(1)-C
distances of 1.915(6), 2.029(6), and 2.112(6) Å and
Ni(2)-C distances of 1.925(6), 2.112(6), and 2.005(6) Å,
affording a geometry reminiscent of Ni(II)-allyl com-
plexes. The formation of the diamagnetic product 9 is
thought to proceed via exchange of dimethylfulvene for
toluene at Ni, followed by electron transfer from Ni to
the fulvene fragment and C-C coupling of the carbon-
based radicals.
Summary
Compound 1 is diamagnetic and is thus formulated
as a Ni(II) product. Nonetheless, it reacts in a facile
manner with a variety of donors such as phosphines,
nitriles, acetylenes, olefins, and ketones to give Ni(I)
compounds. The M-L interaction involves both ligand-
to-metal σ donation and metal-to-ligand π donation.
Electron transfer from the metal to the ligand was
demonstrated in the case of the reaction of 1 with
dimethylfulvene, where C-C coupling gives the diful-
venide bimetallic complex 9.
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.
OM050544F