A diazabutadiene stabilized nickel(0) cyclooctadiene complex: Synthesis, characterization and the reaction with diphenylacetylene

Article abstract of DOI:10.1002/zaac.200500424

The reaction of [Ni(COD)₂] with one equivalent of DAB ^Mes (DAB^Mes = (2,4,6-Me₃C₆H ₂)N=C(Me)-C(Me)=N(2,4,6-Me₃C₆H₂)) affords a mixture of the compound [Ni(DA

Full text of DOI:10.1002/zaac.200500424

DOI: 10.1002/zaac.200500424
A Diazabutadiene stabilized Nickel(0) Cyclooctadiene Complex: Synthesis,
Characterization and the Reaction with Diphenylacetylene
Thomas Schaub and Udo Radius*
Karlsruhe, Institut für Anorganische Chemie der Universität (TH)
Received October 31st, 2005.
Professor Kurt Dehnicke zum 75. Geburtstag gewidmet
Abstract. The reaction of [Ni(COD)2] with one equivalent of
DABMes (DABMes ϭ (2,4,6-Me3C6H2)NϭC(Me)-C(Me)ϭN(2,4,6-
Me3C6H2)) affords a mixture of the compound [Ni(DABMes)2] (2)
and starting material [Ni(COD)2]. The crystallographically charac-
terized, diamagnetic complex 2 can be obtained in a stoichiometric
reaction of [Ni(COD)2] and two equivalents of DABMes. This reac-
tion can be accelerated by addition of 1-chloro-fluorobenzene
or methyl iodide. In the presence of 1-chloro-fluorobenzene,
[Ni(DABMes)(COD)] (3) is available via reaction of [Ni(COD)2] and
one equivalent of DABMes. The crystallographically characterized
complex 3 reacts with diphenylacetylene to afford [Ni(DABMes)-
(Ph-CϵC-Ph)] (4). A long-wavelength absorption band in the UV-
Vis spectrum of this compound has to be assigned to a mixed
MLCT/LLЈCT transition, as quantum chemical calculations reveal.
Keywords: Diazabutadiene complexes; Nickel; Alkyne complexes;
DFT calculations.
Introduction
system is ideally suited to stabilize nickel(0) complexes and
that the application of DAB nickel(0) complexes in various
fields of catalysis has been established.
We became interested into DAB nickel(0) chemistry dur-
ing our latest work on C-C and C-F activation using
N-heterocyclic carbene stabilized complexes of the type
[Ni2(ImR2)4(COD)] (ImR2 ϭ 1,3-di(R)imidazole-2-ylidene)
[5]. [Ni2(ImiPr2)4(COD)] (A) activates the C-F bond of hexa-
fluorobenzene very efficiently and is also an excellent cata-
lyst for the catalytic insertion of diphenyl acetylene into the
Because of their high electronic and coordination mode
flexibility [1, 2], the coordination chemistry of diazabuta-
diene ligands (RNϭC(Me)-C(Me)ϭNR; DABR) has at-
tracted attention over the last decades. This includes un-
usual electron-donor and -acceptor properties of these
ligands, combining the useful features of N-based donor
ligands such as 2,2Ј-bipyridine or 1,10-phenanthroline and
unsaturated acceptor systems such as dienes. Consequently,
these ligands are generally compatible with metal atoms in
both high and low oxidation states. Especially organometal-
lic nickel complexes with these α-diimine ligands have
gained an enormous interest, mainly due to their success as
effective catalysts in olefin polymerization or olefin/CO co-
polymerization [3]. It has been established mainly by Brook-
hart and co-workers, that nickel(II) organyl complexes with
carefully designed diazabutadiene ligands exhibit higher ac-
tivities than classical Ziegler catalysts combined with a
greatly reduced sensibility towards poisoning by polar func-
tions. DAB stabilized nickel complexes date back to the
1960s [1, 2], and especially the groups of Walther and tom
Dieck developed the chemistry of such compounds [4]. In
their work it has been demonstrated that the DAB ligand
* Priv.-Doz. Dr. Udo Radius
Institut für Anorganische Chemie der Universität
Engesserstr., Geb. 30.45
D-76128 Karlsruhe, Germany
Tel: (Int) ϩ 721-608-8097
email: radius@aoc1.uni-karlsruhe.de
www.ak-radius.de
Scheme
1
Complexes [Ni2(ImiPr2)4(COD)] (A), [Ni(ImiPr2)2-
(Biphenylene)] (B) and [NiL2(η4-Biphenylene)] (C).
Z. Anorg. Allg. Chem. 2006, 632, 807Ϫ813
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
807

Th. Schaub, U. Radius
2,2Ј-C-C-bond of biphenylene. As was previously shown for
other nickel(0) complexes [6], the reaction of A with equim-
olar amounts of biphenylene at low temperature proceeds
under insertion of the nickel(0) biscarbene complex frag-
ment into the strained 2,2Ј-C-C-bond to give the complex
[Ni(ImiPr2)2(Biphenylene)] (B). Theoretical calculations on
the reaction path performed on model systems revealed a
probable intermediate of the type [NiL2(η4-Biphenylene)] C
(L ϭ ImiPr2) [5b], which is located at a local minimum on
the energy surface (see Scheme 1).
ligand 1. This diazabutadiene was synthesized according to
a procedure reported by tom Dieck and co-worker [4g] for
other aryl-substituted diazadienes, i.e. via the acid catalyzed
condensation reaction of 2,4,6-trimethyl aniline and 2,3-bu-
tanedione. The molecular structure of 1 (see Figure 1) re-
veals a trans-alignment of the nitrogen atoms in the solid
˚
state with a C(1)ϭN-double bond (bond length 1.278(2) A)
˚
and a C(1)-C(1)Ј single bond (1.500(2) A) in the diazadiene
unit. The CϭN stretching vibration in the infrared spec-
trum of 1 was observed as a strong band at 1638 cmϪ1
.
For the reaction of A with biphenylene, however, there is
no evidence so far for the involvement of such an intermedi-
ate, since this particular insertion into the strained single
bond of biphenylene is very fast on the NMR timescale.
Earlier studies of Eisch and co-workers demonstrated a de-
pendence of the insertion rate on the metal basicity of the
nickel(0) complex fragment involved in the process, and
therefore we aimed at isolating or identifying a η4- coordi-
nated biphenylene nickel complex using a different set of
ligands L. A comparison of the CO stretching vibrations of
different known dicarbonyl complexes of the type
[NiL2(CO)2] [7] revealed that the complex fragment
[Ni(DABR)] is much less basic compared to similar frag-
ments with L ϭ NHC, phosphine, and bipyridyl ligands,
and hence appropriate for our purposes. Furthermore,
cyclobutadiene complexes of the type [Ni(DABR)-
(η4-C4RЈ4)] have been reported previously [8], and thus we
decided to investigate the reaction of a suitable DAB-Ni0
precursor and biphenylene in order to characterize a pos-
sible η4-coordinated intermediate.
Figure 1 ORTEP diagram of the molecular structure of DABMes
(1) in the solid state (ellipsoids set at 40 % probability level).
H atoms have been omitted for clarity.
˚
Selected bond lengths/A and angles/°: C(1)-C(1)Ј: 1.500(2), C(1)-C(2):
1.497(3), N-C(1) 1.278(2), N-C(3): 1.427(2), N-C(1)-C(1)Ј: 116.23(15),
N-C(1)-C(2): 125.75(19), C(1)-N-C(3): 119.79(15).
In order to synthesize a useful precursor of the
[Ni(DABMes)] complex fragment, the nickel bis(cyclo-
octadiene) complex was reacted with one equivalent of the
diazadiene, which resulted in
a mixture of purple
[Ni(DABMes)2] (2) and starting material. The pure diamag-
netic compound 2 can be synthesized from the reaction of
[Ni(COD)2] and two equivalents diazadiene in good yield.
This reaction can be accelerated by addition of 1-chloro-
fluorobenzene or methyl iodide. In the proton NMR spec-
trum of 2, a set of singlets for the methyl groups of the
backbone (Ϫ1.43 ppm), the methyl groups of the arene
rings (2.22 ppm, 2.43 ppm) and for the arene hydrogen
atoms (6.80 ppm) were detected. The mass spectrum of the
isolated purple powder reveals a signal for the molecular
ion, which fragmented under cleavage of the diazadiene
ligand. The UV-Vis spectrum of a 10Ϫ4 M solution of 2 in
Results and Discussuion
Following our work on NHC stabilized complexes, we in-
tended to synthesize complexes of the type [Ni(D-
ABR)(COD)] as a valuable precursor for the [Ni0(DABR)]
complex fragment. Previous work done in the groups of tom
Dieck and Walther [4d, e, f] demonstrated that diazadiene
stabilized Ni0 complexes are accessible via reduction of
nickel(II) precursors in the presence of diazadiene or from
the reaction of [Ni(COD)2] and a corresponding diazadiene.
In the latter case usually the substitution of a second DAB
ligand of an intermediate [Ni(DABR)(COD)] usually pro-
ceeds much faster compared to the first substitution of
COD. The reactions of [Ni(COD)2] and two equivalents of
diazadiene led to persubstituted complexes of the type
[Ni(DAB)2] with some exceptions for diazadienes with steri-
cally very demanding groups substituted at the nitrogen
atom. For the sterically very demanding DABDip (Dip ϭ
2,6 di(isopropyl)phenyl) ligand, tom Dieck et al. reported
the formation of metallic nickel during the reaction of
[Ni(COD)2] with one or two equivalents of the diazadiene [4g],
respectively, and only traces of the complex [Ni(DABDip)-
(COD)] using an excess of the ligand. For other aryl substi-
tuted ligand systems, however, compounds of the type
[Ni(DABAr)2] are known [4g]. Therefore, we decided to use
the sterically less demanding mesityl substituted DABMes
hexane shows a main absorption at λ ϭ 508 nm (εmax
ϭ
2449 1molϪ1cmϪ1) and a absorption of lower intensity at
λ ϭ 762 nm (εmax ϭ 876 1molϪ1cmϪ1) in the visible region.
The presence of two absorption bands in the UV-Vis spec-
tra of bis(diaazadiene) nickel complexes is characteristic for
compounds with a significant distortion from tetrahedral
to square planar (see below) and are Ϫ according to theor-
etical calculations Ϫ due to charge transfer excitations [9].
Crystals suitable for X-ray diffraction have been obtained
from saturated hexane solutions. Complex 2 crystallizes in
the orthorhombic space group Fdd2 with half of the mol-
ecule in the asymmetric unit. The molecular structure of
[Ni(DABMes)2] (2) along with selected bond lengths and
angles is shown in Figure 2.
808
www.zaac.wiley-vch.de
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2006, 807Ϫ813

A Diazabutadiene stabilized Nickel(0) Cyclooctadiene Complex
concept was realized by an addition of equimolar amounts
of methyl iodide or 1-fluoro-chlorobenzene to [Ni(COD)2]
and a subsequent addition of one equivalent of the DABMes
ligand. Following this procedure, [Ni(DABMes)(COD)] (3)
was synthesized in 72 % isolated yield as a dark purple com-
pound. The 1H and 13C NMR spectra of 3 show the signals
typically found for coordinated DABMes and COD ligands
and the signal for the molecular ion in the EI-MS spectrum
of complex 3 was detected. The UV/Vis spectrum of a
10Ϫ4 M solution of 3 in hexane shows absorptions at λ ϭ
280 nm (εmax ϭ 10348 1molϪ1cmϪ1) and at λ ϭ 496 nm
(εmax ϭ 3892 1molϪ1cmϪ1).
Crystals of 3 suitable for X-ray diffraction were grown
from saturated toluene solutions at Ϫ40 °C (see Figure 3).
Complex 3 crystallizes in the monoclinic space group P21/c
with one molecule in the asymmetric unit. The nickel atom
is distorted tetrahedrally coordinated with two nitrogen
atoms of the DABMes ligand and two alkene entities of the
COD ligand. The Ni-N and Ni-C distances are unexcep-
tional. The CϭN distances of the diazadiene ligand of
1.348(11) and 1.332(12) as well as the C-C distances of
1.404(15) differ significantly from the corresponding bond
lengths in uncoordinated 1 and also from those observed
for the molecular structure of 2. A shorter C-C distance
and an elongated C-N bond of the diazadiene ligand is a
result of a more pronounced backbonding to the diazadiene
π* orbital in 3 compared to the bis(diazadiene) complex 2,
which clearly indicates that the metal atom in the
[Ni(COD)] complex fragment is more basic than the metal
atom in [Ni(DABMes)].
Figure 2 ORTEP diagram of the molecular structure of [Ni(DABMes)2]
(2) in the solid state (ellipsoids set at 40 % probability level).
H atoms have been omitted for clarity.
˚
Selected bond lengths/A and angles/°: Ni-N(1): 1.943(6), Ni-N(2): 1.953(5),
N(1)-C(1): 1.316(9), N(1)-C(3): 1.459(7), N(2)-C(12): 1.356(9), N(2)-C(14):
1.432(6), C(1)-C(12): 1.416(6), C(1)-C(2): 1.484(11), C(12)-C(13): 1.501(10),
N(1)-Ni-N(2): 148.44(13), N(1)-Ni-N(1)Ј: 108.8(3), N(2)-Ni-N(2)Ј: 107.8(3),
N(1)-Ni-N(2): 80.45(19).
Molecular structures of complexes [Ni(DABR)2] reported
earlier have shown that dialkyl-substituted derivatives ad-
opt a distorted tetrahedral coordination (D2d) in which the
planes of the chelates are orthogonal with respect to each
other, whereas this angle significantly deviates from 90° for
aryl-substituted derivatives to adopt (pseudo) D2 symmetry
[4f, g, 10]. This deviation presumably reflects the excellent π
accepting properties especially of the aryl substituted ligand
system and a partial oxidation of the nickel(0) atom takes
place, which is connected with a distortion of the coordi-
nation sphere from tetrahedral towards square planar. In 2,
the chelates intersect each other under an angle of 75.0(6)°,
which is much larger (i.e. towards a tetrahedral coordi-
nation) compared to the corresponding dihedral angles
found for [Ni(DABDMP)2] (44.5°, DMP ϭ 2,6-Me2C6H3)
and [Ni(DABDIP)2] (51°). It is also interesting to note that
for the isoelectronic tetraazadiene complex [Ni{(3,5-
Me2C6H3)2N4}2] this dihedral angle is 90° [11]. Since tetra-
azadiene ligands are considered as even better π-electron
acceptors than diazabutadiene ligands other factors may
also be operative. The planes through the aryl rings inter-
sect the C2N2 cores of the ligands under an angle of ap-
proximately 50° (49.6(9)°). This tilting might be expected
for sterical reasons, but also diminishes delocalization
throughout the coordinated ligand system. Within the DAB
core, the C-N bond lengths of the ligand are slightly in-
Figure 3 ORTEP diagram of the molecular structure of [Ni(DABMes)-
(COD)] (3) in the solid state (ellipsoids set at 40 % probability
level). H atoms have been omitted for clarity.
˚
Selected bond lengths/A and angles/°: Ni-N(1): 1.942(8); Ni-N(2): 1.938(7);
Ni-C(23): 2.075(10); Ni-C(26): 2.077(11); Ni-C(27): 2.077(12); Ni-C(30):
2.076(10); N(1)-C(1): 1.348(11); N(2)-C(2): 1.332(12); C(1)-C(2) 1.404(15);
C(27)-C(26): 1.382(16); C(30)-C(23): 1.367(15); N(1)-Ni-N(2): 81.6(3), N(1)-
Ni-C(23): 120.6(4), N(2)-Ni-C(23): 116.8(4), N(1)-Ni-C(30): 99.8(4), N(2)-
Ni-C(30): 151.4(4), N(1)-Ni-C(27): 115.6(4), N(2)-Ni-C(27): 120.9(4), C(23)-
Ni-C(30): 38.5(4), C(23)-Ni-C(27): 102.0(4), C(27)-Ni-C(30): 84.5(4), N(1)-
Ni-C(26): 150.7(4), N(2)-Ni-C(26): 100.2(4), C(23)-Ni-C(26): 85.0(4), C(26)-
Ni-C(30): 92.3(4), C(26)-Ni-C(27): 38.8(4), C(1)-N(1)-C(5): 117.9(7),
Ni-N(1)-C(1): 113.7(6), Ni-N(1)-C(5): 128.1(5), C(2)-N(2)-C(14): 118.1(7),
Ni-N(2)-C(2): 114.7(7), Ni-N(2)-C(14): 126.7(6), N(1)-C(1)-C(2) 115.2(8),
N(2)-C(2)-C(1) 114.6(8).
˚
creased (N(1)-C(1) of 1.316(9) A and N(2)-C(12) of
˚
˚
1.356(9) A vs. 1.278(2) A in 1) and the C-C bonds decreased
˚
(C(1)-C(12) of 1.416(6) vs. 1.500(2) A in 1) compared to the
uncoordinated ligand, which also reflects significant charge
transfer from the nickel(0) atom to the ligand.
Since all attempts to synthesize [Ni(DABMes)(COD)] (3)
starting from DABMes and [Ni(COD)2] failed in first experi-
ments due to a fast second substitution of the COD ligand
in 3, we were interested in a procedure both to differentiate
and to labilize the COD substituents in [Ni(COD)2]. This
Following our work on nickel carbene complexes, we
studied the reaction behavior of complex 3 towards di-
phenylacetylene and biphenylene as well as mixtures thereof.
Z. Anorg. Allg. Chem. 2006, 807Ϫ813
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
809

Th. Schaub, U. Radius
Unfortunately, complex 3 does not react with biphenylene
at all, even if the reaction is carried out in refluxing toluene
for more than a week. There was also no evidence for a
possible nickel complex with an η4-coordinated biphenylene
ligand. In contrast to the nickel precursors described earlier
[5], in which COD acts as a monodentate, bridging ligand,
the COD ligand in 3 chelates the metal atom and can not
readily be replaced by biphenylene. Reaction mixtures of
biphenylene and diphenylacetylene, however, react
smoothly to afford a blue green material, which turned out
to be the alkyne complex [Ni(DABMes)(Ph-CϵC-Ph)] (4).
Compound 4 was synthesized separately either from the re-
action of 3 with an equimolar amount of diphenylacetylene
or from the reaction of [Ni(COD)2] with one equivalent of
DABMes and one equivalent of diphenylacetylene. Complex
4 shows a simple proton and carbon NMR spectrum, which
is in accordance with a monomeric complex of C2v sym-
metry. The EI mass spectrum of 4 reveals a signal for the
molecular ion. In the UV-Vis spectrum of 4, an absorbtion
at 666 nm (εmax ϭ 2424 1molϪ1cmϪ1) was observed which
can be assigned to a metal to ligand and/or ligand to ligand
charge transfer (see below).
than the CϭC stretching vibration of unsymmetrically sub-
stituted acetylenes. The molecular structure of 4 is in much
closer agreement with a CϭC bond stretching vibration of
unconjugated disubstituted cis-alkenes. Hence, a nickelacy-
clopropene (or nickelirene) structure with a nickel(ll) oxi-
dation state seems to be a more important resonance struc-
ture contributor than a resonance structure where the nickel
center is viewed as in a Ni0 oxidation state. A similar situ-
ation was observed in other nickel diphenyl acetylene com-
plexes [5, 12].
The DAB stabilized nickel complexes reported here are
brightly colored, ranging from purple to blue green in the
solid as well as in solution. The absorption spectra are
dominated by two broad bands of medium intensity in the
visible region and an intense band in the UV region. In
agreement with earlier work by Stufkens et al. [9] we can
assign two long-wavelength bands to charge-transfer tran-
sitions (CT) to the π* orbitals of the diazadiene ligands
and the UV bands to ligand-centred π-π* transitions. Ad-
ditionally, the occurrence of mixed MLCT/LLЈCT (ligand-
to-ligand charge transfer) transitions instead of pure
MLCT transitions have to be discussed for the alkyne com-
plex due to contributions of the co-ligands to the frontier
orbitals of the complex [13]. To investigate the electronic
structure of the alkyne complex in more detail, DFT calcu-
lations have been performed on the full compound
[Ni(DABMes)(Ph-CϵC-Ph)] (4) as well as on a significantly
reduced model of this complex, [Ni(HDABH)(H-CϵC-H)]
(4Ј) (HDABH ϭ HNϭC(H)-C(H)ϭNH). The molecular
structures were calculated on the RIDFT/BP/SVP level of
theory using the TURBOMOLE set of programs. For com-
pound 4, the HOMO has almost exclusively d-Orbital
character, whereas the HOMO-1 shows significant admix-
ture of the alkyne π֊-orbital and of one of the DAB
π*-Orbitals (see Figure 5).
Crystals suitable for X-ray diffraction have been obtained
from saturated diethyl ether solutions at Ϫ40 °C (see Fig-
ure 4). The nickel atom of 4 is essentially planar coordi-
nated with both the DAB ligand nitrogen atoms and the
carbon atoms of the alkyne entity. The C-C-vector (C(23)-
C(24)) of the alkyne is aligned within the plane defined by
the nickel atom and the nitrogen atoms of the DABMes li-
˚
gand. The average Ni-C separation of 1.852 A is compar-
able with Ni-C σ-bonds involving sp2-hybridized carbon
˚
centers. The C-C separation of 1.297(8) A is indicates the
presence of a CϭC rather than a CϵC bond. Furthermore,
complex 4 displays a sharp absorption at 1752 cmϪ1 in its
infrared spectrum, shifted substantially to lower frequencies
Figure 4 ORTEP diagram of the molecular structure of [Ni(DABMes)-
(Ph-CϵC-Ph)] (4) in the solid state (ellipsoids set at 40 % probabi-
lity level). H atoms have been omitted for clarity.
Figure 5 The orbitals HOMO-1 and LUMO of [Ni(DABMes)-
(Ph-CϵC-Ph)] 4 (left side) and the MO scheme of [Ni(HDABH)-
(H-CϵC-H)] 4Ј.
˚
Selected bond lengths/A and angles/°: Ni-N(1): 1.916(4), Ni-N(2): 1.911(5),
Ni-C(23): 1.849(5), Ni-C(24): 1.854(5), N(1)-C(1): 1.323(7), N(2)-C(2):
1.313(6), N(1)-C(14): 1.448(6), N(2)-C(5): 1.460(6), C(1)-C(2): 1.444(7),
C(23)-C(24): 1.297(8), N(1)-Ni-N(2): 81.37(19), C(23)-Ni-C(24): 41.0(2),
N(1)-Ni-C(23): 160.4(2), N(1)- Ni-C(24): 119.4(2), N(2)-Ni-C(23): 118.2(2),
N(2)-Ni-C(24): 159.2(2), C(1)-N(1)-Ni: 115.7(4), C(14)-N(1)-Ni: 123.4(3),
C(2)-N(2)-Ni: 115.8(3), C(5)-N(2)-Ni: 123.6(3), N(1)-C(1)-C(2): 113.0(5),
N(2)-C(2)-C(1): 113.9(5), C(23)-C(24)-C(31): 141.5(5), C(24)-C(23)-C(25):
145.7(5).
To gain more insight into the nature of the electronic
transitions, the lowest singlet excitation energies have been
calculated. For comp1ex 4 we obtain a transition at 649 nm,
810
www.zaac.wiley-vch.de
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2006, 807Ϫ813

A Diazabutadiene stabilized Nickel(0) Cyclooctadiene Complex
Synthesis of DABMes (1). Formic acid (2 ml) was added to a solu-
tion of 2,4,6-trimethyl aniline (43.6 ml, 0.30 mol) in 90 ml meth-
anol. Under stirring, 2,3-butanedione (13.2 ml, 0.15 mol) was ad-
ded slowly at room temperature and the product starts to precipi-
tate. The reaction mixture was stirred over night and the product
was filtered off and washed twice with small portions of methanol.
Yield 68.0 g (75 %); yellow powder. Crystals suitable for X ray dif-
fraction were grown from saturated toluene solutions at Ϫ40 °C.
IR (KBr/cmϪ1: 2971 m, 2910 m, 2849 m, 2727 w, 1737 w, 1638 s, 1477 s,
1363 s, 1211 s, 1119 s, 853 s, 292 m, 540 m. Ϫ 1H-NMR (C6D6): δ ϭ 1.99 (s,
12 H, Ar-CH3), 2.07 (s, 6 H, NϭC-CH3), 2.25 (s, 6 H, Ar-CH3), 6.85 (s, 4 H,
Ar-H). Ϫ 13C-NMR (C6D6): δ ϭ 16.5 (NϭCCH3), 18.7 (Aryl-o-CH3), 21.6
(Aryl-p-CH3), 125.3 (Aryl-o-C), 129.9 (Aryl-m-C), 133.1 (Aryl-p-C), 147.5
(Aryl-i-C), 169.2 (NϭC).
which is close to the experimentally observed transition at
666 nm. The calculated singlet excitation predominantly
consists of a transition from HOMO-1 to the LUMO of
complex 4 (see Figure 5, left side). The ground state one-
electron energies and percentage composition of selected
highest occupied and lowest unoccupied molecular orbitals
have also been calculated for the reduced model system un-
1
der C2v symmetry and a similar A1 transition can be as-
signed, albeit at significantly higher energies (λ ϭ 435 nm)
due to the modified ligand system. The dominant contri-
butions to this band are transitions from orbital 5b2
(89.0 %) to the LUMO 6b2, which is predominately DAB
π* in character (see Figure 5, right side). Therefore, these
transitions have mixed character, in which the contribution
from the alkyne ligand cannot be neglected for the full as
well as for the model system and the corresponding tran-
sitions should be assigned as mixtures of MLCT/LЈLCT
transitions. In the investigated systems the character of the
LUMO is only moderately influenced by the variation of
the alkyne coligand. More substantial changes are observed
in the composition of the unoccupied orbitals at higher en-
ergy levels, which have larger contributions of the alkyne
coligand.
In conclusion, we have synthesized a novel diazabuta-
diene nickel(0) cyclooctadiene complex, which might be a
useful precursor for further studies on the reactivity of diaz-
adiene stabilized nickel complexes. First investigations have
shown that this compound does not react with biphenylene
under ambient conditions, but that the COD ligand is read-
ily displaced by good donating ligands such as diphenyl-
acetylene. Quantum chemical calculations on the resulting
alkyne complexes reveal a low energy band of the alkyne
complex in the UV-Vis spectrum, that has to be assigned to
a mixed MLCT/LLЈCT transition instead of pure MLCT
transitions.
Synthesis of [Ni(DABMes)2] (2). DABMes (640 mg, 2.00 mmol) and
[Ni(COD)2] (270 mg, 1 mmol) were dissolved in 40 ml THF and
methyl iodide (0.062 ml, 1.00 mmol) was added at room tempera-
ture. The reaction mixture was stirred over night and filtered over
a pad of celite afterwards. All volatiles were removed in vacuo, the
solid residue was suspended in 20 ml hexane and the purple prod-
uct was filtered off and dried in vacuo. A second fraction of the
product was obtained by cooling the mother liquor to Ϫ40 °C over
12 h. Combined yield: 415 mg (0.59 mmol, 59 %), purple powder.
Crystals suitable for X ray diffraction were grown from saturated
hexane solutions at Ϫ40 °C. C36H38N2Ni [698.6 g/mol]. Ϫ Calcd.
(found): C 75.54 (75.44), H 8.07 (8.02), N 8.01 (8.12) %. EI-MS m/z
(%): 698 (16) [M]ϩ; 378 (19) [M-DABMes]ϩ.
IR (KBr/cmϪ1): 2993 (s), 2943 (s), 2906 (s), 2854 (s), 2725 (w), 1777 (w),
1746 (w), 1720 (w), 1692 (w), 1656 (w), 1642 (w), 1573 (w), 1555 (w), 1473
(vs), 1384 (s), 1354 (s), 1302 (vs), 1212 (s), 1163 (m), 1147 (w), 1121 (w),
1105 (w), 1033 (w), 1009 (w), 988 (m), 873 (m), 859 (m), 843 (m), 721 (w),
633 (m), 611 (m), 389 (w). Ϫ 1H-NMR (C6D6): δ ϭ Ϫ1.43 (s, 12H, NϭC-
CH3), 2.22 (s, 24 H, Ar-CH3), 2.43 (s, 12H, Ar-CH3), 6.80 (s, 8 H, Ar-H). Ϫ
13C-NMR (C6D6): δ ϭ 19.38 (Aryl-o-CH3), 21.61 (DAB-CH3), 22.71 (Aryl-
p-CH3), 129.52 (Aryl-m-C), 129.85 (Aryl-o-Cm), 133.69 (Aryl-p-C), 140.46
(Aryl-i-C), 156.68 (DAB-NϭC). Ϫ UV-Vis: λmax (ε)/nm: 277 (9786), 508
(2449), 762 (876).
Synthesis of [Ni(DABMes)(COD)] (3). DABMes (3.20 g, 10.0 mmol)
and [Ni(COD)2] (2.70 g, (10.0 mmol) were dissolved in 100 ml tolu-
ene and 1-chloro-fluorobenzene (0.74 ml, 10.0 mmol) was added at
room temperature. The reaction mixture was stirred over night and
all volatiles were removed in vacuo afterwards. The resulting solid
was suspended in hexane and the product was filtered off and dried
in vacuo. A second fraction of the product was obtained by cooling
the mother liquor to Ϫ40 °C for several days. Combined yield:
3.50 g (7.20 mmol; 72 %), dark purple powder. Crystals suitable for
X ray diffraction were grown from saturated toluene solutions at
Ϫ40 °C. Ϫ EI-MS m/z (%): 486 (45) [M-H]ϩ; 378 (100) [M-COD]ϩ.
IR (KBr/cmϪ1): 2915 (s), 2856 (m), 1644 (m), 1576 (m), 1472 (s), 1352 (s),
1232 (s), 1105 (m), 985 (m), 843 (m); 567 (m). Ϫ 1H-NMR (C6D6): δ ϭ
Ϫ0.47 (s, 6 H, NϭC-CH3), 1.58 (m, 4 H, COD-CH2), 2.10 (s, 12 H, Ar-CH3),
2.36 (s, 6H, Ar-CH3), 2.38 (m, 4 H, COD-CH2), 3.81 (s, 4 H, COD-CH),
7.00 (s, 4 H, Ar-H). Ϫ 13C-NMR (C6D6): δ ϭ 18.75 (Aryl-o-CH3), 19.371
(DAB-CH3), 21.98 (Aryl-p-CH3), 31.59 (COD-CH2), 86.63 (COD-CH),
128.35 (Aryl-m-C), 129.77 (Aryl-o-Cm), 133.35 (Aryl-p-C), 146.36 (Aryl-i-C),
152.79 (DAB-NϭC). Ϫ UV-Vis: λmax (ε)/nm: 280 (10348), 496 (3892).
Experimental Section
General methods and instrumentation All air/moisture sensitive
manipulations were performed using standard Schlenk-line and
drybox (N2) techniques. Solvents were predried and distilled from
sodium (toluene), potassium (thf), sodium-potassium alloy (1:3 w/w)
(diethyl ether) and lithium aluminium hydride (hexane) under N2.
Solvents were distilled at atmospheric pressure prior to use. Deuter-
ated solvents were dried over potassium (C6D6) under N2.
1H- and 13C{1H}-NMR spectra were recorded on a Bruker AMX
300 or AV 400 spectrometer. Spectra are referenced internally to
residual protio-solvent (1H) or solvent (13C) resonances and are
reported relative to tetramethylsilane (δ ϭ 0.00 ppm). Chemical
shifts are quoted in δ (ppm) and coupling constants in Hertz. IR
spectra were recorded on a Bruker IFS28 spectrometer as KBr pel-
lets. All data are quoted in wavenumbers (cmϪ1). Mass spectra were
recorded on a Varian MAT 3830 spectrometer and the data are
quoted as their mass/charge (m/z) ratios. UV-VIS spectra were re-
corded on a Perkin Elmer Lambda 900 as 10Ϫ4 M solutions in hex-
ane; ε is quoted in molϪ1cmϪ1. Elemental analyses were carried out
by the analytical laboratory at the University of Karlsruhe (TH).
Synthesis of [Ni(DABMes)(Ph-CϵC-Ph)] 4. A solution of diphenyl-
acetylene (1.60 g, 8.97 mmol) in 20 ml toluene was added at room
temperature to a solution of [Ni(COD)2] (2.47 g, 8.97 mmol) and
DABMes (2.87 g, 8.97 mmol) in 30 ml toluene. The resulting blue-
green reaction mixture was stirred for an hour at room temperature
and afterwards all volatile material was removed in vacuo. The re-
maining solid was suspended in 30 ml hexane, the product was fil-
tered off, washed with 5 ml hexane and dried in vacuum. Yield:
Literature preparations Ni(COD)2 [14].
Z. Anorg. Allg. Chem. 2006, 807Ϫ813
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
811

Th. Schaub, U. Radius
3.90 g (78 %), green powder. Crystals suitable for X ray diffraction
were grown from saturated diethyl ether solutions at Ϫ 40 °C.
C36H38N2Ni [557.4 g/mol]. Ϫ Calcd. (found): C 77.57 (77.59), H
6.87 (6.77), N 5.03 (4.91) %. Ϫ EI-MS m/z (%):556.1 (18) [M-H]ϩ;
378.1 (53) [MϪPh-CϵC-Ph]ϩ.
IR (KBr/cmϪ1): 3063 (m), 2903 (m), 2842 (m), 1752 (m) ν(CϵC), 1592 (m),
1538 (m), 1447 (s), 1378 (s), 1333 (s), 1226 (s), 967 (s), 837 (s), 753 (s), 693
(s), 235 (s). Ϫ 1H-NMR (C6D6): δ ϭ Ϫ0.03 (s, 6 H, NϭC-CH3), 2.22 (s,
12 H, Ar-CH3), 2.41 (s, 6 H, Ar-CH3), 7.00 (m, 4 H, Ar-H), 7.25 (m, 10 H,
Ar-H). Ϫ 13C-NMR (C6D6): δ ϭ 19.18 (DAB-Aryl-o-CH3), 19.56 (DAB-
CH3), 21.92 (DAB-p-CH3), 126.11 (Alkyne-i-C), 126.99 (DAB-o-C), 128.51
(Alkyne-p-C), 128.71 (Alkyne-o-C), 130.13 (DAB-m-C), 130.28 (Alkyne-m-C),
131.40 (Alkyne-C), 134.77 (DAB-p-C), 152.58 (DAB-i-C), 159.51 (DAB-Nϭ
C). Ϫ UV-Vis: λmax (ε)/nm: 280 (12652), 296 (9599), 374 (1258), 666 (2424).
temperature device. Data were collected at 203 K. The images were
processed with the Stoe software packages and equivalent reflec-
tions were merged. Corrections for Lorentz-polarization effects and
absorption were performed if necessary and the structures were
solved by direct methods. Subsequent difference Fourier syntheses
revealed the positions of all other non-hydrogen atoms, and hydro-
gen atoms were included in calculated positions. Extinction correc-
tions were applied as required. Crystallographic calculations were
performed using SHELXS-97 and SHELXL-97 [22].
Acknowledgments. This work was financially supported by the
University Karlsruhe (TH), the Fonds der Chemischen Industrie
and the Deutsche Forschungsgemeinschaft. We thank Professor D.
Fenske for his continuing support and interest in our work.
Computational details
References
All calculations were carried out with the DFT implementation of
the TURBOMOLE program package [15]. For the DFT calcu-
lations we used the BP86 functional [16], SVP basis sets and the
RI-J approximation [17Ϫ19]. The equilibrium structures of the
complexes were optimized at the RIDFT level using a SVP basis.
Analytic second derivatives were calculated with theprogram
AOFORCE [20] using the RI-J approximation. The DFT-BP86 cal-
culations for the excitation energies were performed with the ESCF
program [21].
[1] G. Van Koten, K. Vrieze, Adv. Organomet. Chem. 1982, 21,
151.
[2] K. Vrieze, J. Organomet. Chem. 1986, 300, 307.
[3] (a) G. J. P. Britovsek, V. C. Gibson, D. F. Wass, Angew. Chem.
1999, 111, 448; Angew. Chem. Int. Ed. 1999, 38, 428; (b) S. D.
Ittel, L. K. Johnson, M. Brookhart, Chem. Rev. 2000, 100,
1169; (c) S. Mecking, Angew. Chem. 2001, 113, 550; Angew.
Chem. Int. Ed. 2001, 40, 534; (d) A. Michalak, T. Ziegler, Or-
ganometallics 2001, 20, 1521.
[4] for DAB stabilized Ni0 complexes see for example: (a) H.
Bock, H. tom Dieck, Angew. Chem. 1966, 78, 549; Angew.
Chem. Int. Ed. 1966, 5, 520; (b) A. L. Balch, R. H. Holm, J.
Am. Chem. Soc. 1966, 88, 5201; (c) D. Walther, Z. Anorg. Allg.
Chem. 1974, 405, 8; (d) D. Walther, Z. Anorg. Allg. Chem.
1977, 431, 17; (e) H. tom Dieck, M. Svoboda, J. Kopf, Z.
Naturforsch. 1978, 33b, 1381; (f) M. Svoboda, H. tom Dieck,
C. Krüger, Y. H. Tsay, Z. Naturforsch. 1981, 36b, 814; (g) H.
tom Dieck, M. Svoboda, T. Greiser, Z. Naturforsch. 1981, 36b,
823; (h) R. Diercks, L. Stamp, H. tom Dieck, Chem. Ber. 1984,
117, 1913; (i) R. Diercks, H. tom Dieck, Chem. Ber. 1985, 118,
428; (j) T. Schleis, T. P. Spaniol, J. Okuda, J. Heinemann, R.
Mülhaupt, J. Organomet. Chem. 1998, 569, 159; (k) J. W.
Strauch, G. Erker, G. Kehr, R. Fröhlich, Angew. Chem. 2002,
114, 2662; Angew. Chem. Int. Ed. 2002, 41, 2543.
Details on the crystal structure determinations of
DABMes (1), [Ni(DABMes)2] (2),
[Ni(DABMes)(COD)] (3), and
[Ni(DABMes)(Ph-CϵC-Ph)] (4)
CCDC-287384 to CCDC-287387 contain the supplementary crys-
tallographic data for the structures of compounds 1Ϫ4. These data
can be obtained free of charge at www.ccdc.cam.ac.uk/conts/
retrieving.html [or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (internat.)
ϩ44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
Crystal data collection and processing parameters are given in
Table 1. Crystals were immersed in a film of perfluoropolyether oil
on a glass fiber and transferred to a Stoe-IPDS diffractometer
(Ag-Kα radiation; compounds 1, 2, 3) or a STOE-STADI4-CCD
(Mo-Kα radiation, compounds 4), equipped with a FTS AirJet low
[5] (a) T. Schaub, U. Radius, Chem. Eur J. 2005, 11, 5024; (b) T.
Schaub, U. Radius, Tetrahedron Lett. 2005, 46, 8195; (c) T.
Schaub, U. Radius, unpublished.
Table 1 X-ray data collection and processing parameters.
1
2
3
4
Formula
C11H14
160.23
orthorhombic
Pbca
16.1438(16)
7.3948(10)
16.5750(16)
Ϫ
1978.7(4)
8
N
C22H28N2Ni0.5
349.82
orthorhombic
Fdd2
20.4340(19)
25.708(4)
14.6029(13)
Ϫ
7671.1(15)
16
C30H40N2Ni
487.35
monoclinic
P21/c
10.6828(4)
30.3688(15)
8.2622(3)
96.646(5)
2662.44(19)
4
C36H38N2Ni
557.39
orthorhombic
Pna21
21.975(4)
13.509(3)
10.201(2)
Ϫ
3028.4(10)
4
Formula weight
Crystal system
Space group
˚
a / A
˚
b / A
˚
c / A
β / °
3
˚
V / A
Z
µ / mmϪ1
0.041
0.291
0.398
0.667
Tot./Indep. reflns.
4933/1396
1089
113
4926/2649
1953
230
10462/4166
2551
306
16387/4949
3299
360
a)
Observed reflns.
Parameters
c, d
Final R b), wR2
0.0449, 0.1151
0.0459, 0.0852
0.0826, 0.2166
0.0566, 0.0728
a) wReflections with I > 2 σ(I); b) R ϭ ΣʈFoΗϪΗFcʈ/ΣΗFoΗ; c wR2 ϭ {Σ[w(Fo2 Ϫ Fc2-)2]/Σ[w(Fo2)2]}1/2
;
d) For data with I > 2 σ(I).
812
www.zaac.wiley-vch.de
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2006, 807Ϫ813

A Diazabutadiene stabilized Nickel(0) Cyclooctadiene Complex
[6] (a) J. J. Eisch, A. M. Piotrowski, K. I. Han, C. Krüger, Y. H.
Tsay, Organometallics 1985, 4, 224; (b) H. Schwager, S.
Spyroudis, K. P. C. Vollhardt, J Organomet. Chem. 1990, 382,
191; (c) B. L. Edelbach, D. A. Vicic, W. D. Jones, Organomet-
allics 1998, 17, 4784; (d) B. L. Edelbach, R. J. Lachicotte, W.
D. Jones, Organometallics 1999, 18, 4040; (e) B. L. Edelbach,
R. J. Lachicotte, W. D. Jones, Organometallics 1999, 18, 4660;
(f) C. Müller, R. J. Lachicotte, W. D. Jones, Organometallics
2002, 21, 1975.
[7] CO stretching vibrations of dicarbonyl complexes of the type
[L2Ni(CO)2]: (a) ref [5]: L ϭ ImiPr2: (1927, 1847 cmϪ1), (b) J.
Chatt, F. A. Hart, J. Chem. Soc. 1960, 1378: L ϭ bipy (1950,
1861 cmϪ1); (c) C. A. Tolman, J. Am. Chem. Soc. 1970, 92,
2956: L ϭ PiPr3 (1984, 1922 cmϪ1), L ϭ PMe3 (1990,
1926 cmϪ1) L ϭ PPh3 (1994, 1936 cmϪ1); (d) ref [4a]: L ϭ
DABOMe (2012, 1946 cmϪ1); (e) ref [4j]: L ϭ DABDip (2014
1954 cmϪ1).
[15] (a) R. Ahlrichs, M. Bär, M. Häser, H. Horn, C. Kölmel, Chem.
Phys. Lett. 1989, 162, 165; (b) M. Häser, R. Ahlrichs, J. Com-
put. Chem. 1989, 10, 104; (c) M. von Arnim, R. Ahlrichs, J.
Comput. Chem. 1998, 19, 1746.
[16] (a) A. D. Becke, Phys. Rev. A 1988, 38, 3098; (b) J. P. Perdew,
Phys. Rev. B 1986, 33, 8822; erratum: J. P. Perdew, Phys. Rev.
B 1986, 34, 7406.
[17] (a) O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346; (b)
K. Eichkorn, O. Treutler, O. Öhm, M. Häser, R. Ahlrichs,
Chem. Phys. Lett. 1995, 240, 283; (c) K. Eichkorn, F. Weigend,
O. Treutler, R. Ahlrichs, Theor. Chem. Acc. 1997, 97, 119.
[18] (a) K. Eichkorn, O. Treutler, H. Öhm, M. Häser, R. Ahlrichs,
Chem. Phys. Lett. 1995, 242, 652; (b) F. Haase, R. Ahlrichs, J.
Comput. Chem. 1993, 14, 907; (c) F. Weigand, M. Häser,
Theor. Chem. Acc. 1997, 97, 331; (d) F. Weigand, M. Häser,
H. Patzelt, R. Ahlrichs, Chem. Phys. Lett. 1998, 294, 143.
[19] A. Schäfer, H. Horn, R. Ahlrichs, J. Chem. Phys. 1992, 97,
2571.
[8] H. Hoberg, C. Fröhlich, J. Organomet. Chem. 1981, 209, C69.
[9] (a) P. C. Servaas, D. J. Stufkens, A. Oskam, Inorg. Chem. 1989,
28, 1774; (b) P. C. Servaas, D. J. Stufkens, A. Oskam, Inorg.
Chem. 1989, 28, 1780.
[20] P. Deglmann, F. Furche, R. Ahlrichs, Chem. Phys. Lett. 2002,
362, 511.
[21] (a) R. Bauernschmitt, M. Häser, O. Treutler, R. Ahlrichs,
Chem. Phys. Lett. 1997, 264, 573; (b) R. Bauernschmitt, R.
Ahlrichs, Chem. Phys. Lett. 1996, 256, 454; (c) R. Bauernsch-
mitt, R. Ahlrichs, J. Chem. Phys. 1996, 104, 9047; (d) H. Weiss,
R. Ahlrichs, Häser, J. Chem. Phys. 1993, 99, 1262; (e) F.
Furche, R. Ahlrichs, C. Wachsmann, E. Weber, A. Sobanski,
F. Vögtle, S. Grimme, J. Am. Chem. Soc. 2000, 122, 1717; (f)
F. Furche, Dichtefunktionalmethoden für elektronisch angeregte
Zustände, Dissertation, Universität Karlsruhe, 2002.
[22] (a) G. M. Sheldrick, SHELXS-97, Program for Crystal Struc-
ture Solution, Universität Göttingen, 1997; (b) G. M. Sheld-
rick, SHELXL-97, Program for Crystal Structure Refinement,
Universität Göttingen, 1997.
[10] (a) H. Görls, D. Walther, J. Sieler, Cryst. Res. Technol. 1987,
22, 1145; (b) W. Bonrath, K. R. Pörschke, R. Mynott, C.
Krüger, Z. Naturforsch. 1990, 45b, 1647.
[11] P. Overbosch, G. van Koten, O. Overbee, Inorg. Chem. 1982,
21, 2373.
[12] (a) J. J. Eisch, X. Ma, J. N. Gitua, C. Krüger, Eur. J. Inorg.
Chem. 2001, 77; (b) R. Waterman, G. L. Hillhouse, Organome-
tallics 2003, 22, 5182.
´
ˇ
[13] A. Klein, M. P. Feth, H. Bertagnolli, S. Zaalis, Eur. J. Inorg.
Chem. 2004, 2784.
[14] W. A. Herrmann, A. Salzer (Eds.), Synthestic Methods of Or-
ganometallic and Inorganic Chemistry (Herrmann/Brauer),
Vol. 1, p. 157.
Z. Anorg. Allg. Chem. 2006, 807Ϫ813
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
813