Dinuclear [RNi(oxam)NiR] complexes (oxam = N1,N2-bis(2-pyridylmethyl)-N3,N4-bis (2,4,6-trimethylphenyl)-oxalamidinate; R = Me, Ph, C≡CH, C≡CPh): Reactions of the methyl complex and formation of [Li(THF)]2</

Article abstract of DOI:10.1021/om000960u

The reaction between 1 equiv of [{(acac)Ni}₂(A)] and 2 equiv of LiR in THF afforded the binuclear organometallic complexes [(RNi)₂(A)] (A: N¹,N²-bis(2-pyridylmethyl)-N³,N⁴-bis (2,4,6-trimet

Full text of DOI:10.1021/om000960u

Organometallics 2001, 20, 4221-4229
4221
Din u clea r [RNi(oxa m )NiR] Com p lexes (oxa m )
N1,N2-bis(2-p yr id ylm eth yl)-N3,N4-bis(2,4,6-tr im eth ylp h en yl)-
oxa la m id in a te; R ) Me, P h , CtCH, CtCP h ): Rea ction s of
th e Meth yl Com p lex a n d F or m a tion of
†
[Li(THF )]2Li2Ni2Me8 a n d [Li(THF )]4Ni2Me8
Dirk Walther,* Michael Stollenz, and Helmar Go¨rls
Institut fu¨r Anorganische und Analytische Chemie der Friedrich-Schiller-Universita¨t J ena,
D-07743 J ena, Germany
Received November 13, 2000
The reaction between 1 equiv of [{(acac)Ni}2(A)] and 2 equiv of LiR in THF afforded the
binuclear organometallic complexes [(RNi)2(A)] (A: N1,N2-bis(2-pyridylmethyl)-N3,N4-bis-
(2,4,6-trimethylphenyl)oxalamidinate; 1: R ) Me; 2: R ) Ph). Analogously, 3b (R ) CtC-H
was formed from [{(acac)Ni}2(A)] and sodium acetylide. The reaction of 1 with phenylacety-
lene resulted in the formation of complex 3a (R ) CtC-Ph), accompanied by the evolution
of methane. Compounds 1-3 were characterized by 1H and 13C NMR spectroscopy, elemental
analysis, and mass spectroscopy. In addition, the molecular structures of 1 and 3b were
determined by X-ray crystallography. The NMR spectra of the complexes showed very simple
patterns, thus indicating that only one isomer is present in solution containing a highly
symmetrical structure with planar Ni(II) centers. X-ray studies confirmed that two Ni(II)
centers are connected via the oxalamidinato bridge A, which coordinates in a tridentate
fashion at each Ni atom. The fourth position at the metal center is occupied by the organic
groups R. Compound 1 reacts with an excess of LiMe in THF, yielding [Li(THF)]2Li2Ni2Me8
(5). Upon recrystallization, the THF-enriched complex [Li(THF)]4Ni2Me8 (6) was isolated.
Both complexes were characterized by X-ray crystallography and 1H/ 13C NMR spectroscopy.
Both 5 and 6 are highly symmetrical compounds in which each planar Ni(II) center is
surrounded by four methyl groups. The Ni‚‚‚Ni separations are relatively long (3.167(1) and
3.142(1) Å, respectively), reflecting the absence of a metal-metal bond between those two
metal centers. Furthermore, agostic Li-H interactions stabilize the structure in a way similar
to that in the corresponding Cr(II) compound [Li4(THF)4Cr2Me8], in which very short contacts
have been found (Cr‚‚‚Cr distance 1.968(2) Å).
In tr od u ction
favored due to the anionic nature of the oxam ligands,
which are poor π-acceptor ligands and thus cannot
stabilize Ni(0) species.
In a preliminary paper we described the first homo-
and heterobinuclear nickel(II) complexes as well as the
first representatives of heterotri- and tetrametallic
complexes in which the metal ions are connected via
bridging oxalic amidinates ligands (“oxam”).1 A series
of these complexes containing acetylacetonato ligands
as terminating groups have shown the ability to catalyze
the oligomerization or polymerization of ethylene in the
presence of MAO.
Since it is likely that di- or oligonuclear organo-
metallic species containing R-Ni units linked by oxam
bridges are involved in these catalytic reactions, we
were interested in investigating the organometallic
chemistry of such oligometallic species. We focused on
the N1,N2-bis(2-pyridylmethyl)-N3,N4-bis(2,4,6-trimeth-
ylphenyl)oxalamidinate ligand (A), reasoning that this
ligand would form dinuclear alkyl-, aryl-, and alkinyl-
Ni(II) complexes of the type [(RNi)2(A)], in which each
planar nickel is surrounded by three N donor groups of
the oxam ligand. This arrangement should inhibit the
formation of coordination polymers, which was observed
when oxam ligands without additional donor groups in
Surprisingly, some of the dinuclear complexes with
oxam ligands also catalyzed the selective cross coupling
between R-X and R′MgX, whereas, according to the
generally accepted mechanism of this reaction, the key
step of the catalytic cycle is postulated to be the
reductive elimination of R-R′, which forms Ni(0).2 In
the case of oxamNi(II) complexes, this reductive elimi-
nation of R-R′ is not expected to be energetically
(2) (a) Negishi, E.; Liu, F. Metal-catalyzed Cross-coupling Reactions;
Diederich, F., Stang, P. J ., Eds.; Wiley-VCH: Weinheim, 1998; Vol.
34, and references therein. (b) Ca´rdenas, D. J . Angew. Chem. 1999,
111, 3201; Angew. Chem. Int. Ed. 1999, 38, 3018, and references
therein. (c) Negishi, E.; Takahashi, T.; Baba, S.; van Horn, D. E.;
Okukado, N. J . Am. Chem. Soc. 1987, 109, 2393. (d) Negishi, E.,
Takahashi, T.; Akiyoshi, K. J . Organomet. Chem. 1987, 334, 181. (e)
Amatore, C.; Azzabi, M.; J utand, A. J . Am. Chem. Soc. 1991, 113, 8375.
(f) Hartwig, J . F.; Paul, F. J . Am. Chem. Soc. 1995, 117, 5373.
† This work is dedicated to Prof. Rudi Taube (Halle, Germany) on
the occasion of his 70th birthday.
(1) Do¨hler, T.; Go¨rls, H.; Walther, D. J . Chem. Soc., Chem. Commun.
2000, 945.
10.1021/om000960u CCC: $20.00 © 2001 American Chemical Society
Publication on Web 08/25/2001

4222 Organometallics, Vol. 20, No. 20, 2001
Sch em e 1. F or m a tion of th e Com p lexes 1-5
Walther et al.
the sidearms were used. Furthermore, lower π-acceptor
properties of ligand A compared with oxam ligands
bearing four aryl substituents at the oxal amidinato
moiety should stabilize the Ni-R bonds toward reduc-
tive elimination and homolytic splitting to form low-
valent nickel.
reaction of 1 with an excess of LiMe results in the
displacement of the oxam ligand and the formation of
the dimeric anionic methyl complexes 5 and 6, respec-
tively.
Resu lts
To the best of our knowledge, di- or oligonuclear
σ-organometal complexes bridged by oxam ligands have
not yet been reported in the literature. In general, very
little is known about the organometallic chemistry of
oxam-based compounds. The first organometallic com-
pound of the type({Cp2Ti}2[oxam]) was described by
Floriani.3 Recently, complexes of the type Cp2Ti(oxam)-
Mo(CO)4 have been synthesized and structurally char-
acterized by Do¨ring and Beckert.4 Moreover, coordina-
tion compounds containing oxam ligands are also
relatively rare5-8 since the ligands tend to form ill-
defined coordination polymers.9
Syn th esis, Str u ctu r e, a n d Rea ction s of th e Com -
p lexes 1-3. The reaction of [{(acac)Ni}2(A)]1,28 with
LiCH3 in THF at -78 °C (ratio 2:1) resulted in the
formation of an orange solution. Upon evaporation of
the solvent, dissolution of the residue in toluene, and
workup the pure dinuclear methyl nickel(II) compound
1 could be isolated in 56% yield (Scheme 1). Single
crystals of 1 were grown from toluene.
The diamagnetic orange complex 1 is readily soluble
in toluene or THF and is thermally stable even for
several hours in toluene solution at 100 °C. According
In this article we describe the synthesis and struc-
tures of the first dinuclear organometallic compounds
in which an oxam ligand acts as bridge between two
organometallic R-Ni(II) fragments (R ) Me, Ph, HCtC,
PhCtC) (Scheme 1). Furthermore, we report on some
reactions of the methyl complex 1. Surprisingly, the
(10) Allen, F. H.; Kennard, O.; Taylor, R. Acc. Chem. Res. 1983, 16,
146.
(11) Klein, H.-F.; Wiemer, T.; Menu, M.-J .; Dartiguenave, M.;
Dartiguenave, Y. Inorg. Chim. Acta 1988, 154, 21.
(12) Klein, H.-F.; Wiemer, T.; Menu, M.-J .; Dartiguenave, M.;
Dartiguenave, Y. Inorg. Chim. Acta 1991, 189, 45.
(13) Klein, H.-F.; Wiemer, T.; Menu, M.-J .; Dartiguenave, M.;
Dartiguenave, Y. Inorg. Chim. Acta 1991, 189. 35.
(14) Selected references. (a) Kaiser, S. W.; Saillant, R. B.; Butler,
W. M.; Rasmussen, P. G. Inorg. Chem. 1976, 15, 2681. (b) Haddad, M.
S.; Duesler, E. N.; Hendrickson, D. N. Inorg. Chem. 1979, 18, 141. (c)
Garcia, M. P.; Lopez, A. M.; Esteruealas, M. A.; Lahoz, F. J .; Oro, L.
A. Chem. Commun. 1988, 793. (d) Garcia, M. P.; Lopez, A. M.;
Esteruealas, M. A.; Lahoz, F. J .; Oro, L. A. J . Chem. Soc., Dalton Trans.
1990, 3465. (e) Esteruealas, M. A.; Lahoz, F. J .; Lopez, A. M.; Onate,
E.; Oro, L. A.; Ruiz, N.; Sola, E.; Tolosa, J . I. Inorg. Chem. 1996, 35,
7811. (f) de Souza Lemos, S.; Bessler, K. E.; Schulz Lang, E. Z. Anorg.
Allg. Chem. 1998, 624, 30. (g) de Souza Lemos, S.; Bessler, K. E.; Schulz
Lang, E. Z. Anorg. Allg. Chem. 1998, 624, 701. (h) Rau, S.; Ruben, M.;
Bu¨ttner, T.; Temme, C.; Dautz, S.; Go¨rls, H.; Rudolph, M.; Walther,
D.; Brotkorb, A.; Duati, M.; O’Connor, C.; Vos, J . G. J . Chem. Soc.,
Dalton Trans. 2000, 3649. (i) Rau, S.; Bu¨ttner, T.; Temme, C.; Ruben,
M.; Go¨rls, H.; Walther, D.; Duati, M.; Fanni, S.; Vos, J . G. Inorg. Chem.
2000, 39, 1621.
(3) Pasquali, M.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. J . Am.
Chem. Soc. 1979, 101, 4740.
(4) Feeling, P.; Do¨ring, M.; Knoch, F.; Beckert, R.; Go¨rls, H. Chem.
Ber. 1995, 128, 405
(5) Do¨ring, M.; Go¨rls, H.; Beckert, R. Z. Anorg. Allg. Chem. 1994,
620, 551.
(6) Beckert, B.; Vorwerk, S.; Lindauer, D.; Do¨ring, M. Z. Naturforsch.
1993, 48b, 1186.
(7) Do¨ring, M., Fehling, P.; Go¨rls, H.; Imhof, W.; Beckert, R.,
Lindauer, D. J . Prakt. Chem. 1999, 341, 748.
(8) Ruben, M.; Rau, S.; Skirl, A.; Krause, K.; Go¨rls, H.; Walther,
D.; Vos, J . G. Inorg. Chim. Acta 2000, 303, 206.
(9) (a) Hofman, W. E. Proc. Indiana Acad. Sci. 1969, 79, 129, Chem.
Abstr. 1970, 73, 126513r. (b) Papavil, E. Anal. Stiint. Univ. J asi, Sect.
110 1964, 115; Chem. Abstr. 1965, 63, 14351h.

Dinuclear [RNi(oxam)NiR] Complexes
Organometallics, Vol. 20, No. 20, 2001 4223
to a DTA measurement, 1 starts to decompose at 274
°C in the solid state. Analysis and a mass spectrum
confirmed its composition. In the mass spectrum the
dinuclear complex ion [{(CH3)Ni}2(oxam)]+ (m/z ) 648)
1
was detected. The H NMR spectrum of 1, recorded in
THF-d8 at room temperature, showed one singlet of the
methyl protons of the Ni-Me group at δ ) -1.35 ppm
and two singlets for the methyl mesityl groups at δ )
2.22 (p-methyl) and 2.43 ppm (o-methyl). The relative
intensities of these resonances are 1:1:2. In addition to
the signals corresponding to the protons of the aromatic
rings between 6.65 and 7.85 ppm, the 1H NMR spectrum
shows a singlet of the CH2 group at 3.62 ppm, which is
ascribed to the CH2 group.
The 13C NMR spectrum in THF-d8 also showed a very
simple pattern. The resonance for the carbon of the Ni-
Me groups appeared at δ ) -7.5 ppm, and the reso-
nances of the mesityl-Me carbons were found at 19.1
and 21.0 ppm, respectively. Furthermore, the signal for
the CH2 carbon was observed at 53.3 ppm. In addition,
10 resonances in the region of the sp2-carbons between
121.2 and 168.9 ppm were observed. This is the expected
number of signals in this region for a symmetrical
structure in solution and corresponds to five signals for
the inequivalent aromatic CH groups (121.2, 122.6,
127.6, 136.3, and 149.0 ppm), four signals for the
inequivalent quarternary C atoms of the aromatic
substituents (133.5, 135.7, 144.4, and 163.1 ppm), and
one signal for the equivalent oxalamidinato carbons. We
assume that the signal at 168.9 ppm belongs to the
latter.
F igu r e 1. Molecular structure of complex 1. Selected bond
distances (Å) and bond angles (deg): Ni-N1 1.905(2), Ni-
N2 1.916(2), Ni-N3 1.912(2), Ni-C8 1.950(3), C1-N1
1.323(3), C1A-N2 1.341(3), C1-C1A 1.506(5), C2-C3
1.514(4), C2-N1 1.459(3), C9-N2 1.435(3), C8-Ni-N1
176.7(1), C8-Ni-N2 96.5(1), C8-Ni-N3 95.7(1), N1-Ni-
N2 83.83(9), N1-Ni-N3 84.18(9), N2-Ni-N3 167.38(9),
N1A-C1A-N2 133.7(2), N1-C1-C1A 111.9(3), C1-N1-
C2 126.8(2), C1A-N2-C9 119.8(2). Symmetry transforma-
tions used to generated equivalent atoms: A -x+1, -y+1,
-z+1.
fashion to bridge two nickel ions. Each metal ion is in a
planar environment created by three N atoms from the
bridging ligand and one carbon of the methyl group. The
double metallacyclic ring containing the N2C-CN2 unit
is essentially planar (deviation 0.002 Å). The C-N bonds
of the oxalamidinate framework are almost equiv-
alent within experimental error (C1-N1 1.323(3) Å,
C1A-N2 1.341(3) Å), indicating a high double-bond
character due to a complete electron delocalization over
the two CN2 units. The C1-C1A bond distance of the
C2N2 unit (1.506(5) Å) is that of a single bond; bond
angles around both carbons are typical for sp2 hybrid-
ization.
The two methyl groups coordinated to the Ni centers
on the opposite sides of the oxam bridge lie trans to each
other. The Ni-C bonds (1.950(3) Å) are relatively short
compared with the average bond lengths of 2.06 Å for
this type of bonding.10-13 Of particular interest in this
connection is the compound [(Me3P)NiMe]2(oxalate),
synthesized and characterized by Klein.13 In this com-
plex the [(Ni(CH3)(PMe3)] fragments are bridged by the
oxalate which forms a planar five-membered chelate
ring with each nickel atom. Furthermore, the methyl
groups lie trans to each other. Remarkably, the Ni-C
distance (1.899(4) Å) in this complex is shorter than in
1.
A search in the Cambridge Data Base showed that
numerous X-ray structures of dinuclear complexes
containing similar bridging ligands such as bis-imid-
azolate14 and bipyrimidine have been published.15 How-
ever, to the best of our knowledge, neither planar Ni
complexes nor Ni-σ-organo compounds with these ligands
were characterized by X-ray crystallography. In the (µ2-
2,2′-imidazolato)bis(1,4,8,11-tetra-azacyclotetradecane)-
dinickel(II) cation containing nickel(II) in an octahedral
environment the Ni-N(imidazolate) bonds are much
longer (2.192 and 2.150 Å) than those in 1 (1.905(2) and
1.916(2) Å).16 This is also the case in octahedral di-
nuclear bispyrimidine nickel complexes.17
The molecular structure of single crystals isolated
from toluene was determined by an X-ray analysis
(Figure 1).
The complex consists of a bimetallic centrosymmetric
unit in which the oxam ligand acts in a bis-chelating
(15) Selected references: (a) Brewe, G.; Sinn, E. Inorg. Chem. 1985,
24, 4580. (b) Real, A.; Zarembowitch, J .; Kahn, O.; Solans, X. Inorg.
Chem. 1987, 26, 2939. (c) Sletten, J . Daraghmeh, H.; Lioret, F.; J ulve,
M. Inorg. Chim. Acta 1998, 279, 127. (d) Mikuriya, M. Fukumoto, H.;
Kako, T. Inorg. Chem. Commun. 1998, 1, 225. (e) Baumann, F. Stange,
A., Kaim, W. Inorg. Chem. Commun. 1998, 1, 305. (f) De Munno, G.;
J ulve, M.; Lioret, F.; Faus, J .; Caneschi, A. J . Chem. Soc., Dalton Trans.
1994, 1175. (g) Castro, I.; Sletten, J .; Glaerum, L. K.; Lioret, F.; Faus,
J .; J ulve, M. J . Chem. Soc., Dalton Trans. 1994, 2777. (h) De Munno,
G.; Viau, G.; Lioret, F.; Faus, J . Inorg. Chim. Acta 1997, 257, 121. (i)
Klein, A.; Kaim, W.; Hornung, F. M.; Fiedler, J . Zalis, S. Inorg. Chim.
Acta 1997, 264, 269. (k) Vogler, C.; Hausen, H.-D.; Kaim, W.;
Kohlmann, S.; Kramer, H. E. A.; Rieker, J . Angew. Chem., Int. Ed.
Engl. 1989, 28, 1659. (l) Schwach, M.; Hausen, H.-D.; Kaim, W. Chem.
Eur. J . 1996, 2, 446.
(16) Tadokoro, M.; Sato, K.; Shiomi, D.; Takui, T.; Itoh, K. Mol.
Cryst. Liq. Cryst. Sci. Technol., Sect. A 1997, 306, 49.
(17) de Munno, G.; J ulve, M.; Lioret, F.; Derory, A. J . Chem. Soc.,
Dalton Trans. 1993, 1179.
(18) Taube, R.; Honymus, G. Angew. Chem. 1975, 87, 291.
(19) Kurras, E.; Otto, J . Organom. Chem. 1965, 4, 114.
(20) Krause, J .; Marx, G.; Scho¨dl, G. J . Organomet. Chem. 1970,
21, 159.
(21) Hao, S.; Gambarotta, S.; Bensimon, C. J . Am. Chem. Soc. 1992,
114, 3556.
(22) Hao, S.; Song, J .-I.; Berno, P.; Gambarotta, S. Organometallics
1994, 13, 1326.
(23) Cotton, F. A.; Troup, J . M.; Webb, D. H.; Williamson, G.;
Wilkinson, J . J . Am. Chem. Soc. 1974, 96, 3824.
(24) Cotton, F. A.; Gage, L. D.; Mertis, L. W.; Shive, G.; Wilkinson,
J . J . Am. Chem. Soc. 1976, 98, 6922.
(25) Wyrwa, R.; Go¨rls, H. Z. Anorg. Allg. Chem. 1999, 625, 1904.
(26) Bauer, R. Ber. Dtsch. Chem. Ges. 1907, 40, 2650.
(27) (a) Lindauer, D.; Beckert, R.; Do¨ring, M.; Fehling, P.; Go¨rls, H.
J . Prakt. Chem. 1995, 337, 143. (b) Langer, P.; Do¨ring, M.; Wuckelt,
J .; Go¨rls, H. Eur. J . Inorg. Chem. 2001, 805.
(28) Walther, D.; Stollenz, M.; Bo¨ttcher, L.; Go¨rls, H. Z. Anorg. Allg.
Chem., in press.

4224 Organometallics, Vol. 20, No. 20, 2001
Walther et al.
The phenyl complex 2 was prepared in a manner
similar to that for 1 from 2 equiv of LiPh, dissolved in
a cyclohexane/diethyl ether mixture, with 1 equiv of
[{(acac)Ni}2(A)] at -78 °C in THF. After workup 2 could
be obtained as orange crystals in excellent yields (90%).
It is even more thermally stable in the solid state than
the corresponding methyl complex 1. A DTA measure-
ment of single crystals of 2 showed that the decomposi-
tion started at 336 °C.
The mass spectrum (molecular ion m/z ) 772) and
NMR spectra also suggest that a dimeric compound
similar to 1 is formed. As expected for a symmetric
coordination of the dianionic bridging ligand at the
Ni(II) ions, two 1H NMR resonances of the two mesityl
methyl groups at 2.05 and 2.44 ppm and one singlet for
the CH2 protons at 3.62 ppm with the expected intensity
ratio of approximately 3:6:2 were observed. The aro-
matic protons resonate between 6.41 and 7.45 ppm.
In the high-field region of the 13C NMR spectrum (in
THF-d8 at room temperature) two signals for the methyl
carbons of the mesityl group at δ ) 19.4 and 20.8 ppm
as well as one resonance for the CH2 group at δ ) 53.5
ppm were observed. These signals appear in the same
region as the corresponding signals in compound 1.
Furthermore, 13 13C signals for the aromatic substitu-
ents and one resonance of the equivalent carbons of the
oxalamidinato framework were observed for compound
2. The total number of 17 signals in the 13C spectrum
of 2 reflects not only the C2-symmetry observed in the
ligand itself but also the equivalence of the two phenyl
groups bonded to each nickel(II) center. This is in
agreement with a symmetric structure of the complex
in solution depicted in Scheme 1.
F igu r e 2. Molecular structure of complex 3b. Selected
bond distances (Å) and bond angles (deg): Ni-N1 1.890(3),
Ni-N2 1.872(3), Ni-N3 1.904(4), Ni-C17 1.856(4), C1-
N1A 1.326(5), C1-N2 1.319(5), C1-C1A 1.492(8), C2-N2
1.456(5), C2-C3 1.484(6), N1-C8 1.435(5), C17-C18
1.216(6), C18-H18 1.00(6), C17-Ni-N1 95.6(2), C17-Ni-
N2 177.5(2), C17-Ni-N3 95.7(2), N1-Ni-N2 84.5(1), N1-
Ni-N3 168.6(1), N2-Ni-N3 84.3(1), N1A-C1-N2 133.8(4),
C1-N2-C2 127.5(3), C1A-N1-C8 120.3(3), C17-C18-
H18 164(4). Symmetry transformations used to generated
equivalent atoms: A -x+1, -y+2, -z+1.
caption. The coordination environment of the Ni atoms
is nearly planar (deviation 0.003 Å), with the alkynyl
ligands lying trans to each other. The Ni-C(sp) bond
lengths in 3b are significantly shorter than the Ni-
C(sp3) bond distance in the methyl complex 1 (1,
1.950(2); 3b, 1.890(3) Å).
Reaction of complex 1 in phenylacetylene at room
temperature resulted in the formation of the corre-
sponding phenylacetylide complex 3a together with the
development of methane, which was indicatad by head-
space gas chromatography.
Other relevant bond lengths and angles fall in the
range of typical values. Most of them are very close to
those of complex 1; for example the CN bond distances
of the oxalamidinato framework are almost equivalent
within the experimental error (average distance 1.323
Å) and the C-C bond length corresponds to a single
bond (1.492(8) Å).
Single crystals of 3a were also grown from toluene at
-18 °C. Since the compound contains disordered toluene
(leading to R1obs ) 0.110), only the structure motif will
be discussed here, showing without doubt that the solid-
state structure of 3a is similar to that of 3b. The
acetylide ligands in 3a lie trans to each other, the oxam
moiety is planar, and the two nickel atoms show planar
geometry. This is in agreement with the results of the
NMR spectroscopic measurements in solution.
Since dinuclear σ-organo-nickel complexes containing
oxam bridges are possibly involved in catalytic cross
coupling reactions,1 we investigated the stoichiometric
reaction of 1 with bromobenzene-d5 to get a deeper
insight into the reactivity of both metal centers. Cleav-
age of the Ni-Me bonds at room temperature in
brombenzene-d5 proceeded slowly to yield toluene-d5 in
reasonable yields (46%). Removing the solvent to dry-
ness followed by extraction of the resulting solid with
diethyl ether gave a brown powder (yield ca. 90 wt %).
According to its 1H NMR spectrum this product con-
tained the dimeric bromo complex [(BrNi)2A] (4) in 80%
purity together with an unidentified byproduct.
The orange acetylide complex 3b was prepared from
sodium acetylide (suspended in xylene and oil) and
[{(acac)Ni}2(A)] (ratio 2:1) at -78 °C in THF. After
workup, 3b was obtained in 56% yield. Upon recrystal-
lization from toluene single crystals of 3b, suitable for
an X-ray diffraction analysis, were grown (Figure 2).
NMR studies in THF-d8 confirm that both complexes
3a and 3b have very similar structures in solution. In
1
the H NMR spectrum of 3a the proton signals for the
mesityl methyl groups were observed at δ ) 2.24 and
2.64 ppm. The methylene protons resonated at 3.69 ppm.
These signals showed the expected intensities of ap-
proximately 3:6:2. The corresponding signals in 3b
appeared at 2.20, 2.57, and 3.58 ppm. Additionally, a
singlet at δ ) 0.93 ppm was found in 3b that was
assigned to the two protons of the two acetylide sub-
stituents.
In the high-field region of the 13C NMR spectrum of
3a three sharp resonances were found at δ ) 19.5, 21.0
(methyl mesityl), and 54.5 ppm (methylene). The corre-
sponding signals in 3b appeared at 19.5, 21.1, and 54.3
ppm. Furthermore, two signals for the alkynyl carbons
(at 103.3 and 106.2 ppm) were observed in the 13C NMR
spectum of 3a (in 3b, 90.7 and 95.2 ppm).
The solid-state structure of 3b is shown in Figure 2.
Relevant bond lengths and angles are listed in the figure
1H NMR monitoring of this reaction in bromobenzene-
d5 as solvent shows that, in the first step of the reaction,

Dinuclear [RNi(oxam)NiR] Complexes
Organometallics, Vol. 20, No. 20, 2001 4225
Sch em e 2. Rea ction of 1 w ith Br om oben zen e-d 5 to F or m 4 a n d F or m a tion of 1 fr om 4 a n d LiMe
a new signal in the methyl region appeared at δ ) -0.99
ppm, in addition to the singlet for the methyl groups in
the starting compound 1 appearing in bromobenzene-
d5 at lower field (at δ ) - 0.94 ppm) than in THF-d8 (δ
) -1.35 ppm). The new signal in the methyl region
suggests the formation of a mixed bromo-methyl com-
plex as an intermediate (Scheme 2). After 9 days both
signals disappeared, and the resonances of the bromo
equiv of [{(acac)Ni}2(A)] with 8 equiv of LiMe in THF
at -78 °C.
NMR measurements of 5 at room temperature in
benzene-d6 clearly show that only one highly sym-
metrical isomer is present in solution. In addition to the
resonances of the coordinated THF (at δ ) 1.17 and 3.53
ppm), only one signal for the methyl groups bound to
the metal center was observed, which gives rise to a
1
1
complex 4 appeared in the H NMR spectrum together
singlet at δ ) -0.80 ppm in the H NMR spectrum and
to a signal at δ ) - 5.3 ppm in the 13C NMR spectrum.
Since also only one signal at δ ) 2.17 ppm was observed
in the 7Li NMR spectrum of 5 in benzene-d6, we can
assume that the THF ligands coordinated to two of the
four Li atoms undergo a rapid exchange at room
temperature.
with an unidentified minor product. Furthermore, com-
pound 4 undergoes a clean reaction with 2 equiv of LiMe
in THF at -78 °C, resulting in the formation of the
dimethyl complex 1 (Scheme 2). From these stoichio-
metric reactions, we conclude that cross coupling reac-
tions between LiMe and bromobenzene can proceed at
both Ni(II) centers.
F or m a tion of [Li(THF )]2Li2Ni2Me8 (5) a n d [Li-
(THF )]4Ni2Me8 (6). To find out if complexes of the type
[(R-Ni)2(oxam)] are able to form organometallic anionic
complexes that, in principle, could play a role as
intermediates in catalytic cross coupling reactions,2a,f
we reacted methyllithium with 1 (ratio 2:1) in THF at
-78 °C.
The 1H NMR spectrum of the reaction mixture
showed the unreacted complex 1 as main product (ca.
90%). Surprisingly, after keeping the solution at -18
°C for one week a small amount of an oxam-free methyl
complex of the composition [Li(THF)]2Li2Ni2Me8 (5)
crystallized from the reaction mixture. Using a 6:1 ratio
between LiMe and 1 we could isolate 5 in good yields
(69%) crystallizing from toluene as a brown microcrys-
talline compound. Yellow crystals of the THF-enriched
complex [Li(THF)]4Ni2Me8 (6) were isolated upon re-
crystallization of 5 from THF instead of toluene. The
complexes 5 and 6 are extremely air-sensitive and even
pyrophoric. 5 is even more reactive toward traces of air
and moisture than 6. However, in the absence of air,
the two complexes are stable at 20 °C in the solid state.
Compound 5 could also be obtained by the reaction of 1
Compared to 5, compound 6 gives a slightly downfield-
shifted singlet for the methyl groups at δ ) -0.61 in
the 1H NMR spectrum. In contrast, the 13C NMR
spectrum shows a high-field-shifted singlet at δ ) -6.2
ppm. The integration of the multiplet resonances of
coordinated THF (δ ) 1.25 and 3.62 ppm) shows the
presence of two additional coordinated molecules of THF
by comparison with 5. As expected for a symmetrical
structure, only one signal at δ ) 1.98 ppm was found
7
in the Li NMR spectrum.
Upon recrystallization of 5 from toluene, single crys-
tals were obtained suitable for X-ray crystallographic
determination. The crystal structure confirmed the
highly symmetrical structure in solution indicated by
NMR spectroscopy. Figure 3 shows the dimeric molec-
ular structure with selected bond lengths and angles
in the figure caption.
Each nickel ion in 5 is surrounded by four methyl
groups in a square-planar geometry. The eight methyl
groups of the dimer form a cube. The Ni‚‚‚Ni separation
is relatively long (3.167(1) Å), reflecting the absence of
a metal-metal bond between those two metal centers.
The two monomeric NiMe4 units are held together by
four bridging Li ions. Each Li atom interacts with the

4226 Organometallics, Vol. 20, No. 20, 2001
Walther et al.
F igu r e 3. Molecular structure of complex 5. Selected bond
distances (Å) and bond angles (deg): Ni-C1 2.009(2), Ni-
C2 2.017(2), Ni-C3 2.016(2), Ni-C4 2.008(2), Li1-C1
2.368(4), Li1-C2A 2.375(4), Li1-C3A 2.388(4), Li1-C4
2.367(4), Li1-O1 1.995(3), Li2-C1A 2.292(4), Li2-C2A
2.359(4), Li2-C3 2.266(4), Li2-C4 2.297(4), C1-Ni-C2
88.92(8), C1-Ni-C3 168.88(9), C1-Ni-C4 90.00(9), C2-
Ni-C3 90.76(8), C2-Ni-C4 168.28(9), C3-Ni-C4 88.05(8).
Average bond distances (Å) and average bond angles
(deg): Li1-H 2.08(3), Li1-C 2.374(4), Li2-H 2.05(3),
Li2-C 2.303(4), Ni-C 2.012(2), Li1-H-C 96(2), Li2-H
92(2). Symmetry transformations used to generated equiva-
lent atoms: A -x+1, -y+2, -z+1.
F igu r e 4. Molecular structure of complex 6. Selected bond
distances (Å) and bond angles (deg): Ni-C1 2.005(5), Ni-
C2 2.005(5), Ni-C3 1.994(5), Ni-C4 2.011(5), Li1-C1
2.339(9), Li1-C2A 2.353(9), Li1-C3A 2.364(9), Li1-C4
2.367(9), Li1-O1 2.050(8), Li2-C1 2.339(9), Li2-C2
2.363(9), Li2-C3A 2.358(9), Li2-C4A 2.372(9), Li2-O2
2.075(8), C1-Ni-C2 89.5(2), C1-Ni-C3 166.6(2), C1-Ni-
C4 89.6(2), C2-Ni-C3 88.9(2), C2-Ni-C4 167.4(2), C3-
Ni-C4 89.0(2). Average bond distances (Å) and average
bond angles (deg): Li1-H 2.04(8), Li1-C 2.335(9), Li2-H
2.04(8), Li2-C 2.358(9), Ni-C 2.003(5), Li1-H-C 95(2),
Li2-H-C 97(2). Symmetry transformations used to gener-
ated equivalent atoms: A -x, -y+1, -z+1.
carbon atoms of four methyl groups, forming two Ni1-
CH3-Li-CH3-Ni2 bonds; however two distinct types
of lithium environments are present: Two of the lithium
atoms are additionally bound to a THF ligand, while
the other two lithium atoms do not coordinate THF.
The C-Li(THF) distances (average 2.374(5) Å) are
significantly longer than those of the C-Li bonds
(average 2.304 Å). In addition, agostic interactions
between one hydrogen atom of a methyl group and Li
(Li1-H ) 2.08(3) and Li2-H ) 2.054(3) Å) are certainly
present. The Li-H-C angles confirm this agostic in-
teractions (96(2)° and 95(2)°, respectively).
The solid-state structure of [Li4(THF)4Ni2Me8] (6),
determined by an X-ray analysis of single crystals, is
very similar to that of 5. The only remarkable difference
is that each lithium in 6 coordinates one THF ligand,
leading to four pentavalent lithium atoms. Conse-
quently, all C- Li distances are almost equivalent
within experimental error, in contrast to those found
in 5. Figure 4 shows the molecular structure of 6 and
shows a list of selected bond distances and angles.
A complex Li2[NiMe4](THF)2 of the same analytical
composition as 6 which was assumed to be monomeric
was obtained by Taube in 1975.18 Since, however,
neither spectroscopic nor X-ray data were determined
for this compound, its structure is still unkown. We
assume, however, that this complex is probably identical
to 6.
is in agreement with Gambarotta’s conclusion for the
corresponding Cr complex. On the other hand, very
large Ni‚‚‚Ni separations were found in both 5 and 6
(3.167(1) and 3.142(1) Å, respectively), in contrast to the
very short Cr‚‚‚Cr distance (1.968(2) Å) in the corre-
sponding Cr complex. This demonstrates that a short
M‚‚‚M contact is no prerequisit for the stabilization of
dimeric complexes of the composition [M2(Me)8]n-. In the
analogous Pt complex also a very large M‚‚‚M separation
was found (3.384(1) Å).25
In summary, we can conclude that the structural
principle [Li4(solv)nM2Me8] is a general stabilizing
principle which can be realized not only in organo-
metallic complexes of d-electon-deficient metals (Cr, Mo,
or in the case of Re(III) as [Li2(solv)2Re2Me8]) but also
in complexes with d-electron-rich metals (such as Ni or
Pt).
Con clu sion s
The planar dinuclear complexes 1-3 are the first
representatives of σ-organo-nickel compounds bridged
by an oxam-type ligand. Compound 1 reacts at room
temperature with phenylacetylene to form the corre-
The solid-state structure of 6 is very similar to the
structures reported for the corresponding Cr(II), Mo(II),
and Re(III) complexes.20-24 [Li(THF)]4Cr2Me8 was first
synthesized by Kurras and Otto in the 1960s.19 An early
structural characterization of this compound by an
X-ray crystallographic study suggested the existence of
a Cr-Cr quadrupole bond.20 However, a reinvestigation
of its structure by Gambarotta has shown that the very
short Cr‚‚‚Cr contact is just the result of favorable
geometrical features.21-22
1
sponding phenylacetylide complex 3a . H NMR moni-
toring of the reaction between 1 and bromobenzene-d5
results in the formation of the corresponding bromide
complex 4 and toluene-d5 as final products, which
indicates that both metal centers react independingly
and one after the other. Furthermore, complete dis-
placement of the oxalamidinato ligand in 1 by employing
an excess of LiMe leads to the formation of the cluster
compounds [Li(THF)]2Li2Ni2Me8 (5) and [Li(THF)]4Ni2-
Me8 (6), respectively. The solid-state structures of com-
pounds 5 and 6 clearly demonstrate that the driving
force for the dimerization of two Ni(Me)4 units lies in
the formation of bridges between methyl groups coor-
The X-ray analyses of both 5 and 6 indicate that the
driving force for the stabilization of the dimeric com-
pound is certainly the formation of agostic Li-H bonds
between the four Li atoms and the methyl groups. This

Dinuclear [RNi(oxam)NiR] Complexes
Organometallics, Vol. 20, No. 20, 2001 4227
meta], 6.93 [t (3J HH ) 6.4 Hz), 2 H, CH, 5-pyridyl], 7.52 [t (3J HH
) 7.7 Hz), 2 H, CH, 4-pyridyl], 7.85 [d (3J HH ) 5.8 Hz), 2 H,
CH, 6-pyridyl]. Signals for the toluene included in the com-
plex: 2.32 [s, ca. 1 H, CH3, according to 0.3 toluene per dimeric
unit], 7.07-7.22 [m, CH, toluene]. 13C NMR (50 MHz, THF-
d8): δ -7.5 [CH3, Ni-CH3], 19.1 [CH3, mes ortho], 21.0 [CH3,
mes para], 53.3 [CH2], 121.2 [CH, 3-pyridyl], 122.6 [CH,
5-pyridyl], 127.6 [CH, mes meta], 133.5, 135.7 [C], 136.3 [CH,
4-pyridyl] ], 144.4 [C], 149.0 [CH, 6-pyridyl], 163.1, 168.9[C].
MS (DEI): m/z (rel intensity, %) 648 [M+, 25], 633 [(M - CH3)+,
77], 618 [(M - 2CH3)+, 83].
dinated at different metal centers and Li(THF) frag-
ments. The Ni1-CH3-Li-CH3-Ni2 bonds are addi-
tionally stabilized by Li-H agostic interactions. These
interactions can be considered as a general stabilizing
principle for organometallics of the type [Li4(solv)nM2-
Me8] in which the M‚‚‚M separations can be very
different.
In general, organometallic complexes, described in
this paper such as compounds 1-3, may be of consider-
able interest as starting material for the controlled
synthesis of either new organometallic compounds or
oligonuclear metal compounds containing adjustable
numbers of metal centers. In addition, these complexes
can be viewed as models for intermediates in catalytic
cross coupling reactions in which the two redox-active
metal centers of dinuclear oxam complexes are involved.
Single crystals of 1 containing two molecules of noncoordi-
nated toluene per dimeric unit suitable for an X-ray analysis
were grown from toluene at -18 °C.
Com p lex 2. The compound was prepared as a yellow solid
analogously to 1 from [{(acac)Ni}2(A)] (0.578 g, 0.71 mmol)
using LiPh in a mixture of 70:30 cyclohexane/diethyl ether (0.9
mL, 1.44 mmol). Yield: 0.495 g (90%). The dried complex
contained 0.3 mol of toluene per dimeric unit, determined by
1H NMR spectroscopy. Anal. Calcd for C44H44N6Ni2‚0.3 C7H8:
C, 69.05; H, 5.83; N, 10.48, Ni, 14.64. Found: C, 69.37; H, 5.79;
Exp er im en ta l Section
1
Gen er a l P r oced u r es. All manipulations were carried out
by using Schlenk techniques under an atmosphere of argon.
Prior to use, tetrahydrofurane, diethyl ether, and toluene were
dried over potassium hydroxide and distilled over Na/benzo-
phenone. 2-Aminopicoline, 1.6 M solutions of lithium methyl
in diethyl ether, and phenyllithium in cyclohexane/diethyl
ether (70:30) (Fluka) were used as received, and phenylacety-
lene and bromobenzene were distilled prior to use using
standard methods. Sodium acetylide was used as a 18 wt %
slurry in xylene and oil (95% purity, ABCR).
N, 10.24; Ni, 14.74. H NMR (200 MHz, THF-d8): δ 2.05 [s, 6
H, CH3, mes para], 2.44 [s, 12 H, CH3, mes ortho], 3.62 [s, 4
H, CH2], 6.41 [s, 4 H, CH, mes meta], 6.42-6.46 [m, 6 H, CH,
phenyl meta, para], 6.64-6.71 [m, 4 H, 3,5-pyridyl], 7.05 [d
(3J HH ) 5.7 Hz), 2 H, CH, 6-pyridyl], 7.27 [d (3J HH ) 6.4 Hz),
2 H, CH, phenyl ortho], 7.45 [t (3J HH ) 7.6 Hz), 2 H, CH,
4-pyridyl]. Signals for the toluene included in the complex:
2.32 [s, ca. 1 H, CH3, according to 0.3 toluene per dimeric unit],
7.07-7.22 [m, CH, toluene]. 13C NMR (50 MHz, THF-d8): δ
19.4 [CH3, mes ortho], 20.8 [CH3, mes para], 53.5 [CH2], 121.1
[CH, pyridyl], 121.8 [CH, phenyl], 122.6 [CH, pyridyl], 124.9
[CH, phenyl], 127.3 [CH, mes meta], 133.4 [C], 134.9 [C], 136.9
[CH, 4-pyridyl], 137.1 [CH, phenyl ortho], 144.2 [C], 152.0 [CH,
6-pyridyl], 162.0, 163.8, 168.4 [C]. MS (DEI): m/z (rel intensity,
%) 772 [M+, 4], 695 [(M - Ph)+, 1], 618 [(M - 2Ph)+, 1].
Com p lex 3a . Complex 1 (0.381 g, 0.56 mmol) was dissolved
in phenylacetylene (30 mL) and stirred at room temperature
for 1 week. After removing the solvent in vacuo, the solid was
washed with n-heptane and dried in vacuo. Complex 3a was
obtained as an orange microcrystalline solid. Yield: 0.287 g
(62%). Anal. Calcd for C48H44N6Ni2: C, 70.11; H, 5.39; N, 10.22;
Ni, 14.28. Found: C, 70.25; H, 5.42; N, 9.98; Ni, 14.19. 1H NMR
(200 MHz, THF-d8): δ 2.24 [s, 6 H, CH3, mes para], 2.64 [s,
12 H, CH3, mes ortho], 3.69 [s, 4 H, CH2], 6.63-6.66 [m, 2 H,
CH, 3-pyridyl], 6.74 [s, 4 H, CH, mes meta], 6.77-7.09 [m, 12
H, CH, phenyl, 5-pyridyl], 7.63 [t (3J HH ) 7.7 Hz), 2 H, CH,
4-pyridyl], 8.87 [d (3J HH ) 5.9 Hz), 2 H, CH, 6-pyridyl]. 13C
NMR (50 MHz, THF-d8): δ 19.5 [CH3, mes ortho], 21.0 [CH3,
mes para], 54.5 [CH2], 103.3 [C, alkyne],106.2 [C, alkyne], 121.1
[CH, 3-pyridyl], 123.0 [CH, 5-pyridyl], 124.7, 127.6, 127.8 [CH,
mes meta, phenyl], 129.7 [C], 132.0 [CH mes meta, phenyl],
134.3, 135.5 [C], 138.3 [CH, 4-pyridyl], 144.6 [C], 153.8 [CH,
6-pyridyl], 164.5, 167.4 [C]. MS (DEI): m/z (rel intensity, %)
820 [M+, 2], 718 [(M - phenylacetylide)+, 100], 618 [(M - 2
phenylacetylide)+, 4].
1H and 13C spectra were recorded on a Bruker AC 200 F
spectrometer (7Li NMR: Bruker DRX 400). Mass spectra were
recorded on a Finnigan MAT SSQ 710. Values for m/z are for
the most intense peak of the isotope envelope. The measured
isotopic pattern for the nickel-containing species is in good
agreement with the calculated isotopic pattern using the
program ICIS (version 8.2.1, Finnigan). Elemental analyses
were performed with Leco CHNS-932. Since both 5 and 6 are
extremely reactive and pyrophoric, C, H analyses could not
be carried out. Ni analyses were obtained by titration of a
solution in dilute hydrochloric acid with 0.01 M EDTA using
murexid as indicator. Li analyses were performed by atomic
absorption spectroscopy. For 5, only the Li:Ni ratio was deter-
mined since the substance started to decompose after 2 min
when it was dried by oil pump vacuum at room temperature.
The ligand N,N′-bis(2-pyridylmethyl)-1,2-bis(2,4,6-trimeth-
ylphenylimino)ethane-1,2-diamine (H2A) was prepared accord-
ing to described methods;26,27 the complex [{(acac)Ni}2(A)] was
obtained following the procedure described in refs 1 and 28.
Com p lex 1. A solution of [{(acac)Ni}2(A)] (4.049 g, 4.95
mmol) in THF (170 mL) was stirred at -78 °C. LiMe (6.4 mL,
10.24 mmol), dissolved in diethyl ether, was added dropwise.
After stirring the solution at room temperature overnight, the
solvent was removed in vacuo. The residue was extraxted with
toluene (170 mL). The extract was filtered, and the residue
was washed with toluene (50 mL). The clear orange solution
was concentrated under vacuum (ca. 10 mL), and diethyl ether
(80 mL) was added. An orange precipitate was formed. After
keeping it at -18 °C overnight, the precipitate was filtered
off, washed with diethyl ether (25 mL), and dried under
vacuum (5 h) at room temperature. An orange solid was
obtained. Yield: 1.866 g (56%) of 1. Recrystallization from
toluene and standing overnight at -18 °C yielded orange
crystals of 1, including 0.3 mol toluene per mol complex
Single crystals of 3a containing four noncoordinated mol-
ecules of toluene per dimeric unit suitable for an X-ray analysis
were grown from toluene at -18 °C.
Com p lex 3b. A solution of [{(acac)Ni}2(A)] (0.987 g, 1.21
mmol) in THF (150 mL) was stirred at -78 °C. Sodium
acetylide (0.119 g, 2.48 mmol), suspended in oil and xylene,
was added dropwise. After stirring the suspension at room
temperature overnight, the solvent was removed in vacuo.
Then toluene (150 mL) was added. The precipitate was filtered
and washed twice with toluene (50 mL). After concentrating
the solution to 2 mL, diethyl ether (40 mL) was added. 3b
crystallized as an orange compound. It was filtered off, washed
twice with diethyl ether (20 mL), and dried in vacuo. Yield:
0.454 g (56%). Anal. Calcd for C36H36N6Ni2: C, 64.53; H, 5.42;
N, 12.54; Ni, 17.52. Found: C, 64.38; H, 5.59; N, 11.98; Ni,
(determined by NMR spectroscopy). Anal. Calcd for C34H40
-
N6Ni2‚0.3C7H8: C, 63.97; H, 6.31; N, 12.40; Ni, 17.32. Found:
C, 63.62; H, 6.01; N, 12.06; Ni, 17.16. 1H NMR (200 MHz, THF-
d8): δ -1.35 [s, 6 H, CH3, Ni-CH3], 2.22 [s, 6 H, CH3, mes
para], 2.43 [s, 12 H, CH3, mes ortho], 3.62 [s, 4 H, CH2], 6.65
[d (3J HH ) 7.9 Hz), 2 H, CH, 3-pyridyl], 6.71 [s, 4 H, CH, mes

4228 Organometallics, Vol. 20, No. 20, 2001
Walther et al.
17.64. 1H NMR (200 MHz, THF-d8): δ 0.93 [s, 2 H, alkyne],
2.20 [s, 6 H, CH3, mes para], 2.57 [s, 12 H, CH3, mes ortho],
3.58 [s, 4 H, CH2], 6.65 [s, 4 H, CH, mes meta], 6.72 [d (3J HH
) 7.9 Hz), 2 H, CH, 3-pyridyl], 6.97 [t (3J HH ) 5.9 Hz), 2 H,
CH, 5-pyridyl], 7.58 [t (3J HH ) 7.5 Hz), 2 H, CH, 4-pyridyl],
8.85 [d (3J HH ) 5.9 Hz), 2 H, CH, 6-pyridyl]. 13C NMR (50 MHz,
THF-d8): δ 19.5 [CH3, mes ortho], 21.1 [CH3, mes para], 54.3
[CH2], 90.7 [C, alkyne], 95.2 [C, alkyne], 121.0 [CH, 3-pyridyl],
122.8 [CH, 5-pyridyl], 125.9 [CH, mes meta], 134.1, 135.4 [C],
138.1 [CH, 4-pyridyl], 144.5 [C], 153.8 [CH, 6-pyridyl], 164.4,
167.4 [C]. MS (neg. DCI/H2O): m/z (rel intensity, %) 668 [M+,
100], 643 [(M - acetylide)+, 2].
of 3b, the whole compound 5 and for the methyl groups of 6
the hydrogen atoms were located by difference Fourier syn-
thesis and refined isotropically. The hydrogen atoms of the
other structures and for the THF molecules of 5 were included
at calculated positions with fixed thermal parameters. All non-
hydrogen atoms were refined anisotropically.29 XP (SIEMENS
Analytical X-ray Instruments, Inc.) was used for structure
representations. The toluene molecules of 3a and 3b are
disordered. The disorder could be solved. Due to the high R
value in the case of 3a (R1obs ) 0.110), the crystallographic
data of 3a will not be published here. Additional information
is given in ref 35.
Cr ysta l Da ta for 1:34 C34H40N6Ni2‚2C7H8, fw ) 834.41 g
mol-1, brown prism, size 0.19 × 0.12 × 0.10 mm3, triclinic,
space group P1h, a ) 8.3999(3) Å, b ) 11.7368(5) Å, c )
13.0598(6) Å, R ) 103.617(2)°, â ) 107.802(2)°, γ ) 108.26(2)°,
Single crystals of 3b containing two molecules of toluene
per dimeric unit suitable for an X-ray analysis were grown
from toluene at -18 °C.
Com p lex 4. This compound was obtained by reacting
perdeuterated bromobenzene-d5 with 1 in bromobenzene-d5 in
an NMR tube (9 days at room temperature) and characterized
by comparison with an authentic sample (prepared from 1
equiv of Li2A and 2 equiv of (Ph3P)2NiBr2 in THF28) via 1H
V ) 1083.18(8) Å3, T ) -90 °C, Z ) 1, Fcalcd ) 1.279 g cm-3
,
µ(Mo KR) ) 9.09 cm-1, F(000) ) 442, 7206 reflections in
h(-10/10), k(-15/13), l(-16/16), measured in the range 3.35°
e θ e 27.47°, completeness θmax ) 96.4%, 4774 independent
reflections, Rint ) 0.020, 4274 reflections with Fo > 4σ(Fo), 223
1
NMR spectroscopy. H NMR (200 MHz, bromobenzene-d5): δ
parameters, 0 restraints, R1obs ) 0.050, wR2 ) 0.141, R1all
2.10 [s, 6 H, CH3, mes para], 2.80 [s, 12 H, CH3, mes ortho],
3.39 [s, 4 H, CH2], 5.74-5.79 [m, 2 H, CH, 3-pyridyl], 6.16-
6.23 [m, 2 H, CH, 5-pyridyl], 6.65 [m, 6 H, CH, mes meta,
4-pyridyl], 8.66-8.69 [m, 2 H, CH, 6-pyridyl]. 1H NMR (200
MHz, benzene-d6): δ 2.13 [s, 6 H, CH3, mes para], 2.92 [s, 12
H, CH3, mes ortho], 3.36 [s, 4 H, CH2], 5.20-5.25 [m, 2 H, CH,
obs
) 0.057, wR2all ) 0.147, GOOF ) 1.012, largest difference peak
and hole 0.836/-0.534 e Å-3
.
Cr ysta l Da ta for 3b:34 C36H36N6Ni2‚4C7H8, fw ) 1038.66
g mol-1, brown prism, size 0.18 × 0.16 × 0.12 mm3, monoclinic,
space group P21/c, a ) 11.019(2) Å, b ) 12.329(2) Å, c )
20.850(3) Å, â ) 103.69(2)°, V ) 2752.1(8) Å3, T ) -90 °C, Z
) 2, Fcalcd ) 1.253 gcm-3, µ(Mo KR) ) 7.29 cm-1, F(000) ) 1100,
5844 reflections in h(-13/13), k(-15/0), l(-26/0), measured in
the range 2.42° e θ e 27.42°, completeness θmax ) 90.9%, 5694
independent reflections, Rint ) 0.019, 3876 reflections with Fo
3-pyridyl], 5.78-5.86 [m, 2 H, CH, 5-pyridyl], 6.14 [t (3J HH
)
7.9 Hz), 2 H, CH, 4-pyridyl], 6.71 [s, 4 H, CH, mes meta], 8.92
[d (3J HH ) 5.9 Hz), 2 H, CH, 6-pyridyl]. MS (DEI): m/z (rel
intensity, %) 776 [M+, 0.07], 697 [(M - Br)+, 0.13], 618 [(M -
2Br)+, 0.06], 560 [(M - Ni - 2Br)+, 3.68].
Upon evaporation of the solvent the reaction mixture was
extracted with diethyl ether. The remaining residue (yield ca.
90 wt %) contained 4 in 80% purity, together with an
unidentified byproduct.
> 4σ(Fo), 287 parameters, 0 restraints, R1obs ) 0.062, wR2
obs
) 0.1763, R1all ) 0.114, wR2all ) 0.203, GOOF ) 1.039, largest
difference peak and hole 1.605/-0.777 e Å-3
.
Cr ysta l Da ta for 5:34 C16H40Li4Ni2O2, fw ) 409.66 g mol-1
,
brown prism, size 0.18 × 0.16 × 0.12 mm3, triclinic, space
group P1h, a ) 6.9022(3) Å, b ) 8.4718(5) Å, c ) 10.1497(6) Å,
R ) 110.586(3)°, â ) 97.200(3)°, γ ) 97.684(3)°, V ) 541.02(5)
Å3, T ) -90 °C, Z ) 1, Fcalcd ) 1.257 g cm-3, µ(Mo KR) ) 17.42
cm-1, F(000) ) 220, 3645 reflections in h(-8/8), k(-9/10), l(-
12/13), measured in the range 3.03° e θ e 27.47°, completeness
θmax ) 97.7%, 2404 independent reflections, Rint ) 0.022, 2211
reflections with Fo > 4σ(Fo), 189 parameters, 0 restraints, R1obs
) 0.027, wR2 ) 0.082, R1all ) 0.031, wR2 ) 0.086, GOOF
Com p lex 5. To a stirred solution of 1 ( 0.333 g, 0.49 mmol)
in THF (60 mL) was added dropwise LiMe, dissolved in diethyl
ether (2.0 mL, 3.20 mmol), at -78 °C. The reaction mixture
was stirred for 24 h and allowed to warm to room temperature.
Then the reaction mixture was filtered. The residue was
washed with toluene (2 × 15 mL). Concentrating the solution
to 5 mL and standing for 1 week gave brown crystals. They
were washed with toluene (2 mL) and pentane (5 mL) and
dried in vacuo for 2 min. Yield: 0.139 g (69%). Anal. Calcd for
obs
all
) 1.015, largest difference peak and hole 0.375/-0.405 e Å-3
.
C
16H40Li4Ni2O2: Molar ratio Li:Ni ) 4.0:2.0. Found: Li:Ni )
4.1:2.0. 1H NMR (200 MHz, benzene-d6): δ -0.80 [s, 24 H,
CH3], 1.17 [m, 8 H, CH2], 3.53 [m, 8 H, CH2]. 13C NMR (50
MHz, benzene-d6): δ -5.3 [CH3], 25.2 [CH2], 68.4 [CH2]. 7Li
NMR (156 MHz, benzene-d6): δ 2.17.
Cr ysta l Da ta for 6:34 C24H56Li4Ni2O4, fw ) 553.87 g mol-1
,
yellow prism, size 0.20 × 0.18 × 0.12 mm3, triclinic, space
group P1h, a ) 8.5892(8) Å, b ) 8.9512(8) Å, c ) 11.0999(9) Å,
R ) 111.184(6)°, â ) 107.343(8)°, γ ) 91.881(7)°, V ) 750.0(1)
Å3, T ) -90 °C, Z ) 1, Fcalcd ) 1.226 g cm-3, µ(Mo KR) ) 12.79
cm-1, F(000) ) 300, 4990 reflections in h(-10/11), k(-10/11),
l(-14/14), measured in the range 3.77° e θ e 27.53°, com-
Single crystals of 5, suitable for an X-ray analysis, were
isolated upon recrystallization from toluene at -18 °C. The
reaction to form 5 can also be carried out using 1 equiv of
[{(acac)Ni}2(A)] as starting material, which was reacted with
8 equiv of LiMe following the above procedure.
pleteness θmax ) 95.6%, 3311 independent reflections, Rint
)
0.032, 2963 reflections with Fo > 4σ(Fo), 202 parameters, 0
Com p lex 6. Complex 5 was recrystallized from THF. After
keeping the solution overnight at -20 °C yellow crystals of 6
were isolated. Yield: 60%. Anal. Calcd for C24H56Li4Ni2O4: Li,
5.01; Ni, 21.20. Found: Li, 5.43; Ni, 21.63. 1H NMR (200 MHz,
benzene-d6): δ -0.61 [s, 24 H, CH3], 1.25 [m,16 H, CH2], 3.62
[m, 16 H, CH2]. 13C NMR (50 MHz, benzene-d6): δ -6.2 [CH3],
25.4 [CH2], 68.2 [CH2]. 7Li NMR (156 MHz, benzene-d6): δ
1.98.
X-r a y Cr ysta llogr a p h y. The intensity data for the com-
pound 3b were collected on a Nonius CAD4 diffractometer and
for the other compounds on a Nonius KappaCCD diffrac-
tometer, using graphite-monochromated Mo KR radiation.
Data were corrected for Lorentz and polarization effects, but
not for absorption.29-31 The structures were solved by direct
methods (SHELXS32) and refined by full-matrix least-squares
techniques against Fo2 (SHELXL-9733). For the acetylide group
(29) MOLEN, An Interactive Structure Solution Procedure; Enraf-
Nonius: Delft, The Netherlands, 1990.
(30) COLLECT, Data Collection Software; Nonius B.V., Nether-
lands, 1998.
(31) Otwinowski, Z.; Minor W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode. In Methods in Enzymology, Vol. 276,
Macromolecular Crystallography, Part A; Carter, C. W., Sweet, R. M.,
Eds.; Academic Press: San Diego, 1997; pp 307-326.
(32) Sheldrick, G. M. Acta Crystallogr. Sect. A 1990, 46, 467-473.
(33) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Ger-
many, 1993.
(34) Further details of the crystal structure investigations are
available on request from the director of the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, GB-Cambridge CB2 1 EZ, on
quoting the depository number CCSD-150911 (1), CCSD-164309 (3b),
CCSD-150913 (5), and CCSD-150914 (6), the names of the authors,
and the journal citation.
(35) CCSD-150912 (3a ) (private communication).

Dinuclear [RNi(oxam)NiR] Complexes
Organometallics, Vol. 20, No. 20, 2001 4229
restraints, R1obs ) 0.086, wR2 ) 0.143, R1all ) 0.101, wR2
Su p p or tin g In for m a tion Ava ila ble: X-ray structural
information for complexes 1, 3, 5, and 6. This material
is available free of charge via the Internet at http://
pubs.acs.org.
obs
all
) 0.148, GOOF ) 1.188, largest difference peak and hole
0.706/-0.730 e Å-3
.
Ack n ow led gm en t. We are grateful to the Deutsche
Forschungsgemeinschaft and the Fonds fu¨r Chemische
Industrie for support of this research.
OM000960U