Synthesis and characterization of the unusual cluster [Ni 2(GaAr′)2(η1:η1- μ2-C2H4)]: Ready addition of ethylene to Ni(COD)(GaAr′)2 at 25 °c and 1 atmosphere

Article abstract of DOI:10.1016/j.jorganchem.2010.11.043

The nickel (0) compound Ni(COD)(GaAr′)₂ (Ar′ = C₆H₃-2,6-(C₆H₃-2,6-i-Pr ₂)₂), 1, was synthesized by the reaction of Ni(COD) ₂ (COD = 1,5-cyclooctadiene) with (GaAr′)₂. Compound 1 reacted with ethylene at 25 °C and at 1 atm pressure to give the bimetallic cluster [Ni₂(GaAr′)₂(η¹: η¹-μ₂-C₂H₄)], 2, through the incorporation of one molecule of ethylene and displacement of COD. The structure of 2 featured an unusual Ni₂Ga₂C₂ core bicyclic structure in which the C₂H₄ moiety bridges the Ga···Ga edge of a Ga₂Ni₂ tetrahedron. The galliums each carry an η¹-bonded Ar′ substituent which complexes the nickel atom by an η⁶-π interaction with one of its flanking Ar' rings.

Full text of DOI:10.1016/j.jorganchem.2010.11.043

Journal of Organometallic Chemistry 696 (2011) 2217e2219
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and characterization of the unusual cluster
[Ni2(GaAr0)2(h1 h1
: -m2-C2H4)]: Ready addition of ethylene
ꢀ
to Ni(COD)(GaAr0)2 at 25 C and 1 atmosphere
*
Oracio Serrano, Elke Hoppe, James C. Fettinger, Philip P. Power
Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
a r t i c l e i n f o
a b s t r a c t
The nickel (0) compound Ni(COD)(GaAr0)2 (Ar0 ¼ C6H3e2,6-(C6H3-2,6-i-Pr2)2), 1, was synthesized by the
reaction of Ni(COD)2 (COD ¼ 1,5-cyclooctadiene) with (GaAr0)2. Compound 1 reacted with ethylene at
Article history:
Received 2 September 2010
Received in revised form
22 November 2010
25 ꢀC and at 1 atm pressure to give the bimetallic cluster [Ni2(GaAr0)2(h1 h1
: -m2-C2H4)], 2, through the
incorporation of one molecule of ethylene and displacement of COD. The structure of 2 featured an
unusual Ni2Ga2C2 core bicyclic structure in which the C2H4 moiety bridges the Ga$$$Ga edge of a Ga2Ni2
tetrahedron. The galliums each carry an h1-bonded Ar0 substituent which complexes the nickel atom by
Accepted 24 November 2010
Keywords:
Gallium
Nickel
an h6
ep interaction with one of its flanking Ar’ rings.
Ó 2010 Elsevier B.V. All rights reserved.
Arene
Ethylene addition
Bimetallic cluster
1. Introduction
However, metalemetal bonded organometallic complexes of
neutral aryl rings are rare. A Ni2(C6H6)3 species has been detected
through mass spectroscopy of a mixture of Nin(benzene)m clusters
generated in the phase gas by laser vaporization but no stable
examples are known [12]. Herein, we describe the unexpected
The chemistry of transition metal complexes with
aromatic rings is of key importance in modern coordination and
organometallic chemistry. The discovery of ferrocene, [Fe(h5
p-bonds to
-
C5H5)2], essentially simultaneously by several groups, its structural
recognition by Wilkinson, Woodward and Fischer initiated the field
of modern organometallic chemistry [1,2]. In addition, the first
example of a metal complex of a neutral arene, bis(benzene)chro-
synthesis of the compound [Ni2(GaAr0)2(h1 h1
: -m2-C2H4)] which
incorporates a (arene)nickelenickel(arene) entity.
2. Experimental
mium, [Cr(h
6-C6H6)2], was reported four years later by Fischer and
Hafner [2]. Since that time, ionic and neutral metallocenes and
bis (arenes) [3,4], including ansa-bridged and half-sandwich type
complexes have been studied intensively by experimental and
theoretical investigations [5e8]. Recent examples of interesting
2.1. Materials and methods
All manipulations were carried out using modified Schlenk
techniques under an atmosphere of N2 or in a Vacuum Atmo-
spheres HE-43 drybox. All solvents were dried and degassed three
times prior to use. The compound (GaAr0)2 was prepared according
to literature procedures. Ni(COD)2 was used as received from Strem.
1H and 13C NMR were recorded on Varian 300 spectrometer and
referenced to known standards. X-ray quality crystals of 1 and 2
were covered with a layer of hydrocarbon oil. A suitable crystal was
selected, attached to a glass fiber, and placed in the cold tempera-
ture stream. The data were collected near 90 K using a Bruker
metal complexes stabilized by
first organometallic zinc(I) compound, [(
p
earene interactions include the
h
5-C5Me5)ZneZn(h5
-
C5Me5)] [9] containing the first stable ZneZn bond in a molecular
complex, the sandwich complexes containing monolayer palladium
sheets, [Pd3(C7H7)Cl3]þ and [Pd5(naphthanacene)2(toluene)]þ [10],
the mixed-valent [Fe(0)(NHC)(p8 h4 4-COT)Fe(I)(p6 5-COT)2]2
- ,h -h
species and the tri-iron cluster Fe3(COT)3 (COT ¼ 1,3,5,7-cyclo-
octatetraene), which was obtained by the fusion of three molecules
of Fe(COT) catalyzed by N-heterocyclic carbenes (NHC) [11].
SMART 1000 diffractometer and Mo K
a
(
l
¼ 0.71073 Å) radiation.
Absorption corrections were applied using SADABS [13]. The
structures were solved by use of Direct Methods in SHELXS [14] and
refined by the full-matrix least-squares procedure in SHELXL. All
* Corresponding author.
E-mail address: pppower@ucdavis.edu (P.P. Power).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.11.043

2218
O. Serrano et al. / Journal of Organometallic Chemistry 696 (2011) 2217e2219
Table 1
Selected crystallographic data for compounds 1 and 2.
Compound
1
2
Formula
C71H93Ga2Ni
1144.6
Red/plate
Triclinic
C62H78Ga2Ni2
1080.10
Green/block
Orthohombic
Pbca
18.875(5)
16.526(4)
34.479(8)
90
90
90
107.55(4)
8
Formula weight
Crystal color-habit
Crystal system
Space group
a (Å)
ꢀ
Pı
12.169(1)
12.920(1)
21.674(2)
78.967(2)
78.316(2)
70.439(2)
3116.1(5)
2
Scheme 1. Synthesis of Ni(COD)(GaAr0)2 (1) and [Ni2(GaAr0)2(h1 h1
: -m2-C2H4)] (2).
b (Å)
c (Å)
a
b
g
(ꢀ)
(ꢀ)
(ꢀ)
(Ar0 ¼ C6H3-2,6-(C6H3-2,6-i-Pr2)2) and Ni(COD)2, Scheme 1. The
structure of 1, was determined by single crystal X-ray diffraction,
and shows that it has a distorted tetrahedral coordination geometry
in which the nickel atom is complexed by two gallanediyls and
a COD ligand, Fig.1. The Ga(1)-NieGa(2) angle is 101.64(4)ꢀ which is
similar to that in the bis gallium (I) triazenido derivative Ni(COD)
[Ga{(N(Ar)2)CNR2}]2 (Ar¼ C6H3Pri2-2,6; R ¼ cyclohexyl) gallanediyl
complex [15]. The GaeNi bond lengths 2.201(4) and 2.205(4) Å are
among the shortest bond distances reported for gallanediyl nickel
species (usual range 2.329(9)e2.476(10) Å) [16], which is presum-
V (Å3)
Z
Crystal size (mm)
0.12 ꢂ 0.2 ꢂ 0.03
0.44 ꢂ 0.37 ꢂ 0.32
Density d(calcd) (g cmꢁ3
)
1.220
1.334
Absorption coefficient
No. Reflns
No. of obs Rflns (I > 2
m
(mmꢁ1
)
1.197
28683
11301
0.034
1.718
3441
2608
0.107
s
(I))
R1
wR2; all data
0.093
0.2157
ably due to the two-coordination at gallium and the good s-donor
non hydrogen atoms were refined anisotropically, while hydrogens
were placed at calculated positions and included in the refinement
by using a riding model. Some details of the data collection and
refinement are given in Table 1. Further details are in the
supplementary material.
character of the GaAr’ ligand [16,17]. The shortness of the bonds is
exceeded by the 2.1700(4) Å observed for the GaeNi distance in
Ni{GaC(SiMe3)3}4 [18].
Synthesis of Ni(COD)(GaAr0)2, (1). A deep green benzene solu-
tion (15 mL) of Ar0GaGaAr0 (0.336 g, 0.36 mmol) was added drop-
wise to
a yellow solution of (10 mL) Ni(COD)2 (0.098 g,
0.359 mmol). The solution became red immediately and was stirred
for 1 h at room temperature, the volatiles were removed under
reduced pressure. The red solid was dissolved in hexane, concen-
trated and cooled to ca. ꢁ20 ꢀC. After 3 days the product 1 was
obtained as red crystals. Yield: 0.190 g (83%). m.p. ¼ 260 ꢀC
(decomp). 1H NMR (C6D6): 7.29 (t, 1H, 3JHH ¼ 6.6 Hz, CHAr), 7.19 (m,
3H, CHAr), 7.03 (d, 1H, 3JHH ¼ 6.6 Hz, CHAr), 3.51 (bs, 1H, CH, COD),
3
3.11 (sept, 2H, JHH ¼ 6.8 Hz, CH(CH3)2), 2.02 (br. m, 1H, CH2, cod),
1.85 (br. m, 1H, CH2, COD),1.21 (d, 3H, 3JHH ¼ 7.2 Hz, CH(CH3)2), 1.06
(d, 12H, JHH ¼ 6.8 Hz, CH(CH3)2). 13C NMR (C6D6): 168.8 (i-C6H3),
147.05 (o-Dipp), 143.6, 139.7, 128.9 (CH, Ar), 128.8 (CH, Ar), 123.9
(CH, Ar), 72.1 (CH, COD), 32.3 (CH2, COD), 30.6 (CH, CH(CH3)2), 25.1
(CH3, CH(CH3)2), 23.9 (CH3, CH(CH3)2).
Synthesis of [Ni2(GaAr0)2(h1 h1
: -m2-C2H4)], (2). A solution of Ni
Fig. 1. Thermal ellipsoid (30%) plot of Ni(COD)(GaAr0)2 (1). The iso-propyl groups of the
flanking aryl rings of the terphenyl substituent and hydrogen atoms are not shown.
Selected bonds lengths (Å) and angles (deg): Ni(1)eGa(2) 2.201(4), Ni(1)eGa(1) 2.205
(4), C(61)eNi(1) 2.111(2), C(62)eNi(1) 2.085(2), C(65)eNi(1) 2.122(2), C(66)eNi(1)
2.087(2); Ga(2)eNi(1)eGa(1) 101.642(14), C(62)eNi(1)eC(66) 102.47(10), C(66)e
Ni(1)eC(61) 86.61(10), C(62)eNi(1)eC(65) 86.20(10), C(61)eNi(1)eC(65) 94.89(9).
(COD)(GaAr0)2 (0.156 g, 0.25 mmol) in hexane or benzene (15 mL)
was treated with excess ethylene at room temperature and atmo-
spheric pressure. Within 10 min the color of the solution changed
to deep green and stirring was continued for 1 h. The solution was
cooled to ca. ꢁ20 ꢀC, under an atmosphere of ethylene for 3 days
which afforded 1 as green plates. Yield: 0.45 g (17%). m.p. ¼ 137 ꢀC
(decomp.). 1H NMR (C6D6, 297 K):
d
¼ 0.7 (d, 3JHH ¼ Hz, 7H), 0.8 (d,
Reaction of this compound with excess ethylene in hexane or
benzene at room temperature and atmospheric pressure led to an
immediate color change from deep red to green. Cooling the
solution under an ethylene atmosphere gave 2 as green blocks in
moderate yield (Scheme 1). The structure of 2 was determined by
X-ray crystallography (Fig. 2).
This reaction was investigated as part of our studies of the
addition of alkenes, alkynes or small molecules (e.g. H2 or NH3) to
Ar0GaGaAr0 which have been of interest over the last few years [17].
These have shown that Ar0GaGaAr0 added two equivalents of an
olefin or alkyne to yield the cycloalkanes or cycloalkenes and
hydrogen or ammonia its yield the hydride or amide compounds
[Ar0Ga(R)(R0)]2 (R ¼ R0 ¼ alkane, alkene or hydride; R ¼ hydride,
R0 ¼ amide) [17]. For 2 the core structure shows that the cyclo-
octadiene ligand has been completely displaced and that just one
3
3
3JHH ¼ Hz, 7H), 1.0 (d, JHH ¼ Hz, 7H), 1.1 (d, JHH ¼ Hz, 7H), 1.3 (d,
3
3JHH ¼ Hz, 1H), 1.4 (d, JHH ¼ Hz, 7H), 2.5 (sept, 3JHH ¼ Hz, 1H), 2.6
(sept, 3JHH ¼ Hz, 1H), 2.8 (sept, 3JHH ¼ Hz, 1H), 2.9 (sept, 3JHH ¼ Hz,
3
3
2H), 3.1 (sept, JHH ¼ Hz, 1H), 5.2 (d, JHH ¼ Hz, 1H), 6.07 (d,
3
3
3JHH ¼ Hz, 1H), 6.09 (d, JHH ¼ Hz, 1H), 6.3 (d, JHH ¼ Hz, 1H), 7.2
(18 H). 13C NMR (C6D6, 297 K):
22.9, 24.6, 25.0, 21.1, 25.6, 29.2, 29.5, 29.9, 30.0, 30.1, 83.3, 97.1,
102.0, 121.4, 121.5, 122.1, 122.2, 122.3, 124.8, 125.8, 126.6, 128.2,
140.7, 141.1, 142.2, 145.0, 146.1, 146.4, 146.6, 168.6.
d
¼ 13.9 (CH2eCH2), 19.8, 21.9, 22.5,
3. Results and discussion
The red complex Ni(COD)(GaAr0)2 (1, COD ¼ 1,5-cyclooctadiene)
was synthesized by the reaction of the digallene Ar0GaGaAr0

O. Serrano et al. / Journal of Organometallic Chemistry 696 (2011) 2217e2219
2219
Acknowledgment
The support of this work by the National Science Foundation is
gratefully acknowledged. O.S. thanks the CONACYT (México) for
a postdoctoral fellowship. E.H. thanks the German Research Foun-
dation (DFG) for financial support.
Appendix A. Supplementary information
CCDC-791693 and 791694 contain the crystallographic data for 1
and 2. These data are available free of charge from the Cambridge
Crystallographic Data Center via www.ccdc.cam.ac.uk/data_request/cif.
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In summary, we have shown that a low-valent compound Ni(0)-
Ga(I), Ni(COD)(GaAr0)2 (1), readily undergoes addition of one
molecule of ethylene at room temperature and 1 atm pressure to
give (arene)nickelenickel(arene) [Ni2(GaAr0)2(h1 h1
: -m2-C2H4)] (2)
complex.