Synthesis and structure of new compounds with Zn-Ga bonds. Insertion of the gallium(I) bisimidinate Ga(DDP) into Zn-X (X = CH3, CI) and the homoleptic complex cation [Zn(GaCp*)4]2+

Article abstract of DOI:10.1021/ic7013804

Insertion reactions of the low-valent group 13 bisimidinate ligand Ga(DDP) {DDP = 2-[(2,6-diisopropylphenyl)-amino]-4-[(2,6-diisopropylphenyl)imino]-2- pentene} into Zn-Me and Zn-Cl bonds are reported. The reaction of ZnMe ₂ with 2 equiv of Ga(

Full text of DOI:10.1021/ic7013804

Inorg. Chem. 2007, 46, 9481−9487
Synthesis and Structure of New Compounds with Zn
−Ga Bonds:
Insertion of the Gallium(I) Bisimidinate Ga(DDP) into Zn
−X (X ) CH3,
+
†
Cl) and the Homoleptic Complex Cation [Zn(GaCp*)4]2
Andreas Kempter, Christian Gemel, Thomas Cadenbach, and Roland A. Fischer*
Anorganische Chemie II, Organometallics & Materials, Ruhr-UniVersita¨t Bochum,
D-44780 Bochum, Germany
Received July 11, 2007
Insertion reactions of the low-valent group 13 bisimidinate ligand Ga(DDP)
amino]-4-[(2,6-diisopropylphenyl)imino]-2-pentene into Zn Me and Zn Cl bonds are reported. The reaction of
ZnMe2 with 2 equiv of Ga(DDP) yields the double-insertion product [ (DDP)GaMe 2Zn] (1), whereas the insertion
of Ga(DDP) into the Zn Cl bond of ZnCl2 in tetrahydrofuran (THF) leads to the monoinsertion product [ (DDP)-
GaCl THF·Ga(DDP) Zn(THF)(
ZnCl(THF)2] (2). Treatment of 2 with Na[BArF] results in the salt [ -Cl)]2[BArF]2 (3),
Ga-bonded compounds 1 3 were
{DDP ) 2-[(2,6-diisopropylphenyl)-
}
−
−
{
}
−
{
}
{
}
µ
with two Cl atoms bridging the Zn centers. The structural features of the Zn
−
−
compared with related complexes and in particular with the compound [Zn(GaCp*)4][BArF]2 (4), which was synthesized
by the reaction of ZnMe2, [H(OEt2)2][BArF], and GaCp* in fluorobenzene. The complex cation [Zn(GaCp*)4]2 of 4
+
relates to previously reported d10 analogues [M(GaCp*)4] (M
)
Ni, Pd, Pt). All new compounds were fully characterized
by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction analysis.
1. Introduction
during the past decade. For example, the neutral NHC
analogue (NHC ) nitrogen heterocyclic carbene) gallium-
(I) bisimidinate ligand [Ga(DDP)] {DDP ) 2-[(2,6-diiso-
propylphenyl)amino]-4-[(2,6-diisopropylphenyl)imino]-2-
pentene} stabilizes low-coordinated, very electron-rich d10
M0 centers (Ni,13 Pd, and Pt2), which allow typical oxidative
addition reactions of hydrogen, organosilanes, and benzene.
Similarly, the anionic congeners to [Ga(DDP)], namely, the
five-membered heterocycle [Ga{[N(Ar)C(H)]2}]- (Ar ) 2,6-
iPr2C6H3), have been introduced as NHC analogue ligands
A continuous motif in metal-organic coordination chem-
istry has been exploring the bonding of the heavier group
13 and 14 elements E to p-, d-, and f-block metal fragments
MLn featuring direct M-E bonds.1 The availability of neutral
as well as anionic nucleophilic carbenoid group 13 organyls
[EIR]a (R ) bulky organic group; a ) 0, -1)1-4 as free
ligands boosted the research on the synthesis and reactivity
of their complexes with late transition metals (Fe,5,6 Ru,7
Co,8,9 Rh,10,11 Ni,12-15 Pd,2,16-18 Pt2,14,18 Cu, Ag,19 and Au20,21
)
(9) Aldridge, S.; Baker, R. J.; Coombs, N. D.; Jones, C.; Rose, R. P.;
Rossin, A.; Willock, D. J. Dalton Trans. 2006, 3313-3320.
(10) Kempter, A.; Gemel, C.; Hardman, N. J.; Fischer, R. A. Inorg. Chem.
2006, 45, 3133-3138.
† Organo group 13 complexes of transition metals. XLVIII. Part
XLVII: Reference 13.
* To whom correspondence should be addressed. E-mail:
roland.fischer@rub.de. Fax: (+49)234 321 4174.
(1) Linti, G.; Schno¨ckel, H. Coord. Chem. ReV. 2000, 285-319.
(2) Kempter, A.; Gemel, C.; Fischer, R. A. Chem.sEur. J. 2007, 13,
2990-3000.
(3) Fischer, R. A.; Weiss, J. Angew. Chem., Int. Ed. 1999, 38, 2831-
2850.
(4) Baker, R. J.; Jones, C. Coord. Chem. ReV. 2005, 249, 1857-1869.
(5) Baker, R. J.; Jones, C.; Platts, J. A. Dalton Trans. 2003, 3673-3674.
(6) Jones, C.; Aldridge, S.; Gans-Eichler, T.; Stasch, A. Dalton Trans.
2006, 5357-5361.
(7) Steinke, T.; Cokoja, M.; Gemel, C.; Kempter, A.; Krapp, A.; Frenking,
G.; Zenneck, U.; Fischer, R. A. Angew. Chem., Int. Ed. 2005, 44,
2943-2946.
(8) Jutzi, P.; Neumann, B.; Reumann, G.; Stammler, H.-G. Organome-
tallics 1998, 17, 1305-1314.
(11) Steinke, T.; Gemel, C.; Cokoja, M.; Winter, M.; Fischer, R. A. Dalton
Trans. 2005, 55-62.
(12) Steinke, T.; Gemel, C.; Cokoja, M.; Winter, M.; Fischer, R. A. Angew.
Chem., Int. Ed. 2004, 43, 2299-2302.
(13) Kempter, A.; Gemel, C.; Fischer, R. A.; Cadenbach, T. Organome-
tallics 2007, 4257-4264.
(14) Green, S. P.; Jones, C.; Stasch, A. Inorg. Chem. 2007, 46, 11-13.
(15) Baker, R. J.; Jones, C.; Platts, J. A. J. Am. Chem. Soc. 2003, 125,
10534-10535.
(16) Steinke, T.; Gemel, C.; Winter, M.; Fischer, R. A. Angew. Chem. 2002,
114, 4955-4957.
(17) Kempter, A.; Gemel, C.; Fischer, R. A. Chem. Commun. 2006, 1551-
1553.
(18) Steinke, T.; Gemel, C.; Winter, M.; Fischer, R. A. Chem.sEur. J.
2005, 11, 1636-1646.
10.1021/ic7013804 CCC: $37.00
Published on Web 10/05/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 22, 2007 9481

Kempter et al.
Scheme 1. Synthesis of Compounds 1-3 (R ) 2,6-iPr2C6H3)
by Jones et al.4-6,9,15,19,22-26 The M-E bonding in all of these
compounds has been extensively studied by quantum chemi-
cal methods on various levels of theory.27-29 In general, one
should note that the M-E bond is dominated by electrostatic
effects, leading to M(δ-) and E(δ+) polarization due to the
very strong σ-donor properties of the [EIR]a ligands.30 The
π(M-E) back-bonding is typically rather weak, and its
contribution to the bonding heavily depends on the particular
types of σ/π donor/acceptor properties of the supporting
group R. As an extreme case, the complex cation [GaPt-
(GaCp*)4]+ may be quoted here. This complex features a
naked Ga+ cation in a terminal position bonded to the 18-
electron closed-shell [Pt(GaCp*)4]. The calculations point
toward equally strong electrostatic and covalent σ and π
acceptor interactions but without any σ-donor influence
caused by the remaining lone pair at the GaI center.31,32
Looking at the large number of M-E complexes of these
types of ligands reported to date, the elements of the Zn
group, Zn, Cd, and Hg, have so far remained elusive. Two
examples with very short Hg-In interactions are known,33
whereas no molecular complexes of Hg and Cd with the
lighter group 13 ligands [AlIR]a or [GaIR]a have been isolated
and characterized so far. Most recently, however, Jones et
al. communicated on the salt elimination reaction of
[Ga{[N(Ar)C(H)]2}]- with N,N-chelated zinc chloride com-
plexes to give the very first examples of compounds featuring
a Zn-Ga bond.23 This report prompted us to present here
our results on the synthesis and structural characterization
of some related new compounds with Zn-Ga bonds, namely,
[{(DDP)GaMe}2Zn] (1), [{(DDP)GaCl}ZnCl(THF)2] (2),
[{THF‚Ga(DDP)}Zn(THF)(µ-Cl)]2[BArF]2 (3), and [Zn-
(GaCp*)4][BArF]2 (4) (THF ) tetrahydrofuran; [BArF] )
[B{C6H3(CF3)2}4]).
three-coordinated Ga centers.4,19,23,24 In addition, the substitu-
tion of weakly bound neutral ligands such as olefins is
possible, leading to anionic complexes.14 Also, the insertion
of [Ga{[N(Ar)C(H)2}]- into metal-halide bonds is observed
but invariably leads to the elimination of the paramagnetic
GaII dimers.34 In contrast to that, the related neutral six-
membered heterocycle [Ga(DDP)] typically inserts into
metal-halide bonds to give neutral complexes with a
M-Ga-X motif (X ) halide), and four-coordinated GaI
centers, as we have recently reported for RhI 10 as well as
AuI 20complexes.Theformallyanionicfragment[Ga(Cl)(DDP)]-
coordinated to a formally cationic metal center can thus be
viewed as being isolobal to phosphanes PR3 or arsanes AsR3
with similar bonding properties and a four-coordinated ligator
atom.
2.1. Insertion Reaction of [Ga(DDP)] into Zn-CH3 and
Zn-Cl Bonds. The reaction of [Ga(DDP)] with Me2Zn in
a ratio of 2:1 in fluorobenzene at room temperature gives
(19) Green, S. P.; Jones, C.; Mills, D. P.; Stasch, A. Organometallics 2007,
26, 3424-3430.
(20) Kempter, A.; Gemel, C.; Fischer, R. A. Inorg. Chem. 2005, 44, 163-
165.
(21) Anandhi, U.; Sharp, P. R. Angew. Chem., Int. Ed. 2004, 43, 6128-
6131.
(22) Baker, R. J.; Farley, R. D.; Jones, C.; Kloth, M.; Murphy, D. M. J.
Chem. Soc., Dalton Trans. 2002, 3844-3850.
(23) Jones, C.; Rose, R. P.; Stasch, A. Dalton Trans. 2007, 2997-2999.
(24) Arnold, P. L.; Liddle, S. T.; McMaster, J.; Jones, C.; Mills, D. P. J.
Am. Chem. Soc. 2007, 129, 5360-5361.
(25) Jones, C.; Mills, D. P.; Platts, J. A.; Rose, R. P. Inorg. Chem. 2006,
45, 3146-3148.
(26) Green, S. P.; Jones, C.; Lippert, K. A.; Mills, D. P.; Stasch, A. Inorg.
Chem. 2006, 45, 7242-7251.
(27) Sundermann, A.; Reiher, M.; Schoeller, W. W. Eur. J. Inorg. Chem.
1998, 305-310.
(28) Uddin, J.; Boehme, C.; Frenking, G. Organometallics 2000, 19, 571-
582.
(29) Reiher, M.; Sundermann, A. Eur. J. Inorg. Chem. 2002, 1854-1863.
(30) Uddin, J.; Frenking, G. J. Am. Chem. Soc. 2001, 123, 1683-1693.
(31) Buchin, B.; Gemel, C.; Cadenbach, T.; Fernandez, I.; Frenking, G.;
Fischer, R. A. Angew. Chem., Int. Ed. 2006, 45, 5207-5210.
(32) Aldridge, S. Angew. Chem., Int. Ed. 2006, 45, 8097-8099.
(33) Gabbai, F. P.; Schier, A.; Riede, J.; Sladek, A.; Goerlitzer, H. W.
Inorg. Chem. 1997, 36, 5694-5698.
2. Results and Discussion
Using the anionic five-membered heterocycles of the type
[Ga{[N(Ar)C(H)2}]- as ligands evidently implies the sub-
stitution of halides from appropriate metal precursors via salt
elimination reactions resulting in neutral complexes with
(34) Baker, R. J.; Farley, R. D.; Jones, C.; Mills, D. P.; Kloth, M.; Murphy,
D. M. Chem.sEur. J. 2005, 11, 2972-2982.
9482 Inorganic Chemistry, Vol. 46, No. 22, 2007

Synthesis and Structure of New Compounds with Zn-Ga Bonds
Figure 1. Mercury plots of 1 (left) and 2 (right). H atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg) of 1: Zn1-Ga1 2.4631(7),
Zn1-Ga2 2.4609(7), Ga1-C100 1.995(3), Ga2-C200 1.984(4), Ga1-N11 2.027(3), Ga1-N12 2.012(3), Ga2-N21 2.027(3), Ga2-N22 1.998(3), N11-
C3 1.322(4), N12-C1 1.327(4), N21-C32 1.325(4), N22-C30 1.323(4); Ga1-Zn1-Ga2 173.61(2), N11-Ga1-N12 90.86(11), N21-Ga2-N22 91.18-
(12), Zn1-Ga1-C100 121.14(10), Zn1-Ga2-C200 122.00(11); C100-Ga1-Ga2-C200 93.4. Selected bond lengths (Å) and angles (deg) of 2: Ga-Zn
2.3920(6), Zn-O1 2.098(2), Zn-Cl1 2.2016(14), Ga-Cl2 2.2820(10), Ga-N1 1.965(2), N1-C1 1.335(3); N1-Ga-N1* 94.18(13), Zn-Ga-Cl2 111.31-
(3), Cl1-Zn-Ga 138.07(4), O1-Zn-O1* 87.26(17); Cl1-Ga-Zn-Cl1 180.0.
the insertion product 1 as orange-red crystals in yields of
around 80% (Scheme 1). Compound 1 was found to be air-
sensitive in solution as well as in the solid state but can be
stored in an inert gas atmosphere for several weeks without
decomposition. The compound is well soluble in common
aprotic organic solvents like hexane, THF, or benzene.
Several attempts to remove the methyl groups of 1 by
protonation with [H(OEt2)2][BArF] in fluorobenzene aiming
at methane elimination and thus leading to the salt [{(DDP)-
Ga}2Zn][BArF]2 as a potential product were not successful.
Instead, the deposition of a gray, obviously metallic pre-
cipitate was observed. Because no well-defined products
could be isolated and characterized, no further attempts to
optimize the conditions were undertaken.
depending on the coordination number at the group 13 metal,
and the distance does not simply reflect the bond order. In
the course of the reaction, the [Ga(DDP)] ligand inserts into
the Zn-Me bond, giving a distorted tetrahedral geometry at
the Ga center. The {MeGa(DDP)} moieties are oriented
perpendicular to each other (torsion angle C100-Ga1-Ga2-
C200: 93.4°) to minimize steric strain in the complex.
Averaging to 1.99 Å, the Ga-Me bond distances are
distinctly longer than those in [Me2Ga(DDP)] (av 1.75 Å)35
but more similar to that of [(Me)(Cl)Ga(DDP)] [1.956(2)
Å],36 the observation of which can be interpreted as an effect
of the lower oxidation state and thus less electrophilic
character of the Ga atom in 1. The Ga-N bond distances of
1.998(3)-2.027(3) Å are in agreement with that explanation
and are only slightly shorter than that in free [Ga(DDP)]
(av 2.054 Å)37 but similar to that found in [{(DDP)Ga}Au-
{Ga(DDP)Cl}] [1.984(6) Å for the {Ga(DDP)Cl} moiety].20
In contrast to the insertion of [Ga(DDP)] into the Zn-C
bond of ZnMe2, the reaction of ZnCl2 with [Ga(DDP)] in a
THF solution does not give the congener of 1, namely, the
compound [{(DDP)GaCl}2Zn]. Rather, the compound 2 is
obtained in quite good yields even in the case of a larger
excess of [Ga(DDP)] (Scheme 1). The presence of the
coordinating solvent THF instead of fluorobenzene may favor
the formation of Zn-THF adducts and thus four-coordinated
Zn species. The increased steric bulk of the DDP ligand (cone
angle of ca. 270°) in comparison with [Ga{[N(Ar)C(H)]2}]-
(cone angle of ca. 180°) is likely to disfavor the formation
of [{(DDP)GaCl}2Zn(THF)2] as the hypothetical double-
insertion product, which, however, would compare with the
known a four-coordinated compound [(tmeda)Zn{Ga{[N(Ar)C-
The 1H NMR spectrum of 1 in CDCl3 at room temperature
displays one set of signals for the DDP ligand, with a reduced
i
(Cs) symmetry (e.g., two signals for the Pr-CH protons,
indicative of a lack of rotation around the C-N bond of the
i
aryl group). The Pr-CH3 protons give rise to four distinct
doublet signals at 1.28, 1.24, 1.22, and 1.09 ppm, whereas a
signal at -0.45 ppm can be assigned to the protons of the
methyl groups bound to the Ga atoms. The 13C NMR
spectrum is in good agreement with these results. Deep-
orange-red crystals of 1 suitable for single-crystal X-ray
analysis were obtained by crystallization from n-hexane at
-30 °C overnight. The molecular structure of 1 in the solid
state is shown in Figure 1 (left). In addition, Figure 1 (right)
shows the molecular structure of 2, the synthesis and
characterization of which are discussed below.
Compound 1 shows a linear two-coordination of the central
Zn atom by the Ga atoms [Ga-Zn-Ga ) 173.61(2)°] with
equal Ga-Zn bond distances of 2.4631(7) and 2.4609(7) Å.
These bond lengths are significantly longer than those in
[{iPr2NC[N(Ar)]2}ZnGa{[N(Ar)C(H)]2}] [2.3230(7) Å] but
comparable to those in [(tmeda)Zn{Ga{[N(Ar)C(H)]2}}2] [Ar
) 2,6-iPr2C6H3; 2.4491(17) and 2.4307(17) Å].23 In general,
the M-E bond distances can vary over quite a large range
(35) Stender, M.; Eichler, B. E.; Hardman, N. J.; Power, P. P.; Prust, J.;
Noltemeyer, M.; Roesky, H. W. Inorg. Chem. 2001, 40, 2794-2799.
(36) Singh, S.; Ahn, H. J.; Stasch, A.; Jancik, V.; Roesky, H. W.; Pal, A.;
Biadene, M.; Herbst-Irmer, R.; Noltemeyer, M.; Schmidt, H.-G. Inorg.
Chem. 2006, 45, 1853-1860.
(37) Hardman, N. J.; Eichler, B. E.; Power, P. P. Chem. Commun. 2000,
1991-1992.
Inorganic Chemistry, Vol. 46, No. 22, 2007 9483

Kempter et al.
(H)]2}}2].23 Several attempts to react ZnCl2 with [Ga(DDP)]
in fluorobenzene as a very polar, inert but noncoordinating
solvent did not give any isolable products. Thus, the solvent-
free congeners to 2 and 3 (vide infra) remain a synthetic
challenge. Compound 2 is soluble in THF, Et2O, or CHCl3
and can be stored in the solid state in an inert gas atmosphere
for several days without decomposition. The 1H NMR
spectrum of 2 in CDCl3 shows one signal for the DDP-
backbone proton at 5.27 ppm as well as signals indicating a
C2V symmetry around the {Ga(DDP)} moiety, which is not
in accordance with the solid-state structure discussed below.
Obviously, the chloro ligands exchange fast in solution,
leading to coalescence of the DDP signals. However, even
at low temperature (-60 °C), no significant splitting of the
signals could be observed.
Pale-yellow prismatic crystals of 2 were grown by storing
the solution at -30 °C overnight. The molecular structure
of 2 in the solid state is shown in Figure 1 (right). Compound
2 crystallizes in the monoclinic space group P21/m, with only
half of the molecule in the elemental cell and the THF ligand
at the Zn being disordered, showing two THF moieties
rotated by around 65.6°. The Zn atom is coordinated in a
distorted tetrahedral geometry by two THF molecules, the
chloro fragment, and the {ClGa(DDP)} fragment. The Zn-
Cl bond [2.2016(14) Å] is slightly longer than those in the
parent compound [(THF)2ZnCl2] [2.176(2) and 2.184(2) Å]38
but is well in the range for other Zn-Cl bonds reported in
the literature. The same is true for the Zn-O bond distance,
which is 2.098(2) Å in 2 and slightly longer than those in
[(THF)2ZnCl2] [2.009(5) and 2.016(5) Å]. Interestingly, the
Ga-Zn bond distance of 2.3920(6) Å is slightly shorter than
that in 1 [2.4609(7) Å] and is well shortened with respect to
four-coordinated Zn complex [(tmeda)Zn{Ga{[N(Ar)C-
(H)]2}}2] [2.4491(17) and 2.4307(17) Å] but significantly
longer than that in [{iPr2NC[N(Ar)]2}ZnGa{[N(Ar)C(H)]2}]
[2.3230(7) Å], which features three-coordinated Zn.23 These
results indicate that the difference in the Zn-Ga bond length
can be attributed to steric interactions of the coordinated
group 13 ligands rather than being primarily related to the
Zn coordination numbers, as was previously suggested for
the five-membered heterocycle complexes.23 The two Cl
atoms, the Ga atom, and the Zn atom are coplanar (torsion
angle Cl-Ga-Zn-Cl: 180°), with the Cl atoms being in
the trans position to each other. Whereas the Ga-Cl bond
distance [2.2820(10) Å] is significantly longer than those in
[(DDP)GaCl2] [2.218(1) and 2.228(1) Å],35 it is similar to
those in other LnM[Ga(DDP)Cl] complexes such as [(Ph3P)-
Au{Ga(DDP)Cl}] [2.290(2) Å], [{(DDP)Ga}Au{Ga(DDP)-
Cl}] [2.2837(16) Å],20 or [(COE)(benzene)Rh{(DDP)GaCl}]
[2.321(2) Å],10 respectively (COE ) cyclooctene). The
comparably long Ga-Cl distance is in good agreement with
the fluxional behavior of the chloro ligand observed in
solution.
storing the solution overnight at -30 °C, colorless needles
of [{THF·Ga(DDP)}Zn(THF)(µ-Cl)]2[BArF]2 (3) were ob-
tained in 72% yield (Scheme 1). No further reaction was
observed upon the addition of another 1 equiv of Na[BArF]
to 3. Compound 3 can be stored in an inert gas atmosphere
for several days without decomposition and was found to
be soluble only in polar solvents such as THF or fluoroben-
zene but not in hexane or toluene, which matches with the
1
ionic nature of the product. Again, the H NMR spectrum
of 3 in fluorobenzene at room temperature shows only one
set of signals for a C2V-symmetric {Ga(DDP)} moiety. This
is in agreement with a fast exchange of the axially coordi-
nated THF molecule, further supported by two broad signals
for the THF ligands observed at 3.51 and 1.53 ppm,
respectively. Similar NMR features were previously reported
for the Au compound [{(DDP)Ga·THF}2Au][BArF], which
also shows only signals for a {Ga(DDP)} moiety in a C2V-
symmetric coordination.20
Colorless needles, suitable for single-crystal X-ray dif-
fraction analysis could be obtained by cooling a saturated
solution of 3 in fluorobenzene to -30 °C overnight.
Compound 3 crystallizes in the triclinic space group P1h with
half of the molecule in the asymmetric unit. The molecular
structure of 3 is depicted in Figure 2 and consists of a planar
Zn2Cl2 core, with the two Cl atoms bridging the Zn centers.
The Zn atoms show a distorted tetrahedral environment. The
Zn-Cl bond distances are 2.3520(16) Å (Zn-Cl) and
2.3652(18) Å (Zn-Cl*), similar to those found in the halide-
bridged complexes [{Me3Si)3Si}Zn(THF)(µ-Cl)]2 (2.36 and
2.40 Å) or [{(Me3Si)3Ge}Zn(THF)(µ-Cl)]2 (2.36 and 2.40
Å).39 Whereas the Zn-Ga [2.3960(11) Å] bond distance is
similar to those found in 2 [2.3920(6) Å] and therefore in
between those found for [(tmeda)Zn{Ga{[N(Ar)C(H)]2}}2]
[2.4491(17) and 2.4307(17) Å] and for [{iPr2NC[N(Ar)]2}-
ZnGa{[N(Ar)C(H)]2}] [2.3230(7) Å],23 the Zn-O bond
distance [2.021(4) Å] is slightly shorter than that in 2 [2.098-
(2) Å] but comparable to [(THF)2ZnCl2] [2.009(5) and 2.016-
(5) Å].38 Similar to the situation discussed at [{(DDP)Ga‚
THF}2Au][BArF],10 the electrophilicity of the Ga center
increases according to the coordination to the metal center.
This is reflected in the weak coordination of a THF molecule
to each Ga atom perpendicular to the least-squares plane of
the heterocycle. The behavior of the Ga center of the {Ga-
(DDP)} moiety to act as a Lewis acid if a Lewis base
approaches from above the ring plane corresponds well with
the theoretical findings of Reiher and Sundermann.29 The
THF moieties coordinated to Zn and Ga are perpendicularly
oriented to each other (torsion angle O-Ga-Zn-O: 90.08°),
with the Ga-O bond distance in 3 [2.098(2) Å] being slightly
shorter than that in [{(DDP)Ga‚THF}2Au][BArF] (av 2.16
Å).10
In contrast to [Ga(DDP)], [GaCp*] does not react with
Me2Zn in either THF or fluorobenzene. However, when
[H(OEt2)2][BArF] and Me2Zn were previously mixed in a
2.1 mole ratio at -30 °C and the resulting colorless solution,
presumably containing solvated Zn2+ cations and/or [Zn2+]-
2.2. Cationic Complex with Zn-Ga Bonds. When 2 is
reacted with 1 equiv of Na[BArF] in THF or fluorobenzene,
no color change or precipitation took place. However, on
(38) Dashti, A.; Niediek, K.; Werner, B.; Neumueller, B. Z. Anorg. Allg.
Chem. 1997, 623, 394-402.
(39) Nanjo, M.; Oda, T.; Mochida, K. J. Organomet. Chem. 2003, 672,
100-108.
9484 Inorganic Chemistry, Vol. 46, No. 22, 2007

Synthesis and Structure of New Compounds with Zn-Ga Bonds
Figure 2. Mercury plot of 3. H atoms and [BArF]- anions are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ga-N1 1.926(5), Ga-N2
1.942(5), Ga-O1 2.105(4), Ga-Zn 2.3960(11), Zn-O2 2.021(4), Zn-Cl1 2.3520(16), Zn-Cl1* 2.3652(18), N1-C1 1.332(7), N2-C3 1.320(7); N1-
Ga-N2 96.8(2), O1-Ga-Zn 107.43(13), Cl1-Zn-Cl1* 92.96(6), O2-Zn-Ga 116.13(12); O1-Ga-Zn-O2 90.07(18).
Scheme 2. Synthesis of Compound 4
[BArF]2 ion aggregates, was warmed to room temperature
and then GaCp* added, colorless crystals of 4 could be
obtained by slow diffusion of hexane into the concentrated
solution overnight (Scheme 2). It should be noted that no
reaction was observed when using [Zn(Otf)2] (Otf )
-
CF3SO3 ) as the alternative Zn source. Besides the signals
1
for the [BArF]- anion, the H NMR spectrum of 4 in CD2-
Cl2 at room temperature expectedly shows only one signal
for the coordinated GaCp* moieties at 2.03 ppm, which is
in agreement with a presumably dynamic and highly sym-
metric homoleptic compound with η5 coordination of the Cp*
rings in solution. The molecular structure of 4 in the solid
state is shown in Figure 3.
Figure 3. Mercury plot of the homoleptic complex cation [Zn(GaCp*)4]2+
of 4. H atoms and [BArF]- anions are omitted for clarity. Selected bond
lengths (Å) and angles (deg): Zn-Ga1 2.4036(6), Zn-Ga2 2.4111(6),
Ga1-Cp*centroid 1.861, Ga1-Cp*centroid 1.850; Ga1-Zn-Ga2 107.440(18),
Ga1*-Zn-Ga2 108.510(17), Ga2-Zn-Ga2* 111.18(3), Ga1-Zn-Ga1*
113.80(3).
Compound 4 crystallizes in the monoclinic space group
C2/c, with some CF3 groups of the [BArF] anion being
slightly disordered. The Zn atom is coordinated by four Ga
atoms in a distorted tetrahedral fashion. In contrast to the
previously reported homoleptic complexes [M(GaCp*)4] (M
) Ni, Pd, and Pt),40,41 which exhibit nearly ideal tetrahedral
Ga-M-Ga angles of around 109°, the Ga-Zn-Ga angles
in 4 vary from 107.44 to 113.80°, possibly because of
packing effects of the [BArF]- anion in the unit cell. The
Zn-Ga bond distances are 2.4036(6) and 2.4111(6) Å; these
distances are shorter than those in 1 [2.4609(7) Å] or
[(tmeda)Zn{Ga{[N(Ar)C(H)]2}}2] [2.4491(17) and 2.4307-
(17) Å] but comparable to the ones in 2 [2.3920(6) Å] or 3
[2.3960(11) Å]. The Cp*centroid-Ga distances range between
1.850 and 1.861 Å and are thus significantly shortened in
comparison to the corresponding distance of the free [(η5-
Cp*)Ga] (2.08 Å)42 and the complexes [M(GaCp*)4] [M )
Ni (2.00 Å), Pd (2.02 Å), and Pt (1.99 Å)].40,41 Similar
Cp*centroid-Ga distances are found in [Cp*GaFe(CO)4] (1.86
Å)43 or [(C6F5)3BGaCp*] (1.865 Å), for example.44 This
shortened Cp*centroid-Ga distance indicates the increased
electrostatic interaction and the strong σ donation of the Ga
(42) Loos, D.; Baum, E.; Ecker, A.; Schno¨ckel, H. Angew. Chem., Int. Ed.
1997, 36, 860-862.
(43) Jutzi, P.; Reumann, G. J. Chem. Soc., Dalton Trans. 2000, 2237-
2244.
(44) Hardman, N. J.; Power, P. P.; Gorden, J. D.; Macdonald, C. L. B.;
Cowley, A. H. Chem. Commun. 2001, 1866-1867.
(40) Gemel, C.; Steinke, T.; Weiss, D.; Cokoja, M.; Winter, M.; Fischer,
R. A. Organometallics 2003, 22, 2705-2710.
(41) Jutzi, P.; Neumann, B.; Schebaum, L. O.; Stammler, A.; Stammler,
H.-G. Organometallics 1999, 18, 4462-4464.
Inorganic Chemistry, Vol. 46, No. 22, 2007 9485

Kempter et al.
lone pair to the Zn2+ cation. The Cp* moieties are nearly
symmetrically η5-bonded to the Ga centers [Ga1-C bond
distances 2.197(4)-2.225(4) Å; Ga2-C bond distances
2.203(4)-2.236(4) Å], but a substantial deviation from
linearity is observed for the Cp*centroid-Ga-Zn vectors (165°
and 170°). This deviation is known for other [M(GaCp*)]
(M ) Ni, Pd, and Pt) complexes and is caused by repulsive
intramolecular interactions between the Cp* methyl groups
of different Cp*Ga ligands (cone angle ∼ 112°).
appropriate amount of the commercially available (Fluka) and as-
received alkyl in hexane or C6H5F. ZnCl2 was purchased from
Riedel-de-Haen and used as received. Elemental analyses were
performed by the Microanalytical Laboratory of the Ruhr-Univer-
sita¨t Bochum. NMR spectra were recorded on a Bruker Avance
DPX-250 spectrometer (1H NMR, 250.1 MHz; 13C NMR, 62.9
MHz) in C6D6 at 298 K, if not stated otherwise. Chemical shifts
are given relative to tetramethylsilane and were referenced to the
solvent resonances as internal standards.
All crystal structures were measured on an Oxford Excalibur 2
diffractometer using Mo KR radiation (λ ) 0.710 73 Å). The
structures were solved by direct methods using SHELXS-97 and
refined against F 2 on all data by full-matrix least squares with
SHELXL-97. Details to the data collection, structure solutions, and
refinements of the new compounds 1-4 are available as Supporting
Information (see below).
3. Conclusion
We have successfully synthesized and structurally char-
acterized several new examples of compounds with Zn-Ga
bonds by insertion of the bulky bisimidinate Ga(DDP) into
Zn-Me and Zn-Cl bonds. Thus, the reaction of ZnMe2 with
[Ga(DDP)] yields the insertion product [{(DDP)GaMe}2Zn]
(1), with two {MeGa(DDP)} moieties coordinating to the
Zn center. Compound 1 exhibits a perpendicular orientation
of the {MeGa(DDP)} moieties in the solid state, which is
explained by the steric bulk of the DDP ligand. The complex
[{(DDP)GaCl}Zn(Cl)(THF)2] (2), synthesized by the reaction
of ZnCl2 with [Ga(DDP)] in THF, only shows a single
insertion of one [Ga(DDP)] moiety into one Zn-Cl bond.
In contrast to the related reaction with the anionic five-
membered heterocycle [Ga{[N(Ar)C(H)]2}]-, the Cl remains
coordinated at the Ga center and allows subsequent substitu-
tion reactions. Thus, salt elimination of 2 with Na[BArF]
yields the cationic complex [{THF·Ga(DDP)}Zn(THF)(µ-
Cl)]2[BArF]2 (3). The rather strong electrophilicity of the
coordinated Ga center of the [Ga(DDP)] ligand in cationic
complexes becomes visible by the axial coordination of THF
molecules to each Ga center in 3. Additionally, the reaction
of Me2Zn with [H(OEt2)2][BArF] and [GaCp*] yield in the
compound [Zn(GaCp*)4][BArF]2 (4), featuring the homo-
leptic complex cation [Zn(GaCp*)4]2+, which represents the
Zn analogue of the well-known neutral homoleptic com-
plexes [M(GaCp*)4] (M ) Ni, Pd, and Pt). This example
nicely illustrates the Lewis base bonding properties of
[GaCp*] to metal cations similar to those of classical Werner-
type complexes such as [Zn(NH3)4]2+.
4.2. Synthetic Procedures and Analytical Data. [{(DDP)-
GaMe}2Zn] (1). A sample of [Ga(DDP)] (200 mg, 0.41 mmol)
was dissolved in 5 mL of fluorobenzene at room temperature. A
volume of 1.66 mL of a 0.25 M solution of ZnMe2 in fluorobenzene
was added slowly. The reaction mixture turned to deep-orange and
was stirred for an additional 1 h at room temperature. The solvent
was removed in vacuo, and the orange-yellow solid was redissolved
in ca. 2 mL hexane. Cooling the solution to -30 °C overnight gave
1
deep-orange-red crystals of 1 in 178 mg yield (81%). H NMR
(CDCl3, 25 °C): δ 7.28-7.13 (m, 12H, Ar), 5.24 (s, 2H, γ-CH),
3.55 (sept, 4H, CH(Me)2, JHH ) 6.72 Hz), 3.07 (sept, 4H, CH(Me)2,
JHH ) 6.85 Hz), 1.85 (s, 12H, CH3), 1.28 (d, 12H, CH(Me)2, JHH
) 7.02 Hz), 1.24 (d, 12H, CH(Me)2, JHH) 6.93 Hz), 1.22 (d, 12H,
CH(Me)2, JHH ) 6.57 Hz), 1.09 (d, 12H, CH(Me)2, JHH ) 6.78
Hz), -0.49 (s, 6H, GaMe). 13C NMR (CDCl3, 25 °C): δ 169.3
(CN), 145.7 (CMe), 142.7 (Ar), 139.7 (Ar), 127.1 (Ar), 124.9 (Ar),
123.5 (Ar), 97.1 (γ -C), 28.9 (CHMe2), 27.7 (CHMe2), 26.8 (CMe),
24.8 (CMe), 24.1 (CHMe2). 23.7 (CHMe2), 23.7 (CHMe2), 1.0
(GaMe). Elem anal. Calcd (found) for C60H88Ga2N4Zn: C, 67.34
(69.69); H, 8.29 (8.57); N, 5.24 (5.06).
A typical experimental approach to remove the methyl groups
of 1 was as follows: 100 mg (0.093 mmol) of 1 was dissolved in
5 mL of C6H5F, and [H(OEt2)2][BArF] (100 mg, 0.093 mmol) was
added at room temperature. After the resulting solution was stirred
for 2 min, a gray/black insoluble precipitate formed. Additionally,
performing the reaction at lower temperature (-30 °C) did not
change the outcome of the reaction.
[{(DDP)GaCl}Zn(Cl)(THF)2] (2). Samples of ZnCl2 (55 mg,
0.41 mmol) and [Ga(DDP)] (200 mg, 0.41 mmol) were dissolved
in 5 mL of THF at room temperature. The pale-yellow solution
was stirred for 1 h, the solvent was reduced to ca. 2 mL, and the
mixture was then stored at -30 °C overnight. Big colorless
4. Experimental Section
4.1. Methods and Techniques. All manipulations were carried
out in an atmosphere of purified Ar using standard Schlenk and
glovebox techniques. Hexane, Et2O, toluene, and THF were dried
using an mBraun Solvent Purification System, and fluorobenzene
and benzene were dried by passing through a column filled with
activated Al2O3. Deuterated solvents (CDCl3 and C6D6) are used
as received, dried over an activated molecular sieve (4 Å), and
degassed by bubbling dried Ar through the solvents. The final H2O
content in all solvents was checked by Karl Fischer titration and
did not exceed 5 ppm. The starting compounds [Ga(DDP)],37
GaCp*,8 [H(OEt2)2][BArF],45 and Na[BArF]46,47 ([BArF] ) [B{C6H3-
(CF3)2}4]) were prepared and purified according to literature
methods. Solutions of Me2Zn were prepared by dissolving an
1
prismatic crystals of 2 were obtained in 250 mg yield (79%). H
NMR (CDCl3, 25 °C): δ 7.34-7.20 (m, 6H, Ar), 5.27 (s, 1H,
γ -CH), 3.83 (br t, 8H, THF), 3.24 (sept, 4H, CH(Me)2, JHH) 6.78
Hz), 1.90 (br., 14 H, overlapping signal of THF and CH3), 1.33 (d,
12H, CH(Me)2, JHH ) 6.70 Hz), 1.18 (d, 12H, CH(Me)2, JHH
)
6.84 Hz). 13C NMR (CDCl3, 25 °C): δ 171.5 (CN), 144.4 (CMe),
137.9 (Ar), 127.9 (Ar), 124.5 (Ar), 97.1 (γ -C), 68.7 (THF), 28.5
(THF), 25.5 (CMe), 25.1 (CMe), 24.8 (CHMe2), 23.9 (CHMe2).
Elem anal. Calcd (found) for C37H57Cl2GaN2O2Zn: C, 57.87
(57.89); H, 7.48 (7.56); N, 3.65 (3.98).
(46) Reger, D. L.; Little, C. A.; Lamba, J. J. S.; Brown, K. J.; Krumper, J.
R.; Bergman, R. G.; Irwin, M.; Fackler, J. P., Jr. Inorg. Synth. 2004,
34, 5-8.
(45) Brookhart, M.; Grant, B.; Volpe, A. F., Jr. Organometallics 1992,
11, 3920-3922.
(47) Yakelis, N. A.; Bergman, R. G. Organometallics 2005, 24, 3579-
3581.
9486 Inorganic Chemistry, Vol. 46, No. 22, 2007

Synthesis and Structure of New Compounds with Zn-Ga Bonds
[{(DDP)Ga·THF}Zn(Cl)(THF)]2[BArF]2 (3). A mixture of 100
mg of 2 (0.127 mmol) with 1 equiv of Na[BarF] (100 mg, 0.127
mmol) in THF or fluorobenzene was stirred at room temperature
for 1 h. By cooling the colorless solution to -30 °C overnight,
room temperature and an excess of [GaCp*] (4.5 equiv, 182 mg,
0.89 mmol) was added. After the reaction mixture was stirred for
ca. 30 min, the solvent was reduced to approximately 2 mL.
Diffusion of ca. 10 mL of hexane overnight gave colorless crystals
of 4. Yield: 196 mg (76%). 1H NMR (CD2Cl2, 25 °C): δ 7.73 (br
t, 16H, BArF), 7.57 (br s, 8H, BArF), 2.03 (s, 60H, Cp*). 13C NMR
(CD2Cl2, 25 °C): δ 163.5 (q, J ) 50 Hz, BArF), 135.4 (BArF),
129.5 (q, J ) 31.5 Hz, BArF), 127.3 (BArF), 123.3 (C5Me5), 118.1
(BArF), 10.0 (C5Me5). Elem anal. Calcd (found) for C104H84B2F48-
Ga4Zn: C, 47.83 (47.38); H, 3.24 (3.51).
1
colorless needles of 3 were obtained in 72% yield (173 mg). H
NMR (7:1 C6H5F/C6D6, 25 °C): δ 8.33 (br, 16H, BArF), 7.63 (s,
8H, BArF), 7.36-6.50 (overlying signals of FPh and aromatic
protons, not interpretable), 5.24 (s, 2H, γ-CH), 3.51 (br s, 16H,
THF), 2.78 (sept, 8H, CHMe2, JHH ) 6.76 Hz), 1.60 (s, 12H, CCH3),
1.53 (br m, 16H, THF), 1.16 (d, 24H, CHMe2, JHH ) 6.82 Hz),
1.09 (d, 24H, CHMe2, JHH ) 6.81 Hz). 13C NMR (7:1 C6H5F/C6D6,
25 °C): Because of the large 13C NMR signals for the solvent, no
assignment of the 13C NMR signals of the aromatic carbons of this
sample could be done. δ 98.7 (γ-C), 68.5 (THF), 28.5 (CHMe2),
25.5 (THF), 25.1 (CMe), 23.9 (CHMe2), 23.5 (CHMe2). Elem anal.
Calcd (found) for C138H138B2Cl2F48Ga2N4O4Zn2: C, 51.94 (52.08);
H, 4.36 (4.35); N, 1.76 (1.66).
Acknowledgment. This work was supported by the Fonds
der Chemischen Industrie, Germany. A.K. and T.C. are
grateful for a Ph.D. fellowship granted by the Fonds der
Chemischen Industrie.
Supporting Information Available: Crystallographic data file
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
[Zn(GaCp*)4][BArF]2 (4). A sample of 200 mg of [H(OEt2)2]-
[BArF] (0.198 mmol) was dissolved in 5 mL of C6H5F and cooled
to -30 °C. After the addition of 0.1 mL of a 2 M solution of Me2-
Zn in toluene under vigorous stirring, the solution was warmed to
IC7013804
Inorganic Chemistry, Vol. 46, No. 22, 2007 9487