Binuclear zinc complexes with radical-anionic diimine ligands

Article abstract of DOI:10.1021/om900291x

The reactions of (dpp-BIAN)Zn-Zn(dpp-BIAN) (1) with PhC=CH and of [(dpp-BIAN)Zn(μ-I)]₂ (2) with potassium hydride yield the binuclear complexes [(dpp-BIAN)Zn(μ-C=CPh)]₂ (3) and [(dpp-BIAN)Zn(w-H)]₂ (4), respectively (dpp-B

Full text of DOI:10.1021/om900291x

Organometallics 2009, 28, 3863–3868 3863
DOI: 10.1021/om900291x
Binuclear Zinc Complexes with Radical-Anionic Diimine Ligands
Igor L. Fedushkin,* Olga V. Eremenko, Alexandra A. Skatova, Alexander V. Piskunov,
Georgi K. Fukin, and Sergey Yu. Ketkov
G. A. Razuvaev Institute of Organometallic Chemistry of Russian Academy of Sciences, Tropinina 49, 603950
Nizhny Novgorod, GSP-445, Russian Federation
Elisabeth Irran and Herbert Schumann*
€
Institut fu€r Chemie der Technischen Universitat Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany
Received April 17, 2009
The reactions of (dpp-BIAN)Zn-Zn(dpp-BIAN) (1) with PhCtCH and of [(dpp-BIAN)-
Zn(μ-I)]2 (2) with potassium hydride yield the binuclear complexes [(dpp-BIAN)Zn(μ-CtCPh)]2 (3)
and [(dpp-BIAN)Zn(μ-H)]2 (4), respectively (dpp-BIAN=1,2-bis[(2,6-diisopropylphenyl)imino]
acenaphthene). Complex 3 is also obtained by thermal dehydrogenation of [dpp-BIAN(H)]Zn-
(CtCPh) (5), which in turn can be prepared by reacting ZnI2 with equimolar amounts of [dpp-BIAN-
(H)]Na and PhCtCNa. The paramagnetic compounds 3 and 4 have been characterized by ESR
spectroscopy; the diamagnetic complex 5, by 1H NMR spectroscopy. The molecular structures of 3
and 4 have been determined by single-crystal X-ray diffraction. The electronic structure of complex 4
has been examined by DFT.
Introduction
Na2 with anhydrous ZnCl2. Complex 2 is obtained by
reacting dpp-BIAN with granulated zinc and 0.5 equiv of
iodine in THF. In contrast to alkali8,9 and alkaline earth
metals,10 metallic zinc does not reduce dpp-BIAN in the
absence of iodine.
In 2004, Carmona and co-workers reported on the pre-
paration of (C5Me5)Zn-Zn(C5Me5),1 the first stable molec-
ular compound containing a Zn-Zn bond. In the following
years, further zinc-zinc-bonded complexes such as the
ketiminate derivative [{HC(CMeNAr)2}Zn-Zn{HC(CMe-
NAr)2}] (Ar=2,6-iPr2C6H3),2 the dizincocene [(C5Me4Et)-
Zn-Zn(C5Me4Et)],3 and the terphenyldizinc compound
Ar0Zn-ZnAr0 (Ar0=C6H3-2,6-(C6H3-2,6-iPr2)2)4 have been
synthesized. In 2007, we reported on the synthesis and
molecular structure of the binuclear zinc complexes (dpp-
BIAN)Zn-Zn(dpp-BIAN) (1) and of [(dpp-BIAN)Zn(μ-I)]2
(2),5 both containing the diimine ligand dpp-BIAN in its
radical-anionic form (dpp-BIAN=1,2-bis[(2,6-diisopropyl-
phenyl)imino]acenaphthene). The ESR spectra of solutions
of 1 confirm the existence of direct Zn-Zn bonds. Com-
pound 1 is easily accessible by reaction of (dpp-BIAN)-
In the literature concerning zinc-zinc complexes (two
reviews have been published just recently6,7) mostly the
preparation, structure, and DFT calculations of such com-
pounds are described. So far, data on reactivity of these
compounds are scarce. The reactions of (C5Me5)Zn-Zn-
(C5Me5) with water or tBuOH give C5Me5H, Zn(OH)2, and
highly crystalline zinc metal.3b CNXyl reacts with (C5Me5)-
Zn-Zn(C5Me5) to give the iminoacyl product (Scheme 1)
and metallic zinc.3b The reaction of (C5Me5)Zn-Zn(C5Me5)
with 4-dimethylaminopyridine (dmap) occurs with retention
of the Zn-Zn bond and affords the product (Scheme 1) with
two molecules of dmap being coordinated to one of the zinc
atoms in a geminal fashion.11 Protonation of (C5Me5)Zn-
Zn(C5Me5) with [((2,4,6-Me3C6H2)N(Me)C)2CH]H (Mes-
nacnacH) gives the dizinc complex (Mesnacnac)Zn-Zn-
(Mesnacnac) (Scheme 1).12
*To whom correspondence should be addressed. E-mail: (I.L.F.)
igorfed@iomc.ras.ru; (H.S.) schumann@chem.tu-berlin.de.
(1) Resa, I.; Carmona, E.; Gutierrez-Puebla, E.; Monge, A. Science
2004, 305, 1136.
(2) Wang, Y.; Quillian, B.; Wei, P.; Wang, H.; Yang, X.-J.; Xie, Y.;
King, R. B.; von Schleyer, P. R.; Schaefer, H. F.; Robinson, G. H. J. Am.
Chem. Soc. 2005, 127, 11944.
(6) Grirrane, A.; Resa, I.; Rodrıguez, A.; Carmona, E. Coord. Chem.
Rev. 2008, 252, 1532.
(3) (a) del Rıo, D.; Galindo, A.; Resa, I.; Carmona, E. Angew. Chem.,
Int. Ed. 2005, 44, 1244. (b) Grirrane, A.; Resa, I.; Rodriguez, A.;
Carmona, E.; Alvarez, E.; Gutierrez-Puebla, E.; Monge, A.; Galindo,
A.; Del Rio, D.; Andersen, R. A. J. Am. Chem. Soc. 2007, 129, 693. (c)
Zhu, Z.; Brynda, M.; Wright, R. J.; Fischer, R. C.; Merrill, W. A.;
Rivard, E.; Wolf, R.; Fettinger, J. C.; Olmstead, M. M.; Power, P. P. J.
Am. Chem. Soc. 2007, 129, 10847.
(7) Carmona, E.; Galindo, A. Angew. Chem., Int. Ed. 2008, 47, 6526.
(8) Fedushkin, I. L.; Skatova, A. A.; Chudakova, V. A.; Fukin, G. K.
Angew. Chem., Int. Ed. 2003, 42, 3294.
(9) Fedushkin, I. L.; Skatova, A. A.; Chudakova, V. A.; Cherkasov,
V. K.; Fukin, G. K.; Lopatin, M. A. Eur. J. Inorg. Chem. 2004, 2, 388.
(10) Fedushkin, I. L.; Skatova, A. A.; Chudakova, V. A.; Fukin, G.
K.; Dechert, S.; Schumann, H. Eur. J. Inorg. Chem. 2003, 18, 3336.
€
€
(4) Zhu, Z.; Wright, R. J.; Olmstead, M. M.; Rivard, E.; Brynda, M.;
Power, P. P. Angew. Chem., Int. Ed. 2006, 45, 5807.
(5) Fedushkin, I. L.; Skatova, A. A.; Ketkov, S. Y.; Eremenko, O. V.;
Piskunov, A. V.; Fukin, G. K. Angew. Chem., Int. Ed. 2007, 46, 4302.
(11) Schuchmann, D.; Westphal, U.; Schulz, S.; Florke, U.; Blaser,
D.; Boese, R. Angew. Chem., Int. Ed. 2009, 48, 807.
(12) Schulz, S.; Schuchmann, D.; Westphal, U.; Bolte, M. Organo-
metallics 2009, 28, 1590.
r
2009 American Chemical Society
Published on Web 06/15/2009
pubs.acs.org/Organometallics

3864 Organometallics, Vol. 28, No. 13, 2009
Scheme 1. Reactivity of (C5Me5)Zn-Zn(C5Me5)
Fedushkin et al.
Scheme 2. Synthesis of Complex 3
Scheme 3. Synthesis of Complex 5
Surprisingly, (Mesnacnac)Zn-Zn(Mesnacnac) cannot be
prepared by reduction of (Mesnacnac)ZnX (X=Cl, I)13 with
alkali metals, a method that has been successfully applied for
the synthesis of the related ketiminate derivative [{HC(CMe-
NAr)2}Zn-Zn{HC(CMeNAr)2}] (Ar=2,6-iPr2C6H3).2
Here we report on the reactions of (dpp-BIAN)Zn-Zn-
(dpp-BIAN) (1) with phenylacetylene and of the iodine-
bridged dimer [(dpp-BIAN)Zn(μ-I)]2 (2) with potassium
hydride.
complexes is the addition of proton acidic substrates to give
diamagnetic amido-imino complexes, for instance in the
reaction of (dpp-BIAN)Mg(THF)3 with phenylacetylene
yielding [dpp-BIAN(H)]MgCtCPh(L)n,16 we decided to test
the reactivity of 1 toward phenylacetylene.
Results and Discussion
Since (dpp-BIAN)Zn-Zn(dpp-BIAN) (1) contains the
dpp-BIAN ligand in the redox-active radical-anionic form,8
two main reaction pathways are expected for this compound:
(i) reactions causing oxidation or reduction of the dpp-BIAN
ligand and (ii) reactions that involve the Zn-Zn bond while
maintaining the oxidation state of the dpp-BIAN ligand.
In 2007, Yang et al. reported on the isolation of Na2[(dpp-
DAD)Zn-Zn(dpp-DAD)]14 (dpp-DAD=1,4-bis(2,6-diiso-
propylphenyl)-1,3-diazadiene), a complex in which the Zn-
Zn bond is supported by dianionic diimine ligands. They
prepared the complex by reduction of (dpp-DAD)ZnCl2
with 3 equiv of sodium. Stimulated by this result, we reduced
1 with 2 equiv of sodium in diethyl ether in order to obtain
the analogous complex Na2[(dpp-BIAN)Zn-Zn(dpp-
BIAN)] with dianionic dpp-BIAN ligands. However, this
reaction proceeds with formation of (dpp-BIAN)Na2(Et2O)3
and probably metallic zinc.
Due to the ability of dpp-BIAN to act as dianionic ligand
dpp-BIAN2-, one can expect that in solutions of 1 an
equilibrium between (dpp-BIAN)Zn-Zn(dpp-BIAN) and
two (dpp-BIAN)Zn(L)n moieties will exist. The solvated
mononuclear zinc complex (dpp-BIAN)2-Zn2+(L)n is an
analogue of the known magnesium complexes (dpp-
BIAN)2-Mg2+(L)n (L=Et2O, n=2; L=THF, n=3).10,15
Since one of the typical reactions of these magnesium
Synthesis of [(dpp-BIAN)Zn(μ-CtCPh)]2 (3), [(dpp-
BIAN)Zn(μ-H)]2 (4), and [dpp-BIAN(H)]Zn(CtCPh) (5).
In contrast to the above reflections, the reaction of (dpp-
BIAN)Zn-Zn(dpp-BIAN) (1) with phenylacetylene in THF
does not produce an amido-imino complex of the type [dpp-
BIAN(H)]ZnCtCPh(L)n, but proceeds with formation of
the binuclear zinc complex 3 and elimination of hydrogen.
Compound 3 is also the product of the thermal dehydro-
genation of 5 in refluxing THF (Scheme 2). Since 5 is
thermally quite stable under these conditions, the dehydro-
genation reaction takes several days. However, the reaction
can be accelerated by addition of benzophenone, which
might act as a trap of hydrogen. Both reactions afford
complex 3 as deep red crystals.
Compound 5 itself has been prepared in a two-step one-
pot reaction from phenylacetylene, (dpp-BIAN)Na2-
(Et2O)3,8 and ZnI2 in diethyl ether (Scheme 3).
Unfortunately, the isolated air- and moisture-sensitive,
deep blue almost black crystals of 5 were not suitable for
X-ray structure analysis, but the constitution of 5 was
confirmed by its 1H NMR spectrum. In free dpp-BIAN
and all its metal complexes, the steric conditions cause an
orthogonal arrangement of the N-bonded phenyl rings with
respect to the acenaphthene plane and an arrangement of the
isopropyl substituents of the phenyl groups at different
sides of the phenyl ring planes. Hence, two times four
NMR equivalent methyl groups will give rise for two dou-
€
(13) Schulz, S.; Eisenmann, T.; Westphal, U.; Schmidt, S.; Florke, U.
Z. Anorg. Allg. Chem. 2009, 635, 216.
(14) (a) Yang, X.-J.; Yu, J.; Liu, Y.; Xie, Y.; Schaefer, H. F.; Liang,
Y.; Wu, B. Chem. Commun. 2007, 2363. (b) Yu, J.; Yang, X.-J.; Liu, Y.;
Pu, Zh.; Li, Q.-S.; Xie, Y.; Schaefer, H. F.; Wu, B. Organometallics 2008,
27, 5800.
1
blet signals in the H NMR spectrum of such compounds.
(15) Fedushkin, I. L.; Skatova, A. A.; Hummert, M.; Schumann, H.
Eur. J. Inorg. Chem. 2005, 8, 1601.
(16) Fedushkin, I. L.; Khvoinova, N. M.; Skatova, A. A.; Fukin, G.
K. Angew. Chem., Int. Ed. 2003, 42, 5223.

Article
Organometallics, Vol. 28, No. 13, 2009 3865
Table 1. Crystal and Refinement Data for 3 and 4
3
4
empirical formula
M
T/K
C
100H102N4Zn2
C86H98N4Zn2
1318.42
150(2)
1490.60
100(2)
crystal system
space group
monoclinic
P2(1)/n
15.8637(8)
15.0628(7)
17.0662(8)
90
93.2260(10)
90
4071.5(3)
2
1.216
monoclinic
P21/c
16.2063(3)
15.1241(3)
15.2238(3)
90
104.4886(18)
90
3612.77(12)
2
1.212
˚
a/A
˚
b/A
˚
c/A
R/deg
β/deg
γ/deg
3
˚
V/A
Z
dcalc/Mg m-3
μ(Mo KR)/mm-1
F(000)
0.639
1580
0.711
1404
cryst size/mm
θ range/deg
0.28 ꢀ 0.27 ꢀ 0.20 0.23 ꢀ 0.22 ꢀ 0.18
1.80-25.50
-19 e h e 19
-18 e k e 18
-20 e l e 20
33 048
2.92-25.00
-19 e h e 19
-17 e k e 17
-18 e l e 17
33 012
h, k, l
reflns collected
indep reflns
R(int)
7546
0.0288
6356
0.0621
data/restraints/params
GOF
R1/wR2(I > 2σ(I))
R1/wR2(all data)
largest diff peak, hole/e A
7546/9/689
1.059
0.0311/0.0772
0.0396/0.0805
0.497/-0.178
6356/0/418
1.003
0.0461/0.1005
0.0795/0.1118
0.522/-0.368
Figure 1. ESR spectra of complexes 3 (a) and 4 (b) (toluene,
150 K).
-3
˚
Scheme 4. Synthesis of Complex 4
components due to the splitting on the four equivalent N
nuclei (I=1, simulated A^(N)=6.5 G). The spectra also show
half-field signals (Δms=2), which are typical for biradicals.
On the basis of the spectral parameters the distance between
the unpaired electrons in 3 and 4 has been calculated to be
˚
˚
7.67 A (D=61.0 G) and 7.76 A (D=59.5 G), respectively.
These data agree well with the results of the X-ray structure
analyses.
This situation will not be maintained if the proton is fixed to
one of the two nitrogen atoms. In this case all eight methyl
groups are nonequivalent. However, if the proton in dpp-
BIAN(H) is localized symmetrically between the two nitro-
gen atoms and out of the acenaphthene plane, one can expect
two methine proton signals and four doublets for the CH3
Molecular Structures of Compounds 3 and 4. The crystal
and structure refinement data of 3 and 4 are listed in Table 1,
and their molecular structures are depicted in Figures 2
and 3. The molecules of 3 and 4 are centrosymmetric dimers
with an inversion center localized in the middle between the
two zinc atoms. In both molecules the zinc atoms are
coordinated tetrahedrally. Just as the ESR data, the molec-
ular parameters of 3 and 4 confirm the radical-anionic
character of the dpp-BIAN ligands. While in free dpp-
BIAN17 the distances N(1)-C(1) and N(2)-C(2) (both
1
groups. The H NMR spectrum of 5, recorded in THF-d8,
shows a singlet for the proton of the dpp-BIAN(H) ligand at
δ=6.45 ppm and four doublet signals for the protons of the
eight methyl groups of the isopropyl substituents at δ=1.44,
1.32, 1.06, and 0.96 ppm. These findings correspond with
those obtained for the magnesium complex [dpp-BIAN(H)]-
MgCtCPh(THF)216 and confirm the existence of the proton
and its delocalization between the two nitrogen atoms of the
dpp-BIAN system. The two pairs of equivalent isopropyl
methine protons give rise to two septets at δ = 3.96 and
3.72 ppm. The high-field septet partially overlaps with the
signal of the solvent THF-d8.
˚
1.282(4) A) correspond to a carbon-nitrogen double bond
˚
and the C(1)-C(2) distance (1.534(6) A) is typical for a single
carbon-carbon bond, in 3 and 4 the N(1)-C(1) and N(2)-
C(2) bonds are elongated and the respective C(1)-C(2)
distance is shortened compared to free dpp-BIAN (3:
(C(1)-N(1) 1.3365(15), C(2)-N(2) 1.3291(15), C(1)-C(2)
˚
1.4408(16) A); 4: (C(1)-N(1) 1.319(4), C(2)-N(2) 1.338(4),
˚
C(1)-C(2) 1.437(4) A). According to the symmetry of the
LUMO of dpp-BIAN, these structural changes correspond
with the population of this orbital by an electron.
[(dpp-BIAN)Zn(μ-H)]2 (4) has been prepared by reaction
of [(dpp-BIAN)Zn(μ-I)]2 (2) with 2 equiv of potassium
hydride in THF and was isolated as deep red crystals by
crystallization from toluene (Scheme 4). The IR spectrum
of complex 4 reveals the Zn-H stretching vibrations at
In 3 as well as in 4 the planes of the two acenaphthenedii-
mine units run parallel to each other and orthogonal to
the plane of the respective four-membered metalacycle
formed by the atoms Zn(1) and Zn(1a) and the bridging
carbon atoms (3) or bridging hydrogen atoms (4). In 3 the
distances of the zinc atoms to the bridging carbon atoms are
1534 cm-1
.
The ESR spectra of the paramagnetic compounds 3 and 4
(Figures 1a and 1b), recorded in toluene at 150 K, prove
the biradical character of both complexes. In both cases,
one electron is localized on each of the two diimine ligands.
The additional hyperfine structure was observed for D^
(17) Fedushkin, I. L.; Chudakova, V. A.; Fukin, G. K.; Dechert, S.;
Hummert, M.; Schumann, H. Russ. Chem. Bull. Int. Ed. 2004, 53, 2744.

3866 Organometallics, Vol. 28, No. 13, 2009
Fedushkin et al.
Figure 2. Molecular structure of 3. Thermal ellipsoids are drawn at 40% probability. The hydrogen atoms are omitted. Selected bond
˚
lengths (A) and angles (deg): Zn(1)-N(1) 2.0063(10), Zn(1)-N(2) 1.9996(10), Zn(1)-C(37) 1.9840(12), Zn(1)-C(37a) 2.2569(12),
Zn(1) Zn(2) 2.7816(3), C(1)-N(1) 1.3365(15), C(2)-N(2) 1.3291(15), C(1)-C(2) 1.4408(16), C(37)-C(38) 1.2099(17); N(1)-
3 3 3
Zn(1)-N(2) 86.56(4), C(37)-Zn(1)-C(37a) 98.30(4), N(1)-Zn(1)-C(37) 125.09(4), N(1)-Zn(1)-C(37a) 114.93(4), N(2)-Zn(1)-
C(37) 120.73(4), Zn(1)-C(37)-Zn(1a) 81.70(4), Zn(1)-C(37)-C(38) 170.08(11), Zn(1)-C(37a)-C(38a) 108.22(9).
Figure 3. Molecular structure of 4. Thermal ellipsoids are drawn at 40% probability. The hydrogen atoms except H(1) and H(1a)
˚
are omitted. Selected bond lengths (A) and angles (deg): Zn(1)-N(1) 1.994(2), Zn(1)-N(2) 2.012(2), Zn(1)-H(1a) 1.67(3), Zn(1)-H(1)
1.88(3), Zn(1) Zn(2) 2.4785(6), C(1)-N(1) 1.319(4), C(2)-N(2) 1.338(4), C(1)-C(2) 1.437(4); N(1)-Zn(1)-N(2) 85.67(9), H(1)-
3 3 3
Zn(1)-H(1a) 91.7(13), N(1)-Zn(1)-H(1) 115.1(8), N(1)-Zn(1)-H(1a) 121.0(10), N(2)-Zn(1)-H(1a) 132.3(9).
quite different (Zn(1)-C(37) 1.9840(12), Zn(1)-C(37a)
(108.22(9)ꢀ) correspond with a nearly linear and a nearly
right-angled Zn-CtCPh arrangement. The comparison of
the bonding situation in 3 with that in [{(TMEDA)Na-
(CtCPh)2Zn(tBu)}2],19 also a complex in which the zinc
atoms are bridged by CtCPh ligands (Zn-C(tC) 2.118(5)
˚
2.2569(12) A). The long Zn(1)-C(37a) bond as well as the
˚
elongation of the C(37a)-C(38a) bond (1.2099(17) A) com-
pared to the length of the CtC bond in free phenylacetylene
(1.188(2) A)18 may be explained by π-electron donation from
˚
˚
the ethynyl bond into vacant zinc orbitals. The angles Zn-
C(37)-C(38) (170.08(11)ꢀ) and Zn(1)-C(37a)-C(38a)
and 2.292(5) A; Zn-CtC 158.0(5)ꢀ and 121.4(4)ꢀ), shows
(19) Clegg, W.; Garcia-Alvarez, J.; Garcia-Alvarez, P.; Graham, D.
V.; Harrington, R. W.; Hevia, E.; Kennedy, A. R.; Mulvey, R. E.; Russo,
L. Organometallics 2008, 27, 2654.
(18) Weiss, H.-C.; Blaser, D.; Boese, R.; Doughan, B. M.; Haley, M.
M. Chem. Commun. 1997, 1703.

Article
Organometallics, Vol. 28, No. 13, 2009 3867
donation of the s lone pair of the hydrogen anion to the
vacant Zn level (97.6% s, 1.8% p, 0.2% d). The natural
charge of Zn is 1.44 e, thus being 0.60 e more positive than
in 1.5 Each bridging hydrogen atom bears a natural charge
of -0.63 e, compensating the decrease in the metal electron
density and providing a more ionic character of the bonding
between the (dpp-BIAN)ZnH monomers in 4 than between
the (dpp-BIAN)Zn monomers in 1.
Experimental Section
General Remarks. Compounds 3, 4, and 5 are sensitive to air
and moisture. Therefore all manipulations concerning their
preparation and identification were carried out under vacuum
using Schlenk techniques. The solvents THF, diethyl ether,
benzene, and toluene were dried by distillation from sodium/
benzophenon. THF-d8 (Aldrich) used for the NMR measure-
ments was dried with sodium/benzophenone at ambient tem-
perature just prior to use and was condensed under vacuum into
the NMR tube already containing the sample. The IR spectra
were recorded on a FSM-1201 spectrometer; the 1H NMR
spectra, on a Bruker DPX-200 NMR spectrometer. The ESR
spectra were obtained using a Bruker EMX instrument
equipped with an ER 041X microwave bridge.
Figure 4. HOMO, HOMO-1, and HOMO-11 R orbitals of 4
from DFT calculation.
that the coordination of the ethynyl ligands is less sym-
metric in 3 than in [{(TMEDA)Na(CtCPh)2Zn(tBu)}2]. In
[{(TMEDA)Li(CtCPh)2Zn(tBu)}2(TMEDA)],19 in which
two phenylethynyl groups bridge a zinc and a lithium atom,
the two Zn-C(tCPh) bonds show nearly the same length
˚
(2.0495(18) and 2.0738(18) A), whereas the bond angles Zn-
CtC(Ph) correspond with those in 3 (Zn-CtC 173.64(15)ꢀ
and 105.37(16)ꢀ).
Like the molecules of 3, the molecules of 4 show different
Synthesis of [(dpp-BIAN)Zn(μ-CtCPh)]2 (3). Method A. To a
solution of 1 (0.54 g, 0.48 mmol) in THF (30 mL) was added
phenylacetylene (0.10 g, 0.960 mmol). During 48 h of reflux the
color of the reaction mixture changed from gold-red to cherry-
red. The solid that remained after evaporation of the solvent
under vacuum was crystallized from benzene, giving red crystals
of 3. Yield: 0.19 g (27%). Mp > 257 ꢀC (dec). Anal. Found (%):
C 80.31, H 7.20. Calcd for C100H102N4Zn2 (1490.60 g/mol) (%):
C 80.58, H 6.90. IR (Nujol): 3058 w, 3031 w, 2089 m, 1808 w,
1596 w, 1534 s, 1361 m, 1319 s, 1254 m, 1184 m, 1157 w, 1146 w,
1107 w, 1080 w, 1057 w, 1038 w, 1011 w, 961 w, 946 w, 934 w,
865 m, 819 m, 803 m, 784 m, 761 s, 592 w, 534 m, 453 m,
411 s cm-1. Method B. To a solution of compound 5 (0.67 g,
1 mmol) in THF (40 mL) was added benzophenone (0.09 g,
0.5 mmol). In the course of 20 h reflux, the mixture changed
color from deep blue to cherry-red. Then the solvent was
evaporated under vacuum. Crystallization of the residual solid
from benzene gave red crystals of 3. Yield: 0.25 g (34%).
Synthesis of [(dpp-BIAN)Zn(μ-H)]2 (4). To a solution of 2
(prepared from 0.5 g (1 mmol) of dpp-BIAN,5 0.13 g (0.5 mmol)
of iodine, and an excess of the granulated zinc in THF (30 mL))
was added potassium hydride (0.04 g, 1 mmol). In the course of
18 h stirring of the mixture at room temperature its color
changed from cherry-red to red-brown. After evaporation of
the solvent under vacuum the residue was dissolved in toluene
(30 mL) and filtered off from precipitated KI. Reduction in the
volume of the solution and cooling caused precipitation of 0.44 g
(67%) of 4 as red-brown crystals. Mp > 263 ꢀC (dec). Anal.
Found (%): C 78.08, H 7.81. Calcd for C86H98N4Zn2 (1318.42 g/
mol): C 78.35, H 7.49. IR (Nujol): 1534 s, 1318 m, 1257 m,
1184 m, 1154 w, 1103 w, 1080 m, 1057 m, 1034 w, 934 m, 864 w,
distances between the zinc atoms and the bridging ligands
˚
(Zn(1)-H(1) 1.88(3) and Zn(1)-H(1a) 1.67(3) A). In the
other two hydrogen-bridged binuclear zinc complexes
known so far, Ar0Zn(μ-H)2ZnAr0 (Ar0 = C6H3-2,6-(C6H3-
4
˚
2,6-iPr2)2); Zn-H (1.67(2) and 1.79(3) A) and [{HC(CMe-
NAr)2}Zn(μ-H)]2 (Ar=2,6-Me2C6H3);20 Zn-H (1.766 A),
˚
the difference in the length of the Zn-H bonds is consider-
ably smaller or even zero. The Zn-H bonds in 4 are
also remarkably longer than the terminal Zn-H bonds in
21
˚
[Me2N(CH2)2N(Me)ZnH]2 (1.62 A) or [(Me3PN)ZnH]4
(1.50 A).22 Due to the small ionic radius of the hydride ion,
˚
˚
the Zn Zn separation in 4 (2.4785(6) A) is smaller than in 3
3 3 3
˚
(2.7816(3) A). However, both distances exceed the range of
6
˚
direct zinc-zinc bonds (2.29-2.40 A).
The electronic structure of 4 was examined by DFT23
calculations at the B3LYP/6-31G* level using the molecule
with unsubstituted phenyl fragments as a model system.
Recently, we used such calculations to study the Zn-Zn
bonding in 1.5 The triplet ground-state configuration of 4 is
11.0 kcal mol-1 more stable than the lowest singlet state,
which agrees well with the ESR data obtained for 4. The key
MOs of 4 are depicted in Figure 4. Like in 1, the two highest
semi-occupied MOs of the triplet system of 4 are localized on
the dpp-BIAN ligands, but in contrast to 1 (HOMO and
HOMO-1; -3.95 eV), in 4 these MOs are not degenerate
(HOMO, -3.89 and HOMO-1, -4.08 eV). The R HOMO
and HOMO-1 in 4 are mainly localized on the atoms of the
diimine fragments and partially on the bridging hydrogen
atoms. The degenerate R HOMO-11 and HOMO-12
(-6.75 eV) are responsible for the Zn-H-Zn bonding.
According to the natural bond orbital (NBO) analysis, the
covalent contribution to the Zn-H bonding arises from the
819 m, 799 c, 757 s, 692 m, 668 w, 634 m, 542 m cm-1
.
[dpp-BIAN(H)]Zn(CtCPh) (5). To a solution of Na2(dpp-
BIAN) (freshly prepared from 0.046 g (1 mmol) of Na and 0.5 g
(1 mmol) of dpp-BIAN in Et2O (30 mL)) was added phenyla-
cetylene (0.102 g, 1 mmol). The color of the reaction mixture
changed instantly from deep green to deep blue. To this mixture
was added a solution of ZnI2 (prepared prior to use from excess
zinc metal and iodine (0.254 g, 1 mmol) in Et2O (20 mL)), and
the NaI formed was filtered off. In the course of 1 day, 5 (0.73 g,
86%) separates from the mother liquor as deep blue crystals.
Mp>275 ꢀC (dec). Anal. Found (%): C 75.92, H 7.88. Calcd for
C54H71N2ZnO2 (845.55 g/mol): C 76.71, H 8.46. IR (Nujol):
3258 w, 3054 w, 2096 m, 1931 w, 1804 w, 1673 w, 1589 m, 1519 s,
1362 m, 1319 m, 1258 s, 1185 m, 1108 m, 1058 m, 1039 w, 1008 w,
(20) Hao, H.; Cui, C.; Roesky, H. W.; Bai, G.; Schmidt, H.-G.;
Noltemeyer, M. Chem. Commun. 2001, 1118.
(21) Bell, N. A.; Moseley, P. T.; Shearer, H. M. M.; Spencer, C. B.
Chem. Commun. 1980, 359.
(22) Krieger, M.; Neumueller, B.; Dehnicke, K. Z. Anorg. Allg.
Chem. 1998, 624, 1563.
(23) The geometry optimization, single-point calculation, and NBO
analysis were performed using the Gaussian 03 package (see Supporting
Information).

3868 Organometallics, Vol. 28, No. 13, 2009
Fedushkin et al.
935 w, 916s, 870w,850 w, 820 m, 800 m, 785 w, 758 s, 693 s, 665w,
SADABS24 was used to perform area-detector scaling
and absorption corrections. The structures were solved
by direct methods using SHELXS-9725 and refined by
full-matrix least-squares techniques against F2o using
SHELXL-97.26 All non-hydrogen atoms were refined aniso-
tropically. The hydrogen atoms were placed in calculated
positions and assigned to an isotropic displacement para-
627 w, 596 w, 546 s, 535 s, 493 w, 454 m, 408 s cm-1 1 H NMR
.
(THF-d8): δ 7.35 (d, 1 H, Ar, J=7.8 Hz), 7.29-7.10 (m, 4 H, Ar),
6.97-6.88 (m, 2 H, Ar), 6.85-6.73 (m, 3 H, Ar), 6.45 (s, 1 H,
NH), 6.12 (d, 1 H, Ar J=7.0 Hz), 5.81 (d, 1 H, Ar, J=6.0 Hz),
3.96 (br sept, 2 H, CH), 3.72 (br sept, 2 H, CH), 1.44 (d, 6 H,
CH3(iPr), J=6.5Hz),1.32 (d, 6H, CH3(iPr), J=6.5 Hz), 1.06(brs,
6 H, CH3(iPr)), 0.96 (d, 6 H, CH3(iPr), J=6.8 Hz).
2
˚
meter of 0.08 A .
X-ray Crystal Structure Determination of Compounds 3 and 4.
The crystal data of 3 were collected at 100 K on a Bruker
SMART APEX diffractometer; those of 4, at 150 K on an
Oxford Diffraction Xcalibur S Sapphire diffractometer using
Acknowledgment. This work was supported by the
Russian Foundation for Basic Research (Grant No.
07-03-00545), the Alexander von Humboldt Foundation
(Partnership Project TU Berlin-IOMC RAS), and the
Fonds der Chemischen Industrie.
˚
graphite-monochromated Mo KR (λ=0.71073 A) radiation.
(24) Sheldrick, G. M. SADABS, Empirical Absorption Correction
€
€
€
Program; Universitat Gottingen: Gottingen, Germany, 1996.
(25) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure
Supporting Information Available: Full details of the X-ray
structural analyses of compounds 3 and 4 and full reference for
the Gaussian 03 program are available free of charge via the
Internet at http://pubs.acs.org.
€
€
€
Solution; Universitat Gottingen: Gottingen, Germany, 1990.
(26) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
€
€
€
Refinement; Universitat Gottingen: Gottingen, Germany, 1997.