New insight into the three-coordinate divalent germanium compounds L2Ge∑ (L2 = PhNC(Me)CHC(Me)Nph, ∑ = Cl, I, Me, OMe). Structural, photoelectron spectroscopic, and theoretical analysis

Article abstract of DOI:10.1021/om030154y

An experimental and theoretical study of the heteroleptic divalent germanium compounds containing the bidentate coordinating monoanionic β-diketiminate ligand L²Ge∑ (L² = PhNC-(Me)CHC(Me)NPh; ∑ = Cl (1), I (2), Me (3), OMe (4)) has been performed in this contribution. The new stable germanium(II) compounds 3 and 4 have been synthesized by reaction of 1 with RLi (R = Me, OMe) and fully characterized. The crystal structures of 1-3 and their electronic structures have been determined by X-ray diffraction and UV-photoelectron spectroscopy (UPS), respectively. DFT calculations on 1 and 3 were carried out at the B3LYP level of theory. Natural bond orbital analysis for the model molecules 1′ and 3′ (without phenyl) gives information on the Ge-∑ bonding. It turns out from the NMR, mass spectroscopy, and X-ray molecular geometry properties together with the ab initio calculations that the three-coordinated germanium(II) compound L²GeX is best described by a model structure corresponding to a divalent germanium species weakly coordinated with the halide group, L²Ge⁺...X^-. This view is confirmed by the particularly low energetic values of the X atom lone-pair ionizations.

Full text of DOI:10.1021/om030154y

Organometallics 2003, 22, 3143-3149
3143
New In sigh t in to th e Th r ee-Coor d in a te Diva len t
Ger m a n iu m Com p ou n d s L2GeΣ (L2 )
P h NC(Me)CHC(Me)NP h , Σ ) Cl, I, Me, OMe). Str u ctu r a l,
P h otoelectr on Sp ectr oscop ic, a n d Th eor etica l An a lysis
Isabelle Saur,† Karinne Miqueu,† Ghassoub Rima,† J acques Barrau,*,†
Virginie Lemierre,‡ Anna Chrostowska,‡ J ean-Marc Sotiropoulos,‡ and
Genevie`ve Pfister-Guillouzo*,‡
He´te´rochimie Fondamentale et Applique´e, UMR 5069, Universite´ Paul Sabatier,
118, route de Narbonne, F-31062 Toulouse Cedex 4, France, and Laboratoire de
Physico-Chimie Mole´culaire, UMR 5624, Universite´ de Pau et des Pays de l’Adour,
Av. de l’Universite´, BP 1155, F-64013 Pau Cedex, France
Received March 4, 2003
An experimental and theoretical study of the heteroleptic divalent germanium compounds
containing the bidentate coordinating monoanionic â-diketiminate ligand L2GeΣ (L2 ) PhNC-
(Me)CHC(Me)NPh; Σ ) Cl (1), I (2), Me (3), OMe (4)) has been performed in this contribution.
The new stable germanium(II) compounds 3 and 4 have been synthesized by reaction of 1
with RLi (R ) Me, OMe) and fully characterized. The crystal structures of 1-3 and their
electronic structures have been determined by X-ray diffraction and UV-photoelectron
spectroscopy (UPS), respectively. DFT calculations on 1 and 3 were carried out at the B3LYP
level of theory. Natural bond orbital analysis for the model molecules 1′ and 3′ (without
phenyl) gives information on the Ge-Σ bonding. It turns out from the NMR, mass
spectroscopy, and X-ray molecular geometry properties together with the ab initio calculations
that the three-coordinated germanium(II) compound L2GeX is best described by a model
structure corresponding to a divalent germanium species weakly coordinated with the halide
group, L2Ge+‚‚‚X-. This view is confirmed by the particularly low energetic values of the X
atom lone-pair ionizations.
In tr od u ction
of three-coordinate divalent germanium L2GeX deriva-
tives (X ) Cl (1), I (2)) with the â-diketiminato L2
)
This work is part of our systematic investigation of
the heavier group 14 element analogues of carbenes
>M(II) (M ) Ge, Sn, Pb). After our previous extensive
research on thermally stable or transient germylenes,1
we initiated, a few years ago, the synthesis and char-
acterization of divalent compounds of germanium, tin,
and lead, supported by amine-substituted phenolate2a-c
and salen2d-f ligands; we recently turned to the â-di-
ketiminato ligand framework as a promising template
for stabilizing divalent M14 compounds. The chemistry
of this family of ligand is now well-developed.3 In our
initial publication,4a we described the preparation,
characterization, and various aspects of the chemistry
PhNC(Me)CHC(Me)NPh ligand.4 Here, we present syn-
theses and characterizations of the new compounds L2-
GeMe (3) and L2GeOMe (4) and, to investigate the
peculiar role that this ligand and the Σ substituents play
in these compounds, we analyze (i) the solid-state
structures of 1-3 and (ii) the electronic structure of
these compounds by density functional theory (DFT) (for
1 and 3) and by UV photoelectron spectroscopy (PES)
(for 1-3). While this work was in progress, the prepara-
tion and the structures of a few other germylated
compounds with a diketiminato ligand bearing a steri-
cally demanding substituent at the nitrogen atoms were
reported.5
* To whom correspondence should be addressed. E-mail: J .B.,
barrau@chimie.ups-tlse.fr; G.P.-G., genevieve.pfister@univ-pau.fr.
† Universite´ Paul Sabatier.
(4) (a) Akkari, A.; Byrne, J . J .; Saur, I.; Rima, G.; Gornitzka, H.;
Barrau, J . J . Organomet. Chem. 2001, 622, 190. (b) Chrostowska, A.;
Lemierre, V.; Pigot, T.; Pfister-Guillouzo, G. Saur, I.; Miqueu, K.; Rima,
G.; Barrau, J . Main Group Met. Chem. 2002, 25, 469. (c) Saur, I.; Rima,
G.; Gornitzka, H.; Miqueu, K.; Barrau, J . Organometallics 2003, 22,
1106. (d) Saur, I.; Rima, G.; Miqueu, K.; Gornitzka, H.; Barrau, J . J .
Organomet. Chem. 2003, 672, 77.
(5) (a) Ayers, A. E.; Klapo¨tke, T. M.; Dias, H. V. R. Inorg. Chem.
2001, 40, 1000. (b) Ding, Y.; Roesky, H. W.; Noltemeyer, M.; Schmidt,
H. G.; Power, P. P. Organometallics 2001, 20, 1190. (c) Ding, Y.; Hao,
H.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H. G. Organometallics
2001, 20, 4806. (d) Ding, Y.; Ma, Q.; Roesky, H. W.; Herbst-Irmer, R.;
Uson, I.; Noltemeyer, M.; Schmidt, H.-G. Organometallics 2002, 21,
5216. (e) Ding, Y.; Ma, Q.; Uso¨n, I.; Roesky, H. W.; Noltemeyer, M.;
Schmidt, H. G. J . Am. Chem. Soc. 2002, 124, 8542.
‡ Universite´ de Pau et des Pays de l’Adour.
(1) Barrau, J .; Rima, G. Coord. Chem. Rev 1998, 593, 178 and
references therein.
(2) (a) Barrau, J .; Rima, G.; El Amraoui, T. Organometallics 1998,
17, 607. (b) Barrau, J .; Rima, G.; El Amraoui, T. J . Organomet. Chem.
1998, 570, 163. (c) Barrau, J .; Rima, G.; El. Amraoui, T. J . Organomet.
Chem. 1998, 561, 167. (d) Agustin, D.; Rima, G.; Gornitzka, H.; Barrau,
J . J . Organomet. Chem. 1999, 592, 1. (e) Agustin, D.; Rima, G.;
Gornitzka, H.; Barrau, J . Main Group Met. Chem. 1997, 20, 791. (f)
Agustin, D.; Rima, G.; Gornitzka, H.; Barrau, Eur. J . Inorg. Chem.
2000, 693.
(3) Bourget-Merle, L.; Lappert, M. F.; Severn, J . R. Chem. Rev. 2002,
102, 3031 and references quoted therein.
10.1021/om030154y CCC: $25.00 © 2003 American Chemical Society
Publication on Web 06/27/2003

3144 Organometallics, Vol. 22, No. 15, 2003
Saur et al.
Sch em e 1
Ta ble 1. Selected 1H a n d 13C{1H} NMR (C6D6) Da ta
for 1-4
L2Ha
1a
2a
3
4
F igu r e 1. Solid-state structure of L2Ge(Cl) (1) (ellipsoids
are drawn at the 50% probability level). Hydrogen atoms
are omitted for clarity. Selected bond lengths (Å) and bond
angles (deg): Ge-N(1) ) 1.955(2), Ge-N(2) ) 1.965(1),
Ge-Cl ) 2.340(6), N(2)-C(9) ) 1.337(2), N(1)-C(7) )
1.338(2), C(9)-C(8) ) 1.390(2), C(8)-C(7) ) 1.391(2); N(1)-
Ge-N(2) ) 90.28(6), N(1)-Ge-Cl ) 93.55(5), N(2)-Ge-
Cl ) 94.95(4).
1H NMR (δ, ppm)
CH
Me
4.77
1.80
5.07 (5.39)b
1.61 (1.96)b
5.23 (5.64)b
1.56 (2.05)b
4.78
1.63
4.84
1.69
13C NMR (δ, ppm)
103.9
23.49
CH
Me
98.14
20.77
102.1
23.75
98.49
20.84
101.5
23.12
a
b
Reference 4a. δ in CDCl3.
peaks of compounds 1, 3, and 4 are detected with
intensities of 45, 9, and 13% of the [L2Ge]+ base peaks,
respectively, indicating the relative stabilities of these
molecular ions in the gas phase. The low degree of ion
pairing in 2 [L2Ge]+‚‚‚I- is revealed in the gas phase
by the absence of the molecular ion M•+ peak in the
mass spectrum (EI), the larger and more prominent
peak corresponding in this case to [L2Ge]+. It is note-
worthy that this cationic L2Ge+ species4a and the
comparable cationic aminotroponiminate [(iPr2)ATI]-
Ge+ 6 have been isolated, which confirms the high
stability of such cationic derivatives of germanium(II)
with supporting polydentate ligands.
The structures of compounds 1-3 were determined
by single-crystal X-ray diffraction. Crystals of 1 and 2
(yellow) and 3 (red) suitable for single-crystral analysis
were obtained from a toluene solution at -30 °C within
3 days. The solid-state structures are shown in Figures
1-3. Crystallographic data and processing parameters
are given in Table 2. The X-ray single-crystal figures of
1-3 display the monomeric structures of all compounds.
The structure of 1 was briefly reported in a preliminary
account,4b and the structural features of the iodo (2) and
methyl (3) congeners are quite similar. In all these
divalent species, the germanium center is at the apex
of a distorted trigonal pyramid. Perusal of the germa-
nium-ligand atom distances suggests that the ligand
is essentially symmetrically bound to the germanium
in 1-3. The five ligand atoms are almost coplanar, the
planarity being confirmed by the fact that the sums of
the internal angles for the six-membered L2Ge rings are
713° (1), 717° (2), and 708° (3), respectively. The side
views of the three compounds (Figure 4) show that the
iodo germylene 2 has the most planar C3N2 ring (x )
0.04 Å; y ) 0.35 Å), whereas the methylgermylene 3 has
the greatest deviation from planarity (x ) 0.15 Å; y )
0.62 Å). Due to their steric hindrance, the two phenyl
rings are found almost orthogonal to the C3N2 plane in
1-3. In all these compounds, the average Ge-N bonds
(1.955-2.022 Å) are between N-Ge donor-acceptor
bonds (2.050-2.110 Å)5a,7 and covalent N-GeII bonds
(1.870-1.890 Å).5a,8 The Ge-N bond lengths of L2GeMe
(2.010(4), 2.022(4) Å) are longer than those in L2GeX
Resu lts a n d Discu ssion
1. Syn th esis of Com p ou n d s 3 a n d 4 a n d Str u c-
tu r es of 1-3. Compounds 3 and 4 were isolated as
orange-red crystalline solids in high yields (75-90%)
from the metathesis reactions of 1 with 1 equiv of MeLi
or MeOLi in toluene (Scheme 1) and were fully charac-
terized by elemental analysis, EI-MS, and multinuclear
NMR spectroscopy.
The divalent germanium species 3 and 4 are soluble
in aromatic and polar solvents and are stable under an
inert atmosphere for a long time, while the halide
analogues 1 and 2 show a lower solubility (specially 2)
in aromatic solvents, perhaps as a result of a more ionic
structure.
The 1H and 13C NMR spectra of 3 and 4 were
consistent with their formula. Both 1H and 13C NMR
data corresponding to the L2 unit are very similar for
1-4 (Table 1). As in the case of the free ligand, the
equivalence of methyl and phenyl groups indicates the
presence of Cs symmetry in solution for 3 and 4. 1H
NMR resonances of the methine and methyl ring of 1-4
(Table 1) show a downfield and an upfield shift, respec-
tively, relative to those of L2H. 13C NMR chemical shifts
are also different, the methine and methyl carbons being
downfield for 1-4 compared to those corresponding to
the L2H free ligand (Table 1). It is noteworthy that the
1
resonances of the methine proton and carbon in H and
13C NMR of L2GeMe (δ(1H) 4.78 ppm; δ(13C) 98.49 ppm)
show an upfield shift compared to the corresponding
resonances of L2GeOMe (δ(1H) 4.84 ppm; δ(13C) 101.5
ppm) and a much more upfield shift compared to those
of L2GeCl (δ(1H) 5.07 ppm; δ(13C) 102.1 ppm). For
L2GeI, the chemical shifts are downfield (δ(1H) 5.23
ppm; δ(13C) 103.9 ppm) compared to those in 1, 3, and
4; this may be the result of an increased positive charge
at the germanium (or on the ligand backbone) due to a
weakly coordinated iodide anion. The chemical shifts for
1 and 2 vary strongly with the solvent; polar solvents
lead to strong deshielding, probably as a result of a
solvent-dependent polarization of the Ge‚‚‚X contact
(Table 1).
The mass spectra of 1-4 show in all cases that the
base peak corresponds to [L2Ge]+. The molecular ion M•+
(6) Dias, R. H. V.; Wang, Z. J . Am. Chem. Soc. 1997, 117, 44650.

Three-Coordinate Divalent Germanium Compounds
Organometallics, Vol. 22, No. 15, 2003 3145
Ta ble 2. Cr ysta l Da ta a n d Str u ctu r e Refin em en t Deta ils for 1,a 2, a n d 3
1
2
3
empirical formula
fw
C
17H17ClGeN2
C17H17GeIN2
448.82
C18H20GeN2
336.95
357.37
cryst syst
space group
a (Å)
b (Å)
orthorhombic
P212121
8.8117(5)
13.5830(8)
13.8910(8)
-
1662.60(17)
4
1.428
orthorhombic
P212121
7.283(1)
8.805(1)
26.107(3)
-
1674.2(3)
4
1.781
triclinic
P1h
7.371(2)
9.173(3)
13.049(4)
82.716(6)
827.5(4)
2
c (Å)
â (deg)
V (Å3)
Z
calcd density (Mg/m3)
1.352
1.846
0.1 × 0.2 × 0.6
1.66-24.11
3950
abs coeff (mm-1
cryst size (mm)
)
1.998
3.669
0.3 × 0.4 × 0.5
2.10-29.45
11 373
0.1 × 0.2 × 0.5
1.56-26.37
9788
θ range for data (deg)
no. of rflns
no. of indep rflns
abs cor
4266 (Rint ) 0.0198)
semiempirical
0.6641
192
1.048
0.0219
0.0508
0.352, -0.184
3409 (Rint ) 0.0514)
semiempirical
0.5489
192
0.996
0.0327
0.0763
0.817, -0.778
2593 (Rint ) 0.0455)
semiempirical
0.6643
193
1.005
0.0521
0.1412
1.227, -0.872
min/max transmission
no. of params
goodness of fit on F2
R1b (I > 2σ(I))
wR2c (all data)
largest diff peak, hole (e Å-3
)
Reference 4b. R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2
.
a
b
2
F igu r e 2. Solid-state structure of L2Ge(I) (2) (ellipsoids
are drawn at the 50% probability level). Hydrogen atoms
are omitted for clarity. Selected bond lengths (Å) and bond
angles (deg): Ge-N(1) ) 1.971(4), Ge-N(2) ) 1.959(4),
Ge-I ) 2.778(6), N(1)-C(1) ) 1.345(6), N(2)-C(3) )
1.351(6), C(1)-C(2) ) 1.391(7), C(2)-C(3) ) 1.397(7); N(1)-
Ge-N(2) ) 91.83(17), N(1)-Ge-I ) 98.37(12), N(2)-Ge-I
) 92.98(12).
F igu r e 3. Solid-state structure of L2Ge(Me) (3) (ellipsoids
are drawn at the 50% probability level). Hydrogen atoms
are omitted for clarity. Selected bond lengths (Å) and bond
angles (deg): Ge-N(1) ) 2.022(4), Ge-N(2) ) 2.010(4),
Ge-C(18) ) 2.014(6), N(1)-C(1) ) 1.332(6), N(2)-C(3) )
1.350(6), C(1)-C(2) ) 1.411(6), C(2)-C(3) ) 1.395(7); N(1)-
Ge-N(2) ) 88.81(15), N(1)-Ge-C(18) ) 94.1(2), N(2)-Ge-
C(18) ) 96.08(2).
(X ) I, 1.959(4), 1.971(4) Å; X ) Cl, 1.955(2), 1.965(1)
Å); this is probably due to the different inductive effects
of the various substituents. Interestingly for L2GeMe,
although the Ge-N(1) and the Ge-N(2) distances are
identical, the N(1)-C(1) and C(2)-C(3) distances are
slightly shorter than N(2)-C(3) and C(1)-C(2), respec-
tively, indicating an alternating, more localized distri-
bution of electrons in the ligand than for L2GeCl and
L2GeI. The N(1)-Ge-N(2) bond angles for 1-3 are close
to 90°; this angle increases from L2GeMe (88.8°) to L2-
GeCl (90.3°) and L2GeI (91.8°), and these variations are
the result of both electronic and steric effects of the Σ
substituents. For the previously described L′2GeCl
compounds (L′2 ) ArNC(Me)CHC(Me)NAr; Ar ) 2,6-i-
Pr2C6H3)5b a lengthening of the Ge-N bonds (1.99, 1.99
F igu r e 4. Side view of 1-3: R ) Cl (1), I (2), Me (3).
Å) is observed compared to those in L2GeCl; these bond
elongations can be attributed to the increased steric
demand of the bulky aryl groups of the â-diketiminato
ligand in these compounds. The Ge-C distance in 3
(2.014(6) Å) is in the normal range for divalent com-
pounds (Ge-C ) 1.989-2.067 Å),9a-c while the Ge-X
lengths in 1 and 2 (1, 2.340(6) Å; 2, 2.778(6) Å) are
(7) (a) Schmidt, H.; Keitemeyer, S.; Neumann, B.; Stammler, H. G.;
Schoeller, W. W.; J utzi, P. Organometallics 1998, 17, 2149. (b) Veith,
M.; Becker, S.; Huch, V. Angew. Chem., Int. Ed. Engl. 1989, 28, 1237.
(c) Veith, M.; Becker, S.; Huch, V. Angew. Chem., Int. Ed. Engl. 1990,
20, 216.
(8) (a) Chorley, R. W.; Hitchkock, P. B.; Lappert, M. F.; Leung, W.
P.; Power, P. P.; Olmstead, M. M. Inorg. Chim. Acta 1992, 198-200,
203. (b) Veith, M.; Hobein, P.; Ro¨sler, R. Z. Naturforsch. 1989, 1067.

3146 Organometallics, Vol. 22, No. 15, 2003
Saur et al.
Ta ble 3. Ca lcu la ted (B3LYP /6-311G(d ,p ))
Geom etr ica l P a r a m eter s (Dista n ces in Å a n d
An gles in d eg) for L2GeCl (1) a n d L2GeMe (2)
L2GeCl (1)a
L2GeMe (3)
Ge-N
2.03, 2.03
2.36
1.33, 1.33
1.40, 1.40
89.4
2.07, 2.07
2.04
1.33, 1.33
1.41, 1.41
89.0
Ge-Σ
N-C
C-C
N(1)-Ge-N(2)
N-Ge-Σ
94.9, 94.8
93.9, 93.8
a
Reference 4b.
normal for three-coordinated germanium(II) com-
pounds.5a,9d-f These last values are ∼10% longer than
the average of previously observed Ge-X distances in
various dicoordinated germanium(II) and german-
ium(IV) compounds (Ge-Cl ) 2.11-2.20 Å; Ge-I )
2.50-2.55 Å);9g-k this impressive margin reflects mainly
the change in coordination at the germanium and
probably also a halide bonded medium-strongly to the
germanium center: L2Ge+‚‚‚X-.
2. UV-P h otoelectr on Sp ectr oscop y Stu d ies w ith
Den sity F u n ction a l Th eor y Su p p or t. For a better
understanding of the electronic structure and effect of
the substituents Σ at the germanium of such com-
pounds, we were particularly interested in (i) experi-
mental UV-photoelectron spectroscopy of 1-3 and (ii)
in NBO population and total atomic charge analyses of
1 and 3. In a preliminay paper,4b we briefly described
the electronic (UV-photoelectron and DFT calculations)
and the molecular (X-ray crystallography) structures of
L2H and L2GeCl; consequently, the experimental and
theoretical studies are extended here to the iodo- and
methyl-substituted species 2 and 3, respectively.
Table 3 shows calculated geometrical parameters for
L2GeMe (3) and, for comparison, those of L2GeCl (1).
These calculated parameters agree well with the avail-
able X-ray experimental data (Figures 1 and 3). For 1
and 3 the calculations predict that the five ligand atoms
are quasi planar, the germanium and the C(H) atoms
being above the C3N2 plane (Figure 4) as denoted by
the X-ray structure; the electronic delocalization within
the ligand is also theoretically found. The two calculated
σGe-N bonds are found to be identical but slightly longer
(as the Ge-Σ bonds) than the experimental X-ray values
obtained for 1 and 3 (Table 3 and Figures 1 and 3).
The Becke3LYP method reproduces properly the
experimentally characterized molecular structures of
both 1 and 3; we used this theoretical description for
assignments of the experimental IP recorded by He I
and He II photoelectron spectroscopy for 1-3.
F igu r e 5. He I and He II photoelectron spectra (IP in
eV): (a) L2Ge(Cl) (1) and Molden25 visualization of the two
first molecular orbitals; (b) L2Ge(I) (2).
The He I and He II photoelectron spectra of L2GeI
(Table 4, Figure 5b) display three well-resolved bands
at 7.4, 7.9, and 8.2 eV, followed by one band at 8.9 eV
and a broader one centered at 9.25 eV with a shoulder
at 9.7 eV. Other less intense bands appear at higher
energies (10.3, 10.6 eV). The two first ionization poten-
tials at 7.4 and at 7.9 eV (Figure 5b) correspond, as for
the chlorine derivative (Table 4, Figure 5a), to the
molecular orbitals having a strong participation of the
germanium and iodine lone pairs in interaction with the
π(π3L) orbital of the ligand. This assignment is confirmed
by the decrease of the intensity of the IP using He II
Ta ble 4. Exp er im en ta l Ion iza tion P oten tia ls a n d KS En er gies (in eV) a n d th e Na tu r e of Molecu la r Or bita ls
for L2GeCl (1) a n d L2GeI (2)
IP
KS
L2GeCl (1)a calcdb
nature of MO
L2GeCl (1)a exptl
L2GeI (2) exptl
nature of MO
π3L - (nGe - nσ
-5.94
-6.38
-6.87
π3L - (nGe - nσ
)
7.5
8.4
8.7
7.4
7.9
8.2
8.9
9.25
9.7 sh
)
I
Cl
hemi
hemi
nGe + π3L - nCl
nGe + π3L - nI
peri
æ-b1
nI
nI
- æ-a2
hemi
-7.17; -7.18; -7.24
-7.34; -7.46
-8.57
æ+b1; æ-a2 - nClperi; æ+a2
9.25
9.7
10.15
10.8
11.05
æ-b1; æ+b1; æ+a2; æ-a2
hemi
nClperi; nCl
π2L
π2L
-9.02
σ+GeN - σGeCl
10.3
10.6
σ+Ge-N - σGe-I
GeN
-9.16
σ-
σ-
GeN
a
b
Reference 4b. ∆SCF )7.43 eV; see the Experimental Section.

Three-Coordinate Divalent Germanium Compounds
Organometallics, Vol. 22, No. 15, 2003 3147
Ta ble 5. Exp er im en ta l Ion iza tion P oten tia ls a n d
KS En er gies (in eV) a n d th e Na tu r e of Molecu la r
Or bita ls for L2GeMe (3)
L2GeMe (3) calcda KS
nature of MO
L2GeMe (3) exptl IP
-4.89
nGe - σCH - π3L
6.7
7.7
8.5
9.1
9.7
3
-5.97
π3L+ nGe
-6.67
æ-b1
-6.94; -7.11; -7.12
-8.16
æ+b1; æ-a2; æ+a2
σ+
- σGeCH
GeN
3
-8.23
-8.71
π2L
GeN
σ-
10.5
a
∆SCF) 6.48 eV; see the Experimental Section.
radiation. The significant decrease in the intensity of
the two bands corresponding to the higher energies 8.2
and 8.9 eV, on He II radiation, is also unambiguously
indicative of the participation of the iodine lone pair
orbitals. The band at 9.25 eV is associated with ejection
of electrons of the phenyl substituent (orthogonal sub-
stituent). The shoulder at 9.7 eV and the ionizations at
10.3 and 10.6 eV can be attributed to the π2L (πCN
antisymmetric combination), σ+
(with iodine partici-
GeN
pation), and σ-
orbitals ionizations, respectively.
GeN
Concerning the ionizations of the lone pairs on the
halogen atoms, it is noteworthy that lower energies are
needed for L2GeCl (9.7 eV (nCl)) and L2GeI (8.9, 8.2 eV-
F igu r e 6. He I photoelectron spectrum of L2Ge(Me) (3)
(IP in eV) and Molden25 visualization of the first two
molecular orbitals.
(nI)) (Table 4) than for the corresponding dihalogerma-
10,11
nium(II) compounds GeX2
(GeCl2, 12.69 (a1, σ+Cl),
12.58 (b2, π+Cl), 11.70 (a2, π-Cl), 11.44 (b1, σ-Cl), average
It is noteworthy that we were unable to record an
intense He II spectrum of 3.
12.10 eV; GeI2, 10.62 (a1, σ+ ), 10.62 (b2, π+ ), 9.83 (a2,
I
I
π- ), 9.50 (b1, σ- ), average 10.14 eV). This is indicative
I
I
Natural bond orbital12 analysis for the model (without
phenyl substituents) molecules 1′ and 3′ gives informa-
tion on the Ge-Σ bonding. It confirms that the contri-
bution (80%) of the chlorine is higher than that of the
CH3 moiety (72%) to form the Ge-Σ bonds. The ligand
backbone does not form a perfectly planar system;
accordingly, it is difficult to estimate the electron
density distribution in the π orbitals but the analysis
of the pπ natural bond orbital population denotes an
electron density loss of 0.2 and 0.1 e for 1′ and 3′,
respectively, indicating a donation to the germanium
atom.
of more highly charged halogen atoms in compounds 1
and 2 than in dihalides GeX2.
Replacement of a halogen atom by a methyl group
causes a decrease in IP values. Table 5 lists Kohn-Shan
energies and corresponding experimental values. The
spectrum of 3 (Figure 6) displays four resolved bands
followed by a broad signal. On the basis of calculations,
the two bands at low energies (6.7 and 7.7 eV) are
assigned to the ionizations of the germanium lone pair
in combination with the ligand π system (6.7 eV, nGe
-
σCH -π3L; 7.7 eV, π3L+ nGe). It is noteworthy that, in
3
contrast to that observed for the chlorine derivative 1,
the participation of the germanium lone pair (nGe) and
of the (π3L) ligand are prominent, in the associated
molecular orbitals, respectively. The bands at 8.5 and
9.1 eV are associated with the ionizations of the phenyl
groups. The broad massif at 9.7-10.5 eV corresponds
to three ionizations: two originating from the σGe-N
bonds and the other from the π2L system of the ligand.
Considering the total atomic charges (Table 6) for 1
and 3, it appears that the substituent at the germanium
is negatively charged, depending on the nucleophilicity
of Σ. The comparison with the chlorine charges found
for GeCl2 (-0.266) shows in the case of the compound 1
a more important chlorine atom charge (-0.474); these
results are in accord with the experimental IPs (vide
supra). Moreover, the total charges of the ligand are in
good agreement with the NMR data, in particular
considering the chemical shift of the methine proton
C(H); the C(H) atom, being highly involved in the π
homo orbital of the L2GeΣ species, is very sensitive to
the electron delocalization on the germanium atom
(particularly in 1 and 2).
(9) (a) Al-J uaid, S. S.; Avent, A. G.; Eaborn, C.; Hill, M. S.; Hitchcock,
P. B.; Patel, D. J .; Smith, J . D. Organometallics 2001, 20, 1223. (b)
J utzi, P.; Becker, A.; Stammler, H. G.; Neumann, B. Organometallics
1997, 10, 1647. (c) J utzi, P.; Keitemeter, S.; Neumann, B.; Stammler,
H. G. Organometallics 1999, 18, 4778. (d) J utzi, P.; Keitemeyer, S.;
Neumann, B.; Stammler, A.; Stammler, H. G. Organometallics 2001,
20, 42. (e) Inoguchi, Y.; Okui, S.; Mochida, K.; Itai, A. Bull. Chem. Soc.
J pn. 1985, 58, 974. (f) Stobart, S. R.; Churchill, M. R.; Hollander, F.
J .; Youngs, W. J . J . Chem. Soc., Chem. Commun. 1979, 911. (g) Moreno,
Y.; Nakamura, Y.; Iijima, T. J . Chem. Phys. 1960, 32, 643. (h) Drake,
J . E.; Hencher, J . L.; Shen, Q. Can. J . Chem. 1977, 55, 1104. (i) Walz,
L.; Thiery, D.; Peters, E. M.; Wendel, H.; Scho¨nher, E.; Wojnowski, M.
Z. Kristallogr. 1993, 208, 207. (j) Filipou, A. C.; Portius, P.; Philip-
popoulos, A. I. Organometallics 2002, 21, 653. (k) Pu, L.; Olmstead,
M. M.; Power, P. P.; Schiemenz, B. Organometallics 1998, 17, 5602.
(10) J onkers, G.; Van der Kerk, S. M.; De Lange, C. A. Chem. Phys.
1982, 70, 69.
Con clu sion
All these data suggest that a L2GeX (X ) halide)
compound is better described as a N2Ge divalent ger-
(12) (a) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988,
88, 899. (b) Foster, J . P.; Weinhold, F. J . Am. Chem. Soc. 1980, 102,
7211.
(11) J onkers, G.; Van der Kerk, S. M.; Mooyman, R.; De Lange, C.
A.; Snijders, J . G. Chem. Phys. Lett. 1983, 94, 585.

3148 Organometallics, Vol. 22, No. 15, 2003
Saur et al.
Ta ble 6. Ca lcu la ted (B3LYP /6-311G(d ,p )) Tota l
Atom ic Ch a r ges (Mu llik en ) for L2GeCl (1) a n d
L2GeMe (3)
was warmed to room temperature and stirred for 2 h. Filtra-
tion and storage of the remaining solution in a -30 °C freezer
for 3 days afforded orange-red crystals of 3 (0.19 g, 83%). 3:
mp 80-84 °C. 1H NMR (C6D6): δ 0.74 (s, 3H, CH3), 1.63 (s,
6H, 2CH3), 4.78 (s, 1H, CH), 6.88-7.10 (m, 10H, C6H5). 13C
NMR (C6D6): δ 11.88 (CH3), 20.84 (2CH3), 98.49 (CH), 125.81
(m aryl C), 126.87 (p aryl C), 128.46 (o aryl C), 147.00 (Cquat),
163.26 (C-N). MS: m/z 338 [M]•+. Anal. Calcd for C18H20N2-
Ge: C, 64.16; H, 5.98; N, 8.31. Found: C, 64.37; H, 5.90; N,
7.92.
Syn th esis of L2GeOMe (4). A solution of 1 (0.24 g, 0.66
mmol) in toluene (15 mL) was added dropwise to a stirred
suspension of MeOLi (0.25 g, 0.66 mmol) in toluene (15 mL)
at -78 °C. The reaction mixture was warmed to room tem-
perature and stirred for 2 h. The precipitate was filtered off,
and the solvent of the resulting solution was removed under
vacuum to yield 4 as an orange-red solid (0.2 g, 87%). 4: mp
total charge
total charge
atom
Σ ) Cl
Σ ) Me
atom
Σ ) Cl
Σ ) Me
Ge
N1
N2
C7
C(H)
C9
0.655
-0.615
-0.621
0.269
0.617
-0.607
-0.609
0.250
Σ
-0.474
0.196
0.197
0.120
0.120
0.090
-0.284
0.157
0.157
0.109
0.110
0.083
Ph(N1)
Ph(N2)
Me(C7)
Me(C9)
H(C8)
1
81-85 °C. H NMR (C6D6): δ 1.69 (s, 6H, 2CH3), 3.92 (s, 3H,
-0.203
0.268
-0.232
0.248
OCH3), 4.84 (s, 1H, CH), 6.84-7.13 (m, 10H, C6H5). 13C NMR
(C6D6): δ 23.12 (CH3), 52.75 (OCH3), 101.48 (CH), 125.81 (m
aryl C), 126.87 (p aryl C), 128.46 (o aryl C), 146.37 (Cquat),
163.47 (C-N). MS: m/z 354 [M]•+. Anal. Calcd for C18H20N2-
OGe: C, 61.25; H, 5.71; N, 7.94. Found: C, 61.64; H, 5.85; N,
7.80.
manium more or less coordinated with an halide group,
-
N2Ge+‚‚‚X-, than a XGe+‚‚‚N2 species, as postulated
in our preliminary report. Suggestion of such a qualita-
tive model for these three-coordinate germanium(II)
species is more particularly supported by the following
observations: (i) the downfield chemical shift of the C(H)
ring proton, which varies strongly with the nature of X
and presents a solvatochromic behavior, (ii) the long
Ge-X distances, (iii) the low ionization potentials of the
halogen lone pairs, which indicate particularly charged
atoms, and (iv) the presence of the molecular [L2Ge]+
ion in the gas phase, which proves its high stability. In
this model the anion/cation separation and thus even-
tual delocalization of the positive charge on the L2Ge
ring depends on the nature of X. Moreover, though the
π electrons of the L2Ge ring system appear to be mostly
delocalized on nitrogen and carbon atoms, it seems
possible to assume a weak π ligand f σ*Ge-X interaction
(negative hyperconjugation), permitting a ligand-to-
germanium transfer of π-electron density. A further
extension of this study to other group 14 elements,
â-diketiminate, and X ligands is now in progress in
order to specify the electronic organization in these
species.
UV-P h otoelectr on Sp ectr oscop y. Photoelectron spectra
were recorded on an Helectros 0018 spectrometer and moni-
tored by a microcomputer system supplemented by a D-A
converter. The spectra contain 2000 points and are accurate
to 0.1 eV. They were recorded with 21.21 eV He I and 40.81
eV He II irradiation as a photon source and calibrated on the
well-known helium autoionization at 4.98 eV and nitrogen
autoionizations at 15.59 and 16.98 eV. It is worth mentioning
that, on going from He I to He II ionization energies, the bands
arising from ejection of an electron from an orbital localized
on second or third row decrease in intensity. These relative
intensity changes are attributed to variations in the one- and
two-center contributions to the photoionization cross-sections
of the corresponding molecular orbitals.14
Com p u ta tion a l Meth od s. The calculations were per-
formed using the Gaussian 98 program package.15 The opti-
mization and vibrational analyses were carried out with
density functional theory (DFT) using the B3LYP16 functional
in conjunction with a 6-311G(d,p) basis set.
The influence of the basis17 set chosen on the KS energy
levels being important, we applied the 6-311G basis set for
calculations on 1 and 3, but we could not do the same for 2
because no 6-311G basis is available for iodine.
Exp er im en ta l Section
(13) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals; Pergamon Press: New York, 1985.
Gen er a l P r oced u r es. All manipulations were carried out
under an argon atmosphere with the use of standard Schlenk
and high-vacuum-line techniques. Solvents were distilled from
conventional drying agents and degassed twice prior to use.13
1H NMR spectra were recorded on a Bruker AC 80 spectrom-
eter operating at 80 MHz (chemical shifts are given in ppm
(δ) relative to Me4Si) and 13C spectra on a AC-200 MHz
spectrometer operating at 62.9 MHz; the multiplicity of the
13C NMR signals was determined by the APT technique. Mass
spectra were recorded on a Nermag R10-10H or a Hewlett-
Packard 5989 instrument operating in the electron impact
mode at 70 eV, and samples were contained in glass capillaries
under argon. IR spectra were obtained on a Perkin-Elmer 1600
FT-IR. Irradiations were carried out at 25 °C by using a low-
pressure mercury immersion lamp in a quartz tube. Melting
points were taken on a hot-plate microscope apparatus from
Leitz Biomed. Elemental analyses (C, H, N) were performed
at the Microanalysis Laboratory of the Ecole Nationale Su-
pe´rieure de Chimie de Toulouse.
(14) (a) Schweig, A.; Thiel, W. J . Electron Spectrosc. Relat. Phenom.
1974, 3, 27. (b) Schweig, A.; Thiel, W. Mol. Phys. 1974, 27, 265.
(15) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.,
J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; J ohnson, B. G.; Chen,
W.; Wong, M. W.; Andres, J . L.; Head-Gordon, M.; Replogle, E. S.;
Pople, J . A. Gaussian 98, revision A.7; Gaussian, Inc.: Pittsburgh, PA,
1998.
(16) (a) Parr, R. G.; Yang, W. Functional Theory of Atoms and
Molecules; Oxford University Press: New York, 1989. (b) Becke, A. D.
Phys. Rev. 1988, 38, 3098. (c) Becke, A. D. J . Chem. Phys. 1993, 98,
5648. (d) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. 1988, B37, 785.
(17) (a) J oante´guy, S.; Pfister-Guillouzo, G.; Chermette, H. J . Phys.
Chem. 1999, 103, 3505. (b) Frish, M. J .; Trucks, G. W.; Cheeseman, J .
R. Systematic Model Chemistries Based on Density Functional
Theory: Comparison with Traditional Models and with Experiment.
In Recent Development and Applications of Modern Density Functional
Theory, Theoretical and Computational Chemistry; Semminario, J . M.,
Ed.; Elsevier Science: Amsterdam, 1996; Vol. 4, pp 679-707.
Syn th esis of L2GeMe (3). A solution of MeLi (0.42 mL,
1.6 M in ether) was added to a stirred solution of 1 (0.24 g,
0.67 mmol) in toluene (25 mL) at -78 °C. The reaction mixture

Three-Coordinate Divalent Germanium Compounds
Organometallics, Vol. 22, No. 15, 2003 3149
Recent works18-21 have shown that ꢀiKS can be linked to
experimental vertical ionization potentials (IPv) by the uniform
data for 1-3 are presented in Table 2. All data were collected
at low temperatures on a Bruker-AXS CCD 1000 diffractome-
ter with Mo KR radiation (λ ) 0.710 73 Å). The structures were
solved by direct methods by means of SHELXS-9723 and
refined with all data on F2 by means of SHELXL-97.24 All non-
hydrogen atoms were refined anisotropically. The hydrogen
atoms of the molecules were geometrically idealized and
refined using a riding model. Full details of the crystal-
lographic analysis of 2 and 3 are given in the Supporting
Information.
exptl
shift x. The value of x is taken as x ) |-ꢀi(HOMO) - IPv
|.
This approach gives a good agreement with experimental
values and is justified by the fact that the first calculated
vertical ionization potential IPvcalcd (as the difference ET(cation)
- ET(neutral molecule)) lies very close to experimental values.
Stowasser and Hoffman22 have recently shown that the
localizations of KS orbitals are very similar to those obtained
after HF calculations. Thus, it is possible to determine the
nature of the first ionizations and to interpret the photoelec-
tron spectra unambiguously.
Ack n ow led gm en t. We thank the IDRIS (CNRS,
Orsay, France) for calculation facilities and P. Baylere
for technical assistance.
∆SCF is the first vertical ionization potential IP1vcalcd, which
is calculated as the difference ET(cation) - ET(neutral mol-
ecule).
X-r a y Cr ysta l Str u ctu r e Deter m in a tion of Com p ou n d s
1-3. Suitable yellow (1, 2) and red (3) crystals for X-ray
diffraction experiments were obtained at low temperature (-20
°C) by cooling concentrated toluene solutions of 1-3. Crystal
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tallographic data and structure refinement details, atomic
coordinates and displacement parameters, and bond lengths
and angles for the crystal structures of compound 2 and 3 and
calculation files (Z matrix, repulsion, and total energies: ZPE
correction) for 1 and 3. This material is available free of charge
via the Internet at http://pubs.acs.org.
(18) Arduengo, A. J .; Bock, H.; Chen, H.; Denk, M.; Dixon, D. A.;
Green, J . C.; Hermann, W. A.; J ones, N. L.; Wagner, M.; West, R. J .
Am. Chem. Soc. 1994, 116, 6641.
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Tetrahedron 1999, 55, 3767. (b) Muchall, H.; Werstiuk, N.; Choudury,
B.; Ma, J .; Warkentin, J .; Pezacki, J . Can. J . Chem. 1998, 76, 238. (c)
Muchall, H.; Werstiuk, N.; Choudury, B. Can. J . Chem. 1998, 76, 221.
(20) Muchall, H.; Rademacher, P. J . Mol. Struct. 1998, 471, 189.
(21) Miqueu, K.; Sotiropoulos, J .-M.; Pfister-Guillouzo, G.; Rana-
ivonjatovo, H.; Escudie´, J . J . Mol. Struct. 2001, 545, 139.
OM030154Y
(23) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(24) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1997.
(25) Schaftenaar, G.; Noordik, J . H. J . Comput. Aided Mol. Des.
2000, 14, 123.
(22) Stowasser, R.; Hoffmann, R. J . Am. Chem. Soc. 1999, 121, 3414.