Reactivity studies of a GeI?GeI compound with and without cleavage of the ge?ge bond

Article abstract of DOI:10.1021/ic100501e

This Communication describes two strikingly different reactivities of a digermylene [{PhC(NtBu)₂}₂Ge₂] (1) featuring a Ge^I?Ge^I single bond. In the reaction with azobenzene, 1 affords the oxidative addition product LGeN(Ph)N(Ph)GeL [2; L = PhC(NtBu) ₂], with simultaneous cleavage of the Ge?Ge bond, whereas treatment of 1 with Fe₂(CO)₉ yields the Lewis acid?base adduct LGe[Fe(CO)₄]Ge[(Fe(CO)₄]L (3). Both compounds were characterized by single-crystal X-ray diffraction, NMR spectroscopy, electrospray ionization mass spectrometry, and elemental analysis.

Full text of DOI:10.1021/ic100501e

5786 Inorg. Chem. 2010, 49, 5786–5788
DOI: 10.1021/ic100501e
Reactivity Studies of a GeI-GeI Compound with and without Cleavage
of the Ge-Ge Bond
Sakya S. Sen, Daniel Kratzert, Daniel Stern, Herbert W. Roesky,* and Dietmar Stalke
€
€
€
Institut fu€r Anorganische Chemie, Universitat Gottingen, Tammannstrasse 4, 37077 Gottingen, Germany
Received March 16, 2010
˚
This Communication describes two strikingly different reactivities of
a digermylene [{PhC(NtBu)2}2Ge2] (1) featuring a GeI-GeI single
bond. In the reaction with azobenzene, 1 affords the oxidative
addition product LGeN(Ph)N(Ph)GeL [2; L = PhC(NtBu)2], with
simultaneous cleavage of the Ge-Ge bond, whereas treatment
of 1 with Fe2(CO)9 yields the Lewis acid-base adduct LGe[Fe-
(CO)4]Ge[(Fe(CO)4]L (3). Both compounds were characterized
by single-crystal X-ray diffraction, NMR spectroscopy, electrospray
ionization mass spectrometry, and elemental analysis.
1. They are 2.63(8) and 2.57(5) A, respectively, and hence
much closer to the bond length found in a Ge-Ge single
5
˚
bond (2.61 A mean). The reactivity of digermynes has been
studied extensively,6 but to the best of our knowledge, the
reactivity of a germanium(I) dimer where the Ge-Ge bond
length has to be regarded as a single bond has not been
reported so far. Furthermore, a detailed theoretical calcula-
tion proposed that 1 features two stereoactive lone pairs,
which prefer to remain nonbonded at each germanium
atom.3 Fueled by this unprecedented electronic structure,
we embarked to study the reactivity of 1. Unequivocally, this
The synthesis of alkyne analogues (REER) of the heavier
congeners (E=Si-Pb) was only recently accomplished. In
2002, Power and co-workers reported the first carmine red-
orange digermyne [RGeGeR; R = 2,6-Trip2C6H3 (Trip =
2,6-iPr2C6H3)] by means of a tailor-made terphenyl-
substituted starting material.1a Following this, Jones et al.
reported the amidinato- and guanidinato-stabilized germa-
nium(I) dimer {Ge(Piso)}2 and {Ge(Giso)}2 [Piso=(ArN)2-
CtBu, Giso=(ArN)2CNiPr2, Ar=2,6-iPr2C6H3].2 Recently,
we successfully synthesized the first gauche-bent amidinato-
stabilized germanium(I) dimer [PhC(NtBu)2]2Ge2 (1) with
the tBu substituents on the nitrogen atoms.3 The series was
extended when Driess et al. documented a unsymmetrically
substituted digermylene with a GeI-GeI bond [LGe-GeL0,
L= C(Me)CHC(Me)N(2,6-iPr2-C6H3), L0 = CH(CMeNR)2,
R = 2,6-iPr2C6H3) R=2,6-iPr2C6H3].4 The main difference
in Power’s digermyne and the other germanium(I) dimers is
the central Ge-Ge bond length. Inspection of structural data
(5) Determined by the survey of the Cambridge Crystallographic Data-
base.
(6) (a) Cui, C.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 2004,
126, 5062–5063. (b) Cui, C.; Brynda, M.; Olmstead, M. M.; Power, P. P. J. Am.
Chem. Soc. 2004, 126, 6510–6511. (c) Power, P. P. Appl. Organomet. Chem.
2005, 19, 488–493. (d) Spikes, G. H.; Fettinger, J. C.; Power, P. P. J. Am. Chem.
Soc. 2005, 127, 12232–12233. (e) Cui, C.; Olmstead, M. M.; Fettinger, J. C.;
Spikes, G. H.; Power, P. P. J. Am. Chem. Soc. 2005, 127, 17530–17541.
(f) Power, P. P. Organometallics 2007, 26, 4362–4372. (g) Rivard, E.; Power,
P. P. Inorg. Chem. 2007, 46, 10047–10064. (h) Power, P. P. Nature 2010, 463,
171–177.
(7) All manipulations were carried out in an inert atmosphere of N2 using
standard Schlenk techniques and in a N2-filled glovebox. (a) 2: A mixture of 1
(0.2 g, 0.33 mmol) and PhNNPh (0.06g, 0.33 mmol) in toluene (20 mL) was
stirred at room temperature overnight. The solvent was removed under
reduced pressure, and the remaining powder was washed with n-hexane
(10 mL). Further recrystallization from toluene (5 mL) at room temperature
afforded colorless crystals of 2 (0.16 g, 61.5%). Mp: 148-155 ꢀC. Elem anal.
Calcd for C42H56Ge2N6 (790.20): C, 63.84; H, 7.14; N, 10.64. Found: C,
64.16; H, 8.04; N, 10.35. 1H NMR (300 MHz, C6D6, 25 ꢀC): δ 1.25 (s, 36 H,
tBu), 7.26-7.33 (m, 10 H, Ph), 6.85-7.50 (m, 20 H, Ph). 13C{1H} NMR
(125.75 MHz, C6D6, 25 ꢀC): δ 32.47(CMe3), 53.81 (CMe3), 123.29, 125.64,
127.54, 127.81, 128.00, 128.10, 128.19, 128.29, 128.41, 128.44, 128.51, 128.53,
129.15, 129.25, 129.27, 129.51, 131.08, 136.37, 140.88 (Ph), 166.08 (NCN).
EI-MS: m/z 790 [Mþ](100%). (b) 3: THF (40 mL) was added to the mixture
of 1 (0.2 g, 0,33 mmol) and diiron nonacarbonyl (0.24 g, 0.67 mmol) at
ambient temperature under N2. After stirring for 40 h, the initially light-
orange solution became darker in color to ultimately afford a garnet-brown
solution. The solvent was then removed in vacuum, and the residue was
extracted with toluene (30 mL). The insoluble solid was filtered off. The
garnet-brown filtrate was concentrated and stored at -30 ꢀC in a freezer to
yield a red-brown solid of 3 (0.52 g, 61%). Mp: 180-185 ꢀC. Elem anal.
Calcd for C38H46Fe2Ge2N4O8 (943.67): C, 48.36; H, 4.91; N, 5.94. Found: C,
47.51; H, 4.33; N, 5.85. 1H NMR (200 MHz, C6D6, 25 ꢀC): δ 1.41 (s, 36H,
tBu), 7.56-7.82 (m, 5H, Ph). 13C{1H} NMR (125.75 MHz, C6D6, 25 ꢀC): δ
31.3 (CMe3), 54.9 (CMe3), 127.8, 128.2, 128.3, 129.2, 130.0, 130.7 (Ph), 171.1
(NCN), 220.5 (CO). IR (Nujol, cm-1): ν 2029 (m), 1974 (s), 1920 (s) (CO).
EI-MS: m/z (%) 943 [Mþ] (100).
1
˚
of the latter affords the Ge-Ge bond distance as 2.28(6) A,
which is commonly interpreted as a double bond because it is
significantly shorter than a single bond. Differently are the
Ge-Ge bond distances in Jones’ germanium(I) dimer and in
*To whom correspondence should be addressed. E-mail: hroesky@
gwdg.de.
(1) (a) Stender, M.; Phillips, A. D.; Wright, R. J.; Power, P. P. Angew.
Chem. 2002, 114, 1863–1865. Angew. Chem., Int. Ed. 2002, 41, 1785-1787.
(b) Power, P. P. Chem. Commun. 2003, 2091–2101.
(2) Green, S. P.; Jones, C.; Junk, P. C.; Lippert, K.-A.; Stasch, A. Chem.
Commun. 2006, 3978–3980.
€
(3) Nagendran, S.; Sen, S. S.; Roesky, H. W.; Koley, D.; Grubmuller, H.;
Pal, A.; Herbst-Irmer, R. Organometallics 2008, 27, 5459–5463.
(4) Wang, W.; Inoue, S.; Yao, S.; Driess, M. Chem. Commun. 2009, 2661–
2663.
r
pubs.acs.org/IC
Published on Web 06/01/2010
2010 American Chemical Society

Communication
Inorganic Chemistry, Vol. 49, No. 13, 2010 5787
mentioning that a similar kind of Ge-Ge bond cleavage was
reported by Power et al. when RGeGeR [R=2,6-Trip2C6H3
(Trip =2,6-iPr2C6H3)] was reacted with azobenzene.8c In
addition to that, the Ge-N bond lengths [1.882(4) and
˚
˚
1.875(4) A] and the N-N bond distance [1.45(3) A] in
RGe{(Ph)NN(Ph)}GeR coincide very well with those of 2.
Both germanium atoms are tricoordinate and each exhibit a
distorted trigonal-pyramidal geometry with a stereochemi-
cally active lone pair at one apex. The three other sites at the
germanium atom are occupied by the two nitrogen atoms of
the amidinato ligand and one nitrogen atom of the bridging
azobenzene. The coordination of the nitrogen atoms is
P
Figure 1. Anisotropic displacement parameters, depicted at the 50%
probability level of 2. Hydrogen atoms and two toluene lattice molecules
are omitted for clarity. All four tBu groups are rotationally disordered
almost planar with angular sums
The Ge-N bond length [1.905(3) A] is within the range found
—N3,4 of 359.8(2)ꢀ.
˚
for other germanium(II) amides.9
˚
about the N-C axis. Selected bond lengths [A] and angles [deg]: N2-Ge1
2.050(3), Ge1-N3 1.911(3), Ge2-N4 1.902(3), N3-C12 1.401(4),
N3-N4 1.436(4); C28-N5-Ge2 91.1(2), C24-N5-Ge2 133.1(2),
C28-N6-Ge2 92.7(2), C35-N6-Ge2 136.3(3), N4-Ge2-N5
105.6(13), N4-Ge2-N6 103.6(14), C12-N3-Ge1 134.5(2), N4-N3-
Ge1 110.8(2), C18-N4-Ge2 132.7(2), N3- N4-Ge2 110.9(2), C1-
N1-Ge1 93.0(2), C39-N1-Ge1 135.4(3), C1-N2-Ge1 91.7(2), C8-
N2-Ge1 134.2(2), N3-Ge1-N1 104.4(13), N3- Ge1-N2 105.1(12),
N1-Ge1-N2 64.1(12).
Additionally, 2 was characterized by NMR spectroscopy,
electron impact mass spectrometry (EI-MS), elemental ana-
lysis. The H NMR spectrum of 2 exhibited three sets of
resonances, one from the tBu protons of the amidinato
ligand, the second one of the phenyl rings of the same ligand,
and the third one of the phenyl substituents of azobenzene.
In the EI-MS spectrum, the molecular ion appeared as
the most abundant peak with the highest relative intensity at
m/z 790.
1
Scheme 1. Preparation of 2
In the aforementioned experiment, the Ge-Ge bond in 1
was cleaved by insertion of azobenzene. However, we were
curious to see a reactivity where the Ge-Ge bond will remain
intact. In order to obviate such a possibility and minimize the
opportunity of cleavage, we wantedtoemploy the lonepair at
the GeI atom in bonding. According to Pearson’s hard and
soft acids and bases concept, 1 can be considered as a soft
base.10 So, the simplest idea is to treat 1 with a soft Lewis acid
and check whether it can form the Lewis acid-base adduct.
Therefore, diiron nonacarbonyl, Fe2(CO)9, with iron in the
formal oxidation state zero, was judiciously chosen as a
probe to investigate the reaction behavior. It is known to
form metal complexes with N-heterocyclic silylene.11 In our
case, the reaction successfully affords the target complex,
a unique example of a Lewis acid-base adduct employing
both germanium(I) centers with adjacent lone pairs as Lewis
bases.
is of great interest to both organic and organometallic
chemists. Our initial results are reported herein.
In order to derivatize 1, a reaction was performed with
azobenzene (PhNdNPh) in a 1:1 molar ratio in toluene at
room temperature (Scheme 1). This afforded 2 as colorless
crystals in good yield.7a The product is stable under an
inert atmosphere and soluble in organic solvents like ether,
toluene, and tetrahydrofuran (THF).
The molecular graph from the crystal structure determina-
tion of 2 is shown in Figure 1.8 Compound 2 crystallizes in the
monoclinic space group Pbcn. The most striking result of the
reaction is the unambiguous cleavage of the Ge-Ge bond
and the insertion of the substituted N2 motif of the azo-
benzene. The formal oxidation state of both germanium atoms
The treatment of 1 with 2 equiv of Fe2(CO)9 in THF for 1
day afforded 3 (Scheme 2).7b After the reaction, the solvent
was removed in vacuum and the residue extracted with
toluene. The insoluble solid was filtered off, and the filtrate
was concentrated and stored at -30 ꢀC in a freezer to yield
red crystals of 3, suitable for the X-ray diffraction study.
The solid-state structure of 3 is shown in Figure 2.8 3
crystallizes in the centrosymmetric monoclinic space group
C2/c. The most striking feature of the structure is the
˚
in 2 is increased to 2þ. The N-N bond distance of 1.44(4) A
is consistent with the interpretation as a single bond.9 In
addition, the N-C bond distances remain unchanged. There-
fore, the reaction of 1 with PhNdNPh has to be regarded as
an oxidative addition with simultaneous Ge-Ge bond clea-
vage. As a result, 2 is a molecular chain containing four
elements each with a lone pair of electrons. Here it is worth
˚
unbroken Ge-Ge bond. This bond length is 2.55(5) A and,
˚
hence, is reduced a little in comparison to 1 [2.57(5) A]. In 3,
each germanium atom binds to two nitrogen atoms from the
monoanionic chelating amidinato ligand, to another GeI
atom, and to a Fe(CO)4 moiety, leaving the germanium atom
(8) (a) Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1993, 26, 615–619.
(b) Stalke, D. Chem. Soc. Rev. 1998, 27, 171–176. (c) Sheldrick, G. M. Acta
Crystallogr., Sect. A 2008, 64, 112–122. Shock-cooled crystals were selected
and mounted under nitrogen atmosphere using X-TEMP2. The structure was
solved by direct methods (SHELXS) and refined against F2 using full matrix least
squares methods of SHELXL. Crystal data for 2: Mr = 881.23, orthorhombic,
space group Pbcn, a = 16.831(2) Å, b = 17.077(3) Å, c = 32.576(5) Å, V =
9364(2) Å3, Z = 8, Fcalcd = 1.250 g/cm3, μ(Mo KR) = 1.323 mm-1, T = 100(2) K,
R1 = 0.0531 [I > 2σ(I)], wR2 = 0.1374. Crystal data for 3: Mr = 943.71,
monoclinic, space group C2/c, a = 21.491(2) Å, b = 10.420(1) Å, c = 18.889(2) Å,
β = 105.965(1)ꢀ, V = 4066.9(7) Å3, Z = 4, Fcalcd = 1.541 g/cm3, μ(Mo KR) = 2.217
mm-1, T = 100(2) K, R1 = 0.0249 [I > 2σ(I)], wR2 = 0.0638.
˚
(9) (a) The N-N bond length in (H3Si)2NN(SiH3)2 is 1.46 A: Glidewell,
C.; Rankin, D. W. H.; Robiette, A. G.; Sheldrick, G. M. J. Chem. Soc. A
1970, 318–320. (b) Veith, M.; Rammo, A. Z. Anorg. Allg. Chem. 2001, 627,
662–668.
(10) (a) Pearson, R. J. Science 1966, 151, 172–177. (b) Pearson, R. J. J. Am.
Chem. Soc. 1963, 85, 3533–3539.
(11) Yang, W.; Fu, H.; Wang, H.; Chen, M.; Ding, Y.; Roesky, H. W.;
Jana, A. Inorg. Chem. 2009, 48, 5058–5060.

5788 Inorganic Chemistry, Vol. 49, No. 13, 2010
Sen et al.
˚
is 2.34(4) A, which is very similar to those found in
˚
LGe(OH)Fe(CO)4 [2.33(1) A; L = HC(CMeNAr)2 with
Ar = 2,6-i Pr2C6H3]12a and [η3-(μ-tBuN)2(SiMeNtBu)2)-
12b
˚
GeFe(CO)4] [2.348(1) A]
and also slightly longer com-
˚
pared with that of LGe(Cl)Fe(CO)4 [2.29(2) A; L =
HC(CMeNPh)2.12c In all of the mentioned examples, the
Fe(CO)4 fragment is bonded to germanium atoms in the
formal oxidation state of 2þ. However, to the best of our
knowledge, 3 is the first example where the Fe(CO)4 moiety
is attached to a germanium atom in the formal oxidation
state of 1þ.
Additionally, 3 was characterized by mass spectrometry,
NMR spectroscopy, and elemental analysis. All obtained
data are in accordance with the structure of 3. The 1H NMR
spectrum of 3 shows a singlet at 1.41 ppm for the 36 protons
of four tBu groups and another multiplet for 10 aromatic
protons (7.56-7.82 ppm). In the 13C NMR spectrum, the
chemical shift of the carbonyl group in 3 (220.56 ppm) is
similar to that observed for the N-heterocyclic silylene
complex with Fe(CO)4.11 The molecular ion in the EI-MS
spectrum appeared as the most abundant peak at m/z 943.
Carbonyl stretching frequencies are used as a probe to
compare the electronic properties of a series of complexes.
The CO stretching frequencies of 3 [2029 (m), 1974 (s), and
1920 (s) cm-1] are very similar to those of LGe(OH)Fe(CO)4
[L=HC(CMeNAr)2 with Ar=2,6-i Pr2C6H3; 2039 (s), 1956
Figure 2. Anisotropic displacement parameters, depicted at the 50%
probability level of 3. Hydrogen atoms are omitted for clarity. Selected
bond lengths [A] and angles [deg]:Ge1-Ge1A 2.5512(5), Ge1-N1
1.9623(16), Ge1-N2 1.9817(16), Fe2-C16 1.791(2), Fe2-Ge1 2.3402(4);
C18-Fe2-C19 92.34(9), N1-Ge1-N2 66.60(6), N1-Ge1-Fe2
118.44(5), N2-Ge1-Fe2 114.94(5), N1-Ge1-Ge1A 111.66(5), N2-
Ge1-Ge1A 108.00(5), Fe2-Ge1-Ge1A 123.211(10).
˚
Scheme 2. Preparation of 3
(s), and 1942 (s) cm-1 12a
and the N-heterocyclic sily-
]
lene complex with Fe(CO)4 [2026 (m), 1949 (s), and 1899
(s) cm-1].11
In summary, we have shown for the first time two con-
trasting reactivities of a germanium(I) dimer featuring a
Ge-Ge single bond toward azobenzene and diiron non-
acarbonyl. In the former case, cleavage of the Ge-Ge bond
occurs to form a vicinal digermahydrazine derivative,
whereas in the latter case, a Lewis acid-base adduct is
formed, keeping the Ge-Ge bond intact. Further reactivity
studies are ongoing in our laboratory and will be reported in
due course.
four-coordinate in a distorted tetrahedral coordination geo-
metry. Each iron atom is centered in a trigonal-bipyramidal
polyhedron; four sites are occupied by carbonyl groups and
one by a germanium atom. The FeI-GeI bond distance in 3
Acknowledgment. This work was supported by the
Deutsche Forschungsgemeinschaft.
(12) (a) Pineda, L. W.; Jancik, V.; Colunga-Valladares, J. F.; Roesky, H.
W.; Hofmeister, A.; Magull, J. Organometallics 2006, 25, 2381–2383. (b) Saur,
I.; Rima, G.; Miqueu, K.; Gornitzka, H.; Barrau, J. J. Organomet. Chem. 2003,
672, 77–85. (c) Veith, M.; Becker, S.; Huch, V. Angew. Chem. 1990, 102,
186–188. Angew. Chem., Int. Ed. Engl. 1990, 29, 216-218.
Supporting Information Available: Crystallographic data in
CIF format for 2 and 3. This material is available free of charge
via the Internet at http://pubs.acs.org.