Isolable metallo-germylene and metallo-stannylene σ-complexes with iron

Article abstract of DOI:10.1021/om9005802

Conversion of the β-diketiminato Ge(II) chloride LGeCl [L = CH{CMe(NAr)}₂, Ar = 2,6-ⁱPr₂C₆H ₃] (1) and its tin homologue LSnCl (2) with the anionic iron complex K[Fe(η⁵-C₅H₅

Full text of DOI:10.1021/om9005802

5032 Organometallics 2009, 28, 5032–5035
DOI: 10.1021/om9005802
Isolable Metallo-Germylene and Metallo-Stannylene σ-Complexes with
Iron
Shigeyoshi Inoue and Matthias Driess*
€
Institute of Chemistry: Metalorganic and Inorganic Materials, Technische Universitat Berlin, Sekr. C2,
Strasse des 17. Juni 135, 10623 Berlin, Germany
Received July 6, 2009
Conversion of the β-diketiminato Ge(II) chloride LGeCl [L=CH{CMe(NAr)}2, Ar=2,6-iPr2C6H3]
(1) and its tin homologue LSnCl (2) with the anionic iron complex K[Fe(η5-C5H5)(CO)2] leads to the
iron-germylene LGeFe(η5-C5H5)(CO)2 (3) and iron-stannylene LSnFe(η5-C5H5)(CO)2 (4), respectively.
The compounds 3 amd 4 were characterized by NMR, IR, and UV-vis spectroscopy as well as
theoretical studies. The structure of 3 was also determined by X-ray crystallography. The experimental
and computed structures show clealy that the Fe-E (E=Ge, Sn) bond is a single bond in compounds 3
and 4. They represent the isolable iron-germylene and -stannylene σ-complexes. Notably, compound 3 is
the first example of iron-germylene σ-complexes ever characterized by X-ray analysis.
Chart 1. Metallo-germylenes and -stannylenes
Introduction
Since the first striking isolation of germylenes and stanny-
lenes by Lappert and co-workers in 1974,1 low-valent germa-
nium and tin compounds have attracted considerable interest
during the last three decades.2 Germylenes and stannylenes
R2E: (E = Ge, Sn; R=amido, alkyl, aryl) are suitable ligands
for the synthesis of transition metal complexes with potential
applications in homogeneous catalysis. The ability of ER2
systems to serve as σ-donors and π-acceptors toward transi-
tion metal centers can be tuned by the nature of the substit-
uents R. While numerous carbene-like transition metal com-
plexes of the type MdER2 have been reported, only a few
examples of isolable metallo-germylenes and -stannylenes
with a M-E(II) σ-bond and a bent M-E-R configuration
(M=transition metal, E=Ge, Sn) have been synthesized to
date.3-5 The latter type of metallo-ylidenes are interesting and
represent congeners of as yet unknown σ-metallocarbenes
[M]-C-R. In 1994, Jutzi and Leue synthesized the first
metallogermylene derivatives of iron Ia,b (Chart 1), but the
latter have not been characterized structurally.3 The metallo-
germylenes IIa,b4 and metallostannylenes IIIa-f5 have been
reported by Power and co-workers and structurally character-
ized by X-ray diffraction (Chart 1). Interestingly, Tilley and
co-workers reported the tautomerization of the osmium
stannylene complex Cp*(iPr3P)(H)OsdSn(H)R to give the
osmostannylene IV, which has been characterized by means of
spectroscopy (Chart 1).6 Pandey and co-workers reported on
the electronic structure and bonding features of metalloger-
mylenes and metallostannylenes by theoretical studies.7 The
latter results suggested that the π-bonding contribution in
metallo-ylidenes is smaller than those in metal-ylidynes, while
*To whom correspondence should be addressed. Phone: þ49(0)30-
314-22265. Fax: þ49(0)30-314-29732. E-mail: matthias.driess@tu-ber-
lin.de. Website: http://www.driess.tu-berlin.de.
(1) (a) Harris, D. H.; Lappert, M. F.; Pedley, J. B.; Sharp, G. J. J.
Chem. Soc., Dalton Trans. 1976, 945. (b) Davidson, P. J.; Harris, D. H.;
Lappert, M. F. J. Chem. Soc., Dalton Trans. 1976, 2268.
(2) For reviews of the chemistry of heavier group 14 carbene analo-
gues see: (a) Barrau, J.; Rima, G. Coord. Chem. Rev. 1998, 178-180,
593. (b) Tokitoh, N.; Okazaki, R. Coord. Chem. Rev. 2000, 210, 251. (c)
Kira, M. J. Organomet. Chem. 2004, 689, 4475. (d) Weidenbruch, M. Eur.
J. Inorg. Chem. 1999, 373. (e) Klinkhammer, K. W. In Chemistry of
Organic Germanium, Tin and Lead Compounds; Rappoport, Z., Ed.; Wiley:
New York, 2002; Vol. 2, pp 283-357. (f) Veith, M. Angew. Chem., Int. Ed.
Engl. 1987, 26, 1. (g) K€uhl, O. Coord. Chem. Rev. 2004, 248, 411. (h) Hill,
N. J.; West, R. J. Organomet. Chem. 2004, 689, 4165. (i) Gehrhus, B.;
Lappert, M. F. J. Organomet. Chem. 2001, 617, 209. (j) Nagendran, S.;
Roesky, H. W. Organometallics 2008, 27, 457.
(3) Jutzi, P.; Leue, C. Organometallics 1994, 13, 2898.
(4) Pu, L.; Twamley, B.; Haubrich, S. T.; Olmstead, M. M.; Mork, B.
V.; Simons, R. S.; Power, P. P. J. Am. Chem. Soc. 2000, 122, 650.
(5) Eichler, B. E.; Phillips, A. D.; Haubrich, S. T.; Mork, B. V.;
Power, P. P. Organometallics 2002, 21, 5622.
(6) Hayes, P. G.; Gribble, C. W.; Waterman, R.; Tilley, T. D. J. Am.
Chem. Soc. 2009, 131, 4606.
(7) (a) Pandey, K. K.; Lein, M.; Frenking, G. J. Am. Chem. Soc. 2003,
ꢀ
125, 1660. (b) Pandey, K. K.; Liedos, A. Inorg. Chem. 2009, 48, 2748.
r
pubs.acs.org/Organometallics
Published on Web 08/18/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 17, 2009 5033
Figure 1. ORTEP drawing of compound 3, top view (left) and side view (right). Thermal ellipsoids are shown with 30% probability,
and hydrogen atoms have been omitted for clarity. Compound 3 is disordered; only the major positions are shown here.
The composition and constitution of 3 and 4 were char-
acterized by elemental analysis and spectrocopy, as well as
X-ray diffraction analysis.10 The 1H NMR spectra of 3 and 4
display resonance signals from the cyclopentadienyl and the
γ-CH protons of the C3N2M (M = Ge (3), Sn (4)) ring in an
intensity ratio of 5:1. Furthermore, four signals for methyl
groups of isopropyl groups and two siganals for the CH
of isopropyl groups are observed. It is suggested that there is
no free rotation around the N-C bond of the Ar group due
to steric hindrance. This pattern is similar to those observed
for LGeCl 1 and LSnCl 2.8 Compound 4 was also character-
ized by 119Sn NMR spectroscopy, which revealed a singlet at
δ=-645 ppm. Apparently, the 119Sn nucleus in 4 is more
shielded than that in the precursor 2 (δ=-224 ppm). In the
UV-vis spectra, absorption bands are observed at 428 and
410 nm for 3 and 4, respectively, which can be assigned to
n-p transitions. This pattern is similar to that observed for
metallogermylenes II and metallostannylenes III.4,5 In addi-
tion, the infrared spectra of 3 and 4 in KBr revealed each two
expected strong stretching vibration modes in the carbonyl
region. The observed stretching frequencies of 3 (1968 and
1918 cm-1) and 4 (1961 and 1907 cm-1) resemble that of
related compounds and are in good agreement with the
DFT-calculated values (3:1977 and 1933 cm-1; 4: 1978 and
1945 cm-1). Moreover, compared with iron-substituted
germylenes Ia (1969 and 1920 cm-1) and Ib (2004 and 1950
cm-1),3 the β-diketiminato germylene and stannylene li-
gands are slightly stronger σ-donors than aryl-substituted
germylene ligands.
Scheme 1. Synthesis of 3 and 4
the σ-bonding contribution in the former compounds is
larger than those in the metallo-ylidynes. Up to now, no
structural characterization of an iron-germylene and -stanny-
lene complex has been reported. We report here the synthesis
and isolation of the new iron-germylene and -stannylene
complexes 3 and 4, starting from the N-heterocyclic E(II)
chloride precursors 1 (E=Ge) and 2 (E=Sn), respectively.
The molecular structure of 3 has also been elucidated by
X-ray diffraction.
Results and Discussion
Synthesis of LGeFe(η5-C5H5)(CO)2 and LSnFe(η5-C5H5)-
(CO)2. The N-heterocyclic β-diketiminato Ge(II) chloride
LGeCl [L=CH{CMe(NAr)}2, Ar=2,6-iPr2C6H3] (1) and its
tin homologue 2 were employed as precursors for the synth-
esis of the iron-germylene 3 and -stannylene 4, respectively
(Scheme 1).8 Thus 1 was allowed to react with 1 molar equiv
of anionic iron complex K[Fe(η5-C5H5)(CO)2]9 in diethyl
ether at ambient temperature, affording a dark red solution,
from which dark red crystals of the desired iron-germylene
LGeFe(η5-C5H5)(CO)2 (3) can be isolated in 71% yield. In
a similar manner, treatment of LSnCl (2) with K[Fe(η5-
C5H5)(CO)2] yields the corresponding iron complex LSnFe-
(η5-C5H5)(CO)2 (4) in 53% yield (Scheme 1).
X-ray Structure Analysis. The molecular structure of 3 is
shown in Figure 1. Two carbonyl ligands, a cyclopentadienyl
ligand, and the β-diketiminato germylene ligand are coordi-
nating to the iron center of 3. The Ge-Fe bond length of
˚
2.4961(17) A in 3 is longer than typical Ge-Fe single bonds;
5
˚
for example, 2.357(4) A is found in Cl2Ge[Fe(η -C5H5)-
(CO)2]
2.080(4) A) are longer than those of LGeCl 2 (1.988(4) and
11
.
The Ge-N bond lengths of 3 (2.059(4) and
2
˚
(8) Ding, Y.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G.;
Power, P. P. Organometallics 2001, 20, 1190.
€
(9) Dulich, F.; Muller, K.-H.; Ofial, A. R.; Mayr, H. Helv. Chim. Acta
(10) See the Supporting Information.
(11) Bush, M. A.; Woodward, P. J. Chem. Soc. A 1967, 1833.
2005, 88, 1754.

5034 Organometallics, Vol. 28, No. 17, 2009
Inoue and Driess
Table 2. Crystal and Refinement Data for 3
empirical formula
M
cryst syst
C36H46FeGeN2O2
667.19
monoclinic
P21/n
9.0894(2)
21.8257(5)
17.4797(4)
90
102.984(2)
90
3379.01(13)
4
1.312
1.352
28 511
5925
0.064
4055
486
space group
˚
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
reflns collected
indep reflns
Figure 2. Molecular orbitalsof3, HOMO(left) andHOMO-11-
(right). DFT calculations were performed at the B3LYP level
using the 6-31G(d) basis set for Ge, N, C, and H atoms and the
LANL2DZ level for the Fe atom.
R(int)
reflns with I > 2σ(l)
Data/params
final R indices [I > 2σ(I)], R1
R indices (all data), wR2
0.0825
0.1537
determined by X-ray analysis. The structural features of 4 are
quite similar to those of 3; however, the X-ray data were not
sufficient for further discussion.
Theoretical Calculations. In order to obtain more informa-
tion about the electronic structure and bonding nature of 3
and 4, we performed quantum chemical calculations at the
gradient-corrected DFT level using the exchange-correla-
tion functional B3LYP of the geometries of 3 and 4, as initial
structures that were obtained by X-ray crystallographic
analysis.13 The HOMO of 3 represents mainly the lone pair
at the Ge(II) atom with somewhat in-plane pseudo-π-bond-
ing contributions (Figure 2, left). The HOMO-11 of 3 shows
mainly the Ge-Fe σ-bonding orbital (Figure 2, right).
Molecular orbitals of 4 are shown in Figure 3. The HOMO
and HOMO-11 of 4 are fairly similar to those of 3 (HOMO,
right; HOMO-11, left).
Figure 3. Molecular orbitalsof4, HOMO(left) andHOMO-11-
(right). DFT calculations were performed at the B3LYP level
using the 6-31G(d) basis set for Ge, N, C, and H atoms and the
LANL2DZ level for the Fe and Sn atoms.
As expected from the geometric features, there is no pure
π-bonding orbital in 3 and 4. An NBO analysis of 3 and 4
shows that the σ-type E-Fe orbitals are highly filled (3:
1.68e, 4: 1.72e) and strongly polarized toward the iron atom
(Fe = 72.29% in 3, 78.11% in 4). Furthermore, the E-Fe
bond of 3 and 4 consists of highly overlapped np-valence
orbitals of E (3: Ge 4s 10.53%, 4p 89.37%, 4: Sn 5s 8.33%, 5p
91.67%). Additionally, the single σ-bond character of 3 and 4
is supported by the WBI values of the E-Fe bond (0.7031 (3)
and 0.6084 (4)). In fact, the electronic features and molecular
orbitals of 4 are similar to those of 3. The molecular orbital
characteristics of the iron-germylene and -stannylene deri-
vatives presented here are in good agreement with those
reported by Pandey and co-workers.7
˚
Table 1. Selected Bond Distances (A) and Angles (deg) in Com-
pound 3
Ge1-Fe1
2.496(2)
N2-Ge1-N1
88.92(16)
Ge1-N1
2.059(4)
2.080(4)
1.807(10)
1.738(11)
N2-Ge1-Fe1
N1-Ge1-Fe1
C4-N2-Ge1
C2-N1-Ge1
110.86(12)
109.91(12)
115.3(3)
Ge1-N2
Fe1-C35(carbonyl)
Fe1-C36(carbonyl)
120.0(3)
˚
1.997(4) A), probably owing to the steric congestion around
the Ge(II) atom. The C3N2 plane of the C3N2Ge ring in the
compound 3 is nearly planar, but the Ge atom is out of the
plane by 32.7°. The angle between the Ge-Fe bond and the
Ge1-N1-N2 plane is 102.9°. The large distorted structure
of 3 is consistent with the presence of a lone pair on the
germanium atom. Accordingly, it is obvious that the bending
feature of 3 is different from germylyne complexes. For
instance, the structures of germylyne complexes having a
triple bond between the transition metal and germanium
atom show a nearly linear structure (bent angles around
172.0-178.9°).4,12 The structure of 4 was unambiguously
Conclusions
In this work, we investigated the synthesis and character-
ization of novel iron-germylene complex 3 and iron-stanny-
lene complex 4. The facile synthesis and stability of 3
and 4 may be attributed to the stabilizing property of the
N-heterocyclic β-diketiminato substituent. They represent
isolable iron-germylene and -stannylene σ-complexes. No-
tably, compound 3 is the first example of an iron-germylene
σ-complex that is structurally characterized. The compounds
3 and 4 are unique because not only are they the first isolable
(12) (a) Simons, R. S.; Power, P. P. J. Am. Chem. Soc. 1996, 118,
11966. (b) Filippou, A. C.; Philippopoulos, A. I.; Portius, P.; Neumann, D. U.
Angew. Chem., Int. Ed. 2000, 39, 2778. (c) Filippou, A. C.; Portius, P.;
Philippopoulos, A. I. Organometallics 2002, 21, 653. (d) Filippou, A. C.;
Portius, P.; Philippopoulos, A. I.; Rohde, H. Angew. Chem., Int. Ed. 2003,
42, 445. (e) Filippou, A. C.; Philippopoulos, A. I.; Schnakenburg, G.
Organometallics 2003, 22, 3339.
(13) Calculations were carried out using the Gaussian 03, Revision
E.01 series of programs, and also see the Supporting Information.

Article
Organometallics, Vol. 28, No. 17, 2009 5035
metallo-germylene and metallo-stannylene σ-complexes
with iron, but also they may lead to novel iron germylyne-
and stannylyne-complexes. For example, Power and co-
workers have synthesized germylyne complexes from metal-
logermylenes by photolysis or thermolysis reactions.4 The
reactivity of 3 and 4, including the synthesis of germylyne or
stannylyne complexes, is currently under investigation.
LSnFe(η5-C5H5)(CO)2 (4). To a mixture of LSnCl 2 (819 mg,
1.432 mmol) and K[Fe(η5-C5H5)(CO)2] (312 mg, 1.444 mmol)
was added dry Et2O (25 mL), and then the reaction mixture was
stirred at room temperature for 4 h. Volatiles were removed
under reduced pressure and the residue was extracted with
hexane (50 mL). The filtrate was concentrated and stored at
-30 °C for 2 days, yielding 4 as dark red crystals (543 mg, 0.759
mmol, 53%). Mp: 140 °C (dec). 1H NMR (400.13 MHz, C6D6,
298 K): δ 1.06 (d, 3JHH = 7 Hz, 12 H, CHMe2), 1.15 (d, 3JHH
=
7 Hz, 12 H, CHMe2), 1.38 (d, 3JHH = 7 Hz, 12 H, CHMe2), 1.42
(d, 3JHH = 7 Hz, 12 H, CHMe2), 1.71 (s, 6 H, NCMe), 3.37 (sep,
3JHH = 6.8 Hz, 2 H, CHMe2), 3.83 (s, 5 H, CpH), 3.96 (sep,
3JHH = 6.8 Hz, 2 H, CHMe2), 4.78 (s, 1 H, γ-CH), 7.05-7.16
(m, 6 H, 2,6-iPr2C6H3). 13C{1H} NMR (100.61 MHz, C6D6, 298
K) δ 23.8 (NCMe), 25.3, 25.4, 25.5, 26.6 (CHMe2), 28.2, 28.5
(CHMe2), 83.6 (Cp), 95.8 (γ-C), 125.1, 125.4, 126.5, 142.6,
143.8, 144,3 (2,6-iPr2C6H3) 169.0 (NCMe), 214.9 (CO). 119Sn
NMR (C6D6, 298 K): δ -645 ppm. UV-vis λ [nm]: 435 (2600),
588 (100). IR (KBr, cm-1): 511 (w), 580 (w), 645 (w), 744 (m),
771 (m), 791 (m), 840 (w), 936 (w), 1001 (w), 1017 (m), 1057 (w),
1099 (m), 1172 (w), 1264 (m), 1316 (s), 1385 (s), 1436 (s), 1463
(m), 1519 (m), 1551 (s), 1623 (w), 1908 (s), 1961 (s), 2867 (w),
2927 (m), 2961 (s), 3057 (w), 3436 (w). Anal. (%) Calcd for
C36H46FeSnN2O2: C, 60.62; H, 6.50; N, 3.93. Found C, 60.78;
H, 6.39; N, 3.96.
Experimental Section
General Considerations. All experiments and manipulations
were carried out under dry oxygen-free nitrogen using standard
Schlenk techniques or in an MBraun inert atmosphere glovebox
containing an atmosphere of purified nitrogen. Solvents were
dried by standard methods and freshly distilled prior to use. The
starting materials LGeCl 1,8 LSnCl 28 (L=HC[C(Me)NAr]2,
Ar=2,6-iPr2C6H3), and K[Fe(η5-C5H5)(CO)2]9 were prepared
according to literature procedures. The NMR spectra were
1
recorded on a Bruker AV 400 spectrometer. The H and 13C-
{1H} NMR spectra were referenced to the residual solvent
signals as internal standards, and the 119Sn NMR spectra was
referenced to SnMe4 as an external standard. Abbreviations:
s=singlet; d=doublet; t=triplet; sept=septet; mult=multi-
plet; br = broad.
LGeFe(η5-C5H5)(CO)2 (3). To a mixture of LGeCl 1 (1.013 g,
1.93 mmol) and K[Fe(η5-C5H5)(CO)2] (417 mg, 1.93 mmol) was
added dry Et2O (30 mL), and then the reaction mixture was
stirred at room temperature for 4 h. Volatiles were removed
under reduced pressure, and the residue was extracted with
hexane (50 mL). The filtrate was concentrated and stored at
-30 °C for 2 days, yielding 3 as dark red crystals (913.8 mg, 1.37
mmol, 71%). Mp: 151 °C (dec). 1H NMR (400.13 MHz, C6D6,
Single-Crystal X-ray Structure Determinations. Crystals were
each mounted on a glass capillary in perfluorinated oil and
measured in a cold N2 flow. The data of compounds 3 were
collected on an Oxford Diffraction Xcalibur S Sapphire at 150 K
˚
(Mo KR radiation, λ = 0.71073 A). The structures were solved
by direct methods and refined on F2 with the SHELX-9714
software package. The positions of the H atoms were calculated
and considered isotropically according to a riding model. The
Ge atom and Fe atom in 3 are disordered over two orientations.
298 K): δ 1.07 (d, 3JHH = 7 Hz, 12 H, CHMe2), 1.11 (d, 3JHH
=
7 Hz, 12 H, CHMe2), 1.51 (d, 3JHH=7 Hz, 12 H, CHMe2), 1.57
(d, 3JHH=7 Hz, 12 H, CHMe2), 1.61 (s, 6 H, NCMe), 3.77-4.01
(m, 4 H, CHMe2), 3.88 (s, 5 H, CpH), 4.63 (s, 1 H, γ-CH),
7.08-7.13 (m, 6 H, 2,6-iPr2C6H3). 13C{1H} NMR (100.61
MHz, C6D6, 298 K): δ 24.3 (NCMe), 25.8, 25.9, 26.0, 26.5
(CHMe2), 27.9, 29.3 (CHMe2), 85.0 (Cp), 95.0 (γ-C), 125.7,
125.9, 127.3, 141.6, 144.8, 145,5 (2,6-iPr2C6H3) 168.7 (NCMe),
217.4 (CO). UV-vis λ [nm]: 428 (2150), 582 (100). IR (KBr,
cm-1): 441 (w), 509 (m), 571 (m), 645 (m), 747 (m), 758 (w), 795
(m), 818 (m), 842 (w), 932 (w), 984 (m), 1053 (w), 1103 (m), 1155
(s), 1240 (s), 1314 (s), 1376 (s), 1436 (m), 1461 (m), 1522 (m), 1548
(m), 1611 (w), 1648 (w), 1910 (s), 1966 (s), 2868 (w), 2928
(w), 2962 (m), 3056 (w), 3483 (w). Anal. (%) Calcd for
C36H46FeGeN2O2: C, 64.80; H, 6.95; N, 4.20. Found: C,
64.57; H, 6.85; N, 4.14.
Acknowledgment. Financial support from the Deut-
sche Forschungsgemeinschaft, the Alexander von Hum-
boldt Foundation, and JSPS (fellowship for S.I.) is grate-
fully acknowledged.
Supporting Information Available: Details of the crystal
structure determination for 3 (CIF) and tables with the Carte-
sian coordinates of the optimized geometries of 3 and 4. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(14) Sheldrick, G. M. SHELX-97, Program for Crystal Structure
€
€
Determination; Universitat Gottingen: Germany, 1997.