Isomerization of an N-heterocyclic germylene to an azagermabenzen-1-ylidene and its coupling to a unique bis(germylene)

Article abstract of DOI:10.1021/om100383y

N-Heterocyclic germylene LGe [L = CH{(C=CH₂)(CMe)(N(aryl)) ₂}, aryl = 2,6-ⁱPr₂C₆H₃] 1 reacts with HN(C₆F₅)₂ solely to give the 1,4-addition product L′GeN(C₆F₅)₂ 2 (L′ = CH(CMe)₂[N(aryl)]₂), which contains a Ge(II)-N(C₆F₅)₂ moiety. In contrast, HN(SiMe₃)₂ does not add to 1 but induces isomerization of 1 to generate the first N(aryl)H-substituted, heteroaromatic azagermabenzen-1-ylidene intermediate. The latter readily undergoes 1,4-addition to a second equivalent of 1 to form the unprecedented bis(germylene) 3, which contains two-and three-coordinate Ge(II) centers. The isomerization process and the nature of the six π-electron aromatic character of the C₄NGe heterocycle in 2 are explored and supported by DFT calculations.

Full text of DOI:10.1021/om100383y

Organometallics 2010, 29, 5353–5357 5353
DOI: 10.1021/om100383y
Isomerization of an N-Heterocyclic Germylene to an
Azagermabenzen-1-ylidene and Its Coupling to a Unique Bis(germylene)§
Shenglai Yao,† Xinhao Zhang,‡ Yun Xiong,† Helmut Schwarz,‡ and Matthias Driess*,†
†
€
Institute of Chemistry: Metalorganics and Inorganic Materials, Technische Universitat Berlin, Sekr. C2,
Strasse des 17 Juni 135, 10623 Berlin Germany, and Organic Chemistry, Technische Universitat Berlin,
‡
€
Sekr. C4, Strasse des 17 Juni 135, 10623 Berlin, Germany
Received April 30, 2010
N-Heterocyclic germylene LGe [L = CH{(CdCH2)(CMe)(N(aryl))2}, aryl = 2,6-iPr2C6H3] 1 reacts
with HN(C6F5)2 solely to give the 1,4-addition product L0GeN(C6F5)2 2 (L0 = CH(CMe)2[N(aryl)]2),
which contains a Ge(II)-N(C6F5)2 moiety. In contrast, HN(SiMe3)2 does not add to 1 but induces
isomerization of 1 to generate the first N(aryl)H-substituted, heteroaromatic azagermabenzen-1-ylidene
intermediate. The latter readily undergoes 1,4-addition to a second equivalent of 1 to form the unprece-
dented bis(germylene) 3, which contains two- and three-coordinate Ge(II) centers. The isomerization
process and the nature of the six π-electron aromatic character of the C4NGe heterocycle in 2 are
explored and supported by DFT calculations.
Introduction
of stable germanium(II) complexes A1k,3 and C4 (Scheme 1),
and these findings initiated renewed interest in investigating
N-heterocyclic Ge(II) systems with two- and three-coordi-
nate Ge atoms. Recently, we succeeded in the synthesis and
isolation of a new type of Ge(II) heterocycle, the cyclopenta-
dienide analogue D,5 via reduction of A (X = Cl)6a by
elemental potassium and subsequent ring contraction. More-
over, we prepared the N-heterocyclic germylene 17 through
dehydrohalogenation of A. Interestingly, the betaine-like ger-
mylene 1 reacts readily with 1,2-dibromoethane, affording the
bis(bromogermylene) B as a yellow solid.7 While the Ge(II)
centers in A and B are stabilized additionally by intramole-
cular NfGe coordination, the significant stabilization of C
and D originates from a heteroaromatic six π-electron delo-
calization over the respective ring systems. However, in con-
trast to C and D, while containing dicoordinate Ge(II) and
enjoying a planar structure with potentially six π-electrons,
DFT calculations indicate no heteroaromatic character for 1.7
Rather, reactivity investigations of germylene 1 revealed that
the ylide-like betaine resonance structure 10 (Scheme 1) plays
an important role and determines largely its intriguing reac-
tivity toward electrophiles. For instance, reaction of 1 with
trimethylsilyl triflate (Me3SiOTf, OTf = OSO2CF3) leads
exclusively to a 1,4-addition product, with addition of the
Me3Si group to the nucleophilic carbon atom of the terminal
methylene moiety and OTf to the electrophilic Ge(II) site,
affording a Ge(II) complex of type A.7 Germylene 1 is even
capable of activating N-H bonds of ammonia, giving the
The preparative chemistry and reactivity of divalent,
two-coordinate germanium(II) compounds (germylenes)
have received considerable interest due to their carbene-
like properties.1 Most of the isolable germylenes are stabi-
lized kinetically by sterically demanding substituents and/
or thermodynamically by both π-electron-donating and
σ-electron-withdrawing substituents (amido ligands, etc.)
bonded to the divalent germanium(II) atom. In some cases,
heteroaromatic six π-electron delocalization may also con-
tribute to the remarkable stabilization of N-heterocyclic
germylenes.2
Using β-diketiminate ligands, bearing sterically congested
aryl substituents at the nitrogen atoms, enabled the synthesis
§ Part of the Dietmar Seyferth Festschrift. Dedicated to Professor Dietmar
Seyferth.
*To whom correspondence should be addressed. Phone: þ49(0)30-
314-22265. Fax: þ49(0)30-314-29732. E-mail: matthias.driess@
tu-berlin.de. Website: http://www.driess.tu-berlin.de.
(1) Recent reviews: (a) Veith, M. Angew. Chem., Int. Ed. Engl. 1987,
ꢀ
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26, 1. (b) Barrau, J.; Escudie, J.; Satge, J. Chem. Rev. 1990, 90, 283. (c)
Neumann, W. P. Chem. Rev. 1991, 91, 311. (d) Dias, H. V. R.; Wang, Z.; Jin,
W. Coord. Chem. Rev. 1998, 176, 67. (e) Weidenbruch, M. Eur. J. Inorg.
Chem. 1999, 373. (f) Tokitoh, N.; Okazaki, R. Coord. Chem. Rev. 2000, 210,
251. (g) Recent advances in structural chemistry of organic germanium, tin
and lead compounds. Klinkhammer, K. W. In The Chemistry of Organic
Germanium, Tin and Lead Compounds, Vol. 2; Rappoport, Z., Ed.; Wiley:
New York, 2002; Chapter 4, pp 284-332. (h) K€uhl, O. Coord. Chem. Rev.
2004, 248, 411. (i) Saur, I.; Alonso, S. G.; Barrau, J. J. Appl. Organomet.
Chem. 2005, 19, 414. (j) Leung, W. P.; Kan, K. W.; Chong, K. H. Coord.
Chem. Rev. 2007, 251, 2253. (k) Nagendran, S.; Roesky, H. W. Organo-
metallics 2008, 27, 457. (l) Mizuhata, Y.; Sasamori, T.; Tokitoh, N. Chem.
Rev. 2009, 109, 3479. (m) Lappert, M. F. Main Group Metal Chem. 1994,
17, 184.
(4) Stender, M.; Phillips, A. D.; Power, P. P. Inorg. Chem. 2001, 40,
5314.
€
(5) Wang, W.; Yao, S.; van Wullen, C.; Driess, M. J. Am. Chem. Soc.
(2) (a) Leites, L. A.; Bukalov, S. S.; Zabula, A. V.; Garbuzova, I. A.;
Moser, D. F.; West, R. J. Am. Chem. Soc. 2004, 126, 4114, and
references therein. (b) Tuononen, H. M.; Roesler, R.; Dutton, J. L.;
Ragogna, P. J. Inorg. Chem. 2007, 46, 10693.
(3) Yao, S.; Brym, M.; Merz, K.; Driess, M. Organometallics 2008, 27,
3601.
2008, 130, 9640.
(6) (a) Ding, Y.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G.
Organometallics 2001, 20, 1190. (b) Jana, A.; Objartel, I.; Roesky, H. W.;
Stalke, D. Inorg. Chem. 2009, 48, 798.
(7) Driess, M.; Yao, S.; Brym, M.; van Wullen, C. Angew. Chem., Int.
Ed. 2006, 45, 4349.
€
r
2010 American Chemical Society
Published on Web 06/22/2010
pubs.acs.org/Organometallics

5354 Organometallics, Vol. 29, No. 21, 2010
Yao et al.
Scheme 1. Germylenes A, B, C, D, and 1
Figure 1. Molecular structure of 2. Thermal ellipsoids are
drawn at a 50% probability level. Hydrogen atoms are omitted
˚
for the sake of clarity. Selected bond lengths [A] and angles [deg]:
Scheme 2. Synthesis of 2 and 3 from Germylene 1
Ge1-N2 1.987(2), Ge1-N1 1.990(2), Ge1-N3 2.054(2), N1-
C2 1.338(2), C1-C2 1.500(2), N2-C4 1.339(2), C2-C3 1.390(3),
N3-C30 1.395(2), N3-C41 1.422(2), C3-C4 1.390(3), C4-C5
1.506(2), N2-Ge1-N1 92.03(6), N2-Ge1-N3 104.76(6), N1-
Ge1-N3 104.67(6), C2-N1-Ge1 126.3(1), C4-N2-Ge1
125.8(1), N1-C2-C3 123.0(2), N1-C2-C1 119.4(2), C30-
N3-C41 116.7(1), C30-N3-Ge1 139.9(1), C41-N3-Ge1
103.0(1).
hedral geometry. Two sites are occupied by nitrogen atoms
from the β-diketiminate ligand, and one site is occupied by
the exocyclic N atom of the N(C6F5)2 group. The lone pair of
electrons occupies presumably the remaining coordination
site of the tetrahedron. While the bond lengths within the
C3N2Ge ring of 2 are comparable to those found in related
same type of 1,4-addition product A (X = NH2).6b Likewise,
germylene 1 reacts also with the secondary amine HN(C6F5)2,
to give the amido-substituted germylene 2 as an expected 1,4-
addition product. To our surprise, HN(SiMe3)2 exhibits dif-
ferent behavior, serving as a catalyst for the rearrangement of
1 to an azagermabenzen-1-ylidene intermediate, which under-
goes coupling with one additional molecule of 1 to give the
unique bis(germylene) 3 (Scheme 2). The latter features both
two- and three-coordinate Ge(II) moieties connected by an
N(aryl) group. Herein we describe the facile addition of secon-
dary amine HN(C6F5) to givethe Ge(II)-amido complex 2 and
the remarkably different result for the conversion 1 f 3 in the
presence of HN(SiMe3)2.
˚
structures, the exocyclic Ge1-N3 distance of 2.054(2) A,
however, is about 0.2 A longer than the corresponding
˚
6b
˚
Ge-N bond length (1.845(2) A) in A (X = NH2), pre-
sumably due to the electron-withdrawing character of the
electronegative N(C6F5)2 subunit, which favors an enhanced
Geþ-N- polarization.
We further probed HN(SiMe3)2 as a potential substrate
for 1,4-addition to 1. We assumed that, if addition of the
amine occurs at all, the desired process would be relatively
slow because of the more demanding steric congestion of the
amino group as compared to N(C6F5)2. In fact, conversion
of 1 in the presence of a catalytic amount (12 mol %) of
bis(trimethylsilyl)amine occurs with only moderate progress,
irrespective of the polarity of the nonprotic organic solvent
used (hexane, diethyl ether, or benzene), and it takes about
three weeks for the complete conversion of 1. Notably, no
significant change has been observed by using additional
amounts of bis(trimethylsilyl)amine. Moreover, at elevated
temperature the reaction led to a complex mixture. Unexpec-
tedly, the novel bis(germylene) 3 crystallized at room tem-
peraturein hexaneas yellow crystalsand was isolated from the
reaction mixture in 48% yield (Scheme 2). In accordance with
its 1H and 13C NMR spectroscopic features and mass spectro-
metric data, 3 constitutes a coupling product that contains
two different Ge(II) subunits as distinct N-heterocyclic li-
gands. The most notable resonances in the 1H NMR spectrum
of 3 recorded in d8-THF are two doublets in the aromatic
proton region at δ = 7.06 and 6.69 ppm with 4JHH = 2.8 Hz.
Results and Discussion
Bis(pentafluorophenyl)amine reacts readily with 1 in hex-
ane at room temperature, affording the expected 1,4-addition
product 2 (Scheme 2). As reported earlier, similar reactions
have been observed for 1 employing different substrates.6b,7,8
Compound 2 has been isolated as yellow crystals in 91% yield
and has been fully characterized by spectroscopic means (see
below).
The molecular structure of 2 obtained from a single-crystal
X-ray diffraction analysis (Figure 1) revealed, as expected,
that the three-coordinate Ge atom adopts a pseudo-tetra-
€
(8) (a) Yao, S.; van Wullen, C.; Driess, M. Chem. Commun. 2008,
5393. (b) Jana, A.; Objartel, I.; Roesky, H. W.; Stalke, D. Inorg. Chem. 2009,
48, 7645. (c) Jana, A.; Schulzke, C.; Roesky, H. W. J. Am. Chem. Soc. 2009,
131, 4600.

Article
Organometallics, Vol. 29, No. 21, 2010 5355
Figure 2. (a) Molecular structure of 3. Thermal ellipsoids are
drawn at a 50% probability level. Hydrogen atoms are omitted
for the sake of clarity. (b) The six-membered C4NGe ring is
Figure 3. Potential energy surface for the isomerization 1 f 1b.
To compare with TS1a/1b, the energy of NH3 was added to 1,
TS1/1a, 1a, and 1b. [Relative energies (with zero-point energy
corrections) are given in kcal mol-1 and the bond distances
˚
disordered over two orientations. Selected bond lengths [A] and
angles [deg]: Ge1-N3 1.959(3), Ge1-N1 2.038(3), Ge1-N2
2.073(3), Ge2-C30 1.869(5), Ge2-N4 1.919(9), N1-C2
1.343(4), N2-C4 1.310(4), N2-C12 1.456(4), N3-C31
1.405(5), N4-C33 1.334(9), C2-C3 1.381(5), C3-C4 1.398(5),
C30-C31 1.397(6), C31-C32 1.407(6), C32-C33 1.380(7),
N3-Ge1-N1 105.1(1), N3-Ge1-N2 105.4(1), N1-Ge1-N2
88.7(1), C30-Ge2-N4 95.6(3), C31-C30-Ge2 126.5(4),
C30-C31-C32 122.5(4), C(30)-C(31)-N(3) 124.2(5), C(31)-
N(3)-Ge(1) 137.6(3).
˚
in A.]
Scheme 3. Proposed DFT-Based Mechanism for the Isomeriza-
tion of 1, via 1a and 1b, and Its Coupling (1,4-Addition) with
1 to Give 3
The latter could be unambiguously assigned to a R-CH and its
adjacent γ-CH proton in 3, respectively, indicating the pre-
sence of an heteroaromatic six π-electron system (see below).
However, the structure of 3 could be unequivocally deter-
mined only by a single-crystal X-ray diffraction analysis
(Figure 2). Compound 3 crystallizes in the triclinic space
group P1 and consists of two six-membered N-heterocyclic
germylenes connected by an N(aryl) group. While one of the
germylene subunits in 3 represents a complex of type A with a
six-membered C3N2Ge ring and a three-coordinate Ge(II)
site, the other one corresponds to a unique azagermabenzen-
1-ylidene heterocycle that contains a six-membered C4NGe
ring bearing a two-coordinate Ge(II) center. The six-membered
C3N2Ge ring in 3 is slightly puckered, and the geometric
parameters are quite similar to those of related complexes of
type A, including an N(H)aryl-substituted (aryl = 2,6-iPr2-
C6H3) derivative,5 which resulted as a side product from the
reduction of the corresponding chloro Ge(II) complex6a with
elemental potassium. However, the Ge1-N3 bond length
˚
distance of 1.919(9) A lies very close to those Ge-N bonds
(1.894(2) A) found in cation B as reported by Power and co-
˚
workers.4 Accordingly and in line with NMR data, this
suggests aromatic character for the novel C4NGe ring system
resulting from a planar (Huckel-like) heteroaromatic six π-
€
electron delocalization. This notion is supported by density
functional theory (DFT) calculations, which reproduced
well the geometric parameters of 3. In fact, the calculated
negative NICS values for 3 (NICS(0) = -1.6 ppm, NICS(1)
= -3.9 ppm) clearly indicate significant aromatic stabilization
in the C4NGe ring. In contrast, no aromatic stabilization is
predicted for the C3N2Ge ring, as shown by the computed
positive NICS values (NICS(0) = 3.5 ppm, NICS(1) = 2.3
ppm), owing to the presence of three-coordinate Ge(II) in the
type A germylene subunit. Compound 3 represents a unique
bis(germylene) bearing the first heteroleptic, two-coordinate
Ge(II) center in a six-membered C4NGe ring system with only
one adjacent nitrogen donor atom and stabilized additionally
by six π-electron delocalization.
˚
(1.959(3) A) in 3 is slightly longer than that in the N(H)aryl
˚
derivative mentioned above (1.906(2) A), owing to the larger
steric congestion of 3. The most noteworthy structural
feature of 3 concerns the planar six-membered C4NGe ring
derived from a rearangement of the β-diketiminate-like
ligand in precursor 1. The C4NGe ring is orthogonally
positioned to the C3N2Ge ring and disordered over two
orientations in a population ratio of 0.74:0.26 (Figure 2b);
only the major form is shown in Figure 2a. Interestingly, the
C-C distances within the C4NGe ring are similar to one
˚
another (1.397(6), 1.407(6), and 1.380(7) A), thus suggesting
the presence of strongly delocalized π-bonds. In addition, the
˚
Ge2-C30 distance of 1.869(5) A is significantly shorter than
In order to rationalize the formation of 3, which obviously
occurs via isomerization of 1 in the presence of HN(SiMe3)2
that of a normal Ge-C single-bond length, and the Ge2-N4

5356 Organometallics, Vol. 29, No. 21, 2010
Yao et al.
4
and its subsequent coupling with another molecule of 1, DFT
calculations have been performed. The proposed mechanism
involving the reactive intermediates 1a and 1b and part of the
calculated potential energy surface are shown in Scheme 3
and Figure 3, respectively. The isomerization is initiated by a
nucleophilic attack of the methylene subunit in resonance
structure 10 to the Ge(II) center and the concomitant forma-
tion of an excocyclic imine group to give the intermediate 1a.
The barrier for the isomerization step 1 f 1a was calcu-
lated to 29.4 kcal mol-1, thus indicating a slow but yet achie-
vable process at room temperature. 1a is ca. 9.4 kcal mol-1
higher in energy than 1 due to sacrificing one of the stabiliz-
ing N-Ge interactions. However, transient 1a can undergo
an imine-enamine tautomerization by transferring a proton
from C1 to N1 to give 1b; the latter gains extra stabilization
through six π-electron delocalization. Such a proton-transfer
process can be accelerated in the presence of a suitable base.
With NH3, acting as an external model to mimic HN(SiMe3)2,
7.06 (d, JHH = 2.8 Hz, 1 H, R-CH), 6.89 - 7.32 (m, 12 H,
2,6-iPr2C6H3). 13C{1H}NMR (100.61 MHz, D8-THF, 298 K): δ
24.1, 26.0, 26.2, 27.2, 28.3, 28.7, 29.7, 30.4 (iPr, NCMe); 97.3, 110.1
(γ-C); 152.1 (R-C); 124.2 - 153.8 (2,6-iPr2C6H3); 160.7, 170.3
(NCMe). Anal. (%) Calcd for C58H82N4Ge2: C 71.20; H 8.24; N
5.73. Found: C 70.97; H 8.27; N 5.37. EI-MS: m/z (%) 978 (0.5,
[M]þ), 490 (33, [1/2M]þ), 475 (100, [1/2M - Me]þ).
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 2 and 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-979 soft-
ware package. The positions of the H atoms were calculated and
considered isotropically according to a riding model.
˚
˚
2: triclinic, space group P1, a= 10.8593(3) A, b= 13.1638(4) A,
˚
c = 14.4489(3) A, R = 92.576(2)°, β = 101.490(2)°, γ =
102.174(2)°, V = 1970.39(9) A , Z = 2, Fcalc = 1.413 Mg/m3,
3
˚
μ(Mo KR) = 0.858 mm-1, 16 016 collected reflections, 6886
crystallographically independent reflections [Rint = 0.0142],
6064 reflections with I > 2σ(l), θmax = 25°, R(Fo) = 0.0264
the relative energy of TS1a/1b amounts to 28.8 kcal mol-1
,
2
which is slightly lower than that of TS1/1a. The N1 atom of
the NH(aryl) moiety in 1b is sterically less congested than that
of HN(SiMe3)2 and thus easily accessible for a 1,4-addition to
1 to give the bis(germylene) 3.
(I > 2σ(l)), wR(Fo ) = 0.0716 (all data), 506 refined parameters.
˚
3: triclinic, space group P1, a = 11.403(3) A, b = 14.520(2) A,
˚
˚
c = 18.793(3) A, R = 78.926(12)°, β = 82.882(17)°, γ =
78.326(16)°, V = 2978.7(10) A , Z = 2, Fcalc = 1.187 Mg/m3,
3
˚
μ(Mo KR) = 1.050 mm-1, 23 925 collected reflections, 10 182
crystallographically independent reflections [Rint = 0.0489],
5230 reflections with I > 2σ(l), θmax = 25°, R(Fo) = 0.0455
Experimental Section
2
(I > 2σ(l)), wR(Fo ) = 0.0938 (all data), 787 refined parameters.
General Considerations. All experiments were carried out
under dry, oxygen-free dinitrogen using standard Schlenk tech-
niques or in an MBraun inert atmosphere drybox containing an
atmosphere of purified nitrogen. Solvents were dried by standard
methods and freshly distilled prior to use. The starting material
LGe was prepared according to literature procedures.7 1H, 13C,
and 19F NMR spectra were recorded with the Bruker spectro-
meters ARX 200 and AV 400, respectively. EI-MS spectra were
taken on a Finnigan-MAT 955 instrument. Elemental analyses
were performed on a FlashEA 1112 CHNS analyzer.
Computational Details
All calculations were performed at the B3LYP level of
theory10 as implemented in the Gaussian03 program package.11
The geometry of compound 2 was optimized with the basis sets
BSI (def2-TZVP for Ge, N, and the C atoms at the two core rings
C4GeN, C3GeN2,12 and with 6-31G for the other atoms). The
NICS values were calculated by the GIAO method with the
Ahlrichs basis set BSII, with VTZ for all the elements.13 The ring
centers were defined by a nonweighted mean of the atom co-
ordinates. The ring plane is defined as the plane through the ring
center for which the sum of the squares of the distance of that
plane to the positions of the atoms forming the ring is minimal.
The positions of the NICS centers are aligned through the ring
center and are orthogonal to the ring plane. All relevant oordi-
nates can be found in the Supporting Information.
Syntheses. Compound 2. A solution of HN(C6F5)2 (0.29 g,
0.81 mmol) inhexane (10mL) was added toa solutionof1 (0.40 g,
0.81 mmol) in hexane (15 mL) at room temperature. The brown-
red color of the reaction mixture changed to yellow immediately.
After concentration and cooling to -20 °C for 24 h, compound 2
crystallized from the solution as yellow crystals (0.62 g, 0.74
mmol, 91%). Mp: 191 °C (dec). 1H NMR (200.13 MHz, C6D6,
298 K): δ 1.06 (d, 3JHH = 7 Hz, 6 H, CHMe2), 1.12 (d, 3JHH
=
7 Hz, 6 H, CHMe2), 1.13 (d, 3JHH = 7 Hz, 6 H, CHMe2), 1.23 (d,
3JHH = 7 Hz, 6 H, CHMe2), 1.52 (s, 6 H, CMe), 3.03 (sept., 2 H,
3JHH = 7 Hz, CHMe2), 3.37 (sept., 2H, 3JHH = 7 Hz, CHMe2),
5.01 (s, 1 H, γ-CH), 7.02-7.20 (m, br, 6 H, aroma-H). 13C{1H}
NMR (50.61 MHz, C6D6, 298 K): δ 24.4, 24.7, 24.8, 25.7, 28.3,
29.3 (iPr, NCMe), 101.7 (γ-C), 125.0-146.2 (2,6-iPr2C6H3,
C6F5), 167.8 (NCMe). 19F{1H} NMR (188.31 MHz, C6D6, 298
K): δ -146 (br), -149 (br), -165.5 (br). Anal. (%) calcd for
C41H41N3GeF10: C 58.74; H 4.93; N 5.01. Found: C 59.31; H
5.05; N 4.96. EI-MS: m/z (%) 491 (15, [M - N(C6F5)2]þ), 475(73,
[M - N(C6F5)2 - Me]þ), 349 (100, [N(C6F5)2]þ).
To study the isomerization 1 f 1a f 1b, the two-layer ONIOM-
(B3LYP/BSIII: B3LYP/3-21G) approach was employed.14 As
shown in Figure 3, the higher layer consists of the core ring and
was calculated with basis sets BSIII (6-311Gþ(d,p) for N and
6-311Gþ(d,p) for other elements). The lower layer consists of the
(9) Sheldrick, G. M. SHELX-97, Program for Crystal Structure
€
€
Determination; Universitat Gottingen: Germany, 1997.
(10) (a) Lee, C.; Yang, W.; Parr, R. G Phys. Rev. B: Condens. Matter
1988, 37, 785. (b) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(11) Frisch, M. J.; et al. et al. Gaussian, Inc.: Wallingford, CT, 2004.
(12) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7,
3297.
(13) Schafer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97,
2571.
Compound 3. To a solution of 1 (0.47 g, 0.96 mmol) in hexane
(20 mL) was added HN(SiMe3)2 (12 mol %) at room temperature.
During the course of 3 weeks yellow crystals of compound 3 were
1
formed (0.23 g, 0.23 mmol, 48%). Mp: 181 °C (dec). H NMR
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(200.13 MHz, D8-THF, 298 K): δ 0.10 (d, JHH = 7 Hz, 6 H,
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=
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1.25 (d, 3JHH = 7 Hz, 6 H, CHMe2), 1.31 (d, 3JHH = 7 Hz, 6 H,
CHMe2),1.75(s,6H,CMe),2.18(s,3H,CMe),2.53(sept.,3JHH
=
7 Hz, 2 H, CHMe2), 2.30 (sept., 3JHH = 7 Hz, 2 H, CHMe2), 3.39
(sept., 3JHH = 7 Hz, 2 H, CHMe2), 3.59 (sept., 3JHH = 7 Hz, 2 H,
CHMe2), 5.27 (s, 1 H, γ-CH), 6.69 (d, 4JHH = 2.8 Hz, 1 H, γ-CH),
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Article
Organometallics, Vol. 29, No. 21, 2010 5357
two substituents (2,6-iPr2C6H3-), as calculated with the 3-21G
basis sets. The quality of the two-layer scheme was tested with the
S-value,14g,15 and we obtained for 1, TS1/1a, 1a, TS1a/1b, and 1b
the following data: -5.2879, -5.2815, -5.2826, -5.2817, and
-5.2898 hartree, indicating that the two-layer ONIOM setup is
reasonable. Frequency calculations were carried out for all opti-
mized structures with the same method to verify the nature of the
stationary points on the potential-energy surfaces and to obtain the
zero-point energy corrections.
Acknowledgment. Financial support from the Deutsche
Forschungsgemeinschaft (DR 226/17-1) and the Fonds
der ChemischenIndustrie isgratefully acknowledged. X.Z.
is grateful to the Alexander von Humboldt-Stiftung for a
postdoctoral fellowship. We thank Burkhard Butschke for
support in the NICS calculations.
Supporting Information Available: Crystallographic data for
2 and 3 (CIF); details of NICS calculations and coordinates of
optimized structure. This material is available free of charge via
the Internet at http://pubs.acs.org.
(15) Morokuma, K.; Musaev, D. G.; Vreven, T.; Basch, H.; Torrent,
M.; Khoroshun, D. V. IBM J. Res. Dev. 2001, 45, 367.