Mechanistic study of stepwise methylisocyanide coupling and C-H activation mediated by a low-valent main group molecule

Article abstract of DOI:10.1021/ja4003553

An experimental and DFT investigation of the mechanism of the coupling of methylisocyanide and C-H activation mediated by the germylene (germanediyl) Ge(Ar^Me6)₂ (Ar^Me6 = C₆H ₃-2,6(C₆H₂-2,4,6-Me₃)₂) showed that it proceeded by initial MeNC adduct formation followed by an isomerization involving the migratory insertion of the MeNC carbon into the Ge-C ligand bond. Addition of excess MeNC led to sequential insertions of two further MeNC molecules into the Ge-C bond. The insertion of the third MeNC leads to methylisocyanide methyl group C-H activation to afford an azagermacyclopentadienyl species. The X-ray crystal structures of the 1:1 (Ar^Me6)₂GeCNMe adduct, the first and final insertion products (Ar^Me6)GeC(NMe)Ar^Me6 and (Ar^Me6) GeC(NHMe)C(NMe)C(Ar^Me6)NMe were obtained. The DFT calculations on the reaction pathways represent the first detailed mechanistic study of isocyanide oligomerization by a p-block element species.

Full text of DOI:10.1021/ja4003553

Article
pubs.acs.org/JACS
Mechanistic Study of Stepwise Methylisocyanide Coupling and C−H
Activation Mediated by a Low-Valent Main Group Molecule
Zachary D. Brown,† Petra Vasko,‡ Jeremy D. Erickson,† James C. Fettinger,† Heikki M. Tuononen,*,‡
and Philip P. Power*,†
†Department of Chemistry, University of California, 1 Shields Avenue, Davis, California 95616, United States
‡Department of Chemistry, University of Jyvaskyla, P.O. Box 35, FI-40014 Jyvaskyla, Finland
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: An experimental and DFT investigation of the mechanism of the
coupling of methylisocyanide and C−H activation mediated by the germylene
Me6
(germanediyl) Ge(ArMe )2 (Ar
= C6H3-2,6(C6H2-2,4,6-Me3)2) showed that it
6
proceeded by initial MeNC adduct formation followed by an isomerization
involving the migratory insertion of the MeNC carbon into the Ge−C ligand bond.
Addition of excess MeNC led to sequential insertions of two further MeNC
molecules into the Ge−C bond. The insertion of the third MeNC leads to
methylisocyanide methyl group C−H activation to afford an azagermacyclopenta-
dienyl species. The X-ray crystal structures of the 1:1 (ArMe )2GeCNMe adduct, the first and final insertion products
6
Me6
Me6
Me6
(ArMe )GeC(NMe)Ar and (Ar )GeC(NHMe)C(NMe)C(Ar )NMe were obtained. The DFT calculations on the reaction
6
pathways represent the first detailed mechanistic study of isocyanide oligomerization by a p-block element species.
Scheme 1. Transition-Metal Mediated Coupling of
Isocyanides
INTRODUCTION
■
The metal-mediated coupling and polymerization of unsaturated
organic molecules are important industrial processes, and the
polymers obtained are of great practical importance.1−4 In
particular, the synthesis of heterocycles resulting from coupling
and cycloaddition reactions of isocyanides with other hetero-
element unsaturated species is a widely used technique.5
Groundbreaking work by Passerini6 and Ugi7−9 led to a dramatic
expansion of the study of cyanide and isocyanide coupling
chemistry, most notably their metal catalyzed oligomerization
and polymerization reactions.10−12 However, knowledge of their
mechanistic details remains limited. Some of the earliest coupling
reactions were shown to be mediated by Grignard reagents13 and
other main group metal halides,14,15 but most of the work on the
mechanism of catalytic coupling of isocyanides has involved
transition-metal complexes either of the group 10 noble metals
or various first row transition-metal complexes.16,17
Yamamoto and co-workers first recognized that cobalt and
nickel complexes displayed high catalytic activity toward
isocyanides.16 Nolte and Drenth examined the mechanism of
the coupling reactions and concluded that the Lewis-acidic
character of the metal center is essential to the propagation of
polymerization (Scheme 1).17 The expansion of the catalytic
work to the main group elements was first realized for the electro-
positive metals of groups 1 and 2.18−20 Isocyanide coordination
to alkali metal cations, followed by nucleophilic attack of alkyl or
amido groups, was reported by Walborsky and Lappert to form
lithioaldimine18 and β-diketiminate19,20 complexes respectively.
Subsequent coupling and migratory insertion reactions of iso-
cyanides into metal−ligand and metal−metal bonds of main
group complexes have been reported, but mechanistic
information on these reactions is scarce.21−26
Recently, we reported the synthesis of the adduct (ArMe6)2GeCNBut,
which underwent isobutene elimination under mild conditions
to give the hydride/cyanide (ArMe6)2Ge(H)CN.27 We now
report the isolation and structural characterization of a series of
compounds arising from the insertion reactions of the simplest
isocyanide, MeNC, with the germylene Ge(ArMe )2 (Ar
=
Me6
6
C6H3-2,6(C6H2-2,4,6-Me3)2)28 and supply details of the mechanism
of the subsequent transformation. We show that the simple adduct
(ArMe )2GeCNMe (1)isformedinthefirst instance, whereupon the
6
coordinated methylisocyanide molecule in 1 then undergoes a
spontaneous migratory insertion into one of the Ge−C(Ar) bonds
to form the structural isomer (ArMe )Ge(μ-CNMe)(Ar ) (1′).
Me6
6
Received: January 31, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/ja4003553 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
obtained due to the low solubility of 1′. λmax (ε): 377 nm. IR (ATR) ν(C−
Scheme 2. Formation of 3″ via Migratory Insertion of
N): 1710 cm−1 (m).
Methylisocyanide
Me6
(ArMe )GeC(NHMe)C(NMe)C(Ar )NMe (3″). To a stirred slurry of
6
Ge(ArMe )2 (0.35 g, 0.5 mmol) in hexane (20 mL) methylisocyanide
6
(5 mmol) was added at room temperature. The purple color of the
solution became yellow, and the reaction mixture was allowed to stir at
room temperature for 2 days, whereupon the color of the solution
changed to deep red. All of the volatile components were removed under
reduced pressure, and the reddish oil was extracted with ∼20 mL
pentane and filtered via a filter tip cannula. Free Ge(ArMe
) was
2
6
separated from the product by overnight storage of the dilute pentane
solution at ca. −18 °C. The mother liquor was decanted from the solids,
and the volume of the solution was reduced by half. Storage at ca. −18 °C
overnight yielded deep red crystals of 3″. Yield: 23% (0.09 g). Mp: 158 °C
If the germylene is treated with excess isocyanide, two additional
molecules of methylisocyanide are incorporated into 1′ to form
(dec). 1H NMR (400 MHz, C6D6, 25 °C): δ 1.98 (3H, s, CNMe or ArMe ),
6
2.07 (3H, s, CNMe or ArMe ), 2.08 (6H, s, o-Me), 2.10, 2.11, 2.13, 2.21,
6
2.26, 2.34 (all s, 3H, CNMe or ArMe ), 4.56 (1H, q, N−H), 6.24 (1H, d,
6
Me6
(ArMe )GeC(NHMe)C(NCH2)C(Ar )NMe, (3″) (Scheme 2)
6
JHH = 7.5 Hz, m-C6H3), 6.59 (2H, br, m-Mes) 6.76 (2H, br, m-Mes), 6.79
(2H, br, m-Mes), 6.88 (2H, d, JHH = 7.5 Hz, m-C6H3) 6.96 (1H, dd,
p-C6H3), 6.98 (2H, d, JHH = 7.5 Hz, m-C6H3), 7.02 (1H, dd, p-C6H3),
7.16 (2H, m, NCH2). 13C NMR spectrum could not be obtained due to
the low solubility of 3″. λmax (ε): 343 nm, 421 nm. IR (ATR) ν(CC)
639 cm−1 (br), ν(CN) 1729 cm−1 (br).
via a two-fold insertion intermediate. The isolation of intermediates
1, 1′, andthefinal product 3″ coupled with a detailed computational
study of the mechanism by density functional theory (DFT) provide
new insights on the migratory insertion and oligomerization
reactions of isocyanides with main group complexes.
(ArMe )2SnCNMe. Methylisocyanide (5 mmol) was added via a syringe
6
to a stirred solution of Sn(ArMe )2 (0. 37 g, 0.5 mmol) in ∼20 mL of a 1:1
6
EXPERIMENTAL SECTION
■
pentane toluene mixture. The reaction mixture was allowed to stand at
ca. −78 °C for 2 weeks, after which time a yellow power precipitated
from the purple solution. The solid was maintained at ca. −78 °C via
cooling in a dry ice/acetone bath, while the mother liquor was decanted
off and an FTIR spectrum could quickly be obtained before complete
General Experimental Procedures. All manipulations were
carried out by using Schlenk techniques under an atmosphere of N2.
All solvents were distilled from NaK and degassed prior to use.
Ge(ArMe
) ) were prepared according to literature
and Sn(ArMe
6
6
2
2
procedures.28 Methylisocyanide was prepared by literature methods and
stored as a 1 M solution in hexane.29 1H NMR spectra were obtained on
Varian Inova 400 and 600 MHz spectrometers and referenced to the
residual protons in the solvent. Melting points were measured in glass
capillaries sealed under N2 by using a Mel-Temp II apparatus and are
uncorrected. Infrared spectra were recorded using attenuated total
reflectance (ATR) on a Bruker Tensor-27 infrared spectrometer.
Variable temperature UV−vis data were recorded on a Cary 300 Scan
spectrometer attached to a Cary Temperature Controller.
dissociation of MeNC and conversion of the yellow powder to a purple
1
solid, which was confirmed to be Sn(ArMe )2 by H NMR spectroscopy;
6
decomp.: ca. −50 °C (free CNMe and Sn(ArMe )2). IR (ATR): ν(C−N)
6
2197 cm−1.
X-ray Crystallographic Data Collection. Crystals of 1, 1′, and 3″
suitable for single crystal X-ray diffractometry were removed from a
Schlenk flask under a stream of N2 and immediately covered with a layer
of hydrocarbon oil. A single crystal was selected, attached to a glass fiber
on a copper pin, and placed in the cold N2 stream of the diffractometer.
Data were collected based upon a single component, processed with
SAINT,30 and corrected for Lorentz and polarization effects and
absorption using Blessing’s method as incorporated into the program
SADABS.31 The structures were determined by direct methods using
the program XS.32 Refinement of the structure was achieved using the
program XL.32 All of the nonhydrogen atoms were located initially or
from one difference-Fourier map least-squares cycle, and convergence
proceeded quickly with all of the hydrogen atoms located from a
subsequent difference-Fourier map. See SI for more details.
(ArMe )2GeCNMe (1). Method A: Methylisocyanide (1.5 mmol) was
6
added to a stirred slurry of Ge(ArMe )2 (0.35 g, 0.5 mmol) in hexane
6
(15 mL) at room temperature. The solution was allowed to stir until all
the solids had dissolved and the purple color of the solution had faded to
a homogeneous yellow (∼15 min). The reaction mixture was stored
overnight at ∼7 °C to yield yellow crystals of 1 suitable for X-ray
diffraction studies. If allowed to stand at ∼7 °C for more than 3 days, the
color of the solution changed to deep red to yield mixtures of 1 and 3″.
Method B: Methylisocyanide (2 mmol) was added to a stirred slurry of
Ge(ArMe )2 (0.35 g, 0.5 mmol) in pentane (30 mL) at room temperature.
6
The colorofthesolutionbecameyellow immediately. All volatile materials
were immediately removed to afford 1 as a yellow powder in quantitative
yield. Method A yield: 60% (0.22 g). Mp: 186 °C (red oil). Due to high
fluxionality, 1H and 13C NMR spectra could not be obtained even with
cooling to −50 °C. λmax (ε): 297 nm. IR (ATR) ν(C−N): 2161 cm−1 (m).
Details of DFT Calculations. All calculations were done with
Turbomole v6.3 program.33 The geometries of studied systems were
optimized with DFT using the hybrid PBE1PBE exchange−correlation
functional34 in combination with the TZVP basis sets.35 Due to the size
of terphenyl ligands in experimental compounds, calculations were
performed for model systems with smaller phenyl substituents. All
reported energy values represent reaction enthalpies at 0 K.
In addition to the mechanism discussed in the main text, a number of
other pathways were investigated via the calculations. For example,
addition of the second equivalent of isocyanide to the germanium prior
to phenyl migration resulted in Ge−C bond breaking and simple
shuffling of the coordinated isocyanides. If, on the other hand, the
second equivalent of methylisocyanide was reacted directly with the
carbon in the coordinated isocyanide, coupling of the two isocyanides to
a free diamine was observed. Similarly, an attack of the third equivalent
of a methylisocyanide to a carbon atom in the azagermacyclobutene
intermediate led to a C−C bond formation and to a structure with a
three-membered CNN ring with no apparent further reactivity. The
possibility of hydrogen transfer occurring before the formation of 3′Ph
was also tested computationally, but it resulted only in a formation of a
five-membered ring with no apparent further reactivity. Hence, the
(ArMe )Ge(CNMe)(Ar ) (1′). To a stirred slurry of Ge(Ar )2 (0.35 g,
0.5 mmol) in hexane (20 mL) methylisocyanide (0.75 mmol) was added
at room temperature. The purple color of the solution became yellow, and
the reaction mixture was allowed to stir at room temperature overnight,
whereupon the color of the solution changed to deep red. All of the
volatiles were removed under reduced pressure, and the reddish oil was
extracted with ∼20 mL pentane and filtered via a filter tip cannula. Free
Me6
Me6
6
Ge(ArMe )2 and complex 1 were separated from the product by overnight
6
storage of the dilute pentane solution at ca. −18 °C. The mother liquor
was decanted from the solids and the volume of the solution was reduced
by half and stored at ca. −18 °C overnight to yield deep-red crystals of 1′.
Yield: 29% (0.11 g). Mp: 186 °C (red oil). 1H NMR (600 MHz, C6D6,
25 °C): δ 1.85 (3H, br, p-Me), 1.89 (3H, s, N-Me), 2.21 (6H, s, o-Me),
2.31 (6H, br, o-Me), 2.37 (3H, s, p-Me), 6.58 (1H, br, m-Mes), 6.77 (1H,
s, m-Mes), 6.82 (4H, d, JHH = 7.5 Hz, m-C6H3), 7.02 (1H, t, JHH = 7.5 Hz,
p-C6H3), 7.11 (1H, t, JHH = 7.5 Hz, p-C6H3). 13C NMR could not be
B
dx.doi.org/10.1021/ja4003553 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
mechanism discussed in the main text was the only plausible reac-
tion pathway connecting 1 to 3″Ph which could be identified
computationally.
proportional to the M−C bond strength but that the back-
bonding interaction in complex 1 plays a large role in the strength
of the dative bond.37
To suppress the subsequent isocyanide insertions which lead
to the formation of 3″, only 1.5 equiv of MeNC was added to a
solution of the germylene to produce the one-fold insertion
product, 1′. X-ray quality red crystals of 1′ (structure, Figure 1)
had a Ge(1)−C(1) bond length of 2.046(4) Å, which is very
RESULTS AND DISCUSSION
■
Treatment of a purple solution of Ge(ArMe )2 with an excess of
6
MeNC immediately yielded a bright yellow solution, indicative of
theformation of the adduct species, 1. Storage of this solution atca.
−18 °C yielded X-ray quality yellow crystals of the germylene−
isocyanide adduct (see Figure 1 for structural details). The bond
close to that in Ge(ArMe )2 (cf. 2.033(4) Å). The Ge(1)−C(49)
6
bond length of 2.022(5) Å is also very similar to that of the Ge−
C(1) bond. The C(1)−Ge(1)−C(49) bond angle of 107.4(2) °
is less than that (114.4(2)°) in Ge(ArMe )2.28 The C(49)−N(49)
6
bond length of 1.271(5) Å in the isocyanide indicates the
conversion of the triple bond to a double bond, and the lowering
of the bond order is confirmed by a decrease in the C−N stretching
frequency to 1710 cm−1 in comparison to the 2165 cm−1 in 1.
Additionally, the nitrogen lone pair is now datively bound to the
germanium through the p-orbital of the germylene. The Ge(1)−
N(49) distance (2.104(4) Å) is long,38 and the dative bond creates
an acute Ge(1)−C(49)−N(49) angle of 75.6(3) ° at C(49). These
two factors, coupled with a broadened 1H NMR spectrum for 1′ are
indicative of a relatively weak Ge−N bond that is dissociating in
solution. Overall, the structural and spectroscopic data do not
strongly support a side-on, π-bonded model for the CN double
bond of the ArMes6CNMe unit with Ge(1).
In order to understand the initial migratory insertion of MeNC
into the Ge(1)−C(Ar) bond, we examined the possible reaction
pathway (Scheme 3) for the formation of 3″ by use of DFT (see
Supporting Information, SI) and via the isolation of the
intermediates 1 and 1′ and the product 3″. The model complex,
Ge(C6H5)2, was used to study the reaction pathway computa-
tionally. Although the replacement of bulky terphenyl groups
with the significantly smaller phenyls will certainly have some
effect on the calculated energies, it is unlikely to have a major
effect on the mechanism, especially in view of the relatively small
size of CNMe. The formation of the model adduct species 1Ph
was found to be more stable than the free starting materials. A
transition state (TS-1Ph) was found for the formation of 1′Ph
which involves the concerted migration of the isocyanide
molecule into the Ge−C(Ph) bond. We hypothesize that the
insertion reaction depends on having a highly activated,
electron-rich germanium atom, and removal of this electron
density is accomplished by either dissociating to the free
starting materials or migratory insertion of the isocyanide
molecule. The activation energy for this process is predicted
to be less than the energy gained from the dative bond
formation, and the coordination number at the germanium
is maintained through a weak dative interaction with the
β-nitrogen of the imino moiety.
As mentioned earlier, the N−Ge dative bond in 1′ is relatively
weak, and in the presence of excess isocyanide, it is readily broken
and is replaced by a second isocyanide molecule which possesses
a greater electron-donating capability than the imino-nitrogen.
The second adduct species, 2Ph, undergoes a further migratory
insertion process (TS-2Ph) in a manner similar to the first
insertion, yielding an azagermacyclobutene complex 2′Ph which,
like 1′Ph, possesses a dative interaction between the γ-nitrogen
and germanium. As before, formation of an isocyanide adduct
complex of 2′Ph is energetically favored and is rapidly followed by
a third migration of MeNC to yield the heterocyclic complex
3′Ph. The C−H bond activated complex, 3″Ph, is predicted
to be more stable than 3′Ph by 49 kJ mol−1 and adopts
a cyclopentadienyl-type structure after hydrogen transfer.
Figure 1. Thermal ellipsoid (30%) drawing of 1 (left) and 1′ (right).
Carbon-bound hydrogen atoms and a cocrystallized hexane molecule
(in 1′) are not shown for clarity. Selected bond lengths (Å) and angles
(°) 1: Ge(1)−C(1) 2.057(3), Ge(1)−C(25) 2.060(3), Ge(1)−C(49)
2.028(4), C(49)−N(49) 1.164(5), N(49)−C(50) 1.422(5), C(1)−
Ge(1)−C(25) 116.6(1), C(Ar)−Ge(1)−C(49) (ave) 96.4(1), Ge(1)−
C(49)−N(49) 156.6(3). 1′: Ge(1)−C(1) 2.046(4), Ge(1)−C(49)
2.021(5), Ge(1)−N(49) 2.104(4), C(49)−C(25) 1.496(4), C(49)−
N(49) 1.271(5), N(49)−C(50) 1.465(6), C(1)−Ge(1)−C(49)
107.4(2), Ge(1)−C(49)−N(49) 75.6(3), C(49)−N(49)−C(50)
128.2(4), Ge(1)−N(49)−C(50) 155.2(3), C(25)−C(49)−Ge(1)
150.4(3).
dissociation energy for 1 was found to be −20 kJ mol−1 by Van’t
Hoff analysis of the variable temperature UV−vis spectrum, and it
exists in equilibrium with free MeNC and Ge(ArMe )2. If the
6
reaction is continued overnight, the yellow solution changes to
deep red, and the three-fold insertion product, 3″, can be isolated
in moderate yield (∼25%).
Adduct formation is often an initial step in the reaction of main
group species with unsaturated molecules, and synergistic
interactions between main group species and the frontier orbitals
of the ligand propagate further reaction.36 The infrared spectrum
of 1 shows a slight shift of the C−N stretching band to higher
frequency (2165 cm−1) in comparison to the free isocyanide
(cf. 2161 cm−1), indicative of n → π* back-bonding between
the germanium(II) lone pair and the π* orbital of the isocyanide
ligand. These data are in good agreement with the spectrum
t
of (ArMe )2GeCNBu , in which the C−N stretching band is
6
5 cm−1 lower in frequency.27 In contrast, the tin congener of 1,
(ArMe )2SnCNMe, can only be isolated at low temperatures with
6
use of a 10-fold excess of MeNC and readily dissociates to
Sn(ArMe )2 and MeNC above ca. −50 °C. Although the bonding
6
between MeNC and Sn(ArMe )2 is weak, the C−N stretching
6
band in the infrared spectrum of (ArMe )2SnCNMe is shifted by
6
36 cm−1 to higher frequency. The direct comparison between
isoleptic tetrylene−isocyanide adducts does not support the view
that hypsochromic shift of the C−N stretching band is directly
C
dx.doi.org/10.1021/ja4003553 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
Scheme 3. Calculated Reaction Pathway for the formation 3″Ph
The final product 3″Ph is predicted to be favored over the tris-imino
complex 3′Ph for steric reasons. We hypothesize that there is
considerable steric strain placed on the α and β imine bonds by the
aryl ligands, and the bond reduction allows these bonds to bend
inward away from the bulky aryl ligands. Relief of this bond strain,
coupled with the energy gained by allowing the C−N bond to freely
rotate away from the germanium-bound ligands, is sufficient to
overcome the calculated activation energy of 72 kJ mol−1.
Deep-red crystals of 3″ suitable for X-ray diffraction were
isolated from a concentrated pentane solution, and the structure
is shown in Figure 2. The diene fragment comprised of N(49)−
C(49)−C(51)−C(53) is twisted 13.7(4) ° from planarity, and
the sum of angles within the five membered ring is 560.5°. The
C(51)−N(51) and C(53)−N(53) bond lengths are 1.413(3)
and 1.345(5) Å, and the contracted distance of the sp2−sp3
C(53)−N(53) bond is indicative of conjugation between the
nitrogen lone pair and the unsaturated heterocycle. The
conjugation is further supported by broadening of the 1H NMR
spectrum for the amido and alkenyl protons. The C(49)−N(49)
bond (1.333(3) Å) maintains its imido character, and the Ge(1)−
N(49) (1.968(2)) is short for germanium bound dative bonds
(cf. 2.104(4) Å in 1′). We attribute the increased strength of the
germanium−nitrogen dative bond toa decreasein the steric bulk at
the germanium atom as well as ability for the γ isocyanide fragment
to freely coordinate without causing undue bond strain as in 1′.
Migratory insertion reactions have been reported by our group for
the reaction of CO with germylenes, although no CO adduct
analogues of 1′ could be isolated.39 Driess and co-workers have
also reported coupling reactions for isocyanides with silylenes
Figure 2. Thermal ellipsoid (30%) drawing of 3″. Carbon-bound
hydrogen atoms of the m-terphenyl ligands are not shown for clarity.
Selected bond lengths (Å) and angles (°): Ge(1)−C(1) 2.036(3),
Ge(1)−C(53) 1.992(3), Ge(1)−N(49) 1.968(2), C(49)−N(49)
1.333(3), N(49)−C(50) 1.455(3), C(25)−C(49) 1.510(3), C(49)−
C(51) 1.423(4), C(51)−N(51) 1.413(3), N(51)−C(52) 1.265(4),
C(51)−C(53) 1.401(4), C(53)−N(53) 1.345(4), N(53)−C(54)
1.460(4), C(1)−Ge(1)−C(53) 107.9(1), C(1)−Ge(1)−N(49)
108.5(1), Ge(1)−N(49)−C(49) 111.4(2), Ge(1)−C(53)−C(51)-
110.2(2), C(51)−N(51)−C(52) 120.1(3), C(49)−N(49)−C(50)
123.8(2).
stabilized by β-diketiminate ligands, but at present, no mechanistic
information is available for these reactions.40
D
dx.doi.org/10.1021/ja4003553 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
(23) MacMillan, S. N.; Tanski, J. M.; Waterman, R. Chem. Commun.
2007, 4172−4174.
CONCLUSION
■
In conclusion, we have prepared an azagermacyclopentadienyl
species by the three-fold insertion of methylisocyanide into the
germanium−carbon bond of a diarylgermylene. Additionally, we
have isolated key intermediates in this reaction which, along with
DFT calculations, have provided further insight for the coupling
reactions of unsaturated organic molecules with heavy carbene
analogues. Further study of coupling reactions between 1 and
other substrates is underway as well as investigations into
catalytic capabilities of the migratory insertion reactions.
(24) Porchia, M.; Ossola, F.; Rossetto, G.; Zanella, P.; Brianese, N. J.
Chem. Soc. Chem. Commun. 1987, 550−551.
(25) Uhl, W.; Schutz, U.; Hiller, W.; Heckel, M. Chem. Ber. 1994, 127,
̈
1587−1592.
(26) Uhl, W.; Hahn, I.; Schutz, U.; Pohl, S.; Saak, W.; Martens, J.;
̈
Manikowski, J. Chem. Ber. 1996, 129, 897−901.
(27) Brown, Z. D.; Vasko, P.; Fettinger, J. C.; Tuononen, H. M.; Power,
P. P. J. Am. Chem. Soc. 2012, 134, 4045−4048.
(28) Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P.
Organometallics. 1997, 16, 1920−1925.
(29) Schuster, R. E.; Scott, J. E.; Casanova, J. Organic Syntheses 1973,
772−774.
ASSOCIATED CONTENT
■
S
* Supporting Information
(30) Blessing, R. H. Acta Crystallogr. 1995, A51, 33−38.
(31) Sheldrick, G. M. SADABS (Siemens Area Detector Absorption
Correction), version 2008/3; Universitat Gottingen: Gottingen,
1
Crystallographic information files for 1, 1′, and 3″; H NMR
spectra for 1′ and 3′; temperature-dependent UV−vis spectra for
1; tables of crystallographic data and collection parameters for 1,
1′, and 3″. Computational details for 1Ph, 1′Ph, 2Ph, TS-2Ph, 2′Ph,
3Ph, TS-3′Ph, and 3″Ph. This material is available free of charge via
the Internet at http://pubs.acs.org.
̈
̈
̈
Germany.
(32) Sheldrick, G. M. SHELXS97 and SHELXL97; Universitat
̈
Gottingen: Gottingen, Germany, 1997.
̈
̈
(33) TURBOMOLE, v6.3; University of Karlsruhe and Forschungszen-
trum Karlsruhe GmbH: Karlsruhe, Germany, 2011; http://www.
turbomole.com.
AUTHOR INFORMATION
Corresponding Author
pppower@ucdavis.edu; heikki.m.tuononen@jyu.fi
Notes
■
(34) (a) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996,
77, 3865−3868. (b) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev.
Lett. 1997, 78, 1396. (c) Perdew, J. P.; Ernzerhof, M.; Burke, K. J. Chem.
Phys. 1996, 105, 9982−9985. (d) Adamo, C.; Barone, V. J. Chem. Phys.
1999, 110, 6158−6170.
The authors declare no competing financial interest.
(35) Schafer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100,
̈
5829−5835.
ACKNOWLEDGMENTS
■
(36) Li, J.; Hermann, M.; Frenking, G.; Jones, C. Angew. Chem., Int. Ed.
2012, 51, 8611−8614.
We thank the U.S. Department of Energy (DE-FG02-
07ER46475), the Academy of Finland and the Technology
Industries of Finland Centennial Foundation for funding.
(37) For further discussion, see: Nakamoto, K. Infrared and Raman
Spectra of Inorganic and Coordination Compounds, 4th ed.; Wiley: New
York, 1986.
(38) cf. 1.968(2) Å in the structure of 3’’ and ge−N = 1.876(5) Å in the
Ge{N(SiMe3)2}2: Chorley, R. W.; Hitchcock, P. B.; Lappert, M. F.;
Leung, W.-P.; Power, P. P.; Olmstead, M. M. Inorg. Chim. Acta. 1992,
188-200, 203−209.
(39) Wang, X. P.; Zhu, Z. L.; Peng, Y.; Lei, H.; Fettinger, J. C.; Power,
P. P. J. Am. Chem. Soc. 2009, 131, 6912−6913.
(40) Xiong, Y.; Yao, S.; Driess, M. Chem.Eur. J. 2009, 15, 8542−
8547.
REFERENCES
■
(1) Suginome, M.; Ito, Y. Adv. Polym. Sci. 2004, 171, 77−136.
(2) Marcilly, C. J. Catal. 2003, 216, 47−62.
(3) Malpass, D. Introduction to Industrial Polyethylene; Wiley-Scrivener:
Hoboken/Salem, 2010.
(4) Millich, F. Macromol. Rev. 1980, 15, 207−253.
(5) Fruhauf, H.-W. Chem. Rev. 1997, 97, 523−596.
̈
(6) Passerini, M.; Ragni, G. Gazz. Chim. Ital. 1931, 61, 964−969.
(7) Domling, A.; Ugi, I. Angew. Chem., Int. Ed. 2000, 112, 3300−3344.
̈
(8) Ugi, I. Angew. Chem., Int. Ed. 1962, 1, 8−21.
(9) Ugi, I.; Steinbruckner, C. Chem. Ber. 1961, 94, 734−742.
̈
(10) Denmark, S. E.; Fan, Y. J. Org. Chem. 2005, 70, 9667−9676.
(11) Biggs-Houck, J. E.; Younai, A.; Shaw, J. T. Curr. Opin. Chem. Biol.
2010, 14, 371−386.
(12) Lygin, A. V.; de Meijere, A. Angew. Chem., Int. Ed. 2010, 49, 9094−
9124.
(13) Ugi, I.; Fetzer, U. Chem. Ber. 1961, 94, 2239−2243.
(14) Yamamoto, Y.; Hagihara, N. Nippon Kagaku Zasshi 1968, 89,
898−900.
(15) Stackman, R. W. J. Macromol. Sci. Chem. 1968, A2, 225−236.
(16) Yamamoto, Y.; Takizawa, T.; Hagihara, N. Nippon Kagaku Zasshi
1966, 87, 1355−1359.
(17) Kamer, P. C. J.; Nolte, R. J. M.; Drenth, W.; Nijs, H. L. L. M.;
Kanters, J. A. J. Mol. Catal. 1988, 49, 21−32.
(18) Walborsky, H. M.; Morrison, W. H.; Niznik, G. E. J. Am. Chem.
Soc. 1970, 92, 6675−6676.
(19) Hitchcock, P. B.; Lappert, M. F.; Layh, M. Angew. Chem., Int. Ed.
1999, 38, 501−504.
(20) Hitchcock, P. B.; Lappert, M. F.; Layh, M. Chem. Commun. 1998,
201−202.
(21) Li, X.; Ni, C.; Song, H.; Cui, C. Chem. Commun. 2006, 1763−
1765.
(22) Cook, K. S.; Piers, W. E.; Hayes, P. G.; Parvez, M. Organometallics
2002, 21, 2422−2425.
E
dx.doi.org/10.1021/ja4003553 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX