Intermolecular C-H insertions and cyclization reactions involving a stable germylene [4]

Full text of DOI:10.1021/ja0026408

982
J. Am. Chem. Soc. 2001, 123, 982-983
of C-H insertion may be Lewis acid-catalyzed.24 This situation
is similar to that of transition metal alkane C-H activation
chemistry prior to 1969 when many intramolecular “tuck-in”
examples of C-H activation were known, but no intermolecular
examples had yet been discovered.26
Intermolecular C-H Insertions and Cyclization
Reactions Involving a Stable Germylene
Karla A. Miller,† Thomas W. Watson,† John E. Bender, IV,‡
Mark M. Banaszak Holl,*,† and Jeff W. Kampf†
Bis[bis(trimethylsilyl)methyl]germylene (1)27 inserts into the
R-C-H bond of acetonitrile in the presence of tetrahydrofuran
(THF) and LiCl, MgCl2, or LiBr to yield [(Me3Si)2CH]2GeH-
(CH2CN) (2) quantitatively as monitored by 1H NMR spec-
troscopy (Scheme 1). The initially bright yellow solution faded
to a clear, pale yellow color as the reaction proceeded to
completion. Similar reactivity was observed for propionitrile,
phenyl acetonitrile, and succinonitrile to yield [(Me3Si)2CH]2GeH-
[CH(CH3)CN] (3), [(Me3Si)2CH]2GeH[CH(C6H5)CN] (4), and
[(Me3Si)2CH]2GeH[CH(CN)CH2CN] (5), respectively.
The UniVersity of Michigan
Ann Arbor, Michigan 48109-1055
Brown UniVersity, ProVidence, Rhode Island 02912
ReceiVed July 18, 2000
A great deal of chemical research has focused upon C-H
activation and insertion reactions in hopes of developing general
methods for introducing functionality into a variety of organic
molecules.1,2 One such area of interest has been the development
of insertion and activation chemistry for the R-C-H bonds in
organonitriles. A number of transition and lanthanide metal-based
chemistries have been previously reported.3-13 In this paper, novel
germylene-based intermolecular C-H insertions are reported for
acetonitrile, phenyl acetonitrile, propionitrile, and succinonitrile.
While exploring the generality of germylene insertion into the
R-C-H of bond nitriles, it was discovered that adiponitrile
cyclizes in a fashion reminiscent of the Thorpe-Zeigler reac-
tion.14,15 However, an unprecedented C-CN bond breaking step
leading to the formation of a Ge-CN bond also occurs.
Although germylenes are known to insert into a variety of
bonds including Si-H,16 Ge-H,17 and C-X bonds,18-22 both
C-H and C-C bonds are generally unreactive to germylenes.
To the best of our knowledge, only two cases of germylene
insertion into any type of C-H bond have been reported, both of
which were intramolecular.23-25 Jutzi demonstrated that this type
The presence of THF and specific salts was essential for the
insertion reaction. The effect of solvent and salt has been most
extensively explored for the reaction with acetonitrile. For this
substrate, no reaction occurred over a 1 week period at 20 °C
when benzene, diethyl ether, or 1,4-dioxane were used as solvents
in the absence of added salt. However, when 0.5 mol equiv of
THF was added to the reaction mixture in benzene, the reaction
slowly proceeded to ∼5% completion after 3 days at 20 °C as
1
estimated by H NMR spectroscopy. The reaction rate was also
dramatically affected by added salt. In THF solvent, the reaction
is complete within 2 and 20 min, respectively, if g0.2 equiv of
MgCl2 or LiCl are added. Upon addition of 1.0 equiv LiBr the
reaction is complete in 1 h. When the reaction was run in the
presence of Bu4NCl, side reactions occurred, and only a trace of
C-H insertion product was observed. Reactions run in THF
without added salt exhibit variable reaction rates, from 30 min
to >1 week, depending upon the batch of 1 employed. This
variability in rate is likely caused by trace MgCl2 impurities in
the starting material.
† The University of Michigan.
‡ Brown University.
Insertion products 2-5 were characterized by 1H and 13C NMR
spectroscopy, IR and mass spectroscopies. Elemental analyses
(1) Herrmann, W. A.; Cornils, B. Applied Homogeneous Catalysis with
Organometallic Compounds; VCH: Weinheim, Germany, 1996; Vol. 2.
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(3) Sto¨ckigt, D.; Sen, S.; Schwartz, H. Organometallics 1994, 13, 1465-
1469.
1
were successfully obtained for 2 and 3. For 2, the H NMR
spectrum shows two singlets at 0.11 and 0.13 ppm for the four
sets of SiMe3 protons and one doublet at -0.26 ppm (3JH-H
)
(4) Wilson, K.; Cooper, B.; Buckner, S. Rapid Commun. Mass Spectrom.
1993, 7, 844-847.
3.2 Hz) for the two CH(SiMe3)2 protons, indicating a plane of
symmetry in the germane. An A2M2X spin system was used to
simulate the Ge-H proton yielding a triplet of triplets centered
at 4.67 ppm with (3JH-H ) 2.0 and 3.2 Hz). For 3, four singlets
at 0.074, 0.12, 0.16, and 0.26 ppm for the SiMe3 group and two
resonances at -0.23 and 0.066 ppm for the two CH(SiMe3)2
groups indicate the absence of a plane of symmetry. The lack of
symmetry results in a ABM3PX spin system for the Ge-H
multiplet centered at 4.53 ppm giving a doublet of doublet of
doublets (3JH-H ) 1.0, 1.6, and 4.0 Hz). The IR spectrum of 2
shows key bands at 2027 (Ge-H) and 2230 (CtN) cm-1. For 3,
IR bands at 2019 (Ge-H) and 2220 (CtN) cm-1 are observed.
Spectroscopic details for complexes 4 and 5 follow the same
general patterns and are available with full experimental details
in the Supporting Information.
(5) Fujita, E.; Creutz, C. Inorg. Chem. 1994, 33, 1729-1730.
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6019-6020.
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1289.
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2291-2302.
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1990, 29, 420-422.
(13) Gibson, J.; Haire, R. J. Phys. Chem. A 1998, 102, 10746-10753.
(14) Schaefer, J.; Bloomfield, J. Org. React. 1967, 15, 1-203.
(15) Taylor, E.; McKillop, A. The Chemistry of Cyclic Enaminonitriles
and ortho-Amino Nitriles; Wiley: New York, 1970.
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(17) Becerra, R.; Boganov, S.; Egorov, M.; Faustov, V.; Nefedov, O.;
Walsh, R. J. Am. Chem. Soc. 1998, 120, 12657-12665.
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373, 11-19.
The ORTEP diagram derived from the X-ray crystal structure
of 2 is shown in Figure 1. The molecule sits on the 2-fold special
position in the Aba2 space group with the rotation axis going
through Ge and N1. Thus, the two -CH(SiMe3)2 groups are
crystallographically equivalent, and the -CH2CN and H moieties
are disordered. A 50% site occupancy was used to model both
the disorder of the -CH2CN group and to calculate the Ge-H
using a riding model. 2 has a roughly tetrahedral geometry with
(21) Ko¨cher, J.; Lehnig, M.; Neumann, W. Organometallics 1988, 7, 1201-
1207.
(22) Schriewer, M.; Neumann, W. J. Am. Chem. Soc. 1983, 105, 897-
901.
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C17-C20.
(24) Jutzi, P.; Schmidt, H.; Neumann, B.; Stammler, H. Organometallics
1996, 15, 741-746.
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2nd ed.; Wiley: New York, 1994.
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10.1021/ja0026408 CCC: $20.00 © 2001 American Chemical Society
Published on Web 01/11/2001

Communications to the Editor
J. Am. Chem. Soc., Vol. 123, No. 5, 2001 983
Scheme 1
a Ge-CH2CN bond length of 1.911(9) Å and CH-Ge-CH2CN
bond angles of 121.2(3)° and 110.1(4)°.
and 2.37 in the 1H NMR spectrum. The new compound is assigned
as the imine tautomer (7).
Recent theoretical studies by Su and Chu have addressed the
issue of germylene insertion into C-H bonds.28 Their studies
suggest insertion into C-H bonds is favored by germylenes with
bulky, electropositive substituents, consistent with the observations
reported in this paper. The presence of electronegative or π-
donating ligands was predicted to inhibit C-H insertion reactions,
and we have not observed the same C-H insertion activity for
the closely related germylene Ge[N(SiMe3)2]2. Su and Chu suggest
that molecules containing unactivated C-H bonds such as
methane should be susceptible to insertion reactions by ger-
mylenes. We have not observed such activity to date using stable
germylenes; however, the predictions certainly provide a challenge
for future work in this area. The critical role of salt observed in
these reactions is reminiscent of carbenoid chemistry and suggests
that mechanistic pathways for these reactions may be quite
different from those explored theoretically by Su and Chu.
Intermolecular C-H insertion by a stable germylene into the
R-CH bond of acetonitrile, propionitrile, phenyl acetonitrile, or
succinonitrile occurs when employing THF/salt solutions under
mild reaction conditions in excellent yields. Furthermore, reaction
of germylene with adiponitrile results in ring closure and cleavage
of a C-CN bond to yield the germanium-trapped cyclopentene
cyanamide. Modification of the germylene ligand set should allow
an expansion of the type of C-H bonds amenable to insertion
reactions. Continued research into the mechanism of this reaction,
particularly the role of salt effects, and exploration of a wider
variety of substrates is planned.
The reaction of 1 with adiponitrile (NC(CH2)4CN) gave
cyclized product 6, bis[bis(trimethylsilyl)methyl]-cyano-N-(1-
cyclopentenyl)amino germane. The structure of 6 was determined
using H and 13C NMR, H-1H COSY, H-13C HETCOR, and
IR spectroscopies as well as GC/MS. The IR spectrum shows
bands at 3344 (N-H), 2192 (CtN), and 1644 (CdC) cm-1. The
1H NMR spectrum shows two singlets at 0.20 and 0.31 ppm for
the SiMe3 protons and a singlet at -0.021 ppm for the CH(SiMe3)2
protons. The ring protons are accounted for by a triplet at 2.23
ppm (3JH-H ) 7.2 Hz) for dC(N)CH2, a quintet at 1.75 ppm
(3JH-H ) 7.2 Hz) for CH2CH2CH2; a triplet of doublets at 2.44
ppm (3JH-H ) 2.0 and 7.2 Hz) for dCHCH2CH2; and a broad
singlet at 5.04 ppm corresponding to CdCH. The amine proton
was observed as a broad singlet at 2.32 ppm. GC/MS of the
hydrolysis of 6 showed formation of cyclopentanone, suggesting
that the product is the germylene trapped cyclopentene cyanamide,
not cyclohexeneamine. Upon sublimation at 80 °C, the N-H
feature is no longer present in either the 1H NMR or IR spectra,
a new IR band assigned to CdN is observed at 1680 cm-1, and
the two pair of symmetric ring CH2 groups are observed at 1.44
1
1
1
Acknowledgment. We thank A. Ashe, Kyle Litz, and R. Noyori for
helpful discussions. The Research Corporation is thanked for support of
this research. M.M.B.H. is grateful for support as an Alfred P. Sloan
Research Fellow.
Supporting Information Available: Full experimental and spectro-
scopic details are provided for all compounds reported (PDF). An X-ray
crystallographic file in CIF format for compound 2. This material is
available free of charge via the Internet at http://pubs.acs.org.
Figure 1. X-ray crystal structure of Ge[CH(SiMe3)2]2[H][CH2CN] (1).
Selected bond lengths (Å) and angles (deg): Ge-C1, 1.911(9); C1-C2,
1.443(15); C2-N1, 1.153(13); Ge-C3, 1.956(4); C1-Ge-C3, 121.2(3);
C1-Ge-C3A, 110.1(4); C3-Ge-C3A, 113.9(3); Ge-C1-C2, 115.2(7);
C1-C2-N1, 177(1).
JA0026408
(28) Su, M.-D.; Chu, S.-Y. J. Am. Chem. Soc. 1999, 121, 4229-4237.