Addition of Isocyanides to Tetramesityldigermene: A Comparison of the Reactivity between Surface and Molecular Digermenes

Article abstract of DOI:10.1002/chem.201602222

The reaction of benzyl isocyanide, tert-butyl isocyanide, and 2,6-dimethylphenyl isocyanide with tetramesityldigermene (Mes₂Ge=GeMes₂) was examined. Whereas the addition of benzyl isocyanide gave the C?NC activation product, Mes₂Ge(CH₂Ph)Ge(CN)Mes₂, tert-butyl isocyanide, and 2,6-dimethylphenyl isocyanide did not give stable adducts, rather the rate of conversion of the digermene to the corresponding cyclotrigermane was accelerated. A comparison between the reactivity of the isocyanides with Mes₂Ge=GeMes₂and the Ge(100)-2×1 surface was made and some insights into the surface chemistry are offered.

Full text of DOI:10.1002/chem.201602222

DOI: 10.1002/chem.201602222
Full Paper
&
Inorganic Chemistry
Addition of Isocyanides to Tetramesityldigermene: A Comparison
of the Reactivity between Surface and Molecular Digermenes
Nada Y. Tashkandi, Emily E. Cook, Jeremy L. Bourque, and Kim M. Baines*[a]
Abstract: The reaction of benzyl isocyanide, tert-butyl isocy-
anide, and 2,6-dimethylphenyl isocyanide with tetramesityl-
digermene (Mes2Ge=GeMes2) was examined. Whereas the
addition of benzyl isocyanide gave the CÀNC activation
product, Mes2Ge(CH2Ph)Ge(CN)Mes2, tert-butyl isocyanide,
and 2,6-dimethylphenyl isocyanide did not give stable ad-
ducts, rather the rate of conversion of the digermene to the
corresponding cyclotrigermane was accelerated. A compari-
son between the reactivity of the isocyanides with Mes2Ge=
GeMes2 and the Ge(100)-2”1 surface was made and some
insights into the surface chemistry are offered.
Introduction
The functionalization of silicon and germanium surfaces is of
particular interest due to the prevalence of these two semicon-
ductors in the microelectronics industry.[1] One of the major
challenges facing surface scientists is the elucidation of the
exact structures present on the surface after functionalization.
This is of primary importance if the initial adducts are to be
used as linkers for the attachment of a secondary layer. We
have demonstrated that for the Si- and Ge(100)-2”1 recon-
structed surfaces, molecular disilenes and digermenes can be
used as effective models for understanding the reactivity of
the surface dimers.[2] For example, we have recently reported
on the addition of organic cyanides to disilenes[3] and diger-
menes[4] and have demonstrated that a comparison of the mo-
lecular and surface chemistries provides important insights not
possible by looking at either system in isolation. More recently,
the addition of isocyanides to the Ge(100)-2”1 surface has
been described and now we report on the comparative
chemistry of the molecular system.
The chemiadsorption of tert-butyl isocyanide[5] and 1,4-phen-
ylene diisocyanide[6] on the Ge(100)-2”1 reconstructed surface
has been investigated. Although three possible reaction prod-
ucts were considered, a Lewis base adduct 1, a [2+1] cycload-
duct 2, and a [2+2] cycloadduct 3 (Scheme 1), only the Lewis
acid adduct 1 is believed to be present on the surface as de-
termined by FTIR spectroscopy, temperature-programmed de-
sorption and DFT calculations.
Scheme 1.
Scheme 2.
has also been reported.[8] tert-Butyl isocyanide reacts with di-
germene 4 to give the germyl cyanide 5 through loss of H2C=
C(CH3)2 and cleavage of the Ge=Ge double bond (Scheme 2).[7]
Herein, the addition of benzyl, tert-butyl, and 2,6-dimethyl-
phenyl isocyanide to tetramesitydigermene (Mes2Ge=GeMes2;
6) is reported to further explore the addition of isocyanides to
digermenes and to make a comparison to the analogous
chemistry on the Ge(100)-2”1 surface.
Molecularly, only one reaction between an isocyanide and
a simple digermene has been reported to date,[7] although the
reaction between a tetragermabutadiene and an isocyanide
Results
The addition of excess of benzyl isocyanide to a THF solution
[a] N. Y. Tashkandi, E. E. Cook, J. L. Bourque, Prof. K. M. Baines
Department of Chemistry, University of Western Ontario
London, Ontario, N6A 5B7 (Canada)
of tetramesityldigermene (6) at room temperature gave a dark-
orange oil upon removal of the solvent. H NMR spectroscopic
1
analysis of the crude product revealed that 7 is the only prod-
uct formed. The mass spectrum of 7 revealed a molecular ion
at m/z: 756.2388, which is consistent with a 1:1 adduct be-
E-mail: kbaines2@uwo.ca
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201602222.
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tween digermene 6 and benzyl isocyanide. Two sets of signals
assigned to mesityl groups were evident in both the H and
first known example of a digermyl cyanide, and thus, no direct
comparisons for the wavenumber of the CN stretching vibra-
tion exist; however, the wavenumber for the CN stretching vi-
bration of 7 is most similar to that of the germyl cyanide
Ar2GeH(CN) (Ar=C6H3-2,6-(C6H2-2,4,6-Me3)2) which has a hydro-
gen geminal to the cyano group (2177 cmÀ1).[11]
1
the 13C{1H} NMR spectra of 7. One of the signals assigned to
a methyl on the mesityl substituent 2.24 ppm) appeared as
a very broad singlet. In the 13C-1H HMBC spectrum of 7, a corre-
lation between the signal assigned to the ipso-C of the Mes
group in the 13C dimension and the signal assigned to the two
hydrogens of the benzyl moiety was observed. Notably, an imi-
nodigermirane structure analogous to 2 would not be expect-
ed to give rise to such a correlation. Unambiguous identifica-
tion of 7 in the solid state was obtained from X-ray crystallo-
graphic methods. The product was identified as 2-benzyl-
1,1,2,2-tetramesityldigermyl cyanide (Scheme 3 and Figure 1).
The N1-C1-Ge1 angle is slightly bent at 174.07(17)8 and the
C20-Ge2-Ge1 angle of 96.85(5)8 deviates substantially from the
standard tetrahedral angle of 1098. All remaining bond lengths
and angles in 7 are within normal ranges.
X-ray crystallography revealed that the C1–N1 fragment in 7
was disordered, with a reverse of the atom order (cyanide
versus isocyanide) in a 91 to 9% ratio, although the presence
of the isomeric mixture was not evident by IR or NMR spec-
troscopy at 258C. Attempts to separate the isomer with the N
bonded to the germanium by using Et3B were not successful
possibly due to the low concentration of the isomer with the
N bonded to the germanium in comparison to 7. The thermal
stability of 7 was investigated by heating a [D8]THF solution of
7 to 1458C in the presence of dimethylbutadiene (DMB); 7 was
recovered unchanged.
The addition of 2,6-dimethylphenyl- or tert-butyl isocyanide
to a THF solution of tetramesityldigermene did not result in
the formation of an adduct, even upon prolonged heating at
1008C. Interestingly, both isocyanides accelerated the conver-
sion of digermene
6 to hexamesitylcyclotrigermane (8)
(Scheme 4). In comparison, when a solution of 6 and 8 (1:1
Scheme 3.
Scheme 4.
ratio) was left to stir at room temperature for three weeks, the
ratio of digermene 6 to the cyclotrigermane 8 increased slight-
ly to 1.0:1.3; after two weeks of refluxing in THF, the ratio of di-
germene 6 to cyclotrigermane 8 changed to 1.0:7.1.[2d] In con-
trast, in the presence of 2,6-dimethylphenyl or tert-butyl isocy-
anide, the conversion of digermene 6 to 8 was accelerated;
the conversion is nearly complete after one week at room tem-
perature. As a control experiment, the addition of tert-butyl
isocyanide to cyclotrigermane 8 did not show any reaction
after stirring at room temperature for one week.
Figure 1. Displacement ellipsoid plot of 7. Ellipsoids are at the 50% proba-
bility level and hydrogen atoms and disorder at C1–N1 were omitted for
clarity. Selected bond lengths [Š] and angles [8]: Ge1ÀC1=1.9759(18), Ge1À
Ge2=2.5031(3), Ge2ÀC20=2.0120(18), C1ÀN1=1.142(2); C1-Ge1-
Ge2=100.98(5), C2-Ge1-C11 =107.80(7), C27-Ge2-C36=114.21(7), C20-Ge2-
Ge1=96.85(5), N1-C1-Ge1=174.07(17).
The reaction between digermene 6 and 2,6-dimethylphenyl
isocyanide was monitored in [D8]THF in a J. Young tube. A so-
lution of digermene 6 dissolved in [D8]THF was monitored si-
multaneously as a control experiment. The amount of 8 pres-
ent in each solution, relative to an internal standard, was plot-
ted against time (see Figure S10 in the Supporting Informa-
tion). Clearly, the presence of 2,6-dimethylphenyl isocyanide
has a significant effect on the rate of conversion of digermene
6 to cyclotrigermane 8 with a significant amount of cyclotriger-
mane observed even after 20 h. The accelerated conversion of
digermene 6 to 8 in the presence of an anionic gallium N-het-
erocyclic carbene (NHC) analogue has previously been report-
ed.[12]
The IR spectrum of 7 revealed a weak absorption at
2168 cmÀ1 which falls just outside the frequency range for CN
stretching vibrations in germyl cyanides (2177–2225 cmÀ1; see
Table S2 in the Supporting Information); the range of frequen-
cies for CN stretching vibrations for germyl cyanides occurs at
lower wavenumbers compared to the typical range for organic
cyanides (2260–2240 cmÀ1).[9] The absorption at 2168 cmÀ1 for
7 occurs at a much higher wavenumber compared to the ab-
sorption for the isocyanide functional group in germyl isocya-
nides (Ph(3Àx)MexGeNC 2088Æ2 cmÀ1).[10] Digermane 7 is the
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Discussion
A possible pathway for the formation of adduct 7 begins with
the coordination of the isocyanide carbon to one of the ger-
manium atoms of digermene 6 to afford the donor adduct 9,
followed by cleavage of the alkyl nitrogen bond to give
a benzyl carbocation, which can then recombine with the
germyl anion to yield 7 (Scheme 5). The formation of 9 is rea-
Scheme 6.
and represent a rare example of a Lewis base-catalysed reac-
tion of a ditetrelene.[3,18]
Scheme 5.
Following a strategy used by Power,[11] attempts to isolate
an adduct between tert-butyl isocyanide and digermene 6 in
the presence of excess isocyanide failed; however, a 1:1
adduct between the isocyanide and the digermene was ob-
served by mass spectrometry. In an effort to provide evidence
for the formation of Mes2Ge: as an intermediate along the re-
action pathway, the reaction was repeated in the presence of
DMB. When a THF solution of digermene 6, 2,6-dimethylphenyl
isocyanide, and a large excess of DMB was stirred at room tem-
perature overnight, the formation of germacyclopentenes 11
and 12 was observed. The formation of 11 provides convincing
evidence for the formation of dimesitylgermylene during the
reaction as germacyclopentane 11 is the well-known product
of the reaction between dimesitylgermylene and DMB.[19] Fur-
thermore, 12 is the well-known trapping product of mesityl(tri-
mesitylgermyl)germylene, the rearrangement product of diger-
mene 6.[19] Notably, a THF solution of digermene 6 was stirred
in the presence of excess DMB at room temperature for three
weeks and 12 was observed as the only product indicating
that digermene 6 does not dissociate to give monomeric ger-
mylene under these reaction conditions.[2d]
sonable; a similar coordination motif was reported in the addi-
tion of tert-butyl isocyanide[11] or methyl isocyanide[13] to the
germylene GeAr2 (Ar=C6H3-2,6-(C6H2-2,4,6-Me3)2) and in the ad-
dition of isocyanides to the bis(terphenyl)digermyne in which
the terphenyl group is C6H3-2,6-(C6H3-2,6-iPr2)2).[14,15] Stable
Lewis base adducts of disilenes have also been reported.[16] Ac-
tivation of the C-isocyanide bond by a ditetrelene is unprece-
dented although activation of the CÀNC bond of isocyanides
by silylenes[17] and germylenes[7,11] has been previously report-
ed. On the basis of computational studies, for the formation of
a germyl cyanide in the addition of tert-butyl isocyanide to
a bis(terphenyl)-substituted germylene was proposed to take
place by heterolytic bond cleavage.[11] The relative energies of
the donor adduct 9 and the isolated product 7 were calculated
using DFT methods at the M06/6-311 +G*//B3LYP/6-31G* level
of theory; the energies of 9 and 7 were lower than that of the
reactants at À13.0 and À236.5 kJmolÀ1, respectively.
The formation of cyclotrigermane 8 in the presence of 2,6-
dimethylphenyl and tert-butyl isocyanide can also be explained
by assuming initial coordination of the bulky isocyanide to the
digermene (Scheme 6). Loss of dimesitylgermylene from 9
would result in the formation of the germylene-isocyanide
complex 10. Complex 10 is likely in equilibrium with the free
isocyanide and germylene; the reversible complexation of ger-
mylenes with Lewis bases has been reported.[11,13] Dimesitylger-
mylene could then dimerize to form digermene 6 (path A) or
react with digermene 6 to produce cyclotrigermane 8 (path B).
Evidently, cyclotrigermane 8 acts as a thermodynamic sink in
the reaction. A similar reaction pathway was proposed for the
formation of 8 by the addition of an anionic gallium heterocy-
clic carbene to digermene 6.[12] In the reaction of 6 with the
bulky isocyanides, the isocyanides are acting as catalysts, accel-
erating the conversion of digermene 6 to cyclotrigermane 8
The addition of tert-butyl isocyanide to digermene
4
(Scheme 2)[7] appears to be analogous to the addition of tert-
butyl isocyanide to tetramesityldigermene, even though the
outcomes of the reaction are quite different; in one case, the
reactivity of the free germylene appears to dominate (when
the substituents on the starting digermene are mesityl), where-
as, in the other case, the product appears to be derived from
the germylene–donor complex (when the substituents on the
starting digermene are silyl). The initial step for formation of 5
was also proposed to occur by coordination of the isocyanide
carbon to one of the germanium atoms of digermene 4 to
give a structure analogous to 9. Cleavage of the germanium–
germanium bond forms a germylene–isocyanide complex anal-
ogous to 10, which then undergoes elimination of isobutene
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to give 5. The difference in the reactivity of digermenes 4 and
6 towards tert-butyl isocyanide may be attributed to the varia-
tion in the relative concentrations of the reagents and/or the
relative rate constants for the reactivity of the free germylene
and the germylene–donor complexes in each case. The sub-
stituents on germanium will play a role in governing the reac-
tivity; the silyl substituents are expected to stabilize a germy-
lene–isocyanide complex through negative hyperconjuga-
tion,[20] whereas the mesityl substituents will not.
The interaction between Lewis bases and digermenes to
give complexes such as 9 and their subsequent reactivity has
received little attention. On the basis of several reports in the
literature, a continuum of reactivity is apparent. Strong Lewis
bases, such as N-heterocyclic carbenes or their main group an-
alogues, are able to form stable donor–germylene complexes
analogous to 10 through extrusion of a germylene from the in-
itial complex.[12,21] Weak Lewis bases, such as cyanides, are pro-
posed to form an intermediate donor–digermene complex
(e.g. 9) and, although the reactivity of the digermene is influ-
enced, extrusion of a germylene does not occur.[4] Molecules
with moderate Lewis basicity, such as isocyanides, exhibit both
um, p-back donation can occur; however, the orbital interac-
tion must be quite significant before a decrease in the wave-
number of n(CN) is observed relative to the uncomplexed iso-
cyanide. Clearly, a good understanding of the position of the
modes of reactivity; however, the formation of the germylene– CN absorption requires a detailed analysis of the natural orbi-
donor complex (e.g. 10) is reversible and, under these condi-
tions, chemistry of the germylene can also be observed.
tals of chemical valence and/or the orbital interaction energies.
With a shift to higher frequency compared to tBuNC and the
expected lack of back-bonding from germanium, a wavenum-
ber of 2192 cmÀ1 for 1 is reasonable. The value compares ex-
tremely well with the calculated stretching frequency for
tBuNC absorbed onto a Ge15H16 cluster (2192 cmÀ1).[5] However,
given the known range of CN stretching frequencies for
germyl cyanides (2177–2225 cmÀ1; see Table S2 in the Support-
ing Information), it also seems entirely reasonable and possible
that the structure on the Ge(100)-2”1 surface might be analo-
gous to 7 and not the Lewis acid–base donor adduct. Notably,
the Ge(100)-2”1 surface dimer is statically buckled at room
temperature. The “up” atom exhibits a nucleophilic character
since it possesses most of the electron density and the “down”
atom is expected to exhibit significant electrophilic character
since it possesses the least electron density.[23] This buckling
may influence the reactivity of the Ge(100)-2”1 surface and
lead to a stable Lewis acid–base adduct (i.e., to form the
donor adduct 1) in contrast to producing a C–N activation
product analogous to 7.
Bent and co-workers observed a shift to lower frequency for
n(CN) of the surface adducts upon increased coverage of
tBuNC on the Ge(100) surface and attributed the shift to
a weakening of adjacent adsorbate–surface bonds upon com-
plexation.[5] An alternative explanation involves cleavage of the
former surface Ge–Ge bond, followed by complexation at the
second germanium site giving two adjacent isocyanide-com-
plexed GeII centres (i.e., structures analogous to 10/15). With
a lone pair at germanium, the CN stretching frequency would
be expected to be lower compared to 1.
Comparison between the structure of the digermene-isocya-
nide adduct 7 and the isocyanide adduct on the Ge(100)-
2”1 surface 1
The reactivity of tert-butyl isocyanide toward the Ge(100)-2”
1 surface revealed the formation of 1, which is similar in struc-
ture to intermediate 9 in the molecular system, and thus, is
quite reasonable.[5] Although the authors considered the possi-
ble formation of cycloadducts on the surface, a CÀN bond acti-
vation adduct similar to 7 was not identified as a potential
product.[5,6] The FTIR spectroscopic data for 7 can be directly
compared to the data obtained for 1. Bent et al. observed two
notable absorptions in the FTIR spectrum of the Ge(100) sur-
face after exposure to tert-butyl isocyanide: 2192 cmÀ1 at low
coverage and 2179 cmÀ1 at high coverage. Both adsorptions
were assigned to the CN stretching vibration of Lewis acid-
base adduct 1.[5] The wavenumber for the CN stretching vibra-
tion for the surface adduct is blueshifted compared to that of
the free tert-butyl isocyanide CN stretching vibration at
2134 cmÀ1. Only a few examples of the CN stretching vibration
in isocyanides coordinated to germanium have been pub-
lished: 2092 cmÀ1 for 13,[14] 2113 cmÀ1 for 14,[15] 2132 cmÀ1 for
15 (R=tBu),[11] and 2165 cmÀ1 for 15 in which R=Me;[13] how-
ever, it is difficult to make a meaningful comparison between
the CN stretching frequencies of these complexes and that of
the surface adduct. Tuononen has published a detailed compu-
tational analysis of the orbital interactions in germylene–isocy-
anide complexes and the influence of complexation on the
characteristic stretching frequency of the isocyano functional
group.[22] In the absence of any p-type back-bonding, an in-
crease in the wavenumber compared to the n(CN) of the un-
complexed isocyanide is noted. With a lone pair on germani-
Finally, the addition of tert-butyl isocyanide to digermene 6
did not result in the formation of a stable adduct in contrast
to the surface chemistry. The underlying germyl substituents
on the germanium dimers of the Ge(100)-2”1 surface are in
a cis-bent geometry. In contrast, digermene 6 possesses bulky
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mesityl substituents oriented in a trans-bent geometry.[2d] The
increased bulk of the substituents on digermene 6 likely pre-
vents the formation of a stable adduct with bulky isocyanides.
Addition of benzyl isocyanide to digermene 6
Ge3Mes6 (100 mg, 0.107 mmol) was placed in a quartz tube[25] and
dissolved in THF (5 mL) and then irradiated (l=350 nm) in
a quartz Dewar[25] at À608C for approximately 18 h to a give
yellow solution. The bright yellow solution of digermene 6 (0.084
mol) was transferred to a round-bottomed flask. Additional THF
was added (5.0 mL) followed by a THF solution of benzyl isocya-
nide (1.05 mL, 0.082m, 0.086 mmol). After stirring for 30 min at
room temperature, the solution became dark orange. The solution
was stirred overnight. The THF was then removed under vacuum
and a dark-orange oil was obtained. Product 7 was purified by
crystallization from saturated solution of hexanes at À228C to give
7 as a white solid (14 mg, 23%). Compound 7: 1H NMR (C6D6,
600 MHz): d=7.03–6.98 (m, 2H, Ph o-H), 6.95- 6.87 (m, 3H, Ph m-
and p-H), 6.61 (s, 8H, Mes m-H), 3.63 (brs, 2H, CH2), 2.33 (s, 12H,
Mes o-CH3), 2.24 (brs, 12H, Mes o-CH3),[26] 2.05, 2.04 (each s, 12H
total Mes p-CH3); 13C NMR (C6D6, 100 MHz): d=143.93 (brs, Mes o-
C), 143.44 (Mes o-C), 139.72 (Ph i-C), 139.17 (Mes p-C), 138.66 (Mes
p-C), 136.15 (Mes i-C), 134.36 (Mes i-C), 130.16 (CN), 130.02 (Ph m-
CH), 129.93 (Mes m-CH), 129.90 (Mes m-CH), 127.8[27] (Ph p-CH),
125.31 (Ph o-CH), 31.84 (brs, CH2), 25.73 (brs, Mes o-CH3), 25.15
(brs, Mes o-CH3), 20.86 (Mes p-CH3), 20.83 (Mes p-CH3); FTIR (thin
film, cmÀ1): n=3016 (s), 2922 (s), 2855 (s), 2168 (w), 1601 (s), 1556
(m), 1451 (s), 1405 (m), 1378 (m), 1289 (m), 1216 (m), 1029 (m), 848
(s), 758 (s), 698 cmÀ1 (m); HR-ESI-MS for C44H5170Ge2N+Na+ calcd:
756.2388; found: 756.2404. Details of the crystallographic analysis
can be found in the Supporting Information.
Conclusions
In conclusion, digermene 6 reacts with benzyl isocyanide to
form the unprecedented CÀN bond activation product, 2-
benzyl-1,1,2,2-tetramesityldigermyl cyanide (7). In the presence
of the bulkier 2,6-dimethylphenyl or tert-butyl isocyanide, the
isocyanides act as catalysts and the conversion of digermene 6
to cyclotrigermane 8 is accelerated. The observed results can
be understood in terms of an initial coordination of the isocya-
nide to the digermene 6 to give a donor complex 9
(Scheme 6). If the isocyanide substituent is small, activation of
the CÀN bond occurs with the germanium–germanium bond
remaining intact. Alternatively, if the isocyanide substituent is
large, dissociation occurs to form a germylene-isocyanide coor-
dination complex and a germylene, which can undergo subse-
quent reaction. The results of these experiments suggest that
Lewis bases may have a significant influence on the reactivity
of digermenes.
By examination of the reactivity of a molecular digermene
towards isocyanides, a previously unknown reaction pathway
was revealed, namely CN bond activation by a digermene, and
this reaction pathway should be considered in the studies of
the addition of isocyanides to the Ge(100)-2”1 surface. Fur-
thermore, the formation of adjacent isocyanide–germylene
complexes was offered as an additional possibility for the
structure of the surface adducts at high coverage. With our re-
sults, new options for the structures of adducts on the
Ge(100)-2”1 surface have been elucidated illustrating the ben-
efits of the comparative chemistry of molecular and surface di-
germenes.
Thermal stability of 7
Compound 7 (13 mg, 0.017 mmol) was dissolved in [D8]THF in a J.
Young tube and excess DMB (4 drops) was added to the solution.
The J. Young tube was placed in an oil bath at 1008C for 20 h. The
solution was allowed to cool to room temperature and then ana-
1
lyzed by H NMR spectroscopy. Compound 7 appeared unchanged.
The J. Young tube was subsequently placed in an oil bath at 1458C
for 18.5 h. After cooling to room temperature, the solution was an-
alyzed by 1H NMR spectroscopy; once again, 7 appeared un-
changed. The [D8]THF and excess DMB were then removed from
the solution under vacuum and the white solid was redissolved in
C6D6. In addition to the signals assigned to 7, a number of signals
were observed from 1.72–1.85 ppm inferring that some decompo-
sition had occurred. The mixture was separated by preparative TLC
(silica gel, 1:1 CH2Cl2/hexanes). Compound 7 was recovered as a col-
ourless solid.
Experimental Section
General
All experiments were carried out under an atmosphere of argon or
nitrogen using standard Schlenk techniques or a glove box. THF
was purified by passage through a column of alumina and was de-
gassed and stored over 4 Š molecular sieves prior to use. C6D6 was
distilled from lithium aluminum hydride, degassed and stored over
4 Š molecular sieves prior to use. [D8]THF was stored over 4 Š mo-
lecular sieves. Liquid isocyanides were degassed and stored over
Addition of 2,6-dimethylphenyl isocyanide to digermene 6
Ge3Mes6 (49 mg, 0.053 mmol) was dissolved in THF (4.0 mL) and ir-
radiated at À408C overnight in a Pyrex Schlenk tube. The bright
yellow solution of 6 (0.079 mmol) was transferred to a round-bot-
tomed flask. Additional THF was added (4.0 mL) followed by a THF
solution of 2,6-dimethylphenyl isocyanide (1.03 mL, 0.076m,
0.079 mmol). The solution was stirred at room temperature and
[24]
4 Š molecular sieves prior to use. Ge3Mes6 was synthesized ac-
cording to the literature procedures. All other chemicals were pur-
chased from commercial sources and used without further purifica-
tion, except as noted above.
1
monitored by H NMR spectroscopy. After 5 days, the ratio of 6/8
was determined to be approximately 1.0:14 by integration of the
signals at 6.71 (6, 8H) and 6.67 ppm (8, 12H) in C6D6.
NMR spectra were recorded on a Varian Inova 400 or Inova
600 MHz NMR spectrometer using C6D6 or [D8]THF as the solvent.
The NMR standards used are as follows: 1H NMR spectra were refer-
enced to residual C6D5H (7.15 ppm) or [D7]THF 3.58 ppm); 13C NMR
spectra were referenced to the central transition of C6D6
(128.00 ppm). FTIR spectra were recorded as thin films using
a Bruker Tensor 27 Spectrometer (resolution of 4 cmÀ1). ESI-TOF
mass spectra were obtained using a Micromass LCT instrument.
Monitoring the conversion of digermene 6 to 8 in the pres-
ence of 2,6-dimethylphenyl isocyanide
Ge3Mes6 (35 mg, 0.037 mmol) was dissolved in [D8]THF (1.4 mL)
and irradiated at À408C overnight in a Pyrex Schlenk tube. The
Chem. Eur. J. 2016, 22, 14006 –14012
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bright-yellow solution of 6 (0.056 mmol) was divided equally and
transferred to two NMR tubes (0.028 mmol of 6 in each tube). A
[D8]THF solution of 2,6-dimethylphenyl isocyanide was added
(0.30 mL, 0.076m, 0.023 mmol) to one of the NMR tubes. The reac-
Keywords: germanium · inorganic chemistry · isocyanide
ligands · main-group elements · surface chemistry
1
tions were monitored using H NMR spectroscopy. The ratio of 6/8
[1] For recent reviews, see: a) Functionalization of Semiconductor Surfaces
(Eds.: F. Tao, S. Bernasek), Wiley, Hoboken, 2012; b) J. S. Kachian, K. T.
Wong, S. F. Bent, Acc. Chem. Res. 2010, 43, 346; c) R. J. Hamers, Annu.
Rev. Anal. Chem. 2008, 1, 707; d) P. W. Loscutoff, S. F. Bent, Annu. Rev.
was determined at intervals by integration of the signals at 6.75 (6,
8H) and 6.64 ppm (8, 12H) in [D8]THF. The [D7]THF signal at
3.58 ppm was used as an internal standard. After 6 days, the
[D8]THF was removed and the mixture was redissolved in C6D6. The
ratio of 6/8 was determined to be approximately 1.0:3.1 by inte-
gration of the signals at 6.71 (6, 8H) and 6.67 ppm (8, 12H).
´
Phys. Chem. 2006, 57, 467; e) A. Bilic, J. R. Reimers, N. S. Hush, in Proper-
ties of Single Organic Molecules on Crystal Surfaces (Eds.: P. Grütter, W.
Hofer, F. Rosei), Imperial College Press, London, 2006; f) X. Lu, M. C. Lin,
Int. Rev. Phys. Chem. 2002, 21, 137; g) S. F. Bent, J. Phys. Chem. B 2002,
106, 2830; h) S. F. Bent, Surf. Sci. 2002, 500, 879; i) J. M. Buriak, Chem.
Rev. 2002, 102, 1271; j) R. J. Hamers, S. K. Coulter, M. D. Ellison, J. S.
Hovis, D. F. Padowitz, M. P. Schwartz, C. M. Greenlief, J. N. Russell, Jr.,
Acc. Chem. Res. 2000, 33, 617.
Addition of 2,6-dimethylphenyl isocyanide to digermene 6
in the presence of DMB
[2] a) N. Y. Tashkandi, F. Parsons, J. Guo, K. M. Baines, Angew. Chem. Int. Ed.
2015, 54, 1612; Angew. Chem. 2015, 127, 1632; b) J. A. Hardwick, L. C.
Pavelka, K. M. Baines, Dalton Trans. 2012, 41, 609; c) K. L. Hurni, K. M.
Baines, Chem. Commun. 2011, 47, 8382; d) K. L. Hurni, P. A. Rupar, N. C.
Payne, K. M. Baines, Organometallics 2007, 26, 5569; e) S. E. Gottschling,
K. K. Milnes, M. C. Jennings, K. M. Baines, Organometallics 2005, 24,
3811; f) S. E. Gottschling, M. C. Jennings, K. M. Baines, Can. J. Chem.
2005, 83, 1568; g) M. S. Samuel, K. M. Baines, J. Am. Chem. Soc. 2003,
125, 12702; h) M. S. Samuel, H. A. Jenkins, D. W. Hughes, K. M. Baines,
Organometallics 2003, 22, 1603.
Ge3Mes6 (25 mg, 0.026 mmol) was dissolved in THF (2.2 mL) and ir-
radiated at À408C overnight in a Pyrex Schlenk tube. The bright-
yellow solution of 6 (0.035 mmol) was transferred to a round-bot-
tomed flask. Additional THF was added (2.0 mL) followed by a THF
solution of 2,6-dimethylphenyl isocyanide (0.46 mL, 0.076m,
0.035 mmol) and excess DMB (0.40 mL, 100 equiv). After stirring at
room temperature for 21.5 h, an aliquot was removed and exam-
ined by H NMR spectroscopy. The ratio of 11/12 was determined
to be approximately 1.0:2.2 by integration of the signals at 1.73
(11, 6H) and 1.65 ppm (12, 6H) in C6D6.
1
[3] J. A. Hardwick, K. M. Baines, Chem. Eur. J. 2015, 21, 2480.
[4] J. A. Hardwick, K. M. Baines, Angew. Chem. Int. Ed. 2015, 54, 6600;
Angew. Chem. 2015, 127, 6700.
[5] B. Shong, K. Wong, S. F. Bent, J. Am. Chem. Soc. 2014, 136, 5848.
[6] B. Shong, E. Sandoval, A. M. Crow, S. F. Bent, J. Phys. Chem. Lett. 2015, 6,
1037.
[7] V. Y. Lee, K. McNeice, Y. Ito, A. Sekiguchi, Chem. Commun. 2011, 47,
3272.
[8] G. Ramaker, W. Saak, D. Haase, M. Weidenbruch, Organometallics 2003,
22, 5212.
[9] D. L. Pavia, G. M. Lampman, G. S. Kriz, Introduction to Spectroscopy, 3rd
ed., Thomson Learning, Toronto, 2001.
[10] P. M. Treichel, D. B. Shaw, J. Organomet. Chem. 1977, 139, 21.
[11] Z. D. Brown, P. Vasko, J. C. Fettinger, H. M. Tuononen, P. P. Power, J. Am.
Chem. Soc. 2012, 134, 4045.
[12] P. A. Rupar, M. C. Jennings, K. M. Baines, Can. J. Chem. 2007, 85, 141.
[13] Z. D. Brown, P. Vasko, J. D. Erickson, J. C. Fettinger, H. M. Tuononen, P. P.
Power, J. Am. Chem. Soc. 2013, 135, 6257.
Addition of tert-butyl isocyanide to digermene 6
Ge3Mes6 (55 mg, 0.059 mmol) was dissolved in THF (5.0 mL) and ir-
radiated at À408C overnight in a Pyrex Schlenk tube. The bright-
yellow solution of 6 (0.088 mmol) was transferred to a round-bot-
tomed flask. Additional THF was added (5.0 mL) followed by a THF
solution of tert-butyl isocyanide (1.00 mL, 0.088m, 0.088 mmol).
The solution was stirred at room temperature and monitored by
1H NMR spectroscopy. After 4 days, the ratio of 6/8 was determined
to be approximately 1.0:4.2 by integration of the signals at 6.71 (6,
8H) and 6.67 ppm (8, 12H) in C6D6.
Addition of excess tert-butyl isocyanide to digermene 6
[14] C. Cui, M. M. Olmstead, J. C. Fettinger, G. H. Spikes, P. P. Power, J. Am.
Chem. Soc. 2005, 127, 17530.
Ge3Mes6 (55 mg, 0.059 mmol) was dissolved in THF (5.0 mL) and ir-
radiated at À408C overnight in a Pyrex Schlenk tube. The bright-
yellow solution of 6 (0.088 mmol) was transferred to a round-bot-
tomed flask. Additional THF was added (5.0 mL) followed by a solu-
tion of tert-butyl isocyanide dissolved in THF (5.00 mL, 0.079m,
0.4 mmol). The solution was stirred at room temperature and
monitored by H NMR spectroscopy. The H NMR spectrum of the
crude solution revealed broad signals of Ge3Mes6 plus some low-in-
tensity signals. Mass spectrometry revealed a signal which was as-
signed to a 1:1 adduct between digermene 6 and tert-butyl isocya-
nide. ESI-TOF for C41H5370Ge2N+H+ calcd: 700.2747; found:
700.2741. The low-intensity signals disappeared after a few days;
only Ge3Mes6 was recovered after a week as determined by
1H NMR spectroscopy.
[15] G. H. Spikes, P. P. Power, Chem. Commun. 2010, 46, 943.
[16] a) R. Fischer, J. Baumgartner, G. Kickelbick, C. Marschner, J. Am. Chem.
Soc. 2003, 125, 3414; b) M. Zirngast, M. Flock, J. Baumgartner, C.
´
Marschner, J. Am. Chem. Soc. 2008, 130, 17460; c) K. Leszczynska, K.
Abersfelder, A. Mix, B. Neumann, H.-G. Stammler, M. J. Cowley, P. Jutzi,
D. Scheschkewitz, Angew. Chem. Int. Ed. 2012, 51, 6785; Angew. Chem.
2012, 124, 6891.
1
1
[17] Y. Xiong, S. Yao, M. Driess, Chem. Eur. J. 2009, 15, 8542.
[18] J. S. Han, T. Sasamori, Y. Mizuhata, N. Tokitoh, Chem. Asian J. 2012, 7,
298.
[19] K. M. Baines, J. A. Cooke, C. E. Dixon, H. W. Liu, M. R. Netherton, Organo-
metallics 1994, 13, 631.
[20] J. B. Lambert, Y. Zhao, R. W. Emblidge, L. A. Salvador, X. Liu, J.-H. So,
E. C. Chelius, Acc. Chem. Res. 1999, 32, 183.
[21] P. A. Rupar, M. C. Jennings, P. J. Ragogna, K. M. Baines, Organometallics
2007, 26, 4109.
[22] A. Mansikkamäki, P. P. Power, H. M. Tuononen, Organometallics 2013, 32,
6690.
Acknowledgements
[23] Y. Qu, J. Han, in Functionalization of Semiconductor Surfaces (Eds.: F. Tao,
S. Bernasek), Wiley, Hoboken, 2012, Chapter 3.
[24] a) W. Ando, T. Tsumuraya, J. Chem. Soc. Chem. Commun. 1987, 1514;
b) T. Tsumuraya, Y. Kabe, W. Ando, J. Organomet. Chem. 1994, 482, 131.
[25] A quartz tube and Dewar were used but Pyrex glassware can also be
used.
We thank NSERC (Canada) for funding and a scholarship to
J.L.B. and King Abdul Aziz University (Saudi Arabia) for a schol-
arship to N.Y.T.
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[26] 1H NMR: d=2.24 (Mes o-CH3); 13C NMR: d=143.93 (Mes o-C), 136.15
(Mes i-C) have been assigned to the mesityl groups closest to the
benzyl ring on the basis of correlations to the broad 1H signal at
[27] Chemical shift extracted from the H– C gHSQC spectrum.
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Received: May 10, 2016
Published online on August 16, 2016
13
2.24 ppm observed in the 1H– C gHMBC spectrum.
Chem. Eur. J. 2016, 22, 14006 –14012
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