The addition of amides to group 14 (di)-metallenes

Article abstract of DOI:10.1039/c1dt11450f

The addition of a series of primary and secondary amides to the group 14 (di)metallenes Mes₂SiSiMes₂, Mes₂GeGeMes ₂ and (Me₃Si)₂SiC(OSiMe₃)R, where R = t-Bu or R = 1-Ad, was examined. In general, the addition of primary and N-methyl amides gave amide adducts whereas the addition of N-phenyl amides gave imidate adducts. The regiochemistry of the additions was highly dependent upon the substituent bonded to the amide nitrogen. We propose that the formation of the adducts proceeds by way of a zwitterionic intermediate. The reactivity of tetramesityldigermene towards amides is used to predict the structure of the amide adducts formed on the Ge(100)-2 × 1 surface.

Full text of DOI:10.1039/c1dt11450f

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PAPER
The addition of amides to group 14 (di)-metallenes†
Julie A. Hardwick, Laura C. Pavelka and Kim M. Baines*
Received 1st August 2011, Accepted 6th September 2011
DOI: 10.1039/c1dt11450f
The addition of a series of primary and secondary amides to the group 14 (di)metallenes
Mes2Si SiMes2, Mes2Ge GeMes2 and (Me3Si)2Si C(OSiMe3)R, where R = t-Bu or R = 1-Ad, was
examined. In general, the addition of primary and N-methyl amides gave amide adducts whereas the
addition of N-phenyl amides gave imidate adducts. The regiochemistry of the additions was highly
dependent upon the substituent bonded to the amide nitrogen. We propose that the formation of the
adducts proceeds by way of a zwitterionic intermediate. The reactivity of tetramesityldigermene towards
amides is used to predict the structure of the amide adducts formed on the Ge(100)-2 ¥ 1 surface.
results obtained from the addition of amides to digermene 2 were
Introduction
compared to the chemistry of amides at the Ge(100)-2 ¥ 1 surface.
A series of acet- and benzamides and their N-methyl, -phenyl
or -benzyl derivatives were examined in this study to give broad
insight into their reactivity. The amides utilized were acetamide,
benzamide, N-methylacetamide (NMA), N-methylbenzamide
(NMB), N-phenylacetamide (NPA), N-phenylbenzamide (NPB)
and N-benzylbenzamide (NBB). In general, doubly-bonded sili-
con and germanium compounds react with amines through the
NH bond to give silyl or germyl amines, respectively, and with
Interest in the functionalization of semiconductor surfaces using
organic molecules has increased dramatically within the last
decade because of potential applications in electronics, nanotech-
nology, sensors and other important technologies.1 For develop-
ment, it is critical to be able to determine the exact structure of
the adduct at the interface since elaboration of the organic layer
will depend on the functional groups present. Surface analytical
techniques exhibit limitations in the unambiguous identification
of the structure of surface adducts. For example, in a recent study,
the addition of primary and secondary amides to the Ge(100)-2
¥ 1 surface was examined for potential application in the area
of biosensors; however, it was impossible to determine the exact
structure of the adducts using multiple internal reflectance (MIR)-
FTIR spectroscopy.2 Based on our previous work,3 we believe that
the group 14 dimetallenes, tetramesityldisilene (Mes2Si SiMes2,
1)4 and tetramesityldigermene (Mes2Ge GeMes2, 2)5 are reason-
able molecular models for the Si and Ge(100)-2 ¥ 1 surfaces,
respectively, since the reactivity of the molecular dimetallenes
mirrors that of the corresponding surfaces.3 Given the limitations
of surface analytical techniques in determining the exact structure
of the amide adducts on the Ge(100)-2 ¥ 1 surface,2 we were
motivated to examine the reactivity of digermenes with amides.
Although group 14 (di)metallenes, R2M ER2, where M = Si, Ge
and E = C, Si, Ge, are known to react with a variety of compounds
that contain functional groups related to amides,6–8 we were
surprised to learn that the addition of amides to (di)metallenes
remains completely unexplored. Thus, the addition of a series
of primary and secondary alkyl and aryl amides to disilene 1,
digermene 2, and two Brook silenes, (Me3Si)2Si C(OSiMe3)R,
where R = t-Bu (3a) or R = 1-Ad (3b) was examined. The
carbonyl compounds through either the a-CH and/or C
O
bond, to give ene addition products and/or (di)metalloxetanes.
Therefore, the formation of an amide (4), an imidate (5), and/or a
(di)metalloxetane (6) can be expected in the addition of amides to
(di)metallenes (Scheme 1). Furthermore, rotameric isomers may
be observed for amides (4) and E/Z isomers may be observed in
the case of imidates (5).
Scheme 1 Possible amide adducts of (di)metallenes and their isomers.
(Di)metalloxetanes (6) should be identifiable by 1H NMR
1
spectroscopy; however, H NMR spectroscopy cannot be used
Department of Chemistry, University of Western Ontario, London, Ontario,
Canada, N6A 5B7. E-mail: kbaines2@uwo.ca; Fax: (519) 661-3022;
Tel: (519) 661-2111, Ext. 86302
† CCDC reference number 778245. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1dt11450f
to distinguish between regioisomers 4 and 5 because there are
no diagnostic 1H chemical shifts or splitting patterns between the
expected amides (4) and imidates (5). Likewise, IR spectroscopy is
not expected to be useful since imidate C N stretching vibrations
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(1676–1630 cm-1)9 fall within the typical range for an amide C
O
the C–N bond at room temperature. For imidates 5-SiCa(V–VII),
only one stereoisomer was observed by 1H NMR spectroscopy.
Compound 4-SiCa(I) also formed upon the addition of ac-
etamide to a C6D6 solution containing a mixture of pivaloyl-
tris(trimethylsilyl)silane, silene 3a, and its dimer in the dark
(Scheme 3). Under these conditions, the time for completion of the
reaction was dependent upon the rate of dissociation of the dimer
to 3a and the crude product was contaminated with significant
amounts of acylsilane. Conversely, co-irradiation of the acylsilane
and acetamide resulted in the clean, quantitative formation of 4-
SiCa(I) (Scheme 2), and thus, was the preferred method for the
addition of amides to silenes 3a/b.
stretching vibration (1680–1630 cm-1).10 The large chemical shift
dispersions of 29Si (-180 to 250 ppm)11 and 13C (0 to 220 ppm),10
however, may allow 29Si and 13C NMR spectroscopy to be useful
in the identification of amide (4)/imidate (5) regioisomers.
Results
A three-component naming system was devised for the amide
adducts to accommodate the four (di)metallenes studied, the three
possible types of addition products (amide, imidate, cycloaddi-
tion), and the seven different amides examined. The first part of
the name refers to the type of adduct (4 for amide, 5 for imidate,
6 for cycloadduct). The second part of the name refers to the
(di)metallene involved, ME where M = Si or Ge and E = C, Si,
or Ge. Since two different silenes were examined, a lower case
a indicates the use of silene 3a and a lower case b indicates
the use of silene 3b. The third part of the name is a Roman
numerical character that refers to the specific amide examined
(I for acetamide, II for benzamide, III for NMA, IV for NMB, V
for NPA, VI for NPB and VII for NBB). For example, 4-SiCa(II)
represents an adduct in the amide form from the reaction between
silene 3a and benzamide.
Reactivity of silenes
Irradiation of a benzene solution containing amide (~1 eq.) and
pivaloyl- or 1-adamantylcarbonyltris(trimethylsilyl)silane gave ei-
ther a clear, pale yellow or colourless solution. Analysis of the
1
Scheme 3 Addition of acetamide to silene 3a in the dark.
crude product by H NMR spectroscopy revealed the presence
of amides 4-SiCa(I–IV) and 4-SiCb(I,IV) or imidates 5-SiCa(V–
VII) (Scheme 2). Only one product derived from the addition of the
amide to the silene was formed in each reaction; the reactions were
completely regioselective. Furthermore, only one set of signals was
observed in the 1H NMR spectra of amides 4-SiCa(I–IV) and 4-
SiCb(I,IV), suggesting that either one rotameric isomer is formed
in each case or that the amide functionality is freely rotating about
Adducts 4-SiCa(I–IV), 5-SiCa(V–VII) and 4-SiCb(I,IV) slowly
hydrolyzed either upon attempted purification by chromatography
or upon exposure to atmospheric moisture; therefore, the adducts
were characterized without purification. The adducts were identi-
fied by 1H, 13C, gCOSY, 1H–13C gHSQC and gHMBC and 1H–29Si
gHMBC NMR spectroscopy and mass spectrometry. Compound
4-SiCa(I) was also identified by IR spectroscopy. Since the spectral
features which led to the structural assignment of 4-SiCa(I–IV),
5-SiCa(V–VII), and 4-SiCb(I,IV) were essentially the same, only
details of the assignment of the structure of 4-SiCa(I) will be
discussed.
The mass spectrum of 4-SiCa(I) revealed a molecular ion (M +
H+) located at m/z 392, which is consistent with a 1 : 1 adduct
between acetamide and silene 3a (plus a hydrogen). The presence
of an amide [NH(C O)CH3] moiety in 4-SiCa(I) was clearly
apparent from the 1H and 13C NMR and IR data. The 1H NMR
spectrum of 4-SiCa(I) displayed a sharp singlet at 1.70 ppm and
a broad singlet at 4.59 ppm, which integrated to 3H and 1H,
respectively. The 13C NMR spectrum of 4-SiCa(I) revealed signals
at 24.70 and 174.81 ppm, which are indicative of a saturated carbon
and a carbonyl moiety, respectively. The 13C chemical shift of an
amide C O typically resonates between 155 and 185 ppm10 while
that of a silyl imidate O–C N appears further upfield between 140
and 160 ppm.12 In the 1H–13C gHSQC spectrum of 4-SiCa(I), the
1H signal at 1.70 ppm showed a correlation to the 13C signal at 24.70
1
1
ppm and, in the H–13C gHMBC spectrum, the same H signal
showed a correlation to the 13C signal at 174.81 ppm; thus, the
1H and 13C signals were assigned to a CH3(C O) moiety. The 1H
Scheme 2 Addition of amides to silenes 3a and 3b.
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Table 1 Selected 13C and 29Si chemical shifts of 4-SiCa(I–IV), 5-SiCa(V–
VII), and 4-SiCb(I,IV)
signal at 4.59 ppm did not show correlations to any other 1H or 13
C
signals. This signal was, thus, assigned to an NH. Furthermore, the
IR spectrum of 4-SiCa(I) displayed strong absorptions at 3337 and
1628 cm-1, which are consistent with the NH and C O stretching
vibrations of a secondary amide.10 There were four chemical shifts
dCa/ppm dSib/ppm
1
observed in the H–29Si gHBMC spectrum of 4-SiCa(I); the 29Si
Compound
Amide
signal at -23.9 ppm was assigned to the central (Me3Si)2Si silicon
based on the observed correlations. Bis(trimethylsilyl) substituted
29Si atoms bonded to nitrogen13 resonate upfield of those bonded
to oxygen14 by 15–20 ppm.
The molecular structure of 4-SiCa(I) was determined by X-ray
crystallography (Fig. 1). It was difficult to distinguish between
the two possible regioisomers (4-SiCa(I) or 5-SiCa(I)) from the
structure alone since nitrogen and oxygen atoms are similar
in electron density and hydrogen atoms are difficult to locate.
4-SiCa(I)
Acetamide 174.81
Benzamide 171.86
-23.9
-22.2
-14.4
-15.2
4.0
4.3
1.0
Amide
Amide
Amide
Amide
Imidate
Imidate
Imidate
Amide
Amide
4-SiCa(II)
4-SiCa(III)
4-SiCa(IV)
5-SiCa(V)
5-SiCa(VI)
NMA
NMB
NPA
177.37
177.68
162.23
159.43
161.63
NPB
5-SiCa(VII) NBB
4-SiCb(I)
4-SiCb(IV)
Acetamide 174.88
NMB 177.52
-24.2
-15.5
a Signal assigned to the unsaturated, non-aromatic carbon atom:
R¢¢NCOR¢. b Signal assigned to the functionalized central silicon atom:
(Me3Si)2Si.
˚
However, the C(4)–O(5) bond length of 1.241(2) A is more
consistent with the average length of an amide C O bond (1.231
16
A)15 than the average length of an imidate C N bond (1.277 A)
˚
˚
˚
and the Si(2)–N(3) bond length of 1.793(2) A is more consistent
15
˚
with a typical Si–N bond length (1.714 A) than a typical Si–
silicon atoms of the adducts resonated in two distinct ranges:
1.0 to 4.3 ppm and -14.4 to -24.2 ppm (Table 1). The 13C and
29Si NMR spectral data suggest that two different isomers were
formed; compounds with 13C chemical shifts of 176 4 ppm
and 29Si chemical shifts between -14.4 and -24.2 ppm [4-SiCa(I–
IV) and 4-SiCb(I,IV)] were assigned silyl amide structures and
compounds with 13C chemical shifts of 161 2 ppm and 29Si
chemical shifts between 1.0 and 4.3 ppm. [5-SiCa(V–VII)] were
assigned silyl imidate structures.
15
˚
O bond length (1.631 A). In the molecular structure of 4-
SiCa(I), the amide oxygen, O(5), is adjacent to the central silicon
atom, Si(2). The analogous rotational isomer is preferred in N-
trialkylsilyl acetamides (CH3CONHSiR3).17 Thus, the X-ray data,
combined with the 13C NMR (174.81 ppm), 29Si NMR (-23.9
ppm) and IR spectral data (3337 and 1628 cm-1), allows us to
confidently assign the structure of 4-SiCa(I) to the amide, rather
than the imidate isomer.
Reactivity of Mes2Si SiMes2 (1) and Mes2Ge GeMes2 (2)
The addition of acetamide (I), benzamide (II), NMA (III), NMB
(IV), NPA (V), NPB (VI) and NBB (VII) to disilene 1 in
THF at room temperature gave 4-SiSi(I,II) and 5-SiSi(III–VII),
contaminated with small amounts of Mes2Si(OH)Si(H)Mes2,18a
(Mes2SiH)2,19 Mes2SiH2,20 and excess starting amide (Scheme 4).
Compounds Mes2Si(OH)Si(H)Mes2, (Mes2SiH)2 and Mes2SiH2
were identified by comparison of the 1H NMR spectral data to the
values reported in the literature. Silanol Mes2Si(OH)Si(H)Mes2
was likely formed by the addition of adventitious water to disilene
1. (Mes2SiH)2 and Mes2SiH2 are often present in trace amounts
in the disilene precursor, Mes2Si(SiMe3)2, and are commonly
observed in reactions involving 1. The addition of acetamide
(I), benzamide (II), NMA (III), NPA (V) and NPB (VI) to
Fig. 1 Molecular structure of 4-SiCa(I) (30% probability level). All
˚
hydrogen atoms are omitted for clarity. Selected bond lengths (A)
and angles (◦): C(1)–Si(2) 1.924(2), Si(2)–N(3) 1.793(2), Si(2)–Si(20)
2.3612(8), Si(2)–Si(16) 2.3678(9), N(3)–C(4) 1.349(3), C(4)–O(5) 1.241(2),
C(4)–C(6) 1.501(3); N(3)–C(4)–C(6) 118.0(2), O(5)–C(4)–N(3) 121.1(2),
O(5)–C(4)–C(6) 120.8(2), N(3)–Si(2)–Si(16) 105.72(6), N(3)–Si(2)–Si(20)
100.80(6), N(3)–Si(2)–C(1) 103.08(9), Si(20)–Si(2)–Si(16) 110.36(3).
To determine the regiochemistry of the remaining silene-amide
adducts, the 13C chemical shifts of the unsaturated, non-aromatic
carbons and the 29Si chemical shifts of the functionalized central
silicon atoms were compared to those of amide 4-SiCa(I) (Table
1). The unsaturated, non-aromatic carbons of 4-SiCa(I–IV) and
4-SiCb(I,IV) resonated at 176 4 ppm, whereas the same carbons
in 5-SiCa(V–VII) resonated upfield at 161 2 ppm. The central
Scheme 4 Addition of amides to disilene 1 and digermene 2.
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Table 2 Selected 13C and 29Si chemical shifts of 4-SiSi(I,II), 5-SiSi(III–
VII), 4-GeGe(I–III), and 5-GeGe(V,VI)
Typically, broad signals are obtained for simple compounds and
for larger, more complex molecules, the signals become too broad
to observe.23 However, based on the 13C NMR spectral data, we
assign the structures of 4-GeGe(I–III) to germyl amides and 5-
GeGe(V,VI) to germyl imidates.
Compound
Amide
dCa/ppm dSib/ppm
4-SiSi(I)
Acetamide
Benzamide 168.93
NMA
NMB
NPA
NPB
NBB
Acetamide
Benzamide 169.72
NMA
NPA
NPB
171.65
-20.5
-19.6
-7.5
-5.2
-4.7
-2.2
-4.6
—
—
—
—
—
Amide
Amide
Imidate
Imidate
Imidate
Imidate
Imidate
Amide
Amide
Amide
Imidate
Imidate
Discussion
4-SiSi(II)
5-SiSi(III)
5-SiSi(IV)
5-SiSi(V)
5-SiSi(VI)
5-SiSi(VII)
4-GeGe(I)
4-GeGe(II)
4-GeGe(III)
5-GeGe(V)
5-GeGe(VI)
157.89
157.77
157.14
155.52
158.15
172.40
The (di)metallenes examined in this study contain either a non-
polar Si Si or Ge Ge bond (1 or 2, respectively) or a relatively
non-polar Si C bond (3a and 3b). In general, their reactivity
towards amides was quite similar. The addition of amides to 1, 2
and 3a/b resulted in the formation of a single regioisomer in all
cases: an amide or an imidate. Cycloaddition between the C
O
175.69
160.90
158.44
bond of the amide and the M E bond of the (di)metallene was
not observed. The primary amides, acetamide (I) and benzamide
(II), reacted with the (di)metallenes to give amide adducts and
the N-phenyl amides [NPA (V) and NPB (VI)] and NBB (VII)
reacted with the (di)metallenes to give imidate adducts (Scheme
5). Interestingly, the N-methyl amides, NMA (III) and NMB (IV),
reacted with the silenes/digermene to give amide adducts, whereas
they reacted with disilene 1 to give imidate adducts.
a Signal assigned to the unsaturated, non-aromatic carbon atom:
R¢¢NCOR¢. b Signal assigned to the non-Mes2SiH silicon atom.
digermene 2 in THF at room temperature gave 4-GeGe(I–
III) and 5-GeGe(V,VI) contaminated with small amounts of
Mes2Ge(OH)Ge(H)Mes2,21 presumably formed by the addition
of trace amounts of water to the digermene, and excess starting
amide (Scheme 4).
With the exception of the addition of NMA to digermene 2,22
only one product derived from the addition of the amide to 1 or 2
was formed in each case; the reactions were completely regioselec-
tive. Similar to silyl amides 4-SiCa(I–IV) and 4-SiCb(I,IV), the 1H
NMR spectra of 4-SiSi(I,II) and 4-GeGe(I,II) revealed only one
set of signals for each compound. For silyl imidates 5-SiSi(III–
VII) and germyl imidates 5-GeGe(V,VI), only one stereoisomer
was obtained.
Compounds 4-SiSi(I,II), 5-SiSi(III–VII), 4-GeGe(I–III) and
5-GeGe(V,VI) were identified by NMR spectroscopy and mass
spectrometry. Compounds 4-SiSi(I,II) were also identified by
IR spectroscopy. A summary of the 13C chemical shifts of the
unsaturated, non-aromatic carbons of 4-SiSi(I,II), 5-SiSi(III–
VII), 4-GeGe(I–III)and 5-GeGe(V,VI) and the 29Si chemical shifts
of the non-Mes2SiH silicon atoms of 4-SiSi(I,II) and 5-SiSi(III–
VII) are presented in Table 2.
The unsaturated, non-aromatic carbons of 4-SiSi(I,II) and 4-
GeGe(I–III) resonated at 172 4 ppm, whereas the corresponding
carbons of 5-SiSi(III–VII) and 5-GeGe(V,VI) resonated upfield
at 158 3 ppm. Furthermore, the non-Mes2SiH silicons of 4-
SiSi(I,II) both resonated at ~ -20 ppm and those of 5-SiSi(III–
VII) resonated downfield between -2.2 and -7.5 ppm. These data
Scheme 5 Summary of the addition of amides to (di)metallenes 1,2,3a/b.
suggest that two distinct isomers are formed; compounds with 13
C
For the silyl and germyl amides, either one rotameric isomer
was formed or the amide functionality is freely rotating about
the C–N bond at room temperature. In N-trialkylsilyl12c,17,24a and
N-trimethylgermyl amides25 the most abundant rotameric isomer
has the pseudo Z-configuration, the same configuration observed
in the structure of 4-SiCa(I) (Fig. 1) and is likely preferred since
it places the amide oxygen within close range of an oxophilic
silicon or germanium atom. For the silyl and germyl imidates, only
one stereoisomer was formed. Similarly, no evidence for a second
isomer was observed in the formation of trialkylsilyl imidates
[R¢C(OSiR3)NR¢¢].12c,24a The imidate adducts derived from the
(di)metallenes most likely have the E-configuration because this
chemical shifts of 172 4 ppm (and 29Si chemical shifts around -20
ppm) were assigned silyl/germyl amide structures and compounds
with 13C chemical shifts of 158 3 ppm (and 29Si chemical shifts
within -2.2 and -7.5 ppm) were assigned silyl/germyl imidate
structures (Table 2).
Although 29Si NMR spectroscopy can be used to help distin-
guish between the isomers of 4-SiSi(I,II) and 5-SiSi(III–VII), the
isomers of compounds 4-GeGe(I–III) and 5-GeGe(V,VI) cannot
be easily distinguished using 73Ge NMR spectroscopy since the
73Ge nucleus has a spin of 9/2 and is not very sensitive. Few
germanium compounds have been characterized by this technique.
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minimizes steric interactions between the R¢¢ substituent and the
bulky substituents on the (di)metallene.
imidate form, in this case, by hindering rearrangement to the amide
form (vide infra).
Although
compounds
containing
and silyl
silyl
imidate
amide
[SiOC-
Acetamide (I) and NMA (III) are similar in structure: NMA
contains a methyl group in place of a hydrogen atom on the amide
nitrogen. The increased bulk of the methyl group of NMA did
not alter the reaction pathway in the case of silene 3a; acetamide
and NMA both reacted with 3a to give silyl amides. However,
in the reaction between disilene 1 and NMA, the difference
in the bulkiness of the substituent was sufficient to alter the
regiochemistry of the reaction: acetamide reacted with 1 to give a
silyl amide, whereas NMA reacted with 1 to give a silyl imidate.
Similar results were obtained for the reaction between benzamide
and NMB and silene 3a (both gave silyl amides) and benzamide
and NMB and disilene 1 (benzamide gave an silyl amide, whereas
NMB gave a silyl imidate) indicating that the size of the substituent
on the amide nitrogen (R¢¢) has a greater influence on the reaction
pathway than the substituent bonded to the carbonyl carbon (R¢).
All previously reported N-trimethylgermyl amides exist in the
amide form suggesting that, in general, germanium prefers the
amide form over the imidate form.25 Similarly, digermene 2
reacted with acetamide and benzamide to give an amide adduct.
Digermene 2 reacted with NMA to give an amide adduct rather
than an imidate adduct as observed with the analogous disilene
(1). Ge–Ge single bonds (Ge–Ge single bond range: 2.457–2.463
[SiNR¢¢(C O)R¢]12b–d,17,24,26
(R¢) NR¢¢]12,17a,24,27 moieties have been reported previously,
adducts 4-SiCa(I–IV), 5-SiCa(V–VII), 4-SiCb(I,IV), 4-SiSi(I,II),
and 5-SiSi(III–VII) are the first silyl amides and imidates prepared
by the direct addition of amides to silenes and disilenes. Germyl
amides have also been prepared,25 although not by the direct
addition of an amide to a digermene. Germyl imidates were
unknown prior to this work.
Related compounds containing N-trialkylsilyl groups, such as
SiMe3 or SiMe2t-Bu, exist as amides (A), imidates (B), or isomeric
mixtures (Scheme 6); the position of the equilibrium is strongly
dependent upon the nature of the substituents.12c,d,17,24 In general,
if the substituent attached to nitrogen enhances the p-character
of the C–N bond, the amide form is preferred, whereas if the
opposite is true, the imidate form is favoured.12c,24b Thus, when the
substituent bonded to nitrogen (R¢¢) is an alkyl group, the amide
form (A) is observed; however, when R¢¢ is an aryl group, imidates
(B) or isomeric mixtures are observed. The imidate isomer also
contains a strong Si–O bond, which undoubtedly contributes to its
thermodynamic stability. The substituent bonded to the carbonyl
carbon (R¢) does not appear to have a strong influence on the
equilibrium. Finally, the effect of increasing the steric bulk at
silicon was examined for a series of N-silyl-N-phenyl formamides
(HCONPhSiR3, R = alkyl or aryl).28 Increasing the size of the
substituents within the silyl group greatly affected the amide–
imidate equilibrium. Compounds containing the silyl groups, Sii-
Pr3 and SiPh2i-Bu, existed exclusively in the imidate form, whereas
compounds containing less bulky substituents at silicon existed as
amide–imidate mixtures.
A)7b are longer than Si–Si single bonds (average Si–Si single bond
˚
11
length: 2.34 A) and Ge–O bonds are weaker than Si–O bonds.8i
˚
Both factors may play a role in stabilizing the amide form over
the imidate form in digermene adducts. The reaction of N-phenyl
amides V–VI with 2 gave germyl imidates consistent with both the
results obtained for disilene 1 and silenes 3a/b; the amide isomer
was not apparent. Again, stabilization by resonance may account
for the formation of the imidate isomer.
The possibility that an equilibrium between the amide and
the tautomeric imidic acid accounts for the observed reactivity
was considered. However, it was concluded that the difference
in reactivity between primary and N-phenyl amides is likely not
due to the presence of free imidic acid in solution, since the
amide–imidic acid equilibrium typically lies strongly in favour of
the amide form (k-1 ꢀ k1) (Scheme 7).16,29 Polar solvents may
lead to an increase in the imidic acid concentration; however,
the reactions reported here were conducted in benzene or THF,
solvents that are not expected to greatly influence the amide–imidic
acid equilibrium. Furthermore, if the rate of OH insertion (k3)
was much greater than the rate of NH insertion (k2), then imidate
products would be expected to form in all reactions; clearly, this
is not the case.
Scheme 6 Amide–imidate equilibrium of N-trialkylsilyl compounds.
In contrast to the reported N-trialkylsilyl amide/imidate sys-
tems, the analogous trimethylgermyl compounds with either a
hydrogen or an aryl group at nitrogen exist only in the amide
form, which has been attributed to a smaller difference between
Ge–O and Ge–N bond strengths compared to Si–O and Si–N
bond strengths.25
In congruence with previous work,12c,24b,28 our results show that
the substituents on the amide nitrogen (R¢¢) and the nature of the
(di)metallene have a significant influence on the regiochemistry
of the reactions whereas the substituent on the carbonyl carbon
(R¢) has little or no discernable influence. The addition of N-
phenyl amides [NPA (V) and NPB (VI)] to the (di)metallenes
leads exclusively to imidate adducts; delocalization of the electron
density on nitrogen by the phenyl group leading to a reduction
in the strength of the (O )C–N p bond appears to stabilize the
imidate form over the amide form.12c,24b The addition of NBB
to disilene 1 and silene 3a also gave silyl imidates; likely, steric
interactions between the (di)metallene substituents and the benzyl
group on the amide nitrogen (R¢¢) played a role in stabilizing the
Scheme 7 Amide–imidic acid equilibrium.
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The addition of aldehydes to disilene 13f ,8a,c,30 and silenes
3a/b8a,b proceeds by way of a biradical intermediate whereas
the addition of aldehydes to digermenes3e proceeds by way of
a zwitterion.8i The amide oxygen is more nucleophilic than the
carbonyl oxygen of an aldehyde; thus, we propose that the addition
of amides to (di)metallenes 1–3 begins with initial coordination
of the amide oxygen to the (di)metallene to give a zwitterionic
complex (Scheme 8). This is the expected regiochemistry for the
formation of a complex for silenes; the regioselective complexation
of alcohols,8c carbonyl compounds, amines and nitriles to polar
silenes has been proposed previously.6 Although no direct evidence
for complexation to silene 3a or b has been obtained thus far,
the relatively non-polar silenes do contain Si C bonds that are
polarized towards the silenic carbon (albeit, to a lesser extent
than the polar silenes). Thus, weak complexation at the silenic
silicon is reasonable in the case of silenes 3a/b. Furthermore,
complexation of the amide oxygen at the silenic silicon would lead
to the formation of a strong Si–O bond. After the formation of
the complex (with 1,2 or 3a/b), the basic portion of the complex
(R2E-) may then intramolecularly abstract the amidic hydrogen
(via a six-membered ring transition state) to give an imidate (5).
The imidates resulting from the addition of primary (R¢¢ = H) or
N-methyl amides (R¢¢ = CH3) may then undergo intramolecular
rearrangement to give formal NH insertion products (4) (Scheme
8). A similar pathway has been proposed for the addition of amides
to the Ge(100)-2 ¥ 1 surface.2
been observed because abstraction of the weakly acidic hydrogen
is favoured.
There are two reports in the literature that describe the addition
of amides to the Ge(100)-2 ¥ 1 surface2,33 and no reports
of the addition of amides to the Si(100)-2 ¥ 1 surface. Bent
and co-workers reported that the addition of tertiary amides
to the Ge(100)-2 ¥ 1 surface at room temperature resulted in
coordination of the amides to the Ge surface through the oxygen
atom in each case, as determined by MIR-FTIR spectroscopy.33
The experimental results were supported by DFT calculations.
The addition of primary and secondary amides (formamide, N-
methylformamide (NMF) and N-methylacetamide (NMA)) to
the Ge surface at room temperature resulted in the formation
of two types of products: a 1 : 1 association complex, where one
Ge atom is coordinated to the amide oxygen and the other Ge
atom is weakly bound to the NH (7) and a covalently bound
Ge–O (8a) or Ge–N (8b) species that is also coordinated to a Ge
atom of an adjacent dimer through a nitrogen or oxygen atom,
respectively (Scheme 9).2 Surface adducts 8a (imidate) and 8b
(amide) could not be distinguished by MIR-FTIR spectroscopy; it
is not known if a mixture of 8a and 8b forms on the surface or if one
regioisomer is preferred.2 In comparison, the addition of primary
amides (acetamide and benzamide) and NMA to digermene 2
gave germyl amides (4-GeGe(I–III)) and the addition of N-phenyl
amides (NPA and NPB) gave germyl imidates (5-GeGe(V,VI)), as
determined by NMR spectroscopy. Digermoxetane formation was
not observed on the Ge surface or with the digermene.
Scheme 9 Proposed adducts of primary and secondary amides formed
on the Ge(100)-2 ¥ 1 surface.
Based on our results and what is known about N-
trimethylgermyl amides,25 we propose that the reactions on the
Ge surface are regioselective and that amide adduct 8b forms, not
8a. Although the addition of N-aryl amides to the Ge surface has
not been attempted, we predict that imidate adducts similar in
structure to 8a would form preferentially.
Scheme
(di)metallenes.
8
Proposed mechanism for the addition of amides to
Although amides are structurally related to esters, 3a/b31 and
132 are unreactive towards simple esters (i.e. ethyl acetate, methyl
benzoate). There are two likely factors which contribute to the
greater reactivity of amides: the enhanced nucleophilicity of the
carbonyl oxygen of amides and the weakly acidic amidic hydrogen
which can be abstracted through a six-membered cyclic transition
state. Furthermore, cycloaddition between the C O bond of the
amide and the M E bond of the (di)metallene may not have
Summary
The addition of primary and secondary amides to silenes 3a/b,
disilene 1 and digermene 2 was investigated; the reactions were
completely regioselective. The structures of the adducts were
determined unambiguously using 13C and 29Si NMR spectroscopy
as the primary diagnostic tools. The silenes and the dimetallenes
were similar in reactivity towards primary and N-phenyl amides;
614 | Dalton Trans., 2012, 41, 609–621
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Table 3 Reaction conditions and product ratios for the formation of 4-
SiCa(I–IV), 5-SiCa(V–VII), and 4-SiCb(I,IV)
primary amides reacted with the (di)metallenes to give silyl
and germyl amides (4) and N-phenyl amides reacted with the
(di)metallenes to give silyl and germyl imidates (5). On the other
hand, N-methyl amides reacted with 2 and 3a/b to give silyl
and germyl amides (4), but reacted with 1 to give silyl imidates
(5). The selectivity is strongly influenced by the substituent
bonded to the amide nitrogen (R¢¢). In general, the imidate
form was observed when R¢¢ = aryl and the amide form was
observed when R¢¢ = alkyl; however, steric interactions between the
substituents on the amide and the (di)metallene also influenced
the regiochemistry. The silyl and germyl amides likely have the
pseudo Z-configuration; however, the exact configuration of the
isomers cannot be established based on our data, except in the
case of silene-acetamide adduct 4-SiCa(I), for which the molecular
structure was obtained. For the silyl and germyl imidates, only
one stereoisomer was observed, likely the E-isomer. Prior to this
work, the direct addition of amides to (di)metallenes had not been
explored and germyl imidates had not been synthesized.
We propose that the reaction of amides with group 14
(di)metallenes begins with coordination of the amide carbonyl
to either silicon or germanium of the (di)metallene followed by
abstraction of the amidic hydrogen to give an imidate which may
rearrange to the amide based on the nature of the substituent at
nitrogen.
Digermene 2 and the germanium dimers on the Ge(100)-2 ¥
1 surface are comparable in reactivity towards primary and N-
methyl amides. Although IR spectroscopy cannot be used to
distinguish between Ge–O bonded imidates and Ge–N bonded
amides on the surface, our results suggest that the addition of
primary and N-methyl amides to the Ge surface will result in a
single regioisomer, likely a germyl amide. Currently, there are no
examples of the addition of amides to the Si(100)-2 ¥ 1 surface.
Based on our results for the molecular system, we believe that the
addition of amides to the Si surface will be regioselective. Primary
amides will likely give silyl amides and N-aryl amides will likely
give silyl imidates.
3, mmol Starting amide tirr/h
Product ratioa
3a, 0.09
3a, 0.09
3a, 0.09
3a, 0.09
3a, 0.09
3a, 0.09
3a, 0.09
3b, 0.05
3b, 0.07
Acetamide
Benzamide
NMA
NMB
NPA
NPB
NBB
Acetamide
NMB
36
36
14–20
14–20
36
36
14–20
45
4-SiCa(I) : swa : sa
4-SiCa(II) : sa
4-SiCa(III) : swa : sa
4-SiCa(IV) : sa
5-SiCa(V) : sa
100 : 1 : 19
28 : 1
84 : 1 : 17
4 : 1
9 : 1
14 : 1
4 : 1
8 : 1
100 : 1 : 1
5-SiCa(VI) : sa
5-SiCa(VII) : sa
4-SiCb(I) : sa
14
4-SiCb(IV) : swa : sa
a swa = silene–water adduct, sa = starting amide.
using a Bruker Vector 33 or Tensor 27 FTIR spectrometer. EI
and CI mass spectra were obtained using a Finnigan MAT model
8400 instrument (70 eV). ESI-TOF mass spectra were obtained on
a Micromass LCT instrument. Mass spectral data are reported in
mass-to-charge units, m/z, with ion identity and peak intensities
(%) in parentheses. Photolyses of Mes2Si(SiMe3)2 and Mes6Ge3
were performed in a Rayonet photochemical reactor (Southern
New England Ultraviolet Co.) equipped with 254 or 350 nm
lamps using quartz or Pyrex glassware, respectively. Solutions of
Mes2Si(SiMe3)2 and Mes6Ge3 were cooled during irradiation using
a dry-ice/isopropanol slurry or a dry-ice/acetone slurry, respec-
tively. Photolyses of (Me3Si)3SiCO(t-Bu) and (Me3Si)3SiCO(1-Ad)
were carried out using three 100 W mercury spot lamps (Blak-Ray
B-100AP series; l > 350 nm◦). Samples were immersed in water,
inside a water-cooled (~8–20 C)39 Pyrex immersion well. Melting
point data are uncorrected.
Addition of amides to silenes 3a and 3b. Equimolar amounts
of acylsilane and amide were placed in an NMR tube and C6D6
(~0.5 mL) was then added. The reaction mixture was irradiated for
1
several hours; the progress of the reaction was monitored by H
NMR spectroscopy. In the case of acetamide, benzamide, NPA and
NPB, the amide was not entirely soluble in C6D6; thus, the contents
of the NMR tube were mixed once during the irradiation period.
In all cases, a pale yellow or colourless solution was obtained after
irradiation; no acylsilane was present in the solution as determined
by 1H NMR spectroscopy. All product mixtures contained starting
amide and/or ~1% or less of (Me3Si)2Si(OH)CH(OSiMe3)(t-Bu)8a
or (Me3Si)2Si(OH)CH(OSiMe3)(1-Ad).40 The specific conditions
and product ratios for each reaction are given in Table 3. Attempts
to purify the adducts by chromatography resulted in hydrolysis
and, with the exception of 4-SiCa(I,II) and 4-SiCb(I), the adducts
hydrolyzed upon exposure to atmospheric moisture; therefore, the
adducts were characterized without purification. Single crystals
of 4-SiCa(I) were obtained by the slow evaporation of a C6D6
solution (see X-Ray experimental section).
Experimental
General
All experiments were carried out under an atmosphere of argon
or nitrogen using standard Schlenk techniques34 or a glove box.
Hexanes and THF were purified using standard procedures.35
˚
C6D6 was distilled from LiAlH4, degassed, and stored over 4 A
molecular sieves. Acetamide was dissolved in acetone, dried over
MgSO4, filtered, and the solvent was removed under vacuum.
Benzamide was recrystallized from ethanol and then benzene.
All other chemicals were purchased from commercial sources
and used without further purification. (Me3Si)3SiCO(t-Bu),36a,c
38
1
(Me3Si)3SiCO(1-Ad),36a,b Mes2Si(SiMe3)2,37 and Mes6Ge3 were
4-SiCa(I): H NMR (C6D6, 600 MHz) d 4.59 (br s, 1H, NH),
prepared according to literature procedures.
4.30 (s, 1H, OCH), 1.70 (s, 3H, CH3), 1.01 (s, 9H, t-Bu), 0.36 (s, 9H,
SiMe3), 0.26 (s, 9H, SiMe3), 0.16 (s, 9H, OSiMe3); 13C NMR (C6D6,
150 MHz) d 174.81 (C O), 78.70 (OCH), 35.73 (C(CH3)3), 28.76
(C(CH3)3), 24.70 (CH3), 1.16 (SiMe3), 0.91 (SiMe3), 0.59 (SiMe3);
29Si NMR (C6D6) d 14.8 (OSiMe3), -15.7 (SiMe3), -16.5 (SiMe3),
-23.9 ((Me3Si)2Si); IR (cm-1) 3337 (s, NH), 2953 (s), 2897 (m),
2864 (w), 1628 (s, C O), 1433 (m), 1361 (w), 1263 (m), 1245 (s),
1058 (s), 1026 (m), 835 (s), 744 (m), 691 (m); CI-MS m/z 392
NMR spectra were recorded on a Varian Mercury 400, Inova
400 or 600 MHz NMR spectrometer using C6D6 as the solvent.
1
The NMR standards used are as follows: H NMR spectra were
referenced to residual C6D5H (7.15 ppm); 13C NMR spectra were
referenced to the central transition of C6D6 (128.00 ppm); 29Si
NMR spectra (1H–29Si gHMBC) were externally referenced to
Me4Si (0 ppm). FTIR spectra were recorded (cm-1) as thin films
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(M + H+, 5%), 376 ((M - Me)+, 73%), 306 (57%), 302 ((M -
OSiMe3)+, 32%), 263 (57%), 248 (100%), 232 ((M - CH(OSiMe3)(t-
(Ph m-C), 128.18 (Ph m-C), 123.09 (Ph p-C), 122.18 (Ph o-C),
78.54 (OCH), 36.15 (C(CH3)3), 28.83 (C(CH3)3), 1.46 (OSiMe3),
0.95 (SiMe3), 0.81 (SiMe3); 29Si NMR (C6D6) d 15.0 (OSiMe3), 4.3
((Me3Si)2Si), -16.0 (SiMe3), -16.8 (SiMe3); EI-MS m/z 529 (M+,
0.5%), 514 (M+ - Me, 3%), 456 (M+ - SiMe3, 6%), 444 (11%), 386
(100%), 370 (M+ - CH(OSiMe3)(t-Bu), 20%), 180 (PhN CPh+,
Bu))+, 34%), 73 (SiMe3 , 25%); high-resolution CI-MS for
+
C16H42Si4NO (M + H+) (m/z) calc. 392.2293, found 392.2295.
4-SiCa(II): 1H NMR (C6D6, 600 MHz) d 7.95–7.87 (m, 2H, Ph
o-H), 7.10–7.02 (m, 3H, Ph p-H, Ph m-H), 5.74 (br s, 1H, NH),
4.51 (s, 1H, OCH), 1.06 (s, 9H, t-Bu), 0.39 (s, 9H, SiMe3), 0.33 (s,
9H, SiMe3), 0.09 (s, 9H, OSiMe3); 13C NMR (C6D6, 150 MHz) d
171.86 (C O), 135.91 (Ph i-C), 131.49 (Ph p-C), 128.81 (Ph m-C),
127.48 (Ph o-C), 78.82 (OCH), 35.83 (C(CH3)3), 28.84 (C(CH3)3),
1.14 (OSiMe3), 0.97 (SiMe3), 0.74 (SiMe3); 29Si NMR (C6D6) d
15.3 (OSiMe3), -15.4 (SiMe3), -16.0 (SiMe3), -22.2 ((Me3Si)2Si);
EI-MS m/z 452 (M+ - H, 2%), 438 (M+ - Me, 20%), 380 (M+ -
SiMe3, 7%), 368 (11%), 310 (100%), 294 (M+ - CH(OSiMe3)(t-Bu),
+
79%), 73 (SiMe3 , 9%); high-resolution EI-MS for C27H47Si4O2N
(M+) (m/z) calc. 529.2684, found 529.2673.
1
5-SiCa(VII): H NMR (C6D6, 600 MHz) d 7.46–7.39 (m, 2H,
Ph o-H), 7.37–7.30 (m, 2H, Ph o-H), 7.26–7.19 (m, 2H, Ph m-H),
~7.14–6.98 (m, Ph m-H, Ph p-H),42 4.59 (s, 1H, OCH), 4.44 (s,
2H, CH2), 1.11 (s, 9H, t-Bu), 0.40 (s, SiMe3),41 0.36 (s, SiMe3),41
0.16 (s, OSiMe3);41 13C NMR (C6D6, 150 MHz) d 161.63 (C N),
141.18 (Ph i-C), 133.51 (Ph),43 129.57 (Ph),43 128.56 (Ph),43 128.51
(Ph),43 128.25 (Ph o-C), 128.07 (Ph o-C), 126.95 (Ph),43 78.51
(OCH), 54.59 (CH2), 36.28 (C(CH3)3), 28.75 (C(CH3)3), 1.59
(OSiMe3), 0.85 (SiMe3 ¥ 2); 29Si NMR (C6D6) d 14.8 (OSiMe3),
1.0 ((Me3Si)2Si), -16.4 (SiMe3), -17.5 (SiMe3); CI-MS m/z 542
(M - H+, 0.4%), 528 ((M - Me)+, 2%), 516 (1%), 470 ((M -
SiMe3)+, 5%), 458 (8%), 400 (100%), 384 ((M - CH(OSiMe3)(t-
Bu))+, 15%), 263 (7%), 211 (34%), 191 (21%); high-resolution
CI-MS for C28H48Si4O2N (M - H+) (m/z) calc. 542.2762, found
542.2775.
+
14%), 73 (SiMe3 , 32%); high-resolution EI-MS for C21H42Si4NO2
(M+ - H) (m/z) calc. 452.2293, found 452.2281.
4-SiCa(III): 1H NMR (C6D6, 600 MHz) d 4.52 (br s, 1H, OCH),
2.57 (br s, 3H, NCH3), 1.71 (br s, 3H, CH3), 1.02 (br s, 9H, t-Bu),
0.37 (s, SiMe3),41 0.34 (br s, SiMe3),41 0.18 (s, OSiMe3);41 13C NMR
(C6D6, 150 MHz) d 177.37 (br, C O), 77.71 (br, OCH), 36.25 (br,
C(CH3)3, NCH3), 28.68 (C(CH3)3), 21.36 (br, CH3), 1.75, 1.65, 1.59
(OSiMe3, SiMe3 ¥ 2); 29Si NMR (C6D6) d 14.5 (OSiMe3), -14.4
((Me3Si)2Si), -17.2 (SiMe3 ¥ 2); EI-MS m/z 405 (M+, 0.4%), 390
(M+ - Me, 10%), 332 (M+ - SiMe3, 15%), 320 (43%), 262 (100%),
246 (M+ - CH(OSiMe3)(t-Bu), 60%), 207 (49%), 191 (64%); high-
resolution EI-MS for C17H43Si4O2N (M+) (m/z) calc. 405.2371,
found 405.2371.
1
4-SiCb(I): H NMR (C6D6, 600 MHz) d 4.60 (br s, 1H, NH),
4.24 (s, 1H, OCH), 2.01–1.92 (br m, 4H, Ad), 1.73 (s, 3H, CH3),
1.74–1.62 (br m, Ad),44 0.40 (s, 9H, SiMe3), 0.28 (s, 9H, SiMe3),
0.18 (s, 9H, OSiMe3); 13C NMR (C6D6, 150 MHz) d 174.88
(C O), 79.90 (OCH), 41.39 (Ad), 37.80 (Ad), 37.37 (Ad), 29.02
(Ad), 24.78 (CH3), 1.25 (OSiMe3), 1.04 (SiMe3), 0.71 (SiMe3); 29Si
NMR (C6D6) d 14.8 (OSiMe3), -15.6 (SiMe3), -16.4 (SiMe3), -24.2
((Me3Si)2Si); high-resolution CI-MS for C22H48Si4O2N (M + H+)
(m/z) calc. 470.2762, found 470.2745.
4-SiCa(IV): 1H NMR (C6D6, 600 MHz) d 7.47–7.38 (m, 2H, Ph
o-H), 7.12–7.01 (m, 3H, Ph m-H, Ph p-H), 4.71 (br s, 1H, OCH),
2.79 (br s, 3H, CH3), 1.09 (s, 9H, t-Bu), 0.42 (s, 9H, SiMe3), 0.38
(s, 9H, SiMe3), 0.22 (s, 9H, OSiMe3); 13C NMR (C6D6, 150 MHz)
d 177.68 (br, C O), 137.04 (br, Ph i-C), 129.64 (Ph p-C), 128.37
(Ph m-C), 127.84 (Ph o-C), 77.99 (OCH), 38.30 (br, CH3), 36.41
(C(CH3)3), 28.68 (C(CH3)3), 1.75 (OSiMe3, SiMe3 ¥ 2); 29Si NMR
(C6D6) d 14.9 (OSiMe3), -15.2 ((Me3Si)2Si), -16.9 (SiMe3 ¥ 2);
CI-MS m/z 466 (M - H+, 1%), 452 ((M - Me)+, 6%), 394 ((M -
SiMe3)+, 12%), 382 (33%), 324 (100%), 308 ((M - CH(OSiMe3)(t-
Bu))+, 63%), 207 (92%), 191 (94%), 118 (PhC N(CH3)+, 99%);
high-resolution CI-MS for C22H44Si4O2N (M - H+) (m/z) calc.
466.2449, found 466.2434.
5-SiCa(V): 1H NMR (C6D6, 600 MHz) d 7.18–7.12 (m, 2H, Ph
m-H), 6.93–6.89 (m, 1H, Ph p-H), 6.85–6.80 (m, 2H, Ph o-H), 4.43
(s, 1H, OCH), 1.62 (s, 3H, CH3), 1.07 (s, 9H, t-Bu), 0.38 (s, 9H,
SiMe3), 0.35 (s, 9H, SiMe3), 0.22 (s, 9H, OSiMe3); 13C NMR (C6D6,
150 MHz) d 162.23 (C N), 149.44 (Ph i-C), 129.36 (Ph m-C),
123.25 (Ph p-C), 121.65 (Ph o-C), 78.66 (OCH), 36.08 (C(CH3)3),
28.78 (C(CH3)3), 17.26 (CH3), 1.50 (OSiMe3), 1.00 (SiMe3), 0.65
(SiMe3); 29Si NMR (C6D6) d 14.6 (OSiMe3), 4.0 ((Me3Si)2Si), -16.3
(SiMe3), -17.0 (SiMe3); EI-MS m/z 467 (M+, 1%), 452 (M+ - Me,
3%), 394 (M+ - SiMe3, 6%), 382 (15%), 324 (100%), 308 (M+ -
CH(OSiMe3)(t-Bu), 22%), 262 (12%), 207 (19%), 191 (19%), 118
(PhN C(CH3)+, 60%); high-resolution EI-MS for C22H45Si4O2N
(M+) (m/z) calc. 467.2527, found 467.2524.
4-SiCb(IV): 1H NMR (C6D6, 600 MHz) d 7.50–7.43 (m, 2H, Ph
o-H), 7.12–7.03 (m, 3H, Ph m-H, Ph p-H), 4.65 (br s, 1H, OCH),
2.84 (br s, 3H, CH3), 2.02–1.97 (m, Ad),44 1.90–1.82 (m, Ad),44
1.78–1.63 (m, Ad),44 0.45 (s, 9H, SiMe3), 0.42 (s, 9H, SiMe3), 0.24
(s, 9H, OSiMe3); 13C NMR (C6D6, 100 MHz)45 d 177.52 (C O),
137.32 (Ph i-C), 129.59 (Ph p-C), 128.40 (Ph m-C), 127.75 (Ph
o-C), 79.33 (OCH), 40.82 (Ad), 38.49 (CH3), 37.42 (Ad), 29.13
(Ad), 1.89 (br, OSiMe3, SiMe3 ¥ 2); 29Si NMR (C6D6) d 14.9
(OSiMe3), -15.5 ((Me3Si)2Si), -16.7 (SiMe3), -16.9 (SiMe3); EI-
MS m/z 544 (M+ - H, 1%), 530 (M+ - Me, 4%), 472 (M+ - SiMe3,
24%), 397 (6%), 382 (3%), 355 (18%), 339 (14%), 324 (100%),
308 (M+ - CH(OSiMe3)(t-Bu), 22%), 265 (18%), 207 (77%), 118
(PhC N(CH3)+, 51%), 73 (SiMe3 , 57%); high-resolution EI-MS
+
for C28H50Si4O2N (M+ - H) (m/z) calc. 544.2919, found 544.2900.
Addition of amides to disilene 1
Mes2Si(SiMe3)2 (50 mg, 0.12 mmol) was dissolved in hexanes
◦
(5 mL) and irradiated (l = 254 nm) at -78 C for ~9 hr.37 The
hexanes were then removed; a yellow solid was obtained. The
yellow solid was dissolved in THF (6 mL) and the solution was
either used in a single reaction (0.06 mmol Mes2Si SiMes2) or
divided in half and used in two separate reactions (0.03 mmol
Mes2Si SiMes2 per reaction). The solid amides were dissolved in
THF (1 mL) then added to the disilene solution. For NMA, a single
drop of amide was added to the disilene solution. The reaction
mixtures were stirred at room temperature and the progress of
5-SiCa(VI): 1H NMR (C6D6, 600 MHz) d 7.52–7.47 (m, 2H, Ph
o-H), 7.08–7.03 (m, 2H, Ph m-H), 6.90–6.85 (m, 5H, Ph m-H, Ph
p-H, Ph o-H), 6.85–6.80 (m, 1H, Ph p-H), 4.64 (s, 1H, OCH), 1.13
(s, 9H, t-Bu), 0.45 (s, 9H, SiMe3), 0.38 (s, 9H, SiMe3), 0.19 (s, 9H,
OSiMe3); 13C NMR (C6D6, 150 MHz) d 159.43 (C N), 148.77
(Ph i-C), 132.62 (Ph i-C), 130.13 (Ph p-C), 129.83 (Ph o-C), 129.44
616 | Dalton Trans., 2012, 41, 609–621
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Table 4 Reaction conditions for the formation of 4-SiSi(I,II) and 5-
(6%), 163 (9%), 121 (9%), 69 (11%); high-resolution EI-MS for
C38H49Si2NO (M+) (m/z) ca◦lc. 591.3353, found 591.3339.
SiSi(III–VII)
1
4-SiSi(II): Mp 198–205 C (decomp.); H NMR (C6D6, 600
Starting amide,
mmol
Reaction
time
MHz) d 7.86–7.81 (m, 2H, Ph o-H), 7.09–7.01 (m, 3H, Ph m-H,
Ph p-H), 6.693 (s, 4H, Mes m-H), 6.686 (s, 4H, Mes m-H), 6.52
(s, 1H, NH), 5.82 (s, 1H, SiH, 1JSiH = 184 Hz, 2JSiH = 10 Hz), 2.38
(s, 12H, Mes o-CH3), 2.35 (s, 12H, Mes o-CH3), 2.08 (s, 6H, Mes
p-CH3), 2.07 (s, 6H, Mes p-CH3); 13C NMR (C6D6, 150 MHz) d
168.93 (C O), 145.46 (Mes o-C), 144.45 (Mes o-C), 139.08 (Mes
p-C), 138. 96 (Mes p-C), 136.97 (Ph i-C), 132.52 (Mes i-C), 131.24
(Mes i-C, Ph p-C), 130.05 (Mes m-C), 129.29 (Mes m-C), 128.75
(Ph m-C), 127.38 (Ph o-C), 24.77 (Mes o-CH3), 24.67 (Mes o-
CH3), 21.03 (Mes p-CH3), 20.96 (Mes p-CH3);29Si NMR (C6D6) d
-19.6 (Mes2SiN), -52.6 (Mes2SiH); IR (cm-1) 3450 (w, NH), 3350
(w, NH), 3025 (m), 2965 (s), 2922 (s), 2854 (m), 2732 (w), 2142
(m, SiH), 1681 (s, C O), 1605 (s), 1583 (w), 1551 (w), 1498 (w),
1451 (s), 1409 (s), 1289 (w), 1265 (m), 1237 (m), 1183 (w), 1029
Mes2Si SiMes2, mmol
Product
0.03
0.03
0.03
0.03
0.06
0.06
0.03
Acetamide, 0.05
Benzamide, 0.03
NMA, ~0.2
NMB, 0.03
NPA, 0.06
NPB, 0.06
14–18 h
14–18 h
14–18 h
8 d
2 d
4 d
4-SiSi(I)
4-SiSi(II)
5-SiSi(III)
5-SiSi(IV)
5-SiSi(V)
5-SiSi(VI)
5-SiSi(VII)
NBB, 0.02
6 d
each reaction was monitored by 1H NMR spectroscopy. The
specific conditions for each reaction are given in Table 4. The
crude products of 4-SiSi(I,II) and 5-SiSi(III–VI) were light yellow
solids and 5-SiSi(VII) was a yellow solid. All of the crude products
contained Mes2Si(H)Si(OH)Mes2,18a (Mes2SiH)2,19 Mes2SiH2,20
starting amide, and small amounts of grease and/or other
impurities. Compounds 4-SiSi(I,II) and 5-SiSi(V,VI) were purified
by preparative thin layer chromatography; however, 5-SiSi(V,VI)
partially hydrolyzed on the plate to give Mes2Si(OH)Si(H)Mes2
and starting amide, which co-eluted and could not be separated
from the products. Compounds 5-SiSi(III,IV) were relatively
stable towards atmospheric moisture, but hydrolyzed upon chro-
matography, and thus, were characterized without purification.
Compound 5-SiSi(VII) also hydrolyzed upon chromatography
and was purified by trituration with hexanes. The crude product
ratios, purification conditions, and yields for each reaction are
given in Table 5.
(s); EI-MS m/z 653 (M+, 8%), 638 (M+ - Me, 9%), 518 (M+
-
Me - MesH, 4%), 386 (M+ - Mes2SiH, 100%), 283 (Mes2SiOH+,
13%); high-resolution EI-MS for C43H51Si2NO (M+) (m/z) calc.
653.3509, found 653.3507.
5-SiSi(III): 1H NMR (C6D6, 600 MHz) d 6.76 (s, 4H, Mes m-H),
1
2
6.68 (s, 4H, Mes m-H), 5.72 (s, 1H, SiH, JSiH = 181 Hz, JSiH
=
11 Hz), 2.58 (s, 3H, NCH3), 2.44 (s, 12H, Mes o-CH3), 2.33 (s,
12H, Mes o-CH3), 2.12 (s, 6H, Mes p-CH3), 2.08 (s, 6H, Mes p-
CH3), 1.59 (s, 3H, CH3); 13C NMR (C6D6, 100 MHz) d 157.89
(C N), 145.52 (Mes o-C), 144.41 (Mes o-C), 138.67 (Mes p-C),
138.57 (Mes p-C), 134.16 (Mes i-C), 131.57 (Mes i-C), 129.61
(Mes m-C), 128.95 (Mes m-C), 35.94 (NCH3), 24.71 (Mes o-CH3),
24.32 (Mes o-CH3), 21.08 (Mes p-CH3), 21.00 (Mes p-CH3), 15.15
(CH3); 29Si NMR (C6D6) d -7.5 (Mes2SiO), -55.4 (Mes2SiH); EI-
MS m/z 605 (M+, 3%), 590 (M+ - Me, 6%), 486 (M+ - Mes,
2%), 338 (M+ - Mes2SiH, 100%), 283 (Mes2SiOH+, 38%), 266
(Mes2Si+, 18%), 177 (43%), 147 (MesSi+, 15%); high-resolution
EI-MS for C39H51Si2NO (M+) (m/z) calc. 605.3509, found
605.3520.
4-SiSi(I): 1H NMR (C6D6, 400 MHz) d 6.71 (s, 4H, Mes m-H),
6.64 (s, 4H, Mes m-H), 5.76 (s, 1H, SiH, 1JSiH = 184 Hz), 5.44 (br s,
1H, NH), 2.36 (s, 12H, Mes o-CH3), 2.26 (s, 12H, Mes o-CH3), 2.09
(s, 6H, Mes p-CH3), 2.06 (s, 6H, Mes p-CH3), 1.73 (s, 3H, CH3); 13
C
NMR (C6D6, 150 MHz) d 171.65 (vbr, C O), 145.37 (Mes o-C),
144.46 (br, Mes o-C), 139.1 (br, Mes p-C), 138.96 (Mes p-C), 132.3
(vbr, Mes i-C), 131.0 (vbr, Mes i-C), 130.02 (br, Mes m-C), 129.26
(Mes m-C), 26.43 (vbr, CH3),46 24.63 (Mes o-CH3), 24.46 (Mes o-
CH3), 21.03 (Mes p-CH3), 20.93 (Mes p-CH3); 29Si NMR (C6D6) d
-20.5 (Mes2SiN), -54.2 (Mes2SiH); IR (cm-1) 3450 (w, NH), 3350
(w, NH), 3022 (m), 2963 (m), 2921 (s), 2858 (m), 2730 (w), 2139
(m, SiH), 1703 (s), 1670 (m, C O), 1604 (s), 1549 (w), 1449 (s),
1407 (s), 1375 (m), 1302 (w), 1263 (w), 1233 (m), 1027 (s); EI-MS
m/z 591 (M+, 3%), 576 (M+ - Me, 15%), 456 (5%), 434 (6%), 415
(3%), 324 (M+ - Mes2SiH, 100%), 283 (Mes2SiOH+, 15%), 206
5-SiSi(IV): 1H NMR (C6D6, 600 MHz) d 7.31–7.25 (m, 2H, Ph
o-H), 7.11–6.99 (m, Ph m-H, Ph p-H),42 6.75 (s, 4H, Mes m-H),
1
2
6.68 (s, 4H, Mes m-H), 5.86 (s, 1H, SiH, JSiH = 182 Hz, JSiH
=
11 Hz), 2.74 (s, 3H, CH3), 2.49 (s, 12H, Mes o-CH3), 2.35 (s, 12H,
Mes o-CH3), 2.10 (s, 6H, Mes p-CH3), 2.08 (s, 6H, Mes p-CH3);
13C NMR (C6D6, 100 MHz) d 157.77 (C N), 145.49 (Mes o-C),
144.43 (Mes o-C), 138.65 (Mes p-C), 138.58 (Mes p-C), 134.28
(Mes i-C), 133.43 (Ph i-C),43 131.83 (Mes i-C), 129.62 (Mes m-C),
Table 5 Crude and purified product ratios and yields for 4-SiSi(I,II) and 5-SiSi(III–VII)
Compound
Crude product ratio
Purification method
Purified product, yield
4-SiSi(I)
33 : 2 : 1 : 1 : 28a
100 : 1 : 2 : 5 : 57a
29 : 5 : 1 : 1 : 60a
20 : 11 : 1 : 1 : 19a
33 : 5 : 1 : 2 : 22a
TLC (silica gel, 100% CH2Cl2)
TLC (silica gel, 100% CH2Cl2)
Characterized without purification
Characterized without purification
TLC (silica gel, 3 : 7
CH2Cl2–hexanes)
TLC (silica gel, 4 : 6
White solid 6 mg, 34%
White solid 9 mg, 46%
4-SiSi(II)
5-SiSi(III)
5-SiSi(IV)
5-SiSi(V)
—
—
White solid 7 : 4 : 1b 20 mg total
5-SiSi(VI)
5-SiSi(VII)
25 : 4 : 2 : 1 : 12a
White solid 5 : 2 : 1b 17 mg total
CH2Cl2-hexanes)
Trituration with hexanes
14 : 14 : 1 : 1 : 21 : 4c
Yellow solid 18 : 16 : 1 : 1 : 5a
47
aa
=
amide adduct, dswa
=
disilene–water adduct, sa
=
starting amide.a aa : dswa : (Mes2SiH)2 : Mes2SiH2 : sa. b aa : dswa : sa.
c aa : dswa : (Mes2SiH)2 : Mes2SiH2 : sa : 1.
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128.99 (Mes m-C), 128.92 (Ph p-C),43 128.31 (Ph m-C),43 128.04
(Ph o-C),43 37.02 (CH3), 24.85 (Mes o-CH3), 24.63 (Mes o-CH3),
21.07 (Mes p-CH3), 21.00 (Mes p-CH3); 29Si NMR (C6D6) d -5.2
(Mes2SiO), -54.7 (Mes2SiH); EI-MS m/z 667 (M+, 3%), 652 (M+
- Me, 5%), 400 (M+ - Mes2SiH, 100%), 283 (Mes2SiOH+, 91%),
266 (Mes2Si+, 24%), 178 (38%), 118 (PhC N(CH3)+, 37%); high-
resolution EI-MS for C44H53Si2NO (M+) (m/z) calc. 667.3666,
found 667.3653.
Table 6 Reaction conditions for the formation of 4-GeGe(I–III) and 5-
GeGe(V–VI)
Reaction
time
Mes2Ge GeMes2, mmol
Amide, mmol
Product
0.04
0.04
0.04
0.04
0.04
acetamide, 0.05
benzamide, 0.05 14–18 h
NMA, 0.05
NPA, 0.04
NPB, 0.04
14–18 h
4-GeGe(I)
4-GeGe(II)
4-GeGe(III)
5-GeGe(V)
5-GeGe(VI)
14–18 h
3 d
3 d
5-SiSi(V): 1H NMR (C6D6, 600 MHz) d 7.12–7.07 (m, 2H, Ph
m-H), 6.87–6.83 (m, 1H, Ph p-H), 6.74 (s, 4H, Mes m-H), 6.68 (s,
4H, Mes m-H), 6.54–6.49 (m, 2H, Ph o-H), 5.74 (s, 1H, SiH, 1JSiH
=
2
182 Hz, JSiH = 11 Hz), 2.47 (s, 12H, Mes o-CH3), 2.33 (s, 12H,
Mes o-CH3), 2.11 (s, 6H, Mes p-CH3), 2.07 (s, 6H, Mes p-CH3),
1.71 (s, 3H, CH3); 13C NMR (C6D6, 150 MHz) d 157.14 (C N),
149.42 (Ph i-C), 145.51 (Mes o-C), 144.33 (Mes o-C), 138.95 (Mes
p-C), 138.76 (Mes p-C), 133.42 (Mes i-C), 131.12 (Mes i-C), 129.65
(Mes m-C), 129.10 (Ph m-C), 128.99 (Mes m-C), 122.71 (Ph p-C),
120.66 (Ph o-C), 24.81 (Mes o-CH3), 24.27 (Mes o-CH3), 21.08
(Mes p-CH3), 20.99 (Mes p-CH3), 17.41 (CH3); 29Si NMR (C6D6)
d -4.7 (Mes2SiO), -55.8 (Mes2SiH); EI-MS m/z 667 (M+, 1%),
652 (M+ - Me, 5%), 400 (M+ - Mes2SiH, 100%), 283 (Mes2SiOH+,
75%); high-resolution EI-MS for C44H53Si2NO (M+) (m/z) calc.
667.3666, found 667.3654.
divided in half and used in two separate reactions (0.04 mmol
Mes2Ge GeMes2 per reaction). The solid amides were dissolved
in THF (0.5–1 mL) then added to the digermene solution. For
NMA, one drop of amide (~0.2 mmol) was dissolved in THF
(2 mL) and 0.5 mL of the NMA solution was added to the
digermene solution. The reaction mixtures were stirred at room
temperature and the progress of each reaction was monitored
by 1H NMR spectroscopy. The specific conditions for each
reaction are given in Table 6. All of the crude products contained
Mes2Ge(H)Ge(OH)Mes2,21 starting amide, and small amounts
of grease and/or other impurities. All adducts hydrolyzed upon
chromatography and upon exposure to atmospheric moisture.
Compounds 4-GeGe(I,III) were characterized without purifica-
tion; 4-GeGe(II) and 5-GeGe(V,VI) were purified by trituration
with hexanes. The crude product ratios, purification conditions,
and product ratios after purification for each reaction are given in
Table 7.
1
5-SiSi(VI): H NMR (C6D6, 600 MHz) d 7.45–7.38 (m, 2H,
Ph o-H), 7.01–6.97 (m, 2H, Ph m-H), 6.90–6.85 (m, 3H, Ph m-
H, Ph p-H), 6.78–6.74 (m, 1H, Ph p-H), 6.73 (s, 4H, Mes m-H),
6.71 (s, 4H, Mes m-H), 6.46–6.40 (m, 2H, Ph o-H), 5.93 (s, 1H,
1
2
SiH, JSiH = 184 Hz, JSiH = 11 Hz), 2.52 (s, 12H, Mes o-CH3),
2.36 (s, 12H, Mes o-CH3), 2.11 (s, 6H, Mes p-CH3), 2.10 (s, 6H,
Mes p-CH3); 13C NMR (C6D6, 150 MHz) d 155.52 (C N), 148.32
(Ph i-C), 145.51 (Mes o-C), 144.44 (Mes o-C), 138.87 (Mes p-C),
138.78 (Mes p-C), 138.69,43 133.78 (Mes i-C), 132.92 (Ph i-C),
131.45 (Mes i-C), 129.67 (Mes m-C), 129.50 (Ph o-C), 129.05,
129.02 (Mes m-C, Ph m-C), 128.05 (Ph p-C), 127.92,43 122.60 (Ph
p-C), 121.36 (Ph o-C), 24.92 (Mes o-CH3), 24.68 (Mes o-CH3),
21.07 (Mes p-CH3), 21.01 (Mes p-CH3); 29Si NMR (C6D6) d -2.2
(Mes2SiO), -54.8 (Mes2SiH); EI-MS m/z 729 (M+, 2%), 714 (M+ -
Me, 2%), 652 (M+ - Ph, 2%), 462 (M+ - Mes2SiH, 81%), 400 (28%),
283 (Mes2SiOH+, 100%); high-resolution EI-MS for C49H55Si2NO
(M+) (m/z) calc. 729.3822, found 729.3830.
4-GeGe(I): 1H NMR (C6D6, 600 MHz) d 6.73 (s, 4H, Mes m-H),
6.69 (s, 4H, Mes m-H), 6.26 (s, 1H, GeH), 5.06 (s, 1H, NH), 2.38
(s, 12H, Mes o-CH3), 2.31 (s, 12H, Mes o-CH3), 2.08 (s, 6H, Mes p-
CH3), 2.07 (s, 6H, Mes p-CH3), 1.67 (s, 3H, CH3); 13C NMR (C6D6,
150 MHz) d 172.40 (C O), 144.09 (Mes o-C), 143.07 (Mes o-C),
138.55 (Mes p-C), 138.22 (Mes p-C), 137.81 (Mes i-C), 135.82 (Mes
i-C), 129.87 (Mes m-C), 129.15 (Mes m-C), 25.23 (CH3), 24.72
(Mes o-CH3), 24.36 (Mes o-CH3), 20.96 (Mes p-CH3), 20.86 (Mes
p-CH3); high-resolution ESI-TOF for C38H4970Ge2NONa (M +
Na+) (m/z) calc. 698.2197, found 698.2202.
1
4-GeGe(II): H NMR (C6D6, 600 MHz) d 7.82–7.75 (m, 2H,
1
5-SiSi(VII): H NMR (C6D6, 600 MHz) d 7.34–7.29 (m, 2H,
Ph o-H), 7.09–6.98 (m, Ph p-H, Ph m-H),42 6.70 (s, 4H, Mes m-
H), 6.69 (s, 4H, Mes m-H), 6.31 (s, 1H, GeH), 6.23 (br s, 1H,
NH), 2.39 (s, 12H, Mes o-CH3), 2.37 (s, 12H, Mes o-CH3), 2.07 (s,
12H, Mes p-CH3); 13C NMR (C6D6, 100 MHz) d 169.72 (C O),
144.10 (Mes o-C), 143.08 (Mes o-C), 138.62 (Mes p-C), 138.30
(Mes p-C), 137.54 (Mes i-C), 137.08 (Ph i-C), 135.71 (Mes i-C),
130.84 (Ph p-C), 129.97 (Mes m-C), 129.20 (Mes m-C), 128.63 (Ph
m-C), 127.43 (Ph o-C), 24.78 (Mes o-CH3), 24.46 (Mes o-CH3),
20.96 (Mes p-CH3), 20.90 (Mes p-CH3); high-resolution ESI-TOF
for C43H5170Ge2NONa (M + Na+) (m/z) calc. 760.2353, found
760.2355.
Ph o-H), 7.15–7.07 (m, 4H, Ph o-H, Ph m-H), 7.07–6.99 (m, 3H,
Ph m-H, Ph p-H), 6.72 (s, Mes m-H),44 6.69 (m, 5H, Mes m-H, Ph
p-H), 5.83 (s, 1H, SiH, 1JSiH = 181 Hz, 2JSiH = 11 Hz), 4.35 (s, 2H,
CH2), 2.48 (s, 12H, Mes o-CH3), 2.30 (s, Mes o-CH3),44 2.12 (s, 6H,
Mes p-CH3), 2.08 (s, 6H, Mes p-CH3); 13C NMR (C6D6, 100 MHz)
d 158.15 (C N), 145.52 (Mes o-C), 144.62 (Mes o-C), 141.35 (Ph
i-C), 139.00 (Mes p-C),48 138.80 (Mes p-C),48 134.00 (Mes i-C),
131.46 (Mes i-C), 129.79 (Mes m-C), 129.27 (Ph),43 128.99 (Mes
m-C), 128.45 (Ph),43 128.16 (Ph),43 127.76 (Ph o-C), 127.36 (Ph ¥
2),43 126.16 (Ph),43 54.20 (CH2), 24.89 (Mes o-CH3), 24.60 (Mes o-
CH3), 21.05 (Mes p-CH3 ¥ 2); 29Si NMR (C6D6) d -4.6 (Mes2SiO),
-55.1 (Mes2SiH); high-resolution EI-MS for C50H57Si2NO (M+)
(m/z) calc. 743.3979, found 743.3954.
4-GeGe(III):22 1H NMR (C6D6, 600 MHz) d 6.71, 6.70 (both
s, 8H, Mes m-H), 6.59 (s, 1H, GeH), 2.54 (s, 3H, CH3), 2.40 (s,
12H, Mes o-CH3), 2.35 (s, 12H, Mes o-CH3), 2.08 (s, 6H, Mes
p-CH3), 2.07 (s, 6H, Mes p-CH3), 1.59 (s, 3H, CH3); 13C NMR
(C6D6, 100 MHz) d ~175.69 (br, C O),48 143.97 (Mes o-C),
143.84 (Mes o-C), 139.22 (Mes i-C),48 138.81 (Mes i-C),48 138.22
(Mes p-C),48 137.74 (Mes p-C),48 129.86 (Mes m-C),43 129.04 (Mes
m-C),43 35.06 (NCH3), 25.02 (Mes o-CH3), 24.42 (Mes o-CH3),
Addition of amides to digermene 2
Mes6Ge3 (50 mg, 0.05 mmol) was dissolved in THF (10 mL) and
irradiated (l = 350 nm) at -78 ◦C for ~9 h.3b The solution was then
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Table 7 Crude and purified product ratios for 4-GeGe(I–III) and 5-GeGe(V,VI)
Compound
Crude product
Crude product ratio
Purification method
Purified product and ratio
—
4-GeGe(I)
White solid
White solid
White solid
Light yellow solid
Orange solid
26 : 1 : 1a
33 : 1 : 14a
5 : 2 : 1a
Characterized without purification
Trituration with hexanes
Characterized without purification
Trituration with hexanes
47
4-GeGe(II)
4-GeGe(III)
5-GeGe(V)
5-GeGe(VI)
White solid 7 : 1 : 2a
—
10 : 1 : 10a
5 : 1 : 10 : 5b
White solid 11 : 1 : 1a
47
Trituration with hexanes
Yellow solid 20 : 2 : 1 a47
aa = amide adduct, dgwa = digermene–water adduct, sa = starting amide.a aa : dgwa : sa. b aa : dgwa : sa : 2.
21.27 (CH3), 20.96 (Mes p-CH3),43 20.82 (Mes p-CH3);43 CI-MS
m/z 696 (M + H+, 72Ge74Ge, 4%), 649 (5%), 577 (M - Mes +
H+, 8%), 529 (17%), 385 (Mes274Ge(H)N(CH3)COCH3, 63%),
312 (Mes274Ge, 19%), 265 (Mes74GeN(CH3)(COCH3), 100%), 192
(20%); high-resolution CI-MS for C39H5270Ge2NO (M + H+) (m/z)
calc. 690.2521, found 690.2515.
Table 8 Crystal data collection and structure refinement parameters for
4-SiCa(I)
Empirical formula
C16H41NO2Si4
391.86
150(2)
0.71073
Orthorhombic
Pbca
9.77160(10)
19.9934(3)
25.5683(3)
4995.22(11)
8
1.042
0.246
1728
0.50 ¥ 0.20 ¥ 0.10
2.04–27.48
-12 to 12, -25 to 25, -32 to 33
10797/5720 [Rint = 0.0511]
99.9
Semi-empirical from
equivalents
Mr
T/K
˚
l/A
Crystal system
Space group
5-GeGe(V): 1H NMR (C6D6, 600 MHz) d 7.14–7.08 (m, 2H, Ph
m-H), 6.89–6.83 (m, 1H, Ph p-H), 6.72 (s, 8H, Mes m-H), 6.53 (s,
1H, GeH), 6.49–6.46 (m, 2H, Ph o-H), 2.414, 2.411 (both s, 24H,
Mes o-CH3), 2.094 (s, 6H, Mes p-CH3), 2.088 (s, 6H, Mes p-CH3),
1.71 (s, 3H, CH3); 13C NMR (C6D6, 100 MHz) d 160.90 (C N),
150.00 (Ph i-C), 143.87 (Mes o-C), 143.25 (Mes o-C), 138.83 (Mes
i-C), 138.50 (Mes p-C), 138.26 (Mes p-C), 136.36 (Mes i-C), 129.65
(Mes m-C), 129.05 (Mes m-C, Ph m-C), 122.46 (Ph p-C), 121.40 (Ph
o-C), 24.98 (Mes o-CH3), 24.27 (Mes o-CH3), 20.98 (Mes p-CH3),
20.94 (Mes p-CH3), 17.12 (CH3); high-resolution ESI-TOF for
C44H5470Ge2NO (M + H+) (m/z) calc. 752.2690, found 752.2697.
˚
a/A
˚
b/A
˚
c/A
3
˚
V/A
Z
Dc/Mg m-3
m/mm-1
F(000)
Crystal size/mm
q range for data collection/◦
Limiting indices, hkl
Reflections collected/unique
Completeness to q = 27.48◦ (%)
Absorption correction
1
5-GeGe(VI): H NMR (C6D6, 400 MHz) d 7.51–7.47 (m, 2H,
Ph o-H), 7.07–7.00 (m, Ph m-H),42 6.89–6.84 (m, 3H, Ph m-H,
Ph p-H), 6.81–6.76 (m, Ph p-H),44 6.73 (s, 4H, Mes m-H), 6.72 (s,
4H, Mes m-H), 6.67 (s, GeH),44 6.53–6.48 (m, 2H, Ph o-H), 2.45,
2.44 (both s, 24H, Mes o-CH3), 2.093, 2.089 (both s, 12H, Mes
p-CH3); 13C NMR (C6D6, 100 MHz) d 158.44 (C N), 149.20 (Ph
i-C), 143.86 (Mes o-C), 143.33 (Mes o-C), 138.88 (Mes i-C), 138.54
(Mes p-C), 138.32 (Mes p-C), 136.48 (Mes i-C), 133.66 (Ph i-C),
129.73, 129.70 (Mes m-C, Ph o-C), 129.43 (Ph p- or m-C), 129.10,
129.08 (Mes m-C, Ph m-C), 128.08 (Ph m- or p-C), 122.23 (Ph
p-C), 121.65 (Ph o-C), 25.04 (Mes o-CH3), 24.51 (Mes o-CH3),
21.00 (Mes p-CH3), 20.96 (Mes p-CH3); high-resolution ESI-
TOF for C49H5670Ge2NO (M + H+) (m/z) calc. 814.2847, found
814.2842.49
Max., min. transmission
Refinement method
0.9758, 0.8870
Full-matrix least-squares on
F2
Data/restraints/parameters
GOOF on F2
5720/0/221
1.021
R1 = 0.0480, wR2 = 0.1146
R1 = 0.1017, wR2 = 0.1314
0.350 and -0.512
Final R indices [I > 2s(I)]
R indices (all data)
Largest diff. peak and hole/e A
-3
˚
Fourier syntheses allowed the remaining atoms to be located.
All of the non-hydrogen atoms were refined with anisotropic
thermal parameters. The hydrogen atom positions were calculated
geometrically and were included as riding on their respective
carbon atoms.
X-Ray experimental
Acknowledgements
Crystals of 4-SiCa(I) suitable for single-crystal X-ray diffraction
analysis were obtained by the slow evaporation of a C6D6 solution.
A colourless block was mounted on a Nylon loop. Data were
collected at low temperature (-123 ◦C) on a Nonius Kappa-
CCD area detector diffractometer with COLLECT. The unit cell
parameters were calculated and refined from the full data set.
Crystal cell refinement and data reduction were carried out using
HKL2000 DENZO-SMN.50 Absorption corrections were applied
using HKL2000 DENZO-SMN (SCALEPACK). A summary of
the crystal data collection and refinement parameters for 4-SiCa(I)
are listed in Table 8.
We thank the Natural Sciences and Engineering Research Council
of Canada and the University of Western Ontario for financial
support and Paul A. Rupar for the X-ray structure of 4-SiCa(I).
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42 Due to overlap with 1H signals of the starting amide, the 1H signal
integrated to a higher value than expected.
43 Due to overlap within the 1H–13C gHMBC and gHSQC spectra,
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44 Due to overlap with 1H signals of impurities, the 1H signal integrated
to a higher value than expected.
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45 Due to overlap within the 1H–13C gHMBC spectrum, all 13C signals
due to the adamantyl substituent could not be located.
46 The 13C chemical shift was determined from the 1H–13C gHSQC
spectrum of 4-SiSi(I).
49 The sample may have contained minor amounts of a 2 : 1 adduct
between NPB and digermene 2. In addition to a molecular ion at m/z
820 (M + H+, 74Ge72Ge), the low-resolution ESI-TOF mass spectrum
of 5-GeGe(VI) contained a signal at m/z 1039, which is consistent with
Mes474Ge72Ge + 2NPB + Na+.
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47 An isolated yield was not measured due to the limitations of the balance
within the glove box.
48 Due to overlap within the 1H–13C gHMBC spectrum, assignment is
tentative.
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Dalton Trans., 2012, 41, 609–621 | 621
©