Utilizing steric bulk to stabilize molybdenum aminogermylyne and aminogermylene complexes

Article abstract of DOI:10.1021/om301144h

Two extremely bulky bis(aryl)amines, HN(Ar*)(Ph) (HL^Ph) and HN(Ar*)(Mes) (HL^Mes) (Ar* = C₆H ₂{C(H)Ph₂}₂Me-2,6,4; Mes = mesityl), have been prepared by palladium-catalyzed cross-coupling reactions and structurally characterized. These have been utilized in the preparation of the amido-germanium(II) chlorides, [L^PhGeCl] and [L^MesGeCl]. Reactions of these, and the known complex, [L′GeCl] (L′ =-N(Ar*)(SiMe₃)), with Na[CpMo(CO)₃] have afforded the first examples of structurally characterized two-coordinate molybdenum substituted germylenes, [Cp(CO)₃MoGeN(Ar*)(R)] (R = SiMe ₃ or Ph). The former readily eliminates a molecule of CO when heated or irradiated with UV light to give an unprecedented amino-germylyne complex, [Cp(CO)₂Moi-≡GeN(Ar*)(SiMe₃)]. The spectroscopic and structural data for this complex, in combination with the results of computational studies, show that this compound is best viewed as having a bent Mo-Ge triple bond, with little multiple bond character to its Ge-N interaction. Computational studies have also indicated that the Mo-Ge-N bending in the complex is due to the extreme steric bulk of its amido substituent.

Full text of DOI:10.1021/om301144h

Article
pubs.acs.org/Organometallics
Utilizing Steric Bulk to Stabilize Molybdenum Aminogermylyne and
Aminogermylene Complexes
Jamie Hicks,† Terrance J. Hadlington,† Christian Schenk,†,‡ Jiaye Li,† and Cameron Jones*,†
†School of Chemistry, Monash University, P.O. Box 23, Melbourne, Victoria, 3800, Australia
‡Im Neuenheimerfeld 270, Anorganische Chemie, Universitat Heidelberg, 69120, Heidelberg, Germany
̈
S
* Supporting Information
ABSTRACT: Two extremely bulky bis(aryl)amines, HN(Ar*)-
(Ph) (HLPh) and HN(Ar*)(Mes) (HLMes) (Ar* = C6H2{C(H)-
Ph2}2Me-2,6,4; Mes = mesityl), have been prepared by palladium-
catalyzed cross-coupling reactions and structurally characterized.
These have been utilized in the preparation of the amido-
germanium(II) chlorides, [LPhGeCl] and [LMesGeCl]. Reactions of
these, and the known complex, [L′GeCl] (L′ = −N(Ar*)(SiMe3)),
with Na[CpMo(CO)3] have afforded the first examples of
structurally characterized two-coordinate molybdenum substituted germylenes, [Cp(CO)3MoGeN(Ar*)(R)] (R = SiMe3 or
Ph). The former readily eliminates a molecule of CO when heated or irradiated with UV light to give an unprecedented amino-
germylyne complex, [Cp(CO)2MoGeN(Ar*)(SiMe3)]. The spectroscopic and structural data for this complex, in
combination with the results of computational studies, show that this compound is best viewed as having a bent Mo−Ge
“triple” bond, with little multiple bond character to its Ge−N interaction. Computational studies have also indicated that the
Mo−Ge−N bending in the complex is due to the extreme steric bulk of its amido substituent.
unknown. At the outset of this study, it was clear that amino
substituents of considerable steric bulk would be required to
stabilize these target molecules. In this respect, we have recently
developed an extremely bulky class of amido ligands, for
example, N(Ar*)(SiMe3) L′ (Ar*= C6H2{C(H)Ph2}2Me-
2,6,4),5 which we believed would fit the bill. These ligands
have allowed us entry to a variety of unprecedented low
coordinate group 13 and 14 metal amide complexes, which
include one-coordinate group 13 metal(I) amides, [L′M:] (M =
Ga, In, or Tl),6 monomeric chloro-tetrelenes [L′ECl] (E = Ge
or Sn),5 a singly bonded amido-digermyne [L′Ge-GeL′],7 the
low coordinate metal(II) cations [L′E:]+ (E = Ge or Sn),8 and
the acyclic boryl-germylene [L′Ge{B(DAB)}] (DAB =
{DipNCH}2; Dip = C6H3Pri2-2,6).9 Here, we report the use
of such bulky amides in the preparation of the first example of a
transition-metal aminotetrelyne, and two related metallo-
germylene complexes.
INTRODUCTION
■
The chemistry of transition-metal carbyne complexes, LnM
CR, is extensively developed and such species have found
numerous synthetic and other applications.1 In recent years,
considerable efforts have been made to extend this work to the
preparation of heavier group 14 analogues of this important
compound class, viz. the transition-metal tetrelynes LnMER
(E = Si, Ge, Sn, or Pb), and to investigate their chemistry.2
These studies have largely been restricted to the group 6
metals, and examples of complexes are now known that
incorporate triple bonds between those metals and all of the
heavier group 14 elements. In all cases, sterically bulky aryl or
alkyl substituents are required to kinetically stabilize the ME
bonds of the complexes. It is interesting to note that, whereas
complexes of the type, LnMER, invariably have essentially
linear MEC fragments, the closely related heavier alkyne
analogues, REER, have trans-bent CEE fragments and
decreasing EE bond orders (ranging from below 3 to close to
1) as the group is descended.3
RESULTS AND DISCUSSION
■
The first report of a transition-metal germylyne complex,
[Cp(CO)2MoGeAr′] (Ar′ = C6H3Mes2-2,6; Mes = mesityl),
came from the group of Power.2a This compound was readily
prepared via the elimination of NaCl and CO below 0 °C in the
reaction of the terphenyl substituted chloro-germylene,
[Ar′GeCl], with Na[CpMo(CO)3]. Considering that we have
previously shown that our bulky amide ligands, for example, L′,
have similar steric profiles and stabilizing properties to
Related to carbyne complexes are transition-metal amino-
carbynes, LnMCNR2. However, as these have planar amino
substituents, their bonding typically exhibits a significant
contribution from their 2-azavinylidene canonical form,
4
Ln MCN+R2. While this can affect the π-acidity and
reactivity of the aminocarbyne ligand relative to that of
organocarbynes, transition-metal aminocarbyne complexes do
have synthetic value. Because of this, and because of the
increasing interest in transition-metal tetrelynes, we sought to
prepare examples of closely related aminotetrelyne complexes,
LnMENR2, which, to the best of our knowledge, are
−
Received: November 26, 2012
© XXXX American Chemical Society
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substituted terphenyls,5−8 we initially targeted amino-germy-
lyne analogues of Power’s germylyne complex, [Cp-
(CO)2MoGeAr′]. This strategy was seen as having the
additional advantage of allowing structural and spectroscopic
comparisons between the two molecule classes.
structures. Some information can obtained from their IR
spectra (Nujol mulls), which, in the cases of 1 and 2, display a
series of strong CO stretching bands in the ranges of 1966−
1830 and 1972−1867 cm−1, respectively. These can be
compared to the values reported for related metalla-tetrelenes,
for example, [Cp(CO)3Mo−SnAr′] (1960−1875 cm−1),11
which are thought to exhibit minimal donation from filled
transition-metal-based orbitals into the empty p orbital at the
group 14 metal center. This view has been reinforced by
computational studies on models of the experimental
compounds.12 The infrared spectrum of 3 exhibits two strong
CO stretching bands centered at 1926 and 1823 cm−1.
Interestingly, these bands occur at similar positions to those
seen for the closely related germylyne complex, [Cp-
(CO)2MoGeAr′] (1930 and 1872 cm−1).2a It might be
thought that, if there was a significant bonding contribution
from the heterovinylidene resonance form of 3 (viz. [Cp-
While suitable chloro-germylene precursors (e.g., [L′GeCl])
to the target germylyne complexes were available to us, we
wished to extend their range to systems that incorporated bulky
amide ligands that are free of silyl substituents. This desire
stemmed from the results of other studies within our group that
have shown that the N−Si linkage of L′ and related ligands can
be susceptible to cleavage. To this end, palladium-catalyzed
cross-coupling reactions, based on a literature procedure,10
were employed to prepare the new, very bulky bis(aryl)
secondary amines, HN(Ar*)(Ph) (HLPh) and HN(Ar*)(Mes)
(HLMes), in good yields. These compounds were spectroscopi-
cally and crystallographically characterized (see the Supporting
Information for ORTEP diagrams). It is of note that HLPh and
HLMes are likely the most bulky bis(aryl)amines produced via
cross-coupling reactions, and therefore, the route used to access
them may well be generally applicable to a wide range of similar
amines. Deprotonation of the amines with BunLi and
subsequent treatment with GeCl2·dioxane led to good yields
of the chlorogermylenes, [LPhGeCl] and [LMesGeCl]. The two
complexes were spectroscopically characterized, though their X-
ray crystal structures could not be obtained.
(CO)2 MoGeN+(Ar*)(SiMe3)]), these bands might
−
occur at lower wavenumbers. This is because the Mo center
of that form should be more electronically satisfied than that in
the germylyne form, [Cp(CO)2MoGeN(Ar*)(SiMe3)],
thereby leading to a weakening of its C−O bonds relative to
those in the germylyne form. This may well suggest that the
germylyne resonance form of 3 predominates. It is noteworthy
that, although generally higher frequency bands are seen for
related complexes incorporating more π-acidic, carbyne and
aza-vinylidene ligands, the trend to lower frequency CO
stretching bands for aza-vinylidene complexes relative to
carbyne complexes is well-established.4 A pertinent comparison
here is between [Cp(CO)2MoC(C6H3Me2-2,6)] (ν = 1992
The 1:1 reactions of [L′GeCl], [LPhGeCl], or [LMesGeCl]
with Na[CpMo(CO)3] in toluene/THF mixtures led to varying
outcomes. Whereas the reaction involving [LMesGeCl] afforded
an unidentifiable mixture of products, the other two reactions
gave good yields of the orange, crystalline metalla-germylene
complexes, 1 and 2 (Scheme 1). It is worth noting that these
13
and 1919 cm−1) and [Cp(CO)2 MoCN+Et2] (ν = 1952
−
and 1866 cm−1).14
To shed further light on the bonding in 1−3, their X-ray
crystal structures were determined. As compound 2 is
essentially isostructural to 1, only the molecular structure of
1 is depicted in Figure 1 (see Table 1 for metrical parameters of
1 and 2, and the Supporting Information for an ORTEP
diagram of 2). Compounds 1 and 2 represent the first examples
Scheme 1. Preparation of Compounds 1−3 (Ar* =
C6H2{C(H)Ph2}2Me-2,6,4)
two complexes are resistant to CO elimination in solution and
the solid state under ambient conditions. This contrasts to the
implied intermediate in the synthesis of [Cp(CO)2Mo
GeAr′], viz. [Cp(CO)3Mo−GeAr′], which could not be
isolated and eliminated CO at well below room temperature.
At this stage, it is not known why 1 is more resistant to CO
elimination than [Cp(CO)3Mo−GeAr′], though this elimi-
nation can be induced by heating its toluene solutions at reflux
for 1 h, or irradiating benzene solutions of the compound with
UV light (λ = 254 nm) for 20 min. Both processes give rise to
essentially quantitative yields of the orange amino-germylyne
complex, 3. In contrast, heating or irradiating solutions of 2 led
to decomposition and the formation of HLPh as the only
identifiable product in each case.
Figure 1. Thermal ellipsoid plot (25% probability surface) of the
molecular structure of 1 (hydrogen atoms omitted). Selected metrical
parameters are given in Table 1.
Compounds 1−3 are all thermally very stable solids, and
their spectroscopic data are consistent with their proposed
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Table 1. Selected Interatomic Distances (Å) and Angles
a
(deg) for 1−3
1
2
3
Mo−Ge
Ge−N
2.7377(3)
(2.814)
2.7100(4)
2.2811(4)
(2.317)
1.812(2)
(1.844)
2.006(1)
155.81(8)
(160.3)
124.5(2)
359.9
1.8871(18)
(1.899)
1.879(2)
Mo−Cpcentroid
M−Ge−N
2.023(1)
118.80(5)
(121.3)
2.013(1)
115.90(7)
Si/C−N−C
Σ angles at N
114.61(13)
359.9
112.6(2)
360.0
a
Selected metrical parameters for the calculated (B3LYP/6-311G(d)/
LANL2DZ) gas-phase structures of 1 and 3 are given in parentheses.
of structurally characterized two-coordinate molybdenum
substituted germylenes, though one three-coordinate example
has been reported,15 and several two-coordinate stannylene and
plumbylene complexes are known.11,16 The Mo−Ge bond
lengths in the compounds (1: 2.7377(3) Å; 2: 2.7100(4) Å) are
close to those calculated for [Cp(CO)3Mo−GeMe] (2.716 Å,
B3LYP),12a and to the sum of the single bond covalent radii for
the two elements (2.74 Å).17 In addition, they are similar to the
W−Ge single bond distance (2.681(3) Å) in the related
tungsten germylidene, [Cp(CO)3W−Ge(C6H3Trip2-2,6)]
(Trip = C6H2Pri3-2,4,6).2b These comparisons suggest that
there is little multiple bond character to the Mo−Ge bonds in 1
and 2. Moreover, their Ge−N distances (1: 1.8871(18) Å; 2:
1.879(2) Å) are longer than that in the precursor complex,
[LGe′Cl] (1.855(3) Å). Although a small degree of N → Ge π-
donation was calculated for the latter complex,5 similar π-
donations are unlikely to be significant in 1 and 2, especially
when it is considered that the sum of the single bond covalent
radii for Ge and N is 1.91 Å.17 That said, the dihedral angles
formed between the SiCNGe/C2NGe and NGeMo least-
squares planes (1: 12.3°; 2: 11.0°) are conducive to N−Ge π-
bonding. The angles at germanium (1: 118.80(5)°; 2:
115.90(7)°) strongly suggest the presence of a stereochemically
active lone pair of electrons in both complexes, as has been
calculated for [Cp(CO)3Mo−GeMe] (Mo−Ge−C: 109.8°,
B3LYP).12a There are no significant Ge−phenyl interactions in
either compound (closest Ge···Cphenyl distances, 1: 3.16 Å; 2:
3.34 Å).
The molecular structure of monomeric 3 is depicted in
Figure 2. The compound has a Ge−Mo distance (2.2811(4) Å)
that is only slightly longer than the Ge−Mo triple bond in
[Cp(CO)2MoGeAr′] (2.271(1) Å). Furthermore, it is
shorter than the calculated bond length in [Cp(CO)2Mo
GeMe] (2.309 Å, B3LYP),12a and is 0.45 Å shorter than the
Ge−Mo distance in 1. In fact, the Ge−Mo distance in 3 is
shorter than those in the majority of known molybdenum
germylynes (seven structurally characterized examples18),
which are typically greater than 2.3 Å, for example, trans-
[(Me3P)4ClMoGeAr′] (2.3041(3) Å).2p This is despite the
fact that the Mo−Ge−N angle in 3 (155.81(8)°, cf. 118.80(5)°
in 1) is significantly distorted from linear, which should not
allow for optimal σ- and π-orbital overlap between the Mo and
Ge centers. This distortion likely arises from steric buttressing
between the CpMo(CO)2 fragment and the two closest phenyl
substituents of the Ar* moiety. If the Mo−Ge−N angle in 3
was linear, this buttressing would be significantly increased. The
Ge−N distance in the compound (1.812(2) Å) is slightly
Figure 2. Thermal ellipsoid plot (25% probability surface) of the
molecular structure of 3 (hydrogen atoms omitted). Selected metrical
parameters are given in Table 1.
shorter than that in 1 (1.8871(18) Å), which may signify some
double bond character to that interaction, and thus some
contribution from the [Cp(CO)2−MoGeN+(Ar*)-
(SiMe3)] canonical form to the bonding in 3. However, for
this to be optimal, the Mo−Ge−N fragment would again need
to be linear. The above comparisons of the structural and
spectroscopic properties of 3 with related compounds suggest
that its amino-germylyne canonical form predominates, at least
in the solid state.
To ascertain the extent of multiple bonding in 3, quantum-
chemical calculations (B3LYP/6-311G(d)/LANL2DZ and
BP86/6-311G(d)/LANL2DZ) were carried out on 1 and 3
in the gas phase. In both cases, their geometries optimized to be
close to those in the experimental solid-state structures, but
with slightly overestimated Ge−Mo and Ge−N distances (see
Table 1 for selected metrical parameters from the B3LYP
calculations). It is of note that the calculated geometries include
similar arrangements of the phenyl groups about the metal
centers, and similar dihedral angles between the SiCNGe and
CpcentroidMoGe least-squares planes, to those in the solid-state
structures. Analysis of the frontier orbitals of 1 revealed an
electronic structure similar to those of related germylenes, for
example, [L′GeCl]5 and [Cp(CO)3MoGeMe].12a That is, the
HOMO has significant Ge lone pair character, whereas the
LUMO is consistent with an empty p orbital at germanium
(Figure 3). Furthermore, the p-orbital lone pair at the N center
is associated with HOMO-6, and there does not appear to be
any significant overlap between this and the empty p orbital at
the Ge center. In contrast, there is no obvious Ge lone pair in 3,
and the σ component of the Ge−Mo bond is seemingly
distributed between several MOs. However, the HOMO and
HOMO-2 have character reminiscent of orthogonal Mo−Ge π-
bonding orbitals (N.B. the HOMO-1 is a largely metal-based
orbital), whereas the LUMO is characteristic of a Mo−Ge π*-
antibonding orbital. As was the case with 1, there are no MOs
that suggest any significant Ge−N π-bonding in the molecule.
This picture of the electronic structure of 1 is in accord with the
structural and spectroscopic data, which are in line with it
possessing a bent “triple” bond with little Ge−N multiple bond
character.
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Figure 3. (a) LUMO, (b) HOMO, and (c) HOMO-6 of 1; (d) LUMO, (e) HOMO, and (f) HOMO-2 of 3 (B3LYP/6-311G(d)/LANL2DZ).
So as to provide some quantification of the Mo−Ge and Ge−
N bond orders in 3, comparative Wiberg bond index (WBI)
calculations (B3LYP/6-311G(d)/LANL2DZ) were carried out
on 1 and 3. Although the Mo−Ge WBI values obtained for the
compounds (1: 0.50; 3: 1.50) are half those that might be
expected for single and triple bonds, respectively, the ratio of
the two values is exactly 1:3. Indeed, these values are very close
to those calculated at the same level of theory for [Cp-
(CO)3MoGeMe] and [Cp(CO)2MoGeMe] (viz. 0.50 and
1.46),12a the latter of which has a near linear Mo−Ge−C
fragment and a Mo−Ge triple bond. Although the Ge−N WBI
for 3 (0.59) is larger than that for 1 (0.48), it is not greatly so
and does not indicate a significant increase in multiple bond
character on going from 1 to 3. As was proposed to be the case
for [Cp(CO)3MoGeMe] and [Cp(CO)2MoGeMe],12a the
low WBI values for the Mo−Ge (and Ge−N) bonds of 1 and 3
are most likely due to the divergent electronegativities of the
elements within their MoGe(N) fragments. This gives rise to
significant polarization of the bonds (natural charges: 1, Mo
−1.49, Ge 1.27, N −1.43; 3, Mo −1.53, Ge 1.51, N −1.35) and
likely reduces the covalent component of the Mo−Ge and Ge−
N bonds at the expense of their electrostatic component.
Although the extent of this was not calculated in the current
study, it is of note that a previous energy decomposition
analysis (EDA) analysis of [Cp(CO)2MoGeMe] showed
that the covalent and electrostatic components of its Mo−Ge
bond are almost equivalent.12a
Quantum-chemical calculations (B3LYP/6-311G(d)/
LANL2DZ and BP86/6-311G(d)/LANL2DZ) were also
carried out on sterically reduced models of 1 and 3, viz.
[Cp(CO)3MoGeN(Ph)(SiMe3)] 1a and [Cp(CO)2Mo
GeN(Ph)(SiMe3)] 3a, with the purpose of determining the
influence the bulky Ar* substituent has on the geometries of
the molecules containing that group. Whereas the geometry of
1a (Mo−Ge 2.77 Å, Ge−N 1.88 Å, Mo−Ge−N 119.6°,
B3LYP) optimized to be similar to those of the experimental
and calculated structures of 1, the optimized geometry of 3a
(Mo−Ge 2.31 Å, Ge−N 1.84 Å, Mo−Ge−N 170.4°, B3LYP)
D
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and volatiles were removed in vacuo to give a brown solid, which was
washed with hexane (2 × 10 mL) to afford HLPh as a pale brown solid
(1.60 g, 68%). N.B. X-ray quality crystals were obtained by slow
has a significantly more obtuse Mo−Ge−N angle than that
calculated for 3. This difference is in line with our proposal that
the steric bulk of the amido group of 3 hinders its Mo−Ge−N
moiety from approaching linearity. Interestingly, despite this,
the calculated Mo−Ge distances in 3 and 3a are almost
identical, which suggests that the difference in the Mo−Ge−N
angles between the two compounds does not greatly affect their
respective Mo−Ge bond orders. This was confirmed by further
calculations on 3a, which yielded a WBI for the Mo−Ge bond
of the compound of 1.60 (cf. 0.56 for 1a), which is only slightly
greater than that for 3. Similarly, the WBI for the Ge−N bond
of 3a (0.68, cf. 0.74 for 1a) is only slightly larger than that for 3.
1
evaporation of a solution of HLPh in hexane. mp: 142−145 °C. H
NMR (499 MHz, C6D6, 298 K): δ = 1.87 (s, 3H, ArCH3), 4.39 (s, 1H,
NH), 5.84 (s, 2H, Ph2CH), 6.34−7.02 (m, 27H, ArH). 13C{1H} (75.5
MHz, C6D6): δ = 21.4 (ArCH3), 52.4 (Ph2CH), 113.1, 118.5, 126.6,
128.6, 129.81, 130.4, 135.9, 136.8, 143.5, 144.2, 144.8, 147.7 (Ar-C).
IR ν/cm−1 (ATR): 3415(NH, m), 1493(s), 1452(m), 1314(m),
1249(m), 1176(m), 872(w), 802(w), 750(m), 698(s). MS/ESI m/z
+
(%): 516.1 (M+, 52), 440.2 (Ar*NH2 , 28), 169.0 (Ph2CH+, 100). Acc.
mass calcd for C39H34N (MH+): 516.2686. Found: 516.2679.
Preparation of HN(Ar*)(Mes) (HLMes). This compound was
prepared similarly to HLPh, but using Ar*NH2 (5.00 g, 11.37 mmol),
ButOK (1.66 g, 14.79 mmol), bromomesitylene (1.47 g, 7.39 mmol),
and [(IPr)Pd(Im)] catalyst (0.185 g, 2.5 mol %) in the initial stages of
the reaction, and [(IPr)Pd(Im)] (0.185 g, 2.5 mol %) and
bromomesitylene (1.47 g, 7.39 mmol) in the latter stages of the
reaction. HLMes was isolated as a pale brown powder (4.95 g, 78%).
N.B. X-ray quality crystals were obtained by slow evaporation of a
CONCLUSIONS
■
In summary, salt elimination reactions of amido germanium(II)
chloride complexes with Na[CpMo(CO)3] have afforded the
first examples of structurally characterized two-coordinate
molybdenum substituted germylenes, [Cp(CO)3MoGeN-
(Ar*)(R)] (R = SiMe3 or Ph). One of these readily eliminates
a molecule of CO when heated or irradiated with UV light to
give an unprecedented amino-germylyne complex, [Cp-
(CO)2MoGeN(Ar*)(SiMe3)], in excellent yield. The
spectroscopic and structural data for this complex, in
combination with the results of computational studies, show
that this compound is best viewed as having a bent Mo−Ge
“triple” bond, with little multiple bond character to its Ge−N
interaction. Computational studies have also indicated that the
Mo−Ge−N bending in the complex is due to the extreme steric
bulk of its amido substituent. We are currently examining the
further chemistry of [Cp(CO)2MoGeN(Ar*)(SiMe3)] and
comparing it with that of transition-metal amino-carbyne
complexes. Our efforts in this direction will be reported in
due course.
1
solution of HLMes in diethyl ether. mp: 250−254 °C. H NMR (499
MHz, C6D6, 298 K): δ = 1.61 (s, 6H, o-CH3 mesityl), 1.88 (s, 3H,
ArCH3), 2.18 (s, 3H, p-CH3 mesityl), 4.32 (s, 1H, NH), 5.73 (s, 2H,
Ph2CH), 6.73 (s, 2H, m-ArH), 6.82−7.05 (m, 22H, ArH). 13C{1H}
(75.5 MHz, C6D6): δ = 18.9 (o-CH3, mesityl), 20.8 (p-CH3, mesityl),
21.2 (ArCH3), 52.9 (Ph2CH), 126.3, 126.6, 128.6, 129.3, 129.7, 130.0,
130.1, 132.3, 138.3, 139.1, 139.3, 144.2 (Ar-C). IR ν/cm−1 (ATR):
3402(NH, w), 1492(m), 1445(m), 1328(m), 1276(w), 1236(w),
1160(w), 761(w), 745(w), 696(s). MS/ESI m/z (%): 558.2 (M+, 20),
169.0 (Ph2CH+, 26). Acc. mass calcd for C42H40N (MH+): 558.3155.
Found: 558.3151.
Preparation of [LPhGeCl]. LiBun (1.33 mL of a 1.6 M solution in
hexane) was added to a solution of HLPh (1.00 g, 1.94 mmol) in THF
(50 mL) at −80 °C over 5 min. The reaction mixture was warmed to
room temperature and stirred for 4 h. The resultant solution was then
added to a solution of GeCl2·dioxane (0.494 g, 2.13 mmol) in THF
(10 mL) at −80 °C. The resultant solution was warmed to room
temperature and stirred for 12 h, whereupon volatiles were removed in
vacuo. The residue was extracted with toluene (35 mL), the extract
was filtered, and volatiles were removed in vacuo to give [LPhGeCl] as
a pale yellow solid (0.78 g, 65%). mp: 94−96 °C. 1H NMR (499 MHz,
C6D6, 298 K): δ = 1.89 (s, 3H, ArCH3), 5.69 (s, 2H, Ph2CH), 6.89−
7.45 (m, 27H, ArH). 13C{1H} (75.5 MHz, C6D6): δ = 21.4 (ArCH3),
52.7 (Ph2CH), 119.5, 122.6, 128.6, 129.5, 129.8, 130.5, 130.6, 137.2,
139.7, 143.9, 142.3, 149.1 (Ar-C). IR ν/cm−1 (ATR): 1492(m),
1445(m), 1308(w), 1256(w), 1231(w), 1177(w), 1122(w), 907(w),
884(w), 750(m), 696(s). MS/EI m/z (%): 515.2 (Ar*(Ph)NH+, 100),
439.1 (Ar*NH+, 6), 167.0 (Ph2CH+, 9).
EXPERIMENTAL SECTION
General Methods. All manipulations were carried out using
standard Schlenk and glovebox techniques under an atmosphere of
high-purity dinitrogen. THF, hexane, and toluene were distilled over
■
1
potassium, while dichloromethane was distilled over CaH2. H and
13C{1H} NMR spectra were recorded on Bruker AvanceIII 400 or
Varian Inova 500 spectrometers and were referenced to the resonances
of the solvent used. 29Si{1H} NMR spectra were recorded on a Bruker
AvanceIII 400 spectrometer and were referenced to external SiMe4.
Mass spectra were obtained from the EPSRC National Mass
Spectrometric Service at Swansea University. FTIR spectra were
recorded using a Perkin-Elmer RX1 spectrometer as Nujol mulls
between NaCl plates, or on solid samples using an Agilent Cary 630
attenuated total reflectance (ATR) spectrometer. Microanalyses were
carried out by the Science Centre, London Metropolitan University.
Reproducible microanalyses of [LPhGeCl] and 2 could not be obtained
as recrystallization of both consistently led to contamination with small
amounts (ca. 5−10%) of the free amine, HLPh. Melting points were
determined in sealed glass capillaries under dinitrogen and are
uncorrected. The compounds Ar*NH2,19 [(IPr)Pd(Im)] (IPr =
:C{N(Dip)C(H)}2; Im = 1-methylimidazole),10 [L′GeCl],5 and
Na[CpMo(CO)3]20 were prepared by literature procedures. All
other reagents were used as received.
Preparation of [LMesGeCl]. This compound was prepared
similarly to [LPhGeCl] but using BunLi (1.85 cm3 of a 1.6 M solution
in hexane), HLMes (1.50 g, 2.69 mmol), and GeCl2·dioxane (0.686 g,
2.96 mmol). [LMesGeCl] was obtained as a pale yellow solid (1.29 g,
72%). mp: 155−157 °C. 1H NMR (499 MHz, C6D6, 298 K): δ = 1.81
(s, 3H, ArCH3), 2.06 (s, 3H, p-CH3 mesityl), 2.27 (br. s, 6H, o-CH3
mesityl), 6.14 (br. s, 2H, Ph2CH), 6.65−7.08 (m, 24H, ArH). 13C{1H}
(75.5 MHz, C6D6): δ = 20.6 (p-ArCH3 mesityl), 21.0 (ArCH3), 26.7
(br., o-ArCH3 mesityl), 51.8 (br., Ph2CH), 127.2 (br.), 129.0 (br.),
130.8 (br.), 131.1 (br.), 132.3 (br.), 133.0, 133.2, 134.6, 142.5, 143.0,
145.2 (br.), 147.2 (Ar-C). IR ν/cm−1 (ATR): 1433(m), 1369(w),
1235(w), 1216(m), 881(m), 863(bw), 881(m), 756(w), 697(s). MS/
EI m/z (%): 665.1 (M+, 2), 557.2 (Ar*(Mes)NH+, 100), 167.0
(Ph2CH+, 22). Acc. mass calcd for C42H38Cl70GeN: 661.1930. Found:
661.1934.
Preparation of [Cp(CO)3MoGeL′] (1). To a solution of [L′GeCl]
(0.200 g, 0.323 mmol) in toluene (30 mL) was added a solution of
Na[CpMo(CO)3] (0.104 g, 0.389 mmol) in THF (3 mL) at −80 °C
over 5 min. The reaction produced an immediate color change from
pale yellow to orange. The mixture was warmed to room temperature
and stirred for 4 h, whereupon volatiles were removed in vacuo. The
residue was extracted with toluene (20 mL), and the extract was
Preparation of HN(Ar*)(Ph) (HLPh). Ar*NH2 (2.00 g, 4.56
mmol), ButOK (0.665 g, 5.93 mmol), bromobenzene (0.465 g, 2.96
mmol), and [(IPr)Pd(Im)] catalyst (0.074 g, 2.5 mol %) were
dissolved in toluene (50 mL) and heated at reflux for 2 h. The reaction
was allowed to cool, whereupon second portions of [(IPr)Pd(Im)]
(0.074 g, 2.5 mol %) and bromobenzene (0.465 g, 2.96 mmol) were
added. The reaction was heated at reflux for a further 2 h and allowed
to cool, and volatiles were removed in vacuo. The residue was
extracted with dichloromethane (3 × 25 mL), the extract was filtered,
E
dx.doi.org/10.1021/om301144h | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
filtered and concentrated to ca. 5 mL. Hexane (30 mL) was added to
produce an orange precipitate of 1, which was isolated by filtration
(0.155 g, 58%). N.B. X-ray quality crystals of 1 were obtained by
recrystallizing this solid from a mixture of THF and hexane. mp: 236−
239 °C. 1H NMR (499 MHz, C6D6, 298 K): δ = 0.79 (s, 9H,
Si(CH3)3), 1.84 (s, 3H, ArCH3), 4.69 (s, 5H, CpH), 6.38 (s, 2H,
Ph2CH), 6.89−7.31 (m, 22H, ArH). 13C{1H} NMR (126 MHz,
C6D6): δ = 5.0 (Si(CH3)3), 21.1 (ArCH3), 52.4 (Ph2CH), 96.0 (Cp-
C), 126.7, 126.9, 128.6, 128.7, 130.3, 130.9, 131.9, 134.3, 143.5, 143.7,
144.9, 145.3 (Ar-C), 226.1 (br., CO). 29Si{1H} NMR (80 MHz, C6D6)
δ = 1.31 (s). IR υ/cm−1 (Nujol): 1966(s, CO str.), 1891(s, CO str.),
1850(sh., CO str.), 1842(s, CO str.),1830(sh., CO str.), 1598(m),
1031(m), 876(s), 847(s), 807(s), 750(m), 701(s), 604(m), 587(m),
555(m), 516(m), 473(m). MS/EI m/z (%): 801.2 (M+ − CO, 4),
details of data collections, and refinement are given in Table S1
(Supporting Information).
Computational Studies. DFT calculations were performed with
the Gaussian 09 package.22 Geometry optimizations were carried out
using either the B3LYP23 or the BP8624 density functional, in
combination with the 6-311G(d) basis set25 for C, H, Si, N, Ge, and O
atoms, and the LANL2DZ basis set26 for Mo atoms. All structural
geometries were optimized to a minimum energy showing no
imaginary frequencies. The optimized geometries obtained from the
B3LYP and BP86 calculations were similar. Therefore, only the B3LYP
results are discussed here (see the Supporting Information for
geometries optimized at the BP86 level of theory). NBO orbital
analyses and the Wiberg bond indices were calculated using the
program packages Gaussian 0922 and NBO 3.127 at the very same
combination of functional and basis sets as above.
745.2 (M+ − 3(CO), 7), 511.2 (Ar*(SiMe3)NH+, 100), 439.2
+
(Ar*NH2
,
33), 167.0 (Ph2CH+, 86). Anal. Calcd for
C44H41GeMoNO3Si: C, 63.79%; H, 4.99%; N, 1.69%. Found: C,
63.81%; H, 5.02%; N, 1.73%.
ASSOCIATED CONTENT
* Supporting Information
Crystallographic data as CIF files for all crystal structures;
ORTEP diagrams for 2, HLPh, and HLMes; and further details of
the crystallographic and computational studies. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
Preparation of [Cp(CO)3MoGeLPh] (2). To a solution of
[LPhGeCl] (0.200 g, 0.321 mmol) in toluene (30 mL) was added a
solution of Na[CpMo(CO)3] (0.103 g, 0.385 mmol) in THF (3 mL)
at −80 °C over 5 min. The reaction produced an immediate color
change from pale yellow to orange. The mixture was warmed to room
temperature and stirred for 4 h, whereupon volatiles were removed in
vacuo. The residue was extracted with warm hexane (100 mL), the
extract was filtered, and volatiles were removed in vacuo to give 2 as an
orange solid (0.130 g, 48%). N.B. X-ray quality crystals of 2 were
obtained by recrystallizing this solid from warm hexane. mp: 164−168
°C. 1H NMR (499 MHz, C6D6, 298 K): δ = 1.90 (s, 3H, ArCH3), 4.52
(s, 5H, CpH), 6.24 (s, 2H, Ph2CH), 6.93−7.88 (m, 27H, ArH).
13C{1H} NMR (126 MHz, C6D6): δ = 21.4 (ArCH3), 51.9 (Ph2CH),
94.9 (Cp-C), 120.5, 123.5, 126.6, 126.8, 128.2, 128.4, 128.6, 129.2,
129.3, 130.1, 130.8, 131.4, 137.0, 143.5, 145.3, 152.3 (Ar-C), 225.0 (br.
CO). IR υ/cm−1 (Nujol): 1972(s, CO str.), 1941(s, CO str.), 1902(s,
CO str.), 1860(sh., CO str.), 1867(s, CO str.), 1597(m), 1014(s),
868(m), 798(s), 746(m), 699(s), 605(m), 579(m). MS/ES(+ve) m/z
(%): 833.1 (M+, 2).
AUTHOR INFORMATION
Corresponding Author
*E-mail: cameron.jones@monash.edu.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was supported by the Australian Research
Council (grant to C.J.) and the U.S. Air Force Asian Office
of Aerospace Research and Development (grant FA2386-11-1-
4110 to C.J.). The EPSRC is also thanked for access to the UK
National Mass Spectrometry Facility.
Preparation of [Cp(CO)2MoGeL′] (3). Method A. Compound
1 (0.200 g, 0.241 mmol) was dissolved in toluene (20 mL) and heated
at reflux for 1 h. Volatiles were removed in vacuo to give 3 as an
analytically pure orange solid (0.189 g, 98%). N.B. X-ray quality
crystals of 3 were obtained by recrystallizing this solid from a mixture
of THF and hexane.
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C6D6, 298 K): δ = 0.36 (s, 9H, Si(CH3)3), 1.83 (s, 3H, ArCH3), 4.88
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str.), 1853(s, CO str.), 1598(m), 1030(m), 872(m), 831(m), 788(m),
761(m), 746(m), 711(m), 700(s), 604(m), 555(m), 546(m). MS/EI
m/z (%): 801.2 (M+, 45), 745.2 (M+ − 2(CO), 88), 511.2
+
(Ar*(SiMe3)NH+, 47), 439.2 (Ar*NH2 , 33), 167.0 (Ph2CH+, 56).
Anal. Calcd for C43H41GeMoNO2Si: C, 64.52%; H, 5.16%; N, 1.75%.
Found: C, 64.41%; H, 5.20%; N, 1.79%.
X-ray Crystallography. Crystals of 1−3, HLPh, and HLMes suitable
for X-ray structural determination were mounted in silicone oil.
Crystallographic measurements were carried out at 123 K using an
Oxford Gemini Ultra diffractometer using a graphite monochromator
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anisotropic with hydrogen atoms included in calculated positions
(riding model), except the amino proton of HLMes, the positional and
isotropic thermal parameters of which were freely refined. Crystal data,
F
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dx.doi.org/10.1021/om301144h | Organometallics XXXX, XXX, XXX−XXX