Structural evidence of strong calcium-π interactions to aryl substituents stabilized by coexistent agostic bonds to alkyl groups

Article abstract of DOI:10.1021/om500135g

Metalation of 1-(2-furanylmethyl)-(1a) and 1-(2-pyridylmethyl)-2-tert- butyl-3-(2,6-diisopropylphenyl)-1,3-diazaprop-2-ene (1b) with n-butyllithium and potassium bis(trimethylsilyl)amide in tetrahydrofuran (THF) yields the corresponding lithium (2a,b) and potassium derivatives (3a,b), with the alkali metals binding to the furanylmethylamido and pyridylmethylamido pockets. The calcium derivatives are accessible via a metathetical approach of the potassium complexes with calcium iodide in THF. Whereas bis[1-(2-furanylmethyl)-2-tert- butyl-3-(2,6-diisopropylphenyl)-1,3-diazaallyl]calcium (4a) precipitates as a thf adduct, bis[1-(2-pyridylmethyl)-2-tert-butyl-3-(2,6-diisopropylphenyl)-1,3- diazaallyl]calcium (4b) crystallized without solvent coligands. Instead of coordinated solvent molecules, strong calcium-π interactions to an aryl group saturate the coordination sphere. Bidentate 1,2-dimethoxyethane (DME), however, is able to replace this side-on bound aryl group, leading to the dme adduct of bis[1-(2-pyridylmethyl)-2-tert-butyl-3-(2,6-diisopropylphenyl)-1,3-diaallyl] calcium (4c). In all of these s-block metal complexes, strong agostic interactions between the cations and the tert-butyl groups stabilize these complexes.

Full text of DOI:10.1021/om500135g

Article
pubs.acs.org/Organometallics
Structural Evidence of Strong Calcium−π Interactions to Aryl
Substituents Stabilized by Coexistent Agostic Bonds to Alkyl Groups
Claas Loh, Susanne Seupel, Helmar Gorls, Sven Krieck, and Matthias Westerhausen*
̈
Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University, Jena Humboldtstrasse 8, D-07743 Jena, Germany
S
* Supporting Information
ABSTRACT: Metalation of 1-(2-furanylmethyl)- (1a) and 1-(2-pyridylmethyl)-
2-tert-butyl-3-(2,6-diisopropylphenyl)-1,3-diazaprop-2-ene (1b) with n-butyllithium
and potassium bis(trimethylsilyl)amide in tetrahydrofuran (THF) yields the
corresponding lithium (2a,b) and potassium derivatives (3a,b), with the alkali
metals binding to the furanylmethylamido and pyridylmethylamido pockets.
The calcium derivatives are accessible via a metathetical approach of the potassium
complexes with calcium iodide in THF. Whereas bis[1-(2-furanylmethyl)-2-tert-
butyl-3-(2,6-diisopropylphenyl)-1,3-diazaallyl]calcium (4a) precipitates as a thf
adduct, bis[1-(2-pyridylmethyl)-2-tert-butyl-3-(2,6-diisopropylphenyl)-1,3-
diazaallyl]calcium (4b) crystallized without solvent coligands. Instead of
coordinated solvent molecules, strong calcium−π interactions to an aryl group
saturate the coordination sphere. Bidentate 1,2-dimethoxyethane (DME),
however, is able to replace this side-on bound aryl group, leading to the dme adduct of bis[1-(2-pyridylmethyl)-2-tert-butyl-3-
(2,6-diisopropylphenyl)-1,3-diaallyl]calcium (4c). In all of these s-block metal complexes, strong agostic interactions between the
cations and the tert-butyl groups stabilize these complexes.
Scheme 1. Coordination Modes of N,N′-Bis(2,6-
INTRODUCTION
■
diisopropylphenyl)pivalamidinate at Lithium, Potassium, and
Calcium with syn (Left) and anti Configurations (Right)
Interactions between metal cations and π systems play an
important role in chemistry, pharmacy, and biology depending
on the softness and hardness of the cations.1 Calcium cations
are considered as quite hard Lewis acids, comparable with lithium
cations on the basis of the charge-to-surface ratios of the cations
(electrostatic surface potential as quotient q/a of charge q and
surface area a of the cation, calculated as 4πr2). Whereas
cation−π interactions are common for the heavy alkali metal
ions, lithium cations favor an environment of hard Lewis bases
(such as ethers and amines). Nevertheless, intramolecular strain
is able to restrict the accessibility of the cations for ethers such
as tetrahydrofuran (THF), and complexes with a lithium−π
interaction to an aryl group can be stabilized and structurally
characterized.2 Thus, the anti configuration of N,N′-bis(2,6-
diisopropylphenyl)pivalamidinate enforces this kind of bonding,
whereas in the corresponding calcium complex, this amidinate
adopts a heavily strained syn configuration avoiding calcium−π
interactions (Scheme 1). Similar observations were made for the
anilides3 and phenylphosphanides4 of the alkaline-earth metals;
whereas the barium complexes aggregate not only via bridging
nitrogen and phosphorus atoms but also via barium−π interac-
tions to phenyl groups, calcium derivatives avoid this latter kind
of bonding.
the treatment of several cardiovascular diseases, and on the basis
of NMR experiments calcium−π interactions to the phenyl
group have been proposed.5 On the basis of vibrational spectra
and as supported by DFT studies, even calcium ions sandwiched
between phenyl groups of the Phe-Phe ligand (L-phenylalanyl-L-
phenylalanine) have been suggested.6
In chemistry numerous theoretical investigations have been
performed in order to clarify the interaction between calcium (in
all possible oxidation states) and arenes. The interaction energy
between elemental calcium and benzene in the electroneutral π
complex [Ca(η6-C6H6)]0 is very small, with values of 1.30 and
3.28 kJ mol−1 (Table 1).7 Kang estimated a binding energy of the
calcium−benzene complex of 14.5 kJ mol−1, but the formation of
the bis(benzene)calcium sandwich complex [Ca(η6-C6H6)2]0
Despite the challenges in identifying and verifying calcium−π
interactions to aryl groups, this bonding type has been assumed
in pharmacy and biology on the basis of NMR and other
spectroscopic data. The calcium channel antagonist verapamil
(α-isopropyl-α-(N-methyl-N-homoveratryl-γ-aminopropyl)-3,4-
dimethoxyphenylacetonitrile hydrochloride) is used clinically in
Received: February 6, 2014
Published: March 7, 2014
© 2014 American Chemical Society
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Article
an increasing number n of calcium-bound water molecules (n = 1,
273.3 kJ mol−1; n = 2, 224.5 kJ mol−1, n = 3, 173.1 kJ mol−1).14
Furthermore, methyl substituents at the arene enhance its
electron density and, consequently, the calcium−π interaction
energy increases as well.16,17
Table 1. Interaction Energies BE between Calcium and Arene
as well as Distances between the Alkaline-Earth Metal and
the Side-on-Bound Arene in Complexes of the Type
a
[(η6-arene)Ae]n+
Aen+
arene
BE/kJ mol−1 Ae−X/pm method ref
Transfer of these theoretical results into experimental
chemistry requires an environment with Lewis basic reaction
conditions because the highly ionic nature of calcium com-
pounds poses solubility challenges which can only be circum-
vented in polar solvents such as THF. The binding energies of
the Ca−O bonds in complexes lie approximately in the same
order of magnitude as the calcium−π interactions. In the thf
adducts [(thf)4CaI2], [(thf)Ca(Cp)I], and [(thf)2Ca(Cp)I]
(Cp = cyclopentadienide) Ca−O binding energies of 108.7,
114.6, and 104.0 kJ mol−1, respectively, have been calculated,18
which again are much smaller than the Ca−O binding energy in
the cationic water adduct [Ca(OH2)]2+ (240.0 kJ mol−1).14
Side-on coordination of π systems to calcium(II) ions is
observed for aromatic anions such as cyclopentadienyl,19
phospha- and arsacyclopentadienyl,20,21 cyclooctatetraenediyl,22
benzyl,23 and fluorenyl,24 with the metallocenes as the most
prominent compound class of this kind. The inverse sandwich
complex [{(thf)3CaI}2(μ-C6H3-1,3,5-Ph3)] represents the only
isolated molecular calcium(I) complex up to now.25 Here, the
bridging 1,3,5-triphenylbenzene radical anion carries two
negative charges. Neutral calcium-bound π systems are very
rare; side-on-coordinated bis(trimethylsilyl)butadiyne at deca-
methylcalcocene exhibits Ca−C distances of 264(2) and 266 (2)
pm to the butadiyne moiety.26 In pentafluorophenylcalcium
triazenide with bulky aryl groups at the triazenide anion, one
side-on-oriented aryl group is observed, whereas the strontium
and barium derivatives show two alkaline-earth-metal−π
interactions to aryl groups. Due to steric constrictions, one aryl
group acts as a cap to the calcium center with large Ca···Carene
contacts of more than 301 pm despite the low coordination
number of 4, leading to extremely short Ca−Othf and Ca−CC6F5 σ
bonds of only 230.8(5) and 249.9(11) pm, respectively.27
Furthermore, the product of the reaction of Ba[P(SiMe3)2]2 with
diphenylbutadiyne yields a complex with barium−π interactions
to remaining alkyne moieties,28 whereas the homologous calcium
compound shows another reaction pathway.20
Stabilization of side-on-bound aryl groups to calcium(II)
requires some preconditions. Due to the fact that organocalcium
derivatives contain strongly heteropolar bonds and can be
considered as ionic compounds, polar and Lewis basic solvents
ensure the solubility of these saltlike complexes. Bulky sub-
stituents are mandatory in order to prevent aggregation and
oligomerization via bridging Lewis bases. Suitable anions include
the 1,3-diazaallyl systems with bulky N-bound aryl substituents;29
large alkyl (amidinates) or diorganylamino groups (guanidinates)
at the carbon atom in the 2-position stabilize the needed anti
orientation of the aryl groups. Thus far, only 1,3-diazaallyl anions
with a syn configuration have been reported in the calcium-based
coordination chemistry of amidinates30−33 and guanidinates33−35
as well as 2-diphenylphosphanyl-1,3-diazaallyl anions.36,37 In addi-
tion, asymmetrically substituted amidinates have already been
studied as hydrophosphanylation reagents.38 In addition to
shielding substituents at the nitrogen atoms, highly electronegative
donor atoms maintain a large positive charge on the calcium atom
(which is required to stabilize the calcium−π interactions),
whereas organyl groups show a significant covalent bond
contribution and, hence, reduce the positive charge on the
metal atom. On the basis of our previous work, we altered the
0
0
0
Ca
Ca
Ca
benzene
benzene
benzene
benzene
benzene
1.30
3.28
∼500
378.5
B3LYP
B3LYP
7a
7b
8
b
c
14.5
226.5
226.5
263.6
266.3
247.2
246.5
283.1
235.9
286.1
289.9
294.6
254.7
255.1
255.8
255.9
261.0
257.8
262.2
VASP
[(η6-C6H6)Ca]
Ca+
67.05
111.2
B3LYP
B3LYP
B3LYP
MP2
8
0
10
10
12
13
14
15
14
14
14
12
12
12
12
12
12
12
d
Ca+
phenyl
101.1
Ca2+
benzene
benzene
benzene
benzene
benzene
benzene
benzene
benzene
benzene
benzene
benzene
benzene
benzene
benzene
308.78
326.89
330.87
340.16
272.26
224.51
173.05
167.00
160.25
151.00
150.21
141.84
139.33
133.05
Ca2+
B3LYP
B3LYP
B3LYP
B3LYP
B3LYP
B3LYP
MP2
b
be
Ca2+
Ca2+
[(H2O)Ca]2+
[(H2O)2Ca]2+
[(H2O)3Ca]2+
[(NC)Ca]+
[ClCa]+
,
be
,
be
,
MP2
[FCa]+
[(HO)Ca]+
[HCa]+
[(H2N)Ca]+
[(H3C)Ca]+
MP2
MP2
MP2
MP2
MP2
a
b
c
X represents the centroid of the arene ring. Ca−C distance. Vienna
d
ab initio simulation program (VASP). Triplet [(η6-C6H5)Ca]+ complex.
e
Average value.
from calcium and two benzene molecules shows a much
larger binding energy of the overall process (Ca + 2 C6H6) of
134.1 kJ mol−1.8 However, the reaction of calcium vapor with
benzene leads to C−H activation and yields the extremely
sensitive phenylcalcium hydride via insertion of a calcium atom
into a C−H bond.9 Enhancement of the positive charge on
calcium also enhances the interaction energy between Ca+ and
benzene, and an interaction energy of 111.2 kJ mol−1 has been
determined for the π complex [Ca(η6-C6H6)]+.10 In agreement
with the experimental studies of Mochida et al.9 the σ-bond
energy of 256.6 kJ mol−1 of Ca+ to a phenyl radical moiety in
[Ca−C6H5]+ is much larger than the π interaction between
Ca+ and a phenyl unit, suggesting a preference for σ-based
interactions.10 Quantum chemical studies of the neutral dimer
[Ca−C6H5]2 show that the calcium−π interaction to the phenyl
group of the other molecule is favored in comparison to the
formation of a Ca−Ca bond.11
Extensive investigations have been performed on the
interaction of Ca2+ with benzene. Depending on the basis sets
and quantum chemical methods, interaction energies between
292.3 and 340.2 kJ mol−1 have been estimated.12−15 Decreasing
size of the alkaline-earth-metal atoms significantly enhances
the interaction energy between Ae2+ and benzene due to smaller
metal−carbon distances; thus, these energies are roughly 50%
larger for the magnesium derivative. However, addition of
another calcium-bound anionic Lewis base lowers the interaction
energy significantly. Depending on X in complexes of the type
[(η6-C6H6)CaX]+ the interaction energy between Ca2+ and
benzene decreases to 133.1 (X = CH3), 139.3 (X = NH2), 151.0
(X = F), 160.3 (X = Cl), and 167.0 kJ mol−1 (X = CN).12 Not
only anions but also neutral Lewis bases reduce the interaction
energy. In complexes of the type [(η6-C6H6)Ca(OH2)n]2+ the
binding energy between calcium(II) and benzene decreases with
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calcium bis[bis(2,6-diisopropylphenyl)amidinates]2,33 by sub-
stitution of a 2,6-diisopropylphenyl group with furanylmethyl or
pyridylmethyl substituents. This alteration enhances the
denticity of these bases, offers a suitable coordination pocket
for calcium ions, and also allows the remaining N-bound aryl
group to turn toward the cation. Furthermore, electron-donating
groups (such as alkyl) at the aryl substituent enhance both the
steric shielding and electron density of the π system and, due
to the latter effect, additionally strengthen the calcium−π
interactions.
RESULTS AND DISCUSSION
■
A procedure similar to that presented for the preparation of 4a
gave the calcium derivative 4b according to eq 4 with a yield of
Synthesis. The preparation of bulky tridentate ligands was
achieved in the style of a reported protocol.38 2,6-Diisopropyl-
phenylamine (Dipp-NH2) in anhydrous pyridine was treated
with pivaloylchloride yielding Dipp-N(H)−C(O)tBu according
to eq 1. The reaction of this amide with thionyl chloride gave
86%. Suitable metalation reagents are KH and KN(SiMe3)2.
Surprisingly, a thf-free calcium complex was isolated after the
metathesis reaction with [(thf)4CaI2], despite the fact that this
compound was synthesized in the strong Lewis base THF. Again,
several carbon nuclei showed two resonances, supporting two
significantly different coordination modes of the amidinate
anions.
Whereas monodentate thf bases were not able to replace the
calcium(II)−π interaction to one of the Dipp groups, the reac-
tion of bidentate dme with 4b irreversibly yielded the cor-
responding adduct 4c with hexacoordinate calcium atoms (eq 5).
nearly quantitatively Dipp-NCCl(tBu), which was treated
either with 2-furanylmethylamine (H2NCH2-Fu) or with 2-
pyridylmethylamine (H2NCH2-Py), leading to the formation of
the desired Dipp-NC(tBu)N(H)CH2-Fu (1a) and Dipp-N
C(tBu)N(H)CH2-Py (1b) in moderate yields of approximately
60%.
The N−H functionalities of these compounds 1 are very
acidic, and metalation was achieved with n-butyllithium and
potassium bis(trimethylsilyl)amide in hydrocarbons according to
eq 2. The resulting alkali-metal complexes were only sparingly
soluble in these solvents and could easily be isolated by filtration.
Recrystallization from 1,2-dimethoxyethane (DME) or tetrahy-
drofuran yielded the crystalline lithium (R = 2-furanyl (2a), 64%;
R = 2-pyridyl (2b), 82%) and potassium complexes (R = 2-
furanyl (3a), 61%; R = 2-pyridyl (3b), 73%).
For the synthesis of calcium complexes a metathetical
approach was chosen. The potassium derivatives 3a,b were
treated with calcium iodide in tetrahydrofuran (eq 3), giving 4a
with a yield of 37%. THF turned out to be the ideal solvent,
because potassium iodide is insoluble in this ether whereas the
thf adduct [(thf)4CaI2] is soluble, ensuring homogeneous reac-
tion conditions. NMR data of the isolated crystalline compound
showed that a thf adduct formed during this reaction. In the
13C{1H} NMR spectrum two sets of resonances were observed
for the calcium complex 4a, already pointing toward two struc-
turally different amidinates.
This observation nicely underlines the results of the quantum
chemical investigations summarized in the Introduction. The
calcium(II)−π interaction is favored if only one Ca−O bond
to an ether molecule can be realized (due to steric shielding of
the calcium ion). However, a small bidentate ether forms two
Ca−O bonds, and hence, this complex rearranges and offers a
coordination site for the dme molecule. The formation of the π
complex 4b requires an anti configuration of the amidinate anion,
which is facilitated by the bulky tert-butyl group at the 2-position
of the 1,3-diazaallyl moiety.
Molecular Structures. The anions (deprotonated 1a,b)
offer three donor atoms for coordination chemistry to cations.
Former investigations of the coordination behavior of the 3-(2-
furanyl)-5-(2-pyridyl)pyrazolate anion toward mono- and divalent
cations showed that the pyridyl-involving coordination site is
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favored.39 The neutral 3-(2-furanyl)-5-(2-pyridyl)pyrazole forms
tetramers in the solid state via hydrogen bridges between
pyrazole and pyridyl aza bases, whereas the furanyl group is not
involved in the hydrogen bridge network.40 Due to the bulkiness
of the substituents monomeric molecules of 1a,b crystallize
without formation of intermolecular hydrogen bridges. The
molecular structures and numbering schemes of 1a,b are shown
in Figure 1. The N-bound substituents show a syn configuration
derivatives 2a,b the amidinate anions bind in a bidentate fashion
via N1 and O1, forming a five-membered ring with the lithium
atom, as depicted in Figure 2. The coordination spheres of
the lithium atoms is saturated by two thf molecules (2a) or a
bidentate dme molecule (2b), leading to distorted-tetrahedral
environments.
In complexes 3a,b the amidinate anions bind in a very similar
manner to the soft potassium atom; however, one-dimensional
coordination polymers form via intermolecular η6 coordina-
tion of the potassium cations to Dipp groups of neighboring
molecules. A part of this strandlike structure is depicted in
Figure 3. The dme ligand of 3a shows a two-site disorder,
suggesting that there is only moderate crowding at the alkali
metal. In order to saturate the coordination spheres, one methyl
group of the tert-butyl substituent points toward the potassium
atom, thus forming strong agostic bonds. The K···C distances to
this methyl group (3a, K1···C5 324.0(2) pm; 3b, K1···C11
325.2(2) pm) lie in the same range as the intermolecular
potassium−π interactions to the Dipp group (3a, K···C between
315.5(2) and 329.7(1) pm; 3b, K···C between 318.5(2) and
343.4(2) pm).
In contrast to the lithium and potassium derivatives 2a,b and
3a,b, which show rather similar structural features, the calcium
derivatives crystallize with significantly different structures.
Whereas 4a precipitates as a thf adduct, complex 4b does not
form a thf complex. The molecular structure and numbering
scheme of the calcium complex 4a is depicted in Figure 4.
One amidinate anion (ligand B) acts as a tridentate base, and the
other anion (ligand A) binds in a bidentate fashion via the
furanylmethylamido unit. Due to rather small bite angles, the
coordination sphere of the calcium atom significantly deviates
from an octahedron. The different coordination modes influence
the structural data. Ligand B shows characteristic features of an
amidinate anion such as equal N1B−C1B and N2B−C1B bond
lengths of 132.7(3) and 133.8(3) pm as well as rather similar
Ca1−N1B (235.3(2) pm) and Ca1−N2B (239.1(2) pm)
distances. Equalization of the N1A−C1A (135.0(3) pm) and
N2A−C1A (130.6(3) pm) bond lengths is less pronounced. The
Ca−O distances vary within a large, although characteristic,
range and have values of 235.3(2) (thf), 253.4(2) (ligand A), and
260.8(2) pm (ligand B).
Substitution of the furanyl base by a pyridyl base strengthens
the Lewis basic behavior. In the ether-free complex 4b the ligands
bind as bidentate chelates via the pyridylmethylamido function-
alities, as also observed for the alkali-metal compounds. The
molecular structure and the numbering scheme are depicted in
Figure 5. The Ca1−N bond lengths vary within a narrow range
of 239.1(2)−244.5(2) pm with only a small effect of the nega-
tive charge. The most interesting feature is the intramolecular
calcium−π interaction to the Dipp group of ligand B, whereas
the Dipp substituent of ligand A is turned to the periphery of the
molecule. The Ca1−CDipp distances vary between 276.4(2) and
313.5(2) pm (average value 295.8 pm) with a calcium−centroid
distance of 260.9 pm. The shortest distance is observed to the
ipso carbon atom C12B and the longest to the meta carbon
C14B. The Ca1−C12B distance is only slightly larger
(approximately 5−10%) than Ca−C σ-bond lengths of
arylcalcium complexes of the type [(L)nCa(Aryl)X] (250−266
pm depending on L and X, L = neutral Lewis base such as ethers
Figure 1. Molecular structures and numbering schemes of (a) 1a and
(b) 1b. Compound 1b contains two molecules in the asymmetric unit,
but only molecule A is depicted. The ellipsoids represent a probability of
40%; C-bound H atoms are omitted for the sake of clarity.
due to steric repulsion with the tert-butyl group. This orientation
leads to severe distortions of the coordination spheres of the
atoms of the 1,3-diazapropene fragment, and all bond angles
within the CDipp−N−C−N−CCH units are significantly widened.
2
The 1,3-diazapropene clearly shows N−C single and double
bonds with values of approximately 136 and 128 pm, whereas the
N−C distances to the external N-bound groups are greater than
141 pm.
The furanyl and pyridyl bases function as donors, and
deprotonated 1a,b act as bidentate chelate ligands toward the
alkali metals lithium (2a,b) and potassium (3a,b). In Tables 2
and 3, structural parameters of the 1-(2-furanylmethyl)- and the
1-(2-pyridylmethyl)-2-tert-butyl-3-(2,6-diisopropylphenyl)-1,3-
diazaallyl anions, respectively, are compared in order to study the
influence of the metal atom on these amidinates. In the lithium
and amines, X = halide or pseudohalide such as Br−, I−, PPh2 ,
−
N(SiMe3)2 ).41 As observed also for the alkali-metal derivatives
−
of this 3-(2,6-diisopropylphenyl)-2-tert-butyl-1-(2-pyridylmethyl)-
1,3-diazapropenide, the tert-butyl group turns one methyl group
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Table 2. Structural Data (Bond Lengths in pm and Angles in deg) of the 1-(2-Furanylmethyl)-2-tert-butyl-3-(2,6-
diisopropylphenyl)-1,3-diazaallyl Anions Bound at Hydrogen (1a), Lithium (2a), Potassium (3a), and Calcium (4a)
a
1a
2a (A)
Li
2a (B)
Li
3a
4a (A)
Ca
4a (B)
Ca
M
H
K
O1−M
N1−M
N1−C1
N1−C6
N2−M
N2−C1
N2−C11
C1−C2
N1−C6−C7
C1−N1−C6
N1−C1−N2
N1−C1−C2
N2−C1−C2
C1−C2−C3
C1−C2−C4
C1−C2−C5
C1−N2−C11
N2−C11−C12
N2−C11−C16
C12−C11−C16
213.9(5)
199.0(4)
133.8(3)
146.4(3)
216.8(4)
199.5(4)
133.2(2)
146.9(3)
270.3(1)
279.5(1)
132.1(2)
146.3(2)
253.4(2)
238.8(2)
135.0(3)
147.3(3)
260.8(2)
235.3(2)
132.7(3)
145.6(3)
239.1(2)
133.8(3)
140.8(3)
155.4(4)
109.0(2)
128.3(2)
111.4(2)
124.1(2)
124.3(2)
110.8(3)
107.1(2)
113.9(2)
131.8(2)
119.2(2)
120.6(2)
119.6(2)
87(2)
137.2(2)
146.5(2)
128.0(2)
141.2(2)
153.7(2)
111.3(1)
128.2(1)
128.2(2)
113.8(1)
118.1(1)
108.4(1)
111.0(1)
110.3(1)
124.7(1)
118.3(1)
120.5(2)
121.0(1)
131.7(2)
139.1(2)
154.8(3)
109.2(2)
117.1(2)
131.9(2)
113.8(2)
114.2(2)
111.0(2)
108.1(2)
111.7(2)
126.7(2)
121.6(2)
118.8(2)
119.2(2)
131.7(2)
138.8(2)
154.9(3)
109.0(2)
116.8(2)
132.0(2)
114.1(2)
113.7(2)
112.5(2)
107.4(2)
111.4(2)
127.7(2)
121.8(2)
118.7(2)
119.1(2)
133.3(2)
138.4(2)
155.3(2)
110.6(1)
117.7(1)
132.9(1)
114.8(1)
112.1(1)
107.9(1)
110.8(1)
112.8(1)
126.7(1)
122.63(1)
119.0(1)
118.0(1)
130.6(3)
139.6(3)
155.4(4)
110.0(2)
116.0(2)
132.5(2)
115.4(2)
111.9(2)
106.5(2)
114.5(2)
109.8(2)
130.9(2)
122.9(2)
117.0(2)
119.3(2)
a
For compound 2a A and B distinguish between two crystallographically independent molecules, and at divalent calcium the two ligands are
distinguised by the letters A and B.
Table 3. Structural Parameters (Bond Lengths in pm and Angles in deg) of the 1-(2-Pyridylmethyl)-2-tert-butyl-3-(2,6-
a
diisopropylphenyl)-1,3-diazaallyl Anions Bound at Hydrogen (1b), Lithium (2b), Potassium (3b), and Calcium (4b,c)
1b (A)
1b (B)
2b
3b
4b (A)
Ca
4b (B)
Ca
4c (A)
Ca
4c (B)
Ca
M
H
H
Li
K
N1−M
N3−M
N1−C1
N1−C6
N2−C1
N2−C12
C1−C2
N1−C6−C7
C1−N1−C6
N1−C1−N2
N1−C1−C2
N2−C1−C2
C1−C2−C3
C1−C2−C4
C1−C2−C5
C1−N2−C12
N2−C12−C13
N2−C12−C17
C13−C12−C17
87(4)
89(4)
196.1(3)
200.8(3)
133.6(2)
145.8(2)
131.6(2)
138.9(2)
154.9(2)
112.1(1)
116.2(1)
132.2(1)
115.9(1)
112.0(1)
113.6(1)
109.4(1)
107.9(1)
131.3(1)
122.6(1)
117.9(1)
118.7(1)
283.1(1)
275.7(1)
131.9(2)
146.5(2)
133.4(2)
138.2(2)
155.6(2)
109.3(1)
118.1(1)
133.2(2)
114.8(1)
111.7(1)
112.9(1)
110.3(1)
107.6(2)
128.6(1)
118.4(1)
123.2(1)
118.0(1)
239.1(2)
244.5(2)
134.6(2)
147.6(2)
131.3(2)
138.8(2)
155.3(2)
112.8(1)
116.2(1)
132.2(2)
116.7(1)
111.0(1)
114.6(1)
109.1(1)
108.3(1)
130.2(1)
122.7(2)
117.7(2)
119.2(2)
242.9(2)
243.9(2)
135.7(2)
146.0(2)
131.4(2)
139.2(2)
155.1(2)
114.6(1)
119.9(1)
121.5(2)
125.3(2)
113.2(1)
110.1(2)
112.8(2)
109.9(2)
119.2(1)
119.4(2)
121.1(2)
119.3(2)
244.8(2)
248.1(2)
135.6(3)
146.5(3)
130.9(3)
139.3(3)
154.9(3)
114.8(2)
114.7(2)
132.0(2)
114.4(2)
113.6(2)
108.9(2)
110.9(2)
111.9(2)
129.0(2)
121.2(2)
119.2(2)
119.1(2)
244.3(2)
247.6(2)
135.5(3)
146.6(3)
130.8(3)
139.4(3)
155.1(3)
114.8(2)
114.9(2)
132.2(2)
114.7(2)
113.1(2)
111.7(2)
110.3(2)
108.8(2)
130.3(2)
118.5(2)
121.2(2)
119.7(2)
135.7(4)
144.3(4)
128.1(4)
140.8(4)
154.0(4)
109.9(3)
130.0(3)
128.5(3)
114.1(3)
117.4(3)
112.1(3)
107.5(3)
110.2(3)
126.3(3)
118.4(3)
120.3(3)
120.6(3)
135.5(4)
145.1(4)
128.5(4)
141.3(4)
153.9(4)
109.4(2)
129.1(3)
129.0(3)
113.7(3)
117.4(3)
109.6(3)
109.1(3)
110.8(3)
128.7(3)
117.9(3)
120.7(3)
120.6(3)
a
For compound 1b two crystallographically independent molecules are distinguished by the letters A and B, and at divalent calcium two ligands are
distinguished by A and B.
toward the calcium center (Ca1···C3A 294.3(2) pm, Ca···H3A
264(2) and Ca···H3B 247(2) pm), thus blocking the attack of an
ether solvent molecule.
The attraction between the calcium atom and the side-on-
bound Dipp group of ligand B clearly affects the intraligand
bonding parameters. Whereas the C1A−N3A--C12A bond angle
of 130.1(1)° is widened due to steric reasons, the C1B−N3B−
C12B angle of ligand B shows a significantly smaller value of
119.1(1)°. The calcium−π interaction also leads to a narrowing
of the N1−C1−N3 bond angles; whereas steric requirements
enforce a large value of 132.3(2)° for ligand A, a much more
acute angle of 121.6(2)° is observed for ligand B.
Whereas ether-free compound 4b was crystallized from a
THF solution, the availability of bidentate DME yielded the
corresponding ether adduct 4c. The molecular structure and
numbering scheme of this complex is depicted in Figure 6.
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Figure 4. Molecular structure and numbering scheme of 4a. The
calcium-bound amidinate ligands are distinguished by the letters A and
B. The ellipsoids represent a probability of 40%; H atoms are neglected
for the sake of clarity.
Figure 2. Molecular structures and numbering schemes of (a) 2a and
(b) 2b. The asymmetric unit of 2a consists of two molecules A and B;
only molecule A is depicted. The ellipsoids represent a probability of
40%; H atoms are neglected for the sake of clarity.
Figure 5. Molecular structure and numbering scheme of 4b. The
amidinate ligands are distinguished by the letters A and B; only ligand B
shows a strong intramolecular calcium−π interaction to an aryl group.
The ellipsoids represent a probability of 40%; H atoms are neglected for
the sake of clarity.
Figure 6. Molecular structure and numbering scheme of 4c. The
amidinate ligands are distinguished by the letters A and B; H atoms are
not shown. The ellipsoids represent a probability of 40%. The distortion
of the octahedral environment of the calcium center arising from the
rather small bite angles of the bidentate ligands is clearly shown.
Figure 3. Cutouts of the strand-like structures of (a) 3a and (b) 3b. The
ellipsoids represent a probability of 40%; H atoms are omitted for the
sake of clarity. The intermolecular potassium−π interaction to a Dipp
group is clearly shown.
Due to the crowded environment of the calcium center, rather
large Ca−O (average Ca−O 252.8 pm) and Ca−N distances
(average Ca−N 246.2 pm) are observed. As found for the alkali metal
compounds, the bulky ligands bind via the 2-pyridylmethylamido
pockets and the demanding Dipp substituents are turned to the
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periphery of the molecule. Due to the rather small bite angles of
the ligands, the octahedral environment of the calcium atom is
severely distorted. On the basis of the centrosymmetric space
group, the solid state consists of a racemate of Λ and Δ isomers.
Scheme 2 gives a drawing of the Δ isomer.
Table 4. Structural Parameters (Bond Lengths in pm and
Angles in deg) of the Intramolecular Bonds between the s-
Block Metal Ions and the tert-Butyl Groups Based on X-ray
a
Structure Determinations
b
b
complex
M
Li
M···C
M···H
M···H−C
π(M−X)
2a
305.5(5) (A),
290.2(5) (B)
225 (A),
220 (B)
139.0 (A),
Scheme 2. Schematic Drawing of the Δ Isomer of 4c
127.9 (B)
2b
3a
Li
K
273.6(3)
324.0(2)
222(2)
112.2(1)
273(2),
288(2)
112.9(4),
102.5(4)
293.3(2)
296.4(2)
3b
K
325.2(2)
270(2),
295(2)
99.3(2),
114.8(2)
4a
4b
Ca 297.0(3)
Ca 294.3(2)
249, 262
109.4, 100.9
247(3),
264(3)
98.1(6),
108.6(6)
260.9(1)
4c
Ca 350.3(2),
352.7(2),
265, 268,
265, 262
145.7, 144.5,
144.8,
144.8
349.5(2),
347.2(2)
Agostic Bonding. The interactions of C−H, C−C, and
Si−C σ bonds with metal atoms play important roles in (often
catalytic) activation of those bonds. Recently, an impressive
example was presented with alkane coordination at a potassium
cation in a dinuclear complex with a rigid hydrophobic pocket;
the shortest K···C contacts vary between 321.5(5) and
362(3) pm.42 Depending on the nature of these bonds, agostic
and anagostic bonds are distinguished.43 The agostic bonds can
be considered as a closed three-center−two-electron interaction,
leading to M···H−C bond angles between 90 and 140° and
short M···H distances. In contrast, the anagostic interaction is
characterized by larger M···H−C bond angles of 110−170° and
also by longer M···H contacts. Whereas the agostic interaction is
a closed three-center bond, the anagostic interaction can be
regarded as an open three-center−two-electron bond and is
based on electrostatic attraction between the metal cation and
slightly negative hydrogen atoms.
Due to the fact that the structure determinations were of
excellent quality, the hydrogen atoms that are involved in this
type of interaction were found in the electron density map and
free isotropic refinement of the positional parameters of the
H atoms allowed interpretation of the nature of Ca···H−C inter-
actions of the tert-butyl groups. Relevant structural parameters
are summarized in Table 4. A cutout of the structure of 4b is
depicted in Figure 7. The Ca···H−C bond angles adopt typical
values for agostic bonds with rather short Ca···H and Ca···C
bonds of 256 (average value) and 294.3(2) pm, respectively, with
the Ca···C distance being comparable to the Ca−C values of
the calcium−π interactions. After addition of bidentate 1,2-
dimethoxyethane and formation of complex 4c, an open three-
center−two-electron Ca···H−C bond forms with characteristic
parameters of an anagostic bonding situation. Thus, the obtuse
Ca···H−C angle of 145° significantly elongates the Ca···C bond
by 55 pm to an average value of 349.9 pm.
a
For comparison reasons, also the inter- (M = K) or intramolecular
distances (M = Ca) between the metal atom M and the centroid X of
the side-on bound Dipp group (metal−π interaction) are added (last
b
column). Values with standard deviations refer to isotropically refined
hydrogen atoms, whereas values without esd values refer to H atoms
which were included at ideal positions with fixed C−H bond lengths
and refined with the riding model.
lithium (2a ,b) and potassium derivatives (3a,b). In order to
produce single-crystal material, an ether exchange proves to be
advantageous and the dme adducts readily form after addition of the
bidentate ether. The furanylmethyl- and pyridylmethyl-substituted
amidinates exhibit coordination behavior very similar to that of
the alkali metals. Treatment of calcium iodide in THF with the
potassium complexes yields the thf adduct of bis[1-(2-furanylmethyl)-
2-tert-butyl-3-(2,6-diisopropylphenyl)-1,3-diazaallyl]calcium (4a)
and, unexpectedly, solvent-free bis[1-(2-pyridylmethyl)-2-tert-butyl-
3-(2,6-diisopropylphenyl)-1,3-diazaallyl]calcium (4b). Even re-
crystallization of 4b from THF does not lead to the formation of
a thf adduct. However, addition of bidentate 1,2-dimethoxyethane
irreversibly yields the corresponding dme adduct 4c.
The bulky tert-butyl group in the 2-position compensates the
preference of certain configurations (Scheme 3). Thus, in 1a,b,
the N-bound substituents show a syn configuration as a Z isomer.
This isomeric structure is maintained in alkali-metal complexes.
The hard lithium and calcium cations as well as the soft potas-
sium cation favor the coordination to the furanylmethylamido
and pyridylmethylamido pockets rather than a binding to the
amidinate units. In the calcium compound 4a, one ligand ex-
presses the same orientation, whereas the other acts as a tridentate
ligand with a syn and E arrangement of the substituents. In calcium
derivative 4b the syn and Z form is realized for one ligand, whereas
the other prefers an anti and Z arrangement. Finally, in 4c
isomerism of the ligands is observed to be similar to that for the
alkali-metal derivatives. An anti and E oriented isomer was not
found in the solid state due to strong steric repulsive forces
between the tert-butyl group and the bulky Dipp substituent.
The soft potassium ion forms intermolecular π interactions to
the aryl substituent, leading to strandlike structures in the solid
state. It is remarkable that in all these metal complexes one
methyl group of the tert-butyl moiety is directed toward the metal
center. This arrangement effectively shields the metal center and
stabilizes low ether contents in the vicinities of the s-block metals.
Due to the excellent quality of the structure determinations
(which allowed localization of the hydrogen atoms in a difference
These calcium complexes impressively demonstrate the
structural features of agostic and anagostic interactions between
an alkaline-earth metal and an alkyl group. These attractive forces
also have an effect on the bond angles of the tert-butyl group. Due
to these interactions, the tetrahedral environment of the
quaternary carbon atom C2 (see Table 3) is slightly distorted.
CONCLUSION
■
Metalation of 1-(2-furanylmethyl)- (1a) and 1-(2-pyridylmethyl)-
2-tert-butyl-3-(2,6-diisopropylphenyl)-1,3-diazaprop-2-ene (1b)
succeeds with good yields in tetrahydrofuran with n-butyllithium
and potassium bis(trimethylsilyl)amide, giving the corresponding
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with a distance of 260.9 pm between the alkaline-earth metal and
the centroid of the arene. The structural parameters nicely
correlate to quantum chemical predictions of side-on-bound
benzene at calcium ions. These quantum-chemical studies of
complexes of the type [(η6-arene)Ca(L)n]2+ and [(η6-arene)-
CaX]+ (L = neutral Lewis base, X = anionic Lewis base) suggest
that the calcium−π interaction energy is slightly larger in com-
parison to Ca−Othf binding energies; however, if two Ca−O
bonds can be formed, the formation of an ether complex is
favored as observed for 4c after addition of bidentate dme. These
considerations clarify the role of the 1-(2-pyridylmethyl)-2-tert-
butyl-3-(2,6-diisopropylphenyl)-1,3-diazaallyl anion. The ligand
has to be designed to offer an aryl moiety in the predetermined
distance to the metal center in order to obtain sufficiently large
metal−π interaction energy competitive with the Ca−Oether
binding energy. In addition, bulky groups have to limit the
access of the metal center by strong and hard Lewis bases (such
as ethers) because this π interaction seems to be competitive only
with a single Ca−Oether bond. This requirement is fulfilled by the
tert-butyl groups in the vicinity of the calcium atom, shielding the
metal center and saturating the coordination sphere by strong
agostic bonds.
Returning to the initially discussed importance of s-block
metal−π interactions in chemistry, pharmacy, and biology, the
requirements for stabilizing such bonds might be generalized. On
the one hand, soft potassium ions prefer soft π systems such as
side-on-bound arene or aryl ligands, in agreement with the
Pearson concept of hard and soft acids and bases. On the other
hand, hard metal ions such as Ca2+ are able to show rather strong
metal−π interactions if the competition with more than one hard
Lewis base is excluded by steric factors.
EXPERIMENTAL SECTION
Figure 7. Clarification of the agostic interactions between the calcium
atom Ca1 and the tert-butyl group in complex 4b (top, dashed lines) as
well as of the anagostic interactions between Ca1 and the tert-butyl
groups in 4c (bottom, dashed lines). The ellipsoids represent a
probability of 40%; H atoms are drawn with arbitrary radii. When the
centroid X1A of the Dipp group and the C3 atom of the tert-butyl group
are considered as single ligands, the distorted-octahedral environment of
Ca1 in 4b can be recognized.
■
General Considerations. All manipulations were carried out under
an inert nitrogen atmosphere using standard Schlenk techniques.
Solvents were dried over KOH and distilled over sodium/
benzophenone under a nitrogen atmosphere; deuterated THF and
benzene were dried over sodium, degassed, and saturated with nitrogen.
The yields given are not optimized. 1H and 13C{1H} NMR spectra were
recorded on Bruker AC 200, AC 400, and AC 600 spectrometers.
Chemical shifts are reported in parts per million relative to Me4Si as an
external standard. The residual signals of [D8]THF, chloroform, and
[D6]benzene were used as internal standards. Due to the air and
moisture sensitivity, combustion analyses were challenging. Despite the
fact that V2O5 was added, the values of the combustion analysis
occasionally deviate from theoretical values, presumably due to
carbonate formation and partial loss of intercalated solvent.
Scheme 3. Possible anti (Top Row) and syn Configurations
(Bottom Row) of the Diazaallyl Anions (R = 2-Furanyl (Fu),
2-Pyridyl (Py)) as Z (Left Column) or E Isomers (Right
Column) with Respect to the CN Double Bond Shown
Synthesis of Dipp-NC(tBu)N(H)CH2-Fu (1a). Dipp-NH2
(9.6 mL, 49.8 mmol) in 80 mL of anhydrous pyridine and pivaloyl
chloride (6.2 mL, 50.4 mmol) gave 11.58 g (44.3 mmol, 89%) of Dipp-
N(H)CO(tBu). The purity of the product was controlled by NMR
spectroscopy. The reaction of Dipp-N(H)CO(tBu) (11.58 g, 44.3
mmol) with SOCl2 (10 mL, 137.8 mmol) yielded 11.65 g (41.6 mmol,
94%) of pure Dipp-NCCl(tBu). The reaction of Dipp-NCCl(tBu)
(11.65 g, 41.6 mmol) and NH2CH2-Fu (4.08 g, 42.0 mmol) led to Dipp-
NC(tBu)N(H)CH2-Fu (8.33 g, 24.5 mmol, 58%). Physical data of 1a
are as follows. Mp: 340.5 K. 1H NMR (CDCl3, 296.2 K, 400.075 MHz):
δ 1.18 (d, 3JH,H = 6.8 Hz, 6H, iPr CH3), 1.21 (d, 3JH,H = 7.2 Hz, 6H, iPr
CH3), 1.32 (s, 9H, tBu CH3), 3.06 (sept, 3JH,H = 6.8 Hz, 2H, iPr CH),
3.79 (d, 3JH,H = 5.2 Hz, 2H, −CH2−), 4.53 (broad, 1H, NH), 5.96 (d,
3JH,H = 2.8 Hz, 1H, Fu o-CH), 6.25 (dd, 3JH,H = 3.0 Hz, 3JH,H = 1.8 Hz,
1H, Fu m-CH), 6.90 (dd, 3JH,H = 7.4 Hz, 3JH,H = 7.4 Hz, 1H, Dipp p-CH),
7.00 (d, 3JH,H = 7.6 Hz, 2H, Dipp m-CH), 7.26 + 7.29 (m, Fu OCH).
13C{1H} NMR (CDCl3, 296.8 K, 100.599 MHz): δ 22.6 + 23.2 (iPr
CH3), 28.5 (iPr CH), 29.2 (tBu CH3), 38.9 (tBu C), 40.9 (−CH2−),
106.9 (Fu o-C), 110.4 (Fu m-C), 121.3 (Dipp p-C), 122.2 (Dipp m-C),
Fourier synthesis and their free isotropic refinement), the
geometry and structural parameters of the M···H−C contacts are
available, verifying the existence of strong agostic bonds.
Ether-free calcium complex 4b is shielded by strong intra-
molecular calcium−π interactions to one aryl (Dipp) substituent
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137.4 (Dipp o-C), 142.2 (Fu OCH), 146.2 (Dipp i-C), 152.1 (Fu i-C),
156.4 (qC). 1H NMR (C6D6, 296.5 K, 400.075 MHz): δ 1.19 (s, 9H, tBu
CH3), 1.30 (d, 3JH,H = 6.8 Hz, 12H, iPr CH3), 3.90 (sept, 3JH,H = 6.8 Hz,
2H, iPr CH), 3.37 (d, 3JH,H = 4.4 Hz, 2H, −CH2−), 4.36 (m, broad, 1H,
NH), 5.68 (d, 3JH,H = 3.0 Hz, 1H, Fu o-CH), 5.92 (dd, 3JH,H = 3.0 Hz,
3JH,H = 1.8 Hz, 1H, Fu m-CH), 6.93 (d, 3JH,H = 1.2 Hz, 1H, Fu O−CH),
Fu o-CH), 6.18 (s, 1H, Fu m-CH), 6.50 (broad, 1H, Dipp p-CH), 6.75
(broad, 2H, Dipp m-CH), 7.24 (s, 1H, Fu OCH). 13C{1H} NMR
([D8]THF, 297.0 K, 100.613 MHz): δ 22.8 + 23.9 (iPr CH3), 29.1 (iPr
CH), 30.7 (broad, tBu CH3), 40.1 (broad, tBu C), 44.6 (broad, −CH2−),
59.0 (DME CH3), 72.8 (DME CH2), 105.9 (broad, Fu o-C), 110.9 (Fu
m-C), 118.4 (broad, Dipp p-C), 121.8 (Dipp m-C), 137.4 (Dipp o-C),
141.6 (broad, Fu OCH), 151.0 (Dipp i-C), 158.4 (Fu i-C), 160.8 (qC).
IR (pure): ν (cm−1) 2956 w, 2928 sh, 2868 vw, 1507 w, 1483 vs, 1446 m,
1421 vs, 1404 m, 1373 m, 1352 m, 1311 s, 1244 m, 1216 vw, 1204 vw,
1156, 1143 w, 1052 m, 1010 m, 933 w, 914 m, 796 m, 779 s, 749 w, 723 s,
597 w, 528 vw. MS (Micro-ESI in THF + MeOH): m/z (%) 379 (24)
[M + H − dme]+, 341 (100) [L + H]+. Anal. Calcd for C26H41KN2O3
(468.71): C, 66.63; H, 8.81; N, 5.98. Found: C, 66.84; H, 8.25; N, 7.17.
Synthesis of [(thf)Ca{(Dipp-N)C(tBu)NCH2-Fu}2] (4a). In 70 mL
of THF, the reactants 1a (0.379 g, 1.11 mmol), KN(SiMe3)2 (0.404 g,
2.02 mmol), and CaI2 (0.366 g, 1.25 mmol) were combined and stirred
for 24 h. Recrystallization from toluene and storage at −20 °C for several
days led to the formation of 4a as colorless crystals. Yield: 0.324 g (0.41
mmol, 37%). Physical data of 4a are as follows. Dec pt: above 379 K. 1H
NMR (C6D6, 297.4 K, 400.075 MHz): δ 1.01 (d, 3JH,H = 6 Hz, 6H, iPr
CH3), 1.16 (m, 4H, THF CH2), 1.20−1.67 (m, broad, 36H, iPr CH3 +
tBu CH3), 1.24 (s, tBu CH3), 1.35 (d, 3JH,H = 6.8 Hz, iPr CH3), 1.46 (dd,
3JH,H = 8.6 Hz, 3JH,H = 8.6 Hz, iPr CH3), 1.57 (s, tBu CH3), 3.26 (m, 4H,
THF OCH2), 3.42 + 3.62 (m, broad, 4H, iPr CH), 4.37 + 4.71 (m, 4H,
−CH2−), 5.43 + 5.63 (s, broad, 2H, Fu o-CH), 5.78 + 6.08 (s, broad, 2H,
Fu m-CH), 6.98−7.40(m, 8H, Dipp p-CH + Dipp m-CH + Fu OCH).
13C{1H} NMR (C6D6, 296.9 K, 100.599 MHz): δ 23.1 + 23.3 + 24.0 (iPr
CH3), 25.3 (THF, CH2), 28.4 + 28.9 (iPr CH), 29.9 + 30.7 (tBu CH3),
40.9 + 41.9 (tBu C), 45.4 + 46.4 (−CH2-), 68.5 (THF OCH2), 104.2 +
104.6 (Fu o-C), 111.3 + 112.0 (Fu m-C), 118.2 + 121.2 (Dipp p-C),
123.7 (broad, Dipp m-C), 137.0 + 140.3 (Dipp o-C), 140.1 + 140.5 (Fu
OCH), 152.0 + 158.4 (broad, Dipp i-C), 158.2 + 158.5 (Fu i-C), 164.8 +
175.8 (qC). IR (pure): ν (cm−1) 2959 m, 2928 sh, 2869 w, 1734 vw, 1699
vw, 1680 sh, 1665 sh, 1648 vs, 1588 w, 1554 vs, 1505 vs, 1457 vs, 1429 vs,
1397 w, 1318 s, 1256 m, 1212 m, 1164 m, 1147 w, 1075 w, 1017 m, 987
w, 968 w, 935 sh, 315 s, 876 w, 803 m, 799 sh, 792 sh, 763 m, 749 vs,
732 m, 715 s, 679 vw, 601 sh, 592 w. MS (DEI): m/z (%) 719 (45)
[M − dme]+, 675 (25) [M − iPr − dme]+, 379 (100) [M − L − dme]+,
340 (70) [L]+, 298 (87) [L − iPr]+, 244 (31) [L − FMA]+, 81 (97)
[FMA − NH]+, 42 (48) [iPr]+. Anal. Calcd for C48H70N4O3Ca
(791.184): C, 72.87; H, 8.92, 7.08. Found: C, 71.14; H, 8.61; N, 7.29.
Synthesis of Dipp-NC(tBu)N(H)CH2-Py (1b). The reaction of
Dipp-NCCl(tBu) (6.10 g, 21.8 mmol) with NH2CH2-Py (2.25 mL,
21.9 mmol) gave Dipp-NC(tBu)N(H)CH2Py (4.8 g, 13.6 mmol,
62%). Physical data of 1b are as follows. Mp: 374 K. 1H NMR (CDCl3,
297.2 K, 400.075 MHz): δ 1.16 (d, 3JH,H = 6.8 Hz, 6H, iPr CH3), 1.18 (d,
7.05 (dd, 3JH,H = 8.2 Hz, 3JH,H = 7.0 Hz, 1H, Dipp p-CH), 7.14 (d, 3JH,H
=
7.6 Hz, Dipp, 2H, m-CH). 13C{1H} NMR (C6D6, 297.1 K, 100.599
MHz): δ 22.6 + 23.5 (iPr CH3), 29.0 (iPr CH), 29.1 (tBu CH3), 38.9
(tBu C), 41.0 (−CH2−), 106.9 (Fu o-C), 110.6 (Fu m-C), 122.0 (Dipp
p-C), 122.7 (Dipp m-C), 137.4 (Dipp o-C), 142.2 (Fu O-CH), 146.5
(Dipp i-C), 152.5 (Fu i-C), 156.2 (qC). 1H NMR ([D8]THF, 297.2 K,
400.075 MHz): δ 1.13 (d, 3JH,H = 6.8 Hz, 6H, iPr CH3), 1.17 (d, 3JH,H
=
6.8 Hz, 6H, iPr CH3), 1.31 (s, 9H, tBu CH3), 3.02 (sept, 3JH,H = 6.8 Hz,
2H, iPr CH), 3.85 (d, 3JH,H = 5.6 Hz, 2H, −CH2−), 5.41 (m, broad, 1H,
NH), 5.94 (d, 3JH,H = 2.8 Hz, 1H, Fu o-CH), 6.22 (dd, 3JH,H = 3.0 Hz,
3JH,H = 1.8 Hz, 1H, Fu m-CH), 6.77 (dd, 3JH,H = 7.6 Hz, 3JH,H = 7.6 Hz,
3
1H, Dipp p-CH), 6.92 (d, JH,H = 7.6 Hz, Dipp, 2H, m-CH), 7.31 (d,
3JH,H = 1.6 Hz, 1H, Fu OCH). 13C{1H} NMR ([D8]THF, 297.0 K,
100.599 MHz): δ 22.6 + 23.6 (iPr CH3), 29.3 (iPr CH), 29.4 (tBu CH3),
39.7 (tBu C), 41.1 (−CH2−), 106.9 (Fu o-C), 110.9 (Fu m-C), 121.6
(Dipp p-C), 122.6 (Dipp m-C), 137.5 (Dipp o-C), 142.7 (Fu OCH),
147.4 (Dipp i-C), 154.0 (Fu i-C), 157.0 (qC). IR (pure): ν (cm−1) 3420
vw (N−H), 2961 m, 2927 sh, 2867 w, 1650 s, 1587 w, 1503 s, 1452 m,
1431 m, 1397 w, 1381 vw, 1364 w, 1330 m, 1277 w, 1255 m, 1226 sh,
1214 m, 1163 m, 1145 m, 1077 w, 1017 m, 933 w, 912 m, 885 vw, 824 w,
797 m, 763 s, 746 vs, 715 w, 681 vw, 643 vw, 600 w. MS (Micro-ESI in
CHCl3 + MeOH, C22H32N2O): calcd 341.259289, found 341.259390.
Anal. Calcd for C22H32N2O (340.51): C, 77.60; H, 9.47; N, 8.22. Found:
C, 78.25; H, 10.49; N, 8.48.
Synthesis of [(thf)2Li{(Dipp-N)C(tBu)NCH2-Fu}] (2a). A 1.5 M
solution of nBuLi in hexane (1.2 mL, 1.8 mmol) was added to a solution
of 1a (0.50 g, 1.5 mmol) in 20 mL of pentane at −78 °C. While it was
warmed to room temperature, the solution changed from colorless via
orange to red. The solution was stirred for 4 h; meanwhile, formation of
a pale orange solid was observed. This precipitate was collected by
filtration, consisting of the solvent-free lithium salt (0.405 g, 1.17 mmol,
87%). Recrystallization of 0.20 g (0.58 mmol) of [Li{(Dipp-N)C(tBu)-
NCH2-Fu}] from 0.2 mL of THF and storage at −20 °C for several days
gave 2a as colorless crystals. Yield: 0.182 g (0.37 mmol, 64%). Physical
data of 2a are as follows. Dec pt: above 488 K. 1H NMR (C6D6, 297.0 K,
400.130 MHz): δ 1.32 (m, 8H, THF CH2), 1.46 (broad, 12H, iPr CH3),
1.60 (broad, 9H, tBu CH3), 3.38 (m, 8H, THF OCH2), 3.74 (broad, 2H,
iPr CH), 4.41 (broad, 2H, −CH2−), 5.56 (s, 1H, Fu o-CH), 5.90 (s, 1H,
Fu m-CH), 6.68 (broad, 1H, Fu O−CH), 7.05 (m, 1H, Dipp p-CH),
7.22 (m, 2H, Dipp m-CH). 13C{1H} NMR (C6D6, 297.0 K, 100.613
MHz): δ 23.4 + 24.3 (broad, iPr CH3), 25.5 (THF CH2), 28.7 (broad,
iPr CH), 31.3 (broad, tBuCH3), 40.3 (broad, tBu C), 47.5 (broad,
−CH2−), 68.1 (THF OCH2), 104.0 (Fu o-C), 111.5 (Fu m-C), 117.7
(broad, Dipp p-C), 121.8 (broad, Dipp m-C), 138.1 (broad, Dipp o-C),
139.4 (broad, Fu OCH), 152.7 (broad, Dipp i-C), 160.2 (broad, Fu i-C).
IR (pure): ν (cm−1) 2957 s, 2869 w, 2361 vw, 1653 m, 1587 vw, 1559 vw,
1539 vw, 1492 s, 1457 m, 1428 s, 1390 w, 1357 m, 1343m, 1328 m, 1309
w, 1248 w, 1211 w, 1188 vw, 1162 vw, 1143 w, 1107 vw, 1075 w, 1012 m,
975 m, 929 w, 884 vs, 804 m, 794 m, 761 vs, 726 sv, 684 vw, 667 vw, 608
vw, 594 w, 505 w, 433 w. MS (Micro-ESI in THF + MeOH): m/z (%)
347 (4) [M + H]+, 341 (100) [L + H]+. Anal. Calcd for C30H47N2O3Li
(490.65): C, 73.44; H, 9.65; N, 5.71. Found: C, 71.52; H, 9.32; N, 5.70.
Synthesis of [(dme)K{(Dipp-N)C(tBu)CH2-Fu}] (3a). A solution
of 1a (0.946 g, 2.78 mmol) in 8 mL of toluene was added at room
temperature to a solution of KN(SiMe3)2 (0.556 g, 2.79 mmol)
dissolved in 15 mL of toluene. A white precipitate formed, and the
solution changed from colorless to orange-brown. After the mixture was
stirred overnight, the solid was collected and recrystallized from 0.5 mL
of DME. Storage at 5 °C for several days gave 3a as colorless crystals.
Yield: 0.797 g (1.7 mmol, 61%). Physical data of 3a are as follows. Dec
pt: above 437 K. 1H NMR ([D8]THF, 297.0 K, 400.130 MHz): δ 1.10
(d, 3JH,H = 6.8 Hz, 6H, iPr CH3), 1.16 (d, 3JH,H = 6.8 Hz, 6H, iPr CH3),
1.26 (s, 9H, tBu CH3), 3.20 (broad, 2H, iPr CH), 3.27 (s, 6H, DME
CH3), 3.43 (s, 4H, DME CH2), 3.88 (s, 2H, −CH2−), 5.80 (broad, 1H,
3JH,H = 6.8 Hz, 6H, iPr CH3), 1.39 (s, 9H, tBu CH3), 3.06 (sept, 3JH,H
=
6.8 Hz, 2H, iPr CH), 3.82 (d, 3JH,H = 4 Hz, 2H, −CH2−), 6.21 (broad,
1H, NH), 6.80 (d, 3JH,H = 7.6 Hz, 1H, Py o-CH), 6.92 (dd, 3JH,H = 8.2 Hz,
3JH,H = 7.2 Hz, 1H, Dipp p-CH), 7.01 (d, 3JH,H = 7.6 Hz, 2H, Dipp m-
CH), 7.12 (dd, 3JH,H = 7.0 Hz, 3JH,H = 5.2 Hz, 1H, Py p-CH), 7.53 (ddd,
3JH,H = 7.7 Hz, JH,H = 7.7 Hz, JH,H = 1.7 Hz, 1H, Py m-CH), 8.51
3
4
(d, JH,H = 4.4 Hz, 1H, Py N−CH). 13C{1H} NMR (CDCl3, 297.0 K,
3
100.599 MHz): δ 22.6 + 23.2 (iPr CH3), 28.5 (iPr CH), 29.4 (tBu CH3),
39.1 (tBu C), 47.0 (−CH2−), 121.1 (Dipp p-C), 121.9 (Dipp m-C),
122.0 (Py o-C), 122.1 (Py p-C), 136.5 (Py m-C), 137.9 (Dipp o-C),
146.9 (Dipp i-C), 148.9 (Py N-CH), 156.8 (Py i-C), 157.1 (qC). H
1
NMR (C6D6, 297.2 K, 400.075 MHz): δ 1.27 (d, 3JH,H = 6.8 Hz, 6H, iPr
CH3), 1.33 (d, 3JH,H = 6.8 Hz, 6H, iPr CH3), 1.47 (s, 9H, tBu CH3), 3.34
(sept, 3JH,H = 6.8 Hz, 2H, iPr CH), 3.82 (d, 3JH,H = 4 Hz, 2H, −CH2−),
6.12 (d, 3JH,H = 7.8 Hz, 1H, Py o-CH), 6.46 (dd, 3JH,H = 6.8 Hz, 3JH,H
=
5.2 Hz, 1H, Py p-CH), 6.69 (m, broad, 1H, NH), 6.76 (ddd, 3JH,H = 7.7
Hz, 3JH,H = 7.6 Hz, 4JH,H = 1.7 Hz, 1H, Py m-CH), 7.11−7.20 (m, 3H,
Dipp p-CH + Dipp m-CH), 8.24 (d, JH,H = 4.8 Hz, 1H, Py NCH).
3
13C{1H} NMR (C6D6, 297.1 K, 100.599 MHz): δ 22.6 + 23.6 (iPr CH3),
29.0 (iPr CH), 29.4 (tBu CH3), 39.3 (tBu C), 47.1 (−CH2−), 121.7
(Dipp p-C), 121.8 (Py o-C), 121.9 (Py p-C), 122.5 (Dipp m-C), 136.2
(Py m-C), 138.1 (Dipp o-C), 147.5 (Dipp i-C), 148.7 (Py NCH), 156.6
(Py i-C), 157.0 (qC). 1H NMR ([D8]THF, 297.0 K, 400.130 MHz): δ
1488
dx.doi.org/10.1021/om500135g | Organometallics 2014, 33, 1480−1491

Organometallics
Article
1.13 (d, 3JH,H = 6.8 Hz, 12H, iPr CH3), 1.38 (s, 9H, tBu CH3), 3.06 (sept,
3JH,H = 6.8 Hz, 2H, iPr CH), 3.86 (d, 3JH,H = 4.4 Hz, 2H, −CH2−), 6.50
(m, broad, 1H, NH), 6.81−6.84 (m, 2H, Py o-CH + Dipp p-CH), 6.94
(d, 3JH,H = 8.4 Hz, 2H, Dipp m-CH), 7.13 (dd, 3JH,H = 6.2 Hz, 3JH,H = 6.2
Hz, 1H, Py p-CH), 7.56 (ddd, 3JH,H = 7.6 Hz, 3JH,H = 7.6 Hz, 4JH,H = 1.6
Hz, 1H Py m-CH), 8.47 (d, 3JH,H = 4.4 Hz, 1H, Py N−CH). 13C{1H}
NMR ([D8]THF, 297.1 K, 100.599 MHz): δ 22.6 + 23.6 (iPr CH3), 29.3
(iPr CH), 29.6 (tBu CH3), 39.8 (tBu C), 47.8 (−CH2−), 121.7 (Dipp p-
C), 122.4 (Py o-C + Py p-C), 122.9 (Dipp m-C), 137.2 (Py m-C), 138.1
(Dipp o-C), 147.9 (Dipp i-C), 149.6 (Py NCH), 157.5 (Py i-C), 157.9
(qC). IR (pure): ν (cm−1) 3379 w (NH), 2961 w, 2924 sh, 2866 vw,
1649 vs, 1589 w, 1570 w, 1499 m, 1479 m, 1451 w, 1432 s, 1395 vw,
1381 vw, 1357 w, 1330 w, 1258 w, 1227 vw, 1207 w, 1151 vw, 1060 vw,
1045 vw, 997 vw, 949 w, 935 sh, 802 w, 786 w, 753 vs, 730 w, 680 vw, 555
w, 529 w, 431 m, 422 sh, 414 sh. MS (Micro-ESI in MeOH, C23H33N3):
calcd 352.275273, found 352.276130. Anal. Calcd for C23H33N3
(351.53): C, 78.58; H, 9.46; N, 11.95. Found: C, 78.04; H, 10.09; N,
11.74.
153.1 (Dipp i-C), 162.7 (qC). IR (pure): ν (cm−1) 2955 w, 2866 vw,
1653 vw, 1591 w, 1570 vw, 1488 vs, 1458 m, 1434 m, 1420 vs, 1402 m,
1372 w, 1362 w, 1350 w, 1322 m, 1299 w, 1246 w, 1216 w, 1095 vw,
1049 m, 1002 w, 934 vw, 832 vw, 810 vw, 782 w, 762 vs, 746 m, 730 vw,
637 vw, 621 w, 556 vw, 534 vw, 463 w, 437 w, 425 w. MS (Micro-ESI in
THF + MeOH): m/z (%) 390 (60) [M + H − dme]+, 352 (37) [L + H]+,
244 (100) [L + H − AMP]+. Anal. Calcd for C27H42KN3O2 (479.74): C,
67.60; H, 8.82; N, 8.76. Found: C, 67.53; H, 8.85; N, 10.35.
Synthesis of [Ca{(Dipp-N)C(tBu)NCH2-Py}2] (4b). The reaction
of 3b (2.8 g, 7.97 mmol), KN(SiMe3)2 (1,59 g, 7.97 mmol), and CaI2
(1.21 g, 4.12 mmol) in 70 mL of THF led to the formation of 4b. Storage
of a saturated toluene solution at −20 °C gave the colorless crystalline
product. Yield: 2.62 g (3.54 mmol, 86%). Physical data of 4b are as
follows. Dec pt: above 406 K. 1H NMR (C6D6, 297.0 K, 600.130 MHz):
δ 0.69−1.71 (m, broad, 42H, iPr CH3 + tBu CH3), 1.41 (s, tBu CH3),
1.77 (s, tBu CH3), 3.41−3.74 (m, broad, 4H, iPr CH), 4.79−5.16 (m,
broad, 4H, −CH2−), 6.24 (dd, 3JH,H = 6.3 Hz, 3JH,H = 6.3 Hz, 2H, Py p-
CH), 6.36−6.48 (m, broad, 2H, Py o-CH), 6.64−7.44 (m, broad, 8H, Py
m-CH + Dipp CH), 7.72 + 7.79 (m, 2H, broad, Py N−CH). 13C{1H}
NMR (C6D6, 297.0 K, 150.903 MHz): δ 21.75 + 22.9 + 23.7 + 24.2
(broad, iPr CH3), 28.9 (broad, iPr CH), 31.1 (tBu CH3), 39.6 + 41.3
(broad, tBu C), 54.5 + 55.7 (broad, -CH2-), 117.7 + 120.7 + 120.9 +
121.0 + 122.0 + 122.5 + 123.7 + 125.0 + 125.7 (Dipp CH + Py o-CH +
Py p-CH), 136.9 (Dipp o-CH), 137.7 (Py m-CH), 141.2 + 141.7 (broad,
Dipp o-CH), 146.5 + 148.0 (Py N-CH), 152.6 + 156.1 (Dipp i-C), 164.3
(qC), 165.1 + 165.7 (Py i-C), 172.4 (qC). IR (pure): ν (cm−1) 2955 m,
2919 sh, 2867 vw, 1653 w, 1603 w, 1588 vw, 1570 w, 1543 vs, 1502 s,
1479 m, 1459 m, 1435 m, 1421 m, 1359 w, 1377 w, 1345 m, 1293 w,
1257 m, 1200 w, 1158 w, 1107 w, 1083 m, 1053 w, 1012 w, 999 m, 933
vw, 879 vw, 834 vw, 804 w, 787 w, 774 m, 757 sh, 748 m, 737 m, 634 vw,
549 vw. MS (DEI): m/z (%) = 741 (17) [M]+, 698 (13) [M − iPr]+, 389
(10) [M − L]+, 351 (52) [L]+, 308 (100) [L − iPr]+, 294 (20) [L − tBu]+,
244 (44) [L − AMP]+, 186 (49) [Dip-NC]+, 175 (42) [Dipp-N]+, 92
(46) [Ph-N]+. Anal. Calcd for C46H64CaN6·C7H8 (833.25): C, 76.40; H,
8.87; N, 10.10. Found: C, 76.94; H, 9.36; N, 12.01.
Synthesis of [(dme)Ca{(Dipp-N)C(tBu)NCH2-Py}2] (4c). The
reaction of 1b (0.354 g, 1.01 mmol), KN(SiMe3)2 (0.412 g, 2.07 mmol),
and CaI2 (0.391 g, 1.33 mmol) in tetrahydrofuran led to the formation of
4b. Recrystallization from 0.5 mL of DME and storage at 5 °C for several
days gave 4c as colorless crystals. Yield: 0.283 g (0.34 mmol, 34%).
Physical data of 4c are as follows. Dec pt: above 424 K. 1H NMR (C6D6,
297.0 K, 600.130 MHz): δ 0.92−1.88 (m, broad, 42H, iPr CH3 + tBu
CH3), 3.07 (s, 6H, DME CH3), 3.16 (s, 4H, DME CH2), 3.36−3.66 (m,
broad, 4H, iPr CH), 4.20−5.20 (m, broad, 4H, −CH2−), 6.21−6.60 (m,
broad, 4H, Py o-CH + Py p-CH), 6.70−6.89 (m, broad, 2H, Py m-CH),
6.97−7.37 (m, broad, 6H, Dipp CH), 7.63−7.91 (m, broad, Py NCH).
13C{1H} NMR (C6D6, 297.0 K, 150.903 MHz): δ 22.0 + 23.0 + 24.0
(broad, iPr CH3), 29.0 (broad, iPr CH), 31.1 (tBu CH3), 39.8 + 41.2
(broad, tBu C), 54.5 + 55.5 (broad, −CH2−), 59.0 (DME, CH3), 71.8
(DME, CH2), 117.6 + 120.5 + 121.0 + 121.9 + 122.6 + 123.6 + 125.1
(Dipp CH + Py o-CH + Py p-CH), 136.8 (Dipp o-CH), 137.7 (Py m-
CH), 141.4 (broad, Dipp o-CH), 146.6 + 147.9 (broad, Py NCH), 152.6
+ 155.7 (broad, Dipp i-C), 164.4 (qC), 165.1 + 165.6 (Py i-C), 172.3
(qC). IR (pure): ν (cm−1) 2656 m, 2920 sh, 2868 vw, 1652 s, 1590 w,
1562 w, 1534 vs, 1506 m, 1478 m, 1457 m, 1432 s, 1405 sh, 1379 w, 1356
sh, 1334 m, 1301 w, 1288 w, 1259 m, 1207 w, 1165 w, 1142 sh, 1102 w,
1061 m 998 w, 936w, 864 w, 802 w, 775 m, 754 vs, 736 sh, 718 sh, 623 w.
MS (DEI): m/z (%) 741 (38) [M − dme]+, 698 (22) [M − iPr − dme]+,
389 (14) [M − L − dme]+, 351 (27) [L]+, 308 (100) [L − iPr]+, 294
(10) [L − tBu]+, 244 (33) [L − AMP]+, 186 (39) [Dipp-NC]+, 175
(35) [Dipp-N]+, 92 (91) [Ph-N]+, 57 (30) [tBu]+. Anal. Calcd for
C50H74N6O2Ca (831.25): C, 72.25; H, 8.97; N, 10.11. Found: C, 70.54;
H, 8.57; N, 10.50.
Synthesis of [(dme)Li{(Dipp-N)C(tBu)NCH2-Py}] (2b). A sol-
ution of nBuLi (0.74 mL, 1.84 mmol, 2.5 M) in hexane was added
at −78 °C to a solution of 1b (0.538 g, 1.53 mmol) dissolved in 30 mL of
heptane. While it was warmed to room temperature, the solution
changed to brown-red. After the mixture was stirred for 67 h, 0.56 mL of
DME was added and a solid precipitated immediately. The pale yellow-
green solid was collected and recrystallized from 1 mL of DME. Storage
at 5 °C for several days led to 2b as colorless crystals. Yield: 0.559 g
(1.25 mmol, 82%). Physical data of 2b are as follows. Dec pt: above
375 K. 1H NMR ([D8]THF, 297.6 K, 400.075 MHz): δ 1.09 (d, 3JH,H
=
6.8 Hz, 6H, iPr CH3), 1.10 (d, 3JH,H = 6.8 Hz, 6H, iPr CH3), 1.30 (s, 9H,
tBu CH3), 3.27 (s, 6H, DME CH3), 3.32 (sept, 3JH,H = 6.8 Hz, 2H, iPr
CH), 3.43 (s, 4H, DME CH2), 4.22 (s, 2H, −CH2−), 6.44 (t, 3JH,H = 7.6
Hz, 1H, Dipp p-CH), 6.68−6.70 (broad, 1H, Py o-CH), 6.71 (d, 3JH,H
=
3
3
7.6 Hz, 2H, Dipp m-CH), 7.05 (ddd, JH,H = 6.2 Hz JH,H = 6.2 Hz,
4JH,H = 0.8 Hz, 1H, Py p-CH), 7.49 (ddd, 3JH,H = 7.7 Hz, 3JH,H = 7.7 Hz,
4JH,H = 1.9 Hz, 1H Py m-CH), 8.31 (dd, 3JH,H = 5.0 Hz, 4JH,H = 0.8 Hz,
1H, Py N−CH). 13C{1H} NMR ([D8]THF, 298.2 K, 100.599 MHz): δ
22.9 + 24.1 (iPr CH3), 29.0 (iPr CH), 31.5 (tBu CH3), 40.4 (tBu C), 57.4
(−CH2), 59.0 (DME CH3), 72.8 (DME CH2), 116.1 (Dipp p-C), 120.9
(Dipp m-C) 121.3 (Py o-C), 123.3 (Py p-C), 137.3 (Py m-C), 137.4
(Dipp o-C), 147.8 (Py NCH), 154.1 (Dipp i-C), 165.4 (Py i-C), 167.8
(qC). IR (pure): ν (cm−1) 2954 w, 2865 sh, 1653 vw, 1599 w, 1571 w,
1534 vs, 1479 m, 1457 m, 1425 s, 1417 s, 1385 m, 1367 m, 1345 s,
1315 w, 1285 w, 1259, w, 1243 w, 1216 w, 1195 m, 1171 w, 1153 w,
1139 vw, 1123 m, 1106 w, 1084 vs, 1028 w, 1013 w, 977 vw, 951 m, 932
w, 885 vw, 867 m, 834 vw, 814 w, 796 w, 783 w, 7.63 m, 767 vs, 734 m,
725 m, 682 vw, 646 w, 620 w, 586 w, 561 w, 535 w, 504 m, 430 m. MS
(Micro-ESI in CHCl3 + MeOH): m/z (%) 358 (17) [M + H − dme]+,
352 (100) [L + H]+, 244 (48) [L + H − AMP]+. Anal. Calcd for
C29H47N3O3Li (492.65): C, 70.70; H, 9.62; N, 8.53. Found: C, 70.56; H,
9.16; N, 9.11.
Synthesis of [(dme)K{(Dipp-N)C(tBu)NCH2-Py}] (3b). A solution
of 1b (0.51 g, 1.45 mmol) dissolved in 10 mL of toluene was added at
room temperature to a solution of KN(SiMe3)2 (0.29 g, 1.45 mmol)
dissolved in 10 mL of toluene. A white precipitate formed, and the
solution changed from colorless via yellow to green. After the mixture
was stirred overnight, the solid was collected. Recrystallization from
0.5 mL of DME and storage at 5 °C for several days gave 3b as colorless
crystals. Yield: 0.51 g (1.06 mmol, 73%). Physical data of 3b are as
1
follows. Dec pt: above 344 K. H NMR ([D8]THF, 297.0 K, 400.130
MHz): δ 1.11 (d, 3JH,H = 6.8 Hz, 6H, iPr CH3), 1.14 (d, 3JH,H = 6.8 Hz,
6H, iPr CH3), 1.28 (s, 9H, tBu CH3), 3.22−3.28 (m, 2H, iPr CH), 3.28
(s, 6H, DME CH3), 3.44 (s, 4H, DME CH2), 3.98 (s, 2H, −CH2−), 6.50
(m, broad, 1H, Py o-CH), 6.73 (d, 3JH,H = 7.6 Hz, 1H, Dipp p-CH), 6.77
(d, 3JH,H = 7.6 Hz, 2H, Dipp m-CH), 6.98 (dd, 3JH,H = 6.0 Hz 3JH,H = 6.0
Hz, 1H, Py p-CH), 7.43 (dd, 3JH,H = 7.4 Hz, 3JH,H = 7.4 Hz, 1H Py m-
CH), 8.32 (d, 3JH,H = 4.0 Hz, 1H, Py NCH). 13C{1H} NMR ([D8]THF,
297.0 K, 100.613 MHz): δ 23.0 + 24.1 (iPr CH3), 29.1 (iPr CH), 31.2
(broad, tBu CH3), 40.4 (tBu C), 53.9 (−CH2), 59.0 (DME CH3), 72.3
(DME CH2), 116.7 (broad, Dipp p-C), 121.5 (Py o-C + Dipp m-C),
123.7 (Py p-C), 136.8 (Py m-C), 137.7 (Dipp o-C), 149.0 (Py N-CH),
Structure Determinations. The intensity data for the compounds
were collected on a Nonius KappaCCD diffractometer using graphite-
monochromated Mo K radiation. Data were corrected for Lorentz and
polarization effects but not for absorption effects.44,45 The structures
were solved by direct methods (SHELXS)46 and refined by full-matrix
least-squares techniques against Fo (SHELXL-97).46 The hydrogen
2
atoms bound at the amine group N1 of compound 1b and all hydrogen
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Article
atoms of compounds 1a−3a (with the exception of the disordered dme
molecule), 3b, and 4b were located by difference Fourier synthesis and
refined isotropically. The hydrogen atoms of 4a and 5b were included at
calculated positions with fixed thermal parameters. All nondisordered,
non-hydrogen atoms were refined anisotropically.46 XP (SIEMENS
Analytical X-ray Instruments, Inc.)47 was used for structure
representations.
(12) Cheng, Y.-H.; Liu, L.; Fu, Y.; Chen, R.; Li, X.-S.; Guo, Q.-X. J.
Phys. Chem. A 2002, 106, 11215−11220.
(13) Reddy, A. S.; Sastry, G. N. J. Phys. Chem. A 2005, 109, 8893−8903.
(14) Reddy, A. S.; Zipse, H.; Sastry, G. N. J. Phys. Chem. B 2007, 111,
11546−11553.
(15) Dinadayalane, T. C.; Hassan, A.; Leszczynski, J. Theor. Chem. Acc.
2012, 131:1131, 1−11.
(16) Cheng, J.; Zhu, W.; Tang, Y.; Xu, Y.; Li, Z.; Chen, K.; Jiang, H.
Chem. Phys. Lett. 2006, 422, 455−460.
ASSOCIATED CONTENT
* Supporting Information
■
(17) Gapeev, A.; Dunbar, R. C. J. Phys. Chem. A 2000, 104, 4084−4088.
(18) Harvey, M. J.; Hanusa, T. P. Organometallics 2000, 19, 1556−
1566.
S
CIF files giving crystallographic data for 1a,b, 2a,b, 3a,b, and
4a−c (excluding structure factors). This material is available free
of charge via the Internet at http://pubs.acs.org. Crystallographic
data have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publications CCDC-983887
for 1a, CCDC-983888 for 1b, CCDC-983889 for 2a, CCDC-
983890 for 2b, CCDC-983891 for 3a, CCDC-983892 for 3b,
CCDC-983893 for 4a, CCDC-983894 for 4b, and CCDC-
983895 for 4c. Copies of the data can be obtained free of charge
on application to the CCDC, 12 Union Road, Cambridge CB2
1EZ, U.K. (e-mail: deposit@ccdc.cam.ac.uk).
(19) (a) Jutzi, P. Adv. Organomet. Chem. 1986, 26, 217−295. (b) Jutzi,
P. J. Organomet. Chem. 1990, 400, 1−17. (c) Hanusa, T. P. Polyhedron
1990, 9, 1345−1362. (d) Hanusa, T. P. Chem. Rev. 1993, 93, 1023−
1036. (e) Burkey, D. J.; Hanusa, T. P. Comments Inorg. Chem. 1995, 17,
41−77. (f) Hays, M. L.; Hanusa, T. P. Adv. Organomet. Chem. 1996, 40,
117−170. (g) Bridgeman, A. J. J. Chem. Soc., Dalton Trans. 1997, 2887−
2893. (h) Jutzi, P.; Burford, N. Chem. Rev. 1999, 99, 969−990.
(i) Hanusa, T. P. Organometallics 2002, 21, 2559−2571.
(20) Westerhausen, M.; Digeser, M. H.; Noth, H.; Ponikwar, W.;
̈
Seifert, T.; Polborn, K. Inorg. Chem. 1999, 38, 3207−3214.
(21) (a) Westerhausen, M.; Digeser, M. H.; Guckel, C.; Noth, H.;
̈
̈
Knizek, J.; Ponikwar, W. Organometallics 1999, 18, 2491−2496.
(b) Westerhausen, M.; Birg, C.; Piotrowski, P. Eur. J. Inorg. Chem.
AUTHOR INFORMATION
Corresponding Author
*M.W.: fax, +49 3641 948132; e-mail, m.we@uni-jena.de; web,
http://www.lsac1.uni-jena.de/.
■
2000, 2173−2178. (c) Westerhausen, M.; Guckel, C.; Piotrowski, P.;
̈
Mayer, P.; Warchhold, M.; Noth, H. Z. Anorg. Allg. Chem. 2001, 627,
̈
1741.1750. (d) Wimmer, K.; Birg, C.; Kretschmer, R.; Al-Shboul, T. M.
A.; Gorls, H.; Krieck, S.; Westerhausen, M. Z. Naturforsch. 2009, 64b,
̈
Notes
1360−1368.
The authors declare no competing financial interest.
(22) Walter, M. D.; Wolmershauser, G.; Sitzmann, H. J. Am. Chem. Soc.
̈
2005, 127, 17494−17503.
ACKNOWLEDGMENTS
■
(23) (a) Feil, F.; Harder, S. Organometallics 2000, 19, 5010−5015.
(b) Harder, S.; Feil, F.; Weeber, A. Organometallics 2001, 20, 1044−
This work was supported by the Verband der Chemischen
Industrie (VCI/FCI, Frankfurt/Main, Germany). C.L. is grateful
to the Graduate Academy of the Friedrich Schiller University
Jena for a generous Ph.D. grant. We also thank the German
Research Foundation (DFG, Bonn, Germany) for financial
support in the frame of the project We1561/12. Infrastructure of
our institute was provided by the EU (European Regional
Development Fund, EFRE) and the Friedrich Schiller University
Jena.
1046. (c) Feil, F.; Muller, C.; Harder, S. J. Organomet. Chem. 2003, 683,
̈
56−63. (d) Guino-o, M. A.; Campana, C. F.; Ruhlandt-Senge, K. Chem.
Commun. 2008, 1692−1694.
(24) (a) Feil, F.; Harder, S. Eur. J. Inorg. Chem. 2003, 3401−3408.
(b) Piesik, D. F.-J.; Habe, K.; Harder, S. Eur. J. Inorg. Chem. 2007, 5652−
̈
5661.
(25) (a) Krieck, S.; Gorls, H.; Yu, L.; Reiher, M.; Westerhausen, M. J.
̈
Am. Chem. Soc. 2009, 131, 2977−2985. (b) Krieck, S.; Gorls, H.;
̈
Westerhausen, M. J. Am. Chem. Soc. 2010, 132, 12492−12501.
(26) Williams, R. A.; Hanusa, T. P. J. Am. Chem. Soc. 1990, 112, 2454−
2455.
REFERENCES
■
(27) Hauber, S.-O.; Lissner, F.; Deacon, G. B.; Niemeyer, M. Angew.
(1) (a) Dougherty, D. A. Science 1996, 271, 163−168. (b) Ma, J. C.;
Dougherty, D. A. Chem. Rev. 1997, 97, 1303−1324. (c) Mahadevi, A. S.;
Sastry, G. N. Chem. Rev. 2013, 113, 2100−2138.
(2) Loh, C.; Seupel, S.; Gorls, H.; Krieck, S.; Westerhausen, M. Eur. J.
Inorg. Chem. 2014, DOI: 10.1002/ejic.201301557.
Chem., Int. Ed. 2005, 44, 5871−5875.
(28) Westerhausen, M.; Digeser, M. H.; Noth, H.; Seifert, T.; Pfitzner,
̈
A. J. Am. Chem. Soc. 1998, 120, 6722−6725.
̈
(29) (a) Edelmann, F. T. Adv. Organomet. Chem. 2008, 57, 183−352.
(b) Edelmann, F. T. Adv. Organomet. Chem. 2013, 61, 55−374.
(30) Westerhausen, M.; Schwarz, W. Z. Naturforsch. 1992, 47b, 453−
459.
(3) (a) Gartner, M.; Gorls, H.; Westerhausen, M. Inorg. Chem. 2007,
̈
̈
46, 7678−7683. (b) Gartner, M.; Gorls, H.; Westerhausen, M. Dalton
̈
̈
Trans. 2008, 1574−1582.
(4) (a) Gartner, M.; Gorls, H.; Westerhausen, M. Z. Anorg. Allg. Chem.
(31) Cole, M. L.; Deacon, G. B.; Forsyth, C. M.; Konstas, K.; Junk, P. C.
̈
̈
Dalton Trans. 2006, 3360−3367.
2007, 633, 2025−2031. (b) Gartner, M.; Gorls, H.; Westerhausen, M.
̈
̈
(32) Cole, M. L.; Junk, P. C. New J. Chem. 2005, 29, 135−140.
Inorg. Chem. 2008, 47, 1397−1405.
(33) Glock, C.; Loh, C.; Gorls, H.; Krieck, S.; Westerhausen, M. Eur. J.
̈
(5) Tetreault, S.; Ananthanarayanan, V. S. J. Med. Chem. 1993, 36,
1017−1023.
Inorg. Chem. 2013, 3261−3269.
(34) Barrett, A. G. M.; Crimmin, M. R.; Hill, M. S.; Hitchcock, P. B.;
Lomas, S. L.; Mahon, M. F.; Procopiou, P. A. Dalton Trans. 2010, 39,
7393−7400.
(6) Dunbar, R. C.; Steill, J. D.; Oomens, J. J. Am. Chem. Soc. 2011, 133,
9376−9386.
(7) (a) Zhao, Y. L.; Lin, C. S.; Zhang, R. Q.; Wang, R. S. J. Chem. Phys.
2005, 122, 194322/1−194322/6. (b) Sun, S. L.; Lin, C. S.; Zhang, R. Q.;
Lee, C. S.; Lee, S. T. J. Phys. Chem. B 2005, 109, 12868−12873.
(8) Kang, H. S. J. Phys. Chem. A 2005, 109, 1458−1467.
(9) Mochida, K.; Hiraga, Y.; Takeuchi, H.; Ogawa, H. Organometallics
1987, 6, 2293−2297.
(35) Feil, F.; Harder, S. Eur. J. Inorg. Chem. 2005, 4438−4443.
(36) Crimmin, M. R.; Barrett, A. G. M.; Hill, M. S.; Hitchcock, P. B.;
Procopiou, P. A. Organometallics 2008, 27, 497−499.
(37) Al-Shboul, T. M. A.; Volland, G.; Gorls, H.; Westerhausen, M. Z.
̈
Anorg. Allg. Chem. 2009, 635, 1568−1572.
(38) Hu, H.; Cui, C. Organometallics 2012, 31, 1208−1211.
(39) Schowtka, B.; Gorls, H.; Westerhausen, M. Z. Anorg. Allg. Chem.
(10) Petrie, S. Int. J. Mass Spectrosc. 2003, 227, 33−46.
(11) Westerhausen, M.; Gartner, M.; Fischer, R.; Langer, J.; Yu, L.;
̈
̈
Reiher, M. Chem. Eur. J. 2007, 13, 6292−6306.
2014, DOI: 10.1002/zaac.201300565.
1490
dx.doi.org/10.1021/om500135g | Organometallics 2014, 33, 1480−1491

Organometallics
Article
(40) Kloubert, T.; Muller, C.; Krieck, S.; Schlotthauer, T.; Gorls, H.;
̈
̈
Westerhausen, M. Eur. J. Inorg. Chem. 2012, 5991−6001.
(41) (a) Westerhausen, M.; Langer, J.; Krieck, S.; Fischer, R.; Gorls, H.;
Kohler, M. Top. Organomet. Chem. 2013, 45, 29−72. (b) Westerhausen,
̈
̈
M.; Langer, J.; Krieck, S.; Glock, C. Rev. Inorg. Chem. 2011, 31, 143−184.
(42) Andreychuk, N. R.; Emslie, D. J. H. Angew. Chem. 2013, 125,
1740−1743; Angew. Chem., Int. Ed. 2013, 52, 1696−1699.
(43) Recent reviews: (a) Etienne, M.; Weller, A. S. Chem. Soc. Rev.
2014, 43, 242−259. (b) Saßmannshausen, J. Dalton Trans. 2012, 41,
1919−1923. (c) Green, J. C.; Green, M. L. H.; Parkin, G. Chem.
Commun. 2012, 48, 11481−11503. (d) Brookhart, M.; Green, M. L. H.;
Parkin, G. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 6908−6914. (e) Clot,
E.; Eisenstein, O. Struct. Bonding (Berlin) 2004, 113, 1−36.
(44) Hooft, R. COLLECT, Data Collection Software; Nonius BV, Delft,
The Netherlands, 1998.
(45) Minor, W. Processing of X-ray Diffraction Data Collected in
Oscillation Mode. In Methods in Enzymology; Otwinowski, Z., Carter, C.
W., Sweet, R. M., Eds.; Academic Press: New York, 1997; Vol. 276,
Macromolecular Crystallography, Part A, pp 307−326.
(46) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112−122.
(47) XP; Siemens Analytical X-ray Instruments Inc., Karlsruhe,
Germany, 1990. XP; Siemens Analytical X-ray Instruments Inc.,
Madison, WI, USA, 1994.
1491
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