2,6-diisopropylphenylamides of potassium and calcium: A primary amido ligand in s-block metal chemistry with an unprecedented catalytic reactivity

Article abstract of DOI:10.1021/om4001007

Transamination of KN(SiMe₃)₂ with 2,6-diisopropylphenylamine (2,6-diisopropylaniline) in toluene at ambient temperature yields [K{N(H)Dipp}·KN(SiMe₃)₂] (1) regardless of the applied stoichiometry. Recrystallization of 1 in the presence of tetramethylethylenediamine (TMEDA) and tetrahydrofuran (THF) leads to the formation of [(μ-thf)K₂{N(H)Dipp}₂]_∞ (2), whereas potassium bis(trimethylsilyl)amide remains in solution. Addition of pentamethyldiethylenetriamine (PMDETA) gives [(pmdeta)K{N(H)Dipp}]₂ (3). In contrast to the thf and pmdeta adducts, which lead to dissociation of 1 into homoleptic species, addition of bidentate dimethoxyethane maintains the mixed complex [(dme)K{μ-N(SiMe₃)₂}{μ-N(H)Dipp}K] ₂ (4). A complete transamination of 2,6-diisopropylaniline with KN(SiMe₃)₂ in toluene at 100 C yields [K{N(H)Dipp}] (5), which reacts with CaI₂ to give [(thf)_nCa{N(H)Dipp} ₂] (6), [(pmdeta)Ca{N(H)Dipp}₂] (7), and [(dme) ₂Ca{N(H)Dipp}₂] (8), depending on the solvents and coligands. Excess potassium 2,6-diisopropylphenylamide allows the formation of the calciate [K₂Ca{N(H)Dipp}₄]_∞ (9). Hydroamination of diphenylbutadiyne with 2,6-diisopropylaniline in the presence of catalytic amounts of 9 gives tetracyclic 2,6-diisopropyl-9,11,14,15- tetraphenyl-8-azatetracyclo[8.5.0.0^1,7.0^2,13]pentadeca-3, 5,7,9,11,14-hexaene (10). Solid-state structures are reported for 2-4 and 7-10. Compound 10 slowly rearranges to tetracyclic 5a,9-diisopropyl-2,3,10,11- tetraphenyl-5a,6-dihydro-2a¹,6-ethenocyclohepta[cd]isoindole (11), which is slightly favored according to quantum chemical studies.

Full text of DOI:10.1021/om4001007

Article
pubs.acs.org/Organometallics
2,6-Diisopropylphenylamides of Potassium and Calcium: A Primary
Amido Ligand in s‑Block Metal Chemistry with an Unprecedented
Catalytic Reactivity
Carsten Glock,†,§ Fadi M. Younis,†,§ Steffen Ziemann,† Helmar Gorls,† Wolfgang Imhof,‡ Sven Krieck,†
̈
and Matthias Westerhausen*,†
†Institut fur Anorganische und Analytische Chemie, Friedrich-Schiller-Universitat Jena, Humboldtstrasse 8, D-07743 Jena, Germany
̈
̈
‡Institut fur Integrierte Naturwissenschaften, Abteilung Chemie, Universitat Koblenz-Landau, Universitatsstrasse 1, D-56070 Koblenz,
Germany
̈
̈
̈
S
* Supporting Information
ABSTRACT: Transamination of KN(SiMe3)2 with 2,6-diisopropylphenylamine
(2,6-diisopropylaniline) in toluene at ambient temperature yields [K{N(H)-
Dipp}·KN(SiMe3)2] (1) regardless of the applied stoichiometry. Recrystallization
of 1 in the presence of tetramethylethylenediamine (TMEDA) and tetrahydrofuran
(THF) leads to the formation of [(μ-thf)K2{N(H)Dipp}2]∞ (2), whereas potassium
bis(trimethylsilyl)amide remains in solution. Addition of pentamethyldiethylenetri-
amine (PMDETA) gives [(pmdeta)K{N(H)Dipp}]2 (3). In contrast to the thf and
pmdeta adducts, which lead to dissociation of 1 into homoleptic species, addition of
bidentate dimethoxyethane maintains the mixed complex [(dme)K{μ-N(SiMe3)2}-
{μ-N(H)Dipp}K]2 (4). A complete transamination of 2,6-diisopropylaniline with
KN(SiMe3)2 in toluene at 100 °C yields [K{N(H)Dipp}] (5), which reacts with
CaI2 to give [(thf)nCa{N(H)Dipp}2] (6), [(pmdeta)Ca{N(H)Dipp}2] (7), and
[(dme)2Ca{N(H)Dipp}2] (8), depending on the solvents and coligands. Excess
potassium 2,6-diisopropylphenylamide allows the formation of the calciate [K2Ca{N(H)Dipp}4]∞ (9). Hydroamination of
diphenylbutadiyne with 2,6-diisopropylaniline in the presence of catalytic amounts of 9 gives tetracyclic 2,6-diisopropyl-
9,11,14,15-tetraphenyl-8-azatetracyclo[8.5.0.01,7.02,13]pentadeca-3,5,7,9,11,14-hexaene (10). Solid-state structures are reported for
2−4 and 7−10. Compound 10 slowly rearranges to tetracyclic 5a,9-diisopropyl-2,3,10,11-tetraphenyl-5a,6-dihydro-2a1,6-
ethenocyclohepta[cd]isoindole (11), which is slightly favored according to quantum chemical studies.
to these complexes, which are soluble in tetrahydrofuran
(THF), the 2,2,6,6-tetramethylpiperidylcalcium complexes
express an enormous reactivity and cannot be handled in
THF because of ether degradation processes.9 In contrast to
the case for stable amidomagnesium halides these Hauser-type
bases of calcium show ligand redistribution processes (Schlenk-
type equilibrium) favoring homoleptic calcium bis(amide) and
calcium dihalide.10
Primary anilides of the heavier alkaline-earth metals tend to
form aggregates (Ca) or even polymers (Sr, Ba) in the solid
state and are only sparingly soluble in Lewis basic donor
solvents.11 2,6-Difluoroanilides form more soluble complexes,
but fluorine substituents in metal organic compounds may be
hazardous and decompose spontaneously and violently.12 o-
Alkyl-substituted anilides form monomeric complexes with a
strongly Lewis basic coligand such as hexamethylphosphoric
acid triamide (hmpa), and mononuclear complexes of the type
[(hmpa)3Ae{N(H)Dipp}2] (Dipp = C6H3-2,6-iPr2) were
isolated.3
INTRODUCTION
■
Substituted amides of the electropositive s-block metals
represent valuable reagents for diverse applications such as
metalation, transamination, and amide transfer. Whereas several
reviews exist discussing structures, properties, and reactivity of
alkali-metal amides,1 interest in organyl-substituted alkaline-
earth-metal bis(amides) has been limited mainly to magnesium
derivatives for a long time.2 The homologous heavier alkaline-
earth-metal complexes have attracted attention only for about
the last two decades.3,4 Early attempts gave insoluble, poorly
characterized, and partially pyrophoric alkaline-earth-metal
amides.5 Approximately 20 years ago, the breakthrough
succeeded with the synthesis of the alkaline-earth-metal
bis[bis(trialkylsilyl)amides], which are soluble in common
organic solvents such as ethers and aromatic and aliphatic
hydrocarbons, allowing homogeneous reaction conditions.6
In recent years the portfolio of amides of the heavy alkaline-
earth metals Ae became versatile. Solubility was guaranteed by
substitution of only one trialkylsilyl group of Ae{N(SiMe3)2}2
by an aryl substituent, leading to substituted trimethylsilylani-
lides.3,7 Recently also diphenylamides8 and N-alkylanilides9
have been prepared and structurally characterized. In contrast
Received: February 21, 2013
Published: April 16, 2013
© 2013 American Chemical Society
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Scheme 1. Reaction Scheme for the Synthesis of Potassium, Calcium, and Mixed-Metal 2,6-Diisopropylanilides
Heterobimetallic s-block metal amides exhibit significantly
enhanced reactivity. Mixed alkali-metal−magnesium amides
tend to form inverse crowns which react as highly reactive
metalation reagents,13 whereas the alkali-metal−calcium
derivatives can best be described as alkali-metal calciates due
to the amido transfer from the alkali metal to calcium.9,14−16
The awakened interest in these alkaline-earth-metal amides is
also based on the catalytic activity (for recent general reviews
see ref 17) in hydroamination reactions of carbodiimides,18
alkenes,19,20 and alkynes.16,20 Especially calcium is a very
attractive inexpensive element, due to its worldwide availability
and nontoxicity regardless of the concentration. In many
catalytic applications Ae{N(SiMe3)2}2 was employed as the
precatalyst, intermediately forming the catalytically active
calcium amides. We could demonstrate that often highly
reactive heterobimetallic compounds such as potassium
calciates are required to catalyze the addition of amines to
carbon−carbon multiple bonds.16
etry and tetranuclear [(dme)K{μ-N(SiMe3)2}{μ-N(H)Dipp}-
K]2 (4) was isolated.
More drastic reaction conditions during transamination of
KN(SiMe3)2 with H2N-Dipp gave solvent-free K{N(H)Dipp}
(5), which was used as an amide transfer reagent. The
metathesis reaction of this potassium amide with calcium
diiodide yielded the oily substance [(thf)nCa{N(H)Dipp}2] (6)
in solvents such as THF, hexane, toluene, and mixtures thereof.
The addition of tridentate pmdeta or bidentate dme led to
crystalline [(pmdeta)Ca{N(H)Dipp}2] (7) and [(dme)2Ca{N-
(H)Dipp}2] (8), respectively. Excess potassium 2,6-diisopro-
pylphenylamide yielded the calciate [K2Ca{N(H)Dipp}4]∞ (9),
which precipitated from a THF solution as a solvent-free
coordination polymer.
The influence of the metals on the chemical 1H and 13C{1H}
NMR shifts of the 2,6-diisopropylphenylamide ions is small and
seems to be not especially diagnostic of structure. Therefore, a
detailed discussion is not included and the data are given in the
Supporting Information. 2,6-Diisopropylaniline shows low-
field-shifted 1H NMR resonances of the aryl and amino
hydrogen atoms. For the potassium derivatives these signals are
high-field-shifted; however, the values of the calcium complexes
are very similar. The tertiary CH fragments of the isopropyl
groups show chemical shifts of δ 3.15 and 3.00 for the
potassium and calcium anilides, respectively.
RESULTS AND DISCUSSION
■
Synthesis. Transamination of KN(SiMe3)2 with 2,6-
diisopropylphenylamine (H2N-Dipp) in toluene at room
temperature led to precipitation of [K{N(H)Dipp}·KN-
(SiMe3)2] (1) regardless of the applied stoichiometry. The
formation of a solid precipitate impeded the complete
conversion to potassium 2,6-diisopropylphenylamide. Addition
of Lewis bases often yields smaller and soluble aggregates which
allow spectroscopic characterization. Compound 1 was
dissolved in a mixture of tetramethylethylenediamine
(TMEDA) and tetrahydrofuran (THF), and from this solution
crystals of [(μ-thf)K2{N(H)Dipp}2]∞ (2) precipitated, whereas
potassium bis(trimethylsilyl)amide remained in solution
(Scheme 1). A similar finding was observed upon addition of
a solvent mixture of pentamethyldiethylenetriamine (PMDE-
TA) and THF, yielding crystalline [(pmdeta)K{N(H)Dipp}]2
(3), whereas KN(SiMe3)2 remained in the mother liquor. In
contrast to the thf and pmdeta adducts, which led to
dissociation of 1 into homoleptic species, addition of bidentate
1,2-dimethoxyethane (DME) maintained the mixed stoichiom-
In the 13C{1H} NMR spectra the largest differences are
observed for the ipso-carbon atoms; deprotonation of 2,6-
diisopropylaniline leads to a significant low-field shift. The
formation of heterobimetallic potassium tetrakis(anilido)-
calciate shifts the resonance of the ipso-carbon back toward a
higher field. The influences of the metal and the environment
of the amido functionality (terminal or bridging position) on
the other carbon atoms are very small, and no dependency is
observed for the chemical shifts of the isopropyl groups.
On the basis of NMR parameters structure elucidation is
impossible. All s-block metal amides 1−9 show only one set of
resonances with very similar chemical shifts. This finding is in
agreement with the expectation that in ionic amides the nature
of the metal atoms plays an ancillary role. Dissociation of these
complexes and fast dynamic behavior on the NMR time scale
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(thus breaking up polymeric structures) explain not only this
observation but also solubility in common organic donor
solvents. Due to the fact that information on solution structures
is very limited, we investigated the solid-state structures in
order to verify the formation of homometallic and mixed s-
block metal amides and to study the influence of coordinated
solvent molecules.
Molecular Structures. Schematic representations are given
in Scheme 1, and the molecular structures of the potassium
amides 2−4, and the calcium bis(anilides) 7 and 8 as well as the
coordination polymer 9 are discussed in detail.
The molecular structure and numbering scheme of a section
of polymeric 2 are shown in Figure 1. The central structural
Figure 2. Molecular structure and numbering scheme of 3. The
ellipsoids represent a probability of 40%, and H atoms are omitted for
clarity. The symmetry-equivalent half of the molecule (−x + 2, −y, −z
+ 1) is marked with the letter A. Selected bond lengths (pm): K1−N1
= 291.6(3), K1−N1A = 279.4(3), K1−N2 = 289.2(3), K1−N3 =
296.9(3), K1−N4 = 318.3(3), N1−C1 = 136.3(4).
Figure 1. Section of polymeric 2. The ellipsoids represent a probability
of 40%, and H atoms are neglected for clarity. Symmetry-related atoms
are marked with the letters A−D. Selected bond lengths (pm): K1A−
N1C = 277.9(2), K1A−N2B = 275.4(2), K1A−O1A = 294.7(2),
K2A−N1C = 277.3(2), K2A−N2B = 275.2(2), K2A−O1A =
286.8(2), K1A−C1A = 318.2(2), K1A−C2A = 316.7(2), K1A−C3A
= 314.8(2), K1A−C4A= 313.3(2), K1A−C5A = 313.3(2), K1A−C6A
= 317.3(2), K2A−C13A = 315.0(2), K2A−C14A = 322.0(2), K2A−
C15A = 320.9(2), K2A−C16A = 314.4(2), K2A−C17A = 306.8(2),
K2A−C18A = 306.6(2), N1C−C1C = 135.6(2), N2B−C13B =
135.8(2).
fragment consists of a four-membered K2N2 ring (average K−N
distance 276.4 pm) with a bridging thf ligand between the
potassium atoms. Thus, there exist three bridges between the
alkali-metal atoms, leading to a short K1···K2 contact of only
349.1(1) pm. The dinuclear units are aligned to a one-
dimensional strand via Lewis acid−base interactions between
the soft potassium cations and the π systems of neighboring
anilide moieties.
Enhancing the denticity and base strength of the neutral
coligand allows the isolation of molecular dinuclear potassium
anilides. The molecular structure and numbering scheme of 3
are displayed in Figure 2. The central structural fragment is the
centrosymmetric planar four-membered K2N2 ring with
different K−N bond lengths of 279.4(3) and 291.6(3) pm.
The shorter K−N distance belongs to an interaction between
K1 and an sp2 hybrid orbital of N1, whereas the other
potassium shows a more side-on coordination to the anilide
anion (pz orbital at N1), leading also to rather short contacts to
C1 (314.8(3) pm) and C6 (329.3(3) pm). The nonbonding
trans-annular K1···K1A contact adopts a rather large value of
421.1(1) pm. The coordination sphere of potassium is
saturated by nitrogen bases of the pmdeta ligand, which
shows two short K−N bonds (289.2(3) and 296.9(3) pm) and
one significantly larger K−N distance of 318.3(3) pm.
Figure 3. Molecular structure and numbering scheme of 4. The
ellipsoids represent a probability of 40%, and H atoms are neglected.
The symmetry-related molecule halves (−x + 2, −y + 1, −z) are
distinguished by the letters A and B. Selected bond lengths (pm):
K1A−N1B = 274.2(1), K1A−N2A = 280.9(1), K2A−N1B = 276.3(1),
K2A−N2A = 274.3(1), K2A−O1A = 273.3(1), K2A−O2A =
276.2(1), K1A−C1A = 320.3(1), K1A−C2A = 326.2(1), K1A−C3A
= 323.5(2), K1A−C4A = 318.9(2), K1A−C5A = 315.3(2), K1A−C6A
= 316.1(1), N1A−C1A = 135.9(2), N2A−Si1A = 166.8(1), N2A−
Si2A = 166.8(1).
coordination polymer. Instead, two dinuclear units are
interconnected by contacts between the potassium atoms and
the π systems of the aryl groups. The highly ionic nature of the
K−N interactions leads to strong electrostatic attractions
between the nitrogen atom and the silicon atoms and, hence,
short Si−N2 bonds of 166.8(1) pm due to back-donation of
charge from the nitrogen atom to the silyl groups (hyper-
conjugation into σ*(Si−C) bonds). The short N2−Si bonds
enforce a large Si1−N2−Si2 bond angle of 133.43(8)° due to
repulsive forces between the bulky trimethylsilyl groups. A
similar effect was already discussed for dimeric [KN-
(SiMe3)2]2.21
Crystalline monomeric 2,6-diisopropylanilides of calcium
were obtained with multidentate coligands such as pmdeta and
dme, yielding [(pmdeta)Ca{N(H)Dipp}2] (7) and [(dme)2Ca-
{N(H)Dipp}2] (8), respectively. The molecular structure and
numbering scheme of 7 is displayed in Figure 4. The
pentacoordinate calcium atom binds to two anilide anions
The central four-membered K2N2 ring is also formed for
heteroleptic [(dme)K{μ-N(SiMe3)2}{μ-N(H)Dipp}K]2 (4),
which is shown in Figure 3. The bulky bridging bis-
(trimethylsilyl)amide anions together with bidentate 1,2-
dimethoxyethane hinder the formation of a one-dimensional
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to complex 7. The N−Ca−N angles for the molecules A−D
vary significantly and are larger for A, B, and D despite a larger
coordination number (molecule A, 115.2(2)°; molecule B,
117.6(1)°; molecule C, 88.6(1)°; molecule D, 122.3(1)°),
whereas molecule C deviates from the other molecules and a
very small value is observed. Intramolecular strain leads to
strongly widened Ca−N−C angles, and the four molecules
show different values (molecule A, 156.8(3) and 157.0(3)°;
molecule B, 137.0(3) and 154,6(3)°; molecule C, 147.5(3) and
149.6(3)°; molecule D, 159.2(3) and 137.4(3)°). The flexibility
of the Ca−N−C angles supports the chemical intuition that
electrostatic and steric forces dominate the structure and that
covalent Ca−N bond contributions play insignificant roles.
In heterobimetallic amides the less electropositive metal
commonly binds to the amido ligands, forming a metalate,
whereas the more electropositive metal represents the counter-
cation. We included the heterobimetallic amide with a
potassium to calcium ratio of 2:1 in our structural investigations
because mixed-metal amides often behave differently than the
homometallic congeners.13,14 The K to Ca ratio of 2:1 justifies
considering this derivative as a higher order calciate. Therefore,
the structure of the calciate [K2Ca{N(H)Dipp}4]∞ (9) was
determined and a section of the coordination polymer is
displayed in Figure 6. The calcium atom is in a distorted-
Figure 4. Molecular structure and numbering scheme of 7. The
ellipsoids represent a probability of 40%, and H atoms are not drawn.
Selected bond lengths (pm): Ca1−N1 = 232.4(4), Ca1−N2 =
229.2(5), Ca1−N3 = 259.5(5), Ca1−N4 = 258.0(5), Ca1−N5 =
255.2(5), N1−C1 = 137.5(6), N2−C13 = 137.0(6). Selected bond
angles (deg): N1−Ca1−N2 = 112.9(2), Ca1−N1−C1 = 136.7(3),
Ca1−N2−C13 = 146.1(4).
and a tridentate pmdeta ligand. Due to additional electrostatic
attraction the Ca1−N1 and Ca1−N2 distances to the anilides
are more than 20 pm smaller than those to the pmdeta base. In
addition, the small bite of the nitrogen bases of the pmdeta
ligand (N···N distances) leads to very small N3−Ca1−N4 and
N4−Ca1−N5 bond angles of 70.4(2) and 72.3(2)°. A rather
small N1−Ca1−N2 bond angle of 112.9(2)° is enabled because
the Ca1−N−C angles of the anilide ligands are widened to
136.7(3)° for N1 and 146.1(4)° for N2.
The complex [(dme)2Ca{N(H)Dipp}2] (8) crystallizes in
the centrosymmetric triclinic space group with four molecules
A−D in the asymmetric unit. The molecular structure and
numbering scheme of molecule A is represented in Figure 5.
The hexacoordinate calcium atom is located in a significantly
distorted octahedral environment due to small bites of the dme
ligands and widened N−Ca−N angles. The larger coordination
number of 6 leads to lengthened Ca−N bonds in comparison
Figure 6. Section of the polymeric structure of 9. The ellipsoids
represent a probability of 40%, and H atoms are neglected for clarity .
The letters A (−x, y, −z + 0.5) and B (−x, −y + 2, −z) characterize
symmetry-related atoms. Selected bond lengths (pm): Ca1−N1 =
232.9(3), Ca1−N2 = 239.3(3), K1−N1 = 294.1(3), K1−C1 =
292.9(3), K1−N2 = 287.2(3), K1−C13B = 335.0(3), K1−C14B =
324.1(3), K1−C15B = 308.8(3), K1−C16B = 304.2(4), K1−C17B =
312.1(3), K1−C18B = 327.4(3), N1−C1 = 137.9(4), N2−C13 =
137.9(4). Selected bond angles (deg): N1−Ca1−N2 = 100.3(1), N1−
Ca1−N1A = 152.4(2), N1−Ca1−N2A = 98.6(1), N2−Ca1−N2A =
93.2(1), Ca1−N1−C1 = 155.8(3), Ca1−N1−K1 = 90.5(1), Ca1−
N2−C13 = 127.0(2), Ca1−N2−K1 = 90.93(9).
tetrahedral environment with N−Ca−N angles between
93.2(1) and 153.4(2)°. Despite the small coordination number
of 4, rather large Ca−N bond lengths of 232.9(3) and 239.3(3)
pm are observed due to electrostatic repulsion between the
amide anions and intramolecular steric strain between the bulky
aryl groups of neighboring amido ligands. The flexibility of the
Ca−N−C bond angles (155.8(3) and 127.0(2)°) again
supports the mainly ionic nature of this compound. These
tetrakis(anilido)calciates are interconnected by potassium
countercations that bind to the nitrogen atoms (K−N =
287.2(3) and 294.1(3) pm) and saturate their coordination
sphere by Lewis acid−base interactions to the π systems of the
aryl groups. The remarkable reactivity can be understood on
Figure 5. Molecular structure and numbering scheme of 8. The
ellipsoids represent a probability of 40%, and H atoms are omitted for
clarity reasons. The asymmetric unit contains four molecules A−D;
only molecule A is depicted. Selected bond lengths (pm): Ca1A−N1A
= 230.6(4), Ca1A−N2A = 231.6(4), Ca1A−O1A = 242.5(3), Ca1A−
O2A = 249.6(4), Ca1A−O3A = 242.8(3), Ca1A−O4A = 249.7(3),
N1A−C1A = 136.9(5), N2A−C13A = 138.0(5). Selected bond angles
(deg): N1A−Ca1A−N2A = 115.2(2), Ca1A−N1A−C1A = 156.8(3),
Ca1A−N2A−C13A = 157.0(3).
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a
Table 1. Average Bond Lengths (pm) of Selected Amides of Potassium and Calcium as Well as Their Mixed-Metal Derivatives
compd
[KN(SiMe3)2]2
av Ca−N
av K−N
av Ca−L
av K−L
ref
Potassium Amides
278.7
21
22
23
24
24
24
[(tmeda)KTmp]2
279.2
295.1 (N)
272.0 (O)
292.2 (N)
297.7 (N)
286.8 (O)
301.5 (N)
270.7 (O)
290.5 (N)
[(thf)3KNPh2]2
282.6
[(pmdeta)KNPh2]2
[(pmdeta)KN(iPr)Ph]2
[(dme)2KN(iPr)Ph]2
[(pmdeta)KN(H)Dipp]2
[(diox)1.5KNPh2]∞
282.9
289.1
287.3
285.5
this work
284.6
25
[(tmeda)1.5KNPh2]∞
[{KN(Me)Ph}3]∞
287.4
26
282.4
24
[{(thf)0.5KN(iPr)Ph}2]∞
[{(thf)KN(iPr)Ph}5]∞
[(dme)0.25KN(iPr)Ph]∞
[(thf)KN(H)Dipp]∞
279.7
276.3 (O)
272.9 (O)
278.1 (O)
290.7 (O)
24
280.8
24
281.0
24
276.4
this work
Calcium Amides
[(thf)2Ca{N(SiMe3)2}2]
[(dme)Ca{N(SiMe3)2}2]
[(tmeda)Ca{N(SiMe3)2}2]
[(tmeda)Ca(Tmp)2]
230.2
227.1
231.5
227.5
227.2
236.9
241.5
234.9
232.6
230.4
231.1
231.1
230.8
237.7 (O)
239.7 (O)
259.2 (N)
264.5 (N)
260.2 (N)
246.1 (O)
240.7 (O)
242.7 (O)
235.6 (O)
234.3 (O)
252.9 (N)
246.2 (O)
257.6 (N)
27
28
10
9
[(tmeda)Ca{N(iPr)2}2]
[(dme)2Ca(NPh2)2]
10
8
[(thf)4Ca{N(Me)Ph}2]
[(thf)3Ca{N(iPr)Ph}2]
[(thf)2Ca{N(SiMe3)Dipp}2]
[(thf)2Ca{N(SiMe3)Mes}2]
[(tmeda)Ca{N(SiMe3)Mes}2]
[(dme)2Ca{N(H)Dipp}2]
[(pmdeta)Ca{N(H)Dipp}2]
12
9
7c
7b
7b
this work
this work
Potassium Calciates
[(thf)4K2Ca{N(iPr)Ph}4]
[(tmeda)2K2Ca{N(iPr)Ph}4]
[(thf)3K2Ca(NPh2)4]∞
[K2Ca{N(H)Dipp}4]∞
241.8
244.1
240.3
236.1
268.7
283.7
265.2
9
294.6
15
9
290.7
Tthis work
a
Abbreviations: diox, 1,4-dioxane; Dipp, 2,6-diisopropylphenyl; dme, 1,2-dimethoxyethane; L, neutral Lewis base such as ethers and amines; Me,
methyl; Mes, 2,4,6-trimethylphenyl; Ph, phenyl; pmdeta, pentamethyldiethylenetriamine; Pr, propyl; thf, tetrahydrofuran; tmeda,
tetramethylethylenediamine; Tmp, 2,2,6,6-tetramethylpiperidide.
the basis of a small coordination number of calcium
(accessibility of calcium by the substrate) and of electrostatic
repulsion between the anilide anions (enhancing the nucleo-
philicity and availability of the anilide anions) in addition to
increased nucleophilicity caused by the electron-donating
isopropyl groups.
at benzyl alkali-metal solvates;29 whereas lithium and sodium
ions show the shortest distances to the methylene unit, the
potassium ion prefers a side-on coordination to the aromatic π
system of the phenyl group. This finding supports the notion
that the potassium ion represents a significantly softer cation
than the lighter congeners and the doubly charged calcium ions.
In heterobimetallic amides of potassium and calcium, the amido
anions always bind to the harder divalent calcium ion, forming
tetrakis(amido)calciates with tetracoordinate calcium centers.
Due to the concentration of negative charge in the vicinity of
calcium, neutral Lewis bases such as thf and tmeda bind at
potassium. If the neutral coligands have weak coordination
properties toward K+ ions in comparison to the π systems of
the phenyl groups, interactions between the potassium ion and
the π systems of aryl substituents are operative, often leading to
aggregation and formation of coordination polymers.
Selected structural parameters of potassium and calcium
amides are compared in Table 1. The amides of the heavier
alkali metals and alkaline-earth metals have attracted tremen-
dous interest because they react as highly reactive nucleophiles
and metalation reagents as well as hydroamination catalysts.17
The reactivity can be adjusted with the s-block metals
potassium and calcium or even by employing their hetero-
bimetallic derivatives. Due to a larger size of the potassium ion
and its smaller charge, the Ca−N bonds are generally
significantly shorter than the K−N bonds. Small variations
depend on the coordination number of the s-block metals and
on the bulkiness of the amides and coligands. In solvent-
depleted compounds, the potassium ions also form strong
bonds to the π systems of aryl groups, whereas solvent-free
calcium amides dimerize via bridging amido ligands.28 This π-
philicity of the potassium ion was already investigated in detail
Hydroamination of Diphenylbutadiyne. Hydroamina-
tion is an atom-economic process for the preparation of
substituted amines. However, thermodynamic and kinetic
challenges aggravate the direct nucleophilic attack of the
amine at an electron-rich C−C multiple bond. In addition, the
large energy difference between the N−H and the C−C
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multiple bond and entropic effects are disadvantageous.
Therefore, activation of the C−C multiple bond (by side-on
coordination to transition metals) or of the amine (amide or
imide formation at electropositive metals and lanthanoids) is
required.
Scheme 3. Calciate-Mediated Hydroamination of
Diphenylbutadiyne with 2,6-Diisopropylaniline in
Tetrahydrofuran, Yielding Tetracyclic Imine 10
a
Intermolecular hydroamination of diphenylbutadiyne with
diphenylamine required a very reactive catalyst.16,20 Whereas
the reactivity of the diphenylamides of potassium and calcium
were insufficient to mediate this hydroamination reaction,
catalytic amounts of heterobimetallic [K2Ca(NPh2)4] led to the
formation of singly hydroaminated diphenylbutadiyne.16 In
contrast to this finding, the more nucleophilic N-isopropylani-
lides of potassium and of calcium are able to mediate the
hydroamination of diphenylbutadiyne with N-isopropylaniline.
The potassium-mediated hydroamination of diphenylbutadiyne
with N-isopropylaniline gave small amounts of the side product
1-isopropylphenylamino-2,4-bis(phenylethynyl)-3-phenylnaph-
thalene with a 2:1 stoichiometry of diphenylbutadiyne to
aniline.16
a
See text and Figure 7.
Hydroamination of butadiynes yielding pyrroles succeeds via
a copper(I)-catalyzed addition of aniline to diphenylbutadiyne
(Scheme 2).30 Another strategy for the synthesis of pyrroles
Scheme 2. Copper(I)-Mediated Synthesis of Pyrroles via
Double Hydroamination of Diphenylbutadiyne with Aniline
Figure 7. Ball-and-stick model of 2,6-diisopropyl-9,11,14,15-tetra-
phenyl-8-azatetracyclo[8.5.0.01,7.02,13]pentadeca-3,5,7,9,11,14-hexaene
(10), clarifying the building blocks of this tetracyclic compound (black
and blue, C and N of 2,6-diisopropylaniline; yellow and green, two
diphenylbutadiyne units). The H atoms (light gray) are neglected,
with the exception of those stemming from the aniline.
was developed via the titanium-mediated double hydro-
amination of 1,4-pentadiynes with primary amines.31 If
benzylamine was used in these catalytic hydroamination
reactions, pyridine derivatives were obtained.30−32 Here we
investigated the calcium-mediated hydroamination of diphe-
nylbutadiyne with 2,6-diisopropylaniline. A single hydro-
amination would yield 1,4-diphenyl-1-(2,6-diisopropylanilino)-
but-1-ene-3-yne, and a second intramolecular hydroamination
step could allow the isolation of N-2,6-diisopropylphenylpyr-
role. However, the hydroamination of diphenylbutadiyne with
primary 2,6-diisopropylaniline proceeded surprisingly different
in the presence of catalytic amounts of 9. Similarly to the
observation of the formation of the naphthalene side product,16
1 equiv of aniline reacted with 2 equiv of butadiyne, as shown
in Scheme 3, regardless of the applied stoichiometry. In Figure
7 the color code clarifies the origin of the building blocks (black
and blue, C and N of 2,6-diisopropylaniline; yellow and green,
two diphenylbutadiyne units). This compound cocrystallized
with half a diphenylbutadiyne molecule.
The molecular structure of 10 is displayed in Figure 8. The
labeling of the atoms shows the numbering in accordance with
the chemical name for the inner tetracyclic unit, with the
nitrogen atom N8 being in position 8. For the numbering of
the substituents, the digit of the adjacent ring atom was
expanded by an additional digit to distinguish the carbon atoms
within a substituent.
The nitrogen atom N8 is bound in a five-membered ring with
a C7N8 double bond and a N8−C9 single bond of 131.2(2)
and 141.8(2) pm, respectively. From these values it is obvious
that there is no significant delocalization within the conjugated
system. A vast steric strain is introduced at the C1 atom, which
is a member of all four cycles. This fact leads to severe
deviations from a tetrahedral environment (C−C1−C values
deviate from 101.2(1) to 120.3(2)°) toward a trigonal-
pyramidal environment33 and to a significant elongation of
the C1−C bonds. The adjacent C2 atom even shows stronger
deviations from ideal tetrahedral symmetry. The smallest C1−
C2−C13 angle shows a value of only 95.7(1)° between three
sp3-hybridized carbon atoms and a C2−C13 bond length of
157.5(2) pm. Distortions also widen the angles at the vicinal
diphenylethene fragment with C15−C14−C141 and C14−
C15−C151 values of 129.9(2) and 130.1(2)°, respectively.
The resulting crystalline tetracyclic imine, 2,6-diisopropyl-
9,11,14,15-tetraphenyl-8-azatetracyclo[8.5.0.01,7.02,13]-
pentadeca-3,5,7,9,11,14-hexaene (10), was obtained with a yield
of 82%. The formation of this product does not depend on the
reaction temperature and succeeded in boiling THF and at
ambient temperature; only the reaction period was extended at
lower temperatures.
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thermally controlled Bergman cyclization reactions of non-
conjugated (Z)-hexa-1,5-diyne-3-ene yields p-benzyne with a
triplet ground state,37 whereas photochemically induced
cyclizations follow other pathways.38 The Bergman cyclization
can be triggered by heat39 and by internal amide function-
alities,40 occasionally also metal-mediated.41
A final rearrangement step yields tetracyclic 2,6-diisopropyl-
9,11,14,15-tetraphenyl-8-azatetracyclo[8.5.0.01,7.02,13]-
pentadeca-3,5,7,9,11,14-hexaene (10; 5a,9-diisopropyl-
2,3,10,11-tetraphenyl-5,5a-dihydro-2a1,5-ethenocyclohepta[cd]-
isoindole), containing three chiral carbon atoms at positions 1,
2, and 13. The driving force of this final reorganization of the
molecule, which divides the π system into a shorter conjugated
unit (C3−C12) and an isolated C14C15 double bond, is
release of steric strain between the isopropyl group at C2 and
the phenyl group at C15 (which are oriented to opposite sides
of molecule 10) as well as between neighboring phenyl
substituents. Due to the strained tetracyclic structure only two
enantiomers were observed and characterized by X-ray
crystallography and NMR studies in order to verify the
proposed structure.
During extensive NMR investigations of 10 it was observed
that new resonances developed within a few days that finally
grew to an approximate equimolar ratio with starting 7,15-
diisopropyl-2,3,10,12-tetraphenyl-9-azatetracyclo-
[8.5.0.01,7.02,13]pentadeca-3,5,7,9,11,14-hexaene (10). A com-
plete conversion to 5a,9-diisopropyl-2,3,10,11-tetraphenyl-5a,6-
dihydro-2a1,6-ethenocyclohepta[cd]isoindole (11) and also
purification efforts have failed as of yet. Therefore, the structure
of the rearrangement product 11 was derived from NMR
spectra and DFT calculations. A rearrangement mechanism is
proposed in Scheme 5. This rearrangement breaks and forms a
C−C bond and rearranges the conjugated π system; however,
the number and size of rings as well as double bonds remain
unchanged in the resulting 11, suggesting solely reduction of
intramolecular strain as the driving force for this rearrangement.
Consequently the energy difference between 10 and 11 is
rather small, with 11 being favored by 17.46 kJ mol−1 according
to DFT calculations. A comparison of experimental and
calculated NMR data (Table 2; for assignments see Scheme
6) shows slightly low field shifted resonances. Nevertheless,
experimental parameters are in accordance with the calculated
values. The trends are expressed correctly, clearly supporting
the above suggested interpretation of the experimental findings.
In order to support the proposed reaction mechanisms and
to deduce the importance of steric strain for the rearrangement
step from F to 10 and from 10 to 11, quantum chemical
investigations were performed.
Figure 8. Molecular structure and numbering scheme of 10. The
ellipsoids represent a probability of 40%, and all H atoms are omitted
for clarity. Selected bond lengths (pm): C1−C2 = 156.2(2), C1−C7 =
150.2(2), C1−C10 = 151.6(2), C1−C15 = 154.8(2), C2−C3 =
150.4(3), C2−C21 = 155.2(3), C3−C4 = 134.1(3), C4−C5 =
145.7(3), C5−C6 = 135.2(3), C6−C7 = 144.4(3), C6−C61 =
152.4(3), C7−N8 = 131.2(2), N8−C9 = 141.8(2), C9−C10 =
136.6(3), C9−C91 = 147.9(3), C10−C11 = 145.0(2), C11−C12 =
135.5(3), C11−C111 = 149.0(3), C12−C13 = 151.1(3), C13−C14 =
153.3(3), C14−C15 = 134.2(3), C14−C141 = 147.5(2), C15−C151
= 147.7(3).
Initially it was astonishing that tetracyclic imine 10 with three
chiral carbon atoms formed in such a selective manner. The
proposed reaction mechanism is presented in Scheme 4,
offering two feasible pathways. The first reaction step is the
addition of an anilide to the triple bond of diphenylbutadiyne,
yielding A. Another alkyne inserts into the newly formed
metal−carbon bond (carbometalation step to B). Thereafter, an
intramolecular metalation yields amide C with a metal−
nitrogen bond. The very nucleophilic amido base forms an
imine, and cyclization leads to the formation of the 1,2,4,6-
cycloheptratetraene derivative D with the negative charge at the
5-position (exemplified in Scheme 4 by an M−C bond). This
carbanion reacts with H2N-Dipp, thus regenerating the 2,6-
diisopropylanilido catalyst M{N(H)Dipp} and leading to
intermediate metal-free E. The 1,2,4,6-cycloheptratetraene
fragment is very reactive, due to ring strain caused by the
ketene moiety. Therefore, a cyclization reaction releases this
strain and annihilates the aromatic character of the Dipp group,
resulting in the tricyclic derivative F. Strained 1,2,4,6-cyclo-
heptatetraenes have already attracted much interest and were
prepared and preserved in an argon matrix.34 Isomeric C(CH)6
was intensively investigated by quantum chemical methods as
free molecules35 as well as a hydrocarbon captured in a
molecular container.36 These investigations show that 1,2,4,6-
cycloheptatetraene is favored in comparison to a carbene
embedded in a seven-membered ring.
An alternative pathway allows the protonation of C (and,
hence, the formation of amine G, which is shown here with a
collinear arrangement of the alkyne units requiring a specific
isomerism at the CC double bonds) combined with the re-
formation of the anilido catalyst (Scheme 4). Thereafter, a
Bergman cyclization leads to the formation of the diradical
species H, which also rearranges to the tricyclic imine F,
accompanied by a hydrogen abstraction from the amino
functionality. This hydrogen transfer from the amino unit to
the carbon atom is accompanied by C−C bond formation,
leading to a breakup of the aromaticity of the Dipp group. The
Quantum Chemical Investigations. Total energies Ecorr
with thermal and entropic corrections being applied as well as
the number of imaginary frequencies are summarized in Table
3. We started our investigations on a simplified unsubstituted
model (marked with “_H”; Scheme 4, R = R′ = H). Here
derivative F_H is favored by 64.5 kJ mol−1 in comparison to the
1,2,4,6-cycloheptatetraene intermediate E_H. Surprisingly, the
derivative F_H also is 60.5 kJ mol−1 lower in energy than 10_H
without isopropyl and phenyl groups. Due to the fact that
unsubstituted 11_H is only 17.4 kJ mol−1 lower in energy than
10_H, derivative F_H represents the thermodynamically most
stable product: i.e., in theory the calciate-mediated reaction of
aniline with butadiyne might well end with the formation of
F_H.
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a
Scheme 4. Proposed Mechanism for the Calciate-Mediated Formation of Imine 10
a
R = iPr, R′ = Ph; see text.
groups. Optimization of F_S leads to the highly endothermic
formation of an intermediate in which the neighboring phenyl
substituents performed a formal [2 + 2] cycloaddition reaction,
which is not a productive reaction pathway in the context of the
experimentally observed reaction. Therefore, F_S cannot be
considered as an intermediate in the formation of tetracyclic
10_S and 11_S but might be considered as a transition state.
Moreover, the substituted intermediate E_S is energetically
favored by 13.3 kJ mol−1 in comparison to 10_S and is only 4.3
kJ mol−1 less stable than substituted 11_S. The latter
nevertheless is the thermodynamically most stable isomer if
the substituted derivatives are considered. The alternative
pathway via intermediate G_S is feasible from a theoretical
point of view because substituted G_S is 48.2 kJ mol−1 higher
in energy than 10_S. In summary, the substitution pattern
dramatically disadvantages intermediate F_S, although the
unsubstituted derivative F_H represents the favored molecule if
phenyl and isopropyl groups are neglected. Hence, the reaction
Scheme 5. Rearrangement of 10, Yielding 5a,9-Diisopropyl-
2,3,10,11-tetraphenyl-5a,6-dihydro-2a1,6-
ethenocyclohepta[cd]isoindole (11)
Taking the substituents into account (designated with “_S”;
R = iPr, R′ = Ph), the situation changes significantly. In the final
rearrangement from 10_S to 11_S the situation is similar to
that for the unsubstituted derivatives, with product 11_S again
being favored by 17.6 kJ mol−1. However, the substituted
molecule F_S does not represent a minimum structure, due to
massive intramolecular strain between neighboring phenyl
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is pushed toward the tetracycle 10_S in order to reduce
intramolecular repulsion between adjacent phenyl groups.
Table 2. Comparison of Experimental and Calculated
13C{1H} NMR Shifts of the Central Tetracyclic Units of 10
a
and 11
CONCLUSION
■
10
11
Metalation of 2,6-diisopropylaniline with K[N(SiMe3)2] yields
the corresponding potassium salt [K{N(H)Dipp}·KN-
(SiMe3)2] (1), regardless of the applied stoichiometry. At
elevated temperatures homoleptic K{N(H)Dipp} (5) can be
isolated. The aggregation degree of these potassium anilides
strongly depends on the denticity of the neutral coligand. The
addition of monobasic THF leads to polymeric [(μ-thf)K2{N-
(H)Dipp}2]∞ (2) in the solid state. Bidentate DME is able to
stabilize tetranuclear [(dme)K{μ-N(SiMe3)2}{μ-N(H)Dipp}-
K]2 (4), whereas in the presence of tridentate PMDETA
dinuclear [(pmdeta)K{N(H)Dipp}]2 (3) crystallizes. In all
these solids the four-membered K2N2 ring is the dominating
structural unit which can be interconnected via Lewis acid−
base interactions between the soft potassium cations and the
aryl π-systems.
exptl
DFT
exptl
DFT
181.0
146.2
140.3
139.2
138.9
136.2
135.6
131.6
127.5
126.8
125.5
77.8
185
156
153
146
145
145
144
140
134
134
130
83
170.0
160.4
137.7
136.4
135.9
133.9
131.7
131.3
127.4
127.2
126.9
66.5
174
168
145
144
142
142
141
141
138
138
133
72
72.8
82
57.7
64
58.3
67
48.6
58
These potassium anilides can be used as anilide transfer
reagents. Thus, the metathetical approach with CaI2 in
tetrahydrofuran yields the corresponding calcium bis(2,6-
diisopropylanilide) [(thf)nCa{N(H)Dipp}2] (6), which can be
purified and crystallized as monomeric and mononuclear
complexes after addition of tri- and bidentate coligands such
as pmdeta or dme, yielding [(pmdeta)Ca{N(H)Dipp}2] (7)
and [(dme)2Ca{N(H)Dipp}2] (8), respectively. Excess potas-
sium 2,6-diisopropylphenylamide leads to the formation of the
calciate [K2Ca{N(H)Dipp}4]∞ (9).
a
The assignment of the chemical shifts is depicted in Scheme 6.
1
Scheme 6. Calculated H (Chemical Shifts δ, left) and 13C
NMR Data (Right) of 10 (Top Row) and 11 (Bottom Row)
The potassium tetrakis(anilido)calciate 9 is highly reactive
and enables a calciate-mediated hydroamination of diphenylbu-
tadiyne with 2,6-diisopropylaniline. However, after this reaction
step and a subsequent carbometalation of another butadiyne a
reaction cascade leads to the formation of tetracyclic 2,6-
diisopropyl-9,11,14,15-tetraphenyl-8-azatetracyclo-
[8.5.0.01,7.02,13]pentadeca-3,5,7,9,11,14-hexaene (10), which
slowly rearranges to 5a,9-diisopropyl-2,3,10,11-tetraphenyl-
5a,6-dihydro-2a1,6-ethenocyclohepta[cd]isoindole (11).
EXPERIMENTAL SECTION
■
General Remarks. All manipulations were carried out under an
argon or a nitrogen gas atmosphere using standard Schlenk techniques.
Solvents were dried according to common procedures and distilled
under argon or nitrogen; deuterated solvents were dried with sodium,
degassed, and saturated with an inert gas. KN(SiMe3)2 was purchased
from Aldrich as a solid with a purity of 95% and used without further
purification. Bruker AC 200, Bruker AC 400, and Bruker AC 600
spectrometers were used to record 1H NMR and 13C NMR spectra at
ambient temperature in [D8]THF solutions if no other solvent is
mentioned. All spectra were referenced to deuterated THF as an
internal standard. The anilido complexes were extremely sensitive
toward moisture and air, and therefore, combustion analysis gave no
reliable results.
Table 3. Calculated Energies and Numbers of Imaginary
Frequencies
a
compd
Ecorr (au)
NImag
E_H
E_S
−594.722615
−1754.647508
−594.747172
−594.695420
−1754.624103
−594.724130
−1754.642443
−594.730775
−1754.649164
0
0
0
0
0
0
0
0
0
Synthesis of K{N(H)Dipp}K{N(SiMe3)2} (1). KN(SiMe3)2 (2.15 g,
10.8 mmol) was dissolved in 22 mL of toluene and the solution filtered
prior to use. To this clear, colorless solution was added H2N-Dipp (1.0
mL, 5.3 mmol) via syringe with vigorous stirring at room temperature
to yield a colorless precipitate of 1. After 3 h of stirring, pure 1 was
isolated by filtration, washed twice with 7.5 mL of toluene and finally
with 10 mL of pentane, and then dried in vacuo. Yield: 2.05 g (4.9
mmol, 93%). 1H NMR: δ 6.89 (2H, d, 3JH,H = 7.4 Hz, m-H), 5.84 (1H,
t, JH,H = 7.4 Hz, p-H), 3.41 (1H, s, NH), 3.12 (2H, hept, JH,H = 6.8
Hz, CH), 1.16 (12H, d, 3JH,H = 6.8 Hz, CH3), −0.19 (18H, s, SiCH3).
13C{1H} NMR: δ 156.6 (i-C), 129.7 (o-C), 122.1 (m-C), 106.7 (p-C),
28.2 (CH), 23.1 (iPrCH3), 6.4 (SiCH3).
F_H
G_H
G_S
10_H
10_S
11_H
11_S
3
3
a
For all compounds denoted with the ending “_H”, R = R′ = H; for all
compounds denoted with the ending “_S”, R = iPr, R′ = Ph.
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Synthesis of [(μ-thf)K2{N(H)Dipp}2]∞ (2). This approach was
performed to yield a tmeda adduct. Therefore, 1 (256 mg, 0.6 mmol)
was dissolved in 1.5 mL of a 2:1 mixture of TMEDA and THF, and
this reaction mixture was heated to 60 °C. Crystalline 2 was obtained
overnight from this solution at ambient temperature. 1H NMR: δ 6.57
3.96 (4H, s, NH), 3.03 (8H, hept, 3JH,H = 6.8 Hz, CH), 1.20 (48H, d,
3JH,H = 6.8 Hz, CH3). 13C{1H} NMR: δ 147.4 (i-C), 131.4 (o-C), 122.6
(m-C), 113.8 (p-C), 28.3 (CH), 23.0 (iPrCH3).
Synthesis of 2,6-Diisopropyl-9,11,14,15-tetraphenyl-8-
azatetracyclo[8.5.0.01,7.02,13]pentadeca-3,5,7,9,11,14-hexaene
(10). Diphenylbutadiyne (0.51 g, 2.47 mmol) was dissolved in 12 mL
of THF before 2,6-diisopropylaniline (0.23 mL, 1.26 mmol) and 5 mol
% of the calciate 9 were added, and the mixture was stirred overnight.
A standard workup procedure including hydrolysis with 15 mL of
water, extraction with diethyl ether, drying with sodium sulfate, and
recrystallization from pentane gave 10 as a crude product which
contained half a molecule of diphenylbutadiyne per formula unit. Final
purification was performed via gradient column chromatography over
silica gel, starting with pure aliphatic hydrocarbons followed by a 1:1
mixture of alkanes and ethyl acetate. The residue was recrystallized
from pentane at −20 °C, yielding orange 10 (0.60 g, 1.03 mmol, 82%).
Mp: 122−125 °C. NMR data without phenyl groups are as follows
(for assignment see Scheme 6). 1H NMR (C6D6, 600 MHz, 295 K): δ
6.54 (1H, d, 3JH,H = 6.4 Hz), 6.24 (1H, dd, 3JH,H = 8.6 + 12.1 Hz), 6.14
3
3
(4H, d, JH,H = 7.4 Hz, m-H), 5.81 (2H, t, JH,H = 7.4 Hz, p-H), 3.62
3
(thf), 3.45 (2H, s, NH), 3.15 (4H, hept, JH,H = 6.8 Hz, CH), 1.78
3
(thf), 1.17 (24H, d, JH,H = 6.8 Hz, CH3). 13C{1H} NMR: δ 157.2 (i-
C), 129.6 (o-C), 122.1 (m-C), 106.3 (p-C), 68.1 (thf), 28.3 (CH), 26.3
(thf), 23.3 (CH3).
Synthesis of [(pmdeta)K{N(H)Dipp}]2 (3). 1 (255 mg, 0.6 mmol)
was dissolved in a mixture of 2 mL of PMDETA and 0.3 mL of THF,
and this solution was heated to 60 °C. Standing at room temperature
1
3
yielded crystalline needles of 3. H NMR: δ 6.56 (4H, d, JH,H = 7.4
3
Hz, m-H), 5.78 (2H, t, JH,H = 7.4 Hz, p-H), 3.39 (2H, s, NH), 3.15
(4H, hept, 3JH,H = 6.8 Hz, CH), 2.29−2.44 (CH2-pmdeta), 2.19 + 2.15
(CH3-pmdeta), 1.16 (24H, d, 3JH,H = 6.8 Hz, CH3). 13C{1H} NMR: δ
157.9 (i-C), 129.5 (o-C), 122.1 (m-C), 105.8 (p-C), 58.8 + 57.3 (CH2-
pmdeta), 46.1 + 43.2 (CH3-pmdeta), 28.3 (CH), 23.3 (iPrCH3).
Synthesis of [(dme)K{μ-N(SiMe3)2}{μ-N(H)Dipp}K]2 (4). 1 (316
mg, 0.8 mmol) was dissolved in 1 mL of DME. Subsequent cooling to
5 °C for about 1 week quantitatively resulted in crystalline 4. 1H
NMR: δ 6.58 (4H, d, 3JH,H = 7.4 Hz, m-H), 5.83 (2H, t, 3JH,H = 7.4 Hz,
p-H), 3.43 (2H, s, NH), 3.43 (CH2-dme), 3.27 (CH3-dme), 3.12 (4H,
3
3
(1H, d, JH,H = 8.6 Hz), 5.81 (1H, d, JH,H = 12.1 Hz), 3.96 (1H, d,
3JH,H = 6.4 Hz), 3.62 (1H, hept, JH,H = 6.9 Hz, CH-iPr), 1.89 (1H,
hept, JH,H = 6.9 Hz, CH-iPr), 1.18 (3H, d, JH,H = 6.9 Hz, CH3-iPr),
3
3
3
3
3
0.81 (3H, d, JH,H = 7.0 Hz, CH3-iPr), 0.80 (3H, d, JH,H = 7.0 Hz,
CH3-iPr), 0.52 (3H, d, JH,H = 6.8 Hz, CH3-iPr). 13C{1H} NMR
3
3
hept, 3JH,H = 6.8 Hz, CH), 1.16 (24H, d, JH,H = 6.8 Hz, CH3), −0.19
(C6D6, 150 MHz, 295 K): δ 181.0, 146.2, 140.3, 139.2, 138.9, 136.2,
135.6, 131.6, 127.5, 126.8, 125.5, 77.8, 72.8, 58.3, 30.8, 30.8, 23.1, 22.3,
18.7, 17.7. Anal. Calcd for C44H39N (581.78): C, 90.84; H, 6.76; N,
2.41. Found: C, 90.80; H, 6.90; N, 2.40. MS (EI, m/z (%)): 581 (12)
[M]+, 379 (40) [M − diyne]+, 202 (44) [diyne], 177 (100)
[C12H19N]+, 162 (68) [C12H17]+. IR: 1599 w, 1491 w, 1443 w,
1261 m, 1177 w, 1056 w, 1027 m, 964 w, 917 w, 839 m, 756 s, 693 vs,
662 w, 608 w, 531 w, 417 w cm−1.
(36H, s, SiCH3). 13C{1H} NMR: δ 156.7 (i-C), 129.7 (o-C), 122.1 (m-
C), 106.7 (p-C), 72.6 (CH2-dme), 58.8 (CH3-dme), 28.3 (CH), 23.2
(iPrCH3), 6.5 (SiCH3).
Synthesis of K{N(H)Dipp} (5). H2N-Dipp (0.98 mL, 5.2 mmol)
was added via syringe to a clear colorless solution of KN(SiMe3)2
(1.033 g, 5.2 mmol) in 15 mL of toluene. The resulting suspension
was heated to 100 °C for 18 h, yielding an off-white powder of 5 that
contains only trace amounts of the initial amide. Yield: 1.02 g (4.7
mmol, 91%). 1H NMR: δ 6.55 (2H, d, 3JH,H = 7.4 Hz, m-H), 5.75 (1H,
Synthesis of 5a,9-Diisopropyl-2,3,10,11-tetraphenyl-5a,6-
dihydro-2a1,6-ethenocyclohepta[cd]isoindole (11). In solution
product 10 rearranged with reduction of intramolecular steric strain,
yielding 11. Due to the fact that this compound always contained
significant amounts of 10, characterization was limited to NMR data.
NMR parameters without phenyl groups are as follows (for
3
3
t, JH,H = 7.4 Hz, p-H), 3.36 (1H, s, NH), 3.16 (2H, hept, JH,H = 6.8
Hz, CH), 1.16 (12H, d, 3JH,H = 6.8 Hz, CH3), −0.19 (1.2 H-equ, ∼7%
SiCH3). 13C{1H} NMR: δ 157.6 (i-C), 129.5 (o-C), 122.1 (m-C),
105.5 (p-C), 28.3 (CH), 23.3 (iPrCH3), 6.5 (SiCH3).
1
assignment see Scheme 6). H NMR (C6D6, 600 MHz, 295 K): δ
Synthesis of [(thf)xCa{N(H)Dipp}2] (6). 5 (1.10 g, 5.1 mmol) and
CaI2 (0.75 g, 2.5 mmol) were dissolved in 15 mL of THF.
Immediately, a white precipitate of KI formed that was separated by
filtration over Celite after 2 h of stirring at room temperature. We note
that no crystalline material could be obtained from this solution.
Instead, 6 separated as an oil from diverse solvent mixtures (THF,
toluene, hexane) during cooling.
6.58 (1H, d, 3JH,H = 12.2 Hz), 6.53 (1H, d, 3JH,H = 9.5 Hz), 6.49 (1H,
3
3
dd, JH,H = 7.6 + 12.2 Hz), 6.00 (1H, d, JH,H = 9.5 Hz), 4.64 (1H,
hept, 3JH,H = 7.0 Hz, CH-iPr), 3.91 (1H, d, 3JH,H = 7.5 Hz), 2.03 (1H,
hept, JH,H = 6.9 Hz, CH-iPr), 1.33 (3H, d, JH,H = 7.0 Hz, CH3-iPr),
3
3
3
3
1.28 (3H, d, JH,H = 7.0 Hz, CH3-iPr), 0.86 (3H, d, JH,H = 7.1 Hz,
CH3-iPr), 0.73 (3H, d, JH,H = 6.8 Hz, CH3-iPr). 13C{1H} NMR
3
(C6D6, 150 MHz, 295 K): δ 170.0, 160.4, 137.7, 136.4, 135.9, 133.9,
131.7, 131.3, 127.4, 127.2, 126.9, 66.5, 57.7, 48.6, 29.9, 29.6, 22.6, 22.6,
18.2, 17.5.
Synthesis of [(pmdeta)Ca{N(H)Dipp}2] (7). A 3 mL portion of a
THF solution of 6 was dried in vacuo. Redissolving in 5 mL of
PMDETA and 1.75 mL of THF with heating followed by cooling to
1
Structure Determinations. The intensity data for the compounds
were collected on a Nonius KappaCCD diffractometer using graphite-
monochromated Mo Kα radiation. Data were corrected for Lorentz
and polarization effects but not for absorption effects.42,43
The structures were solved by direct methods (SHELXS44) and
−20 °C overnight yielded colorless crystalline material. H NMR: δ
3
3
6.63 (4H, d, JH,H = 7.4 Hz, m-H), 5.96 (2H, t, JH,H = 7.4 Hz, p-H),
3
3.31 (2H, s, NH), 3.00 (4H, hept, JH,H = 6.8 Hz, CH), 2.29−2.48
3
(CH2-pmdeta), 2.20 + 2.16 (CH3-pmdeta), 1.22 (24H, d, JH,H = 6.8
Hz, CH3). 13C{1H} NMR: δ 156.9 (i-C), 130.4 (o-C), 122.1 (m-C),
108.7 (p-C), 58.8 + 57.3 (CH2-pmdeta), 46.1 + 43.2 (CH3-pmdeta),
29.4 (CH), 23.4 (iPrCH3).
2
refined by full-matrix least-squares techniques against Fo (SHELXL-
9744). The hydrogen atoms of compounds 2 and 10 and the hydrogen
atoms bound to the amide functionalities were located by difference
Fourier synthesis and refined isotropically. The other hydrogen atoms
were included at calculated positions with fixed thermal parameters. All
nondisordered non-hydrogen atoms were refined anisotropically.44
Crystallographic data as well as structure solution and refinement
details are summarized in Table S1 as part of the Supporting
Information. XP (SIEMENS Analytical X-ray Instruments, Inc.) was
used for structure representations.
Synthesis of [(dme)2Ca{N(H)Dipp}2] (8). Crystalline 8 was
obtained when oily 6 was dissolved in a few milliliters of DME and
1
cooled to −20 °C, yielding single crystals of 8. H NMR: δ 6.63 (4H,
d, 3JH,H = 7.4 Hz, m-H), 5.96 (2H, t, 3JH,H = 7.4 Hz, p-H), 3.43 (CH2-
dme), 3.31 (2H, s, NH), 3.28 (CH3-dme), 3.00 (4H, hept, 3JH,H = 6.8
Hz, CH), 1.22 (24H, d, 3JH,H = 6.8 Hz, CH3). 13C{1H} NMR: δ 157.0
(i-C), 130.4 (o-C), 122.1 (m-C), 108.6 (p-C), 72.6 (CH2-dme), 58.8
(CH3-dme), 29.3 (CH), 23.4 (iPrCH3).
Synthesis of [K2Ca{N(H)Dipp}4]∞ (9). 5 (814 mg, 3.8 mmol) and
CaI2 (280 mg, 0.9 mmol) were reacted in 10 mL of THF, and
precipitation of finely divided KI was observed. THF-free crystalline
material was obtained after reduction of the original volume of the
calciate solution to one-third of its original volume, addition of 3 mL
of toluene, and subsequent cooling to −20 °C for 2 weeks. 1H NMR: δ
Computational Methods. Full geometry optimizations (i.e.,
without symmetry constraints) were carried out with the GAUSSIAN
09 program package using throughout the hybrid Hartree−Fock-DFT
approach (B3LYP/6-311G(d,p)).45−47 Stationary points of geometry
optimizations were characterized to be minimum structures according
to the absence of any imaginary modes by applying second-order
derivative calculations. NMR spectra were calculated with the
3
3
6.79 (8H, d, JH,H = 7.4 Hz, m-H), 6.31 (4H, t, JH,H = 7.4 Hz, p-H),
2658
dx.doi.org/10.1021/om4001007 | Organometallics 2013, 32, 2649−2660

Organometallics
Article
continuous set of gauge transformations (CSGT) and the gauge-
independent atomic orbital (GIAO) methods.48 Visualization of any
calculated properties was performed using the program package
GAUSSVIEW.49
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ASSOCIATED CONTENT
* Supporting Information
■
S
Tables, figures, and CIF files giving crystallographic data of the
crystal structure determinations as well as the NMR spectra of
the metal anilides. This material is available free of charge via
the Internet at http://pubs.acs.org. Crystallographic data
(excluding structure factors) have also been deposited with
the Cambridge Crystallographic Data Centre as supplementary
publication CCDC-888141 for 2, CCDC-888142 for 3, CCDC-
888143 for 4, CCDC-888144 for 7, CCDC-888145 for 8,
CCDC-888146 for 9, and CCDC-888147 for 10. 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).
Ibrahim, A. A.; Malik, K. M. A.; Motevalli, M.; Moseler, R.; Powell, H.;
̈
Runnacles, J. D.; Sullivan, A. C. Polyhedron 1990, 9, 2959−2964.
(7) (a) Torvisco, A.; Ruhlandt-Senge, K. Organometallics 2011, 30,
986−991. (b) Gillett-Kunnath, M.; Teng, W.; Vargas, W.; Ruhlandt-
Senge, K. Inorg. Chem. 2005, 44, 4862−4870. (c) Vargas, W.; Englich,
U.; Ruhlandt-Senge, K. Inorg. Chem. 2002, 41, 5602−5608.
(d) Kennedy, A. R.; Mulvey, R. E.; Schulte, J. H. Acta Crystallogr.
2001, C57, 1288−1289. See also related Me2Si(NDipp)2Ae(thf)n:
Yang, D.; Ding, Y.; Wu, H.; Zheng, W. Inorg. Chem. 2011, 50, 7698−
7706.
AUTHOR INFORMATION
Corresponding Author
*M.W.: fax, +49 (0) 3641 9-48102; e-mail, m.we@uni-jena.de.
■
Author Contributions
§These authors contributed equally.
Notes
The authors declare no competing financial interest.
(8) Gartner, M.; Fischer, R.; Langer, J.; Gorls, H.; Walther, D.;
̈
̈
Westerhausen, M. Inorg. Chem. 2007, 46, 5118−5124.
ACKNOWLEDGMENTS
■
(9) Glock, C.; Gorls, H.; Westerhausen, M. Inorg. Chem. 2009, 48,
̈
We are very grateful to Rainer Beckert and Roman Goy for
valuable discussions as well as to the undergraduate student
Thomas Gallert for support in the frame of an advanced
laboratory course. The infrastructure of our institute was
provided by the EU (European Regional Development Fund,
EFRE) and the Friedrich Schiller University Jena. Computing
time provided by the Ohio Supercomputing Centre, Columbus,
OH, is gratefully acknowledged.
394−399.
(10) Glock, C.; Gorls, H.; Westerhausen, M. Inorg. Chim. Acta 2011,
̈
374, 429−434.
(11) Gartner, M.; Gorls, H.; Westerhausen, M. Inorg. Chem. 2007, 46,
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7678−7683.
(12) Gartner, M.; Gorls, H.; Westerhausen, M. Dalton Trans. 2008,
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1574−1582.
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(b) Mulvey, R. E. Organometallics 2006, 25, 1060−1075. (c) Mulvey,
R. E. Chem. Commun. 2001, 1049−1056.
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