Synthesis and structural characterization of lithium, sodium and potassium complexes supported by a tridentate amino-bisphenolate ligand

Article abstract of DOI:10.1016/j.molstruc.2018.03.079

Reactions of methylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol) (1) with one or two equivalents of bulk Li, Na or K metals in THF or DMSO render mono or dialkali metal complexes depending on the stoichiometric ratio of the reactants. The metal-methylamino-N-(2-methylene-4,6-tert-butylphenol)–N-(2-methylene-4,6-tert-butylphenolate) complexes, 2Li, 2Na and 2K, are generated upon the substitution of a single phenol hydrogen of 1. In the solid state, complex 2Na is a dimer due to the establishment of two symmetric hydrogen bonds between two adjacent molecules. The Na center also engages into the formation of a ten-membered metallacycle ring with a butterfly-like structure. Due to dimerization, an intermolecular six-membered core is formed involving two sodium and four oxygen atoms. The weakly coordinated nitrogen atom from the ligand is nearly perpendicular to the hexagonal core. The dimetal-methylamino-N,N′-bis(2-methylene-4,6-di-tert-butylphenolate) complexes, 3Li, 3Na and 3K result from metal substitution of the two phenol hydrogens from ligand 1. The SC-XRD structures of 3Li and 3Na are discreet, each incorporating two metal atoms in different coordination environments. Ten-membered rings with boat-boat conformations are also observed as are rhombic central M₂O₂ cores. The molecular structure of 3K in DMSO shows a higher degree of aggregation. It effectively comprises four K atoms, two ligand backbones and seven solvent molecules forming a central four-membered K₂O₂ ring perpendicular to an eight-membered structure formed also by K and O atoms spanning over the two ligand moieties.

Full text of DOI:10.1016/j.molstruc.2018.03.079

Journal of Molecular Structure 1164 (2018) 248e258
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis and structural characterization of lithium, sodium and
potassium complexes supported by a tridentate amino-bisphenolate
ligand
a
b
b
ꢀ
Clara J. Durango-García , Ernesto Rufino-Felipe , Marcela Lopez-Cardoso ,
b
b, *
ꢀ
~
ꢀ
Miguel-Angel Munoz-Hernandez , Virginia Montiel-Palma
Facultad de Ciencias. Universidad Antonio Narino sede Armenia, Av. Bolívar 49 Norte - 30, Armenia-Quindío, Colombia
Centro de Investigaciones Químicas, Instituto de Investigacion en Ciencias Basicas y Aplicadas, Universidad Autonoma del Estado de Morelos, Av.
Universidad 1001, Col. Chamilpa, Cuernavaca, Morelos 62209 Mexico
a
~
b
ꢀ
ꢀ
ꢀ
a r t i c l e i n f o
a b s t r a c t
Article history:
Reactions of methylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol) (1) with one or two equivalents
of bulk Li, Na or K metals in THF or DMSO render mono or dialkali metal complexes depending on the
stoichiometric ratio of the reactants. The metal-methylamino-N-(2-methylene-4,6-tert-butylphenol)eN-
(2-methylene-4,6-tert-butylphenolate) complexes, 2Li, 2Na and 2K, are generated upon the substitution
of a single phenol hydrogen of 1. In the solid state, complex 2Na is a dimer due to the establishment of
two symmetric hydrogen bonds between two adjacent molecules. The Na center also engages into the
formation of a ten-membered metallacycle ring with a butterfly-like structure. Due to dimerization, an
intermolecular six-membered core is formed involving two sodium and four oxygen atoms. The weakly
coordinated nitrogen atom from the ligand is nearly perpendicular to the hexagonal core. The dimetal-
methylamino-N,N0-bis(2-methylene-4,6-di-tert-butylphenolate) complexes, 3Li, 3Na and 3K result from
metal substitution of the two phenol hydrogens from ligand 1. The SC-XRD structures of 3Li and 3Na are
discreet, each incorporating two metal atoms in different coordination environments. Ten-membered
rings with boat-boat conformations are also observed as are rhombic central M2O2 cores. The molecu-
lar structure of 3K in DMSO shows a higher degree of aggregation. It effectively comprises four K atoms,
two ligand backbones and seven solvent molecules forming a central four-membered K2O2 ring
perpendicular to an eight-membered structure formed also by K and O atoms spanning over the two
ligand moieties.
Received 7 October 2017
Received in revised form
18 March 2018
Accepted 19 March 2018
Available online 20 March 2018
Keywords:
Aminobisphenolate
Alkali metal
Lithium
Sodium
Potassium
SC-XRD
© 2018 Elsevier B.V. All rights reserved.
1. Introduction
attributed this behavior to the coordination modes of K as well as
steric effects [2]. Indeed, in recent years alkali metal complexes
The coordination chemistry of a number of ligands has flour-
ished partly owing to the increasing interest for the development of
efficient catalytic systems for a variety of chemical reactions [1].
Understanding the fundamental aspects of the coordination and
structure of the chemical systems can have a profound impact if
one aims at designing more efficient and environmentally friendly
catalysts. As an illustration, Ma and coworkers reported on a family
of potassium amino-phenolate complexes capable of polymerizing
rac-lactide with high monomer conversions yet poor selectivity and
have been pointed out as successful, innocuous alternatives to the
more expensive transition metals for a variety of applications
[3e5]. Due to their ability to coordinate a wide range of metals,
ligands based on Ne and O-donor atoms, amongst which Schiff
bases and aminophenolates are preferred options, have been
employed as alternatives to non-metallocene olefin and ester
polymerization systems, including biodegradable polymers
[4,6e9]. With regards to aminophenolates, studies including sys-
tematic comparisons between group 1 metals, remain rare [10,11].
In those studies however, it has been noticed that even small
changes in the ligand and solvent result in important differences in
the structure and chemical reactivity of the complexes [12].
In light of this, we now wish to report on the reactivity of the
* Corresponding author.
E-mail address: vmontielp@uaem.mx (V. Montiel-Palma).
https://doi.org/10.1016/j.molstruc.2018.03.079
0022-2860/© 2018 Elsevier B.V. All rights reserved.

C.J. Durango-García et al. / Journal of Molecular Structure 1164 (2018) 248e258
249
tridentate proligand methylamino-N,N-bis(2-methylene-4,6-di-
tert-butylphenol) (1) towards bulk alkali metals Li, Na or K. We
show reactions take place resulting in formal substitution of one or
two of the phenol hydrogens by a metal cation with concomitant
dihydrogen gas release.
66%. 1H NMR (CDCl3, 400 MHz, 298 K),
d
(ppm): 1.32 (s, 18H, CH3),
1.42 (s, 18 H, CH3), 2.60 (s, 3H, NCH3), 3.96 (br s, 2H, CH2), 4.76 (br s,
2H, CH2), 6.81 (d, 4JHH 2.2 Hz, 2H, CHaromatic), 7.18 (d, 4JHH 2.2 Hz, 2H,
CHaromatic). 13C{1H} NMR (CDCl3, 100.61 MHz, 298 K),
d (ppm): 30.0
(CH3), 31.7 (CH3), 46.8 (NCH3), 55.8 (CH2), 126.5 (Caromatic), 127.3
(Caromatic), 128.4 (Caromatic), 129.2 (Caromatic), 141.0 (Caromatic). Anal.
Calcd for C39H64NNaO4: C, 73.89; H, 10.18; N, 2.21. Found: C, 74.08;
H, 10.44; N, 2.28.
2. Materials and methods
2.1. General details
2.5. Synthesis of lithium-methylamino-N-(2-methylene-4,6-tert-
All manipulations were carried out under an atmosphere of
argon using standard Schlenk line techniques or an MBraun glo-
vebox under argon, unless otherwise indicated. All commercial
reagents were purchased from Aldrich or Merck and used as
received. Solvents were distilled under nitrogen from the appro-
priate drying agent. CDCl3 and DMSO-d6 were stored under mo-
lecular sieves. 1H, 13C{1H} and 7Li NMR spectra were recorded either
on a Varian Mercury 200 MHz or a Varian Unity 400 MHz spec-
trometers at room temperature. Elemental analyses were per-
formed using Elementar Vario EL-III equipment. Infrared spectra
were prepared as KBr pellets under argon in a glovebox and were
recorded on a Nicolet 6700 spectrometer.
butylphenol)eN-(2-methylene-4,6-tert-butylphenolate), 2Li
To a Schlenk flask containing a solution of 1 (360 mg, 0.8 mmol)
in 15 mL of THF, 0.8 mmol (6 mg) of finely cut Li were added. The
mixture was refluxed for 48 h under vigorous stirring. After this
time, the reaction mixture was filtered off via cannula to remove
the residual solid. The solution was then dried under vacuum and
the remaining fine white solid crystallized from THF. The white
crystals were not suitable for a SC-XRD experiment. 2Li was ob-
tained as a THF adduct. Yield 68%. 1H NMR (CDCl3, 400 MHz, 298 K),
d: 1.13 (s,18H, CH3),1.34 (s,18H, CH3),1.84 (s, 3H, NCH3), 2.88 (br, u1/
34 Hz, 2H, CH2), 4.17 (br, u1/2 46 Hz, 2H, CH2), 6.71 (br, 2H, CHar-
2
omatic), 7.04 (br, 2H, CHaromatic). 13C{1H} NMR (CDCl3, 100.61 MHz,
2.2. Single crystal X-ray diffraction (SC-XRD)
298 K), d: 140.89 (Caromatic), 137.32 (Caromatic), 133.07 (Caromatic),
125.17 (Caromatic), 123.24 (Caromatic), 121.98 (Caromatic), 63.56 (CH2),
39.55 (NCH3), 35.35 (CeCH3), 34.04 (CeCH3), 32.08 (CH3), 29.84
SC-XRD data for 2Na, 3Li and 3Na were collected using the
program SMART [13] on a Brucker APEX CCD diffractometer with
(CH3). 7Li NMR (CDCl3, 155.45 MHz, 298 K)
d
: ꢀ1.81 (br s). Anal.
monochromatized Mo-K
a
radiation (
l
¼ 0.71073 Å). Cell refine-
Calcd. for C39H64LiNO4: C, 75.81; H, 10.44; N, 2.27. Found: C, 76.25;
H, 9.99; N, 2.38.
ment and data reduction were carried out with the use of the
program SAINT, the program SADABS was employed to make inci-
dent beam, decay and absorption corrections in the SAINT-Plus v.
6.0 suite [14]. Then, the structures were solved by direct methods
with the program SHELXS and refined by full-matrix least-squares
techniques with SHELXL in the SHELXTL v. 6.1 suite [15]. X-ray in-
tensity data for 3K was collected using the program CrysAlisPro on a
four-circle SuperNova, Dual EosS2 CCD diffractometer with mono-
2.6. Synthesis of potassium-methylamino-N-(2-methylene-4,6-
tert-butylphenol)eN-(2-methylene-4,6-tert-butylphenolate), 2 K
To a solution of 1 (200 mg, 0.43 mmol) in 8 mL THF, 17 mg
(0.43 mmol) of finely cut K were added. The reaction mixture was
refluxed for 3 h after which time all the metal had been consumed.
The solution was dried under vacuum, washed three times with
0.5 mL of cold hexane and recrystallized from concentrated THF
rendering a pale yellow solid. 2K was obtained as a THF adduct.
chromatic Cu-K
a
radiation (
l
¼ 1.54184 Å). Cell refinement, data
reduction, incident beam, decay and absorption corrections were
carried out with the use of the program CrysAlisPro. Using Olex 2,
the structure was solved by direct methods with the program
SHELXT and refined by full-matrix least-squares techniques with
SHELXL. Hydrogen atoms were generated in calculated positions
and constrained with the use of a riding model. The final models
involved anisotropic displacement parameters for all non-
hydrogen atoms. The crystal structure data was deposited at the
Cambridge Crystallographic Data Center and further details of the
structure analysis are given in the ESI.
Yield 71%. 1H NMR (CDCl3, 400 MHz, 298 K),
d (ppm): 1.25 (s, 18H,
CH3), 1.35 (s, 18 H, CH3), 2.56 (s, 3H, NCH3), 3.93 (s, 2H, CH2), 4.74 (s,
2H, CH2), 6.77 (d, 4JHH 2.8 Hz, 1H, CHaromatic), 7.13 (d, 4JHH 2.8 Hz, 1H,
4
4
CHaromatic), 7.20 (d, JHH 2.8 Hz, 1H, CHaromatic), 7.26 (d, JHH 2.8 Hz,
1H, CHaromatic). 13C{1H} NMR (CDCl3, 100.61 MHz),
(ppm): 150.3
d
(Caromatic), 148.2 (Caromatic), 142.2 (Caromatic), 136.6 (Caromatic), 125.1
(Caromatic), 123.7 (Caromatic), 123.2 (Caromatic), 122.1 (Caromatic), 122.0
(Caromatic), 118.9 (Caromatic), 116.0 (Caromatic), 53.2 (CH2), 40.1 (NCH3),
35.2 (CeCH3), 34.5 (CeCH3), 31.9 (CH3), 29.9 (CH3). Anal. Calcd for
2.3. Synthesis of proligand methylamino-N,N-bis(2-methylene-4,6-
di-tert-butylphenol), 1
C39H64KNO4: C, 72.06; H, 9.92; N, 2.15. Found: C, 72.11; H, 9.86; N,
2.16.
Methylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol) (1)
was synthesized according to reported procedures [16,17] by
Mannich condensation of methylamine, paraformaldehyde and
2,4-di-tert-butylphenol.
2.7. Synthesis of dilithium-methylamino-N,N'-bis(2-methylene-4,6-
di-tert-butylphenolate), 3Li
200 mg (0.43 mmol) of 1 and 6 mg (0.9 mmol) of oil-free Li were
refluxed in THF for 48 h. Yellow crystals suitable for X-ray analysis
were grown from concentrated THF-hexane solutions at 273 K.
Yield 75%. 3Li was also obtained as a THF adduct. 1H NMR (CDCl3,
2.4. Synthesis of sodium-methylamino-N-(2-methylene-4,6-tert-
butylphenol)eN-(2-methylene-4,6-tert-butylphenolate), 2Na
400 MHz),
d (ppm): 1.18 (s, 18H, CH3), 1.42 (s, 18H, CH3), 1.95 (s, 3H,
Equimolar amounts of Na (0.43 mmol, 10 mg) and 1 (0.43 mmol,
200 mg) were refluxed for 48 h. After this time, the reaction
mixture was filtered off via cannula to remove the unreacted solids.
The solution was then dried under vacuum to yield a fine white
solid. Crystals suitable for SC-XRD were grown from concentrated
THF solutions at 257 K. 2Na was obtained as a THF adduct. Yield
NCH3), 2.73 (d, 2JHH 11.6 Hz, 2H, CH2), 4.11 (d, 2JHH 11.6 Hz, 2H, CH2),
4
4
6.80 (d, JHH 2.2 Hz, 2H, CHaromatic), 7.10 (d, JHH 2.2 Hz, 2H, CHar-
omatic). 13C{1H} NMR (CDCl3, 100.61 MHz),
(ppm): 166.2 (Caromatic),
d
136.9 (Caromatic), 132.3 (Caromatic), 127.3 (Caromatic), 125.6 (Caromatic),
123.0 (Caromatic), 65.1 (CH2), 40.4 (NCH3), 36.1 (CeCH3), 34.5
(CeCH3), 32.7 (CH3), 30.5 (CH3). 7Li NMR (THF-d8, 155.45 MHz,

250
C.J. Durango-García et al. / Journal of Molecular Structure 1164 (2018) 248e258
Scheme 1. The synthesis of compounds 2M (M ¼ Li, Na, K) from proligand 1.
298 K)
d
: 0.3 (br s). 7Li NMR (CDCl3, 155.45 MHz, 298 K)
d
: 0.6 (br
were performed on all three new compounds. Their formulations
are consistent with overall replacement of a single hydrogen atom
from a phenol group in 1 by a metal cation presumably by release of
molecular H2. Crystals of all three new complexes 2 M (M ¼ Li, 2Li;
M ¼ Na, 2Na; M ¼ K, 2 K; Scheme 1) were obtained but only the
sodium derivative 2Na rendered crystals of acceptable quality for a
SC-XRD analysis. The compounds were also characterized by NMR
spectroscopy. The comparisons allowed us to propose analogous
structures for all three compounds.
s), ꢀ0.2 (s). Anal. Calcd. for C43H71Li2NO5: C, 74.21; H, 10.28; N, 2.01.
Found: C, 73.23; H, 9.85; N, 2.19.
2.8. Synthesis of disodium-methylamino-N,N'-bis(2-methylene-4,6-
di-tert-butylphenolate), 3Na
200 mg (0.43 mmol) of 1 and 20 mg (0.9 mmol) of finely cut oil-
free Na were refluxed in THF for 48 h. The green-yellow solid was
washed three times with 0.5 mL of hexane and dried in vacuo for ca.
8 h. Yield 54%. Suitable crystals for SC-XRD analysis were grown
from concentrated THF-hexane solutions at 273 K. 3Na was ob-
tained as a THF adduct. Yield 54%. 1H NMR (CDCl3, 400 MHz, 293 K),
3.1.1. Synthesis of sodium-methylamino-N-(2-methylene-4,6-tert-
butylphenol)eN-(2-methylene-4,6-tert-butylphenolate), 2Na
The off-white solid was obtained in 66% yield. Crystals of 2Na for
SC-XRD spectroscopy were grown from slow evaporation of
concentrated THF solutions. Details of the crystal refinement and
other relevant crystallographic information are given in Table 1 and
ESI. The geometry of the central pentacoordinated Na is trigonal
bipyramid formed by coordination of the metal to four oxygen and
one nitrogen atoms (Fig. 1). The bond angles around Na are only
d
(ppm): 1.29 (s,18H, CH3),1.42 (s,18H, CH3), 2.65 (s, 3H, NCH3), 3.96
4
(br s, 2H, CH2), 4.78 (br s, 2H, CH2), 7.16 (d, JHH 2.2 Hz, 2H, CHar-
omatic), 7.38 (d, JHH 2.2 Hz, 2H, CHaromatic). 13C{1H} NMR (CDCl3,
4
100.61 MHz, 298 K): 29.4 (CH3), 31.4 (CH3), 40.1 (NCH3), 68.2 (CH2),
122.0 (Caromatic), 126.5 (Caromatic), 127.3 (Caromatic), 138.6 (Caromatic),
141.0 (Caromatic), 142.2 (Caromatic). Anal. Calcd. for C43H71NNa2O5: C,
70.94; H, 9.83; N, 1.92. Found: C, 70.91; H, 9.72; N, 1.92.
slightly deviated from ideality (c
value 0.90)1 [18], in contrast to
other related tridentate systems which show large deviations [4]
(Table 2). Indeed, the Na atom coordinates to the three donor atoms
from 1 (two oxygens and one nitrogen), the proligand having lost a
single phenol hydrogen. Additionally, the remaining hydroxyl
moiety forms an intermolecular OeH/O hydrogen bond with the
oxygen atom from a second complex unit, which overall generates a
symmetric dimer (Fig. 1). Intermolecular interactions resulting in
higher aggregation is a phenomenon previously observed in related
systems [7,19e22] but in alkali metal compounds most of them are
due to the formation of M-O bonds [4,23] rather than intermolec-
ular hydrogen bonds as in the present case. However, a related
precedent of hydrogen bond effecting dimerization was reported by
Huang in which tetralithium bisphenolate complexes were
partially hydrolyzed to form dilithium species through hydrogen
bonding [24]. Also Wu reported on the presence of a K system
2.9. Synthesis of tetrapotassium-methylamino-N,N'-bis(2-
methylene-4,6-di-tert-butylphenolate)-[(di-m-dimethyl sulfoxide-
dimethyl sulfoxide- O)-bis(di- O1)-]-tris(dimethyl sulfoxide), 3 K
k
k
200 mg (0.43 mmol) of 1 and 33 mg (0.9 mmol) of oil-free K
were refluxed in 10 mL of THF for 8 h. The brown solid was evap-
orated to dryness by heating to 323 K during 16 h and then washed
three times with 1 mL of hexane and dried in vacuo for 16 h by
heating to 323 K with a water bath. Yield 70%. Adequate crystals for
SC-XRD analysis were grown from concentrated DMSO solutions.
3K was obtained as a DMSO adduct. 1H NMR (DMSO-d6, 400 MHz),
d
(ppm): 1.18 (s, 18H, CH3), 1.34 (s, 18H, CH3), 2.08 (br s, 2H, CH2),
3.49 (br s, 2H, CH2), 3.91 (s, NCH3), 6.72 (br s, 2H, CHaromatic), 6.86 (br
s, 2H, CHaromatic). 13C{1H} NMR (DMSO-d6, 50.31 MHz),
(ppm):
d
stabilized by
a bulky monophenoxide ligand in which two
134.4 (Caromatic), 120.6 (Caromatic), 59.2 (CH2), 40.5 (NCH3), 34.7
(CeCH3), 33.4 (CeCH3), 32.0 (CH3), 29.8 (CH3). Anal. Calcd. for
hydrogen bonds stemming from benzyl alcohol effect dimerization
in the solid state [5]. In the latter system, the geometrical param-
eters of the hydrogen bond interaction were determined as O/O at
2.5491(18) Å, OeH at 0.8755 Å and the angle OeH/O at 164.3ꢁ. In
our case, the corresponding parameters are significantly different:
O2/O1 at 2.444(4) Å, O2eH100 at 1.22(4) Å and O2eH100/O1 at
172(4)o. Thus, the hydrogen bond interaction is stronger in our
system.
C
73H130K4N2O11S7: C, 55.05; H, 8.23; N, 1.76. Found: C, 54.43; H,
8.38; N, 1.60.
3. Results and discussion
3.1. Synthesis of metal-methylamino-N-(2-methylene-4,6-tert-
butylphenol)eN-(2-methylene-4,6-tert-butylphenolate), 2Na, 2Li
and 2 K
To further discuss the SC-XRD molecular structure of 2Na we
1
Equimolar amounts of finely cut metal (Li, Na or K) and 1 were
refluxed in THF in a Schlenk flask under argon. Elemental analyses
Applying Konno's equation to 2Na gives
¼ 1).
c value 0.90, very close to trigonal
bipyramid geometry (ideal value
c

C.J. Durango-García et al. / Journal of Molecular Structure 1164 (2018) 248e258
251
Table 1
Collection parameters for all complexes from SC-XRD studies.
Complex
2Na$2THF
3Li$3THF
3Na3$THF
3 K$7DMSO
Molecular formula
Formula Weight
T/K
C78H124N2Na2O8
1236.76
100(2)
C90H154Li4N2O11
1467.90
100(2)
C86H142N2Na4O10
1455.97
100(2)
C82H154K4N2O14S10
1869.06
100(2)
l
(Å)
0.71073
Triclinic
P-1
10.7304(18)
14.609(2)
14.700(2)
62.139(2)
82.816(3)
70.817(3)
1
0.71073
Monoclinic
P2(1)/n
9.252(3)
16.578(5)
29.137(9)
90
93.575(7)
90
2
0.71073
Monoclinic
P2(1)/n
9.2104(16)
17.977(3)
28.167(5)
90
93.391(4)
90
2
1.54184
Monoclinic
P2(1)/c
33.6316(2)
29.5449(2)
20.88014(13)
90
93.4622(5)
90
8
Crystal system
Space group
a(Å)
b(Å)
c(Å)
a
b
g
Z
r
(ꢁ)
(ꢁ)
(ꢁ)
calcd(g/cm3)
1.091
0.078
1.090
0.069
1.039
0.082
1.199
3.839
Abs. Coeff(mmꢀ1
)
Reflections collected
18553
18092
24758
142403
Independent reflns [Rint
Completeness to qmax
]
6762 [0.0464]
99.3%
6773 [0.1456]
95.9%
8060 [0.0652]
97.5%
40711 [0.0373]
99.9%
Data/restraints/parameters
6762/140/450
1.062
0.1105
7499/358/574
0.884
0.0787
8060/53/443
1.040
0.0990
40711/633/2225
1.053
0.0889
GOFa on F2
R1b (I > 2
wR2c(I > 2
s
)
s
)
0.1276
0.1756
0.2540
0.2391
R1 (all data)
0.1276
0.2121
0.1360
0.0915
wR2(all data)
0.2564
0.2498
0.2837
0.2419
Largest diff. Peak, hole
0.59 & ꢀ0.36
0.22 & ꢀ0.23
0.95 & ꢀ1.0
5.25 & ꢀ2.86
a
GOF ¼ (Sw(Fo2 e F2c)2/(n e p))1/2 where n is the number of data and p is the number of parameters refined.
b
c
R1 ¼ SjjFo e jFcjj/SjFoj.
wR2 ¼ (S (w(F2o e F2c)2)/S (w(F2o)2))1/2
.
Fig. 1. ORTEP drawings of complex 2Na.2THF with thermic ellipsoids at 50% probability level. Most hydrogen atoms are omitted for clarity. (a): View of the dimer generated upon
hydrogen bond formation. (b): View of the central trigonal bipyramid geometry generated around each Na center. Na1eN1 distance is 2.587(4) Ǻ. Other selected bond lengths and
angles are given in Table 2.
will consider only one of the monomers because the dimeric
structure is generated by symmetry (-x,1-y,-z). Two THF molecules
complete the coordination sphere of Na. The equatorial plane
consist of the two oxygen atoms from 1 and one from a coordinated
THF molecule while the axial positions are occupied by the nitrogen
atom from 1 and the oxygen from the second THF molecule. The
angles around the metal center in the equatorial plane are
116.59(12)ꢁ, 118.16(12)ꢁ and 121.88(11)ꢁ while the angle between
the axial atoms is 170.83(12)ꢁ. Due to the presence of the two
hydrogen bonds discussed above, the dimer forms a hexagonal core
comprising two sodium and four oxygen atoms of the two moieties
leaving the nitrogen atoms in close to orthogonal dispositions
(Fig. 2). Regarding bond lengths, the three equatorial NaeO bonds
are 2.312(3), 2.317(3) and 2.334(3) Å, close to the sum of the co-
valent radii NaeO at 2.32(11) [25,26], and as expected significantly
shorter than the axial NaeO4 length at 2.468(3) Å. All of these
lengths are slightly longer than those reported by O'Hara in tetra-
sodium cuboidal systems [12]. Besides, the axial NaeN1 bond
length is 2.587(4) Å, rather elongated with respect to the sum of
covalent radii NaeN at 2.39(11) Å) but in agreement with the
observed distances in related sodium phenolates [27] and bisphe-
nolates [12]. One can also observe metal coordination gives rise to a
ten-membered heterocycle ring comprising two fused six
membered rings in a boat-boat conformation (Fig. 2(b)).
Crystals of 2Na were dissolved in CDCl3 for their solution NMR
analysis (Table 3). The main features in the 1H NMR spectrum are

252
C.J. Durango-García et al. / Journal of Molecular Structure 1164 (2018) 248e258
Table 2
Selected bond lengths (Å) and angles (ꢁ) from the SC-XRD studies of complexes 2Na, 3Li and 3Na.
2Na
3Li
3Na
3K
Na1eO1 2.312(3)
Li1eO1 1.929(9)
Na1eO1 2.274(3)
K1eO5 2.826(3)
Na1eO2 2.317(3)
Na1eO3 2.334(3)
L1-O2 1.923(9)
Li1eO3 1.993(9)
Na1eO2 2.283(3)
Na1eO3 2.289(3)
K1eS3A 3.537(4)
K1eO1 2.618(3)
Na1eO4 2.468(3)
Li1eN1 2.080(9)
Na1eN1 2.417(3)
K1eO2 2.577(2)
Na1eN1 2.587(4)
Li2eO1 1.885(9)
Li2eO2 1.842(9)
Na2eO1 2.197(3)
Na2eO2 2.150(3)
Na2eO4 2.280(5)
Na2eO5 2.294(5)
K1eO11 2.752(3)
K1eN1 2.825(3)
K1eO5 2.826(3)
K2eS3 3.653(1)
K2eO1 2.555(2)
K2eO4 2.707(2)
K2eO6 2.699(3)
K2eO10 2.653(3)
K3eS2 3.766(1)
K3eO5 2.812(3)
K3eS3 3.585(1)
K3eO2 2.812(3)
K3eO3 2.738(2)
K3eO6 2.713(3)
K3eO9 2.691(3)
K4eS3 3.269(1)
O1eNa1eO2 121.88(11)
O1eNa1eO3 118.16(12)
O2eNa1eO3 116.59(12)
O3eNa1eO4 85.94(12)
O3eNa1eN1 84.99(12)
O4eNa1eN1 170.83(12)
Li2eO4A 2.010(9)
Li2eO5A 2.015(9)
O1eLi1eN1 98.3(4)
O1eLi1eO3 129.2(4)
O2eLi1eN1 98.1(4)
O2eLi1eO1 96.5(4)
O2eLi1eO3 114.6(4)
O3eLi1eN1 114.6(4)
O1eLi2eO4A 123.5(5)
O1eLi2eO5A 112.4(4)
O2eLi2eO1 100.9(4)
O2eLi2eO4A 107.1(4)
O2eLi2eO5A 116.6(5)
O4A-Li2-O5A 97.4(4)
O1eNa1eN1 85.1(11)
O1eNa1eO3 144.79(12)
O2eNa1eN1 85.14(11)
O1eNa1eO2 90.07(11)
O2eNa1eO3 117.86(12)
O3eNa1eN1 116.41(13)
O1eNa2eO4 117.02(15)
O1eNa2eO5 110.24(16),
O2eNa2eO1 95.79(12)
O2eNa2eO4 125.98(15).
O2eNa2eO5 114.76(18)
O4eNa2eO5 93.65(18)
K4eO8 2.735(4)
K4eO8A 2.635(14)
K4eO3 2.655(2)
K4eO4 2.667(3)
K5eS8 3.720(1)
K5eO12 2.701(2)
K5eO13 2.620(2)
K5eO17 2.657(3)
K5eN3 2.811(3)
K5eO16 2.797(3)
K5eS10 3.228(1)
K6eO12 2.667(2)
K6eO14 2.551(3)
K6eO18 2.657(4)
K6eO21 2.692(3)
K6eO20 2.857(3)
K6eS10 3.677(1)
K7eS11 3.707(1)
K7eO13 2.680(2)
K7eO15 2.607(2)
K7eO19 2.668(4)
K7eO21 2.671(3)
K7eO20 2.810(3)
K7eS10 3.570(1)
K8eO14 2.650(3)
K8eO15 2.552(3)
K8eN4 2.822(3)
K8eO21 2.692(3)
K8eO20 2.839(3)
K8eS10A 3.617(4)
O1eK1eO5 77.03(8)
O1eK1eS3A 91.03(9).
O1eK1eO11 108.80(8)
O1eK1eN1 78.39(8)
O2eK1eO5 77.48(8)
O2eK1eS3A 87.53(9).
O2eK1eO1 124.83(8)
O2eK1eO11 122.29(8)
O2eK1eN1 75.62(8)
O2eNa2eO4 125.98(15).
O2eNa2eO5 114.76(18)
O4eNa2eO5 93.65(18)
O2eNa2eO1 95.79(12)
O2eNa2eO4 125.98(15).
two equally integrating singlet signals for the methyl hydrogens of
the tert-butyl groups at 1.32 and 1.42. The methylamine hy-
drogens appear as a singlet at 2.60 while for the methylenic hy-
drogens an AB system is observed due to diastereotopic
environment at 3.96 and 4.76 with unresolved couplings (u1/2
34 Hz) (the corresponding signal for the non coordinated ligand
appears at d 3.70 as a sharp singlet). The presence of an AB spin
d
d
system for the methylenic hydrogens can be explained in terms of
the formation upon chelation of a metallacycle ring structure which
generates a diastereotopic environment [16]. Finally for the aro-
matic hydrogens two signals are observed as doublets in the
appropriate region. In the 13C{1H} NMR spectrum the main features
d
a
d
d

C.J. Durango-García et al. / Journal of Molecular Structure 1164 (2018) 248e258
253
Fig. 2. ORTEP drawings of complex 2Na. Non-relevant hydrogen atoms and the labels of the non-relevant carbon atoms have been omitted for clarity. (a): View of the hexagonal
core between two complex moieties. (b): View of the ten-membered ring metallocycle formed upon Na coordination showing a butterfly-like structure in a bent boat-boat
conformation.
Table 3
1H NMR data of complexes 2 M in CDCl3 (400 MHz).
Assignment/Complex
2Na
2Li
2 K
4-tBu
2-tBu
NeCH3
CH2
1.32 (s, 18H)
1.42 (s, 18H)
2.60 (s, 3H)
1.13 (s, 18H)
1.34 (s, 18H)
1.84 (s, 3H)
2.88 (br, 2H)
1.25 (s, 18H)
1.35 (s, 18H)
2.56 (s, 3H)
3.93 (s, 2H)
4.74 (s, 2H)
3.96 (s, br, 2H)
4.76 (s, br, 2H)
0
CH2
4.17 (br, 2H)
4
4
H arom 5
H arom 3
H arom 50
H arom 30
6.81 (d, JHH ¼ 2.2 Hz, 2H)
6.71 (d, 4JHH 2 Hz, 2H)
7.04 (d, 4JHH 2 Hz, 2H)
6.77 (d, JHH 2.8 Hz, 1H)
4
4
7.18 (d, JHH ¼ 2.2 Hz, 2H)
7.13 (d, JHH 2.8 Hz, 1H)
4
7.20 (d, JHH 2.8 Hz, 1H)
4
7.26 (d, JHH 2.8 Hz, 1H)
comprise a sole signal for the methylene carbons at
singlet at 46.8 is assigned to the methylamine carbon. HSQC
1He13C NMR experiments confirm the correlation of the signal at
55.8 in the 13C{1H} dimension with the two methylene hydrogens
at
3.96 and 4.76 in the 1H NMR spectrum. In addition, two signals
for the methyl carbons of the tert-butyl groups at 30.0 and 31.7 are
d
55.8 while a
unresolved couplings (u1/2 34 Hz and u1/2 46 Hz). The latter two
signals correlate with the sole methylene signal at 63.6 in the
d
d
HSQC 1He13C NMR spectrum. It is noteworthy that despite the
similarities in the rest of the spectral signals, the chemical shifts of
the methylene groups in the Li and Na systems are fairly different.
However, this can be explained due to the increased covalence of
the LieO and particularly LieN bonds with respect to their Na
counterparts [28].
d
d
d
present in the 13C{1H} NMR spectrum. The fact that a sole set of
hydrogen and carbon signals is observed is in accordance either
with the preservation of the dimeric structure in CDCl3 solution or
the existence of a fluxional process in which the hydroxyl proton
hops between the two oxygen atoms of the ligand. Indeed, a non-
fluxional monomeric structure would give rise to two sets of car-
bon and hydrogen signals. Unfortunately, due to the low solubility
of the complex in conventional NMR solvents at low temperature,
we were not able to perform variable temperature NMR studies.
However, comparison with the related systems reported in the
literature [2,10,12,27] and the rest of the gathered spectroscopic
evidence, allow us to postulate that in solution a monomeric
structure undergoing dynamic processes prevails (Scheme 2).
Elemental analysis is also in accordance with the formulation but
does not allow to discriminate between a monomeric or dimeric
structure.
3.1.3. Synthesis of potassium-methylamino-N-(2-methylene-4,6-
tert-butylphenol)eN-(2-methylene-4,6-tert-butylphenolate), 2 K
Complex 2K was obtained as a yellow solid in 71% yield after
purification. The 1H NMR spectrum of 2K in CDCl3 solution shows
the signals of the coordinated ligand as singlets at
for the tert-butyl groups; the singlet due to the methylamine hy-
drogens is observed at 2.56 and the two methylene hydrogen
signals are at 3.93 and 4.74. These data are very similar to those of
d 1.25 and 1.35
d
d
complex 2Na. However, in contrast to 2Na where only two signals
for the aromatic hydrogens were observed, in the spectrum of 2K
four aromatic signals are observed as doublets at
and 7.26 with 4JHH 2.8 Hz, each integrating for one hydrogen. In the
13C{1H} NMR spectrum the methylene carbon appears at
53.2 but
d 6.77, 7.13, 7.20
d
the number of signals due to the aromatic carbons have doubled in
comparison to 2Na. We attribute the fact that double number of
aromatic signals in the 1H and 13C NMR spectra of 2K are observed
while the rest of the spectral signals remain very similar to those of
2Na; to a diminished symmetry in 2K caused by a larger more
electropositive Kþ center which engages better than Naþ and Liþ in
a stronger non symmetrical K-Cipso interaction with one of the ipso
carbons bearing the O atom of one of the rings. Although this type
of M-Cipso interactions [2,29,30] are observed in the solid state
structures of all complexes 2M, it is more likely they are preserved
3.1.2. Synthesis of lithium-methylamino-N-(2-methylene-4,6- tert-
butylphenol)eN-(2-methylene-4,6-tert-butylphenolate), 2Li
Comparison of the spectroscopic features of the three 2M
(M ¼ Li, Na, K) complexes prompts us to propose analogue struc-
tures for all three compounds in solution according to the data
given in Tables 3 and 4. Complex 2Li was obtained in 68% yield. In
the 1H NMR spectrum recorded in CDCl3, it shows a singlet signal
for the methylamine hydrogens at
drogens appear as two broad signals at
d
1.84 while the methylene hy-
2.88 and 4.17 with
d

254
C.J. Durango-García et al. / Journal of Molecular Structure 1164 (2018) 248e258
Scheme 2. The proposed structures of complexes 2M in CDCl3 solution.
3.2.1. Synthesis of lithium-methylamino-N,N0-bis(2-methylene-4,6-
di-tert-butylphenolate)-tris(tetrahydrofuran), 3Li
Table 4
13C{1H} NMR data of complexes 2M in CDCl3 (100.61 MHz) (ND ¼ not determined).
The yellow solid was isolated in 75% yield and crystals suitable
for SC-XRD analysis were grown from concentrated THF solutions.
Details of the crystal refinement and other relevant crystallo-
graphic information are given in the ESI. The molecular structure at
173 K demonstrates that effectively Li coordination has taken place
(Fig. 3). It comprises two lithium atoms per ligand moiety. Each
lithium center is bonded to two oxygen atoms of the ligand. One of
them, Li1, possesses a single THF molecule coordinated while Li2
has two THF molecules completing its coordination sphere. The Li1
atom is also bonded to the N atom of the ligand with a LieN bond
distance of 2.080(9) Ǻ. This value is within the expected range of
covalent interactions [24,31]. Furthermore, it is remarkably similar
Assignment/Complex
2Li
2Na
2 K
CH3
CH3
CeCH3
CeCH3
NeCH3
CH2
C arom
C arom
C arom
C arom
C arom
C arom
C arom
C arom
C arom
C arom
C arom
C arom
29.8
32.1
34.0
35.4
39.6
63.6
121.0
123.2
125.2
133.1
137.3
140.9
30.0
31.8
ND
29.9
31.9
34.5
35.2
40.1
53.2
116.0
118.9
122.0
122.1
123.2
123.7
125.1
136.6
142.2
148.2
150.3
ND
ND
46.8
55.8
126.5
127.3
128.4
129.2
141.0
ND
to those reported by Kerton for
a tetralithium diamine-
bisphenolate complex derived of imidazolidine (compare 2.096(4)
and 2.095(4) Å) [19,20]. In complex 3Li, ligand coordination to the
two metals gives rise to the formation of two ring metallacycles. A
central four-membered Li1eO1eLi2eO2 parallelogram is formed
with only slight deviations from the plane (torsion angle ꢀ2.7(6)ꢁ,
plane deviation ꢂ 0.02 Å). The presence of rhombic Li2O2 units is
relatively well known in Li chemistry [19,20,24,32]. It has also been
observed in Na [4,33] and K [2] systems. The geometry around each
lithium center can be described as distorted tetrahedral. Around Li2
the angles are between 97.4(4)ꢁ and 123.5(5)ꢁ, while they are be-
tween 96.5(4)ꢁ and 129.2(4)ꢁ around Li1. A closer look around Li1
reveals relatively close bond lengths with the ipso carbons C15 and
C1 of the ligand backbone at 2.589(9) and 2.663(9) Å respectively,
which are significantly longer than the sum of covalent radii Li-Csp2
at 2.01 (9) Ǻ [25,34], but much shorter than the Van der Waals radii
in solution and are stronger for the more electropositive 2K than in
its lighter analogues. The elemental analysis are in agreement with
the proposed formulation but again do not allow to discern be-
tween the nuclearity of the species. The discussion on M-Cipso in-
teractions will be continued below.
3.2. Synthesis of metal-methylamino-N,N0-bis(2-methylene-4,6-di-
tert-butylphenolate) complexes 3Li, 3Na and 3 K
3.45e3.5 Å [35]. A situation indicative of weak strength
p in-
teractions in the solid state. The analysis of the structure shows the
aromatic rings orient the ipso carbons (C1 or C15) towards the
metal. This type of metal interaction with the ligand ipso carbons
are also observed in Na [12] and K systems [2,29,30].
Regarding the coordination of ligand 1 to Li1 once again one
could state two fused six-membered rings in a boat-boat confor-
mation are generated (Fig. 3). The dihedral angle between the
planes defined by N1eLi1eC30eC15 and N1eLi1eC29eC1 is 37.8ꢁ.
On the other hand, the solid state structure appears to be pre-
served in solution accompanied by a dynamic process. Indeed,
crystals of 3Li were dissolved in CDCl3 and the NMR spectra ac-
quired. In the 1H NMR spectrum one observes the singlets for the
Amounts corresponding to two molar equivalents of finely cut
metal (Li or Na) and 1 were refluxed in THF or in DMSO (K) in a
Schlenk flask under argon. Carrying out the reaction of compound 1
with 2 equiv. of K in THF resulted in a mixture of products, thus we
resorted to use DMSO as solvent. After work-up the formation of
the new compounds 3M (M ¼ Li, 3Li; M ¼ Na, 3Na; M ¼ K, 3K;
Scheme 3); was first envisaged by the disappearance of the hy-
droxyl nOH band in the infrared spectra of the products. Elemental
analysis as well as SC-XRD analysis of all three compounds proved
their formulations are consistent with replacement of the two hy-
drogens of the hydroxyl groups by the corresponding metal atoms
(Scheme 3).

C.J. Durango-García et al. / Journal of Molecular Structure 1164 (2018) 248e258
255
Scheme 3. The synthesis of compounds 3M (M ¼ Li, Na, K) from proligand 1.
tert-butyl hydrogens at
amine protons at
d
1.18 and 1.42, the signal for the methyl-
d
1.95, two doublets for the methylene hydrogens
4.11 and two doublets for the aromatic hydrogens at
6.80 and 7.10. The most important feature is the fact that an AB
d
2.73 and d
d
spin system is again observed for the methylene hydrogens with a
resolved 2JHH of 11.6 Hz (Table 5). On the other hand, in the 13C{1H}
NMR spectrum, six aromatic signals are observed between 166.2 <
d
< 123.0 while only one signal at
In addition, the methylamine carbon is observed at
tert-butyl carbons in the range 36.1 < < 30.5 (Table 6). It is note-
2.73 and 4.11 correlate with the
d
65.1 for the methylene carbon.
d
40.4 and the
d
worthy that the two hydrogens at
d
Table 6
13C{1H} NMR data of complexes 3M in CDCl3 (3Li, 3Na) or in DMSO-d6 (3K) (ND ¼
not determined).
Assignment/Complex
3Li
3Na
3 K
CH3
CH3
30.5
32.7
34.5
36.1
40.4
65.1
123.0
125.6
127.3
132.3
136.9
166.2
29.4
31.4
ND
ND
40.1
68.2
122.0
126.5
127.3
138.6
141.0
142.2
29.8
32.0
33.4
34.7
40.5
59.2
120.6
134.4
ND
CeCH3
CeCH3
NeCH3
CH2
C arom
C arom
C arom
C arom
C arom
C arom
Fig. 3. ORTEP drawing of complex 3Li.3THF. Hydrogen atoms have been omitted for
clarity as have the labels of the carbon atoms. Li1eN1 bond distance is 2.080(9) Å.
Other selected bond lengths and angles are given in Table 2.
ND
ND
ND
Table 5
1H NMR data of complexes 3M in CDCl3 (400 MHz).
Assignment/Complex
3Na
3Li
3 K
4-tBu
2-tBu
NeCH3
CH2
CH2
H arom 5
H arom 3
1.29 (s, 18H)
1.42 (s, 18H)
2.65 (s, 3H)
1.18 (s, 18H)
1.42 (s, 18H)
1.95 (s, 3H)
1.18 (s, 18H)
1.34 (s, 18H)
3.91 (s, 3H)
2.08 (s, 2H)
3.49 (s, 2H)
6.72 (s, 2H)
6.86 (s, 2H)
3.96 (s, br, 2H)
4.78 (s, br, 2H)
2.73 (d, J ¼ 11.6 Hz, 2H)
0
4.11 (d, J ¼ 11.6 Hz, 2H)
4
4
7.16 (d, JHH ¼ 2.2 Hz, 2H)
6.80 (d, JHH ¼ 2.2 Hz, 2H)
4
4
7.38 (d, JHH ¼ 2.2 Hz, 2H)
7.10 (d, JHH ¼ 2.2 Hz, 2H)

256
C.J. Durango-García et al. / Journal of Molecular Structure 1164 (2018) 248e258
sole methylene carbon in the HSQC 1He13C NMR spectrum, in
agreement with the formation of a symmetric metallaycle ring
which restricts rotation of the now diastereotopic methylene
hydrogens.
complex 3Li, in which two signals are found for the methylene
groups and two singlets for aromatic hydrogens. In this case
however, the methylene signals are broad at
d 3.96 and 4.78 with
unresolved couplings unlike its Li analogue. Moreover, the chemical
shifts are quite different from those of complex 3Li (Table 3). In the
13C{1H} NMR spectrum, the methylene carbon appears as a singlet
In the 7Li NMR spectrum recorded in CDCl3 one observes two
signals in a very similar integration ratio at
d
0.6 and ꢀ0.2 (ESI), in
line with the two different chemical environments around the Li
nuclei.
at
two broad signals at
d
68.2 which correlates in the HSQC 1He13C spectrum with the
d
3.96 and 4.78 in the 1H NMR spectrum.
3.2.2. Synthesis of sodium-methylamino-N,N0-bis(2-methylene-4,6-
di-tert-butylphenolate)-tris(tetrahydrofuran), 3Na
3.2.3. Synthesis of tetrapotassium-bis[methylamino-N,N'-bis(2-
methylene-4,6-di-tert-butylphenolate)], 3 K
Attempts at the synthesis of the analogous K derivative of 3Li
and 3Na in THF resulted in a mixture of products which in our
hands proved impossible to separate. However, carrying out the
reaction in DMSO as solvent resulted after 8 h of reflux in the full
consumption of the metal and formation of an insoluble solid. The
solid was recrystallized from a concentrated DMSO solution (yield
70%) from which crystals suitable for an SC-XRD study were ob-
tained. Details of the crystal refinement and other relevant crys-
tallographic information are given in Table 1 and the molecular
structure is shown in Fig. 5. It is observed that two potassium atoms
are coordinated to each ligand fragment but with important dif-
ferences with respect to 3Li and 3Na. In the first place, the structure
shows a higher aggregation consisting of four potassium atoms and
two ligand moieties. As in 3Li and 3Na, two of the four potassium
atoms exhibit bonding interactions with the N atoms of the ligands
at K1eN1 2.825(3) Å and K4eN2 2.874(3) Å also generating a
butterfly-like structure around K1 and K4. These values appear to
be close to the bond lengths range 2.844(3)-2.876(3) Å reported by
Kozak for potassium aminophenolates [36]. Between two of these
structures, a central coplanar four-membered K2O4 parallelogram is
formed, the oxygens stemming from the DMSO solvent and not
from the ligand. Each potassium atom of the central core is bonded
in almost trans disposition to two oxygen atoms, one from each of
the ligands. It is the formation of these bonds that effect the ag-
gregation of two molecules in the solid state. Fairly close contact
distances K-Cipso (bearing the O atoms) are also observed, for
example K1eC1 accounts for 3.123(3) Å indicating a relatively
important interaction comparable to those observed in related
systems [2,29,30,37]. Overall, there are seven molecules of DMSO
coordinated to the four K centers either in a terminal or bridged
fashion. By SC-RXC, Kozak also found seven molecules of THF co-
ordinated to the tetra-potassium compound derived of the related
ligand amino-bisphenolate with a benzyl substituent on the N atom
[36].
A light green solid was obtained in moderate yield after purifi-
cation (54%). Crystals suitable for SC-XRD analysis were grown from
a hexane layered THF solution. Details of the crystal refinement and
other relevant crystallographic information are given in Tables 1
and 2 Fig. 4 shows the molecular structure collected at 173 K. The
structure is very similar to that obtained for complex 3Li, namely
two sodium atoms are coordinated to a modified ligand 1. Once
again, a four membered metallacycle ring O1eNa1eO2eNa2 is
formed. The distorted tetrahedral coordination of Na2 is charac-
terized by angles between 95.79ꢁ and 125.98ꢁ. The central Na1
atom exhibits a 2.417(3) Ǻ bond distance to N1, considerably
shorter than the corresponding in complex 2Na at 2.587(4) Ǻ and
closer to the sum of covalent radii at 2.37(10) Ǻ [25,30]. On the
contrary, the bond lengths of Na1 to the oxygen atoms of the ligand
are 2.274(3) Ǻ and 2.283(3) Ǻ, significantly longer than those of Na2
to the same oxygen atoms (2.150(3) and 2.197(3) Ǻ). The shortest
Na1 to ipso carbon bond distances Na1eC15 2.746 Å and Na1eC1
2.835 Å are also indicative of weak
p NaeC interactions.
As in complex 3Li, the coordination around Na1 generates two
fused heterocycles in a boat-boat conformation and a dihedral
angle between the planes defined by C30eN1eNa1eC15 and
C29eN1eNa1eC1 of 39.7ꢁ, fairly similar to that in 3Li.
Crystals of 3Na were dissolved in CDCl3 and their solution NMR
spectra acquired. The spectra are qualitatively similar to those of
Crystals of 3K were dissolved in DMSO-d6 and analyzed by NMR
spectroscopy in solution. Complex 3K was insoluble in CDCl3.
Despite the different solvent media, the features are very similar to
those described for complex 3Na, namely two signals for the tert-
butyl groups at
two broad methylene signals at
hydrogens at 6.72 and 6.86 as singlets (Tables 4 and 5). The
methylene carbon appears at
59.2 in the 13C NMR spectrum. We
d
1.18 and 1.34, one for the methylamine at
d 3.91,
d
2.08 and 3.49 and two aromatic
d
d
propose these data are in agreement with the equation proposed in
Scheme 4, in which the solid state tetrameric structure is lost giving
rise in DMSO-d6 to a structure analogue to that of complexes 3Li
and 3Na, in which only two K centers are included.
4. Conclusions
Six new alkali metal complexes derived of aminobisphenolate
compound 1 were synthesized from the bulk metals Li, Na and K in
THF or DMSO in moderate to good yields. Step-wise substitution of
one or two of the hydroxyl hydrogens of the ligand was effected by
simple variation of the stoichiometry employed for the reaction.
Fig. 4. ORTEP drawing of complex 3Na.3THF. Hydrogen atoms have been omitted for
clarity as have the labels of the carbon atoms. The Na1eN1 distance is 2.417(3) Ǻ. Other
selected bond lengths and angles are given in Table 2.

C.J. Durango-García et al. / Journal of Molecular Structure 1164 (2018) 248e258
257
Fig. 5. ORTEP drawings of complex 3K.7DMSO. (a): View including only two coordinated DMSO molecules forming the central K2O2 unit. (b): View of the central eight-membered
metallacycle including the four K atoms. Hydrogen atoms are omitted for clarity as have been the labels of the carbon atoms.
Scheme 4. The proposed structures of compound 3K in the solid state and in solution.
The solid state structure of the complex derived from one equiva-
lent of Na, 2Na, exhibits a dimeric structure generated upon for-
mation of intermolecular hydrogen bonds. Although some
precedents of hydrogen bonding effecting dimerization of alkali
metal complexes exist in the literature, this situation remains rare
and to our knowledge it had not previously been observed from
stoichiometric control but upon partial hydrolysis of doubly
deprotonated aminobisphenolates [24] or from inclusion of benzyl
alcohol in system [5].
resulting ten-membered ring, a common feature in the present
systems. Further experimentation is necessary in order to establish
unequivocally the solution state structures.
Declaration
The authors declare no competing financial interest.
Acknowledgments
The reaction with two metal equivalents yields bimetallic
monomeric structures in the solid state for the Li and Na de-
rivatives, 3Li and 3Na, in THF. One of the metals forms a butterfly-
like structure in a boat-boat conformation upon coordination to N
and the two O atoms of the ligand while the second metal atom
adopts a tetrahedral geometry forming part of a LieOeLieO
rhombic unit, a relatively common motif in the chemistry of group
We thank CONACYT for financial support through project CB-
242818.
Appendix A. Supplementary data
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.molstruc.2018.03.079.
1 metals [7]. Weak
p interactions with the ipso carbons bearing the
O atoms of the ligands are also observed. In contrast, the K deriv-
ative synthesized in DMSO presents a more complex structure in
the solid state which can be described as comprising two molecules
bridged by O atoms of the ligand and the coordinated solvent, yet
the butterfly-like boat-boat conformation is also observed in the
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