Zebra reaction or the recipe for the synthesis of heterodimeric zinc complexes

Article abstract of DOI:10.1039/c5dt03883a

A series of asymmetric heterodimeric zinc complexes have been synthesized in a direct reaction between conformationally flexible chiral/achiral homodimers. The cooperative activity of steric factors and coordination codes resulted in an intriguing chiral self-sorting process. Herein, we are reporting our recent exploration of the first example of such a type of reaction.

Full text of DOI:10.1039/c5dt03883a

Dalton
Transactions
View Article Online
View Journal
PAPER
Zebra reaction or the recipe for the synthesis
of heterodimeric zinc complexes†
Cite this: DOI: 10.1039/c5dt03883a
D. Jędrzkiewicz, J. Ejfler,* Ł. John and S. Szafert
Received 5th October 2015,
Accepted 13th November 2015
A series of asymmetric heterodimeric zinc complexes have been synthesized in a direct reaction between
conformationally flexible chiral/achiral homodimers. The cooperative activity of steric factors and coordi-
nation codes resulted in an intriguing chiral self-sorting process. Herein, we are reporting our recent
exploration of the first example of such a type of reaction.
DOI: 10.1039/c5dt03883a
www.rsc.org/dalton
centers bearing different ancillary ligands is possible in one
pot, by means of a simple and efficient procedure with the
Introduction
Zinc complexes with functionalized monoanionic chelating application of the classical zinc aminophenolates.
amino/imino-phenols, i.e. Schiff-base type ligands, have found
widespread applications in coordination chemistry, biological
systems and catalysis.1 The structural motif of the coordinat-
ing ligand for the selected application requires a confor-
Experimental
General materials, methods and procedures
mationally rigid ligand framework, employed for the
All reactions and operations were performed under an inert
atmosphere of N2, while using a glove-box (MBraun) or stan-
dard Schlenk techniques. Reagents were purified using stan-
dard methods: toluene, distilled from Na; hexanes, distilled
from Na; methanol, distilled from Mg; C6D6, distilled from
CaH2. ZnEt2 (1.0 M solution in hexanes), N-α-dimethyl-
benzylamine, N-methylcyclohexylamine, N-dimethylamine (2 M
solution in MeOH), formaldehyde (37% solution in H2O), and
4-tert-butylphenol were purchased from Aldrich and used as
stabilization of the metal center, or on the contrary, flexibility
of the ligand is the priority to achieve the desired molecular
architecture for the metal complexes of an interesting reaction.
Therefore, the precise design of ligands with optimal confor-
mational freedom is of course the first stage of the planned
synthetic strategy but unfortunately sometimes undoable in
practice. Instead, unplanned and unexpected reactivity of even
tedious, well-known complexes could constitute a valuable
support for sophisticated synthesis.
Well-defined alkyl zinc complexes with N, O-donor ligands
confirmed by X-ray analysis are known and usually present
monomeric or dimeric structures.2,3 Recently, we have explored
the combination of functionalized aminophenol ligands with
ZnEt2 for the targeted synthesis of homodimeric complexes.
The experimental data as well as the theoretical DFT calcu-
lations indicate that aminophenolate ligands with a free ortho-
position of the phenol ring prefer the formation of dimeric
alkyl zinc complexes, irrespective of the substrates’ molar
ratio.4a
1
received. H and 13C NMR spectra were collected at the temp-
erature range from 233 to 333 K, while using Bruker ESP 300E
or 500 MHz spectrometers. Chemical shifts are reported in
parts per million and referenced to residual protons in deuter-
ated solvents.
Syntheses
N-[Methyl(2-hydroxy-5-tert-butylphenyl)]-N-methyl-N-(1-phe-
nylethyl)amine (LR-H). To a solution of 1.13 g (7.52 mmol) of
4-tert-butylphenol and 1.10 mL (7.52 mmol) of (R)-(+)-N-α-di-
methylbenzylamine in MeOH (50 mL), 0.80 mL (10.64 mmol)
of formaldehyde (37% solution in H2O) was added. The solu-
tion was stirred and heated under reflux for 24 h until a crude
product precipitated as a white solid. It was collected by fil-
tration, washed with cold methanol and dried in vacuo to give
LR-H. Yield 86% (1.92 g, 6.47 mmol).
Here we are reporting a new type of substrate for the new
synthetic strategy tailored for the acquisition of heterodimeric
zinc complexes. The synthesis of zinc dimers containing metal
Department of Chemistry, University of Wrocław, 14 F. Joliot-Curie, 50-383 Wrocław,
Poland. E-mail: jolanta.ejfler@chem.uni.wroc.pl; Tel: +48 (71) 375 7310
Anal. Calcd (Found) for C20H27NO: C, 80.76 (80.53); H, 9.15
(9.45); N, 4.71 (4.63)%; ESI/MS: 298.2 [M + 1]+; 1H NMR
(500 MHz, CDCl3, RT): δ = 11.18 (br, s, 1H, OH), 7.39–7.27 (m,
†Electronic supplementary information (ESI) available: 1H, 13C, NOESY spectra,
X-ray experimental data and refinement, DFT and DOSY calculations. CCDC
1046690, 1427070, 1046689, 1427071 and 1434203. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c5dt03883a
ArH, 5H), 7.16 (dd, JHH = 8.4, 2.5 Hz, 1H, ArH), 6.92 (d, JHH
=
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
2.4 Hz, 1H, ArH), 6.75 (d, JHH = 8.4 Hz, 1H, ArH), 3.85–3.56 (m, CH3-CH2); 13C NMR (75 MHz, C6D6, RT): δ = 161.5 (ArC-OH,
2H, N-CH2-Ar), 3.79 (q, JHH = 6.9 Hz, 1H, N-CH-Ar), 2.22 (s, 3H, , 2C), 161.3 (ArC-OH, 1C), 161.2 (ArC-OH, 1C), 140.6
N-CH3), 1.51 (d, JHH = 6.9, 3H, CH3-CH), 1.26 (s, 9H, C(CH3)3); (ArC-CH2, 4C), 139.1 (ArC-CH, 1C), 136.8 ( , 1C), 136.5
13C NMR (75 MHz, CDCl3, RT): δ = 155.7 (ArC-OH, 1C), 141.8 (ArC-CH, 1C), (ArC-CH, 1C), 130.6 (ArCH, 2C), 130.5 (ArCH,
(ArC-C, 1C), 140.8 (ArC-CH, 1C), 128.6 (ArCH, 2C), 128.2
(ArCH, 2C), 127.7 (ArCH, 1C), 125.4 (ArCH, 1C), 125.3 (ArCH, ArCH,
, 4C), 130.1 (ArCH, 2C), 128.8 (ArCH, 1C), 128.7 (ArCH,
, 3C), 128.5 (ArCH, ArCH, ArCH, , 12C), 127.3
1C), 121.2 (ArC-CH2, 1C), 115.4 (ArCH, 1C), 62.8 (N-CH-Ar, 1C), (ArCH, 4C), 125.1 (ArC-CH2, 1C), 125.0 (ArC-CH2, 1C), 124.6
58.6 (N-CH2-Ar, 1C), 37.4 (N-CH3, 1C), 34.1 (C(CH3)3, 1C), 31.7 (ArC-CH2, 1C), 123.1 ( , 1C), 120.2 (ArCH, , 2C),
119.9 (ArCH, ArCH, 2C), 65.1 (N-CH-Ar, 1C), 64.2 (N-CH-Ar, 1C),
(C(CH3)3, 3C), 17.5 (CH3-CH, 1C).
LS-H. This compound was prepared in the same manner as 64.1 (N-CH-Ar, 1C), 62.4 (
, 1C), 61.7 (N-CH2-Ar, 1C),
, 1C), 58.1 (N-CH2-Ar, 1C),
, 1C), 35.1 (N-CH3, 1C), 1C), 34.8
, 2C), 33.9 (C(CH3)3,
described above for LR-H but (S)-(−)-N-α-dimethylbenzylamine 61.3 (N-CH2-Ar, 1C), 60.7 (
instead of (R)-(+)-N-α-dimethylbenzylamine was used.
38.8 (N-CH3, 1C), 36.3 (
N-[Methyl(2-hydroxy-5-tert-butylphenyl)]-N-dimethylamine (N-CH3, 1C), 34.0 (C(CH3)3,
(LMe-H). To a solution of 1.50 g (10.00 mmol) of 4-tert-butyl- C(CH3)3, 2C), 31.9 (C(CH3)3,
, 31.8 (C(CH3)3, C(CH3)3,
phenol in MeOH (50 mL), dimethylamine (2 M solution in 6C), 20.2 (CH3-CH-N, CH3-CH-N,
MeOH, 10.00 mmol) and then 1.10 mL (14.63 mmol) of for- CH-N, 1C), 13.6 (CH3-CH2, 1C) 13.5 (CH3-CH2, 1C) 13.4
maldehyde (37% solution in H2O) were added. The solution , 1C) 13.3 (CH3-CH2, 1C), 0.7 ( , 1C), −1.2
was stirred and heated under reflux for 24 h until a crude (CH3-CH2, 1C) −1.6 (CH3-CH2, 1C), −1.7 (CH3-CH2, 1C).
, 3C), 15.3 (CH3-
(
product precipitated as a white solid. It was collected by fil-
[SS-Zn]. This compound was prepared in the same manner
tration, washed with cold methanol and dried in vacuo to give as described above for [RR-Zn] but LS-H instead of LR-H was
LMe-H. Yield 91% (1.89 g, 9.10 mmol). Anal. Calcd (Found) for used.
C13H21NO: C, 75.32 (75.12); H, 10.21 (10.65); N, 6.76 (6.82)%;
[RS-Zn]. [RR-Zn] (0.78 g, 1.00 mmol) and [SS-Zn] (0.78 g,
ESI/MS: 208.2 [M + 1]+; 1H NMR (500 MHz, CDCl3, RT): δ = 1.00 mmol) were dissolved in toluene (20 mL) at room tem-
10.57 (br, s, 1H, OH), 7.20 (dd, JHH = 8.5, 2.5 Hz, 1H, ArH), perature. The solution was stirred and concentrated in vacuo,
6.97 (d, JHH = 2.4 Hz, 1H, ArH), 6.78 (d, JHH = 8.4 Hz, 1H, ArH), then put at −15 °C. After 24 h, the product [RS-Zn] was
3.64 (s, 2H, N-CH2-Ar), 2.33 (s, 6H, N-CH3), 1.30 (s, 9H, obtained as colourless crystals in 87% yield (1.36 g,
C(CH3)3); 13C NMR (75 MHz, CDCl3, RT): δ = 155.7 (ArC-OH, 1.74 mmol). Anal. Calcd (Found) for C44H62N2O2Zn2: C, 67.60
1C), 141.7 (ArC-C, 1C), 125.5 (ArCH, 1C), 125.2 (ArCH, 1C), (67.53); H, 7.99 (8.03); N, 3.58 (3.55)%; 1H NMR (500 MHz,
121.3 (ArC-CH2, 1C), 115.5 (ArCH, 1C), 63.5 (N-CH2-Ar, 1C), C6D6, RT): δ = 7.30 (dd, JHH = 8.4, 2.6 Hz, 2H, ArH), 7.25–7.10
44.7 (N-CH3, 2C), 34.1 (C(CH3)3, 1C), 31.7 (C(CH3)3, 3C).
(m, 10H, ArH), 7.07 (d, JHH = 8.4 Hz, 2H, ArH), 6.87 (d, JHH =
[RR-Zn]. To a solution of LR-H (0.59 g, 2.00 mmol) in 2.5 Hz, 2H, ArH), 5.06 (q, JHH = 7.0 Hz, 2H, N-CH-Ar), 4.86 (d,
hexanes (50 mL), ZnEt2 (2 mL, 2.00 mmol) was added drop- JHH = 12.0 Hz, 2H, N-CH2-Ar), 3.12 (d, JHH = 12.0 Hz, 2H,
wise at room temperature. The solution was stirred until a N-CH2-Ar), 1.99 (s, 6H, N-CH3), 1.68 (d, JHH = 7.0, 6H, CH3-
white solid precipitated. It was filtered off, washed with CH), 1.48 (t, JHH = 8.1 Hz, 6H, CH2-CH3), 1.15 (s, 18H,
hexanes (10 mL) and dried in vacuo. The product was recrystal- C(CH3)3), 0.47 (q, JHH = 8.1 Hz, 4H, CH2-CH3); 13C NMR
lized from toluene at −15 °C to give a crystalline colourless (75 MHz, C6D6, RT): δ = 161.5 (ArC-C, 2C), 140.7 (ArC-C, 2C),
solid. Yield 77% (0.60 g, 0.77 mmol). Anal. Calcd (Found) for 136.3 (ArC-CH, 2C), 130.6 (ArCH, 4C), 128.6 (ArCH, 8C), 128.4
C44H62N2O2Zn2: C, 67.60 (67.49); H, 7.99 (8.06); N, 3.58 (ArCH, 2C), 124.9 (ArC-CH2, 2C), 119.9 (ArCH, 2C), 64.6
1
(3.56)%; H NMR (500 MHz, C6D6, RT): δ = 7.49 (d, JHH = 7.4 (N-CH-Ar, 2C), 61.5 (N-CH2-Ar, 2C), 35.1 (N-CH3, 2C), 33.9
Hz, 2H, ArH,
ArH), 7.27–7.11 (m, 10H, ArH), 7.12 (s, 2H, ArH, ArH), 7.08 (d, (CH2-CH3, 2C), −1.5 (CH2-CH3, 2C).
JHH = 7.6 Hz, 1H, ArH), 7.04 (d, JHH = 8.5 Hz, 1H, ArH), 6.96 (s, [Cy-Zn]. This compound was prepared based on a pre-
2H, ArH,
), 6.86 (s, 2H, ArH, ArH), 5.08 (q, JHH = 6.9, 1H, viously published procedure.4a
N-CH-Ar), 4.94 (s, 1H, N-CH-Ar), 4.84 (d, JHH = 11.8 Hz, 1H, [RCy-Zn]. [RR-Zn] (0.78 g, 1.00 mmol) and [Cy-Zn] (0.74 g,
N-CH2-Ar), 4.80 (d, JHH = 10.1 Hz, 2H, N-CH2-Ar, N-CH2-Ar), 1.00 mmol) were dissolved in toluene (20 mL) at room tem-
4.49 (q, JHH = 6.8 Hz, 1H, N-CH-Ar), 3.95 (s, 2H, perature. The solution was stirred and concentrated in vacuo,
), 3.58 (s, 1H, ), 3.29 (d, JHH = 11.8 Hz, 1H, then put at −15 °C. After 24 h, the product [CyR-Zn] was
N-CH2-Ar), 3.09 (d, JHH = 11.8 Hz, 2H, N-CH2-Ar, N-CH2-Ar), obtained as a white crystalline powder in 91% yield (1.38 g,
), 7.33 (s, 1H, ArH), 7.31 (d, JHH = 8.8 Hz, 1H, (C(CH3)3, 2C), 31.8 (C(CH3)3, 6C), 20.0 (CH3-CH, 2C), 13.6
,
2.61 (s, 3H,
), 2.02 (s, 3H, N-CH3), 1.99 (s, 3H, N-CH3), 1.82 mmol). Anal. Calcd (Found) for C42H64N2O2Zn2: C, 66.40
1.92 (s, 3H, N-CH3), 1.75 (d, JHH = 7.5, 3H, CH3-CH), 1.68 (d, (66.33); H, 8.49 (8.89); N, 3.69 (3.85)%; 1H NMR (500 MHz,
JHH = 7.5, 3H, CH3-CH), 1.66 (d, JHH = 7.5, 3H, CH3-CH), 1.54 C6D6, RT): δ = 7.35 (dd, JHH = 8.3, 2.8 Hz, 1H, ArH), 7.33 (dd,
(t, JHH = 8.1, 3H,
3H, CH3-CH2), 1.31 (t, JHH = 8.1, 3H, CH3-CH2), 1.29 (s, 21H, JHH = 2.7 Hz, 1H, ArH), 7.10 (d, JHH = 8.4 Hz, 1H, ArH), 7.07 (d,
C(CH3)3), CH3-CH2), 1.17 (s, 9H, C(CH3)3), 1.16 (s, 9H, JHH = 8.4 Hz, 1H, ArH), 6.84 (d, JHH = 2.5 Hz, 1H, ArH), 5.07 (q,
C(CH3)3), 0.65–0.57 (m, 2H, ), 0.41 (q, JHH = 8.0, 2H, JHH = 7.0 Hz, 1H, N-CH-Ar), 4.82 (d, JHH = 11.9 Hz, 1H, N-CH2-
CH3-CH2), 0.35 (q, JHH = 8.1, 2H, CH3-CH2), 0.32–0.14 (m, 2H, Ar), 4.61 (d, JHH = 12.2 Hz, 1H, N-CH2-Ar), 3.37 (d, JHH = 12.0 Hz,
), 1.46 (s,
), 1.38 (t, JHH = 8.1, JHH = 8.4, 2.8 Hz, 1H, ArH), 7.24–7.12 (m, 5H, ArH), 7.12 (d,
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
1H, N-CH2-Ar), 3.31–3.23 (m, 1H, N-CH), 3.08 (d, JHH = 12.0 Hz, (ArCH, 1C), 127.5 (ArCH, 1C), 127.3 (ArCH, 1C), 125.2
1H, N-CH2-Ar), 2.26–0.86 (m, 10H, CH2), 1.96 (s, 3H, (ArC-CH2, 1C), 124.5 (ArC-CH2, 1C), 120.3 (ArCH, 2C), 119.8
N-CH3), 1.88 (s, 3H, N-CH3), 1.67 (d, JHH = 7.1, 3H, CH3-CH), (ArCH, 1C), 64.6 (N-CH-Ar, 1C), 63.6 (N-CH2-Ar, 1C), 61.7
1.43 (t, JHH = 8.1 Hz, 3H, CH2-CH3), 1.38 (t, JHH = 8.1 Hz, 3H, (N-CH2-Ar, 1C), 46.9 (N-CH3, 1C), 44.3 (N-CH3, 1C), 35.5
CH2-CH3), 1.36 (s, 9H, C(CH3)3), 1.14 (s, 9H, C(CH3)3), (N-CH3, 1C), 34.1 (C(CH3)3, 1C), 33.9 (C(CH3)3, 1C), 32.0
0.44–0.34 (m, 4H, CH2-CH3, CH2-CH3); 13C NMR (75 MHz, (C(CH3)3, 3C), 31.8 (C(CH3)3, 3C), 19.9 (CH3-CH, 1C), 13.8
C6D6, RT): δ = 161.6 (ArC-OH, 1C), 161.5 (ArC-OH, 1C), 140.5 (CH2-CH3, 1C), 13.3 (CH2-CH3, 1C), −1.7 (CH2-CH3, 1C), −3.6
(ArC-C, 1C), 140.4 (ArC-C, 1C), 136.3 (ArC-CH, 1C), 130.6 (CH2-CH3, 1C).
(ArCH, 2C), 128.7 (ArCH, 1C), 128.5 (ArCH, 4C), 127.5 (ArCH,
1C), 127.3 (ArCH, 1C), 125.1 (ArC-CH2, 1C), 124.9 (ArC-CH2,
Details of X-ray data collection and reduction
1C), 120.0 (ArCH, 2C), 119.9 (ArCH, 1C), 64.6 (N-CH-Ar, 1C),
64.3 (N-CH, 1C), 61.5 (N-CH2-Ar, 1C), 59.7 (N-CH2-Ar, 1C), 36.0
(N-CH3, 1C), 34.9 (N-CH3, 1C), 34.1 (C(CH3)3, 1C), 33.9
(C(CH3)3, 1C), 32.0 (C(CH3)3, 3C), 31.8 (C(CH3)3, 3C), 26.8
(CH2, 2C), 26.4 (CH2, 2C), 25.9 (CH2, 1C), 20.0 (CH3-CH, 1C),
13.7 (CH2-CH3, 1C), 13.4 (CH2-CH3, 1C), −1.3 (CH2-CH3, 1C),
−1.6 (CH2-CH3, 1C).
X-ray diffraction data for a suitable crystal of each sample were
collected using a KUMA KM4 CCD Saphire or Xcalibur CCD
Onyx (see ESI†) with the ω scan technique at 100 K. The data
collection and processing utilized the CrysAlis suite of pro-
grams.5 Space groups were determined based on systematic
absences and intensity statistics. Lorentz polarization correc-
tions were applied. The structures were solved using direct
methods and refined by full-matrix least-squares on F2. All cal-
culations were performed using the SHELXTL-2013 suite of
programs.6 All non-hydrogen atoms were refined with anisotro-
pic displacement parameters. Hydrogen atom positions were
calculated with geometry and not allowed to vary. Thermal
ellipsoid plots were prepared with 30% of probability displace-
ments for non-hydrogen atoms, using the Mercury 3.1
program.7 All data have been deposited with the Cambridge
Crystallographic Data Centre, CCDC: 1046690 for RR-Zn,
1427070 for SS-Zn, 1046689 for RS-Zn, 1427071 for RCy-Zn,
and 1434203 for SMe-Zn.
[Me-Zn]. To a solution of LMe-H (0.41 g, 2.00 mmol) in
hexanes (50 mL), ZnEt2 (2 mL, 2.00 mmol) was added drop-
wise at room temperature. The solution was stirred until a
white solid precipitated. It was filtered off, washed with
hexanes (10 mL) and dried in vacuo. The product was recrystal-
lized from toluene at −15 °C to give a crystalline colourless
solid. Yield 83% (0.50 g, 0.83 mmol). Anal. Calcd (Found) for
C30H50N2O2Zn2: C, 59.90 (59.48); H, 8.38 (8.65); N, 4.66
1
(4.61)%; H NMR (500 MHz, C6D6, RT) δ = 7.34 (dd, JHH = 8.4,
26 Hz, 2H, ArH), 7.01 (d, JHH = 8.3 Hz, 2H, ArH), 7.01 (d, JHH
=
2.6 Hz, 2H, ArH), 4.44 (d, JHH = 11.9 Hz, 2H, N-CH2-Ar), 2.70
(d, JHH = 12.0 Hz, 1H, N-CH2-Ar), 2.38 (s, 6H, N-CH3), 1.79 (s,
6H, N-CH3), 1.33 (s, 18H, C(CH3)3), 1.26 (t, JHH = 8.1 Hz, 6H,
CH2-CH3), 0.28 (q, JHH = 8.1 Hz, 4H, CH2-CH3).
Computational details
All density functional theory (DFT) calculations were per-
formed with Gaussian 03 program suite.8 The geometries of
the complexes and ligands were optimized (Tables, in the
ESI†) using B3LYP density functional theory and the 6-31G**
basis sets, implemented in the Gaussian 03 on all atoms.9,10
The starting geometries of complexes RR-Zn, SS-Zn, RS-Zn,
and RCy-Zn were generated from their crystal structures,
whereas the starting geometries of the adequate monomers
were derived from their optimized complexes. The structures
of all isomers of the calculated complexes were first optimized
in vacuo. Next, to obtain results more relevant to the experi-
ment, calculations were performed in the presence of a
solvent, while using the Polarizable Continuum Model (PCM)
as the SCRF method. Frequency calculations confirmed the
stationary points to be minimal on PES.
13C NMR (126 MHz, C6D6, RT) δ = 161.4 (ArC-OH, 2C), 140.4
(ArC-C, 2C), 127.8 (ArCH, 2C), 127.4 (ArCH, 2C), 124.9
(ArC-CH2, 2C), 120.3 (ArCH, 2C), 63.7 (N-CH2-Ar, 2C), 46.7
(N-CH3, 2C), 44.4 (N-CH3, 2C), 34.0 (C(CH3)3, 2C), 32.0
(C(CH3)3, 6C), 13.5 (CH2-CH3, 2C), −3.9 (CH2-CH3, 2C).
[RMe-Zn]. [RR-Zn] (0.78 g, 1.00 mmol) and [Me-Zn] (0.60 g,
1.00 mmol) were dissolved in toluene (20 mL) at room tem-
perature. The solution was stirred and concentrated in vacuo,
then put at −15 °C. After 24 h the product [CyR-Zn] was
obtained as a white crystalline powder in 88% yield (1.22 g,
1.76 mmol). Anal. Calcd (Found) for C37H56N2O2Zn2: C, 64.26
(64.51); H, 8.16 (8.22); N, 4.05 (4.07)%; 1H NMR (500 MHz,
C6D6, RT) δ = 7.33–7.30 (m, 2H, ArH, ArH), 7.19–7.10 (m, 5H,
ArH), 7.08–7.02 (m, 3H, ArH, ArH), 6.83 (d, JHH = 2.6 Hz, 1H,
ArH), 4.90 (q, JHH = 7.0 Hz, 1H, N-CH-Ar), 4.71 (d, JHH = 12.0
Hz, 1H, N-CH2-Ar), 4.61 (d, JHH = 12.0 Hz, 1H, N-CH2-Ar), 3.07
(d, JHH = 12.0 Hz, 1H, N-CH2-Ar), 2.70 (d, JHH = 12.2 Hz, 1H,
N-CH2-Ar), 2.44 (s, 3H, N-CH3), 1.95 (s, 3H, N-CH3), 1.82 (s, 3H,
N-CH3), 1.69 (d, JHH = 7.1 Hz, 3H, CH3-CH), 1.40 (t, JHH = 8.1
Hz, 3H, CH2-CH3), 1.33 (s, 9H, C(CH3)3), 1.30 (t, JHH = 8.1 Hz,
3H, CH2-CH3), 1.16 (s, 9H, C(CH3)3), 0.42 (q, JHH = 8.2 Hz, 2H,
Theoretical diffusion coefficients (D) have been calculated
for DFT optimized structures according to the procedure
described by us previously.4a
Results and discussion
CH2-CH3), 0.31 (q, JHH = 8.1 Hz, 2H, CH2-CH3). 13C NMR Recently a family of stable aminophenolate zinc homodimers
(126 MHz, C6D6, RT) δ = 161.6 (ArC-OH, 1C), 161.3 (ArC-OH, have been synthesized in our group (Scheme 1). Although in
1C), 140.6 (ArC-C, 1C), 140.4 (ArC-C, 1C), 136.3 (ArC-CH, 1C), the solid state the dimeric structure is clear and determined
130.5 (ArCH, 2C), 128.5 (ArCH, 3C), 128.4 (ArCH, 1C), 128.0 using X-ray analysis, in solution a mixture of homodimeric
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
atoms are typical and comparable with bond lengths and
angles observed for similar earlier described complexes.3,4 The
solid state structures of the zinc complexes shown in Fig. 1–3
and Tables S1–2 (see ESI†) summarize the crystal data for the
structures of all the zinc complexes reported in this paper.
1
The H NMR spectrum of the homodimeric zinc complexes
RR/SS-Zn contains four sets of signals in equivalent ratios (see
Fig. 6 and S5†). The spectrum exhibits integrated sharp
signals, singlets for amine methyl groups (1.99 and 1.92, ppm)
and tert-butyl groups (1.29 and 1.16 ppm), and quartets for
ethyl groups bonded to the zinc centre at 0.41 and 0.35 ppm.
The proton regions, due to the expected methylene doublets
and methyl quartets connected with the methylbenzyl substi-
tuents bonded to nitrogen atoms, are broadened and less
indicative in the spectrum recorded in C6D6 solvent at room
Scheme 1 Synthesis of aminophenolate homodimeric zinc complexes.
a Previously published.4a
isomers has been observed. Therefore, one question is still
emerging from the reaction course, whether the equilibrium
monomer/dimer or the transformation between the dimers is
responsible for the dynamic behavior in the solution, con-
ducted in the mixture of homodimers.
In the Cy-Zn complex described earlier (Scheme 1), the
asymmetry is due to the arrangement of the prochiral ligand
around the metal.4a The chiral variant of this type of ligand
can probably allow stereo-directing substituents to suppress
the number of potential isomers. Therefore, we have modified
the nitrogen atom environments by introducing a bulky
obstruction containing a single configurationally stable stereo-
genic centre.
The synthetic procedure for the preparation of chiral
ligands is a simple Mannich condensation reaction of chiral
amines with phenol and formaldehyde, carried out under
reflux with methanol.
Fig. 1 Molecular structure of RR-Zn. The thermal ellipsoids are drawn
at the 30% probability level. Disorder of tert-butyl groups and H atoms
are excluded for clarity.
These new chiral ligands (LR–H and LS–H) in the direct
reaction with ZnEt2 form aminophenolate zinc complexes RR-
Zn and SS-Zn, respectively, with ease (Scheme 1). In order to
verify the transformation of the potential homodimers, we
intermix RR-Zn and SS-Zn and we expect only the racemic
mixture of the starting complexes. Surprisingly, the symmetric
RS-Zn has been exclusively obtained as the only product.
A lack of these types of well-defined alkyl heterochiral zinc
dimers has been observed but some examples are known as
inactive reservoirs in a scalemic mixture of precatalysts for
asymmetric reactions.11,12 In this context and in the context of
other catalytic applications, the propensity of the formation of
these dimers is now of principal interest.
The molecular structures of RR/SS-Zn and RS-Zn are similar
and form classic dimers with four-coordinated zinc centers
surrounded by chelating aminophenol ligands, i.e. by terminal
nitrogen atoms and two bridged oxygen atoms and ethyl
groups which are located trans to each other. The typical
central core rhomboid Zn2–O2 is nearly planar and this is a
common structural motif in dimeric zinc complexes. All the
bond distances and angles between the zinc and O, N and C
Fig. 2 Molecular structure of SS-Zn. The thermal ellipsoids are drawn
at the 30% probability level. Disorder of tert-butyl groups and H atoms
are excluded for clarity.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
occurs stereoselectively. Homochiral dimerization gives several
possible isomers characterized by the configuration at the
carbon atom (R for LR or S for LS, according to the ligands
used in the synthesis) which is next amplified at nitrogen and
zinc atoms, respectively. The molar ratio of the possible
isomers probably depends on the dynamic processes
which are supposedly evoked by a stereo-directing group,
which leads to the interconversion of the configuration of the
nitrogen atoms, while the coordination motif is being built
(for the possible isomers obtained by these processes, see
Fig. 4 and S23–24†). The consequence of this molecular fitting
is that the homodimeric zinc complex is in equilibrium with
the corresponding dimeric species in which the central Zn–O–
Zn–O rhomboid is intact while the phenol side arm is
dangling. The dynamic behaviour in solution may cause
broadened resonances for the methylene fragments of the side
arms and the methine protons situated on the nitrogen
substituents.
Fig. 3 Molecular structure of RS-Zn. The thermal ellipsoids are drawn
at the 30% probability level, H atoms are excluded for clarity.
When both RR-Zn and SS-Zn coexist in solution, the hetero-
chiral combination between them occurs preferentially and
leads, among other possibilities, solely to RS-Zn possessing an
S/R configuration at the carbon and nitrogen and a Λ and Δ
configuration at the zinc atoms.
temperature. In order to obtain reasonable assignments for
this compound, variable temperature NMR studies were con-
ducted. The features in this spectrum are broadened and
hence became more complex at lower temperatures (see ESI,
Fig. S15†). The variable temperature NMR analysis as well as
NOESY are unable to discern whether the intramolecular
rearrangements or the monomer/dimer equilibrium (or both)
are involved. The DOSY data showed that RR/SS-Zn remain as
dimeric structures in solution (see ESI, Table S11†).
The 1H NMR spectrum of RS-Zn is clear and as anticipated,
there is only one set of well-resolved signals, which proved that
the two ligands adopted the same coordination mode, consist-
ent with the meso structure (Fig. S7†). In contrast to the 1H
NMR spectrum of RR-Zn/SS-Zn, the signals for the RS-Zn
complex could be ascribed exactly to the protons of the methyl-
ene group, represented as two doublets at δ = 4.42 and
2.83 ppm; the next quartet of the methyl group bonded to the
asymmetric carbon atom, assigned at 4.93, and the signals at
δ = 1.04 (triplet) and −0.04 (quartet) correspond to the ethyl
During the first stage of the reaction, invisible in NMR,
ZnEt2 reacts with appropriate chiral ligands forming coordi-
nately unsaturated monomers, however, next the dimerization
Fig. 4 Schematic structure of the selected heterochiral RS-Zn and homochiral RR-Zn isomers.
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
Fig. 5 Relative energies of the RS/RR-Zn isomers in benzene (blue – possible only when one enantiomer of the ligand occurs) and the corres-
ponding molecular codes: green – favorable; red – unfavorable neighborhood of chiral centers.
group bonded to the zinc centre. The pattern of the spectrum the DFT study possessed agreeable configurations of both
is temperature independent (Fig. S16†), thus the RS-Zn dimer carbon and nitrogen atoms (1H NMR signals marked as green
appears to be stable in the solution and this conclusion has and grey, Fig. 6) and is probably the first compound formed
been verified by DOSY experiments which additionally suggest during the dimerization process. The transformation of this
stability of the heterodimeric structural motif in solution.
isomer to the most stable RR-ZnA isomer (signals marked as
For the purpose of comparing the molecular structure red and blue, Fig. 6) is predictable using theoretical
determined using X-ray diffraction and to delineate the possi- calculations.
ble isomers in the solution, the geometrical parameters and
Based on the experimental and calculated NMR spectra (see
relative energies of both homo- and heterodimeric zinc com- Table 1) the homochiral RR-Zn dimer is a mixture of RR-ZnA
plexes were investigated by means of DFT calculations at the and RR-ZnC isomers during mutual transformation (Fig. 6).
B3LYP levels while using the 6-31G** basis set (for details see The previous findings from NMR stating that homochiral
ESI†).
forms are in a balanced equilibrium are fully reinforced by
The structural motifs of all generated isomers are shown in these DFT calculations.
1
Fig. S23–24† (selected in Fig. 6) and their simplified version,
The final H NMR spectra of RS-Zn contain a single set of
indicative of the relations between the neighboring chiral sharp peaks at room temperature that is consistent with the
centres is presented in Fig. 5.
structures in solution that are dimeric, or the rapidly equili-
Considering the zinc dimers, a full comparison of both
homo- and heterochiral dimeric isomers has been achieved.
This analysis indicates differences between the syn- and anti-
related conformations of the homo- and heterochiral series.
The complexes with ethyl groups arranged anti to one another
with respect to the Zn–O2 plane are more favorable compared
to the syn-structures (Fig. 5).
The theoretically determined energies reveal that the experi-
mentally obtained anti-heterodimer RS-Zn is intrinsically the
most stable structure.
In order to decode an experimental NMR spectrum of the
chiral homodimer RR-Zn and to verify which isomers are
detectable in solution, theoretical NMR spectra were computed
with geometries obtained from DFT studies. The results of this
analysis indicated that both the experimental and calculated
NMR signals are best matched to isomers with the lowest
energy, RR-ZnA and RR-ZnC. The RR-ZnC isomer, proposed by
Fig. 6 A fragment of the 1H NMR spectrum of RR-Zn.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
Table 1 Selected 1H NMR chemical shifts for RR-Zn in benzene-d6:
DFT – calculated for optimized structures, EXP – experimental
NMR spectra, the absence of additional resonances potentially
rules out the exclusive formation of heterodimeric species, in
this example RS-Zn. But here, during the titration experiment,
we have observed the formation process of RS-Zn (Fig. 7B),
although the NMR spectrum of the RS-Zn complex (Fig. 7C) is
nearly identical to one of the signal sets corresponding to the
starting homochiral dimer (Fig. 7A). The reaction of the poten-
tially formed monomers that later statistically dimerized is
clear when in the NMR spectrum the presence of the signals
corresponding to the homo- and heterodimeric species could
be observed.3a However, no monomeric species have been
detected as an independent entity, even at low temperatures.
The monomeric forms seem to be absent which was
additionally supported by the highest energy of the generated
monomeric species obtained by DFT calculations (Fig. 5).
This preferred interaction between the components of
opposite chirality leads to the spontaneous selection of enan-
tiomers to form a favored heterochiral product (Scheme 2).
In the chiral self-sorting system discussed here, the pairs of
enantiomers differ only in their relative spatial orientation
derived from their opposite chirality, therefore, typical geo-
metrical factors do not exhibit an overwhelming preponder-
ance. However, a high tendency to form stable dimers and the
flexibility of the amine arm of the ligands are undoubtedly
additional molecular codes that enable particular homodimers
to recognize each other. Therefore, we have focused on the
study of geometrical complementarity together with chiral con-
straint of aminophenolate ligands over the reaction course.
The stable homodimer Cy-Zn appears to be a suitable target
for such investigation because it combines a similar shape to
RR-Zn and the possibility to arrange suitable chirality on nitro-
gen atoms. The reaction between RR-Zn and Cy-Zn gives an
exclusively heterodimeric complex, RCy-Zn, with the expected
structural motif containing a Zn2–O2 rhomboid and each of
the zinc atoms being surrounded by different aminophenolate
ligands.
brating mixtures. But the following question may arise: is the
monomer the real structure of the intermediate species in this
reaction? The experimental and calculated data suggest that
the homodimer transformation is a more tenable heterodimer-
ization pathway. Because the origin of the self-sorting process
of zinc complexes has remained unclear, the crossover titration
experiments in an NMR tube have been undertaken (Fig. 7).
First, to RR-Zn solution in C6D6, SS-Zn has been added in the
sequence of 1/0.5 and 1/1 molar ratio. The racemic mixture of
RR-Zn and SS-Zn should show an unchanged pattern in the
1
Distinctive H NMR signals of RCy-Zn include the methyl-
ene backbone and methine protons at 4.82, 3.08 and 5.07
corresponding to the chiral ligand bonded to the zinc atom. In
addition, the doublets of the methylene protons of the LCy
fragment at 4.61 and 3.37 ppm are visible (see Fig. 8 and S9†).
The chiral clips of the LR fragment constrain the appropri-
ate opposite configuration on the nitrogen atoms of the LCy
part to form the stable heterodimer RCy-Zn.
Accordingly, to ensure fidelity of the self-sorting process, a
sufficient complex for the reaction with chiral RR-Zn could be
the stable achiral homodimer. For this purpose, we have pre-
pared a suitable Me-Zn homodimer with appropriate amino-
phenolate ligands containing nitrogen atoms with two methyl
substituents. As a consequence, in the one pot reaction
between Me-Zn and chiral RR-Zn, the new heterodimer RMe-
Zn has been formed.
The NMR spectrum of this heterodimer shows signals
belonging to the appropriate ligands coordinated to zinc
atoms. The methylene and methine protons are distinguished
in the chiral fragment doublets at 4.70 and 3.07 and a quartet
Fig. 7 The monitoring of the reaction between the chiral dimers by 1H
NMR. RR-Zn and SS-Zn in the following molar ratios: 1/0 (A), 1/0.5 (B),
and 1/1 (C).
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
Scheme 2 Synthesis of aminophenolate heterodimeric zinc complexes – the zebra reaction.
at 4.90 ppm, respectively, and the new methylene signals at in the reaction in the absence of a chiral substrate, in our
4.61 and 2.70 ppm. (see Fig. 9 and S13†). example: Me–Zn and Cy–Zn give the mixture of homo-/
The detailed information describing the structural data in heterodimers.
solution is in the Experimental section and ESI, Fig. S9–12,
Although the X-ray analysis correlates with the structures
S20, 22 and Tables S8, 10†, while the molecular structures of in the solution provided by NMR, the DFT study offers
RCy-Zn and SMe-Zn are presented in Fig. 10 and 11 (for additional information to clarify the heterodimerization
details see ESI: Tables S1–2†).
pathway in the “zebra reaction”. The chiral clips CRNRZn
The selective formation of the heterodimeric zinc com- during homochiral dimerization form a mixture of isomers
plexes has been carried out in a direct reaction between the but two of them which undergo dynamic behavior arise from
chiral homodimer and the chiral/achiral ones. What is more, the competition between chiral and geometrical codes;
RR-ZnA (RCRNΛZnΔZnSNRC) and RR-ZnC (RCRNΛZnΔZnRNRC),
Fig. 8 The monitoring of the reaction between RR-Zn and Cy-Zn by
1H NMR. Cy-Zn and RR-Zn in the following molar ratios: 1/0 (A), 1/0.5 (B),
Fig. 9 Monitoring the reaction between RR-Zn and Me-Zn by 1H NMR.
Me-Zn and RR-Zn in the following molar ratios: 1/0 (A), 1/0.5 (B), 1/1 (C).
1/1 (C).
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
Fig. 12 The proposed mechanism of heterodimer formation. – favor-
able; – unfavorable – switchable relation of chiral centers.
Fig. 10 Molecular structure of RCy-Zn. The thermal ellipsoids are
drawn at the 30% probability level. Disorder of the tert-butyl group and
H atoms are excluded for clarity.
sorting process and the application of these zinc complexes in
catalysis, constitute the subject of our intensive research at the
moment. The findings of our research will be published in a
different paper soon.
Conclusions
The recipe for zinc heterodimers is simple: homodimers,
which are more stable than their monomers (confirmed by a
DFT study during the design process) and one of the homodi-
mers with a chiral clip can form unique heterodimers contain-
ing zinc atoms bearing different ligands.
Acknowledgements
Fig. 11 Molecular structure of SMe-Zn. The thermal ellipsoids are
drawn at the 30% probability level. Disorder of the tert-butyl groups and
H atoms are excluded for clarity.
The authors gratefully acknowledge the National Science
Centre in Poland (Grant NN 204 200640), the Wrocław Centre
for Networking and Supercomputing (http://www.wcss.wroc.
pl), and EU under the European Social Found (project
Academy of development as the key to strengthen human
resources of the Polish economy) for the support of this
research.
respectively. Destabilization of one ligand arm by changing the
nitrogen atom configuration seems to be the driving force of
the reaction between the appropriate dimers (Fig. 12).
The “black horse” RR-Zn can gallop with the “white” one
(opposite chirality SS-Zn) and form the “white and black
zebra”, RS-Zn, presenting the molecular code RCRNΛZnΔZnSNSC.
While when the zinc dimer with the prochiral ligand LCy meets
the “black horse”, it forms RCy-Zn (RCRNΛZnΔZnSN) easily, and
the best is to match with the flexible Me-Zn which gets trans-
formed into RMe-Zn (RCRNΛZnΔZn). What is important to note
is that the two chiral clips, although uncomfortable during the
formation of the homodimers, are crucial for heterodimers,
because the “zebras” (RS-Zn, RCy-Zn and RMe-Zn) with stable
codes are unable to react with each other. This clearly shows
the power of chemistry, because nobody has seen a zebra as
the offspring of two horses but chemistry facilitates the magic.
The new examples with more detailed analysis of the key
structural features, responsible for the chiral-directed self-
Notes and references
1 See for examples: (a) G. Consiglio, S. Failla, P. Finocchiaro,
I. P. Oliveri, R. Purrello and S. Di Bella, Inorg. Chem., 2010,
49, 5134; (b) A. W. Kleij, Dalton Trans., 2009, 4635;
(c) K. Zhang, H. Qian, L. Zhang and W. Huan, Inorg.
Chem., 2015, 54, 675; (d) I. P. Oliveri, G. Malandrino and
S. Di Bella, Inorg. Chem., 2014, 53, 9771; (e) P. Roy,
K. Dhara, M. Manassero, J. Ratha and P. Banerjee, Inorg.
Chem., 2007, 46, 6405; (f) I. Giannicchi, R. Brissos,
D. Ramos, J. de Lapuente, J. C. Lima, A. D. Cort and
L. Rodríguez, Inorg. Chem., 2013, 52, 9245; (g) Y. Sarazin
and J.-F. Carpentier, Chem. Rev., 2015, 115, 3564;
(h) M. I. Childers, J. M. Longo, N. J. V. Zee, A. M. LaPointe
and G. W. Coates, Chem. Rev., 2014, 114, 8129.
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
2 (a) B. M. Chamberlain, M. Cheng, D. R. Moore, T. M. Ovitt,
E. B. Lobovsky and G. W. Coates, J. Am. Chem. Soc., 2001,
123, 3229; (b) M. H. Chisholm, J. C. Huffman and
K. Phomphrai, Dalton Trans., 2001, 3, 222; (c) A. P. Dove,
V. C. Gibson, E. L. Marshall, A. J. P. White and
D. J. Wiliams, Dalton Trans., 2004, 570; (d) F. Drouin,
P. O. Ogadinma, T. J. J. Whitehornr, R. E. Prud’homme and
F. Schaper, Organometallics, 2010, 29; (e) M. H. Chisholm,
N. W. Eilerts, J. C. Huffman, S. S. Iyer, M. Pacold and
K. Phomphrai, J. Am. Chem. Soc., 2000, 122, 11845;
(f) H. Y. Chen, H. Y. Tang and C. C. Lin, Macromolecules,
2006, 39, 3745; (g) Z. Zheng, G. Zhao, R. Fablet,
M. Bouyahyi, C. M. Thomas, T. Roisnel, O. Casagrande Jr.
and J.-F. Carpentier, New J. Chem., 2008, 32, 2279;
(h) G. Labourdette, D. J. Lee, B. O. Patrick, M. B. Ezhova
and P. Mehrkhodavandi, Organometallics, 2009, 28, 1309;
(i) V. Poirier, T. Roisnel, J.-F. Carpentier and J. Sarazin,
Dalton Trans., 2011, 40, 523.
3 (a) C. K. Williams, L. E. Choi, S. K. Breyfogle, W. Nam,
V. G. Young Jr., M. A. Hillmyer and W. B. Tolman, J. Am.
Chem. Soc., 2003, 125, 11350; (b) N. Ikpo, L. N. Saunders,
J. L. Walsh, J. M. B. Smith, L. N. Dawe and F. M. Kerton,
Eur. J. Inorg. Chem., 2011, 35, 5347; (c) J. D. Farwell,
P. B. Hitchcock, M. F. Lappert, G. A. Luinstra,
A. V. Protchenko and X.-H. Wei, J. Organomet. Chem., 2008,
693, 1861; (d) S. Groysman, E. Sergeeva, I. Goldberg and
6 G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystal-
logr., 2008, 64, 112.
7 C. F. Macrae, I. J. Bruna, J. A. Chisholm, P. R. Edgington,
P. Mccabe, E. Pidcock, L. Rodriguez-Monge, R. Taylor,
J. van de Streek and P. A. Wood, J. Appl. Crystallogr., 2008,
41, 466.
8 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers,
K. N. Kudin, V. N. Staroverov, T. Keith, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J. C. Burant,
S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam,
M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev,
A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski,
R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth,
P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski and
D. J. Fox, Gaussian 09 (Revision B.01), Gaussian, Inc., Wall-
ingford CT, 2010.
9 A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
M. Kol, Eur. J. Inorg. Chem., 2006, 14, 2739; (e) V. Poirier, 10 C. Lee, W. Yang and R. G. Parr, Phys. Rev. B: Condens.
T. Roisnel, J.-F. Carpentier and Y. Sarazin, Dalton Trans.,
2009, 9820.
4 (a) D. Jędrzkiewicz, J. Ejfler, N. Gulia, Ł. John and
Matter, 1988, 37, 785.
11 (a) H. S. Jena and V. Manivannan, Inorg. Chim. Acta, 2013,
394, 210; (b) H. S. Jena, RSC Adv., 2014, 4, 3028.
S. Szafert, Dalton Trans., 2015, 44, 13700; (b) J. Ejfler, 12 For selected examples, see: (a) M. Steigelmann, Y. Nisar,
S. Szafert, K. Mierzwicki, L. B. Jerzykiewicz and P. Sobota,
Dalton Trans., 2008, 6556.
5 CrysAlisRED Software, Oxford Diffraction, Wrocław, Poland,
1995–2004.
F. Rominger and B. Goldfuss, Chem. – Eur. J., 2002, 8, 5211;
(b) L. Schiaffino and G. Ercolani, Angew. Chem., Int. Ed.,
2008, 120, 6938; (c) J. Klankermayer, I. D. Gridnev and
J. M. Brown, Chem. Commun., 2007, 3151.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015