Synthesis, characterization, and catalytic studies of (Aryloxido)magnesium complexes

Article abstract of DOI:10.1002/ejic.200901207

The reaction of MgBu₂ with 1 equiv. of four-coordinating (R)-or rac-N,N-bis(3,5-di-tert-butylbenzyl-2-hydroxy)tetrahydrofurfurylamine (R/rac-bpthfa-H₂) gave dinuclear homoleptic [Mg(μ-R/rac-bpthfa)] ₂ (R/rac-2c) as white p

Full text of DOI:10.1002/ejic.200901207

FULL PAPER
DOI: 10.1002/ejic.200901207
Synthesis, Characterization, and Catalytic Studies of (Aryloxido)magnesium
Complexes
Jolanta Ejfler,[a] Katarzyna Krauzy-Dziedzic,[a] Sławomir Szafert,[a]
Lucjan B. Jerzykiewicz,[a] and Piotr Sobota*[a]
Keywords: Aminophenolates / Magnesium / Lactides / Polymerization / Structure elucidation
The reaction of MgBu2 with 1 equiv. of four-coordinating (R)-
characterized by spectroscopic methods and, in the case of
or rac-N,N-bis(3,5-di-tert-butylbenzyl-2-hydroxy)tetrahydro- R-2c and S-2f, by X-ray crystallography. The new complexes
furfurylamine (R/rac-bpthfa-H2) gave dinuclear homoleptic
[Mg(µ-R/rac-bpthfa)]2 (R/rac-2c) as white powders in
54–67% yields. Analogous reactions of MgBu2 with 2 equiv.
of two-coordinating N-(3,5-di-tert-butylbenzyl-2-hydroxy)-
N-methylcyclohexanamine (tbpca-H; 1e-H) and (S)-N-(3,5-
di-tert-butylbenzyl-2-hydroxy)-N,α-dimethylbenzylamine
(S-tbpmpa-H; S-1f-H) gave white crystals of homoleptic mo-
nonuclear compounds of general formula [Mg(L)2] (2e and S-
2f) in 87–89% yields. The resulting aminophenolates were
R/rac-2c, 2e, and S-2f, as well as the previously described
homo- and heteroleptic tetranuclear [Mg(ddbfo)2]4 (2a),
[Mg(thffo)2]4 (2b), [Mg4(µ3-OMe)2(µ,η2-ddbfo)2(µ,η1-ddbfo)2-
(η1-ddbfo)2(MeOH)5]·CH3OH·thf
(3a·CH3OH·thf)
and
[Mg4(µ3,η2-thffo)2(µ,η2-thffo)2(Ph3SiO)2] (4b), were tested in
the polymerization of lactide to reveal good activity only in
the case of mononuclear four-coordinate species grafted with
an external donor, benzyl alcohol.
Some of our previous research has already included the
synthesis of magnesium alkoxides and aryloxides, where we
utilized variety of oxido ligands, including commercially
available 2,3-dihydro-2,2-dimethyl-7-benzofuranol (ddbfo-
H; 1a-H) and tetrahydrofurfuryl alcohol (thffo-H; 1b-H), as
well as aminophenolato ligands bpthfa-H2 (1c-H2),[7]
tbpoa-H (1d-H),[2b] and tbpca-H (1e-H),[2b] which are
shown in Scheme 1.
Introduction
The potential of magnesium alkoxides and aryloxides has
been explored systematically in a variety of chemical pro-
cesses. Among others, numerous catalytic, noncatalytic, or-
ganic, and organometallic reactions, as well as syntheses of
advanced materials are noteworthy.[1] Recently, magnesium
complexes have also gained considerable attention as initia-
tors in the syntheses of biodegradable polymers.[2] Two im-
portant classes of these polymers are polyesters and, in par-
ticular, polylactides (PLAs) due to their wide application
in biomedical and pharmaceutical fields.[3] Although many
strategies have been developed for the preparation of PLAs,
the most effective is the ring-opening polymerization (ROP)
of lactides initiated by metal alkoxides.[4] Among the known
initiators, candidates of primary importance are monomeric
complexes with nontoxic and life-essential metals such as
magnesium.[2,5]
To date, only a few examples of heteroleptic magnesium
compounds that are active as initiators in the ROP of cyclic
esters have been described.[2] Recently, interest has also
been directed towards homoleptic compounds able to act
as initiators for the ROP in the presence of exterior alcohol,
which is extremely interesting from the perspective of poly-
mer chain modification.[6] However, only a few magnesium
alkoxides and aryloxides have a structure proven by X-ray
analysis, which is highly desirable to design well-defined
“single-site” initiators.
It has been shown that reactions of sterically unde-
manding bidentate 1a-H or 1b-H with MgBu2 or magne-
sium turnings yield tetranuclear compounds [Mg(ddbfo)2]4
(2a)[8a] and [Mg(thffo)2]4 (2b),[8b] which have open dicubane
geometry. Both molecules possess two five-coordinate mag-
nesium atoms of trigonal-bipyramidal geometry and two
six-coordinate octahedral metal centers. The most interest-
ing feature of these compounds is the presence of coordina-
tively unsaturated metal sites which can react easily with
methanol or Ph3SiOH to form heteroleptic tetrameric
magnesium complexes [Mg4(µ3-OMe)2(µ,η2-ddbfo)2(µ,η1-
ddbfo)2(η1-ddbfo)2(MeOH)5]·CH3OH·thf
(3a·CH3OH·
thf)[8a]
and
[Mg4(µ3,η2-thffo)2(µ,η2-thffo)2(Ph3SiO)2]
(4b).[8b]
Higher dentate or more bulky bidentate ligands form less
aggregated structures that are usually dimeric and perform
well as initiators in the ROP of lactides. A few important
examples include [(EDBP)Mg(Et2O)], [(EDBP)Mg(thf)]2
[EDBP = 2,2Ј-ethylenebis(4,6-di-tert-butylphenoxido)],[2a]
and a series of dimeric [(L)Mg(µ-OBz)]2 compounds {L =
NNO-ketiminate[2d,2i] or 2,4-di-tert-butyl-6-[1-(3,5-di-tert-
butyl-2-phenoxy)ethyl]phenyl benzenesulfonate},[2h] which
[a] Department of Chemistry, University of Wrocław,
14 F. Joliot-Curie, 50-383 Wrocław, Poland
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(Aryloxido)magnesium Complexes
Scheme 1. Some of the precursors of alkoxido and aryloxido ligands.
were all designed by Lin and co-workers. Another interest-
As shown in Scheme 2 ligands 1e-H or S-1f-H were
ing example, prepared by Cheng et al., is a compound treated with 0.5 equiv. of MgBu2 in toluene or hexanes to
formed in situ from [(BDI)MgN(TMS)2] {BDI = 2-[(2,6- form monomeric tetrahedral compounds [Mg(tbpca)2] (2e)
diisopropylphenyl)amino]-4-[(2,6-diisopropylphenyl)imino]- and [Mg(tbpmpa)2] (S-2f) in 87 and 89% yields, respec-
2-pentene} and paclitaxel, a potent chemotherapeutic tively.
agent, that is most probably a monomeric species and al-
lows incorporation of the agent into the polylactide chain
to form an interesting drug-delivery system.[2g]
In this paper, we report the preparation of a series of
homoleptic magnesium complexes with aryloxido and ami-
nophenolato ligands. The ligands have been varied from
two- to four-dentate in order to evaluate the resulting struc-
tural motifs. The additional donor arm on the nitrogen
atom in the aminophenolato ligands, which could readily
involve dynamic behavior in solution, may be an important
factor for catalytic applications. Preliminary results of the
activity of the compounds in the ROP of lactides are also
reported.
Results and Discussion
Synthesis and Characterization of Complexes
Scheme 2. Synthesis of monomeric magnesium complexes 2e and
S-2f.
The aminophenolato bidentate ligands 1e-H and S-1f-H
appear to be well suited for the synthesis of monomeric
The new complexes 2e and S-2f were isolated as colorless
magnesium complexes. The latter was prepared by Mannich solids, which are readily soluble in hydrocarbons, CH2Cl2,
condensation from (–)-(S)-α,4-dimethylbenzylamine, para- and thf. Their structures were confirmed by elemental
formaldehyde, and 2,4-di-tert-butylphenol in refluxing analysis and NMR spectroscopy, as well as X-ray crystal-
methanol in 54% unoptimized yield as described in the Ex- lography for S-2f.
1
perimental Section. As already described, the reaction of
The H NMR spectra were routine. The spectrum for 2e
1e-H performed in a mixture of solvents (hexane/thf) gave shows one set of resonances for the aryl protons at δ = 7.66
monomeric octahedral [Mg(tbpca)2(thf)2] (5).[2b] It has also and 7.08 ppm, two singlets from the tert-butyl groups at δ =
been demonstrated that the reaction of MgBu2 with 1d-H 1.78 and 1.56 ppm, and a signal arising from the N-methyl
in toluene gave the six-coordinate complex [Mg(tbpoa)2].[2b] protons at δ = 2.02 ppm. The methylene protons from the
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J. Ejfler, K. Krauzy-Dziedzic, S. Szafert, L. B. Jerzykiewicz, P. Sobota
FULL PAPER
phenyl–CH2–N linker appear as broad singlets at δ = 4.12 X-ray Crystallographic Studies
and 3.44 ppm. For S-2f, the signals of the aminophenolato
Colorless, needle-shaped crystals of R-2c·2C6H5CH3·
ligands are broad indicating a fluxional process on the
NMR timescale. The aryl protons of the phenolate ring ap-
pear as broadened singlets at δ = 7.69 and 6.96 ppm. The
methine and methyl protons of the chiral amine substitu-
ents also show broad resonances at δ = 3.54 and 1.84 ppm,
respectively. The signal of the methylene protons from the
phenyl–CH2–N linker appears at δ = 4.21 ppm.
Attempts to introduce alcohols into the monomeric
(aminophenolato)magnesium complexes 2e and S-2f were
unsuccessful. The reactions between 2e or S-2f and EtOH
or benzyl alcohol were monitored by NMR spectroscopy,
which indicated the synthesis of a mixture of products (pre-
sumably due to a reversible reaction), but, after a few days
and after a careful workup, the isolated products were iden-
tified as the homoleptic starting complexes.
CH2Cl2 were obtained by crystallization from a CH2Cl2/
toluene mixture. The detailed structure was determined as
outlined in the Experimental Section. Key metrical param-
eters are listed in Table 1, and the structure is shown in
Figure 1.
Table 1. Selected bond lengths [Å] and angles [°] for R-2c·
2C6H5CH3·CH2Cl2.
Atoms
Distance
Atoms
Distance
Mg(1)–Mg(2)
Mg(1)–O(2)
Mg(1)–O(4)
Mg(2)–O(1)
Mg(2)–O(5)
Mg(2)–N(2)
3.008(3)
1.907(4)
2.014(4)
1.993(4)
1.922(4)
2.205(5)
Mg(1)–O(1)
Mg(1)–O(3)
Mg(1)–N(1)
Mg(2)–O(4)
Mg(2)–O(6)
2.027(4)
2.058(4)
2.208(5)
2.018(4)
2.090(4)
In the next stage of our investigation, the chiral and race- Atoms
Angle
Atoms
Angle
mic aminobis(phenolato) ligands R-1c-H2 and rac-1c-H2
containing additional N,O-donor atoms (going from two-
to four-dentate ligands) were used. Their reactions with
1 equiv. of MgBu2 in toluene at room temperature
cleanly afforded the dimeric magnesium complexes [Mg(R-
bpthfa)]2 (R-2c) and [Mg(rac-bpthfa)]2 (rac-2c) by butane
elimination, as presented in Scheme 3. The complexes were
isolated in good yields (54–67%) as colorless crystals, solu-
ble in hydrocarbons and chlorinated solvents. Compounds
R/rac-2c contain unsaturated five-coordinate metal centers,
are unreactive towards alcohols, and remain stable even in
hot ethanol. Similarly to 2e and S-2f, incorporation of al-
koxido ligands and formation of heteroleptic products were
not observed.
O(1)–Mg(1)–O(2)
O(1)–Mg(1)–O(4)
O(2)–Mg(1)–O(3)
O(2)–Mg(1)–N(1)
O(3)–Mg(1)–N(1)
O(1)–Mg(2)–O(4)
O(1)–Mg(2)–O(6)
O(4)–Mg(2)–O(5)
O(4)–Mg(2)–N(2)
O(5)–Mg(2)–N(2)
162.86(19) O(1)–Mg(1)–O(3)
76.36(15) O(1)–Mg(1)–N(1)
100.49(18) O(2)–Mg(1)–O(4)
95.31(15)
86.65(16)
95.80(16)
138.32(17)
137.85(18)
94.65(16)
136.41(19)
95.88(15)
99.17(17)
80.86(16)
89.35(17)
80.73(16)
77.05(14)
O(3)–Mg(1)–O(4)
O(4)–Mg(1)–N(1)
O(1)–Mg(2)–O(5)
140.29(18) O(1)–Mg(2)–N(2)
163.93(19) O(4)–Mg(2)–O(6)
86.87(16)
89.98(17)
O(5)–Mg(2)–O(6)
O(6)–Mg(2)–N(2)
Mg(1)–O(4)–Mg(2) 96.52(15)
Mg(1)–O(1)–Mg(2) 96.88(15)
Scheme 3. Synthesis of dimeric complexes R/rac-2c.
The 1H NMR spectra of the complexes R/rac-2c are
identical and show one set of resonances for 1 equiv. of the
coordinated bis(phenoxido) ligand, which could be assigned
in detail on the basis of 2D 1H-1H COSY, 1H, and 13C
NMR experiments. Complementary investigations of these
Figure 1. ORTEP view of R-2c·2C6H5CH3·CH2Cl2 (H and disor-
dered atoms are omitted for clarity; the displacement ellipsoids are
drawn at 40% probability level).
The X-ray analysis shows R-2c·2C6H5CH3·CH2Cl2 to be
compounds indicated that the NMR features were essen- a homoleptic molecular dimer. The two magnesium centers
tially unchanged in C6D5CD3, CDCl3, and CD3OD up to are identically coordinated, each surrounded by two bridg-
60 °C.
ing oxygen atoms of two phenoxido ligands coming from
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(Aryloxido)magnesium Complexes
separate aminobis(phenolato) ligands, one terminal phen-
oxido oxygen atom, one nitrogen atom, and one oxygen
atom from the tetrahydrofuran ring.
The pentacoordinate magnesium atoms are in an almost
identical arrangement, that is between trigonal-bipyramidal
and square-pyramidal geometry with a τ parameter of 0.41
for Mg(1) and 0.39 for Mg(2).[9] In both cases the nitrogen
atom resides in the apical position.
Although complexes with pentacoordinate magnesium
are quite commonly observed, only two examples of the
crystallographically characterized species with a coordina-
tion environment similar to R-2c (MgO4N comprising two
bridging phenoxido groups) were found in the CCDC.[10]
The Mg2O2 central core in R-2c·2C6H5CH3·CH2Cl2 is a
distorted rhombohedron with four different Mg–O dis-
tances of 2.027(4) [Mg(1)–O(1)], 2.014(4) [Mg(1)–O(4)],
1.993(4) [Mg(2)–O(1)], and 2.018(4) Å [Mg(2)–O(4)]. The
distances are similar to those found in the magnesium di-
mer with bis(α,α-diarylprolinol) [Mg2(L)2] [Mg–O 1.991(6),
2.031(6), 1.979(6), and 2.016(6) Å].[10a]
Figure 2. View of S-2f (H atoms are omitted for clarity; the dis-
placement ellipsoids are drawn at 40% probability level). Selected
bond lengths [Å] and angles [°]: Mg(1)–O(1) 1.892(3), Mg(1)–O(2)
1.900(3), Mg(1)–N(1) 2.176(4), Mg(1)–N(2) 2.166(3); O(1)–Mg(1)–
O(2) 125.77(15), O(1)–Mg(1)–N(1) 92.68(13), O(1)–Mg(1)–N(2)
105.32(13), O(2)–Mg(1)–N(1) 105.69(14), O(2)–Mg(1)–N(2)
95.71(13), N(1)–Mg(1)–N(2) 136.07(14), Mg(1)–O(1)–C(11)
The terminal Mg–Oaryloxido distances in R-2c·2C6H5CH3·
CH2Cl2 are 1.907(4) and 1.922(4) Å and are typical. Also
typical are the Mg–O–C bond angles for the terminal
aryloxido ligands, which are 134.3(3) and 134.9(3)°, and
suggest a very small π-character in the Mg–Oaryloxido bonds. 129.9(3), Mg(1)–O(2)–C(41) 124.5(2).
Light pink blocks of S-2f were obtained by slow concen-
tration of a hexane solution. The detailed structure was de-
Lactide Polymerization
termined as outlined in Table 1 and described in the Experi-
mental Section. The structure is depicted in Figure 2, and
selected bond lengths and angles are listed in the caption.
Previous research in our group has shown that zinc com-
plexes that incorporate 1e-H are effective initiators for the
The X-ray analysis shows S-2f to be a molecular mono- ROP of lactide.[12] In addition, the monomeric hexacoordi-
mer with the four-coordinate magnesium center surrounded nate magnesium complex 5[2b] was proved to initiate the po-
by two pairs of N,O atoms from two aminophenolato li- lymerization of -lactic acid (-LA) in high conversion
gands forming a distorted tetrahedron. Although such co- within 30 min to afford PLA with a moderate Mw of 8600
ordination seems typical for magnesium, to our surprise, and a polydispersity index (PDI) of 1.12. In this case, the
only one monomeric four-coordinate magnesium amino- NMR end-group analysis of the isolated PLA indicated the
phenolate was found in the CCDC.[11]
presence of hydroxy and aminophenolate ester end groups.
The distances Mg(1)–O(1) and Mg(1)–O(2) in S-2f are Biocompatible metals such as Zn and Mg are of great inter-
1.892(3) and 1.900(3) Å, respectively, and are similar to est in this process because of the propensity for trace
those found in [Mg(2,6-tBu2C6H4O)2(tmeda)] [tmeda = amounts of the catalyst to be incorporated within the poly-
N,N,NЈ,NЈ-tetramethylethylenediamine; Mg–O 1.8803(8) mer.[2d] Therefore, preliminary research exploring the use of
and 1.8817(9) Å]. The Mg(1)–N(1) and Mg(1)–N(2) dis- the above described and characterized aryloxo magnesium
tances in S-2f of 2.176(4) and 2.166(3) Å are a little shorter complexes as initiators for the ROP of lactide. The tetra-
than those in [Mg(2,6-tBu2C6H4O)2(tmeda)] [Mg–N meric complexes 2a–b, 3a, and 4b, as well as dimeric R/rac-
2.2625(11) and 2.2695(11) Å].
2c were tested and proved to be essentially inactive.
Table 2. Polymerization of -lactide with initiators (I) 2e, S-2f, 2e/BnOH, and S-2f/BnOH.[a]
10–3 Mn
10–3 Mn
Conv.[c]
PDI[b]
[b]
Entry
I
[I]/[-LA]/[BnOH]
t (min)
1
2
3
4
5
6
2e
2e
1:100:0
1:50:1
1:100:1
1:100:0
1:50:1
5 d
1 min
5 min
5 d
1 min
10 min
–
–
–
–
6.88
15.58
–
7.20
14.82
7.02
13.37
–
6.59
13.80
96%
92%
–
90%
95%
1.09
1.10
–
1.02
1.08
2e
S-2f
S-2f
S-2f
1:100:1
1
[a] General polymerization conditions: solvent: toluene (10 mL), T = 25 °C, [I] = 0.025. [b] Conversion determined by H NMR spec-
troscopy. [c] Determined by GPC, PDI calibrated with polystyrene standards.
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J. Ejfler, K. Krauzy-Dziedzic, S. Szafert, L. B. Jerzykiewicz, P. Sobota
FULL PAPER
Monomeric tetrahedral aminophenolate compounds 2e chains at one end are terminated by benzyl ester with no
and S-2f were tested next. Although they both showed no sign of transesterification products (the OH proton was not
activity they become extremely active when an external do- observed) (Figure 5).
nor was added as described in Table 2.
Polymerization of -LA initiated by 2e in the presence of
BnOH was very effective, and high conversion was achieved
within 5 min for [2e]/[-LA]/BnOH (1:100:1) (Figure 3).
Figure 5. 13C NMR spectrum of PLA synthesized with the S-2f/
BnOH initiator.
All of the initiator systems exhibit molecular weights in
close agreement with calculated values, and narrow PDIs
are characteristic for well-controlled living propagation.
Conclusions
Figure 3. 1H NMR spectrum of a living oligomer in the ROP of -
LA initiated by 2e in the presence of BnOH.
We have synthesized a new chiral aminophenolato ligand
S-1f-H and four new magnesium aminophenolates R/rac-
2c, 2e, and S-2f. The compounds were characterized by
spectroscopic methods and, in case of R-2c and S-2f, by X-
ray crystallography, thereby enriching the library of well-
defined magnesium aminophenolates. As expected, the
compound with the tetracoordinate R-bpthfa ligand ap-
peared to be dimeric with five-coordinate magnesium
atoms, whereas the compound with the dicoordinate S-
tbpmpa was monomeric with tetrahedral geometry around
the metal atom.
The predictable molecular weights and narrow PDIs of
the obtained PLAs indicate a well-controlled polymeriza-
tion process. The H NMR spectrum of PLA in CD2Cl2
prepared by using [2e]/[-LA]/[BnOH] in 1:10:1 ratio
showed one benzyl ester and one hydroxy chain end sug-
gesting that the initiation occurred through the insertion of
the benzyloxy group into -lactide (Figure 4).
1
All of the new compounds, as well as few polynuclear
magnesium species 2a–b, 3a, and 4b synthesized previously,
were tested in the polymerization of -lactide, and all of
them proved to be essentially inactive. Nevertheless, in the
case of 2e and S-2f, grafting with benzyl alcohol led to
greatly enhanced polymerization activities resulting in high
activity initiators, which gave 92–95% conversion after 5–
10 min, and exclusively linear polymers with low PDI val-
ues, 1.08–1.10. These results clearly support the advantage
of monomeric magnesium species over polynuclear analogs
in lactide polymerization.
Figure 4. 1H NMR spectrum of PLA synthesized with the 2e/
BnOH initiator.
Similar results were obtained for the polymerization of
-LA initiated with S-2f in the presence of BnOH per-
formed at room temperature in toluene. A high conversion
was achieved within 10 min for [S-2f]/[-LA]/[BnOH]
Experimental Section
General Materials and Experimental Procedures: All the reactions
and operations were performed under N2 by using standard
Schlenk techniques. Reagents were purified by standard methods:
1
(1:100:1). The H and 13C NMR spectra of the PLAs ob-
tained in the presence of S-2f showed that the polymer thf was distilled from CuCl, predried with NaOH, and then dis-
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(Aryloxido)magnesium Complexes
tilled from Na/benzophenone. C6H5CH3 was distilled from Na;
CH2Cl2 and CD2Cl2 were distilled from P2O5; hexanes were dis-
tilled from Na; methanol was distilled from Mg; C6D6 and
C6D5CD3 were distilled from CaH2. -LA (98%; Aldrich) was sub-
limed and recrystallized from toluene prior to use. MgBu2 (Aldrich;
1.0  solution in hexanes) and (–)-(S)-α,4-dimethylbenzylamine
(Aldrich, 98%) were used as received. BnOH (Aldrich; Ͼ99%) was
distilled prior to use. Ligands (tbpca-H), R/rac-bpthfa-H2 were pre-
pared according to literature procedures.[2b,7] 1H and 13C NMR
spectra were recorded in the temperature range 298–351 K with
Bruker ESP 300E or 500 MHz spectrometers. Chemical shifts are
reported in ppm and referenced to the signals of residual protons
in deuterated solvents. The weights and number-average molecular
weights of the PLAs were determined by gel permeation
chromatography (GPC) using an HPLC-HP 1090 II with a DAD-
UV/Vis and RI detector HP 1047A, and polystyrene calibration.
Microanalyses were conducted with an ARL Model 3410 + ICP
spectrometer (Fisons Instruments) and a VarioEL III CHNS (in-
house).
cedure analogous to that of R-2c described above. A similar
workup gave rac-2c in 67% yield (3.52 g, 3.14 mmol).
C70H106Mg2N2O6 (1120.23): calcd. C 75.05, H 9.54, N 2.50; found
75.14, H 9.37, N 2.34.
[Mg(1e)2] (2e): To a solution of 1e-H (1.32 g, 4.00 mmol) in toluene
(10 mL) was added MgBu2 (2 mL, 2.00 mmol) dropwise. The reac-
tion mixture was stirred for 24 h, and the solvent was removed to
give a yellow oil. n-Hexane was added (20 mL), and colorless crys-
tals precipitated at room temperature after 1 d. They were collected
by filtration, washed with n-hexane (10 mL), and dried in vacuo to
yield 2e (2.40 g, 87%, 3.50 mmol). C44H72MgN2O2 (685.37): calcd.
C 77.11, H 10.59, N 4.09; found C 76.68, H 10.31, N 3.98. 1H
NMR (C6D6, 298 K): δ = 7.66 (s, 2 H, ArH), 7.08 (s, 2 H, ArH),
4.12 (br. s, 2 H, NCH2Ar), 3.44 (s, 2 H, NCH2Ar), 2.27–2.39 (m,
2 H, C6H11), 2.02 (s, 6 H, NCH3), 1.78 [s, 18 H, C(CH3)3], 1.60–
1.70 (m, 10 H, C6H11), 1.56 [m, 18 H, C(CH3)3], 1.30–1.47 (m, 10
H, C6H11) ppm. 13C NMR (76 MHz, C6D6, 298 K): δ = 25.2 (10
C, C6H11), 25.5 (10 C, C6H11), 29.4 [6 C, C(CH3)3], 31.0 (2 C,
NCH3), 31.5 [6 C, C(CH3)3], 33.3 [2 C, C(CH3)3], 34.7 [2 C,
C(CH3)3], 59.4 (2 C, C6H11), 60.3 (2 C, NCH2Ar) 62.3, 136.8,
134.6, 125.0, 123.5, 121.0 (24 C, Ar) ppm.
Ligand and Complex Synthesis. S-1f-H: To a mixture of 2,4-di-tert-
butylphenol (7.88 g, 38.20 mmol) and (–)-(S)-α,4-dimethylbenzyl-
amine (5.60 mL, 38.06 mmol) in methanol (50 mL) was added a 1.5
molar excess of formaldehyde (4.32 mL, 58.01 mmol, 37% solution
in water). The solution was then stirred and heated under reflux
for 5 d. The solvent was removed to give a yellow oil. Cold meth-
anol was added (10 mL), and the mixture was stirred for 1 h and
cooled to –15 °C. After 1 d, colorless crystals of S-1f-H had
formed. Yield 7.21 g (54%). C24H35NO (353.55): calcd. C 81.53, H
9.98, N 3.96; found C 81.62, H 10.12, N 4.11. 1H NMR (C6D6,
298 K): δ = 7.58 (d, JHH = 2.42 Hz, 1 H, ArH), 7.30–7.14 (m, 5 H,
Ph), 6.93 (d, JHH = 2.42 Hz, 1 H, ArH), 3.60 (br. s, 2 H, NCH2Ar),
3.50 (q, JHH = 6.82 Hz, 2 H, CH), 1.93 (s, 3 H, NCH3), 1.82 [s, 9
H, C(CH3)3], 1.44 [s, 9 H, C(CH3)3], 1.20 (d, JHH = 6.82 Hz, 3 H,
CH3) ppm. 13C NMR (76 MHz, C6D6, 298 K): δ = 19.6 (CHCH3),
29.6 [C(CH3)3], 31.9 [C(CH3)3], 33.8 [C(CH3)3], 35.2 [C(CH3)3],
36.3 (NCH3), 58.9 (CH2), 62.1 (CHCH3), 121.1, 121.6, 122.6,
122.8, 123.4, 123.9, 135.7, 140.2, 140.6, 154.1, 155.0 (12 C, 2Ar)
ppm.
[Mg(S-1f)2] (S-2f): To a solution of S-1f-H (1.36 g, 2.00 mmol) in
n-hexane (10 mL) was added MgBu2 (2.00 mL, 2.00 mmol) drop-
wise. The reaction mixture was stirred for 24 h, and the solvent was
removed to yield a pink oil. n-Hexane was added (20 mL) and,
after additional stirring at room temperature for 24 h, a pink solid
precipitated from the solution. The powder was collected by fil-
tration, washed with n-hexane (10 mL), and dried in vacuo to yield
S-2f (1.68 g, 89%, 2.30 mmol). C48H68MgN2O2 (729.35): calcd. C
79.05, H 9.40, N 3.84; found C 78.95, H 9.53, N 3.94. 1H NMR
(300 MHz, C6D6, 298 K): δ = 7.69 (br. s, 2 H, ArH), 7.16–7.21 (m,
5 H, ArH), 6.96 (br. s, 2 H, ArH), 4.21 (br. s, 4 H, NCH2Ar), 3.54
(br. s, 2 H, CHCH3), 1.93 (s, 6 H, NCH3), 1.84 (br. s, 6 H, CHCH3),
1.82 [s, 18 H, C(CH3)3], 1.45 [m, 18 H, C(CH3)3] ppm. 13C NMR
(76 MHz, C6D6, 298 K): δ = 29.6 [6 C, C(CH3)3], 29.7 [6 C,
C(CH3)3] 31.9 [2 C, C(CH3)3], 34.7 [2 C, C(CH3)3] 35.7 [2 C,
C(CH3)3], 36.4 (2 C, NCH3), 59.2 (CH2), 61.3 (CH), 156.3, 155.1,
141.6, 140.3, 131.2, 129.4, 124.0, 123.5, 122.8, 122.9, 122.1, 121.5,
121.3 (24 C, Ar) ppm.
[Mg(R-1c)]2 (R-2c): To a solution of R-1c-H2 (0.86 g, 1.61 mmol)
in toluene (15 mL) was added MgBu2 (1.61 mL, 1.61 mmol) drop-
wise. The mixture was stirred for 24 h, and the solution was concen-
trated to dryness. n-Hexane was added (25 mL), and the suspension
was stirred for 2 h. The resulting white powder was collected by
filtration, washed with n-hexanes (20 mL) and dried in vacuo to
yield R-2c (0.96 g, 54%, 0.86 mmol). Crystals suitable for X-ray
determination were obtained after recrystallization with n-hexane/
CH2Cl2. C70H106Mg2N2O6 (1120.23): calcd. C 75.05, H 9.54, N
Polymerization Procedure: In a Schlenk flask under argon, a com-
plex I was treated with -LA, [I]/[-LA] = 1:100 in toluene (10 mL).
The reaction mixture was stirred at the desired temperature for the
prescribed time. At certain time intervals, aliquots of about 1 mL
were removed for the determination of the conversion by 1H NMR
spectroscopy. After the reaction was complete, it was quenched
with methanol; the solution was concentrated in vacuo, and the
polymer was precipitated with an excess of cold methanol. A white
product was collected by filtration and dried in vacuo.
1
2.50; found C 74.78, H 9.47, N 2.41. H NMR (C6D6, 298 K): δ =
7.47 (d, JHH = 2.5 Hz, 2 H, ArH), 7.41 (d, JHH = 2.5 Hz, 2 H,
ArH), 7.10 (d, JHH = 2.6 Hz, 2 H, ArH), 6.92 (d, JHH = 2.6 Hz, 2
H, ArH), 4.65–4.73, 4.74–4.80 (2 m, 4 H, CHOCH2C2H4), 4.58–
4.63 (m, 2 H, CHOCH2C2H4), 3.19–3.26, 3.48–3.53 (2 m, 8 H,
CH2Ar), 3.04–3.13 (m, 4 H, NCH2), 2.55–2.60, 2.63–2.72 (2 m, 8
H, CHOCH2C2H4), 1.48, 1.54, 1.56, 1.88 [4 s, 72 H, C(CH3)3] ppm.
Details of X-ray Data Collection and Reduction: X-ray diffraction
data were collected with a KUMA KM4 CCD (ω-scan technique)
diffractometer equipped with an Oxford Cryosystem-Cryostream
cooler.[13] The space groups were determined from systematic ab-
sences and subsequent least-squares refinement. Lorentz and polar-
ization corrections were applied. The structures were solved by di-
rect methods and refined by full-matrix least squares on F2 by using
the SHELXTL package.[14] Non-hydrogen atoms were refined with
anisotropic thermal parameters. Hydrogen-atom positions were
calculated and added to the structure-factor calculations, but were
not refined (Table 3). The tBu groups, C(17)–C(110), C(27)–C(210),
and C(47)–C(410), and both tetrahydrofuran rings in 2e are disor-
dered and were solved with two positions for each moiety. The
13C NMR (76 MHz, C6D6, 298 K):
δ = 28.7, 31.7 (4 C,
CHOCH2C2H4), 29.8, 31.1, 31.9, 32.1 [24 C, C(CH3)3], 33.8, 33.9,
35.0, 35.1 [8 C, C(CH3)3], 55.5 (2 C, NCH2), 65.2, 64.4 (4 C,
CH2Ar), 68.9 (2 C, CHOCH2C2H4), 78.8 (2 C, CHOCH2C2H4),
121.5, 123.4 [4 C, o-C(Ar)-CH2N], 123.9, 125.1 [4 C, m-C(Ar)],
125.4, 127.1 [4 C, m-C(Ar)], 137.0, 137.2 [4 C, o-C(Ar)C(CH3)3],
138.9, 139.7 [4 C, p-C(Ar)C(CH3)3] ppm.
[Mg(rac-1c)]2 (rac-2c): rac-1c-H (2.53 g, 4.72 mmol) and MgBu2
(4.72 mL, 4.72 mmol) were allowed to react according to a pro-
Eur. J. Inorg. Chem. 2010, 3602–3609
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3607

J. Ejfler, K. Krauzy-Dziedzic, S. Szafert, L. B. Jerzykiewicz, P. Sobota
FULL PAPER
Table 3. Summary of crystallographic data for R-2c·2C6H5CH3·CH2Cl2 and S-2f.
R-2c·2C6H5CH3·CH2Cl2
S-2f
Empirical formula
Formula mass
Crystal system
Space group
Temperature [K]
Cell dimensions
a [Å]
C85H124Cl2Mg2N2O6
1389.38
monoclinic
P21
C48H68MgN2O2
729.35
orthorhombic
P212121
120(2)
100(2)
15.3323(10)
14.3051(10)
18.5068(14)
93.379(6)
4052.0(5)
2
10.859(5)
19.999(5)
20.399(5)
90
4430(3)
4
b [Å]
c [Å]
β [°]
V [Å3]
Z
Dcalcd. [g/cm3]
1.139
0.147
1.094
0.078
µ [mm–1]
Crystal dimensions [mm]
Radiation (λ [Å])
Reflections measured
Range/indices (h, k, l)
θ limit [°]
Total no. of unique data
No. of observed data [I Ͼ 2σ(I)]
No. of variables
No. of restraints
Absolute structure parameter
Rint
0.45ϫ0.24ϫ0.18
Mo-Kα (0.71073)
31 061
–18, 18; –17, 16; –22, 22
3.00–25.06
12756
7125
842
17
0.05(13)
0.35ϫ0.20ϫ0.19
Mo-Kα (0.71073)
41 850
–13, 13; –24, 23; –25, 25
2.74–26.11
8678
5522
486
0
–0.1(4)
0.1254
0.0962
R = Σ||Fo| – |Fc||/Σ|Fo| (all, observed)
0.1450, 0.0796
0.1759, 0.1543
0.969
0.1417, 0.0762
0.1653, 0.1447
0.994
2
2 2
4 1/2
wR2 = Σ[w(Fo – Fc ) ]/Σw(Fo
GOOF
)
(all, observed)
Data completeness
0.997
0.947, 0.975
0.54, –0.49
0.993
0.929, 0.966
0.41, –0.24
Absorption correction (Tmin, Tmax
)
∆ρ(max, min) [e/Å3]
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Acknowledgments
The authors would like to thank the Polish State Committee for
Scientific Research (Grants N204 261234 and N205 4036 33) for
support of this research.
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Received: December 14, 2009
Published Online: July 6, 2010
Eur. J. Inorg. Chem. 2010, 3602–3609
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3609