The group 13 metal complexes of sterically-hindered substituted iminophenol: synthesis and structure

Abstract

The dimethyl derivatives of the group 13 metals I–IV were synthesized by interaction of N-(1-(5,7-di-tert-butyl-2-methyl-2,3-dihydrobenzo[d]oxazol-2-yl)ethylidene)-2,6-diisopropylaniline (a) with Me₃M (M = Al (I), Ga (II), In (III), Tl (IV)) in high yield. The obtained complexes were characterized by elemental analysis, ¹H NMR and IR spectroscopy. The structures of II–IV were determined by X-ray single crystal analysis. The compounds II–IV were found to be monomeric in the solid state due to the bulkiness of the tert-butyl and iso-propyl groups in contrast to similar derivatives reported previously.

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Introduction

Schiff base ligands have been extensively studied mainly due to their preparation accessibilities, structural varieties, easily tunable electronic properties and good solubility in common solvents.^1–4 Additionally, they are widely used as antibacterial, antiviral, antifungal agents⁵ and anticancer drugs.^6,7 The versatility of the Schiff base ligands may be illustrated by the tridentate species HL1 (Scheme 1),⁸ which is known to form complexes with Fe(III), Co(III), Ni(II), Zn(II), Cd(II), Ga(III), In(III) and lanthanide(III) ions.^9–16 The complexes of Zn(II), Cd(II), Ga(III) and In(III) show intense luminescence at room temperature and thus have potential applications as photoactive materials.⁹

Scheme 1 Tridentate Schiff base ligand.

The Schiff bases derived from a large number of carbonyl compounds and amines have already been known. However, the studies of their optical properties like luminescence are rare. Recently we have obtained new ligand N-(1-(5,7-di-tert-butyl-2-methyl-2,3-dihydrobenzo[d]-oxazol-2-yl)ethylidene)-2,6-di-iso-propylaniline (a) based on 3-(2,6-di-iso-propylphenylimino)butan-2-one and 2-amino-4,6-di-tert-butylphenol. It have been shown that the compound a in solution exists in equilibrium with the enamine form containing hydroxy group.¹⁷ In this paper we describe the synthetic details, spectral characteristics, X-ray crystal structures and luminescence properties of new group 13 metal complexes with aforementioned ligand a.

Results and discussion

Synthesis and characterization

The N-(1-(5,7-di-tert-butyl-2-methyl-2,3-dihydrobenzo[d]oxazol-2-yl)ethylidene)-2,6-di-iso-propylaniline (a) was obtained by condensation of 2-amino-4,6-di-tert-butylphenol with 3-(2,6-di-iso-propylphenylimino)butan-2-one.¹⁷ This compound (a) smoothly reacts with Me₃M (M = Al, Ga, In, Tl) at room temperature in the ether solution forming dimethylaluminium, dimethylgallium, dimethylindium, dimethylthallium complexes I–IV with high yields (see Scheme 2).

Scheme 2 The synthesis of the complexes I–IV.

The complexes I–IV were isolated as a violet or deep blue solids. The color of the complexes depends from the crystals dispersion of the compounds II–IV. Although the group 13 metal alkyl derivatives are extremely moisture and oxygen sensitive, the obtained compounds are fairly stable on the exposure to the air. The complexes could be left at the inert atmosphere for several months without obvious decomposition. The complexes are slightly soluble in the cold saturated hydrocarbons such as pentane or hexane and very soluble in the aromatic hydrocarbons and THF. It is interesting that the compounds II and III are stable when heated in either coordinating (THF) or non-coordinating (toluene) solvents under vacuum.

All obtained products gave satisfactory elemental analysis results corresponding to the stoichiometric structure Me₂ML [M = Al (I), Ga (II), In (III), Tl (IV), L = 2,4-di-tert-butyl-6-(3-(2,6-di-iso-propylphenylimino)butan-2-ylidene)amino phenolato]. All of compounds decompose at temperatures above 160 °C without melting.

The obtained complexes have been characterized by IR and ¹H NMR spectroscopy. The IR spectra of the complexes I–IV feature the medium to strong distinctive C–H stretch vibration bands and the absence of the N–H signals unlike the IR spectra of free ligand a. The NMR signals of the metal bonded methyl protons in complexes I–IV (Al (−0.33 ppm), Ga (0.11 ppm), In (0.05 ppm), Tl (−0.08 and 0.5 ppm)) are shifted upfield in comparison with the signals of Me₃M (M = Al (−0.36 ppm), Ga (−0.15 ppm), In (−0.24 ppm) in ¹H NMR spectra correspondingly.¹⁸ It is supposed that the coordination of the nitrogen atom to the metal is responsible for the upfield shift of the methyl protons signals.

The confirmation of the molecular structure of the complexes II–IV and the determination of their monomeric or dimeric nature were provided by X-ray diffractometry. Unfortunately, we have not obtained the crystals of I suitable for X-ray analysis due to its rapid precipitation from the reaction mixture. Followed recrystallization of I from various solvents (THF, toluene) is accompanied by changing of the solution color from deep blue to brown and forming of the mixture of several products. The predominant one was found to be amidophenolate derivative V as a product of methyl group migration. Other products have not be identified (Scheme 3).

Scheme 3 The transformation of the complex I in solution.

The formation of the amidophenolate V was proved by NMR. After treatment of I with THF or toluene during 3 days the two fold decreasing of the metal bonded methyl substituent signal intensity (3 : 9 methyl : tert-butyl ratio vs. 6 : 9 one for I) is observed in the ¹H NMR spectrum. Also, the additional ligand bonded methyl signal (2.37 ppm) appears.

In the ¹³C NMR spectrum the signal of the Al–Me group is observed at −7.3 ppm being shifted upfield in comparison with one for I (−6.82 ppm). Also, there is only one signal corresponding to C=N group (171.9 ppm) in the ¹³C NMR spectrum. Finally, there are a lot of carbon signals in the aliphatic and aromatic area of the ¹³C NMR spectrum which can not be unambiguously attributed.

X-ray crystallographic study of II–IV

The results of the X-ray structure analysis show that the molecular structures of II–IV are similar. The molecular structure of II is depicted in Fig. 1. The crystal data and the collection and refinement parameters for II–IV are summarized in Table 1 and the selected interatomic distances (Å) and the bond angles (°) are given in Table 2.

Fig. 1 The molecular structure of II. Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms and Me-fragments of ⁱPr-, ^tBu-groups are omitted.

Table 1 Crystallographic data and structure refinement details for II–IV

	LGaMe2 (II)	LInMe2 (III)	LTlMe2 (IV)
Formula	C32H49GaN2O	C32H49InN2O	C32H49TlN2O
Mr	547.45	592.55	682.10
Crystal size, mm^3	0.10 × 0.10 × 0.05	0.53 × 0.20 × 0.07	0.28 × 0.18 × 0.05
T, K	100(2)	100(2)	100(2)
Crystal system	Monoclinic	Monoclinic	Monoclinic
Space group	P2(1)/c	P2(1)/c	P2(1)/m
a, Å	9.4025(4)	9.3801(7)	9.4850(6)
b, Å	9.5037(4)	9.5414(7)	9.6118(6)
c, Å	34.1500(1)	34.908(3)	17.0918(1)
α, °	90	90	90
β, °	95.9760(1)	97.4420(1)	98.300(1)
γ, °	90	90	90
Cell volume, Å^3	3035.0(2)	3097.9(4)	1541.90(2)
Z	4	4	2
Dcalc, g cm^−3	1.198	1.270	1.469
μ, mm^−1	0.932	0.788	5.262
F000	1176	1248	688
2θ range, °	52	52	54
Index ranges	−11 ≤ h ≤ 11	−11 ≤ h ≤ 11	−12 ≤ h ≤ 12
	−11 ≤ k ≤ 11	−11 ≤ k ≤ 11	−12 ≤ k ≤ 12
	−42 ≤ l ≤ 42	−43 ≤ l ≤ 43	−21 ≤ l ≤ 21
Reflns collected	25 545	25 613	14 206
Independent reflns	5958	6058	3567
Rint	0.0194	0.0403	0.0211
Completeness to θ	99.9	99.2	99.9
Data, restraints and parameters	5958/0/338	6058/12/352	3567/6/336
GooF	1.032	1.158	1.084
R1 (I > 2σ(I))	0.0297	0.0434	0.0167
wR2 (all data)	0.0742	0.1029	0.0399
Largest diff. peak and hole	0.509/−0.343	2.066/−1.054	1.501/−0.619

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Table 2 Selected distances [Å] and angles [°] of complexes II–IV (M = Ga (II), In (III), Tl (IV))

	LGaMe2 (II)	LInMe2 (III)	LTlMe2 (IV)
C(1)–O(1)	1.305(2)	1.307(3)	1.321(3)
C(2)–N(1)	1.403(2)	1.397(3)	1.401(3)
C(1)–C(2)	1.424(2)	1.423(4)	1.439(4)
C(15)–N(1)	1.299(2)	1.298(3)	1.295(3)
C(17)–N(2)	1.278(2)	1.277(3)	1.271(3)
C(15)–C(17)	1.496(5)	1.499(4)	1.500(4)
O(1)–M(1)	1.998(1)	2.196(2)	2.328(2)
N(1)–M(1)	2.099(1)	2.320(2)	2.507(2)
N(2)–M(1)	2.402(1)	2.463(2)	2.634(2)
O(1)–M(1)–N(1)	79.20(5)	72.71(7)	68.90(7)
N(1)–M(1)–N(2)	70.83(5)	67.57(8)	62.91(7)
O(1)–M(1)–N(2)	149.84(4)	140.18(7)	131.80(7)
C(31)–M(1)–C(32)	129.27(7)	136.4(1)	160.7(1)

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X-ray crystallographic study of II

Single crystals of II were obtained by cooling of a saturated ether solution. The complex II crystallizes in the monoclinic space group P(2)1/c. Although a few dimethylgallium complexes were found to be dimeric in the solid state,^19–21 the compound II is monomeric. The gallium atom is five coordinated with distorted trigonal bipyramidal environment. In compound II the nitrogen atoms N(1) and N(2) coordinate to the gallium atom forming intramolecular five-membered rings. Metallacycle Ga(1)N(1)C(15)C(17)N(2) is non planar, the angle between the Ga(1)N(1)N(2) and N(1)C(15)C(17)N(2) planes is 159.5°. Another five-membered ring is formed by Ga(1), O(1), C(1), C(2) and N(1) atoms; this one is planar (maximum deviation of atoms from the plane doesn't exceed 0.1 Å). The Ga(1)–O(1) bond length (1.998(1) Å) is slightly longer than those ones in 4-(N,N-dimethylaminophenolato)dimethylgallium (1.911(2) Å),¹⁹ [3,4-dimethoxyphenylmethyleneimino phenolato]dimethyl gallium (1.921(2) Å),²⁰ (quinolin-8-olate)dimethylgallium (1.868(2) Å),²¹ [N-salicylidene-2-aminopyridine]dimethylgallium (1.917(2) Å),²² bis(3,5-di-tert-butyl-2-((pyridin-2-ylmethylimino)methyl)phenolate)gallium (1.899(2) Å),²³ N,N-ethylene(salicylideneiminato)bis[dimethylgallium] (1.886(2) Å)²⁴ and shorter than those ones in (1-(2-piridyl)methyleneimino-2-naphthonato)dimethylgallium (2.002(4) Å).²⁵ It should be noted that the latter compound exists like II in a monomeric form in the solid state due to the steric hindrances of the naphthyl moiety. The Ga–N distances (2.099(1) Å for Ga(1)–N(1) and 2.402(1) Å for Ga(1)–N(2)) in II are slightly shorter than those ones reported in ref. 20 and 22–25 (2.136(2)–2.316(3) Å) for Ga(1)–N(1) and are longer than those ones in compound obtained in ref. 23 and 24 for Ga(1)–N(2) respectively. These bond distances indicate that the nitrogen atoms are datively bounded to the gallium atom. The difference in Ga–O and Ga–N lengths between the present compound (II) and other ones should be caused by the steric bulkiness two tert-butyl and two iso-propyl groups.

The distances C–C and C–N (C(15)–C(17) 1.496(5) Å, N(1)–C(15) 1.299(2) Å, N(2)–C(17) 1.278(2) Å) forming the diazadiene moiety are corresponding to the bond orders of one and two, respectively.

Crystal structure determination of compounds III and IV

The crystals of III and IV suitable for structural determination were obtained from concentrated hexane solution.

The compound III was found to be isomorphic to II. The structure of the complex IV was resolved and refined in the monoclinic space group P(2)1/m with the cell volume (V = 1541.90(2) ų, c = 17.0918(1) Å) is a half of the cell volume of II and III (II: V = 3035.0(2) ų, c = 34.1500(1) Å, III: V = 3097.9(4) ų, c = 34.908(3) Å). The asymmetric unit cell in IV contains one molecule disordered over two sites. Geometry parameters of the molecules II–IV are close to each other. The distances In–O (2.196(2) Å), In–N (2.320(2), 2.463(2) Å) in III and Tl–O (2.328(2) Å), Tl–N (2.507(2), 2.634(2) Å) in IV are slightly longer than those ones in II (Ga–O: 1.998(1) Å, Ga–N: 2.099(1), 2.402(1) Å) due to the larger covalent radii of indium (1.42 Å) and thallium (1.45 Å) respectively in comparison with gallium (1.22 Å).²⁶ The bond values of the ligand in III and IV are corresponding with those in II (Table 2). As for II, the metallacycles MNCCN in III and IV are non planar. The angles between the MNN and NCCN planes are 159.6° (III) and 157.5° (IV) respectively. It could be noted that MOCCNCCN fragments in III and IV are less distorted in comparison II. The angles between MOCCN and MNCCN planes are 167.9° (II), 169.7° (III) and 169.3° (IV) respectively.

It should be also noted that the compound III is a monomeric in the solid state in contrast to similar indium compound^27,28 as a result of the presence of sterically hindered tert-butyl and iso-propyl groups in the structure.

Caution! Thallium and its compounds are toxic and must be handled with care.

Electrochemical study

On the assumption of the crystal structure determination of the compounds II–IV we have shown that II–IV contain coordinated diazadiene moiety which is potentially able to the one electron reduction. The electrochemical study of IV have been performed to estimate this possibility (compound IV was selected due to the absence of any reactivity of the metal bonded methyl groups).

The cyclic voltammetric study of the complex IV was performed using CH₂Cl₂ as a solvent and tetrabutylammonium perchlorate as supporting electrolyte at the scan rate of 0.2 V s⁻¹. One irreversible reductive response at −1.60 V versus Ag/AgCl/KCl electrode was tentatively assigned to the reduction of coordinated diazadiene fragment of the ligand. The reduction is accompanied by the strong adsorption of reaction products on the electrode surface therefore the evaluation of the electron number and the electrochemical reaction reversibility were complicated. At higher reductive response (−2.054 V) the irreversible reduction of the metal ion is observed.

Photoluminescence (PL) determination

The PL emission spectra of the complexes III and IV were measured as shown on the Fig. 2. The compounds III and IV possess an intense photoluminescence properties at room temperature, which were not observed for I and II. The PL emission data shows that the emission bands are located in the violet region. Their emission maxima lies at 402 and 405 nm with the intensities of 458 and 340 a.u. for complexes IV and III respectively.

Fig. 2 PL emission spectra of III and IV (THF, 3.15 × 10⁻⁶ mol L⁻¹).

Conclusions

In the present work we have described the synthesis of dimethyl derivatives of group 13 metals I–IV. All of obtained complexes were characterized by elemental analysis, NMR and IR spectroscopy. The structures of gallium, indium and thallium compounds II–IV were determined by X-ray single crystal analysis. The compounds II–IV were found to be a monomeric in the solid state due to the bulkiness of the tert-butyl and iso-propyl groups unlike earlier reported derivatives.^19–25 We have reported that aluminium derivative I after recrystallization from various solvents (THF, toluene) undergoes the migration of the methyl group from the metal atom to C=N group of the ligand with the formation of the amidophenolate derivative V. We have found that III and IV possess an intense photoluminescence at room temperature, which was not observed for I and II. It is suggested that complexes III and IV may be potentially used as a photoactive materials.

Experimental

General comments

N-(1-(5,7-Di-tert-butyl-2-methyl-2,3-dihydrobenzo[d]-oxazol-2-yl)ethylidene)-2,6-di-iso-propylaniline (a)¹⁷ and Me₃Tl²⁹ were prepared according to previously described procedures. Solvents were freshly purified by standard methods.³⁰ The Me₃M (M = Al, Ga, In) were used as purchased. All syntheses have been provided in evacuated ampoules.

The NMR spectra were recorded on a “Bruker Avance III” NMR spectrometer (400 MHz) using C₆D₆ as the solvent with tetramethylsilane as the internal standard. IR-spectra were recorded by “Specord M-80”. Elemental analyses were obtained on “EuroEA-3028-HT”. Metal atom percentage was estimated by the pyrolysis of the investigated samples with the followed weighing of the obtained oxides. The PL spectra were recorded on UV-spectrometer “Perkin Elmer UV/VIS Lambda 25” at room temperature.

Electrochemical studies were carried out using an IPC-pro potentiostate in three electrode mode. The glassy carbon (d = 2 mm) disk was used as working electrode; the auxiliary electrode was a platinum-flag electrode. The reference electrode was an Ag/AgCl/KCl (sat.) with watertight diaphragm. All measurements were carried out under argon. The samples were dissolved in the pre-deaerated solvent. The rate scan was 200 mV s⁻¹. The supporting electrolyte 0.1 M [(n-Bu)₄N]ClO₄ (99%, ‘‘Acros”) was doubly recrystallized from the aqueous ethanol and was dried in vacuum at 50 °C for 48 h.

The X-ray data for II–IV were collected on a Bruker Smart Apex diffractometer (graphite-monochromated, MoKα-radiation, ω-scan technique, λ = 0.71073 Å, T = 100(2) K). The structures were resolved by direct methods and were refined on F² using SHELXTL³¹ package. All non-hydrogen atoms were found from Fourier syntheses of electron density and were refined anisotropically. All hydrogen atoms were placed in calculated positions and were refined in the riding model. SADABS³² was used to perform area-detector scaling and absorption corrections. The details of crystallographic, collection and refinement data are shown in Table 1 and corresponding CIF files are available in ESI.

Synthesis

Dimethyl aluminium (2,4-di-tert-butyl-6-(3-(2,6-diisopropylphenylimino)butan-2-ylidene)aminophenolate) (I). Me₃Al (0.144 g, 2 mmol) was added to a solution of a (0.898 g, 2 mmol) in diethyl ether (30 mL). The color immediately changed from colorless to deep blue. The reaction mixture was stirred during 30 min at room temperature, all volatiles were removed and the deep blue crystals were isolated after cooling.

Yields: 0.879 g (87%, based on Me₃Al). Found (%): C, 76.21; H, 9.82; Al, 5.36; N, 5.48. Calculated for C₃₂H₄₉AlN₂O (%): C, 76.15; H, 9.79; Al, 5.35; N, 5.55. ¹H NMR (C₆D₆, δ/ppm, J/Hz): −0.33 (s, 6H, CH₃Al); 0.91 (d, 6H, (CH₃)₂CH, J = 6.85); 1.29 (d, 6H, (CH₃)₂CH, J = 6.85); 1.36 (s, 9H, tBu); 1.52 (s, 3H, CH₃); 1.71 (s, 9H, tBu); 1.80 (s, 3H, CH₃); 2.78 (sept, 2H, (CH₃)₂CH, J = 6.85); 7.08–7.13 (m, 3H, H_arom); 7.20 (d, 1H, H_AmPh, J = 2.22); 7.61 (d, 1H, H_AmPh, J = 2.22). ¹³C NMR (C₆D₆, δ/ppm): −6.82 ((CH₃)₂Al); 18.20; 19.54; 24.00; 24.51; 28.18; 29.04; 31.13; 34.01; 35.35; 115.61; 124.27; 126.90; 130.90; 136.40; 139.87; 141.99; 149.26; 164.32 (C=N); 168.77 (C=N). IR (nujol, ν/cm⁻¹): 465w, 510w, 550m, 589w, 613w, 664s, 683m, 721m, 742m, 770m, 784m, 798s, 847s, 865m, 900w, 919m, 935w, 943w, 982m, 1027w, 1055w, 1134s, 1171s, 1197m, 1209m, 1239m, 1258s, 1307m, 1333m, 1363s, 1443s, 1515s, 1562w, 1627m, 1707w.

Dimethyl gallium (2,4-di-tert-butyl-6-(3-(2,6-diisopropylphenylimino)butan-2-ylidene)aminophenolate (II). Prepared as described for I from a (0.898 g, 2 mmol) and trimethylgallium (0.23 g, 2 mmol). Complex II was isolated as violet crystals from Et₂O.

Yields: 0.910 g (83%, based on Me₃Ga). Found (%): C, 70.25; H, 9.08; Ga, 12.71; N, 5.08. Calculated for C₃₂H₄₉GaN₂O (%): C, 70.20; H, 9.02; Ga, 12.74; N, 5.12. IR (nujol, ν/cm⁻¹): 491w, 515w, 535w, 592m, 612w, 636w, 654w, 677w, 740s, 781s, 790s, 843m, 864m, 911m, 935w, 976s, 1027w, 1050w, 1124s, 1162s, 1192s, 1240s, 1260s, 1308s, 1331m, 1358s, 1376s, 1508m, 1556w, 1598w, 1633m. ¹H NMR (C₆D₆, δ/ppm, J/Hz): 0.11 (s, 6H, (CH₃)₂Ga); 0.94 (d, 6H, (CH₃)₂CH, J = 6.84); 1.21 (d, 6H, (CH₃)₂CH, J = 6.84); 1.35 (s, 9H, tBu); 1.53 (s, 3H, CH₃); 1.76 (s, 9H, tBu); 2.01 (s, 3H, CH₃); 2.66 (sept, 2H, (CH₃)₂CH, J = 6.84); 7.06–7.11 (m, 4H, H_arom); 7.50 (d, 1H, H_arom, J = 2.29). ¹³C NMR (C₆D₆, δ/ppm): −4.22 ((CH₃)₂Ga); 19.72; 20.45; 23.78; 24.34; 28.02; 29.25; 29.59; 31.50; 31.65; 116.37; 123.98; 126.00; 126.92; 130.39; 134.53; 137.99; 140.10; 142.86; 153.56; 164.85 (C=N); 165.56 (C=N).

Dimethyl indium (2,4-di-tert-butyl-6-(3-(2,6-diisopropylphenylimino)butan-2-ylidene)aminophenolate (III). Prepared as described for I from a (0.898 g, 2 mmol) and trimethylindium (0.32 g, 2 mmol). After the removal of ether in vacuo, hexane was added to the crude product. Complex III was isolated as deep blue crystals from hexane.

Yield: 1.020 g (86%, based on Me₃In). Found (%): C, 64.89; H, 8.37; In, 19.39; N, 4.69. Calculated for C₃₂H₄₉InN₂O (%): C, 64.86; H, 8.33; In, 19.38; N, 4.73. ¹H NMR (C₆D₆, δ/ppm, J/Hz): 0.05 (s, 6H, (CH₃)₂In); 0.87 (d, 6H, (CH₃)₂CH, J = 7.8); 1.15 (d, 6H, (CH₃)₂CH, J = 7.8); 1.37 (s, 9H, tBu); 1.48 (s, 3H, CH₃); 1.80 (s, 9H, tBu); 1.94 (s, 3H, CH₃); 2.63 (sept, 2H, (CH₃)₂CH, J = 7.8); 7.02–7.60 (m, 5H, H_arom). ¹³C NMR (C₆D₆, δ/ppm): −6.11 (CH₃)₂In; 20.09; 20.21; 23.88; 24.29; 28.01; 29.37; 31.44; 31.64; 34.03; 35.75; 116.61; 124.03; 126.39; 126.92; 130.53; 133.40; 138.65; 141.17; 142.03; 150.34; 166.67 (C=N); 168.74 (C=N). IR (nujol, ν/cm⁻¹): 487s, 528s, 547w, 587m, 601m, 634w, 649w, 665w, 710s, 760w, 781s, 791s, 840s, 871s, 911s, 935m, 975s, 1004w, 1025w, 1056w, 1125s, 1160s, 1189s, 1200s, 1236m, 1255s, 1283w, 1305m, 1335m, 1366w, 1409w, 1506s, 1534w, 1553m, 1601w, 1629m.

Dimethyl thallium (2,4-di-tert-butyl-6-(3-(2,6-diisopropylphenylimino)butan-2-ylidene)aminophenolate (IV). Prepared as described for III from a (0.898 g, 2 mmol) and trimethylthallium (0.498 g, 2 mmol). Complex IV was isolated as deep blue crystals from hexane.

Yield: 1.118 g (82%, based on Me₃Tl). Found (%): C, 56.38; H, 7.27; N, 4.06; Tl, 29.95. Calculated for C₃₂H₄₉N₂OTl (%): C, 56.34; H, 7.24; N, 4.11; Tl, 29.96. IR (nujol, ν/cm⁻¹): 1631m (C=N), 1593m, 1547m, 1502s, 1364m, 1326m, 1303s, 1277s, 1255s, 1232s, 1190s, 1160s, 1119s, 1051w, 1025w, 976s, 939m, 908m, 871s, 841m, 777s, 732m, 641w, 585m, 532m, 510w, 476m. ¹H NMR (C₆D₆, 400 MHz, δ/ppm, J/Hz): 0.41 (br, s, 3H, Tl(CH₃)₂); 1.03 (d, 6H, (CH₃)₂CH, J = 6.83); 1.20 (d, 6H, (CH₃)₂CH, J = 6.83); 1.39 (br, s, 3H, Tl(CH₃)₂); 1.51 (s, 9H, tBu); 1.61 (s, 3H, CH₃); 1.99 (s, 9H, tBu); 2.18 (s, 3H, CH₃); 2.70 (sept, 2H, (CH₃)₂CH, J = 6.83); 6.99 (d, 1H, H_AmPh, J = 2.52); 7.26 (m, 3H, H_arom); 7.70 (d, 1H, H_arom, J = 2.52). ¹³C NMR (C₆D₆, δ/ppm): 14.35 (CH₃)₂Tl; 19.96 (CH₃); 21.22 (CH₃); 24.04 ((CH₃)₂CH); 27.79 ((CH₃)₂CH); 29.74 ((CH₃)₃CH); 31.83 ((CH₃)₂CH); 33.95 ((CH₃)₂CH); 35.83 ((CH₃)₂CH); 107.38; 114.53; 117.35; 123.83; 125.12; 125.35; 131.66; 133.88; 137.33; 141.45; 143.81; 155.31 (C=N); 168.24 (C=N).

Methyl aluminium (2,4-di-tert-butyl-6-(3-(2,6-diisopropylphenylimido)butan-2-ylidene)aminophenolate (V). The complex I was dissolved in THF/toluene. The blue color disappears during several hours. Solvent was removed in vacuum and residue was dissolved in C₆D₆.

¹H NMR (C₆D₆, δ/ppm, J/Hz): −0.27 (s, 3H, (CH₃)Al); 1.01 (d, 6H, (CH₃)₂CH, J = 6.45); 1.05 (d, 6H, (CH₃)₂CH, J = 6.45); 1.1 (s, 9H, tBu); 1.27 (s, 9H, tBu); 1.67 (s, 6H, (CH₃)_amide); 2.37 (s, 3H, CH₃); 2.54 (sept, 2H, (CH₃)₂CH, J = 6.45); 7.00–7.12 (m, 5H, H_arom).

Acknowledgements

The authors are grateful to the Russian Foundation for Basic Research (projects no. 14-03-31071_mol_a, 15-33-20628-mol_a_ved), the Council for Grants of the President of Russian Federation for Support of Leading Scientific Schools (grant no. NSh 271.2014.3) and Fund competitive support to students, graduate students and young researchers and teachers UNN.

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