Te–Te and Te–C bond cleavage reactions using a monovalent gallanediyl

Abstract

LGa (L = [(2,6-i-Pr₂-C₆H₃)NC(Me)]₂CH) reacts with elemental tellurium with formation of the Te-bridged compound [LGa-μ-Te]₂1, whereas the reactions with Ph₂Te₂ and i-Pr₂Te occurred with cleavage of the Te–Te and Te–C bond, respectively, and subsequent formation of LGa(TePh)₂2 and LGa(i-Pr)Tei-Pr 3. 1–3 were characterized by heteronuclear NMR (¹H, ¹³C, ¹²⁵Te) and IR spectroscopy and their solid state structures were determined by single crystal X-ray analyses.

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Introduction

Univalent LGa containing the sterically crowded β-diketiminate ligand (L = [(2,6-i-Pr₂-C₆H₃)NC(Me)]₂CH)¹ adopts a monomeric structure in the solid state and in solution. The gallium valence shell contains two bond pairs, a lone pair and an empty p-orbital. Therefore, LGa can react as electrophilic and nucleophilic reagent at the gallium atom. Computational calculations predicted that LGa is a good σ-donor but a poor π-acceptor due to the low energy and high s-character of the HOMO, and the large energy difference (95.3–110 kcal mol⁻¹) between the HOMO and the rather diffuse acceptor 4p-orbital (LUMO+1).^2–4 The σ-donor capacity of LGa was experimentally demonstrated for instance with the synthesis of the Lewis acid–base adduct LGa→B(C₆F₅)₃ ⁵ and other p- or d-block metal complexes as well as with the synthesis of a large variety of (late) transition metal complexes.⁶ The latter were shown to be promising reagents for the activation of small molecules such as ethylene and have been used as precursors for the formation of heterometallic clusters,^7,8 which in part can be described as molecular models for alloys.

While the coordination chemistry of LGa has been developed to a far greater extent compared to that of its lighter homologue LAl, its use in the transformation of unsaturated organic substrates has not,^9–11 which most likely results from the weaker reducing properties of LGa. However, LGa was found to react with E–X bonds via insertion of the Ga(I) centre and subsequent formation of covalent Ga–E bonds.¹² This reaction pathway was used for cluster formation reactions via oxidative insertion/reductive elimination processes. The synthesis of molecular gallium–tin intermetallic clusters upon reaction of LGa with SnCl₂ ¹³ as well as two galla-dibismuthenes containing covalent Ga–Bi single-bonds and Bi=Bi double bonds, which were obtained from the reactions of LGa with Bi(OR)₃ (R = O₂SCF₃, C₆F₅),¹⁴ represent remarkable experimental “snapshots” of these reactions. The cluster compounds can be considered as isolated reaction intermediates on the way to full reduction to tin metal and bismuth metal, respectively. The syntheses of these complexes demonstrate the promising potential of LGa to serve as selective reducing agent in the preparation of metalloid clusters and subvalent “metastable” compounds.

In addition to these interesting studies on the synthesis of intermetallic compounds, the capability of LGa in bond activation reactions was also studied. LGa was reacted with a large variety of compounds containing different element–element bonds including dihydrogen¹⁵ as well as electronically unsaturated molecules such as N₂O, organic azides N₃R and elemental sulphur. Many of these reactions were performed in order to synthesize compounds containing multiple bonds to gallium. However, reactions of LGa with N₂O or S₈ yielded the oxo- or sulfido bridged dimers [LGa-μ-E]₂ (E = O, S),¹⁶ while its reaction with N₃SiMe₃ proceeded with formation of a cyclic gallium tetrazole and a gallium imide/azide compound. The most-likely formed reaction intermediate, a monomeric gallium imide LGa=NR,¹⁷ was finally synthesized by reaction of LGa with the sterically encumbered azide Ar*N₃ (Ar* = 2,6-Trip₂-C₆H₃, Trip = 2,4,6-i-Pr₃-C₆H₂) and structurally characterized by single crystal X-ray diffraction.¹⁸

Our long-term interest in the reactivity of low-valent organometallics of group 12 to 16 elements prompted us to start investigations on the general reactivity of LM (M = Al, Ga, In) toward group 15 compounds such as BiEt₃ ¹⁹ as well as tetraalkyldistibanes and dibismuthanes Et₄E₂ (E = Sb, Bi).²⁰ These reactions were found to proceed with cleavage of the Bi–C as well as E–E bond and subsequent formation of LM(Et)BiEt₂ and LM(EEt₂)₂, respectively, in which the Ga atom is oxidized from the formal oxidation state +I to +III. Moreover, oxidative addition reactions of monovalent Zn(I) compounds,²¹ germylenes and stannylenes²² as well as distibanes and dibismuthanes²³ with dichalcogenanes were reported by us. In addition, insertion reactions of elemental chalcogens into metal–metal bonds were observed in reactions with tetraalkyldistibanes and -dibismuthanes.^24,25 We herein report on the reactions of LGa with elemental tellurium as well as diphenylditellane Ph₂Te₂ and diisopropyltellane i-Pr₂Te, which proceeded with Te–Te and Te–C bond cleavage and subsequent formation of compounds containing direct Ga–Te σ-bonds.

Results and discussion

Equimolar amounts of LGa were reacted with elemental tellurium, diphenylditellane Ph₂Te₂ and diisopropyltellane i-Pr₂Te in toluene at ambient temperature, yielding the Te-bridged dimer [LGa-μ-Te]₂1 as well as LGa(TePh)₂2 and LGa(i-Pr)Tei-Pr 3, respectively (Scheme 1). 1–3 are moisture sensitive, yellow to pale yellow crystalline solids but moderately stable toward air. 1 is sparingly soluble in benzene, toluene and n-hexane whereas 2 and 3 are soluble in these solvents.

Scheme 1 Synthesis of 1–3.

The ¹H and ¹³C NMR spectra of 1–3 show the characteristic resonances of the organic entities. ¹H NMR spectral pattern of 1 and 2 are similar to those of LGa and C_2v symmetric molecules related to the β-diketiminate ligands. They exhibit single resonances for the γ-CH (4.59 ppm, 1; 4.76 ppm, 2) and two methyl groups of the C₃N₂Ga rings (1.35 ppm 1; 1.50 ppm 2). The methyl protons of the isopropyl substituents and methine protons appear as two doublets (1.13 & 1.10 ppm 1; 1.48 & 1.08 ppm 2) and a septet (3.33 ppm 1; 3.62 ppm 2), respectively. Due to its low solubility, the ¹³C and ¹²⁵Te NMR resonances of 1 were not intense enough. The ¹³C NMR spectrum of 2 shows 14 signals including the characteristic resonances due to the γ-CH (99.22 ppm) backbone carbon atom, both β-C atoms atoms of the C₃N₂Ga ring (170.63 ppm) and the methine (29.36 ppm) and methyl carbon atoms of isopropyl groups (27.01, 25.44 ppm). Compound 3 shows more distinct ¹H and ¹³C NMR patterns than 1 and 2. Due to the presence of three different substituents at the Ga atom and a hindered rotation about the N–C bonds, the i-Pr groups in 3 are magnetically inequivalent, leading to six doublets (1.87, 1.61, 1.34, 1.31, 1.08, 0.67 ppm) in the ¹H NMR spectrum. The six methine protons of the i-Pr groups appear as four septets (4.16, 3.82, 3.42, 1.04 ppm) with the integral ratios of 2 : 1 : 2 : 1, respectively. Integrals of 2 H belong to the i-Pr methine groups of the L ligand. The γ-CH and two methyl groups of the C₃N₂M ring are in the mirror plane and exhibit only single resonances at 4.67 and 1.51 ppm, respectively. The ¹³C{¹H} NMR spectrum of 3 shows the expected 19 signals and some of them were tentatively assigned to the i-Pr carbons atoms in 3 in the Experimental section. Elemental analyses (C, H, N) of 1–3 confirm the structural compositions and their analytical pure nature. Furthermore, the NMR (¹H, ¹³C, ¹²⁵Te) and IR spectroscopic details are in accordance with the proposed formulations of 1–3.

1–3 are stable in solution and no reduction/decomposition occurs even at 90 °C in C₆D₆. Despite that the first Te–C bond cleavage of i-Pr₂Te occurred smoothly at room temperature, the second Te–C bond couldn't be cleaved by reaction with an additional equivalent of LGa. In contrast, we successfully cleaved the Te–C and Te–Te bonds of Ph₂Te₂ upon reaction with an equimolar amount of the Lewis acid–base adduct LGa→B(C₆F₅)₃ in C₆D₆, which yielded an yellow-orange solution at room temperature within three days. The ¹H NMR spectrum of the reaction mixture shows the presence of four different types of γ-CH protons with different integral ratios (Fig. S11†) and the spectral comparison evidences the presence of traces of 1 (4.57, 3.39 ppm) and 2 (4.76, 3.62 ppm) along with two unknown compounds. Prolonged storage of the reaction mixture (10 days) at room temperature led to pale yellow crystals of 1. During this period the peaks corresponding to 2 gradually decreased. Unfortunately, our efforts to isolate the major component of the reaction mixture (see Fig. S12†) failed since the solution is highly sensitive and decomposes to oily substances. According to the ¹H NMR pattern, the Ga atom in the major product has three different substituents.

Single crystals of 1 were grown separately in benzene and toluene solutions. 1a is the solvent-free compound (obtained from the 1 : 1 reaction of Ph₂Te₂ and LGa→B(C₆F₅)₃) and crystallises in the monoclinic space group P2₁/n, while 1b is its toluene hemi-solvate (obtained from the 1 : 1 reaction of Te and LGa), which crystallises in the monoclinic space group C2/m. Single crystals of 2 were obtained from a freshly prepared n-hexane solution upon storage at room temperature, while single crystals of 3 were grown from saturated toluene solutions at 5 °C. 2 and 3 crystallise in the orthorhombic space groups Pbca (2) and Pnma (3). Fig. 1–3 show the solid state structures of 1a, 2 and 3 and the selected bond lengths and bond angles are given at the figure captions. Table 1 summarizes the crystal data and details of the structural determinations.

Fig. 1 Solid state structure of 1a (thermal ellipsoids are shown at 50% probability levels); H atoms are omitted for clarity. Symmetry generated part in pale colours. Selected bond lengths and angles in Å and °: Te(1)–Ga(1)#1 2.5777(4), Te(1)–Ga(1) 2.5898(4), Ga(1)–N(2) 1.979(2), Ga(1)–N(1) 1.982(2), C(1)–C(2) 1.397(4), C(2)–C(3) 1.397(4), N(1)–C(1) 1.339(4), N(2)–C(3) 1.337(4), N(2)–Ga(1)–N(1) 94.92(10), N(2)–Ga(1)–Te(1)#1 118.56(7), N(1)–Ga(1)–Te(1)#1 115.72(7), N(2)–Ga(1)–Te(1) 114.87(7), N(1)–Ga(1)–Te(1) 115.13(7), Te(1)#1–Ga(1)–Te(1) 98.883(11), C(3)–C(2)–C(1) 128.4(3), N(1)–C(1)–C(2) 123.6(3), N(2)–C(3)–C(2) 124.1(3).

Fig. 2 Solid state structure of 2 (thermal ellipsoids are shown at 50% probability levels); H atoms are omitted for clarity. Selected bond lengths and angles in Å and °: Ga(1)–N(1) 1.950(4), Ga(1)–N(2) 1.971(4), Ga(1)–Te(1) 2.5586(5), Ga(1)–Te(2) 2.6076(6), Te(1)–C(41) 2.114(5), Te(2)–C(31) 2.144(4), N(1)–C(1) 1.342(6), N(2)–C(3) 1.334(5), C(1)–C(2) 1.377(6), C(2)–C(3) 1.406(6), N(1)–Ga(1)–N(2) 97.45(15), N(1)–Ga(1)–Te(1) 110.65(11), N(2)–Ga(1)–Te(1) 114.06(11), N(1)–Ga(1)–Te(2) 110.98(12), N(2)–Ga(1)–Te(2) 109.00(11), Te(1)–Ga(1)–Te(2) 113.587(19), C(1)–C(2)–C(3) 130.5(4), N(1)–C(1)–C(2) 123.5(4), N(2)–C(3)–C(2) 122.7(4).

Fig. 3 Solid state structure of 3 (thermal ellipsoids are shown at 50% probability levels); H atoms are omitted for clarity. Symmetry generated part in pale colours. Selected bond lengths and angles in Å and °: Te(1)–C(18) 2.1983(19), Te(1)–Ga(2) 2.5929(4), Ga(2)–N(1) 1.9739(10), Ga(2)–C(16) 1.9902(17), N(1)–C(1) 1.3321(13), C(1)–C(2) 1.4044(13), N(1)–Ga(2)–N(1)#1 95.66(5), N(1)–Ga(2)–C(16) 115.64(4), N(1)–Ga(2)–Te(1) 112.07(3), C(16)–Ga(2)–Te(1) 105.84(5), C(1)–C(2)–C(1)#1 128.03(14), N(1)–C(1)–C(2) 123.73(11).

Table 1 Crystallographic data of 1a, 1b, 2, and 3

	1a	1b	2	3
a R 1 = ∑(||Fo| − |Fc||)/∑|Fo| (for I > 2σ(I)). b wR2 = {∑[w(Fo^2 − Fc^2)^2]/∑[w(Fo^2)^2]}^1/2. c Goodness of fit = {∑[w(|Fo^2| − |Fc^2|)^2]/(Nobservns − Nparams)}^1/2. w^−1 = σ^2(Fo^2) + (aP)^2 + bP with P = [Fo^2 + 2Fc^2]/3, a and b are constants chosen by the program.
Empirical formula	C58H82Ga2N4Te2	C61.50H86Ga2N4Te2	C41H51GaN2Te2	C35H55GaN2Te
M	1229.91	1275.98	896.75	701.13
Crystal size [mm]	0.280 × 0.220 × 0.180	0.220 × 0.180 × 0.130	0.415 × 0.326 × 0.198	0.200 × 0.190 × 0.100
T [K]	130(1)	100(1)	100(1)	100(1)
Crystal system	Monoclinic	Monoclinic	Orthorhombic	Orthorhombic
Space group	P21/n	C2/m	Pbca	Pnma
a [Å]	14.0688(10)	18.6322(4)	19.1512(8)	16.888(3)
b [Å]	13.8376(10)	20.9742(5)	19.7070(8)	19.798(3)
c [Å]	15.2807(11)	16.4363(4)	20.3343(8)	10.2125(15)
α [°]	90	90	90	90
β [°]	106.759(2)	98.9820(10)	90	90
γ [°]	90	90	90	90
V [Å^3]	2848.5(4)	6344.5(3)	7674.4(5)	3414.5(9)
Z	2	4	8	4
D calc [g cm^−1]	1.434	1.336	1.552	1.364
μ (MoKα [mm^−1])	1.988	1.788	2.237	1.668
Transmissions	0.75/0.50	0.75/0.68	0.75/0.52	0.75/0.63
F(000)	1248	2596	3568	1448
Index ranges	−20 ≤ h ≤ 21	−27 ≤ h ≤ 27	−27 ≤ h ≤ 27	−25 ≤ h ≤ 23
	−20 ≤ k ≤ 20	−28 ≤ k ≤ 31	−27 ≤ k ≤ 26	−30 ≤ k ≤ 26
	−21 ≤ l ≤ 22	−24 ≤ l ≤ 24	−26 ≤ l ≤ 28	−15 ≤ l ≤ 15
θ max [°]	32.618	32.155	30.255	33.202
Reflections collected	43 835	86 728	131 905	77 225
Independent reflections	10 256	11 354	11 268	6666
R int	0.0375	0.0319	0.0446	0.0307
Refined parameters	298	342	415	193
R 1 [I > 2σ(I)]^a	0.0440	0.0223	0.0469	0.0225
wR2 [all data]^b	0.1300	0.0606	0.1249	0.0578
GooF^c	1.081	1.072	1.127	1.046
Δρfinal (max/min) [e Å^−3]	3.763/−1.417	0.986/−0.453	2.287/−1.586	0.677/−0.358

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The Ga atoms in 1a, 1b, 2 and 3 each adopt slightly distorted tetrahedral coordination spheres.‡ The six-membered GaN₂C₃ rings show boat-type conformations, in which the Ga atoms are significantly out of-plane (deviation from best plane of the ligand's backbone: 0.521(3) Å 1a, 0.5853(19) and 0.560(2) Å 1b, 0.721(5) Å 2, 0.6309(18) Å 3) The average Ga–N bond length (1.981(2) Å 1a; 1.992(2) Å 1b; 1.961(4) Å 2; 1.9739(10) Å 3) and N–Ga–N bond angle (94.92(10)° 1a; 95.38(6)° 1b; 97.45(15)° 2; 95.66(5)° 3) as observed for 1, 2 and 3 are almost identical to that of LGa, for which an average Ga–N distance of 2.054(2) Å and a N–Ga–N bond angle of 87.56(6)° was reported.¹ The Te–Ga–Te (98.88(2)° 1a; 100.39(1)° 1b; 113.59(2)° 2) and C–Ga–Te bond angles (105.84(5)° 3) are smaller compared to the N–Ga–N bond angles. The Ga–Te bond lengths (2.5777(4), 2.5898(4) Å 1a; 2.5809(2), 2.5909(2) Å 1b; 2.5586(5), 2.6076(6) Å 2; 2.5929(4) Å 3) are comparable to those reported for [K(OEt₂)₃][(PhTe)₂Ga{[N(2,6-i-Pr₂-C₆H₃)C(H)]₂}] (2.5785(12), 2.6577(10) Å),²⁶ the Te-bridged dimers {[Me₃SiNC(Ph)C(SiMe₃)₂]Ga-μ-Te}₂ (2.570 Å)²⁷ and [i-Pr₂PNP(i-Pr₂)TeGa-μ-Te]₂ (2.5783(7) Å) as well as the six-membered heterocycle [i-Pr₂PNP(i-Pr₂)TeGa-μ-Te]₃ (2.582(2) Å).²⁸ In addition, the mixed Te/carboxylate-bridged compound [R₂Ga₂(μ-Te)(μ-OOCCH₃)₂] (2.534 Å)²⁹ as well as the base-stabilized compounds LGa(TePh)₃ (L = NMe₃, PCy₃), which were obtained from the reaction of base-stabilized gallanes [LGaH₃] with Ph₂Te₂ and which also contain fourfold-coordinated Ga atoms and twofold-coordinated Te atoms, show comparable Ga–Te bond distances of 2.580(1) Å and 2.597(2) Å, respectively.³⁰ In contrast, the Ga–Te bonds in the [MeGa(TePh)₃]⁺ monocation of [(Me₃P)₄Cu][MeGa(TePh)₃] is slightly elongated (2.6406(3) Å).³¹ The same holds for the Ga–Te bonds in four structurally characterized Ga₄Te₄ heterocubanes, which range from 2.67 to 2.72 Å,^32–35 as well as in dimeric compounds of the general type [R₂Ga-μ-TeR]₂, for which Ga–Te bond lengths in the range from 2.67 to 2.76 Å were reported.^36–39 In contrast, slightly shorter Ga–Te bond lengths were reported for {[(Me₃Si)₂CH]₂Ga-μ-Te} (2.5521(4) Å),⁴⁰ [(Me₃Si)₂CH]₂GaTeSi(SiMe₃)₃ (2.535(1) Å),⁴¹ whereas the Ga–Te bonds observed in Ga{TeSi(SiMe₃)₃}₃ (av. 2.496(6) Å)⁴² as well as in Tp^#GaTe (2.422(1)) (Tp^# = tris(3,5-di-tert-butylpyrazolyl)hydroborato), to date the only compound containing a terminal Ga–Te double bond, are significantly shortened.⁴³

Reactions of trivalent group 13 compounds (MR₃, MH₃; M = Al, Ga, In) with elemental chalcogens E or chalcogen sources such as R₃P=E (E = O, S, Se, Te) typically occur with insertion of the chalcogen atom into the M–C/H bond and subsequent formation of dimeric ([R₂M-μ-ER]₂) or tetrameric ([RME]₄) compounds, whereas divalent (R₄M₂) as well as monovalent group 13 compounds RM (M = Al, Ga, In, Tl) react with insertion of the chalcogen atom into the M–M bond.^44–49 In addition, E–Br bond cleavage reactions of PhEBr (E = Se, Te) upon treatment with the monovalent In(I) cluster [(Me₃Si)₃C]₄In₄ ⁵⁰ as well as of Te–Te bond cleavage reactions of Ph₂Te₂ by reaction with Ga(I)²⁶ and In(I) compounds⁵¹ as well as with base-stabilized GaH₃ ³⁰ were reported. However, to the best of our knowledge, the cleavage of the Te–C bond of diorganyltellanes upon reaction with monovalent group 13 compounds RM has never been observed before.

Conclusions

LGa was found to selectively insert into the Te–Te bond of diphenylditellane Ph₂Te₂ as well as one Te–C bond of diisopropyltellane i-Pr₂Te, resulting in the formation of LGa(TePh)₂2 and LGa(i-Pr)Tei-Pr 3. Moreover, its reaction with elemental tellurium yielded the Te-bridged compound [LGa-μ-Te]₂1. We are currently investigating reactions of the somewhat stronger reducing agent LAl with various group 16 precursors. A previous report showed that LAl reacted with elemental sulfur with subsequent formation of [LAl(μ-S₃)]₂, containing an unusual Al₂S₆ ring.⁵²

Experimental

All manipulations were performed in an atmosphere of purified argon using standard Schlenk and glove-box techniques. Toluene and hexane were dried using a mBraun Solvent Purification System. THF was carefully dried over Na/K. Deuterated solvents were dried over activated molecular sieves (4 Å) and degassed prior to use. Anhydrous nature of the solvents was verified by Karl Fischer titration. The ¹H (300 MHz), ¹³C{¹H} (75.5 MHz) and ¹²⁵Te NMR (95 MHz) (δ in ppm) spectra were recorded using a Bruker Avance DPX-300 spectrometer. The ¹H and ¹³C{¹H} spectra were referenced to internal C₆D₅H (¹H: δ = 7.154; ¹³C: δ = 128.39) and C₆D₅CHD₂ (¹H: δ = 2.09; ¹³C: δ = 20.40). ¹²⁵Te NMR spectra were referenced to Na₂TeO₃ in D₂O. The microanalyses were performed at the elemental analysis laboratory of the University of Duisburg-Essen. IR spectra were measured with an ALPHA-T FT-IR spectrometer equipped with a single reflection ATR sampling module. Elemental tellurium and Ph₂Te₂ were commercially available and used as received, whereas i-Pr₂Te was freshly prepared according to a slightly modified procedure described for the synthesis of Te(SiMe₃)₂.⁵³ In necessary cases, the reaction mixtures were filtered using a oven dried Teflon cannula (3.5 mm D) in which one end of the tip was wrapped with Whatman® glass microfiber filters (CAT no. 1823-025) using Teflon tape.

Synthesis of i-Pr₂Te. Et₃BHLi (“superhydride”, 1.0 M in THF, 16.06 mmol, 16.1 mL) was added drop wise to a THF (50 mL) suspension of Te (1.0 g, 7.84 mmol) at 0 °C. After stirring at room temperature for 2 h, a solution of isopropyl bromide (1.976 g, 16.06 mmol, 1.5 mL) in THF (10 mL) was added. The reaction mixture was additionally stirred at room temperature for 2 h and the mixture was filtered through a glass frit. The solvents were removed under reduced pressure (500 mbar) and i-Pr₂Te was distilled at 45 °C (10 mbar). Yield: 72% (1.20 g). ¹H NMR (C₆D₆, 300 MHz): δ 3.18 (sept, –CH(CH₃)₂, 2 H), 1.50 (d, –CH(CH₃)₂, 12 H). ¹³C NMR (C₆D₆, 75 MHz): δ 28.00 (–CH(CH₃)₂), 10.57 (–CH(CH₃)₂).

Synthesis of 1. A mixture of elemental tellurium (0.0393 g, 0.308 mmol) and LGa (0.150 g, 0.308 mmol) in 20 mL of toluene was stirred at ambient temperature for 3 days. The reaction mixture was cannula filtered and the precipitate was extracted twice with 10 mL of hot toluene. Combined filtrates were concentrated to 10 mL and stored at −30 °C for 3 days to afford analytically pure 1 as pale yellow crystals. Yield: 61% (0.115 g). Anal. Calcd for C₅₈H₈₂Ga₂N₄Te₂·toluene: C, 59.05; H, 6.86; N, 4.24. Found: C, 59.70; H, 6.89; N, 4.26%. ¹H NMR (300 MHz, toluene-d₈): δ 7.10 (m, C₆H₃(ⁱPr)₂, 12 H), 4.59 (s, γ-CH–, 2 H), 3.33 (sept, –CH(CH₃)₂, 8 H), 1.35 (s, ArNCCH₃, 12 H), 1.10 (br m, –CH(CH₃)₂, 48 H). IR (neat): ν 2961 (m), 2921 (w), 2859 (w), 1530 (s), 1438 (m), 1381 (s), 1307 (s), 1257 (m), 1177 (m), 1097 (w), 1018 (m), 938 (m), 859 (m), 796 (s), 757 (m), 723 (m), 688 (w), 638 (w), 532 (w), 461 (w) cm⁻¹.

Synthesis of 2. A solution of Ph₂Te₂ (0.168 g, 0.41 mmol) in toluene (2 mL) was added dropwise to a well-stirred toluene (2 mL) solution of LGa (0.2 g, 0.41 mmol). The reaction mixture was stirred at room temperature for 3 h to give a clear yellow solution. The solution was then concentrated to 1 mL, layered with 1 mL of n-hexane and stored at −30 °C to give an analytically pure crystalline precipitate of 2. Single crystals suitable for X-ray diffraction analysis were grown from n-hexane solution. 0.13 g of 2 was dissolved in 4 mL of warm n-hexane and stored at room temperature for 1 day to give yellow crystals suitable for X-ray diffraction analysis. Yield: 73% (0.269 g). Anal. Calcd for C₄₁H₅₁GaN₂Te₂: C, 54.91; H, 5.73; N, 3.12. Found: C, 55.30; H, 5.81; N, 3.13%. ¹H NMR (300 MHz, C₆D₆): δ 7.54 (m, o-H Ph, 4 H), 7.18 (m, C₆H₃(ⁱPr)₂, 6 H), 6.96 (m, p-H Ph, 2 H), 6.78 (m, m-H Ph, 4 H), 4.76 (s, γ-CH–, 1 H), 3.62 (sept, –CH(CH₃)₂, 4 H), 1.50 (s, ArNCCH₃, 6 H), 1.48 (d, –CH(CH₃)₂, 12 H), 1.08 (d, –CH(CH₃)₂, 12 H). ¹³C NMR (75.5 MHz, C₆D₆): δ 170.63 (ArNCCH₃), 145.36 (Ar), 142.05 (Ar), 141.58 (Ar), 128.91 (Ar), 128.21 (Ar), 126.81 (Ar), 125.47 (Ar), 108.69 (Ar), 99.22 (γ-CH–), 29.36 (–CH(CH₃)₂), 27.01 (–CH(CH₃)₂), 25.44 (–CH(CH₃)₂), 24.67 (ArNCCH₃). ¹²⁵Te NMR (95 MHz, C₆D₆): δ −21.94. IR (neat): ν 3051 (w), 2962 (m), 2923 (w), 2863 (w), 1521 (m), 1460 (m), 1366 (m), 1311 (m), 1254 (m), 1169 (w), 1103 (w), 1014 (m), 935 (w), 861 (w), 797 (m), 727 (s), 689 (s), 636 (w), 531 (w), 451 (m) cm⁻¹.

Synthesis of 3. A mixture of i-Pr₂Te (0.068 g, 50 μL, 0.318 mmol) and LGa (0.155 g, 0.318 mmol) in 2 mL of toluene was stirred at ambient temperature for 24 h. The clear solution was concentrated to 1 mL and stored at 5 °C for 3 days to give a large amount of 2 as pale yellow blocks. Yield: 76% (0.169 g). Anal. Calcd for C₃₅H₅₅GaN₂Te: C, 59.96; H, 7.91; N, 4.00. Found: C, 60.10; H, 7.98; N, 3.97%. ¹H NMR (300 MHz, C₆D₆): δ 7.14 (m, C₆H₃(ⁱPr)₂, 6 H), 4.67 (s, γ-CH–, 1 H), 4.16 (sept, –CH(CH₃)₂, 2 H), 3.82 (sept, –TeCH(CH₃)₂, 1 H), 3.42 (sept, –CH(CH₃)₂, 2 H), 1.87 (d, –CH(CH₃)₂, 6 H), 1.61 (d, –CH(CH₃)₂, 6 H), 1.51 (s, ArNCCH₃, 6 H), 1.32 (m, –CH(CH₃)₂, 12 H), 1.08 (d, –CH(CH₃)₂, 6 H), 1.04 (m, –GaCH(CH₃)₂, 1 H), 0.67 (d, –GaCH(CH₃)₂, 6 H). ¹³C NMR (75.5 MHz, C₆D₆): δ 169.78 (ArNCCH₃), 146.22 (Ar), 143.88 (Ar), 142.73 (Ar), 127.74 (Ar), 126.09 (Ar), 124.32 (Ar), 98.25 (γ-CH–), 32.51 (–CH(CH₃)₂), 29.35 (–CH(CH₃)₂), 28.48 (–CH(CH₃)₂), 25.53 (–CH(CH₃)₂), 25.40 (–CH(CH₃)₂), 24.82 (–CH(CH₃)₂), 24.03 (–CH(CH₃)₂), 21.90 (ArNCCH₃), 17.67 (–TeCH(CH₃)₂), 1.79 (–GaCH(CH₃)₂), 1.76 (–GaCH(CH₃)₂). ¹²⁵Te NMR (95 MHz, C₆D₆): δ −115.74. IR (neat): ν 2964 (m), 2919 (w), 2849 (w), 1551 (w), 1521 (m), 1438 (m), 1383 (s), 1312 (m), 1258 (m), 1172 (w), 1098 (m), 1017 (s), 935 (w), 862 (w), 796 (s), 757 (m), 526 (m), 440 (w), 402 (w) cm⁻¹.

Single crystal X-ray diffraction

Crystallographic data of 1–3, which were collected on a Bruker D8 Kappa APEX2 diffractometer (MoK_α radiation, λ = 0.71073 Å) at 130(1) K (1a), 100(1) K (1b), 100(1) K (2) and 100(1) K (3), are summarized in Table 1. The solid-state structures of 1–3 are shown in Fig. 1–3. The structures were solved by Direct Methods (SHELXS-97) and refined anisotropically by full-matrix least-squares on F² (SHELXL-97).^54,55 Absorption corrections were performed semi-empirically from equivalent reflections on basis of multi-scans (Bruker AXS APEX2). The toluene molecule of 1b is disordered via 2/m symmetry. Further solvent molecules that could not be modelled sufficiently were removed by a PLATON/SQUEEZE run.⁵⁶ The crystal quality of 2 was rather low consequently the quantitative results of the model should be carefully assessed. The resolution of the data of 3 was high enough to show a mismatch of the calculated position of H2 and the residual electron density. Consequently H2 was refined freely with its displacement parameter constrained to be 1.2 times U_eq of the connected C atom. Other hydrogen atoms were refined using a riding model or rigid methyl groups.

Acknowledgements

S.S. likes to thank the University of Duisburg-Essen for financial support.

Notes and references

1. N. J. Hardman, B. E. Eichler and P. P. Power, J. Chem. Soc., Chem. Commun., 2000, 1991–1992.
2. N. J. Hardman and P. P. Power, ACS Symp. Ser., 2002, 822, 2–15.
3. C.-H. Chen, M.-L. Tsai and M.-D. Su, Organometallics, 2006, 25, 2766–2773.
4. M. S. Hill, P. B. Hitchcock and R. Pontavornpinyo, J. Chem. Soc., Dalton Trans., 2005, 273–277.
5. N. J. Hardman, P. P. Power, J. D. Gorden, C. L. B. Macdonald and A. H. Cowley, J. Chem. Soc., Chem. Commun., 2001, 1866–1867.
6. C. Gemel, T. Steinke, M. Cokoja, A. Kempter and R. A. Fischer, Eur. J. Inorg. Chem., 2004, 4161–4176.
7. A. Kempter, C. Gemel, T. Cadenbach and R. A. Fischer, Organometallics, 2007, 26, 4257–4264.
8. A. Kempter, C. Gemel and R. A. Fischer, Chem. – Eur. J., 2007, 13, 2990–3000.
9. S. Schulz, Chem. – Eur. J., 2010, 16, 6416–6428.
10. R. J. Baker and C. Jones, Coord. Chem. Rev., 2005, 249, 1857–1869.
11. Y.-C. Tsai, Coord. Chem. Rev., 2012, 256, 722–758.
12. M. Asay, C. Jones and M. Driess, Chem. Rev., 2011, 111, 354–396.
13. G. Prabusankar, A. Kempter, C. Gemel, M.-K. Schröter and R. A. Fischer, Angew. Chem., Int. Ed., 2008, 47, 7234–7237.
14. G. Prabusankar, C. Gemel, P. Parameswaran, C. Flener, G. Frenking and R. A. Fischer, Angew. Chem., Int. Ed., 2009, 48, 5526–5529.
15. A. Seifert, D. Scheid, G. Linti and T. Zessin, Chem. – Eur. J., 2009, 15, 12114–12120.
16. N. J. Hardman and P. P. Power, Inorg. Chem., 2001, 40, 2474–2475.
17. N. J. Hardman and P. P. Power, J. Chem. Soc., Chem. Commun., 2001, 1184–1185.
18. N. J. Hardman, C. Cui, H. W. Roesky, W. H. Fink and P. P. Power, Angew. Chem., Int. Ed., 2001, 40, 2172–2174.
19. C. Ganesamoorthy, D. Bläser, C. Wölper and S. Schulz, J. Chem. Soc., Chem. Commun., 2014, 50, 12382–12384.
20. C. Ganesamoorthy, D. Bläser, C. Wölper and S. Schulz, Angew. Chem., Int. Ed., 2014, 53, 11587–11591.
21. S. Gondzik, S. Schulz, D. Bläser and C. Wölper, J. Chem. Soc., Chem. Commun., 2014, 50, 1189–1191.
22. P. Steiniger, G. Bendt, D. Bläser, C. Wölper and S. Schulz, J. Chem. Soc., Chem. Commun., 2014, 50, 15461–15463.
23. S. Heimann, A. Kuczkowski, D. Bläser, C. Wölper, R. Haak, G. Jansen and S. Schulz, Eur. J. Inorg. Chem., 2014, 4858–4864.
24. S. Heimann, S. Schulz, D. Bläser and C. Wölper, Eur. J. Inorg. Chem., 2013, 4909–4915.
25. S. Heimann, D. Bläser, C. Wölper and S. Schulz, Organometallics, 2014, 33, 2295–2300.
26. R. J. Baker, C. Jones and M. Kloth, J. Chem. Soc., Dalton Trans., 2005, 2106–2110.
27. K. S. Klimek, J. Prust, H. W. Roesky, M. Noltemeyer and H.-G. Schmidt, Organometallics, 2001, 20, 2047–2051.
28. M. C. Copsey and T. Chivers, J. Chem. Soc., Chem. Commun., 2005, 4938–4940.
29. W. Uhl, L. Cuypers, T. Spies, F. Weller, B. Habrecht, M. Conrad, A. Greiner, M. Puchner and J. H. Wendorff, Z. Anorg. Allg. Chem., 2003, 629, 1124–1130.
30. W. J. Grigsby, C. L. Raston, V.-A. Tolhurst, B. W. Skelton and A. H. White, J. Chem. Soc., Dalton Trans., 1998, 2547–2556.
31. O. Kluge and H. Krautscheid, Inorg. Chem., 2012, 51, 6655–6666.
32. S. Schulz, M. Andruh, T. Pape, T. Heinze, H. W. Roesky, L. Häming, A. Kuhn and R. Herbst-Irmer, Organometallics, 1994, 13, 4004–4007.
33. C. H. Harlan, E. G. Gillan, S. G. Bott and A. R. Barron, Organometallics, 1996, 15, 5479–5488.
34. U. App and K. Merzweiler, Z. Anorg. Allg. Chem., 1997, 623, 478–482.
35. W. Uhl, M. Benter, W. Saak and P. G. Jones, Z. Anorg. Allg. Chem., 1998, 624, 1622–1628.
36. M. A. Banks, O. T. Beachley Junior, H. J. Gysling and H. R. Luss, Organometallics, 1990, 9, 1979–1982.
37. C. Schnitter, A. Klemp, H. W. Roesky, H.-G. Schmidt, C. Ropken, R. Herbst-Irmer and M. Noltemeyer, Eur. J. Inorg. Chem., 1998, 2033–2039.
38. M. R. Kopp and B. Neumüller, Z. Anorg. Allg. Chem., 1997, 623, 796–804.
39. O. Kluge, S. Gerber and H. Krautscheid, Z. Anorg. Allg. Chem., 2011, 637, 1909–1921.
40. W. Uhl and U. Schütz, Organometallics, 1995, 14, 1073–1075.
41. W. Uhl, M. Layh, G. Becker, K. W. Klinkhammer and T. Hildenbrand, Chem. Ber., 1992, 125, 1547–1551.
42. S. P. Wuller, A. L. Seligson, G. P. Mitchell and J. Arnold, Inorg. Chem., 1995, 34, 4854–4861.
43. M. C. Kuchta and G. Parkin, Inorg. Chem., 1997, 36, 2492–2493.
44. C. J. Allan and C. L. B. Macdonald, in Comprehensive Inorganic Chemistry II, ed. J. Reedijk and K. Poeppelmeier, Elsevier, Oxford, 2013, vol. 1, pp. 485–566.
45. S. Schulz, in Topics in Organometallic Chemistry, Vol. 41 Modern Organoaluminum Reagents, ed. S. Woodward and S. Dagorne, Springer Verlag, 2013.
46. S. Aldridge, in The Group 13 Metals Aluminum, Gallium, Indium and Thallium, ed. S. Aldridge and A. J. Downs, Wiley, 2011.
47. S. Schulz, in Comprehensive Organometallic Chemistry III, ed. R. H. Crabtree and D. M. P. Mimgos, Compounds of Group 13–15, ed. C. E. Housecroft, Elsevier, 2007, vol. 3.
48. J. A. J. Pardoe and A. J. Downs, Chem. Rev., 2007, 107, 2–45.
49. G. He, O. Shynkaruk, M. W. Lui and E. Rivard, Chem. Rev., 2014, 114, 7815–7880.
50. W. Uhl, F. M. de Andrade, C. Peppe, J. Kösters and F. Rogel, J. Organomet. Chem., 2007, 692, 869–873.
51. C. Peppe, F. Molinos de Andrade and W. Uhl, J. Organomet. Chem., 2009, 694, 1918–1921.
52. Y. Peng, H. Fan, V. Jancik, H. W. Roesky and R. Herbst-Irmer, Angew. Chem., Int. Ed., 2004, 43, 6190–6192.
53. M. R. Detty and M. D. Seidler, J. Org. Chem., 1982, 47, 1354–1356.
54. SHELXS-97, G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystallogr., 1990, 46, 467–473.
55. G. M. Sheldrick, SHELXL-97, Program for Crystal Structure Refinement, Universität Göttingen, 1997 See also: G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystallogr., 2008, 64, 112–122.
56. PLATON/SQUEEZE, P. van der Sluis and A. L. Spek, Acta Crystallogr., Sect. A: Fundam. Crystallogr., 1990, 46, 194–201.

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Footnotes

† Electronic supplementary information (ESI) available: Crystallographic data of 1a, 1b, 2, and 3 and spectroscopic details (¹H, ¹³C, ¹²⁵Te, IR). CCDC 1040132–1040135. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5dt00172b

‡ The crystallographic data of 1a, 1b, 2, and 3 (excluding structure factors) have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication nos. CCDC-1040132 (1a), CCDC-1040134 (1b), CCDC-1040133 (2) and CCDC-1040135 (3).

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