Three at a Time: Step by Step to Heterotermetallic Molecules

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Three at a Time: Step by Step to Heterotermetallic Molecules Tim Heidemann and Sanjay Mathur* Department of Chemistry, Institute of Inorganic Chemistry, Greinstrasse 6, 50939 Cologne, Germany S Supporting Information *

ABSTRACT: New structural motifs in ternary metal alkoxides are demonstrated through synthetic strategies that enable overcoming statistical barriers and solution equilibrium. Tetradentate dimetalate unit, {M2(OiPr)9}− (M = Hf (1), Zr (2)), used to sequester the coordination sphere of the central metal atom (Ba), allowed step-by-step construction of termetallic molecules [{M′(OiPr)4}(HOiPr)Ba{M2(OiPr)9}] (M′ = Al (3), Ga (4), M = Hf; M′ = Al, M = Zr (5)). In contrast to a common “coordinative-fit” approach mainly used for bimetallic compounds, this stepwise rational construction using fast successive salt metathesis reactions circumvents general challenges in the syntheses of termetallic alkoxides by avoiding the thermodynamically preferred formation of bimetallic alkoxide molecules. The presented compounds exhibit for the first time gas phase stable termetallic alkoxide frameworks.

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metals strontium and barium.6 These reactions exhibit metal switching of positions between cadmium and the alkaline earth metal as a characteristic feature, resulting in dimeric compounds of the general composition [{Cd(OiPr)3}M′{M2(OiPr)9}]2 (M′ = Sr, Ba; M = Ti, Zr, Hf), in which the alkaline earth metal is found in the pocket of the dimetalate unit {M2(OiPr)9}− (Figure 1). The observed metal switching acted so far as a limiting factor for possible metal variations in

INTRODUCTION Predicting chemical links in metalorganic synthesis of multimetallic molecules is severely restricted due to complex dynamic equilibria among simpler precursor species and the lack of synthetic rationales. The statistical distribution of metal combinations resulting from these solution equilibria is a general problem in the targeted preparation of termetallic complexes. Very recently this issue was addressed by Akine et al.1 by a carefully designed ligand, selectively binding three different metal ions. However, for potential material scientific applications specific ligand design is time-consuming and gas phase processes as CVD require preferably low molecular masses and gas-phase stability. Availability of synthetic principles demonstrating targeted synthesis of metal-based molecules with three or more different cations is therefore required to foster the development of advanced materials from molecular precursors.2−4 A common rationale for the syntheses of heterometallic alkoxides is based on a kind of “coordinative-fit” approach driven by Lewis acid−base condensations (neutral building blocks, [M(OR)x]) or assembly of ionogenic species (charged building blocks, [M(OR)x+1]−) (x = valence of metal). Intrinsic limitations imposed by charge neutrality constraints and “optimal fit”, which is a function of the ionic size of the metal and bite angle of the ligand, have severely restricted the access to termetallic alkoxides. In this context, stepwise construction of multimetallic assembly is a promising approach as shown for bimetallic alkoxides. However, examples of alkoxide molecules unifying three different metal atoms in a singular framework continue to be extremely rare.5−9 In addition, some of the earlier published results are based on insufficient analytics (often only IR spectroscopy and elemental analysis). A comprehensive study on termetallic alkoxides involves the reaction of iodocadmium dimetalates (Ti, Zr, Hf) with potassium isopropoxo metalates of larger alkaline earth © XXXX American Chemical Society

Figure 1. Metal switching observed in termetallic compounds.5−8 Received: August 25, 2016

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DOI: 10.1021/acs.inorgchem.6b02069 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 2. Rational construction of termetallic alkoxides (left) feasible by step-by-step approach of subsequent salt metathesis reactions, although a bimetallic compound (right) is thermodynamically more favored.

{M2(OiPr)9} (M = Hf, Zr)6 starting with the reaction of [M(OiPr)4iPrOH]217 and KOiPr. A toluene solution of the resulting K{M2(OiPr)9} was reacted with BaI2 in 1:1 molar ratio by refluxing the reaction mixture for 12 h (Scheme 1).

the termetallic species, since only the introduction of strontium or barium to iodo cadmium dimetalates was feasible. This suggested the assumption of an “optimal fit” for the coordinated metal, that needs to be fulfilled to allow an expansion from bi- to termetallic frameworks.

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Scheme 1. Syntheses of Bimetallic Building Blocks

RESULTS AND DISCUSSION The structural motif M2X9− is a versatile building block to sequester large cations that produce stable bimetallic compounds shown by the pioneering contributions of Bradley,10 Mehrotra,11 Caulton,12 and Hubert-Pfalzgraf.13 However, simple mixing of three constituent alkoxides is not an effective strategy in constructing termetallic frameworks as the redistribution of elements lowers the total energy of the system and is therefore thermodynamically more favored, leading preferentially to bimetallic compounds. Therefore, an attempted one-pot synthesis of a termetallic species from [Zr(OiPr)4HOiPr]2, [Ba(hmds)2(THF)2] (hmds = hexamethyldisilazide), and [Al(OiPr)3]4 in excess of isopropyl alcohol only results in the formation of the bimetallic compound [BaZr4(OiPr)16(OH)2] (Figure 2, right) (molecular structure in the Supporting Information), which is a derivative of earlier described [BaZr4(OiPr)18]14 and [BaZr4(OiPr)17(OH)].15 Stepwise construction using fast salt elimination reactions can circumvent these problems, leading to the kinetically favored termetallic species (Figure 2, left), which are transformed to the bimetallic compound only under excessive heating for 5 days at 80 °C in argon atmosphere (see the Supporting Information for NMR comparison). To demonstrate these concepts the bimetallic compounds 1 and 2 were synthesized containing barium already in the pocket of the {M2(OiPr)9}− unit fulfilling the “optimal fit”. A subsequent reaction adding a group 13 metal alkoxo unit resulted in the formation of the termetallic compounds 3−5, which revealed a novel structural motif. Since alkoxide chemistry of zirconium is extensively investigated also in relation to its appearance as a {Zr2(OiPr)9}− unit,16 we focused also on considerably less studied hafnium containing compounds. The bimetallic compounds 1 and 2 were prepared according to the procedure used for the cadmium derivatives ICd-

Suitable single crystals of 1 and 2 were obtained from toluene solution, after filtration of precipitated KI. Both compounds crystallized in the monomeric space group P21/c, displaying the expected dimeric behavior in contrast to the monomeric cadmium derivatives ICd{M2(OiPr)9}. As a consequence of dimerization now all metal atoms exhibit a distorted octahedral coordination (Figure 3). The larger size of barium (Ba2+: 1.49 Å)18 compared to cadmium (Cd2+: 1.09 Å)18 and its therefore preferred larger distance to the dimetalate subunit result in minor changes in bond lengths and angles that are in the expected range.6 The obtained “optimal fit” is visualized by the space-filling model in Figure 3. While all metals of the dimeric unit and all μ2-bridging isopropoxide oxygen atoms are placed on the same plane, the rectangular “Ba2I2” unit was expected to be found perpendicular to this plane. Instead, the proximity of the asymmetric units result in slightly twisted isopropyl groups at the μ2(Ba-O-M) oxygen atoms to reduce sterical hindrance. Geometric restriction of the isopropyl groups then influences additionally the observed angle of the “Ba2I2” unit to the plane, which is found to be reduced to 78.7° (1) and 79.3° (2) against the expected 90° (Supporting Information). The 1H NMR spectrum of 1 and 2 in CDCl3 displayed three septet signals in the methine proton region with an integrated intensity ratio of 5:2:2 and five doublets in the methyl region with a ratio of 2:2:1:2:2. Based on 2 μ3-OiPr, 2 μBaM-OiPr, 1 μMM-OiPr, and 4 terminal OiPr groups a ratio of 2:2:1:4 was expectable, which is also the observed ratio found for the B

DOI: 10.1021/acs.inorgchem.6b02069 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 4. Representative structural motif (hydrogen atoms are omitted for clarity) of [{M′(OiPr)4}(HOiPr)Ba{M2(OiPr)9}] with M′ = Al (3), Ga (4), M = Hf (shown structure is compound 3; for comparison of structures 3−5 see the Supporting Information) and space-filling model visualizing the “optimal fit” for M′ = Al, M = Zr (5) (hydrogen and carbon atoms are omitted).

Figure 3. Molecular structure of [IBa{Hf2(OiPr)9}]2 (1) (hydrogen atoms are omitted for clarity) and space-filling model of [IBa{Zr2(OiPr)9}]2 (2) visualizing the “optimal fit” (hydrogen and carbon atoms are omitted).

monomeric cadmium derivatives [ICd{M2(OiPr)9}] (M = Zr, Hf).6 However, the earlier described tilting of the “Ba2I2” unit and the unequal effect of the bridging unit to the terminal isopropoxy groups in the dimeric compounds 1 and 2 result in further splitting of the corresponding doublet signal in the observed spectra. A following second salt metathesis of KM′(OiPr)4 (freshly prepared by the reaction of KOiPr and M′(OiPr)3; M = Al, Ga) with 1 or 2 in refluxing toluene isopropyl alcohol mixture led, after filtration of precipitated KI, to the termetallic compounds [{M′(OiPr)4}(HOiPr)Ba{M2(OiPr)9}] with M′ = Al (3), Ga (4), M = Hf, and M′ = Al, M = Zr (5) (Scheme 2).

allow the additional coordination of a solvent molecule. The bond lengths and angles in the dimetalate subunit are hardly affected compared to compounds 1 or 2. As commonly observed in confacial bioctahedral alkoxide structures,16 the M−O bond lengths in the {M2(OiPr)9}− units are gradually decreased in the direction M−Oμ3 > M−Oμ2 > M−Oterminal. The Al−O bond lengths are comparable to the parameters found for literature known compounds with {Al(OiPr)4}− units.19,20 While compound 4 (Figure 4) shows the same molecular structure as the aluminum derivatives 3 and 5, it is found to crystallize in the acentric orthorhombic space group Pca21. Crystallization in a less symmetric space group is caused by the larger size of gallium influencing the orientation of the single molecules in the crystal structure and therefore resulting in the loss of the inversion center. The larger ionic radius of gallium is also responsible for minor changes on bond length and angles compared to compound 3. The observed Ga−O bond lengths are comparable to those in other compounds containing a {Ga(OiPr)4}− unit.21 The 1H NMR spectra (500.1 MHz) of 3 and 5 exhibit seven definite separated doublet signals in the methyl proton region in an integrative ratio of 2:2:1:4:2:2:1 (Figure 5) based on expected 14 isopropoxo groups corresponding to the observations in the crystal structure. The methine protons display overlapping septets in a ratio of 2:3:4:4:1. Signals assigned to the coordinating isopropyl alcohol show significant low field shifts compared to free iPrOH, therefore indicating the presence of 7-fold coordinated barium also in solution. The 27 Al NMR spectra of 3 and 5 showed broad singlets at 68 ppm, which is in the typical range of tetrahedral coordinated aluminum.22 A similar 1H NMR (300.1 MHz) pattern is found for compound 4, while stronger signal overlapping is

Scheme 2. Syntheses of Termetallic Alkoxides

The crystallographic data of compounds 1−5 are summarized in the Supporting Information. Compounds 3 and 5 (Figure 4) crystallized from a concentrated benzene solution at room temperature (rt) in colorless prismatic crystals in the orthorhombic space group Pbca. In contrast to previously described termetallic alkoxides6 the compounds are found to be monomeric in the solid state. The structures revealed a novel structural motif with a 7-fold coordination of barium. Besides the tetradentate {M2(OiPr)9}− unit and the bidentate coordinating tetrahedral {Al(OiPr)4}− unit, an additional isopropyl alcohol solvent molecule is coordinated to the barium center to display a distorted capped trigonal prismatic geometry. While the two bulky iodide atoms in 1 and 2 were able to fill one coordination hemisphere of barium, the smaller oxygen atoms of the {Al(OiPr)4}− unit C

DOI: 10.1021/acs.inorgchem.6b02069 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

[BaM 2 (OiPr) 9 ] + , [BaM 2 (OiPr) 7 (OEt) 2 ] + , and [M(OiPr)3(OEt)]+. In addition CHNS elemental analyses were in agreement for all compounds while standard analytical procedures for metal and iodine content in the complexes showed small deviation within the values’ errors.

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CONCLUSIONS In conclusion, the presented study shows the successful syntheses of a new class of termetallic alkoxides with a novel structural motif. The key factor was to use the halide bimetallic alkoxides [IBa{M2(OiPr)9}]2 (M = Hf, Zr) serving as effective building blocks. These avoid the characteristic feature of metal switching observed for previous structures by fulfilling the “optimal fit” requirement and therefore enabling easy expansion to a termetallic framework. In addition the chosen stepwise construction by fast salt elimination reactions favors the kinetic termetallic products over the thermodynamically favored bimetallic compounds obtained by a “coordinative-fit” approach. These results demonstrated the importance of a rational syntheses strategy for termetallic alkoxide frameworks. This work expands the experimental space of metal alkoxide chemistry by enabling deep insight in the processes of termetallic alkoxide formation, which allowed for the first time the targeted syntheses of monomeric rigid compounds unifying three different metals in rather compact molecules. The comparably low molecular mass of the obtained monomeric products is a crucial factor with regard to a future application of termetallic alkoxides as single-source precursors in CVD processes. Besides manifesting the versatility of alkoxometalate units that can be transferred to various metal cations, the synthetic access to multimetallic clusters is of significant value in the synthesis of mixed-metal ceramics such as perovskite, superconductors, and substituted garnets or spinels. Further studies on the diversity of this new system are currently under investigation.

Figure 5. 1H−13C HSQC spectrum of 5 (500.1 MHz, in CDCl3) with detailed view on methyl proton region showing distinct signal correlation.

attributed to the smaller magnetic field intensity of the used spectrometer. The coordination of the solvent molecule in solution in 4 is especially emphasized by the observed correlation signals in a 1 H− 1 H NOESY spectrum. A comparison of 1H NMR spectra (300.1 MHz) of 3−5 (see the Supporting Information) exhibits only minor changes for chemical shifts. A reaction of compound 5 with excess of ethanol for 2 h at room temperature revealed after removal of all volatiles only partial replacement of OiPr to OEt groups. Based on the observed multiplicities and integrative ratios in the 1H NMR spectrum (Supporting Information) only four groups were exchanged, namely, 2 μ3-OR and 2 μ-OR groups, which enabled highest reduction of steric constraints. Extensive heat treatment of 5 in ethanol by heating a sealed sample under argon for 3 d at 80 °C resulted after removal of volatiles again in the formation of [BaZr4(OiPr)16(OH)2], which was also obtained from the one-pot synthesis. These observations strengthen the conclusion that bimetallic [BaZr4(OiPr)16(OH)2] is thermodynamically highly favored. However, the intended termetallic species were accessible as the kinetic product by fast salt metathesis reactions. Electron impact mass spectrometry of compounds 3−5 measured at an ionization energy of 20 eV revealed for the first time for each compound gas-phase stable termetallic fragments. The fragments of the general formula [M′BaM(OiPr)8]+ with metal ratios of 1:1:1 were detected as the base peaks at temperature around 180 °C. Since 27Al is the only isotope of aluminum, the observed isotopic pattern of the fragments for derivatives 3 and 5 gave no conclusive indication for the presence of aluminum and thus for a termetallic fragment. While in full agreement with the calculated isotopic pattern, the reliable evidence for the existence of such gas-phase stable termetallic fragments was obtained from the gallium derivative 4 exhibiting more distinctive isotopic patterns. Further recurring fragments from the termetallic compounds include

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EXPERIMENTAL SECTION

Materials and Methods. All manipulations were carried out in an atmosphere of dry nitrogen (modified Stock vacuum line) using ovendried glass apparatus under strict exclusion of moisture. All solvents were dried over sodium and freshly distilled prior to use. [Zr2(OiPr)4iPrOH]2,12 [Hf2(OiPr)4iPrOH]2,12 [K{Hf2(OiPr)9}],6 [Al(OiPr)3]4,23 and [Ga(OiPr)3]24 were prepared according to literature procedures. Anhydrous barium iodide was obtained from Strem Chemicals Inc. and directly used. NMR spectra were recorded in CDCl3 or C6D6 on a Bruker AVANCE II 300 and Bruker AVANCE III 500 spectrometer. All 1H NMR (300.1 MHz, 500.1 MHz) and 13C NMR (75.5 MHz, 125.7 MHz) chemical shifts are reported in parts per million relative to external tetramethylsilane and are referenced to deuterated chloroform or benzene. 27Al NMR (78.2 MHz) is referenced externally to [Al(H2O)6Cl3]. Elemental analysis (C and H) were carried out using a HEKAtech CHNS EuroEA 3000 Analyzer and a LECO Elemental Analyzer CHN900 with helium as carrier gas. Standard analytical procedures25 were employed to estimate metal and iodine contents in the complexes. Data collection for X-ray crystal structure determination for compounds 1−5 was performed on a STOE IPDS 2 T diffractometer using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). The data were corrected for Lorentz and polarization effects. A numerical absorption correction based on crystal-shape optimization was applied for all data.26 The programs used in this work are Stoe’s XArea,27 including X-RED and X-Shape for data reduction and absorption correction28 and the WinGX suite of programs29 including D

DOI: 10.1021/acs.inorgchem.6b02069 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry SIR-9230 and SHELXL-9731 for structure solution and refinement. The hydrogen atoms were placed in idealized positions and constrained to ride on their parent atoms. As typically observed for heterometallic alkoxides, the thermal ellipsoids of the termetallic compounds 3−5 indicate vibrational disorder on several isopropyl groups, resulting in large Hirshfeld differences. In addition vibrational disorder in compound 4 resulted in a short C−C bond between methine carbon C7 and methyl carbon C8. To achieve a converging structure (shift/su_max = 0.001), ISOR was applied to C8, C27, C62 (3 × ISOR = 18 restraints) and C25 and C26 were refined isotropically (to prevent appearance as nonpositive definite). The Flack parameter of 0.473 was ambiguous, but twinning also helped for convergence of structure. Despite stronger vibrational disorder on isopropyl groups and weaker crystal quality for compound 4, it is in good agreement with the obtained structures of derivatives 3 and 5. [IBa{Hf2(OiPr)9}]2 (1). A fresh sample of K{Hf2(OiPr)9} (4.26 g, 4.58 mmol) was dissolved in 25 mL of toluene and added to a slurry of BaI2 (1.80 g, 4.60 mmol) in 15 mL of THF. The reaction mixture was refluxed with stirring for 12 h, and formed KI was filtered off. The volatiles were removed in vacuum (10−3 mbar) to obtain 1 as a white solid (5.15 g, 97%), which was recrystallized from hot toluene to give transparent rectangular blocks of 1 suitable for X-ray diffraction. Anal. Calcd (%): C, 28.12; H, 5.50; Ba, 11.90; I, 11.00; Hf, 30.95. Found (%): C, 27.85; H, 5.26; Ba, 11.43; I, 10.71; Hf, 30.17. 1H NMR (500.1 MHz, CDCl3, 298 K): δ, 1.21 (d, 3JH−H = 6 Hz, 12 H), 1.24 (d, 3JH−H = 6 Hz, 12 H), 1.31 (d, 3JH−H = 6 Hz, 6 H), 1.35 (d, 3JH−H = 6 Hz, 12 H), 1.55 (d, 3JH−H = 6 Hz, 12 H), 4.45 (m, 3JH−H = 6 Hz, 5 H), 4.46 (m, 3JH−H = 6 Hz, 2 H), 4.54 (m, 3JH−H = 6 Hz, 2 H). 13C{1H} NMR (125.7 MHz, CDCl3, 298 K): δ, 27.42, 27.51, 28.03, 28.16, 28.52 (CH3); 69.64, 69.99, 70.66, 72.02 (CH). 1H NMR (300.1 MHz, C6D6, 298 K): δ, 1.29,1.31 (overlapping d, 3JH−H = 6 Hz, 24 H), 1.39 (d, 3 JH−H = 6 Hz, 6 H), 1.58 (d, 3JH−H = 6 Hz, 12 H), 1.72 (d, 3JH−H = 6 Hz, 12 H), 4.50 (m, 3JH−H = 6 Hz, 4 H), 4.60 (m, 3JH−H = 6 Hz, 3 H),4.70 (m, 3JH−H = 6 Hz, 5 H). 13C{1H} NMR (75.5 MHz, C6D6, 298 K): δ, 26.75, 26.90, 27.38, 27.50, 27.97 (CH3); 69.19, 69.55, 70.08, 71.45 (CH). [IBa{Zr2(OiPr)9}]2 (2). The compound was prepared analogously to 1 by using BaI2 (2.22 g, 5.66 mmol) and K{Zr2(OiPr)9} (4.26 g, 5.66 mmol). Yield: 4.21 g, 76%. Anal. Calcd (%): C, 32.96; H, 6.48; Ba, 14.03; I, 12.96; Zr, 18.64. Found (%): C, 32.89; H, 6.05; Ba, 13.77; I, 12.32; Zr, 18.70. 1H NMR (500.1 MHz, CDCl3, 298 K): δ, 1.23 (d, 3 JH−H = 6 Hz, 12 H), 1.26 (d, 3JH−H = 6 Hz, 12 H), 1.33 (d, 3JH−H = 6 Hz, 6 H), 1.45 (d, 3JH−H = 6 Hz, 12 H), 1.61 (d, 3JH−H = 6 Hz, 12 H), 4.38 (m, 3JH−H = 6 Hz, 5 H), 4.49 (m, 3JH−H = 6 Hz, 2 H), 4.66 (m, 3 JH−H = 6 Hz, 2 H). 13C{1H} NMR (125.7 MHz, CDCl3, 298 K): δ, 26.65, 26.74, 27.21, 27.48, 27.97(CH3); 69.21, 70.06, 71.52 (CH). [{Al(OiPr)4}(HOiPr)Ba{Hf2(OiPr)9}] (3). To a solution of 1 (2.60 g, 2.25 mmol) in 15 mL of toluene was added a solution of KAl(OiPr)4 (0.68 g, 2.26 mmol) (freshly synthesized by the reaction of KOiPr and Al(OiPr)3 in refluxing toluene isopropyl alcohol mixture). The resulting suspension was stirred at rt for 2 h and filtered. The obtained clear solution was reduced in vacuum (10−3 mbar) until the raw product was obtained as a viscous colorless mass. Addition of 4 mL of benzene gave large prismatic crystals of 3 in good yield (2.40 g, 79%) overnight at rt. Anal. Calcd (%): C, 37.37; H, 7.38; Al, 2.00; Ba, 10.17; Hf, 26.44. Found (%): C, 37.01; H, 7.15; Al, 1.90; Ba, 10.12; Hf, 26.12. EI-MS (20 eV, 180 °C) m/z (%, fragment): 1026 (67, [BaHf2(OiPr)9]+), 999 (11, [BaHf2(OiPr)7(OEt)2]+), 817 (100, [AlBaHf(OiPr) 8 ] + ), 402 (17, [Hf(OiPr) 3 (OEt)] + ), 45 (72, [OC2H5]+). 1H NMR (500.1 MHz, CDCl3, 298 K): δ, 1.20 (d, 3 JH−H = 6 Hz, 6 H), 1.27 (d, 3JH−H = 6 Hz, 12 H), 1.30 (d, 3JH−H = 6 Hz, 12 H), 1.35 (d, 3JH−H = 6 Hz, 24 H), 1.36 (d, 3JH−H = 6 Hz, 6 H), 1.40 (d, 3JH−H = 6 Hz, 12 H), 1.51 (d, 3JH−H = 6 Hz, 12 H), 3.91 (sept, 3 JH−H = 6 Hz, 1 H), 4.32 (sept, 3JH−H = 6 Hz, 4 H), 4.40 (sept, 3JH−H = 6 Hz, 4 H), 4.45 (sept, 3JH−H = 6 Hz, 3 H), 4.58 (sept, 3JH−H = 6 Hz, 2 H). 13C{1H} NMR (125.7 MHz, CDCl3, 298 K): δ, 25.42, 26.88, 27.00, 27.09, 27.18, 27.59, 27.88 (CH3); 63.91, 64.75, 68.68, 70.19, 71.60 (CH). 1H NMR (300.1 MHz, C6D6, 298 K): δ, 1.19 (d, 3JH−H =

6 Hz, 6 H), 1.33 (d, 3JH−H = 6 Hz, 24 H), 1.41 (d, 3JH−H = 6 Hz, 12 H), 1.46 (d, 3JH−H = 6 Hz, 30 H), 1.55 (d, 3JH−H = 6 Hz, 12 H), 3.93 (sept, 3JH−H = 6 Hz, 1 H), 4.40−4.71 overlapping (m, 3JH−H = 6 Hz, 13 H). 27Al-NMR (78.2 MHz, benzene-d6, 298 K) δ/ppm: 68. [{Ga(OiPr)4}(HOiPr)Ba{Hf2(OiPr)9}] (4). Compound 4 was prepared analogously to 3 by reacting 1 (2.60 g, 2.25 mmol) with KGa(OiPr)4 (0.78 g, 2.26 mmol). Yield of obtained colorless raw product: 3.07 g, 98%, which was recrystallized from benzene at rt to give transparent rectangular blocks of 4 suitable for X-ray diffraction. Anal. Calcd (%): C, 36.23; H, 7.17. Found (%): C, 36.18; H, 7.10. EI-MS (20 eV, 180 °C) m/z (%, fragment): 1026 (47, [BaHf2(OiPr)9]+), 999 (23, [BaHf2(OiPr)7(OEt)2]+), 859 (100, [GaBaHf(OiPr)8]+), 402 (23, [Hf(OiPr)3(OEt)]+), 45 (61, [OC2H5]+). 1H NMR (300.1 MHz, C6D6, 298 K): δ, 1.15 (d, 3JH−H = 6 Hz, 6 H), 1.34 (d, 3JH−H = 6 Hz, 24 H), 1.44 (d, 3JH−H = 6 Hz, 12 H), 1.48 (d, 3JH−H = 6 Hz, 30 H), 1.57 (d, 3JH−H = 6 Hz, 12 H), 3.92 (sept, 3JH−H = 6 Hz, 1 H), 4.45− 4.64 overlapping (m, 3JH−H = 6 Hz, 9 H), 4.64−4.81 (m, 3JH−H = 6 Hz, 4 H). 13C{1H} NMR (75.5 MHz, C6D6, 298 K): δ, 25.58, 26.94, 27.16, 27.35, 27.82, 28.09 (CH3); 66.05, 68.76, 70.06, 71.39 (CH). [{Al(OiPr)4}(HOiPr)Ba{Zr2(OiPr)9}] (5). Compound 5 was prepared analogously to 3 by reacting 2 (2.30 g, 2.36 mmol) with KAl(OiPr)4 (0.72 g, 2.37 mmol). Yield: 2.20 g, 89%. Transparent rectangular crystals of 5 suitable for X-ray diffraction were obtained from a benzene solution at rt. Anal. Calcd (%): C, 42.92; H, 8.43; Al, 2.29; Ba, 11.68; Zr, 15.52. Found (%): C, 42.27; H, 8.25; Al, 2.02; Ba, 11.50; Zr, 15.45. EI-MS (20 eV, 175 °C) m/z (%, fragment): 849 (53, [BaZr2(OiPr)9]+), 821 (14, [BaZr2(OiPr)7(OEt)2]+), 727 (100, [AlBaZr(OiPr) 8 ] + ), 312 (23, [Zr(OiPr) 3 (OEt)] + ), 45 (69, [OC2H5]+). 1H NMR (500.1 MHz, CDCl3, 298 K): δ, 1.21 (d, 3 JH−H = 6 Hz, 6 H), 1.29 (d, 3JH−H = 6 Hz, 12 H), 1.31 (d, 3JH−H = 6 Hz, 12 H), 1.36 (d, 3JH−H = 6 Hz, 24 H), 1.37 (d, 3JH−H = 6 Hz, 6 H), 1.42 (d, 3JH−H = 6 Hz, 12 H), 1.52 (d, 3JH−H = 6 Hz, 12 H), 3.94 (sept, 3 JH−H = 6 Hz, 1 H), 4.35 (sept, 3JH−H = 6 Hz, 4 H), 4.43 (sept, 3JH−H = 6 Hz, 4 H), 4.48 (sept, 3JH−H = 6 Hz, 3 H), 4.60 (sept, 3JH−H = 6 Hz, 2 H). 13C{1H} NMR (125.7 MHz, CDCl3, 298 K): δ, 25.60, 26.93, 27.01, 27.09, 27.25, 27.70, 27.92 (CH3); 63.92, 64.79, 68.72, 70.22, 71.61 (CH). 1H NMR (300.1 MHz, C6D6, 298 K): δ, 1.19 (d, 3JH−H = 6 Hz, 6 H), 1.32 (d, 3JH−H = 6 Hz, 24 H), 1.41 (d, 3JH−H = 6 Hz, 18 H), 1.47 (d, 3JH−H = 6 Hz, 24 H), 1.56 (d, 3JH−H = 6 Hz, 12 H), 3.95 (sept, 3JH−H = 6 Hz, 1 H), 4.39−4.57 overlapping (m, 3JH−H = 6 Hz, 9 H), 4.57−4.71 (m, 3JH−H = 6 Hz, 4 H).27Al-NMR (78.2 MHz, benzene-d6, 298 K) δ/ppm: 68. [BaZr4(OiPr)16(OH)2] (6). Compound 6 was obtained unintended either from compound 5 after heating a sample for 5 d at 80 °C in toluene or alternatively from a one-pot reaction of equimolar amounts of [Zr(OiPr)4HOiPr]2, [Ba(hmds)2(THF)2], and [Al(OiPr)3]4 in toluene, which was reacted for 36 h at 80 °C. Transparent rectangular crystals of 6 suitable for X-ray diffraction were obtained from a benzene solution at rt. Anal. Calcd (%): C, 39.36; H, 7.78. Found (%): C, 39.12; H, 7.49. 1H NMR (300.1 MHz, C6D6, 298 K): δ, 1.26, 1.28, 1.34, 1.43, 1.50, 1.63 (m, overlapping, CH3), 4.36−4.74 (m, overlapping, CH).

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S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02069. Analytical data including 1D and 2D NMR spectra (PDF) X-ray crystallographic data files for 1−5 (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Tim Heidemann: 0000-0003-2590-9045 E

DOI: 10.1021/acs.inorgchem.6b02069 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Notes

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are thankful to Dr. Corinna Hegemann and Dr. Johannes Schläfer for useful discussion. REFERENCES

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DOI: 10.1021/acs.inorgchem.6b02069 Inorg. Chem. XXXX, XXX, XXX−XXX