HAlCl2 and H2AlCl as Precursors for the Preparation of Compounds

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HAlCl2 and H2AlCl as Precursors for the Preparation of Compounds with Four- and Five-Coordinate Aluminum Mingdong Zhong,†,§ Yashuai Liu,†,‡,§ Subrata Kundu,† Nico Graw,† Jiancheng Li,†,∥ Zhi Yang,‡ Regine Herbst-Irmer,† Dietmar Stalke,*,† and Herbert W. Roesky*,† †

Institut für Anorganische Chemie, Georg-August-Universität, Tammannstrasse 4, 37077 Göttingen, Germany School of Chemical Engineering and Environment, Beijing Institute of Technology, 100081 Beijing, China ∥ State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, 361005 Xiamen, China Downloaded via UNIV AUTONOMA DE COAHUILA on August 7, 2019 at 22:19:29 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

‡

S Supporting Information *

backbone unsaturated NHCs (nPr2Im, iPr2Im, iPr2ImMe, and Dipp2Im, where Im = imidazolin-2-ylidene and Dipp = 2,6diisopropylphenyl) were used in reactions with HBcat and formed Lewis acid−base adducts. While the backbonesaturated NHC Dipp2H2Im resulted in adduct formation, following B−H activation. 10 Complexes with sterically demanding NHC ligands, such as [(IMes)AlH3] (IMes = (HCNMes)2C: and Mes = 2,4,6-Me3C6H2)11 and [(IDip)AlH3] [IDip (often named IPr) = (HCNDip)2C: and Dip = 2,6-iPr2C6H3],12 show NHCs that allow the synthesis of thermally stable aluminum hydride. The synthesis of cyclic alkyl(amino)carbenes (cAACs) was reported in 2005 by Bertrand et al.13 cAACs exhibit superior properties for the stabilization of various unstable complexes, radicals, and elements in their different oxidation states because of their smaller highest occupied molecular orbital−lowest unoccupied molecular orbital energy gap compared to NHCs.14 Traditionally, aluminum hydride complexes were synthesized by the reaction of ligands with H3Al·NR3 through the elimination of H2 or the addition of unsaturated compounds using Al−Hcontaining precursors.15 Jonas and co-workers reported the monomeric complex [C(H)(NAr)2]2AlH (Ar = 2,6-diisopropylphenyl), which can be prepared through H2 elimination in a 2:1 ratio of ArNC(H)N(H)Ar) and [AlH3(NMe3)] or the addition of [AlH3(NMe3)] to ArNCNAr in a ratio of 1:2.16a In 2010, the hydride complexes with low oxidation states of aluminum were formed using a magnesium(I) dimer.16b HAlCl2 and H2AlCl work favorably as precursors for the synthesis of aluminum hydrides complexes. The latter are more suitable, safe, and reliable for such reactions. Furthermore, the intermediates with Al−H and Al−Cl bonds can be easily obtained from HAlCl2 and H2AlCl. Such products have great potential for the synthesis of novel aluminum materials. Radius et al. reported the reaction of NHC-alane adducts with cAACMe, which led to Al−H bond cleavage and the insertion of cAAC into the Al−H bond.17 Herein, we used the favorable HAlCl2 as well as H2AlCl as precursors, in the reaction with cyclic alkyl(amino)carbene (cAAC:), in which the carbene carbon atom undergoes insertion into the Al−H bond to form compounds with four-coordinate aluminum. We

ABSTRACT: Carbenes are known as donor molecules to form with chloroalane adducts, which enhances their aerobic and thermal stabilities. In contrast, the insertion products (cAACH)AlCl2(cAAC) (1) and (cAACH)AlHCl(THF) (2; THF = tetrahydrofuran) have been formed in the reaction of a cyclic alkyl(amino)carbene (cAAC:) with HAlCl2, and H2AlCl, respectively. PhC(NtBu)2Li as the precursor for the reaction with HAlCl2 in a molar ratio of 2:1 can easily form compound [PhC(NtBu)2]2AlH (3) with five-coordinate aluminum. The new products have been studied by spectroscopic methods and single-crystal X-ray diffraction.

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n recent years, main-group metal hydrides have received numerous attention largely because of their potential as hydrogen storage materials for mobile devices that are powered by fuel cells.1−3 Moreover, compounds of aluminum hydride have attracted interest in recent research because of their application in homogeneous catalysis.4 Recently, our group reported on aluminum hydrides such as NacNacAlH2 and NacNacAlH(OSO2CF3) (NacNac = β-diketiminate ligand) that showed excellent catalytic properties in hydroboration and trimethylsilyl cyanation of aldehydes.5 The yield of the products was quantitative, and the amount of catalyst NacNacAlH(OSO2CF3) was very small (∼0.2 mol %). NacNacAl:, an aluminum analogue of a carbene, exhibits a two-coordinate aluminum that possess a metal-centered lone pair, which displays rich oxidative addition chemistry.6 Another active research area is the preparation of four- and fivecoordinate aluminum centers for the application of catalysts in the ring-opening polymerization of lactones and lactides.7 These results motivated further driven investigations for aluminum compounds with different coordination numbers at the aluminum center. We used HAlCl2 and H2AlCl as precursors. Although the structures of these compounds are not known, they are easily prepared by stoichiometric reactions of AlCl3 with LiAlH4.8 N-heterocyclic carbene (NHC)-coordinated chloroalane has been developed to some extent.9 However, the result of the reaction between a carbene and a main-group element hydride depends on the nature of the carbene. For example, the © XXXX American Chemical Society

Received: July 6, 2019

A

DOI: 10.1021/acs.inorgchem.9b02001 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry were also able to prepare compound 3 with five-coordinate aluminum containing an amidinate ligand. When HAlCl2 reacted with cAAC: in a 1:2 molar ratio in tetrahydrofuran (THF), the product (cAACH)AlCl2(cAAC) (1) was produced in good yield (Scheme 1). The structure of

expansion occurred. The structure of 2 was determined by single-crystal X-ray diffraction18 (Figure 2). Compound 2

Scheme 1. Preparation of Compounds 1−3

Figure 2. Asymmetric unit of 2. The anisotropic displacement parameters are depicted at the 50% probability level. No metal-bound hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Al1−H1 1.50(2), Al1−C6 1.999(2), Al1−Cl1 2.1873(12); H1−Al1−C6 118.6(10).

crystallizes in the monoclinic space group P21/c. The hydrogen atom H1 was refined freely. As with compound 1, the aluminum atom shows a slightly distorted tetrahedral coordination geometry, with angles ranging between 99.53(7)° (O1−Al1−Cl1) and 118.6(10)° (H1−Al1−C6). [PhC(NtBu)2]2AlH (3) was readily obtained from the reaction of HAlCl2 with [PhC(NtBu)2]Li in a 1:2 molar ratio. 3 crystallizes in the triclinic space group P1̅. Single-crystal Xray diffraction18 revealed a 5-fold-coordinated aluminum atom (Figure 3). Again, the metal-bound hydrogen atom H1 was

1 was determined by single-crystal X-ray diffraction18 (Figure 1). Compound 1 crystallizes in the monoclinic space group

Figure 3. Asymmetric unit of 3. The anisotropic displacement parameters are depicted at the 50% probability level. Non-metalbound hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Al1−H1 1.55(2), Al1−N1 2.0070(9), Al1−N2 1.9409(11), Al1−N3 1.9578(10), Al1−N4 2.0203(9); N2−Al1−N1 67.44(4), N2−Al1−N3 113.26(4), N1−Al1−N4 171.72(4), H1− Al1−N3 128.0(5), H1−Al1−N4 93.8(5).

Figure 1. Asymmetric unit of 1. The anisotropic displacement parameters are depicted at the 50% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Al1−C1 2.014(2), Al1−C21 2.094(2), Al1−Cl1 2.1549(8), Al1−Cl2 2.1766(8); C1−Al1−C21 124.82(8), C1−Al1−Cl1 112.40(6).

P21/c. The aluminum atom adopts distorted tetrahedral geometry, with the C1−Al1−C21 [124.82(8)°] bond angle showing the largest deviation due to widening induced by the steric bulk of the cAAC ligands. To our surprise, the reaction of H2AlCl with cAAC afforded (cAACH)AlHCl(THF) (2). Furthermore, the reaction of H2AlCl with cAAC in a 1:2 molar ratio resulted in the compound (cAACH)AlCl(cAACH) in a moderate yield, according to the result of mass spectrometry and NMR (see the Supporting Information). Compounds 1 and 2 were stored in THF-d8 at 60 °C for 2 days. However, no cAAC ring

refined freely. The angle between the two amidinato ligands (C1N1N2Al1 and C16N3N4Al1 planes) is 67.25(5)°, which leaves the aluminum atom roughly linearly coordinated by the two nitrogen atoms N1 and N4. The overall geometry of 3 is therefore best described as trigonal-bipyramidal, also indicated by the Addison parameter19 τ = 0.86 (τ = 1 for ideal trigonalbipyramidal geometry). B

DOI: 10.1021/acs.inorgchem.9b02001 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry The treatment of NacNacLi (NacNac = β-diketiminate ligand) with HAlCl2 in a 1:2 molar ratio was not successful, obviously because of the steric bulk of the NacNac ligand. In summary, four-coordinate (1) and five-coordinate (3) aluminum compounds were prepared by the reaction of HAlCl2 with cAAC: and PhC(NtBu)2Li, respectively. The reaction of H2AlCl with cAACMe led to Al−H bond cleavage and the insertion of cAAC into the Al−H bond to afford a four-coordinate aluminum compound (2). Possible catalytic applications of the complexes as well as their reactivity are currently under investigation in our laboratory.

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(3) Graetz, J. New Approaches to Hydrogen Storage. Chem. Soc. Rev. 2009, 38, 73−82. (4) Nikonov, G. I. New Tricks for an Old Dog: Aluminum Compounds as Catalysts in Reduction Chemistry. ACS Catal. 2017, 7, 7257−7266. (5) (a) Yang, Z.; Zhong, M.; Ma, X.; De, S.; Anusha, C.; Parameswaran, P.; Roesky, H. W. An Aluminum Hydride That Functions like a Transition-Metal Catalyst. Angew. Chem., Int. Ed. 2015, 54, 10225−10229. (b) Yang, Z.; Zhong, M.; Ma, X.; Nijesh, K.; De, S.; Parameswaran, P.; Roesky, H. W. An Aluminum Dihydride Working as a Catalyst in Hydroboration and Dehydrocoupling. J. Am. Chem. Soc. 2016, 138, 2548−2551. (c) Bismuto, A.; Thomas, S. P.; Cowley, M. J. Aluminum Hydride Catalyzed Hydroboration of Alkynes. Angew. Chem., Int. Ed. 2016, 55, 15356−15359. (6) (a) Chu, T.; Nikonov, G. I. Oxidative Addition and Reductive Elimination at Main-Group Element Centers. Chem. Rev. 2018, 118, 3608−3680. (b) Bakewell, C.; White, A. J. P.; Crimmin, M. R. Reactions of Fluoroalkenes with an Aluminium(I) Complex. Angew. Chem., Int. Ed. 2018, 57, 6638−6642. (7) (a) Hao, P.; Yang, Z.; Li, W.; Ma, X.; Roesky, H. W.; Yang, Y.; Li, J. Reactivity Studies of LAlH2 (L = HC(CMeNAr)2, Ar = 2,6iPr2C6H3) with 2-Aminobenzenethiol, 2-Aminophenol, and 1,4Dithiane-2,5-diol. Organometallics 2015, 34, 105−108. (b) Postigo, L.; Maestre, M. C.; Mosquera, M. E. G.; Cuenca, T.; Jiménez, G. Aminoarenethiolate Aluminum Complexes: Synthesis, Characterization, and Use in L-Lactide Polymerization. Organometallics 2013, 32, 2618−2642. (c) Ajellal, N.; Carpentier, J.-F.; Guillaume, C.; Guillaume, S. M.; Helou, M.; Poirier, V.; Sarazin, Y.; Trifonov, A. Metal-catalyzed Immortal Ring-Opening Polymerization of Lactones, Lactides and Cyclic Carbonates. Dalton Trans 2010, 39, 8363−8376. (d) Wade, C. R.; Lamprecht, B. J.; Day, V. W.; Belot, J. A. Synthesis and Structural Characterization of Two Five Coordinate Aluminum Alkyl and Bis(trimethylsilyl)amino Complexes Bearing Acyclic Tetradentate Schiff Bases. Polyhedron 2007, 26, 3286−3290. (e) Atwood, D. A.; Harvey, M. J. Group 13 Compounds Incorporating Salen Ligands. Chem. Rev. 2001, 101, 37−52. (8) (a) Schmidt, D. L.; Flagg, E. E. Bis(tetrahydrofuran)-haloalanes. Inorg. Chem. 1967, 6, 1262−1265. (b) Ganesamoorthy, C.; Loerke, S.; Gemel, C.; Jerabek, P.; Winter, M.; Frenking, G.; Fischer, R. A. Reductive Elimination: A Pathway to Low-valent Aluminium Species. Chem. Commun. 2013, 49, 2858−2860. (c) Myers, T. W.; Berben, L. A. Aluminum−Ligand Cooperative N−H Bond Activation and an Example of Dehydrogenative Coupling. J. Am. Chem. Soc. 2013, 135, 9988−9990. (d) Thompson, E. J.; Myers, T. W.; Berben, L. A. Synthesis of Square-Planar Aluminum(III) Complexes. Angew. Chem., Int. Ed. 2014, 53, 14132−14134. (e) Myers, T. W.; Berben, L. A. Aluminium-ligand Cooperation Promotes Selective Dehydrogenation of Formic Acid to H2 and CO2. Chem. Sci. 2014, 5, 2771−2777. (9) Alexander, S. G.; Cole, M. L.; Forsyth, C. M. Tertiary Amine and N-Heterocyclic Carbene Coordinated Haloalanes-Synthesis, Structure, and Application. Chem. - Eur. J. 2009, 15, 9201−9214. (10) Würtemberger-Pietsch, S.; Schneider, H.; Marder, T. B.; Radius, U. Adduct Formation, B-H Activation and Ring Expansion at Room Temperature from Reactions of HBcat with NHCs. Chem. Eur. J. 2016, 22, 13032−13036. (11) Arduengo, A. J.; Dias, H. V. R.; Calabrese, J. C.; Davidson, F. A Stable Carbene-alane Adduct. J. Am. Chem. Soc. 1992, 114, 9724− 9725. (12) Baker, R. J.; Davies, A. J.; Jones, C.; Kloth, M. Structural and Spectroscopic Studies of Carbene and N-Donor Ligand Complexes of Group 13 Hydrides and Halides. J. Organomet. Chem. 2002, 656, 203−210. (13) (a) Lavallo, V.; Canac, Y.; Präsang, C.; Donnadieu, B.; Bertrand, G. Stable Cyclic (Alkyl)(Amino)Carbenes as Rigid or Flexible, Bulky, Electron-Rich Ligands for Transition-Metal Catalysts: A Quaternary Carbon Atom Makes the Difference. Angew. Chem., Int. Ed. 2005, 44, 5705−5709. Lavallo, V.; Canac, Y.; Prasang, C.; Donnadieu, B.; Bertrand, G. Stable Cyclic (Alkyl)(Amino)Carbenes as Rigid or Flexible, Bulky, Electron-Rich Ligands for Transition-

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.9b02001. Detailed synthetic procedures, analytical and characterization data including NMR, elemental analysis, and melting points, and details of crystal structure refinement (PDF) Accession Codes

CCDC 1898149−1898151 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Subrata Kundu: 0000-0002-2308-5452 Zhi Yang: 0000-0002-5732-0326 Regine Herbst-Irmer: 0000-0003-1700-4369 Dietmar Stalke: 0000-0003-4392-5751 Herbert W. Roesky: 0000-0003-4454-1434 Author Contributions §

These authors contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS H.W.R. thanks the DFG for financial support (RO 224/71-1). D.S. thanks the Danish National Research Foundation (DNRF93) funded Center for Materials Crystallography for partial support.

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DEDICATION Dedicated to Professor Chunming Cui on the occasion of his 50th birthday. REFERENCES

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DOI: 10.1021/acs.inorgchem.9b02001 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

θmax = 26.433°, 40922 reflections measured, 5114 independent reflections (Rint = 0.0354), R1 = 0.0463 [I > 2σ(I)], wR2 = 0.1045 (all data), residual density peaks of +0.526 to −0.325 e Å−3, CCDC 1898150. Crystal data for 3 at 100(2) K: C30H47AlN4, Mr = 490.69 g mol−1, 0.326 × 0.324 × 0.134 mm3, triclinic, P1̅, a = 11.027(2) Å, b = 12.575(2) Å, c = 12.850(3) Å, α = 65.28(2)°, β = 74.87(3)°, γ = 64.27(2)°, V = 1451.2(6) Å3, Z = 2, μ(Mo Kα) = 0.094 mm−1, θmax = 27.476°, 81427 reflections measured, 6659 independent reflections (Rint = 0.0313), R1 = 0.0339 [I > 2σ(I)], wR2 = 0.0883 (all data), residual density peaks of +0.350 to −0.249 e Å−3, CCDC 1898151. (19) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C. Synthesis, Structure, and Spectroscopic Properties of Copper(II) Compounds Containing Nitrogen-Sulphur Donor Ligands; the Crystal and Molecular Structure of Aqua[1,7-bis(N-methylbenzimidazol-2’-yl)-2,6 dithiaheptane]copper(II) Perchlorate. J. Chem. Soc., Dalton Trans. 1984, 7, 1349−1356. (20) (a) Stalke, D. Cryo Crystal Structure Determination and Application to Intermediates. Chem. Soc. Rev. 1998, 27, 171−178. (b) Kottke, T.; Stalke, D. Crystal Handling at Low Temperatures. J. Appl. Crystallogr. 1993, 26, 615−619. (21) Bruker Apex CCD and SAINT v8.30C; Bruker AXS Institute Inc.: Madison, WI, 2013. (22) Krause, L.; Herbst-Irmer, R.; Stalke, D. An Empirical Correction for the Influence of Low-Energy Contamination. J. Appl. Crystallogr. 2015, 48, 1907−1913. (23) Krause, L.; Herbst-Irmer, R.; Sheldrick, G. M.; Stalke, D. Comparison of Silver and Molybdenum Microfocus X-ray sources for Single-Crystal Structure Determination. J. Appl. Crystallogr. 2015, 48, 3−10. (24) Sheldrick, G. M. SHELXT−Integrated Space-Group and Crystal-Structure Determination. Acta Crystallogr., Sect. A: Found. Adv. 2015, A71, 3−8. (25) Sheldrick, G. M. Crystal Structure Refinement with SHELXL. Acta Crystallogr., Sect. C: Struct. Chem. 2015, C71, 3−8. (26) Hübschle, C. B.; Sheldrick, G. M.; Dittrich, B. ShelXle: a Qt Graphical User Interface for SHELXL. J. Appl. Crystallogr. 2011, 44, 1281−1284.

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DOI: 10.1021/acs.inorgchem.9b02001 Inorg. Chem. XXXX, XXX, XXX−XXX