English

• 1. INTRODUCTION

  The heterobimetallic complexes were widely reported because they often exhibit a special synergy that makes them more reactive than their homometallic precursors. These heterobimetallic formulations as metalate (ate) reagents are surveyed focusing mainly on containing an alkali metal paired with another metal (alkali metal, magnesium, calcium, zinc, aluminum, gallium, etc)^[1-6].

  The first alkali metal zincate [Na(ZnEt₃)] was announced by Wanklyn in 1959^{[7, 8]}. In recent decades, various types of heterobimetallic complexes were continually reported to selectively functionalize neighbouring meta and para positions of aromatic molecules. For example, Mulvey and co-workers reported a range of lithium aluminates and alkali amide magnesites which had been successfully utilized in metal-hydrogen exchange reactions of challenging weakly acidic aromatic substrates^[9-17]. Mongin′s group provided a series of bimetallic metalate complexes combining lithium with a variety of secondary metals^[18-26]. Wheatley contributed a number of lithium-aluminum complexes^[27-30], of which ⁱBu₃Al(TMP)Li is designed for regionally and chemically selective direct generation of functionalized aromatic compounds^[30].

  Recently, Blair has reported four heterobimetallic (Na/Mg) complexes and revealed the contrasting heterobimetallic deprotonation with homometallic induced ethene elimination reactivity^[31]. A series of lithium aluminates and lithium alkylmagnesiates have been synthesized by our group^[32], such as [{-LiOC(CH₂)₅CH₂N(Me)CH₂CH₂NMe₂}Al(Me)(ⁿBu)CH₃-}_n] (a), [{-LiOC(CH₂)₅CH₂N(Me)CH₂CH₂NMe₂}Al(ⁿBu)₂CH₃-}_n] (b), [{ⁿBu₂Mg{LiOC(CH₂)₅CH₂N(Me)CH₂CH₂NMe₂}}₂] (c) and [{ⁿBuMgOLi[LiOC(CH₂)₅CH₂N(Me)CH₂CH₂NMe₂]₂}₂] (d). Each of complexes a~d was utilized as catalyst in Meerwein-Ponndorf-Verley (MPV) reduction^[33-37] applications of selected carbonyl compound and isopropanol. Hopefully, complex c showed the best catalytic activity of its homometallic magnesium precursor. At the same time, it is worth noting that the catalytic activity of complex a is significantly higher than that of b with similar structure. It would be due to the steric hindrance effect of normal-butyl group for b, which added the steric hindrance of metal center and decreased the attack probability to benzaldehyde. As part of our ongoing studies in the influence of initiators' structures on the catalytic activities and the synergistic effect of heterobimetallic complexes, we report here the synthesis and characterization of a lithium-aluminum complex [{-LiOC-(CH₂)₅CH₂N(Me)CH₂CH₂NMe₂}-AlMe₂CH₃-}_n] (1). Complex 1 was characterized by NMR spectra and single-crystal X-ray diffraction techniques and was used as catalysts in MPV reactions.

  2. EXPERIMENTAL

  2.1 Instruments and reagents

  All experiments were carried out under purified dry nitrogen atmosphere by using standard Schlenk techniques. Solvents were dried and freshly distilled under nitrogen. The carbonyl compounds were distilled, sublimed, or recrystallized before use. MeLi (1.6 M solution in diethyl ether), AlMe₃ (2.0 M solution in hexane) and AlEtCl₂ (1.0 M solution in heptane) were used as purchased from Alfa Aesar. ¹H NMR and ¹³C NMR spectra of the complexes were recorded in THF-D₈ with a Bruker AVANCE Ⅲ HD 600 instrument, using TMS as an internal standard. Melting point was determined on a STUART SMP10 melting point apparatus and uncorrected. Elemental analyses were conducted on a Vario EL-Ⅲ instrument.

  2.2 Synthesis of complex 1, [{-LiOC(CH₂)₅CH₂N(Me)-CH₂CH₂NMe₂}AlMe₂CH₃-}_n]

  Method 1   The ligand HOC(CH₂)₅CH₂N(Me)CH₂CH₂NMe₂ (LH) was prepared with reference to the literature^[38]. To a stirred solution of LH (0.23 g, 1.1 mmol) in diethyl ether (10 mL), AlMe₃ (0.55 mL, 1.1 mmol) was added dropwise at 0 ℃. The solution was slowly warmed to room temperature and stirred for an additional 2 h. Then MeLi (0.69 mL, 1.1 mmol) was added to the reaction mixture at 0 ℃. The mixture was allowed to warm to room temperature and stirred for 2 h. The reaction mixture was filtered and crystallized from tetrahydrofuran-hexane at –5 ℃ to give colourless crystals of complex 1. Yield: 0.24 g (77%).

  Method 2   AlEtCl₂ (2.1 mL, 2.1 mmol) was added dropwise at 0 ℃ to a solution of LH (0.44 g, 2.1 mmol) in diethyl ether (10 mL). The solution was then warmed to room temperature and stirred for 2 h. Then MeLi (2.6 mL, 4.2 mmol) was added to the reaction mixture at 0 ℃. The mixture was allowed to warm to room temperature and stirred for 2 h. Colorless crystals were obtained from tetrahydrofuran-hexane at –5 ℃. Yield: 0.54 g (89%), m. p.: 176~179 ℃. ¹H NMR (THF-D₈, δ/ppm): –1.30 (s, 9H, AlCH₃Li and AlC₂H₆), 0.98~1.02 (m, 1H, C₅H₁₀), 1.09~1.14 (m, 2H, C₅H₁₀), 1.39~1.44 (m, 5H, C₅H₁₀ and NC₂H₆), 1.54 (s, 2H, NC₂H₆), 1.69~1.80 (m, 1H, NC₂H₆), 1.86~1.95 (m, 1H, NC₂H₄N), 2.04~2.15 (m, 6H, C₅H₁₀, NC₂H₆ and C₅H₁₀CH₂), 2.17~2.23 (m, 4H, NCH₃ and NC₂H₄N), 2.46~2.56 (m, 3H, NC₂H₄N and C₅H₁₀CH₂). ¹³C NMR (THF-D₈, δ/ppm): –5.41 (AlCH₃Li and AlC₂H₆), 24.08 (C₅H₁₀), 24.21 (C₅H₁₀), 26.00 (C₅H₁₀), 37.84 (NC₂H₆), 40.99 (NC₂H₆), 46.54 (NCH₃), 57.52 (NC₂H₄N), 57.84 (NC₂H₄N), 64.66 (C₅H₁₀CH₂), 72.11 (C₅H₁₀CO-). ⁷Li NMR (THF-D₈, δ/ppm): 0.73. ²⁷Al NMR (THF-D₈, δ/ppm): 149.55. Anal. Calcd. (%) for C₁₅H₃₃AlLiN₂O: C, 61.83; H, 11.42; N, 9.61. Found (%): C, 61.74; H, 11.75; N, 9.93.

  2.3 General procedure employed for the MPV reaction

  The carbonyl compound (2.0 mmol) and complex 1 (0.1 mmol) were added to a 50 mL Schlenk flask, followed by the addition of isopropanol (0.19 mL, 2.4 mmol). The reaction mixture was then refluxed for 6 hours, and the yield was determined by ¹H NMR spectroscopic study based on the integration in the methylene and the CHO region of the benzyl group.

  2.4 Structure determination

  The crystal of complex 1 was coated in oil and then directly mounted on the diffractometer under a stream of cold nitrogen gas. Single-crystal X-ray diffraction data of complex 1 were collected on a Bruker Smart Apex CCD diffractometer using monochromated MoKα radiation (λ = 0.71073 Å). A total of N reflections were collected by using an ω scan mode. A total of 6698 reflections were collected with 8994 unique ones (R_int = 0.0937), of which 5066 observed reflections with I > 2σ(I) were used in the succeeding refinements. Corrections were applied for Lorentz and polarization effects as well as absorption using multi-scans (SADABS)^[39]. The molecular structure was solved by direct methods and refined on F² by full-matrix least-squares technique (SHELX-97)^[40]. All non-hydrogen atoms were refined with anisotropic displacement parameters, whereas the hydrogen atoms were constrained to parent sites, using a riding mode (SHE-LXTL)^[41]. The final R = 0.0650, wR = 0.1424 (w = 1/[σ²(F_o²) + (0.0231P)² + 5.3400P], where P = (F_o² + 2F_c²)/3), S = 0.988, (Δ/σ)_max = 0.000, (Δρ)_max = 0.363 and (Δρ)_min = –0.346 e/ų. The selected bond lengths and bond angles for complex 1 are given in Table 1.

  Table 1

  

  Table 1.  Selected Bond Lengths (Å) and Bond Angles (°)

  DownLoad: CSV

  Bond	Dist.		Bond	Dist.		Bond	Dist.
  Al(1)–O(1)	1.804(2)		Al(1)–C(13)	1.992(4)		Al(1)–C(14)	1.995(4)
  Al(1)–C(15)	2.015(4)		Al(2)–O(2)	1.800(2)		Al(2)–C(28)	1.996(4)
  Al(2)–C(29)	1.985(4)		Al(2)–C(30)	2.016(4)		Li(1)–O(1)	1.879(6)
  Li(1)–N(1)	2.111(6)		Li(1)–N(2)	2.122(7)		Li(2)–O(2)	1.880(6)
  Li(2)–N(3)	2.099(6)		Li(2)–N(4)	2.106(6)		Li(2)–C(15)	2.428(6)
  Angle	(°)		Angle	(°)		Angle	(°)
  Al(1)–C(15)–Li(2)	165.9(2)		Al(1)–O(1)–Li(1)	118.2(2)		O(1)–Li(1)–N(1)	88.6(2)
  O(1)–Li(1)–N(2)	118.1(3)		N(1)–Li(1)–N(2)	89.0(2)		O(1)–Al(1)–C(15)	106.69(13)
  O(1)–Al(1)–C(13)	114.17(14)		O(1)–Al(1)–C(14)	102.43(13)		C(13)–Al(1)–C(15)	110.61(17)
  C(13)–Al(1)–C(14)	110.84(17)		C(14)–Al(1)–C(15)	111.83(16)		C(15)–Li(2)–N(3)	108.4(2)
  C(15)–Li(2)–N(4)	110.7(3)		O(2)–Li(2)–N(3)	89.1(2)		O(2)–Li(2)–N(4)	115.5(3)
  N(3)–Li(2)–N(4)	89.8(2)		O(2)–Al(2)–C(30)	107.38(13)		O(2)–Al(2)–C(28)	103.06(13)
  O(2)–Al(2)–C(29)	113.93(14)

  3. RESULTS AND DISCUSSION

  3.1 Description of the structure

  The synthesis of complex 1 by ligand LH presented here is shown in Scheme 1, which has two ways. Method 1: Reaction of LH with trimethyl aluminum in diethyl ether results in the facile evolution of methane gas and the formation of colorless solution. Treatment of the solution with equivalent amount of methyl lithium obtained the colorless crystal complex 1 in 77% yield.

  Figure 1

  

  Figure 1.  Synthesis of lithium-aluminum complex 1

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  Method 2: The sequential reaction of LH with equivalent amount of ethylaluminum dichloride and two equivalents of methyl lithium in diethyl ether afforded complex 1 in 89% yield. The yield of this method is obviously better than that of method 1. It is worth noting that the adding sequence of methyl lithium and aluminum reagent is tried to be changed and the expected product is not available.

  Complex 1 crystallizes in triclinic, space group P$ \overline 1 $. The ORTEP drawing of complex 1 indicated that the crystal structure is of one-dimensional polymerization (Fig. a). The fragment of two monomers results from a weak intermolecular bond of lithium atom by Al-bonded methyl-C atom (mean Li(2)–C(15) = 2.428 Å) in the structure unit of 1 (Fig. b), which is similar to that of complexes a and b^[32]. The four-coordinated aluminum atom is surrounded by the oxygen atoms from the ligand and three methyl-C atoms in an approximately tetrahedral geometry in the structure of monomer. The charge on the negative aluminate fragment is offset by that on the metal lithium centre. The geometry around the lithium (Li(1)) atom is three-coordinated with the oxygen (O(1)) atom from ligand and two nitrogen (N(1), N(2)) atoms. The bond distance of Li(2)–C(15) is significantly longer than that in complexes a (2.373 Å) and b (2.337 Å). The Al(1)–C(15) (2.015 Å) is slightly longer than Al(1)–C(13) (1.992 Å) and Al(1)–C(14) (1.995 Å), respectively. Meanwhile, Al(1)–C(15) is slightly longer than that (2.002 and 2.010 Å, respectively) in complexes a and b. Compared with the structures of complexes a and b, there is a greater spatial advantage around aluminum atoms in complex 1.

  Figure 1

  

  Figure 1.  (a) Polymeric chain structure of 1, (b) Structure unit of 1 (at 25% probability level). Hydrogen atoms are omitted for clarity

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  3.2 Complex 1 as catalyst for the MPV reaction

  According to the previous work^{[32, 42, 43]}, the study of the MPV reaction was carried out using selected carbonyl compounds and dry isopropanol catalyzed by the heterobimetallic complex 1. The results are shown in Table 2. Firstly, complex 1 at 5 mol% loading under solvent-free in 6 hours afford 94% yield of benzaldehyde to benzyl alcohol (Table 2, entry 1). Then the electronic effects were examined by employing 4-subsitituted benzaldehyde. 4-Chlorobenzaldehyde of electron-withdrawing group on the phenyl ring gave an obviously better yield than 4-anisaldehyde (97%, 87% yield, Table 2, entries 2 and 3). In addition, citronellal and some α, β-unsaturated aldehydes were also reduced to the corresponding alcohols under our catalytic system in good yield (Table 2, entries 4~6). Due to the conjugative effect, the yield of citronellal was significantly higher than that of cinnamaldehyde and citral. Finally, low active acetophenone and cyclohexanone were also reduced to corresponding alcohols in 78% and 85% yields, respectively (Table 2, entries 7 and 8). The chirality of the product of MPV reaction was further tested. Each of 1-phenylethanol products catalyzed complexes 1~3 was proved to be a racemic mixture, respectively.

  Table 2

  

  Table 2.  Complex 1 Catalyzed MPV Reactions of Selected Carbonyl Compounds^a

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  Entry	Carbonyl compound	Product	Yield (%)b
  1			91c, 94
  2			97
  3			87
  4			95
  5			84
  6			81
  7			78d
  8			85d
  aConditions: reflux, 5 mol% catalyst, solvent-free, 6 h; bdetermined by 1H NMR spectroscopy; c 4 h; ddetermined by GC-MS

  4. CONCLUSION

  In summary, a new heterobimetallic complex 1 was synthesized, characterized and used for catalytic study of MPV reaction. 1 exhibited good catalytic activity for a range of aldehydes and ketones, which could be rapidly and selectively transferred to the corresponding alcohols about 78~97% yield.

  
  
• 1. [1]

     Linton, D. J.; Schooler, P.; Wheatley, A. E. H. Group 12 and heavier group 13 alkali metal'ate complexes. Coord. Chem. Rev. 2001, 223, 53–115. doi: 10.1016/S0010-8545(01)00379-4

  2. [2]

     Haag, B.; Mosrin, M.; Ila, H.; Malakhov, V.; Knochel, P. Regio- and chemoselective metalation of arenes and heteroarenes using hindered metal amide bases. Angew. Chem. Int. Ed. 2011, 50, 9794–9824. doi: 10.1002/anie.201101960

  3. [3]

     Tilly, D.; Chevallier, F.; Mongin, F.; Gros, P. C. Bimetallic combinations for dehalogenative metalation involving organic compounds. Chem. Rev. 2014, 114, 1207–1257. doi: 10.1021/cr400367p

  4. [4]

     Organo-di-Metallic compounds (or reagents) (Ed. : Z. Xi), Springer Cham. 2014.

  5. [5]

     Robertson, S. D.; Uzelac, M.; Mulvey, R. E. Alkali-metal-mediated synergistic effects in polar main group organometallic chemistry. Chem. Rev. 2019, 119, 8332–8405. doi: 10.1021/acs.chemrev.9b00047

  6. [6]

     Coz, E. L.; Roueindeji, H.; Dorcet, V.; Roisnel, T.; Carpentier, J. F.; Sarazin, Y. Heterobimetallic Ba/Li and Ca/Li amides and diphenylmethanide. Dalton Trans. 2019, 48, 5500–5504. doi: 10.1039/C9DT00771G

  7. [7]

     Wanklyn, J. A. Ueber einige neue aethylverbindungen. welche alkalimetalle enthalten. Liebigs Ann. 1858, 108, 67–79. doi: 10.1002/jlac.18581080116

  8. [8]

     Wanklyn, J. A. On some new ethyl-compounds containing the alkalimetals. Proc. R. Soc. London 1859, 9, 341–345. doi: 10.1098/rspl.1857.0084

  9. [9]

     Andrikopoulos, P. C.; Armstrong, D. R.; Kennedy, A. R.; Mulvey, R. E.; O'Hara, C. T.; Rowlings, R. B.; Weatherstone, S. Synthesis and structural characterisation of mixed alkali metal-magnesium mixed ligand alkyl-amido ate complexes. Inorg. Chim. Acta 2007, 360, 1370–1375. doi: 10.1016/j.ica.2006.05.026

  10. [10]

      Mulvey, R. E. Avant-garde metalating agents: structural basis of alkali-metal-mediated metalation. Acc. Chem. Res. 2009, 42, 743–755. doi: 10.1021/ar800254y

  11. [11]

      Mulvey, R. E.; Blair, V. L.; Clegg, W.; Kennedy, A. R.; Klett, J.; Russo, L. Cleave and capture chemistry illustrated through bimetallic-induced fragmentation of tetrahydrofuran. Nat. Chem. 2010, 2, 588–591. doi: 10.1038/nchem.667

  12. [12]

      Martínez-Martínez, A. J.; Kennedy, A. R.; Mulvey, R. E.; O'Hara, C. T. Directed ortho-meta'- and meta-meta'-dimetalations: a template base approach to deprotonation. Science 2014, 346, 834–837. doi: 10.1126/science.1259662

  13. [13]

      Mulvey, R. E.; Robertson, S. D. FascinATES: mixed-metal ate compounds that function synergistically. Top. Organomet. Chem. 2014, 47, 129–158.

  14. [14]

      Kennedy, A. R.; Mulvey, R. E.; Ramsay, D. L.; Robertson, S. D. Heterobimetallic metallation studies of N, N-dimethylphenylethylamine (DMPEA): benzylic C–H bond cleavage/dimethylamino capture or intact DMPEA complex. Dalton Trans. 2015, 44, 5875–5887. doi: 10.1039/C5DT00247H

  15. [15]

      Fuentes, M. Á.; Zabala, A.; Kennedy, A. R.; Mulvey, R. E. Structural diversity in alkali metal and alkali metal magnesiate chemistry of the bulky 2,6-diisopropyl-N-(trimethylsilyl)anilino ligand. Chem. Eur. J. 2016, 22, 14968–14978. doi: 10.1002/chem.201602683

  16. [16]

      Pollard, V. A.; Ángeles, F. M.; Kennedy, A. R.; McLellan, R.; Mulvey, R. E. Comparing neutral (monometallic) and anionic (bimetallic) aluminum complexes in hydroboration catalysis: influences of lithium cooperation and ligand set. Angew. Chem. Int. Ed. 2018, 57, 10651–10655. doi: 10.1002/anie.201806168

  17. [17]

      Gauld, R. M.; Kennedy, A. R.; McLellan, R.; Barker, J.; Reid, J.; Mulvey, R. E. Diverse outcomes of CO₂ fixation using alkali metal amides including formation of a heterobimetallic lithium-sodium carbamato-anhydride via lithium-sodium bis-hexamethyldisilazide. Chem. Commun. 2019, 55, 1478–1481. doi: 10.1039/C8CC08308H

  18. [18]

      L'Helgoual'ch, J. M.; Seggio, A.; Chevallier, F.; Yonehara, M.; Jeanneau, E.; Uchiyama, M.; Mongin, F. Deprotonative metalation of five-membered aromatic heterocycles using mixed lithium-zinc species. J. Org. Chem. 2008, 73, 177–183. doi: 10.1021/jo7020345

  19. [19]

      Snegaroff, K.; L'Helgoual'ch, J. M.; Bentabed-Ababsa, G.; Nguyen, T. T.; Chevallier, F.; Yonehara, M.; Uchiyama, M.; Derdour, A.; Mongin, F. Deprotonative metalation of functionalized aromatics using mixed lithium-cadmium, lithium-indium, and lithium-zinc species. Chem. Eur. J. 2009, 15, 10280–10290. doi: 10.1002/chem.200901432

  20. [20]

      Dayaker, G.; Sreeshailam, A.; Chevallier, F.; Roisnel, T.; Krishna, P. R.; Mongin, F. Deprotonative metallation of ferrocenes using mixed lithium-zinc and lithium-cadmium combinations. Chem. Commun. 2010, 46, 2862–2864. doi: 10.1039/b924939g

  21. [21]

      Sngaroff, K.; Komagawa, S.; Chevallier, F.; Gros, P. C.; Golhen, S.; Roisnel, T.; Uchiyama, M.; Mongin, F. Deprotonative metalation of substituted benzenes and heteroaromatics using amino/alkyl mixed lithium-zinc combinations. Chem. Eur. J. 2010, 16, 8191–8201. doi: 10.1002/chem.201000543

  22. [22]

      Dayaker, G.; Tilly, D.; Chevallier, F.; Hilmersson, G.; Gros, P. C.; Mongin, F. Enantioselective metalation of N, N-diisopropylferrocenecarboxamide and methyl ferrocenecarboxylate using lithium-metal chiral bases. Eur. J. Org. Chem. 2012, 6051–6057.

  23. [23]

      Messaoud, M. Y. A.; Bentabed-Ababsa, G.; Hedidi, M.; Derdour, A.; Chevallier, F.; Halauko, Y. S.; Ivashkevich, O. A.; Matulis, V. E.; Picot, L.; Thiery, V.; Roisnel, T.; Dorcet, V.; Mongin, F. Deproto-metallation of N-arylated pyrroles and indoles using a mixed lithium-zinc base and regioselectivity-computed CH acidity relationship. Beilstein J. Org. Chem. 2015, 11, 1475–1485. doi: 10.3762/bjoc.11.160

  24. [24]

      Nguyen, T. T.; Chevallier, F.; Jouikov, V.; Mongin, F. New Gilman-type lithium cuprate from a copper(Ⅱ) salt: synthesis and deprotonative cupration of aromatics. Tetrahedron Lett. 2009, 50, 6787–6790. doi: 10.1016/j.tetlet.2009.09.100

  25. [25]

      Bayh, O.; Awad, H.; Mongin, F.; Hoarau, C.; Trecourt, F.; Queguiner, G.; Marsais, F.; Blanco, F.; Abarca, B.; Ballesteros, R. Deprotonation of thiophenes using lithium magnesates. Tetrahedron 2005, 61, 4779–4784. doi: 10.1016/j.tet.2005.03.024

  26. [26]

      Mongin, F.; Bucher, A.; Bazureau, J. P.; Bayh, O.; Awad, H.; Trecourt, F. Deprotonation of furans using lithium magnesates. Tetrahedron Lett. 2005, 46, 7989–7992. doi: 10.1016/j.tetlet.2005.09.066

  27. [27]

      Davies, R. P.; Linton, D. J.; Snaith, R.; Wheatley, A. E. H. Selective oxygen capture to give a unique mixed-anion lithium aluminate: the synthesis and solid-state structure of {[PhC(O)N(Me)Al(Me)(Bu^t)OMe]Li·[PhC(O)N(Me)Al(Me)(OBu^t)OMe]Li}₂. Chem. Commun. 2000, 193–194.

  28. [28]

      Armstrong, D. R.; Davies, R. P.; Linton, D. J.; Schooler, P.; Shields, G. P.; Snaith, R.; Wheatley, A. E. H. Selective oxygen capture by lithium aluminates: a solid state and theoretical structural study. J. Chem. Soc. Dalton. 2000, 4304–4311.

  29. [29]

      Davies, R. P.; Linton, D. J.; Schooler, P.; Snaith, R.; Wheatley, A. E. H. Synthesis and solid-state structure of (Li₄Am₃)⁺·{Li[(µ-Me)₂Al(Me)^tBu]₂}^- {Am = [PhNC(Ph)NPh]^-}: a polymeric species incorporating a lithium-nitrogen cluster cation. Eur. J. Inorg. Chem. 2001, 619–622.

  30. [30]

      Naka, H.; Uchiyama, M.; Matsumoto, Y.; Wheatley, A. E. H.; McPartlin, M.; Morey, J. V.; Kondo, Y. An aluminum ate base: its design, structure, function, and reaction mechanism. J. Am. Chem. Soc. 2007, 129, 1921–1930. doi: 10.1021/ja064601n

  31. [31]

      Stevens, M. A.; Hashim, F. H.; Gwee, E. S. H.; Izgorodina, E. I.; Mulvey, R. E.; Blair, V. L. Contrasting synergistic heterobimetallic (Na-Mg) and homometallic (Na or Mg) bases in metallation reactions of dialkylphenylphosphines and dialkylanilines: lateral versus ring selectivities. Chem. Eur. J. 2018, 24, 15669–15677. doi: 10.1002/chem.201803477

  32. [32]

      Hua, Y.; Guo, Z.; Han, H.; Wei, X. N, N, O-Tridentate mixed lithium-magnesium and lithium-aluminum complexes: synthesis, characterization and catalytic activities. Organometallics 2017, 36, 877–883. doi: 10.1021/acs.organomet.6b00921

  33. [33]

      Leng, Y.; Shi, L.; Du, S.; Jiang, J.; Jiang, P. A tannin-derived zirconium-containing porous hybrid for efficient Meerwein-Ponndorf-Verley reduction under mild conditions. Green Chem. 2020, 22, 180–186. doi: 10.1039/C9GC03393A

  34. [34]

      Boit, T.; Mehta, M.; Garg, N. Base-mediated Meerwein-Ponndorf-Verley reduction of aromatic and heterocyclic ketones. Org. Lett. 2019, 21, 6447–6451. doi: 10.1021/acs.orglett.9b02342

  35. [35]

      Alshakova, I.; Foy, H.; Dudding, T.; Nikonov, G. Ligand effect in alkali-metal-catalyzed transfer hydrogenation of ketones. Chem. Eur. J. 2019, 25, 11734–11744. doi: 10.1002/chem.201902240

  36. [36]

      Xiao, Z. Insight into the Meerwein-Ponndorf-Verley reduction of cinnamaldehyde over MgAl oxides catalysts. Molecular Catalysis 2017, 436, 1–9. doi: 10.1016/j.mcat.2017.04.016

  37. [37]

      McNerney, B.; Whittlesey, B.; Cordes, D.; Krempner, C. A well-defined monomeric aluminum complex as an efficient and general catalyst in the Meerwein-Ponndorf-Verley reduction. Chem. Eur. J. 2014, 20, 14959–14964. doi: 10.1002/chem.201404994

  38. [38]

      Hua, Y.; Wang, H.; Guo, Z.; Wei, X. Study on the C–H bond activation of methyl in TMEDA. Journal of Shanxi University (Nat. Sci. Ed. ) 2019, 42, 407–412.

  39. [39]

      Sheldrick, G. M. SADABS Correction Software. University of Göttingen, Göttingen, Germany 1996.

  40. [40]

      Sheldrick, G. M. SHELXS-97, Program for the Solution of Crystal Structure. University of Göttingen: Göttingen, Germany 1997.

  41. [41]

      Sheldrick, G. M. Crystal structure refinement with SHELXL. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3–8. doi: 10.1107/S2053229614024218

  42. [42]

      Hua, Y.; Guo, Z.; Suo, H.; Wei, X. Bidentate N, O-aluminum complexes: synthesis, characterization and catalytic study for MPV reduction reactions. J. Organomet. Chem. 2015, 794, 59–64. doi: 10.1016/j.jorganchem.2015.06.011

  43. [43]

      Han, H.; Guo, Z.; Zhang, S.; Hua, Y.; Wei, X. Synthesis and crystal structures of guanidinatoaluminum complexes and catalytic study for MPV reduction. Polyhedron 2017, 126, 214–219. doi: 10.1016/j.poly.2017.01.030

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  Figure 1  Synthesis of lithium-aluminum complex 1

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  Figure 1  (a) Polymeric chain structure of 1, (b) Structure unit of 1 (at 25% probability level). Hydrogen atoms are omitted for clarity

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  Table 1.  Selected Bond Lengths (Å) and Bond Angles (°)

  Bond	Dist.		Bond	Dist.		Bond	Dist.
  Al(1)–O(1)	1.804(2)		Al(1)–C(13)	1.992(4)		Al(1)–C(14)	1.995(4)
  Al(1)–C(15)	2.015(4)		Al(2)–O(2)	1.800(2)		Al(2)–C(28)	1.996(4)
  Al(2)–C(29)	1.985(4)		Al(2)–C(30)	2.016(4)		Li(1)–O(1)	1.879(6)
  Li(1)–N(1)	2.111(6)		Li(1)–N(2)	2.122(7)		Li(2)–O(2)	1.880(6)
  Li(2)–N(3)	2.099(6)		Li(2)–N(4)	2.106(6)		Li(2)–C(15)	2.428(6)
  Angle	(°)		Angle	(°)		Angle	(°)
  Al(1)–C(15)–Li(2)	165.9(2)		Al(1)–O(1)–Li(1)	118.2(2)		O(1)–Li(1)–N(1)	88.6(2)
  O(1)–Li(1)–N(2)	118.1(3)		N(1)–Li(1)–N(2)	89.0(2)		O(1)–Al(1)–C(15)	106.69(13)
  O(1)–Al(1)–C(13)	114.17(14)		O(1)–Al(1)–C(14)	102.43(13)		C(13)–Al(1)–C(15)	110.61(17)
  C(13)–Al(1)–C(14)	110.84(17)		C(14)–Al(1)–C(15)	111.83(16)		C(15)–Li(2)–N(3)	108.4(2)
  C(15)–Li(2)–N(4)	110.7(3)		O(2)–Li(2)–N(3)	89.1(2)		O(2)–Li(2)–N(4)	115.5(3)
  N(3)–Li(2)–N(4)	89.8(2)		O(2)–Al(2)–C(30)	107.38(13)		O(2)–Al(2)–C(28)	103.06(13)
  O(2)–Al(2)–C(29)	113.93(14)

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  Table 2.  Complex 1 Catalyzed MPV Reactions of Selected Carbonyl Compounds^a

  Entry	Carbonyl compound	Product	Yield (%)b
  1			91c, 94
  2			97
  3			87
  4			95
  5			84
  6			81
  7			78d
  8			85d
  aConditions: reflux, 5 mol% catalyst, solvent-free, 6 h; bdetermined by 1H NMR spectroscopy; c 4 h; ddetermined by GC-MS

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