Strong Lewis Acid Research Articles

Facile synthesis of bidentate boron Lewis acids by pentafluorobenzene elimination

The obtained results reveal simple synthetic approach for bidentate boron Lewis acids with the ‐OB(C6F5)2 acid group and aliphatic or aromatic linkers. Computational results showed comparable FIA for the ‐OB(C6F5)2 site in boron bidentate Lewis acids relative to initial B(C6F5)3. The relative Lewis acid strength of R[OB(C6F5)2]2 (R = C2H4, p‐C6H4, m‐C6H4) was characterized by Gutman‐Becket tests. The elimination of pentafluorobenzene by the reaction of R‐OH with B(C6F5)3 can be used for the synthesis of R‐OB(C6F5)2 derivatives and polydentate strong Lewis acids.

In Situ Generated 1‐Naphthylmethyl Radicals From Bis(1‐Naphthylmethyl)tin Dichlorides: Utilization For C‐C, C‐N, and C‐O Bond‐Forming Reactions

The in situ‐generated 1‐naphthylmethyl radicals from the thermolysis of bis(1‐naphthylmethyl)tin dichlorides combine with persistent organic radicals, 4‐hydroxy‐TEMPO or 4‐oxo‐TEMPO designs C−O bond forming products. Subsequently, the C‐N bond occurs when the 1‐naphthylmethyl radicals unite with nitric oxide (NO) under a nitrogen atmosphere.In contrast, the oxidation instead of the addition reaction predominantly happens in the 1‐naphthylmethyl radicals when nitrogen dioxide contains a high oxidation state nitrogen center, i.e., N(IV) used.The by‐product, dodecanuclear organotin cages, with twelve peripheral naphthyl units, could be isolated from the 4‐hydroxy‐TEMPO reaction. Besides, the synthesis of unsymmetrical diarylmethanes RArCH2 (R = 1‐naphthyl, 2,4,6‐Me3C6H2, 3‐ and 4‐MeC6H4, phenyl, 4‐ClC6H4; Ar = 4‐MeOC6H4, 3,4‐, 2,4‐ and 2,5‐Me2C6H3) in high yields and with good regioselectivity is reported. This new methodology involves the iodine‐mediated thermolysis of bis(arylmethyl)tin dichlorides (RCH2)2SnCl2 and an excess of an arene. This reaction involves homolytic cleavage of Sn–C bonds to give arylmethyl radicals that react with iodine in the presence of SnCl2 to give the corresponding cations, which undergo electrophilic attack on the arene. Functionalised diarylmethanes have wide applications in pharmaceutical, agrochemical, and materials sciences. Alternative synthetic approaches to this class of organic compounds that avoid using a transition‐metal catalyst or a strong Lewis acid are desirable.

PnictogenIIIDications Supported by BZIMPY Ligands.

Two homologous series of pnictogen(III) dications, stabilized by 2,6-bis(benzimidazole-2-yl)pyridine ligands have been prepared. Both series contain PnIII-X moieties (Pn = P, As, Sb, Bi; X = Cl or Ph) and have been fully characterized using spectroscopic methods including X-ray crystallography. The Lewis acidity of these compounds has also been probed by computational methods; the results suggest that the dictations are strong Lewis acids, with the PnCl2+ compounds being more acidic than the PnPh2+ compounds, and with Lewis acidity increasing from P to Bi, in both series. The PhP2+-containing compound was also found to be a versatile PIII transfer reagent, leading to new synthetic routes for various PhP-containing compounds. The redox chemistry of all compounds has also been probed using cyclic voltammetry and chemical reductions. In some cases the resulting PnI moieties could be trapped using diazabutadienes.

Influence of WO3 Content in Phosphated Tungsten-Zirconium Oxide Catalysts on the Catalytic Pathways of Glycerol Transformation.

The catalytic performance of phosphate-stabilized WOx-ZrO2 compositions in gas-phase glycerol dehydration has been investigated. Results show that varying WO3 concentrations direct the process towards either acrolein or allyl alcohol formation. Catalysts with low WOx content exhibit strong Lewis acid sites (Zr4+ and W6+), where these metal ions likely function as redox sites, facilitating glycerol hydrogenolysis to produce allyl alcohol. Higher WO3 concentrations (exceeding 20 wt.%) lead to the shielding of some W6+ and Zr4+ sites by polytungstate surface complexes, which are strong Brønsted acid sites. This alteration promotes glycerol dehydration through the removal of two water molecules, thereby shifting the selectivity towards acrolein formation.

Sulfur-doped CuCo2O4 as a PMS activator: The synergy of oxygen defects and strong Lewis acid sites in boosting the elimination of ciprofloxacin

Herein, the synthesis of sulfur-modified CuCo2O4 (S-CuCo2O4) nanoparticles as a heterogeneous catalyst for peroxymonosulfate (PMS) activation was reported. The S-CuCo2O4 maintained the spinel structure and exhibited rich oxygen vacancies. Also, the presence of S atoms enlarged the specific surface area and created strong Lewis acid sites that both enhanced the adsorption ability toward PMS and CIP. Compared to the corresponding S-doped single oxides and CuCo2O4, the S-CuCo2O4 with the designed molar ratio of S and metal ions to be 10%, i.e., CCS-10, significantly improved the catalytic activity, indicating the synergism between Cu-O-Co bonds, the oxygen vacancies, and the Lewis acid sites. Under the optimal conditions of 0.1g.L-1 CCS-10 dosage, 0.2g.L-1 PMS, and natural pH, the CCS-10/PMS system could remove approximately 87% of CIP and 70% of TOC within 20min at a four-time higher rate than that of the pristine catalyst. This system showed the highest performance in the pH range from weak acidic to weak basic (pH 5.5 - pH 8.5). CCS10/PMS also displayed considerable efficiency in degrading various pollutants belonging to different categories (methylene blue (MB), carbamazepine (CBZ), bisphenol A (BPA), and sulfamethoxazole (SMX)). SO4•–, •OH, O2•–, and 1O2 active species were found to be responsible for CIP elimination. Finally, the PMS residual concentration was recorded to be 0.01g.L-1 after the reaction. Overall, this study could contribute a possible strategy to enhance the heterogeneous catalysts for the removal of organic pollutants.

Bismuth(III) Triflate, Bi(OTf)3: Green and Reusable Catalyst for One‐Pot Synthesis of Fused Nitrogen/Oxygen Heterocycle Derivatives

AbstractThere is an increasing demand for the development of catalytic reagents that are nontoxic due to the growing environmental concerns in the present organic transformation. Bismuth(III) compounds have significant potential as catalysts for a range of organic synthesis due to their low toxicity, strong Lewis acid catalytic activity, and great flexibility. In this research work, a series of various chemically and pharmacologically important six‐membered fused nitrogen‐/oxygen‐based heterocycle derivatives were efficiently prepared via a one‐pot multicomponent reaction starting from aromatic aldehydes, malononitrile, and barbituric acid in presence of green and reusable Lewis catalyst bismuth(III) triflate, that is, Bi(OTf)3 in EtOH/H2O (1:1) media. Bi(OTf)3 has the additional benefit of being reusable catalyst, ready availability, eco‐friendliness, and easy to handle to obtain corresponding products in excellent yields (83%–94%). Structure of all synthesized products was characterized on the basis of FT‐IR, 1H‐NMR, 13C‐NMR, and ESI–MS analysis.

A modified separator based on ternary mixed-oxide for stable lithium metal batteries

Li metal batteries (LMBs) are among the most promising options for next-generation secondary batteries under the rapidly growing demand for high-energy–density electrochemical energy storage. However, the implementation of LMBs are hindered by major obstacles such as dentritic Li deposition and low cycling Coulombic efficiency. A practical functional separator is developed in this study, which consists of a Lewis acidic mixed oxide of ZrO2-SiO2-Al2O3 as a functional coating with anion anchoring ability to modulate ion transport in the vicinity of the Li metal anode, delivering a high Li+ transference number of 0.88 in carbonate electrolytes that suppresses dendrite formation. The strong Lewis acid sites in ZrO2-SiO2-Al2O3 originate from coordinatively unsaturated Zr4+ ions, which immobilize anions and reduce their decomposition rate. This significantly improves the chemical stability of the electrolyte and induces a more stable solid electrolyte interphase layer. The modified separator enables an anode-free cell containing a high-loading LiNi0.8Co0.1Mn0.1O2 cathode to present stable charge and discharge cycling for 150 cycles at 0.5C. By effectively suppressing Li dendrite growth and supporting the long-term operation of anode-free LMBs, this study offers a novel approach to rationally design mixed oxides with high Lewis acidity for functional separators.

Fe-ZSM-5 outperforms Al-ZSM-5 in paraffin cracking by increasing the olefinicity of C3-C4 products

Iron-modified Al-ZSM-5 increases selectivity to propene, a key petrochemical resulting from fluid catalytic cracking (FCC). However, the type and role of active iron species remain unclear, hindering efforts to streamline the design of selective FCC additives. Here, we investigated Al-free Fe-ZSM-5 catalysts containing iron species in the form of framework Fe3+, extra-framework Fe3+, oxidic clusters, and oxide micro aggregates in n-octane cracking (FCC model) to assess their effect on catalytic cracking. DR-UV–Vis spectroscopy, 57Fe Mössbauer Spectroscopy, FTIR studies of pyridine adsorption, and n-octane cracking tests at 500 °C revealed that framework-associated coordinatively unsaturated Fe3+ species, which induce strong Lewis acidity, are responsible for paraffin cracking initiation, whereas bulk iron oxides on the zeolite surface are inactive. In comparison with Al-ZSM-5, Fe-ZSM-5 increases the olefinicity of the valuable C3-C4 fractions (selectivity to propene and butenes) and promotes aromatization reactions due to the lower relative strength of Fe-induced Brønsted acid sites and dehydrogenation properties. As shown by our 57Fe Mössbauer study (performed at −269 °C) of the catalyst in calcined, spent, and regenerated states, Fe-ZSM-5 deactivation is associated with the loss of tetrahedrally coordinated Fe3+ species. Therefore, tuning Fe-ZSM-5 C3-C4 selective FCC additives requires stabilizing framework Brønsted and framework-associated Lewis acid sites while decreasing the concentration of iron oxide species. Ultimately, these findings may enable us to meet the demand for propene derived from FCC cracking, which is expected to grow in the foreseeable future.

Defect Engineering in a Nanoporous Thulium-Organic Framework in Catalyzing Knoevenagel Condensation and Chemical CO2 Fixation.

Defect engineering is an extremely effective strategy for modifying metal-organic frameworks (MOFs), which can break through the application limitations of traditional MOFs and enhance their functionality. Herein, we report a highly robust nanoporous thulium(III)-organic framework, {[Tm2(BDCP)(H2O)5](NO3)·3DMF·2H2O}n (NUC-105), with [Tm(COO)2(H2O)]n chains and [Tm2(COO)4(H2O)8] dinuclears as metal nodes and 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (BDCP) linkers. In NUC-105, each of the four chains of [Tm(COO)2]n and the two rows of [Tm2(COO)4(H2O)8] units is unified by the organic skeleton, resulting in a rectangular nanochannel with dimensions of 15.35 Å × 11.29 Å, which leads to a void volume of 50%. It is worth mentioning that the [Tm2(COO)4(H2O)8] cluster is very rare in terms of its higher level of associated water molecules, implying that the activated host framework can serve as a strong Lewis acid. NUC-105a exhibited great heterogeneous catalytic performance for CO2 cycloaddition with epoxides under the reaction conditions (0.60 mol % NUC-105a, 5.0 mol % n-Bu4NBr, 65 °C, 5 h), ensuring exclusive selectivity and high conversion rates. In addition, NUC-105a's strong catalytic impact on the Knoevenagel condensation of aldehydes and malononitrile can be attributed to the collaboration between the drastically unsaturated Lewis acidic Tm3+ centers and Lewis basic pyridine groups.

Synthesis and Stabilization of Highly Reactive Haloacetylium Ions.

The reactions of selected haloacetyl fluorides with the strong Lewis acids AsF5 and SbF5 were investigated in the aprotic solvent SO2ClF. Depending on the stoichiometric ratio of AsF5 or SbF5 and the haloacetyl fluorides, either O-coordinated adducts or the respective haloacetylium ions were isolated as solids. The compounds were characterized by low-temperature vibrational spectroscopy and single-crystal X-ray diffraction. [CClH2CO][Sb2F11] and [CH2FCO][Sb2F11] crystallize in the monoclinic space group P21 with two formula units per unit cell. The reactivity of the haloacetyl fluorides under Lewis acidic conditions is discussed based on quantum chemical calculations of fluoride ion affinities on the BP/def2SVPP level of theory. The haloacetylium ions are stabilized in the solid-state phase by intermolecular C···F contacts and electron donation of the fluorine ligands of the anions as well as intramolecular hyperconjugation.

Nickel‐Catalyzed Asymmetric Michael Addition of Acyl‐Imidazoles to Acrolein or β‐Ester Enones

AbstractAn enantioselective Michael addition of α‐substituted acyl‐imidazoles to acrolein catalyzed by a nickel‐bisoxazoline complex has been developed. The use of strong Lewis acid TMSOTf as an additive to activate the Michael acceptors proved to be vital to the success of this process. This process tolerates a wide range of acyl‐imidazoles, and a series of conjugate adducts are obtained in high yields and good enantioselectivities. Besides acrolein, β‐ester ennones are also applicable in this process affording the corresponding conjugate adducts in high yields with good diastereoselectivities and enantioselectivites in most cases. The potential utility of the reaction system is confirmed through 2 mmol‐scale reaction and derivatization experiments.

Direct mechanochemical synthesis of nano-LiAlH4 promoted by 0.696 wt% TiCl4 catalyst surface-modified Al powder

LiAlH4, known for its high hydrogen capacity and metastable nature, is a promising hydrogen source under mild conditions. However, its reversible regeneration from stable binary dehydrogenation phases (LiH/Al) is thermodynamically and kinetically hindered. By constructing a homogeneous and highly dispersed molecular layer of TiCl4 on the surface of the Al reactant to enhance the kinetics of the multiphase interfacial reaction, we achieved the direct mechanochemical synthesis of nano-LiAlH4, bypassing the intermediate phase Li3AlH6. Using the strong Lewis acidity of Ti4+, TiCl4 was chemically adsorbed onto the surface of the Al powder through Ti-O-Al bonds, with a loading capacity of only 0.696 wt%. The obtained TiCl4 surface-modified Al powder and LiH were hydrogenated by ball milling for 10 h under hydrogen pressure to synthesize nano-LiAlH4, which was then dehydrogenated at room temperature. This indicates that the crucial effects of the catalytic sites were dispersed on the reactant surface to ensure the local environment of the multiphase absorption/desorption hydrogen reaction interface and promote the reaction kinetics.

Superactivity of Bimetallic CuFeO2 Submicron Particles towards Selective Proteolysis, Depending on their Surface Hydroxyls.

Nano bimetallic oxides as nanoproteases have the great advantages in the heterogeneous hydrolysis of proteins. Here, we report that bimetallic delafossite CuFeO2 submicron particles (CuFeO2 SMPs) display a high protease activity towards selective cleavage of peptide bond involving hydrophobic residue at 25 °C. CuFeO2 SMPs have excellent regeneration performance with high structural stability. The strong Lewis acidity of Fe3+ and the strong nucleophilicity of Cu+ bound hydroxyl groups are both necessary for the high protease activity of CuFeO2 SMPs. Low-valent metal ion has a great advantage in that low-valent Cu+ bound hydroxyl has strong nucleophilicity, resulting in promotion of protein hydrolysis via high-efficient bimetallic catalysis. This study provides evidence that the protease activity of CuFeO2 SMPs depends on metal ion-bound hydroxyls on their surface. Our findings highlight that the valence of metal ions in artificial protease and their surface hydroxyls are two important factors that determine their catalytic efficiency.

First Main‐Group Element Lewis Acid Thionyl Chloride Adduct and its Chemistry

AbstractAlthough the adduct of aluminum trichloride with thionyl chloride has been reported, no thionyl chloride adduct of a main group element Lewis acid or organometallic compound has been structurally characterized. In this communication we present the synthesis and reactivity of the structurally ascertained adduct of thionyl chloride with tris(pentafluoroethyl)gallane as a representative of a main group element Lewis acid. Gallium and indium compounds with electron withdrawing groups, e.g. the pentafluoroethyl ligand, display versatile properties. While gallates and indates, [MR4]−, behave as weakly coordinating anions, neutral gallanes and indanes, MR3, are strong Lewis acids. Salts with the tetrakis(pentafluoroethyl)gallate and ‐indate, [M(C2F5)4]− (M=Ga, In), have recently been studied in detail. In contrast to this, work on the syntheses of the free Lewis superacids M(C2F5)3 (M=Ga, In) is scarce and underdeveloped. The hydrates [M(C2F5)3(OH2)2] proved to be suitable starting materials, particularly due to their thermal stability. Herein we report on synthesis and characterization of reactive adducts, [M(C2F5)3D], with the weak donor molecules (D) SOCl2 and Me3SiF. The effective Lewis acidities of Ga(C2F5)3 and In(C2F5)3 were experimentally determined by the (modified) Gutmann‐Beckett method and their catalytic potential is showcased.

Lignin-MOF hybrid polymetallic composites for selective hydrogenolysis of cellulose derived 5-hydroxymethylfurfural

The development of green, effective and inexpensive catalysts was important for the catalytic transfer hydrogenation of 5-hydroxymethylfurfural (HMF) to prepare 5-methylfurfuryl alcohol (MFA). The assembly of sodium lignosulfonate (LS) with NiCo-MOFs through a simple hydrothermal method was reported, and a series of iron-containing polymetallic hybrid catalysts were investigated. The introduction of iron led to the increase of medium strong acid sites and Lewis acid sites in the catalyst and enhanced the adsorption of furan rings, thus improved the catalytic activity. The effects of calcination temperature, iron content, and reaction parameters (including reaction temperature, pressure, hydrogen donor solvent) were all studied in detail. It was found that HMF could be completely converted over Fe@Ni3Co-MOF-LS, with a MFA yield of 88.75 % under the optimal condition (240 ℃, 2 MPa N2 in 4 h) without the presence of hydrogen. This study provided a new perspective for the utilization of lignin resource as carbon-based catalysts for the production of biomass-derived platform chemicals.

Borane-Catalyzed Enantioselective α-Alkylation of Unactivated 2-Alkylbenzoxazoles with Electron-Deficient Olefins.

Chiral borane-catalyzed reactions have recently emerged as a powerful tool for the enantioselective production of chiral scaffolds. In this study, we demonstrated for the first time that a chiral bisborane catalyst can be used for the α-functionalization of 2-alkylazaarenes; specifically, we accomplished unprecedented highly enantioselective α-alkylation of unactivated 2-alkylbenzoxazoles with electron-deficient olefins. The strong Lewis acidity and the steric bulk of the bisborane catalyst were essential to the observed reactivity and selectivity.

Defect-engineered indium-organic framework displays the higher CO2 adsorption and more excellent catalytic performance on the cycloaddition of CO2 with epoxides under mild conditions.

In order to achieve the high adsorption and catalytic performance of CO2, the direct self-assembly of robust defect-engineered MOFs is a scarcely reported and challenging proposition. Herein, a highly robust nanoporous indium(III)-organic framework of {[In2(CPPDA)(H2O)3](NO3)·2DMF·3H2O}n (NUC-107) consisting of two kinds of inorganic units of chain-shaped [In(COO)2(H2O)]n and watery binuclear [In2(COO)4(H2O)8] was generated by regulating the growth environment. It is worth mentioning that [In2(COO)4(H2O)8] is very rare in terms of its richer associated water molecules, implying that defect-enriched metal ions in the activated host framework can serve as strong Lewis acid. Compared to reported skeleton of [In4(CPPDA)2(μ3-OH)2(DMF)(H2O)2]n (NUC-66) with tetranuclear clusters of [In4(μ3-OH)2(COO)10(DMF)(H2O)2] as nodes, the void volume of NUC-107 (50.7%) is slightly lower than the one of NUC-66 (52.8%). However, each In3+ ion in NUC-107 has an average of 1.5 coordinated small molecules (H2O), which far exceeds the average of 0.75 in NUC-66 (H2O and DMF). After thermal activation, NUC-107a characterizes the merits of unsaturated In3+ sites, free pyridine moieties, solvent-free nanochannels (10.2 × 15.7 Å2). Adsorption tests prove that the host framework of NUC-107a has a higher CO2 adsorption (113.2 cm3/g at 273K and 64.8 cm3/g at 298K) than NUC-66 (91.2 cm3/g at 273K and 53.0 cm3/g at 298K). Catalytic experiments confirmed that activated NUC-107a with the aid of n-Bu4NBr was capable of efficiently catalyzing the cycloaddition of CO2 with epoxides into corresponding cyclic carbonates under the mild conditions. Under the similar conditions of 0.10mol% MOFs, 0.5mol% n-Bu4NBr, 0.5 MP CO2, 60°C and 3h, compared with NUC-66a, the conversion of SO to SC catalyzed by NUC-107a increased by 21%. Hence, this work offers a valuable perspective that the in situ creation of robust defect-engineered MOFs can be realized by regulating the growth environment.

Hydrogenation of inert aromatic compounds under mild conditions catalyzed by confined trimetal sites in porous metal silicate materials

Complete hydrogenation of aromatic compounds is an important subject in various industry fields. However, due to the high stabilization energy of aromatic compounds resulting from their high aromaticity and non-polarity, the hydrogenation reaction is usually performed under harsh reaction conditions in the presence of noble metal-based catalysts. We report herein a porous metal silicate (PMS) material PMS-58, which consists of Cu, Ce and Co trimetal active sites, demonstrating high catalytic activity and selectivity in hydrogenating of a series of aromatic compounds under mild conditions (60 °C and 0.5 MPa H2). PMS-58 is superior to the previously reported non-noble metal-based catalysts and could be favorably compared to noble metal-based catalysts. The unique catalytic properties of PMS-58 are derived from the synergistic work of trimetal sites with Ce species serving as strong Lewis acid sites for dissociation of dihydrogen, Co species stabilizing Cu(I) species, and Cu(I) species playing a crucial role in activating aromatic rings. Therefore, this work provides a new approach in developing highly efficient non-noble metal catalysts for complete hydrogenation of arenes under mild conditions, which could be applied in removal of aromatic compounds in petroleum products.

The Ether‐Adduct of a Lewis Superacidic, Dicoordinate Aluminum Hydride Cation and the Ion Affinities of Solvent‐Adducts

AbstractAluminum reagents are widely used as strong Lewis acids for organic transformations and catalysis. In recent years, a variety of Al‐Lewis superacids could be accessed by preparation of aluminum cations paired with weakly‐coordinating anions or by use of perfluorinated substituents at the metal. While the majority of these Al‐Lewis superacids is composed of a tricoordinate Al‐metal atom, examples for dicoordinate Al species are very scarce. In this study, we report the preparation of [(Mes*)Al(H)(OEt2)]+[Al(ORF)4]− (Mes*=2,4,6‐tBu3‐C6H2, RF=C(CF3)3) by reaction of protonated ether [H(OEt2)2]+[Al(ORF)4]− with [Mes*AlH2]2. Structural analysis supported by computed frontier orbitals and atomic charges reveals that the cation is best described as diethylether adduct of dicoordinate [(Mes*)Al(H)]+ and acts as synthon to this low‐coordinate cation. To incorporate the masking of the coordination site by the ether, the enthalpy of dissociation is included in the computed fluoride‐ and hydride ion affinities (XIA) and entropic effects are treated by defining a “free ion affinity” (fXIA), basing on the Gibbs energy change. Hereby, the Lewis acidity of free Lewis acids as well as their solvent adducts can be estimated.

From Coordination to Noncoordination: Syntheses and Substitution Lability Studies of Titanium Triflato Complexes.

A new concept for obtaining cationic complexes with triflate counteranions from coordinating triflato ligands was developed. Various routes are leading to titanium(IV) and titanium(III) triflato complexes efficiently. The reactions of pentafulvene titanium complexes with either triflic acid or silver triflate give the corresponding titanium(IV) triflato complexes in excellent yields. Hydrolysis of the titanium(IV) bistriflato complexes leads to cationic aqua complexes via displacement of the triflato ligand, which consequently acts as a noncoordinating anion. A functionalized titanium(IV) monotriflato complex was synthesized by insertion of a nitrile into the Ti-C bond and the triflato ligand was displaced by an NHC. While the titanium(IV) complexes are mostly inert toward substrates, the donor-free titanium(III) triflato complex is a strong Lewis acid and forms various adducts with monodentate Lewis bases. The titanium(III) complex was oxidized by reaction with TEMPO, resulting in a diamagnetic titanium(IV) complex. The reaction with bidentate ligands results in cationic titanium(III) complexes due to displacement of the triflato ligand by the bidentate ligands. Treatment with acetone leads to an aldol reaction of two acetone molecules and the formation of a cationic diacetone alcohol complex.