Alexandra A. Skatova

Addition of Alkynes to a Gallium Bis‐Amido Complex: Imitation of Transition‐Metal‐Based Catalytic Systems

Acetylene, phenylacetylene, and alkylbutynoates add reversibly to (dpp-bian)Ga-Ga(dpp-bian) (dpp-bian=1,2-bis[(2,6-diisopropylphenyl)-imino]acenaphthene) to give addition products [dpp-bian(R(1)C=CR(2))]Ga-Ga[(R(2)C=CR(1))dpp-bian]. The alkyne adds across the Ga-N-C section, which results in new carbon-carbon and carbon-gallium bonds. The adducts were characterized by electron absorption, IR, and (1)H NMR spectroscopy and their molecular structures have been determined by single-crystal X-ray analysis. According to the X-ray data, a change in the coordination number of gallium from three [in (dpp-bian)Ga-Ga(dpp-bian)] to four (in the adducts) results in elongation of the metal-metal bond by approximately 0.13 Å. The adducts undergo a facile alkynes elimination at elevated temperatures. The equilibrium between [dpp-bian(PhC=CH)]Ga-Ga[(HC=CPh)dpp-bian] and [(dpp-bian)Ga-Ga(dpp-bian) + 2 PhC≡CH] in toluene solution was studied by (1)H NMR spectroscopy. The equilibrium constants at various temperatures (298≤T≤323 K) were determined, from which the thermodynamic parameters for the phenylacetylene elimination were calculated (ΔG°=2.4 kJ mol(-1), ΔH°=46.0 kJ mol(-1), ΔS°=146.0 J K(-1) mol(-1)). The reactivity of (dpp-bian)Ga-Ga(dpp-bian) towards alkynes permits use as a catalyst for carbon-nitrogen and carbon-carbon bond-forming reactions. The bisgallium complex was found to be a highly effective catalyst for the hydroamination of phenylacetylene with anilines. For instance, with [(dpp-bian)Ga-Ga(dpp-bian)] (2 mol%) in benzene more than 99% conversion of PhNH(2) and PhC≡CH into PhN=C(Ph)CH(3) was achieved in 16 h at 90 °C. Under similar conditions, the reaction of 1-aminoanthracene with PhC≡CH catalyzed by (dpp-bian)Ga-Ga(dpp-bian) formed a carbon-carbon bond to afford 1-amino-2-(1-phenylvinyl)anthracene in 99% yield.

Digallane with Redox-Active Diimine Ligand: Dualism of Electron-Transfer Reactions

The reactivity of digallane (dpp-Bian)Ga-Ga(dpp-Bian) (1), which consists of redox-active ligand 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-Bian), has been studied. The reaction of 1 with I2 proceeds via one-electron oxidation of each of two dpp-Bian ligands to a radical-anionic state and affords complex (dpp-Bian)IGa-GaI(dpp-Bian) (2). Dissolution of complex 2 in pyridine (Py) gives monomeric compound (dpp-Bian)GaI(Py) (3) as a result of a solvent-induced intramolecular electron transfer from the metal-metal bond to the dpp-Bian ligands. Treatment of compound 3 with B(C6F5)3 leads to removal of pyridine and restores compound 2. The reaction of compound 1 with 3,6-di-tert-butyl-ortho-benzoquinone (3,6-Q) proceeds with oxidation of all the redox-active centers in 1 (the Ga-Ga bond and two dpp-Bian dianions) and results in mononuclear catecholate (dpp-Bian)Ga(Cat) (4) (Cat = [3,6-Q](2-)). Treatment of 4 with AgBF4 gives a mixture of [(dpp-Bian)2Ag][BF4] (5) and (dpp-Bian)GaF(Cat) (6), which both consist of neutral dpp-Bian ligands. The reduction of benzylideneacetone (BA) with 1 generates the BA radical-anions, which dimerize, affording (dpp-Bian)Ga-(BA-BA)-Ga(dpp-Bian) (7). In this case the Ga-Ga bond remains unchanged. Within 10 min at 95 °C in solution compound 7 undergoes transformation to paramagnetic complex (dpp-Bian)Ga(BA-BA) (8) and metal-free compound C36H40N2 (9). The latter is a product of intramolecular addition of the C-H bond of one of the iPr groups to the C═N bond in dpp-Bian. Diamagnetic compounds 3, 5, 6, and 9 have been characterized by NMR spectroscopy, and paramagnetic complexes 2, 4, 7, and 8 by ESR spectroscopy. Molecular structures of 2-7 and 9 have been established by single-crystal X-ray analysis.

New high-spin iron complexes based on bis(imino)acenaphthenes (BIAN): synthesis, structure, and magnetic properties

The reactions of iron diiodide with one and two equivalents of the monopotassium salt of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-BIAN) in diethyl ether gave the complexes [(dpp-BIAN)FeI]2 (1) and (dpp-BIAN)2Fe (2), respectively. The bis-ligand complex (tms-BIAN)2Fe (3) was synthesized by the exchange reaction of the monosodium salt of 1,2-bis(trimethylsilylimino)acenaphthene (tms-BIAN) with iron diiodide. The reaction of FeI2 with tms-BIAN affords the chelate complex (tms-BIAN)FeI2 (4), whereas the reaction of FeBr2·2H2O with tms-BIAN is accompanied by elimination of trimethylsilyl groups to form the tris-ligand acenaphthene-1,2-diimine complex [(H2BIAN)3Fe][FeBr3·THF]2 (5) containing two types of iron ions. Compounds 1–5 were characterized by IR spectroscopy and elemental analysis. The molecular structures of 1–5 were determined by single-crystal X-ray diffraction. For high-spin complexes 1–3, the temperature-dependent magnetic susceptibilities were measured in the range of 4–300 K.

Redox‐Active Ligand‐Assisted Two‐Electron Oxidative Addition to Gallium(II)

The reaction of digallane (dpp-bian)Ga-Ga(dpp-bian) (2) (dpp-bian=1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) with allyl chloride (AllCl) proceeded by a two-electron oxidative addition to afford paramagnetic complexes (dpp-bian)Ga(η1 -All)Cl (3) and (dpp-bian)(Cl)Ga-Ga(Cl)(dpp-bian) (4). Treatment of complex 4 with pyridine induced an intramolecular redox process, which resulted in the diamagnetic complex (dpp-bian)Ga(Py)Cl (5). In reaction with allyl bromide, complex 2 gave metal- and ligand-centered addition products (dpp-bian)Ga(η1 -All)Br (6) and (dpp-bian-All)(Br)Ga-Ga(Br)(dpp-bian-All) (7). The reaction of digallane 2 with Ph3 SnNCO afforded (dpp-bian)Ga(SnPh3 )2 (8) and (dpp-bian)(NCO)Ga-Ga(NCO)(dpp-bian) (9). Treatment of GaCl3 with (dpp-bian)Na in diethyl ether resulted in the formation of (dpp-bian)GaCl2 (10). Diorganylgallium derivatives (dpp-bian)GaR2 (R=Ph, 11; tBu, 14; Me, 15; Bn, 16) and (dpp-bian)Ga(η1 -All)R (R=nBu, 12; Cp, 13) were synthesized from complexes 3, 10, Bn2 GaCl, or tBu2 GaCl by salt metathesis. The salt elimination reaction between (dpp-bian)GaI2 (17) and tBuLi was accompanied by reduction of both the metal and the dpp-bian ligand, which resulted in digallane 2 as the final product. Similarly, the reaction of complex 10 with MentMgCl (Ment=menthyl) proceeded with reduction of the dpp-bian ligand to give the diamagnetic complex [(dpp-bian)GaCl2 ][Mg2 Cl3 (THF)6 ] (18). Compounds 11, 12, 13, 15, and 16 were thermally robust, whereas compound 14 decomposed when heated at reflux in toluene to give complex (dpp-bian-tBu)GatBu2 (19). Both complexes 7 and 19 contain R-substituted dpp-bian ligand: in the former compound the allyl group was attached to the imino-carbon atom, whereas in complex 19, the tBu group was situated on the naphthalene ring. Crystal structures of complexes 3, 8, 9, 10, 13, 14, 18, and 19 were determined by single-crystal X-ray analysis. The presence of dpp-bian radical anions in 3, 6, 8, and 10-16 was determined by ESR spectroscopy.

Synthesis and structure of bischelate gallium complexes (dpp-bian)Ga(acac) and (dpp-bian)Ga(2,2´-bipy) (dpp-bian is 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene)

A reaction of digallane [(dpp-bian)Ga—Ga(dpp-bian)] (1) (dpp-bian is the 1,2-bis[(2,6-disopropylphenyl)imino]acenaphthene) with one equivalent of I2 leads to oxidation of (dpp-bian)2– in compound 1 to (dpp-bian)–and gives [(dpp-bian)GaI—GaI(dpp-bian)] (2). In the reaction of compound 2 with two equivalents of (acac)Na, not only exchange of the iodide and acetylacetonate ions takes place, but also a transfer of electrons from the metal—metal bond to dpp-bian with the formation of the complex [(dpp-bian)Ga(acac)] (3), in which the dpp-bian ligand is a dianion. A reaction of digallane 1 with 2,2´-bipyridyl at 200 °C in toluene in a sealed tube leads to the reduction of 2,2´-bipyridyl and gives the complex [(dpp-bian)Ga(bipy)] (4), which contains two different chelate redox-active ligands. The new compounds were characterized by IR (3, 4), NMR (3), and ESR spectra (4), the structures of both derivatives were established by X-ray diffraction.

Europium complexes with 1,2-bis(arylimino)acenaphthenes: a search for redox isomers

Reduction of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-bian, 1) with metallic europium in 1,2-dimethoxyethane (dme) under anaerobic conditions gave a europium(II) complex with the acenaphthene-1,2-diimine dianion, (dpp-bian)Eu(dme)2 (4), in high yield. Oxidation of complex 4 with triphenyltin chloride or 1,2-dibromostilbene afforded the corresponding halogen derivatives [(dpp-bian)Eu(µ-Cl)(dme)]2 (5) and [(dpp-bian)Eu(µ-Br)(dme)]2 (6). The molecular structures of complexes 4–6 were determined by X-ray diffraction. The magnetic moments of complexes 5 and 6 remain constant over a temperature range from 25 to 295 K; they are indicative of the presence of the europium(II) ion and the dpp-bian radical anion in both the complexes.

Hydroamination of alkynes with aromatic amines catalyzed by digallane (dpp-bian)Ga—Ga(dpp-bian)

Digallane (dpp-bian)Ga—Ga(dpp-bian) (1) (dpp-bian is the 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) catalyzes the addition of 4-chloroaniline to some terminal alkynes RC≡CH (R = Bun, Ph, 4-MeC6H4). The reaction orders in each of the substrates were found for the reaction of phenylacetylene with 4-chloroaniline catalyzed by compound 1. The reaction of compound 1 with phenylacetylene in a molar ratio of 1: 10 led to 1-[N-(2,6-diisopropylphenyl)imino]-2-(1-phenylethylidene)acenaphthene (5) and the compound [C12H6(NC6H3Pr2i)(PhC=CH2)(PhC=CH)]Ga(C≡CPh)2 (6). The reaction of digallane 1 with phenylacetylene and aniline in a stoichiometric ratio of 1: 2: 2 gave bis-anilide (dpp-bian)-Ga[N(H)Ph]2 (7) in 40% yield. The compound (PhC≡C)3Ga·THF (9) was obtained by the reaction of three equivalents of sodium phenylacetylide (prepared in situ from phenylacetylene and sodium) with one equivalent of GaCl3 in tetrahydrofuran. Compounds 5—7 and 9 were characterized by IR spectroscopy, 1H NMR spectroscopy was used to characterize products 5, 6, and 9, whereas EPR spectroscopy was used for amide 7. The structures of compounds 5—7 and 9 were determined by single crystal X-ray diffraction analysis.

Formation of carbon-carbon bonds between activated alkynes and diimine ligands in the aluminum complexes

The gallium and aluminum complexes containing the redox-active ligand (dpp-bian)Ga-Ga(dpp-bian) (1), (dpp-bian)Al-Al(dpp-bian) (2), or (dpp-bian)AlI(Et2O) (3) (dpp-bian is 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) react with alkyl butynoates Me-C≡C-CO2R (R = Me, Et) to form C-C bonds between the dpp-bian ligand and alkyne. The reaction of complex 1 with methyl 2-butynoate and 4-chloroaniline in a molar ratio of 1: 2: 2 affords 7-(2,6-diisopropylphenyl)-10-methylacenaphtho[1,2-b]pyridin-8(7H)-one (4) containing no gallium. In the reaction of complex 2 with methyl 2-butynoate, alkyne is inserted into the skeleton of the dpp-bian ligand to form 4-(dpp-AIE)-9-(2,6-diisopropylphenyl)-8-(1,3-dpp-2MBIDP)-3,7-dimethoxy-1,5-dialuma-9-aza-2,6-dioxabicyclo[3.3.1]nonadiene-3,7 (5) (dpp-AIE is 1-[2-(2,6-diisopropylphenylimino)acenaphthen-1(2H)-ylidene]ethyl; 1,3-dpp-2MBIDP is 1,3-bis(2,6-diisopropylphenylimino)-2-methyl-2,3-dihydro-1H-phenalen-2-yl). The reactions of complex 3 with methyl and ethyl 2-butynoates afford dimeric derivatives [-OC(OR)=C(2,3-dpp-1MBIDP)Al(I)-]2 (2,3-dpp-1MBIDP is 2,3-bis(2,6-diisopropylphenylimino)-1-methyl-2,3-dihydro-1H-phenalen-2-yl; R = Me (6), Et (7)). The reaction of complex 3 with methyl 2-butynoate gives the product isomeric to compound 6: [-OC(OCH3)=C(1,3-dpp-2MBIDP)Al(I)-]2 (8), which cleaves THF resulting in complex [-OC(OCH3)=C(1,3-dpp-2MBIDP)Al(OC4H8I)-]2 (9). Complex (dpp-bian)Al(acac) (10), obtained by the reduction of dpp-bian with aluminum in the presence of Al(acac)3 in diethyl ether at ambient temperature, is inert towards acetylene, phenylacetylene, and alkyl butynoates. Compounds 4–7 and 10 were characterized using IR spectroscopy, and compounds 4, 7, and 10 were additionally characterized by 1H NMR spectroscopy. The structures of compounds 4–7, 9, and 10 were determined by X-ray diffraction analysis.

Cycloaddition versus Cleavage of the C=S Bond of Isothiocyanates Promoted by Digallane Compounds with Noninnocent α-Diimine Ligands

Whereas the chemistry of single-bond activation by compounds of the main group elements has undergone some development in recent years, the cleavage of multiple bonds remains underexplored. Herein, the reactions of two digallanes bearing α-diimine ligands, namely, [L1 Ga-GaL1 ] (1, L1 =dpp-dad=[(2,6-iPr2 C6 H3 )NC(CH3 )]2 ) and [L2 Ga-GaL2 ] (2, L2 =dpp-bian=1,2-[(2,6-iPr2 C6 H3 )NC]2 C10 H6 ), with isothiocyanates are reported. Reactions of 1 or 2 with isothiocyanates in 1:2 molar ratio proceeded with [2+4] cycloaddition of the C=S bond across the C2 N2 Ga metallacycle with formation of C-C and S-Ga single bonds to afford [L1 (RN=C-S)Ga-Ga(S-C=NR)L1 ] (3, R=Me; 4, R=Ph) and [L2 (RN=C-S)Ga-Ga(S-C=NR)L2 ] (8, R=allyl; 9, R=Ph). In the cases of 8 and 9, this cycloaddition is reversible. The digallanes reacted with 2 equiv of PhNCS in the presence of Na metal or at high temperatures through a unique reductive cleavage of the C=S bond to yield the disulfide-bridged digallium species [Na(THF)3 ]2 [L1 Ga(μ-S)2 GaL1 ] (5), [L2 Ga(μ-S)2 GaL2 ] (10), and [Na(DME)3 ][L2 Ga(μ-S)2 GaL2 ] (11). Moreover, products 4 and 5 can further react with an excess of isothiocyanate, through cleavage of the C=S bond or cycloaddition, to give the bis- or mono-S-bridged complexes [Na(THF)2 ]2 [L1 (PhN=C-S)Ga(μ-S)2 Ga(S-C=NPh)L1 ] (6) and [L1 (PhN=C-S)Ga(μ-S)Ga(S-C=NPh)L1 ] (7). All the newly prepared compounds were characterized by elemental analysis, single-crystal X-ray diffraction, IR spectroscopy, NMR (3-9) or ESR spectroscopy (11), and DFT calculations.

Syntheses and structures of magnesium, calcium, europium, gallium, and zinc complexes with bis(imino)acenaphthene ligands*

The reduction of 1,2-bis(trimethylsilylimino)acenaphthene and 1,2-bis{[3,5-bis(trifluoromethylphenyl)]imino}acenaphthene with metals gave magnesium, calcium, europium, zinc, and gallium complexes containing radical-anion and dianionic ligands of the 1,2-diiminoacenaphthene type. Their structures were studied by 1H NMR, ESR, and/or single-crystal X-ray analysis. Some chemical transformations of the complexes were carried out.