Reactivity of Transition Metal Gallylene Complexes Toward Substrates with Multiple Carbon-Element Bonds.

Reactivity of transition metal complexes containing the redox-active gallylene (dpp-bian)Ga ligand (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) toward isocyanide, isocyanate, isothiocyanate, and ketene substrates is described. The reaction of [(dpp-bian)GaCr(CO)5] (1) with tBuNC results in a dative complex [(dpp-bian)Ga(CNtBu)Cr(CO)5] (2), while compound [(dpp-bian)GaCr(CO)5]2[Na(THF)2]2 (3) reacts with tBuNC to give the coordination polymer [(dpp-bian)GaCr(CO)5][Na(CNtBu)(THF)]n (5). Treatment of [(dpp-bian)GaCr(CO)5]2[Na(THF)2]2 with an excess of PhNCO results in trimerization of the latter and formation of complex [(dpp-bian)GaCr(CO)5][Na(PhNCO)3(Et2O) (DME)] (4). [(dpp-bian)GaFeCp(CO)2] (7) treated with Ph2CCO or PhNCS results in cycloaddition products [(dpp-bian)(Ph2CCO)GaFeCp(CO)2] (8) and [(dpp-bian)(PhNCS)GaFeCp(CO)2] (9). The formation of 2 and 9 was found to be reversible, which offers a means for facile regulation of transition metal center reactivity and cooperative substrate activation. New compounds were characterized by EPR (2), NMR (4, 8, and 9), and IR spectroscopy (2, 4, 5, 8, and 9). The molecular structures of 2, 4, 5, 8, and 9 were established by single-crystal X-ray diffraction analysis. Electronic structures of the compounds have been examined by DFT calculations.

Reactions of Iso(thio)cyanates with Dialanes: Cycloaddition, Reductive Coupling, or Cleavage of the C═S or C═O Bond.

The dialanes [(dpp-Bian)Al-Al(dpp-Bian)] (1) and [(dpp-dad)Al(THF)-(THF)Al(dpp-dad)] (2) (dpp-Bian = 1,2-[(2,6-iPr2C6H3)NC]2C12H6, dpp-dad = [(2,6-iPr2C6H3)NC(CH3)]2) react with some isothiocyanates, isocyanates, and diphenylketene via [2 + 4] cycloaddition of the C═O or C═S bond across the C═C-N-Al fragment to afford complexes [L(X═C-Y)Al-Al(X═C-Y)L] with an intact Al-Al single bond (3, L = dpp-Bian, X = PhN, Y = O; 4, L = dpp-Bian, X = Ph2C, Y = O; 6, L = dpp-dad, X = BnN, Y = S; 7, L = dpp-dad, X = tBuN, Y = O; 8, L = dpp-dad, X = iPrN, Y = S; and 9, L = dpp-dad, X = CyN, Y = S). A mixed C═N and C═O mode cycloadduct, [(dpp-Bian)(TosN═C-O)Al-Al(TosN-C═O)(dpp-Bian)] 5, was obtained in the reaction of 1 with tosylisocyanate. Heating the solution of 3 resulted in a thermal transformation and a change of the cycloaddition mode from C═O to C═N to give the product [(dpp-Bian)(PhN-C═O)Al(O)Al(PhN-C═O)(dpp-Bian)] 10. The reduction of 7 and 8 with Na yielded the products [Na(THF)n]2[(dpp-dad-H)(X═C-Y)Al]2 (12, X = iPrN, Y = S, n = 2 and 13, X = tBuN, Y = O, n = 3) in which one of the methyl groups of the backbone of the initial dpp-dad ligand was dehydrogenated. When 2 was reacted with the bulky adamantyl isocyanate AdNCO, the C-C coupling of two substrates occurred to form 14 [(dpp-dad)Al(O═C-NAd)2Al(dpp-dad)] in which the coupled dianionic oxamide ligand bridged two Al atoms in a µ,η4-N,O/N,O mode. Moreover, in the presence of 2.0 equiv of Na metal, precursor 2 reacts with tBuNCS, p-TolylNCS, or Me3SiNCO, possibly through the reduced AlI intermediate, to yield the sulfur- or oxygen-bridged dimer [Na(solv)n]2[(dpp-dad)Al(µ-E)]2 (15, E = S, solv = THF, n = 3 and 16, E = O, solv = DME, n = 2) upon C═S or C═O bond cleavage. Dialane 1 reacts with dimethylsulfone to give a Lewis adduct [(dpp-Bian)(Me2SO2)Al]2 (17), which releases dimethylsulfone upon heating. The diamagnetic compounds 3-10 and 12-17 were characterized by NMR and IR spectroscopy. The molecular structures of 3-17 were established by single-crystal X-ray diffraction analysis. Electronic structures of the compounds and possible isomers have been examined by DFT calculations.

Reversible Addition of Carbon Dioxide to Main Group Metal Complexes at Temperatures about 0 °C.

The reaction of dialane [LAl-AlL] (1; L=dianion of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene, dpp-bian) with carbon dioxide results in two different products depending on solvent. In toluene at temperatures of about 0 °C, the reaction gives cycloadduct [L(CO2 )Al-Al(O2 C)L] (2), whereas in diethyl ether, the reaction affords oxo-bridged carbamato derivative [L(CO2 )(Et2 O)Al(µ-O)AlL] (3). The DFT and QTAIM calculations provide reasonable explanations for the reversible formation of complex 2 in the course of two subsequent (2+4) cycloaddition reactions. Consecutive transition states with low activation barriers were revealed. Also, the DFT study demonstrated a crucial effect of diethyl ether coordination to aluminium on the reaction of dialane 1 with CO2 . The optimized structures of key intermediates were obtained for the reactions in the presence of Et2 O; calculated thermodynamic parameters unambiguously testify the irreversible formation of the product 3.

Low-coordinate Sm(II) and Yb(II) complexes derived from sterically-hindered 1,2-bis(imino)acenaphthene (ArBIG-bian).

Reduction of ArBIG-bian (1, 1,2-bis[(2,6-dibenzhydryl-4-methylphenyl)imino]acenaphthene) with an excess of samarium in tetrahydrofuran (thf) and crystallization of the crude product from a thf/toluene mixture affords [(ArBIG-bian)Sm]·C7H8 (2a), which is free of the coordinating solvent. The use of 1,2-dimethoxyethane (dme) as the reaction medium resulted in the same product, [(ArBIG-bian)Sm]·C4H10O2 (2b), which differs from 2a only in the crystal lattice solvent. Reduction of 1 with an excess of ytterbium in dme gives compound [(ArBIG-bian)Yb(dme)]·2.5C7H8 (3), containing a coordinated dme molecule. All three products consist of dianionic ArBIG-bian ligands whose bulky 2,6-(Ph2CH)2-4-Me-C6H2 groups shield effectively the metal atoms. The newly prepared compounds 2a, 2b and 3 were characterized by 1H NMR and IR spectroscopy. The molecular structures of complexes 2a, 2b and 3 have been established by single crystal X-ray analysis. The intramolecular interactions were analysed on the basis of DFT calculations. The temperature dependence of the magnetic susceptibility of 2b and 3 in the region of 2-300 K was studied. The magnetic moments of complex 2b correspond to divalent samarium.

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.

Gallium Hydrides with a Radical-Anionic Ligand.

The reaction of Cl2GaH with a sodium salt of the dpp-Bian radical-anion (dpp-Bian•-)Na (dpp-Bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) affords paramagnetic gallane (dpp-Bian•-)Ga(Cl)H (1). Oxidation of (dpp-Bian2-)Ga-Ga(dpp-Bian2-) (2) with N2O results in the dimeric oxide (dpp-Bian•-)Ga(µ2-O)2Ga(dpp-Bian•-) (3). A treatment of the oxide 3 with phenylsilane affords paramagnetic gallium hydrides (dpp-Bian•-)GaH2 (4) and (dpp-Bian•-)Ga{OSi(Ph)H2}H (5) depending on the reagent's stoichiometry. The reaction of digallane 2 with benzaldehyde produces pinacolate (dpp-Bian•-)Ga(O2C2H2Ph2) (6). In the presence of PhSiH3, the reaction between digallane 2 and benzaldehyde (2: PhSiH3: PhC(H)O = 1:4:4) affords compound 4. The newly prepared complexes 1, 3-6 consist of a spin-labeled diimine ligand-dpp-Bian radical-anion. The presence of the ligand-localized unpaired electron allows the use of the ESR spectroscopy for characterization of the gallium hydrides reported. The molecular structures of compounds 1, 3-6 have been determined by the single-crystal X-ray analysis.

Adaptive behavior of a redox-active gallium carbenoid in complexes with molybdenum.

A gallium(I) carbenoid derived from redox-active diimine 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-bian) in complexes with molybdenum may serve either as a neutral [(dpp-bian)Ga:] or an anionic [(dpp-bian)Ga:](-) two-electron donor depending on the electronic state of the transition metal.

Acenaphthene-1,2-diimine chromium complexes.

The reaction of (dpp-BIAN)Mg(THF)3 (1) with anhydrous CrCl3 in THF at 80 degrees C affords the mixed chromium-magnesium complex (dpp-BIAN)Cr(mu-Cl)3Mg(THF)3 (2). The treatment of 2 with 1,4-dioxane causes the elimination of MgCl2 and the formation of dimeric [(dpp-BIAN)Cr(mu-Cl)(THF)]2 (3). The reaction of (dpp-BIAN)Na2 with CrCl3 gives the chlorine-free compound [Na(THF)6][(dpp-BIAN)2Cr] (4). Paramagnetic complexes 2, 3 and 4 have been characterized by IR and electronic absorption spectroscopy. The magnetic susceptibilities of 2 and 4 have been determined in solution using Evans method. The molecular structures of 2-4 have been established by single crystal X-ray analysis.