Hydro-coupling of isocyanates promoted by 1,2-bis(arylimino)acenaphthene aluminum hydrides.

The interaction of aluminum hydrides [(dpp-bian)AlH2] (1) and [(ArBIG-bian)AlH2(THF)] (2) (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene; ArBIG-bian = 1,2-bis[(2,6-dibenzhydryl-4-methylphenyl)imino]acenaphthene) with isocyanates RNCO (R = Ph, Cy, 3,5-Cl2Ph) proceeds via insertion of two molecules of isocyanates into each Al-H bond with the formation of unique Al carboxamides [(Ar-bian)Al{OC(H)N(R)C(NR)O}2] (Ar = dpp, R = Ph, 3; Ar = ArBIG, R = Ph, 4; Ar = ArBIG, R = Cy, 5; Ar = ArBIG, R = 3,5-Cl2C6H3, 6). In contrast, the reactions of 1 and 2 with an excess of tert-butylisocyanate afford formimidate derivatives [(Ar-bian)Al{OC(H)N(tBu)}2] (Ar = dpp, 7; Ar = ArBIG, 8). The reactions of N,N'-dicyclohexylcarbodiimide with 1 and 2 give [(dpp-bian)Al{(NCy)2CH}2] (9) and [(ArBIG-bian)Al(H){(NCy)2CH}] (10), correspondingly. New compounds 3-10 have been characterized by ESR spectroscopy; their molecular structures have been established by single-crystal X-ray analysis.

Diversity of transformation of heteroallenes on acenaphthene-1,2-diimine aluminum oxide.

The reactions of oxide [(dpp-bian)Al(µ2-O)2Al(dpp-bian)] (1) (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) with phenyl- or cyclohexylisocyanates result in the formation of carbonimidate derivatives [(dpp-bian)Al(µ-O)(µ-RNCO2)Al(dpp-bian)] (R = Ph, 2; Cy, 3). Addition of N,N'-dicyclohexylcarbodiimide to compound 1 leads to the formation of ureate complex [(dpp-bian)Al(µ-O)(µ-(CyN)2CO)Al(dpp-bian)] (4). The reactions of the oxide 1 with pinacolborane and catecholborane afford oxo-bridged hydride [{(dpp-bian)Al(H)}(µ-O){Al(OBpin)(dpp-bian)}] (5) and compound [{(dpp-bian)Al(OBCat)}2(µ-O)] (7), respectively. Insertion of cyclohexylisocyanate into the Al-H bond of compound 5 gives CO insertion product [{(dpp-bian)Al(OC(H)NCy)}(µ-O){Al(OBpin)(dpp-bian)}] (6). New compounds have been characterized by ESR and IR spectroscopy; their molecular structures have been established by single-crystal X-ray analysis. The oxide 1 serves as a catalyst for the hydroboration of heteroallenes (isocyanates, carbodiimides) with pinacolborane.

Reduction of CO2 with Aluminum Hydrides Supported with Ar-BIAN Radical-Anions (Ar-BIAN = 1,2-Bis(arylimino)acenaphthene).

The reactions of H2AlCl with [(dpp-Bian)Na(Et2O)n] and [(ArBIG-Bian)Na(THF)] produce respective aluminum hydrides supported by radical-anionic 1,2-bis(arylimino)acenaphthene ligands, [(dpp-Bian)AlH2] (1) and [(ArBIG-Bian)AlH2(THF)] (2) (dpp-Bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene); ArBIG-Bian = 1,2-bis[(2,6-dibenzhydryl-4-methylphenyl)imino]acenaphthene). The reaction of 1 with CO2 proceeds with reduction of both C═O bonds and results in diolate [{(dpp-Bian)Al(µ-O2CH2)}2] (3). Complex 2 reacts with CO2 to carbonate [{(ArBIG-Bian)Al(µ-OCH2OCO2)}2] (4) that is a result of the insertion of CO2 into the Al-O bond in diolate species formed initially. Aluminum monohydrides [(dpp-Bian)AlH(X)] (X = Cl, 5; Me, 6) react with CO2 to form respective alumoxanes [{(dpp-Bian)AlX}2(µ-O)] (X = Cl, 7 and X = Me, 8). Compounds 1-4, 7, and 8 have been characterized by ESR and IR spectroscopy, and their molecular structures have been determined by single-crystal X-ray analysis.

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.

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.