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

Abstract

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.

Hydroboration of a Diolate Complex Obtained by Carbon Dioxide Capture with Acenaphthenediimine Aluminum Hydride

“…According to the single-crystal X-ray analysis, the N(1)–C(1) and N(2)–C(2) bond lengths for complexes 2 , 3 , and 4 lie in the range of 1.318(9)–1.3436(15) Å (Table S2), which is characteristic for radical-anionic bian ligands. , The aluminum atoms in complexes 2 and 4 are connected via μ 2 -oxo-bridge (O 2– ) with the Al–O bond lengths: Al(1)–O(1) 1.677(5) Å and Al(2)–O(1) 1.691(5) Å for 2 and Al(1)–O(1) 1.6720(10) Å for 4 . The Al–O–Al fragment is linear (177.7(3)° and 180° in 2 and 4 , respectively) as in other dialumoxanes . The coordination number of aluminum atoms in 2 and 4 is four, and the coordination environment is almost an ideal tetrahedron.…”

“…20,21,27 The B−O distances in complex 3) and 1.397(3) Å). 20 In the centrosymmetric dimer 3 (Figure 2), two aluminum atoms are bound by two catecholate ligands: the Al•••Al distance is 3.016(3) Å which excludes a direct metal−metal interaction. The distribution of bond lengths in the OCCO fragment of the catecholate ligand (Table S2) is indicative of the dianion form.…”

“…22 The product of the reaction of 1 with borane dimethyl sulfide (BH S2), which is characteristic for radical-anionic bian ligands. 20,24 The aluminum atoms in complexes 5) and 1.738(5) Å in compounds 2 and 4, respectively. In general, all bond lengths in the coordination sphere of the aluminum atoms in 2 and 4 (Table S2, see the ESI) are in a good agreement with the known four-coordination aluminum complexes.…”

“…In general, all bond lengths in the coordination sphere of the aluminum atoms in 2 and 4 (Table S2, see the ESI) are in a good agreement with the known four-coordination aluminum complexes. 20,21,27 The B−O distances in complex 3) and 1.397(3) Å). 20 In the centrosymmetric dimer 3 (Figure 2), two aluminum atoms are bound by two catecholate ligands: the Al•••Al distance is 3.016(3) Å which excludes a direct metal−metal interaction.…”

“…13−17 Previously, we have demonstrated the diverse reactivity of aluminum complexes of sterically hindered diimine ligands dpp-bian ( For instance, the reaction of dialane [(dpp-bian)Al−Al(dppbian)] with CO 2 results in two different products depending on solvent�a cycloadduct in toluene and an oxo-bridged carbamato derivative in diethyl ether. 18 Acenaphthene-1,2diimine aluminum dihydrides bind CO 2 to form formate, 19 gemdiolate, 20 and carbonate 20 derivatives. Recently, we have carried out the reduction of "captured" CO 2 by BH 3 •NHMe 2 and HBpin 21 (Scheme 1).…”