Facile Benzene Reduction by a Ca²⁺/Al^I Lewis Acid/Base Combination

Abstract

Attempted synthesis of the donor-acceptor complex (BDI)Ca ←Al (BDI) complex by reaction of (BDI)Ca in the form of its B(C F ) salt with (BDI)Al in benzene led to dearomatization of the solvent and formation of (BDI)Ca (C H )Al (BDI) (BDI=CH[C(CH )N-Dipp] , Dipp=2,6-diisopropylphenyl). The C H anion is strongly puckered and its boat form features four long (ca. 1.50 Å) and two short (ca. 1.34 Å) C-C bond distances. The flagpole positions of the C H anion chelate an Al cation giving a norbornadiene-like fragment with Al in the 7-position. The C=C double bonds of this alumina-norbornadiene strongly coordinate to the Ca metal ion. The complex is stable in solution up to 80 °C. Several mechanisms for its formation are discussed including a highly likely frustrated Lewis pair type mechanism in which benzene is activated by the Lewis acid (BDI)Ca followed by nucleophilic attack by the Lewis base (BDI)Al .

Cycloaddition of Dialkylalumanyl Anion toward Unsaturated Hydrocarbons in (1+2) and (1+4) Modes

“…Similarly, the monomeric form of oxygen‐stabilized Al anion F reacted with ethylene to form (1+2) cycloadduct I . On the other hand, B also reacted with a benzene complex of [NacNac‐Ca] + to give an alumanorbornadiene product J . The anionic bicyclic compound H rearranged to the (1+4) product K upon addition of [18]crown‐6 .…”

“…AlÀC2 .1118 (15) 2.1087 (15) 2.1125 (12) 2.1154 (15) 2.059(4) 2.055 (4) 2.060 (3) 2.073 (3) 2.025(3) 2.044(3) C-Al-C 75.10(6) 75.21(6) 81.5 (1) 77.2(1) 88.1 (1) Compd. 4G 1G 2G 3M…”

“…duct J. [15] The anionic bicyclic compound H rearranged to the (1 + 4) product K upon addition of [18]crown-6. [10a] Thus, compounds B and D are examples of Al I compound, which exhibit reactivity for two different modeso fc ycloaddition reaction.…”

“…Compounds 2 and 3 are the first examples of anionic aluminanorbornadiene derivatives. Twon ewly formed AlÀC(bridgehead) bonds of 2 and 3 [2:2 .1118 (15), 2.1087 (15) ; 3:2 .1125(12), 2.1154 (15) ]a re longer than those of the previously reported Al-incorporated bicyclic compounds( L, [20] J, [15] K [10a] ), reflecting the steric repulsion between four trimethylsilyl substituents and benzoannulated moiety in 2 and 3.A saresult, the C-Al-C angles in 2 and 3 [2:7 5.10(6)8; 3:7 5.21(6)8]a re slightly smaller than those of reference compounds. Similart endencies were found in the AlÀCb onds and C-Al-C angles of 4 and trans-5 in comparison with those of reference compounds (G1-G6, [14] H [10a] ).…”

Complexation and Versatile Reactivity of a Highly Lewis Acidic Cationic Mg Complex with Alkynes and Phosphines

“…The high Lewis acidity of these cations may be exploited in molecule activation and could have applications in the rapidly growing field of frustrated Lewis pair (FLP) chemistry . Indeed, a combination of Lewis acidic (BDI)Ca + and Lewis basic (BDI)Al I strikingly dearomatizes C 6 H 6 to formally afford a C 6 H 6 2− species ( IV ) …”