2,6-Diisopropylphenylamides of Potassium and Calcium: A Primary Amido Ligand in s-Block Metal Chemistry with an Unprecedented Catalytic Reactivity

Abstract

Transamination of KN(SiMe3)2 with 2,6-diisopropylphenylamine (2,6-diisopropylaniline) in toluene at ambient temperature yields [K{N(H)Dipp}·KN(SiMe3)2] (1) regardless of the applied stoichiometry. Recrystallization of 1 in the presence of tetramethylethylenediamine (TMEDA) and tetrahydrofuran (THF) leads to the formation of [(μ-thf)K2{N(H)Dipp}2]∞ (2), whereas potassium bis(trimethylsilyl)amide remains in solution. Addition of pentamethyldiethylenetriamine (PMDETA) gives [(pmdeta)K{N(H)Dipp}]2 (3). In contrast to the thf and pmdeta adducts, which lead to dissociation of 1 into homoleptic species, addition of bidentate dimethoxyethane maintains the mixed complex [(dme)K{μ-N(SiMe3)2}{μ-N(H)Dipp}K]2 (4). A complete transamination of 2,6-diisopropylaniline with KN(SiMe3)2 in toluene at 100 °C yields [K{N(H)Dipp}] (5), which reacts with CaI2 to give [(thf)nCa{N(H)Dipp}2] (6), [(pmdeta)Ca{N(H)Dipp}2] (7), and [(dme)2Ca{N(H)Dipp}2] (8), depending on the solvents and coligands. Excess potassium 2,6-diisopropylphenylamide allows the formation of the calciate [K2Ca{N(H)Dipp}4]∞ (9). Hydroamination of diphenylbutadiyne with 2,6-diisopropylaniline in the presence of catalytic amounts of 9 gives tetracyclic 2,6-diisopropyl-9,11,14,15-tetraphenyl-8-azatetracyclo[8.5.0.01,7.02,13]pentadeca-3,5,7,9,11,14-hexaene (10). Solid-state structures are reported for 2–4 and 7–10. Compound 10 slowly rearranges to tetracyclic 5a,9-diisopropyl-2,3,10,11-tetraphenyl-5a,6-dihydro-2a1,6-ethenocyclohepta[cd]isoindole (11), which is slightly favored according to quantum chemical studies.