title: Unprecedented Reaction Pathway of Sterically Crowded Calcium Complexes: Sequential C-N Bond Cleavage Reactions Induced by C-H Bond Activations.
abstract: Five bis(quinolylmethyl)-(1H-indolylmethyl)amine (BQIA) compounds, that is, {(quinol-8-yl-CH2)2NCH2(3-Br-1H-indol-2-yl)} (L1H) and {[(8-R3-quinol-2-yl)CH2]2NCH(R2)[3-R1-1H-indol-2-yl]} (L2-5H) (L2H: R1=Br, R2=H, R3=H; L3H: R1=Br, R2=H, R3=iPr; L4H: R1=H, R2=CH3, R3=iPr; L5H: R1=H, R2=nBu, R3=iPr) were synthesized and used to prepare calcium complexes. The reactions of L1-5H with silylamido calcium precursors (Ca[N(SiMe2R)2]2(THF)2, R=Me or H) at room temperature gave heteroleptic products (L1, 2)CaN(SiMe3)2(1, 2), (L3, 4)CaN(SiHMe2)2(3 a, 4 a) and homoleptic complexes (L3, 5)2Ca (D3, D5). NMR and X-ray analyses proved that these calcium complexes were stabilized through Ca⋅⋅⋅C-Si, Ca⋅⋅⋅H-Si or Ca⋅⋅⋅H-C agostic interactions. Unexpectedly, calcium complexes ((L3-5)CaN(SiMe3)2) bearing more sterically encumbered ligands of the same type were extremely unstable and underwent C-N bond cleavage processes as a consequence of intramolecular C-H bond activation, leading to the exclusive formation of (E)-1,2-bis(8-isopropylquinol-2-yl)ethane.
authors.affiliation: Shanghai Key Laboratory of Functional Materials Chemistry and Laboratory of Organometallic Chemistry, School of Chemistry & Molecular Engineering, East China University of Science and Technology, P.O. Box 310, 130 Meilong Road, 200237, Shanghai, P.R. China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Shanghai Key Laboratory of Functional Materials Chemistry and Laboratory of Organometallic Chemistry, School of Chemistry & Molecular Engineering, East China University of Science and Technology, P.O. Box 310, 130 Meilong Road, 200237, Shanghai, P.R. China.
authors.forename: Haobing
authors.initials: H
authors.lastname: Wang
authors.affiliation: Shanghai Key Laboratory of Functional Materials Chemistry and Laboratory of Organometallic Chemistry, School of Chemistry & Molecular Engineering, East China University of Science and Technology, P.O. Box 310, 130 Meilong Road, 200237, Shanghai, P.R. China.
authors.forename: Haiyan
authors.initials: H
authors.lastname: Ma
keywords: C−H activation; C−N bond cleavage; N ligands; calcium complexes; ring-opening polymerization