Directed Ortho Calciation of 1,3-Bis(3-isopropylimidazol-2-ylidene)benzene

Abstract

The deprotonation of 1,3-bis­(3-isopropylimidazol-2-ylidene)­benzene with Me3SiCH2CaX (X = Br, I) in tetrahydrofuran (THF) yields the ether adducts of the corresponding 2,6-bis­(3-isopropylimidazol-2-ylidene)­phenylcalcium halides (X = Br (1·2thf), I (2·2thf)). The crystallization behavior of 2 can be improved via substitution of ligated thf molecules by tetrahydropyran (thp) ligands, leading to 2·2thp. These heteroleptic complexes 1·2thf and 2·2thp show very small Ca–Cipso bond lengths to the ipso-carbon atoms of the aryl groups. Calciation of 1,3-bis­(3-isopropylimidazol-2-ylidene)­benzene with Ca­(CH2SiMe3)2 in THP leads to the formation of ether-free homoleptic bis­[2,6-bis­(3-isopropylimidazol-2-ylidene)­phenyl]calcium (3). Intramolecular steric strain causes an elongation of the Ca–Cipso bonds to the aryl groups. In all of these complexes, the Ca–Ccarbene distances are significantly larger than those to the ipso-carbon atoms of the aryl groups.

Direct Synthesis of Heavy Grignard Reagents: Challenges, Limitations, and Derivatization

“…The reduction of trimethylsilylmethyl bromide and iodide with activated calcium in tetrahydrofuran yielded the corresponding alkylcalcium iodide ( 2 a ) and bromide ( 2 b ), whereas Me 3 SiCH 2 Cl did not react with activated calcium powder. To enhance the durability of the complexes in ethereal solvents, the thf ligands were exchanged by tetrahydropyran molecules (Scheme ).…”

“…Despite considerable effort, single crystals of cyclopropylcalcium derivatives suitable for X-ray diffraction experiments could not be grown. Relevant 1 HNMR spectroscopic data includes as hielded H a reso- The reduction of trimethylsilylmethyl bromide and iodide with activated calcium in tetrahydrofurany ielded the correspondinga lkylcalcium iodide (2a) [23,24] andb romide (2b), whereas Me 3 SiCH 2 Cl did not react with activated calcium powder. To enhancethe durability of the complexes in ethereal solvents, the thf ligands were exchanged by tetrahydropyran molecules (Scheme 6).…”

NHCs in Main Group Chemistry

“…Complexes 139c , d with the heavier metals strontium and barium have also been isolated. Directed ortho -metalation of 1,3-bis­(NHC)-benzene with the heavy Grignard reagent Me 3 SiCH 2 CaX (X = Br, I) resulted in the calcium complexes 138a , b with the chelating CCC ligand . The bis-coordinated complex 140 was obtained by calciation of the ligand with Ca­(CH 2 SiMe 3 ) 2 .…”

“…Very recently, Westerhausen et al isolated calcium complexes with a chelating CCC 202 (138) and CNC 203 (139) ligand system as well as the bis-coordinated complexes 140 and 141 (Figure 25). Complexes 139c,d with the heavier metals strontium and barium have also been isolated.…”

“…Directed ortho-metalation of 1,3-bis(NHC)-benzene with the heavy Grignard reagent Me 3 SiCH 2 CaX (X = Br, I) resulted in the calcium complexes 138a,b with the chelating CCC ligand. 202 The bis-coordinated complex 140 was obtained by calciation of the ligand with Ca(CH 2 SiMe 3 ) 2 . The 13 3) Å (M = Sr) and 2.925(4) Å (M = Ba)).…”