Affiliation:
1. Inorganic Chemistry Laboratory Department of Chemistry National and Kapodistrian University of Athens Panepistimiopolis Zografou 15771 Athens Greece
2. Equipe Confinement Moléculaire et Catalyse Institut de Chimie de Strasbourg UMR 7177 CNRS Université de Strasbourg 4, rue Blaise Pascal CS-90032, 67081 Strasbourg Cedex France
3. Laboratoire de Chimie Quantique Institut de Chimie de Strasbourg UMR 7177 CNRS Université de Strasbourg 4, rue Blaise Pascal CS-90032, 67081 Strasbourg Cedex France
4. Fédération de Chimie “Le Bel” - UAR2042 BP 296R8 1, rue Blaise Pascal 67008 Strasbourg Cedex France
5. Laboratory of Analytical Chemistry Department of Chemistry National and Kapodistrian University of Athens Panepistimiopolis Zografou 15771 Athens Greece
Abstract
AbstractThe pincer complexes [NiIIBr(CNC)]Br (4), [CrIIIBr3(CNC)] (5 a) and [CrIIIBr2.3Cl0.7(CNC)] (5 b), where CNC=3,3′‐(pyridine‐2,6‐diyl)bis(1‐mesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene), were obtained from the novel ligand CNC, generated in situ from the precursor (CHNCH)Br2 and [NiIIBr2(PPh3)2] or from [CrII{N(SiMe3)2}2(THF)2] and (CHNCH)Br2 by aminolysis, respectively. The tetrahedrally distorted square planar (τ4≅0.30) geometry and the singlet ground state of Ni in 4 were attributed to steric constraints of the CNC backbone. Computational methods highlighted the dependence of the coordination geometry and the singlet‐triplet energy difference on the size of the N‐substituent of the tetrahydropyrimidine wingtips and contrasted it to the situation in 5‐membered imidazolin‐2‐ylidene pincer analogues. The octahedral CrIII metal center in 5 a and 5 b is presumably formed after one electron oxidation from CH2Cl2. 4/MAO and 5 a/MAO were catalysts of moderate activity for the oligomerization and polymerization of ethylene, respectively. The analogous (CH^N^CH)Br2 precursor, where (CH^N^CH)=3,3′‐(pyridine‐2,6‐diylbis(methylene))bis(1‐mesityl‐3,4,5,6‐tetrahydropyrimidin‐1‐ium), was also prepared, however its coordination chemistry was not studied due to the inherent instability of the resulting free C^N^C ligand.