Isomerism in Hexacoordinate Ti(IV) and Zr(IV) Complexes with a Tetradentate ONNO‐Schiff Base Ligand

Abstract

The reactions of [(thf) 2 TiCl 4 ] with sodiated 2,2'-bis[2-hydroxy-3,5-di(tert-butyl)benzylideneamino]-1,1'-biphenyl (1 a) and 2,2'bis[2-hydroxy-3,5-di(tert-butyl)benzylideneamino]-4,4'-dimethyl-1,1'-biphenyl (1 b) yield the corresponding Ti complexes 2 a and 2 b. Similarly, 1 a reacts with [(thf) 2 ZrCl 4 ] to the corresponding Zr derivative 3. For 2 a, a mixture of cis-β and trans isomers were observed in solution whereas the Zr congener exclusively forms the cis-α form. Quantum chemical calculations verify that these isomers are the preferred molecular structures. The crystal structures of cis-β isomeric 2 a and cis-α isomeric 3 have been determined. Metalation of 1 a with Ti(NMe 2 ) 4 yields 2,2'-bis[(2oxido-3,5-di(tert-butyl)phenyl)-dimethylaminomethylamino]-1,1'-biphenyl titanium(IV) (4) with a hexadentate ligand.

Group IV Complexes with Sterically Congested N-Aryl-adamantylcarbamidate Ligands

“…The Ti1 atom shows an unusually small coordination number of four with a slightly distorted tetrahedral environment of the Ti1 atom. The O1−Ti1−N bond angles (average value 112.6(4)°) are larger than the N− Ti1−N values with an average of 106.1 (5)°due to the much larger steric demand of the O-bound amidate ligand.…”

“…Advantageous starting materials for metalation reactions and syntheses of precatalysts are the easily accessible tetrakis­(dialkylamido) compounds M­(NR 2 ) 4 . Thus, the reaction of these group IV amides with tetradentate Jacobsen-type Schiff base ligands with a biphenyl backbone leads to the formation of 2,2′-bis­[(2-oxido-3,5-di­( tert -butyl)­phenyl)-dimethylaminomethylamino]-1,1′-biphenyl titanium­(IV) with a distorted octahedrally coordinated titanium center as depicted in Scheme . The Ti­(IV) atom is effectively shielded by this hexadentate ligand and, hence, catalytically inactive in hydroamination processes.…”