Synthesis and reactivity of Li and TaMe sub(3) complexes supported by N,N'-bis(2,6-diisopropylph enyl)-o-phenylenediamido ligands

• Published in: Dalton transactions : an international journal of inorganic chemistry 2016-06, Vol.45 (26), p.10672-10680
• Main Authors: Janes, Trevor, Xu, Maotong, Song, Datong
• Format: Article
• Language: English
• Subjects: Insertion; Ligands; Lithium; Radicals; Spectroscopy; Synthesis; Tantalum; Toluene
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c6dt01908k

The dilithium complex of N,N'-bis(2,6-diisopropylph enyl)-o-phenylenediamide, [Li sub(2)L(thf) sub(3)], reacts with TaMe sub(3)Cl sub(2) in THF/Et sub(2)O to yield [Li(Et sub(2)O)(thf)LTaMe sub(3)C l] in which the phenylene backbone of L super(2-) is bound eta super(4) to the Ta centre. This dinuclear species reacts with MeLi to yield the tetramethyltantalum complex [Li(Et sub(2)O)(thf)LTaMe sub(4)] . Double deprotonation of N,N'-bis(2,6-diisopropylph enyl)(4,5-dimethyl)-o-phenylenediamine (H sub(2)L') in Et sub(2)O yielded the dilithium complex [Li sub(2)L'(OEt sub(2)) sub(2)]. The two additional methyl groups on L' super(2-) change the observed reactivity towards TaMe sub(3)Cl sub(2): rather than bridging between Ta and Li, ligand oxidation occurs to afford mononuclear [LiL'(OEt sub(2))]. This monolithium radical species, which was characterized by EPR spectroscopy, can also be synthesized using the more conventional oxidant AgBF sub(4). Double deprotonation of H sub(2)L with KCH sub(2)Ph in toluene followed by reaction with TaMe sub(3)Cl sub(2) furnished [TaLMe sub(3)]. Preliminary reactivity studies show [TaLMe sub(3)] reacts with unsaturated substrates N,N'-dicyclohexylcarbodiimide and mesityl azide to undergo migratory insertion into one of the Ta-C bonds: the corresponding amidinate and triazenido ligands are generated. When subjected to UV irradiation, [TaLMe sub(3)] undergoes reduction accompanied by loss of a methyl group to yield the dimeric species [TaLMe sub(2)] sub(2).