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Synthesis and Reductive N−N Bond Cleavage of Neutral and Cationic Titanium (1-Pyridinio)imido Complexes

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journal contribution
posted on 24.12.1998, 00:00 by Mikael Retbøll, Youichi Ishii, Masanobu Hidai
Novel (1-pyridinio)imidotitanium(IV) complexes [Cp‘TiCl2(NNC5H3R2-2,6)] (3a, Cp‘ = Cp, R = H; 3b, Cp‘ = Cp, R = Me; 3c, Cp‘ = Cp*, R = Me) were synthesized in high yield from [Cp‘TiCl3] and [NH2NC5H3R2-2,6][PF6] in the presence of base. Complex 3b could also be prepared from [Cp2TiCl2] and [NH2NC5H3Me2-2,6][PF6] in the presence of 1 equiv of BuLi. Cationic complexes [Cp*Ti(OTf)(NNC5H3Me2-2,6)(bpy)][OTf] (bpy = 2,2‘-bipyridine) (4) and [Cp*Ti(NNC5H3Me2-2,6)(terpy)][OTf]2 (terpy = 2,2‘:6‘,2‘ ‘-terpyridine) (5) were derived from 3c through reaction with AgOTf in the presence of bpy and terpy, respectively. The structures of complexes 3a, 3b, 3c, and 5 were determined by X-ray crystallography. The N−N bond of 3ac could be cleaved by reduction with sodium amalgam, liberating the corresponding pyridines in high yield, while the N−N bond in 4 and 5 could be reductively cleaved by cobaltocene in moderate yield. The N−N bond in 3ac could also be cleaved by cobaltocene in the presence of a proton analogue like Me3SiCl.