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

Novel (1-pyridinio)imidotitanium(IV) complexes [Cp‘TiCl<sub>2</sub>(NNC<sub>5</sub>H<sub>3</sub>R<sub>2</sub>-2,6)] (<b>3a</b>, Cp‘ = Cp, R = H; <b>3b</b>, Cp‘ = Cp, R = Me; <b>3c</b>, Cp‘ = Cp*, R = Me) were synthesized in high yield from [Cp‘TiCl<sub>3</sub>] and [NH<sub>2</sub>NC<sub>5</sub>H<sub>3</sub>R<sub>2</sub>-2,6][PF<sub>6</sub>] in the presence of base. Complex <b>3b</b> could also be prepared from [Cp<sub>2</sub>TiCl<sub>2</sub>] and [NH<sub>2</sub>NC<sub>5</sub>H<sub>3</sub>Me<sub>2</sub>-2,6][PF<sub>6</sub>] in the presence of 1 equiv of BuLi. Cationic complexes [Cp*Ti(OTf)(NNC<sub>5</sub>H<sub>3</sub>Me<sub>2</sub>-2,6)(bpy)][OTf] (bpy = 2,2‘-bipyridine) (<b>4</b>) and [Cp*Ti(NNC<sub>5</sub>H<sub>3</sub>Me<sub>2</sub>-2,6)(terpy)][OTf]<sub>2</sub> (terpy = 2,2‘:6‘,2‘ ‘-terpyridine) (<b>5</b>) were derived from <b>3c</b> through reaction with AgOTf in the presence of bpy and terpy, respectively. The structures of complexes <b>3a</b>, <b>3b</b>, <b>3c</b>, and <b>5</b> were determined by X-ray crystallography. The N−N bond of <b>3a</b>−<b>c </b>could be cleaved by reduction with sodium amalgam, liberating the corresponding pyridines in high yield, while the N−N bond in <b>4</b> and <b>5</b> could be reductively cleaved by cobaltocene in moderate yield. The N−N bond in <b>3a</b>−<b>c</b> could also be cleaved by cobaltocene in the presence of a proton analogue like Me<sub>3</sub>SiCl.