Exploring Alternative Synthetic Routes for the Preparation of Five-Coordinate Diamidoamine Group 4 Metal Complexes

Efficient synthetic routes for the preparation of electrophilic titanium and zirconium complexes featuring a tridentate diamidoamine ligand have been developed. The five-coordinate titanium dichloride complexes [(MesNCH<INF>2</INF>CH<INF>2</INF>)<INF>2</INF>NR]TiCl<INF>2</INF> (R = H (<BO>3</BO>), SiMe<INF>3</INF> (<BO>4</BO>)) are conveniently prepared from the amine elimination reactions of the triamines (MesNHCH<INF>2</INF>CH<INF>2</INF>)<INF>2</INF>NR (R = H (<BO>1</BO>), SiMe<INF>3</INF> (<BO>2</BO>)) with Ti(NEt<INF>2</INF>)<INF>2</INF>Cl<INF>2</INF>. Treatment of Ti(NEt<INF>2</INF>)<INF>4</INF> with 2 equiv of SiMe<INF>3</INF>Cl offers an effective method for the preparation of Ti(NEt<INF>2</INF>)<INF>2</INF>Cl<INF>2</INF>. The corresponding five-coordinate zirconium homologues [(MesNCH<INF>2</INF>CH<INF>2</INF>)<INF>2</INF>NR]ZrCl<INF>2</INF> (R = H (<BO>5</BO>), SiMe<INF>3</INF> (<BO>6</BO>)) are synthesized via the toluene elimination reactions of Zr(benzyl)<INF>2</INF>Cl<INF>2</INF>(Et<INF>2</INF>O)<INF>2</INF> with <BO>1</BO> and <BO>2</BO>, respectively. The thermally unstable and photosensitive Zr(benzyl)<INF>2</INF>Cl<INF>2</INF>(Et<INF>2</INF>O)<INF>2</INF> species may be prepared in situ from the reaction of Zr(benzyl)<INF>4</INF> with 2 equiv of [NEt<INF>3</INF>H]Cl in diethyl ether at 0 °C in the dark. The toluene elimination reaction of Hf(benzyl)<INF>4</INF> with <BO>1</BO> affords the dibenzyl Hf complex [(MesNCH<INF>2</INF>CH<INF>2</INF>)<INF>2</INF>NH]Hf(benzyl)<INF>2</INF>, <BO>7</BO>. The X-ray structural and solution NMR data for <BO>4</BO>, <BO>5</BO>, <BO>6</BO>, and <BO>7</BO> reveal that these electrophilic group 4 metal complexes adopt the facial structure with either a chloride or a η²-benzyl ligand trans to the central amino N atom of the tridentate diamidoamine ligand.