Titanocene and Zirconocene Complexes with Diaminoacetylenes: Formation of Unusual Metallacycles and Fulvene Complexes

Abstract

The reaction of dipiperidinoacetylene (pipC≡Cpip, pip = NC5H10, 1a) with [Cp2Ti(η2-btmsa)] (2) or with [Cp2Zr(η2-btmsa)(py)] (4) (btmsa = bis(trimethylsilyl)acetylene, py = pyridine) afforded the metallacyclopentadienes [Cp2M(C4pip4)] (3, M = Ti; 5, M = Zr), which in the solid state exhibit twisted five-membered metallacycles with an unusual half-chair conformation. In contrast, the sterically more demanding decamethyltitanocene (Cp*2Ti) and -zirconocene (Cp*2Zr) complex fragments can only accommodate one alkyne ligand. Thus, the titanacyclopropene [Cp*2Ti(C2pip2)] (7) was isolated from the reaction of 1a with [Cp*2Ti(η2-btmsa)] (6) or with [Cp*2TiCl] in the presence of magnesium, whereas the zirconacyclopropenes [Cp*2Zr(C2X2)] (8a, X = pip; 8b, X = NC5H9-4-Me; 8c, X = NEt2) were prepared by the reduction of [Cp*2ZrCl2] with magnesium in the presence of 1a, bis(4-methylpiperidino)acetylene (1b), and bis(diethylamino)acetylene (1c), respectively. NMR studies showed that complexes 8 are in equilibrium with ...