Structural and Stereochemical Aspects of the Group 4 Metal Chemistry of Constrained-Geometry 2-(Indenyl)phenoxide Ligation

The reactivity of 2-(inden-3-yl)-4,6-di-tert-butylphenol (1) and its 2-methyl (2), 1,2-dimethyl (3), 2,4,7-trimethyl (4), and 1,2,4,7-tetramethyl (5) derivatives toward group 4 metal dialkylamides has been examined. Reaction of 1 equiv of the phenols 1−4 with the tetrakis(dialkylamido) compounds [M(NR2)4] (M = Ti, R = Me; M = Zr, R = Me, Et; M = Hf, R = Et) has allowed isolation of a series of bis(dialkylamido) compounds:  e.g., [Ti(OC6H2{η5-Ind}-2-But2-4,6)(NMe2)2]. In these compounds the parent phenol was found to be deprotonated at both the phenolic OH and indenyl ring, leading to the elimination of 2 equiv of dialkylamine. Structural studies of eight of these derivatives allow the variation of metal and methyl substitution to be assessed. The metal coordination of the series of compounds is best described as pseudo-tetrahedral, with the indenyl ring occupying one site of a three-legged piano-stool geometry. The M−C(indenyl) distances are consistent with an essentially η5 coordination for all bis(dialk...