Preparation and physical properties of early-late heterobimetallic compounds featuring Ir–M bonds (M = Ti, Zr, Hf)

Abstract

Treatment of Cp*Ir N^tBu (1) with the appropriate metallocene equivalent is an effective route for the preparation of the heterobimetallic complexes Cp*Ir(μ-N^tBu)MCp₂ (2-M, M = Ti, Zr, Hf). The electronic structures of the isostructural series of compounds, 2-M, are described with reference to single-crystal X-ray, Raman, UV-vis, and cyclic voltammetry data. Density functional theory (DFT) calculations were used to aid in the interpretation of this experimental work. Treatment of the zirconium or hafnium congeners with 2,6-lutidinium triflate leads to protonation of the Ir–M bond, to afford Cp*Ir(μ-N^tBu)(μ-H)MCp₂OTf (3-M, M = Zr, Hf). Compound 3-Zr was characterized by single-crystal X-ray diffraction and independently prepared by the reaction of 1 and Cp₂Zr(H)Cl in the presence of Me₃SiOTf. In reactions analogous to those for 2-Zr, 2-Hf reacts with S₈ and aryl azides to insert an S-atom or aryl azide fragment into the metal–metal bond, yielding Cp*Ir(μ-N^tBu)(μ-S)HfCp₂ (6-Hf) and Cp*Ir(μ-N^tBu)(N₃Ph)HfCp₂ (4-Hf), respectively. Heating 4-Hf results in N₂extrusion to form Cp*Ir(μ-N^tBu)(NPh)HfCp₂ (5-Hf). The kinetics of the latter reaction were studied to obtain activation parameters and a Hammett trend; these data are compared to those for the analogous reaction involving Ir–Zr heterobimetallics.