Adduct formation of [(η 7-C 7H 7)Zr(η 5-C 5H 5)] with phosphines and N-heterocyclic carbenes: An experimental and theoretical study

Abstract

The reaction of [(η 7-C 7H 7)Zr(η 5-C 5H 5)] with two Lewis bases, tetramethylimidazolin-2-ylidene and PMe 3, is reported and their stability probed via spectroscopic and theoretical methods. The strongly σ-basic N-heterocyclic carbene forms a stable adduct which has been structurally characterised, whilst the PMe 3 ligand coordinates weakly to the metal centre. Variable temperature 31P NMR spectroscopy has been used to determine the activation energy for this process (Δ G ‡ = 40.5 ± 1.9 kJ mol −1). DFT calculations have been performed on both complexes and the structures discussed. In addition, the enthalpies for the formation of these compounds have been calculated [Δ H 0(Zr–IMe) = −56.3 kJ mol −1; Δ H 0(Zr–PMe 3) = −2.3 kJ mol −1] and show that the N-heterocyclic carbene forms a thermodynamically much more stable adduct than that with PMe 3.