Trigonal prismatic versus octahedral coordination geometry of transition metal dithiolates: Comparison between saturated and unsaturated early transition metal tris(1,2-dithiolate) complexes

Abstract

Reaction of a stoichiometric amount of H2edt/NaHedt (edt = ethane-1,2-dithiolate) with the appropriate metal amide, followed by cation exchange, gave the complexes [NEt4]2[M(edt)3] (M = Ti, 1; Hf, 2) and [AsPh4] [Nb(edt)3]•CH3CN, 3. The structure of 3 has been determined crystallographically (space group; cell dimensions; Z; unique data (I ≥ 3σ (I); R/Rw): [Formula: see text]; a = 9.095(1), b = 14.609(3), c = 15.639(3) Å and α = 60.09(2), β = 80.07(3), γ = 89.89(2)°; z = 2; 1488; 4.3/4.5. The coordination geometry of 3 is severely distorted from the trigonal prismatic (TP) structure found in the analogous Nb(1,2-S2C6H4)3−, which contains an unsaturated 1,2-dithiolate ligand system. The average twist angle between triangular faces is 33.3°. However, on the basis of VT 1H NMR spectroscopy it is argued that the TP form is at most 9–10 kcal mol−1 less stable than the observed geometry. A comparison between the structures of tris-chelate complexes of the early transition metals containing saturated and unsaturated 1,2-dithiolates and related ligands is made, and the factors thought to be responsible for TP vs. octahedral geometry are reviewed and their relative importance assessed. Keywords: structure, trigonal prismatic, 1,2-dithiolate, early transition metals.