Early Transition Metal Complexes Containing 1,2,4-Triazolato and Tetrazolato Ligands:  Synthesis, Structure, and Molecular Orbital Studies

Abstract

Several early transition metal complexes bearing 1,2,4-triazolato and tetrazolato ligands have been prepared by reaction of the pyrazolato complexes Ti(tBu(2)pz)(4-x)Cl(x) (tBu(2)pz = 3,5-di-tert-butylpyrazolato; x = 1, 2) and M(tBu(2)pz)(5-x)Cl(x) (M = Nb, Ta: x = 2, 3) with the sodium or potassium salts derived from 1,2,4-triazoles and tetrazoles. The X-ray structure analysis of Ti(tBu(2)pz)(2)(Me(2)C(2)N(3))(2) shows eta(2)-coordination of the 1,2,4-triazolato ligands, while in Ti(tBu(2)pz)(3)(C(2)H(2)N(3)) and Nb(tBu(2)pz)(3)(Me(2)C(2)N(3))(2) the analogous groups are joined in a eta(1)-fashion in the solid-state structure. Solution NMR studies at different temperatures suggest transition states involving eta(2)-1,2,4-triazolato ligands for the complexes containing eta(1)-1,2,4-triazolato ligands in the solid state. X-ray crystal structures of analogous tetrazolato complexes Ti(tBu(2)pz)(3)(PhCN(4)) and Nb(tBu(2)pz)(3)(PhCN(4))(2) show eta(1)-coordination of the 2-nitrogen atoms of the tetrazolato ligands. Molecular orbital calculations have been carried out on several model titanium complexes and provide detailed insight into the bonding between early transition metal centers and 1,2,4-triazolato and tetrazolato ligands. The eta(2)-coordination mode of 1,2,4-triazolato and tetrazolato ligands is predicted to be more stable than the eta(1)-coordination mode by 13.8-5.2 kcal/mol.

Azide Chemistry – An Inorganic Perspective, Part II[‡][3+2]‐Cycloaddition Reactions of Metal Azides and Related Systems

“…Theoretical results demonstrate that particularly in early transition metal compounds there is a strong thermodynamic preference for this kind of coordination over the η 1 -mode. [198] In order to obtain discrete mononuclear complexes with (slipped) η 2 -bonded tetrazoles/tetrazolates, bulky ancillary ligands are required in the coordination sphere as, for instance, in [K(18-crown-6)](η 2 (N 1 ,N 2 )-N 4 CR) (R = Ph, pyrrolidinyl, Bu t ), [199] or in [Ba (18- [198] For the most part, however, coordinative saturation both in simple binary compounds and in the realm of tetrazole-based metal-organic coordination polymers (MOCPs) (see particularly section 1.3. ), is achieved by tetrazolato bridge formation.…”

Synthesis, Structure, and Properties of Zirconium and Hafnium Complexes Containing η2‐Pyrazolato Ligands

“…We have previously reported that treatment of group 4 and 5 metal chlorides with potassium pyrazolato salts constitutes an excellent synthetic route to the corresponding group 4 and 5 pyrazolato complexes. [12,13] Accordingly, salt metathesis routes to hafnium pyrazolato complexes were explored. Treatment of hafnium tetrachloride with 4 equiv.…”

“…[10c, 11,12] Meyer and co-workers reported a homoleptic zirconium complex with four bulky η 2 -pyrazolato ligands. [11] We have reported the synthesis and structure of several zirconium and hafnium complexes that contain pyrazolato ligands, [12] but have not published any structural studies of the homoleptic pyrazolato complexes.…”

“…[11] We have reported the synthesis and structure of several zirconium and hafnium complexes that contain pyrazolato ligands, [12] but have not published any structural studies of the homoleptic pyrazolato complexes.…”

Synthesis, structure and thermokinetic studies on perchlorate salts of metal complexes containing a formamidine-type ligand

“…Synthesis, structure and thermokinetic studies on perchlorate salts of metal complexes containing a formamidine-type ligand 1…”