Structural Trends in Group 4 Metal Tetraaza Macrocycle Complexes. Molecular Structures of (Me₄taen)Zr(O^tBu)₂ and (Me₄taen)Hf(NMe₂)₂

Abstract

The tetraaza macrocycle complexes (Me4taen)Zr(OtBu)2 (4) and (Me4taen)Hf(NMe2)2 (5) have been prepared and characterized by X-ray crystallography. Both species adopt cis structures with distorted octahedral metal geometries. These structures are similar to that observed earlier for (Me4taen)Zr(NMe2)2 (3) but quite different from the trigonal prismatic structures observed for (Me4taen)ZrCl2 (1) and (Me4taen)Zr(CH2Ph)2 (2). The structures of these d0 (Me4taen)MX2 species are rationalized on electronic grounds. The conformational properties of the Me4taen2- macrocycle and the covalent character of and absence of a strong π-component in the M−X bonds favor trigonal prismatic structures for 1 and 2, whereas M−X π-bonding in 3−5 promotes distortion toward octahedral structures. Compound 4, C22H40N4O2Zr, crystallizes in the triclinic space group P1̄ with a = 9.6080(8) Å, b = 9.7407(8) Å, c = 14.5916(12) Å, α = 92.714(1)°, β = 107.808(1)° γ = 99.810(1)°, and Z = 2. Compound 5, C18H34N6Hf·0.5(C7H8), crystallizes in the triclinic space group P1̄ with a = 9.102(3) Å, b = 11.242(4) Å, c = 13.478(5) Å, α = 108.672(5)°, β = 96.310(5)°, γ = 106.266(6)°, and Z = 2.

“Non‐VSEPR” Structures and Bonding in d0Systems

“…Either structures close to the trigonal prism or characteristically distorted octahedral arrangements have been found for the complexes [MX 2 (Me 4 taen)] (Me 4 taen=5,7,12,14‐tetramethyl‐1,4,8,11‐tetraazacyclotetradeca‐4,6,11,13‐tetraene; M=Zr, Hf) 213. The cavity of the tetradentate macrocyclic ligand Me 4 taen is too small to completely enclose the metal.…”

“…The dihedral angles are close to the trigonal prismatic extreme for X=Cl, CH 2 Ph, with the ligands X each pointing in between two of the nitrogen atoms of the macrocycle. In contrast, in complexes with presumably stronger π‐donors213 (X=N(CH 3 ) 2 , O t Bu) the ligands X eclipse almost two of the macrocyclic nitrogens, creating an octahedral structure distorted in the direction of a doubly capped tetrahedron.…”

Diamido/diamine cyclam-based zirconium and hafnium complexes: Synthesis and characterization

“…This value is certainly a reflex of the bonding properties of the diamidodiamine donor set that may act as a 12 electron donor to the metal centre when both r and p bonds are considered. As a consequence, the chloride ligands behave as pure r donor ligands [32]. Short contact distances between the Cl(1) and H syn atoms located at carbons C(1) and C(3) and one benzylic hydrogen atom, are observed.…”

Synthesis, Characterization, and Magnetic Properties of Iron Complexes Bearing Polydentate Nitrogen Ligands

“…A more sterically hindered amidinate is required or amidinates that can give additional electronic stabilization to the highly electronically unsaturated central metal atoms are required. In this general scenario, nitrogen‐based ligands have been found to be particularly attractive in early and late transition metal systems …”