Self‐Assembly Reactions To Form Multinuclear Zirconium(III) and Titanium(III) Complexes with Imidazole Derivatives as Bridging Ligands

Abstract

Self-assembly reactions with low valent early transition metals, leading to neutral multinuclear complexes are rare. Mostly late transition metals like Pt, Pd or Ru together with Nheterocycles or O-donor-based ligands are used to form supramolecular coordination complexes. This paper reports on selfassembly reactions of low valent titanocene and zirconocene units and five-membered N-heterocycles as bridging ligands. These reactions lead to novel molecular triangles and rectangles with the metal centers marking the vertices. Five different imidazole derivatives and four different metallocene precursors were used. For the first time, molecular triangles and architec-Scheme 1. Molecular quadrangle with pyrazine I and 4,4′-bipyridine II and a combination of both III as bridging ligands.[a]

Recent Synthetic and Catalytic Applications of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes

“…only one trianionic ligand, formed by the above mentioned deprotonation of cyanuric acid or melamine as the starting material . The new aspect in the series described by Beckhaus et al is that three or four (benz)imidazolate anions act as bridging ligands for three or four metal centers …”

Imidazole‐Bridged Tetrameric Group(IV) Heteroleptic Complexes from the Spontaneous Metal‐Ligand Assembly of a Potentially N4‐Tetradentate Ligand

“…The tetrameric structure is obtained through the application of the symmetry elements of the I4 space group in the lattice. The main structural metrics [ d (Zr–N im ) = 2.36 Å; d(Zr–N py ) = 2.495(4) Å; d(Zr–N anilido ) = 2.120(4) Å; d (Zr–NMe 2 ) = 2.09 Å; α(N im –Zr–N im ) = 77.22(13)°; α(N im –Zr–N py ) = 76.55(13)°; α(N im –Zr–N anilido ) = 80.34(14)°] fall in the typical range observed for similar complexes in the CSD containing bridging or terminal, imidazole ligands bound to zirconium(IV) [ d (Zr–N im ) = 2.33 Å; α(N im –Zr–N im ) = 97.3°; α(N im –Zr–N py ) = 74.1°]. Intramolecular C‐H ··· N interactions are present in the molecule between C‐H bonds from methylene or dimethylamido groups and N‐atoms from the same ‐NMe 2 ligands or imidazole [d(C ··· NMe 2 ) = 3.379(6) Å; d(C ··· N im ) = 3.214(7) Å].…”

“…Imidazole (and its derivatives) is one of the most intriguing and stable N‐heterocycles to be employed in coordination chemistry. Due to the ability of its deprotonated form (imidazolate) to act as a bridging ligand with a wide variety of metal ions, it has already provided a number of polymetallic materials and original complex architectures . Starting from our interest in the synthesis and characterization of group IV pyridylamido complexes containing pyrazole, and imidazolate units, we report herein on the synthesis and coordination chemistry of a new imidazolate‐based polydentate N‐ligand.…”

Advantages of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes as Metallocene Sources Towards Other Synthetically used Systems

“…Self‐assembly reactions to multinuclear complexes using group 4 bis(trimethylsilyl)acetylene complexes are possible and were described in detail . Some older examples of C−C coupling reactions with or without C−H bond activation to give tri‐ or tetranuclear complexes were published .…”

“…Starting from Cp 2 Ti(η 2 ‐Me 3 SiC 2 SiMe 3 ) and benzimidazole or 5,6‐dimethylbenzimidazole tetranuclear complexes were formed. The reason could be that with an increased sterical demand of the ligands Cp* and the substituents R=Ph only tri‐ and with the smaller Cp‐ligands and the substituents H or Me the tetranuclear complexes were obtained (Scheme ) …”