Reactions of Low-Valent Titanocene(II) Fragments with trans-4,4′-Azobispyridine (RN═NR, R = C₅H₄N): Formation of Tetranuclear Molecular Squares by trans−cis Isomerization

Abstract

The reactions of the low-valent titanocene sources [Cp* 2 Ti(η 2 -C 2 (TMS) 2 )] (2) and [tBuCp 2 Ti(η 2 -C 2 -(TMS) 2 )] (3) with trans-4,4′-azobispyridine (8) leads to novel supramolecular squares [(Cp* 2 Ti) 4 (µ 2 -N,N′;η 2 -N,N′-C 10 H 8 N 4 ) 2 ] (10) and [(tBuCp 2 Ti) 4 (µ 2 -N,N′;η 2 -N,N′-C 10 H 8 N 4 ) 2 ] (11). These complexes consist of four bent-titanocene corner units and two azo ligands 8. Within this self-assembly process the azo ligands experience a conformational rearrangement from trans to cis. The titanocene moieties are embedded with two different N-donor environments, provided by the pyridyl rings and the azo functionality of 8. Single-crystal X-ray analyses of the tetranuclear compounds 10 and 11 revealed the structural features of these molecular polygons. Exclusively cis-configurated azopyridine units are detected in 10 and 11. Comparison of bond lengths and angles in coordinated and free ligands shows a reduced state of the bridging ligands in the low-valent titanium complexes 10 and 11. In such a way, the N azo -N azo distances are elongated from 1.251(2) Å in 8 to av 1.405(3) Å (10) and 1.434(3) Å ( 11), respectively. The syntheses and attributes of these novel compounds are discussed. From the reaction of [Cp 2 Ti(η 2 -C 2 (TMS) 2 )] (1) with 8, 1,2-bis(4-pyridyl)hydrazine ( 13) was isolated and fully characterized as a subsequent product.

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

“…A highlight in this direction was the coupling of different N-heterocycles, published by Beckhaus and coworkers. [100][101][102][103][104][105][106] As starting complexes Cp 2 Ti(η 2 -btmsa) and Cp* 2 Ti(η 2 -btmsa) were used. For example with pyrazine and Cp* 2 Ti(η 2 -btmsa) by threefold C-C coupling a trinuclear complex and with Cp 2 Ti(η 2 -btmsa) and pyrimidine an octanuclear complex was obtained.…”

Multifunctional mixed ligand metal organic frameworks: X-ray structure, adsorption, luminescence and electrical conductivity with theoretical correlation

“…48 Zn(NO 3 ) 2 ·6H 2 O and 5-hydroxy-1,3-benzenedicarboxylic acid (OH-H 2 -1,3-BDC) were obtained from Sigma-Aldrich Chemicals.…”

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 .…”