Group 4 Transition Metal Sandwich Complexes: Still Fresh after Almost 60 Years

Abstract

Metal sandwich compounds, more commonly known as metallocenes, are some of the most enduring molecules in organometallic chemistry. Beginning with Wilkinson's quest for titanocene, [(η 5 -C 5 H 5 ) 2 Ti], the synthesis and exploration of the electronic structure and reactivity of group 4 metal sandwich complexes have been an ongoing story for almost six decades. This review recounts the historical origins of group 4 metallocenes and highlights synthetic efforts to observe and stabilize formally d 2 metal sandwich compounds. Specific attention is devoted to recent developments in the field, including dinitrogen coordination by various substituted titanocene derivatives as well as our group's interest in bis(indenyl)zirconium and -hafnium compounds.

Cycloheptatrienyl Zirconium Sandwich Complexes with Lewis Basic Phospholyl Ligands (Phosphatrozircenes): Synthesis, Structure, Bonding and Coordination Chemistry

“…In view of the striking metallosupramolecular chemistry based on phosphaferrocenes with more than one P atom in the ring, [48] our studies will also be developed in this direction and hopefully help to validate Chiriks recent statement: "Group 4 Transition-Metal Sandwich Complexes: Still Fresh after Almost 60 Years". [49] Experimental Section General: All synthetic and spectroscopic manipulations were carried out under an atmosphere of prepurified nitrogen, either in a Schlenk apparatus or in a glovebox. Solvents were dried and deoxygenated either by distillation under a nitrogen atmosphere from sodium benzophenone ketyl or by an MBraun GmbH solvent purification system.…”

Crystal structure of an isomeric bis[(η 5:η 1-6,6-di-p-tolylpentafulvene)(η 5-pentamethylcyclopentadienyl)titanium(III)]-μ 2,η 1:η 1-dinitrogen complex, C60H66N2Ti2

“…Besides many early transition metal complexes which are capable to activate and bind molecular nitrogen [5][6][7][8][9], our group reported the easy and smooth formation of dinuclear nitrogen-bridged low-valent titanium complexes [1]. These complexes appear to serve as synthons for di erent titanocenes, due to the weakly activated and displaceable dinitrogen.…”

The influences of electronic effect and isomerization of salalen titanium(iv) complexes on ethylene polymerization in the presence of methylaluminoxane

“…[12][13][14] The strategy of radical polymerization is limited to high-pressure apparatus and forms low-density polyethylene as a result of the high degree of short and long chain branching, as well as hyperbranching. 9 Ethylene coordination polymerization is the most widespread technology, which includes the heterogeneous Ziegler-Natta, 14,15 homogeneous metallocene [16][17][18] and post-metallocene [19][20][21][22] catalysts. Advances in catalyst research with homogeneous catalysts have given rise to new classes of polyethylene, [23][24][25] as these catalysts can provide control over branch structures, [26][27][28] molecular weight and molecular weight distributions.…”