Transitions trihalide compounds

Ziegler-Natta Catalysts (Heterogeneous). These systems consist of a combination of a transition metal compound from groups IV to VIII and an organometallic compound of a group I—III metal.23 The transition metal compound is called the catalyst and the organometallic compound the cocatalyst. Typically the catalyst is a halide or oxyhalide of titanium, chromium, vanadium, zirconium, or molybdenum. The cocatalyst is often an alkyl, aryl, or halide of aluminum, lithium, zinc, tin, cadmium, magnesium, or beryllium.24 One of the most important catalyst systems is the titanium trihalides or tetra-halides combined with a trialkylaluminum compound. 

Redistribution of substituents tends to be especially facile for halides, hydrides, and alkyls of Groups I—III nontransition elements because these compounds are electron-deficient. Bridging groups are present in many of these compounds. Even in the boron trihalides that are not bridged, a bridged transition state making use of the empty valence shell orbitals is possible, so that redistribution can occur with a relatively low activation energy (113) ... 

Halogen exchange in the coordinatively saturated boron trihalide adducts requires either a preliminary dissociative step or an associative interaction different from the doubly halogen-bridged transition state available to three-coordinate boron compounds [Eq. (1)] (113,114). The reactions can be classified as follows. 

I.r. and Raman studies have shown the formation of complexes between tributyl phosphate and both arsenic and antimony tribromides. Cryoscopy in fused arsenic tribromide is reported for a num r of inorganic and organic solutes, showing dTj X values lower than the ideal value, and with dioxan the compound 2AsBr3,3dioxan, melting at 64 °C, is formed. Arsenic and antimony trihalides give a-bonded transition-metal derivatives, such as X2E[Fe(CO)2(Cp)]J, where E = As or Sb and X = Cl or Br, on reaction with metal carbonyl anions or metal carbonyls with metal-metal bonds. ... 

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