Soluble systems metal coordination polymers

There exist a vast number of discrete, polymetallic coordination clusters both of the metal-metal bonded type and linked by a tremendous variety of bridging ligands, notably carboxylates. Such compounds are not coordination polymers but oligomers and hence can be more soluble, more well-defined and easier to characterise than coordination polymers, for which they can serve as useful model systems. We will discuss discrete, self-assembled complexes of semi-protected metal ions that act as hosts in solution or as 3D capsules in the next chapter and we will not cover these systems in detail here except to note in passing a couple of examples that are of particular interest. One particularly prominent cluster is Muij-acetate, the mixed-valence compound... 

In conclusion, electronic density of the transition metal may be influenced, case by case, by the effect of the reaction with aluminum alkyl and, as a result, the carbon-transition metal bond stability, olefin coordination and insertion capacity, stereochemical control of active centre and chain transfer and propagation processes, hence polymer MWD, may also be affected. This is particulary true for soluble catalytic systems for which the existence of active centres as bimetallic complexes is likely. 

There is little information on rates of initiation in coordination polymerization. With the soluble catalyst (7r-CsHs)2TiCl2—AlMejCl for ethylene, Chien [111] reported = 4.99 x 10 1 mole s at 15°C Ei = 15.5 kcal mole ). This was determined from the rate of incorporation of C14 labelled AlMe2 Cl into the polymer. In most systems examined the initiating centres have been preformed and reaction starts immediately. This is the case with Natta type catalysts from transition metal subhalides with the alkyls of aluminium, beryllium and zinc. With some catalysts the rate rises rapidly to a steady value but with others there is a rapid rise to a maximum followed by a decline to a constant rate, the latter being... 

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