Titanium complexes, ROMP

The alkyl-substituted titanium carbene complex 18 reacts with norbornene 24 to form a new titanacycle 25, which can be employed for the ROMP of 24 (Scheme 14.13). The titanacycle generated by the reaction of the Tebbe reagent with 24 is also used as an initiator for the same polymerization [23]. These preformed titanacyclobutanes also initiate ROMP of various other strained olefin monomers [24],... 

Complexes Cp2TiMe2, Cp2TiClMe, CpTiMe3, and Cp2Ti(CH2CMe3)2 catalyze the ROMP of norbornene. The initiation of this process by thermally generated alkylidene titanium species and subsequent formation of titanacyclobutane complexes is proposed. The presence of THF as the solvent can inhibit the ROMP activity.1409 Developments of practical methods to carry out olefination reactions of aldehydes, ketones, and... 

Vinyl ethers are known to react with ruthenium carbene complexes to give the so-called Fischer carbenes which show greatly reduced olefin metathesis activity [13]. Therefore, ethyl vinyl ether is typically use din the nonfunctional termination of most living ROMP reactions using ruthenium initiators. Figure 3.2. When substituted vinyl ethers are employed, functional groups or even complex molecules can be transferred onto the polymer chain end in one step. This type of functional termination reaction works only for ruthenium carbene complexes because titanium, molybdenum, and tungsten carbenes are tolerant toward vinyl ethers. 

The thermal and functional group sensitivity of these complexes limited their application in fiinaional polymer synthesis As better inidators became available, there was litde further research udlizing these very early Ti and Ta complex inidators. However, these early studies provided the foundation for living ROMP. With the titanium systems, it was demonstrated that ... 

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