Abstract A new, convenient preparation of W(CH tBu)(NAr)Cl 2(dme) (Ar = 2,6-diisopropylphenyl) involves treatment of W(NAr)(O tBu) 2(CH 2 tBu) 2 with PCl 5 in dimethoxyethane as a final step. From it a variety of complexes of the type W(CH tBu)(NAr)(OR) 2 (R = alkyl or fluoroalkyl) can be prepared straightforwardly in high yield. Analogous complexes of the type Mo(CH t-Bu)(NAr)(OR) 2 were also prepared. Complexes in which ORO tBu will not react with ordinary olefins, but will react with strained cyclic olefins such as norbornene (NBE) and cyclopentene to give living polymers from which the organic polymer can be cleaved by treatment with aldehydes. Polydispersities for norbornene polymers prepared in this manner are as low as 1.03. Mo(CH tBu)(NAr)(O tBu) 2 also will polymerize endo,endo-5, 6-dicarbomethoxynorbomene (DCNBE) to give homopolymers and block copolymers (with NBE) with polydispersities in the range 1.10–1.15. A bis-CF 3 Feast monomer can be ring-opened and the polymer cleaved with pivaldehyde to give (after pyrolysis) soluble polyenes, tBu(CHCH) 2x+1 tBu. Odd polyenes containing from 7 to 19 double bonds were isolated by column chromatography employing five equivalents of monomer. Triblocks containing a 40-ene (average) central chain, capped by two polynorbornene chains (25 equiv) have been prepared by related techniques. In this case the triblock with the expected molecular weight was observed to form a high molecular weight material that is still soluble. The polymer with the expected molecular weight was separated from the high molecular weight material by column chromatography.