Living polymerization with well‐defined alkylidene catalysts

Alkylidene complexes of the type Mo(CH‐t‐Bu)(NAr)(OR) 2 (Ar = 2, 6‐diisopropylphenyl; OR = O‐t‐Bu, OCMe 2 (CF 3 ), OCMe(CF 3 ) 2 , etc.) can be prepared from a “universal precursor”, Mo(CH‐t‐Bu)(NAr)(triflate) 2 (1, 2‐dimethoxyethane), 1 which can be prepared in three high‐yield steps from ammonium dimolybdate. 2 These complexes serve as initiators for the ring opening metathesis of norbornenes and substituted norbornadienes, 3 or for the polymerization of acetylenes to give polyenes, 4 all in a living manner. The organic polymer can be cleaved upon treatment with an aldehyde. Norbornenes that contain a variety of organic or inorganic functionalities can be polymerized to give essentially monodisperse homopolymers and block copolymers. Recently chiral catalysts have been prepared that will polymerize norbornenes and norbornadienes stereoselectively to give all cis isotactic polymers. 5 Molybdenum catalysts also have been found that will cyclopolymerize dipropargyl derivatives or substituted phenylacetylenes in a living manner. 6 The stereospecific synthesis of all cis, or all trans, tactic polynorbornadienes and polynorbornenes will be discussed in detail, including a proof of tacticity. 7