Ring-opening polymerization of norbornene by a tantalum catalyst: a living polymerization

Controlled Ring-Opening Metathesis Polymerization by Molybdenum and Tungsten Alkylidene Complexes

“…We also found that although endo,endo-5,6-dicarbomethoxynorbornene (DCNBE) could not be polymerized in a controlled manner by W(CHtBu)(NAr)(OtBu) 2 , addition of DCNBE to Mo(CHtBu)(NAr)(OtBu)2 in C 6 D 6 quantitatively converted it (vs. an internal standard) into a living polymer that has an alkylidene Ha signal at 11.64 ppm. 50 and 100 eq of DCNBE can be polymerized by Mo(CIBu)(NAr)(OtBu)2 to give polymers with low polydispersity, characteristic of a living polymerization catalyst system ( Table 1).…”

“…The two steps shown in equation 2 proceed in high yield. W(NAr)(OtBu) 2 entirely analogous to those used originally to prepare the tungsten analog [5]. So far we have not developed a route to the molybdenum catalysts that is as convenient as that we now use for the tungsten catalyst (equations 1-3).…”

“…To our knowledge this is the first report of a controlled polymerization of a nerbornene that is derivatized with an ester functionality, and the first report of polymerization of DCNBE. 2 > W(CHtBu)(NAr)(OtBu) 2 …”

“…The first one by Grubbs [11 is based upon a titanacyclobutane complex in which the rate-limiting step consists of opening of the TiC 3 ring. A tantallacyclobutane complex behaves in a related fashion [2]. Catalyst systems in which alkylidenes are the propagating species are of the type W(CHR)(OCH 2 tBu) 2 X 2 (X = e.g., halide) [3] and W(CHtBu)(NAr)(OtBu) 2 (Ar = 2,6-diisopropylphenyl) [4].…”

“…A tantallacyclobutane complex behaves in a related fashion [2]. Catalyst systems in which alkylidenes are the propagating species are of the type W(CHR)(OCH 2 tBu) 2 X 2 (X = e.g., halide) [3] and W(CHtBu)(NAr)(OtBu) 2 (Ar = 2,6-diisopropylphenyl) [4]. I will discuss some recent developments and applications of chemistry involving M(C-IBu)(NAr)(OtBu) 2 complexes (M = Mo or W).…”