Group 4 Dimethylsilylenebisamido Complexes Bearing the 6‐[2‐(Diethylboryl)phenyl]pyrid‐2‐yl Motif: Synthesis and Use in Tandem Ring‐Opening Metathesis/Vinyl‐Insertion Copolymerization of Cyclic Olefins with Ethylene

Two novel Zr IV ‐ and Hf IV ‐based bisamido complexes bearing the 6‐[2‐(diethylboryl)phenyl]pyrid‐2‐yl motif, that is, [ZrCl 2 {Me 2 Si(DbppN) 2 }(thf)] ( 9 ) and [HfCl 2 {Me 2 Si(DbppN) 2 }(thf) 2 ] ( 10 ) (DbppN=6‐[2‐(diethylboryl)phenyl]pyridine‐2‐amido) have been prepared. Their reactivities have been compared with that of a model precatalyst that does not bear the aminoborane motif. Upon activation with methylalumoxane, precatalysts 9 and 10 are active in the homopolymerization of ethylene (E) yielding high‐density polyethylene (HDPE). In the copolymerization of E with cyclopentene (CPE), for example by the action of 9 , the presence of CPE resulted in a dramatic increase in the polymerization activity of E, while CPE incorporation remained close to or at zero. In the vinyl‐insertion copolymerization of norborn‐2‐ene (NBE) with E by the action of 9 , statistical cyclic olefin copolymers of these two monomers were obtained. At higher NBE concentrations, however, 9 gave rise to reversible ring‐opening metathesis (ROMP)/vinyl‐insertion polymerization (VIP) of NBE with E, resulting in the formation of multi‐block copolymers of the general formula poly(NBE) ROMP ‐ co ‐poly(NBE) VIP ‐ co ‐poly(E). This particular feature of precatalyst 9 , that is, the ability to induce a reversible α‐H elimination/α‐H addition reaction, is attributed to the unique role of the 6‐[2‐(diethylboryl)phenyl]pyrid‐2‐yl ligand. Accordingly, a model precatalyst lacking this ligand does not have the ability to induce α‐H elimination/α‐H addition reactions. The different 11 B NMR shifts of various diethylborylphenylpyrid‐2‐ylamines and ‐amides permit a ranking of the strengths of the BN bonds in these compounds. This strength of the BN bond is correlated with the propensity of 9 /MAO to produce poly(NBE) ROMP ‐ co ‐poly(NBE) VIP ‐ co ‐poly(E) at different temperatures.