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 B-N bonds in these compounds. This strength of the B-N bond is correlated with the propensity of 9/MAO to produce poly(NBE)(ROMP)-co-poly(NBE)(VIP)-co-poly(E) at different temperatures.

Homopolymerization of ethylene, 1-hexene, styrene and copolymerization of styrene with 1,3-cyclohexadiene using (η5-tetramethylcyclopentadienyl)dimethylsilyl(N-Ar')amido-TiCl2/MAO (Ar'=6-(2-(diethylboryl)phenyl)pyrid-2-yl, biphen-3-yl).

The propensity of a half-sandwich (η5-tetramethylcyclopentadienyl) dimethylsilylamido Ti(IV)-based catalyst bearing an auxiliary diethylboryl-protected pyridyl moiety (Ti-8), activated by methylaluminoxane (MAO) to homopolymerize α-olefins such as ethylene, 1-hexene and styrene as well as to copolymerize styrene with 1,3-cyclo-hexadiene is described. The reactivity of Ti-8 was investigated in comparison to a 6-(2-(diethylboryl)phenyl)pyrid-2-yl-free analogue (Ti-3).

Meridional bicyclometalation with iron: a novel way of forming dianionic [C,N,C]-ligands.

Bicyclometalation of aromatic substrates containing imine anchoring groups is achieved with a dimethyliron complex at -70 degrees C; azadiene systems undergo a regiospecific activation of 1,4-CH/N interchanged C-H bonds which may be aromatic or vinylic.

First regioselective cyclometalation reactions of cobalt in arylketones: C-H versus C-F activation.

Phenyl ketones react smoothly under mild conditions with low valent cobalt(i) adducts to form new and stable five-membered cobaltacycles via C-H and C-F activation.

Four- and five-membered cobaltacycles by regioselective cyclometallation of benzyl sulfide derivatives via Co(v) intermediates.

C-H activation through the coordination of a benzyl sulfide anchoring group with a C-S bond cleavage at a Co(v) center constitutes a regiospecific access to four- and five-membered metallacycles under mild conditions.