Reaction between DADZnR2 and either B(C6F5)3 or ZnR2 and [DADH][B(C6F5)4] affords three-coordinate alkyl and amide zinc cations which are active for the ring opening polymerisation of epoxides and e-caprolactone [DAD = (MeC=NC6H3Pri2-2,6)2]

The olefin polymerisation activity of metallocene catalysts strongly depends on the counteranion provided by the activator system. The relative activities of a number of new diborate anions [Z(BAr3)2]- have been quantified (Z = CN, NH2, N(CN)2; Ar = C6F5 or o-C6F4C6F5). The kinetic parameters for the initiation, propagation and termination steps of propene polymerisations catalysed by (SBI)ZrCl2 have been determined using quenched-flow kinetic and batch techniques [SBI = rac-Me2Si(1-Ind)2]. Comparison of two activator systems, (i) CPh3[B(C6F5)4] / triisobutylaluminium (TIBA) and (ii) methylaluminoxane (MAO) shows, surprisingly, that the concentration of species actively involved in chain growth at any one time is comparable for both systems, although the MAO-activated catalyst is about 20 times less active than the borate system. It is concluded that the counteranion remains sufficiently strongly bound to the metal centre throughout the chain growth sequence to modulate the energetics of monomer insertion. A model suggesting that the monomer binding follows an associative interchange (Ia) mechanism is proposed

The versatile reactivity of B(C6F5)3 in alkene polymerization reactions is summarized. Adduct formation with basic anions such as CN– and NH2– gives extremely weakly co- ordinating diborates, which are the basis of some of the most active polymerization catalysts known to date. By contrast, the reaction of B(C6F5)3 with zirconium half-sandwich complexes leads to extensive C6F5 transfer, including the surprising formation of borole-bridged triple decker complexes. Main group alkyls undergo such C6F5 exchange reactions very readily unless donor ligands are present. Borate salts of new three-coordinate zinc alkyl cations proved to be highly effective catalysts for the ring-opening polymerization of epoxides and lactones.

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Summary: The influence of perfluoroborate anions on catalyst activity and stereospecificity has been determined for propene polymerisations at 20–60 °C. For C2‐symmetric ansa‐zirconocenes, activities were strongly ligand‐dependent, with systems activated by TIBA/Ph3C+X−, where TIBA = AliBu3, X = {Z[B(C6F5)3]2}, and Z = CN or NH2, giving significantly higher activities than methylaluminoxane under comparable conditions. For high‐activity catalysts at 60 °C, {H2N[B(C6F5)3]2}− proved superior to {CN[B(C6F5)3]2}−, presumably due to the higher thermal stability of the amidoborate. The influence of counteranions on PP stereospecificity for these catalysts is negligible. On the other hand, the conformationally flexible catalyst, (2‐PhInd)2ZrCl2/TIBA/Ph3C+X−, shows not only a strong anion dependence of its activity, but also significant variation in poly(propylene) isotacticity, mainly due to the formation of small fractions of highly isotactic (mmmm > 70%) PP. This effect was particularly pronounced for {CN[B(C6F5)3]2}− and the dianion, {Ni[CNB(C6F5)3]4}2−.Effect of {CN[B(C6F5)3]2}− and {H2N[B(C6F5)3]2}− on propene polymerisation productivities for zirconocenes 1–8 at 20 °C.imageEffect of {CN[B(C6F5)3]2}− and {H2N[B(C6F5)3]2}− on propene polymerisation productivities for zirconocenes 1–8 at 20 °C.