Michael Rudolf Buchmeiser

The synthesis of a novel, air- and moistures table dicationic palladium (II) complex, Pd(CH₃CON-(2-pyridyl)₂)(CH₃CN)²⁺ ₂(PF₆ ⁻)₂ (1) is described. 1 crystallizes in the mononoclinic space group C2/m, a = 2391.11 (4), b = 1063.34(5), c = 1137.59(6) pm, α = 90°, β = 105.026(2)°, γ = 90°, Z = 4. Its use in the ring-opening polymerization (ROP) of cyclohexene oxide in comparison to the parent catalyst, dichloropalladium di(pyrid-2-yl)amide (2) was investigated. In contrast to 2, 1 shows excellent reactivity in the ROP of cyclohexene oxide, allowing a class-II living polymerization, however, it fails to polymerize propylene oxide.

The synthesis of novel ruthenium‐based metathesis catalysts containing the saturated 1,3‐bis(2,4,6‐trimethylphenyl)‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene ligand, that is, [RuCl₂(NHC){CH‐2‐(2‐PrO)‐5‐NO₂‐C₆H₃}] (1) and [Ru(CF₃COO)₂(NHC){CH‐2‐(2‐PrO)‐5‐NO₂‐C₆H₃}] (2) (NHC=1,3‐bis(2,4,6‐trimethylphenyl)‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene) is described. Both catalysts are highly active in ring‐closing metathesis (RCM) and ring‐opening cross‐metathesis (ROCM). Compound 1 shows moderate activity in enyne metathesis. Compound 2 is not applicable to enyne metathesis since it shows high activity in the cyclopolymerization of diethyl dipropargylmalonate (DEDPM). Poly(DEDPM) prepared by the action of 2 consists of 95 % five‐membered rings, that is, poly(cyclopent‐1‐enevinylene)s, and 5 % of six‐membered rings, that is, poly(cyclohex‐1‐ene‐3‐methylidene)s. The polymerization proceeds in a nonliving manner and results in polyenes with broad polydispersities (1.9≦PDI≦2.3). Supported analogues of 2 were prepared by immobilization on hydroxymethyl‐Merrifield resin and a monolithic support derived from ring‐opening‐metathesis polymerization (ROMP). Catalyst loadings of 1 and 2.5 %, respectively, were obtained. Both supported versions of 2 showed excellent reactivity. With 0.24–2 % of the supported catalysts, yields in RCM and ROCM were in the range of 76–100 %. Leaching of ruthenium was low and resulted in Ru contaminations of the products of less than 0.000014 % (0.14 ppm).

The state of the art and recent developments in the synthesis of supported, well-defined metathesis catalysts are reviewed. In this context, their synthesis, selected properties and application to both polymer and organic chemistry are summarised. Special consideration will be given to aspects of activity [discussed in terms of turnover numbers (TONs) and turn over frequencies (TOFs)], regioselectivity and enantioselectivity as well as stability. The general applicability of these supported catalysts to either high-throughput technology or to the manufacture of continuous flow systems is discussed.