Polyisobutylene Phase-Anchored Ruthenium Complexes
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Summary: The use of polymers in general as ligands or sequestrants for metals has often focused on the use of cross-linked polymers or readily available soluble polar polymers like poly(ethylene glycol). Our work shows that functional nonpolar polymers like polyisobutylene are viable alternatives and can be readily used as phase selectively soluble ligands or sequestrants for commonly used transition metal catalysts. This is illustrated in this work by the synthesis of ligands and sequestrants for ruthenium catalysts widely used in ring-closing-metathesis, cross-metathesis, and ring-opening metathesis polymerization. We show that a polyisobutylene terminally functionalized with a vinyl group can be converted by electrophilic aromatic substitution into species that phase immobilize a benzylidene Ru catalyst precursor, an N-heterocyclic carbene ligand, or that can sequester a Ru complex by conversion of a reactive Ru alkylidene into a phase-immobilized Fischer carbene complex. In all these cases, the Ru complexes that are formed are selectively soluble in a nonpolar or weakly polar phase of a liquid/liquid biphasic system - a system that can be efficiently formed either thermomorphically, by perturbation of an initially miscible solvent mixture, or by extraction. Copyright 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
