Immobilized aza-bis(oxazoline) copper catalysts on SAMs: Selectivity dependence on catalytic site embedding

Aza-bis(oxazoline) copper complexes have been immobilized onto alkanethiol self-assembled monolayers with three different surface orientations and tested in the benchmark cyclopropanation reaction of ethyl diazoacetate and styrene. The three surface orientations were the catalyst backbone above, below, and even with the tail groups of the self-assembled monolayer. Enantioselectivity of the product improved to >90% by immobilization of the catalyst at the monolayer surface and was significantly reduced when the catalyst was imbedded in the monolayer. The catalyst presented above the monolayer surface is a solution mimic in terms of selectivity. The catalytic chips proved to be recyclable. (C) 2009 Elsevier Inc. All rights reserved.