Polymer brushes (PBs) have been used as supports for the immobilization of palladium complexes on silicon surfaces. The polymers were grown by surface-initiated atom-transfer radical polymerization (SI-ATRP) and postdecorated with dipyridylamine (dpa) ligands. The pendant dpa units were in turn complexed with [Pd(OAc)(2)] to afford hybrid catalytic surfaces. A series of catalytic samples of various thicknesses (ca. 20-160 nm) and associated palladium loadings (ca. 10-45 nmol  cm(-2)) were obtained by adjusting the SI-ATRP reaction time and characterized by ellipsometry, X-ray reflectivity, X-ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS). ICP-MS revealed a near-linear relationship between thickness of the polymer brush and palladium content, which confirmed the robustness of the preparation and postmodification sequence presented herein, rendering possible the creation of functional architectures with predefined catalytic potential. The activities of the catalytic PBs were determined by systematically exploring a full range of substrate-to-catalyst ratios in a model palladium(0)-catalyzed reaction. Quantitative transformations were observed for loadings down to 0.03 mol % and a maximum turnover number (TON) of around 3500 was established for the system. Comparison of the catalytic performances evidenced a singular influence of the thickness on conversions and TONs. The limited recyclability of the hairy catalysts has been attributed to palladium leaching.

Catalytic surfaces have been prepared by complexation of palladium on self-assembled terpyridine monolayers on silicon. A reaction-based fluorogenic probe was developed to allow facile visualization of the catalytic potential of the surface. Superior activity of the immobilized catalyst compared with the homogeneous control reactions is demonstrated.

The first trans-selective [3 + 2]-cycloaddition of a new type of donor-acceptor cyclopropane with aldehydes is presented. 2,2-Disubstituted cyclopropanes, bearing an alkyne moiety as the sole donor entity, were transformed to highly substituted tetrahydrofurans in the presence of a catalytic amount of Ca(NTf2)2/Bu4NPF6. The protocol allows for an easy access to tetrahydrofurans bearing a versatile alkyne substituent at the quarternary 2-position under very mild reaction conditions.

The Alkynyl Moiety as a Donor for Donor-Acceptor Cyclopropanes. -A calcium-catalyzed [3 + 2]-cycloaddition of aldehydes with a new type of quaternary donor site cyclopropanes, bearing an alkyne moiety as the sole donor entity, is presented. The method provides an unprecedented general access to highly substituted tetrahydrofurans bearing an alkyne moiety with excellent diastereoselectivities. -(HAUBENREISSER, S.; HENSENNE, P.; SCHROEDER, S.; NIGGEMANN*, M.; Org. Lett. 15 (2013) 9, 2262-2265, http://dx.