Monolayers as Models for Supported Catalysts:  Zirconium Phosphonate Films Containing Manganese(III) Porphyrins

Abstract

Organized monolayer films of a manganese tetraphenylporphyrin have been prepared and used as supported oxidation catalysts. Manganese 5,10,15,20-tetrakis(tetrafluorophenyl-4'-octadecyloxyphosphonic acid) porphyrin (1) has been immobilized as a monolayer film by a combination of Langmuir-Blodgett (LB) and self-assembled monolayer techniques that use zirconium phosphonate linkages to bind the molecule to the surface. Analysis by FTIR, XPS, UV-vis and polarized optical spectroscopy show that the films consist of noninteracting molecules effectively anchored and oriented nearly parallel to the surface. The monolayer films are stable to the solvent and temperature conditions needed to explore organic oxidations. The activity of films of 1 toward the epoxidation of cyclooctene using iodosylbenzene as the oxidant was compared to that of Manganese 5,10,15,20-tetrakis(pentafluorophenyl) porphyrin (2) and 1 under equivalent homogeneous conditions. The immobilized porphyrin 1 shows an enhanced activity relative to either homogeneous reaction. The main difference between 1 and 2 is the four alkyl phosphonate arms in 1 designed to incorporate the porphyrin within the films. The increased activity of immobilized 1 is a combination of the porphyrin structure, which prohibits the formation of mu-oxo dimers even in solution, and a change in conformation when anchored to the surface. The study demonstrates that careful monolayer studies can provide useful models for the design and study of supported molecular catalyst systems.

Metal Phosphonates Applied to Biotechnologies: A Novel Approach to Oligonucleotide Microarrays

“…[41] Our groups have used this chemistry to form monolayer films of organophosphonates with organic groups ranging from simple alkanes [41] to azobenzene, [45] tetrathiafulvalene, [55] phenoxy and biphenoxy groups, [43] and porphyrins. [46] The zirconium phosphonate-modified surfaces can be prepared in different ways, but often involve binding of Zr 4 + ions to phosphorylated groups deposited onto silica [50,51,54,[56][57][58][59][60][61] or gold ( Figure 6). [52,54,56,57,62] Our experience is that exceptionally smooth and uniform films can be gener- Chem.…”

“…2005, 11, 1980 -1988 www.chemeurj.org 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ated on hydrophobic supports by using Langmuir-Blodgett (LB) methods. [41][42][43][44][45][46] The LB process begins with an octadecylphosphonic acid (ODPA) Langmuir monolayer that is deposited onto the hydrophobic solid support in such a way that the hydrophilic acid group (PO 3 H 2 ) is directed away from the support (Figure 7). [41,42] The substrate is then removed from the LB trough and exposed to a solution of Zr 4 + ions that bind to give a monolayer of the zirconated octadecylphosphonic acid (ODPA-Zr).…”

Increased Catalytic Activity of Surface‐Immobilized Palladium Complexes in the Fluorogenic Deprotection of an Alloc‐Derivatized Coumarin

“…Some evidence have been reported on the impact of ordering and orientation of functionalized Langmuir-Blodgett films on catalysis in terms of activity and selectivity. [13][14][15] The stability of cobalt-porphyrin catalysts was significantly improved following immobilization on gold surfaces and their activity in the catalytic oxidation of hydroquinone can possibly be related to the arrangement of the catalyst on the molecular level.[16] Impressively, a palladium surface covered with alkanethiol SAMs showed enhanced regioselectivity towards the reduction of an unsaturated epoxide from 11 to 94 %, despite a loss of 40 % activity compared with the uncoated surface. [17] This effect was attributed to selective binding of the alkene moiety on the coated Pd surface at the expense of the epoxide ring.…”

Geometry of Molecular Motions in Dye Monolayers at Various Coverages

“…Molecular monolayers have applications in a broad range of research fields from optoelectronics, [1][2][3][4][5] to catalysis [6][7][8] to medicine. [9][10][11][12] They are used in many technologies to tune the fundamental properties of pre-existing materials.…”