Multipoint Anchoring of the [18.104.22.168]Metacyclophane Motif to a Gold Surface via Self-Assembly: Coordination Chemistry of a Cyclic Tetraisocyanide Revisited
2008-04-21T00:00:00Z (GMT) by
A one-pot transformation of bis(2-isocyano-3-methylphenyl)ethane affords gram quantities of 8,16,24,32-tetraisocyano[22.214.171.124]metacyclophane (3). The solid state structure of 3 is remarkably close to the lowest energy conformation found on the potential energy landscape for 3 by DFT. In solution, the structure of metacyclophane 3 is mobile but can be locked in a rectangular gauche−anti−gauche−anti conformation by coordination of the isocyanide substituents to the [W(CO)5] units to give [M]4(μ4-η1:η1:η1:η1-3) (5). The tetranuclear [M]4(μ4-η1:η1:η1:η1-3) motif featured in crystallographically characterized 5 may be present in several insoluble complexes of 3 previously described as mononuclear η4 species. A self-assembled monolayer of metacyclophane 3 is formed upon exposing a solution of 3 to the gold(111) surface with no precautions to exclude air or light. The monolayer nature of the film was confirmed by optical ellipsometry. The isocyanide stretching band for 3 shifts from 2119 cm−1 in solution to 2175 cm−1 upon chemisorption to metallic gold. The FTIR spectrum of the film indicates interaction of 3 with the gold surface via all four of its isocyanide anchors. No gold-facilitated oxidation of the −NC junctions was detected under ambient conditions. The energy cost associated with accessing the conformations of 3 suitable for μ4-η1:η1:η1:η1 interaction of the molecule with the Au(111) surface is under 8 kcal/mol, a value that can be easily offset by formation of a gold−isocyanide bond. Two different μ4-η1:η1:η1:η1 coordination arrangements of 3 with respect to gold atoms on the (111) face of the fcc Au lattice are suggested.