Multipoint anchoring of the [2.2.2.2]metacyclophane motif to a gold surface via self-assembly: Coordination chemistry of a cyclic tetraisocyanide revisited

摘要

A one-pot transformation of bis(2-isocyano-3-methylphenyl)ethane affords gram quantities of 8,16,24,32tetraisocyano[2.2.2.2]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)(mu(4)-eta(1):eta(1):eta(1):eta(1)-3) (5). The tetranuclear [M](4)(mu(4)-eta(1):eta(1):eta(1): eta(1)-3) motif featured in crystal log raphically characterized 5 may be present in several insoluble complexes of 3 previously described as mononuclear eta(4) species. A self-assembled monolayer of metacyclophane 3 is formed upon exposing a solution of 3 to the gold(l 11) 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 FIR 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 mu(4)-eta(1):eta(1):eta(1):eta(1) interaction of the molecule with the Au(1 11) surface is under 8 kcal/mol, a value that can be easily offset by formation of a gold-isocyanide bond. Two different mu(4)-eta(1):eta(1):eta(1):eta(1) coordination arrangements of 3 with respect to gold atoms on the (111) face of the fcc Au lattice are suggested.