Two-dimensional supramolecular chemistry with molecular Tinkertoys

Abstract

For some time now (1–5), we have worked on the development of a “molecular construction kit,” analogous to the children's Tinkertoy† construction set, which permits the assembly of complicated objects from a limited set of rods, connectors, and other simple building elements. The idea is to do civil engineering with individual molecular components ranging in size from a few to several dozen A. A somewhat related concept of “molecular Lego,” based on a different set of structural elements, was proposed (7) and developed (8) independently by Stoddard. Both belong to the wider category of “modular chemistry,” in which a small number of mid-sized rigid molecular structural elements are combined into complex structures (9). At the start of our project, a very limited selection of types and lengths of straight terminally functionalized molecular rods and connectors was available. We synthesized additional ones based on the oligomers of [1.1.1]propellane ([ n ]staffanes) (10) and on oligomeric 10-vertex and 12-vertex p -carboranes (11). Other laboratories produced polycubyls (12), oligomers of [2.2.2]propellane (13), additional oligomers of 12-vector carboranes (14), and many rods constructed from the more common p -phenylene and acetylene subunits. A combination of several types of such structural elements permits one to achieve an accurate match to a desired rod length. A recent comprehensive review (15) makes it abundantly clear that after a decade of effort, considerable flexibility exists in the choice of molecular rod lengths and properties. After some initial experiments with point (4) connectors, which function by forming bonds from a central atom to the termini of several rods, we turned our attention to star (4) connectors, which function by forming a bond between each of several star arm termini to the terminus of a rod or of another star arm. Various suitable star connectors such …