Toposelective synthesis of a triply-bridged molecular gyroscope and polymorphogenic behavior of alkylated rotors

In the field of molecular machines, inspiration for molecular design is drawn from macroscopic rotors, such as gears, propellers and turnstiles, in attempts to develop molecules capable of performing functions similar those of these macroscopic objects. The ultimate goal is to develop a molecular assembly, which responds collectively to an external stimulus, thus performing functions analogous to those of their macroscopic counterparts. Recognizing that macroscopic machines are composed of assemblies of gears, pivots, and ratchets arranged in a dose-packed manner, with each component predetermined to perform a specific task, we envision the solid state as the perfect medium for a close-packed molecular assembly in which individual units respond collectively to an external stimulus. Along these lines, chemists have recognized the importance of rotary components in macroscopic objects, and have designed molecules which emulate the shape and rotary dynamics of gears, ratchets, and turnstiles, to name a few.;A major challenge in this endeavor is the successful design of molecules, which experience programmed free rotation in the solid state. With this in mind, we have designed molecules similar in shape and function to macroscopic gyroscopes and compasses in attempts to design programmed rotation in the solid state.;This thesis describes the synthesis and polymorphogenic behavior of polyalkylated molecular gyroscopes and the synthesis of bridged molecular gyroscopes as an attempt to design molecular free-rotors in the solid state. Chapter 1 introduces the concept of molecular machinery, emphasizing the need for rotary units within a molecule, the challenges intrinsic to the development of rotating units within a molecule, as well as elegant proofs of principle towards the design of molecular machines. The work described in Chapter 1 proves the potential for organic compounds to behave in a manner similar to macroscopic objects, and illustrates the need for a fully protected unit "programmed" to rotate, giving a brief description of our group's attempts at the development of crystalline compounds modeled after macroscopic gyroscopes and compasses. Chapter 2 describes the synthesis of a hexa-meta-methoxy molecular gyroscope as a precursor to a fully bridged structure, as well as the detailed study of the polymorphogenic behavior of this gyroscope, for which 7 polymorphs and 6 phase transitions that relate them were observed. Chapter 3 describes the synthesis and properties of alkylated gyroscopes with varying alkyl chain lengths and describes attempts to study the effect of increasing chain length on the solid-state properties of these compounds. The synthesis of various alkyl chain-bridged molecular gyroscopes is described in Chapter 4, emphasizing the preferred meridional/zonal bridged products, highlighting the need for asymmetric precursors to the formation of meridional-bridged molecular gyroscopes. Chapters 2 and 4 have been previously published in peer-reviewed journals, Cryst. Growth and Des. 2006, 6, 866-873, and Org. Lett. 2007, 9, 3559-3561, respectively.