Unsaturated nanodiamonds : synthesis and functionalization of coupled diamondoids as a direct route to nanometer-sized building blocks

Abstract

Nanosciences are currently targeting new materials where carbon-based structures (nanotubes, fullerenes, graphenes and nanodiamonds) are among the most promising ones. The sizes of carbon nanostructure building blocks are now approaching the 1 5 nm scale that is already at the borderline between nanoparticles and single molecules. The wide range of electronic properties in combination with high chemical stability makes diamond potentially most useful material for nanoelectronics and optics, as well as other fields of material sciences.The ability of diamondoids to participate in electron transfer and self-assembling on the surface or to act as good electron emitters due to stability of their radical cations on the metal surface, would make synthesis of such coupled sterically hindered alkenes as highly perspective research topic. In this work we show that this approach allows the preparation of geometrically welldefined nanodiamond particles of up to 2 nm in size from higher diamondoids starting from diamantane, which dimers are not known up to date.In the present doctoral thesis, a series of novel compounds containing diamondoidyl and homocubyl moieties and unsaturated spacers were prepared from respective cage ketones and characterized.Methods of synthesis for diamantanedione-3,8 and diamantanedione-3,10 were developed, as well as optimization of the synthesis of CS-trishomocubane-8-one through newly developed approaches. Also triamantanone-16 was separated from the mixture of oxidation products of triamantane.Two of reductive pairs for McMurry coupling were tested, namely titanium (III) chloride lithium in DME and titanium (IV) chloride zinc in THF. The second tested pair was found to be fully satisfying our needs in respect of simplicity, stability and reaction yields.A number of new unsaturated coupled cage compounds, namely anti- and syn-diamantylidenediamantanes, adamantylidenediamantane-3, adamantylidenetriamantane-8, di(adamantylidene-2)diamantane-3,10, as well as Ci-trans-CS-8-trishomocubylidene-CS-8-trishomocubane, were synthesized in presence of titanium (IV) chloride zinc, separated and characterized by analytical and computational methods. Individual stereoisomers of anti-, syn-diamantylidenediamantane and Ci-trans-CS-8-trishomocubylidene-CS-8-trishomocubane, were separated by fractional recrystallization from hexane. Alternatively the cross-coupled diamondoids separation on silica gel impregnated by silver nitrate was successfully applied.In contrast to diamantanone, where two isomeric products were formed in equal amounts, reductive coupling of CS-trishomocubane-8-one gives a mixture of stereoisomers and it was confirmed that trans-products are favored.It was found by computational methods that terminal hydrogen atoms, neighboring to the carbon atoms of the double bond have destabilizing influence due to repulsive van der Waals interactions.Functionalization of adamantylideneadamantane, anti- and syn-diamantylidenediamantanes under phase transfer catalytic conditions was performed in order to create new building blocks for potential nanoelectronic devices and main components of the reaction mixture (4-bromo-anti- and 4-bromo-syn-diamantylidenediamantane as well as anti- and syn-diamantylidenediamantan-2-ol) were separated where tertiary carbon atom substituted products were formed.Study of the structure/property relationships in synthesized nanodiamond family members opens avenues for studying their potential for molecular electronics. One of the next logical steps in our research would be conversion of substituted sterically hindered alkenes into thiols and self-assembling their monolayers on the metal surfaces. Functionalization of ketones and further introduction them into McMurry reaction would allow us to synthesize disubstituted coupled diamondoids in order to create conductive linkers between two surfaces.