In my thesis, scientific articles and reviews about direct C–H activation via transition-metal-catalysed activation of C–H bonds were examined, with an emphasis on ruthenium catalysis. Firstly, synthesis and characteristics of symmetrical hexaarylbenzenes were discussed. In addition, a possible synthetic pathway for asymmetric hexaarilbenzenes was discussed. Next, arylation mechanism of C–H bond via Ru(II) catalysis was described. Ligands containing nitrogen-coordinating groups were examined along with the complexes that resulted from their coordination to ruthenium catalysts. At the end of my thesis, I planned out the theoretical laboratory work plan that would be done, if it weren’t for the COVID-19 pandemic.