Gold(iii) complexes of 2-tert-butyl-1,10-phenanthroline and of N-(8-quinolinyl)amides: syntheses and structures.

A series of gold(iii) complexes was synthesized by mixing aqueous solutions of [AuCl4]- with organic solutions of the appropriate ligand (2-t-butyl-1,10-phenanthroline ( t-BuPhen), 2,2-dimethyl-N-8-quinolinylpropanamide ( t-BuAQ), or 2-ethyl-N-8-quinolinylbutanamide (3-PentAQ)). This resulted in the respective complexes [( t-BuPhen)AuCl3], [( t-BuAQ)AuCl2], and [(3-PentAQ)AuCl2]. The formation of the latter two complexes involved deprotonation of the amide; however, the inclusion of NaHCO3 (a potential base) in the reaction mixture improved the yields of [( t-BuPhen)AuCl3] and [( t-BuAQ)AuCl2] but not of [(3-PentAQ)AuCl2]. In assessing the crystal structure of [( t-BuPhen)AuCl3], the three chlorides and the less sterically hindered nitrogen of the phenanthroline make a square plane around the gold(iii) center, while the more sterically hindered nitrogen of the phenanthroline is positioned to interact with the gold(iii) in an apical position. Any interaction between gold(iii) and the apical nitrogen is very weak based on their relatively large separation and the lack of much distortion in the square plane. The complexes [( t-BuAQ)AuCl2] and [(3-PentAQ)AuCl2] are both square planar with the organic ligand bound in a bidentate manner through imine and amido donors. In comparing the structures of all these complexes, it is apparent that bond lengths, angles, and degree of bonding are strongly impacted by the sterics associated with the presence of a t-butyl group near the gold(iii) center.