Novel Actinide-Transition Metal Heterobimetallic Complexes Featuring Metal-Metal Bonds

Abstract

Previous research established that complexes containing linkages between uranium or thorium and molybdenum could be prepared if the complexes were supported by a tris(phosphinoamide) ligand system. Attempts were made to replicate these results using the other Group VI metals, chromium and tungsten. A series of Group VI metal precursor complexes were prepared, however these did not show the desired reactivity with the phosphinoamine ligands or actinide tris(phosphinoamide) complexes, resulting only in the tetracarbonyl complexes [W(CO)4(PPh2NHMes)2] (146) and [W(CO)4(PiPr2NHMes)2] (150), which were concluded to be the most stable, thermodynamically favoured products. A photolytic synthesis route resulted in the preparation of the heterobimetallic complexes [(MesNPPh2)UCl(MesNPPh2)2Cr(CO)4] (157) and [(MesNPPh2)UCl(MesNPPh2)2W(CO)4] (159), however the distance between the metals was too large for an interaction to occur. The number of unique, unsupported linkages between actinides and transition metals has been expanded. The novel thorium-rhenium bond was prepared in the complex [Th(TrenDMBS)ReCp2] (162) through the reaction of the thorium TrenDMBS cyclometallate [Th(TrenDMBS,cyclo)]2 (120) with [ReCp2H] (160), and subsequent analysis found Th-Re to be longer, weaker and more ionic than the U-Re bond in the known uranium analogue. [Th(TrenDMBS)RuCp(CO)2] (170) was prepared using 120 and [RuCp(CO)2H] (169), and was found via IR spectroscopy to feature a very similar Ru-CO backbonding profile to the U-Ru analogue. During attempts to prepare complexes featuring U-W and Th-W bonds, the isocarbonyl complexes [Th(TrenDMBS)(THF)(OC)WCp¬(CO)2] (183) and [U(TrenDMBS)(THF)(OC){WCp(CO)2}] (184) were isolated; this was concluded to be due to poor orbital overlap between the metals rather than due to steric influences considering the wide apical pocket of the actinide centres. The homobimetallic complex [W2(CO)10][K-18-c-6(THF)2]2 (182) was prepared, providing the first known structure of the [W2(CO)10]2- moiety. The eclipsed geometry of the solid-state structure was investigated spectroscopically and computationally, revealing that the staggered conformation is energetically favoured and the structure of 182 is likely a result of crystal packing effects.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Stephen Liddle (Supervisor) & David Mills (Supervisor)