Carbonyl fluorides of rhenium and other transition metals.
thesisposted on 19.11.2015, 08:48 by Donald Malcolm. Bruce
Rhenium carbonyl reacts with three moles of XeF2 in Genetron 113 to produce the novel carbonyl fluoride-penta-fluoride complex Re(CO)5F.ReF5 This is decomposed to ReF6 by three further moles of XeF2. The use of proportions intermediate between these gives only mixtures of Re2(CO)10 and Re(CO)5F.ReF5, or Re(CO)5F.ReF5 and ReF6. When HF is used as the solvent, a similar process is indicated, but partial hydrolysis of HF solutions of HF solutions of Re(CO)5F.ReF5 frequently occurred, to give (Re(CO)6)+ (ReOF5)-. No conclusive evidence for Re(CO)5F was found. Re2(CO)10 also forms Re(CO)5F.ReF5 with two moles of ReF6, in HF solution, but with four moles, the new, ionic 1:2 complex (Re (CO)6)+ (Re2F11)- is produced. Re (CO)5F.TaF5 and (Re(CO)6)+(Sb2F11)- were produced by exchange reactions of Re(CO)5F.ReF5 with TaF5 and SbF5 respectively. The oxidation of [(n5 -C5H5) Fe (CO)2]2 with AgF in acetone produced 5 evidence for a new fluoride, (n5-C5H5)Fe(CO)2F. It was surmised that the maintenance of stable (Re(CO)5F) or (Re(CO)6)+ units governs the course of these fluorinations, and that, in general, carbonyl fluorides will only exist with certain, specific, stable units. Analogous units were proposed for other carbonyl fluoride systems, and a general progression for metal carbonyl fluorinations was established, through simple carbonyl fluoride to carbonyl fluoride-pentafluoride complex(es), and finally binary fluoride. The carbonyl fluoride-pentafluoride complex plays a fundamental role in these systems which has no parallel in other organometallic halides, although related complexes are known in a few cases. Full X-ray crystal structures of Re(CO)5F.ReF5 and ?-(Re (CO)6)+ (Re2F11)- were performed, and a partial investigation made of (Re (CO)6)+ (ReOF5)-. Re (CO)5F.ReF5 is an essentially covalent, fluorine-bridged complex whose bond lengths are of value for comparing other fluorine-bridged interactions. Polymorphism is found in (Re(CO)6)+(Re2F11)-. The ?-phase has an ionic lattice, with a centrosymmetric anion. Anion-cation interactions in other structures were discussed.