Article pubs.acs.org/IC
Cite This: Inorg. Chem. 2018, 57, 319−325
Expanding the Chemistry of Rhenium Metal−Metal Bonded Fluoro Complexes: Facile Preparation and Characterization of Paddlewheel Complexes Samundeeswari Mariappan Balasekaran,*,† Alfred P. Sattelberger,†,‡ Adelheid Hagenbach,§ and Frederic Poineau† †
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, Las Vegas, Nevada 89154, United States Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States § Department of Chemistry and Biochemistry, Freie University Berlin, Berlin 14195, Germany ‡
S Supporting Information *
ABSTRACT: Quadruply bonded rhenium(III) dimers with the stoichiometry Re2L4F2 (1, L = hexahydro-2H-pyrimido[1,2a]pyrimidinate (hpp−); 2, L = diphenyl formamidinate (dpf−)) were prepared from the solid-state melt reactions (SSMRs) between (NH4)2[Re2F8]·2H2O and HL. Those compounds were characterized in the solid state by single-crystal X-ray diffraction and in solution by UV−visible spectroscopy and cyclic voltammetry. The compound [Re2(hpp)4F2]PF6 (3) was prepared from the one-electron oxidation of Re2(hpp)4F2 with [Cp2Fe]PF6. Compounds 1−3 are isostructural with the corresponding chloro derivatives. In solution, compound 1 undergoes two one-electron oxidations. Comparison with its higher halogen homologues reveals that Re2(hpp)4F2 (1) is more easily oxidized than its chloro and bromo analogues.
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INTRODUCTION The metal−metal bond chemistry of group 6−8 transitionmetal complexes containing fluoride ligands is poorly developed, and only six complexes have been reported: Mo 2 F 6 (py) 4 , 1 Mo 2 F 4 (PMe 3 ) 4 , 2 (n-Bu 4 N) 2 [Re 2 F 8 ], 3 Re2(hpp)4F2, [Re2(hpp)4F](TFPB)2,4 and Ru2(ap)4F.5 One reason is the lack of availability of metal−metal bonded fluoro precursors which can be easily obtained in high yield. The original preparation of (n-Bu4N)2[Re2F8] is not reproducible,6 while [Mo2F8]4− and [Tc2F8]2− are still unknown. The known Re2(hpp)4F2 and [Re2(hpp)4F](TFPB)2 complexes were both derived from Re2(hpp)4Cl2; their syntheses are complicated, and the complexes were not characterized by spectroscopic techniques.4 A study of the fluoride chemistry of metal−metal bonded complexes will permit a better understanding of the effect of the halogen on structure, bonding, and physical properties. Furthermore, metal−metal bonded fluoro complexes have the potential to be used as fluoride transfer agents in synthetic chemistry. In this context, we revisited the fluoride chemistry of multiply metal−metal bonded systems and started with Re. Recently, we developed a high-yield, reproducible method for the preparation of (NH4)2[Re2F8]·2H2O and K2[Re2F8].6 These salts were prepared from a solid-state melt reaction (SSMR) between (n-Bu4N)2[Re2Cl8] and MHF2 (M = NH4, K). The salts are stable up to 400 °C, insoluble in organic © 2017 American Chemical Society
solvents, and hydrolyze slowly in aqueous solution. The insolubilities of these salts limit their use as precursors in solution reactions. A survey of the literature indicates that a number of metal− metal bonded Re chloro complexes can be obtained from the SSMR between (n-Bu4N)2[Re2Cl8] or Re2(OOCCH3)4Cl2 and protonated ligands.7−10 The protonated ligands used in those reactions have relatively low melting points (
