Synthesis and Structural Characterization of Cationic Rhenium(V) and Technetium(V) Dioxo Complexes Containing Four N-Heterocyclic Carbene Ligands

Abstract

Cationic dioxorhenium and dioxotechnetium complexes of the composition [MO(2)(L(1))(4)](+) (L(1) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) have been prepared from various starting materials and studied spectroscopically and by X-ray crystallography. The metal-carbon distances range from 2.216(4) to 2.232(4) A indicating mainly sigma-bonding.

Synthesis and Structural Characterization of Novel Oxorhenium(V) Complexes Containing N‐Heterocyclic Carbenes

“…Similar values have been reported for the ReϭO vibration in [ReO 2 (1,3- 6 ], [9] and in [ReO 2 (dppe) 2 ][I]. [10] (1)…”

“…[9] Compound 1 is soluble in aromatic hydrocarbons such as benzene or toluene, while compound 2 is insoluble in toluene, dichloromethane, tetrahydrofuran or diethyl ether, and slightly soluble in acetonitrile.…”

Dioxomolybdenum(VI) complexes containing N-heterocyclic carbenes

“…This is in agreement with the results recently published by Abram and co-workers, who observed that the number of NHCs introduced in a series of oxorhenium complexes depends on the electron-donating nature of the carbene, the more electron-donating the carbene, the higher the number of ligands [13]. In this sense, 4,5-dimethyl substituted NHCs always provide complexes with general formula [ReOCl-(NHC) 4 ] 2+ [4,15] (complexes with less than four carbenes could not be obtained), while non-substituted and triazolylidene NHCs provide ReOCl 3 (NHC) 2 [5] and [ReO(OMe)-Cl 2 (NHC)(PPh 3 )], respectively.…”

“…Although most of the NHC-metal complexes reported to date refer to late transition metals in low oxidation states, a few examples concerning the coordination of these ligands to high oxidation state species have been reported [3][4][5]. Regarding the studies of N-heterocyclic carbene complexes of molybdenum, these are scarce, and most of them concern carbonyl molybdenum (0) complexes [6].…”

Technetium and rhenium: coordination chemistry and nuclear medical applications

“…Such ligands have been used in the coordination chemistry of many transition metals for quite a long time, but the first well-characterized rhenium and technetium compounds were not published until 2003. 36 This is surprising, particularly in the light that some of the compounds possess remarkable stability, which is mainly determined by the high sterical demand of the ligands systems, which protect the metal centers and prevent further ligand exchange and/or hydrolysis. The influence of ligand substituents has been carefully studied for oxorhenium(V) complexes with a series of 1,3-dialkyl-4,5-dimethylimidazol-2-ylidenes.…”