Nitridotechnetium(V) Complexes with N-Heterocyclic Carbenes and Unexpected (OSiMe₂OSiMe₂O)^2- Coligands

Reactions of [TcNCl2(PPhR2)3] complexes (R = Me, Et) with 1,3-diethyl-4,5-dimethylimidazol-2-ylidene yield air-stable nitridotechnetium(V) complexes with N-heterocyclic carbenes with up to four of these bulky ligands and, depending on the reaction conditions applied, 1,1,3,3-tetramethyldisiloxane-1,3-diolato coligands which were abstracted from silicon-based grease

Nitridotechnetium(V) Complexes with N-Heterocyclic Carbenes and Unexpected (OSiMe₂OSiMe₂O)^2- Coligands

Reactions of [TcNCl2(PPhR2)3] complexes (R = Me, Et) with 1,3-diethyl-4,5-dimethylimidazol-2-ylidene yield air-stable nitridotechnetium(V) complexes with N-heterocyclic carbenes with up to four of these bulky ligands and, depending on the reaction conditions applied, 1,1,3,3-tetramethyldisiloxane-1,3-diolato coligands which were abstracted from silicon-based grease

Rhenium(V) Complexes with Pentadentate P,N,O Ligands

Novel rhenium(V) complexes were isolated from reactions of [NBu4][ReOCl4] with the potentially pentadentate Schiff base PhP{C6H4-2-(HCN(C6H4-2-OH))}2, H2L1, and the corresponding amine PhP{C6H4-2-(CH2−NH(C6H4-2-OH))}2, H4L2. While the Schiff base undergoes partial hydrolytic decomposition and a redox reaction, the amine remains intact and acts as a pentadentate ligand, which encapsulates the metal atom of the {ReVO}3+ core or stabilizes a {ReVCl}4+ center by the formation of an imido-type ligand system

Rhenium(V) Complexes with Pentadentate P,N,O Ligands

Novel rhenium(V) complexes were isolated from reactions of [NBu4][ReOCl4] with the potentially pentadentate Schiff base PhP{C6H4-2-(HCN(C6H4-2-OH))}2, H2L1, and the corresponding amine PhP{C6H4-2-(CH2−NH(C6H4-2-OH))}2, H4L2. While the Schiff base undergoes partial hydrolytic decomposition and a redox reaction, the amine remains intact and acts as a pentadentate ligand, which encapsulates the metal atom of the {ReVO}3+ core or stabilizes a {ReVCl}4+ center by the formation of an imido-type ligand system

Technetium Complexes with Triazacyclononane

[NBu4][TcOCl4] reacts with ethylene glycol and 1,4,7-triazacyclononane (tacn) in MeOH under the formation of the deep-blue oxotechnetium(V) cation [TcO(OC2H4O)(tacn)]+, which can readily be oxidized by air to give the stable technetium(VII) compound [TcO3(tacn)]+. The reaction with aqueous HCl results in reduction and the formation of the cationic technetium(III) complex [TcCl2(OH2)(tacn)]Cl. The products were isolated in crystalline form and studied spectroscopically and by X-ray diffraction

Nitridotechnetium(V) Complexes with N-Heterocyclic Carbenes and Unexpected (OSiMe₂OSiMe₂O)^2- Coligands

Reactions of [TcNCl2(PPhR2)3] complexes (R = Me, Et) with 1,3-diethyl-4,5-dimethylimidazol-2-ylidene yield air-stable nitridotechnetium(V) complexes with N-heterocyclic carbenes with up to four of these bulky ligands and, depending on the reaction conditions applied, 1,1,3,3-tetramethyldisiloxane-1,3-diolato coligands which were abstracted from silicon-based grease

[Tc(OH₂)(CO)₃(PPh₃)₂]⁺: A Synthon for Tc(I) Complexes and Its Reactions with Neutral Ligands

A scalable synthesis of the novel and highly reactive [Tc­(OH2)­(CO)3­(PPh3)2]+ cation is described. The ligand-exchange chemistry of this compound with neutral ligands coordinating through C, N, O, S, Se, and Te has been explored systematically. The complexes either retain the original mer-trans tricarbonyl core under exclusive exchange of the aqua ligand or form dicarbonyl complexes by thermal decarbonylation. Ligand exchange reactions starting from [Tc­(OH2)­(CO)3­(PPh3)2]+ proceed under mild conditions and are generally almost quantitative. Some of the formed complexes are remarkably stable and inert, while others provide products with one labile ligand for further reactions. The derived complexes of the type [Tc­(L)­(CO)3­(PPh3)2]+ and [Tc­(L)2­(CO)2­(PPh3)2]+ represent an interesting opportunity for the development of 99mTc complexes with potential use in radiopharmacy. The ready displacement of the aqua ligand highlights the synthetic value of [Tc­(OH2)­(CO)3­(PPh3)2]+ as a reactive entry point for further studies in the little explored field of the organometallic chemistry of technetium

Rhenium and Technetium Complexes with <i>N</i>,<i>N</i>-Dialkyl-<i>N</i>‘-benzoylthioureas

N,N-Dialkyl-N‘-benzoylthioureas, HR1R2btu, react under single deprotonation and form air-stable chelate complexes with common rhenium or technetium complexes such as (NBu4)[MOCl4] (M = Re, Tc) or [ReOCl3(PPh3)2]. Compositions and molecular structures of the products are strongly dependent on the precursors used and the reaction conditions applied. Reactions with [ReOCl3(PPh3)2] in CH2Cl2 give complexes of the general formula [ReOCl2(R1R2btu)(PPh3)] (3), with the benzoyl oxygen atom of the chelating benzoylthiourea being trans to the oxo ligand, and/or Re(III) complexes of the composition [ReCl2(R1R2btu)(PPh3)2] (4) with the PPh3 ligands in trans positions to each other. In polar solvents such as MeOH, EtOH or acetone, corresponding reactions without addition of a supporting base only result in intractable brown solutions, from which no crystalline complexes could be isolated. The addition of NEt3, however, allows the isolation of the bis-chelates [ReOCl(R1R2btu)2] (1) in good yields. In this type of complex, one of the chelating R1R2btu- ligands coordinates equatorially, while the second occupies the position trans to the oxo ligand with its oxygen atom. The latter compounds can also be prepared from (NBu4)[ReOCl4] in MeOH when no base is added, while the addition of NEt3 results in the formation of [ReO(OMe)(R1R2btu)2] (5) complexes with the methoxo ligand trans to O2-. Compounds of the type 5 can alternatively be prepared by heating 1 in MeOH with addition of NEt3. A reversible conversion of 5 into oxo-bridged dimers of the composition [{ReO(R1R1btu)2}2O] (6) is observed in water-containing solvents. Starting from (NBu4)[TcOCl4], a series of technetium complexes of the type [TcOCl(R1R2btu)2] (2) could be prepared. The structures of such compounds are similar to those of the rhenium analogues 1. Reduction of 2 with PPh3 in CH2Cl2 gives Tc(III) complexes of the composition [TcCl(R1R2btu)2(PPh3)] (7) having the chloro and PPh3 ligands in cis positions. When this reaction is performed in the presence of excess chelating ligand, the Tc(III) tris-chelates [Tc(R1R2btu)3] (8) are formed

Rhenium(V) Oxo Complexes with N-Heterocyclic Carbenes

Air-stable rhenium(V) oxo complexes are formed when [ReOCl3(PPh3)2] is treated with N-heterocyclic carbenes of the 1,3-dialkyl-4,5-dimethylimidazol-2-ylidene type, LR (R = Me, Et, i-Pr). Complexes of the compositions [ReO2(LR)4]+, [ReOCl(LR)4]2+, or [ReO(OMe)(LR)4]2+ can be isolated depending on the alkyl substituents at the nitrogen atoms of the ligands and the reaction conditions applied. Despite the steric overcrowding of the equatorial coordination spheres of the metal atoms by each of the four carbene ligands, stable complexes with six-coordinate rhenium atoms are obtained. Steric demands of the alkyl groups allow control of the stability of the mono-oxo intermediates. Air-stable cationic complexes of the compositions [ReOCl(LMe)4]2+, [ReOCl(LEt)4]2+, and [ReO(OMe)(LMe)4]2+ have been isolated, whereas reactions of [ReOCl3(PPh3)2] or other rhenium(V) precursors with the more bulky 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (Li-Pr) directly yield the dioxo complex [ReO2(Li-Pr)4]+. X-ray structures of [ReO2(Li-Pr)4][ReO4], [ReO2(Li-Pr)4][PF6], [ReO2(LMe)4][ReO4]0.45[PF6]0.55, [ReO(MeOH)(LMe)4][PF6]2, and [ReOCl(LEt)4][PF6]2 show that the equatorial coordination spheres of the rhenium atoms are essentially planar irrespective of the steric demands of the individual carbene ligands

Rhenium Complexes with Triazine Derivatives Formed from Semicarbazones and Thiosemicarbazones

Benzil bis(semicarbazone), H2L1, reacts with common rhenium(V) nitrido complexes such as [ReNCl2(PPh3)2] or [ReNCl2(PR2Ph)3] (R = Me, Et) under the release of one semicarbazone unit, cyclization, and formation of stable triazine-3-onato complexes of rhenium(V). The resulting 5,6-diphenyltriazine-3-one, HL2, acts as monodentate or chelating, monoanionic ligand depending on the reaction conditions applied. Complexes of the compositions [ReNCl(L2-κN 2,κO)(PR2Ph)2] (R = Me, Et) or [ReN(L2-κN 2,O)(L2-κN 2)(PPh3)2] were isolated. The N2 nitrogen atom is the preferred binding site of the monodentate form of the ligand. This contrasts the behavior of the analogous thione HL3, which preferably coordinates to nitridorhenium(V) centers via the sulfur atom. HL3 is readily formed by the abstraction of methanol from 5-methoxy-5,6-diphenyl-4,5-dihydro-2H-[1,2,4]triazine-3-thione, H2L3OCH3. In the presence of [ReNCl2(PPh3)2] or [ReNCl2(PR2Ph)3] complexes (R = Me, Et), this reaction yields stable complexes of the composition [ReN(L3-κN 2,κS)(L3-κS)(PR2Ph)2] (R = Me, Et, Ph) in good yields. Reduction of the metal atom and formation of the seven-coordinate [Re(PPh3)(L3-κN 2,κS)3] was observed during reactions of H2L3OCH3 with [ReOCl3(PPh3)2] or [ReO2I(PPh3)2], while no rhenium complexes could be isolated during similar reactions with H2L1, although cyclization of the bis(semicarbazone) and the formation of H2L2OEt were observed