Technetium Hydrides Revisited: Syntheses, Structures, and Reactions of [TcH3(PPh3)4] and [TcH(CO)3(PPh3)2]
Optimized synthetic approaches to [TcH3(PPh3)4] (1) and mer-trans-[TcH(CO)3(PPh3)2] (5) as key compounds of the technetium hydrido chemistry are reported. They give access to pure and stable samples of the complexes. The solid-state structures of the two title compounds have been determined. Reacti...
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Veröffentlicht in: | Organometallics 2021-09, Vol.40 (18), p.3095-3112 |
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Sprache: | eng |
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Zusammenfassung: | Optimized synthetic approaches to [TcH3(PPh3)4] (1) and mer-trans-[TcH(CO)3(PPh3)2] (5) as key compounds of the technetium hydrido chemistry are reported. They give access to pure and stable samples of the complexes. The solid-state structures of the two title compounds have been determined. Reactions of [TcH3(PPh3)4] with monodentate basic phosphines such as PMe2Ph or PMe3 lead to mixtures of mixed-phosphine complexes of the compositions [TcH3(PR3) n (PPh3)4–n ] (n = 1–3), from which the mixed-phosphine trihydride complex [TcH3(PPh3)2(PMe3)2] (2) could be isolated. Spectroscopic data and DFT calculations suggest a fluxional structure between a capped trigonal prism and a pentagonal bipyramid. Reactions of the monohydride mer-trans-[TcH(CO)3(PPh3)2] (5) with HX (X = Cl, Br, I) give [TcX(CO)3(PPh3)2] (6) complexes in good yields, while mer-trans-[Tc{η1-O(CR)O}(CO)3(PPh3)2] (7) or cis–trans-[Tc{η2-OO(CR)}(CO)2(PPh3)2] (8) complexes are formed with carboxylic acids depending on the substituent R and the conditions applied. Chelate formation of the formato ligand can also be obtained by thermal decarbonylation of the isolated mer-trans-[Tc(η1-O(CH)O)(CO)3(PPh3)2] (7a) complex. The latter reaction is reversible, and the tricarbonyl compound is reformed when [Tc{η2-OO(CH)}(CO)2(PPh3)2] (8a) is exposed to CO gas. Reactions of [TcH(CO)3(PPh3)2] (5) with phenyl seleninic acid (PhSeOOH) in methanol give the tetranuclear cluster [{Tc(CO)3}3(μ3-OH)(μ2-O(SePh)O)3{Tc(CO)3}] (10) and a small amount of the bridged dinuclear oxalato complex [Tc2(CO)6(ox)(OPPh3)2] (11). The latter compound is the result of a complex reaction, which involves a metal-induced oxidation of methanol to formate and a subsequent C–C coupling of two formato ligands. The plausibility of the proposed mechanism is supported by the fact that the dimeric oxalato complex is much more efficiently formed when the formato complex [Tc{η1-O(CH)O}(CO)3(PPh3)2] (7a) is directly reacted with PhSeOOH. Exclusively the monomeric oxalato complex [Tc(η2-oxH)(CO)2(PPh3)2] (12) is formed during a reaction of mer-trans-[TcH(CO)3(PPh3)2] (5) with oxalic acid. The remaining proton of the Hox– ligand of [Tc(η2-oxH)(CO)2(PPh3)2] (12) can be removed by NEt3, and the ion pair (HNEt3)[Tc(η2-ox)(CO)2(PPh3)2] (13) is formed. |
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ISSN: | 0276-7333 1520-6041 |
DOI: | 10.1021/acs.organomet.1c00274 |