Komplexe mit kohlenstoffsulfiden und -seleniden als liganden: IV. Ein- und zweikernige rhodium—CS2-komplexe und kristallstruktur eines RhSCSC-heterocyclus

The complexes C₅H₅Rh(PMe₃)CS₂(II) and C₅H₅Rh(PMe₂Ph)CS₂(III) are formed in excellent yields in the reaction of C₅H₅Rh(C₂H₄)PR₃(PR₃ = PMe₃, PMe₂Ph) with CS₂ in benzene. The CS₂ ligand in II and III is dihapto-bonded and at least in III is rigid. II reacts with Cr(CO)₅THF and C₅H₅Mn(CO)₂THF to give the binuclear complexes C₅H₅(PMe₃)Rh(SCS)Cr(CO)₅ (IV) and C₅H₅- (PMe₃)Rh(SCS)Mn(CO)₂C₅H₅ (V) in which the CS₂ molecule bridges two different metal atoms. In the reaction of C₅H₅Rh(C₂H₄)PMe₃ and CS₂ under certain conditions a second product of C₅H₅Rh(PMe₃)C₂S₄ (VI) is formed. The cyrstal structure shows that in this complex a five-membered RhSCSC heterocyclic ring is present.     

Basische Metalle. XIII. Ein neuer Syntheseweg für Cyclopentadienyl-Rhodium-Phosphonat- aus Cyclopentadienyl-Rhodium-Phosphit-Komplexen

Basic Metals. XIII. A New Synthesis of Cyclopentadienylrhodium Phosphonate from Cyclopentadienylrhodium Phosphite Complexes C₅H₅Rh[P(OCH₃)₃]₂ reacts with alkali metal iodides MI (M = Li, Na, K) in two stages via the intermediate C₅H₅RhCH₃[P(O)(OCH₃) ₂]P(OCH₃)₃ to the corresponding bisphosphonate complexes C₅H₅RhCH₃[P(O)(OCH₃) ₂]₂M. Their properties suggest that they exist as contact ionpairs rather than dissociated ions. The reaction of C₅H₅RhCH₃[P(O)(OCH₃)₂]₂ Na with HCl in benzene yields the complex C₅H₅RhCH₃[P(O)(OCH₃) ₂]₂H, in which a chelate ligand with a P? O? H? O? P bridge is probably present. The acidic character of the bridging H atom is shown in the reaction with (CH₃)₃PCH₂ which leads to [C₅H₅RhCH₃{P(O)(OCH₃) ₂}₂][P(CH₃)₄]. C₅H₅RhCH₃[P(O)(OCH₃) ₂]₂Tl was formed in the reaction of C₅H₅RhCH₃[P(O)(OCH₃)₂]₂ H and thallium acetylacetonate. The n.m.r. spectra of the new phosphonate complexes are discussed.     

Basische metalle : XXXVI. Die synthese stabiler hydrido(olefin)rhodium-komplexe und von[C5H5Rh(PMe3)(η3-CH3CHC6H5)]PF6

The complexes C₅H₅Rh(PMe₃)C₂H₃R′ (R′  H, Me, Ph) and C₅H₅Rh(PR₃)C₂H₄(PR₃  PMe₂Ph, PPrⁱ₃) are prepared by reaction of[PMe₃(C₂H₃R/t')RhCl]₂ or [PR₃(C₂H₄)RhCl]₂ and TlC₅H₅, respectively. They react with HBF₄ in ether/propionic anhydride to form the BF₄ salts of the hydrido(olefin)rhodium cations [C₅H₅RhH(C₂H₃R′)PR₃]⁺(R  Me; R′  H, Me and R  Prⁱ; R′  H). From C₅H₅Rh(PMe₃)C₂H₃Ph and CF₃COOH/NH₄PF₆ the η³-benzyl complex [C₅H₅Rh(PMe₃)(η³-CH₃CHC₆H₅)]PF₆ is obtained. The reversibility of the protonation reactions is demonstrated by temperature-dependent NMR spectra and by deuteration experiments. The complexes C₅H₅Rh(PMe₃)C₂H₃R′ (R′  H, Ph) and C₅H₅Rh(PMe₂Ph)C₂H₄ react with CH₃I in ether to give the salts [C₅H₅RhCH₃(C₂H₃R′)PR₃]I which in THF or CH₃NO₂ yield the neutral compounds C₅H₅RhCH₃(PR₃)I.     

Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+)

Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.