Der Einfluss von Halogenidionen in der Übergangsmetallkatalyse

Mixed‐Valence Tetrametallic Iridium Chains

“…Under this perspective, complexes [ 2 ] 2+ , [ 3 ] 2+ , and 7 , which feature weakly coordinated acetonitrile, acetone, and thiocyanate ligands (Table 1), shows the more shielded H 6 protons, whereas they are high field shifted for the halide series. For them, the observed trend Cl<Br<I matches well with the expected increase of the Ir−X bond strength (Cl<Br<I) [47] . Noticeably, this trend was also observed in their corresponding 13 C{ 1 H} NMR spectra, where again the more deshielded C 6 carbon was found in the iodide complex 7 (see the Supporting Information).…”

“…For them, the observed trend Cl < Br < I matches well with the expected increase of the IrÀ X bond strength (Cl < Br < I). [47] Noticeably, this trend was also observed in their corresponding 13 C{ 1 H} NMR spectra, where again the more deshielded C 6 carbon was found in the iodide complex 7 (see the Supporting Information).…”

Enantioselective Synthesis of Alcohols and Amines by Iridium‐Catalyzed Hydrogenation, Transfer Hydrogenation, and Related Processes

“…[42] The same group reported that benzyl chloroformate was an excellent imine-activating reagent (Scheme 15a and b). [44] (S)-SegPhos ((S)-45) was the most active among all the ligands tested; several quinolines (10) and isoquinolines (16) activated with chloroformate could be hydrogenated with ee values up to 90 %. In a recent hydrogenation protocol using 45, it was found that certain Brønsted acids (e.g., piperidine·TfOH) used in catalytic amounts were excellent substrate activators for quinolines (10) and quinoxalines (14) (Scheme 15c).…”

“…Catalyst oxidation (that is, from Ir I to Ir III ) occurs by oxidative addition of H 2 or it is mediated by the additive (halides such as I 2 are frequently used additives [16] ). Common substrates are shown in Scheme 3 and classified as N-aryl imines (2,(5)(6)(7), N-alkylimines (8-9), endocyclic imines and N-heteroarenes (10)(11)(12)(13)(14)(15)(16)(17)(18)(19), and N-H imines (20). The development of a general catalytic system for imine hydrogenation is difficult since the substrate selectivity and reactivity are highly dependent on the substituents on the nitrogen atom.…”

The synthesis and crystallographic characterisation of the complexes [RuX(CO)(η2-C,N-C6H5C(H) NC6H4-4Me)(PPh3)2] · CHCl3 (X = Cl, Br, I, F): Evidence for competing Ru–X⋯Cl–CHCl2 and Ru–X⋯HCCl3 interactions in the solid state

“…This trend in the observed m(CO) values observed for 2-F, 2-Cl, 2-Br, 2-I must therefore be a result of both processes. Other evidence for this trend in p-donor strength for the halides (F > Cl > Br > I) to transition metal centres has been noted previously [32]. The compounds 2-Cl, 2-Br, 2-I all show the expected singlet resonance in their 31 P{ 1 H} NMR spectra Table 1, whereas for 2-F a doublet is observed with J PF = 13.5 Hz.…”