Zwitterionische Verwandte kationischer Platinmetallkomplexe: Anwendungen in der stöchiometrischen und katalytischen σ‐Bindungsaktivierung

Zwitterionic Iridium Complexes with P,N‐Ligands as Catalysts for the Asymmetric Hydrogenation of Alkenes

“…In this context, we have recently developed functionalized anionic building blocks 19 a and 19 b (Scheme 2). [26] They resemble structural analogues of the established tetrakis(pentafluoro)-phenylborate (BA C H T U N G T R E N N U N G (C 6 F 5 ) 4 ) and tetrakisA C H T U N G T R E N N U N G [3,5-bis(trifluoromethyl)phenyl]borate (BAr F ), and can easily be introduced in neutral precursors through nucleophilic substitution reactions.…”

“…After the addition of aqueous Na 2 S 2 O 3 (5 %, 20 mL), the mixture was extracted with CH 2 Cl 2 (4 20 mL). The combined organic phases were dried over MgSO 4 General procedure for enantioselective hydrogenations: The precatalyst (usually 1.0 mmol) and substrate (usually 100 mmol) were weighed in a 2 mL screw-cap glass vial equipped with a magnetic stirrer bar and the desired solvent was added (usually 0.5 mL of absolute CH 2 Cl 2 ). Alternatively, stock solutions of the iridium complex and alkene were sometimes used.…”

“…The resulting two-phase system was vigorously stirred for 30 min at room temperature, the phases were allowed to separate, and the aqueous layer was extracted with CH 2 Cl 2 (3 10 mL). The combined organic phases were dried over MgSO 4 General procedure for the preparation of ligands by heteroatom alkylation Compound 45a: PHIM 12 a (577 mg, 1.50 mmol) was added to a suspension of KH (66.2 mg, 1.65 mmol) in absolute THF (15 mL) at 0 8C. After the mixture had been stirred at room temperature until no further gas evolution was detected (about 2 h), pentafluorobenzyl bromide (272 mL, 1.80 mmol) was added dropwise to the now yellow solution at 0 8C.…”

“…[4] The zwitterionic rhodium species 1, which was described by Schrock as early as 1970, [5] was applied by Alper in a multitude of transformations, such as hydroformylations and hydrogenations.…”

Steric, Electronic, and Secondary Effects on the Coordination Chemistry of Ionic Phosphine Ligands and the Catalytic Behavior of Their Metal Complexes

“…Recently, Lombardo and Trombini have discussed a selected number of examples of homogeneous transition metal-based catalysts and organocatalysts in which the presence of an ionic group in the structure of the ligand or catalyst appears to lead to an increase in the observed catalytic activity. [21] The catalytic properties of cationic platinum group metal complexes bearing a ligand containing an anionic functionality, which renders the overall metal complex zwitterionic, have been reviewed by Stradiotto et al [22] Here, we describe the different types of effects on the coordination chemistry of phosphine ligands with respect to a transition metal that may occur upon functionalization of the phosphine backbone with anionic and cationic substituents. In particular, secondary interactions that have been observed with these ligands, and the influence that they exert on the observed catalytic activity or selectivity, are reviewed.…”