Palladium(II), Platinum(II), and Iridium(I) Complexes of 2-Phosphino-1-dimethylaminoferrocenes: A Survey of Structure and Catalysis

Abstract

A series of PdCl 2 , PtCl 2 , and Ir(COD)BAr F complexes bearing a rare class of racemic bidentate 2-phosphino-1-dimethylaminoferrocene ligands were prepared and characterized by NMR spectroscopy and X-ray crystallography. The new complexes displayed a structural trend relating a decrease in heteroatom-metal bond length with an increase in ligand bite angle on going from Ir to Pd and Pt. The PdCl 2 and PtCl 2 complexes were almost isostructural and featured MCl 2 moieties in the plane of the substituted Cp ring of the ligand. In contrast, the Ir(COD) þ complex was distinguished by a bend of the Ir(COD) moiety toward the unsubstituted (Cp 0 ) ring. The latter gave rise to a steric interaction that placed the Cp rings in almost eclipsed conformations. Ligand 8a (2-diphenylphosphino-1-dimethylaminoferrocene) was able to promote Pd-catalyzed Suzuki-Miyaura and Buchwald-Hartwig coupling of aryl chlorides in addition to Ir-catalyzed hydrogenation of electron-deficient and unactivated alkenes. A preliminary intramolecular hydroamination of a terminal alkene using 8a in conjunction with Ir(I) afforded the cyclized product in 64% yield.

Low Pressure Asymmetric Hydrogenation of Quinolines using an Annulated Planar Chiral N‐Ferrocenyl NHC‐Iridium Complex

“…This compound was surprisingly robust and indefinitelys table in af reezer (À15 8 8C) under an inert atmosphere.O xidation of 11 with triphenylcarbenium tetrafluoroborate gave an imidazolinium salt,w hich wasn ot isolated due to its instability. [17] Instead, deprotonation of this NHC precursor with KO-t-Bu in the presence of 0.5 equivalents of [Ir(COD)Cl] 2 afforded Ir(I) complex 12.Coordination of this atypical NHC ligand to iridium was determined initially by 13 CNMR, where ac haracteristic ylidene carbon signal was observed at d = 206. Exposure of 12 to triphenylphosphine in dichloromethane gave the cationic iridium complex 13 upon anion exchange with potassium hexafluorophosphate.…”

“…[12] As part of our ongoing studies of NHC-Ir complexes, [13,14] we were interested in investigating whether an analogue of 1 bearing ac hiral NHC ligand wouldb ec apable of catalyzing the hydrogenation of quinolines in appreciable enantioselectivity,b ut also under similarlym ild conditions.D escribed in this papera re the syntheses of twou nusualm onodentate planar chiral N-ferrocenyl NHC ligands,p reparedb y established stereoselective lithiation of syn-a nd anti-8 (Scheme 2a nd Scheme4). [15] Thed erived ferrocenyl NHC-Ir complexes were characterized crystallographically and/or spectroscopically,a nd found to promote the asymmetric hydrogenation of 2-substituted quinolines under mild conditions (1-5 atm H 2 ,2 58 8 C) in up to 90:10 er.…”

“…[24] Column chromatography was performed on silica gel 60 (70-230 mesh). NMR spectra were obtained on aB ruker Avance 300 or 600 MHz instrument and are referenced to TMS or to the residual proton signal of the deuterated solvent for 1 Hs pectra, and to the carbon multiplet of the deuterated solvent for 13 Cspectra according to published values.E nantiomeric ratios were determined on an Agilent 1100 series HPLC system at l = 254 nm on aC hiralcel ODHc olumn. FT-IR spectra were obtained on an ATIM attson Research Series spectrometer as KBr pellets for solids or on KBr discs for liquids.O ptical rotationsw ere measured on aR udolph Research Autopol III automatic polarimeter.…”

Synthesis of Saturated Heterocycles via Metal-Catalyzed Alkene Hydroamination or Hydroalkoxylation Reactions

“…Other iridium complexes, such as the neutral P,O-phosphino-phenolate complex 71 [58], the cationic P,N-ferrocenyl iridium complex 72 [59], and the bidentate Nheterocyclic carbene complex 73 [60], demonstrated reactivity for intramolecular hydroamination of secondary aminoalkenes, but these more complex catalysts have not yet shown to be advantageous over the simple [Ir(COD)Cl] 2 system in initial reports (Scheme 32). …”

Asymmetric Lithiation of Boron Trifluoride‐Activated Aminoferrocenes: An Experimental and Computational Investigation

“…[14] The resulting carbanions would be expected to have configurational stability in the same way that (À)-sparteine-mediated lithiation of 5 and 6 generates enantiomerically enriched intermediates. Development of a direct asymmetric lithiation protocol for aminoferrocenes would provide rapid access to a set of planar chiral ligands that have not been investigated to their full potential in catalysis [15] because of limitations or lengths of previous synthetic routes. [16] In this paper we report that BF 3 -activated tertiary aminoferrocenes undergo asymmetric lithiation [17] with alkyllithiums in the presence of chiral 1,2-diaminocyclohexane-derived additives.…”