Reaction of [IrCp*Cl2]2 with ferrocenylimines (Fc=NAr, Ar = Ph, p-MeOC6H4) results in ferrocene C-H activation and the diastereoselective synthesis of half-sandwich iridacycles of relative configuration Sp*,RIr*. Extension to (S)-2-ferrocenyl-4-(1-methylethyl)oxazoline gave highly diastereoselective control over the new elements of planar chirality and metal-based pseudo-tetrahedral chirality, to give both neutral and cationic half-sandwich iridacycles of absolute configuration Sc,Sp,RIr. Substitution reactions proceed with retention of configuration, with the planar chirality controlling the metal-centred chirality via an iron-iridium interaction in the coordinatively unsaturated cationic intermediate.

ABSTRACT:Highly diastereoselective lithiation (s-BuLi/TMEDA in Et 2 O, -78 o C, 2 h) of (S)-2-ferrocenyl-4-(substituted)oxazolines followed by addition of MeOH-d 4 , gave up to 95% D incorporation. Subsequent application of alternative lithiation conditions (n-BuLi in THF, -78 o C, 2 h), followed by addition of an electrophile, resulted in a reversal of diastereoselectivity controlled primarily by the high k H /k D value for lithiation (isomer ratio typically between 10:1 and 20:1).Many non-racemic ligands employed in metal catalyzed asymmetric reactions contain more than one element of chirality. For a C 1 -symmetric ligand containing two such elements, diastereoisomers are possible which may result in different reaction product enantioselectivities, and there are a number of examples where the identification of matched and mismatched chirality pairings has been established.

Diastereoselective lithiation of (S)-2-ferrocenyl-4-(1-methylethyl)oxazoline followed by addition of HgCl2 resulted in the formation by transmetallation of an (S,Sp)-configured mercury substituted complex. Addition to this of [Cp*IrCl2]2 and tetrabutylammonium chloride resulted in a second transmetallation reaction and formation of an (S,Sp,RIr)-configured chloride-substituted half-sandwich iridacycle as exclusively a single diastereoisomer. By reversing the lithiation diastereoselectivity by use of a deuterium blocking group an alternative (S,Rp,SIr)-configured iridacycle was synthesised similarly. Use of (R)-Ugi's amine as substrate in the lithiation/double transmetallation sequence gave a (R,Sp,SIr)-configured half-sandwich iridacycle, complexes of this type being previously unavailable by direct cycloiridation. Lithium to gold transmetallation was also demonstrated with the synthesis of an (S,Sp)-configured Au(I) ferrocenyloxazoline derivative. Use of the (S,Rp,SIr)-iridacycle as a catalyst for the formation of a chiral product by reductive amination with azeotropic HCO2H/NEt3 resulted in a racemate.