Enantiopure Planar Chiral and Chiral-at-Metal Iridacycles Derived from Bulky Cobalt Sandwich Complexes

Reaction
of (η5-(S)-2-(4-methyl­ethyl)­oxazolinyl­cyclo­penta­dienyl)-(η4-tetra­phenyl­cyclo­butadiene)­cobalt
with [IrCp*Cl2]2 in acetonitrile with KPF6 and KOt-Bu resulted in S,Sp,SIr and S,Rp,RIr configured acetonitrile and Cp* coordinated cationic iridacycles
(d.r. up to 4.8:1 – kinetic control), the planar chiral configuration
dictating the configuration of the pseudo-tetrahedral iridium-based
stereogenic center. Addition of water to the cycloiridation reaction
resulted in an increase in yield (up to 78%) at the cost of diastereoselectivity.
Use of the corresponding substrate containing a t-Bu rather than an i-Pr substituted oxazoline gave
exclusively the S,Sp,SIr diastereoisomer, and under the same conditions,
(S)-2-ferrocenyl-4-(1,1-di­methyl­ethyl)­oxazoline
cycloiridated to give only the S,Sp,SIr diastereoisomer. Substitution
reactions of the title complexes at iridium proceeded with retention
of configuration, a computational study revealing the proposed coordinatively
unsaturated intermediate of a dissociative mechanism to display a
relatively weak Co–Ir interaction, and a pronounced steric
effect as the basis of stereocontrol.