Monovalent chiral-at-copper complexes: halide-controlled diastereoselectivity

Abstract

An unusual example of diastereoselectivity has been observed in Cu(κ(3)-P,C,P'-1)X complexes where 1 is an asymmetric tridentate ligand containing a bicyclic NHC framework and X is a halide. When X is Cl(-), the S(Cu) isomer is formed selectively whereas when X = I(-) the R(Cu) diastereomer is preferred.

Variable coordination of a chiral diphosphine containing an amidinium/NHC group within its backbone: μ-P,P′, κ2-P,P′ and κ3-P,C,P′ coordination modes

“…This is largely to be expected as d 10 Ag(I) does not tend to form octahedral or square planar complexes and, if 11 is monomeric (although bridging forms of PC NHC P ligands are known 23 only monomeric species were observed in the mass spectrum of 11), then the likely geometry would approximate to tetrahedral as noted for the related [Cu(κ 3 -P,C,P′-1)X] species. 24 The absolute magnitude of the 2 J P-P coupling constant compares well with known tetrahedral phosphine containing complexes of silver(I) such as [AgBr(κ 2 -P,P′-dppp)(κ 1 -P-dpppO)] where a value of 58 Hz is observed. 25 The 1 J P-Ag coupling constants are somewhat larger than those of 253 and 220 Hz observed in [AgBr(κ 2 -P,P′-dppp)(κ 1 -P-dpppO)].…”

“…The related copper(I) systems [Cu(κ 3 -P,C,P′-1)X] show a halidedependant diastereomerism with the R Cu configuration being favoured when X = I − and the S Cu configuration when X = Cl − . 24 The 1 H NMR spectrum of 11 shows no evidence of the presence of more than one isomer although some of the signals in the 1 H NMR spectrum are broadened slightly, most notably for one set of benzylic CH 2 resonances (AB pattern) and one of the methyl signals. The absence of a CH 3 resonance upfield of TMS in the 1 H NMR spectrum would suggest that the preferred isomer of 11 has the S configuration at the metal and that this isomer is formed preferentially.…”

Asymmetric Cationic Phosphines: Synthesis, Coordination Chemistry, and Reactivity

“…The construction of such ligands requires access to chiral forms of the positively charged organic substituent and the phosphorus-containing component. We − and Wilhelm − have already demonstrated the synthetic utility of amidinium species derived from 1,3-diamino-1,2,2-trimethylcyclopentane which made this the obvious candidate for the cationic fragment. The need for a robust, inherently chiral PR 2 group capable of supporting a stable N–P bond to the amidinium led to the selection of 1,3,5,7-tetramethyl-2,4,6-trioxa-8-phosphatricyclo­[3.3.1.1 , ]­decane or Cagephos (CgP) as it satisfied all of the desired criteria. − Our preliminary report detailed the synthesis of the ligand as a diastereomeric mixture as our original attempts at resolution were unsuccessful .…”

Review for chiral-at-metal complexes and metal-organic framework enantiomorphs

“…The catalytic application of the chiral octahedral complexes with cobaltate(III), ruthenium(II), and iridium(III) at metal centers was summarized by Gong et al [32]. Chiral-at-copper complexes were prepared with an asymmetric tridentate ligand while halide was used to control diastereoselectivity after coordinating to the copper center [34]. An octahedral chiral-at-iridium(III) complex catalyzed the enantioselective Friedel-Crafts addition of indoles effectively and the iridium center was considered to act as the coordinately activating center and the source of chirality [35].…”