Diastereoselective Coordination of P‑Stereogenic Secondary Phosphines in Copper(I) Chiral Bis(phosphine) Complexes: Structure, Dynamics, and Generation of Phosphido Complexes

Diastereoselective coordination of racemic secondary phosphines (PHRR′) to Cu­(I) precursors containing chiral bis­(phosphines) (diphos*) was explored as a potential route to P-stereogenic phosphido complexes. Reaction of [Cu­(NCMe)4]­[PF6] with chiral bis­(phospholanes) gave [Cu­(diphos*)2]­[PF6] (diphos* = (R,R)-Me-DuPhos (1), (R,R)-Et-DuPhos (2), or (R,R)-Me-FerroLANE) (3)) or the mono­(chelates) [Cu­(diphos*)­(NCMe) n ]­[PF6] (diphos* = (R,R)-i-Pr-DuPhos, n = 2 (4); diphos* = (R,R)-Me-FerroLANE, n = 1 (5)). Treatment of [Cu­(NCMe)4]­[PF6] with diphos* and PHMe­(Is) (Is = 2,4,6-(i-Pr)3C6H2) gave mixtures of diastereomers of [Cu­((R,R)-i-Pr-DuPhos)­(PHMe­(Is))­(NCMe)]­[PF6] (6) and [Cu­((R,R)-Me-FerroLANE)­(PHMe­(Is))]­[PF6] (7); two of the three expected isomers of the bis­(secondary phosphine) complexes [Cu­((R,R)-i-Pr-DuPhos)­(PhHP­(CH2) n PHPh)]­[PF6] (n = 2 (8); n = 3 (9)) were formed preferentially in related reactions. Reaction of the halide-bridged dimers [Cu­((R,R)-i-Pr-DuPhos)­(X)]2 or [Cu­((R,R)-Me-FerroLANE)­(I)]2 with PHMe­(Is) gave the labile adducts Cu­((R,R)-i-Pr-DuPhos)­(PHMe­(Is))­(X) (X = Cl (10), Br (11), I (12)) and Cu­((R,R)-Me-FerroLANE)­(PHMe­(Is))­(I) (13). Complexes 1, 6, and 8–11 were structurally characterized by X-ray crystallography. Variable temperature NMR studies of 6 and 8 showed that the secondary phosphine ligands underwent reversible dissociation. Deprotonation of 6 or 7 generated the P-stereogenic phosphido complexes Cu­(diphos*)­(PMeIs) (diphos* = (R,R)-i-Pr-DuPhos (14) or (R,R)-Me-FerroLANE) (17)), observed by 31P NMR spectroscopy, but decomposition also occurred. Density functional theory calculations were used to characterize the diastereomers of thermally unstable 17 and the inversion barrier in a model copper-phosphido complex. These observations provided structure–property relationships which may be useful in developing catalytic asymmetric reactions involving secondary phosphines and P-stereogenic copper phosphido intermediates.