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

ABSTRACT

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) nPHPh)][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.