Complexes of the Gilman Reagent with Double Bonds across the π–σ Continuum

Abstract

By using rapid injection NMR at low temperatures, a variety of π-complexes of lithium dimethylcuprate(I) with C−C, C− N, and C−S double bonds have been prepared and characterized. Complexation is generally accompanied by large upfield changes in chemical shift for the substrate carbon atoms bonded to copper. In the case of α,β-unsaturated carbonyl compounds, the changes for the carbonyl carbons are much smaller in magnitude, which is consistent with the usual η 2 representation of these structures. It is possible for one ligand to displace another, and in this way an order of stability can be elucidated. Treatment of selected π-complexes with chlorosilanes or cyanosilanes gives Cu III intermediates.

π-Complexes from acyl cyanides and lithium dimethylcuprate(i)

“…Organocuprates form p-complexes with activated alkenes and alkynes, [1][2][3] which are well-characterized intermediates, thanks to mechanistic studies on the conjugate addition reactions of these useful reagents. 4,5 We were able to extend our preparations of cuprate p-complexes from C-C to C-N double bonds by using isothiocyanates and azachalcones. 4 In an attempt to extend our studies to C-N triple bond complexes, we investigated acyl cyanides and serendipitously discovered the title compounds.…”

Intermediates Formed in the Reactions of Organocuprates with α,β‐Unsaturated Nitriles

“…Presumably, they are less important for the addition to the corresponding nitriles because nitrogen has a lower Li + affinity than oxygen . However, adducts stable at room temperature are predicted to form only if at least two cyano groups are attached to the carbon–carbon double bond of the Michael acceptor, in line with previous NMR spectroscopic experiments …”

First X‐Ray Crystal Structure and Internal Reference Diffusion‐Ordered NMR Spectroscopy Study of the Prototypical Posner Reagent, MeCu(SPh)Li(THF)3

“…[11] Preparation of NMR samples has been described. [10,16] For details of the molecular weight measurements, see the Supporting Information. Reference compounds (internal standards) [21] for these diffusion-ordered NMR studies are shown below: CCDC-928158 (1) contains the supplementary crystallographic data for this paper.…”

“…ORTEP plot (50 % ellipsoids) for 1. Selected bond distances [] and angles [8]: CuÀC, 1.914(3); CuÀS, 2.1797 (7); LiÀS, 2.431(4); LiÀO1, 1.920 (5); LiÀO2, 1.914 (5); LiÀO3, 1.914(4); CÀCuÀS, 176.15 (12); CuÀSÀLi, 98.94 (10).…”