Dinuclear silver(I) and copper(I) complexes with neutral N 2S 2 donor ligands and their reactivities towards CO. Structures in solution ( 1H and INEPT 109Ag NMR) and in the solid (X-ray) of [Ag 2{μ-( R)( S)-1,2-(thiophene-2–CHN) 2cyclohexane} 2](O 3SCF 3) 2

Abstract

The 1/1 reactions of the neutral N 2S 2 donor system ( R)( S)-1,2-(5-R–thiophene-2-CHN) 2–cyclohexane (R = H, 1a or Me, 1b) with [M(O 3SCF 3)] [M = Ag(I) or Cu(I)] yielded ionic complexes, consisting of a dinuclear [M 2( 1) 2] 2+ dication and O 3SCF 3 − monoanions. An X-ray crystallographic study characterized the molecular structure of [Ag 2–( 1a) 2](O 3SCF 3) 2, in the monoclinic unit cell, space group P2 1/ n, with Z = 4; a = 17.26(1), b = 15.08(2), c = 19.960(17) Å, β = 106.15(4)°, V = 4991 Å 3. The structure was refined to R is 0.0704. The two N 2S 2 ligands coor- dinate to the silver(I) centres in a bridging di- bidentate manner with short AgN(imine) [ e.g. Ag(1)N(2), 2.152(10); Ag(1)N(7), 2.162(9); Ag(2)N(3), 2.153(10); Ag(2)N(6), 2.158(10) Å] and long AgS(thiophene) distances [Ag(1)S(1), 2.961(4); Ag(1)S(8), 2.938(4); Ag(2)S(4), 2.928(4); Ag(2)S(5), 2.995(5) Å]. The Ag(1) Ag(I) separation is 2.909(1) Å. In solution the coordination properties of the N 2S 2 ligands to silver(I) and copper(I) have been studied by 1H and INEPT 109Ag NMR spectroscopy. The 1H NMR data revealed, by the presence of two thiophene–imine 1H patterns at 190 K, that at this temperature i) the structural features found for [Ag 2( 1a) 2] 2+ in the solid are retained in solution and ii) the silver(I) and copper(I) complexes have similar structures in solution. Furthermore, the presence of 3J( 1H 107,109Ag) on the imine-H resonances of the silver(I) complexes indicates that at 190 K intermolecular exchange processes are slow on the NMR time scale. From the difference in δ 109Ag of the [Ag 2( 1) 2](O 3SCF 3) 2 complexes, R = H (δ + 678) or Me (δ + 659), it was concluded that weak thiopheneSAg(I) interactions are present, and stabilize the formation of the [M 2( 1) 2] 2+ dications. However, in the reversible reactions of [Cu 2( 1) 2](O 3SCF 3) 2 with carbon monoxide the thiopheneSCu(I) bonds dissociate and neutral complexes are formed having a [{CuCO(O 3SCF 3)} 2{μ−1} 2] type of structure. In these complexes both the carbon monoxide and OSO 2CF 3 groups are terminally coordinated to Cu(I) (R = H, ν(CO), 2089 cm −1; R = Me, ν(CO) = 2087 cm −1 in CH 2Cl 2).