GROUP-11 METAL-IONS IN POLY(DONOR ATOM) ENVIRONMENTS - X-RAY CRYSTAL AND MOLECULAR-STRUCTURE OF [M((R,S)-1,2-(5-R-THIO-2-CH=N)2-C-HX)2](O3SCF3) (M=AG(I), R = ME, THIO = THIOPHENE, C-HX = CYCLOHEXANE) AND SILVER(I) AND COPPER(I) COORDINATION PROPERTIES IN SOLUTION (H-1, AG-109, AND N-15 NMR)-
Vanstein, GC; Vankoten, G; Vrieze, K; Spek, AL; Klop, EA; Brevard, C
The 2/1 reactions of the N2S2 ligand system (R,5)-1,2-(5-R-thio-2-CH=N)2-c-Hx (R = H (1a), Me (1b); thio = thiophene, c-Hx = cyclohexane) with M = Ag(I), Cu(I) yielded stable mononuclear [M(N2S2)2](O3SCF3) complexes. An X-ray crystallographic study of [Ag(lb)2](03SCF3) defined its molecular structure: triclinic, space group P1*, a = 9.900 (4) Å, b = 11.465 (4) Å, c = 19.423 (6) Å, α = 106.10 (3)°, β = 99.95 (3)°, γ = 90.38 (3)°, and Z = 2 for 5124 independent reflections. The structure was refined to R = 3.9%. The N2S2 ligands are coordinated to the group 11 metal center with one thiophene-imine moiety of each ligand via the imine-N atoms N(1) (Ag-N(1) = 2.275 (3) Å) and N(3) (Ag-N(3) = 2.281 (3) Å) while the lone pairs of N(2), S(2), N(4), and S(4) are not pointing toward the silver(I) center. The 1H NMR results revealed that in solution at 190 K the same enantiomeric pair is present as has been found in the solid. From the 15N NMR data, the chemical shifts of the resonances representing the two different imine-N sites, N(1) N(3) and N(2), N(4), as well as the presence of 1J(15N-107 109Ag) on both resonances, unambiguously proved the existence of orbital overlap between Ag(I) and N(1), N(3) as well as with the unfavorably positioned (with respect to the group 11 metal center) N(2) and N(4) donor sites; i.e., all four N donor atoms interact with the Ag center. On the basis of the small difference in 109Ag chemical shifts for the [Ag(1)2]+cations (R = H, Me; Δδ(109Ag) = 1), it is concluded that the thiophene-S-Ag interactions are very weak or are not present. This weak affinity of thiophene-S atoms for group 11 metal centers can be regarded as the main reason for the formation of these mononuclear [M(N2S2)2](O3SCF3) complexes. When stronger donor atoms are present in the “outer” ring system, for instance pyridine-N atoms, resulting in the N4 ligand system, only the dinuclear [M2(N4)2](03SCF3)2 complexes were formed. The copper(I) complex [Cu(lb)2](03SCF3) has in the solid-state a structure similar to that of the corresponding silver(I) complex. The difference in M-N(1) and M-N(3) distances found in the two structures (M = Cu(I), Ag(I)) is caused by the stronger Cu-N(imine) bonds and the smaller ionic radius of copper(I) compared with that of silver(I). In solution (at 190 K) the [Cu(1b)2]+cation exists in at least two different stereoisomeric forms. Above 210 K an intermolecular N2S2 ligand-exchange process occurs in solutions of the [M(N2S2)2](03SCF3) complexes, as demonstrated for [Ag(1)2]+by the loss of 3J(1H-107’109Ag) on the imine-H(A) resonances. 1985, American Chemical Society. All rights reserved.