A Copper(I) Homocubane Collapses to a Tetracapped Tetrahedron Upon Hydride Insertion

The hydrido copper(I) and silver(I) clusters incorporating 1,1-dicyanoethylene-2,2-dithiolate (i-MNT) ligands are presented in this paper. Reactions of M(I) (M = Cu, Ag) salts, [Bu4N](2)[S2CC(CN)(2)], with the anion sources ([Bu4N][BH4] for H-, [Bu4N] [BD4] for D-) in an 8:6:1 molar ratio in THF produce octanuclear penta-anionic Cu(I)/Ag(I) clusters, [Bu4N](8)[M-8(X){S2CC(CN)(2)}(6)] (M = Cu, X = H, 1(H); X = D, 1(D); M = Ag, X = H, 2(H); X = D, 2(D)). They can also be produced from the stoichiometric reaction of M-8(i-MNT)(6)(4-) with the ammonium borohydride. All four compounds have been fully characterized spectroscopically (H-1 and C-13 NMR, IR, UV-vis) and by elemental analyses. The deuteride-encapsulated Cu-8/Ag-8 clusters of D-1 and D-2 are also characterized by H-2 NMR X-ray crystal structures of 1(H) and 2(H) reveal a hydride-centered tetracapped tetrahedral Cu-8/Ag-8 core, which is inscribed within an S-12 icosahedron formed by six i-MNT ligands, each in a tetrametallic tetraconnective (mu(2), mu(2)) bonding mode. The encapsulated hydride in 2(H) is unequivocally characterized by both H-1 and Ag-109 NMR spectroscopies, and the results strongly suggest that the hydride is coupled to eight magnetically equivalent silver nuclei on the NMR time scale. Therefore, a fast interchange between the vertex and capping silver atoms in solution gives a plausible explanation for the perceived structural differences between the Ag-8 geometry deduced from the X-ray structure and the NMR spectra.