Saccharinate as a versatile polyfunctional ligand. Four distinct coordination modes, misdirected valence, and a dominant aggregate structure from a single reaction system

Resumen

The reaction system consisting of copper, saccharinate, and the auxiliary ligands H 2O, PPh 3, and NH 3 produces a sequence of compounds in which saccharinate is coordinated to copper in four distinct manners. The complex trans-[Cu(sacch) 2(H 2O) 4] (2) (produced by thermal dehydration of trans-[Cu(sacch) 2(H 2O) 4] ·2H 2O (1)) reacts with triphenylphosphine in CH 2Cl 2 to produce any or all of three Cu(I) complexes, depending upon conditions. The three Cu(I) compounds are Cu(sacch)(PPh 3) 3 (3), in which saccharinate binds to copper through the carbonyl group of the ligand, Cu(sacch)(PPh 3) 2 (4), in which sacch binds to Cu through its charge-bearing nitrogen atom; and [Cu(sacch)(PPh 3)] 2 (5), a dinuclear complex in which saccharinate bridges two Cu centers through its imidate nitrogen and carbonyl oxygen atoms. Complexes 3-5 can be isolated individually, although in solution they exist in a complex equilibrium which has been examined by NMR spectroscopy. Each of the three Cu(I) products reacts with NH 3 in CH 2Cl 2 solution to produce trans-[Cu(sacch) 2(NH 3) 4] (6), an unstable Cu(II) complex that exhibits misdirected valence at the Cu-N(sacch) bond. Complex 6 evolves spontaneously to [Cu(sacch)(NH 3) 4](sacch)·H 2O (7), which in the solid state is dominated by a supramolecular aggregate of two formula units, linked by hydrogen bonding in which the water molecule plays a central role. Alternative pathways exist to several of the products. The X-ray crystal structure analyses of 3-7 are reported and establish the coordination modes of saccharinate, the misdirected valence in 6, and the supramolecular aggregation in 7. The structure analysis of 7 by single-crystal neutron diffraction is reported and together with the previously reported neutron structure analysis of 1 establishes the substitution of the auxiliary ligand H 2O by NH 3 in the Cu(II) products.