In situ synthesis of trisubstituted methanol ligands and their potential as one-pot generators of cubane-like metal complexes

Two different one Pot routes to a variety of metal cubane compounds are reported; one route is based on an in situ benzilic acid type rearrangement and the other involves in situ nucleophilic attack at a ketone. Diketosuccinic acid in basic solution in the presence of certain divalent metal ions undergoes a benzilic acid type rearrangement to generate the carbon oxyanion, C(CO2-)(3)O-, which serves as a cubane-forming bridging ligand in a series of octanuclear complexes of composition [M-8{C(CO2)(3)O}(4)](H2O)(12) (M=Mg, Mn, Fe, Co, Ni, Zn). At the heart of each of these highly symmetrical aggregates is an M4O4 cubane core, each oxygen component of which is provided by the alkoxo centre of a C-(CO2-)(3)O- ligand. Reaction of 2,2'-pyridil, (2-C5H4N)COCO(2-C5H4N), and calcium nitrate in basic alcoholic solution, which proceeds by a similar benzilic acid type rearrangement, gives the cubane compounds, [Ca4L4(NO3)(4)] in which L = (2-C5H4N)(2)C(COOR)O- (R = Me or Et). Nucleophilic attack by bisulfite ion at the carbonyl carbon atom of 2,2'-dipyridyl ketone in the presence of certain divalent metals generates the electrically neutral complexes, [{(C5H4N)(2)SO3C(OH)}(2)M] (M = Mn, Fe, Co, Ni, Zn and Cd). Cubane-like complexes [M-4-{(C5H4N)(2)SO3C(O)}(4)] (M = Zn, Mn) can be obtained directly from 2,2'-dipyridyl ketone in one-pot reaction systems (sealed tube, 120 degrees C) if a base as weak as acetate ion is present to deprotonate the OH group of the initial [(C5H4N)(2)SO3C(OH)](-) bisulfite addition compound; the [(C5H4N)(2)SO3C(O)](2-) ligand in this case plays the same cubane-forming role as the ligands C(COO-)(3)O- and (2-C5H4N)(2)C(COOR)O- above. When excess sodium sulfite is used in similar one-pot reaction mixtures, the mono-anionic complexes, [M3Na{(C5H4N)(2)SO3C(O)}(4)](-) (M=Zn, Mn, Co) with an M3NaO4 cubane core, are formed directly from 2,2'-dipyridyl ketone.