Formation of a robust Ru sub(4)O sub(4) skeleton with two Ru sub(2)(CO) sub(4) units in criss-cross configuration

Thermolysis of triruthenium dodecacarbonyl Ru sub(3)(CO) sub(12) with picolinic acid, 2-furoic acid and 2-thiophenecarboxylic acid was thoroughly studied. Three ruthenium carbonyl products, Ru sub(4)(CO) sub(8)( mu sub(2)-O, eta super(1)-N-pic) sub(4) (1) (pic = picolinate), [Ru sub(2)(CO) sub(4)(fur) sub(2)] sub(m) (2) (fur = 2-furoate) and [Ru sub(2)(CO) sub(4)(thi) sub(2)] sub(n) (3) (thi = 2-thiophenecarboxylate) were isolated. Single crystal X-ray crystallography revealed that compound 1 is a tetraruthenium cluster with two Ru sub(2)(CO) sub(4) units in an unexpected criss-cross geometry, while compounds 2 and 3 exhibit the classical sawhorse structure. Compound 1 was stable to common donor ligands and formed solvated compounds Ru sub(4)(CO) sub(8)( mu sub(2)-O, eta super(1)-N-pic) sub(4) .H sub(2)O (4) and Ru sub(4)(CO) sub(8)( mu sub(2)-O, eta super(1)-N-pic) sub(4) .CH sub(3)CN (5) in hydrous toluene and acetonitrile, respectively; compounds 2 and 3 converted into monomers Ru sub(2)(CO) sub(4)(fur) sub(2)(H sub(2)O) sub(2) .H sub(2)O (2b) and Ru sub(2)(CO) sub(4)(thi) sub(2)(CH sub(3)OH) sub(2).CH sub(3)OH (3b) in hydrous dichloromethane and acetonitrile, respectively. [Ru sub(2)(CO) sub(4)(pic) sub(2)] sub(2) (1a), Ru sub(2)(fur) sub(2)(CO) sub(6) (2a) and Ru sub(2)(thi) sub(2)(CO) sub(6) (3a) were proposed as the corresponding intermediates of 1-3 based on in situ FT-IR spectroscopy, LC-MS and the molecular structures of the known ruthenium carbonyl carboxylates.