Dicopper(I) Oxalate Complexes Stabilized by Lewis Bases: Potential Precursors for Copper Deposition

The synthesis, characterization, and thermal behavior of the dicopper(I) oxalate complexes
L2Cu2O4C2 (L = Me3SiC⋮CSiMe3 (1), Me3SiC⋮CnBu (2), EtC⋮CEt (3), H2CC(H)SiMe2tBu
(4), H2CC(H)SiEt2Me (5), norbornene (6)) is reported. All complexes can be prepared in a
straightforward manner by the reaction of stoichiometric amounts of Cu2O and oxalic acid
with 2 equiv of the respective alkyne or alkene. The complexes are stable at room
temperature, and in solid form they can be handled in air for some time. Their thermal
behavior was studied by thermal gravimetric analysis (TGA). The order of thermal stability
was found to be 1 > 6 > 4 > 2 ≈ 3 > 5. Decomposition starts between 50 and 100 °C and
is completed between 300 and 350 °C. All compounds fully decompose via an efficient internal
redox process to give elemental copper, CO2, and the free alkyne or alkene ligands, which
makes these new complexes promising precursors for copper deposition (in the case of 4, it
is likely that H2CC(H)SiMe2H and isobutene is formed via β-hydrogen elimination from
H2CC(H)SiMe2tBu). Distinct two- or three-step decomposition sequences for the individual
complexes are revealed by the TGA analyses and are discussed. The single-crystal X-ray
structures of 1 and 3 are reported, which are the first for copper(I)/oxalato compounds. Both
complexes exhibit the anticipated planar dinuclear structure with the oxalate in a μ-1,2,3,4
bridging mode and the alkynes or alkenes as capping ligands.