Organometallic Oligomers Based on 1,8-Diisocyano-p-menthane (dmb):  Syntheses and Characterization of the {[M(diphos)(dmb)]BF₄}_n and {[Pd₂(diphos)₂(dmb)](ClO₄)₂}_n Materials (M = Cu, Ag; diphos = dppe, dppp)

A new strategy to synthesize organometallic oligomers is presented and consists of using the title diisocyanide and chelated metal fragments with bis(diphenylphosphine)alkanes. The title materials are synthesized by reacting the [M(dppe)(BF₄)] and [M₂(dppp)₂](BF₄)₂ complexes (M = Cu, Ag; dppe = bis(diphenylphosphino)ethane, dppp = bis(diphenylphosphino)propane) with dmb and the Pd₂-bonded d⁹−d⁹ Pd₂(dmb)₂Cl₂ dimer with dppe or dppp. The model compounds [M(diphos)(CN-t-Bu)₂]BF₄ (M = Cu, Ag) and [Pd₂(diphos)₂(CN-t-Bu)₂](ClO₄)₂ (diphos = dppe, dppp) have been prepared and characterized as well for comparison purposes. Three of the model compounds were also characterized by X-ray crystallography to establish the diphosphine chelating behavior. The materials are amorphous and have been characterized from the measurements of the intrinsic viscosity, DSC, TGA, and XRD, as well as their capacity for making stand-alone films. The intrinsic viscosity data indicate that the Cu and Pd₂ materials are oligomeric in solution (∼8−9 units), while the Ag materials are smaller. For {[Cu(dppe)(dmb)]BF₄}_n, a glass transition is reproducibly observed at about 82 °C (ΔC_p = 0.43 J/(g deg)), which suggests that these materials are polymeric in the solid state. The Cu and Ag species are luminescent in the solid state at room temperature exhibiting λ_max and τ_e (emission lifetime) around 480−550 nm and 18−48 μs, respectively, while the Pd₂ species are not luminescent under these conditions. During the course of this study, the unsaturated [M₂(dppp)₂](BF₄)₂ starting materials (M = Cu, Ag) were prepared, one of which (M = Ag) was characterized by crystallography. The bridging behavior of the dppp ligand in this case contrasts with the chelating behavior seen for the saturated [Cu(dppp)(CN-t-Bu)₂]BF₄ complex.