Photochemical Synthesis of cis,trans,cis-1,2,3,4-Tetrakis(diphenylphosphanyl)buta-1,3-diene and Its Metal Coordination.

The new bis(bidentate) tetraphosphane cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphanyl)buta-1,3-diene (dppbd) (7) was obtained by applying a photochemical synthetic protocol. The key step of the photochemical reaction consisted of an intramolecular [2+2] cycloaddition involving a C-C double and triple bond of the Pt-dimer species of the formula [Pt2Cl4(dppa)(trans-dppen)] (2) {dppa = 1,2-bis(diphenylphosphanyl)acetylene and dppen = 1,2-bis(diphenylphosphanyl)ethene} leading to [Pt2Cl4(dppbd)] (5). The asymmetrically bridged precursor complex 2 was obtained by combinatorial chemistry. Single crystal X-ray structure analyses of 2 and 5 proved that the intramolecular photochemical reaction occurred. Cyanolysis of 5 gave 7, which was oxidized to dppbdO4 (8). Compounds 7, 8, and the PdII dimer complex [Pd2Cl4(dppbd)] (9) were characterized in the solid state by a single-crystal X-ray structure analysis. Interesting photophysial properties emerged from the UV/Vis spectra acquired for 7 and the dimer Os complexes meso-Δ,Λ/Λ,Δ-[Os2(bpy)4(dppbd)](PF6)4 (10) and rac-Δ,Δ/Λ,Λ-[Os2(bpy)4(dppbd)](PF6)4 (11).