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 [Pt(2)Cl(4)(dppa)(trans‐dppen)] (2) {dppa = 1,2‐bis(diphenylphosphanyl)acetylene and dppen = 1,2‐bis(diphenylphosphanyl)ethene} leading to [Pt(2)Cl(4)(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 Pd(II) dimer complex [Pd(2)Cl(4)(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‐[Os(2)(bpy)(4)(dppbd)](PF(6))(4) (10) and rac‐Δ,Δ/Λ,Λ‐[Os(2)(bpy)(4)(dppbd)](PF(6))(4) (11).