Mn(CO)₂ Complexes of Cyclopentadienyl/Scorpionate Hybrid Ligands

Rare examples of complexes featuring a chelating cyclopentadienyl/scorpionate hybrid ligand are reported. The compounds are obtained by photolytic decarbonylation of K[(OC)₃Mn(C₅H₄-B(pz)(R)R‘)] (1:  R = R‘ = Me; 2:  R = Me, R‘ = pz; 3:  R = R‘ = pz; pz = pyrazol-1-yl), which leads to the constrained-geometry complexes K[(OC)₂Mn(C₅H₄-B(μ-pz)(R)R‘)] (4−6) in quantitative yields. In 4−6, the Mn-coordinating pyrazolyl ring is tethered to the cyclopentadienyl ligand via a borate bridge. According to X-ray crystallography, the molecular frameworks of 4−6 are largely unstrained. The ligand scaffold is thus well adapted to the coordination requirements of the Mn(I) ion. The crystal lattices of 2, 3, and Li[(OC)₃Mn(C₅H₄-BPh₃)] (7) contain dimeric aggregates held together by K⁺-OC σ adducts, K⁺-pz σ adducts, and K⁺-pz π interactions (2, 3) as well as Li⁺-OC σ adducts and Li⁺-phenyl π interactions (7). In none of these cases does the π-electron cloud of the cymantrenyl substituent take part in alkali metal ion complexation.