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)(3)Mn(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)(2)Mn(C5H4-B(mu-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)(3)Mn(C5H4-BPh3)] (7) contain dimeric aggregates held together by K+-OC sigma adducts, K+-pz sigma adducts, and K+-pz pi interactions (2, 3) as well as Li+-OC sigma adducts and Li+-phenyl pi interactions (7). In none of these cases does the pi-electron cloud of the cymantrenyl substituent take part in alkali metal ion complexation.