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(C 5 H 4 -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(C 5 H 4 -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) 3 Mn(C 5 H 4 -BPh 3 )] ( 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.

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The ditopic 1,3-cymantrenediyl-bridged scorpionate K2[(OC)3Mn(C5H3(Bpz3)2)] (3) is available in three steps and good yields starting from cymantrene. Its THF adduct [3(THF)2]2 crystallizes in the form of macrocyclic dimers. Reaction of 3 with BrMn(CO)5 gives access to the trinuclear MnI complex [(OC)3Mn(C5H3(Bpz3Mn(CO)3)2)] (4). Irradiation of 3 in CD3CN for 30 min with a high-pressure mercury lamp (λmax = 510 nm) results in the liberation of one CO molecule and intramolecular Mn-pyrazolyl coordination (mono-ansa-complex K2[(OC)2Mn(C5H3(B(μ-pz)pz2)(Bpz3)]; 5). Upon further irradiation, 5 undergoes demetalation, and the free cyclopentadienyl/scorpionate hybrid ligand K2[C5H4(Bpz3)2] (7) can be isolated from the reaction mixture. 7 has been structurally characterized both as a THF adduct (coordination polymer [7a(THF)2]∞) and as a THF/18-crown-6 adduct (dimer [7a(18-c-6)(THF)2]2).

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