A Basic Strategy for Functionalization of Metal Cyclopentadienyl Complexes: Synthesis, Characterization, and Reactivity of Linear, Butterfly, and Cubic Chromium/Selenium Complexes Containing Functionally Substituted Cyclopentadienyl Ligands

The first examples of linear, butterfly, and cubic Cr/Se complexes containing functionally
substituted Cp ligands have been successfully synthesized by skeleton and functional
transformations of the prefunctionalized Cp metal precursors. For example, (i) the prefunctionalized Cp metal precursors [η5-RC5H4Cr(CO)3]2 (1, R = MeCO; 2, R = MeO2C) reacted
with elemental selenium under the given conditions to afford linear complexes [η5-RC5H4Cr(CO)2]2Se (3, R = MeCO; 4, R = MeO2C), butterfly complexes [η5-RC5H4Cr(CO)2]2Se2 (5,
R = MeCO; 6, R = MeO2C), and cubane clusters (η5-RC5H4)4Cr4Se4 (7, R = MeCO; 8, R =
MeO2C), whereas the linear complexes 3/4 reacted with elemental selenium under appropriate conditions to produce butterfly complexes 5/6 or cubane clusters 7/8; (ii) thermolysis of
a THF solution of butterfly complex 5 or 6 gave rise to cubane cluster 7 or 8, whereas the
THF solution of two butterfly complexes [CpCr(CO)2]2Se2 and 6 under reflux afforded cubane
clusters (η5-MeO2CC5H4)nCp4-nCr4Se4 (n = 0, Cp4Cr4Se4; n = 1, 9; n = 2, 10; n = 3, 11; n =
4, 8); (iii) while cluster 7 reacted with excess NaBH4 to give secondary hydroxy derivative
[η5-MeCH(OH)C5H4]4Cr4Se4 (12), it reacted with Grignard reagent MeMgI and subsequent
hydrolysis of the addition intermediate to afford tertiary hydroxy derivative [η5-Me2C(OH)C5H4]4Cr4Se4 (13); and (iv) the functional transformation of cluster 7 under the action of
Wittig reagent Ph3PCHPh produced cubane cluster [η5-PhCHC(Me)C5H4]4Cr4Se4 (14),
whereas the condensation reaction of 7 with 2,4-dinitrophenylhydrazine yielded phenylhydrazone derivative [η5-2,4-(NO2)2C6H3NHNC(Me)C5H4]4Cr4Se4 (15). Possible pathways for
the reactions leading to functionalized cubane clusters 7−11 are suggested. Furthermore,
77Se NMR techniques were utilized to characterize the new functionalized complexes, whereas
single-crystal X-ray diffraction was employed to confirm the structures of complexes 4, 7, 8,
11, and 12.