Binuclear transition-metal complexes of cyclophanoid cyclopentadienone and cyclopentadienyl ligands

Article abstract of DOI:10.1021/om00109a027

The double-layered cyclophanoid cyclopentadienone 2,3,10,11-tetraphenyltricyclo[12.2.1.1 ^9,12]octadeca-1,3,9,11-tetraene-17,18-dione (7) is obtained by aldol condensation of cyclotetradecane-1,8-dione (8) with 2 equiv of benzil (9). 7 (= L) reacts with Ni(COD)₂, Fe₂(CO)₉, and Cp*Co(C₂H₄)₂ to give the binuclear cyclopentadienone complexes (COD)Ni-L-Ni(COD) (11a), (CO)₃Fe-L-Fe(CO)₃ (11b), and Cp*Co-L-CoCp* (11c). 11a reacts with tetrafluoroboric acid and trifluoromethanesulfonic acid to yield the respective (hydroxycyclopentadienyl)nickel complexes [(COD)Ni-LH₂-Ni(COD)]₂₊·2BF₄^- (14a) and [(COD)Ni-LH₂-Ni(COD)]²⁺·2CF₃SO ₃^- (14b); likewise, (tetracyclone)Ni(COD) (13a) reacts with tetrafluoroboric acid to give the mononuclear hydroxycyclopentadienyl complex [(Ph₄CpOH)Ni]⁺BF₄^- (14e); 11a and 11c react with triethyloxonium tetrafluoroborate to afford the binuclear ethoxycyclopentadienyl complexes [(COD)Ni-LEt₂-Ni(COD)]²⁺·2BF₄ ^- (14c) and [Cp*Co-LEt₂-CoCp*]²⁺·2BF ₄^- (14d). The electrochemical properties of the binuclear (cyclopentadienone)cobalt complex 11c and the binuclear (ethoxycyclopentadienyl)nickel complex 14c are examined; both complexes show interacting redox sites. X-ray structural investigations on 11a show an anti conformation of the two quasi-planar cyclopentadienone rings, the distance between them being approximately 410 pm; each nickel atom is bonded η⁴ to its cyclopentadienone moiety, the Ni-Ni distance being 805 pm; the whole molecule is centrosymmetric (crystal system monoclinic; space group C2/c; a = 2433.1 (10) pm, b = 1425.1 (6) pm, c = 1850.0 (7) pm, β = 97.83 (3)° Z = 4).