Synthesis of 9-anthrylmethyl-functionalised cyclopentadienyl derivatives of rhodium(I) and iridium(I) and study of their luminescence properties

The compound 9-anthrylmethylcyclopentadiene 1 was prepared by reacting 9-bromomethylanthracene with cyclopentadienylsodium and transformed into its thallium(I) derivative on reaction with thallium ethoxide 3. The 9-anthrylmethylcyclopentadienyl (AnCH2C5H4) derivatives of rhodium(I) and iridium(I) of formula [M(η5-AnCH2C5H4)L2] (M=Rh or Ir; L=C2H4, CO, PPh3, C8H14; L2=C7H8, 1,5-C8H12) 4–6 and 9–11 were obtained in good yields by reacting the corresponding rhodium(I) and iridium(I) chlorides with 3. Both [Rh(η5-AnCH2C5H4)(η2-C2H4)2] (4) and [Rh(η5-AnCH2C5H4)(CO)2] (5) react with triphenylphosphine, at 130°C to give [Rh(η5-AnCH2C5H4)(η2-C2H4)(PPh3)] (7) and [Rh(η5-AnCH2C5H4)(CO)(PPh3)] (8). All complexes were characterised by elemental analysis, mass spectrometry, 1H-NMR and FTIR. The structures of two of them, i.e. [Rh(η5-AnCH2C5H4)(η2-C2H4)2] (4) and [Rh(η5-AnCH2C5H4)(CO)2] (5), were elucidated by single crystal X-ray diffraction. Compound 4 crystallises in the triclinic space group P1̄ with a=11.112(1), b=12.065(1), c=15.982(2) Å; α=99.83(1), β=107.86(1), γ=107.22(1)°. V=1865.6(3) Å3. Z=4, Dcalc=1.475 g cm−1, R1=0.0414 [I>2σ(I)], wR2=0.0953. Compound 5 crystallises in the triclinic space group P1̄ with a=12.232(1), b=13.463(1), c=13.488(1) Å; α=61.25(1), β=68.51(1), γ=67.45(1)°. V=1752.5(2) Å3. Z=4, Dcalc=1.570 g cm−1, R1=0.0313 [I>2σ(I)], wR2=0.0795. The UV–vis spectra (280–700 nm) of 1 and of complexes 4–11 were recorded. The spectra of 4–11 are indicative of important interactions between the anthrylic chromophore and the cyclopentadienyl–metal moiety. When excited at 365 nm, 1 results to be an efficient light-emitting molecule, while its derivatives 4–11 are poorly luminescent compounds. Indeed, all complexes exhibit similar fluorescence spectra which are typical of the anthrylic fluorophore but have extremely low intensity (the one observed for 9-methylanthracene was below 5% and taken as the reference compound). The mechanism of fluorescence quenching in the complexes 4–11 is discussed.