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Reductive Coupling of Diynes at Rhodium Gives Fluorescent Rhodacyclopentadienes or Phosphorescent Rhodium 2,2’‐Biphenyl Complexes
Author(s) -
Sieck Carolin,
Tay Meng Guan,
Thibault MarieHélène,
Edkins Robert M.,
Costuas Karine,
Halet JeanFrançois,
Batsanov Andrei S.,
Haehnel Martin,
Edkins Katharina,
Lorbach Andreas,
Steffen Andreas,
Marder Todd B.
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201601912
Subject(s) - rhodium , intersystem crossing , phosphorescence , biphenyl , chemistry , fluorescence , photochemistry , excited state , metal , catalysis , singlet state , organic chemistry , physics , quantum mechanics , nuclear physics
Reactions of [Rh( κ 2 ‐ O , O ‐acac)(PMe 3 ) 2 ] (acac=acetylacetonato) and α,ω‐bis(arylbutadiynyl)alkanes afford two isomeric types of MC 4 metallacycles with very different photophysical properties. As a result of a [2+2] reductive coupling at Rh, 2,5‐bis(arylethynyl)rhodacyclopentadienes ( A ) are formed, which display intense fluorescence ( Φ =0.07–0.54, τ =0.2–2.5 ns) despite the presence of the heavy metal atom. Rhodium biphenyl complexes ( B ), which show exceptionally long‐lived (hundreds of μs) phosphorescence ( Φ =0.01–0.33) at room temperature in solution, have been isolated as a second isomer originating from an unusual [4+2] cycloaddition reaction and a subsequent β ‐H‐shift. We attribute the different photophysical properties of isomers A and B to a higher excited state density and a less stabilized T 1 state in the biphenyl complexes B , allowing for more efficient intersystem crossing S 1 →T n and T 1 →S 0 . Control of the isomer distribution is achieved by modification of the bis‐ (diyne) linker length, providing a fundamentally new route to access photoactive metal biphenyl compounds.