1′,1′′′-Bis(ethynyl)biferrocene as a Linking Group for Gold, Ruthenium, and Osmium Fragments: Synthesis, Solid State Structures, and Electrochemical, UV−Vis, and EPR Spectroscopical Studies

A series of organometallic mono- and disubstituted bis(alkynyl)biferrocenes of type (L n MC≡C)(HC≡C)bfc (L n M = (η 5 -C 5 H 5 )(Ph 3 P) 2 Ru ( 8a ), (η 5 -C 5 H 5 )(Ph 3 P) 2 Os ( 8b ), (η 5 -C 5 H 5 )(dppf)Ru ( 8c ); bfc = 1′,1′′′-biferrocenyl, ((η 5 -C 5 H 4 ) 2 Fe) 2; dppf = 1,1′-bis(diphenyl)phosphanyl ferrocene, (η 5 -C 5 H 4 PPh 2 ) 2 Fe) and (L n MC≡C) 2 bfc (L n M = (Ph 3 P)Au ( 6 ), (η 5 -C 5 H 5 )(Ph 3 P) 2 Ru ( 9a ), (η 5 -C 5 H 5 )(Ph 3 P) 2 Os ( 9b ), (η 5 -C 5 H 5 )(dppf)Ru ( 9c )) have been synthesized from (HC≡C) 2 bfc ( 4 ) with either (Ph 3 P)AuCl ( 5 ) in the presence of HNEt 2 /[CuI] (synthesis of 6 ) or L n MX (L n MX = (η 5 -C 5 H 5 )(Ph 3 P) 2 RuCl ( 7a ); (η 5 -C 5 H 5 )(Ph 3 P) 2 OsBr ( 7b ); (η 5 -C 5 H 5 )(dppf)RuCl ( 7c )) together with [H 4 N]PF 6 and KO t Bu (synthesis of 8 and 9 ), respectively. The structures of 6, 8b, 9a, 9b, and 9c in the solid state were determined by single-crystal X-ray structure analysis, showing unsymmetrical ( 8 ) or symmetrical geometries ( 6, 9 ), with almost eclipsed conformations or approximately midway positions between the fully eclipsed and the fully staggered conformation of the bfc cyclopentadienyl rings and with anti geometry of the linear ethynyl connecting units. UV−vis and NIR spectroscopic measurements suggest a weak interaction between the appropriate metal atoms. The associated radical cations were in situ generated by stepwise chemical oxidation and characterized by continuous wave electron paramagnetic resonance (EPR) investigations in X-band performed at low temperature.