A series of organometallic mono-and disubstituted bis(alkynyl)biferrocenes of type (L n MCtC)-(HCtC)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 MCtC) 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 (HCtC) 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 KOtBu (synthesis of 8 and 9), respectively. The structures of 6, 8b, 9a, 9b, and 9c in the solid state were determined by singlecrystal 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.

Treatment of 1 0 ,1 000 -bis(ethynyl)biferrocene (1) with 2 equiv of FeCl(η 2 -dppe)(Cp*) (2) in the presence of [H 4 N]PF 6 produced the vinylidene complex [1 0 ,1 000 -((Cp*)(η 2 -dppe)FedCdCH) 2 bfc][PF 6 ] 2 (3) (97%, Cp*=η 5 -C 5 Me 5 ; dppe=1,2-bis(diphenylphosphino)ethane; bfc=1 0 ,1 000 -biferrocenyl, (η 5 -C 5 H 4 ) 2 Fe) 2 ), while neutral tetranuclear 1 0 ,1 000 -((Cp*)(η 2 -dppe)Fe-CtC) 2 bfc (4) was obtained from the reaction of 3 with KO t Bu (68%). The IR, 1 H, 13 C, and 31 P NMR, cyclic voltammetry, M€ ossbauer, and UV-vis data were obtained for 4. When reacted with 2 equiv of [FcH]PF 6 or TCNQ, complex 4 provided 4[X] 2 (Fc = 1-ferrocenyl, (η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 ), X = PF 6 , 89%; X = TCNQ = 7,7,8,8tetracyanoquinodimethane, 91%), and 4[PF 6 ] was obtained by reacting 4 with 4[PF 6 ] 2 in a 1:1 molar ratio (76%). Organometallics 4[PF 6 ] 3 (93%) and 4[PF 6 ] 4 (87%) were obtained from the reaction of 4[PF 6 ] 2 with 1 or 2 equiv of Ag [PF 6 ]. For the purpose of reasonable solubility the triflate salts of tri-and tetracationic species 4[OTf] 3 (94%) and 4[OTf] 4 (95%) were synthesized instead of the hexafluorophosphate salts. The structures of 3, 4, and 4[TCNQ] 2 in the solid state were determined by single-crystal X-ray structure analysis. IR and M€ ossbauer spectroscopy of 4[PF 6 ] n (n=0-4) allowed the stepwise observation of the four metal-centered oxidations and established the localized character of the mixedvalence complexes. EPR spectra of 4[PF 6 ] n (n=1, 3) proved the formation of two radicals, one centered on the half-sandwich termini and the other centered on the (ethynyl)biferrocene bridge, indicating that the mediating state is sufficiently low lying to be populated at 66 K. The NIR spectra of the mixedvalent species 4[PF 6 ] n (n=1, 2) and 4[OTf] 3 showed the presence of two bands, and their characteristic parameters are in accord with an electron transfer involving intermediate states. § Part of the Dietmar Seyferth Festschrift. In honor of Prof. Dr. h.c. mult. Dietmar Seyferth for his outstanding contribution as editor to Organometallics.