Published: July 06, 2011 r2011 American Chemical Society 4115 dx.doi.org/10.1021/om200421a | Organometallics 2011, 30, 4115–4122 ARTICLE pubs.acs.org/Organometallics Reversible Reductive Dimerization of Diiron μ-Vinyl Complex via CC Coupling: Characterization and Reactivity of the Intermediate Radical Species Adriano Boni, †,^ Tiziana Funaioli, † Fabio Marchetti,* ,† Guido Pampaloni, † Calogero Pinzino, ‡ and Stefano Zacchini § † Dipartimento di Chimica e Chimica Industriale, Universit  a di Pisa, Via Risorgimento 35, I-56126 Pisa, Italy ‡ CNR-Consiglio Nazionale delle Ricerche, ICCOM, Area della Ricerca, Via G. Moruzzi 1, I-56124 Pisa, Italy § Dipartimento di Chimica Fisica e Inorganica, Universit  a di Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy ^ Scuola Normale Superiore, Piazza dei Cavalieri, I-56126 Pisa, Italy b S Supporting Information ’ INTRODUCTION Carboncarbon couplings on small transition metal units have attracted considerable attention since they may serve as models for related catalytic processes. 1 In this context, the reactivity of hydrocarbyl units, bridging coordinated in di- nuclear iron or ruthenium complexes bearing ancillary cyclo- pentadienyl and/or carbonyl ligands, has been widely investigated. 2 In principle, dinuclear metal species may provide nonconventional reactivity patterns to bridging ligands and offer the possibility of stabilizing coordination fashions, as a consequence of the cooperativity effects of the two metal centers working in concert. 3 A series of intermolecular CC bond forming reactions between hydrocarbyl fragments coordinated to metal complexes have been documented, and they generally lead to an increase of nuclearity with no reversible character. 4 The series includes the coupling of two radical units based on the [Fe 2 Cp 2 (CO) 2 (μ- CO)] frame to give a Fe 4 derivative. 5 Other relevant examples are the reductive dimerization of [Co 4 (CO) 3 (μ 3 -CO) 3 (μ 3 -C 7 H 7 )- (η 5 -C 7 H 9 )] and that of the 19-electron complex FeCp(η 6 - C 6 H 6 ), affording CC bridged dimers, involving respectively the cycloheptatrienyl ligand 6 and the aromatic C6 ring. 7 In the present paper, we report on the redox chemistry (straightforward reversible reduction to a fairly stable radical species, which dimerizes to a CC bridged Fe 4 compound) of the diiron μ-vinyl complex [Fe 2 Cp 2 (CO) 2 (μ-CO){μ-η 1 :η 2 - CHdCH(Ph)}][BF 4 ], [1][BF 4 ], obtained in two steps from the commercial Fe 2 Cp 2 (CO) 4 according to Scheme 1. 8 ’ RESULTS AND DISCUSSION Our interest in the chemistry of hydrocarbyl ligands coordi- nated in diiron and diruthenium complexes 9 prompted us to investigate the reactivity of the formerly described μ-vinyl [Fe 2 Cp 2 (CO) 2 (μ-CO){μ- η 1 : η 2 -CHdCH(Ph)}][BF 4 ], [1]- [BF 4 ]. The nucleophilic additions of a restricted series of nucleophiles (e.g., H  , CN  ) to [1][BF 4 ] were reported to occur at the phenyl-substituted carbon, to afford alkylidene derivatives. 8c Surprisingly, all our attempts to extend this chem- istry to other nucleophiles (e.g., PhLi, LiCtCPh, NEt 3 ) resulted in the formation of a unique product, which was identified as the tetrairon complex [Fe 2 Cp 2 (CO) 2 (μ-CO){μ-CHCH(Ph)}] 2 , 2. On account of the fact that the formation of 2 appears to be the result of the CC homocoupling of a diiron complex derived from the monoelectron reduction of [1][BF 4 ], the best conditions for the synthesis of 2 were found by using a typical monoelectron Received: May 19, 2011 ABSTRACT: The diiron μ-vinyl complex [Fe 2 Cp 2 (CO) 2 (μ-CO){μ-η 1 :η 2 -CHdCH(Ph)}]- [BF 4 ], [1][BF 4 ], reacted with CoCp 2 affording selectively the CC coupling product [Fe 2 Cp 2 (CO) 2 (μ-CO){μ-CHCH(Ph)}] 2 , 2. The cation [1] + was regenerated from 2 in good yield by I 2 -induced oxidative cleavage. The cation [1] + underwent two sequential monoelec- tron reductions, the first one being an electrochemically reversible process that generated the radical species [Fe 2 Cp 2 (CO) 2 (μ-CO){μ-CHCH(Ph)}], [1] • . The latter was characterized by EPR spectroelectrochemistry. The structures of [1] + ,[1] • , and 2 were optimized for the gas phase by DFT calculations. The reaction of [1][BF 4 ] with NEt 3 in the presence of excess PhSSPh gave [Fe 2 Cp 2 (CO) 2 (μ-CO){μ-CHCH(Ph)(SPh)}], 3. The new compounds 2 and 3 were fully characterized by IR and NMR spectroscopy, elemental analysis, and X-ray diffraction studies.