The reactions of FeCl(dppe)Cp* and Ru(CtCCtCH)L 2 Cp′ with Na[BPh 4 ] and 1,8diazabicyclo[5.4.0]undec-7-ene (dbu; 2 equiv) in a mixed thf/NEt 3 solvent afford {Cp*(dppe)-Fe}(CtCCtC){Ru(PP)Cp′} (PP ) dppe, Cp′ ) Cp*, 7; PP ) (PPh 3 ) 2 , Cp′ ) Cp, 8). Cyclic voltammetry shows that these mixed Fe/Ru complexes undergo sequential loss of up to three electrons, with the mono-and dioxidized species being isolated following chemical oxidation. Computational (DFT) and spectroscopic (IR, NMR, ESR, Mo ¨ssbauer) studies are consistent with a polarized ground-state structure with oxidation leading to the gradual evolution of cumulenic character in the FeC 4 Ru moiety and a greater degree of orbital mixing between the Fe, C, and Ru centers than found in the related heterometallic complex [{Cp*(dppe)-Fe}(CtCCtC){Re(NO)(PPh 3 )Cp*}] n+ ([6] n+ ). In contrast to the two-electron oxidation products derived from the diiron complex {Cp*(dppe)Fe}(CtCCtC){Fe(dppe)Cp*} (1) and iron/rhenium complex 6, the dications [7] 2+ and [8] 2+ feature a dominant contribution from a singlet ground state. Thus, while 6 behaves in a manner closely related to 1, 7 and 8 are more closely related to {Cp(Ph 3 P) 2 Ru}(CtCCtC){Ru(PPh 3 ) 2 Cp} (2) and {Cp*(dppe)Ru}-(CtCCtC){Ru(dppe)Cp*} (3), clearly demonstrating the pronounced role that choice of metal as well as formal electron count can play in tuning the electronic and magnetic properties of this fascinating class of compound.

International audienceThe complexes [Fe2(CO)6{μ-SCH2N(R)CH2S}] (R = CH2CH2OCH3, 1a; R = iPr, 1b) and [Fe2(CO)6(μ-pdt)] 2 (pdt = S(CH2)3S) are structural analogues of the [2Fe]H subsite of [FeFe]H2ases. Electrochemical investigation of 1 and 2 in MeCN–[NBu4][PF6] under Ar and under CO has demonstrated that the reduction can be resolved into two one-electron transfer steps by using fast scan cyclic voltammetry. At slow scan rates the reduction of 1 tends towards a two-electron process owing to the fast disproportionation of the anion, while the two-electron reduction of 2 is clearly favoured in the presence of CO. Substitution of a CO ligand in 2 by a N-heterocyclic carbene results in the destabilisation of the anion. Thus, in MeCN–, thf- or CH2Cl2–[NBu4][PF6], the electrochemical reduction of Fe2(CO)5LNHC(μ-pdt)] 3 (LNHC = 1,3-bis(methyl)-imidazol-2-ylidene, 3a; 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene, 3b) occurs in a single-step, two-electron process at moderate scan rates; under appropriate conditions this process can be separated into two one-electron steps. Density Functional Theory calculations successfully rationalize the effects of the S-to-S linkage on the electrochemistry of the complexes

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Hydrogenation of CO: The reaction of [U(η‐C8H6{SiiPr3‐1,4}2)(η‐Cp*)] in toluene with CO and H2 at subambient to ambient temperature and pressure affords the methoxide complex [U(η‐C8H6{SiiPr3‐1,4}2)(η‐Cp*)OMe].

An intramolecular 1,2(α)-H migration in a saturated ruthenium stannylene complex, to form a ruthenostannylene complex, involves a reversal of the role for a coordinated stannylene ligand, from that of an electron donor to an acceptor in the transition state. This change in the bonding properties for a stannylene group, with a simple molecular motion, lifts the usual requirement for generation of an unsaturated metal center in migration chemistry.

The sequential conversion of [OsBr(cod)Cp*] (9) to [OsBr(dppe)Cp*] (10), [Os([=C=CH2)(dppe)Cp*]PF6 ([11]PF6), [Os(C triple bond CH)(dppe)Cp*] (12), [{Os(dppe)Cp*}2{mu-(=C=CH-CH=C=)}][PF6]2 ([13](PF6)2) and finally [{Os(dppe)Cp*}(2)(mu-C triple bond CC triple bond C)] (14) has been used to make the third member of the triad [{M(dppe)Cp*}2(mu-C triple bond CC triple bond C)] (M = Fe, Ru, Os). The molecular structures of []PF6, 12 and 14, together with those of the related osmium complexes [Os(NCMe)(dppe)Cp*]PF6 ([15]PF6) and [Os(C triple bond CPh)(dppe)Cp*] (16), have been determined by single-crystal X-ray diffraction studies. Comparison of the redox properties of 14 with those of its iron and ruthenium congeners shows that the first oxidation potential E1 varies as: Fe approximately Os < Ru. Whereas the Fe complex has been shown to undergo three sequential 1-electron oxidation processes within conventional electrochemical solvent windows, the Ru and Os compounds undergo no fewer than four sequential oxidation events giving rise to a five-membered series of redox related complexes [{M(dppe)Cp*}2(mu-C4)]n+ (n = 0, 1, 2, 3 and 4), the osmium derivatives being obtained at considerably lower potentials than the ruthenium analogues. These results are complimented by DFT and DT DFT calculations.

Treatment of [Cp*(dppe)Fe−CC-1-naphthyl] (3) with [CpRu(NCCH 3 ) 3 ](PF 6 ) (2(PF 6 )) in CH 2 Cl 2 provides the heterobinuclear complex [Cp*(dppe)Fe−CC-1-(η 6 -C 10 H 7 )RuCp](PF 6 ) in 80% isolated yield (Cp = η 5 -C 5 H 5 , Cp* = η 5 -C 5 Me 5 , dppe = 1,2-bis(diphenylphosphino)-ethane). Complexation of the CpRu + arenophile fragment specifically takes place onto either the substituted naphthyl ring A or on the unsubstituted ring B, providing isomers 1A(PF 6 ) and 1B(PF 6 ) in a 70/30 ratio. Under the same conditions, complexation of the cationic vinylidene 3H(PF 6 ) or the iron(III) complex 3(PF 6 ) affords 1A(PF 6 ) and 1B(PF 6 ) in a 30/70 ratio upon deprotonation of the dicationic vinylidenes 1AH(PF 6 ) 2 and 1BH(PF 6 ) 2 and monoelectronic reduction of the dicationic acetylides 1A(PF 6 ) 2 and 1B(PF 6 ) 2 , respectively. The new compounds were characterized by NMR, IR, cyclic voltammetry, and UV−vis methods. The X-ray crystal structures show that the (η 6 -arene)Ru distances lengthen according to the following sequence of compounds: 1B(PF 6 ), 1B(PF 6 ) 2 , and 1A(PF 6 ). It is found that the isomerization of 1A(PF 6 ) into 1B(PF 6 ) can be achieved at 20°C upon activation of the (η 6 -arene)Ru bond by one-electron oxidation of the remote iron center and assistance from a coordinating solvent molecule. The experimental data have been analyzed with the support of theoretical calculations performed at the density functional theory (DFT) level. It is proposed that the reaction pathway involves a transition state in which the CpRu + entity is η 3 -coordinated to the naphthyl rings in an exocyclic manner in a position opposite to the alkynyl iron moiety. Theoretical results also reflect the ability of the transition state to accommodate coordinating solvent molecules such as acetonitrile to lower the activation energy barrier of the haptotropic rearrangement.

Hydrierung von CO: Die Reaktion von [U(η‐C8H6{SiiPr3‐1,4}2)(η‐Cp*)] in Toluol mit CO und H2 unterhalb und unter Normalbedingungen liefert den Methoxid‐Komplex [U(η‐C8H6{SiiPr3‐1,4}2)(η‐Cp*)OMe].