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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Gamma,delta-unsaturated ketones undergo two very different stereoselective cyclization reactions mediated by samarium(II) iodide depending upon the alcohol cosolvent used in the reaction. Switching between an unprecedented aldol spirocyclization and a novel cyclobutanol-forming process can be achieved simply by changing the alcohol cosolvent from methanol to tert-butyl alcohol. [reaction: see text]

The bis(phosphido)-bridged complex [Fe(2)(mu-PPhH)(2)(CO)(6)] (1) undergoes double deprotonation to give the phosphorus-centered dianionic derivative [Fe(2)(mu-PPh)(2)(CO)(6)](2)(-) (2) which in turn reacts with the tertiary base RN(CH(2)Cl)(2) to give [Fe(2)[(PPhCH(2))(2)NR](CO)(6)] (3) in moderate yield. Treatment of 3 with HBF(4).Et(2)O affords the N-protonated species [Fe(2)[(PPhCH(2))(2)NHR](CO)(6)] BF(4) (4). The structural changes to the heavy atom skeleton of 3 arising from protonation are slight, the most obvious being a ca. 0.03 Alengthening of the N-C bonds.

Reaction of the bis-isonitrile complex [Mo2Cp2(μ-SMe)3(t-BuNC)2](BF4) (1) with n-BuLi (in hexane) produced the dealkylated derivative [Mo2Cp2(μ-SMe)3(t-BuNC)(CN)] (2) in quantitative yield. However, upon treatment with either NaOH (suspension) or (Me4N)OH (in MeOH), 1 was converted into a mixture of 2 and the μ-alkylidyne species [Mo2Cp(μ-SMe)3{μ-(η5-C5H4)(t-BuN)CN(t-Bu)C}] (3), in which a deprotonated Cp and both isonitrile ligands of 1 are now linked by new carbon−carbon and carbon−nitrogen bonds.

Treatment of [PtMe2(bu2bpy)] (bu2bpy = 4,4‘-di-tert-butyl-2,2‘-bipyridine) with B(C6F5)3 in the presence of the ligand L gives, under anhydrous conditions, [PtMeL(bu2bpy)][MeB(C6F5)3] {L = CO (1a), C2H4 (2a), PPh3 (3a)}. Similar reactions performed in the presence of H2O afford [PtMeL(bu2bpy)][HOB(C6F5)3] {L = CO (1b), C2H4 (2b), PPh3 (3b)}. In the absence of L, the treatment of [PtMe2(bu2bpy)] with B(C6F5)3 and H2O gives [Pt{HOB(C6F5)3}Me(bu2bpy)] (4), the first published example of a hydroxytris(pentafluorophenyl)borate complex. All of the complexes are fully characterized by NMR and IR spectroscopy and, in the case of complex 4, by an X-ray analysis which confirms the attachment of the [HOB(C6F5)3]- ligand to the square-planar platinum atom via a Pt−O bond of 2.062(2) Å. We propose that, in the presence of water, B(C6F5)3 forms an adduct [H2OB(C6F5)3] (which acts as a strong acid H[HOB(C6F5)3]) and this then protonates a Pt−Me bond of [PtMe2(bu2bpy)] forming CH4 and [PtMe(bu2bpy)]+[HOB(C6F5)3]-. This protonolysis methodology provides an alternative route to the well-established electrophilic methyl-ligand abstraction by B(C6F5)3 for the production of late transition-metal cations.