Dithiolate Complexes of Manganese and Rhenium: X-ray Structure and Properties of an Unusual Mixed Valence Cluster Mn3(CO)6(μ-η2-SCH2CH2CH2S)3

Chirality-Guided Isomerization of Mn2S2 Diamond Core Complexes: A Mechanistic Study

Occasioned by the discovery of a ligand transfer from M(N₂S₂) to Mn^I in Mn(CO)₅Br, the resulting H₂N₂S₂ ligand-tethered dimanganese complex, (μ₄-N,N'-ethylenebis(mercaptoacetamide))[Mn₂(CO)₆], was found to have myriad analogues of the type (μ-S-E)₂[Mn₂(CO)₆], making up an under-studied class containing Mn₂S₂ rhombs. The attempt to synthesize a nontethered version resulted in a solid-state structure in an anti-conformation. However, a direct comparison of the Fourier-transform infrared spectra of the tethered versus nontethered complexes in combination with theoretical frequency calculation suggested the coexistence of syn- and anti-isomers and their interconversion in solution. Analysis of the syn- versus anti-version of the dimanganese components led to the understanding that whereas the anti-form exists as centrosymmetric RS isomers, the syn-form is restricted by C₂ symmetry to be either RR or SS. Molecular scrambling experiments indicated monomeric, pentacoordinate, 16-e^- (S-O)Mn(CO)₃ intermediates with lifetimes sufficiently long to sample R and S monomers. Density functional theory analysis of the mechanistic pathway and a kinetic study corroborated that the proposed isomerization involves the cleavage and reformation of the dimeric structures.

Electronic Communication in Binuclear Osmium- and Iridium-Polyhydrides

Reactions of polyhydrides OsH₆(PⁱPr₃)₂ (1) and IrH₅(PⁱPr₃)₂ (2) with rollover cyclometalated hydride complexes have been investigated in order to explore the influence of a metal center on the MH_n unit of the other in mixed valence binuclear polyhydrides. Hexahydride 1 activates an ortho-CH bond of the heterocyclic moiety of the trihydride metal–ligand compounds OsH₃{κ²-C,N-[C₅RH₂N-py]}(PⁱPr₃)₂ (R = H (3), Me (4), Ph (5)). Reactions of 3 and 4 lead to the hexahydrides (PⁱPr₃)₂H₃Os{μ-[κ²-C,N-[C₅RH₂N-C₅H₃N]-N,C-κ²]}OsH₃(PⁱPr₃)₂ (R = H (6), Me (7)), whereas 5 gives the pentahydride (PⁱPr₃)₂H₃Os{μ-[κ²-C,N-[C₅H₃N-C₅(C₆H₄)H₂N]-C,N,C-κ³]}OsH₂(PⁱPr₃)₂ (8). Pentahydride 2 promotes C—H bond activation of 3 and the iridium-dihydride IrH₂{κ²-C,N-[C₅H₃N-py]}(PⁱPr₃)₂ (9) to afford the heterobinuclear pentahydride (PⁱPr₃)₂H₃Os{μ-[κ²-C,N-[C₅H₃N-C₅H₃N]-N,C-κ²]}IrH₂(PⁱPr₃)₂ (10) and the homobinuclear tetrahydride (PⁱPr₃)₂H₂Ir{μ-[κ²-C,N-[C₅H₃N-C₅H₃N]-N,C-κ²]}IrH₂(PⁱPr₃)₂ (11), respectively. Complexes 6–8 and 11 display HOMO delocalization throughout the metal–heterocycle-metal skeleton. Their sequential oxidation generates mono- and diradicals, which exhibit intervalence charge transfer transitions. This notable ability allows the tuning of the strength of the hydrogen–hydrogen and metal–hydrogen interactions within the MH_n units.

The influence of a metal center on the MH_n unit of the other in binuclear osmium- and iridium-polyhydride complexes bearing rollover cyclometalated bipyridines as a bridging ligand has been studied.

Mono- and Dinuclear Manganese Carbonyls Supported by 1,8-Disubstituted (L = Py, SMe, SH) Anthracene Ligand Scaffolds

Presented herein is a synthetic scheme to generate symmetric and asymmetric ligands based on a 1,8-disubstituted anthracene scaffold. The metal-binding scaffolds were prepared by aryl chloride activation of 1,8-dichloroanthracene using Suzuki-type couplings facilitated by [Pd(dba)2] as a Pd source; the choice of cocatalyst (XPhos or SPhos) yielded symmetrically or asymmetrically substituted scaffolds (respectively): namely, Anth-SMe2 (3), Anth-N2 (4), and Anth-NSMe (6). The ligands exhibit a nonplanar geometry in the solid state (X-ray), owing to steric hindrance between the anthracene scaffold and the coupled aryl units. To determine the flexibility and binding characteristics of the anthracene-based ligands, the symmetric scaffolds were complexed with [Mn(CO)5Br] to afford the mononuclear species [(Anth-SMe2)Mn(CO)3Br] (8) and [(Anth-N2)Mn(CO)3Br] (9), in which the donor moieties chelate the Mn center in a cis fashion. The asymmetric ligand Anth-NSMe (6) binds preferentially through the py moieties, affording the bis-ligated complex [(Anth-NSMe)2Mn(CO)3Br] (10), wherein the thioether-S donors remain unbound. Alternatively, deprotection of the thioether in 6 affords the free thiol ligand Anth-NSH (7), which more readily binds the Mn center. Complexation of 7 ultimately affords the mixed-valence Mn(I)/Mn(II) dimer of formula [(Anth-NS)3Mn2(CO)3] (11), which exhibits a fac-{Mn(CO)3} unit supported by a triad of bridging thiolates, which are in turn ligated to a supporting Mn(II) center (EPR: |D| = 0.053 cm(-1), E/|D| = 0.3, Aiso = -150 MHz). All of the metal complexes have been characterized by single-crystal X-ray diffraction, IR spectroscopy and NMR/EPR measurements-all of which demonstrate that the meta-linked, anthracene-based ligand scaffold is a viable approach for the coordination of metal carbonyls.

New insights into the chemistry of di- and trimetallic iron dithiolene derivatives. Structural, Mössbauer, magnetic, electrochemical and theoretical studies

Reaction of Fe3(CO)12 with 1,2-dithiolene HSC6H2Cl2SH affords a mixture of complexes [Fe2(CO)6(μ-SC6H2Cl2S)] 1, [Fe2(SC6H2Cl2S)4] 2 and [Fe3(CO)7(μ3-SC6H2Cl2S)2] 3. In the course of the reaction the trimetallic cluster 3 is first formed and then converted into the known dinuclear compound 1 to afford finally the neutral diiron tetrakis(dithiolato) derivative 2. Compounds 2 and 3 have been studied by Mössbauer spectroscopy, X-ray crystallography and theoretical calculations. In compound 2 the metal atoms are in an intermediate-spin Fe(III) state (S(Fe) = 3/2) and each metal is bonded to a bridging dithiolene ligand and a non-bridging thienyl radical (S = 1/2). Magnetic measurements show a strong antiferromagnetic coupling in complex 2. Cyclic voltammetry experiments show that the mixed valence trinuclear cluster 3 undergoes a fully reversible one electron reduction. Additionally, compound 3 behaves as an electrocatalyst in the reduction process of protons to hydrogen.

Electrocatalytic proton reduction catalyzed by a dimanganese disulfide carbonyl complex containing a redox-active internal disulfide bond

A dimanganese complex containing a redox-active elongated disulfide bond electrocatalyses proton reduction.

Precursors to [FeFe]-hydrogenase models: syntheses of Fe2(SR)2(CO)6 from CO-free iron sources

This report describes routes to iron dithiolato carbonyls that do not require preformed iron carbonyls. The reaction of FeCl 2, Zn, and Q 2S 2C n H 2 n (Q (+) = Na (+), Et 3NH (+)) under an atmosphere of CO affords Fe 2(S 2C n H 2 n )(CO) 6 ( n = 2, 3) in yields >70%. The method was employed to prepare Fe 2(S 2C 2H 4)( (13)CO) 6. Treatment of these carbonylated mixtures with tertiary phosphines, instead of Zn, gave the ferrous species Fe 3(S 2C 3H 6) 3(CO) 4(PR 3) 2, for R = Et, Bu, and Ph. Like the related complex Fe 3(SPh) 6(CO) 6, these compounds consist of a linear arrangement of three conjoined face-shared octahedral centers. Omitting the phosphine but with an excess of dithiolate, we obtained the related mixed-valence triiron species [Fe 3(S 2C n H 2 n ) 4(CO) 4] (-). The highly reducing all-ferrous species [Fe 3(S 2C n H 2 n ) 4(CO) 4] (2-) is implicated as an intermediate in this transformation. Reactive forms of iron, prepared by the method of Rieke, also combined with dithiols under a CO atmosphere to give Fe 2(S 2C n H 2 n )(CO) 6 in modest yields under mild conditions. Studies on the order of addition indicate that ferrous thiolates are formed prior to the onset of carbonylation. Crystallographic characterization demonstrated that the complexes Fe 3(S 2C 3H 6) 3(CO) 4(PEt 3) 2 and PBnPh 3[Fe 3(S 2C 3H 6) 4(CO) 4] feature high-spin ferrous and low-spin ferric as the central metal, respectively.