Automated iterative Csp3-C bond formation.

Fully automated synthetic chemistry would substantially change the field by providing broad on-demand access to small molecules. However, the reactions that can be run autonomously are still limited. Automating the stereospecific assembly of Csp3-C bonds would expand access to many important types of functional organic molecules1. Previously, methyliminodiacetic acid (MIDA) boronates were used to orchestrate the formation of Csp2-Csp2 bonds and were effective building blocks for automating the synthesis of many small molecules2, but they are incompatible with stereospecific Csp3-Csp2 and Csp3-Csp3 bond-forming reactions3-10. Here we report that hyperconjugative and steric tuning provide a new class of tetramethyl N-methyliminodiacetic acid (TIDA) boronates that are stable to these conditions. Charge density analysis11-13 revealed that redistribution of electron density increases covalency of the N-B bond and thereby attenuates its hydrolysis. Complementary steric shielding of carbonyl π-faces decreases reactivity towards nucleophilic reagents. The unique features of the iminodiacetic acid cage2, which are essential for generalized automated synthesis, are retained by TIDA boronates. This enabled Csp3 boronate building blocks to be assembled using automated synthesis, including the preparation of natural products through automated stereospecific Csp3-Csp2 and Csp3-Csp3 bond formation. These findings will enable increasingly complex Csp3-rich small molecules to be accessed via automated assembly.

Defect Engineering in Composition and Valence Band Center of Y2(YxRu1-x)2O7-δ Pyrochlore Electrocatalysts for Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) takes place in various types of electrochemical devices that are pivotal for the conversion and storage of renewable energy. This paper describes a strategy in the design of solid-state structures of OER electrocatalysts through controlling the cation substitution on the active metal site and consequently valence band center position of site-mixed Y2(YxRu1-x)2O7-δ pyrochlore to achieve high catalytic activity. We found that partially replacing the B-site Ru4+ cation with A-site Y3+ in pyrochlore-structured Y2Ru2O7-δ modifies the oxidation state of B-site Ru from 4+ to 5+, as observed by electron paramagnetic resonance (EPR) spectroscopy but does not continuously increase the oxygen vacancy concentration in these oxygen substoichiometric compositions, as quantified by thermogravimetric analysis (TGA) decomposition studies. We found the increased Ru oxidation state leads to a downshift in valence band center. X-ray photoelectron spectroscopy (XPS) analysis was performed to quantitatively determine the optimal band center to be ∼1.27 eV below the Fermi energy level based on the analysis of the valence band edge of these Ru-based Y2(YxRu1-x)2O7-δ OER electrocatalysts. This work highlights that defect engineering can be a practical, effective approach to the optimization of oxidation state and electronic band center for high OER catalytic performance in a quantitative manner.

Assembly and Disassembly of Supramolecular Hypervalent Iodine Macrocycles via Anion Coordination.

This study explores the dynamic self-assembly and disassembly of hypervalent iodine-based macrocycles (HIMs) guided by secondary bonding interactions. The reversible disassembly and reassembly of HIMs are facilitated through anion binding via the addition of tetrabutylammonium (TBA) salts or removal of the anion by the addition of silver nitrate. The association constants for HIM monomers with TBA(Cl) and TBA(Br) are calculated and show a correlation with the strength of the iodine-anion bond. A unique tetracoordinate hypervalent iodine-based compound was identified as the disassembled monomer. Last, the study reveals the dynamic bonding nature of these macrocycles in solution, allowing for rearrangement and participation in dynamic bonding chemistry.

Exfoliable Transition Metal Chalcogenide Semiconductor NbSe2I2.

As the field of exfoliated van der Waals electronics grows to include complex heterostructures, the variety of available in-plane symmetries and geometries becomes increasingly valuable. In this work, we present an efficient chemical vapor transport synthesis of NbSe2I2 with the triclinic space group P1̅. This material contains Nb-Nb dimers and an in-plane crystallographic angle γ = 61.3°. We show that NbSe2I2 can be exfoliated down to few-layer and monolayer structures and use Raman spectroscopy to test the preservation of the crystal structure of exfoliated thin films. The crystal structure was verified by single-crystal and powder X-ray diffraction methods. Density functional theory calculations show triclinic NbSe2I2 to be a semiconductor with a band gap of around 1 eV, with similar band structure features for bulk and monolayer crystals. The physical properties of NbSe2I2 have been characterized by transport, thermal, optical, and magnetic measurements, demonstrating triclinic NbSe2I2 to be a diamagnetic semiconductor that does not exhibit any phase transformation below room temperature.

Formation of Red Elemental Selenium from Seleniferous Oxyanions: Deoxygenation by a Homogeneous Iron Catalyst.

Seleniferous oxyanions are groundwater contaminants from both anthropogenic and natural sources, while pure amorphous selenium nanoparticles have a variety of industrial applications. Biology can achieve the multicomponent 6 e-/8 H+ reduction of selenate to amorphous selenium using multiple metalloenzymes, like selenate and selenite reductase. Inspired by biology, we developed a new homogeneous system that can generate pure elemental selenium with no caustic waste. The stoichiometric reductions of selenate, selenite, and selenium dioxide with an iron(II) complex produced an iron(III)-oxo and red elemental selenium, the latter of which has been characterized by a variety of spectroscopic techniques. The catalytic reduction of SeO42- and SeO32- directly to amorphous Se and isolated as Se=PPh3 is reported with a turnover number of 12 and 7, respectively.

Insights into the Mechanism of CO2 Electroreduction by Molecular Palladium-Pyridinophane Complexes.

Herein, we report the synthesis, characterization, and electrocatalytic CO2 reduction activity of a series of Pd(II) complexes supported by tetradentate pyridinophane ligands. In particular, we focus on the electrocatalytic CO2 reduction activity of a Pd(II) complex supported by the mixed hard--soft donor ligand 2,11-dithia[3.3](2,6)pyridinophane (N2S2). We also provide spectroscopic evidence of a CO-induced decomposition pathway for the same catalyst, which provides insights into catalyst poisoning for molecular Pd CO2 reduction electrocatalysts.

Synthesis, Spectroscopy, and Structure of [FeRu(µ-dithiolate)(CN)2(CO)4]2.

The salt [K(18-crown-6)]2[Ru(CN)2(CO)3] ([K(18-crown-6)]2[1]) was generated by the reaction of Ru(C2H4)(CO)4 with [K(18-crown-6)]CN. An initial thermal reaction gives [Ru(CN)(CO)4]-, which, upon ultraviolet (UV) irradiation, reacts with a second equiv of CN-. Protonation of [1]2- gave [HRu(CN)2(CO)3]- ([H1]-), which was isolated as a single isomer with mutually trans cyanide ligands. The complex cis,cis,cis-[Ru(pdt)(CN)2(CO)2]2- ([2]2-) was prepared by the UV-induced reaction of [1]2- with propanedithiol (pdtH2). The corresponding iron complex cis,cis,cis-[Fe(pdt)(CN)2(CO)2]2- ([3]2-) was prepared similarly. The pdt complexes [2]2- and [3]2- were treated with Fe(benzylideneacetone)(CO)3 to give, respectively, [RuFe (µ-pdt)(CN)2(CO)4]2- ([5]2-) and [Fe2(µ-pdt)(CN)2(CO)4]2- ([4]2-). The pathway from [3]2- to Fe2 complex [4]2- implicates intermetallic migration of CN-. In contrast, the formation of [5]2- leaves the Ru(CN)2(CO) center intact, as confirmed by X-ray crystallography. The structure of [5]2- features a "rotated" square-pyramidal Fe(CO)2(µ-CO) site. NMR measurements indicate that the octahedral Ru site is stereochemically rigid, whereas the Fe site dynamically undergoes turnstile rotation. 57Fe Mössbauer spectral parameters are very similar for rotated [5]2- and unrotated Fe2 complex [4]2-, indicating the insensitivity of that technique to both the geometry and the oxidation state of the Fe site. According to cyclic voltammetry, [5]2- oxidizes at E1/2 ∼ -0.8 V vs Fc+/0. Electron paramagnetic resonance (EPR) measurements show that 1e- oxidation of [5]2- gives an S = 1/2 rhombic species, consistent with the formulation Ru(II)Fe(I), related to the Hox state of the [FeFe] hydrogenases. Density functional theory (DFT) studies reproduce the structure, 1H NMR shifts, and infrared (IR) spectra observed for [5]2-. Related homometallic complexes with both cyanides on a single metal are predicted to not adopt rotated structures. These data suggest that [5]2- is best described as Ru(II)Fe(0). This conclusion raises the possibility that for some reduced states of the [FeFe]-hydrogenases, the [2Fe]H site may be better described as Fe(II)Fe(0) than Fe(I)Fe(I).

Quasi-One-Dimensional Transition-Metal Chalcogenide Semiconductor (Nb4Se15I2)I2.

The discovery of new low-dimensional transition-metal chalcogenides is contributing to the already prosperous family of these materials. In this study, needle-shaped single crystals of a quasi-one-dimensional (1D) material, (Nb4Se15I2)I2, were grown by chemical vapor transport, and the structure was solved by single-crystal X-ray diffraction (XRD). The structure has 1D (Nb4Se15I2)n chains along the [101] direction, with two I- ions per formula unit directly bonded to Nb5+. The other two I- ions are loosely coordinated and intercalated between the chains. Individual chains are chiral and stack along the b axis in opposing directions, giving space group P21/c. The phase purity and crystal structure were verified by powder XRD. Density functional theory calculations show (Nb4Se15I2)I2 to be a semiconductor with a direct band gap of around 0.6 eV. Resistivity measurements of bulk crystals and micropatterned devices demonstrate that (Nb4Se15I2)I2 has an activation energy of around 0.1 eV, and no anomaly or transition was seen upon cooling. Low-temperature XRD shows that (Nb4Se15I2)I2 does not undergo a structural phase transformation from room temperature to 8.2 K, unlike related compounds (NbSe4)nI (n = 2, 3, or 3.33), which all exhibit charge-density waves. This compound represents a well-characterized and valence-precise member of a diverse family of anisotropic transition-metal chalcogenides.

Ligand Modifications Produce Two-Step Magnetic Switching in a Cobalt(dioxolene) Complex.

Mononuclear monodioxolene valence tautomeric (VT) cobalt complexes typically exist in their low spin (l.s.) CoIII (cat2- ) and high spin (h.s.) CoII (sq⋅- ) forms (cat2- =catecholato, and sq⋅- =seminquinonato forms of 3,5-di-t Bu-1,2-dioxolene), which reversibly interconvert via temperature-dependent intramolecular electron transfer. Typically, the remaining four coordination sites on cobalt are supported by a tetradentate ligand whose properties influence the temperature at which VT occurs. We report that replacing one chelating pyridyl arm of tris(2-pyridylmethyl)amine (tpa) with a weaker field ortho-anisole moiety facilitates access to a third magnetic state, and examine a series of related complexes. Variable temperature crystallographic, magnetic, calorimetric, and spectroscopic studies support that this third state is consistent with l.s. CoII (sq⋅- ). Thus, our ligand modifications not only provide access to the VT transition from l.s. CoIII (cat2- ) to l.s. CoII (sq⋅- ), but at higher temperatures, the complex undergoes spin crossover from l.s. CoII (sq⋅- ) to h.s. CoII (sq⋅- ), representing the first example of two-step magnetic switching in a mononuclear monodioxolene cobalt complex. We hypothesize that ligand dynamicity may facilitate access to the rarely observed l.s. CoII (sq⋅- ) intermediate state, suggesting a new design criterion in the development of stimulus-responsive multi-state molecular switches.

Organometallic Fe2(µ-SH)2(CO)4(CN)2 Cluster Allows the Biosynthesis of the [FeFe]-Hydrogenase with Only the HydF Maturase.

The biosynthesis of the active site of the [FeFe]-hydrogenases (HydA1), the H-cluster, is of interest because these enzymes are highly efficient catalysts for the oxidation and production of H2. The biosynthesis of the [2Fe]H subcluster of the H-cluster proceeds from simple precursors, which are processed by three maturases: HydG, HydE, and HydF. Previous studies established that HydG produces an Fe(CO)2(CN) adduct of cysteine, which is the substrate for HydE. In this work, we show that by using the synthetic cluster [Fe2(µ-SH)2(CN)2(CO)4]2- active HydA1 can be biosynthesized without maturases HydG and HydE.

Synthesis and Dynamics of Ferrous Polychalcogenides [Fe(Ex)(CN)2(CO)2]2- (E = S, Se, or Te).

Elemental chalcogens react with [Fe(CN)2(CO)3]2- to give the following ferrous derivatives: [K(18-crown-6)]2[Fe(S5)(CN)2(CO)2], [K(18-crown-6)]2[Fe(S2)(CN)2(CO)2], [K(18-crown-6)]2[Fe(Se4)(CN)2(CO)2], [K(18-crown-6)]2[Fe(Te2)(CN)2(CO)2], and (NEt4)2[Fe(Te2)(CN)2(CO)2]. While these complex anions crystallized in a single stereochemistry (i.e., trans dicyanides or cis dicyanides), they isomerize in solution upon irradiation. The results are benchmarked by the corresponding studies on benzyl thiolate [K(18-crown-6)]2[Fe(SBn)2(CN)2(CO)2].

Homoleptic Rhodium Pyridine Complexes for Catalytic Hydrogen Oxidation.

The homoleptic rhodium pyridine complex [Rh(py)4]+ ([1]+) is prepared from simple precursors. Lacking good π-acceptor ligands but being sterically protected, [1]+ reversibly oxidizes to colorless [Rh(py)4(thf)2]2+. This monomeric S = 1/2 Rh(II) complex activates H2 to give [HRh(py)4L]2+, which can also be generated by protonation of [1]+. The Rh(III)-H bond is weak, being susceptible to H atom abstraction as well as deprotonation. These results underpin a novel catalytic system for the oxidation of H2 by ferrocenium.

Computational and Experimental Investigations of the Fe2(µ-S2)/Fe2(µ-S)2 Equilibrium.

Density functional theory (DFT) calculations on Fe2S2(CO)6-2n(PMe3)2n for n = 0, 1, and 2 reveal that the most electron-rich derivatives (n = 2) exist as diferrous disulfides lacking an S-S bond. The thermal interconversion of the FeII2(S)2 and FeI2(S2) valence isomers is symmetry-forbidden. Related electron-rich diiron complexes [Fe2S2(CN)2(CO)4]2- of an uncertain structure are implicated in the biosynthesis of [FeFe]-hydrogenases. Several efforts to synthesize electron-rich derivatives of Fe2(µ-S2)(CO)6 (1) are described. First, salts of iron persulfido cyanides [Fe2(µ-S2)(CO)5(CN)]- and [Fe2(µ-S2)(CN)(CO)4(PPh3)]- were prepared by the reactions of NaN(tms)2 with 1 and Fe2(µ-S2)(CO)5(PPh3), respectively. Alternative approaches to electron-rich diiron disulfides targeted Fe2(µ-S2)(CO)4(diphosphine). Whereas the preparation of Fe2(µ-S2)(CO)4(dppbz) was straightforward, that of Fe2(µ-S2)(CO)4(dppv) required an indirect route involving the oxidation of Fe2(µ-SH)2(CO)4(dppv) (dppbz = C6H4-1,2-(PPh2)2, dppv = cis-C2H2(PPh2)2). DFT calculations indicate that the oxidation of Fe2(µ-SH)2(CO)4(dppv) produces singlet diferrous disulfide Fe2(µ-S)2(CO)4(dppv), which is sufficiently long-lived as to be trapped by ethylene. The reaction of 1 and dppv mainly afforded Fe2(µ-SCH=CHPPh2)(µ-SPPh2)(CO)5, implicating a S-centered reaction.

Modulation of π-stacking modes and photophysical properties of an organic semiconductor through isosteric cocrystallization.

We report on the control of π-stacking modes (herringbone vs slipped-stack) and photophysical properties of 9,10-bis((E)-2-(pyridin-4-yl)vinyl)anthracene (BP4VA), an anthracene-based organic semiconductor (OSC), by isosteric cocrystallization (i.e., the replacement of one functional group in a coformer with another of "similar" electronic structure) with 2,4,6-trihalophenols (3X-ph-OH, where X = Cl, Br, and I). Specifically, BP4VA organizes as slipped-stacks when cocrystallized with 3Cl-ph-OH and 3Br-ph-OH, while cocrystallization with 3I-ph-OH results in a herringbone mode. The photoluminescence and molecular frontier orbital energy levels of BP4VA were effectively modulated by the presence of 3X-ph-OH through cocrystallization. We envisage that the cocrystallization of OSCs with minimal changes in cocrystal formers can provide access to convenient structural and property diversification for advanced single-crystal electronics.

Surprising Condensation Reactions of the Azadithiolate Cofactor.

Azadithiolate, a cofactor found in all [FeFe]-hydrogenases, is shown to undergo acid-catalyzed rearrangement. Fe2 [(SCH2 )2 NH](CO)6 self-condenses to give Fe6 [(SCH2 )3 N]2 (CO)17 . The reaction, which is driven by loss of NH4+ , illustrates the exchange of the amine group. X-ray crystallography reveals that three Fe2 (SR)2 (CO)x butterfly subunits interconnected by the aminotrithiolate [N(CH2 S)3 ]3- . Mechanistic studies reveal that Fe2 [(SCH2 )2 NR](CO)6 participate in a range of amine exchange reactions, enabling new methodologies for modifying the adt cofactor. Ru2 [(SCH2 )2 NH](CO)6 also rearranges, but proceeds further to give derivatives with Ru-alkyl bonds Ru6 [(SCH2 )3 N][(SCH2 )2 NCH2 ]S(CO)17 and [Ru2 [(SCH2 )2 NCH2 ](CO)5 ]2 S.

Reactions of [Fe6C(CO)14(S)]2-: Cluster Growth, Redox, Sulfiding.

Redox reactions, substitutions, and metalations are reported for the iron carbido sulfide [Fe6C(CO)14(S)]2- ([1]2-). Dianion [1]2- oxidized to [Fe6C(CO)16(S)]0 ([2]0) upon treatment with of [Fe(C5H5)2]BF4 or HBF4 (H2 formation) under an atmosphere of CO. Reaction of [2]0 with tBuNC gave [Fe6C(S)(CO)13(tBuNC)5], consisting of Fe5C(CO)13 and [Fe(tBuNC)5]2+ subunits linked by a µ3-S2-. The Fe7CS cluster [Fe7C(CO)17(S)]2- formed upon treatment of (Ph4P)2[1] with Fe(benzylideneacetone)(CO)3. The Fe7 species is an edge-fused cluster with [Fe6C(CO)10(µ-CO)4] and Fe(CO)3 subunits joined by µ3-S and two Fe-Fe bonds. The analogous reaction using Mo(CO)4(norbornadiene) gave [MoFe6C(CO)18(S)]2-. In this cluster, the Mo center is located in the octahedral subunit. Treatment of [1]2- with SO2 afforded [Fe6C(S)(SO2)(CO)13]2-. This cluster features an Fe6C core decorated with µ3-S and µ2-SO2 ligands. These experiments were undertaken in an effort to connect organometallic clusters to FeMoco.

Super- and Ferroelastic Organic Semiconductors for Ultraflexible Single-Crystal Electronics.

Like silicon, single crystals of organic semiconductors are pursued to attain intrinsic charge transport properties. However, they are intolerant to mechanical deformation, impeding their application in flexible electronic devices. Such contradictory properties, namely exceptional molecular ordering and mechanical flexibility, are unified in this work. We found that bis(triisopropylsilylethynyl)pentacene (TIPS-P) crystals can undergo mechanically induced structural transitions to exhibit superelasticity and ferroelasticity. These properties arise from cooperative and correlated molecular displacements and rotations in response to mechanical stress. By utilizing a bending-induced ferroelastic transition of TIPS-P, flexible single-crystal electronic devices were obtained that can tolerate strains (ϵ) of more than 13 % while maintaining the charge carrier mobility of unstrained crystals (µ>0.7 µ0 ). Our work will pave the way for high-performance ultraflexible single-crystal organic electronics for sensors, memories, and robotic applications.

Iron Carbide-Sulfide Carbonyl Clusters.

Described is the preparation of the first iron carbide-sulfides. The cluster [Fe6C(CO)15(SO2)]2- ([2]2-), which is generated quantitatively from [Fe6C(CO)16]2- ([1]2-), was O-methylated to give the sulfinite [2Me]-. Demethoxylation of [2Me]- with BF3 gave the face-capped octahedral cluster Fe6C(CO)15(SO) (3). In solution, 3 spontaneously converted to the sulfide Fe6C(CO)16(S) (4), an edge-fused double cluster with Fe5C and Fe3S subunits. Although 4 undergoes 1e- reduction reversibly, 2e- reduction (or base hydrolysis) of 4 gives closo-[Fe6C(CO)14(S)]2- ([5]2-). The synthetic entries into the Fe6CS x manifold may underpin the preparation of active-site analogues of the FeMoco and FeVco cofactors.

Redox and "Antioxidant" Properties of Fe2(µ-SH)2(CO)4(PPh3)2.

The chemistry of Fe2(µ-SH)2(CO)4(PPh3)2 (2HH) is described with attention to S-S coupling reactions. Produced by the reduction of Fe2(µ-S2)(CO)4(PPh3)2 (2), 2HH is an analogue of Fe2(µ-SH)2(CO)6 (1HH), which exhibits well-behaved S-centered redox. Both 2HH and the related 2MeH exist as isomers that differ with respect to the stereochemistry of the µ-SR ligands (R = H, Me). Compounds 2HH, 2MeH, and 2 protonate to give rare examples of Fe-SH and Fe-S2 hydrides. Salts of [H2]+, [H2HH]+, and [H2MeH]+ were characterized crystallographically. Complex 2HH reduces O2, H2O2, (PhCO2)2, and Ph2N2, giving 2. Related reactions involving 1HH gave uncharacterizable polymers. The differing behaviors of 2HH and 1HH reflect stabilization of the ferrous intermediates by the PPh3 ligands. When independently generated by the reaction of 2HH with 2,2,6,6-tetramethyl-1-piperidinyloxy, 2* quantitatively converts to 2 or, in the presence of C2H4, is trapped as the ethanedithiolate Fe2(µ-S2C2H4)(CO)4(PPh3)2. Evidence is presented that the Hieber-Gruber synthesis of 1 involves polysulfido intermediates [Fe2(µ-S n)2(CO)6]2- ( n > 1). Two relevant experiments are as follows: (i) protonation of [Fe4(µ-S)2(µ-S2)CO)12]2- gives 1 and 1HH, and (ii) oxidation of 1HH by sulfur gives 1.

Synthetic Designs and Structural Investigations of Biomimetic Ni-Fe Thiolates.

Described are the syntheses of several Ni(µ-SR)2Fe complexes, including hydride derivatives, in a search for improved models for the active site of [NiFe]-hydrogenases. The nickel(II) precursors include (i) nickel with tripodal ligands: Ni(PS3)- and Ni(NS3)- (PS33- = tris(phenyl-2-thiolato)phosphine, NS33- = tris(benzyl-2-thiolato)amine), (ii) traditional diphosphine-dithiolates, including chiral diphosphine R,R-DIPAMP, (iii) cationic Ni(phosphine-imine/amine) complexes, and (iv) organonickel precursors Ni( o-tolyl)Cl(tmeda) and Ni(C6F5)2. The following new nickel precursor complexes were characterized: PPh4[Ni(NS3)] and the dimeric imino/amino-phosphine complexes [NiCl2(PCH═NAn)]2 and [NiCl2(PCH2NHAn)]2 (P = Ph2PC6H4-2-). The iron(II) reagents include [CpFe(CO)2(thf)]BF4, [Cp*Fe(CO)(MeCN)2]BF4, FeI2(CO)4, FeCl2(diphos)(CO)2, and Fe(pdt)(CO)2(diphos) (diphos = chelating diphosphines). Reactions of the nickel and iron complexes gave the following new Ni-Fe compounds: Cp*Fe(CO)Ni(NS3), [Cp(CO)Fe(µ-pdt)Ni(dppbz)]BF4, [( R,R-DIPAMP)Ni(µ-pdt)(H)Fe(CO)3]BArF4, [(PCH═NAn)Ni(µ-pdt)(Cl)Fe(dppbz)(CO)]BF4, [(PCH2NHAn)Ni(µ-pdt)(Cl)Fe(dppbz)(CO)]BF4, [(PCH═NAn)Ni(µ-pdt)(H)Fe(dppbz)(CO)]BF4, [(dppv)(CO)Fe(µ-pdt)]2Ni, {H[(dppv)(CO)Fe(µ-pdt)]2Ni]}BF4, and (C6F5)2Ni(µ-pdt)Fe(CO)2(dppv) (DIPAMP = (CH2P(C6H4-2-OMe)2)2; BArF4- = [B(C6H3-3,5-(CF3)2]4-)) Within the context of Ni-(SR)2-Fe complexes, these new complexes feature new microenvironments for the nickel center: tetrahedral Ni, chirality, imine, and amine coligands, and Ni-C bonds. In the case of {H[(dppv)(CO)Fe(µ-pdt)]2Ni}+, four low-energy isomers are separated by ≤3 kcal/mol, one of which features a biomimetic HNi(SR)4 site, as supported by density functional theory calculations.