Mn₃ Single-Molecule Magnets and Mn₆/Mn₉ Clusters from the Use of Methyl 2‑Pyridyl Ketone Oxime in Manganese Phosphinate and Phosphonate Chemistry

The syntheses, structures, and magnetochemical properties are reported for five new Mn clusters: [Mn^III₃O­(O₂PPh₂)₃­(mpko)₃]­(ClO₄) (<b>1</b>), [Mn^III₃O­(O₂PPh₂)₃­(ppko)₃]­(ClO₄) (<b>2</b>) [Mn^III₆O₂(OMe)₄­(O₂PPh₂)₄(mpko)₄]­(ClO₄)₂ (<b>3</b>), [Mn^III₈Mn^IIO₆(O₂CMe)₇­(O₃PPh)₂(mpko)₃(H₂O)] (<b>4</b>), and [Mn^III₂Mn^IIO­(mpko)₃­(H₂O)₄(ClO₄)₂]­(ClO₄) (<b>5</b>), where mpko^– (or ppko^–) is the anion of methyl (or phenyl) 2-pyridyl ketone oxime. <b>1</b> was obtained by carboxylate substitution on [Mn^III₃O­(O₂CMe)₃­(mpko)₃]­(ClO₄) by treatment with diphenylphosphinic acid (Ph₂PO₂H). The comproportionation reaction between Mn­(ClO₄)₂ and NBuⁿ₄MnO₄ in the presence of Ph₂PO₂H and ppkoH in EtOH, or mpkoH in MeOH, led to <b>2</b> and <b>3</b>, respectively. <b>4</b> was obtained as was <b>3</b>, but with phenylphosphonic acid (PhPO₃H₂) instead of Ph₂PO₂H. <b>5</b> was obtained by aerial oxidation of Mn­(ClO₄)₂ in the presence of mpkoH. <b>1</b> and <b>2</b> contain a triangular Mn₃ core, <b>3</b> comprises the fusion of two Mn₃ units of <b>1</b> by MeO^– bridges, and <b>4</b> has a cagelike structure. <b>5</b> is similar to <b>1</b> in possessing a triangular core. Variable-temperature, solid-state direct-current (dc) and alternating-current (ac) magnetic data were collected on <b>1</b>–<b>5</b>: <b>1</b> and <b>2</b> exhibit ferromagnetic Mn····Mn exchange interactions, <i>S</i> = 6 ground states, and are new single-molecule magnets (SMMs). <b>3</b>–<b>5</b> possess <i>S</i> = 4, ⁵/₂, and ⁵/₂ ground states, respectively, from dominant antiferromagnetic interactions. Fits of dc magnetization data in the 1.8–10.0 K and 10–70 kG ranges gave <i>D</i> and <i>g</i> values of: −0.29(2) cm^–1 and 1.94(1) for <b>1</b>, −0.38(2) cm^–1 and 1.99(1) for <b>2</b>, −0.29(2) cm^–1 and 1.96(1) for <b>3</b>, −1.26(4) cm^–1 and 1.99(2) for <b>4</b>, −1.41(4) cm^–1 and 1.98(2) for <b>5</b>, where <i>D</i> is the axial zero-field splitting parameter

Magnetostructural Correlation for High-Nuclearity Iron(III)/Oxo Complexes and Application to Fe₅, Fe₆, and Fe₈ Clusters

The synthesis and characterization are reported of two new polynuclear Fe^III complexes containing the anion of 8-hydroxyquinoline (hqnH), an N,O-chelating ligand. The complexes are [Fe₈O₄(O₂CPh)₁₀(hqn)₄(OMe)₂] (<b>1</b>) and [Fe₆O₂(OH)₂(O₂CPh)₁₀(hqn)₂] (<b>2</b>) and were obtained from reactions in MeOH (<b>1</b>) or H₂O (<b>2</b>) using either low-nuclearity preformed clusters or simple metal salts as starting materials. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out and indicate <i>S</i> = 0 and <i>S</i> = 5 ground states for <b>1</b> and <b>2</b>, respectively. In order to rationalize the ground states of these and other higher-nuclearity Fe^III/O clusters, a magnetostructural correlation (MSC) has been developed specifically for polynuclear Fe^III/O systems that predicts the exchange interaction constant (<i>J</i>_<i>ij</i>) between two Fe^III atoms based on the Fe–O distances and Fe–O–Fe angles at monoatomically bridging ligands. This correlation was refined using selected tri- and tetranuclear complexes in the literature for which both crystal structures and reliable experimentally determined <i>J</i>_<i>ij</i> values were available. The predictive capability of the MSC was evaluated by rationalizing the ground-state spins of <b>1</b>, <b>2</b>, and other Fe₅–Fe₈ clusters, simulating the dc magnetic susceptibility data of polynuclear Fe^III complexes, and fitting experimental dc magnetic susceptibility vs <i>T</i> data. The latter fits were evaluated to identify and eliminate systematic errors, and this allowed a protocol to be developed for application of this MSC to other polynuclear Fe^III/oxo clusters

Magnetostructural Correlation for High-Nuclearity Iron(III)/Oxo Complexes and Application to Fe₅, Fe₆, and Fe₈ Clusters

The synthesis and characterization are reported of two new polynuclear Fe^III complexes containing the anion of 8-hydroxyquinoline (hqnH), an N,O-chelating ligand. The complexes are [Fe₈O₄(O₂CPh)₁₀(hqn)₄(OMe)₂] (<b>1</b>) and [Fe₆O₂(OH)₂(O₂CPh)₁₀(hqn)₂] (<b>2</b>) and were obtained from reactions in MeOH (<b>1</b>) or H₂O (<b>2</b>) using either low-nuclearity preformed clusters or simple metal salts as starting materials. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out and indicate <i>S</i> = 0 and <i>S</i> = 5 ground states for <b>1</b> and <b>2</b>, respectively. In order to rationalize the ground states of these and other higher-nuclearity Fe^III/O clusters, a magnetostructural correlation (MSC) has been developed specifically for polynuclear Fe^III/O systems that predicts the exchange interaction constant (<i>J</i>_<i>ij</i>) between two Fe^III atoms based on the Fe–O distances and Fe–O–Fe angles at monoatomically bridging ligands. This correlation was refined using selected tri- and tetranuclear complexes in the literature for which both crystal structures and reliable experimentally determined <i>J</i>_<i>ij</i> values were available. The predictive capability of the MSC was evaluated by rationalizing the ground-state spins of <b>1</b>, <b>2</b>, and other Fe₅–Fe₈ clusters, simulating the dc magnetic susceptibility data of polynuclear Fe^III complexes, and fitting experimental dc magnetic susceptibility vs <i>T</i> data. The latter fits were evaluated to identify and eliminate systematic errors, and this allowed a protocol to be developed for application of this MSC to other polynuclear Fe^III/oxo clusters

Catalytic Enantioselective Synthesis of Amino Skipped Diynes

The Cu-catalyzed synthesis of nonracemic 3-amino skipped diynes via an enantiodetermining C–C bond formation is described using StackPhos as ligand. Despite challenging issues of reactivity and stereoselectivity inherent to these chiral skipped diynes, the reaction tolerates an extremely broad substrate scope with respect to all components and provides the title compounds in excellent enantiomeric excess. The alkyne moieties are demonstrated here to be useful synthetic handles, and 3-amino skipped diynes are convenient building blocks for enantioselective synthesis

Design, Preparation, and Implementation of an Imidazole-Based Chiral Biaryl P,N-Ligand for Asymmetric Catalysis

A new strategy for increasing the barrier to rotation in biaryls has been developed that allows for the incorporation of 5-membered aromatic heterocycles into chiral atropisomers. Using this concept, an imidazole-based biaryl P,N-ligand has been designed and prepared as a single enantiomer. This ligand performs exceptionally well in the enantioselective A³-coupling, demonstrating the potential of this new design element

Design, Preparation, and Implementation of an Imidazole-Based Chiral Biaryl P,N-Ligand for Asymmetric Catalysis

A new strategy for increasing the barrier to rotation in biaryls has been developed that allows for the incorporation of 5-membered aromatic heterocycles into chiral atropisomers. Using this concept, an imidazole-based biaryl P,N-ligand has been designed and prepared as a single enantiomer. This ligand performs exceptionally well in the enantioselective A³-coupling, demonstrating the potential of this new design element

Incorporation of Axial Chirality into Phosphino-Imidazoline Ligands for Enantioselective Catalysis

A complementary strategy for ligand tuning that enables controlling ligand conformation is described here. The concept is demonstrated with new ligands that are employed in the catalytic enantioselective preparation of the highly important C2-aminoalkyl five-membered heterocycle motif. The alkynylation/cyclization sequence developed here is convergent, highly modular, and allows for a complementary scope to the heteroarylation of imines. This new ligand platform should offer new possibilities for expanding the use of PHIM-type ligands in a large variety of new transformations

Design, Preparation, and Implementation of an Imidazole-Based Chiral Biaryl P,N-Ligand for Asymmetric Catalysis

A new strategy for increasing the barrier to rotation in biaryls has been developed that allows for the incorporation of 5-membered aromatic heterocycles into chiral atropisomers. Using this concept, an imidazole-based biaryl P,N-ligand has been designed and prepared as a single enantiomer. This ligand performs exceptionally well in the enantioselective A³-coupling, demonstrating the potential of this new design element

Mn₈ Cluster with Ferrocene-1,1′-Dicarboxylate Ligation: Single-Molecule Magnetism with Multiple External Redox Centers

The syntheses, structures, and magnetic properties are reported of a new Mn₈ cluster obtained from the reaction of ferrocene-1,1′-dicarboxylic acid (fdcH₂) with [Mn₁₂O₁₂(O₂CMe)₁₆(H₂O)₄] and mononuclear Mn salts under different conditions and limited light exposure. The product was obtained in two forms: [Mn₈O₄(fdc)₆(DMF)₂(H₂O)₂] (<b>1</b>) and [Mn₈O₄(fdc)₆(DMF)₄] (<b>2</b>), differing in the bound solvent ligands. The structures are otherwise almost identical, comprising very similar cores that both contain 4Mn^III and 4Mn^II atoms bridged by four O^2– ions and six fdc^2– groups. The [Mn^III₄Mn^II₄(μ₄-O)₄] cores have virtual <i>T</i>_<i>d</i> symmetry and can be described as a central [Mn^III₄(μ₄-O)₄]⁴⁺ cubane unit whose four O^2– ions are μ₄, because they each attach to an external Mn^II atom. Peripheral ligation about the core is provided by six bridging fdc^2– groups and the terminal solvent ligands, one each on the Mn^II atoms. The differences in solvent ligands between <b>1</b> and <b>2</b>, and different packing from the different crystal space groups, lead to significant differences in metric parameters within the core, which are reflected in significantly different magnetic properties. Variable-temperature, solid-state dc and ac susceptibility measurements reveal the clusters to be predominantly antiferromagnetically coupled, and to possess ground state spin values of <i>S</i> = 5 and <i>S</i> = 2 for <b>1</b> and <b>2</b>, respectively. The difference in ground states is assigned to the small but distinct structural differences seen in the central cubane. Alternating current (AC) susceptibility data indicate <b>1</b> and <b>2</b> to be new single-molecule magnet, and this was confirmed by magnetization versus direct current (DC) field scans on a single crystal of <b>1</b>·4DMF·4H₂O, which exhibited hysteresis

New Structural Types of Mn₁₆ Single-Molecule Magnets: W‑Shaped Topology from Reductive Aggregation

Two new Mn₁₆ clusters are reported: [Mn₁₆O­₁₀­(OH)₃­(OMe)₈(O₂CPhBu^t)₁₇(MeOH)₅] (<b>2</b>) and [Mn₁₆O₁₆(OMe)₆­(O₂CPh)₁₂­(NO₃)₄(MeOH)₂(H₂O)₄] (<b>3</b>). The complexes were obtained by reductive aggregation of MnO₄^– in CH₂Cl₂/MeOH, and oxidation of Mn^II and preformed (N^<i>n</i>Bu₄)­[Mn₄^IIIO₂(O₂CPh)₉(H₂O)] with Ce^IV, respectively. The core of <b>2</b> has a Mn₁₆^III core with an unusual 1:2:3:4:3:2:1 layer structure and a W-shaped pleated topology, whereas <b>3</b> contains a central 2 × 3 Mn₆^IV planar grid held within a nonplanar Mn₁₀^III loop and is a rare example of a complex with nitrate ions bridging like carboxylate ions. Variable-temperature, solid-state dc susceptibility, and ac susceptibility studies reveal that <b>2</b> and <b>3</b> possess <i>S</i> = 12 and <i>S</i> = 8 ground states, respectively. Fits of dc magnetization data collected over a temperature range of 1.8–4.0 K and a magnetization range of 0.1–4 T were fit to give <i>S</i> = 12, <i>D</i> = −0.16(2) cm^–1, <i>g</i> = 1.98(3) for <b>2</b> and <i>S</i> = 8, <i>D</i> = −0.22(1) cm^–1, <i>g</i> = 1.99(2) for <b>3</b>, where <i>D</i> is the axial zero-field splitting parameter. The ac in-phase (χ_M^′<i>T</i>) susceptibility below 15 K confirmed the ground-state spin values of <b>2</b> and <b>3</b>, as determined from dc data, and the appearance of frequency-dependent out-of-phase (χ_M^″) signals revealed that both complexes are new single-molecule magnets (SMMs). Fits of the ac data gave <i>U</i>_eff = 49.7(1) K and τ₀ = 4.32 × 10^–9 s for <b>2</b> and <i>U</i>_eff ≈ 14.0 ± 2 cm^–1 and τ₀ ≈ 3.2 ± 0.5 × 10^–8 s for <b>3</b>, where <i>U</i>_eff is the effective barrier to magnetization relaxation and τ₀ is the pre-exponential factor. Thus, complexes <b>2</b> and <b>3</b> are two new members of a growing family of Mn₁₆ clusters, and two new examples of high-nuclearity SMMs, with the <i>U</i>_eff for <b>2</b> approaching the value for the prototypical SMM family, [Mn₁₂O₁₂(O₂CR)₁₆(H₂O)₄]