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Synthesis and Reactivity of Nickel Hydride Complexes of an α‑Diimine Ligand

Reaction of L⁰NiBr₂ with 2 equiv of NaH yielded the Ni^II hydride complex [(L^•–)­Ni­(μ-H)₂Ni­(L^•–)] (<b>1</b>) (L = [(2,6-<i>i</i>Pr₂C₆H₃)­NC­(Me)]₂; L⁰ represents the neutral ligand, L^•– is its radical-anionic form, and L^2– denotes the dianion) in good yield. Stepwise reduction of complex <b>1</b> led to a series of nickel hydrides. Reduction of <b>1</b> with 1 equiv of sodium metal afforded a singly reduced species [Na­(DME)₃]­[(L^•–)­Ni­(μ-H)₂Ni­(L^•–)] (<b>2a</b>) (DME = 1,2-dimethoxyethane), which contains a mixed-valent core [Ni­(μ-H)₂Ni]⁺. With 2 equiv of Na a doubly reduced species [Na­(DME)]₂[L^2–Ni­(μ-H)₂NiL^2–] (<b>3a</b>) was obtained, in which each monoanion (L^•–) in the precursor <b>1</b> has been reduced to L^2–. By using potassium as the reducing agent, two analogous species [K­(DME)₄]­[(L^•–)­Ni­(μ-H)₂Ni­(L^•–)] (<b>2b</b>) and [K­(DME)]₂[L^2–Ni­(μ-H)₂NiL^2–] (<b>3b</b>) were obtained. Further treatment of <b>3b</b> with 2 equiv of K led to a trinuclear complex [K­(DME)­(THF)]₂K₂[L^2–Ni­(μ-H)₂Ni­(μ-H)₂NiL^2–] (<b>4</b>), which contains one Ni^II and two Ni^I centers with a triplet ground state. When <b>1</b> and <b>3a</b> were warmed in toluene or benzene, respectively, three reverse-sandwich dinickel complexes, [(L^•–)­Ni­(μ-η³:η³-C₇H₈)­Ni­(L^•–)] (<b>5</b>) and [Na­(DME)]₂[L^2–Ni­(μ-η³:η³-C₆H₅R)­NiL^2–] (<b>6</b>: R = CH₃; <b>7</b>: R = H), were isolated. Reaction of <b>1</b> with Me₃SiN₃ gave the N₃-bridged complex [(L^•–)­Ni­(μ-η¹-N₃)₂Ni­(L^•–)] (<b>8</b>). The crystal structures of complexes <b>1</b>–<b>8</b> have been determined by X-ray diffraction, and their electronic structures have been fully studied by EPR/NMR spectroscopy

Synthesis and Reactivity of Nickel Hydride Complexes of an α‑Diimine Ligand

Reaction of L⁰NiBr₂ with 2 equiv of NaH yielded the Ni^II hydride complex [(L^•–)­Ni­(μ-H)₂Ni­(L^•–)] (<b>1</b>) (L = [(2,6-<i>i</i>Pr₂C₆H₃)­NC­(Me)]₂; L⁰ represents the neutral ligand, L^•– is its radical-anionic form, and L^2– denotes the dianion) in good yield. Stepwise reduction of complex <b>1</b> led to a series of nickel hydrides. Reduction of <b>1</b> with 1 equiv of sodium metal afforded a singly reduced species [Na­(DME)₃]­[(L^•–)­Ni­(μ-H)₂Ni­(L^•–)] (<b>2a</b>) (DME = 1,2-dimethoxyethane), which contains a mixed-valent core [Ni­(μ-H)₂Ni]⁺. With 2 equiv of Na a doubly reduced species [Na­(DME)]₂[L^2–Ni­(μ-H)₂NiL^2–] (<b>3a</b>) was obtained, in which each monoanion (L^•–) in the precursor <b>1</b> has been reduced to L^2–. By using potassium as the reducing agent, two analogous species [K­(DME)₄]­[(L^•–)­Ni­(μ-H)₂Ni­(L^•–)] (<b>2b</b>) and [K­(DME)]₂[L^2–Ni­(μ-H)₂NiL^2–] (<b>3b</b>) were obtained. Further treatment of <b>3b</b> with 2 equiv of K led to a trinuclear complex [K­(DME)­(THF)]₂K₂[L^2–Ni­(μ-H)₂Ni­(μ-H)₂NiL^2–] (<b>4</b>), which contains one Ni^II and two Ni^I centers with a triplet ground state. When <b>1</b> and <b>3a</b> were warmed in toluene or benzene, respectively, three reverse-sandwich dinickel complexes, [(L^•–)­Ni­(μ-η³:η³-C₇H₈)­Ni­(L^•–)] (<b>5</b>) and [Na­(DME)]₂[L^2–Ni­(μ-η³:η³-C₆H₅R)­NiL^2–] (<b>6</b>: R = CH₃; <b>7</b>: R = H), were isolated. Reaction of <b>1</b> with Me₃SiN₃ gave the N₃-bridged complex [(L^•–)­Ni­(μ-η¹-N₃)₂Ni­(L^•–)] (<b>8</b>). The crystal structures of complexes <b>1</b>–<b>8</b> have been determined by X-ray diffraction, and their electronic structures have been fully studied by EPR/NMR spectroscopy

Two Stable Phosphorus-Containing Four-Membered Ring Radical Cations with Inverse Spin Density Distributions

Two phosphorus-containing four-membered ring radical cations <b>1</b>^•+ and <b>2</b>^•+ have been isolated and characterized by UV–vis absorption spectroscopy, electron paramagnetic resonance (EPR), and single-crystal X-ray diffraction. Compared with neutral molecules <b>1</b> and <b>2</b>, radical <b>1</b>^•+ has elongated P–P bonds and more pyramidalized phosphorus atoms, while shortened P–N_ring distances and larger angles around phosphorus centers are observed for <b>2</b>^•+. EPR studies indicate that for <b>1</b>^•+ spin density mainly resides on the exocyclic nitrogen atoms with very minor contribution from endocyclic phosphorus atoms, while the situation is opposite for <b>2</b>^•+. Such an inverse spin density distribution is controlled by the exocyclic substituents, which is supported by DFT calculations

Two Stable Phosphorus-Containing Four-Membered Ring Radical Cations with Inverse Spin Density Distributions

Two phosphorus-containing four-membered ring radical cations <b>1</b>^•+ and <b>2</b>^•+ have been isolated and characterized by UV–vis absorption spectroscopy, electron paramagnetic resonance (EPR), and single-crystal X-ray diffraction. Compared with neutral molecules <b>1</b> and <b>2</b>, radical <b>1</b>^•+ has elongated P–P bonds and more pyramidalized phosphorus atoms, while shortened P–N_ring distances and larger angles around phosphorus centers are observed for <b>2</b>^•+. EPR studies indicate that for <b>1</b>^•+ spin density mainly resides on the exocyclic nitrogen atoms with very minor contribution from endocyclic phosphorus atoms, while the situation is opposite for <b>2</b>^•+. Such an inverse spin density distribution is controlled by the exocyclic substituents, which is supported by DFT calculations

Alkali Metal and Zinc Complexes of a Bridging 2,5-Diamino-1,4-Benzoquinonediimine Ligand

Two alkali metal complexes of a bridging 2,5-diamino-1,4-benzoquinonediimine ligand (dipp-dabqdiH₂), [(thf)₂Li­(μ-dipp-dabqdi)­Li­(thf)₂] (<b>1</b>) and [(dme)_1.5Na­(μ-dipp-dabqdi)­Na­(dme)_1.5]_<i>n</i> (<b>2</b>, dme = 1,2-dimethoxyethane), have been synthesized by the reaction of dipp-dabqdiH₂ with Li^<i>n</i>Bu or sodium metal. In addition, treatment of 1,2,4,5-tetrakis­(2,6-diisopropylamino)­benzene (dipp-tabH₄) with potassium metal in dme afforded the complex [(dme)₂K­(μ-dipp-tabH₂)­K­(dme)₂] (<b>3</b>). X-ray crystal diffraction analyses revealed that complexes <b>1</b> and <b>3</b> have dinuclear structures, while the sodium complex <b>2</b> aggregates to a one-dimensional polymer through bridging dme ligands. With increasing ion radius, the coordination number of the alkali metal (Li, Na, and K) increases from four to five to six, while the coordination geometry changes from distorted tetrahedral to square pyramidal and further to octahedral in <b>1</b>, <b>2</b>, and <b>3</b>, respectively. The salt metathesis reactions of <b>1</b> and <b>2</b> with anhydrous ZnCl₂ yielded the ion-contacted zinc complexes [(thf)₃Li­(μ-Cl)­ClZn­(μ-dipp-dabqdi)­ZnCl­(μ-Cl)­Li­(thf)₃] (<b>4</b>), [(dme)₂Li­(μ-Cl)­ClZn­(μ-dippdabqdi)­ZnCl­(μ-Cl)­Li­(dme)₂] (<b>5</b>), and [(dme)₂Na­(μ-Cl)₂Zn­(μ-dipp-dabqdi)­Zn­(μ-Cl)₂Na­(dme)₂] (<b>6</b>), respectively. The ligand exists as the dianionic form in compounds <b>1</b>–<b>6</b> upon double deprotonation, and a complete electronic delocalization (except for <b>3</b>) of the quinonoid π-system is observed between the metal centers over the two NCCCN halves of the ligand. The electronic structures of the complexes were studied by density functional theory (DFT) computations

Stable Tetraaryldiphosphine Radical Cation and Dication

Salts containing tetraaryldiphosphine radical cation <b>1</b>^<b>•+</b> and dication <b>1</b>^<b>2+</b> have been isolated and structurally characterized. Radical <b>1</b>^<b>•+</b> has a relaxed pyramidal geometry, while dication <b>1</b>^<b>2+</b> prefers a planar, olefin-like geometry with a two-electron π bond. The alteration of the geometries of the tetraaryldiphosphine upon oxidation is rationalized by the nature of the bonding. The EPR spectrum showed that the spin density of radical <b>1^•+</b> is mainly localized on phosphorus atoms, which is supported by theoretical calculation

Stable Tetraaryldiphosphine Radical Cation and Dication

Salts containing tetraaryldiphosphine radical cation <b>1</b>^<b>•+</b> and dication <b>1</b>^<b>2+</b> have been isolated and structurally characterized. Radical <b>1</b>^<b>•+</b> has a relaxed pyramidal geometry, while dication <b>1</b>^<b>2+</b> prefers a planar, olefin-like geometry with a two-electron π bond. The alteration of the geometries of the tetraaryldiphosphine upon oxidation is rationalized by the nature of the bonding. The EPR spectrum showed that the spin density of radical <b>1^•+</b> is mainly localized on phosphorus atoms, which is supported by theoretical calculation