Heterometallic Potassium Rare-Earth-Metal Allyl and Hydrido Complexes Stabilized by a Dianionic (NNNN)-Type Macrocyclic Ancillary Ligand

The macrocyclic diamino diamine (1,7-Me₂TACD)­H₂ (1,7-Me₂TACD = 1,7-dimethyl-1,4,7,10-tetraazacyclododecane, 1,7-Me₂[12]­aneN₄), reacted under propylene elimination with [Ln­(η³-C₃H₅)₃(diox)] (Ln = Y, La) to give the mono­(allyl) complexes [(1,7-Me₂TACD)­Ln­(η³-C₃H₅)]₂ (Ln = Y (<b>1a</b>), La (<b>1b</b>)). A single-crystal X-ray diffraction study shows <b>1b</b> to be a centrosymmetric dimer with lanthanum atoms bridged by one of the two amido nitrogen atoms. Complexes <b>1a</b>,<b>b</b> were treated with 2 equiv of the potassium allyl KC₃H₅ to give the corresponding heterometallic allyl complexes [(1,7-Me₂TACD)­Ln­(η³-C₃H₅)₂K­(THF)]_<i>n</i> (Ln = Y (<b>2a</b>), La (<b>2b</b>)). A single-crystal X-ray diffraction study revealed that <b>2a</b>,<b>b</b> are polymeric in the solid state with allyl ligands bridging the metal centers in addition to the presence of μ₂-amido functions of the 1,7-Me₂TACD ligand. Hydrogenolysis of the yttrium compound <b>2a</b> with 1 bar of H₂ led to the formation of the heterometallic Y₄K₂ hydrido complex [(1,7-Me₂TACD)₂Y₂H₃K­(THF)₂]₂ (<b>3a</b>), which can also be synthesized from a 1:1 mixture of <b>1a</b> and KC₃H₅ with 1 bar of H₂. A single-crystal X-ray diffraction study of <b>3a</b> revealed a dimer of heterotrinuclear Y₂K trihydride aggregate. Treatment of <b>2b</b> with 1 bar of H₂ afforded the heptanuclear La₃K₄ heptahydrido complex [(1,7-Me₂TACD)₃La₃H₇K₄(THF)₇] (<b>3b</b>)

Formation of a Cationic Calcium Hydride Cluster with a “Naked” Triphenylsilyl Anion by Hydrogenolysis of Bis(triphenylsilyl)calcium

Protonolysis of bis­(triphenylsilyl)­calcium [Ca­(SiPh₃)₂(THF)₄] (<b>1</b>; THF = tetrahydrofuran) with the NNNN-type macrocyclic amido triamine (Me₃TACD)H (TACD = 1,4,7-triazacyclododecane) gave the heteroleptic calcium complex [Ca­(Me₃TACD)­SiPh₃] (<b>2</b>) in quantitative yield. Hydrogenolysis of <b>2</b> gave the cationic tricalcium dihydride cluster [Ca₃H₂(Me₃TACD)₃]⁺(SiPh₃)⁻·2THF (<b>4a</b>) in high yield with concomitant formation of HSiPh₃. In the crystal, <b>4a</b> consists of a cluster cation and a free triphenylsilyl anion. ¹H NMR spectroscopy and deuterium labeling experiments confirmed the selective cleavage of dihydrogen by the highly polar Ca–Si bond in <b>1</b>

Heterometallic Potassium Rare-Earth-Metal Allyl and Hydrido Complexes Stabilized by a Dianionic (NNNN)-Type Macrocyclic Ancillary Ligand

The macrocyclic diamino diamine (1,7-Me₂TACD)­H₂ (1,7-Me₂TACD = 1,7-dimethyl-1,4,7,10-tetraazacyclododecane, 1,7-Me₂[12]­aneN₄), reacted under propylene elimination with [Ln­(η³-C₃H₅)₃(diox)] (Ln = Y, La) to give the mono­(allyl) complexes [(1,7-Me₂TACD)­Ln­(η³-C₃H₅)]₂ (Ln = Y (<b>1a</b>), La (<b>1b</b>)). A single-crystal X-ray diffraction study shows <b>1b</b> to be a centrosymmetric dimer with lanthanum atoms bridged by one of the two amido nitrogen atoms. Complexes <b>1a</b>,<b>b</b> were treated with 2 equiv of the potassium allyl KC₃H₅ to give the corresponding heterometallic allyl complexes [(1,7-Me₂TACD)­Ln­(η³-C₃H₅)₂K­(THF)]_<i>n</i> (Ln = Y (<b>2a</b>), La (<b>2b</b>)). A single-crystal X-ray diffraction study revealed that <b>2a</b>,<b>b</b> are polymeric in the solid state with allyl ligands bridging the metal centers in addition to the presence of μ₂-amido functions of the 1,7-Me₂TACD ligand. Hydrogenolysis of the yttrium compound <b>2a</b> with 1 bar of H₂ led to the formation of the heterometallic Y₄K₂ hydrido complex [(1,7-Me₂TACD)₂Y₂H₃K­(THF)₂]₂ (<b>3a</b>), which can also be synthesized from a 1:1 mixture of <b>1a</b> and KC₃H₅ with 1 bar of H₂. A single-crystal X-ray diffraction study of <b>3a</b> revealed a dimer of heterotrinuclear Y₂K trihydride aggregate. Treatment of <b>2b</b> with 1 bar of H₂ afforded the heptanuclear La₃K₄ heptahydrido complex [(1,7-Me₂TACD)₃La₃H₇K₄(THF)₇] (<b>3b</b>)

Hydroboration and Deoxygenation of CO₂ Mediated by a Gallium(I) Cation

Hydroboration of CO2 to formoxy borane occurs under ambient conditions in acetonitrile using pinacolborane HBpin in the presence of gallium­(I) cation [(Me4TACD)­Ga]­[BAr4] (1; Me4TACD = N,N′,N″,N′′′-tetramethyl-1,4,7,10-tetraazacyclododecane; Ar = C6H3-3,5-Me2). Slow turnover was accompanied by side reactions including ligand scrambling of HBpin to give BH3(CH3CN) and crystalline B2pin3. When 1 was reacted with CO2 alone, the formation of the gallium­(III) carbonato complex [(Me4TACD)­Ga­(κ2-O2CO)]­[BAr4] (3) along with CO was observed. This complex was assumed to form via the unstable oxido cation [(Me4TACD)­Ga=O]+ (4). Reaction of 1 with N2O in the presence of BPh3 confirmed the formation of the oxido cation, which was spectroscopically characterized as a triphenylborane adduct [(Me4TACD)­Ga=O­(BPh3)]­[BAr4] (4·BPh3). CO was also detected when CO2 was reacted with 1 in the presence of HBpin, suggesting that compound 3 may also be formed in initial stages of catalysis. Compound 3 reacts with HBpin to give formoxy borane, borane redistribution products, and an unidentified Me4TACD-containing species 5, which was also observed in “catalytic” runs starting from 1, HBpin, and CO2. Hydroboration of CO2 using HBpin with slow turnover and competitive ligand scrambling was also observed in the presence of gallium­(III) hydride dication [(Me4TACD)­GaH]­[BAr4]2 (2), which is unreactive toward CO2 in the absence of HBpin

Bis(allyl)gallium Cation, Tris(allyl)gallium, and Tetrakis(allyl)gallate: Synthesis, Characterization, and Reactivity

A series of cationic, neutral, and anionic allylgallium complexes has been isolated and fully characterized. It includes neutral [Ga­(η¹-C₃H₅)₃(L)] (<b>1</b>, L = THF; <b>2</b>, L = OPPh₃), cationic [Ga­(η¹-C₃H₅)₂(THF)₂]⁺[A]⁻ (<b>3</b>, [A]⁻ = [B­(C₆F₅)₄]⁻; <b>4</b>, [A]⁻ = [B­(C₆H₃Cl₂)₄]⁻), as well as anionic [Cat]⁺[Ga­(η¹-C₃H₅)₄]⁻ (<b>5</b>, [Cat]⁺ = K⁺; <b>6</b>, [Cat]⁺ = [K­(dibenzo-18-<i>c</i>-6]⁺; <b>7</b>, [Cat]⁺ = [PPh₄]⁺). Binding modes of the allyl ligand in solution and in the solid state have been studied comparatively. Single crystal X-ray analyses revealed a four-coordinate neutral gallium center in <b>2</b>, a five-coordinate cationic gallium center in <b>4</b> and [<b>4</b>·THF], and a four-coordinate anionic gallium center with a bridging μ₂-η¹:η² coordination mode of the allyl ligand in <b>6</b>. The reactivity of this series of allylgallium complexes toward benzophenone and <i>N</i>-heteroaromatics has been investigated. Counterion effects have also been studied. Reactions of <b>1</b> and <b>5</b> with isoquinoline revealed the first examples of organogallium complexes reacting under 1,2-insertion with pyridine derivatives

Layer-by-Layer Assembly of Partially Sulfonated Isotactic Polystyrene with Poly(vinylamine)

The stereoregular synthetic polymer isotactic polystyrene bearing partially sulfonated groups (SiPS) was used as a layer-by-layer assembled thin film for the first time. When a low molecular weight compound was employed as the pair for the alternative layer-by-layer (LbL) assembly, the frequency shift was very small using quartz crystal microbalance (QCM) analysis, whereas poly­(vinylamine) (PVAm) formed an effective pair for the construction of LbL films with SiPS. When it was neutralized, SiPS was not assembled, probably due to the loss of effective polymer–polymer interactions. The ionic strength conditions revealed a slight difference of the assembly behavior on the isotactic polymer as compared to the atactic one. The assembled LbL film showed the same peaks over the range from 1141 to 1227 cm^–1 and 700 cm^–1 in the FT-IR/ATR spectra as the bulk complex of SiPS/PVAm, and the thickness on one side was calculated at 76 nm by QCM analysis. The surface roughness of the film was also observed by AFM

Cationic Zirconium Hydrides Supported by an NNNN-Type Macrocyclic Ligand: Synthesis, Structure, and Reactivity

An air- and light-sensitive, but thermally stable tris­[(trimethylsilyl)­methyl]­zirconium complex containing an NNNN-type macrocyclic ligand [Zr­(Me₃TACD)­(CH₂SiMe₃)₃] (<b>1</b>; Me₃TACD = Me₃[12]­aneN₄: 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane) was prepared by reacting [Zr­(CH₂SiMe₃)₄] with (Me₃TACD)­H. Reaction of the zirconium tris­(alkyl) <b>1</b> with a Lewis or Brønsted acid gave a dialkyl cation with a weakly coordinating anion [Zr­(Me₃TACD)­(CH₂SiMe₃)₂]­[A] [A = Al­{OC­(CF₃)₃}₄ (<b>2a</b>), B­{3,5-C₆H₃(CF₃)₂}₄ (<b>2b</b>), B­(3,5-C₆H₃Cl₂)₄ (<b>2c</b>), and BPh₄) (<b>2d</b>)]. Hydrogenolysis of <b>2a</b>–<b>2c</b> resulted in the formation of the dinuclear tetrahydride dication [{Zr­(Me₃TACD)­(μ-H)₂}₂]­[A]₂ (<b>3a</b>–<b>3c</b>). Compounds <b>1</b>–<b>3</b> were characterized by multinuclear NMR spectroscopy, and the solid-state structures of <b>1</b>, <b>2c</b>, and <b>3b</b> were established by single-crystal X-ray diffraction studies. The dinuclear hydride complex <b>3b</b> exhibits a quadruply bridged {Zr₂(μ-H)₄} core in solution and in the solid state with a relatively short Zr···Zr distance of 2.8752(11) Å. Density functional theory computations at the B3PW91 level reproduced this structure (Zr···Zr distance of 2.900 Å). The cationic hydride complex <b>3b</b> reacted with excess carbon monoxide in tetrahydrofuran at room temperature to give ethylene in 25% yield based on <b>3b</b>. Upon analysis of ¹³C NMR spectra of the reaction mixture using ¹³CO, oxymethylene and enolate complexes were detected as intermediates among other complexes

Cationic Zirconium Hydrides Supported by an NNNN-Type Macrocyclic Ligand: Synthesis, Structure, and Reactivity

An air- and light-sensitive, but thermally stable tris­[(trimethylsilyl)­methyl]­zirconium complex containing an NNNN-type macrocyclic ligand [Zr­(Me₃TACD)­(CH₂SiMe₃)₃] (<b>1</b>; Me₃TACD = Me₃[12]­aneN₄: 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane) was prepared by reacting [Zr­(CH₂SiMe₃)₄] with (Me₃TACD)­H. Reaction of the zirconium tris­(alkyl) <b>1</b> with a Lewis or Brønsted acid gave a dialkyl cation with a weakly coordinating anion [Zr­(Me₃TACD)­(CH₂SiMe₃)₂]­[A] [A = Al­{OC­(CF₃)₃}₄ (<b>2a</b>), B­{3,5-C₆H₃(CF₃)₂}₄ (<b>2b</b>), B­(3,5-C₆H₃Cl₂)₄ (<b>2c</b>), and BPh₄) (<b>2d</b>)]. Hydrogenolysis of <b>2a</b>–<b>2c</b> resulted in the formation of the dinuclear tetrahydride dication [{Zr­(Me₃TACD)­(μ-H)₂}₂]­[A]₂ (<b>3a</b>–<b>3c</b>). Compounds <b>1</b>–<b>3</b> were characterized by multinuclear NMR spectroscopy, and the solid-state structures of <b>1</b>, <b>2c</b>, and <b>3b</b> were established by single-crystal X-ray diffraction studies. The dinuclear hydride complex <b>3b</b> exhibits a quadruply bridged {Zr₂(μ-H)₄} core in solution and in the solid state with a relatively short Zr···Zr distance of 2.8752(11) Å. Density functional theory computations at the B3PW91 level reproduced this structure (Zr···Zr distance of 2.900 Å). The cationic hydride complex <b>3b</b> reacted with excess carbon monoxide in tetrahydrofuran at room temperature to give ethylene in 25% yield based on <b>3b</b>. Upon analysis of ¹³C NMR spectra of the reaction mixture using ¹³CO, oxymethylene and enolate complexes were detected as intermediates among other complexes

Mixed Alkyl Hydrido Complexes of Zinc: Synthesis, Structure, and Reactivity

The (NNNN)-type macrocycle 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane (Me₃TACD, 1,4,7-Me₃[12]­aneN₄) reacted with 1 equiv of ZnEt₂ under ethane elimination to give the mononuclear ethyl complex [(Me₃TACD)­ZnEt] (<b>1</b>). Upon treatment of (Me₃TACD)H with 2 equiv of ZnEt₂, the dinuclear complex [(Me₃TACD)­(ZnEt)­(ZnEt₂)] (<b>2</b>) was formed, which was converted with an additional 1 equiv of (Me₃TACD)H to <b>1</b>. Reaction of <b>1</b> with PhSiH₃ led to the formation of a tetranuclear ethyl hydrido complex [{(Me₃TACD)­ZnEt}₂(ZnEtH)₂] (<b>3</b>). Single-crystal X-ray diffraction study revealed <b>3</b> to be a centrosymmetric dimer featuring two [(Me₃TACD)­ZnEt] units coordinated to a [Zn­(μ-H)₂Zn] core via amido nitrogen atoms of the Me₃TACD ligands. Substitution of the two [(Me₃TACD)­ZnEt] units in <b>3</b> by N-heterocyclic carbene IMes [1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene] gave [(IMes)­ZnEtH]₂ (<b>4b</b>). The mixed alkyl hydrido complexes [(IMes)­ZnRH]₂ (R = Me, <b>4a</b>; Et, <b>4b</b>) were alternatively synthesized in quantitative yield by reacting [(IMes)­ZnR₂] (R = Me, Et) with [(IMes)­ZnH₂]₂ in 2:1 ratio. Methyl complex <b>4a</b> reacted with CO₂ (<i>p</i>(CO₂) = 0.5 bar) under facile insertion of CO₂ into Zn–H bonds to give dinuclear formate complex [(IMes)­ZnMe­(O₂CH)]₂ (<b>5a</b>). Treatment of <b>4b</b> with CO₂ (<i>p</i>(CO₂) = 0.5 bar) afforded a mixture of di- and trinuclear formate complexes [(IMes)­ZnEt­(O₂CH)]₂ (<b>5b</b>) and [(IMes)₂Zn₃Et₃(O₂CH)₃] (<b>6</b>) under elimination of one IMes as CO₂ adduct <b>IMes</b>·<b>CO</b>_<b>2</b>

Mixed Alkyl Hydrido Complexes of Zinc: Synthesis, Structure, and Reactivity

The (NNNN)-type macrocycle 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane (Me₃TACD, 1,4,7-Me₃[12]­aneN₄) reacted with 1 equiv of ZnEt₂ under ethane elimination to give the mononuclear ethyl complex [(Me₃TACD)­ZnEt] (<b>1</b>). Upon treatment of (Me₃TACD)H with 2 equiv of ZnEt₂, the dinuclear complex [(Me₃TACD)­(ZnEt)­(ZnEt₂)] (<b>2</b>) was formed, which was converted with an additional 1 equiv of (Me₃TACD)H to <b>1</b>. Reaction of <b>1</b> with PhSiH₃ led to the formation of a tetranuclear ethyl hydrido complex [{(Me₃TACD)­ZnEt}₂(ZnEtH)₂] (<b>3</b>). Single-crystal X-ray diffraction study revealed <b>3</b> to be a centrosymmetric dimer featuring two [(Me₃TACD)­ZnEt] units coordinated to a [Zn­(μ-H)₂Zn] core via amido nitrogen atoms of the Me₃TACD ligands. Substitution of the two [(Me₃TACD)­ZnEt] units in <b>3</b> by N-heterocyclic carbene IMes [1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene] gave [(IMes)­ZnEtH]₂ (<b>4b</b>). The mixed alkyl hydrido complexes [(IMes)­ZnRH]₂ (R = Me, <b>4a</b>; Et, <b>4b</b>) were alternatively synthesized in quantitative yield by reacting [(IMes)­ZnR₂] (R = Me, Et) with [(IMes)­ZnH₂]₂ in 2:1 ratio. Methyl complex <b>4a</b> reacted with CO₂ (<i>p</i>(CO₂) = 0.5 bar) under facile insertion of CO₂ into Zn–H bonds to give dinuclear formate complex [(IMes)­ZnMe­(O₂CH)]₂ (<b>5a</b>). Treatment of <b>4b</b> with CO₂ (<i>p</i>(CO₂) = 0.5 bar) afforded a mixture of di- and trinuclear formate complexes [(IMes)­ZnEt­(O₂CH)]₂ (<b>5b</b>) and [(IMes)₂Zn₃Et₃(O₂CH)₃] (<b>6</b>) under elimination of one IMes as CO₂ adduct <b>IMes</b>·<b>CO</b>_<b>2</b>