Cobalt(II) silanethiolato complexes with dimethylpyridines: crystal structures and spectroscopic studies

Cobalt(II) tri-tert-butoxysilanethiolates with 2,5-dimethylpyridine, 3,4-dimethylpyridine and 3,5- dimethylpyridine co-ligands have been synthesized by reaction of bimetallic [Co{μ-SSi(O ^t Bu)₃}{SSi(O ^t Bu)₃}(NH₃)]₂ with the appropriate pyridines. The complexes were characterized by elemental analysis, single-crystal X-ray structure determination, IR and UV–Vis spectroscopy. These complexes are tetra- or penta-coordinated with CoN₂S₂ and CoNO₂S₂ cores, respectively.     

Organometallic Cerium Complexes from Tetravalent Coordination Complexes

The use of tetravalent cerium alkoxides, nitrates, and triflates was studied as a direct route to [Ce^IV(carbene)] complexes. Protonolysis reactions between 1H‐imidazolium‐ or imidazoline (=4,5‐dihydro‐1H‐imidazole)‐containing alkoxide proligands HL (L=OCMe₂CH₂[1‐C(NCHCHNⁱPr)]) and HL^S (L^S=OCMe₂CH₂[1‐C(NCH₂CH₂NⁱPr)]) and Ce^IV tert‐butoxide, triflate, and nitrate compounds were studied to target [Ce^IV(N‐heterocyclic carbene)] complexes (of unsaturated and saturated carbenes, resp.). Instead, tetravalent cerium imidazolium [(O^tBu)₃Ce(μ‐O^tBu)₂(μ‐HL)Ce(O^tBu)₃], or imidazolinium adducts [(O^tBu)₃Ce(μ‐O^tBu)₂(μ‐HL^S)Ce(O^tBu)₃] were isolated. However, the salt metathesis of cerium triflate with KL provided a simple route to [CeL₄], which was significantly improved if an external oxidant, benzoquinone, was included in the mixture to maintain oxidation‐state integrity. Likewise, the salt metathesis of cerium triiodide with KL and added benzoquinone provided a straightforward route to [CeL₄].     

A family of four-coordinate iron(II) complexes bearing the sterically hindered tris(pyrazolyl)borato ligand Tp(tBu,Me)

A new family of 14‐electron, four‐coordinate iron(II) complexes of the general formula [Tp^tBu,MeFeX] (Tp^tBu,Me is the sterically hindered hydrotris(3‐tert‐butyl‐5‐methyl‐pyrazolyl) borate ligand and X=Cl ( 1 ), Br, I) were synthesized by salt metathesis of FeX₂ with Tp^tBu,MeK. The related fluoride complex was prepared by reaction of 1 with AgBF₄. Chloride 1 proved to be a good precursor for ligand substitution reactions, generating a series of four‐coordinate iron(II) complexes with carbon, oxygen, and sulphur ligands. All of these complexes were fully characterized by conventional spectroscopic methods and most were characterized by single‐crystal X‐ray crystallographic analysis. Magnetic measurements for all complexes agreed with a high‐spin (d⁶, S=2) electronic configuration. The halide series enabled the estimation of the covalent radius of iron in these complexes as 1.24 Å.     

Dioxygen affinities of Schiff base cobalt(II) complexes with aza-crown or morpholino pendants

Abstract  

Schiff base Co(II) complexes, CoL₂¹–CoL₂⁶ with aza-crown or morpholino pendants were synthesized. The oxygenation constants (KO₂) of these complexes in MeOCH₂CH₂OMe solution were measured over the range of −5 to 25 °C, and the thermodynamic parameters (∆H ⁰, ∆S ⁰) for oxygenation were calculated based on these KO₂ values. The effects of different substituents on the Schiff base ligand with respect to the modulation of O₂-binding capability were explored. The results indicate that the dioxygen affinities of the Co(II) complexes are much more enhanced by aza-crown pendants than that by morpholino pendants, and the O₂-binding capabilities of the aza-crown pendants complexes can also be enhanced by adding Na⁺ cations.     

Yttrium Siloxide Complexes Bearing Terminal Methyl Ligands: Molecular Models for Ln−CH3 Terminated Silica Surfaces

Surface organometallic chemistry (SOMC) on silica materials is a prominent approach for the generation of highly active heterogenized polymerization catalysts. Despite advanced methods of characterization, the elucidation of the catalytically active surface species remains a challenging task. Alkylated rare‐earth metal siloxide complexes can be regarded as molecular models of respective covalently bonded alkylated surface species, primarily used for 1,3‐diene polymerization. Here, we performed both salt metathesis reactions of [Y(MMe₄)₃] (M = Al, Ga) with [K{OSi(OtBu)₃}] and alkylation reactions of [Y{OSi(OtBu)₃}₃]₂ with AlMe₃. The obtained complexes [Y(CH₃)[(AlMe₂){OSi(OtBu)₃}₂](AlMe₄)]₂, [Y(CH₃)[(AlMe₂){OSi(OtBu)₃}₂]‐{OSi(OtBu)₃}], [Y{OSi(OtBu)₃}₃(μ‐Me)Y(μ‐Me)₂Y{OSi(OtBu)₃}₂(AlMe₄)], and [Y(CH₃)(GaMe₄){OSi(OtBu)₃}]₂ represent rare examples of organoyttrium species with terminal methyl groups. The formation and purity of the mixed methyl/siloxy yttrium complexes could be enhanced by treating [Y(MMe₄)₃] with [K(MMe₂){OSi(OtBu)₃}₂]_n (M=Al: n=2; M=Ga: n=∞). Complexes [K(MMe₂){OSi(OtBu)₃}₂]_n were obtained by addition of [K{OSi(OtBu)₃}] to [Me₂M{OSi(OtBu)₃}]₂. Deeper insight into the fluxional behavior of the mixed methyl/siloxy yttrium complexes in solution was gained by ¹H and ¹³C NMR spectroscopic studies at variable temperature and ¹H–⁸⁹Y HSQC NMR spectroscopy.     

Siloxyaluminate and Siloxygallate Complexes as Models for Framework and Partially Hydrolyzed Framework Sites in Zeolites and Zeotypes

Anionic molecular models for nonhydrolyzed and partially hydrolyzed aluminum and gallium framework sites on silica, M[OSi(OtBu)₃]₄⁻ and HOM[OSi(OtBu)₃]₃⁻ (where M=Al or Ga), were synthesized from anionic chlorides Li{M[OSi(OtBu)₃]₃Cl} in salt metathesis reactions. Sequestration of lithium cations with [12]crown-4 afforded charge-separated ion pairs composed of monomeric anions M[OSi(OtBu)₃]₄⁻ with outer-sphere [([12]crown-4)₂Li]⁺ cations, and hydroxides {HOM[OSi(OtBu)₃]₃} with pendant [([12]crown-4)Li]⁺ cations. These molecular models were characterized by single-crystal X-ray diffraction, vibrational spectroscopy, mass spectrometry and NMR spectroscopy. Upon treatment of monomeric [([12]crown-4)Li]{HOM[OSi(OtBu)₃]₃} complexes with benzyl alcohol, benzyloxide complexes were formed, modeling a possible pathway for the formation of active sites for Meerwin–Ponndorf–Verley (MPV) transfer hydrogenations with Al/Ga-doped silica catalysts.     

SYNTHESIS AND COMPLEX FORMATION OF NOVEL 12-MEMBERED MACROCYCLIC (E,E)-DIOXIMES

Abstract

Dibenzo[e,k]-2,3-bis(hydroxyimino) 1.4.7.10-tetrathia-2,3,8,9-tetrahydrocyclododecine (S₄H₂) and dibenzo-[e,k]-2,3-bis(hydroxyimino)-1,4-dithia-7,10-dioxa-2,3,8,9- tetrahydrocyclododecine (O₂S₂H₂) have been prepared from (E,E)-dichloroglyoxime, 2,3,8,9-dibenzo-1,4,7,10-tetrathiadecane (DTT) and 2,3,8,9-Dibenzo-4,7-dioxa-1,10-dithiadecane (DDD) which was synthesized by treating 1,2-bis(o-aminophenoxy)ethane with HNO₂ and potassium ethylxsanthate. The structures of these vic-dioximes have been determined as the (E,E)-forms according to ¹H-NMR and IR data. Only mononuclear complexes with a metal-ligand ratio of 1:2 have been isolated with Co(II), such as [(S₄H)₂Co(III)L′Cl] and [(O₂S₂H)₂Co(III)L′Cl]; Cu(II) forms only trinuclear complexes. Reaction of the mononuclear complexes with Pd(II) gives heterotrinuclear complexes.     

Multinuclear NMR Spectroscopic Characterization of Vanadium(V) Alkylperoxo Complexes VO(OOtBu)k(OnBu)3-k, where k = 1, 2, 3

Using ⁵¹V, ¹⁷O, ¹³C and ¹H NMR spectroscopy, vanadium(V) alkylperoxo complexes VO(OOtBu)_k(OnBu)_3-k, where k = 1, 2 and 3, were characterized in the reaction of VO(OnBu)₃ with tBuOOH in CH₂Cl₂.     

Dioxygen Activation by Non‐Adiabatic Oxidative Addition to a Single Metal Center

A chromium(I) dinitrogen complex reacts rapidly with O₂ to form the mononuclear dioxo complex [Tp^tBu,MeCr^V(O)₂] (Tp^tBu,Me=hydrotris(3‐tert‐butyl‐5‐methylpyrazolyl)borate), whereas the analogous reaction with sulfur stops at the persulfido complex [Tp^tBu,MeCr^III(S₂)]. The transformation of the putative peroxo intermediate [Tp^tBu,MeCr^III(O₂)] (S=³/₂) into [Tp^tBu,MeCr^V(O)₂] (S=¹/₂) is spin‐forbidden. The minimum‐energy crossing point for the two potential energy surfaces has been identified. Although the dinuclear complex [(Tp^tBu,MeCr)₂(μ‐O)₂] exists, mechanistic experiments suggest that O₂ activation occurs on a single metal center, by an oxidative addition on the quartet surface followed by crossover to the doublet surface.     

Neue Koordinations-Motive bei Cyclothiazeno-Komplexen von Molybdän und Wolfram. Die Kristallstrukturen von [{Mo(N3S2)(Cl)(OtBu)2}{Mo(O)(N3S2)(OtBu)}]2 und [W(N3S2)2(LiCl){N≡W(NPPh3)3}2]

New Coordination Motives at Cyclothiazeno Complexes of Molybdenum and Tungsten. Crystal Structures of [{Mo(N₃S₂)(Cl)(O^tBu)₂}{Mo(O)(N₃S₂)(O^tBu)}]₂ and [W(N₃S₂)₂(LiCl){N≡W(NPPh₃)₃}₂] The metalla cyclothiazeno complexes (Cyclo-1λ⁶-metalla-3,5-dithia-2,4,6-triazino complexes) [{Mo(N₃S₂)(Cl) · (O^tBu)₂}{Mo(O)(N₃S₂)(O^tBu)}]₂ ( 1 ) and [W(N₃S₂)₂(LiCl) · {N≡W(NPPh₃)₃}₂] ( 2 ) are formed from [MoCl₃(N₃S₂)]₂ and LiO^tBu in toluene, and from [WCl₃(N₃S₂)]₂ and LiNPPh₃ in THF, respectively. The complexes form moisture sensitive, black ( 1 ) or brown ( 2 ) crystals, which we characterized by crystal structure analyses. 1 · Toluene: Space group P 1, Z = 1, lattice dimensions at –83 °C: a = 934.2(1), b = 964.4(1), c = 1700.3(1) pm; α = 83.54(1)°, β = 78.35(1)°, γ = 71.56(1)°, R₁ = 0.0339. 2 · 1.625 Toluene · 0.75 THF: Space group P 1, Z = 4, lattice dimensions at –80 °C: a = 1313.8(1), b = 2896.8(2), c = 3384.9(3) pm; α = 82.42(1)°, β = 88.71(1)°, γ = 77.28(1)°, R₁ = 0.0603.     

Nickel(II) tri-tert-butoxysilanethiolates with N-heterocyclic bases as additional ligands: Synthesis, molecular structure and spectral studies

Three heteroleptic, neutral nickel(II) tri-tert-butoxysilanethiolates with monodentate heterocyclic bases (pyridine, 2-methylpyridine and 3,5-dimethylpyridine) serving as additional ligands have been prepared following the same synthetic procedure. The complexes were characterized by single crystal X-ray structure determination and elemental analysis. For complexes 1 and 2, FT-IR and UV-Vis spectroscopy have been additionally recorded.Three different coordination motifs have been observed in these complexes. Molecules building tetragonal crystals of [Ni{SSi(O^tBu)₃}₂(C₅H₅N)] (1) feature Ni(II) coordinated by two S,O-chelating tri-tert-butoxysilanethiolato residues and one N atom of pyridine in a strongly distorted trigonal bipyramidal environment. The complex [Ni{SSi(O^tBu)₃}₂(C₆H₇N)₂] (2) forms triclinic crystals and its core atoms adopt a planar geometry with Ni(II) in the middle of the N₂S₂ plane. Molecules of complex [Ni{SSi(O^tBu)₃}₂(C₇H₉N)₂(H₂O)] (3) form orthorhombic crystals with penta-coordinated Ni(II) in a distorted tetragonal pyramidal NiN₂OS₂ environment. Complex 2 roughly mimics one of the two metal centers in the active site of the ACS/CODH enzyme.     

13C and1H NMR spectroscopic characterization of titanium(IV) alkylperoxo complexes Ti(OOtBu)n(OiPr)4?n with n=1, 2, 3, 4

Using¹³C and¹H NMR spectroscopy, titanium(IV) alkylperoxo complexes Ti(OOtBu)_n(OiPr)_4−n with n=1, 2, 3 and 4 were characterized in the reaction of Ti(OiPr)₄ withtBuOOH in CH₂Cl₂ and CDCl₃.     

Cation‐Mediated Conversion of the State of Charge in Uranium Arene Inverted‐Sandwich Complexes

Two new arene inverted‐sandwich complexes of uranium supported by siloxide ancillary ligands [K{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 3 ) and [K₂{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 4 ) were synthesized by the reduction of the parent arene‐bridged complex [{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 2 ) with stoichiometric amounts of KC₈ yielding a rare family of inverted‐sandwich complexes in three states of charge. The structural data and computational studies of the electronic structure are in agreement with the presence of high‐valent uranium centers bridged by a reduced tetra‐anionic toluene with the best formulation being U^V–(arene^4?)–U^V, KU^IV–(arene^4?)–U^V, and K₂U^IV–(arene^4?)–U^IV for complexes 2 , 3 , and 4 respectively. The potassium cations in complexes 3 and 4 are coordinated to the siloxide ligands both in the solid state and in solution. The addition of KOTf (OTf=triflate) to the neutral compound 2 promotes its disproportionation to yield complexes 3 and 4 (depending on the stoichiometry) and the U^IV mononuclear complex [U(OSi(OtBu)₃)₃(OTf)(thf)₂] ( 5 ). This unprecedented reactivity demonstrates the key role of potassium for the stability of these complexes.     

Allylic Peroxidations with Bis(2‐pyridylimino)isoindolato‐Cobalt and ‐Iron Complexes

Several novel substituted bis(2‐pyridylimino)isoindolato (BPI) cobalt(II) and iron(II) complexes [M(BPI)(OAc)(H₂O)] (M = Co: 1 ‐ 6, Fe: 7) have been synthesized by reaction of bis(2‐pyridylimino)isoindole derivatives with the corresponding metal(II) acetates. Reaction of 1‐6 with 1.5 ‐ 2 molar equivalents of t‐BuOOH gave the corresponding alkylperoxocobalt(III) complexes [Co(BPI)(OAc)(OOtBu)] (10 ‐ 15). Using an aqueous solution of t‐BuOOH (70 %), cyclohexene was selectively catalytically oxidized to the dialkylperoxide cyclohex‐2‐ene‐1‐t‐butylperoxide.     

Spectral, magnetic and thermal investigations of some d-electron element 3-methoxy-4-methylbenzoates

Conditions for the preparation of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) 3-methoxy-4-methylbenzoates were investigated and their quantitative composition and magnetic moments were determined. The IR spectra and powder diffraction patterns of the complexes prepared of general formula M(C₉H₉O₃)₂·nH₂O (n=2 for Mn, Co n=1 for Ni, Cu, n=0 for Zn, Cd) were prepared and their thermal decomposition in air was studied. Their solubility in water at 293 K is of the order 10^–2 (Mn)–10^–4 (Cu) mol dm^–3. IR spectra of the prepared 3-methoxy-4-methylbenzoates suggest that carboxylate groups are bidentate bridging. The magnetic moments for the paramagnetic complexes of Mn(II), Co(II), Ni(II) and Cu(II) attain values 5.50, 4.45, 3.16 and 1.79 B. M., respectively. During heating the hydrated complexes lose crystallization water molecules in one step and then the anhydrous complexes decompose directly to oxides MO and Mn3O4. Only Co(II) complex decomposes to Co₃O₄ with intermediate formation CoO.     

Heteroleptic Square Planar Cobalt(I/II) Complexes

Reduction of the cobalt(II) chloride complex, Ph₂B(^tBuIm)₂Co(THF)Cl ( 1 ) in the presence of ^tBuN≡C affords the diamagnetic, square planar cobalt(I) complex Ph₂B(^tBuIm)₂Co(C≡N^tBu)₂ ( 2 ). This is a rare example of a 16-electron cobalt(I) complex that is structurally related to square planar noble metal complexes. Accordingly, the electronic structure of 2 , as calculated by DFT, reveals that the HOMO is largely d_z² in character. Complex 2 is readily oxidized to its cobalt(II) congener [Ph₂B(^tBuIm)₂Co(C=N^tBu)₂]BPh₄ ( 3 -BPh₄), whose EPR spectral parameters are characteristic of low-spin d⁷ with an unpaired electron in an orbital of d_z² parentage. This is also consistent with the results of DFT calculations. Despite its 16-electron configuration and the d_z² parentage of the HOMO, the only tractable reactions of 2 involve one electron oxidation to afford 3 .     

Synthesis and characterizations of bis(phenoxy)‐amine tin(II) complexes for ring‐opening polymerization of lactide

A series of tin(II) complexes supported by N₂O₂ bis(phenol)‐amine ligands were prepared from the reactions of the corresponding ligands with Sn[N(SiMe₃)₂]₂ in benzene at room temperature. The ligands were designed to have different substituted group at the ortho‐position on the aryl rings (R = ^tBu, CH₃) and N‐containing side arm (E = ? CH₂NEt₂ and pyridine) giving a variation of tin(II) complexes (R = ^tBu, E = CH₂NEt₂, 2a ; R = ^tBu, E = py, 2b ; R = CH₃, E = CH₂NEt₂, 2c ; R = CH₃, E = py, 2d ). All complexes were characterized by NMR spectroscopy and single‐crystal X‐ray analysis. The single‐crystal X‐ray crystallography revealed that all complexes have a monomeric four‐coordinate tin center with a distorted seesaw structure. All complexes are active for solvent‐free polymerization of l ‐lactide at 120 °C giving poly(l ‐lactide) with narrow to moderate dispersity (Ð = 1.12–1.56). In the presence of benzyl alcohol during the polymerization, the resulting polymer was found to be linear having benzyl alcohol as the end group while, in the absence of benzyl alcohol, the polymer was cyclic. The large ^tBu group at the ortho‐position was found to decrease polymerization activity while the more basic ? CH₂NEt₂ group was found to increase the polymerization activity. The polymerization of rac‐lactide under a similar condition gave PLA having a slight heterotactic bias for all catalysts. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2104–2112     

Ein neuer Aluminium/Nickel/Oxo‐Cluster: [Ni(acac)OAl(OtBu)2]4

A New Aluminum/Nickel/Oxo‐Cluster: [Ni(acac)OAl(OtBu)₂]₄ When bis(tert‐butoxy)alane (tBu‐O)₂AlH is allowed to react with nickeldiacetylacetonate at elevated temperature a new nickel/aluminum/oxo cluster [Ni(acac)OAl(OtBu)₂]₄ is formed together with aluminum acetylacetonate Al(acac)₃ and some other products. The metal/oxo cluster is isolated by crystallization and structurally fully characterized by X‐ray diffraction analysis. The molecule [Ni(acac)OAl(OtBu)₂]₄ contains an eight membered Al₄O₄ cycle, to which eight mutually edge sharing NiO₂Al cycles are fused. The overall point symmetry of the metal/oxo cluster is almost S₄. While the aluminum atoms are tetrahedrally surrounded by oxygen ligands (mean distances Al‐O in‐between 1, 730(6) and 1, 789(6) Å)), the nickel atoms are in a square pyramidal coordination sphere of oxygen atoms (Ni‐O_axial = 1.938(6) Å, Ni‐O_basal = 2.056(9) Å; all polyhedra are distorted). The nickel atoms have a d⁸ high spin electron configuration (μ_eff = 3.32 B.M.).     

Potential Precursors for Terminal Methylidene Rare-Earth-Metal Complexes Supported by a Superbulky Tris(pyrazolyl)borato Ligand

A series of solvent-free heteroleptic terminal rare-earth-metal alkyl complexes stabilized by a superbulky tris(pyrazolyl)borato ligand with the general formula [Tp^tBu,MeLnMeR] have been synthesized and fully characterized. Treatment of the heterobimetallic mixed methyl/tetramethylaluminate compounds [Tp^tBu,MeLnMe(AlMe₄)] (Ln=Y, Lu) with two equivalents of the mild halogenido transfer reagents SiMe₃X (X=Cl, I) gave [Tp^tBu,MeLnX₂] in high yields. The addition of only one equivalent of SiMe₃Cl to [Tp^tBu,MeLuMe(AlMe₄)] selectively afforded the desired mixed methyl/chloride complex [Tp^tBu,MeLuMeCl]. Further reactivity studies of [Tp^tBu,MeLuMeCl] with LiR or KR (R=CH₂Ph, CH₂SiMe₃) through salt metathesis led to the monomeric mixed-alkyl derivatives [Tp^tBu,MeLuMe(CH₂SiMe₃)] and [Tp^tBu,MeLuMe(CH₂Ph)], respectively, in good yields. The SiMe₄ elimination protocols were also applicable when using SiMe₃X featuring more weakly coordinating moieties (here X=OTf, NTf₂). X-ray structure analyses of this diverse set of new [Tp^tBu,MeLnMeR/X] compounds were performed to reveal any electronic and steric effects of the varying monoanionic ligands R and X, including exact cone-angle calculations of the tridentate tris(pyrazolyl)borato ligand. Deeper insights into the reactivity of these potential precursors for terminal alkylidene rare-earth-metal complexes were gained through NMR spectroscopic studies.     

A Comparative Study on the Thermodynamics of Halogen Bonding of Group 10 Pincer Fluoride Complexes

The thermodynamics of halogen bonding of a series of isostructural Group 10 metal pincer fluoride complexes of the type [(3,5-R₂-^tBuPOCOP^tBu)MF] (3,5-R₂-^tBuPOCOP^tBu=κ³-C₆HR₂-2,6-(OPtBu₂)₂ with R=H, tBu, COOMe; M=Ni, Pd, Pt) and iodopentafluorobenzene was investigated. Based on NMR experiments at different temperatures, all complexes 1-tBu (R=tBu, M=Ni), 2-H (R=H, M=Pd), 2-tBu (R=tBu, M=Pd), 2-COOMe (R=COOMe, M=Pd) and 3-tBu (R=tBu, M=Pt) form strong halogen bonds with Pd complexes showing significantly stronger binding to iodopentafluorobenzene. Structural and computational analysis of a model adduct of complex 2-tBu with 1,4-diiodotetrafluorobenzene as well as of structures of iodopentafluorobenzene in toluene solution shows that formation of a type I contact occurs.