Development of more labile low electron count Co(I) sources: mild, catalytic functionalization of activated alkanes using a [(Cp*Co)2-μ-(η4:η4-arene)] complex

Catalytic transfer dehydrogenation of silyl protected amines, requiring sp(3) C-H bond activation, is mediated by a bridging arene complex of the type [(Cp*Co)(2)-μ-(η(4):η(4)-arene)] under mild conditions. Mechanistic and qualitative rate studies establish the compound as a more reactive Co(I) source when compared to other known Cp*Co(I) complexes.     

C-H activation of arenes and heteroarenes by early transition metallaborane, [(Cp*Ta)2B5H11] (Cp* = η5-C5Me5)

C-H activation of arenes and heteroarenes has been achieved by a hydrogen rich tantalaborane cluster [(Cp*Ta)(2)B(5)H(11)] that leads to the formation of C-H functionalized products. Furthermore, we examined the reaction of substituted thiophene and pyrrole derivatives with tantalaborane which provided a convenient and efficient route to regio-defined C-H functionalized heteroarenes.     

Halogenation of the Hexaphosphabenzene Complex [(Cp*Mo)2(μ,η6:η6-P6)]: Snapshots on the Reaction Progress

The oxidation of [(Cp*Mo)₂(μ,η⁶:η⁶-P₆)] ( 1 ) with halogens or halogen sources was investigated. The iodination afforded the ionic complexes [(Cp*Mo)₂(μ,η³:η³-P₃)(μ,η¹:η¹:η¹:η¹-P₃I₃)][X] (X=I₃⁻, I⁻) ( 2 ) and [(Cp*Mo)₂(μ,η⁴:η⁴-P₄)(μ-PI₂)][I₃] ( 3 ), while the reaction with PBr₅ led to the complexes [(Cp*Mo)₂(μ,η³:η³-P₃)(μ-Br)₂][Cp*MoBr₄] ( 4 ) [(Cp*MoBr)₂(μ,η³:η³-P₃)(μ,η¹-P₂Br₃)] ( 5 ) and [(Cp*Mo)₂(μ-PBr₂)(μ-PHBr)(μ-Br)₂] ( 6 ). The reaction of 1 with the far stronger oxidizing agent PCl₅ was followed via time- and temperature-dependent ³¹P{¹H} NMR spectroscopy. One of the first intermediates detected at 193 K was [(Cp*Mo)₂(μ,η³:η³-P₃)(μ-PCl₂)₂][PCl₆] ( 8 ) which rearranges upon warming to [(Cp*Mo)₂(μ-PCl₂)₂(μ-Cl)₂] ( 9 ), [(Cp*MoCl)₂(μ,η³:η³-P₃)(μ-PCl₂)] ( 10 ) and [(Cp*Mo)₂(μ,η⁴:η⁴-P₄)(μ-PCl₂)][Cp*MoCl₄] ( 11 ), which could be isolated at room temperature. All complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy and their electronic structures were elucidated by DFT calculations.     

A homometallic tricapped cubane cluster: [(Cp*Mo)4B4H4(μ4-BH)3] (Cp* = η5-C5Me5)

The reaction of [Cp*MoCl(4)] with an excess of LiBH(4), followed by thermolysis with tellurium powder in toluene, afforded a tricapped cubane cluster, [(Cp*Mo)(4)B(4)H(4)(μ(4)-BH)(3)] (1), which represents an unprecedented metal-rich metallaborane cluster with a cubane core containing 58 cluster valence electrons (cve) and three metal-metal bonds.     

C-H activation by a mononuclear manganese(III) hydroxide complex: synthesis and characterization of a manganese-lipoxygenase mimic?

Lipoxygenases are mononuclear non-heme metalloenzymes that regio- and stereospecifically convert 1,4-pentadiene subunit-containing fatty acids into alkyl peroxides. The rate-determining step is generally accepted to be hydrogen atom abstraction from the pentadiene subunit of the substrate by an active metal(III)-hydroxide species to give a metal(II)-water species and an organic radical. All known plant and animal lipoxygenases contain iron as the active metal; recently, however, manganese was found to be the active metal in a fungal lipoxygenase. Reported here are the synthesis and characterization of a mononuclear Mn(III) complex, [Mn(III)(PY5)(OH)](CF(3)SO(3))(2) (PY5 = 2,6-bis(bis(2-pyridyl)methoxymethane)pyridine), that reacts with hydrocarbon substrates in a manner most consistent with hydrogen atom abstraction and provides chemical precedence for the proposed reaction mechanism. The neutral penta-pyridyl ligation of PY5 endows a strong Lewis acidic character to the metal center allowing the Mn(III) compound to perform this oxidation chemistry. Thermodynamic analysis of [Mn(III)(PY5)(OH)](2+) and the reduced product, [Mn(II)(PY5)(H(2)O)](2+), estimates the strength of the O-H bond in the metal-bound water in the Mn(II) complex to be 82 (+/-2) kcal mol(-)(1), slightly less than that of the O-H bond in the related reduced iron complex, [Fe(II)(PY5)(MeOH)](2+). [Mn(III)(PY5)(OH)](2+) reacts with hydrocarbon substrates at rates comparable to those of the analogous [Fe(III)(PY5)(OMe)](2+) at 323 K. The crystal structure of [Mn(III)(PY5)(OH)](2+) displays Jahn-Teller distortions that are absent in [Mn(II)(PY5)(H(2)O)](2+), notably a compression along the Mn(III)-OH axis. Consequently, a large internal structural reorganization is anticipated for hydrogen atom transfer, which may be correlated to the lessened dependence of the rate of substrate oxidation on the substrate bond dissociation energy as compared to other metal complexes. The results presented here suggest that manganese is a viable metal for lipoxygenase activity and that, with similar coordination spheres, iron and manganese can oxidize substrates through a similar mechanism.     

Ditantalum dinitrogen complex: reaction of H2 molecule with "end-on-bridged" [Ta(IV)]2(μ-η(1):η(1)-N2) and Bis(μ-nitrido) [Ta(V)]2(μ-N)2 complexes

To elucidate (i) the physicochemical properties of the {(η(5)-C(5)Me(5))[Ta(IV)](i-Pr)C(Me)N(i-Pr)}(2)(μ-η(1):η(1)-N(2)), I, [Ta(IV)](2)(μ-η(1):η(1)-N(2)), and {(η(5)-C(5)Me(5))[Ta(V)](i-Pr)C(Me)N(i-Pr)}(2)(μ-N)(2), II, [Ta(V)](2)(μ-N)(2), complexes; (ii) the mechanism of the I → II isomerization; and (iii) the reaction mechanism of these complexes with an H(2) molecule, we launched density functional (B3LYP) studies of model systems 1, 2, and 3 where the C(5)Me(5) and (i-Pr)C(Me)N(i-Pr) ligands of I (or II) were replaced by C(5)H(5) and HC(NCH(3))(2), respectively. These calculations show that the lower-lying electronic states of 1, [Ta(IV)](2)(μ-η(1):η(1)-N(2)), are nearly degenerate open-shell singlet and triplet states with two unpaired electrons located on the Ta centers. This finding is in reasonable agreement with experiments [J. Am Chem. Soc. 2007, 129, 9284-9285] showing easy accessibility of paramagnetic and diamagnetic states of I. The ground electronic state of the bis(μ-nitrido) complex 2, [Ta(V)](2)(μ-N)(2), is a closed-shell singlet state in agreement with the experimentally reported diamagnetic feature of II. The 1-to-2 rearrangement is a multistep and highly exothermic process. It occurs with a maximum of 28.7 kcal/mol free energy barrier required for the (μ-η(1):η(1)-N(2)) → (μ-η(2):η(2)-N(2)) transformation step. Reaction of 1 with H(2) leading to the 1,4-addition product 3 proceeds with a maximum of 24.2 kcal/mol free energy barrier associated by the (μ-η(1):η(1)-N(2)) → (μ-η(2):η(1)-N(2)) isomerization step. The overall reaction 1 + H(2) → 3 is exothermic by 20.0 kcal/mol. Thus, the addition of H(2) to 1 is kinetically and thermodynamically feasible and proceeds via the rate-determining (μ-η(1):η(1)-N(2)) → (μ-η(2):η(1)-N(2)) isomerization step. The bis(μ-nitrido) complex 2, [Ta(V)](2)(μ-N)(2), does not react with H(2) because of the large energy barrier (49.5 kcal/mol) and high endothermicity of the reaction. This conclusion is also in excellent agreement with the experimental observation [J. Am Chem. Soc. 2007, 129, 9284-9285].     

Synthesis,spectra and crystal structure of a dinuclear manganese(χ) complex [(NTB)Mn(μ-O)]2(ClO4)4 · 2H2O

A novel dinuclear manganese(χ) complex [(NTB)Mn(μ-O)]₂(ClO₄)₄?·?2H₂O (1) (NTB?=?tris(2-benzimidazolylmethyl) amine) has been synthesized and characterized. The crystal structure is determined by single crystal X-ray diffraction. The compound crystallizes in the monoclinic system, space group C2/c with a?=?18.3461(1), b?=?15.4170(1), c?=?21.0141(1)?Å, β?=?90.5290(1)°, V?=?5943.4(8)?ų, Z?=?4 and R ₁?=?0.0789 for 5729 observed reflections. Two manganese atoms are bridged by two oxygen atoms forming a dinuclear complex. The results of interaction between 1 and H₂O₂ indicated that hydrogen peroxide destroyed the Mn₂O₂ unit of 1.     

The Superbulky Pn Ligand Complexes [CpBIGFe(η5−P5)] and [(CpBIGFe)2(μ,η4:4-P4)]—Synthesis and Characterization

Abstract

A new synthesis of [Cp^BIGFe(CO)₂]₂ 3 (Cp^BIG = C₅(4-ⁿBuC₆H₄)₅) was developed starting from Cp^BIGNa and FeCl₂ in the presence of CO. Reaction of this product with P₄ leads to the two new P_n ligand complexes [Cp^BIGFe(η⁵-P₅)] 1b and [(Cp^BIGFe)₂(μ,η^4:4-P₄)] (4) containing the highly sterically demanding Cp^BIG ligand. Depending on the solvent, different ratios of 1b:4 are obtained. The products 1b, 3, and 4 were characterized by spectroscopic methods as well as by X-ray diffraction.     

Synthesis of a vinylcarbynetetrairon complex. Crystal and molecular structure of [(C5H5)2(CO)2Fe2(μ-CO)]2- (μ-C5H3)+BF4−

The diiron vinyl ether carbyne complex [(C₅H₅)(CO)Fe]₂(μ-CO)- (μ-CCHCHOCH₂CH₃)⁺ BF₄⁻ (1) reacted with the diiron ethenylidene complex [(C₅H₅)(CO)Fe]₂(μ-CO)(μ-CCH₂) (2) to yield the tetrairon complex [(C₅H₅)₂(CO)₂Fe₂(μ-CO)]₂(μ-C₅H₃⁺BF₄⁻ (3) which was characterized by spectroscopy and by single crystal X-ray diffraction.     

Synthesis and the fluxional behavior of the 30-electron cationic iron-molybdenum triple-decker complex with a central pentaphospholyl ligand, [(η-C7H7)Mo(μ-η:η-P5)Fe(η-C5Me5)]BF4

The reaction of [(η-C₇H₇)Mo(MeCN)₃)]BF₄ with (η-C₅Me₅)Fe(η-P₅) afforded the new 30-electron triple-decker complex [(η-C₇H₇)Mo(μ-η:η-P₅)Fe(η-C₅Me₅)]BF₄. Studies of the temperature dependence of the¹H NMR spectra demonstrated that the resulting compound contains a fluxional cyclohepatrienyl ligand. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1374–1376, July, 1999.     

Synthesis, characterization, and reactivity of a novel μ-η2:η2-diselenidodicopper(II) complex

The first μ-η(2):η(2)-diselenidodicopper(II) complex has been obtained in the reaction of a copper(I) complex with N,N',N″-tribenzyl-cis,cis-1,3,5-triaminocyclohexane and elemental selenium. The structure and reactivity of the complex is described.     

Water oxidation catalyzed by a new tetracobalt-substituted polyoxometalate complex: [{Co4(μ-OH)(H2O)3}(Si2W19O70)]11-

A new polyoxometalate of earth adundant elements [{Co(4)(μ-OH)(H(2)O)(3)}(Si(2)W(19)O(70))](11-) has been synthesized, characterized and shown to be a water oxidation catalyst. The initial catalytic complex is unstable and slowly undergoes hydrolysis. The hydrolysis products have been isolated and characterized, and their catalytic water oxidation activity is assessed.     

STRUCTURE OF TRANS-SYN-BIS-[(η-(CH_3)_2CHC_5H_4)Mo (μ-S)(μ-SC(CH_3)_3)]

<正> Mr = 648.75, triclinic, space group P1 , a = 10.087(4), b = 12.686(5), c = 14.222(6) A, α= 104.83(3)°, β = 124.61(4)°, γ = 90.98(3)°, V = 1417.22A3, Z = 2, De = 1.520 Mg.m-3, (MoKα)= 0.71069A, μ(MoKα) = 11.597 cm-1, F(000) = 664, room temperature. Final R=0.0424 for 5705 observed reflections. In the molecule two metal atoms are bonded togetherin a cavity surrounded by Ugands. Pour sulphur atoms are in bridging positions and in the same plane perpendicular to the metal-metal vector with the two t-butylthiolato ligands being in mutu-syn positions.     

Properties of a New 58-Electron Butterfly [Pt4(μ2-dpam)3(μ2-CO)3(η1-dpam)]2+ Cluster

A new organometallic cluster [Pt₄(₂-dpam)₃(₂-CO)₃(¹-dpam)] X₂ (X=CF₃CO ₂ ^- ; 4a) was prepared from a reaction between Pt(dpam)(CF₃CO₂)₂ and CO in a methanol (water mixture). The PF ₆ ^- salt 4b is obtained from an anion exchange with NH₄PF₆ in methanol. Dark red crystals suitable for X-ray crystallography (X=PF ₆ ^- ) revealed the commonly encountered butterfly structure for a 58-electron Pt cluster (angle between the two Pt₃ planes =95.36(8)°, nonbonding Pt...Pt distance =3.094(1) Å). The structure consists of two edge sharing Pt₃ triangles, a small one 'Pt₃(₂-dpam) ₃ ²⁺ and a larger one Pt₃(₂-CO)₃(L)₃ where L=As group. The Extended Huckel Molecular Orbital calculations (EHMO) have been rationalized from interactions of two L and PtL ₂ ²⁺ fragments onto the planar triangular Pt₃(₂-CO)₃L₃ cluster (L = AsH₃). The compound is luminescent at 77 K with a structureless band located at 690 nm (_e=3.2 ±0.2s). Finally, the ¹H NMR spectra are interpreted, particularly with respect to fluxionality and presence of two isomers. X-ray data for 4b: orthorhombic, C c2a, a=26.320(9), b=27.613(6), c=28.891(4) Å, V=20998(9) ų, Z=4, D(calc.)=1.925 Mg/m³.     

The Potential of the Diarsene Complex [(C5H5)2Mo2(CO)4(μ,η2-As2)] as a Connector Between Silver Ions

The reaction of the organometallic diarsene complex [Cp₂Mo₂(CO)₄(μ,η²-As₂)] ( B ) (Cp = C₅H₅) with Ag[FAl{OC₆F₁₀(C₆F₅)}₃] (Ag[FAl]) and Ag[Al{OC(CF₃)₃}₄] (Ag[TEF]), respectively, yields three unprecedented supramolecular assemblies [(η²- B )₄Ag₂][FAl]₂ ( 4 ), [(μ,η¹:η²- B )₃(η²- B )₂Ag₃][TEF]₃ ( 5 ) and [(μ,η¹:η²- B )₄Ag₃][TEF]₃ ( 6 ). These products are only composed of the complexes B and Ag^I. Moreover, compounds 5 and 6 are the only supramolecular assemblies featuring B as a linking unit, and the first examples of [Ag^I]₃ units stabilized by organometallic bichelating ligands. According to DFT calculations, complex B coordinates to metal centers through both the As lone pair and the As−As σ-bond thus showing this unique feature of this diarsene ligand.     

Synthesis and characterisation of a pyrazine bridged bis-allyl ruthenium(IV) complex. Crystal structure of [{(η3:η3-C10H16)RuCl2}2(μ-C4H4N2)]·2CHCl3

The reaction of pyrazine with the ruthenium(IV) bis-allyl dimer [(η³:η³-C₁₀H₁₆)RuCl(μ-Cl)]₂ gives the bridged binuclear complex [{(η³:η³-C₁₀H₁₆)RuCl₂}₂(μ-C₄H₄N₂)] in high yield. The complex has been characterised by ¹H NMR spectroscopy and by a single-crystal X-ray diffraction study.     

Tetracarbonyliron adducts of Cp2Cr2(CO)4(μ-η2-P2). Syntheses and crystal structures of Cp2Cr2(CO)4P2[Fe(CO)4] m (m=1 and 2)

Cp₂Cr₂(CO)₄( - ² - P₂), 1, reacts with one molar equivalent of Fe₂(CO)₉ in THF to yield the mono- and di-iron complexes, Cp₂Cr₂(CO)₄P₂[Fe(CO)₄], 2, (16.5% yield) and Cp₂Cr₂(CO)₄P₂[Fe(CO)₄]₂, 3, (16.9% yield), as dark magenta brown and dark greenish brown crystals, respectively. Both complexes were characterized by single-crystal X-ray diffraction analysis. Crystal data –2: space group =P2₁/c,a=17.024(1) Å,b=8.180(1) Å,c=30.891(2) Å, =100.953(5)°,V=4223.4(7)ų,Z=8, 3743 observed reflections,R _F=0.033; 3: space group P1,a=10.209(2) Å,b=10.212(2) Å,c=15.989(3) Å, =106.93(1)°, =91.87(1)°, =119.50(1)°,V=1356.5(4) ų,Z=2, 3489 observed reflections,R _F=0.029.     

Crystal Structure of catena-[(Tetrakis-μ2-acetato-μ2-4,4'-bipyridine) dicopper(Ⅱ)] Acetonitrile Solvate

The title compound,[Cu2(CH3COO)4(C8H10N2)]n·nCH3CN1 (C8H10N2,4,4'-bipy = 4,4'-bipyridine),has been solvothermally synthesized in CH3CN and characterized by X-ray diffraction.The crystal is of monoclinic,space group Cc with a = 22.626(6),b = 14.012(4),c =15.106(4) (A),β = 107.610(3)°,V = 4565(2) (A)3,C20H23Cu2N3O8,Mr = 560.49,Z = 8,Dc = 1.631 g/cm3,μ = 1.914 mm-1,Flack parameter = 0.48(1),F(000) = 2288,R = 0.042 and wR = 0.)98 for 8887 observed reflections (I ＞ 2σ(I)).It consists of nearly linear one-dimensional chains [Cu2(CH3COO)4(C8H10N2)]n derived from paddle-wheel [Cu2(CH3COO)4] unit linked by 4,4'-bipy,and CH3CN as guest molecule regularly decorates between the chains.