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Three novel tridentate pyridazine phenolate ligands were prepared in high yields by Schiff-base condensation of salicylic aldehyde with various pyridazine hydrazines (substituent R in the 6 position: R = Cl (HL(Cl)), (t)Bu (HL((t)Bu)), or tol (HL(tol))). They react with [ReOCl(3)(OPPh(3))(SMe(2))] to form rare mononuclear trans-dichloro oxo complexes of general formula [ReOCl(2)(L(R))] with R = tol (1), (t)Bu (2), or Cl (3) as confirmed by single-crystal X-ray diffraction analyses of 1 and 2. They were found to be catalysts for oxidation of cyclooctene to the corresponding epoxide by tert-butyl hydroperoxide (TBHP). Extensive UV-vis and NMR spectroscopic investigations followed by evaluation using the powerful Mauser method revealed mechanistic details. This showed the catalyst precursor [ReOCl(2)(L)] (2) to be transformed into the rhenium(VII) compound [ReO(3)L] (4) in a two-step reaction via intermediate INT which is tentatively assigned to [ReO(2)L]. Confirmation gave the isolation of 4 by reaction of 2 with excess of TBHP. Monitoring the catalytic oxidation reaction by UV-vis spectroscopy clearly excludes the two rhenium(V) compounds 2 and INT from being the catalytically active species as their formation is several orders of magnitude faster than the observed catalytic epoxidation reaction., (© 2011 American Chemical Society)

Heating of 6-methylpyridazine-3-thione (HPn(Me)) and 6-tert-butylpyridazine-3-thione (HPn(tBu)) with potassium borohydride in diphenylmethane in a 3:1 ratio gave two new scorpionate ligands K[HB(Pn(Me))(3)] and K[HB(Pn(tBu))(3)]. Single crystal X-ray diffraction analysis of the methyl derivative K[HB(Pn(Me))(3)] revealed a dimeric species with one potassium atom coordinated by six sulfur atoms of two scorpionate ligands and a second potassium atom coordinated by three nitrogen atoms of one of the two ligands as well as by three water molecules. The reaction of K[HB(Pn(tBu))(3)] with nickel(II) chloride or cobalt(II) chloride in CH(2)Cl(2) led to the new boratrane compounds [M{B(Pn(tBu))(3)}Cl] (M = Ni 1, Co 3) where a formal reduction of the metal ions to Ni(I) and Co(I), respectively, and activation of the B-H bond occurred. Similar reactivity was observed by employing K[HB(Pn(R))(3)] (R = Me, tBu) and nickel(II) chloride in water. Reaction with cobalt(II) chloride in water also gave boratrane compounds [Co{B(Pn(R))(3)}(Pn(R))] (R = tBu 4, Ph 5), but instead of a chloride a bidentate pyridazinethionate ligand from a defragmentated scorpionate is found in the molecules. The molecular structures of all nickel and cobalt compounds were determined by single crystal X-ray diffraction analyses confirming the formation of boratranes in compounds 1-5. Magnetic measurements confirm the reduced oxidation states and the paramagnetic character of the Ni(I) and Co(I) complexes. Supportive DFT studies were carried out for a better understanding of the electronic nature of the metal-boron bond of the boratrane complexes., (© 2011 American Chemical Society)

We synthesized and characterized a set of new oxorhenium(V) complexes coordinated by various pyrazole containing phenol (L1-L3) and naphthol ligands (L4-L7). Depending on the starting material, we were able to selectively synthesize monosubstituded or disubstituted complexes of the type [ReOBr(2)L(PPh(3))] (1-7; L = L1-L7) and [ReOClL(2)] (L = L1 8; L2 9; L4 10; L6 11), respectively. All complexes are stable to air and moisture, both in solid state as well as in solution. Furthermore, the cationic oxorhenium(V) complex [ReO(L1)(2)(NCMe)](OTf) (8a) was obtained upon chloride abstraction with silver triflate from 8. All new complexes were able to catalyze the epoxidation of cis-cyclooctene in yields up to 64%. The ease of preparation and their tolerance to air and moisture, as well as the simple ligand modifications, make them an interesting class of novel catalysts. An attempted reduction of perchlorate ClO(4)(-) with complex 8 was unsuccessful. Molecular structures of complexes 1, 4, 6, 7, 8, 8a, 10, and 11 were determined by single crystal X-ray diffraction analyses., (© 2011 American Chemical Society)

The asymmetric molybdenum(VI) dioxo complexes of the bis(phenolate) ligands 1,4-bis(2-hydroxybenzyl)-1,4-diazepane, 1,4-bis(2-hydroxy-4-methylbenzyl)-1,4-diazepane, 1,4-bis(2-hydroxy-3,5-dimethylbenzyl)-1,4-diazepane, 1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-1,4-diazepane, 1,4-bis(2-hydroxy-4-flurobenzyl)-1,4-diazepane, and 1,4-bis(2-hydroxy-4-chlorobenzyl)-1,4-diazepane (H(2)(L1)-H(2)(L6), respectively) have been isolated and studied as functional models for molybdenum oxotransferase enzymes. These complexes have been characterized as asymmetric complexes of type [MoO(2)(L)] 1-6 by using NMR spectroscopy, mass spectrometry, elemental analysis, and electrochemical methods. The molecular structures of [MoO(2)(L)] 1-4 have been successfully determined by single-crystal X-ray diffraction analyses, which show them to exhibit a distorted octahedral coordination geometry around molybdenum(VI) in an asymmetrical cis-β configuration. The Mo-O(oxo) bond lengths differ only by ≈0.01 Å. Complexes 1, 2, 5, and 6 exhibit two successive Mo(VI)/Mo(V) (E(1/2), -1.141 to -1.848 V) and Mo(V)/Mo(IV) (E(1/2), -1.531 to -2.114 V) redox processes. However, only the Mo(VI)/Mo(V) redox couple was observed for 3 and 4, suggesting that the subsequent reduction of the molybdenum(V) species is difficult. Complexes 1, 2, 5, and 6 elicit efficient catalytic oxygen-atom transfer (OAT) from dimethylsulfoxide (DMSO) to PMe(3) at 65 °C at a significantly faster rate than the symmetric molybdenum(VI) complexes of the analogous linear bis(phenolate) ligands known so far to exhibit OAT reactions at a higher temperature (130 °C). However, complexes 3 and 4 fail to perform the OAT reaction from DMSO to PMe(3) at 65 °C. DFT/B3LYP calculations on the OAT mechanism reveal a strong trans effect., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Treatment of [MoO(N-t-Bu)Cl(2)(dme)] (dme = dimethoxyethane) with 2 equiv of the potassium salts of Schiff base ligands of the type KArNC(CH(3))CHC(CH(3))O afforded oxo imido molybdenum(VI) compounds [MoO(N-t-Bu)L(2)] {1, with Ar = phenyl (L(Ph)), 2 with Ar = 2-tolyl (L(MePh)), 3 with Ar = 2,6-dimethylphenyl (L(Me2Ph)) and 4 with Ar = 2,6-diisopropylphenyl (L(iPr2Ph))}. We have also prepared related bisimido complexes [Mo(N-t-Bu)(2)L(2) (5 with L = L(Ph), 6 with L = L(MePh), and 7 with L = L(Me2Ph)) by treatment of [Mo(N-t-Bu)(2)Cl(2)(dme)] with 2 equiv of the potassium salt of the respective ligand. 1, 3, 5, and 6 were characterized via single crystal X-ray diffraction. The oxo imido complexes exhibit oxygen atom transfer (OAT) reactivity toward trimethyl phosphine. Kinetic data were obtained for 1 and 3 by UV/vis spectroscopy revealing decreased OAT reactivity in comparison to related dioxo complexes with the same Schiff base ligands and decreased reactivity of 1 versus 3. Cyclic voltammetry was used to probe the electronic situation at the molybdenum center showing reversible reduction waves for 3 and [MoO(2)(L(Me2Ph))(2)] at comparable potentials while 1 exhibits a significant lower potential. Density functional theory (DFT) calculations showed a higher electron density on oxygen in the oxo imido complexes.

Rhenium(V) oxo complexes of the type [ReOX(L)(2)] (1-7; X = Cl, Br) containing beta-ketiminate ligands (L = CH(3)C(O)CH(2)C(NAr)CH(3): Ar = Ph (APOH), 2-MePh (MPOH), 2,6-Me(2)Ph (DPOH), 2,6-(i)Pr(2)Ph (DiPOH)) have been prepared by reaction of [ReOX(3)(OPPh(3))(SMe(2))] (X = Cl, Br) with the lithium salts of the corresponding ligands. All compounds have been spectroscopically characterized, showing [ReOX(DiPO)(2)] (X = Cl (1), Br (5)), [ReOX(DPO)(2)] (X = Cl (2), Br (6)), and [ReOX(APO)(2)] (X = Cl (4), Br (7)) to be isomerically pure, in contrast to complex [ReOCl(MPO)(2)] (3), which exhibits a mixture of isomers. Compounds 2, 3, 5, and 7 were crystallographically characterized, showing similar octahedral coordination spheres with trans O horizontal lineRe-O and cis O horizontal lineRe-Cl bonds. However, the coordination of the nitrogen atoms vs each other is found to be cis or trans. Compounds 2 and 5 showed a trans-N,N configuration, for compound 3 both isomers (trans-N,N 3 and cis-N,N 3) were structurally characterized, and 7 gave a cis-N,N configuration. Compounds 1-6 are catalyst precursors for the epoxidation of cis-cyclooctene with 3 equiv of tert-butyl hydroperoxide (TBHP). Yields of the formed epoxide were up to 55% with all precursors, except with 2 and 6, where only up to 13% of epoxide was obtained under analogous conditions.

A series of new molybdenum(VI) dioxo complexes of the type [MoO(2)ClL(X)] with potentially monoanionic phenolate ligands L(X) (L = 4,6-di-tert-butyl-2-{[(X)methylamino]methyl}-phenolate; L(OMe), where X = 2'-methoxyethyl; L(SEt), where X = 2'-ethylthioethyl; L(NEt2), where X = 2'-diethylaminoethyl; and L(NMe2), where X = 2'-dimethylaminoethyl) have been synthesized as models for molybdoenzymes. All molybdenum complexes were readily accessible by employing the eta(2)-coordinate pyrazolate complex [MoO(2)Cl(eta(2)-t-Bu(2)pz)]. The nitrogen ligand can easily be exchanged by the monoanionic phenolate ligands L(X) in toluene at room temperature, leading to monosubstituted complexes 1-4 as yellow to red powders in good yields. Suitable single crystals for X-ray diffraction analysis of complexes 2 and 3 were obtained from a concentrated benzene solution. Both complexes reveal a six-coordinate molybdenum atom in a distorted octahedral surrounding, with a tridentate fac coordination of the ligand. Additionally, the complexes were characterized by elemental analysis; IR, UV/vis, and NMR spectroscopy; and mass spectrometry. For complexes 1 and 2, only one isomer can be detected in solution, whereas complexes 3 and 4 reveal the formation of two isomers in a 1:1 ratio for 3 and in a 1:3 ratio for 4. Optimized geometries and relative free energies of all possible isomers have been established by DFT calculations, indicating two isomers in solutions of 3 and 4 to be two types of facially coordinated complexes. Furthermore, this is supported by gauge-independent atomic orbital calculations of the (1)H NMR shifts with a high correlation of experimental and calculated shifts for the fac compounds. Oxygen atom transfer reactions of 1 to PMe(3) quickly form monooxo molybdenum compound cis,mer-[MoOCl(2)(PMe(3))(3)].

A series of octahedral dioxomolybdenum(VI) complexes of the type [MoO(2)L(2)] {L = 4-Ar-pent-2-en-ol; L(i-Pr2Ph) with Ar = 2,6-diisopropylphenyl (1); L(Me2Ph) with Ar = 2,6-dimethylphenyl (2), L(MePh) with Ar = 2-methylphenyl (3) and with Ar = phenyl (4)} and dioxotungsten(VI) compounds [WO(2)L(2)] {L(i-Pr2Ph) (5); L(Me2Ph) (6) and L(MePh) (7)} with Schiff bases have been synthesized as models for oxotransferases. Spectroscopic characterization in solution shows with the sterically encumbered ligands L(i-Pr2)Ph and L(Me2)Ph isomerically pure products whereas the ligand with only one substituent in ortho position at the aromatic ring L(MePh) revealed a dynamic mixture of three isomers as confirmed by variable temperature NMR spectroscopy. Single crystal X-ray diffraction analyses of compounds 1, 2, and 4 and showed them to be in the N,N-trans conformation consistent with the larger steric demand at nitrogen. Oxygen atom transfer (OAT) properties towards trimethylphosphine were investigated leading to the isolation of two mononuclear molybdenum(IV) compounds [MoO(PMe(3))(L(Me2Ph))(2)] (8) and [MoO(PMe(3))(L(MePh))(2)] (9) as confirmed by spectroscopic and crystallographic means. The kinetics of OAT between complex [MoO(2)(L(Me2Ph))(2)] (2) and PMe(3) was investigated by UV/Vis spectroscopy under pseudo-first-order conditions revealing single-step reactions with Eyring values of DeltaH(double dagger) = +60.79 kJ mol(-1) and DeltaS(double dagger) = -112 J mol(-1) K(-1) and a first-order dependence of phosphine consistent with a slow nucleophilic attack of the phosphine showing the octahedral geometries of this system to be unfavorable for OAT. Compound 1 showed no OAT reactivity towards PMe(3) emphasizing the influence of sterical properties. Furthermore, the reactivity of the reduced compounds [MoO(PMe(3))(L(Me2Ph))(2)] (8) and [MoO(PMe(3))(L(MePh))(2)] (9) towards molecular oxygen was investigated leading, in the case of 8, to the substitution of PMe(3) by O(2) under formation of the peroxo compound [MoO(O(2))(L(Me2Ph))(2)] (10). In contrast, the analogous reaction employing 9 led to oxidation forming the dioxo compound [MoO(2)(L(MePh))(2)] (3).

Tris(dimethylamino)silyl substituted aniline HNPh{Si(NMe2)3} (1) was prepared in high yield by metathesis reaction of lithium anilide with tris(dimethylamino)chlorosilane. 1 reacts with 1 equiv of n-butyl lithium at elevated temperatures to yield the corresponding lithium salt [LiNPh{Si(NMe2)3}] (2). Treatment of 1 with 2 equiv of n-butyl lithium leads to dilithiated compounds [Li2N(C6H4){Si(NMe2)3}]4 (3a) or [Li2(THF)2N(C6H4){Si(NMe2)3}]2 (3b) depending on the solvent used for crystallization, the former being crystallized in heptane, the latter in tetrahydrofuran (THF). Single crystal analyses of 3a and 3b confirm the occurrence of two lithium atoms per ligand, where the anilino nitrogen atom and one ortho carbon atom of the phenyl group are deprotonated. In both cases organolithium compounds with polynuclear lithium cores are formed. The molecular structure of 3a represents the first example of an organolithium compound consisting of a Li8 core that forms a polyhedron in which two trigonal prisms share one square face and are twisted by 90 degrees. Such a polyhedron is known in mathematics as the Johnson solid J26 or as Gyrobifastigium and is rare in chemistry. The coordinating carbon atoms are situated above the other square faces with three close contacts and one slightly longer contact to four lithium atoms. Furthermore, the central four lithium atoms form an Li4N4 square with almost linear N-Li-N bonds, a rare structural situation. The molecular structure of 3b shows each lithium atom to be additionally coordinated by a molecule of THF compared to that of 3a. Thus, a dimeric structure is found with a Li4 core that forms a planar parallelogram. The carbon atoms are found in close contact to a triangular Li3 face on each side of the Li4 plane.

Treatment of [MoO2(eta2-Pz)2] (Pz = 3,5-di-tert-butylpyrazolate) with the diketiminate ligand NacNacH (NacNac = CH[C(Me)NAr]2-, Ar = 2,6-Me2C6H3) at 55 degrees C leads under reduction of the metal to the formation of the dimeric molybdenum(V) compound [{MoO2(NacNac)}2] (1). The compound was characterized by spectroscopic means and by X-ray crystal structure analysis. The dimer consists of a [Mo2O4]2+ core with a short Mo-Mo bond (2.5591(5) A) and one coordinated diketiminate ligand on each metal atom. The reaction of [MoO2(eta2-Pz)2] with NacNacH in benzene at room temperature leads to a mixture of 1 and the monomeric molybdenum(VI) compound [MoO2(NacNac)(eta2-Pz)] (2). From such solutions, yellow crystals of 2 suitable for X-ray structural analysis were obtained revealing the coordination of one bidentate NacNac and one eta2-coordinate Pz ligand. This renders the two oxo groups inequivalent. Further high oxidation state molybdenum compounds containing the NacNac ligand were obtained by the reaction of [Mo(NAr)2Cl2(dme)] (Ar = 2,6-Me2C6H3) and [Mo(N-t-Bu)2Cl2(dme)] (dme = dimethoxyethane) with 1 equiv of the potassium salt NacNacK forming [Mo(NAr)2Cl(NacNac)] (3) and [Mo(N-t-Bu)2Cl(NacNac)] (4), respectively, in good yields. The X-ray structure analysis of 3 revealed a penta-coordinate compound where the geometry is best described as trigonal-bipyramidal.

Substitution reactions of rhenium(V) oxo precursors [ReOCl3(PPh3)2] or [NBu4][ReOCl4] with the bidentate acetylacetone-derived ketoamine ligands APOH = 4-anilino-3-penten-2-one, DPOH = 4-[2,6-dimethylanilino]-3-penten-2-one, and MTPOH = 4-[2-(methylthio)anilino]-3-penten-2-one gave the complexes [ReO(APO)Cl2(PPh3)] (1), [ReO(DPO)Cl2(PPh3)] (2), and [NBu4][ReOLCl3] (3, L = APO; 4, L = DPO; 5, L = MTPO), respectively. All complexes exhibit only one ketoamino chelate, independent of the amount of ligand added to the rhenium precursors. The complexes were characterized by 1H and 13C NMR spectroscopy. X-ray crystal structures of the complexes 1, 2, 4, and 5, including that of MTPOH, were determined, revealing the trans position of the two oxygen atoms and the trans-Cl,Cl conformation in 1 and 2, in contrast to most other rhenium complexes of this type where the cis-Cl,Cl conformation is observed. Coordination of the potentially tridentate ligand MTPOH in 5 is bidentate with a dangling thioether substituent. Compound 2 shows catalytic activity in the oxidation of cis-cyclooctene with tert-butylhydroperoxide.

Molybdenum(IV) monooxo compound that contains bis(beta-ketiminato) ligands activates molecular oxygen forming a molybdenum(VI) monooxo peroxo compound, representing a new entry into molybdenum peroxo derivatives.

Stepwise addition of one equivalent of n-butyllithium and trimethylsilyl chloride to 2-tert-butylmercaptoaniline affords the new ligand 1-(Me3SiNH)-2-(t-BuS)C6H4 (LH), that reacts with one equivalent of butyllithium to its lithium salt LLi. Dioxodichloromolybdenum [MoO2Cl2] and dioxodichlorotungsten dimethoxyethane [WO2Cl2(dme)] react in tetrahydrofuran solution at low temperature with two equivalents LLi to monomeric dioxomolybdenum(VI) [MoO2L2] (1) and dioxotungsten(VI) complex [WO2L2] (2) employing two bidentate amido thioether ligands. The crystallographic determination of the molecular structures of 1 and 2 show evidence for M...S contacts. The reaction of [MoO2Cl2] with LLi in tetrahydrofuran solution at room temperature leads next to 1 to two compounds where silyl group migration from nitrogen to oxygen atoms occurs forming [Mo(=NL')2(OSiMe)2] (3) and [Mo(=NL')2(OSiMe3)L] (4, L' = N-2-t-BuSC6H4) as determined by NMR spectroscopy. Compound 4 was isolated in low yield and its molecular structure determined by X-ray crystallography. Higher yields of a bisimido complex can be obtained by the direct reaction of one equivalent of LLi with [Mo(NAr)2Cl2(dme)] (Ar = 2,6-Me2C6H4) forming [Mo(NAr)2LCl] (5).

The complex [[(eta 5-C5Me5)(Ph3P)Ir(mu-H)2]2Ag2(OSO2CF3)2], containing the Ag2(2+)-ion, has been synthesized; crystallographic and spectroscopic data are described.

Molybdenum dioxo compounds [MoO2Cl(eta 2-pz)] and [MoO2(eta 2-pz)2] with pz = eta (2)-3,5-di-tert-butylpyrazolate have been synthesized; crystallographic data, catalytic activity, and oxo transfer properties are described.

Reaction of bis(2-aminoethyl)(3-aminopropyl)amine with C(6)F(6) and K(2)CO(3) in DMSO yields unsymmetrical [(C(6)F(5))HNCH(2)CH(2)](2)NCH(2)CH(2)CH(2)NH(C(6)F(5)) ([N(3)N]H(3)). The tetraamine acts as a tridentate ligand in complexes of the type H[N(3)N]Re(O)X (X = Cl 1, Br 2) prepared by reacting Re(O)X(3)(PPh(3))(2) with [N(3)N]H(3) and an excess of NEt(3) in THF. Addition of 1 equiv of TaCH(CMe(2)Ph)Br(3)(THF)(2) to 1 gives the dimeric compound H[N(3)N]ClReOReBrCl[N(3)N]H (3) in quantitative yield that contains a Re(V)[double bond]O[bond]Re(IV) core with uncoordinated aminopropyl groups in each ligand. Addition of 2 equiv of TaCH(CMe(2)Ph)Cl(3)(THF)(2) to 1 leads to the chloro complex [N(3)N]ReCl (4) with all three amido groups coordinated to the metal, whereas by addition of 2 equiv of TaCH(CMe(2)Ph)Br(3)(THF)(2) to 2 the dibromo species H[N(3)N]ReBr(2) (5) with one uncoordinated amino group is isolated. Reduction of 4 under an atmosphere of dinitrogen with sodium amalgam gives the dinitrogen complex [N(3)N]Re(N(2)) (6). Single-crystal X-ray structure determinations have been carried out on complexes 1, 3, 5, and 6.

The 3,5-di-tert-butylpyrazolato (3,5-tBu(2)pz) derivatives of aluminum [(eta(1),eta(1)-3,5-tBu(2)pz)(mu-Al)R(1)R(2)](2) (R(1) = R(2) = Me 1; R(1) = R(2) = Et, 2; R(1) = R(2) = Cl, 3; R(1) = R(2) = I, 4; [(eta(2)-3,5-tBu(2)pz)(3)Al], 5; [Al(2)(eta(1),eta(1)-3,5-tBu(2)pz)(2)(mu-E)(C triple bond CPh)(2)] (E = S (6), Se (7), Te (8)) have been prepared in good yield. Compounds 1 and 2 were obtained by the reactions of H[3,5-tBu(2)pz] with Me(3)Al and Et(3)Al, respectively. Reaction of [(eta(1),eta(1)-3,5-tBu(2)pz)(mu-Al)H(2)](2) with the pyrazole H[3,5-tBu(2)pz] gave [(eta(2)-3,5-tBu(2)pz)(3)Al] (5). The reaction of [(eta(1),eta(1)-3,5-tBu(2)pz)(mu-Al)R(2)](2) (R = H, Me) and I(2) yielded 4, while the reaction of 1 equiv of K[3,5-tBu(2)pz] and AlCl(3) afforded 3. In addition, the reaction of [Al(2)(eta(1),eta(1)-3,5-tBu(2)pz)(2)(mu-E)H(2)] and HC triple bond CPh gave 6, 7, and 8. All compounds have been characterized by elemental analysis, NMR, and mass spectroscopy. The molecular structure analyses of compounds 1, 3, 6, and 7 by X-ray crystallography showed that complexes 1 and 3 are dimeric with two eta(1),eta(1)-pyrazolato groups in twisted conformation while 6 and 7 with two eta(1),eta(1)-pyrazolato groups display a boat conformation.