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Borate Ligands (borate + ligand)
Selected AbstractsA New Synthesis of Charge-Neutral Tris-Pyrazolyl and -Methimazolyl Borate LigandsCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2010Philip Abstract The dimethylamine in the adducts [(HNMe2)B(azolyl)3] (azolyl=methimazolyl, pyrazolyl), obtained by reaction of the azole with B(NMe2)3, can readily be substituted with a range of nitrogen donors to provide new charge-neutral, tripodal ligands in high yield. This observation has led to a revision of an earlier interpretation of the mechanism of the formation of these species. The donor properties of the ligands [(nmi)B(azolyl)3] (nmi=N -methylimidazole) have been compared with their anionic analogues [HB(azolyl)3], by synthesis of their manganese(I),tricarbonyl complexes and comparison of their infrared ,CO energies. This comparison indicates that the new neutral ligands are only marginally weaker donors than the corresponding anionic hydrotris(azolyl)borate ligands. This may be explained by the ability of the attached nmi ring to stabilize a positive charge remotely from the coordinated metal, which may also account for the fact that the [(nmi)B(pyrazolyl)3] ligand is a substantially stronger donor than the similarly neutral tris(pyrazolyl)methane ligand. [source] Synthesis of New Tripodal Tri-Functionalized Hydrotris(indazol-1-yl)borate Ligands and X-ray Structures of Their Cyclopentadieneruthenium ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2006Alexandre Carella Abstract Two new tripodal ligands designed to anchor complexes onto surfaces have been synthesized. They integrate ester or thioether functions at the 6-position of the indazoles. Potassium hydrotris[6-(ethoxycarbonyl)indazolyl]borate and potassium hydrotris{6-[(ethylsulfanyl)methyl]indazolyl}borate exhibit three pendant groups oriented to anchor complexes onto an oxide and a metallic surface, respectively. Their complexation with [RuCp(CH3CN)3]PF6 yielded two piano-stool-shaped complexes that were characterized by X-ray diffraction. Comparison with the synthesized unfunctionalized analog showed that the three 6-substituted functions do not interfere with the coordination site and are particularly well oriented for surface deposition.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] New Bis(mercaptoimidazolyl)(pyrazolyl)borate Ligands and Their Zinc Complex ChemistryEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2003Mouhai Shu Abstract Nine new tripodal NS2 ligands of the bis(mercaptoimidazolyl)(pyrazolyl)borate type with varying 3-R-mercaptoimidazolyl moieties were prepared as their potassium salts. Treatment with zinc salts yielded the complex types L·Zn,Cl, L·Zn,I, L·Zn,ONO2, L·Zn,OClO3 and [L·Zn(imidazole)]ClO4. Attempts at the formation of L·Zn,OH or cationic L·Zn complexes resulted in dismutation and formation of ZnL2 complexes. Hydrolytic destruction yielded one [OZn4(thiooimidazolate)6] complex. The ZnS2NO coordination which is present in the enzyme-substrate complex of alcohol dehydrogenase could be successfully modelled by an [L·Zn(C2H5OH)]+ complex. The L·Zn,X complexes showed very low catalytic activity in the dehydrogenation of 2-propanol or the hydrogenation of p -nitrobenzaldehyde. The new compounds were identified by a total of 12 structure determinations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Ethyl[tris(3- tert -butyl-5-methylpyrazol-1-yl)hydridoborato]zinc(II)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2010Mukesh Kumar The X-ray crystal structure of the title compound, [Zn(C2H5)(C24H40BN6)], or TptBu,MeZnEt [TptBu,Me is tris(3- tert -butyl-5-methylpyrazolyl)hydridoborate], reveals a distorted tetrahedral geometry around the Zn atom. The Zn center is coordinated by three N atoms of the borate ligand and by one C atom of the ethyl group. The present structure and other tetrahedral Tp zinc alkyl complexes are compared with similar Ttz ligands (Ttz is 1,2,4-triazolylborate), but no major differences in the structures are noted, and it can be assumed that variation of the substitution pattern of Tp or Ttz ligands has little or no influence on the geometry of alkylzinc complexes. Refinement of the structure is complicated by a combination of metric pseudosymmetry and twinning. The metrics of the structure could also be represented in a double-volume C -centered orthorhombic unit cell, and the structure is twinned by one of the orthorhombic symmetry operators not present in the actual structure. The twinning lies on the borderline between pseudomerohedral and nonmerohedral. The data were refined as being nonmerohedrally twinned, pseudomerohedrally twinned and untwinned. None of the approaches yielded results that were unambiguously better than any of the others: the best fit between structural model and data was observed using the nonmerohedral approach which also yielded the best structure quality indicators, but the data set is less than 80% complete due to rejected data. The pseudomerohedral and the untwinned structures are complete, but relatively large residual electron densities that are not close to the metal center are found with values up to three times higher than in the nonmerohedral approach. [source] Bis(tetraphenylphosphonium) (hexasulfido-2,2S1,S6)di-,-sulfido-disulfido-1,2S -tungsten(VI)zinc(II) acetone solvateACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2009Azizolla Beheshti The title complex, (C24H20P)2[WZnS4(S6)]·C3H6O or (Ph4P)2[WS2(,-S)2{Zn(S6)}]·Me2CO, was unexpectedly obtained on attempted recrystallization of a mixed tungten,zinc complex of a tris(pyrazolato)borate ligand. The two metal centres of the anion have distorted tetrahedral coordination and the two tetrahedra share one S...S edge; tungsten is additionally coordinated by two terminal sulfide ligands and zinc by a chelating S62, ligand, which has one central S,S bond significantly longer than the other four, a pattern found to be consistent for this ligand. This is the first reported example of a tetrahedral zinc centre bridging an edge of a single tetrathiotungstate(VI) or tetrathiomolybdate(VI) anion, although there are many previous examples with other metals. [source] Structure, Electrochemistry and Hydroformylation Catalytic Activity of the Bis(pyrazolylborato)rhodium(I) Complexes [RhBp(CO)P] [P = P(NC4H4)3, PPh3, PCy3, P(C6H4OMe-4)3]EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2004Anna M. Trzeciak Abstract Rhodium complexes of formula [RhBp(CO)P] [Bp = bis(pyrazolylborate), P = P(NC4H4)31, PPh32, PCy33, P(C6H4OMe-4)34] have been prepared by exchange of the acetylacetonate (acac,) ligand in [Rh(acac)(CO)P] complexes. The spectroscopic and electrochemical properties as well as X-ray data of [Rh(acac)(CO)P] and [RhBp(CO)P] complexes have been compared with the aim to estimate the relative donor properties of both anionic ligands (acac, and Bp,). The cyclic voltammetric results indicate that the Bp, ligand behaves as a much stronger electron donor than acac, and a value of the Lever EL ligand parameter identical to that of the pyrazolate ligand (,0.24 V vs. NHE for each coordinating arm) is proposed for the bis- and tris(pyrazolyl)borate ligands, whereas P(C6H4OMe-4)3 is also shown to have an identical EL value (0.69 V) to that of P(NC4H4)3. An improved linear relationship between the oxidation potential and the sum of the ligand EL values for square-planar RhI complexes is also obtained and adjusted values for the Lever SM and IM parameters for the RhI/RhII redox couple are given. The trans influence of phosphanes was not observed in crystals of complexes 2 and 3, in contrast to analogous acetylacetonato complexes in which the Rh,O bonds differ by ca. 0.04,0.06 Å. Complexes 1,4 are very attractive precursors for hydroformylation catalysts and yields of aldehydes of 80,87% have been obtained with all complexes without extra phosphane as co-catalyst. During the hydroformylation reaction, however, small amounts of a catalytically inactive [RhBp(CO)2] complex were formed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] A Spirocyclic Chiral Borate for Catalytic Enantioselective Nozaki-Hiyama Allylation of KetonesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Xin-Ren Huang Abstract A new class of chiral spirocyclic borate ligands 5a,d with a rigid borocycle has been developed. The catalyst formed from chromium(II)- 5a promotes the highly efficient enantioselective Nozaki,Hiyama allylation of alkyl and aryl ketones using allyl bromide. The scope of the present method is shown to be wide, and it affords an efficient access to chiral tertiary homoallylic alcohols. [source] A New Synthesis of Charge-Neutral Tris-Pyrazolyl and -Methimazolyl Borate LigandsCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2010Philip Abstract The dimethylamine in the adducts [(HNMe2)B(azolyl)3] (azolyl=methimazolyl, pyrazolyl), obtained by reaction of the azole with B(NMe2)3, can readily be substituted with a range of nitrogen donors to provide new charge-neutral, tripodal ligands in high yield. This observation has led to a revision of an earlier interpretation of the mechanism of the formation of these species. The donor properties of the ligands [(nmi)B(azolyl)3] (nmi=N -methylimidazole) have been compared with their anionic analogues [HB(azolyl)3], by synthesis of their manganese(I),tricarbonyl complexes and comparison of their infrared ,CO energies. This comparison indicates that the new neutral ligands are only marginally weaker donors than the corresponding anionic hydrotris(azolyl)borate ligands. This may be explained by the ability of the attached nmi ring to stabilize a positive charge remotely from the coordinated metal, which may also account for the fact that the [(nmi)B(pyrazolyl)3] ligand is a substantially stronger donor than the similarly neutral tris(pyrazolyl)methane ligand. [source] | ||||||||||