1,2-Borotropic shifts and B-N bond cleavage reactions in molybdenum hydrotris(3-isopropylpyrazolyl)borate chemistry: Mixed-valence MoMo2 and pyrazole-rich oxo-Mo complexes

Red-black [Tp^iPr∗Mo^VO]₂(μ-O)(μ-Mo^VIO₄) (1, Tp^iPr∗ = hydrobis(3-isopropylpyrazolyl)(5-isopropylpyrazolyl)borate) has been isolated as a by-product in the synthesis of NEt₄[Tp^iPrMo(CO)₃] (Tp^iPr = hydrotris(3-isopropylpyrazolyl)borate) and characterized by spectroscopic and X-ray crystallographic techniques. The trinuclear, mixed-valence complex contains two distorted octahedral anti-Tp^iPr∗Mo^VO centers bridged by bent oxo (Mo-O-Mo av. 158.7°) and tetrahedral κO,κO′-molybdate ligands. The complex contains a six-membered, non-planar Mo₃(μ-O)₃ core and two 1,2-borotropically-shifted Tp^iPr∗ ligands (with the shifted pyrazolyl trans to Mo^V=O). Aerial decomposition of solid NEt₄[Tp^iPrMo(CO)₃] produces sky-blue, diamagnetic Tp^iPrMoO(ⁱPrpz)(ⁱPrpzH) (2, ⁱPrpz^- = 3-isopropylpyrazolate, ⁱPrpzH = 3-isopropyl-2H-pyrazole). Molecules of 2 feature a tridentate fac-Tp^iPr ligand and mutually cis terminal oxo (MoO = 1.665(2) Å) and monodentate ⁱPrpz⁻ and ⁱPrpzH ligands. The latter are formed by B-N bond cleavage of Tp^iPr. The complex can also be synthesized by reacting NEt₄[Tp^iPrMo(CO)₃] with excess 3-isopropylpyrazole and dioxygen at 100 °C. Cleavage of the B-N bond(s) of Tp^iPr was also observed in the formation of Tp^iPrMoO(SPh)(ⁱPrpzH) (3) as a by-product in the synthesis of Tp^iPrMoO₂(SPh). In the monohydrate, 3 exhibits a distorted octahedral geometry defined by a tridentate fac-Tp^iPr ligand and mutually cis terminal oxo (MoO = 1.676(3) Å) and monodentate SPh⁻ and ⁱPrpzH ligands. The pyrazole β-NH group is observed to participate in a hydrogen-bond to the lattice water molecule. The complex can be synthesized in high yield by reducing Tp^iPrMoO₂(SPh) by HSPh or PPh₃ in the presence of excess 3-isopropylpyrazole.     

Isovalent and mixed-valent molybdenum complexes containing Mo(μ-E)(μ-S2)Mo (E = O, S) core units

The reactions of Tp^iPrMoO(SR)(NCMe) (Tp^iPr = hydrotris(3-isopropylpyrazolyl)borate) with propylene sulfide in toluene result in the formation of the diamagnetic, isovalent Mo(V) complex, [Tp^iPrMo^VO]₂(μ-S)(μ-S₂). This complex and its previously reported μ-oxo analog, [Tp^iPrMo^VO]₂(μ-O)(μ-S₂), react with cobaltocene to produce one-electron-reduced, mixed-valent complexes, [CoCp₂][{Tp^iPrMo^IV,VO}₂(μ-E)(μ-S₂)] (E = S or O, respectively). All complexes have been isolated and characterized by microanalysis, mass spectrometry, IR and ¹H NMR or EPR spectroscopies, and X-ray crystallography. Neutral [Tp^iPrMo^VO]₂(μ-S)(μ-S₂) exhibits a pseudo-C₂ symmetric structure, with distorted octahedral anti oxo-Mo(IV) centers coordinated by Tp^iPr and linked by μ-sulfido and μ-disulfido ligands. A similar structure is adopted by the anion in mixed-valent [CoCp₂][{Tp^iPrMo^IV,VO}₂(μ-S)(μ-S₂)]; this compound adopts a hexagonal, supramolecular structure with columns of tight ion-pairs with interactions, interconnected through weaker contacts to three neighboring columns. The structure contains large interstitial voids filled with lattice solvent molecules. EPR investigation of the mixed-valent complexes gave rise to unusually broad signals with no evident hyperfine splitting. The synthesis and characterization of a number of cis-dioxo-Mo(VI) precursors are also reported.     

Dinuclear metal phosphonates and -phosphates

The reaction of Cu(II) or Cd(II) salts with 2,4,6-iPr₃C₆H₂PO₃H₂, 2,4,6-iPr₃C₆H₂CH₂PO₃H₂ or 2,6-iPr₂C₆H₃OPO₃H₂ in the presence of strong chelating nitrogen ligands such as 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 2-pyridylpyrazole (pypz) or 3,5-dimethyl pyrazole (dmpz) as the ancillary ligands afforded dinuclear copper or cadmium complexes [Cu₂(2,4,6-iPr₃C₆H₂PO₃H)₄(bpy)₂] (4), [Cu₂(2,6-iPr₂C₆H₃OPO₃H)₂(bpy)₂(OAc)₂(CH₃OH)₂]·(CH₃OH) (5), [Cd₂(2,6-iPr₂C₆H₃OPO₃H)₄ (bpy)₂(CH₃OH)₂]·2(CH₃OH) (6), [Cd₂(2,6-iPr₂C₆H₃OPO₃H)₄(phen)₂] (7), [Cu₂(2,6-iPr₂C₆H₃OPO₃H)₂(PyPz)₂(CH₃OH)₂] (8) and [Cu₂(2,4,6-iPr₃C₆H₂CH₂PO₃H)₂(DMPz)₂Cl₂]·(CH₃OH) (9) The molecular structures of 4-7 are grossly similar. The common structural features in these complexes are that the two metal centers are bridged by two bidentate [RPO₂(OH)]⁻ ligands generating a central eight-membered ring. Each of the metal centers also contains a chelating nitrogen ligand and a monodentate phosphonate or a phosphate ligand. In 5 and 6 other terminal ancillary ligands are also present. In compound 8, each of the two copper centers contains a monodentate [RPO₂(OH)]⁻ ligand along with a molecule of methanol. The two coppers are bridged by two monoanionic pyridylpyrazole ligands. The molecular structure of 9 is similar to that of 4-7. However, in 9 each of the two copper centers contain only terminal monodentate ligands in the form of two chlorides and a pyrazole. Magnetic studies on all of these copper complexes reveal an anti-ferromagnetic behavior at low temperatures. In addition, these complexes were found to be artificial nucleases and can convert supercoiled pBR322 DNA form I into nick form II in 1 min in the presence of an external oxidant through a hydrolytic and/or an oxidative pathway.     

Nickel promoted C-H, C-C and C-O bond activation in solution

Reaction of NiI₂ with the PCP-ligand {1-Et-2,6-(CH₂PⁱPr₂)₂-C₆H₃} (1) results in selective activation of the strong sp²-sp³ aryl-ethyl bond to afford the aryl-nickel complex [Ni{2,6-(CH₂PⁱPr₂)₂-C₆H₃}I] (2), whereas reaction of NiI₂ with {1,3,5-(CH₃)₃-2,6-(CH₂PⁱPr₂)₂-C₆H} (4) leads to the formation of the benzylic complex [Ni{1-CH₂-2,6-(CH₂PⁱPr₂)₂-3,5-(CH₃)₂-C₆H}I] (5) by selective C-H bond activation. Thermolysis of 5 results in formation of [Ni{2,6-(CH₂PⁱPr₂)₂-3,5-(CH₃)₂-C₆H}I] (6) by activation of the sp²-sp³ C-C bond. The identity of the new 16-electron complexes 2 and 6 was confirmed by reaction of NiI₂ with {1,3-(CH₂PⁱPr₂)₂-C₆H₄} (3) and {1,3-(CH₃)₂-4,6-(CH₂PⁱPr₂)₂-C₆H₂} (7), respectively, lacking the aryl-alkyl groups between the “phosphines arms” (alkyl=ethyl, methyl). Complexes 2 and 5 have been fully characterized by X-ray analysis. Nickel-based activation of an unstrained C-O single bond was observed as well. Reaction of the aryl-methoxy bisphosphine {1-OMe-2,6-(CH₂PⁱPr₂)₂-C₆H₃} (8) with NiI₂ results in the formation of the phenoxy complex [Ni{1-O-2,6-(CH₂PⁱPr₂)₂-C₆H₃}I] (9) by selective sp³-sp³ C-O bond activation.     

New coordination polymer based on salpn Schiff base and azide bridging ligands: Synthesis and structural characterization of {Na[Co(μ-salpn)(μ1,1-N3)2]}n (H2salpn = N,N′-bis(salicylidene)-1,3-diaminopropane)

One-pot reaction of cobalt(II) nitrate hexahydrate Co(NO₃)₂ · 6H₂O with H₂salpn (N,N′-bis(salicylidene)-1,3-diaminopropane) in presence of a large excess of sodium azide (NaN₃) gives the new Co(III) compound {Na[Co^III(μ-salpn)(μ_1,1-N₃)₂]}_n (1), which was characterized by single crystal X-ray diffraction analysis. The crystal structure shows polymeric 1D complex generated by the hexadentate Schiff base salpn²⁻ and two crystallographically different azide ligands. The two nitrogen atoms of the salpn ligand are bonded to the cobalt(III) ion while each phenoxo oxygen atom is bonded to the same Co(III) ion and to two equivalent sodium ions. Each azide ligand acts with the end-on bridging coordination mode between Co(III) and Na(I) ions. The Co(III) ion adopts a distorted octahedral geometry arising from two oxygen and two nitrogen atoms of the salpn ligand and from two nitrogen atoms of the two crystallographically different azide ligands in trans positions. Such [Co(salpn)(N₃)₂] entities are connected each other by sodium ions through four oxygen atoms of two equivalent Schiff base ligands and two nitrogen atom of the two different azide ligands to generate the 1D structure of 1.     

Sheet and chain polymeric transition metal complexes formed by N,N-o-phenylenedimethylenebis(pyridin-4-one)

The preparations are reported of the ‘extended reach’ ligand N,N^′-o-phenylene-dimethylenebis(pyridin-4-one) (o-XBP4) and of a range of its metal complexes with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II), two of which have been shown by X-ray studies to have polymeric structures. In the compound [Mn(o-XBP4)(H₂O)₂(NO₃)](NO₃) the o-XBP4 ligands link ‘Mn(H₂O)₂(NO₃)’ units into chains which are then cross-linked into sheets by the bridging action of the coordinated nitrate. In [Cu(o-XBP4)(NO₃)₂] chains are also formed by the bridging action of the o-XBP4 ligands but here they simply pack trough-in-trough with no nitrate cross-linking. X-band EPR spectra are reported for these and the other Mn and Cu compounds as are relevant spectroscopic results for the other complexes.     

A new bonding mode for the bicyclic guanidinate, [hpp], in the tetrametallic yttrium oxide cluster, Y4(hpp)8Cl2(μ4-O)

Oxygen incorporation in the product of the reaction between YCl₃ and the lithium salt of 1,3,4,6,7,8-hexahydro-2Hpyrimido[1,2-a]pyrimidine (hppH) afforded the tetrametallic cluster Y₄(hpp)₈Cl₂(μ₄-O), in which four of the guanidinate anions are involved in a previously unreported μ,η²,η²-bridging mode between two metal centres.     

Mononuclear and dinuclear iridium and heterodinuclear iridium-rhodium complexes derived from 1,4-C6H4(CCSiMe3)2 as precursor

The labile iridium(I) precursor trans-[IrCl(C₈H₁₄)(PiPr₃)₂] (2), prepared in situ from [IrCl(C₈H₁₄)₂]₂ (1) and PiPr₃, reacted with equimolar amounts of 1,4-C₆H₄(CCSiMe₃)₂ (3) at 60 °C to give the mononuclear vinylidene complex trans-[IrCl(CC(SiMe₃)C₆H₄CCSiMe₃)(PiPr₃)₂] (4). From 2 and 3 in the molar ratio of 2:1, the dinuclear compound trans,trans-[(PiPr₃)₂ClIr(CC(SiMe₃)C₆H₄C(SiMe₃)C)IrCl(PiPr₃)₂] (5) was obtained. Reaction of 4 with [RhCl(PiPr₃)₂]₂ (6) at room temperature afforded the heterodinuclear alkyne(vinylidene) complex trans,trans-[(PiPr₃)₂ClIr(CC(SiMe₃)C₆H₄CCSiMe₃)RhCl(PiPr₃)₂] (7), which on heating at 45 °C was converted to the bis(vinylidene) isomer trans,trans-[(PiPr₃)₂ClIr(CC(SiMe₃)C₆H₄C(SiMe₃)C)RhCl(PiPr₃)₂] (8).     

Synthesis and reactivity of five- and six-coordinate hydrido(vinyl) iridium(III) complexes

The reaction of the dihydrido iridium(III) precursor [IrH₂(Cl)(PiPr₃)₂] (5) with internal alkynes RCC(CO₂Me) (R = Me, CO₂Me) afforded the five-coordinate hydrido(vinyl) complexes [IrH(Cl){(E)-C(R)CH(CO₂Me)}(PiPr₃)₂] (6, 7), via insertion of the alkyne into one of the IrH bonds. Compounds 6 and 7 are also accessible by careful hydrogenation of the alkyne iridium(I) derivatives trans-[IrCl{RCC(CO₂Me)}(PiPr₃)₂] (9, 10), the latter being prepared from in situ generated trans-[IrCl(C₈H₁₄)(PiPr₃)₂] and RCC(CO₂Me). UV irradiation of 6 (R = CO₂Me) led to the formation of the isomer [IrH(Cl){κ²(C,O)-C(CO₂Me)CHC(OMe)O}(PiPr₃)₂] (3) having the vinyl ligand coordinated in a bidentate fashion. While 6 reacted with acetonitrile and CO to afford the six-coordinate iridium(III) compounds [IrH(Cl){(E)-C(CO₂Me)CH(CO₂Me)}(L′)(PiPr₃)₂] (11, 12), treatment of 6 with LiC₅H₅ gave the half-sandwich-type complex [(η⁵-C₅H₅)IrH{(E)-C(CO₂Me)CH(CO₂Me)}(PiPr₃)] (13) by, the loss of one PiPr₃. The reaction of 3 with CO under pressure resulted in the formation of [IrH(Cl){(Z)-C(CO₂Me)CH(CO₂Me)}(CO)(PiPr₃)₂] (14) in which, in contrast to the stereoisomer 12, the two CO₂Me substituents are trans disposed.     

Dimeric palladium and platinum complexes isolated in Lewis-acidic media

The synthesis and X-ray characterization of binuclear dipalladium(I) and diplatinum(I) p-xylene complexes [Pd₂(η⁶-C₈H₁₀)₂(μ-Cl/Br)₂(GaCl₃)₂] (1) and [Pt₂(η⁶-C₈H₁₀)₂(Ga₂Br₇)₂] (5) are reported. It was established that the toluene ligands in the palladium complex [Pd₂(η⁶-C₇H₈)₂(GaCl₄)₂] (3) can be substituted by naphthalene without disruption of the metal-metal bond. The reaction of 3 with Pd(PPh₃)₄ leads to the formation of a dipalladium(II) μ-diphenylphosphido compound [Pd₂(μ-PPh₂)(PPh₃)₄] (GaCl₄)₂ · 4(C₇H₈) (4), most likely also involving a bridging μ-H⁻ ligand.     

Ferromagnetic trinuclear carbonato-bridged and tetranuclear hydroxo-bridged Cu(II) compounds with 4,4′-dimethyl-2,2′-bipyridine as ligand. X-ray structure, spectroscopy and magnetism

A controlled synthesis, characterisation and single-crystal X-ray analysis of two novel copper(II) compounds with the ligand 4,4′-dimethyl-2,2′-bipyridine (abbreviated dmbipy) is described. In a CO₂ atmosphere, with sodium hydroxide added, the carbonato-bridged triangular trinuclear compound [Cu₃(dmbipy)₆(μ₃-CO₃)](BF₄)₄(C₂H₅OH)(H₂O) (1) is obtained. Compound 1 crystallises in the monoclinic space group P2₁/n with a=16.169(6), b=23.351(11), c=21.312(7) Å, β=91.26(3), Z=4. The three copper ions are connected via the oxygen atoms from the symmetrically bridging carbonato group, resulting in a triangular array of copper atoms. Each copper has a distorted square-pyramidal environment with a basal plane formed by three nitrogen atoms of the two chelating bipyridine groups and the oxygen atom of the bridging carbonato group (Cu-N/O distances about 2.0 Å). The apical position at each copper is occupied by the fourth nitrogen atom of the bipyridines with distances varying from 2.100(11) to 2.146(11) Å. In all other experimental conditions the tetranuclear hydroxo-bridged compound [Cu₄(dmbipy)₄(μ₃-OH)₂(μ-OH)₂(H₂O)₂](BF₄)₄(H₂O)₄ (2) is obtained. Compound 2 crystallises in the monoclinic space group P2₁/c with a=13.274(8), b=21.685(7), c=11.266(7) Å, β=107.71(4), Z=2. The structure consists of two bis(hydroxo)-bridged dinuclear planar units which are connected with long Cu-O bonds to form a tetranuclear unit. Each Cu ion has a similar square-pyramidal coordination geometry: the equatorial plane of each Cu ion consists of two nitrogen atoms of the dmbipy ligand (Cu-N distances 1.945-2.003 Å), and two bridging hydroxo oxygen atoms (Cu-O distances 1.945-1.973 Å). The apical position of Cu1 is occupied by an oxygen atom of a water molecule with a distance of 2.262 Å. The second copper atom, Cu2, has the apical position occupied by an oxygen atom of a bridging hydroxo group at a distance of 2.349 Å; this bond is responsible for the formation of the tetranuclear unity. Compound 1 exhibits a ferromagnetic interaction between the copper ions with a J=29.3 cm⁻¹ and a very weak ferromagnetic intercluster interaction with zj′=2.4 cm⁻¹. Compound 2 also exhibits a ferromagnetic interaction between the copper ions with a J=31.1 cm⁻¹ and an overall magnetic interaction between the two dimeric units J′=8.76 cm⁻¹     

Synthesis and reactivity of tin amide complexes

A terminal tin amide and a terminal tin anilide complex, (BDI)SnN(iPr₂) and (BDI)SnN(H)Ar (Ar = 2,6-ⁱPr₂C₆H₃), respectively, have been synthesized utilizing the bulky β-diketiminate ligand, [{N(2,6-ⁱPr₂C₆H₃)C(Me)}₂CH]⁻, or BDI, to stabilize the low coordinate divalent tin metal center. Only (BDI)SnN(iPr₂) reacts with phenylacetylene to yield (BDI)SnCCPh, but both species react with methyl triflate to give (BDI)SnOTf and carbon dioxide, resulting in the formation of (BDI)SnOC(O)N(iPr₂) and (BDI)SnOC(O)N(H)Ar.     

Cyanoscorpionates: Co(II), Mn(II), and Ni(II) complexes coordinated only through the cyano group

New complexes have been synthesized of scorpionate ligands with cyano substituents in the 4-positions of the pyrazoles and tert-butyl substituents in the 3-positions of the pyrazoles. Reaction of Co²⁺, Mn²⁺, and Ni(cyclam)²⁺ (cyclam = 1,4,8,11-tetraazacyclotetradecane) with Tp^t-Bu,4CN in a 1:2 ratio produced new octahedral metal complexes of the form (Tp^t-Bu,4CN)₂ML₄ (L₄ = (H₂O)₄, (H₂O)₂(MeOH)₂, or cyclam). Unlike the sandwich complexes previously isolated with Tp^Ph,4CN, the crystal structures showed none of the pyrazole nitrogen atoms coordinated to the metal. Rather, the metal is coordinated to one CN nitrogen atom from each ligand, with two Tp anions coordinated trans to each other around the metal center. This leaves the Tp pyrazole nitrogen atoms open for another metal to coordinate, which could to lead to heterometallic complexes, new coordination polymers, as well as the framework for supramolecular complexes.     

Structural characterization of zirconium isopropoxide precursors modified by di- and trichloroacetic acids

Reactions of Zr(OⁱPr)₄(PrⁱOH) with di- and trichloroacetic acid in 1:1 molar ratio in toluene gave the products Zr₂(μ-OⁱPr)₂(μ-OOCCHCl₂)(OⁱPr)₄(OOCCHCl₂)(HOⁱPr) (1) and Zr₂(μ-OⁱPr)₂(μOOCCCl₃)(OⁱPr)₄(OOCCCl₃)(HOⁱPr) (2), respectively, in quantitative yields. The molecular geometry of both (1) and (2) is constituted by a slightly distorted edge-shared bioctahedron and both have almost similar bond dimensions. Addition of dichloroacetic acid in 1:2 molar ratio to Zr(OⁱPr)₄(HOⁱPr) in toluene although yielded the bis-substituted crude product Zr(OⁱPr)₂(OOCCHCl₂)₂(HOⁱPr) (3) but its solution in toluene left for crystallization formed a tri-nuclear oxo product Zr₃(μ₃-O)(μ-OⁱPr)₂(μ-OOCCHCl₂)₃(η-OOCCHCl₂)₂(OⁱPr)₃ (3a). The three zirconium atoms in the structure of (3) are forming an isosceles triangle with a triply bridged oxo moiety at its center.     

The reactivity of [Pt2(μ-S)2(PPh3)4] towards difunctional chloroacetamide alkylating agents: Formation of cyclized or bridged products

The reactions of [Pt₂(μ-S)₂(PPh₃)₄] towards some bis(chloroacetamide) alkylating agents have been investigated. Reaction with one mole equivalent of the hydrazine-derived compound ClCH₂C(O)NHNHC(O)CH₂Cl led to the cyclized product [Pt₂{SCH₂C(O)NHNHC(O)CH₂S}(PPh₃)₄]²⁺ which showed two different PPh₃ environments in the ³¹P{¹H} NMR spectrum, as a result of non-fluxional behavior of the dithiolate ligand in solution. Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with the ortho and para isomers of the phenylenediamine-derived bis(chloroacetamides) ClCH₂C(O)NHC₆H₄NHC(O)CH₂Cl gave tetrametallic complexes containing two {Pt₂S₂} moieties spanned by the CH₂C(O)NHC₆H₄NHC(O)CH₂ group. Both the ortho and para isomers were crystallographically characterized; in the ortho isomer there is intramolecular CO···H-N and S···H-N hydrogen bonding involving the two amide groups.     

Palladium(II) and platinum(II) monoselenocarboxylates: Synthesis, spectroscopy, structure and their use as molecular precursors for metal selenides

Treatment of MCl₂(P^∩P) or MCl₂(PⁿPr₃)₂ with two equivalents of ArCOSeK readily yields cis-[M(SeCOAr)₂(P^∩P)] and trans-[M(SeCOAr)₂(PⁿPr₃)₂], respectively (M = Pd or Pt; Ar = Ph or 4-MeC₆H₄; P^∩P = dppm, dppe, dppp). The reaction of Pd(SeCOAr)₂(dppe) with PdCl₂(dppe) in the presence of NaBPh₄ in methanol gave a tri-nuclear ionic complex, [Pd₃(μ₃-Se)₂(dppe)₃][BPh₄]₂. These complexes were characterized by UV-Vis, IR and NMR spectroscopy. The complex [Pt(SeCOPh)₂(dppp)] has been structurally characterized by X-ray crystallography. The coordination environment around square planar platinum atom is defined by chelating dppp ligand and two unidentate selenocarboxylates bonded through selenium atoms. Pyrolysis of [Pd(SeCOAr)₂(PⁿPr₃)₂] either in tri-n-butylphosphate (TBP) (at 200 °C) or in the solid state (furnace heating at 350 °C) gave Pd₁₇Se₁₅.     

Synthesis, crystal structure, spectroscopic and magnetic properties of doubly and triply bridged dinuclear copper(II) compounds containing di-2-pyridylamine as a ligand

The dihydroxo-bridged dinuclear copper(II) compound [Cu₂(dpyam)₂(μ-OH)₂]I₂ (1) and the triply bridged dinuclear copper(II) compounds with a formato bridge [Cu₂(dpyam)₂(μ-O₂CH)(μ-OH)(μ-OMe)](ClO₄) (2) and [Cu₂(dpyam)₂(μ-O₂CH)(μ-OH)(μ-Cl)](ClO₄) · 0.5H₂O (3) (in which dpyam=di-2-pyridylamine) have been synthesized and their crystal structures determined by X-ray crystallographic methods. All three compounds are either centrosymmetric, or have a symmetry plane in the molecule. Compound 1 contains the [Cu₂(dpyam)₂(μ-OH)₂]⁺ unit and iodide anions. Each copper(II) ion is in a slightly tetrahedrally distorted square planar coordination with the square plane consisting of two nitrogen atoms of the dpyam ligand and two bridging hydroxo groups. The Cu-I distances of 3.321 Å are quite long and only involve a weak semi-coordination. Compound 2 contains a triply bridged dinuclear copper(II) species, the coordination environment around each copper(II) ion involves a distorted trigonal-bipyramidal CuN₂O₃ chromophore. In the dinuclear unit of compound 3, the triply bridged copper(II) ions show a distorted trigonal-bipyramidal coordination of the CuN₂O₂Cl chromophore. The Cu-Cu distances are 2.933(2), 3.023(1) and 3.036(1) Å for compounds 1, 2 and 3, respectively.The magnetic susceptibility measurements, measured from 5 to 280 K, revealed a weak antiferromagnetic interaction between the Cu(II) atoms for compound 1 with a singlet-triplet energy gap (J) of −15.3 cm⁻¹, whereas compounds 2 and 3 are ferromagnetic with J=62.5 and 79.1 cm⁻¹, respectively.     

Syntheses and crystal structures of mononuclear and dinuclear (pentamethylcyclopentadienyl)iridium(III) complexes containing 2-mercaptobenzimidazole

A reaction of [Cp*IrCl₂]₂ {Cp* = η⁵-C₅(CH₃)₅} and 2-mercaptobenzimidazole (H₂bimt) in methanol in a 1:2 molar ratio gave a yellow complex of [Cp*IrCl₂(H₂bimt)]·CH₃OH (1). In compound 1 the H₂bimt acts as a monodentately S-donating (κS) ligand. A similar reaction of [Cp*IrCl₂]₂ and H₂bimt in the presence of NaOCH₃ (molar ratio of 1:2:2) gave an orange product (2) on addition of excess amount of NH₄PF₆. Compound 2 was composed of an unsymmetrical dinuclear complex cation, [(Cp*IrCl)₂(μ-Hbimt)(μ-H₂bimt)]⁺, a PF₆⁻ anion, and water molecules of crystallization. In the complex cation, H₂bimt bridges two Ir^III centers by S atom in the μ-κS:κS mode, while the monodeprotonated Hbimt⁻ ligand bridges via S and N atoms in the μ-κS:κN¹ mode.     

N-Heterocyclic carbene gold(I) and silver(I) adducts of [Pt2(μ-S)2(PPh3)4]

Reaction of the metalloligand [Pt₂(μ-S)₂(PPh₃)₄] with the N-heterocyclic carbene (NHC) complexes IPrAuCl, IMesAuCl and IMesAgCl in methanol gave the first examples of metal adducts of [Pt₂(μ-S)₂(PPh₃)₄] that contain NHC ligands, namely [Pt₂(μ-S)₂(PPh₃)₄AuL]⁺ (L = IPr, IMes) and [Pt₂(μ-S)₂(PPh₃)₄AgIMes]⁺. The complexes were isolated as hexafluorophosphate salts. Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with excess IPrAuCl in refluxing methanol yielded only the mono-adduct, in contrast to the behaviour with the gold(I) phosphine complex Ph₃PAuCl, which undergoes double addition giving [Pt₂(μ-SAuPPh₃)₂(PPh₃)₄]²⁺. The X-ray structure of [Pt₂(μ-S)₂(PPh₃)₄AuIPr]PF₆ was determined and reveals that the ‘free’ sulfide is substantially sterically protected by the IPr ligand, accounting for the low reactivity towards addition of a second AgIPr⁺ moiety.     

Structural variations in dinuclear model hydrolases and hydroxamate inhibitor models: synthetic, spectroscopic and structural studies

Reactions of the structural model hydrolases [M₂(OAc)₄(H₂O)(Im)₄]; M=Mn (E^′); M=Co (D^′); M=Ni (B^′) and [M₂(OPiv)₄(H₂O)(tmen)₂]; M=Mn (E″); M=Co (D″); M=Ni (B″) with a number of hydroxamic acids, RHA (aceto- (R=CH₃), benzo- (R = C₆H₅) and N-phenylacetohydroxamic acid (NPhAHA)) gave a series of hydroxamate dibridged complexes [M₂(OAc)(RA)₂(Im)₄][OTf] and [M₂(OPiv)(RA)₂(tmen)₂][OTf]; M=Co, Ni, in which the bridging hydroxamates exhibit a novel bonding mode in which the deprotonated hydroxamate hydroxyl bridges the two metal centres only. The formation of this type of structure by NPhAHA is the first example involving a secondary hydroxamic acid. These complexes are good structural models of the acetohydroxamate-inhibited C³¹⁹A variant of Klebsiella aerogenes urease (KAU) and their structures are close to those previously reported for complexes containing tmen capping ligands. Reaction with glutarodihydroxamic acid leads to hydroxylamine elimination and formation of a dimer containing deprotonated N-hydroxyglutarimide as bridging ligand but in this case the structure contains pentacoordinated Co(II) and only one bridging acetate in contrast to the tmen-based series where the analogous complex contains hexacoordinated Co(II) and two bridging acetates. Reaction of [Mn₂(OAc)₂(μ-OAc)₂(μ-H₂O)(tmen)₂] with acetohydroxamic acid (AHA) gave the first structurally characterized manganese hydroxamate, [Mn₂(OAc)₃(AA)(tmen)₂] with the same bridging/chelating mode of hydroxamate bonding as in the analogous cobalt and nickel complexes, although only one bridging hydroxamate occurs in the manganese complex in contrast to the two bridging hydroxamates in the cobalt and nickel complexes. The isolation of the dimanganese hydroxamate bridged complex suggests that hydroxamic acids may also inhibit the dimanganese based metallohydrolase, arginase.