Monomeric oxovanadium(IV) compounds of the general formula cis-[V(IV)(=O)(X)(L(NN))(2)](+/0) [X = OH(-), Cl(-), SO(4)(2)(-) and L(NN) = 2,2'-bipyridine (bipy) or 4,4'-disubstituted bipy

Reaction of [V(IV)OCl(2)(THF)(2)] in aqueous solution with 2 equiv of AgBF(4) or AgSbF(6) and then with 2 equiv of 2,2'-bipyridine (bipy), 4,4'-di-tert-butyl-2,2'-bipyridine (4,4'-dtbipy), or 4,4'-di-methyl-2,2'-bipyridine (4,4'-dmbipy) affords compounds of the general formula cis-[V(IV)O(OH)(L(NN))(2)]Y [where L(NN) = bipy, Y = BF(4)(-) (1), L(NN) = 4,4'-dtbipy, Y = BF(4)(-) (2.1.2H(2)O), L(NN) = 4,4'-dmbipy, Y = BF(4)(-) (3.2H(2)O), and L(NN) = 4,4'-dtbipy, Y = SbF(6)(-) (4)]. Sequential addition of 1 equiv of Ba(ClO(4))(2) and then of 2 equiv of bipy to an aqueous solution containing 1 equiv of V(IV)OSO(4).5H(2)O yields cis-[V(IV)O(OH)(bipy)(2)]ClO(4) (5). The monomeric compounds 1-5 contain the cis-[V(IV)O(OH)](+) structural unit. Reaction of 1 equiv of V(IV)OSO(4).5H(2)O in water and of 1 equiv of [V(IV)OCl(2)(THF)(2)] in ethanol with 2 equiv of bipy gives the compounds cis-[V(IV)O(OSO(3))(bipy)(2)].CH(3)OH.1.5H(2)O (6.CH(3)OH.1.5H(2)O) and cis-[V(IV)OCl(bipy)(2)]Cl (7), respectively, while reaction of 1 equiv of [V(IV)OCl(2)(THF)(2)] in CH(2)Cl(2) with 2 equiv of 4,4'-dtbipy gives the compound cis-[V(IV)OCl(4,4'-dtbipy)(2)]Cl.0.5CH(2)Cl(2) (8.0.5CH(2)Cl(2)). Compounds cis-[V(IV)O(BF(4))(4,4'-dtbipy)(2)]BF(4) (9), cis-[V(IV)O(BF(4))(4,4'-dmbipy)(2)]BF(4) (10), and cis-[V(IV)O(SbF(6))(4,4'-dtbipy)(2)]SbF(6) (11) were synthesized by sequential addition of 2 equiv of 4,4'-dtbipy or 4,4'-dmbipy and 2 equiv of AgBF(4) or AgSbF(6) to a dichloromethane solution containing 1 equiv of [V(IV)OCl(2)(THF)(2)]. The crystal structures of 2.1.2H(2)O, 6.CH(3)OH.1.5H(2)O, and 8.0.5CH(2)Cl(2) were demonstrated by X-ray diffraction analysis. Crystal data are as follows: Compound 2.1.2H(2)O crystallizes in the orthorhombic space group Pbca with (at 298 K) a = 21.62(1) A, b = 13.33(1) A, c = 27.25(2) A, V = 7851(2) A(3), Z = 8. Compound 6.CH(3)OH.1.5H(2)O crystallizes in the monoclinic space group P2(1)/a with (at 298 K) a = 12.581(4) A, b = 14.204(5) A, c = 14.613(6) A, beta = 114.88(1) degrees, V = 2369(1), Z = 4. Compound 8.0.5CH(2)Cl(2) crystallizes in the orthorhombic space group Pca2(1) with (at 298 K) a = 23.072(2) A, b = 24.176(2) A, c = 13.676(1) A, V = 7628(2) A(3), Z = 8 with two crystallographically independent molecules per asymmetric unit. In addition to the synthesis and crystallographic studies, we report the optical, infrared, magnetic, conductivity, and CW EPR properties of these oxovanadium(IV) compounds as well as theoretical studies on [V(IV)O(bipy)(2)](2+) and [V(IV)OX(bipy)(2)](+/0) species (X = OH(-), SO(4)(2)(-), Cl(-)).     

Synthesis and structure of a series of new d(1)-Aryl imido-vanadium(IV) complexes stabilized by n-donor ligands

A family of new coordination vanadium(IV) compounds supported by a terminal or bridged aryl imido ligand are reported. Reaction of V(NMe(2))(4) with anilines ArNH(2), where Ar = 2,6-i-Pr(2)-C(6)H(3), 2,6-Me(2)-C(6)H(3), Ph, 2,6-Cl(2)-C(6)H(3), and C(6)F(5), afforded the diamagnetic imido-bridged complexes [V(NAr)(NMe(2))(2)](2) (1a-e). Chlorination of 1a-e with trimethylchlorosilane afforded complexes 2a-e formulated as [V(=NAr)Cl(2)(NHMe(2))(x)()](n)(). One-pot reaction of V(NMe(2))(4) with ArNH(2) in the presence of an excess of trimethylchlorosilane gave the five-coordinate compound [V(=NAr)Cl(2)(NHMe(2))(2)] (3a-e). Reaction of 3a-e with pyridine, bipyridine (bipy), or N,N,N',N'-tetramethylethylenediamine (tmeda) gave respectively the six-coordinate tris- or bis(pyridine) adducts [V(=NAr)Cl(2)(Py)(3)] (4a-e) or [V(=NAr)Cl(2)(Py)(2)(NHMe(2))] (5a), bipyridine complexes [V(=NAr)Cl(2)(bipy)(NHMe(2))] (5a-e) and [V(=NAr)Cl(2)(bipy)(Py)] (9a), and tmeda adduct [V(=NAr)Cl(2)(tmeda)(NHMe(2))] (10a). Moreover, five-coordinate complexes free of NHMe(2) ligands, such as [V(=NAr)Cl(2)(Py)(2)] (5a), [V(=NAr)Cl(2)(bipy)] (8a), and [V(=NAr)Cl(2)(tmeda)] (11a), were directly prepared starting from precursors 2a-e. All compounds were totally characterized by spectroscopic methods (IR, (1)H NMR for diamagnetic complexes, and EPR for paramagnetic complexes), elemental analysis, magnetism, and single-crystal X-ray diffraction studies for 1b, 3a, 3d, 4b, 4d, 7c, 10a, and 11a.     

Investigation of mixed oxidation state cyanide-bridged Re(V)oxo (acac(2)en/pn) and Re(I)(bipy)(CO)3 complexes

A series of cyanide-bridged complexes that combine a low-valent photoacceptor rhenium(I) metal center with an electroactive midvalent rhenium(V) complex were prepared. The synthesis involved the preparation of novel asymmetric rhenium(V) oxo compounds, cis-Re(V)O(CN)(acac(2)en) (1) and cis-Re(V)O(CN)(acac(2)pn) (2), formed by reacting trans-[Re(V)O(OH(2))(acac(2)en)]Cl or trans-Re(V)O(acac(2)pn)Cl with [NBu(4)][CN]. The μ-bridged cyanide mixed-oxidation Re(V)-Re(I) complexes were prepared by incubating the asymmetric complexes, 1 or 2, with fac-[Re(I)(bipy)(CO)(3)][OTf] to yield cis-[Re(V)O(acac(2)en)(μ-CN-1κC:2κN)-fac-Re(I)(bipy)(CO)(3)][PF(6)] (3) and [cis-Re(V)O(acac(2)pn)(μ-CN-1κC:2κN)-fac-Re(I)(bipy)(CO)(3)][PF(6)] (4), respectively.     

Coordination and Redox Chemistry of Substituted-Polypyridyl Complexes of Ruthenium

The complexes [Ru(tpy)(acac)(Cl)], [Ru(tpy)(acac)(H(2)O)](PF(6)) (tpy = 2,2',2"-terpyridine, acacH = 2,4 pentanedione) [Ru(tpy)(C(2)O(4))(H(2)O)] (C(2)O(4)(2)(-) = oxalato dianion), [Ru(tpy)(dppene)(Cl)](PF(6)) (dppene = cis-1,2-bis(diphenylphosphino)ethylene), [Ru(tpy)(dppene)(H(2)O)](PF(6))(2), [Ru(tpy)(C(2)O(4))(py)], [Ru(tpy)(acac)(py)](ClO(4)), [Ru(tpy)(acac)(NO(2))], [Ru(tpy)(acac)(NO)](PF(6))(2), and [Ru(tpy)(PSCS)Cl] (PSCS = 1-pyrrolidinedithiocarbamate anion) have been prepared and characterized by cyclic voltammetry and UV-visible and FTIR spectroscopy. [Ru(tpy)(acac)(NO(2))](+) is stable with respect to oxidation of coordinated NO(2)(-) on the cyclic voltammetric time scale. The nitrosyl [Ru(tpy)(acac)(NO)](2+) falls on an earlier correlation between nu(NO) (1914 cm(-)(1) in KBr) and E(1/2) for the first nitrosyl-based reduction 0.02 V vs SSCE. Oxalate ligand is lost from [Ru(II)(tpy)(C(2)O(4))(H(2)O)] to give [Ru(tpy)(H(2)O)(3)](2+). The Ru(III/II) and Ru(IV/III) couples of the aqua complexes are pH dependent. At pH 7.0, E(1/2) values are 0.43 V vs NHE for [Ru(III)(tpy)(acac)(OH)](+)/[Ru(II)(tpy)(acac)(H(2)O)](+), 0.80 V for [Ru(IV)(tpy)(acac)(O)](+)/[Ru(III)(tpy)(acac)(OH)](+), 0.16 V for [Ru(III)(tpy)(C(2)O(4))(OH)]/[Ru(II)(tpy)(C(2)O(4))(H(2)O)], and 0.45 V for [Ru(IV)(tpy)(C(2)O(4))(O)]/[Ru(III)(tpy)(C(2)O(4))(OH)]. Plots of E(1/2) vs pH define regions of stability for the various oxidation states and the pK(a) values of aqua and hydroxo forms. These measurements reveal that C(2)O(4)(2)(-) and acac(-) are electron donating to Ru(III) relative to bpy. Comparisons with redox potentials for 21 related polypyridyl couples reveal the influence of ligand changes on the potentials of the Ru(IV/III) and Ru(III/II) couples and the difference between them, DeltaE(1/2). The majority of the effect appears in the Ru(III/II) couple. ()A linear correlation exists between DeltaE(1/2) and the sum of a set of ligand parameters defined by Lever et al., SigmaE(i)(L(i)), for the series of complexes, but there is a dramatic change in slope at DeltaE(1/2) approximately -0.11 V and SigmaE(i)(L(i)) = 1.06 V. Extrapolation of the plot of DeltaE(1/2) vs SigmaE(i)(L(i)) suggests that there may be ligand environments in which Ru(III) is unstable with respect to disproportionation into Ru(IV) and Ru(II). This would make the two-electron Ru(IV)O/Ru(II)OH(2) couple more strongly oxidizing than the one-electron Ru(IV)O/Ru(III)OH couple.     

Unusual reactivity of the [Re(V)O]3+ core: syntheses and characterization of novel rhenium halide complexes with n-methyl-o-diaminobenzene

The reactions of 1 or 2 equiv of N-methyl-o-diaminobenzene with trans-[ReOX(3)(PPh(3))(2)] (X = Cl, Br) in refluxing chloroform gave oxo-free rhenium complexes [Re(VI)X(4)(NC(6)H(4)NHCH(3))(OPPh(3))] (X = Cl, 3; X = Br, 6), [Re(V)X(2)Y(NC(6)H(4)NHCH(3))(PPh(3))(2)] (X, Y = Cl, 4; X = Br, Y = Cl, 7), [Re(IV)Cl(2)(NHC(6)H(4)NCH(3))(2)] (5), and [Re(IV)Br(3)(NHC(6)H(4)NCH(3))(PPh(3))] (8). All complexes were characterized by elemental analysis, (1)H NMR and IR spectroscopy, cyclic voltammetry, EPR spectroscopy, and X-ray crystallography. The complexes all display distorted octahedral coordination geometry. For Re(IV) complexes 5 and 8, the ligands coordinate in the benzosemiquinone diimine form. In Re(VI) complexes 3 and 6 and the Re(V) complexes 4 and 7, the ligands coordinate in the dianionic monodentate imido form. The EPR spectra of Re(VI) species 3 and 6 in dichloromethane solution at room temperature exhibit the characteristic hyperfine pattern of six lines, with evidence of strong second-order effects. The IR spectra of the complexes are characterized by Re=N and Re-N stretching bands at ca. 1090 and 540 cm(-)(1), respectively. The Re(IV) and Re(V) complexes display well-resolved NMR spectra, while the Re(VI) complexes exhibit no observable spectra, due to paramagnetism. The cyclic voltammograms of complexes 3 and 6 display Re(VII)/ Re(VI) and Re(VI)/Re(V) processes, those of 4 and 7 exhibit Re(VI)/Re(V) and Re(V)/Re(IV) couples, and those of 5 and 8 are characterized by Re(V)/Re(IV) and Re(IV)/Re(III) processes.     

Synthetically persistent, self assembled [V(IV)2V(V)4] polyoxovanadates: facile synthesis, structure and magnetic analysis

Slow diffusion in a H-tube at room temperature of a methanolic solution of [VO(acac)(2)] (Hacac = acetylacetone) and 1,10-phenanthroline (phen) or 2,2'-bipyridine (bipy) into an aqueous solution of sodium pyrophosphate (Na(4)P(2)O(7)) resulted in the serendipitous formation of X-ray quality crystals of mixed-valent, hexameric oxovanadates of general formula [V(6)O(12)(OCH(3))(4)(L)(4)]·solv [L = 1,10-phenanthroline (phen) for 1· 2CH(3)OH · 4H(2)O (1a), and 2,2'-bipyridine (bipy) for 2· 4H(2)O (2a)]. These were characterized by single-crystal X-ray diffraction, IR, elemental and thermogravimetric analysis (TGA). A facile, rationalized synthetic route for the isolation of 1a and 2a could be established following structural determination, involving NaOH in place of Na(4)P(2)O(7) as pH modulator. The use of distilled water (pH 7) as methanolic co-solvent also resulted in crystallization of the two complexes, proving the presence of a base in the reaction scheme is not vital, with slightly pH-depended yields noted for 2a only. A survey of the literature revealed the occurrence of several other procedures, from classical methods to hydrothermal routes, leading to different solvates of 1, the crystal structure of 2 being unreported in any form to date. The precise nature of the molecular assembly in these type of hybrid organic-inorganic poly-vanadates is contradictory in published reports. On the basis of newly acquired high resolution crystal data and supported by magnetic investigation of the samples, we propose herein a formulation as [(V(IV)O)(2)(V(V)O(2))(4)(μ(3)-O)(2)(μ-OCH(3))(4)(L)(4)], with two oxovanadyl(IV) and four dioxovanadyl(V) units per molecule. A net ferromagnetic coupling between the two isolated V(IV) metal centers was measured with literature-consistent J values of +16.1(1) and +19.7(1) cm(-1) for 1a and 2a, respectively [H = -JS(A)·S(B) + S(A)·D·S(B) + βH (g(A)S(A) + g(B)S(B))], suggesting that crystal packing forces do not significantly influence the magnetic properties of this class of materials. A facile route toward the synthesis of the fully-oxidized [V(V)(4)O(8)(CH(3)O)(4)(bipy)(2)] and [V(V)(4)O(6)(CH(3)O)(6)(acac)(2)] tetraoxovanadates is also reported.     

Synthesis and Characterization of Six-Coordinate Nitrido Complexes of Vanadium(V), Chromium(V), and Manganese(V). Isolation of a Dinuclear, Mixed-Valent &mgr;-Nitrido Chromium(III)/Chromium(V) Species

Photolysis of a series of octahedral monoazido complexes of the type [LM(III)(didentate ligand)(N(3))](n)(+)X(n) of vanadium(III), chromium(III), and manganese(III) in the solid state or in solution yields quantitatively the corresponding six-coordinate nitrido complexes [LM(V)(didentate ligand)(N)](n)(+)X(n) and 1 equiv of dinitrogen. L represents the macrocycle 1,4,7-triazacyclononane or its N-methylated derivative (L'), the didentate ligands are pentane-2,4-dionate (acac), 2,2,6,6-tetramethylheptane-3,5-dionate (tacac), picolinate (pic), phenanthroline (phen), and oxalate (ox), and X(-) represents perchlorate or hexafluorophosphate. The following nitrido complexes were prepared: [LV(V)(N)(acac)](ClO(4)) (6), [LCr(V)(N)(acac)](ClO(4)) (13), [LCr(V)(N)(tacac)](ClO(4)) (14), [LCr(V)(N)(pic)](ClO(4)) (15), [LCr(V)(N)(phen)](ClO(4))(2) (16), [LCr(V)(N)(ox)] (19), [L'Mn(V)(N)(acac)]PF(6) (21). Photolysis of [LCr(III)(N(3))(ox)] (17) in the solid state produces the &mgr;-nitrido-bridged mixed-valent species [L(2)Cr(2)(ox)(2)(&mgr;-N)](N(3)) (18). The structures of the precursor complex [L'Mn(acac)(N(3))]BPh(4) (20), of 13, and of [L'Mn(V)(N)(acac)]BPh(4) (21) have been determined by X-ray crystallography. Complex 13 crystallizes in the orthorhombic space group Pnma, with cell constants a = 27.187(5) ?, b = 9.228(2) ?, c = 7.070(1) ?, V = 1773.7(6) ?(3), and Z = 4; complex 20 crystallizes in the triclinic space group P&onemacr; with a = 14.769(5) ?, b = 16.83(1) ?, c = 16.96(1) ?, alpha = 108.19(5) degrees, beta = 105.06(4) degrees, gamma = 99.78(4) degrees, V = 3719(2) ?(3), and Z = 4; and complex 21 crystallizes in the monoclinic space group P2(1)/n with a = 10.443(3) ?, b = 16.035(4) ?, c = 21.463(5) ?, beta = 95.76(1) degrees, V = 3575.9(14) ?(3), and Z = 4. The Cr(V)&tbd1;N and Mn(V)&tbd1;N distances are short at 1.575(9) and 1.518(4) ?, respectively, and indicate a metal-to-nitrogen triple bond.     

Rhenium complexes with 2-(diphenylphosphinomethyl)aniline: formation of a cyclic, trinuclear oxorhenium(V) core

Reactions of 2-(diphenylphosphinomethyl)aniline, H(2)L(2), with (NBu(4))[ReOCl(4)] yield different oxo rhenium(V) complexes depending on the conditions applied. This comprises monomeric compounds such as [ReOCl(3)(H(2)L(2))] (1), [ReOCl(2)(OMe)(H(2)L(2))] (2), or [ReO(2)(H(2)L(2))(2)]Cl (5) as well as the dimeric μ-oxo complex [{ReOCl(2)(H(2)L(2))}(2)]O] (3) and the oxo-bridged trimer [{ReOCl(H(2)L(2))}O](3) (4). The latter compound represents the first example of a hitherto unknown trinuclear, cyclic oxo(V) core. [{ReOCl(H(2)L(2))}O](3) contains a tensed 6-membered metallacycle, which readily undergoes rearrangements and reactions with additional ligands. Compounds of the compositions 5 and [ReO(2)(H(2)L(2))(H(2)L(1))]Cl (6) were isolated either from the decomposition of 4 in CH(2)Cl(2)/n-pentane or from reactions with 2-(diphenylphosphino)aniline, H(2)L(1).     

Ability of a Au(III)-N unit to bond two aurophilically interacting gold(I) centers

The monohapto neutral 2-(diphenylphosphino)aniline (PNH(2)) complexes [Au(C(6)F(5))(2)X(PNH(2))] (X = C(6)F(5) (1), Cl (2)) have been obtained from [Au(C(6)F(5))(3)(tht)] or [Au(C(6)F(5))(2)(micro-Cl)](2) and PNH(2), and the cationic [Au(C(6)F(5))(2)(PNH(2))]ClO(4) (3) has been similarly prepared from [Au(C(6)F(5))(2)(OEt(2))(2)]ClO(4) and PNH(2) or from 2 and AgClO(4). The neutral amido complex [Au(C(6)F(5))(2)(PNH)] (4) can be obtained by deprotonation of 3 with PPN(acac) (acac = acetylacetonate) or by treatment of the chloro complex 2 with Tl(acac). It reacts with [Ag(OClO(3))(PPh(3))] or [Au(OClO(3))(PPh(3))] to give the dinuclear species [Au(C(6)F(5))(2)[PNH(MPPh(3))]]ClO(4) (M = Ag (5), Au (6)). The latter can also be obtained by reaction of equimolar amounts of 3 and [Au(acac)(PPh(3))]; when the molar ratio of the same reagents is 1:2, the trinuclear cationic complex [Au(C(6)F(5))(2)[PN(AuPPh(3))(2)]]ClO(4) (7) is obtained. The crystal structures of complexes 2-4 and 7 have been established by X-ray crystallography; the last-mentioned displays an unusual Au(I)-Au(III) interaction.     

Binuclear (salen)osmium phosphinidine and phosphiniminato complexes

The preparation of a number of binuclear (salen)osmium phosphinidine and phosphiniminato complexes using various strategies are described. Treatment of [Os(VI)(N)(L(1))(sol)](X) (sol = H(2)O or MeOH) with PPh(3) affords an osmium(IV) phosphinidine complex [Os(IV){N(H)PPh(3)}(L(1))(OMe)](X) (X = PF(6)1a, ClO(4)1b). If the reaction is carried out in CH(2)Cl(2) in the presence of excess pyrazine the osmium(III) phosphinidine species [Os(III){N(H)PPh(3)}(L(1))(pz)](PF(6)) 2 can be generated. On the other hand, if the reaction is carried out in CH(2)Cl(2) in the presence of a small amount of H(2)O, a μ-oxo osmium(IV) phosphinidine complex is obtained, [(L(1)){PPh(3)N(H)}Os(IV)-O-Os(IV){N(H)PPh(3)}(L(1))](PF(6))(2)3. Furthermore, if the reaction of [Os(VI)(N)(L(1))(OH(2))]PF(6) with PPh(3) is done in the presence of 2, the μ-pyrazine species, [(L(1)){PPh(3)N(H)}Os(III)-pz-Os(III){N(H)PPh(3)}(L(1))](PF(6))(2)4 can be isolated. Novel binuclear osmium(IV) complexes can be prepared by the use of a diphosphine ligand to attack two Os(VI)≡N. Reaction of [Os(VI)(N)(L(1))(OH(2))](PF(6)) with PPh(2)-C≡C-PPh(2) or PPh(2)-(CH(2))(3)-PPh(2) in MeOH affords the binuclear complexes [(MeO)(L(1))Os(IV){N(H)PPh(2)-R-PPh(2)N(H)}Os(IV)(L(1))(OMe)](PF(6))(2) (R = C≡C 5, (CH(2))(3)6). Reaction of [Os(VI)(N)(L(2))Cl] with PPh(2)FcPPh(2) generates a novel trimetallic complex, [Cl(L(2))Os(IV){NPPh(2)-Fc-PPh(2)N}Os(IV)(L(2))Cl] 7. The structures of 1b, 2, 3, 4, 5 and 7 have been determined by X-ray crystallography.     

Redox-noninnocence of the S,S'-coordinated ligands in bis(benzene-1,2-dithiolato)iron complexes

The electronic structures of complexes of iron containing two S,S'-coordinated benzene-1,2-dithiolate, (L)(2)(-), or 3,5-di-tert-butyl-1,2-benzenedithiolate, (L(Bu))(2)(-), ligands have been elucidated in depth by electronic absorption, infrared, X-band EPR, and Mossbauer spectroscopies. It is conclusively shown that, in contrast to earlier reports, high-valent iron(IV) (d(4), S = 1) is not accessible in this chemistry. Instead, the S,S'-coordinated radical monoanions (L(*))(1)(-) and/or (L(Bu)(*))(1)(-) prevail. Thus, five-coordinate [Fe(L)(2)(PMe(3))] has an electronic structure which is best described as [Fe(III)(L)(L(*))(PMe(3))] where the observed triplet ground state of the molecule is attained via intramolecular, strong antiferromagnetic spin coupling between an intermediate spin ferric ion (S(Fe) = (3)/(2)) and a ligand radical (L(*))(1)(-) (S(rad) = (1)/(2)). The following complexes containing only benzene-1,2-dithiolate(2-) ligands have been synthesized, and their electronic structures have been studied in detail: [NH(C(2)H(5))(3)](2)[Fe(II)(L)(2)] (1), [N(n-Bu)(4)](2)[Fe(III)(2)(L)(4)] (2), [N(n-Bu)(4)](2)[Fe(III)(2)(L(Bu))(4)] (3); [P(CH(3))Ph(3)][Fe(III)(L)(2)(t-Bu-py)] (4) where t-Bu-py is 4-tert-butylpyridine. Complexes containing an Fe(III)(L(*))(L)- or Fe(III)(L(Bu))(L(Bu)(*))- moiety are [N(n-Bu)(4)][Fe(III)(2)(L(Bu))(3)(L(Bu)(*))] (3(ox)()), [Fe(III)(L)(L(*))(t-Bu-py)] (4(ox)()), [Fe(III)(L(Bu))(L(Bu)(*))(PMe(3))] (7), [Fe(III)(L(Bu))(L(Bu)(*))(PMe(3))(2)] (8), and [Fe(III)(L(Bu))(L(Bu)(*))(PPr(3))] (9), where Pr represents the n-propyl substituent. Complexes 2, 3(ox)(), 4, [Fe(III)(L)(L(*))(PMe(3))(2)] (6), and 9 have been structurally characterized by X-ray crystallography.     

Chelated hydrazido(3-)rhenium(V) complexes: on the way to the nitrido-M(V) core (M = Tc, Re)

Neutral and asymmetrical hydrazido(3-)rhenium(V) heterocomplexes of the type [Re(eta(2)-L(4))(L(n))(PPh(3))] (eta(2)-L(4) = NNC(SCH(3))S; H(2)L(1) = S-methyl beta-N-((2-hydroxyphenyl)ethylidene)dithiocarbazate, 1, H(2)L(2) = S-methyl beta-N-((2-hydroxyphenyl)methylidene)dithiocarbazate, 2) are prepared via ligand-exchange reactions in ethanolic solutions starting from [Re(V)(O)Cl(4)](-) in the presence of PPh(3) or from [Re(V)(O)Cl(3)(PPh(3))(2)]. The distorted octahedral coordination sphere of these compounds is saturated by a chelated hydrazido group, a facially ligated ONS Schiff base, and PPh(3). Reduction-substitution reactions starting from [NH(4)][Re(VII)O(4)] in acidic ethanolic mixtures containing PPh(3) and H(2)L(n) (or its dithiocarbazic acid precursor H(3)L(4)) produce another example of chelated hydrazido(3-) rhenium(V) derivative, namely [Re(eta(2)-L(4))Cl(2)(PPh(3))(2)], 3. On the contrary, the N-methyl-substituted dithiocarbazic acid H(2)L(3) reacts with perrhenate to give the known nitrido complex [Re(N)Cl(2)(PPh(3))(2)]. Rhenium(V) complexes incorporating the robust eta(2)-hydrazido moiety represent key intermediates helpful for the comprehension of the reaction pathway which generates nitridorhenium(V) species starting from oxo precursors. An essential requirement for the stabilization of such chelated hydrazido-Re(V) units is the triple deprotonation at the hydrazine nitrogens, thereby providing efficient pi-electron circulation in the resulting five-membered ring. The thermal stability of these units is affected by the nature of the anchoring donor, thione sulfur ensuring stronger chelation than nitrogen and oxygen. The eta(2)-hydrazido complexes are characterized by conventional physicochemical techniques, including the X-ray crystal structure determination of 1 and 3.     

Redox-induced terpyridyl substitution in the Os(VI)-hydrazido complex, trans-[Os(VI)(tpy)(Cl)(2)(NN(CH(2))(4)O)](2+)

Reaction between the Os(VI)-hydrazido complex, trans-[Os(VI)(tpy)(Cl)(2)(NN(CH(2))(4)O)](2+) (tpy = 2,2':6',2"-terpyridine and O(CH(2))(4)N(-) = morpholide), and a series of N- or O-bases gives as products the substituted Os(VI)-hydrazido complexes, trans-[Os(VI)(4'-RNtpy)(Cl)(2)(NN(CH(2))(4)O)](2+) or trans-[Os(VI)(4'-ROtpy)(Cl)(2)(NN(CH(2))(4)O)](2+) (RN(-) = anilide (PhNH(-)); S,S-diphenyl sulfilimide (Ph(2)S=N(-)); benzophenone imide (Ph(2)C=N(-)); piperidide ((CH(2))(5)N(-)); morpholide (O(CH(2))(4)N(-)); ethylamide (EtNH(-)); diethylamide (Et(2)N(-)); and tert-butylamide (t-BuNH(-)) and RO(-) = tert-butoxide (t-BuO(-)) and acetate (MeCO(2)(-)). The rate law for the formation of the morpholide-substituted complex is first order in trans-[Os(VI)(tpy)(Cl)(2)(NN(CH(2))(4)O)](2+) and second order in morpholine with k(morp)(25 degrees C, CH(3)CN) = (2.15 +/- 0.04) x 10(6) M(-)(2) s(-)(1). Possible mechanisms are proposed for substitution at the 4'-position of the tpy ligand by the added nucleophiles. The key features of the suggested mechanisms are the extraordinary electron withdrawing effect of Os(VI) on tpy and the ability of the metal to undergo intramolecular Os(VI) to Os(IV) electron transfer. These substituted Os(VI)-hydrazido complexes can be electrochemically reduced to the corresponding Os(V), Os(IV), and Os(III) forms. The Os-N bond length of 1.778(4) A and Os-N-N angle of 172.5(4) degrees in trans-[Os(VI)(4'-O(CH(2))(4)Ntpy)(Cl)(2)(NN(CH(2))(4)O)](2+) are consistent with sp-hybridization of the alpha-nitrogen of the hydrazido ligand and an Os-N triple bond. The extensive ring substitution chemistry implied for the Os(VI)-hydrazido complexes is discussed.     

Synthesis, characterization, and reactivity of mononuclear O,N-chelated vanadium(IV) and -(III) complexes of methyl 2-Aminocyclopent-1-ene-1-dithiocarboxylate based ligand: reporting an example of conformational isomerism in the solid state

Vanadium(IV) and -(III) complexes of a tetradentate N(2)OS Schiff base ligand H(2)L [derived from methyl 2-((beta-aminoethyl)amino)cyclopent-1-ene-1-dithiocarboxylate and salicylaldehyde] are reported. In all the complexes, the ligand acts in a bidentate (N,O) fashion leaving a part containing the N,S donor set uncoordinated. The oxovanadium(IV) complex [VO(HL)(2)] (1) is obtained by the reaction between [VO(acac)(2)] and H(2)L. In the solid state, compound 1 has two conformational isomers 1a and 1b; both have been characterized by X-ray crystallography. Compound 1a has the syn conformation that enforces the donor atoms around the metal center to adopt a distorted tbp structure (tau = 0.55). Isomer 1b on the other hand has an anti conformation with almost a regular square pyramidal geometry (tau = 0.06) around vanadium. In solution, however, 1 prefers to be in the square pyramidal form. A second variety of vanadyl complex [VO(L(cyclic))(2)](I(3))(2) (2) with a new bidentate O,N donor ligand involving isothiazolium moiety has been obtained by a ligand-based oxidation of the precursor complex 1 with iodine. Preliminary X-ray and FAB mass spectroscopic data of 2 have supported the formation of a heterocyclic moiety by a ring closure reaction involving a N-S bond. Vanadium(III) complex [V(acac)(HL)(2)] (3) has been obtained through partial ligand displacement of [V(acac)(3)] with H(2)L. Compound 3 has almost a regular octahedral structure completed by two bidentate HL ligands along with an acetylacetonate molecule. Electronic spectra, magnetism, EPR, and redox properties of these compounds are reported.     

The first acetimino complexes of Rh(III). 4-imino-2-methylpentan-2-amino-Rh(III) complexes through metal-assisted intramolecular aldol-type condensation of two acetimino ligands

[Rh(Cp)Cl(mu-Cl)](2) (Cp = pentamethylcyclopentadienyl) reacts (i) with [Au(NH=CMe(2))(PPh(3))]ClO(4) (1:2) to give [Rh(Cp)(mu-Cl)(NH=CMe(2))](2)(ClO(4))(2) (1), which in turn reacts with PPh(3) (1:2) to give [Rh(Cp)Cl(NH=CMe(2))(PPh(3))]ClO(4) (2), and (ii) with [Ag(NH=CMe(2))(2)]ClO(4) (1:2 or 1:4) to give [Rh(Cp)Cl(NH=CMe(2))(2)]ClO(4) (3) or [Rh(Cp)(NH=CMe(2))(3)](ClO(4))(2).H(2)O (4.H(2)O), respectively. Complex 3 reacts (i) with XyNC (1:1, Xy = 2,6-dimethylphenyl) to give [Rh(Cp)Cl(NH=CMe(2))(CNXy)]ClO(4) (5), (ii) with Tl(acac) (1:1, acacH = acetylacetone) or with [Au(acac)(PPh(3))] (1:1) to give [Rh(Cp)(acac)(NH=CMe(2))]ClO(4) (6), (iii) with [Ag(NH=CMe(2))(2)]ClO(4) (1:1) to give 4, and (iv) with (PPN)Cl (1:1, PPN = Ph(3)P=N=PPh(3)) to give [Rh(Cp)Cl(imam)]Cl (7.Cl), which contains the imam ligand (N,N-NH=C(Me)CH(2)C(Me)(2)NH(2) = 4-imino-2-methylpentan-2-amino) that results from the intramolecular aldol-type condensation of the two acetimino ligands. The homologous perchlorate salt (7.ClO(4)) can be prepared from 7.Cl and AgClO(4) (1:1), by treating 3 with a catalytic amount of Ph(2)C=NH, in an atmosphere of CO, or by reacting 4with (PPN)Cl (1:1). The reactions of 7.ClO(4) with AgClO(4) and PTo(3) (1:1:1, To = C(6)H(4)Me-4) or XyNC (1:1:1) give [Rh(Cp)(imam)(PTo(3))](ClO(4))(2).H(2)O (8) or [Rh(Cp)(imam)(CNXy)](ClO(4))(2) (9), respectively. The crystal structures of 3 and 7.Cl have been determined.     

A new class of ferromagnetically-coupled mixed valence vanadium(IV/V) polyoxometalates

Reaction of [V(VI)OCl(2)(thf)(2)] with a bidentate nitrogen-donor ligand (L: phen=1,10-phenanthroline, 5-mephen=5-methyl-1,10-phenanthroline, bipy=2,2'-bipyridine, 5,5'-me(2)bipy=5,5'-dimethyl-2,2'-bipy) in methyl alcohol, in the presence of triethylamine, leads to the formation of hexameric [V(2) (IV)V(4) (V)] oxo-alkoxo-vanadates of the general formula [V(6)O(12)(mu(2)-OCH(3))(4)(L)(4)].x H(2)O [L=phen (1.4 H(2)O), 5-mephen (2.6 H(2)O), bipy (3.4 H(2)O), 5,5'-me(2)bipy (4.H(2)O)]. X-ray structure analysis of 1.2 H(2)O and 4.8 CH(3)OH revealed a pair of V(3)O(13)N(4) trimeric units sharing two corners, with a centrosymmetric planar V(6)-core. In addition, a fully oxidized V(V) species [V(V) (4)O(8)(OCH(3))(2)(mu(3)-OCH(3))(2)(5,5'-me(2)bipy)(2)].3 CH(3)OH (5.3 CH(3)OH) was isolated from the reaction mixture used for the synthesis of 4.H(2)O. The crystal structure of 5.3 CH(3)OH revealed a dicubane-like framework with two missing vertices. Electron paramagnetic resonance (EPR) and variable temperature magnetic susceptibility studies for the hexamers 1.4 H(2)O and 3.4 H(2)O showed the complete localization of the single 3d electrons on the V(IV) ions and unusual ferromagnetic interaction between the two paramagnetic vanadium(IV) ions separated by a distance of about 5.1 A. Furthermore, intermolecular antiferromagnetic interactions through pi-contacts of phenyl rings were observed for these species below 8 K. The ferromagnetic exchange coupling observed in the hexanuclear compounds 1.4 H(2)O and 3.4 H(2)O is also discussed using ab initio UHF calculations on a model compound. The value of the exchange coupling constant (3.7 cm(-1)) for this model compound, calculated using the broken symmetry approach, is in good agreement, both in sign and magnitude, with the experimental J values (6.00 cm(-1) for 1.4 H(2)O and 8.54 cm(-1) for 3.4 H(2)O).     

Formation of a dinuclear imido complex from the reaction of a ruthenium(VI) nitride with a ruthenium(II) hydride

The treatment of [Ru(L(OEt))(N)Cl(2)] (1; L(OEt)(-) = [Co(η(5)-C(5)H(5)){P(O)(OEt)(2)}(3)](-)) with Et(3)SiH affords [Ru(L(OEt))Cl(2)(NH(3))] (2), whereas that with [Ru(L(OEt))(H)(CO)(PPh(3))] (3) gives the dinuclear imido complex [(L(OEt))Cl(2)Ru(μ-NH)Ru(CO)(PPh(3))(L(OEt))] (4). The imido group in 4 binds to the two ruthenium atoms unsymmetrically with Ru-N distances of 1.818(6) and 1.952(6) ?. The reaction between 1 and 3 at 25 °C in a toluene solution is first order in both complexes with a second-order rate constant determined to be (7.2 ± 0.4) × 10(-5) M(-1) s(-1).     

Reaction of an osmium(VI) nitrido complex with cyanide: formation and reactivity of an osmium(III) hydrogen cyanamide complex

Reaction of [Os(VI)(N)(L(1))(Cl)(OH(2))] (1) with CN(-) under various conditions affords (PPh(4))[Os(VI)(N)(L(1))(CN)(Cl)] (2), (PPh(4))(2)[Os(VI)(N)(L(2))(CN)(2)] (3), and a novel hydrogen cyanamido complex, (PPh(4))(2)[Os(III){N(H)CN}(L(3))(CN)(3)] (4). Compound 4 reacts readily with both electrophiles and nucleophiles. Protonation and methylation of 4 produce (PPh(4))[Os(III)(NCNH(2))(L(3))(CN)(3)] (5) and (PPh(4))[Os(III)(NCNMe(2))(L(3))(CN)(3)] (6), respectively. Nucleophilic addition of NH(3), ethylamine, and diethylamine readily occur at the C atom of the hydrogen cyanamide ligand of 4 to produce osmium guanidine complexes with the general formula [Os(III){N(H)C(NH(2))NR(1)R(2)}(L(3))(CN)(3)](-) , which have been isolated as PPh(4) salts (R(1) = R(2) = H (7); R(1) = H, R(2) = CH(2)CH(3) (8); R(1) = R(2) = CH(2)CH(3) (9)). The molecular structures of 1-5 and 7 and 8 have been determined by X-ray crystallography.     

On the reactivity of mononuclear iron(V)oxo complexes

Ferric tetraamido macrocyclic ligand (TAML)-based catalysts [Fe{C(6)H(4)-1,2-(NCOCMe(2)NCO)(2)CR(2)}(OH(2))]PPh(4) [1; R = Me (a), Et (b)] are oxidized by m-chloroperoxybenzoic acid at -40 °C in acetonitrile containing trace water in two steps to form Fe(V)oxo complexes (2a,b). These uniquely authenticated Fe(V)(O) species comproportionate with the Fe(III) starting materials 1a,b to give μ-oxo-(Fe(IV))(2) dimers. The comproportionation of 1a-2a is faster and that of 1b-2b is slower than the oxidation by 2a,b of sulfides (p-XC(6)H(4)SMe) to sulfoxides, highlighting a remarkable steric control of the dynamics. Sulfide oxidation follows saturation kinetics in [p-XC(6)H(4)SMe] with electron-rich substrates (X = Me, H), but changes to linear kinetics with electron-poor substrates (X = Cl, CN) as the sulfide affinity for iron decreases. As the sulfide becomes less basic, the Fe(IV)/Fe(III) ratio at the end of reaction for 2b suggests a decreasing contribution of concerted oxygen-atom transfer (Fe(V) → Fe(III)) concomitant with increasing electron transfer oxidation (Fe(V) → Fe(IV)). Fe(V) is more reactive toward PhSMe than Fe(IV) by 4 orders of magnitude, a gap even larger than that known for peroxidase Compounds I and II. The findings reinforce prior work typecasting TAML activators as faithful peroxidase mimics.     

o-Iminobenzosemiquinonato complexes of Mn(III) and Mn(IV). Synthesis and characterization of [Mn(III)(L(ISQ))(2)(L(AP))] (S(t) = 1) and [Mn(IV)(L(ISQ))(2)(L(AP)-H)] (S(t) = 1/2)

From the reaction of [Mn(III)(3)(micro-O)(micro-CH(3)CO(2))(6)]CH(3)CO(2) (manganese(III) acetate) and 2-anilino-4,6-di-tert-butylphenol (1:3) in methanol under anaerobic conditions, dark brown-black crystals of [Mn(III)(L(ISQ))(2)(L(AP))] (1) were obtained in approximately 30% yield. (L(AP))(-) represents the closed-shell o-aminophenolate(-) form of the above ligand, and (L(ISQ))(-) is the monoanionic pi radical form o-iminobenzosemiquinonate(-) (S(rad) = 1/2). Complex 1 can be deprotonated at the (L(AP))(-) ligand and one-electron-oxidized by air, yielding crystals of [Mn(IV)(L(ISQ))(2)(L(AP)-H)] (2), where (L(AP)-H)(2-) represents the closed-shell, dianionic o-amidophenolate(2-) form of the above ligand. The structures of 1 and 2 have been determined by X-ray crystallography at 100 K. The protonation and oxidation levels of the ligands and of the metal ions have been unequivocally established: both complexes contain two pi radical ligands, 1 contains a Mn(III) ion, and 2 contains a Mn(IV) ion. The spins of the radicals (S(rad) = 1/2) couple strongly antiferromagnetically with the d(4) and d(3) configuration of the Mn ions in 1 and 2, respectively, yielding the observed ground states of S = 1 for 1 and S = (1)/(2) for 2. This has been established by temperature-dependent susceptibility measurements (2-300 K) and S- and X-band EPR spectroscopy.