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.     

Reactions of acetonitrile coordinated to a nitrosylruthenium complex with H2O or CH(3)OH under mild conditions: structural characterization of imido-type complexes

The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) (bpy = 2,2'-bipyridine) in H(2)O at room temperature proceeded to afford two new nitrosylruthenium complexes. These complexes have been identified as nitrosylruthenium complexes containing the N-bound methylcarboxyimidato ligand, cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+), and methylcarboxyimido acid ligand, cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+), formed by an electrophilic reaction at the nitrile carbon of the acetonitrile coordinated to the ruthenium ion. The X-ray structure analysis on a single crystal obtained from CH(3)CN-H(2)O solution of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](PF(6))(3) has been performed: C(22)H(20.5)N(6)O(2)P(2.5)F(15)Ru, orthorhombic, Pccn, a = 15.966(1) A, b = 31.839(1) A, c = 11.707(1) A, V = 5950.8(4) A(3), and Z = 8. The structural results revealed that the single crystal consisted of 1:1 mixture of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+) and cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+) and the structural formula of this single crystal was thus [Ru(NO)(NH=C(OH(0.5))CH(3))(bpy)(2)](PF(6))(2.5). The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) in dry CH(3)OH-CH(3)CN at room temperature afforded a nitrosylruthenium complex containing the methyl methylcarboxyimidate ligand, cis-[Ru(NO)(NH=C(OCH(3))CH(3))(bpy)(2)](3+). The structure has been determined by X-ray structure analysis: C(25)H(29)N(8)O(18)Cl(3)Ru, monoclinic, P2(1)/c, a = 13.129(1) A, b = 17.053(1) A, c = 15.711(1) A, beta = 90.876(5) degrees, V = 3517.3(4) A(3), and Z = 4.     

4,4'-dithiodipyridine as a bridging ligand in osmium and ruthenium complexes: the electron conductor ability of the -S-S- bridge

The compounds [Ru(NH(3))(5)(dtdp)](TFMS)(3), [Os(NH(3))(5)(dtdp)](TFMS)(3), [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](TFMS)(6), [(NH(3))(5)Os(dtdp)Ru(NH(3))(5)](TFMS)(3)(PF(6))(2), and [(NH(3))(5)Os(dtdp)Fe(CN)(5)] (dtdp = 4,4'-dithiodipyridine, TFMS = trifluoromethanesulfonate) have been synthesized and characterized by elemental analysis, cyclic voltammetry, electronic, vibrational, EPR, and (1)H NMR spectroscopies. Changes in the electronic and voltammetric spectra of the ion complex [Os(NH(3))(5)(dtdp)](3+) as a function of the solution pH enable us to calculate the pK(a) for the [Os(NH(3))(5)(dtdpH)](4+) and [Os(NH(3))(5)(dtdpH)](3+) acids as 3.5 and 5.5, respectively. The comparison of the above pK(a) data with that for the free ligand (pK(1) = 4.8) provides evidence for the -S-S- bridge efficiency as an electron conductor between the two pyridine rings. The symmetric complex, [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](6+), is found to exist in two geometric forms, and the most abundant form (most probably trans) has a strong conductivity through the -S-S- bridge, as is shown by EPR, which finds it to have an S = 1 spin state with a spin-spin interaction parameter of 150-200 G both in the solid sate and in frozen solution. Further the NMR of the same complex shows a large displacement of unpaired spin into the pi orbitals of the dttp ligand relative to that found in [Os(NH(3))(5)(dtdp)](3+). The comproportionation constant, K(c) = 2.0 x 10(5), for the equilibrium equation [Os(II)Os(II)] + [Os(III)Os(III)] right harpoon over left harpoon 2[Os(II)Os(III)] and the near-infrared band energy for the mixed-valence species (MMCT), [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](5+) (lambda(MMCT) = 1665 nm, epsilon = 3.5 x 10(3) M(-)(1) cm(-)(1), deltanu(1/2) = 3.7 x 10(3) cm(-)(1), alpha = 0.13, and H(AB) = 7.8 x 10(2) cm(-)(1)), are quite indicative of strong electron delocalization between the two osmium centers. The electrochemical and spectroscopic data for the unsymmetrical binuclear complexes [(NH(3))(5)Os(III)(dtdp)Ru(II)(NH(3))(5)](5+) (lambda(MMCT) = 965 nm, epsilon = 2.2 x 10(2) M(-)(1) cm(-)(1), deltanu(1/2) = 3.0 x 10(3) cm(-)(1), and H(AB) = 2.2 x 10(2) cm(-)(1)) and [(NH(3))(5)Os(III)(dtdp)Fe(II)(CN)(5)] (lambda(MMCT) = 790 nm, epsilon = 7.5 x 10 M(-)(1) cm(-)(1), deltanu(1/2) = 5.4 x 10(3) cm(-)(1), and H(AB) = 2.0 x 10(2) cm(-)(1)) also suggest a considerable electron delocalization through the S-S bridge. As indicated by a comparison of K(c) and energy of the MMCT process in the iron, ruthenium, and osmium complexes, the electron delocalization between the two metal centers increases in the following order: Fe < Ru < Os.     

Synthesis of Polysiloxane-Bound (Ether-phosphine)palladium Complexes. Stoichiometric and Catalytic Reactions in Interphases(1)

The reaction of two equiv of the monomeric ether-phosphine O,P ligand (MeO)(3)Si(CH(2))(3)(Ph)PCH(2)-Do [1a(T(0)()), 1b(T(0)())] {Do = CH(2)OCH(3) [1a(T(0)())], CHCH(2)CH(2)CH(2)O [1b(T(0)())]} with PdCl(2)(COD) yields the monomeric palladium(II) complexes Cl(2)Pd(P approximately O)(2) [2a(T(0)())(2)(), 2b(T(0)())(2)()]. The compounds 2a(T(0)())(2)() and 2b(T(0)())(2)() are sol-gel processed with variable amounts (y) of Si(OEt)(4) (Q(0)()) to give the polysiloxane-bound complexes 2a(T(n)())(2)()(Q(k)())(y)(), 2b(T(n)())(2)()(Q(k)())(y)() (Table 1) {P approximately O = eta(1)-P-coordinated ether-phosphine ligand; for T(n)() and Q(k)(), y = number of condensed T type (three oxygen neighbors), Q type (four oxygen neighbors) silicon atoms; n and k = number of Si-O-Si bonds; n = 0-3; k = 0-4; 2a(T(n)())(2)()(Q(k)())(y)(), 2b(T(n)())(2)()(Q(k)())(y)() = {[M]-SiO(n)()(/2)(OX)(3)(-)(n)()}(2)[SiO(k)()(/2)(OX)(4)(-)(k)()](y)(), [M] = (Cl(2)Pd)(1/2)(Ph)P(CH(2)Do)(CH(2))(3)-, X = H, Me, Et}. The complexes 2b(T(n)())(2)()(Q(k)())(y)() (y = 4, 12, 36) show high activity and selectivity in the hydrogenation of 1-hexyne and tolan. The dicationic complexes [Pd(P&arcraise;O)(2)][SbF(6)](2) [3a(T(0)())(2)(), 3b(T(0)())(2)()] are formed by reacting Cl(2)Pd(P approximately O)(2) with 2 equiv of a silver salt {P&arcraise;O = eta(2)-O&arcraise;P-coordinated ether-phosphine ligand; 3a(T(0)())(2)(), 3b(T(0)())(2)() = [M]-SiOMe(3); [M] = {[Pd(2+)](1/)(2)P(Ph)(CH(2)CH(2)OCH(3))(CH(2))(3)-}{SbF(6)} (a), {[Pd(2+)](1/)(2)P(Ph)(CH(2)CHCH(2)CH(2)CH(2)O)(CH(2))(3)-}{SbF(6)} (b)}. Their polysiloxane-bound congeners 3a(T(n)())(2)(), 3b(T(n)())(2)() {[M]-SiO(n)()(/2)(OX)(3)(-)(n)} are obtained if a volatile, reversible bound ligand like acetonitrile is employed during the sol-gel process. The bis(chelate)palladium(II) complexes 3a(T(n)())(2)(), 3b(T(n)())(2)() are catalytic active in the solvent-free CO-ethene copolymerization, producing polyketones with chain lengths comparable to those obtained with chelating diphosphine ligands. The polysiloxane-bound palladium(0) complexes 5a(T(n)())(2)()(Q(k)())(4)(), 5b(T(n)())(2)()(Q(k)())(4)() {[M]-SiO(n)()(/)(2)(OX)(3)(-)(n)}(2)[SiO(k)()(/2)(OX)(4)(-)(k)](4), [M] = [(dba)Pd](1/)(2)P(Ph)(CH(2)Do)(CH(2))(3)-} undergo an oxidative addition reaction with iodobenzene in an interphase with formation of the complexes PhPd(I)(P approximately O)(2).4SiO(2) [6a(T(n)())(2)()(Q(k)())(4)(), 6b(T(n)())(2)()(Q(k)())(4)()] {[M]-SiO(n)()(/)(2)(OX)(3)(-)(n)](2)[SiO(k)()(/2)(OX)(4)(-)(k)](4), [M] = [PhPd(I)](1/2)P(Ph)(CH(2)Do)(CH(2))(3)-}, which insert carbon monoxide into the palladium-aryl bond even in the solid state.     

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.     

Imido Complexes Derived from the Reactions of Niobium and Tantalum Pentachlorides with Primary Amines: Relevance to the Chemical Vapor Deposition of Metal Nitride Films

Reactions of niobium and tantalum pentachlorides with tert-butylamine (>/=6 equiv) in benzene afford the dimeric imido complexes [NbCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2) (90%) and [TaCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2) (79%). The niobium complex exists as two isomers in solution, while the tantalum complex is composed of three major isomers and at least two minor isomers. Analogous treatments with isopropylamine (>/=7 equiv) give the monomeric complexes NbCl(2)(N(i)Pr)(NH(i)Pr)(NH(2)(i)Pr)(2) (84%) and TaCl(2)(N(i)Pr)(NH(i)Pr)(NH(2)(i)Pr)(2) (84%). The monomeric complexes are unaffected by treatment with excess isopropylamine, while the dimeric complexes are cleaved to the monomers MCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)(2) upon addition of excess tert-butylamine in chloroform solution. Treatment of niobium and tantalum pentachlorides with 2,6-diisopropylaniline affords insoluble precipitates of [NH(3)(2,6-(CH(CH(3))(2))(2)C(6)H(3))](2)[NbCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))] (100%) and [NH(3)(2,6-(CH(CH(3))(2))(2)C(6)H(3))](2)[TaCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))] (100%), which react with 4-tert-butylpyridine to afford the soluble complexes [4-t-C(4)H(9)C(5)H(4)NH](2)[NbCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))] (45%) and [4-t-C(4)H(9)C(5)H(4)NH](2)[TaCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))] (44%). Sublimation of [NbCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2), MCl(2)(N(i)Pr)(NH(i)Pr)(NH(2)(i)Pr)(2), and [NH(3)(2,6-(CH(CH(3))(2))(2)C(6)H(3))](2)[MCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))] leads to decomposition to give [MCl(3)(NR)(NH(2)R)](2) as sublimates (32-49%), leaving complexes of the proposed formulation MCl(NR)(2) as nonvolatile residues. By contrast, [TaCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2) sublimes without chemical reaction. Analysis of the organic products obtained from thermal decomposition of [NbCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2) showed isobutylene and tert-butylamine in a 2.2:1 ratio. Mass spectra of [NbCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2), [TaCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2), and [NbCl(3)(N(i)Pr)(NH(2)(i)Pr)](2) showed the presence of dimeric imido complexes, monomeric imido complexes, and nitrido complexes, implying that such species are important gas phase species in CVD processes utilizing these molecular precursors. The crystal structures of [4-t-C(4)H(9)C(5)H(4)NH](2)[NbCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))], [NbCl(3)(N(i)Pr)(NH(2)(i)Pr)](2), [NbCl(3)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))(NH(2)(2,6-(CH(CH(3))(2))(2)C(6)H(3)))](2), and [TaCl(3)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))(NH(2)(2,6-(CH(CH(3))(2))(2)C(6)H(3)))](2) were determined. [4-t-C(4)H(9)C(5)H(4)NH](2)[NbCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))] crystallizes in the space group P2(1)/c with a = 12.448(3) ?, b = 10.363(3) ?, c = 28.228(3) ?, beta = 94.92(1) degrees, V = 3628(5) ?(3), and Z = 4. [NbCl(3)(N(i)Pr)(NH(2)(i)Pr)](2) crystallizes in the space group P2(1)/c with a = 9.586(4) ?, b = 12.385(4) ?, c = 11.695(4) ?, beta = 112.89(2) degrees, V = 1279.0(6) ?(3), and Z = 2. [NbCl(3)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))(NH(2)(2,6-(CH(CH(3))(2))(2)C(6)H(3)))](2) crystallizes in the space group P2(1)/n with a = 10.285(3) ?, b = 11.208(3) ?, c = 23.867(6) ?, beta = 97.53 degrees, V = 2727(1) ?(3), and Z = 2. [TaCl(3)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))(NH(2)(2,6-(CH(CH(3))(2))(2)C(6)H(3)))](2) crystallizes in the space group P2(1)/n with a = 10.273(1) ?, b = 11.241(2) ?, c = 23.929(7) ?, beta = 97.69(2) degrees, V = 2695(2) ?(3), and Z = 2. These findings are discussed in the context of niobium and tantalum nitride film depositions from molecular precursors.     

Solid state and solution studies of lanthanide(III) complexes of cyclohexanetriols, models of the coordination sites found in sugars

This report covers studies in trivalent lanthanide complexation by two simple cyclohexanetriols that are models of the two coordination sites found in sugars and derivatives. Several complexes of trivalent lanthanide ions with cis,cis-1,3,5-trihydroxycyclohexane (L(1)()) and cis,cis-1,2,3-trihydroxycyclohexane (L(2)()) have been characterized in the solid state, and some of them have been studied in organic solutions. With L(1)(), Ln(L)(2) complexes are obtained when crystallization is performed from acetonitrile solutions whatever the nature of the salt (nitrate or triflate) [Ln(L(1)())(2)(NO(3))(2)](NO(3)) (Ln = Pr, Nd); [Ln(L(1)())(2)(NO(3))H(2)O](NO(3))(2) (Ln = Eu, Ho, Yb); [Ln(L(1)())(2)(OTf)(2)(H(2)O)](OTf) (Ln = Nd, Eu). Lanthanum nitrate itself gives a mixed complex [La(L(1)())(2)(NO(3))(2)][LaL(1)()(NO(3))(4)] from acetonitrile solution while [La(L(1)())(2)(NO(3))(2)](NO(3)) is obtained using dimethoxyethane as reaction solvent and crystallization medium. With L(2)(), Ln(L)(2) complexes have also been crystallized from methanol solution [Ln(L(2)())(2)(NO(3))(2)]NO(3), (Ln = Pr, Nd, Eu). Single-crystal X-ray diffraction analyses are reported for these complexes. Complex formation in solution has been studied for several triflate salts (La, Pr, Nd, Eu, and Yb) with L(1 )()and L(2)(), respectively in acetonitrile and in methanol. In contrast to the solid state, both structures Ln(L) and Ln(L)(2) equilibrate in solution, as was demonstrated by low-temperature (1)H NMR and electrospray ionization mass spectrometry experiments. Competing experiments in complexing abilities of L(1)() and L(2)() with trivalent lanthanide cations have shown that only L(2)() exhibits a small selectivity (Nd > Pr > Yb > La > Eu) in methanol.     

Redox reactivity of photogenerated osmium(II) complexes

Powerful reductants [Os(II)(NH(3))(5)L](2+) (L = OH(2), CH(3)CN) can be generated upon ultraviolet excitation of relatively inert [Os(II)(NH(3))(5)(N(2))](2+) in aqueous and acetonitrile solutions. Reactions of photogenerated Os(II) complexes with methyl viologen to form methyl viologen radical cation and [Os(III)(NH(3))(5)L](3+) were monitored by transient absorption spectroscopy. Rate constants range from 4.9 × 10(4) M(-1) s(-1) in acetonitrile solution to 3.2 × 10(7) (pH 3) and 2.5 × 10(8) M(-1) s(-1) (pH 12) in aqueous media. Photogeneration of five-coordinate Os(II) complexes opens the way for mechanistic investigations of activation/reduction of CO(2) and other relatively inert molecules.     

Self-assemblies of new rigid angular ligands and metal centers toward the rational construction and modification of novel coordination polymer networks

Self-assemblies of rigid angular ligands with 120 degrees molecular angle and metal centers have been investigated with the aim of achieving the rational construction and modification of coordination polymer structures. The reactions of Co(NCS)(2) with 1,3-bis(trans-4-styrylpyridyl)benzene (L(1)()), 2,6-bis(trans-4-styrylpyridyl)pyridine (L(2)()), 1,3-bis(trans-4-styrylpyrimidyl)benzene (L(3)()), and 1,3-bis(trans-4-styrylquinoly)benzene (L(4)()) afford complexes [Co(L(1)())(2)(NCS)(2)]( infinity ) (1), [Co(L(2)())(2)(NCS)(2)]( infinity ) (2), Co(L(3)())(2)(NCS)(2)(CH(3)OH)(2) (3), and [Co(L(4)())(NCS)(2)]( infinity ) (4), respectively. The resulting complexes exhibit open framework, stairlike hydrogen-bonded chain and single-stranded helical coil structures, which are controlled by the variation of the geometry around the coordination site in ligands. Moreover, the coordination of L(1)() and L(2)() to Mn(hfac)(2) (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate) yields single-stranded helical coordination polymers of [Mn(L(1)())(hfac)(2)]( infinity ) (5) and [Mn(L(2)())(hfac)(2)]( infinity ) (6), respectively.     

Multinuclear platinum(II)-amine complexes containing bis(aminopropyl)dicarba-closo-dodecaborane(12) ligands

Treatment of the bridging bidentate 1,Z-bis(aminopropyl)-1,Z-dicarba-closo-dodecaborane(12)(1,Z-bis(aminopropyl)-1,Z-carborane) ligands of the type 1,Z-[H(2)N(CH(2))(3)](2)-1,Z-C(2)B(10)H(10)(L(1), Z= 7, 5) or (L(2), Z= 12, 6) with two equivalents of trans-[PtClI(2)(NH(3))](-), followed by halogen ligand metathesis with AgOTf and HCl((aq)) afforded the novel diplatinum(II)-amine species cis-[[PtCl(2)(NH(3))](2)L(n)](7(n= 1) or 8(n= 2), respectively). Similarly, the reaction of L(1) or L(2) with the labile trans-[PtCl(dmf)(NH(3))(2)](+) afforded trans-[[PtCl(NH(3))(2)](2)L(n)](OTf)(2)(9(n= 1) or 10(n= 2), respectively) in good yield and purity. However, isolation of the analogous 1,2-carborane complexes was not possible owing to decomposition reactions that led to extensive degradation of the carborane cage and reduction of the metal centre. The mixed dinuclear complex [cis-[PtCl(2)(NH(3))]-L(1)-trans-[PtCl(NH(3))(2)]]OTf (19) was prepared by treatment of the Boc-protected amine ligand 1-[(Boc)(2)N(CH(2))(3)]-7-[H(2)N(CH(2))(3)]-1,7-C(2)B(10)H(10)(L(3), 15) with trans-[PtCl(dmf)(NH(3))(2)](+) to yield trans-[PtCl(NH(3))(2)L(3)]OTf (16), followed by acid deprotection of the pendant amine group, complexation with trans-[PtClI(2)(NH(3))](-), and halogen ligand metathesis using AgOTf and HCl((aq)). A novel trinuclear species containing 5 was prepared by the addition of two equivalents of 15 to the labile precursor cis-[Pt(dmf)(2)(NH(3))(2)](2+) followed by acid deprotection of the pendant amine groups. Further complexation with two equivalents of trans-[PtClI(2)(NH(3))](-) followed by halogen ligand metathesis using AgOTf and HCl((aq)) afforded the triplatinum(II)-amine species [cis-[Pt(NH(3))(2)(L(1))(2)]-cis-[PtCl(2)(NH(3))](2)](OTf)(2)(23). Complexes 7-10, 19 and 23 represent the first examples of multinuclear platinum(ii)-amine derivatives containing carborane cages. Preliminary in vitro cytotoxicity studies for selected complexes are also reported.     

Unprecedented chemical transformation of benzaldehyde semicarbazone mediated by osmium

para-Nitrobenzaldehyde semicarbazone (O(2)N(para)-C(6)H(4)C(H)=N-NH-CO-NH(2)) undergoes unprecedented chemical transformation during its reaction with [Os(PPh(3))(2)(CO)(2)(HCOO)(2)] in different alcoholic (R'OH, R' = CH(2)CH(2)OCH(3), CH(2)CH(3), CH(2)CH(2)CH(3), and CH(2)CH(2)CH(2)CH(3)) solvents whereby the NH(2) group of the semicarbazone ligand is displaced by a OR' group provided by the solvents. The transformed semicarbazone ligand binds to osmium as a bidentate N,O-donor forming five-membered chelate ring to afford complexes of type [Os(PPh(3))(2)(CO)(H)(L-OR')], where L-OR' refers to the transformed semicarbazone ligand. Structure of the [Os(PPh(3))(2)(CO)(H)(L-OCH(2)CH(2)OCH(3))] complex has been determined by X-ray crystallography. All the [Os(PPh(3))(2)(CO)(H)(L-OR')] complexes are diamagnetic and show characteristic (1)H NMR signals. They also show intense absorptions in the visible and ultraviolet region. Cyclic voltammetry on the complexes shows an irreversible oxidative response within 0.69-0.88 V versus SCE.     

Ligand influence over the formation of dinuclear [2+2] versus trinuclear [3+3] Cu(I) Schiff base macrocyclic complexes

The preparation and characterization of three new macrocyclic ligands with pendant arms based on the [2+2] condensation of isophthalaldehyde and the corresponding triamine substituted at the central N-atom is reported. None of these new macrocyclic ligands undergo any equilibrium reaction, based on imine hydrolysis to generate [1+1] macrocyclic formation or higher oligomeric compounds, such as [3+3], [4+4], etc., at least within the time scale of days. This indicates the stability of the newly generated imine bond. In sharp contrast, the reaction of the [2+2] macrocyclic Schiff bases with Cu(I) generates the corresponding dinuclear Cu(I) complexes [Cu(2)(L(1))](2+), 1(2+); [Cu(2)(L(2))(CH(3)CN)(2)](2+), 2(2+); and [Cu(2)(L(3))(CH(3)CN)(2)](2+), 3(2+), together with their trinuclear Cu(I) homologues [Cu(3)(L(4))](3+), 4(3+); [Cu(3)(L(5))(CH(3)CN)(3)](3+), 5(3+); and [Cu(3)(L(6))(CH(3)CN)(3)](3+), 6(3+), where the [2+2] ligand has undergone an expansion to the corresponding [3+3] Schiff base that is denoted as L(4), L(5), or L(6). The conditions under which the dinuclear and trinuclear complexes are formed were analyzed in terms of solvent dependence and synthetic pathways. The new complexes are characterized in solution by NMR, UV-vis, and MS spectroscopy and in the solid state by X-ray diffraction analysis and IR spectroscopy. For the particular case of the L(2) ligand, MS spectroscopy is also used to monitor the metal assisted transformation where the dinuclear complex 2(2+) is transformed into the trinuclear complex 5(3+). The Cu(I) complexes described here, in general, react slowly (within the time scale of days) with molecular oxygen, except for the ones containing the phenolic ligands 2(2+) and 5(3+) that react a bit faster.     

Synthesis and properties of oxo-carboxylato- and dioxo-bridged diosmium complexes of tris(2-pyridylmethyl)amine

A series of oxo-bridged diosmium complexes with tpa ligand (tpa = tris(2-pyridylmethyl)amine) are synthesized. The hydrolytic reaction of the mononuclear osmium complex [Os(III)Cl(2)(tpa)]PF(6) in aqueous solution containing a sodium carboxylate yields a μ-oxo-μ-carboxylato-diosmium(III) complex, [Os(III)(2)(μ-O)(μ-RCOO)(tpa)(2)](PF(6))(3) (R = C(3)H(7) (1), CH(3) (2), or C(6)H(5) (3)). One-electron oxidation of 1 with (NH(4))(2)Ce(IV)(NO(3))(6) gives a mixed-valent [Os(III)Os(IV)(μ-O)(μ-C(3)H(7)COO)(tpa)(2)](PF(6))(4) complex (4). A mixed-valent di-μ-oxo-diosmium complex, [Os(III)Os(IV)(μ-O)(2)(tpa)(2)](PF(6))(3) (5), is also synthesized from 1 in an aerobic alkaline solution (pH 13.5). All the complexes exhibit strong absorption bands in a visible-near-infrared region based on interactions of the osmium dπ and oxygen pπ orbitals of the Os-O-Os moiety. The X-ray crystallographic analysis of 1, 3, and 4 shows that the osmium centers take a pseudo-octahedral geometry in the μ-oxo-μ-carboxylato-diosmium core. The mixed-valent osmium(III)osmium(IV) complex 4 has a shorter osmium-oxo bond and a larger osmium-oxo-osmium angle as compared with those of the diosmium(III) complex 1 having the same bridging carboxylate. Crystal structure of 5 reveals that the two osmium ions are bridged by two oxo groups to give an Os(2)(μ-O)(2) core with the significantly short osmium-osmium distance (2.51784(7) ?), which is indicative of a direct osmium-osmium bond formation with the bond order of 1.5 (σ(2)π(2)δ(2)δ*(2)π*(1) configuration). In the electrochemical studies, the μ-oxo-μ-carboxylato-diosmium(III) complexes exhibit two reversible Os(III)Os(III)/Os(III)Os(IV) and Os(III)Os(IV)/Os(IV)Os(IV) oxidation couples and one irreversible redox wave for the Os(III)Os(III)/Os(II)Os(III) couple in CH(3)CN. The irreversible reductive process becomes reversible in CH(3)CN/H(2)O (1:1 Britton-Robinson buffer; pH 5-11), where the {1H(+)/2e(-)} transfer process is indicated by the plot of the redox potentials against the pH values of the solution of 1. Thus, the μ-oxo-μ-butyrato-diosmium(III) center undergoes proton-coupled electron transfer to yield a μ-hydroxo-μ-butyrato-diosmisum(II) species. The di(μ-oxo) complex 5 exhibits one reversible Os(III)Os(IV)/Os(IV)Os(IV) oxidation process and one reversible Os(III)Os(IV)/Os(III)Os(III) reduction process in CH(3)CN. The comproportionation constants K(com) of the Os(III)Os(IV) states for the present diosmium complexes are on the order of 10(19). The values are significantly larger when compared with those of similar oxo-bridged dimetal complexes of ruthenium and rhenium.     

Structures, host-guest chemistry and mechanism of stepwise self-assembly of M4L6 tetrahedral cage complexes

The ligand L(bip), containing two bidentate pyrazolyl-pyridine termini separated by a 3,3'-biphenyl spacer, has been used to prepare tetrahedral cage complexes of the form [M(4)(L(bip))(6)]X(8), in which a bridging ligand spans each of the six edges of the M(4) tetrahedron. Several new examples have been structurally characterized with a variety of metal cation and different anions in order to examine interactions between the cationic cage and various anions. Small anions such as BF(4)(-) and NO(3)(-) can occupy the central cavity where they are anchored by an array of CH···F or CH···O hydrogen-bonding interactions with the interior surface of the cage, but larger anions such as naphthyl-1-sulfonate or tetraphenylborate lie outside the cavity and interact with the external surface of the cage via CH···π interactions or CH···O hydrogen bonds. The cages with M = Co and M = Cd have been examined in detail by NMR spectroscopy. For [Co(4)(L(bip))(6)](BF(4))(8) the (1)H NMR spectrum is paramagnetically shifted over the range -85 to +110 ppm, but the spectrum has been completely assigned by correlation of measured T(1) relaxation times of each peak with Co···H distances. (19)F DOSY measurements on the anions show that at low temperature a [BF(4)](-) anion diffuses at a similar rate to the cage superstructure surrounding it, indicating that it is trapped inside the central cage cavity. Furthermore, the equilibrium step-by-step self-assembly of the cage superstructure has been elucidated by detailed modeling of spectroscopic titrations at multiple temperatures of an acetonitrile solution of L(bip) into an acetonitrile solution of Co(BF(4))(2). Six species have been identified: [Co(2)L(bip)](4+), [Co(2)(L(bip))(2)](4+), [Co(4)(L(bip))(6)](8+), [Co(4)(L(bip))(8)](8+), [Co(2)(L(bip))(5)](4+), and [Co(L(bip))(3)](2+). Overall the assembly of the cage is entropy, and not enthalpy, driven. Once assembled, the cages show remarkable kinetic inertness due to their mechanically entangled nature: scrambling of metal cations between the sites of pure Co(4) and Cd(4) cages to give a statistical mixture of Co(4), Co(3)Cd, Co(2)Cd(2), CoCd(3) and Cd(4) cages takes months in solution at room temperature.     

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.     

Osmabenzenes from the reactions of a dicationic osmabenzyne complex

Treatment of the osmabenzyne Os([triple bond]CC(SiMe(3))=C(Me)C(SiMe(3))=CH)Cl(2)(PPh(3))(2) (1) with 2,2'-bipyridine (bipy) and thallium triflate (TlOTf) produces the thermally stable dicationic osmabenzyne [Os([triple bond]CC(SiMe(3))=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)](OTf)(2) (2). The dicationic osmabenzyne 2 reacts with ROH (R = H, Me) to give osmabenzene complexes [Os(=C(OR)CH=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)]OTf, in which the metallabenzene ring deviates significantly from planarity. In contrast, reaction of the dicationic complex 2 with NaBH(4) produces a cyclopentadienyl complex, presumably through the osmabenzene intermediate [Os(=CHC(SiMe(3))=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)]OTf. The higher thermal stability of [Os(=C(OR)CH=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)]OTf relative to [Os(=CHC(SiMe(3))=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)]OTf can be related to the stabilization effect of the OR groups on the metallacycle. A theoretical study shows that conversion of the dicationic osmabenzyne complex [Os([triple bond]CC(SiMe(3))=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)](OTf)(2) to a carbene complex by reductive elimination is thermodynamically unfavorable. The theoretical study also suggests that the nonplanarity of the osmabenzenes [Os(=C(OR)CH=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)]OTf is mainly due to electronic reasons.     

Gas-phase coordination complexes of dipositive plutonyl, PuO2(2+): chemical diversity across the actinyl series

We report the first transmission of solvent-coordinated dipositive plutonyl ion, Pu(VI)O(2)(2+), from solution to the gas phase by electrospray ionization (ESI) of plutonyl solutions in water/acetone and water/acetonitrile. ESI of plutonyl and uranyl solutions produced the isolable gas-phase complexes, [An(VI)O(2)(CH(3)COCH(3))(4,5,6)](2+), [An(VI)O(2)(CH(3)COCH(3))(3)(H(2)O)](2+), and [An(VI)O(2)(CH(3)CN)(4)](2+); additional complex compositions were observed for uranyl. In accord with relative actinyl stabilities, U(VI)O(2)(2+) > Pu(VI)O(2)(2+) > Np(VI)O(2)(2+), the yields of plutonyl complexes were about an order of magnitude less than those of uranyl, and dipositive neptunyl complexes were not observed. Collision-induced dissociation (CID) of the dipositive coordination complexes in a quadrupole ion trap produced doubly- and singly-charged fragment ions; the fragmentation products reveal differences in underlying chemistries of plutonyl and uranyl, including the lower stability of Pu(VI) as compared with U(VI). Particularly notable was the distinctive CID fragment ion, [Pu(IV)(OH)(3)](+) from [Pu(VI)O(2)(CH(3)COCH(3))(6)](2+), where the plutonyl structure has been disrupted and the tetravalent plutonium hydroxide produced; this process was not observed for uranyl.     

Formation of μ-dinitrogen (salen)osmium complexes via ligand-induced N···N coupling of (salen)osmium(VI) nitrides

Treatment of [N(n)Bu(4)][Os(VI)(N)Cl(4)] with a stoichiometric amount of H(2)L (L = N,N'-bis(salicylidene)-o-cyclohexylenediamine dianion) in the presence of PF(6)(-) or ClO(4)(-) in MeOH affords [Os(VI)(N)(L)(OH(2))](PF(6)) 1a and [Os(VI)(N)(L)(CH(3)OH)](ClO(4)) 1b, respectively. The structure of 1b has been determined by X-ray crystallography and the Os≡N bond distance is 1.627(3) ?. In the presence of a N-donor heterocyclic ligand in CH(3)CN, 1a reacts at room temperature to afford the mixed-valence μ-N(2) (salen)osmium species [(X)(L)Os(III)-N≡N-Os(II)(L)(X)](PF(6)), 2-14 (X = py 2; 4-Mepy 3; 4-(t)Bupy 4; pz 5; 3-Mepz 6; 3,5-Me(2)pz 7; Im 8; 1-MeIm 9; 2-MeIm 10; 4-MeIm 11; 1,2-Me(2)Im 12; 2-Meozl 13; 4-MeTz 14). These complexes are formed by ligand-induced N···N coupling of two [Os(VI)≡N](+) to give initially [Os(III)-N(2)-Os(III)](2+), which is then reduced to give the more stable mixed-valence species [Os(III)-N(2)-Os(II)](+). Cyclic voltammograms (CVs) of 2-14 show two reversible couples, attributed to Os(III,III)/Os(III,II) and Os(III,II)/Os(II,II). The large comproportionation constants (K(com)) of (5.36-82.3) × 10(13) indicate charge delocalization in these complexes. The structures of 3 and 14 have been determined by X-ray crystallography, the salen ligands are in uncommon cis-β configuration. Oxidations of 4 and 14 by [Cp(2)Fe](PF(6)) afford the symmetrical species [(X)(L)Os(III)-N≡N-Os(III)(L)(X)](PF(6))(2) (X = 4-(t)Bupy 15; 4-MeTz 16). These are the first stable μ-N(2) diosmium(III,III) complexes that have been characterized by X-ray crystallography.     

Enhancement of metal-metal coupling at a considerable distance by using 4-pyridinealdazine as a bridging ligand in polynuclear complexes of rhenium and ruthenium

Novel polynuclear complexes of rhenium and ruthenium containing PCA (PCA = 4-pyridinecarboxaldehyde azine or 4-pyridinealdazine or 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene) as a bridging ligand have been synthesized as PF(6-) salts and characterized by spectroscopic, electrochemical, and photophysical techniques. The precursor mononuclear complex, of formula [Re(Me(2)bpy)(CO)(3)(PCA)](+) (Me(2)bpy = 4,4'-dimethyl-2,2'-bipyridine), does not emit at room temperature in CH(3)CN, and the transient spectrum found by flash photolysis at lambda(exc) = 355 nm can be assigned to a MLCT (metal-to-ligand charge transfer) excited state [(Me(2)bpy)(CO)(3)Re(II)(PCA(-))](+), with lambda(max) = 460 nm and tau < 10 ns. The spectral properties of the related complexes [[Re(Me(2)bpy)(CO)(3)}(2)(PCA)](2+), [Re(CO)(3)(PCA)(2)Cl], and [Re(CO)(3)Cl](3)(PCA)(4) confirm the existence of this low-energy MLCT state. The dinuclear complex, of formula [(Me(2)bpy)(CO)(3)Re(I)(PCA)Ru(II)(NH(3))(5)](3+), presents an intense absorption in the visible spectrum that can be assigned to a MLCT d(pi)(Ru) --> pi(PCA); in CH(3)CN, the value of lambda (max) = 560 nm is intermediate between those determined for [Ru(NH(3))(5)(PCA)](2+) (lambda(max) = 536 nm) and [(NH(3))(5)Ru(PCA)Ru(NH(3))(5)](4+) (lambda(max) = 574 nm), indicating a significant decrease in the energy of the pi-orbital of PCA. The mixed-valent species, of formula [(Me(2)bpy)(CO)(3)Re(I)(PCA)Ru(III)(NH(3))(5)](4+), was obtained in CH(3)CN solution, by bromine oxidation or by controlled-potential electrolysis at 0.8 V in a OTTLE cell of the [Re(I),Ru(II)] precursor; the band at lambda(max) = 560 nm disappears completely, and a new band appears at lambda(max) = 483 nm, assignable to a MMCT band (metal-to-metal charge transfer) Re(I) --> Ru(III). By using the Marcus-Hush formalism, both the electronic coupling (H(AB)) and the reorganization energy (lambda) for the metal-to-metal intramolecular electron transfer have been calculated. Despite the considerable distance between both metal centers (approximately 15.0 Angstroms), there is a moderate coupling that, together with the comproportionation constant of the mixed-valent species [(NH(3))(5)Ru(PCA)Ru(NH(3))(5)](5+) (K(c) approximately 10(2), in CH(3)CN), puts into evidence an unusual enhancement of the metal-metal coupling in the bridged PCA complexes. This effect can be accounted for by the large extent of "metal-ligand interface", as shown by DFT calculations on free PCA. Moreover, lambda is lower than the driving force -DeltaG degrees for the recombination charge reaction [Re(II),Ru(II)] --> [Re(I),Ru(III)] that follows light excitation of the mixed-valent species. It is then predicted that this reverse reaction falls in the Marcus inverted region, making the heterodinuclear [Re(I),Ru(III)] complex a promising model for controlling the efficiency of charge-separation processes.