Titanium and niobium imido complexes stabilized by heteroscorpionate ligands

The reaction of [Ti(NR)Cl(2)(py)(3)](R = (t)Bu, p-tolyl, 2,6-C(6)H(3)(i)Pr(2)) with [{Li(bdmpza)(H(2)O)}(4)][bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate] and [{Li(bdmpzdta)(H(2)O)}(4)][bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate] affords the corresponding complexes [Ti(NR)Cl(kappa(3)-bdmpzx)(py)](x = a, R = (t)Bu 1, p-tolyl 2, 2,6-C(6)H(3)(i)Pr(2) 3; x = dta, R =(t)Bu 4, p-tolyl , 2,6-C(6)H(3)(i)Pr(2) 6), which are the first examples of imido Group 4 complexes stabilized by heteroscorpionate ligands. The solid-state X-ray crystal structure of 1 has been determined. The titanium centre is six-coordinate with three fac-sites occupied by the heteroscorpionate ligand and the remainder of the coordination sphere being completed by chloride, imido and pyridine ligands. The complexes are 1-6 fluxional at room temperature. The pyridine ortho- and meta-proton resonances show evidence of dynamic behaviour for this ligand and variable-temperature NMR studies were carried out in order to study their dynamic behaviour in solution. The complexes [Nb(NR)Cl(3)(py)(2)](R = (t)Bu, p-tolyl, 2,6-C(6)H(3)(i)Pr(2)) reacted with [{Li(bdmpza)(H(2)O)}(4)] and (Hbdmpze)[bdmpze = 2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide], the latter with prior addition of (n)BuLi, to give the complexes [Nb(NR)Cl(2)(kappa(3)-bdmpzx)](x = a, R =(t)Bu 7, p-tolyl 8, 2,6-C(6)H(3)(i)Pr(2) 9; x = e, R = (t)Bu 10, p-tolyl 11, 2,6-C(6)H(3)(i)Pr(2)) 12 and these are the first examples of imido Group 5 complexes with heteroscorpionate ligands. The structures of these complexes have been determined by spectroscopic methods.     

Titanium isopropoxide complexes of a series of sterically demanding aryloxo based [N2O2]2- ligands as precatalysts for ethylene polymerization

Several titanium isopropoxide complexes [N,N'-bis(2-oxo-3-R(1)-5-R(2)-phenylmethyl)-N,N'-bis(methylene-p-R(3)-C(6)H(4))-ethylenediamine]Ti(O(i)Pr)(2) [R(1) = t-Bu, R(2) = Me, R(3) = H (1b); R(1) = R(2) = t-Bu, R(3) = H, (2b); R(1) = R(2) = Cl, R(3) = H, (3b), R(1) = t-Bu, R(2) = Me, R(3) = Cl (4b); R(1) = R(2) = t-Bu, R(3) = Cl, (5b); R(1) = R(2) = R(3) = Cl, (6b)] supported over sterically demanding aryloxy based [N(2)O(2)]H(2) ligands have been designed as precatalysts for the ethylene polymerization. Specifically, the 1b-6b complexes, when treated with methylaluminoxane (MAO) under 88 ± 0.5 psi of ethylene at 30 °C for 3 h, produced polyethylene polymers of high molecular weight (M(w) = ca. 7.2-8.3 × 10(5) g mol(-1)) having broad molecular weight distribution (PDI = ca. 13.1-14.6). The 1b-6b complexes were conveniently synthesized from the direct reaction of the [N(2)O(2)]H(2) ligands, 1a-6a, with Ti(O(i)Pr)(4) in 69-86% yield.     

New titanium complexes with symmetric or asymmetric cis-9,10-dihydrophenanthrenediamide ligands formed through sequential intramolecular C-C bond-forming reactions

A series of new titanium(IV) complexes with symmetric or asymmetric cis-9,10-dihydrophenanthrenediamide ligands, cis-9,10-PhenH(2)(NR)(2)Ti(O(i)Pr)(2) [PhenH(2) = 9,10-dihydrophenanthrene, R = 2,6-(i)Pr(2)C(6)H(3) (2a), 2,6-Et(2)C(6)H(3) (2b), 2,6-Me(2)C(6)H(3) (2c)], cis-9,10-PhenH(2)(NR(1))(NR(2))Ti(O(i)Pr)(2) [R(1) = 2,6-(i)Pr(2)C(6)H(3), R(2) = 2,6-Et(2)C(6)H(3) (2d); R(1) = 2,6-(i)Pr(2)C(6)H(3), R(2) = 2,6-Me(2)C(6)H(3) (2e)], and [cis-9,10-PhenH(2)(NR(1))(2)][o-C(6)H(4)(CH=NR(2))]TiO(i)Pr [R(1) = 2,6-(i)Pr(2)C(6)H(3), R(2) = 2,6-Et(2)C(6)H(3) (3a); R(1) = 2,6-(i)Pr(2)C(6)H(3), 2,6-Me(2)C(6)H(3) (3b)], have been synthesized from the reactions of TiCl(2)(O(i)Pr)(2) with o-C(6)H(4)(CH=NR)Li [R = 2,6-(i)Pr(2)C(6)H(3), 2,6-Et(2)C(6)H(3), 2,6-Me(2)C(6)H(3)]. The symmetric complexes 2a-2c were obtained from the reactions of TiCl(2)(O(i)Pr)(2) with 2 equiv of the corresponding o-C(6)H(4)(CH=NR)Li followed by intramolecular C-C bond-forming reductive elimination and oxidative coupling processes, while the asymmetric complexes 2d-2e were formed from the reaction of TiCl(2)(O(i)Pr)(2) with two different types of o-C(6)H(4)(CH=NR)Li sequentially. The complexes 3a and 3b were also isolated from the reactions for complexes 2d and 2e. All complexes were characterized by (1)H and (13)C NMR spectroscopy, and the molecular structures of 2a, 2b, 2e, and 3a were determined by X-ray crystallography.     

Syntheses, solid-state structures, and solution studies by VT 31P NMR of [Zn[Se2P(OEt)2]2] infinity and [Zn2[Se2P(OiPr)2]4

Complexes [Zn[Se(2)P(OEt)(2)](2)]( infinity ) (1) and [Zn(2)[Se(2)P(O(i)Pr)(2)](4)] (2) are prepared from the reaction of Zn(ClO(4))(2).6H(2)O and (NH(4))[Se(2)P(OR)(2)] (R = Et and (i)Pr) in a molar ratio of 1:2 in deoxygenated water at room temperature. Positive FAB mass spectra show m/z peaks at 968.8 (Zn(2)L(3)(+)) and 344.8 (ZnL(+)) for 1 and m/z at 1052.8 (Zn(2)L(3)(+)) for 2. (1)H NMR spectra exhibit chemical shifts at delta 1.43 and 4.23 ppm for 1 and 1.41 and 4.87 ppm for 2 due to Et and (i)Pr group of dsep ligands. While the solid-state structure of compound 1 is a one-dimensional polymer via symmetrically bridging dsep ligands, complex 2 in the crystalline state exists as a dimer. In both 1 and 2, zinc atoms are connected by two bridging dsep ligands with an additional chelating ligand at each zinc atom. The dsep ligands exhibit bimetallic biconnective (micro(2), eta(2)) and monometallic biconnective (eta(2)) coordination patterns. Thus, each zinc atom is coordinated by four selenium atoms from two bridging and one chelating dsep ligands and the geometry around zinc is distorted tetrahedral. The Zn-Se distances range between 2.422 and 2.524 A. From variable-temperature (31)P NMR studies it has been found that monomer and dimer of the complex are in equilibrium in solution via exchange of bridging and chelating ligands. However, at temperature above 40 degrees C the complex exists as a monomer and shows a very sharp peak while with lowering of the temperature the percentage of dimer increases gradually at the expense of monomer. Below -90 degrees C the complex exists as a dimer and two peaks are observed with equal intensities which are due to bridging and chelating ligands. (77)Se NMR spectra of both complexes at -30 degrees C exhibit three doublets due to the presence of monomer and dimer in solution.     

Robust chiral zirconium alkoxide initiators for the room-temperature stereoselective ring-opening polymerisation of rac-lactide

Chiral Schiff bases (1H to 4H) and a series of their Group 4 metal alkoxide complexes [(R-1)2Ti(O(i)Pr)2, (R-2)2Ti(O(i)Pr)2, (R-1)(2)Zr(O(i)Pr)2, (R-2)2Zr(O(i)Pr)2, (R-3)2Zr(O(i)Pr)2, (R-4)2Zr(O(i)Pr)2, (S-1)2Zr(O(i)Pr)2 and (rac-1)2Zr(O(i)Pr)2] have been prepared and characterised by 1H, and 13C NMR spectroscopy. In solution, both Lambda and Delta isomers were observed, suggesting a low degree of chiral induction from the ligand. One ligand (R-4H) and three complexes [Delta-(R,R-2)2Ti(O(i)Pr)2, Lambda-(R,R-1)2Zr(O(i)Pr)2 and Delta-(R,R-3)2Zr(O(i)Pr)2] have also been characterised by single crystal X-ray diffraction. All complexes were found to have a pseudo-octahedral alpha-cis geometry. The complexes were tested as initiators for the ring-opening polymerisation of rac-lactide in solution and in the melt. The titanium complexes are inactive in solution and afford atactic polylactide in the melt. Zr(iv) complexes afford heterotactically enriched polylactide both in toluene solution (at 20 degrees C and 80 degrees C) and in the melt. Polymerisations were generally found to be well-controlled, giving predictable molecular weights and low molecular weight distributions. Ligand variation (substituents and/or chirality) has little effect on either the activity or selectivity of initiators. Zirconium initiators were found to be unusually robust as they were able to maintain well-controlled polymerisation following addition of water to reactions in solution and when using unpurified monomer for reactions in the melt.     

Trans --> cis isomerization of trans-[(dppm)2Ru(H)(L)][BF4] (L = P(OR)3) complexes: preparation of cis-[(dppm)2Ru(eta2-H2)(L)][BF4]2

A series of new dicationic dihydrogen complexes of ruthenium of the type cis-[(dppm)(2)Ru(eta(2)-H(2))(L)][BF(4)](2) (dppm = Ph(2)PCH(2)PPh(2); L = P(OMe)(3), P(OEt)(3), PF(O(i)Pr)(2)) have been prepared by protonating the precursor hydride complexes cis-[(dppm)(2)Ru(H)(L)][BF(4)] (L = P(OMe)(3), P(OEt)(3), P(O(i)Pr)(3)) using HBF(4).Et(2)O. The cis-[(dppm)(2)Ru(H)(L)][BF(4)] complexes were obtained from the trans hydrides via an isomerization reaction that is acid-accelerated. This isomerization reaction gives mixtures of cis and trans hydride complexes, the ratios of which depend on the cone angles of the phosphite ligands: the greater the cone angle, the greater is the amount of the cis isomer. The eta(2)-H(2) ligand in the dihydrogen complexes is labile, and the loss of H(2) was found to be reversible. The protonation reactions of the starting hydrides with trans PMe(3) or PMe(2)Ph yield mixtures of the cis and the trans hydride complexes; further addition of the acid, however, give trans-[(dppm)(2)Ru(BF(4))Cl]. The roles of the bite angles of the dppm ligand as well as the steric and the electronic properties of the monodentate phosphorus ligands in this series of complexes are discussed. X-ray crystal structures of trans-[(dppm)(2)Ru(H)(P(OMe)(3))][BF(4)], cis-[(dppm)(2)Ru(H)(P(OMe)(3))][BF(4)], and cis-[(dppm)(2)Ru(H)(P(O(i)Pr)(3))][BF(4)] complexes have been determined.     

Heterobimetallic Bi(III)-Ti(IV) coordination complexes: synthesis and solid-state structures of BiTi4(sal)6(mu-OiPr)3(OiPr)4, and the cyclic isomers Bi4Ti4(sal)10(mu-OiPr)4(OiPr)4 and Bi8Ti8(sal)20(mu-OiPr)8(OiPr)8

The reaction of a 1:2 mixture of bismuth(III) salicylate with titanium(IV) isopropoxide in refluxing toluene has been investigated and found to proceed with ligand exchange to produce the new heterobimetallic complexes BiTi(4)(sal)(6)(mu-O(i)Pr)(3)(O(i)Pr)(4) (1), Bi(4)Ti(4)(sal)(10)(mu-O(i)Pr)(4)(O(i)Pr)(4) (2), and Bi(8)Ti(8)(sal)(20)(mu-O(i)Pr)(8)(O(i)Pr)(8) (3). Complex 1 is the major product, while 2 and 3 were identified as minor products from the reaction. Compound 1 is produced pure and in high yield by employing stoichiometric amounts of reagents; its crystal structure consists of a [Ti(4)(sal)(6)(O(i)Pr)(7)](3)(-) ion capped by a Bi(3+) ion. Complexes 2 and 3 exhibit cyclic ring structures of bismuth and titanium atoms showing crystallographically imposed inversion symmetry. Both structures occlude large quantities of lattice solvent. The compositional and structural parameters from the single crystal studies indicate that complexes 2 and 3 may represent sequential steps in a ligand exchange process between the two metal species, while the reactivity patterns that were observed provide clues about the solution state structure of bismuth(III) salicylate itself. The 2D COSY (1)H NMR spectrum of 1 indicates retention of the asymmetric structure in solution as evidenced by the presence of 14 diastereotopic isopropoxide methyl resonances.     

Interplay between lead carboxylate and Ti or Zr isopropoxides in solution routes to perovskites: synthesis, molecular structures and reactivity of single source non-oxo Pb-Zr and Pb-Ti carboxylatoalkoxides supported by 2-ethylhexanoate ligands

The reactions between Ti(O(i)Pr)(4) and Zr(2)(O(i)Pr)(8)(HO(i)Pr)(2), respectively, and lead 2-ethylhexanoate Pb(O(2)CC(7)H(15))(2) have been investigated at rt and by heating. The initial mixed-metal species, characterized by single-crystal X-Ray diffraction, were adducts namely Pb(4)Zr(4)(mu-O(2)CR')(8)(mu-OR)(6)(mu(3)-OR)(2)(OR)(8)(OHR)(2) and Pb(2)Ti(4)(mu-O(2)CR')(4)(mu-OR)(6)(mu(3)-OR)(2)(OR)(8) (R' = CHCH(Et)C(2)H(4)Me, R = (i)Pr) independently of the stoichiometry used. They are the first Pb-Ti and Pb-Zr non-oxo carboxylatoalkoxides reported. is also the first Pb-Zr species based on an alkoxide-carboxylate ligand set matching the PbZrO(3) stoichiometry. Both structures are centrosymmetric with six-coordinate transition metals, as required for the perovskite, and are based on triangular M(2)Pb cores (M = Zr, Ti). The lead centers display quite high coordination numbers, six and seven. The thermal and hydrolytic condensation reactions of and were investigated. Heat treatment of and elimination of the volatiles under vacuum afforded Pb(2)Ti(3)(mu(4)-O)(mu(3)-O)(mu-O(2)CC(7)H(15))(2)(mu-O(i)Pr)(6)(O(i)Pr)(4) resulting from extrusion of Ti(O(i)Pr)(4) and scrambling of carboxylate ligands. Characterization of the various compounds was achieved by elemental analysis, FT-IR, (1)H and (207)Pb NMR.     

The role of neutral coligands on the stabilization of mono-Tp(i)Pr2 U(III) complexes

The reaction of [UI(3)(THF)(4)] with 1 equiv of KTp()i(Pr)()2 in toluene in the presence of several neutral coligands allowed the synthesis of a novel family of mono-Tp()i(Pr)()2 complexes, [UI(2)Tp()i(Pr)()2(L)(x)()] [L = OPPh(3), x = 1 (3); L = C(5)H(5)N, x = 2 (4); L = Hpz()t(Bu,Me), x = 2 (5); and L = bipy, x = 1 (6)]. The adduct with THF, [UI(2)Tp()i(Pr)()2(THF)(2)(-)(3)] (1), could also be isolated by reacting [UI(3)(THF)(4)] with 1 equiv of KTp()i(Pr)()2 in tetrahydrofuran. However, complex 1 is not a good starting material to enter into the mono-Tp()i(Pr)()2 U(III) complexes as it decomposes in solution, leading to mixtures of U(III) species coordinated with Hpz()i(Pr)()2. The solid-state structures of 3, 4, and 6 were determined by single-crystal X-ray diffraction and revealed that this family of mono-Tp()i(Pr)()2 complexes can be six- (3) or seven-coordinated (4 and 6), depending on the nature of the neutral coligand. Complex 3 displays distorted octahedral coordination geometry, while 4 and 6 display distorted pentagonal bipyramid and capped octahedral geometries, respectively. Complexes 3 and 6 are static in solution, and the patterns of the (1)H NMR spectra are consistent with the C(s)() symmetry found in the solid state. The other complexes (1, 4, and 5) are fluxional, but the dynamic processes involved can be slowed by decreasing the temperature.     

Ruthenium agostic (phosphinoaryl)borane complexes: multinuclear solid-state and solution NMR, X-ray, and DFT studies

The reactivity of the (o-phosphinophenyl)(amino)borane compound HB(N(i)Pr(2))C(6)H(4)(o-PPh(2)) prepared from Li(C(6)H(4))PPh(2) and HBCl(N(i)Pr(2)) toward the bis(dihydrogen) complex RuH(2)(H(2))(2)(PCy(3))(2) (1) was studied by a combination of DFT, X-ray, and multinuclear NMR techniques including solid-state NMR, a technique rarely employed in organometallic chemistry. The study showed that the complex RuH(2){HB(N(i)Pr(2))C(6)H(4)(o-PPh(2))}(PCy(3))(2) (3), isolated in excellent yield as yellow crystals and characterized by X-ray diffraction, led in solution to PCy(3) dissociation and formation of an unsaturated 16-electron complex RuH(2){HB(N(i)Pr(2))C(6)H(4)(o-PPh(2))}(PCy(3)) (4), with a hydride trans to a vacant site. In both cases, the (phosphinoaryl)(amino)borane acts as a bifunctional ligand through the phosphine moiety and a Ru-H-B interaction, thus featuring an agostic interaction.     

Molybdenum(VI) dioxo and oxo-imido complexes of fluorinated β-ketiminato ligands and their use in OAT reactions

Substitution of a methyl by a trifluoromethyl moiety in well-known β-ketimines afforded the ligands (Ar)NC(Me)CH(2)CO(CF(3)) (HL(H), Ar = C(6)H(5); HL(Me), A r= 2,6-Me(2)C(6)H(3); HL(iPr), Ar = 2,6-(i)Pr(2)C(6)H(3)). Subsequent complexation to the [MoO(2)](2+) core leads to the formation of novel complexes of general formula [MoO(2)(L(R))(2)] (R = H, 1; R = Me, 2; R = iPr, 3). For reasons of comparison the oxo-imido complex [MoO(N(t)Bu)(L(Me))(2)] (4) has also been synthesized. Complexes 1-4 were investigated in oxygen atom transfer (OAT) reactions using the substrate trimethylphosphine. The respective products after OAT, the reduced Mo(IV) complexes [MoO(PMe(3))(L(R))(2)] (R = H, 5; R = Me, 6; R = iPr, 7) and [Mo(N(t)Bu)(PMe(3))(L(Me))(2)] (8), were isolated. All complexes have been characterized by NMR spectroscopy, and 1-4 also by cyclic voltammetry. A positive shift of the Mo(VI)-Mo(V) reduction wave upon fluorination was observed. Furthermore, molecular structures of complexes 2, 4, 5, and 8 have been determined via single crystal X-ray diffraction analysis. Complex 8 represents a rare example of a Mo(IV) phosphino-imido complex. Kinetic measurements by UV-vis spectroscopy of the OAT reactions from complexes 1-4 to PMe(3) showed them to be more efficient than previously reported nonfluorinated ones, with ligand L' = (Ar)NC(Me)CH(2)CO(CH(3)) [MoO(2)(L')(2)] (9) and [MoO(N(t)Bu)(L')(2)] (10), respectively. Thermodynamic activation parameters ΔH(?) and ΔS(?) of the OAT reactions for complexes 2 and 4 have been determined. The activation enthalpy for the reaction employing 2 is significantly smaller (12.3 kJ/mol) compared to the reaction with the nonfluorinated complex 9 (60.8 kJ/mol). The change of the entropic term ΔS(?) is small. The reaction of the oxo-imido complex 4 to 8 revealed a significant electron-donating contribution of the imido substituent.     

Preparation of Ti(IV) fluoride N-heterocyclic carbene complexes

1,3,4,5-Tetramethylimidazol-2-ylidene (L(Me)) and 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (L(iPr )) readily form complexes of trans-TiF4(L(Me))2 (1) and of trans-TiF4(L(iPr))2 (4) with TiF4 in THF, respectively. Complex 1 has been used as a precursor for preparing the Ti(IV) fluoride carbene complexes [{TiF2(L(Me))(NEt 2)}2(mu-F)2] (2) and (TiF4(L(Me))2)(NacNacLi) (3) (NacNac = HC(CMeN(2,6- iPr2C6H3))2). Complex 2 was prepared from the reaction of 1-3 equiv of 1 and 1 equiv of Ti(NEt2)4 or by reacting TiF4 with Ti(NEt2)4 and L(Me) in toluene. Complex 3 has been prepared from 1 and NacNacLi in toluene. Reaction of 1 and AlMe3 in toluene results in ligand transfer and formation of AlMe3(L(Me)). Complex 4 is unstable in solution at room temperature and degrades with formation of [HL(iPr)][TiF5(L(iPr))] (5). Complexes 1, 2.2CH2Cl2, 4, and 5 were characterized by single crystal X-ray structural analysis, elemental analysis, IR and NMR spectroscopy, and mass spectrometry. The relative basicities of L(Me), L (iPr), and the donor ligands THF, pyridine, DMSO, and H2O as well as [Cl](-) and [F](-) toward the Ti(IV) pentafluoride anion were established by NMR and confirmed by density functional theory (DFT) calculations. L(Me) and L(iPr ) are more basic than the mentioned molecular donors and more basic than chloride, however less basic than fluoride.     

Structural diversity in solvated lithium aryloxides. Syntheses, characterization, and structures of [Li(OAr)(THF)x]n and [Li(OAr)(py)x]2 complexes where OAr = OC6H5, OC6H4(2-Me), OC6H3(2,6-(Me))2, OC6H4(2-Pr(i)), OC6H3(2,6-Pr(i)))2, OC6h4(2-Bu(t)), OC6H3(2,6-Bu(t)))2

A series of sterically varied aryl alcohols H-OAr [OAr = OC6H5 (OPh), OC6H4(2-Me) (oMP), OC6H3(2,6-(Me))2 (DMP), OC6H4(2-Pr(i)) (oPP), OC6H3(2,6-(Pr(i)))2 (DIP), OC6H4(2-Bu(t)) (oBP), OC6H3(2,6-(Bu(t)))2 (DBP); Me = CH3, Pr(i) = CHMe2, and Bu(t) = CMe3] were reacted with LiN(SiMe3)2 in a Lewis basic solvent [tetrahydrofuran (THF) or pyridine (py)] to generate the appropriate "Li(OAr)(solv)x". In the presence of THF, the OPh derivative was previously identified as the hexagonal prismatic complex [Li(OPh)(THF)]6; however, the structure isolated from the above route proved to be the tetranuclear species [Li(OPh)(THF)]4 (1). The other "Li(OAr)(THF)x" products isolated were characterized by single-crystal X-ray diffraction as [Li(OAr)(THF)]4 [OAr = oMP (2), DMP (3), oPP (4)], [Li(DIP)(THF)]3 (5), [Li(oBP)(THF)2]2, (6), and [Li(DBP)(THF)]2, (7). The tetranuclear species (1-4) consist of symmetric cubes of alternating tetrahedral Li and pyramidal O atoms, with terminal THF solvent molecules bound to each metal center. The trinuclear species 5 consists of a six-membered ring of alternating trigonal planar Li and bridging O atoms, with one THF solvent molecule bound to each metal center. Compound 6 possesses two Li atoms that adopt tetrahedral geometries involving two bridging oBP and two terminal THF ligands. The structure of 7 was identical to the previously reported [Li(DBP)(THF)]2 species, but different unit cell parameters were observed. Compound 7 varies from 6 in that only one solvent molecule is bound to each Li metal center of 7 because of the steric bulk of the DBP ligand. In contrast to the structurally diverse THF adducts, when py was used as the solvent, the appropriate "Li(OAr)(py)x" complexes were isolated as [Li(OAr)(py)2]2 (OAr = OPh (8), oMP (9), DMP (10), oPP (11), DIP (12), oBP (13)) and [Li(DBP)(py)]2 (14). Compounds 8-13 adopt a dinuclear, edge-shared tetrahedral complex. For 14, because of the steric crowding of the DBP ligand, only one py is coordinated, yielding a dinuclear fused trigonal planar arrangement. Two additional structure types were also characterized for the DIP ligand: [Li(DIP)(H-DIP)(py)]2 (12b) and [Li2(DIP)2(py)3] (12c). Multinuclear (6,7Li and 13C) solid-state MAS NMR spectroscopic studies indicate that the bulk powder possesses several Li environments for "transitional ligands" of the THF complexes; however, the py adducts possess only one Li environment, which is consistent with the solid-state structures. Solution NMR studies indicate that "transitional" compounds of the THF precursors display multiple species in solution whereas the py adducts display only one lithium environment.     

Cadmium amido alkoxide and alkoxide precursors for the synthesis of nanocrystalline CdE (E = S, Se, Te)

The synthesis and characterization of a family of alternative precursors for the production of CdE nanoparticles (E = S, Se, and Te) is reported. The reaction of Cd(NR2)2 where NR2 = N(SiMe3)2 with n HOR led to the isolation of the following: n = 1 [Cd(mu-OCH2CMe3)(NR2)(py)]2 (1, py = pyridine), Cd[(mu-OC6H3(Me)(2)-2,6)2Cd(NR2)(py)]2 (2), [Cd(mu-OC6H3(CHMe2)(2)-2,6)(NR2)(py)]2 (3), [Cd(mu-OC6H3(CMe3)(2)-2,6)(NR2)(py)]2 (4), [Cd(mu-OC6H2(NH2)(3)-2,4,6)(NR2)(py)]2 (5), and n = 2 [Cd(mu-OC6H3(Me)(2)-2,6)(OC6H3(Me)(2)-2,6)(py)2]2 (6), and [Cd(mu-OC6H3(CMe3)(2)-2,6)(OC6H3(CMe3)(2)-2,6)(THF)]2 (7). For all but 2, the X-ray crystal structures were solved as discrete dinuclear units bridged by alkoxide ligands and either terminal -NR2 or -OR ligands depending on the stoichiometry of the initial reaction. For 2, a trinuclear species was isolated using four mu-OR and two terminal -NR2 ligands. The coordination of the Cd metal center varied from 3 to 5 where the higher coordination numbers were achieved by binding Lewis basic solvents for the less sterically demanding ligands. These complexes were further characterized in solution by 1H, 13C, and 113Cd NMR along with solid-state 113Cd NMR spectroscopy. The utility of these complexes as "alternative precursors" for the controlled preparation of nanocrystalline CdS, CdSe, and CdTe was explored. To synthesize CdE nanocrystals, select species from this family of compounds were individually heated in a coordinating solvent (trioctylphosphine oxide) and then injected with the appropriate chalcogenide stock solution. Transmission electron spectroscopy and UV-vis spectroscopy were used to characterize the resultant particles.     

Phosphato, chromato, and perrhenato complexes of titanium(IV) and zirconium(IV) containing Kläui's tripodal ligand

Treatment of titanyl sulfate in dilute sulfuric acid with 1 equiv of NaL(OEt) (L(OEt)(-) = [(eta(5)-C(5)H(5))Co{P(O)(OEt)(2)](3)](-)) in the presence of Na(3)PO(4) and Na(4)P(2)O(7) led to isolation of [(L(OEt)Ti)(3)(mu-O)(3)(mu(3-)PO(4))] (1) and [(L(OEt)Ti)(2)(mu-O)(mu-P(2)O(7))] (2), respectively. The structure of 1 consists of a Ti(3)O(3) core capped by a mu(3)-phosphato group. In 2, the [P(2)O(7)](4-) ligands binds to the two Ti's in a mu:eta(2),eta(2) fashion. Treatment of titanyl sulfate in dilute sulfuric acid with NaL(OEt) and 1.5 equiv of Na(2)Cr(2)O(7) gave [(L(OEt)Ti)(2)(mu-CrO(4))(3)] (3) that contains two L(OEt)Ti(3+) fragments bridged by three mu-CrO(4)(2-)-O,O' ligands. Complex 3 can act as a 6-electron oxidant and oxidize benzyl alcohol to give ca. 3 equiv of benzaldehyde. Treatment of [L(OEt)Ti(OTf)(3)] (OTf(-) = triflate) with [n-Bu(4)N][ReO(4)] afforded [[L(OEt)Ti(ReO(4))(2)](2)(mu-O)] (4). Treatment of [L(OEt)MF(3)] (M = Ti and Zr) with 3 equiv of [ReO(3)(OSiMe(3))] afforded [L(OEt)Ti(ReO(4))(3)] (5) and [L(OEt)Zr(ReO(4))(3)(H(2)O)] (6), respectively. Treatment of [L(OEt)MF(3)] with 2 equiv of [ReO(3)(OSiMe(3))] afforded [L(OEt)Ti(ReO(4))(2)F] (7) and [[L(OEt)Zr(ReO(4))(2)](2)(mu-F)(2)] (8), respectively, which reacted with Me(3)SiOTf to give [L(OEt)M(ReO(4))(2)(OTf)] (M = Ti (9), Zr (10)). Hydrolysis of [L(OEt)Zr(OTf)(3)] (11) with Na(2)WO(4).xH(2)O and wet CH(2)Cl(2) afforded the hydroxo-bridged complexes [[L(OEt)Zr(H(2)O)](3)(mu-OH)(3)(mu(3)-O)][OTf](4) (12) and [[L(OEt)Zr(H(2)O)(2)](2)(mu-OH)(2)][OTf](4) (13), respectively. The solid-state structures of 1-3, 6, and 11-13 have been established by X-ray crystallography. The L(OEt)Ti(IV) complexes can catalyze oxidation of methyl p-tolyl sulfide with tert-butyl hydroperoxide. The bimetallic Ti/ Re complexes 5 and 9 were found to be more active catalysts for the sulfide oxidation than other Ti(IV) complexes presumably because Re alkylperoxo species are involved as the reactive intermediates.     

High hydride count rhodium octahedra, [Rh6(PR3)6H12][BArF4]2: synthesis, structures, and reversible hydrogen uptake under mild conditions

A new class of transition metal cluster is described, [Rh(6)(PR(3))(6)H(12)][BAr(F)(4)](2) (R = (i)Pr (1a), Cy (2a); BAr(F)(4) = [B{C(6)H(3)(CF(3))(2)}(4)](-)). These clusters are unique in that they have structures exactly like those of early transition metal clusters with edge-bridging pi-donor ligands rather than the structures expected for late transition metal clusters with pi-acceptor ligands. The solid-state structures of 1a and 2a have been determined, and the 12 hydride ligands bridge each Rh-Rh edge of a regular octahedron. Pulsed gradient spin-echo NMR experiments show that the clusters remain intact in solution, having calculated hydrodynamic radii of 9.5(3) A for 1a and 10.7(2) A for 2a, and the formulation of 1a and 2a was unambiguously confirmed by ESI mass spectrometry. Both 1a and 2a take up two molecules of H(2) to afford the cluster species [Rh(6)(P(i)Pr(3))(6)H(16)][BAr(F)(4)](2) (1b) and [Rh(6)(PCy(3))(6)H(16)][BAr(F)(4)](2) (2b), respectively, as characterized by NMR spectroscopy, ESI-MS, and, for 2b, X-ray crystallography using the [1-H-CB(11)Me(11)](-) salt. The hydride ligands were not located by X-ray crystallography, but (1)H NMR spectroscopy showed a 15:1 ratio of hydride ligands, suggesting an interstitial hydride ligand. Addition of H(2) is reversible: placing 1b and 2b under vacuum regenerates 1a and 2a. DFT calculations on [Rh(6)(PH(3))(6)H(x)()](2+) (x = 12, 16) support the structural assignments and also show a molecular orbital structure that has 20 orbitals involved with cluster bonding. Cluster formation has been monitored by (31)P{(1)H} and (1)H NMR spectroscopy, and mechanisms involving heterolytic H(2) cleavage and elimination of [HP(i)Pr(3)](+) or the formation of trimetallic intermediates are discussed.     

Modeling dioxygen-activating centers in non-heme diiron enzymes: carboxylate shifts in diiron(II) complexes supported by sterically hindered carboxylate ligands

General synthetic routes are described for a series of diiron(II) complexes supported by sterically demanding carboxylate ligands 2,6-di(p-tolyl)benzoate (Ar(Tol)CO(2)(-)) and 2,6-di(4-fluorophenyl)benzoate (Ar(4-FPh)CO(2)(-)). The interlocking nature of the m-terphenyl units in self-assembled [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (L = C(5)H(5)N (4); 1-MeIm (5)) promotes the formation of coordination geometries analogous to those of the non-heme diiron cores in the enzymes RNR-R2 and Delta 9D. Magnetic susceptibility and M?ssbauer studies of 4 and 5 revealed properties consistent with weak antiferromagnetic coupling between the high-spin iron(II) centers. Structural studies of several derivatives obtained by ligand substitution reactions demonstrated that the [Fe(2)(O(2)CAr')(4)L(2)] (Ar' = Ar(Tol); Ar(4-FPh)) module is geometrically flexible. Details of ligand migration within the tetracarboxylate diiron core, facilitated by carboxylate shifts, were probed by solution variable-temperature (19)F NMR spectroscopic studies of [Fe(2)(mu-O(2)CAr(4-FPh))(2)-(O(2)CAr(4-FPh))(2)(THF)(2)] (8) and [Fe(2)(mu-O(2)CAr(4-FPh))(4)(4-(t)BuC(5)H(4)N)(2)] (12). Dynamic motion in the primary coordination sphere controls the positioning of open sites and regulates the access of exogenous ligands, processes that also occur in non-heme diiron enzymes during catalysis.     

Cobalt(III) carbonate and bicarbonate chelate complexes of tripodal tetraamine ligands containing pyridyl donors: the steric basis for the stability of chelated bicarbonate complexes

The synthesis and characterization (X-ray crystallography, UV/vis spectroscopy, electrochemistry, ESI-MS, and (1)H, (13)C, and (59)Co NMR) of the complexes [Co(L)(O(2)CO)]ClO(4)xH(2)O (L = tpa (tpa = tris(2-pyridylmethyl)amine) (x = 1), pmea (pmea = bis((2-pyridyl)methyl)-2-((2-pyridyl)ethyl)amine) (x = 0), pmap (pmap = bis(2-(2-pyridyl)ethyl)(2-pyridylmethyl)amine) (x = 0), tepa (tepa = tris(2-(2-pyridyl)ethyl)amine) (x = 0)) which contain tripodal tetradentate pyridyl ligands and chelated carbonate ligands are reported. The complexes display different colors in both the solid state and solution, which can be rationalized in terms of the different ligand fields exerted by the tripodal ligands. Electrochemical data show that [Co(tepa)(O(2)CO)](+) is the easiest of the four complexes to reduce, and the variation in E(red.) values across the series of complexes can also be explained in terms of the different ligand fields exerted by the tripodal ligands, as can the (59)Co NMR data which show a chemical shift range of over 2000 ppm for the four complexes. [Co(pmea)(O(2)CO)](+) is fluxional in aqueous solution, and VT NMR spectroscopy ((1)H and (13)C) in DMF-d(7) (DMF = dimethylformamide) over the temperature range -25.0 to 75.0 degrees C are consistent with inversion of the unique six-membered chelate ring. This process shows a substantial activation barrier (DeltaG(#) = 58 kJ mol(-1)). The crystal structures of [Co(tpa)(O(2)CO)]ClO(4)xH(2)O, [Co(pmea)(O(2)CO)]ClO(4).3H(2)O, [Co(pmap)(O(2)CO)]ClO(4), and [Co(tepa)(O(2)CO)]ClO(4) are reported, and the complexes containing the asymmetric tripodal ligands pmea and pmap both crystallize as the 6-isomer. The carbonate complexes all show remarkable stability in 6 M HCl solution, with [Co(pmap)(O(2)CO)](+) showing essentially no change in its UV/vis spectrum over 4 h in this medium. The chelated bicarbonate complexes [Co(pmea)(O(2)COH)]ZnCl(4), [Co(pmap)(O(2)COH)][Co(pmap)(O(2)CO)](ClO(4))(3), [Co(pmap)(O(2)COH)]ZnCl(4)xH(2)O, and [Co(pmap(O(2)COH)]ZnBr(4)x2H(2)O can be isolated from acidic aqueous solution, and the crystal structure of [Co(pmap)(O(2)COH)]ZnCl(4)x3H(2)O is reported. The stability of the carbonate complexes in acid is explained by analysis of the crystallographic data for these, and other slow to hydrolyze chelated carbonate complexes, which show that the endo (coordinated) oxygen atoms are significantly hindered by atoms on the ancillary ligands, in contrast to complexes such as [Co(L)(O(2)CO)](+) (L = (NH(3))(4), (en)(2), tren, and nta), which undergo rapid acid hydrolysis and which show no such steric hindrance.     

Diverse lanthanide coordination polymers tuned by the flexibility of ligands and the lanthanide contraction effect: syntheses, structures and luminescence

Two new flexible exo-bidentate ligands were designed and synthesized, incorporating different backbone chain lengths bearing two salicylamide arms, namely 2,2'-(2,2'-oxybis(ethane-2,1-diyl)bis(oxy))bis(N-benzylbenzamide) (L(I)) and 2,2'-(2,2'-(ethane-1,2-diylbis(oxy))bis(ethane-2,1-diyl))bis(oxy)bis(N-benzylbenzamide) (L(II)). These two structurally related ligands are used as building blocks for constructing diverse lanthanide polymers with luminescent properties. Among two series of lanthanide nitrate complexes which have been characterized by elemental analysis, TGA analysis, X-ray powder diffraction, and IR spectroscopy, ten new coordination polymers have been determined using X-ray diffraction analysis. All the coordination polymers exhibit the same metal-to-ligand molar ratio of 2?:?3. L(I), as a bridging ligand, reacts with lanthanide nitrates forming two different types of 2D coordination complexes: herringbone framework {[Ln(2)(NO(3))(6)(L(I))(3)·mC(4)H(8)O(2)](∞) (Ln = La (1), and Pr (2), m = 1, 2)} as type I,; and honeycomb framework {[Ln(2)(NO(3))(6)(L(I))(3)·nCH(3)OH](∞) (Ln = Nd (3), Eu (4), Tb (5), and Er (6), n = 0 or 3)} as type II, which change according to the decrease in radius of the lanthanide. For L(II), two distinct structure types of 1D ladder-like coordination complexes were formed with decreasing lanthanide radii: [Ln(2)(NO(3))(6)(L(II))(3)·2C(4)H(8)O(2)](∞) (Ln = La (7), Pr (8), Nd (9)) as type III, [Ln(2)(NO(3))(6)(L(I))(3)·mC(4)H(8)O(2)·nCH(3)OH](∞) (Ln = Eu (10), Tb (11), and Er (12), m, n = 2 or 0) as type IV. The progressive structural variation from the 2D supramolecular framework to 1D ladder-like frameworks is attributed to the varying chain length of the backbone group in the flexible ligands. The photophysical properties of trivalent Sm, Eu, Tb, and Dy complexes at room temperature were also investigated in detail.     

Lanthanide complexes of chiral 3 + 3 macrocycles derived from (1R,2R)-1,2-diaminocyclohexane and 2,6-diformyl-4-methylphenol

The enantiopure amine macrocycle H(3)L, as well as the parent macrocyclic Schiff base H(3)L1, the 3 + 3 condensation product of (1R,2R)-1,2-diaminocyclohexane and 2,6-diformyl-4-methylphenol, are able to form mononuclear complexes with lanthanide(III) ions. The lanthanide(III) complexes of H(3)L have been studied in solution using NMR spectroscopy and electrospray mass spectrometry. The NMR spectra indicate the presence of complexes of low C(1) and C(2) symmetry. The (1)H and (13)C NMR signals of the Lu(III) complex obtained from H(3)L have been assigned on the basis of COSY, TOCSY, NOESY, ROESY and HMQC spectra. The NMR data reveal unsymmetrical binding of lanthanide(III) ion and the presence of a dynamic process corresponding to rotation of Lu(III) within the macrocycle. The [Ln(H(4)L)(NO(3))(2)](NO(3))(2)(Ln = Sm(III), Eu(III), Dy(III), Yb(III) and Lu(III)) complexes of the cationic ligand H(4)L(+) have been isolated in pure form. The X-ray analysis of the [Eu(H(4)L)(NO(3))(2)](NO(3))(2) complex confirms the coordination mode of the macrocycle determined on the basis of NMR results. In this complex the europium(III) ion is bound to three phenolate oxygen atoms and two amine nitrogen atoms of the monoprotonated macrocycle H(4)L(+), as well as to two axial bidendate nitrate anions. In the presence of a base, mononuclear La(III), Ce(III) and Pr(III) complexes of the deprotonated form of the ligand L(3-) can be obtained. When 2 equivalents of Pr(III) are used in this synthesis Na(3)[Pr(2)L(NO(3))(2)(OH)(2)](2)NO(3).5H(2)O is obtained. The NMR, ES MS and an X-ray crystal model of this complex show coordination of two Pr(III) ions by the macrocycle L. The X-ray crystal structure of the free macrocycle H(3)L1 has also been determined. In contrast to macrocyclic amine H(3)L, the Schiff base H(3)L1 adopts a cone-type conformation resembling calixarenes.