Pentacoordinate nickel(II) complexes double bridged by phosphate ester or phosphinate ligands: spectroscopic, structural, kinetic, and magnetic studies

The bis(phosphatediester)-bridged complexes [[Ni([12]aneN(3))(mu-O(2)P(OR)(2))](2)](PF(6))(2) [[12]aneN(3)=Me(3)[12]aneN(3), 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene; R=Me (1), Bu (2), Ph (3), Ph-4-NO(2) (4); [12]aneN(3)=Me(4)[12]aneN(3), 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene; R=Me (5), Bu (6), Ph (7), Ph-4-NO(2) (8)] were prepared by hydrolysis of the phosphate triester with the hydroxo complex [[Ni([12]aneN(3))(mu-OH)](2)](PF(6))(2) or by acid-base reaction of the dialkyl or diaryl phosphoric acid and the above hydroxo complex. The acid-base reaction was also used to synthesise the phosphinate-bridged complexes [[Ni([12]aneN(3))(mu-O(2)PR(2))](2)](PF(6))(2) [[12]aneN(3)=Me(3)[12]aneN(3), R=Me (9), Ph (10); [12]aneN(3)=Me(4)[12]aneN(3), R=Me (11), Ph (12)]. The molecular structures of complexes 2, 3 and 12 were established by single crystal X-ray diffraction studies. The eight-membered rings defined by the nickel atoms and the bridging ligands show distorted twist-boat, chair and boat-boat conformations in 2, 3 and 12, respectively. The experimental susceptibility data for compounds 2, 3 and 12 were fitted by least-squares methods to the analytical expression given by Ginsberg. The best fit was obtained with values of J=-0.11 cm(-1), D=-9.5 cm(-1) and g=2.20 for 2; J=-0.97 cm(-1), D=-9.3 cm(-1) and g=2.21 for 3; and J=-0.14 cm(-1), D=-11.9 cm(-1) and g=2.195 for 12. The magnetic-exchange pathways must involve the phosphate/phosphinate bridges, because these favour antiferromagnetic interactions. The observation of a higher exchange parameter for compound 3 is a consequence of a favourable disposition of the O-P-O bridges. The kinetics for the hydrolysis of TNP (tris(4-nitrophenyl)phosphate) with the dinuclear nickel(II) hydroxo complex [[Ni(Me(3)[12]aneN(3))(mu-OH)](2)](PF(6))(2) was studied by UV-visible spectroscopy. The proposed mechanism for TNP-promoted hydrolysis can be described as one-substrate/two-product, and can be fitted to a Michaelis-Menten equation.     

AlMe3 and ZnMe2 adducts of a titanium imido methyl cation: a combined crystallographic, spectroscopic, and DFT study

A combined experimental and DFT study of the reactions of the titanium imido methyl cation [Ti(NtBu)(Me3[9]aneN3)Me]+ (4+) with AlMe3 and ZnMe2 is described. Reaction of 4+ with AlMe3 gave [Ti(NtBu)(Me3[9]aneN3)(mu-Me)2AlMe2]+ (7+), the first structurally characterized AlMe3 adduct of a transition metal alkyl cation and a model for the presumed resting state in MAO-activated olefin polymerizations. Reaction of 4+ with ZnMe2 also gave a methyl-bridged heterobinuclear species, namely [Ti(mu-NtBu)(Me3[9]aneN3)(mu-Me)2ZnMe]+ (8+), the first directly observed ZnMe2 adduct of a transition metal alkyl cation. At room temperature, all three metal-bound methyls of 8+ underwent rapid exchange with those of free ZnMe2, whereas at 233 K only the terminal Zn-Me group exchanged significantly. Addition of AlMe3 to 8+ quantitatively formed 7+ and ZnMe2. Reaction of 4+ with Cp2ZrMe2 gave [Ti(NtBu){Me2(mu-CH2)[9]aneN3}(mu-CH2)ZrCp2]+ (10+) via a highly selective double C-H bond activation reaction in which both alkyl groups of Cp2ZrMe2 were lost. DFT calculations on models of 7+ confirmed the approximately square-based pyramidal geometries for the bridging methyl groups. Calculations on 8+ found that the formation of the Ti(mu-Me)2Zn moiety is assisted by an Nimide-->Zn dative bond. DFT calculations for the sterically less encumbered methyl cation [Ti(NMe)(H3[9]aneN3)Me]+ found strong thermodynamic preferences for adducts featuring Nimide-->M (M = Al or Zn) interactions. This offers insight into recently observed structure-productivity trends in MAO-activated imido-based polymerization catalysts. Calculations on the metallocenium adducts [Cp2Ti(mu-Me)2AlMe2]+ and [Cp2Ti(mu-Me)2ZnMe]+ are described, each showing alpha-agostic interactions for the bridging methyl groups. For these systems and the imido ones, the coordination of AlMe3 to the corresponding monomethyl cation is ca. 30 kJ mol-1 more favorable than for ZnMe2.     

Triisopropyltriazacyclononane copper(II): an efficient phosphodiester hydrolysis catalyst and DNA cleavage agent

A 6000-fold rate enhancement has been observed for the hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) in the presence of 0.2 mM Cu(i-Pr(3)[9]aneN(3))(2+) at pH 9.2 and 50 degrees C. In a direct comparison, the rate of hydrolysis of BNPP is accelerated at least 60-fold over the previously reported catalyst Cu([9]aneN(3))(2+). As observed for Cu([9]aneN(3))(2+), hydrolysis is selective for diesters over monoesters. Hydrolysis of BNPP by Cu(i-Pr(3)[9]aneN(3))(2+) is catalytic, exhibiting both rate enhancement and turnover. The reaction is inhibited by both p-nitrophenyl phosphate and inorganic phosphate. The reaction is first-order in substrate and half-order in metal complex, with a k(1.5) of 0.060 +/- 0.004 M(-1/2) s(-1) at 50 degrees C. The temperature dependence of the rate constant results in a calculated activation enthalpy (Delta H(++) of 51 +/- 2 kJ mol(-1) and activation entropy (Delta S(++)) of -110 +/- 6 J mol(-1) K(-1). The kinetic pK(a) of 7.8 +/- 0.2 is close to the thermodynamic pK(a) of 7.9 +/- 0.2, consistent with deprotonation of a coordinated water molecule in the active form of the catalyst. The active catalyst [Cu(i-Pr(3)[9]aneN(3))(OH)(OH(2))](+) is in equilibrium with an inactive dimer, and the formation constant for this dimer is between 216 and 1394 M(-1) at pH 9.2 and 50 degrees C. Temperature dependence of the dimer formation constant K(f) indicates an endothermic enthalpy of formation for the dimer of 27 +/- 3 kJ mol(-1). The time course of anaerobic DNA cleavage by Cu(i-Pr(3)[9]aneN(3))(2+) is presented over a wide range of concentrations at pH 7.8 at 50 degrees C. The concentration dependence of DNA cleavage by Cu([9]aneN(3))(2+) and Cu(i-Pr(3)[9]aneN(3))(2+) reveals a maximum cleavage efficiency at sub-micromolar concentrations of cleavage agent. DNA cleavage by Cu(i-Pr(3)[9]aneN(3))(2+) is twice as efficient at pH 7.8 as at pH 7.2.     

Titanium tert-butoxyimido compounds

The synthesis and molecular and electronic structures of the first tert-butoxyimido complexes of titanium (TiNO(t)Bu functional group) are reported, featuring a variety of mono- or poly-dentate, neutral or anionic N-donor ligands. Reaction of Ti(NMe(2))(2)Cl(2) with (t)BuONH(2) gave good yields of Ti(NO(t)Bu)Cl(2)(NHMe(2))(2) (1). Compound 1 serves as an excellent entry point into new tert-butoxyimido complexes by reaction with a variety of fac-N(3) donor ligands, namely, Me(3)[9]aneN(3) (trimethyl-1,4,7-triazacyclononane), HC(Me(2)pz)(3) (tris(3,5-dimethylpyrazolyl)methane), or Me(3)[6]aneN(3) (trimethyl-1,3,5-triazacyclohexane) to give Ti(NO(t)Bu)(Me(3)[9]aneN(3))Cl(2) (2), Ti(NO(t)Bu){HC(Me(2)pz)(3)}Cl(2) (3), or Ti(NO(t)Bu)(Me(3)[6]aneN(3))Cl(2) (4) in good yield. It was found that 4 could be converted into Ti(NO(t)Bu)Cl(2)(py)(3) (5) in very good yield by reaction with an excess of pyridine. Compound 5 is effective in a range of salt metathesis reactions with lithiated amide or pyrrolide ligands, and reacts with Li(2)N(2)N(py), Li(2)N(2)N(Me), LiN(pyr)N(Me(2)), or Li(2)N(2)(pyr)N(Me) to give Ti(N(2)N(py))(NO(t)Bu)(py) (6), Ti(N(2)N(Me))(NO(t)Bu)(py) (7), Ti(N(pyr)N(Me(2)))(NO(t)Bu)Cl(py)(2) (9), or Ti(N(2)(pyr)N(Me))(NO(t)Bu)(py)(2) (10) in moderate to good yields (N(2)N(py) = (2-NC(5)H(4))C(Me)(CH(2)NSiMe(3))(2); N(2)N(Me) = MeN(CH(2)CH(2)NSiMe(3))(2); N(pyr)N(Me(2)) = Me(2)NCH(2)(2-NC(4)H(3)); N(2)(pyr)N(Me) = MeN{CH(2)(2-NC(4)H(3))}(2)). Compounds 7, 9, and 10 reacted with 2,2'-bipyridyl by pyridine exchange reactions forming Ti(N(2)N(Me))(NO(t)Bu)(bipy) (8), Ti(N(pyr)N(Me(2)))(NO(t)Bu)Cl(bipy) (11), and Ti(N(2)(pyr)N(Me))(NO(t)Bu)(bipy) (12). Ten tert-butoxyimido compounds, namely, 1-6, 11, and 12, have been structurally characterized revealing approximately linear Ti-N-O(t)Bu linkages with Ti-N distances [range 1.686(2)-1.734(2) ?] that are generally intermediate between those in the homologous alkylimido and phenylimido analogues, and shorter than in the diphenylhydrazido counterparts. Density functional theory (DFT) studies on the model compounds Ti(NR)Cl(2)(NHMe(2))(2) (1_R; R = OMe, Me, Ph, NMe(2)) confirmed this trend and found that the destabilizing effect of the -OMe oxygen 2p(π) lone pair on one of the Ti-N π-bonds in 1_OMe is comparable to that of the occupied phenyl ring π orbitals in the phenylimido homologue 1_Ph but much less than for the -NMe(2) nitrogen lone pair in 1_NMe(2).     

Mixed-valent [FeIV(mu-O)(mu-carboxylato)2FeIII]3+ core

The symmetrically ligated complexes 1, 2, and 3 with a (mu-oxo)bis(mu-acetato)diferric core can be one-electron oxidized electrochemically or chemically with aminyl radical cations [*NR3][SbCl6] in acetonitrile yielding complexes which contain the mixed-valent [(mu-oxo)bis(mu-acetato)iron(IV)iron(III)]3+ core: [([9]aneN3)(2FeIII2)(mu-O)(mu-CH3CO2)2](ClO4)2 (1(ClO4)2), [(Me3[9]aneN3)(2FeIII2)(mu-O)(mu-CH3CO2)2](PF6)2 (2(PF6)(2)), and [(tpb)(2FeIII2)(mu-O)(mu-CH3CO2)2] (3) where ([9]aneN3) is the neutral triamine 1,4,7-triazacyclononane and (Me3[9]aneN3) is its tris-N-methylated derivative, and (tpb)(-) is the monoanion trispyrazolylborate. The asymmetrically ligated complex [(Me3[9]aneN3)FeIII(mu-O)(mu-CH3CO2)2FeIII(tpb)](PF6) (4(PF6)) and its one-electron oxidized form [4ox]2+ have also been prepared. Finally, the known heterodinuclear species [(Me3[9]aneN3)CrIII(mu-O)(mu-CH3CO2)2Fe([9]aneN3)](PF6)2 (5(PF6)(2)) can also be one-electron oxidized yielding [5ox]3+ containing an iron(IV) ion. The structure of 4(PF6).0.5CH3CN.0.25(C2H5)2O has been determined by X-ray crystallography and that of [5ox]2+ by Fe K-edge EXAFS-spectroscopy (Fe(IV)-O(oxo): 1.69(1) A; Fe(IV)-O(carboxylato) 1.93(3) A, Fe(IV)-N 2.00(2) A) contrasting the data for 5 (Fe(III)-O(oxo) 1.80 A; Fe(III)-O(carboxylato) 2.05 A, Fe-N 2.20 A). [5ox]2+ has an St = 1/2 ground state whereas all complexes containing the mixed-valent [FeIV(mu-O)(mu-CH3CO2)2FeIII]3+ core have an St = 3/2 ground state. M?ssbauer spectra of the oxidized forms of complexes clearly show the presence of low spin FeIV ions (isomer shift approximately 0.02 mm s(-1), quadrupole splitting approximately 1.4 mm s(-1) at 80 K), whereas the high spin FeIII ion exhibits delta approximately 0.46 mm s(-1) and DeltaE(Q) approximately 0.5 mm s(-1). M?ssbauer, EPR spectral and structural parameters have been calculated by density functional theoretical methods at the BP86 and B3LYP levels. The exchange coupling constant, J, for diiron complexes with the mixed-valent FeIV-FeIII core (H = -2J S1.S2; S(1) = 5/2; S2 = 1) has been calculated to be -88 cm(-1) (intramolecular antiferromagnetic coupling) and for the reduced diferric form of -75 cm(-1) in reasonable agreement with experiment (J = -120 cm(-1)).     

Probing the effects of ligand structure on activity and selectivity of Cr(III) complexes for ethylene oligomerisation and polymerisation

A series of distorted octahedral Cr(III) complexes containing tridentate S-, S/O- or N-donor ligands comprised of three distinct architectures: facultative {S(CH(2)CH(2)SC(10)H(21))(2) (L(1)) and O(CH(2)CH(2)SC(10)H(21))(2) (L(2))}, tripodal {MeC(CH(2)S(n)C(4)H(9))(3) (L(3)), MeC(CH(2)SC(10)H(21))(3) (L(4))} and macrocyclic {(C(10)H(21))[9]aneN(3) (L(5)), (C(10)H(21))(3)[9]aneN(3) (L(6)), with [9]aneN(3)=1,4,7-triazacyclononane} are reported and characterised spectroscopically. Activation of [CrCl(3)(L)] with MMAO produces very active ethylene trimerisation, oligomerisation and polymerisation catalysts, with significant dependence of the product distribution upon the ligand type present. The properties of the parent [CrCl(3)(L)] complexes are probed by cyclic voltammetry, UV-visible, EPR, EXAFS and XANES measurements, and the effects upon activation with Me(3)Al investigated similarly. Treatment with excess Me(3)Al leads to substitution of Cl ligands by Me groups, generation of an EPR silent Cr species (consistent with a change in the oxidation state of the Cr to either Cr(II) or Cr(IV)) and substantial dissociation of the neutral S and S/O-donor ligands.     

Highly efficient ethylene polymerisation by scandium alkyls supported by neutral fac-kappa3 coordinated N3 donor ligands

Reaction of [M(CH2SiMe3)3(THF)2] (M = Sc or Y) with the neutral fac-kappa3 N3 donor ligands (L) Me3[9]aneN3 or HC(Me2pz)3 gave the corresponding trialkyls [M(L)(CH2SiMe3)3]; activation of the scandium congeners with B(C6F5)3 in the presence of ethylene afforded highly active polymerisation catalysts (Me3[9]aneN3 = 1,4,7-trimethyltriazacyclononane).     

Scandium alkyl and amide complexes containing a cyclen-derived (NNNN) macrocyclic ligand: synthesis, structure and ring-opening polymerization activity toward lactide monomers

Cyclic polyamine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, (Me(3)TACD)H (= Me(3)[12]aneN(4)), reacted with [K{N(SiHMe(2))(2)}] in benzene-d(6) to give [K{(Me(3)TACD)SiMe(2)N(SiHMe(2))}] (1) under hydrogen evolution. Single-crystal X-ray diffraction of 1 shows a dinuclear structure in the solid state, featuring a bridging μ-amido and a weak β-agostic Si-H bond. 1,7-Dimethyl-1,4,7,10-tetraazacyclododecane (Me(2)TACD)H(2) (= Me(2)[12]aneN(4)) and (Me(3)TACD)H were reacted with [Sc{N(SiHMe(2))(2)}(3)(thf)] in benzene-d(6) to give [{(Me(2)TACD)SiMe(2)N(SiHMe(2))}Sc{N(SiHMe(2))(2)}] (2) and [(Me(3)TACD)Sc{N(SiHMe(2))(2)}(2)SiMe(2)] (3), respectively. Both compounds are monomeric in solution and X-ray diffraction studies showed the scandium metal centers to be six-coordinate. The scandium alkyl complex [Sc(Me(3)TACD)(CH(2)SiMe(3))(2)] (4) was obtained by reacting (Me(3)TACD)H with [Sc(CH(2)SiMe(3))(3)(thf)] in benzene-d(6). The scandium amide complexes 2 and 3 catalyzed the ring-opening polymerization (ROP) of meso-lactide to give syndiotactic polylactides.     

Well-defined imidotitanium alkyl cations: agostic interactions, migratory insertion vs.[2+2] cycloaddition, and the first structurally authenticated AlMe(3) adduct of any transition metal alkyl cation

The imidotitanium alkyl cations [Ti(NtBu)(Me3[9]aneN3)R]+ (R = Me (3+) or CH2SiMe3(4+)) possess either a very weak alpha-agostic or beta-Si-C agostic interactions, respectively, according to 13C and 29Si NMR and DFT studies; reaction of (4+) with iPrNCNiPr gives totally selective insertion into the Ti-alkyl bond; reaction of 3+ with AlMe3 gives the first structurally characterised AlMe3 adduct of a transition metal alkyl cation (Me3[9]aneN3 = 1,4,7-trimethyltriazacyclononane).     

Oxamidate-bridged dinuclear five-coordinate nickel(II) complexes: a magneto-structural study

The preparation, spectroscopic characterization, and magnetic study of three new oxamidate-bridged nickel(II) dinuclear complexes of formulas ([Ni(Me3[12]aneN3)]2(mu-oa))(PF6)2 (1), ([Ni(Me3[12]aneN3)]2(mu-dmoa))(PF6)2 (2), and ([Ni(Me3[12]aneN3)]2(mu-dpoa))(PF6)2 (3) (Me3[12]aneN3 = 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene, oa = oxamidate, dmoa = N,N'-dimethyloxamidate, and dpoa = N,N'-diphenyloxamidate) are reported. The crystal structures of two of them (1 and 3) have been determined. 1 and 3 crystallize in the monoclinic system, space group P2(1)/c, with Z = 2 and a = 7.901(4) A, b = 13.597(6) A, c = 17.565(10) A, and beta = 96.46(4) degrees for 1 and a = 13.854(3) A, b = 17.469(4) A, c = 12.543(3) A, and beta = 116.22(3) degrees for 3. The structures of 1 and 3 consist of dinuclear ([Ni(Me3[12]aneN3)]2(mu-oa))2+ and ([Ni(Me3[12]aneN3)]2(mu-dpoa))2+ cations and hexafluorophosphate anions. Each nickel in 1-3 is five-coordinate, and the substitution of the hydrogen atom of the amidate nitrogen of 1 by a methyl (2) or a phenyl (3) group causes a significant modification of the stereochemistry of the nickel(II) ions from square pyramidal toward trigonal bipyramidal (tau values of 0.12 and 0.48 for 1 and 3, respectively). The NOESY spectrum of 3 has allowed us to achieve the assignment of the phenyl protons of the N,N'-diphenyloxamidate. The value of magnetic coupling between the two nickel(II) ions across the oxamidate bridge [J = -57.0 (oa, 1), -38.0 (dmoa, 2) and -30.5 cm(-1) (dpoa, 3)] is very sensitive to this stereochemical change, and its variation is explained on the basis of orbital considerations. DFT type calculations have been performed to analyze and substantiate the trend of the magnetic coupling in 1-3.     

Synthesis, characterization, and activity in ethylene polymerization of silica supported cationic cyclopentadienyl zirconium complexes

Cp*ZrMe3 reacts with silica pretreated at 800 degrees C, SiO(2-(800)) through two pathways: (a) protolysis of a Zr-Me group by surface silanols and (b) transfer of a methyl group to the surface by opening of strained siloxane bridges, in a relative proportion of ca. 9/1, respectively, affording a well-defined surface species [([triple bond]SiO)ZrCp*(Me)2], 3, but with two different local environments 3a, [([triple bond]SiO)ZrCp*(Me)2][[triple bond]Si-O-Si[triple bond]], and the other with 3b, [structure: see text]. The reaction of the species 3 with B(C6F5)3 is controlled by this local environment and gives three surface species [([triple bond]SiO)ZrCp*(Me)](+)[MeB(C6F5)3]- [[triple bond]Si-O-Si[triple bond]], 4a (20%), [([triple bond]SiO)ZrCp*(Me)](+)[(Me)B(C6F5)3]- [[triple bond]Si-Me], 4b (10%), and [([triple bond]SiO)2ZrCp*](+)[(Me)B(C6F5)(3)](-)[[triple bond]Si-O-Si[triple bond]], 5 (70%). On the contrary, the reaction of Cp*Zr(Me)3, Cp2Zr(Me)2 with [[triple bond]SiO-B(C6F5)3](-)[HNEt2Ph]+, 6, leads to a unique species [([triple bond]SiO)B(C6F5)3](-)[Cp*Zr(Me)2.NEt2Ph]+, 7, and [([triple bond]SiO)ZrCp2](+)[(Me)B(C6F5)3]-, 9 respectively. The complexes 4 and 7 are active catalysts in ethylene polymerization at room temperature, 93 and 67 kg PE mol Zr1- atm(-1) bar(-1), respectively, indicating that covalently bounded Zr catalyst 4 is slightly more active than the "floating" cationic catalyst 7.     

Crystal Structures of Two New Monoprotonated Products of 1,4,7-trimethyl- 1,4,7-triazacyclononane: (Me3 [9] aneN3H ) (SO3CF3) and (Me3 [9] aneN3H) I

Two new monoprotonated products of macrocyclic polyamine 1,4,7-trimethyl- 1,4,7-triazacyclononane (Me3 [9]aneN3), (Me3 [9]aneN3H) (SO3CF3) 1 (C10H22N3O3SF3, Mr=321.36) and (Me3[9]aneN3H)I 2 (C9H22N3I, Mr=299.20) were obtained by the reactions of Me3[9]aneN3 and yttrium triflate or ytterbium diiodide as the unexpected products. The crystal structures of compounds 1 and 2 have been determined. Crystal 1is orthorhombic, space group P212121(#19), a =12. 609(3), b=13. 531(1), c=9.225(3) A, V=1573.9(7) A3, Z=4, Dc=1. 356g/cm3, μ=2.47cm- 1, F (000) = 680 and R= 0. 052, Rw= 0. 052 for 807 unique reflections with I＞ 2σ(I). Crystal 2 belongs to the orthorhombic system with space group P212121 (# 19), a=11.417(2), b=13.099(3), c=8.762(2) A, V=1310.5(4) A3, Z=4, Dc=1. 516 g/cm3, μ= 24.14 cm-1, F(000)=600 and R=0. 035, Rw=0. 042 for 1427 u-nique reflections with I＞3σ(I). The two structures contain the same cyclic framework in which the acid proton is bonded to an amine nitrogen. This proton exhibits strong intramolecular hydrogen bonds with the other two nitrogen atoms. The methyl groups are directed away from the ring cavity. The bond distance between acid proton and an amine nitrogen in compound 2 is extremely short. The bond angles for 1 and 2 also exhibit obvous diversity inside of triazacyclononae.     

Crystal Structures of Two New Monoprotonated Products of 1,4,7 trimethyl-1,4,7-triazacyclononane: (Me_3〔9〕aneN_3H)(SO_3CF_3) and (Me_3〔9〕aneN_3H)I

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Synthesis, structures, and DFT bonding analysis of new titanium hydrazido(2-) complexes

The reaction of 1,1-diphenylhydrazine with Ti(NMe2)2Cl2 produced the monomeric terminal titanium hydrazido(2-) species Ti(NNPh2)Cl2(HNMe2)2 (1) in near-quantitative yield. The reaction of Ti(NMe2)2Cl2 with the less sterically demanding ligand precursors 1,1-dimethylhydrazine or N-aminopiperidine gave the dimeric mu-eta2,eta1-bridged compounds Ti2(mu-eta2,eta1-NNMe2)2Cl4(HNMe2)2 (2) and Ti2[mu-eta2,eta1-NN(CH2)5]2Cl4(HNMe2)3 (3). The X-ray structures of 2 and 3 showed the formation of N-H...Cl hydrogen bonded dimers or chains, respectively. The reaction of 1 with an excess of pyridine formed [Ti(NNPh2)Cl2(py)2]n (4, n = 1 or 2). The reaction of the tert-butyl imido complex Ti(N(t)Bu)Cl2(py)3 with either 1,1-dimethylhydrazine or N-aminopiperidine again resulted in the formation of hydrazido-bridged dimeric complexes, namely Ti2(mu-eta2,eta1-NNMe2)2Cl4(py)2 (5, structurally characterized) and Ti2[mu-eta2,eta1-NN(CH2)5]2Cl4(py)2 (6). Compounds 1 and 4 are potential new entry points into terminal hydrazido(2-) chemistry of titanium. Compound 1 reacted with neutral fac-N3 donor ligands to form Ti(NNPh2)Cl2(Me3[9]aneN3) (7), Ti(NNPh2)Cl2(Me3[6]aneN3) (8), Ti(NNPh2)Cl2[HC(Me2pz)3] (9, structurally characterized), and Ti(NNPh2)Cl2[HC(n)Bupz)3] (10) in good yields (Me3[9]aneN3 = trimethyl-1,4,7-triazacyclononane, Me3[6]aneN3 = trimethyl-1,3,5-triazacyclohexane, HC(Me2pz)3 = tris(3,5-dimethylpyrazolyl)methane, and HC((n)Bupz)3 = tris(4-(n)butylpyrazolyl)methane). DFT calculations were performed on both the model terminal hydrazido compound Ti(NNPh2)Cl2[HC(pz)3] (I) and the corresponding imido compounds Ti(NMe)Cl2[HC(pz)3] (II) and Ti(NPh)Cl2[HC(pz)3] (III). The NNPh2 ligand binds to the metal center in an analogous manner to that of terminal imido ligands (metalligand triple bond), but with one of the Ti=N(alpha) pi components significantly destabilized by a pi interaction with the lone pair of the N(beta) atom. The NR ligand sigma donor ability was found to be NMe > NPh > NNPh2, whereas the overall (sigma + pi) donor ability is NMe > NNPh2 > NPh, as judged by fragment orbital populations, Ti-N atom-atom overlap populations, and fragment-charge analysis. DFT calculations on the hydrazido ligand in a mu-eta2,eta1-bridging mode showed involvement of the N=N pi electrons in donation to one of the Ti centers. This TiN2 interaction is best represented as a metallocycle.     

Synthetic, X-ray Structure, Electron Paramagnetic Resonance, and Magnetic Studies of the Manganese(II) Complex of 1-Thia-4,7-diazacyclononane ([9]aneN(2)S)

Reaction of manganese(II) perchlorate hexahydrate with a methanol solution of 1-thia-4,7-diazacyclononane ([9]aneN(2)S) resulted in the isolation of the manganese(II) complex [Mn([9]aneN(2)S)(2)](ClO(4))(2). The X-ray structure of this complex is reported: crystal system orthorhombic, space group Pbam, No. 55, a = 7.937(2) ?,b = 8.811(2) ?, c = 15.531(3) ?, Z = 2, R = 0.0579. The complex is high spin (S = (5)/(2)) with an effective magnetic moment (&mgr;(eff)) 5.82 &mgr;(B) at 298 K and 5.65 &mgr;(B) at 4.2 K. Computer simulation of the Q-band EPR spectrum of [Mn([9]aneN(2)S)(2)](ClO(4))(2) yields g = 1.99 +/- 0.01, |D| = 0.19 +/- 0.005 cm(-)(1), and E/D = 0.04 +/- 0.02. For the analogous hexaamine complex [Mn([9]aneN(3))(2)](ClO(4))(2) ([9]aneN(3) = 1,4,7-triazacyclononane) analysis of the EPR spectra produced the following values: g = 1.98 +/- 0.01, |D| = 0.09 +/- 0.003 cm(-)(1), and E/D = 0.1 +/- 0.01. The spin Hamiltonian parameters for [Mn([9]aneN(2)S)(2)](ClO(4))(2) derived from the EPR spectra produced a good fit to the magnetic susceptibility data.     

Encapsulation of metal cations and anions within the cavity of bis(1,4,7-triazacyclononane) receptors

The synthesis and characterisation of a new bis([9]aneN3) ligand (L4) containing two [9]aneN3 macrocyclic moieties separated by a 2,6-dimethylenepyridine unit is reported. A potentiometric and 1H NMR study in aqueous solution reveals that ligand protonation occurs on the secondary amine groups and does not involve the pyridine nitrogen. The coordination properties toward Cu(II), Zn(II), Cd(II) and Pb(II) were studied by means of potentiometric and UV spectrophotometric measurements. The ligand can form mono- and binuclear complexes in aqueous solution. In the 1 : 1 complexes, the metal is sandwiched between the two [9]aneN3 moieties and the pyridine N-donor is coordinated to the metal, as actually shown by the crystal structure of the compound [ZnL4](NO3)2.CH3NO2. L4 shows a higher binding ability for Cd(II) with respect to Zn(II), probably due to a better fitting of Cd(II) ion inside the cavity generated by the two facing [9]aneN3 units. The formation of binuclear complexes is accompanied by the assembly of OH-bridged M2(OH)x (x = 1-3) clusters inside the cavity defined by the two facing [9]aneN3 units, and pyridine is not involved in metal coordination. A potentiometric and (1)H NMR study on the coordination of halogenide anions by L4 and its structural analogous L3 in which the two [9]aneN3 units are separated by a shorter quinoxaline linkage, shows that bromide is selectively recognised by L4, while chloride is selectively bound by L3. Such a behaviour is discussed in terms of dimensional matching between the spherical anions and the cavities generated by the two [9]aneN3 units of the receptors.     

Electron-Transfer Reactions of Re(CO)(5): Atom-Transfer-Concerted Mechanism vs Bimetallic Intermediate Formation

Flash photochemically generated Re(CO)(5) reacts with halide complexes, Cu(Me(4)[14]-1,3,8,10-tetraeneN(4))X(+), Cu(Me(2)pyo[14]trieneN(4))X(+), and Ni(Me(2)pyo[14]trieneN(4))X(+) (X = Cl, Br, I) and ion pairs, [Co(bipy)(3)(3+), X(-)]. The rate constants for the electron transfers have values, k approximately 10(9) M(-1) s(-1), close to expectations for processes with diffusion-controlled rates. Reaction intermediates, probably bimetallic species, were detected in electron-transfer reactions of Re(CO)(5) with Cu(Me(6)[14]dieneN(4))X(+), (X = Cl, Br, I). In the absence of the halides X(-), the electron-transfer reactions between Re(CO)(5) and these complexes are slow, k < 10(6) M(-1) s(-1). The results are discussed in terms of inner-sphere pathways, namely an atom-transfer-concerted mechanism. The mediation of bimetallic intermediates in the electron transfer is also considered.     

A new macrocyclic cryptand with squaramide moieties: an overstructured Cu(II) complex that selectively binds halides: synthesis, acid/base- and ligational behavior, and crystal structures

The synthesis and characterization of the novel 24,29-dimethyl-6,7,15,16-tetraoxotetracyclo-[19.5.5.0(5,8).0(14,17)]-1,4,9,13,18,21,24,29-octaazaenatriaconta-Delta(5,8),Delta(14,17)-diene (L) are reported. Molecule L incorporates two squaramide functions in a overstructured chain connecting two opposite nitrogen atoms of the Me(2)[12]aneN(4) polyaza macrocyclic base to obtain a cage topology. The basicity and binding properties of L towards Cu(II) were determined by means of potentiometric measurements in aqueous solution (298.1+/-0.1 K, I=0.15 mol dm(-3)). Molecule L behaves as a diprotic base under the experimental conditions employed and forms only mononuclear Cu(II) complexes in which the squaramide moieties are not involved in the stabilization of the metal ion that is stabilized by the amine functions of the polyaza base inside the three-dimensional cavity. The [CuL](2+) species was tested as a host for the series of halide anions. UV-visible spectrophotometric experiments permitted the determination of the addition constants of halides to the Cu(II)-complexed species. The [CuL](2+) species binds the anions F(-), Cl(-), and Br(-) by forming the [CuLX](+) species, but does not bind the biggest I(-) anion. A trend of selectivity as a function of the hydrogen-bonding capability as well as the dimensions of the anion were established; the maximum value of selectivity was for addition of the F(-) anion (log K=4.8). This selectivity is due to the presence of the overstructured chain containing the squaramide groups up to the Me(2)[12]aneN(4) macrocyclic base. The squaramide groups, by providing hydrogen-bond contacts, permit the [CuL](2+) species to selectively bind these anions through the formation of a hydrogen-bond network with F(-) and Cl(-). The crystal structures of the [CuLF](+) and [CuLCl](+) cations support the results obtained in aqueous solution.     

Synthesis and properties of one-dimensional Ni(Ⅱ) and Ni(Ⅱ)Cu(Ⅱ) complexes linked by hydrogen bond

Four dithiooxalato (Dto) bridged one-dimensional Ni(ll) and Ni(ll)Cu(ll) complexes (Me6[14]dieneN4)Ni2(Dto)2) (1), (Me6[14]dieneN4)CuNi(Dto)2 (2), (Me6[14]aneN4)Ni2(Dto)2 (3), and (Me6[14]aneN4)CuNi(Dto)2(4), were synthesized. These complexes have been characterized by elemental analysis, IR, UV and ESR spectra. The crystal structure of complex 3 was determined. It crystallizes in the monoclinic system, space group C2/c with a = 2.2425(4) nm, b = 1.0088(2) nm, c=1.4665(3) nm, β= 125.32(3)° ;Z=4; R = 0.076, Rw = 0.079. In the complex, Ni(1) coordinates four sulphur atoms of two Dto ligands in plane square environment. Ni(2) lies in the center of mac-rocyclic ligand. For Dto ligand, two sulphur atoms coordinate Ni(1), and O(1) coordinates Ni(2) and forms weak coordination bond. O(2) is linked to N(2) of macrocyclic ligand through hydrogen bond.     

Reaction of vinyl chloride with late transition metal olefin polymerization catalysts

The reactions of vinyl chloride (VC) with representative late metal, single-site olefin dimerization and polymerization catalysts have been investigated. VC coordinates more weakly than ethylene or propylene to the simple catalyst (Me(2)bipy)PdMe(+) (Me(2)bipy = 4,4'-Me(2)-2,2'-bipyridine). Insertion rates of (Me(2)bipy)Pd(Me)(olefin)(+) species vary in the order VC > ethylene > propylene. The VC complexes (Me(2)bipy)Pd(Me)(VC)(+) and (alpha-diimine)Pd(Me)(VC)(+) (alpha-diimine = (2,6-(i)Pr(2)[bond]C(6)H(3))N[double bond]CMeCMe[double bond]N(2,6-(i)Pr(2)[bond]C(6)H(3))) undergo net 1,2 VC insertion and beta-Cl elimination to yield Pd[bond]Cl species and propylene. Analogous chemistry occurs for (pyridine-bisimine)MCl(2)/MAO catalysts (M = Fe, Co; pyridine-bisimine = 2,6-[(2,6-(i)Pr(2)[bond]C(6)H(3))N[double bond]CMe](2)-pyridine) and for neutral (sal)Ni(Ph)PPh(3) and (P[bond]O)Ni(Ph)PPh(3) catalysts (sal = 2-[C(H)[double bond]N(2,6-(i)Pr(2)-C(6)H(3))]-6-Ph-phenoxide; P[bond]O = [Ph(2)PC(SO(3)Na)[double bond]C(p-tol)O]), although the initial metal alkyl VC adducts were not detected in these cases. These results show that the L(n)MCH(2)CHClR species formed by VC insertion into the active species of late metal olefin polymerization catalysts undergo rapid beta-Cl elimination which precludes VC polymerization. Termination of chain growth by beta-Cl elimination is the most significant obstacle to metal-catalyzed insertion polymerization of VC.