Oxidation of 1-Methyl-1-phenylhydrazine with Oxidovanadium(V)-Salan Complexes: Insight into the Pathway to the Formation of Hydrazine by Vanadium Nitrogenase.

A series of oxidovanadium(V) complexes [VO(L-κ4O,N,N,O)(OR)] (1a, R = Et, L = L1; 1b, R = Me, L = L1; 2, R = Me, L = L2; 3, R = Me, L = L3) were synthesized by the σ-bond metathesis reaction between [VO(OR)3] and the linear diaminebis(phenol) derivatives H2L (salans) containing different para-substituents on the phenoxo group [CMe3CH2CMe2, L1; Me, L2; Cl, L3]. As shown by X-ray crystallography complexes 1a, 1b, and 2 exhibit cis-α geometry, do have a stereogenic vanadium center, and exist as a racemic mixture of the Δ cis-α and Λ cis-α enantiomers. In solution, as demonstrated by 1H and 51V NMR investigations, the structures of complexes 1-3 are consistent with their solid state. The reactions of 1b, 2, and 3 with NH2NMePh in n-hexane afforded the oxidovanadium(IV) [VO(L-κ4O,N,N,O)] (4, L1; 5, L2; 6, L3) and 1,4-dimethyl-1,4-diphenyl-2-tetrazene (Me2Ph2N4) (7) as the main products together with a small amount of hydrazido(2-) vanadium(V) [V(L3-κ4O,N,N,O)(NNMePh)(OMe)] (8). Proposed reaction course for the oxidation of NH2NMePh by 1b-3 is discussed. Compounds 4-8 were characterized by chemical and physical techniques including the X-ray crystallography for 4, 7, and 8. The solid-state (powder) electron paramagnetic resonance spectra and magnetic features strongly indicate that complexes 4-6 are formed as a mixture of a mononuclear (S = 1/2) and a dinuclear (S = 1) species.

Investigation of vanadium(III) and vanadium(IV) compounds supported by the linear diaminebis(phenolate) ligands: correlation between structures and magnetic properties.

A family of oxidovanadium(iv) compounds containing linear diaminebis(phenolate (salans) L1-5 ligands (L1 = [MeNCH2CH2NMe(CH2-4-CMe2CH2CMe3-C6H3O)2]2-; L2 = [MeNCH2CH2NMe(CH2-4-CH3-C6H3O)2]2-; L3 = [MeNCH2CH2NMe(CH2-4-Cl-C6H3O)2]2-; L4 = {MeNCH2CH2NMe[CH2-4,6-(CH3)2-C6H2O]2}2-; and L5 = {MeNCH2CH2NMe[CH2-4,6-(Br)2-C6H2O]2}2-) and non-oxidovanadium(iii) with L2,4 and acac ligands has been prepared and characterized by chemical and physical techniques. Reactions of [VO(acac)2] with ligand precursors H2L2,4 in toluene or hexane afforded vanadium(iii) compounds [V(L-κ4ONNO)(acac)] (1, L2; 2, L4), while the use of acetonitrile or ethanol led to the formation of dimeric oxidovanadium(iv) [(VO)2(µ-L-κ4ONNO)2] (3, L1; 4, L2; 5, L3) and monomeric [VO(L-κ4ONNO)] (6, L4, 7, L5) compounds. As shown by X-ray crystallography, compounds 1 and 2 are monomeric, in which the chelating ligands afford octahedral cis-α geometry at the vanadium center. In the dimeric structures of 3-5, the six-coordinate vanadium centers are bridged via two oxygen atoms of the L1-3 ligands while the L4,5 ligands generate square pyramidal structures of the monomeric 6 and 7 compounds. HFEPR studies allowed the determination of the spin Hamiltonian parameters of the S = 1 spin state of the monomeric V(iii) and dimeric V(iv), and S = ½ in monomeric V(iv) compounds. Magnetic measurements of 3-5 indicated weak ferromagnetic metal-metal exchange interactions. A reaction course for the deoxygenation and reduction of vanadyl-salan compounds is proposed.

Magnesium, zinc and aluminium complexes supported by tripodal diaminebis(aryloxido) ligands: synthesis, solid state and solution structure.

The reactions of the diaminebis(aryloxido) ligand precursors [Me2NCH2CH2N(CH2-4-R-C6H3OH)2] [R = C(CH3)2CH2C(CH3)3, H2L(1); R = CH3, H2L(2)] with Mg(n)Bu2, ZnEt2 and AlEt3 create complexes of general formula [M2(µ-L-κ(4)O,N,N,O)2] (M = Mg, 1a for L(1) and 1b for L(2); M = Zn, 2a for L(1) and 2b for L(2)) and [Al2(µ-L-κ(3)O,N,N,O)2Et2] (3 for L(1)) in good yields. Compounds 1a-3 were characterized by NMR spectroscopy and ESI-MS experiments. The definitive molecular structure of 1b·CH2Cl2, 2a·H2O, 2b·CH2Cl2 and 3 was provided by a single-crystal analysis and revealed their dimeric nature with an M2O2 planar core. The L(1) and L(2) ligands coordinate as the dianions in a tetradentate/bridging manner in 1b, 2a, 2b and in a tridentate/bridging mode in 3. The NMR spectra showed that the solid state of these compounds is essentially retained in solution.

Vanadate complexes bearing an imidazolidine-bridged bis(aryloxido) ligand: synthesis and solid state and solution structure.

A new imidazolidine-bridged bis(aryloxido) ligand precursor (H(2)L) [H(2)L = 2,2'-(imidazolidine-1,3-diylbis(methylene))bis(4-(1,1,3,3-tetramethylbutyl-2-yl)phenol)] was prepared in a relatively high yield (∼60%) via a single-step Mannich condensation of 4-(1,1,3,3-tetramethylbutyl)phenol, ethylenediamine and paraformaldehyde at 2:1:3 molar ratio and characterized by chemical and physical techniques including X-ray crystallography. Reactions of H(2)L with [VO(OEt)(3)] at 1:1 and 1:2 molar ratios in toluene afforded [V(L-κ(3)O,N,N,O)(O)(OEt)] (1) and [V(2)(µ-L-κ(4)O,N,N,O)(µ-OEt)(2)(O)(2)(OEt)(2)] (2), respectively. Alcoholysis of 1 with EtOH enables elimination of one molecule of H(2)L and the formation of 2. Compounds 1 and 2 were characterized by IR and NMR spectroscopy as well as ES-MS experiments. The definitive molecular structure of 2 was provided by a single-crystal analysis and revealed its dinuclear nature, featuring two octahedral vanadium centres bridged by both OEt groups and the L ligand. The (51)V, (1)H and (13)C NMR spectra as well as ES-MS showed that 2 does not stay intact in solution and undergoes dissociation to give 1 and [VO(OEt)(3)].

Lithium complexes supported by tripodal diaminebis(aryloxido) ligands: synthesis and structure.

The diaminebis(aryloxido) ligand precursors H(2)L(1) and H(2)L(2) [H(2)L(1) = Me(2)NCH(2)CH(2)N(CH(2)-4-CMe(2)CH(2)CMe(3)-C(6)H(3)OH)(2); H(2)L(2) = Me(2)NCH(2)CH(2)N(CH(2)-4-Me-C(6)H(3)OH)(2)] were synthesized by a straightforward single-step Mannich condensation. Their reactions with 2 molar equivalents of MeLi in thf afforded [Li(4)(µ-L-κ(4)O,N,N,O)(2)(thf)(2)] (1a, L(1); 1b, L(2)) and unexpectedly small amounts (∼9%) of [Li(6)(µ-L-κ(4)O,N,N,O)(2)(µ(3)-Cl)(2)(thf)(4)]·thf (2a·thf; L(1); 2b·thf, L(2)). Stoichiometric reactions of LiCl, MeLi and ligand precursors H(2)L led to the formation of 2a and 2b in high yield (∼80%). All compounds were characterized by chemical and physical techniques including X-ray crystallography for H(2)L(1), H(2)L(2), 1b, 2a and 2b.

Zirconium and hafnium complexes of the thio(bisphenolato) ligand: synthesis, structural characterization and testing as 1-hexene polymerization catalysts.

Thio(bisphenolato) complexes of the type [M2(mu-tbop-kappa3O,S,O)2Cl4] [M = Zr 1, Hf 2 and tbop = 2,2-thiobis{4-(1,1,3,3-tetramethyl-butyl)phenolate}] were prepared by HCl elimination from tbopH2 and MCl4. Substitution of the chlorides in 1 and 2 by 2,6-diisopropylphenolato groups (dipp) generates new compounds [M2(mu-tbop-kappa3O,S,O)2(dipp)4] (M = Zr 3, Hf 4). The structures of 1-4 were confirmed by NMR spectroscopy; complexes 3 and 4 were further investigated by X-ray crystallography. These studies showed 1-4 to be dimers either in the solid state or in solution and to have metal centers adopting distorted octahedral geometry. However treatment of MCl4 with [Al2(mu-OEt)2(tbop-kappa3O,S,O)2] or [Al2(mu-tbop-kappa3O,S,O)2Me2] gave heterotrinuclear complexes [M(tbop-kappa3O,S,O)2Cl2(mu-AlX2)2] (M = Zr, X = Cl 5, X = Me 7 and M = Hf, X = Cl 6, X = Me 8) for which the single-crystal X-ray diffraction analysis showed zirconium and hafnium centers to have eight-coordinate dodecahedral geometry. Complexes 1-6 after activation with aluminium alkyls and supporting on MgCl2 showed a lack of activity in the ethene polymerization process and moderate activity towards 1-hexene producing high molecular weight atactic poly(1-hexenes).

Synthesis, structural studies and reactivity of vanadium complexes with tridentate (OSO) ligand.

The direct reaction between [VCl(3)(thf)3] or [VO(OEt)3] and 2,2'-thiobis{4-(1,1,3,3-tetramethyl-butyl)phenol (tbopH(2)) leads to the formation of [V(2)(micro-tbop-kappa(3)O,S,O)2Cl(2)(CH(3)CN)(2)] (1).4CH(3)CN or [V(2)(micro-OEt)2(O)2(tbop-kappa(3)O,S,O)2] (2), respectively, in high yield. Compounds 1 and 2 were characterized by chemical and physical techniques including X-ray crystallography and variable temperature magnetic susceptibility studies (J = -29.1 cm(-1)) for 1. Complexes 1 and 2 were supported on MgCl2 and when activated with aluminium alkyls, were found to effectively polymerize ethene to produce polyethylene with a narrow molecular weight distribution M(w)/M(n) approximately 3.