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Masatatsu Suzuki

Publications and source records attributed to Masatatsu Suzuki.

16 recordsLinked to original sources
PubMed2006

Sequential reaction intermediates in aliphatic C-H bond functionalization initiated by a bis(mu-oxo)dinickel(III) complex.

The reaction of [Ni2(OH)2(Me2-tpa)2]2+ (1) (Me2-tpa = bis(6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine) with H2O2 causes oxidation of a methylene group on the Me2-tpa ligand to give an N-dealkylated ligand and oxidation of a methyl group to afford a ligand-based carboxylate and an alkoxide as the final oxidation products. A series of sequential reaction intermediates produced in the oxidation pathways, a bis(mu-oxo)dinickel(III) ([Ni2(O)2(Me2-tpa)2]2+ (2)), a bis(mu-superoxo)dinickel(II) ([Ni2(O2)2(Me2-tpa)2]2+ (3)), a (mu-hydroxo)(mu-alkylperoxo)dinickel(II) ([Ni2(OH)(Me2-tpa)(Me-tpa-CH2OO)]2+ (4)), and a bis(mu-alkylperoxo)dinickel(II) ([Ni2(Me-tpa-CH2OO)2]2+ (5)), was isolated and characterized by various physicochemical measurements including X-ray crystallography, and their oxidation pathways were investigated. Reaction of 1 with H2O2 in methanol at -40 degrees C generates 2, which is extremely reactive with H2O2, producing 3. Complex 2 was isolated only from disproportionation of the superoxo ligands in 3 in the absence of H2O2 at -40 degrees C. Thermal decomposition of 2 under N2 generated an N-dealkylated ligand Me-dpa ((6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine) and a ligand-coupling dimer (Me-tpa-CH2)2. The formation of (Me-tpa-CH2)2 suggests that a ligand-based radical Me-tpa-CH2* is generated as a reaction intermediate, probably produced by H-atom abstraction by the oxo group. An isotope-labeling experiment revealed that intramolecular coupling occurs for the formation of the coupling dimer. The results indicate that the rebound of oxygen to Me-tpa-CH2* is slower than that observed for various high-valence bis(mu-oxo)dimetal complexes. In contrast, the decomposition of 2 and 3 in the presence of O2 gave carboxylate and alkoxide ligands, respectively (Me-tpa-COO- and Me-tpa-CH2O-), instead of (Me-tpa-CH2)2, indicating that the reaction of Me-tpa-CH2* with O2 is faster than the coupling of Me-tpa-CH2* to generate ligand-based peroxyl radical Me-tpa-CH2OO*. Although there is a possibility that the Me-tpa-CH2OO* species could undergo various reactions, one of the possible reactive intermediates, 4, was isolated from the decomposition of 3 under O2 at -20 degrees C. The alkylperoxo ligands in 4 and 5 can be converted to a ligand-based aldehyde by either homolysis or heterolysis of the O-O bond, and disproportionation of the aldehyde gives a carboxylate and an alkoxide via the Cannizzaro reaction.

Catalysis↗
PubMed2005

Structure and dioxygen-reactivity of copper(I) complexes supported by bis(6-methylpyridin-2-ylmethyl)amine tridentate ligands.

The structure and dioxygen-reactivity of copper(I) complexes R supported by N,N-bis(6-methylpyridin-2-ylmethyl)amine tridentate ligands L2R[R (N-alkyl substituent)=-CH2Ph (Bn), -CH2CH2Ph (Phe) and -CH2CHPh2(PhePh)] have been examined and compared with those of copper(I) complex (Phe) of N,N-bis[2-(pyridin-2-yl)ethyl]amine tridentate ligand L1(Phe) and copper(I) complex (Phe) of N,N-bis(pyridin-2-ylmethyl)amine tridentate ligand L3(Phe). Copper(I) complexes (Phe) and (PhePh) exhibited a distorted trigonal pyramidal structure involving a d-pi interaction with an eta1-binding mode between the metal ion and one of the ortho-carbon atoms of the phenyl group of the N-alkyl substituent [-CH2CH2Ph (Phe) and -CH2CHPh2(PhePh)]. The strength of the d-pi interaction in (Phe) and (PhePh) was weaker than that of the d-pi interaction with an eta2-binding mode in (Phe) but stronger than that of the eta1 d-pi interaction in (Phe). Existence of a weak d-pi interaction in (Bn) in solution was also explored, but its binding mode was not clear. Redox potentials of the copper(I) complexes (E1/2) were also affected by the supporting ligand; the order of E1/2 was Phe>R>Phe. Thus, the order of electron-donor ability of the ligand is L1Phe<L2R<L3Phe. This was reflected in the copper(I)-dioxygen reactivity, where the reaction rate of copper(I) complex toward O2 dramatically increased in the order of R<R<R. The structure of the resulting Cu2/O2 intermediate was also altered by the supporting ligand. Namely, oxygenation of copper(I) complex R at a low temperature gave a (micro-eta2:eta2-peroxo)dicopper(II) complex as in the case of Phe, but its O-O bond was relatively weakened as compared to the peroxo complex derived from Phe, and a small amount of a bis(micro-oxo)dicopper(III) complex co-existed. These results can be attributed to the higher electron-donor ability of L2R as compared to that of L1Phe. On the other hand, the fact that Phe mainly afforded a bis(micro-oxo)dicopper(III) complex suggests that the electron-donor ability of L2R is not high enough to support the higher oxidation state of copper(III) of the bis(micro-oxo) complex.

Journal Article↗
PubMed2005

Synthesis and reactivity of a (mu-1,1-hydroperoxo)(mu-hydroxo)dicopper(II) complex: ligand hydroxylation by a bridging hydroperoxo ligand.

A new tetradentate tripodal ligand (L3) containing sterically bulky imidazolyl groups was synthesized, where L3 is tris(1-methyl-2-phenyl-4-imidazolylmethyl)amine. Reaction of a bis(mu-hydroxo)dicopper(II) complex, [Cu2(L3)2(OH)2]2+ (1), with H2O2 in acetonitrile at -40 degrees C generated a (mu-1,1-hydroperoxo)dicopper(II) complex [Cu2(L3)2(OOH)(OH)]2+ (2), which was characterized by various physicochemical measurements including X-ray crystallography. The crystal structure of 2 revealed that the complex cation has a Cu2(mu-1,1-OOH)(mu-OH) core and each copper has a square pyramidal structure having an N3O2 donor set with a weak ligation of a tertiary amine nitrogen in the apex. Consequently, one pendant arm of L3 in 2 is free from coordination, which produces a hydrophobic cavity around the Cu2(mu-1,1-OOH)(mu-OH) core. The hydrophobic cavity is preserved by hydrogen bondings between the hydroperoxide and the imidazole nitrogen of an uncoordinated pendant arm in one side and the hydroxide and the imidazole nitrogen of an uncoordinated pendant arm in the other side. The hydrophobic cavity significantly suppresses the H/D and 16O/18O exchange reactions in 2 compared to that in 1 and stabilizes the Cu2(mu-1,1-OOH)(mu-OH) core against decomposition. Decomposition of 2 in acetonitrile at 0 degrees C proceeded mainly via disproportionation of the hydroperoxo ligand and reduction of 2 to [Cu(L3)]+ by hydroperoxo ligand. In contrast, decomposition of a solid sample of 2 at 60 degrees C gave a complex having a hydroxylated ligand [Cu2(L3)(L3-OH)(OH)2]2+ (2-(L3-OH)) as a main product, where L3-OH is an oxidized ligand in which one of the methylene groups of the pendant arms is hydroxylated. ESI-TOF/MS measurement showed that complex 2-(L3-OH) is stable in acetonitrile at -40 degrees C, whereas warming 2-(L3-OH) at room temperature resulted in the N-dealkylation from L3-OH to give an N-dealkylated ligand, bis(1-methyl-2-phenyl-4-imidazolylmethyl)amine (L2) in approximately 80% yield based on 2, and 1-methyl-2-phenyl-4-formylimidazole (Phim-CHO). Isotope labeling experiments confirmed that the oxygen atom in both L3-OH and Phim-CHO come from OOH. This aliphatic hydroxylation performed by 2 is in marked contrast to the arene hydroxylation reported for some (mu-1,1-hydroperoxo)dicopper(II) complexes with a xylyl linker.

Journal Article↗
PubMed2005

Structural and spectroscopic characterization of (mu-hydroxo or mu-oxo)(mu-peroxo)diiron(III) complexes: models for peroxo intermediates of non-heme diiron proteins.

(mu-Hydroxo or oxo)(mu-1,2-peroxo)diiron(III) complexes having a tetradentate tripodal ligand (L) containing a carboxylate sidearm [Fe2(mu-OH or mu-O)(mu-O2)(L)2]n+ were synthesized as models for peroxo-intermediates of non-heme diiron proteins and characterized by various physicochemical measurements including X-ray analysis, which provide fundamental structural and spectroscopic insights into the peroxodiiron(III) complexes.

Biomimetic Materials↗
PubMed2003

Ligand effect on reversible conversion between copper(I) and bis(mu-oxo)dicopper(III) complex with a sterically hindered tetradentate tripodal ligand and monooxygenase activity of bis(mu-oxo)dicopper(III) complex.

A new sterically hindered tetradentate tripodal ligand (Me2-etpy) and its labeled analogue having deuterated methylene groups (d4-Me2-etpy) were synthesized, where Me2-etpy is bis(6-methyl-2-pyridylmethyl)(2-pyridylethyl)amine. Copper(I) complexes [Cu(Me2-etpy or d4-Me2-etpy)]+ (1 and 1-d4, respectively) reacted with dioxygen at -80 degrees C in acetone to give bis(mu-oxo)dicopper(III) complexes [Cu2(O)2(Me2-etpy or d4-Me2-etpy)2](2+) (1-oxo and 1-d4-oxo, respectively), the latter of which was crystallographically characterized. Unlike a bis(mu-oxo)dicopper(III) complex with a closely related Me2-tpa ligand having a 2-pyridylmethyl pendant, 1-oxo possessing a 2-pyridylethyl pendant is not fully formed even under 1 atm of O2 at -80 degrees C and is very reactive toward the oxidation of the supporting ligand. Thermal decomposition of 1-oxo gave an N-dealkylated ligand in yield approximately 80% based on a dimer and a corresponding aldehyde. The deuterated ligand d4-Me2-etpy greatly stabilizes the bis(mu-oxo)dicopper(III) complex 1-d4-oxo, indicating that the rate determining step of the N-dealkylation is the C-H bond cleavage from the methylene group. The reversible conversion between 1-d4 and 1-d4-oxo in acetone is dependent on the temperature, and the thermodynamic parameters (DeltaH and DeltaS) of the equilibrium were determined to be -53 +/- 2 kJ mol(-1) and -187 +/- 10 J mol(-1) K(-1), respectively. The effect of the 2-pyridylethyl pendant in comparison with the 2-pyridylmethyl and 6-methyl-2-pyridylmethyl pendants on the physicochemical properties of the copper(I) and bis(mu-oxo)dicopper(III) species is discussed.

Algorithms↗
PubMed2002

Synthesis, structures, and magnetic properties of heterodimetal bis(mu-hydroxo)chromium(III)nickel(II) complexes with Tpa derivatives having sterically bulky substituents.

A series of heterodinuclear bis(mu-hydroxo)chromium(III)nickel(II) complexes was newly prepared: [(phen)(2)Cr(mu-OH)(2)Ni(tpa)](ClO(4))(3) x 0.5H(2)O (1), [(phen)(2)Cr(mu-OH)(2)Ni(Me-tpa)](ClO(4))(3) x 2H(2)O (2), [(phen)(2)Cr(mu-OH)(2)Ni(Me(2)-tpa)](ClO(4))(3) x 2H(2)O (3), and [(phen)(2)Cr(mu-OH)(2)Ni(Me(3)-tpa)](ClO(4))(3) x 3H(2)O (4), where phen is 1,10-phenanthroline and tpa, Me-tpa, Me(2)-tpa, and Me(3)-tpa are tris(2-pyridylmethyl)amine, [(6-methyl-2-pyridyl)methyl]bis(2-pyridylmethyl)amine, bis[(6-methyl-2-pyridyl)methyl](2-pyridylmethyl)amine, and tris[(6-methyl-2-pyridyl)methyl]amine, respectively. X-ray crystallography revealed that the structures of 1-4 resemble one another having an edge-shared bioctahedral structure with a Cr(mu -OH)(2)Ni unit (crystal data: 1 x C(2)H(5)OH, triclinic, P1, a = 13.179(4) A, b = 13.685(4) A, c = 14.260(4) A, alpha = 84.95(2) degrees, beta = 77.65(1) degrees, gamma = 90.21(2) degrees, V = 2502(1) A(3), Z = 2, R = 0.103, R(w) = 0.097; 2 x C(2)H(5)OH, triclinic, P1, a = 13.214(2) A, b = 13.657(2) A, c = 14.417(3) A, alpha = 95.205(5) degrees, beta = 102.583(4) degrees, gamma =90.720(3) degrees, V = 2527.3(8) A(3), Z = 2, R = 0.090, R(w) = 0.122; 3 x C(2)H(5)OH, triclinic, P1, a = 13.276(2) A, b =13.696(2) A, c = 14.454(2) A, alpha = 95.640(3) degrees, beta = 102.821(4) degrees, gamma = 90.174(3) degrees, V = 2549.5(6) A(3), Z = 2, R= 0.087, R(w)= 0.119; 4, triclinic, P1, a = 10.8916(9) A, b = 14.268(2) A, c = 17.522(2) A, alpha = 84.498(9) degrees, beta = 74.313(7) degrees, gamma = 72.402(7) degrees, V = 2498.6(5) A(3), Z = 2, R = 0.060, R(w)= 0.088). Chromium and nickel ions are coordinated by two phen's and Me(n)-tpa, respectively, to complete a distorted octahedral coordination sphere. Introduction of the 6-methyl group(s) onto the pyridyl group(s) results in the elongation of the Ni-N bond distances due to an unfavorable steric interaction between the methyl group and the bridging hydroxide group: systematic elongation of the Ni-N bond distances and the Cr ...Ni separations accompanied by an increase in the Cr-O-Ni angles was observed as the number of the methyl groups increases. Variable-temperature magnetic susceptibility measurements of 1-4 (4.2-300 K) indicated that magnetic interactions between Cr(III) and Ni(II) ions are systematically modulated from a very weak antiferromagnetic interaction to a ferromagnetic interaction as the number of the methyl groups increases; the exchange integrals J's for 1-4 are estimated to be -1.4, +0.0, +4.1, and +7.4 cm(-1), respectively. The magneto-structural relationship is discussed in terms of the change in the magnetic orbital energies of nickel(II) centers arising from the change in the Ni-N bond distances.

Journal Article↗
PubMed1996

Preparation, Structure, and Properties of Bis(&mgr;-oxo)dirhenium(III,IV) and -dirhenium(IV) Complexes of Tris(2-pyridylmethyl)amine and Its (6-Methyl-2-pyridyl)methyl Derivatives.

A series of bis(&mgr;-oxo)dirhenium complexes, [Re(2)(&mgr;-O)(2)(L)(2)](PF(6))(n)() (L = tris(2-pyridylmethyl)amine (tpa), n = 3 (1), n = 4 (1a); L = ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine (Metpa), n = 3 (2), n = 4 (2a); bis((6-methyl-2-pyridyl)methyl)(2-pyridylmethyl)amine (Me(2)tpa), n = 3 (3), n = 4 (3a)), have been prepared and characterized by several physical methods. X-ray crystallographic studies for 2, 2a.2CH(3)CN.2H(2)O (2a'), and 3a' (ReO(4)(-) salt), include the first structural determinations of (i) the bis(&mgr;-oxo)-Re(III)Re(IV) complex (2) and (ii) the pair of Re(III)Re(IV) and Re(IV)(2) complexes (2 and 2a'). All the complexes have a centrosymmetric structure, suggesting that the mixed-valence state 2 is of structurally delocalized type. The Re-Re distances for 2, 2a.2CH(3)CN.2H(2)O, and 3a' are 2.426(1), 2.368(1), and 2.383(1) Å, respectively, being consistent with the bond order of 2.5 (sigma(2)pi(2)delta(2)delta) for 2 and 3 (sigma(2)pi(2)delta(2)) for the others. Methyl substitution on the pyridyl moiety of the ligands has no significant influence to the overall structure. Cyclic voltammetry of 1 shows two reversible redox waves at -0.77 ((III,III)/(III,IV)) and 0.09 V ((III,IV)/(IV,IV)) vs Ag/AgCl in acetonitrile. The potentials are slightly more positive for 2 (-0.66 and 0.14 V) and 3(-0.64 and 0.20 V). No proton-coupled redox behavior was observed on addition of p-toluenesulfonic acid. Complexes, 1a, 2a, and 3a show a strong visible absorption band at 477 nm (epsilon, 9200 dm(3) mol(-)(1) cm(-)(1)), 482 (11200), and 485 (8700), respectively, which is assigned to the pi-pi transition within the Re(2)(&mgr;-O)(2) core. For the mixed-valence complexes 1, 2, and 3, a strong band is observed in the longer wavelength region (556-572 nm). Crystal data: 2, monoclinic, space group C2/c (No.15), a = 11.799(2) Å, b = 19.457(3) Å, c = 21.742(4) Å, beta = 98.97(1) degrees, Z = 4; 2a', triclinic, space group P&onemacr; (No. 2), a = 13.151(3) Å, b = 13.535(2) Å, c = 10.243(3) Å, alpha = 104.37(2) degrees, beta = 109.02(2) degrees, gamma = 106.87(1) degrees, Z = 1; 3a', monoclinic, space group P2(1)/n (No. 14), a = 13.384(3) Å, b = 14.243(2) Å, c = 13.215(6) Å, beta = 106.88(2) degrees, Z = 2.

Journal Article↗
PubMed1996

Structural and Electrochemical Comparison of Copper(II) Complexes with Tripodal Ligands.

A series of copper(II) complexes with tripodal polypyridylmethylamine ligands, such as tris(2-pyridylmethyl)amine (tpa), ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine (Me(1)tpa), bis((6-methyl-2-pyridyl)methyl)(2-pyridylmethyl)amine (Me(2)tpa), and tris((6-methyl-2-pyridyl)methyl)amine (Me(3)tpa), have been synthesized and characterized by X-ray crystallography. [Cu(H(2)O)(tpa)](ClO(4))(2) (1) crystallized in the monoclinic system, space group P2(1)/a, with a = 15.029(7) Å, b = 9.268(2) Å, c = 17.948(5) Å, beta = 113.80(3) degrees, and Z = 4 (R = 0.061, R(w) = 0.059). [CuCl(Me(1)tpa)]ClO(4) (2) crystallized in the triclinic system, space group P&onemacr;, with a = 13.617(4) Å, b = 14.532(4) Å, c = 12.357(4) Å, alpha = 106.01(3) degrees, beta = 111.96(2) degrees, gamma = 71.61(2) degrees, and Z = 4 (R = 0.054, R(w) = 0.037). [CuCl(Me(2)tpa)]ClO(4) (3) crystallized in the monoclinic system, space group P2(1)/n, with a = 19.650(4) Å, b = 13.528(4) Å, c = 8.55(1) Å, beta = 101.51(5) degrees, and Z = 4 (R = 0.071, R(w) = 0.050). [CuCl(Me(3)tpa)][CuCl(2)(Me(3)tpa)]ClO(4) (4) crystallized in the monoclinic system, space group P2(1)/a, with a = 15.698(6) Å, b = 14.687(7) Å, c = 19.475(4) Å, beta = 97.13(2) degrees, and Z = 4 (R = 0.054, R(w) = 0.038). All the Cu atoms of 1-4 have pentacoordinate geometries with three pyridyl and one tertiary amino nitrogen atoms, and a chloride or aqua oxygen atom. Nitrite ion coordinated to the Cu(II) center of Me(1)tpa, Me(2)tpa, and Me(3)tpa complexes with only oxygen atom to form nitrito adducts. The cyclic voltammograms of [Cu(H(2)O)(Me(n)()tpa)](2+) (n = 0, 1, 2, and 3) in the presence of NO(2)(-) in H(2)O (pH 7.0) revealed that the catalytic activity for the reduction of NO(2)(-) increases in the order Me(3)tpa << Me(2)tpa << Me(1)tpa < tpa complexes.

Journal Article↗