Yoshitaka Tatsuno

Preparation of optically active peralkyldiphosphines and their use, as the rhodium(I) complex, in the asymmetric catalytic hydrogenation of ketones

Abstract Two types of the optically active peralkyldiphosphine, 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(dialkylphosphino)butane (Rdiop 3) and N-(N′-substituted carbamoyl-4-dicyclohexylphosphino-2-dicyclohexylphosphinomethylpyrrolidine (R-Cycapp 8), have been prepared by various synthetic methods. Rhodium(I) complexes of 3 and 8 showed high catalytic activity for hydrogenation of various kinds of prochiral ketones, which were reduced smoothly to the corresponding optically active hydroxy compounds, under hydrogen at atmospheric pressure and ambient temperature. The neutral rhodium(I) complexes (diphosphine-RhN) hydrogenated α-ketoamides and α-ketopantolactone in fairly high optical yields (66–77%ee). In the hydrogenation of N-(α-ketoacyl)-α-amino esters, the Cydiop-RhN catalyst showed a marked contrast to the diop-RhN system; in the hydrogenation of the methyl ester of N-(phenylglyoxyl)-(S)-α-phenylalanine, 72%de was attained with little double asymmetric induction by the chiral center in the substrate.

Mechanistic aspects of catalytic hydrogenation of ketones by rhodium(I)-peralkyldiphosphine complexes

Mechanistic aspects of the hydrogenation of ketones employing cationic rhodium(I) complexes [Rh((i-Pr)2P(CH2)4P(i-Pr)2)(NBD)]ClO4 (NBD = norbornadiene) and [Rh(CyDIOP)(NBD)]ClO4 (CyDIOP = 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(dicyclohexylphosphino)butane) and a neutral complex, “Rh-(CyDIOP)Cl” were studied. The cationic complex-catalyzed hydrogenation of the poor coordinating simple ketone substrates followed a rate equation r0 = kobs[Rh][ketone]0[H2]0 and showed an unusual negative temperature dependence of the reaction rate. The hydrogenation of the chelating substrate PhCOCONHCH2Ph followed a rate equation r0 = kobs[Rh][H2] with the activation parameters Ea 5.51 kcal mol−1, ΔH‡308 4.90 kcal mol−1, ΔS‡308 −32.0 e.u. ([Rh((i-Pr)2P(CH2)4P(i-Pr)2)(NBD)]ClO4 catalyst); Ea 5.36 kcal mol−1, ΔH‡308 4.75 kcal mol−1, ΔS‡308 − 30.9 e.u. ([Rh(CyDIOP)(NBD)]ClO4 catalyst). For the neutral complex-catalyzed hydrogenation of PhCOCONHCH2Ph, the rate equation r0 = [Rh]0.25[ketone]0[H2]0 was obtained with the activation parameters (Ea 3.99 kcal mol−1 ΔH‡308 3.38 kcal mol−1, ΔS‡308 −43.0 e.u.). Several intermediate complexes in the cationic complex-catalyzed hydrogenation were also detected spectroscopically or isolated. On the basis of these observations, a general reaction scheme was proposed.

Heteropolyvanadates as catalysts for oxygenation of 3,5-Di-t-butylcatechol

Abstract Three heteropolyvanadates, [PV 14 O 42 ] 9− (6), [MnV 13 O 38 ] 7− (7) and [NiV 13 O 38 ] 7− (8) efficiently catalyzed the oxygenation of 3,5-di-t-butylcatechol (1) with dioxygen to give 2,4-di-t-butylmuconic acid anhydride (2), 4,6-di-t-butyl-2-pyrone (3), 3,5-di-t-butyl- o -benzoquinone (4) and the quinone dimer 3,4a,6,8-tetra-t-butyl-4a,10a-dihydrodibenzo- p -dioxin-1,2-dione (5).The 18 O labeling experiments revealed that oxygen atoms involved in the oxygenated products 2 and 3 came from dioxygen and not from the oxyanions present in the heteropolyvanadates. Reaction of 6 with an excess of 1 under dinitrogen resulted in the formation of the blue complex [V(DBSQ)(DBcatH) 2 ] 2 (13), which was assumed to be the reaction intermediate complex in the catalysis on the basis of its reactivity and spectroscopic data. The reaction mechanism for the oxygenation of 1 catalyzed by heteropolyvanadates was discussed.

A new rhodium trinuclear complex containing highly protected hydroxo groups, [{Rh(binap)}3(µ3-OH)2]CIO4, responsible for deactivation of the 1,3-hydrogen migration catalyst of allylamine [binap = 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl]

A new stable rhodium trinuclear complex, [{Rh(binap)}3(µ3-OH)2]ClO4[binap = 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl](2), formed when water deactivates the RhI–binap complex catalysed asymmetric 1,3-hydrogen migration of allylamine, has been isolated; and X-ray structural analysis of the deuterium derivative [{Rh[(+) binap]}3(µ3-OD)2]ClO4 revealed a unique structure with two highly protected µ3-hydroxo groups.

Preparation of new chiral peralkyldiphosphines as efficient ligands for catalytic asymmetric hydrogenation of α-dicarbonyl compounds

New chiral peralkyldiphosphines (5) containing a pyroolidine ring have been prepared by a new method, which is widely applicable to transformation of known chiral diphosphines into the corresponding cyclohexyl analogues; asymmetric hydrogenation of α-dicarbonyl compounds catalysed by rhodium complexes of (5) proceeds smoothly under mild conditions (1 atm H2; 35°C) to give moderate optical yields.

Crystal structure of di-µ-sulphur dioxide-pentakis(t-butyl isocyanide)-triangulo-tripalladium–dibenzene

A single-crystal X-ray analysis on the title compound revealed an interesting cluster structure involving SO2 bridging.

Diazoalkane–nickel(0) complexes

The preparation, characterisation, and thermal decomposition of a series of the title complexes are reported.

Oxygen exchange between the Fe(IV)O heme and bulk water for the A2 isozyme of horseradish peroxidase

Resonance Raman spectra were observed for compound II of horseradish peroxidase A2, and the Fe(IV)O stretching Raman line was identified at 775 cm−1. This Raman line shifted to 741 cm−1 upon a change of solvent from H2 16O to H2 18O, indicating occurrence of the oxygen exchange between the Fe(IV)O heme and bulk water. The oxygen exchange took place only at the acidic side of the heme‐linked ionization with pK a = 6.9.

Vanadium catalyzed oxygenation of 4,6-di-tert-butylpyrogallol. A model reaction for intradiol dioxygenase

Abstract Recently, we have reported the intradiol cleavage of 3,5-di tert -butylcatechol with molecular oxygen catalyzed by several vanadium complexes as a model reaction for intradiol dioxygenase [1]. Although the enzymatic [2] or the base catalyzed [3] cleavage of pyrogallol are known, metal catalyzed oxygenation of pyrogallol have not been reported yet. Here we wish to report vanadium catalyzed oxygenation of 4,6-di- tert -butylpyrogallol ( 1 ) and discuss the reaction mechanism based on the isotopic labelling experiment and the structure of the isolated reaction intermediate complex. Oxidation of 1 (0.1 M in CH 2 Cl 2 ) in the presence of a catalytic amount of VO(salen) (1 mol%) with molecular oxygen at room temperature for 20 h produced 3,5-di- tert -butyl-2-pyrone-6-carboxylic acid ( 2 ) (41%), 3,5-di- tert -butyl-5-hydroxy-2-furanone ( 3 ) (8%) besides a quinone dimer ( 4 ) (24%) [see eqn. (1)]. These products were characterized from elemental analyses, IR, 1 H NMR and mass spectra. 18 O isotopic labelling experiments indicated that 18 O atoms were incorporated into 2 (one atom) and 3 (two atoms) and that an 18 O atom in 2 was located in the carboxylic acid moiety, but not in the lactone moiety. These facts suggest that the main product 2 is formed by rearrangement of an intermediate ( 5 ) arising from the intradiol ring cleavage of 1 just as in the enzymatic reaction [see eqn. (2)]. As the compound 5 corresponds by Hamilton [4] in the enzyme reaction, the vanadium catalyzed oxygenation of the pyrogallol 1 proceeds via the Hamilton intermediate similarly to oxygenation of 3,5-di- tert -butylcatechol [1]. Reaction of 1 with VO(salen) under nitrogen atmosphere gave a complex ( 6 ) as a black brown powder (mp 135-40°C, dec.) which showed a similar catalytic activity for the oxygenation of 1 to that of VO(salen) [see eqn. (3)]. Based on the elemental analyses, IR, and ESR spectra, the structure of 6 was proposed as shown in Fig. 1. Thus, VO(salen) + 2·1 → 6 the complex 6 can be regarded as a model complex for the enzyme-substrate complex. Coordination of the pyrogallol monoanion to the metal ion leading to the activation of the substrate is essential for the oxygenation of 1.

Preparation and structure of [Rh{(?5-C5H4(2-C5H4N))(?5-C5H4PPh2)}(cod)]PF6 and [Ir(H){Fe[?5-C5H3(2-C5H4N)](?5-C5H4PPh2)}(cod)]PF6; a Rh I complex having a C?H ? Rh I interaction and a hydrido Ir III complex (where cod = cyclo-octa-1,5-diene)

A rhodium complex (2) of [Fe{η5-C5H4(2-C5H4N)}(η5-C5H4PPh2)] contains a C–H ⋯ RhI interaction, which shows a marked high-frequency shift in the 1H NMR spectrum, whereas the corresponding iridium complex forms an iridium(III) hydrido complex (3), resulting from the oxidative addition of the C–H bond.