Hidetake Seino

Catalytic functions of cubane-type M4S4 clusters

Catalysis by the cubane-type Fe4S4 cluster has been found in metalloproteins such as biotin synthase, aconitase, and IspH, whereas some synthetic M4S4 clusters show catalytic activities for biologically related reactions or various types of organic transformations. This minireview summarizes recent progress in the chemistry of catalytic functions of cubane-type M4S4 clusters.

Two-dimensional metamagnet composed of cyano-bridged CuII-WV bimetallic assembly.

Two-dimensional cyanide-bridged copper(II) octacyanotungstates(V), [(Cu(3-CNpy)2(H2O))2(Cu(3-CNpy)2(H2O)2)(W(CN)8)2] (3-CNpy = 3-cyanopyridine) (1) and [(Cu(4-CNpy)2)2(Cu(4-CNpy)2(H2O)2)(W(CN)8)2] x 6H2O (4-CNpy = 4-cyanopyridine) (2), were prepared and these compounds exhibited metamagnetic behavior with Néel temperatures of 8.0 K (1) and 4.4 K (2).

Reactivities of the coordinated organonitriles in molybdenum(0) and tungsten(0) phosphine complexes: protonation of the nitrile carbon and cleavage of the CN triple bond

Abstract The molybdenum and tungsten dinitrogen-organonitrile complexes trans-[M(N2)(NCR)(dppe)2] (2, MMo; 4, MW; RPh, C6H4Me-p, C6H4OMe-p, Me; dppePh2PCH2CH2PPh2) underwent double protonation at the nitrile carbon atom with loss of N2 and a change in oxidation state to +4 on treatment with hydrochloric acid to afford the cationic imido complexes trans-[MCl(NCH2R)(dppe)2]+. The solid-state structure of trans-[WCl(NCH2CH3)(dppe)2][PF6]·CH2Cl2 was determined by single-crystal X-ray analysis. Protonation of complexes 2 by fluoroboric acid or hydrobromic acid also formed the similar imido complexes trans-[MoX(NCH2R)(dppe)2]+ (XF, Br). In contrast, the dinitrogen complex trans-[Mo(N2)2(dppe)2] reacted with two equiv. of benzoylacetonitrile, a nitrile with acidic CH hydrogen atoms, to give the nitrido complex trans-[Mo(N)(NKCCHCOPh)(dppe)2] (12), which was accompanied by evolution of dinitrogen and the formation of 1-phenyl-2-propen-1-one in high yields. For complex 12, the zwitterionic structure, where the anionic enolate ligand PhC(O+)CHCN coordinates to the cationic Mo(IV) center through its nitrogen atom, was confirmed by spectroscopic measurements and single-crystal X-ray analysis. A unique intermolecular aromatic CH⋯O hydrogen bonding was observed in that crystal structure. Complex 12 is considered to be formed via the cleavage of the CN triple bond of benzoylacetonitrile on the metal. A reaction mechanism is proposed, which includes the double protonation of the nitrile carbon atom of the ligating benzoylacetonitrile on a low-valent molybdenum center.

Polymers with Multishape Memory Controlled by Local Glass Transition Temperature

A multishape memory polymer with flexible design capabilities is fabricated by a very simple method. Local glass transition temperatures of a loosely cross-linked polymer film are changed by immersing sections of the film in a cross-linker solution with a different concentration. Each section memorizes a temporary shape, which recovers its permanent shape at a different recovery temperature depending on the local glass transition temperature. As a base polymer, we chose a network polymer prepared by a Diels-Alder reaction between poly(2,5-furandimethylene succinate) (PFS) and 1,8-bis-maleimidotriethyleneglycol (M2). Quintuple shape memory behavior was demonstrated by a PFS/M film with four sections with distinct glass transition temperatures. The number of temporary shapes was determined by the number of different M2 solutions. Furthermore, owing to the reversibility of the Diels-Alder reaction, the permanent shape was rewritable.

Heterolytic H2 activation by rhodium thiolato complexes bearing the hydrotris(pyrazolyl)borato ligand and application to catalytic hydrogenation under mild conditions.

Thiolato complexes of Rh(III) bearing a hydrotris(3,5-dimethylpyrazolyl)borato ligand (Tp(Me2)) have been prepared, and their reactivity toward H(2) has been investigated. The bis(thiolato) complex [Tp(Me2)Rh(SPh)(2)(MeCN)] (1) reacted with 1 atm H(2) at 20 degrees C to produce the hydrido-thiolato complex [Tp(Me2)RhH(SPh)(MeCN)] (2) and PhSH via heterolytic cleavage of H(2). This process is reversible and in equilibrium in THF and benzene. The bis(selenolato) complex [Tp(Me2)Rh(SePh)(2)(MeCN)] (4) was also converted to [Tp(Me2)RhH(SePh)(MeCN)] and PhSeH under 1 atm H(2), but the equilibrium largely shifted to 4. Reaction of the dithiolato complex [Tp(Me2)Rh(bdt)(MeCN)] (3; bdt = 1,2-C(6)H(4)S(2)) with H(2) occurred in the presence of amine, giving the anionic hydrido complex [Tp(Me2)RhH(bdt)](-) and an equimolar amount of ammonium cations. Catalytic activity for hydrogenation has been examined under 1 atm H(2) at 20-50 degrees C. While 1, 2, and 4 slowly hydrogenated styrene at similar rates at 50 degrees C, activities for the hydrogenation of N-benzylideneaniline increased in the order, 2 < 1 < 4. Complex 3 was found to be the most active and selective catalyst for hydrogenation of imines, and thus a variety of imines were reduced at 20 degrees C under 1 atm H(2), with the C=C and C=O bonds in the substrate molecules completely preserved. An ionic mechanism was involved to explain such high chemoselectivity.

Crystal structure of Ce(IV)/dipicolinate complex as catalyst for DNA hydrolysis

The structures of Ce4+ complexes that are active for DNA hydrolysis were determined for the first time by X-ray crystallography. The crystals were prepared from a 1:2 mixture of Ce(NH4)2(NO3)6 and dipicolinic acid (2,6-pyridinedicarboxylic acid). Depending on the recrystallization conditions, three types of crystals were obtained. Some of the Ce4+ ions in these complexes have enough coordinated water molecules that can directly and indirectly participate in the catalysis. The distances between the Ce4+ and the dipicolinate ligand are considerably shorter than those in the corresponding La3+ and Ce3+ complexes. On the other hand, the distances between the Ce4+ and its coordinated water are similar to those for the La3+ and Ce3+ complexes. In a proposed mechanism of DNA hydrolysis, the scissile phosphodiester linkage is notably activated by coordination to Ce4+ and attacked by the Ce4+-bound hydroxide. The process is further assisted by acid catalysis of Ce4+-bound water.

Syntheses and reactivities of hydrosulfido- or sulfido-bridged heterobimetallic complexes containing Group 6 and Group 9 metals

Reactions of [Cp2M(SH)2] (M = Mo 1, W 2) with one equiv of [IrH2(PPh3)2(Me2CO)2][PF6] in acetone at room temperature under 1 atm of H2 afforded the hydrosulfido–hydrido complexes [Cp2M(μ-SH)2IrH2(PPh3)2][PF6] (M = Mo 4, W 5), whereas those of 1 and 2 with [RhH2(PPh3)2(Me2CO)(EtOH)][PF6] 6 resulted in the formation of [Cp2Mo(μ-SH)2Rh(PPh3)2][PF6] 7 and [Cp2W(μ-S)2Rh(PPh3)2][PF6] 8. X-Ray analyses have been undertaken to clarify the detailed structure of [Cp2Mo(μ-SH)2IrH2(PPh3)2][BPh4] derived from 4 along with 7 and 8. Bimetallic complexes 4, 5, 7, and 8 catalysed the hydrogenation of alkynes such as 1-octyne and tert-butyl propiolate at room temperature under 1 atm of H2, yielding 1-octene and tert-butyl acrylate as the major products, respectively. In both reactions, the Mo–Rh complex 7 showed the highest catalytic activity, although even the reactions using 7 are much slower than those catalyzed by the mononuclear Rh complex 6.

Preparation of mononuclear and dinuclear Rh hydrotris(pyrazolyl)borato complexes containing arenethiolato ligands and conversion of the mononuclear complexes into dinuclear Rh–Rh and Rh–Ir complexes with bridging arenethiolato ligands

Reactions of [Tp*Rh(coe)(MeCN)](; Tp*= HB(3,5-dimethylpyrazol-1-yl)(3); coe = cyclooctene) with one equiv. of the organic disulfides, PhSSPh, TolSSTol (Tol = 4-MeC(6)H(4)), PySSPy (Py = 2-pyridyl), and tetraethylthiuram disulfide in THF at room temperature afforded the mononuclear Rh(III) complexes [Tp*Rh(SPh)(2)(MeCN)](3a), [Tp*Rh(STol)(2)(MeCN)](3b), [Tp*Rh(eta(2)-SPy)(eta(1)-SPy)](6), and [Tp*Rh(eta(2)-S(2)CNEt(2))(eta(1)-S(2)CNEt(2))](7), respectively, via the oxidative addition of the organic disulfides to the Rh(I) center in 1. For the Tp analogue [TpRh(coe)(MeCN)](2, Tp = HB(pyrazol-1-yl)(3)), the reaction with TolSSTol proceeded similarly to give the bis(thiolato) complex [TpRh(STol)(2)(MeCN)](4) as a major product but the dinuclear complex [[TpRh(STol)](2)(micro-STol)(2)](5) was also obtained in low yield. Complex 3 was treated further with the Rh(III) or Ir(III) complexes [(Cp*MCl)(2)(micro-Cl)(2)](Cp*=eta(5)-C(5)Me(5)) in THF at room temperature, yielding the thiolato-bridged dinuclear complexes [Tp*RhCl(micro-SPh)(2)MCp*Cl](8a: M = Rh, 8b: M = Ir). Dirhodium complex [TpRhCl(micro-STol)(2)RhCp*Cl](9) was obtained similarly from 4 and [(Cp*RhCl)(2)(micro-Cl)(2)]. Anion metathesis of 8a proceeds only at the Rh atom with the Cp* ligand to yield [Tp*RhCl(micro-SPh)(2)RhCp*(MeCN)][PF(6)](10), when treated with excess KPF(6) in CH(2)Cl(2)-MeCN. The X-ray analyses have been undertaken to determine the detailed structures of 3b, 4, 5, 6, 7, 8a, 9, and 10.

Syntheses of a series of trinuclear MIr2 or pentanuclear MIr4 bimetallic bis(selenido) and selenido-sulfido clusters (M = Pd, Pt, Fe, Co) from diiridium μ-bis(hydroselenido) and μ-hydroselenido-hydrosulfido complexes [{(η5-C5Me5)IrCl}2(μ-SeH)(μ-EH)] (E = Se, S)

Abstract Reactions of a diiridium μ-bis(hydroselenido) complex [Cp*IrCl(μ-SeH) 2 IrCp*Cl] ( 1a ; Cp*=η 5 -C 5 Me 5 ) with [MCl 2 (cod)] (M=Pd, Pt; cod=1,5-cyclooctadiene), FeCl 2 , and CoCl 2 readily afforded the bimetallic selenido clusters containing a trinuclear or a pentanuclear cores [(Cp*Ir) 2 (MCl 2 )(μ 3 -Se) 2 ] (M=Pd, Pt ( 5 ), Fe ( 6 )) and [(Cp*Ir) 4 Co(μ 3 -Se) 4 ][CoCl 3 (MeCN)] 2 ( 8 ). Cluster 6 was converted to the latter-type bow-tie cluster [(Cp*Ir) 4 Fe(μ 3 -Se) 4 ][BPh 4 ] 2 ( 7 ) by treatment with an additional amount of 1a and excess NaBPh 4 . Novel μ-hydroselenido–hydrosulfido complex [Cp*IrCl(μ-SeH)(μ-SH)IrCp*Cl] ( 3 ) was obtained by the reaction of [Cp*IrCl(μ-Cl) 2 IrCp*Cl] with one equiv of H 2 Se generated in situ from a NaSeH/HCl aq. mixture, followed by that with H 2 S gas. Treatment of 3 with a range of transition metal compounds has shown that 3 can serve as a good precursor to synthesize a series of mixed-chalcogenido clusters in a rational manner; selenido–sulfido clusters derived from 3 include [(Cp*Ir) 2 (MCl 2 )(μ 3 -Se)(μ 3 -S)] (M=Pd, Pt, Fe ( 14 )), [(Cp*Ir) 2 {PtCl(PPh 3 )}(μ 3 -Se)(μ 3 -S)]Cl ( 13 ), [(Cp*Ir) 4 Co(μ 3 -Se) 2 (μ 3 -S) 2 ][CoCl 3 (MeCN)] 2 ( 15 ), and [(Cp*Ir) 4 Fe(μ 3 -Se) 2 (μ 3 -S) 2 ][BPh 4 ] 2 . To determine the detailed structures, X-ray analyses have been undertaken for 5 ·1/2ClCH 2 CH 2 Cl, 6 , 7 , 8 , 13 ·CH 2 Cl 2 , 14 , and 15 ·CH 2 Cl 2 .

Reactions of tetraphosphine complex [Mo {meso-o-C6H4(PPhCH2CH2PPh2)2}(Ph2PCH2CH2PPh2)] with nitrile, CO, and isocyanide

When treated with three equivalents of PhCN in benzene at room temperature, [Mo(η 4 - P 4 )(dppe)] ( 1 ) containing a linear tetraphosphine meso - o -C 6 H 4 (PPhCH 2 CH 2 PPh 2 ) 2 ( P 4 ) as well as a diphosphine Ph 2 PCH 2 CH 2 PPh 2 (dppe) afforded a nitrile complex [Mo(PhCN)( fac -η 3 - P 4 )(dppe)] ( 2 ), whereas treatment of 1 with CO (1 atm) in benzene at room temperature resulted in the formation of a 1:1 mixture of the CO analogue of 2 [Mo(CO)( fac -η 3 - P 4 )(dppe)] and a bis(carbonyl) complex cis -[Mo(CO) 2 (η 4 - P 4 )]. In contrast, reactions of 1 with XyNC (Xy=2,6-Me 2 C 6 H 3 ) gave more diversified products varying from mono(isocyanide) to tris(isocyanide) complexes. Thus, reaction of 1 with an equimolar amount of XyNC gave a mixture of two isomers of mono(isocyanide) complex [Mo(XyNC)( fac -η 3 - P 4 )(dppe)] ( 5 and 6 ) along with a bis(isocyanide) complex cis -[Mo(XyNC) 2 (η 4 - P 4 )] ( 7 ). It has also been found that mono(isocyanide) complexes 5 and 6 are treated further with one equivalent of XyNC at elevated temperatures to form the expected bis(isocyanide) complex 7 as well as the other bis(isocyanide) complex trans -[Mo(XyNC) 2 (η 2 - P 4 )(dppe)] ( 8 ). By heating in solution, the latter was converted into the former. From the reaction of 7 with excess XyNC, a tris(isocyanide) complex [Mo(XyNC) 3 ( fac -η 3 - P 4 )] was obtained. The X-ray analyses have disclosed the detailed structures for 2 , 5 , 7 , and 8 .