Masanobu Hidai

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.

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 .

Novel catalytic hydrogenolysis of silyl enol ethers by the use of acidic ruthenium dihydrogen complexes

Abstract Treatment of 1-trimethylsilyloxy-1-cyclohexene (1a) in the presence of a catalytic amount of the acidic dihydrogen complex [RuCl(η2-H2)(dppe)2]OTf (4a) [dppe=1,2-bis(diphenylphosphino)ethane, OTf=OSO2CF3] (10 mol.%) under 1 atm of H2 in anhydrous ClCD2CD2Cl at 50xa0°C for 8 h afforded cyclohexanone (3a) and Me3SiH in quantitative NMR yields. Silyl enol ethers such as 1-triethylsilyloxy-1-cyclohexene (1b), 1-t-butyldimethylsilyloxy-1-cyclohexene (1c), and other trimethylsilylethers (1d, 1e, and 1f) reacted similarly with H2 to afford the corresponding ketones and trialkylsilanes. The direct proton transfer from H2 to the trimethylsilyl enol ethers (1a and 1d–1f) was confirmed by the experiments employing D2 gas, where α-monodeuterated ketones (3a′ and 3d′–3f′) were obtained in high yields. The enantioselective protonation of prochiral silyl enol ethers with 1 atm of H2 by employing [RuCl(η2-H2)((S)-BINAP)2]OTf (4e) [BINAP=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl] and [RuCl(η2-H2)((R, R)-CHIRAPHOS)2]OTf (4f) [CHIRAPHOS=2,3-bis(diphenylphosphino)butane] showed that no enantioselectivity was observed in either catalytic or stoichiometric protonation reactions under various reaction conditions. The reaction of [RuHCl(dppe)2] (5a) with one equivalent of Me3SiOTf under 1 atm of H2 produced rapidly 4a, concurrent with the formation of Me3SiH. Based on these studies, the mechanism for this novel hydrogenolysis of silyl enol ethers is proposed which involves heterolytic cleavage of the coordinated H2 on the ruthenium atom caused by the nucleophilic attack of the oxygen atom of enol ethers to give ketones and Me3SiOTf, and the subsequent reaction of the resultant complex 5a with Me3SiOTf under 1 atm of H2 to regenerate the original dihydrogen complex 4a. On the other hand, the stoichiometric reaction of a lithium enolate 6e with one equivalent of 4e at −78xa0°C in CH2Cl2 under 1 atm of H2 afforded 2-methyl-1-tetralone (3e) with 75% ee (S) in >95% yield, together with the formation of [RuHCl((S)-BINAP)2] (5e).

Preparation of chalcogenolato-bridged dinuclear Tp*Rh–Cp*Ru complexes (Tp*= hydrotris(3,5-dimethylpyrazol-1-yl)borate, Cp*=η5-pentamethylcyclopentadienyl) and binding of dioxygen to their Ru sites

Reactions of [Tp*Rh(coe)(MeCN)](1; Tp*= hydrotris(3,5-dimethylpyrazol-1-yl); coe = cyclooctene) with one equiv of diphenyl dichalcogenides PhEEPh (E = Se, Te) afforded the mononuclear Rh(III) complexes [Tp*Rh(EPh)(2)(MeCN)](2b: E = Se; 2c: E = Te), as reported previously for the formation of [Tp*Rh(SPh)(2)(MeCN)](2a) from the reaction of 1 and PhSSPh. Complexes 2a-2c were treated with the Ru(II) complex [(Cp*Ru)(4)(mu(3)-Cl)(4)](Cp*=eta(5)-C(5)Me(5)) in THF at room temperature, yielding the chalcogenolato-bridged dinuclear complexes [Tp*RhCl(mu-EPh)(2)RuCp*(MeCN)](3). Complex 3a (E = S) in solution was converted slowly into a mixture of 3a and the sterically less encumbered dinuclear complex [Tp*RhCl(SPh)(mu-eta(1)-S-eta(6)-Ph)RuCp*](4a) at room temperature. In 4a, one SPh group binds only to the Rh center as a terminal ligand, while the other SPh group bridges the Rh and Ru atoms by coordinating to the former at the S atom and to the latter with the Ph group in a pi fashion. The Se analogue 3b also underwent a similar transformation under more forcing conditions, e.g. in benzene at reflux, whereas formation of the mu-eta(1)-Te-eta(6)-Ph complex was not observed for the Te analogue 3c even under these forcing conditions. When complexes 3 was dissolved in THF exposed to air, the MeCN ligand bound to Ru was substituted by dioxygen to give the peroxo complexes [Tp*RhCl(mu-EPh)(2)RuCp*(eta(2)-O(2))](5a: E = S; 5b: E = Se; 5c: E = Te). X-Ray analyses have been undertaken to determine the detailed structures for 2c, 3a, 3b, 4a, 5a, 5b, and 5c.

Mono(sulfido)-bridged mixed-valence nitrosyl complex: protonation and oxidative addition of iodine across the Ir(II)–Ir(0) bond

Treatment of [Cp*IrH(SH)(PMe3)] (Cp* = eta5-C5Me5) with [IrCl2(NO)(PPh3)2] in the presence of triethylamine yielded the sulfido-bridged Ir(II)Ir0 complex [Cp*Ir(PMe3)(mu-S)Ir(NO)(PPh3)], which further reacted with I2 and triflic acid to give the diiodo complex [Cp*Ir(PMe3)(mu-I)(mu-S)IrI(NO)(PPh3)] and the hydrido complex [Cp*Ir(PMe3)(mu-H)(mu-S)Ir(NO)(PPh3)][OSO2CF3], respectively.