Kazuhide Tani

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.

Asymmetric epoxidation of hydrocarbon olefins by tert-butyl hydroperoxide with molybdenum(VI) catalysts in the presence of optically active diols. Application to the asymmetric synthesis of (3S)-2,3-oxidosqualene

Catalytic enantioselective epoxidation of prochiral olefins without functional groups was achieved by tert-BuOOH using Mo(O)2(acac)2-optically active diols as catalysts.

Half‐Metallocene Tantalum Complexes Bearing Methyl Methacrylate (MMA) and 1,4‐Diaza‐1,3‐diene Ligands as MMA Polymerization Catalysts

Activation with AlMe3 at low temperature converts half-metallocene complexes of tantalum with methyl methacrylate (MMA) and diazadiene ligands such as [Cp*Ta(η2 -Cy-DAD)(η4 -MMA)] (structure shown) into effective catalysts for the polymerization of MMA. Polymerization is complete after 10 min at -20°C and gives a poly(methyl methacrylate) of narrow polydispersity. Cp*=η5 -C5 H5 , Cy-DAD=1,4-dicyclohexyl-1,4-diaza-1,3-butadiene.

Synthesis, characterisation and structure of square-planar palladium(II) complexes with phosphine–pyridine hybrid ligands o-Ph2PC6H4CH2O(CH2)nC5H4N-2 (n= 1–3). Isolation of the first transition-metal complex with a trans-chelating bidentate PN ligand

The reaction of Na2[PdCl4] or [PdCl2(PhCN)2] with an equimolar amount of new bidentate hybrid ligands having a P and a N donor atom capable of trans chelation, o-Ph2PC6H4CH2O(CH2)nC5H4N-2 (n= 1–3), gave mainly the 1 : 1 complex [PdCl2{o-Ph2PC6H4CH2O(CH2)nC5H4N-2}]. Depending on the length of the backbone connecting the phosphino and the pyridyl groups, cis- or trans-co-ordinated complexes were mainly formed; when n= 1 the cis complex 1 was formed, but the ligands with longer bridges gave the trans complexes 2 and 3 respectively as the main products. From the reaction of the palladium(II) complex with o-Ph2PC6H4CH2O(CH2)nC5H4N-2 (n= 2 or 3) the trinuclear complexes [Pd3Cl6{o-Ph2PC6H4CH2O-(CH2)nC5H4N-2}2]4(n= 2) and 5(n= 3) were also obtained as minor products and the cis-chelated complexes analogous to 1 could not be isolated. The reaction of Na2[PdCl4] with 2 equivalents of o- Ph2PC6H4CH2O(CH2)3C5H4N-2 gave quantitatively the 1 : 2 complex trans-[PdCl2{o-Ph2PC6H4CH2O-(CH2)3C5H4N-2}2]7 in which the ligand is bound only through the P atom. This complex is in equilibrium with the trans 1 : 1 complex 3 in solution, dissociating one molecule of the ligand (Keq= 5.6 × 10–3 mol dm–3, 35 °C). On heating in CH2Cl2-tetrahydrofuran or diethyl ether, 3 partially isomerised to the dinuclear complex [Pd2Cl4{µ-o-Ph2PC6H4CH2O(CH2)3C5H4N-2}2]6, in which the hybrid ligands act as bridges. The crystal structures of 1, 3 and 6 were determined; 3 is the first example of a transition-metal complex with a trans-spanning chelate phosphine-pyridine hybrid ligand. The reaction of the ligand o-Ph2PC6H4CH2-O(CH2)3C5H4N-2 with K2[PtCl4], in contrast to the palladium complexes, always gave the 1 : 2 complex trans-[PtCl2{o-Ph2PC6H4CH2O(CH2)3C5H4N-2}2]8 in good yield regardless of the ligand: Pt ratio. It did not dissociate in solution and the trans-chelated complex analogous to 3 could not be isolated even from the reaction of K2[PtCl4] with an equimolar amount of the ligand o-Ph2PC6H4CH2O(CH2)3C5H4N-2.

Convenient synthesis of anionic dinuclear ruthenium(II) complexes [NR2H2][{RuCl(diphosphine)}2(μ-Cl)3] [diphosphine=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl, 2,2′-bis(di(p-tolyl)phosphino)-1,1′-binaphthyl, and 1,2-bis(diphenylphosphino)benzene]: crystal structure of [NEt2H2][{RuCl(1,2-bis(diphenylphosphino)benzene)}2(μ-Cl)3]

Abstract We report a practical one-pot synthesis of dialkylammonium salts of anionic dinuclear ruthenium complexes having chelating diphosphine ligands, BINAPs and DPB, with formula of [NEt2H2][{RuCl(diphosphine)}2(μ-Cl)3] [2a: diphosphine=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl; 6a: 2,2′-bis(di(p-tolyl)phosphino)-1,1′-binaphthyl; 8a: 1,2-bis(diphenylphosphino)benzene]. Treatment of cationic ruthenium complexes, [RuCl(η6-p-cymene)(diphosphine)]Cl (4) with a slight excess of NEt2H2Cl (5a) afforded 2a, 6a, and 8a in quantitative yields. Similar reactions with various dialkylammonium salts 5b–f gave the corresponding salts, [NR2H2][{RuCl(diphosphine)}2(μ-Cl)3]. A one-pot mixture of BINAP or its derivative, [RuCl2(η6-arene)]2, and NR2H2Cl produced salts of the anionic dinuclear complexes which can be applied as catalysts for the asymmetric hydrogenation of ketonic substrates such as acetol and methyl acetoacetate with high activity and high enantioselectivity. The anionic face-sharing bioctahedral structure of these complexes was confirmed by the X-ray analysis of 8a, which has two hydrogen bonds between two NH of the diethylammonium cation and two terminal chloro-ligands.

Synthesis and reactions of coordinatively unsaturated 16-electron chalcogenolate complexes, Ru(EAr) 2(η6-arene) and cationic binuclear chalcogenolate complexes, [(η6-arene) Ru(μ-EPh)3 Ru(η6-arene)]PF6

Abstract Coordinatively unsaturated 16-electron ruthenium-selenolate complexes (η6-arene)Ru(Se-2,4,6-C6H2Me3)2 [arene =p=CH3C6H4(CHMe2) (5b), C6Me6 (5c)] have been prepared by treating [((η6-arene)RuCl2]2 (1) with sodium salt of 2,4,6-trimethylphenyl-selenolate in methanol. The complexes 5 are compared with the thiolate complexes such as (η6-arene)Ru(SAr)2 [SAr = 2,6-dimethylbenzenethiolate (2), SAr = 2,4,6-tri(isopropyl)benzenethiolate (3), (SAr)2 = 1,2-benzenedithiolate (4); arene = C6H6 (a), p-CH3C6H4(CHMe2) (b), C6Me6 (c)], which have been recently prepared by us. However, the tellurolate analog has not been obtained in similar manner. These selenolate complexes are dark green, being ascribed to the LMCT band [pπ(Se)→ dπ*(Ru)]. The absorption bands of S are red-shifted compared to the thiolate complexes. In contrast to the bulky substituted chalcogenolate ligand system, the reaction of 1 with PhENa followed by the addition of KPF6 resulted in the formation of the cationic binuclear chalcogenolate complexes [(η6-arene)Ru(μ-E-Ph)3Ru(η6-arene)](PF6) [E=Se (7), E = Te (8); arene = p-CH3C6H4(CHMe2) (b) C6Me6 (c)]. Reactions of the 16-electron thiolate and selenolate complexes with σ-donor molecules such as DMSO, hydrazine and ammonia along with some electrophiles were investigated. DMSO can coordinate with the thiolate complex 2a to give a DMSO adduct of 9, which was characterized spectroscopically and crystallographically. The strength of complexation of hydrazine and ammonia to the thiolate and selenolate complexes 2, 3, 4c and 5 depends on the effective electron deficiency of the ruthenium supported by η6-arene ligand and two chalcogenolate ligands. Two new hydrazine complexes (η6-C6H6)Ru(η1-NH2)(S-2,6-C6H3Me2)2 (10a) and [(η6-C6Me6)Ru(S2C6H4)]2(μ-NH2NH2) (16) were crystallographically characterized. The observed two different coordination modes, mononuclear η1-hydrazine and binuclear μ-hydrazine, were the results of the combined steric effect of the arene and the thiolate coligands as well as the NH …S hydrogen bonding.

Stereoselective reaction of ±-7-Phenyldinaphtho[2,1-b;1′,2′-d]phosphole with an optically active palladium complex. Molecular structure and fluxional behavior of Pd(S)- C6H4CH(CH3)N(CH3)2(P)-PPh(C20H12) Cl

Abstract Reaction of ±-7-phenyldinaphtho[2,1- b ;1′,2′- d ]phosphole ( 1 ) with one-half equivalent of an optically active palladium complex, Pd[( S )-C 6 H 4 CH(CH 3 )N(CH 3 ) 2 ](μ-Cl) 2 (( S )- 3a ), proceeded stereoselectively to give one of the diastereomers, Pd( S )-C 6 H 4 CH(CH 3 )N(CH 3 ) 2 ( P )-PPh(C 20 H 12 )Cl (( S )( P ) 4a ), accompanying racemization of 1 . The X-ray crystallographic analysis of ( S ( P )- 4a determined the absolute configuration of the coordinated phosphole unequivocally to be P . The fluxional behavior of 4a and the related complex is also discussed.

Vanadium(II) complexes as efficient reagents for direct construction of asymmetric quaternary carbons from carbonyl compounds

Abstract Direct geminal diallylation of propiophenone with allyl bromide has been achieved in the presence of vanadium(II) species. By applying this method, direct construction of asymmetric quaternary carbons from propiophenone has been accomplished. Strong oxophilicity of the low-valent vanadium facilitated the deoxygenative reaction. The present reaction is characteristic of vanadium complexes.

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.