Shiro Matsukawa

A structure-activity relationship for pincer palladium(II) complexes: influence of ring-size of metallacycles on the activity in allylic alkylation

A series of new palladium(II) complexes derived from the well-known pincer complex [PdCl{(C 6 H 3 )(OP i Pr 2 ) 2 -2,6}] were synthesised: [PdX{(C 6 H 3 )(OP i Pr 2 ) 2 -2,6}] (X=Br − , I − , OAc − , OTf − ). A novel PCP′ pincer ligand 1-( i Pr 2 PO)-3-( i Pr 2 POCH 2 )(C 6 H 4 ) was prepared and complexed to palladium(II) to give [PdX{(C 6 H 3 )(OP i Pr 2 )-2-(CH 2 OP i Pr 2 )-6}] (X=Cl − , I − , OAc − , OTf − , BF 4 − ). The X-ray structure of [PdCl{(C 6 H 3 )(OP i Pr 2 )-2-(CH 2 OP i Pr 2 )-6}] was solved and is discussed. These complexes were applied to the catalytic reaction of cinnamyl acetate with sodium dimethyl malonate in order to evaluate the influence of the ligand structure and co-ordinating or non-co-ordinating anions on the regioselectivity. A detailed analysis shows that palladium(II) complexes of the unsymmetrical PCP′ bis(phosphinito) ligand are much more active when compared to related complexes of the symmetrical PCP bis(phosphinito) ligand. The origin of this difference in activity is discussed.

Stereomutation and apicophilicity of diastereomeric spirophosphoranes (10-P-5)

Abstract The apicophilicity for a series of monodentate groups were determined by deducing activation parameters of equilibration between diastereomeric spirophosphoranes bearing a Martin ligand and a modified Martin ligand. The equilibration was shown to be an intramolecular process and the order of apicophilicity of the groups turned out to be OMe≈H>COMe≈SMe>NMe2>Me>n-Bu on the basis of activation enthalpy. The involvement of π-conjugation type interactions was revealed by X-ray structures of symmetric analogs bearing COMe (acceptor) and NMe2 (donor) groups.

Pentacoordinate organoantimony compounds that isomerize by turnstile rotation.

Two stereoisomers of pentacoordinate antimony compounds (stiboranes) with a new rigid tridentate ligand were synthesized, and the isomerization was found to proceed by the turnstile rotation (TR) mechanism with the tridentate ligand as a trio and the two monodentate ligands as a pair.

Stereospecific stilbene formation from β-hydroxy-α, β-diphenylethylphosphoranes. Mechanistic proposals based upon stereochemistry

Abstract All four diastereomers of β-hydroxy-α,β-diphenylethylspirophosphoranes bearing two Martin ligands were prepared from a P–H (equatorial) spirophosphorane. Treatment of these phosphoranes with t-BuOK or t-BuONa at low temperature (ca. −40°C) led to the formation of stilbene with complete stereospecificity. In half of the cases the reaction proceeded quantitatively, whereas the other half gave rise to retro-aldol reaction with the formation of varying amounts of benzaldehyde and benzylphosphorane. A kinetic examination revealed that of the four the quantitatively proceeding reaction that gives cis-stilbene was the fastest. Based on the experimental observations, a mechanistic rationale for the previously reported Wittig-type reaction of exceptionally high Z-selectivity using an ethoxycarbonylmethylspirophosphorane is presented.

The first enantiomerically pure, C2-symmetric spiroselenurane: 3,3,3′,3′-tetramethyl-1,1′-spirobi[3H,2,1]-benzoxaselenole

Abstract The enantiomers of a C2-symmetric spirobisalkoxyselenurane, 3,3,3′,3′-tetramethyl-1,1′-spirobi[3H,2,1]-benzoxaselenole, have been isolated for the first time via chromatographic resolution of the racemate using a chiral HPLC column. The isomers were further characterized by 1H NMR and CD spectroscopic measurements.

Some reactions of O-equatorial spirophosphoranes bearing the bidentate ligand based on decafluoro-3-phenyl-3-pentanol

Some reactions of O-equatorial and O-apical methylphosphoranes bearing two bidentate ligands consisted of 1,1,1,2,2,4,4,5,5,5-decafluoro-3-phenyl-3-pentanol were examined. Not only the O-apical phosphorane, but also the O-equatorial isomer did not react with MeLi as a nucleophile at the phosphorus center. This should be due to the steric bulkiness of the C 2 F 5 group. For both isomers, deprotonation at the methyl group was achieved using Superbase (t-BuOK/n-BuLi) to give the corresponding α-anion, which was treated with several electrophiles to afford new phosphorane derivatives. The O-equatorial and O-apical phosphoranes having a β-hydroxyethyl group as the monodentate ligand were synthesized. It was found that under basic conditions, the O-apical phosphorane could be converted into the O-equatorial isomer via hexacoordinate phosphate intermediates.

Synthesis and structure of hypervalent boron (10-B-5) compounds bearing a 2,6-(p-tolyloxymethyl)benzene tridentate ligand

Several organoboron compounds having a tridentate ligand based on 2,6-bis(p-tolyloxymethyl)benzene (5) were prepared. X-ray crystallography revealed that the distances between the central boron and both oxygen atoms of the tridentate ligand varied from 2.50 A to 3.16 A. The boron atom of the pinacolato derivative (5a) was found to be tricoordinated, whereas those of the diphenyl (5b) and the catecholato derivative (5c) were pentacoordinated, although these molecular structures were unsymmetrical. Compound 5c was found to have the strongest B[sbnd]O interactions among this series because the B[sbnd]O distances of 5c (av. 2.60 A) are shorter than those for 5b (av. 2.65 A), and this could mainly come from the electronic effect of the substituents at the boron atom.

The NCN-Type Pincer Complex of Palladium(II) with a 2,6-Bis(2-pyridyl)-4-tert-butylbenzene Tridentate Ligand: Synthesis, Structure and Catalytic Activity in the Mizoroki-Heck Reaction

The reaction of 1-bromo-4-tert-butyl-2,6-diiodobenzene with 2-pyridylzinc chloride in the presence of catalytic Pd(PPh 3 ) 4 afforded an NCN-type pincer palladium(II) complex with two pyridine donors. The structure of the complex was determined by X-ray crystallography. The complex was found to catalyze the Mizoroki-Heck reaction at 250 °C under aerobic conditions.

Synthesis and Characterization of Antiapicophilic Arsoranes and Related Compounds

Utilizing bulky bidentate ligand systems with C(2)F(5) and n-C(3)F(7) groups, antiapicophilic arsoranes (5b and 5c, respectively) were synthesized. A kinetic study on the isomerization of these arsoranes to their more stable isomers showed that the barriers increased in the order of CF(3) < C(2)F(5) < n-C(3)F(7) in accord with their steric bulk. It was also revealed that the degree of freezing isomerization was larger for the change from CF(3) to C(2)F(5) than from C(2)F(5) to n-C(3)F(7), obvious from the differences in activation free energy at 363 K of 1.6 and 0.3 kcal mol(-1), respectively. X-ray structural analysis of several precursors of these two systems disclosed the unique structures of these compounds.

Solution and Crystal Structure of a Hexacoordinate Phosphoranate Bearing Two Martin Ligands and Two Methyl Groups

A hexacoordinate phosphoranate bearing two Martin ligands and two methyl groups was synthesized by the reaction of the monocyclic phosphorane bearing a hydroxy group with KH, and was crystallized in the presence of 18-crown-6 ether. The crystal structure of the phosphoranate could be regarded as an intermediate model in the reaction of the O-equatorial methylphosphorane with a methyl anion.