Hideo Kurosawa

Organopalladium complexes containing palladiumpalladium bonds

Abstract This review covers recent achievements in the field of organopalladium chemistry involving PdPd bonds. Several new aspects are reported with regard to the role of PdPd bonds in catalysis, especially new binding modes and transformations of unsaturated hydrocarbons on a PdPd bond.

Discrete Sandwich Compounds of Monolayer Palladium Sheets

Despite the abundance of “sandwich” complexes, in which two cyclic aromatic hydrocarbon ligands flank a metal center, this motif has not been extended to sheets of multiple metal atoms. We prepared and isolated two such compounds. In the first, three palladium centers form a planar triangular array, capped by chlorides, between two cycloheptatrienyl ligands. In the second, a pentapalladium sheet adopts an edge-sharing triangle-trapezoid skeleton between two naphthacene rings. The compounds were characterized by x-ray crystallography and nuclear magnetic resonance spectroscopy. The nature of bonding in the clusters was analyzed by quantum calculations.

Synthesis and reaction of ruthenium(II) complexes containing heteroatom donor (O, N, and P) tethered to η6-arene ring

Abstract Synthesis of ruthenium(II) complexes chelated by the η6-arene ring and a pendent donor atom (O, N, and P) is described. The alcohol-containing η6-arene ruthenium complexes [Ru{η6-C6H5(CH2)3OH}(PR3)Cl2] (1a R=Ph; 1b R=Et) and [Ru{η6-C6H5(CH2)3OH}L2Cl]BF4 (2a L2=2,2′-bipyridine; 2b L2=1,10-phenanthroline; 2c L2=2,2-bis[4(R)-phenyl-1,3-oxazolon-2-yl]propane, (R)-bpop) were prepared by treatment of [Ru{η6-C6H5(CH2)3OH}Cl2]2 with tertiary phosphines or N,N′-chelate ligands/NaBF4, respectively. Addition of 1 equiv. of AgBF4 to a solution of complexes 1 or 2 gave alcohol chelate complexes [Ru{η6:η1-C6H5(CH2)3OH}(PR3)Cl]BF4 (3a–b) or [Ru{η6:η1-C6H5(CH2)3OH}L2](BF4)2 (4a–c), respectively. Although stable in MeOH, the alcoholRu chelate bond of 3 and 4 was cleaved by Cl− ion. Treatment of 4 with bases (OH−, R3N) led to abstraction of the hydroxy proton to give alkoxy chelate complexes [Ru{η6:η1-C6H5(CH2)3O}L2]BF4 (5a–c). In CH2Cl2 acidity of the hydroxy proton in 4c was revealed to be comparable to that of N-methylbenzylammonium cation (pKa in H2O, ca. 11). Amino chelate complexes [Ru{η6:η1-C6H5(CH2)nNH2}(PPh3)Cl]BF4 (7a n=3; 7b n=2) were prepared by treatment of ammonium complexes [Ru{η6-C6H5(CH2)nNH3Cl}(PPh3)Cl2] (6a n=3; 6b n=2) with 1 equiv. of NaOH and NaBF4. 7 were stable to the attack of Cl− ion. In contrast, the similar treatment of dimethylammonium derivative [Ru{η6-C6H5(CH2)3NMe2HCl}(PPh3)Cl2] (8) with KOH gave a non-chelate complex [Ru{η6-C6H5(CH2)3NMe2}(PPh3)Cl2] (9). Phosphorous chelate complexes [Ru{η6:η1-C6H5(CH2)3OPPR2}Cl2] (10a R=Ph; 10b R=iPr) were prepared by reaction of [Ru{η6-C6H5(CH2)3OH}Cl2]2, PPR2Cl, and EtNiPr2. Treatment of 10b with AgBF4 and CO (1 atm) gave the cationic carbonyl complex [Ru{η6:η1-C6H5(CH2)3OPiPr2}(CO)Cl]BF4 (11).

Preparation and properties of monoalkylthallium derivatives

Abstract Several monomethyl- and monoethylthallium derivatives have been synthesized for the first time. Methylthallium dicarboxylates are found to decompose when heated or treated with halide anions to give thallous ion and methyl esters of carboxylic acids, methanol or methyl halides. From the structural studies on RTl(Ox)2 and RTl(OOCC3H7-iso)2 (R = CH3 and C2H5) in solution, it is suggested that these compounds have penta-coordinated thallium atoms.

Reductive Coupling of Metal Triangles in Sandwich Complexes

The one-electron reduction of [Pd3(C7H7)2(CH3CN)3][BF4]2 in acetonitrile resulted in the formation of the dimer dication [Pd6(C7H7)4(CH3CN)4][BF4]2, whose structure containing a novel bitriangle hexapalladium skeleton was determined by X-ray crystallographic analysis. The dimer is stable in CD3CN at ambient temperature for several days but is highly air-sensitive. Similarly, the cycloheptatriene tripalladium complex [Pd3(C7H7R)2(CH3CN)3][BF4]2 (R = H, t-Bu) dimerized upon one-electron reduction. Both monomer and dimer of cycloheptatriene complexes were structurally determined by X-ray crystallographic analyses.

Transition-metal-catalyzed carbon - heteroatom three-component cross-coupling reactions: A new concept for carbothiolation of alkynes

The deep-seated understanding of flexible ligand behavior of thiolate on transition-metals has paved the way to achieve metal-catalyzed carbothiolations of terminal alkynes. The strategy of the reaction is quite simple: 1) generation of the complex with C-Pt-S fragments formed after the Pd-catalyzed C-S bond-forming cross-coupling reaction, 2) insertion of an alkyne into Pt-S bond to form the complex with a C-Pt-C fragment, and 3) C-C bond-forming reductive elimination.

Preparation and properties of novel palladium compounds containing a thiomethoxymethyl group

Abstract Oxidative addition of chloromethyl methyl sulfide to Pd(Ph 3 P) 4 provided a good yield of Pd(Ph 3 P) 2 (CH 2 SCH 3 )Cl (I) whose 1 H NMR and molecular weight data showed that dissociation of either the phosphine or the chloride ligand occurs in CH 2 Cl 2 solution. In accord with such equilibria, repeated crystallization of I from CH 2 Cl 2 and Et 2 O gradually removed the triphenylphosphine set free in these solvents to give the monomeric complex. Pd(Ph 3 P)(CH 2 SCH 3 )Cl (III), while treatment of 1 with NH 4 PF 6 in CH 2 Cl 2 and acetone gave the cationic complex [Pd(Ph 3 P) 2 (CH 2 SCH 3 ]PF 6 (II), 1 H NMR spectra of II and III are discussed in terms of a three-membered chelate structure arising from coordination of sulfur with palladium

Redox-induced reversible metal assembly through translocation and reversible ligand coupling in tetranuclear metal sandwich frameworks

Sandwich structures formed by metal atoms intercalated between sp(2)-carbon planes can be found either in metal-graphite-based materials or discrete multinuclear sandwich complexes. Their reactivity, and in particular their dynamic behaviour, has recently attracted interest both from a structural and a practical aspect, for example in catalysis. However, progress in this area has been rather slow, and it remains difficult to elucidate their structure and behaviour at the molecular level. Here, we report two sandwich complexes--in which four palladium centres are incorporated between two π-conjugated ligands--which exhibit two modes of redox-switchable structural changes. In the first complex, the tetrapalladium chain is split by oxidation into two well-separated dipalladium units. This motion is reversed on reduction. In the second complex, reversible carbon-carbon coupling occurs between the ligands during the redox process.

Synthesis and structure of cationic η3-allenyl/propargylpalladium complexes

Abstract Treatment of η 1 -allenyl- or η 1 -propargylpalladium bis(triphenylphosphine) chloride with AgBF 4 or NaBPh 4 afforded cationic η 3 -allenyl/propargylpalladium complexes. The molecular structure and some properties of the η 3 -allenyl/propargylpalladium were revealed.

π-allylmetal chemistry : V. New π-allylpalladium(II) complexes as models of key intermediates in allylic alkylation

Abstract Novel complexes of the type Pd(π-all)(Ar)(L) (all = CH 2  CMeCH 2 , MeCHCHCH 2 , EtO 2 CCHCHCH 2 ; Ar = C 6 Cl 5 , 2,3,5,6-C 6 HCl 4 ; L = PPh 3 , SbPh 3 ) were prepared and characterized by 1 H NMR spectroscopy. These were shown to be particularly good model compounds for mechanistic studies of allylic alkylation via π-allylpalladium complexes. Reductive elimination of these complexes proceeds by a unimolecular, concerted pathway to give, in a regio- and stereo-selective fashion, quantitative yields of allylpolychlorobenzenes.