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On the basis of the 1,2,3,4-tetrahydrofluorenyl ligand, a simple approach was developed to new effective rhodium catalysts for the construction of C-C and C-N bonds. The halide compounds [(η5 -tetrahydrofluorenyl)RhX2 ]2 (2 a: X=Br; 2 b: X=I) were synthesized by treatment of the bis(ethylene) derivative (η5 -tetrahydrofluorenyl)Rh(C2 H4 )2 (1 a) with halogens. An analogous reaction of the cyclooctadiene complex (η5 -tetrahydrofluorenyl)Rh(cod) (1 b) with I2 is complicated by the side formation of [(cod)RhI]2 . The reaction of 2 b with 2,2'-bipyridyl leads to cation [(η5 -tetrahydrofluorenyl)Rh(2,2'-bipyridyl)I]+ (3). The halide abstraction from 2 a,b with thallium or silver salts allowed us to prepare sandwich compounds with incoming cyclopentadienyl, dicarbollide and mesityleneligands [(η5 -tetrahydrofluorenyl)RhCp]+ (4), (η5 -tetrahydrofluorenyl)Rh(η-7,8-C2 B9 H11 ) (5), and [(η5 -tetrahydrofluorenyl)Rh(η-mesitylene)]2+ (6). The structures of 1 b, 2 b ⋅ 2I2 , 3PF6 , 4TlI4 , 5, and [(cod)RhI]2 were determined by X-ray diffraction. Compounds 2 a,b efficiently catalyze the oxidative coupling of benzoic acids with alkynes to selectively give isocoumarins or naphthalenes, depending on the reaction temperature. Moreover, they showed moderate catalytic activity in other annulations of alkynes with aromatic compounds (such as benzamide, acetanilide, etc.) which proceed through CH activation. Compound 2 b also effectively catalyzes the reductive amination of aldehydes and ketones in the presence of carbon monoxide and water via water-gas shift reaction, giving amines in high yields (67-99 %).

The reaction of the bromide complexes [CpCo(μ-1,3-C3B2Me5)MBr2]2 [M = Rh (1), Ir (2); Cp = cyclopentadienyl] with AgBF4 in acetonitrile affords the tris(acetonitrile) μ-diborolyl triple-decker complexes [CpCo(μ-1,3-C3B2Me5)M(MeCN)3]2+ [Rh (3), Ir (4)]. The labile nitromethane solvates [CpCo(μ-1,3-C3B2Me5)M(MeNO2)3]2+, generated in a similar way, react with benzene and its methylated derivatives to give the arene triple-decker complexes [CpCo(μ-1,3-C3B2Me5)M(arene)]2+ [M = Rh (5), Ir (6); arene = C6H6 (a), 1,2,4,5-Me4C6H2 (b), C6Me6 (c)]. The structures of 5b(BF4)2, 5c(BF4)2, 6b(BF4)2 and 6c(BF4)2 were determined by X-ray diffraction. The electron-transfer ability of the arene complexes was ascertained by electrochemical techniques. In general, they are able to undergo two separate one-electron reductions reversibly. DFT calculations revealed structural changes caused by redox processes and satisfactorily predicted the redox potentials. The second reduction is accompanied by a η6 η4 hapticity change of the arene ligand. Energy decomposition analysis revealed that the Rh–benzene bond in cation 5a is weaker than in cyclopentadienyl analogues [(C5R5)Rh(C6H6)]2+; however, 5a proved to be the least reactive in benzene replacement with acetonitrile and mesitylene.

The reaction of CpCo(1,3-C3B2Me5H) (1) with CpTl affords the thallium derivative CpCo(1,3-C3B2Me5)Tl (2). The structures of 1 and 2 were determined by X-ray diffraction at 100 K. An “extra” hydrogen atom in 1 occupies a C–H···B bridging position. According to DFT calculations, 1 exists as a mixture of two enantiomers with an enantiomerization barrier of only 0.5 kcal mol–1. The transition state has Cs symmetry with an endo-CH hydrogen atom. The isomeric iso-1with the Co–H···B bridge is less stable than 1 by 10 kcal mol–1.The formation of 1 and iso-1 from C3B2Me5H and CpCo(C2H4)2 have almost equal activation energies. The isomerization of iso-1 to 1 was shown to proceed as a two-step hydrogen transfer. The bonding of the “extra” hydrogen atom in the related CHB-bridged carborane nido-2,3,5-C3B3R5H2 and metallacarboranes M(C5R5)(C3B2R′5H) (R, R′ = H, Me; M = Co, Rh, Ir) as well as their hydridic isomers MH(C5R5)(C3B2R′5) was compared. According to energy decomposition analysis, the bonding of the parent anion [CpCo(1,3-C3B2H5)]– with metal cations becomes stronger in the following order: K+ < Na+ < Tl+ < Li+ < [RuCp]+. The attractive interactions between the [CpCo(1,3-C3B2H5)]– and Tl+ fragments are 68 % electrostatic and 32 % covalent.

The pathophysiology of asthma is complex and engages cascades of events in the cytokine network. We, therefore, investigated the impact of bronchial allergen challenge in humans on the cytokine profile of circulating lymphocytes. Peripheral blood samples from 10 patients with allergic asthma were collected before and 24 h after allergen provocation. Patients who mounted a late-phase reaction were designated dual responders opposite to single responders. Whole blood cells were stimulated by mitogen and intracellular interleukin (IL)-4 and interferon (IFN)-gamma were detected by flow cytometry. The allergen challenge induced a decrease in IL-4+CD4+ cells in the patients (P = 0.05), and a significant decrease (P0.05) in IFN-gamma+CD4+ cells was noted in single, but not dual, responders. In addition, there was a significant difference (P0.01) with respect to the changes in the IFN-gamma+CD4+ cells comparing dual and single responders. No corresponding changes were observed in CD8+ cells. The data suggest a possible on-going traffic of IFN-gamma and IL-4+CD4+ lymphocytes into the bronchial mucosa in relation to an allergen challenge and generate the hypothesis that a difference exists between single and dual responders in this respect. Because the CD4+IFN-gamma-producing cells have the capacity to downregulate the T-helper type 2 response, a reduced capacity in this aspect might contribute to the pathophysiology in dual responders.

Stacking reactions of the dicationic fragments [LM]2+ (LM = (η-C6H6)Ru, (η-C6H3Me3)Ru, or (η-C5Me5)Rh) with the complex (η-C5H5)Co(η-C4H4BCy) (Cy = cyclo-C6H11) afforded new dicationic 30-electron triple-decker complexes [(η-C5H5)Co(μ-η:η-C4H4BCy)ML](BF4)2 containing a cyclohexyl-substituted borole ligand in the central position.

Hexanuclear rhodium carbonyl cluster, Rh6(CO)16, catalyzes benzene hydroxylation with hydrogen peroxide in acetonitrile solution. Phenol and (at lower concentration) quinone are formed with the maximum attained total yield and turnover number 17% and 683, respectively. Certain other rhodium carbonyl complexes, containing cyclopentadienyl ligands, Rh2Cp2(CO)3 and Rh3(CpMe)3(CO)3, are less efficient catalysts. Cyclopentadienyl derivatives of rhodium which do not contain the carbonyl ligands, Rh(CpMe5)(CH2CH2)2, RhCp(cyclooctatetraene) and Rh2Cp2(cyclooctatetraene) turned out to be absolutely inactive in the benzene hydroxylation. Styrene is transformed into benzaldehyde and (at lower concentration) acetophenone and 1-phenylethanol. Copyright © 2008 John Wiley & Sons, Ltd.