Thiophene Ligands

A number of nonsulfur-containing bis(oxazolines) ligands with numerous structural diversities have been designed by several groups and successfully 

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Cp(CO)2Re(THF) forms the complex 105 upon reaction with thiophene (89JA8753, 910M2436). Similar species are known for 2- and 3-methyl-, 2,5-dimethyl, and tetramethylthiophene (91IC1417). Thiophene in 105 is S-coordi-nated, and the sulfur atom is pyramidal. Treatment of 105 with Fc2(CO)9 produces 106, where the thiophene ligand is bridge-coordinated via the sulfur atom to rhenium and four carbon atoms of the dienic system with iron (the coordination mode). The pyramidal nature of the sulfur atom is preserved. The -coordination of thiophene separates the dienic and sulfur counterparts of the ligand and decreases the TT-electron delocalization, which leads to the enhanced basicity of the sulfur atom. 

Scheme 2.15 Cu-catalysed 1,4-addition of ZnEt2 to chalcone with oxazoline-cyclo-penta[h]thiophene ligands.

Scheme 6.4 Bis(oxazolines)thiophene ligands for Cu-catalysed cyclopropanations of alkenes with EDA.

Another class of chiral diphosphine ligands bearing two interconnected thiophene rings, has been successfully developed by Sannicolo et al. These bis(diphenylphosphino)[Z)]thiophene ligands, called tetraMe-BITIANP and... 

Scheme 8.30 Hydrogenations of a- and P-keto esters with Ci-symmetric diphosphine-thiophene ligand.

Scheme 8.31 Hydrogenations of P-keto esters with diphosphine-thiophene ligand.

Cl-symmetric hgands diphosphine-thiophene ligand 264-5 monosulfoximine hgands 192-3 C2-symmetric hgands 9 biheteroaromahc diphosphines 193 bis(sulfonamide) hgands 145-6 bis(sulfoximine) hgands 42-3,190-3... 

The hemilabile phosphino-ester and phosphino-thiophene ligands (139)-(142) behave like monodentate phosphine under catalytic conditions.476... 

An important step in the HDS process is postulated to be loss of aromaticity of the thiophene ligand, -coordination of thiophene in [Mn(CO)3(r>5-thiophene)]+ has been found to activate the 2-position of the ring to... 

The (S) thiophene ligand is very weakly coordinated (equation 4). Thiophene itself is bound less... 

Recently, Ewen et al. have designed C2-, Cj-, and Ci-symmetric catalysts bearing heterocycle-condensed Cp ligands, as illustrated in Scheme 9, which add electronic effects to the stereocontrol. ° The complexes, containing isopropylidene-bridged cyclopentadienyl and cyclopentyl thiophene ligands, show activity... 

One of the most successful preparative routes for r -bonded metal complexes of thiophenes has been the chemical or electrochemical reduction of the corresponding 18e 1)5 Ru, Rh, and Ir precursors [58-64] upon addition of two extra electrons to complexes like Cp Ir( ri -Th), the thiophenic ligand necessarily transforms from a 6e-donor into a 4e-donor situation in order to avoid oversaturation at the metal center, as exemplified for Cp Ir(2,5-Me2T) in Eq. 2.16. 

P. Mills, S. Korlaim, M.E. Bussell, M.A. Reynolds, M.V. Ovchinnikov, R.J. Angelici, C. Stinner, T. Weber R. Prins (2001). J. Phys. Chem. A, 105, 4418-4429. Vibrational study of organometallic complexes with thiophene ligands Models for adsorbed thiophene on hydrodesulfurization catalysts. 

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