Tris pentamethylcyclopentadienyl Systems

With the isolation of [UCp 3] accomplished, the next target was what promised to be even harder, the synthesis of the uranium(IV) species [UCp 3Cl] and related compounds. [UCp 3] underwent oxidation with HgF2, forming [UCp 3F], and reaction with a stoichiometric amount of PhCl, forming [UCp 3Cl] reaction of [UCp 3] with 2 molecules of PhCl afforded [UCp 2Cl2]. 

The structure of [UCp 3] has trigonal planar coordination of U similarly in [UCp 3Cl] the three ring centroids are coplanar with U, and with a very long U-Cl bond at 2.90 A - compare 2.637 A in [U(C5Me4H)3Cl]. 

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An even more crowded system is present in the first tris-pentamethylcyclopentadienyl lanthanide complex Cpj Sm obtained (Evans et al. 1991a) as byproduct of the reaction... 

Systems which fulfil these conditions are tris(2,2 -bipyridyl)rhodium complexes [63] and, more effectively, substituted or unsubstituted (2,2 -bipyridyl) (pentamethylcyclopentadienyl)-rhodium complexes [64], Electrochemical reduction of these complexes at potentials between — 680 mV and — 840 mV vs SCE leads to the formation of rhodium hydride complexes. Strong catalytic effects observed in cyclic voltammetry and preparative electrolyses are... 

The successful synthetic application of this electroenzymatic system has first been shown for the in-situ electroenzymatic reduction of pyruvate to D-lactate using the NADH-dependent D-lactate dehydrogenase. Electrolysis at — 0.6 V vs a Ag/AgCl-reference electrode of 50 mL of a 0.1 M tris-HCL buffer of pH 7.5 containing pentamethylcyclopentadienyl-2,2 -bipyridinechloro-rhodium(III) (1 x 10 3 M), NAD+ (2 x 10 3 M), pyruvate (2 x 10 2 M), 1300 units D-lactate dehydrogenase (divided cell, carbon foil electrode) after 3 h resulted in the formation of D-lactate (1.4 x 10 2 M) with an enantiomeric excess of 93.5%. This means that the reaction occurred at a rate of 5 turnovers per hour with respect to the mediator with a 70% turnover of the starting material. The current efficiency was 67% [67],... 

The ferrocene/ferricinium ion electrode. For nonaqueous electrochemistry, IUPAC recommends47 the use of the ferrocene/ferricinium ion [Fen(Cp)2/ Fen(Cp)2 , HCp = cyclopentadiene] couple as an internal standard. The couple has been chosen because its potential is largely independent of the solvent (E° = +0.40 V vs. NHE in water 3 and +0.69, +0.72, +0.76, and +0.68 V vs. NHE in MeCN, DMF, py, and Me2SO, respectively).48 The ferricinium ion is unstable in some organic solvents because of decomposition.49,50 Recently the use of bis(pentamethylcyclopentadienyl) iron(II) has been proposed to avoid the problem.51 The Fen(Cp)2/Fem(Cp)2 couple cannot be used as an internal standard for some systems due to overlapping waves.52 In these cases other compounds such as tris-(l,10-phenanthroline)iron(II),4 cobalto-... 

Kawabe, M. MurataM. Synthesis of block graft copolymer with syndiospecific living polymerization of styrene derivatives by (trimethyl)pentamethylcyclopentadienyl titanium/tris(pentafluorophenyl) borane/trioctylaluminium catalytic system. Macromol. Chem. Phys. 2001, 202,1799-1805. 

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