Rhodium complexes ferrocenyl

Recently a novel chiral ferrocene-based amidinato ligand and its rhodium complexes have been described. The chiral N,N -bis(ferrocenyl)-substituted formamidine (N,N -bis[(S)-2- (lR)-l-(diphenylphosphino)ethyl ferrocen-l-yl]for-mamidine was prepared from commercially available (IR)-l-(dimethylamino) ethyl ferrocene by a multistep procedure in an overall yield of 29%. Deprotonation of the ligand with -butyllithium followed by addition of [RhCl2(COD)2] as illustrated in Scheme 167 yielded the corresponding (formamidinato)rhodium(l)... 

The dithiophosphonic acid monoesters, RP(OR )(S)SH can be conveniently prepared by cleavage of dimeric, cyclic diphosphetane disulfides, [RP(S)S]2 with alcohols, silanols, or trialkylsilylalcohols180 and then can be converted into metal complexes M[SPR(OR )]2 without isolation.181 The substituted ferrocenyl anion, (N3C6H4CH20)(CpFeC5H4)PS2 has been prepared in two steps from P4Sio, ferrocene and hydroxymethylbenzotriazole (and its salt was used for the preparation of some nickel and rhodium complexes).182 Zwitter-ionic ferrocenylditiophosphonates,... 

For asymmetric hydrosilylation of ketones a rhodium complex coordinated with the ferrocenyl(dimethyl)phosphine 3b has been reported to be more effective than other ferrocenylphosphines to give optically active alcohols (up to 49% ee) after hydrolysis (Scheme 2-49) [7]. 

More recently, a rran.y-chelating asymmetric ferrocenyl phosphine (abbreviated as TRAP) has been developed [63]. The rhodium complex of TRAP catalyzes asymmetric Michael additions of a-cyanocarboxylates in high enantioselectivity (72-89 % ee) (eq (18)) [64]. Because these Michael reactions proceed via a A -bound enolato complex [65], the reaction center on the enolato ligand is far from the metal center. Thus, a CLv-chelating phosphine cannot control the direction of electrophilic attack. The reaction with c/.y-chelating phosphines gives only a poor enantiomeric excess (BINAP, 17 % ee DIOP, 12 % ee CHIRAPHOS, 3 % ee). 

Catechol is an intermediate for the synthesis of racemic adrenaline which, although quite medicinally active, can be resolved (ref. 36) in 71% yield to afford the more active R(-) enantiomer, the natural form, which can also be derived quantitatively by asymmetric reduction (ref. 37) of the synthetic precursor, adrenalone as the hydrochloride by catalytic hydrogenation in methanol containing the rhodium complex of (R)-o[(S)-1 ,2-bis(diphenylphosphine)ferrocenyl]ethyl alcohol. Adrenalone is obtained by the acylation of catechol with chloroacetyl chloride to afford 3,4-dihydroxy-w-chloroacetophenone followed by reaction with methylamine. 

Figure 7.2 The rhodium complex reported by Hayashi and coworkers [11]. (Fc = ferrocenyl).

Rhodium complexes with the ferrocenyl ligand (i ,5)-Cy2PF-PPh2 (109) have been shown to catalyse asymmetric hydroalkynylation of norbornadienes with <99.9% ee A hydroxorhodium complex with (R)-Segphos (110) has been shown to catalyse the hydroarylation of 3-pyrrolines (111) with arylboroxines (112) under neutral conditions to give 3-arylpyrrolidines (113) (<96% ee) ... 

Methods for achieving enantioselective reduction of prochiral ketones are always of interest. This can be achieved by asymmetric hydrogenation of corresponding enol diphenylphosphinates using a cationic rhodium complex of (/ )- -[(5)-r,2-bis(diphenylphosphino)-ferrocenyl]ethanol. Although optical yields of up to 78% are reported, only simple ketonic substrates were used further developments, therefore, would be welcome. 

Schnyder A, Togni A, Wiesli U (1997) Electronic effects in asymmetric catalysis. Synthesis and structure of model rhodium complexes containing ferrocenyl ligtmds for use in the hydroboration reaction. Organometallics 16 255-260... 

These complexes can be isolated in some cases in others they are generated in situ from appropriate precursors, of which diazo compounds are among the most important. These compounds, including CH2N2 and other diazoalkanes, react with metals or metal salts (copper, palladium, and rhodium are most commonly used) to give the carbene complexes that add CRR to double bonds. Ethyl a-diazoacetate reacts with styrene in the presence of bis(ferrocenyl) bis(imine), for example, to give ethyl 2-phenylcyclopropane-l-carboxylate. Optically active complexes have... 

A broad screening of ligands and ionic liquids was carried out by Feng et al. [104]. For rhodium-catalyzed hydrogenation of enamides the best catalysts were found to be the rhodium-ferrocenyl-diphosphine complexes with taniaphos, josiphos, walphos and mandyphos as ligands (Fig. 41.9). 

A Cr(VI) sulfoxide complex has been postulated after interaction of [CrOjtClj] with MejSO (385), but the complex was uncharacterized as it was excessively unstable. It was observed that hydrolysis of the product led to the formation of dimethyl sulfone. The action of hydrogen peroxide on mesityl ferrocencyl sulfide in basic media yields both mesityl ferrocenyl sulfoxide (21%) and the corresponding sulfone (62%) via a reaction similar to the Smiles rearrangement (165). Catalytic air oxidation of sulfoxides by rhodium and iridium complexes has been observed. Rhodium(III) and iridium(III) chlorides are catalyst percursors for this reaction, but ruthenium(III), osmium(III), and palladium(II) chlorides are not (273). The metal complex and sulfoxide are dissolved in hot propan-2-ol/water (9 1) and the solution purged with air to achieve oxidation. The metal is recovered as a noncrystalline, but still catalytically active, material after reaction (272). The most active precursor was [IrHClj(S-Me2SO)3], and it was observed that alkyl sulfoxides oxidize more readily than aryl sulfoxides, while thioethers are not oxidized as complex formation occurs. 

A bimetallic Rh-Re catalyst (9) is effective for related hydrogenations shown in equation (16) that works best if R = R = H (ee 82-98%). The X-ray structure of the racemic complex was determined. Chiral derivatives of the more familiar ferrocenyl phosphines are effective in the rhodium-catalyzed hydrogenation of... 

Complexes of different dendrimers with rhodium that contained ferrocenyl phosphine ligands on the surface, 52-53, were also active in hydrogenation. They catalyzed dimethylacetone hydrogenation at an optical selectivity of 98%, which is comparable to the selectivity of a low molecular weight analogue [113, 123, 124]. 

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