TangPhos ligand

Recently, high enantioselectivity was obtained in the rhodium-catalyzed hydrogenation of a-aryl enamides and E/Z-isomeric mixtures of y9-substituted enamides. Tab. 1.3 lists some examples for the hydrogenation of a-phenylenamide and the /Z-isomeric mixture of yS-methyl-a-phenylenamide. A P-chiral ligand, TangPhos, proved to be particularly efficient for the rhodium-catalyzed hydrogenation of enamides, given the excellent enantioselectivity and reactivity, with up to 10000 turnovers. 

Yun and co-workers reported the Cu-catalysed enantioselective hydroboration of styrene with pinacolborane using the ligand TangPhos (Scheme 8.32). 

The 1-t-butylphospholane sulfide intermediate to TangPhos was also used to prepare the P,N ligands 48 by reacting the lithium complex with C02 and then oxazoline formation with a range of chiral amino alcohols [69b, 74]. The Ir complexes of these ligands have been successfully used in the reduction of / -methylcinnamic esters (80-99% ee) and methylstilbene derivatives (75-95% ee), a particularly challenging class of unfunctionalized olefins [4 c]. 

Several phospholane-based ligands have shown a wide substrate scope beyond the standard examples represented in Table 24.2. Both Et-FerroTANE 61 [147] and TangPhos 46 [69 b, 71] have been successfully applied to a diverse range of methyl and ethyl />-aryl-dehydroamino acids containing various aromatic substituents, whilst catASium M 20a [95] has been used for the reduction of numerous yS-alkyl-dehydroamino acid esters. 

Recent results have shown that a number of other commercially available ligands can be expected to have industrial potential for the hydrogenation of dehydro a-amino acid derivatives. However, it must be pointed out that in most cases model substrates and not industrially relevant targets have been investigated until now. Chiral Quest has shown that Rh-TangPhos as well as Rh-f-Ke-talPhos (for structures, see Fig. 37.9) were able to hydrogenate a variety of a-de-hydro amino acid derivatives with ee-values of 98->99%, TONs of up to 10000... 

In contrast to dehydro a-amino acids, the hydrogenation of acetylated /1-dehy-droamino acid derivatives has only recently been of industrial interest and, accordingly, no applications on a larger scale have yet been reported. Several ligands such as certain phospholanes or phosphoramidites might have industrial potential, but until now these have only been tested on model substrates under standard conditions [50]. Chiral Quests TangPhos and Binapine (Fig. 37.10) have been shown to hydrogenate several acetylated dehydro / -amino acid derivatives with ee-values of 98-99% and TONs of 10000 at r.t., 1 bar [3, 47]. 

A highly regio- and enantio-selective hydroformylation of alkenes, such as PhCH= CH2, CH2=CHCH2CN, and CH2=CHOAc, catalysed by ruthenium complexes with (g) 2,5-disubstituted phospholane ligands has been reported. With (83) as the ligand, the turnover rates over 4000 h-1 at 80 °C, have been attained.108 (Acac)Rh(CO)2-TangPhos [Tangphos = (84)] has been developed as a new enantioselective catalyst for asymmetric hydroformylation of norbornene and other [2.2.1]-bicyclic alkenes (55-92% ee).109... 

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