Ligands PHANEPHOS

When we first ventured into the field of [2.2]paracyclophane ligand synthesis, successful applications of such ligands were relatively rare [2]. The most prominent example was clearly the PHANEPHOS ligand developed by Rossen and Pye [3], who have found several successful applications in asymmetric hydrogenation reactions. A comprehensive survey of [2.2]paracyclophane-based ligands can be found in recent reviews [4, 5]. 

The studies on copper complexes demonstrated that the phanephos ligand (see Fig. 2) can be successfully applied to engineer highly luminescent Cu(i) complexes. The rigid [Cu(dmp)(phanephos)] complex displays a high luminescence quantum yield of 0.8 at ambient temperature. In contrast to the long-lived phosphorescence of 240 ps at low temperature, the ambient-temperature emission represents a thermally activated delayed fluorescence with a decay time of 14 ps. ... 

More recent work employing diphosphine ligands has focused on both new substrates for hydroboration and also new hydroborating agents. Specifically, Gevorgyan has successfully employed cyclopropenes 56 as substrates, with pinacolboranes 13 as the borane source.20 Impressive enantioselectivities were obtained with a range of diphosphines, for example, with rhodium complexes of NORPHOS (>99% ee), PHANEPHOS (97% ee), BINAP (94% ee), and Tol-BINAP (96% ee), all with near perfect m-selectivity (see Scheme 8). 

The ligands tested were tol-binap, dipamp, P-phos, xyl-P-phos, binam, phanephos and xyl-phanephos with the results lised in Table E Table 2 shows the effect which... 

The diamine ligands that have shown the most consistent usage are DPEN (145) and diapen (146). The best bisphosphines ligands used to date have been axial bisphosphines ligands, such as BINAP (3a), tol-BINAP (3b), xyl-BINAP (3c),23 188 xyl-PhanePhos (127b),162 163 and xyl-P-Phos (120c).153... 

A novel series of atropisomeric ligands uses a paracyclophane backbone. Rhodium and ruthe-nium-PhanePhos catalysts have performed well in the asymmetric hydrogenation of enamide esters, (3-keto esters, and especially arylketones with JST catalysts (Duloxetine). 

Respectable results for the ruthenium chelate-catalyzed reduction of y9-ketoesters were also obtained by Pye [49] with 2.2-PHANEPHOS (24) and Imamoto [50] with 10a as the ligand. 

S R ratio = 5 1) [22]. Yanada and Yoneda constructed the deazaflavinophane 26, which exhibits complete facial selectivity in its oxidation and reduction reactions, e.g. the reduction with NaBD to afford 27 [23], Belokon and Rozen-berg used scalemic 4-formyl-5-hydroxy[2.2]para-cyclophane (FHPC) 28 in the synthesis of a-ami-no acids (ee 45-98 %) [24], An alternative approach to FHPC was more recently reported by Hopf [25]. Other interesting advances in the area of chiral cyclophanes include the homochir-al [2.2]paracyclophane-derived amino acids 29 and 30 [26], as well as (5)-PHANEPHOS (31) [27], which has been shown to be an effective ligand for highly enantioselective Ru-catalyzed asymmetric hydrogenations of -ketoesters and... 

A Merck group reported an interesting kinetic resolution of a racemic di-bromocyclophane via Pd-catalyzed amination [91]. While BINAP was a poor ligand for the reaction in terms of selectivity, the C2-symmetric cyclophane-derived PHANEPHOS (17) proved to be optimal. Reaction of the cyclophane derivative with benzylamine afforded the unreacted dibromide in 45% ee after 37% conversion, corresponding to a selectivity factor of 12, Eq. (78). 

Recently the first use of the paracyclophane backbone for the placement of two diphenylphosphano groups to give a planar chiral C2-symmetric bisphos-phane was reported [102]. The compound 159 abbreviated as [2.2]PHANEPHOS was used as a ligand in Rh-catalyzed hydrogenations. The catalytic system is exceptionally active and works highly enantioselective [ 103]. The preparation of [2.2]PHANEPHOS starts with rac-4,12-dibromo[2.2]paracyclophane (rac-157), which was metalated, transmetalated and reacted with diphenylphosphoryl chloride to give racemic bisphosphane oxide (rac-158). Resolution with diben-zoyltartaric acid and subsequent reduction of the phosphine oxides led to the enantiomerically pure ligand 159. 

Although the first P-chiral bisphosphane (DIPAMP) was developed by Knowles over 30 years ago, the discovery of new efficient P-chiral bisphosphanes has been slow partly because of the difficulties in ligand synthesis. Pye and Rossen have developed a planar chiral bisphosphine ligand, [2.2]-PHANEPHOS 40, based on a paracyclophane backbone.37 The ligand has shown excellent enantioselectivity in Rh- and Ru-catalyzed hydrogenations. 

Scheme 20.9 Structures of ruthenium-diamine catalysts with PhanePhos and HexaPhemp ligands.

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