Biaryl diphosphines

Chan has discovered a completely atropdiasteroselective synthesis of a biaryl diphosphine by asymmetric intramolecular Ullmann coupling or Fe(m)-promoted oxidative coupling. A chiral atropisomeric biaryl bisphosphine ligand 2 was synthesized through this central-to-axial chirality transfer.38 Recently, a xylyl-biaryl bisphosphine ligand, Xyl-TetraPHEMP, was introduced by Moran, and is found to be effective for the Ru-catalyzed hydrogenation of aryl ketone.39... 

R)-l,2-Propanediol is an intermediate for (S)-oxafloxazin, a bactericide which until recently was sold as a racemate. The (R)-diol is now produced by Takasago via hydrogenation of hydroxyacetone (see Fig. 37.23) using a Ru-Tol-binap catalyst on a 50 t y 1 scale [92 b[. Recently, it was reported that segphos - a newly developed biaryl diphosphine - shows even better results, achieving >98% ee and TON and TOF of 10000 and 1400 h, respectively [16, 93]. 

I.4.I.2. Amino, Hydroxy, and Phenylthio Ketones Asymmetric hydrogenation of amino ketones, in either a neutral or hydrochloride form, has extensively been studied. Both Rh(I) and Ru(II) complexes with an appropriate chiral diphosphine give a high enantioselectivity. As described in Scheme 1.42, a-aminoacetophenone hydrochloride is hydrogenated using a cationic Rh complex with (R)-MOC-BIMOP, an unsymmetricaJ biaryl diphosphine, to give the... 

The reductions of /i,<5-dikcU)cslcrs 51 with ruthenium/BINAP catalysts result in formation of the /raw.v-diols 52 in high selectivity and e.e. Experiments have revealed that it is likely that the reduction takes place via the coordination of both ketones to the metal—the selectivity matches that obtained in the reduction of /1-diketones222. Biaryl diphosphines closely related in structure to BINAP have also given excellent results223. Other excellent... 

A brief statistical summary of their application is presented in Table 1. It is easy to see that about the same number of Rh- and Ru-catalyzed processes have been reported. However, while for Ru-catalyzed hydrogenation reactions biaryl diphosphines are applied almost exclusively this ligand class has barely been applied in Rh-catalyzed processes we here all the other ligand types shown in Fig. 2 have been successful. 

In comparison to Rh, the chemistry of Ru is more complex, and a broader variety of Ru precursors has actually been used on a regular basis (see Fig. 8). On the other hand, with some notable exceptions, only atropisomeric biaryl diphosphines, all inspired by binap, have led to effective catalysts. Much of this chemistry has been developed by the Noyori group, some of it in collaboration with Takasago [61]. For these Ru diphosphine complexes, the presence or absence of either chloride or bromide ions dominates their catalytic properties. Halides containing Ru complexes... 

Ru/diphosphine/diamine were shown by Noyori (For a recent account see [87]) to be effective hydrogenation catalysts of ketones without a- or (3-functionality. The absolute configurations of the P P and N N ligands have to be matched. The technology has been licensed by several companies using various biaryl diphosphines but it is not clear whether it is already used for concrete manufacturing purposes. 

Mori, R, Fukawa, N., Noguchi, K., Tanaka, K. (2011). Asymmetric synthesis of axially chiral biaryl diphosphine ligands by rhodium-catalyzed enantioselective intramolecular double [2+2+2] cycloaddition. Organic Letters, 13, 362-365. 

The cationic rhodium(I)/axially chiral biaryl diphosphine complex catalyzed the enantioselective desymmetrization of symmetric dialkynylphosphine oxides via rhodium-catalyzed [2- -2-1-2] cycloaddition with 1,6-diynes to give / -stereogenic alkynylphosphine oxides (Scheme 4.50) [53]. This method was also applied to... 

The [24-24-2] cycloaddition was also used to synthesize biaryl diphosphines (Scheme 2.56) [107]. A double [2- -2- -2] cycloaddition of l,4-bis(diphenylphosphino)buta-l,3-diyne 2.162 to diyne 2.161 in the presence of cationic Rh(I) and Ag/binap as a catalyst afforded biaryl diphosphine oxides 2.163 in high yield and with excellent enantioselectivity. Reduction with trichlorosilane/phosphite led to the corresponding... 

A similar approach, but through a stepwise double [2-l2-l2] cycloaddition (Scheme 2.57), was used for the highly enantioselective synthesis of axially chiral biaryl diphosphine oxides [100, 108, 109]. 

Scheme 2.57 Enantioselective synthesis of axially chiral biaryl diphosphine dioxides by stepwise double [24-24-2] cycloaddition using a rbodium-catalyst.

Doherty, S., Knight, J.G., Smyth, C.H., Harrington, R.W. and Clegg, W. (2007) Rhodium-catalyzed double [24-24-2] cycloaddition of 1,4-bis (diphenylphosphinoyl)buta-l,3-diyne with tethered diynes a modular, highly versatile single-pot synthesis of NU-BIPHEP biaryl diphosphines. Organic Letters, 9(23), 4925-4928. 

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