Phosphine aminophosphine

Mixed Phosphine-Phosphoramidites and Phosphine-Aminophosphine Ligands... 

Fig. 27.5 Mixed phosphine-phosphoramidites and phosphine-aminophosphine ligands.

Pt(II) complexes generally give hydroformylation products with higher asymmetric induction than Rh(I) complexes. A Pt(II)-SnCl2 complex with a chiral phosphine, aminophosphine, or phosphinite also catalyzes the hydroformylation of styrene in up to 86% optical yield (115). Stille noticed that the PtCl2(bppm)-SnCl2 combined catalyst is... 

The chiral, hybrid phosphine-aminophosphine ligand (113) has been applied in the Rh-catalyzed asymmetric hydrogenation of various dimethyl a-benzoyloxyethenephosphonates (114) bearing (3-aryl, (3-alkyl and (3-alkoxy substituents in high enantioselectivities (ee up to 97%) (Scheme 39). 

This chapter will also deal with compounds containing two or three phosphinous amide units, which, for simpUcity, will be named here as bis(amino-phosphanes) or tris(aminophosphanes) but not with phosphinous amides containing other additional organophosphorus functionaUties as, for instance, the so-called aminophosphine phosphinites (AMMP), which have been the subject of increasing attention in the Uterature dealing with catalytic asymmetric transformations and have been treated in other reviews [2,3]. 

The alcoholysis and transamination of various aminophosphines have been studied as functions of the basicity of the attacking nucleophile and the substituents on phosphorus. As might be expected the reaction is facilitated by electron-withdrawing groups on phosphorus. The hydrolysis of tris(dimethylamino)phosphine (90) to phosphorous acid has been investigated using thin-layer chromatography and the amides (91) and (92) have been identified as intermediates. 

The bidentate phosphine dppe (l,2-bis(diphenylphosphino)ethane) and the aminophosphine eddp (2-aminoethyl-diphenylphosphine) form mixed ligand (N, P, O) complexes such as Co(acac) (edpp)2 and Co(acac)(en)(dppe). A preference for trans N-Co-P and P-Co-P configurations over N-Co-N was found for the bis(edpp) complexes.925... 

This section essentially catalogs some of the newer catalyst systems that have not been considered in the previous sections. A number of the catalysts are certainly derived from more established ones (e.g., use of chelated aminophosphine ligand instead of two monodentate phosphines... 

Another ligand, the potential of which has only recently been exploited, is Bo-Phoz (35). This ligand is an aminophosphine as well as a phosphine (see also Section 23.7). It has shown high selectivities and activities with enamides and itaconates [154, 155]. 

Tomioka and co-workers (175) showed that monodentate aminophosphines are moderately effective in mediating the conjugate addition of diethylzinc to enones. The precatalyst is generated from Cu(OTf)2 and 2 equiv of phosphine 240. Optimal selectivities are obtained in the conjugate addition of diethylzinc to dimethylcyclo-hexenone, affording the adduct in 70% ee and 80% yield, Eq. 141. 

FIGURE 1.28 Chromatograms of the HPLC enantiomer separation of Z-protected a-aminophosphinic acids (a,b) and phosphinic acid-ilr-dipeptide (c) on (a and b) a 0-9-(tert-butylcarbamoyl)quinidine CSP and (c) corresponding 0-9-(fcrr-butylcarbamoyl)qninine-CSP, respectively. Experimental conditions Column dimensions, 150 mm x 4 mm ID mobile phase, methanol-50 mM sodium phosphate buffer (80 20 v/v) (pHa 5.6) temperature, 40°C flow rate, 1 mLmin detection, UV at 250 nm and optical rotation detection (ORD). (Reproduced from M. Lammerhofer et ah, Tetrahedron Asymmetry, 14 2557 (2003). With permission.)... 

An interesting synthetic approach to thietanes is the selective desulfurization of cyclic disulfides.The treatment of dithiolanes with a diethyl-aminophosphine results in a ring contraction to thietanes, (Eq. 19). This has been demonstrated with a-lipoic acid, a coenzyme with a dithiolane structure involved in the biological oxidation of pyruvic acid. The reaction is proposed to be initiated by the electrophilic attack of the phosphorus on the ring sulfur atom, resulting in the formation of an acyclic internal phosphonium salt, which by subsequent elimination of a phosphine sulfide, closes to the four-membered ring. °... 

To our knowledge, the first examples of asymmetrically substituted monocyclic phosphoranes are 60 and 61, described by Moriarty et al.135 and involving the reaction of a substituted o-benzoquinone136,137 (Scheme 6) on an aminophosphine (59), itself obtained by alcoholysis of 58 with l-( — )-menthol. In contrast to the amino phosphine 53 (Scheme 5), 59 is a mixture of the diastereoisomers 59a and b, and its reaction with 3,5-di-tert-butyl-l,2-benzoquinone yields two diastereoisomeric phosphoranes, 60a and b. Finally, alcoholysis of the P(V)—NR2 bond138 in 60a and b leads to 61a and b or 62. 

---