Phosphorus ligands bidentate

Fig. 31.10 Comparison of rate (schematic) and enantioselec-tivity for mono- and bidentate phosphorus ligands on 1 mM scale, (a) a-Dehydroamino ester, 2 bar H2 (b) jS-dehydroami-no ester, 10 bar H2.

Bidentate phosphorus ligands based on BINOL, such as phosphonite 23, phosphites 24 and 25, and phosphoramidite 26 (Tab. 7.2), with various bridging units were introduced by the groups of Reetz, Chan, and Waldmann [48-50]. Excellent enantioselectivities - up to 96% for ligand 23, for instance - were found. 

When an unsymmetrical diyne is used, two regjoisomers of ortho and meta isomers are formed. Then, by choosing the bidentate phosphorus ligand (DPPE or DPPE (l,l -bis(diphenylphosphino)ferrocene), the ratio of their formation could be controlled from 1 4 to 7 1 (Scheme 11.2) [12]. 

Slagt, V.F., van Leeuwen, P.W.N.M. and Reek, J.N.H. (2007) Supramolecular bidentate phosphorus ligands based on bis-zinc(ii) and bis-tin(lV) porphyrin building blocks. Dalton Trans., 2302-2310. 

It was shown (17) that phosphine exchange occurred in [AuMe(PR3)l complexes, but species with a coordination number greater than two were not observed, even with bidentate phosphorus ligands. Although such species were not observed, an associative mechanism was thought to be operative (16, 18). With trimethylphosphite also, only the two-coordinate complex [AuMe P(OMe)3 l was detected in solution (19). 

Addition of 2-butyne to [CpMo(dppe)2][PF6] displaces one dppe chelate to yield the cationic alkyne complex, [CpMo(dppe)(MeC=CMe)][PF6]-[Eq. (14)] (66). The replacement of a bidentate phosphorus ligand with a single 2-butyne donor is a comment on the propensity of Mo2+ to bind alkynes. 

CO groups in silyl-transition-metal carbonyls can be replaced by PR3 groups or bidentate phosphorus ligands ... 

The infrared spectra of many organocopper compounds have been reported (40, 41, 73, 75, 77) and compared favorably with the respective covalently bound organic halides. Bidentate phosphorus ligands coordinate more strongly with arylcopper compounds than monodentate ligands (41, 75, 281e). Substantial modification of the ligand spectrum is also seen in the infrared spectra of arylcopper complexes with bipy-ridyl or 1,10-phenanthroline (41). 

Bidentate phosphorus ligands coordinated to metal ions may be more suitable for hydrogenation processes than for carbonylation processes the competition of CO as a ligand would then be excluded. 

Macrocyclizfltion by allylatiort-alkylation.12 The key step in a synthesis of the antibiotic A26771B (3) is cyclization of the substrate 1 using 0,N-bis(trimethylsilyl)acetamide (1, 61 2, 30 3, 23-24) as base and Pd[P(C6H5)3]4 as catalyst. In addition a bidentate phosphorus ligand is essential. The highest yields were obtained with 1,4-bis(diphenylphosphine)butane (dppb). 

Electrochemical experiments on bidentate phosphorus ligands indicate that ligands with reduction potentials more positive than - IV (versus SCE) form long-lived 19-electron species with cobalt carbonyls, whereas ligands with more negative potentials form reactive species. For example, with a reduction potential of -0.7 V, bis(diphenylphosphino)maleic anhydride was expected to form a stable species with cobalt carbonyls, a prediction confirmed by its synthesis. ... 

Related dimeric trihydrides containing various bidentate phosphorus ligands have been prepared by treatment of [PtCl2L2] with AgBF4, fol-... 

The enantioselective reduction of N acetyl enamides has a rich history and several substrate classes of N acetyl enamides can now be reliably converted to enantiopure amines (>99% ee) using rhodium based catalysts. The field has bifurcated over the past 10 years with the utility of monodentate versus bidentate ligands at the fore of the discussion. In Chapter 8, Zhou lays a strong foundation for the monodentate phosphorus ligand accomplishments and challenges. Chapter 9 provides a wonder fill complement by Zheng, who fully summarizes the bidentate phosphorus ligand literature over the past 10 years. 

Bisphosphines are oxidized to the monooxides, thus bidentate phosphorus ligands of mixed oxidation states are readily accessible. 

Activation of C-H Bonds by Bidentate Phosphorus Ligand Complexes of Iron... 

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