Optically active phosphine ligands, especially C 2 -symmetric diphosphine ligands, have played an important role in various metal-catalyzed asymmetric transformations, and numerous phosphine ligands have been prepared for the development of effective catalytic asymmetric processes. [1] Dramatic results from Knowles and co-workers with the C 2 -symmetric P-chiral ligand 1,2-ethanediylbis[(2-methoxyphenyl)phenylphosphane] (dipamp) for Rh-catalyzed hydrogenations opened up this field of asymmetric catalysis. [2] However, it took nearly two decades for other groups to develop efficient methods to prepare C 2 -symmetric P-chiral diphosphine ligands, largely as a result of the synthetic difficulties in the construction of the P-chiral P centers. [3,4] Nevertheless, some C 2 -symmetric Pchiral diphosphine ligands, such as BisP*, [4a] MiniPhos, [4b] TangPhos, [4c] DiSquareP*, [4d] DuanPhos, [4e] and QuinoxP*, [4f] which exhibit almost perfect enantioselectivity in some Rhcatalyzed asymmetric hydrogenations, have been developed recently. However, a major drawback in many of the requisite synthetic methods (developed by the groups of Imamoto, [3a] JugØ, [3b] Corey, [3c] Evans, [3e] and Livinghouse [3g] ) is that either only one enantiomer of the ligand is readily accessible owing to the nature of the chiral auxiliaries used in the formation of the chiral center or there is a need for tedious diastereomeric derivatization, separation, and deprotection sequences.Ferrocene-based phosphine ligands are well documented. [5] They are more amenable to asymmetric catalysis than many other types of chiral ligands as a result of their easy accessibility and derivatization as well as special electronic and steric properties. Indeed, several families of ferrocenebased phosphine ligands with subtle structural variations have been developed in the last few years. Most of these ligands incorporate both C-centered chirality and planar chirality, and they have proved to be highly effective in numerous asymmetric reactions. In stark contrast, much less attention has been paid to P-chiral phosphines that bear ferrocenyl groups, [3k,l, 5] doubtless as a result of the previous difficulties in their synthesis. Very recently, we reported a highly stereoselective and modular synthesis of ferrocene-based P-chiral phosphine ligands using a simple and straightforward strategy, that is, reaction of a chiral organometallic reagent with a dichlorophosphine, followed by a second organometallic reagent; several families of new ferrocene-based P-chiral phosphine ligands have been developed. [6] Herein, we describe the highly stereoselective synthesis of a new ferrocenebased C 2 -symmetric diphosphine ligand 1 (TriFer). To the best of our knowledge, ligand 1 is the first class of C 2 -symmetric diphosphine that combines C-centered, P-centered, and planar chirality. Most importantly, unprecedented enantioselectivities have been achieved with ligand 1 for the Rhcatalyzed asymmetric hydrogenation of a-substituted cinnamic acids, a class of ver...

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The Massbauer spectra of in binary glasses of SnO and Si%, in varying proportions of between 16.8 and 71.5 mol% SnO. have been obtained at 77 K. From these spectra the tin was found to be predominantly in the 2"' state. The isomer shift and the quadrupole splitting were both significantly p a t e r than those in crystalline SnO and were found to decrease with increasing tin content. which also corresponds to decreasing molar volume. A second series of spectra of two of the san&.s was taken at temperatures between 10 and 300 K. These spectra show a decrease in shift with temperature which was the same for the two samples and which could only partly be accounted for by the second-order Doppler shift. The remainder was ascribed to the temperature dependence of the isomer shih. By using these data together with the measured expansivity and increase in density with tin content. it was possible CO wrrect the isomer shift for the effects of the change in volume, and it was found that the volumesorrected isomer shift inereared with increasing tin content. This showed that there was an increase in s-electron density at the tin nuclei. while the accompanying decrease in quadrupole splitting showed a decrease in the p-electron character, as expected for a decrease in covalency. From the decrease in absorption area with temperature the Debye temperature of tin was estimated to be -190 K, which is slightly less than that of crystalline SnO, and decreased with increasing tin content, All the data suggest that the Sn-0 bonds become progressively less covalent as more tin is added to SnO-Si% glasses, and possibly indicate a change from 4-fold to &fold co-ordination.A third series of spectra was obtained for the glass containing 40.9 mol% of SnO after a series of heat trements. The spectra show changes in the oxidation state of the tin which depended upon the different conditions applied.

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