Trans-phosphine arrangements

The trans-phosphine arrangement is presumed to support strong binding of olefin ligands and thus impede respective homogeneous catalyses. In order to systematically investigate the phosphine effect on the catal3 tic performance of Re(I)... 

The mechanism of hydrogenation of enamides by rhodium catalysts with monoden-tate phosphorous ligands was investigated computationally by means of the functional M05-2X taking into account the role of trans intermediates. Since the study suggested that cis intermediates played the major role in the mechanism of the reaction, the results with monodentate phosphorous ligands needed interpretation without involvement of structures with rrun -phosphine arrangements. ... 

Complex 4a (see Fig. 1) differs from these catalytically active complexes only in the substitution of the complexed olefin molecules and hydrogen atom by a 7r-allyl group. The ligands in these square-planar molecules can adopt two different arrangements around the central nickel atom The olefin can either be trans (31a) or cis (31b) to the phosphine molecule. Because precedent exists for both these arrangements [e.g., 12 (84) and 30 (82)]. it is difficult to decide which of the two structures (31a or 31b) represents the catalytically active species. It is of course possible that the differences observed in the catalytic properties of systems having different ligands L and Y (Section IV) is due (at least in part) to differences in the population of 31a and 31b. 

Bismuth phosphine complexes represent a substantial component of the established phosphine complexes of heavier p-block elements, and an excellent overview has presented an important bonding model for these systems (7). The observed structures are considered as trigonal-pyramidal BiX3 units with three secondary trans bonds. If the acceptor orbitals are the Bi-X trans arrangement is expected, as the relationship between the trans X-Bi-P bond distances. The shortest Bi-P distance [2.7614(2) vs 2.866(3) A] is trans to the longer Bi-Br distance [3.403(1) vs 2.9916(1) A], as the only arrangement that will allow the phosphine ligands to occupy trans... 

Strukul and co workers recently prepared a series of cis and trans isomers of the platinum- t-butyl peroxide complexes Pt(R)(OOBu )L2 (R = CF3, Ph, etc. L = tertiary phosphine). The X-ray crystal structure of the franx-[Pt(Ph)(OOBu )(PPh5)2] (88) revealed a square-planar arrangement with... 

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