Phosphine, tris stereochemistry

Phosphine, tris(dimethyldithiocarbamato)-stereochemistry, 81 structure, 82 Phosphines ligands history, 21 oxides... 

A"-Ray structure determinations (see Chapter 11 for details) have been reported for triphenylphosphine oxide, tri-o-tolylphosphine oxide, sulphide, and selenide, and for cw-2,2,3,4,4-pentamethyl-l-phenylphos-phetan-1-oxide (5). Electron spectroscopic studies of phosphorus oxychloride and thiophosphoryl chloride in the gaseous state, and n.m.r., i.r., and u.v. spectra of phosphine sulphides have appeared. Dipole moments have been used to define the stereochemistry of 2-cyanoethylphosphine oxides, such as (6), which is shown in its preferred conformation. 

Another situation is found for the stereochemistry of the products which are obtained from the reaction of [Re02(py)4]Cl with tris(hydroxymethyl)phosphine (THP) which yields both the cis-and traro-isomers of [ReO(py)2(THP)2] (74) with a clear preference for the cw-compound (74b) at longer reaction times, whereas the trara-compound (75) could be isolated exclusively with the more bulky bis(hydroxymethyl)phenylphosphine ligand (Scheme 6). ... 

The formation of both 12 and 13 during the reduction of 4 in the presence of triphenylphosphine indicated not only that one-half of an equivalent of the added phosphine was taken up, but also that the intermediate formed is the bisphosphine complex, (< 3P) JRhCl, proposed as the reactive intermediate in hydrogenation runs using 1 as the catalyst (1). This assumption is further supported by the fact that the product stereochemistry (cis/trans = 2.0) and lack of double bond isomerization observed on hydrogenation of 7 with this reaction mixture corresponds directly with the data obtained on hydrogenation of 7 using pre-hydro-genated 1 (3). When the reduction of 4 was repeated in the presence of tri-p-tolyphosphine, the carbonyl complex formed was isolated and shown by PMR spectroscopy to contain 1.5 equivalents of triphenylphosphine and 0.5 equivalent of the tri-p-tolyphosphine, as expected. 

The transmetallation step (iii) is certainly the most enigmatic part of the catalytic cycle. Generally, it is assumed to be rate limiting, and several mechanisms are proposed depending on the solvent. An open transition state with inversion of the stereochemistry would arise with polar solvents which are able to stabilize the transient partial charges , whereas a cyclic transition state with retention of the stereochemistry would arise in less polar solvents. It should be noted that the nature of the ligands on the palladium may influence dramatically the kinetics of the transmetallation step. A 1000-fold rate enhancement was observed when replacing triphenylphosphine by tri(2-furyl)phosphine . However, the dissociative or associative nature of the substitution on the palladium is stiU under discussion . ... 

Uranium, tetrathiocyanatotetrakis[tris-(dimethylamino)phosphine oxidc]-structure, 87 Uranium(VI) complexes liquid-liquid extraction of, 541 Uranyl complexes six-coordinate compounds structure, 53 stereochemistry, 74 Uranyl ions photoreactivity, 408 Urea... 

The influence which the other ligands have on the alkylation of d complexes is illustrated by the addition of methyl iodide to the tris(phos-phine)-rhodium complex (XL) (82a) but not to the similar complex RhCl(CO)(PPh3)2 in which a CO group has replaced a phosphine. However, the analogous iridium complex IrCl(CO)(PPh3)2 reacts with methyl iodide (see Section II,B) (2J, 41, 67), The rhodium adduct (XLI) is novel inasmuch as it contains two molecules of methyl iodide, the second apparently being bound through iodine (82a). The detailed stereochemistry... 

Studies of mono- and di-nucleotides using n.m.r. spectroscopy have reported chemical shifts and coupling constants. Both and n.m.r. spectroscopy were used to examine the stereoisomeric spirophosphoranes obtained by the joint action of tris(dimethyIamino)phosphine and carbon tetrachloride on 3-0-benzyl-l, 2-O-isopropylidene-ot-D-gluco- and -allo-furanose (see Vol. 9, p. 47), and, in conjunction with n.m.r. spectroscopy, the stereochemistries of 1,2-substituted 6-deoxy-6-halogeno-D-glucofuranose 3,5-phosphates. ... 

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