Phosphine tertiary, isomerization

Replacement of CO in MeCOMn(CO)5 with PPh3 seems to have little effect on the rate of the decarbonylation. As shown in Table IV, MeCO-Mn(CO)4PPh3 (an isomeric mixture) reacts only slightly faster than MeCOMn(CO)5 after provision is made for the difference in temperature 169). However, a recent kinetic study on the decarbonylation of CpMo-(CO)2L(COMe) (L = a tertiary phosphine) has shown that both inductive and steric properties of L are important 19a). Sterically demanding and weakly a-bonding phosphines increase the reaction rate. 

Efforts to tune the reactivity of rhodium catalysts by altering structure, solvent, and other factors have been pursued.49,493 50 Although there is (justifiably) much attention given to catalysts which provide /raor-addition processes, it is probably underappreciated that appropriate rhodium complexes, especially cationic phosphine complexes, can be very good and reliable catalysts for the formation of ( )-/3-silane products from a air-addition process. The possibilities and range of substrate tolerance are demonstrated by the two examples in Scheme 9. A very bulky tertiary propargylic alcohol as well as a simple linear alkyne provide excellent access to the CE)-/3-vinylsilane products.4 a 1 In order to achieve clean air-addition, cationic complexes have provided consistent results, since vinylmetal isomerization becomes less competitive for a cationic intermediate. Thus, halide-free systems with... 

We subsequently reported that altering the structure of the aryl groups of the tertiary phosphine can indeed produce a more effective catalyst [10]. Thus, replacement of Ph with o-Tol (PF-PPh2 -> PF-P(o-Tol)2) furnishes a ligand that provides improved enantioselectivity and yield for the rhodium-catalyzed isomerization of F-allylic alcohols (Tab. 4.1). 

Tertiary Phosphine Complexes Redox Linked cis-trans Isomerism. 390... 

Both the rhodium and the cobalt complexes catalyze olefin isomerization as well as olefin hydroformylation. In the case of the rhodium(I) catalysts, the amount of isomerization decreases as the ligands are altered in the order CO > NR3 > S > PR3. When homogeneous and supported amine-rhodium complexes were compared, it was found that they both gave similar amounts of isomerization, whereas with the tertiary phosphine complexes the supported catalysts gave rather less olefin isomerization than their homogeneous counterparts (44, 45). 

Phospholes can behave as simple two electron donors, in the same way as tertiary phosphines, and most of the transition metals have been complexed to phospholes. For example, ruthenium(II) forms a series of complexes [(Phole)2 Ru(CO)2C12] and [(Phole)3 Ru(CO)C12]. The formation of the tris phosphole complex attests to their small size. Because of the ring structure an unusual isomerism has been observed, with the rings either in the basal plane of the square pyramidal complex or normal to the basal plane (Figure 23). 

The products of oxidative addition of acyl chlorides and alkyl halides to various tertiary phosphine complexes of rhodium(I) and iridium(I) are discussed. Features of interest include (1) an equilibrium between a five-coordinate acetylrhodium(III) cation and its six-coordinate methyl(carbonyl) isomer which is established at an intermediate rate on the NMR time scale at room temperature, and (2) a solvent-dependent secondary- to normal-alkyl-group isomerization in octahedral al-kyliridium(III) complexes. The chemistry of monomeric, tertiary phosphine-stabilized hydroxoplatinum(II) complexes is reviewed, with emphasis on their conversion into hydrido -alkyl or -aryl complexes. Evidence for an electronic cis-PtP bond-weakening influence is presented. 

Isomerization of Secondary Alkyl lridium(lll) Complexes Containing Tertiary Phosphines... 

We conclude that in octahedral alkyliridium(III) complexes the presence of tertiary phosphines favors exclusively the n -alkyl over the corresponding secondary alkyl, irrespective of the size or basicity of the phosphine. This preference is probably largely electronic in origin, but steric factors cannot be ruled out. A key step that generates a vacant coordination site for both alkyl-group migration and isomerization in octahedral tertiary phosphine complexes of rhodium(III) and iridium(III) is dissociation of halide ion. 

Musco has also investigated the dimerization of butadiene. He found that COj enhances the catalytic effect of tertiary phosphine-palladium complexes in the syntheses of 1,3, 7-octatriene and in the subsequent isomerization to 2, 4, 6-octauiene 1299]. 

Dichloro(l, 3-propanediyl)platinum and its bis(pyridine) derivative have been studied by a number of authors. Dichloro(l,3-propanediyl)platinum, and the corresponding substituted 1,3-propanediyl platinum compounds release the parent cyclopropane on treatment with potassium cyanide, potassium iodide, a tertiary phosphine, carbon monoxide, and other ligands.2,6 Reduction by means of hydrogen or lithium aluminum hydride yields chiefly isomeric substituted propanes. Dichlorobis(pyridine)(l,3-propanediyl)platinum in refluxing benzene yields a pyridinium ylid complex, - (CH3CH2CHNC5Hs)-PtpyCla. 

Although boron is more accurately described as a metalloid rather than a metal, this section is concluded by two papers that describe the structures and bonding in several organoboron/organophosphorus compounds that display ylidic character. The X-ray structure of 9-borylanthracene (88) shows that only one of the diisopropylphosphine moieties is bonded to the boron in the solid state. However, H NMR evidence shows that an intramolecular bond-switching process takes place very rapidly in solution. The structures of a series of borabenzene adducts of phosphorus ylides, iminophosphoranes and tertiary phosphines have also been determined. Treatment of l-chloro-3,5-dimethyl-2-(trimethylsilyl)-l,2-dihydroborinine (89) with methylenetriphenylphosphorane (90) produces (triphenylphosphonio)methanide-3,5-dimethylborabenzene (91). However, if the reaction sequence is reversed and (90) is treated with (89), then (trimethylsilyl)(triphenylphosphonio)methanide-3,5-dimethylborabenzene (92) is obtained (Scheme 26). Treatment of an isomeric mixture of l-chloro(trimethyl-silyl)dihydroborinines (93) with N-(triphenylphosphoranylidene)aniline (94) produces iV-(triphenylphosphonio)anilide-borabenzene (95) (Scheme 27). Crystal structures of (91), (92) and (95) show that the P-C or P-N bonds are... 

The complex [Co(dmgh)(NO)] would be expected to react in the same fashion as the compounds just discussed, but under comparable conditions (e.g., in the presence of Lewis bases) it gives a mixture of nitrato and nitro products (192). The factors that infiuence the proportion of nitro and nitrato products have not been established by mechanistic studies, but a possible pathway involves the isomerization of the peroxy intermediate (35) to the nitrato species (37), as indicated in Fig. 20, or by further oxidation of the nitro product. Recent studies (193) have shown that the nitro complex is a reactive intermediate in the formation of [RuCl(N03)(bpy)2]. Tertiary phosphine complexes of the platinum metals also tend to give nitrato products (194)-. 

Reactions of [MnfRKCOIj] with tertiary phosphines, PR3, are extensive and range from the very early studies of Mawby et al. (122), Noack et al. (104), and Bannister et al. (123) to the far more recent studies of Cotton et al. (96,107,114) and Andersen and Moss (16-18). In the first study reported on this type of reaction, Mawby et al. (122) reacted [Mn(CH3)(CO)5] with PPh3 and P(OPh>3 in THF. The products of the reaction were the tertiary phosphine-substituted acyl complexes, c/.v-[Mn-(C0CH3)(C0)4(PR3)]. Similar results were subsequently obtained by other workers in the field (67,123-126). The later results also demonstrated the presence of the trans isomer of the phosphine-substituted acyl products. Noack et al. (104) reported a study of the isomerization process. Bannister et al. conducted a rather extensive study on the reaction of [Mn(R)(CO)5] (R = CH3, CeHs) with a range of nucleophiles (123). The results for [Mn(CH3)(CO)5] are shown in Table III. Thus, the reaction of [Mn(CH3)(CO)5] (and [Mn(Ph)(CO)j]) with phosphites gave disubstituted products. Similar results were obtained in subsequent studies on this type of reaction (21,41,67,99). 

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