Allylic complexes, properties

Curtis and Eisenstein355 have made a molecular orbital analysis of the regioselectivity of the addition of nucleophiles to 77-allyl complexes and on the conformation of the 773-allyl ligand in [MoX(CO)2L2(773-allyl)] type complexes. A detailed study of the chirality retention in rearrangements of complexes of the type [MX(CO)2(dppe)(rj3-C3H5)] has been made.356 Studies of the photoelectron spectra,357 electrochemical properties,358 infrared spectroelectrochemistry,359 and fast atom bombardment mass spec-... 

Variable temperature H NMR spectroscopy of a series of Sc and Y metallocene allyl complexes indicates flux-ional (see Fluxional Molecule and Structure Property Maps for Inorganic Solids) behavior involving C-C... 

The synthesis and properties of 7r-allyl transition metal complexes have been discussed elsewhere (127-129). We shall draw attention to the most interesting properties of n-allyl complexes such as structure, coordinative unsaturation of the metal, and the ability of the 77-allyl ligand to enter into intermolecular rearrangements. 

As the first catalytically active allyl-lanthanide compounds, the tetrakis(allyl) complexes Li[Ln(C3H5)4] dioxane, with Ln = Ce, Nd, Sm, Gd, and Dy, have been described [47]. More recently the field of allyl-lanthanide chemistry was extended considerably by the synthesis of the neutral tris(allyl) compounds of lanthanum and neodymium, LnlCsHj), n dioxane (Ln = La, n = 1.5 Ln = Nd, n = 1) from the tetrakis(allyl) complexes by abstraction of allyllithium with tri(ethyl)boron according to eqs. (1) and (2) [48]. For the catalytic properties of the allylneodymium(III) complexes, see [106],... 

In reactions which do not proceed via a /weyo-n-allyl complex, almost complete stereoselectivity in favor of the product with retenlion of configuration is observed, but regioselectivity may cause problems. The electron-withdrawing properties of the alkyl substituenl in the allylic aceiatc 22 is responsible for the exclusive formation of the distal product 2354 rather than its steric demand, since the nucleophile approaches the ir-allyl complex trans to the substituent. After further derivatization, the products 23 can be converted to polyfused ring systems by an intramolecular tandem palladium ene-Heck insertion reaction. 

Nickel(II) forms many relatively stable allyl complexes. In the case of Pt(II), the situation is reversed numerous, stable olefin compounds are known, while allyl complexes are quite scarce. Intermediate properties are exhibited by Pd(II) which forms many of both olefin and allyl complexes. However, allyl complexes are more stable because they may be obtained from olefin complexes at higher temperatures. This suggests that in 7r-complexes, the chemical properties of Pd(II) more closely resemble those of Ni(II) than Pt(II). 

These elements form homoleptic allyl complexes as well as alkenyl compounds with mixed coordination spheres. These compounds are also sensitive to air and proton containing solvents (Table 7.8). They decompose at low temperatures, for example, the compound [Ta(C3115)4] is stable only in saturated hydrocarbon solutions below 273 K. The complexes [Nb(allyl)4] and [Ta(allyl)4] are paramagnetic. The complex [V(C3H5)3] has pyrophoric properties. Halogen and cyclopentadienyl allyl complexes are more stable. In the compound [V(C3H5)cp2] the allyl forms a a bond to the central atom thus, it acts as an ligand. 

The Occurrence of tt-Allyl and Related Complexes All complexes in this class reported prior to January 1st, 1964, are given in Table IV. It is convenient when discussing the preparation and properties of 7r-allylic complexes to separate them into two categories. The... 

The Properties of -n-Allyl Transition Metal Complexes a. Stability. The thermal stability of w-allylic complexes varies from the very stable complexes of palladium, which are often stable above 200° C, to the very unstable and incompletely characterized tris(7r-allyl) complexes of chromium and iron. Most 7r-allylic complexes are oxidized by atmospheric oxygen, especially in solution. An extreme example is bis(7r-allyl)nickel which spontaneously ignites in air. However, many 7r-allylic complexes only show decomposition in air after several hours exposure. 

The spectra and the general properties of the lithium and magnesium allyl complexes indicate that they are essentially covalent compounds. However, in contrast, the sodium and potassium allyl complexes appear to be essentially salts. 

A variety of cations of the type (FpO—CRa), in which the carbonyl oxygen of an aldehyde, ketone, ester, or amide is complexed with an Fp+ residue, has been prepared as salts by reactions of the carbonyl compound with Fpg or FpBr in the presence of AgfPFg] and by displacement reactions of [Fp( y-iso-butene)]+ [BF4] the crystal structure of the [PFe]- salt of the 3-methylcyclo-hexanone complex has been determined. The n.m.r, spectra of complexes of the type [Fp( y-ene)]+ have been analysed,and the utility of such cations and related Fp(iy -allyl) complexes in organic synthesis has been further exploited. - In comparison with the properties of FpCH2CH=CH2,... 

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