Metal ylides

Synthesis of metal ylide complex and their application in polymer chemistry. 

The insertion reactivity of the electrophilic iridium methylene species 57 was noted above. A cationic iridium methylene complex is also the likely intermediate in the thermal rearrangement of Ir(=CH2)I(CO)(PPh3)2 to the ortho-metallated ylide complex 75 ([Pg.167]

A mechanistic picture which reconciles the experimental results is given in Scheme 24. It is assumed that both the heteroatom and the double bond of the allyl halide compete for an electrophilic metal carbene. Heteroatom attack yields a metalated ylide 129, which may go on to ylide 131 by demetalation and/or to allylmetal complex 130. Symmetry-allowed [2,3] rearrangement of 131 accounts for product 132, and metal elimination from 130 gives rise to products 132 and 133, corresponding to [2,3] and [1,2] rearrangement, respectively, as well as haloacetate (if R3 = CHc ). 

Among four main directions of the chemical transformations of betaines of the first group, which are presented in Scheme 38, isomerization to metallated ylides (direction A), retro-Wittig type decomposition (direction... 

Materials science, 228, 297-306 Metallated ylides, 78-81, 86, 87 Metallocenes, 1-2, 7, 10 MOCVD (metal organic chemical vapor deposition), 228, 257-258, 265, 298, 300, 301... 

Keywords Nitrogen Phosphorus Sulfur Transition metal Ylide... 

Although, in principle, the chemistry here reported should be centered on the late transition metals, sometimes we will jump the frontier between late and middle or early transition metal since this line could be more or less diffuse and could change as a function of the history. At least seven different coordination modes have been identified (I-VII, Scheme 3) as the main bonding modes. In modes I and II the ylide behaves as neutral and monodentate, bonded exclusively through the Ca atom (kC mode) this is the case for simple ylides and carbodipho-sphoranes. Mode 111 covers the variants of a metallated ylide, that is, a situation in which the metal replaces a substituent of the ylide and transforms it into an anionic ligand. 

We have previously stated that an ylide could be considered the coupling product of a singlet carbene with a nucleophile. Therefore, it seems logical that the reaction of a metallic carbene with a nucleophile would give a metal bonded ylide and, in fact, this is a quite useful method to prepare metallated ylides. Even more, in some cases coordinated ylides have been used as masked caibenes [85]. Complexes (26) (Scheme 9, M = Cr, W), which contain a pyridinium yhde, are conveniently prepared by reaction of the corresponding carbenes [(CO)5M=C(OEt) R] with 1,2- or 1,4-dihydropyridines. During the reaction an unprecedented hydride... 

The attack of nucleophiles on unsaturated ligands or functional groups bonded to metallic centers, exemplified in Scheme 9 (reaction of metallic carbenes with phosphines or pyridines) or in Scheme 15 (Wittig reaction) can be extended to a wide variety of reagents. Two main groups of reactions can be considered (1) those in which the nucleophile is an ylide and (2) those in which the nucleophile is a phosphine (and less commonly other nucleophiles). Usually these reactions give metallated ylides (type III), that is, species in which the ylide substituents are metallic centers. 

Treatment of 2-(benzylideamino)propanoate with NEt3 and metal halides other than LiBr leads to N-metalated azomethine ylides (Scheme 11.11) (87). Although N-sodiated ylides generated by using Nal/NEta afford the Michael adduct as the major product in reactions with methyl crotonate, other metalated ylides produce... 

Methyl (naphthylideneamino)acetate undergoes dimerization to produce a mixture of two diastereomeric imidazolidines when treated with Mg(C104)2 or C0CI2 (89). Other imines can also be used as acceptor molecules (Scheme 11.12). With the exception of azomethine ylides incorporating sodium and titanium ions, other N-metalated ylides undergo highly endo-selective cycloadditions with a,p-unsaturated... 

Enantiocontrolled anti-selective Michael additions of the metalated ylides derived from a-(alkylideneamino)alkanoates are attractive as a new synthetic route to enantiomers of a-amino esters. Although there are a variety of chiral glycine equivalents available, only the enolates derived from 1,4-dihydropyrazine have been successfully applied to asymmetric Michael additions (Scheme 11.22) (103-105). In these reactions, the diastereoselectivities are high. 

The oxygen as heteroatom in ethers or carbonyl compounds is weak to moderate Lewis base. Nevertheless, a highly reactive metal carbene complex can interact with the oxygen to generate oxygen ylide. The interaction between ether and metal carbene functional groups is believed to be rather weak as demonstrated by the facts that other metal carbene reactions, such as G-H insertion and cyclopropanation, can proceed in ethereal solvents." These experiments demonstrate that the formation of the metal ylide is much less favored in the equilibrium shown in Equation (1). ... 

The alkylidenephosphoranes are among the most powerful bases known, and the displacement of a coordinated ligand is a useful method for the preparation of transition metal ylide complexes. 

A very stable type of organocopper compound, a metalated ylide, is obtained from the reaction between copper(I) chloride and trimethyl-methylenephosphorane in an aromatic solvent. The compound is soluble in aromatic and chlorocarbon solvents and can be sublimed 256a). 

Phosphines, as nucleophiles, add to many unsaturated substrates giving metallated ylides. Scheme 17 collects some representative examples of the addition of phosphines to carbyne complexes, giving (57) [132], to allenylidenes (58) [133], rr-alkenyls (59) [134], or CT-alkynyls (60) [135]. Moreover, reaction of phosphines with jt-aUcenes [136] and n-alkynes (61)-(64) [137-140] have also been reported. It is not possible to explain in depth each reaction, but the variety of resulting products provides an adequate perspective about the synthetic possibilities of this type of reactions. 

Miscellaneous. Tetramethylphosphonium salts have been generated from methylenetrimethylphosphorane by treatment with acid in inert solvent, or with ammonium salts in inert solvents or in aqueous ethanol. Details have appeared of the preparation of ]8y-unsaturated ketones using lithiated phen-acylidenetriphenylphosphorane. Alkylation of the metallated ylide (32) has... 

Extending his elegant work on multiphosphorus-ylide systems, Schmidbaur " - has prepared (8) and (9) by phosphinylation of the ylidic-anion (7), pure (8) and (9) can be obtained and both compounds form alkali metal-ylide complexes. 

The cycloaddition of in sitM-generated azomethine yhdes with electron-deficient alkenes is a useful method for the generation of stereodefined, substituted pyrrolidines, and there has been some recent interest in the development of a catalytic asymmetric variant. While a variety of methods for the generation of azomethine ylides have been developed, treatment of an a-iminoester (8.200) with an amine base in the presence of metal salts is the process most commonly employed in the asymmetric variant, which generally uses an enantiomerically pure metal complex of copper, silver or zinc to give an N-metallated ylide (8.201) (Figure 8.6). ... 

Trimethylphosphine is a ligand of proven utility in oiganometallic chemistry. However, because of its expense when purchased from commercial sources (Strero Chemicals) or its poor to moderate yidds when isolated as the silver iodide adduct [AgI(PMe3)l4, its potential is not fully realized. Frequently, large quantities of the phosphine are required, for example, as a reactive solvent or in the field of lanthanide and actinide chemistry, wherein the lability of the phosphine ligand may require crystallization from neat tri-methylphosphine. Similar considerations apply in exploratory synthetic early transition metal chemistry. In transition metal ylide chemistry, access to quantities of PMea is also very desirable, particularly when excess ylide is required. The volatility of PMe3 facilitates work-up of reaction mixtures and... 

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