Ylide complexes

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

The ylide complexes Ph3PC5H4M(CO)3 (M = Mo, W) are also able to add BF3. Solutions of these complexes in CH2CI2 can be titrated tensimetrically with BF3 at 0°C and - 78°C. The titration curves suggest that the reactions between the metal complexes and BF3 are reversible. The red adducts are air stable. 

The diamagnetic ylide complexes 34 have been obtained from the reaction of electron-deficient complexes [MoH(SR)3(PMePh2)] and alkynes (HC=CTol for the scheme), via the formal insertion of the latter into the Mo-P bond. The structural data show that 34 corresponds to two different resonance-stabilized ylides forms 34a (a-vinyl form) and 34b (carbene ylide form) (Scheme 17) [73]. Concerning the group 7 recent examples of cis ylide rhenium complexes 36 cis-Me-Re-Me) have been reported from the reaction of the corresponding trans cationic alkyne derivatives 35 with PR" via a nucleophilic attack of this phosphine at the alkyne carbon. 

Works developed by Navarro and coworkers for the palladium and stabilized ylides complexes have been extended to the platinum chemistry (Scheme 25) [97,98]. 

Complexes containing the ylide ligand can be also obtained by reaction of the yellow solution of ylides (prepared by addition of butyllithium to tetrahydrofurane or diethylether solutions of the phosphonium salt) with [AulCfiFs) (tht)]. The weak ligand tht is replaced and the ylide complex is obtained (Equation 3.5) [70]. 

Uson, R., Laguna, A., Laguna, M. and Uson, A. (1983) A new route for the synthesis of gold(I) and gold(III) pentafluorophenyl(ylide) complexes. Inorganica Chimica Acta, 73(1),... 

Trzcinskabancroft, B., Knachel, H., Dudis, D., Delord, T.J. and Marler, D.O. (1985) Experimental And Theoretical-Studies Of Dinudear Gold(I) And Gold(II) Phosphorus Ylide Complexes - Oxidative Addition, Halide Exchange, And Structural-Properties Including The Crystal And Molecular-Structures Of [Au (CH2)2PPh2]2 And [Au(CH2)2PPh2]2(CH3) Bri. Journal of the American Chemical Society, 107(24), 6908-6915. 

It was shown that complexes 19 of the zwitterionic precursors of ortho-quinone methides and a bis(sulfonium ylide) derived from 2,5-di hydroxyl 1,4 benzoquinone46 were even more stable than those with amine N-oxides. The bis(sulfonium ylide) complexes were formed in a strict 2 1 ratio (o-QM/ylide) and were unaltered at —78 °C for 10 h and stable at room temperature under inert conditions for as long as 15—30 min (Fig. 6.18).47 The o-QM precursor was produced from a-tocopherol (1), its truncated model compound (la), or a respective ortho-methylphenol in general by Ag20 oxidation in a solution containing 0.50-0.55 equivalents of bis(sulfonium ylide) at —78 °C. Although the species interacting with the ylide was actually the zwitterionic oxidation intermediate 3a and not the o-QM itself, the term stabilized o-QM was introduced for the complexes, since these reacted similar to the o-QMs themselves but in a well defined way without dimerization reactions. 

Scheme 11 Gold(III) and mixed Gold(I)/Gold(III) ylide complexes.

This reaction closely resembles the formation of ylide complex 8 from the stable rhenium methylene 7 (24) ... 

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]

Ylide complexes of gold are unique in that they exhibit an exceptional chemical and thermal stability, which facilitates preparative and structural work very considerably. It was in this class of compounds that a large variety of true organogold(ll) and mixed valence organogold(l)/(lIl) complexes was discovered. These are rare in the remainder of organogold chemistry. 

Unusual aurophilic bonding between gold in different oxidation states appears to be responsible for the adduct formation between (G6F5)3Au and cyclic ylide complexes with gold in the oxidation state +1 and +2 and in related compounds with an ionic structure (Scheme 24)155-157... 

Formulas of phosphonium/sulfonium ylide complexes should be written with onium charges at the P or S atoms and negative charges at the metal atom, but for the sake of convenience and clarity, these charges are omitted. 

Substrates with two labile substituents such as (tht)AuCl can be converted into ylide complexes in two steps. An example of this type is the product [(Ph3PGH2)2Au]+C104 obtained upon the reaction with two ylides, followed by anion exchange. The cation with its linear CH2-Au-CH2 core unit crystallizes with the tetracyanochinodimethane anion as a green crystalline product.1... 

Cyclic dinuclear ylide complexes have also been prepared with sulfur ylides. The reactions of (dppm)(AuCl)2 or (dppe)(AuCl)2 with trimethylsulfoxonium tetrafluoroborate and base under phase-transfer conditions gave the products shown in Scheme 42. Auration of the dppm ligand leads to the byproducts.27... 

Structure and bonding in cyclic ylide complexes have been studied extensively in earlier experimental and theoretical work.2 There is general agreement that transannular aurophilic bonding has a significant influence on the stability and reactivity of this family of compounds. There is also evidence for inter -molecular aurophilic bonding between these auracycles, but the number of examples is still limited (Scheme 43) 27455-i57,i8i... 

Cyclic ylide complexes are readily oxidized not only by aggressive reagents like elemental halogens but also by milder oxidants like disulfides, or even mercaptanes in the presence of molecular oxygen, as shown for a reaction with pyridine-2-thiol in air (Equation (34)).182 A similar reaction is known to take place with thiuramdi-dulfides.2,180... 

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