Ylide complexes formation

For the rate-limiting ylide complex formation no isotope effects are expected for epoxide carbons. The observed 13C KIEs (Figure 20) rules out that formation of ylide is kinetically important, because effects of Cl and C2 atoms are different than unity. The normal isotope effect of Cl corresponds to the C-O bond breakage in the rate-limiting step. The inverse isotope effect of C2 suggests that the C2-0 bond became stranger in transition state than in substrate. 

Increased interest in the chemistry of ylides has produced X-ray structures for compounds 123 (R = OMe) (91T5277) and 138 (92H(34)1005), while possibilities of complex formation have led to structures for bidentate copper complex of 135 (94JCS(D)2651), monodentate copper complex of the 3-phenyltria-zolopyridine 139, monodentate (through N2) dinitrato ligand of 3-methyl-triazolopyridine 140 (99MI4), and dinitrato bidentate copper complex of... 

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

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... 

The ylide complex Pt[Au CH2P(S)Ph2 2]2 380 exhibits a structure similar to that of the analogous Pb derivative (see Section 2.4.4), with a linear Au-Pt-Au skeleton, transannular d8-d10 Au-Pt interaction of3.034(1) A, and extended one-dimensional chain polymer formation through weak intermolecular d10-d10 interactions [Au-Au 3.246 A] [34]. Oxidation of 380 or adduct formation resulted in discrete molecular... 

The oxonium ylide mechanism requires a bifunctional acid-base catalyst. The validity of the oxonium ylide mechanism on zeolites was questioned459,461,464 because zeolites do not necessarily possess sufficiently strong basic sites to abstract a proton from the trimethyloxonium ion to form an ylide. It should, however, be pointed out, as emphasized by Olah,447,465 that over solid acid-base catalysts (including zeolites) the initial coordination of an electron-deficient (i.e., Lewis acidic) site of the catalysts allows formation of a catalyst-coordinated dimethyl ether complex. It then can act as an oxonium ion forming the catalyst-coordinated oxonium ylide complex (10) with the participation of surface bound CH30 ions ... 

In cases where an alkyl has no (5 hydrogens (or no accessible ]8 hydrogen), an important alternative process, a elimination, can occur. M. L. H. Green40 has proposed the process shown in Scheme 3 to explain the formation of the ylide complex shown. Another interesting example (Scheme 4) is due to Shaw.6 It is not known whether Schrock s62 remarkable chemistry (equation 45), which led to the first examples of carbenes not stabilized by heteroatoms, also goes via a elimination or, perhaps more likely, by deprotonation of an alkyl at the a position by an organolithium reagent or other base. 

This activation process can be assumed to be the initial step in the formation of dinuclear copper(II) acetylide complexes, as first proposed by Bohlmann and coworkers 40 years ago (Scheme 6) [10f]. Deprotonated alkyne units 11 (or the corresponding JT-complexes 10) generated therein, stepwise displace the negatively charged counter ions of copper(II) salt dimers (12). The dinuclear copper(II) acet-ylide complex which finally results (14) collapses to the coupled product under reductive elimination of copper(I). The existence of higher-order copper acetylide... 

Formation of sulphur ylide complexes of Pt(Pd) of type [PtX2(R2S)Sy] (X = Cl, Br or I R = Me, Et Sy = Me(Ph)SCHC(0)C6H4Cl-p) has been reported.105 The v(CO) band of the metal complexes occurs at higher frequencies than in the free ylide, and in addition spin-spin coupling between the ylide methine proton and the 195Pt nucleus is observed, which is indicative of the Pt—C bond (47). 

C KIEs experiments were supposed to help distinguishing the rate-limiting formation of an epoxide-carbene ylide complex 52 versus a rate-limiting deoxygenation process. 

Both the cis and trans forms of [Pt(PPh3)2(I)CH2Cl] (57) react with PPh3 to give the ylide complex, ci5-[ Pt(PPh3)2(Cl )CH2PPh3]+ (58) (Scheme 19) 134,135). The novelty of the reaction in Scheme 19 is the specific formation of 58, which involves the migration of Cl from C to Pt with loss of I-... 

From carbodiphosphoranes R3P=C=PR3 and dialkyl-gold(III) halides, cyclic ylide complexes containing four Au-C <7-bonds are obtained in a multiple transylidation reaction (equation 24). Related thiophosphorus ylides and sulfonium and sulfoxonium ylides are equally effective in the formation of Au-C <7-bonds, and a series of analogous gold thiophosphonium and sulfoxonium-methyhde complexes is available (equations 25-27). ... 

Formation of Carbon-Transition and Inner Transition Metal Bond 105 5.8.2.S.7. Ylide Complexes... 

Complex formation takes place immediately when the methylene-trimethylphosphorane is added. A yellow sohd can be crystallized from the reaction solution in high yield, microanalysis of which shows a Ni/ylide A/ylide B complex with 1/1/1 stoichiometry. 

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