Xylylene complexes

Although the o-xylylene complex is thermally unstable, it was characterized at — 50 °C by its 1H- and 13C-NMR spectra showing the exocyclic methylene at 5 = 5.04,4.42 ppm (JH) and 5 = 144.8 ppm (13C) using C6D5CD3 as the solvent. Its reaction with benzoyl chloride on the exocyclic carbon leaves a very acidic methylene group which transfers a proton onto the adjacent methylene unit. The double bond is benzoylated again in in situ and a di-cation of the [bis(arene)Fe]2+ type is obtained [47] Scheme VIII. 

An additional notable mode of the reactivity of these quinone methide complexes is formation of metal stabilized p- and o-xylylenes.10... 

Vigalok, A. Shimon, L. J. W. Milstein, D. Methylene arenium cations via quinone methides and xylylenes stabilized by metal complexation. J. Am. Chem. Soc. 1998, 120, 477 183. 

Whether [6]radialenes have a potential as novel ligands for metal complexes remains to be seen. A first example of a successful complexation is provided by 150, which reacts with tris(acetonitrile)tricarbonylchromium in dioxane at room temperature to give the ortho-xylylene chromium complex 175 in excellent yield (83%) (equation 23)105. 

From these examples, one should recognize that the building of the complex steroid skeleton of estrone has been made rather simple when various o-xylylene generation and trapping methods are applied ll5 118). 

The formation of the heterocycle 1 from the xylylene-bis-phosphonium salt 2 and PCI3 proceeds via a detectable intermediate 3 in a cascade of condensation reactions that is terminated by spontaneous heterolysis of the last remaining P-Cl bond in a cyclic bis-ylide-substituted chlorophosphine formed (Scheme 1) [15]. The reaction scheme is applicable to an arsenic analogue of 1 [15] and to bis-phosphonio-benzophospholides with different triaryl-, aryl-alkyl- and aryl-vinyl-phosphonio groups [16, 18, 19], but failed for trialkylphosphonio-substituted cations here, insufficient acidity prohibited obviously quantitative deprotonation of the phosphonium salts, and only mixtures of products with unreacted starting materials were obtained [19]. The cations were isolated as chloride or bromide salts, but conversion of the anions by complexation with Lewis-acids or metathesis was easily feasible [16, 18, 19] and even salts with organometallic anions ([Co(CO)4] , [CpM(CO)3] (M=Mo, W) were accessible [20]. 

C2H,N, Pyridine, 3,5-dimethyl-palladium complex, 26 210 CbHsNO, Benzoyl isocyanide chromium com-C HbO, Ethanone, 1-phenyl-manganese complex, 26 156-158 CBH, 02, Methyl benzoate chromium complex, 26 32 C H i, o-Xylylene magnesium complex, 26 147 ChH P, Phosphine, dimethylphenyl-iron complex, 26 61 ruthenium complex, 26 273 ChH12, 1,5-Cyclooctadiene iridium complex, 26 122 ruthenium complexes, 26 69-72, 253-256 ChH OjPS, 2-Butenedioic acid, 2-(dimethylphosphinothioyl)-dimethyl ester, manganese complex, 26 163... 

Figure 2. Experimental (A isomer) and computed (A isomer) low energy structures of the dicopper(I) complex of the macrocyclic Schiff-base ligand with para-xylylene spacer groups, and computed energy barrier (confirmed by NMR spectroscopy).125126...

The electron transfer photochemistry of benzocyclobutenes in the presence of dienophiles exhibits another interesting feature of CIP reactions [93]. For example, charge transfer irradiation of the EDA complex composed of 1,2-diphenylbenzocy-clobutene (36) and TCNE (IS) leads to the CIP (36 15 ), of which 36 spontaneously ring-opens to the o-xylylene (37) radical cation, followed by the collapse of the new CIP (Eqs. (20, 21)), leading to the Diels-Alder adduct 39 in high yield and with high efficiency. 

The cationic hexamethylbenzene ruthenium complex 254 can be depro-tonated by treatment with t-BuOK to give the ruthenium complexes 255 and 256 in which the r 4-o-xylylene ligand is coordinated via its exocyclic diene (Scheme 23). Protonation of 255 gives the dication 15c, whereas protonation of 256 produces the fluxional tj3-benzyl derivative 257 which is stabilized by an agostic C—H bond (156,157). 

In order to increase the extension of the concave surface of cyclotriveratrylene, and to obtain potentially useful host structures, Cram and coworkers have synthesised cavitands 60-65 [33]. In these compounds the additional walls (e.g., the o-xylylene units in 60) are conformationally very mobile in solution. On crystallization from CH2Cl2-cyclohexane, 60 afforded a complex with one CH2C12 molecule inside the host cavity. The stereoview in Fig. 9 shows that two of the o-xylylene walls are turned upward from the cavity bottom and the third outward. 

Figure 3,108 Synthesis of iridium(l) and rhodium(l) carbene complexes with bis-carbenes possessing an o-xylylene scaffold.

Half-sandwich see Half-sandwich Complexes) complexes Cp Nb j -o-(CH2)2C6H4 Cl2 andCp Ta( 7 -Ci4Hio)Cl2 with an extended conjngated jj -diene ligand snch as o-xylylene and anthracene have been prepared from the reactions of Cp MCl4 with o-C6H4(CH2MgCl)2 and Mg(anthracene)(THF)3, respectively. ... 

The catalytic activities of Nb and Ta complexes Cp M() -diene)Cl2 (M = Nb, Ta diene = 1,3-butadiene, isoprene, 2,3-dimethyl-l,3-butadiene) activated by MAO have been compared. They both give polyethylene with very narrow polydispersities at low temperature (Mw/M as low as 1.05). The Nb complexes are superior to the Ta complexes in terms of the catalyst activity and the polydispersity. Cp Ta(o-xylylene)Cl2/MAO is twice as catalytically active and the molecular weight distribution of the polyethylene is much narrower than that using Cp M( -l,3-butadiene)Cl2/MAO as catalysts. ... 

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