Complexes methyl

The benzyhc complex has been synthesized at low temperatures and may owe its stabiUty to possible multihapto coordination, Tj —Tj, of the benzyl ligand. The methyl complex is stable even up to room temperature. Six of the methyl groups are hydrogen-bonded to the Li atom to stabilize this highly charged species. This compound is very reactive with and CO. However, there is no concrete stmctural data for the final products of such reactions. 

Two forms of the methyl complex have been characterized by X-ray diffraction the Rh-C distances differ slightly at 1.97 and 2.01 A, though the sp coordination geometry is the same. 

From the invariance of the coupling constant 2J(SiP) between HMPA-P and Si over a wide temperature range (compounds 4-7, 9-11) a rigid coordination of the HMPA to silicon can be deduced. Only in the case of the methyl complex 6 above 25 °C is the beginning of exchange of HMPA observed. However, a fast exchange of the coordinated acetonitrile at room temperature has been found for 12. 

Fe—N4 plane displacements of over 0.15 A, consistent with low spin Fe(lll) centers." The Fe—C bond lengths in the iron(lll) complexes are shorter (less than 2 A) than that in the iron(Il) complex (greater than 2 A). The shorter bond length for the phenyl complex Fe(TPP)Ph relative to the methyl complex Fe(TAP)Me is consistent with a stronger aryl Fe—C bond in the former. 

The addition of cyclohexyl isocyanide to several palladium(II) methyl complexes has proven particularly interesting 169, 170). From... 

The photochemically active bands of methylcobalamin have been identified as the intense hands due to -n—n transitions within the conjugated corrin ring, and the following quantum yields (< ) were obtained A = 490 nm, Similar quantum yields ( = 0.3-0.5) were also obtained for the photolysis of methylcobalamin in acid, where the base has been displaced and protonated, and the complex is present as a mixture of the methylaquo and five coordinate methyl complexes (/40). The effect of varying the second axial ligand on the rate of photolysis by white light has also been studied (134). 

The above results show that the reactions of all organocobalt(III) complexes with Hg(II) ions so far reported share several features in common. The reaction proceeds by an Se2 mechanism and the rate is reduced [compared to that of the simple aquated Hg(II) ion with the methyl complex] by (1) complexing of the Hg(II), e.g., with chloride, (2) increased substitution on the a-carbon, and (3) reduced electron donation from the cis and/or trans ligands. 

Enzymatic methylation of homocysteine (HSCHjCHjCHNHjCOOH) by methylcobalamin to give methionine (CH3SCH2CH2CHNH2COOH) was discovered in 1962 by Woods and co-workers, who also noticed the occurrence of a much slower, nonenzymatic reaction giving the same products. Methylcobinamide showed the same activity as the cobalamin in both the enzymatic and nonenzymatic reactions (72, 7/). It was subsequently discovered that HS, MeS , PhS , and w-BuS will dealkylate a variety of methyl complexes [DMG, DMG-BF2, DPG, G, salen, (DO)(DOH)pn, cobalamin] and even ethyl-Co(DMG)2 complexes to give the thioethers, and it was suggested that the reaction involved transfer of the carbonium ion to the attacking thiolate 161, 164), e.g.,... 

Catalytic hydrogenation with platinum liberates the hydrocarbon from methylcobalamin (57) and from alkyl-Co-DMG complexes (161), but not from pentacyanides with primary alkyl, vinyl, or benzyl ligands, though the cr-allyl complex yields propylene (109). Sodium sand gives mixtures of hydrocarbons with the alkyl-Co-salen complexes (64). Dithioerythritol will liberate methane from a variety of methyl complexes [cobalamin, DMG, DMG-BF2, G, DPG, CHD, salen, and (DO)(DOH)pn] (156), as will 1,4-butanedithiol from the DMG complex (157), and certain unspecified thiols will reduce DMG complexes with substituted alkyl ligands (e.g., C0-CH2COOH ->CH3C00H) (163, 164). Reaction with thiols can also lead to the formation of thioethers (see Section C,3). 

The methyl complex [BpBut]AlMe2 undergoes rearrangement upon heating at ca. 100°C to give the more stable isomer, [rj2-H2B(3-Butpz)(5-Butpz)]AlMe2, as shown in Eq. (18). 

Table 9-10. Experimental binding energies D0 [kcal/mol] for the cationic methyl complexes of the 3d elements and deviations from these data obtained at various levels of theory. Calculated values include a uniform zero point vibrational energy correction of 2.6 kcal/mol. 

Holthausen, M. C., Heinemann, C., Cornehl, H. H., Koch, W., Schwarz, H., 1995, The Performance of Density-Functional/Hartree-Fock Hybrid Methods Cationic Transition-Metal Methyl Complexes MCHt (M = Sc - Cu, La, Hf - Au) , J. Chem. Phys., 102, 4931. 

Studies have been carried out on the methylated complex [H3C-Niin(17)(H20)]2+, which is obtained from the reaction of methyl radicals (generated by pulse radiolysis) with [Ni(17)]2+. The volumes of activation are consistent with the coherent formation of Ni—C and Ni—OH2 bonds, as expected for the generation of a Ni111 complex from a square planar Ni11 precursor.152 The kinetics of reactions of [H3C-Niin(17)(H20)] + involving homolysis, 02 insertion and methyl transfer to Crn(aq) have been determined, and intermediates have been considered relevant as models for biological systems.153 Comparing different alkyl radicals, rate constants for the... 

The hydride-methyl complex OsH(Me)(CO)2(P Pr3)2 reacts with electrophilic reagents. The reaction products depend on the nature of the reagent (Scheme 39). Whereas the reaction with iodine gives almost quantitatively the diiodide OsI2(CO)2(P,Pr3)2, the reaction with a five-fold excess of phenylacetylene does not lead to the formation of the previously mentioned bis-alkynyl complex... 

Figure 97 The structure of the strontium bis(phosphinimino)methyl complex 183.

The use of weakly coordinating and fluorinated anions such as B(C6H4F-4)4, B(C6F5)4, and MeB(C6F5)3 further enhanced the activities of Group 4 cationic complexes for the polymerization of olefins and thereby their activity reached a level comparable to those of MAO-activated metallocene catalysts. Base-free cationic metal alkyl complexes and catalytic studies on them had mainly been concerned with cationic methyl complexes, [Cp2M-Me] +. However, their thermal instability restricts the use of such systems at technically useful temperatures. The corresponding thermally more stable benzyl complexes,... 

Enhanced stability is often detrimental to reactivity, and it came as no surprise that 6 did not react with 150 psi of H2 at 25 °C. When reacted with BH3 THF, was reduced to (n-C5H5)Re(N0)-(PPh3)(CH3) (7) (eq i). Methyl complex 7 could also be obtained by reduction of 2 with NaBHi,. However, since the prospects for reduction chemistry relevant to the fate of catalyst-bound formyls seemed bleak, we began to investigate other facets of the chemistry of fi. 

An excellent example of this sequence was illustrated in the reaction of CpRe(C0)2(N0)+ with NaBHu which under carefully controlled conditions produced the formyl, the hydroxymethyl and the methyl complexes, successively.— —... 

Thermolysis of the tantalum-phenyl/methyl complex 114 led to the formation of the Ta-benzyne complex 115 and the elimination of CH4.58 Similar to the reaction of the Ni-benzyne complex 85, one molecule of C02 could be incorporated into the carbon-tantalum bond to form the tantalumcycle 116 as shown in Scheme 40.59... 

The observation of stable Pt(IV) alkyl hydrides upon protonation of Pt(II) alkyls has provided support for the idea that the methane which had been observed in earlier studies (89-92) of protonation of Pt(II) methyls could be produced via a reductive elimination reaction from Pt(IV). An extensive study of protonation of Pt(II) methyl complexes was carried out in 1996 (56) and an excellent summary of these results appeared in a recent review article (14). Strong evidence was presented to support the involvement of both Pt(IV) methyl hydrides and Pt(II) cr-methane complexes as intermediates in the rapid protonolysis reactions of Pt(II) methyls to generate methane. The principle of microscopic... 

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