Alkyl ligands stability

Qualitative Comparison of the Stability of Pentacyanides [RCo(CNj)] " Containing Primary, Secondary, and Tertiary Alkyl Ligands"... 

The same order of the relative stability is observed also for the initial product of the migratory insertion step, with the endo alkyl(silyl) complex, 9a, being more stable than the exo one, 9b, by -4.2 kcal/mol. A rearrangement of the Tj1-alkyl ligand leads to a T) coordination of the... 

Typical n-alkyl ligand densities that can be achieved with -alkylchlorosi lanes are within the range of 2.5-3.2pmolm-2, whilst with disilazanes, ligand densities approaching the limited values can be reached under optimized conditions, i.e. between 3.50 and 4.20 pmolm-2. Surface-modified zirconia or other metal oxide based RPC sorbents can be similarly prepared by either of the above two strategies. Compared to n-alkylsilicas, these ceramic RPC sorbents show different selectivities with synthetic peptides, as well as different chemical stability profiles. Consequently, RPC sorbents based on these types on surface-modified, porous metal oxide materials fulfill useful and complementary roles, but at this point in time, have achieved a more limited range of applications for the resolution of synthetic peptides due to their limited availability. 

Comparison between the half-wave potentials (equations 2 to 4) of [Cr(CNR)6](PF6)2, e.g. for R = Bu , -1.04, -0.28 and 0.84 V (versus SCE),22 with those for [Cr(CNPh)6](PF6)2, i.e. -0.35, 0.25 and 1.00 V,20 shows that alkyl and aryl isocyanides favour respectively the higher and the lower oxidation states as expected from the greater a-donor and weaker jr-acceptor capabilities of the alkyl over the aryl isocyanides. Similarly, the phosphines in the mixed ligand complexes (Table 3), 23 relative to isocyanide ligands, stabilize the Cr111 oxidation state. The great difference in the relative stabilities of Cr—C bonds in the cyano and phenyl isocyanide complexes is indicated by the magnitude of the shift (ca. 2.0 V) between the Cr(CN) "/Cr(CN)r (-1.130 V) and the Cr(CNPh)i+/Cr(CNPh)i+ reduction potentials.28... 

Terminal monoalkenes were alkylated by stabilized carbanions (p a 10-18) in the presence of 1 equiv. of palladium chloride and 2 equiv. of triethylamine, at low temperatures (Scheme l).1 The resulting unstable hydride eliminate to give the alkene (path b), or treated with carbon monoxide and methanol to produce the ester (path c).2 As was the case with heteroatom nucleophiles, attack at the more substituted alkene position predominated, and internal alkenes underwent alkylation in much lower (=30%) yield. In the absence of triethylamine, the yields were very low (1-2%) and reduction of the metal by the carbanion became the major process. Presumably, the tertiary amine ligand prevented attack of the carbanion at the metal, directing it instead to the coordinated alkene. The regiochemistry (predominant attack at the more sub-... 

They are sensitive to light, air, and moisture. Alkyl compounds stabilized by donor ligands are significantly more stable, for example (18-1-VII)15 and (18-I-VIII).16 The linear L—Ag—C arrangement is typical. 

The migration of an alkyl ligand to a coordinated CO generates a coordinatively unsaturated species (21-XXIXa) which can be stabilized either by the solvent (S) or as a r -bound acyl (21-XXIXb) by coordination of the oxygen to the metal. In general, several mechanistic pathways are therefore possible ... 

Certain simple alkyls are stabilized by the presence of either phosphine or amide ligands, thus ... 

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