Methyl group alkyl ligand

The best titanium mediator appears to be methyltitanium triisopropoxide, yet good yields are also obtained with titanium tetraisopropoxide and chlorotitanium triisopropoxide. The methyl group on titanium serves as a dummy alkyl ligand which is eliminated as methane after hydride transfer from the... 

Fig. 35. (a) Correlation between the photolysis rate of halomethyl-cobalamins and the electronegativity of the alkyl ligand. (The electronegativity values are shown as the sums of the Pauling electronegatives of the atoms attached to the methyl carbon.) (b) Correlation between pKa for displacement of benzimidazole and alkyl group electronegativity for a series of halomethyl-cobalamins... 

As described previously, the two dimethyl amino methyl groups on the 2,6-position of the phenyl ring of teluride 161 act as internal ligands (Koten s arms) and stabilize the cation generated at the central Te atom (see Equation 44). Furukawa and co-workers subsequently showed that these Koten s arms also activate the molecule to release alkyl substituents which are attached to the central chalcogen atom <1995JA10153> and <1997BCJ2571>. For example,... 

Scheme 10.1S. Dummy ligands selective transfer of the methyl (or alkyl, alkenyl, aryl) group in preference to transfer of the alkynyl group.

As previously mentioned, the catalyst precursors in aprotic solvents generally contain a Pd-alkyl moiety for immediate insertion of CO without the need of activators. In some cases, bis-halide Pd" precursors have been employed in conjunction with activators such as methyl aluminoxane (MAO), which is able to replace one halide ligand with a methyl group and to create a free coordination site at the metal [17]. 

---