Ligands electron-rich

A palladium catalyst with a less electron-rich ligand, 2,2-dipyridyl-methylamine-based palladium complexes (4.2), is effective for coupling of aryl iodides or bromides with terminal alkynes in the presence of pyrrolidine and tetrabutylammonium acetate (TBAB) at 100°C in water.37 However, the reactions were shown to be faster in NMP solvent than in water under the reaction conditions. Palladium-phosphinous acid (POPd) was also reported as an effective catalyst for the Sonogashira cross-coupling reaction of aryl alkynes with aryl iodides, bromides, or chlorides in water (Eq. 4.18).38... 

The diphosphines 29-31 induced low asymmetries (8-15% ee) irrespective of the reaction conditions. The more electron-rich ligand (R, R)-32 gave (R)- 1-phenylethanol with a much-improved 65% ee (entry 1). Conversely, the application of the more electron-poor diphosphine (R, R)-33 resulted in the (A)-enantiomer, but with the same level of enantioselection (entry 2), highlighting the importance of the electron density of the phosphorus center on the... 

The Suzuki-Miyaura reactions with relatively inert arylchloride are known to require palladium complexes possessing highly electron-rich ligands which favor the oxidative addition of the arylchloride into Pd(0)-complex (Scheme 11) [67-69]. Herrmann et al. showed that the utilization of NHC ligands with bulky substituents... 

The observation of a bonding arrangement of the type shown in Fig. 20a in (AlO)2-centred dimers is a recurrent feature of aluminium hydroxides and organooxides of simple, electron rich ligands [44, 99, 110, 125, 134, 204, 205, 214-231]. Those more complex dimers which have been noted take two main forms both polydentate terminal and bridging ligands allow multiple interactions with the Group 13 metal centres. 

These structural changes involve the donor group of a donor-bridge-acceptor system it was therefore expected that a more electron-donating (electron rich) ligand at the donor metal would increase the molecular hyperpolarizability. This was confirmed in the substitution of cyclopentadie-nyl by the more electron-rich indenyl group for [Ru(C= CCf)H4-4-... 

The presence of electron rich ligands in the coordination sphere of the metal increases the rate of oxidative-addition. 

Starting from pent-4-yn-l-ols,the previously described catalytic system led to a mixture of lactone and cyclic enol ether [41]. However, in the presence of (Cp)ruthenium complexes bearing an electron-rich ligand such as tris(p-methoxyphenyl)phosphine in the presence of a large excess of the same ligand [system A], the selective formation of lactones was obtained. A simple modification of the catalyst precursor such as the switch to the electron-deficient... 

Many proteolytic enzymes utilize metal ions in their active site for catalyzing specific hydrolytic reactions [26]. Consequently, quite a number of electron-rich ligands for the complexation of specific metal ions [27] have been designed. Hydrolytic reactions mediated by such complexes have also been examined in order to obtain insight into the mechanisms responsible for this kind of catalysis [28]. These studies provided a basis for understanding certain actions of the... 

Using nickel catalysts of electronically tuneable phosphinite ligands, 105, an equally dramatic electronic effect on enantioselectivity has been observed (Scheme 37). An e.e. of 16% using an electron-rich ligand can be improved to 85-91% e.e. using an otherwise similar electron-poor ligand. This is the best e.e. observed for this reaction. 

The chemistry of 2,3-dihydrobenzo[ ]furan 257 discussed herein is focused on the furan part, rather than on the phenyl part, where its chemistry is similar to that of benzenoid molecules. For the chemistry based on the furan part, the frequent reports are related to the C-O bond cleavage. For example, by using an electron-rich ligand-based PCys/ Ni(acac)2 as a catalyst, 2,3-dihydrobenzo[ ]furan 257 was employed to couple aryl groups to afford biaryl compounds, as can be seen in Equation (150) <2004AGE2428>. 

---