Substituted pyrrolyl ligands

In the same year, Breit [6, 7] published a prehminary report concerning the use of tris(l-pyrrolyl)phosphine in Rh-catalyzed hydroformylation of styrene. Although only poor conversion was observed (CO/H2 = 1 1, 50 bar 20 °C), from this point pyrrol-substituted phosphorus ligands dominated the research that followed. 

Fluoroarene-Cr(CO)2L complexes 33p [L = CO, PPh3, P(OPh)3, P(pyrrolyl)3, P(pyrolyl)2 (NMeBn)], where L is a potential linker ligand for solid-phase synthesis, have been evaluated with regard to the rates of nucleophilic substitution by amines [35]. The preparative and kinetic results indicate that SNAr reactions on tris(pyrrolyl)phosphine-modified fluoroar-enechromium complexes proceed rapidly and with high efficiency, and are thus appropriate for the development of solid-phase versions for use in combinatorial synthesis (Scheme 18). 

Spectroscopic and crystallographic techniques were used to good effect in the study of pyridazines. Spectrophotometry and H NMR spectroscopy were used to investigate the ligand substitution reactions of pyridazine in Pt(II) coordination complexes <07M1>. The electron densities and tautomeric equilibria of 6-(2-pyrrolyl)pyridazin-3-one 11 and 6-(2-pyrrolyl)pyridazin-3-thione 12 <07ARK114>. Optical, dielectric and x-ray diffraction studies of pyridazine perchlorate showed distinct structural differences between phases <07MI086219>. 

A set of nine ligands 20-28 based on the rigid acenaphthenechinone backbone containing N-N bonded peripheral substituents were synthesized (Chart 3.2). Variations include the 2,5-substitution pattern of pyrrole and the degree of annela-tion. In addition, one example of a mixed hgand with one N-pyrrolyl and one N-aryl substituent was obtained. AU these compounds are yellow or red air-stable sohds with spectroscopic properties in line with their structural features. 

Kinetics of CO substitution on 17 -heterocyclic complexes of Mn(CO)3 were measured. Of the N-, C-, P-, and As-heterocycles, only the N-heterocycles undergo substitution by phosphines. This is attributed to the greater electronegativity of N. Both 3,4-dimethylpyrrolyl and 2,5-dimethylpyrrolyl complexes substitute by an associative mechanism, but the former also undergoes substitution by a ligand-independent path. The proposed mechanism involves 17 — 77 coordination of the heterocycle (Scheme 2). The rates of substitution for these complexes are slower than that for [Mn(r7 -pyrrolyl)(CO)3], but [Mn(T7 -3,4-dimethylpyrrolyl)(CO)3] substitutes ca. 100 times faster than [Mn(T7 -2,5-dimethylpyrrolyl)(CO)3],... 

---