Novel Chelating Phosphonite Ligands: Syntheses, Structures, and Nickel-Catalyzed Hydrocyanation of Olefins

Abstract

A series of sterically tuned chelating bisarylphosphonite ligands with a cis-1,2-(bi)cycloalkane spacer and cyclic phosphonite moieties was synthesized. The spacer as well as the phosphacycles were modified to investigate their influence in the nickel-catalyzed hydrocyanation of styrene and 1,3-butadiene and the isomerization of 2-methyl-3-butenenitrile. NMR studies detect only catalytically active (P ∩ P)Ni(COD) species and no hints of the formation of catalytically inactive dibisphosphonite complexes (P ∩ P) 2 Ni are found. In the hydrocyanation of styrene, these catalysts are highly active (93% conversion) and highly regioselective (99.9% iso) at moderate catalyst concentrations (1 mol %). They also proved to be very active in the hydrocyanation of butadiene with turnover numbers of 644 and turnover frequencies of 426 h -1 at low catalyst concentrations (0.1 mol %). Moreover, they very efficiently catalyze the isomerization of 2-methyl-3-butenenitrile to the linear 3-pentenenitrile.

Phosphonite Ligand Design for Nickel‐Catalyzed 2‐Methyl‐3‐butenenitrile Isomerization and Styrene Hydrocyanation

“…By applying as little as 0.8 mol % of catalyst, a yield of 43 % of 2PPN could be reached within 16 h at a reaction temperature of 60 °C 17. Although full conversion was not achieved, the result is quite remarkable, since, to our knowledge, phosphonite ligands in styrene hydrocyanation—with the exception of 20 —require catalyst loadings of 5 mol % and higher in order to achieve satisfying yields 11. 18…”

“…31 P NMR spectroscopy showed the exclusive formation of a pair of doublets ( δ =189.3 and 193.3 ppm, J =61.0 Hz; free ligand: δ =179.7 and 182.1 ppm, J =13.7 Hz); The increased coupling constant and the downfield shift of the signals clearly indicate the formation of mono‐chelate nickel(0) complex 19 . Due to broadening of the signals in 1 H NMR spectra, the question whether cod in [( 15 )Ni(cod)] is bound in a η 2 ‐coordination mode or rather adopts a η 4 ‐coordination mode, as previously reported for a chelating phosphonite ligand,11 remains unclear.…”

“…There are only a few reported examples for the utilization of chelating phosphonite ligands in the literature 10. However, a modular system ( 2 ; Figure 1) recently developed in our group, bearing cycloalkanes as ligand backbones, showed excellent activities in 1,3‐butadiene and styrene hydrocyanation, as well as in 2M3BN isomerization 11. It therefore seemed attractive to also synthesize and investigate phosphonite derivatives with dihydroanthracene‐based ligand backbones ( 3 ; Figure 1).…”

The Primary Phosphine Renaissance

“…1.9); these are typically reactive electrophilic reagents and enantiopure examples would be especially valuable for synthetic operations [36]. A library of phosphonites [58][59][60] could then be prepared by reaction of these dichlorophosphines with the appropriate alcohols and phenols in the presence of a tertiary amine base, and our exemplar targets were phosphonites based on enantiopure binol as shown in Fig. 1.10.…”

Backbone Diversity Analysis in Catalyst Design

“…Despite the fact that this is a well known process, catalyst optimisation remains a challenge. [32,33] We focus here on the second step, the hydrocyanation of 3-pentenenitrile to adiponitrile (Figure 3, bottom).…”