Iminoarylphosphites with ferrocenylidene and cymantrenylidene fragments: Coordination properties and use in palladium-catalysed asymmetric allylic substitution

Ferrocenyliminophosphites as Easy‐to‐Modify Ligands for Asymmetric Catalysis

“…Noteworthy is the asymmetric arrangement of this ligand, which manifests itself in the fact that each carbon atom exhibits its own signal. This seems to be due to the influence of the bulky organophosphorus ligand, which causes a distortion of the geometry of the metal complex 6f. Comparison of the 13 C NMR spectral parameters of the free and coordinated ( R a)‐ 7 revealed substantial downfield coordination shifts of the signals for the CH=N carbon atom (Δ δ C = 12.1 ppm).…”

“…So, the amination with pyrrolidine with 2b gave ee values up to 73 % (Table 3, Entry 30), and the alkylation with dimethyl malonate with 2a – c produced ee values up to 88 % 6c,6d. Acyclic iminophosphites 3a , b and 4a , b were found to be even more efficient; they gave rise to almost quantitative chemical and optical yields in the enantioselective Pd‐catalysed C*–C and C*–S bond formation reactions with substrate 19 6e,6f…”

“…In the Pd‐catalysed allylic alkylation of the monosubstituted substrate 1‐(4‐chlorophenyl)allyl methyl carbonate and the unhindered linear substrate ethyl 3‐penten‐2‐yl carbonate the binol‐ and phenol‐based acyclic iminophosphites produced very similar results. At the same time, in the Pd‐catalysed allylic alkylation of 1,3‐diphenyl‐2‐propenyl acetate the ligands with 2,6‐disubstituted phenyl moieties were found to be much better stereoselectors and the best one was ligand 3a 6f. However, in contrast to the alkylation of 19 , for 1‐(4‐chlorophenyl)allyl methyl carbonate ( 16 ) enantioselectivities are higher when more sterically demanding substituents in the ortho positions of the phenyl rings are present ( i Pr > Me).…”

“…However, in contrast to the alkylation of 19 , for 1‐(4‐chlorophenyl)allyl methyl carbonate ( 16 ) enantioselectivities are higher when more sterically demanding substituents in the ortho positions of the phenyl rings are present ( i Pr > Me). In addition, the iminophosphites with a biphenyl backbone 2a – c were discovered to be less efficient than their binaphthyl analogues in the Pd‐catalysed allylic alkylation of the monosubstituted and unhindered linear substrates and more efficient in the Pd‐catalysed allylation of bulky substrate 19 6c,6d,6f…”

“…All reactions were carried out under a dry argon atmosphere in freshly dried and distilled solvents; Et 3 N and pyrrolidine were twice distilled from KOH and then over a small amount of LiAlH 4 before use. Ligands ( S a)‐ 1 , ( R a)‐ 1 ,6a 2b 6c 3a ,6b 3b ,6f 4a 6e and their cationic cis ‐chelate complexes [Pd(allyl)( L )]BF 4 were prepared as described earlier. Phosphorylating reagent ( S a)‐ or ( R a)‐2‐chloro‐dinaphtho[2,1‐ d :1′,2′‐ f ][1,3,2]dioxaphosphepine ( 5 )16 and iminoalcohol ( 2S )‐2‐(ferrocenylideneamino)‐3,3‐dimethylbutan‐1‐ol ( 6 )6e were synthesised by using literature procedures.…”