A 2,2′,6,6′-tetraphosphinobiphenyl

Abstract

The first example of a 2,2',6,6'-tetraphosphinobiphenyl was prepared and used as a ligand in a dinuclear palladium(II) complex. The close proximity of the two complex fragments induces a coupling pathway allowing the allosteric communication between the two palladium complex fragments.

Syntheses of P –aryl- and P –alkyl substituted 2,2′,6,6′–tetraphosphanyl–1,1′–biphenyls

“…In our first experiments we used n BuLi for generating the dilithiated species 6a [20]. It turned out, that this method is very case sensitive and results differ between experiments.…”

“…The crude products can be further purified by means of recrystallization from ethanol. All of the dibromo-substituted phosphines 4 were remarkably stable towards oxidation in air [25,31].…”

“…Ethanol was purified by distillation from magnesium and acetonitrile by distillation from calcium hydride. The following compounds: 2,2 0 -dibromo-4,4 0 methyl-6,6 0 -diiodobiphenyl 3 [22e24], diphosphanes 4a-c [20,25] as well as tetraphosphane 1a [20] were synthesized following published procedures. All other chemicals were purchased by commercial suppliers and were used without further purification.…”

“…[4,10e18] Despite the large number of known 2,2 0 -diphosphanyl-1,1 0 -biphenyls the number of reported examples of 2,2 0 ,6-triphosphanyl biphenyls is limited to a few ones. [6,19] Only in 2012, the first example of a 2,2 0 ,6,6 0 -tetraphosphanyl biphenyl 1a was reported by our group (Scheme 1) [20] The synthetic procedure was facilitated by two consecutive double halogen/lithium exchange and electrophilic quenching reactions starting from 2,2 0 -diiodo-6,6 0 -dibromobiphenyl 3 (Scheme 2). So far we only reported the synthesis of the symmetric 2,2 0 ,6,6 0 -tetrakis(diisopropylphosphanyl)biphenyl 1a and the related dinuclear palladium complex 2a.…”

“…We found that the phosphine donors in 1a are sterically hindered and can only be accessed by reactive palladium salts. Moreover the two chelating coordination sites interact with each other by allosteric interactions [20]. Herein we report a closer look at the limits of the employed synthesis strategy and the coordination behavior of homo as well as mixed substituted 2,2 0 ,6,6 0 -tetraphosphanyl biphenyls towards the common Pd 2þ precursor Pd(COD)Cl 2 (see Scheme 3).…”