Efficient, Nickel‐Catalysed Kumada–Tamao–Corriu Cross‐ Coupling with a Calix[4]arene‐Diphosphine Ligand

Abstract

Abstract:The dynamic complex cis-P,P'-(h 5 -cyclopentadienyl)-{5, 17-bis(diphenylphosphino)-25,26,27, 28-tetrabenzyloxycalix[4]arene}nickel(II) tetrafluoro-A C H T U N G T R E N N U N G borate (2) in which the PNiP plane undergoes a rapid fanning motion was assessed in the cross-coupling reacting between phenylmagnesium bromide (PhMgBr) and aryl halides (ArX). TOFs, of up to 21250 mol(converted ArBr)·mol(2), were obtained with electron-rich as well as congested bromoarenes using catalyst loadings as low as 1 10À3 mol%, provided that the reactions were carried out at 100 8C in dioxane with a PhMgBr/ArX ratio of 2:1. The high activities observed contrast with those observed for triphenylphosphine-based catalysts and furthermore, outperforms the fastest diphosphinebased catalysts reported, a behaviour which is likely to rely on a bite angle effect.

Unusually Large Bite Angle of a Distally Diphosphanylated Calix[4]arene Chelator

“…The value of the P-Ni-P angle, 104.6°, is close to that found in two related [Ni(η 5 -C 5 H 5 )(CALDIP)]BF 4 complexes. [17,22] The room temperature 1 H and 31 P NMR spectra are in accord with C 2v symmetry, which actually reflects a fast fanning motion of the P-Ni-P plane about the P···P axis similar to that previously reported for several [MX 2 (CALDIP)] (X = halide) and [M(η 5 -C 5 H 5 )(CALDIP)] complexes. [16,17] In this process the nickel atom moves between two positions on either side of the calixarene axis.…”

“…These complexes were found to operate as remarkably efficient catalysts in carbon-carbon coupling reactions. [17][18][19][20][21][22] Their high reactivity was attributed to the relatively large ligand bite angle (100-110°), which may favour a reductive elimination step in the catalytic cycle through steric effects involving the phosphorus substituents. A factor likely to enhance this effect is the fanning motion of the P-M-P plane in solution.…”

Crystal structure of 5,17-bis-cyano-25,26,27,28-tetrapropyloxy-calix[4]arene, C42H46N2O4

“…In the solid state, the calix [4]arene cavity adopts a typical pinched cone conformation [1][2][3], with interplanar angles between opposite phenoxy rings of 21.2°and 76.2°, respectively. The separations between the aromatic para-carbon atoms of opposite phenolic rings are 4.26 and 9.97 Å, respectively.…”

Resorcin[4]arene‐Derived Mono‐ and Diphosphines in Suzuki Cross‐Coupling

“…The increased performance of 3 vs. that of 2 possibly arises from its partial conversion into P,P-chelate complexes in which the ligand displays a large bite angle, [49] this latter feature being known, as already mentioned above, to promote reductive elimination in cross-coupling reactions. [46][47][48] Molecular mechanics calculations (SPAR-TAN) indeed show that in hypothetical [PdX 2 (3)] chelate complexes (X = halide, aryl), be they square planar or tetrahedral, the corresponding PMP angles are significantly larger than in conventional ML 2 X 2 complexes. Here the resulting strain generated within [a]…”

“…It is now commonly accepted that an increase of the PMP angle in [Pd(phosphine) 2 XY] complexes favours the reductive elimination step in C À C coupling reactions. [46][47][48] Formation of such species do, of course, not prevent from forming P,O-chelated intermediates.…”