A comparison of MOP-phosphonite ligands and their applications in Rh(i)- and Pd(ii)-catalysed asymmetric transformations

Abstract

Six chiral MOP-phosphonites have been synthesised and compared via experimental and computational methods in an effort to quantify their differing structural and electronic profiles. They were found to be electron-poor ligands in comparison to their arylphosphine analogues and have a larger trans influence in square planar Pt(ii) complexes. Four [Rh(L)(η:η-cod)Cl] complexes were synthesised and characterised by NMR, HRMS and X-ray crystallography. Two [Rh(L)]BF complexes were prepared where one ligand acts as a chelating P,C-π-donor; detailed NMR studies demonstrated a hemilabile η-coordination mode, which in one case was confirmed by X-ray crystallography. Rh(i) complexes were used as catalysts in asymmetric hydrogenation and hydroformylation reactions and in the addition of phenyl boronic acid to an isatin. Pd(ii) complexes were successfully employed in asymmetric Suzuki-Miyaura cross-coupling reactions yielding binaphthyl products. Two [Pd(L)Cl] complexes were synthesised and characterised by X-ray crystallography, both adopting cis orientations, with one of the complexes crystallising as two pseudo-polymorphs.

Inverting Conventional Chemoselectivity in Pd-Catalyzed Amine Arylations with Multiply Halogenated Pyridines

“…On the basis of the preceding correlations, we considered heteroatom substituents at phosphorus. Unlike phosphonites ([RP­(OR′) 2 ]), which are uniformly weak σ-donors and strong π-acceptor ligands, the electronic properties of the corresponding bis­(dialkyl­amino)­phosphines are highly tunable. For instance, the Tolman electronic parameter (υ CO ) measured for trans -L 2 Rh­(CO)­Cl spans from 2007 cm –1 for PhP­(pyrrolyl) 2 to 1949 cm –1 for PhP­(pyrrolidinyl) 2 .…”

Rh(I) Complexes in Catalysis: A Five-Year Trend

“…Monophosphonites have thus been rather disregarded, in this respect, although they represent good substrates that can be diversely functionalized in order to tune their steric and electronic properties, affording effective catalysts for different processes. To evaluate this, a series of enantiomerically pure MOP-based structures have been prepared [30] (Figure 1), bearing -H or -OMe groups as the substituents on the 2 position of the binaphthyl backbone, and phenyl or diphenyl groups on the phosphonate moiety to increase the bulkiness of the ligand. The relative cationic Rh(I) complexes were thoroughly studied for their coordination features, using both experimental and computational data to quantify their stereoelectronic donor properties.…”