| Abstract
| - The solid-state structures for [Rh((S)-MeO-Biphep)(P{OMe}3)2)]BF4 and PdBr(p-NCC6H4)((S)-MeO-Biphep) deviate markedly from square-planar geometry. DFT calculations on a series of systematically varied complexes reveal attractive aromatic ring π−π interactions to be important.
- The solid-state structure of the cationic MeO-Biphep Rh(I) compound [Rh((S)-MeO-Biphep)(P{OMe}3)2)]BF4 (3) has been determined by X-ray diffraction. The four P-donors deviatemarkedly from square-planar geometry, with the phosphite ligands P2 and P2‘ ca. ±0.61(7)Å from the P1−Rh−P1‘ plane. This distortion resembles that found for PdBr(p-NCC6H4)((S)-MeO-Biphep) (1). Density functional calculations on a series of systematically variedmodels of 1 reveal three major components to be responsible for the observed distortionfrom square-planar geometry: (i) attractive aromatic ring π−π interactions, (ii) electronicstabilization of coplanar aromatic rings in pseudo-trans positions, and (iii) P-phenyl andMeO-Biphep-phenyl intraligand repulsive steric interactions. Additional DFT studies on thep-tolyl-Binap analogue of 1, PdBr(p-NCC6H4)((R)-p-Tol-Binap) (2), explain the source of theextremely long Pd−P2 bond distance, 2.437(1) Å, in 2. Despite the structural similaritybetween 1 and 2, the calculations rationalize the observation of a pronounced distortionfrom a square-planar geometry in the former that is essentially absent in the latter.
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