Tripod‐Rhodium‐COD‐Komplexe: Synthese, Struktur, Dynamik und Katalyse

Abstract

Tripod Rhodium COD Complexes: Synthesis, Structure, Dynamics and Catalysis The reaction of the tripod ligands R′C(CH2PR2)3 (1a–c) and X2POCH[CH2P(Ph)2]2 (2a–c) with [RhI(COD)Cl]2] is investigated. It yields tripod rhodium COD complexes [(1a–c)RhI(COD)]Y (3a–c) and [(2a–c)RhI(COD)]Y [4a–c; Y = B(Ph)4, PF6]. The tripod ligand is coordinated by all three donor groups in each case, irrespective of the different donor capabilities of the coordinating groups. The solid state structure of compounds 3a–c and 4a is determined by X‐ray analysis. The observed coordination polyhedra delineate the variation from the idealized trigonal bipyramide to an idealized quadratic pyramide. In solution the analysis of the NMR spectra shows a rapid intramolecular interconversion according to a turnstile pseudo rotation. The complexes 3a and 4a are found to be catalysts for the hydrogenation of prochiral olefines.

Synthesis, Immobilization, MAS and HR‐MAS NMR of a New Chelate Phosphine Linker System, and Catalysis by Rhodium Adducts Thereof

“…The cation incorporating the Rh center is well defined, and overall the structure of 18 resembles the analogous Si‐triphos21a and triphos21b Rh structures. The coordination of all three phosphine groups of 16 is obvious, as it is the case in an analogous methoxy‐norbornadienyl Rh complex,22 as well as, for example, in various other tripod Rh23a and Cu23b complexes, and Sn,23c Ir,23d and Rh23e complexes with borate tripod ligands. In contrast to these systems, 18 needs two counteranions to satisfy the positive charges of the Rh(I) center and the phosphonium ligand.…”

Preparation, Characterization, and Performance of Tripodal Polyphosphine Rhodium Catalysts Immobilized on Silica via Hydrogen Bonding

“…In particular, the magnetic equivalence of the three phosphorus atoms in the fast-exchange regime (A 3 pattern) has been related to a fast rearrangement between square-pyramidal (SQ) and trigonal-bipyramidal (TBP) structures. ,20b In the slow motion regime, either of these limiting structures would give rise to an AM 2 pattern which can only be envisaged in the 31 P spectrum of 1 at −100 °C. Due to the geometrical constraints of the tripodal ligand, no five-coordinate metal complex with triphos can assume a perfect SQ or TBP conformation in the solid state; the complexes invariably adopt more or less distorted geometries depending on the coligands. , Unfortunately, we were unable to grow crystals of either 1 or 2 suited for an X-ray analysis and thus we cannot assign a preferential coordination geometry to either complex in the solid state. A distorted TBP structure has been determined, however, for the iridium derivative (sulfos)Ir(cod), which has been characterized by X-ray methods (Figure )…”

Dynamic coordinative exchange in rhodium(I) complexes of chiral diphosphines bearing pendant pyridyl donor groups

“…In contrast, no obvious weak coordination of an additional third donor atom is apparent in P,PЈ,PЉcoordinated rhodium/COD analogues of which a small number have been reported. 19 The relatively weak coordination in 2 may therefore be explained by the strain induced when the tridentate coordination mode is adopted, however the P(1)-Rh(1)-P(2), P(1)-Rh(1)-N(133) and P(2)-Rh(1)-N(133) interbond angles of 83.19(3), 75.38 (6), and 81.73(6)Њ respectively bear a close resemblance to those in its fac-P,PЈ,NЈcoordinated Mo(CO) 3 derivative (81.00, 73.27 and 79.17Њ respectively) where a strong N-coordination is observed. 18 Alternatively, this weak coordination may simply be explained by a reluctance of the rhodium to increase its formal electron count and coordination number and thus its electron density, especially via coordination of a relatively poor π-acceptor such as a nitrogen atom.…”