ISSN:
0009-2940
Keywords:
η3-Allylrhodium complexes, preparation with Grignard reagents
;
η3-Benzylrhodium complexes, antara- and suprafacial rearrangements in solution
;
Unsymmetrical η3-benzyl-to-metal bonding in the solid state
;
Rhodium, η1-benzyl(carbonyl) compound
;
Rhodium, monomeric square-planar η2-carboxylato complexes
;
η3-Allyl(η1-carboxylato)hydridometal intermediates, formation by oxidative addition
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
η3-Allyl and η3-Benzyl Rhodium Complexes: Synthesis, Structure Dynamic, and Reactions with Carboxylic AcidsThe (η3-allyl)rhodium complexes [Rh(η3-2-RC3H4)(PiPr3)2] (3-5) have been prepared in 70-90% yield from the in situ generated chlororhodium precursor [RhCl(PiPr3)2] (2) and 2-RC3H4MgX. On a similar route, the corresponding ethene(phosphane) derivative [Rh(η3-2-MeC3H4)(PiPr3)] (9) has been obtained. Compound 9 smoothly reacts with PiPr3 and PMe3 to give 4 (R = Me) and [Rh(η3-2-MeC3H4)(PMe3)-(PiPr3)] (10), respectively. In contrast to the η3-allyl complexes which are configurationally stable, the η3-benzyl analogues [Rh(η3-CH2C6H4R) (PiPr3)2] (11, 12), prepared from 2 and 4-RC6H4CH2MgCl, are highly fluctional in solution. At room temperature, an antarafacial (π-δ-π) as well as a suprafacial rearrangement occurs, the first one of which is frozen out at 263 K. On cooling to 193 K, the faster process (equally designated as a metallotropic shift) is also slowed down, and the rigid structure of 11 and 12 is observed. The ΔG* values for the antara and suprafacial rearrangements of 11 and 12 which have been determined from the 1H- and 31P-NMR spectra at variable temperature are 60.0 ± 1.5 and 39.5 ± 1.0 kJ/mol, respectively. The η3-benzyl compound 11 reacts even at -78°C with CO to give the monocarbonylrhodium(I) complex trans-[Rh(η1-CH2C6H5)(CO)(PiPr3)2] (13). Treatment of 3,4, or 11 with RCO2H (R = CF3, CH3, C6H5, C6H4-4-OMe, C6H4-4-NO2) affords the monomeric η2-carboxylatorhodium(I) compounds [Rh(η2-O2CR) (PiPr3)2] (14-18) almost quantitatively. If the reaction of 3 or 4 with CF3CO2H is performed at -20°C in pentane, the octahedral (η3-allyl)hydrido complexes [Rh(η3-2-RC3H4)(H)(η1-O2CCF3)(PiPr3)2] (19, 20) are isolated. The crystal structures of 12 (at 223 K) and of 15 (at 298 K) have been determined by X-ray diffraction studies. They confirm that the η3-benzyl ligand is highly unsymmetrically and the acetato ligand completely symmetrically bound to the [Rh(PiPr3)2] unit.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19941270106
