η³‐Allyl‐ und η³‐Benzyl‐Rhodiumkomplexe: Synthese, Strukturdynamik und Reaktionen mit Carbonsäuren

Abstract

-and suprafacial rearrangements in solution I Unsymmetrical q3-benzyl-to-metal bonding in the solid state / Rhodium, q'-benzyl(carbony1) compound / Rhodium, monomeric square-planar q2-carboxylato complexes / q3-Allyl(q I-carboxy1ato)hydridometal intermediates, formation by oxidative addition q3-Allyl and q3-Benzyl Rhodium Complexes: Synthesis, Structure Dynamic, and Reactions with Carboxylic AcidsThe (q3-ally1)rhodium complexes [Rh(q3-2-RC3H4)(PiPr3),] (3-5) have been prepared in 70-90% yield from the in situ generated chlororhodium precursor [RhCl(PiPr,),] (2) and 2-RC,H,MgX. On a similar route, the corresponding ethene-(phosphane) derivative [Rh(i13-2-MeC3H4)(C2H4)(PiPr3)] (9) has been obtained. Compound 9 smoothly reacts with PiPr3 and PMe, to give 4 (R = Me) and [Rh(q3-2-MeC3H4)(PMe3)-(PiPr,)] (lO), respectively. In contrast to the q3-allyl complexes which are configurationally stable, the q3-benzyl analogues [Rh(i13-CH2C6H4R)(PiPr3),] (11, 12), prepared from 2 and 4-RC6H4CH2MgC1, are highly fluctional in solution. At room temperature, an antarafacial (71-0-71) 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 AG* values for the antara and suprafacial rearrangements of 11 and 12 which have been determined from the 'H-and ,lP-NMR spectra at variable temperature are 60.0 ? 1.5 and 39.5 ? 1.0 kJ/mol, respectively. The q3-benzyl compound 11 reacts even at -78°C with CO to give the monocarbonylrhodium(1) complex trans-[Rh(q '-CH2C6H,) (CO) (PiPr3),] (13). Treatment of 3,4, or 11 with RC0,H (R = CF3, CH3, C6H5, C6H4-4-OMe, C6H4-4-N02) affords the monomeric q2-carboxylatorhodium (1)

The Scope of Catalytic Asymmetric Hydroboration/Oxidation with Rhodium Complexes of 1,1′‐(2‐Diarylphosphino‐1‐naphthyl)isoquinolines

“…[19] For vinylarenes, the weight of evidence suggests that the cycle follows the pathway outlined in Scheme 3, in which the hydride transfers regiospecifically to give a benzylic borane, possibly h 3 , which in turn undergoes reductive elimination with the formation of the hydroboration product. [20] This representation is in agreement with a DFT theoretical treatment. [21] Any attempt to rationalise the enantioselectivity further must consider the hydride transfer step in more depth, since the configuration of the new stereogenic centre is set at that stage.…”

Mono‐ and Dinuclear Rhodium and Iridium Complexes with Chiral Phospholanes as Ligands

“…The 31 P NMR spectra of 1 and 2 display a sharp doublet with a large 1 J Rh,P coupling constant of 196.2 Hz (1) and 198.0 Hz (2) that is characteristic for a Rh(PR 3 ) 2 moiety with the P-donors in a cis arrangement. [4,7] The 1 H NMR spectra of 1 and 2 show two signals for the protons of the different methyl groups of the phospholane units but are otherwise quite complicated due to the overlap of the resonances for the CH 2 and CH protons of the five-membered ring. Similar observations have also been made for the other Isophos and Phephos complexes described in this paper and thus the corresponding 1 H NMR spectroscopic data will not be discussed.…”

Reactivity of Rhodium–Triflate Complexes with Diphenylsilane: Evidence for Silylene Intermediacy in Stoichiometric and Catalytic Reactions

“…Reactions of [Rh(iPr 3 P) 2 8 ]toluene (0.5 mL) was treated with a mixture of Ph 2 SiH 2 (5.5 mg, 0.03 mmol) and styrene (3 mg, 0.03 mmol) at À30 8C. The color of the solution immediately changed from deep violet to brown.…”

“…[4] whereas values for 1 J-(Rh,P) higher than 130 Hz usually indicate Rh I structures. [5] A doublet of triplets is observed in the [8] with HSiPh 2 OTf [7a] (see Scheme 1). This last reaction resulted in several other products due to side reactions, such as both SiÀH and SiÀOTf addition followed by SiÀC coupling, and compound 4 was formed in about 15 % yield (by NMR spectroscopy).…”