Optically Active Transition-Metal Complexes. 9.¹A General Stereoselective Route to α-Chiral (R)-Tricarbonyl(η⁶-ethylbenzene)chromium Complexes. Novel Organometallic Phosphine Catalysts for the Asymmetric Hydrovinylation Reaction

Abstract

Treatment of (R)-[{α-(dimethylamino)ethyl}-η6-benzene]Cr(CO)3 with esters of chloroformic acid leads to stereoselective substitution of the dimethylamino group for a chloro substituent. The reaction can be extended to systems in which the chromium arene complex, after metalation, is diastereoselectively substituted in the ortho position with carbon and silicon electrophiles to generate planar chirality. The chloro group in turn can be replaced stereoselectively for various phosphorus, nitrogen, and oxygen nucleophiles. Both substitution reactions in the benzylic position proceed via retention of configuration. The addition of cyanide is not stereospecific. The phosphine derivatives are efficient catalysts for the enantioselective hydrovinylation of styrene to 3-phenyl-1-butene. X-ray crystal structures establish the absolute configuration of (R)-[(α-chloroethyl)η6-benzene]Cr(CO)3, (R)-[{α-(diphenylphosphanyl)ethyl}-η6-benzene]Cr(CO)3, and (pS,S)-[1-(α-cyanoethyl)-2-methyl-η6-benzene]Cr(CO)3.

Cationic Nickel Complexes with Weakly Coordinating Counterions and Their Application in the Asymmetric Cycloisomerisation of 1,6‐Dienes

“…[15,16] In order to evaluate the influence of the anion on regio-and enantioselectivities at different conversions, it is again important to ensure that intrinsic effects are observed and selectivities are not affected by secondary isomerisation and/or kinetic resolution of the primary product as occasionally observed in hydrovinylation reactions. [20] Comparing the selectivities obtained with catalyst 3c at different conversions in the present and previous studies [10] show that no variation occurs within experimental error (cv ¼ 37%:…”

The Stereospecific Ligand Exchange at a Pseudo‐Benzylic T‐4 Iridium Centre in Planar‐Chiral Cycloiridium (η6‐Arene)tricarbonylchromium Complexes

“…[40][41][42][43] In most cases, retention of configuration is observed. [44] In the present report, we deal with the first rational use of this concept with a class of Ir III pseudo-tetrahedral complexes in line with our endeavour to develop novel stereospecific methods of synthesis of chiral-at-metal metallacycles. In previous reports, it was shown that the reaction of a planar-prochiral ligand such as 2-[tricarbonyl(h 6 -phenyl)chromium]pyridine with pseudo-tetrahedral complexes such as [(MCl 2 Cp*) 2 ] (M = Rh, Ir; Cp* = pentamethylcyclopentadienyl) [26,[45][46][47][48] or octahedral compounds such as [{Ru(CO) 2 Cl 2 } n ] [25,49] would selectively lead to the anti isomer.…”

Novel Chiral 1,3‐Diamines by a Highly Modular Umpolung Strategy Employing a Diastereoselective Fluorination–Nucleophilic Aromatic Substitution Sequence

“…[12] The starting material for the synthesis of Daniphos is [(R)-(1-phenyl)ethyldimethylamine]tricarbonylchromium (1). [14] Our approach to chiral 1,3-diphosphanes or similar derivatives employed a successive electrophilic exchange of the ring proton in the 2-position followed by a nucleophilic exchange of the dimethylamino group via a chloro intermediate.…”

“…[18] An elegant recent example by Imamoto demonstrated that an optically active BH 3 -protected secondary phosphide could be attached to benzenetricarbonylchromium in this manner. [19] By the time Imamoto's paper appeared, we had also found that compound 2 could be employed for the synthesis of planar-chiral 1,3-P,N-ligands by nucleophilic substitution with lithium phosphides, especially those bearing unusual phosphane moieties which cannot be introduced via the classic electrophilic route [12] due to the lack of availability of the appropriate chlorophosphane (e.g. the phobane isomers).…”

“…Because the fluorine atom has to be introduced stereoselectively, en-antio-and diastereoselective fluoro-functionalization remains a field of continuing chemical research. [11] We have recently investigated the chemistry of chiral diphosphanes (the "Daniphos" ligands), [12] based on an optically active [η 6 -arene]tricarbonylchromium backbone, [13] and have found many applications for them in homogeneous catalysis, where they rival the better-known and industrially important Josiphos ligands.…”