153956-40-2Relevant academic research and scientific papers
Diastereoselectivity in the reaction of RCH2C[CH2P(Ar)(Li)]3 with electrophiles: Enhancement of diastereoselective control by η3-coordination in RCH2C[CH2P(Ar)(Li)]3Mo(CO)3
Buechner, Michael,Huttner, Gottfried,Winterhalter, Ute,Frick, Axel
, p. 1379 - 1392 (2007/10/03)
Following a procedure developed for RCH2C[CH2P(Ar)(Li)]3 (la) as the starting compound, various tripod ligands RCH2C-[CH2P(Ar)2]3 (1) have been transformed into the trilithiotriphosphides RCH2C[CH2P(Ar)(Li)]3 by reductive cleavage of their P-Ar bonds by metallic lithium. The triphosphides are readily protonated to produce RCH2C[CH2P(Ar)(H)]3 (2). Reaction of RCH2C[CH2P(Ar)(Li)]3 with various electrophiles R'-Hal leads to the two diastereomers of RCH2C[CH2P-(Ar)(R′)]3 (6) with an (RRR/SSS : RRS/SSR) ratio close to the statistical value of 1:3, except when Ar = Ph and R′ = Bzl, where the RRS/SSR diastereomer is obtained almost exclusively. In contrast, the reaction of RCH2C[CH2P(Ar)(Li)]3)-Mo(CO)3 (4) with electrophiles R′-Hal tends to favour the formation of the homochiral RRR/SSS diastereomers. The triphosphide coordination compounds 4 are available by two different routes: either the complexes {RCH2C[CH2P-(Ar)(H)]3]Mo(CO)3, obtained from 2 and (CH3CN)3Mo(CO)3, are deprotonated by MeLi, or the trilithiotriphosphides RCH2C[CH2P(Ar)(Li)]3 are reacted with (CH3CN)3Mo(CO)3 to produce 4 in high yields. The ratio in which the two diastereomeric forms of 5 are obtained depends on the nature of the electrophile: the greatest diastereomeric discrimination is obtained for Ar = Ph, R = Ph,′ = Bzl, where the homochiral RRR/SSS enantiomeric pair is produced in a fourfold excess relative to the RRS/SSR pair. Two-dimensional NMR spectra and simulations of one-dimensional spectra are used to ascertain the diastereomeric excess in each case. X-ray analyses of three compounds of type 5 (5d, Ar = Ph, R = H,′ = Bzl; 5k, Ar = 3,5-Me2C6H3, R = H,′ = Bzl; 51, Ar = Ph, R = Ph,′ = Bzl) indicate the remarkable conformational stability of the tripod metal scaffolding, with the conformations observed for these three compounds in three different solid-state environments being closely similar, even with respect to the torsional arrangement of the phosphorus-bound benzyl groups. WILEY-VCH Verlag GmbH,.
Chirale Tripodliganden: Die Eintopfreaktion MeC(CH2PPh2)3 MeC(CH2P(Ph)(R))3; Zwischenstufen, diastereoselektive Kontrolle und Komplexchemie
Walter, Olaf,Klein, Thomas,Huttner, Gottfried,Zsolnai, Laszlo
, p. 63 - 82 (2007/10/02)
The tripod ligand H3CC(CH2PPh2)3, 1, reacts with lithium metal to produce H3CC(CH2PPhLi)3, 2, in good yields.Compound 2 crystallizes in the form of 2*4THF*MeN(CH2CH2NMe2)2.The crystal structure of this adduct shows bridging as well as terminal phosphorous-coordination of lithium.Compound 2 reacts with electrophiles RX to give H3CC(CH2P(Ph)(R))3, 3 (R = H, Me, Et, iPr, CH2Ph, 3a-e).The transformation 1 2 3 can be performed in a one-pot reaction.While the chiral compounds 3 may be characterized as such, their reaction with (CH3CN)3Mo(CO)3 yields theeasy-to-characterize coordination compounds H3CC(CH3P(Ph)(R))3Mo(CO)3, 5.NMR analysis of 3 and 5 shows that from the two diastereomeric forms of 3 (the enantiomeric pair SSR/RRS and the pair SSS/RRR) only the SSR/RRS-diastereomer is formed with R = CH2Ph (3e, 5e).In the other cases (R = H, Me, Et, iPr) a statistical 3:1 mixture of the two diastereomers is formed.These findings are further corroborated by X-ray analyses of H3CC(CH2P(Ph)(Et))3Mo(CO)3, 5c, and H3CC(CH2P(Ph)(CH2Ph))3Mo(CO)3, 5e.The remarkable facts reported in this paper are the ease with which the chiral tripod ligands H3CC(CH2P(Ph)(R))3, 3, are prepared, and the evidence that their formation may well involve diastereoselective control.
