Chirale tripodliganden: Die eintopfreaktion MeC(CH 2PPh 2) 3 → MeC(CH 2P(Ph)(R)) 3; Zwischenstufen, diastereoselektive kontrolle und komplexchemie

Abstract

The tripod ligand H 3CC(CH 2PPh 2) 3, 1, reacts with lithium metal to produce H 3CC(CH 2PPhLi) 3, 2, in good yields. Compound 2 crystallizes in the form of 2· 4THF·MeN(CH 2CH 2NMe 2) 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 H 3CC(CH 2 P(Ph)(R)) 3, 3 (R = H, Me, Et, iPr, CH 2Ph, 3a–3e). 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 (CH 3CN) 3Mo(CO) 3 yields the easy-to-characterize coordination compounds H 3CC(CH 2P(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 = CH 2Ph ( 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 H 3CC(CH 2P(Ph)(Et)) 3Mo(CO) 3, 5c, and H 3CC(CH 2P (Ph)(CH 2Ph)) 3Mo(CO) 3, 5e. The remarkable facts reported in this paper are the ease with which the chiral tripod ligands H 3 CC(CH 2P(Ph)(R)) 3, 3, are prepared, and the evidence that their formation may well involve diastereoselective control.