Syntheses of Novel C2-Symmetric Chiral Bidentate Bis(N-heterocyclic carbene) Ligands and Their Molybdenum Complexes

Abstract

Novel chiral bis(N-heterocyclic carbene) was prepared starting from (S,S)- and (R,R)-1,2-bis(1-hydroxypropyl)benzene. The chiral bis(N-heterocyclic carbene) (NHC) ligand formed C2-symmetric chiral complex of molybdenum formulated as cis-[Mo(CO)4{bis(NHC)}].

N-heterocyclic carbene complexes of Group 6 metals

“…17 M(0) carbonyl complexes with chelating di-NHC ligands[73,74,[113][114][115].Mo-23 (Figure 2.18), reported by Hahn et al in 2000, has been prepared from the reaction between electron-rich olefin and Mo(CO) 4 (η 4 -norbornadiene) in THF. It shows an approximately octahedral geometry with Mo-C carbene bond length of 2.234(3) Å.…”

Synthesis of bis(N-heterocyclic carbene) palladium complexes derived from (S,S)-1,2-bis(1-hydroxypropyl)benzene

“…As described in the Introduction, we have recently reported the preparation of chiral o-xylylene-bridged bis(imidazolium) pro-ligands, which were obtained in two-steps from 3, and their molybdenum complexes [13]. Then, we next examined the preparation of the bis(imidazol-2-ylidene) complex of palladium.…”

“…All reagents were commercially available and used without further purification. Compound (R,R)-1 was prepared according to the literature method [13]. Melting points were determined on a Stuart Scientific melting point apparatus SMP3 and are uncorrected.…”

“…1 H NMR (500 MHz, CD 2 Cl 2 ) d 0.73 (t, J ¼ 7.6 Hz, 6H, 2 Â CH 3 ), 2.00e2.12 (m, 2H, CH 2 ), 2.22e2.31 (m, 2H, CH 2 ), 3.91 (s, 6H, 2 Â NeCH 3 ), 5.86 (t, J ¼ 7.6 Hz, 2H, 2 Â CH), 6.65 (d, J ¼ 1.3 Hz, 2H, ImH), 6.90 (d, J ¼ 1.3 Hz, 2H, ImH), 7.53e7.56 (m, 2H, ArH), 7.66e7.69 (m,2H,ArH). 13 C NMR (125 MHz, CD 2 Cl 2 ) d 11.4 (CH 3 ), 29.4 (CH 2 ), 39.5 (NeCH 3 ), 61.4 (CH), 118. 6, 118.9, 128.6, 129.6 (aromatic) …”

“…Although two NHCs in these ligands located in cisposition, the complex showed C 1 -symmetric structure. We have also reported novel chiral o-xylylene-bridged bis(imidazol-2-ylidene) ligands derived from enantiomerically pure 1,4-diol, 1,2-bis (1-hydroxypropyl)benzene (3), and their molybdenum complexes [13]. These molybdenum complexes showed cis-C 2 -symmetric structure in octahedral geometry.…”