title: Alkyl Grignard cross-coupling of aryl phosphates catalyzed by new, highly active ionic iron(ii) complexes containing a phosphine ligand and an imidazolium cation.
abstract: A novel family of ionic iron(ii) complexes of the general formula [HL][Fe(PR'3)X3] (HL = 1,3-bis(2,6-diisopropylphenyl)imidazolium cation, HIPr, R' = Ph, X = Cl, 2; HL = HIPr, R' = Cy, X = Cl, 3; HL = HIPr, R' = Ph, X = Br, 4; HL = HIPr, R' = Cy, X = Br, 5; HL = 1,3-bis(2,4,6-trimethylphenyl)imidazolium cation, HIMes, R' = Cy, X = Br, 6) was easily prepared via a stepwise approach in 88%-92% yields. In addition, an ionic iron(ii) complex, [HIPr][Fe(C4H8O)Cl3] (1), has been isolated from the reaction of FeCl2(THF)1.5with one equiv. of [HIPr]Cl in 90% yield and it can further react with one equiv. of PPh3or PCy3, affording the corresponding target iron(ii) complex 2 or 3, respectively. All these complexes were characterized by elemental analysis, electrospray ionization mass spectrometry (ESI-MS),1H NMR spectroscopy and X-ray crystallography. These air-insensitive complexes 2-6 showed high catalytic activities in the cross-coupling of aryl phosphates with primary and secondary alkyl Grignard reagents with a broad substrate scope, wherein [HIPr][Fe(PCy3)Br3] (5) was the most effective. Complex 5 also catalyzes the reductive cross-coupling of aryl phosphates with unactivated alkyl bromides in the presence of magnesium turnings and LiCl, as well as the corresponding one-pot acylation/cross-coupling sequence under mild conditions.
authors.affiliation: The Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, People's Republic of China. sunhm@suda.edu.cn.
authors.forename: Zhuang
authors.initials: Z
authors.lastname: Li
authors.forename: Ling
authors.initials: L
authors.lastname: Liu
authors.forename: Hong-Mei
authors.initials: HM
authors.lastname: Sun
authors.forename: Qi
authors.initials: Q
authors.lastname: Shen
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang