Cyclopentadienyl Molybdenum(II) N,C-Chelating Benzothiazole-Carbene Complexes: Synthesis, Structure, and Application in Cyclooctene Epoxidation Catalysis

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• 作者：Zhe Wang ; Sin Wee Benny Ng ; Lu Jiang ; Wen Jin Leong ; Jin Zhao ; T. S. Andy Hor
• 刊名：Organometallics
• 出版年：2014
• 出版时间：May 27, 2014
• 年：2014
• 卷：33
• 期：10
• 页码：2457-2466
• 全文大小：443K
• 年卷期：v.33,no.10(May 27, 2014)
• ISSN：1520-6041

文摘

A series of new benzothiazolyl-imidazolium salts 1鈥?b>3 (1-(benzothiazol-2-yl)-3-methylimidazolium chloride (1); 1-(benzothiazol-2-yl)-3-benzylimidazolium chloride (2); 1-(benzothiazol-2-yl)-3-allylimidazolium chloride (3)) have been prepared from nucleophilic substitution of 2-chlorobenzothiazole by imidazoles. They serve as the precursors of hybrid N-heterocyclic carbene (NHC) ligands L1鈥?b>L3 (L1 = 1-(benzothiazolin-2-yl)-3-methylimidazol-2-ylidene; L2 = 1-(benzothiazolin-2-yl)-3-benzylimidazol-2-ylidene; L3 = 1-(benzothiazolin-2-yl)-3-allylimidazol-2-ylidene). Reactions of 1鈥?b>3 with Ag<sub>2sub>O result in Ag(I) NHC complexes 4鈥?b>6 [Ag(L)(渭-Cl)]<sub>2sub> (L = L1, 4; L = L2, 5) and Ag(L3)Cl (6), in which L1鈥?b>L3 act as monodentate carbene ligand with a benzothiazolyl pendant. Subsequent transmetalation of 4鈥?b>6 with CpMo(CO)<sub>3sub>Br (Cp = cyclopentadienyl) and anion exchange reaction with AgX (X = BF<sub>4sub>, PF<sub>6sub>, or OTf) give complexes [CpMo(CO)<sub>2sub>(L)]<sub>2sub>[Ag<sub>2sub>Br<sub>4sub>] (L = L1, 7a; L = L2, 8a; L = L3, 9a) and [CpMo(CO)<sub>2sub>(L)][X] (L = L1, X = BF<sub>4sub>, 7b; L = L2, X = BF<sub>4sub>, 8b; X = PF<sub>6sub>, 8c; X = OTf, 8d; L = L3, X = BF<sub>4sub>, 9b), whose structures are reported herein. The ligands L1鈥?b>L3 show their versatility by switching to be N,C-chelating in these Mo(II) complexes. The chelation of the hybrid NHC ligand results in shorter Mo鈥揅<sub>carbenesub> bonds (2.14鈥?.16 脜) comparing with known Mo(II) NHC complexes in the literature. These complexes are active toward cyclooctene epoxidation with tert-butyl hydroperoxide (TBHP) affording up to 90% yield of epoxide (for 8b) in 3 h at 55 掳C.