2,6-Dibromo-iodobenzene (3). This compound was prepared by a modified literature procedure. 1 A solution of NaNO 2 (7.97 g, 115 mmol) in H 2 O (60 mL) was added dropwise to a suspension of 2,6-dibomoaniline (26.3 g, 105 mmol) in aqueous HCl (100 mL, 12 M) at 0 °C. The mixture turned orange. The mixture was stirred at 0 °C for 90 min to afford an opaque red mixture. Additional NaNO 2 (2.11 g, 30.5 mmol) was added. The mixture was stirred for an additional 45 min at 0 °C and then filtered through a plug of glass wool into an ice-cooled jacketed addition funnel. The resulting red solution was added dropwise to a stirred solution of KI (173 g, 1.02 mol) in H 2 O (260 mL) at 20 °C to form a foamy black mixture. The mixture was stirred at 20 °C for 2 h. Aqueous Na 2 SO 3 (114 mL, 1.00 M, 114 mmol) was added and the mixture turned clear yellow. Methylene chloride (200 mL) was added and the mixture was stirred for 7 h. The mixture was separated and the aqueous layer was extracted with CH 2 Cl 2 (2 x 250 mL). The organic fractions were combined and washed with aqueous KOH (100 mL, 1 M), and dried over MgSO 4. The solvent was removed under vacuum. The resulting red solid was recrystallized from hot ethanol to afford 2,6-dibromoiodobenzene as off-white needles in two crops (total yield 32 g, 84%).
Molybdenum cis-dioxo bis-phenolate ONO complexes were synthesized and have been shown to be active for DODH. Catalysts were screened for activity at 190 °C and ambient pressure, and appreciable alkene yields of up to 59% were obtained.
Reactions between Mo(NAr)(CHR)(Me2Pyr)-(OTPP) (Ar = 2,6-i-Pr2C6H3, R = H or CHCMe2Ph, Me2Pyr = 2,5-dimethylpyrrolide, OTPP = O-2,3,5,6-Ph4C6H) and CH2=CHX where X = B(pin), SiMe3, N-carbazolyl, N-pyrrolidinonyl, PPh2, OPr, or SPh lead to Mo(NAr)(CHX)-(Me2Pyr)(OTPP) complexes in good yield. All have been characterized through X-ray studies (as an acetonitrile adduct in the case of X = PPh2). The efficiencies of metathesis reactions initiated by Mo(NAr)(CHX)(Me2Pyr)(OTPP) complexes can be rationalized on the basis of steric factors; electronic differences imposed as a consequence of X being bound to the alkylidene carbon do not seem to play a major role. Side reactions that promote catalyst decomposition do not appear to be a serious limitation for Mo=CHX species.
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