Abstract
Reaction of 3,3’,4,4’-tetramethyl-1,1’-diphosphaferrocene 1 with an excess of benzoyl chloride and AlCl3 afforded a ~1:1 mixture of meso- and rac-2,2’-dibenzoyl-3,3’,4,4’-tetramethyl-1,1’diphosphaferrocenes 2, which were separated by column chromatography. The less polar diastereomer was transformed into its bis-W(CO)5- complex 3. The single crystal X-ray study revealed that this complex contains the meso-2 ligand. Therefore, the more polar diastereomer must be rac-2. It has been suggested that the splitting pattern of the phospholyl protons signal in the 1 H NMR spectra can be used for stereochemistry assignments.
Highlights
Friedel-Crafts acylation of ferrocene constitutes a direct synthetic route to monoacyl- and and heteroannular 1,1’-diacylferrocenes,[1] versatile starting materials in syntheses of numerous ferrocene derivatives.[2,3,4,5,6,7] Friedel-Crafts acylation of 1,1’-diphosphaferrocene gives, depending on the reaction conditions, either 2-acyl- or heteroannular 2,2’-diacyl derivatives.[8]
The stereoisomers were separated via column chromatography
Benzoyl chloride (0.81 ml, 6.75 mmol) and AlCl3 (0.85 g, 6.22 mmol) in dichloromethane ( 5 ml) were stirred at rt for 5 min and 3,3’,4,4’-tetramethyl-1,1’-diphosphaferrocene (690 mg, 2.48 mmol) was added and to the resulting mixture was stirred at rt for 4h
Summary
Friedel-Crafts acylation of ferrocene constitutes a direct synthetic route to monoacyl- and and heteroannular 1,1’-diacylferrocenes,[1] versatile starting materials in syntheses of numerous ferrocene derivatives.[2,3,4,5,6,7] Friedel-Crafts acylation of 1,1’-diphosphaferrocene gives, depending on the reaction conditions, either 2-acyl- or heteroannular 2,2’-diacyl derivatives.[8]. Mathey et al.[8] separated stereoisomers of 2,2’-diacetyl-3,3’,4,4’-tetramethyl-1,1’-diphosphaferrocene by column chromatography but were unable to asses their stereochemistry.
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