Carbohydratocarbene Complexes of Manganese and Rhenium

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Abstract
The cationic carbyne complexes [Cp(CO)2MCR]+ [BX4]− [M = Mn, X = F: R = Ph (1), Tol (2); M = Re, X = 3,5‐C6H2(CF3)2: R = Ph (3)] add the anion of monodeprotonated protected mannofuranose (4a), glucofuranose (4b), and fructopyranose (4c) to the carbyne carbon atom to form the carbohydratocarbene complexes 5a–c, 6a, b, and 7a. With 5b, 5c, and 6b the addition proceeds with retention of configuration at the anomeric center. Due to inversion of configuration in the deprotonation step the complexes 5a, 6a, and 7a are obtained as β‐glycosides. The carbene ligand is oxidatively cleaved from the metal by trimethylamine N‐oxide or air. Cleavage of the C(carbene)O bond with reformation of the cation of the carbyne complex 2 is achieved by reaction of 6a with BCl3. Photolysis of [Cp(CO)2MnC(Ph)OEt] in the presence of L affords the carbene complexes [Cp(CO)(L)MnC(Ph)OEt] [L = P(OMe)3 (11), P(Tol)3 (12)]. Ethoxide abstraction from 11 and 12 by BF3 gives the chiral cationic carbyne complexes [Cp(CO)(L)MnCPh]+[EF4]− (13, 14) which add 4a to form the corresponding mannofura‐nosylcarbene complexes (15, 16). When 0.5 equivalents of 4a are employed in the reaction with 13, 14 the ratio of diastereomers is 3:2, both for 15 and 16. Complex 11 was characterized by an X‐ray structural analysis.

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