d6 and d8 Metal Carbonyl Complexes of 7,7-Dimethoxy-5,6-dimethylidenebicyclohept-2-ene. Stereoselective Hydroformylation of an Complex

Article abstract of DOI:10.1002/hlca.19850680130

Reaction of 7,7-dimethoxy-5,6-dimethylidenebicyclo<2.2.1>hept-2-ene (2) with various metal carbonyls and their derivatives gave the η²-M(CO)4 (M=Fe (17), Ru (18), η⁴-M(CO)3 (M= Fe (19x, 19n), Ru (20n), and η²-M(CO)5 and η⁶-M(CO)3 (M=Cr, Mo, W) complexes.The trigonal bipyramidal η²-M(CO)4 complexes present an exceptional C_3v symmetry at the metal with the C,C-double bond in an axial position.In all the η²-complexes, this double bond is stereospecifically coordinated by its exo-face.The exo- vs endo-η⁴-Fe(CO)3 configuration was established by chemical correlation (hydrolysis, hydrogenation) with the corresponding complexes (24x, 24n) of 7,7-dimethoxy-2,3-dimethylidenebicyclo<2.2.1>heptane (5).The relative rates of hydrolysis (AcOH/H2O 2:1, 50 deg C) of ligands 2 and 5 and of complexes 19x, 19n, 24x, and 24n to the corresponding ketones showed an acceleration effect only when the metal is coordinated to the exo-face.This was attributed to an F-strain effect on the leaving group of the substrate.Compound 17 was further metallated by giving the bimetallic isomers 21xn and 21xx.The endocyclic C,C-double bond of the latter can be stereospecifically hydroformylated (1 atm CO, AcOH/H2O, 25 deg C) giving 29x (49percent).Hydroformylation of 17 gave the corresponding uncoordinated aldehydes 30x/30n in better yields (76percent) but with lower selectivity (3:1).These are the first examples of hydroformilation of an isolated complex.