1,3-DIPOLAR CYCLOADDITION TO THE C=X-M FRAGMENT .13. REGIOSELECTIVITYIN THE REACTIONS OF MONONUCLEAR IMINOKETONE COMPLEXES FE(CO)(3)((T)BU-N=C(H)-C(R)=O) (R=PH, ME) WITH THE ASYMMETRIC ALKYNE METHYL PROPYNOATE

The reaction of complexes Fe(CO)(3)((t)Bu-N=C(H)-C(R)=O) (6a: R=Ph, 6b : R=Me) with one equivalent of methyl propynoate (MP) under an atmosph ere of CO, at -30 degrees C (R=Ph) or -50 degrees c (R=Me) results in formation of the Fe(CO)(3)(butenolide) complexes (9a,b), which have be en characterized spectroscopically (IR, H-1, C-13 NMR) and by elementa l analysis. The spectroscopic properties indicate that one of the poss ible regio-isomers is exclusively formed. INEPT and 2D heteronuclear c orrelation NMR techniques show that in the regio-isomer obtained the f ormer ketone carbon atom is C-C bonded to the carbon atom that in the alkyne bore the electron-withdrawing ester group. When the complexes F e(CO)(3)((t)Bu-N=C(H)-C(R)=O) (6a,b) are treated with two equivalents of MP at -30 degrees C in the absence of CO, the tricyclic complexes 1 2a,b are formed in moderate yield. the molecular structure of complex 12b has been determined by a single-crystal X-ray diffraction study. I t contains three five-membered rings, with the two fused metallacycles sharing three common carbon atoms with the third, a gamma-lactone rin g, thus forming the tricyclic moiety. The coordination geometry around the central iron atom is distorted octahedral, with the dianionic tri dentate ligand occupying three facial positions. The fact that complex es 12 can also be obtained in high yield by irradiation of the corresp onding Fe(C)(3)(butenolide) (9) in the presence of an excess of MP str ongly supports the proposed reaction mechanism in which the second alk yne is initially pi-coordinated and subsequently coupled with the pi-c oordinated double bond of the butenolide heterocycle.