SYNTHESIS AND PROPERTIES OF (ETA(2)-C,X) CHELATE ARYLCARBENE COMPLEXES [FE(C(5)ME(5))(L)(ETA(2)-C(OME)C6H4-O-X)][OTF] (L=CO, PME(3), X=OME,CL)

The methoxycarbene complexes [Fe(C(5)Me(5))(CO)(2){=C(OMe)C6H4-o-X}][O Tf] (2a, X = OMe; 2b, X = Cl) are good precursors of the corresponding (eta(2)-C,X) chelate carbene complexes [Fe((5)Me(5))(CO){eta(2)-C(OMe )C6H4-o-X}[Otf] (OTf = CF3SO3) (5a,6). The eta(2)-chloro derivative 5b has been characterized by X-ray diffration, confirming the formation of a five-membered ring metallacycle. All the new carbene complexes, i ncluding the nonheteroatom-stabilized carbene complex Fe(C(5)Me(5))(Co )(2){=C(H)C6H4-o-OMe}][OTf] (4a), have been fully characterized by H-1 and C-13 NMR spectrocopy. The lability of the chelating o-substituent is chemically demonstrated by the formation of the corresponding neut ral iodo carbene complexes [Fe(C(5)Me(5))(CO)(I){eta(1)-C(OMe)C6H4-o-X }] (6a,b), the competitive O-demethylation process being thus inhibite d. Selective ligand exchange reactions of 5a,b afford various substitu ted complexes such as (5))(CO)(n)(PMe(3)){eta(x)-C(OMe)C6H4-o-OMe}][OT f] (11, n = 1, x = 1; 12, n = 0, x = 2); the mono- and bis(acetonitril e) complexes C(5)Me(5))(L)(CH3CN){eta(1)-C(OMe)C6H4-o-Cl}][OTf] (14, L = CH3CN; 15, L = CO) have been also synthesized. The reactivity of 5a toward NaBH4 is highly dependent on the solvent. Specific hydride add ition occurs in 9:1 THF-MeOH to give the expected complex [Fe(C(5)Me(5 ))(CO){eta(2)-CH(OMe)C6H4-o-OMe}] (9) as a single diastereoisomer, whi le reduction in pure THF affords the organoborohydride complex [Fe(C(5 )Me(5))(CO){eta(2)-H2BHCH2C6H4-o-OMe}] (10). The latter reaction invol ves a formal insertion of BH3 into a Fe-C bond, promoted by the potent ial vacant coordination site. The carbene ligand is easily displaced a nd recovered as free carbonyl-containing organic substrates (aldehyde or ester) from both types of carbene complexes upon bubbling of O-2.