SYNTHESIS, STRUCTURE, AND REACTIVITY OF IRIDACYCLOHEXADIENONE AND IRIDAPHENOL COMPLEXES

Iridacyclohexadienone complexes, a new class of unsaturated six-member ed metallacycles, have been synthesized, and their reactions with acid s have been investigated. Treatment of CH=C(Me)-CH=C (Me)-CH=Ir(PMe3)( 3) (''iridabenzene'' 1) with nitrous oxide produces the iridacyclohexa dienone complex CH=C(Me)-CH=C- (Me)-C(O)-Ir(PMe3)(3)(H) (2), which upo n stirring in diethyl ether solution slowly isomerizes to 5-eta-2,4-di methylpenta-1,3-dien-5-oyl)Ir(PMe3)(3) (3). Treatment of 2 with methyl trifluoromethanesulfonate leads to removal of the metal hydride and p roduction of CH=C(Me)-CH=C(Me)-C(O)-Ir(PMe3)(3)(O3SCF3) (4). In aceton e solution, 4 forms an equilibrium mixture with a ring-contracted irid acyclopentadiene isomer, [CH=C(Me)-CH=C(Me)-Ir(PMe3)(3)(CO)]+O3SCF3- ( 5). Treatment of 4 with trimethylphosphine generates the tetrakis(trim ethylphosphine)iridacyclohexadienone complex [CH=C(Me)-CH=C(Me)-C(O)-I r(PMe3)(4)]+O3SCF3- (6). Iridacyclohexadienone 2 reacts with trifluoro methanesulfonic acid to produce the iridacyclopentene complex [CH2-C(M e)=CH-CH(Me)-Ir(P Me-3)(3)(CO)]+O3SCF3- (7). In contrast, treatment of iridacyclohexadienones 4 and 6 with trifluoromethanesulfonic acid lea ds to protonation of oxygen and production of the corresponding ''irid aphenols'' 8 and 10. When 4 is treated with trifluoroacetic acid, an i ridaphenol product is again generated (compound 9), but in this case t he phenol proton forms an intramolecular hydrogen bond with the carbon yl oxygen of the trifluoroacetate ligand. The ring protons in compound s 8, 9, and 10 exhibit downfield H-1 NMR chemical shifts consistent wi th aromatic character. Compounds 3, 4, 6, 7, 8, and 9 have been struct urally characterized by single-crystal X-ray diffraction.