Reactivity of an iridapyrylium and oxapentadienyl-rhodium-phosphine chemistry

The reactivity of an aromatic oxametallacycle, iridapyrylium ( 4), with a variety of substrates has been studied and is found to follow predominantly two different paths. Treatment of 4 with 2-electron donor reagents such as methyl lithium and hydride reagents results in addition at the metal center to produce octahedral Ir(III) complexes that possess an iridaoxacyclohexa-1,3-diene ring system. Alternatively, unsaturated molecules such as terminal alkynes, methylacrylate, and sulphur dioxide undergo [4+2] cycloadditions in the presence of 4. The addition occurs across iridium and the central carbon atom of the ring to yield complexes with an iridaoxacyclohexa-1,4-diene ring system. The structure of the sulphur dioxide adduct has been confirmed via X-ray diffraction.;Oxapentadienyl chemistry has been extended from iridium phosphine complexes to analogous rhodium phosphine systems. Treatment of [(PR3) 2RhCl]2 (R=Me, Et) with potassium oxapentadienide leads to the formation of (1,2,3-eta-5-oxapentadienyl)Rh(PR3)2 (63 R=Me; 64 R=Et) as a mixture of anti and syn isomers. Likewise, addition of potassium 2,4-dimethyloxapentadienide to [(PR 3)2RhCl]2 (R=Me, Et) produces (1,2,3-eta-2,4-dimethyl-5-oxapentadienyl)Rh(PR 3)2 (65 R=Me; 66 R=Et). In compounds 65 and 66 the ligand is predominately in the anti configuration and also shows hindered rotation around the C3-C4 bond when cooled to -70°C yielding two rotamers, U-shaped and S-shaped.;Treatment of 63 with one equivalent of PMe3 yields the trisphosphine complex (1,2,3-eta-5-oxapentadienyl)Rh(PMe3) 3 67. The similar compound (1,2,3-eta-2,4-dimethyl-5-oxapentadienyl)Rh(PMe 3)3 69 could be formed at room temperature from 65 and PMe3, but not isolated due to decomposition when placed under vacuum. The addition of PEt3 to 64 yields the triethylphosphine analogue of 67, but only at low temperature. No corresponding complex could be formed with PEt3 and 66 . However, treatment of 66 with electrophiles such as methyl triflate and tetrafluoroboric acid leads to 18-electron Rh(III) complexes [(eta5-2,4-dimethyl-5-oxapentadienyl)Rh(PEt3) 2(R)]+[X]- (70 R=Me, X=SO3CF3; 71 R=H, X=BF4). Further treatment of 70 with PPNCl produces (1,2,3-eta-5-oxapentadienyl)Rh(PEt 3)2(Me)(Cl) 72, which has the ligand in the syn geometry. Treatment of 71 with PPNCl leads to formation of [(PEt3)2RhCl]2.;The structures of 63, 67, and 70 have been confirmed by X-ray diffraction.