Crystal structures of two unusual, high oxidation state, 16-electron iridabenzenes

Abstract

Treatment of carbonyl(1,2-diphenylpenta-1,3-dien-1-yl-5-ylidene)bis(triphenylphosphane)iridium, [IrCO(—C(Ph)=C(Ph)—CH=CH—CH=)(PPh3)2], with either bromine or iodine produced dibromido(1,2-diphenylpenta-1,3-dien-1-yl-5-ylidene)(triphenylphosphine)iridium(III), [IrBr2{—C(Ph)=C(Ph)—CH=CH—CH=}(PPh3)], (I), and (1,2-diphenylpenta-1,3-dien-1-yl-5-ylidene)diiodido(triphenylphosphane)iridium(III), [IrI2{—C(Ph)=C(Ph)—CH=CH—CH=}(PPh3)], (II), respectively, which are two rare examples of 16-electron metallabenzenes. Structural elucidation of (I) and (II) reveals that these isotypic iridabenzenes are unusual, not only in their electron count, but also in their coordination sphere of the IrIII atom where they contain an apparent open coordination site. The crystal structures of (I) and (II) confirm that the molecules are complexes containing five-coordinated IrIII with only one triphenylphosphine group bound to the iridium atom, unambiguously proving that the molecules are indeed 16-electron, high-oxidation-state iridabenzenes. The coordination geometry of the IrIII atom in both structures can be best described as a distorted square pyramid with the P, two Br (or I) and one C atom in the basal plane and another C atom in the apical position.

Keywords

• Iridabenzene
• metallabenzene
• aromaticity
• oxidation state
• coordinatively unsaturated
• crystal structure