Steric Influence on the Reactivity of the (<i>o</i>-Carboranedithiolato)iridium(III) Complex [Ir(<i>η</i>⁵-C₅Me₅)(<i>η</i>²-S₂C₂B₁₀H₁₀)]: New Types of Addition Reactions Involving Cyclometalation or Isomerization

Abstract

The reactivity of the mononuclear 16-electron iridadithiolene ring complex Cp*Ir(S2C2B10H10) (1) toward alkynes, a diazoalkane, and quadricyclane has been investigated. Reaction of 1 with an excess of alkyne resulted in the incorporation of one alkyne molecule, giving Cp*Ir[o-BC2B9H9SS{η2-(R1HCCR2)}-S] (2: R1 = H, R2 = Ph, 2a; R1 = COOCH3, R2 = COOCH3, 2b), containing a cyclometalated four-membered metallacycle ring of Ir−B−C−S and a coordinating alkenethiol group. Reaction of 1 with (trimethylsilyl)diazomethane resulted in the formation of the bicyclic iridium metal complex Cp*Ir[o-BC2B9H9SS(CH2SiMe3)-S,S‘] (3), in which cyclometalation of a coordinated dithiolato ligand at the iridium(III) metal center has occurred, accompanied by transfer of the methylene group to one end of the sulfur atom of the dithiolato ligand. The X-ray structures of 2a and 3 are reported. In both complexes, the central iridium atom is coordinated to the boron atom in a three-legged piano-stool structure. On the other hand, the reaction of 1 with quadricyclane afforded the addition product Cp*Ir[C2B10H10SS{η1-(CHCH)C5H6}-S] (4), formed through the isomerization of a quadricyclane unit. The six-membered metallacyclic compound 4 was proven by the X-ray structure determination of the complex. Interestingly, the reaction of LiCabN,S (LiCabN,S = C2B10H10(LiS)(CH2NMe2)-N,S-) with [Cp*IrCl2]2 yielded the cyclometalated compound Cp*Ir[o-BC2B9H9S(CH2NMe2)-N,S] (5). The structure of 5 was determined by X-ray diffraction analysis, exhibiting a three-legged piano-stool structure consisting of a four-membered metallacyclic ring of Ir−B−C−S and a five-membered metallacyclic ring due to intramolecular coordination of a B,N-chelating ligand system.