Steric influence on the reactivity of the (o-carboranedithiolato)iridium(III) complex [Ir(eta(5)-C5Me5) (eta(2)-S2C2B10H10)]: New types of addition reactions involving cyclometalation or isomerization

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 i ncorporation of one alkyne molecule, giving Cp*Ir[o-BC2B9H9SS{eta(2)-((RHC) -H-1=CR2)}-S] (2: R-1 = H, R-2 = Ph, 2a; R-1 = COOCH3, R-2 = COOCH3, 2b), c ontaining a cyclometalated four-membered metallacycle ring of Ir-B-C-S and a coordinating alkenethiol group. Reaction of 1 with (trimethylsilyl)diazom ethane resulted in the formation of the bicyclic iridium metal complex Cp*I r[o-BC2B9H9SS(CH2SiMe3)-S,S'] (3), in which cyclometalation of a coordinate d dithiolato ligand at the iridium(III) metal center has occurred, accompan ied 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. Tn both complexes, the central iridium atom is coordinated to the boron atom in a t hree-legged piano-stool structure. On the other hand, the reaction of 1 wit h quadricyclane afforded the addition product. Cp*Ir[C2B10H10SS{eta(1)-(CH= CH)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 LiCab(N,S) (L iCab(N,S) = C2B10H10(LiS)(CH2NMe2)-N,S-) with [Cp*IrCl2](2) yielded the cyc lometalated compound Cp*Ir[o-BC2B9H9S(CH2NMe2)-N,S] (5). The structure of 5 was determined by X-ray diffraction analysis, exhibiting a three-legged pi ano-stool structure consisting of a four-membered metallacyclic ring of Ir- B-C-S and a five-membered metallacyclic ring due to intramolecular coordina tion of a B,N-chelating ligand system.