Steric Influence on the Reactivity of the (o-Carboranedithiolato)iridium(III) Complex [Ir(η⁵-C₅Me₅)(η²-S₂C₂B₁₀H₁₀)]:  New Types of Addition Reactions Involving Cyclometalation or Isomerization

The reactivity of the mononuclear 16-electron iridadithiolene ring complex Cp*Ir(S 2 C 2 B 10 H 10 ) ( 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 -BC 2 B 9 H 9 SS{ η 2 -(R 1 HC CR 2 )}- S ] ( 2: R 1 = H, R 2 = Ph, 2a; R 1 = COOCH 3, R 2 = COOCH 3, 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 -BC 2 B 9 H 9 SS(CH 2 SiMe 3 )- 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[C 2 B 10 H 10 SS{ η 1 -(CH CH)C 5 H 6 }- 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 (LiCab N,S = C 2 B 10 H 10 (LiS)(CH 2 NMe 2 )- N,S - ) with [Cp*IrCl 2 ] 2 yielded the cyclometalated compound Cp*Ir[ o -BC 2 B 9 H 9 S(CH 2 NMe 2 )- 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.