Reactions of 16-Electron Iridium(III) Dithiolene Complexes with Diazoalkanes: Formation and Properties of Novel Mononuclear and Binuclear Alkylidene Adducts of Iridium Dithiolene Complexes

Some 16-electron pentacoordinated iridium dithiolene complexes were synthesized by the
reactions of [Cp*Ir(Cl)(μ-Cl)]2 (Cp* = C5Me5) with 1,3-dithiol-2-one derivatives. The iridium
dithiolene complex [Cp*Ir{S2C2(COOMe)2}] (1) reacted with ethyl diazoacetate or (trimethylsilyl)diazomethane to give the 1:1 alkylidene adducts of iridium dithiolene complexes
(R = COOEt (3a), SiMe3 (3b)), respectively. The structures
of complexes 3a,b were determined by X-ray crystal structure analyses:  the COOEt unit of
complex 3a is located at the exo position with respect to the iridadithiolene ring, and the
SiMe3 group of complex 3b is located at the corresponding endo position with respect to the
same ring. In solution, the endo (3b-1) and exo (3b-2) isomers of complex 3b were observed.
In an electrochemical investigation, the oxidized species of the exo isomer (3b-2+) was
isomerized to the stable endo isomer (3b-1+). The reaction of complex 1 with diazomethane
gave the novel 2:2 methylene adduct of a binuclear iridium dithiolene complex (4). This complex 4 has a five-membered iridadithiolene ring and a six-membered iridacycle. The dimeric complex 4 was
also formed from the desilylation of the monomeric complex 3b with TBAF. The complex
(5a) that includes a six-membered iridacycle
was obtained by the reaction of the alkylidene-bridged complex 3a with trimethyl phosphite.
The reactions of complex 3b with HCl gave [Cp*Ir(Cl){S(SCH2SiMe3)C2(COOMe)2}] (6b) due
to Ir−C bond cleavage.