Synthesis and Reactivity of Ir(CO)(η²-C₂R₂)(η⁵-C₉H₇) (R = Ph, Tol). Alkyne Coupling and Arene C−H Bond Activation Forming a Substituted Butadiene Ligand

Abstract

The reaction of Ir(CO)(η2-C8H14)(η5-C9H7) with excess C2R2 (R = Ph, Tol) in benzene at reflux leads to a mixture containing Ir(CO)(η2-C2R2)(η5-C9H7) (1a, R = Ph; 1b, R = Tol), Ir2(CO)2(μ-C2R2)(η5-C9H7)2 (2a, R = Ph; 2b, R = Tol), and Ir(η4-HC4R4R‘)(η5-C9H7) (3a, R = Ph, R‘ = Ph; 3b, R = Tol, R‘ = Ph). Conducting the reaction in benzene-d 6, toluene, or m-xylene leads to 1 and 2 and Ir(η4-DC4R4R‘)(η5-C9H7) (3c, R = Tol, R‘ = C6D5) or Ir(η4-HC4R4R‘)(η5-C9H7) (3d, R = Ph, R‘ = C6H4Me; 3e, R = Ph, R‘ = C6H3Me2; 3f, R = Tol, R‘ = C6H4Me). The structures of compounds 2a and 3b have been determined by X-ray diffraction. Compound 2a contains a dimetallacyclobutene framework with the CO ligands adopting a trans orientation with respect to the Ir2C2 mean plane. The indenyl ligands take positions opposite the carbonyls at each Ir center. Compound 3b contains a 1-phenyl-1,2,3,4-tetratolyl-1,3-butadiene ligand formed through both alkyne coupling and CH bond activation of the solvent benzene. The direct reactions of 1 with excess Ir(CO)(η2-C8H14)(η5-C9H7) or C2R2 lead to higher yields of 2 or 3, respectively.

Formation of metal–carbon σ-bonds via reactions of alkynes with iridium and their reactivity toward carbon–carbon bond formation with neighboring hydrocarbyl ligands

“…( 1)) [8,9]. Metal-alkynyls have drawn much attention [10][11][12] since they are probably the key intermediates for metalmediated oligomerization of alkynes that produces diverse forms of unsaturated oligomeric hydrocarbons such as cross-conjugated poly-olefin [3], poly-enynes [13,14], alkyne polymers [15] and aromatic com-pounds [14,16]. In the metal-mediated oligomerization of alkynes, metal-hydrido moiety M-H also plays important roles being involved in the insertion step of an alkyne into the M-C bond (M−H + RC≡CH → M−CH=CHR [3]) and the termination step to give products (M(H)R → M + RH).…”