High-Valent Iridium Complexes Containing a Tripodal Bis- Cyclometalated CNC Ligand

Iridium complexes containing a bis-cyclometalated tripodal CANAC ligand have been synthesized, and their redox property and reactivity have been studied. The previously reported intermediate (1) prepared from IrCl3 center dot xH2O and bis(4-(tert-butyl)phenyl)methyl)pyridine (H2Bubnpy) has been used as a starting material for synthesis of Ir(CANAC) complexes. Treatment of 1 with CO, xylNC (xyl = 2,6-dimethylphenyl), PCy3 (Cy = cyclohexyl), and the Kla''ui tripodal ligand Na[Co(ri5-C5H5){P(O)(OEt)2}3] (NaLOEt) afforded [H3dtpny][Ir(Bubnpy)(CO)Cl2] (2), [Ir(Bubnpy)(CNxyl)2Cl] (3), [Ir(Bubnpy)(PCy3)Cl] (4), and [Ir(Bubnpy)(LOEt)] (6), respectively. Reaction of 5-coordinated 4 with CO gave the adduct [Ir(Bubnpy)(PCy3)Cl(CO)] (5). Treatment of 1 and 4 with [Ru(LOEt)(N)Cl2] afforded the respective heterometallic mu-nitrido complexes [(H2O)Cl(Bubnpy)Ir(mu-N)Ru(LOEt)Cl2] (7) and [(PCy3)Cl(Bubnpy)Ir(mu-N)Ru(LOEt)Cl2] (8). The Ir-N [1.887(5) angstrom] and Ru-N [1.661(5) angstrom] distances in 7 are indicative of the Ir(V)=N=Ru(IV) resonance structure. The cyclic voltammogram of 6 in CH2Cl2 displayed a reversible couple at ca. 0 V vs Fc+/0 (Fc = ferrocene) that is assigned as the Ir(IV/III) couple. Oxidation of 6 with Ag(OTf) (OTf- = triflate) afforded 6 center dot OTf that exhibited an EPR signal in CH2Cl2 at 4 K with gx = 2.06, gy = 1.91, and gz = 2.84 and Ir(IV) (I = 3/2) hyperfine coupling constants Axx, Ayy, and Azz of 60, 40, and 18 G, respectively, consistent with the Ir(IV) formulation. Treatment of 4 with PhICl2 yielded [Ir(Bubnpy)(PCy3)Cl2] (9), whereas the reaction of 7 with PhICl2 yielded mixed-valence [Cl2(Cl2Bubnpy)Ir(mu-N)Ru(LOEt)Cl2] (10) that contains a chlorinated CANAC ligand. DFT calculations indicated that the spin density in 10 is mostly found at the Ir atom, the chloride ligands, and a phenyl ring of the CANAC ligand. 1 and 4 can catalyze the oxidation of cyclooctene with PhIO, possibly via an Ir-oxo or Ir-PhIO active intermediate. The results of this work highlight the ability of the dianionic tripodal CANAC ligand to stabilize high-valent iridium.