Synthesis and Reactivity of Heptamethylcyclohexadienyl Rhodium(III) Complexes

Abstract

We report the synthesis and reactivity of the halfsandwich rhodium(III) complexes with the fully methylated cyclohexadienyl ligand C 6 Me 7 , which is analogous to the classical Cp*. The starting complex [(C 6 Me 7 )RhCl 2 ] 2 (4) was obtained in high yield (92%) by the reaction of [(cyclooctene) 2 RhCl] 2 with the readily available 6-methylenehexamethylcyclohexadiene-1,4 (C 6 Me 6 CH 2 ) followed by addition of HCl. Reactions of complex 4 with common two-electron ligands L gave the expected adducts (C 6 Me 7 )RhCl 2 L (L = pyridine, P(OEt) 3 , PPh 3 ) in high yields (80−90%). At the same time, the interaction of 4 with the stronger ligand t BuNC led to the replacement of the C 6 Me 7 ligand. The cationic complex [(C 6 Me 7 )Rh(dppe)Cl]PF 6 and the dicationic complex [(C 6 Me 7 )Rh(C 6 Me 6 )](BF 4 ) 2 were obtained by abstraction of chlorides from 4 with TlPF 6 or AgBF 4 in the presence of the corresponding ligands. The reaction of 4 with 2-phenylpyridine in the presence of CsOAc proceeded via CH activation and gave the cyclometalated product (C 6 Me 7 )Rh(C 6 H 4 -Py)Cl in 85% yield. Accordingly, the catalytic reaction of 2phenylpyridine with 3-hexyne in the presence of 4 (5 mol %) gave the 9,10-diethyl-8a-azaphenanthrene cation in 61% yield. However, the catalytic efficientcy of 4 was lower than that of the classical catalyst [Cp*RhCl 2 ] 2 , possibly because the displacement of the cyclohexadienyl ligand interrupted the catalytic cycle. The DFT calculations suggested that the electrondonating ability of cyclic π ligands in the rhodium complexes (C n R n )RhCl 2 CO decreases in the order C

Iridium-Catalyzed Hydrogenation of a Phenoxy Radical to the Phenol: Overcoming Catalyst Deactivation with Visible Light Irradiation

“…The driving force accounting for the conversion of B to Ir-Int is likely the formation of the Ir–C and O–H bonds at the expense of the C–H and Ir–O bonds as well as steric pressure from the tert -butyl groups. The vacant coordination site for the tautomerization may arise either from pyridine dissociation ,− or a change in hapticity of the [C 5 Me 5 ] ring. , Addition of another equivalent of 1 results in abstraction of a hydrogen atom from Ir1-Int , either from the α-carbon from iridium or a phenolic O–H bond. An additional equivalent of 1 promotes another H-atom abstraction likely derived from the subsequent radical coupling reaction to generate Ir1-DHBF as the final product.…”