Synthesis, reactivity, and structures of cationic η6-arene carbonyl complexes of rhenium(I). Crystal and molecular structures of the two isoelectronic 1,3,5-trimethylbenzene tricarbonyl complexes of rhenium(I) and tungsten(0)

Abstract

Cationic arene derivatives of tricarbonylrhenium(I), less methyl substituted than hexamethylbenzene, of general formula [Re(CO)₃{C₆H_6–n(CH₃)_n}]⁺ with [AlBr₄]^–, [BPh₄]^–, or [Re₂l₈]^2– as counter anion, have been isolated. The crystal and molecular structure of the trimethylbenzene complex [Re(CO)₃{1,3,5-C₆H₃(CH₃)₃}][AlBr₄] has been solved by X-ray diffraction methods: monoclinic, space group P2₁/a, with unit-cell dimensions a= 15.687(3), b= 12.876(3), c= 9.690(2)Å, β= 101.95(2)°, and Z= 4; R= 0.046 for 1 220 observed reflections. The corresponding neutral tungsten(0) complex [W(CO)₃{1,3,5-C₆H₃(CH₃)₃}] is monoclinic, space group P2₁/a, with unit-cell dimensions a= 8.959(2), b= 16.979(3), c= 8.797(2)Å, β= 118.46(2)°, and Z= 4; R= 0.036 for 861 observed reflections. Both complexes have an eclipsed orientation of the carbonyl groups with respect to the methyl substituents on the ring. Reduction of [Re(CO)₃{1,3,5-C₆H₃(CH₃)₃}]⁺ with [BH₄]^– afforded the trimethyl-substituted cyclohexadienyl complex, [Re(CO)₃{1,3,5-C₆H₄(CH₃)₃}].