Reaction of Cp~*(CO)_2Re=Re(CO)_2Cp~* with Dimethyl Acetylenedicarboxylate Produces a 3,4-Dimetallacyclobutene Which Undergoes Photochemical Isomerization to a 2,4-Dimetallabicyclo[ 1.1.0]butane

摘要

The reaction of Cp~*(CO)_2Re=Re(CO)_2Cp~* (1) with dimethyl acetylenedicarboxylate (DMAD) produced the 3,4-dimetallacyclobutene Cp~*(CO)_2Re(μ-η~1,η~1-CH_3O_2CC=CCO_2CH_3)Re(CO)_2Cp~* (2). Photochemical rearrangement of 2 produced Cp~*(CO)_2Re(μ-η~2,η~2-CH_3O_2CC≡CCO_2CH_3)Re(CO)_2Cp~* (3), in which both Cp~*(CO)_2Re units are coordinated to the alkyne. Upon heating at 72℃, 3 was converted (t_(1/2) ≈ 120 min) to a 78:22 equilibrium mixture of 2:3. Photolysis of 3 in a Rayonet photoreactor (maximum emission 300 nm) resulted in CO loss and formation of Cp~*(CO)Re(μ-η~2,η~2-CH_3O_2CC≡CCO_2CH_3)(μ-CO)Re(CO)Cp~* (4). Compounds 2, 3, and 4 were characterized by X-ray crystallography: 2, orthorhombic, Pcba, a = 14.480(3) A, b = 16.246(3) A, c = 26.027(3) A, Z = 8, D_c = 1.946 Mg/m~3; 3, monoclinic, C2/c, a = 12.854(2) A, b = 14.729(3) A, c = 16.650(3) A, β = 108.188(12)°, Z = 4, D_c = 1.989 Mg/m~3; 4, trigonal, P3(2), a = 16.277(2) A, b = 16.277(2) A, c = 9.408(3) A, α = 90°, β = 90°, γ = 120°, Z = 3, D_c = 2.005 Mg/m~3.