Photochemically induced reactions of decacarbonyldimanganese(0)

Photolysis at ca. 350 nm of Mn₂(CO)₁₀ in the presence of each of I₂, CH₃I, SnI₄, CuCl₂ - 2 H₂O, HgX₂ (X  Cl, Br or I), C₆H₅HgI, η⁵-C₅H₅Cr(NO)₂Cl, (η⁵-C₅H₅)₂Cr₂(NO)₄ and [Co₂(CNCH₃)₁₀](BF₄)₄, generally under N₂ or CO in several organic solvents (mainly cyclohexane and THF), was investigated. The observed photoreactions are best rationalized in terms of initial homolytic cleavage of the MnMn bond. In the presence of a halogen (X)-containing compound, the resultant Mn(CO)₅· radical abstracts X to yield Mn(CO)₅X. These reactions are characterized by high quantum efficiencies (generally, _φ-Mn2(CO)10?0.36). Following the abstraction, the remaining metal-containing species (usually a radical), SnCl₃·, CuCl, HgX·, C₆H₅Hg· or η⁵-C₅H₅Cr(NO)₂·, undergoes further abstraction of halogen by Mn(CO)₅·, coupling with the Mn(CO)₅· or ligand substitution. Isolated metal-containing products include SnI₂, Cu, Mn(CO)₅HgX, Hg, [Mn(CO)₅]₂Hg and η⁵-C₅H₅Cr(CO)₂NO. Photolysis of Mn₂(CO)₁₀ in the presence of each of the metal-metal bonded compounds, (η⁵-C₅H₅)₂Cr₂(NO)₄ and [Co₂(CNCH₃)₁₀](BF₄)₄, does not give the respective heterodinuclear combinations, (η⁵-C₅H₅)(NO)₂CrMn(CO)₅ and [(CH₃NC)₅CoMn(CO)₅]²⁺, as detectable or isolable species; instead, η⁵-C₅H₅Cr(CO)₂NO, Mn(CO)₄NO, Mn₂(CO)₉CNCH₃, and [Mn(CO)(CNCH₃)₅]₊ are among the isolated products. The photoreaction between Mn₂(CO)₁₀ and CH₃I provides a convenient synthesis of Mn(CO)₅I.