MnCl3 was claimed to be a dark solid and produced by the reaction of "anhydrousmanganese(III) acetate" and liquidhydrogen chloride at −100 °C and decomposes above -40 °C.[3] Other claims involved reaction ofmanganese(III) oxide, manganese(III) oxide-hydroxide, and basic manganese acetate withhydrochloric acid. Given recent investigations however, such claims have been disproved or called into serious doubt.[4] Specifically, all known compounds containing MnCl3 are known to be solvent or ligand-stabilizedadducts.
MnCl3 can be stabilized by complexation to diverseLewis bases, as has been established over the course of many years of study.[4]Meta stableacetonitrile-solvated Mn(III)Cl3 can be prepared at room temperature by treating[Mn12O12(OAc)16(H2O)4] withtrimethylsilyl chloride.[5] The treatment of permanganate salts with trimethylsilylchloride generates solutions containing Mn(III)–Cl species for alkene dichlorination reactions;[6][7][8] electrocatalytic methods that use Mn(III)–Cl intermediates have been developed for the same purpose.[9][10]
The reaction of manganese dioxide with hydrochloric acid intetrahydrofuran gives MnCl3(H2O)(THF)2.[4]Manganese(III) fluoride suspended in THF reacts withboron trichloride, giving MnCl3(THF)3 which has the appearance of dark purple prisms.[4] This compound has a monoclinic crystal structure, reacts with water, and decomposes at room temperature.[4]
The most readily handled of this series of adducts isMnCl3(OPPh3)2.[11]
Another common manganese(III) chloride compound is the pentachloromanganate(III) dianion. It is usually charge balanced withcounterion(s) liketetraethylammonium.[12] The pentachloromanganates are typically green in color, light sensitive, maintainpentacoordination in solution, and have S = 2 ground states at room temperature.[12][13] Crystal structures of pentachloromanganate indicate the anion issquare pyramidal.[14][15] Tetraethylammonium pentachloromanganate(III), [Et4N]2[MnCl5], can be prepared and isolated by treating suspension of[Mn12O12(OAc)16(H2O)4] indiethyl ether withtrimethylsilylchloride, collecting the resulting purple solid in the dark, and then treating this solid with 0.6 M solution oftetraethylammonium chloride.[5] The green product is air stable but should be kept in the dark.
Somemanganese compounds with macrocyclic tetradentate coordination can stabilize the manganese(III) monochloride, Mn(III)–Cl, moiety.Jacobson's catalyst is an example of a coordination compound containing the Mn(III)–Cl moiety and is stabilized byN,N,O,O coordination from asalen ligand. Jacobson's catalyst and related Mn(III)–Cl complexes react with O-atom transfer reagents to form high-valent Mn(V)O that are reactive in alkeneepoxidation.Tetraphenylporphyrin Mn(III)Cl is a related commercially available compound.
^Wiberg, Egon; Holleman, A. F.; Wiberg, Nils (2001).Inorganic chemistry. Nils Wiberg, A. F. Holleman (1st English ed.). San Diego: Academic Press. p. 1411.ISBN0-12-352651-5.OCLC48056955.
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