Manganese complexes carboxylates

Tetranuclear manganese(III) carboxylate complexes have three different configurations for their metal centers fused open cubane, planar, or butterfly (see Figure 22). There is only one example of the first type namely [Mn4Q2(OAc)2(BSP)2] (105). The Mn Mn separations in (105) vary between 2.875(1)A and 3.122(1)A. Variable temperature magnetic measurements for (105) indicated weak antiferromagnetic interactions (/=—10.0cm and / = —3.7cm ) between the manganese(III) centers. Cyclic voltammetry of (105) in methanol shows one quasireversible oxidation wave at 0.01 V and two quasireversible reduction waves at about —0.4 V and —0.7 V vs. SCE. 

Butterfly tetranuclear manganese(III) carboxylate complexes are monoanionic with the exception of the bpy complex. An example of a butterfly core complex is (Bu 4N)[Mn402(02CPh)7-(imac)2]-5CH3CN (108). 

Manganese(lII) carboxylate complexes of nuelearity>5 are limited and are summarized in Table 10. The first hexanuclear complex, [Mn602(02CCMe3)i4] (109), was prepared from Mn(N03)3 and excess pivalic acid in dioxane. This neutral eomplex has an [Mn6(//4-0)2(/U3-02CCMe3)4-(/t-02CCMe3)6] core with both bridging and monodentate pivalates. All manganese centers have a distorted octahedral environment. 

Employing asymmetric pentadentate ligands, such as H3-4-X-bhedsd (H3-4-X-bhedsd = A-(4-X-salicylidene)-A, iV -bis(2-hydroxyethyl)ethylenediamine and X = Q, Br, or OMe) (Figure 18), gave hexanuclear manganese(III) carboxylate complexes with an [Mn6(//3-0)2(//-0Me)6] + core. 

The mechanism of the reaction of the alcohol (or water) with the acyl complex to produce ester (or acid) and regenerate the cobalt hydride complex is not known. Because the reaction of the analogous manganese complex with alcohols is known to proceed through a hemiacetal-like complex, this mechanism has been written for the carboxylation reaction (equation 42). 

Thus, 1 seems to be a true catalyst rather then a new kind of free radical initiator. This behavior is in contrast to the behavior of related manganese complexes. For example, Mn(II) carboxylates are known to decompose CHP during autoxidation of cumene l dinuclear Mn(III) complexes decompose tetralin hydroperoxide during oxidation of tetralin (an inner-sphere Mn-alkyl hydroperoxide intermediate has been proposed) trinuclear, carboxylate and oxo-bridged complexes containing Mn(II) were found to decompose CHP during the catalyzed oxidation of cumene. 

Vinyl polymerization using metallocomplexes commonly proceeds by a radical pathway and rarely involves an ionic mechanism. For instance, metal chelates in combination with promoters (usually halogenated hydrocarbons) are known as initiators of homo- and copolymerization of vinylacetate. Similar polymer-bound systems are also known [3]. The polymerization mechanism is not well understood, but it is believed to be not exclusively radical or cationic (as polymerization proceeds in water). The macrochelate of Cu with a polymeric ether of acetoacetic acid effectively catalyzes acrylonitrile polymerization. Meanwhile, this monomer is used as an indicator for the radical mechanism of polymerization. Mixed-ligand manganese complexes bound to carboxylated (co)polymers have been used for emulsion polymerization of a series of vinyl monomers. Macromolecular complexes of Cu(N03)2 and Fe(N03)3 with diaminocellulose in combination with CCI4 are active in polymerization of MMA, etc. 

Manganese(III) palmitate was found to be a selective catalyst for the conversion of dialkyl ketones to carboxylic acids at temperatures of 110 or greater [276]. A single carboxylic add could be formed from synunetrical ketones [276]. The ease with which manganese complexes convert aldehydes to carboxylic acids (Section 13) is utilized in this conversion. 

Malononitrile s. 1,1-Dinitriles Malonyl chlorides s. a-Di-carboxylic acid chlorides Manganese(II) chloride 17, 68 Manganese complex compounds, ar. 16,813... 

Interestingly, manganese does not readily form the hydrazinium complex although manganese hydrazine carboxylate hydrate and hydrazine complexes are formed. 

Brechin et al. have recently reported a new class of single-molecule magnets with a nonanuclear manganese core. The reaction of a reduced basic carboxylate compound, [Mn30(0Ac)6(py)3], with l,l,l-tris(hydroxymethyl)ethane (H3thme) afforded the Mn 3Mn 4Mn 2 complex... 

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