Tris-chelated compounds

Another set of reactions that has received considerable attention is that ui which optically active complexes, especially tris(chelate) compounds racemize ... 

Related to jS-diketones are metalla-/ -diketones, whose distinctive chemistry is a recent development. In these, the methine group of a conventional diketonate is replaced with an organometallic moiety such as m-Mn(CO)4, m-Re(CO)4, /<2c-Mn(CO)3(RNC) or C5H5Fe(CO).519 Exemplary is Al Mn(MeCO)2(CO)4 3, which is prepared in a two-step synthesis. Addition of methyllithium to Mn(CO)5COMe forms Li[Mn(MeCO)2(CO)4] which, when treated with aluminum chloride, provides the tris(chelate) compound.520 An X-ray study showed that the MnC202Al ring is essentially planar with Mn—C(acyl) bond distances indicative of a bond order of ca. 1.2. The O—O bite distance, 2.73 A, is about the same as that of acetylacetonate in Al(MeCOCHCOMe)3.521 As in the... 

Hydroxycarboxylate compounds of Mn111 are known for salicylates and various aliphatic acids.299 Some crystalline solids have been isolated, including bis-chelate species of the salicylates M[Mn(X-sal)2L2] (L = H20, py) but the only tris-chelate compound isolated is the black Cs3[Mn (CF2)2C(0)COO 3]. Various red or green crystalline solids also are known with tartrate ligands and they are reasonably robust, but no structural data are available. 

Similar green or brown tris-chelated compounds are described283 for many of the usual range of available / -diketonates, the most stable compound being that formed with the sexadentate ligand (124).318... 

Tris-chelated compounds with three symmetrical bidendate ligands (in inorganic chemistry these are the prototypical tris-chelate complexes of transition metals) can also be conceived as three-bladed propellers with their helicities specified accordingly. 

In a later publication Tor et al. reported for the first time that coordination compounds, such as tris-chelate Ru(II) complexes, are good substrates for C-C... 

Rhenium(III) tris-chelates are formed by the reaction of 2-(diphenylphosphinomethyl)-4-methylphenol, PpOH (258a), or 2-diphenylphosphinophenol, P2-OH (258b) with [ReCl3(PPh3)2(CH3CN)] in a 1 3 ratio. [Re(Pi-0)3] is stable as solid and in solutions while [Re(P2-0)3] is easily oxidized in air giving the rhenium(V) 0x0 complex [Re0(P2-0)2(0P2-0]. This behavior is also reflected in the electrochemical behavior of the compounds, where each one well-defined redox couple for one-electron oxidation and reduction steps are observed for both compounds. A second oxidative wave (Re /Re ) is only reversible for [Re(Pi-0)3]. 

A series of compounds has been isolated with thiobenzoylhydrazine. The reaction with perrhenate in acidic solution yields after recrystallization from DMF the neutral tris-chelate [Re(NHNC(S)Ph)3] DMF, which is also formed from [ReOCl3(PPh3)2] in neutral ethanol/benzene... 

From equation (30), whether a tris chelate is formed depends on the donor ability of the ligand. Several vanadium(IV) complexes with 1,2-dihydroxybenzenes formed from solutions of the ligand, VOSO4 and thallium(I) acetate.498 The compounds are of two types (I) T12[V(RC6H302)3] (R = H, 3-Me, 4-Me, 3-MeO) and (II) T12[V0(RC6H302)2] (R = CHO). 

The question might be asked Are there similar mechanisms for changing the configuration of molecules without breaking bonds in molecules with coordination numbers other than 3 and 5 The answer is yes. One of the most important series of inorganic compounds consists of six-coordinate chelate compounds exemplified by the tris(ethylenediamine)cobalt(lIl) ion. Because of the presence of the three chelate rings, the ion is chiral and racemization can take place by a mechanism that is closely related to atomic inversion or Berry pseudorotaiion (the mechanism for six-coordination is termed the Bailar twist see Chapter 13k... 

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