Diketonate complexes

Lanthanide(III) ions form three distinct types of complexes with 1,3-diketones (p-diketones) (a) tris complexes with a metal-to-ligand ratio of 1 3, (b) Lewis-base adducts of tris complexes, and (c) tetrakis complexes with a metal-to-ligand ratio of 1 4 (Binnemans, 2005a). It is very difficult to obtain pure monomeric tris complexes, because the coordination number of the lanthanide ion in this type of compounds is six and this is too low for saturation of the first coordination sphere of a trivalent lanthanide ion (except for tris complexes of very bulky 1,3-diketones). Therefore, most of the tris complexes form either dimeric (or even oligomeric or polymeric) complexes, or they form hydrates. The water molecules act as Lewis bases and by addition of 

TABLE 11 Thermal Behavior of the Lanthanide Complexes P-Enaminoketone L13H of the A/-Alkyl 

crystalline phase SmA, smectic phase SmX, unidentified smectic phase 1, isotropic liquid.  

CHAPTER 4 COVALENT (x-TYPE) LIGANDS BOUND THROUGH METAL-HETEROATOM BONDS 

Transition-Metal-Boryl Complexes (Written with Dr. Jaciyn M. Murphy) 

Transition-metal-boryl complexes contain a covalent bond between a metal and three-coordinate boron. Boryl complexes are a subset of the variety of ligands containing a single boron atom that would encompass borane, boryl, and borene ligands. Of this group, boryl complexes are the most abundant. 

Boryl complexes participate in a variety of catalytic processes, including transition-metal-catalyzed hydroboration and diboration of olefin and acetylene C-C ir-bonds (Chapter 16) and tihe functionalization of alkane and arene C-H bonds (Chapter 17). The chemistry of these complexes has been developed primarily since 1990. A body of literature on metal-boiyl complexes was published in the 1960s, but the structures of these compounds were apparently misassigned in the absence of modem X-ray crystallographic and NMR methods. Boryl complexes of all transition metals except for group 3 (Sc, Y, and La) and group 4 (Ti, Zr, Hf) metals - have been isolated. A majority of transition-metal boryl-complexes contain late metals. 

Free ftom a transition metal, tiie boryl group is highly basic. The first fuUy diaracter-ized alkali metal boryl anion was reported in 2006 by Yamashita, Nozaki and co-workers. Previous studies on the generation of boryl anions have not been reproduced. Theoretical studies imply that much of the charge on a free boryl anion would actually reside on the substituents, and that the boron would bear positive charge.  

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Champmartin D and Rubini P 1996 Determination of the 0-17 quadrupolar coupling constant and of the C-13 chemical shielding tensor anisotropy of the CO groups of pentane-2,4-dione and beta-diketonate complexes in solution. NMR relaxation study/norg. Chem. 35 179-83... 

Dithiolium salts and dithio- 3-diketone complexes of the transition metals. T. N. Lockyer and R. L. Martin, Prog. Inorg. Chem., 1980, 27, 223-324 (198). 

Carbon bonded 8-diketone complexes. D. Gibson, Coord. Chem. Rev., 1969,4,225-240 (30). 

Tris(bipyridyl) complexes structure, 1, 63 Tris(diketonate) complexes structure, 1,65 Trisdithiolencs metal complexes synthesis, 2, 597... 

Strontium titanate (SrXi03) by reacting titanium isopropoxide and a strontium beta-diketonate complex at 600-850°C and 5 Xorr. 

Balog, M., Schieber, M., Michman, M., andPatai, S., Zirconium and Hafnium Oxides by Thermal Decomposition of Zirconium and Hafnium Diketonate Complexes in the Presence and Absence of Oxygen, J. Electrochem. Soc., 126(7) 1203-1207 (1979)... 

Strontium titanate (SrTi03) has a large dielectric constant of 12, and a high refractive index with potential opto-electronic applications. It is deposited by MOCVD from titanium isopropoxide and a strontium beta-diketonate complex at 600-850°C and 5 Torr.t" " ... 

A key step proposed in the radical chain mechanism for the formation of the formyl complex is the coordination of CO to the Rh(OEP)- monomer, to give an intermediate carbonyl complex, Rh(OEP)(CO)- which then abstracts hydride from Rh(OEP)H to give the formyl product.This mechanism was proposed without direct evidence for the CO complex, and since then, again from the research group of Wayland, various Rh(fl) porphyrin CO complexes, Rh(Por)(CO), have been observed spectroscopically along with further reaction products which include bridging carbonyl and diketonate complexes. 

Other examples of this synthetic strategy are known for example, a recent zirconium polymer by Illingsworth and Burke (8), who joined amine side groups of a zirconium bis(quadridentate Schiff-base) with an acid dianhydride to give amide linkages. Once again, caution is necesary, as Jones and Power (2) learned when they attempted to link metal bisO-diketonates) with sulfur halides that is, they obtained insoluble metal sulfides because the p-diketone complexes which they used were fairly labile and the insolubility drove the reactions to completion in the wrong direction. 

Tc(III), Tc(IV) and Tc(V) P-diketonate complexes are stable in acid solution. In fact, when a chloroform solution of TcCl2(acac)2 was shaken with 1 M hydrochloric acid solution, no detectable change in the distribution ratio of the complex - defined as the ratio of the concentration of technetium in the organic phase to that in the aqueous phase - was observed over a 24 h period [26]. However, when the technetium complexes were backextracted into aqueous alkaline solution, decomposition occurred [26-29]. In all the cases studied, spectrophotometric investigation revealed that pertechnetate was formed quantitatively as a final product. 

In closing, recovery of technetium from waste solution should be touched upon. Studies of the base hydrolysis of technetium P-diketone complexes revealed that all of the complexes studied decompose in an alkaline solution even at room temperature, until technetium is finally oxidized to pertechnetate. These phenomena are very important for the management of technetium in waste solutions. Since most metal ions precipitate in alkaline solution, only technetium and some amphoteric metal ions can be present in the filtrate [29]. A further favorable property of pertechnetate is its high distribution coefficient to anion exchangers. Consequently, it is possible to concentrate and separate technetium with anion exchangers from a large volume of waste solution this is especially effective using an alkaline solution [54],... 

MetalIa-/3-diketonate complexes, such as 1, are conveniently prepared by reacting acylmetal carbonyl complexes with strong bases that can also react as nucleophiles, such as organolithium, Grignard, or boron hydride reagents [Eq. (1)]. These reactions can be followed by IR spectroscopy. 

Casey et al. have studied the decarbonylation reactions of [cis-(OC)4M(MeCO)(PhCO)], in which M is Mn or Re (16,17). These complexes lose a carbonyl ligand to form five-coordinate intermediates of the type [(OC)3M(MeCO)(PhCO)]. Reversible methyl migration proceeds much more rapidly than does phenyl migration. In the course of these studies, a phosphine substituted rhena-/3-diketonate complex, [fac-(OC)3(Et3P)Re(MeCO) (PhCO)], was prepared. 

Because the interligand C—C coupling of the acyl carbon donor atoms in metalla-/3-diketonate complexes [Eq. (8)] is such a general (though unusual) reaction that occurs very facilely, we have proposed (without proof) a formal description of how this type of coupling might take place (44,50). This formalism has been adopted by others to explain the C—C coupling shown in Eq. (10) (47). 

Figure 6.15. Perfluorinated =-diketonate complex used for a variety of oxidation reactions (M = Ni)[55] or...

A helical arrangement within columns was also found for other metal 3-diketonate complexes provided with chiral side chains (32) by Serrano and co-workers.35,36 These compounds form rectangular columnar mesophases with helical order within the columns. A spin-coated sample of 32 showed a positive exciton-splitted signal in the CD spectra, which was interpreted as a left-handed (M) helix. Annealing of the film resulted in much higher optical activities and a shift of the absorption maxima. The observed optical changes clearly point to a chiral organization of the columns in the mesophase. 

The Eu—0 (diketonate) distances vary from 2.32 to 2.37 A and agree very well with other lanthanide-/S-diketonate complexes and with eight coordinated Eu(DPM)3(Py)2 complex (see later). Eu—0 (sulphoxide) distance is 2.40 A. The sulphoxide ring is puckered by 35° and the S—0 has equitorial conformation. 

The distortion in [Lu(DPM)3(NCeH7)] stems from the fact that the Lu—N bond (2.492 A) is 0.25 A longer than the average Lu—O distance of 2.238 A, while the average chelate bite remains at 2.74 A Hke other /S-diketonate complexes. Such distortion is not uncommon. Even when all seven atoms are oxygens, a long M—O distance contributes to the distortion of the coordination polyhedron as in the case of [Dy(DPM)3(OH2)] (57), where the Dy—O (water) is longer by 0.11 A compared to the Dy—O (chelate) bond. 

There is, however, no hydrogen bonding present in [Lu(DPM)3 (NC6H7)] complex in contrast to many other /3-diketonate complexes described above (83—85), where H-bonding is an important feature in the structure. AH inter-molecular 0—0 contacts are above 4 A and the shortest intermolecular distance involving C, O and N atoms is 3.55 A (86). 

It is noteworthy to mention that the two water molecules in [Ho(HNIC)3 (0112)2] " cationic complex are occupying trans-positions across the diagonal of a square face (Fig. 21) while they occupy cis (vicinal positions in [M(NIC)3(OH2)2] dimers and in diketonate complexes described earlier. 

The tetrakis- 8-diketonate complexes of the lanthanides constitute an important stereoisomer in the dodecahedral geometry. The four diketonate ligands are found to span the four g-edges of the dodecahedron (Fig. 22) (146, 147). In other do-... 

Immobilization of Rare-Earth Metal Alkoxide and -Diketonate Complexes... 

The efficient and selective catalysis of some Diels-Alder reactions by lanthanide P-diketonate complexes has been known since 1975 [226, 227]. The fluorinated p-diketonate complexes Ln(fod)3 (cf. Scheme 12.5) selectively catalyze the Danishefsky transformation (Scheme 12.23) as a consequence of their mild Lewis acidity. Importantly, zeolites and Lewis acid modified silica or alumina also catalyze Diels-Alder reactions [228-232]. 

Silica-grafted group 3 and lanthanide silylamides have been used as precursor to surface (3-diketonate complexes [(=SiO) Ln( Bu-COCHCO- C3F7)m(THF)i]... 

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