Complex organometallic

Organometallic Complexes. The compounds [(7t-Cp)V(RC02)2] (R = Me, Bz or CF3) involve dimeric molecules, and magnetic studies have indicated that strong metal-metal interactions exist within these dimers. 

Vanadium(iv) Complexes.—Aqueous electron-transfer reactions involving V as a reductant have been reviewed. 

Pruchnik, S. Wajda, and E. Kwaskowska-Chec, Roczniki Chem., 1971, 45, 537. 

The study of cyclopentadienyl complexes is of interest in relation to the carcinostatic properties of the metallocene dihalides MX2CP2, [100—102], as well as the possible tissue imaging properties of the iron and especially ruthenium complexes RuCp2 [28]. The Fe(Cp)2 also has some antitumour activity [103] and is of interest as a radiosensitizer (Chapter 8). 

However, other factors such as relative lability may be more determinant of activity, especially as alteration of halide (leaving group ) in the 

TI defined as LD50/ED75, where ED is effective dose. 

Ti series does not produce dramatic effects, unlike the case of the platinum amines. The metallocenes are expected to be more labile than Group 8—10 complexes, and this is borne out by hydrolysis studies where polymeric products from both halide and cyclopentadienyl loss have been isolated [102—104]. Interestingly, differences between the complexes have been observed — the Ti and V complexes lose Cp much more readily than Mo, for example [115, 116]. The relative lack of toxic side effects (nonnephrotoxic) may well be a reflection of the fact that, especially in aqueous medium, decomposition products may be unreactive, unlike those of the platinum systems. 

The different behavior of [V(0)(acac)2] in comparison to [Co(acac)2 (N02)2] , and especially acac displacement by nucleic acid bases with NH groups also emphasizes the different chemistry involved [118]. The reactivity of )8-diketonate complexes is indeed relevant due to the demonstrated antitumour activity of the benzoylacetonato (complexes [TiX2(Bzacac)2] (X = halide, OR) (119). Indeed, one complex from this new series of Ti complexes, budotitane diethoxybis(l-phenylbutane-l,3-dionato)titanium(IV), X = OEt is receiving limited clinical trials in Europe. 

It is in the synthesis of organometallic complexes that the metal-atom technique shows its greatest utility. From metal vapors, many complexes may be synthesized on a macroscale that are difficult, if not impossible, to prepare by standard, wet-chemical techniques 64, 65). In this section, we shall illustrate the vast potential that the method has in this area, although, to be sure, it is evident throughout this entire review. 

Benzene, benzene-d , and fluorobenzene were found (770, 777) to react with chromium, cobalt, iron, and nickel atoms on codeposition in the neat ligand at 77 K, or in argon matrices at 10-12 K. IR studies of the products indicated that the initial reaction of these transition-metal atoms with an aromatic system is 7r-complex formation. Studies of ligand concentration-effects showed that the chromium-atom reaction is approximately second-order with respect to benzene, yielding the previously known (782) complex (CeH6)2Cr, whereas, with the other metals, the reaction is first-order, yielding MfCsHs), M = Co, Fe, or Ni. The absence of CrfCeH ) is probably a reflection of (a) the fact that the 

Far-Inprared Bands and Shifts of the vC=C Stretching and SC-H o.p. Bending Vibrations of Benzene upon Complexation (171) 

Complexation with polyaromatic systems has also been observed. For instance, M(naphthalene)z, M = Cr 88,183), Mo (183), V 183), or Ti 183) may be synthesized in a solution reactor with the appropriate, metal vapors at liquid-nitrogen temperature. The Cr/naphthalene complex is less stable (dec. 160°C) than Cr(C6He)2 (m.p. 283-284° C). In fact, the naphthalene ligand is sufficiently labile to allow reaction under mild conditions, to afford CrL (L = CO or Bu NC), or Cr(naphth)L3 [L = PF3, PfOMels, or PMes]. The Mo, V, and Ti species are equally reactive. Analogous 1-methylnaphthalene complexes were also isolated (783). In addition, the complexes shown in Fig. 38 were synthesized by reaction, at the temperature of liquid nitrogen, of Cr atoms with 1,4-diphenylbutane 35, 201, 202). Analogous complexes were formed with 1,5-diphenylbutane 202). 

Lagowski et al. (79) synthesized a very large series of bis(arene) Cr(0) compounds, thereby providing a good example of the use of metal-atom chemistry in synthesizing homologous series of compounds 

MeNC inserts into M—Q bonds of both NbClj and TaCls to give the corresponding pale-brown [MCl4 C(Cl)=NMe (CNMe)] products which appear to be dimeric in MeCN. These complexes have a strong i.r. absorption in the range 2286— 2271 cm characteristic of the v(N=Q stretch of the coordinated MeNC group which, in the niobium derivative, may be displaced by 

Buchler and K. Rohbock, Inorg. Nuclear Chem. Letters, 1972, 8, 1073. 

DeKock et al. have studied the bonding in [ti -C5H5)2M( jl-X)]2 compounds where M = Zr (X = I, PH2, and NH) and M = Ti (X = Cl). PCMODEL software and MMX force field were used to determine the importance of steric effects on the geometry of these molecules. No details are given about the potential energy terms or the origin of the parameters. The authors concluded that Zr—Zr distance is controlled by an interplay of sterics and electronics. 

As noted earlier, ir-type ligands coordinated to metals present a particular challenge to the design of a molecular mechanics model. Recently, the MM2 force field has been adapted to model (T) -allyl)palladium moieties. To avoid extensive reprogramming, Norrby et al. utilize the dummy atom to act as a 

This force field has also been used to explain the bent geometry of [M((CH3)5C5)2] complexes (M = calcium, strontium, barium, samarium, europium, or ytterbium). However, Hollis et al. set the ring carbon—dummy-dummy—ring carbon dihedral (as described by Doman et al.44) and dummy— metal-dummy bending force constants to zero. Thus, the force field is a points-on-a-sphere model. As one might expect, the calculated structures were 

The SHAPES force field has been implemented in CHARMM and used to examine the structures of several square planar rhodium complexes. This force field is based on angular overlap considerations and treats angular distortions for a variety of geometries. Spherical internal coordinates and Fourier potential functions form the basis for the description of these molecular shapes. The parameters for this force field were derived from normal coordinate analysis, ab initio calculations, and structure-based optimizations. The average rms deviation for bond lengths was 0.026 A, and the average rms deviation for bond angles was 3.2°. 

Albinati et al. have studied the three-dimensional structure of PtCl2L and PdCl2L metal complexes [P,N bidentate L=(p-CH3CgH4)2PCH2CH(Pr )NHCH2- 

Duchateau and coworkers have employed the hydroxysilsesquioxane (c-C5H9)7Si80i2(0H) and triphenylsilanol as model supports for silica-grafted olefin polymerization catalysts [5]. Treatment of [Cp MCfi] (M=Ti, Zr Cp =C5H3(SiMe3)2) 

no solvent). The grafted catalyst proved to be highly active, with equilibrium reached in less than Ih. A TOP of 0.25molmoT s was attained, which corresponds to one of the best rates observed for a Re metathesis catalyst. Also observed during the metathesis reaction was the evolution of approximately 1 equivalent of a 1 3 mixture of 3,3-dimethylbutene and 4,4-dimethyl-2-pentene, which arises from the cross-metathesis of the neopentyl ligand of the grafted complex and propene. 

Transition Metal Single Site Catalysts-From Homogeneous to Immobilized Systems 

The isotropic shifts of the UB and 13C nuclear resonances and the e.s.r. spectrum of M[Crin 2,3-Me2-2,3-C2B9H2 2] (M = Cs or Et4N) salts have been determined and used to suggest that the mode of electron delocalization within this anion is primarily ligand-to-metal charge transfer.214 

Treatment of Cr02Cl2(bipy) with aqueous HC1 has been shown to produce CrOCl2(bipy), which was characterized by i.r. spectral and conductance measurements.219 

The crystal structure of [Cr(CH2CMe2Ph)4] has been determined and the CrIV atom shown to be co-ordinated by a slightly distorted tetrahedron of carbon atoms (Cr—C = 205 pm).220 The e.s.r. spectrum of tetrakis-(l-norbornyl)chromium(iv) has been recorded for the compound contained in organic glasses at low temperatures. 

Lavielle, H. Kessler, A. Hatterer, Bull. Soc. chim. France, 1973, 1918. 

In most of these glasses the complex apparently assumes several conformations which are distinguishable by their zero-field parameters.221 

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Mashima K, Nakayama Y and Nakamura A 1997 Recent trends in polymerization of a-olefins catalyzed by organometallic complexes of early transition metals Adv. Polym. Sc/. 133 1-54... 

A concise summary of chemistry of technologically important reactions catalysed by organometallic complexes in solution. Cornils B and Herrmann W A (eds) 1996 Applied Homogeneous Catalysis with Organometallio Compounds (Weinheim VCH) A two-volume, multiauthored account with emphasis on industrial applications. 

Figure 2-61. a) The bonding in organometallic complexes (e.g., ferrocene) cannot be expressed adequately by a connection table, b) A new representation has to account for all the valence electrons of Iron,... 

Organometallic Complexes. Wemer-type complexes of chromium and long-chain carboxyflc acids, eg, stearic acid, are water repeUents for fabrics of natural and synthetic fibers. The complexes have a smaU market in the textile industry. 

Benzodiazepines as antianxiety agents, 1, 170 as anticonvulsants, 1, 166 organometallic complexes, 7, 604 as sedatives, 1, 166 IH- 1,2-Benzodiazepines conversion to 3H-1,2-benzodiazepines, 7, 604 synthesis, 7, 597, 598, 604 3H-1,2-Benzodiazepines acid-catalyzed reactions, 7, 601 nucleophilic reactions, 7, 604 oxidation, 7, 603 synthesis, 7, 596 thermal reactions, 7, 600 5H-1,2-Benzodiazepines photochemical reactions, 7, 599 synthesis, 7, 603... 

Precipitation is often applied to the removal of most metals from wastewater including zinc, cadmium, chromium, copper, fluoride, lead, manganese, and mercury. Also, certain anionic species can be removed by precipitation, such as phosphate, sulfate, and fluoride. Note that in some cases, organic compounds may form organometallic complexes with metals, which could inhibit precipitation. Cyanide and other ions in the wastewater may also complex with metals, making treatment by precipitation less efficient. A cutaway view of a rapid sand filter that is most often used in a municipal treatment plant is illustrated in Figure 4. The design features of this filter have been relied upon for more than 60 years in municipal applications. 

The structure of the organometallic complex lithium tetramethylborate LiBMc4 is discussed on pp. 127-8 alongside that of polymeric BeMc2 with which it is isoelectronic. 

Sometimes coordination of SO2 to an organometallic complex is followed by intramolecular insertion of SO2 into the M-C a bond. e.g. 

The Hoch-Campbell aziridine synthesis entails treatment of ketoximes with excess Grignard reagents and subsequent hydrolysis of the organometallic complex. ... 

The first ri -transition metal organometallic complexes 272 were made from Li(Mc4C4ESiMe3) (E = Si, Ge) and Cp HfC (98JA8245). Species 272 (E = Si) with trimethylphosphine forms the Hf-PMc3-adduct. 

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