Tungsten complexes monomeric

Although distibenes, the antimony analogues of azo compounds, have never been isolated as free, monomeric molecules (130), a tungsten complex, tritungsten pentadecacarbonyl[p.2-Tj -diphenyldistibene] [82579-41-7] C2yH2Q025Sb2W2, has been prepared by the reductive dehalogenation of phenyldichlorostibine (131) ... 

The use of /r-hydroxo or ju-alkoxo bridged polynuclear complexes of chromium, molybdenum, tungsten, or rhenium in this route leads to the formation of monomeric bis(NHC) complexes, to the elimination of hydrogen, and to the partial oxidation of the metal [Eq.(ll)]. Chelating and nonchelating imidazolium salts as well as benzimidazolium and tetrazolium salts can be used. 

There are two general procedures for the preparation of monomeric W11 complexes.269 In one, substituted tungsten carbonyls are oxidized by halogens under controlled conditions as exemplified by equations (18) and (19). In the second, W(CO)6 is first oxidized by Cl2 or Br2 at low temperature, followed by reaction of the oxidized product with the appropriate ligands. This preparative procedure is exemplified by equation (20). 

Hexaalkoxides are only known for the two elements tungsten and uranium. In both cases, physical and spectroscopic data are consistent with monomeric, octahedral complexes. Tungsten hexaalkoxides are pale yellow or colorless substances that readily sublime and exhibit the expected H NMR and mass spectra.189 The totally symmetric v(W—O) stretch occurs between 530 and 600 cm-1 in the IR spectrum, depending on the alkyl substituents. In contrast, the homoleptic phenoxide W(OPh)6 is intense red in color due to the presence of a strong oxygen-to-metal charge transfer band in this d° complex which absorbs in the visible part of the spectrum.36... 

Bis(adamantylimido) compounds, with monomeric chromium(VI) complexes, 5, 348 Bis(alkene) complexes conjugated, Rh complexes, 7, 214 mononuclear Ru and Os compounds, 6, 401 -02 in Ru and Os half-sandwich rj6-arenes, 6, 538 with tungsten carbonyls and isocyanides, 5, 685 Bis(u-alkenylcyclopentadienyl) complexes, with Ti(II), 4, 254 Bis(alkoxide) nitrogen-donor complexes, with Zr(IV), 4, 805 Bis(alkoxide) titanium alkynes, in cross-coupling, 4, 276 Bis(alkoxo) complexes, with bis-Cp Ti(IV), 4, 588 Bis[alkoxy(alkylamino)carbene]gold complexes, preparation, 2, 288... 

The chemistry of Lewis acids is quite varied, and equilibria such as those shown in Eqs. (28) and (29) should often be supplemented with additional possibilities. Some Lewis acids form dimers that have very different reactivities than those of the monomeric acids. For example, the dimer of titanium chloride is much more reactive than monomeric TiCL (cf., Chapter 2). Alkyl aluminum halides also dimerize in solution, whereas boron and tin halides are monomeric. Tin tetrachloride can complex up to two chloride ligands to form SnCL2-. Therefore, SnCl5 can also act as a Lewis acid, although it is weaker than SnCl4 [148]. Transition metal halides based on tungsten, vanadium, iron, and titanium may coordinate alkenes, and therefore initiate polymerization by either a coordinative or cationic mechanism. Other Lewis acids add to alkenes this may be slow as in haloboration and iodine addition, or faster as with antimony penta-chloride. 

Two tungsten alkylidyne polymers [W(sC-(4-NCsH2-3,5-Me2))(0 Bu)3] (34) and [W(=C-(3-NC5H4))(0 Bu)3] (35) displayed emission at 635 and 640 nm, respectively, in the solid state at 77 K." Under similar conditions, the monomeric [W(=CR)(0 Bu)3] (R = aryl, alkyl) complexes were nonemissive. It was proposed that the [W=C-pyridine] TT-system contributed significantly to the frontier orbitals of these luminescent polymeric materials. 

The crystal structure of 2-lithiated l-methyl-l,3-benzazaphosphole 35 showed it to have a dimeric structure with two THF molecules associated with each lithium. The two lithium atoms and the two C-2 atoms form a four-membered ring <20020M912>. In contrast, the N-lithiated derivative of 2,5-dimethyl-l//-l,3-benzazaphosphole exists as a monomeric species 36 in the solid state <2002JOM(646)113>. The carbene-type complex 37 derived from the lithiated species 35 on reaction with tungsten hexacarbonyl was also studied by X-ray crystallography. 

The monomeric tungsten(IV) phenoxide and thiolate complexes [W(0-2,6-C6H3R2)]4] (R = Me, /-Pr) and [W(S-t-Bu)4] were produced by the reaction of [WCl4(Et2S)2] and the corresponding phenolate or thiolate anion.133,134 The phenolate complexes exhibited nearly square planar geometry. 

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