Molybdenum derivatives

Mineral fillers and additives aluminium trihydrate (ATH), magnesium hydroxide and boron derivates are the best known but tin derivates, ammonium salts, molybdenum derivates and magnesium sulphate heptahydrate are used to varying extents and nanofillers are developing. 

MoOCl2(02)(OPR3)2, 10, one of the few examples of mono-peroxo molybdenum derivatives, has been isolated and characterized in the solid state . These derivatives are fairly unstable and the crystal structures obtained derive from a mixture with their reduction products Mo02(Cl2)(OPR3)2. 

As has been shown recently, a partial reduction of some molybdenum derivatives can occur spontaneously on storage via oxidation of the organic radical. Thus, molybdenum (VI) oxoisopropoxide transforms completely in 2 months according to the equation ... 

Displacement of trimethylphosphite from (CpMo(MeC=CR)[P-(OMe)3]2 + with anionic sulfur nucleophiles produces neutral monoalkyne molybdenum derivatives [Eq. (22)] (74). Methoxide has also been incorporated into monoalkyne cyclopentadienyl derivatives [Eq. (23)] (75). 

The metal-alkyne bonding parameters of molecules of the type CpML-(RC=CR)X are similar to those of other classes of four-electron donor alkynes in Table I. Both cationic and neutral derivatives with cyclopen-tadienyl (Cp = t75-C5H5) or indenyl (tj5-C9H7) illustrate the structural regularities of these molecules. The preponderance of molybdenum derivatives relative to tungsten reflects more extensive and diverse synthetic chemistry with molybdenum to date. 

In the absence of interaction with other hgands or orbitals, the back-bonding interaction in the yz plane for the 6 = 90° orientation would be degenerate with that in the xz plane for the 6 = 0° orientation. Thus, for the chromium and molybdenum derivatives M(CO)5 (ethylene), there would be no preference for either the yz or the xz plane. In fact, at this level of approximation, no barrier would be expected for a rotation from the yz to the xz plane, that is, the interaction with a linear combination of xz and yz would also be equivalent in energy. 

This expansion of interest was very well supported by Climax Molybdenum Company. The company obviously had a vested interest in increasing utilisation of molybdenite or any molybdenum derivatives, but the methods which it used from the early years were a model of responsible technical encouragement. Samples suitable for lubrication studies were made available, and circulation of technical papers. 

DICARBONYL-ii-CYCLOPENTADIENYLNITROSYL-MOLYBDENUM AND BIS(DIHAL0-J7-CYCLOPENTADIENYLNITROSYL-MOLYBDENUM) DERIVATIVES... 

The tungsten derivative W(f/ -C5H5)Me(CO)3 is much less reactive than the molybdenum analogue in the PPhj-promoted insertion of CO. While the molybdenum derivative [reaction (b)] reacts in acetonitrile at RT, the corresponding tungsten derivative does not react under the same conditions. For the reaction in acetonitrile, the rate constants (s ) are as follows W, (3.5 0.5) x 10 , 82°C Mo, (5 + 1) x 10 , SO C. No quantitative data are available for chromium, owing to the thermal lability of Cr((tf -CsH5)Me(CO)3, but qualitatively chromium resembles molybdenum. 

The second band for the chromium and molybdenum derivatives is assigned to the 2E2g ion state. In the case of tungsten, this band is split into two spin-orbit components, 2E2 ( ) and 2E2 ( ), as a result of the greater spin-orbit coupling constant for the third-row transition metal. 

Additional evidence for reversible CO loss from several carbene complexes such as 11-15 was obtained from kinetic measurements of CO exchange rates determined by C NMR. The results are summarized in Table 1. For the phenylmethoxycarbene complexes (11-13), CO dissociation from the tungsten complex is seen to be much slower than for the chromium and molybdenum derivatives. Changing the methoxy to a phenyl group (14 versus 13) increases the exchange rate which can be understood in terms of the reduced 7r-donor ability of... 

T-Bonded Complexes of Some Heteroatom Boranes with Iron and Molybdenum Derivatives, T. Yamamoto and L. J. Todd, J. Organometal. Chem., 67, 75 (1974). 

A comparatively large number of molybdenum derivatives with the empirical formula A Mo P O, where A is usually a Group 1 or Group II metal, have been studied and characterised by crystal structure determination. These include [46-50]... 

The n-cycloheptatrienyl molybdenum derivatives (274 R = H or Me) have been prepared from [(PhR)Mo(C3H5)Cl]2 (R = H or Me) and used to prepare a wide variety of new n-cycloheptatrienyl molybdenum compounds. Unexpected fluxional behaviour in hexacarbonyl(jt-cycloheptadienyl)(7i-cycloheptatrienyl)triruthenium... 

In order to gain some insight into the reactivity of bridging vinylidenes 4a and 4b, electrochemical studies have been carrried out. The cyclic voltammograms reveal that both the molybdenum and timgsten vinylidenes are readily oxidized. Molybdenum derivative 4a exhibits a quasi-reversible redox couple at E1/2 = +0.64 V vs. SCE (AEp = 270 mV at 100 mV/sec). The accompanying cathodic response indicates that the oxidized species is somewhat unstable, as ip /ip = 0.7. 

Several molybdenum derivatives can be prepared using a thiolate. A stable monomeric 7r-allyl molybdenum derivative has been obtained by the metathesis ... 

Our group has prepared a number of [Leu Enkephalin derivatives with organometallic compounds attached to the N terminus via amide bond formation. In addition to the ferrocenoyl derivative 27 and the related cobaltocenium derivative 28 [61], we have also published the synthesis and characterization of two molybdenum derivatives 29 and 30 (see Schemes 5.13 and 5.14) [62]. In all cases, the enkephalin was prepared by standard solid phase peptide synthesis (SPPS) techniques the by Fmoc strategy. For compounds 27-29, the metal complex was attached to the deprotected N terminus of the peptide as the final step on the solid support. Subsequent cleavage from the resin was achieved by cone. NHj solution in MeOH (27 and 29) or cone. TFA (28), respectively, in accordance with... 

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