MoCl, Molybdenum

Molybdenum(V) compounds generally occur as mononuclear or dinuclear species. Molybdenum pentachloride [10241-05-1] MoCl, formed by combination of the elements, serves as a usebil and reactive starting material (Fig. 1). MoCl has a dinuclear stmcture (Fig. 3) in the soHd state but is mononuclear in the gas phase. In solution or in the soHd state the compound, actually Mo2C1 q (Fig- 3a), is readily hydroly2ed in air to form MoOCl ... 

Representative compounds for the +4 oxidation state are shown in Figure 4. The violet tetravalent molybdenum dioxide [18868-43 ] M0O2, is formed by the reduction of M0O3 with H2 at temperatures below which Mo metal is formed or M0O3 is volatile (ca 450°C). MoCl [13320-71 -3] is formed upon treatment of M0O2 at 250°C with CCl (see Fig. 1). 

Although molybdenum is an essential element, excess levels can have deleterious effects. The LD q and TLV values of the most common Mo compounds are Hsted in Table 3 (63,64). In general the toxicity of Mo compounds is considered to be low. For example, M0S2 has been found to be virtually nontoxic even at high levels. Certain Mo compounds such as MoCl and Mo(CO), have higher toxicity because of the chemical nature and reactivity of these compounds rather than the Mo content. Supplementary dietary Cu ", thiosulfate, methionine, and cysteine have been shown to be effective in alleviating Mo toxicity in animals. 

The first kinetic study of the aquation of [MoCl ] to [MoClgfHjO)] = 87 min at 0 °C) has been reported. No conclusive proof that the final product is [Mo(H20)g] could be obtained, and the spectral profile reported earlier for [Mo(H20)e] is not considered to preclude the existence of dimeric molybdenum(iii) species. The reaction of [WCl (MeCN)2] with... 

Reaction with potassium chloride in fused state or in the presence of iodine monochloride forms molybdenum hexachloride anion, MoCle , which forms salts such as K2M0CI6 ... 

The same configuration has been reported also for molybdenum pentachloride,7 MoCl , antimony pentachloride,80 SbCli, and the tri-methylstibine dihalides,81 (CH ) 3bX. Molybdenum pentachloride... 

Tables I and II summarize the structural studies of mononuclear and binuclear vinylidene complexes, and Table III those of propadienylidene complexes which had been reported to mid-1982. As can be seen, the C=C bond lengths range from 1.29 to 1.38 A, and the M-C bond (1.7-2.0 A) is considerably shorter than those found in alkyl or simple carbene complexes. Both observations are consistent with the theoretical picture outlined above, and in particular, the short M-C bonds confirm the efficient transfer of electron density to the n orbitals. In mononuclear complexes, the M—C=C system ranges from strictly linear to appreciably bent, e.g., 167° in MoCl[C=C(CN)2][P(OMe3)2]2(fj-C5H5) these variations have been attributed to electronic rather than steric factors. In the molybdenum complex cited, the vinylidene ligand bends towards the cyclopentadienyl ring (111).

For both modern reagents PIFA and MoCls an inner-sphere radical transfer is expected, as depicted in Scheme 7. The Lewis acidic additives involved in the PIFA-mediated transformation create an iodonium species that forms a Jt-com-plex 26 with the substrate this subsequently leads to an electron transfer. In contrast, the electrophilic molybdenum chloride most probably coordinates to the oxygen atoms of the donor functions which will then start the transformation. Smooth conversions are obtained if the substituent R" adjacent to the donor (27) is another methoxy group or a bulky moiety. 

Specific procedures for the synthesis of M0CI4, MoCl, and M0CI2 are described in the sections that follow. Other methods of synthesis are also summarized in these sections. Procedures for the synthesis of M0CI5 have been given in Inorganic Syntheses 7, 167 (1963) and 9, 135 (1967). The industrial method is the direct chlorination of metal and is recommended in some laboratories.12-18 A convenient laboratory technique is the liquid-phase reaction system that uses refluxing thionyl chloride and molybdenum (VI) oxide.14... 

Presumably because of its lower electronegativity, bromine can stabilize Mo(V) as MoOBr8 but not Mo (VI) as MoOBr4. There are no reported molybdenum oxide iodides and no lower-valent [molybdenum(V) or molybdenum(IV)] oxide fluorides. The combination of oxygen plus chlorine can stabilize Mo (VI) in both M0O2CI2 and MoOCU, but MoCl is apparently unstable at room temperature. 

Molybdenum (III) chloride, MoCl, has a molecular weight of 202.32. The dark red compound is stable when protected from... 

The X-ray crystal structure of [ MoCl(CO)2(dppmSe) 2][Mo6019] 4MeN02 was reported in 1988224 by Colton et al. The molybdenum is seven-coordinate with a slightly distorted capped octahedral geometry, with a carbonyl ligand in the unique capping position. In 1991, the molecular structure of the dibromo complex [MoBr2(CO)2(i71-dppm)(7j2-dppm)] was reported.225... 

Reaction of [MoCl(S2CNR2)3] (R = Me, Et) with silver triflate afforded diamagnetic [Mo2(dtc)6][OTf]2 which could act as the source of tris(dithiocarbamato)Mo cations in the synthesis of [MoL(dtc)3]"+ (n = 0, L = Cl, I, N3 n = 1, L = O, NCMe, PR3). The molybdenum atom in paramagnetic seven-coordinate [Mo(PMe2Ph)(S2CNEt2)3][OTf has pentagonal-bipyramidal coordination with an apical phosphine ligand. 

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