Molybdenum complexes arene

Bis(Tj6-jV,-/V-dimethylaniline)molybdenum has been prepared in good yield by cocondensation of molybdenum atoms with a fifty-fold excess of Af,Af-dimethyl-aniline vapor on a liquid nitrogen cooled surface. This method has been extended to the synthesis of other molybdenum arene complexes and is at present the only synthetic route to such compounds. 

As well as organic chiral auxiliaries, organometallic fragments have found some application as chiral auxiliaries in conjugate addition reactions. Particularly noteworthy are chiral molybdenum allyl complexes [69], chiral iron complexes [70], and planar chiral arene chromium species [71]. 

Molybdenum and tungsten atoms seem to react with alkylbenzenes more efficiently than chromium atoms yields of 30 to 50% are reported (113). Conventional routes to the synthesis of tungsten-arene complexes are difficult and inefficient so that the ability to prepare these compounds in high yield via tungsten atoms is of special significance. Unfortunately, tungsten has a very high vaporization temperature and the scale of work with its vapor is necessarily limited. 

Corazza, F., Floriani, C., Chiesi-Villa, A., Guastini, C., The oxo-molybdenum(Vl) group over a calixarene-oxo surface— calix[4]arene complexing inorganic and organic functionalities. J. Chem. Soc., Chem. Commun. 1990, 640. 

Some examples of polynuclear polymeric metal arene complexes, obtained by cryosynthetic reactions from tin, titanium, vanadium, chromium, and molybdenum, are represented [202,542,543]. However, the preparative possibilities of such syntheses are not yet clear [201,202]. 

Hexacarbonylchromium(O) is readily attacked by chlorine giving CrCb, CO, and COCI2. Bromine and iodine do not attack Cr(CO)6 to any substantial extent at room temperature. The chromium tricarbonyl arene complexes, Cr(CO)3( -arene), are readily oxidized at room temperature by I2 to give Cris this is a conveitient preparative method for the anhydrous iodide. Although the oxidation of the tricarbonyl arene derivatives of chrontium with I2 does not show evidence of intermediate carbonyl complexes in oxidation states >0, the corresponding molybdenum(O) compounds give a series of carbonyl iodides of molybdenum(II), for example, the ionic [Mo(CO)3 ( ) -arene)]I. 

There are two different general classes of rr-bound arene-containing complexes of molybdenum the monoarene complexes [() -arene)Mo(CO)3] or the h/i-arene complexes [()] -arene)2Mo]. The solid-state structures of both classes of compound show that the bond lengths around the arene ligand are equivalent. This clearly means that the arene does not bond as a friene through localized electron pairs. 

A variety of transition metals, for example, chromium, molybdenum, tungsten, iron, vanadium, manganese, and rhodium can be used to prepare relatively stable j -arene complexes (see Arene Complexes). Reactions of j -arene chromium tricarbonyl complexes have been extensively examined, and numerous reviews are available. Although chromium complexes are by far the most utilized in organic synthesis, complexes of iron and manganese are emerging as potentially useful alternatives. 

Detailed vibrational assignments have been carried out on arene chromium and arene molybdenum tricarbonyl complexes (18, 19). Splitting of the E band in the carbonyl region was observed for substituted benzene chromium tricarbonyl complexes but not in (CgHg)Cr(CO)3 itself, showing that the concept of local symmetry (Cg ) is of very restricted validity when discussing the C—O stretching vibrations in such complexes (18). 

An alternative synthetic procedure is to use Metal Vapor Synthesis (MVS) see Metal Vapor Synthesis of Transition Metal Compound ). This method of preparation is hindered by the high boiling point of molybdenum and the expense of the MVS apparatus. It does, however, allow a greater range of functionalized Ais-arene complexes to be synthesized. ... 

With the exception of the labile complexes of condensed aromatics, the metal-arene bond in (arene)Mn(CO)3 complexes is very robust. It is more difficult to cleave than that in the neutral arene complexes of chromium and molybdenum and requires strongly oxidative conditions such as DDQ in refluxing acetonitrile. 

Radius, U. Attner. J. Dinuclear molybdenum(III) and tungsten(III) calix[4]arene complexes — Metal-metal triple 27. bonds supported by bridging calix[4]arene ligands. Eur. J. 

T -Arene complexes containing late metals have been known for many years, but the scope and utility of these complexes have increased in recent years. Copper(I) and silver form labile arene complexes of various stoichiometries that are apparently T -arene complexes. A few of these complexes have been structurally characterized. More recently, a large number of V-arene and heteroarene complexes of osmium, rhenium, molybdenum, and tungsten have been prepared for the purpose of dearomatization of the arene or heteroarenes. Two examples are shown in Figure 2.33. This dearomatization creates a diene or vinyl unit that imdergoes the organic chemistry of ttiese isolated units, instead of the chemistry of an arene. n -Arene complexes of rhodium and platinum have been characterized structurally and studied in the context of their likely intermediacy in the oxidative addition of arene C-H bonds. ... 

Arene chromium tricarbonyl complex Molybdenum carbonyl complex Mo(CO)g... 

Chromium, Molybdenum and Tungsten.- The use of metal vapour syntheses continues to dominate the reports of new arene complexes including new complexes of Cr, W and Re with benzene and... 

A molybdenum(II) arene complex results from the reaction of... 

Complexation of metals to preformed polymers is a useful methodology for the synthesis of polymers incorporating metals into their backbones or sidechains. In 1984 the complexation of a molybdenum tricarbonyl complex to approximately 25% of the arenes in polyparaphenylene (PPP), was reported. This polymer displayed shifts in its IR spectrum similar to that of potassium-doped PPP. 

MoO -A /gOg, MoOj-S/Og U2O2-AI2O2 Arene chromium tricarbonyl complex Molybdenum carbonyl complex Mo(COk... 

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