Tungsten atom

JOM(400)149 96BSCF33]. The complex 164 is the first known t] -phospholyl species. The tungsten atoms have a coordination number of 9, and the carbon atoms of the phospholyl ring are coplanar. The phosphorus atom deviates from the plane of carbon atoms by 0.015 nm. The basic difference between the Ti -cyclopentadienyl and ri -phospholyl complexes is the existence of a low-lying LUMO localized mainly at the phosphorus atom. 

The function of the tetraethyltin is to create vacant sites so that coordination of alkene molecules becomes possible, and to change the oxidation state of the tungsten atom from +6 to +4. Similar behavior of the aluminum compound in the system WCL-CgHsAlCb is not probable, because it has been demonstrated that WCle-AlClg is also an active catalyst (22, 44), which suggests that C2H5AICI2 functions as a Lewis acid. Vacant sites can be created by a Lewis acid as follows ... 

The cr2 tta triple bond between molybdenum and tungsten atoms developing the chemistry of an inorganic functional group. M. H. Chisholm, Angew. Chem., Int. Ed. Engl., 1986,25,21 (70). 

It is interesting to note that there are strings of tungsten atoms WII in the A15 crystals with each atom between two very near neighbors the interatomic distance 2.519 A. leads to the bond number n = 1.35. 

The tetragonal crystal WSi2 (Zachariasen, 1927) may serve as another example. Each silicon atom forms five bonds with surrounding silicon atoms at 2-633 A and five bonds with tungsten atoms at the same distance. Each tungsten atom forms ten bonds with silicon atoms at 2-633 A and four bonds with tungsten atoms at... 

Using an electron-gun source, tungsten atoms were reacted with benzene, toluene, or mesitylene at 77 K, to form the expected (arene)2W complex (42) in a yield of 30%, compared with the —2% yield from the previously published, bis(benzene)W synthesis (32). These arene complexes are reversibly protonated, to give the appropriate [(T7-arene)2WH] species. By using the same technique, the analogous, niobium complexes were isolated (43). 

The products are, in turn, starting materials for a rich chemistry, only superficially explored to date. The phosphorus atoms serve as Lewis bases toward metals. Coordination complexes with one or two tungsten atoms have been isolated (Eq. 34). They also readily undergo insertion reactions... 

Activation of carbon-hydrogen bonds bv tungsten atoms... 

Co-condensation of tungsten atoms with a mixture of cyclohexane and PMe3 gives a mixture a products shown in Figure 6 12 6). The identity of the... 

In a more remarkable experiment in which tungsten atoms are co-condensed with a mixture of cyclopentane and PMe3 the major component was identified as [W(T -C5H5) (PMe3)H5] (Figure 7) (22.). The other species... 

Figure 7 Reaction of tungsten atoms with cyclopentane, (i and iv) Co-condensation at -196 °C (ii) Cyclopenta-diene in benzene at 60 °C and (iii) Dihydrogen at 50 atm.

Alkane activation by metal atoms by osmium atoms, 273-274 by rhenium atoms, 265-271 by tungsten atoms, 270-272 description, 265 Alkane elimination reactions, processes, 20,22... 

Figure 4. The central Wk(i -H)a0lk skeleton of the centrosymmetric (0- -Pr)H molecule emphasizing the octahedral geometries of the tungsten atoms.

Structures known to form with either metal also form with the entire intermediate range of mixed-metal combinations 180). Both molybdenum and tungsten form the heptametalate [M7O24]6 in aqueous solution. The existence of mixed heptametalates has been shown by the application of 170 NMR 182) and 183W NMR spectroscopy 180). In fact, molybdenum can replace any or all of the tungsten atoms in [W7O24]6 so that at least 19 mixed-metal structures can be observed 180). Approximate relative stability constants have been determined for the intermediate species in the series... 

The dinitrogen molecule bridges the two tungsten atoms, each of which assumes a four-legged piano stool geometry. 

---