Molybdenum complexes dinitrosyl

Molybdenum dinitrosyl complexes with the general formula Mo(NO)2(CHR) (0R )2(A1C12)2 have been found to be active in a variety of metathesis reactions [110]. New alkylidenes could be identified. Variations such as Mo(NO)2(CHMe) (RC02)2 also are known [111]. Complexes of this type are believed to be more reduced than typical d° species discussed here, although they appear to be much more active as metathesis catalysts than typical Fischer-type carbene complexes. 

A. ALKYL AND ARYL(tjs-CYCLOPENTADIENYL)DINITROSYL CHROMIUM, MOLYBDENUM, AND TUNGSTEN COMPLEXES... 

An important use of dinitrosyl complexes of molybdenum has been as catalyst precursors in the alkene disproportionation reaction. Thus [MoCl2(NO)2L2] (L = PPh3 or py) together with AlCl2Et forms an active homogeneous catalyst for alkene disproportionation. The catalysis appears to require loss of NO from the metal and the field has been reviewed.19,31... 

These complexes are generally prepared by methods similar to those employed for the dinitrosyl compounds, treatment of a low-valent molybdenum compound with NO or a nitrosyl derivative being the principal method. Compounds and major physical properties are collected in Table 3. 

A number of unusual structural features have been noted. The ruthenium porphyrin formed by reaction of triruthenium dodecacarbonyl with an N, AT-vinyl-bridged tetraphenylporphyrin involves disruption of a pyrrole C-N bond to give a product in which the ruthenium is bound to two pyrrole N atoms, the C and N atoms of the ruptured pyrrole ring, and two mutually cis carbonyl ligands. The remaining pyrrole N is uncoordinated.613 Mutually cis configurations have also been found for the dicarbonyl complex of molybdenum tetraphenylporphyrin and for some dinitrosyl porphyrins. 

The chemistry of the dicarbonyl(7 -cyclopentadienyl)nitrosyl and the chloro-(i7 -cyclopentadienyl)dinitrosyl complexes of chromium, molybdenum, and tungsten [i.e., fT -CsHs)M(CO)j(NO)] and [(i7 -CsHs)M(NO)2Cl] has not been studied extensively, partly because of the various difficulties associated with their preparation. The procedures described below are of general applicability to all three metals and lead to the desired compounds in high yields. The carbonyl nitrosyl complexes are the synthetic precursors of the chloro nitrosyl complexes and so their preparation is described first. 

B. CHLORO(t7 -CYCLOPENTADIENYL)DINITROSYL complexes of CHROMIUM, MOLYBDENUM, AND TUNGSTEN... 

B2F,MoN C,Hi2, Molybdenum(II), te-trakis(acetonitrile)dinitrosyl-, cis-, bis[tetrafluoroborate(l -)], 26 132 02B2F,N4 VC Hi2, Tungsten(II), te-trakis(acetonitrile)dinitrosyl-, cis-, bis[tetrafluoroborate(l -)], 26 133 O2CH24 Formic acid, rhenium complex, 26 112... 

The ability of the nitrosyl ligand to behave as an electron pair reservoir has also been considered to play an important part in certain catalytically active systems. The vacant site provided by isomerization of the ligand could enable an unsaturated organic molecule to enter the transition metal s coordination sphere, thus forming an active intermediate. Examples of catalysis by nitrosyl complexes include the hydrogenation of alkenes by Rh(NO)L3 species and the dimerization of dienes in the presence of Fe(CO)2(NO)2 or Fe(n-C3Hs)(CO)2NO. Certain molybdenum dinitrosyl complexes, such as MoCljfNOljfPPhjlj, have also been found to provide very efficient alkene dismutation catalysts. ... 

Hexacoordinated mixed-ligand dinitrosyl complexes of molybdenum(O) of the composition [Mo(NO)2(L)(OH)] with a variety of Schiff base ligands have been reported [3]. Such complexes are readily obtained by a single-step reaction between molybdate(VI) and the ligand in presence of hydroxylaminehydrochloride in a dimethylformamide solvent. A ds-octahedral structure has been observed in these complexes, as shown in Figure 12. 

---