Molybdenum complexes ligand substitution

V. Solvent Exchange and Ligand Substitution on Some Molybdenum and Tungsten Cluster Complexes... 

An interesting allylic substitution reaction of ( )-cinnamyl methyl carbonate 143 has been examined by Pfaltz s group. The use of a molybdenum complex of ligand 144 resulted in 145 in 88% yield with an ee of 99% [for the (R) isomer] (Fig. 9.45). 

Support-bound transition metal complexes have mainly been prepared as insoluble catalysts. Table 4.1 lists representative examples of such polymer-bound complexes. Polystyrene-bound molybdenum carbonyl complexes have been prepared for the study of ligand substitution reactions and oxidative eliminations [51], Moreover, well-defined molybdenum, rhodium, and iridium phosphine complexes have been prepared on copolymers of PEG and silica [52]. Several reviews have covered the preparation and application of support-bound reagents, including transition metal complexes [53-59]. Examples of the preparation and uses of organomercury and organo-zinc compounds are discussed in Section 4.1. 

Ligand exchange reactions with nitrido molybdenum complex 56 has been documented (Eq. (19)). Treatment of 56 with 2 equiv. of HX (X = Cl or Br) leads to the formation of 57 which, following treatment with triethylamine, afforded 58, wherein a halide has been substituted for the azide ligand found in 56 [27]. The introduction of a nitride onto a Mov complex has been carried out by treatment of Mom or Mo ... 

The gradual substitution of the phenyl groups in the phosphine ligand for ferro-cenyl subunits affords the diferrocenyl- and triferrocenyl-phosphinepentacarbonyl-molybdenum complexes, respectively. With respect to the redox pathway shown in Fig. 7-11, each added ferrocenyl ligand involves the appearance of a further one-electron oxidation [50]. The relevant redox potentials are given in Table 7-7. 

The first reported diazenido metal complex was obtained by King and Bisnette (1964) by ligand exchange, as shown in (10-5) one of the three carbonyl groups in the molybdenum complex 10.20 was replaced by an aryldiazenido ligand (10.21) in tetrahydrofuran. The 18-electron Mo configuration requires the aryldiazenido ligand to be a three-electron donor the anionic complex 10.20 becomes a neutral product (10.21) by this substitution. 

---