Ligand cyclopentadienyl imido

Alkoxides and imido are used as anionic ligands in zirconium and titanium catalysts for the polymerisation of alkenes, sometimes as the only anions, but often in combination with cyclopentadienyl ligands. Imides linked to cyclopentadienyl groups form part of the single-site catalyst developed by Dow (Chapter 10) (Figure 1.9, 1). In very different titanium catalysts, namely those used for epoxidation of alkenes, also alkoxide ligands are used (Chapter 14). 

Figure 2.7 Parallels in the chemistry of cyclopentadienyl, aryloxide, amido and imido ligands...

Thermolysis of ()) -cyclopentadienyl)bis(neopentyl)(tri-methylphosphine)vanadium(I) (82) in the presence of 1,2-bis(dimethylphosphuio)ethane leads to the formation of the Schrock-type see Schrock-type Carbene Complexes) alkylidene vanadium complex (83), which is supported by X-ray crystallographic analysis (Scheme 45). " The imido vanadium complex (84) is converted to the corresponding alkylidene complex (86) on treatment with ben-zylidene(triphenyl)phosphorane (85) via substitution of the phosphine ligand (Scheme 46). ... 

Exploiting the Isolobal Relationship Between Cyclopentadienyl and Imido Ligands... 

The isolobal analogy between cyclopentadienyl and imido ligands held promise for the development of new a-olefin polymerisation catalysts based on imido ligation. However, our early endeavours were to prove disappointing. Cationic... 

In contrast to the tantalum compounds considered above, the niobium complexes can exist as conformers of different stability at low temperatures. For example, in the H NMR spectrum of complex 4, the intensity ratio between the signals of the conformers is about 3 1 [ 32 ]. The crystal structures of the bis-amido compound 5 and the methylamido compound 6 all show that the lone pair of the amido ligand lies preferentially in the equatorial binding plane of the cyclopentadienyl and imido ligands, a conformation due to the ir bonding interaction of the lone pair with the niobium centre. If rotation about the Nb-Namido bond becomes slow on the NMR time scale then two conformers will be observed, one with the amido proton oriented toward the cyclopentadienyl ring and one with it oriented away. It is supposed that the major conformer is that with the amido proton oriented toward the cyclopentadienyl ring, which minimizes the steric interactions present [32]. 

The metals bonded to two cyclopentadienyls (Cp) in a pentahapto mode form the metallocenes (see Chap. 11 also describing the Cp-M orbitals). In many other families of compounds, the metal is bonded to only one Cp or derivative. Common examples of this category include ternary families containing, besides the Cp-type ligand, carbonyls, phosphines, nitrosyls, hydrides, 0x0, imido, methyls, etc. - ... 

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