Hafnium amides

Metal dialkylamides were reviewed by Bradley in 1972.61 A comprehensive list of all zirconium and hafnium amides reported prior to 1979 may be found in the book by Lappert et al.62... 

Scheme 2. Pathways for the formation of the hafnium amides from azides and hafnium hydrides. Reprinted with permission from Organometallics 1, 1025. Copyright (1982) American Chemical Society.

The chemistry of zirconium and hafnium amides has been investigated further 101) using the general reactions of (1) metal amide with excess protic compound, (2) metal amide with a stoichiometric amount of protic compound, and (3) the reaction of a metal chloride with lithium dimethyl amide. The comyiounds jirepared are listed in Table V. They are all monomeric. Hafnium amides have not been described before, although there is a reference by Bradley (7fl) to the reaction of hafnium amide with carbon disulfide and metal carbonyls. 

MUanov, A., Bhakta, R., Bannemann, A., Becker, H., Thomas, R., Ehrhart, R, Winter, M., Devi, A. (2006) Guanidinate-stabilized monomeric hafnium amide complexes as promising precursors for MOCVD of Hf02. Inorganic Chemistry, 45,11008-11018. 

In other studies, the combination of alkoxides and chlorides, or alkoxides and amides without oxidant have been used to deposit hafnium silicate thin films by ALD [3,7],... 

Table 15 Complexes of Ziiconium(IV) and Hafnium(IV) Halides with Sulfoxides, Selenoxides, Amides, Af-Oxides, P-Oxides and Related Ligands...

Fig. 12.5 Symyx high-throughput primary screen, in which arrays of metal-ligand combinations are rapidly surveyed for olefin polymerization activity. In this example, a 1-octene primary screen was used to discover a new amide ether-based hafnium catalyst.

Recent Group IV chemistry has seen an upsurge in the number of amide derived species, and this has included fluoride derivatives. None of these compounds are of oxidation state -(-III or less, which are the subject of this review, but refer to titanium, zirconium or hafnium where the metal is the +IV state [1,9-12] and, consequently, not covered here. 

The amides of zirconium and hafnium, M(NR2)4, like the alkoxides, are associated. The degree of association depends on the nature of R. Zr(NMe2)4 (mp 70 °C, bp 80 °C at 0.05 mmHg) in the sohd state adopts the amide-bridged dimeric structure Zr2(/u.-NMe2)2(NMe2)6. A monomer-dimer equilibrium is estabhshed in solution but only the monomer exists in the gas phase. Gas-phase electron diffraction data indicate that the N atoms are coplanar, as a result of N to Zr p to donation seep Bonding). ... 

Hafnium(IV) bis(perfluorooctanesulfonyl)amide complex Hf[N(S02C8F17)2]4 is a highly reactive and recyclable Lewis add catalyst in Friedel-Crafts acylation and Prins reactions in fluorous biphasic systems at low catalyst loadings (<1 mol%) (Equation 4.23). In these reactions, Hf[N(S02C8F17)2]4 is selectively soluble in the fluorous phase and can be recovered after reaction by simple phase separation. In addition, the catalyst can be reused without any loss of activity [44],... 

Acylation of anisole with A AN is carried out in a mixture of GALDEN SV 135, a suitable fluorous solvent, and chlorobenzene in the presence of hafnium tetra[bis(perfluorooctanesulfonyl)amide] (1% mol) at 70°C-120°C for 1 to 5 h, giving para-methoxyacetophenone in 80% yield and 100% selectivity. It is significant to underline that aluminum chloride gives the mentioned product in only 2% yield under the present mild reaction conditions. The catalyst can be very easily recycled by directly reusing the lower fluorous catalytic phase in the successive reaction with another mixture of reactants, affording the product more than three times without decrease in catalytic activity. The catalytic process can be applied to dimethoxybenzenes and mesitylene with both aliphatic and aromatic acyl chlorides and anhydrides (80%-97% yield). Benzoylation of toluene gives para-methylbenzophenone in 35% yield. 

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