Hafnium carbonyls

Zero- and Subvalent Zirconium and Hafnium Carbonyl Complexes 699... 

In contrast to the vast number of mono- and multinuclear binary carbonyl complexes of the transition metals, no isolable binary carbonyls of titanium, zirconium, or hafnium have been reported. 

Like zirconium, the first fully characterized carbonyl complex of hafnium was reported in 1976 by Thomas and Brown (6). This complex, bis(i7-cyclopentadienyl)dicarbonylhafnium (3) was prepared via the reductive carbonylation of Cp2HfCl2 using sodium amalgam. While the reaction proceeded to give a moderate yield of 3 (30%), this corresponded to only 60 mg of isolated product. 

As mentioned already, new methylidene-group IV metal complexes have been prepared and were subsequently used in nucleophilic additions to carbonyl electrophiles (Scheme 43).53 In contrast to titanium and zirconium, the reaction of methylidene hafnium dichloride 97 benzophenone stopped at the first stage (i.e., addition). The tertiary alcohol was obtained in 73% yield, while the corresponding alkene was formed only as minor product. 

Zirconium and hafnium dialkylamides are highly reactive compounds. They undergo (i) protolytic substitution reactions with reagents such as alcohols, cyclopentadiene and bisftrimethylsilyOamine 63 64 (ii) insertion reactions with C02, CS2, COS, nitriles, phenyl isocyanate, methyl isothiocyanate, carbodiimides and dimethyl acetylenedicarboxylate 69-72 and (iii) addition reactions with metal carbonyls.73 These reactions are summarized with reference to Zr(NMe2)4 in Scheme 1. 

Triphenylsilyl zirconium and hafnium derivatives have been prepared from the silyl lithium species. Triphenylsilyl bis(cyclopentadienyl) zirconium chloride undergoes carbonyl insertion under pressure of carbon monoxide (100 psi) to give the corresponding acyl zirconium species which, upon treatment with anhydrous hydrogen chloride in a benzene matrix at —196 °C and warming to room temperature, gives rise to formyl triphenylsilane55. 

Fig. 16. Molecular geometry of the dipolar carbonyl hafnium complex 131.

C-H bonds in hydrogenation reactions, 276-277 C-Si bonds, 73 Carbonyl complexes, 184 Carbonyl hafnium complex, 144 Carbonylation of aryl halides, 271-272 Carbonylation reactions in ionic liquids, 271... 

The hexacarbonylmetalates(-II) of group 4 can be synthesized by reducing the tetrachlorides with potassium in the presence of a cryptand. In the case of hafnium, the starting material is a tertiary-phosphine-carbonyl complex of the zerovalent metal (see equations 52 and 53). The cryptand/(metal cation) system, characterized by a large mass and a low charge density, presumably has a stabilizing effect on the carbonyl anion. Reactions of equations (52) and (53) are carried out with CO at atmospheric pressure. ... 

Dihydro derivatives of zirconium(IV) and hafnium(IV), formula M(r/ -CjH5)2H2, react with CO at low temperature to give a carbonyl adduct characterized by a CO... 

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. 

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