Hafnium complexes carbonates

In contrast, exposure of 14-VE (diene)MCp Cl complexes (M = Zr, Hf) to CO (1 atm) results in the formation of cyclopentadienes70. The mechanism proposed for this transformation was elucidated with a carbon labeled CO ( CO) as requiring an initial coordination of CO to generate a (diene)MCp (CO)Cl complex 153 (Scheme 37). For the hafnium complex, the intermediate 153 (M = Hf) was observed by infrared spectroscopy. Insertion of CO into the a2, jt diene generates a metallacyclohexenone, which undergoes reductive elimination to generate the dimeric metallaoxirane species 154. -Hydride elimination from 154 (M = Zr, Hf) followed by 1,2-elimination produces substituted cyclopentadienes and the polymeric metal-oxide 155. Treatment of (diene)TiCp Cl with CO leads to isolation of the metallaoxirane complex 154 (M = Ti). 

This complex, unlike the simple homoalkyls of uranium 133), is stable at room temperature but decomposes without melting at 85 °C. The NMR spectrum of the diamagnetic complex confirms the presence of a Th—C a bond coordinated through the methylene carbon [t, 8.90 ppm singlet (2) t, 3.60 ppm doublet (2) t, 3.15— 2.60 ppm multiplet (3)]. Both the NMR and infrared spectra are in accordance with those of the presumably isostructural tetrabenzylzirconium and hafnium complexes. Also reported was the thorium(III) complex (C6H5CH2)3Th-THF. 

Dimethylbutadiene)HfCp (Cl)] (74c) reacts with one molar equivalent of acetylene to yield the unusual product 87. This is probably formed by a conventional butadiene/alkyne coupling at the Group 4 metal center, followed by an intramolecular alkene insertion into the adjacent hafnium to carbon cr-bond. The resulting alkylidene complex (86) then rapidly dimerizes to yield the observed final product (see Scheme 28), that was characterized by X-ray diffraction.96... 

The zirconium and hafnium complexes of trifluoroacetyl-acetone are white crystalline solids, insoluble in water but soluble in benzene, cyclohexane, and carbon tetrachloride. The hafnium complex melts at 128 to 129° and the zirconium complex at 130 to 131°. The complexes have been subjected to gas-phase chromatography and may be sublimed at 115° at a pressure of 0.05 mm. The proton magnetic resonance spectra of the compounds dissolved in carbon tetrachloride show single peaks in the methyl and methylene regions. The peaks appear at 2.20 and 6.00 p.p.m. (5) relative to tetramethylsilane (internal reference) for the zirconium complex and at 2.20 and 5.97 p.p.m. for the hafnium complex. 

As expected, the strong-field 7r-acidic ligand, carbon monoxide, has also been used to isolate zero-valent zirconium and hafnium complexes. This area has been a subject of relatively long-standing interest and has been reviewed.7 Chemistry outside of this review will be the focus of this section. 

Knobloch DJ, Lobkovsky E, Chirik PJ. Dinitrogen cleavage and functionalization by carbon monoxide promoted by a hafnium complex. Nat Chem. 2010 2 30-35. 

For future discussions, it is also important to know that the fluorenyl-Zr-cyclo-pentadienyl bond angle in the zirconium complex 1 is 118.6° (119.4° for hafnium complex 2) and deviates by about 10° from the ideal tetrahedral angle of 109.5° (tetrahedral formed around the bridging carbon and the bonds with its four substituents, two methyl groups plus fluorenyl and cyclopentadienyl groups) and a Cl-Zr-Cl bond angle of 98.2° (Cl-Hf-Cl = 97.5°). 

Esterification of carboxylic acids with alcohols, including bulky secondary ones, by equimolar di-2-thienyl carbonate (2-DTC) in the presence of a catalytic amount of 4-(dimethylamino)pyridine in toluene solvent at room temperature followed by addition of a catalytic amount of hafnium(IV) trifluoromethanesulfonate, Hf(OTf)4, afforded the corresponding esters in good to high yields. In step 1 (Scheme 1), interaction of the acid and 2-DTC (1) produces the thienyl ester (2) with evolution of CO2 and formation of 2(5H)-thiophenone (3). In step 2, the added Hf(OTf)4 forms with (2) an activated complex (4), alcoholysis of which yields the ester (5) and a further molecule of 2(5H)-thiophenone.1 The procedure was also effective for converting [Pg.48]

---