Photolysis of diphenylzirconocene and 2,3-bis(methylene)bicyclo[2.2.2]octane in toluene at -25 °C yields biphenyl and (2,3-bis(methylene)bicyclo[2.2.2]octane)zirconocene (lg) (67.5% isolated yield).1g exhibits dynamic NMR spectra indicating rapid alternation of diene faces coordinated to zirconium (ring-flip mechanism). This degenerate intramolecular rearrangement is characterized by an extremely low activation barrier (⊿G≠-131°C = 7.1 ± 0.3 kcal/mol). 1g crystallizes in space group P1̄with a = 7.215(1) Å, b = 9.654(1) Å, c = 11.831(1) Å, α = 94.97(1)°, β = 91.81(1)°, and γ = 103.22(1)°. The X-ray structure determination reveals a pronounced metal alkyl character of the (diene)ZrCp2 moiety. Accordingly, 1g is easily reduced electrochemically to give a Zr(III) radical anion (7) observed by esr (g = 1.990; a(H) = 2.976 G; a(Zr) = 18.36 G).
The reactions of tBuN = VCl2 · DME with LiX (X = NHtBu, NR2, OSiPh3, SR, Alkyl, Cp) have been studied. LiNHtBu and LiCH3 furnish the binuclear diamagnetic tert-butylimido-vanadium( IV) compounds [(μ-NtBu)2V2X4]; in all other cases only the vanadium(V) compounds tBuN=VX3 and tBuN=VCpCl2 formed by disproportionation reactions of vanadium(IV) can be isolated. The syntheses of various mononuclear amido tert-butylimido-vanadium(V) complexes as well as of the binuclear complexes [μ-NtBu)2V2(NtBu)2Cl2] and [(μ-0)V2(NtBu)2Cp2Cl2] are also described. All compounds obtained have been characterized by 51V NMR spectroscopy. tBuN=V(OMe)3 was investigated by X-ray diffraction analysis; the molecular structure has been found to be that of a binuclear vanadium(V) complex with two bridging methoxo ligands.
Universal vitamin D supplementation is controversial. Preventative examinations and public health initiatives in former East Germany that included vitamin D prophylaxis for children were regulated by official recommendations and guidelines. The aim of this study is to analyse the impact of a standardised nationwide guideline for universal supplementation with 400 International Units (IU) vitamin D3/day during the first year of life on clinical and biochemical parameters and the influence of surrounding factors.
This is a cross-sectional analysis looking at data from a field study of 3481 term-born children during their first year of life that was conducted in 1989.
There were no significant clinical signs of rickets. 25 hydroxyvitamin D (25(OH)D) (mean and SEM, total analyses n=572) after birth (n=28) was 36(7) nmol/L, at 1 month 64(4) nmol/L (n=70, p<0.0001), 91(5) nmol/L at 3 months (n=95, p<0.0001), 65(8) nmol/L at 8 months (n=21, p=0.005) and ranged between 33 and 109 nmol/L until 12 months. Less than 0.2% of analyses revealed pathological levels for calcium or phosphate. Alkaline phosphatase (ALP) levels (n=690) were >1500 U/L (95th percentile) in 3.6%. Participants were on breastmilk or vitamin D-free formula, with solids added from 6 months of age. There were seasonal variations in 25(OH)D levels with a rise during spring and autumn. Thus this analysis is unique as sun exposure and supplementation can be considered as the only vitamin D sources.
We conclude that universal supplementation with 400 IU of vitamin D3 during the first year of life is safe and provides sufficient 25(OH)D levels in Germany.