Mononuclear iron(III) species with end-on and side-on peroxide have been proposed or identified in the catalytic cycles of the antitumor drug bleomycin and a variety of enzymes, such as cytochrome P450 and Rieske dioxygenases. Only recently have biomimetic analogues of such reactive species been generated and characterized at low temperatures. We report the synthesis and characterization of a series of iron(II) complexes with pentadentate N5 ligands that react with H 2 O 2 to generate transient low-spin Fe III −OOH intermediates. These intermediates have low-spin iron(III) centers exhibiting hydroperoxo-to-iron(III) charge-transfer bands in the 500−600-nm region. Their resonance Raman frequencies, ν O-O , near 800 cm -1 are significantly lower than those observed for high-spin counterparts. The hydroperoxo-to-iron(III) charge-transfer transition blue-shifts and the ν O-O of the Fe−OOH unit decreases as the N5 ligand becomes more electron donating. Thus, increasing electron density at the low-spin Mononuclear iron(III) peroxide species are implicated as intermediates in the mechanisms of oxygen activating biomolecules such as cytochrome P450, 1 heme oxygenase, 2 the antitumor drug bleomycin, 3 and Rieske dioxygenases, 4,5 as well as superoxide reductases from anaerobic bacteria. [6][7][8][9] Experimental evidence for some of these intermediates has

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Monodentate phosphoramidites based on BINOL or substituted BINOL are excellent ligands for the rhodium-catalysed asymmetric hydrogenation of olefins. Very high enantioselectivities were obtained with MonoPhos (7a) the simplest member of this class, a ligand that is prepared in a single step from BINOL and HMPT. Turnover numbers up to 6000 have been obtained in the hydrogenation of dehydroamino acid derivatives. Enantioselectivities in the hydrogenation of dehydroamino acids are solvent dependent; in non-protic solvents they range from 95 ± 99%. Itaconic acid and its dimethyl ester could be hydrogenated with 96 and 94% e.e., respectively. Hydrogenation of aromatic enamides gave the corresponding acylated amines in 86 ± 94% e.e. Several analogous phosphoramidite ligands have been prepared. Surprisingly, bidentate ligands gave poorer results, both in terms of rate as well as enantioselectivity. Taddol-based phosphoramidites led to poor e.e. and slow rates. Methyl substituents at the 3,3'-position of BINOL led to a sharply reduced rate and a somewhat lower enantioselectivity. Bromo substituents at the 6,6'-position led to a slightly reduced rate but little effect was seen on enantioselectivity. Use of octahydro-MonoPhos (11) gave results that were very similar to those obtained with 7a. The rate of the reaction is dependent on the hydrogen pressure, however, the enantioselectivity is not affected. The rate of the dehydroamino acid hydrogenation also increases if the ligand to rhodium ratio is reduced from 2.2 to 1.5 or even to 1.0; yet, there is no deleterious effect on the enantioselectivity. Catalytic activity ceases with L/Rh 3 when dehydroamino acid derivatives were used as substrate. The reaction shows a positive non-linear effect, which confirms the presence of Rh-complexes with more than one ligand. Following the hydrogenation of methyl 2-acetamidocinnnamate with Rh(nbd) 2 BF 4 /7a by electrospray mass spectrometry showed the presence of several rhodium species. Notable are the presence of [Rh(7a)] 3 and [Rh(7a)] 4 . There is at present insufficient evidence to conclude if the active catalytic species carries one or two ligands. In view of the low cost of MonoPhos this invention might well lead to a broader application of asymmetric olefin hydrogenation for the production of enantiopure amino acids and amines.

Functional models for iron-bleomycin Roelfes, J.G.; Lubben, M; Leppard, S.W; Schudde, E.P.; Hermant, R.M.; Hage, R.; Wilkinson, E.C.; Que, L.; Feringa, B.L.; Que Jr., Lawrence

The synthesis of the amines la-f by hydrogenation of the corresponding imines 4a-f occurs with a diastereoselectivity ranging from 33% to higher than 90%. The absolute configurations of lb-f have been determined by either X-ray analysis (lb and lc), chemical correlation (le and If), or correlation via 1H NMR shifts (Id).The difference in the observed diastereoselectivities is rationalized by a mechanism in which the hydrogenation occurs exclusively at the less hindered side of the imines, which results in the formation of amines 1 from the anti and of amines 2 from the syn imines.Chiral amines constitute a class of compounds that have a wide application in organic chemistry as resolving agents1 and chiral building blocks,2 as well as chiral auxiliaries in stereoselective synthesis.3 Naturally occurring amines such as brucine, ephedrine, and amino acids, as well as synthetic amines such as -methylbenzylamine and 2amino-l-butanol, are frequently used. An advantage of the use of natural chiral amines is that they occur in an optically pure form, while for the synthetic amines a resolution procedure or a stereoselective synthesis is necessary. However, a drawback of the first class is that they often are only available in one enantiomeric form.

Herein, we report the automated parallel synthesis of solution-phase libraries of phosphoramidite ligands for the development of enantioselective catalysts. The ligand libraries are screened in situ in the asymmetric rhodium-catalyzed addition of arylboronic acids to aldehydes and imines. It is shown that the described methodology results in the straightforward discovery of leads for highly efficient enantioselective catalysts.

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A new direct functionalization of N-methylanilino-methylpolystyrene (a = 0.31 ) with p-nitrobenzenediazonium chloride yields an azastilbene modified polystyrene with excellent solubility properties.iii