the known carbide clusters can be viewed as derived from an Fe4C cluster, while the heterometallic nitride cluster can be viewed as derived from an Ru4N cluster. The metal-metal bonds in the Ru4 framework are considerably stronger than those in the Fe4 framework, and substitution of another metal into the Ru4 framework could have a smaller effect on the overall stability of the metal framework than substitution of a different metal into the Fe4 framework. Thus, when one Rh atom replaces one Fe atom in [Fe4C(CO)12]2", the overall perturbation of the electronic structure of the cluster is much larger than when one Fe atom replaces one Ru atom in [Ru4N(CO)12]~, and it is perhaps not surprising that in the former case one isomer is strongly preferred. ConclusionsA comparison of the electronic structures of [Fe4C(CO)12]2", [Fe4N(CO)12]", and Fe40(C0)i2 shows that the major consequence of changing the interstitial atom from carbon to nitrogen to oxygen is a significant weakening of the bonds between the interstitial atom and the wingtip metal atoms. Because of the small size of the O atom, the -Fe interactions may not be sufficient to maintain the same butterfly cluster geometry as that observed for [Fe4C(CO)12]2" and [Fe4N(CO)12]". The [Ru4N-(CO)12J-anion is found to be isostructural with [Fe4N(CO)12]" and [Os4N(CO)12]". The only major difference in the electronic structures of [Fe4N(CO)12]" and [Ru4N(CO)12]" is the increased strength of the metal-metal bonds in [Ru4N(CO)12]~. The electronic structures of the two isomers of [FeRu3N(CO)12]" are found to be very similar. Substitution of Fe into the Ru4 framework of [Ru4N(CO)12]' results in relatively small perturbations of the electronic structure of the cluster, and this probably accounts for the occurrence of the two isomers. Protonation of each of the nitride clusters results in a hydride cluster in which the hydrogen bridges the hinge metal atoms. In each case, this product can be associated with the presence of a high-energy cluster framework bonding orbital that is localized across the hinge of the cluster.Acknowledgment. The portion of this research that was carried out at the University of Minnesota was supported by a grant from the National Science Foundation. Supplementary Material Available: Lists of the temperature factors, H atom positions, and all distances and angles (12 pages); a list of the structure factors (22 pages). Ordering information is given on any current masthead page.

Mono-, bis-, and tris(sulfito) complexes of Fe(III), produced during the reaction of aquated Fe(III) and S(IV) oxides, undergo two successive redox reactions and produce Fe(II), S042-, and S2062-. Spectrophotometric and kinetic measurements as well as ion chromatographic analyses of the reaction products were performed under the conditions 2.5 X 10-4 < [Fe(III)] < 6 X 10-3 M, 5 X 10-4 < [total S(IV)] < 3 X 10~2 , 1.3 5 pH < 2.9, 13 < T < 40 °C, and 0.1 M ionic strength. First-order rate constants for the first redox step are 0.14, 0.10, and 0.055 s"1 11at pH = 2.5 and 25 °C for the tris-, bis-, and mono(sulfito) complexes, respectively. A pH dependence with a maximum rate constant at pH = 2.2 was observed. The second redox step has a rate constant of 0.01 s"1 and exhibits only a slight pH dependence. Oxygen does not effect these steps but does initiate a more rapid redox reaction prior to the two steps mentioned before. It drastically affects the total amount of S(IV) oxidized to S042" and S2062". The mechanistic aspects of the reported data are discussed in reference to the suggested complex formation mechanism (part 1) and results reported in the literature.

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Two novel carbohydrate-derived pyridyl (PYOX)-and cyclopropyl (CYBOX)-substituted oxazoline ligands were prepared from D-glucosamine hydrochloride and 1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy-β-D-glucopyranose hydrochloride in two steps, respectively. The sugar-annulated PYOX ligand formed a stable metal complex with Pd(II), which was fully characterized by NMR spectroscopy and X-ray crystallography. NMR and X-ray analysis revealed a change of the conformation in the sugar moiety upon complexation with the palladium(II) species. Both glycosylated ligands resulted in high asymmetric induction (up to 98% ee) upon application as chiral ligands in the Pd-catalyzed allylic alkylation of rac-1,3-diphenylallyl acetate with dimethyl malonate (Tsuji-Trost reaction). Both ligands provided mainly the (R)-enantiomer of the alkylation product.

SummaryIn the present work, we describe a convenient synthesis of spiro-fused D-fructo- and D-psico-configurated oxazoline ligands and their application in asymmetric catalysis. The ligands were synthesized from readily available 3,4,5-tri-O-benzyl-1,2-O-isopropylidene-β-D-fructopyranose and 3,4,5-tri-O-benzyl-1,2-O-isopropylidene-β-D-psicopyranose, respectively. The latter compounds were partially deprotected under acidic conditions followed by condensation with thiocyanic acid to give an anomeric mixture of the corresponding 1,3-oxazolidine-2-thiones. The anomeric 1,3-oxazolidine-2-thiones were separated after successive benzylation, fully characterized and subjected to palladium catalyzed Suzuki–Miyaura coupling with 2-pyridineboronic acid N-phenyldiethanolamine ester to give the corresponding 2-pyridyl spiro-oxazoline (PyOx) ligands. The spiro-oxazoline ligands showed high asymmetric induction (up to 93% ee) when applied as chiral ligands in palladium-catalyzed allylic alkylation of 1,3-diphenylallyl acetate with dimethyl malonate. The D-fructo-PyOx ligand provided mainly the (R)-enantiomer while the D-psico-configurated ligand gave the (S)-enantiomer with a lower enantiomeric excess.