Main group sulfides

The MEG method seems to be of considerable general utility even for compounds in which one would expect considerable covalency, so long as the structure is relatively compact and does not involve important angular variables. For example, the geometries of main-group sulfides and nitrides are predicted fairly accurately by this method (Muhihausen and... 

The progress on S-C bond activation, which covers the reduction of a C-S bond to a C-H bond, cross coupling reaction of sulfides with main group organometaUic nucleophiles, ring opening reactions of thietanes and thiiranes, and desulfurization of thiols, sulfides, and thiophenes has already been reviewed elsewhere [6-10], and... 

The lone pair MO of the free amine and phosphine possesses at symmetry in Cjt, local symmetry. As anticipated, this MO undergoes considerable stabilization as coordination to the metal occurs. The lone pair stabilization energies of amines have been found to be greater than those of phosphines with respect to main group acceptors such as BH3, O, and S (32, 113, 210). The sulfide ligands feature two MOs with significant lone pair character. 

These complexes are the first examples of multifunctional catalysts and demonstrate impressively the opportunities that can reside with the as yet hardly investigated bimetallic catalysis. The concept described here is not limited to lanthanides but has been further extended to main group metals such as gallium [31] or aluminum [32]. In addition, this work should be an incentive for the investigation of other metal-binaphthyl complexes to find out whether polynuclear species play a role in catalytic processes there as well. For example, the preparation of ti-tanium-BINOL complexes takes place in the presence of alkali metals [molecular sieve ( )]. A leading contribution in this direction has been made by Kaufmann et al, as early as 1990 [33], It was proven that the reaction of (5)-la with monobromoborane dimethyl sulfide leads exclusively to a binuclear, propeller-like borate compound. This compound was found to catalyze the Diels-Alder reaction of cyclopentadiene and methacrolein with excellent exo-stereoselectivity and enantioselectivity in accordance with the empirical rule for carbonyl compounds which has been presented earlier. 

Barthelmehs, K. L., G. V. Gibbs, and M. B. Boisen, Jr. (1990). Bond length and bonded radii variations in sulfide molecules and crystals containing main group elements a comparison with oxides. Amer. Mineral 74, 620-26. 

Catalytic reactions have the advantage over the methods discussed so far in that the chiral catalyst need not be added in stoichiometric amounts, but only in very small quantities, which is important if not only the metal (very often a precious one) but also the chiral ligand are expensive. Among the ferrocenes, phosphines are by far the most important catalysts for stereoselective reactions, and are covered in Chapter 2 of this book. We will therefore focus here mainly on the catalytic applications of chiral ferrocenes not containing phosphine groups. Only recently, some progress has been made with such compounds, mainly with sulfides and selenides, and with amino alcohols in the side chain (for this topic, see Chapter 3 on the addition of dialkyl zinc to aldehydes). 

Main group element derivatives containing three or four ferrocenyl thiolate ligands are accessible from the corresponding element chlorides and Fc-SLi. Thus, the reaction of PCI3 with a suspension of 3 equivalents Fc-SLi in toluene — THF (3 1) leads to tris(ferrocenyl thiolato) phosphine, P(SFc)3 the oxide and sulfide, P(0)(SFc)3 and P(S)(SFc)3, are formed as side-products in addition to Fc-SS-Fc. The corresponding tris (ferrocenyl thiolato) element compounds As(SFc)3 and Sb(SFc)3 are also known the antimony derivative decomposes under the influence of either air or light [235]. 

They compute Laplacian and bond critical point properties of sulfide bonds containing first- and second-row main group M-cations and compare them with oxide bonds. The Laplacian maps of the distributions show that the VSCC of the sulfide anion is highly polarised and extends into the internuclear region of the M-S bonds, coalescing with the VSCCs of the more electronegative first-row cations. On the other hand, maps for a corresponding set of oxide molecules show that the oxide anion tends to be less polarised and more locally concentrated in the vicinity of its valence shell, particularly when bonded to second-row M-cations. 

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