Triple directed metal oxidation

The preparation of stable complexes with transition metal-phosphorus triple bonds is of fundamental importance and constitutes a novel field of coordination chemistry. The contribution of B.P. Johnson, G. Balazs, and M. Scheer reports the synthesis and isolation of such complexes for transition metals in high oxidation states in contrast, the corresponding complexes with transition metals in low oxidation states were found to exist only as highly reactive intermediates. A synthetic concept to generate directly such intermediates is documented. The present knowledge of the reactivity pattern of all these types of compounds is summarized in chapter 1. 

VIBRATIONAL SPECTROSCOPY Infrared and Raman spectroscopies have proven to be useful techniques for studying the interactions of ions with surfaces. Direct evidence for inner-sphere surface complex formation of metal and metalloid anions has come from vibrational spectroscopic characterization. Both Raman and Fourier transform infrared (FTIR) spectroscopies are capable of examining ion adsorption in wet systems. Chromate (Hsia et al., 1993) and arsenate (Hsia et al., 1994) were found to adsorb specifically on hydrous iron oxide using FTIR spectroscopy. Raman and FTIR spectroscopic studies of arsenic adsorption indicated inner-sphere surface complexes for arsenate and arsenite on amorphous iron oxide, inner-sphere and outer-sphere surface complexes for arsenite on amorphous iron oxide, and outer-sphere surface complexes for arsenite on amorphous aluminum oxide (Goldberg and Johnston, 2001). These surface configurations were used to constrain the surface complexes in application of the constant capacitance and triple layer models (Goldberg and Johnston, 2001). 

With Zn Lewis acids, only single a-insertion of alkynes (—> 42) is observed, while with AlMes double alkenylation (— 43) dominates. It is proposed that oxidative Ni(0) insertion to the 2-CH bond, hydronickelation of the triple bond, alkenyl transfer to C-2 of the pyridine, and reductive Ni-elimination are the decisive steps in the catalytic cycle, (d) The pyridyl residue may serve as a directing group in C-H insertion reactions of phenyl substituents at pyridine mediated by transition metals like Cu and Pd. For instance, 2-phenylpyridine can be regioselectively halogenated, acetoxylated, and cyanided (- products 44, 45, and 47) in the presence of Cu(OAc)2 [92] or amidated — 46) in the presence of Pd(OAc)2 [93] ... 

Soft bases either have lone pairs on atoms of the second or later row of the periodic table (e.g.. Cl, Br , and PPhs) or have double or triple bonds (e.g., CN , C2H4, and benzene) directly adjacent to the donor atom. Soft acids can come from the second or later row of the periodic table (e.g., Hg +) or contain atoms that are relatively electropositive (e.g., BH3) or are metals in a low (<2) oxidation state (e.g., Ni(0), Re(I), Pt(II), andTi(II)). Organometallic chemistry is dominated by soft-soft interactions, as in metal carbonyl, alkene, and arene chemistry, while traditional coordination chemistry involves harder metals and ligands. 

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