Complexation to metals

Several metal complexes have been described with urea, thiourea or dimethyl derivatives [49,50]. We will focus in this section on the coordination chemistry of substituted ureas and thioureas used as neutral Ugands as well as many ureato and thioureato anions complexed to metal centres. 

Beside these catalytically active metallophosphine dendrimers (see above), preliminary studies on the chemical properties of phoshorus-based dendrimers complexed to metals such as platinum, palladium and rhodium have been described by Majoral, Caminade and Chaudret [21], They showed that these macromolecules (see Scheme 13) could be useful for the (in situ) generation of metallodendrimer catalysts. 

Very recently, spectroscopic investigations have provided evidence that at least two types of molecular NO can exist simultaneously on transition metal surfaces (12,15.19,20, 21, 22), thus supporting the interesting possibility that the rich diversity of nitrosy1-metal chemistry extends from metal complexes to metal surfaces. Two states of molecular NO have been observed on Ru(001) by electron energy loss spectroscopy (EELS) (13), and also by X-ray photo-... 

Functionalized oxetanes 11, with R = indenyl or fluorenyl and X = PR2, have been prepared and studied in detail by 1H, 13C, and 31P NMR spectroscopy <2001EJI949>. They were then converted into tripod ligands via a nucleophilic ring opening for complexation to metal ions. 

According to several workers (8,9,18) the interaction of Lewis acids and crotylnickel halides involves transfer of a halide from the r-allylic complex to metal halide... 

A high CO pressure would shift equilibrium (4.3) to the left and the catalytic reaction would become slower. In this complex CO is a far better ligand than an alkene. On the other hand the reaction uses CO as a substrate, so it cannot be omitted. Furthermore, low pressures of CO may lead to decomposition of the cobalt carbonyl complexes to metallic cobalt and CO, which is also undesirable. Finally, the product alcohol may stabilize divalent cobalt species which are not active as a catalyst ... 

Reactions with Metal Complexes. The reactions of acetylenes with metal complexes or ions to give ir-bonded adducts is well known (e.g., eq. 47). We have therefore investigated the reactions of 1 with a host of metal complexes to determine if the MosMo triple bond would form similar "ir-complexes" to metals. 

Carbene species can be stabilized by complexation to metals and transferred to olefinic substrates in catalytic reactions. Although the main industrial application of carbenes is in metathesis (Chapter 6), an important application in the area of fine chemicals is to asymmetric cyclopropanation. 

Figure 2.46 Molecular structure of [ Nd(L °)3(THF) 2(ir-bpm)],hydrogen atoms are omitted. Displacement ellipsoids are drawn at the 50% prohahihty level [26a]. (Reprinted with permission from G. Zucchi, O. Maury, R Thuery and M. Ephritikhine, Structural diversity in neodymium hipyrimidine compounds with near infrared luminescence from mono- and binuclear complexes to metal-organic frameworks, Inorganic Chemistry, 47, 10398-10406, 2008. 2008 American Chemical Society.)...

The key reaction of this 1-octanol process is telomerization of butadiene with a palladium complex catalyst. Known attempts to commercialize the palladium complex-catalyzed telomerization have failed, in spite of great efforts, for the following reasons (1) palladium complex catalysts are thermally unstable and tbe catalytic activity markedly decreases when, as a means of increasing the thermal stability, the ligand concentration is increased (2) a sufficiently high reaction rate to satisfy industrial needs cannot be obtained (3) low selectivity and (4) distillative separation of reaction products and unreacted butadiene from the reaction mixture causes polymeric products to form and the palladium complex to metallize. Kuraray succeeded in 1991 in commercializing the production of 1-octanol using hydrodimerization of butadiene. 

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