O , precursors

Dimethylindene derivatives were hydroaluminated with BujAlH using Ni(acac)2 as the nickel(O) precursor (Scheme 2-13) [9]. Hydroalumination of the trisubstituted double bond in 9 was also achieved, although more forcing conditions... 

For unsaturated lactones containing an endocyclic double bond also the two previously described mechanisms are presumably involved and the regio-selectivity of the cyclocarbonylation is governed by the presence of bulky substituents on the substrate. Inoue and his group have observed that the catalyst precursor needs to be the cationic complex [Pd(PhCN)2(dppb)]+ and not a neutral Pd(0) or Pd(II) complex [ 148,149]. It is suggested that the mechanism involves a cationic palladium-hydride that coordinates to the triple bond then a hydride transfer occurs through a czs-addition. Alper et al. have shown that addition of dihydrogen to the palladium(O) precursor Pd2(dba)3/dppb affords an active system, in our opinion a palladium-hydride species, that coordinates the alkyne [150]. 

As cyclic amines are at the heart of medicinal chemistry, there is always interest in new methods for their preparation. Marco Ciufoiini of the Universitc Claude Bernard in Lyon reports (Organic. Lett. 5 4943, 2003) the preparation of a series of dihydro indole derivatives, exemplified here by 3, 6, and 9, by free radical cyclization of an N-O precursor. The N-O precursor can be prepared from the corresponding bromide, as illustrated by the conversion of 1 to 2 and of 4 to 5. Alternatively, a radical precursor such as 8 can be prepared separately. The generated radical is then trapped by 7 to make a new radical, that cyclizcs to 9. 

To date, only nickel, palladium, and platinum have formed homoleptic metal(O) isocyanide clusters. This may be due to two factors, either the greater tendency to nucleation in the group or simply the ready access to the highly labile metal(O) precursors M(COD)2 [M = Ni (137), Pt (138)]. 

Figure 4, Steady-shear viscosity versus shear rate for PDM-PMAS. Key O, precursor A, Nc = 10 O, = 12 , Nc = 14 A, Nc = 16 and 9, Nc = 18. Nc is the number of side-chain carbon atoms.

The crystal structure of this complex is not known, but the structure of the tris(dibenzylideneacetone)dipalladium(o) precursor has been reported [167, 168]. The two palladium atoms have a trigonal planar geometry arising from bonding to the olefinic groups of the three ligands. 

Multi-nuclear NMR (H, C, O) - Precursor and Solution /, s Structure, bonding environment 50, 55... 

Both the Mg/Al/La/0 and Mg/Al/Ce/0 precursors give XRD patterns corresponding to the presence of a hydrotalcite-like structure and a Me hydroxy carbonate phase (Me = La, Ce). The La containing material is much better crystallized than the Ce containing one. The Mg/Al/Zr/0 precursor is characterised by a pattern similar to that of the Zr/O precursor, indicating the absence of any crystalline precipitate. In this case, therefore, the presence of Zr hinders the development of the crystalline hydrotalcite-like precursor. 

After the specimens were loaded into the furnace tube, they were heated in Nj to 700°C, prior to introduction of ethane. With the tube still maintained at 700°C, ethane was admitted at a flow rate of 94 cmJ/min and the reaction allowed to continue for periods of between 1.0 to 6.0 hours. The weight of deposited carbon was determined by difference of the starting and final specimen weights. In addition, the chemical state of iron in the FeO and f O ) precursors was determined by room temperature Mossbauer spectroscopy after 2.Oh of reaction in ethane at 700°C. 

The product of a VOC s concentration and its OH rate constant will determine in an approximate manner its relative role as an ozone precursor. A species with a large concentration will not necessarily be an important O, precursor if it is unreactive conversely, another compound with a small concentration can be important if it is extremely reactive. (An example is methane, typically the most abundant VOC in the atmosphere but of negligible importance in producing ozone on urban or regional scales because of its extremely low reactivity.) An airmass can have a large total VOC concentration but a low ozone-producing capacity if the VOCs present are relatively unreactive. 

It is to be expected that such phases may also control the later crystallization of SiC by heterogeneous nucleation. Such effects have been described in [150, 165, 166] concerning the crystallization of Si-C-(O) precursors containing metals like Ti, Zr, Al, i.e., precursor systems from which different types of Tyranno fibers are formed [167]. In the case of the Al-containing system it was observed that - under the given unusual conditions - SiC polytype 2H is stabilized by AI2OC which is isostructural to SiC 2H. 

Higher molecular weight oligomers and polymers are obtained when ethylene is reacted with P—0 chelate catalysts synthesized by the oxidative addition of phosphorus ylides to zerovalent nickel compounds in the presence of triphenylphosphine or other ligands. " As shown in eq 9, the catalysts are easily prepared from keto—ylides by oxidative addition of a P—Ph bond to a nickel(O) precursor like Ni(COD)2. " In this manner, a wide... 

Another early popular NP synthetic method used the thermal decomposition of metal(O) precursors in the form of, for instance, metal carbonyls (Fe, Co, Ni, Ru, Rh, Ir) in the presence of stabilizing polymers [8e- ]. This method was not only useful for catalytic purposes, but in 1996 Hess and Parker [8h] and Thomas [8i] also reported in on the ferromagnetic properties (ferrofluids) and used the thermal... 

The preparation comprises the following steps synthesis of the V/P/O catalyst precursor, preparation of the 5 wt% Si02 solution of PSA, preparation and spray drying of the V/P/O precursor-PSA slurry, calcination and activation. 

C. P. Kubiak, R. Eisenberg, Molecular A frames. Synthesis from binuclear rhodium(O) precursors and catalytic activity in the water gas shift reaction and alkyne hydrogenation, J. Am. Chem. Soc. 102 (1980) 3637-3639. 

Scheme 7.8 Scheme for the fabrication of hierarchical MoS /PANI nanowires through facile polymerization and hydrothermal treatment of MOjOj lC H NlyH O precursor. Panels are reproduced with permission [115], Copyright 2013, Wiley. 

The most often used palladium(O) precursors are Pd2(dba)3 or Pd(dba)2 (dba = dibenzylidenacetone this is released during the formation of the active complex). 

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