Nicholas complex

To achieve exclusive 1,2-additions (see 12) the triple bond has to be hidden in a Nicholas complex [3]. This complexation not only protects the triple bond but... 

These data give a very strong encouragement to look for intramolecular epoxide cleavage in the presence of a cobalt complexed triple bond since this Nicholas complex has been shown to strongly favor a positive charge in the a-position to this complexed triple bond. 

It is certainly noteworthy that this highly regioselective complex directed endo-mode cyclization was shown to be absolutely independent of the electronic properties of the triple bond substituent This means that one can switch from electron poor to electron rich substituents by employing the Nicholas complex. 

Melikyan GG, Nicholas KM (1995) The Chemistry of Metal-Alkyne Complexes. In Stang... 

Years earlier, Nicholas and Ladoulis had found another example of reactions catalyzed by Fe2(CO)9 127. They had shown that Fe2(CO)9 127 can be used as a catalyst for allylic alkylation of allylic acetates 129 by various malonate nucleophiles [109]. Although the regioselectivites were only moderately temperature-, solvent-, and substrate-dependent, further investigations concerned with the reaction mechanism and the catalytic species were undertaken [110]. Comparing stoichiometric reactions of cationic (ri -allyl)Fe(CO)4 and neutral (rj -crotyl ace-tate)Fe(CO)4 with different types of sodium malonates and the results of the Fe2(CO)9 127-catalyzed allylation they could show that these complexes are likely no reaction intermediates, because regioselectivites between stoichiometric and catalytic reactions differed. Examining the interaction of sodium dimethylmalonate 75 and Fe2(CO)9 127 they found some evidence for the involvement of a coordinated malonate species in the catalytic reactions. With an excess of malonate they... 

Not surprisingly, the cobalt-complexed ether products obtained by the Nicholas reaction can be subjected directly to the Pauson-Khand sequence (Scheme 7).244... 

An amorphous material sometimes referred to as amorphous poly(ethylene oxide), aPEO, consists of medium but randomly-variable length segments of poly(ethylene oxide) joined by methyleneoxide units. Fig. 5.13 (Wilson, Nicholas, Mobbs, Booth and Giles, 1990). These methyleneoxide units break up the regular helical pattern of poly(ethylene oxide) and in doing so suppress crystallisation. The aPEO host polymer and its salt complexes can crystallise below room temperature, but this is not detrimental to the properties of the polymer-salt complexes at or above room temperature. Similarly, dimethyl siloxy units have been introduced between medium length poly(ethylene oxide) units to produce an amorphous polymer. Fig. 5.14 (Nagoka, Naruse, Shinohara and Watanabe, 1984). 

An EU COST project under action D23 Metachem Metalaboratories for Complex Computational Applications in Chemistry . Project number D23/0001/01 European Metalaboratory for multireference quantum chemical methods (01/02/200118/07/2005). Participants P. Carsky, J. Pittner (J. Heyrovsky Institute, Prague, Czech Republic), 1. Hubac (Comenius University, Slovakia), S. Wilson (Rutherford Appleton Laboratory, UK), W. Wenzel (Universitat Dortmund Germany), L. Meissner (Nicholas Copernicus University Poland), V. Staemmler (Ruhr Universitat Bochum Germany), C. Tsipis (Aristotle University of Thessaloniki, Greece), A. Mavridis (National and Kapodistrian University of Athens, Greece). 

Interestingly, seven-membered conjugated diyne complex 16 is produced by the acid-promoted Nicholas reaction of the dicobalt-coordinated bispropargylic complex (Equation (7)). The cyclization proceeds via an intramolecular coupling reaction between a propargyiic cation and an alkene produced after dehydration. The molecular structure of seven-membered diyne complex 16 is confirmed by X-ray analysis, although the decomplexation is not successfully carried out. 

In 1993, Nicholas and his co-worker developed the stereospecific propargylic alkylation of chiral propargylic alcohols 30 with enol silanes 31 by using a stoichiometric amount of [Co2(CO)5L] (L = phosphite), but separation procedures of the produced diastereoisomers are necessary twice on the way to obtain the compounds specifically alkylated at the propargylic position 32 (Scheme 5). In 2001, Montana and his co-worker reported the diastereo-selective Nicholas alkylation of propargylic acetal complexes 33 bearing a chiral auxiliary with various enol silanes 34 (Equation (14)). A high diastereoselectivity is observed, but unfortunately, only low to moderate enantioselec-tivities are achieved in all cases. 

Combinatorial chemistry and solid-phase synthesis have evolved in the last decade to become one of the most important techniques to save time for drug discovery. To reach its full potential, the solid-phase synthesis has to incorporate many versatile organometallic reactions developed over recent several decades. The first example of the Nicholas reaction on solid phase was reported by Kann and his co-workers in 2002, which involves the reaction of polymer-bound cobalt complexes 51 with various carbon-centered nucleophiles in the presence of a Lewis acid to... 

Pierre-Joseph Macquers Elemens de chimie th orique, (1749) and Elemens de chimie practique (1751) became the first significant French successor to Nicholas Lemerys Cours de chymie, first published in 1675. Unlike earlier works it was an attempt to offer chemistry for its own sake, independent of medicine. It was intended for the absolute Novice in Chymistry to lead him from the most simple truths. .. to the most complex. Hence he begins with the elements, then moves on to saline substances (acids, alkalies, and their combinations) the volatile sulphureous spirit, sulphur, phosphorus, and the neutral salts, which have an earth or a fixed alkali for their bases. Then on to the metals, which are scarcely more compounded than the saline ... 

Lander, Eric S., and Nicholas J. Schork. 1994. "Genetic Dissection of Complex Traits." Science 265 2037-48. 

Nicholas anthracite, we investigated the effect of particle size on the rate of volatile matter release at constant temperature from other anthracites. In all cases H2 represented a large fraction of the total volatile matter released. Evolution rates were measured at 800°C. on 5.5-gram samples. As previously discussed, at 800°C. plots of the volume of volatile matter released vs. the log of time gave straight lines, with the slope of these lines (dq/d log t) being a measure of the relative rate of volatile matter release. Results are summarized in Table III and Figure 10. The effect of particle size on volatile matter release rate is complex and depends upon the anthracite studied. However, in every case particle size has a pronounced effect on volatile matter release rate at constant temperature. 

In a closely related study, complex 26, where L = PPh3, has been prepared in the absence of water by Nicholas and its structure has been determined by X-ray crystallography (Fig. 12)(104). Investigations employing a Rh-D complex, coupled with the lack of sensitivity of the reaction to H20, led these researchers to propose a route involving rhodium promoted reductive disproportionation of C02 followed by hydrogen transfer from Rh to the oxygen of the coordinated carbonate (Scheme 9) (105). 

Furthermore, as shown in Figure 3.9, Nicholas and coworkers isolated azodioxide complex 37 as a reactive intermediate, which could be characterized by X-ray crystal structure analysis [132, 133], Isotope labeling studies established complex 37 to be indeed the catalytically active species. 

Prior to these recent studies Nicholas and coworkers reported on the Fe2(CO)9-catalyzed reaction between allylic acetates and sodium dimethylmalonate (Scheme 7.26) [39]. Detailed mechanistic studies indicated that the Fe(0) complex acts as a precatalyst that is activated in situ upon reaction with the nucleophile. The... 

Gregorio et al., 1998). T-cap in turn interacts in vitro with the stretch-dependent IsK ion channel (Furukawa et al., 2001), MLP (Knoll et al., 2002), and myostatin (Nicholas et al., 2002). The titin Zl-Z2/T-cap complex may function as a versatile adaptor complex that couple titin s N-terminus to myofibrillar signaling. 

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