Treatment with zero-valent metals

Information concerning the pathways and products of reactions of polyhalogenated solvents with zero-valent metals may be critical to the success of in situ treatment techniques. Fennelly and Roberts (1998) have investigated the reduction of 1,1,1-trichloroethane (1,1,1 -TCA) by Fe(O) and Zn(O) and by two bimetallic (nickel/iron and copper/iron) reductants. The following products were detected at measurable concentrations as intermediates and/or final products ... 

In a one-step treatment of the zero-valent metals a /-butyl substituted pentafulvalene derivative yielded penta-fulvalenyl dilanthanide(ll) sandwich complexes (Ln = Sm, Yb). A two-electron transfer of a lanthanide to the pentafulvalene (= Pf), a system with 10 7t-electrons, gave a Pf2 dianion (Scheme 41).216... 

Historically, vinylidene complexes of zero-valent pentacarbonyl Group 6 metals appeared as a fleeting intermediate for the preparation of Fischer-type carbene complexes. Probably the first example of the formation of such a pentacarbonyl vinylidene complex of a Group 6 metal was proposed in 1974 by Fischer et al, who examined the reaction of pentacarbonyl[hydroxy(methyl)carbene] chromium 1 with dicyclohexylcarbodiimide(DCC) [3]. Thus, treatment of 1 with DCC in CH2CI2 at —20°C rt gave a novel azetidinylidene complex 2 in 47% yield. As a possible... 

With this end in view, phenyldimcthylsilyl tri-n-butylstannane was added under the influence of zero-valent palladium compound with high regioselectivity and in excellent yield to the acetylene 386 to give the metallated olefin 387 (Scheme 56). The vinyl lithium carbanion 388 generated therefrom, was then converted by reaction with cerium(lll) chloride into an equilibrium mixture (1 1) of the cerium salts 389 and 390 respectively. However, the 1,2-addition of 389 to the caibonyl of 391, which in principle would have eventually led to ( )-pretazettine, did not occur due to steric reasons — instead, only deprotonation of 391 was observed. On the other hand, 390 did function as a suitable nucleophile to provide the olefinic product 392. Exposure of 392 to copper(II) triflate induced its transformation via the nine membered enol (Scheme 55) to the requisite C-silyl hydroindole 393. On treatment with tetrafluoroboric acid diethyl ether complex in dichloromethane, compound 393 suffered... 

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), a photosynthetic inhibitor that is used in large quantities for weed control in com and sorghum, has been treated electrochemically in aqueous solution on reticulated vitreous carbon cathode in the presence of noble-metal catalysts (Stock and Bunce 2002). Elec-trocatalytic hydrogenolysis to 2-ethylamino-4-isopropylamino-s-triazine occurs in quantitative yield, and is most efficient with Pd-based catalysts. Current efficiency increases with increasing atrazine and catalyst concentration, and decreasing current density. The Authors observed a time lag between the start of the electrolysis and the appearance of the dechlorinated products, which was attributed to the absorption of hydrogen by the palladium lattice. As alternative to the electrochemical treatment, the degradation of chlorinated triazines by zero-valent-iron was already mentioned (Dombek et al. 2004). 

Oxidative addition of an allyl halide to a zero-valent complex (method D) or treatment of a trifluorophosphine metal late complex with an allylic halide followed by loss of PF3 (method E) have also been briefly reported. 

Alkynyl Grignard reagents may not give such good yields as alkali metal derivatives. Also, treatment of the zero-valent compound (Ph3P)4Pt with BrC CPh gives the mono-alkynyl (Ph3P)2Pt(C CPh)Br [46a]. 

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