Me 2 NC 2 H 4 C 5 Me 4 Li reacts with Cr(THF) 3 Cl 3 to give (η 1 :η 5 -Me 2 NC 2 H 4 C 5 Me 4 )CrCl 2 , in which the complexation of the N-donor atom to the metal atom has been confirmed by X-ray crystallography. A series of related compounds, e.g. (η 1 :η 5 -cyclo-C 4 H 8 NSiMe 2 OSiMe 2 C 5 H 4 )-CrCl 2 , has been prepared by varying the substituents on the organic ligand. Further reaction with organomagnesium reagents leads to formation of the corresponding dialkyl-Cr complexes. Related species have been prepared containing imine-, alkoxy-, and alkylthiosubstituted cyclopentadienyl groups as well as the C-donor ligand tetramethylimidazol-2ylidene. Treatment of these compounds with methylalumoxane (MAO) leads to the formation of highly active catalysts for the oligomerization, polymerization, and copolymerization of ethylene.
An oligomeric gold(III) compound containing dicarbanionic chelating 4,4'-di-tert-butylbiphenyl was prepared via transmetallation using the corresponding organotin(IV) compound. The reactivity of the chloro-bridged oligomer with various species including neutral N-, P-, and C-donor ligands as well as monoanionic S- and Se-ligands was investigated. Some of the products were characterised by X-ray crystallography. The photophysical properties of two derivatives were studied.
A series of both mono- and dinuclear gold(I) phosphine complexes containing monoanionic seleno- and thiosemicarbazones as ligands were prepared and fully characterized by spectroscopic methods and, in some cases, by single crystal X-ray diffraction. The in vitro anti-malaria activity of some of these compounds was investigated in chloroquine sensitive strains of Plasmodium falciparum. The IC(50) results show that the sulfur containing compounds exhibit activity similar to that of chloroquine, whilst the selenium derivatives display only moderate anti-malaria activity.
-arene}] (3; R 1,2,4-tri-tert-butyl) is described. A unique feature of the compound is its h 4 :h 4 antifacial-coordinated arene ligand, which displays complete planarity, as determined by X-ray crystallography, and represents the first example of its kind. In 3 two opposite carbon atoms of the arene moiety are bonded to both cobalt centers. To probe possible reasons for arene lability in this complex we compared arene exchange with benzene and azulene in 3 and in the related complex [{(h 5 -Cp -arene}] 4 were performed with the semiempirical ZINDO approximation. From a crossover exchange experiment between 1, 3, benzene, and azulene it was deduced that arene exchange in these tripledeckers proceeds by a dissociative pathway involving mononuclear {(h 5 -Cp R )Co} intermediates (R Me 5 , 1,2,4-tri-tert-butyl). The formation of the mixed triple-decker 13 as main product in this experiment is highly indicative for this type of ligand substitution. Such a mechanism is described herein, for the first time, for ligand exchange in tripledecker complexes.
The dinuclear gold(I) compound [Au2(μ-C10H6){μ-Ph2P(CH2)2PPh2}] was prepared in high yield by the reaction of 1,8-bis(trimethylstannyl)naphthalene with [Au2Cl2(μ-Ph2P(CH2)2PPh2)]. Oxidative addition with halogens results in the formation of the dihalodigold(II) complexes [Au2(X)2(μ-C10H6){μ-Ph2P(CH2)2PPh2}] (X = Cl, Br, I) containing a gold−gold bond.
A straightforward synthesis of cyclopropenylidene-stabilized phosphenium cations 1 a–g through the reaction of [(iPr2N)2C3+Cl]BF4 with secondary phosphines is described. Their donor ability was evaluated by analysis of the CO stretching frequency in Rh complexes [RhCl(CO)L2](BF4)2 and electrochemical methods. The cyclopropenium ring induces a phosphite-type behavior that can be tuned by the other two substituents attached to the phosphorus atom. Despite of the positive charge that they bear, phosphenium cations 1 a–g still act as two-electron donor ligands, forming adducts with PdII and PtII precursors. Conversely, in the presence of Pd0 species, an oxidative insertion of the Pd atom into the Ccarbene–phosphorus bond takes place, providing dimeric structures in which each Pd atom is bonded to a cyclopropenyl carbene while two dialkyl/diaryl phosphide ligands serve as bridges between the two Pd centers. The catalytic performance of the resulting library of PtII complexes was tested; all of the cationic phosphines accelerated the prototype 6-endo-dig cyclization of 2-ethynyl-1,1′-biphenyl to afford pentahelicene. The best ligand 1 g was used in the synthesis of two natural products, chrysotoxene and epimedoicarisoside A
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