Homoleptic alkyl complexes

UV irradiation of the homoleptic alkyl complexes of chromium was found to give homolysis of the Cr—alkyl bonds and the generation of free radicals 17, 45, 46). When Cr(nor)4 was irradiated with near-UV light in CCU/hexane mixtures, clean changes in the UV-visible absorption spectrum resulted and norbornane, 1-chloronorbornane, and hexachloroeth-ane were produced [Eq. (56)] (45). An orange, chromium-containing solid... 

Like Cr, W is able to form a variety of neutral, mononuclear, homoleptic alkyl complexes, in this case in oxidation states as high as six. Treatment of WClg with only 3 equiv of LiMe in ethereal solution affords the (sometimes explosively) labile WMe. ... 

Discussion of the chemistry of carbon-based ligands is selective in order to emphasize more recent aspects of coordination chemistry. As a result, this section focuses on homoleptic alkyl complexes, as well as alkylidene and alkylidyne species that do not contain cyclopentadienyl or related ligands. Acyl (rj2-C,0-RCO) and iminoacyl (r/2-C./V-RCNR ) ligands are not discussed generally. These and other aspects of carbon-based ligands can be found in Comprehensive Organometallic Chemistry I and II.4 5... 

Allyl Complexes. Allyl complexes of uranium are known and are usually stabilized by cyclopentadienyl ligands. AEyl complexes can be accessed via the interaction of a uranium halide and an allyl grignard reagent. This synthetic method was utilized to obtain a rare example of a "naked" homoleptic allyl complex, U(T -C2H )4 [12701 -96-17, which decomposes at 0°C. Other examples, which are more stable than the homoleptic allyl complex have been synthesized, ie, U(allyl)2(OR)2 (R = alkyl), U(allyl)2X (X = halide), and U(allyl)(bipy)2. 

Hydrocarbyl Complexes. Stable homoleptic and heteroleptic uranium hydrocarbyl complexes have been synthesized. Unlike the thorium analogues, uranium alkyl complexes are generally thermally unstable due to P-hydride elimination or reductive elimination processes. A rare example of a homoleptic uranium complex is U(CH(Si(CH2)3)2)3, the first stable U(I11) homoleptic complex to have been isolated. A stmctural study indicated a triganol... 

Examples of silver(l) alkyl and alkenyl (including aryl) complexes have been known from as early as 1941 6-9 however, the number of examples is fairly limited with respect to that of the heavier congeners, copper(l) and gold(l). Such a phenomenon can readily be attributed to the relatively low stability of this class of complexes, both photochemically and thermally. Simple homoleptic alkyl and alkenyl complexes of silver(i) are known to be very unstable under ambient temperature and light, and successful isolation of this class is fairly limited and mainly confined to those involving perfluoroorganics.10 The structures and the metal-carbon bond-dissociation energies for... 

Homoleptic germylenes, preparation and properties, 3, 773 Homoleptic lanthanide(II) alkyl compounds, properties, 4, 4 Homoleptic manganese aryl complexes, preparation, 5, 816 Homoleptic manganese isonitrilates, preparation, 5, 773—774 Homoleptic molybdenum complexes, preparation and characteristics, 5, 514... 

Homoleptic tetrazincates, characteristics, 2, 346 Homoleptic titanium(III) complexes, with -ligands, 4, 282 Homoleptic trizincates, characteristics, 2, 345 Homoleptic vanadium(III) alkyl complexes synthesis and structure, 5, 12 VMes3 reactivity, 5, 12... 

Similar to homoleptic dithiolene complexes, alkylation of Cp2M(S2C2Z2) results in the alkyl group being added to the ligand sulfur atom (Eq. 28) (131). 

Homoleptic tetrabenzyl complexes are prepared by reaction between ThCLt and benzyllithinm in THF solntion at low temperature (eqnation 53)d It is nnlikely that these complexes are -alkyls, since the X-ray stmctnre of Cp Th(CH2Ph)3 revealed mnltihapto coordination of the benzyl ligand. ... 

The first example of a nentral homoleptic nra-ninm(III) alkyl complex was prepared by reaction of bis(trimethylsilyl)methyllithinm with a monomeric nraninm aryloxide, U(0-2,6-t-Bn2C6H3)3, in hydrocarbon solntion (eqnation 54)d Attempts to prepare... 

Osmium forms a wide variety of alkyl and aryl complexes including homoleptic alkyl and aryl complexes and many complexes with ancillary carbonyl (see Carbonyl Complexes of the Transition Metals), cyclopentadienyl (see Cyclopenta-dienyl), arene (see Arene Complexes), and alkene ligands (see Alkene Complexes). It forms stronger bonds to carbon and other ligands than do the lighter elements of the triad. Because of this, most reactions of alkyl and aryl osmium complexes are slower than the reactions of the corresponding ruthenium complexes. However, because osmium is more stable in higher oxidation states, the oxidative addition (see Oxidative Addition) of C-H bonds is favored for osmium complexes. The rate of oxidative addition reactions decreases in the order Os > Ru Fe. 

Homoleptic aryl-lanthanides are less studied then alkyl complexes. After the first lanthanide aryl complex [Li(THF)4][Lu(C6H3-2,6-Me2)4], neutral triphenyllantha-nides Ph3Ln(THF)3 (Ln = Er, Tm, Yb) were synthesized in THF by reaction of metallic lanthanides with Ph2Hg or... 

Neutral and cationic homoleptic (see Homoleptic Compound) tnngsten-isocyanide complexes W(CNR)6 and [W(CNR)y] + (R = alkyl, aryl) are known, and W(CO)e (CNR) (n=l-3) complexes may be prepared from W(CO)6 and excess isocyanide in the presence of catalytic amounts of C0CI2 or PdO. Iso-cyanides are isoelecfronic with CO and also insert into the W-R bonds of alkyl complexes (see Alkyl Complexes). For instance, the alkyl-nitrosyl complexes Cp W(NO)(X)(CH2Bfr) (X = NHBfr, OBfr) react with CNBu to afford -iminoacyl complexes, and the isocyanide complexes, Cp W(CO)2(Me)(CNR) (10, R = alkyl), rearrange to afford either -iminoacyl Cp W(CO)2( -MeCNR)(ll) or ij -l-azaallyl Cp W(CO)2( -CH2CHNR) (12) derivatives, depending upon the reaction conditions (equation 4). ... 

With the exception of the metallation reaction in Eq. (4), little chemistry has been reported for homoleptic lanthanide complexes. With four to six reactive alkyl sites per metal center, these compounds are potentially much more reactive than the bis(cyclopentadienyl)alkyl compounds described in Section IV,B. This is an area of future growth in the organolanthanide held. 

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