Anionic alkyl complexes

The reduced alkyl complexes are reoxidized by O2 to the iron(lll) alkyls. The corresponding diamagnetic phthalocyanine iron(ll) alkyl complexes, rFe(Pc)R), were prepared by two-electron reduction of Fe(Pc) by LiAIFl4 to give [Fe(Pc) (actually the Fe(I) phthalocyanine radical anion) followed by reaction with Mel, Etl or i-PrBr. The methyl compound, [Fe(Pc)CHi] was characterized by X-ray crystallography. ... 

One-electron reduction of the iron(lll) alkyl complexes forms the diamagnetic iron(ll) alkyl anions [Fe(Por)R. The iron(ll) anions do not react with oxygen directly, but are first oxidized by O2 to the corresponding alkyliron(III) complexes, Fe(Por)R, which then insert O2 as described above. 

Iron hydride complexes can be synthesized by many routes. Some typical methods are listed in Scheme 2. Protonation of an anionic iron complex or substitution of hydride for one electron donor ligands, such as halides, affords hydride complexes. NaBH4 and L1A1H4 are generally used as the hydride source for the latter transformation. Oxidative addition of H2 and E-H to a low valent and unsaturated iron complex gives a hydride complex. Furthermore, p-hydride abstraction from an alkyl iron complex affords a hydride complex with olefin coordination. The last two reactions are frequently involved in catalytic cycles. 

All of the reactions described above use anionic alkyl metal complexes as stoichiometric reductants. Cationic zirconium catalyst 58 was shown to re-ductively cyclize a variety of 1,5-dienes to give both mono- and bicyclic silane products when H3SiPh was employed as the stoichiometric reductant (Scheme 10) [32]. Poor yields due to competing polymerization processes were observed when less substituted dienes were employed. It is likely that... 

The active species of the metallocene/MAO catalyst system have now been established as being three-coordinated cationic alkyl complexes [Cp2MR] + (14-electron species). A number of cationic alkyl metallocene complexes have been synthesized with various anionic components. Some structurally characterized complexes are presented in Table 4 [75,76], These cationic Group 4 complexes are coordinatively unsaturated and often stabilized by weak interactions, such as agostic interactions, as well as by cation-anion interactions. Under polymerization conditions such weak interactions smoothly provide the metal sites for monomers. 

The use of weakly coordinating and fluorinated anions such as B(C6H4F-4)4, B(C6F5)4, and MeB(C6F5)3 further enhanced the activities of Group 4 cationic complexes for the polymerization of olefins and thereby their activity reached a level comparable to those of MAO-activated metallocene catalysts. Base-free cationic metal alkyl complexes and catalytic studies on them had mainly been concerned with cationic methyl complexes, [Cp2M-Me] +. However, their thermal instability restricts the use of such systems at technically useful temperatures. The corresponding thermally more stable benzyl complexes,... 

Fig. 15. Correlation between hydrogen bond strength and iGluRl/2 vs 3/4 selectivity among willardiines. Unsubstituted/alkylated willardiines and azawillardiines lie in one series, halo-genated derivatives in another. The strength of anion-water complex is calculated as E[ArO(-)] + E[H20] - E[ArO(-)...HOH] at B3LYP/6-311+G(d,p).

Nucleophilic acyl complexes can be 0-alkylated with hard electrophiles to yield the corresponding alkoxy- or (acyloxy)carbene complexes. The first carbene complex ever isolated [61] was prepared by this route the intermediate, anionic acyl complex was generated by addition of phenyllithium to tungsten hexacarbonyl (Figure 2.3). 

The formation of the heterocycle 1 from the xylylene-bis-phosphonium salt 2 and PCI3 proceeds via a detectable intermediate 3 in a cascade of condensation reactions that is terminated by spontaneous heterolysis of the last remaining P-Cl bond in a cyclic bis-ylide-substituted chlorophosphine formed (Scheme 1) [15]. The reaction scheme is applicable to an arsenic analogue of 1 [15] and to bis-phosphonio-benzophospholides with different triaryl-, aryl-alkyl- and aryl-vinyl-phosphonio groups [16, 18, 19], but failed for trialkylphosphonio-substituted cations here, insufficient acidity prohibited obviously quantitative deprotonation of the phosphonium salts, and only mixtures of products with unreacted starting materials were obtained [19]. The cations were isolated as chloride or bromide salts, but conversion of the anions by complexation with Lewis-acids or metathesis was easily feasible [16, 18, 19] and even salts with organometallic anions ([Co(CO)4] , [CpM(CO)3] (M=Mo, W) were accessible [20]. 

Alkylcadmium alkoxides, 11 399-400 alkylperoxides, 11 399-400 anions, 11 370-371 halides, 11 377 solvated, 11 392-394 Alkylcalcium halides, solvated, 11 390 Alkyl complexes, osmium, 37 239-242 Alkyl copper compounds, 17 140, 142, 143 Alkyl derivatives, phosphoniuilic halides and, 1 363... 

In the first, Fe(CO)5 is converted into the carbonyl hydride anion by reductive decarboxylation following initial OH" attack on a carbonyl carbon (55). The carbonyl group is thus oxidized to carbonate in basic medium. The second reaction, (3) (56), is one of E. O. Fischer s celebrated carbene forming reactions (57). Phenyl lithium reacts with Cr(CO)6 leading to an anionic acyl complex. A subsequent alkylation step using Me30+ yields the methoxy-phenylcarbene complex Cr(CO)5(CPh(OMe)). 

Especially for alkyl halides 6 the transfer of a single electron from the metal center is facile and occurs at the halide via transition state 6C, which stabilizes either by direct abstraction of the halide to a carbon-metal complex radical pair 6D or via a distinct radical anion-metal complex pair 6E. This process was noted early but not exploited until recently (review [45]). Alkyl tosylates or triflates are not easily reduced by SET, and thus Sn2 and/or oxidative addition pathways are common. The generation of cr-radicals from aryl and vinyl halides has been observed, but is rarer due to the energy requirement for their generation. Normally, two-electron oxidative addition prevails. 

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