Mixed-alkylated complexes

Table 28 Structural parameters of heterobimetallic Ln/Al complexes featuring different alkylated aluminum centers ( mixed-alkylated complexes )... 

A tridentate bis(amido)phosphine ligand, (MejSiNFlCFlgCF PPh, is employed to prepare several Zr(iv) complexes including the dichloride, dialkyl, and mixed alkyl complexes 190, via standard amine elimination and alkylation methodologies.165 The mixed methyl benzyl dialkyl complex shows a distorted trigonal bipyramid in which the methyl group is in the apical position trans to phosphorus and the 7]2-benzyl group is cis to phosphorus. Related... 

Zirconium oxalates exist as compounds, double compounds, and mixed oxalato complexes (165,195,225—226). When the carboxylate ligand is a longer alkyl chain, the materials often are called zirconium soaps. 

A further dramatic comparison of the comparative reactivities of chromium alkyls in diverse oxidation states was furnished by another set of benzyl complexes. [7] Shown below, these three compound are isomers, yet they range in oxidation state from Cr to Cr °. Of the three, only the mixed-valent complex Cp G0i-ti n3-Bz)Cr(Bz)Cp, containing a Bivalent chromium bound to an T)3-benzyl and a ni-benzyl ligand, catalyzed the polymerization of ethylene. 

Synthesis and Chemistry of Mixed Imido-Alkyl Complexes. . . 181... 

Mixed alkyl)dichalcogenocarbamate complexes as precursors for ternary materials... 

As shown in Scheme 4-6, the reaction proceeds via a Ti(IV) mixed-ligand complex A bearing allyl alkoxide and TBHP anions as ligands. The alkyl peroxide is electrophilically activated by bidentate coordination to the Ti(IV) center. Oxygen transfer to the olefinic bond occurs to provide the complex B, in which Ti(IV) is coordinated by epoxy alkoxide and r-butoxide. In complex B,... 

Alternatively, CO2 can be used as source of CO. Indeed, it is well known that low-valent transition metal complexes can catalyze the chemical or electrochemical reduction of CO2 into CO. This approach was used to generate the mixed nickel complex Ni°bpy(CO)2 by the electrochemical reduction of Nibpy in NMP or DMF in the presence of CO2. The reduced complex can react with alkyl, benzyl, and allylhalides to give the symmetrical ketone along with the regeneration of Nibpy ". A two-step method alternating electroreduction and chemical coupling leading to the ketone has thus been set up (Scheme 9) [126,127]. 

The tetrahedral structure of these surface alkyl complexes on MCM-41(5oo) has been highlighted by XANES a sharp, intense pre-edge peak at 4969.6 0.3 eV is characteristic of an electronic transition of titanium, from the Is energetic level to molecular orbitals mixing 3d and 4p of Ti with the orbitals of the Ugands, in a complex where titanium is in a tetrahedral symmetry [28-31]. The same argument can be applied for species obtained from alcoholysis of 2a and 2b, especially using tert-butanol. 

In contrast, the analogous diethyl-diselenocarbamates (dsc) have been shown to be poor sources for the deposition of ZnSe or CdSe films. Under similar reaction conditions (10 -10 Torr, 370-420° C) the diethyl dsc precursors give films of the metal selenide heavily contaminated with selenium [108]. However the mixed alkyl dsc complex Eq. 4 have been used successfully to deposit thin films of CdSe or ZnSe [109,110]. 

Figure 21, Proposed model of adsorbed chiral selector (A-alkylproline)- Cu(U)-[free amino acid] mixed chelate complex, The lipophilized proline selector is held in position via intercalation of the alkyl chain. Case A the alkyl part of the mixed chelate complex is fixed by hydrophobic interactions with stationary phase (RP-J). Case B the complex formation is stabilized by other types of hydrophobic attraction. Chiral recognition and elution order is therefore not only dependent on the simple and isolatedly viewed chelate complex stability. In general, retention and chiral recognition in chiral LC is based on mixed-mode adsorption/dcsorption processes which act synergisticallv and also antagonistically with respect to the observed chiral resolution and intermolecular complex formation.

Comparison between the half-wave potentials (equations 2 to 4) of [Cr(CNR)6](PF6)2, e.g. for R = Bu , -1.04, -0.28 and 0.84 V (versus SCE),22 with those for [Cr(CNPh)6](PF6)2, i.e. -0.35, 0.25 and 1.00 V,20 shows that alkyl and aryl isocyanides favour respectively the higher and the lower oxidation states as expected from the greater a-donor and weaker jr-acceptor capabilities of the alkyl over the aryl isocyanides. Similarly, the phosphines in the mixed ligand complexes (Table 3), 23 relative to isocyanide ligands, stabilize the Cr111 oxidation state. The great difference in the relative stabilities of Cr—C bonds in the cyano and phenyl isocyanide complexes is indicated by the magnitude of the shift (ca. 2.0 V) between the Cr(CN) "/Cr(CN)r (-1.130 V) and the Cr(CNPh)i+/Cr(CNPh)i+ reduction potentials.28... 

Mixed cyanoisonitrile complexes have been reported to result from the reaction of Ag4[W(CN)8] with RNC (R = Me, Et, Prn, Pr Bu and CPh3).264 The resulting [W(CN)4(CNR)4] complexes are dodecahedral, with the more strongly jt accepting isonitrile ligands occupying the B position. These complexes can also be obtained by the reaction of the silver salt with alkyl iodide.255... 

In the (—)-DAIB-catalyzed reaction of diethylzinc and benzaldehyde, the rate is first-order in the amino alcohol. The initial alkylation rate is influenced by the concentration of diethylzinc and benzaldehyde but soon becomes unaffected by increased concentration. Thus, under the standard catalytic reaction conditions, the reaction shows saturation kinetics the rate is zeroth order with respect to both dialkylzinc reagent and aldehyde substrate. These data support the presence of the equilibrium of A-D, and alkyl transfer occurs intramolecularly from the dinuclear mixed-ligand complex D. This is the stereo-determining and also turnover-limiting step. 

Tetrakis(alkyl isocyanide) complexes of nickel(O), Ni(CNR)4, and the mixed isocyanide complexes with phosphines and unsaturated molecules are strictly analogous to the corresponding carbonyl complexes.23,24 They are generally more stable than [Ni(CN)4]4-. Mixed isocyanide complexes have been prepared by the reaction of Ni(cod)2 and CNBu followed by reaction with the appropriate phosphine or unsaturated molecules (alkenes, arylnitroso compounds, azo compounds, etc.) as outlined in equations (7) and (S).25... 

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