Alkyl complexes features

Sequentially, the same group developed a variety of rare-earth metal bis(alkyl) complexes featuring NPN ligands (Scheme 26). Under the assistance of borate... 

Steric hindrance may hamper the correct stereochemistry required for 13-elimination, and perhaps this can be used to stabilise our metal alkyl complex. In the modem polymerisation catalysts for polypropene this feature has actually been observed, which leads to higher molecular weight polymers. This now forms part of the design of new catalysts. 

Important features favoring the reductive elimination reaction have been discussed based on theoretical and experimental studies [128-130]. The reductive elimination of an azohum salt from a palladium NHC alkyl complex (Fig. 13) proceeds under direct formation of Pd° in an exothermic process with a low activation barrier [128]. The coligands at the palladium atom play an important role. It has been shown that the Caikyi-Pd-CNHC angle becomes more acute during the reductive elimination to allow for an optimal orbital overlap of the groups to be... 

Like rare-earth metal hydride and alkyl complexes [141, 206, 207], silylamide derivahves catalyze the hydrosilylation of alkenes and dienes with phenylsilane [208-210]. Accordingly, materials [Ln N(SiMe3)2 3] AS-380.7oo (12a-d, Table 12.3) featuring monopodal bis(silylamide) surface complexes have been exploited as catalysts for the reaction of 1-hexene and styrene with PhSiH3 (Scheme 12.20) [118]. 

The extension to other cases is straightforward but tedious, and the principal results for low-spin octahedral species are summarised in Table 2, which shows some interesting features. At this level of discussion, R loss is never assisted. The question of demotion only arises where the t2g subshell is less than full. Two-electron demotion is is only possible for R loss from cf , cf, and systems, and in all of these it is actually term-term assisted. R" loss is assisted by the demotion of one electron fotd, d, or d curves, but among these it is only term-term assisted for d. R loss is clearly assisted by the demotion of a single electron for all d" (n < 6), but is only term-term assisted for n = 1 and n = 2. (These predictions are quite different from those of Ref. which refers exclusively to second order terms in R loss). The only configurations with n < 6 for which no process shows first order term-term assistance are d and d. This is a gratifying result and tends to promote confidence in the usefulness of the theory. The relative ease of preparation of Cr(III) alkyl complexes has often been noted and t/ is exemplified by the Co(IV) alkyls now known to be accessible by electrochemical oxidation of Co(III) Presumably a parallel chemistry of Fe(III) awaits discovery. 

In a proton NMR experiment in which 1,4-pentadiene was added to a solution of HNi[P(OMe)3]4, it was possible to watch the isomerization of 1,4- to 1,3-pentadiene, followed by formation of l,3-dimethyl-7t-allyl complexes (53). The observation of 7t-allyl products in the reaction of the hydride with the conjugated diene, but not in the ff-alkyl intermediates involved in isomerization, illustrates the much greater stability of zr-allyl complexes of nickel compared to tr-alkyls, a feature which is also observed in the hydrocyanation reactions. 

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

Cationic Cp2M(R)(L)+ complexes exhibit a variety of interesting structural features which result from the high Lewis acidity of the cationic (P metal centers. The first simple alkyl complex of this type to be structurally characterized was [(CsH5)2Zr(CH3)(THF)][BPh4] (3, Fig. 2) (32). The... 

The above-mentioned features of ylides, together with the ability to form ylide anions, and their ease of synthesis make them exciting and versatile ligands for transition metal chemistry [8]. Ylides have outstanding potential with respect to fhe formation of transition metal-carbon bonds, because a major reaction path for fhe decomposition of such moieties, i.e. j5-H ehmination, is blocked by the phospho-nium group, a significant difference in comparison wifh simple alkyl complexes [Eqs. (2) and (3) Fig. 1.1]. 

It should be noted that complexes of types VII-5 or VII-7 can be easily prepared by the method initially described in [30a-d], The chloride complex Pt"Cl4 - reacts at room temperature in aqueous solution with alkyl iodide to produce a o-alkyl complex of platinum(IV). Methyl [30a], ethyl [30b,c], and acetonyl [30d] complexes of Pt(IV) have been prepared by this method. An interesting feature of the reaction is that the sixth coordination site in the octahedral molecule of the product is occupied by water, while the T ion is bound to another molecule of the platinum(II) complex (Ptlj and analogous products are formed and precipitate) ... 

---