Alkyls hydrocarbyl ligands

When the hydrocarbyl ligand is 1° alkyl, the reaction proceeds with overall retention of configuration to produce RHgX and L FeX. When R = IIP or benzyl, race-mization is the stereochemical outcome and the products are RX and L FeHgX. Apparently two pathways are operative in this example. Path e (Schemes 8.9 and 8.11) gives retention by a reductive elimination pathway. As R becomes substituted with groups that can stabilize a carbocation, path d (Schemes 8.9 and 8.11) takes over to produce free R+ that picks up X from HgX3. ... 

An early theoretical study suggested that better 0 donors are eliminated more easily from cA-MR(R )L2 type complexes [8]. However, this prospect is now known to be applicable only to a dialkyl complex series [e.g., Me > Et > Pr > Bu]. Thus the rate of reductive elimination is rather sensitive to the other factors, especially to the orbital hybridization of hydrocarbyl ligands. In general, the reactivity decreases in the order [hydrido (s)alkenyl (sp ) > aryl (sp ) 3> alkynyl (sp) > alkyl (sp )]. While a Jt-allyl ligand ranks middle, its behavior in reductive elimination will be described separately in Section 9.4. 

The synthesis of stable actinide complexes containing only alkyl, aryl, or alkenyl (hydrocarbyl) ligands has been an Important goal since the early 1940 s [5]. However, reactions such as eq.(l) are known to yield... 

Abstract Square-planar palladium(II) and platinum(II) complexes with a high-lying filled d 2 orbital can act as metalloligands for Lewis-acidic metal centers such as d ° and s cations. This behavior is promoted by hard ligands such as a-bound hydrocarbyl ligands. A wide diversity of structural motifs based on this kind of donor-acceptor metal-metal bonds has been discovered in the last decades. This chapter reviews the coordination chemistry of metalloligands derived from alkyl, aryl, alkynyl, and carbene complexes of palladium(II) and platinum(II). The specific reactivity of the resulting bimetallic complexes is also addressed. 

This section covers developments concerning synthesis and reactivity of organometallic iron complexes having a 7 -bound hydrocarbyl ligand, whose a-carbon atom is considered as rp -hybridized, and their formal derived insertion products (acyis, iminoacyis). Iron complexes ligated both by 77 - and 77 - ( = 2 ) hydrocarbyl ligands such as the 77 -alkyl-77 -allyl compounds or the benzene-coordinated acyl complex [Fe PhCH(=0) (C0)3] 4" will be... 

Coordination catalysts of formula (I), where M is Pd, Q is an alkyl, S is a halogen, R1 is H or an alkyl (1-4 carbon atoms), preferably a methyl group, and R2 is a hydrocarbyl (1-4 carbon atoms), preferably a methyl group, may be made by the reaction of the corresponding 1,5-cyclooctadiene (COD) Pd complex with the appropriate diimine. When M is Ni, (I) can be made by the displacement of another ligand, such as a dialkylether or a polyether such as 1,2-dimethoxyethane, by an appropriate diimine ... 

The word hydrocarbyl is used to describe a a-bonded hydrocarbon ligand that may be an alkyl, aryl, or vinyl group, for example. 

Electrophilic abstraction of a portion of a a-bound hydrocarbyl or a coordinated 7t ligand may occur. The trityl cation, Ph3C+, is a commonly-used electrophile for this task. Equation 8.73 provides an example of abstraction at the (3 position of an alkyl ligand to provide an rf-alkene complex,102 a useful route for the synthesis of these compounds. 

Transmetallafion transfers a hydrocarbyl or hydrido ligand from one metal to another. Since the transmetallation generates a new transition metal alkyl, it constitutes one of the most important elementary processes in molecular catalysis. 

Many additional routes to metal-alkyl complexes other than transmetallation and alkylation are discussed in later chapters of this text. For example, metal-alkyl complexes are generated by insertion of an olefin into a metal-hydride or or metal-hydrocarbyl species. Such insertion reactions are discussed in Chapter 9, but an example of the synthesis of a zirconium alkyl by olefin insertion into a zirconium hydride is shown in Equation 3.9. Metal-alkyl complexes are also generated by nucleophilic attack on coordinated olefins (Equation 3.10) or carbene ligands (Equation 3.11). These reactions are presented in detail in Chapter 11. 

A vacant coordination site is created during the forward insertion reaction of Equation 9.1, and a vacant coordination site must be present for the reverse reaction to occur. This mechanism makes it necessary for coordinatively saturated (18-electron) metal-alkyl complexes to dissociate a ligand prior to 3-hydrogen and 3-hydrocarbyl elimination reactions. 

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