Bonded organic ligands

and (c) a schematic representation of Mo(r -C3H5)(Ti -CH2CHCHCH2)(r -C5H5). Colour code Ru, pale grey Mo, red C, dark grey P, orange H, white. 

The extent of back-donation to R2C=CR2 is influenced by the nature of R, and is enhanced by electron-withdrawing groups such as CN. In the extreme, the 7r-contribution to the C—C bond is completely removed and the complex becomes a metallacyclopropane ring. Structures 23.19a and 23.19b show limiting bonding schemes. In 23.19a, 

The bonding description for a coordinated alkene can be extended to other unsaturated organic ligands. Polyalkenes may be non-conjugated or conjugated. In complexes of non-conjugated systems (e.g. cycloocta-1,5-diene (cod), 23.20, or 

Alkenes, R2C=CR2, tend to bond to metal centres in a side-on (i.e. r ) manner and behave as 2-electron donors. The 

The allyl ligand, [C3H5] (24.26), coordinates in an ri -mode, using the two occupied tt-MOs (bonding and non-bonding) as donors and the 7t -MO as an acceptor 

In solution, complexes with rr-bonded organic ligands are often fluxional, with rotation of the ligand being a common dynamic process (see structure 24.55, Fig. 24.19 and scheme 24.98). Variable-temperature NMR spectroscopy is used to study such phenomena. 

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Solvated transition metal cations containing weakly bonded organic ligands are potentially useful as intermediates in preparative coordination chemistry. The coordinated solvent molecules provide solubility of the compounds in various organic solvents, and they can be replaced readily by other ligands with better donor properties.1, 2 The preparation of mononuclear transition metal complexes with weakly bonded anions has been described previously3 and preparative applications of such complexes have been reviewed.4... 

The data collected in the Tables 4-6 require several comments. In some cases the metal-organic product of the insertion step has been investigated directly. In other cases this was not possible, because immediate -hydrogen abstraction from the a-bonded organic ligand led to a hydrido-metal species and an unsaturated product molecule, e.g. (cf. Table 4, last example) ... 

Transmetalation of jt-allyl transition metal complexes and of the complexes with related C3 ligands proceeds via unique pathways that are not found in the intermolecular transfer of -bonded organic ligands. Rich information about stereochemistry of unsymmetrically substituted rt-allyl ligands of Pd complexes provides a useful probe to investigate details of the reaction mechanism. Cationic jr-allylpalladium(II) complex reacts with ethylene-coordinated Pt(0) complex to afford the jr-allylplatinum(II) complex and Pd(0) complex via transfer of the allyl ligand from Pd to Pt (Eq. 5.57). 

The stability of the bonded organic ligand on a reversed-phase column depends on the type and acidity... 

Scheme 10.4 Schematic illustration of covalently bonding organic ligand/catalyst on the MS by (a) one-step and (b) two-step method.

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