Ligands alkyl- or aryl

The complexes discussed in the review generally comprise five- or six-coordinate complexes containing tr-alkyl or aryl ligands. This contrast with transition metal organometallic porphyrin complexes which provide, in addition to cr-bonded... 

This class of compound is represented by the dicyanoiodate(I) anion, involving a pseudohalide rather than an alkyl or aryl ligand. The linear ion, with I—C distance of 2.302 A, has been characterized in the compound K[I(CN)2]C6H12N202, resulting from reaction of an aqueous solution of KCN with an ethanolic solution of ICN. The diimino oxalic acid diethyl ester molecule apparently stabilizes the structure.56... 

Apart from the platinum and nickel compounds with cr-bonded alkyl or aryl ligands, Chatt s group reported between 1961 and 1966 the synthesis of an impressive series of related cobalt(II), iron(II), rhodium(III), iridium(III), rhe-nium(III) and rhenium(V) complexes [39-42]. The paramagnetic cobalt(II) and iron(II) derivatives MR2(PR 3)2 were stable when R was an aryl group with... 

For a long time it was thought that binary complexes of transition metals containing only o-alkyl- or aryl ligands could be thermodynamically stable only if they are coordinatively saturated (18 electron rule). A series of illuminating papers by Wilkinson 26), Lappert27) and others 28) dispelled this fallacy. It became clear that transition metal alkyls can decompose via kinetically low energy pathways such as P-hydride elimination or abstraction, but rarely via primary metal-carbon homolysis. Mechanisms and theories of decomposition have been proposed and reviewed 29). 

Nucleophilic substitution at silicon, as described in previous sections, usually proceeds through five- or possibly six-coordinated silicon intermediates or transition states. For silicon bearing the common alkyl or aryl ligands, the barrier to formation of such extracoordinated intermediates is quite low. In these examples bimolecular substitution is so facile that unimolecular substitution, even in the most favourable cases, is so slow by comparison as to be unobservable. 

Recently it has been shown [45] that C-H bonds of (terminal) methyl groups in alkyl or aryl ligands can be oxidatively added to coordinatively unsaturated, com-plexed metal ions, as in... 

Most of transmetalation between main group metal compounds and transition metal complexes leads to the formation of a transition metal-carbon bond. The reaction which causes alkyl or aryl ligand transfer from transition metal to main group element is much less common. Olefin polymerization catalyzed by a metallocene catalyst is sometimes accompanied by chain transfer caused by the transfer of the growing polymer end from Ti or Zr to an A1 compound that is used as the cocatalyst (Scheme 5.23) [139,140]. 

Once again, the trans cr-bonding alkyl or aryl ligand exerts a powerful influence on the M-N-O bond angle. Studies on transient intermediates during photolysis of Ru-NO nitrosyls have revealed different modes of binding (and dissociation) of coordinated NO at the ruthenium centers. Metastable NO linkage isomers have been observed for MNO (M = Fe, Ru, Os) and for MNO ° complexes of Ni, as well as for FeNO iron nitrosyl porphyrins [208-212]. 

Subsequent studies on the reactivities of neutral and cationic alkyl- and aryl- palladium complexes revealed that the creation of a vacant site adjacent to the alkyl or aryl ligand causes marked enhancement in reactivity toward j8-hydrogen migration. The implications of these results on the fundamental processes of the transition metal alkyls and aryls with the mechanisms of Pd-catalyzed organic synthesis, such as arylation of olefins and carbonylation of aryl halides, have been discussed. 

Per definitionem, organometallic compounds are distinguished by an often reactive metal-carbon bond. Typical organic ligands are carbon monoxide CO, polyh to-coordinated n systems such as olefins or aromatics, and h -coordinated alkyl or aryl ligands [1]. 

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