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Eighteen-electron complexes

Eicosyl phobanes, HP-NMR and HP-IR studies, 1, 490-491 EIEs, see Equilibrium isotope effects Eighteen-electron complexes, ligand substitution in, 1, 96 Eighteen-electron rule... [Pg.100]

MoH4(Ph2PCH2CH2PPh2)2] is a coordinatively-saturated, eighteen-electron complex. Clearly binding protons to the molybdenum cannot alter the... [Pg.486]

Each Mn in Mn2(CO)io would therefore be called an eighteen-electron system. Eighteen-electron complexes have the EAN of a noble gas and the corresponding stability. [Pg.24]

Eighteen-electron complexes react more slowly than similar complexes with either more or less electrons. The eighteen-electron rule explains why some reactions are associative and others dissociative. Complexes in which the metal has sixteen or less valence electrons tend to react by associative mechanisms, since the metal has vacant low-energy orbitals which can be used to form a bond with the entering ligand. This orbital can accept an electron pair from an entering ligand and provide a path for associative substitution. Substitution reactions in square planar complexes illustrate this point, reaction (40). [Pg.113]

It is interesting that two eighteen-electron complexes which are extremely similar to Ni(CO)4, Co(CO)3NO and Fe(CO)2(NO)2, react rapidly with CO in a second-order process. This is explained by the ability of NO to accept a pair of electrons from the metal and in this way vacate a low-energy metal orbital suitable for accepting a pair of electrons from an entering ligand, reaction (42). [Pg.114]

Addition reactions. Certain square planar c/ (sixteen-electron) complexes such as [RhH(CO)L2] play a particularly important role in catalysis. These are sixteen-electron systems, having two less electrons than needed to complete a noble gas electronic configuration. It should not be surprising that such complexes add one ligand to become eighteen-electron complexes, reaction (18). [Pg.128]

In a formal sense, these are oxidation reactions, because rhodium(l) is oxidized to rhodium(ni). These are also addition reactions because two ligands are added to square planar sixteen-electron systems which are transformed into octahedral eighteen-electron complexes. These reactions can also be viewed as an insertion reaction (see (4) below) in which a metal atom is inserted into a bond between two nonmetals. [Pg.129]

The series of reactions above is a simple catalytic cycle for the water gas shift reaction, CO + H2O CO2 + H2. (a) What is the oxidation state of rhodium in each complex in the cycle (b) Indicate whether each complex is a sixteen- or eighteen-electron complex, (c) Which of these classes of reactions does each step of the cycle illustrate addition, elimination, oxidative addition, reductive elimination, insertion, or deinsertion ... [Pg.136]

Eighteen-electron complexes can also undergo associative substitution. Such complexes usually contain a ligand capable of rearranging and accepting an extra pair of electrons, so that the metal can avoid a 2(te configuration. Nitrosyls, with their... [Pg.110]

Eighteen-electron complexes can undergo associative substitution without forming an unfavorable 20e intermediate if a ligand can rearrange to leave a 2e vacancy to allow L to bind. Nitrosyls, with their 3e linear to le bent rearrangements, can do this. For example, Mn(CO)4(/m-NO) shows a second-order rate law (Eq. 4.37) and a negative entropy of activation, AS, as expected for Eq. 4.36. [Pg.122]

When using the eighteen electron rule, we need to remember that square-planar complexes of centers are associated with a 16 electron configuration in the valence shell. If each ligand in a square-planar complex of a metal ion is a two-electron donor, the 16 electron configuration is a natural consequence. The interconversion of 16-electron and 18-electron complexes is the basis for the mode of action of many organometallic catalysts. One of the key steps is the reaction of a 16 electron complex (which is coordinatively unsaturated) with a two electron donor substrate to give an 18-electron complex. [Pg.173]

There are ammoniates of PtCl2, of halides of other platinum metals and of cobalt and nickel, too, some of which have been mentioned before in, Section 50. The cobalt complexes clearly show the importance of the completed d shells for the stability of the complex. Non complex compounds of trivalent cobalt are very unstable. Solutions of divalent cobalt in ammonia, however, are readily oxidized by air, because the NH3 complex of trivalent cobalt Co(NH3)6 3+ClT has eighteen electrons used in bond formation, whereas the ion Co(NH3) + would have nineteen electrons. [Pg.228]

Eighteen Electron Rule rule noting that coordination complexes with eighteen electrons are stable electrons from both metal species and ligand donor species are counted... [Pg.280]

For case (1) complexes, examples of which include many first transition series compounds (Table 8.8.3), the lt2g orbitals are essentially nonbonding and A0 is small. In other words, the 2eg orbitals are only slightly antibonding and they may be occupied without much energy cost. Hence, there is little or no restriction on the number of d electrons and the eighteen-electron rule has no influence on these complexes. [Pg.288]

Table 8.3 3. Three types of complexes in relation to the eighteen-electron rule... Table 8.3 3. Three types of complexes in relation to the eighteen-electron rule...
Multiple products with formula Cp 2Mo2S4 arise in the reaction of 2 with sulfur (185). One of these has structure 70. A similarly complex reaction occurs for 3, while the product of reacting 3 with selenium is 71 (186). On the other hand, a pentasulfide (72 ) is formed (187) when 1 is treated with an excess of sulfur. Its structure is interesting the five sulfur atoms adopt a planar configuration. Eighteen-electron configurations are attained in 72 provided a Cr=Cr bond is accepted. [Pg.142]

Eighteen-electron rule — An electron-counting rule to which an overwhelming majority of stable diamagnetic transition metal complexes adhere. The number of non-bonded electrons at the metal plus the number of electrons in the metal-ligand bonds should be 18. The 18-electron rule in transition metal chemistry is a full analogue of the Lewis octet rule . [Pg.181]

Ligand exchange of [Pt(P(OR)3)4] with free phosphite is dissociative, as expected for an 18-electron complex see Eighteen Electron Compounds). [Pt(PF3)4] is very stable and does not react with potential substrates for oxidative addition. [Pg.3892]

A versatile reductive complexation method that leads directly to cycloalkene Ru complexes consists of treatment of RUCI3 with activated Zn in ethanol or methanol (or mixtures with THF) in the presence of an alkene (Scheme 17)." " Starting from a diene, a dehydrogenation is required to provide the metal with 18 valence electrons see Eighteen Electron Compounds), and this is accomplished by hydrogenating one of the cycloalkenes to a monoalkene, which as the weakest ligand is replaced by another diene. An extension of this... [Pg.4155]


See other pages where Eighteen-electron complexes is mentioned: [Pg.91]    [Pg.12]    [Pg.91]    [Pg.12]    [Pg.172]    [Pg.26]    [Pg.16]    [Pg.13]    [Pg.19]    [Pg.120]    [Pg.398]    [Pg.398]    [Pg.224]    [Pg.221]    [Pg.288]    [Pg.289]    [Pg.198]    [Pg.1314]    [Pg.15]    [Pg.67]    [Pg.257]    [Pg.825]    [Pg.859]    [Pg.1146]    [Pg.1530]    [Pg.2042]    [Pg.3338]    [Pg.3588]    [Pg.4140]    [Pg.4151]    [Pg.4986]   
See also in sourсe #XX -- [ Pg.712 , Pg.731 , Pg.732 , Pg.735 ]




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