D-metal complex

Martell, A. E. Hancock, R. D. Metal Complexes in Aqueous Solution, Plenum Press New York, 1996... 

Harmon RE., Dabrowiak JC., Brown DJ., Gupta SK., Herbert M., and Chitharanjan D. Metal Complexes of 1-Substituted 3-Hydroxyureas. Journal of Medicinal Chemistry, 1970, 13(3), 577-579. 

A d-mctal ion may also be responsible for color, as is apparent from the varied colors of many d-metal complexes (see Chapter 16). Two types of transitions may be involved. In one, which is called a d-to-d transition, an electron is excited from a d-orbital of one energy to a d-orbital of higher... 

A currently popular alternative to the ah initio method is density functional theory, in which the energy is expressed in terms of the electron density rather than the wave-function itself. The advantage of this approach is that it is less demanding computationally, requires less computer time, and in some cases—particularly for d-metal complexes—gives better agreement with experimental values than other procedures. 

Square brackets are commonly used to indicate the presence of a d-metal complex. 

The Lewis bases attached to the central metal atom or ion in a d-metal complex are known as ligands they can be either ions or molecules. An example of an ionic ligand is the cyanide ion. In the hexacyanoferrate(II) ion, [Fe(CN)6]4, the CN- ions provide the electron pairs that form bonds to the Lewis acid Fe2+. In the neutral complex Ni(CO)4, the Ni atom acts as the Lewis acid and the ligands are the CO molecules. 

Because the color of a d-metal complex depends on the identity of the ligands as well as that of the metal, impressive changes in color often accompany substitution reactions (Fig. 16.17). 

There are two major theories of bonding in d-metal complexes. Crystal field theory was first devised to explain the colors of solids, particularly ruby, which owes its color to Cr3+ ions, and then adapted to individual complexes. Crystal field theory is simple to apply and enables us to make useful predictions with very little labor. However, it does not account for all the properties of complexes. A more sophisticated approach, ligand field theory (Section 16.12), is based on molecular orbital theory. 

The colors that we have described arise from d-d transitions, in which an electron is excited from one d-orbital into another. In a charge-transfer transition an electron is excited from a ligand onto the metal atom or vice versa. Charge-transfer transitions are often very intense and are the most common cause of the familiar colors of d-metal complexes, such as the transition responsible for the deep purple of permanganate ions, Mn04 (Fig. 16.33). 

Name and write formulas for d-metal complexes (Toolbox 16.1 and Example 16.1). 

Use the spectrochemical series to predict the effect of a ligand on the color, electron configuration, and magnetic properties of a d-metal complex (Examples 16.4 and 16.5). 

Very recently, the yttrium hydride [2,2 -bis(tert-butyldimethylsilylamido)-6,6 -di-methylbiphenyl]YH(THF) 2 (36), conveniently generated in situ from [2,2 -bis(tert-butyldimethylsilylamido)-6,6 -dimethylbiphenyl]YMe(THF)2 (35) demonstrated its high catalytic activity in olefin hydrosilylation. This system represents the first use of a d° metal complex with non-Cp ligands for the catalytic hydrosilylation of olefins. Hydrosilylation of norbornene with PhSiHs gave the corresponding product (37) of 90% ee (Scheme 3-15) [43]. 

ELECTROCHEMICAL ACTIVITY OF CARBONS MODIFIED BY d-METAL COMPLEXES WITH ETHANOLAMINES... 

This model was proposed by Bursten [82] in 1982. It assumes a linear correlation (with a negative slope) between the HOMO energy and the oxidation potential of octahedral d metal complexes of the type [ML Lg ] (L = stronger jr-acceptor than L ), this potential (viz. HOMO energy) being determined in an additive way by the effects B) of all the L and (6 — n)L ligands and by the effects (C) of the ligands, xL and (4 — x)L, that r-interact with the metal d,r orbital comprised in the HOMO of the complex (Eq. 29 in which depends on the metal atom, in particular its oxidation state, and trivially on the solvent and reference electrode). 

The calculations of ethene MCD parameters described in the previous section provided a number of insights into the best way to calculate MCD spectra but were lacking in some areas. In particular, ethene only gives rise to terms. We shall now turn to a series of highly symmetric tetrahedral d° metal complexes, including the permanganate and dichromate ions, where A as well as terms are involved. 

Dissociative Activation in the Substitution Reactions of Four-coordinate, Planar d Metal Complexes 320... 

Simple protonation is not expected in the case of formally d° metal complexes, as the metal has no lone pairs, but the proton may attack an M—H bonding electron pair and lead to products (equation 11). The protonation of many complexes of alkenes and other unsaturated hydrocarbons often occurs at carbon, not at the metal (e.g. equation 2852). 

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