Transition metal complexes coordination hybrid orbitals

Transition metal atoms coordinated by dithiocarbamate ligands through four sulfur atoms have both electronic (free d-orbitals) and steric (free octahedral sites) propensity to form adducts with nitrogen bases, since nitrogen atoms have one sp -hybrid orbital, which is occupied by the lone pair of stereochem-ically active electrons. To characterize newly prepared adducts of dimethyl-, diethyl- and morpholinedithiocarbamate zinc(II) complexes with cyclic N-donor bases, such as pyridine, piperidine, hexamethyleneimine and morpholine, compounds 28-35 have been prepared and studied by and CP/MAS... 

Abstract A variety of structural types of transition metal complexes containing a-borane ligands are reviewed. Their structure and bonding are discussed. Compared with other types of a-complexes, a-borane complexes display quite different structural and bonding properties because of the electron unsaturated boron center in the a-borane ligands in the precoordination state. The availability of an sp3-hybridized orbital at the boron center allows stronger back-donation interaction without breaking the coordinated B-H bond. The role played by a-borane complexes in hydroboration and borylation reactions has also been reviewed. 

Two other, closely related, consequences flow from our central proposition. If the d orbitals are little mixed into the bonding orbitals, then, by the same token, the bond orbitals are little mixed into the d. The d electrons are to be seen as being housed in an essentially discrete - we say uncoupled - subset of d orbitals. We shall see in Chapter 4 how this correlates directly with the weakness of the spectral d-d bands. It also follows that, regardless of coordination number or geometry, the separation of the d electrons implies that the configuration is a significant property of Werner-type complexes. Contrast this emphasis on the d" configuration in transition-metal chemistry to the usual position adopted in, say, carbon chemistry where sp, sp and sp hybrids form more useful bases. Put another way, while the 2s... 

Pauling further extended the sp"dm hybridization approach to the d-block compounds.3 By varying the relative importance of p and d orbitals, Pauling was able to construct hybrid orbitals that rationalized the geometries and magnetic properties of many transition-metal coordination complexes. For example, the square-planar... 

In the coordinated anionic polymerizations with Group I—III metal alkyls alone, monomer coordination involves overlap of the olefinic jr-electrons with vacant sp3 hybrid orbitals. Since this interaction is very weak it is most effective with easily polarized monomers. In the coordination polymerizations with Ziegler type catalysts, stronger monomer coordination is obtained by overlap of jr-electrons with vacant -orbitals of the transition metal component. The complexes have structures of the type proposed by Dewar (199b) and by Chatt and Duncanson (200) and applied to Ziegler type catalysts by Cossee (201) (Fig. 6). The olefin yr-electrons overlap with the orbital of... 

In organometallic complexes of alkenes, where a transition metal uses an empty d orbital to coordinate to the n bond of the alkene, the vinyl carbons move upfield to the range of 8 7-110, varying widely and depending on the exact structure of the complex.5 The reasons for this upfield shift include both shielding by the electron-rich electropositive metal, and a change in hybridization of the vinyl carbons toward less s character (i.e., more sp3 like). 

Hybridization in an octahedral complex in the valence bond model of coordination ompound the formation of bonds to an octahedral transition metal ion would involve six d sp h /hrid orbitals. In the approach used here the diff( ring syininetry properties of the s, thii p, p and p.. and the d, and d orbitals used in bonding are explicitly taken into account. However, the 3 all of the p and two ol the d metal valence shell orbitals are otill used in o-bond tormation. 

For an octahedral complex the jr-bonding leads in the (d2sp3) hybridization model to an increase in the number of electrons in the group of d orbitals which may be treated by Slater s rules, as well as to an increase of electrons in the next outer shell. As it is probable that the jr-coordinated electrons may not be completely assigned to the transition metal ion, and as the more accurate tables of Clementi 108> contain only values for neutral atoms, the resulting effect can... 

It cannot yet be claimed that the experimental evidence for such distortions from tetrahedral coordination is so well established as for the octahedral case, but this is largely attributable to the comparative rarity of structures in which transition-metal ions occur in a tetrahedral environment. There appear to be no examples of tetrahedral coordination about d3 and d ions, and only fragmentary information is available for d8 and d9 ions. It may be recalled that tetrahedral coordination was anticipated by Pauling 11 A) for paramagnetic 4-covalent complexes of nickel(II) on the grounds that, since all the d orbitals are occupied by electrons from the metal, the covalent bonding must occur through sp3 hybridized orbitals. It is now known that many formally 4-covalent complexes are, in fact,... 

Alkynyl complexes contain metal-carbon bonds in which the metal is bound to the sp-hybridized carbon at the terminus of a metal-carbon triple bond. The materials properties of these complexes have been investigated extensively. The properties of these complexes include luminescence, optical nonlinearity, electrical conductivity, and liquid crystallinity. These properties derive largely from the extensive overlap of the metal orbitals with the ir-orbitals on the alkynyl ligand. The M-C bonds in alkynyl complexes appear to be considerably stronger than those in methyl, phenyl, or vinyl complexes. Alkynyl complexes are sometimes prepared from acetylide anions generated from terminal alkynes and lithium bases (e.g., method A in Equation 3.42), but the acidity of alkynyl C-H bonds, particularly after coordination of the alkyne to the transition metal, makes it possible to form alkynyl complexes from alkynes and relatively weak bases (e.g., method B in Equation 3.42). Alkynyl copper complexes are easily prepared and often used to make alkynylnickel, -palladium, or -platinum complexes by transmetallation (Equation 3.43). This reaction is a step in the preparation of Ni, Pd, or Pt alkynyl complexes from an alkyne, base, and a catalytic amoimt of Cul (Equation 3.44). This protocol for... 

Carbene is a liable intermediate in organic reactions however, if it coordinates to a transition element, the coordination bond is stable and it is able to be isolated as a complex. Singlet carbene ( CX2) forms an sp hybrid orbital, has six electrons with two p-orbitals, and a third orbital remains as vacant (p orbital). When the carbene forms a complex, lone pair electrons of one of the sp hybrid orbitals a-donates to the metal atom and 7T-electrons of the metal back-donate to the vacant orbital p, of the carbon atom (a-donation rr-back donation). Therefore, this MC bond should thus exhibit partial double bond character. However, as the p, vacant orbital which is used for back donation didn t have enough acceptor orbitals available for the back-donation process, the double bond character is thought to be small [53]. 

A range of compounds has been synthesized by double-salt metathesis in which a two-coordinate, substituent-free gallium atom sits in an essentially linear environment between two transition metals. Compounds of the form (q -CjRjjjdppejFeGaMjCO) (M = Fe, n = 4j M = Cr, W, = 5 R = H, Me) may be accessed via reactions of (q -CjRjjjdppejFeGaCl with carbonylmetallate dianions K2[M(C0) ] [186-188, 244]. In such complexes, the bridging gallium atom is formally sp-hybridized and hence has two vacant p-orbitals, which may accept electron density from metal d-orbitals... 

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