D Transition metals

Application of a New Tight-Binding Total Energy Method to 4-d Transition Metals and Compounds... 

The mechanism of the poisoning effect of nickel or palladium (and other metal) hydrides may be explained, generally, in terms of the electronic theory of catalysis on transition metals. Hydrogen when forming a hydride phase fills the empty energy levels in the nickel or palladium (or alloys) d band with its Is electron. In consequence the initially d transition metal transforms into an s-p metal and loses its great ability to chemisorb and properly activate catalytically the reactants involved. 

Stereochemical aspects of reactions of complexes of d° transition metals with multiply bonded ligands. Y. V. Kokunov and Y. A. Buslaev, Coord. Chem. Rev., 1982, 47,15-40 (120). 

Oxalamidinate anions represent the most simple type of bis(amidinate) ligands in which two amidinate units are directly connected via a central C-C bond. Oxalamidinate complexes of d-transition metals have recently received increasing attention for their efficient catalytic activity in olefin polymerization reactions. Almost all the oxalamidinate ligands have been synthesized by deprotonation of the corresponding oxalic amidines [pathway (a) in Scheme 190]. More recently, it was found that carbodiimides, RN = C=NR, can be reductively coupled with metallic lithium into the oxalamidinate dianions [(RN)2C-C(NR)2] [route (c)J which are clearly useful for the preparation of dinuclear oxalamidinate complexes. The lithium complex obtained this way from N,N -di(p-tolyl)carbodiimide was crystallized from pyridine/pentane and... 

Table 20-1 Oxidation States Displayed by the 3 d Transition Metals ...

Cyclometallation reactions of 6-(thienyl)-2,2 -bipyridine with d transition metal ions. Journal of the Chemical Society, Dalton Transactions, (14), 2251. 

Deng, L., Ziegler, T., 1997, Theoretical Study of the Oxidation of Alcohols to Aldehyde by d° Transition-Metal-Oxo Complexes Combined Approach Based on Density Functional Theory and die Intrinsic Reaction Coordinate Method , Organometallics, 16, 716. 

F.E. Mabbs and D. Collison, Electron Paramagnetic Resonance of d Transition Metal Compounds, Elsevier, Amsterdam, 1992. 

As a typical case, olefin-metal complexation is described first. Alkene complexes of d° transition metals or ions have no d-electron available for the 7i-back donation, and thus their metal-alkene bonding is too weak for them to be isolated and characterized. One exception is CpfYCH2CH2C(CH3)2CH=CH2 (1), in which an intramolecular bonding interaction between a terminal olefinic moiety and a metal center is observed. However, this complex is thermally unstable above — 50 °C [11]. The MO calculation proves the presence of the weak metal-alkene bonding during the propagation step of the olefin polymerization [12,13]. 

Evangelisti and Brechin [13]. The results of their work can help determine which of the d-transition metals are most suitable as cometals, if appropriate to the synthetic routes pursued. 

Dichalcogenolene ligands form complexes with main group and d transition metal ions.103 Bis( 1,2-dithiolene) complexes have been obtained for metals, such as Cr, Mn, Ni, Cu, Zn, for the first row, Pd, Ag, and Cd for the second row, and Pt, Au, and Hg for the third row. Homoleptic /ra(l,2-dithiolcnc) complexes have been obtained for Ti, V, Cr, Zr, Nb, Mo, Tc, Ru, Ta, W, Re, and Os. Fe and Co have been found both in bis and /ra(l,2-dithiolene) complexes, although /ra(l,2-dithiolene) complexes containing these metal ions... 

Scheme 6.1 Elementary steps for the hydrogenation of olefins with d° transition-metal complexes.

Water exchange on main group and d-transition metal ions... 

IV. Water Exchange on Main Group and d-Transition Metal Ions... 

The larger Mg " " ion is hexa-coordinated. The water exchange rate for [Mg(H20)6] " (40) lies between those of the d-transition metals [Co(H20)6] + and [Ni(H20)e] + (Tables I and Table II), and reflects the order of ionic radii of these three ions. The measured activation volume is... 

A better insight into the mechanistics of water exchange on the 2nd and 3rd row d-transition metal ions came from quantum chemical calculations 87). For the rhodium(III) ion two transition states have been obtained, one for the dissociative and one for the interchange mechanisms, whereas for the... 

Recently, the oxidative addition of C2-S bond to Pd has been described. Methyl levamisolium triflate reacts with [Pd(dba)2] to give the cationic palladium complex 35 bearing a chiral bidentate imidazolidin-2-ylidene ligand [120]. The oxidative addition of the levamisolium cation to triruthenium or triosmium carbonyl compounds proceeds also readily to yield the carbene complexes [121], The oxidative addition of imidazolium salts is not limited to or d transition metals but has also been observed in main group chemistry. The reaction of a 1,3-dimesitylimidazolium salt with an anionic gallium(I) heterocycle proceeds under formation of the gaUium(III) hydrido complex 36 (Fig. 12) [122]. 

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