Four GENERAL TRANSITION METAL COMPOUNDS

The first part of the present volume complements and extends the collection of magnetic susceptibility data for coordination and organometallic transition metal compounds which was presented as volume II/2 of the New Series of Landolt-Bdrnstein tables [21]. The literature covered here adds directly to that included in the previous volume [21] and extends to the end of 1968. It is expected that the series of volumes on magnetic data of transition metal compounds will be continued by supplementary volumes, each covering two years of literature. The extensive amount of magnetic data in this volume from a period of between four and five years as compared to the data in volume II/2 (which covers the years 1899 to 1964) reflects the general increase in the number of scientific publications. 

MOMEC is a force field for describing transition metal coordination compounds. It was originally parameterized to use four valence terms, but not an electrostatic term. The metal-ligand interactions consist of a bond-stretch term only. The coordination sphere is maintained by nonbond interactions between ligands. MOMEC generally works reasonably well for octahedrally coordinated compounds. 

In general M and M may differ or be the same and X may be NR2, OR, a halide, SR, S, 0, etc. The use of Group I metal amides in the synthesis of other metal amides (equations 12-19) provides one class of this type of reaction. A four-center transition state can in most cases be invoked and in studies of the ligand redistributions between Ti(NMe2)4 and Ti(OR)4 compounds (R = Bu and Pr ) activation parameters are consistent with this view.226,227... 

These early successes with carbonyl complexes of rhenium encouraged me to undertake systematic research on the carbon monoxide chemistry of the heavy transition metals at our Munich Institute during the period 1939-45, oriented towards purely scientific objectives. The ideas of W. Manchot, whereby in general only dicarbonyl halides of divalent platinum metals should exist, were soon proved inadequate. In addition to the compounds [Ru(CO)2X2] (70), we were able to prepare, especially from osmium, numerous di- and monohalide complexes with two to four molecules of CO per metal atom (29). From rhodium and iridium (28) we obtained the very stable rhodium(I) complexes [Rh(CO)2X]2, as well as the series Ir(CO)2X2, Ir(CO)3X, [Ir(CO)3]j (see Section VII,A). With this work the characterization of carbonyl halides of most of the transition metals, including those of the copper group, was completed. 

A general review by Cundy et al. (76) on silicon-transition metal complexes has appeared, and again, we select only a few molecules to highlight different properties and chemistry within an isoelectronic group. In the four examples (Cp)Mn(CO)2(/u-H)Si(F)(Ph)2 (30), (Cp)Fe(CO)2Si-(F)(Ph)2 (31), (Cp)Mn(CO)2(M-H)Si(Cl)3 (32), and (Cp)Fe(CO)2Si(Cl)3 (33), compounds 30-31 and 32-33 are isoelectronic pairs based on the total number of valence electrons. Compounds 30 and 32 also form a related pair with respect to the three-center, two-electron Si—H—Mn interactions. 

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