Open shell organometallics: a general analysis of their electronic structure and reactivity

Abstract

Transition metal organometallic compounds that contain fewer than 18-electrons and two or more unpaired electrons are generally excluded from treatises of either Werner-type coordination compounds or organometallic chemistry. However, they can be seen as the bridge filling the gap between these two traditional areas of coordination chemistry. Their magnetic and optical properties are reminiscent of the Werner-type complexes, whereas their chemical reactivity parallels that of the lower-valent organometallics. Spin state change phenomena are of paramount importance in this area. This paper provides a broad perspective of this area, with particular attention to: (i) how the ground state properties can be related to the metal and ligands nature; (ii) under which circumstances the often inappropriately invoked concept of ''spin block'' is meaningful; (iii) the spin acceleration concept; (iv) how the coordination sphere affects the topology of the reaction coordinate in the vicinity of spin crossing points; and (v) the effect of spin state changes on reaction selectivities.

Synthesis, Structure, and Electrochemical Properties of Sterically Protected Molybdenum Trihydride Redox Pairs: A Paramagnetic “Stretched” Dihydrogen Complex?

“…[16] The steric bulk of the PMe 3 and 1,2,4-C 5 H 2 tBu 3 ligands, in combination with the electron-pairing stabilization provided by the spin-quartet state, [42,43] accounts for the absence of solvent coordination to complex 5 a. The oxidatively induced reductive elimination of compounds containing two one-electron ligands ([M(X)(Y)], leading to the elimination of X À Y) has previously been demonstrated for dialkyl complexes [M(R) 2 ] to give the alkane coupling product R À R [18,[44][45][46][47][48][49][50] and for alkyl-hydride complexes [M(R)(H)] to give the corresponding alkane RÀH, [18,47] plus products originating from [M] + .…”

A new local density functional for main-group thermochemistry, transition metal bonding, thermochemical kinetics, and noncovalent interactions

“…The addition of this data set is prompted by the increasing attention being paid by many workers to the relative energies of spin states of transition metal systems because of the importance of spin states for structures, properties, and chemical reactivities of organometallic complexes and for functional nanotechnology. [52][53][54][55][56][57][58][59][60][61][62] Holthausen made a systematic study 63 of the ability of density functionals to predict 3d-4s excitation energies in transition metal cations and found that some functionals, even though performing well for main group atomization energies, show large errors for transition metal atomic excitation energies. Because we seek a functional that is accurate for both main-group and transition metal chemistry, our small database has both types of atoms.…”

Reaktivität von Chromkomplexen unter Spinkontrolle

“…[15] Ein Wechsel des Spinzustandes zwischen den Oxidationsstufen ist jedoch durchaus möglich und könnte sogar zu einem beschleunigten Reaktionsschritt führen, wenn ein Spinwechsel ausreichend schnell verläuft. [16] Theoretische Studien von solchen spinverbotenen Reaktionen sind viel aufwändiger. In den letzten Jahren wurden erhebliche Fortschritte in diesem Zusammenhang gemacht, aber bisher noch nicht auf Reaktionsschritte in Schema 1 ausgeweitet.…”