SiH and CH Activation by Transition Metal Complexes: A Step Towards Isolable Alkane Complexes?

Abstract

The recognition of the fundamental contributions by G. A. Olah on the elucidation of the structure of nonclassical carbocations, in the form of the award of the Nobel prize for chemistry, has recently emphasized the importance of electron-deficient bonds in the understanding of chemical bonding in organic chemistry. In the field of coordination chemistry, the formulation of electrondeficient bonds has been used for some time to describe nonclassical interactions between atoms. Traditional ligands in coordination chemistry such as amines and phosphanes bond to metal centers through their lone pair of electrons. Synergistic bonding effects dominate in the coordination of Jr-bonded ligands such as alkenes. In the mid-1980s the discovery of dihydrogen complexes having side-on coordination of H, gave fresh impetus to transition metal chemistry as well as to the understanding of the interaction of o-coordinating ligands with transition metals. In the meantime, transiton metal complexes can be obtained with a variety of ocoordinated X-H fragments, and their mode of bonding can be understood by a common and quite general model. The chemistry of o-bound silane ligands is particularly varied and well-investigated. These silane ligands enable the investigation of a large range of G-coordinated metal complex fragments up to complete oxidative addition with cleavage of the Si-H bond and formation of silyl(hydrid0) complexes, which has thus also widened our general understanding of the bonding of other o-bound ligands. Whilst there is a large range of isolable and stable H, and SiR, complexes available, there are no such alkane analogues known at present. Only when the C-H bond is part of a ligand that is already directly bonded to the transition metal center will the resulting chelate effect stabilize this agostic C-H-M interaction. The complexation of SiH, , the simplest heavier homologue of CH,, was achieved recently. This is a further step towards the understanding of the factors which govern o-complexation of ligands at transition metal centers.

Hard Carbon Coatings: The Way Forward

“…In addition the elastic limit is much lower than for diamond, and the adhesion can be very poor on many substrates. 23 It can modify the hydrogen-carbon strength, and can influence the recombination or selective etching (e.g., by atomic nitrogen) of the bonded hydrogen, leading to the rejection of hydrogen. 15 Because hydrogen is monovalent, the hydrogen atom cannot be an interconnecting element with a strong covalent bond on each side of the chain.…”

Strength of Si–H ⋯ B charge-inverted hydrogen bonds in 1-silacyclopent-2-enes and 1-silacyclohex-2-enes

“…For example, in case of Y being a transition metal, this interaction is called an agostic bond [10][11][12][13] or a σ interaction [12][13][14][15][16][17] depending on a specific situation, whereas if Y is an electron-deficient element (as, for example, boron), this type of interaction was called a "charge-inverted hydrogen bond" (CIHB) [11][12][13][18][19][20][21][22][23][24][25]. Therefore, the electron-deficient Si-H-B bridge (this term was being used by Wrackmeyer et al [1][2][3][4]) in investigated systems in fact represents one of the examples of intramolecular charge-inverted hydrogen bonds (IMCIHB).…”

Methane activation by chromium oxide cations in the gas phase: A theoretical study

“…CH bond activation of methane and alkanes is the subject of considerable interest in recent transition metal catalytic chemistry 1–9. Gas‐phase experimental and theoretical investigations were by wide and large exploited as sources of complementary information.…”