Agostic Interactions in d⁰Metal Alkyl Complexes

Abstract

The phenomenon of agostic interactions is reviewed and the nature of the interaction is revisited. A historical perspective is followed by an overview of experimental techniques used to diagnose agostic behavior, and previous interpretations of agostic bonding are presented. A series of simple metal alkyl complexes is considered and a new model for the phenomenon in d(0) systems is developed which sets them apart from agostic late-transition-metal complexes. Factors such as the valence electron count and coordination number of the metal center are revealed to be unimportant in facilitating the interaction in most d(0) systems. The charge density distribution in several transition-metal alkyl complexes is explored by experimental and theoretical techniques, including the powerful "Atoms in Molecules" approach. Local charge concentrations are shown to play an important role in the agostic interaction. Finally, we demonstrate for the first time a way to manipulate and control the magnitude and disposition of such local charge concentrations, and hence the strength of agostic interactions in d(0) metal alkyl complexes.

Highly branched unsaturated polyethylenes achievable using strained imino-cyclopenta[b]pyridyl-nickel precatalysts

“…1 H NMR (CDCl3, 400 MHz, TMS): δ 7.80 (d, J = 8.0 Hz, 1H), 7.49 (d, J = 8.0 Hz, 1H), 2.97 (s, 2H), 1.28 (s, 6H). 13 C NMR (CDCl3,100 MHz,TMS): δ 208.2,153.3,153.1,145.9,137.7,128.8,45.0,40.1,25. [b]pyridin-7-one (7.84 g, 0.040 mol), NaOH (1.90 g, 0.048 mol) and 10% Pd/C (0.80 g) in methanol (80 mL) was stirred under an atmosphere of hydrogen for 8 h at ambient temperature. The mixture was then filtered and extracted with CH2Cl2 (3× 50 mL).…”

Methyl Complexes of the Transition Metals

“…152 Computational studies of agostic interactions in early and late transition metal complexes have been reported in the last years. [153][154] Characterization of such interactions may in some cases, particularly with α-agostic interactions, require NMR and theoretical analysis, in addition to X-ray diffraction data, since the latter technique may not be precise enough to reveal the activation of the bridging C-H bond. 148 As an example, a series of heterobimetallic complexes of rhodium and osmium with bridging methyls have been characterized by X-ray diffraction and NMR.…”

“…156 An additional support for the agostic interaction was that the 1 H chemical shift δ of the bridging methyl increased in samples with monodeuterated bridges, as a result of the isotopic perturbation resonance (IPR) effect. 153 The effect of the bridging ligand on the nature of the metal-metal bond and the bond order has been studied in detail by Baik, Frieser and Parkin 144,157 using dimolybdenum complexes. 158 According to their analysis, the resulting effect of a bridging methyl (or H) ligand can be seen as the protonation of one of the metal-metal bonds.…”

Anagostic Interactions under Pressure: Attractive or Repulsive?

“…4, Figure 4a) and signals the electron-deficient nature of the respective M•••H'ago-C moieties in 2 and 4. [17] ) and a BCP is even lacking in case of 4. [18] The weakness of the agostic interaction in 2 also becomes obvious by direct comparison with the d 8 …”