The reaction of the copper(I) β-diketiminate copper complex {(Cu(BDI Mes )) 2 (μ-C 6 H 6 )} (BDI Mes = N,N′-bis(2,4,6trimethylphenyl)pentane-2,4-diiminate) with the low-valent group 13 metal β-diketiminates M(BDI Dip ) (M = Al or Ga; BDI Dip = N,N′-bis(2,6-diisopropylphenyl)pentane-2,4-diiminate) in toluene afforded the complexes {(BDI Mes )CuAl(BDI Dip )} and {(BDI Mes )-CuGa(BDI Dip )}. These feature unsupported copper−aluminum or copper−gallium bonds with short metal−metal distances, Cu−Al = 2.3010(6) Å and Cu−Ga = 2.2916(5) Å. Density functional theory (DFT) calculations showed that approximately half of the calculated association enthalpies can be attributed to London dispersion forces.

Conspectus Interactions between sterically crowded hydrocarbon-substituted ligands are widely considered to be repulsive because of the intrusion of the electron clouds of the ligand atoms into each other’s space, which results in Pauli repulsion. Nonetheless, there is another interaction between the ligands which is less widely publicized but is always present. This is the London dispersion (LD) interaction which can occur between atoms or molecules in which dipoles can be induced instantaneously, for example, between the H atoms from the ligand C–H groups. These LD interactions are always attractive, but their effects are not as widely recognized as those of the Pauli repulsion despite their central role in the formation of condensed matter. Their relatively poor recognition is probably due to the relative weakness (ca. 1 kcal mol–1) of individual H···H interactions owing to their especially strong distance dependence. In contrast, where there are numerous H···H interactions, a collective LD energy equaling several tens of kcal mol–1 may ensue. As a result, in some molecules the latent importance of the LD attraction energies emerges and assumes a prominence that can overshadow the Pauli effects (e.g., in the stabilization of high-oxidation-state transition-metal alkyls, inducing disproportionation reactions, or in the stabilization of otherwise unstable bonds). Despite being known for over a century, the accurate quantification of individual H···H LD effects in molecular species is a relatively recent phenomenon and at present is based mainly on modified DFT calculations. A few leading reviews summarized these earlier studies of the C–H···H–C LD interactions in organic molecules, and their effects on the structures and stabilities were described. LD effects in sterically crowded inorganic and organometallic molecules have been recognized. The author’s interest in these LD effects arose fortuitously over a decade ago during research on sterically crowded heavier main-group element carbene analogues and two-coordinate, open-shell (d1–d9) transition-metal complexes where counterintuitive steric effects were observed. More detailed explanations of these effects were provided by dispersion-corrected DFT calculations in collaboration with the groups of Tuononen and Nagase (see below). This Account describes our development of these initial results for other inorganic molecular classes. More recently, the work has led us to move to the planned inclusion of dispersion effects in ligands to stabilize new molecular types with theoretical input from the groups of Vasko and Grimme (see below). Our approach sought to use what Grimme has described as dispersion effect donor (DED) groups (i.e., spatially close-lying, densely packed substituents either as ligands (e.g., −C6H2-2,4,6-Cy3, Cy = cyclohexyl) or as parts of ligands (e.g., a Cy substituent) that produce relatively large dispersion energies to stabilize these new compounds. We predict that the future design of sterically crowding hydrocarbon ligands will include the ...

A series of alkali metal 1‐adamantoxide (OAd1) complexes of formula [M(OAd1)(HOAd1)2], where M=Li, Na or K, were synthesised by reduction of 1‐adamantanol with excess of the alkali metal. The syntheses indicated that only one out of every three HOAd1 molecules was reduced. An X‐ray diffraction study of the sodium derivative shows that the complex features two unreduced HOAd1 donors as well as the reduced alkoxide (OAd1), with the Ad1 fragments clustered together on the same side of the NaO3 plane, contrary to steric considerations. This is the first example of an alkali metal reduction of an alcohol that is inhibited from completion due to the formation of the [M(OAd1)(HOAd1)2] complexes, stabilized by London dispersion effects. NMR spectroscopic studies revealed similar structures for the lithium and potassium derivatives. Computational analyses indicate that decisive London dispersion effects in the molecular structure are a consequence of the many C−H⋅⋅⋅H−C interactions between the OAd1 groups.

Ethyl and amide zinc thioureides [L1ZnEt]2 (1), [L1*ZnEt]2 (2) and [L1Zn(N(SiMe3)2)]2 (3) have been synthesised from the equimolar reaction of thiourea ligands (HL1 = iPrN(H)CSNMe2 and HL1* = PhN(H)CSNMe2) with diethyl zinc and zinc...