The reaction of 1 equiv of the dimeric lithium salt of a new London dispersion effect donor ligand {Li(C 6 H 2 -2,4,6-Cy 3 )•OEt 2 } 2 (Cy = cyclohexyl) with SnCl 2 afforded the distannene {Sn(C 6 H 2 -2,4,6-Cy 3 ) 2 } 2 (1). The distannene remains dimeric in solution, as indicated by its room-temperature 119 Sn NMR signal (δ = 361.3 ppm) and its electronic spectrum, which is invariant over the temperature range of −10 to 100 °C. The formation of the distannene, which has a short Sn−Sn distance of 2.7005(7) Å and greatly enhanced stability in solution compared to that of other distannenes, is due to increased interligand London dispersion (LD) attraction arising from multiple close approaches of ligand C−H moieties across the Sn−Sn bond. DFT-D4 calculations revealed a dispersion stabilization of dimer 1 of 38 kcal mol −1 and a dimerization free energy of ΔG dimer = −6 kcal mol −1 . In contrast, the reaction of 2 equiv of the similarly shaped but less bulky, less hydrogen-rich Li(C 6 H 2 -2,4,6-Ph 3 )•(OEt 2 ) 2 with SnCl 2 yielded the monomeric stannylene Sn(C 6 H 2 -2,4,6-Ph 3 ) 2 (2), which is unstable in solution at ambient temperature.

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.

The synthesis, molecular structures, and spectroscopic details of a series of isocyanide and nitrile complexes of the early first-row transition-metal tris­(silyl)­amides M­{N­(SiMe3)2}3 (M = Ti, V) are reported. Previously, first-row transition-metal tris­(silyl)­amides were generally thought to be incapable of forming complexes with Lewis bases due to their excessive steric crowding. However, it is now shown that simple treatment of the base-free trisamides with 2 equiv of an isocyanide or nitrile base at room temperature results in the formation of the trigonal bipyramidal complexes Ti­{N­(SiMe3)2}3(1-AdNC)2 (1), Ti­{N­(SiMe3)2}3(CyNC)2 (2), Ti­{N­(SiMe3)2}3(Bu t NC)2 (3), Ti­{N­(SiMe3)2}3(PhCN)2 (4), V­{N­(SiMe3)2}3(1-AdNC)2 (5), V­{N­(SiMe3)2}3(CyNC)2 (6), V­{N­(SiMe3)2}3(Bu t NC)2 (7), and V­{N­(SiMe3)2}3(PhCN)2 (8), which incorporate two donor ligands (1-AdNC = 1-adamantyl isocyanide, CyNC = cyclohexyl isocyanide, Bu t NC = tert-butyl isocyanide, PhCN = benzonitrile). All complexes display a characteristic increase in the frequency of the multiple bonded C–N stretching mode which is observed to be in the range of 2170–2190 cm–1 for the isocyanide complexes 1–3 and 5–7 and at 2250 cm–1 for the nitrile complex 8. This effect was not observed for the titanium nitrile complex 4, suggesting weak binding of the donor to titanium. Paramagnetic 1H NMR studies showed these complexes to have detectable, though extremely broadened, signals attributable to the trimethylsilyl groups of the amide ligands (δ = ca. 2.8 ppm for titanium isocyanide complexes, ca. 4.5–4.7 ppm for vanadium isocyanide complexes). A variable-temperature 1H NMR study showed that in solution these complexes exist as mixtures of the five-coordinate species and a putative four-coordinate species coordinating a single Lewis basic ligand. Electronic spectroscopy indicated that the vanadium complexes 5–8 bind the Lewis bases more strongly than the corresponding titanium complexes, where the spectra of complexes 1–4 are essentially identical to the base-free Ti­{N­(SiMe3)2}3 at the temperatures and concentrations studied. In contrast to these results, no corresponding complexes were detected for the metal silylamides M­{N­(SiMe3)2}3 (M = Cr, Mn, Fe, or Co) when treated with the isocyanide or nitrile bases.

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.

Treatment of Fe­{N­(SiMe3)2}2 with 2 equiv of the appropriate phenol or thiol affords the dimers {Fe­(OC6H2-2,6-Bu t 2-4-Me)2}2 (1) and {Fe­(OC6H3-2,6-Bu t 2)2}2 (2) or the monomeric Fe­{SC6H3-2,6-(C6H3-2,6-Pr i 2)2}2 (3) in moderate to excellent yields. Recrystallization of 1 and 2 from diethyl ether gives the corresponding three-coordinate ether complexes Fe­(OC6H3-2,6-Bu t 2-4-Me)2(OEt2) (4) and Fe­(OC6H3-2,6-Bu t 2)2(OEt2) (5). In contrast, no diethyl ether complex is formed by the dithiolate 3. The 1H NMR spectra of 4 and 5 show equilibria between the ether complexes and the base-free dimers. A comparison of these spectra with those of the dimeric 1 and 2 allows an unambiguous assignment of the paramagnetically shifted signals. Treatment of 1 with excess ammonia gives the tetrahedral diammine Fe­(OC6H2-2,6-Bu t 2-4-Me)2(NH3)2 (6). Ammonia is strongly coordinated in 6, with no apparent loss of ammine ligand either in solution or upon heating under low pressure. In contrast, significantly weaker ammonia coordination is observed when dithiolate 3 is treated with excess ammonia, which gives the diammine Fe­{SC6H3-2,6-(2,6-Pr i 2-C6H3)2}2(NH3)2 (7). Complex 7 readily loses ammonia either in solution or under reduced pressure to give the monoammine complex Fe­{SC6H3-2,6-(2,6-Pr i 2-C6H3)2}2(NH3) (8). The weak binding of ammonia by iron thiolate 7 reflects the likely behavior of the proposed iron–sulfur active site in nitrogenases, where release of ammonia is required to close the catalytic cycle.