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Simple silyl ethers like O(SiMe3)2 in contrast to normal ethers are inert to metal bonding; however, a "naked", highly Lewis-acidic, cationic Mg species enforces complexation. DFT calculations indicate that agostic interactions and van der Waals attraction significantly contribute to the stability of this first example of unsupported metal silyl ether coordination.

Reaction of the trityl cation in [Ph3C+]­[B­(C6F5)4 –] with the n-butyl anion in (BDI)­MgnBu led to ß-hydride abstraction and formation of Ph3CH, 1-butene, and [(BDI)­Mg+]­[B­(C6F5)4 –] (1) (BDI = CH­[C­(CH3)­N-Dipp]2; Dipp = 2,6-diisopropylphenyl). The “naked” Mg center in 1 is weakly bound to B­(C6F5)4 – through two Mg···F interactions. Addition of arenes to 1 gave strongly bound cationic magnesium π–arene complexes (BDI)­Mg+·arene in good yields arene = benzene (94%), toluene (74%), m-xylene (82%), and mesitylene (63%). 1,2,4,5-Tetramethylbenzene is too bulky to give a coordination complex. Crystal structures of these π-arene complexes show η3–arene–Mg interactions for the smaller arenes (benzene, toluene and m-xylene). In each case, the coordination sphere was filled by an additional Mg···F interaction. For mesitylene, η6-coordination was found, leaving no space at the metal for supplementary Mg···F interaction. Dissolved in C6D5Br, all arene complexes are in association–dissociation equilibrium: (BDI)­Mg+ + arene ⇄ (BDI)­Mg+·arene. For the most strongly bound mesitylene ligand, a decoalescence of the 1H NMR resonances was reached at −20 °C, each species giving separate signals. From the temperature dependency of this equilibrium, the following thermodynamic parameters have been deduced: ΔH 0 = −6.9 kcal·mol–1 and ΔS 0 = −28.2 cal·mol–1·K–1. DFT calculations reveal that the Mg···arene bonding is mainly electrostatic of nature with only little charge transfer from arene to Mg2+ (ca. 0.05 e) and a slight polarization of π-electron density toward the metal. Substitution of benzene in (BDI)­Mg+·C6H6 for mesitylene is exothermic by −11.7 kcal/mol; however, including the B­(C6F5)4 – counterion in the calculation gave an energy gain of −2.2 kcal/mol. This clearly demonstrates that weakly coordinating anions can affect these Mg···arene interactions substantially.

The reaction of (tBuBDI)­ZnEt with [Ph3C+]­[B­(C6F5)4 −] yielded the cation (tBuBDI)­Zn+ (tBuBDI = CH­[C­(tBu)­N-DIPP]2, DIPP = 2,6-diisopropylphenyl). The cation is sterically too shielded to interact with the ion B­(C6F5)4 – but forms complexes with arenes (benzene, toluene, m-xylene) or halobenzenes (PhX: X = F, Cl, Br, I). Crystal structures of these complexes are compared with those of the corresponding Mg complexes. Although Mg2+ and Zn2+ are of equal size, the Zn···arene and Zn···XPh contacts are generally 0.1–0.2 Å shorter than comparable contacts to (tBuBDI)­Mg+. This originates from differences in bond character: bonding to Mg has a more electrostatic nature. A major difference between Mg and Zn is observed for PhF complexation. While the hard Mg2+ cation prefers Mg···FPh bonding, the softer Zn2+ shows a Zn···(π)­PhF interaction. Heavier halobenzenes with softer halogens (Cl, Br, I) show Zn···XPh bonding. DFT calculations on (tBuBDI)­Zn+···XPh (X = F, Cl, Br, I) show decreasing Zn···X–Ph angles from PhF to PhI on account of the increase in the halogen’s σ-hole. Zn···XPh interactions result in C–X bond lengthening, but C–X bond activation is less pronounced than in corresponding Mg···XPh complexes. Weak (tBuBDI)­Zn+···XPh bonding could not be detected in solution but is believed to play a role in the functionalization of organohalides by Zn reagents.