MgCl and Mg₂Cl₂: From Theoretical and Thermodynamic Considerations to Spectroscopy and Chemistry of Species with MgMg Bonds

Abstract

Recently, compounds containing metal-metal bonds between main-group elements have attracted interest to a surprising extent. [1][2][3][4][5] In spite of the latest structural results for two crystalline Mg 2 R 2 compounds (R1 = [ArNC(NiPr 2 )NAr] À ; R2 = [{ArNCMe} 2 CH] À ; Ar= 2,6-diisopropylphenyl, iPr = isopropyl) [2] and in spite of a number of theoretical contributions on molecules with MgÀMg bonds, [10][11][12] several important questions still remain to be answered, for example, concerning the unexpected disproportionation stability of the abovementioned Mg I compounds. Herein, we present the following results: 1) On the basis of quantum-chemical-assisted thermodynamic calculations, a feasible synthesis of radical monomeric Mg I halides at temperatures near 900 8C is presented.2) The nature of the MgÀMg bond is investigated by spectroscopic examination of MgCl and its linear dimer Mg 2 Cl 2 in solid inert-gas matrixes; the MgÀMg dissociation energy is obtained. 3) By comparing the thermodynamics of Mg 2 Cl 2 (1), Mg 2 Cp 2 (2, Cp = cyclopentadienyl), and a model compound Mg 2 R* 2 (3, R* = C(NH 2 )(NCH 3 ) 2 ) analogous to crystalline Mg 2 (R1) 2 , the enormous disproportionation stability of the latter compound is explained. For further investigations, for example in the field of metal-rich Mg n R m clusters (n > m), the synthesis of reactive starting materials like MgCl is absolutely necessary. Initial results on the synthesis of MgCl are reported.After the first evidence for stable alkaline earth

Experimentally Based DFT Calculations on the Hindered Disproportionation of [Al4Cp*4]: Formation of Metalloid Clusters as Intermediates on the Way to Solid Al Prevents the Decomposition of a Textbook Molecule

“…Therefore, we suppose that the formation of metalloid [Zn n Cp* m ] clusters is a real challenge because the decomposition of [Zn 2 Cp* 2 ] requires too high a temperature, at which point any [(ZnCp*) n ] cluster (radical or closed‐shell species) will also decompose. A similar scenario to [Zn 2 Cp* 2 ] may be expected for the so far unknown [Mg 2 Cp* 2 ] molecule with its strong MgMg σ bond,43 similar to that of Mg 2 Cl 2 , which has a bond strength of about 190 kJ mol −1 as determined experimentally 44…”

Investigations of the Nature of ZnII−SiII Bonds

“…However,a midinates often bind more strongly to am etal center than C 5 H 5 À . [15] Silylene L,w hich was synthesized in ar ational approach by the reaction of KC 5 Me 5 and{ PhC(NtBu) 2 }ClSi in THF (Scheme 2), has now been fully characterized. It is readily soluble in common organic solvents such as THF, Et 2 O, toluene, and pentane.…”

“…Ligand L can formally be regarded as the amidinate mimic of [(η 5 ‐C 5 Me 5 ) 2 Si]. However, amidinates often bind more strongly to a metal center than C 5 H 5 − . Silylene L , which was synthesized in a rational approach by the reaction of KC 5 Me 5 and {PhC(N t Bu) 2 }ClSi in THF (Scheme ), has now been fully characterized.…”

Isomeric Al2R4, Mg2R2 Species and Oligomerisation Products: Investigation of Al–Al and Mg–Mg σ Bonding

“…Compound 14 is isoelectronic with the neutral molecule (Mg 2 Cl 2 ) 2 , where the magnesium centres have the rare oxidation state of Mg I . Although Mg 2 Cl 2 has been characterised theoretically [9] and, very recently, experimentally, [18] nothing is known about oligomeric species. Therefore, we have optimised the structure of (Mg 2 Cl 2 ) 2 (12) (D 2h symmetry, 1 A g state) in comparison with the two monomeric conformers, 13a and 13b, which are shown in Figure 11.…”

“…The stabilisation energies starting from Mg(g) and MgCl 2 (g) are so large that, for a reaction of MgCl 2 (g) with solid Mg(s) in a nonpolar solvent, an exothermic reaction to (Mg 2 Cl 2 ) x with x Ն 4 should proceed since the vaporisation enthalpy of Mg(s) is only 148 kJ mol -1 . [14] Furthermore, since Mg 2 Cl 2 could be obtained under matrix conditions recently, [18] there may be a chance to gain further stabilisation via an oligomerisation process that finally may end up with solid MgCl. Theoretical and experimental work on this subject is a challenge for future investigations.…”