Unsupported Mg–Alkene Bonding

Abstract

The first intermolecular early main group metal–alkene complexes were isolated. This was enabled by using highly Lewis acidic Mg centers in the Lewis base‐free cations (MeBDI)Mg+ and (tBuBDI)Mg+ with B(C6F5)4− counterions (MeBDI=CH[C(CH3)N(DIPP)]2, tBuBDI=CH[C(tBu)N(DIPP)]2, DIPP=2,6‐diisopropylphenyl). Coordination complexes with various mono‐ and bis‐alkene ligands, typically used in transition metal chemistry, were structurally characterized for 1,3‐divinyltetramethyldisiloxane, 1,5‐cyclooctadiene, cyclooctene, 1,3,5‐cycloheptatriene, 2,3‐dimethylbuta‐1,3‐diene, and 2‐ethyl‐1‐butene. In all cases, asymmetric Mg–alkene bonding with a short and a long Mg−C bond is observed. This asymmetry is most extreme for Mg–(H2C=CEt2) bonding. In bromobenzene solution, the Mg–alkene complexes are either dissociated or in a dissociation equilibrium. A DFT study and AIM analysis showed that the C=C bonds hardly change on coordination and there is very little alkene→Mg electron transfer. The Mg–alkene bonds are mainly electrostatic and should be described as Mg2+ ion‐induced dipole interactions.

Cationic Aluminium Complexes as Catalysts for Imine Hydrogenation

“…The neutral (BDI)AlR 2 complexes were converted into (BDI)AlR + cations by reaction with [Ph 3 C + ][B(C 6 F 5 ) 4 − ] in the polar but weakly coordinating solvent chlorobenzene (Scheme 1). Like observed previously in the syntheses of comparable (BDI)Mg + cations [14–17] or (BDI)Zn + cations, [18] the colour change from dark orange towards pale yellow or colourless indicated completion of the reaction. Purification of the borate salts, however, was challenging and afforded the laborious development of individual procedures for each individual complex.…”

“…[10][11][12][13] Our group has been interested in molecule activation with highly Lewis acidic cationic main group metal complexes. [14][15][16][17][18][19] We recently reported that Jordan's cationic β-diketiminate aluminium complex, ( Me,DIPP BDI)AlMe + , can be used as a highly Lewis acidic component in FLP activation of alkynes or CO 2 . [20] Attempts to convert these stoichiometric reactions to a catalytic protocol failed.…”

Lewis Acidic Cationic Strontium and Barium Complexes

“…Upon addition of a number of mono-and bis-alkenes, the first unsupported group 2 metal alkene complexes could be isolated and were fully characterized. [48] Increasing the bulk of the β-diketiminate ligand allowed for isolation of the full series of Mg•••XPh complexes (X=F, Cl, Br, I). [49] It was shown that the coordinated benzene ligand in (BDI)Ca + • C 6 H 6 is activated for nucleophilic attack: reaction with the low-valent Al l species (BDI)Al gave 1,4addition to benzene resulting in a species containing the nonplanar, anti-aromatic C 6 H 6 2À anion which can be seen as a (BDI) Ca + cation interacting with an alumina-norbornadiene (III).…”

“…The very high Lewis acidity of their metal centers was not only demonstrated by bonding of π‐ arenes including benzene, toluene and m ‐xylene, [42–45] but also by coordination of 3‐hexyne [46] and hexamethyldisiloxane, [47] a silyl ether normally inert to metal bonding ( II ). Upon addition of a number of mono‐ and bis ‐alkenes, the first unsupported group 2 metal alkene complexes could be isolated and were fully characterized [48] . Increasing the bulk of the β‐diketiminate ligand allowed for isolation of the full series of Mg⋅⋅⋅XPh complexes (X=F, Cl, Br, I) [49] .…”

Cationic Heterobimetallic Mg(Zn)/Al(Ga) Combinations for Cooperative C–F Bond Cleavage

“…[32][33][34][35] We and others recently reported as eries of cationic bdiketiminate alkaline earth (Ae) metal complexes (IV) [36,37] which, being free of additional Lewis bases,d isplay high Lewis acidity. [38][39][40] It was shown that ac ombination of the Lewis acidic cation ( Me BDI)Ca + and Roeskysl ow-valent bdiketiminate Al I complex ( Me BDI)Al [41] is able to reduce benzene (V). [42] Mixing ( Me BDI)Al with [( Me BDI)Ca(m-H)] 2 led to C À Ha ctivation of benzene (VI)t og ive ( Me BDI)Al-(H)Ph.…”