Low-coordinate Potassium Alkoxide - an Efficient Trap for Arenes: the Role of Ηn Non-Covalent Bonding in Substrate Activation for C-H Bond Metalation

Metalation of bulky tris(2-(piperidin-1-yl-methyl)phenyl)methanol [(C5H10N)CH2C6H4-o]3COH with (Me3Si)2NK in Et2O results in a dimeric potassium alkoxide {[(C5H10N)CH2C6H4-o]3C(μ2-O)K(Et2O)}2 (1). The Et2O molecule can be removed from the K+ coordination sphere affording coordinatively unsaturated alkoxide species which readily traps π-donor molecules. In the presence of excess arene, the reactions result in ηn-π-complexes, retaining in the crystal state a dimeric core {[(C5H10N)CH2C6H4-o]3C(μ2-O)K(ηn-arene)}2 (arene = C6H6 (2), CH3C6H5 (3), C10H8 (4)). With C6H5OMe and C6H5NMe2 molecules containing competing n- and π-donating sites, the reactions proceed differently: the former coordinates to K+ through an oxygen lone pair resulting in {[(C5H10N)CH2C6H4-o]3C(μ2-O)K(κ1-O(Me)C6H5)}2 (5) while for the latter, π-arene interaction turns out to be preferable, yielding {[(C5H10N)CH2C6H4-o]3C(μ2-O)K(η2-C6H5NMe2)}2 (6). The reactions with equimolar amounts of benzene or thiophene afford coordination polymers [{[(C5H10N)CH2C6H4-o]3C(μ2-O)K}2(μ-C6H6)]n (7) and [{[(C5H10N)CH2C6H4-o]3C(μ2-O)K}2(μ-C4H4S)]n (8), in which benzene and thiophene molecules are μ-bridging two K+ ions. The treatment of {[(C5H10N)CH2C6H4-o]3C(μ2-O)K(η2-CH3C6H5))}2 with Me3SiCH2Li or n-BuLi (1.2 eq.) in hexane at 20 °C results in the facile metalation of the Me group of toluene, forming [PhCH2K]n and lithium alkoxide. This model reaction provides a deeper insight into the probable mechanism of metalation of CH bonds under Lochmann-Schlosser superbasic conditions, and the role and the nature of the synergistic effect of two metals. The calculations and QTAIM analysis were performed for 1-8 and model molecules as well.