Alkali metal influences in aluminyl complexes. Issue 33 (29th July 2022)

• Record Type: Journal Article
• Authors: Grams, Samuel; Mai, Jonathan; Langer, Jens; Harder, Sjoerd
• Is Part Of: Dalton transactions. Volume 51:Issue 33(2022)
• Page Start: 12476
• Page End: 12483
• Publication Date: 2022-07-29
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d2dt02111k
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Aluminyl complexes over the full series of alkali metals crystallize as dimers. The alkali metal influences structure, dimerization energies and reactivity. Abstract : The previously reported potassium aluminyl complex [(BDI-H)Al − K + ]2 was converted in Li + or Na + salts by a salt metathesis reaction with Li(BPh4 ) or Na(BPh4 ), respectively; BDI-H = dianionic [(DIPP)N–C(Me)C(H)–C(CH2 )–N(DIPP) 2− ] and DIPP = 2, 6-diisopropylphenyl. The Rb and Cs aluminyl complexes were obtained by reaction of (BDI)Al with RbC8 or CsC8 ; BDI = HC[C(Me)N(DIPP)]2 . Crystal structures of two monomers, (BDI-H)Al − Li + ·(Et2 O)2 and (BDI-H)Al − Na + ·(Et2 O)(TMEDA), and four dimers [(BDI-H)Al − M + ]2 (M = Li, Na, Rb, Cs) are discussed. Lewis base-free dimers [(BDI-H)Al − M + ]2 crystallize either as slipped dimers (Li +, Na + ) in which each Al center features only one Al–M contact or as a symmetric dimer (K +, Rb +, Cs + ) in which the cation bridges both Al centers. The dimer with the largest cation (Cs + ) shows Cs⋯CH2 C interactions between dimers, resulting in a coordination polymer. AIM and charge analysis reveal highly ionic Al–M bonds with strong polarization of the Al lone-pair towards the smaller cation Li + and Na + . The Al–M bonds become weaker from Li to Cs. Calculated dimerization energies suggest that in apolar solvents only complexes with the heavier metals Rb and Cs may be in a monomer–dimer equilibrium. This is confirmed by DOSY measurements in benzene. Dimeric aluminyl complexes with heavier alkali metals (K-Cs) react with benzene to give a double C–H activation in para -positions.