The first example of an intermolecular weak (agostic)γ-methyl-metal interaction: the low temperature single crystal X-ray and neutron diffraction structure of (MgR2)∞[R = CH(SiMe3)2]

Abstract

The crystalline homoleptic magnesium alkyl (MgR₂)_∞[R = CH(SiMe₃)₂], derived from Mg(OC₆H₂Bu^t₂-2,6-Me-4)₂ and 2LiR, is shown by low temperature X-ray (190 K) and neutron (15 K) diffraction to have the structure [Mg{CH(SiMe₃)[SiMe₂(µ-Me)]}R]_∞, with the MgC₂C′ unit coplanar (C′ refers to µ-C′H₃ of a neighbouring Mg′R₂ moiety), Mg-C 2.117(4) and 2.105(4)Å, short Mg ⋯ C [2.535(4)Å] and Mg′⋯ H [2.333(4), 2.414(5), and 2.516(4)Å] contacts, and the bridging methyl group adopting a pseudo trigonal bipyramidal arrangement [Mg ⋯ C(H)₃-Si: Mg′⋯ C-Si 172.3(2)°, <H-C-H> 110.4°, and a longer {1.915(8)Å} C-Si bond than those {av.1.877(6)Å} not involved in a Mg contact].