Alkali-metal alkylberyllium alkoxides

Abstract

Three series of alkali-metal t-butoxyberyllate complexes are described, including MBe(OBu^t)₃(M = Li, Na, K, Rb, or Cs), [MEtBe(OBu^t)₂]₂(M = Li or Na), and [MEt₂Be(OBu^t)]₂(M = Na or K). The series MBe(OBu^t)₃ is formed from MOBu^t and Be(OBu^t)₂, from Na₂BeH₄ and Bu^tOH, or from K and Be(OBu^t)₂ in Bu^tOH. The Li and Rb complexes crystallise from benzene though the others are insoluble in that solvent. The Li and Na complexes dissolve in bis(2-methoxyethyl) ether yielding hexane-soluble 1:1 monomeric co-ordination complexes. The LiBe(OSiMe₃)₃ and LiBe(OBu^t)₂(OCEtMe₂) complexes are dimeric in benzene solution. In contrast, LiBe(OCEt₃)₃ exists in a dimer-monomer equilibrium in benzene solution. The series [MEtBe(OBu^t)₂]₂ are conveniently prepared from EtLi and Be(OBu^t)₂ or from NaOBu^t and EtBeOBu^t. Replacement of the ethyl group in the former with a t-butyl group yields dimeric [LiBu^t(OBu^t)₂]₂, though Li₂Bu^t₂Be(OBu^t)₂ has a degree of association of between 1 and 2 in benzene solution. Complexes of the type [MEt₂Be(OBu^t)]₂ are readily prepared from equimolar mixtures of NaOBu^t or KOBu^t with Et₂Be, though Rb₂Et₃Be₂(OBu^t)₃ is isolated from equimolar portions of RbOBu^t and Et₂Be. Sodium diethyl t-butoxyberyllate reacts with toluene or mesitylene giving red K₅Et₃Be₃(OBu^t)₄(PhCH₂)₄ or orange diamagnetic K₃Et₂Be₂(OBu^t)₂(mesityl)₂, respectively. The rubidium complex gives red Rb₅Et₃Be₃(OBu^t)₂(mesityl)₄ on reaction with mesitylene. Sparingly benzene-soluble LiBu^tBe(NMe₂)₂ is also described.