Syntheses and structures of new alkali-metal boraamidinates and ferrocenyl aminoboranes

Abstract

The ferrocenyl bis(amino)boranes FcB[N(H)R]₂ (Fc = ferrocenyl; 1a, R = ^tBu, 1b, R = Dipp) and 1,1′-Fc{B[N(H)^tBu]₂}₂ (2) are obtained by the reactions of [Li][N(H)R] with the corresponding ferrocenyl dibromoboranes FcBBr₂ and 1,1′-Fc(BBr₂)₂. In a similar manner 1,4-[N(H)^tBu]₂BC₆H₄B[N(H)^tBu]₂ (3) is prepared in good yield by treatment of 1,4-Br₂BC₆H₄BBr₂ with five equivalents of [Li][N(H)^tBu] in toluene. Compound 3 is converted to the highly air-sensitive tetralithio derivative [Li₄][1,4-(N^tBu)₂BC₆H₄B(N^tBu)₂] (4), by deprotonation with ⁿBuLi in hexanes. Alkali-metal derivatives of a monoanionic boraamidinate [M][PhB(NDipp){N(H)Dipp}] [M = Li (5), K (6)] are produced by reactions of PhB[N(H)Dipp]₂ with one equivalent of ⁿBuLi in hexanes or [K][CH₂Ph] in THF, respectively. The use of two equivalents of [K][CH₂Ph] generates the dipotassium reagent [K₂][PhB(NDipp)₂] (7) in excellent yield. The X-ray structures of 1a, 1b, 2, 4·6THF, 5·2THF and 7·3THF were determined. The complex 4·6THF incorporates one terminal and one bridging THF molecule for each Li⁺ cation. The boraamidinate ligand in 5·2THF is connected in an N-monodentate fashion to the Li⁺ cation, which is solvated by two THF molecules. In the solid state 7·3THF forms an extended structure as a result of η¹-amide–η⁶-arene coordination to the two K⁺ cations, which are coordinated by one or two THF molecules, respectively.