Sodium Aminodiboranates Na(H₃BNR₂BH₃): Structural and Spectroscopic Studies of Steric and Electronic Substituent Effects

Abstract

We describe the syntheses of a series of sodium aminodiboranate salts, Na(H 3 B−NR 2 −BH 3 ), with different substituents on nitrogen, including sodium salts of the unsubstituted aminodiboranate, H 3 B−NH 2 −BH 3 − , and of the N-substituted anions H 3 B−NRR′−BH 3 − , where NRR′ = NHMe, NHEt, NH(SiMe 3 ), NEt 2 , N(i-Pr) 2 , N(SiMe 3 ) 2 , NMe(i-Pr), NMe(t-Bu), NMe-(SiMe 3 ), and the pyrrolidide and piperidide derivatives NC 4 H 8 , NC 5 H 10 , and NC 5 H 8 -cis-2,6-Me 2 . The compounds have been characterized by 1 H and 11 B NMR spectroscopy and IR spectroscopy; crystallographic studies have been carried out for the unsolvated N,N-dimethylaminodiboranate salt Na-(H 3 B−NMe 2 −BH 3 ) and several sodium aminodiboranate salts in which the sodium ions are solvated with ethers (dioxane, diglyme, tetrahydrofuran, and 12-crown-4) or amines (N,N,N′,N′tetramethylethylenediamine). One of the structures contains a rare example of an ether ligand in which one oxygen atom bridges between two metal ions. General structural and spectroscopic trends as a function of the substituents on nitrogen are discussed.

Structural and Spectroscopic Studies of Steric and Electronic Substituent Effects in a Series of Magnesium Aminodiboranates Mg[(BH3)2NMeR]2

“…The 11 B NMR spectra of 1–4 each consist of a 1:3:3:1 quartet at δ −11.82, −13.24, −14.08, and −14.80, respectively, with 1 J BH coupling constants of about 90 Hz. For the corresponding sodium salts, electron-donating substituents on the nitrogen atom deshield the 11 B NMR shift, whereas sterically bulky substituents shield the 11 B NMR shift; these empirical trends also appear to apply to the magnesium compounds. The 1 H NMR spectra are as expected (see the Experimental Section).…”

“…MgBr 2 was used as received from Aldrich. Sodium aminodiboranate salts were synthesized following previously reported procedures. , Magnesium dimethylaminodiboranate, 1 , was synthesized by the previously reported procedure . Microanalyses were performed by the University of Illinois Microanalytical Laboratory.…”

“…12,13 The attractive features of metal complexes of the DMADB anion have prompted us to explore the preparation of magnesium complexes of other aminodiboranate anions bearing a variety of substituents on nitrogen, which we have previously synthesized as sodium salts. 14 Varying the groups on the nitrogen atom may enable the preparation of new magnesium CVD precursors with greater volatility and improved reaction characteristics compared to Mg(DMADB) 2 . Tuning the physical and chemical properties of a CVD precursor by varying substituents has often led to improved CVD processes.…”

The Influence of Phosphorus Substituents on the Structures and Solution Speciation of Trivalent Uranium and Lanthanide Phosphinodiboranates

“…Our goal was to determine how a stepwise decrease in substituent size, especially from t Bu to i Pr to Et, affects the solid state and solution structures of f-element PDB complexes. 23 Here, we report the synthesis and characterization of i Pr-PDB complexes with U 3+ (U- i Pr), Nd 3+ (Nd- i Pr), Sm 3+ (Sm- i Pr), Tb 3+ (Tb- i Pr), and Er 3+ (Er- i Pr) as well as Et-PDB complexes with U 3+ (U-Et) and Nd 3+ (Nd-Et). Our results show how steric and metal-size-induced variations in B–P–B angles, as quantified using single-crystal XRD and supporting density functional theory (DFT) calculations, appear to control the extent of oligomerization of trivalent f-element PDB complexes in solution.…”