Synthesis and Characterization of Calcium N,N-Dimethylaminodiboranates as Possible Chemical Vapor Deposition Precursors
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- 作者：Andrew C. Dunbar ; Gregory S. Girolami
- 刊名：Inorganic Chemistry
- 出版年：2014
- 出版时间：January 21, 2014
- 年：2014
- 卷：53
- 期：2
- 页码：888-896
- 全文大小：334K
- ISSN：1520-510X
文摘
The reaction of CaBr<sub>2sub> with 2 equiv of sodium N,N-dimethylaminodiboranate, Na(H<sub>3sub>BNMe<sub>2sub>BH<sub>3sub>) in Et<sub>2sub>O at 0 掳C followed by crystallization and drying in vacuum yields the unsolvated calcium compound Ca(H<sub>3sub>BNMe<sub>2sub>BH<sub>3sub>)<sub>2sub>, 1. Before the vacuum drying step, the colorless crystals obtained by crystallization consist of the diethyl ether adduct Ca(H<sub>3sub>BNMe<sub>2sub>BH<sub>3sub>)<sub>2sub>(Et<sub>2sub>O)<sub>2sub>, 2. If the reaction of CaBr<sub>2sub> with 2 equiv of Na(H<sub>3sub>BNMe<sub>2sub>BH<sub>3sub>) is carried out in the more strongly coordinating solvent tetrahydrofuran (thf), the solvate Ca(H<sub>3sub>BNMe<sub>2sub>BH<sub>3sub>)<sub>2sub>(thf)<sub>2sub>, 3, is obtained. This compound does not desolvate as easily in vacuum as the diethyl ether compound 2. Treating the thf adduct 3 with 1,2-dimethoxyethane (dme), bis(2-methoxyethyl) ether (diglyme), or N,N,N鈥?i>,N鈥?tetramethylethylenediamine (tmeda) in thf affords the new compounds Ca(H<sub>3sub>BNMe<sub>2sub>BH<sub>3sub>)<sub>2sub>(dme), 4, Ca(H<sub>3sub>BNMe<sub>2sub>BH<sub>3sub>)<sub>2sub>(diglyme), 5, and Ca(H<sub>3sub>BNMe<sub>2sub>BH<sub>3sub>)<sub>2sub>(tmeda), 6, respectively, in greater than 60% yields. Treatment of 3 with 2 equiv of the crown ether 12-crown-4 in thf affords the charge-separated salt [Ca(12-crown-4)<sub>2sub>][H<sub>3sub>BNMe<sub>2sub>BH<sub>3sub>]<sub>2sub>, 7. Crystal structures of all the Lewis base adducts are described. Compounds 2鈥?b>6 all possess chelating 魏<sup>2sup>-BH<sub>3sub>NMe<sub>2sub>BH<sub>3sub>-魏<sup>2sup> groups, in which two hydrogen atoms on each boron center are bound to calcium. Compound 7 is the only ionic compound in the series; the Ca atom is completely encapsulated by two 12-crown-4 rings, and the anions are charge-separated counterions within the unit cell. When heated, the dme, diglyme, and tmeda compounds 4, 5, and 6 melt without decomposition, and can be sublimed readily under reduced pressure (1 Torr) at 90 掳C (4) and 120 掳C (5, 6). The dme adduct is one of the most volatile calcium compounds known, and is a promising CVD precursor for the growth of calcium-containing thin films.