Synthesis and Characterization of Strontium ,-Dimethylaminodiboranates as Possible Chemical Vapor Deposition Precursors.

The reaction of SrBr with 2 equiv of sodium -dimethylaminodiboranate (DMADB; Na(HBNMeBH)) in EtO at 0 °C followed by crystallization and drying under vacuum gives the unsolvated strontium compound Sr(HBNMeBH) (). Before the vacuum-drying step, the colorless crystals obtained by crystallization consist of the diethyl ether adduct Sr(HBNMeBH)(EtO) (). If the reaction of SrBr with 2 equiv of Na(HBNMeBH) is carried out in the more strongly coordinating solvent thf, the solvate Sr(HBNMeBH)(thf) () is obtained. Treating the thf adduct with 1,2-dimethoxyethane (dme), bis(2-methoxyethyl) ether (diglyme), or ,''-tetramethylethylenediamine (tmeda) in thf affords the new compounds Sr(HBNMeBH)(dme) (), Sr(HBNMeBH)(diglyme) (), and Sr(HBNMeBH)(tmeda) (), respectively, in greater than 60% yields. Treatment of with 2 equiv of the crown ether 12-crown-4 affords the charge-separated salt [Sr(HBNMeBH)(12-crown-4)][HBNMeBH] (). Crystal structures of all the Lewis base adducts are described. Compounds - all possess chelating κ-BHNMeBH-κ groups, in which two hydrogen atoms on each boron center are bound to strontium. Compound is dinuclear because each metal atom is also coordinated to one hydrogen atom on a BHNMeBH ligand that chelates to the neighboring metal center. Compound possesses an unusual κ-BHNMeBH group owing to the near-complete encapsulation of the Sr atom by two 12-crown-4 molecules; the other BHNMeBH anion is a charge-separated counterion. When they are heated, the diglyme and tmeda compounds and melt without decomposition and can be sublimed readily under reduced pressure (1 Torr) at 120 °C. The diglyme and tmeda adducts are some of the most volatile strontium compounds known and are promising candidates as CVD precursors for the growth of strontium-containing thin films.