Volatility, High Thermal Stability, and Low Melting Points in Heavier Alkaline Earth Metal Complexes Containing Tris(pyrazolyl)borate Ligands

Abstract

Treatment of MI(2) (M = Ca, Sr) or BaI(2)(THF)(3) with 2 equiv of potassium tris(3,5-diethylpyrazolyl)borate (KTp(Et2)) or potassium tris(3,5-di-n-propylpyrazolyl)borate (KTp(nPr2)) in hexane at ambient temperature afforded CaTp(Et2)(2) (64%), SrTp(Et2)(2) (64%), BaTp(Et2)(2) (67%), CaTp(nPr2)(2) (51%), SrTp(nPr2)(2) (75%), and BaTp(nPr2)(2) (39%). Crystal structure determinations of CaTp(Et2)(2), SrTp(Et2)(2), and BaTp(Et2)(2) revealed monomeric structures. X-ray structural determinations for strontium tris(pyrazolyl)borate (SrTp(2)) and barium tris(pyrazolyl)borate ([BaTp(2)](2)) show that SrTp(2) exists as a monomer and [BaTp(2)](2) exists as a dimer containing two bridging Tp ligands. The thermogravimetric analysis traces, preparative sublimations, and melting point/decomposition determinations demonstrate generally very high thermal stabilities and reasonable volatilities. SrTp(2) has the highest volatility with a sublimation temperature of 200 degrees C/0.05 Torr. [BaTp(2)](2) is the least thermally stable with a decomposition temperature of 330 degrees C and a percent residue of 46.5% at 450 degrees C in the thermogravimetric analysis trace. SrTp(Et2)(2), BaTp(Et2)(2), CaTp(nPr2)(2), SrTp(nPr2)(2), and BaTp(nPr2)(2) vaporize as liquids between 210 and 240 degrees C at 0.05 Torr. BaTp(Et2)(2) and BaTp(nPr2)(2) decompose at about 375 degrees C, whereas MTp(Et2)(2) and MTp(nPr2)(2) (M = Ca, Sr) are stable to >400 degrees C. Several of these new complexes represent promising precursors for chemical vapor deposition and atomic layer deposition film growth techniques.

Advances in alkaline earth-nitrogen chemistry

“…Here, we provide only a brief overview of the different ligand types and the main characteristics of the relevant complexes that have not previously been reviewed. Interest in these compounds arises from their applications in atomic layer deposition (ALD) as precursors for electronic materials, and as catalysts and bioorganometallic applications [150,[169][170][171]. As multiple recent reviews are available on the topic, the following discussion will be brief.…”

“…The competition between solvent coordination and metal stabilization through M· · ·H-B interaction is illustrated by the three magnesium complexes [Mg 2 (Bp) 2 Cl 2 (thf) 3 compounds are more stable than many known Group II CVD precursors, but they were less thermally stable than the corresponding Tp complexes described below [150,174].…”

Highly Fluorinated Tris(indazolyl)borate Silylamido Complexes of the Heavier Alkaline Earth Metals: Synthesis, Characterization, and Efficient Catalytic Intramolecular Hydroamination

“…The Sr1ÀN5 bond trans to the amido is significantly longer (2.7629 (16) [45,46] The Sr1ÀN7 bond (2.4219 (18) ) is slightly shorter than the related bond length reported for the four-coordinate complexes [{BDI}Sr{N(SiMe 3 ) 2 }(thf)] [39] and [{N^N}Sr{N(SiMe 3 ) 2 }(thf)] [13] (2.446 (2) and 2.463(2) , respectively), outlining the electron-withdrawing properties of the fluorinated {F 12 As reported for lanthanides [47][48][49][50][51] and Ae complexes, [52] proposed for 4 (see the Supporting Information).…”

Unusual stoichiometry control in the atomic layer deposition of manganese borate films from manganese bis(tris(pyrazolyl)borate) and ozone

“…ALD uniquely enables the stoichiometry control, since the depositions are conducted below the thermal decomposition temperatures of CaTp 2 , SrTp 2 , and Ba(TpEt 2 ) 2 [<400 C (Ref. 28)]. The intermediate physisorbed precursor monolayers replicate the 2:1 boron to metal precursor stoichiometry in the thin films upon treatment with the water coreactant, and the MB 2 O 4 layers are stable to B 2 O 3 loss at <400 C. [29][30][31] ALD affords conformal coverage of nanoscale features and enables subnanometer control of film thicknesses because of the self-limited growth mechanism.…”