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Date of Award
Charles H. Winter
A series of heavy alkaline earth complexes containing TpR2-based ligands has been synthesized, structurally characterized, and their properties were investigated. Salt metathesis routes involving MI2 (M = Ca, Sr, Ba) with either KTpEt2 or KTpnPr2 afforded MTpEt22 or MTpnPr22 in good to moderate yields. All of these complexes are volatile and exceptionally thermally stable, and have acceptable properties for use as group 2 atomic layer deposition (ALD) precursors. In addition, a series of group 2 complexes containing BpR2-based ligand systems were synthesized. Treatment of MI2 (M = Ca, Sr, Ba) with two equivalents of TlBptBu2, KBp, and KBpiPr2 in tetrahydrofuran at ambient temperature afforded MBptBu22(THF)n, MBp2(THF)n, and MBpiPr22(THF)2, respectively. In the MBptBu2 complexes, the BptBu2 ligands undergo deformation in order to avoid intraligand and interligand tert-butyl group steric repulsions. Some of the BptBu2 complexes have enough volatility and thermal stability to be used as ALD or CVD precursors, however, the Bp and BpiPr2 complexes decompose prior to volatilization. The thermolysis of three equivalents of CaBp2(THF)2 at 190-200 °C/0.05 Torr afforded one equivalent of CaTp2 and two equivalents of TpCaBH4 in good yields. Treatment of TpCaBH4 with methanol and ethanol, followed by the appropriate work up procedure, led to the isolation of [(TpCa(MeOH)2)2(μ-B(OMe)4)][B(OMe)4] and [(TpCaB(OEt)3O)3B]·EtOH, respectively. The ALD film growth of MB2O4 (M = Ca, Sr, Ba) has been demonstrated using CaTp2, SrTp2, or BaTpEt22 and water. For the ALD growth of BaB2O4, an ALD window was observed from 250-375 °C with a growth rate of 0.23 Å/cycle. In the ALD growth of CaB2O4 and SrB2O4, an ALD window was observed from 300-375 °C, respectively, with a consistent growth rate of approximately 0.36 and 0.47 Å/cycle, respectively. In the temperature versus growth rate plots for CaTp2, SrTp2, and BaTpEt2, precursor saturation occurred at ≥ 3.0, ≥ 3.0, and ≥ 1.0 s, respectively. Elastic recoil detection analysis (ERDA) of representative samples within the ALD windows indicated that the films were consistent with the composition of MB2O4, which demonstrates that TpR2-based ligands are able to act as a single source precursor for metal and boron, and confer a precise 2:1 boron/metal ratio.
Saly, Mark J., "The Synthesis, Structure, And Properties Of Group 2 Poly(pyrazolyl)borates And Their Use For The Atomic Layer Deposition Of Group 2 Borates" (2010). Wayne State University Dissertations. Paper 184.