Solution Reactions of a Bis(pyrrolylaldiminate)copper(II) Complex with Peralkyl Zinc, Aluminum, and Boron Reagents: Investigation of the Pathways Responsible for Copper Metal Deposition

The solution reactions of bis( N -isopropylpyrrolylaldiminate)copper(II) (CuL 2 ) with AlMe 3, BEt 3, and ZnEt 2 have been studied. In all cases, reduction occurs in two stages via a stable copper(I) pyrrolylaldiminate complex (Cu 2 L 2 ), with each stage initiated by copper alkyl complex formation. Reduction from “LCuR” (R = Me or Et) occurs with release of R 2 or L−R, consistent with bimolecular C−C or C−N bond-forming reductive elimination. At room temperature or below, copper deposition from “CuMe” occurs exclusively via reductive elimination of ethane, whereas decomposition of “CuEt” yields ethylene, ethane, and hydrogen, indicative of both β-hydride elimination and reductive elimination. The reaction byproducts [Cu 2 L 2 ], [LAlMe 2 ], [L 2 AlMe], [AlL 3 ], [LBEt 2 ], [LZnEt], [ZnL 2 ], L−Me, and L−Et were synthesized independently and isolated as pure compounds. All compounds are thermally stable, with the exception of LZnEt, which undergoes ligand redistribution to form ZnL 2 and ZnEt 2 in solution and as a solid at elevated temperatures. With the exception of [LZnEt] and [Cu 2 L 2 ], these complexes are also volatile; monoligated [LAlMe 2 ] and [LBEt 2 ] are particularly volatile, and therefore more desirable as byproducts in ALD or pulsed-CVD.