Robotic Lepidoptery: Structural Characterization of (mostly) Unexpected Palladium Complexes Obtained from High-Throughput Catalyst Screening

In the course of a high-throughput search for optimal combinations of bidentate ligands with Pd(II) carboxylates to generate oxidation catalysts, we obtained and crystallographically characterized a number of crystalline products. While some combinations afforded the anticipated (L-L)Pd(OC(O)R)(2) structures (L-L = bipyridine, tmeda; R = CH3, CF3). many gave unusual oligometallic complexes resulting from reactions such as C-H activation (L-L = sparteine), P-C bond cleavage (L-L = 1,2-bis(diphenylphosphino)ethane, and C-C bond formation between solvent (acetone) and ligand (L-L = 1,4-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene). These findings illustrate potential pitfalls of screening procedures based on assuming uniform, in situ catalyst self-assembly.