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[Ru­(Cp)­(PPh 2NBn 2)­(MeCN)]­PF6 (1; PPh 2NBn 2 = 1,5-benzyl-3,7-phenyl-1,5-diaza-3,7-diphosphacyclooctane) and [Ru­(Cp)­(dppp)­(MeCN)]­PF6 (2; dppp = 1,3-bis­(diphenylphosphino)­propane) are both active toward the acceptorless dehydrogenation of benzylamine (BnNH2) and N-heterocycles. The two catalysts have similar activities but different selectivities for dehydrogenation products. Independent synthesis of a [Ru­(Cp)­(PPh 2NBn 2)­(NH2Bn)]­PF6 adduct (3) reveals the presence of a hydrogen bond between the bound amine and the pendent base of the PPh 2NBn 2 ligand. Preliminary mechanistic studies reveal that the benzylamine adduct is not an on-cycle catalyst intermediate.

High-throughput screening offers major opportunities to accelerate the discovery and optimization of homogeneously catalyzed reactions. A general method for acquisition of reaction profiles through a high-throughput quenching (HTQ) approach is described, which gives a more accurate picture of catalyst performance, e.g., total productivity, induction periods, selectivity and lifetime, than the customary analysis at a fixed, arbitrary time.

The synthesis of a new tripodal ligand family that contains tertiary amine groups in the second-coordination sphere is reported. The ligands are tris(amido)amine derivatives, with the pendant amines attached via a peptide coupling strategy. They were designed to function as new molecular catalysts for the oxygen reduction reaction (ORR), in which the pendant acid/base group could improve the catalyst performance. Two members of the ligand family were each metalated with cobalt(II) and zinc(II) to afford trigonal-monopyramidal complexes. The reaction of the cobalt complexes [Co(L)](-) with dioxygen reversibly generates a small amount of a cobalt(III) superoxo species, which was characterized by electron paramagnetic resonance (EPR) spectroscopy. Protonation of the zinc complex Zn[N{CH2CH2NC(O)CH2N(CH2Ph)2}3)](-) ([Zn(TN(Bn))](-)) with 1 equiv of acid occurs at a primary-coordination-sphere amide moiety rather than at a pendant basic site. The addition of excess acid to any of the complexes [M(L)](-) results in complete proteolysis and formation of the ligands H3L. These undesired reactions limit the use of these complexes as catalysts for the ORR. An alternative ligand with two pyridyl arms was also prepared but could not be metalated. These studies highlight the importance of the stability of the primary-coordination sphere of ORR electrocatalysts to both oxidative and acidic conditions.

New entries to the [Ru(Cp/Cp*)(P R 2 N R' 2 )(MeCN)]PF 6 catalyst family were synthesized, including a Cp complex (R=Cy; R'=Ph) and two Cp* complexes (R=Cy, Ph; R'=Ph). These and other derivatives were used for the intramolecular hydroamination of 2-ethynylaniline to elucidate trends in catalytic lifetime and rate. The readily accessible [Ru(Cp)(P Cy 2 N Ph 2 )(MeCN)]PF 6 derivative showed comparable lifetime to [Ru(Cp)(P tÀ Bu 2 N Ph 2 )(MeCN)] PF 6 , the previous optimal catalyst. Donor-free 'active' catalysts, [Ru(Cp/Cp*)(P Cy 2 N Ph 2 )]PF 6 , were prepared and their thermal stability was assessed. The relatively high stability of the Cp derivative was explained by the capacity of the P Cy 2 N Ph 2 ligand to coordinate in a k 3 -(P,P,Ar) mode, which protects the lowcoordinate species. This coordination mode is inaccessible with the Cp* derivative. Additionally, [Ru(Cp*)(P Cy 2 N Ph 2 )]PF 6 readily activated the CÀ Cl bond of the solvent dichloromethane. Variable time normalization analysis (VTNA) revealed that the indole product inhibited the catalyst [Ru(Cp)(P Cy 2 N Ph 2 )(MeCN)] PF 6 , which slowed catalytic rates.

The chemistry of a palladium­(II) complex containing both an alkyl– and an aryl–palladium bond is reported. The reaction of [Pd­(CH2CMe2C6H4)­(MesNCHCHNMes)] with bromine or iodine leads to reductive elimination of 1,1-dimethylcyclobutabenzene with formation of [PdX2(MesNCHCHNMes)] (X = Br, I). However, the reaction with hydrogen peroxide gives [Pd­(CH2CMe2C6H4O)­(MesNCHCHNMes)] by overall oxygen atom insertion into the aryl–palladium rather than the alkyl–palladium bond. This complex [Pd­(CH2CMe2C6H4O)­(MesNCHCHNMes)] reacts with bromine, iodine, or hydrogen peroxide to give 3,3-dimethyl-2,3-dihydrobenzofuran and the corresponding complex [PdX2(MesNCHCHNMes)]. The mechanisms of reaction and basis for selectivity are discussed. The results support the view that oxygen atom insertion is a mechanistically viable pathway for selective catalytic oxidation of hydrocarbons by the green oxidant hydrogen peroxide.

The first successful use of the PN (1,5-R'-3,7-R-1,5-diaza-3,7-diphosphacyclooctane) ligand family toward an organic synthesis is described. The precatalysts [Ru(Cp)(PN)(MeCN)]PF are active toward cyclization of 2-ethynylbenzyl alcohol at low catalyst loading and mild temperatures. Catalyst performance however is limited by both low conscription and by competitive deactivation.