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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 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.

A bidentate nitrogen-donor ligand with an appended phenol group, CHNCH[double bond, length as m-dash]N-2-CHOH, H(L1) was treated with a palladium cycloneophyl complex [Pd(CHCMeCH)(COD)], with both Pd-aryl and Pd-alkyl bonds, to give a Pd-alkyl complex, [Pd(CHCMeCH)(κ-N,N',O-OCHN[double bond, length as m-dash]CH(2-CHN))], 1. The cleavage of the Pd-aryl bond and the deprotonation of the ligand phenol to afford a bound aryloxide, indicates facile Pd-aryl bond protonolysis. Deuterium labelling experiments confirmed that the ligand phenol promotes protonolysis and that the reverse, aryl C-H activation, occurs under very mild reaction conditions (within 10 min at room temperature). An unusual isomerization of the Pd-alkyl complex 1 to a Pd-aryl complex, [Pd(CH(2-t-Bu))(κ-N,N',O-OCHN[double bond, length as m-dash]CH(2-CHN))], 2, was observed to give an equilibrium with [2]/[1] = 9 after 5 days in methanol. The isomerization requires that both aryl C-H activation and Pd-alkyl protonolysis steps occur. The very large KIE value (k/k = ca. 40) for isomerization of 1 to 2, suggests a concerted S2-type mechanism for the Pd-alkyl protonolysis step.

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.

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.