A catalytic cascade system for CO2 hydrogenation to MeOH under acidic conditions is described. The reaction uses three catalysts which promote stepwise formation and conversion of formic acid and formate ester intermediates. The activities and decomposition pathways of different catalyst candidates for each step were investigated. The combination Ru­(H)2[P­(CH2CH2PPh2)3]/Sc­(OTf)3/Ir­(tBuPCP)­(CO) was found to be the most active for CO2 hydrogenation to MeOH. An overall TON of 428 was achieved after 40 h at 155 °C in EtOH, resulting in a high concentration of MeOH (1.07 M). Catalyst speciation studies upon completion of the reaction indicated that the carbonyl complexes [Ru­[P­(CH3CH2PPh2)3]­(H)­(CO)]­(OTf), Ir­(tBuPCP)­(H)­(CO)­(OTf), and [Ir­(tBuPCP)­(H)­(CO)2]­(OTf) were formed as the major metal-containing species. Notably, [Ru­[P­(CH3CH2PPh2)3]­(H)­(CO)]­(OTf) was found to be inactive for CO2 hydrogenation, limiting the productivity of the reaction.

A series of phosphine-diimine ligands were synthesized by the condensation of 2-(diphenylphosphino)aniline (PNH2) with a variety of formyl and ketopyridines. Condensation of PNH2 with acetyl- and benzoylpyridine yielded the Ph2P(C6H4)N═C(R)(C5H4N), respectively abbreviated PN(Me)py and PN(Ph)py. With ferrous halides, PN(Ph)py gave the complexes FeX2(PN(Ph)py) (X = Cl, Br). Condensation of pyridine carboxaldehyde and its 6-methyl derivatives with PNH2 was achieved using a ferrous template, affording low-spin complexes [Fe(PN(H)py(R))2](2+) (R = H, Me). Dicarbonyls Fe(PN(R)py)(CO)2 were produced by treating PN(Me)py with Fe(benzylideneacetone)(CO)3 and reduction of FeX2(PN(Ph)py) with NaBEt3H under a CO atmosphere. Cyclic voltammetric studies show that the [FeL3(CO)2](0/-) and [FeL3(CO)2](+/0) couples are similar for a range of tridentate ligands, but the PN(Ph)py system uniquely sustains two one-electron reductions. Treatment of Fe(PN(Ph)py)X2 with NaBEt3H gave active catalysts for the hydroboration of 1-octene with pinacolborane. Similarly, these catalysts proved active for the addition of diphenylsilane, but not HSiMe(OSiMe3)2, to 1-octene and vinylsilanes. Evidence is presented that catalysis occurs via iron hydride complexes of intact PN(Ph)py.

A family of CoCl2(PNpy) complexes were prepared, where PNpy = 2-iminopyridyl-phosphine ligands derived from aminoalkyl and aminoaryl phosphines and 2-keto- and 2-formylpyridines. Reduction of CoCl2(PNpy) complexes in the presence of PPh3 gave CoH­(PNpy)­(PPh3) and CoMe­(PNpy)­(PPh3), which were active for hydrofunctionalization of alkenes. According to DFT calculations, the CoMe­(PNpy)­(PPh3) complexes are best described as Co­(II) derivatives of the anion [PNpy]−, with a labile PPh3 coligand. Metalation of Na­[Ph2PC2NHpy] gave the dimers [CoCl­(Ph2PC2NHpy)]2. Monomeric complexes catalyze hydrosilylation of 1-octene with Ph2SiH2, with the CoCl2(iPr2PC3NHpy)/2NaBEt3H system exhibiting the highest rate and selectivity for anti-Markovnikov product. In situ NMR studies established the following: (i) silanes protonolyze catalyst precursors to give the Co-silyl complexes Co­(SiR3)­(Ph2PC6H4NPhpy)­(PPh3), (ii) alkenes compete with PPh3 to give Co­(SiHPh2)­(Ph2PC6H4NPhpy)­(η2-alkene), (iii) ethylene inserts into the Co–Si bond to give Co­(CH2CH2SiR3)­(Ph2PC6H4NPhpy)­(PPh3).

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Selective C–H activation of benzene and n-octane under mild conditions by a pincer IrIII carboxylate complex, (CCCMesityl)­Ir­(OAc)2(OH2) (1a), is described. A kinetic study of benzene activation was undertaken, and the resulting Eyring analysis informed the design of a tButylCCCMethyl-ligated IrIII carboxylate, which exhibited a ΔG ⧧ value for the reaction lower than that observed for 1a. Elimination of the aquo ligand was found to further lower the ΔG ⧧ value of benzene activation, enabling C–H activation by IrIII at temperatures as low as 30 °C.

The cover picture shows the catalytic conversion of amines or nitroarenes with alcohols into useful amino compounds by [P,N,O]‐RuII complexes in a one‐pot reaction, which is a sustainable cycle in organic synthesis. The ruthenium(II) complexes serving as catalysts in this work were prepared by complexation of RuII precursors with various [P,N,O] ligands and were characterized by spectroscopic methods and X‐ray crystallography. These investigations provided some insight into ligand effects on the metal ions. Details are discussed in the article by C.‐C. Lee et al. on p. 4801 ff.

Coordination and Catalytic Activity of Ruthenium Complexes Containing Tridentate P,N,O Ligands. -Synthesis and characterization of seven ruthenium complexes bearing PNO ligands are reported. One complex is found to be an efficient catalyst for the reductive amination of amines with alcohols. In terms of turnover frequency for this reaction, the results are comparable or better than previously reported ruthenium(II) systems. -(LEE, C.-C.; CHU, W.-Y.; LIU, Y.-H.; PENG, S.-M.; LIU*, S.-T.; Eur. J. Inorg. Chem. 2011, 31, 4801-4806, http://dx.