Palladium(II) aminoiminophosphoranate complexes as cross-coupling catalysts

Versatile Reactivity of Half-Sandwich Rhodium(III) Iminophosphonamide Complexes

Novel 18e̅ and 16e̅ pentamethylcyclopentadienyl rhodium(III) complexes [(η⁵-C₅Me₅)RhX(NPN)] (1a,b, X = Cl; 2a-c, X = PF₆, BAr₄^F) with chelating zwitterionic iminophosphonamide (NPN) ligands (Ph₂P(NR)(NR'); a, R = R' = p-Tol; b, R = p-Tol, R' = Me; c, R = R' = Me) were synthesized and characterized by single-crystal X-ray diffraction. In the 16e̅ complexes 2, the rhodium (Rh) atom is efficiently stabilized by π-donation of unshared N electrons, thus hampering coordination of the external ligands and rendering the 18e̅ complexes labile. Due to low coordination enthalpy, the cationic 18e̅ monocarbonyl and pyridine adducts 2a·L are stable only at low temperatures. At room temperature, 2·CO adducts readily give stable carbonyl-carbamoyl complexes [(η⁵-C₅Me₅)Rh(CO){(CO(NR')Ph₂P(NR)}]⁺ (4) formed as a result of CO insertion into the Rh-N bond, thus showing high nucleophilicity of the N atoms in 18e̅ complexes. High basicity of the Na⁺NPN^- precursors caused side deprotonation of the η⁵-C₅Me₅ ligand during the synthesis of 1 that yields unstable fulvene Rh(I) complexes [(η⁴-C₅Me₄CH₂)Rh{Ph₂P(NR)(NR')₂}] (3a,b). Complex 3a undergoes a facile reaction with isoprene to yield an unusual [(η⁵:η¹-C₅Me₄(CH₂)C(Me)═CHCH₂)Rh(NPN)] complex─the first example of intermolecular 1,4-metallacycloaddition of diene to the Rh-fulvene complex.

RuII complexes of 1,2,3-triazole appended tertiary phosphines, [P(Ph){(o-C6H4)(1,2,3-N3C(Ph)CH}2] and [P(Ph){o-C6H4(CCH)-(1,2,3-N3-Ph)}2]: highly active catalysts for transfer hydrogenation of carbonyl/nitro compounds and for α-alkylation of ketones

The synthesis of two new 1,2,3-triazole appended monophosphines [P(Ph){(o-C₆H₄)(1,2,3-N₃C(Ph)CH}₂] (1) and [P(Ph){o-C₆H₄(CCH)(1,2,3-N₃-Ph)}₂] (2) and their Ru^II complexes is described. The reactions of 1 and 2 with [Ru(PPh₃)₃Cl₂] in a 1 : 1 molar ratio produced cationic complexes 3 and 4, respectively. Both the complexes showed very high catalytic activity towards transfer hydrogenation, nitro reduction, and α-alkylation reactions and afforded the corresponding products in good to excellent yields. The free energy of β-hydride elimination from the respective Ru-alkoxide intermediates, a key mechanistic step common to all the three catalytic pathways, was calculated to be close to ergoneutral by density functional theory-based calculations, which is posited to rationalize the catalytic activity of 3. The reduction of aromatic nitro compounds was found to be highly chemoselective and produced the corresponding amines as major products even in the presence of a carbonyl group. The triazolyl-N2 coordinated Ru^II-NPN complex 3 showed better catalytic activity compared to the triazolyl-N3 coordinated complex 4.

Redox behaviour of ([fc(NPiPr2)2]Fe)2, formation of an iron–iron bond and cleavage of azobenzene

The redox behaviour of the dimeric tetrairon complex, ([fc(NPⁱPr₂)₂]Fe)₂ (where fc(NPⁱPr₂)₂ = 1,1′-(C₅H₄NPⁱPr₂)₂Fe) has been investigated.