The synthesis and characterization of original NHC ligands based on an imidazo[1,5‐a]pyridin‐3‐ylidene (IPy) scaffold functionalized with a flanking barbituric heterocycle is described as well as their use as tunable ligands for efficient gold‐catalyzed C−N, C−O, and C−C bond formations. High activity, regio‐, chemo‐, and stereoselectivities are obtained for hydroelementation and domino processes, underlining the excellent performance (TONs and TOFs) of these IPy‐based ligands in gold catalysis. The gold‐catalyzed domino reactions of 1,6‐enynes give rise to functionalized heterocycles in excellent isolated yields under mild conditions. The efficiency of the NHC gold 5Me complex is remarkable and mostly arises from a combination of steric protection and stabilization of the cationic AuI active species by ligand 1Me.

The direct α-methylation of ketones with methanol under hydrogen borrowing conditions using a well-defined manganese PN3P pre-catalyst was, for the first time, achieved.

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The appropriate combination of methacrylate polymers permits the synthesis of a soluble polymer for use in ruthenium(II)-catalyzed asymmetric transfer hydrogenation reactions. Using a 7:3 copolymer of a poly(ethylene glycol) ester and a hydroxyethyl ester, a derived ruthenium(II)/norephedrine complex catalyses reduction of acetophenone in up to 95% yield and 81% ee.

The synthesis of the bifunctional iminophosphorane-NHC (1) based on the imidazo[1,5-a]pyridin-3ylidene (IPy) platform is reported. Its imidazo[1,5-a]pyridinium salt precursor [1•H](X) was readily obtained by an efficient three-component coupling reaction between 5bromoimidazo[1,5-a]pyridinium bromide, sodium azide, and triphenylphosphine according to a SN Ar /Staudinger reaction sequence. The stable free carbene 1 was generated by deprotonation of [1•H](X) with potassium bis(trimethylsilyl)amide, and its coordination ability toward various transitionmetals was evaluated, either upon direct metalation of the free carbene or by transmetalation from a silver(I) NHC complex. While the ligand 1 is singly bounded through the carbene carbon atom in the latter complex, it behaves as a chelating bidentate ligand in all other complexes that were prepared, including the cationic and neutral palladium(II) complexes [Pd(allyl)(κ 2 C,N -1)](OTf) ([5](OTf)) and [PdCl 2 (κ 2 C,N -1)] (7), and the cationic rhodium(I) complexes [Rh(cod)(κ 2 C,N -1)](OTf) ([8](OTf)) and [Rh(CO) 2 (κ 2 C,N -1)](OTf) ([9](OTf)), generating stable 5-membered metallacycles. IR ν CO measurements carried out on the complex [Rh(CO) 2 (κ 2 C,N -1)](OTf) ([9](OTf)) show evidence of the strong donating character of the iminophosphorane-NHC ligand 1.

The straightforward synthesis of tethered η 5 -oxocyclohexadienyl Ru(II) complexes is presented. Pioneering results in catalysis show that these original half-sandwich Ru(II) complexes allow the effective isomerization of allylic alcohols under mild conditions without further additives; η 5 -oxocyclohexadienyl ruthenium complexes may be considered as a new class of catalysts. R uthenium is one of the most intensively used metals in catalysis, 1 partly due to its lower price compared to other noble metals but also because a wide span of highly stable Rubased catalysts can be prepared. A relevant example is Shvo's catalyst I (Figure 1), 2 a cyclopentadienone-ligated diruthenium complex that efficiently promotes a number of environmentally friendly and atom-economical chemical transformations. 3 Shvo et al. proposed that I thermally dissociates into two monoruthenium active species, the 18-electron II species and the remaining elusive 16-electron III complex (Figure 1).Half-sandwich Ru(II) complexes with η 6 -arene ligands IV (Figure 2) are also efficient catalysts or catalyst precursors for a wide range of reactions, and the scope of their applications has considerably increased in the past decades. 1 Especially, their corresponding configurationally stable piano-stool tethered complexes 4 have found great interest in asymmetric catalysis. 4a,5 Within the family of six-membered rings coordinated in an η n -hapto mode to a transition metal, η 5 -oxocyclohexadienyl ligands have been relatively little studied. 6,7 To the best of our knowledge there is no example of a catalytically active halfsandwich ruthenium complex V with an η 5 -oxocyclohexadienyl as ligand (Figure 2). 6 Indeed, half-sandwich Ru-based η 5 -oxocyclohexadienyl complexes are very scarce, and their corresponding tethered complexes unknown. 8 Herein, we describe the straightforward preparation of the first tethered η 5 -oxocyclohexadienyl half-sandwich ruthenium-(II) complexes. We furthermore probed the catalytic activity of this new class of Ru(II) complexes in the redox isomerization of allylic alcohols.As shown in Scheme 1, complex 1 9 reacted quantitatively ( 31 P NMR) with 1 equiv of CsF followed by the addition of Figure 1. Shvo's catalyst I and its thermal dissociation products II and III.Figure 2. Half-sandwich-Ru(II) η 6 -arene IV and η 5 -oxocyclohexadienyl complexes V.Communication pubs.acs.org/Organometallics

The reduction of imines to amines via transfer hydrogenation was achieved promoted by phosphine‐free manganese(I) catalyst. Using isopropanol as reductant, in the presence of tBuOK (4 mol %) and manganese complex [Mn(CO)3Br(κ2N,N‐PyCH2NH2)] (2 mol %), a large variety of aldimines (30 examples) were typically reduced in 3 hours at 80 °C with good to excellent yield.

Unexpected room temperature luminescence is observed and rationalized by highly challenging excited state calculations for a functionalized phosphine ligand coordinated on the [Ru(bpy)(tpy)](2+) core.