Tridentate NNN Ligand Associating Amidoquinoline and Iminophosphorane: Synthesis and Coordination to Pd and Ni Centers

Arene displacement, C-H activation and acetonitrile insertion reactions enabled by coordination of a functionalized iminophosphorane to a RuII-p-cymene scaffold

Reaction of a sterically demanding iminophosphorano-phosphine, Ph2PCH2Ph2PNAr* (here onwards referred to as PCPNAr*; Ar* = 2,6-dibenzhydryl-4-methylphenyl), (1) with [Ru(η6-p-cymene)Cl2]2 yielded three different types of complex, [RuCl2{(η6-p-cymene)(PCPNAr*)-κ1-P}] (2), [RuCl{(P(O)CPNAr*)(κ2-N,C)(C-η6-arene)}] (3) and [RuCl{(POCPNAr*)(κ2-N,C-o)(C-η6-arene)}] (4), depending on the reaction conditions via CH activation, tethered η6-arene coordination, ortho-metallation or PN bond cleavage/rearrangement reactions. Interestingly, a similar reaction in CH3CN in the presence of AgBF4 resulted in the insertion of CH3CN into the PN bond to form a novel metallacycle [Ru(NCMe)3{(PC2PN(CH3)CNAr*)-κ3-N,N,P}][BF4]2 (5) containing 4- and 5-membered rings via an aza-Wittig type reaction. Complex 4 showed very good catalytic activity in the transfer hydrogenation of carbonyl compounds.

Mono and Dinuclear Palladium Pincer Complexes of NNSe Ligand as a Catalyst for Decarboxylative Direct C-H Heteroarylation of (Hetero)arenes

This report describes the synthesis of a new NNSe pincer ligand and its mono- and dinuclear palladium(II) pincer complexes. In the absence of a base, a dinuclear palladium pincer complex (C1) was isolated, while in the presence of Et3 N base a mononuclear palladium pincer complex (C2) was obtained. The new ligand and complexes were characterized using techniques like 1 H, 13 C{1 H} nuclear magnetic resonance (NMR), fourier transform infrared (FTIR), high-resolution mass spectrometry (HRMS), ultraviolet-visible (UV-Visible), and cyclic voltammetry. Both the complexes showed pincer coordination mode with a distorted square planar geometry. The complex C1 has two pincer ligands attached through a Pd-Pd bond in a dinuclear pincer fashion. The air and moisture-insensitive, thermally robust palladium pincer complexes were used as the catalyst for decarboxylative direct C-H heteroarylation of (hetero)arenes. Among the complexes, dinuclear pincer complex C1 showed better catalytic activity. A variety of (hetero)arenes were successfully activated (43-87 % yield) using only 2.5 mol % of catalyst loading under mild reaction conditions. The PPh3 and Hg poisoning experiments suggested a homogeneous nature of catalysis. A plausible reaction pathway was proposed for the dinuclear palladium pincer complex catalyzed decarboxylative C-H bond activation reaction of (hetero)arenes.

FeII complexes supported by an iminophosphorane ligand: synthesis and reactivity

The synthesis of iron complexes supported by a mixed phosphine-lutidine-iminophosphorane (PPyNP) ligand was carried out. While bidentate κ2-N,N coordination was observed for FeCl2, pincer coordination modes were adopted at cationic iron centers, either through dechlorination of [LFe(PPyNP)Cl2] (1) or direct coordination of PPyNP to Fe(OTf)2. Reaction with tert-butylisocyanide gave access to the diamagnetic octahedral complex [Fe(PPyNP)(CNtBu)3]X2 (X = OTf (4), Cl (4')). Both 1 and 4 were shown to undergo deprotonation of the phosphinomethyl group, but the resulting complexes were not active for the dehydrogenative coupling of hexan-1-ol. The hydrosilylation of acetophenones was catalyzed at room temperature with 1 mol% of a catalyst generated in situ from cationic PPyNP-supported iron triflate complexes and KHBEt3.

Construction of N-Acyliminophosphoranes via Iron(II)-Catalyzed Imidization of Phosphines with N-Acyloxyamides

Employing FeCl₂ as a cheap and readily available catalyst, a facile imidization of phosphines with N-acyloxyamides is described, affording synthetically useful N-acyliminophosphoranes with high functional group tolerance. The transformation is easily performed under an air atmosphere at room temperature and could be scaled up to gram scale with a catalyst loading of 1 mol %. The iminophosphoranyl moiety in the product was further utilized as an effective directing group for controllable ortho C(sp²)-H bond amidations under Rh(III) catalysis.

Reaction of Phosphines with 1-Azido-(2-halogenomethyl)benzene Giving Aminophosphonium-Substituted Indazoles

The reaction between a 1-azido-(2-halogenomethyl)benzene and a phosphine gives different products depending on the nature of the halogen, the phosphine itself, and the solvent employed. While PPh₃ (2 equiv) reacts with the chloro reagent in toluene to give the expected iminophosphorane-phosphonium adduct, trialkylphosphines (PCy₃ and PEt₃) surprisingly furnish an aminophosphonium substituted by a zwitterionic indazole. The bicyclic product can also form from PPh₃ using the bromo reagent in acetonitrile. A mechanism is proposed for this cyclization based on DFT calculations.

Reversible nickel-metallacycle formation with a phosphinimine-based pincer ligand

Pincer ligands have a remarkable ability to impart control over small molecule activation chemistry and catalytic activity; therefore, the design of new pincer ligands and the exploration of their reactivity profiles continues to be a frontier in synthetic inorganic chemistry. In this work, a novel, monoanionic NNN pincer ligand containing two phosphinimine donors was used to create a series of mononuclear Ni complexes. Ligand metallation in the presence of NaOPh yielded a nickel phenoxide complex that was used to form a mononuclear hydride complex on treatment with pinacolborane. Attempts at ligand metallation with NaN(SiMe3)2 resulted in the activation of both phosphinimine methyl groups to yield an anionic, cis-dialkyl product, in which dissociation of one phosphinimine nitrogen leads to retention of a square planar coordination environment about Ni. Protonolysis of this dialkyl species generated a monoalkyl product that retained the 4-membered metallacycle. The insertion of 2,6-dimethylphenyl isocyanide (xylNC) into this nickel metallacycle, followed by proton transfer, generated a new five-membered nickel metallacycle. Kinetic studies suggested rate-limiting proton transfer (KIE ≥ 3.9 ± 0.5) from the α-methylene unit of the putative iminoacyl intermediate.