1,2,3-Triazole based ligands with phosphine and pyridine functionalities: synthesis, PdII and PtII chemistry and catalytic studies

Structural Diversity and Rare η1 Cu-C Interactions in CuI Complexes of 1,2,3-Triazole-Functionalized Bisphosphines

This manuscript describes the synthesis of copper complexes of 1,2,3-triazolyl-phosphines: o-Ph2P(C6H4){1,2,3-N3CC6H5)C(PPh2)} (L1), (C6H5){1,2,3-N3C(C6H4(o-PPh2))-C(PPh2)} (L2), 3-Ph2P(C5H3N){1,2,3-N3C(C6H5)C(PPh2)} (L3), o-Ph2P(C6H4){1,2,3-N3C(C5H5N)C(PPh2)} (L4), and {(3,5-Ph2PC6H4-o)21,2,3-N3CCH} (L5). The reactions of L1-L3 with CuI salts afforded dimeric complexes having the general formula [Cu2(μ -X)2L2] (L = L1, X = Cl, Br and I: 1 - 3; L= L2, X = Cl, Br and I: 4- 6; L = L3; X = Cl, Br, and I: 7-9). The reaction of L4 with CuI in a 1:2 molar ratio afforded 1D-coordination polymer [{(CuI)2{o-Ph2P(C6H4){1,2,3-N3C(C5H5N)C(PPh2)}-μ-((k1-N)(k2-P,P))}}]n (10). The reaction of L5 with cuprous halides (CuX) (X = Br, I) yielded mononuclear complexes [CuX{(3,5-Ph2PC6H4-o)21,2,3-N3CCH}-κ2P,P] (X = Br, 12; I, 13). Crystal structures of complexes 12 and 13 showed close interactions between CuI and the triazole C7 carbon. These relatively short Cu···C7 separations may be due to the η1-C interaction (dπ-pπ bond) between the triazolic carbon atom (via pz orbital) and CuI or three-centered two-electron interaction between CuI and the triazolic C-H bond. The existence of the Cu···C interaction was further evinced by the QTAIM analysis in compounds 12 and 13.

Catalytic utility of PNN-based MnI pincer complexes in the synthesis of quinolines and transfer hydrogenation of carbonyl derivatives

This manuscript describes the synthesis of a triazolyl-pyridine-based phosphine, N-((diphenylphosphaneyl)methyl)-N-methyl-6-(1-phenyl-1H-1,2,3-triazol-4-yl)pyridin-2-amine, [2,6-{(PPh2)CH2N(Me)(C5H3N)(C2HN3C6H5)}] (1) (here onwards referred to as PNN) and its cationic and neutral MnI complexes and catalytic applications. The reaction of 1 with Mn(CO)5Br afforded a cationic complex [Mn(CO)3(PNN)]Br (2), which is highly stable in solid state, but in solution it gradually loses one of the CO groups to form a neutral complex [Mn(CO)2(PNN)Br] (3). Complex 2 on treatment with AgBF4 also yielded a cationic complex [Mn(CO)3(PNN)]BF4 (4). These complexes efficiently promoted the synthesis of quinoline derivatives via acceptor-less dehydrogenative coupling of 2-aminobenzyl alcohol and ketones, with complex 3 showing the highest activity with a very low catalyst loading (0.03 mol%) at 110 °C. Complex 3 (0.5 mol%) also showed excellent catalytic activity in the transfer hydrogenation of ketones and aldehydes to form respective secondary and primary alcohols.

Cationic and Neutral PdII and PtII Pincer Complexes of Phosphinamino-Triazolyl-Pyridine [PN(H)N]: Pincer Ligand-Stabilized Palladium Nanoparticles and Their Catalytic Annulation of Internal Alkynes to Indenones

We describe the synthesis of a triazolyl-pyridine-based aminophosphine, N-(diphenylphosphaneyl)-6-(1-phenyl)-1H-(1,2,3-triazol-4-yl)pyridine-2-amine [2,6-{(PPh₂)-N(H)(C₅H₃N)(C₂HN₃C₆H₅)}] [1, PN(H)N hereafter], and its palladium and platinum complexes and their catalytic application. The reaction of 1 with [M(COD)Cl₂] (M = Pd or Pt) afforded the cationic complex [(MCl){PN(H)N}-κ³-P,N,N]Cl [M = Pd (2) or Pt (3)]. Alternatively, compounds 2 and 3 were also synthesized by treating [2,6-{H₂N(C₅H₃N)(C₂HN₃C₆H₅)}] (A) with [M(COD)Cl₂] (M = Pd or Pt), followed by the addition of stoichiometric amounts of PPh₂Cl and Et₃N. The neutral, dearomatized complexes [(MCl){PNN}-κ³-P,N,N] [M = Pd (4) or Pt (5)] were prepared by the deprotonation of the NH of 2 and 3 with 1 equiv of ^tBuOK. Compounds 4 and 5 were also synthesized stepwise by treating [2,6-{H₂N(C₅H₃N)(C₂HN₃C₆H₅)}] (A) with [M(COD)Cl₂] (M = Pd or Pt) to give intermediate complexes [{MCl₂}2,6-{NH₂(C₅H₃N)(C₂HN₃C₆H₅)-κ²-N,N}] [M = Pd (B) or Pt (C)], which were subsequently phosphinated. The in situ-generated PNN ligand-stabilized Pd nanoparticles from compound 2 catalyzed the annulation of o-bromobenzaldehyde with alkynes to yield indenone derivatives. Mechanistic investigations suggested that the reaction was catalyzed by Pd nanoparticles (Pd@2) generated from compound 2 and proceeded through sequential oxidative addition, alkyne insertion, and reductive elimination steps to produce indanone products.

Novel 1,2,3-triazolyl phosphine with a pyridyl functionality: synthesis, coinage metal complexes, photophysical studies and Cu(I) catalyzed C-O coupling of phenols with aryl bromides

This manuscript describes the synthesis and coinage metal complexes of pyridine appended 1,2,3-triazolyl-phosphine [2-{(C₆H₄N)(C₂(PPh₂)N₃C₆H₅)}] (1), photophysical studies and their catalytic application. The reactions of 1 with copper salts afforded dimeric complexes [{Cu(μ₂-X)}₂{2-(C₆H₄N)(C₂(PPh₂)N₃C₆H₅)}₂] (2, X = Cl; 3, X = Br; and 4, X = I). The crystal structure indicates that the Cu⋯Cu distance in 4 (2.694 Å) is significantly shorter than that in complexes 3 (3.0387 Å) and 2 (3.104 Å), indicating strong cuprophilic interactions which is also supported by NBO calculations, signifying the involvement of 3d_z² orbitals from each Cu atom contributing to the bonding interaction. The fluorescence studies on complexes 2-4 carried out in the solid state showed broad emission bands around 560 nm on excitation at λ_ex = 420 nm. Complex 4 on treatment with two equivalents of 1,10-phenanthroline yielded a mononuclear complex 5 which showed almost complete quenching of fluorescence in the solid state, clearly indicating that the emissive properties of 4 are mainly due to the Cu⋯Cu interaction, along with (M + X)LCT. The reactions of 1 with silver salts led to the isolation of dimeric complexes [{Ag(μ₂-X)}₂{2-(C₆H₄N)(C₂(PPh₂)N₃C₆H₅)}₂] (6, X = Cl; 7, X = Br; and 8, X = I) in good yield. The reaction between 1 and [AuCl(SMe₂)] yielded [{AuCl}{2-(C₆H₄N)(C₂(PPh₂)N₃C₆H₅)}] (9). The molecular structures of 2-5 and 7-9 were confirmed by single crystal X-ray analysis. The complex 4 is found to be an excellent catalyst for C-O coupling under mild conditions.