Versatile Production of Novel PNP Based Metal Complexes Applicable as Water Reduction Catalysts Showing CH/M as Well as CH/π Interactions

Abstract

Several PNP‐type ligands of the form bis(dianisylphosphanylmethyl)alkylamine, where alkyl is methyl, ethyl, isopropyl, and benzyl (1–4), have been coordinated to Co(II), Ni(II), Pd(II), and Pt(II) (5–26). This series of water reduction catalysts (WRC) has been characterized by single‐crystal X‐ray structure analysis, multinuclear and 2D NMR spectroscopy, mass spectrometry and a computational study. Intramolecular contact approaches show differences depending on hetero‐ or homoleptic complexes. Both solid state and solution structures indicate an enhancement of steric pressure for the latter. As a consequence CH/M as well as CH/π interactions appear in the X‐ray structures and 1H NMR spectra. They can also be clearly identified by quantum mechanical calculations on a B3LYP level. Since these WRC contain proton relays due to the used PNP‐ligands, they are prone to proton coupled electron transfer (PCET) during photocatalysis. The different steric pressure influences their reorganisation energy. Obviously, the observed intramolecular contact approaches should be regarded as a tool for the design of future WRC.

Insights into Proton Coupled Electron Transfer in the Field of Artificial Photosynthesis

“…Catalysts of the type [M(II)Cl 2 (PNP−C1], [M(II)(MeCN) 2 (PNP−C1] 2+ , [M(II)(PNP−C1) 2 ] 2+ , and [M(II)Cl(PNP−C2] + (M=Pt 2+ , Pd 2+ , Ni 2+ , and Co 2+ ) show an effective photochemical production of hydrogen, when combined with the well‐known photosensitiser [Ir(III)(bpy)(ppy) 2 ](PF 6 ) and triethylamine as sacrificial donor [21a,b] . PNP‐ligands exhibit a very versatile preparative and coordination chemistry [21c] .…”

The influence of trinuclear complexes on light-induced hydrogen production

“…6, blue) was calculated, and the resulting incident photon conversion efficiency (IPCE, see ESI †) for trimetallic 8b is 2.1%. In order to make this calculation of the IPCE possible, a calibration of the photoreactor by actinometry has been performed (see the ESI, † pages [12][13][14][15][16][17].…”

“…So far, several PNP complexes with different backbones and metal centres have been investigated in our group. 5,6,15,16 To highlight the positive effect of multinuclear WRCs in comparison to mononuclear species, the TONs of the most promising and structurally similar tri-and mononuclear WRCs were compared. The mononuclear complex [Pd(ACN) 2 (PNP-C1-Me)](BF 4 ) 2 , with only one palladium centre, was studied by W. Viertl et al 6 The complex offered a TON of 2289 when irradiated in the presence of the same [Ir(bpy)(ppy) 2 ](PF 6 ) chromophore as for the analogous trinuclear complex 8b.…”

“…Moreover, anisyl phosphines exhibit enhanced catalytic stability compared to phenyl phosphine analogues. 5,6,15,16 Another beneficial preparative side effect is that the educt di-ortho anisyl phosphine is a powder and easy to handle in comparison to its easily inflammable diphenyl phosphine relative, which makes it attractive for larger scale reactions. Similar systems of the monoand bis-ligand with phenyl instead of anisyl groups already exist.…”

Phospha-Mannich reactions of RPH2, R2PH, and R3P

“…Entry R R' Yield, % δ P , ppm 55 [281] -28.1 (CDCl 3 ) (-)*** [142] -27.7 for Ph 2 PCH 2 -(CDCl 3 ) 32 [148] -34.8 (CDCl 3 ) Me 78 [282] -42.7 (C 7 H 8 ) Et 84 [283] -44.0 (CD 2 Cl 2 ) i-Pr 79 [283] -42.1 (CD 2 Cl 2 ) 81 [283] -41.6 (CD 2 Cl 2 ) 74 [148] -44.5 (CDCl 3 ) Et Me > 70, [284] 71, [285,286] 84 [263] -31.0 (CD 3 CN) Et n-Bu 47 [285] -32.2 (CD 3 CN) Et t-Bu 65 [287] -29.3 (C 6 D 5 Br) Et 84 [263] -33.0 (THF-d 8 )…”