PNN′ & P₂NN′ ligandsviareductive amination with phosphine aldehydes: synthesis and base-metal coordination chemistry

Abstract

Phosphorus-donor “arms” are readily added to amines in order to enable sturdy base metal coordination.

A One-Step Preparation of Tetradentate Ligands with Nitrogen and Phosphorus Donors by Reductive Amination and Representative Iron Complexes

“…Synthesis of Unsymmetrical NPP 2 ′ and NP 3 Ligands. Our group has previously reported the synthesis of chiral P-NH-P′ 55 and achiral PNN′ and P 2 NN′ ligands 33 via reductive amination of primary amines with phosphine aldehydes generated in situ via phosphonium dimers. The synthesis of novel unsymmetrical tripodal ligands NPP 2 ′ adopts a similar synthetic strategy where the primary amine starting material is 2-(diphenylphosphino)ethylamine (1; Scheme 3).…”

“…Recently, our lab reported the synthesis of tetradentate P 2 NN′-Cy and P 2 NN′-Ph ligands and an iron complex FeCl 2 (P 2 NN′-Ph). 33 Here, we report the synthesis of iron complexes where the ligand bears cyclohexyl substituents at phosphorus. One equivalent of the P 2 NN′-Cy ligand reacts with FeCl 2 in THF to give the octahedral complex FeCl 2 (P 2 NN′-Cy) (8; Scheme 5).…”

“…90 Bis[N-(2-(dicyclohexylphosphino)ethyl)-N-(pyridin-2-ylmethyl)amine (P 2 NN′-Cy) and FeCl 2 (P 2 NN′-Ph) were prepared according to their literature procedure. 33 NMR spectra were obtained at ambient temperature and pressure using a 400 MHz Varian MercuryPlus NMR spectrometer (400.00 MHz for 1 H, 161.98 MHz for 31 P, 128.4 MHz for 11 B, and 376.1 Hz for 19 F), an Agilent 500 MHz spectrometer with a OneNMR H/F{X} Probe (500 MHz for 1 H, 126 MHz for 13 C, 202 MHz for 31 P, and 160 MHz for 11 B), or an Agilent DD2-600 MHz spectrometer (600 MHz for 1 H, 151 MHz for 13 C, and 242 MHz for 31 P) unless stated otherwise. The 1 H and 13 C NMR were measured relative to partially deuterated solvent peaks.…”

“…Increased flexibility can be achieved by lengthening the ethylene spacers to propylene in order to accommodate larger atoms like Mo(0) . Unsymmetrical tetradentate ligands have also been reported where one phosphorus donor is substituted for an additional nitrogen donor, resulting in an open-chain P 2 N 2 framework if the nitrogen donors are geometrically equivalent, or a P 2 NN′ framework if they are not . Chiral, open-chain P 2 N 2 tetradentate ligands have been shown to be very useful ligands for the asymmetric transfer hydrogenation of polar bonds. − Chiral, macrocyclic P 2 N 2 ligands have also been reported and are useful for similar asymmetric catalytic hydrogenations. − …”

Recent Progress with Pincer Transition Metal Catalysts for Sustainability

“…After the first family of PCP complexes was synthetized by Shaw in 1976 [7], numerous research groups have applied this concept for almost all types of homogeneously catalyzed chemical reactions. A myriad of novel complexes with different pincer arms have been synthetized and characterized, including a vast family of carbene pincers [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23], PNP [24][25][26][27][28][29], PNN [30,31], POP [32], PCP [33][34][35][36][37][38], SNS [39,40], NCN [41], NSiN [42], CNC [43], CNN [44], NNN [45], as well as sulfur- [46][47][48], silicon- [49,50], selenium- [51,52], and boron-functionalized [53,…”