Iron PCP Pincer Complexes in Three Oxidation States: Reversible Ligand Protonation To Afford an Fe(0) Complex with an Agostic C–H Arene Bond

Abstract

In the current investigation, the reaction of Fe(CO) with the ligand precursor 2-chloro-N,N-bis(diisopropylphosphanyl)-N,N-diethylbenzene-1,3-diamine (P(C-Cl)P- iPr) (1) was investigated. When a suspension of Fe(CO) and 1 in CHCN was transferred in a sealed microwave glass vial and stirred for 18 h at 110 °C the complex [Fe(PCP- iPr)(CO)Cl] (2) was obtained. In an attempt to prepare the hydride Fe(II) complex [Fe(PCP- iPr)(CO)H] (3), 2 was reacted with 1 equiv of Li[HBEt] in THF. Instead of ligand substitution, this complex underwent a one electron reduction which led to the formation of the low-spin d Fe(I) complex [Fe(PCP- iPr)(CO)] (4). Exposure of a benzene solution of 4 to NO gas (1 bar) at room temperature affords the diamagnetic complex [Fe(PCP- iPr)(CO)(NO)] (5). This is the first iron PCP nitrosyl complex. Protonation of 5 with HBF·EtO affords the cationic Fe(0) complex [Fe(κ P,CH,P-P(CH)P- iPr)(CO)(NO)]BF (6) which features an η-C-H agostic bond. Even with relatively weak bases such as NEt the agostic C-H bond can be deprotonated with reformation of the starting material 5. Therefore, protonation of 5 is completely reversible.

Synthesis and characterization of xylene-based group-six metal PCP pincer complexes

“…Deuterated solvents were dried over 4 Å molecular sieves. The synthesis of (2-bromo-1,3-phenylene)bis(methylene)bis(diisopropylphosphane) (P(C-Br)P CH2 -iPr) (1) was carried according to the literature [8]. 1 H, 13 C{ 1 H}, and 31 P{ 1 H} NMR spectra were recorded on Bruker AVANCE-250 and 400 spectrometers.…”

“…Here we utilize the oxidative addition of the C-Br bond of the ligand precursor (2-bromo-1,3-phenylene)bis(methylene) bis(diisopropylphosphane) (P(C-Br)P CH2 -iPr) (1) to the hexacarbonyl complexes [M(CO) 6 ] (M=Cr, Mo, W) as synthetic entry into group-six metal PCP pincer complexes. This procedure has been successfully applied recently for the synthesis of several Cr, Mo, W, Mn, and Fe PCP complexes bearing NR (R = alkyl) linkers [8,9]. X-ray structures of the Mo and W complexes are presented.…”

Azanone (HNO): generation, stabilization and detection

“…126 NOstabilization by complexes with pincer scaffolds is far better known. Several structural analyses of this kind of species exist in bibliography, 124,[127][128][129][130][131][132][133] along with reports of their catalytic activity. [134][135][136] Within our group, several rhodium-based pincer ligand systems have been studied (the most relevant are highlighted in Figure 3b).…”

Structure and Reactivity of NO/NO+/NO−Pincer and Porphyrin Complexes

“…However, this conception has been changed in time through reports of different reactions where transformations centered on the pincer ligand allowed different types of reactivities. [10,13] Some of the transformations consist of hemilability of one of the ligand arms, [14][15][16][17][18][19][20][21] formation of CÀ H agostic interactions, [22] dearomatization of aryl systems, [23] and even reversible collapse of the pincer platform. [24] However, the broad scope of pincer complexes greatly contrasts with that of pincer nitrosyl complexes, which have comparably been far less consistently studied.…”