Preparation of Ni(cod)₂ Using Light as the Source of Energy

Abstract

A convenient method to prepare Ni­(cod)2 from Ni­(acac)2 using light as the source of energy is reported. In the first step of this process, xanthone is reductively dimerized upon irradiation of solar or LED light in 2-propanol to form a vicinal diol possessing a highly sterically congested C–C bond. In the second step, a ketyl radical derived from the diol reacts with Ni­(acac)2, ultimately reducing nickel­(II) to nickel(0), which is bound by 1,5-cyclooctadiene (COD) to produce Ni­(cod)2. This new method obviates the need for hazardous reductants such as diisobutylaluminum hydride (DIBAH) and sodium.

Transmetalation Reactions of Aromatic Dilithionickelole: Synthesis of Heterobimetallic Complexes Featuring Metalloles as Diene Ligands

“…Complexes 2-6 were all characterized by 1 H and 13 C NMR spectroscopy and some selected NMR data was summarized in Table 2. In the 1 H NMR spectra of 2-6, the Me and TMS groups on the metalloles exhibit two single peaks with an area ratio of 1 : 3.…”

“…The signals for the Me groups in 2-6 (1.46-1.95 ppm) are all upfield shifted compared to that of 1 (2.26 ppm), [5a] indicating the absence of the strong deshielding effect of aromatic metallole as in 1. In the 13 was not observed probably due to the coupling with 45 Sc (I = 7/ 2). [11c] The chemical shifts of the olefinic carbons on the CODs in 2-6 are comparable to that of Ni(COD) 2 (89.7 ppm) [13] and decrease in the following sequence: 3 > 4 > 6 > 5 > 2.…”

“…In the 13 was not observed probably due to the coupling with 45 Sc (I = 7/ 2). [11c] The chemical shifts of the olefinic carbons on the CODs in 2-6 are comparable to that of Ni(COD) 2 (89.7 ppm) [13] and decrease in the following sequence: 3 > 4 > 6 > 5 > 2. As these complexes have similar coordination spheres around Ni, the electron population on the olefinic carbons of COD should reflect the electron-donating ability of the metallole ligands, which is in the reverse order: 2 > 5 > 6 > 4 > 3.…”

Sustainable System for Hydrogenation Exploiting Energy Derived from Solar Light

“…The system consists of two separate steps. Solar energy is captured and chemically stored in the first step; exposure of a solution of an aryl ketone in ethanol to solar light causes dimerization of the aryl ketone to store energy in an arising sterically strained vicinal diol. , In the second step, the chemical energy stored in the diol is released and used for hydrogenation; the diol offers hydrogen to alkenes and splits back to the aryl ketone, which is easily recovered and reused repeatedly for capturing solar energy. Thus, the aryl ketone acts as a solar-driven hydrogen carrier to mediate the net transfer of hydrogen from ethanol to alkenes.…”

“…For the first step, the literature procedure for photodimerization of benzophenone , was slightly modified for a practical efficiency and convenience; a solution of azaxanthone 1 (2.00 g, 10.1 mmol) in ethanol (350 mL, used as received from commercial sources) was put in a plastic bag with low oxygen permeability, deaerated by sparging with argon gas, and sealed by heating (Scheme a). The bag was set in an untarnished stainless-steel tray, which was placed on a rooftop of a building on a fine or occasionally cloudy day and exposed to solar light at ambient temperature.…”