A new anthraquinoid ligand for the iron-catalyzed hydrosilylation of carbonyl compounds at room temperature: new insights and kinetics

Abstract

The reaction of 1-((2-(pyridin-2-yl)ethyl)amino)anthraquinone with either Fe(HMDS)2 or Li(HMDS)/FeCl2 allowed the preparation of a new anthraquinoid-based iron(ii) complex active in the hydrosilylations of carbonyls. The new complex Fe(2)2 was characterized by single-crystal X-ray diffraction, infrared spectroscopy, NMR, and high resolution mass spectrometry (electrospray ionization). Superconducting quantum interference device (SQUID) magnetometry established no spin crossover behavior with an S = 2 state at room temperature. This complex was determined to be an effective catalyst for the hydrosilylation of aldehydes and ketones, exhibiting turnover frequencies of up to 63 min-1 with a broad functional group tolerance by just using 0.25 mol% of the catalyst at room temperature, and even under solvent-free conditions. The aldehyde hydrosilylation makes it one of the most efficient first-row transition metal catalysts for this transformation. Kinetic studies have proven first-order dependences with respect to acetophenone and Ph2SiH2 and a fractional order in the case of the catalyst.

Iron-Catalyzed Homogeneous Hydrosilylation of Ketones and Aldehydes: Advances and Mechanistic Perspective

“…Continuing our work on Fe-catalyzed hydrosilylation, a new iron(II) complex was synthesized bearing an anthraquinonederived ligand substituted with a 2-pyridylethylamino arm "AQ Et Py" (Scheme 10), which showed excellent activity toward carbonyl hydrosilylation. 38 Employing Fe(AQ Et Py) 2 as a catalyst, aromatic aldehydes were reduced to primary alcohols using 0.25 mol % of catalyst at room temperature in very short times (Scheme 10). Substrates bearing an electron- donating substituent on the aromatic ring proceeded faster than those with electron-withdrawing groups, but in all cases the hydrosilylations were completed in less than 60 min.…”

“…In our group, we have recently reported the use of anthraquinone-derived tridentate NNO ligands for the synthesis of iron(II) complexes with high activity as hydrosilylation catalysts. 37,38 Preliminary results on the hydrosilylation of acetophenone were obtained employing an iron-based pre-catalyst with a picolylamino-substituted anthraquinone ligand "AQPic" (Figure 4). 37 Continuing our work on Fe-catalyzed hydrosilylation, a new iron(II) complex was synthesized bearing an anthraquinone-derived ligand substituted with a 2-pyridylethylamino arm "AQ Et Py" (Scheme 10), which showed excellent activity towards carbonyl hydrosilylation.…”

“…37 Continuing our work on Fe-catalyzed hydrosilylation, a new iron(II) complex was synthesized bearing an anthraquinone-derived ligand substituted with a 2-pyridylethylamino arm "AQ Et Py" (Scheme 10), which showed excellent activity towards carbonyl hydrosilylation. 38 Employing 307…”

“…In our group, we have recently reported the use of anthraquinone-derived tridentate NNO ligands for the synthesis of iron­(II) complexes with high activity as hydrosilylation catalysts. , Preliminary results on the hydrosilylation of acetophenone were obtained employing an iron-based precatalyst with a picolylamino-substituted anthraquinone ligand “AQPic” (Figure ). The amount of Fe­(II) precatalyst Fe­(AQPic) 2 was initially set to 0.25 mol %, obtaining a 52% conversion into 2-phenylethanol after 1 h of reaction (or 80% after 24 h) at room temperature using (EtO) 2 MeSiH as a reductant.…”

“…Continuing our work on Fe-catalyzed hydrosilylation, a new iron­(II) complex was synthesized bearing an anthraquinone-derived ligand substituted with a 2-pyridylethylamino arm “AQ Et Py” (Scheme ), which showed excellent activity toward carbonyl hydrosilylation . Employing Fe­(AQ Et Py) 2 as a catalyst, aromatic aldehydes were reduced to primary alcohols using 0.25 mol % of catalyst at room temperature in very short times (Scheme ).…”