Comparing Well-Defined Manganese, Iron, Cobalt, and Nickel Ketone Hydrosilylation Catalysts

Abstract

A brief review of manganese-catalyzed hydrosilylation is presented along with a personal account of how the design for the highly active catalyst, ( Ph2PPr PDI)Mn, was conceived. The reductive transformations achieved using this catalyst are described and put into further context by comparing the observed activities with those attained for leading late first-row transition-metal catalysts.Key words: catalysis, hydrosilylation, ketones, manganese, ligands Due to the cost and relative toxicity associated with homogeneous precious metal catalysts, 1 the search for sustainable alternatives that operate with competitive activities, selectivities, and lifetimes has continued to intensify. 2 Much of this effort has centered around the development of late first-row transition-metal (Mn, Fe, Co, and Ni) catalysts, 3 as these metals are earth-abundant and far less expensive than their precious metal counterparts. 4 While a wide range of organic transformations have been targeted, 5 the development of first-row metal hydrosilylation catalysts remains of interest to the polysilane industry 2b since platinum catalysts have long been used to prepare silicone coatings and elastomers. 6 With this in mind, my colleagues and I recently reported the development of a well-defined manganese complex that is capable of mediating ketone hydrosilylation with turnover frequencies (TOF) of up to 76,800 h -1 at ambient temperature. 7

Conversion of Carbon Dioxide to Methanol Using a C–H Activated Bis(imino)pyridine Molybdenum Hydroboration Catalyst

“…31,32,36 For this reason, we refrain from assigning the Ph2PPr PDI chelate of 3 as redox-active (i.e., reduced by one or more electrons), even though Ph2PPr PDI is known to accept electrons when bound to formally zerovalent Mn. 37,38 Having isolated and characterized 3, its reduction to an appropriate catalyst precursor was explored. Adding an excess of K/Hg to 3 in THF afforded a green solution after 3 d at ambient temperature.…”

Iron Catalysis: Historic Overview and Current Trends

“…Enantioselective versions of these reductions have been reported as well [77,78], as highlighted by Thierry Ollevier in [79]. The hydrosilylation of alkenes is also a reduction reaction and allows access to a variety of silanes; the hydrosilylation of carbonyl units affords silyl ethers, which can subsequently be hydrolyzed to give the corresponding alcohols [80,81].…”

Bench‐Stable Cobalt Pre‐Catalysts for Mild Hydrosilative Reduction of Tertiary Amides to Amines and Beyond

“…Due to the skyrocketing prices of these metals, the development of more economical non‐precious metal based catalysts has been an intensive area of research in the last decade . In this regard, earth abundant base transition metal catalysts (Mn, Fe, Co, Ni) have become very attractive alternatives to conventional precious metal systems, Whereas, a series of base metal catalysts have been developed for hydrosilylation of alkenes, alkynes, aldehydes, ketones– and even esters, the examples of application of simple commercially available bench‐stable systems are still scarce ,,. Base‐metal catalyzed hydrosilative reduction of amides is even more challenging, and there is only a handful of reported examples, most of which require rather high temperatures (≥100 °C) and long reaction times,…”