Hydrosilylation of Ketones: From Metal-Organic Frameworks to Simple Base Catalysts (original) (raw)

2010, Chemistry - An Asian Journal

The catalytic reduction of carbon À heteroatom multiple bonds under mild conditions constitutes an important transformation in organic synthesis and the pharmaceutical as well as agrochemical industry. [1] Obviously, high selectivity and broad tolerance towards functional groups are key factors for the acceptance and application of novel methodologies. In addition to molecular hydrogen and hydrogen transfer reagents, [2] hydrosilanes are commonly used as reducing agents. Since the early reports three decades ago, [4] the asymmetric and non-asymmetric hydrosilylations of prochiral ketones relied mainly on precious-metal-based catalysts, such as rhodium, ruthenium, and iridium. However, less-expensive metals, such as titanium, tin, and copper were explored, too. [11] More recently, efforts have been devoted to the development of more-benign and available bio-relevant metal catalysts based on iron [12] and zinc complexes. [13] Notably, silanes have also been used as reducing reagents in the presence of acid, [14] fluoride ions, or base, [14a, 15b, 16] although in many cases harsh reaction conditions and large amounts of salt or base were required. Clearly, each of these procedures has its merits as well as limitations. Either the cost of the metal catalyst, toxicity of the residual metal in the product, operational difficulties (such as low temperature À50 to À70 8C), or the use of complex ligand systems limit their applications. Hence, the development of novel catalysts continues to attract academic and industrial interest.