Henry Rzepa's Blog Chemistry with a twist

October 2, 2009

Full circle with carbon hypervalencies

The previous post talked about making links or connections. And part of the purpose for presenting this chemistry as a blog is to expose how these connections are made, or or less as it happens in real time (and not the chronologically sanitized version of discovery that most research papers are). So each post represents an evolution or mutation from the previous one. To recapitulate, we have seen how the idea of cyclopentadienyl anion as a ligand for a dipositive carbon atom has evolved. Let us move in yet another direction; the cyclobutadienyl dianion.  This ligand has recently been shown to bind Mg2+ (DOI: 10.1002/ejic.200800066), so why not He2+? And picking up again the previous theme, we will then protonate the bound complex. The result now is a monocation, and it has the C4v-symmetric structure shown below (DOI: 10042/to-2438). This bears some resemblance to pyramidane, a neutral  C5H4 compound with hemispherical carbon reported in 2001 (DOI: 10.1021/jp011642r) which is also a stable minimum in the potential energy surface.


September 18, 2009

Spotting the unexpected: Anomeric effects

Chemistry can be very focussed nowadays. This especially applies to target-driven synthesis, where the objective is to make a specified molecule, in perhaps as an original manner as possible. A welcome, but not always essential aspect of such syntheses is the discovery of new chemistry. In this blog, I will suggest that the focus on the target can mean that interesting chemistry can get over-looked (or if observed, not fully exploited in subsequent publications). Taking a synthesis-oriented publication at (almost) random entitled Synthesis of 1-Oxadecalins from Anisole Promoted by Tungsten (DOI: 10.1021/ja803605m) which appeared in 2008, the following molecule appears as one of the (many) intermediates.


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