Reproducibility is the hallmark of reliable science. Reproducible synthetic procedures are of central importance in the chemical sciences, yet >= 12% of syntheses submitted to publications that explicitly check procedures before their publication, such as Inorganic Syntheses and Organic Syntheses, are reported as having to be rejected since the submitted synthesis could not be repeated. In the present contribution paper we re-examine our own 2012 synthesis of [Ir(1,5-COD)(mu-H)](4) which, frustratingly, we were unable to reproducible once the first author of the original publication completed his stent in our labs. We detail the approach we took to uncover the problems in the synthesis, a key step in which was constructing a "paper mechanism" that led to the key hypothesis of what was going wrong in our attempts to repeat the published synthesis. The results have led to an improved synthesis, one shown to be reproducible by a second researcher working only from the detailed written procedure. Also detailed are the 4 conceptual Steps that were used to find the main problems in the synthesis, as well as the 7 specific alternative hypotheses that were involved and 20 experimental trials which discovered the missing detail in the original synthesis-the previously unknown need to employ a closed reaction system-and which led to the present, further improved synthesis which we demonstrate can be reproduced by an independent researcher with no prior Schlenk-technique experience working from only the written procedure. The hard-won insight of the need for a closed system is likely of broader significance and applicability to analogous syntheses involving metal-reductions by LiBEt3H and probably other anionic hydrides. A summary and conclusion section is included, one striving toward assisting the design and reporting of more reproducible syntheses in the chemical sciences. (C) 2015 Elsevier B.V. All rights reserved.