Molybdenum-102, level scheme

Simple 1,3-dienes also undergo a thermal monocyclopropanation reaction with methoxy(alkyl)- and methoxy(aryl)carbene complexes of molybdenum and chromium [27]. The most complete study was carried out by Harvey and Lund and they showed that this process occurs with high levels of both regio-and diastereoselectivity. The chemical yield is significantly higher with molybdenum complexes [27a] (Scheme 7). Tri- and tetrasubstituted 1,3-dienes and 3-methylenecyclohexene (diene locked in an s-trans conformation) fail to react [28]. The monocyclopropanation of electronically neutral 1,3-dienes with non-heteroatom-stabilised carbene complexes has also been described [29]. 

One possible reaction scheme, an elaboration of the so-called Chatt cycle, results in the nitrogenase cycle shown in Figure 6.16.51 The cycle shown operates between molybdenum oxidation states Mo(0) and Mo(IV), but others have been proposed that operate between Mo(II) and Mo(VI) levels. 

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