Reactions of Cp(2)Mo(2)(Co)(4) with Organo Nitrogen Compounds (Molybdenum, Alkylidene).

Abstract

This research has involved the investigation of the reactivity of Cp(,2)Mo(,2)(CO)(,4)(Mo(TBOND)Mo) 29 with various organo nitrogen compounds, including diazoalkanes, azo compounds, and azides. The work with diazoalkanes was begun by Lou Messerle who obtained the complex Cp(,2)Mo(,2)(CO)(,4)(N(,2)CPh(,2)) 33 from the reaction of Ph(,2)CN(,2) with 29. Under either thermolytic or photolytic conditions, 33 looses nitrogen to form the u-alkylidene complex Cp(,2)Mo(,2)(CO)(,4)(u-CPh(,2)) 35. An x-ray analysis of 35 revealed that one of the phenyl groups is involved in a (pi) donation to a Mo atom, resulting in a Mo-Mo single bond. If this donation could be avoided, then from electron counting arguments, a complex with a Mo=Mo double bond would result. In order to eliminate this interaction, stereochemical restraints were placed on the aryl groups of the diazoalkane. The reaction of 9-diazofluorene with 29 proceeded with loss of nitrogen to yield the complex Cp(,2)Mo(,2)(CO)(,4)(u-C(,13)H(,8))(Mo=Mo) 40. An x-ray analysis showed that the fluorenylidene lig and is perpendicular to and symmetrically bridges the Mo=Mo double bond (Mo-Mo distance = 2.798(1) (ANGSTROM)). The complex 40 proved to be unreactive towards CO, C(,2)H(,4), and various acetylenes, but did react with H(,2) to form fluorene and 29. This can be compared with 35 which reacted with CO, C(,2)H(,4), acetylenes, and H(,2) under very mild conditions. A fragment molecular orbital analysis (EHMO method) indicated that the LUMO of 40 lies at a significantly higher energy than that of 35. Also, the LUMO of 35 is largely localized on one Mo atom and is ideally hybridized to bond an incoming nucleophile. In order to observe what effects the organic substituents may have on the reactivity, diethyldiazomalonate was allowed to react with 29. A 40% yield of Cp(,2)Mo(,2)(CO)(,4)(N(,2)C(CO(,2)Et)(,2)) 64 was isolated. From an x-ray analysis, it was found that the diazoalkane is acting as a chelating six electron donor, thus completely displacing the Mo-Mo triple bond. Each Mo atom in 64 is bonded to a different nitrogen atom, and one Mo is involved in a five membered metallacycle via an sp('2) CO of the diazoalkane. Similar results were obtained in the reaction of 29 with diethyl azodicarboxylate. A quantitative yield of Cp(,2)Mo(,2)(CO)(,4)(C(,2)H(,5)O(,2)CN(,2)CO(,2)C(,2)H(,5)) 105 was obtained in which the azo lig and is behaving as a chelating six electron donor. The structure of 105 consists of two edge sharing five membered metallacycles in which there is no longer a metal-metal bonding interaction. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI