(Cyclopentadienyl)nitrosyhnanganese Compounds: The Original Molecules Containing Bridging Nitrosyl Groups

The (cyclopentadienyl)nitrosylmanganese derivatives CP2-Mn-2(NO)(2)(CO). (n = 2, 1, 0), CP2Mn2(NO)(3)X (X = NO2, (7C51-15), CpMn(NO)(2), CP2Mn2(NO)(4), and CP3Mn3(NO)4 have been investigated by using density functional theory. Six structures are found for Cp2Mn2(NO)(2)(CO)(2) with various combinations of terminal and bridging carbonyl and nitrosyl groups within ca. 3 kcal/mol of each other indicating a highly fluxional system. A triplet-state triply bridged structure is predicted to be the global minimum for CP2Mn2(NO)(2)(CO), just as it is for the isoelectronic CP2Fe2(CO)3. For CP2Mn2(NO)(2) a doubly bridged triplet structure is predicted to lie ca. 30 kcal/mol below the corresponding singlet structure, unlike the isoelectronic CP2Fe2(CO)(2). The structures predicted for CP2Mn(p-NO)2(NO)X (X = NO2 and 9'-C5H5) and CP3Mn3(ll-NO)(3)(113-NO) are close to the experimentally known structures. The monomer CpMn(NO)(2), with a favorable 18-electron configuration for the manganese atom, is predicted to be unstable with respect to dimerization to Cp2Mn2(mu-NO)(2)(NO)(2), for which two structures are found of similar energy. One CP2Mn2(p-NO)2(NO)2 structure has a non-bonding Mn...Mn distance of ca. 3.1 angstrom and linear terminal MnNO units, whereas the other CP2Mn2(mu-NO)(2)-(NO)(2) structure has a single-bond Mn-Mn distance of ca. 2.5 angstrom and bent terminal MnNO units. In CP2Mn(p-NO)(2)(NO)(mu-Cp) the Mn-2(p-NO)(2) unit is unsymmetrical, with significantly different (by ca. 0.2 A) Mn-N bond lengths to each side. However, in CP2Mn2(NO)(2)(CO)n (n = 2, 1, 0) and CP2Mn2(p-NO)(2)(NO)(2) the Mn-2(mu-NO)(2) units are symmetrical, with essentially the same Mn-N bond lengths to both sides. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)