NO bond cleavage and N2 activation reactions of the Nitrosyl-Bridged complex [Mo2Cp2(µ-PtBu2)(µ-NO)(NO)2]

The title compound was prepared through a three-step procedure starting with the hydride complex [Mo₂Cp₂(µ-H)(µ-P^tBu₂)(CO)₄], which was first dehydrogenated through reaction with HBF₄·OEt₂ to give the unsaturated complex [Mo₂Cp₂(µ-P^tBu₂)(CO)₄](BF₄) (Mo=Mo), which displays a transoid structure according to experimental (Mo-Mo = 2.8283(7) Å) and Density Functional Theory studies. The latter was then reacted with NO to give the dinitrosyl derivative [Mo₂Cp₂(µ-P^tBu₂)(CO)₂(NO)₂](BF₄), which in turn was further decarbonylated and nitrosylated upon reaction with [N(PPh₃)₂]NO₂ to give the title nitrosyl-bridged complex (Mo-Mo = 2.905(1) Å). This complex displayed a structure comparable to that of its PCy₂-bridged analogue, with similar pyramidalization of the bridging nitrosyl, but a more pronounced folding of the central MoPMoN skeleton and bending of terminal nitrosyls. It also displayed a similar NO bond activation chemistry, as shown by its reactions with HBF₄·OEt₂ to give the nitroxyl-bridged complex [Mo₂Cp₂(µ-P^tBu₂)(µ-k¹:η²-HNO)(NO)₂](BF₄) (HNO = 1.330(8) Å), with P(OEt)₃ to give the phosphoraniminate-bridged complex [Mo₂Cp₂(µ-P^tBu₂){µ-NP(OEt)₃}(NO)₂], and with Na(Hg) to give the amide-bridged derivative [Mo₂Cp₂(µ-P^tBu₂)(µ-NH₂)(NO)₂]. Under a nitrogen atmosphere, however, the latter reaction also gave a minor side product identified as the dinitrogen-bridged derivative [Mo₄Cp₄(µ-P^tBu₂)₂(µ₄-N₂)(NO)₄]. This tetranuclear complex displays a dinitrogen molecule bridging four metal atoms in the novel µ₄-k¹:k¹:k¹:k¹ coordination mode, with strong metal-nitrogen interactions taking the N₂ ligand to the diazendiide (N₂^2-) limit (NN = 1.241(3) Å).