N O bond cleavage and N2 activation reactions of the Nitrosyl-Bridged complex [Mo2Cp2(µ-P Bu2)(µ-NO)(NO)2]

• The title complex adds N 2 upon reduction to unveil a novel µ 4 N 2 coordination mode. • N O bond cleavage of the title complex occurs upon reduction or addition of P(OEt) 3 . • The title complex displays a significant pyramidalization of its bridging NO ligand. • Unsaturated cations [Mo 2 Cp 2 (µ-PR 2 )(CO) 4 ] + display an asymmetric transoid structure. The title compound was prepared through a three-step procedure starting with the hydride complex [Mo 2 Cp 2 (µ-H)(µ-P t Bu 2 )(CO) 4 ], which was first dehydrogenated through reaction with HBF 4 ·OEt 2 to give the unsaturated complex [Mo 2 Cp 2 (µ-P t Bu 2 )(CO) 4 ](BF 4 ) (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 [Mo 2 Cp 2 (µ-P t Bu 2 )(CO) 2 (NO) 2 ](BF 4 ), which in turn was further decarbonylated and nitrosylated upon reaction with [N(PPh 3 ) 2 ]NO 2 to give the title nitrosyl-bridged complex (Mo-Mo = 2.905(1) Å). This complex displayed a structure comparable to that of its PCy 2 -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 N O bond activation chemistry, as shown by its reactions with HBF 4 ·OEt 2 to give the nitroxyl-bridged complex [Mo 2 Cp 2 (µ-P t Bu 2 )(µ- k 1 : η 2 -HNO)(NO) 2 ](BF 4 ) (HN O = 1.330(8) Å), with P(OEt) 3 to give the phosphoraniminate-bridged complex [Mo 2 Cp 2 (µ-P t Bu 2 ){µ-NP(OEt) 3 }(NO) 2 ], and with Na(Hg) to give the amide-bridged derivative [Mo 2 Cp 2 (µ-P t Bu 2 )(µ-NH 2 )(NO) 2 ]. Under a nitrogen atmosphere, however, the latter reaction also gave a minor side product identified as the dinitrogen-bridged derivative [Mo 4 Cp 4 (µ-P t Bu 2 ) 2 (µ 4 -N 2 )(NO) 4 ]. This tetranuclear complex displays a dinitrogen molecule bridging four metal atoms in the novel µ 4 - k 1 : k 1 : k 1 : k 1 coordination mode, with strong metal-nitrogen interactions taking the N 2 ligand to the diazendiide (N 2 2- ) limit (N N = 1.241(3) Å). Synopsis The title complex displays a bridging nitrosyl with significant pyramidalization at its N atom, and undergoes N O bond cleavage in reactions with P(OEt) 3 and Na(Hg), to give phosphoraniminate- and amide-bridged derivatives, respectively. Reduction under nitrogen also yields a tetranuclear complex with a dinitrogen molecule bound in a novel coordination mode.