trans-Bis(dinitrogen)bis[1,2-bis(diphenylphosphino)ethane]molybdenum(0) is a coordination complex with the formula Mo(N<sub>2</sub>)<sub>2</sub>(dppe)<sub>2</sub>. It is a relatively air stable yellow-orange solid. It is notable as being the first discovered dinitrogen complex of molybdenum.
Mo(N<sub>2</sub>)<sub>2</sub>(dppe)<sub>2</sub> is an octahedral complex with idealized D<sub>2h</sub> point group symmetry. The dinitrogen ligands are mutually trans across the metal center. The Mo-N bond has a length of 2.01 ÃÂ , and the N-N bond has a length of 1.10 ÃÂ . This length is close to the free nitrogen bond length, but coordination to the metal weakens the N-N bond making it susceptible to electrophilic attack.
The first synthetic route to Mo(N<sub>2</sub>)<sub>2</sub>(dppe)<sub>2</sub> involved a reduction of molybdenum(III) acetylacetonate with triethylaluminium in the presence of dppe and molecular nitrogen.
A higher yielding synthesis involves a four-step process. In the first step, molybdenum(V) chloride is reduced by acetonitrile (CH<sub>3</sub>CN) to give [MoCl<sub>4</sub>(CH<sub>3</sub>CN)<sub>2</sub>]. Acetonitrile is displaced by tetrahydrofuran (THF) to give [MoCl<sub>4</sub>(THF)<sub>2</sub>]. This Mo(IV) compound is reduced by tin powder to [MoCl<sub>3</sub>(thf)<sub>3</sub>]. The desired compound is formed in the presence of nitrogen gas, dppe ligand, and magnesium turnings as the reductant:
The terminal nitrogen is susceptible to electrophilic attack, allowing for the fixation of nitrogen to ammonia in the presence of acid. In this way, Mo(N<sub>2</sub>)<sub>2</sub>(dppe)<sub>2</sub> serves as a model for biological nitrogen fixation. Carbon-nitrogen bonds can also be formed with this complex through condensation reactions with ketones and aldehydes, and substitution reactions with acid chlorides. The terminal nitrogen can also be silylated.