Bis(dinitrogen)bis(1,2-bis(diphenylphosphino)ethane)molybdenum(0)
# Bis(dinitrogen)bis(1,2-bis(diphenylphosphino)ethane)molybdenum(0)

trans-Bis(dinitrogen)bis[1,2-bis(diphenylphosphino)ethane]molybdenum(0) is a coordination complex with the formula $Mo(N_2)_2(dppe)_2.$ It is a relatively air stable yellow-orange solid. It is notable as being the first discovered dinitrogen containing complex of molybdenum.

## Structure

$Mo(N_2)_2(dppe)_2$ is an octahedral complex with idealized $D_{2h}$ point group symmetry. The dinitrogen ligands are mutually trans across the metal center. The Mo-N bond has a length of 2.01 Å, and the N-N bond has a length of 1.10 Å. 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.

## Synthesis

The first synthetic route to $Mo(N_2)_2(DPPE)_2$ involved a reduction of molybdenum(III) acetylacetonate with triethylaluminium in the presence of dppe and nitrogen.

A higher yielding synthesis involves a four-step process. In the first step, molybdenum(V) chloride is reduced by acetonitrile $(CH_3CN)$ to give $[MoCl_4(CH_3CN)_2].$ Acetonitrile is displaced by tetrahydrofuran (THF) to give $[MoCl_4(THF)_2].$ This Mo(IV) compound is reduced by tin powder to $[MoCl_3(thf)_3].$ The desired compound is formed in the presence of nitrogen gas, dppe ligand, and magnesium turnings as the reductant:

    3 Mg + 2 $MoCl_3(THF)_3$ + 4 $Ph_2PCH_2CH_2PPh_2$ + 4 $N_2$ → 2 $trans-[Mo(N_2)_2(Ph_2PCH_2CH_2PPh_2)_2]$ + 3 $MgCl_2$ + 6 THF

## Reactivity

The terminal nitrogen is susceptible to electrophilic attack, allowing for the fixation of nitrogen to ammonia in the presence of acid. In this way, $Mo(N_2)_2(dppe)_2$ 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.

