An essential process in nitrogen fixation is cleavage of molecular nitrogen. [1] Several studies using model systems have confirmed that metal nitrides can be formed from coordinated dinitrogen providing that at least six electrons are available to formally reduce the N 2 unit to two N 3À ligands. [2] To date, all well-characterized molecular examples of metal nitride formation from dinitrogen have involved intermediates containing multiple metal atoms. Therefore, comparisons have been made to the polymetallic FeMoco active site in nitrogenase enzymes, and activated iron surfaces in the Haber process. [3] Herein we report a completely new way to form metal nitrides from coordinated dinitrogen that involves simple organoborane addition to a dinuclear tantalum dinitrogen complex. Because this result is quite unrelated to either biological or industrial nitrogen fixation, we suggest that a new paradigm for both cleaving and functionalizing coordinated dinitrogen is now available.
We have reported the facile preparation of [{(NPN)Ta} 2 -(m-H) 2 (m-h 1 :h 2 -N 2 )] (1; where NPN ¼ (PhNSiMe 2 CH 2 ) 2 PPh), [4] from the spontaneous reaction of N 2 gas with the dinuclear tantalum(iv)±hydride precursor [{(NPN)Ta} 2 (m-H) 4 ]. Equation (1) shows the 1:1 reaction between dark brown 1 and a THF solution of 9-borabicyclononane (9-BBN), which proceeds to completion over a few hours at room temperature to give orange [{(NPN)Ta(H)}(m-H) 2 (m-N 2 -BC 8 H 14 ){Ta(NPN)}] (2), in almost quantitative yield.