To Split or Not to Split: [AsCCAs]-Coordinated Mo, W, and Re Complexes and Their Reactivity toward Molecular Dinitrogen

Abstract

Molybdenum, tungsten, and rhenium halides bearing a 2,2′-( i Pr 2 As) 2 -substituted diphenylacetylene ([AsCCAs], 1-As) were prepared and reduced under an atmosphere of dinitrogen in order to activate the latter substrate. In the case of molybdenum, a diiodo (2-As) and a triiodo molybdenum precursor (5) were equally suited for reductive N 2 splitting, which led to the isolation of [AsCCAs]Mo�N(I) (3-As) in each case. For tungsten, [AsCCAs]-WCl 3 (6) was reduced under N 2 to afford {[AsCCAs]WCl 2 } 2 (N 2 ) (7), which is best described as a dinuclear π 8 δ 4 -configured μ-(η 1 : η 1 )-N 2 -bridged dimer. Attempts to reductively cleave the N 2 unit in 7 did not lead to the expected tungsten nitride (8), which had to be prepared independently via the treatment of 7 with sodium azide. To arrive at a π 10 δ 4 -configured N 2 -bridged dimer in a tetragonally distorted ligand environment, [AsCCAs]ReCl 3 (9) was reduced in the presence of N 2 . As expected, a μ-(η 1 : η 1 )-N 2 -bridged dirhenium species, namely, {[AsCCAs]ReCl 2 } 2 (N 2 ) (10), was formed, but found to very quickly decompose (presumably via loss of N 2 ), not only under reduced pressure, but also upon irradiation or heating. Hence, an alternative synthetic route to the originally envisioned nitride, [AsCCAs]Re�N(Cl) 2 (11), was developed. While all the aforementioned nitrides (3-As, 8, and 11) were found to be fairly robust, significantly different stabilities were noticed for {[AsCCAs]MCl 2 } 2 (N 2 ) (7 for M = W, 10 for M = Re), which is ascribed to the electronically different MN 2 M cores (π 8 δ 4 for 7 vs π 10 δ 4 for 10) in these μ-(η 1 : η 1 )-N 2 -bridged dimers.

Synthesis of Collidine from Dinitrogen via a Tungsten Nitride

“…Under an atmosphere of N 2 , green solutions of 2b were found to rapidly turn yellowish to afford a μ-(η 1 :η 1 )-N 2 -bridged dimer ( 4 ) in nearly quantitative yields (see Figure ). Numerous attempts to further reduce 4 using harsh reductants (KC 8 , Na/K, or K/KI), however, were unsuccessful, and the initially expected nitride was detectable by neither NMR nor IR spectroscopy. Along these lines, it needs to be mentioned that nitrides of type 3 and N 2 -dimers of type 4 are easily distinguishable by 183 W– 1 H HMBC NMR spectroscopy and by comparative IR analysis as illustrated in Figure .…”