Substituent Effects in the Hydrosilylation of Coordinated Dinitrogen in a Ditantalum Complex:  Cleavage and Functionalization of N₂

Abstract

The dinitrogen complex ([NPN]Ta)2(mu-eta1:eta2-N2)(mu-H)2, 1, (where [NPN] = (PhNSiMe2CH2)2PPh) undergoes hydrosilylation with primary and secondary alkyl- and arylsilanes, giving a new N-Si bond and a new terminal tantalum hydride derived from one Si-H unit. Various primary silanes can be employed to give isolable complexes of the general formula ([NPN]TaH)(mu-N-N-SiH(n)R(3-n))(mu-H)2(Ta[NPN]) (5, R=Bu, n = 2; 9, R=Ph, n = 2). Analogous complexes featuring secondary silanes are not isolable, because these products, and 5 and 9, are uniformly unstable toward reductive elimination of bridging hydrides as H2, followed by cleavage of the N-N bond to give ([NPN]TaH)(mu-N)(mu-N-SiH(n)R(3-n))(Ta[NPN]) (6, R=Bu, n = 2; 10, R=Ph, n = 2; 15, R=Ph, n = 1; 16, R=Ph and Me, n = 1). The bridging nitrido ligand in these complexes is itself a substrate for a second hydrosilylation when n = 2, and schemes leading to Ta(IV) complexes of the general formula ([NPN]Ta)2(mu-N-SiH2R)(mu-N-SiH2R') via elimination of H2 are reported (4, R=R'=Bu; 12, R=Bu, R' = Ph; 13, R=Bu, R' = CH2CH2SiH3). At this point, the general reaction manifold for these compounds ramifies, with distinct outcomes occurring for different R groups-[NPN] ligand amide migration from Ta to RSi affords 11, whereas stable complex 6 rearranges to give 7, in the presence of excess silane. Ethanediylbissilane reacts with 1 to give 14, isostructural to 7.

Dinitrogen Cleavage by a Diniobium Tetrahydride Complex: Formation of a Nitride and Its Conversion into Imide Species

“…Subsequent treatment with boranes, silanes, and zirconium hydrides resulted in NÀN bond cleavage of the coordinated N 2 molecule. [16,17] For 2, the cleavage proceeded spontaneously and did not require external reducing agent. This process corresponds to an overall six-electron reduction of N 2 , in which two electrons are initially stored in a metal-metal bond, and four additional electrons are provided by H 2 elimination.…”

Dinitrogen activation by group 4 and group 5 metal complexes supported by phosphine-amido containing ligand manifolds

“…Unfortunately, this potential catalytic cycle was not realized, but in the process of this investigation, the extraordinary reactivity of 13.3 with E-H reagents was revealed. For example, we have reported that 13.3 is capable of undergoing hydroboration [68,69], hydroalumination [70], hydrosilylation [71][72][73] and zirconocene insertion [74] reactions, all of which result in new nitrogen-element (N-E) bond formation [44,67]. An overview of the reactivity of 13.3 towards these reagents is illustrated in Scheme 14.…”

Fused Spirocyclic Imidazolone Ketals

“…[8][9][10][11][12][13][14][15][16][17] Removal of dihydrogen (H 2 ) through oxidation leads one to think about the "peroxycarbene" 4. Although likely not persistent, its valence tautomers (structures 5-7) begin to resemble heteroatom-functionalized architectures of tricyclic-fused natural products and promise both interesting structures and chemistry.…”