Reaction of the N-tosylaziridines (p-CH(3)C(6)H(4)SO(2))NCH(2)CHR (1a, R = H; 1b, R = Me; 1c, R = n-Bu; 1d, R = i-Pr) with (bpy)Ni(cod) (2; bpy = 2,2'-bipyridine; cod = 1,5-cyclooctadiene) or (bpy)NiEt(2) (3) results in elimination of cod or butane from 2 and 3, respectively, and oxidative addition of an aziridine C-N bond to give the azametallacyclobutane complexes (bpy)Ni(NTosCHRCH(2)) (4a, R = H; 4b, R = Me; 4c, R = n-Bu; 4d, R = i-Pr) as maroon solids in 50-70% isolated yields. The structure of 4b exhibits a puckered four-membered azametallacycle containing a pyramidal nitrogen and with Ni-N(1) = 1.911(5) A; the tosyl group on N and the methyl substituent on the adjacent C are disposed in an anti conformation. The monodeuterated aziridine syn-(p-CH(3)C(6)H(4)SO(2))NCHDCH-n-Bu (1e) reacts with either 2 or 3 to give (bpy)Ni[NTosCH(n-Bu)CHD] (4e) in 60-65% yield, having an anti arrangement of the methine and methylene protons in the azametallacycle, and indicates that >95% inversion of stereochemistry has occurred at the methylene carbon during the oxidative-addition reaction. When the azametallacyclobutane complexes 4a-e are exposed to oxygen, oxidatively induced reductive elimination ensues, giving the free aziridines in 30-60% isolated yields. In the oxidation of 4e, the product aziridine is spectroscopically identical to its parent, 1e, indicating the elimination that forms the C-N bond also proceeds with inversion of stereochemistry (approximately 92% by (1)H NMR) at the methylene carbon.

The transformation of acid chlorides (RC(O)Cl) to organic nitriles (RC[triple bond]N) by the terminal niobium nitride anion [N[triple bond]Nb(N[Np]Ar)3]- ([1a-N]-, where Np = neopentyl and Ar = 3,5-Me2C6H3) via isovalent N for O(Cl) metathetical exchange is presented. Nitrido anion [1a-N]- is obtained in a heterodinuclear N2 scission reaction employing the molybdenum trisamide system, Mo(N[R]Ar)3 (R = t-Bu, 2a; R = Np, 2b), as a reaction partner. Reductive scission of the heterodinuclear bridging N2 complexes, (Ar[R]N)3Mo-(mu-N2)Nb(N[Np]Ar)3 (R = t-Bu, 3b; R = Np, 3c) with sodium amalgam provides 1 equiv each of the salt Na[1a-N] and neutral N[triple bond]Mo(N[R]Ar)3 (R = t-Bu, 2a-N; R = Np, 2b-N). Separation of 2-N from Na[1a-N] is readily achieved. Treatment of salt Na[1a-N] with acid chloride substrates in tetrahydrofuran (THF) furnishes the corresponding organic nitriles concomitant with the formation of NaCl and the oxo niobium complex O[triple bond]Nb(N[Np]Ar)3 (1a-O). Utilization of 15N-labeled 15N2 gas in this chemistry affords a series of 15N-labeled organic nitriles establishing the utility of anion [1a-N]- as a reagent for the 15N-labeling of organic molecules. Synthetic and computational studies on model niobium systems provide evidence for the intermediacy of both a linear acylimido and niobacyclobutene species along the pathway to organic nitrile formation. High-yield recycling of oxo 1a-O to a niobium triflate complex appropriate for heterodinuclear N2 scission has been developed. Specifically, addition of triflic anhydride (Tf2O, where Tf = SO2CF3) to an Et2O solution of 1a-O provides the bistriflate complex, Nb(OTf)2(N[Np]Ar)3 (1a-(OTf)2), in near quantitative yield. One-electron reduction of 1a-(OTf)2 with either cobaltocene (Cp2Co) or Mg(THF)3(anthracene) provided the monotriflato complex, Nb(OTf)(N[Np]Ar)3 (1a-(OTf)), which efficiently regenerates complexes 3b and 3c when treated with the molybdenum dinitrogen anions [N2Mo(N[t-Bu]Ar)3]- ([2a-N2]-) or [N2Mo(N[Np]Ar)3]- ([2b-N2]-), respectively.

Nitride NW(N[i-Pr]Ar)3 (1, Ar = 3,5-C6H3Me2) was synthesized in two steps from known NW(O-t-Bu)3 (41% overall yield). Complex 1 is the tungsten congener of NMo(N[i-Pr]Ar)3, a known molecule that has been synthesized using N2 as the nitrido nitrogen source, but which undergoes no reaction with pivaloyl chloride. Compound 1 undergoes metathesis with pivaloyl chloride at 25 degrees C to form the corresponding nitrile in 97% yield. Another substrate examined in this work was the labeled acid chloride 1-Ad13C(O)Cl (Ad = adamantyl). The "(O)Cl" moiety is transferred to tungsten forming an oxo-chloride, (Ar[i-Pr]N)3W(O)Cl (3), as the final tungsten product; both 1 and 3 were characterized structurally by X-ray diffraction. An intermediate observed in the nitrile-forming reaction was characterized spectroscopically to be a tungsten acylimido complex. The latter assignment was substantiated by the synthesis and structural characterization of the compound (Ar[i-Pr]N)3W(NC(O)CF3)(O2CCF3) (2m). In addition, density functional theory calculations performed using ADF lent insight into the thermochemistry of the overall process.

Dedicated to Professor Philip P. PowerThe terminal, anionic niobium phosphide (P 3À ) complex Na [P Nb(N[Np]Ar) 3 ] (Na-1; Np= neopentyl, Ar = 3,5-Me 2 C 6 H 3 ) has served as a platform for the construction of multiply bonded, phosphorus-containing moieties as both complexed ligands and free entities. [1][2][3][4][5] Exemplifying the latter is the synthesis of phosphaalkynes (RCP) and [O Nb{N(Np) [5] We envisioned that a similar method could be employed to synthesize new transition-metal phosphide complexes, given the availability of a suitable reaction partner for Na-1. We recently reported an attractive candidate for this application: the tungsten oxide/chloride complex, [O(Cl)W{N(iPr)Ar} 3 ] (3).[6] In a reaction similar to Equation (1), complex 3 is prepared by treating the corresponding nitride complex [NW{N(iPr)Ar} 3 ] (4) with pivaloyl chloride (tBuC(O)Cl), and is quantitatively obtained as a blood-red, highly lipophilic solid of sufficient purity for further synthetic studies. We hypothesized that in the presence of Na-1, 3 would behave as an "inorganic acid chloride", engaging Na-1 by elimination of NaCl. With subsequent intermetal exchange of P and O ligands, the known oxidoniobium complex 2 would be generated as well as a new terminal phosphide complex [P W{N(iPr)Ar} 3 ] (5). Several examples of installing multiply bonded ligands (oxide, imide, and alkylidene) by intermetal ligand exchange have been reported; [7][8][9][10][11][12][13][14][15][16] herein, we extend this concept to the terminal phosphide functional group.Our hypothesis was tested by treating a yellow-orange, ethereal solution of Na-1 with a red, ethereal solution of 3 at À35 8C, following in situ preparation of 3 from 4 and removal of tBuCN. Upon stirring for two hours at 22 8C, an orangebrown, homogeneous solution was obtained. Following solvent removal under reduced pressure the product mixture was dissolved in C 6 D 6 . [17]Separation of 5 from NaCl was trivial; however, separation of 5 from coproduct 2 at first proved difficult, owing to their similar solubility properties. This was initially overcome by applying the Pasteur method, [18] whereby mixtures of crystalline 2 and 5 were manually separated.A more efficient method of separating 5 from coproduct 2 was achieved by in situ conversion of 2 to the bistriflate complex [(TfO) 2 Nb{N(Np)Ar} 3 ] (6, Tf = CF 3 SO 2 ), [5] a complex that is only sparingly soluble in common hydrocarbon solvents. Accordingly, treatment of a 1:1 mixture of 2 and 5 in Et 2 O with neat triflic anhydride (Tf 2 O, 1 equiv) at room temperature resulted in a color change from orange-brown to yellow-brown over several minutes as a yellow precipitate formed. Following solvent removal under reduced pressure, the product mixture was dissolved in C 6 D 6 . The 1 H NMR spectrum of the product mixture revealed clean and selective production of 6, with 5 remaining unperturbed. The 31 P{ 1 H} NMR spectrum displayed only the downfield signal associated with 5, thus confirming its role as a spectator in this react...

The kinetics of the oxidative addition of PhSeSePh and PhTeTePh to the stable 17-electron complex *Cr(CO)3C5Me5 have been studied utilizing stopped-flow techniques. The rates of reaction are first-order in each reactant, and the enthalpy of activation decreases in going from Se (deltaH(double dagger) = 7.0 +/- 0.5 kcal/mol, deltaS(double dagger) = -22 +/- 3 eu) to Te (deltaH(double dagger) = 4.0 +/- 0.5 kcal/mol, deltaS(double dagger) = -26 +/- 3 eu). The kinetics of the oxidative addition of PhSeH and *Cr(CO)3C5Me5 show a change in mechanism in going from low (overall third-order) to high (overall second-order) temperatures. The enthalpies of the oxidative addition of PhE-EPh to *Cr(CO)3C5Me5 in toluene solution have been measured and found to be -29.6, -30.8, and -28.9 kcal/mol for S, Se, and Te, respectively. These data are combined with enthalpies of activation from kinetic studies to yield estimates for the solution-phase PhE-EPh bond strengths of 46, 41, and 33 kcal/mol for E = S, Se, and Te, respectively. The corresponding Cr-EPh bond strengths are 38, 36, and 31 kcal/mol. Two methods have been used to determine the enthalpy of hydrogenation of PhSeSePh in toluene on the basis of reactions of HSPh and HSePh with either *Cr(CO)3C5Me5 or 2-pyridine thione. These data lead to a thermochemical estimate of 72 kcal/mol for the PhSe-H bond strength in toluene solution, which is in good agreement with kinetic studies of H atom transfer from HSePh at higher temperatures. The reaction of H-Cr(CO)3C5Me5 with PhSe-SePh is accelerated by the addition of a Cr radical and occurs via a rapid radical chain reaction. In contrast, the reaction of PhTe-TePh and H-Cr(CO)3C5Me5 does not occur at any appreciable rate at room temperature, even in the presence of added Cr radicals. This is in keeping with a low PhTe-H bond strength blocking the chain and implies that H-TePh < or = 63 kcal/mol. Structural data are reported for PhSe-Cr(CO)3C5Me5 and PhS-Cr(CO)3C5Me5. The two isostructural complexes do not show signs of an increase in steric strain in terms of metal-ligand bonds or angles as the Cr-EPh bond is shortened in going from Se to S. Bond strength estimates of the PhE-H and PhE-EPh derived from density functional theory calculations are in reasonable agreement with experimental data for E = Se but not for E = Te. The nature of the singly occupied molecular orbital of the *EPh radicals is calculated to show increasing localization on the chalcogenide atom in going from S to Se to Te.