7784-42-1Relevant articles and documents
Pnictogen-hydride activation by (silox)3Ta (silox = tBu3SiO); Attempts to circumvent the constraints of orbital symmetry in N2 activation
Hulley, Elliott B.,Bonanno, Jeffrey B.,Wolczanski, Peter T.,Cundari, Thomas R.,Lobkovsky, Emil B.
, p. 8524 - 8544 (2010/12/18)
Activation of N2 by (silox)3Ta (1, silox = tBu3SiO) to afford (silox)3Ta=N-N=Ta(silox) 3 (12-N2) does not occur despite ΔG°cald = -55.6 kcal/mol because of constraints of orbital symmetry, prompting efforts at an independent synthesis that included a study of REH2 activation (E = N, P, As). Oxidative addition of REH 2 to 1 afforded (silox)3HTaEHR (2-NHR, R = H, Me, nBu, C6H4-p-X (X = H, Me, NMe2); 2-PHR, R = H, Ph; 2-AsHR, R = H, Ph), which underwent 1,2-H2- elimination to form (silox)3Ta=NR (1=NR; R = H, Me, nBu, C6H4-p-X (X = H (X-ray), Me, NMe2, CF 3)), (silox)3Ta=PR (1=PR; R = H, Ph), and (silox) 3Ta=AsR (1=AsR; R = H, Ph). Kinetics revealed NH bond-breaking as critical, and As > N > P rates for (silox)3HTaEHPh (2-EHPh) were attributed to (1) ΔG°calc(N) calc(P) ～ ΔG°calc(As); (2) similar fractional reaction coordinates (RCs), but with RC shorter for N P～As. Calculations of the pnictidenes aided interpretation of UV-vis spectra. Addition of H2NNH2 or H2N-N(cNC2H3Me) to 1 afforded 1=NH, obviating these routes to 12-N2, and formation of (silox)3MeTaNHNH2 (4-NHNH2) and (silox) 3MeTaNH(-cNCHMeCH2) (4-NH(azir)) occurred upon exposure to (silox)3Ta=CH2 (1=CH2). Thermolyses of 4-NHNH2 and 4-NH(azir) yielded [(silox)2TaMe](μ- NαHNβ)(μ-NγHN δH)[Ta(silox)2] (5) and [(silox)3MeTa] (μ-η2-N,N: η1-C-NHNHCH2CH 2CH2)[Ta(κ-O,C-OSitBu2CMe 2CH2)(silox)2] (7, X-ray), respectively. (silox)3Ta=CPPh3 (1=CPPh3, X-ray) was a byproduct from Ph3PCH2 treatment of 1 to give 1=CH 2. Addition of Na(silox) to [(THF)2Cl3Ta] 2(μ-N2) led to [(silox)2ClTa](μ-N 2) (8-Cl), and via subsequent methylation, [(silox) 2MeTa]2(μ-N2) (8-Me); both dimers were thermally stable. Orbital symmetry requirements for N2 capture by 1 and pertinent calculations are given.
GASEOUS DIELECTRICS WITH LOW GLOBAL WARMING POTENTIALS
-
, (2010/12/31)
A dielectric gaseous compound which exhibits the following properties: a boiling point in the range between about ?20° C. to about ?273° C.; non-ozone depleting; a GWP less than about 22,200; chemical stability, as measured by a negative standard enthalpy of formation (dHf0); a toxicity level such that when the dielectric gas leaks, the effective diluted concentration does not exceed its PEL; and a dielectric strength greater than air.
Laser spectroscopy and dynamics of the jet-cooled AsH2 free radical
He, Sheng-Gui,Clouthier, Dennis J.
, p. 1 - 9 (2009/02/02)
The A2A1-X2B1 electronic transition of the jet-cooled AsH2 free radical has been studied by laser-induced fluorescence (LIF), wavelength-resolved emission, and fluorescence lifetime measurements. The radical was produced by a pulsed electric discharge through a mixture of arsine (AsH3) and high pressure argon at the exit of a pulsed valve. Nine vibronic bands wereidentified by LIF spectroscopy in the 505-400 nm region, including a lo ng progression in the bending mode and two bands (101 and 101201) involving the excited state As-H symmetric stretch. Single vibronic level emission spectra showed similar activity in the bending and symmetric stretching frequencies of the ground state. High-resolution spectra of the 000 band exhibited large spin splittings and small, resolved arsenic hyperfine splittings, due to a substantial Fermi contact interaction in the excited state. The rotational constants obtained in the analysis gave effective molecular structures of r″0 = 1.5183(1) ?, θ″0=90.75(1) ° and r′0=1.4830(1) ?, θ′0= 123.10(2)°. The excited state fluorescence lifetimes vary dramatically with rovibronicstate, from a single value of 1.4 μs to many with lifetimes less tha n 10 ns, behavior which the authors interpret as signaling the onset of a predissociative process near the zero-point level of the ground state.
