### Abstract

Activation of N_{2} by (silox)_{3}Ta (1, silox = ^{t}Bu_{3}SiO) to afford (silox)_{3}Ta=N-N=Ta(silox) _{3} (1_{2}-N_{2}) 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 REH_{2} activation (E = N, P, As). Oxidative addition of REH _{2} to 1 afforded (silox)_{3}HTaEHR (2-NHR, R = H, Me, ^{n}Bu, C_{6}H_{4}-p-X (X = H, Me, NMe_{2}); 2-PHR, R = H, Ph; 2-AsHR, R = H, Ph), which underwent 1,2-H_{2}- elimination to form (silox)_{3}Ta=NR (1=NR; R = H, Me, ^{n}Bu, C_{6}H_{4}-p-X (X = H (X-ray), Me, NMe_{2}, CF _{3})), (silox)_{3}Ta=PR (1=PR; R = H, Ph), and (silox) _{3}Ta=AsR (1=AsR; R = H, Ph). Kinetics revealed NH bond-breaking as critical, and As > N > P rates for (silox)_{3}HTaEHPh (2-EHPh) were attributed to (1) ΔG°_{calc}(N) < ΔG° _{calc}(P) ∼ ΔG°_{calc}(As); (2) similar fractional reaction coordinates (RCs), but with RC shorter for N < P∼As; and (3) stronger TaE bonds for N > P∼As. Calculations of the pnictidenes aided interpretation of UV-vis spectra. Addition of H_{2}NNH_{2} or H_{2}N-N(^{c}NC_{2}H_{3}Me) to 1 afforded 1=NH, obviating these routes to 1_{2}-N_{2}, and formation of (silox)_{3}MeTaNHNH2 (4-NHNH_{2}) and (silox) _{3}MeTaNH(-^{c}NCHMeCH_{2}) (4-NH(azir)) occurred upon exposure to (silox)_{3}Ta=CH_{2} (1=CH_{2}). Thermolyses of 4-NHNH_{2} and 4-NH(azir) yielded [(silox)_{2}TaMe](μ- N_{α}HN_{β})(μ-N_{γ}HN _{δ}H)[Ta(silox)_{2}] (5) and [(silox)_{3}MeTa] (μ-η^{2}-N,N: η^{1}-C-NHNHCH_{2}CH _{2}CH_{2})[Ta(κ-O,C-OSi^{t}Bu_{2}CMe _{2}CH_{2})(silox)_{2}] (7, X-ray), respectively. (silox)_{3}Ta=CPPh_{3} (1=CPPh_{3}, X-ray) was a byproduct from Ph_{3}PCH_{2} treatment of 1 to give 1=CH _{2}. Addition of Na(silox) to [(THF)_{2}Cl_{3}Ta] _{2}(μ-N_{2}) led to [(silox)_{2}ClTa](μ-N _{2}) (8-Cl), and via subsequent methylation, [(silox) _{2}MeTa]_{2}(μ-N_{2}) (8-Me); both dimers were thermally stable. Orbital symmetry requirements for N_{2} capture by 1 and pertinent calculations are given.

Original language | English (US) |
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Pages (from-to) | 8524-8544 |

Number of pages | 21 |

Journal | Inorganic Chemistry |

Volume | 49 |

Issue number | 18 |

DOIs | |

State | Published - Sep 20 2010 |

Externally published | Yes |

### ASJC Scopus subject areas

- Physical and Theoretical Chemistry
- Inorganic Chemistry

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## Cite this

_{3}Ta (silox =

^{t}Bu

_{3}SiO); Attempts to circumvent the constraints of orbital symmetry in N

_{2}activation.

*Inorganic Chemistry*,

*49*(18), 8524-8544. https://doi.org/10.1021/ic101147x