## Abstract

The reaction mechanisms of model complexes[p_{2}n_{2}]Zr(μ-η ^{2}NNH)(μ-H)Zr[p_{2}n_{2}], B1 (A7), [p_{2}n_{2}](H)Zr(μ-η^{2}-NNH)Zr[p _{2}n_{2}], B11 (A3), [p_{2}n_{2}]Zr(μ-η ^{2}-cis-HNNH)(μ-H)Zr(H)[p_{2}n_{2}], C1 (B3), [p_{2}n_{2}](H)Zr(μ-η^{2}-cis-HNNH)Zr(H)[p _{2}n_{2}], C4 (B13), [p_{2}n_{2}](H)Zr(μ-η^{2}-trans-HNNH)Zr (H)[p_{2}n_{2}], C7 (B21), where [p_{2}n_{2}] = [(PH_{3})(NH_{2})], with molecular hydrogen have been studied using density functional theory and compared with those for [p_{2}n_{2}]Zr(μ-η^{2}-N_{2})Zr[p _{2}n_{2}], A1. The addition of a H_{2} molecule to B1 (A7) (i.e., the addition of the second H_{2} to A1) takes place with a 19.5 kcal/mol barrier, which is about 2 kcal/mol smaller than that for the first H_{2} addition Al + H_{2} → A7 reaction. From B3, product of B1 + H_{2}, the process proceeds via either channel I.a, the reverse reaction B3 → B1 + H_{2}, or/and channel I.b, the dihydrogen elimination B3 → [p_{2}n_{2}]Zr(μ-η^{2}-cis-HNNH)Zr[p _{2}n_{2}] (A15) + H_{2}, with barriers of 11.7 and 21.5 kcal/mol, respectively. Since addition of the first H_{2} to A1 is known to occur at laboratory conditions, one predicts that the addition of the H_{2} to B1 (A7) will also be feasible under proper experimental conditions. Once A15 is produced, reaction leads to [p_{2}n_{2}]Zr(μ-NH)(μ-NH_{2})(μ-H)Zr[p _{2}n_{2}] (B8) via formation of [p_{2}n_{2}]Zr(μ-NH)_{2}Zr[p_{2}n _{2}], A17, which was kinetically unreachable by A1 + H_{2} because of a very high barrier separating it from A7. Addition of H_{2} to the intermediate complex B11 (A3) leads to B13, where the N-H bonds are located cis to each other. Subsequently, B13 most likely rearranges to complex B3 and follows the reactions of B3. Addition of the third H_{2} molecule to A1 is found to be kinetically less favorable than the first two.

Original language | English |
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Pages (from-to) | 3393-3403 |

Number of pages | 11 |

Journal | Organometallics |

Volume | 19 |

Issue number | 17 |

DOIs | |

State | Published - 21 Aug 2000 |

Externally published | Yes |

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_{2}]Zr(μ-η

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_{2})Zr[P

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_{2}] activate more than one hydrogen molecule? A theoretical sudy'. Together they form a unique fingerprint.