Bonding, activation, and protonation of dinitrogen on a molybdenum pentaphosphine complex Comparison to <i>trans</i>-bis(dinitrogen) and -nitrile dinitrogen complexes with tetraphosphine coordination
Bibliographic record
Abstract
The molybdenum-N2 pentaphosphine complex [Mo(N2)(dpepp)(dppm)] (1) containing a bi- and a tridentate phosphine ligand (dpepp = PhP(CH2CH2PPh2)2, dppm = Ph2PCH2PPh2) has been prepared and characterized. By protonation of 1 with triflic acid the NNH2 complex [Mo(NNH2)(dpepp)(dppm)](CF3SO3)2 (2) is formed without loss of the pentaphosphine coordination. The electronic properties of 1 and 2 and their 15N and (or) 2H counterparts are investigated by NMR, IR, and Raman spectroscopy coupled to DFT frequency and NMR shift calculations. Force constants are evaluated from experimental frequencies and isotope shifts by the quantum chemistry based normal coordinate analysis procedure (QCB-NCA). The results for the N2 complex 1 are compared with those obtained earlier for bis(dinitrogen) and trans-nitrile dinitrogen systems. Importantly, the N2 in the pentaphosphine complex is more strongly activated compared to corresponding bis(dinitrogen) compounds and more weakly activated compared to trans-nitrile N2 systems. The activation of the NNH2 ligand in complex 2 is similar to trans-nitrile systems and weaker compared to corresponding NNH2 complexes with coordinated anions like [MoF(NNH2)(dppe)2](BF4). These results are discussed based on the relative donoracceptor properties of the respective trans ligands, demonstrating the influence of σ donation and π acceptance on the activation of N2 in transition metal complexes.Key words: nitrogen fixation, phosphine complexes, NMR shifts, DFT calculations, normal coordinate analysis.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".