Probing the Dichotomy of Square Planar d¹⁰ Complexes: Geometric and Electronic Structure of Nickel π-Complexes
Bibliographic record
Abstract
Ni π-complexes are widely postulated as intermediates in organometallic chemistry. However, the nature of the bonding in such complexes has not been extensively studied. Herein, we probe the geometric and electronic structure of a series of nickel π-complexes using a combination of 31 P NMR, Ni K-edge XAS, Ni K β XES, and supporting density-functional computations. These complexes are best described as square planar d 10 complexes with π-backbonding acting as the dominant factor in the M-L bond to the π ligand. The degree of backbonding correlates with both 2 J PP and the energy of the clearly observable Ni 1s→4p z pre-edge transition in the Ni K-edge XAS data. The degree of backbonding is determined by the energy of the π* ip ligand acceptor orbital: unactivated olefinic ligands tend to be poor π-acids whereas ketones, aldehydes, and esters allow for greater backbonding. The strength of the backbonding from the neutral Ni(dtbpe) molecular fragment is dramatically increased via σ donation from the diphosphine ligands. In fact, in unactivated pi complexes, backbonding is dominated by charge donation from the phosphines, which allows for strong backdonation even though the metal centre retains a formal d 10 electronic configuration. We describe this interaction as a formal 3-centre-4-electron (3c-4e) interaction where the nickel centre mediates charge transfer from the phosphine σ-donors to the π* ip ligand acceptor orbital. The implications of this unusual bonding motif are described with respect to both geometric structure and reactivity.
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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".