First Direct Structural Comparison of Complexes of the Same Metal Fragment to Ketenes in Both C,C- and C,O-Bonding Modes
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Bibliographic record
Abstract
Using a series of Ir(I) and Rh(I) ketene complexes, conclusions about the structure and bonding of complexes of the fundamentally important ketene ligand class are reached. In a unique comparison of X-ray structures of the same metal fragment to ketenes in both the eta(2)-(C,C) and the eta(2)-(C,O) binding mode, the Ir-Cl bond distances in complexes of trans-Cl(Ir)[P(i-Pr)(3)](2) to phenylketene [4, eta(2)-(C,C)] and diphenylketene [2a, eta(2)-(C,O)] are 2.371(3) and 2.285(2) A, respectively. This would be consistent with greater trans influence of a ketene ligand bound to a metal through its C=C bond than one connected by its C=O bond. Back-bonding of Ir(I) and Rh(I) to diphenylketene was assessed using trans-Cl(M)[P(i-Pr)(3)](2)[eta(2)-(C,O)-diphenylketene] (2a and 2d). Most bond lengths and angles are identical, but slightly greater back-bonding by Ir(I) is suggested by the somewhat greater deformation of the ketene C=C=O system [C-C-O angles are 136.6(4) and 138.9(4) in the Ir and Rh cases 2a and 2d, respectively]. Syntheses of new labeled ketenes Ph(2)C=(13)C=O and Ph(2)C=C=(18)O and their Ir(I) and Rh(I) complexes are reported, along with the generation of an Ir(I) complex of PhCH=(13)C=O. The effects of isotopic substitution on infrared absorption data for ketene complexes are presented for the first time. Preliminary normal coordinate mode analysis allowed definitive assignment of absorptions ascribed to the C-O stretching frequencies of coordinated ketenes, which are near the absorptions for aromatic ring systems commonly found as substituents on ketenes. For free diphenylketene and four of its complexes and a phenylketene complex characterized by X-ray diffraction, the magnitude of the (13)C-(13)C coupling between the two ketene carbons is correlated to carbon-carbon bond distance.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 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) | 0.000 | 0.000 |
Machine scores (provisional)
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Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
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