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I have never seen any Carbonyl Oxygen acting as a ligand. But a naive intution says that since carbonyl oxygen has two lone pairs, it should act as a donor atom, donating one of its lone pairs as shown below:

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In general can aldehydes and ketones act as a monodentate ligand? If no, then what's the reason?

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Examples are known. Coordination can take place through the oxygen atom, as shown in the question, or through the carbonyl pi bond so as to form a metal-carbon-oxygen triangle. See, among others, Huang and Gladysz 1. A couple sample figures from the reference are given below.

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Reference

  1. Yo Hsin Huang and J. A. Gladysz (1988). "Aldehyde and ketone ligands in organometallic complexes and catalysis". _J. Chem. Educ. 65, 4, 298. https://doi.org/10.1021/ed065p298
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  • $\begingroup$ Nice downvote there. Would be better if you could give ideas on how to improve this answer. $\endgroup$ Commented Apr 5, 2023 at 12:10
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Yes, there are numerous examples. Check out some of them:

  1. Chemistry in Acetone Complexes of Metal Dications:  A Remarkable Ethylene Production Pathway Jianhua Wu, Dan Liu, Jian-Ge Zhou, Frank Hagelberg, Sung Soo Park, and Alexandre A. Shvartsburg The Journal of Physical Chemistry A 2007 111 (22), 4748-4758 DOI: 10.1021/jp068574z
  2. $\ce{[M(Ac)6^2+][A−]2}$ where M is Mg(II), Ca(II), Sr(II), Mn(II), Fe(II), Co(II), Ni(II), and Zn(II); and $\ce{A−}$ is $\ce{FeCl4−}$ and $\ce{InCl4−}$: Driessen, W.L. and Groeneveld, W.L. (1969), Complexes with ligands containing the carbonyl group. Part I: Complexes with acetone of some divalent metals containing tetrachloro-ferrate(III) and -indate(III) anions. Recl. Trav. Chim. Pays-Bas, 88: 977-988.DOI: 10.1002/recl.19690880811
  3. Troepol'skaya, T.V., Sitdikov, R.A., Titova, Z.S. et al. Synthesis and structure of complexes of acetone acylhydrazones with some transition metals. Russ Chem Bull 29, 903–907 (1980). DOI: 10.1007/BF00958804
  4. $\ce{[Fe(C19H25N5)(C3H6O)(H2O)2](BF4)2·2C3H6O}$: Kilner, C. A. & Halcrow, M. A. (2006). An unusual example of a linearly coordinated acetone ligand in a six-coordinate iron(II) complex. Acta Cryst. C62, m437–m439. (Link)
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