title: On the relation between carbonyl stretching frequencies and the donor power of chelating diphosphines in nickel dicarbonyl complexes.
abstract: The relation between spectroscopic observables and the detailed metal-ligand bonding features in chelation complexes is addressed using both experimental and state-of-the-art theoretical and computational methods. We synthesized and characterized a set of six nickel dicarbonyl complexes of general formula [Ni(CO)2(PP)], where PP is an atropoisomeric chelating diphosphine ligand. The analysis of the obtained experimental data and the basicity and oxidative potentials of the free ligands suggests a close relation between the donor ability of the chelating ligand and the carbonyl stretching frequencies observed in the complexes. We then use theory to unravel the detailed mechanisms of chelation-bond formation in terms of partial charge flows between the molecular orbitals of the fragments. By extending the promising, recently published natural orbitals for chemical valence/charge displacement (NOCV/CD) analysis scheme we provide a thorough, quantitative description of the several charge fluxes following the metal-ligand bond formation and demonstrate that the carbonyl stretching frequencies in the considered complexes selectively respond to the σ-donation charge flow from the phosphorus lone pairs of the ligands, with the frequency shift being in quantitative correlation with the extent of the ligand-to-metal charge transfer.
authors.affiliation: Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy. marco.fuse@sns.it sergio.rampino@sns.it.
authors.forename: Marco
authors.initials: M
authors.lastname: Fusè
authors.affiliation: Dipartimento di Scienze Farmaceutiche, Università di Milano, Via Golgi 19, 20133 Milano, Italy.
authors.forename: Isabella
authors.initials: I
authors.lastname: Rimoldi
authors.affiliation: Dipartimento di Scienze Farmaceutiche, Università di Milano, Via Golgi 19, 20133 Milano, Italy.
authors.forename: Edoardo
authors.initials: E
authors.lastname: Cesarotti
authors.affiliation: Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy. marco.fuse@sns.it sergio.rampino@sns.it.
authors.forename: Sergio
authors.identifier: http://orcid.org/0000-0001-8525-7777
authors.initials: S
authors.lastname: Rampino
authors.affiliation: Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy. marco.fuse@sns.it sergio.rampino@sns.it.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Barone