Linearly Bridging N2 versus CO: Chemical Bonding and Spin-Controlled Reactivity.

The synthesis of the linearly N-2 bridged, dichromium complex [(mu-N-2){Cr(PNP)}(2)] (PNP=N((CHCHPBu2)-Bu-t)(2)) is reported. Experimental and computational data favor a three-spin electronic structure model with high-spin Cr-II ions that are antiferromagnetically coupled to an N-2(2-) bridge due to spin-polarized backbonding. Reaction with CO gave isocarbonyl complex [(PNP)(CO)(2)Cr(mu-CO)Cr(PNP)] and [(PNP)(CO)(2)Cr(mu-N-2)Cr(PNP)] could be trapped as intermediate. The latter is best described by a (ls-Cr-I)(N-2(-))(hs-Cr-II) ground state model, while more covalent bonding with the CO bridge is reflected by a (ls-Cr-0)(CO0)(hs-Cr-II) electronic structure description. The selectivity of the carbonylation reaction is attributed to a spin transition after binding of the first CO ligand to [(mu-N-2){Cr(PNP)}(2)].

Automated summary

The synthesis of a linearly N-2 bridged, dichromium complex is described. Experimental and computational data support a three-spin electronic structure model with high-spin Cr-II ions antiferromagnetically coupled to an N-2(2-) bridge due to spin-polarized backbonding. The selectivity of the carbonylation reaction is attributed to a spin transition after binding of the first CO ligand.