Synthesis of [Ru3(CO)9(μ-dppf){P(C4H3E)3}] (E = O, S) and thermally induced cyclometalation to form [(μ-H)Ru3(CO)7(μ-dppf){μ3-(C4H3E)2P(C4H2E)}] (dppf = 1,1′-bis(diphenylphosphino)ferrocene)

• Formation of new triruthenium dppf/PR3 complexes.
• Thermally-induced cyclometalation of furyl or thienyl ligand.
• DFT calculations to probe equatorial-axial isomerism.
• Windshield-wiper fluxionality probed by NMR and DFT.

The new clusters [Ru3(CO)9(μ-dppf){P(C4H3E)3}] (1, E = O; 2, E = S) have been prepared from the Me3NO-induced decarbonylation of [Ru3(CO)10(μ-dppf)] in the presence of PFu3 (E = O) and PTh3 (E = S), respectively. Upon thermolysis in benzene, the major products are the cyclometalated clusters [(μ-H)Ru3(CO)7(μ-dppf){μ3-(C4H3E)2P(C4H2E)}] (3, E = O; 4, E = S). This thermolytic behavior is in marked contrast to that previously noted for the analogous bis(diphenylphosphino)methane (dppm) complexes [Ru3(CO)9(μ-dppm){P(C4H3E)3}], in which both carbon–hydrogen and carbon–phosphorus bond activation yields furyne- and thiophyne-capped clusters. The crystal structures of 1, 3 and 4 are presented and reveal that phosphine migration has occurred during the transformation of 1,2 into 3,4, respectively. The possible relation of the observed reactivity to the relative flexibilities of the diphosphine ligands is discussed. Density functional calculations have been performed on the model cluster [Ru3(CO)9(μ-Me4-dppf){P(C4H3O)3]}], and these data are discussed relative to the ground-state energy differences extant between the different isomeric forms of this cluster. The dynamic NMR behavior displayed by the metalated thienyl ring in cluster 4 has also been investigated by computational methods, and the free energy of activation for the “windshield wiper” motion of the activated thienyl moiety determined.

The new clusters [Ru3(CO)9(μ-dppf){P(C4H3E)3}] (E = O, S) rearrange upon heating to give cyclometalated clusters [(μ-H)Ru3(CO)7(μ-dppf){μ3-(C4H3E)2P(C4H2E)}], behavior that is in marked contrast to the analogous dppm complexes in which both carbon-hydrogen and carbon-phosphorus bond activation yields furyne- and thiophyne-capped clusters. This difference in reactivity is probed by DFT calculations.Figure optionsDownload as PowerPoint slide