Synthesis of ruthenium phenylindenylidene, carbyne, allenylidene and vinylmethylidene complexes from (PPh3)3−4RuCl2: A mechanistic and structural investigation

The reaction of (Ph3P)3RuCl2 with 1,1-diphenyl-2-propyn-1-ol was investigated in various solvents. The reaction in thf under reflux is reported to produce the (PPh3)2Cl2Ru(3-phenylindenylidene) complex (3) which has undergone rearrangement of the allenylidene C3-spine. We have improved the reliability of the reported synthesis by adding acetyl chloride which converts the formed water of the reaction and thus increases the acidity of the reaction solution. Without the additive, we observed the exclusive formation of an intermediate of the transformation and identified it as dinuclear (PPh3)2ClRu(μ-Cl)3(PPh3)2RuCCCPh2 complex (5). The reaction of (Ph3P)3−4RuCl2 with 1,1-diphenyl-2-propyn-1-ol in CH2Cl2 or C2H4Cl2 under reflux in the presence of excess conc. aqueous HCl afforded the new, neutral (PPh3)2Cl3RuC–CHCPh2 carbyne complex (7), an HCl adduct of previously elusive (PPh3)2Cl2RuCCCPh2 complex 6 in high yields. In contrast to the formation of complex 3, the reaction in a non-coordinating solvent did not afford the rearrangement of the allenylidene C3-spine. Complex 7 was converted into complex 3 in thf under reflux under loss of a molecule HCl. Complex 7 was converted with triethylamine under loss of HCl to complex 6. Pentacoordinate complex 6 was crystallized in the presence of O-donor ligands (EtOH, MeOH and H2O) to give hexacoordinate (PPh3)2Cl2(ROH)RuCCCPh2 (R = H, CH3, C2H5) complexes (9)–(11) with the O-donor coordinating in trans-position to the allenylidene moiety. The reaction of complex 7 with 2 equiv. of 4-(N,N-dimethylamino)pyridine (DMAP) gave hexacoordinate (PPh3)2Cl2(DMAP)RuCCCPh2complex (12) with one molecule DMAP also coordinating in trans-position to the allenylidene group. Methanol and acetic acid in the absence of strong bases afforded the Fischer-carbene complexes (PPh3)2Cl2RuC(OCH3)–CHCPh2 (14) and (PPh3)2Cl2RuC(OAc)–CHCPh2 (15) where the nucleophile added to the α-carbon atom. The structures of complexes 5, 7, 9–11, 14, and 15 were solved via X-ray crystallography.

Graphical abstractA reliable synthesis of a 3-phenylindelylidene ruthenium complex is described. An allenylidene and a carbyne intermediate of this reaction have been isolated. The carbyne intermediate was reacted with bases and nucleophiles to give allenylidene and Fischer-carbene complexes. X-ray crystal structures were obtained from eight new complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide