Chalcogenoacyl-bridged derivatives of the unsaturated carbyne complex [Mo 2 ( η 5 -C 5 H 5 ) 2 ( μ -CPh)( μ -PCy 2 )(CO) 2 ]

Abstract

The 32-electron benzylidyne-bridged complex [Mo 2 Cp 2 (-CPh)(-PCy 2)CO) 2 ] reacted with elemental chalcogens E n (E = S, Se) at 333 K to give the corresponding derivatives trans-[Mo 2 Cp 2 {- 2 : 2-C(Ph)E}(-PCy 2)(CO) 2 ], following from addition of a chalcogen atom to the Mo 2 C face of the central Mo 2 PC core in the parent compound, whereby a 5-electron donor, bridging chalcogenoacyl ligand was formed (MoMo = 2.8662(5) Å, CS = 1.757(5) Å in the thioacyl complex). These thermally stable products did not undergo decarbonylation under irradiation with visible-UV light, but instead rearranged into the corresponding cis-dicarbonyl isomers cis-[Mo 2 Cp 2 {- 2 : 2-C(Ph)E}(-PCy 2)(CO) 2 ] (MoMo = 2.9208(5) Å, CS = 1.745(5) Å in the thioacyl complex), in a process where no reaction intermediates were detected. The coordination of the chalcogenoacyl ligand in the cis-dicarbonyl isomers is analogous to that observed in the corresponding trans isomers, and involves the selective positioning of the 3-electron donor chalcogen atom trans to the bridging phosphanyl ligand, a structural trend common to related complexes with isoelectronic  2 : 2 bridging groups such as iminoacyl, formimidoyl and diphosphenyl ligands.