Organic chemistry of dinuclear metal centres. Part 9. Diruthenium complexes of buta-1,3-diene. X-Ray crystal structure of [Ru2(CO)2(µ-s-trans-η2:η2′-CH2CHCHCH2)(η-C5H5)2]

Abstract

Heating [Ru₂(CO)(µ-CO){µ-C(O)C₂Ph₂}(η-C₅H₅)₂] with buta-1,3-diene in toluene gives [Ru₂(CO)(µ-CO)₂(η²-CH₂CHCHCH₂)(η-C₅H₅)₂] which upon photolysis yields [Ru₂(CO)₂(µ-s-trans-η²:η^2′-CH₂CHCHCH₂)(η-C₅H₅)₂] and [Ru₂(CO)(µ-CO)(µ-σ:η³-CHCHCHCH₃)(η-C₅H₅)₂], the latter arising from a new transformation of the diene. These complexes cannot be obtained directly from [Ru₂(CO)₄(η-C₅H₅)₂], but photolysis of [Ru₂(CO)₄(η-C₅Me₅)₂] with buta-1,3-diene affords the analogues [Ru₂(CO)₂(µ-s-trans-η²:η^2′-CH₂CHCHCH₂)(η-C₅Me₅)₂] and [Ru₂(CO)(µ-CO)₂(η²-CH₂CHCHCH₂)(η-C₅Me₅)₂]. Heating [Ru₃H₃(CO)₃(η-C₅H₅)₃] with buta-1,3-diene in toluene gives [Ru₂(CO)(µ-CO)₂(η²-CH₂CHCHCH₂)(η-C₅H₅)₂] and [Ru₂(CO)₂(µ-s-trans-η²:η^2′-CH₂CHCHCH₂)(η-C₅H₅)₂], or[Ru₂(CO)(µ-CO)(µ-σ:η³-CHCHCHCH₃)(η-C₅H₅)₂] depending on minor modification of the conditions. The molecular structure of [Ru₂(CO)₂(µ-s-trans-η²:η^2′-CH₂CHCHCH₂)(η-C₅H₅)₂] has been determined by X-ray diffraction. The structure was solved by heavy-atom methods and refined by least squares to give a final R 0.038 for 838 unique, observed diffractometer data. Crystals are monoclinic, space group I2, with Z= 2 in a unit cell of dimensions a= 11.544(6), b= 7.841(4), c= 8.622(4)Å, and β= 103.36(4)°. The molecule consists of a (CO)(η-C₅H₅)Ru–Ru(η-C₅H₅)(CO) unit with trans CO and η-C₅H₅ ligands, symmetrically bridged by a buta-1,3-diene ligand in the s-trans conformation so that each Ru atom is η² co-ordinated. Compared to unco-ordinated buta-1,3-diene and other complexes with s-trans-buta-1,3-diene similarly co-ordinated, the terminal CC bonds are significantly elongated [1.486(15)Å], consistent with substantial back-donation to the diene lowest unoccupied molecular orbital and depopulation of the diene highest occupied molecular orbital.