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:η2′-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:η2′-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:η2′-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:η2′-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.