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Photolysis of [Ru2(CO)4(η-C5R52] (R = H or Me) in the presence of allene yields complexes [(η-C5R5)(CO)2RuCH 2C(CH2)C(CH2)CH2Ru(CO)2(η-C5R5)] and [Ru2(CO)2{(μ-C(Me)CHCH2CCH2)}(η-C5Me5)2], containing dimers of allene derived by C(2)C(2) and C(1)C(1) coupling, respectively. The molecular structure of [Ru2(CO)2 (μ-C(Me)CHCH2)CCH2(η-C5Me5)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 0.047 for 4678 unique, observed diffractometer data. Crystals are monoclinic, space group P21 /c, with Z = 8 in a unit cell of dimensions a = 10.403(8), b = 28.804(27), c = 19.882(18) A, β = 117.14(6)°. The molecule is based on a trans-(η-C5Me5)(CO)RuRu(CO)(η-C5Me5) unit with one terminal and one semi-bridging carbonyl ligand This unit is bridged by a linear MeCCHCH2CCH2 six-carbon chain which is η2-bound to one ruthenium through two σ-bonds, making a metallacyclopentene ring, and to the other through an η2-interaction of an exocyclic double bond. The formation of the allene dimer products is attributed to the attack of Ru(CO)2(η-C5R5) radicals upon the C(1) or C(2) carbon of allene, followed by dimerization of the radicals so formed. The μ-allene species [Ru2(CO)2(μ-CH2CCH2)(η-C5H5)2] is obtained by photolysis of the μ-vinylidene complex [Ru2(CO)3(μ-CCH2)(η-C5H5)2] in acetonitrile, followed by the addition of diazomethane. |
