Organic chemistry of dinuclear metal centres—X. Dimerization of allene at a diruthenium centre; X-ray crystal structure of [Ru 2(CO) 2{ (μ-C(Me)CHCH 2CCH 2)}(η-C 5Me 5) 2

Abstract

Photolysis of [Ru 2(CO) 4(η-C 5R 5 2] (R = H or Me) in the presence of allene yields complexes [(η-C 5R 5)(CO) 2RuCH 2C(CH 2)C(CH 2)CH 2Ru(CO) 2(η-C 5R 5)] and [Ru 2(CO) 2{(μ-C(Me)CHCH 2CCH 2)}(η-C 5Me 5) 2], containing dimers of allene derived by C(2)C(2) and C(1)C(1) coupling, respectively. The molecular structure of [Ru 2(CO) 2 (μ-C(Me)CHCH 2)CCH 2(η-C 5Me 5) 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 P2 1 / c, with Z = 8 in a unit cell of dimensions a = 10.403(8), b = 28.804(27), c = 19.882(18) Å, β = 117.14(6)°. The molecule is based on a trans-(η-C 5Me 5)(CO)RuRu(CO)(η-C 5Me 5) unit with one terminal and one semi-bridging carbonyl ligand This unit is bridged by a linear MeCCHCH 2CCH 2 six-carbon chain which is η 2-bound to one ruthenium through two σ-bonds, making a metallacyclopentene ring, and to the other through an η 2-interaction of an exocyclic double bond. The formation of the allene dimer products is attributed to the attack of Ru(CO) 2(η-C 5R 5) radicals upon the C(1) or C(2) carbon of allene, followed by dimerization of the radicals so formed. The μ-allene species [Ru 2(CO) 2(μ-CH 2CCH 2)(η-C 5H 5) 2] is obtained by photolysis of the μ-vinylidene complex [Ru 2(CO) 3(μ-CCH 2)(η-C 5H 5) 2] in acetonitrile, followed by the addition of diazomethane.