Variable Co-ordination behaviour of ethyne and other alkynes towards the diruthenium complexes [Ru2(µ-CO)-(CO)4{(RO)2PN(Et)P(OR)2}2] and [Ru2(µsb-CO)2(CO)2-{(RO)2PN(Et)P(OR)2}2](sb = semi-bridging, R = Me or Pri)
Abstract
The reaction of ethyne with [Ru2(µ-CO)(CO)4{(RO)2PN(Et)P(OR)2}2] in toluene at 80 °C or with [Ru2(µsb-CO)2(CO)2{(RO)2PN(Et)P(OR)2}2](R = Me or Pri, sb = semi-bridging), in toluene at room temperature, affords almost exclusively the ethenediyl-bridged species [Ru2(µ-σ2-HC![[double bond, length half m-dash]](https://www.rsc.org/images/entities/char_e006.gif)
CH)(CO)4{(RO)2-PN(Et)P(OR)2}2] for R = Me and the vinylidene-bridged product [Ru2(µ-σ-CCH2)(CO)4{(RO)2-PN(Et)P(OR)2}2] for R = Pri; a second, minor product is also formed in each of these reactions and was identified as [Ru2(µ-σ-CCH2)(CO)4{(MeO)2PN(Et)P(OMe)2}2] and [Ru2(µ-σ2-HCCH)(CO)4-{(PriO)2PN(Et)P(OPri)2}2] respectively. The reactions of [Ru2(µ-CO)(CO)4{(RO)2PN(Et)P(OR)2}2] and [Ru2(µsb-CO)2(CO)2{(RO)2PN(Et)P(OR)2}2] with the terminal alkynes MeC![[triple bond, length half m-dash]](https://www.rsc.org/images/entities/char_e007.gif)
CH, PhCCH and MeO2CCCH also afford mixtures of alkenediyl- and vinylidene-bridged products with the relative yields of these isomers being dependent on the identity of the alkyne and of the bridging diphosphazane ligand. On the other hand reaction with the internal alkyne MeO2CCCCO2Me gives solely the alkenediyl-bridged product [Ru2(µ-σ2-MeO2CCCCO2Me)(CO)4{(RO)2PN(Et)P(OR)2}2] irrespective of the diphosphazane ligand involved. Possible mechanisms for the formation of the two types of products are described. The crystal structure of [Ru2(µ-σ2-HCCH)(CO)4{(MeO)2PN(Et)P(OMe)2}2] is reported.
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