Solid–gas reactions of metal carbonyl clusters. Hydrogenation of 1,4-cyclohexadiene and hex-3-yne in the presence of H 4Ru 4(CO) 12, Ru 3(CO) 12 or Ru 3(CO) 3(μ-CO)(μ 3-CO)(μ 3-‖-C 2Ph 2)(η-C 5H 5) 2

Abstract

The clusters H 4Ru 4(CO) 12 ( 1), Ru 3(CO) 12 ( 2) and Ru 3(CO) 3(μ-CO)(μ 3-CO)(μ 3-‖-C 2Ph 2)(η-C 5H 5) 2 ( 3), which are homogeneous hydrogenation catalysts for alkynes and cyclic dienes, have been investigated in solid–gas hydrogenation reactions. The clusters were deposited on porous glass discs in a new reaction vessel and reacted with the vapours of 1,4-cyclohexadiene or hex-3-yne and dihydrogen, giving monoenes selectively. The apparatus is easy to use and allows the collection and analysis of the gaseous phase with time; limitations are discussed. The reactions are catalytic, with low turnover numbers (TON). Sublimation of the clusters and of reaction products onto the glass walls of the apparatus, formation and recondensation of metal fragments and/or of metallacyclic derivatives were observed during the experiments. The behaviour of the clusters under solid–gas conditions was found to be similar to that under homogeneous conditions. Comparable organometallic intermediates or byproducts have been isolated suggesting that the same reaction pathways occur. This work shows for the first time that electronically saturated clusters in the solid state can react with mixtures of gases under relatively mild conditions.