Reversible Transformation between Methylene and Methylidyne-Hydride Moieties on the Ru₁₀C₂Framework

Abstract

Oxidative substitution of [Ru10C2(CO)22(NBD)]2- with ferrocenium ion and diazomethane forms a methylene compound, Ru10C2(CO)22(NBD)(μ-CH2), in which the methylene ligand symmetrically bridges two adjacent apical ruthenium centers in the edge-fused bioctahedral Ru10C2 framework. A methylidyne tautomer, Ru10C2(CO)22(NBD)(CH)(H), is formed reversibly at 80 °C.

Investigations by13C NMR Spectroscopy of Ethene-Initiated Catalytic CO Hydrogenation

“…Current thinking suggests that formation of the putative CH 2(ad) or CH (ad) from CO involves the deoxygenation of CO to give a surface carbide, followed by a stepwise hydrogenation. The deoxygenation step is found in the formation of carbides from carbonyl clusters , and in other model organometallic reactions. , Although stoichiometric reactions of coordinated CO with H 2 to give directly CH 2 or CH liganded to a metal have not yet been reported, such reductions using LiAlH 4 , NaBH 4 , or hydrosilanes and the addition of H to a metal carbide giving either a methylidyne CH (ad) or a methylene CH 2(ad) are known. ,, …”

“…21,31,[35][36][37] Thus, most authors have discussed mechanisms involving methylene as the propagating monomer; however, recently an alternative proposal has been made, with the polymerization involving sequential methylidyne and hydride {CH (ad) + H (ad) } addition. Surface studies, in particular HREELS measured in vacuo at very low temperature, provide good evidence for the formation of >CH 2(ad) from diazomethane, CH 2 I 2 , CH 2 ClI, various hydrocarbon precursors (methane, ethene), [72][73][74][75] and also CO, 33 on clean surfaces [Ru(0001), Ni (111), Pt (111), Rh (111), etc.]. However, the methylene appears only to be stable below ca.…”

“…The deoxygenation step is found in the formation of carbides from carbonyl clusters 108,109 and in other model organometallic reactions. 110,111 Although stoichiometric reactions of coordinated CO with H 2 to give directly CH 2 or CH liganded to a metal have not yet been reported, such reductions using LiAlH 4 , NaBH 4 , 112 or hydrosilanes 113 and the addition of H to a metal carbide giving either a methylidyne CH (ad) or a methylene CH 2(ad) are known. 80,114,115 Since model organometallic complexes indicate facile equilibration between CH 2 and CH ligands, it is likely that this will also be true for surface species.…”