Linear Hydrocarbon Chain Growth from a Molecular Diruthenium Carbide Platform

The formation of linear hydrocarbon chains by sequential coupling of C1 units on the metal surface is the central part of the Fischer–Tropsch (F-T) synthesis. Organometallic complexes have provided numerous models of relevant individual C–C coupling events but have failed to reproduce the complete chain lengthening sequence that transforms a linear C n hydrocarbon chain into its C n+1 homologue in an iterative fashion. In this work, we demonstrate stepwise growth of linear C n hydrocarbon chains and their conversion to their C n+1 homologues via consecutive addition of CH2 units on a molecular diruthenium carbide platform. The chain growth sequence is initiated by the formation of a μ-η1:η1-CCH2 ligand from a C + CH2 coupling between the μ-carbido complex [(Cp*Ru)2(η-NPh)­(μ-C)] (1; Cp* = η5-C5Me5) and Ph2SCH2. Then, the chain propagates via a general CCHR + CH2 coupling and subsequent hydrogen-assisted isomerization of the resulting allene ligand μ-η1:η3-H2CCCHR to a higher vinylidene homologue μ-η1:η1-CCH­(CH2)­R. By repeating this reaction sequence, up to C6 chains have been synthesized in a stepwise fashion. The key step of this chain homologation sequence is the selective hydrogenation of the μ-η1:η3-allene unit to the corresponding μ-alkylidene ligand. Isotope labeling and computational studies indicate that this transformation proceeds via the hydrogenation of the allene ligand to a terminal alkene form and its isomerization to the μ-alkylidene ligand facilitated by the coordinatively unsaturated diruthenium platform.