Selective Activation of CH Bonds in Polar Vinyl Olefins and Coupling of Ethylene to the Activated Carbon Atoms in Pentaruthenium Complexes

Metal carbonyl clusters of groups 8-10: synthesis and catalysis

In this review article, we discuss advances in the chemistry of metal carbonyl clusters (MCCs) spanning the last three decades, with an emphasis on the more recent reports and those involving groups 8-10 elements. Synthetic methods have advanced and been refined, leading to higher-nuclearity clusters and a wider array of structures and nuclearities. Our understanding of the electronic structure in MCCs has advanced to a point where molecular chemistry tools and other advanced tools can probe their properties at a level of detail that surpasses that possible with other nanomaterials and solid-state materials. MCCs therefore advance our understanding of structure-property-reactivity correlations in other higher-nuclearity materials. With respect to catalysis, this article focuses only on homogeneous applications, but it includes both thermally and electrochemically driven catalysis. Applications in thermally driven catalysis have found success where the reaction conditions stabilise the compounds toward loss of CO. In more recent years, MCCs, which exhibit delocalised bonding and possess many electron-withdrawing CO ligands, have emerged as very stable and effective for reductive electrocatalysis reactions since reduction often strengthens M-C(O) bonds and since room-temperature reaction conditions are sufficient for driving the electrocatalysis.

Synthesis, Structures, and Transformations of Bridging and Terminally-Coordinated Trimethylammonioalkenyl Ligands in Zwitterionic Pentaruthenium Carbido Carbonyl Complexes

Reactions of the pentaruthenium cluster complexes Ru₅(μ₅-C)(CO)₁₅ (5), Ru₅(μ₅-C)(CO)₁₄[μ-η²-O═C(NMe₂)](μ-H) (6), and Ru₅(μ₅-C)(CO)₁₅Cl(μ-H) (7) with ethyne (C₂H₂) in the presence of Me₃NO yielded the zwitterionic complexes Ru₅(μ₅-C)(CO)₁₃[μ-η²-CHCH(NMe₃)] (8), Ru₅(μ₅-C)(CO)₁₃[μ-η²-O═C(NMe₂)](η¹-E-CH═CH(NMe₃)(μ-H) (9), and Ru₅(μ₅-C)(CO)₁₃Cl[η¹-E-CH═CH(NMe₃)](μ-H) (11). Each product contains a positively charged trimethylammonioethenyl ligand, CH═CH(⁺NMe₃), that is derived from a 2-trimethylammonioethenide, ^-CH═CH(⁺NMe₃), zwitterion that formally has a positive charge on the nitrogen atom and a negative charge on the terminal enyl carbon atom. The trimethylammonioethenyl ligand, CH═CH(⁺NMe₃) in 8 is a η²-ligand that bridges a Ru-Ru bond on a basal edge of the square-pyramidal Ru₅ cluster by a combination of σ + π cooordination of the ethenyl group. Compounds 9 and 11 each contain a η¹-terminally coordinated [η¹-E-CH═CH(⁺NMe₃)] ligand with an E stereochemistry at the C═C double bond in open Ru₅ cluster complexes. Compound 9 was decarbonylated to yield the compound Ru₅(μ₅-C)(CO)₁₂[μ-η²-O═C(NMe₂)][μ-η²-CH═CH(NMe₃)](μ-H) (10) containing a η²-bridging CHCH(⁺NMe₃) ligand. Compound 10 was converted back to 9 by the addition of CO. Two zwitterionic products, Ru₅(μ₅-C)(CO)₁₄[η¹-E-CH═CH(NMe₃)] (12) and Ru₅(μ₅-C)(CO)₁₅[η¹-E-CH═CH(NMe₃)] (13), were obtained by the addition of CO to 8. Compound 12 is an intermediate en route to 13. Compound 12 contains a terminally coordinated η¹-E-CH═CH(⁺NMe₃) ligand on one of the basal Ru atoms of a square-pyramidal Ru₅ cluster. Compound 13 also contains a terminally coordinated η¹-E-CH═CH(⁺NMe₃) ligand on the wing-tip bridging Ru atom of a butterfly Ru₄C cluster. Treatment of 6 with methyl propiolate (HC≡CCO₂Me) yielded the zwitterionic complex Ru₅(μ₅-C)(CO)₁₃[μ-η²-O═C(NMe₂)][η¹-E-(MeO₂C)C═C(H)NMe₃](μ-H) (14) that is structurally similar to 9 but contains a η¹-E-(MeO₂C)C═C(H)(⁺NMe₃) ligand. Compound 14 eliminated the NMe₃ group to yield the compounds Ru₅(μ₅-C)(CO)₁₃[μ-η²-O═C(NMe₂)][μ-η²-(MeO₂C)HC═CH] (15) which contains a bridging methoxycarbonyl-substituted alkenyl ligand and the known compound Ru₅(μ₅-C)(CO)₁₃[μ-η²-O═C(NMe₂)](HNMe₂)(μ-H) (16).