Alkene Hydrogenations by Soluble Iron Nanocluster Catalysts

Abstract

The replacement of noble metal technologies and the realization of new reactivities with earth-abundant metals is at the heart of sustainable synthesis.Alkene hydrogenations have so far been most effectively performed by noble metal catalysts. This study reports an iron-catalyzedh ydrogenation protocol for tri-and tetra-substituted alkenes of unprecedented activity and scope under mild conditions (1-4 bar H 2 ,2 08 8C). Instructive snapshots at the interface of homogeneous and heterogeneous iron catalysis were recorded by the isolation of novel Fe nanocluster architectures that act as catalyst reservoirs and soluble seeds of particle growth.

A Manganese Nanosheet: New Cluster Topology and Catalysis

“…[1] Unlike graphene,t ransition-metal nanosheets are very challenging to prepare owing to the lack of convenient metal precursors,t he preference for three-dimensional geometries,a nd the generally high reactivity of metal monolayers. [3,4] From ac onceptual viewpoint, 3D metal nanoclusters are models of the bulk material. Thev ast majority of transition-metal clusters contain six or more metal atoms in three-dimensional cluster geometries.…”

“…Small 2D metal nanoclusters can be viewed as intermediate stages of the growth of soluble metals or metal ions towards metallic monolayers ( Figure 1). [3] Recently,O hki and coworkers and our group have shown that the reaction of easily available transition-metal amide precursor complexes M{N(SiMe 3 ) 2 } 2 (M = Co,Fe) with commercial hydride sources (diisobutylaluminium hydride,D ibal-H;p inacolborane, HBpin) is ac onvenient strategy to access new topologies of low-valent transition-metal nanoclusters in high yields.Planar Co 4 ,C o 7 ,F e 4 ,F e 6 ,a nd Fe 7 clusters have been isolated and characterized. [4] An example of ap lanar,C O-free cluster is the oligohydride Rh 7 wheel (type A, Figure 1), which contains aplanar Rh core that mimics aM (111) monolayer.…”

“…[5] Flat metal clusters exhibit unique magnetic properties and distinct catalytic activities owing to the electronic,m agnetic,a nd steric communication between the neighboring metals in the plane.P olynuclear metal carbonyl species are by far the most studied class of 2D and 3D clusters;t hey exhibit strong coordination of the CO ligands to the metals,a re coordinatively saturated, and thus provide not the best models for metal clusters and surfaces under other, CO-free conditions. [3] Given the synthetic ease of the formation of the precursors and clusters,t he use of simple hydrides as initiators of cluster growth, and the high yields of the resultant nanoclusters,w e set out to further explore the potential of such facile procedures for the preparation of carbonyl-ligand-free transition-metal nanoclusters with new topologies.H erein, we report the synthesis of al ow-valent manganese nanosheet with ah itherto unknown arrangement of six Mn atoms in an early planar ladder-type architecture (C). [3] Recently,O hki and coworkers and our group have shown that the reaction of easily available transition-metal amide precursor complexes M{N(SiMe 3 ) 2 } 2 (M = Co,Fe) with commercial hydride sources (diisobutylaluminium hydride,D ibal-H;p inacolborane, HBpin) is ac onvenient strategy to access new topologies of low-valent transition-metal nanoclusters in high yields.Planar Co 4 ,C o 7 ,F e 4 ,F e 6 ,a nd Fe 7 clusters have been isolated and characterized.…”

“…[3] We surmised that an equimolar reaction of the related manganese complex Mn[N(SiMe 3 ) 2 ] 2 (1) [6] with ahydride reagent would afford the coordinatively highly unsaturated species [Mn{N(SiMe 3 ) 2 }H]. [3] We surmised that an equimolar reaction of the related manganese complex Mn[N(SiMe 3 ) 2 ] 2 (1) [6] with ahydride reagent would afford the coordinatively highly unsaturated species [Mn{N(SiMe 3 ) 2 }H].…”

“…[3] The unprecedented planar growth might be adirect consequence of the steric bulk of the hmds ligands,which effectively shield the half spaces above and below the metal plane.The Mn À Mn bond lengths (2.85622(3)-2.97627(3) )a re in the range of Mn À Mn bonds in other Mn clusters. Single-crystal X-ray analysis of 2 revealed an unprecedented ladder-type Mn 6 nanocluster containing four m 2 -bridging N(SiMe 3 ) 2 and two terminal N(SiMe 3 ) 2 ligands (Scheme 1, middle).…”