Saturday May 5th – Presentations

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Development of electronic unsaturation in transition metal cluster complexes: Addition of Pt(IPr) groupings as sterically demanding ligands

Vincent J Zollo Jr, Sedigheh Etezadi, Burjor Captain

University of Miami

08:45 AM
Inorganic Chemistry

Nature has utilized catalytic properties of transition metals all throughout time seen electron transport in oxidative and reductive pathways and the centers of enzymes found in every form of life. On the lab bench, we try to mimic the action through analogous species using a synthetic approach. The development of electronic unsaturation in transition metal complexes has been widely studied for its role in small molecule activation and catalysis. The 14 electron compound Pt(SnBut3)(IPr)(H), 1 [IPr = N,N’-bis-(2,6-(diisopropyl) phenyl)imidazole-2-ylidene] was reacted with transition metal carbonyl cluster complexes. This yielded numerous mixed-metal cluster compounds structurally determined by single crystal x-ray diffraction, mass and NMR spectroscopy. The reaction between 1 and Ru56-C)(CO)15 resulted in three mixed-metal clusters: PtRu56-C)(IPr)(CO)15, 2 Pt2Ru56-C)(IPr)2(CO)15 , 3 H2PtRu55-C)(IPr)(CO)14 it was shown 2 was able to activate H2, while 3 showed dynamic activity in solution. The progression of the development of unsaturated complexes was furthered using M3(CO)12 (M = Fe, Ru, Os) starting reagents. Seven new mixed-metal cluster complexes were synthesized. Working under the assumption each metal obeys the 18 e- rule, unsaturation was found amongst most species. Moving down the triad, the reaction of 1 with Fe3(CO)12 afforded triangular Fe-Pt complexes: PtFe2(IPr)(CO)9, 4 and Pt2Fe(IPr)2(CO)6, 5. The reaction of 1 with Ru3(CO)12 resulted with a trigonal bipyramid structure Pt2Ru3(IPr)2(CO)12, 6.  The reaction of Os3(CO)12 with 1 is the most interesting. This gave mono and bis Pt(IPr) equatorial adducts: PtOs3(IPr)(CO)12, 7 and Pt2Os3(IPr)2(CO)12, 8 and a dihydride Pt(IPr) adduct, (µ-H)2PtOs3(IPr)(CO)10, 9. Most notable formed is the asymmetric raft, PtOs4(IPr)2(CO)12, 10 as well as its carbonyl substitution product PtOs4(IPr)(CO)13, 11 . This increased development of unsaturated species serves as a platform for prominent pre-cursor catalysts to those found in nature.  The synthesis, characterization, and application will be further discussed with insight to the complex bonding of sterically demanding ligands.

Ligand-induced ground state spin changes in Ce3Mn8 perovskite model clusters

Thai Son Cao, Khalil A. Abboud, and George Christou

Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL 32611

09:05 AM
Inorganic Chemistry

The AMnO3 manganites (A = main group or lanthanide metal) with a perovskite structure are under intense study because of their fascinating properties, such as multiferroicity, colossal magnetoresistance, piezoelectricity, and magnetoelasticity. We recently reported the molecular cluster [Ce3Mn8O8(O2CPh)18(HO2CPh)2], henceforth Ce3Mn8, with a structure related to the perovskite repeating unit and which provided insight into the origin of perovskite properties by possessing the same spin vector configurations as the C-type AF perovskites (AF = antiferromagnetic). It also has A-type AF low-lying excited states, suggesting that small structural changes could alter the ground state of the molecule to A-type AF; such changes are common in perovskites under different pressures and temperatures. To investigate this, we have synthesized derivatives of the Ce3Mn8 cluster in which Cl or Me substituents have been introduced into the ortho position of the benzoate ligands to introduce some structural perturbations. This presentation will describe the syntheses and structures of these 2-Cl-Ph and 2-Me-Ph derivatives, and the analysis of their magnetic properties to assess whether their ground states have changed.

Study of tri-t-butyl tin hydride complexes of transition metals towards activation of small molecules

Sedigheh Etezadi, Burjor Captain

University of Miami

09:25 AM
Inorganic Chemistry

We have been actively pursuing the chemistry of transition metal complexes containing sterically demanding tin ligands. The ability of tin compounds to modify both heterogeneous and homogeneous catalysts is known and our recent efforts center on utilizing the reagent But3SnH to investigate the influence of this ligand, which combines a steric profile similar to that of PBut3, with functional reactivity at the Sn-H bond. These properties of the SnBut3 ligand allow preparation of new complexes and comparison of their structures and reactivities with less encumbered tri-alkyl stannanes. This has allowed fine-tuning of the strained molecular geometry at the coordinatively unsaturated site and study of how that influences small molecule activation. Reversible H2 binding and activation, H2-D2 scrambling to form HD, C-H activation of bound ligands and solvents, catalytic hydrogenation, and catalytic hydrostannylation have all been observed for select complexes. In addition, a range of metal cluster complexes incorporating stannane moieties have been prepared and structurally characterized. The bulky SnBut3 group can serve as a reagent in the hydrostannylation reactions of alkynes to furnish vinylstannanes of high regio- and stereochemical specificity. The potential role of designed and selectively modified stannane ligands has been demonstrated by power and others but full utilization of the added dimension that stannanes bring to catalyst design remains a goal for future exploration. In this manner, we synthesized the new
14-electron unsaturated complex Pt(IPr)(SnBut3)(H), which was shown to undergo facile reactions with small molecules as well as function as a catalyst,
is an active and highly selective catalyst in more than one arena, where the bulky SnBut3 group first serves as a ligand and imparts electronic unsaturation about the platinum metal center, and also serves at facilitating catalytic reactions due to its versatility to eliminate and hence generate reactive sites on the transition metal center.

Design and synthesis of concentration gradient Prussian blue analogues

Su Kyung Jeon, Daniel R. Talham

Department of Chemistry, University of Florida

10:15 AM
Inorganic Chemistry

Analogues within the Prussian blue family of coordination polymer networks are studied for wide ranging applications including electrochromics, ion storage for battery electrodes, magnetism and light-switchable magnetism, as well as for biomedical agents and in catalysis.  A new architecture of coordination polymer particles, concentration gradient Prussian blue analogues, is introduced in this presentation. In these particles, a gradient between two single phases of PBA is achieved by varying the occupancy of divalent metals from core to the surface within the particle. The synthetic conditions under which uniform gradient particles can be reproducibly synthesized will be described. In addition, discussion of systems that behave well and those that show new behavior is presented. The concentration gradient particles are compared to analogous single phase and core-shell heterostructure particles.

Catalytic Synthesis of Cyclic Polymer via Ring Expansion Metathesis Polymerization.

Vineet K. Jakhar, Muhammad T. Jan, Poppy W. J. P. Disney, Khalil A. Abboud, Adam S. Veige

University of Florida

10:35 AM
Inorganic Chemistry

This report describes an approach to building Mo complexes featuring metal-carbon multiple bonds using a trianionic pincer ligand. Treating [tBuOCO]MoNMe2(NHMe2)2, a d2 Mo(IV) ion, with terminal alkynes (H–C≡CR, R = tBu, Ph, and SiMe3) produces in quantitative yield the corresponding metallocyclopropylidene complexes. X-Ray diffraction studies on a single crystal of these complexes reveal three notable features: (1) a highly distorted hexacoordinate Mo(VI) center, (2) a metallocyclopropene fragment, and (3) a highly distorted CH group in the metallocyclopropene unit. These complexes are capable of polymerizing norbornene via ring expansion metathesis polymerization (REMP) to yield highly cis-syndiotactic cyclic polynorbornene (poly(NBE)). The tacticity of the polymer was determined by examination of 1H and 13C{1H} NMR spectra of the polymer in solution. Polymerization conducted at ambient temperature generated >98% cis, >98% syndiotactic poly(NBE) over 21 h. The timeframe was reduced to 6-10 h by gradually increasing the temperature to 60 °C, which led to a decrease in cis to trans ratio (>93, cis).

Growth mechanisms of Prussian blue analogue nanoparticles in surfactant-free synthesis

Jiamin Liang, Carissa H. Li, Daniel R. Talham

Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, United States

10:55 AM
Inorganic Chemistry

The growth mechanism of Prussian blue analogue (PBA) nanoparticles synthesized via surfactant-free coprecipitation has been investigated. This study suggests that PBA nanoparticles form via different mechanisms, depending on composition.  Particles of the rubidium cobalt hexacyanometallate(III) series, RbCoM’ PBA with M’ = Cr, Fe, Co, form through a complex nonclassical growth mechanism, whereas rubidium nickel hexacyanometallate(III), RbNiM’ PBA with M’ = Cr, Fe, Co, nanoparticles form via a classical dissolution-recrystallization growth process. Factors affecting the growth behavior including reaction time and precursor concentration have been probed using transmission electron microscopy (TEM), real-time conductance measurement and dynamic light scattering (DLS). Although nanoscale and mesoscale Prussian blue analogue particles are used in many areas of study, including magnetism, battery cathodes, electrochromics and catalysis, this is the first detailed analysis of their particle growth mechanisms.