Search

Heterogenization of catalytically important homogeneous catalysts on solid supports has become an expanding area of research. PNN and PONOP ruthenium pincer complexes were immobilized on a silica poly(allylamine) composite, BP-1 by a two-step Mannich reaction. The complexes on BP-1 were characterized by solid state NMR, FT-IR, elemental analysis, and metal digestion studies. Model solution experiments were carried out to determine the site of electrophilic substitution on the pyridine ring of the pincer complexes and revealed substitution in both the meta - and para -position. The catalytic reactivity of immobilized (PNN)RuH(Cl)(CO) and (PONOP)RuH(Cl)(CO) on BP-1 was studied for the dehydrogenative coupling of alcohols to esters with the liberation of H 2 . Moderate to good ester yields were realized with both immobilized systems without using the base required for the homogeneous reaction and also in the presence of KOH. The homogeneous model reactions required a base for ester formation. The amine functionality on BP-1 served as the base to generate the active pincer catalyst on the BP-1 surface. Both immobilized catalysts were recycled for multiple alcohol reaction cycles. Four-step control experiments were carried out using an alcohol and both immobilized systems. The results revealed the heterogeneity of the alcohol catalysis by both BP-1-Ru-PNN and BP-1-Ru-PONOP systems. This study has opened a new catalytic methodology for reactions where base is required for catalyst activation, by using a solid support with basic functionality. [ABSTRACT FROM AUTHOR]

Immobilization of catalytically active transition metal complexes on silica polyamine composite (SPC) surfaces offers many advantages for applications in catalysis particularly for catalyst recovery and reuse. We report here the immobilization of PONOP pincer complexes of Ru, Rh, Ni and Pd on the poly(allylamine) SPC, BP-1 using the Mannich reaction. Three different methods have been investigated for synthesizing the PONOP pincer transition metal complexes on BP-1: 1) direct reaction of the preformed pincer complexes using a two step Mannich reaction; 2) immobilization of the PONOP ligand using the Mannich reaction followed by the addition of a transition metal compound of a given metal; 3) the stepwise construction of PONOP on BP-1 followed by addition of a transition metal compound. The immobilized complexes on BP-1 were characterized by FT-IR, solid-state CPMAS 13 C and 31 P NMR, as well as elemental analysis. Anchoring of the complexes on BP-1 was also evaluated by the metal loading data obtained from the digestion of the loaded composites followed by Atomic Absorption Spectroscopy (AAS) or Inductively Coupled Plasma Atomic Emission Spectroscopy (ICPAES). The results showed that method 1 works better for the loading of pincer complexes on the SPC than methods 2 and 3. In the case of the Ru and Ni pincer complexes reasonable agreement with the phosphorous analysis was realized, while for the Pd complex values were high relative to the loading predicted from the phosphorus analysis, indicating the formation of the Pd nanoparticles on the surface during immobilization. For the Rh and Ru immobilized complexes with methods 2 & 3, metal loading was lower than the phosphorous analysis and this is attributed to entrained triphenylphosphine from the starting rhodium and ruthenium complexes based on the 13 C and 31 P CPMAS NMR data. Solution experiments using the PONOP pincer ligand and the Ru(PONOP) complex with n-butyl amine were conducted to model the site of electrophilic aromatic substitution on the pyridine ring. It was found that substitution both meta - and para -to the nitrogen takes place and this helped in the interpretation of the solid-state data. [ABSTRACT FROM AUTHOR]

The synthesis, structure and photophysical properties of the complexes [Ru[(CO)(TFA) (PPh 3 ) 2 (L)][(L = ppy = 2-phenylpyridine, ( 1a ); L = 2–(p–tolyl)pyridine] ( 1b ), are reported. The complexes were characterized by UV-VIS, IR and NMR and by single-crystal X-ray diffraction techniques. We also report the synthesis, structure and photophysical properties of [Ru(CO)(L)(PPhMe 2 ) 2 (L′)] + [PF 6 ] − [L′ = bipyridine, L = TFA, ( 3a ); L = H, ( 3b ) and L = H, L′ = 4,4′-dimethlyl bipyridine ( 3c )]. These compounds were characterized by UV-VIS, IR and NMR techniques and by a single crystal X-ray diffraction in the case of 3a. The solid state structure of [Ru(Me 2 PhP) 2 (CO) 2 (TFA) 2 (2) which is the starting material for the synthesis 3a - 3c is also reported to verify the trans relationship of the less bulky PPhMe 2 and for comparison with the previously reported PPh 3 analogs. The purpose of this study was to determine the impact, if any, of replacing bpy with ppy in the case of 1a and alkylation of the benzene ring in the case of 1b on the photophysical and electrochemical properties compared to related Ru(bpy) complexes. In contrast to the bpy analogs 1a and 1b showed reversible 1e − oxidations and blue-shifted MLCT absorptions. In the case of 3a - 3c we were interested in the effect on the photophysical properties of substituting PPh 3 with the less bulky but more electron donating PPhMe 2 . There were only minor changes in the photophysical and electrochemical properties relative to the previously reported PPh 3 analogs. [ABSTRACT FROM AUTHOR]

The reaction of the benzothiazolate-capped triosmium clusters Os 3 (CO) 9 (μ 3 ,η 2 -C 7 H 3 NSR)(μ-H) ( 1a , R = H; 1b , R = Me) with PPh 3 proceeds readily at room temperature with a μ 3 ,η 2 → μ,η 2 hapticity change in the benzothiazolate heterocycle to furnish Os 3 (CO) 9 (PPh 3 )(μ,η 2 -C 7 H 3 NSR)(μ-H) ( 2a , R = H; 2b , R = Me) in high yields. X-ray crystallography has confirmed the regiospecific nature of this reaction where the PPh 3 ligand is bound to the osmium atom that serves as the coordination site for the hydride and the metalated-carbon atom associated with the edge-bridged benzothiazolate ligand. The thermolysis of 2a and 2b in boiling toluene affords several new Os 3 clusters as a result of ligand isomerization, decarbonylation, and ortho metalation of the ancillary PPh 3 ligand. The new products have been isolated and characterized by a combination of spectroscopic methods and X-ray crystallography in the case of 3b , 4b , 5b and 6b . Clusters 3b and 4b are isomers of 2b and differ in the location of the hydride and PPh 3 ligands relative to the benzothiazolate moiety. Electronic structure calculations on the isomeric clusters 2b , 3b , and 4b confirm that 2b is the kinetic product of ligand substitution, accounting for its rearrangement to the latter two isomers upon heating. Cluster 5b contains a face-capping benzothiazolate moiety and is shown by DFT calculations to derive from a site-selective loss of an axial CO group in 4b . Cluster 6a,b formed from 5a,b as a result of further decarbonylation with concomitant ortho metalation of one of the phenyl groups of the coordinated PPh 3 ligand. [ABSTRACT FROM AUTHOR]

Reactions of Ru3(CO)10(µ-dppf) (1) (dppf = 1,1'-bis(diphenylphosphino)ferrocene), Ru3(CO)10(µ-dppm) (2) (dppm = bis(diphenylphosphino)methane), and the orthometalated derivative Ru3(CO)9{µ3- PPhCH2PPh(C6H4)} (3) with silanes (Ph3SiH, Et3SiH, Ph2SiH2) are reported. Treatment of 1 with Ph3SiH and Ph2SiH2 at room temperature leads to facile Si--H bond activation to afford Ru3(CO)9(µ-dppf)(SiPh3)(µ-H) (4) (60% yield) and Ru3(CO)9(µ-dppf)(SiPh2H)(µ-H) (6) (53% yield), respectively. The reaction of 1 with Ph3SiH has been investigated by electronic structure calculations, and these data have facilitated the analysis of the potential energy surface leading to 4. Compound 1 does not react with Et3SiH at room temperature but reacts at 68 °C to give Ru3(CO)9(µ-dppf)(SiEt3)(µ-H) (5) in 45% yield. Reaction of 2 with Ph3SiH at room temperature yields two new products: Ru3(CO)9(µ-dppm)(SiPh3)(µ-H) (7) in 40% yield and Ru3(CO)6(µ3-O)(µ-dppm)(SiPh3)(µ- H)3 (8) in 15% yield. Interestingly, at room temperature compound 7 slowly reverts back to 2 in solution with decomposition and liberation of Ph3SiH. Complex 8 can also be prepared from the direct reaction between 7 and H2O. Similar reactions of 2 with Et3SiH and Ph2SiH2 give only intractable materials. The orthometalated compound 3 does not react with Ph3SiH, Et3SiH and Ph2SiH2 at room temperature but does react at 66 °C to give Ru3(µ-CO)(CO)7{µ3- PPhCH2PPh(C6H4)}(SiR2R¹)(µ- H)](9, R = R' = Ph, 71% yield; 10, R = R' = Et, 60% yield; 11, R = Ph, R' = H, 66% yield) by activation of the Si--H bond. Compounds 4 and 8--11 have been structurally characterized. In 4, both the dppf and the hydride bridge a common Ru--Ru vector, whereas NMR studies on 7 indicate that two ligands span different Ru--Ru edges. Compound 8 contains a face-capping oxo moiety, a terminally coordinated SiPh3 ligand, and three bridging hydride ligands, whereas 9--11 represent simple oxidative addition products. In all of the compounds examined, the triruthenium framework retains its integrity and the silyl groups occupy equatorial sites. [ABSTRACT FROM AUTHOR]