Selective HCOOH decomposition to H2/CO2 on Au: Au species catalyze HCOOH dehydrogenation at higher rates than on Pt, previously considered the most active metal. Dehydrogenation occurs through formate decomposition limited by H2 desorption on Au species undetectable by TEM. CO did not form (<10 ppm), making products suitable for low‐temperature fuel cells.

À , E= PPh 2 and SPh} tethered to a trialkoxysilane moiety through a carbamate linkage were immobilized on ordered mesoporous silicas SBA-15 and MCM-41 using a grafting process. The resulting hybrid materials were characterized by IR spectroscopy, solid-state CP/MAS NMR ( Si), and elemental analyses. These analyses showed the integrity of the pincer-metal complexes on the supports, which highlights their stability under the applied immobilization conditions. An H-bonding interaction between the carbamate carbonyl group of the complex and free silanol groups on the silica surface was also established. The hybrid materials were found to act as Lewis acid catalysts in the aldol reaction between methyl isocyanoacetate and benzaldehyde. SBA-15 modified with the PCP-pincer Pd complex was used in up to five runs without loss of activity. Control experiments showed the true heterogeneous nature of the catalyst in this reaction. Nitrogen physisorption data, XRD, and TEM/EDX analyses of the hybrid materials revealed that the mesoporous structure of these materials was retained during the immobilization process as well as during catalysis.

Abstract2,6-Bis[(dimethylamino)methyl]phenyl (NCN-pincer) palladium(II) and platinum(II) complexes tethered to a trialkoxysilane coupling agent through a carbamate linkage were immobilized on various types of silica using a grafting or a sol-gel process. The resulting hybrid materials were characterized by IR spectroscopy (DRIFT) and solid state CP/MAS NMR ( 13 C and 29 Si). Based on these analyses, H-bond interactions between the carbamate carbonyl group of the complex and the free silanol groups on silica surface were established. The palladium-based materials were tested for their activity as Lewis acid catalysts in the aldol reaction between methyl isocyanoacetate and benzaldehyde. It was found that these materials can indeed be applied as catalysts in this reaction. Their repetitive reuse showed an inferior catalytic efficacy, which presumably was caused by a reconstitution of the silica support. These studies also revealed that simple silver-based salts are active catalysts in this aldol reaction.

a b s t r a c tVarious para-OH functionalized ECE-pincer metal complexes [MX(ECE-OH)L n ] (ECE-OH = [C 6 H 2 (CH 2 E) 2 -2,6-OH-4] À , E = NMe 2 , PPh 2 and SPh) were synthesized. The X-ray crystal structures of neutral [PdCl(SCS-OH)], [PdCl(NCN-OH)], and cationic [Pd(PCP-OH)(MeCN)](BF 4 ) are reported. The neutral halide complexes exhibit self-assembly to form polymeric chains via H-bonding involving the para-OH group as donors and the halide ligand on the metal as acceptors. Moreover, the halide ligand can be replaced by a monomeric aryloxy-O ligand leading to the formation of a covalently bonded dimer. The crystal structure of such a dimer derived from [PdI(NCN-OH)] is reported. Furthermore, these pincer-metal complexes were tethered through a carbamate linker to a siloxane functionality with the aim to be immobilized on a silica support. The crystal structure of a siloxane-functionalized [PtI(NCN-Z)] complex exemplifies how other H-bonding interactions not involving the metal-halide groupings can lead to polymeric networks as well.

Monodisperse magnetizable colloidal silica particles in a stable dispersion have been functionalized with a homogeneous catalyst: a PCP-pincer Pd-complex. In a proof-of-principle experiment we demonstrate the catalytic activity of the colloids in a C-C bond formation reaction. Advantages of the magnetic silica carriers are the large surface-to-volume ratio and the easy recovery by magnetic separation. After magnetic separation, the catalyst-loaded particles are readily redispersed for further use. r

Silicatein protein filaments isolated from marine demosponges have been used to influence the condensation of siloxanes bearing organometallic pincer complexes. The siliceous material is formed under remarkably mild conditions and the organometallic pincer becomes an intrinsic part of the silica. The immobilisation of a metal pincer, which acts as a sensor and initial results on the immobilisation of a pre-catalytic pincer species are reported.

Catalysis O 0020Catalytic Performance of Symmetrical and Unsymmetrical Sulfur-Containing Pincer Complexes: Synthesis and Tandem Catalytic Activity of the First PCS-Pincer Palladium Complex. -A new arene-based unsymmetrical PCS pincer ligand is prepared and tested in the Pd-catalyzed aldol reaction of isocyanoacetate (I) with benzaldehyde (II). The catalytic activity of the new ligand is comparable to that of the corresponding symmetrical SCS ligand as it enters the catalytic cycle as precatalyst, but it behaves different from the symmetrical PCP ligand. The tandem coupling of allylic chlorides (V) and (X) or vinyloxirane (XV) with hexamethyldistannane and aldehyde (VI) or sulfonylimine (VIII) is efficiently catalyzed by the Pd-PCS complex as it catalyzes the formation of an allylstannane as well as its addition to aldehydes/imines. In contrast, the symmetrical PCP ligand is not effective in allylstannane formation. Thus, desymmetrization and electronic fine-tuning of pincer complexes can lead to unexpected synergistic effects and the development of new catalytic domino reactions. -(GAGLIARDO, M.; SELANDER, N.; MEHENDALE, N. C.; VAN KOTEN, G.; KLEIN GEBBINK*, R. J. M.; SZABO, K. J.; Chem. Eur. J. 14 (2008) 16, 4800-4809; Fac. Sci., Chem. Biol. Org. Chem., Utrecht Univ., NL-3584 CH Utrecht, Neth.; Eng.) -Mischke 40-026