A wide array of forms of palladium has been utilized as precatalysts for Heck and Suzuki coupling reactions over the last 15 years. Historically, nearly every form of palladium used has been described as the active catalytic species. However, recent research has begun to shed light on the in situ transformations that many palladium precatalysts undergo during and before the catalytic reaction, and there are now many suggestions in the literature that narrow the scope of types of palladium that may be considered true “catalysts” in these coupling reactions. In this work, for each type of precatalyst, the recent literature is summarized and the type(s) of palladium that are proposed to be truly active are enumerated. All forms of palladium, including discrete soluble palladium complexes, solid-supported metal ligand complexes, supported palladium nano- and macroparticles, soluble palladium nanoparticles, soluble ligand-free palladium, and palladium-exchanged oxides are considered and reviewed here. A considerable focus is placed on solid precatalysts and on evidence for and against catalysis by solid surfaces vs. soluble species when starting with various precatalysts. The review closes with a critical overview of various control experiments or tests that have been used by authors to assess the homogeneity or heterogeneity of catalyst systems.

On the Nature of the Active Species in Palladium Catalyzed Mizoroki–Heck and Suzuki–Miyaura Couplings – Homogeneous or Heterogeneous Catalysis, A Critical Review

Cyclometalated phosphine-based pincer complexes: Mechanistic insight in catalysis, coordination, and bond activation

Since the first reports in the late 1970s on transition metal complexes contain- ing pincer-type ligands—named after the particular coordination mode of these ligands—these systems have at- tracted increasing interest owing to the unusual properties of the metal centers imparted by the pincer ligand. Typical- ly, such a ligand comprises an anionic aryl ring which is ortho,ortho-disubsti- tuted with heteroatom substituents, for example, CH2NR2 ,C H 2PR2 or CH2SR, which generally coordinate to the met- al center, and therefore support the MC s bond. This commonly results in a terdentate and meridional coordina- tion mode consisting of two metalla- cycles which share the MC bond. Detailed studies of the formation and the properties of a large variety of pincers containing platinum group metal complexes have provided direct access to both a fundamental under- standing of a variety of reactions in organometallic chemistry and to a range of new applications of these complexes. The discovery of alkane dehydrogenation catalysts, the mecha- nistic elucidation of fundamental transformations (for example, CC bond activation), the construction of the first metallodendrimers for sustain- able homogeneous catalysis, and the engineering of crystalline switches for materials processing represent only a few of the many highlights which have emanated from these numerous inves- tigations. This review discusses the synthetic methodologies that are cur- rently available for the preparation of platinum group metal complexes con- taining pincer ligands and especially emphasizes different applications that have been realized in materials science such as the development and engineer- ing of sensors, switches, and catalysts.

Platinum Group Organometallics Based on “Pincer” Complexes: Sensors, Switches, and Catalysts

The potential of palladacycles: more than just precatalysts

s of Papers, 221st ACS National Meeting, San Diego, CA, April 1-5, 2001; American Chemical Society:Washington, DC, 2001; INOR287. (b) Dijkstra, H. P.; Slagt, M. Q.; McDonald, A.; Kruithof, C. A.; Kreiter, R.; Mills, A. M.; Lutz, M.; Spek, A. L.; Klopper, W.; van Klink, G. P. M.; van Koten, G. Eur. J. Inorg. Chem. 2003, 830. (c) Mehendale, N. C.; Bezemer, C.; van Walree, C. A.; Klein Gebbink, R. J. M.; van Koten, G. J. Mol. Catal. A 2006, 257, 167. (d)Mehendale, N. C.; Sietsma, J. R. A.; de Jong, K. P.; vanWalree, C. A.; Gebbink, R. J. M. K.; van Koten, G. Adv. Synth. Catal. 2007, 349, 2619. (e) Mehendale, N. C.; Lutz, M.; Spek, A. L.; Klein Gebbink, R. J. M.; van Koten, G. J. Organomet. Chem. 2008, 693, 2971. (f)McDonald, A. R.; Dijkstra, H. P.; Suijkerbuijk, B.M. J. M.; van Klink, G. P. M.; van Koten, G.Organometallics 2009, 28, 4689. (g) McDonald, A. R.; Franssen, N.; van Klink, G. P. M.; van Koten, G. J. Organomet. Chem. 2009, 694, 2153. (h) O’Leary, P.; vanWalree, C. A.; Mehendale, N. C.; Sumerel, J.; Morse, D. E.; Kaska, W. C.; van Koten, G.; Klein Gebbink, R. J. M. Dalton Trans. 2009, 4289. (164) Gimenez, R.; Swager, T. M. J. Mol. Catal. A 2001, 166, 265. (165) Poyatos, M.; Marquez, F.; Peris, E.; Claver, C.; Fernandez, E. New J. Chem. 2003, 27, 425. (166) Yu, K.; Sommer, W.; Weck, M.; Jones, C. W. J. Catal. 2004, 226, 101. (167) Sommer,W. J.; Yu, K.; Sears, J. S.; Ji, Y.; Zheng, X.; Davis, R. J.; Sherrill, C. D.; Jones, C. W.; Weck, M. Organometallics 2005, 24, 4351. (168) Brookhart, M.; Huang, Z.; MacArthur, A. H.; Carson, E. C.; Goldman, A.; Scott, S. L.; Vicente, B. C. Abstracts of Papers, 239th ACS National Meeting, San Francisco, CA, March 21-25, 2010; American Chemical Society: Washington, DC, 2010; CATL-79. (169) del Pozo, C.; Corma, A.; Iglesias, M.; Sanchez, F. Organometallics 2010, 29, 4491.

Dehydrogenation and related reactions catalyzed by iridium pincer complexes

High yield olefination of a wide scope of aryl chlorides catalyzed by the phosphinito palladium PCP pincer complex: [PdCl{C6H3(OPPri2)2-2,6}]

The PCP pincer complex, IrH2{C6H3-2,6-(CH2P-t-Bu2)2} (1) catalyzes the transfer dehydrogenation of primary and secondary alcohols Dehydrogenation occurs across the CO bond rather than the CC bon

Selective dehydrogenation of alcohols and diols catalyzed by a dihydrido iridium PCP pincer complex

High Yield Olefination of a Wide Scope of Aryl Chlorides Catalyzed by the Phosphinito Palladium PCP Pincer Complex: [PdCl{C6H3(O-P(iPr)2)2-2,6}].

The PCP pincer complex, IrH2{C6H3-2,6-(CH2P-t-Bu2)2} (1) catalyzes the transfer dehydrogenation of primary and secondary alcohols. Dehydrogenation occurs across the CO bond rather than the CC bon...

Cathleen Yung

Papers

High yield olefination of a wide scope of aryl chlorides catalyzed by the phosphinito palladium PCP pincer complex: [PdCl{C6H3(OPPri2)2-2,6}]

Selective dehydrogenation of alcohols and diols catalyzed by a dihydrido iridium PCP pincer complex

High Yield Olefination of a Wide Scope of Aryl Chlorides Catalyzed by the Phosphinito Palladium PCP Pincer Complex: [PdCl{C6H3(O-P(iPr)2)2-2,6}].

Selective Dehydrogenation of Alcohols and Diols Catalyzed by a Dihydrido Iridium PCP Pincer Complex.