From the experimental crystal structure and ab initio calculations on resveratrol and its derivatives, structural features of mechanistic importance are described. The molecular structure reveals the relative coplanarity of the trans-stilbene skeleton, and the molecular packing in the solid state shows an extensive hydrogen bond network that elucidates the flip-flop motion of the three hydroxyl groups that alternately form and break H bonds with each of the neighboring phenolic oxygens. The dynamic behavior provoked by the alternation of hydrogen bond formation and breaking can result in the ready mobility of up to three hydrogen atoms per resveratrol molecule that can be transferred to reactive oxidants that are rich in electron density. In addition, theoretical studies confirm the planarity of resveratrol as well as for half of the molecule of a condensation dimeric derivative of resveratrol, trans-sigma-viniferin. Furthermore, these studies show the p-4'-OH group to be more acidic compared to the other two m-OH groups. These features correlate with the biological activity of resveratrol as an antioxidant and support earlier studies showing H-atom transfer to be the dominant mechanism by which phenolic antioxidants intercept free radicals.

Triamidoamine-supported zirconium phosphido complexes, (N 3 N)ZrPRR 0 (N 3 N=N(CH 2 CH 2 -NSiMe 3 ) 3 3-; R = alkyl, aryl; R 0 = R, H), have been shown to catalyze the hydrophosphination of terminal alkynes as well as that of symmetric aryl and alkyl carbodiimides. A mechanism based on insertion of the substrate into the Zr-P bond is proposed on the basis of competition experiments and model examples of stoichiometric insertion reactions of polar, small-molecule substrates possessing CdO, CdN, CtN, and CdS functionalities into the Zr-P bond. Molecular structures of the insertion products (N 3 N)ZrNdC(PHCy)Ph (4), (N 3 N)ZrNdC(PPh 2 )Ph (5), and (N 3 N)ZrPhNC-(O)PPh 2 (11), as well as (N 3 N)Zr[η 2 (N,N)-( i PrN) 2 C(PPh 2 )] (9), a key intermediate in the catalytic hydrophosphination of carbodiimides, have been determined.

The paramagnetic complexes (TmtBu)CoX (X = Cl, Br, I) have been readily prepared and structurally characterized and provide a convenient entry into cobalt(II) tris(mercaptoimidazolyl)borate chemistry. A number of derivatives, including mononuclear triphenylphosphine adducts [(TmtBu)Co(PPh3)]X and dinuclear compounds [Co2(TmtBu)2X]Y, have been prepared in order to ascertain whether cobalt is a reliable surrogate for zinc in biological systems, particularly in sulfur-rich coordination environments. The structure of the first cobaltaboratrane is also reported.

A general, two-step procedure is reported for the modular synthesis of a series of palladium complexes of chelating Chugaev-type diaminocarbene ligands via metal-templated addition of hydrazines to alkylisocyanides. This method afforded high yields of (dicarbene)palladium dihalide complexes with methyl, isopropyl, cyclohexyl, and tert-butyl substituents by addition of hydrazine to the corresponding alkylisocyanide, and analogous backbone-substituted complexes were prepared by palladium-templated addition of methylhydrazine to methylisocyanide. The complexes were fully characterized by IR, 1H NMR, and 13C NMR spectroscopies. X-ray crystallographic analyses of four (dicarbene)palladium dibromide complexes revealed structural similarities with complexes of imidizole-based N-heterocyclic carbenes (NHCs), characterizing these chelating ligands as strongly donating, resonance-stabilized diaminocarbenes. To examine whether these ligands are amenable to cross-coupling catalyst optimization via systematic ligand modification, a set of 10 (dicarbene)palladium dihalide complexes was tested as precatalysts in the Suzuki−Miyaura coupling of bromobenzene with phenylboronic acid. Substantial variations in catalytic activity were observed, and a backbone-substituted palladium dicarbene complex derived from methylhydrazine was identified as the most active precatalyst. Catalyst activities did not correlate with ligand sterics, and subtle electronic perturbation of carbene donor ability by the alkyl groups is proposed to be the origin of the differences in activity. The optimized catalyst was found to give high yields in Suzuki−Miyaura cross-couplings of electron-poor aryl chlorides and a range of aryl bromides, although elevated temperatures (120 °C) were necessary. Coupling reactions conducted open to air showed little formation of homocoupling byproduct and minimal loss of yield in most cases, identifying the optimized system as a rare example of an air-tolerant Suzuki−Miyaura catalyst. This study highlights the importance of a modular ligand design in fine-tuning the activity of a homogeneous catalyst.