The performance of a wide variety of DFT exchange-correlation functionals for a number of late-transition-metal reaction profiles has been considered. Benchmark ab-initio reference data for the prototype reactions Pd + H2, Pd + CH4, Pd + C2H6 (both C-C and C-H activation), and Pd + CH3Cl are presented, while ab-initio data of lesser quality were obtained for the catalytic hydrogenation of acetone and for the low-oxidation-state and high-oxidation-state mechanisms of the Heck reaction. "Kinetics" functionals such as mPW1K, PWB6K, BB1K, and BMK clearly perform more poorly for late-transition-metal reactions than for main-group reactions, as well as compared to general-purpose functionals. There is no single "best functional" for late-transition-metal reactions, but rather a cluster of several functionals (PBE0, B1B95, PW6B95, and TPSS25B95) that perform about equally well; if main-group thermochemical performance is additionally considered, then B1B95 and PW6B95 emerge as the best performers. TPSS25B95 and TPSS33B95 offer attractive performance compromises if weak interactions and main-group barrier heights, respectively, are also important. In the ab-initio calculations, basis set superposition errors (BSSE) can be greatly reduced by ensuring that the metal spd shell has sufficient radial flexibility in the high-exponent range. Optimal HF percentages in hybrid functionals depend on the class of systems considered, increasing from anions to neutrals to cations to main-group barrier heights; transition-metal barrier heights represent an intermediate situation. The use of meta-GGA correlation functionals appears to be quite beneficial.

[reaction: see text] [cis-Ru(II)(dmp)2(H2O)2]2+ (dmp = 2,9-dimethylphenanthroline) was found to be a selective oxidation catalyst using hydrogen peroxide as oxidant. Thus, primary alkenes were very efficiently oxidized via direct carbon-carbon bond cleavage to the corresponding aldehydes as an alternative to ozonolysis. Secondary alkenes were much less reactive, leading to regioselective oxidation of substrates such as 4-vinylcyclohexene and 7-methyl-1,6-octadiene at the terminal position. Primary allylic alcohols were chemoselectively oxidized to the corresponding allylic aldehydes, e.g., geraniol to citral.

We studied the scope and limitations of a tandem intramolecular Nicholas/Pauson-Khand strategy for the synthesis of tricyclic oxygen- and nitrogen-containing heterocycles. This methodology enables conversion of simple acyclic starting materials into a series of previously unknown heterocyclic architectures. For the preparation of cyclic ethers (Z = O), tricyclic [5,6,5]- through [5,9,5]-systems (m = 1, n = 1-4) are available with the [5,7,5]- and [5,8,5]-systems amenable to quick and efficient synthesis. Tricyclic [5,7,5]- and [5,8,5]-amine-containing (Z = NTs) heterocycles can be successfully prepared. Attempts to make larger ring systems (Z = O, m = 2; Z = O, n = 5; or Z = NTs, n = 4-5) or prepare lactones via Nicholas reactions with carboxylic acid nucleophiles (available via oxidation of alcohol nucleophiles, Z = O) result in decomposition or dimerization. The latter process enables formation of 14-, 16-, and 18-membered ring diolides when using carboxylic acid nucleophiles. We also investigated the use of chiral amine promoters in the Pauson-Khand step but found no asymmetric induction.

[reaction: see text] Simple acyclic enynes can be easily converted into tricyclic ethers upon treatment with Co2(CO)8 followed by Nicholas and Pauson-Khand reactions. Tricyclic [5,8,5]- and [5,7,5]-systems can be prepared in high overall yields in only seven synthetic steps.

[reaction: see text] We have developed a new strategy for the preparation of diolides using a cascade of Nicholas reactions. The carboxylic acid nucleophiles in these reactions are virtually unstudied participants in transformations of this type. Using this methodology, a 16-membered cobalt-complexed cyclic diyne is available in 28% yield over eight steps (an average of 85% per step). We can also easily access the uncomplexed diolide in one additional step.