The ability of the terpyridine ligand to stabilize alkyl complexes of nickel has been central in obtaining a fundamental understanding of the key processes involved in alkyl-alkyl cross-coupling reactions. Here, mechanistic studies using isotopically labeled (TMEDA)NiMe(2) (TMEDA = N,N,N',N'-tetramethylethylenediamine) have shown that an important catalyst in alkyl-alkyl cross-coupling reactions, (tpy')NiMe (2b, tpy' = 4,4',4' '-tri-tert-butylterpyridine), is not produced via a mechanism that involves the formation of methyl radicals. Instead, it is proposed that (terpyridine)NiMe complexes arise via a comproportionation reaction between a Ni(II)-dimethyl species and a Ni(0) fragment in solution upon addition of a terpyridine ligand to (TMEDA)NiMe(2). EPR and DFT studies on the paramagnetic (terpyridine)NiMe (2a) both suggest that the unpaired electron resides heavily on the terpyridine ligand and that the proper electronic description of this nickel complex is a Ni(II)-methyl cation bound to a reduced terpyridine ligand. Thus, an important consequence of these results is that alkyl halide reduction by (terpyridine)NiR(alkyl) complexes appears to be substantially ligand based. A comprehensive survey investigating the catalytic reactivity of related ligand derivatives suggests that electronic factors only moderately influence reactivity in the terpyridine-based catalysis and that the most dramatic effects arise from steric and solubility factors.

A number of new ionic titanocene compounds have been isolated and characterized. These exhibit significant cytotoxicity against a number of different human tumor cell lines including a defined cisplatin-resistant cell line. One of the compounds is an order of magnitude more active than its nonfunctionalized equivalent.

The reaction of cis-Fe(dmpe) 2 H 2 (1) with 13 C-labeled carbon dioxide (CO 2 ) was inVestigated, and trans-[Fe(dmpe) 2 (CO)H] • [HCO 3 ] (5) was identified as a reaction byproduct. Both the carbonyl ligand and the bicarbonate anion are deriVed from CO 2 , and this effectiVely constitutes a disproportionation of CO 2 to CO and CO 3 2-. trans-[Fe(dmpe) 2 (CO)H].[HCO 3 ] (5) was characterized by crystallography and by NMR spectroscopy.