The complete basis set method CBS-QB3 was used in conjunction with the CPCM solvation model to predict both the absolute and relative pKa's of 12 nucleophilic carbenes in dimethyl sulfoxide (DMSO), acetonitrile (MeCN), and water. Average absolute pKa values in DMSO ranged from 14.4 +/- 0.16 for 3-methylthiazol-2-ylidene (12) to 27.9 +/- 0.23 in the case of bis(dimethylamino)carbene (11), while values in MeCN were determined to be between 25.7 +/- 0.16 (12) and 39.1 +/- 0.25 (11). Relative pKa calculations yielded similar results. Calculations in aqueous solution gave pKa's between 21.2 +/- 0.2 (12) and 34.0 +/- 0.3 (11). Excellent agreement between calculated and experimental pKa's was obtained for the few cases where experimental numbers are available, confirming that this theoretical approach may be used to calculate highly accurate pKa values.

No abstract

The highly accurate complete basis set method CBS-QB3 has been used in conjunction with the conductor-like polarized continuum (CPCM) method to predict the aqueous pKa values for the three different hydrogen atoms in the imidazolium cation. Excellent agreement was obtained with the available experimental values. The pKa for the deprotonation of imidazole was also calculated and found to be quite different from the experimental estimate. The protocol for the pKa calculation was carefully analyzed and some recommendations made about the choice of levels of theory.

The treatment of the hydrazine complex cis-[Fe(N(2)H(4))(dmpe)(2)](2+) with base afforded the diazene complex cis-[Fe(N(2)H(2))(dmpe)(2)]. This reaction is reversed by the treatment of the diazene complex with a mild acid, while treatment of the hydrazine complex with a mixture of KOBu(t) and Bu(t)Li afforded the dinitrogen complex [Fe(N(2))(dmpe)(2)].

No abstract

Acetylido methyl ruthenium(II) complexes, trans-Ru(CtCR)(CH 3 )(dmpe) 2 , were synthesized in a single metathesis reaction from trans-Ru(CH 3 ) 2 (dmpe) 2 at ambient temperature; at elevated temperatures the reaction yields trans-Ru(CtCR) 2 (dmpe) 2 . Addition of a second terminal acetylene to a methanol solution of trans-Ru(CtCR)(CH 3 )(dmpe) 2 results in the formation of trans-Ru(CtCR)(CtCR′)(dmpe) 2 .

A series of dinuclear and trinuclear, acetylide-bridged ruthenium(II) complexes was synthesized by the condensation of terminal acetylenes with methyl ruthenium complexes. Dinuclear ruthenium(II) complexes trans,trans-(RCtC)Ru(dmpe) 2 (μ-CtCC 6 H 4 CtC)Ru(CtCR 0 )(dmpe)

Terminal acetylenes react with cis-RuMe 2 (PMe 3 ) 4 to form the bis(acetylido) complexes cis/trans-Ru(CϵCR) 2 (PMe 3 ) 4 in good yield. The structures of trans-2 (R = Ph), cis-3