A new N-heterocyclic carbene architecture comprising a 1,4-naphthoquinone annulated to 1,3-dimesitylimidazolylidene (NpQ-NHC) was synthesized in two high yielding steps from commercially available starting materials. The free NpQ-NHC was characterized (solution and solid-state) and was used to synthesize various Rh and Ag complexes that ranged in pi-electron density. Enabled by the quinone moiety, the pi-systems of these complexes were analyzed using infrared spectroscopy and cyclic voltammetry. In contrast to previous reports, pi-backbonding was found to be non-negligible and was directly influenced by the metal's electronic character.

Thermally-reversible covalent polymers featuring dynamic carbon-carbon double bonds and tunable molecular weights were prepared from difunctional carbenes; addition of transition metal complexes to these materials afforded the respective main-chain organometallic polymers.

To investigate effects of redox-active functional groups on the coordination chemistry and electronic properties of N-heterocyclic carbenes (NHCs), we prepared a series of complexes comprising 1,3-diferrocenylimidazolylidene and -benzimidazolylidene (1 and 2, respectively), 1-ferrocenyl-3-methyl-and 1,3-diphenyl-5-ferrocenylbenzimidazolylidene (3 and 4, respectively), N,N 0 -diisobutyldiaminocarbene[3]ferrocenophane (FcDAC), and 1,3-dimesitylnaphthoquinoimidazolylidene (NqMes) ligands and coordinated [Ir(COD)Cl] (COD = 1,5-cyclooctadiene), [Ir(CO) 2 Cl], and [M(CO) 5 ] (M=Cr, Mo, W) units. The coordination chemistry of the aforementioned NHCs was investigated by X-ray crystallography, and their electronic properties were studied by NMR and IR spectroscopy, as well as electrochemistry. No significant variation in ν CO was observed among metal carbonyl complexes supported by 2-4 and FcDAC, indicating that the number (one vs two) of redoxactive groups, the location (N atom vs backbone) of the redox-active group, and carbene ring identities (strained six-membered, nonaromatic vs five-membered, heteroaromatic) did not have a significant effect on ligand electron-donating ability. Because the shifts in ν CO upon oxidation of 1-3 and FcDAC were similar in magnitude but opposite in sign to NqMes, we conclude that the enhancement or attenuation of ligand donating is primarily Coulombic in origin (i.e., due to the molecule acquiring a positive or negative charge).

The phosphine 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane, which we will condense to DAPTA, and its oxide have been fully characterized both in solution and in the solid state. These compounds were prepared by acylation of 1,3,5-triaza-7-phosphaadamantane (PTA) and its oxide with acetic anhydride. The nonionic compounds were found to be soluble in most common organic solvents, in addition to possessing extremely large molar solubilities in water. Indeed, the molar solubility of DAPTA was shown to be 7.4 M, which is 4 time more soluble than the commonly utilized water-soluble phosphine, triply meta-sulfonated triphenylphosphine (TPPTS). In the case of DAPTA this enhanced water solubility is attributed to a strong interaction of water with the amide nitrogen−CO bond dipole as revealed by a large red shift of the νC  O vibration on going from a weakly interacting solvent such as CH2Cl2 to water. This latter observation is supported by the short average amide nitrogen−carbonyl carbon bond distance of 1.375 Å as determined via X-ray crystallography, indicative of a strong Coulombic interaction between the nitrogen and carbon atoms. To assess the metal to phosphorus binding characteristics of DAPTA, several group 10 and group 6 complexes were prepared and their M−P bond distances were shown to be quite similar with those of their PTA analogues. For examples, the W−P bond distance in W(CO)5DAPTA of 2.492(3) Å is comparable to that previously reported for W(CO)5PTA of 2.4976(15) Å and slighter shorter than that found in W(CO)5PMe3 (2.516(2) Å). Accordingly, the PTA ligand has generally been characterized as possessing donor properties similar to that of PMe3. Consistent with these bonding parameters determined in the solid state, all three tungsten pentacarbonyl complexes have nearly identical ν(CO) frequencies in solution.

A new, high-yielding synthesis of 3,3Ј,4,4Ј-tetrachlorobiphenyl was developed, facilitating access to a new family of fluorescent 5,5Ј-bibenzimidazolium salts bearing phenyl or bulky tertiary alkyl N-substituents. Deprotonation of these salts afforded the respective 5,5Ј-bibenzimidazolylidenes in excellent isolated yields (Ն86 %), which were characterized in the solid state and solution. Treatment of these ditopic ligands with [Rh(COD)Cl] 2 (COD = 1,5-cyclooctadiene) afforded bimetallic complexes composed of two Rh atoms connected through a bis(carbene) linker. Electrochemical analyses of these complexes revealed single, quasi-reversible oxidations at E 1/2 = +0.54 to +0.59 V (vs. SCE) arising from the