Patterned monolayers of neutral and charged functionalized manganese arene complexes on a highly ordered pyrolytic graphite surface.

Complex patterns: The arene manganese tricarbonyl complexes [Mn(eta(5)-2,5-didodecoxy-1,4-semiquinone)(CO)(3)] and [Mn(eta(6)-1,4-dioctyloxybenzene)(CO)(3)] BF(4) form patterned monolayers on the surface of highly ordered pyrolytic graphite (HOPG), as a result of hydrogen-bonding, hydrophobic, and electrostatic interactions, leading to an ordered 2D array of manganese atoms or ions.

Pi-bonded quinonoid transition-metal complexes.

Coordination of the carbocyclic ring of hydroquinones to electrophilic transition-metal fragments such as Mn(CO)3+ and Rh(COD)+ produces stable pi-bonded eta6-complexes that are activated to facile reversible deprotonation of the -OH groups. The deprotonations are accompanied by electron transfer to the transition metal, which acts as an internal oxidizing agent or electron sink. With manganese as the metal, the resulting eta5-semiquinone and eta4-quinone complexes have been used to synthesize one- two- and three-dimensional polymeric metal-organometallic coordination networks. With rhodium as the metal, the pi-quinonoid complexes have been demonstrated to play a unique role in multifunctional C-C coupling catalysis and in the synthesis of new organolithium reagents. Both classes of pi-quinonoid complexes appear to have significant applications in nanochemistry by providing an excellent vehicle for templating the directed self-assembly of nanoparticles into functional materials.

Organometallic crystal engineering of [(1,4- and 1,3-hydroquinone)Rh(P(OPh)3)2]BF4 by charge assisted hydrogen bonding.

The ionic complexes [(1,4- and 1,3-hydroquinone)Rh(P(OPh)3)2]BF4 form porous organometallic structures dictated by charge assisted hydrogen bonding.

An anionic rhodium eta4-quinonoid complex as a multifunctional catalyst for the arylation of aldehydes with arylboronic acids.

The pi-bonded rhodium quinonoid complex, K+[(1,4-benzoquinone)Rh(COD)]-, functions as a good catalyst for the coupling of arylboronic acid and aldehydes to afford diaryl alcohols. The catalysis is heterobimetallic in that both the transition metal and concomitant alkali metal counterion play an integral part in the reaction. In addition, the anionic quinonoid catalyst itself plays a bifunctional role by acting as a ligand to the boronic acid and as a Lewis acid receptor site for the transferring aryl group.

Chemical and electrochemical reduction of polyarene manganese tricarbonyl cations: hapticity changes and generation of syn- and anti-facial bimetallic eta4,eta6-naphthalene complexes.

(Eta6-naphthalene)Mn(CO)(3)(+) is reduced reversibly by two electrons in CH(2)Cl(2) to afford (eta4-naphthalene)Mn(CO)(3)(-). The chemical and electrochemical reductions of this and analogous complexes containing polycyclic aromatic hydrocarbons (PAH) coordinated to Mn(CO)(3)(+) indicate that the second electron addition is thermodynamically easier but kinetically slower than the first addition. Density functional theory calculations suggest that most of the bending or folding of the naphthalene ring that accompanies the eta6 --> eta4 hapticity change occurs when the second electron is added. As an alternative to further reduction, the 19-electron radicals (eta6-PAH)Mn(CO)(3) can undergo catalytic CO substitution when phosphite nucleophiles are present. Chemical reduction of (eta6-naphthalene)Mn(CO)(3)(+) and analogues with one equivalent of cobaltocene affords a syn-facial bimetallic complex (eta4,eta6-naphthalene)Mn(2)(CO)(5), which contains a Mn-Mn bond. Catalytic oxidative activation under CO reversibly converts this complex to the zwitterionic syn-facial bimetallic (eta4,eta6-naphthalene)Mn(2)(CO)(6), in which the Mn-Mn bond is cleaved and the naphthalene ring is bent by 45 degrees . Controlled reduction experiments at variable temperatures indicate that the bimetallic (eta4,eta6-naphthalene)Mn(2)(CO)(5) originates from the reaction of (eta4-naphthalene)Mn(CO)(3)(-) acting as a nucleophile to displace the arene from (eta6-naphthalene)Mn(CO)(3)(+). Heteronuclear syn-facial and anti-facial bimetallics are formed by the reduction of mixtures of (eta6-naphthalene)Mn(CO)(3)(+) and other complexes containing a fused polycyclic ring, e.g., (eta5-indenyl)Fe(CO)(3)(+) and (eta6-naphthalene)FeCp(+). The great ease with which naphthalene-type manganese tricarbonyl complexes undergo an eta6 --> eta4 hapticity change is the basis for the formation of both the homo- and heteronuclear bimetallics, for the observed two-electron reduction, and for the far greater reactivity of (eta6-PAH)Mn(CO)(3)(+) complexes in comparison to monocyclic arene analogues.

Supramolecular metal-organometallic coordination networks based on quinonoid pi-complexes.

The use of organometallic pi-complexes in the coordination-directed self-assembly of polymeric structures is a new area with many potential applications. Supramolecular metal-organometallic coordination networks (MOMNs), which are described herein, consist of metal ion or metal cluster nodes connected by bifunctional "organometalloligands" that serve as spacers. The organometalloligand utilized in this work is the stable anionic complex (eta(4)-benzoquinone)Mn(CO)(3)(-) (p-QMTC), which binds through both quinone oxygen atoms to generate MOMNs having both backbone and pendant metal sites. In many cases the MOMNs are obtained as neutral and thermally stable solids, with molecular structures that depend on the geometrical and electronic requirements of the metal nodes, the solvent, and the presence of organic spacers. Redox-active quinone-based organometallic pi-complexes permit the construction of an impressive range of coordination network architectures and hold much promise for the development of functional materials.

A coordination network containing metal-organometallic secondary building units based on pi-bonded benzoquinone complexes.

In DMSO-MeOH solvent the complex [(eta 4-benzoquinone)Mn(CO)3]- (QMTC) reacts with Mn2+ ions to produce the coordination polymer (Mn2[(eta 4-benzoquinone)Mn(CO)3]4(DMSO))n, which consists of dimanganese secondary building units interconnected by QMTC spacers.

Metal-Mediated Self-Assembly of π-Bonded Benzoquinone Complexes into Polymers with Tunable Geometries.

Coordination of Mn(CO)3+ to the π system in hydroquinone facilitates proton loss to afford benzoquinone complexes. Subsequent σ coordination of the benzoquinone oxygen atoms to added metal ions results in neutral one-, two-, or three-dimensional quinoid polymers. The geometrical requirements of the metal ion and the presence of added "spacer" ligands dictate the type of polymer formed.

H-Bonding Interactions in the Epoxidation of Alkenylammonium Salts with Dimethyldioxirane and m-Chloroperbenzoic Acid: A Kinetic Study.

The epoxidation rate constants for the reaction of allylic and homoallylic primary and quaternary ammonium salts with DMDO (1b) and m-CPBA (2), as well as the stereochemical outcome of these reactions, were determined. The presence of an ionic functional group in the substrate complicates the kinetic study of the reaction. However, k(0) can be determined from the k(obs) values measured in solutions with different ionic strengths. The order of magnitude of the rate constants is the same for the epoxidation of primary and quaternary homoallylic ammonium salts, while primary allylic ammonium salts react more than 10 times faster than their quaternary counterparts. High syn-diastereoselectivity is achieved in the epoxidation of the primary allylic salt 3aH(+)() while the quaternary allylic ammonium salt 5a(+)() gives equimolecular (m-CPBA) or predominantly anti(DMDO) mixtures of diastereomers. These results are consistent with the existence of hydrogen bond interaction between the protic substrates and the oxidant.