Dwight A. Sweigart

Electrophilic reactivity of coordinated cyclic π-hydrocarbons

Abstract A large number of transition metal complexes are known that contain cyclic π -hydrocarbon ligands. In many cases, coordination to the metal imparts significant electrophilic character to the hydrocarbon. In this review, the electrophilic properties of cyclic dienyl and triene complexes are examined. Featured reactions with nucleophiles include (1) single and double addition to the coordinated ring, (2) substitution of a ring substituent, e.g. chloride, (3) deprotonation of the coordinated ring or a side chain, (4) ligand substitution and (5) single electron transfer. The mechanistic aspects of these reactions are discussed with regard to electrophilic and nucleophilic reactivity, regiochemistry, stereochemistry, and detailed reaction pathways. The mechanistic principles are illustrated by selected synthetic applications.

Synthesis and electrophilic reactivity of dicarbonylnitrosyl(cyclohexadienyl)manganese cations: double nucleophilic addition to coordinated arenes

Synthese des cations (cyclohexadienyl)Mn(CO)(NO)L + par traitement de (cyclohexadienyl)Mn(CO) 2 L (L=CO, PBu 3 ) avec NOPF 6 . Mecanisme des reactions de ces cations avec les nucleophiles

A coordination network containing metal–organometallic secondary building units based on π-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.

Incorporation of Fe3O4 Nanoparticles into Organometallic Coordination Polymers by Nanoparticle Surface Modification

Surface-modified Fe(3)O(4) nanoparticles (NPs) can be obtained by substituting [(eta(5)-semiquinone)Mn(CO)(3)] for oleylamine surface protecting groups. The resulting NP can function as a nucleus or template to generate crystalline coordination polymers that contain superparamagnetic Fe(3)O(4) NPs. Hybridized magnetic properties can be obtained by introducing paramagnetic metal nodes, such as Mn(2+), into the polymers (see picture).

π-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 π-bonded η6-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 η5-semiquinone and η4-quinone complexes have been used to synthesize one- two- and three-dimensional polymeric metal–organometallic coordination networks. With rhodium as the metal, the π-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 π-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.

η6-Hydroquinone and catechol complexes of manganese tricarbonyl. 0olecular structure of [(η6-hydroquinone) Mn(CO)3]2SiF6

Abstract The reaction of ( η 6 -acenaphthene)Mn(CO) 3 + with hydroquinone and catechol affords the stable π-bonded complexes ( η 6 -hydroquinone)Mn(CO) 3 + ( 1 ) and ( η 6 -catechol)Mn(CO) 3 + ( 2 ). The X-ray structure of [ 1 ] 2 SiF 6 shows an approximately planar arene ligand with the -OH substituents strongly hydrogen bonded to fluorine atoms in the SiF 6 2− anion. Deprotonation of 1 and 2 by NEt 3 yields the corresponding π-bonded semiquinone complexes.

Dependence of the electrophilicity of coordinated cyclic π-hydrocarbons on the metal in the chromium, manganese, and iron triads

Abstract Phosphorus nucleophiles rapidly add to the coordinated arene in [(arene-M(CO) 3 ] + (M = Mn, Re) and [(arene) 2 M] 2+ (M = Fe, Ru, Os). Kinetic data for these reactions are reported. It is suggested that π-bonding is important in determining the dependence of the coordinated ring electrophilicity on the metal within a given triad. The relationship between ring activation and reduction potential of the organometallic electrophile is discussed. It is shown that phosphites as compared to phosphines are much more reactive towards a metal centered electrophile than towards a carbon electrophile

Physically Separated References for Diffusion Coefficient-Formula Weight (D-FW) Analysis of Diffusion-Ordered NMR Spectroscopy (DOSY) in Water

Development and application of physically separated references for aqueous (1)H DOSY diffusion coefficient-formula weight (D-FW) correlation analysis is reported. Commercially available biological buffers (Tris and HEPES) and a water-soluble alcohol (tert-butanol) were used as physically separated references for a Ru and a Mn complex in D(2)O. This extension of DOSY D-FW analysis expands its applicability to a wide variety of water-soluble molecules or metal complexes, with particular application to green chemistry.

The synthesis and electrophilic reactivity of manganese tricarbonyl complexes of the C-ring aromatic diterpenoid methyl O-methylpodocarpate

Abstract The aromatic ring in the diterpenoid methyl O -methylpodocarpate (podo) coordinates readily to the Mn(CO) 3 + moiety to afford in high yield a nearly 1:1 isometric distribution of [( η 6 -podo)Mn(CO) 3 ] BF 4 ([ 2 ]BF 4 ), in which the metal is situated on the α or β face. The nucleophiles PhLi, PhMgBr, MeLi, MeMgCl, LiCH 2 C(O)CMe 3 and NaBH 4 were found to add cleanly to the activated aromatic ring in 2 + to give neutral cyclohexadienyl complexes. Nucleophilic addition occurs predominantly meta to the OMe substituent in the case of the α-isomer of 2 + , and at both ortho and meta sites in the case of the β-isomer. The X-ray structure is reported for a typical α- meta and a typical β- ortho cyclohexadienyl product, namely β -( η 5 -podo · Ph)Mn(CO) 3 and α -( η 5 -podo · CH 2 C(O)CMe 3 )Mn(CO) 3 . The high yield and regioselectivity of the nucleophilic additions suggests that the manganese-mediated functionalization of aromatic diterpenes and steroids will prove to provide a useful synthetic methodology.

Manganese-mediated synthesis of cis-disubstituted cyclohexadienes via double nucleophilic addition to coordinated arenes

Abstract The addition of carbon donor nucleophiles to (arene)Mn(CO) 2 L + (L=CO, P(OPh) 3 , PMe 3 ), followed by replacement of a CO with NO + , affords monofunctionalized (cyclohexadienyl)Mn(CO)(NO)L + complexes ( 12 ). A study has been made of nucleophilic addition to 12 to yield cyclohexadiene complexes ( 13 ). The yield of the reaction of 12 with soft stabilized carbon donors (e.g. NaCH(CO 2 Et)CN) improves substantially when the ligand LCO is replaced by LP(OPh) 3 or PMe 3 . Hydride donors give good yields of monofunctionalized cyclohexadiene complexes regardless of the nature of L. When L≠CO, significant chiral discrimination takes place and the product is obtained as a mixture of diastereomers. Oxidation of the (cyclohexadiene)Mn(CO)(NO)L complexes with FeCl 3 or Me 3 NO generates the free hydrocarbon ligand as cis -disubstituted cyclohexa-1,3-dienes or cyclohexen-1-ones, the latter resulting from hydrolysis of a methoxy substituent. Hard carbon donors such as LiPh and LiMe attack a CO in 12 , ultimately converting to trans -disubstituted cyclohexadienes. This work shows that the manganese- mediated double nucleophilic addition to arenes can be an efficient route to functionalized cyclohexadienes.