Mechanistic and Synthetic Organic/Organometallic Chemistry

Areas of current research emphasis:

Carbocations; arenium ions; onium ions; superacid chemistry and catalysis; organofluorine and organophosphorus chemistry; cyclophanes; annulenes; multinuclear and 2D-NMR; electrophilic aromatic substitution; synthetic methods and applications specially in superacid media; chemistry in ionic liquids; host-guest chemistry and molecular recognition in solution (NMR) and in the gas phase (mass spectrometry); cation/molecule cluster ions; computational chemistry (semi-empirical, ab initio, DFT, GIAO-NMR) as adjunct to experiment.

Research in the Laali laboratory focuses on multifaceted projects which combine (to various degrees) synthetic, structural/mechanistic, spectroscopic, and theoretical approaches to solving diverse problems in organic chemistry. Several projects are in biological chemistry and materials chemistry focus areas.

a) Biological electrophiles in particular carbocations derived from Polycyclic Aromatic Hydrocarbons (PAHs): Emphasis is on direct studies of model persistent carbocations derived from various classes of PAHs with varied degrees of biological activity. These projects combine synthetic chemistry with superacid chemistry and modern NMR techniques. In most cases theory is applied as adjunct to experimental work. Work in this category is being extended to Hetero-PAHs (X = N, S) in projects that emphasize both mechanistic carcinogenesis (focusing on the electrophilic intermediates in particular carbocations) and the PAH-onium salts (for example azonium salts from aza-PAH) as anti-cancer agents that intercalate into DNA.

b) Novel organic conducting materials: Work under this umbrella brings together cyclophane chemistry, carbocation/onium ion chemistry and organofluorine chemistry to tailor projects in materials chemistry and self-assembly. Fluorinated cyclophanes, janusenes, and onium cations are the main building blocks for designing various assemblies. A major goal is to achieve extended charge delocalization within pi-stacks in rigid cyclophanes. A current joint program focuses on synthesis of cyclophane-based liquid crystals LCs and discotic LCs.

c) “Green Chemistry”: Utility of “Ionic Liquids” as environmentally friendly solvents and as Lewis acid in fundamentally important synthetic transformations of industrial importance. Recent published studies from this laboratory have emphasized aromatic nitration and fluorination.

d) Organophosphorus Chemistry: Utilizing phosphaalkynes and phosphaalkene as building blocks for novel cations and molecules: Research in this category focuses on electrophilic and cycloaddition chemistry of kinetically stabilized phosphaalkynes and their cyclooligomers, such as tetraphosphacubane, metal-complexed phosphaalkenes, and on multinuclear NMR and structural studies of novel phosphonium ions derived from phosphaalkynes, tetraphosphacubanes and phosphirenes. Joint projects focusing on the gas phase synthesis and ion-molecule reactions of novel P/C cations are also available.

e) Molecular Recognition and Guest-Host (HG) chemistry: Non-covalent forces in particular cation-pi and pi-pi interactions are exploited to create host-guest complexes. Electrospray Mass Spectrometry and NMR are used to detect the formation of cation-molecule cluster ions and to probe HG interactions. Current projects focus on PAH/metal ions, calixarenes/onium ions, crown-ethers/onium ions.

Selected Publications

1. Laali, Kenneth K.; Chun, Joong-Hyun; Okazaki, Takao; Kumar, Subodh; Borosky, Gabriela L.; Swartz, Carol. Electrophilic Chemistry of Thia-PAHs: Stable Carbocations (NMR and DFT), S-Alkylated Onium Salts, Model Electrophilic Substitutions (Nitration and Bromination), and Mutagenicity Assay. Journal of Organic Chemistry (2007), 72(22), 8383-8393.

2. Laali, Kenneth K.; Arrica, Maria A.; Okazaki, Takao; Harvey, Ronald G. Substituent Effects in Benz[a]anthracene Carbocations: A Stable Ion, Electrophilic Substitution (Nitration, Bromination), and DFT Study. Journal of Organic Chemistry, (2007), 72, 6786-6775.

3. Laali, Kenneth K.; Okazaki, Takao; Bunge, Scott D. N-(Trifluoromethylsulfonyl)aryloxy-trifluoromethylsulfoximines [ArO-SO(CF3):NTf] and N-Aryltriflimides Ar-N(Tf)2 by Thermal and Photolytic Dediazoniation of [ArN2][BF4] in [BMIM][Tf2N] Ionic Liquid: Exploiting the Ambident Nucleophilic Character of a "Nonnucleophilic" Anion. Journal of Organic Chemistry (2007) , 72, 6758-6762.

4. Okazaki , Takao; Laali, Kenneth K. Intermediates of Halogen Addition to Phenylethynes and Protonation of Phenylethynyl Halides. Open Halovinyl Cations, Bridged Halonium, or Phenyl-Bridged Ions: A Substituent Effect Study by DFT and GIAO-DFT. Journal of Organic Chemistry (2006), 71(26), 9643-9650.

5. Brule, Cedric; Holmer, Stephanie; Krechanin, Seth; Laali, Kenneth K. Sterically crowded azulene-based dication salts as novel guests: synthesis and complexation studies with crown ethers and calixarenes in solution and in the gas phase. Organic & Biomolecular Chemistry (2006), 4(16), 3077-3084.

6. Laali, Kenneth K.; Hupertz, Scott; Temu, Alice G.; Galembeck, Sergio E. Electrospray mass spectrometric and DFT study of substituent effects in Ag + complexation to polycyclic aromatic hydrocarbons (PAHs). Organic & Biomolecular Chemistry (2005), 3(12), 2319-2326

7. Laali, Kenneth K.; Sarca, Viorel D.; Okazaki, Takao; Brock, Aaron; Der, Paul. Triflic acid-catalyzed adamantylation of aromatics in [BMIM][OTf] ionic liquid; synthetic scope and mechanistic insight. Organic & Biomolecular Chemistry (2005), 3(6), 1034-1042.

8. Esteves, Pierre M.; Laali, Kenneth K.. In Search of Phosphavinyl Cations: A DFT Study of Electrophilic Attack on Phosphaacetylenes. Organometallics (2004), 23, 3701-3713

9. Okazaki, Takao; Laali, Kenneth K.; Zajc, Barbara; Lakshman, Mahesh K.; Kumar, Subodh; Baird, William M.; Dashwood, Wan-Mohaiza. Stable ion study of benzo[a]pyrene (BaP) derivatives: 7,8-dihydro-BaP, 9,10-dihydro-BaP and its 6-halo derivatives, 1- and 3-methoxy-9,10-dihydro- BaP-7(8H)-one, as well as the proximate carcinogen BaP 7,8-dihydrodiol and its dibenzoate, combined with a comparative DNA binding study of regioisomeric (1-, 4-, 2-) pyrenylcarbinols. Organic & Biomolecular Chemistry (2003), 1(9), 1509-1516.

10. Laali, Kenneth K.; Okazaki, Takao. NMR of persistent carbocations from polycyclic aromatic hydrocarbons (PAHs). Annual Reports on NMR Spectroscopy (2002), 47 149-214.