Welcome Professor Lin to direct our group!

2 Self-introduction Name: Yulei.Hao Hometown: Shou County in Anhui Province Mother school: Hefei University of Technology 合肥工业大学 Grade: First-year graduate

σ-Aromaticity Review and σ-Aromaticity investigation of 3MRs transition metal alkylidene complexes Reportor: Yulei Hao Advisor: Jun Zhu

Introduction of σ-Aromaticity 1 Computed methods 2 Results and Discussion 3 Further work 4 4

Dewar firstly proposed the concept of σ- Aromaticity to explain the anomalous behavior of cyclopropane such as the upfield 1 HNMR chemical shift (1.25ppm to 0.22ppm), small difference of CSE (conventional strain energy) compared with cyclobutane, 27.5 kcal mol -1 and 26.5 kcal mol -1 respectively. He concluded that σ-Aromaticity energy compensate the high strain energy, and σ- ring induce the diamagnetic property. 5 Introduction of σ-Aromaticity 1 cyclopropane σ-Conjugation and σ-Aromaticity M. J. Dewar, Bull. Soc. Chim. Belg. 1979, 88, Figure1. Magnetic lines of force in cyclopropane.

6 Introduction of σ-Aromaticity 1 The two structure models of cyclopropane Walsh Coulson and Moffitt three trignal near-sp 2 methylene carbenes three bent C(sp 3 )-C(sp 3 )bonds

7 author concept Method or conclusion 1979Dewarσ-Aromaticity proposed σ-ring current and aromaticity energy 1985Cremer electron density and surface delocalization ab initio caculation 1996SchleyerNICS values absolute magnetic shieldings coputed at ring centers 2001Schleyer intrinsic bond energy evaluate ASE (11.3 kal.mol -1 ) 2002SchleyerISEsimple way to evaluation ASE 2005SchleyerECRE(extra cyclic resonance energy) evaluation ASE and correlated well with NICS 2007Folwerσ-ring current coupled Hatree-Fock "ipsocentric" 2009 Wu Wei and Schleyer VBSCF motheod, ECRE small σ-ASE (3.5 kal mol -1 ) Introduction of σ-Aromaticity 1 Table1. the deveiopment of cyclopropane of σ-Aromaticity and evaluation criteria.

8 J. Am. Chem. Soc. 1996, 118, Introduction of σ-Aromaticity 1 Theoretical Determination of Molecular Structure and Conformation Three-Membered Rings: Bent Bonds, Ring Strain, and Surface Delocalization J. Am. Chem. Soc. 1985, 107, 13, Nucleus-Independent Chemical Shifts: A Simple and Efficient Aromaticity Probe Is Cyclopropane Really the s-Aromatic Paradigm? Chem. Eur. J. 2009, Theoretical Bond Energies: A Critical Evaluation J. Phys. Chem. A 2001, 105, References: The ring current in cyclopropane Theor. Chem. Acc. 2007, 118, Recommendations for the Evaluation of Aromatic Stabilization Energies Org. Lett. 2002, 4, An Energetic Measure of Aromaticity andAntiaromaticity Basedon the Pauling–Wheland Resonance. Chem. Eur. J. 2006, 12,

9 Org. Lett.Vol. 2002, 4, Recommendations for the Evaluation of Aromatic Stabilization Energies ISE: isomeric stabilization energy The differences between a methyl derivative of the aromatic system and its nonaromatic exocyclic methylene isomer. Introduction of σ-Aromaticity 1

10 ECRE: extra cyclic resonance energy The RE (resonance energy) difference between a fully cyclic aromatic compound and appropriate acyclic model. Introduction of σ-Aromaticity 1 An Energetic Measure of Aromaticity and Antiaromaticity Based on the Pauling–Wheland Resonance. Chem. Eur. J. 2006, 12,

11 Introduction of σ-Aromaticity 1 a b Fig. 3 a Current density map for cyclopropane. b the sum of localised C–H bonds of the cyclopropane molecule. The current induced in the plane of the carbon nuclei by a perpendicular external magnetic field is calculated at the (CTOCD-DZ/ 6-31G**//RHF/6-31G**) level. The ring current in cyclopropane. Patrick W. Fowler Theor. Chem. Acc. 2007, 118,

12 Computed Methods 2 Opt DFT: B3LYP Base sets: 6-31G* and LanL2DZ NICS DFT: B3LYP Base sets: G** and LanL2DZ ASE DFT: B3LYP Base sets: 6-31G* and LanL2DZ

13 Results and Discussion 3

14 Results and Discussion 3

15 NICS(0)NICS(0) ZZ NICS(1) a NICS(1) ZZ b Table 2. NICS values [ppm] of non-metal rings1-3 and alkylidene compelexes rings a, b These are the average values of above and below center(0) 1Å. Results and Discussion 3

16 Results and Discussion 3 Fig. 4 Comparison of NICS(0) with NICS(1), and NICS(0) ZZ with NICS(1) ZZ based on the result in table 2. Benzene

17 Results and Discussion 3

18 Further work 4 Try to find other ways to evaluate σ-Aromaticity energy by VB. Explain the NICS results reasonably.

19 Thank you !