aromatic compounds. In this chapter, we have shown that it is possible to differentiate between aromatic and antiaromatic planar conjugated rings by analyzing
how the crossed delocalization terms changes when adding or removing a pair of
electrons. Using multicenter electron delocalization measures, we have verified the
4n Baird rule, although our results have been inconclusive about the validity of
Soncini-Fowler’s extension of Baird’s rule. We have also confirmed the validity of
the 2(n + 1)
2 and 2n
2 + 2n + 1 (S = n + ½) rules of spherical aromaticity for closed
and open-shell species, respectively. Finally, we have shown the existence of a
connection between the 4n + 2 Hückel rule for two-dimensional aromaticity in
planar conjugated rings and the 4n + 2 Wade-Mingos rule for three-dimensional
aromaticity in boranes.
Acknowledgments This work has been supported by the Ministerio de Economía y
Competitividad (MINECO) of Spain (Projects CTQ2014-54306-P and CTQ2013-41236-ERC) and
the Generalitat de Catalunya (project 2014SGR931, Xarxa de Referència en Química Teòrica i
Computacional, and ICREA Academia 2014 prize for M.S.). F.F. acknowledges financial support
of the Beatriu de Pinós programme from AGAUR for the postdoctoral grants BP_A_00339 and
BP_A2_00022. The EU under the Marie Curie Career Integration grant PCI09-GA-2011-294240
(E.M.) and the FEDER grant UNGI10-4E-801 (European Fund for Regional Development) have
also funded this research.
References
1. Li X, Kuznetsov AE, Zhang H-F, Boldyrev A, Wang L-S (2001) Observation of all-metal
aromatic molecules. Science 291:859–861
2. Zhai H-J, Averkiev BB, Zubarev DY, Wang L-S, Boldyrev AI (2007) δ Aromaticity in
[Ta 3 O 3 ]
−
. Angew Chem Int Ed 46:4277–4280
3. Boldyrev AI, Wang L-S (2005) All-metal aromaticity and antiaromaticity. Chem Rev
105:3716–3757
4. Feixas F, Matito E, Poater J, Solà M (2013) Metalloaromaticity. WIREs Comput Mol Sci
3:105–122
5. Tsipis CA (2005) DFT study of “all-metal” aromatic compounds. Coord Chem Rev 249:2740–
2762
6. Jiménez-Halla JOC, Matito E, Robles J, Solà M (2006) Nucleus-independent chemical shift
(NICS) profiles in a series of monocyclic planar inorganic compounds. J Organomet Chem
691:4359–4366
7. Stanger A (2006) Nucleus-independent chemical shifts (NICS): distance dependence and
revised criteria for aromaticity and antiaromaticity. J Org Chem 71:883–893
8. Schleyer PvR, Manoharan M, Wang ZX, Kiran B, Jiao HJ, Puchta R, van Eikema
Hommes NJR (2001) Dissected nucleus-independent chemical shift analysis of π-aromaticity
and antiaromaticity. Org Lett 3:2465–2468
9. Poater J, Fradera X, Duran M, Solà M (2003) The delocalization index as an electronic
aromaticity criterion. Application to a series of planar polycyclic aromatic hydrocarbons.
Chem Eur J 9:400–406
10. Matito E, Duran M, Solà M (2005) The aromatic fluctuation index (FLU): a new aromaticity
index based on electron delocalization. J Chem Phys 122:014109; Erratum íbid.(2006)
125:059901
332
F. Feixas et al.
how the crossed delocalization terms changes when adding or removing a pair of
electrons. Using multicenter electron delocalization measures, we have verified the
4n Baird rule, although our results have been inconclusive about the validity of
Soncini-Fowler’s extension of Baird’s rule. We have also confirmed the validity of
the 2(n + 1)
2 and 2n
2 + 2n + 1 (S = n + ½) rules of spherical aromaticity for closed
and open-shell species, respectively. Finally, we have shown the existence of a
connection between the 4n + 2 Hückel rule for two-dimensional aromaticity in
planar conjugated rings and the 4n + 2 Wade-Mingos rule for three-dimensional
aromaticity in boranes.
Acknowledgments This work has been supported by the Ministerio de Economía y
Competitividad (MINECO) of Spain (Projects CTQ2014-54306-P and CTQ2013-41236-ERC) and
the Generalitat de Catalunya (project 2014SGR931, Xarxa de Referència en Química Teòrica i
Computacional, and ICREA Academia 2014 prize for M.S.). F.F. acknowledges financial support
of the Beatriu de Pinós programme from AGAUR for the postdoctoral grants BP_A_00339 and
BP_A2_00022. The EU under the Marie Curie Career Integration grant PCI09-GA-2011-294240
(E.M.) and the FEDER grant UNGI10-4E-801 (European Fund for Regional Development) have
also funded this research.
References
1. Li X, Kuznetsov AE, Zhang H-F, Boldyrev A, Wang L-S (2001) Observation of all-metal
aromatic molecules. Science 291:859–861
2. Zhai H-J, Averkiev BB, Zubarev DY, Wang L-S, Boldyrev AI (2007) δ Aromaticity in
[Ta 3 O 3 ]
−
. Angew Chem Int Ed 46:4277–4280
3. Boldyrev AI, Wang L-S (2005) All-metal aromaticity and antiaromaticity. Chem Rev
105:3716–3757
4. Feixas F, Matito E, Poater J, Solà M (2013) Metalloaromaticity. WIREs Comput Mol Sci
3:105–122
5. Tsipis CA (2005) DFT study of “all-metal” aromatic compounds. Coord Chem Rev 249:2740–
2762
6. Jiménez-Halla JOC, Matito E, Robles J, Solà M (2006) Nucleus-independent chemical shift
(NICS) profiles in a series of monocyclic planar inorganic compounds. J Organomet Chem
691:4359–4366
7. Stanger A (2006) Nucleus-independent chemical shifts (NICS): distance dependence and
revised criteria for aromaticity and antiaromaticity. J Org Chem 71:883–893
8. Schleyer PvR, Manoharan M, Wang ZX, Kiran B, Jiao HJ, Puchta R, van Eikema
Hommes NJR (2001) Dissected nucleus-independent chemical shift analysis of π-aromaticity
and antiaromaticity. Org Lett 3:2465–2468
9. Poater J, Fradera X, Duran M, Solà M (2003) The delocalization index as an electronic
aromaticity criterion. Application to a series of planar polycyclic aromatic hydrocarbons.
Chem Eur J 9:400–406
10. Matito E, Duran M, Solà M (2005) The aromatic fluctuation index (FLU): a new aromaticity
index based on electron delocalization. J Chem Phys 122:014109; Erratum íbid.(2006)
125:059901
332
F. Feixas et al.