1. MICROWAVE SPECTRA, MOLECULAR STRUCTURE AND AROMATIC CHARACTER OF BN-NAPHTHALENE (4A,8A-AZABORANAPHTHALENE)
AARON M. PEJLOVAS, STEPHEN G. KUKOLICH, University of Arizona
ARTHUR J. ASHE III, University of Michigan,
ADAM M. DALY,
University of Arizona .
ISMS – 16 – P1531

2. B-N substitution in AROMATIC Molecules
How aromatic is AZABORINE?
S. Y. Liu – > OSU
PLANAR MOLECULE 0 = 0.02 amuÅ2
BOND LENGTH 1.45Å BETWEEN SINGLE AND DOUBLE BOND LENGTH
C) eqQ’s CONSISTENT WITH PARTIAL DELOCALIZATION of p ELECTRONS
Parameters for BN-NAPTHALENE
synthesis by A. J. Ashe 2014
PLANAR MOLECULE 0 = amuÅ2
B-N BOND 1.47(2) Å, BETWEEN SINGLE AND DOUBLE BOND LENGTH
C) eqQ’s CONSISTENT WITH PARTIAL DELOCALIZATION of p ELECTRONS 2 2 2

3.  Synthesis of BN-naphthalene.13
Allyltributylstannane and boron trichloride > diallylboron chloride
treat with diallylamine then trimethylamine > 1:1 addition product.
Ring closing produces the bicyclic BN-heterocycle.
React this with Pd-black > mixture of BN-naphthalene and BN-tetralin, separated by column chromatography on silica gel
a) BCl3 b) HN(C3H5)2 c) NEt3 d) cat. (Cy3P)2(PhCH)RuCl2 e) Pd black
13. Rohr, A. D.; Kampf, J. W.; Ashe, A. J., III Organometallics 2014, 33, 1318. 3 3

4.  Microwave Measurements
Flygare-Balle Spectrometer – Homodyne Detection, BN napthalene room temp
Isotopologues > normal with 10B, 11B, and all unique single 13C and the 15N (with 11B), in natural abundance
Measurements 3-11 GHz > 1982 Spectrometer
Measurements 2-3 GHz > BIG Spectrometer – 2011 > 48” dia. Mirrors, 35” diff. pump

5. Measured lines 2-11 GHz
Example transitions > 10B14N (129 pulsed beam cycles),
11B14N 13C4 or 13C12 (2436 pulsed beam cycles), and
11B15N (7803 pulsed beam cycles)

6. J′ Ka’ Kc’ F’ J″ Ka” Kc” F” obs o-c 1 1 1 3 0 0 0 2 3896.0701 0.0000
Measured rotational transitions for the 11B15N isotopologue.. Values shown are in MHz. Only A, B, and C were fit with these transitions.
J′ Ka’ Kc’ F’
J″ Ka” Kc” F”
obs
o-c
0.0000
0.0003
0.0025 6

7. Experimental and calculated parameters for (11B14N-naphthalene).
Basis sets - B3LYP/aug-cc-pVTZ, B3LYP/aug-cc-pVQZ, MP2/aug-cc-pVTZ
and B97D/aug-cc-pVTZ 7

8. Experimental and calculated parameters for (11B14N-naphthalene).
Basis sets - B3LYP/aug-cc-pVTZ, B3LYP/aug-cc-pVQZ, MP2/aug-cc-pVTZ
and B97D/aug-cc-pVTZ Azaborine shown for comparison 8

9.  Structure Fit
Inertial Defect Δ = amu Å2 , so planar structure and C2v symmetry assumed
10 variable parameters describing relative positions (cartesian coordinates) of heavy atoms
H atom coordinates relative to bonded atom from B3LYP calculation
The standard deviation for the structure fit was MHz
Uncertainties in heavy atom coordinates > ±0.005 Å. 9 9

10.  Structure and Atom Cooridinates
a (calc.)
b (calc.)
a (exp.)
b (exp.)
Krait-|a|
Krait-|b| C1
-2.390
-0.741
-2.400
-0.743
2.397(7)
0.743(2) C2
-1.188
-1.369
-1.203
-1.373
1.193(1)
1.372(1) C3
-1.371
1.461
-1.354
1.466
1.376(1)
1.464(1) C4
-2.490
0.681
-2.499
0.689
2.496(8)
0.684(2)
B17
0.000
0.806
0.796
0.279(5)
0.795(2)
N18
-0.669
-0.674
0.08*i(2)
0.675(2) 10 10

11. r(B-N) Interatomic Distances Microwave Fit Value (Å)
 Comparison of B-N bond distances for BN-naphthalene and other molecules with the B-N bond.
 The B-N bond lengths agree where there is -donation from the N p- orbital to the empty p-orbital of B.
 This results in some double bond character which shortens the bond length.
r(B-N) Interatomic Distances
Microwave Fit Value (Å)
Calculated Value (Å)
BN-naphthalenea
1.470
1.475
1,2-dihydro-azaborineb
1.45
1.437
BN-cyclohexenec -
1.40
H3NBF3d
1.59
BH3NH3e
1.6576
H2NBH2f
1.391
HCN-BF3g
2.47 11

12.  Quadrupole Coupling & Townes-Dailey analysis -(Stew Novick slide)
Extended Towned-Dailey analysis of Azaborine by Novick
(S. E. Novick, J. Mol. Spectrosc. 267, (2011), 13–18)
NITROGEN populations of the sp2 and 2pz orbitals in azaborine.
STO-3G
npz
1.00
1.20
1.40
1.50
1.60
2.00
1.58
ng1 (nH)
0.91
1.11
1.31
1.41
1.51
1.91
1.28
ng2 + ng3 (nC+nB)
1.76
2.16
2.56
2.76
2.96
3.76
2.52
ntotal about N
4.47
5.27
5.67
6.07
7.67
5.38
Occupations
Townes-Dailey
NBO
N (pz)
1.3
1.4
1.45
NB (sp2)
1.5
1.6
NC+NC (sp2)
2.3
2.5
2.6
Ntotal
5.0
5.4
5.6
Charge
0.0
-0.43
-0.63
Electron orbital occupations for NITROGEN in BN-naphthalene > very similar to occupations for 1,2-dihydro-1,2-azaborine, which behaves very similar to other aromatic N-containing molecules such as pyrrole.
SIGNIFICANT AROMATIC CHARACTER for BN napthalene and Azaborine 12 12

13.  Quadrupole Coupling & Townes-Dailey analysis -(Stew Novick slide)
Extended Towned-Dailey analysis of Azaborine by Novick
(S. E. Novick, J. Mol. Spectrosc. 267, (2011), 13–18)
nitrogen electron populations of the sp2 and 2pz orbitals in azaborine.
STO-3G
npz
1.00
1.20
1.40
1.50
1.60
2.00
1.58
ng1 (nH)
0.91
1.11
1.31
1.41
1.51
1.91
1.28
ng2 + ng3 (nC+nB)
1.76
2.16
2.56
2.76
2.96
3.76
2.52
ntotal about N
4.47
5.27
5.67
6.07
7.67
5.38
Occupations
Townes-Dailey
NBO
N pz
1.3
1.4
1.45
NB (sp2)
1.5
1.6
NC+NC (sp2)
2.3
2.5
2.6
Ntotal
5.0
5.4
5.6
Charge
0.0
-0.43
-0.63
Electron orbital occupations for N in BN-naphthalene > very similar to occupations for 1,2-dihydro-1,2-azaborine, which behaves very similar to other aromatic N-containing molecules such as pyrrole.
SIGNIFICANT AROMATIC CHARACTER for BN napthalene and Azaborine 13 13

14.  Arthur Ashe III, UNIVERSITY of MICHIGAN
Acknowledgements:
 Arthur Ashe III, UNIVERSITY of MICHIGAN
 Lu Kang, KENNISAW STATE UNIVERSITY (for help with early measurements on this molecule
 N$F – We thank the National Science Foundation for Grants CHE , CHE 14 14

15. ISMS – 16 – P1531