Multiple intra-molecular hydrogen bonds in 2,4-di-tert-butyl-6-[N-(2,6- diisopropylphenyl)-P,P-diphenylphosphorimidoyl]phenol

Article abstract of DOI:10.1107/S0108270111009267

The title compound, C₃₈H₄₈NOP, isolated from the reaction of (2-diphenyl-phosphanyl-4,6-di-tert-butyl)phenol with 2,6-di-iso-propyl-phenyl -azide at 273 K, can act as an N,O-bidentate ligand. Crystal structure analysis shows a deviat

Full text of DOI:10.1107/S0108270111009267

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
and tert-butyl groups on the phenol unit. As part of our efforts
in the development and structural studies of these molecules,
we report the synthesis and X-ray crystal structure of (I),
supported by density functional theory (DFT) calculations.
ISSN 0108-2701
Multiple intramolecular hydrogen
bonds in 2,4-di-tert-butyl-6-[N-(2,6-
diisopropylphenyl)-P,P-diphenyl-
phosphorimidoyl]phenol
Jong-Dae Lee,a Il-Hwan Suhb and Sang Ook Kangc*
aDepartment of Chemistry, College of Natural Sciences, Chosun University, Gwangju
501-759, Republic of Korea, bReSEAT Program, Korea Institute of Science and
Technology Information, 335 Eoeun-dong, Yuseong-gu, Daejeon 305-806, Republic
of Korea, and cDepartment of Advanced Materials Chemistry, Korea University,
Sejong Campus, Chungnam 339-700, Republic of Korea
Correspondence e-mail: sangok@korea.ac.kr
Received 30 January 2011
Accepted 10 March 2011
Online 12 April 2011
The title compound, C38H48NOP, isolated from the reaction of
(2-diphenylphosphanyl-4,6-di-tert-butyl)phenol with 2,6-diiso-
propylphenyl azide at 273 K, can act as an N,O-bidentate
ligand. Crystal structure analysis shows a deviation from ideal
tetrahedral symmetry around the P atom. The molecule exists
as a monomer in the solid state, whose conformation is
stabilized via multiple intramolecular hydrogen bonds.
Geometric parameters from both experimental and theore-
tical calculations are compared.
As shown in Fig. 1 and Table 1, compound (I) has five
intramolecular hydrogen bonds. The strong O1—H1Á Á ÁN1
˚
hydrogen-bond OÁ Á ÁN distance of 2.601 (2) A is in good
Comment
The search for nonmetallocene transition metal complexes to
catalyse olefin polymerization has resulted in a wide range of
new catalysts based on new or known ancillary ligands
(Hlatky, 2000; Gibson & Spitzmesser, 2003). In recent years,
there has been considerable and growing interest in the
coordination chemistry of sterically hindered phosphinimine
and phosphiniminate complexes (Masuda et al., 2003; Cristau
et al., 2002; Said et al., 2001). Among these, titanium
complexes bearing phosphinimide ligands have been shown by
Stephan et al. (2003) to be highly active ethylene poly-
merization catalysts. At the same time, Fujita and co-workers
(Mitani et al., 2002, 2003) developed a series of group IV metal
complexes containing bis(phenoxyimine) ligands, and these
complexes have proved to be excellent precatalysts for olefin
polymerization. Subsequently, Zhang and co-workers (Qi et
al., 2005; Qi & Zhang, 2006) reported that group IV metal
complexes with phenoxy–phosphinimine ligands reacted
similarly. Intrigued by the possibility that increasing the bulk
of the N-containing substituents could improve catalytic
activity, we investigated the use of the title compound, (I),
containing the bulky 2,6-diisopropylphenyl group on atom N1
Figure 1
The molecular structure of (I), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 30% probability level, and H
atoms (except for H1, H12C, H14C, H33 and H36) and the minor
component of the disordered tert-butyl group have been omitted for
clarity. Dashed lines indicate intramolecular hydrogen bonds.
Acta Cryst. (2011). C67, o151–o153
doi:10.1107/S0108270111009267
# 2011 International Union of Crystallography o151

organic compounds
˚
agreement with the values of 2.580 (6) and 2.619 (6) A
reported for (1Z,3Z)-1,4-di(pyridin-2-yl)buta-1,3-diene-2,3-
˚
´
diol (Osmiałowski et al., 2002), and 2.600 (2) and 2.540 (2) A
in bis[2-(2-hydroxy-3-methoxybenzylideneamino)phenolato-
the calculation of total energy. The calculations were carried
out using the B3LYP/6-31+G(d) level of theory. As shown in
Table 2, the atomic bond lengths including P calculated by
DFT are slightly longer than those from the X-ray data, and it
may safely be said that all the rest are similar. However,
improved agreement might be obtained if still higher level
basis sets were used, at the expense of additional computa-
tional time.
¨
ꢀO]dimethylsilane (Bohme & Fels, 2010). The six-membered
N1/P1/C2/C1/O1/H1 ring, containing the phosphinimine unit
and the O1—H1Á Á ÁN1 hydrogen bond, is planar to within
˚
0.042 (1) A and nearly coplanar with the phenoxy ring, with a
dihedral angle of 2.9 (3)ꢀ. The remainder of the hydrogen
bonds are weak and occur between the heteroatoms (O1 and
N1) and the alkyl substituents [C—H of –C(CH3)3 and
–CH(CH3)2] of the aromatic rings, with CÁ Á ÁO distances
Experimental
2,4-Di-tert-butyl-6-[N-(2,6-diisopropylphenyl)-P,P-diphenylphosphor-
imidoyl]phenol, (I), was obtained in a two-step synthesis, as indicated
in the reaction scheme in the Comment.
˚
varying from 2.912 (3) to 3.021 (3) A. These hydrogen bonds
appear to play an important role in controlling the molecular
conformation of (I). Presumably, the additional steric
requirement of the bulky 2,6-diisopropylphenyl substituent
prevents the formation of intermolecular hydrogen bonds. In
For the preparation of (I), a solution of 2,6-diisopropylphenyl
azide (0.61 g, 3 mmol) in tetrahydrofuran (THF, 10 ml) was added
dropwise to a solution of 4,6-di-tert-butyl-2-(diphenylphosphanyl)-
phenol (1.17 g, 3 mmol) in THF (10 ml) at 273 K and the resulting
mixture stirred for 12 h at room temperature. The solvent was
evaporated and a crude product obtained. Pure pale-yellow crystals
of (I) were obtained after recrystallization from toluene at 263 K and
these were dried in vacuo (yield 87%; m.p. 356–358 K). Analysis
found: C 80.69, H 8.54, N 2.51%; calculated for C38H48NOP: C 80.67,
H 8.55, N 2.48%.
i
˚
fact, the closest intermolecular contact [O1Á Á ÁH10A = 2.88 A;
symmetry code: (i) x + 1, y, z] suggests that the molecular
packing of (I) is governed only by van der Waals forces. There
are also no significant intermolecular ꢁ–ꢁ interactions in the
structure as the shortest centroid–centroid distance between
˚
any parallel phenyl rings is greater than 5 A. Examination of
the structure with PLATON (Spek, 2009) showed that there
are solvent-accessible voids in the crystal structure.
Crystal data
C38H48NOP
Mr = 565.74
Triclinic, P1
a = 9.4999 (15) A
b = 11.9323 (19) A
˚
c = 15.247 (3) A
ꢂ = 88.658 (3)ꢀ
ꢃ = 76.925 (3)ꢀ
ꢄ = 89.380 (3)ꢀ
3
˚
The P1 N1 bond distance in (I) [1.5826 (18) A] is similar
˚
to the value of 1.592 (2) A in 2-methoxy-3-methyl-6-[(tri-
phenylphosphoranylidene)amino]pyrimidin-4(3H)-one and
˚
V = 1683.0 (5) A
Z = 2
˚
Mo Kꢂ radiation
ꢅ = 0.11 mmÀ1
T = 293 K
0.40 Â 0.10 Â 0.10 mm
˚
1.588 (2) A in 3-methyl-2-methylthio-6-[(triphenylphosphor-
˚
anylidene)amino]pyrimidin-4(3H)-one (Low et al., 1998).
Recently, however, Hayes and co-workers reported a 4,6-
bis[N-(2,4,6-trimethylphenyl)-P,P-diphenylphosphorimidoyl]-
dibenzofuran system, and this compound displayed a signifi-
cant difference in the P N bond distances [1.549 (1) and
Data collection
Bruker SMART 1000 CCD area-
detector diffractometer
Absorption correction: integration
(SADABS; Sheldrick, 2008)
Tmin = 0.957, Tmax = 0.989
22883 measured reflections
8349 independent reflections
4194 reflections with I > 2ꢆ(I)
Rint = 0.053
˚
1.565 (1) A; Ireland et al., 2010]. In comparison with the
structure of (I), the P N bonds of the dibenzofuran system
are shortened as a result of the presence of sterically less
hindered methyl groups instead of isopropyl groups on the
phenyl ring attached to the phosphinimine N atom. As shown
in Table 2 and Fig. 1, the range of angles around the P1 atom
[104.92 (9)–115.89 (10)ꢀ] in (I) indicates a distorted tetra-
hedral geometry. These values are similar to the range of
105.50 (9)–118.22 (13)ꢀ observed in the pyrimidinone com-
pounds (Low et al., 1998). The dibenzofuran compound also
shows comparable bond angles [100.54 (7)–116.31 (7)ꢀ;
Ireland et al., 2010] around the P center even in the absence of
strain.
Refinement
R[F2 > 2ꢆ(F2)] = 0.052
wR(F2) = 0.157
S = 1.02
8349 reflections
420 parameters
H atoms treated by a mixture of
independent and constrained
refinement
À3
˚
Áꢇmax = 0.24 e A
Áꢇmin = À0.38 e A
À3
˚
One of the tert-butyl groups is disordered over two orientations.
Two positions were defined for the methyl groups at atoms C8, C9,
and C10 and the site-occupation factors of the two orientations were
constrained to sum to unity. The major orientation (atom labels with
the suffix ‘A’) has an occupation of 0.619 (12). All C—C bonds
involving the disordered C atoms were restrained to a similar length
All four aromatic rings of (I) are planar, with a maximum
˚
deviation of 0.027 (2) A for atom C27 from the least-squares
plane defined by atoms C27–C32. The phenoxy ring is almost
perpendicular to the C21–C26 phenyl ring attached to atom
P1, with a dihedral angle of 89.48 (7)ꢀ, and the dihedral angle
between the C15–C20 phenyl ring attached to atom P1 and the
C27–C32 phenyl ring attached to atom N1 is 42.21 (10)ꢀ.
A molecular orbital calculation was performed using the
GAUSSIAN03 package (Frisch et al., 2004). The geometries
obtained from the X-ray analysis were used in the input file for
˚
within a tolerance s.u. value of 0.005 A.
Aromatic H atoms were included in the model in idealized sp2
˚
geometries, with C—H = 0.93 A and with Uiso(H) = 1.2Ueq(C).
Methyl H atoms were included in the model in sp3 geometries found
˚
from difference Fourier syntheses, with C—H = 0.96 A and with
Uiso(H) = 1.5Ueq(C). The remaining H atoms (H1, H33 and H36)
were found in an electron-density difference map and were allowed
to refine both positionally and isotropically. The final difference map
ꢁ
o152 Lee et al. C38H48NOP
Acta Cryst. (2011). C67, o151–o153

organic compounds
Table 1
Hydrogen-bond geometry (A, ).
ORTEP-3 for Windows (Farrugia, 1997); software used to prepare
material for publication: SHELXL97.
ꢀ
˚
D—HÁ Á ÁA
D—H
HÁ Á ÁA
DÁ Á ÁA
D—HÁ Á ÁA
This work was supported by a Korea University grant in
2010.
O1—H1Á Á ÁN1
0.99 (3)
0.96
0.96
1.03 (2)
0.96 (2)
1.63 (3)
2.38
2.31
2.52 (2)
2.48 (2)
2.601 (2)
3.021 (3)
2.948 (3)
2.912 (3)
2.935 (3)
163 (2)
124
123
101.6 (15)
109.0 (15)
C12—H12CÁ Á ÁO1
C14—H14CÁ Á ÁO1
C33—H33Á Á ÁN1
C36—H36Á Á ÁN1
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: FN3077). Services for accessing these data are
described at the back of the journal.
Table 2
Comparison of selected geometric parameters (A, ) with those derived
from DFT calculations.
ꢀ
˚
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Lee et al. C38H48NOP o153