Structural tuning of the imido bonds in (Arylimido)vanadium(V) compounds

Article abstract of DOI:10.1246/cl.2007.1486

Structural characterization of (arylimido)vanadium(V) compounds was demonstrated to elucidate the ligand effect on the nature of the imido bonds. In the case of the triisopropoxide ligand, the nitrogen of the imido bond is suggested to possess an sp-hybridized character although the participation of an sp²-hybridized character is indicated with the imido nitrogen derived from the triethanolaminate ligand. Copyright

Full text of DOI:10.1246/cl.2007.1486

1486
Chemistry Letters Vol.36, No.12 (2007)
Structural Tuning of the Imido Bonds in (Arylimido)vanadium(V) Compounds
Toshiyuki Moriuchi,ꢀ Kenta Ishino, and Toshikazu Hiraoꢀ
Department of Applied Chemistry, Graduate School of Engineering,
Osaka University, Yamada-oka, Suita, Osaka 565-0871
(Received September 13, 2007; CL-071008; E-mail: hirao@chem.eng.osaka-u.ac.jp, moriuchi@chem.eng.osaka-u.ac.jp)
Structural characterization of (arylimido)vanadium(V) com-
and bridging isopropoxide ligands in apical positions, is formed
in the crystal packing. The V(1)–V(1ꢀ) internuclear distance of
˚
3.29 A indicates the absence of any bonding interaction between
pounds was demonstrated to elucidate the ligand effect on the
nature of the imido bonds. In the case of the triisopropoxide li-
gand, the nitrogen of the imido bond is suggested to possess
an sp-hybridized character although the participation of an
sp2-hybridized character is indicated with the imido nitrogen
derived from the triethanolaminate ligand.
ꢀ
˚
the metals. The axial V(1 )–O(1) bond is 0.36 A longer than the
equatorial V(1)–O(1) bond in the bridging isopropoxy group.
The long axial V–O distance trans to the imido ligand suggests
a weaker coordination. On the other hand, only one kind of iso-
1
propyl resonance was detected in the H NMR spectrum of 1a,
indicating that 1a appears to be monomeric in CD2Cl2. The
˚
Since the initial work of (imido)vanadium(V) complexes by
Preuss,1 Maatta,2 and Horton groups,3 (imido)vanadium(V)
complexes have been focused on, to design a catalyst for olefin
polymerization,4 C–H activation,3b,3c,5 and others1e,1f,6 because
the imido ligands are known to be a particularly suitable ligand
for stabilization of transition-metal complexes in high oxidation
states through extensive ligand-to-metal ꢀ donation.7 The steric
and electronic properties of vanadium centers are expected to be
influenced by coordination environment. We herein report the
structural tuning of the imido bonds in (arylimido)vanadium(v)
compounds.
The reaction of VO(OiPr)3 with 4-phenoxyphenyl isocya-
nate without solvent at 140 ꢁC afforded the (arylimido)vana-
dium(V) triisopropoxide 1a, [(C6H4–O–C6H4N)V(OiPr)3], in
76% yield. Structural characterization of 1a was performed by
the single-crystal X-ray structure determination as depicted in
Figure 1a.8 A dimeric structure, in which each vanadium atom
is coordinated in a trigonal-bipyramidal geometry with the imido
V(1)–N(1) distance of 1.673(2) A and the nearly linear V(1)–
N(1)–C(1) angle of 176.4(2)ꢁ suggest the nitrogen of the imido
bond to possess an sp-hybridized character. The twist angle ꢁ
defined as the angle between the least-squares plane of the
benzene ring and the C(ipso)–imido bond is considered to be
controlled by the imido bond. The almost perpendicular twist
angle ꢁ was observed in the case of 1a (94.97(8)ꢁ). These
results suggest that the nitrogen of the imido bond is closely
explained by an sp-hybridized character with a double V=N
bond and the lone pair of electrons might be localized in a nitro-
gen p orbital, which is likely to interact with metal ꢀ-acceptor
orbitals and aryl ꢀ orbitals.
The ligand effect was investigated more as follows. To pre-
vent the dimerization, triethanolamine was used as a basal ligand
which is expected to affect the nature of the imido moiety by
trans influence based on the donor ability of triethanolamine
nitrogen.9 The ligand exchange reaction of 1a with triethanol-
amine in CH2Cl2 at room temperature afforded the desired
O
O
R
R
O
O
O
O
O
O
O
O
O
O
N
N
N
N
N
N
V
V
V
V
V
V
N
N
N
O
O
O
O
O
O
O
O
2a: R = O
2b: R = O
1b
1a
3a: R = CH2
3b: R = CH2
(a)
(b)
O1
V1*
O1
N1
V1
N2
O2
C1
N1
O4
C1
V1 O1*
O3
O2
O3
O4
N
V
N
O
N
V
O
O
sp-hybridized nitrogen
sp2-hybridized nitrogen
ꢁ
˚
Figure 1. Molecular structure of (a) 1a and (b) 1b (hydrogen atoms are omitted for clarity). Selected bond lengths (A) and angles ( ):
1a; V(1)–N(1) 1.673(2), V(1)–O(1) 1.852(2), V(1)–O(2) 1.786(2), V(1)–O(3) 1.780(2), V(1)–O(1ꢀ) 2.213(2), C(1)–N(1) 1.380(3),
C(1)–N(1)–V(1) 176.4(2), N(1)–V(1)–O(1ꢀ) 173.17(8), 1b; V(1)–N(1) 1.682(4), V(1)–N(2) 2.216(3), V(1)–O(1) 1.829(4), V(1)–
O(2) 1.830(3), V(1)–O(3) 1.832(4), C(1)–N(1) 1.383(6), C(1)–N(1)–V(1) 167.0(3), N(1)–V(1)–N(2) 175.9(2).
Copyright Ó 2007 The Chemical Society of Japan

Chemistry Letters Vol.36, No.12 (2007)
1487
(arylimido)vanadium(V) triethanolaminate 1b, [(C6H4–O–C6-
H4N)V(TEA)], in 86% yield. The crystal structure of 1b
revealed the imido structure with the V(1)–N(1) distance of
References and Notes
1
a) F. Preuss, W. Towae, Z. Naturforsch., B 1981, 36, 1130. b)
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ꢁ
˚
1.682(4) A and the bent V(1)–N(1)–C(1) angle of 167.0(3) ,
Hausler, Z. Naturforsch., B 1987, 42, 881. d) F. Preuss, H.
¨
in which a monomeric structure with a pseudo-trigonal-
bipyramidal geometry around the metal center was observed
(Figure 1b).8 The vanadium atom is pulled out of the plane
formed by triethanolamine oxygen atoms in the direction of
the imido nitrogen. The three equatorial vanadium–oxygen bond
distances are statistically identical. The benzene ring of 1b is
close to parallel to the least-squares plane of the C(ipso)–imido
bond (ꢁ ¼ 27:8ð1Þꢁ). Furthermore, the longer imido bond and
more bent angle of 1b probably due to the donor ability of the
triethanolamine nitrogen were observed as compared with 1a.
From these results, the contribution of an sp2-hybridized charac-
ter is suggested in the case of the imido nitrogen of 1b, wherein
the filled imido ꢀ orbital seems to interact with aryl ꢀ orbitals.
The basal ligand was demonstrated to control the nature of the
imido bonds. Furthermore, the CH–ꢀ interaction between the
phenyl moiety of one molecule and the aryl moiety of another
molecule was observed to form the dimer in the crystal packing.
51V NMR measurements were performed in order to clarify
the electronic environment of the vanadium atoms. 51V chemical
shift of the triisopropoxide 1a in CD2Cl2 was observed at
ꢂ614 ppm. On the contrary, the triethanolaminate 1b showed
51V chemical shift at ꢂ310 ppm probably due to the donor
ability of the triethanolamine nitrogen.
The bimetallic (arylimido)vanadium(V) triisopropoxide 2a,
[(OiPr)3V(NC6H4–O–C6H4N)V(OiPr)3], connected by the oxy
spacer and 3a, [(iPrO)3V(NC6H4–CH2–C6H4N)V(OiPr)3], con-
nected by the methylene spacer could be obtained in 62% and
51% yields by the reaction with 4,40-oxybis(phenyl isocyanate)
or 4,40-methylenebis(phenyl isocyanate), respectively. The
bimetallic (arylimido)vanadium(V) triisopropoxide 2a and 3a
are suggested to be present as a monomeric structure in CD2Cl2
by the 1H NMR studies. The ligand-exchange reaction of 2a
and 3a with triethanolamine in CH2Cl2 at room temperature
led to the formation of the (arylimido)vanadium(V) triethanol-
aminates, [(TEA)V(NC6H4–O–C6H4N)V(TEA)] (2b) and
[(TEA)V(NC6H4–CH2–C6H4N)V(TEA)] (3b), in 90% and
94% yields, respectively. 51V chemical shifts of 2 and 3 (2a:
ꢂ617 ppm, 3a: ꢂ621 ppm, 2b: ꢂ312 ppm, 3b: ꢂ315 ppm) are
almost identical with the corresponding monomeric compound
1. These results indicate that the electronic environment around
the vanadium atoms of 2 and 3 are likely to be almost the same
as that of 1, suggesting no interaction between the vanadium
centers in solution.
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4
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8
a) D. E. Wigley in Progress in Inorganic Chemistry, ed. by
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Crystal data for 1a: C21H30N1O4V1, Mr ¼ 411:41, triclinic,
ꢀ
space group P1 (No. 2), a ¼ 9:1115ð7Þ, b ¼ 9:7377ð6Þ, c ¼
˚
14:1306ð9Þ A,
ꢂ ¼ 95:699ð2Þꢁ,
ꢁ ¼ 91:858ð3Þꢁ, ꢃ ¼
ꢁ
3
ꢁ
˚
113:789ð5Þ , V ¼ 1137:9ð1Þ A , Z ¼ 2, T ¼ 2:0 C, Dcalcd
¼
In conclusion, the (arylimido)vanadium(V) compounds
were synthesized and characterized structurally. The basal li-
gand was found to control the nature of the imido bonds. The
imido nitrogen of the triisopropoxide 1a depends on an sp-hybri-
dized character although the contribution of an sp2-hybridized
character was suggested in the case of the triethanolaminate
1b. Studies on the application of the (arylimido)vanadium(V)
complexes as a catalyst are now in progress.
1:201 g cmꢂ3, ꢄ(Mo Kꢂ) = 4.59 cmꢂ1
, Mo Kꢂ radiation
˚
(ꢅ ¼ 0:71069 A), R1 ¼ 0:052, wR2 ¼ 0:150. CCDC-656969
for 1a. Crystal data for 1b: C18H21N2O4V1, Mr ¼ 380:32,
monoclinic, space group P21=n (No. 14), a ¼ 10:9590ð9Þ,
ꢁ
˚
b ¼ 10:8442ð9Þ, c ¼ 15:2471ð9Þ A, ꢁ ¼ 100:609ð2Þ , V ¼
3
1781:0ð2Þ A , Z ¼ 4, T ¼ 4:0 ꢁC, Dcalcd ¼ 1:418 g cmꢂ3
,
˚
ꢄ(Mo Kꢂ) = 5.81 cmꢂ1, Mo Kꢂ radiation (ꢅ ¼ 0:71069 A),
R1 ¼ 0:062, wR2 ¼ 0:172. CCDC-656970 for 1b.
D. C. Crans, H. Chen, O. P. Anderson, M. M. Miller, J. Am.
Chem. Soc. 1993, 115, 6769.
˚
9
Thanks are due to the Analytical Center, Graduate School
of Engineering, Osaka University, for the use of the NMR
instruments.
10 Supporting Information is available electronically on the CSJ-
Journal Web site, http://www.csj.jp/journals/chem-lett/.
Published on the web (Advance View) November 17, 2007; doi:10.1246/cl.2007.1486