Formation of novel phosphide dichloride Zr complex from trichloride Zr complex with a secondary phosphine-pendant cyclopentadienyl ligand: Structure of [{η5-C5H4(CH2) 2PMes-κP}ZrCL2(N-methylimidazole)2] (Mes = 2,4,6-trimethylphenyl)

Article abstract of DOI:10.1246/cl.2003.70

The reaction of [{η⁵-C₅H₄(CH₂) ₂P(H)Mes-κP}ZrCl₃(tht)] (1; Mes = 2,4,6-trimethylphenyl; tht = tetrahydrothiophene) with 1 equiv of NaCPh₃, followed by treatment with N-methylimidazole gave a novel phosphide-pendant dichloride complex [{η⁵-C₅H₄(CH₂) ₂PMes-κP}ZrCl₂(N-methylimidazole)₂] (4) with liberation of HCPh₃. The product (4) is the first dichloride terminal phosphide Zr complex characterized by X-ray crystallographic analysis.

Full text of DOI:10.1246/cl.2003.70

70
Chemistry Letters Vol.32, No.1 (2003)
Formation of Novel Phosphide Dichloride Zr Complex from Trichloride Zr Complex
with a Secondary Phosphine-pendant Cyclopentadienyl Ligand: Structure of
[{ꢀ5-C5H4(CH2)2PMes-ꢁPgZrCl2(N-methylimidazole)2] (Mes = 2,4,6-Trimethylphenyl)
Takeshi Ishiyama, Tsutomu Mizuta, Katsuhiko Miyoshi,ꢀ and Hiroshi Nakazawaꢀy
Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526
yDepartment of Chemistry, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585
(Received October 18, 2002; CL-020890)
The reaction of [{ꢀ5-C5H4(CH2)2P(H)Mes-ꢁPgZrCl3(tht)]
(1; Mes =2,4,6-trimethylphenyl; tht =tetrahydrothiophene) with
1 equiv of NaCPh3, followed by treatment with N-methylimida-
zole gave a novel phosphide-pendant dichloride complex [{ꢀ5-
C5H4(CH2)2PMes-ꢁPgZrCl2(N-methylimidazole)2] (4) with lib-
eration of HCPh3. The product (4) is the first dichloride terminal
phosphide Zr complex characterized by X-ray crystallographic
analysis.
Intensive studies have been continued on dihalide and dialkyl
complexes of early transition metals which serve as Kaminsky-
type precatalysts in olefin polymerization.1a{c Since it was
reported that titanium complexes with an amide-pendant cyclo-
pentadienyl ligand, [(ꢀ5-C5Me4SiMe2NtBu-ꢁN)TiL2] (L = Cl,
alkyl group) called constrained-geometry catalysts (CGC), are
effective in olefin copolymerization,1a analogous phosphide-
pendant cyclopentadienyl complexes have currently attracted
much attention with respect to comparison with the above amide
complexes.2a{d However, it is often difficult to prepare early
transition-metal phosphide complexes antagonistic to the HSAB
principle.3a{c For example, the conventional salt-elimination
reaction of ZrCl4 with the lithium phosphide ligand
Li2C5Me4SiMe2PR (R = Cy, 2,4,6-trimethylphenyl (Mes)) did
not give any products of the [(ꢀ5-C5Me4SiMe2PR-ꢁP)ZrCl2]
type.2b,4 For group 4 transition-metal complexes of this type, only
the diamide complexes [(ꢀ5-C5Me4ER2PCy-ꢁP)M(NR’2)2] (M
= Ti, ER2 = CMe2, SiMe2, R0 = Me; M = Zr, ER2 = CH2, CMe2,
SiMe2, R0 = Et) have been recently prepared via the salt-
elimination reaction by Erker et al.2a{c
We recently prepared the Zr and Hf complexes with an
ethylene-linked secondary phosphine-cyclopentadienyl ligand
[{ꢀ5-C5H4(CH2)2P(H)Mes-ꢁPgMCl3(tht)] (M = Zr (1), Hf; tht =
tetrahydrothiophene),5 which are expected to be useful starting
complexes to terminal phosphide complexes6a{b and phosphide-
bridged multinuclear complexes as well.6c In this paper, we
report the synthesis of the dichloride Zr complex with a
phosphide-pendant cyclopentadienyl ligand through tritylation
of 1 followed by liberation of a trityl-H coupling product, and
describe the molecular structure of its N-methylimidazole
derivative (4).
Scheme 1.
suggesting quantitative formation of a phosphide complex.
Taking account of the negative results obtained previously in
the salt-elimination reaction with an alkali-metal phosphide2b,4
and our recent findings in the reaction of 1 with LiCH2SiMe3,7 we
propose that the present reaction proceeds as shown in Scheme 1;
the reaction firstly affords not a sodium phosphide but a secondary
phosphine monotrityl complex (2) as an undetectable intermedi-
ate, which liberates immediately the trityl-H coupling product
(CHPh3) to give a phosphide dichloride complex (3), which is
probably solvated with THF’s. The concomitantly formed CHPh3
1
was detected by the H NMR spectrum. Though the phosphide
complex (3) could not be isolated because of its high solubility
similar to that of CHPh3, it is expected toserve as a good precursor
of a series of phosphide-pendant complexes. In order to convert it
into an isolable derivative, N-methylimidazole was added to a
solution containing 3 to result in narrow isolation of a highly air-
and moisture-sensitive bis(N-methylimidazole)complex (4,
40%).8 The product was identified by the 1H, 13C, and 31P
NMR spectra and the single-crystal X-ray diffraction analysis.9
The red single crystals of 4 were obtained from its THF/
hexane solution. An asymmetric unit consists of two independent
molecules. A THF molecule involved is disordered. One of the
enantiomers is shown in Figure 1. The Zr atom possesses a
distorted octahedral coordination. The two chloride groups
coordinate to the Zr center in trans positions. The Zr–P bond
distance (2.600 A) and the low-field 31P NMR resonance
ꢀ
The reaction of 1 with 1 equiv of NaCPh3 in ether/THF was
examined (Scheme 1). The 31P NMR spectrum without proton
irradiation showed a singlet at 236.2 ppm only, at the expense of a
broad doublet at À86:7 ppm (JPH ¼ 213 Hz) attributed to the
THF-solvated starting complex (1) with the secondary phosphine
moiety freed from the Zr center.5 The spectral change indicates
that the product has a Zr–P covalent bond but not a P–H bond,
(162.8 ppm, s) point to an appreciable double bond character in
the Zr–P bond.3a The sum of bond angles around the phosphorus
atom (341.7ꢁ) indicates the phosphorus atom bearing some sp2
character.3a The phosphide-pendant complex (4) is one of a few
examples of group 4 transition-metal complexes with a hetero-
chelate ligand containing a phosphide group.2a{c,10a{b
Copyright Ó 2003 The Chemical Society of Japan

Chemistry Letters Vol.32, No.1 (2003)
71
3
a) E. Hey-Hawkins, Chem. Rev., 94, 1661 (1994). b) E. Hey-
Hawkins, in ‘‘Comprehensive Organometallic Chemistry II,’’ ed.
by E. W. Abel, F. G. A. Stone, and G. Wilkinson, Pergamon, Oxford
(1995), Vol. 4, pp 512–518. c) D. W. Stephan, Angew. Chem., Int.
Ed., 39, 314 (2000).
4
5
6
T. Koch, S. Blaurock, F. B. Somoza, Jr., A. Voigt, R. Kirmse, and E.
Hey-Hawkins, Organometallics, 19, 2556 (2000).
T. Ishiyama, H. Nakazawa, and K. Miyoshi, J. Organomet. Chem.,
648, 231 (2002).
a) W. Malisch, N. Gunzelmann, K. Thirase, and M. Neumayer, J.
Organomet. Chem., 571, 215 (1998). b) W. Malisch, U.-A. Hirth, K.
Grun, and M. Schmeußer, J. Organomet. Chem., 572, 207 (1999). c)
¨
R. D. Adams, in ‘‘Comprehensive Organometallic Chemistry II,’’
ed. by E. W. Abel, F. G. A. Stone, and G. Wilkinson, Pergamon,
Oxford (1995), Vol. 10, pp 1–22 and references cited therein.
The reaction of 1 with 3 equiv of LiCH2SiMe3 gave quantitatively a
trialkyl complex [{ꢀ5-C5H4(CH2)2P(H)MesgZr(CH2SiMe3)3]
with the P–H bond intact, showing that the carbanion attacks
preferentially not the P–H moiety but the Zr center.
7
8
(4): A solution of NaCPh3, generated in situ (0.36 mmol) in 20 ml of
ether, was slowly added to a solution of 1 (0.19 g, 0.36 mmol) in
25 ml of THF at room temperature. The reaction mixture was stirred
for 30 min and then the solvents were removed in vacuo. The
residue was dissolved in 20 ml of toluene and the solution was
filtered. To the filtrate was slowly added a solution of N-
methylimidazole (0.039 g, 0.47 mmol) in 10 ml of THF (addition
of 2equivalent or more of N-methylimidazole gave rise to
decomposition of the product). After stirring for 10 min, the
solution was reduced in volume in vacuo, and then the residue was
washed with ether, followed by drying in vacuo to yield a red
powder of 4 (40% based on 1, 0.082g). 1H NMR (300 MHz, C6D6):
ꢂ 8.33 (s, 1H, imidazole), 8.23 (s, 1H, imidazole), 8.10 (s, 1H,
imidazole), 8.00 (s, 1H, imidazole), 6.74 (s, 2H, m-H in Mes or Cp),
6.67 (s, 2H, m-H in Mes or Cp), 6.17 (s, 2H, Cp), 5.84 (s, 1H,
imidazole), 5.69 (s, 1H, imidazole), 3.41 (m, 2H, PCH2 or CpCH2),
3.21–3.08 (m, 2H, PCH2 or CpCH2), 2.70 (s, 6H, o-Me in Mes),
2.15 (s, 6H, MeN), 2.08 (s, 3H, p-Me in Mes). 13C NMR (75.5 MHz,
C6D6): ꢂ 144.0 (s, imidazole), 143.3 (s, imidazole), 143.2(s,
imidazole), 141.3 (s, imidazole), 139.9 (d, JPC ¼ 3:7 Hz, aromatic-
C in Mes), 138.1 (s, 1-C in Cp), 136.0 (d, JPC ¼ 1:9 Hz, aromatic-C
in Mes), 131.5 (br-s, aromatic-C in Mes), 129.9 (s, aromatic-C in
Mes), 119.0 (s, imidazole or 2,5- or 3,4-C inCp), 117.4 (s, imidazole
or 2,5- or 3,4-C in Cp), 116.0 (s, imidazole or 2,5- or 3,4-C in Cp),
112.1 (s, imidazole or 2,5- or 3,4-C in Cp), 37.5 (s, CpCH2), 32.5 (s,
MeN), 32.4 (s, MeN), 27.7 (d, JPC ¼ 19:8 Hz, PCH2), 24.0 (d,
JPC ¼ 9:9 Hz, o-Me in Mes), 20.9 (s, p-Me in Mes). 31P NMR
(121.5 MHz, C6D6): ꢂ 162.8 (s).
Figure 1. ORTEP drawing of 4. Ellipsoids are shown at 50%
probability level. Hydrogen atoms are omitted for clarity.
ꢀ
Selected bond distances (A) and bond angles (deg): Zr1–P1,
2.600(2); Zr1–Cl1, 2.537(2); Zr1–Cl2, 2.563(2); Zr1–N1,
2.429(5); Zr1–N3, 2.366(5); Zr1–P1–C7, 110.3(3); Zr1–P1–C8,
119.4(2); C7–P1–C8, 111.9(3).
In this way, the novel phosphide-pendant dichloride Zr
complex (3) is successfully generated via tritylation of the
trichloride Zr complex with a secondary phosphine-pendant
cyclopentadienyl ligand, followed by elimination of CHPh3.
There have appeared only a few reports on such a unique synthetic
method utilizing the reaction of an alkyl complex with a P–H
functionalized phosphine to prepare a phosphide complex.11a{c In
contrast, most phosphide complexes of group 4 transition metals
have been prepared by the conventional salt-elimination re-
actions,2a{c,3a{c which did not work at all in our study. The present
mild synthetic method may have a potential to introduce a
phosphide ligand into many kinds of metal complexes. The
phosphide complex obtained here and some related complexes
are now under investigation with respect to their reactivities
involving catalytic activities in olefin polymerization. Details of
characterization of 4 and related complexes will be reported
elsewhere.
9
Crystallographic data for 4Á(thf)0:5: formula C26H35Cl2N4O0:5PZr;
ꢁ
ꢀ
fw ¼ 604:69; triclinic; P1 (No. 2); a ¼ 8:0490ð2Þ A, b ¼
ꢀ
ꢀ
16:4160ð3Þ A,
c ¼ 21:9390ð6Þ A,
ꢃ ¼ 81:054ð1Þꢁ,
ꢄ ¼
We acknowledge financial support (14654123 and
14044071) from Ministry of Education, Science, Sports, and
Culture, Japan.
ꢁ
ꢁ
ꢀ 3
88:255ð1Þ , ꢅ ¼ 89:857ð1Þ , V ¼ 2862:3ð1Þ A ; Z ¼ 4; Dcalcd
¼
1:403 g/cm3. Out of a total of 12393 reflections measured, 7776
reflections with 2:00ꢆðIÞ < I and 2ꢇ < 50:00ꢁ, were used in the
refinement, and the structure was solved by direct methods and
expanded using Fourier techniques: R ðRwÞ ¼ 0:071 (0.115). The
measurement was made on a Mac Science DIP2030 imaging plate
References and Notes
1
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ꢀ
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