Bis(amido)cyclodiphosph(III)azane hafnium complexes and their activation by tris(perfluorophenyl)borane

Article abstract of DOI:10.1021/om0492303

Bis(amido) hafnium complexes [(RN)(t-BuNP)]₂HfCl₂ (R = 2,6-i-Pr₂C₆H₃ (5), 2,5-t-Bu₂C ₆H₃ (6)) bearing a N-tert-butyl cyclodiphosph(III)azane bridge were prepared by direct metalation of corresponding ligand precursors with HflNMe₂)₄ followed by chlorination by Me ₃SiCl. Complexes 5 and 6 and the already known [(t-BuN)(t-BuNP)] ₂HfCl₂ (4) were subsequently converted to their methyl derivatives [(RN)(t-BuNP)]₂HfMe₂ by the alkylation by MeMgBr in Et₂O. The solid state structure of [t-BuN)(t-BuNP)] ₂HfMe₂ (7) reveals a highly distorted trigonal-bypiramidal configuration at the metal center. Activation of the dimethyl complexes with B(C₆CeFs₆)₃ led to the generation of corresponding cationic species, which were investigated by ¹H, ¹³C, ³¹P, and ¹⁹F NMR. In the solid state, the metal center of {[(t-BuN)(t-BuN)(tBuNP)]₂HfMe(μ-M)B(C ₆F₆)₃ has a distorted trigonal-bypiramidal configuration and the {MeB(C₆F₅)₃]^- anion is only weakly coordinated with cationic hafnium. In deuterobenzene solution {[(t-BuN)(t-BuNP)]₂HfMe(μ-Me)B(C₆F ₅)₃}, like in the solid state, exhibited C_s symmetry as a result of the additional coordination of the high electrophilic hafnium atom with one of the nitrogens of the P₂N₂ ring. This additional metal-ligand interaction in solution is absent in the case of the activated complexes 8 and 9, having bulky aryl substituents. The compounds 4 and 7 revealed moderate catalytic activity in the ethene polymerization, while hafnium complexes bearing aryl groups remained inactive in the same conditions.

Full text of DOI:10.1021/om0492303

1336
Organometallics 2005, 24, 1336-1343
Bis(amido)cyclodiphosph(III)azane Hafnium Complexes
and Their Activation by Tris(perfluorophenyl)borane
Kirill V. Axenov, Martti Klinga, Markku Leskela¨, and Timo Repo*
Laboratory of Inorganic Chemistry, Department of Chemistry, University of Helsinki,
PO Box 55, FIN-00014, Finland
Received October 5, 2004
Bis(amido) hafnium complexes [(RN)(t-BuNP)]2HfCl2 (R ) 2,6-i-Pr2C6H3 (5), 2,5-t-Bu2C6H3
(6)) bearing a N-tert-butyl cyclodiphosph(III)azane bridge were prepared by direct metalation
of corresponding ligand precursors with Hf(NMe2)4 followed by chlorination by Me3SiCl.
Complexes 5 and 6 and the already known [(t-BuN)(t-BuNP)]2HfCl2 (4) were subsequently
converted to their methyl derivatives [(RN)(t-BuNP)]2HfMe2 by the alkylation by MeMgBr
in Et2O. The solid state structure of [(t-BuN)(t-BuNP)]2HfMe2 (7) reveals a highly distorted
trigonal-bypiramidal configuration at the metal center. Activation of the dimethyl complexes
with B(C6F5)3 led to the generation of corresponding cationic species, which were investigated
by 1H, 13C, 31P, and 19F NMR. In the solid state, the metal center of {[(t-BuN)(t-BuNP)]2HfMe-
(µ-Me)B(C6F5)3} has a distorted trigonal-bypiramidal configuration and the [MeB(C6F5)3]-
anion is only weakly coordinated with cationic hafnium. In deuterobenzene solution
{[(t-BuN)(t-BuNP)]2HfMe(µ-Me)B(C6F5)3}, like in the solid state, exhibited Cs symmetry as
a result of the additional coordination of the high electrophilic hafnium atom with one of
the nitrogens of the P2N2 ring. This additional metal-ligand interaction in solution is absent
in the case of the activated complexes 8 and 9, having bulky aryl substituents. The compounds
4 and 7 revealed moderate catalytic activity in the ethene polymerization, while hafnium
complexes bearing aryl groups remained inactive in the same conditions.
Introduction
on perfluoroarylboranes and salts of arylammonium
cations with noncoordinating anions are widely used in
investigation of activation of metallocenes,7 constrained
geometry,8 and nonmetallocene complexes.9 Due to the
high instability of activated species, they are generated
and investigated mainly in situ by different NMR
techniques.4,7-9 These cationic complexes facilitate di-
rect insight and offer fundamental information on the
catalytically active species, leading to new opportunities
for rational development of homogeneous polymeriza-
tion catalyts.4 The catalytic species formed during the
activation process can exhibit a geometry differing from
the one of the parent complex, i.e., configuration of the
central atom and/or coordination of the activator. There-
fore, knowing the structural features of the catalyst
precursor is not enough, and it appears necessary to
study the activation reaction of the precatalyst and the
The basic discovery in the middle 1970s that group 4
metallocene dichlorides can be activated with methyl-
aluminoxanes (MAO)1 has provided a solid basis for the
development of homogeneous single-center polymeriza-
tion catalysts. Therefore, during the last 30 years we
have witnessed significant advances in the design of
organometallic and inorganic complexes and their ap-
plication in R-olefin polymerization.2,3 The function of
MAO in the activation process is rather well established
and includes the alkylation of the catalyst precursor
followed by the formation of a cationic metal center by
alkyl abstraction.2a
Since the advent of MAO, new strong Lewis acid
activators displaying similar and even higher efficiency
were reported to be valuable cocatalysts for homoge-
neous Ziegler-Natta olefin polymerization systems.4
Started by Chen, Marks,5 and Ewen,6 activators based
(5) (a) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1994,
116, 10015. (b) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc.
1991, 113, 3623.
(6) Ewen, J. A.; Elder, M. J. Eur. Patent Appl. 0,427,697, 1991; U.S.
Pat. 5,561,092, 1996.
* To whom correspondence should be addressed. E-mail: timo.repo@
helsinki.fi. Fax: +358-(0)9-19150198.
(1) Andersen, A.; Cordes, H.-G.; Herwig, J.; Kaminsky, W.; Merck,
A.; Mottweiler, R.; Pein, J.; Sinn, H.; Vollmer, H.-J. Angew. Chem.
1976, 88, 689; Angew. Chem., Int. Ed. Engl. 1976, 15, 630.
(2) For metallocenes: (a) Kaminsky, W.; Arndt, M. In Applied
Homogeneous Catalysis with Organometallic Compounds; Cornils, B.,
Herrmann, W. A., Eds.; VCH: Weinheim, 1996; Vols. 1 and 2. (b) Alt,
H. G.; Ko¨ppl, A. Chem. Rev. 2000, 100, 1205. (c) Brintzinger, H. H.;
Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem.
1995, 107, 1255; Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
(3) For nonmetallocene catalysts: (a) Britovsek, J. P.; Gibson, V.
C.; Wass, D. F. Angew. Chem. 1999, 111, 448; Angew. Chem., Int. Ed.
1999, 38, 428. (b) Gibson, V. C.; Spitzmesser, K. Chem. Rev. 2003, 103,
283.
(7) (a) Ref 5. (b) Bochmann, M.; Lancaster, S. J. Organometallics
1994, 13, 2235. (c) Temme, B.; Erker, G.; Karl, J.; Luftmann, H.;
Frohlich, R.; Kotila, S. Angew. Chem., Int. Ed. Engl. 1995, 34, 1755.
(d) Karl, J.; Erker, G.; Frohlich, R. J. Am. Chen. Soc. 1997, 119, 11165.
(8) (a) Chen, Y.-X.; Marks, T. J. Organometallics 1997, 16, 3649.
(b) Chen, Y.-X.; Fu, P.-F.; Stern, C. L.; Marks, T. J. Organometallics
1997, 16, 5958.
(9) (a) Aizenberg, M.; Turculet, L.; Davis, W. M.; Schattenmann, F.;
Schrock, R. R. Organometallics 1998, 17, 4795. (b) Horton, A. D.; de
With, J.; van der Linden, A. J.; van de Weg, H. Organometallics 1996,
15, 2672. (c) Warren, T.; Schrock, R. R.; Davis, W. M. Organometallics
1998, 17, 308. (d) Baumann, R.; Schrock, R. R. J. Organomet. Chem.
1998, 557, 69. (e) Baumann, R.; Davis, W. M.; Schrock, R. R. J. Am.
Chem. Soc. 1997, 119, 3830.
(4) Chen, Y.-X.; Marks, T. J. Chem. Rev. 2000, 100, 1391.
10.1021/om0492303 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/12/2005

Bis(amido) Hafnium Complexes
Organometallics, Vol. 24, No. 6, 2005 1337
Chart 1
Experimental Section
All manipulations were done under inert argon atmosphere
using standard Schlenk techniques or in a glovebox. The
hydrocarbon and ethereal solvents were refluxed over sodium
and benzophenone, distilled, and stored under argon with
sodium flakes. Dichloromethane was refluxed with CaH2
powder and distilled before use. Deuterated solvents were
carefully dried (CD2Cl2 with P4O10 and deuterobenzene with
sodium) and stored over molecular sieves in a glovebox. Mass
spectra were measured on a JEOL SX102 spectrometer, and
the 1H and 13C NMR spectra were recorded on a Varian Gemini
200 MHz spectrometer and referenced relative to CHDCl2 (5.28
and 53.73 ppm, respectively) or C6D5H (7.24 and 128.0 ppm,
respectively). 31P NMR spectra were collected with Bruker
AMX 400 and Bruker Avance DRX 500 spectrometers and
referenced relative to an external standard (85% H3PO4
solution). 19F NMR spectra were recorded with a Bruker
Avance DRX 500 spectrometer and referenced relative to
CFCl3. Elemental analyses were performed by Analytische
Laboratorien (Prof. Dr. H. Malissa und G. Reuter) GmbH,
Lindlar, Germany. Chlorotrimethylsilane (Fluka), tris(per-
fluorophenyl)borane (Strem), n-BuLi (Aldrich), and MeMgBr
(Aldrich) were used as received. Hf(NMe2)4 (Strem) was
dissolved in a fixed amount of dry toluene and used as a stock
solution. Methylalumoxane (MAO, 30 wt % solution in toluene)
was received from Borealis Polymers Oy. Ligand precursors
actual structure of the catalytic species generated under
conditions resembling those used during the polymer-
ization process.4
Zirconium, hafnium, and titanium cis-bis(tert-butyl-
amido) complexes bearing a cyclodiphosph(III)azane
bridge (structure A, Chart 1) have recently attracted
attention as homogeneous catalyst precursors for ethene
polymerization.10-12 Nevertheless, the presence of an
electron-rich phosphor-nitrogen cycle in the vicinity of
metal center raises the question of the determination
of the site of MAO coordination during the activation
step. Presumably, an aluminum species can also coor-
dinate to phosphorus(III) atoms and, as a result, ini-
tiate the decomposition of the catalyst.11
Recently we reported on new cis-bis(amino)cyclo-
diphosph(III)azanes bearing bulky arylamine substit-
uents and their Ti and Zr derivatives (structure B,
Chart 1).13,14 After MAO activation, these catalysts
showed an increased stability if compared with tert-
butylamido-substituted analogues and high activity in
ethene polymerization. It was also established that
stability of the catalysts, displayed average activities,
and properties of the produced polyethylene depend on
the size and nature of the amido substituents. A rational
explanation can reside in the more or less efficient
protection of the central metal atom provided by amido
substituents of different bulkiness toward monomer
and/or cocatalyst (MAO) coordination.14 Among group
4 transition metals, the most stable alkyl derivatives
are those of hafnium,4 and their use can thus permit
precise structural determination of in situ generated
cationic species and too fast decomposition of the
generated cationic species can be avoided.
13
[(t-BuNH)(t-BuNP)]215 (1), cis-[(2,6-i-Pr2C6H3NH)(t-BuNP)]2
(2), and cis-[(2,5-t-Bu2C6H3NH)(t-BuNP)]213 (3) were prepared
according to literature procedures.
[(t-BuN)(t-BuNP)]2HfCl2 (4) was prepared according to a
modified literature procedure.12 A hexane solution of n-BuLi
(1.6 M, 18 mL, 28 mmol) was added via a syringe to a solution
of 1 (4.5 g, 13 mmol) in THF (30 mL) at -50 °C. After 20 min,
the reaction mixture was allowed to warm to room tempera-
ture and refluxed during 3 h. All volatiles were removed in
vacuo, and toluene (30 mL) was added. Solid HfCl4 (4.14 g, 13
mmol) was added with vigorous stirring to the toluene suspen-
sion, and the resulting mixture was refluxed during 1 day. All
volatiles were removed in vacuo, and the solid residue was
extracted by a toluene-hexane mixture, followed by filtration.
Evaporation of the solvents from the filtrate under reduced
pressure gave a yellow crystalline solid (6.04 g, 78%). Anal.
Calcd for C16H36Cl2HfN4P2: C, 32.25; H, 6.09. Found: C, 32.12;
H, 6.09. 1H NMR (200 MHz, C6D6, 29 °C): δH 1.37 (s, 18H,
t-Bu, P2N2 cycle), 1.49 (s, 18H, t-Bu). 31P{1H} NMR (202 MHz,
C6D6, 21 °C): δP 102.03 (s). MS(EI): m/z (%) 596 (35, M+), 580
(90, M+ - CH3), 525 (25, M+ - 2Cl), 352 (60, ligand).
[(2,6-i-Pr2C6H3N)(t-BuNP)]2HfCl2 (5). Hf(NMe2)4 (2.39 g,
6.75 mmol) in toluene (25 mL) was added to the toluene (30
mL) solution of cis-[(2,6-i-Pr2C6H3NH)(t-BuNP)]2 (2) (3.75 g,
6.75 mmol) and refluxed overnight. Excess of Me3SiCl (7.3 mL,
6.23 g, 57.3 mmol) was further added via a syringe to the
resulting yellow solution at room temperature and stirred
overnight. All volatiles were then removed in vacuo, and the
residue was extracted three times with a mixture of hexane
(30 mL) and CH2Cl2 (10 mL) followed by filtration of extracts.
Solvents were then removed under vacuum, and a yellow
sticky material residue was obtained (4.12 g, 76%). This
complex absorbs solvents so strongly that even under harsh
drying conditions they cannot be removed completely. Several
attempts were made to get proper elemental analysis data,
but in all of them the increased content of carbon was detected.
Anal. Calcd for C32H52Cl2HfN4P2: C, 47.80; H, 6.52; N, 6.97.
Accordingly, to get insight into the activation step of
cis-bis(amido)cyclodiphosph(III)azane group 4 metal
complexes, and to understand the true nature of the
activated catalyst precursor, the synthesis of new cis-
bis(amido)cyclodiphosph(III)azane Hf methyl complexes
was undertaken, and their activation by perfluorophen-
ylborane was investigated by means of NMR and X-ray
diffraction techniques.
(10) Grocholl, L. P.; Stahl, L.; Staples, R. J. Chem. Commun. 1997,
1465.
1
Found: C, 48.39; H, 6.63; N, 7.30. H NMR (200 MHz, C6D6,
(11) Moser, D. F.; Carrow, C. J.; Stahl, L.; Staples, R. J. J. Chem.
Soc., Dalton Trans. 2001, 1246.
29 °C): δH 1.37 (s, 18H, t-Bu), 1.42 (d, 24H, CH3, i-Pr), 3.97
(m, 4H, CH, i-Pr), 7.19 (m, 4H, H-Ar), 7.28 (2H, H-Ar).
13C{1H} NMR (50.3 MHz, C6D6, 29 °C): δC 24.17 (CH3, i-Pr),
(12) Moser, D. F.; Grocholl, L.; Stahl, L.; Staples, R. J. J. Chem.
Soc., Dalton Trans. 2003, 1402.
(13) Axenov, K. V.; Klinga, M.; Leskela¨, M.; Kotov, V. V.; Repo, T.
Eur. J. Inorg. Chem. 2004, 695.
(14) Axenov, K. V.; Klinga, M.; Leskela¨, M.; Kotov, V. V.; Repo, T.
Eur. J. Inorg. Chem. 2004, 4702.
(15) Hill, T. G.; Haltiwanger, R. C.; Thompson, M. L.; Katz, S. A.;
Norman, A. D. Inorg. Chem. 1994, 33, 1770.

1338 Organometallics, Vol. 24, No. 6, 2005
Axenov et al.
29.17 (t, CH, i-Pr), 31.36 (t, JPC ) 6.5 Hz, CH3, t-Bu), 51.60 (t,
JPC ) 14.5 Hz, C, t-Bu), 123.98 (Ar), 136.37 (Ar), 140.96 (Ar),
144.57 (Ar). 31P{1H} NMR (202 MHz, C6D6, 21 °C): δP 115.63
(s). MS (EI): m/z (%) 804 (5, M+), 732 (10, M+ - 2Cl), 556 (20,
ligand).
[(2,5-t-Bu2C6H3N)(t-BuNP)]2HfMe2 (9). Solutions of
MeMgBr in Et2O (3M, 1.5 mL, 4.5 mmol) and [(2,5-t-
Bu2C6H3N)(t-BuNP)]2HfCl2 (6) (1.8 g, 2.1 mmol) in Et2O (20
mL) were combined and treated as described above, and
separation of the product was carried out as reported for 7.
The Hf complex was isolated as a yellow-brown solid (1.40 g;
81.4%). Anal. Calcd for C38H66HfN4P2: C, 55.70; H, 8.12; N,
[(2,5-t-Bu2C6H3N)(t-BuNP)]2HfCl2 (6) was synthesized
similarly to 5 from a toluene (20 mL) solution of cis-[(2,5-
tBu2C6H3NH)(tBuNP)]2 (3) (3.11 g, 5.07 mmol) and Hf(NMe2)4
(1.8 g, 5.07 mmol) in toluene (19 mL). Excess Me3SiCl (6.7 mL,
5.68 g, 43.10 mmol) was added with a syringe to the resulting
yellow solution at room temperature. After overnight stirring
all volatiles were removed in vacuo, and the residue was
extracted several times with a mixture of hexane (20 mL) and
CH2Cl2 (10 mL). After filtration of the extracts, solvents were
removed under reduced pressure to yield a pale yellow solid
(3.60 g, 82%). Anal. Calcd for C36H60Cl2HfN4P2: C, 50.26; H,
7.03; N, 6.51. Found: C, 50.54; H, 7.56; N, 6.92. 1H NMR (200
MHz, C6D6, 29 °C): δH 1.45 (s, 36H, t-BuAr), 1.57 (s, 18H,
1
6.84. Found: C, 55.61; H, 8.03; N, 6.68. H NMR (200 MHz,
C6D6, 29 °C): δH 0.38 (s, 6H, CH3), 1.45 (s, 36H, t-BuAr), 1.57
1
2
(s, 18H, t-Bu), 7.00 (dd, 2H, J ) 6.2 Hz, J ) 2.2 Hz, 4-H-
Ar), 7.38 (2H, 3-H-Ar), 8.26 (dd, 2H, 1J ) 3.3 Hz, 2J ) 2.2
Hz, 6-H-Ar). 13C{1H} NMR (50.3 MHz, C6D6, 29 °C): δC 31.0
(CH3, 5-t-BuAr), 31.33 (t, JPC ) 6.5 Hz, CH3, t-Bu), 31.53 (CH3,
2-t-BuAr), 34.00 (C, 5-t-BuAr), 34.50 (C, 2-t-BuAr), 51.71 (t,
JPC ) 13.5 Hz, C, t-Bu), 62.64 (CH3), 113.83 (Ar), 114.50 (Ar),
117.18 (Ar), 131.19 (Ar), 141.90 (d, J ) 9.9 Hz, Ar), 150.02 (t,
J ) 1.2 Hz, Ar). 31P{1H} NMR (202 MHz, C6D6, 21 °C): δP
98.70 (s). MS(EI): m/z (%) 774 (2, M+ - t-Bu), 612 (45, ligand).
In Situ Generation of [(t-BuN)(t-BuNP)]2Hf(Me)MeB-
(C6F5)3 (10). In a glovebox, an NMR tube was charged with
[(t-BuN)(t-BuNP)]2HfMe2 (7) (40 mg, 72 µmol), B(C6F5)3 (36.9
mg, 72 µmol), and 0.6 mL of C6D6 at room temperature and
shaken vigorously. The product was investigated only by NMR
methods because of its high thermal instability and very high
air and moisture sensitivity. Crystals suitable for X-ray
analysis were grown by layer recrystallization from a toluene-
1
2
t-Bu), 7.00 (dd, 2H, J ) 6.2 Hz, J ) 2.2 Hz, 4-H-Ar), 7.38
1
2
(2H, 3-H-Ar), 8.26 (dd, 2H, J ) 3.3 Hz, J ) 2.2 Hz, 6-H-
Ar). 13C{1H} NMR (50.3 MHz, C6D6, 29 °C): δC 31.0 (CH3, 5-t-
BuAr), 31.33 (t, JPC ) 6.6 Hz, CH3, t-Bu), 31.53 (CH3,
2-t-BuAr), 34.00 (C, 5-t-BuAr), 34.50 (C, 2-t-BuAr), 51.7 (t, JPC
) 13.73 Hz, C, t-Bu), 113.83 (Ar), 114.50 (Ar), 117.17 (Ar),
131.18 (Ar), 138.90 (d, J ) 9.9 Hz, Ar), 150.10 (t, J ) 1.2 Hz,
Ar). 31P{1H} NMR (202 MHz, C6D6, 21 °C): δP 99.80 (s).
MS(EI): m/z (%) 862 (2, M+), 804 (10, M+ - t-Bu), 613 (90,
ligand).
1
hexane mixture at -20 °C. H NMR (200 MHz, C6D6, 29 °C):
δH 0.87 (s, 3H, CH3Hf), 1.00 (s, 9H, t-Bu, P2N2 cycle), 1.07 (s,
9H, t-Bu, P2N2 cycle), 1.13 (s, 18H, t-Bu), 2.93 (br s, 3H, CH3B).
13C{1H} NMR (50.3 MHz, C6D6, 29 °C): δC 30.86 (m, BCH3),
[(t-BuN)(t-BuNP)]2HfMe2 (7). A solution of MeMgBr in
Et2O (3M, 2.3 mL, 6.9 mmol) was added via syringe to a
solution of [(t-BuN)(t-BuNP)]2HfCl2 (4) (2.0 g, 3.36 mmol) in
Et2O (30 mL) at -50 °C. The reaction mixture was allowed to
warm to room temperature, and the stirring was continued
overnight. All volatiles were removed in vacuo, and the solid
residue was extracted with hexane, followed by filtration in
the glovebox through Teflon filters. The resulting clear hexane
solution was then evaporated off in vacuo, and a white-yellow
crystalline solid (1.76 g; 94.6%) was isolated. Crystals suitable
for X-ray analysis were obtained by recrystallization of 7 from
Et2O at -20 °C. The compound revealed high sensitivity to
moisture, air, and elevated temperatures, and therefore it
turn out to be difficult to obtain reliable elemental analysis
data. To confirm the complex composition HR-MS was per-
formed instead (see Supporting Information). Anal. Calcd for
C18H42HfN4P2: C, 38.95; H, 7.63; N, 10.10. Found: C, 38.32;
H, 7.27; N, 9.45. 1H NMR (200 MHz, C6D6, 29 °C): δH 0.62 (s,
6H, CH3), 1.38 (s, 18H, t-Bu, P2N2 cycle), 1.54 (d, J ) 0.73 Hz,
18H, t-Bu). 13C{1H} NMR (50.3 MHz, C6D6, 29 °C): δC 30.44
(t, JPC ) 6.1 Hz, CH3, t-Bu, P2N2 cycle), 34.35 (d, JPC ) 9.2
Hz, CH3, t-Bu), 54.0 (t, JPC ) 12.2 Hz, C, t-Bu, P2N2 cycle),
57.35 (d, JPC ) 16.0 Hz, C, t-Bu), 59.34 (t, J ) 0.8 Hz,
CH3). 31P{1H} NMR (202 MHz, C6D6, 21 °C): δP 108.3 (s).
MS(EI): m/z (%) 555 (2, M+), 541 (8, M+ - CH3), 349 (90,
ligand). HR-MS(EI): m/z calcd for C17H39N4P2Hf (M+ - CH3)
539.2090; observed 539.2110, error 4.2 ppm.
33.70 (t, JPC ) 11.0 Hz, CH3, t-Bu, P2N2 cycle), 33.80 (d, JPC
)
9.2 Hz, CH3, t-Bu), 58.7 (d, JPC ) 11.8 Hz, C, t-Bu), 59.6 (t,
JPC ) 6.5 Hz, C, t-Bu, P2N2 cycle), 59.8 (HfCH3), br signals
126.7 (B-CAr), 135.0 (PhF), 139.9 (PhF), 147.0 (PhF), 151.8
(PhF). 31P{1H} NMR (202 MHz, C6D6, 21 °C): δP 91.54 (s). 19
F
NMR (470 MHz, C6D6, 21 °C): δF -132.6 (d, JFF ) 22.3 Hz,
o-F, C6F5), -159.0 (t, JFF ) 20.7 Hz, m-F, C6F5), -163.9 (t, JFF
) 19.0 Hz, p-F, C6F5).
Preparation of other cationic complexes was done in a
manner similar to that described for 10, and formation of the
cationic complexes was followed by NMR methods (see Sup-
porting Information).
Single-Crystal X-ray Diffraction Studies. Crystal data
of compounds 7 and 10 were collected with a Nonius Kap-
paCCD area-detector diffractometer at 173(2) K using Mo KR
radiation (graphite monochromator), 0.71073 Å. Data reduc-
tion: COLLECT.16 Absorption correction: SADABS.17 Solution
and refinement: SIR-2002.18 Graphics: SHELXTL/PC.19 All
non-hydrogen atoms were refined anisotropically and the hy-
drogen atoms were refined on calculated positions. The dis-
placement factors of the H atoms were 1.2× (1.5×) that of the
host atom.
Results and Discussion
Synthesis of Complexes. On the basis of our earlier
studies on cis-bis(amido)cyclodiphosph(III)azane com-
plexes of group 4 transition metals, the ligand substit-
uents have a significant influence on initial catalytic
activity, stability of the catalytic species, and quality of
the polymers produced.13,14 To investigate the activation
process more closely, hafnium complexes of cis-bis-
(amino)cyclodiphosph(III)azane ligands were obtained,
[(2,6-i-Pr2C6H3N)(t-BuNP)]2HfMe2 (8). Solutions of
MeMgBr in Et2O (3 M, 2.0 mL, 6.0 mmol) and [(2,6-i-Pr2C6H3N)-
(t-BuNP)]2HfCl2 (5) (2.0 g, 2.49 mmol) in Et2O (20 mL) were
combined and treated as described above. Separation of the
product was carried out as reported for 7. The Hf complex
was isolated as a yellow oil (1.70 g; 89.5%). Anal. Calcd for
C34H58HfN4P2: C, 53.50; H, 7.66; N, 7.34. Found: C, 53.87;
H, 7.78; N, 7.13. 1H NMR (200 MHz, C6D6, 29 °C): δH 0.38 (s,
6H, CH3), 1.38 (s, 18H, t-Bu), 1.42 (d, 24H, CH3, i-Pr), 3.97
(m, 4H, CH, i-Pr), 7.20 (m, 4H, H-Ar), 7.27 (2H, H-Ar).
13C{1H} NMR (50.3 MHz, C6D6, 29 °C): δC ) 24.17 (CH3, i-Pr),
28.43 (CH3), 29.08 (t, CH, i-Pr), 31.36 (t, JPC ) 6.5 Hz, CH3,
t-Bu), 51.60 (t, JPC ) 14.5 Hz, C, t-Bu), 123.99 (Ar), 136.37
(Ar), 140.97 (Ar), 144.57 (Ar). 31P{1H} NMR (202 MHz, C6D6,
21 °C): δP 115.57 (s). MS (EI): m/z (%) 763 (1, M+), 731 (1,
M+ - 2CH3), 556 (30, ligand).
(16) Nonius. COLLECT; Nonius BV: Delft, The Netherlands, 2002.
(17) Sheldrick, G. M. SADABS; University of Go¨ttingen: Germany,
1996.
(18) Burla, M. C.; Camalli, M.; Carrozzini, G. L.; Cascarano, G.;
Giacovazzo, C.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 2003, 36,
1103.
(19) Sheldrick, G. M. SHELXTL, Version 5.10; Bruker AXS Inc.:
Madison, WI, 1997.

Bis(amido) Hafnium Complexes
Organometallics, Vol. 24, No. 6, 2005 1339
Scheme 1
Table 1. Crystallographic Data for Complexes 7
and 10
as their alkylated derivatives are more stable than the
corresponding zirconium complexes. For this purpose,
ligand precursors with different amino substituents
were prepared: [(t-BuNH)(t-BuNP)]2 (1) was synthe-
sized according to an earlier published literature pro-
cedure,15 while [(2,6-i-Pr2C6H3NH)(t-BuNP)]2 (2) and
[(2,5-t-Bu2C6H3NH)(t-BuNP)]2 (3), having bulky aryl
substituents, were obtained via a synthetic method
lately developed in our laboratory.13 The dichloro hafni-
um complex of 1 was prepared by deprotonation of the
ligand precursor with butyllithium and subsequent
treatment of the lithium salt with HfCl4 as reported
earlier.12 On the other hand, direct metalation of the
sterically hindered ligands 2 and 3 with Hf(NMe2)4
turned out to be the most efficient method leading to
complex synthesis (Scheme 1). The intermediate bis-
(amido)Hf(NMe2)2 species were not isolated, but 1H
NMR and 31P NMR showed that metalation occurred
selectively, and only the desired hafnium amido deriva-
tives were identified in 1H NMR. Conversion of the
tetra(amido) hafnium complexes to the corresponding
dichloride derivatives was carried out by using a large
excess of Me3SiCl. As expected, the bonding between the
metal center and the ligand was protected efficiently
enough, and only substitution of the NMe2 groups
occurred.20 The dichloro hafnium complexes [(2,6-i-
Pr2C6H3N)(t-BuNP)]2HfCl2 (5) and [(2,5-t-Bu2C6H3N)-
(t-BuNP)]2HfCl2 (6) were isolated in good yields (Scheme
1). The 1H NMR spectra of 5 and 6 revealed an apparent
C2v symmetry in solution, as all the alkyl and aromatic
protons were equivalent. Moreover, NMR data of these
hafnium complexes were in accordance with those
observed for their Ti and Zr analogues.13,14
7
10
formula
fw
C
18H42N4P2Hf
C36H42N4P2F15BHf
1066.98
P21/c
554.99
P212121
9.916(1)
15.327(1)
16.582(2)
90
space group
a, Å
12.168(1)
19.986(1)
17.984(1)
103.561(2)
4251.6(5)
1.667
b, Å
c, Å
â, deg
V, Å3
2520.2(4)
1.463
dcalc, g cm-3
Z
4
4
µ, cm-1
Flack param
λ, Å
4.275
2.627
0.001(7)
0.71073
173(2)
0.0304
0.0511
0.71073
173(2)
0.0497
0.1211
T, K
Ra
Rw
b
a R ) ∑||Fo| - |Fc||/∑|Fo| for observed reflections [I > 2σ(I)]. b Rw
2
2
) {∑[w(Fo - Fc )2]/∑[w(Fo2)2]}1/2 for all data.
Reaction of the dichloro hafnium derivatives 4-6 with
MeMgBr provided the dimethyl hafnium complexes 7-9
with high yield (Scheme 1). During the isolation process,
7-9 proved to be highly soluble in aliphatic solvents
and exhibited high thermal stability, but were highly
air and moisture sensitive. The entire purification
process was consequently undertaken in a glovebox so
as to avoid the formation of hydrolysis and oxidation
products, otherwise easily formed. 1H and 13C NMR
measurements of the dimethyl complexes 7-9 gave
spectra similar to the dichloro analogues, pointing out
that 7-9 are also C2v symmetric in solution. Moreover,
the methyl substituents were found to be chemically
equivalent. Recrystallization of complex 7 from a satu-
rated diethyl ether solution at -20 °C yielded yellow
crystals suitable for X-ray diffraction analysis. The
crystallographic and structural data are collected in
Tables 1 and 2.
(20) For the synthesis of bis(amido) group IV metal complexes see:
(a) Armistead, L. T.; White, P. S.; Gagne, M. R. Organometallics 1998,
17, 216. (b) Scollard, J. D.; McConville, D. H.; Vittal, J. J. Organo-
mnetallics 1997, 16, 4415. (c) Schrock, R. R.; Baumann, R.; Reid, S.
M.; Goodman, J. T.; Stumpf, R.; Davis, W. M. Organometallics 1999,
18, 3649.
In the solid state, complex 7 adopts structural fea-
tures similar to those reported for Zr and Ti bis(amido)-

1340 Organometallics, Vol. 24, No. 6, 2005
Axenov et al.
Table 2. Selected Structural Parameters for
Complexes 7 and 10
7
10
Distances, Å
1.698(3)
1.787(3)
1.748(4)
2.709(3)
2.207(5)
2.254(5)
P1-N1
1.688(5)
1.802(5)
1.776(5)
2.734(2)
2.228(6)
P1-N3
P1-N4
P1-P2
Hf1-C21
Hf1-C22
Hf1-C61
Hf1-N1
Hf1-N2
Hf1-N3
C61-B1
C31-B1
2.473(5)
2.096(5)
2.081(4)
2.315(4)
1.673(8)
1.659(8)
2.078(3)
2.097(3)
2.428(3)
Figure 1. ORTEP plot of 7 with thermal ellipsoids drawn
at the 50% probability level. All hydrogen atoms were
omitted for clarity.
Angles, deg
79.19(16)
93.05(15)
122.59(12)
104.2(2)
N3-P1-N4
78.8(2)
N1-P1- N3
N1-Hf1-N2
C21-Hf1-C22
C21-Hf1-C61
C21-Hf1-N1
C61-Hf1-N1
C21-Hf1-N3
C61-Hf1-N3
Hf1-N3-P1
Hf1-C61-B1
C31-B1-C61
C31-B1-C51
94.0(2)
permit the separation and isolation of the products,
spectroscopic characterization was made in situ. Mixing
7 and B(C6F5)3 in CD2Cl2 in an NMR tube led to the
instant reaction, and a clear transparent orange solution
was obtained.24 In 1H NMR, the singlet arising from the
Hf-CH3 groups of 7 (δH ) 0.62 ppm) was then split into
a sharp singlet corresponding to the cationic Hf-CH3
(δH ) 0.04 ppm) and a broad singlet ascribed to B-CH3
(δH ) 0.43 ppm).25 The conversion of B(C6F5)3 to a
noncoordinating [MeB(C6F5)3]- anion is supported by
19F NMR (∆δ(m,p-F) ) 2.56).26 However, the reaction
proved to be rather unselective, as the 31P NMR
spectrum displayed three signals corresponding to as
many different species (see Supporting Information). A
first peak at δP ) 109.8 ppm represents the parent
complex 7, the second signal at δP ) 91.1 ppm is
characteristic of the cationic complex, and a third signal
was shifted upfield at δP ) 34.8 ppm (vide infra).
When the reaction was carried out in deuterated
benzene, the immediate precipitation of a yellow solid
was observed, and the remaining bright yellow solution
slowly darkened with time. This implies a decreased
solubility but a higher stability of the hafnium cation
in hydrocarbon solvents compared to CD2Cl2. According
to 31P NMR the reaction proceeded with high selectivety,
as only one phosphorus peak (δP ) 91.54 ppm) appeared
in the spectrum. The 1H NMR spectrum also exhibited
two peaks instead of the initial Hf-CH3 singlet: a broad
singlet shifted to δH ) 2.93 ppm (B-CH3) and a sharp
one at δH ) 0.87 ppm (cationic Hf-CH3) (Figure 2). The
enormous downfield shift of the Me-B group signal
indicates the strong coordination of the MeB(C6F5)3
anion via the Hf-Me-B bridge. The 19F NMR data also
proved the presence of the coordinated [MeB(C6F5)3]-
anion (∆δ(m,p-F) ) 4.13) and corroborated the synthe-
sis of {[(t-BuN)(t-BuNP)]2HfMe(µ-Me)B(C6F5)3} (10)
(Scheme 2).
128.79(17)
100.4(2)
112.0(2)
99.62(17)
105.97(19)
153.61(18)
86.14(18)
172.6(4)
112.8(5)
102.3(4)
111.47(16)
106.52(16)
86.66(12)
cyclodiphosph(III)azanes10-14 and resembles the struc-
ture of the [(t-BuN)(t-BuNP)]2HfCl2 parent complex.12
The central Hf atom has a distorted trigonal bipyrami-
dal configuration defined by two amido-hafnium bonds,
two hafnium-methyl bonds, and an additional coordi-
nation of metal with one of the imino nitrogen atoms
from the cyclodiphosph(III)azane ring (Figure 1). The
amido nitrogens as well as the methyl substituents are
positioned close to the corners of an ideal tetrahedron,
and the N-Hf-N angle is 122.59(12)° and Me-Hf-Me
is 104.2(2)°. The length of the Hf-N3 bond and P-Namido
bonds are elongated compared to the parent dichloro
complex (2.428(3) vs 2.394(9) Å and 1.698(3) vs
1.648(9) Å, respectively).21 This illustrates the decreased
Lewis acid character of the hafnium in compound 7. It
can be explained that in dichloro complexes the electron
density is moved from the metal toward the very
electronegative chlorine atoms, while in the alkyl de-
rivatives this effect is much weaker because of the
smaller electronegativity of the carbon.22 In 7, the
Hf-CH3 bonds have an average length of 2.231(5) Å,
which is usual for Hf-alkyl bond lengths; in [NON]Hf-
(CH2CMe3)2, bearing 2,4,6-trimethylphenyl groups, it is
reported to be 2.225(7) Å.23
Generation of Cationic Species. The bis(amido)-
dimethyl hafnium complexes 7-9 were reacted with
B(C6F5)3 in order to better understand the formation of
cationic bis(amido) hafnium complexes and to ascertain
the structure of the activated species. As the high
instability of the produced cationic complexes did not
(24) The color of this solution changed to brown during approxi-
mately 30 min, which indicated high instability of such complexes in
halogenated solvents.
(25) Two different methyl groups were also detected in the 13C NMR
spectrum (multiplet at δC ) 21.3 ppm and singlet at δC ) 58.15 ppm
(21) Similar trends were described for pentacoordinated [NON]ZrX2
(X ) Cl or Me) complexes, bearing tert-butyl groups. The Zr-O bond
was elongated from 2.336(3) Å in [NON]ZrCl2 to 2.418(3) Å in alkyl Zr
complex. See ref 20c.
(22) Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry:
Principles of Structure and Reactivity; Harper Collins College Publish-
ers: New York, 1993.
(23) Liang, L.-C.; Schrock, R. R.; Davis, W. M. Organometallics 2000,
19, 2526.
vs signal at δC ) 59.34 ppm for parent complex). A triplet at δC )
29.98 ppm (JPC ) 6.1 Hz) and a doublet at δC ) 33.60 ppm (JPC ) 6.5
Hz) can be assigned for the t-BuNimino groups. However, due to fact
that the reaction was unselective and a decomposition of 7/B(C6F5)3
occurred during the measurement, several indefinite signals appeared.
(26) The value of ∆δ(m,p-F) (19F NMR) is a good probe of coordina-
tion of [MeB(C6F5)3]- to cationic d0 metals (values of 3-6 ppm indicate
coordination; <3 ppm indicates noncoordination). See: Horton, A. D.;
de With, J. Chem. Commun. 1996, 1375.

Bis(amido) Hafnium Complexes
Organometallics, Vol. 24, No. 6, 2005 1341
Figure 2. 1H NMR (200 MHz, C6D6, 29 °C) spectrum of the hafnium cationic species formed in deuterobenzene by the
reaction of [(t-BuN)(t-BuNP)]2HfMe2 with B(C6F5)3.
Scheme 2
hafnium and the other methyl group remained without
apparent changes (2.228(6) vs 2.254(5) Å in the parent
complex 7). The methyl-boron bond is short (1.673(8)
Å)27 and the configuration of the boron atom is close to
tetrahedral, with CBC angles varying from 102.4(4)° to
116.1(5)°. This emphasizes the increased contribution
of sp3 hybridization, which is common for anionic
tetracoordinated boron. The charge-separated character
of this complex is unambiguously established by the
much longer Zr-CH3 (bridging) distance than the
Zr-CH3 (terminal) distance and the relatively normal
B-CH3 distances. The B‚‚‚CH3‚‚‚Hf bonding (B-C-Hf
angle is 172.6(4)°) can here be considered as ionic and
10 in the solid state as a tight ion pair ([LHfMe]+-
[MeB(C6F5)3]-), where the hafnium cation is weakly
associated with a boronate anion through a highly
unsymmetrical Hf-CH3-B bridge.28
As a result of the abstraction of one of its methyl
groups, hafnium acquires a high Lewis acid character,
which is materialized in the shortening of the Hf-Nimino
bond (2.315(4) vs 2.428(3) Å in [(t-BuN)(t-BuNP)]2HfMe2
vs 2.394(9) Å in [(t-BuN)(t-BuNP)]2HfCl2) and in an
increased degree of puckering of the phosph(III)azane
cycle. This distortion of the diphosph(III)azane cycle
prompts the electron-rich imino nitrogen atoms to get
closer to the cationic hafnium center, as it can be seen
from the distance between the metal center and the
noncoordinated imino nitrogen (N4), which is much
shorter than in 7 (2.765(5) Å in 10 vs 3.000(5) Å in 7)
and resembles the Hf-N4 distance in [(t-BuN)-
(t-BuNP)]2HfCl2 (2.793 Å).12
Figure 3. ORTEP plot of 10 with thermal ellipsoids drawn
at the 50% probability level. All hydrogen atoms, except
hydrogens at the CH3-B group, were omitted for clarity.
As activated nonmetallocene complexes are generally
characterized by their poor stability (which usually is
synonymous with high reactivity), their solid state
structures have scarcely been reported in the litera-
ture.4,9 However, crystals of 10 suitable for X-ray analy-
sis were successfully grown from a toluene-hexane
layer at -20 °C. The ORTEP diagram is presented in
Figure 3, and crystallographic data as well as selected
structural parameters are collected in Tables 1 and 2,
respectively.
In 10 hafnium is pentacoordinated, which is a com-
mon feature for bis(amido)cyclodiphosph(III)azane com-
plexes in the solid state, and the distorted trigonal-
bipyramidal configuration is achieved as a result of an
additional Hf1-N3 bonding from the diphosph(III)azane
ring. The coordination of B(C6F5)3 to one of the hafnium
methyl groups significantly elongated the Hf-Me dis-
tance (2.473(5) Å), while the bond length between the
1H NMR spectra in C6D6 show that 10 adopts Cs sym-
metry in solution: the coordination of B(C6F5)3 reduces
the complex symmetry as the methyl groups are ren-
dered nonequivalent. In addition, two different signals
1
in the H NMR corresponding to the t-BuNimino groups
denote their chemical nonequivalence (Figure 2), which
is noteworthy, as the parent complex 7 is strictly
C2v-symmetric in solution. We assume that this phe-
nomenon arises from the increased Lewis acidity of the
(27) This value indicates that [MeB(C6F5)3]- is weakly coordinated
to the hafnium cation. See ref 5a.
(28) Marks, T. J.; Kolb, J. R. Chem. Rev. 1977, 77, 263.

1342 Organometallics, Vol. 24, No. 6, 2005
Axenov et al.
Scheme 3
metal center, which favors in solution the formation of
an additional coordination from the diphosph(III)azane
cycle in a manner similar to that displayed in the solid
state structure of 10.
Stability of in situ formed cationic hafnium species
was reported to be improved in deuterated benzene by
coordination with the electron-donating solvent mol-
ecules.29 In a similar manner, 10 bearing relatively
small tert-butyl groups can be stabilized in noncoordi-
nating deuterated dichloromethane by intermolecular
donor-acceptor interactions of the highly electrophilic
cationic hafnium with phosphorus(III) free electron
pairs of a second hafnium cationic complex. This is
illustrated by the 31P NMR spectrum of the B(C6F5)3-
activated [(t-BuN)(t-BuNP)]2HfMe2 in CD2Cl2, with the
appearance of the largely upfield peak at 34.8 ppm.30
Likewise, dimethyl complexes 8 and 9 were treated
with B(C6F5)3 in deuterobenzene, and in both cases, a
phase separation occurred from the very unstable
(quickly darkening) solution, verifying that a reaction
did occur. According to 1H, 31P, and 19F NMR, the
deuterobenzene phases contained mainly the unreacted
parent complexes and B(C6F5)3, and only minor amounts
of the noncoordinated [MeB(C6F5)3]- anion (10%,
∆δ(m,p-F) ) 2.39 for 8 and 5%, ∆δ(m,p-F) ) 2.5 for 9)
were detected in 19F NMR, clearly indicating that the
activation was not quantitative.
acidity of the hafnium center is lower than in 10,
presumably due to additional donation of electron
density from the aryl substituents through the amido
nitrogen atoms.
On the basis of the experimental data, it seems that
in deuterated benzene the cationic species resulting
from the addition of the boron activator to the hafnium
complex precipitate as a denser oily phase, while only
the unreacted parent complex and B(C6F5)3 with a small
amount of product can be detected in the solvent phase.
It can be inferred from 1H NMR measurement that the
red oily phase contains the desired activated complex
with a large amount of coordinated deuterated ben-
zene.29 In CD2Cl2, the formed cationic compounds
remain soluble in the solvent and can thus be investi-
gated by means of NMR methods. In this same solvent,
the rate of activation, as well as decomposition, was
accelerated, and the presence of the parent hafnium
complex could not be detected.
Polymerization Activity. Complex [(t-BuN)-
(t-BuNP)]2HfCl2 and its methyl derivative showed a
moderate ethene polymerization activity after activation
by MAO or B(C6F5)3, respectively, while no activity was
observed in the case of complexes 5 and 6 bearing bulky
aromatic substituents and their methyl analogues 8 and
9 under the same conditions.32 This difference in po-
lymerization behavior can be explained by the poor
ability of Hf complexes bearing bulky aryl groups to be
activated in aromatic hydrocarbon solvents (vide supra).
Furthermore, the different geometry and coordination
number adopted in solution by the complexes bearing
tert-butyl and bulky aryl substituents after boron
activation can also have a detrimental effect on the rates
of monomer coordination, insertion, and â-H elimina-
tion.
To ascertain their exact nature, the resulting red oily
precipitates were separated from the solvent phase and
dissolved in CD2Cl2.31 In fact, from 1H NMR, 8/B(C6F5)3
and 9/B(C6F5)3 possess two different Hf-Me groups: a
sharp singlet at δH ) 0.26 ppm corresponds to the
methyl not coordinated to boron, while a broader one
at δH ) 0.43 ppm can be assigned to the Hf-Me-B
1
group. Concerning the ligand framework, H and 13C
NMR spectra displayed a molecular symmetry similar
to the parent Hf dimethyl complexes. The 31P NMR
spectrum displayed only a slight upfield shifting after
the addition of the boron activator: δP ) 114.74 vs
115.56 ppm for 8 and δP ) 98.25 vs 98.67 ppm for 9. In
19F NMR, peaks corresponding to the noncoordinated
[MeB(C6F5)3]- (∆δ(m,p-F) ) 2.56 for 8; ∆δ(m,p-F) ) 2.58
for 9) were recorded (see Supporting Information). These
data clearly underline that the additional cyclodiphos-
ph(III)azane imino nitrogen coordination to hafnium
observed for 10 is not occurring in the case of B(C6F5)3
activation of 8 and 9 (Scheme 3) and that the Lewis
(29) For arene coordination to the positively charged IVb group
metal atom see: (a) Ref 4. (b) Gillis, D. J.; Tudoret, M.-J.; Baird, M.
C. J. Am. Chem. Soc. 1993, 115, 2543. (c) Gillis, D. J.; Quyoum, R.;
Tudoret, M.-J.; Wang, Q.; Jeremic, D.; Roszak, A. W.; Baird, M. C.
Organometallics 1996, 15, 3600. (d) Lancaster, S. J.; Robinson, O. B.;
Bochmann, M. Organometallics 1995, 14, 2456.
(30) The coordination of the complex species, where the transition
metal reveals electron pair acceptor properties, with cyclodiphosph-
(III)azane ligands via P(III) atoms leads in 31P NMR to the upfield
shift of the signals corresponding to those coordinated phoshorus
atoms. See: (a) Hitchcock, P. B.; Lappert, M. F.; Layh, M. Eur. J. Inorg.
Chem. 1998, 751. (b) Scherer, O. J.; Quintus, P.; Kaub, J.; Sheldrick,
W. S. Chem. Ber. 1987, 120, 1463. (c) Jenkins, L. S.; Willey, G. R.
Dalton Trans. 1979, 777. (d) Reddy, V. S.; Krishnamurthy, S. S.;
Nethaji, M. Dalton Trans. 1995, 1933. (e) Scherer, O. J.; Krieger, K.
D. Z. Naturforsch., Ser. B 1982, 37B, 1041.
(31) In the first part of the experiments the reagents were mixed
in CD2Cl2, as was described for [(t-BuN)(t-BuNP)]2HfMe2 and B(C6F5)3.
In the second part the red liquid product obtained in deuterobenzene
was separated from the solvent phase and dissolved in dichlorodeu-
teromethane. In both cases identical NMR spectra were observed.
There was little difference in peak shifts due to solvent change (from
C6D6 to CD2Cl2).
Conclusions
Two new bis(amido)cyclodiphosph(III)azane dichloro
hafnium complexes bearing bulky aryl groups were
synthesized and were converted to their dimethyl
derivatives, as well as [(t-BuN)(t-BuNP)]2HfCl2, with
MeMgBr. Both dichloro and dimethyl complexes were
found to be C2v symmetric in solution, on account of the
absence of chemically nonequivalent groups. After
B(C6F5)3 activation, the hafnium derivatives showed
different properties (geometry, coordination number,
activation and decomposition rates) depending on the
(32) Polymerization conditions: steel autoclave, volume of the
polymerization toluene 200 mL, MAO/Hf ratio 1000 or Hf/B(C6F5)3 ratio
1 (with addition of TIBA as a scavenger TIBA/Hf 500), polymerization
temperature 50 °C for MAO activation and 30 °C for borane activation,
ethene pressure 3.8 bar.

Bis(amido) Hafnium Complexes
Organometallics, Vol. 24, No. 6, 2005 1343
reaction solvent and the nature of their amido substit-
uents. It appeared that in deuterated benzene the
activated complexes were more stable than in deu-
terated dichloromethane, but the activation was faster
in the latter solvent. B(C6F5)3-activated [(t-BuN)-
(t-BuNP)]2HfMe2 readily produced pentacoordinated
highly Lewis acidic hafnium species in both solvents,
and in deuterobenzene a strong hafnium cation-bor-
onate anion coordination occurred. Conversely, the
activation of the aryl-substituted hafnium complexes
was not quantitative, and the additional hafnium-
ligand coordination was not observed in solution. Pre-
sumably, the electron-rich aryl substituents donate
electron density to the hafnium center via the amide
nitrogens and therefore reduce its Lewis acidity. These
results are in good agreement with the ethene polym-
erization results previously reported for zirconium
dichloride analogues: the tert-butyl-substituted complex
gave higher polymerization activity than the aryl-
substituted ones after their activation with MAO.
Acknowledgment. Support of this work by Acad-
emy of Finland (project 204408) and Finnish National
Technology Agency (TEKES) (project 209739) is grate-
fully acknowledged. Great thanks to Pascal Castro for
helpful discussion and manuscript correction.
Supporting Information Available: Listings of spectral
data of compounds 5, 6, and 7; activation of complexes with
spectral characteristics observed. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM0492303