(NH)-phosphanylamido- and (PH)-phosphoraneiminato transition-metal complexes: Syntheses, structures, and computational studies

Article abstract of DOI:10.1021/om000967b

Reactions of aminobis(diorganylamino)phosphanes (R₂N)₂PNH₂ (R = iPr (a), Cy (b)) with Cp₂MCl₂ (M = Ti, Zr, Hf), CpTiCl₃, and TiCl₄ lead to the formation of the transition-metal complexes (R₂N)₂PN(H)MCp₂Cl (M = Ti (1b), Zr (2a,b), Hf (3a,b)) (R₂N)₂P(H)NTiCpCl₂ (8a,b), and (R₂N)₂P(H)NTiCl₃ (10a,b), respectively. The influence of electronic effects of the metal fragment on the resulting equilibrium between the (NH)-phosphanylamido and the tautomeric (PH)-iminophosphorane form is presented in detail. Computational studies unambiguously confirm the experimental results. The molecular structures of 2a, 3a, and 8b have been determined by single-crystal X-ray diffraction.

Full text of DOI:10.1021/om000967b

1770
Organometallics 2001, 20, 1770-1775
(NH)-P h osp h a n yla m id o- a n d (P H)-P h osp h or a n eim in a to
Tr a n sition -Meta l Com p lexes: Syn th eses, Str u ctu r es, a n d
Com p u ta tion a l Stu d ies†
Michael Raab,‡ Andreas Sundermann,§ Gerold Schick,‡ Armin Loew,‡
Martin Nieger,‡ Wolfgang W. Schoeller,§ and Edgar Niecke*,‡
Institut fu¨r Anorganische Chemie der Universita¨t Bonn, Gerhard-Domagk-Strasse 1,
53121 Bonn, Germany, and Fakulta¨t fu¨r Chemie der Universita¨t, Postfach 100131,
33501 Bielefeld, Germany
Received November 14, 2000
Reactions of aminobis(diorganylamino)phosphanes (R2N)2PNH2 (R ) iPr (a ), Cy (b)) with
Cp2MCl2 (M ) Ti, Zr, Hf), CpTiCl3, and TiCl4 lead to the formation of the transition-metal
complexes (R2N)2PN(H)MCp2Cl (M ) Ti (1b), Zr (2a ,b), Hf (3a ,b)) (R2N)2P(H)NTiCpCl2 (8a ,b),
and (R2N)2P(H)NTiCl3 (10a ,b), respectively. The influence of electronic effects of the metal
fragment on the resulting equilibrium between the (NH)-phosphanylamido and the tauto-
meric (PH)-iminophosphorane form is presented in detail. Computational studies unambigu-
ously confirm the experimental results. The molecular structures of 2a , 3a , and 8b have
been determined by single-crystal X-ray diffraction.
1. In tr od u ction
we have reported the reactions of aminobis(dicyclohexyl-
amino)phosphane, (Cy2N)2PNH2, with trialkylalanes
and dialkylaluminum hydrides. The strong acidic char-
acter of the Al center led to the formation of bis-
(dicyclohexylamino)iminophosphorane-trialkylalane
Lewis acid base adducts (Cy2N)2P(H)N(H)AlR3 (R ) Me,
Et, tBu) and dimeric bis(dicyclohexylamino)iminophos-
phorane-dialkylalane heterocycles [(Cy2N)2P(H)NAlR2]2
(R ) Me, Et), respectively.6 This corresponds to the
results of previous experimental and theoretical inves-
tigations on the isomerization of (NH)-aminophosphanes
R2P(NH)R′ to (PH)-iminophosphoranes.7
In this context, we have recently published the
reactions of aminobis(diorganylamino)phosphanes with
group 4 bis(cyclopentadienyl)-substituted complexes,8,9
leading to the formation of an equilibrium between the
(NH)-phosphanylamido species A and the tautomeric
(PH)-iminophosphorane form B (Scheme 1).
Substituted-cyclopentadienyl early-transition-metal
complexes have been investigated intensively due to
their potential as alkene polymerization catalysts.1 In
attempts to develop comparable systems with accessible
catalytic activity, several research groups have devel-
oped alternative ligands for early-metal systems with
similar reactivities such as carbolyl, C2B9H11,2 or the
phosphoraneiminato group, R3PN-, which have been
described as isolobal with the cyclopentadienyl ligand.3
In particular, early-transition-metal complexes, which
stabilize the phosphorane ligand, have been the subject
of a variety of experimental and theoretical studies.4
Furthermore, efforts to substitute the transition-
metal center by main-group-metal fragments have
drawn considerable attention.5 Within our own studies,
† Dedicated to Professor Kurt Dehnicke on the occasion of his 70th
birthday.
In the present paper, we report on experimental and
computational studies of ligand effects on the NH/PH-
tautomerization in (NH)-phosphanylamido and (PH)-
phosphoraneiminato group 4 transition-metal com-
plexes.
‡ Institut fu¨r Anorganische Chemie der Universita¨t Bonn.
§ Fakulta¨t fu¨r Chemie der Universita¨t.
(1) (a) Cornills, B.; Herrmann, W. A. In Applied Homogeneous
Catalysis with Organometallic Compounds; Wiley-VCH: Weinheim,
Germany, 1999. (b) Bochmann, M. J . Chem. Soc., Dalton Trans. 1996,
255. (c) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;
Waymouth, R. Angew. Chem. 1995, 107, 1255; Angew. Chem., Int. Ed.
Engl. 1995, 34, 1143.
(2) (a) Bei, X.; Kreuder, C.; Swenson, D. C.; J ordan, R. F.; Young,
V. G., J r. Organometallics 1998, 17, 1085. (b) Crowther, D. J .; Swenson,
D. C.; J ordan, R. F. J . Am. Chem. Soc. 1995, 117, 10403. (c) Kreuder,
C.; J ordan, R. F.; Zhang, H. Organometallics 1995, 14, 2993.
(3) Ru¨benstahl, T.; Weller, F.; Wocadlo, S.; Massa, W.; Dehnicke,
K. Z. Anorg. Allg. Chem. 1995, 621, 953.
(5) (a) Dehnicke, K.; Weller, F. Coord. Chem. Rev. 1997, 158, 103.
(b) Ong, C. M.; McKarns, P.; Stephan, D. W. Organometallics 1999,
18, 4197. (c) Aparna, K.; McDonald, R.; Ferguson, M.; Cavell, R. G.
Organometallics 1999, 18, 4241. (d) Dagorne, S.; J ordan, R. F.; Young,
V. G., J r. Organometallics 1999, 18, 4619.
(6) Schulz, S.; Raab, M.; Nieger, M.; Niecke, E. Organometallics
2000, 19, 2616.
(4) (a) Dehnicke, K.; Stra¨hle, J . Polyhedron 1989, 8, 707. (b)
Dehnicke, K.; Krieger, K.; Massa, W. Coord. Chem. Rev. 1999, 182,
19. (c) Stephan, W. D.; Stewart, J . C.; Gue´rin, F.; Spence, R. E. v. H.;
Xu, W.; Harrison, D. G. Organometallics 1999, 18, 1116. (d) Stephan,
W. D.; Gue´rin, F.; Spence, R. E. v. H.; Koch, L.; Gao, X.; Brown, S. J .;
Swabey, J . W.; Wang, Q.; Xu, W.; Zoricak, P.; Harrison, D. G.
Organometallics 1999, 18, 2046. (e) Gue´rin, F.; Stewart, J . C.; Beddie,
C.; Stephan, W. D. Organometallics 2000, 19, 2994. (f) Gue´rin, F.;
Stephan, W. D. Angew. Chem. 2000, 112, 1354. (g) Carraz, C. A.;
Stephan, W. D. Organometallics 2000, 19, 3791. (h) Diefenbach, A.;
Bickelhaupt, F. M. Z. Anorg. Allg. Chem. 1999, 625, 892. (i) Sunder-
mann, A.; Schoeller, W. W. J . Am. Chem. Soc. 2000, 122, 4729.
(7) See, e.g.: (a) Schmidpeter, A.; Ebeling, J . Angew. Chem. 1968,
80, 197; Angew. Chem., Int. Ed. Engl. 1968, 7, 197. (b) Schmidpeter,
A.; Rossknecht, H. Angew. Chem. 1969, 81, 572; Angew. Chem., Int.
Ed. Engl. 1969, 8, 614. (c) Romanenko, V. D.; Ruban, A. V.; Kalibab-
chuk, N. N.; Iksanova, S. V.; Markovski, L. N. J . Gen. Chem. USSR
(Engl. Transl.) 1981, 51, 1475. (d) O’Neal, H. R.; Neilson, R. H. Inorg.
Chem. 1984, 23, 1372. (e) Sudhakar, P. V.; Lammertsma, K. J . Am.
Chem. Soc. 1991, 113, 1899.
(8) Schick, G.; Loew, A.; Nieger, M.; Airola, K.; Niecke, E. Chem.
Ber. 1996, 129, 211.
(9) Schick, G.; Raab, M.; Gudat, D.; Nieger, M.; Niecke, E. Angew.
Chem. 1998, 110, 2486; Angew. Chem., Int. Ed. Engl. 1998, 37, 2390.
10.1021/om000967b CCC: $20.00 © 2001 American Chemical Society
Publication on Web 03/30/2001

NH/ PH Tautomerization
Sch em e 1
Organometallics, Vol. 20, No. 9, 2001 1771
pentane and diethyl ether (2b), and pentane (3b) were added
to the residue. The precipitated LiCl was filtered off and the
solvent removed under vacuum. 1b and 3b were crystallized
from diethyl ether and 2b from diethyl ether/toluene (2:1) at
-30 °C. 1b: yield 0.83 g (67%); mp 139 °C. 31P{1H} NMR
1
(C6D6): δ 100.6 (s). H NMR (C6D6): δ 6.22 (s, 10H, Cp), 2.73
(m, 4H, NCH), 1.9-0.9 (m, 40H, CH2). 13C NMR (C6D6): δ
2
3
114.4 (s, Cp), 55.7 (d, J CP ) 9.3 Hz, PNC), 36.1 (d, J CP ) 8.2
3
Hz, PNCC), 35.5 (d, J CP ) 5.6 Hz, PNCC), 34.8 (s, PNCCC),
27.6 (s, PNCCCC). Anal. Calcd (found) for C34H55ClN3PTi: C,
2. Exp er im en ta l Section
65.85 (65.79); H, 8.94 (8.85); N, 6.78 (6.70). 2b: yield 1.20 g
2.1. Gen er a l Con sid er a tion s. All manipulations were
performed with the exclusion of air and moisture under argon
employing standard Schlenk techniques. Solvents were dried
by using standard procedures. Cp2TiCl2, Cp2ZrCl2, Cp2HfCl2,
1
(91%); mp 135 °C. 31P{1H} NMR (C6D6): δ 94.0 (s). H NMR
(C6D6): δ 6.20 (s, 10H, Cp), 3.40 (m, 4H, NCH), 1.6-0.9 (m,
2
40H, CH2). 13C NMR (C6D6): δ 114.5 (s, Cp), 55.6 (d, J CP
)
)
3
3
9.2 Hz, PNC), 35.9 (d, J CP ) 5.3 Hz, PNCC), 35.3 (d, J CP
10
and TiCl4 were used as received. CpTiCl3 and (R2N)2PNH2
6.9 Hz, PNCC), 27.9 (s, PNCCC), 25.8 (s, PNCCCC). Anal.
Calcd (found) for C34H55ClN3PZr: C, 61.55 (61.44); H, 8.35
(8.28); N, 6.33 (6.29). 3b: yield 0.45 g (61%); mp 103 °C. 31P-
(R ) iPr, Cy)8 were prepared by literature methods. A Bruker
AMX 300 spectrometer was used for NMR spectroscopy. 1H
and 13C{1H} spectra were referenced to internal C6D5H (δ(1H)
7.154, δ(13C) 128.0) and 31P to external H3PO4. Mass spectra
were recorded on a VG Masslab 12-250 spectrometer in the
electron impact mode (EI). Melting points were observed in
sealed capillaries and were not corrected. Elemental analyses
were performed at the Mikroanalytisches Labor der Univer-
sita¨t Bonn.
1
{1H} NMR (C6D6): δ 95.4 (s). H NMR (C6D6): δ 6.19 (s, 10H,
Cp), 2.60 (m, 4H, NCH), 2.0-0.9 (m, 40H, CH2). 13C NMR
2
(C6D6): δ 112.5 (s, Cp), 53.6 (d, J CP ) 8.9 Hz, PNC), 34.4 (d,
3
3J CP ) 4.1 Hz, PNCC), 33.6 (d, J CP ) 4.1 Hz, PNCC), 27.2 (s,
PNCCC), 26.2 (s, PNCCCC). Anal. Calcd (found) for C34H55
ClHfN3P: C, 54.40 (54.36); H, 7.38 (7.31); N, 5.60 (5.49).
-
Gen er a l Syn th esis of (iP r 2N)2P (H)NTiCp Cl2 (8a ) a n d
(Cy2N)2P (H)NTiCp Cl2 (8b). To a solution of aminobis(di-
organylamino)phosphane (a , 0.48 g; b, 0.82 g; 2 mmol of each)
in THF (20 mL) was added n-butyllithium (1.43 mL, 2.3 mmol,
1.6 M in hexane) at -40 °C (8a ) and -10 °C (8b), respectively,
and the mixture was stirred for 15 min (8b, 45 min). Then, a
solution of cyclopentadienyltitanium trichloride (0.44 g, 2
mmol) in THF (20 mL) was added dropwise at -78 °C (8b,
-40 °C). The mixture was slowly warmed to room tempera-
ture. The solvent was removed under reduced pressure. A
mixture of pentane and toluene (8b, pentane and diethyl ether)
was added to the residue. The precipitated LiCl was filtered
off and the solvent removed under vacuum. 8a ,b were crystal-
lized from toluene and diethyl ether (2:1) at -30 °C. 8a : yield,
0.68 g (79%); mp 114 °C. 31P NMR (C6D6): δ -16.1 (dquin,
2.2. Gen er a l Syn th esis of (iP r 2N)2P N(H)Zr Cp 2Cl (2a )
a n d (iP r 2N)2P N(H)HfCp 2Cl (3a ). To a solution of aminobis-
(diisopropylamino)phosphane (0.48 g, 2 mmol) in THF (20 mL)
was added n-butyllithium (1.43 mL, 2.3 mmol, 1.6 M in
hexane) at -30 °C. The mixture was stirred and warmed to
-10 °C within 1 h. Then, a solution of dicyclopentadienyl-
metallocene dichloride (2a , 0.58 g; 3a , 0.76 g; 2 mmol for each)
in THF (20 mL) was added dropwise at -78 °C. The mixture
was warmed to room temperature. After the solvent was
removed under reduced pressure, a mixture of pentane and
diethyl ether (1:1) was added to the residue. The precipitated
LiCl was filtered off and the solvent removed under vacuum.
Both compounds were recrystallized from a 2:1 mixture of
diethyl ether and toluene (2a , -30 °C; 3a , -78 °C). 2a : yield
0.88 g (88%); mp 132 °C. 31P{1H} NMR (CDCl3): δ 90.4 (s). 1H
3
1J PH ) 549 Hz, J PH ) 19.1 Hz). 1H NMR (C6D6): δ 7.27 (d,
3
NMR (CDCl3): δ 6.19 (s, 10H, Cp), 3.30 (d, J HP ) 14.2 Hz,
3
1J PH ) 549 Hz, 1H, PH), 6.41 (s, 5H, Cp), 3.40-3.25 (m, J HH
3
3J HH ) 6.7 Hz, 4H, NCH), 1.41 (d, J HH ) 6.7 Hz, 12H, CH3),
) 6.8 Hz, 4H, NCH), 1.31 (d, 3J HH ) 6.8 Hz, 12H, CCH3), 0.99
3
1.36 (d, J HH ) 6.7 Hz, 12H, CH3). 13C NMR (CDCl3): δ 114.5
3
(d, J HH ) 6.8 Hz, 12H, CCH3). 13C NMR (C6D6): δ 115.4 (s,
(s, Cp), 44.8 (d, 2J CP ) 11.4 Hz, PNC), 24.7 (s, PNCC). MS (180
2
3
Cp), 45.6 (d, J CP ) 5.8 Hz, PNC), 23.8 (d, J CP ) 3.0 Hz,
°C/70 eV): m/z 502 (3) [M+], 467 (4) [M+ - Cl], 437 (1) [M+
-
3
PNCC), 22.9 (d, J CP ) 3.0 Hz, PNCC). MS (200 °C/70 eV):
Cp], 402 (5) [M+ - N(iPr)2], 367 (3) [M+ - N(iPr)2 - Cl], 255
(22) [ClZrCp2+], 100 (100) [N(iPr)2+]. Anal. Calcd (found) for
m/z 430 (3) [M+], 395 (2) [M+ - Cl], 330 (7) [M+ - N(iPr)2],
247 (6) [M+ - CpTiCl2], 183 (4) [CpTiCl2+],100 (100) [N(iPr)2].
Anal. Calcd (found) for C17H34Cl2N3PTi: C, 47.46 (47.35); H,
7.97 (7.91); N, 9.77 (9.70). 8b: yield 0.98 g (83%); mp 125 °C.
C
22H39ClN3PZr: C, 52.51 (52.45); H, 7.81 (7.75); N, 8.35 (8.28).
3a : yield 0.98 g (83%); mp 123 °C. 31P{1H} NMR (CDCl3): δ
92.8 (s). 1H NMR (CDCl3): δ 6.04 (s, 10H, Cp), 3.46 (m, 4H,
31P NMR (C6D6): δ -15.2 (dquin, J PH ) 550 Hz, J PH ) 16.5
1
3
3
3
NCH), 1.26 (d, J HH ) 6.8 Hz, 12H, CH3), 1.15 (d, J HH ) 6.8
Hz, 12H, CH3). 13C NMR (CDCl3): δ 110.1 (s, Cp), 46.5 (d, 2J CP
) 5.4 Hz, PNC), 25.7 (s, PNCC), 23.1 (s, PNCC). MS (180 °C/
1
1
Hz). H NMR (C6D6): δ 7.26 (d, J PH ) 550 Hz, 1H, PH), 6.58
(s, 5H, Cp), 3.20 (m, 4H, PNCH), 1.9-0.9 (m, 40H, CH2). 13C
2
NMR (CDCl3): δ 115.4 (s, Cp), 54.7 (d, J CP ) 4.9 Hz, PNC),
70 eV): m/z 590 (2) [M+], 547 (6) [M+ - N(iPr)], 513 (2) [M+
-
3
3
34.8 (d, J CP ) 2.7 Hz, PNCC), 34.1 (d, J CP ) 1.9 Hz, PNCC),
Cl - iPr], 490 (45) [M+ - N(iPr)2], 390 (25) [M+ - (N(iPr)2)2],
343 (52) [HfCp2Cl+], 247 (5) [M+ - Cp2HfCl], 100 (100)
[N(iPr)2+]. Anal. Calcd (found) for C22H39ClHfN3P: C, 44.75
(44.66); H, 6.66 (6.61); N, 7.12 (7.08).
27.3 (s, NCCC), 26.0 (s, NCCCC). Anal. Calcd (found) for
C
29H50Cl2N3PTi: C, 58.99 (58.87); H, 8.54 (8.47); N, 7.12 (7.01).
Syn th esis of (iP r 2N)2P (H)NTiCl3 (10a ) a n d (Cy2N)2P -
(H)NTiCl3 (10b). To a solution of aminobis(diorganylamino)-
phosphane (a , 0.36 g; b, 0.62 g; 1.5 mmol of each) in THF (20
mL) was added triethylamine (0.16 mL, 1.5 mmol) at -30 °C.
This mixture was added dropwise to a solution of titanium
tetrachloride (0.28 g, 1.5 mmol) in THF at -78 °C and warmed
to room temperature within 2 h. After the solvent was removed
under reduced pressure, hexane (20 mL) was added to the
residue. The precipitated ammonium chloride was filtered off,
and 10a ,b were crystallized from this solution at -60 °C. 10a :
yield 0.38 g (61%); mp 92 °C. 31P NMR (CDCl3): δ -11.6
Gen er a l Syn t h esis of (Cy2N)2P N(H )TiCp 2Cl (1b ),
(Cy2N)2P N(H )Zr Cp 2Cl (2b ), a n d (Cy2N)2P N(H )H fCp 2Cl
(3b). To a solution of aminobis(dicyclohexylamino)phosphane
(0.41 g, 1 mmol) in THF (15 mL) was added n-butyllithium
(0.63 mL, 1.1 mmol, 1.6 M in hexane) at -10 °C. The mixture
was stirred at this temperature for 1 h, and then a solution of
dicyclopentadienylmetallocene dichloride (1b, 0.25 g; 2b, 0.29
g; 3b, 0.38 g; 1 mmol of each) in THF (15 mL) was added
dropwise at -40 °C. The mixture was warmed to room
temperature within 2 h, and the solvent was removed under
reduced pressure. Mixtures of pentane and toluene (1b ),
1
3
1
(dquin, J PH ) 582 Hz, J PH ) 15.9 Hz). H NMR (CDCl3): δ
1
7.88 (d, J PH ) 582 Hz, 1H, PH), 3.72 (m, 4H, NCH), 1.64 (d,
3
3J HH ) 6.8 Hz, 6H, CCH3), 1.56 (d, J HH ) 6.8 Hz, 6H, CCH3),
(10) Chandra, K.; Sharma, R. K.; Kumar, N.; Garg, B. S. Chem. Ind.
1980, 288.
1.44 (d, 3J HH ) 6.8 Hz, 6H, CCH3), 1.32 (d, 3J HH ) 6.8 Hz, 6H,

1772 Organometallics, Vol. 20, No. 9, 2001
Raab et al.
Ta ble 1. Cr ysta llogr a p h ic Da ta a n d Mea su r em en ts for (iP r 2N)2P N(H)Zr Cp 2Cl (2a ), (iP r 2N)2P N(H)HfCp 2Cl
(3a ), a n d (Cy2N)2P (H)NTiCp Cl2 (8b)
2a
3a
8b
mol formula
fw
C
22H39ClN3PZr
C22H39ClHfN3P
590.47
C29H50Cl2N3PTi‚0.5(toluene)
636.56
503.20
cryst syst
space group
a, Å
b, Å
monoclinic
P21/c (No. 14)
15.4818(4)
10.2902(3)
16.2080(5)
monoclinic
P21/c (No. 14)
15.4475(3)
10.2903(2)
16.2122(4)
triclinic
P1h (No. 2)
8.9411(3)
10.5678(3)
19.6517(4)
102.374(2)
93.787(2)
108.596(2)
1700.81(8)
2
c, Å
R, deg
â, deg
106.785(2)
106.945(1)
γ, deg
V, Å3
2472.10(12)
4
2456.20(9)
4
Z
radiation (wavelength, Å)
Mo KR (0.710 73)
Mo KR (0.710 73)
Mo KR (0.710 73)
µ, mm-1
0.630
4.417
0.481
temp, K
123(2)
1.352
123(2)
1.591
123(2)
1.243
D
calcd, g cm-3
cryst dimens (mm)
2θmax, deg
min/max transmissn
no. of rflns recorded
no. of nonequiv rflns recorded
Rint
0.20 × 0.07 × 0.04
0.25 × 0.15 × 0.10
0.25 × 0.15 × 0.10
50.0
56.66
56.6
0.8697, 0.9037
27 880
4348
0.4038, 0.6781
49 761
6116
22 855
6061
0.027
0.052
0.059
no. of params/restraints
256/1
0.0328, 0.0741
1.08
256/1
0.0211, 0.0480
0.99
400/403
0.0353, 0.1046
1.08
R1,a wR2b
goodness of fitc
final max, min ∆F, e Å-3
0.690, -0.328
0.914, -1.086
0.413, -0.322
R1 ) ∑(||Fo| - |Fc||)/∑|Fo| (for I > 2σ(I)). wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2
.
c Goodness of fit ) {∑[w(|Fo | - |Fc |)2]/(Nobservns
-
a
b
2
2
2
N
params)}1/2
.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 2a , 3a , a n d 8b
CCH3). 13C NMR (CDCl3): δ 46.1 (d, 2J CP ) 5.7 Hz, PNC), 23.8
3
3
(d, J CP ) 3.0 Hz, PNCC), 22.7 (d, J CP ) 2.3 Hz, PNCC). MS
(180 °C/70 eV): m/z 400 (18) [M+], 365 (15) [M+ - Cl], 300
(20) [M+ - N(iPr)2], 246 (5) [M+ - TiCl3], 147 (9) [M+ - TiCl3
Compound 2a
P1-N1
P1-N2
P1-N3
1.722(2)
1.699(2)
1.701(2)
Zr1-N1
2.067(2)
2.497(1)
2.226a
Zr1-Cl1
- N(iPr)2], 100 (100) [N(iPr)2+]. Anal. Calcd (found) for C12H29
-
Zr1-Cp(centroid)
Cl3N3PTi: C, 35.98 (35.84); H, 7.30 (7.19); N, 10.49 (10.36).
10b: yield 0.67 g (79%); mp 105 °C. 31P NMR (C6D6): δ -16.4
N1-P1-N2
N1-P1-N3
N2-P1-N3
103.5(1)
101.3(1)
105.9(1)
P1-N1-Zr1
N1-Zr1-Cl1
137.6(1)
100.8(1)
1
3
(dquin, J PH ) 587 Hz, J PH ) 15.8 Hz). 1H NMR (C6D6): δ
1
7.00 (d, J PH ) 587 Hz, 1H, PH), 3.00 (m, 4H, NCH), 1.9-1.3
(m, 40H, CH2). 13C NMR (C6D6): δ ) 55.2 (d, J CP ) 5.0 Hz,
2
Compound 3a
3
3
PNC), 34.8 (d, J CP ) 2.7 Hz, PNCC), 33.6 (d, J CP ) 1.9 Hz,
PNCC), 27.0 (s, NCCC), 25.6 (s, NCCCC). MS (300 °C/16 eV):
m/z 559 (2) [M+], 524 (4) [M+ - Cl], 476 (4) [M+ - Cy], 406
(35) [M+ - TiCl3], 180 (75) [NCy2+]. Anal. Calcd (found) for
C24H45Cl3N3PTi: C, 51.40 (51.32); H, 8.09 (8.00); N, 7.49 (7.36).
X-r a y Str u ctu r e Solu tion a n d Refin em en t. Crystal-
lographic data for 2a , 3a , and 8b are summarized in Table 1,
and selected bond lengths and angles are given in Table 2.
Figures 1-3 show the ORTEP diagrams of the solid-state
structures of 2a , 3a , and 8b. Data were collected on a Nonius
Kappa-CCD diffractometer. Structures were solved by direct
methods (SHELXS-97)11 and refined by full-matrix least
squares on F2 (SHELXL-97).12 All non-hydrogen atoms were
refined anisotropically, and hydrogen atoms, localized by
difference electron density determination, used a riding model
(coordinates of H(N) and H(P) free). An empirical absorption
correction was applied for 2a and 3a ; in 8b one solvent
molecule (toluene) and a cyclohexyl group are disordered.
P1-N1
P1-N2
P1-N3
1.718(2)
1.696(2)
1.704(2)
Hf1-N1
2.052(2)
2.467(1)
2.209a
Hf1-Cl1
Hf1-Cp(centroid)
N1-P1-N2
N1-P1-N3
N2-P1-N3
103.4(1)
101.7(1)
105.9(1)
P1-N1-Hf1
N1-Hf1-Cl1
137.4(1)
99.8(1)
Compound 8b
P1-N1
P1-N2
P1-N3
Ti1-N1
1.592(2)
Ti1-Cp(centroid)
Ti1-Cl1
Ti1-Cl2
2.061(1)
2.306(1)
2.314(1)
1.643(2)
1.649(2)
1.781(2)
N1-P1-N2
N1-P1-N3
N2-P1-N3
P1-N1-Ti1
115.4(1)
N1-Ti1-Cl1
N1-Ti1-Cl2
Cl1-Ti1-Cl2
102.8(1)
104.4(1)
103.0(1)
111.6(1)
109.6(1)
152.0(1)
a
Average M1-Cp(centroid) distance.
Compounds 1a ,b-3a ,b can be stored at -30 °C for
weeks without decomposition, and no rearrangement to
the (PH)-phosphoraneiminato-substituted tautomers
4a ,b-6a ,b is detected at this temperature.
3. Resu lts a n d Discu ssion
The addition of Cp2MCl2 (M ) group 4 metal) to a
solution of aminobis(dialkylamino)phosphane, (R2N)2-
PNH2 (R ) iPr (a ), Cy (b)), and n-butyllithium in THF
afford the (NH)-phosphanylamido-substituted transi-
tion-metal complexes 1-3 (Scheme 2).
The constitution of 1a ,b-3a ,b follows from the high-
1
resolution mass spectra and the 31P, H, and 13C NMR
spectra. Compared to the 31P NMR resonances of the
starting materials,8 the observed phosphanylamido-
complexes 1b, 2a ,b, and 3a ,b show a downfield shift of
the P(III) atoms (1b, 100.6 ppm; 2a , 90.4 ppm; 2b, 94.0
ppm; 3a , 92.8 ppm; 3b, 95.4 ppm).
(11) Sheldrick, G. M. SHELXS-97, Program for Structure Solution.
Acta Crystallogr., Sect. A 1990, 46, 467.
(12) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1997.

NH/ PH Tautomerization
Organometallics, Vol. 20, No. 9, 2001 1773
Sch em e 3
3a , 1.718 Å) differ only slightly from those observed for
(iPr2N)2PN(H)TiCpCl2 (P1-N1 ) 1.723 Å), previously
obtained in our group,8 and fall in the typical range of
PIII-N single-bond lengths.13 The M1-N1-P1 bond
angles (2a , 137.6°; 3a , 137.4°), the planarity of N1, and
the M1-N1 distance (2a , 2.067 Å; 3a , 2.052 Å) suggest
some kind of π-interaction between the nitrogen and the
transition metal.
F igu r e 1. ORTEP plot (50% probability level) showing the
solid-state structure and atom-numbering scheme for 2a .
Heating 1-3 gently to 50 °C in polar solvents leads
to the formation of the PH tautomers 4-6, indicated
by the occurrence of 31P NMR resonances significantly
shifted upfield (4b, -3.9 ppm; 5a , -7.4 ppm; 5b, -4.7
ppm; 6a , 0.1 ppm; 6b, 1.7 ppm) and characteristic P,H
coupling constants (1J HP = 550 Hz).14 The reactions
afford mixtures of the “NH” and the “PH” isomers, and
4-6 cannot be isolated in a pure form, indicating a slow
establishment of the equilibrium. Heating the mixture
up to higher temperatures or for a longer period leads
to decomposition.
Metalation of aminobis(diorganylamino)phosphanes
(R2N)2PNH2 (R ) iPr, Cy) with n-butyllithium and
subsequent reaction with CpTiCl3 gives the (PH)-
phosphoraneiminato-substituted complexes 8a,b (Scheme
3), proven by the significant shielding of the phosphorus
atoms (8a , -16.1 ppm; 8b, -15.2 ppm) in the 31P NMR
spectra and typical P,H coupling constants (8a , 549 Hz;
8b, 550 Hz). The formation of the NH tautomers 7a ,b
is not detected, even at low temperatures. This corre-
sponds well with the stronger Lewis acidity of the mono-
compared to the bis(cyclopentadienyl) fragment.
Single crystals of 8b, suitable for X-ray structure
determination, were obtained from a diethyl ether/
toluene solution. The structure (Figure 3, Table 1)
undoubtedly proves the presence of the (PH)-iminophos-
phorane form in the solid state, as expected from the
multinuclear NMR studies.
F igu r e 2. ORTEP plot (50% probability level) showing the
solid-state structure and atom-numbering scheme for 3a .
Sch em e 2
The P1-N1 bond lengths of 1.592 Å lies in the upper
range for PN double bonds.15 Compared to the single
bond covalent distances, the Ti1-N1 distance (1.781 Å)
is significantly shortened. This corresponds well with
the data found for the similar Ph3PNTiCpCl2 complex.16
The M1-N1-P1 bond angle of 152.0° is not consistent
with most common descriptions of the bonding situation
in phosphoraneiminato complexes with linear M-N-P
arrangements (161-177°) or a bent M-N-P moiety
(13) Trinquier, G.; Ashby, M. T. Inorg. Chem. 1994, 33, 1306.
(14) (a) Schmidpeter, A.; Eberling, J .; Stary, H.; Weingand, C. Z.
Anorg. Allg. Chem. 1972, 394, 171. (b) Krishnamurthy, S. S.; Woods,
M. Annu. Rep. NMR Spectrosc. 1987, 19, 175.
(15) Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Claren-
don: Oxford, U.K., 1984.
The molecular structures of 2a and 3a are further
proven by crystal structure analysis (Figures 1 and 2,
Table 1). The transition metals feature a distorted-
tetrahedral coordination by two η5-coordinated cyclo-
pentadienyl ligands, a chlorine atom, and the amido
nitrogen atom. The P1-N1 bond lengths (2a , 1.722 Å;
(16) Latham, I. A.; Leigh, G. J .; Huttner, G.; J ibril, I. J . Chem. Soc.,
Dalton Trans. 1986, 377.

1774 Organometallics, Vol. 20, No. 9, 2001
Raab et al.
Ta ble 3. Rela tive En er gies (∆E in k J m ol-1) of th e
Tw o Ta u tom er s Accor d in g to Eq 1 for [RR′P HN]-
Ion sa
R
R′
∆E
R
R′
NH2
N(CH3)2
∆E
H
H
H
NH2
130.9
109.4
NH2
N(CH3)2
99.0
98.7
a
Values for ∆E + zero point vibrational energy correction are
given in parentheses.
developed with Becke’s three-parameter exchange func-
tional17 and the Lee-Young-Parr correlation func-
tional.18 As basis sets the relativistically corrected
effective core potentials of Stevens, Basch, and Krauss19
with a double-ú basis expansion for the valence space
were used, augmented by one set of polarization func-
tions (of d type) for the heavy (non-hydrogen) main-
group elements (SBK(d) basis). The use of polarization
functions is imperative to get a correct description of
the strongly polar P-N bond. For all anions this basis
set was augmented by a set of diffuse s and p functions
(SBK(d+diff)) to account for the larger extent of the
MOs in these molecules. All stationary points were
verified as local minima by inspection of the eigenvalues
of the corresponding Hessian matrices (calculated at the
DFT level as well). All calculations were performed
using the Gaussian 98 package of programs.20
F igu r e 3. ORTEP plot (50% probability level; disordered
parts omitted for clarity) showing the solid-state structure
and atom-numbering scheme for 8b.
Sch em e 4
4.2. Com p u ta tion a l Resu lts. To give support to the
experimental results, DFT calculations have been per-
formed on several model compounds. Within these
models the organic residues of the amino groups have
been replaced by hydrogen atoms. The determination
of the relative energy ∆E of the tautomers (as given by
eq 1) was the main objective of our calculations, because
an experimental measurement of ∆E is difficult.
(R2P)NH- h (R2HP)N- + ∆E
(1)
For the uncoordinated anion RR′PHN-, the NH
tautomer in equilibrium 1 is clearly favored. The size
of ∆E depends on the number of amino groups at the
phosphorus atom. This is demonstrated in Table 3. To
mimic the experimental situation more closely, also the
effect of dimethylamino substitution was considered.
Accordingly, the electronegative groups such as NRR′
(R,R′ ) H, CH3) decrease the energy difference between
the tautomers, though the sign of ∆E is not altered. The
replacement of the hydrogens by methyl groups does not
affect the equilibrium between both anionic structural
isomers.
(130-140°).4a But, as recently demonstrated by Bick-
elhaupt, the variation of the bond angle over 50° is
associated with a change on the potential energy surface
of less than 2 kcal/mol.4h This indicates a great influence
of the different substituents in the R3PN- fragment and
the surroundings in the solid state on the observed
M-N-P angle and explains the unusual situation in
8b.
At least, (R2N)2PNH2 species (R ) iPr, Cy) are reacted
with titanium tetrachloride and triethylamine in THF
(Scheme 4). As expected, no NH tautomers 9a ,b are
accessible and only the PH compounds 10a ,b are
formed, due to the increasing electrophilicity at the
metal center compared to the cyclopentadienyl-substi-
tuted fragments CpMCl2 and Cp2MCl.
It is different if the anion is coordinated to a transition
metal complex fragment. Because of the coordination
(17) Becke, A. D. J . Chem. Phys. 1993, 98, 5648.
In the 31P NMR spectra, the presence of the PH form
is again confirmed by the observation of the typical
shielding of the phosphorus atoms (10a , -11.6 ppm;
10b, -16.4 ppm) and the occurrence of characteristic
P,H coupling constants (10a , 582 Hz; 10b, 587 Hz). The
proposed constitution and the high thermal stability of
10a ,b are further proven by the results of mass spec-
troscopy. In both cases, the highest observed peaks
correspond with the molecular ions.
(18) Lee, C.; Young, W.; Parr, R. G. Phys. Rev. 1988, B37, 785.
(19) (a) Stevens, W. J .; Basch, H.; Krauss, M. J . Chem. Phys. 1984,
81, 6026. (b) Stevens, W. J .; Krauss, M.; Basch, H.; J asien, P. G. Can.
J . Chem. 1992, 70, 612.
(20) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.,
J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; J ohnson, B. G.; Chen,
W.; Wong, M. W.; Andres, J . L.; Head-Gordon, M.; Replogle, E. S.;
Pople, J . A. Gaussian 98, revision A.3; Gaussian, Inc.: Pittsburgh, PA,
1998.
4. Com p u ta tion a l Stu d ies
4.1. Com p u ta tion a l Meth od s. All molecules were
fully optimized at the B3LYP level. This method is

NH/ PH Tautomerization
Organometallics, Vol. 20, No. 9, 2001 1775
Ta ble 4. Rela tive En er gies (∆E in k J m ol-1) for
Ta ble 5. Ca lcu la ted Bon d Len gth s (Å) a n d An gles
(d eg) for MClxCp 3-x(NP H(N′H2)2) a n d
MClxCp 3-x(NP H(NH2)2) vs MClxCp 3-x(NHP (NH2)2)a
MClxCp 3-x(NHP (N′H2)2) (TS ) tr a n sition sta te)
M
Ti
x
∆E
a
M
x
M-N
P-N
P-N′
M-Cl
P-N-M
3
2
1
-24.9 (-22.4)/31.0 (24.9)b
-9.7 (-10.6)
NH Tautomer
2.249b
2.220b
2.405b
2.380b
2.383b
2.360b
111.9
139.2
112.7
139.4
112.3
139.5
33.3 (29.5)
Ti
Zr
Hf
3
1.914
1.850
2.074
2.007
2.050
1.985
1.724
1.775
1.722
0.772
1.772
1.770
1.760
3 (TS)
3
1.714
1.769
1.721
1.772
1.723
Zr
3
2
1
-32.9 (-31.2)/51.8 (45.5)b
-9.7 ( -11.0)
28.2 (24.5)
-35.0 (-33.4)/56.9 (50.1)b
-12.9 (-14.5)
26.4 (22.4)
3 (TS)
3
3 (TS)
Hf
3
2
1
Ti
Zr
Hf
2
2
2
1.901
2.049
2.026
1.772
1.765
1.765
1.719
1.727
1.728
2.282b
2.429b
2.397b
135.2
134.8
135.9
a
Values for ∆E + zero point vibrational energy correction are
b
given in parentheses. The first entry is the relative energy of
the NH transition state, and the second entry is the relative energy
of the corresponding minimum. For molecular structures, see
Figure 4.
Ti
Zr
Hf
1
1
1
1.960
2.101
2.073
1.740
1.736
1.737
1.735
1.737
1.737
2.443
2.520
2.486
141.5
138.8
139.1
PH Tautomer
Ti
Zr
Hf
3
3
3
1.772
1.933
1.913
1.588
1.573
1.569
1.677
2.240b
2.400b
2.375b
143.9
178.8
178.5
1.685
1.686
Ti
Zr
Hf
2
2
2
1.803
1.957
1.938
1.582
1.569
1.561
1.682
1.689
1.692
2.318b
2.449b
2.419b
137.7
150.8
170.8
Ti
Zr
Hf
1
1
1
1.859
2.000
1.980
1.556
1.555
1.552
1.708
1.701
1.703
2.472
2.542
2.506
142.5
152.4
154.1
a
b
Average P-N′ distance. Average M-Cl distance.
The calculated structures are in good agreement with
the experimental findings and give support to the
reliability of our results.
F igu r e 4. Molecular structure of complexes MCl3NHP-
(NH2)2: (left) NH tautomer; (right) PH tautomer, transition
state; (top) NH tautomer, minimum. The NH tautomer is
the most favorable configuration for this complex.
5. Con clu sion s
The syntheses and structures of different group 4
transition-metal complexes of the type (R2N)2PN(H)-
MCpnCl3-n and the tautomeric (R2N)2P(H)NMCpnCl3-n
are presented. The formation of the (NH)-phosphanyl-
amido or the (PH)-iminophosphorane form is dependent
on the Lewis acidity of the transition-metal fragment.
A stronger acidic character of the metal center stabilizes
the PH form. This corresponds to the results previously
obtained for similar reactions with several aluminum
trialkyls and dialkylaluminum hydrides.
Computational studies ambiguously confirm the experi-
mental results and can be summarized as follows: to
stabilize the PH tautomer, a π-acceptor binding to the
nitrogen atom is necessary. If this atom/fragment is only
a σ-acceptor (e.g., a proton), the NH form is the
energetically favored tautomer. Cyclopentadienyl ligands
compete with the phosphoraneiminato ligand for the
acceptor orbitals of the transition-metal atom. If the
transition-metal complex fragment contains two Cp
ligands, its acidity is not sufficient to stabilize the PH
tautomer. For the NH-PH tautomerization, all ele-
ments of group 4 have similar acceptor strengths.
the relative stability of the phosphoraneiminato form
-
(eq 1, right) is promoted. If the anion NPH(NH2)2 is
coordinated to a complex fragment of sufficient π-acid-
ity, the equilibrium is shifted to the right-hand side, the
outcome increasing with the Lewis acidity of the transi-
tion metal fragment. This is shown in Table 4 for several
complexes with elements of group 4.
The calculated relative energies show that the π-acid-
ity of the complex fragment and therefore the stability
of the PH form depends on the number of π-donor
ligands coordinated to the transition-metal atom. As a
consequence, the stability of the PH tautomer increases
in the order MCp2Cl < MCpCl2 < MCl3. Here, one has
to take into account that the expected structure of the
complex Cl3M(NH)P(NH2)2 is only a transition state on
the energy hypersurface. In the corresponding minimum
-
structure NHP(NH2)2 acts as a bidentate ligand. As
shown in Figure 4, also one of the amino groups
coordinates to the highly Lewis acidic transition metal
center. This intramolecular stabilization is the only
possibility for the isolated complex; in condensed matter,
we expect intermolecular reactions (e.g., dimer forma-
tion) to be more important for the saturation of the
coordination sphere of the transition metal center.
The relative stability of the “NH” vs the “PH” form
also depends on the choice of the transition metal.
Therefore, we explored complexes of all elements of
group 4. According to our calculations, Hafnium is the
best choice to stabilize the PH form, though the differ-
ences between the transition metals are rather small.
Selected structural parameters from the optimization
are given in Table 5.
Ack n ow led gm en t. Financial support was given by
the Deutsche Forschungsgemeinschaft (DFG) and the
Fonds der Chemischen Industrie.
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
distances, bond angles, anisotropic temperature factor param-
eters, and fractional coordinates for 2a , 3a , and 8b. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM000967B