Monodentate σ-N and Bidentate σ-N,σ-N′ Coordination of 1,1-Bis((N-p-tolylimino)diphenylphosphoranyl)ethane, CHCH3(PPh2=NC6H4-4-CH 3)2, to Platinum(II)

Article abstract of DOI:10.1021/ic950748w

The new ligand, 1,1-bis((N-p-tolylimino)diphenylphosphoranyl)ethane (1,1-BIPE), 1, has been synthesized by means of a Staudinger reaction of 1,1-bis(diphenylphosphino)ethane (1,1-dppe) with 2 equiv of p-tolylazide. Bridgesplitting reactions of Pt₂

Full text of DOI:10.1021/ic950748w

1518
Inorg. Chem. 1996, 35, 1518-1528
Monodentate σ-N and Bidentate σ-N,σ-N′ Coordination of
1,1-Bis((N-p-tolylimino)diphenylphosphoranyl)ethane, CHCH3(PPh2dNC6H4-4-CH3)2, to
Platinum(II)
Mandy W. Avis,† Cornelis J. Elsevier,*,† Nora Veldman,‡ Huub Kooijman,‡ and
Anthony L. Spek*,‡
Van’t Hoff Research Institute, Anorganisch Chemisch Laboratorium, Universiteit van Amsterdam,
Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands, and Bijvoet Center for
Biomolecular Research, Vakgroep Kristal- en Structuurchemie, Universiteit Utrecht,
Padualaan 8, 3584 CH Utrecht, The Netherlands
ReceiVed June 15, 1995X
The new ligand, 1,1-bis((N-p-tolylimino)diphenylphosphoranyl)ethane (1,1-BIPE), 1, has been synthesized by
means of a Staudinger reaction of 1,1-bis(diphenylphosphino)ethane (1,1-dppe) with 2 equiv of p-tolylazide. Bridge-
splitting reactions of Pt2Cl4(PR3)2 with 1 readily afforded σ-N monodentate complexes, [PtCl2(PR3){1,1-BIPE-
σN}] (2a, PR3 ) PEt3; 2b, PR3 ) PMe2Ph). Conversion of 2 into the six-membered platinacycle [PtCl(PR3){1,1-
BIPE-σN,σN′}]+[X]- (3) (X ) Cl, PtCl3(PR3), BF4) took place after prolonged stirring, its reaction rate being
strongly dependent on the type of phosphine (>5 days for 2a in the presence of NaBF4, 1 h for 2b) and the
1
metal-to-ligand ratio. The compounds 1, 2, and 3 have been fully characterized by H, 31P{1H}, and 13C{1H}
NMR and IR spectroscopy, elemental analysis, or FAB mass spectroscopy. The molecular structures of CHCH3-
(PPh2dNC6H4-4-CH3)2 (1) and [PtCl(PMe2Ph){(N(pTol)dPPh2)2CHCH3}]+[Cl]- (3b) have been determined by
X-ray crystallography. Crystal data for 1: space group P21/c with a ) 8.9591(5) Å, b ) 19.1961(12) Å, c )
21.9740(9) Å, â ) 105.069(4)°, V ) 3649.1(3) Å3, and Z ) 4. The structure refinement converged to R ) 0.080
and Rw ) 0.109. Crystal data for 3b: monoclinic, space group P21/c with a ) 12.4021(7) Å, b ) 16.9705(11)
Å, c ) 23.760(2) Å, â ) 109.544(5)°, V ) 4712.7(5) Å3, and Z ) 4. The structure refinement converged to R1
) 0.057, wR2 ) 0.122. Variable temperature NMR spectroscopy has revealed that complexes 3 exclusively
adopt a twisted boat conformation with the methyl group in equatorial position at low temperature, in agreement
with the solid state structure of 3b as determined by X-ray crystallography. Boat-to-boat inversion is assumed
to take place at temperatures above 293 K. Furthermore, for 3, hindered rotation of one of the p-tolyl substituents
on nitrogen has been established at low temperatures.
Introduction
Monitoring the reactions by NMR revealed that the initial
step in the formation of the N,C chelates involves a nucleophilic
attack by a nitrogen donor atom, giving an intermediate
[PtX2(PR3){N(R′)dPPh2CH2PPh2dN(R′)}] (A), containing σ-N
monodentate BIPM (Scheme 1),4 which reacts further by a 1,3-
H-shift from the methylene carbon atom in A to the noncoor-
dinated nitrogen atom, giving intermediate B (not observed) and
subsequent fast dissociation of the ligand isomer (C). The final
product (D) is formed by recombination of C with PtX3(PR3)-.4
The selectivity of the reactions of BIPM with Pt(II), in
contrast to its reactions with Rh(I) and Ir(I),3 has been explained
in terms of an increased polarity of the σ-N-coordinated NdP
group in A, resulting in an increased acidity of the methylene
hydrogen atoms, which may shift easily to the noncoordinated
nitrogen atom.4 Also the fact that Pt-C bond formations are
thermodynamically more favorable than Pt-N bonds probably
results in a preference for N,C chelation of BIPM to Pt. This
has been confirmed by a reaction where twofold excess of the
Pt(II) precursor was used, which afforded a relatively stable
six-membered platinacycle by N,N′ coordination of BIPM which
finally converted into the thermodynamically more stable four-
membered platinacycle.4
In connection with recent investigations on the coordination
behavior of bis(iminophosphoranyl)methanes (BIPM), H2C-
(PPh2dNR′)2 toward the transition metals tungsten(VII),1 os-
mium(VIII),2 rhodium(I), and iridium(I),3 we have extended this
line of research to platinum(II) and palladium(II). Previous
reports have shown that reactions of NSiMe3-substituted BIPM
ligand with WX6 (X ) Cl, F) and OsO4 resulted in the formation
of N,N′-coordinated six-membered metallacycles by splitting
of the reactive N-Si bonds.1,2 Reaction of N-aryl substituted
BIPM with halide bridged Rh and Ir dimers, however, gave
mixtures of two products, in which the ligand acts as a σ-N,
σ-N′ chelate in one isomer and as a N,C chelate in the other.3
Interestingly, similar reactions of BIPM (R′ ) aryl) with Pt2X4-
(PR3)2 (X ) Cl, Br; PR3 ) PEt3, PMe2Ph) proceeded much
more selectively, since stable N,C chelated four-membered
platinacycles (Scheme 1, D) were formed exclusively.4
* To whom correspondence should be addressed: C.J.E., correspondence
regarding the paper; A.L.S., correspondence regarding the crystallography.
† Universiteit van Amsterdam.
‡ Universiteit Utrecht.
X Abstract published in AdVance ACS Abstracts, February 15, 1996.
(1) Katti, K. V.; Seseke, U.; Roesky, H. W. Inorg. Chem. 1987, 26, 814.
(2) Katti, K. V.; Roesky, H. W.; Rietzel, M. Z. Anorg. Allg. Chem. 1987,
553, 123.
We have been looking for ways to obtain (if possible
exclusively) platinum(II) complexes containing a N,N′ chelating
bis(iminophosphoranyl)alkane fragment. Hence, in order to
retard the H-shift and subsequent C coordination we have
modified the bis(iminophosphoranyl)methane ligand by substi-
tuting the bridging CH2 group by a CHCH3 group. This
(3) Imhoff, P.; van Asselt, R.; Elsevier, C. J.; Zoutberg, M. C.; Stam, C.
H. Inorg. Chim. Acta 1991, 184, 73.
(4) Avis, M. W.; Vrieze, K.; Kooijman, H.; Veldman, N.; Spek, A. L.;
Elsevier, C. J. Inorg. Chem. 1995, 34, 4093.
0020-1669/96/1335-1518$12.00/0 © 1996 American Chemical Society

σ-N Coordination to Pt(II)
Inorganic Chemistry, Vol. 35, No. 6, 1996 1519
Scheme 1. Reaction Sequence in the Formation of Four-Membered Platinacycles (D), Containing N,C-Coordinated BIPMa
a
An asterisk denotes recombination of dissociation fragment PtX2(PR3) with X- of D).
complexes are given in Tables 4-6 under results, and in the preparative
modification will introduce more steric hindrance around the
central carbon atom and hence favor stabilization of σ-N,σ-N′-
coordinated species, and at the same time the inductive
electronic effect of the methyl substituent in the CHCH3 moiety
will result in a decreased acidity of the methine proton.
In this paper we report the synthesis of 1,1-bis(N-p-tolyl-
imino)diphenylphosphoranyl)ethane (1,1-BIPE, 1), CHCH3-
(PPh2dNC6H4-4-CH4)2, and its reactions with Pt2Cl4(PR3)2.
descriptions below.
Synthesis of 1,1-Bis((N-p-tolylimino)diphenylphosphoranyl)-
ethane (1,1-BIPE) (1). To a stirred solution of 713 mg (1.79 mmol)
of 1,1-dppe in 15 mL of toluene was added dropwise a solution of 480
mg (3.60 mmol) of p-tolylazide in 5 mL of toluene at 60 °C. After 4
h at 60 °C, during which N2 gas evolved, the solvent was removed in
vacuo. To the brownish residue 60 mL of pentane was added, which
resulted in precipitation of a white solid after 1 h of stirring. The
precipitate was washed with pentane (2 × 20 mL) and dried in vacuo,
yielding 1.10 g (1.8 mmol, 99%) of a white powder 1. IR (Nujol):
ν(PdN) ) 1341 cm-1. Anal. Calcd. for C40H38N2P2: C, 78.93; H,
6.30; N, 4.60; P, 10.18. Found: C, 78.99; H, 6.34; N, 4.53; P, 10.23.
Crystals (colorless needles) suitable for X-ray crystal structure deter-
mination were obtained by diffusion of pentane into a toluene solution
of 1 after 4 days at 20 °C and 1 atm.
Experimental Section
All preparations were carried out under an atmosphere of dry nitrogen
using standard Schlenk techniques at 20 °C, unless stated otherwise.
The solvents were dried and distilled prior to use. 1H and 31P{1H}
NMR spectra were obtained on Bruker AC 100, AMX 300, and WH
5005 instruments (operating at 100.13/300.13/500.14 MHz and 40.53/
121.50/202.45 MHz, respectively) using SiMe4 and 85% H3PO4,
respectively, as the external standards, with positive values (in ppm)
to high frequency of the standard in all cases. 13C{1H}NMR data were
obtained on a Bruker AMX 300 instrument (operating at 75.48 MHz)
using SiMe4 as the external standard. Elemental analysis were carried
out by Dornis und Kolbe Mikroanalytisches Laboratorium, Mu¨lheim
a.d. Ruhr, Germany. Infrared spectra, using KBr pellets and Nujol
mulls, were recorded on a Perkin-Elmer 283 or a Mattson Galaxy 3000
spectrophotometer.5 FAB Mass spectroscopy was carried out by the
Institute for Mass Spectroscopy at the University of Amsterdam. The
compounds 1,1-bis(diphenylphosphino)ethane (1,1-dppe),6 p-tolylazide7
and Pt2Cl4(PR3)2 (PR3) PEt3, PMe2Ph)8 were synthesized according
to literature procedures. Data relating to the characterization of the
Synthesis of [PtCl2(PEt3){1,1-BIPE-σN}] (2a). To a solution of
37.6 mg (0.05 mmol) of Pt2Cl4(PEt3)2 in 10 mL of CH2Cl2 was added
59.6 mg (0.10 mmol) of 1. After 10 min of stirring at 20 °C, the yellow
solution was evaporated to dryness. The residue was washed with cold
pentane (0 °C, 2 × 20 mL) and dried in vacuo, yielding 95 mg (98%)
of a yellow powder, 2a. IR(KBr): ν(PdN) ) 1335 (br) and 1235
cm-1 (m). Anal. Calcd. for C46H53N2P3Cl2Pt: C, 55.65; H, 5.38; N,
2.82; P, 9.36. Found: C, 55.36; H, 5.48; N, 2.73; P, 9.30. FAB mass
found: m/z ) 957 (M - Cl) (M, calcd for C46H53N2P3Cl2Pt: 992.9).
[PtCl2(PMe2Ph){1,1-BIPE-σN}] (2b) was synthesized in the same
way, yielding 99% 2b after 10 min of stirring in CH2Cl2 at 20 °C and
evaporation to dryness. IR (KBr): ν(PdN) ) 1334 (br) and 1236 cm-1
(m). FAB mass found: m/z ) 977 (M - Cl) (M, calcd for C48H49N2P3-
Cl2Pt: 1012.9).
Synthesis of [PtCl(PEt3){1,1-BIPE-σN,σN′}]+[BF4]- (3a). To a
solution of 395.7 mg (0.65 mmol) of 1 and 249.7 mg (0.33 mmol) of
Pt2Cl4(PEt3)2 in 20 mL of CH2Cl2 was added a 10-fold excess of NaBF4,
and the mixture was stirred for 24 h at 20 °C. The product, obtained
by filtration and subsequent evaporation of the solvent, contained
(5) Located at the University of MissourisColumbia.
(6) Lee, C. L.; Yang, Y. P.; Rettig, S. J.; James, B. R.; Nelson, D. A.;
Lilga, M. A. Organometallics 1986, 5, 2220.
(7) Ugi, L.; Perlinger, H.; Begringer, L. Chem. Ber. 1958, 91, 2330.
(8) Goodfellow, R. J.; Venanzi, L. M. J. Chem. Soc. 1965, 7533.

1520 Inorganic Chemistry, Vol. 35, No. 6, 1996
Avis et al.
Table 1. Crystallographic Data for 1‚Toluene and 3b‚THF
approximately 23% 3a and 77% 2a. Continued stirring of this mixture
in CH2Cl2 with freshly added NaBF4 (ca. 100 mg) gave 77% 3a and
23% 2a and some decomposition after 5 days. Compound 2a was
completely washed out with Et2O (2 × 20 mL), giving a residue
consisting of 3a and some decomposition. Recrystallization out of CH2-
Cl2/Et2O (1:3) at 20 °C gave 155 mg of pure 3a (23%). IR (KBr):
ν(PdN) ) 1247 and 1225 cm-1. Anal. Calcd. for C46H53BN2F4P3-
ClPt: C, 52.91; H, 5.12; N, 2.68; P, 8.90. Found: C, 52.75; H,
5.19; N, 2.75; P, 8.95. FAB mass found: m/z ) 957.3 (M+, calcd for
C46H53N2P3ClPt: 957.4).
1
3b
formula
mw
space group
cryst syst
a, Å
b, Å
c, Å
C40H38N2P2‚0.5C7H8
654.77
P21/c
monoclinic
8.9591(5)
19.1961(12)
21.9740(9)
105.069(4)
3649.1(3)
4
C48H49Cl2N2P3Pt‚C4H8O
1084.94
P21/c
monoclinic
12.4021(7)
16.9705(11)
23.760(2)
109.544(5)
4712.6(6)
â, deg
V, Å3
Z
[PtCl(PEt3){1,1-BIPE-σN,σN′}]+[PtCl3(PEt3)]- (3a′). To a solu-
tion of 106.2 mg (0.17 mmol) of 1 in 15 mL of CH2Cl2 was added
134.0 mg (0.17 mmol) of Pt2Cl4(PEt3)2, and the mixture was stirred
for 18 h. Evaporation of the solvent resulted in a yellow powder, 240
mg (0.35 mmol, 99.9%) of 3a′. IR (Nujol): ν(PdN) ) 1248 and 1219
4
D
calcd, g cm-3
1.192
1.529
F(000)
µ, cm-1
data set
Ra
1388
2192
13.1 (Cu KR)
-11:7, 0:24, -27:27
0.080 [for 5234Fo >
5.0σ(Fo)]
32.6 (Mo KR)
-10:16, 0:22, -30:28
0.057 [for 6850 Fo >
4.0σ(Fo)]
cm-1 FAB mass found: m/z ) 957.3 (M+, calcd for C46H53N2P3-
.
ClPt: 957.4).
[PtCl(PMe2Ph){1,1-BIPE-σN,σN′}]+[Cl]- (3b). To a solution of
179.1 mg (0.29 mmol) of 1 in 10 mL of CH2Cl2 was added 118.9 mg
(0.15 mmol) of Pt2Cl4(PMe2Ph)2, and the mixture was stirred for 1 h
at 20 °C. The product was obtained by evaporation of the solvent,
yielding 294 mg (0.29 mmol, 99%) of 3b. IR (KBr): ν(PdN) )
1251 and 1230 cm-1. FAB mass found: m/z ) 977 (M+, calcd for
C48H49N2P3ClPt: 977.4). Crystals suitable for X-ray crystal structure
determination were obtained by diffusion of pentane into a THF/CH2-
Cl2 solution of 3b at 20 °C at 1 atm for 7 days.
b
Rw
0.109
wR2c
0.1215
1.00
S
1.28
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑[w(||Fo| - |Fc||)2]/[∑[w(Fo2)]]1/2
.
2
2
c wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo )2]]1/2
.
variance), for 404 parameters and 5234 reflections with Fo > 5σ(Fo).
Hydrogen atoms were included in the refinement on calculated positions
(C-H ) 0.98 Å) riding on their carrier atoms. All non-hydrogen atoms
were refined with anisotropic thermal parameters; the hydrogen atoms
were refined with one common isotropic displacement parameter.
Weights were introduced in the final refinement cycles. The unit cell
contains two toluene molecules disordered over the inversion centers.
No discrete atom model could be fitted. The BYPASS procedure13
was used to take this electron density into account. The application of
BYPASS made refinement more stable. The solvent accessible areas
have a total volume of 550 Å3. A total density of 100 electrons was
counted in this area, consistent with two toluene molecules. The final
difference Fourier showed no residual density outside -0.78 and +0.89
e Å-3. Neutral atom scattering factors were taken from Cromer and
Mann,14 with anomalous dispersion corrections taken from Cromer and
Liberman.15
Compound 3b. Yellowish crystals of 3b, 0.3 × 0.3 × 0.05 mm,
were mounted on a Lindemann-glass capillary and placed on an Enraf-
Nonius CAD4-T diffractometer on rotating anode in the cold dinitrogen
stream (150 K). Data were collected in ω/2θ mode, λ(MoKR) )
0.71073 Å (monochromator), with θ in the range 1.5-27.5°. Scan
angle was ∆ω ) 0.66 + 0.35 tan θ°. Unit cell dimensions and standard
deviations were obtained by least-squares fit (SET4)9 of the setting
angles of 25 reflections in the range 11.6° < θ < 14.0°. The unit cell
parameters were checked for the presence of higher lattice symmetry.10
Three standard reflections were monitored periodically (24h2h, 22h4, 15h2h)
and showed approximately 4% variation in intensity during the 44 h
of data collection. The data were scaled accordingly. Intensity data
were corrected for Lorentz, polarization, and absorption effects (an
empirical absorption/extinction correction was applied (DIFABS16
correction range 0.725-1.00)) and averaged into a unique set of
reflections. Total data of 15 022 reflections were collected of which
10 778 were independent (Rint ) 0.0382).
Alternative Method. Stirring a mixture of 90 mg (0.15 mmol) of
1 and 61 mg (0.07 mmol) of Pt2Cl4(PMe2Ph)2 in 10 mL of THF at 70
°C for 4.5 h gave the same product 3b after workup with pentane,
yielding 111 mg (73%).
[PtCl(PMe2Ph){1,1-BIPE-σN,σN′}]+[PtCl3(PMe2Ph)]- (3b′) was
synthesized from 172.4 mg (0.25 mmol) of 1,1-BIPE (1) and 229.4
mg (0.25 mmol) of Pt2Cl4(PMe2Ph)2 (M:L ) 1:1) in 20 mL of CH2-
Cl2. The solution was stirred for 1 h and evaporated to 5 mL. Addition
of 40 mL of pentane resulted in the precipitation of 3b′, which was
washed with pentane (20 mL) and dried in vacuo. Yield: 344 mg
(87%). IR (KBr): ν(PdN) ) 1250 cm-1 (br). Anal. Calcd.for
C56H60N2P4 Cl4Pt2: C, 47.47; H, 4.72; N, 1.98; P, 8.72. Found: C,
47.28; H, 4.33; N, 1.92; P, 8.61.
Variable temperature NMR studies were carried out on solutions
of 0.035 mmol of 3a in 0.5 mL of CDCl3 at 233-330 K or of 0.035
mmol of 3b in 0.4 mL of CD2Cl2 at 233-293 K. Subsequently, 2.8
µL (0.035 mmol) of pyridine was added to the CDCl3 solution of 3a at
330 K, which gave no reaction and no exchange processes occurred.
X-ray Crystal Structure Determinations of 1 and 3b. Crystal
data and experimental procedures on both crystal structures are collected
in Table 1.
Compound 1. Transparent colorless crystals, 0.3 × 0.3 × 0.6 mm,
suitable for X-ray structure determination, were mounted on a Linde-
mann-glass capillary and placed on an Enraf-Nonius CAD4-F diffrac-
tometer at 298 K. Data were collected in ω/2θ mode, λ(Cu KR) )
1.54184 Å (Ni-filtered), with θ in the range 2.1-75.0°. Scan angle
was ∆ω ) 0.55 + 0.14 tan θ°. Unit cell dimensions and standard
deviations were obtained by least-squares fit (SET4)9 of the setting
angles of 25 reflections in the range 18.4° < θ < 23.7°. Reduced-cell
calculations did not indicate higher lattice symmetry.10 Three standard
reflections were monitored periodically (2h14, 1h24h, 2h1h4) and showed
approximately 14% decay during the 91 h of data collection. The data
were scaled accordingly. Intensity data were corrected for Lorentz,
polarization, but not for absorption, and averaged into a unique set of
reflections. Total data of 11 303 reflections were collected of which
7503 were independent (Rint ) 0.0778). The structure was solved by
direct methods (SHELXS86).11 Refinement on F was carried out by
full-matrix least-squares techniques (SHELX76);12 final R value 0.080,
Rw ) 0.109, w ) 1/{σ2(F) + 0.000248F2], S ) 1.28 (based on the
The structure was solved by automatic Patterson methods and
subsequent difference Fourier synthesis (DIRDIF-92).17 Refinement
on F2 was carried out by full-matrix least-squares techniques (SHELXL-
93);18 final R1 value 0.057 for 555 parameters and 6850 reflections
with I > 2.0σ(I), wR2 ) 0.122 for all 10 778 reflections, S ) 0.996
2
and w ) 1/{σ2(Fo) + 0.0514P2] where P ) (Max(Fo ,0) + 2Fc2)/3. All
(13) van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.
(14) Cromer, D. T.; Mann, J. B. Acta Crystallogr. 1968, A24, 321.
(15) Cromer, D. T.; Liberman, D. J. Chem. Phys. 1970, 53, 1891.
(16) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(17) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; Garc´ıa-
Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. The DIRDIF
program system; Technical report of the Crystallography Laboratory;
University of Nijmegen: Nijmegen, The Netherlands, 1992.
(18) Sheldrick, G. M. SHELXL-93 Program for crystal structure refinement.
University of Go¨ttingen, Germany, 1993.
(9) Boer, J. L. de; Duisenberg, A. J. M. Acta Crystallogr. 1984, A40,
C410.
(10) Spek, A. L. J. Appl. Crystallogr. 1988, 21, 578.
(11) Sheldrick, G. M. SHELXS86 Program for crystal structure determi-
nation. University of Go¨ttingen, Germany, 1986.
(12) Sheldrick, G. M. SHELX76 Program for crystal structure determina-
tion. University of Cambridge, Cambridge, 1976.

σ-N Coordination to Pt(II)
Inorganic Chemistry, Vol. 35, No. 6, 1996 1521
Scheme 2. Complex Formation of 2 and 3a
a
Conditions (20 °C): (i) 5 min in CH2Cl2; (ii) +NaBF4, more than 5 days in CH2Cl2 (3a); + 0.5 equiv of Pt2Cl4(PEt3)2, 18 h in CH2Cl2 (3a′);
1 h in CH2Cl2 (3b); + 0.5 equiv of Pt2Cl4(PMe2Ph)2 (3b′).
reflections were considered observed during refinement. Anisotropic
thermal parameters were used for all non-hydrogen atoms. Hydrogen
atoms were included in the refinement cycle at calculated positions,
riding on their carrier atoms. The hydrogen atoms were refined with
a fixed isotropic thermal parameter amounting to 1.5 (methyl-H) or
1.2 times (all other H’s) the value of the equivalent isotropic thermal
parameter of the carrier atoms. Weights were introduced in the final
refinement cycles. A final difference Fourier showed no residual
density outside -0.78 and +2.03 e Å-3. Neutral scattering factors and
anomalous dispersion corrections were taken from ref 19.
N atoms instead. 1,1-BIPE is quite soluble in THF, benzene,
toluene, chloroform, and dichloromethane, slightly soluble in
Et2O, but not soluble in apolar solvents like pentane. In the
solid state, 1 is thermally stable for at least 1 year when stored
under N2 at 20 °C, but decomposition occurs within a couple
of weeks when it is exposed to moist air. The 1,1-BIPE ligand
(1) has been fully characterized by 1H, 31P{1H}, and 13C{1H}-
NMR and infrared spectroscopy, elemental analysis, and an
X-ray crystal structure determination.
All geometrical calculations and the ORTEP illustrations were
performed with PLATON.20 Computing was conducted on a DEC-
station 5000 cluster.
Formation of Complexes 2 and 3. 1,1-BIPE (1) reacted
rapidly and quantitatively with the halide-bridged platinum
dimers Pt2Cl4(PR3)2 (PR3 ) PEt3, PMe2Ph) in dichloromethane
at 20 °C to give mononuclear platinum(II) complexes 2a or 2b,
in which 1,1-BIPE is σ-N monodentate coordinated (Scheme
2, eq i).
Prolonged stirring of the reaction mixture eventually resulted
in the selective formation of cationic six-membered platinacycles
3a,3b or 3a′,3b′, by σ-N,σ-N′ coordination of 1,1-BIPE (Scheme
2, eq ii), irrespective of whether a metal-to-ligand (M:L) ratio
of 1:1 or 2:1 is used. The rate of the conversion reaction of 2
into 3 was found to depend strongly on the type of phosphine
and the M:L ratio (vide infra).
Results and Discussion
Synthesis of 1,1-BIPE (1). A Staudinger reaction (eq 1),
similar as reported previously for the synthesis of analogous
bis(iminophosphoranyl)methanes (BIPM),21,22 was used to
synthesize the new 1,1-bis((N-p-tolylimino)diphenylphospho-
ranyl)ethane ligand (1,1-BIPE, 1), containing a methyl sub-
stituent on the carbon atom bridging the two PdN moieties.
Ph2PCH(Me)PPh2 + 2p-tolyl-N3 f
p-Tol-NdPh2PCH(Me)PPh2dN-p-Tol + 2N2 (1)
Complexes 2 and 3 are air-stable yellow solids, readily soluble
in THF, CH2Cl2, CHCl3, toluene, benzene, and Et2O and
moderately soluble in pentane at 20 °C, but only slightly soluble
in pentane when cooled down. In solution, the complexes 2
and 3 decompose in air, by reaction with H2O and CO2. The
platinum complexes 2a,b and 3a,b,a′,b′ have been fully
characterized by 1H, 31P{1H}, and 13C{1H}NMR, infrared, and
FAB mass spectroscopy, elemental analysis, and an X-ray crystal
structure determination of 3b.
Complexes 2a and 2b, [PtCl2(PR3){1,1-BIPE-σN}], represent
the first isolable complexes in which the potentially bi- or even
tridentate bis(phosphinimine) ligand of the type R′NdPR2-
CHR′′PR2dNR′ is monodentate coordinated. Recently, the
formation of an analogous thermally less stable Pt complex,
[PtCl2(PEt3){BIPM-σN}] (A, Scheme 1), containing a σ-N
monodentate coordinated bis((N-p-tolylimino)diphenylphospho-
ranyl)methane ligand (BIPM), has been observed by NMR.4
Although many coordination complexes containing related
1
Compound 1 was obtained in quantitative yield. Other
methods, through deprotonation of BIPM by NaH,22 and
subsequent reaction with 1 equiv MeI, as has been reported
earlier for the synthesis of CHMe(PR2dS)2,23 did not result in
methylation of the bridging carbon, but of one of the terminal
(19) Wilson, A. J. C. (ed.), International Tables for Crystallography;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992; Vol.
C.
(20) Spek, A. L. Acta Crystallogr. 1990, A46, C34.
(21) (a) Gilyarov, V. A.; Kovtun, V. Y.; Kabachnik, M. I. IzV. Akad. Nauk
SSSR, Ser. Khim. 1967, 5, 1159. (b) Kovtun, V. Y.; Gilyarov, V. A.;
Kabachnik, M. I. IzV. Akad. Nauk SSSR, Ser. Khim. 1972, 11, 2612.
(c) Aquair, A. M.; Beisler, J. J. Organomet. Chem. 1964, 29, 1660.
(d) Appel, R.; Ruppert, I. Z. Anorg. Allg. Chem. 1974, 406, 131.
(22) Imhoff, P.; van Asselt, R.; Elsevier, C. J.; Vrieze, K.; Goubitz, K.;
van Malssen, K. F.; Stam, C. H. Phosphorus Sulfur 1990, 47, 401.
(23) Grim, S. O.; Mitchell, J. D. Inorg. Chem. 1977, 16, 1762.

1522 Inorganic Chemistry, Vol. 35, No. 6, 1996
Avis et al.
ligands of the type XdPR2CHR′PR2dY, with X,Y ) S, O,
and Se; R ) alkyl, aryl; and R′ ) H, Me, and PR2dX are
known,24-29 to our knowledge only two similar types of
stable monodentate coordinated species have been reported,
i.e. (C6F5)3Au{SdPPh2CH2PPh2dS}29a and [Fe(C5H5)(CO)2-
{XdPPh2(CH2)nPPh2dX}]BF4 (X ) S, Se; n ) 1-3).29b The
isolation of the complexes 2a,b has demonstrated that the σ-N-
coordinated Pt(1,1-BIPE) complex is thermally more stable than
the σ-N-coordinated Pt-BIPM complex, which is clearly caused
by the methyl substituent on the central carbon atom in 1,1-
BIPE.
Complex 2a (PR3 ) PEt3) is stable in solution; no further
reaction is observed within 24 h at 20 °C. Treatment of a
solution of 2a with NaBF4 resulted in only 23% conversion into
the six-membered platinacycle 3a after 24 h. In contrast,
complex 2b (PR3 ) PMe2Ph) converts completely within 1 h
(in CH2Cl2 at 20 °C) into complex 3b (Scheme 2, eq ii). The
much slower conversion of 2a into 3a as compared to the fast
conversion of 2b into 3b might be explained by the slightly
larger steric hindrance exerted by the triethylphosphine (cone
angle ) 132°) relative to the dimethylphenylphosphine (cone
angle ) 122°),30 which slows down the substitution of chloride
cis to PEt3 via intramolecular attack of the second N atom.
Note that the large difference in conversion rate between 2a
and 2b is true for trans complexes only. A cis geometry for 2
(PR3 trans to the Pt-Cl bond) is unlikely because this would
have resulted in a faster dissociation of the Pt-Cl bond in 2a
relative to 2b, as the trans effect of PEt3 > PMe2Ph.
Figure 1. ORTEP 30% probability plot of 1 (PLATON).20 Hydrogens
are omitted for clarity.
Table 2. Selected Interatomic Distances (Å) and Angles (deg) for 1
(Esd’s in Parentheses)
Bond Lengths
P(1)-N(1)
P(1)-C(8)
P(1)-C(14)
P(1)-C(20)
N(1)-C(1)
C(20)-C(21)
1.559(3)
1.820(4)
1.814(4)
1.827(3)
1.380(4)
1.529(5)
P(2)-N(2)
P(2)-C(29)
P(2)-C(35)
P(2)-C(20)
N(2)-C(22)
1.553(3)
1.820(4)
1.819(4)
1.835(4)
1.393(5)
Bond Angles
When the metal-to-ligand (M:L) ratio of the reaction is
changed to 2:1, the ionic dinuclear complexes [PtCl(PR3)-
{(N(pTol)dPPh2)2CHCH3-σN,σN′}][PtCl3(PR3)] (3a′: PR3 )
PEt3) and (3b′: PR3 ) PMe2Ph) are formed. Clearly, the
reactions of 1,1-BIPE (1) with Pt2Cl4(PR3)2 result in the selective
formation of six-membered platinacycles 3a,b or 3a′,b′ as the
final products, independent of whether a 1:1 or a 2:1 (M:L)
ratio is used. This is in sharp contrast to an earlier report which
showed that the reactions of BIPM with Pt2Cl4(PR3)2 resulted
in the exclusive formation of four-membered platinacycles by
N,C coordination of BIPM.4 In that case, N,N′ coordination
of BIPM only took place in an intermediate complex formed
in a 2:1 reaction, which reacted further to give a N,C-coordinated
product.4 We have not found such a conversion for the six-
membered platinacycles 3, not even after reflux, which indicates
that N,C coordination of 1,1-BIPE is disfavored by the presence
of a methyl substituent on the central carbon atom. Previous
investigations have shown that the N,C coordination of BIPM
occurs concomitantly with, or is preceded by, a H-shift (Scheme
1), which obviously is not taking place for the complexes 2a,b.
This finding is in keeping with the less acidic character of the
methine H atom in the σ-N-coordinated 1,1-BIPE ligand as
P(1)-N(1)-C(1)
N(1)-P(1)-C(8)
N(1)-P(1)-C(14)
N(1)-P(1)-C(20)
C(8)-P(1)-C(14)
C(8)-P(1)-C(20)
C(14)-P(1)-C(20)
P(1)-C(20)-C(21)
P(2)-C(20)-C(21)
133.4(2)
P(2)-N(2)-C(22)
N(2)-P(2)-C(29)
N(2)-P(2)-C(35)
N(2)-P(2)-C(20)
C(29)-P(2)-C(35)
C(20)-P(2)-C(29)
C(20)-P(2)-C(35)
P(1)-C(20)-P(2)
130.5(2)
113.54(16)
117.95(16)
106.57(15)
105.14(16)
105.22(16)
107.61(16)
111.0(2)
115.63(16)
116.17(16)
105.22(15)
105.01(16)
104.42(16)
109.75(16)
112.39(19)
113.9(2)
Torsion Angles
N(1)-P(1)-C(20)-P(2) -53.8(2) P(1)-C(20)-P(2)-N(2) -50.2(2)
N(1)-P(1)-C(20)-C(21) 75.1(3) C(21)-C(20)-P(2)-N(2) -177.5(2)
C(1)-N(1)-P(1)-C(20) -174.5(3) C(20)-P(2)-N(2)-C(22) -166.3(3)
compared to the methylene H atoms in the Pt-BIPM complex
(A, Scheme 1), due to the inductive effect of the methyl group
on the central carbon. The decreased acidity of free 1,1-BIPE
has also been established by its diminished reactivity toward
NaH in comparison to BIPM.31 Furthermore, the steric effect
exerted by the Me substituent will disfavor the formation of a
four-membered Pt-N-P-C metallacycle.
X-ray Crystal Structure of CHCH3(PPh2dNC6H4-4-CH3)2
(1). The molecular structure of 1 and the adopted numbering
scheme are shown in Figure 1. Selected bond distances and
angles are listed in Table 2. The unit cell contains four
molecules of 1 and two molecules of toluene, which was used
as the solvent for crystallization. Compound 1 consists of two
enantiotopic (p-tolylimino)diphenylphosphoranyl units attached
to a prochiral ethane-1,1-diyl moiety. The P-N bond lengths
(1.559(3) and 1.553(3) Å) are slightly shorter than found for
the related bis(iminophosphoranyl)methane (BIPM) compounds,
i.e in CH2(PR2dNC6H4-4-R′)2 (1.566-1.568 Å for R ) Ph and
R′ ) Me, or 1.580(4) Å for R ) Me and R′ ) NO2),22 but are
comparable with the P-N distances normally found for other
phosphinimines, ranging from 1.50 to 1.64 Å.32 The P-Calkyl
(24) Browning, J.; Beveridge, K. A.; Bushnell, G. W.; Dixon, K. R. Inorg.
Chem. 1986, 25, 1987.
(25) Abbassioun, M. S.; Chaloner, P. A.; Claver, C.; Hitchcock, P. B.;
Masdeu, A. M.; Ruiz, A.; Saballs, T. J. Organomet. Chem. 1991, 403,
229.
(26) Browning, J.; Bushnell, G. W.; Dixon, K. R.; Hilts, R. W. J.
Organomet. Chem. 1992, 434, 241.
(27) (a) Grim, S. O.; Kettler, P. B.; Merola, J. S. Inorg. Chim. Acta 1991,
85, 57. (b) Grim, S. O.; Kettler, P. B.; Thoden, J. B. Organometallics
1991, 10, 2399.
(28) (a) Browning, J.; Bushnell, G. W.; Dixon, K. R. Inorg. Chem. 1981,
20, 3912. (b) Browning, J.; Bushnell, G. W.; Dixon, K. R.; Pidcock,
A. Inorg. Chem. 1983, 22, 2226. (c) Browning, J.; Dixon, K. R.; Hilts,
D. W. Organometallics 1989, 8, 552. (d) Berry, D. E.; Browning, J.;
Dixon, K. R.; Hilts, R. W.; Pidcock, A. Inorg. Chem. 1992, 31, 1479.
(29) (a) Laguna, A.; Laguna, M.; Rojo, A.; Fraile, M. N. J. Organomet.
Chem. 1986, 315, 269. (b) Schumann, H. J. Organomet. Chem. 1987,
320, 145.
(31) Avis, M. W.; Elsevier, C. J.; Ernsting, J. M.; Vrieze, K.; Veldman,
N.; Spek, A. L.; Katti, K. V.; Barnes, C. L. Submitted for publication
in Organometallics.
(30) Tolman, C. A. Chem. ReV. 1977, 77, 3, 313.

σ-N Coordination to Pt(II)
Inorganic Chemistry, Vol. 35, No. 6, 1996 1523
Table 3. Selected Interatomic Distances (Å) and Angles (deg) for
3b (Esd’s in Parentheses)
Around Pt
Pt-P(3)
Pt-Cl(1)
2.234(2)
2.293(3)
Pt-N(1)
Pt-N(2)
2.052(5)
2.131(7)
Within Phosphine
P(3)-C(41)
P(3)-C(47)
1.813(8)
1.802(9)
P(3)-C(48)
1.819(7)
Within Ligand
P(1)-N(1)
P(1)-C(8)
P(1)-C(14)
P(1)-C(20)
N(1)-C(1)
C(20)-C(21)
1.611(5)
1.806(7)
1.806(8)
1.821(7)
1.443(8)
1.545(10)
P(2)-N(2)
P(2)-C(28)
P(2)-C(22)
P(2)-C(20)
N(2)-C(34)
1.618(6)
1.795(7)
1.826(7)
1.825(8)
1.433(10)
Around Pt
Cl(1)-Pt-P(3)
Cl(1)-Pt-N(1)
Cl(1)-Pt-N(2)
88.71(8)
176.63(15) P(3)-Pt-N(2)
N(1)-Pt-N(2)
88.4(2)
174.68(15)
93.95(14)
Figure 2. ORTEP 30% probability plot of 3b (PLATON).20 The
89.12(18) P(3)-Pt-N(1)
hydrogen atoms, the Cl- and the THF solvent are omitted.
Within Ligand
Pt-N(1)-P(1)
Pt-N(1)-C(1)
P(1)-N(1)-C(1)
N(1)-P(1)-C(8)
118.8(3)
118.1(4)
121.2(5)
113.4(3)
Pt-N(2)-P(2)
110.6(3)
118.5(5)
bonds (1.835(4) and 1.827(3) Å) are almost similar to the ones
reported for the analogous BIPM compounds (1.81-1.83
Å),22 or the P-C single bonds in (Me3Si)2CdPPh2CHdPPh2-
CH(SiMe3)2 (1.762(4) and 1.821(4) Å),33 but are shorter than
the average P-C bonds in, for instance, [HC(PR2dS)3] (1.883
Å).34 The geometry around the two phosphorus atoms and
C(20) is approximately tetrahedral. The P(1)-C(20)-P(2)
angle (112.39(19)°) is somewhat smaller than found for BIPM
(115.2(1)°),22 due to the steric effect of the methyl group on
C(20).
Pt-N(2)-C(34)
P(2)-N(2)-C(34) 124.1(5)
N(2)-P(2)-C(28) 112.9(3)
N(2)-P(2)-C(22) 116.8(3)
N(2)-P(2)-C(20) 105.6(3)
C(28)-P(2)-C(22) 105.9(3)
C(28)-P(2)-C(20) 108.8(4)
C(22)-P(2)-C(20) 106.6(3)
N(1)-P(1)-C(14) 111.6(3)
N(1)-P(1)-C(20) 106.3(3)
C(8)-P(1)-C(14)
C(8)-P(1)-C(20)
C(14)-P(1)-C(20) 107.6(4)
P(1)-C(20)-C(21) 114.2(5)
P(2)-C(20)-C(21) 112.7(5)
106.9(4)
110.8(3)
P(1)-C(20)-P(2)
112.3(4)
The relatively short N-C bonds (1.380(4) Å and 1.393(5)
Å), the wide P-N-C angles (133.4(2)° and 130.5(2)°) and the
planarity of the P-N-aryl moiety (the least-squares planes
through the p-tolyl substituents on the N atoms in 1 make angles
of 0.94(17) and 7.82(17)° with the phosphinimine PdN bonds),
are features that have been observed also for the related BIPM
compounds22 and other phosphinimines,32a indicating that
electron delocalization takes place over the PdN bond, which
is extended to the π-system of the p-tolyl groups on both N
atoms in 1.
X-ray Crystal Structure of [PtCl(PMe2Ph){(N(p-Tol)d
PPh2)2CHCH3}]Cl (3b). The atom labeling scheme and the
structure of a single molecule of compound 3b are shown in
Figure 2. The unit cell also contains THF, but this has been
omitted in the figure. Selected bond distances and angles are
listed in Table 3. The planarity of the coordination geometry
around platinum has been determined by a least-squares plane
analysis through the atoms Pt, Cl(1), P(3), N(1), and N(2), which
showed deviations from the plane of -0.021(1), -0.064(2),
0.063(2), -0.069(5), and 0.069(6) Å, respectively. The 1,1-
bis(iminophosphoranyl)ethane ligand in 3b is bidentate coor-
dinated by both N atoms. The Pt-N bonds, 2.052(5) and
2.131(7) Å, differ considerably in length, with the longer bond
trans to the PMe2Ph ligand, in keeping with the larger trans
influence of the phosphine. Such features have been previously
observed for the Pt-S bonds in S,S′-coordinated [PtCl(PEt3)-
{(SdPPh2)3C}].24 The Pt-Cl(1), 2.293(3) Å, and Pt-P(3),
2.234(2) Å, bond lengths in 3b are in agreement with the
distances normally found for such bonds trans to N σ-donor
atoms.4,31,35,36 The X-ray crystal structure clearly shows that
the six-membered chelate ring Pt-N(1)-P(1)-C(20)-P(2)-
N(2) has a boat conformation, with the H atom on C(20) in
axial and the methyl group in equatorial position. A ring-
puckering analysis resulted in a puckering amplitude (Q) of
1.187(5) Å, Θ of 82.2(2)°, and φ of 338.1(2)°, in agreement
with the description as a twisted boat conformation.37
The bite angle N(1)-Pt-N(2), 88.4(2)°, is close to optimum
and is similar to the N-Rh-N angle, 88.3(5)°, in N,N′-
coordinated [Rh(COD){(N(pTol)dPPh2)2CH2}]+.3 Within the
N,N′ coordinated 1,1-BIPE ligand in 3b both PdN bonds
(1.611(5) and 1.618(6) Å) are elongated when compared to those
in the free ligand 1 and represent normal bond distances for
coordinated phosphinimine ligands.3,4,31,38-40 Most features such
as the P(1)-C(20)-P(2) angle of 112.3(4) Å, which is indicative
for an approximate tetrahedral geometry around C(20), and the
P-C(20) bond lengths are similar to those observed for 1, [Rh-
(COD){(N(pTol)dPPh2)2CH2}]+,3 and [Rh(COD){(SdPPh2)2-
CH2}]+.25 The least-squares planes through the p-tolyl sub-
stituents on the N atoms in complex 3b are not in plane with
the phosphinimine PdN bonds, but make an angle of 44.2(3)°
and 21.3(4)° to it, which is in contrast to the almost planarity
of the PdNstolyl moiety in the free ligand 1 (vide supra). Also,
a significant lengthening of the N-C bonds has occurred, from
(36) Hartley, F. R. Chem. Soc. ReV. 1973, 2, 163.
(37) Boeyens, J. C. A. J. Cryst. Mol. Struct. 1978, 8, 317.
(38) (a) Imhoff, P.; Elsevier, C. J. J. Organomet. Chem. 1989, 361, C61.
(b) Elsevier, C. J.; Imhoff, P. Phosphorus Sulfur 1990, 49, 405. (c)
Imhoff, P.; Nefkens, S. C. A.; Elsevier, C. J.; Vrieze, K.; Goubitz,
K.; Stam, C. H. Organometallics 1991, 10, 1421. (d) Imhoff, P.; van
Asselt, R.; Ernsting, J. M.; Vrieze, K.; Elsevier, C. J. Organometallics
1993, 12, 1523. (e) Imhoff, P.; Gu¨lpen, J, H.; Vrieze, K.; Elsevier, C.
J.; Smeets, W. J. J.; Spek, A. L. Inorg. Chim. Acta 1995, 235, 77.
(39) Katti, K. V.; Cavell, R. G. Inorg. Chem. 1990, 291, 808.
(40) (a) Miller, J. S.; Visscher, M. O.; Caulton, K. G. Inorg. Chem. 1974,
13, 1632. (b) Phillips, F. L.; Skapski, A. C. J. Chem. Soc., Dalton
Trans. 1976, 1448. (c) Abel, E. W.; Mucklejohn, S. A. Z. Naturforsch.,
B 1978, 33, 339. (d) Dapporto, P.; Denti, G.; Dolcetti, G.; Ghedini,
M. J. Chem. Soc., Dalton Trans. 1983, 779. (e) Mronga, N.; Weller,
F.; Dehnicke, K. Z. Anorg. Allg. Chem. 1983, 502, 35.
(32) (a) Allen, C. W. Coord. Chem. ReV. 1994, 130, 137. (b) Dehnicke,
K.; Stra¨hle, J. Polyhedron 1989, 8, 6, 707.
(33) Appel, R.; Haubrich, G.; Knoch, F. Chem. Ber. 1984, 117, 2063.
(34) Colquhoun, I. J.; McFarlane, W.; Bassett, J. M.; Grim, S. O. J. Chem.
Soc., Dalton Trans. 1981, 1645.
(35) Albinati, A.; Lianza, F.; Muller, B.; Pregosin, P. S. Inorg. Chim. Acta
1993, 208, 119.

1524 Inorganic Chemistry, Vol. 35, No. 6, 1996
Table 4. 31P NMR Data for the Compounds 1-3a
Avis et al.
compd
solvent/temp, K
δ(P)
δ(PA), 1J(Pt,PA)
δ(PB), 2J(Pt,PB)
δ(PC), 2J(Pt,PC)
δ(PD), 1J(Pt,PD)
3J(PA,PB)
2J(PB,PC)
1
C6D6/293
6.6 (s)
8.2 (s)
CD2Cl2/293
CD2Cl2/293
CDCl3/293
CD2Cl2/285
CDCl3/233
CD2Cl2/253
CDCl3/253
2a
2b
1.0 (d), 3455
-24.5 (d), 3490
1.2 (d), 3579
39.4 (dd), 61
40.3 (dd), 62
27.9 (dd)
6.1 (d)
6.5 (d)
31.4 (d), 60
31.8 (d),c nr
32.3 (d),c 56
32.4 (d),c nr
13.1
14.5
3.6
4.5
4.0
12.4
12.3
12.1
12.1
3a
3a′ b
3b
2.1 (s),c 3554
28.3 (dd)c
28.9 (d)c
2.8 (s), 3690
2.5
-20.4 (s),c 3643
3b′
-20.4 (s),c 3650
28.8 (d)c
-21.4 (s), 3790
a Measured at 40.53 or 121.48 MHz, unless noted otherwise. All J values in Hz. Multiplicity labels and abbreviations: br ) broad, s ) singlet,
d ) doublet, dd ) doublet of doublet, nr ) not resolved. b Recorded at 202.5 MHz. c Slightly broadened at 293 K.
Table 5. 1H NMR Data for 1-3a
c
compd
1f
δ(alkyl-P)b
δ(CH-CH3)
δ(CH)d
3.72 (m)
δ(4-CH3)
δ(C6H4-N)e
δ(Ph/Ar-o,m,p)
1.42 (dt, 7.4, 16.7)
2.15 (s)
6.36 (d, 4H)
6.73 (d, 4H)
6.58 (d, 2H)
6.69 (m, 4H)
6.87 (d, 2H)
(o)
7.4 (m, 12H)
7.7, 7.9 (m, 8H)
6.9-8.1 (m, 18H)
9.18 (dd, 2H-ortho)
2ag
1.15 (dt)
1.91 (m)
1.77 (dt, 7.0, 17.4)
5.57 (m)
2.01 (s)
2.23 (s)
2bh
1.80 (d)
1.92 (d)
1.03 (dt)
1.44 (m)
1.00 (dt)
1.36 (m)
(o)
5.50 (m)
2.04 (s)
2.25 (s)
2.23 (s)
2.25 (s)
2.19 (s)
2.21 (s)
6.5-7.9 (m, 26H)
9.27 (m, 2H-ortho)
7.0-8.3 (m, 22H)
3af,i
1.34 (dt, 7.3, 17.8)
1.28 (dt, 7.1, 17.9)
5.75 (tq, 7.3, 19.1)
5.71 (tq, 7.1, 18.7)
6.94 (d, 2H)
233K
3a′g,j
233K
3bf
223K
3b′ k
213K
6.16 (d, 1H)
6.69 (d, 1H)
6.92 (d, 2H)
(o)
7.28 (d, 1H)
8.46 (d, 1H)
7.0-8.3 (m, 22H)
6.8-8.4 (m, 28H)
1.00 (dt)
1.53 (br)
1.01 (dt)
1.42 (m)
1.45 (br)
5.8 (br)
2.21 (vs)
∼1.4 (o)
5.72 (m)
2.19 (s)
2.22 (s)
6.05 (d, 1H)
6.56 (d, 1H)
6.91 (d, 2H)
(o)
8.50 (d, 1H)
6.9-8.4 (m, 23H)
1.68 (d)
1.87 (d)
1.58 (d)
1.84 (d)
1.41 (br dt)
(o)
2.18 (s)
2.22 (s)
2.15 (s)
2.17 (s)
6.5-8.8 (m, 33H)
6.8-8.8 (m, 30H)
1.32 (dt, 7.0, 18.2)
6.78 (tq, 7.0, 19.2)
5.66 (d, 1H)
6.33 (d, 1H)
8.55 (d, 1H)
(o)
1.8 (br)
1.47 (br)
nr
nr
2.17 (s)
2.20 (s)
2.16 (s)
2.17 (s)
6.6-8.7 (m)
1.64 (d)
1.70 (d)
1.37 (dt, 6.9, 18.2)
5.47 (d, 1H)
6.28 (d, 1H)
6.65 (d, 1H)
8.56 (d, 1H)
6.8-8.6 (m, 34H)
a Measured at 300.13 MHz in CDCl3 at 293 K, unless stated otherwise. J values in Hz. Multiplicity labels and abbreviations: br ) broad, s )
singlet, d ) doublet, dd ) doublet of doublet, dt ) doublet of triplet, m ) multiplet, nr ) not resolved, o ) obscured by overlap, tq ) triplet of
3
3
quartet. b For Et3P: δ(P-CH2-CH3) (dt) and δ(P-CH2-CH3) (m) are given successively, with coupling constants J(H,H) ) 7.5 Hz, J(P,H) )
15.0 Hz, and J(P,H) ) nr. For Me2PhP: δ(P-CH3) (d) with J(P,H) ≈ 8.7-11.8 Hz. c 3J(H,H) and J(P,H) are given in parentheses. d 3J(H,H)
and 2J(P,H) are given in parentheses. e 3J(H,H) ≈ 6.3-8.3 Hz. Remaining or obscured protons are included under next column: δ(Ar). f Recorded
in CD2Cl2. g Measured at 500.13 MHz. h Measured at 100.13 MHz. i BF4 salt. j δ(P-alkyl) for the counterion [PtCl3(PEt3)]- is found at 1.17 (dt)
2
2
3
2
and 1.90 (dq). k δ(P-alkyl) for the counterion [PtCl3(PMe2Ph)]- is found at 1.81 (d, J(P,H) ) 11.9 Hz).
1.386(5) Å (1) to 1.438(9) Å (3b) (averages), which is likely
due to a shift of electron density from the PdN groups to the
metal. These two effects might also be caused by severe steric
interference between the aromatic groups on N and the PR3 and
Cl ligand on Pt. The chloride anion, Cl(2), has short nonbonding
contact distances with H(19), H(20), H(27), and H(48C). Short
intramolecular distances exist between the Pt(1) center and
H(20), 2.844(7) Å, Pt‚‚‚H(2), 2.916(7), Å, and Pt‚‚‚H(39), 3.141-
(9) Å.
31P NMR Spectroscopy. 1,1-BIPE shows a 31P resonance
frequency at 7 ppm, which is higher than that of BIPM (0
ppm).22 A similar trend has also been found for CHCH3-
(PPh2dS)2 (δ(P) ) 46.6 ppm) relative to CH2(PPh2dS)2 (δ(P)
) 34.6 ppm).28d The 31P NMR of complexes 2, where three
resonances are found, shows strong similarities to the 31P NMR
data of the analogous σ-N coordinated Pt-BIPM complex
reported earlier.4 The low frequency doublet resonance with
1J(Pt,P) of 3455-3490 Hz and 3J(PA,PB) of ca. 14 Hz is
unambiguously assigned to the phosphine PAR3 trans to the
coordinated NdPB group. The doublet at about 6.3 pm lies at
approximately the same 31P frequency as the free ligand 1 and
is therefore directly assigned to the noncoordinated PCdN group.
Spectroscopic Characterization of Compounds 1-3. 31P-
{1H}, 1H, and 13C{1H} NMR data for the compounds 1, 2, and
3 are given in Tables 4-6, respectively. Selected IR data
(Nujol, KBr) are given in the experimental section.

σ-N Coordination to Pt(II)
Inorganic Chemistry, Vol. 35, No. 6, 1996 1525
Table 6. 13C NMR Data for 1, 2a, and 3aa
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
1
36.8 (t, 75)
12.3 (s) 130.0 (d, 83)
131.2 (d, 92)
133.4 (vt, 4) 128.9 (m)b
132.0 (s)
132.1 (s)
149.1 (s)
123.3 (m, 9)b 129.8 (s) 126.6 (s) 20.9 (s)
133.9 (vt, 4)b
2a 35.7 (dd, 83, 70) 15.1 (m) 130.8 (d, 93)
133.2 (m)
128.1 (d, 13) 131.7 (d, 2) 149.1 (d, 3) 123.7 (d, 17) 129.9 (s) 127.0 (s) 21.0 (s)
128.7 (d, 13) 132.3 (d, 2)
131.3 (dd, 73, 7)
3a 34.2 (vt, 79)
11.2 (s) 118.1 (d, 87)
135.4 (d, 9) 130.8 (d, 12) 135.1 (d)e
145.8 (s)
123.2 (s)
131.2 (s)f 134.1 (s) 21.4 (s)g
118.5 (dd, 88, 3) 136.0 (d, 9) 131.5 (d, 12) 135.5 (d)e
128.6 (d, 12)
C12A
C12B
C13
C14
C15
C16
C17
C18
C19
C20
C21
2a 15.0 (d, 39) 8.3 (d, 3) 123.5 (d, 87)
135.8 (d, 10) 129.0 (d, 12) 132.5 (d, 3) 148.3 (s) 125.4 (d, 12) 128.5 (s) 128.8 (s) 20.7 (s)
124.6 (dd, 90)d 137.4 (d, 11) 129.4 (d, 11) 133.2 (d, 3)c
3a 14.6 (d, 38) 8.8 (d, 3) 126.9 (dd, 84, 5) 132.9 (d, 10) 129.6 (d, 12) 134.6 (d)e
146.1 (s) 125.4 (d, 13) 129.9 (s) 132.1 (s) 21.4 (s)g
127.4 (dd, 91, 5) 133.3 (d, 10) 129.7 (d, 12) 134.9 (d)e
a Measured at 75.48 MHz in CD2Cl2 at 293 K (1, 2a) or 233 K (3a). nJ(P,C) (in Hz) is given in parentheses. The atom labeling scheme is given
above. b Second order multiplet: vt ) virtual triplet, m ) multiplet, virtual couplings are given where possible. c C16 obscured by C4. d 3J(P,C) e
2 Hz. e 4J(P,C) was not resolved. f One C9 atom of the interacting p-tolyl group. The other C9 atom is obscured. g C11 and C21 are overlapping.
The high frequency resonance, a doublet of doublet at ca. 40
reaction of either of the two PdN groups of the N,N′
coordinated 1,1-BIPE ligand for pyridine. Evidence obtained
from 1H NMR (vide infra) points to conformational changes of
the six-membered platinacycle at temperatures above 293 K.
ppm, is attributed to PB of the coordinated PBdN group, based
2
on the observed J(Pt,P) coupling of 61-62 Hz, and mutual
spin-spin couplings with PA and PC. The large high frequency
shift of ∆δ(PB) ≈ 33 ppm falls within the range usually found
for coordination complexes of phosphinimines.3,4,31,32,38,39,41
Complexes 3 show three (3a,3b) or four (3a′,3b′) 31P
resonances at 293 K. The signals at 32.5 ppm (2J(Pt,PC) )
56-60 Hz) and 28.5 ppm (2J(Pt,PB) ≈ 0 Hz) are unambiguously
assigned to PC and PB, respectively, based on normal trans
influence criteria. This is confirmed by the X-ray crystal
structure of 3b, which has pointed out that the Pt-N bond trans
to Cl is indeed shorter than that trans to PR3. Further proof
for the trans PA-Pt-NdPB disposition is supplied by the Pt
complexes 3a and 3a′ (PAR3 ) PEt3), which show small
3J(PA,PB) of about 3 Hz. For related six-membered platinacycles
of the type [Pt(PPh3)2{NRdPPh2NdCPhNR′}],42 similar
3J(PPh3,P) trans couplings of 2.7-2.8 Hz have been reported,
whereas cis couplings range from 0 to 1.9 Hz.
1H NMR Spectroscopy (Table 5). In the 1H NMR spectra
of the 1,1 BIPE ligand (1), a characteristic multiplet (triplet of
quartet) is found for the methine-H at 3.72 ppm, which shifts
to higher frequencies upon mono- (5.5-5.6 ppm) or bidentate
(5.7-6.8 ppm) coordination of the ligand in the complexes 2
and 3, respectively. The methyl substituent on the central C
atom is found as a double triplet at about 1.3-1.8 ppm for 1-3,
meaning that its resonance frequency and also its coupling
pattern are hardly influenced by the coordination mode of the
1,1-BIPE ligand. As evidenced by the two doublets between
1.80 and 1.92 ppm for 2b, 3b, and 3b′, the methyl groups of
the PMe2Ph ligand on Pt are diastereotopic due to the chirality
of the central C atom of the σ-N- and the σ-N,σ-N′-coordinated
1,1-BIPE ligands in 2a,b and 3a,b,a′,b′, respectively. Interest-
ingly, for the σ-N monodentate coordinated complexes 2a and
2b, a striking high frequency resonance is observed in the region
9.1-9.3 ppm (dd), the integral corresponding to two phenyl-H
atoms, which can be understood in terms of intermittant
intramolecular interactions of the two Hortho atoms of one phenyl
ring on P with a Cl ligand or with the Pt center (by rotation
around the P-Ph bond). For a related Pt-phosphinimine
complex, reported earlier by Vicente et al., trans-[PtCl2-
{N(dPPh3)C(Ph)dCHCO2R}(NCPh)], an X-ray structural analy-
sis has shown that indeed one of the phenyl groups on P is
close to one of the axial positions of the Pt center, resulting in
short intramolecular distances between Hortho and Pt.43
The two resonances in the high frequency region between
28 and 33 ppm are slightly broadened at 293 K (for 3a′, 3b,
and 3b′), but do not show significant increases in broadening
or coalescence at temperatures up to 330 K. This observation
indicates that a slow dynamic process on the NMR time scale
might be at hand, indeed the peaks due to PB and PC become
sharp at low temperature. Addition of 1 equiv of pyridine to a
solution of 3a in CDCl3 in an NMR tube did not result in a
broadening of the 31P signals belonging to PB and PC, in a
temperature range from 293 to 330 K, which indicates that the
dynamic process does not involve a substitution or exchange
(41) Katti, K. V.; Cavell, R. G. Organometallics 1991, 10, 539.
(42) Roesky, H. W.; Scholz, U.; Noltemeyer, M. Z. Z. Anorg. Allg. Chem.
1989, 576, 255.
(43) Vicente, J.; Chicote, M.-T.; Ferna´ndez-Baeza, J.; Lahoz, F. J.; Lo´pez,
J. A. Inorg. Chem. 1991, 30, 3617.

1526 Inorganic Chemistry, Vol. 35, No. 6, 1996
Avis et al.
Scheme 3. Possible Dynamic Processes for 3b and 3b′ a
a
Key: (i) boat-to-boat inversion (occurring) and (ii) N1,N2 exchange (not occurring). Substituents on N and P have been omitted for clarity.
1
The variable temperature H NMR spectra (Table 5) for the
six-membered platinacycles 3a′,b and 3b′ show slightly broad-
ened signals belonging to the bridging ethane-1,1-diyl group at
293 K accompanying the broadening as observed in the 31P
NMR for 3a′,b and 3b′(vide supra). The signals sharpen up at
low temperature. As complexes 3b and 3b′ show two sharp
methyl resonances for the PMe2Ph ligand over the whole
temperature range from 213 to 330K, an N,N′ exchange process
as depicted in Scheme 3 by steps (ii) can be excluded, since
such a process would lead to inversion of configuration at the
methine carbon atom (R T S) and should hence reveal
broadening or coalescence of the two diastereotopic P-Me
signals at high temperature, which is not observed. This is
confirmed by 31P NMR (vide supra).
compared to E. Such features have been reported for six-
membered platina- and palladacycles containing flexible nitrogen
donor ligands bridged by methylene and ethane-1,1-diyl groups.44
Also, as can be seen from Scheme 3, presence of E and F in
solution would have resulted in additional PMe2Ph signals (c
and d), since F is a diastereomer of E. As mentioned before,
only two sharp doublets (a and b) for PMe2Ph are observed
over the whole temperature range. We therefore infer that the
boat-to-boat inversion of 3 is a slow process up to 330 K and
that the equilibrium lies completely on the side of conformer E
at low temperature; i.e., the concentration of conformer F is
too low to be observed. Comparison with the related complex
[PtCl(PEt3){(N(pTol)dPPh2)2CH2-N,N′}]+[PtCl3(PEt3)]-, for
which rapid boat-to-boat inversion of the six-membered plati-
nacycle has been demonstrated,4 shows that the increased steric
hindrance around the central carbon atom in complex 3 is
responsible for the slow ring-flip to conformer F. Molecular
CPK models have shown that indeed significant steric interac-
tions between the Me group and the Ph groups on the
phosphorus atoms exist during an enforced boat-to-boat inver-
sion. Furthermore, for organic six-membered ring systems it
is generally known that an equatorial position of sterically
demanding Me-groups is preferred.
However, the observations are consistent with a dynamic
process involving conformational changes within the six-
membered ring as depicted in Scheme 3(i), E T F. As rotation
about the P-N double bonds is blocked, chair-type conformers
cannot occur and hence conformational changes are restricted
to boat-to-boat inversion only. Such a ring flip results in an
exchange of equatorial and axial positions of the hydrogen and
methyl group on the central carbon, which accounts for the
1
broadness of these signals in the H NMR. The fact that one
set of sharp signals is observed for the CHCH3 group at low
temperature indicates that one conformer is favored. A boat-
to-boat inversion is also consistent with the 31P NMR as PB
and PC do not average, but minor broadening is expected, also
for PA.
The low temperature 1H NMR spectra (Figure 3) of the six-
membered platinacycles (3a,b) revealed another fluxional
process too. When the samples are cooled, the 1H NMR spectra
of 3a,3b,3a′ and 3b′ (Table 5 and Figure 3) show that two
doublets (a,b) appear at 8.5 and ca. 7.3 ppm (obscured) and
two doublets (a′,b′) in the region 5.5-6.8 ppm, the doublet
splitting being due to 3J(Ha,Hb) coupling within a C6H4 moiety
as established by 1H{31P} NMR spectroscopy, and each signal
corresponding to one proton. It appears that one of the N-p-
tolyl groups has lost its rotational freedom by intramolecular
interaction of either of the Hortho atoms (Ha) with the Cl ligand
or with the Pt(II) center, causing the large downfield shift to
8.5 ppm.45 The remaining three protons of the C6H4 moiety
have become anisochronous. Fast rotation of the p-tolyl group
at temperatures g293 K results in coalescence to give broad
In view of the relatively high CH frequency (5.7-6.8 ppm)
and the hardly changing C-CH3 frequency for 3, as compared
to the corresponding signals for 1,1-BIPE (1), we have deduced
that the most favored species in solution assumes conformation
E. The axial position of the methine hydrogen atom could cause
the observed high frequency shift for this group due to its
proximity to the platinum center. The structure in solution is
therefore in agreement with the solid state structure, as
authenticated by the X-ray crystal structure determination of
3b. Clearly, the concentration of conformer F in solution is
too low to be observed, as an axial position of the methyl group
in F would have resulted in a significant high frequency shift
of this methyl and a much lower CH resonance frequency as
(44) (a) Byers, P. K.; Canty, A. J. Organometallics 1990, 9, 210. (b) Byers,
P. K.; Canty, A. J.; Honeyman, R. T.; Watson, A. A. J. Organomet.
Chem. 1990, 385, 429.

σ-N Coordination to Pt(II)
Inorganic Chemistry, Vol. 35, No. 6, 1996 1527
Figure 4. Representation of the pTol-NdPPh2CH(Me)PPh2dN-pTol
ligand (1), viewed through the P-C-P plane.
C(Ph)dCHCO2R}], respectively.43 The shielding of the Cipso
atoms on P and N (C13 and C17), as well as the C(1) atom, is
obviously the result of a stronger polarization of the coordinated
PdN group and concomitant delocalization of electron density
in the aryl groups on N and P as compared to the noncoordinated
one. Similar observations have been made on going from
Ph3PdNPh to [Ph3PNHPh]+[Br]-.46
The 13C NMR spectrum of 3a shows that C1 has shifted to
an even lower frequency as compared to 1 and 2a. The
Ph2PdN-pTol part (C13-C21), which is coordinated trans to
PEt3 in 3a, has virtually the same 13C resonances as in 2a, except
for the phenyl ortho-carbons (C14) which showed a high
frequency shift of 3-4 ppm for 2a as a result of an intramo-
lecular interaction with the chloride ligand or the platinum
1
center, which is in agreement with the observation in the H
NMR (vide supra). For the newly coordinated Ph2PdN-pTol
moiety trans to chloride in 3a an extreme low frequency shift
is observed for C3 and a somewhat smaller one for C7, which
clearly indicates that the polarization of the PdN bond trans to
chloride is larger than in the PdN bond trans to PEt3. All other
carbons show deshielding effects upon coordination similar as
noted above for 2a.
Figure 3. 1H NMR spectra of 3b at 223, 253, and 293 K showing the
anisochronicity of the ortho- and meta-protons of the p-tolyl group at
low temperatures. Note that at 223 K two signals are found at 8.5
ppm: a broad signal (•) belonging to ortho-H of Ph (see 293 K) and a
doublet (a) belonging to one ortho-H of pTol. (* ) diethyl ether).
IR Spectroscopy. The ligand 1 shows a characteristic
medium absorption at 1341 cm-1, corresponding well with the
ν(PdN) stretch vibrations in the region 1282-1344 cm-1
reported for (N-aryl)phosphinimines21ab,47 and the bis(imino-
phosphoranyl)methane (BIPM) ligands.22
signals at 7.0 ppm (aav) and 6.7 ppm (bav, obscuring δ(CH)),
found at the approximate average chemical shifts of Ha, Ha′
and Hb, Hb′.
Interestingly, for the earlier reported N,N′-coordinated Pt-
BIPM complex,4 no intramolecular interactions as in 3 have
been observed, even at low temperature. We suspect that this
might be caused by a difference in folding of the six-membered
chelate ring in the boat conformers of [PtCl(PEt3){BIPM-
σN,σN′}]+[PtCl3(PEt3)]- 4 and [PtCl(PR3){1,1-BIPE-σN,σN′}]+X-
(3), due to the larger steric effect of the bridging CHCH3 group
in 3.
Complexes 2 show absorptions at 1330 and 1235 cm-1
,
corresponding to the noncoordinated and coordinated PdN
groups, respectively, when compared to ν(PdN) of 1 and earlier
reported σ-N coordinated Pt- and Pd-phosphinimine complexes,
e.g. trans-[PtCl2{N(dPPh3)C(Ph)dCHCO2R}(NtCPh)],43 [PdCl-
(µ-Cl){N(aryl)dPPh3}]2,48 and [PdCl2{N(aryl)dPPh3}(NtCPh)]48
with absorptions between 1238 and 1296 cm-1
.
For the complexes 3, two signals are found for ν(PdN) in
the region 1219-1251 cm-1. The low frequency shift of 90-
122 cm-1 is more pronounced than found for the analogous
N,N′-coordinated Rh- and Ir-BIPM complexes,3 but fall within
range of other complexes containing phosphinimine ligands,
which act as two-electron donors.38,39,47,48
13C NMR Spectroscopy (Table 6). The 13C{1H} NMR
spectrum of 1 shows a triplet at 36.8 ppm (1J(P,C) ) 75 Hz),
characteristic for the central carbon atom (C1). Similar values
have been reported for the corresponding carbon atom in bis-
(iminophosphoranyl)methane (BIPM) (30.5 ppm, 1J(P,C) ) 63.5
Hz)22 and the bis-sulfide analogue of 1,1-BIPE, CHCH3-
(PPh2dS)2 (41.1 ppm, 1J(P,C) ) 43 Hz).26 The Cipso,Cortho, and
Cmeta of the P-phenyl groups and also the Cortho atoms of the
p-tolyl substituent on N show double sets of resonance signals,
indicating that these aryl groups are magnetically inequivalent,
in keeping with their diastereotopicity (Figure 4).
The assignment of the 13C resonance signals, belonging to
the noncoordinated PPh2dN-pTol part (C3-C11) and co-
ordinated PPh2dN-pTol moiety (C13-C21) in complex 2a, is
in agreement with relevant 13C NMR data of 1 and the
structurally related complex, trans-[PtCl2(NtCPh){N(dPPh3]-
Conclusion
The free 1,1-bis((N-p-tolylimino)diphenylphosphoranyl)-
ethane ligand resembles the structure of the bis(iminophospho-
ranyl)methane analogues both in solution and in the solid state,
as evidenced by the close similarities in spectroscopic and X-ray
crystallographic data. However, a tremendous change in
coordination behavior to Pt(II) is observed as a consequence of
the presence of an additional methyl group on the central carbon
atom in 1,1-BIPE. Stable platinum(II) complexes containing
σ-N monodentate 1,1-BIPE (2) and σN,σN′-chelated 1,1-BIPE
(45) Deshielding of aromatic protons by interaction with adjacent halogens
is well known,44 but here an intramolecular interaction with Pt is
perhaps more likely, since the X-ray crystal structure analysis of 3b
shows a short distance (2.916(7)Å) between the ortho-H(2) of the
p-tolyl group cis to PMe2Ph and Pt.
(46) Albright, T. A.; Freeman, W. J.; Schweizer, E. E. J. Am. Chem. Soc.
1975, 97, 940.
(47) Abel, E. W.; Mucklejohn, S. A. Phosphorus Sulfur 1981, 9, 235.
(48) Fukui, M.; Itoh, K.; Ishii, Y. Bull. Chem. Soc. Jpn. 1975, 48, 2044.

1528 Inorganic Chemistry, Vol. 35, No. 6, 1996
Avis et al.
(3) could be isolated, which is in sharp contrast to the instability
of analogous Pt-BIPM complexes.4 We have established that
the thermal stabilization is largely due to electronic effects of
the additional methyl group in 1,1-BIPE, which decreases the
relative acidity of the methine proton in 1,1-BIPE as compared
to the methylene hydrogen atoms in BIPM, as proven by the
reluctance of 2 and 3 to undergo an H-shift from the methine
carbon to one of the nitrogen atoms (an essential step in the
formation of N,C coordinated four-membered metallacyclic Pt-
BIPM complexes).4
(SON) with financial aid from the Netherlands Organization
for Scientific Research (NWO). M.W.A. and C.J.E. wish to
thank Prof. K. Vrieze for his support of this work and Prof. K.
V. Katti and co-workers of the Radiology and Chemistry
Department of the University of MissourisColumbia for helpful
discussions and use of their facilities.
Supporting Information Available: Tables giving further details
of the structure determination, including crystallographic data atomic
coordinates for both the non-hydrogen and the hydrogen atoms, bond
lengths and angles, and thermal parameters for 1 and 3b (18 pages).
Ordering information is given on any current masthead page.
Acknowledgment. This work was supported in part (A.L.S.
and N.V.) by the Netherlands Foundation of Chemical Research
IC950748W