Remarkably stable titanium complexes containing terminal alkylidene, phosphinidene, and imide functionalities

Article abstract of DOI:10.1021/om0490583

PNP pincer-type complexes of titanium(III) and -(IV) have been prepared, characterized, and proven to be remarkably stable, despite having terminal alkylidene, phosphinidene, and imide functionalities.

Full text of DOI:10.1021/om0490583

1390
Organometallics 2005, 24, 1390-1393
Communications
Remarkably Stable Titanium Complexes Containing
Terminal Alkylidene, Phosphinidene, and Imide
Functionalities
Brad C. Bailey,† John C. Huffman,† Daniel J. Mindiola,*,† Wei Weng,‡ and
Oleg V. Ozerov‡
Department of Chemistry and Molecular Structure Center, Indiana University,
Bloomington, Indiana 47405, and Department of Chemistry, Brandeis University, MS015,
415 South Street, Waltham, Massachusetts 02454
Received November 30, 2004
Summary: PNP pincer-type complexes of titanium(III)
and -(IV) have been prepared, characterized, and proven
to be remarkably stable, despite having terminal alkyli-
dene, phosphinidene, and imide functionalities.
nature of these terminal functionalities. Recently, our
group has illustrated the use of the sterically demanding
Nacnac (Nacnac ) [Ar]NC(Me)CHC(Me)N[Ar]-, Ar )
2,6-(CHMe2)2C6H3) ligand for the preparation of low-
coordinate titanium complexes possessing terminal
alkylidene,6 imide,7 and phosphinidene8 ligands. Despite
the Nacnac ligand being an attractive template in
stabilizing low-coordinate titanium systems having
terminal metal-ligand multiply bonded scaffolds, this
type of ligand is often fraught with undesirable side
reactions due to the inherent reactivity of the imine
functionality.6,7,9 Other drawbacks with the Nacnac
ligand include electrophilic attack of the NCCCN γ-C
atom and C-H abstraction reactions that occur at both
the NCCCN â-C and nitrogen aryl groups.9
High-oxidation-state early-transition metal-carbon,1
-phosphorus,2 and -nitrogen3 multiple bonds play a
crucial role in many transformations that are ubiquitous
to chemists. Despite the extensive list of transition-
metal alkylidenes, only a handful of group 4 transition-
metal alkylidenes1,4 and phosphinidenes2,5 have been
prepared, which is likely due to the highly reactive
* To whom correspondence should be addressed. E-mail: mindiola@
indiana.edu.
† Indiana University.
‡ Brandeis University.
To avoid such obstacles, we employed the PNP pincer-
type ligand (PNP ) N[2-P(CHMe2)2-4-Me-C6H3]2-).10
The PNP ligand provides a “hybrid-type” coordination
environment combining both a hard amide and two soft
phosphine donors fixed in a meridional geometry. In
addition, this ancillary support is impervious to the
intramolecular cross-metathesis (or alternatively re-
ferred to as Wittig-type) reactions often encountered
with sterically demanding â-diketiminate-based com-
plexes such as (Nacnac)TidCHtBu(OTf)6 and (Nacnac)-
(1) Schrock, R. R. Chem. Rev. 2002, 102, 145-179.
(2) (a) Lammertsma, K.; Vlaar, M. J. M. Eur. J. Org. Chem. 2002,
1127-1138 and references therein. (b) Cowley, A. H. Acc. Chem. Res.
1997, 30, 445-451 and references therein. (c) Cowley, A. H.; Barron,
A. R. Acc. Chem. Res. 1988, 21, 81-87. (d) Mathey, F. Angew. Chem.,
Int. Ed. 2003, 42, 1578-1604 and references therein.
(3) (a) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239-482. (b)
Nugent, W. A.; Mayer, J. M. In Metal-Ligand Multiple Bonds; Wiley:
New York, 1988.
(4) (a) Fryzuk, M. D.; Mao, S. S. H.; Zaworotko, M. J.; MacGillivray,
L. R. J. Am. Chem. Soc. 1993, 115, 5336-5337. (b) Fryzuk, M. D.;
Duval, P. B.; Mao, S. S. H.; Zaworotko, M. J.; MacGillivray, L. R. J.
Am. Chem. Soc. 1999, 121, 2478-2487. (c) Fryzuk, M. D.; Duval, P.
B.; Patrick, B. O.; Rettig, S. J. Organometallics 2001, 20, 1608-1613.
(d) Barger, P. T.; Santarsiero, B. D.; Armantrout, J.; Bercaw, J. E. J.
Am. Chem. Soc. 1984, 106, 5178-5186. (e) Cheon, J.; Rogers, D. M.;
Girolami, G. S. J. Am. Chem. Soc. 1997, 119, 6804-6813. (f) Ivin, K.
J.; Rooney, J. J.; Stewart, C. D.; Green, M. L. H.; Mahtab, R. J. Chem.
Soc., Chem. Commun. 1978, 604-606. (g) Rice, G. W.; Ansell, G. B.;
Modrick, M. A.; Zentz, S. Organometallics 1983, 2, 154-157. (h) van
der Heijden, H.; Hessen, B. J. Chem. Soc., Chem. Commun. 1995, 145-
146. (i) Meinhart, J. D.; Anslyn, E. V.; Grubbs, R. H. Organometallics
1989, 8, 583-589. (j) Gilliom, L. R.; Grubbs, R. H. Organometallics
1986, 5, 721-724. (k) Hartner, F. W., Jr.; Schwartz, J.; Clift, S. M. J.
Am. Chem. Soc. 1983, 105, 640-641. (l) Weng, W.; Yang, L.; Foxman,
B. M.; Ozerov, O. V. Organomeatllics 2004, 23, 4700-4705. Attempts
to prepare group 4 alkylidene species have been reported: (m)
Wengrovius, J. H.; Schrock, R. R. J. Organomet. Chem. 1981, 205, 319-
327.
(5) (a) Hou, Z. M.; Stephan, D. W. J. Am. Chem. Soc. 1992, 114,
10088-10089. (b) Hou, Z. M.; Breen, T. L.; Stephan, D. W. Organo-
metallics 1993, 12, 3158-3167. (c) Breen, T. L.; Stephan, D. W. J. Am.
Chem. Soc. 1995, 117, 11914-11921. (d) Graham, T.; Stephan, D. W.
Private communication. (e) Urnezius, E.; Lam, K.-C.; Rheingold, A.
L.; Protasiewicz, J. D. J. Organomet. Chem. 2001, 630, 193-197. Other
Zr phosphinidene complexes have been isolated by trapping experi-
ments: (f) Mahieu, A.; Igau, A.; Majoral, J.-P. Phosphorus Sulfur 1995,
104, 235-239.
TidPR(CH2 Bu) (R ) C6H11, 2,4,6-iPr3C6H2).8 A true
t
representation of the robust nature of the PNP skeleton
was demonstrated recently by Ozerov and co-workers,
(6) (a) Basuli, F.; Bailey, B. C.; Tomaszewski, J.; Huffman, J. C.;
Mindiola, D. J. J. Am. Chem. Soc. 2003, 20, 6052-6053. (b) Basuli,
F.; Bailey, B. C.; Watson, L. A.; Tomaszewski, J.; Huffman, J. C.;
Mindiola, D. J. Organometallics, in press.
(7) Basuli, F.; Bailey, B. C.; Huffman, J. C.; Mindiola, D. J. Chem.
Commun. 2003, 1554-1555.
(8) Basuli, F.; Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J. J.
Am. Chem. Soc. 2003, 34, 10170-10171.
(9) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev. 2002,
102, 3031-3066.
(10) The PNP ligand has been used in the chemistry of group 9 and
10 metals, and JP-P values have been reported. (a) Fan, L.; Foxman,
B. M.; Ozerov, O. V. Organometallics 2004, 23, 326-328. (b) Ozerov,
O. V.; Guo, C.; Fan, L.; Foxman, B. M. Organometallics 2004, 23, 5573-
5580. (c) Ozerov, O. V.; Guo, C.; Papkov, V. A.; Foxman, B. M. J. Am.
Chem. Soc. 2004, 126, 4792-4793. (d) Fan, L.; Yang, L.; Guo, C.;
Foxman, B. M.; Ozerov, O. V. Organometallics 2004, 23, 4778-4787.
The PNP relative bis(2-diphenylphosphino)amide has also been re-
ported: (e) Liang, L.-C.; Lin, J.-M.; Hung, C.-H. Organometallics 2003,
22, 3007-3009.
10.1021/om0490583 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/25/2005

Communications
Scheme 1. Synthesis of Complexes 1-3
Organometallics, Vol. 24, No. 7, 2005 1391
Toluene solutions of complex 1 react smoothly with 2
equiv of neopentyllithium at -35 °C over 1 h to afford
a red solution. Upon removal of the salts and recrys-
tallization from cold (-35 °C) saturated pentane solu-
t
tions, red-brown crystalline (PNP)Ti(CH2 Bu)2 (2) is
obtained in 52% yield (Scheme 1). A single-crystal X-ray
diffraction study of 2 agrees with the proposed con-
nectivity and displays no significant R-H interactions
in the solid state,11 while Evans magnetic susceptibility
measurements are in accord with a titanium(III) species
(µeff ) 2.11 µΒ). The room-temperature X-band solution
EPR spectrum of 2 reveals not only hyperfine coupling
of the unpaired electron to the titanium center (Aiso
)
10.5 G) but also superhyperfine coupling to the proximal
phosphorus atoms (Aiso ) 10.1 G) and the nitrogen (Aiso
) 34.9 G) and super-superhyperfine coupling to all four
R-H’s on the neopentyl ligands (Aiso ) 1.7 G).11 Alter-
natively, it was found that complex 2 can be prepared
in a “one pot” synthesis of Li(PNP) and TiCl3(THF)3,
t
followed by the addition of 2 equiv of LiCH2 Bu after
12 h (63% yield based on TiCl3(THF)3).11
To promote R-abstraction6 and form (PNP)TidCHtBu-
(OTf) (3), complex 2 was oxidized with AgOTf at -35
°C in pentane. Upon filtration of the Ag0 mirror, complex
3 is generated quantitatively on the basis of the
combination of 1H, 31P, 13C, and 13C{31P} NMR spectra.11
Diagnostic spectroscopic features for 3 include a 13C
NMR resonance centered at 301 ppm, which is consis-
tent with a terminal CR-alkylidene ligand.1,4,6 The R-H
in which they reported the isolation of a terminal
zirconium alkylidene-alkyl complex (PNP)ZrdCHPh-
(CH2Ph).4l Herein, the following paper demonstrates
that the PNP ligand can be incorporated readily onto
Ti and that such a template can stabilize terminal
alkylidene, phosphinidene, and imide functionalities.
In contrast to the Zr chemistry,4l attempts to integrate
the alkylidene functionality directly on Ti(IV) proved
difficult, inasmuch as treatment of (PNP)TiCl3, prepared
directly from TiCl4 and Li(PNP), with alkyl Grignard
reagents (2-3 equiv) led to undesired reduction instead
of alkylation.11 This difference between the reactivities
of (PNP)ZrCl3 and (PNP)TiCl3 is not surprising, since
reduction of MIV to MIII should be more facile for M )
Ti than for the heavier congener M ) Zr.
To avoid redox pathways during the transmetalation
process, we resorted to an approach that worked well
previously for the preparation of titanium alkylidenes
with the Nacnac system: alkylation of a TiIII precursor
followed by one-electron oxidation. To prepare the Ti-
(III) precursor (PNP)TiCl2 (1), a toluene solution of Li-
(PNP) was cooled to -35 °C and added dropwise to a
cold toluene suspension of TiCl3(THF)3. After 12 h and
upon removal of salts, a violet powder of (PNP)TiCl2 (1)
was isolated in 58% yield (Scheme 1). Satisfactorily
elemental analysis and isolation of X-ray-quality single
crystals has so far eluded us; however, the room-
temperature X-band EPR measurements of 1 in THF
displayed a giso value of 1.949 and well-resolved hyper-
fine and superfine coupling to titanium (Aiso ) 17.4 G)
and both phosphorus atoms (Aiso ) 8.8 G), respectively.
When purple solids of 1 are dissolved in THF, the
solutions turn red, suggesting that coordination of the
solvent might be occurring to form a putative (PNP)-
TiCl2(THF) complex, but coordination appears to be
weak and reversible, since red solids turn back to purple
under reduced pressure. It is also possible that complex
1 could exist as a dimer in the absence of coordinating
solvents. However, we have found that complex 1
(possibly (PNP)TiCl2(THF) or the dimer) readily ab-
stracts Cl from CCl4 to afford (PNP)TiCl3.11
1
is significantly downfield (8.42 ppm) in the H NMR
spectrum, and the low JC-H value of 102.6 Hz for the
alkylidene resonance lends support to an R-agostic
interaction being present in solution. The 31P NMR
spectrum of 3 displays two doublets centered at 33.6
and 24.2 ppm (JP-P ) 55 Hz), which would be in
agreement with the molecule retaining C1 symmetry in
solution. This JP-P coupling constant is low in compari-
son to similar chelate trans-phosphine systems (100-
300 Hz)4l,10,12 and is thus indicative of the phosphines
being significantly skewed from a strict trans geometry
(P-Ti-P ) 180°). Such a geometrical constraint is
arguably a result of the aryl motifs in the PNP ligand
or is based on an electronic reason involving a compro-
mise between the soft P and hard Ti and N atoms.
Rigidity is probably more pronounced in this class of
ligand than in the SiPNP ligand system utilized by
Fryzuk and co-workers (SiPNP
) N[SiMe2CH2P-
(tBu)2]2-).13 Interestingly, compound 3 resembles an
electron-deficient and unsaturated version of Schrock
and Baumann’s complex (NON)TidCHtBu(PMe3)2 (NON
) [iPrN-o-C6H4]2O2-).15
X-ray-quality single crystals of 3 were slowly grown
from pentane at room temperature (Figure 1).16 The
molecular structure of 3 reveals a short TidC bond
(1.883(7) Å) and a metal center residing in a pseudo-
trigonal-bipyramidal geometry with “trans-like” phos-
(12) (a) Crabtree, R. H. The Organometallic Chemistry of the
Transition Metals, 3rd ed.; Wiley-Interscience: New York, 2001; pp
260-262.
(13) (a) Fryzuk, M. D.; Mao, S. S. H.; Zaworotko, M. J.; MacGillivray,
L. R. J. Am. Chem. Soc. 1993, 115, 5336-5337. (b) Fryzuk, M. D.;
Duval, P. B.; Mao, S. S. H.; Zaworotko, M. J.; MacGillivray, L. R. J.
Am. Chem. Soc. 1999, 121, 2478-2487.
(14) Baumann, R.; Stumpf, R.; Davis, W. M.; Liang, L.-C.; Schrock,
R. R. J. Am. Chem. Soc. 1999, 121, 7822-7836.
(15) Basuli, F.; Bailey, B. C.; Huffman, J. C.; Baik, M.; Mindiola,
D. J. J. Am. Chem. Soc. 2004, 7, 1924-1925.
(11) See the Supporting Information for complete experimental,
crystallographic, and DFT calculation details.

1392 Organometallics, Vol. 24, No. 7, 2005
Communications
Figure 1. Molecular structures of 3 and 4 with thermal ellipsoids at the 50% probability level. All H atoms, with the
exception of the R-H on C(31), and the O2SCF3 and iPr methyl groups on the P atoms and aryl positions (complex 4) have
been omitted for clarity. Next to each structure are the DFT calculations (HOMO and LUMO for 3 and HOMO-1 and
HOMO for 4) depicting bonding interactions involving the TidC and TidP linkages.
Scheme 2. Formation of Phosphinidene 4 and
phines (148.43(8)°). The distorted Ti(1)dC(31)-C(32)
angle (157.6(6)°) coupled with the low R-C JC-H (vide
Imido 5 from 3a
supra) and short Ti-H distance (2.09(6) Å) are all
consistent with an R-H agostic interaction being present
in complex 3.1,14
It was presaged by the nucleophilic character of the
R-carbon in early-transition-metal alkylidenes1,8,15 that
complex 3 would undergo R-H migration reactions with
primary phosphide or amide reagents. Given the low
number of terminal titanium phosphinidenes,5d,8 we
proceeded to treat 3 with 1 equiv of LiPHTrip (Trip )
2,4,6-iPr3C6H2). Upon addition, the solution rapidly
changed color from red to purple concomitant with
a Legend: (i) LiXHAr is added to 3 in Et2O at -35 °C.
generation of LiOTf. Large purple blocks of (PNP)Tid
t
PTrip(CH2 Bu) (4) were isolated in 70% yield from
tions of 4 exhibit three inequivalent phosphorus reso-
nances resolving into three doublets of doublets centered
at 31 (JP-P ) 40 and 12 Hz), 37 (JP-P ) 44 and 40 Hz),
and 237 ppm (JP-P ) 44 and 12 Hz). The 31P NMR
pentane at -35 °C (Scheme 2).17 Formation of 4 likely
proceeds via the hypothetical alkylidene-phosphide
complex (PNP)TidCHtBu(PHTrip), which undergoes
R-H migration to furnish the TidP linkage in 4. Solu-
(17) Crystal data for 4: C54H92NP3Ti, Mw ) 896.10, triclinic, space
group P1h, a ) 10.4954(10) Å, b ) 14.5554(14) Å, c ) 19.3081(18) Å, R
) 107.202(2)°, â ) 103.737(2)°, γ ) 95.098(2)°, V ) 2696.5(4) Å3, T )
125(2) K, Z ) 2, Dc ) 1.104 Mg m-3, µ(Mo ΚR) ) 0.281 mm-1, 20 639
(16) Crystal data for 3:
C32H50F3NO3P2STi, Mw ) 695.63, mono-
clinic, space group P21/n, a ) 9.823(2) Å, b ) 20.914(6) Å, c ) 18.009-
(5) Å, â ) 103.524(6)°, V ) 3597.4(16) Å3, T ) 122(2) K, Z ) 4, Dc )
1.284 Mg m-3, µ(Mo ΚR) ) 0.432 mm-1, 8035 unique reflections (F >
4σ(F)), 2160 observed reflections (Rint ) 0.2052). Final R1(I > 2σ(I)) )
0.0698 and wR2(all data) ) 0.1312. All hydrogen atoms were located
in subsequent Fourier maps. Attempts to refine all hydrogen atoms
were not successful. Although all were refined to qualitatively correct
positions, there were several in which the C-H distance was as large
as 1.26 Å and angles were similarly distorted. For this reason all
hydrogen atoms with the exception of that on C(31) were placed in
ideal positions and refined as riding atoms with relative isotropic
displacement parameters. The hydrogen on C(31) was allowed to vary
isotropically to verify its correct assignment.
unique reflections (F > 4σ(F)), 13 889 observed reflections (Rint
)
0.1657). Final R1(I > 2σ(I)) ) 0.0463 and wR2(all data) ) 0.1194. The
structure was found as proposed with 11/2 pentane solvent molecules
in the asymmetric cell. Two regions of disorder indicated that solvent
was present in the cell, and the solvent was modeled using partial-
occupancy on carbon atoms. One of the two sites resulted in a
reasonable model, while the other (located at a center of inversion at
1/2, 1/2, 1/2) was not readily modeled. All non-hydrogen atoms were
refined with anisotropic displacement parameters. All nonsolvent
hydrogen atoms were located in subsequent Fourier maps and included
as isotropic contributors in the final cycles of refinement.

Communications
Organometallics, Vol. 24, No. 7, 2005 1393
Table 1. Comparison of Experimental Data and
Theoretical Results (B3LYP Level of Theory)
substituent was changed to Me), all bond angles and
distances remained relatively close to those of the actual
compound, suggesting that steric interactions do not
appear to be a prerequisite for the stability of 3. Unlike
(Nacnac)TidCHtBu(OTf),6 the LUMO of compound 3
has mostly TidC π* character without too much ligand
contribution.
Theoretical investigations of 4, on the other hand,
displayed results in contrast with those for 3. Although
the actual compound of 4 closely reproduces the bond
angles and distances seen in the crystal structure (Table
1), the geometry of the model appears sensitive to any
structural simplifications. More specifically, when the
iPr groups on the PNP, the phosphinidene aryl, and the
neopentyl group were simplified to methyl groups, the
TidP bond length was comparable (2.23 Å) but the Tid
P-Cipso angle deviated severely (127.7°).11 Careful ex-
amination of the frontier orbitals on the actual com-
pound of 4 suggest that a pseudo TitP bond can be in
fact conceivable, since the HOMO and HOMO-1 display
orthogonal TidP π bond sets (Figure 1). On the basis of
this argument it is proposed that sterically demanding
substituents appear to enforce sp hybridization of P in
4.
bond length (Å) or angle (deg)
exptl from X-ray data
calcd
Compound 3
1.883(7)
Ti1-C31
1.85
Ti1-N5
2.034(5)
2.06
P2-Ti1-P8
Ti1-C31-C32
148.43(8)
157.6(6)
148.4
147.0
Compound 4
2.2066(4)
Ti1-P31
2.19
Ti1-N9
2.1023(11)
2.0847(14)
163.44(4)
2.14
Ti1-C47
Ti1-P31-C32
P2-Ti1-P16
2.08
164.2
137.7
137.409(15)
resonance centered at 237 ppm is strong evidence of a
linear phosphinidene structure.18
As with 3, the molecular structure of 4 also exhibits
a pseudo-trigonal-bipyramidal titanium center, but with
the PNP phosphine donors being more acutely oriented
(137.49(15)°). The TidP distance is exceedingly short
(2.2066(4) Å) in comparison to the two dative Ti-PiPr2
distances in the same system (2.60-2.61 Å; Figure 1)
but is similar to the only structurally characterized
titanium phosphinidene complex, (Nacnac)TidPMes*-
In conclusion, the robust “(PNP)Ti” scaffold has been
t
(CH2 Bu) (Mes* ) 2,4,6-tri-tert-butylphenyl).8 Complex
shown to stabilize terminal ligands such as [CR2]2-
,
4 also contains an obtuse TidP-Cipso angle of 163.44-
(4)°, which suggests that there might be some significant
amount of multiple-bond character between P and Ti.
[PAr]2-, and [NAr]2-. Unlike titanium â-diketiminate
complexes having alkylidene and phosphinidene ligands,
this pincer-based class of compounds does not appear
to generate unstable kinetic products and thus offers
an attractive opportunity to study the chemical reactiv-
ity of the metal-ligand multiple bond.
t
In contrast to (Nacnac)TidPMes*(CH2 Bu), complex 4
is kinetically and thermally stable, which is rather
remarkable, considering the hard-soft mismatch among
these elements. We have also determined that complex
3 reacts cleanly with LiNHAr (Ar ) 2,6-(CHMe2)2C6H3)
to afford the titanium nitrogen analogue of 4, namely
Acknowledgment. For financial support of this
research D.J.M. thanks Indiana UniversitysBloom-
ington, the Camille and Henry Dreyfus Foundation, and
the National Science Foundation (CAREER Award,
Grant No. CHE-0348941). B.C.B. acknowledges the
Department of Education for a GAANN Fellowship and
Prof. M.-H. Baik for insightful comments and discus-
sions. Acknowledgment is made by O.V.O. and W.W. to
Brandeis University, to Research Corp., and to the
donors of the Petroleum Research Fund, administered
by the American Chemical Society, for partial support
of this research. We also thank the reviewers for
insightful comments.
t
(PNP)TidNAr(CH2 Bu) (5), as red blocks in 78% yield
(Scheme 2).11
To probe why complexes 3 and 4 are much more stable
than the Nacnac analogues, DFT calculations were
carried out on the actual compound for each system.11
Theoretical values closely match the experimental
parameters obtained from the X-ray data (Table 1). For
3, the HOMO displays strictly TidC π bond character,
while the LUMO is the TidC π* orbital, which lies high
in energy relative to the HOMO (Figure 1; ∆E ) 3.441
eV). Upon significant simplification of the model for 3
i
(the Pr groups were changed to Me, and the tBu
Supporting Information Available: Text, tables, and
figures giving complete experimental details (1-5), CIF files
giving crystallographic data (2-5), and text, tables, and figures
giving theoretical data (3 and 4). This material is available
free of charge via the Internet at http://pubs.acs.org.
(18) Group 4-6 transition-metal complexes having a bent geometry
at the terminal phosphinidene ligand exhibit 31P NMR spectral
resonances >330 ppm.2,5 In contrast, linear phosphinidene ligands of
the early transition metals (e.g. Ti, Ta, and W) have been reported to
have 31P NMR resonances between 270 and 170 ppm.2,8 However, we
are not entirely confident about making discriminations between linear
and bent phosphinidene geometries from just the 31P NMR spectro-
scopic data.
OM0490583