A New Water-Soluble Phosphine Derived from 1,3,5-Triaza-7-phosphaadamantane (PTA), 3,7-Diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane. Structural, Bonding, and Solubility Properties

Article abstract of DOI:10.1021/om0343059

The phosphine 3,7-diacetyle-1,3,7-triaza-5-phosphabicyclo[3.3.1.] was investigated. These compounds were prepared by acylation of 1,3,5-triaza-7- phosphaadamantane (PTA) and its oxide with acetic anhydride. The nonionic compounds were found to be soluble in most common organic solvents, in addition to possessing extremely large molar solubilities in water. Restricted rotation about the amide nitrogen-carbonyl carbon bond is observed.

Full text of DOI:10.1021/om0343059

Organometallics 2004, 23, 1747-1754
1747
A New Wa ter -Solu ble P h osp h in e Der ived fr om
1,3,5-Tr ia za -7-p h osp h a a d a m a n ta n e (P TA),†
3,7-Dia cetyl-1,3,7-tr ia za -5-p h osp h a bicyclo[3.3.1]n on a n e.
Str u ctu r a l, Bon d in g, a n d Solu bility P r op er ties
Donald J . Darensbourg,* Cesar G. Ortiz, and J ustin W. Kamplain‡
Department of Chemistry, Texas A&M University, College Station, Texas 77843
Received November 18, 2003
The phosphine 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane, which we will
condense to DAPTA, and its oxide have been fully characterized both in solution and in the
solid state. These compounds were prepared by acylation of 1,3,5-triaza-7-phosphaadaman-
tane (PTA) and its oxide with acetic anhydride. The nonionic compounds were found to be
soluble in most common organic solvents, in addition to possessing extremely large molar
solubilities in water. Indeed, the molar solubility of DAPTA was shown to be 7.4 M, which
is 4 time more soluble than the commonly utilized water-soluble phosphine, triply meta-
sulfonated triphenylphosphine (TPPTS). In the case of DAPTA this enhanced water solubility
is attributed to a strong interaction of water with the amide nitrogen-CO bond dipole as
revealed by a large red shift of the νCdO vibration on going from a weakly interacting solvent
such as CH2Cl2 to water. This latter observation is supported by the short average amide
nitrogen-carbonyl carbon bond distance of 1.375 Å as determined via X-ray crystallography,
indicative of a strong Coulombic interaction between the nitrogen and carbon atoms. To
assess the metal to phosphorus binding characteristics of DAPTA, several group 10 and
group 6 complexes were prepared and their M-P bond distances were shown to be quite
similar with those of their PTA analogues. For examples, the W-P bond distance in
W(CO)5DAPTA of 2.492(3) Å is comparable to that previously reported for W(CO)5PTA of
2.4976(15) Å and slighter shorter than that found in W(CO)5PMe3 (2.516(2) Å). Accordingly,
the PTA ligand has generally been characterized as possessing donor properties similar to
that of PMe3. Consistent with these bonding parameters determined in the solid state, all
three tungsten pentacarbonyl complexes have nearly identical ν(CO) frequencies in solution.
Ch a r t 1
In tr od u ction
Aqueous organometallic chemistry has received much
attention in recent years due to the many advantages
an aqueous medium presents to stoichiometric and
catalytic reactions.1 Water’s copious and nontoxic na-
ture, along with its distinct physical properties, makes
it an ideal solvent for numerous processes from an
industrial point of view. With regard to its physical
properties, its high heat capacity enables it to effectively
distribute heat from exothermic reactions, and its
immiscibility with many organic compounds allows it
to serve as part of a biphasic system where products
can be easily separated from water-soluble catalysts by
a simple extraction process. The latter procedure is the
foundation of the Ruhrchemie-Rhoˆne Poulenc hydro-
formylation process of lower molecular weight olefins,
in which the triply meta-sulfonated triphenyl phosphine
ligand, TPPTS, is used with rhodium as the active metal
center.1,2 This and other tertiary water-soluble phos-
phines (WSP) have been the most widely used class of
water-soluble ligands in aqueous catalysis due to their
neutral donating ability, which can effectively stabilize
the metal center throughout the catalytic cycles (Chart
1). Furthermore, these phosphines can participate in the
reduction of the metal center in such processes as
carbon-carbon bond formation reactions, where group
† The IUPAC name for PTA is 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]-
decane.
* Correspondingauthor.Fax: (979)845-0158.E-mail: djdarens@mail.chem.
tamu.edu.
‡ NSF-REU participant from Oklahoma Christian University.
(1) For extensive reviews on aqueous catalysis, see: (a) J oo´, F.
Aqueous Organometallic Catalysis; Kluwer: Dordrecht, 2001. (b)
Cornils, B., Herrmann, W. A., Eds. Aqueous-Phase Organometallic
Catalysis. Concepts and Applications; Wiley-VCH: Weinheim, 1998.
(c) Horva´th, I. T., J oo´, F., Eds. Aqueous Organometallic Chemistry and
Catalysis; NATO ASI 3/5; Kluwer: Dordrecht, 1995. (d) Sinou, D. Top.
Curr. Chem. 1999, 206, 41.
(2) Cornils, B. Org. Process Res. Dev. 1998, 2, 121.
10.1021/om0343059 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 03/09/2004

1748 Organometallics, Vol. 23, No. 8, 2004
Darensbourg et al.
10 metals, M2+, are reduced to the active M0 species.
Apart from TPPTS, a variety of WSPs have appeared
through the years, and their catalytic potential has been
investigated. Of main importance to our work is the
water-soluble and air-stable 1,3,5-triaza-7-phosphaada-
mantane (PTA) ligand, which owes its water solubility
to hydrogen bonding of the nitrogen atoms to water
(Chart 1).3 Due to its small cone angle (102°) and
excellent donating ability (comparable to PMe3), it has
received much attention as a potential ligand for
catalytic reactions such as in the monophasic4 and
biphasic5 hydrogenation of alkenes and aldehydes.
In addition, various other derivatives of PTA have
also been synthesized but remain relatively unexplored.
For example, the sulfone derivative of PTA, 2-thia-1,3,5-
triaza-7-phosphaadamantane-2,2-dioxide (PASO2), was
previously prepared by Daigle,6 and its binding to group
6 metals7 was illustrated in our laboratories. However,
to our surprise, the PASO2 derivative possesses very
limited water solubility. Shortly after Daigle’s initial
synthesis of PTA, a series of reactions of PTA similar
to those observed for its hexamethylenetetramine ana-
logue were carried out by Siele. These included nitra-
tion,8 nitrosation,9 and acetylation.10 At that time, it was
noted that PTA reacts with acetic anhydride to provide
the acetylated product 3,7-diacetyl-1,3,7-triaza-5-phos-
phabicyclo[3.3.1]nonane (1).11 Nevertheless, no other
studies of this phosphine, which we will call DAPTA,
have been reported. Due to the need for a larger variety
of water-soluble phosphines to serve as ligands to low-
valent metal complexes rendering them soluble in
water, we have chosen to investigate DAPTA for this
purpose. Herein, we report the complete characteriza-
tion of 1 and its corresponding oxide (2). In addition,
several metal complexes were prepared and character-
ized in solution by IR/NMR spectroscopy, and in the
solid state via X-ray crystallography, to assess the
nature of the metal-phosphorus bond. The water
solubility of 1 was measured and compared with other
commonly utilized water-soluble phosphines, including
its PTA analogue.
one ketyl. In the preparation of 1 and 2, deionized water was
used. Cr(CO)6 and W(CO)6 precursors were purchased from
Aldrich Chemical Co., with the latter being sublimed prior to
use. Ni(COD)2 was purchased from Strem Chemical Co. and
used without further purification. PTA and its oxide were
prepared following the literature method.3 Although the
preparations of 1 and 2 have been previously described by
Siele, the syntheses are included herein for completeness
purposes.11 The salicylaldimine used in the preparation of 4
was prepared according to the literature procedure.12
X-ray data were collected on a Bruker CCD diffractometer
and covered more than a hemisphere of reciprocal space by a
combination of three sets of exposures; each exposure set had
a different æ angle for the crystal orientation, and each
exposure covered 0.3° in ω. The structures were solved by
direct methods. The absolute configuration of compound 1,
determined in the noncentrosymmetric space group P2(1),
1
could not be accurately assessed. H, 13C, and 31P NMR data
were obtained using a Varian Unity+ 300 MHz NMR instru-
ment. 1H and 13C chemical shifts were referenced according
to the deuterated solvent used. The 31P chemical shifts were
referenced using an external 85% H3PO4 sample. Elemental
analyses were conducted by Canadian Microanalytical Inc.
P reparation of3,7-Diacetyl-1,3,7-triaza-5-phosphabicyclo-
[3.3.1]n on a n e (DAP TA) (1).11 In a 250 mL round-bottom
flask equipped with a dropping funnel, PTA (6.25 g, 39.6 mmol)
was dissolved in 80 mL of water. To this solution, maintained
at 0 °C, was added dropwise acetic anhydride (12.1 g, 119
mmol) with stirring over a period of 20 min. The solution was
allowed to stand for 30 min, and the solvent was removed
under vacuum, leaving behind a white solid. The product was
purified by recrystallization from acetone and obtained in 47%
1
yield. H NMR (300 MHz, CDCl3, δ): 1.96 (s, 6H, C(O)CH3),
4
2
4.12 (d, J PC ) 9.3 Hz, 4H, NCH2N), 4.67 (d, J PC ) 13.2 Hz,
2
2H, PCH2N), 4.85 (d, J PC ) 13.2 Hz, 2H, PCH2N), 5.63 (d,
2J PC ) 13.8 Hz, 2H, PCH2N). 13C NMR (75 MHz, CDCl3, δ):
20.9 (C(O)C), 62.03 (N-C-N), 67.0 (P-C-N), 70.1 (P-C-N),
169.0 (C(O)). 31P (121 MHz, CDCl3, δ): -78.5. IR (νCdO): 1642
cm-1 (CH2Cl2), and 1608 cm-1 (H2O).
P r ep a r a tion of 3,7-Dia cetyl-1,3,7-tr ia za -5-p h osp h a bi-
cyclo[3.3.1]n on a n e 5-Oxid e (2).11 The preparation of 2 was
achieved by the acylation of PTA oxide using a synthetic
protocol analogous with that employed for the synthesis of 1,
in a 41% yield. Similar to 1, the ligand readily dissolves in
water and polar organic media such as methylene chloride and
THF. 1H NMR (300 MHz, CDCl3, δ): 2.11 (s, 6H, C(O)CH3),
2
4
3.27 (m, J HH ) 16.2 Hz, J PH ) 6.60 Hz, J HH ) 3.22 Hz, 1H),
Exp er im en ta l Section
2
3.74 (d, J HH ) 7.20 Hz, 2H), 3.81 (dd, J PH ) 7.50 Hz, J HH
)
3.00 Hz, 1H), 3.87 (d, 2J HH ) 14.4 Hz, 1H), 4.40 (t, 2J HH ) 14.4
Ma ter ia ls a n d Meth od s. Unless otherwise indicated, all
reactions were carried out under an inert argon atmosphere
using standard Schlenk and drybox techniques. Prior to their
use, all organic solvents were distilled from sodium benzophen-
2
2
Hz, 1H), 4.87 (d, J HH ) 14.1 Hz, 1H), 5.50 (t, J HH ) 16.2 Hz,
1H), 5.71 (d, 2J HH ) 14.4 Hz, 1H). 13C NMR (75 MHz, D2O, δ):
21.9, 21.5 (C(O)CH3), 42.0 (d, J PC ) 67.1 Hz, P-C-N), 46.7
(d, J PC ) 64.1 Hz, P-C-N), 53.4 (d, J PC ) 62.2 Hz, P-C-
N), 62.0 (d, J PC ) 6.86 Hz, N-C-N), 66.9 (d, J PC ) 6.49 Hz,
N-C-N), 169.5 (C(O)), 170.1 (C(O)). 31P NMR (121 MHz,
CDCl3, δ): 2.20.
1
1
1
4
4
(3) (a) Daigle, D. J .; Peppermann, A. B.; Vail, S. L. J . Heterocycl.
Chem. 1974, 11, 407. (b) Daigle, D. J . Inorg. Synth. 1998, 32, 40.
(4) (a) Darensbourg, D. J .; J oo´, F.; Na´dasdi, L.; Be´nyei, A. Cs. J .
Organomet. Chem. 1996, 512, 45. (b) Smolenski, P.; Pruchnik, F. P.
Appl. Organomet. Chem. 1999, 13, 829.
(5) (a) Darensbourg, D. J .; J oo´, F.; Kannisto, M.; Katho´, A.; Reiben-
spies, J . H.; Daigle, D. J . Inorg. Chem. 1994, 33, 200. (b) Darensbourg,
D. J .; J oo´, F.; Kannisto, M.; Katho´, A.; Reibenspies, J . H. Organome-
tallics 1992, 11, 1990. (c) Darensbourg, D. J .; Stafford, N. W.; J oo´, F.;
Reibenspies, J . H. J . Organomet. Chem. 1995, 455, 99.
(6) Daigle, D. J .; Boudreaux, G. J .; Vail, S. L. J . Chem. Eng. Data
1976, 21, 240.
(7) (a) Darensbourg, D. J .; Yarbrough, J . C.; Lewis, S. J . Organo-
metallics 2003, 22, 2050.
(8) Hale, G. C. J . Am. Chem. Soc. 1925, 47, 2754.
(9) (a) Bachmann, W. E.; Horton, W. J .; J enner, E. L.; MacNaughton,
N. W.; Scott, L. B. J . Am. Chem. Soc. 1951, 73, 2769. (b) Bachmann,
W. E.; Deno, N. C. J . Am. Chem. Soc. 1951, 73, 2777.
(10) (a) Warman, M.; Siele, V. I.; Gilbert, E. E. J . Heterocycl. Chem.
1973, 10, 97. (b) Siele, V. I.; Warman, M.; Gilbert, E. E. J . Heterocycl.
Chem. 1974, 11, 237.
P r ep a r a tion of Ni(DAP TA)4 (3). To a Schlenk flask
containing Ni(COD)2 (0.120 g, 0.436 mmol), in approximately
20 mL of toluene, was added 1 (0.400 g, 1.75 mmol), in 5 mL
of methanol, via cannula. The resulting clear solution was
stirred for 3 h, leading to the formation of a white precipitate.
The white solid was collected by filtration, washed with 2 × 5
mL of ether, and dried under vacuum. Yield: 94.1%. 1H NMR
(300 MHz, CD2Cl2, δ): 2.09 (s, 12H, C(O)CH3), 2.13 (s, 12H,
1
C(O)CH3), 3.11 (d, J HH ) 14.4 Hz, 4H, NCHN), 3.48 (s, 8H,
1
PCH2N), 3.69 (d, J HH ) 15.3 Hz, 4H, PCHNC(O)), 4.06 (d,
(12) (a) Grubbs, R. H.; Wang, C.; Friedrich, S.; Younkin, T. R.; Li,
R. T.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149.
(b) Grubbs, R. H.; Younkin, T. R.; Connor, E. F.; Henderson, J . I.;
Friedrich, S.; Bansleben, D. A. Science 2000, 287, 460.
(11) Siele, V. I. J . Heterocycl. Chem. 1977, 14, 337.

Water-Soluble Phosphine Derived from PTA
Organometallics, Vol. 23, No. 8, 2004 1749
1J HH ) 13.8 Hz, 4H, PCHNC(O)), 4.28 (d, 1J HH ) 15.0 Hz, 4H,
NCHN), 4.65 (d, 1J HH ) 14.1 Hz, 4H, PCHNC(O)), 4.99 (d, 1J HH
1
) 14.1 Hz, 4H, PCHNC(O)), 5.25 (d, J HH ) 15.0 Hz, 4H,
1
NCHN), 5.82 (d, J HH ) 14.4 Hz, 4H, NCHN). 13C NMR (75
MHz, CD2Cl2, δ): 21.5 (C(O)CH3), 22.2 (C(O)CH3), 46.4 (N-
C-N), 51.3 (N-C-N), 56.4 (P-C-N), 62.4 (P-C-NC(O)), 67.7
(P-C-NC(O)), 169.4 (C(O)), 169.8 (C(O)). 31P NMR (121 MHz,
CD2Cl2, δ): -28.3. IR (CH2Cl2): 1643 cm-1 (ν(CdO)). Anal.
Calcd for C36H64N12O8P4Ni: C, 44.34; H, 6.56; N, 17.24.
Found: C, 44.77; H, 6.57; N, 16.65.
P r ep a r a tion of P a lla d iu m Sa licyla ld im in a to DAP TA
Com p lex (4). To a 50 mL Schlenk flask containing (TMEDA)-
Pd(CH3)2 (150 mg, 0.594 mmol) in 10 mL of toluene at -30 °C
was introduced via cannula DAPTA (136 mg, 0.594 mmol) in
5 mL of methanol. To this mixture, the salicylaldimine (208
mg, 0.594 mmol) in 10 mL of toluene at -30 °C was slowly
cannulated into the flask, and the solution was stirred for 30
min. The temperature was raised to room temperature, and
the light red solution was further stirred overnight. Subse-
quently, the solvent was removed in vacuo until approximately
5 mL remained, and 20 mL of cold (-78 °C) pentane was
added, resulting in the formation of a yellow precipitate. The
solid was collected by cold cannula filtration and washed (3 ×
5 mL) with cold (-78 °C) pentane, affording 4 in 96.8% yield.
F igu r e 1. Molar water solubility of selected tertiary water-
soluble phosphines.
via a 100 µL syringe with stirring. In a typical experiment,
75 µL of water was needed to completely dissolve 100 mg of 1.
Solubility measurements were repeated several times to yield
an average value for the molar solubility of 1 in water of 7.4
M.
Resu lts a n d Discu ssion
3
1H NMR (300 MHz, C6D6, δ): -0.14 (d, J PH ) 3.60 Hz, 3H,
The synthesis of DAPTA and other PTA derivatives
was first reported by Siele in 1977.11 The ligand is easily
prepared by direct acylation of PTA in water with acetic
anhydride at 0 °C (eq 1).
3
3
Pd-CH3), 0.97 (dd, J HH ) 6.60 Hz, J HH ) 2.70 Hz, 6H, CH-
3
3
(CH3)2), 1.29 (dd, J HH ) 6.60 Hz, J HH ) 6.00 Hz, 6H, -C(O)-
3
CH3), 1.80 (d, J HH ) 6.60 Hz, 6H, CH(CH3)2), 2.97-3.02 (m,
3
1H, DAPTA), 3.24-3.34 (m, 5H, DAPTA), 3.51 (d, J HH
)
14.10, 1H, DAPTA), 3.62-3.67 (m, 1H, DAPTA), 4.21 (d, 3J HH
) 13.80 Hz, 1H, DAPTA), 4.23-4.51 (m, 1H, DAPTA), 6.75
(d, 3J HH ) 2.7 Hz, 1H, Ar), 7.11-7.15 (m, 2H, Ar), 7.48 (d, 3J HH
) 2.7 Hz, 1H, Ar), 7.55 (d, J PH ) 11.4 Hz, 1H, HCdN). 13C
4
2
NMR (75 MHz, C6H6, δ): -7.65 (d, J PC ) 12.2 Hz, Pd-CH3),
1
21.09, 22.78, 24.56, 28.23, 37.28 (d, J PC ) 22.05 Hz, P-C-
N), 41.97 (d, 1J PC ) 19.73 Hz, P-C-N), 47.13 (d, 1J PC ) 24.30
4
Surprisingly, the water solubility of DAPTA was
found to be approximately 7.4 M, making it one of the
most water-soluble phosphine ligands thus far re-
ported.1 A comparison of the water solubility of 1 to its
parent, PTA, and the sulfonated triphenylphosphine
derivatives (i.e., TPPMS and TPPTS)13 illustrates its
superior water solubility characteristic (Figure 1). Ad-
ditionally, the ligand readily dissolves in common
organic solvents such as methylene chloride, acetone,
and alcohols (e.g., methanol and ethanol), making it a
very versatile ligand that may be used in a variety of
solvents.
Hz, P-C-N), 61.50 (d, J PC ) 4.50 Hz, C(O)CH3), 66.61 (d,
4J PC ) 4.50 Hz, C(O)CH3), 116.63, 119.75, 123.60, 123.68,
125.53, 127.06, 128.40, 128.74, 129.17, 133.49, 134.44, 140.69
3
(d, J PC ) 9.15 Hz, CdN), 146.91, 168.46 (CdO), 169.23 (Cd
O). 31P NMR (121 MHz, C6D6, δ): -24.12. IR (CH2Cl2): ν(Cd
O) ) 1605 cm-1. Anal. Calcd for C29H39N4O3PCl2Pd: C, 49.79;
H, 5.57; N, 8.01. Found: C, 50.06; H, 5.61; N, 7.94.
P r ep a r a tion of M(CO)5(DAP TA) (M ) W (5), Cr (6))
Com p lexes. The replacement of a single CO molecule was
achieved by the photochemical reaction of M(CO)6 in THF.
After photolyzing W(CO)6 (0.200 g, 0.57 mmol) in 100 mL of
THF, this solution was cannulated over to a flask containing
1 (0.130 g, 0.57 mmol), in 10 mL of THF. The resulting solution
was stirred for 1 h followed by removal of the solvent in vacuo.
The solid was sublimed to remove any excess W(CO)6. The
synthesis of 6 was achieved in an analogous manner. Both
complexes are colorless and were cystallized and isolated by
the slow evaporation of THF from the corresponding solution,
resulting in good yields (>80%). Complexes 5 and 6 are
insoluble in water and nonpolar organic solvents (e.g., hexane,
pentane), but readily dissolve in polar media (e.g., chloroform,
THF).
The previously reported NMR data for 1 by Siele were
obtained on a 60 MHz instrument, and therefore, no
detailed splitting patterns or coupling constants were
provided. Here, we wish to point out some of these key
1
features by examining the H, 13C, and 31P spectra of
the phosphine. All of the 1H NMR resonances associated
with the methylene carbons exhibit phosphorus coupling
(xJ PH, x ) 2, 4) on the order of 13 Hz. The methyl
hydrogens on the acyl functionality (C(O)CH3) are
observed as a singlet at 1.96 ppm. In the 13C NMR
spectrum in CDCl3, the acyl carbons NC(O)CH3 are
displayed by a single resonance at 168.96 ppm, which
is contrary to what is expected for the anti conformation
(vide infra). On the other hand, both the 13C and 1H
NMR spectra of 1 indicate a mixture of conformers
present in aqueous solution. For example, the 13C NMR
resonances (NC(O)CH3) occur at 172.2 and 171.7 ppm,
Com p lex 5. 13C NMR (75 MHz, CD2Cl2, δ): 195.19 (t, dd,
1J WC ) 127.75 Hz, 2J PC ) 7.16 Hz, CO (trans)), 199.07 (d, 2J PC
) 21.19 Hz, CO (eq)). 31P NMR (121 MHz, CD2Cl2, δ): -47.7
(t, 1J WP ) 228.52 Hz). Anal. Calcd for C14H16N3O7PW: C, 30.40;
H, 2.92; N, 7.60. Found: C, 30.30; H, 2.94; N, 7.57. IR (CHCl3,
cm-1): 1650 (νCdO, DAPTA), 1944 (E), 2076 (A1).
Com p lex 6. 31P NMR (121 MHz, CD2Cl2, δ): -5.79. Anal.
Calcd for C14H16N3O7PCr: C, 39.92; H, 3.83; N, 9.97. Found:
C, 40.09; H, 3.85; N, 9.98. IR (CHCl3, cm-1): 1658 (νCdO
,
DAPTA), 1940 (E).
Wa ter Solu bility of 1. The extent of water solubility of 1
was assessed by placing a small, accurately weighed quantity
of the ligand in a vial followed by the slow addition of water
(13) (a) Kuntz, E. G. CHEMTECH 1987, 17, 570. (b) Kuntz, E. G.
French Patent 2314910, 20.06, 1975. (c) Kuntz, E. G. US Patent Re
31812, 29.05, 1982.

1750 Organometallics, Vol. 23, No. 8, 2004
Darensbourg et al.
Ta ble 1. Cr ysta llogr a p h ic Da ta for Com p lexes 1, 2,
4, 5, a n d 6
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d s 1, 2, 4, 5, a n d 6a
1
2
4
5
6
Compound 1
P(1)-C(1)
P(1)-C(2)
P(1)-C(3)
N(2)-C(6)
C(6)-O(1)
1.736(15)
1.707(14)
1.742(14)
1.373(18)
1.224(15)
C(6)-C(8)
N(3)-C(7)
C(7)-O(2)
C(7)-C(9)
1.524(19)
1.377(18)
1.258(14)
1.483(19)
cryst
syst
space
mono-
ortho-
triclinic
mono-
ortho-
clinic
rhombic
clinic
rhombic
P2(1)
Pbca
P1h
P2(1)/c
Pbca
group
V, Å3
Z
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
T, K
535.3(11) 2224(4)
2
6.191(7)
10.431(12) 11.121(13) 15.620(4) 12.922(3) 13.693(14)
8.407(10) 23.51(3)
3350.3(16) 1843.8(7) 3633(7)
4
8
4
8
P(1)-C(1)-N(2)
P(1)-C(2)-N(3)
P(1)-C(3)-N(1)
118.5(9)
119.9(10)
115.0(10)
C(1)-N(2)-C(6)
C(2)-N(3)-C(7)
116.0(10)
124.7(11)
8.506(10) 12.530(4) 12.000(2) 11.836(13)
17.576(5) 13.238(3) 22.41(2)
77.533(5)
85.937(5) 116.076(4)
88.832(5)
110
1.570
99.59(2)
Compound 2
P(1)-C(1)
P(1)-C(2)
P(1)-C(3)
P(1)-O(3)
N(2)-C(6)
1.816(3)
1.827(3)
1.797(3)
1.492(3)
1.365(4)
C(6)-O(1)
C(6)-C(8)
N(3)-C(7)
C(7)-O(2)
C(7)-C(9)
1.227(4)
1.500(5)
1.360(4)
1.236(4)
1.499(4)
110
1.422
110
1.465
110
1.993
110
1.541
d(calc),
g/cm3
abs coeff, 0.242
mm-1
0.245
6.17
0.960
7.93
6.393
5.26
0.759
3.09
R,a %
[I >
10.59
P(1)-C(1)-N(2)
P(1)-C(2)-N(3)
P(1)-C(3)-N(1)
111.80(18)
114.57(19)
106.19(18)
C(1)-N(2)-C(6)
C(2)-N(3)-C(7)
118.5(2)
123.3(2)
2σ(I)]
Rw,a %
19.23
6.86
10.24
6.49
4.66
a
2 1/2
R ) ∑||Fo| - |Fc||/∑Fo and RwF ) {[∑w(Fo - Fc)2]/∑wFo
}
.
Complex 4
Pd(1)-C(1)
Pd(1)-N(1)
2.029(8)
2.080(6)
Pd(1)-P(1)
Pd(1)-O(1)
2.209(2)
2.077(5)
Sch em e 1
C(1)-Pd(1)-O(1)
P(1)-Pd(1)-C(1)
O(1)-Pd(1)-N(1)
175.4(3)
88.5(3)
90.9(2)
P(1)-Pd(1)-O(1)
P(1)-Pd(1)-N(1)
86.91(16)
177.82(17)
Compound 5
P(1)-C(1)
P(1)-C(2)
P(1)-C(3)
W(1)-P(1)
W(1)-C(10)
N(2)-C(6)
C(6)-O(1)
C(6)-C(8)
1.840(11) W(1)-C(11)
1.849(10) W(1)-C(12)
1.845(11) N(3)-C(7)
2.053(13)
1.999(13)
1.348(13)
1.230(12)
1.519(15)
2.032(13)
2.040(13)
2.492(3)
C(7)-O(2)
with the latter being about one-fourth the intensity of
the former. The two acyl groups adopt an anti confor-
mation in the solid state (vide infra), with the barrier
to rotation of the N-C(O) bond generally ascribed to
the π electronic resonance model of an amide (A and B
in Scheme 1).14a This experimental rotational barrier
is expected to be about 18-19 kcal/mol.14b-d More recent
ab initio computations assign a large part of the
rotational stability of the N-C bond to a Coulombic
interaction via the σ system between the N and carbonyl
C atoms (C in Scheme 1).14e Further upfield are the
resonances pertaining to the P-C-N carbons, which fall
at 67.0 and 70.1 ppm, respectively. Those associated
with the N-C-N carbons are found at 62.0 ppm.
Dissolving 1 in CH2Cl2 and allowing the slow diffusion
of pentane into the solution over several days at -20
°C resulted in quality crystals for X-ray diffraction. The
crystallographic data and selected bond distances and
angles are presented in Table 1 and Table 2, respec-
tively. A thermal ellipsoid representation of 1 is shown
in Figure 2. In the solid state, the C(O)CH3 groups are
anti with respect to each other. The N(2)-C(6) and
N(3)-C(7) bond distances were found to be short when
compared to other N-C bond distances, with values of
1.373(18) and 1.377(18) Å, respectively, and resemble
a Schiff base (NdC) double bond (Scheme 1). The P(1)-
C(1) bond distance was found to be approximately 0.03
Å longer than the P(1)-C(2) counterpart, but is never-
theless significantly shorter than that found in the P-C
bond lengths of PTA (i.e., 1.857(3) Å).15
2.049(14) C(7)-C(9)
1.344(13) W(1)-C(13)
1.224(13) W(1)-C(14)
1.535(15)
P(1)-C(1)-N(2)
P(1)-C(2)-N(3)
P(1)-C(3)-N(1)
C(11)-W(1)-P(1) 90.0(3)
C(12)-W(1)-P(1) 92.7(4)
117.6(7)
112.4(7)
109.8(7)
C(1)-N(2)-C(6)
C(2)-N(3)-C(7)
C(10)-W(1)-P(1)
119.1(9)
124.5(9)
176.1(3)
C(10)-W(1)-C(11) 88.3(4)
C(10)-W(1)-C(12) 90.8(5)
Compound 6
P(1)-C(1)
P(1)-C(2)
P(1)-C(3)
Cr(1)-P(1)
Cr(1)-C(10)
N(2)-C(6)
C(6)-O(1)
C(6)-C(8)
1.853(3)
1.839(3)
1.836(3)
Cr(1)-C(11)
Cr(1)-C(12)
N(3)-C(7)
1.910(4)
1.902(4)
1.359(4)
1.227(4)
1.512(5)
1.902(4)
1.903(4)
2.3562(19) C(7)-O(2)
1.863(4)
1.359(4)
1.233(4)
1.504(5)
C(7)-C(9)
Cr(1)-C(13)
Cr(1)-C(14)
P(1)-C(1)-N(2)
P(1)-C(2)-N(3)
P(1)-C(3)-N(1)
C(11)-Cr(1)-P(1) 89.31(12)
C(12)-Cr(1)-P(1) 94.56(11)
113.8(2)
114.93(19) C(2)-N(3)-C(7)
109.9(2)
C(1)-N(2)-C(6)
124.7(3)
118.2(2)
173.55(10)
C(10)-Cr(1)-P(1)
C(10)-Cr(1)-C(11) 87.37(15)
C(10)-Cr(1)-C(12) 91.00(14)
a
Estimated standard deviations are given in parentheses.
As evident from the space-filling model, the rigid
nature of the ligand creates a cavity within the cage
structure (Figure 3). The phosphorus atom is clearly
exposed, allowing for easy binding to a metal center.
Additionally, the acyl-free nitrogen and oxygen atoms
are also exposed, which facilitates hydrogen bonding to
the surrounding aqueous environment. The calculated
cone angle was found to be similar to that reported for
PTA, having a value of about 102°.16
(14) (a) Yamada, S. J . Org. Chem. 1996, 61, 941. (b) Sunner, B.;
Piette, L. H.; Schneider, W. G. Can. J . Chem. 1960, 38, 681. (c) Kamei,
H. Bull. Chem. Soc. J pn. 1968, 41, 2269. (d) Drakenberg, T.; Forsen,
S. J . Phys Chem. 1970, 74, 1. (e) Wiberg, K. B.; Breneman, C. M. J .
Am. Chem. Soc. 1992, 114, 831.
The phosphine oxide species 2 was also fully charac-
terized in solution and in the solid state. This derivative
(15) Fluck, E.; Fo¨rster, J .; Weidlein, J .; Hidiche, E. Z. Naturforsh.
1977, 32b, 409.
(16) Delerno, J . R.; Trefonas, L. M.; Darensbourg, M. Y.; Majeste,
R. J . Inorg. Chem. 1976, 15, 816.

Water-Soluble Phosphine Derived from PTA
Organometallics, Vol. 23, No. 8, 2004 1751
F igu r e 4. Shielding effects on geminal protons by acyl
group in DAPTA oxide (2).
F igu r e 2. Thermal ellipsoid representation of DAPTA (1)
showing 50% probability ellipsoids.
F igu r e 5. Thermal ellipsoid representation of DAPTA
oxide (2) showing 50% probability ellipsoids.
F igu r e 3. Space-filling model of DAPTA (1) showing (a)
front and (b) side view.
gen. The two CdO signals reside at 169.45 and 170.09
ppm with an absence of 31P coupling.
is easily prepared from PTA oxide employing the same
synthetic strategy used in the synthesis of 1 (eq 2).
Allowing a concentrated CH2Cl2 solution of 2 to stand
at -20° C over a period of two weeks resulted in the
formation of large, colorless, single crystals. Using these
crystals for X-ray analysis, a solid state structure of 2
was obtained. Crystallographic data and selected bond
distances and angles are provided in Tables 1 and 2,
respectively. A thermal ellipsoid representation of 2 is
shown in Figure 5. A key feature in the solid state, as
was also observed in complexes 5 and 6, is the P(1)-
C(Y) (Y ) 1-3) bond distances. Upon coordination of
the ligand to a metal or in its oxidized form, these bond
lengths are approximately 0.09 Å longer than those
observed in 1. However, the N(2)-C(6) and N(3)-C(7)
are nearly identical when compared to its parent, as is
the case for many of the other bond distances. The P(1)-
O(3) bond distance is found to have a value of 1.492(3)
Å. In the space-filling model, the ligand also possesses
the cavity observed in 1 with the oxygen atom coordi-
nated to phosphorus fully exposed for binding (Figure
6). The other oxygen atoms as well as the acyl-free
nitrogen is also exposed, similar to 1.
Spectroscopically, 2 is similar to its parent. Although
difficult to interpret, the 1H NMR spectrum displays
coupling between geminal hydrogens. For example, the
proton (HA) associated with the N-CH-N framework
and in the axial position is shielded more by the syn
CdO group residing on the adjacent nitrogen and
therefore is located further downfield at 5.71 ppm.
Meanwhile, its geminal hydrogen, residing in the equa-
torial position, is less shielded and appears further
2
upfield with a common J HH coupling constant (i.e., 14.4
Hz) (Figure 4). 31P coupling is observed for the P-CH2-N
protons, located at 3.27 ppm, and is on the order of 6.60
Hz. Similar to 1, the 13C NMR spectrum is also easy to
interpret and displays several signals with 31P coupling.
For example, the P-C-N carbons are located at 41.99,
Several complexes incorporating 1 were synthesized
to illustrate the binding mode and strength of this
phosphine. PTA complexes of group 10 metals have been
previously reported and were found to be readily soluble
in water. Of main interest is the nickel(0) PTA complex,
Ni(PTA)4, which can be synthesized from Ni(COD)2 and
4 equiv of PTA in a toluene/methanol solution. Using
1
46.72, and 53.40 ppm with J PC constants of 62-67 Hz.
The coupling between these hydrogens and phosphorus
illustrates the pronounced electronic effect of oxy-

1752 Organometallics, Vol. 23, No. 8, 2004
Darensbourg et al.
F igu r e 6. Space-filling model of DAPTA oxide (2) showing
(a) front and (b) side view.
F igu r e 7. Thermal ellipsoid representation of 4 showing
50% probability ellipsoids.
Sch em e 2
CH(CH3)2 hydrogens. The ν(CdO) stretch was found to
be located at 1605 cm-1, which is approximately a 50
cm-1 shift to lower frequency from that of the free
ligand. Additionally, a rotation barrier exists about the
N-C(O)CH3 bonds, as two sets of signals are observed
in the 13C NMR spectrum for the C(O)CH3 groups.
Allowing the slow diffusion of pentane into a toluene
solution of 4 at -20 °C resulted in X-ray quality crystals.
Crystallographic data and selected bond distances and
angles are shown in Tables 1 and 2, respectively. A
thermal ellipsoid representation of 4 is presented in
Figure 7. The solid state structure of the complex is
nearly identical to its PTA analogue, with the Pd(1)-
P(1) bond distances being the same in both complexes
(i.e., 2.209(2) and 2.211(3) Å for 4 and the PTA analogue,
respectively).18 The palladium metal center adopts the
standard square-planar geometry, as the C(1)-Pd(1)-
O(1) and P(1)-Pd(1)-N(1) bond angles are found to
have values of 175.4(3)° and 177.82(17)°, respectively.
Group 6 pentacarbonyl complexes of DAPTA were also
prepared by the typical reaction protocol of photolyzing
a THF solution of M(CO)6 (M ) W, Cr) to produce the
M(CO)5(THF) intermediate. Following the in situ for-
mation of M(CO)5(THF), a THF solution of 1 was added,
yielding the M(CO)5(DAPTA) (M ) W (5), Cr (6))
complexes in good yields (eq 4). For the tungsten
this methodology, the Ni(DAPTA)4 (3) derivative was
prepared (eq 3).
toluene/methanol
Ni(DAPTA)
Ni(COD)2 + 4 DAPTA
8
+
4
2 h, rt
3
2 COD (3)
The product was characterized by 1H, 13C, and 31P NMR
as well as elemental analysis. Unfortunately, 3 is not
soluble in water or alcoholic solvents such as methanol
or ethanol, but is readily soluble in chlorinated organic
solvents such as methylene chloride. The insoluble
nature of the complex in water is surprising due to the
high water solubility of 1 and Ni(PTA)4 (0.291 M).17 The
IR spectrum displays the ν(CdO) stretch at 1643 cm-1
,
which is nearly identical to the ν(CdO) stretch of the
free ligand in CH2Cl2. The 13C NMR spectrum displays
the two signals due to the acyl carbons at 169.8 and
169.4 ppm, respectively, while the 1H NMR contains
many signals that are split by phosphorus and geminal
coupling. Attempts to grow suitable crystals in CH2Cl2
have failed due to the formation of spherical crystals,
all of which did not diffract upon exposure to X-ray
radiation.
Another group 10 metal complex bearing 1 is the
salicylaldiminato palladium complex 4. This derivative
was prepared using the synthetic methodology employed
for the synthesis of palladium salicylaldiminato PTA
complexes (Scheme 2).18 In solution, the complex is very
similar to its PTA analogue. For example, the ketimine
derivative, 5, the ν(CdO) stretch associated with bound
1 was found to be located at 1663 cm-1 in THF, a 10
cm-1 shift to higher energy when compared to the free
ligand. In the 195-200 ppm region of the 13C NMR, the
two signals pertaining to the M-CO carbons are ob-
served with pronounced 31P and 183W coupling. The
signal at 195.2 ppm, due to the equatorial carbonyls,
has a J WC and J PC coupling of 127.8 and 7.3 Hz,
respectively. The resonance at 199.1 ppm, derived from
the axial carbonyl, exhibits a 31P coupling of 21.2 Hz
with no visible 183W coupling due to the lower signal
4
hydrogen, HCdN, exhibits J PH coupling on the order
of 11.4 Hz, which is slightly larger than that reported
for the PTA analogue (i.e., 10.5 Hz). The isopropyl
groups on the aniline moiety are perpendicular to the
plane and exhibit a rotation barrier, as two sets of
1
signals are observed in the H NMR spectrum for the
1
2
(17) Darensbourg, D. J .; Decuir, T. J .; Stafford, N. W.; Robertson,
J . B.; Draper, J . D.; Reibenspies, J . H.; Katho´, A.; J oo´, F. Inorg. Chem.
1997, 36, 4218.
(18) Darensbourg, D. J .; Ortiz, C. G.; Yarbrough, J . C. Inorg. Chem.
2003, 42, 6915.

Water-Soluble Phosphine Derived from PTA
Organometallics, Vol. 23, No. 8, 2004 1753
F igu r e 8. Thermal ellipsoid representation of W(CO)5-
(DAPTA) (5) showing 50% probability ellipsoids.
F igu r e 9. Thermal ellipsoid representation of Cr(CO)5-
(DAPTA) (6) showing 50% probability ellipsoids.
intensity. The 31P resonance is located at -47.7 ppm,
to the equatorial carbonyls. The Cr(1)-P(1) bond dis-
tance was found to be 2.3562(19) Å, which is ap-
proximately 0.01 Å shorter than that found in the
Cr(CO)5PMe3 analogue.19b,c Furthermore, the pro-
nounced tilt associated with the phosphine ligand and
the equatorial carbonyl plane observed for the PTA and
PASO2 tungsten pentacarbonyl derivatives is not present
in complexes 5 and 6.7
an approximate 25 ppm upfield shift from the free
1
ligand, with J WP coupling of 228.5 Hz, which is similar
to that observed for the W(CO)5(PTA) (1J WP ) 218.2 Hz)
and W(CO)5(PASO2) (1J WP ) 228.9 Hz) complexes.7
Colorless crystals suitable for X-ray diffraction were
isolated by the slow evaporation of THF from a corre-
sponding solution of the complex at room temperature.
Crystallographic data and selected bond distances and
angles for the complex are presented in Tables 1 and 2,
respectively. A thermal ellipsoid representation of the
complex showing 50% probability is shown in Figure 8.
The tungsten metal center exhibits a slightly distorted
octahedral coordination, with the C(12)-W(1)-C(13),
C(10)-W(1)-P(1), and C(11)-W(1)-C(14) bond angles
having values of 179.7(5)°, 176.1(3)°, and 177.3(5)°,
respectively. The pronounced shorter W-Cax bond dis-
tance observed for the axial carbonyl in the W(CO)5-
(PTA) and W(CO)5(PASO2) complexes is not observed
in 5.7 All W-C bond distances have an average value
of 2.044 Å. The W(1)-P(1) bond distance is very similar
to the PTA analogue, with a value of 2.492(3) Å, and is
shorter than the W-P distance of 2.516 Å of the
trimethylphosphine analogue, W(CO)5(PMe3).19a
Con clu d in g Rem a r k s
The cage-opening reaction of PTA and its oxide with
acetic anhydride to provide the corresponding acylated
products 1 and 2, respectively, has been revisited. In
this report we have fully characterized these derivatives
in solution by 1H/13C/31P NMR and infrared spec-
troscopies, as well as in the solid state by X-ray
crystallography. As anticipated, restricted rotation about
the amide nitrogen-carbonyl carbon bond is observed,
which is consistent with the short N-C(O) bond dis-
tances determined in these derivatives. Phosphine 1 was
shown to possess excellent solubility in water (7.4 M),
much greater than that of its PTA analogue. In ac-
cordance with the water solubility of 1, its νCdO vibration
in water occurs at 1608 cm-1, some 34 cm-1 to lower
energy than that observed in weakly interacting organic
solvents. This is indicative of a strong interaction of the
amide nitrogen-CO bond dipole with water.
The binding ability of DAPTA (1) toward a variety of
metal centers was shown to be very much comparable
to that of the parent PTA ligand, which in turn
compares favorably with the air-sensitive PMe3 ligand.
This is evident in the M-P bond distances observed in
corresponding metal complexes of 1 and PTA. For
example, the W-P bond distances in (CO)5W(PTA),
(CO)5W(DAPTA), and (CO)5WPMe3 are 2.4976(15), 2.492-
(3), and 2.516(3) Å, respectively. Further evidence for
the relative binding abilities of 1 and PTA was provided
by the similarities in the ν(CO) vibrational modes in
M(CO)5L derivatives, where M ) Cr or W and L ) 1 or
Using the same crystal growth technique, crystals of
6 suitable for X-ray analysis were obtained. Crystal-
lographic data and selected bond distances and angles
are presented in Tables 1 and 2, respectively. A thermal
ellipsoid representation showing 50% probability of the
complex is provided in Figure 9. The chromium metal
center exhibits a slightly distorted octahedral geometry,
with the C(12)-Cr(1)-C(13), C(10)-Cr(1)-P(1), and
C(11)-Cr(1)-C(14) bond angles having values of 175.55-
(14)°, 173.55(10)°, and 177.30(14)°, respectively. Al-
though not observed in 5, the axial Cr(1)-C(10) distance
is appreciably shorter than the equatorial Cr-CO, with
a value of 1.863(4) Å. This is approximately 0.04 Å
shorter than the average Cr-C bond distance pertaining
(19) (a) Cotton, F. A.; Darensbourg, D. J .; Kolthammer, B. W. S.
Inorg Chem. 1981, 20, 4440. (b) Davies, M. S.; Pierens, R. K.; Aroney,
M. J . J . Organomet. Chem. 1993, 458, 141. (c) Lee, K. J .; Brown, T. L.
Inorg. Chem. 1992, 31, 289.

1754 Organometallics, Vol. 23, No. 8, 2004
Darensbourg et al.
PTA.20 Unexpectedly, the Ni(DAPTA)4 (3) derivative,
which is highly soluble in organic solvents, exhibits no
solubility in water, whereas its Ni(PTA)4 analogue is
very water soluble. We will continue our efforts to obtain
X-ray quality crystals of this derivative in hopes that
its solid state structure will shed some light on this
puzzling issue. Finally, it should be possible to synthe-
size other phosphine ligands via this cage-opening
reaction, which possess a wide range of solubility and
metal-binding properties.21,22
Ack n ow led gm en t. Financial support from the Na-
tional Science Foundation (CHE 02-34860 and CHE 98-
07975 for purchase of X-ray equipment) and the Robert
A. Welch Foundation is greatly appreciated.
Note Ad d ed a fter ASAP . In the version of the paper
originally posted on the web on March 9, 2004, Figures
5 and 6 were incorrectly repeated as Figures 2 and 3.
The version that now appears is correct.
Su p p or tin g In for m a tion Ava ila ble: Complete details of
the X-ray diffraction studies on compounds 1, 2, and 4-6. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(20) Darensbourg, M. Y.; Daigle, D. J . Inorg. Chem. 1975, 14, 1217.
(21) An alternative cage-opened PTA derivative which serves as a
chelating ligand has been reported by Schmidbaur and co-workers.22
(22) Assmann, B.; Angermaier, K.; Paul, M.; Riede, J .; Schmidbaur,
H. Chem. Ber. 1995, 128, 891.
OM0343059