Water-soluble organometallic compounds. 7.1 further studies of 1,3,5-triaza-7-phosphaadamantane derivatives of group 10 metals, including metal carbonyls and hydrides

Article abstract of DOI:10.1021/ic981243j

The syntheses of Ni(PTA)₄ (5), Pd(PTA)₄ (6), and Pt(PTA)₄ (8) are accomplished through the reduction of the M^IICl₂ salts in water with excess 1,3,5-triaza-7-phosphaadamantane (FTA). The products are obtained as partially protonated derivatives with protonation occurring at the nitrogen atoms of the bound PTA ligands. Crystal structures illustrating the monoprotonated and bis-protonated derivatives of 8, [Pt(PTA)₃(PTAH)][Cl] (1S) and [Pt(PTA)₂-(PTAH)₂][BF₄]₂ (2S), are reported. The crystal structure of an intermediate along the reduction pathway, [PdCl-(PTA)₃][Cl] (7), is also presented, showing a trans influence whereby the Pd-P bond length trans to the Cl^- ligand is shorter, 2.238(3) ?, than the average Pd-P bond length cis to the Cl^- ligand, 2.334(2) A. Complex 8 is also protonated at the metal center to form [(H)Pt(PTA)₄][X], where X = Cl^-, BF₄^-, HCO₃^-, and C₃H₅CO₂^-, through the addition of weak acids such as CO₂/H₂O, NH₄Cl, PTAH⁺Cl^-, HPy⁺BF₄^-, and crotonic acid. Addition of strong acids such as HCl or HBF₄ results in protonation at the PTA ligands. Thereby, the Pt metal center is shown to have a pK_a between 7.44 and 9.25. The bound PTA ligands on complex 8 have a pK_a below 4.69 but above 2.12. Ni(CO)_4-n(PTA)_n derivatives are also reported for n = 3 (9), 2 (10), and 1 (11). Using IR data of 11, PTA is determined to have an electronic parameter (χ) as defined by Tolman to be 15.3 cm^-1, indicating PTA to be slightly less donating than PPh₃, where χ = 12.8 cm^-1. Complex 10 is crystallized out of a MeOH/ether solution maintained at -15 °C and characterized by X-ray crystallography. It is a distorted tetrahedron and has a crystallographically determined Tolman cone angle of PTA of 103°. Monitored reactions of Ni(PTA)₄ with CO in water via in situ IR techniques show that the rate observed for the dissociation of PTA to provide Ni(CO)-(PTA)₃ is 7.92 × 10^-4 s^-1 at 20 °C. This rate, along with ³¹P NMR results, indicates that the M (PTA)₄ complexes exhibit little dissociation and slow exchange of the bound PTA ligands.

Full text of DOI:10.1021/ic981243j

Inorg. Chem. 1999, 38, 2473-2481
2473
Water-Soluble Organometallic Compounds. 7.1 Further Studies of
1,3,5-Triaza-7-Phosphaadamantane Derivatives of Group 10 Metals, Including Metal
Carbonyls and Hydrides
Donald J. Darensbourg,* Jeffrey B. Robertson, David L. Larkins, and Joseph H. Reibenspies
Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012
ReceiVed October 23, 1998
The syntheses of Ni(PTA)4 (5), Pd(PTA)4 (6), and Pt(PTA)4 (8) are accomplished through the reduction of the
MIICl2 salts in water with excess 1,3,5-triaza-7-phosphaadamantane (PTA). The products are obtained as partially
protonated derivatives with protonation occurring at the nitrogen atoms of the bound PTA ligands. Crystal structures
illustrating the monoprotonated and bis-protonated derivatives of 8, [Pt(PTA)3(PTAH)][Cl] (1S) and [Pt(PTA)2-
(PTAH)2][BF4]2 (2S), are reported. The crystal structure of an intermediate along the reduction pathway, [PdCl-
(PTA)3][Cl] (7), is also presented, showing a trans influence whereby the Pd-P bond length trans to the Cl-
ligand is shorter, 2.238(3) Å, than the average Pd-P bond length cis to the Cl- ligand, 2.334(2) Å. Complex 8
-
is also protonated at the metal center to form [(H)Pt(PTA)4][X], where X ) Cl-, BF4-, HCO3-, and C3H5CO2
,
through the addition of weak acids such as CO2/H2O, NH4Cl, PTAH+Cl-, HPy+BF4-, and crotonic acid. Addition
of strong acids such as HCl or HBF4 results in protonation at the PTA ligands. Thereby, the Pt metal center is
shown to have a pKa between 7.44 and 9.25. The bound PTA ligands on complex 8 have a pKa below 4.69 but
above 2.12. Ni(CO)4-n(PTA)n derivatives are also reported for n ) 3 (9), 2 (10), and 1 (11). Using IR data of 11,
PTA is determined to have an electronic parameter (ø) as defined by Tolman to be 15.3 cm-1, indicating PTA to
be slightly less donating than PPh3, where ø ) 12.8 cm-1. Complex 10 is crystallized out of a MeOH/ether
solution maintained at -15 °C and characterized by X-ray crystallography. It is a distorted tetrahedron and has
a crystallographically determined Tolman cone angle of PTA of 103°. Monitored reactions of Ni(PTA)4 with CO
in water via in situ IR techniques show that the rate observed for the dissociation of PTA to provide Ni(CO)-
(PTA)3 is 7.92 × 10-4 s-1 at 20 °C. This rate, along with 31P NMR results, indicates that the M0(PTA)4 complexes
exhibit little dissociation and slow exchange of the bound PTA ligands.
Introduction
bases in the latter ligand to afford the ionic ligands PTAMe+
and PTAH+, respectively, thus providing additional solubility
properties in water.
Although phosphine ligands containing sulfonated aryl groups
(e.g., TPPTS, 1) have dominated the ligands utilized in water-
solubilizing organometallic derivatives, there is an increase in
the number of investigations involving other types of substituents
on phosphines which impart water solubility. For example, these
+
include cationic ammonium groups (Ph2PCH2CH2NMe3 and
+ 2-5
Cy2PCH2CH2NMe3
)
and carboxylated aromatic groups
(2).6 Among the nonionic aliphatic phosphine ligands which
offer greater basicities are tris(hydroxymethylphosphine), P-
(CH2OH)3,7,8 (HOCH2)2PC6H4P(CH2OH)2,9 and PTA (3).10-12
It is also possible to alkylate or protonate one of the nitrogen
* Corresponding author. E-mail: djdarens@mail.chem.tamu.edu.
(1) Part 6: Darensbourg, D. J.; Decuir, T. J.; Stafford, N. W.; Robertson,
J. B.; Draper, J. D.; Reibenspies, J. H.; Katho´, A.; Joo´, F. Inorg. Chem.
1997, 36, 4218.
(2) Smith, R. T.; Ungar, R. K.; Baird, M. C. Transition Met. Chem. 1982,
7, 288.
(3) Smith, R. T.; Baird, M. C. Inorg. Chim. Acta 1982, 62, 135.
(4) Smith, R. T.; Ungar, R. K.; Sanderson, L. J.; Baird, M. C. Organo-
metallics 1983, 2, 1138.
(5) Mohr, B.; Lynn, D. M.; Grubbs, R. H. Organometallics 1996, 15,
4317.
We have been extensively associated with the development
of the PTA ligand in aqueous organometallic chemistry and
catalysis.13-16 Pertinent to these efforts it is of importance to
(10) PTA (1,3,5-triaza-7-phosphatricyclo [3.3.1.13, 7] decane) is commonly
referred to as 1,3,5-triaza-7-phosphaadamantane. Some authors prefer
to condense this ligand’s name to TPA.
(6) Hoots, J. E.; Rauchfuss, T. B.; Wrobleski, D. A. Inorg. Synth. 1982,
21, 175.
(7) Ellis, J. W.; Harrison, K. N.; Hoye, P. A. T.; Orpen, A. G.; Pringle,
P. G.; Smith, M. B. Inorg. Chem. 1992, 31, 3026.
(8) Hoye, P. A. T.; Pringle, P. G.; Smith, M. B.; Worboys, K. J. Chem.
Soc., Dalton Trans. 1993, 269.
(11) Daigle, D. J. Inorg. Synth. 1998, 32, 40.
(12) Darensbourg, D. J.; Decuir, T. J.; Reibenspies, J. H. In Aqueous
Organometallic Chemistry and Catalysis; Horva´th, I. T., Joo´, F., Eds.;
NATO ASI Series 3, High Technology; Kluwer: Dordrecht, The
Netherlands, 1995; pp 61-77.
(13) Darensbourg, D. J.; Joo´, F.; Kannisto, M.; Katho´, A.; Reibenspies, J.
H. Organometallics 1992, 11, 1990.
(9) Katti, K. V. Current Sci. 1996, 70, 219.
10.1021/ic981243j CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/21/1999

2474 Inorganic Chemistry, Vol. 38, No. 10, 1999
Darensbourg et al.
note that the 1,3,5-triaza-7-phosphaadamatane ligand was orig-
inally synthesized by Daigle et al. and was given the abbrevia-
tion PAA.17 During the same time period Darensbourg and
Daigle described in a report the synthesis and characterization
of a variety of metal carbonyl derivatives of this ligand, where
it was given the abridged designation PTA.18 In addition, the
X-ray structure of one of these derivatives, Mo(CO)5PTA, was
subsequently reported,19 followed by the X-ray structure of the
free ligand, PTA.20
Recent efforts from our laboratories have focused on the
group 10 metal derivatives of PTA.1 In part the impetus for
these investigations stems from the widespread use of related
metal derivatives as catalysts or catalyst precursors in a variety
of chemical transformations, many of which may be carried out
in an aqueous medium. For example, carbon-carbon coupling
reactions have been successfully performed in aqueous solution
or aqueous-organic biphasic systems. In addition to the Heck
reaction (eq 1),21 several other cross-coupling reactions have
We have previously reported the synthesis of M(PTA)4 (M
) Ni, Pd, Pt) derivatives by several well-known procedures,
i.e., Ni(cod)2 plus PTA, reduction of PdCl2 or PtCl2 with
hydrazine in the presence of PTA, and Pt(PPh3)4/PTA ligand
exchange.1 Herein, we wish to communicate a facile synthetic
method for these metal derivatives from their respective halide
salts in water using excess phosphine as reductant. In addition,
the preparation of a series of Ni(CO)4-n(PTA)n (n ) 1-3)
complexes derived from the ligand substitution reactions of
Ni(PTA)4 and CO is described, along with the X-ray structure
of one of these, Ni(CO)2(PTA)2. Finally, a water-soluble plati-
num hydride species originating from the reaction of Pt(PTA)4
and weak acids (e.g., carbonic acid) has been synthesized and
1
characterized by H, 31P, and 195Pt NMR spectroscopies.
Experimental Section
Methods and Materials. All reactions were performed under an
inert atmosphere unless otherwise stated. NiCl2 and PdCl2 were
purchased from Aldrich Chemicals and Johnson-Matthey Chemicals,
respectively, and used without further purification. PtCl2 was purchased
from Strem Chemicals and Pressure Chemical and used without further
purification. 1,3,5-triaza-7-phosphaadamantane (PTA) was synthesized
according to the procedure developed by Daigle and co-workers.11 CO
was purchased from Matheson and Liquid Carbonic Specialty Gases.
Crotonic acid and tetrafluoroboric acid were purchased from Aldrich.
Ammonium chloride was purchased from J. T. Baker. CO2 was
purchased from Praxair. Hydrochloric acid and phosphoric acid were
purchase from EM. All were used without further purification.
PTAH+Cl- was prepared by treating PTA with an equimolar amount
of 0.1 M HCl. The solvent was removed in vacuo to yield a white
powder (31P NMR (D2O): δ ) -91 ppm). Pyridinium tetrafluoroborate
was prepared by treating pyridine with tetrafluoroboric acid in ether,
followed by isolation of the precipitate. Water was degassed through
a nitrogen purge for at least 45 min prior to use. Methanol was
purchased from Fischer Scientific and stored over and distilled from
Mg/I2 prior to use. Ether was purchased from Fisher Scientific, stored
over Na/benzophenone, and distilled before use. D2O, MeOH-d4, and
THF-d8 were purchased from Cambridge Isotopes Laboratories. D2O
was stored in an airtight flask under N2 at all times. MeOH-d4 and
THF-d8 were stored in a drybox. 31P NMR spectra were recorded on a
Varian Unity 300 spectrometer, and 85% H3PO4 (δ ) 0.0 ppm) was
used as an external reference. 195Pt NMR spectra were recorded on a
Varian XL200 broadband spectrometer employing aqueous K2PtCl4 (δ
) -1630 ppm) as an external reference. Infrared samples were recorded
on a Mattson 6021 Galaxy Series FT-IR in a 0.01 mm CaF2 cell for
water samples and a 0.1 mm CaF2 cell for MeOH samples. Monitored
kinetic reactions were done using an ASi Applied Systems ReactIR
1000 Electronics Module. The p[H] measurements involving PTA were
carried out at 25.0 ( 0.1 °C at a constant ionic strength (µ ) 0.100 M)
adjusted with KCl in doubly distilled, deionized water, with careful
exclusion of oxygen and carbon dioxide. These experiments were
performed by Dr. Tara Decuir in the laboratories of Professor A.
Martell, employing the experimental setup and procedure previously
described in detail.30 Elemental analysis were carried out by Canadian
Microanalytical Service, Ltd.
been carried out under these conditions, including Suzuki22 and
Stille23 coupling processes. Carbonylation of benzyl chloride
has also been shown to be catalyzed by water-soluble phosphine
complexes of palladium in a biphasic system.24 In all of these
processes a zerovalent metal complex is the catalytically active
species, which is often produced in situ from the corresponding
MIIX2L2 derivative.
Herrmann and co-workers have prepared the homoleptic
TPPTS complexes of the zerovalent group 10 metals where the
coordination number of the metal was found to increase with
increasing metal size, i.e., Ni(TPPTS)3, Pd(TPPTS)3, and Pt-
(TPPTS)4.25 This trend is consistent with the greater steric
requirements of the TPPTS ligand26 as compared to PPh3,27
where the analogous group 10 metal complexes exhibit four-
coordination. More recently, Pringle and co-workers have syn-
thesized and fully characterized the zerovalent group 10 metal
derivatives M[P(CH2OH)3]4.7 In addition there are several re-
ports of water-soluble phosphine complexes of group 10 metals
in the +2 oxidation state, including cis- and trans-PtCl2-
(TPPTS)2,25 MCl2[P(CH2OH)3]2 (M ) Ni, Pd, Pt),7,28 and
hydroxy metal bis(phosphine) complexes of Pd and Pt.29
(14) Darensbourg, D. J.; Joo´, F.; Kannisto, M.; Katho´, A.; Reibenspies, J.
H.; Daigle, D. J. Inorg. Chem. 1994, 33, 200.
(15) Darensbourg, D. J.; Stafford, N. W.; Joo´, F.; Reibenspies, J. H. J.
Organomet. Chem 1995, 488, 99.
(16) Joo´ F.; Na´dasdi, L.; Be´nyei, A. C.; Darensbourg, D. J. J. Organomet.
Chem. 1996, 512, 45.
(17) Daigle, D. J.; Pepperman, A. B., Jr.; Vail S. L. Heterocycl. Chem.
1974, 11, 407.
(18) Darensbourg, M. Y.; Daigle, D. J. Inorg. Chem. 1975, 14, 1217.
(19) DeLerno, J. R.; Trefonas, L. M.; Darensbourg, M. Y.; Majeste, R. J.
Inorg. Chem. 1976, 15, 816.
(20) Fluck, E.; Fo¨rster, J. E.; Weidlein, J.; Ha¨dicke, E. Z. Naturforsch.
Teil B 1977, 32, 499.
(21) Kiji, J.; Okano, T.; Hasegawa, T. J. Mol. Catal. A 1995, 97, 73.
(22) Casalnuovo, A. L.; Calabrese, J. C. J. Am. Chem. Soc. 1990, 112,
4324.
(23) Zhang, H.-C.; Daves, G. D., Jr. Organometallics 1993, 12, 1499.
(24) Okano, T.; Uchida, I.; Nakagaki, T.; Konishi, H.; Kiji, J. J. Mol. Catal.
1989, 54, 65.
Dichlorobis(1,3,5-triaza-7-phosphaadamantane)nickel(II), 4. A
0.346 g (1.46 mmol) sample of NiCl2 and 0.470 g (2.98 mmol) of PTA
were weighed out into a Schlenk flask. Then 20 mL of MeOH was
added, resulting in the formation of a blue solution. The solution was
allowed to stir for 2 days during which time a red precipitate formed.
The precipitate was collected on a sintered glass frit and washed with
MeOH and ether. The powder was dried in vacuo, and 0.547 g (85%
(25) Herrmann, W. A.; Kellner, J.; Riepl, H. J. Organomet. Chem. 1990,
389, 103.
(26) (a) Darensbourg, D. J.; Bischoff, C. J.; Reibenspies, J. H. Inorg. Chem.
1991, 30, 1144. (b) Bartik, T.; Bartik, B.; Hanson, B. E.; Guo, I.;
To´th, I. Organometallics 1993, 12, 164.
(28) Chatt, J.; Leigh, G. J.; Slade, R. W. J. Chem. Soc., Dalton Trans.
1973, 2021.
(29) Reddy, V. S.; Katti, K. V.; Barnes, C. L. J. Chem. Soc., Dalton Trans.
1996, 1301.
(27) (a) Tolman, C. A. Chem. ReV. 1977, 77, 313. (b) Immirzi, A.; Musco,
(30) Martell, A. E.; Motekaitis, R. J. Determination and Use of Stability
Constants, 2nd ed.; VCH Publishers: New York, 1992.
A. Inorg. Chim. Acta 1977, 25, L41.

Water-Soluble Organometallic Compounds
Inorganic Chemistry, Vol. 38, No. 10, 1999 2475
yield) of the product was isolated. Anal. Calcd for NiCl2P2C12H24N6:
C, 32.47; H, 5.45; N, 18.93. Found: C, 32.45; H, 5.42; N, 18.74.
Tetrakis(1,3,5-triaza-7-phosphaadamantane)nickel(0), 5. To 0.203
g (0.85 mmol) of NiCl2 and 0.739 g (4.71 mmol) of PTA was added
4 mL of H2O. Immediately, the solution became a dark blue ink color.
This color began to change to red as 8 mL of MeOH was added. The
red/orange solution was allowed to stir for 8 h. During this time, the
orange color faded and a white precipitate formed. The precipitate was
collected on a sintered glass frit. It was washed three times with MeOH
and twice with ether. It was allowed to dry in vacuo, and 0.436 g (74%
yield) of the white product was isolated. 31P NMR revealed a singlet
at -44.8 ppm in D2O.
Tetrakis(1,3,5-triaza-7-phosphaadamantane)palladium(0), 6. A
0.107 g portion of PdCl2 (0.680 mmol) and 0.534 g of PTA (3.4 mmol,
5 equiv) were weighed out into a Schlenk flask. The flask was evacuated
and backfilled with nitrogen. Then 5 mL of distilled water was added
via syringe. The resulting solution was a deep orange/brown color. It
was allowed to stir overnight. The mixture was filtered through Celite
to remove any metallic palladium, and then the solvent was removed.
Twenty milliliters of MeOH was added, and the resulting mixture was
filtered to yield a tan precipitate and a yellow filtrate. The solid was
washed several times with 5 mL aliquots of MeOH, followed by a 5
mL aliquot of ether. The product was allowed to dry in vacuo. A 0.283
g (57% yield) portion of white/gray product was isolated. 31P NMR
(D2O): δ ) -56.5 ppm (s).
[PdCl(PTA)3]Cl, 7. The synthesis of this compound has been
described previously.1 Bright yellow needles were obtained from a
methanol/0.1 M HCl solution of 7 (5:1 mL/mL) allowed to stand
overnight. These needles were isolated and redissolved in methanol/
0.1 M HCl. This solution was stored at 5 °C for 2 months until yellow
crystals suited to X-ray diffraction appeared. 31P NMR (D2O): δ )
-47 ppm.
Tetrakis(1,3,5-triaza-7-phosphaadamantane)platinum(0), 8. A
0.169 g portion of PtCl2 (0.637 mmol) and 0.600 g of PTA (3.82 mmol,
6 equiv) were weighed out into a Schlenk flask, and 10 mL of distilled
water was added via syringe. Initially, the solution was an orange color
and contained a precipitate. After a few hours the precipitate disap-
peared, and the orange color faded to yellow. The solution was allowed
to stir for 2 days and was then filtered through Celite to remove any
metallic platinum. The solution was taken to dryness in vacuo and 10
mL of MeOH was added to redissolve the solid. The addition of 20
mL of ether caused an off-white precipitate to form. This was collected
on a sintered glass frit and washed extensively with ether and allowed
to dry in vacuo. The solid (0.432 g) was isolated in a drybox. 31P NMR
(D2O): δ ) -70 (JPt-P ) 3699 Hz), and -80 ppm (JPt-P ) 2357 Hz),
showing a mixture of two products.
Reaction of PtCl2 and PTA under Acidic Conditions. PtCl2 (0.169
g, 0.635 mmol) and PTA (0.6 g, 3.82 mmol, 6 equiv) were combined
in a Schlenk flask which was evacuated and backfilled with N2. Initially,
10 mL of 0.1M HCl (degassed) was added to the flask, causing the
formation of a clear, orange solution. After 15 min, another 30 mL of
0.1 M HCl was added. The solution immediately lost the orange color,
which faded to a light yellow. After stirring for 2 days, the volume
was removed in vacuo, and 20 mL of MeOH was added. The resulting
white precipitate was isolated on a sintered glass frit. 31P NMR (D2O):
δ ) -47 ppm (broad).
Reaction of PtCl2 and PTA under a CO2 Atmosphere. PtCl2
(0.169 g, 0.635 mmol) and PTA (0.6 g, 3.82 mmol, 6 equiv) were
weighed out into a 10 mL Schlenk flask. H2O (3 mL) and D2O (3 mL)
were added under a nitrogen atmosphere. The solution was allowed to
stir for 2 days. 31P NMR (D2O): δ ) -80 ppm (JPt-P ) 2361 Hz).
31P NMR Experiments of Pt(PTA)4 Reactions with Acids. Pt-
(PTA)4 + H3PO4. Pt(PTA)4 (30 mg 3.65 × 10-5 mol) was weighed
out into a 5 mm NMR tube, and 1 mL of D2O was added via syringe,
followed by 2.47 µL (3.6 × 10-5 mol) of H3PO4. 31P NMR (D2O): δ
) -70 ppm (JPt-P ) 3701 Hz).
Pt(PTA)4 + PTAH+Cl-. Pt(PTA)4 (30 mg, 3.65 × 10-5 mol) was
weighed out into a 5 mm NMR tube, and 0.021 g (1.09 × 10-4 mol)
of PTAH+Cl- was dissolved in 1 mL of D2O and cannulated into the
NMR tube. 31P NMR (D2O): δ ) -80 ppm (JPt-P ) 2357 Hz).
Pt(PTA)4 + CO2. Pt(PTA)4 (0.030 g, 3.65 × 10-5 mol) was weighed
out into a 5 mm NMR tube, and 0.9 mL of D2O was added. CO2 gas
was bubbled through the solution for 5 min. 31P NMR (D2O): δ )
-74 (JPt-P ) 3604 Hz), -80 ppm (JPt-P ) 2357 Hz). -74 ppm:-80
ppm ratio ) 0.0300.
Pt(PTA)4 + NH4Cl. Pt(PTA)4 (30 mg, 3.65 × 10-5 mol) was
weighed out into a 5 mm NMR tube, and 0.0021 g (3.96 × 10-5 mol)
of NH4Cl was dissolved in 1 mL of D2O and cannulated into the NMR
tube. 31P NMR (D2O): δ ) -74 (JPt-P ) 3591 Hz), -80 ppm (JPt-P
) 2357 Hz). -74 ppm:-80 ppm ratio ) 2.96.
Pt(PTA)4 + C3H5CO2H. Pt(PTA)4 (0.030 g, 6.0 × 10-5 mol) was
weighed out into a 5 mm NMR tube, and 0.012 g (1.39 × 10-4mol) of
crotonic acid was weighed out into a Schlenk flask. D2O (0.8 mL) was
added to the Schlenk flask. This solution was cannulated into an NMR
tube under an inert atmosphere. 31P NMR (D2O): δ ) -70 (JPt-P
)
3681 Hz), -80 ppm (JPt-P ) 2357 Hz). -80 ppm:-70 ppm ratio )
3.88.
Pt(PTA)4 + 2,3-Dichlorophenol. Pt(PTA)4 (0.030 g, 3.65 × 10-5
mol) was weighed out into a 5 mm NMR tube. 2,3-Dichlorophenol
(0.012 g, 7.18 × 10-5 mol) was weighed out into a Schlenk flask. An
0.8 mL amount of D2O was added to the Schlenk flask. This solution
was cannulated into an NMR tube under an inert atmosphere. 31P NMR
(D2O), δ -74 ppm, JPt-P ) 3592 Hz; δ -80 ppm, JPt-P ) 2355 Hz;
-80 ppm:-74 ppm ratio ) 1.5.
Carbonyltris(1,3,5-triaza-7-phosphaadamantane)nickel(0), 9. Ni-
(PTA)4 (0.300 g, 0.457 mmol) was weighed out into a 100 mL Schlenk
flask, and the flask was evacuated and back-filled with a CO
atmosphere. To the flask was added 55 mL of methanol, and the
resulting slurry was allowed to stir at room temperature. After 5 min,
all of the precipitate had dissolved and the CO atmosphere was quickly
replaced with a nitrogen atmosphere to prevent further substitution.
The volume was reduced in vacuo until approximately one-third of
the initial volume remained. During this time, a white solid precipitated
out of solution. Ether (60 mL) was added and the flask was placed in
the freezer overnight. The white precipitate was collected on a frit,
washed with ether, and allowed to dry in vacuo. The product was
isolated as a white powder (0.208 g, 85% yield) in a drybox. IR
(MeOH): 1945 cm-1 31P NMR (MeOH-d4): δ ) -47.2 ppm (s). Anal.
.
Calcd for NiC19N9OH36P: C, 40.89; H, 6.50; N, 22.58. Found: C,
40.36; H, 6.43; N, 22.19.
Dicarbonylbis(1,3,5-triaza-7-phosphaadamantane)nickel(0), 10.
In a typical synthesis, Ni(PTA)4 (0.300 g, 0.437 mmol) was placed in
a Schlenk flask, and 35 mL of MeOH was added under a CO
atmosphere. The mixture was heated to 50 °C and allowed to stir
overnight. The mixture was filtered through Celite and the MeOH
removed in vacuo. H2O (20 mL) was added, and the white precipitate
which resulted was collected on a frit and washed with ether. After
drying in vacuo overnight, the product (0.142 g, 76% yield) was isolate
in the drybox as a white solid. IR (MeOH): 2012, 1956 cm-1 31P NMR
.
(MeOH-d4): δ ) -50.7 ppm. Anal. Calcd for NiC14N6O2H24P2: C,
39.19; H, 5.64; N, 19.59. Found: C, 38.92; H, 5.54; N, 19.44. Crystals
of the product were grown by dissolving the isolated powder in a
minimum amount of MeOH in a large test tube. The MeOH was then
layered with ether and allowed to sit at room temperature for 3 days,
at which time small feathery crystals grew. The tube was then placed
in a freezer at -15 °C. After approximately 1 week, crystals suitable
for X-ray diffraction appeared.
Triscarbonyl(1,3,5-triaaza-7-phosphaadamantane)nickel(0), 11.
Ni(PTA)4 (200 mg, 0.291 mmol) was weighed out into a 100 mL
Schlenk flask. The flask was evacuated and backfilled with a CO
atmosphere. Toluene (80 mL) was added, and CO was allowed to flow
through the flask for approximately 0.5 h. The flask was then sealed
off and heated to 50 °C in an oil bath. The reaction was monitored
periodically for 1 week. The mixture was filtered through a sintered
glass frit. The solvent was evaporated in vacuo, which yielded trace
Pt(PTA)4 + Pyridinium Tetrafluoroborate. Pt(PTA)4 (30 mg, 3.65
× 10-5mol) was weighed out into a 5 mm NMR tube, and 0.0142 g
(7.30 × 10-5 mol) of pyridinium tetrafluoroborate was dissolved in 1
mL of D2O and cannulated into the NMR tube. 31P NMR (D2O): δ )
-80 ppm (JPt-P ) 2357 Hz).
amounts of a yellow/white powder. IR (toluene): 2068, 1993 cm-1
.

2476 Inorganic Chemistry, Vol. 38, No. 10, 1999
Darensbourg et al.
Table 1. Crystallographic Data and Data Collection Parameters for Complexes 7, 10, 1S, and 2S
complex
7
10
1S
2S
empirical formula
fw
C19H42Cl2N9OP3Pd
682.83
P21/c
2856.3(10)
4
C24H60ClN12O6P4Pt
967.26
Fd3h
C24H56B2F8N12O4P4Pt
1069.40
C2/c
8478(3)
8
C15H28N6NiO3P2
461.08
Cmca
4119.5(14)
8
space group
V (Å3)
7818.5(13)
8
Z
D
calc (Mg m3)
1.588
1.643
1.676
1.487
a (Å)
b (Å)
c (Å)
10.796(3)
21.255(3)
12.677(2)
90
100.49(2)
90
293(2)
1.036
0.710 73
5.71
19.8476(19)
19.8476(19)
19.8476(19)
90
90
90
193(2)
3.874
0.710 73
5.70
25.079(5)
21.639(4)
17.325(4)
90
115.61(3)
90
173(2)
8.349
1.541 84
8.28
23.046(5)
7.508(2)
23.808(5)
90
90
90
193(2)
1.125
0.710 73
4.98
R (deg)
â (deg)
γ (deg)
T (K)
µ(Mo KR) (mm-1
wavelength (Å)
RF (%)a
)
R
wF (%)a
17.40
11.32
17.71
13.13
2
a RF ) ∑||Fo| - |Fc||/∑Fo and RwF ) {[∑w(Fo - Fc)2]/∑wFo ]1/2
.
Scheme 1
31P NMR (THF-d8): δ ) -54 ppm. This complex was more readily
prepared from the reaction of Ni(CO)4 and PTA in toluene solution.
Monitored Kinetics of Ni(PTA)4 + CO in Water. In a typical
run, CO was bubbled through water for approximately 1 h, and 15 mL
of this solution was transferred via syringe into the reaction vessel.
The reaction vessel contained the IR probe and was maintained under
an atmosphere of CO at a constant temperature via an external bath.
The solution was then allowed to equilibrate to the desired temperature
for 5 min. A total of 256 background scans were taken, and the
instrument was setup to take 64 scans every 50 s. The run was started
and four scans were taken before the Ni(PTA)4 (2.33 × 10-4 mol in 5
mL of degassed water) was introduced via syringe to the reaction vessel.
The appearance of a product υ(CO) band at 1945 cm-1 was followed
over time. The reaction was monitored until it was determined that all
of the Ni(PTA)4 had reacted to form Ni(CO)(PTA)3.
1). The reaction solution immediately turned blue followed by
changing to red, subsequently resulting in a colorless solution.
The identity of the blue transient species is most likely an
octahedral Ni(II) complex containing PTA ligands bound via a
nitrogen atom, since amine complexes of this type are charac-
teristically blue in color.31 Although there are no documented-
complexes of PTA bound via a nitrogen atom, the measured
pKa of 5.70 ( 0.01 of a nitrogen-bound proton in PTAH+ would
suggest it to be a suitable ligand toward Ni(II). Nevertheless,
we observed no apparent reaction between NiCl2 and the weaker
nitrogen base analogue hexamethylenetetraamine (pKa ) 4.89),
in aqueous solution. The red intermediate has been identified
as NiCl2(PTA)2, (4) by way of an independent synthesis of this
derivative in anhydrous methanol. On the other hand, this latter
Ni(II) derivative was shown to be quite unstable in an aqueous
methanol solution with regard to forming the reduced Ni(PTA)4
(5) species along with 1 equiv of PTAdO (31P NMR at -2.32
ppm).
X-ray Structural Determinations. Crystal data and details of data
collection are given in Table 1. In addition, crystallographically deter-
mined parameters for the singly and doubly protonated Pt(PTA)4 deriv-
atives, namely, [Pt(PTA)3(PTAH)][Cl] (1S) and [Pt(PTA)2(PTAH)2]-
[BF4]2 (2S), are contained in the Supporting Information. A yellow
needle of [Pd(PTA)3Cl]Cl and a white needle of Ni(CO)2(PTA)2 were
mounted on glass fibers with epoxy cement at room temperature and
cooled in a liquid nitrogen cold stream. Preliminary data collection
was performed on a Nicolet R3m/v X-ray diffractometer (Mo KR, λ )
0.71073 Å radiation). Cell parameters were calculated from the least-
squares fitting of the setting angles for 24 reflections. ω scans for several
intense reflections indicated acceptable crystal quality. Data were
collected for 4.0° e 2θ g 50°. Three control reflections, collected every
97 reflections, showed no significant trends. Background measurements
by stationary-crystal and stationary-counter techniques were taken at
the beginning and end of each scan for half the total scan time. Lorentz
and polarization corrections were applied to 4627 reflections for [Pd-
(PTA)3Cl]Cl and 1603 reflections for Ni(CO)2(PTA)2. A total of 4627
unique reflections for [Pd(PTA)3Cl]Cl and 1603 for Ni(CO)2(PTA)2,
with |I| g 2.0s(I), were used in further calculations. The structure was
solved by direct methods [SHELXS program package, Sheldrick
(1993)]. Full-matrix least-squares anisotropic refinement for all non-
hydrogen atoms yielded; R ) 6.35, Rw ) 18.82, and S ) 1.036 for
[Pd(PTA)3Cl]Cl, and R ) 4.98, Rw ) 13.13, and S ) 1.021 for Ni-
(CO)2(PTA)2. Hydrogen atoms were placed in idealized positions with
isotropic thermal parameters fixed at 0.08. Neutral-atom scattering
factors and anomalous scattering correction terms were taken from
International Tables for X-ray Crystallography.
The Ni(PTA)4 which was prepared by this route in a purified
yield of 74% has a single 31P NMR signal at -44.8 ppm in
D2O. This 31P chemical shift is slightly downfield from that of
Ni(PTA)4 prepared in toluene/methanol from the ligand sub-
stitution reaction of Ni(cod)2 and PTA of -45.7 ppm.1 This
downfield shift is indicative of partially protonated PTA ligands
in the nickel(0) product obtained in Scheme 1, which is
consistent with the production of 2 equiv of HCl during this
+
process. The completely protonated Ni(PTAH)4 cation, pre-
pared from Ni(PTA)4 in 0.1 M HCl and crystallographically
characterized, exhibits a 31P NMR chemical shift further
downfield at -41.9 ppm.
Results and Discussion
The palladium analogue to complex 5 is similarly prepared
from PdCl2 and 5 equiv of PTA in an aqueous solution in a
Zerovalent Group 10 Metal M(PTA)4 Derivatives. The
tetrakis(1,3,5-triaza-7-phosphaadamantane)nickel(0) complex
was readily synthesized from the room-temperature reaction of
NiCl2 and excess PTA in an aqueous methanol solution (Scheme
(31) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th ed.;
John Wiley and Sons: New York, 1988; p 744.

Water-Soluble Organometallic Compounds
Inorganic Chemistry, Vol. 38, No. 10, 1999 2477
(0.062 Å. The Pd-P bond trans to the chloride ligand is
observed to be significantly shorter, 2.238(3) Å, as compared
to the average Pd-P bond length cis to the Cl- ligand, 2.334-
(2) Å. That is, the cation exhibits a notable trans influence, much
like that seen in the platinum derivative.32 The average Cl-
Pd-Pcis and Pcis-Pd-Ptrans bond angles were found to be 84.30-
(8)° and 95.79(8)°, respectively, whereas the Pcis-Pd-Pcis bond
angle was determined to be 168.37(9)°. The water molecule
was shown to be involved in a hydrogen-bonding motif with
the nitrogen atoms of adjacent cations (N‚‚‚O distances are 2.863
and 2.913 Å with a N-O-N angle of 121.2°). Similarly, the
chloride anion is hydrogen-bonded to methanol with a Cl‚‚‚O
distance of 3.098 Å and a C-O-Cl angle of 101.1°.
The reaction of platinum dichloride with excess PTA in an
aqueous solution over the period of 2 days underwent a color
change from orange to yellow prior to affording the off-white,
zerovalent platinum complex. However, the definitive identifica-
tion of the product(s) resulting from this reaction was not as
straightforward as that of the other group 10 metals. That is,
this process provided two platinum(0) species in an overall yield
of 82%. These two platinum derivatives exhibited sharp, singlet
31P NMR resonances in D2O at -70 (JPt-P ) 3699 Hz) and
-80 ppm (JPt-P ) 2357 Hz) in a ratio of 1.7 to 1. The former
31P signal is readily assignable to the expected product, a
partially protonated at nitrogen Pt(PTA)4 derivative. Recall that
Figure 1. Molecular structure of complex 7 (thermal ellipsoids at 50%
probability).
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complex
7
Pd(1)-Cl(1)
Pd(1)-P(1)
Pd(1)-P(2)
Pd(1)-P(3)
O(1M)-C(1M)
2.375(3)
2.330(2)
2.238(3)
2.338(2)
1.38(2)
N-C(ave)a
N-C(ave)b
P(1)-C(ave)
P(2)-C(ave)
P(3)-C(ave)
1.491[11]
1.472[11]
1.846[9]
1.852[8]
1.851[9]
4+
Pt(PTA)4 and Pt(PTAH)4 haVe 31P NMR chemical shifts at
-74.5 and -69.1 ppm, respectiVely.1
Upon the addition of an aqueous solution of [Et4N][OH] to
the mixture of platinum(0) species in water, a single 31P
resonance at -74.5 ppm appeared. Hence, both derivatives are
related to Pt(PTA)4 via a protonation process. It is important to
reiterate here that the Pt(PTAH)4Cl4 complex (crystals grown
from Pt(PTA)4 in 0.1 HCl) has been crystallographically defined
to be a tetrahedral species with one N atom of each PTA ligand
protonated as evidence by an analysis of the C-N bond dis-
tances in the bound PTA ligands.12 Therefore, it follows that
the other platinum derivative is protonated at an alternative site,
most likely at the metal center. Indeed several research groups
have reported zerovalent group 10 metal derivatives protonated
at the metal site.7,33-36
Cl(1)-Pd(1)-P(1)
Cl(1)-Pd(1)-P(2)
Cl(1)-Pd(1)-P(3)
84.23(8) P(1)-Pd(1)-P(2)
174.43(8) P(1)-Pd(1)-P(3)
84.37(8) P(2)-Pd(1)-P(3)
97.72(8)
168.37(9)
93.85(8)
Pd(1)-P(1)-C(ave) 118.8[3]
Pd(1)-P(2)-C(ave) 119.1[3]
Pd(1)-P(3)-C(ave) 118.6[3]
a Carbon bonded to one nitrogen atom and one phosphorus atom.
b Carbon bonded to two nitrogen atoms.
yield of 57%. However, the synthesis of this derivative requires
a longer reaction period of about 12 h. As in the case of the
nickel complex, the 31P NMR signal in D2O of this Pd(PTA)4,
(6) complex was downfield at -56.5 ppm relative to the
unprotonated derivative (-58.7 ppm), again indicative of some
protonation of the bound PTA ligands. Previously we have
reported upon the reductive synthesis (PdCl2 plus excess PTA)
of the Pd(PTA)4 complex in ethanol/water where a cationic Pd-
(PTA)3Cl+ intermediate species was isolated and characterized
spectroscopically as its chloride salt.1 Herein, we have obtained
X-ray quality crystals of this derivative, complex 7. The [Pd-
(PTA)3Cl][Cl] salt was crystallized from methanol/water with
one molecule each of CH3OH and H2O in the crystal lattice
and shown to be isomorphous with its platinum analogue
previously reported by Muir and co-workers.32
Yellow crystals suitable for X-ray diffraction were obtained
from a concentrated aqueous methanol solution of complex 7
maintained at 5 °C for several days. These crystals were
extremely air sensitive, turning orange followed by decomposi-
tion upon minimal exposure to moist air. Crystallographic data
and data collection parameters are listed in Table 1. A thermal
ellipsoid view of the cation of complex 7 is depicted in Figure
1, along with the atomic numbering scheme. Bond distances
and bond angles of specific interest are found in Table 2. The
geometry about the palladium center in the cation, Pd(PTA)3Cl+,
is approximately square planar, where the average deviation
from the plane defined by the four ligand and Pd atoms is
From these observations it is evident that the kinetically
controlled site of protonation of Pt(PTA)4 is at the nitrogen
atoms of the PTA ligands. That is, the addition of an excess of
strong aqueous acids such as hydrochloric led to formation of
the well-characterized Pt(PTAH)4Cl4 derivative. However, if a
much weaker acid is employed such as [PTAH][Cl] (pKa )
1
5.70) or carbonic acid (pKa ) 6.37), the PTA ligands are not
protonated and only the 31P NMR resonance at -80 ppm is
observed. [The bound PTA ligands would be anticipated to be
less basic than those of free PTA, which we haVe determined
to haVe a pKa of 5.70. For example, PTAdO has a measured
pKa of 2.52.] It is of importance to note that in the synthesis of
Pt(PTA)4 by the aqueous reduction of PtCl2 in excess PTA the
HCl produced in this process is partially consumed by free
PTA, thereby leading to two protonating reagents and subse-
quently two different protonated platinum species. From one
of these preparations we have isolated crystals of a Pt(PTA)4
complex protonated at one of the nitrogen atoms of PTA, i.e.,
[Pt(PTA)3(PTAH)][Cl] (1S), as determined by X-ray crystal-
(33) Cariati, F.; Ugo, R.; Bonati, F. Inorg. Chem. 1966, 5, 1128.
(34) Drinkard, W. C.; Eaton, D. R.; Jesson, J. P.; Lindsey, R. V., Jr. Inorg.
Chem. 1970, 9, 392.
(35) Shunn, R. A. Inorg. Chem. 1970, 9, 394.
(36) Miedaner, A.; DuBois, D. L.; Curtis, C. J. Organometallics 1993, 12,
299.
(32) Muir, M. M.; Muir, J. A.; Alyea, E. C.; Fisher, K. J. J. Crystallogr.
Spectrosc. Res. 1993, 23, 745.

2478 Inorganic Chemistry, Vol. 38, No. 10, 1999
Darensbourg et al.
Figure 2. (A) 195Pt NMR spectrum of [(H)Pt(PTA)4][Cl] in 3:1 H2O/
D2O. (B) 195Pt NMR spectrum of [(D)Pt(PTA)4][Cl] in D2O.
Figure 4. Variable temperature 31P NMR of [(H)Pt(PTA)4][BF4] and
excess PTA in D2O at (A) 80 °C, (B) 65 °C, and (C) 25 °C.
thusfar not obtained crystals of this platinum derivative proto-
nated at the metal center, X-ray structures of several such species
synthesized via NaBH4 reduction of Pt(II) derivatives have been
reported.36-38 These platinum cations display distorted trigonal
bipyramidal or capped tetrahedral coordination in the solid state.
Furthermore, 31P NMR studies reveal the phosphorus nuclei to
be undergoing a rapid fluxional process on the NMR time scale,
even at low temperatures. However, a static trigonal bipyramidal
Figure 3. 1H NMR spectrum of [(H)Pt(PTA)4][Cl] in 3:1 H2O/D2O.
lography. Structural parameters for complex 1S are essentially
the same as those previously reported for the [Pt(PTAH)4][Cl]4
derivative.1
That this species is protonated at the platinum center is clearly
demonstrated by both 195Pt and 1H NMR spectroscopies. Figure
2 depicts the 195Pt NMR spectra for the protonated and
+
structure for the HPt[P(CH2OH)3]4 derivative in CD3OD has
been assigned at -78 °C on the basis of 31P NMR studies.7
This increase in the barrier to intramolecular phosphine ex-
change in this instance is thought to result from hydrogen
bonding between the coordinated P(CH2OH)3 ligands. In ad-
dition, 31P NMR studies of other platinum hydride derivatives
obtained from NaBH4 reduction of Pt(II) complexes containing
tripodal phosphine ligands reveal trigonal bipyramidal structures
in solution.39-41
+
deuterated HPt(PTA)4 species in water. As seen in Figure 2,
superimposed on the platinum nucleus being split by four-
equivalent phosphine ligands into a quintet (JPt-P ) 2362 Hz)
are the Pt-H(JPt-H ) 565 Hz) and Pt-D(JPt-D ) 87 Hz)
couplings. Although there is some overlap in the 195Pt NMR
chemical shifts for Pt(II) and Pt(0) species, the chemical shift
+
found for HPt(PTA)4 at -6289 ppm is more typical of a
platinum(0) species. The 1H NMR spectrum of the HPt(PTA)4
+
The metal site is more basic than the bound PTA nitrogen
atoms and therefore the thermodynamic site for protonation of
the Pt(PTA)4 species in water. Nevertheless, rapid protonation
of the nitrogen atoms of the PTA ligands of Pt(PTA)4 by strong
acids inhibits protonation at the metal center. Indeed when 1
equiv of aqueous HCl is slowly added dropwise to an aqueous
solution of Pt(PTA)4, protonation occurs predominantly at the
metal center. We have been able to better define the basicity of
the metal center in Pt(PTA)4 by employing acids of various
strengths under conditions of kinetic control. In this manner
the extent of protonation at the nitrogen atoms of PTA Vs the
platinum center as a function of the pKa of the added acid was
determined by 31P NMR (-70 vs -80 ppm signals, respec-
tively). Of course, the fact that these processes are carried out
cation in water exhibits a signal at -14.3 ppm split into a quintet
by four magnetically equivalent phosphine ligands (2JP-H ) 28.0
Hz). In addition, the 195Pt satellites appear with a coupling
constant of JPt-H ) 567 Hz (see Figure 3). Similarly, the 31P
NMR spectrum of this derivative, a singlet at -80 ppm in H2O,
displays a 2JP-H value of 28.0 Hz. Furthermore, low-temperature
31P NMR spectra determined in CD3OD revealed the phosphine
ligands to be magnetically equivalent at temperatures as low as
-80 °C, indicative of a rapid intramolecular ligand exchange
process. Correspondingly, at elevated temperatures in aqueous
solution rapid intermolecular ligand exchange occurs between
the HPt(PTA)4+ cation and free PTA, as evidenced by 31P NMR
spectroscopy (see Figure 4).
All attempts to grow crystals of the [HPt(PTA)4][X] salt with
various anions have thusfar been unsuccessful. For example,
crystals of the partially protonated derivative, [Pt(PTA)2-
(PTAH)2][BF4]2 (2S), were obtained from the reaction of Pt-
(PTA)4 and [PTAH][BF4] in water/methanol and characterized
by X-ray diffaction (see the Supporting Information). The metric
parameters determined were quite similar to those previously
reported for the [Pt(PTAH)4][Cl]4 derivative.1 Although we have
(37) Bruggeller, P. Inorg. Chem. 1990, 29, 1742.
(38) Gieren, V. A.; Bruggeller, P.; Hofer, K.; Hubner, T.; Ruiz-Perez, C.
Acta Crystallogr., Sect. C 1989, 45, 196.
(39) Bruggeller, P. Inorg. Chim. Acta 1987, 129, L27.
(40) Peter, M.; Probst, M.; Peringer, P.; Mu¨ller, E. P. J. Organomet. Chem.
1991, 410, C29.
(41) Handler, A.; Peringer P.; Mu¨ller, E. P. J. Organomet. Chem. 1991,
412, 451.

Water-Soluble Organometallic Compounds
Inorganic Chemistry, Vol. 38, No. 10, 1999 2479
Scheme 2
Table 3. IR and NMR Data for Ni(CO)x(PTA)4-x Complexes
in water allows for the use of a wide range of well-defined acid
strengths. The summary of our findings are shown in Scheme
2. As indicated by these results, the metal center in Pt(PTA)4 is
fairly basic with a pKa value greater than 7.44 but less than
9.25. We have tentatiVely defined the pKa of the metal
protonated species to be 7.89 by the titration method described
for free PTA.
Carbonyl Derivatives of Ni(PTA)4. In this study we have
examined the production of carbonyl derivatives of Ni(PTA)4
via ligand substitution reactions for two reasons. First, catalytic
processes involving 18-electron catalyst precusors of Ni(PR3)4
derivatives generally require phosphine dissociation prior to
substrate binding and reacting; hence, it is important to establish
the rates of PTA dissociation in aqueous solution. Second, the
electronic and steric properties of the PTA ligand have been
defined on the basis of comparisons with group 6 metal carbonyl
derivatives.18,19 The availability of Ni(CO)4-n(PTA)n complexes
would allow for a more direct comparison with Tolman’s
parameters, which are based on an extensive series of Ni-
(CO)3PR3 derivatives.27a
complex
Ni(PTA)4
Ni(CO)(PTA)3
Ni(CO)2(PTA)2
IR(υCO) (cm-1
)
31P NMR (ppm)
solvent
-46
-48
-50
H2O
H2O
MeOH
1945
2012
1956
2001
1944
2006
1946
2069
1994
2068
1993
2071
1997
THF
CH2Cl2
THF
Ni(CO)3(PTA)
-55
toluene
CH2Cl2
average υ(CO) value and the 31P NMR chemical shift increase
in frequency and shift upfield, respectively, with an increase in
the number of CO ligands in the complex. The Tolman elec-
tronic parameter derived from the value of the υ(CO) A1 band
observed in CH2Cl2 for Ni(CO)3PTA suggests that the PTA
ligand is much less electron-donating than PMe3.42 The υ(CO)
vibrational modes exhibit significant shifts to lower frequncies
in going from water or methanol as solvent to less polar organic
solvents. For example, the symmetric and asymmetric υ(CO)
vibrations in the Ni(CO)2(PTA)2 derivative appear at 2012 and
1955 cm-1 in H2O or MeOH and shift to 2001(2006) and 1944
(1946)cm-1 in THF (CH2Cl2). On the other hand, the calculated
angle (θ) between the two CO ligands’ Ni-C-O vectors
determined from the absolute intensity ratio of the symmetric
and asymmetric υ(CO) vibrations was found to be quite similar,
i.e., 104.4° (THF), 103.2° (CH2Cl2), and 107.6° (MeOH).43
These calculated angles are somewhat less obtuse than that
experimentally observed in complex 10 in the solid state (117.5°)
(vide infra). This underestimation of the calculated OC-Ni-
CO angle is a consequence of an enhancement of the intensity
of the symmetric υ(CO) vibrational mode relative to the asym-
metric mode as a result electronic migration in the phosphine-
Ni π-bonding framework during the former vibration.43
Synthesis of the carbonyl derivatives of Ni(PTA)4 was
accomplished by way of the reaction described in eq 2. The
Ni(PTA)4 + excess CO solvent8 Ni(CO)4-n(PTA)n (2)
initial substitution step is quite fast (vide infra). However,
substitution of one PTA ligand by CO greatly retards the rate
of dissociation of the second PTA ligand. That is, this latter
substitution process takes place over a 12 h reaction period in
methanol at 50 °C. The Ni(CO)(PTA)3 product (9) is quite
soluble in water, whereas the Ni(CO)2(PTA)2 product (10) is
only slightly water-soluble but very soluble in methanol.
Substitution of a third PTA ligand by CO to provide Ni-
(CO)3PTA (11) occurs extremely slowly at ambient temperature
in toluene/methanol, requiring about 1 week to go to completion.
Complex 11 is not water-soluble and only slightly soluble in
methanol, but is quite soluble in organic solvents such as THF
or toluene. Alternatively, this complex is more readily prepared
via the reaction of Ni(CO)4 with 1 equiv of PTA, a process
which takes place on the time scale of minutes. Hence, the
successiVe replacement of the PTA ligands in Ni(PTA)4 occurs
at a decelerated rate, and concomitantly the reaction products
possess greatly reduced solubilities in water and enhanced
solubilities in nonpolar organic solVents.
The solid-state structure of one of these derivatives, complex
10, was determined by X-ray crystallography. Crystals suitable
for X-ray diffraction were obtained from a methanol solution
of the complex layered with ether and maintained at -15 °C
for several days. Crystallographic data and data collection
(42) Tolman, C. A. J. Am. Chem. Soc. 1970, 92, 2953.
(43) (a) Darensbourg, D. J. Inorg. Chem. 1972, 11, 1606. (b) Darensbourg,
D. J.; Brown, T. L. Imorg. Chem. 1968, 7, 959.
These complexes were all characterized by υ(CO) infrared
and 31P NMR spectroscopies (see Table 3). As anticipated, the

2480 Inorganic Chemistry, Vol. 38, No. 10, 1999
Darensbourg et al.
Figure 5. Molecular structure of complex 10 (thermal ellipsoids at
50% probability).
Table 4. Selected Bond Lengths (Å) and Angles (deg) for Complex
10
Figure 6. Overlay of IR spectra of Ni(PTA)4 + CO in H2O at 20 °C,
and monitored appearance of Ni(CO)(PTA)3 υ(CO) vibration at 1945
Ni(1)-C(1)
Ni(1)-C(2)
Ni(1)-P(1)
Ni(1)-P(1)#1
P(1)-C(3)
P(1)-C(4)
P(1)-C(5)
N(3)-C(5)
N(3)-C(7)
1.767(6)
1.758(9)
2.1853(13)
2.1853(12)
1.838(5)
1.839(5)
1.848(5)
1.466(6)
1.458(6)
N(3)-C(8)
N(2)-C(4)
N(2)-C(6)
N(2)-C(7)
N(1)-C(3)
N(1)-C(6)
N(1)-C(8)
O(3)-C(1M)
O(3)-C(1M)#2
1.467(6)
1.479(6)
1.456(7)
1.463(6)
1.472(6)
1.478(7)
1.468(6)
1.405(12)
1.405(12)
cm-1
.
C(2)-Ni(1)-C(1)
C(1)-Ni(1)-P(1)
C(1)-Ni(1)-P(1)#1
C(3)-P(1)-C(4)
C(4)-P(1)-C(5)
C(4)-P(1)-Ni(1)
117.5(3)
C(2)-Ni(1)-P(1)
110.56(12)
103.43(13) C(2)-Ni(1)-P(1)#1 110.56(12)
103.43(13) P(1)-Ni(1)-P(1)#1 110.96(8)
97.5(2)
96.1(2)
126.1(2)
C(3)-P(1)-C(5)
C(3)-P(1)-Ni(1)
C(5)-P(1)-Ni(1)
96.9(2)
115.7(2)
118.9(2)
C(1M)-O(3)-C(1M)#2 131.3(13)
Symmetry transformations used to generate equivalent atoms: #1,
-x, y, z; #2, x, -y, -z + 1.
parameters are listed in Table 1. A thermal ellipsoid view of
the complex is found in Figure 5, along with the atomic
numbering scheme. Selected bond distances and bond angles
are compiled in Table 4. The geometry about the nickel center
is that of a slightly distorted tetrahedron with metal-ligand bond
angles of C-Ni-P (ave. 107°), P-Ni-P (110.96(8)°), and
C-Ni-C (117.5(3)°). The average Ni-CO bond distance is
1.763[8] Å and the Ni-P bond length is 2.185(1) Å. These
bonding parameters are consistent with those in other bispho-
sphine carbonyl derivatives of Ni(CO)4.44 However, as would
be anticipated on steric grounds, the P-Ni-P angles in the more
bulky PCy344a and PPh344c derivatives are more obtuse at 123°
and 117°, respectively. The corresponding Ni-P bond distances
of 2.261 and 2.221 Å, respectively, are significantly longer than
those observed herein for the PTA derivative with the Ni-C
distances of 1.746 and 1.763 Å being quite similar for all three
derivatives. The crystallographically defined Tolman cone angle
as described in ref 19 was calculated to be 103°.
Figure 7. Reaction profile of Ni(PTA)4 + CO in H2O at 20 °C, and
monitored appearance of Ni(CO)(PTA)3 υ(CO) vibration at 1945 cm-1
.
in turn, is inserted into a glass reaction vessel which is externally
cooled or heated. The υ(CO) vibrational mode in the product,
Ni(CO)(PTA)3, at 1945 cm-1 was used to follow the progress
of the reaction (Figure 6). As depicted in Figure 7, substitution
of a second PTA ligand in Ni(CO)(PTA)3 is much slower than
that of the first, i.e., the absorbance for the 1945 cm-1 peak
increases and levels off with no diminution during the course
of the substitution process. The reaction was shown to be first-
order in metal complex, as indicated by the linearity of the
logarithic plot of (Abs∞ - Abst) vs time (Figure 8). Consistent
with the qualitative observations noted during the preparations
of these carbonyl derivatives of Ni(PTA)4, the rate of PTA
The rate of PTA substitution in Ni(PTA)4 by carbon monoxide
in aqueous solution was determined by employing an infrared
probe for real time, in situ monitoring of the reaction’s progress.
The system consists of a dedicated interferometer, which is
coupled through a stainless steel optical conduit with a ZnSe
support element to a silicon disk probe (SiComp). This probe,
substitution in complex 10 is quite fast in water with a kobs
)
7.92 × 10-4 s-1 at 20 °C. Because of the low solubility of CO
in water, even at high pressure, the PTA substitutional process
is retarded by small quantities of PTA ligand in solution, or in
other words, the reaction product (PTA) retards the CO
substitution process. The low solubility of CO in aqueous vs
organic solvents is a real limitation in investigating mechanistic
aspects of these process, e.g., the [CO] in water [(1.13-1.09)
× 10-3 M at 1.2-10.5 atm]45 is not only much lower than that
in organic solvents but does not vary significantly at modest
(44) (a) Del Pra, A.; Zanotti, G.; Pandolfo; Segala, P. Cryst. Struct.
Commun. 1981, 10, 7. (b) Baacke, M.; Morton, S.; Stelzer, O.;
Sheldrick, W. S. Chem. Ber. 1980, 113, 1343. (c) Kruger, C.; Tsay,
Y.-H. Cryst. Struct. Commun. 1974, 3, 455. (d) Ficker, R.; Hiller,
W.; Regius, C. T.; Hoffman, P. Z. Kristallogr. 1996, 211, 62.

Water-Soluble Organometallic Compounds
Inorganic Chemistry, Vol. 38, No. 10, 1999 2481
shift value of -6289 ppm suggests these complexes to be
protonated Pt(0) derivatives as opposed to Pt(II) hydrides. By
way of comparison with acids of well-defined pKa values in
water, the pKa of this platinum hydride is estimated to be greater
than 7.44 but less than 9.25. On the other hand, the pKa of the
protonated nitrogen atoms of bound PTA ligands is less than
5.70. These protonated platinum salts were shown to possess
magnetically equivalent phosphine ligands at a temperature as
low as -80 °C in CD3OD by 31P NMR, indicative of a fast
intramolecular exchange processes. Furthermore, at elevated
temperatures (>50 °C) fast intermolecular phosphine exchange
between the HPt(PTA)4+ cation and free phosphine in aqueous
solution was observed.
+
It is of interest to compare the pKa defined for the HPt(PTA)4
cation in aqueous solution with other values determined in
closely related complexes. For example, the water-soluble Pt-
[P(CH2OH)3]4 complex has been protonated by water which
would indicate the platinum center to be much more basic than
in the PTA analogue reported herein.7 This in turn would dictate
that the P(CH2OH)3 ligand is a much better donor than PTA,
for Angelici has shown that there is a strong correlation between
the enthalpies of protonation (∆HHM) of metal phosphine
complexes and the phosphine’s basicity.48 Related to this, the
pKa of HPt[P(OMe)3]4+ has been estimated at 11 in H2O from
data determined in acetonitrile.49 On the basis of our studies,
this pKa value would appear to be too high since the P(OMe)3
ligand is a weaker donor than PTA.
Finally, the synthesis and characterization of a series of
Ni(CO)4-n(PTA)n derivatives has allowed for an assessment of
the electronic and steric parameters for the PTA ligand according
to Tolman’s original definitions.27a That is, based on the υ-
(CO) A1 vibrational frequency of Ni(CO)3PTA in methylene
chloride, the PTA ligand is shown to be less donating to the
Ni(0) center than PPh3. This was a bit unexpected, since previous
comparisons with molybdenum and iron carbonyl derivatives,
as well as metal carbonyl cluster derivatives,50 have suggested
the PTA ligand to be similar to PMe3.18 On the other hand, the
steric requirements (cone angle) of PTA, as determined by X-ray
crystallography for the Ni(CO)2(PTA)2 derivative, was computed
to be 103°. This value is indistinguishable from that defined
for this parameter based on crystallographic data for the Mo-
(CO)5PTA complex.19
Figure 8. Ln(Abs∞ - Abst) vs t (min) plot of Ni(PTA)4 + CO in H2O
at 20 °C.
CO pressures. Nevertheless, in a reaction carried out in 1 equiv
of PTA the measured rate constant was an order of magnitude
smaller than that observed with no added PTA. This observation
is totally consistent with a dissociative (D) pathway for the
substitution of a phosphine ligand in an 18-electron metal
complex by a weakly nucleophilic incoming CO ligand.46
The relatively slow rate of PTA dissociation in Ni(PTA)4 in
aqueous medium is consistent with the observation that, upon
adding excess PTA to solutions of 5, 6, and 8, sharp 31P NMR
signals are observed for both the complexes and free ligand.
This is indicative of slow dissociative phosphine exchange on
the NMR time scale. The aforementioned observation, coupled
with the absence of a 31P resonance for free PTA in the 31P
NMR spectra of M(PTA)4 derivatives, is as anticipated for the
dissociative equilibrium depicted in eq 3, which has been shown
to be governed by steric rather than electronic effects.47 That
is, for the small, tight-binding PTA ligand in group 10 M(PTA)4
species, there is little or no dissociation and slow exchange.
M(PR3)4 h M(PR3)3 + PR3
Comments and Conclusions
(3)
Herein we have described the synthesis of water-soluble,
zerovalent group 10 metal tetrakis-phosphine derivatives from
the reaction of the corresponding metal(II) chloride salt and
excess PTA in aqueous solution with concomitant production
of PTAdO. These M(PTA)4 derivatives were shown by 31P
NMR studies to have little to no phosphine dissociation and to
undergo slow exchange with free PTA in water. Unlike the
nickel and palladium derivatives, the Pt(PTA)4 complex was
found to be readily protonated at the metal center by weak
aqueous acids such as carbonic acid and pyridinium tetrafluo-
roborate to provide [HPt(PTA)4][X] salts. The 195Pt chemical
Acknowledgment. Financial support of this research by the
National Science Foundation (Grant 96-15866) and the Robert
A. Welch Foundation is greatly appreciated. The experimental
contributions of Dr. A. Katho´ and Dr. Tara Decuir to this
research effort are gratefully acknowledged.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of complexes 7, 10, 1S,
and 2S. This material is available free of charge via the Internet at
http://pubs.acs.org.
IC981243J
(45) International Critical Tables, McGraw-Hill: New York, 1928; Vol.
3, p 260.
(48) Angelici, R. J. Acc. Chem. Res. 1995, 28, 51.
(49) Kristja´nsdo´ttir, S. S.; Norton, J. R. Transition Metal Hydrides; Dedieu,
A., Ed.; VCH Publishers: New York, 1992; p 309.
(50) Darensbourg, D. J.; Beckford, F. A.; Reibenspies, J. H. J. Cluster
Chem., in press.
(46) (a) Darensbourg, D. J. AdV. Organomet. Chem. 1982, 21, 113. (b)
Howell, J. A. S.; Burkinshaw, P. M. Chem. ReV. 1983, 83, 557.
(47) Tolman, C. A.; Seidel, W. C.; Gosser, L. W. J. Am. Chem. Soc. 1974,
96, 53.