Terminal platinum(II) phosphide complexes: Synthesis, structure, and thermochemistry

Article abstract of DOI:10.1021/om9708891

A series of terminal Pt(II) phosphide complexes Pt(dppe)(Me)(PRR′) (R = H; R′ = Mes* (1), R′ = Mes (2), R′ = Ph (3), R′ = Cy (4); R = R′ = Mes (5); R = R′ = Ph (6); R = R′ = Cy (7); R = R′ = Et (8); R = Ph, R′ = i-Bu (9)) has been prepared by proton transfer from the appropriate phosphine to the methoxide ligand of Pt(dppe)(Me)(OMe) (10) (dppe = Ph₂PCH₂-CH₂PPh₂; Mes* = 2,4,6-(t-Bu)₃C₆H₂; Mes = 2,4,6-Me₃C₆H₂; Cy = cyclo-C₆H₁₁). Complexes 1 and 2 were also made by deprotonation of the cations [Pt(dppe)(Me)(PH₂Ar)][BF₄] (Ar = Mes* (13); Ar = Mes (14)). For comparison to 1, the arylthiolate and aryloxide complexes Pt(dppe)(Me)(EMes*) (E = S (11); E = O (12)) were also prepared from 10. NMR studies of the proton-transfer equilibria between Pt(dppe)(Me)(X), Pt(dppe)(Me)(Y), and the acids HY and HX (see Bryndza, H. E.; Fong, L. K.; Paciello, R. A.; Tam, W.; Bercaw, J. E. J. Am. Chem. Soc. 1987, 109, 1444-1456 and Bryndza, H. E.; Domaille, P. J.; Tam, W.; Fong, L. K.; Paciello, R. A.; Bercaw, J. E. Polyhedron 1988, 7, 1441-1452) provide an approximate partial ranking of Pt-P bond strengths in this series: Pt-PHPh > Pt-PHMes > Pt-PHMes*; Pt-PPh₂ > Pt-PMes₂. Complementary solution calorimetry investigations probe the role of entropie effects on the equilibria. Both steric and electronic factors appear to be important in controlling relative Pt-P bond strengths. The Pt-S bonds in 11 and Pt(dppe)(Me)(SPh) are stronger than the analogous Pt-P bonds in 1 and 3. Complexes 1 and 5·THF were structurally characterized by X-ray crystallography.

Full text of DOI:10.1021/om9708891

652
Organometallics 1998, 17, 652-660
Ter m in a l P la tin u m (II) P h osp h id o Com p lexes: Syn th esis,
Str u ctu r e, a n d Th er m och em istr y
Denyce K. Wicht, Sara N. Paisner, Belinda M. Lew, and David S. Glueck*
6128 Burke Laboratory, Department of Chemistry, Dartmouth College,
Hanover, New Hampshire 03755
Glenn P. A. Yap, Louise M. Liable-Sands, and Arnold L. Rheingold
Department of Chemistry, University of Delaware, Newark, Delaware 19716
Christopher M. Haar and Steven P. Nolan
Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148
Received October 14, 1997
A series of terminal Pt(II) phosphido complexes Pt(dppe)(Me)(PRR′) (R ) H; R′ ) Mes*
(1), R′ ) Mes (2), R′ ) Ph (3), R′ ) Cy (4); R ) R′ ) Mes (5); R ) R′ ) Ph (6); R ) R′ ) Cy
(7); R ) R′ ) Et (8); R ) Ph, R′ ) i-Bu (9)) has been prepared by proton transfer from the
appropriate phosphine to the methoxide ligand of Pt(dppe)(Me)(OMe) (10) (dppe ) Ph2PCH2-
CH2PPh2; Mes* ) 2,4,6-(t-Bu)3C6H2; Mes ) 2,4,6-Me3C6H2; Cy ) cyclo-C6H11). Complexes
1 and 2 were also made by deprotonation of the cations [Pt(dppe)(Me)(PH2Ar)][BF4] (Ar )
Mes* (13); Ar ) Mes (14)). For comparison to 1, the arylthiolate and aryloxide complexes
Pt(dppe)(Me)(EMes*) (E ) S (11); E ) O (12)) were also prepared from 10. NMR studies of
the proton-transfer equilibria between Pt(dppe)(Me)(X), Pt(dppe)(Me)(Y), and the acids HY
and HX (see Bryndza, H. E.; Fong, L. K.; Paciello, R. A.; Tam, W.; Bercaw, J . E. J . Am.
Chem. Soc. 1987, 109, 1444-1456 and Bryndza, H. E.; Domaille, P. J .; Tam, W.; Fong, L.
K.; Paciello, R. A.; Bercaw, J . E. Polyhedron 1988, 7, 1441-1452) provide an approximate
partial ranking of Pt-P bond strengths in this series: Pt-PHPh > Pt-PHMes >
Pt-PHMes*; Pt-PPh2 > Pt-PMes2. Complementary solution calorimetry investigations
probe the role of entropic effects on the equilibria. Both steric and electronic factors appear
to be important in controlling relative Pt-P bond strengths. The Pt-S bonds in 11 and
Pt(dppe)(Me)(SPh) are stronger than the analogous Pt-P bonds in 1 and 3. Complexes 1
and 5‚THF were structurally characterized by X-ray crystallography.
In tr od u ction
metal complex catalysts.3 Many phosphido-bridged
dinuclear complexes of these metals have been re-
ported,4 but the more reactive terminal phosphido
ligands, which are of greater relevance to the processes
mentioned above, are less common, and little is known
about the structure and properties of these compounds.5
We report here synthetic, structural, and thermody-
namic studies of a series of terminal Pt(II) phosphido
compounds and of some related arylthiolate and aryl-
oxide complexes, which provide information about the
relative Pt-X bond strengths in this series of anionic
ligands.
Phosphido complexes of the group 10 metals are
important proposed intermediates in catalytic phosphi-
nation1 and hydrophosphination2 reactions and in P-C
cleavage processes that deactivate phosphine-containing
(1) (a) Hillhouse, J . H. Abstracts of Papers, 212th ACS National
Meeting, Orlando, FL, 1996; American Chemical Society: Washington,
DC, 1996; ORG329. (b) Hillhouse, J . H. U.S. Patent No. 5550295 (to
Cytec), 1996. (c) Beletskaya, I. P.; Veits, Y. A.; Leksunkin, V. A.; Foss,
V. L. Bull. Russ. Acad. Sci., Div. Chem. Sci. 1992, 41, 1272-1274. (d)
Cai, D.; Payack, J . F.; Bender, D. R.; Hughes, D. L.; Verhoeven, T. R.;
Reider, P. J . J . Org. Chem. 1994, 59, 7180-7181. (e) Herd, O.; Hessler,
A.; Hingst, M.; Tepper, M.; Stelzer, O. J . Organomet. Chem. 1996, 522,
69-76. (f) Tunney, S. E.; Stille, J . K. J . Org. Chem. 1987, 52, 748-
753. (g) Veits, Y. A.; Karlstedt, N. B.; Beletskaya, I. P. Russ. J . Org.
Chem. 1994, 30, 70-73. (h) Veits, Y. A.; Karlstedt, N. B.; Nasonova,
N. S.; Borisenko, A. A.; Beletskaya, I. P. Russ. J . Org. Chem. 1994,
30, 515-523.
(2) (a) Wicht, D. K.; Kourkine, I. V.; Lew, B. M.; Nthenge, J . M.;
Glueck, D. S. J . Am. Chem. Soc. 1997, 119, 5039-5040. (b) Pringle, P.
G.; Brewin, D.; Smith, M. B.; Worboys, K. In Aqueous Organometallic
Chemistry and Catalysis; Horvath, I. T., J oo, F., Eds.; Kluwer:
Dordrecht, 1995; Vol. 5, pp 111-122. (c) Hoye, P. A. T.; Pringle, P. G.;
Smith, M. B.; Worboys, K. J . Chem. Soc., Dalton Trans. 1993, 74, 269-
274. (d) Pringle, P. G.; Smith, M. B. J . Chem. Soc., Chem. Commun.
1990, 1701-1702. (e) Harrison, K. N.; Hoye, P. A. T.; Orpen, A. G.;
Pringle, P. G.; Smith, M. B. J . Chem. Soc., Chem. Commun. 1989,
1096-1097. (f) Nagel, U.; Rieger, B.; Bublewitz, A. J . Organomet.
Chem. 1989, 370, 223-239.
(3) (a) For a review of metal-mediated P-C cleavage reactions, see:
Garrou, P. E. Chem. Rev. (Washington, D.C.) 1985, 85, 171-185. For
selected recent examples involving the group 10 metals, see: (b) Louie,
J .; Paul, F.; Hartwig, J . F. Organometallics 1996, 15, 2794-2805. (c)
Hartwig, J . F.; Richards, S.; Baranano, D.; Paul, F. J . Am. Chem. Soc.
1996, 118, 3626-3633. (d) Kong, K.-C.; Cheng, C.-H. J . Am. Chem.
Soc. 1991, 113, 6313-6315. (e) Morita, D. K.; Stille, J . K.; Norton, J .
R. J . Am. Chem. Soc. 1995, 117, 8576-8581 and references therein.
(f) Archambault, C.; Bender, R.; Braunstein, P.; De Cian, A.; Fischer,
J . Chem. Commun. 1996, 2729-2730. (g) Novak, B. M.; Wallow, T. I.;
Goodson, F.; Loos, K. Polym. Prepr. 1995, 36, 693-694. (h) Wallow, T.
I.; Novak, B. M. Polym. Prepr. 1993, 34, 1009-1010. (i) Wallow, T. I.;
Seery, T. A. P.; Goodson, F. E., III.; Novak, B. M. Polym. Prepr. 1994,
35, 710-711. (j) Widenhoefer, R. A.; Zhong, H. A.; Buchwald, S. L. J .
Am. Chem. Soc. 1997, 119, 6787-6795.
S0276-7333(97)00889-3 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/30/1998

Terminal Platinum(II) Phosphido Complexes
Organometallics, Vol. 17, No. 4, 1998 653
Sch em e 1a
Most of the new platinum complexes were formed
quantitatively from methoxide 10 and isolated in high
yields as orange, yellow, or white solids after recrystal-
lization (see the Experimental Section for details).
These complexes were also stable in solution. However,
reaction of 10 with diethylphosphine gave several
byproducts in addition to complex 8, which appears to
be unstable in solution and could not be obtained pure.
Similarly, the cyclohexylphosphido complex 4 could not
be purified, and the mixed arylalkylphosphido complex
9 decomposed in solution at room temperature. The
complexes were characterized by spectroscopic tech-
niques and elemental analyses. The 31P NMR spectra
are particularly diagnostic and are given in Table 1. The
1
cations 13 and 14 show J PH values much larger than
those in the free phosphine (380 and 404 Hz)7 and large
a
[Pt] ) Pt(dppe).
2
trans J P-P couplings (400 and 392 Hz) similar to that
in the cationic tertiary phosphine complex8 [Pt(dppe)-
(Me)(PPh3)]+ (380 Hz). In addition, complex 13 shows
a P-H stretch9 in the IR spectrum at 2416 cm-1 and a
PH2 signal in the 1H NMR spectrum (THF-d8) at δ 6.07.
The neutral compounds show characteristically small
Resu lts a n d Discu ssion
In connection with our studies of Pt-catalyzed hydro-
phosphination of acrylonitrile, we have previously com-
municated the synthesis of the terminal Pt(II) phosphi-
do complexes Pt(dppe)(Me)(PRR′) (R ) H; R′ ) Mes*
(1), R ) R′ ) Mes (5) (dppe ) Ph2PCH2CH2PPh2; Mes*
) 2,4,6-(t-Bu)3C6H2; Mes ) 2,4,6-Me3C6H2)) as shown
in Scheme 1.2a The two-step synthesis of 1 by complex-
ation and deprotonation of supermesitylphosphine has
been extended to mesitylphosphine to afford [Pt(dppe)-
(Me)(PH2Mes)][BF4] (14) and Pt(dppe)(Me)(PHMes) (2)
(Scheme 1). A more convenient synthetic method
involves treatment of the methoxide6 Pt(dppe)(Me)-
(OMe) (10) with a phosphine to provide methanol and
the phosphido complexes Pt(dppe)(Me)(PRR′) 1-9 (R )
H; R′ ) Mes (2), R′ ) Ph (3), R′ ) Cy (4); R ) R′ ) Ph
(6); R ) R′ ) Cy (7); R ) R′ ) Et (8); R ) Ph, R′ ) i-Bu
(9); Cy ) cyclo-C6H11, Scheme 1). This approach also
affords the arylthiolate and aryloxide complexes Pt-
(dppe)(Me)(EMes*) (E ) S (11); E ) O (12); Scheme 1).
Significantly, the reactions of 10 with phosphines and
the thiol proceed quantitatively with 1 equiv of added
HX; the consequences of the position of these equilibria
are considered in more detail below. Formation of
aryloxide complex 12 is somewhat less clean, but again
in this case the equilibrium qualitatively favors the
products.
2
1
trans J P-P and J Pt-P couplings to the phosphido
ligands, as previously observed for platinum5 and for
other metal phosphido complexes10 and rationalized in
terms of low s-character in the Pt-P bond. These
observations further suggest that the phosphido P is
pyramidal with a stereochemically active lone pair and
that a planar phosphido ligand involved in Pt-P
multiple bonding is not present.11
In addition, the primary phosphido complexes show
P-H stretches in the IR spectra from 2279 to 2232 cm-1
.
1
The P-H protons in these complexes give rise to H
NMR signals ranging from 5.07 to 3.06 ppm, which show
coupling to all three phosphorus nuclei and an ad-
ditional Pt-H coupling of ∼60 Hz. The one-bond P-H
couplings of ∼200 Hz are much smaller than those
observed in cations 13 and 14 and similar to those in
the free primary phosphines. Despite the bulky ligands
employed, no restricted rotation of the Mes or Mes*
1
groups is observed at room temperature by H NMR.
The new arylthiolate and aryloxide complexes 11 and
12 are spectroscopically similar to the previously re-
ported Pt(dppe)(Me)(SPh),8 Pt(dppe)(Me)(O-p-MeOC6H4),8
and Pt(dppe)(Me)(O-p-Tol).12
Appleton and Bennett8 have reported NMR data for
a series of Pt(dppe)(Me)(X) complexes and shown that
the trans influence of the X group correlates with the
Pt-P coupling of the dppe phosphorus trans to X. Using
this criterion, the terminal phosphido ligand in this
series has a large trans influence similar to that of an
alkyl group (Table 1). The relative trans influence of
(4) (a) Review: Carty, A. J .; MacLaughlin, S. A.; Nucciarone, D. In
Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis; Verkade,
J . G., Quin, L. D., Eds.; VCH: Deerfield Beach, FL, 1987; pp 559-
619. Selected recent references: (b) Sommovigo, M.; Pasquali, M.;
Leoni, P.; Englert, U. Inorg. Chem. 1994, 33, 2686-2688. (c) Leoni,
P.; Pasquali, M.; Sommovigo, M.; Albinati, A.; Lianza, F.; Pregosin, P.
S.; Ruegger, H. Organometallics 1994, 13, 4017-4025. (d) Sommovigo,
M.; Pasquali, M.; Marchetti, F.; Leoni, P.; Beringhelli, T. Inorg. Chem.
1994, 33, 2651-2656. (e) Kourkine, I. V.; Chapman, M. B.; Glueck, D.
S.; Eichele, K.; Wasylishen, R. E.; Yap, G. P. A.; Liable-Sands, L. M.;
Rheingold, A. L. Inorg. Chem. 1996, 35, 1478-1485. (f) Maslennikov,
S. V.; Glueck, D. S.; Yap, G. P. A.; Rheingold, A. L. Organometallics
1996, 15, 2483-2488. (g) Leoni, P.; Manetti, S.; Pasquali, M. Inorg.
Chem. 1995, 34, 749-752.
(7) 1J PH in metal-coordinated primary phosphines is usually larger
than in the free ligand, see: Kourkine, I. V.; Maslennikov, S. V.;
Ditchfield, R.; Glueck, D. S.; Yap, G. P. A.; Liable-Sands, L. M.;
Rheingold, A. L. Inorg. Chem. 1996, 35, 6708-6716 and references
therein, and also ref 10.
(5) See ref 2a and (a) Cecconi, F.; Ghilardi, C. A.; Midollini, S.;
Moneti, S.; Orlandini, A.; Scapacci, G. Inorg. Chim. Acta 1991, 189,
105-110. (b) Maassarani, F.; Davidson, M. F.; Wehman-Ooyevaar, I.
C. M.; Grove, D. M.; van Koten, M. A.; Smeets, W. J . J .; Spek, A. L.;
van Koten, G. Inorg. Chim. Acta 1995, 235, 327-338. (c) Handler, A.;
Peringer, P.; Muller, E. P. J . Chem. Soc., Dalton Trans. 1990, 3725-
3727. (d) David, M.-A.; Glueck, D. S.; Yap, G. P. A.; Rheingold, A. L.
Organometallics 1995, 14, 4040-4042. (e) Schafer, H.; Binder, D. Z.
Anorg. Allg. Chem. 1988, 560, 65-79. For related dihydrodiphosphete
and phospholene complexes, see: (f) Sillett, G.; Ricard, L.; Patois, C.;
Mathey, F. J . Am. Chem. Soc. 1992, 114, 9453-9457.
(8) Appleton, T. G.; Bennett, M. A. Inorg. Chem. 1978, 17, 738-
747.
(9) Nakamoto, K. Infrared Spectra of Inorganic and Coordination
Compounds, 4th ed.; J ohn Wiley and Sons: New York, 1986.
(10) Deeming, A. J .; Doherty, S.; Marshall, J . E.; Powell, J . L.;
Senior, A. M. J . Chem. Soc., Dalton Trans. 1993, 1093-1100.
(11) See refs 5 and 10. For somewhat different observations in a
square-planar Rh-phosphido complex, see: Dahlenburg, L.; Hock, N.;
Berke, H. Chem. Ber. 1988, 121, 2083-2093.
(6) Bryndza, H. E.; Calabrese, J . C.; Wreford, S. S. Organometallics
1984, 3, 1603-1604.
(12) Holland, P. L.; Andersen, R. A.; Bergman, R. G.; Huang, J .;
Nolan, S. P. J . Am. Chem. Soc. 1997, 119, 12800-12814.

654 Organometallics, Vol. 17, No. 4, 1998
Ta ble 1. 31P NMR Da ta for [P t(d p p e)Me(X)]n + (1-14)a ,b
Wicht et al.
X
δ(PR2)
J Pt-P (PR2)
J PP (trans)
J PP (cis)
δ(dppe) (trans)
δ(dppe) (cis)
J Pt-P (trans)
J Pt-P (cis)
PHMes* (1)c
PHMes (2)
PHPh (3)
-71.1
-88.4
-53.2
-27.1
-56.4
-7.8
863
806
819
131
137
143
137
172
144
108
130
134
12
46.5
49.9
49.8
51.3
45.1
47.8
46.0
48.1
48.0
36.0
45.9
35.2
54.7
57.6
47.4
48.7
51.0
49.6
34.0
45.0
39.3
47.1
45.3
37.4
46.2
47.0
50.8
52.4
1956
1978
2039
1870
1993
1932
1608
1643
1805
3356
3053
3914
2979
2956
1756
1813
1842
1842
1870
1825
1836
1915
1871
1852
1758
1848
1627
1724
PHCy (4)
846
PMes2 (5)
PPh2 (6)
1239
1039
948
911
946
18
22
5
PCy2 (7)d
-15.6
-6.1
PEt2 (8)
PPh(i-Bu) (9)
OMe (10)e
SMes* (11)
OMes* (12)
PH2Mes* (13)
PH2Mes (14)
-29.9
12
-66.8
-76.7
2700
2469
400
392
17
20
a
Temperature ) 22 °C. Chemical shifts in ppm, external ref 85% H3PO4, coupling constants in hertz. For 13 and 14, n ) 1; for 1-12,
b
c 1
n ) 0. Solvents: C6D6 for 1-9, 11, and 12; THF-d8 for 10 and 13; MeCN for 14. Trans and cis are with respect to the X group.
J
:
PH
213 (1), 199 (2), 201 (3), 183 (4), 380 (13), 404 (14). J PP(cis, dppe) ) 5. e Bryndza, H. E.; Calabrese, J . C.; Marsi, M.; Roe, D. C.; Tam, W.;
d
Bercaw, J . E. J . Am. Chem. Soc. 1986, 108, 4805-4813.
the phosphido groups falls in the order X ) PCy2 > PEt2
> PPh(i-Bu) > PHCy > PPh2 > PHMes* > PHMes >
PMes2 > PHPh. Values for the mono- and dialkylphos-
phido groups are substantially lower, while the remain-
ing mono- and diarylphosphides have similar trans
influences. In the series of primary arylphosphido
groups it appears that alkyl substitution slightly in-
creases the trans influence, consistent with the presence
of a more electron-rich aryl group. However, this effect
is reversed in the secondary arylphosphides. The
coordinated primary phosphines in 13 and 14 exhibit a
trans influence slightly less than that of PPh3 and
P(OPh)3 (J Pt-P ) 2743 and 2718 Hz).8 The aryloxide
and thiolate ligands are relatively low in the series and
follow the trans influence order PHMes* > SMes* >
OMes*. Comparison of the 31P NMR data for these
complexes shows that the SMes* group has a larger
F igu r e 1. ORTEP diagram of Pt(dppe)(Me)(PHMes*) (1)
showing 30% probability thermal ellipsoids. Hydrogen
atoms are omitted for clarity.
trans influence than the SPh ligand, but the opposite
trend is observed for the aryloxides; the J Pt-P(trans, dppe)
values are 3380 (SPh), 3053 (SMes*), 3840 (O-p-
MeOC6H4), 3811 (O-p-Tol), and 3914 (OMes*).
1
31P NMR data, these phosphido ligands have a similar
trans influence; the Pt-P(trans,dppe) bond lengths of 2.273-
(5) (1) and 2.287(2) Å (5‚THF) are the same within
experimental error. The Pt-P(dppe) bond lengths in 1
(2.273(5) Å trans to PHMes* and 2.273(4) trans to Me)
are the same, although the NMR data suggest Me has
a slightly larger trans influence in this case. The data
for 5‚THF are more consistent with the NMR results,
since the Pt-P(dppe) bond distance trans to PMes2
(2.287(2) Å) is significantly shorter than the one trans
to Me (2.308(2) Å). The Pt-P(dppe) bond length (trans
to Me) in 5‚THF (2.308(2) Å) is significantly longer than
that in 1 (2.273(4) Å); this may be a steric effect to avoid
destabilizing interactions of the PMes2 and dppe PPh2
groups. The Pt-C(Me) bond lengths in the two struc-
tures (2.13(2) (1) and 2.122(9) Å (5‚THF)) are the same
within experimental error.
X-r a y Cr ysta llogr a p h ic Stu dies. The crystal struc-
tures of phosphido complexes 1 and 5 (as a THF solvate)
have been determined (ORTEP diagrams are shown in
Figures 1 and 2). Table 2 contains details of the data
acquisition and solution and refinement of the struc-
tures, Table 3 contains selected bond lengths and angles,
and additional information is provided in the Experi-
mental Section and the Supporting Information.
Both complexes contain roughly square-planar Pt(II)
centers, with the usual constraints imposed by the
chelating dppe ligand. The dppe bite angle (85°) is the
same in the two cases, and other angles at Pt are close
to the ideal 90°, except for the Me-Pt-PHMes* angle
of 97.2(6)°, which is a bit bigger than the corresponding
93.0(2)° angle in the PMes2 case. This is balanced out
by the Me-Pt-P(dppe) angles of 89.2(6)° and 92.0(2)°,
respectively.
Consistent with the conclusions from the 31P NMR
data, the PMes2 phosphorus in 5 is pyramidal (the sum
of the angles at P is 333.9°; compare with 328.5° for a
tetrahedral and 360° for a planar atom). The P-H atom
in 1 was not located, but the Pt-P-C(Ar) angle of 116.8-
(6)° in this complex is similar to that in 5 and consistent
with a similar structure in the two cases. Similarly,
large angles have been observed in related metal-
The Pt-PMes2 bond distance (2.351(2) Å) is signifi-
cantly shorter than the Pt-PHMes* one (2.378(5) Å),
although the absolute difference is small. These bond
lengths are similar to those previously found for termi-
nal Pt(II) phosphido complexes.13 Consistent with the
(13) Compare Pt(PPh3)(CO)[Mes*PC(O)PMes*] (ref 5d), 2.321(7) and
2.337(7) Å, and the related dihydrodiphosphete complex Pt(PPh3)2-
[PPhCPh)CPhPPh] (ref 5f), 2.288(2) and 2.282(2) Å.

Terminal Platinum(II) Phosphido Complexes
Organometallics, Vol. 17, No. 4, 1998 655
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Ter m in a l P la tin u m P h osp h id o Com p lexes
1 a n d 5‚THF
1
5‚THF
Pt-PR2
2.378(5)
2.273(5)
2.273(4)
2.13(2)
2.351(2)
2.287(2)
2.308(2)
2.122(9)
1.846(8)
1.854(9)
Pt-P (dppe, trans)
Pt-P (dppe, cis)
Pt-Me
P-C(Ar)
1.90(2)
P-Pt-PR2
C-Pt-PR2
P-Pt-P
88.9(2)
97.2(6)
85.0(2)
89.2(6)
116.8(6)
90.04(8)
93.0(2)
84.80(8)
92.0(2)
116.2(3)
116.9(2)
100.8(4)
C-Pt-P
Pt-P-Ar
C(Ar)-P-C(Ar)
reported extensive solution NMR studies of the equi-
libria in eq 1.18 A brief summary of their results follows.
Pt(dppe)(Me)(OMe) + HX h
Pt(dppe)(Me)(X) + MeOH (1)
F igu r e 2. ORTEP diagram of Pt(dppe)(Me)(PMes2)‚THF
(5‚THF) showing 30% probability thermal ellipsoids. The
THF solvent molecule and hydrogen atoms are omitted for
clarity.
(1) For a range of X groups, this reaction was ap-
proximately thermoneutral; assuming that entropy ef-
fects can be neglected, the measured equilibrium con-
stant, along with literature values for the H-X and
H-OMe bond strengths, provides information on rela-
tive Pt-OMe and Pt-X bond strengths. (2) For several
weak acids HX, a remarkable correlation is found
between Pt-X and H-X bond strengths. (3) Some X
groups do not obey the correlation; in these cases (X )
SH, CN) the Pt-X bond is stronger than predicted, and
these observations were rationalized as involving either
π-bonding (to cyanide) or particularly favorable soft-
soft interactions with the second-row substituent sulfur.
As mentioned above, methoxide 10 is consumed on
reaction with 1 equiv of phosphine or thiol in the
formation of the phosphido complexes 1-9 and the
thiolate 11, as well as the known Pt(dppe)(Me)(SPh)8
(eq 1). Thus, the phosphido and thiolate groups do not
obey the Pt-X/H-X bond strength correlation previ-
ously established for bonds between the Pt(dppe)(Me)
fragment and the first-row atoms C, N, and O. As for
SH and CN, these Pt-X bonds to second-row atoms are
stronger than predicted.
Ta ble 2. Cr ysta llogr a p h ic Da ta for
P t(d p p e)(Me)(P HMes*) (1) a n d
P t(d p p e)(Me)(P Mes2) (5‚THF )
1
5‚THF
formula
fw
C
45H57P3Pt
C49H57OP3Pt
949.95
885.90
space group
a, Å
b, Å
P212121
P21/c
14.1610(10)
14.502(3)
22.634(6)
20.591(3)
11.295(3)
18.851(4)
99.23(1)
4328(2)
4
c, Å
â, deg
V, Å3
4648(2)
4
Z
cryst color, habit
D(calc), g cm-3
µ(Mo KR), cm-1
temp, K
2θ scan range, deg
data collected (h, k, l)
no. of rflns collected
yellow rod
1.265
31.48
298(2)
4.0-45.0
orange block
1.458
33.90
238(2)
4.0-45.0
-15, +15, +24 (22, -12, +19
4240
6978
4321
4.46
no. of indpt obsd rflns (4σ(Fo)) 3180
R(F), %a
4.78
11.80
R (wF2), %a
10.29
Information on the relative Pt-X bond strengths for
second-row substituents was obtained from 31P NMR
studies of the equilibria shown in eq 2 in THF solvent.
Quantity minimized ) R(wF2) ) ∑[w(Fo2 - Fc2)2]/∑[(wFo2)2]1/2
R ) ∑∆/∑(Fo), ∆ ) |(Fo - Fc)|.
;
a
phosphido complexes.14 Comparison of the structure of
5 with those of PHMes2 (sum of angles at P ) 323°)15
and PMes3 (sum of angles at P ) 329.1°)16 suggests that
the distortion of the PMes2 pyramid observed in 5‚THF
is mainly a consequence of steric effects. The P-C(Mes)
bond lengths in these three structures are not signifi-
cantly different, so coordination to Pt does not signifi-
cantly perturb the P-C bonds, as might be expected if
the phosphido ligand were acting as a π-acceptor.17
NMR a n d Ca lor im etr ic Stu d ies of P r oton -Tr a n s-
fer Rea ction s. Bryndza, Bercaw and co-workers have
Pt(dppe)(Me)(PRR′) + HX h
Pt(dppe)(Me)(X) + PHRR′ (2)
X ) phosphide or thiolate
Some such reactions were approximately thermoneu-
tral, allowing measurement of the equilibrium constants
at room temperature (Chart 1). Details of the experi-
mental measurements and estimation of error limits are
described in the Experimental Section. In most cases,
the equilibria could be approached from either side and
(14) For example, the sum of the bond angles at the di-tert-
butylphosphido group in CpRe(NO)(PPh3)[P(t-Bu)2] is 332.1°, see:
Buhro, W. E.; Zwick, B. D.; Georgiou, S.; Hutchinson, J . P.; Gladysz,
J . A. J . Am. Chem. Soc. 1988, 110, 2427-2439.
(17) (a) Dunne, B. J .; Morris, R. B.; Orpen, A. G. J . Chem. Soc.,
Dalton Trans. 1991, 653-661. (b) Orpen, A. G.; Connelly, N. G.
Organometallics 1990, 9, 1206-1210. (c) Reference 7.
(18) (a) Bryndza, H. E.; Fong, L. K.; Paciello, R. A.; Tam, W.; Bercaw,
J . E. J . Am. Chem. Soc. 1987, 109, 1444-1456. (b) Bryndza, H. E.;
Domaille, P. J .; Tam, W.; Fong, L. K.; Paciello, R. A.; Bercaw, J . E.
Polyhedron 1988, 7, 1441-1452.
(15) Bartlett, R. A.; Olmstead, M. M.; Power, P. P.; Sigel, G. A. Inorg.
Chem. 1987, 26, 1941-1946.
(16) Blount, J . F.; Maryanoff, C. A.; Mislow, K. Tetrahedron Lett.
1975, 11, 913-916.

656 Organometallics, Vol. 17, No. 4, 1998
Wicht et al.
mol),19 PH2Me (two separate studies have reported
either between 74 and 79.5 kcal/mol20 or 79.3 kcal/
mol),21 and PHMe2 (77.3 kcal/mol)21 are known. As-
suming that P-H bond strengths in mono- and diaryl-
phosphines follow trends similar to those observed for
E-H bonds19,22,23 (E ) C, H, N, O, S), it is likely that
they decrease in the order H-PHPh > H-PHMes >
H-PHMes* for the primary arylphosphines, and
H-PPh2 > H-PMes2 for the secondary ones. The
relative P-H bond strengths in alkyl-, aryl-, and mixed
alkylarylphosphines are difficult to predict, but the P-H
bonds in the primary phosphines are probably stronger
than those in the secondary phosphines in this series;
this assumption is supported by data for the meth-
ylphosphines and by analogy to amines. Similarly,
although S-H BDE’s in a variety of substituted thiophe-
nols have been reported,23 that for Mes*SH is unknown;
it is likely to be significantly lower than the PhSH value
of 79.1 kcal/mol.
Ch a r t 1. Equ ilibr iu m Con sta n ts for P r oton
Tr a n sfer Rea ction sa
THF, 22 °C, from 31P NMR.
a
Ta ble 4. F r ee En er gy a n d En th a lp y Ch a n ges
(k ca l/m ol) for th e Rea ction a
In general, the reaction of a secondary phosphido
complex [Pt]-PR2 ([Pt] ) Pt(dppe)(Me)) with a primary
phosphine to give a primary phosphido complex and a
secondary phosphine (eq 3) favors the products, despite
the energetic cost associated with making a secondary
P-H bond at the expense of a primary one. This
Pt(dppe)(Me)(PMes2) + HX h
Pt(dppe)(Me)(X) + PHMes2
X
NMRb
calorimetryc
PHMes*
PPh2
PHPh
-4.2(8)
-5.3(8)
-8.8(9)
-10.5(9)
-4.0(1)
-4.6(1)
-6.0(2)
-10.2(1)
Pt(dppe)(Me)(PR2) + PH2R′ h
Pt(dppe)(Me)(PHR′) + PHR2 (3)
SMes*
a
In THF. b 31P NMR, 22 °C. c Solution calorimetry, 30 °C.
suggests that these reactions are controlled by the
relative Pt-P bond strengths. These in turn clearly
depend on steric effects, with bonds to smaller phos-
phido ligands being thermodynamically favored. Rel-
evant cone angles reported by Tolman24 and others
include those for PH2Ph (101°), PH2Mes (110°),7 PH2-
Mes* (132°),25 PH2Cy (115°),26 PHPh2 (128°), PHCy2
(143°),27 and PHMes2 (170°).27 For primary arylphos-
phido complexes, the Pt-P bond strengths follow the
order Pt-PHPh > Pt-PHMes > Pt-PHMes*; a similar
gave reproducible results for the equilibrium constants.
Equilibria were established quickly, and a relatively
narrow concentration range was required for reasons
of solubility and 31P NMR detection limits. Measure-
ments involving alkylphosphido complexes 4 and 9 were
hampered by decomposition (see Experimental Section),
but the results obtained are internally consistent and
also agree with the results from complementary solution
calorimetry studies (see below).
In other cases, the position of the equilibria was far
to one side, preventing direct NMR measurement of Keq.
Estimates of the equilibrium constants for such “ir-
reversible” reactions were obtained from the products
of individual equilibrium constants in a ladder (Chart
1). Such transformations were also studied directly by
solution calorimetry in THF at 30 °C starting with the
dimesitylphosphido complex 5. Comparison of the
results obtained with these complementary techniques
(Table 4) shows relatively good agreement, despite the
slightly different temperatures employed, and is con-
sidered in detail below. Although the reactions de-
scribed above reach equilibrium in minutes to hours,
the aryloxide complex 12 reacted much more slowly. For
example, 12 did not react with PHMes2 in THF at room
temperature in 1 day; after 6 days at 50 °C, 12 was
consumed and 5 formed. However, under these condi-
tions, some decomposition occurs. Complex 12 also
reacted quantitatively with PH2Mes* and Mes*SH upon
heating under similar conditions to give 1 and 11, again
with some decomposition.
steric trend is seen for diarylphosphides (Pt-PPh2
>
Pt-PMes2). In these cases, the predicted decrease in
P-H bond energies with increasing substitution on the
aryl group(s) is apparently outweighed by effects on the
Pt-P bonds. Similarly, dicyclohexylphosphido complex
7 is consumed on reaction with diethylphosphine to give
mainly diethylphosphido complex 8 plus decomposition
products; this reaction is presumably controlled mostly
by steric effects.
(19) Berkowitz, J .; Ellison, G. B.; Gutman, D. J . Phys. Chem. 1994,
98, 2744-2765.
(20) Berger, S.; Brauman, J . I. J . Am. Chem. Soc. 1992, 114, 4737-
4743.
(21) McKean, D. C.; Torto, I.; Morrisson, A. R. J . Phys. Chem. 1982,
86, 307-309.
(22) (a) McMillen, D. F.; Golden, D. M. Annu. Rev. Phys. Chem. 1982,
33, 493-532. (b) Bordwell, F. G.; Cheng, J .-P.; J i, G.-Z.; Satish, A. V.;
Zhang, X. J . Am. Chem. Soc. 1991, 113, 9790-9795. (c) Bordwell, F.
G.; Zhang, X.-M.; Cheng, J .-P. J . Org. Chem. 1993, 58, 6410-6416.
(d) Bordwell, F. G.; Zhang, X. M. J . Phys. Org. Chem. 1995, 8, 529-
535. (e) Bordwell, F. G.; Liu, W.-Z. J . Am. Chem. Soc. 1996, 118,
10819-10823.
(23) Bordwell, F. G.; Zhang, X.-M.; Satish, A. V.; Cheng, J .-P. J . Am.
Chem. Soc. 1994, 116, 6605-6610.
(24) Tolman, C. A. Chem. Rev. (Washington, D.C.) 1977, 77, 313-
Further quantitative analysis of these results requires
several assumptions, some necessary because of the
limited data available on organophosphorus thermo-
chemistry. Very few P-H bond strengths have been
reported; in fact, only those for PH3 (83.9 ( 0.5 kcal/
348.
(25) Kourkine, I. V.; Chapman, M. B.; Glueck, D. S.; Eichele, K.;
Wasylishen, R. E.; Yap, G. P. A.; Liable-Sands, L. M.; Rheingold, A. L.
Inorg. Chem. 1996, 35, 1478-1485.
(26) Brown, T. L. Inorg. Chem. 1992, 31, 1286-1294.
(27) McFarlane, W.; Regius, C. T. Polyhedron 1997, 16, 1855-1861.

Terminal Platinum(II) Phosphido Complexes
Organometallics, Vol. 17, No. 4, 1998 657
In proton-transfer reactions involving the secondary
phosphines PHPh2, PHPh(i-Bu), and PHCy2, increasing
aryl substitution on the Pt-phosphido group is ener-
getically preferred. This trend could be due to hard-
soft considerations (soft arylphosphides are expected to
bind more strongly to soft Pt(II) than hard alkylphos-
phides). Differences in relative Pt-P bond strengths
could also be described by an electrostatic model in
which phenyl substituents on phosphorus are preferred
because they stabilize partial negative charge on the
phosphido ligand.12 However, differences in P-H bond
strengths surely also contribute to the values of these
equilibrium constants and may be more important than
Pt-P bonding. The position of the equilibria between
2, 4, and the phosphines PH2Mes and PH2Cy also
appears to reflect these factors, given the similar steric
demands of these ligands, while the PHPh substituent
may be favored in comparison to both of them for steric
reasons.
Related experimental observations suggest that Pt-S
bond strengths in this system are stronger than the
analogous Pt-P ones. Treatment of the primary
arylphosphido complexes 1 and 3 with stoichiometric
amounts of the arylthiols Mes*SH and PhSH led to
quantitative formation of the thiolates 11 and Pt(dppe)-
(Me)(SPh), respectively, along with PH2Mes* and PH2-
Ph. Even on addition of excess phosphine to these
thiolate complexes, formation of 1 and 3 was not
observed. However, an equilibrium between 3, 11, PH2-
Ph, and Mes*SH could be accessed from either side
(Chart 1). The reaction of 3 with PhSH (eq 4) allows
estimation of relative Pt-SPh and Pt-PHPh bond
strengths in this system. Given that the PhS-H BDE
measurements is for the bulkiest ligands (conversion of
dimesitylphosphido complex 5 to PHMes* complex 1 or
SMes* complex 11), and the smaller PHPh and PPh2
complexes are thermodynamically favored more than
would be expected from the reaction enthalpy results;
the discrepancy is largest for the smallest ligand, PHPh.
The order of magnitude of the presumed entropic effects
is similar to that observed by Bryndza and co-workers18
in the equilibrium between RuCp*(PMe3)2(OH), diphen-
ylamine, RuCp*(PMe3)2(NPh2), and water, where the
entropic contribution to the equilibrium free energy at
25 °C was -1.8 kcal/mol.
As described above, the Pt-PHMes* bond is slightly
longer than the Pt-PMes2 one in the solid state. For
Pt(II) complexes of tertiary phosphines, 1J Pt-P correlates
with the Pt-P distance,29 and the same effect is
observed here (1J Pt-P ) 863 Hz for 1 and 1239 Hz for
5). Because the appropriate P-H BDE’s are not known,
however, our data do not provide information on relative
Pt-P bond strengths in these compounds for possible
correlation with the bond lengths.30
Con clu sion s
Data for the series of phosphido complexes 1-9 show
that the terminal phosphido ligand contains a pyramidal
phosphorus, that the Pt-P bond has low s character,
and that the phosphido ligand has a large trans influ-
ence, comparable to that of an alkyl group; the strongest
trans-influence ligands in the phosphido series are those
with electron-releasing alkyl groups. Complementary
NMR and calorimetry studies of proton-transfer equi-
libria suggest that the Pt-P bonds in 1-9 are weaker
than analogous Pt-S bonds and also provide some
information on entropic contributions to the equilibria.
Stronger Pt-P bonds are formed by smaller ligands. For
ligands of comparable steric bulk, in equilibria between
alkyl- and arylphosphido complexes and the analogous
phosphines, arylphosphides are energetically favored;
this effect may reflect changes in the Pt-P bond as well
as P-H BDE differences. Because current knowledge
of organophosphorus thermochemistry is limited, more
work in this field is required to separate these effects.
Pt(dppe)(Me)(PHPh) + PhSH h
Pt(dppe)(Me)(SPh) + PH2Ph (5)
is 79.1 kcal/mol and assuming conservative upper
bounds for the energy of this reaction (-4 kcal/mol) and
for the H-PHPh BDE (82 kcal/mol) suggests that the
Pt-SPh bond is at least 1 kcal/mol stronger than the
Pt-PHPh one. As above, this difference can be ratio-
nalized either on hard-soft or on electrostatic grounds
(the more electronegative S can stabilize negative
charge better than P).
Exp er im en ta l Section
A similar comparison of Pt-O and Pt-X bond
strengths is complicated by the sluggish reactivity of
aryloxide complex 12, which precluded measurements
of equilibrium constants involving this compound. Com-
plex 12 reacts with PH2Mes* and Mes*SH to afford 1
and 11 respectively, suggesting that for these ligands
of comparable steric demand, Pt-S and Pt-P bonds are
stronger than the Pt-O one. However, the E-H bonds
involved in these reactions may have equal or greater
importance, since the H-OMes* BDE of 82.3 kcal/mol28
is likely to be significantly greater than the analogous
P-H and S-H bond strengths.
Since the NMR equilibrium studies measure the free
energy of reaction and the calorimetric ones only the
reaction enthalpy, differences between the two sets of
results evident in Table 4 may be ascribed to the entropy
term. The best agreement between the two types of
Gen er a l. All manipulations were carried out under a
nitrogen atmosphere using either standard Schlenk apparatus
or a glovebox. Solvents were distilled from sodium benzophe-
none (toluene, THF, ether, petroleum ether) or from CaH2
(methylene chloride) and stored under nitrogen. NMR spectra
were obtained at the following frequencies (MHz) 31P, 121.4;
13C, 75.4; 1H, 299.9 and are referenced either via internal
solvent peaks to TMS or to an external standard of 85% H3-
PO4. Coupling constants are reported in hertz. IR spectra
were recorded in KBr pellets, and peaks are reported in cm-1
.
Elemental analyses were done by Schwarzkopf Labs, Wood-
side, NY. The following were prepared by literature proce-
dures: PH2Mes*,31 Mes*SH,32 PH2Mes,15 PHMes2,15 Pt(dppe)-
(29) Mather, G. G.; Pidcock, A.; Rapsey, G. J . N. J . Chem. Soc.,
Dalton Trans. 1973, 2095-2099.
(30) Ernst, R. D.; Freeman, J . W.; Stahl, L.; Wilson, D. R.; Arif, A.
M.; Nuber, B.; Ziegler, M. L. J . Am. Chem. Soc. 1995, 117, 5075-5081.
(31) Cowley, A. H.; Norman, N. C.; Pakulski, M. Inorg. Synth. 1990,
27, 235-240.
(28) Bordwell, F. G.; Zhang, X. M. J . Phys. Org. Chem. 1995, 8, 529-
535.
(32) Davis, F. A.; J enkins, R. H., J r.; Rizvi, S. Q. A.; Yocklovich, S.
G. J . Org. Chem. 1981, 46, 3467-3474.

658 Organometallics, Vol. 17, No. 4, 1998
Wicht et al.
(Me)(Cl),33 Pt(dppe)(Me)(OMe),6 and Pt(dppe)(Me)(SPh).8
PH(Ph)(i-Bu) was a gift from Cytec Canada and was prepared
by Hillhouse’s method.1a,b
perature over 2 days. These crystals were washed with
petroleum ether and vacuum-dried to give 254 mg of a light
yellow solid (71% yield). A second recrystallization from
benzene/THF/petroleum ether at room temperature gave
analytically pure light yellow crystals. Alternatively, addition
of LiN(SiMe3)2 to a THF solution of cation 14 also gave 2,
according to 31P NMR.
[P t(d p p e)(Me)(P H2Mes*)][BF 4] (13). To a solution of Pt-
(dppe)(Me)(Cl) (505 mg, 0.78 mmol) in CH2Cl2 (15 mL) was
added a slurry of AgBF4 (151 mg, 0.78 mmol) in CH3CN (3
mL). Immediate reaction occurred, as indicated by the forma-
tion of a white precipitate. PH2Mes* (239 mg, 0.86 mmol)
dissolved in CH2Cl2 (3 mL) was then added to the solution.
The reaction mixture was allowed to stir overnight in the dark
at room temperature. The yellow solution was filtered, and
the solvent was removed in vacuo to give a pale yellow solid.
The solid was dissolved in a minimal amount of THF, and
petroleum ether was added to the THF solution. Cooling of
this solution to -25 °C yielded 702 mg (92%) of pale yellow
[Pt(dppe)(Me)(PH2Mes*)][BF4].
1H NMR (∼5:1 C6D6/THF-d8): δ 7.7-7.5 (br, 8H, Ar), 7.11-
1
3
7.08 (m, 12H, Ar), 6.72 (2H, Mes), 3.77 (ddd, J PH ) 199, J PH
) 13, 8, 2J Pt-H ) 64, 1H, PH), 2.50 (6H, o-Me), 2.12 (3H, p-Me),
2.1-1.8 (br, 4H, CH2), 0.59 (m, J Pt-H ) 68, 3H, Pt-Me). Since
the complex is sparingly soluble, the 13C NMR spectrum was
not recorded. IR: 2915, 2279, 1434, 1102, 1028, 998, 878, 852,
823, 744, 692, 531, 485. Anal. Calcd for C36H39P3Pt: C, 56.91;
H, 5.18. Found: C, 56.78; H, 5.06.
P t (d p p e)(Me)(P HP h ) (3). Pt(dppe)(Me)(OMe) (100 mg,
0.156 mmol) was suspended in C6D6 (1 mL), and phenylphos-
phine (17 µL, 0.16 mmol) was added by syringe. The suspen-
sion turned red at the solid-solution interface on addition then
1H NMR (THF-d8): δ 7.77-7.52 (br m, 22H, Ar), 6.07 (d,
1J PH ) 380, 2H, PH2), 2.84-2.74 (m, 4H, CH2), 1.45 (18H,
2
o-CMe3), 1.28 (9H, p-CMe3), 0.28-0.21 (m, J Pt-H ) 60, 3H,
1
yellow as all the solid dissolved. The 31P and H NMR spectra
Pt-Me). 13C{1H} NMR (THF-d8): δ 156.5 (quat Ar), 154.0
(quat Ar), 134.6-134.2 (m, Ar), 132.9 (Ar), 130.7-130.2 (m,
Ar), 129.8 (quat Ar), 129.1 (quat Ar), 128.3 (quat Ar), 124.4
(d, 3J C-P ) 10, Ar), 39.1 (o-CMe3), 36.0 (p-CMe3), 33.6 (o-CMe3),
showed complete conversion to 3. The solution was decanted,
filtered through Celite, and crystallized by addition of petro-
leum ether. White solid (65 mg, 58%) formed over 2 days at
room temperature; it was washed with petroleum ether and
dried in a vacuum. A second recrystallization from THF/
petroleum ether at -20 °C gave yellow crystals for analysis.
1H NMR (C6D6): δ 7.70-7.64 (m, 6H, Ar), 7.55-7.49 (m,
31.4 (p-CMe3), 30.8-29.1 (m, dppe CH2), 2.5 (dm, 2J C-P(trans)
72, J C-Pt ) 510, Pt-Me). IR: 2416 (PH), 1054 (BF4). Anal.
Calcd for C45H58BF4P3Pt: C, 55.51; H, 6.00. Found: C, 55.29;
H, 6.19.
)
1
1
3
4H, Ar), 7.06-6.94 (m, 15H, Ar), 4.42 (ddd, J PH ) 201, J PH
[P t(d p p e)(Me)(P H2Mes)][BF 4] (14) was prepared simi-
larly and identified by 31P NMR (Table 1) but not isolated or
further characterized.
2
) 15, 6, J Pt-H ) 57, 1H, PH), 1.90-1.72 (m, 4H, CH2), 1.28
(m, J Pt-H ) 67, 3H, Pt-Me). 13C{1H} NMR (C6D6): δ 145.3-
145.0 (m, Ar), 135.5 (dd, J ) 3, 14, Ar), 134.4-133.7 (m, Ar),
132.0 (d, J ) 44, Ar), 130.9 (Ar), 129.0 (m, Ar), 127.5 (d, J )
5, Ar), 125.1 (Ar), 31.5-30.8 (m, CH2), 1.2 (dm, J PC ) 86, Pt-
Me). IR: 3050, 2919, 2873, 2256, 1579, 1482, 1435, 1411, 1308,
1185, 1159, 1102, 1068, 1026, 998, 877, 820, 742, 692, 652,
531, 484. Anal. Calcd for C33H33P3Pt: C, 55.23; H, 4.64.
Found: C, 54.96; H, 4.75.
P t(d p p e)(Me)(P HMes*) (1). To a solution of [Pt(dppe)-
(Me)(PH2Mes*)][BF4] (13) (133 mg, 0.14 mmol) in THF (8 mL)
was added LiN(SiMe3)2 (23 mg, 0.14 mmol) dissolved in THF
(3 mL). The reaction mixture immediately turned bright
yellow. The solvent was removed in vacuo, and the yellow
residue was washed with 3 1 mL portions of petroleum ether.
The solid was dried under vacuum to yield 112 mg (93%) of
yellow Pt(dppe)(Me)(PHMes*). Alternatively, to a solution of
Pt(dppe)(Me)(OMe) (200 mg, 0.31 mmol) dissolved in THF (10
mL) was added a solution of PH2Mes* (96 mg, 0.34 mmol)
dissolved in THF (5 mL). The solution immediately became
bright yellow and was allowed to stir at room temperature for
1 h. The solvent was removed under vacuum and the yellow
residue was washed with 3 1 mL portions of petroleum ether.
The solid was redissolved in a minimal amount of THF and
filtered. Petroleum ether was added to the THF solution, and
cooling of the solution to -25 °C yielded 144 mg (50%) of
product. Crystals for X-ray crystallography were grown from
THF/petroleum ether at -25 °C.
P t(d p p e)(Me)(P HCy) (4). PH2Cy (19 mg, 0.16 mmol) was
added to a slurry of Pt(dppe)(Me)(OMe) (100 mg, 0.16 mmol)
in C6D6 (1 mL). The reaction mixture immediately became a
homogeneous yellow solution, and NMR confirmed formation
of 4 and methanol, along with unidentified impurities. The
solution was filtered through Celite, layered with petroleum
ether, and cooled to -25 °C to give a light yellow powder, 45
mg (40%). Recrystallization from THF/petroleum ether or
toluene/ether was not successful in purifying this material.
1H NMR (C6D6): δ 7.77-7.71 (m, 4H, Ph), 7.63-7.57 (m,
4H, Ph), 7.10-7.01 (m, 12H, Ph), 3.06 (dddd, J PH ) 6, 18, 183,
J HH ) 9, J Pt-H ) 54, 1H, PH), 2.42-2.38 (m, 2H), 2.04-1.78
(m, 4H), 1.76-1.0 (m, 9H, Cy), 1.32 (m, J Pt-H ) 55, 3H, Pt-
Me). 13C{1H} NMR (C6D6): δ 134.4-134.3 (m, Ph), 134.0-
133.7 (m, Ph), 133.6-133.3 (m, Ph), 132.9-132.3 (m, Ph), 130.8
(Ph), 129.2-128.8 (m, Ph), 34.1 (m), 31.6-30.9 (m), 29.9-29.5
(m), 29.3-29.2 (m), 27.2, -3.2 (dd, J PC ) 8, 88, J Pt-C ) 583,
Pt-Me). IR: 3050, 2916, 2842, 2232, 1483, 1434, 1102, 819,
745, 693, 531, 484.
1H NMR (C6D6): δ 7.77 (br, 4H, Ar), 7.71 (2H, Ar), 7.48 (br,
4H, Ar), 7.17-7.08 (m, 6H, Ar), 6.97-6.94 (m, 6H, Ar), 5.07
1
3
3
2
(ddd, J P-H ) 213, J P-H ) 9, J P-H ) 6, J Pt-H ) 66, 1H, PH),
1.96 (9H, p-CMe3), 1.90-1.76 (br m, 4H, CH2), 1.39 (18H,
o-CMe3), 0.56-0.50 (m, J Pt-H ) 68, 3H, Pt-Me). 13C{1H}
2
NMR (C6D6): δ 154.8 (quat Ar), 146.2 (quat Ar), 138.8-138.6
(m, quat Ar), 138.1-137.9 (m, quat Ar), 134.4-134.1 (br m,
Ar), 133.9 (Ar), 133.8 (Ar), 132.6-131.8 (m, Ar), 130.8 (Ar),
129.0 (Ar), 128.9 (Ar), 121.2 (Ar), 39.3 (o-CMe3), 35.3 (p-CMe3),
P t(d p p e)(Me)(P Mes2) (5). PHMes2 (49 mg, 0.18 mmol)
dissolved in THF (2 mL) was added to a solution of Pt(dppe)-
(Me)(OMe) (115 mg, 0.18 mmol) dissolved in THF (10 mL).
The reaction mixture immediately became bright orange. The
solvent was removed under vacuum, and the orange solid was
washed 3 times with 1 mL portions of petroleum ether. The
solid was redissolved in a minimal amount of THF and filtered.
Petroleum ether was added to the THF solution, and the
solution was cooled to -25 °C to yield 133 mg (84%) of orange
Pt(dppe)(Me)(PMes2), isolated as a THF solvate. Successive
recrystallization from THF/petroleum ether as described yielded
X-ray quality crystals.
4
33.9 (d, J CP ) 7, o-CMe3), 32.1 (p-CMe3), 29.9-28.9 (m, dppe
CH2), 0.8 (dd, 2J CP(trans) ) 83, 2J CP(cis) ) 7, 1J CPt ) 600, Me). IR:
2265 (PH). Anal. Calcd for C45H57P3Pt: C, 61.00; H, 6.50.
Found: C, 60.64; H, 6.67.
P t(d p p e)(Me)(P HMes) (2). Pt(dppe)(Me)(OMe) (300 mg,
0.47 mmol) was suspended in THF (10 mL), and mesitylphos-
phine (90 mg, 0.59 mmol) was added by syringe. On addition,
the suspended solid immediately solubilized to give a yellow
solution, which was filtered through Celite and layered with
petroleum ether. Light yellow crystals formed at room tem-
1H NMR (C6D6): δ 7.66-7.58 (br m, 8H, Ar), 7.03-6.91 (m,
12H, Ar), 6.71 (4H, Ar), 2.70 (12H, o-Me), 2.13 (6H, p-Me),
1.83-1.78 (br m, 4H, CH2), 0.90-0.83 (m, 2J Pt-H ) 69, 3H, Me).
(33) Clark, H. C.; J ablonski, C. R. Inorg. Chem. 1975, 14, 1518-
1526.

Terminal Platinum(II) Phosphido Complexes
Organometallics, Vol. 17, No. 4, 1998 659
2
1
13C{1H} NMR (C6D6): δ 143.8 (d, J CP ) 13, quat Ar), 141.0
127.2 (m, Ar), 125.0-124.9 (m, Ar), 37.2 (d, J CP ) 22, CH2-
2
4
(quat Ar), 140.5 (quat Ar), 133.9 (br, Ar), 133.8 (Ar), 130.9 (Ar),
130.2 (Ar), 129.2 (Ar), 129.1 (Ar), 128.2 (Ar), 128.0 (Ar), 28.4-
27.9 (m, dppe CH2), 26.1 (d, 3J CP ) 14, o-Me), 21.4 (p-Me), -0.3
(dd, J CP(trans) ) 85, J CP(cis) ) 5, Me, Pt satellites were not
resolved). IR: 2923, 1952, 1892, 1814, 1598, 1430, 1184, 1058,
999, 873, 843, 741, 693, 639, 531. Anal. Calcd for C45H49P3-
Pt: C, 61.56; H, 5.63. Found: C, 61.43; H, 5.95.
CH), 31.5-30.8 (m, dppe CH2), 29.8 (dd, J CP ) 13, J CP ) 7,
CH2CH), 29.6-29.1 (m, dppe, CH2), 25.2-25.1 (CHMe2), 3.3
(dm, J C-P(trans) ) 87, J C-Pt ) 603, Pt-Me). Anal. Calcd for
37H41P3Pt: C, 57.43; H, 5.35. Found: C, 56.95; H, 5.41.
2
1
2
2
C
P t(d p p e)(Me)(SMes*) (11). A solid mixture of Pt(dppe)-
(Me)(OMe) (100 mg, 0.156 mmol) and Mes*SH (60 mg, 0.22
mmol) was dissolved in a mixture of 12 mL of THF and 3 mL
of petroleum ether. The resulting light orange solution was
filtered through Celite, and the solvents were removed under
vacuum from the filtrate. Recrystallization from THF/
petroleum ether at -20 °C gave 100 mg of a beige solid (72%
yield). A second recrystallization from THF/petroleum ether
gave analytically pure white needles.
1H NMR (C6D6): δ 8.06-8.00 (m, 4H, Ar), 7.74 (2H, Ar),
7.50-7.42 (m, 4H, Ar), 7.22-7.08 (m, 6H, Ar), 6.95-6.92 (m,
6H, Ar), 2.11 (18H, o-t-Bu), 1.9-1.7 (br m, 4H, CH2), 1.40 (9H,
P t(d p p e)(Me)(P P h 2) (6). A solution of diphenylphosphine
(30 mg, 0.16 mmol) in 1 mL of THF was added to a slurry of
Pt(dppe)(Me)(OMe) (88 mg, 0.14 mmol) in 2 mL of THF. The
mixture immediately became lemon-yellow and homogeneous.
The solution was filtered through Celite, layered with petro-
leum ether, and cooled to -20 °C to give yellow powder, which
was washed with petroleum ether and dried in a vacuum (84
mg, 76% yield). A second recrystallization from THF/petro-
leum ether at -20 °C gave yellow needles, which rapidly
desolvated to an analytically pure yellow powder.
1H NMR (C6D6): δ 7.77-7.52 (m, 12H), 7.07-6.95 (m, 18H),
1.88-1.77 (m, 4H, CH2), 1.22 (m, 3H, J Pt-H ) 68, Pt-Me). 13C-
{1H} NMR (C6D6): δ 136.3 (dd, J ) 4, 18, Ar), 134.7-133.8
(m, Ar), 132.4 (d, J ) 10, Ar), 131.1-130.6 (m, Ar), 129.3-
129.1 (m, Ar), 127.8-127.5 (m, Ar), 125.6 (Ar), 30.6-28.4 (m,
CH2, dppe), 4.9-3.7 (m, Pt-Me. Due to the low solubility of
this complex in C6D6, no Pt satellites were observed for this
peak). IR: 3050, 1578, 1482, 1435, 1186, 1102, 1025, 998, 877,
819, 744, 693, 531, 483. Anal. Calcd for C39H37P3Pt: C, 59.01;
H, 4.71. Found: C, 58.74; H, 4.52.
3
3
1
p-t-Bu), 0.32 (dd, J PH ) 7.2, J PH ) 5.4, J Pt-H ) 62, 3H, Me).
13C{1H} NMR (C6D6): δ 154.5 (d, J ) 2.3, o-Ar), 145.8 (p-Ar),
138.5 (d, J ) 4.5, Ar), 138.3 (d, J ) 4.5, Ar), 134.3 (d, J )
11.9, Ar), 133.9 (d, J ) 11.4, Ar), 132.6 (d, J ) 41, Ar), 131.0
(d, J ) 9.1, Ar), 130.6 (d, J ) 51, Ar), 129.0 (d, J ) 4.1, Ar),
128.9 (d, J ) 4.5, Ar), 121.8 (m-Ar), 39.6 (CMe3), 35.3 (CMe3),
32.9 (CMe3), 32.3 (CMe3), 31.6 (m, CH2), 27.6 (m, CH2), 4.8 (dd,
2J PC ) 86, J PC ) 7.2, J PtC ) 570, Pt-Me). IR: 3052, 2947,
1589, 1483, 1435, 1385, 1352, 1239, 1208, 1103, 1041, 876, 818,
745, 692, 532, 487. Anal. Calcd for C45H56SP2Pt: C, 60.99;
H, 6.38. Found: C, 60.64; H, 6.46.
2
1
P t(d p p e)(Me)(P Cy2) (7). A solution of dicyclohexylphos-
phine (55 mg, 0.28 mmol) in 1 mL of THF was added to a slurry
of Pt(dppe)(Me)(OMe) (160 mg, 0.25 mmol) in 2 mL of THF.
The mixture immediately became orange and homogeneous.
The solution was filtered through Celite, layered with petro-
leum ether, and cooled to -20 °C to give yellow chunks, which
were washed with petroleum ether and dried in a vacuum.
Several crops of a yellow crystalline solid were obtained;
although a yellow oil initially forms, crystals grow slowly over
several days (total 145 mg, 72% yield). Two more recrystal-
lizations from THF/petroleum ether at -20 °C gave yellow
needles, which rapidly desolvated to analytically pure yellow
powder.
P t(d p p e)(Me)(OMes*) (12). Addition of Mes*OH (170 mg,
0.65 mmol) to a slurry of Pt(dppe)(Me)(OMe) (200 mg, 0.31
mmol) in 8 mL of THF gave a light yellow solution with a little
suspended white solid. After 3 days, 31P NMR showed that
12 was the major species present, with several minor impuri-
ties. The reaction mixture was filtered through Celite. The
solvent was removed from the light yellow filtrate, and the
residue was recrystallized from THF/petroleum ether at -20
°C to give a yellow solid, which was washed with petroleum
ether and dried under vacuum to give 222 mg (82% yield) of a
free-flowing yellow powder. White crystals suitable for el-
emental analysis were obtained by slow evaporation of a C6D6
solution.
1H NMR (C6D6): δ 7.81-7.74 (m, 4H, Ar), 7.63-7.57 (m,
4H, Ar), 7.16-7.02 (m, 12H, Ar), 2.6-2.1 (br, 4H), 2.0-1.7 (br,
11H), 1.6-1.2 (br, 11H), 1.46 (m, J Pt-H ) 71, 3H, Pt-Me). 13C-
{1H} NMR (C6D6): δ 134.8-134.6 (m, Ar), 134.0-133.7 (m,
Ar), 133.2-133.0 (m, Ar), 132.6-132.5 (m, Ar), 130.8-130.5
(m, Ar), 129.2-129.0 (m, Ar), 128.5 (obscured by C6D6, Ar),
1H NMR (C6D6): δ 7.86-7.80 (m, 3H, Ar), 7.60-7.42 (m,
6H, Ar), 7.16-6.99 (m, 13H, Ar), 1.86 (18H, o-t-Bu), 1.8-1.6
3
3
(br m, 4H, CH2), 1.49 (9H, p-t-Bu), 0.46 (dd, J PH ) 3, J PH
)
7.8, J Pt-H ) 51, 3H, Me). 13C{1H} NMR (C6D6): δ 139.9 (d, J
) 1.4, Ar), 136.4 (d, J ) 1.9, Ar), 134.5 (d, J ) 11.6, Ar), 133.9
(d, J ) 2.8, Ar), 133.7 (d, J ) 11.2, Ar), 133.4 (d, J ) 36.7, Ar),
131.3 (d, J ) 2.3, Ar), 131.0 (d, J ) 1.9, Ar), 130.3 (d, J )
61.4, Ar), 129.1 (d, J ) 8.4, Ar), 129.0 (d, J ) 10.7, Ar), 121.6
(Ar), 37.0 (o-CMe3), 34.9 (p-CMe3), 32.9 (p-CMe3), 32.8 (o-CMe3),
1
35.9-35.5 (m, Cy/dppe), 28.0 (Cy), -1.0 (d, J PC ) 91, J Pt-C
)
629, Pt-Me). IR: 2920, 2844, 1435, 1102, 1065, 819, 747, 698,
531. Anal. Calcd for C39H49P3Pt: C, 58.12; H, 6.14. Found:
C, 58.05; H, 6.27.
2
30.9-30.1 (m, CH2), 27.1-26.6 (m, CH2), 10.4 (dd, J PC ) 90,
P t(d p p e)(Me)(P Et2) (8) was generated as the major com-
ponent of a mixture from Pt(dppe)(Me)(OMe) and PHEt2 as
described above in C6D6 or THF and characterized by 31P NMR
(Table 1). This material could not be isolated in pure form.
P t (d p p e)(Me)[P (P h )(i-Bu )] (9). PH(Ph)(i-Bu) (187 mg,
1.13 mmol) was added to a stirring slurry of Pt(dppe)(Me)-
(OMe) (480 mg, 0.750 mmol) in THF (10 mL). The reaction
mixture immediately became a bright yellow homogeneous
solution and was concentrated in vacuo to approximately 5 mL.
Petroleum ether (5 mL) was added, and the solution was cooled
to -25 °C overnight to give 462 mg (80%) of a bright yellow
product. 1H NMR (THF-d8): δ 7.82-7.76 (m, 2H, Ar), 7.67-
7.61 (m, 3H, Ar), 7.39-7.21 (br m, 15H, Ar), 6.92-6.78 (m,
5H, Ar), 2.32-2.20 (m, 4H, dppe CH2), 1.80-1.74 (m, 2H, CH2-
2J PC ) 7.5, Pt-Me, Pt satellites were not observed due to low
concentration of the sample). IR: 2945, 1436, 1418, 1253,
1104, 878, 745, 692, 532, 492. Anal. Calcd for C45H56OP2Pt:
C, 62.12; H, 6.50. Found: C, 62.00; H, 6.25.
X-r a y Cr ysta llogr a p h ic Stu d ies. For 1, crystal, data
collection, and refinement parameters are given in Table 2. A
suitable crystal was selected and mounted on the tip of a glass
fiber with epoxy cement. The unit-cell parameters were
obtained by the least-squares refinement of the angular
settings of 24 reflections (20° e 2θ e 25°).
The systematic absences in the diffraction data are uniquely
consistent for orthorhombic space group P212121. The struc-
ture was solved using direct methods, completed by subsequent
difference Fourier syntheses, and refined by full-matrix least-
squares procedures. An empirical absorption correction was
applied, based on a Fourier series in the polar angles of the
incident and diffracted beam paths, and was used to model
an absorption surface for the difference between the observed
and calculated structure factors.34 The absolute configuration
3
CH), 1.42-1.30 (m, 1H, CH2CH), 0.72 (d, J HH ) 6, 6H,
2
CHMe2), 0.47-0.40 (m, J Pt-H ) 69, 3H, Pt-Me). 13C{1H}
1
NMR (C6D6): δ 149.6 (apparent dt, J CP ) 34, J Pt-C ) 5, quat
Ar), 134.8 (Ar), 134.7 (Ar), 134.5 (Ar), 134.5-134.2 (m, Ar),
1
134.1-133.7 (m, Ar), 132.5 (d, J CP ) 41, quat Ar), 132.2 (d,
1J CP ) 41, quat Ar), 130.85 (Ar), 129.2-128.8 (m, Ar), 127.3-

660 Organometallics, Vol. 17, No. 4, 1998
Wicht et al.
of the structure has been determined (Flack parameter )
-0.02(2)). All non-hydrogen atoms were refined with aniso-
tropic displacement coefficients. The hydrogen atom on the
phosphido phosphorus atom could not be located from the
difference map and was ignored. All other hydrogen atoms
were treated as idealized contributions.
Solu tion Ca lor im etr ic Stu d ies. Only materials of high
purity as indicated by NMR spectroscopy were used in the
calorimetric experiments. Monitoring of the reactions of 5 in
THF by 31P NMR showed clean, rapid, and quantitative
formation of the products, usually within minutes, under the
experimental calorimetric conditions. Calorimetric measure-
ments were performed using a Calvet calorimeter (Setaram
C-80) which was periodically calibrated using the TRIS reac-
tion35 or the enthalpy of solution of KCl in water.36 This
calorimeter has been previously described,37 and typical
procedures are described below. Experimental enthalpy data
are reported with 95% confidence limits.
For 5‚THF, the procedure was similar (Table 2), except the
systematic absences in the diffraction data are uniquely
consistent for the reported space group P21/c. A semiempirical
absorption correction was applied to the data set. A tetrahy-
drofuran solvent molecule was located in the asymmetric unit.
Two peaks remaining in the difference map (max ) 2.7 e Å-3
)
were located 1.1 Å from the platinum atom and were consid-
ered as noise peaks. All non-hydrogen atoms were refined with
anisotropic displacement coefficients. Hydrogen atoms were
treated as idealized contributions.
All software and sources of the scattering factors are
contained in the SHELXTL (5.03) program library (G. Sheld-
rick, Siemens XRD, Madison, WI).
In a representative experimental trial, the mixing vessels
of the Setaram C-80 were cleaned, dried in an oven maintained
at 120 °C, and then taken into the glovebox. A sample of Pt-
(dppe)(Me)(PMes2) (5, 21.0 mg, 23.9 µmol) was charged into
the lower vessel, which was closed and sealed with 1.5 mL of
mercury. A solution of Mes*SH (11.1 mg, 39.9 µmol) in THF
(4.0 mL) was added, and the remainder of the cell was
assembled, removed from the glovebox, and inserted into the
calorimeter. The reference vessel was loaded in an identical
fashion with the exception that no platinum complex was
added to the lower vessel. After the calorimeter had reached
thermal equilibrium at 30.0 °C (ca. 2 h), it was inverted,
thereby allowing the reactants to mix. The reaction was
considered complete after the calorimeter had once again
reached thermal equilibrium (ca. 2 h). Control reactions with
Hg and protonating reagents show no reaction. The enthalpy
of proton exchange (-10.2 ( 0.1 kcal/mol) listed in Table 4
represents the average of at least three individual calorimetric
determinations with all species in solution. The enthalpy of
solution of Pt(dppe)(Me)(PMes2) (-3.2 ( 0.1 kcal/mol) in neat
THF was determined using an identical methodology.
NMR Equ ilibr iu m Stu d ies. Typ ica l P r oced u r e. At
ambient temperature, to a solution of Pt(dppe)(Me)(PHPh) (3,
22 mg, 0.031 mmol) in ∼0.8 mL of THF in an NMR tube was
added PH2Mes (20 mg, 0.13 mmol) via syringe. Integrated
intensities from the 31P NMR spectra of the dppe region were
used to calculate the relative amounts of 3 and the product 2
present, while the amounts of the phosphines PH2Ph and PH2-
Mes were calculated from the mass balance; these quantities
were used to obtain the equilibrium constant. The phosphines
were also observed by 31P NMR, but integration of these
resonances was usually unreliable due to the large excess of
phosphine present. Generally, equilibria could be approached
from either side, giving consistent results. Equilibria were
usually reached soon after mixing, and the position of equi-
librium did not change over a period of days, although minor
decomposition was frequently observed on standing for an
extended period. Control experiments using known amounts
of 2 and 3 (or the other complexes as appropriate) showed that
the 31P NMR integrals gave a reliable measure of the ratios of
Pt complexes present, and controls using an internal standard
(PPh3O) showed that the reactions were quantitative. The
equilibrium constants listed in Chart 1 are the average of at
least three independent determinations. Error limits have
been estimated from the deviation of these measurements, as
well as from estimates of errors in weighing and integration.
The equilibrium constants involving phenyl(isobutyl)phosphido
complex 9 are the least reliable quantitatively, since some
decomposition in these reaction mixtures was consistently
observed; a similar problem was observed with cyclohexyl-
phosphido complex 4.
Ack n ow led gm en t. We thank Dartmouth College,
the donors of the Petroleum Research Fund, adminis-
tered by the American Chemical Society, the NSF
CAREER program, the Exxon Education Foundation,
and DuPont for support. B.M.L. acknowledges an NSF-
REU fellowship. We thank J ohnson Matthey/Alfa/Aesar
for loans of platinum salts, Dr. J ohn Hillhouse (Cytec
Canada) for gifts of phosphines, and Drs. Henry Brynd-
za, Robert G. Bergman, and Patrick Holland for helpful
discussions and sharing results before publication. The
work in New Orleans was supported by NSF Grant No.
CHE-963116.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and structure refinement, atomic coordinates, bond
lengths and angles, anisotropic displacement coefficients, and
H-atom coordinates for 1 and 5‚THF (19 pages). Ordering
information is given on any current masthead page.
(34) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158-166.
(35) Ojelund, G.; Wadso¨, I. Acta Chem. Scand. 1968, 22, 1691-1699.
(36) Kilday, M. V. J . Res. Natl. Bur. Stand. (U.S.) 1980, 85, 467-
481.
(37) (a) Nolan, S. P.; Hoff, C. D.; Landrum, J . T. J . Organomet.
Chem. 1985, 282, 357-362. (b) Nolan, S. P.; Lopez de la Vega, R.; Hoff,
C. D. Inorg. Chem. 1986, 25, 4446-4448.
OM9708891