Synthetic, Structural, and Solution Calorimetric Studies of Pt(CH3)2(PP) Complexes

Article abstract of DOI:10.1021/om990962i

Reaction enthalpies of the complex (COD)PtMe₂ (1; COD = η⁴-1,5-cyclooctadiene) with an extensive series of bidentate phosphines (dpype, dppf, diop, dppe, dppb, dppp, dpmcb, depe, dmpe, dcpce) have been measured by solution calorimetry. The relative stabilities of the resulting complexes PtMe₂(PP) are determined by a combination of the donor and bite angle/ steric properties of the bidentate phosphine ligand. In general, good a donor ligands with small bite angles result in more thermodynamically stable complexes. Additionally, the molecular structures of 1, Pt(Me)₂(pype) (2), Pt(Me)₂(dppf) (3), Pt(Me)₂(diop) (4), Pt(Me)₂-(dppe) (6), Pt(Me)₂(dpmcb) (9), and Pt(Me)₂(Et₂dppp) (13) have been determined by single-crystal X-ray diffraction. No correlation between the thermochemical results and the structural parameters, e.g, M-P distance (as observed in other systems), is apparent in this class of complexes.

Full text of DOI:10.1021/om990962i

Organometallics 2000, 19, 1427-1433
1427
Syn th etic, Str u ctu r a l, a n d Solu tion Ca lor im etr ic Stu d ies
of P t(CH3)2(P P ) Com p lexes†
Dale C. Smith, J r., Christopher M. Haar, Edwin D. Stevens, and
Steven P. Nolan*
Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148
William J . Marshall and Kenneth G. Moloy
Central Research and Development Department, E. I. du Pont de Nemours & Co., Inc.,
Experimental Station, P.O. Box 80328, Wilmington, Delaware 19880-0328
Received December 6, 1999
Reaction enthalpies of the complex (COD)PtMe2 (1; COD ) η4-1,5-cyclooctadiene) with an
extensive series of bidentate phosphines (dpype, dppf, diop, dppe, dppb, dppp, dpmcb, depe,
dmpe, dcpce) have been measured by solution calorimetry. The relative stabilities of the
resulting complexes PtMe2(PP) are determined by a combination of the donor and bite angle/
steric properties of the bidentate phosphine ligand. In general, good σ donor ligands with
small bite angles result in more thermodynamically stable complexes. Additionally, the
molecular structures of 1, Pt(Me)2(pype) (2), Pt(Me)2(dppf) (3), Pt(Me)2(diop) (4), Pt(Me)2-
(dppe) (6), Pt(Me)2(dpmcb) (9), and Pt(Me)2(Et2dppp) (13) have been determined by single-
crystal X-ray diffraction. No correlation between the thermochemical results and the
structural parameters, e.g, M-P distance (as observed in other systems), is apparent in
this class of complexes.
In tr od u ction
factors: a steric factor, typically Tolman’s cone angle
for the ligand involved, and an electronic factor which
Thermochemical measurements have been applied for
some time to the quantitative assessment of metal-
ligand interactions in organometallic systems.1 We have
been investigating the steric and electronic contribu-
tions present in tertiary phosphine and arsine based
organoruthenium,2 organorhodium,3 organoplatinum,4
and organoiron5 systems by means of solution calorim-
etry. We present in this paper the first thermochemical
studies on a series of organoplatinum bis(phosphine)
complexes formed by the general reaction given in
Scheme 1. The complexes of the type (COD)PtRX (COD
) η4-1,5-cycloocadiene; R, X ) aryl, alkyl, halide) are
well-studied.6 The substitutional lability of COD renders
these compounds convenient sources of organoplat-
inum fragments for coordination to phosphine ligands.
Calorimetric measurements on related Pt(Me2)(L)2
(L ) monodentate phosphine) complexes4 have been
explained in terms of contributions from two separate
is highly dependent on the ligand.7 In light of these
(2) For organoruthenium systems see: (a) Smith, D. C., J r.; Haar,
C. M.; Luo, L.; Li, C.; Cucullu, M. E.; Malher, C. H.; Nolan, S. P.;
Marshall, W. J .; J ones, N. L.; Fagan, P. J . Organometallics 1999, 18,
2357-2361. (b) Li, C.; Serron, S.; Nolan, S. P. Organometallics 1996,
15, 4020-4029. (c) Serron, S. A.; Luo, L.; Li, C.; Cucullu, M. E.; Nolan,
S. P. Organometallics 1995, 14, 5290-5297. (d) Serron, S. A.; Nolan,
S. P. Organometallics 1995, 14, 4611-4616. (e) Luo, L.; Li, C.; Cucullu,
M. E.; Nolan, S. P. Organometallics 1995, 14, 1333-1338. (f) Cucullu,
M. E.; Luo, L.; Nolan, S. P.; Fagan, P. J .; J ones, N. L.; Calabrese, J . C.
Organometallics 1995, 14, 289-296. (g) Luo, L.; Zhu, N.; Zhu, N. J .;
Stevens, E. D.; Nolan, S. P.; Fagan, P. J . Organometallics 1994, 13,
669-675. (h) Li, C.; Cucullu, M. E.; McIntyre, R. A.; Stevens, E. D.;
Nolan, S. P. Organometallics 1994, 13, 3621-3627. (i) Luo, L.; Nolan,
S. P. Organometallics 1994, 13, 4781-4786. (j) Luo, L.; Fagan, P. J .;
Nolan, S. P. Organometallics 1993, 12, 4305-4311. (k) Nolan, S. P.;
Martin, K. L.; Stevens, E. D.; Fagan, P. J . Organometallics 1992, 11,
3947-3953.
(3) For organoiron systems see: (a) Li, C.; Stevens, E. D.; Nolan, S.
P. Organometallics 1995, 14, 3791-3797. (b) Li, C.; Nolan, S. P.;
Organometallics 1995, 14, 1327-1331. (c) Luo, L.; Nolan, S. P. Inorg.
Chem. 1993, 32, 2410-2415. (d) Luo, L.; Nolan, S. P. Organometallics
1992, 11, 3947-3951.
(4) Haar, C. M.; Nolan, S. N.; Marshall, W. J .; Moloy, K. G.; Prock,
A.; Giering, W. P. Organometallics 1999, 18, 474-479.
(5) For organorhodium systems see: (a) Haar, C. M.; Huang, J .;
Nolan, S. P. Organometallics 1998, 17, 5018-5024. (b) Huang, J .; Haar,
C. M.; Nolan, S. P.; Marshall, W. J .; Moloy, K. G. J . Am. Chem. Soc.
1998, 120, 7806-7815. (c) Serron, S.; Nolan, S. P.; Moloy, K. G.
Organometallics 1996, 15, 534-539.
(6) See for example: Anderson, G. K. In Comprehensive Organo-
metallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon: Oxford, U.K., 1995; Vol. 9, pp 431-531.
(7) (a) Tolman, C. A. Chem. Rev. 1977, 77, 313-348. (b) Manzer, L.
E.; Tolman, C. A. J . Am. Chem. Soc. 1975, 97, 1955-1956. (c) Tolman,
C. A.; Reutter, D. W.; Seidel, W. C. J . Organomet. Chem. 1976, 117,
C30-C33.
* To whom correspondence should be addressed. E-mail: snolan@
uno.edu.
† Contribution No. 7838 from Du Pont.
(1) (a) Nolan, S. P. Bonding Energetics of Organometallic Com-
pounds. In Encyclopedia of Inorganic Chemistry; King, R. B., Ed.;
Wiley: New York, 1994. (b) Hoff, C. D. Prog. Inorg. Chem. 1992, 40,
503-561. (c) Martinho Simo˜es, J . A.; Beauchamp, J . L. Chem. Rev.
1990, 90, 629-688. (d) Marks, T. J ., Ed. Bonding Energetics In
Organotransition Metal Compounds; ACS Symposium Series 428;
American Chemical Society: Washington, DC, 1990. (e) Marks, T. J .,
Ed. Bonding Energetics In Organotransition Metal Compounds. Poly-
hedron Symp. Print 1988, 7. (f) Skinner, H. A.; Connor, J . A. In
Molecular Structure and Energetics; Liebman, J . F., Greenberg, A.,
Eds.; VCH: New York, 1987; Vol. 2, Chapter 6.
10.1021/om990962i CCC: $19.00 © 2000 American Chemical Society
Publication on Web 03/10/2000

1428 Organometallics, Vol. 19, No. 7, 2000
Smith et al.
Sch em e 1
Ta ble 1. En th a lp ies of Su bstitu tion in THF a t 30
previous results on monodentate ligands, and the
importance of chelating phosphorus ligands in coordina-
tion/organometallic chemistry and catalysis,8 we decided
to conduct a thermochemical and structural study on
the related bis(phosphine) PtMe2 complexes. In this
report, thermochemical measurements are compared to
determine some of the possible factors affecting the
structures and relative stability of the Pt(Me)2(PP)
complexes.
°C for P t(Me)2(COD) + P ∼P f P t(Me)2(P ∼P ) + COD
a
a
(P∼P)
∆Hrxn
(P∼P)
∆Hrxn
complex ligand (kcal/mol)
complex ligand (kcal/mol)
2
3
4
5
6
7
dpype
dppf
(+)-diop -25.7(1)
dppb
dppe
dppp
-21.7(1)
-24.3(2)
8
9
10
11
12
dppv
dpmcb -31.4(3)
depe
dmpe
dcpe
-30.7(3)
-35.6(3)
-36.4(2)
-37.2(2)
-26.4(3)
-29.9(1)
-30.5(4)
a
Enthalpy values are provided with 95% confidence limits.
Resu lts a n d Discu ssion
are singlets with 195Pt satellites (1J PtP, ) 1779-2180
Hz, within the typical range for cis-bis(phosphine)
species).4 It is interesting to note that the 31P{1H}
Or ga n op la t in u m Syn t h eses. All organoplatinum
complexes were prepared in a similar manner from
PtMe2(COD) (1) using a stoichiometric amount of the
appropriate bis(phosphine) ligand in either CH2Cl2 or
THF according to Scheme 1. In all cases, the reaction
proceeded rapidly, except in the case of 13, which
required a slightly elevated temperature. All new
compounds were found to be mononuclear complexes
and are readily soluble in both THF and CH2Cl2.
NMR Sp ectr oscop y. Included in the Experimental
1
chemical shifts, J PtP values, and the Pt-Cmethyl chemi-
cal shifts are highly dependent on the identity of the
2
chelating bis(phosphine) ligand. However, the J PtH
coupling constants are insensitive to variation of the bis-
(phosphine) ligand. These observations are consistent
with 31P{1H} and 1H NMR spectroscopy studies on
previously reported Pt(Me)2(PR3)2 complexes.4
Str u ctu r e Deter m in a tion a n d Cr ysta llogr a p h ic
Da ta . In an effort to clarify the relationship between
phosphine ligand steric and electronic properties and
the thermochemistry (see below), single-crystal X-ray
diffraction analyses of cis-(COD)PtMe2 1, and the bis-
(phosphine) adducts 2-4, 6, 9, and 13 were performed.
Crystallographic information for all seven compounds,
including cell dimensions and details of the data col-
lection, are given in Table 2. The ORTEP diagrams of
1-4, 6, 9, and 13 are given in Figures 1-7. In their
gross structural features, all cis-PtMe2(PP) complexes
1
Section are the 31P{1H} and H NMR data for all new
compounds investigated in the present study. The
multinuclear NMR data are typical of square-planar
platinum with a cis arrangement of phosphine and
1
methyl ligands. The Pt-Cmethyl resonances appear in H
spectra as phosphorus-coupled multiplets with 195Pt
satellites (2J PtH ) 69-72 Hz), while 31P{1H} resonances
(8) Dierkes, P.; van Leeuwen, P. W. M. N. J . Chem. Soc., Dalton
Trans. 1999, 1519-1529.

Pt(CH3)2(PP) Complexes
Organometallics, Vol. 19, No. 7, 2000 1429
Ta ble 2. Selected Bon d Len gth s a n d An gles in th e
In n er Coor d in a tion Sp h er e of th e Com p lexes
a
P t(Me)2(L)2
P-Pt-P,
trans-C-Pt-P,
complex
Pt-P, Å
Pt-C, Å
deg
deg
2
2.241(1)
2.238(1)
2.2916(8)
2.2954(9)
2.2743(5)
2.2954(5)
2.246(2)
2.254(2)
2.261(1)
2.265(1)
2.102(5)
2.114(5)
2.094(3)
2.102(4)
2.1009(18)
2.1066(19)
2.108(7)
2.112(6)
2.109(5)
2.106(6)
84.73(5)
100.77(3)
98.022(18)
86.01(7)
95.39(5)
95.82(4)
177.2(2)
176.4(2)
3
4
173.42(11)
168.95(10)
173.18(7)
170.96(7)
177.5(2)
176.6(2)
174.8(2)
174.7(2)
172.99(11)
174.51(13)
6
9
13
2.2562(13) 2.156(4)
2.2620(12) 2.258(4)
F igu r e 3. ORTEP diagram of 3 with ellipsoids drawn at
50% probability.
a
Complete structural details are provided as Supporting In-
formation.
F igu r e 1. ORTEP diagram of 1 with ellipsoids drawn at
50% probability.
F igu r e 4. ORTEP diagram of 4 with ellipsoids drawn at
50% probability.
F igu r e 2. ORTEP diagram of 2 with ellipsoids drawn at
50% probability.
are typical for square-planar Pt(II) complexes. Average
Pt-P bond lengths range from a maximum of 2.294 Å
in 3 to a minimum of 2.240 Å in 2, as shown in Table 2.
All complexes investigated are rigorously square planar
at platinum. Average Pt-Cmethyl distances span a range
from 2.098 Å (3) to 2.207 Å (13) and appear somewhat
less sensitive to the identity of the phosphine ligand;
however, the responses of P(1)-Pt-P(2) and C(1)-Pt-
C(2) are opposite, as expected. For comparison, the Pt-
Cmethyl bond distances in the structure of PtMe2(COD)
(1) are 2.056(6) and 2.069(6) Å, and these distances are
shorter on average than most of the bis(phosphine)
F igu r e 5. ORTEP diagram of 6 with ellipsoids drawn at
50% probability.
complexes. The P(1)-Pt-P(2) angle generally opens up
with increasing chelate “bite” of the bis(phosphine)
ligand accompanied by an increase in the Pt-P bond
distance.
Solu tion Ca lor im etr y. As determined by both 1H
and 31P{1H} NMR spectroscopy, the reaction illustrated
by Scheme 1 is notably fast, clean, and quantitative for
a wide variety of chelating bis(phosphine) ligands at 30
°C. Of the 13 ligands examined for the reaction in

1430 Organometallics, Vol. 19, No. 7, 2000
Smith et al.
more thermodynamically stable complexes while the
isosteric ligand dpype, which also possesses a five-
membered ring, gives the lowest enthalpy of the series
due to its weak donor properties. A similar enthalpic
trend was observed for the related PtMe2(PR3)2 com-
plexes with monodentate phosphine ligands.4 Other
trends are not well-defined and will require further
investigation. For instance, it is notable that the two
ligands with the largest bite angles (dppf ≈ (+)-diop ≈
100°) give reaction enthalpies 5-10 kcal/mol lower than
the five- and six-membered-ring chelates. However, no
relationship is found between the enthalpies of reaction
and the average Pt-P bond lengths or P(1)-Pt-P(2)
angles of the complexes, and no clear correlation be-
tween the C-Pt-C angle and the enthalpy is evident.
Other relationships between the enthalpy of reaction
and the metrical parameters are not straightforward,
suggesting that other factors (e.g., steric, electronic,
reorganization, or solvation) are operative and influence
the structural chemistry of this system.17
F igu r e 6. ORTEP diagram of 9 with ellipsoids drawn at
50% probability.
Comparison between model bis(monodentate) and
chelating ligand complexes can afford a gauge of the
“strain energy” present in chelating systems.2a In this
platinum system, such a comparison involving (diphenyl-
phosphino)ethylene and (+)-diop with the Me2Pt(PPh2-
Me)24 complex (as a model system with no strain energy;
since there is no metallacyclic structure, there is no
strain) is possible. Any difference in enthalpy of reaction
is then attributed to the strain energy in the metalla-
cyclic complex. Observed differences between (diphenyl-
phosphino)ethylene (-29.9 kcal/mol) and 2 equiv of
PPh2Me (-29.0 kcal/mol) is very small, indicating
almost no strain in the metallacycle. On the other hand,
(+)-diop (-25.7 kcal/mol) shows signs of strain on the
order of 3 kcal/mol. This strain energy is of the same
order as that found for seven-membered metallacycles
in the (PP)Mo(CO)4 systems investigated by Hoff and
co-workers.1b
F igu r e 7. ORTEP diagram of 13 with ellipsoids drawn at
50% probability.
Scheme 1, forming the complexes PtMe2(dpype) (2),
PtMe2(dppf) (3),9 PtMe2((+)-diop) (4), PtMe2(dppb) (5),10,11
PtMe2(dppe) (6),10-12 PtMe2(dppp) (7),10,11 PtMe2(dppv)
(8), PtMe2(dpmcb) (9), PtMe2(depe) (10),13 PtMe2(dmpe)
(11),14,15 and PtMe2(dcpe) (12),16 only Et2dppp failed to
react under these conditions, requiring 24 h at 40 °C to
give complete ligand substitution to form 13. All com-
plexes in this series possess identical coordination
environments at platinum. Therefore, any variation in
structures and the enthalpy of reaction should be due
chiefly to the steric/bite angle and electronic effects of
the phosphine ligand. As shown in Table 1, the enthal-
pies of substitution range from -21.7(1) kcal/mol for 2
to -37.2(2) kcal/mol for 12. The overall order of stability
is as follows: dpype < dppf < (+)-diop < dppb < dppe
< dppp < dppv < dpmcb < depe <dmpe < dcpe. As the
Tolman electronic scale7 predicts, the relative stabilities
of the resulting complexes are strongly influenced by
the electronic donor properties of the bidentate phos-
phine ligand if no larger steric factors are present. For
example, better σ donors, e.g., dmpe, depe and dcpe, give
The present enthalpy data allow for comparison to
prior thermochemical studies for reactions of a common
chelating bis(phosphine) ligand in the Cp′Ru(PP)Cl2g,h
(Cp′ ) Cp* ) η5-C5Me5 or Cp ) η5-C5H5) and (PP)Ru-
18
(allyl)2 (allyl ) 2-methylpropenyl) systems. The rela-
tive order of stability of the resulting complexes in the
Cp*Ru(PP)Cl,2g CpRu(PP)Cl,2h and (PP)Ru(allyl)2 sys-
18
tems follow a similar trend as for the PtMe2(PP) system.
A good correlation (R ) 0.96) is found for the plot of
∆Hrxn versus ∆Hrxn for a series of common PP ligand
substitution reactions in the CpRu(PP)Cl and PtMe2(PP)
systems, and the plot is presented in Figure 8. Similarly,
for reactions of the same PP ligand in the Cp*(PP)RuCl
and PtMe2(PP) systems a good correlation (R ) 0.97) is
found and is illustrated in Figure 9. However, compari-
son of ∆Hrxn versus ∆Hrxn of the PtMe2(PP) and the
(PP)Ru(allyl)2 systems only yields a fair correlation (R
) 0.91), as illustrated in Figure 10; the reason for the
weaker correlation may be due to the steric and elec-
tronic differences attributed to the ancillary ligands.
Another informative system for comparison is the (PP)-
(9) Thorn, D. L.; Fultz, W. C. J . Phys. Chem. 1989, 93, 1234-1243.
(10) Appleton, T. G.; Bennett, M. A.; Tomkins, I. B. J . Chem. Soc.,
Dalton Trans. 1976, 5, 439-446.
(11) Hietkamp, S. J . Organomet. Chem. 1979, 169, 107-113.
(12) Hooton, K. A.; Stufkens, D. J .; Vrieze, K. J . Chem. Soc. A 1970,
1896-1900.
(13) Holtcamp, M. W.; Labinger, J . A.; Bercaw, J . E. Inorg. Chim.
Acta 1997, 265, 117-125.
(14) Alcock, N. W.; Brown, J . M.; MacLean, T. D. J . Chem. Soc.,
Chem. Commun. 1984, 24, 1689-1690.
(15) Gregory, P. R.; White, S.; Roddick, D. M. Organometallics 1998,
17, 4493-4499.
(17) Huang, J .; Haar, C. H.; Nolan, S. P.; Marshall, W. J .; Moloy,
K. G. J . Am. Chem. Soc. 1998, 120, 7806-7815.
(18) Smith, D. C., J r.; Cadoret, J .; Stevens, E. D.; Nolan, S. P.
Manuscript submitted for publication.
(16) Fischer, R. A.; Kaesz, H. D.; Khan, S. I.; Muller, H. J . Inorg.
Chem. 1990, 29, 1601-1602.

Pt(CH3)2(PP) Complexes
Organometallics, Vol. 19, No. 7, 2000 1431
F igu r e 8. Comparison between enthalpies of ligand
substitution in the CpRu(PP)Cl system and PtMe2(PP)
systems. R ) 0.96; slope ) 1.1 ( 0.2.
F igu r e 11. Comparison between enthalpies of ligand
substitution in the (PP)Fe(CO)3 system and PtMe2(PP)
systems. R ) 0.96; slope ) 1.2 ( 0.2.
(PP)Fe(CO)3 and PtMe2(PP) systems is presented in
Figure 11. Importantly, the thermochemical compari-
sons between these organoplatinum, organoruthenium,
and organoiron systems illustrate that common elec-
tronic and steric factors of the bis(phosphine) ligands
affect the thermodynamic stability of metallacyclic
complexes.
Con clu sion
Single-crystal X-ray diffraction studies of several
PtMe2(PP) systems have been performed in order to
correlate structural parameters regarding the chelate
bite of the bis(phosphine) ligand. Among this series of
complexes, the reaction enthalpies correlate well with
established donor properties of phosphine ligands.4,7 The
relative stabilities of the resulting complexes are strongly
influenced by the electronic donor properties of the
bidentate phosphine ligand with better σ donors, result-
ing in more thermodynamically stable complexes. How-
ever, other relationships between the enthalpy of reac-
tion and resulting metrical parameters are not forthright,
suggesting that other factors influence the structural
chemistry of this system.17
F igu r e 9. Comparison between enthalpies of ligand
substitution in the Cp*Ru(PP)Cl system and PtMe2(PP)
systems. R ) 0.97; slope ) 1.0 ( 0.1.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations involving
organoplatinum complexes were performed under an inert
atmosphere of argon, using standard high-vacuum or Schlenk
techniques, or in a MBraun glovebox containing less than 1
ppm of oxygen and water. Only materials of high purity as
indicated by NMR spectroscopy were used in the calorimetric
experiments. Multinuclear NMR spectra were recorded using
a Gemini 300 MHz or Oxford 400 MHz spectrometer. Calori-
metric measurements were performed using a Calvet calorim-
eter (Setaram C-80) which was periodically calibrated using
the TRIS reaction20 or the enthalpy of solution of KCl in
water.21 The calorimeter has been previously described.22,23 The
experimental enthalpies for these two standard reactions
compared very closely to literature values. All phosphine
F igu r e 10. Comparison between enthalpies of ligand
substitution in the (PP)Ru(allyl)2 system and PtMe2(PP)
systems. R ) 0.91; slope ) 1.4 ( 0.3.
Fe(CO)3 system,19 since the chelating phosphine ligands
should have similar steric environments about the metal
center. As expected, the relative orders of stability of
the resulting complexes of both PtMe2(PP) and (PP)Fe-
(CO)3 systems are similar. For reactions of common PP
ligands in the (PP)Fe(CO)3 and PtMe2(PP) systems a
good correlation (R ) 0.96) is found. This linear rela-
tionship between ∆Hrxn for PP ligand substitution in the
(20) Ojelund, G.; Wadso¨, I. Acta Chem. Scand. 1968, 22, 1691-1699.
(21) Kilday, M. V. J . Res. Natl. Bur. Stand. (U.S.) 1980, 85, 467-
481.
(22) Nolan, S. P.; Hoff, C. D.; Landrum, J . T. J . Organomet. Chem.
1985, 282, 357-362.
(23) Nolan, S. P.; Lopez de la Vega, R.; Hoff, C. D. Inorg. Chem.
1986, 25, 4446-4448.
(19) Li, C.; Cucullu, M. E.; McIntyre, R. A.; Stevens, E. D.; Nolan,
S. P. Organometallics 1994, 13, 3221-3627.

1432 Organometallics, Vol. 19, No. 7, 2000
Smith et al.
Ta ble 3. Cr ysta llogr a p h ic Da ta for th e Com p lexes P t(Me)2(L∼L)
1
2
3
4
6
9‚2.5THF
13
formula
fw
cryst syst
space group
a, Å
b, Å
c, Å
R, Å
C
10H18Pt
C20H26N4P2Pt
579.49
monoclinic
P21/c
14.317(4)
8.981(1)
16.274(5)
90
C36H34FeP2 Pt
779.51
triclinic
P1h
9.3697(12)
9.3757(12)
18.135(2)
92.089(3)
104.105(3)
103.106(3)
0.036
C33H38O2P2 Pt
723.66
C28H28P2Pt
621.57
monoclinic
P21/n
8.521(5)
14.612(2)
19.895(2)
90
C43H56P2PtO2.5
869.96
orthorhombic
Pbcn
24.914(1)
13.850(1)
22.694(1)
90
90
90
0.020
0.020
C33H40P2Pt
693.68
monoclinic
P21/n
11.1982(7)
20.1754(13)
13.9257(9)
90
112.011(2)
90
333.33
monoclinic
P21/c
8.134 (2)
18.105(4)
7.3117 (19)
90
115.708(5)
90
0.041
orthorhombic
P212121
10.9150(7)
16.2899(11)
17.0011(11)
90
90
90
0.021
0.031
â, deg
γ, deg
Ra
94.24(3)
90
0.029
90.67(3)
90
0.035
0.029
0.060
a
Rw
0.114
0.025
0.081
0.028
goodness of fit
0.91
0.90
1.03
0.74
0.87
0.55
0.90
a
2
R ) ∑(||Fo| - |Fc||)/∑|Fo|; Rw ) ∑w(|Fo| - |Fc|)2/∑w|Fo| .
ligands used in these studies were purchased from Aldrich or
Strem or prepared by the literature methods.24,25
2.15-2.25 (m, 4 H, PCH2), 6.10-7.20 (m, 16 H, pyrl). 31P{1H}
NMR (CD2Cl2): δ 109.71 (s, pseudo d, J PtP ) 2180 Hz). Anal.
Calcd for C28H28P2Pt: C, 54.11; H, 4.54. Found: C, 54.19; H,
4.44.
NMR Titr a tion s. Prior to every set of calorimetric experi-
ments involving a new ligand, a precisely measured amount
((0.1 mg) of (COD)PtMe2 was placed in an NMR tube along
with CD2Cl2 and >1.2 equiv of ligand. Both 1H and 31P{1H}
NMR spectra were measured within 1 h of mixing; both
indicated the reactions were clean and quantitative. These
conditions are necessary for accurate and meaningful calori-
metric results and were satisfied for all reactions investigated.
Solu tion Ca lor im etr y. In a representative experimental
trial, the mixing vessels of the Setaram C-80 were cleaned,
dried in an oven maintained at 145 °C, and then taken into
the glovebox. A sample of (COD)PtMe2 (20.2 mg, 0.0539 mmol)
was massed into the lower vessel, which was closed and sealed
with 1.5 mL of mercury. A solution of 7 (30.1 mg, 0.0751 mmol)
in CH2Cl2 (4 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 phosphine show no reaction. The enthalpy of ligand
substitution (-30.5 ( 0.4 kcal/mol) listed in Table 1 represents
the average of at least three individual calorimetric determi-
nations with all species in solution. The enthalpy of solution
of (COD)PtMe2 (+5.8 ( 0.1 kcal/mol) in CH2Cl2 was deter-
mined using identical methodology.4
Syn th esis of P tMe2((+)-DIOP ) (4). Yield: 104 mg (73.6%)
as yellow blocks. 1H NMR (CD2Cl2): δ 0.187 (m, 6 H, Pt(CH3)2,
J PtCH ) 69 Hz), δ 1.1 (s, 6 H, O2CCH3), 3.10-3.20 (m, 4 H,
3
PCH2), 3.70-3.85 (m, 2 H, OCH), 7.15-7.85 (m, 20 H, Ph).
31P{1H} NMR (CD2Cl2): δ 9.23 (s, pseudo d, J PtP ) 1832 Hz).
Anal. Calcd for C33H38O2P2Pt‚H2O: C, 53.44; H, 5.44. Found:
C, 53.70; H, 5.39.
Syn th esis of P tMe2(d p p v) (8). Yield: 144 mg (77.4%) as
1
orange prisms. H NMR (CD2Cl2): δ 0.667 (m, 6 H, Pt(CH3)2,
J PtCH ) 71 Hz), 7.10-7.80 (m, 2 H, HCdCH; 20 H, Ph).
3
31P{1H} NMR (CD2Cl2): δ 56.82 (s, pseudo d, J PtP ) 1779 Hz).
Anal. Calcd for C28H28P2Pt: C, 54.11; H, 4.54. Found: C, 54.19;
H, 4.44.
Syn th esis of P tMe2(d p m cb) (9). Yield: 94 mg (61.7%) as
colorless crystals. 1H NMR (CD2Cl2): δ 0.17 (m, 6 H, Pt(CH3)2,
J PtCH ) 69 Hz), 1.32 (t, 4 H, PCH2), 1.2-1.4 (m, 4 H, (CH2)3),
3
1.52 (q, 2 H, (CH2)3), 7.05-7.89 (m, 20 H, Ph). 31P{1H} NMR
(CD2Cl2): δ 5.76 (s, pseudo d, J PtP ) 1821 Hz). Anal. Calcd for
C
32H36P2Pt‚2H2O: C, 53.85; H, 5.65. Found: C, 54.33; H, 5.33.
Syn th esis of P tMe2(Et2d p p p ) (13). The reaction mixture
was heated to 50 °C for 18 h. Yield: 108 mg (60.1%) as colorless
1
needles. H NMR (CD2Cl2): δ 0.16 (m, 6 H, Pt(CH3)2, J PtCH
)
3
70 Hz), 2.30 (m, 4 H, PCH2), 1.07 (q, 4 H, CH2), 0.26 (s, 6 H,
CH3), 7.1-8.0 (m, 20 H, Ph). 31P{1H} NMR (CD2Cl2): δ 4.25
(s, pseudo d, J PtP ) 1874 Hz). Anal. Calcd for C33H40P2Pt: C,
57.14; H, 5.81. Found: C, 57.48; H, 6.04.
X-r a y Str u ctu r a l An a lyses of 1-4, 6, 9, a n d 13. For each
compound, a suitable crystal was mounted on the glass fiber
of a goniometer head in a random orientation and placed in
the cold stream of N2 in an automated diffractometer using
Mo KR radiation. The cell dimensions were determined in each
case from at least 25 centered reflections, and data were
collected. Standard reflections were monitored during data
collection. An azimuthal absorption correction was applied in
all structures. The structures of 1-4, 9, and 13 were deter-
mined from data collected on an Enraf-Nonius CAD4 diffrac-
tometer equipped with Mo KR radiation and a low-temperature
apparatus (150 K), while the structure of 6 was determined
on a Bruker Smart 1K CCD system with equipped with Mo
KR radiation and a low-temperature apparatus. The structures
were solved by direct methods using either the SHELXS or
MULTAN program. Each structure was refined in a full-matrix
least-squares refinement on F, using anomalous terms for Pt
and P, with all non-hydrogen atoms refined anisotropically.
In each case, hydrogen atoms were located from a Fourier
difference map and used as the basis of H atom positions in
the final structure. All the structures have idealized and fixed
H atoms, after attempts to refine them proved unsatisfactory.
The absolute configuration of 4 was determined by refining a
Flack parameter, which confirms the proper structural as-
Syn th esis of Dim eth ylbis(ph osph in e)platin u m (II) Com -
p lexes. Unless otherwise noted, all new complexes were
prepared according to the following typical procedure. PtMe2-
(COD)26 (1) and PtMe2(dppf)9 (3) were prepared by literature
methods.
Syn th esis of P tMe2(d p yp e) (2). In the glovebox, a Schlenk
tube equipped with a magnetic stir bar was charged with
(COD)PtMe2 (77.9 mg, 0.234 mmol), dpype (82.8 mg, 0.234
mmol), and THF (5 mL). The vessel was sealed, removed from
the glovebox, and interfaced to a Schlenk line, where the
reaction mixture was stirred for ∼2 h. The volatile components
were removed in vacuo, and the residue was triturated several
times with CH2Cl2 (3-5 mL) to ensure complete removal of
cyclooctadiene. The colorless to off-white residue was then
taken up in a minimum of CH2Cl2. Layering with pentane
afforded orange prisms of 2 after 1 day. Yield: 106 mg (77.9%).
1H NMR (CD2Cl2): δ 1.02 (m, 6 H, Pt(CH3)2, J PtCH ) 72 Hz),
3
(24) Marcone, J . E.; Moloy, K. G. J . Am. Chem. Soc. 1998, 120,
8527-8528.
(25) Bianchini, C.; Lee, H. M.; Meli, A.; Moneti, S.; Vizza, F.; Fontani,
M.; Zanello, P. Macromolecules 1999, 32, 4183-4193.
(26) Clark, H. C.; Manzer, L. E. J . Organomet. Chem. 1975, 59, 411-
428.

Pt(CH3)2(PP) Complexes
Organometallics, Vol. 19, No. 7, 2000 1433
signment. ORTEP diagrams of each structure are given in
Figures 1-7. Selected bond distances and angles are given in
Table 2, and crystallographic data are given in Table 3.
Positional and equivalent isotropic parameters for all non-
hydrogen atoms are given in the Supporting Information.
and Du Pont (Educational Aid Grant) for financial
support of this research.
Su p p or tin g In for m a tion Ava ila ble: Details of the crys-
tal structure determination for complexes 1-4, 6, 9, and 13.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Ack n ow led gm en t. S.P.N. acknowledges the Na-
tional Science Foundation (Grant No. CHE-9985213)
OM990962I