Chelating P,N versus P,P ligands: Differing reactivity of donor-stabilized pt(η2-PhC≡CPh) complexes toward diphenylacetylene

Article abstract of DOI:10.1021/om010924a

The thermal activation of the η²-diphenylacetylene complex (PN)Pt(η²-PhC≡CPh) (1) (PN = (diisopropylphosphinodimethylamino)ethane leads to the formation of the platinacyclopenta-2,4-diene compound (PN)Pt(CPh)₄ (3), which c

Full text of DOI:10.1021/om010924a

1118
Organometallics 2002, 21, 1118-1123
Ch ela tin g P ,N ver su s P ,P Liga n d s: Differ in g Rea ctivity
of Don or -Sta bilized P t(η2-P h CtCP h ) Com p lexes Tow a r d
Dip h en yla cetylen e
Christian Mu¨ller, Rene J . Lachicotte, and William D. J ones*
Department of Chemistry, University of Rochester, Rochester, New York 14627
Received October 22, 2001
The thermal activation of the η2-diphenylacetylene complex (PN)Pt(η2-PhCtCPh) (1) (PN
) (diisopropylphosphinodimethylamino)ethane leads to the formation of the platinacyclo-
penta-2,4-diene compound (PN)Pt(CPh)4 (3), which can be quantitatively obtained by reaction
of 1 with 1 equiv of diphenylacetylene. Two transient intermediates are observed by 31P
NMR spectroscopy during the course of the latter reaction. These species were independently
synthesized and characterized. Hexaphenylbenzene is catalytically generated by reaction
of 1 in the presence of excess diphenylacetylene. In contrast, no reaction of diphenylacetylene
with (dippe)Pt(η2-PhCtCPh) (2) (dippe ) bis(diisopropylphosphino)ethane) was observed.
In tr od u ction
triles,7b,c olefins,4c,8 or alkynes.7 These systems not only
act as good σ-donors but provide considerable π-acceptor
capabilities to stabilize the electron-rich metal center.
However, much less attention has been paid to bidentate
mixed donor systems as ligands for late transition metal
alkyne complexes. We have recently reported on the
synthesis of the Pt(0)-diphenylacetylene complex (PN)-
Pt(η2-PhCtCPh) (1) bearing a hemilabile P,N-hybrid
ligand (PN ) (diisopropylphosphinodimethylamino)-
ethane).9 Because the dimethylamino group lacks in
π-acceptor capability, the coordinative M-NR2 bond is
considered to be labile.10 This situation should lead not
only to an intrinsic instability of the (PN)Pt(η2-alkyne)
complex but also to an enhanced reactivity of the metal
center toward substrates.
Alkyne complexes of late transition metals play an
important role in the cyclotrimerization reaction of
acetylenes to benzene derivatives.1 Generally, the inser-
tion of an alkyne into the M-η2-acetylene bond initially
leads to a metalacyclopenta-2,4-diene and subsequently
to larger metalacyclic complexes and benzene deriva-
tives, respectively. This reaction is known for many
compounds of d8-d10 metals, such as Fe, Co, Ni, Ru,
Rh, Pd, and Ir.2 However, insertion reactions in corre-
sponding Pt(0)-alkyne complexes are much less com-
mon but have been reported in a few cases.3
Zerovalent Pt complexes are typically isolated with
ligands such as phosphines,4 imines,5 amides,6 isoni-
We report here on the thermal activation of (PN)Pt-
(η2-PhCtCPh) and on the reductive coupling reaction
of diphenylacetylene with the Pt-η2-alkyne bond. A
comparison with the system (dippe)Pt(η2-PhCtCPh)
(dippe ) bis(diisopropylphosphino)ethane), which con-
tains a chelating bisphosphino ligand, was carried out.
(1) (a) Lautens, M.; Klute, W.; Tam, W. Chem. Rev. 1996, 96, 49.
(b) Grotjahn, D. B. In Comprehensive Organometallic Chemistry II;
Abel. E. W., Stone, F. G. A., Wilkinson, G., Eds.; Elsevier Science Ltd:
Oxford, 1995; Vol. 12, p 741. (c) Schore, N. E. In Comprehensive
Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press
Ltd: Oxford, 1991; Vol. 5, p 1129. (d) Schore, N. E. Chem. Rev. 1988,
88, 1081. (e) Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl. 1984,
23, 539.
(2) See for example: (a) Eisch, J . J .; Ma, X.; Han, K. I.; Gitua, J .
N.; Kru¨ger, C. Eur. J . Inorg. Chem. 2001, 77, and references therein.
(b) Ca´mpora, J .; Palma, P.; Carmona, E. Coord. Chem. Rev. 1999, 193-
195, 207, and references therein. (c) Otsuka, S.; Nakamura, A. Adv.
Organomet. Chem. 1976, 14, 245, and references therein.
(3) (a) Tom Dieck, H.; Fendesak, G.; Munz, C. Polyhedron 1991, 10,
255. (b) Tom Dieck, H.; Munz, C.; Mu¨ller, C. J . Organomet. Chem. 1990,
384, 243. (c) Boag, N. M.; Dias, G. H. M.; Green, M.; Spencer, J . L.;
Stone, F. G. A.; Vicente, J . J . Chem. Soc., Dalton Trans. 1981, 1981.
(4) (a) Hasebe, K.; Kamite, J .; Mori, T.; Katayama, H.; Ozawa, F.
Organometallics 2000, 19, 2022. (b) Anderson, G. K.; Lumetta, G. J .;
Siria, J . W. J . Organomet. Chem. 1992, 434, 253. (c) Osborn, J . A.;
Wilkinson, G.; Mrowca, J . J . Inorg. Synth. 1990, 28, 77. (d) Hackett,
M.; Ibers, J . A.; Whitesides, G. M. J . Am. Chem. Soc. 1988, 110, 1436.
(e) Hackett, M.; Whitesides, G. M. J . Am. Chem. Soc. 1988, 110, 1449.
(f) Ros, R.; Michelin, R. A.; Bataillard, R.; Roulet, R. J . Organomet.
Chem. 1978, 161, 75. (g) Smart, L. E.; Browning, J .; Green, M.; Laguna,
A.; Spencer, J . L.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1977,
1777. (h) Chatt, J .; Rowe, G. A.; Williams, A. A. Proc. Chem. Soc. 1957,
208. (i) Allen, A. D.; Cook, C. D. Can. J . Chem. 1964, 42, 1063.
(5) (a) Klein, R. A.; Witte, P.; van Belzen, R.; Fraanje, J .; Goubitz,
K.; Numan, M.; Schenk. H.; Ernsting, J . M.; Elsevier, C. J . Eur. J .
Inorg. Chem. 1998, 319. (b) De Felice, V.; De Renzi, A.; Ruffo, F.;
Tesauro, D. Inorg. Chim. Acta 1994, 219, 169.
Resu lts a n d Discu ssion
P r ep a r a tion a n d Ch a r a cter iza tion of Don or -
Sta bilized P t(η2-P h CtCP h ) Com p lexes. Reaction of
(7) (a) Green, M.; Grove, D. M.; Howard, J . A. K.; Spencer, J . L.;
Stone, F. G. A. J . Chem. Soc., Chem. Commun. 1976, 759. (b) Boag,
N. M.; Green, M.; Grove, D. M.; Howard, J . A. K.; Spencer, J . L.; Stone,
F. G. A. J . Chem. Soc., Dalton Trans. 1980, 2170. (c) Boag, N. M.;
Green, M.; Howard, J . A. K.; Spencer, J . L.; Stansfield, R. F. D.;
Thomas, M. D. O.; Stone, F. G. A.; Woodward, P. J . Chem. Soc., Dalton
Trans. 1980, 2182.
(8) Schager, F.; Haack, K.-J .; Mynott, R.; Rufin˜ska, A.; Po¨rschke,
K.-R. Organometallics 1998, 17, 807.
(9) Mu¨ller, C.; Iverson, C. N.; Lachicotte, R. J .; J ones, W. D. J . Am.
Chem. Soc. 2001, 123, 9718. For the concept of hemilability see for
example: (a) J effrey, J . C.; Rauchfuss, T. B. Inorg. Chem. 1979, 18,
2658. (b) Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40,
680. (b) Mu¨ller, C.; Vos, D.; J utzi, P. J . Organomet. Chem. 2000, 600,
127. (c) Slone, C. S.; Weinberger, D. A.; Mirkin, C. A. Prog. Inorg. Chem.
1999, 48 233. (d) Okuda, J . Comments Inorg. Chem. 1994, 16 185.
(10) Pearson, R. G.; Scott, A. In Survey of Progress in Chemistry;
Academic Press: New York, 1969; Chapter 1.
(6) Park. S.; Hedden, D.; Rheingold, A. L.; Roundhill, D. M. Orga-
nometallics 1986, 5, 1305.
10.1021/om010924a CCC: $22.00 © 2002 American Chemical Society
Publication on Web 02/12/2002

Chelating P,N versus P,P Ligands
Organometallics, Vol. 21, No. 6, 2002 1119
F igu r e 2. Molecular structure of (dippe)Pt(PhCtCPh) (2)
(ORTEP diagram; 30% probability ellipsoids).
F igu r e 1. Molecular structure of (PN)Pt(PhCtCPh) (1)
(ORTEP diagram; 30% probability ellipsoids).
Ta ble 1. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 1
(COD)Pt(η2-PhCtCPh)7b with 1 equiv of PN11 or dippe12
afforded the η2-diphenylacetylene complexes (PN)Pt(η2-
PhCtCPh) (1) and (dippe)Pt(η2-PhCtCPh) (2), respec-
tively (eq 1). These compounds were obtained as orange,
Bond Lengths
Pt(1)-N(11)
Pt(1)-P(11)
Pt(1)-C(11)
Pt(1)-C(21)
2.221(8)
2.247(2)
2.054(9)
1.994(9)
C(11)-C(21)
C(21)-C(31)
C(11)-C(91)
1.312(13)
1.458(13)
1.443(13)
Bond Angles
37.8(4) Pt(1)-P(11)-C(181) 104.1(3)
C(21)-Pt(1)-C(11)
C(21)-Pt(1)-P(11) 123.6(3) Pt(1)-N(11)-C(171) 111.0(6)
C(11)-Pt(1)-N(11) 114.3(3) C(21)-C(11)-C(91)
N(11)-Pt(1)-P(11) 84.3(2) C(11)-C(21)-C(31)
142.7(9)
143.3(9)
Ta ble 2. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 2
Bond Lengths
air- and moisture-sensitive solids in high yields, and
their synthesis has recently been described in detail.9
1 and 2 have been further characterized by single-
crystal X-ray diffraction. The molecular structures of 1
and 2 are illustrated in Figures 1 and 2, and selected
bond lengths and angles are listed in Tables 1 and 2,
respectively. The structural analyses revealed the ex-
pected distorted square-planar geometry at the metal
center with the alkyne ligand in the P-Pt-N and
P-Pt-P plane. The elongated CtC bonds and the
bending of the CtC-C angles compared to free diphen-
ylacetylene13 reflect major contribution of π* back-
donation.2c,7b,14 The C-C triple bond distances and
bending angles are similar to those reported for (PPh3)2-
Pt(η2-PhCtCPh).15
Pt(1)-P(1)
Pt(2)-P(2)
Pt(1)-C(15)
Pt(1)-C(16)
2.2577(9)
2.2672(10)
2.029(3)
C(15)-C(16)
C(15)-C(17)
C(16)-C(23)
1.301(5)
1.464(5)
1.452(4)
2.047(3)
Bond Angles
C(15)-Pt(1)-C(16) 37.24(13) C(2)-P(2)-Pt(1)
C(15)-Pt(1)-P(1) 158.28(10) P(1)-Pt(1)-P(2)
C(16)-Pt(1)-P(2) 121.05(10) C(15)-C(16)-C(23) 140.7(3)
C(1)-P(1)-Pt(1) 109.72(12) C(16)-C(15)-C(17) 144.4(3)
108.76(12)
86.84(3)
Th er m a l Activa tion Rea ction s of 1 a n d 2. We
have recently shown that 1 and 2 undergo migration of
the metal center with subsequent insertion into the
C-Ph bond upon irradiation with UV light.9 We were
also interested in the reactivity of the η2-diphenylacetyl-
ene complexes under thermal conditions. A solution of
1 in C6D6 was heated to T ) 70 °C, and the reaction
was monitored by 31P NMR spectroscopy. Within 3 days
the starting material was quantitatively consumed
while a major species was formed in ∼50% spectroscopic
yield. This compound 3 was obtained as a colorless solid
after recrystallization from pentane/CH2Cl2 at T ) -30
°C. The 31P{1H} NMR spectrum of 3 showed a singlet
at δ ) 52.8 ppm with Pt satellites (1J Pt-P ) 2228 Hz).
The significantly smaller coupling constant compared
to the starting material (1J Pt-P ) 3647 Hz) implies
(11) Werner, H.; Hampp, A.; Peters, K.; Peters, E. M.; Walz, L.; von
Schnering, H. G. Z. Naturforsch. 1990, 45b, 1548.
(12) (a) Fryzuk, M. D.; J ones, T.; Einstein, F. W. B. Organometallics
1984, 3, 185. (b) Burg, R. J .; Chatt, J .; Hussain, W.; Leigh, G. J . J .
Organomet. Chem. 1979, 182, 203.
(13) The CtC bond length in free diphenylacetylene is 1.198(4) Å:
Mavriris, A.; Moustakali-Mavridis, I. Acta Crystallogr. 1977, B33, 3612.
(14) (a) Bartik, T.; Happ, B.; Iglewsky, M.; Bandmann, H.; Boese,
R.; Heimbach, P.; Hoffmann, T.; Wenschuh, E. Organometallics 1992,
11, 1235. (b) Rosenthal, U., Schulz, W. J . Organomet. Chem. 1987,
321, 103. (c) Tatsumi, K.; Hoffmann, R.; Templeton, J . L. Inorg. Chem.
1982, 21, 466. (d) Hey, E.; Weller, F.; Dehnicke, K. Z. Anorg. Allg.
Chem. 1984, 514, 18. (e) Dewar, M. J . S.; Ford, G. P. J . Am. Chem.
Soc. 1979, 101, 783. (f) Hartley, F. R. Angew. Chem. 1972, 84, 657. (g)
Nelson, J . H.; Wheelock, K. S.; Cusachs, L. C.; J onassen, H. B. J . Am.
Chem. Soc. 1969, 91, 7005. (h) Greaves, E. O.; Lock, C. J . L.; Maitlis,
P. M. Can. J . Chem. 1968, 46, 3879. (i) Dewar, M. J . S. Bull. Soc. Chim.
Fr. 1951, 18, C79. (j) Chatt, J .; Duncanson, L. A. J . Chem. Soc. 1953,
2939.
1
substituents σ-bonded to the Pt center. In the H NMR
(15) Glanville, J . O.; Stewart, J . M.; Grim, S. O. J . Organomet. Chem.
1967, 7, P9.

1120 Organometallics, Vol. 21, No. 6, 2002
Mu¨ller et al.
F igu r e 4. 31P NMR spectrum (162 MHz) of the reaction
of 1 with diphenylacetylene at t ) 23 h (T ) 78 °C).
Figu r e 3. Molecular structure of (PN)Pt(CPh)4 (3) (ORTEP
diagram; 30% probability ellipsoids).
Sch em e 1
Ta ble 3. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 3
Bond Lengths
Pt(1)-N(1)
Pt(1)-P(1)
Pt(1)-C(14)
Pt(1)-C(11)
C(11)-C(12)
C(12)-C(13)
2.273(9)
2.291(4)
2.078(12)
1.982(12)
1.389(17)
1.488(16)
C(13)-C(14)
C(14)-C(33)
C(13)-C(27)
C(12)-C(21)
C(11)-C(15)
1.350(16)
1.477(17)
1.465(15)
1.504(15)
1.478(17)
Bond Angles
N(1)-Pt(1)-P(1)
82.7(3)
80.6(5)
C(13)-C(14)-Pt(1) 114.2(8)
C(14)-Pt(1)-C(11)
C(14)-Pt(1)-N(1)
C(11)-Pt(1)-P(1)
98.8(4)
98.0(4)
Pt(1)-C(11)-C(12) 116.0(8)
C(11)-C(12)-C(13) 114.4(10) Pt(1)-N(1)-C(1)
C(12)-C(13)-C(14) 114.8(10) Pt(1)-P(1)-C(2)
111.3(7)
103.4(5)
spectrum resonances were observed for four unique
phenyl groups. In particular, four sets of ortho-phenyl
protons were detected. A crystal of 3 suitable for X-ray
diffraction was obtained by slow recrystallization from
pentane/CH2Cl2 at T ) -30 °C. The molecular structure
of 3 is illustrated in Figure 3, and selected bond lengths
and angles are listed in Table 3. The structural analysis
revealed that 3 is the platinacycle (PN)Pt(CPh)4. The
C-C distances C(11)-C(12) and C(13)-C(14) are
1.389(17) and 1.350(16) Å and therefore very similar to
the value of 1.337(6) Å for a simple CdC double bond.16
However, the bond length C(12)-C(13) of 1.488(16) Å
is indicative of a single bond between two double
bonds.16 These values suggest that the platinacycle 3
has a localized double-bond system and is best described
as a platinacyclopenta-2,4-diene complex. The formation
of 3 by thermolysis of 1 is only possible if compound 1
partially decomposes to provide free diphenylacetylene.
To show whether this phenomenon is due to the
intrinsic instability of 1, a solution of 2 in C6D6 was
heated to T ) 70 °C and monitored by 31P NMR
spectroscopy. Interestingly, the η2-diphenylacetylene
complex 2, which contains the chelating bisphosphino
ligand dippe, does not lead to a metalacyclic product.
Even at prolonged heating at T ) 100 °C no reaction or
decomposition of 2 was observed.
Stimulated by these observations, we were interested
in the thermolysis of 1 in the presence of 1 equiv of
diphenylacetylene. We found that a 1:1 mixture of 1 and
diphenylacetylene can easily be generated in situ by
reaction of Pt(η2-PhCtCPh)27a,b with 1 equiv of the P,N
ligand in C6D6 according to Scheme 1. The orange
solution was heated to T ) 100 °C and monitored by
31P NMR spectroscopy. The starting material was
indeed quantitatively converted to 3 within 42 h.
Surprisingly, two transient intermediates were observed
during the course of the reaction. The 31P NMR spec-
trum recorded after t ) 23 h (reaction temperature T )
78 °C) is illustrated in Figure 4. A singlet at δ ) 32.3
ppm with Pt satellites (1J Pt-P ) 3336 Hz) was observed
for intermediate I, while a singlet at δ ) 49.8 ppm with
broad Pt satellites (1J Pt-P ) 2608 Hz) was detected for
intermediate II. Again, the smaller Pt-P coupling
constant of intermediate II compared to an η2-alkyne
complex suggests the presence of substituents σ-bonded
to the metal center. We were able to synthesize and
characterize I and II independently; reaction of (COD)-
Pt(η2-PhCtCPh) with 2 equiv of the P,N ligand in C6D6
led to the formation of the bisphosphino complex
(NP)2Pt(η2-PhCtCPh) (4), which was quantitatively
(16) Gastinger, R. G.; Rausch, M. D., Sullivan, D. A.; Palenik, G. J .
J . Am. Chem. Soc. 1976, 98, 719.

Chelating P,N versus P,P Ligands
Organometallics, Vol. 21, No. 6, 2002 1121
Ta ble 4. Selected Bon d Len gth s (Å), Dista n ces (Å),
a n d Bon d An gles (d eg) for 5
Bond Lengths/Distances
Pt(1)-N(1)
Pt(1)-P(2)
Pt(1)-C(25)
Pt(1)-C(28)
C(25)-C(26)
C(26)-C(27)
C(27)-C(28)
2.245(5)
2.2908(15)
2.023(6)
2.098(6)
1.422(7)
1.494(8)
1.381(8)
Pt(1)‚‚‚Pt(2)
Pt(2)-C(25)
Pt(2)-C(26)
Pt(2)-C(27)
Pt(2)-C(28)
Pt(2)-C(11)
Pt(2)-C(12)
C(11)-C(12)
3.0640(3)
2.359(5)
2.222(5)
2.241(5)
2.361(5)
2.008(6)
1.995(6)
1.294(8)
Bond Angles
82.05(14) Pt(1)-C(25)-C(26) 117.1(4)
78.0(2) C(25)-C(26)-C(27) 112.7(5)
99.39(16) C(26)-C(27)-C(28) 113.5(5)
P(1)-Pt(1)-N(1)
C(25)-Pt(1)-C(28)
C(25)-Pt(1)-P(1)
C(28)-Pt(1)-N(1)
Pt(1)-N(1)-C(2)
Pt(1)-P(1)-C(1)
100.7(2)
111.7(4)
103.9(2)
C(11)-Pt(2)-C(12)
37.7(2)
C(13)-C(11)-C(12) 145.3(6)
C(11)-C(12)-C(19) 147.0(6)
Pt(1)-C(28)-C(27) 115.6(4)
F igu r e 5. Molecular structure of (PN)Pt(CPh)4Pt(η2-PhCt
CPh) (5) (ORTEP diagram; 30% probability ellipsoids).
of 3.064 Å is considered to be too long for a bonding
interaction. To the best of our knowledge, this structural
motif of a Pt(0) complex has not been reported in the
literature so far. However, a related dinuclear Ni(0)/
Ni(II) complex was described by Po¨rschke. In this
compound, an ethyne ligand bridges the metal centers
of a donor-stabilized nickelacyclopenta-µ-2,4-diene com-
plex and a (dippe)Ni(0) fragment.17
obtained as a yellow, air- and moisture-sensitive oil (eq
2). 4 was characterized by 1H and 31P NMR spectroscopy
The platinacyclopenta-2,4-diene complex 3 turned out
to be an intermediate in the catalytic formation of
hexaphenylbenzene by (PN)Pt(η2-PhCtCPh) (eq 4). A
as well as elemental analysis. The 31P NMR data of 4
are identical with those observed for intermediate I. In
complex 4 the two P,N molecules act as monodentate
ligands with coordination to the metal center via the
diisopropylphosphino group. Intermediate II, however,
was synthesized by reaction of 2 equiv of Pt(η2-PhCt
CPh)2 with 1 equiv of the P,N ligand at T ) 70 °C in
solution of (PN)Pt(η2-PhCtCPh) and excess diphenyl-
acetylene in C6D6 was heated at T ) 100 °C and
1
C6D6 (eq 3). The product 5 with identical H and 31P
1
monitored by H and 31P NMR spectroscopy. Initially,
the quantiative formation of the platinacyclopenta-2,4-
diene complex was observed. Hexaphenylbenzene was
then catalytically generated, although this reaction
turned out to be very slow (1 turnover/20 days). How-
ever, once quantitatively formed, 3 remained the only
intermediate observed by 31P NMR spectroscopy during
the course of the catalytical reaction.
In contrast to the results mentioned above, insertion
reactions of diphenylacetylene into the Pt-alkyne bond
in (dippe)Pt(η2-PhCtCPh) (2) were not observed. Heat-
ing a solution of 2 plus diphenylacetylene at T ) 100
NMR data as intermediate II was isolated as a dark
red solid from the reaction mixture in 68% yield.
Crystals suitable for X-ray diffraction were obtained
after recrystallization from C6D6/pentane at room tem-
perature. The molecular structure of 5 is illustrated in
Figure 5, and selected bond lengths, distances, and
angles are listed in Table 4. The structural analysis
revealed that the intermediate II (5) is a platinacyclo-
penta-2,4-diene complex of Pt(0). The Pt(0)-diphenyl-
acetylene fragment is η4-coordinated to the metalacycle
in a half-sandwich fashion. On complexation, the bond
distances C(25)-C(26) and C(27)-C(28) in the metala-
cycle are slightly elongated by approximately 0.03 Å
compared to the CdC double bonds in the free platina-
cyclopenta-2,5-diene system. The Pt(1)-Pt(2) distance
1
°C for 6 days showed no change in the H and 31P NMR
spectra.
Mech a n istic Con sid er a tion s. We assume that the
initial step in the formation of the metallacycle 3 is the
displacement of the amino group by a second alkyne
with subsequent C-C coupling and recoordination of the
nitrogen donor to the metal center (Scheme 2). This
assumption is based on the fact that compound 2,
containing two strong σ-donor as well as strong π-ac-
ceptor phosphorus ligands, does not react with diphen-
(17) Po¨rschke, K.-R. Angew. Chem., Int. Ed. Engl. 1987, 26, 1288.

1122 Organometallics, Vol. 21, No. 6, 2002
Mu¨ller et al.
Sch em e 2
F igu r e 6. Distribution of species 1, 3, I (4), and II (5) in
the reaction of 1 with diphenylacetylene (T ) 78 °C) ([, 1;
2, 3; 9, 4; b, 5).
Sch em e 3
Con clu sion s
The Pt(0) complex (PN)Pt(η2-PhCtCPh) reacts with
diphenylacetylene to form quantitatively the metalacy-
clic product (PN)Pt(CPh)4. Two transient intermediates
are observed during the course of the reaction and were
independently synthesized and characterized. Interme-
diate I turned out to be a Pt(η2-PhCtCPh) complex with
two P,N ligands attatched to the metal center via the
phosphorus donor. In intermediate II a Pt(η2-PhCtCPh)
fragment is η4-coordinated to the double-bond system
of the final product, the metalacycle (PN)Pt(CPh)4. In
contrast, no reaction at all is observed in the corre-
sponding bisphosphino-substituted complex (dippe)Pt-
(η2-PhCtCPh). These studies demonstrate that the P,N
ligand is labile not only at the nitrogen but at the
phosphorus atom also. This enhanced lability, compared
to the dippe analogue, results in far more varied
reactivity as summarized in this report. Ultimately
thermodynamics takes over and a single simple meta-
lacycle product is formed.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were carried
out under a nitrogen atmosphere, either on a high-vacuum line
using modified Schlenk techniques or in a Vacuum Atmo-
spheres Corporation glovebox unless otherwise stated. The
solvents were commercially available and distilled from dark
purple solutions of benzophenone ketyl. A Siemens-SMART
three-circle CCD diffractometer was used for the X-ray crystal
structure determinations. The elemental analyses were ob-
ylacetylene at all. However, an equilibrium between 1
and compound 4, which contains two P,N ligands, must
also exist according to the data obtained by 31P{1H}
NMR spectroscopy (Figure 4). The remaining fragment
“Pt(η2-PhCtCPh)” would react very fast with the met-
allacycle 3 to form the second intermediate 5 (Scheme
3). This is consistent with the observation that the
relative amounts of 4 and 5 remain almost equal during
the course of the reaction. The highest concentrations
of 4 and 5 were detected after 2.5 h of thermolysis. The
latter reaction is also reversible, leading again to a
decrease of 5 as well as 4 to form the final product 3
quantitatively after approximately 68.5 h at T ) 78 °C.
A distribution of species plot is shown in Figure 6. The
amount of the starting material 1 decreases rapidly at
the beginning of the reaction. The intermediates 4 and
5 are formed early in the reaction, whereas the metal-
lacycle 3 is formed comparatively slow. These data are
consistent with a complex rapid equilibration of species
prior to a slower formation of product.
1
tained from Desert Analytics. H, 13C{1H}, and 31P{1H} NMR
spectra were recorded on
a Bruker AMX-400 or Bruker
Avance-400 spectrometer, and all 1H chemical shifts are
reported relative to the residual proton resonance in the
deuterated solvents. (PN)Pt(η2-PhCtCPh),9 (dippe)Pt(η2-PhCt
CPh),9 (COD)Pt(PhCtCPh),7b Pt(PhCtCPh)2,7a,b (iPr)2PCH2-
CH2NMe2 (PN),11 and (iPr)2PCH2CH2P(iPr)2 (dippe)12 were
synthesized according to published procedures.
P r ep a r a t ion of (P N)P t (CP h )4 (3). (Diisopropylphos-
phinodimethylamino)ethane) (6.7 µL, 0.032 mmol) was added
dropwise to a solution of Pt(η2-PhCtCPh)2 in C6D6 (0.5 mL).
A bright yellow solution was formed and was transferred to
an NMR tube. The 31P NMR spectrum was recorded im-
mediately and showed the quantitative formation of 1 and 1
equiv of diphenylacetylene. The solution was then heated to
T ) 100 °C and the starting material was quantitatively
converted to 3 within 42 h. The solvent was removed in vacuo,

Chelating P,N versus P,P Ligands
Organometallics, Vol. 21, No. 6, 2002 1123
and the remaining solid was recrystallized from pentane/CH2-
dark red solid was formed. 5 was formed in ∼95% spectroscopic
yield within 21 h. The volume was reduced in vacuo to ∼0.1
mL, and 2 mL of petroleum ether was added. The red solid
was filtered, washed with petroleum ether, and dried in vacuo.
Yield: 18.0 mg (0.016 mmol, 68%). 1H NMR (THF-d8): δ (ppm)
0.80 (m, 2 H, -CH-), 0.89 (m, 3 H, iPr), 0.99 (dd, 3J H-P ) 10.6
Hz, 3J H-H ) 6.8 Hz, 3 H, iPr), 1.22 (dd, 3J H-P ) 18.1 Hz, 3J H-H
Cl2 (6:1) at T ) -30 °C. 3 was obtained as a colorless solid.
1
Yield: 15.6 mg (0.021 mmol, 66%). H NMR (C6D6): δ (ppm)
3
3
i
0.62 (dd, J H-P ) 10.7 Hz, J H-H ) 6.9 Hz, 6 H, Pr), 0.76 (m,
i
2 H, -CH-), 1.07 (m, 2 H, P-CH2-), 1.16 (m, 6 H, Pr), 1.63
(m, 2 H, N-CH2-), 2.02 (s, br, 6 H, N-CH3), 6.67 (t, 2 H,
m-C6H5), 6.85-6.97 (m, 6 H, 2×m-C6H5, 4×p-C6H5), 6.96 (t, 2
3
i
3
3
H, m-C6H5), 7.08 (t, 2 H, m-C6H5), 7.24 (d, J H-H ) 8.0 Hz, 2
) 6.9 Hz, 3 H, Pr), 1.37 (dd, J H-P ) 17.9 Hz, J H-H ) 7.9 Hz,
H, o-C6H5), 7.28 (d, 3J H-H ) 7.4 Hz, 2 H, o-C6H5), 7.33 (d, 3J H-H
3 H, Pr), 1.50 (m, 2 H, P-CH2-), 1.93 (s, br, 3 H, N-CH3),
i
3
) 7.0 Hz, 2 H, o-C6H5), 7.44 (d, J H-H ) 7.5 Hz, 2 H, o-C6H5).
2.30 (m, 2 H, N-CH2-), 2.38 (s, br, 3 H, N-CH3), 6.61-6.85
(m, 12 H, phenyl-H), 7.20 (pt, 4 H, phenyl-H), 7.31 (pt, 7 H,
phenyl-H), 7.38 (d, 3J H-H ) 7.2 Hz, 2 H, o-C6H5), 7.72 (d, 3J H-H
13C{1H} NMR (C6D6): δ (ppm) 16.2 (d, 2J C-P ) 18.9 Hz, -CH-
2
CH3), 17.9 (d, J C-P ) 6.4 Hz, -CH-CH3), 22.4, 22.5, 22.6,
2
3
22.7 (P-CH2-; -CH-), 49.3 (N-CH3), 67.5 (d, J C-P ) 7.4
) 6.8 Hz, 1 H, o-C6H5), 7.80 (d, J H-H ) 7.4 Hz, 4 H, o-C6H5).
Hz, N-CH2-), 123.4, 123.8, 124.2, 126.8, 127.3, 127.5, 128.5,
129.3 (Ph-C), 130.0 (d, J ) 2.3 Hz, Ph-C), 131.0 (Ph-C),
139.6, 143.8 (d, J ) 6.5 Hz), 152.6 (d, J ) 4.9 Hz), 154.3 (d, J
) 4.7 Hz), 155.9 (d, J ) 4.7 Hz), 157.2, 166.5, 167.6 (vinylic-
C, ipso-Ph-C). 31P NMR (C6D6): δ (ppm) 52.8 (s, with platinum
31P NMR (THF-d8): δ (ppm) 49.9 (s, with platinum satellites,
1J Pt-P ) 2661 Hz). Anal. Calcd for C52H54NPPt2 (1114.17
g/mol): C, 56.06; H, 4.89; N, 1.26. Found: C, 56.43; H, 4.81;
N, 1.12.
Th er m olysis of 1. An equimolar solution of 1 and diphen-
ylacetylene was prepared by adding (iPr)2PCH2CH2NMe2 (6.4
µL, 0.03 mmol) to a solution of Pt(PhCtCPh)2 (16.8 mg, 0.03
mmol) in C6D6 (0.5 mL). The orange solution was transferred
to a resealable NMR tube and heated to T ) 78 °C. The
reaction was monitored by 1H and 31P NMR spectroscopy. 3
was quantitatively formed after 68.5 h.
1
satellites, J Pt-P ) 2228 Hz). Anal. Calcd for C38H44NPPt
(740.82 g/mol): C, 61.61; H, 5.99; N, 1.89. Found: C, 61.83;
H, 6.22; N, 1.96.
P r ep a r a tion of (NP )2P t(η2-P h CtCP h ) (4). A solution of
(iPr)2PCH2CH2NMe2 (11.3 µl, 0.054 mmol) in CD2Cl2 (0.5 mL)-
was cooled to T ) -30 °C and added to a precooled vial
containing (COD)Pt(PhCtCPh) (12.4 mg, 0.026 mmol). A
yellow solution was formed, and the reaction was monitored
by 31P NMR spectroscopy. 4 was quantitatively generated
within 8 h. The solvent and all volatile compounds were
removed in vacuo. 4 was isolated as a yellow, air- and
moisture-sensitive oil. 1H NMR (C6D6): δ (ppm) 1.05 (dd, 3J H-P
) 12.8 Hz, 3J H-H ) 6.9 Hz, 6 H, iPr, m, 4 H, -CH-), 1.20 (dd,
Th er m olysis of 2. Diphenylacetylene (3.2 mg, 0.018 mmol)
was added to a solution of 2 (10.9 mg, 0.017 mmol) in C6D6
(0.5 mol). The orange solution was transferred to a resealable
NMR tube and heated to T ) 100 °C. The reaction was
1
monitored by H and 31P NMR spectroscopy. No reaction was
observed within 6 days.
Catalytic For m ation of Hexaph en ylben zen e. (iPr)2PCH2-
CH2NMe2 (5.8 µL, 0.027 mmol) was added to a solution of Pt-
(PhCtCPh)2 (15.1 mg, 0.027 mmol) in C6D6 (0.5 mL). Diphen-
ylacetylene (53.7 mg, 0.3 mmol) was added, and the orange
solution was transferred to a sealable NMR tube and heated
to T ) 100 °C. The reaction was monitored by 1H and 31P NMR
spectroscopy. A total of 40 mg (74%) hexaphenylbenzene was
isolated after 150 days of thermolysis.
3
i
3J H-P ) 15.1 Hz, J H-H ) 7.2 Hz, 6 H, Pr), 2.07 (m, 4 H,
P-CH2-), 2.12 (s, br, 12 H, N-CH3), 2.52 (m, br, 4 H,
3
N-CH2-), 7.00 (t, J H-H ) 6.6 Hz, 2 H, p-C6H5), 7.19 (t, 4 H,
m-C6H5), 7.53 (d, J H-H ) 7.1 Hz, 4 H, o-C6H5). 13C{1H} NMR
3
(C6D6): δ (ppm) 18.9 (s, with platinum satellites, 3J C-Pt ) 19.7
Hz, -CH-CH3), 20.2 (m, -CH-CH3), 25.2 (m, P-CH2-), 27.2
(m, -CH-), 45.2 (N-CH3), 56.1 (s, with platinum satellites,
3J C-Pt ) 22.0 Hz, N-CH2-), 125.0, 128.6, 131.9 (Ph-C), 140.4
(m, tC-Ph). 31P NMR (C6D6): δ (ppm) 32.3 (s, with platinum
Ack n ow led gm en t is made to the U.S. Department
of Energy, grant FG02-86ER13569, for their support of
this work. C.M. thanks the Deutsche Forschungsge-
meinschaft (DFG) for a postdoctoral fellowship.
1
satellites, J Pt-P ) 3336 Hz). Anal. Calcd for C34H58N2P2Pt
(751.93 g/mol): C, 54.31; H, 7.77; N, 3.73. Found: C, 53.60;
H, 7.83; N, 3.48.
P r ep a r a tion of (P N)P t(CP h )4P t(η2-P h CtCP h ) (5). Pt-
(η2-PhCtCPh)2 (13.0 mg, 0.024 mmol) was dissolved in C6D6
(0.5 mL). (iPr)2PCH2CH2NMe2 (5.0 µl, 0.024 mmol) was added,
and an orange solution was formed. This solution was trans-
ferred to a vial containing more Pt(PhCtCPh)2 (13.0 mg, 0.024
mmol). The orange solution, which slowly turned dark orange,
was transferred to an NMR tube and heated to T ) 70 °C.
The reaction was monitored by 31P NMR spectroscopy. During
the course of the reaction the color changed to dark red and a
Su p p or tin g In for m a tion Ava ila ble: Details of data
collection parameters, bond lengths, bond angles, fractional
atomic coordinates, and anisotropic thermal parameters for
1, 2, 3, and 5. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM010924A