(R2PC2H4PR2)Pd 0-1-alkyne complexes

Article abstract of DOI:10.1021/om9702035

Displacement of the ethene ligand in (d¹PPe)Pd(C₂H₄) (dⁱppe = ⁱPr₂PC₂H₄P_iPr ₂) by 1-alkynes RC≡CH affords the mononuclear complexes (dⁱPPe)Pd(RC≡CH) (R = Me (2a), Ph (3a), CO₂-Me (4), SiMe₃ (5)). The molecular structure of 3a has been determined by X-ray crystallography. Mononuclear 2a and 3a have been reacted with stoichiometric amounts of (dⁱPPe)Pd(η¹-C₃H₅)₂ as a source for [(dⁱppe)Pd⁰] to yield the dinuclear derivatives {(dⁱppe)-Pd}₂(RC≡=CH) (R = Me (2b), Ph (Sb)). By the reaction Of (dⁱPPe)Pd(C₂H₄) with difunctional vinylacetylene the mononuclear complex (dⁱppe)Pd{(l,2-η²)-RC≡CH} (R = CH=CH₂ (6a)) is formed, which is in equilibrium with isomeric (dⁱppe)Pd{(3,4-η²)-H₂C=CHC≡CH}(6b). Addition of [dⁱPPe)Pd⁰] to 6a,b yields dinuclear {(dⁱPPe)Pd}₂(μ-RC≡CH) (R = CH≡CH₂ (6c)). Reaction of (dⁱppe)Pd(C₂H₄) with butadiyne affords (dⁱppe)Pd(η²-HC≡=CC≡CH) (7c). From dippe, Pt(cod)₂, and C₄H₂ the Pt homologue has also been synthesized and thus, together with the already known Ni derivative, the series (dⁱppe)M(η²-HC≡CC≡CH) (M = Ni (7a), Pd (7c), Pt (7f)) is now complete. When 7c and [(dⁱppe)Pd⁰] are combined, the dinuclear complex {(dⁱppe)Pd}₂(γ-RC≡CH) (R = C≡CH (7e)) is formed in solution, whereas isomeric {(dⁱppe)Pd}₂{μ(l,2-η²):(3,4-η ²)-HC≡CC≡CH} (7d) is present in the solid state. The preparation of the Pd⁰-1-alkyne complexes refutes the conventional wisdom that this type of compound is inherently unstable. By reaction of (dⁱppe)Pd(C₂H₄) with internal alkynes C₂R₂ the complexes (dⁱPPe)Pd(RC≡CR) (R = Me (8a), Ph (9), CO₂Me (10), SiMe₃ (11)) have also been prepared. Combining 8a with [(dⁱPPe)Pd⁰] affords dinuclear {(dⁱppe)Pd}₂(μ-MeC≡CMe) (8b). Finally, solution thermolysis of 2b and 8b gives rise to dinuclear alkyne-free Pd₂(dⁱPPe)₂ (12).

Full text of DOI:10.1021/om9702035

4276
Organometallics 1997, 16, 4276-4286
(R2P C2H4P R2)P d 0-1-Alk yn e Com p lexes
Frank Schager, Werner Bonrath, Klaus-Richard Po¨rschke,* Magnus Kessler,
Carl Kru¨ger, and Klaus Seevogel
Max-Planck-Institut fu¨r Kohlenforschung, D-45466 Mu¨lheim an der Ruhr, Germany
Received March 11, 1997X
Displacement of the ethene ligand in (dippe)Pd(C2H4) (dippe ) iPr2PC2H4PiPr2) by 1-alkynes
RCtCH affords the mononuclear complexes (dippe)Pd(RCtCH) (R ) Me (2a ), Ph (3a ), CO2-
Me (4), SiMe3 (5)). The molecular structure of 3a has been determined by X-ray crystal-
lography. Mononuclear 2a and 3a have been reacted with stoichiometric amounts of
(dippe)Pd(η1-C3H5)2 as a source for [(dippe)Pd0] to yield the dinuclear derivatives {(dippe)-
Pd}2(µ-RCtCH) (R ) Me (2b), Ph (3b)). By the reaction of (dippe)Pd(C2H4) with difunctional
vinylacetylene the mononuclear complex (dippe)Pd{(1,2-η2)-RCtCH} (R ) CHdCH2 (6a )) is
formed, which is in equilibrium with isomeric (dippe)Pd{(3,4-η2)-H2CdCHCtCH} (6b).
Addition of [(dippe)Pd0] to 6a ,b yields dinuclear {(dippe)Pd}2(µ-RCtCH) (R ) CHdCH2 (6c)).
Reaction of (dippe)Pd(C2H4) with butadiyne affords (dippe)Pd(η2-HCtCCtCH) (7c). From
dippe, Pt(cod)2, and C4H2 the Pt homologue has also been synthesized and thus, together
with the already known Ni derivative, the series (dippe)M(η2-HCtCCtCH) (M ) Ni (7a ),
Pd (7c), Pt (7f)) is now complete. When 7c and [(dippe)Pd0] are combined, the dinuclear
complex {(dippe)Pd}2(µ-RCtCH) (R ) CtCH (7e)) is formed in solution, whereas isomeric
{(dippe)Pd}2{µ-(1,2-η2):(3,4-η2)-HCtCCtCH} (7d ) is present in the solid state. The prepara-
tion of the Pd0-1-alkyne complexes refutes the conventional wisdom that this type of
compound is inherently unstable. By reaction of (dippe)Pd(C2H4) with internal alkynes C2R2
the complexes (dippe)Pd(RCtCR) (R ) Me (8a ), Ph (9), CO2Me (10), SiMe3 (11)) have also
been prepared. Combining 8a with [(dippe)Pd0] affords dinuclear {(dippe)Pd}2(µ-MeCtCMe)
(8b). Finally, solution thermolysis of 2b and 8b gives rise to dinuclear alkyne-free
Pd2(dippe)2 (12).
Sch em e 1
In tr od u ction
Previous reports on the reaction of Pd0 complexes with
1-alkynes give the impression that the preferred reac-
tion path is oxidative addition to yield PdII alkynyl
hydrides.1 It appears, however, that the major obstacle
in the synthesis of Pd0-1-alkyne complexes has been
the scarcity of appropriate starting complexes rather
than an inherent instability of this type of complex. In
this context we have recently reported on novel (R2-
i
PC2H4PR2)Pd0 alkene and ethyne complexes (R ) Pr,
tBu; alkene ) C2H4, 1,5-hexadiene, 1,5-cyclooctadiene).2
When Pd(η3-C3H5)2 and Pd(η3-2-MeC3H4)2 are reacted
below -30 °C with bidentate iPr2PC2H4PiPr2 (dippe), the
PdII η1-allyl compounds (dippe)Pd(η1-C3H5)22 and (dippe)-
Pd(η1-2-MeC3H4)23 are produced. Above -30 °C the allyl
substituents couple with reduction of PdII to form
various labile (dippe)Pd0-1,5-hexadiene or -2,5-di-
methyl-1,5-hexadiene complexes, which have in part
been isolated. Addition of ethene furnishs uniformly the
stable complex (dippe)Pd(C2H4), and by the reaction of
the latter with ethyne mononuclear (dippe)Pd(C2H2) (1a )
is obtained (Scheme 1). These complexes can also be
prepared in one-pot reactions. Combination of 1a with
any of the aforementioned (dippe)PdII,0 complexes pro-
duces dinuclear {(dippe)Pd}2(µ-C2H2) (1b ). Similar
t
reactions carried out with Bu2PC2H4PtBu2 (dtbpe) as
the phosphane component afford (dtbpe)Pd(C2H4),
(dtbpe)Pd(C2H2), and {(dtbpe)Pd}2(µ-C2H2).2,4 Besides
Pd(η3-C3H5)2 and Pd(η3-2-MeC3H4)2, the complexes (η5-
C5H5)Pd(η3-C3H5) and (tmeda)PdMe2 may serve alter-
natively as starting materials.
On the basis of the chemistry described above we set
out to tackle the problem of the synthesis of Pd0-1-
alkyne complexes. We have confined the studies to
dippe as an exemplary ligand to Pd because of the
excellent properties it generally confers to products with
respect to stability, solubility, and crystallizability. We
report here on, to the best of our knowledge, the first
X Abstract published in Advance ACS Abstracts, August 15, 1997.
(1) (a) Chukhadzhyan, G. A.; EÄ voyan, Z. K.; Melkonyan, L. N. Zh.
Obshch. Khim. 1975, 45, 1114; J . Gen. Chem. USSR (Engl. Transl.)
1975, 45, 1096. (b) Maitlis, P. M.; Espinet, P.; Russell, M. J . H.
Comprehensive Organometallic Chemistry; Pergamon: Oxford, U.K.,
1982; Vol. 6, p 254. (c) Davies, J . A. Comprehensive Organometallic
Chemistry II; Pergamon: Oxford, U.K., 1995; Vol. 9, p 316.
(2) Krause, J .; Bonrath, W.; Po¨rschke, K.-R. Organometallics 1992,
11, 1158.
(4) The molecular structures of (dtbpe)Pd(HCtCH) (CtC ) 1.20(1)
Å) and {(dtbpe)Pd}2(µ-HCtCH) (CtC ) 1.28(1) Å) have been deter-
mined.3 Goddard, R.; Krause, J .; Po¨rschke, K.-R. Unpublished results.
(3) Krause, J . Dissertation, Universita¨t Du¨sseldorf, 1993.
S0276-7333(97)00203-3 CCC: $14.00 © 1997 American Chemical Society

(R2PC2H4PR2)Pd0-1-Alkyne Complexes
Organometallics, Vol. 16, No. 20, 1997 4277
Sch em e 2
The mononuclear complexes 4 and 5 are stable in
solution at ambient temperature. When solutions of
complexes 2a and 3a are warmed to 20 °C, additional
signals arise in the NMR spectra which are attributed
to the dinuclear derivatives {(dippe)Pd}2(µ-RCtCH) (R
) Me (2b), Ph (3b)). Complex 2b has been obtained in
pure form by depleting propyne from the ethereal
solution of 2a under vacuum. Furthermore, complexes
2b and 3b have been synthesized by reacting 2a and
3a with an equimolar amount of (dippe)Pd(η1-C3H5)2.
The latter thermolyzes into (dippe)Pd(η2-C6H10) and
thus serves as a source for [(dippe)Pd0]. (dippe)Pd(η2-
C6H10) is more reactive than (dippe)Pd(C2H4), for which
the coupling reactions with (dippe)Pd(RCtCH) are
incomplete. It appears without doubt that also 4 and 5
will react with [(dippe)Pd0] to form the corresponding
dinuclear complexes.
The colorless or faintly colored crystalline complexes
are isolated in 80-90% yield. The melting points of the
mononuclear complexes are relatively low (30-81 °C),
while those of the dinuclear complexes are somewhat
higher (70-110 °C). When a THF-d8 solution of 2a ,b
is kept at 20 °C for several days, a slow decomposition
proceeds to afford a mixture of products. Of these, the
dinuclear alkyne-free complex 12 (see below) has been
identified by its characteristic high-field 31P NMR
singlet (δP 33.7).
Although the mononuclear complexes 4 and 5 are
stable in solution when pure, they are destabilized by
additional 1-alkyne. When to a solution (THF-d8, 20
°C) of the mononuclear complexes 2a , 3a , 4, and 5 about
4 equiv of the corresponding 1-alkyne is added, for 3a
and phenylacetylene a slight decomposition is observed
after 1 day. However, for 5 and (trimethylsilyl)acety-
lene some decomposition is observable already after 1
h, and the situation is similar for 2a and added propyne.
For 4 and propiolic acid methyl ester decomposition is
the most rapid and proceeds largely within 1 h. Thus,
the following qualitative sequence of increased desta-
bilization (increased reactivity) has been established:
isolated5 Pd0-1-alkyne complexes and also some new
Pd0 complexes with internal alkynes.6 While related
Ni(0)-1-alkyne complexes7 are still scarce, the group
of Pt(0)-1-alkyne complexes8 is quite broad.
Resu lts
(d ip p e)P d 0 Com p lexes w ith MeCtCH, P h CtCH,
MeO2CCtCH, a n d Me3SiCtCH (2-5). While the
methyl group in propyne is electron-donating (“nonac-
tivated alkyne”), the phenyl or ester substituents in
phenylacetylene and propiolic acid methyl ester are
electron-withdrawing (“activated alkyne”), whereas the
electronic effect of the Me3Si substituent in (tri-
methylsilyl)acetylene is a priori difficult to assess.
When (dippe)Pd(C2H4) is reacted with an excess of these
1-alkynes in pentane or diethyl ether at e0 °C, the
ethene ligand is readily displaced and, upon cooling to
-78 °C, the mononuclear (dippe)Pd0-1-alkyne com-
plexes 2a , 3a , 4, and 5 are obtained (Scheme 2).
Although the complexes can also be prepared by one-
pot reactions of any of the PdII complexes mentioned in
the Introduction with dippe and the 1-alkyne (cf. Scheme
1), the reaction of isolated (dippe)Pd(C2H4) with 1-alkyne
appears to be favorable.
3a /HCtCPh < 5/HCtCSiMe3 ≈ 2a /HCtCMe <
4/HCtCCO2Me
It is deemed that decomposition is initiated by the
oxidative addition of a 1-alkyne C-H bond to (dippe)-
Pd0(1-alkyne), giving rise to a PdII/IV alkynyl hydride
intermediate. Further reaction with 1-alkyne may lead
to 1-alkyne oligomerization.9 For the given [(dippe)Pd0]
system the formation of various oligomers is indicated
(5) For IR spectroscopically characterized species obtained by co-
condensation of Pd atoms and 1-alkynes, see: Zoellner, R. W.;
Klabunde, K. J . Chem. Rev. 1984, 84, 545 and literature cited therein.
(6) (a) Schager, F. Diplomarbeit, Universita¨t Du¨sseldorf, 1995. (b)
Schager, F.; Po¨rschke, K.-R. GECOM-CONCOORD 1995, University
of Rennes, May 28-J une 1, 1995; St J acut de la Mer, France. (c)
Schager, F. Planned Dissertation (1997).
(7) (a) (bpy)Ni(CO)2(PhCtCH) (unknown structure): Herrera, A.;
Hoberg, H.; Mynott, R. J . Organomet. Chem. 1981, 222, 331. (b)
(Me3P)2Ni(PhCtCH): Po¨rschke, K.-R.; Mynott, R.; Angermund, K.;
Kru¨ger, C. Z. Naturforsch., B: Anorg. Chem., Org. Chem. 1985, 40,
199. (c) (Ph3P)2Ni(PhCtCH): Po¨rschke, K.-R.; Tsay, Y.-H.; Kru¨ger, C.
Angew. Chem. 1985, 97, 334; Angew. Chem., Int. Ed. Engl. 1985, 24,
323. Rosenthal, U.; Schulz, W. J . Organomet. Chem. 1987, 321, 103.
Bartik, T.; Happ, B.; Iglewsky, M.; Bandmann, H.; Boese, R.; Heim-
bach, P.; Hoffmann, T.; Wenschuh, E. Organometallics 1992, 11, 1235.
(d) Chetcuti, M. J . Comprehensive Organometallic Chemistry II;
Pergamon: Oxford, U.K., 1995; Vol. 9, p 129.
(8) Selected references: (a) Allen, A. D.; Cook, C. D. Can. J . Chem.
1964, 42, 1063. Harbourne, D. A.; Stone, F. G. A. J . Chem. Soc. A 1968,
1765. Nelson, J . H.; J onassen, H. B.; Roundhill, D. M. Inorg. Chem.
1969, 8, 2591. Tripathy, P. B.; Roundhill, D. M. J . Organomet. Chem.
1970, 24, 247. Mann, B. E.; Shaw, B. L.; Tucker, N. I. J . Chem. Soc. A
1971, 2667. Furlani, A.; Carusi, P.; Russo, M. V. J . Organomet. Chem.
1974, 67, 315. Empsall, H. D.; Shaw, B. L. Stringer, A. J . J . Chem.
Soc., Dalton Trans. 1976, 185. J agner, S.; Hazell, R. G.; Rasmussen,
S. E. J . Chem. Soc., Dalton Trans. 1976, 337. Butler, G.; Eaborn, C.;
Pidcock, A. J . Organomet. Chem. 1981, 210, 403. (b) Hartley, F. R.
Comprehensive Organometallic Chemistry; Pergamon: Oxford, U.K.,
1982; Vol. 6, p 691. Young, G. B. Comprehensive Organometallic
Chemistry II; Pergamon: Oxford, U.K., 1995; Vol. 9, p 564.
1
by the H NMR spectra. Of these oligomers the cyclic
11
trimer10 1,3,5-C6H3(COOMe)3 has been identified. No
NMR signals for PdII/IV alkynyl hydride species have
been observed.
(9) For examples of Pd-catalyzed oligo- or polymerization of terminal
alkynes, see: (a) Odaira, Y.; Hara, M.; Tsutsumi, S. Technol. Rep.
Osaka Univ. 1965, 16, 325; Chem. Abstr. 1966, 65, 10670f. (b) Maitlis,
P. M. Acc. Chem. Res. 1976, 9, 93 and references cited therein. (c)
Simionescu, C. I.; Percec, V.; Dumitrescu, S. J . Polym. Sci., Polym.
Chem. Ed. 1977, 15, 2497. (d) Sabourin, E. T. J . Mol. Catal. 1984, 26,
363. (e) Ishikawa, M.; Ohshita, J .; Ito, Y.; Minato, A. J . Organomet.
Chem. 1988, 346, C58. (f) Dzhemilev, U. M.; Khusnutdinov, R. I.;
Shchadneva, N. A.; Nefedov, O. M.; Tolstikov, G. A. Izv. Akad. Nauk
SSSR, Ser. Khim. 1989, 2360; Bull. Acad. Sci. USSR, Div. Chem. Sci.
(Engl. Transl.) 1990, 2171. (g) Trost, B. M.; Sorum, M. T.; Chan, C.;
Harms, A. E.; Ru¨hter, G. J . Am. Chem. Soc. 1997, 119, 698.
(10) It will be shown in a separate paper that [(iPr3P)Pd0] regio- and
stereospecifically catalyzes the oligomerization of 1-alkynes to form
linear trimers.3 Krause, J .; Schager, F.; Po¨rschke, K.-R. 32nd Inter-
national Conference on Coordination Chemistry, Santiago, Chile, Aug
24-29, 1997.

4278 Organometallics, Vol. 16, No. 20, 1997
Schager et al.
(1.287(7) Å) and (dippe)Pt(HCtCH) (1.37(3) Å),15 in
agreement with a relatively weak back-bonding strength
of Pd0. The deviation of the phenyl substituent from
collinearity with the alkyne C atoms in 3a (36.2°) is of
intermediate magnitude (A, 35°; B, 44°). In 3a the
plane of the phenyl group is tilted toward the Pd
coordination plane by 20°, which may be caused by
crystal-packing effects.
Sp ectr oscop ic P r op er ties of 2-5. Complexes 2-5
1
have been characterized by their MS, IR, and H, 13C,
and 31P NMR spectra. In the EI mass spectra the
mononuclear Pd0-1-alkyne complexes 2a , 3a , 4, and 5
(vaporization temperature 20-50 °C) display the mo-
lecular ions which fragment by cleavage of the 1-alkyne
ligands to afford [(dippe)Pd]+ (m/ e 368) as common base
ion.16 With respect to the dinuclear alkyne complexes
2b and 3b (120 °C), the molecular ion has been observed
only for the phenylacetylene derivative 3b, but both
complexes give rise to the dinuclear alkyne-free ion
[Pd2(dippe)2]+ (12+, m/ e 736). The latter monomerizes
into [(dippe)Pd]+, which represents the base ion for 2b.
F igu r e 1. Molecular structure of complex 3a . Selected
bond distances (Å): Pd-P1 ) 2.294(1), Pd-P2 ) 2.301(1),
Pd-C1 ) 2.028(5), Pd-C2 ) 2.062(4), C1-C2 ) 1.246(7).
Selected bond and dihedral angles (deg): P1-Pd-P2 )
87.2(1), P1-Pd-C1 ) 116.6(1), P1-Pd-C2 ) 152.1(1), P2-
Pd-C1 ) 156.2(1), P2-Pd-C2 ) 120.8(1), C1-C2-C3 )
143.8(5), C2-C1-H1 ) 149(3), Pd,P1,P2/Pd,C1,C2 ) 0.6,
Pd,C1,C2/(C3-C8) ) 20.2.
In the IR spectra (Table 1) of the mononuclear (dippe)-
Pd0-1-alkyne complexes 2a , 3a , 4, and 5 the 1-alkyne
C-H stretching band is shifted from about 3300 ( 30
cm-1 for the free alkyne to 3085 ( 25 cm-1, correspond-
ing to a coordination shift of ∆ν(C-H) ) 210 ( 25 cm-1
.
For 2a , 3a , and 4 the CtC stretching bands are shifted
to 1735 ( 25 cm-1, corresponding to ∆ν(CtC) ) 395 (
15 cm-1. For 4, of course, the observed value ∆ν(CtC)
may be somewhat influenced by the occurrence of
vibrational coupling of the CtC and CdO groups
(ν(CdO) 1667 cm-1) in the coordinated alkyne, different
from the situation in the free alkyne. Significantly
Molecu lar Str u ctu r e of (d ippe)P d(P h CtCH) (3a).
The molecular structure of 3a (Figure 1) has been
determined by X-ray crystallography. Due to the mono-
substitution of the alkyne ligand and the nonplanar
(dippe)Pd chelate ring, the molecular point symmetry
is C1. The (dippe)Pd fragment of 3a displays features
similar to those in other (dippe)Pd complexes.12,13 Thus,
the P1-Pd-P2 angle of 87.2(1)° and the P-Pd bond
lengths of 2.294(1) and 2.301(1) Å compare very well
with the mean values (angle 87.17° and bond length
2.304 Å) for the compounds in refs 12 and 13. However,
the “bite angle” P1-Pd-P2 in 3a is significantly smaller
than for the Pd0-alkyne complexes with monodentate
phosphanes (Ph3P)2Pd(MeO2CCtCCO2Me)14a (A, 107°)
and {(c-C6H11)3P}2Pd(F3CCtCCF3)14b (B, 111°), result-
ing in a higher donor strength for the dippe ligand.
Consequently, the Pd-P bond length is distinctly shorter
than for A (2.33 Å (mean)) and B (2.36 Å (mean)), and
the coordination geometry at the TP-3 Pd0 center in 3a
is exactly planar (Pd,P1,P2/Pd,C1,C2 0.6°), whereas for
A (10°) and B (3°) larger distortions from planarity are
observed. In 3a the coordinated CtC bond C1-C2
(1.246(7) Å) is relatively short (uncoordinated CtC:
1.18-1.20 Å), while the length of Pd-C (Pd-C1 )
2.028(5), Pd-C2 ) 2.062(4) Å) is of the same magnitude
as for A (CtC ) 1.28 Å; Pd-C ) 2.06 Å (mean)) and B
(CtC ) 1.27 Å; Pd-C ) 2.05 Å (mean)). In particular,
the coordinated CtC bond is less elongated than for the
corresponding Ni0 and Pt0 complexes (dippe)Ni(HCtCH)
smaller values ∆ν(CtC) are observed for 1a (355 cm-1
)
and 5 (326 cm-1), for which ν(CtC) values for the
uncoordinated alkynes are particularly low.
When the alkyne ligand of the Pd0-1-alkyne com-
plexes is coordinated to a second (dippe)Pd0 fragment,
additional “complementary” coordination shifts to lower
wavenumbers are observed, resulting uniformly for 1b-
3b in an absorption band ν(C-H) 3060 ( 5 cm-1 and in
a total CtC bond complexation shift ∆ν(CtC) 600 (
20 cm-1. Although a direct comparison of Pd0-1-alkyne
and corresponding Ni0-1-alkyne7 and Pt0-1-alkyne8
complex IR data would only be meaningful if the same
phosphane ligand (dippe) was applied, it is evident from
a qualitative examination of the available data that the
coordination shifts ∆ν(C-H) and ∆ν(CtC) are distinctly
smaller for the Pd0-1-alkyne complexes than for the
Ni0- and Pt0-1-alkyne derivatives.
In the 1H and 13C NMR spectra (Table 2) of the
mononuclear complexes 1a -3a , 4, and 5 the alkyne
tCH and -Ct resonances are shifted by ∆δH ) 3.9-
4.7 ppm and ∆δC ) 28-45 ppm to low field as compared
to the uncoordinated alkyne (for 5, ∆δC(SiCt) ) 21.2
ppm appears to be exceptionally small). When the
dinuclear derivatives 1b-3b are formed from 1a -3a ,
(11) The Aldrich Library of 13C and 1H FT NMR Spectra; 1st
ed.; Aldrich Chemical: Milwaukee, WI 1993; p 1282 (spectrum for
11,598-3).
(12) (a) Krause, J .; Pluta, C.; Po¨rschke, K.-R.; Goddard, R. J . Chem.
Soc., Chem. Commun. 1993, 1254. (b) Krause, J .; Haack, K.-J .;
Po¨rschke, K.-R.; Gabor, B.; Goddard, R.; Pluta, C.; Seevogel, K. J . Am.
Chem. Soc. 1996, 118, 804.
(13) (a) Goddard, R.; Hopp, G.; J olly, P. W.; Kru¨ger, C.; Mynott, R.;
Wirtz, C. J . Organomet. Chem. 1995, 486, 163. (b) Schager, F.;
Seevogel, K.; Po¨rschke, K.-R.; Kessler, M.; Kru¨ger, C. J . Am. Chem.
Soc. 1996, 118, 13075.
(14) (a) McGinnety, J . A. J . Chem. Soc., Dalton Trans. 1974, 1038.
(b) Farrar, D. H.; Payne, N. C. J . Organomet. Chem. 1981, 220, 239.
(15) (a) Haack, K.-J . Dissertation, Universita¨t Du¨sseldorf, 1994. (b)
Kru¨ger, C.; Goddard, R. Unpublished results.
(16) In the EI mass spectra the fragmentation of (dippe)Pd0- and
(dtbpe)Pd0-alkene/alkyne complexes is initiated by loss of the alkene
or alkyne ligand to produce the PdI radical ions [(dippe)Pd]+ and [(dt-
bpe)Pd]+. The PdI ions fragment by radical substituent cleavage to
afford the PdII ions [(iPr2PC2H4PiPr)Pd]+ and [(tBu2PC2H4PtBu)Pd]+
,
which successively eliminate propene or 2-methylpropene to yield [(H2-
PC2H4PH)Pd]+. In contrast, for [(dippe)M]+ and [(dtbpe)M]+ (M ) Ni,
Pt) alkene elimination proceeds with preservation of the MI radical
ion character.

(R2PC2H4PR2)Pd0-1-Alkyne Complexes
Organometallics, Vol. 16, No. 20, 1997 4279
Ta ble 1. Selected IR (Ra m a n ) Da ta for th e Alk yn e Liga n d s of th e Mon o- a n d Din u clea r (d ip p e)P d 0-Alk yn e
Com p lexes 1-6 a n d 8-11
ν(C-H) (cm-1
)
ν(CtC) (cm-1
)
free alkyne
coord alkyne
∆ν
free alkyne
1974 (Ra)a
coord alkyne
1619
∆ν
1a
3374 (Ra) syma
3289 asyma
3125 sym
3085 asym
3065 symb
3107
3058
3062
3055
3087
3099
249
204
309
227
276
229
236
186
194
355
1b
2a
2b
3a
3b
4
1370
1756
1528
1720
1524
1718d
1710
604
384
612
390
586
409
326
3344/23c
3291
2152/27c
2110
3273
3293
2127
2036
5
6a
6c
3298
3087
211
(218)
2105
1717
1498
388
607
3080e
8a
8b
9
10
11
2240 (Ra)
1862
1618
1827
1811d
1771
378
622
396
437
339
2223 (Ra)
2248 (Ra)
2110 (Ra)
a
b
d
Gaseous ethyne. Very weak band; hard to detect. c Gaseous propyne; P and R branches. Band involves C-C and C-O stretchings.
e Assignment uncertain due to olefinic C-H bands occurring in the same region.
Ta ble 2. Selected 1H, 13C, a n d 31P NMR Da ta for th e Mon o- a n d Din u clea r (d ip p e)P d 0-Alk yn e Com p lexes
1-6 a n d 8-11a
δH(tCH)
δC(-Ct)
δC(tCH)
coord
alkyne
free
alkyne
coord
alkyne
free
alkyne
coord
alkyne
free
alkyne
1J (CH)d
coord alkyne
∆δH
∆δC
∆δC
δP
2J (PP)d
1a
1b
2a b
2bb
3a
3b
4
6.91
5.75
6.21
5.44
7.36
5.78
7.34
7.26
7.13
5.49
2.40
1.80
3.44
4.51
3.35
4.41
3.64
3.92
2.34
3.85
4.68
3.83
2.19
106.6
67.7
96.4
67.7
107.7
66.6
112.2
121.3
109.8
65.5
71.9
68.3
79.2
34.7
-4.2
28.1
-0.6
28.5
-12.6
35.6
31.5
30.4
-13.9
211
200
212
196
211
198
210
212
69.5
59.9
116.0
85.4
129.4
92.2
117.5
116.3
123.5
88.5
106.6
84.9
80.0
84.9
36.0
5.4
44.5
7.3
42.1
21.2
40.7
5.7
31.7
10.0
36.0
47.8
20.7
68.0, 67.8
59.3, 57.3e
70.6, 67.5
61.3, 55.1e
74.2, 71.3
68.5, 65.9
69.9, 68.4
61.1, 57.7e
67.1c
58.0
67.5
75.7
63.4
45
34
3.49
2.58
3.30
75.4
95.1
82.8
76.6
89.8
79.4
19
46
32
5
6a c
6cc
8a
8bb
9
74.9
126.1
122.7
134.7
90.1
74.9
114.0
10
11
a
b
d
Solvent THF-d8, temperature 27 °C. Temperature -30 °C. c Temperature -80 °C. Coupling constant in hertz. e Approximate values
of a nonsimulated AA′BB′ spin system.
an opposite shift to high field is observed, so that the
coordination chemical shifts17 ∆δH and ∆δC are now
markedly smaller and even become negative for the
unsubstituted alkyne C atom. For mononuclear 2a , 3a ,
4, and 5 ABX spin systems are observed for the tCH
(A, B ) 31P; X ) 1H) and the tCH and -Ct resonances
(A, B ) 31P; X ) 13C), and for dinuclear 2b and 3b the
corresponding nuclei give rise to well-resolved A2B2X
multiplets (“triplet of triplets”). In agreement with this,
the 31P NMR spectra display sharp AB (2a , 3a , 4, 5) or
AA′BB′ (2b, 3b) multiplets. When the solution of 2a ,b
is warmed from -30 to 27 °C, the HCtCCH3 ligand
resonances are slightly broadened but the multiplet
patterns are maintained.18 It follows from these fea-
tures that for both mono- and dinuclear complexes the
coordination of the 1-alkyne to the (dippe)Pd0 moieties
can be considered to be rigid on the NMR time scale
(Cs symmetry). For 2a ,b the spectra indicate a “starting
slow rotation” at ambient temperature.
With regard to the coupling constant 1J (CH) of the
1-alkyne ligand, it has been found that it is lowered from
about 250 Hz for the uncoordinated 1-alkyne to about
211 Hz in the mononuclear complexes (1a , 2a , 3a , 4, 5)
and to e200 Hz in the dinuclear derivatives (1b, 2b,
3b).
(d ip p e)P d 0-Vin yla cetylen e Com p lexes (6a -c).
After we had established that 1-alkynes indeed form
stable complexes with Pd0, it was of further interest to
explore how the reactivity of the terminal CtC bond is
influenced by conjugation to a CdC or CtC bond. For
this purpose we studied [(dippe)Pd0] coordination com-
pounds with vinylacetylene and butadiyne (see below).
When vinylacetylene is added to a pentane solution
of (dippe)Pd(C2H4) at -78 °C, colorless crystals of 6a ,b
precipitate in almost quantitative yield. According to
the IR spectrum this precipitate consists of a roughly
4:1 mixture of complex isomers in which the enyne
ligand is coordinated by either the CtC bond (6a ) or
the CdC bond (6b) to Pd0 (Scheme 3). Thus, the major
isomer 6a displays absorption bands (Table 1) at 3087
and 1717 cm-1 for the η2-CtCH moiety and further
(17) The 1H and 13C coordination chemical shift, i.e., the change in
chemical shift which the alkyne experiences upon coordination to a
metal center, is defined by ∆δ ) δligand - δfree alkyne. Thus, typical alkyne
coordination shifts to lower field are positive, whereas those to higher
field are negative. J olly, P. W.; Mynott, R. Adv. Organomet. Chem.
1981, 19, 257.
(18) The 31P AB signals of 2a coalesce at 27 °C due to the very small
difference in chemical shifts.

4280 Organometallics, Vol. 16, No. 20, 1997
Schager et al.
Sch em e 3
Sch em e 4
bands at 3010 and 1582 cm-1 for the uncoordinated
CHdCH2 function (cf. vinylacetylene: 3106, 3016 (dC-
H) and 1599 (CdC) cm-1), whereas absorption bands
at 3317 and 2068 cm-1 are attributed to the uncoordi-
nated CtCH moiety of the η2-CHdCH2 isomer 6b. The
same mixture of isomers is isolated when the reaction
is carried out in diethyl ether at 20 °C and the product
is crystallized at -30 or -78 °C. The η2-CtCH isomer
6a is considered to be thermodynamically slightly more
stable than the η2-CHdCH2 isomer 6b. The presence
of 6b in the solid is deemed to result from a crystal-
lization effect. According to the 1H and 31P NMR
spectra, a solution (THF-d8) of 6a ,b at -80 °C contains
almost exclusively 6a but an increasing amount of 6b
(40%) is formed when the solution is warmed to ambient
temperature. Complex 6a ,b is only moderately soluble
in THF at low temperature and is even less so in diethyl
ether. It slowly decomposes as a solid (mp 76 °C) at 20
°C and is somewhat less stable in solution. By solution
thermolysis (20 °C) some dinuclear 6c but no 12 (see
below) is formed. In the EI mass spectrum 6a ,b exhibit
a molecular ion (m/ e 420, 6%) which fragments by
cleavage of the enyne ligand to afford the base ion
[(dippe)Pd]+ (m/ e 368).
compared to uncoordinated vinylacetylene. Most strongly
affected are the protons dCH- (δH 3.12) and dCHZHE
(δH 2.49, 2.36) of the coordinated vinyl group. The tCH
resonance (δH 2.63) is still in the range expected for
uncoordinated alkynes, and the moderate high-field
shift is explained by a weakened conjugation between
CtC and the (now coordinated) CdC bond. An assign-
ment of the dippe resonances of 6b is difficult to achieve
because of the expected low symmetry and the presence
of the isomer mixture.
In the 31P NMR spectrum (27 °C) the isomers 6a and
6b display sharp AB spin systems. For 6b the signals
are at somewhat higher field and 2J (PP) ) 43 Hz is
larger than for 6a (32 Hz), indicating that in 6b more
charge remains at the Pd atom due to a weaker electron
withdrawal induced by the vinyl group as compared to
that by the alkyne moiety in 6a .
It follows from the NMR spectra that in the complexes
neither the alkyne ligand (6a ) nor the vinyl ligand (6b)
rotates rapidly about the bond axis to [(dippe)Pd0].
Furthermore, the isomerization reaction 6a h 6b
(Scheme 3) is slow at 20 °C on the NMR time scale and
no exchange of 6a ,b with uncoordinated vinylacetylene
has been detected (1H NMR). In compliance with other
exchange reactions of oligofunctional alkenes (butadi-
ene, isoprene,19 p-benzoquinone, cyclooctadiene, 1,5-
hexadiene,2 stannacyclopentadiene,12b cyclooctatetraene6c)
at TP-3 Pd0 we suppose that the slow isomerization 6a
h 6b proceeds by an intramolecular mechanism via a
T-4 Pd0 transition state (Scheme 4).
In the solution 1H NMR spectrum (-80 °C) the
acetylenic proton of 6a gives rise to a low-field doublet
of doublets (δH 7.13) due to different couplings
3
3J (PH)trans and J (PH)cis. Both the chemical shift and
the multiplet structure are typical for (dippe)Pd0-1-
alkyne complexes (Table 2). Concerning the vinyl
protons, the signal of CH2dCH- is also at relatively low
field (δH 6.97) but for the terminal protons (δH 5.40
(dCHHZ), 5.25 (dCHEH)) the changes in the chemical
shift are less pronounced as compared to uncoordinated
vinylacetylene (δH 3.30 (HCt), 5.81 (-CHd), 5.65
(dCHHZ), 5.50 (dCHEH)). Similarly, the 13C NMR
signals for the coordinated CtC bond at δC 123.5 (tC-)
and 109.8 (tCH) (Table 2) are at significantly lower
field from the corresponding signals of uncoordinated
vinylacetylene (δC 82.8 (tC-), 79.4 (tCH)) and display
The fact that in mononuclear 6a ,b the [(dippe)Pd0]
fragment is coordinated to the CtC bond (6a ) or the
CdC bond (6b) led to the expectation that in a dinuclear
derivative (6c) the [(dippe)Pd0] fragments were coordi-
nated to both CtC and CdC bonds. This is, however,
not true. When the ethereal solution of 6a ,b is treated
at 0 °C with an equimolar amount of (dippe)Pd(η2-
C6H10), generated in situ from (dippe)Pd(η1-C3H5)2,
orange crystals of the dinuclear vinylacetylene complex
6c are obtained (-78 °C) (Scheme 3). As follows from
the MS, IR, and NMR data, the [(dippe)Pd0] fragments
in 6c are coordinated exclusively to the CtC bond.
2
distinctly different couplings J (PC)trans (ca. 65 Hz) and
2J (PC)cis (ca. 4 Hz), whereas the vinyl signals at δC 128.1
(-CHd) and 120.7 (dCH2) are close to those of unco-
ordinated vinylacetylene (δC 117.5 (-CHd), 128.4
(dCH2)). Furthermore, the dippe ligand 1H and 13C
signals of 6a indicate Cs symmetry of the complex (the
mirror plane passing through Pd, both P atoms, and the
vinylacetylene skeleton), in agreement with a coordi-
nated CtC bond, whereas for 6b (coordinated unsym-
metrical CdC bond) C1 symmetry is expected.
(19) (a) Benn, R.; J olly, P. W.; J oswig, T.; Mynott, R.; Schick, K.-P.
Z. Naturforsch., B: Anorg. Chem., Org. Chem. 1986, 41, 680. (b)
Topalovic, I. Dissertation, Universita¨t Siegen, 1990. (c) Benn, R.; Betz,
P.; Goddard, R.; J olly, P. W.; Kokel, N.; Kru¨ger, C.; Topalovic, I. Z.
Naturforsch., B: Anorg. Chem., Org. Chem. 1991, 46, 1395.
In contrast, for the vinylacetylene ligand in 6b (20
°C) all 1H resonances are shifted to higher field as

(R2PC2H4PR2)Pd0-1-Alkyne Complexes
Organometallics, Vol. 16, No. 20, 1997 4281
The mass spectrum of 6c displays M+, the alkyne-
free ion [Pd2(dippe)2]+ (12+, see below) typical for
{(dippe)Pd}2(µ-alkyne) complexes, and the base ion
[(dippe)Pd]+. In the IR spectrum a band at 1498 cm-1
can be assigned to the bridging 1-alkyne ligand, whereas
ν(CdC) 1600 cm-1 corresponds to the uncoordinated
Sch em e 5
1
vinyl group. In the H NMR spectrum (-80 °C) of 6c
the tCH resonance at δH 5.49 represents a triplet of
triplets due to the couplings to two pairs of formally
trans- and cis-positioned P atoms. The signal of
CH2dCH- is shifted further to low field (δH 7.16), but
the signals of the terminal vinyl protons (δH 4.79
(dCHHZ), 4.32 (dCHEH)) are at relatively high field (cf.
6a ). Correspondingly, the 13C resonances of tC- (δC
88.5) and tCH (δC 65.5) are of the magnitude (cf. Table
2) and display phosphorus couplings as expected for a
µ-alkyne ligand. For the uncoordinated vinyl group the
-CHd signal is shifted further to low field (δC 142.7)
and the dCH2 signal is shifted further to high field (δC
104.1) in the following sequence: uncoordinated viny-
lacetylene f 6a f 6c. The high-field location and the
AA′BB′ multiplet of the 31P signals are also indicative
of a {(dippe)Pd}2(µ-1-alkyne) complex.
At 27 °C the vinylacetylene 1H signals and the 31P
NMR signals are significantly broadened, indicating a
dynamic structure of 6c. The structural dynamics of
6c are intramolecular and are not due to cleavage of
one [(dippe)Pd0] fragment, as evidenced by the fact that
for a mixture of 6c and 6a ,b (27 °C) the NMR signals
of the latter remain sharp. Taking into account that
3b, which is strongly related to 6c, is structurally rigid,
we exclude the possibility that the dynamics of 6c are
represented by a simple rotation of the [(dippe)Pd0]
groups about the coordination axis to the CtC bond.
Instead, we suggest that one of the [(dippe)Pd0] frag-
ments in 6c migrates to the vinyl bond and there the
[(dippe)Pd0] fragment rotates about the coordination
axis to the (more weakly coordinated) CdC bond. By
return to the CtC bond the pairwise corresponding
nuclei of the dippe ligand have equilibrated (Scheme 4).
The dynamics of the [(dippe)Pd0] fragments in 6c
proceed more easily than in 6a due to an increased
charge at the vinylacetylene ligand. We finally note
that at 20 °C a slow solution thermolysis of 6c starts
which does not produce alkyne-free 12 (as for 3a ,b
(“activated alkyne”)), although 2a ,b and 8a ,b (“nonac-
tivated alkynes”) do.
Complexes 7a ,c,f, as solids and in solution, are stable
at ambient temperature for several days. In the EI
mass spectra the molecular ions are observed. Cleavage
of the butadiyne ligand affords [(dippe)M]+ as base
ions.16 The IR and 1H and 13C NMR data of the
butadiyne ligands of 7a ,c,f are compiled in Table 3.
Concerning the IR spectra, the most characteristic are
ν(C-H) and ν(CtC) of the coordinated CtC bond, for
which the wavenumbers are largest for 7c, lowest for
7f, and intermediate for 7a , consistent with an increase
in the back-bonding ability in the series Pd0 < Ni(0) <
1
Pt(0).23a,24 With respect to the H and 13C NMR data,
the downfield complexation shifts of the resonances of
the coordinated HCtC bonds are smallest for 7c. In a
comparison of 7a and 7f, the proton resonance of 7f (δH
8.41) is at an exceedingly low field but the 13C reso-
nances are almost coincident.
For 7a ,c,f the 31P NMR spectra display AB type spin
systems. It follows from the NMR spectra that all
complexes are rigid (relative to the NMR time scale)
with respect to both a rotation of the coordinated CtC
bond about the bond axis to the metal and an exchange
of coordinated and uncoordinated CtC bonds.
When 7c is reacted with (dippe)Pd(η2-C6H10), gener-
ated in situ from (dippe)Pd(η1-C3H5)2, a brown solution
is obtained (0 °C) from which the dinuclear Pd0-
butadiyne complex 7d crystallizes at -78 °C over the
course of several weeks (Scheme 6). Complex 7d is
fairly stable (dec pt >65 °C). The composition is
confirmed by the EI mass spectrum (130 °C), which
displays the molecular ion (m/ e 786). Loss of the
butadiyne ligand affords 12+, which monomerizes into
[(dippe)Pd]+. Complex 7d corresponds to the structur-
ally characterized Ni analogue 7b, as follows from
(dippe)M0-Bu tadiyn e Com plexes (7a -f). We have
already communicated that butadiyne is coordinated at
Ni(0) to form the mono- and dinuclear complexes
(iPr2P(CH2)nPiPr2)Ni(η2-HCtCCtCH) (n ) 2 (7a ), 3)
and {(iPr2P(CH2)nPiPr2)Ni}2{µ-(1,2-η2):(3,4-η2)-HCtCCt
CH} (n ) 2 (7b), 3), which have also been structurally
characterized.20 In addition, for n ) 2 (dippe) mono-
nuclear derivatives of the heavier homologues (dippe)M-
(η2-HCtCCtCH) (M ) Pd (7c), Pt (7f)) have been
synthesized.6,21 When 1 mol equiv of butadiyne is added
to the colorless pentane solution of (dippe)Pd(C2H4) at
-30 °C, off-white microcrystals of 7c precipitate in 93%
yield. Similarly, the reaction of dippe/Pt(cod)2 (cod )
1,5-cyclooctadiene)22 and butadiyne affords yellow-
orange cubes of 7f (75%) (Scheme 5).
(22) The reaction of stoichiometric amounts of Pt(cod)2 and dippe
in diethyl ether (20 °C) affords (dippe)Pt(η2-cod), which has been
spectroscopically characterized.15a
(23) Related complexes are as follows. (a) (Ph3P)2Pd{C2(COOMe)2}:
Greaves, E. O.; Maitlis, P. M. J . Organomet. Chem. 1966, 6, 104.
Greaves, E. O.; Lock, C. J . L.; Maitlis, P. M. Can. J . Chem. 1968, 46,
3879 ((Ph3P)2Pd(C2Ph2) is not isolable, see also ref 23c). (b)
(Ph2PC2H4PPh2)Pd{C2(COOMe)2}: Moseley, K.; Maitlis, P. M. J . Chem.
Soc., Dalton Trans. 1974, 169. (c) For (Ph3P)2Pd and (Cy3P)2Pd
complexes with hydroxy- and alkoxyalkynes, see: Krause, H.-J . Z.
Anorg. Allg. Chem. 1982, 490, 141. (d) (Cy2PC2H4PCy2)Pd{C2-
(COOMe)2}: Schick, K.-P. Dissertation, Universita¨t Bochum, 1982.
J olly, P. W. Angew. Chem. 1985, 97, 279; Angew. Chem., Int. Ed. Engl.
1985, 24, 283. Pan, Y.; Mague, J . T.; Fink, M. J . Organometallics 1992,
11, 3495. See also ref 27. For (Cy2PC2H4PCy2)Pd(C2Ph2) and {(Cy2-
PC2H4PCy2)Pd}2(µ-C2Ph2), see ref 27. (e) Although (iPr3P)2Pd(C2H2)3,12
has been isolated, (iPr3P)2Pd(C2Ph2) appears to be unstable. Cestaric,
G. Diplomarbeit, Universita¨t Du¨sseldorf, 1996.
(20) Bonrath, W.; Po¨rschke, K.-R.; Wilke, G.; Angermund, K.;
Kru¨ger, C. Angew. Chem. 1988, 100, 853; Angew. Chem., Int. Ed. Engl.
1988, 27, 833.
(24) (a) Farrar, D. H.; Payne, N. C. J . Organomet. Chem. 1981, 220,
251. (b) Rosenthal, U.; Oehme, G.; Go¨rls, H.; Burlakov, V. V.; Polyakov,
A. V.; Yanovsky, A. I.; Struchkov, Y. T. J . Organomet. Chem. 1990,
389, 251.
(21) Bonrath, W. Dissertation, Universita¨t Bochum, 1988.

4282 Organometallics, Vol. 16, No. 20, 1997
Schager et al.
Sch em e 6
concurring butadiyne ligand IR and NMR data (Table
3). Again, the coordination shifts of the butadiyne
ligand IR bands and NMR resonances are smaller for
7d than for 7b, in agreement with a lower back-bonding
strength of Pd0 as compared to Ni(0). The dippe NMR
signals of 7d indicate C2v or C2h symmetry in solution.
Thus, the two [(dippe)Pd] moieties in 7d are coordinated
at different CtC bonds of a bridging butadiyne ligand.
When a THF-d8 solution of 7d is kept at -80 °C, a
slow isomerization takes place to afford 7e. The isomer-
ization is complete after about 1 week. According to the
1H and 13C NMR spectra (Table 3) the [(dippe)Pd]
moieties in 7e are coordinated to the same CtC bond
of a bridging butadiyne ligand (similar to the case for
2b, 3b, and 6c). Thereby, a rather rigid structure
results, and the symmetry of the complex is lowered to
Cs. When the solution of 7e is warmed to 0 °C, the
isomerization is only partially reversed. It has not been
attempted to isolate 7e. Apparently, isomers 7d and
7e are in slow equilibrium and subtle effects determine
which one is preferred. While 7e is thermodynamically
favored in solution, crystallization affords 7d .
(d ip p e)P d 0 Com p lexes w ith MeCtCMe, P h CtC-
P h , MeO2CCtCCO2Me, a n d Me3SiCtCSiMe3 (8-
11). For reasons of comparison we have also prepared
some (dippe)Pd0 complexes with internal alkynes. The
substituents of these alkynes are of the same kind as
in the case of the 1-alkyne complexes 2-5. When to a
solution of (dippe)Pd(C2H4) in pentane or diethyl ether
2-butyne (0 °C), tolane, acetylenedicarboxylic acid di-
methyl ester, and bis(trimethylsilyl)acetylene (all 20 °C)
are added, colorless off-white crystals of the mono-
nuclear complexes 8a and 9-11 are obtained in 80-
90% yield (Scheme 7).23 Solutions of 9-11 are stable
at 20 °C for at least several days. Complex 8a partially
eliminates 2-butyne in solution to produce small amounts
of dinuclear 8b. The latter has been prepared in a pure
state by treating 8a with (dippe)Pd(η2-C6H10), obtained
in situ from (dippe)Pd(η1-C3H5)2, to afford yellow crystals
of 8b in 85% yield.25 When a solution of 8b in THF-d8
is kept at 20 °C for a few hours, the 31P NMR spectrum
shows, besides the singlet of 8b (δP 56.4, 70%), ad-
ditional singlets of equal intensity (each 15%) for
mononuclear 8a (δP 67.1) and dinuclear alkyne-free 12
(δP 33.7) due to an equilibrium between these complexes
(Scheme 8). No byproducts are detected. Complex 12
(25) Without question dinuclear derivatives of 9-11 can also be
prepared by applying a procedure similar to that for 8b, although this
has not been attempted by us.

(R2PC2H4PR2)Pd0-1-Alkyne Complexes
Organometallics, Vol. 16, No. 20, 1997 4283
composition and purity of the complexes. The 13C
Sch em e 7
resonances of the (quaternary) CtC atoms represent for
9 an ABX multiplet and for 10 a doublet (2J (PC)trans
)
74 Hz; 2J (PC)cis is very small). Thus, different couplings
to trans and cis 31P nuclei are observed in agreement
with a static CtC bond coordination in these complexes.
Concerning the 2-butyne complexes 8a ,b, the 13C
multiplet structure of the 2-butyne CtC atoms has not
been sufficiently resolved to allow an unequivocal as-
signment to a certain spin system (ABX, A2X, A2B2X,
or A4X). However, the CH3 1H resonance of the 2-bu-
tyne ligand in mononuclear 8a (δH 2.51) also represents
an ABX multiplet, whereas the corresponding CH3
signal of dinuclear 8b (δH 2.86) is a sharp A4X quintet
at 27 °C (unresolved at -30 °C). It is concluded from
these spectra that at ambient temperature and relative
to the NMR time scale the rotation of the (dippe)Pd0
moieties about the bond axis to the 2-butyne ligand is
slow for 8a (similar as for the propyne complex 2a ) but
rapid for 8b (in contrast to 2b). The anticipated bond
rotation in 8b is presumably due to the increased charge
at the bridging CtC bond, resulting from the inductive
effect of two Me substituents and back-bonding from two
Pd0 centers.
Sch em e 8
Discu ssion
We have described a series of novel mono- and
dinuclear (dippe)Pd0-1-alkyne complexes (2-7) and also
some derivatives with internal alkynes (8-11). Al-
though the former are in general thermally somewhat
less stable than the latter, the Pd0-1-alkyne complexes
should not be regarded as particularly unstable, in
contrast to prior perception. The following features of
the complexes are worth emphasizing:
(a) The relatively small and “fixed” bite of the dippe
ligand at Pd0 (87.2°), as compared to monodentate
phosphanes and to bidentate ligands R′2P(CH2)nPR′2 (n
> 2) forming larger chelate rings, contributes to the
stabilization of the complexes because of an increased
back-donation from Pd0 to the alkyne ligand. Thus, no
alkyne ligand dissociation has been observed on the
NMR time scale, in contrast to, e.g., extensive alkyne
ligand dissociation of (iPr3P)2Pd(C2Ph2).23e
(b) As one might expect, alkyne coordination to the
[(dippe)Pd0] fragment is generally weaker for alkynes
with electron-donating substituents and stronger for
those with electron-withdrawing substituents. Thus, in
solution the mononuclear complexes 2a and 8a slowly
eliminate propyne or 2-butyne to form the dinuclear
complexes 2b and 8b as primary products. Similarly,
while monophenyl-substituted 3a slowly eliminates
PhC2H to form 3b, the tolane derivative 9 is stable. In
contrast, for COOMe- and SiMe3-substituted alkynes
the mononuclear complexes (4, 10 and 5, 11) are stable.
For the mononuclear Pd0-alkyne complexes the IR
and 13C NMR complexation shifts ∆ν(CtC) and ∆δ-
(CtC) respectively display an approximately linear
correlation with the inductive effect substituent con-
stant σI29a of R.29b The data confirm similar correlations
established before for related alkyne complexes.30
is exceedingly soluble in ordinary solvents and has not
been isolated so far.26 It is assumed that 12 is analo-
gous to the structurally characterized Pd2{µ-(c-C6H11)2-
PC2H4P(c-C6H11)2}2.27
P r op er ties of 8-11. The melting points of the
mono- and dinuclear 2-butyne complexes 8a ,b (about
80 °C) and of the Me3SiCtCSiMe3 complex 11 (50 °C)
are rather low, whereas those of the other derivatives
are higher (9, 166 °C; 10, 101 °C). Solutions of 9-11
and added alkyne (C2Ph2, C2(COOMe)2, or C2(SiMe3)2)
show no reaction at 20 °C over several days,28 in
contrast to the corresponding 1-alkyne complexes. In
the EI mass spectra of the mononuclear complexes (8a ,
9-11) the molecular ions are observed, whereas for
dinuclear 8b the largest detected ion is alkyne-free [(di-
ppe)2Pd2]+ (12+, 23%). In the IR spectra (Table 1) the
CtC stretching frequencies of the disubstituted alkyne
ligands occur at 1840 ( 30 cm-1 (11, 1771 cm-1) and
thus, as expected, are at higher wavenumbers than for
the 1-alkyne complexes. The complexation shift ∆ν-
(CtC) of the disubstituted alkyne ligands, however, is
of magnitude similar to that for the corresponding
1-alkyne complexes.
1
The H and 31P NMR spectra of 9-11 (Table 2) are
not very informative and serve only to confirm the
(26) In solution, Pd2(µ-dippe)2 (12; C28H64P4Pd2, Mr ) 737.6) has been
encountered before by various groups. (a) Hopp, G.; J olly, P. W.;
Krause, J .; Po¨rschke, K.-R. Unpublished results. (b) When an ethereal
solution of (dippe)Pd{η2-CH2dC(Me)C2H4C(Me)dCH2}, obtained from
(dippe)Pd(η1-2-MeC3H4)2 at 20 °C, is evaporated to dryness, the color
3
changes to deep red. In the 1H and 31P NMR spectra (THF-d8) of the
residue the signals of 12 are observed: 1H NMR (200 MHz, 27 °C) δ
1.80 (8 H, PCH), 1.75 (8 H, PCH2), 1.26, 1.22 (each 24 H, diastereotopic
Me); 31P NMR δ 33.7; EI-MS (70 eV, 160 °C) m/ e 736 (M+).15a (c)
Fryzuk, M. D.; Clentsmith, G. K. B.; Rettig, S. J .; Ha¨gele, G.
Organometallics 1996, 15, 2083.
(27) Pan, Y.; Mague, J . T.; Fink, M. J . J . Am. Chem. Soc. 1993, 115,
3842. Landtiser, R.; Pan, Y.; Fink, M. J . Phosphorus, Sulfur Silicon
Relat. Elem. 1994, 93-94, 393.
(28) C6(COOMe)6, the cyclotrimer of C2(COOMe)2, can easily be
excluded because of the absence of the corresponding 1H NMR signal
(δH 3.88). Diercks, R.; tom Dieck, H. Z. Naturforsch., B: Anorg. Chem.,
Org. Chem. 1984, 39, 180.
(29) (a) Charton, M. Prog. Phys. Org. Chem. 1981, 13, 119. (b) For
unsymmetrical alkynes, σI and ∆δ(CtC) are defined as σI ) {σI(R1) +
σI(R2)}/2 and ∆δ(CtC) ) {∆δ(C1) + ∆δ(C2)}/2, respectively.
(30) (a) Herberich, G. E.; Okuda, J . Chem. Ber. 1984, 117, 3112. (b)
Rosenthal, U.; Schulz, W. J . Organomet. Chem. 1987, 321, 103.
Rosenthal, U.; Oehme, G.; Burlakov, V. V.; Petrovskii, P. V.; Shur, V.
B.; Vol’pin, M. E. J . Organomet. Chem. 1990, 391, 119.

4284 Organometallics, Vol. 16, No. 20, 1997
Schager et al.
(KBr): see Table 1. 1H NMR (200 MHz, -30 °C): δ 6.21 (m,
1 H, tCH), 2.64 (m, 3 H, tCMe), propyne; 2.0 (4 H, PCH and
P′CH), 1.6 (4 H, PCH2 and P′CH2), 1.1 (four unresolved signals
24 H, Me), dippe. 13C NMR (100.6 MHz, -80 °C): δ 116.6 [1
(c) As determined by NMR, the mononuclear (dippe)-
Pd0-alkyne complexes of ethyne, 1-alkynes, and inter-
nal alkynes are rigid (27 °C) with respect to a possible
alkyne ligand rotation about the bond axis to Pd0. While
this also holds for dinuclear 1b (ethyne) and largely for
2b (propyne), a corresponding rotation indeed takes
place in the case of 8b, where the 2-butyne ligand is
relatively electron-rich.
(d) With respect to possible secondary reactions,
initiated for example by a C-H activation step of the
1-alkyne, the pure (dippe)Pd0-1-alkyne complexes are
surprisingly stable. Such a reaction has to be taken into
account only when an excess of the 1-alkyne is present,
thereby facilitating an anticipated C-H addition of a
further alkyne molecule to the initially formed 16e
complex by an associative mechanism. This secondary
reaction is especially severe for the MeO2CCtCH
complex 4, which may explain why former attempts to
synthesize such complexes had failed. Secondary reac-
tions are retarded by carrying out the synthesis of the
complexes at low temperature.
2
2
2
C, J (PC)trans ) 52.5 Hz, J (PC)cis ) 24.3 Hz, J (CH) ) 9 Hz,
tCMe], 96.4 [1 C, 1J (CH) ) 212 Hz, 2J (PC)trans ) 56.0 Hz,
3
3
2J (PC)cis ) 2.9 Hz, tCH], 17.6 [1 C, J (PC) ) 19.1 Hz, J (PC)
) 12.4 Hz, Me], propyne; 26.0, 25.9 [each 1 C, 1J (PC) ) 4.8
Hz, PCH and P′CH], 22.7, 22.3 [each 1 C, 1J (PC) ) 18 Hz,
PCH2 and P′CH2], 20.3 [4 C, 2J (PC) ) 10.5 Hz, set of
diastereotopic Me], 18.9 [4 C, 2J (PC) ) 15.3 Hz, set of
diastereotopic Me], dippe. 31P NMR (81 MHz, -30 °C): see
Table 2. 31P NMR (81 MHz, 27 °C): δ 68.2 (coalesced signal).
{(d ip p e)P d }2(µ-MeCtCH) (2b). An ethereal solution (5
mL) of 2a (409 mg, 1.0 mmol) is combined at -78 °C with a
cream-colored suspension of (dippe)Pd(η1-C3H5)2 (451 mg, 1.0
mmol) in diethyl ether (10 mL). When the mixture is warmed
to 0 °C, a yellow solution is obtained from which off-white
crystals separate at -30/-78 °C. The product is isolated as
described above and dried under vacuum at 0 °C: yield 620
mg (80%); mp 70 °C dec. Anal. Calcd for C31H68P4Pd2
(777.6): C, 47.88; H, 8.81; P, 15.93; Pd, 27.37. Found: C,
47.83; H, 8.82; P, 15.76; Pd, 27.53. EI-MS (120 °C): m/ e (%)
736 (12+, 3), 368 ([(dippe)Pd]+, 100), 40 ([MeCtCH]+, 50). IR
(KBr): see Table 1. 1H NMR (300 MHz, -30 °C): δ 5.44 [tt,
In conclusion, due to the electronic and steric proper-
ties (strong chelate effect) of the dippe ligand the
[(dippe)Pd0] fragment withstands a lowering of the
phosphane ligation from L2Pd0 to L-Pd0 or phosphane-
free Pd0, which are considered to be catalytically more
active species,10,23b and as a result L2Pd0-1-alkyne
complexes are easily isolable.31
3
3
1 H, J (PH)trans ) 18 Hz, J (PH)cis ) 6 Hz, tCH], 2.92 [t, 3 H,
4J (PH) ) 8 Hz, tCMe], propyne; 2.0-1.7 (four unresolved
signals, 8 H, PCH), 1.5-1.3 (four unresolved signals, 8 H,
PCH2), 1.1-0.8 (eight unresolved signals, 48 H, Me), dippe.
2
13C NMR (75.5 MHz, -30 °C): δ 85.4 [tt, 1 C, J (PC)trans ) 47
2
1
Hz, J (PC)cis ) 6 Hz, tCMe], 67.7 [tt, 1 C, J (CH) ) 196 Hz,
2J (PC)trans ) 46 Hz, 2J (PC)cis ) 7 Hz, tCH], ∼26 (obscured
CH3), propyne; 25.9 (8 C, four unresolved signals PCH), 22.7
(4 C, PCH2 and P′CH2), 21.1, 20.8, 20.3, 20.0, 19.6 (each 2 C),
18.9 (4 C), 18.7 (2 C, Me), dippe. 31P NMR (121.5 MHz, -30
°C): see Table 2.
Exp er im en ta l Section
To exclude oxygen and moisture, all operations were con-
ducted under an atmosphere of argon by standard Schlenk
techniques. Pd(η3-C3H5)2,32 Pd(η3-2-MeC3H4)2,32 (dippe)Pd(η1-
C3H5)2,2 (dippe)Pd(η1-2-MeC3H4)2,3 (dippe)Pd(C2H4),2 and Pt-
(cod)233 were prepared by published procedures. Microanalyses
were performed by the Mikroanalytisches Labor Kolbe, Mu¨l-
heim, Germany. 1H NMR spectra (δ relative to internal TMS)
were measured at 200, 300, and 400 MHz, 13C NMR spectra
(δ relative to internal TMS) at 50.3, 75.5, and 100.6 MHz, and
31P NMR spectra (δ relative to external 85% aqueous H3PO4)
at 81, 121.5, and 162 MHz on Bruker AM-200, WM-300, and
WH-400 instruments. For all NMR spectra solutions of the
compounds in THF-d8 were used. EI mass spectra were
recorded at 70 eV on a Finnigan MAT 8200, IR spectra on
Nicolet FT 7199 and Magna-IR 750 spectrometers, and Raman
spectra on a Coderg LRT 800 spectrometer (excitation by argon
ion laser at 4880 Å).
(d ip p e)P d (MeCtCH) (2a ). To the colorless pentane solu-
tion (10 mL) of (dippe)Pd(C2H4) (1.984 g, 5.0 mmol) is added
propyne (1 mL, 17.6 mmol) at -30 °C. The mixture is warmed
to 0 °C, whereupon the color changes to orange. After filtration
(D4 glass frit) to remove insoluble impurities, orange micro-
crystals separate at -78 °C. The mother liquor is cannulated
away from the solid. The latter is subsequently washed twice
with cold pentane and dried under vacuum at -30 °C: yield
1.62 g (79%); mp 38 °C dec. Anal. Calcd for C17H36P2Pd
(408.8): C, 49.94; H, 8.88; P, 15.15; Pd, 26.03. Found: C,
49.66; H, 9.15; P, 15.10; Pd, 25.91. EI-MS (50 °C): m/ e (%)
408 (M+, 10), 368 ([(dippe)Pd]+, 100), 40 ([MeCtCH]+, 78). IR
(d ip p e)P d (P h CtCH) (3a ). To a colorless solution of (di-
ppe)Pd(C2H4) (794 mg, 2.0 mmol) in diethyl ether (10 mL) is
added PhCtCH (0.5 mL, 4.5 mmol) at 0 °C. When the solution
is cooled to -30/-78 °C, colorless crystals are obtained, which
are isolated as described above and dried under vacuum at 20
°C: yield 735 mg (78%); mp 81 °C. Anal. Calcd for C22H38P2-
Pd (470.9): C, 56.11; H, 8.13; P, 13.15; Pd, 22.60. Found: C,
56.21; H, 7.99; P, 13.21; Pd, 22.60. EI-MS (50 °C): m/ e (%)
470 (M+, 6), 368 ([(dippe)Pd]+, 100), 102 ([PhCtCH]+, 94). IR
(KBr): see Table 1. 1H NMR (200 MHz, 27 °C): δ 7.51 (CâH),
3
7.17 (CγH), 7.01 (CδH, C6H5), 7.36 [dd, 1 H, J (PH)trans ) 30.8
Hz, 3J (PH)cis ) 16.5 Hz, tCH], alkyne; 2.1 (4 H, PCH and
P′CH), 1.7 (4 H, PCH2 and P′CH2), 1.1 (four unresolved signals,
24 H, Me), dippe. 13C NMR (50.3 MHz, 27 °C): δ 133.0 (1 C,
CR), 131.9 (2 C, Câ), 128.5 (2 C, Cγ), 126.0 (1 C, Cδ, C6H5), 129.4
(1 C, tC- quaternary), 107.7 [1 C, 2J (PC)trans ) 64 Hz, 2J (PC)cis
1
3
) 3 Hz, tCH], alkyne; 27.1 [2 C, J (PC) ) 11.3 Hz, J (P′C) )
1
3
4.4 Hz, PCH], 26.4 [2 C, J (P′C) ) 10.5 Hz, J (PC) ) 3.5 Hz,
P′CH], 23.8 [1 C, 1J (PC) ) 20.1 Hz, 2J (P′C) ) 17.4 Hz, PCH2],
1
2
23.0 [1 C, J (P′C) ≈ J (PC) ≈ 17 Hz, P′CH2], 20.8, 20.8, 19.7,
19.4 (each 2 C, Me), dippe. 31P NMR (81 MHz, 27 °C): see
Table 2.
Cr ysta l Str u ctu r e Deter m in a tion of 3a . A crystal
(yellow plates) of dimensions 0.32 × 0.53 × 0.53 mm was used
for X-ray crystallography. Preliminary examination and data
collection were performed at 20 °C with Mo KR radiation (λ )
0.710 69 Å) on an Enraf-Nonius CAD4 diffractometer equipped
with
a graphite incident beam monochromator. Crystal
data: C22H38P2Pd, Mr ) 470.86, monoclinic, space group P21/n
(No. 14), a ) 12.0451(14) Å, b ) 15.1265(14) Å, c ) 14.382(3)
Å, â ) 110.467(12)°, V ) 2455.0(6) Å3, Z ) 4, Dcalcd ) 1.274 g
cm-3, absorption coefficient 0.889 mm-1, F(000) ) 984, no
absorption correction. A total of 5807 measured reflections,
5593 unique, were obtained using an ω-2θ scan technique
with a scan rate of 1-5° min-1 (in ω). The structure was
solved by SHELXS-8634 and refined by SHELXL-9335 (on F2)
to a final R1 ) 0.0375, wR2 ) 0.0891 (observed reflections).
(31) Concerning Pd0 ligated by monodentate phosphanes, besides the
isolated (Me3P)2Pd(HCtCH)12 and (iPr3P)2Pd(HCtCH)12 we have
characterized (Me3P)2Pd(Me3SiCtCH) in solution (NMR).3
(32) See ref 2 and literature cited therein.
(33) (a) Mu¨ller, J .; Go¨ser, P. Angew. Chem. 1967, 79, 380; Angew.
Chem., Int. Ed. Engl. 1967, 6, 364. (b) Green, M.; Howard, J . A. K.;
Spencer, J . L.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1977, 271.
(c) Herberich, G. E.; Hessner, B. Z. Naturforsch., B: Anorg. Chem.,
Org. Chem. 1979, 34, 638. (d) Crascall, L. E.; Spencer, J . L. Inorg.
Synth. 1990, 28, 126.

(R2PC2H4PR2)Pd0-1-Alkyne Complexes
Organometallics, Vol. 16, No. 20, 1997 4285
{(d ip p e)P d }2(µ-P h CtCH) (3b). An ethereal solution (5
mL) of 3a (471 mg, 1.0 mmol) is combined at -78 °C with a
suspension of (dippe)Pd(η1-C3H5)2 (451 mg, 1.0 mmol) in diethyl
ether (10 mL), and the mixture is warmed to 20 °C (15 min).
The resulting orange solution is filtered to remove some
insoluble impurities. Cooling the solution to -78 °C affords
orange intergrown needles, which are isolated as described
above and dried under vacuum at 20 °C: yield 665 mg (79%);
mp 110 °C dec. Anal. Calcd for C36H70P4Pd2 (839.7): C, 51.49;
H, 8.40; P, 14.75; Pd, 25.35. Found: C, 51.42; H, 8.34; P, 14.73;
Pd, 25.47. EI-MS (120 °C): m/ e (%) 838 (M+, 2), 736 (12+, 3),
368 ([(dippe)Pd]+, 44), 102 ([PhCtCH]+, 41). IR (KBr): see
Table 1. 1H NMR (300 MHz, 27 °C): δ 7.48 (CâH), 6.89 (CγH),
6.61 (CδH, C6H5), 5.78 [tt, 1 H, 3J (PH)trans ) 19.5 Hz, 3J (PH)cis
) 5.7 Hz, tCH], alkyne; 2.1-1.8 (4 unresolved signals, 8 H,
PCH), 1.6-1.4 (4 unresolved signals, 8 H, PCH2), 1.22 (12 H),
is added at -30 °C vinylacetylene (1 mL, 13.6 mmol). When
the solution is cooled to -78 °C, colorless crystals form, which
are separated as described above and dried under vacuum at
-30 °C: yield 810 mg (96%); mp 76 °C dec. Anal. Calcd for
C
18H36P2Pd (420.9): C, 51.37; H, 8.62; P, 14.72; Pd, 25.29.
Found: C, 51.33; H, 8.64; P, 14.78; Pd, 25.28. EI-MS (50 °C):
m/ e (%) 420 (M+, 6), 368 ([(dippe)Pd]+, 100), 52
([H2CdCHCtCH]+, 96).
6a : IR (KBr) 3087 (H-Ct coord), 3009 (H-C) free), 1717
1
(CtC coord), 1582 cm-1 (CdC free); H NMR (400 MHz, -80
3
3
°C) δ 7.13 [dd, 1 H, J (PH)trans ) 30.5 Hz, J (PH)cis ) 17.0 Hz,
2
tCH], 6.97 (m, 1 H, dCH-), 5.40 [m, 1 H, J (HH) ) 2.5 Hz,
3J (HH) ) 16.2 Hz, dCHHZ], 5.25 [dd, 1 H, J (HH) ) 2.5 Hz,
2
3J (HH) ) 9.4 Hz, dCHEH], alkyne, 2.19, 2.06 (each m, 2 H,
PCH and P′CH), 1.7 (4 H, PCH2 and P′CH2), 1.06 (four
unresolved signals, 24 H, Me), dippe; 13C NMR (100.6 MHz,
1.12 (12 H), 1.02 (12 H), 0.85 (6 H), 0.74 (6 H), CH3, dippe. 13
C
-80 °C) δ 128.1 [dd, 1 C, 3J (PC)trans ) 17.2 Hz, 3J (PC)cis
)
NMR (75.5 MHz, 27 °C): δ 148.7 [tt, 3J (PC)trans ) 8 Hz,
3J (PC)cis ) 3 Hz, CRH], 130.7 (CâH), 127.1 (CγH), 121.1 (CδH,
C6H5), 92.2 [tt, 2J (PC)trans ) 50.4 Hz, 2J (PC)cis ) 5.6 Hz, -Ct],
66.6 [m, 1J (CH) ) 197.5 Hz, tCH], alkyne; 26.6, 26.3, 26.1,
25.7 (each 2 C, PCH), 23.2, 22.3 (each 2 C, PCH2), 21.3, 21.1,
20.2, 19.9, 19.8, 19.6, 18.6, 18.1 (each 2 C, CH3), dippe. 31P
NMR (121.5 MHz, 27 °C): see Table 2.
10.9 Hz, -CHd], 123.5 [dd, 1 C, 2J (PC)trans ) 63.0 Hz, 2J (PC)cis
2
) 3.8 Hz, tC-], 120.7 (1 C, dCH2), 109.8 [dd, 1 C, J (PC)trans
) 65.8 Hz, J (PC)cis ) 3.8 Hz, tCH], alkyne; 27.1, 26.0 (each
2
2 C, PCH and P′CH), 23.1, 21.8 (each 1 C, PCH2 and P′CH2),
20.7, 20.2, 18.7, 18.7 (each 2 C, Me), dippe; 31P NMR (162 MHz,
-80 °C), see Table 2.
6b: IR (KBr) 3317 (H-Ct free), 2069 cm-1 (CtC free); 1H
NMR (200 MHz, 27 °C) δ 3.12 (m, 1 H, dCH-), 2.63 (m, 1 H,
tCH), 2.49, 2.36 (each m, 1 H, dCHHZ and dCHEH), alkyne,
dippe signals as for 6a ; 31P NMR (81 MHz, 27 °C) δ 66.8, 60.4
[2J (PP) ) 43 Hz].
{(d ip p e)P d }2(µ-H2CdCHCtCH) (6c). An ethereal solu-
tion (15 mL) of 6a ,b (421 mg, 1.0 mmol) is added at -78 °C to
(dippe)Pd(η1-C3H5)2 (451 mg, 1.0 mmol), and the mixture is
warmed to 0 °C (5 min). The resulting orange solution is
filtered to remove insoluble impurities. At -78 °C orange
crystals are obtained, which are isolated as described above
and dried under vacuum at -30 °C: yield 625 mg (79%); dec
pt >55 °C. Anal. Calcd for C32H68P4Pd2 (789.6): C, 48.68; H,
8.68; P, 15.69; Pd, 26.95. Found: C, 48.61; H, 8.66; P, 15.83;
Pd, 26.95. EI-MS (100 °C): m/ e (%) 788 (M+, 1), 736 (12+, 6),
368 ([(dippe)Pd]+, 100). IR (KBr): 3080, 3041 (alkyne and
olefinic CH), 1498 (µ-CtC), 1600 cm-1 (noncoordinated CdC).
1H NMR (200 MHz, -80 °C): δ 7.16 (m, 1 H, dCH-), 5.49 [tt,
1 H, 3J (PH)trans ) 18.7 Hz, 3J (PH)cis ) 6.2 Hz, tCH], 4.79 [dd,
(d ip p e)P d (MeO2CCtCH) (4). To the colorless solution of
(dippe)Pd(C2H4) (794 mg, 2.0 mmol) in diethyl ether (5 mL) is
added at -30 °C an ethereal solution (5 mL) of MeO2CCtCH
(0.5 mL, 5.6 mmol). When the solution is concentrated under
vacuum to a volume of 4 mL, a tan microcrystalline precipitate
is obtained (-30 °C), which is isolated as described above and
dried under vacuum at 0 °C: yield 790 mg (87%); mp 56 °C.
Anal. Calcd for C18H36O2P2Pd (452.9): C, 47.74; H, 8.01; O,
7.07; P, 13.68; Pd, 23.50. Found: C, 47.90; H, 7.95; P, 13.62;
Pd, 23.38. EI-MS (40 °C): m/ e (%) 452 (M+, 2), 368 ([(dippe)-
Pd]+, 100). IR (KBr): 1667, 1175 cm-1 (CO2Me); for alkyne
ligand, see Table 1. 1H NMR (200 MHz, 27 °C): δ 7.36 [dd, 1
3
3
H, J (PH)trans ) 28.7 Hz, J (PH)cis ) 19.1 Hz, HCt], 3.61 (s, 3
H, Me), alkyne; 2.0 (4 H, PCH and P′CH), 1.7 (4 H, PCH2 and
P′CH2), 1.1 (four unresolved signals, 24 H, Me), dippe. 13C
NMR (75.5 MHz, 27 °C): δ 169.9 [dd, 1 C, 3J (PC)trans ) 18 Hz,
3J (PC)cis ) 13 Hz, COOMe], 117.5 [d, 1 C, 2J (PC)trans ) 62.1
2
2
Hz, J (PC)cis ) 3.1 Hz, -Ct], 112.2 [d, 1 C, J (PC)trans ) 71.2
Hz, 2J (PC)cis ) 2.0 Hz, 1J (CH) ) 210 Hz, tCH], 50.9 (1 C,
OMe), alkyne; 25.9 (2 C, PCH), 25.7 (2 C, P′CH), 23.0 (1 C,
PCH2), 22.7 (1 C, P′CH2), 20.3, 19.9, 19.3, 19.2 (each 2 C, Me),
dippe. 31P NMR (81 MHz, 27 °C): see Table 2.
2
3
1 H, J (HH) ) 2.0 Hz, J (HH) ) 16.5 Hz, dCHHZ], 4.32 [dd,
2
3
1 H, J (HH) ) 2.0 Hz, J (HH) ) 9.4 Hz, dCHEH], alkyne; 1.9
(four unresolved signals, 8 H, PCH), 1.5 (four unresolved
signals, 8 H, PCH2), 1.30-0.80 (eight unresolved signals, 48
H, Me), dippe. 13C NMR (50.3 MHz, -80 °C): δ 142.7 (m, 1 C,
(d ip p e)P d (Me3SiCtCH) (5). To the colorless solution of
(dippe)Pd(C2H4) (782 mg, 2.0 mmol) in pentane (10 mL) is
added at -30 °C Me3SiCtCH (0.5 mL, 3.5 mmol). At -78 °C
off-white crystals slowly separate (1 day), which are isolated
as described above and dried under vacuum at 0 °C: yield 847
mg (92%); mp 30 °C. Anal. Calcd for C19H42P2PdSi (467.0):
C, 48.87; H, 9.07; P, 13.27; Pd, 22.79; Si, 6.01. Found: C,
48.78; H, 8.99; P, 13.25; Pd, 22.65; Si, 6.11. EI-MS (20 °C):
m/ e (%) 466 (M+, 6), 368 ([(dippe)Pd]+, 100), 98 ([Me3-
SiCtCH]+, 5), 83 ([Me2SiCtCH]+, 40). IR (KBr): 1238, 855/
34 cm-1 (SiMe3); for alkyne ligand, see Table 1. 1H NMR (200
2
-CHd), 104.1 (m, 1 C, dCH2), 88.5 [tt, 1 C, J (PC)trans ) 48.0
2
2
Hz, J (PC)cis ) 5.2 Hz, tC-], 65.5 [m, 1 C, J (PC)trans ) 53.2
Hz, tCH], alkyne; 26.1 (four unresolved signals, 8 C, PCH),
22.3 (two resolved signals, 4 C, PCH2), 20.9, 19.8, 18.9, 18.5
(each 4 C, Me), dippe. 31P NMR (81 MHz, -80 °C): see Table
2.
(d ip p e)P d (η2-HCtCCtCH) (7c). To the colorless pentane
solution (10 mL) of (dippe)Pd(C2H4) (794 mg, 2.0 mmol) is
added butadiyne (0.35 mL, 5.1 mmol) at -30 °C. At -78 °C
off-white microcrystals precipitate, which are isolated as
described above and dried at -30 °C under vacuum: yield 780
mg (93%); mp 55 °C dec. Anal. Calcd for C18H34P2Pd (418.8):
C, 51.62; H, 8.18; P, 14.79; Pd, 25.41. Found: C, 51.40; H,
7.87; P, 14.98; Pd, 25.62. EI-MS (70 °C): m/ e (%) 418 (M+,
2), 368 ([(dippe)Pd]+, 56), 50 (C4H2, 100). IR (KBr): 3314
(tC-H free), 3075 (weak, tC-H coord), 2066 (CtC free),
1690 cm-1 (CtC coord). 1H NMR (400 MHz, -30 °C): δ 7.19
[m, 1 H, 3J (PH)trans ) 31.0 Hz, 3J (P′H)cis ) 21.7 Hz, tCH
coord], 4.10 [m, 1 H, 5J (PH) ) 4 Hz, 5J (HH) ) 1 Hz, tCH
free], alkyne; 2.1 (4 H, PCH and P′CH), 1.7 (4 H, PCH2 and
P′CH2), 1.21, 1.18, 1.12, 1.03 (each m, 6 H, Me), dippe. 13C
NMR (75.5 MHz, -30 °C): δ 112.8 [1 C, 2J (PC)trans ) 72.9 Hz,
3
3
MHz, 27 °C): δ 7.26 [dd, 1 H, J (PH)trans ) 32.6 Hz, J (PH)cis
) 15.1 Hz, tCH], 0.19 (s, 9 H, SiMe3), alkyne; 2.0 (4 H, PCH
and P′CH), 1.65 (4 H, PCH2 and P′CH2), 1.16, 1.09, 1.04, 0.98
(each, 6 H, Me), dippe. 13C NMR (50.3 MHz, 27 °C): δ 121.3
2
2
[1 C, J (PC)trans ) 46.2 Hz, J (PC)cis ) 9.6 Hz, tCH], 116.3 [1
C, 2J (PC)trans ) 36.6 Hz, 2J (PC)cis ) 8.7 Hz, -Ct], 2.0 (3 C,
1
SiMe3), alkyne; 26.7 (4 C, PCH and P′CH), 24.2 [1 C, J (PC)
) 20.9 Hz, 2J (P′C) ) 17.4 Hz, PCH2], 23.1 [1 C, 1J (P′C) ) 17.4
Hz, 2J (PC) ) 15.7 Hz, P′CH2], 21.1, 20.6, 19.7, 19.4 (each 2 C,
Me), dippe. 31P NMR (81 MHz, 27 °C): see Table 2.
(d ip p e)P d (H2CdCHCtCH) (6a ,b). To the colorless solu-
tion of (dippe)Pd(C2H4) (794 mg, 2.0 mmol) in pentane (20 mL)
1
2J (P′C)cis ) 2.3 Hz, J (CH) ) 210 Hz, tCH coord], 106.9 [1 C,
(34) Sheldrick, G. M. SHELXS-86. Acta Crystallogr., Sect. A 1990,
46, 467.
(35) Sheldrick, G. M. SHELXL-93, Program for Crystal Structure
Refinement; Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1993.
2J (P′C)trans ) 66.2 Hz, tC- coord], 86.6 [1 C, 4J (P′C)trans
)
1
3
7.6 Hz, J (CH) ) 249.5 Hz, tCH free], 80.7 [1 C, J (P′C)trans
) 19.3 Hz, 3J (PC)cis ) 8.1 Hz, tC- free], alkyne; 26.0, 25.8

4286 Organometallics, Vol. 16, No. 20, 1997
Schager et al.
(each 2 C, PCH and P′CH), 22.8, 22.2 (each 1 C, PCH2 and
P′CH2), 20.2, 20.0, 19.1, 19.0 (each 2 C, Me), dippe. 31P NMR
(162 MHz, -30 °C): δ 70.2, 68.6 [2J (PP) ) 25 Hz].
mp 80 °C dec. Anal. Calcd for C32H70P4Pd2 (791.6): C, 48.55;
H, 8.91; P, 15.65; Pd, 26.89. Found: C, 48.48; H, 9.12; P, 15.57;
Pd, 26.86. EI-MS (100 °C): m/ e (%) 736 (12+, 23), 368
([(dippe)Pd]+, 85), 219 ([iPr2PC2H4PiPr]+, 88), 54 ([MeCtCMe]+,
70), 43 (100). IR (KBr): see Table 1. 1H NMR (400 MHz, -30
°C): δ 2.86 (quint, 6 H, tCMe), 2-butyne; 1.95 (unresolved, 8
H, PCH), 1.44 (unresolved, 8 H, PCH2), 1.10, 1.00 (each 24 H,
Me), dippe. 13C NMR (100.6 MHz, -30 °C): δ 84.9 (“t”, 2 C,
tC-), 18.9 (“d”, 2 C, Me), 2-butyne; 26.2, 25.6 (each 4 C, PCH),
23.8 (4 C, PCH2), 22.5, 22.5, 20.8, 20.0 (each 6 C, diastereotopic
Me), dippe. 31P NMR (162 MHz, -30 °C): see Table 2.
(d ip p e)P d (P h CtCP h ) (9). To a colorless solution of
(dippe)Pd(C2H4) (397 mg, 1.0 mmol) in diethyl ether (5 mL) is
added an ethereal solution (5 mL) of PhCtCPh (210 mg, 1.2
mmol) at 20 °C. Colorless crystals precipitate, which are
isolated as described (-30 °C) and dried under vacuum (20
°C): yield 755 mg (87%); mp 166 °C. Anal. Calcd for C28H42P2-
Pd (547.0): C, 61.48; H, 7.74; P, 11.32; Pd, 19.45. Found: C,
61.39; H, 7.65; P, 11.42; Pd, 19.46. EI-MS (95 °C): m/ e (%)
546 (M+, 10), 368 ([(dippe)Pd]+, 100), 178 ([C2Ph2]+, 83). IR
(KBr): see Table 1. 1H NMR (400 MHz, 27 °C): δ 7.60 (4 H),
7.22 (4 H), 7.04 (2 H), C2Ph2; 2.13 (m, 4 H, PCH), 1.68 (m, 4
H, PCH2), 1.12, 1.05 (each m, 12 H, diastereotopic Me), dippe.
13C NMR (100.6 MHz, 27 °C): δ 138.2 (2 C, CR), 130.2 (4 C,
Câ), 128.3 (4 C, Cγ), 125.5 (2 C, Cδ), 126.1 (2 C, tC-), C2Ph2;
{(d ip p e)P d }2{µ-(1,2-η2):(3,4-η2)-HCtCCtCH} (7d ). An
ethereal solution (15 mL) of 7c (419 mg, 1.0 mmol) is added
at -78 °C to solid (dippe)Pd(η1-C3H5)2 (451 mg, 1.0 mmol). The
mixture is warmed to 0 °C for 5 min, and the resulting brown
solution is filtered. Over the course of several weeks brown
crystals separate at -78 °C, which are isolated as described
above and dried under vacuum at -30 °C: yield 640 mg (81%);
dec pt >65 °C. Anal. Calcd for C32H66P4Pd2 (787.6): C, 48.80;
H, 8.45; P, 15.73; Pd, 27.02. Found: C, 48.68; H, 8.44; P, 15.65;
Pd, 27.15. EI-MS (130 °C): m/ e (%) 786 (M+, <1), 736 (12+,
4), 368 ([(dippe)Pd]+, 28), 219 ([iPr2PC2H4PiPr]+, 100). IR
(KBr): see Table 3. 1H NMR (300 MHz, -85 °C; for tCH see
Table 3): δ 2.0 (8 H, PCH and P′CH), 1.6 (8 H, PCH2 and
P′CH2), 1.2-0.9 (48 H, four unresolved signals, Me), dippe. 13
C
NMR (75.5 MHz, -85 °C; for tC- and tCH see Table 3): δ
26.2, 25.7 (each d, 4 C, PCH and P′CH), 22.8, 21.9 (each m, 2
C, PCH2 and P′CH2), 20.4, 18.9 (each d, 8 C, pair of unresolved
diastereotopic CH3), dippe. 31P NMR (121.5 MHz, -85 °C): δ
68.0, 64.4 (AA′BB′ spin system).
{(d ip p e)P d }2{µ-(1,2-η2)-HCtCCtCH} (7e). 1H NMR (300
3
3
MHz, -85 °C): δ 5.37 [tt, 1 H, J (PH)trans ) 17.5 Hz, J (PH)cis
) 7.0 Hz, tCH coord], 2.93 [t, 1 H, 5J (PH) ) 3.7 Hz, tCH
free], alkyne; 2.12 (2 H), 2.03 (2 H), 1.96 (4 H, four kinds of
PCH), 1.5 (8 H, PCHaHb and P′CHaHb), 1.25-0.9 (unresolved,
48 H, 8 signals of CH3 expected), dippe. 13C NMR (75.5 MHz,
-85 °C; for butadiyne see Table 3): δ 26.0, 25.9, 25.6, 25.4
(each 2 C, four types of PCH), 22.5, 21.5 (each 2 C, PCH2 and
P′CH2), 20.8 (4 C), 20.3 (2 C), 19.4 (4 C), 18.6 (6 C, eight types
of CH3), dippe. 31P NMR (121.5 MHz, -85 °C): δ 62.6, 58.7
(AA′BB′ spin system).
2
26.8 [4 C, 1J (PC) ) 7.6 Hz, PCH], 22.8 [“t”, 2 C, 1J (PC) ≈ J (PC)
≈ 18.1 Hz, PCH2], 20.5, 19.0 (each 4 C, diastereotopic Me),
dippe. 31P NMR (162 MHz, 27 °C): see Table 2.
(d ip p e)P d (MeO2CCtCCO2Me) (10). To a solution of
(dippe)Pd(C2H4) (791 mg, 2.0 mmol) in diethyl ether (10 mL)
is added at 0 °C an ethereal solution (10 mL) of MeO2-
CCtCCO2Me (0.5 mL, 4.1 mmol). Colorless crystals form,
which are isolated as described above and dried under vacuum
(20 °C): yield 920 mg (90%); mp 101 °C. Anal. Calcd for
C20H38O4P2Pd (510.9): C, 47.02; H, 7.50; O, 12.53; P, 12.13;
Pd, 20.83. Found: C, 47.09; H, 7.46; P, 11.98; Pd, 20.71. EI-
MS (90 °C): m/ e (%) 510 (M+, 4), 368 ([(dippe)Pd]+, 100). IR
(KBr): 1679, ∼1190 cm-1 (CO2Me); for alkyne ligand, see Table
1. 1H NMR (400 MHz, 27 °C): δ 3.64 (s, 6 H, CO2Me), alkyne;
2.06 (m, 4 H, PCH), 1.78 (m, 4 H, PCH2), 1.14, 1.07 (each 12
H, diastereotopic Me), dippe. 13C NMR (100.6 MHz, 27 °C): δ
167.9 (2 C, CO2Me), 122.7 (2 C, tC-), 51.1 (2 C, CO2Me),
(d ip p e)P t(η2-HCtCCtCH) (7f). To the colorless suspen-
sion of Pt(cod)2 (822 mg, 2.0 mmol) and dippe (525 mg, 2.0
mmol) in diethyl ether (40 mL) is added at -30 °C butadiyne
(0.14 mL, 2.0 mmol). When the mixture is stirred, a burgundy
red solution results, from which yellow-orange cubes separate
at -78 °C. These are isolated as described above and dried
under vacuum at -30 °C: yield 760 mg (75%), dec pt >0 °C.
Anal. Calcd for C18H34P2Pt (507.5): C, 42.59; H, 6.76; P, 12.21;
Pt, 38.44. Found: C, 42.92; H, 7.10; P, 12.11; Pt, 38.08. EI-
MS (74 °C): m/ e (%) 507 (M+, 40), 457 ([(dippe)Pt]+, 100). IR
(KBr): see Table 3. 1H NMR (200 MHz, -30 °C; for C4H2
signals see Table 3): δ 2.1 (4 H, PCH and P′CH), 1.70, 1.64
(each m, 2 H, PCH2 and P′CH2), 1.18, 1.10, 1.03, 1.00 (each
m, 6 H, Me), dippe. 13C NMR (75.5 MHz, -30 °C; for C4H2
signals see Table 3): δ 26.6, 26.1 (each 2 C, PCH and P′CH),
24.6, 24.1 (each 1 C, PCH2 and P′CH2), 19.9, 19.6, 18.9, 18.8
(each 2 C, Me), dippe. 31P NMR (121.5 MHz, -30 °C): δ 77.5,
77.2 [J (PtPA) ) 3074 Hz, J (PtPB) ) 3231 Hz, 2J (PP) ) 42.8
Hz].
1
2
alkyne; 25.9 (4 C, PCH), 22.9 [2 C, J (PC) ) 20 Hz, J (PC) )
17 Hz, PCH2], 19.9, 19.3 (each 4 C, diastereotopic Me), dippe.
31P NMR (162 MHz, 27 °C): see Table 2.
(d ip p e)P d (Me3SiCtCSiMe3) (11). To the colorless solu-
tion of (dippe)Pd(C2H4) (794 mg, 2.0 mmol) in diethyl ether (5
mL) is added Me3SiCtCSiMe3 (0.5 mL, 2.2 mmol) at 20 °C.
When the solution is cooled to -78 °C (1 day), off-white cubes
crystallize, which are separated as described above and dried
under vacuum at 20 °C: yield 850 mg (79%); mp 50 °C dec.
Anal. Calcd for C22H50P2PdSi2 (539.2): C, 49.01; H, 9.35; P,
11.49; Pd, 19.74; Si, 10.42. Found: C, 48.75; H, 9.28; P, 11.41;
Pd, 19.92; Si, 10.55. EI-MS (40 °C): m/ e (%) 538 (M+, 8), 368
([(dippe)Pd]+, 100), 170 ([C2(SiMe3)2]+, 4). IR (KBr): 1239, 861/
36 (SiMe3); for alkyne ligand, see Table 1. 1H NMR (200 MHz,
27 °C): δ 0.22 (s, 18 H, SiMe3), alkyne; 2.04 (m, 4 H, PCH),
1.65 (m, 4 H, PCH2), 1.08, 1.07 (each m, 12 H, diastereotopic
Me), dippe. 13C NMR (50.3 MHz, 27 °C): δ 134.7 [“t”, 2 C,
(d ip p e)P d (MeCtCMe) (8a ). To a colorless solution of
(dippe)Pd(C2H4) (1.98 g, 5.0 mmol) in pentane (10 mL) is added
at 0 °C 2-butyne (1 mL, 12.8 mmol). The resulting light orange
solution is cooled to -78 °C, and within 1 day off-white crystals
separate which are isolated as described above and dried under
vacuum at 0 °C: yield 1.71 g (81%); mp 79 °C. Anal. Calcd
for C18H38P2Pd (422.9): C, 51.13; H, 9.06; P, 14.65; Pd, 25.17.
Found: C, 51.10; H, 9.20; P, 14.65; Pd, 24.98. EI-MS (60 °C):
m/ e (%) 422 (M+, 11), 368 ([(dippe)Pd]+, 100), 54 ([MeCtCMe]+,
25). IR (KBr): see Table 1. 1H NMR (200 MHz, -80 °C): δ
2.51 (m, 6 H, tCMe), 2-butyne; 1.85 (m, 4 H, PCH), 1.67 (m,
4 H, PCH2), 1.06 (24 H, set of diastereotopic Me), dippe. 13C
NMR (50.3 MHz, 27 °C): δ 106.6 (“t”, 2 C, tC-), 16.1 (“t”, 2
C, Me), 2-butyne; 26.1 (4 C, PCH), 23.4 (2 C, PCH2), 20.3, 19.4
(each 6 C, diastereotopic Me), dippe. 31P NMR (81 MHz, -80
°C): see Table 2.
2
2J (PC)trans ≈ J (PC)cis ≈ 20 Hz, CtC], 2.3 (6 C, SiMe3), alkyne;
27.2 [4 C, 1J (PC) ) 6.5 Hz, PCH], 23.4 [“t”, 2 C, 1J (PC) ≈
2J (P′C) ≈ 18 Hz, PCH2], 21.4, 19.3 (each 4 C, diastereotopic
Me), dippe. 31P NMR (81 MHz, 27 °C): δ 63.4 [3J (SiP) ) 16
Hz].
Ack n ow led gm en t. We thank the Volkswagen-Stif-
tung and the Fonds der Chemischen Industrie for
financial support.
{(d ip p e)P d }2(µ-MeCtCMe) (8b). A pentane solution (5
mL) of 8a (423 mg, 1.0 mmol) is combined with a cream-colored
suspension of (dippe)Pd(η1-C3H5)2 (451 mg, 1.0 mmol) in
pentane (10 mL) at -78 °C. When the mixture is warmed to
20 °C, an orange-red solution is obtained from which yellow
crystals separate at -30/-78 °C. The product is isolated as
described and dried under vacuum at 0 °C: yield 670 mg (85%);
Su p p or tin g In for m a tion Ava ila ble: Tables of data col-
lection information, anisotropic thermal parameters, atom
coordinates and U values, and bond lengths and angles for 3a
(4 pages). Ordering information is given on any current
masthead page.
OM9702035