Planar tetranuclear and dumbbell-shaped octanuclear palladium complexes with bridging silylene ligands

Article abstract of DOI:10.1002/anie.200804728

(Chemical Equation Presented) An uncommon structure: The novel title compounds (see scheme) were prepared and fully characterized. The tetranuclear complex contains a hexagonal Pd₄Si₃ core involving one central Pd atom, three outer Pd atoms, and three bridging Si atoms within the same plane, whereas the dumbbell-shaped octanuclear Pd complex is composed of two Pd₄Si₃ groups bridged by a diphosphine ligand.

Full text of DOI:10.1002/anie.200804728

Communications
DOI: 10.1002/anie.200804728
Coordination Modes
Planar Tetranuclear and Dumbbell-Shaped Octanuclear Palladium
Complexes with Bridging Silylene Ligands**
Tetsuyuki Yamada, Akane Mawatari, Makoto Tanabe, Kohtaro Osakada,* and Tomoaki Tanase
Late-transition-metal complexes with silylene (SiR2) ligands
have attracted considerable attention since the proposal of
platinum–silylene intermediates in the [PtCl2(PEt3)2]-cata-
lyzed reactions that convert organodisilanes into oligosilanes
and the cyclic adducts into alkynes.[1] Mononuclear silylene
complexes of platinum[2] and other late transition metals[3]
were not isolated until some years later, probably because of
porates four Pd centers and three bridging SiPh2 ligands
[Eq. (1)]. The accompanying formation of [Pd(SiPh2H)2-
(dmpe)][13] (3) was also detected. Reaction of [Pd(PCy3)2]
with 3 yields 2 as one of the products.
=
the extremely high reactivity of most M Si double bonds.
Dinuclear complexes of late transition metals with bridging
silylene ligands are more common.[4] The dinuclear platinum
complex [{Pt(PR3)}2(m-SiHPh2)2] (PR3 = PPh3, PCy3 etc.) has
been reported.[5] However, in spite of the stable coordination
of bridging silylene ligands, complexes containing three or
more metal atoms with bridging Si ligands have few prece-
dents,[6] and those known are stabilized by electron-with-
drawing CO and CNR ligands.[7] Braddock-Wilking and co-
workers[8] and our group[9,10] have reported zero-valent
triangular Pt3 complexes, stabilized by bridging silylene and
phosphine ligands. Chen, Shimada, and Tanaka employed 1,2-
disilabenzene as a ligand and prepared trinuclear Pd com-
plexes supported by the Si ligands.[11]
Herein, we report the synthesis and unexpected structure
of a planar tetranuclear Pd0 complex with three bridging SiPh2
ligands as well as facile exchange of the bridging silylene
ligands to yield a dumbbell-shaped octapalladium complex
composed of two Pd4 units bridged by a diphosphine ligand.
These complexes, composed of Pd0 centers and electron-
donating Si and phosphine ligands, possess a unique planar
{Pd4Si3} core.
The molecular structure of 2 was determined by single-
crystal X-ray diffraction (Figure 1).[14] Complex 2 has a
hexagonal {Pd4Si3} core incorporating one central Pd atom,
Heating a mixture of a dipalladium complex with bridging
diphenylsilyl ligands, [{Pd(PCy3)}2(m-h2-SiHPh2)2] (1),[12] and
1,2-bis(dimethylphosphino)ethane (dmpe) in toluene at 808C
produced [Pd{Pd(dmpe)}3(m3-SiPh2)3] (2; 54%), which incor-
[*] T. Yamada, A. Mawatari, Dr. M. Tanabe, Prof. K. Osakada
Chemical Resources Laboratory, Tokyo Institute of Technology
4259 Nagatsuta, Midori-ku, Yokohama, 226-8503 (Japan)
Fax: (+81)45-924-5224
Figure 1. ORTEP representation of 2 viewed from (a) above and (b) in
the plane of the {Pd4Si3} core. Thermal ellipsoids are set at 50%
probability. Hydrogen atoms and solvent molecules are omitted for
À
clarity. Selected bond lengths [ꢀ] and angles [8]: Pd1 Pd2 2.7122(3),
E-mail: kosakada@res.titech.ac.jp
À
À
À
À
Pd1 Pd3 2.7358(2), Pd1 Pd4 2.7326(2), Pd1 Si1 2.2521(8), Pd1 Si2
À
À
À
Prof. T. Tanase
Department of Chemistry, Faculty of Science
Nara Women’s University
2.2649(8), Pd1 Si3 2.2674(8), Pd2 Si2 2.5351(8), Pd2 Si3 2.5052(8),
À
À
À
À
Pd3 Si1 2.5210(6), Pd3 Si3 2.5398(8), Pd4 Si1 2.5456(7), Pd4 Si2
2.5116(8); Si1-Pd1-Si2 119.96(2), Si1-Pd1-Si3 119.88(2), Si2-Pd1-Si3
120.03(3).
Kitauoya-higashi-machi, Nara 630-8506 (Japan)
[**] This work was financially supported by Grants-in-Aid for Scientific
Research for Young Chemists (No. 19750043), for Scientific
Research (No. 1925008), and for Scientific Research on Priority
Areas (No. 19027018), from the Ministry of Education, Culture,
Sport, Science, and Technology Japan. We thank Rieko Kobayashi
(Tokyo Institute of Technology) for experimental assistance.
Pdcent, three outer Pd atoms, Pdout, and three bridging Si atoms
arranged within the same plane; the six Pdout-Pdcent-Si bond
À
angles add up to a total of 359.98(2)8. The Pdcent Si bond
lengths, 2.2521(8)–2.2674(8) ꢀ, are comparable to those of
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200804728.
=
Pd Si bonds in a mononuclear Pd complex with two non-
568
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2009, 48, 568 –571

Angewandte
Chemie
bridging silylene
ligands,
[Pd{SiKC(SiMe3)2CH2CH2CL -
center at the midpoint of the two carbon atoms of the bridging
(SiMe3)2}2], (2.263(1) and 2.260(2) ꢀ),[15] and are shorter
dmpe ligand (Figure 2).[14] The phenyl substituents are
oriented away from the {Pd4Si3} unit to avoid steric conges-
À
than the Pd Si single bonds of
3
(2.3548(9) and
2.3550(7) ꢀ).[13] The Pdcent Pdout bond lengths in
2
À
À
(2.7122(3)–2.7358(2) ꢀ) are within the range of Pd Pd bond
lengths in neutral tripalladium clusters (2.6207(4)–
3.000(5) ꢀ).[16] The two Pdcent-Si-Cipso angles (122.39(8)–
127.5(1)8) and the Cipso-Si-Cipso angle (109.1(1)–110.1(1)8)
around each Si atom add up to approximately 3608. These
bond parameters suggest that three SiPh2 ligands are bonded
to the central palladium atom giving rise to Si centers with
distorted trigonal-bipyramidal geometries.[17] A similar m3-
coordination mode has recently been reported for germylene
(GeR2) and stannylene (SnR2) ligands to three Ru atoms
[Ru3(CO)8(m-SPh)2(m3-EPh2)(EPh3)2] (E = Ge, Sn).[18] The
{Pd4Si3} core is stabilized by bonds between Pdout and Si
À
atoms that are weaker than Pdcent Si bonds, in addition to a
d10–d10 interaction between the Pdcent and Pdout atoms.[19] The
31P{1H} NMR spectrum of 2 displayed a single signal (d =
À2.41 ppm) flanked by satellite signals of 29Si nuclei (J-
(P,Si) = 22 Hz). The 29Si{1H} NMR signal of 2 was detected as
a multiplet at d = 195 ppm. The downfield Si NMR spectro-
scopic shifts in the range of d = 200–370 ppm were attributed
to the paramagnetic shielding effect of the bridging silylene
coordination with metal–metal bonds.[4a] Shimada and co-
workers have recently described a multinuclear complex
containing a {Pd4Si5} framework composed of a planar Pd4Si3
core, similar to 2, and two additional Si ligands at the central
Figure 2. ORTEP representation of 4 with thermal ellipsoids set at
50% probability. The complex has an inversion center at the midpoint
between two carbon atoms of the bridging dmpe ligand. Atoms with
asterisks are crystallographically equivalent to those having the same
number without asterisks. Hydrogen atoms, except for SiH hydrogen
atoms, and solvent molecules are omitted for clarity. Selected bond
À
À
lengths [ꢀ] and angles [8]: Pd1 Pd2 2.7659(2), Pd1 Pd3 2.7988(3),
À
À
À
À
Pd1 Pd4 2.7785(3), Pd1 Si1 2.3152(9), Pd1 Si2 2.3292(9), Pd1 Si3
À
À
À
2.3075(9), Pd2 Si2 2.5706(9), Pd2 Si3 2.5114(9), Pd3 Si1 2.448(1),
À
À
À
À
Pd3 Si3 2.5134(9), Pd4 Si1 2.495(1), Pd4 Si2 2.5078(9), Pd1 P1
2.3399(8); Si1-Pd1-Si2 109.62(3), Si1-Pd1-Si3 109.64(3), Si2-Pd1-Si3
108.20(3).
Pd atom.[20] The Pdcent Si bond lengths of the {Pd4Si3} plane
À
(2.3265(13) and 2.2944(9) ꢀ) are significantly longer than the
corresponding bonds in 2.
The reaction of H2SiPh2 with 2 (5 equivalents) at room
temperature afforded a mixture of 2 and 3 in 3:1 ratio. This
result indicates that the silylene ligands in 2 can be converted
into SiHPh2 ligands with degradation of the tetranuclear
{Pd4Si3} framework. Treatment of 2 with a threefold molar
excess of H3SiPh produced an octanuclear Pd complex,
[(Pd{Pd(dmpe)}3{m3-SiHPh}3)2(m-dmpe)] (4: 76%), accompa-
nied by the elimination of H2SiPh2 [Eq. (2)].
tion. Pdcent deviates from the {Pd4Si3} plane by 0.62 ꢀ. The
À
À
Pdcent Pdout (2.7659(2)–2.7988(3) ꢀ) and Pdcent Si bond
lengths (2.3075(9)–2.3292(9) ꢀ) of 4 are elongated compared
with the corresponding bonds of 2. The 13C{1H} NMR
spectrum of 4 at À608C indicated the presence of PCH2 and
P(CH3)2 groups of bridging dmpe ligands (d = 31.3 and
22.8 ppm) and the P(CH3)2 groups of the chelating dmpe
ligands at the inside and outside of the dumbbell-shaped
structure (d = 15.3 and 14.2 ppm). The 1H NMR signal
corresponding to the SiH hydrogen atom is detected at d =
8.13 ppm, which is shifted downfield compared with the SiH
hydrogen of organosilanes, in a similar fashion to the
=
mononuclear silylene complexes, [Cp*(CO)(H)Ru Si(H){C-
(SiMe3)3}] (d = 9.14 ppm; Cp* = C5Me5)[22] and [Cp*-
[23]
=
(iPr3P)(H)Os Si(H){C6H2iPr3-2,4,6}] (d = 12.1 ppm).
The
downfield shift of the SiH hydrogen signals is characteristic of
sp2 hybridization of the Si atom.[24]
The 31P{1H} NMR spectrum of 4, at À608C in [D8]THF
(Figure 3a), is consistent with the crystal structure of 4. Two
31P{1H} NMR signals at d = 7.34 and À15.2 ppm are detected
with an intensity ratio of approximately 6:1, and are assign-
able to the phosphine nuclei of chelating (PA) and bridging
(PB) dmpe ligands, respectively. The addition of an equimolar
amount of dmpe to the solution of 4 gave rise to new signals at
d = 7.81 (PC), À15.6 (PD), and À49.7 ppm (PE), accompanied
by free dmpe (d = À47.5 ppm, Figure 3b). Two doublets at
d = À15.6 and À49.7 ppm, with the same coupling constant
(J(P,P) = 23 Hz), were assigned to the coordinated (PD) and
The reaction appears to involve exchange of the bridging
SiPh2 ligands with the SiHPh group derived from H3SiPh[21]
and subsequent bridging coordination of a dmpe ligand to the
central Pd atom of the resultant [Pd{Pd(dmpe)}3(m3-SiHPh)3]
intermediate. Complex 4 has a crystallographic inversion
Angew. Chem. Int. Ed. 2009, 48, 568 –571
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
569

Communications
Keywords: bridging ligands · coordination modes · P ligands ·
.
palladium · Si ligands
[1] a) K. Yamamoto, H. Okinoshima, M. Kumada, J. Organomet.
Chem. 1970, 23, C7 – C8; b) K. Yamamoto, H. Okinoshima, M.
Kumada, J. Organomet. Chem. 1971, 27, C31 – C32.
[2] a) S. D. Grumbine, T. D. Tilley, J. Am. Chem. Soc. 1993, 115,
7884 – 7885; b) G. P. Mitchell, T. D. Tilley, Angew. Chem. 1998,
110, 2602 – 2605; Angew. Chem. Int. Ed. 1998, 37, 2524 – 2526;
c) J. D. Feldman, G. P. Mitchell, J.-O. Nolte, T. D. Tilley, J. Am.
Chem. Soc. 1998, 120, 11184 – 11185; d) J. D. Feldman, G. P.
Mitchell, J.-O. Nolte, T. D. Tilley, Can. J. Chem. 2003, 81, 1127 –
1136.
Figure 3. 31P{1H} NMR spectra at À608C in [D8]THF of a) 4 and b) the
reaction mixture after the addition of bis(dimethylphosphino)ethane
(dmpe, 1 equivalent) to the solution of 4.
[3] a) P. D. Lickiss, Chem. Soc. Rev. 1992, 21, 271 – 279; b) C. Zybill,
H. Handwerker, H. Friedrich, Adv. Organomet. Chem. 1994, 36,
229 – 281; c) M. Okazaki, H. Tobita, H. Ogino, Dalton Trans.
2003, 493 – 506; d) R. Waterman, P. G. Hayes, T. D. Tilley, Acc.
Chem. Res. 2007, 40, 712 – 719.
[4] a) H. Ogino, H. Tobita, Adv. Organomet. Chem. 1998, 42, 223 –
290; b) J. Y. Corey, J. Braddock-Wilking, Chem. Rev. 1999, 99,
175 – 292; c) P. Braunstein, N. M. Boag, Angew. Chem. 2001, 113,
2493 – 2499; Angew. Chem. Int. Ed. 2001, 40, 2427 – 2433; d) K.
Osakada, M. Tanabe, Bull. Chem. Soc. Jpn. 2005, 78, 1887 – 1898;
e) S. Shimada, M. Tanaka, Coord. Chem. Rev. 2006, 250, 991 –
1011.
terminal (PE) atoms, respectively of the dmpe ligand bonded
to the central Pd atom . The product was identified as a
tetranuclear palladium complex with a dangling dmpe ligand,
[Pd(dmpe){Pd(dmpe)}3(m3-SiHPh)3] (5) [Eq. (3)], based on
the multinuclear NMR spectra. The product mixture con-
tained 4 and 5 in a 6:94 ratio. However, purification of 5 by
recrystallization was not feasible. The above NMR spectro-
scopic data indicate that the octanuclear structure of complex
4 does not change in solution, although the addition of dmpe
converts it into the tetranuclear complex 5. A similar reaction
[5] M. Auburn, M. Ciriano, J. A. K. Howard, M. Murray, N. J. Pugh,
J. L. Spencer, F. G. A. Stone, P. Woodward, J. Chem. Soc. Dalton
Trans. 1980, 659 – 666.
[6] a) A. Brookes, S. A. R. Knox, F. G. A. Stone, J. Chem. Soc. A
1971, 3469 – 3471; b) S. G. Anema, S. K. Lee, K. M. Mackay,
B. K. Nicholson, J. Organomet. Chem. 1993, 444, 211 – 218; c) C.
Evans, G. J. Harfoot, J. S. McIndoe, C. J. McAdam, K. M.
Mackay, B. K. Nicholson, B. H. Robinson, M. L. Van Tiel, J.
Chem. Soc. Dalton Trans. 2002, 4678 – 4683; d) C. Evans, B. K.
Nicholson, J. Organomet. Chem. 2003, 665, 95 – 100.
[7] a) Metal–Metal Bonds and Clusters in Chemistry and Catalysis
(Ed.: J. P. Fackler), Plenum, New York, 1990; b) D. A. Admas,
F. A. Cotton, Catalysis by Di- and Polynuclear Metal Cluster
Complexes, Wiley, New York, 1998; c) Clusters and Colloids
(Ed.: G. Schmid), VCH, Weinheim, 1994.
[8] a) J. Braddock-Wilking, J. Y. Corey, K. Dill, N. P. Rath, Organo-
metallics 2002, 21, 5467 – 5469; b) J. Braddock-Wilking, J. Y.
Corey, L. M. French, E. Choi, V. J. Speedie, M. F. Rutherford, S.
Yao, H. Xu, N. P. Rath, Organometallics 2006, 25, 3974 – 3988.
[9] K. Osakada, M. Tanabe, T. Tanase, Angew. Chem. 2000, 112,
4219 – 4221; Angew. Chem. Int. Ed. 2000, 39, 4053 – 4055.
[10] We reported the complex as the first example of a Pt0 complex
with Si ligands, but, in fact, a mononuclear Pt0 complex with a
nonbridging silylene ligand had been found earlier. See ref. [2b].
[11] W. Chen, S. Shimada, M. Tanaka, Science 2002, 295, 308 – 310.
[12] M. Tanabe, T. Yamada, K. Osakada, Organometallics 2003, 22,
2190 – 2192.
of dmpe with an equimolar dinickel complex, having a dmpe
ligand that bridges two metal centers, was reported to
produce the mononuclear complex with pendant dmpe at
the apical position of the metal centers.[25]
In summary, we obtained the tetra- and octanuclear Pd0
complexes with novel and unique structures using simple and
common ligands, namely, SiPh2, SiHPh, and dmpe. The
former complex had a stable structure in solution, but the
addition of PhSiH3 induced rapid exchange of the Si ligands
and production of an octanuclear complex. Four Pd0 centers
having three bridging silylene ligands are expected to show
unique chemical properties, which are of continuing interest
in this study.
[13] M. Tanabe, A. Mawatari, K. Osakada, Organometallics 2007, 26,
2937 – 2940.
[14] Crystallographic data for (2)·C6H14: C60H92P6Pd4Si3; Mr =
1509.09; crystal size 0.18 ꢁ 0.33 ꢁ 0.65 mm3; monoclinic; P21/c;
a = 13.614(2), b = 27.398(4), c = 18.687(3) ꢀ; b = 99.218(2)8; V=
6880(2) ꢀ3; Z = 4; 1calcd = 1.457 gcmÀ3
; ; F-
m = 1.2552 mmÀ1
(000) = 3072, T= 133 K; Rigaku Saturn CCD area detector
equipped with monochromated MoKa radiation (l = 0.71070 ꢀ);
variables = 750; 50104 reflections measured (2qmax = 55.08);
15569 independent reflections (Rint = 0.034); R1 = 0.0295;
wR2 = 0.0730; GOF = 1.021. Crystallographic data for
(4)·2C6H14: C90H176P14Pd8Si6; Mr = 2711.73; crystal size 0.43 ꢁ
0.68 ꢁ 0.75 mm3; monoclinic; P21/c; a = 14.231(2), b = 18.514(2),
Received: September 27, 2008
Published online: December 15, 2008
c = 22.498(3) ꢀ; b = 98.047(2)8; V= 5869(2) ꢀ3; Z = 2; 1calcd
=
570
www.angewandte.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2009, 48, 568 –571

Angewandte
Chemie
1.534 gcmÀ3
;
m = 1.4874 mmÀ1
;
F(000) = 2756; T= 133 K;
[19] a) R. J. Puddephatt, Polyhedron 1990, 9, 2767 – 2802; b) P. D.
Rigaku Saturn CCD area detector equipped with monochro-
mated MoKa radiation (l = 0.71070 ꢀ); variables = 629; 39847
reflections measured (2qmax = 55.08); 13084 independent reflec-
tions(Rint=0.024); R1 = 0.0413; wR2 = 0.1177; GOF = 0.980.
CCDC 702935 (2) and 702937 (4) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Harvey, J. Cluster Sci. 1993, 4, 377 – 402; c) D. Imhof, L. M.
Venanzi, Chem. Soc. Rev. 1994, 23, 185 – 193; d) A. D. Burrows,
D. M. P. Mingos, Coord. Chem. Rev. 1996, 154, 19 – 69; e) W.
Schuh, P. Braunstein, M. Bꢂnard, M.-M. Rohmer, R. Welter, J.
Am. Chem. Soc. 2005, 127, 10250 – 10258.
[20] S. Shimada, Y.-H. Li, Y.-K. Choe, M. Tanaka, M. Bao, T.
Uchimaru, Proc. Natl. Acad. Sci. USA 2007, 104, 7758 – 7763.
[21] W.-D. Wang, R. Eisenberg, Organometallics 1992, 11, 908 – 912.
[22] M. Ochiai, H. Hashimoto, H. Tobita, Angew. Chem. 2007, 119,
8340 – 8342; Angew. Chem. Int. Ed. 2007, 46, 8192 – 8194.
[23] P. G. Hayes, C. Beddie, M. B. Hall, R. Waterman, T. D. Tilley, J.
Am. Chem. Soc. 2006, 128, 428 – 429.
[24] a) R. S. Simons, J. C. Gallucci, C. A. Tessier, W. J. Youngs, J.
Organomet. Chem. 2002, 654, 224 – 228; b) J. D. Feldman, J. C.
Peters, T. D. Tilley, Organometallics 2002, 21, 4065 – 4075.
[25] S. Shimada, M. L. N. Rao, M. Tanaka, Organometallics 1999, 18,
291 – 293.
[15] C. Watanabe, T. Iwamoto, C. Kabuto, M. Kira, Angew. Chem.
2008, 120, 5466 – 5469; Angew. Chem. Int. Ed. 2008, 47, 5386 –
5389.
[16] D. Kovala-Demertzi in Metal Clusters in Chemistry, Vol. 1 (Eds.:
P. Braunstein, L. A. Oro, P. R. Raithby), Wiley-VCH, Weinheim,
1999, pp. 399 – 416.
[17] Y. Apeloig in The Chemistry of Organic Silicon Compounds
(Eds.: S. Patai, Z. Rappoport), Wiley, Chichester, 1989.
[18] S. E. Kabir, A. K. Raha, M. R. Hassan, B. K. Nicholson, E.
Rosenberg, A. Sharmin, L. Salassa, Dalton Trans. 2008, 4212 –
4219.
Angew. Chem. Int. Ed. 2009, 48, 568 –571
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
571