Sila- and germaplatinacycles produced from a stepwise E-E bond forming reaction

Article abstract of DOI:10.1021/om900201y

A study was conducted to demonstrate the production of sila- and germaplatinacycles from a stepwise E-E bond forming reaction. Two alternative pathways for the formation of E-E bonds were demonstrated. These alternative pathways started from bis(silyl) or bis(germyl)platinum complexes, either through a platinum-silyllene or -germylene intermediate or through a reductive-elimination and oxidative-addition pathway. It was demonstrated that reaction of 9,9-dihydridosilafluorene (H₂SiC₁₂H ₈) with the chelating phosphine complex (dppe)PtMe²⁸ ₂ in ca. 4:1 ratio in toluene-d₈ resulted in the formation of the bis(silyl)platinum complex (dppe)Pt(SiHC₁₂H₈) ₂. The novel platinatetetrasilacycle 4 was also obtained as a minor product in 8% in the form of a yellow solid when the reaction was carried out at 75 °C for a period of 19 hours.

Full text of DOI:10.1021/om900201y

4098 Organometallics 2009, 28, 4098–4105
DOI: 10.1021/om900201y
Sila- and Germaplatinacycles Produced from a Stepwise E-E Bond
Forming Reaction
Janet Braddock-Wilking,* Teresa Bandrowsky, Ngamjit Praingam, and Nigam P. Rath
Department of Chemistry and Biochemistry and the Center for Nanoscience, University of Missouri-St.
Louis, St. Louis, Missouri 63121
Received March 17, 2009
Introduction
whereas reactions with late transition metal catalysts
have been postulated to involve a cycle of oxidative-
addition/reductive-elimination steps6 but could also in-
volve a sequence of oxidative-addition/reductive-elimina-
tion steps, R-hydride abstraction, and migration of ER3
groups between the metal and the E center in LnMd
ER2 intermediates.4,7 The migration of a group from the
metal to the silylene silicon center has been observed
with a number of different metal systems.7b,8 Two alterna-
tive pathways for the formation of E-E bonds starting
from bis(silyl) or bis(germyl)platinum complexes, either
through a platinum-silylene or -germylene intermediate
or through a reductive-elimination/oxidative-addition path-
way, are shown in Scheme 1. Limited examples of dehydro-
coupling of hydrosilanes with late transition metal catalysts
such as those containing platinum are known.9 The forma-
tion of Ge-Ge bonds catalyzed by late transition metal
complexes is less common compared to silicon due to the
decreased reactivity of the M-Ge bond compared to the
M-Si bond.10
The preparation of transition metal complexes contain
ing bonds to the heavier group 14 elements, E=Si, Ge,
and Sn, has received considerable attention over the last
several decades. Complexes containing transition metal-
silicon bonds1 are by far the most abundant, but many
examples are also known for M-Ge and M-Sn contain-
ing complexes2 (M = transition metal). The most versatile
method for the preparation of complexes containing a M-E
bond involves activation of an E-H bond by the metal
center.3 Metal-promoted activation of the E-H bonds
in hydrosilanes, hydrogermanes, and hydrostannanes is
also important in dehydrocoupling reactions,4 as well as
addition of E-H bonds to unsaturated organic substrates
(e.g., hydrosilylation).4h,5 The dehydrocoupling of E-H
bonds catalyzed by many early transition metal complexes
is thought to proceed by a sigma-bond metathesis route,4b
*To whom correspondence should be addressed. E-mail: wilking-
j@umsl.edu.
We previously reported the preparation of the diger-
mane complex (Ph3P)2HPt-GeAr2GeAr2-PtH(PPh3)2 as
one of the major products formed from the reaction of
germafluorene with (Ph3P)2Pt(η2-C2H4) through a formal
dehydrocoupling reaction (eq 1).11 A similar diplatinum
digermane complex, [(Et3P)2HPtGeAr2GeAr2PtH(PEt3)2],
was reported by Banaszak-Holl and co-workers.12 These
reactions likely proceed through pathway a in Scheme 1.
Related Ge-Ge bond forming reactions or 1,2-migrations
(1) (a) Tilley, T. D. Transition-Metal Silyl Derivatives. In The Chem-
istry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; J. Wiley
and Sons: New York, 1989; pp 1415-1477. (b) Tilley, T. D. Appendix to
Transition-Metal Silyl Derivatives. In The Silicon-Heteroatom Bond; Patai,
S., Rappoport, Z., Eds.; J. Wiley and Sons: New York, 1991; pp 309-364.
(c) Schubert, U. Transition Met. Chem. 1991, 16, 136–144. (d) Eisen, M. S.
Transition-Metal Silyl Complexes. In The Chemistry of Organic Silicon
Compounds; 1998; Vol. 2 (Pt. 3), pp 2037-2128. (e) Aylett, B. J. Adv. Inorg.
Chem. Radiochem. 1982, 25, 1–133. (f) Osakada, K.; Tanabe, M. Bull.
Chem. Soc. Jpn. 2005, 78, 1887–1898.
(2) For a review of early work see: (a) Mackay, K. M.; Nicholson,
B. K. In Comprehensive Organometallic Chemistry; Wilkinson, G.,
Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1982;
Vol. 6, pp 1043-1114. (b) Colomer, E.; Corriu, R. J. P. Top. Curr. Chem.
1981, 96, 80-107.
(6) Curtis, M. D.; Epstein, P. S. Adv. Organomet. Chem. 1981, 19,
213–255.
(7) (a) Ojima, I.; Inaba, S.-I.; Kogure, T. J. Organomet. Chem. 1973,
55, C7–C8. (b) Yamamoto, K.; Okinoshimia, H.; Kumada, M. J.
Organomet. Chem. 1970, 23, C7–C8.
(8) (a) Ogino, H.; Tobita, H. Adv. Organomet. Chem. 1998, 42, 223-
290, and references therein. (b) Waterman, R.; Hayes. P. G.; Tilley, T. D.
Acc. Chem. Res. 2007, 40, 712-719, and references therein. (c) Sharma,
H. K.; Pannell, K. H. Chem. Rev. 1995, 95, 1351-1374, and references
therein.
(9) (a) Chauhan, B. P. S.; Shimizu, T.; Tanaka, M. Chem. Lett. 1997,
785–786. (b) Tanaka, M.; Kobayashi, T.-a.; Hayashi, T.; Sakakura, T.
Appl. Organomet. Chem. 1988, 2, 91–92. (c) Brown-Wensley, K. A.
Organometallics 1987, 6, 1590–1591.
(3) Corey, J. Y.; Braddock-Wilking, J. J. Chem. Rev. 1999, 99, 175–
292.
(4) For recent reviews see: (a) Corey, J. Y. Adv. Organomet. Chem.
2004, 51, 1–52. (b) Tilley, T. D. Comments Inorg. Chem. 1990, 10,
37–51. (c) Braunstein, P.; Morise, X. Chem. Rev. 2000, 100, 3541–
3552. (d) Gauvin, F.; Harrod, J. F.; Woo, H. G. Adv. Organomet. Chem.
1998, 42, 363–405. (e) Reichl, J. A.; Berry, D. H. Adv. Organomet. Chem.
1999, 43, 197–265. (f) Yamashita, H.; Tanaka, M. Bull. Chem. Soc. Jpn.
1995, 68, 403–419. (g) Clark, T. J.; Lee, K.; Manners, I. Chem.;Eur.
J. 2006, 12, 8634–8648. (h) Kim, B.-H.; Woo, H.-G. Adv. Organomet.
Chem. 2005, 52, 143–174. (i) Tilley, T. D. Acc. Chem. Res. 1993, 26,
22–29.
(5) (a) Smith, N. D.; Mancuso, J.; Lautens, M. Chem. Rev. 2000, 100,
3257–3282. (b) Roy, A. K. Adv. Organomet. Chem. 2007, 55, 1–59. (c)
Marciniec, B. Coord. Chem. Rev. 2005, 249, 2374–2390. (d) Suginome,
M.; Ito, Y. Chem. Rev. 2000, 100, 3221–3256. (e) Ojima, I.; Li, Z.; Zhu, J.
Recent Advances in Hydrosilylation and Related Reactions. In The
Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.;
John Wiley and Sons: New York, 1998; p 1687.
(10) Ozawa, F.; Hikida, T.; Hasebe, K.; Mori, T. Organometallics
1998, 17, 1018–1024.
(11) White, C. P.; Braddock-Wilking, J.; Corey, J. Y.; Xu, H.;
Redekop, E.; Sedinkin, S.; Rath, N. P. Organometallics 2007, 26,
1996–2004.
(12) Bender, J. E.; Litz, K. E.;Giarikos, D.;Wells, N. J.;Banaszak-Holl,
M. M.; Kampf, J. W. Chem.;Eur. J. 1997, 3, 1793–1796.
r
pubs.acs.org/Organometallics
Published on Web 06/25/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 14, 2009 4099
involving PtdGe species have been reported by Barrau,13
Scheme 1
Yamashita,14a and Mochida.14b,15-17
pathway a in Scheme 1. A number of bis(silyl)platinum1,3
and bis(germyl)platinum12,13,14a,15-17,22 phosphine com-
plexes have been reported previously.
Mochida and co-workers reported the room-temperature
formation of a Ge-Ge bond in cis-(Ph3P)2Pt(H)[GeH(Mes)
GeH2Mes] from cis-(Ph3P)2Pt(GeH2Mes)2 (Mes = 2,4,6-
C6H2).16 A related platinum(disilyl) complex, (Ph3P)2Pt(H)-
(SiPh2SiPh2H), was found to be stable only at low tempera-
ture and underwent a rapid 1,2-migration of a silyl group to
give the bis(silyl)complex (Ph3P)2Pt(SiPh2H)2 at -40 °C.18
In contrast, the related germanium complex (Ph3P)2Pt(H)-
(GePh2GePh2H) was found to be stable in toluene or ben-
zene solution.17 Ishii and co-workers have reported the
preparation of stable dihydridogermyl(hydrido)platinum
complexes, cis-P2Pt(H)(GeH2Trip) (Trip=9-triptycyl; P2=
(Ph3P)2, dppe, dcpe). The dppe complex was found to under-
go a thermolysis reaction to produce the digermyl(hydrido)-
platinum complex (dppe)Pt(H)(Ge(HTrip)GeH2Trip).19 The
reaction pathway for the latter complex via reductive elimination
of digermane (pathway b, Scheme 1) was preferred since Tilley
has reported that 1,2-migrations in four-coordinate Pt-Si com-
plexes without prior ligand dissociation are unfavorable.20
Recently, Osakada and co-workers reported the pre-
paration of novel mono- and dinuclear germapallada-
cycles from a Ge-Ge bond forming reaction that was
promoted by palladium (Scheme 2).21 The dipalladium
germacycle was the major product when the starting bis
(germyl)palladium complex was heated in toluene. How-
ever, upon treatment of the bis(germyl)palladium com-
plex with excess Ph2GeH2 and heat, the monopalladium
germacycle was the major product. Both reactions were
proposed to proceed through the digermyl(hydrido)palla-
dium phosphine complex (dmpe)Pd(H)(GePh2GePh2H) via
Five-membered metallacycles containing a transition metal
or main group metal and two or more group 14 elements (Si or
Ge) have been prepared by a variety of synthetic pathways.
For example, reactions involving oxidative addition of E-
H bonds at a transition metal center have produced ME4
complexes as reported by Osakada,21 Mochida,17 Schram,23
and Barrau.13a,13c Barrau and co-workers have also synthesized
a number of cyclic complexes, L2Pt[GeMe2XGeMe2] (L =
PPh3, diphos;X=(CH2)n, S, O, NPh, (η5-C5H4)2Fe) by reaction
of bis(chlorogermyl)platinum complexes with alkali-metal
reagents.13a,13b Marschner and co-workers have prepared
Cp2M[Si(SiMe3)2(SiMe)2Si(SiMe3)2] complexes (M = Zr,
Hf) and related Mg metallacycles from a salt-elimination reac-
tion.24,25 Mochida and co-workers have suggested the formation
of PdGe4 metallacycles from the palladium-catalyzed ring-open-
ing reactions of tetragermetanes and the subsequent addition
reactions with alkynes.26 Bochkarev et al. reported the prepara-
tion of aYbGe4 metallacycle from the reaction of elemental
Yb and Ph2GeCl2 in THF.27 Herein, we report the preparation
of two platinacycles containing five-membered PtE4 rings,
(dppe)Pt(ER2)4 (ER2 = SiC12H8 or GeC12H8), from the step-
wise thermal reaction of H2ER2 with (dppe)PtMe2.
Results and Discussion
Reaction of 9,9-dihydridosilafluorene (H2SiC12H8, 1)
28
with the chelating phosphine complex (dppe)PtMe2 (2)
in ca. 4:1 ratio in toluene-d8 at 70 °C resulted in the forma-
tion of the bis(silyl)platinum complex (dppe)Pt(SiHC12H8)2
as an orange solid in 56% yield (eq 2). However, when the
reaction was carried out at 75 °C for a period of 19 h, the
(13) (a) Barrau, J.; Rima, G.; Cassano, V. Main Group Met. Chem.
ꢀ
1996, 19, 283–299. (b) Barrau, J.; Rima, G.; Cassano, V.; Satge, J.
Organometallics 1995, 17, 5700–5703. (c) Barrau, J.; Rima, G.; Cassano,
ꢀ
V.; Satge, J. Inorg. Chim. Acta 1992, 198-200, 461–467.
(14) For additional examples of PtdGe formation via 1,2-migration
of groups from Ge to Pt see: (a) Yamashita, H.; Kobayashi, T-a.;
Tanaka, M.; Samuels, J. A.; Streib, W. E. Organometallics 1992, 11,
2330–2333. (b) Mochida, K.; Fukushima, T.; Suzuki, M.; Hatanaka, W.;
Takayama, M.; Usui, Y.; Nanjo, M.; Akasaka, K.; Kudo, T.; Komiya,
S. J. Organomet. Chem. 2007, 692, 395–401.
(15) For examples of Pt- or Pd-catalyzed Ge-Ge bond formation see:
(a) Komoriya, H.; Kako, N.; Nakadaira, Y.; Mochida, K. J. Organomet.
Chem. 2000, 611, 420–432. (b) Mochida, K.; Karube, H.; Nanjo, M.;
Nakadaira, Y. Organometallics 2005, 24, 4734–4741. (c) Mochida, K.;
Wada, T.; Suzuki, K.; Hatanaka, W.; Nishiyama, Y.; Nanjo, M.; Sekine,
A.; Ohashi, Y.; Sakamoto, M.; Yamamoto, A. Bull. Chem. Soc. Jpn.
2001, 74, 123–137.
(21) Tanabe, M.; Ishikawa, N.; Hanzawa, M.; Osakada, K. Organo-
metallics 2008, 27, 5152–5158.
(22) See for example: (a) Brooks, E. H.; Glockling, F. Chem.
Commun. 1965, 510. (b) Brooks, E. H.; Glockling, F. J. Am. Chem.
Soc. (A) 1966, 1241–1243. (c) Usui, Y.; Fukushima, T.; Nanjo, M.;
Mochida, K.; Akasaka, K.; Kudo, T.; Komiya, S. Chem. Lett. 2006, 35,
810–811.
(23) (a) Lemanski, M. F.; Schram, E. P. Inorg. Chem. 1976, 15, 1489–
1492. (b) For the preparation of a related PtSi3 complex see: Hengge, E.;
Pollhammer, G. Z. Chem. 1983, 23, 251–252.
(24) Kayser, C.; Kickelbick, G.; Marschner, C. Angew. Chem., Int.
Ed. 2002, 41, 989–992.
(16) Arii, H.; Nanjo, M.; Mochida, K. Organometallics 2008, 27,
4147–4151.
(25) Gaderbauer, W.; Zirngast, M.; Baumgartner, J.; Marschner, C.
Organometallics 2006, 25, 2599–2606.
(17) Usui, Y.; Hosotani, S.; Ogawa, A.; Nanjo, M.; Mochida, K.
Organometallics 2005, 24, 4337–4339.
(26) Mochida, K.; Hirakue, K.; Suzuki, K. Bull. Chem. Soc. Jpn.
2003, 76, 1023–1028.
(18) Arii, H.; Takahashi, M; Noda, A.; Nanjo, M.; Mochida, K.
Organometallics 2008, 27, 1929–1935.
(19) Nakata, N.; Fukazawa, S.; Ishii, A. Organometallics 2009, 28,
534–538.
(20) (a) Mitchell, G. P.; Tilley, T. D. Angew. Chem., Int. Ed. 1998, 37,
2524–2526. (b) Feldman, J. D.; Mitchell, G. P.; Nolte, J. O.; Tilley, T. D.
Can. J. Chem. 2003, 81, 1127–1136.
(27) Bochkarev, L. N.; Makarov, V. M.; Zakharov, L. N.; Fukin,
G. K.; Yanovsky, A. I.; Struchkov, Y. T. J. Organomet. Chem. 1995, 490,
C29–C31.
(28) (a) Hooton, K. A. J. Chem Soc. (A) 1970, 1896–1900.
(b) Appleton, T. G.; Bennett, M. A.; Tomkins, I. B. J. Chem. Soc.
Dalton 1976, 439–446. (c) Hietkamp, S.; Stufkens, D. J.; Vrieze, K. J.
Organomet. Chem. 1979, 169, 107–113.

4100 Organometallics, Vol. 28, No. 14, 2009
Braddock-Wilking et al.
Scheme 2
novel platinatetrasilacycle 4 was obtained as a minor product
in 8% yield as a yellow solid (eq 2).
but was accelerated by heating at 323 K. The initial products
observed at room temperature in the 31P{1H} NMR spec-
trum were assigned to the bis(germyl) platinum complex
(dppe)Pt(GeAr2H)2 (7) at δ 56.9 (1JPtP = 2139 Hz) and three
products that were assigned to six-coordinate complexes
based on the chemical shift to higher field and significantly
1
reduced JPtP coupling values (<1350 Hz).29 These high-
field resonances were assigned to six-coordinate complexes
that would arise from the oxidative-addition of H2GeAr2 (5)
to (dppe)PtMe2 (2) and the subsequent six-coordinate
complexes that would result after reductive elimination of
CH4 or MeGeAr2H followed by oxidative addition of a
second molecule of 5. The 31P NMR chemical shifts and
tentative assignments for the six-coordinate complexes
are 30.6 and 24.9 ppm (C, (dppe)Pt(CH3)(H)2(GeAr2H);
26.1 and 25.8 ppm (D, (dppe)Pt(CH3)(H)(GeAr2H)2); and
16.1 ppm (E, (dppe)Pt(CH3)2(H)(GeAr2H)). The unreacted
platinum complex 2 (δ 46.8, 1JPtP=1779 Hz) was also present
in a significant amount in the reaction solution.
The 1H NMR spectrum of 3 in CD2Cl2 exhibited a Si-H
resonance at 5.23 ppm (2JPtH = 83 Hz) in addition to the aryl
and methylene proton signals of the complex. The 31P{1H}
NMR spectrum of 3 shows a singlet with platinum satellites
at 59.3 ppm (1JPtP = 1704 Hz) and a similar shift for 4 at
57.6 ppm (1JPtP = 1683 Hz). The molecular structure of
4 was confirmed by X-ray crystallography (vide infra).
The corresponding reaction between 9,9-dihydridogerma-
fluorene 5 and the platinum complex 2 in toluene-d8 at lower
temperature (50 °C) produced the platinatetragermacycle
6 as the major product in 55% yield (eq 3). The molecular
structure of 6 was confirmed by X-ray crystallography (vide
infra). The 1H and 31P{1H} NMR spectra of 6 were similar to
those of 4, but the phosphorus resonance of 6 appeared at
55.9 ppm and exhibited a significantly larger Pt-P coupling
of 1JPtP = 2177 Hz compared to 4. The bis(germyl)platinum
complex 7 was observed at the early stages of the reaction, as
determined by NMR spectroscopy (vide infra). Complex 7
was isolated as the major product in 67% yield in a separate
experiment involving the reaction of 2 with 5 in toluene-d8 at
27 °C in the presence of 2 equiv of CD3CN (vide infra).
As the reaction mixture was heated gradually to 323 K, a
number of new resonances emerged while some of the
1
original resonances slowly disappeared in both the H and
31P{1H} NMR spectra, and no new resonances assignable to
six-coordinate intermediates were observed. The sequential
appearance of five new sets of doublet resonances in the 31P
{1H} NMR spectra in the region of 50-60 ppm during the
course of the reaction indicated the formation of unsymme-
trical complexes (labeled as products A, B, F, H, and I in
Figure 1 and Supporting Information). This supports a
stepwise process in the formation of the metallacycle 6.
A reaction pathway similar to the one proposed by
Osakada and co-workers for the formation of the related
palladacycle, (dmpe)Pd(GePh2)4, starting from the bis(ger-
21
myl)palladium complex (dmpe)Pd(GePh2H)2 may be oc-
curring in the formation of the platinum metallacycle
6 through a stepwise sequence beginning with the bis(ger-
myl)platinum complex 7 as shown in Scheme 1. Dissociation
of a phosphine group from 7, followed by a 1,2-hydride
migration from Ge to Pt, would produce the germylene-
platinum intermediate as shown in Scheme 3. A subsequent
1,2-migration of a (GeAr2H) group from Pt to the germy-
lene followed by recoordination of the phosphine to plati-
num would generate the complex (dppe)Pt(H)(GeAr2-
GeAr2H). However, dissociation of a phosphine unit in a
chelating phosphine would be less favorable than a complex
containing a monodentate phosphine. Another possible
(29) See for example: (a) Braddock-Wilking, J.; Corey, J. Y.;
Trankler, K. A.; Xu, H.; French, L. M.; Praingam, N.; White, C.; Rath,
N. P. Organometallics 2006, 25, 2859–2871. (b) Shimada, S.; Rao, M. L.
N.; Li, Y.-H.; Tanaka, M. Organometallics 2005, 24, 6029–6036. (c)
Shimada, S.; Tanaka, M.; Honda, K. J. Am. Chem. Soc. 1995, 117, 8289–
8290. (d) Heyn, R. H.; Tilley, T. D. J. Am. Chem. Soc. 1992, 114, 1917–
1919. (e) Packett, D. L.; Syed, A.; Trogler, W. C. Organometallics 1988,
7, 159–166.
The thermolysis reaction of 2 with an excess of 5 was
also performed in toluene-d8 and produced a number of
complexes during the course of the reaction as determined
by 1H and 31P{1H} NMR spectroscopy (Figure 1). The
reaction proceeded to a small extent at room temperature

Article
Organometallics, Vol. 28, No. 14, 2009 4101
Figure 1. 31P{1H} NMR data collected during the reaction of 2 + 5 showing (a) the full spectrum at 300 K, 20 min after mixing.
Expanded regions between 47 and 63 ppm and 11-35 ppm collected at (b, c) 300 K, 20 min; (d, e) 310 K, 1 h 50 min; (f, g) 323 K, 3 h 23
min; (h, i) 300 K after heating, 7 h. The expanded spectra are scaled to the largest peak.
Scheme 3
route would involve reductive elimination of the digermane
HAr2Ge-GeAr2H from 7 followed by subsequent oxidative-
addition of the Ge-H bond by (dppe)Pt. Reaction between
H2GeAr2 (5) and (dppe)Pt(H)(GeAr2GeAr2H) either by an
oxidative-addition reaction involving a Ge-H bond of 5 or
more likely through a pathway involving a sigma-bond
metathesis reaction followed by elimination of H2 would
produce (dppe)Pt(GeAr2H)(GeAr2GeAr2H). A similar se-
quence of steps would then ultimately generate the complex
(dppe)Pt(H)[(GeAr2)3GeAr2H]. The latter complex could
then undergo a final step involving intramolecular oxida-
tive-addition of the terminal Ge-H bond at the Pt atom or
react by a σ-bond methathesis step to give product 6 along
with elimination of H2. The 31P{1H} NMR spectra collected
during the course of the reaction of 2 + 5 showed several sets
of doublet resonances (Figure 1) that may be due to Pt
(germyl)(di- or trigermyl) or Pt(hydridro)(germyl) com-
plexes as shown in Scheme 3. However, no NMR evidence
was observed for the presence of either platinum-germylene
or four-coordinate or six-coordinate (hydrido)platinum(ger-
myl) species, but this may be due to high instability or
reactivity of these complexes. Deuterium labeling studies
for the reaction of 5-d2 with 2 did not provide any new NMR
2
signals in the H spectrum that were not observed in the

4102 Organometallics, Vol. 28, No. 14, 2009
Braddock-Wilking et al.
reaction of 5 with 2 as determined by 1H NMR spectroscopy.
1
A singlet was observed in the H NMR spectrum from the
beginning of the reaction that may be due to the digermane
HAr2Ge-GeAr2H,30 but signals due to other possible reduc-
tive-elimination products, H(GeAr2)xH (x = 3-4), were not
assigned. Complexes containing smaller [Pt(GeAr2)3] or
larger [Pt(GeAr2)5] metallacycles were not observed in the
reaction, and this is probably due to the formation of the
thermodynamically favorable five-membered metallacycle
in 6. The formation of the metallacycles 4 and 6 and
21
(dmpe)Pd(GePh2)4 appear to be influenced by the use of
chelating phosphine groups at the metal center and not the
substituents at the group 14 center. Attempts to trap any
platinum-germylene intermediates with 1,3-dimethyl-2-imi-
dazolidinone (DMI) or CD3CN were unsuccessful.31 In the
reaction with added DMI, complex 6 was isolated in 30%
yield, and an unidentified product was observed in solution
after heating at 323 K that exhibited a singlet resonance with
Pt satellites at δ 57.3 in the 31P{1H} NMR spectrum (1JPtP
=
2013 Hz). In the reaction with 1 equiv of CD3CN, the
formation of the major product 7 suggests that the CD3CN
may interfere with the reaction pathway by reversible co-
ordination to the germylene center in the intermediate
species (Ph2PCH2CH2PPh2)(H)Pt(dGeAr2)(GeAr2H). This
would make the subsequent germyl migration to the germy-
lene center unfavorable, thus inhibiting the reaction from
proceeding further. In fact, only a minor amount of 6
(<10%) was produced from this reaction.
Figure 2. Molecular structure of 4 (with thermal ellipsoids shown
˚
at the 50% probability level). Selected bond distances (A) and angles
(deg): Pt(1)-P(1)=2.294(2), Pt(1)-P(2)= 2.3042(19), Pt(1)-Si(1)
= 2.346(3), Pt(1)-Si(2) = 2.375(3), Si(1)-Si(4) = 2.365(3), Si(3)-
Si(4) = 2.327(3), Si(2)-Si(3) = 2.357(4); P(1)-Pt(1)-P(2) = 85.32
(8), Si(1)-Pt(1)-Si(2) = 88.85(7), P(1)-Pt(1)-Si(2) = 169.46(8),
P(2)-Pt(1)-Si(1)=164.23(9), Pt(1)-Si(1)-Si(4)=122.23(13), Pt-
(1)-Si(2)-Si(3)=121.04(13), P(1)-Pt(1)-Si(1) = 96.17(9), P(2)-
Pt(1)-Si(2)=92.37(9), Si(2)-Si(3)-Si(4)=100.57(13), Si(1)-Si(4)-
Si(3) = 99.40(13).
X-ray Crystallography. The molecular structures of 4, 6, and
7 were determined by X-ray crystallography and are shown in
Figures 2-4, respectively. Both structures 4 and 6 contain two
five-membered rings in puckered envelope conformations. The
two five-membered rings in 4 and 6 are twisted relative to each
other by 9.6° and 1.6°, respectively. The platinum centers in
4, 6, and 7 exhibit a distorted square-planar environment.
˚
The Pt-Si bond distances of 4 (2.34-2.37 A) fall in the
range of known Pt-Si single bonds3 and are similar to those
32
observed in (dppe)Pt(SiHiPr2)2, [(dppe)Pt(μ-SiPh2)]2,33
and {(dppe)Pt[μ-SiH(IMP)]}2.34 As expected, the Pt-Ge
˚
distances for 6 and 7 (2.43-2.44 A) are similar to those
reported for (dppe)Pt(GeMePh2)2,15c cis-(PhMe2P)2Pt-
(GeR3)2 (GeR3 = GeMePh2, GeMe2Ph),15c and (dmpe)Pt-
15c
(GeMePh2)2 but are slightly longer than the Pt-Si dis-
tances in 4 due to the larger size of Ge compared to Si.
The digermaplatinacycle complex (Ph3P)2Pt[GePh2(Si-
Me3)2GePh2] showed significantly longer Pt-Ge distances
17
˚
(2.49 A) compared to 6.
˚
The Pt-P distances in 4 and 7 (2.28-2.30 A) are similar
15c
to those observed for (dppe)Pt(GeMePh2)2
and are
˚
only marginally longer than those in complex 6 (2.27 A),
resulting from the smaller trans influence of Ge compared
to Si; likewise, larger Pt-P coupling values were observed
Figure 3. Molecular structure of 6 (with thermal ellipsoids shown
˚
at the 50% probability level). Selected bond distances (A) and angles
(deg): Pt(1)-P(1)=2.2711(15), Pt(1)-P(2) = 2.2768(15), Pt(1)-Ge
(1)=2.4426(7), Pt(1)-Ge(4)=2.4384(7), Ge(1)-Ge(2)=2.4383(9),
Ge(2)-Ge(3) = 2.3964(9), Ge(3)-Ge(4) = 2.4434(9); P(1)-Pt(1)-
P(2)=86.05(5), Ge(1)-Pt(1)-Ge(4)=90.61(2), P(1)-Pt(1)-Ge(4)
= 170.36(4), P(2)-Pt(1)-Ge(1)=174.51(4), P(1)-Pt(1)-Ge(1) =
92.10(4), P(2)-Pt(1)-Ge(4) = 92.09(4), Pt(1)-Ge(1)-Ge(2) =
118.72(3), Pt(1)-Ge(4)-Ge(3) = 120.43(3), Ge(1)-Ge(2)-Ge(3)
= 101.79(3), Ge(2)-Ge(3)-Ge(4) = 98.67(3).
€
(30) Lui, Y.; Ballweg, D.; Muller, T.; Guzei, I. A.; Clark, R. W.; West,
R. J. Am. Chem. Soc. 2002, 124, 12174–12181.
(31) (a) For the preparation of a donor-stabilized iron-silylene com-
plex with DMI see: Corriu, R. J. P.; Lanneau, G. F.; Chauhan, B. P. S.
Organometallics 1993, 12, 2001–2003. (b) For the preparation of a
donor-stabilized ruthenium-silylene complex with CH3CN see: Strauss,
D. A.; Tilley, T. D.; Rheingold, A. L.; Geib, S. J. J. Am. Chem. Soc. 1987,
109, 5872–5873.
(32) Pham, E. K.; West, R. Organometallics 1990, 9, 1517–1523.
(33) Tanabe, M.; Ito, D.; Osakada, K. Organometallics 2008, 27,
2258–2267.
for 6 and 7 (1JPtP=2177, and 2131 Hz, respectively) com-
pared to 4 (1JPtP =1683 Hz) and are consistent with the
stronger trans influence of silicon. The dihedral angle for the
(34) Braddock-Wilking, J.; Levchinsky, Y.; Rath, N. P. Inorg. Chim.
Acta 2002, 330, 82–88.

Article
Organometallics, Vol. 28, No. 14, 2009 4103
1,3-Dimethyl-2-imidazolidinone (DMI) was purchased from
Aldrich Chemical Co. and degassed before use. 9,9-Dihydrido-
germafluorene11 was prepared by the lithium aluminum hydride
reduction of dichlorogermafluorene,30 and 9,9-dideuterogerma-
fluorene was prepared from an analogous reaction by reduction
of Cl2GeC12H8 with LiAlD4. 9,9-Dihydridosilafluorene was
prepared by a literature method.37 The platinum complex
(dppe)PtMe228 was prepared by a modified literature procedure
using (cod)PtMe2 and dppe in toluene.38 The 1H and 31P {1H}
NMR spectra were recorded on a Bruker ARX-300 MHz and
Bruker ARX-500 MHz at room temperature unless otherwise
specified. Proton chemical shifts (δ) were referenced to the
residual peaks of the solvents used. Phosphorus chemical shifts
are referenced relative to external H3PO4. Infrared spectra were
recorded on a Thermo-Nicolet Avatar 360 ESP FT-IR spectro-
meter. Elemental analysis determinations were obtained from
Atlantic Microlabs, Inc., Norcross, GA. X-ray crystallographic
determinations were performed on a Bruker Apex II diffract-
ometer equipped with a CCD area detector.
Figure 4. Molecular structure of 7 (thermal ellipsoids shown at
˚
the 50% probability level). Selected bond distances (A) and
General Procedure for the Addition Reactions. In a drybox, a
solution of the platinum precursor (dppe)PtMe2 was prepared in
C7D8 in a vial. In a separate vial, H2SiC12H8 or H2GeC12H8 was
dissolved in C7D8 and then added dropwise to the (dppe)PtMe2
solution. The reaction mixture was transferred to a NMR tube
and heated in the NMR probe or in an oil bath. NMR data were
collected at various reaction times after addition.
angles (deg): Pt(1)-P(1)=2.2893(8), Pt(1)-P(1)#1=2.2893(8),
Pt(1)-Ge(1) = 2.4346(4), Pt(1)-Ge(1)#1=2.4347(4), Ge(1)-
H(1)=1.49(3); P(1)-Pt(1)-P(1)#1 = 85.58(4), Ge(1)-Pt(1)-
Ge(1)#1 = 82.347(17), P(1)-Pt(1)-Ge(1)#1 = 96.91(2), P(1)
#1-Pt(1)-Ge(1) = 96.91(2), P(1)-Pt(1)-Ge(1) = 169.90(2),
P(1)#1-Pt(1)-Ge(1)#1 = 169.90(1).
Preparation of (dppe)Pt(SiHC12H8)2 (3). To a solution of
(dppe)PtMe2 (0.064 g, 0.10 mmol, 2) in 0.5 mL of C7D8 was
added a solution of H2SiC12H8 (0.080 g, 0.44 mmol, 1) in 1 mL of
C7D8. The sample was heated at 70 °C in an oil bath for 16 h. An
orange solid (3, 55 mg, 56% yield) precipitated and was washed
with pentane and then dried. 1H NMR data (300 MHz,
CD2Cl2): δ 7.50-6.80 (br, overlapping resonances, aromatic
planes composed of P1-Pt-P10 and Ge1-Pt-Ge10 for 7
is 14.9°. The Si-Si35 and Ge-Ge36 distances in the ring
in complexes 4 and 6, respectively, are within the expected
range.
There are a few examples of structurally characterized
complexes containing a five-membered MSi4 or MGe4 ring
including Cp2M(SiMe2)4 (M=Zr and Hf),24 (THF)2Mg-
(SiMe3)4,25 (dmpe)Pd(GePh2)4,21 and (THF)4Yb(GePh2)4.27
2
H), 5.23 (s, JPtH = 83 Hz, SiH), 1.88 (br, m, CH2). 31P{1H}
1
NMR data (121 MHz, CD2Cl2): δ 59.3 (s, JPtP = 1704 Hz).
Selected IR data (solid, cm-1): ν 2044 (Si-H). Anal. Calcd for
C50H42P2PtSi2: C, 62.81; H, 4.43. Found: C, 62.24; H, 4.46.
Preparation of (dppe)Pt(SiC12H8)4 (4). To a solution of (dppe)
PtMe2 (0.028 g, 0.045 mmol, 2) in 0.5 mL of C7D8 was added a
solution of H2SiC12H8 (0.030 g, 0.16 mmol, 1) in 0.75 mL of
C7D8. The sample was heated at 75 °C for 19 h in an oil bath.
A yellow crystalline solid (4, 5 mg, 8% yield) formed and was
washed with benzene and then dried. 1H NMR data (500 MHz,
CD2Cl2): δ 7.80-6.90 (br, overlapping resonances, aromatic H),
1.89 (br, m, CH2). 31P{1H} NMR data (202 MHz, CD2Cl2):
Conclusion
The thermolysis of sila- and germafluorene (1 and
5, respectively) with (dppe)PtMe2 (2) produced new five-
membered metallacycles (dppe)Pt(ER2)4 (E = Si (4), Ge (6);
R = C12H8). The use of the chelating dppe ligand at Pt
facilitates the E-E bond forming reaction starting from
(dppe)Pt(ER2H)2 (3 and 7, respectively). The reaction path-
way of 4 and 6 likely involves PtdE intermediates formed
from silyl or germyl group migrations and a series of
oxidative-addition or sigma-bond metathesis steps, as sug-
gested by multinuclear NMR spectroscopy.
1
δ 57.6 (s, JPtP=1683 Hz). Attempts to obtain a significant
quantity of analytically pure 4 were unsuccessful.
Reaction of H2GeC12H8 (5) with (dppe)PtMe2 (2). Formation
of (dppe)Pt(GeC12H8)4 (6). To a solution of (dppe)PtMe2 (0.046
g, 0.074 mmol, 2) in 0.4 mL of C7D8 was added H2GeC12H8
(0.045 g, 0.22 mmol, 5) in 0.4 mL of C7D8 at room temperature.
Then the temperature was raised to 50 °C and maintained for
3.25 h. After heating, the sample tube contained a yellow
solution and a light yellow crystalline solid. The solid was
dissolved in CD2Cl2 and analyzed by NMR spectroscopy. Pale
yellow crystals of 6 containing one molecule of CD2Cl2 solvate
were isolated from the NMR sample and were suitable for X-ray
Experimental Section
General Procedures. All reactions were carried out under
an argon atmosphere using standard Schlenk techniques
or a drybox. The solvents THF, diethyl ether, and methy-
lene chloride were distilled according to standard proce-
dures. The NMR solvents, toluene-d8, benzene-d6, and methy-
lene-d2, were purchased from Cambridge Isotopes, Inc., and
degassed by freeze/thaw pump cycles and dried over acti-
vated molecular sieves. Acetonitrile-d3 was obtained as 1 g
vials from Cambridge Isotopes Inc. and used as received.
crystallographic analysis. Anal. Calcd for C74H56P2PtGe4
3
CD2Cl2: C, 57.02; H, 3.83. Found: C, 57.82; H, 3.93. In a
separate reaction, (dppe)PtMe2 (0.048 g, 0.077 mmol, 2) and
H2GeC12H8 (0.052 g, 0.23 mmol, 5) in ca. 1.0 mL of C7D8 were
heated for approximately 3 h at 50 °C. Complex 6 was isolated as
a light yellow solid in 55% yield (63 mg). Anal. Calcd for
C74H56P2PtGe4: C, 59.04; H, 3.78. Found: C, 59.01; H, 3.97.
(35) (a) Corey, J. Y. In The Chemistry of Organic Silicon Compounds,
Part 1; Patai, S., Rappoport, Z., Eds.; John Wiley & Sons: New York,
1989; Chapter 1. (b) Sheldrick, W. S. In The Chemistryof Organic Silicon
Compounds, Part 1; Patai, S., Rappoport, Z., Eds.; John Wiley & Sons:
New York, 1989; Chapter 3.
(37) (a) Chang, L. S.; Corey, J. Y. J. Organomet. Chem. 1986, 307, 7–
14. (b) For a recent preparation of 1,1-dichlorosilafluorene see: Liu, Y.;
Stringfellow, T. C.; Ballweg, T.; Guzei, I. A.; West, R. J. Am. Chem. Soc.
2002, 124, 49–57.
(38) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411–
428.
€
(36) See for example: (a) Drager, V. M.; Ross, L. Z. Anorg. Allg.
Chem. 1980, 460, 207–216. (b) Drager, V. M.; Ross, L. Z. Anorg. Allg.
€
Chem. 1980, 469, 115–122.

4104 Organometallics, Vol. 28, No. 14, 2009
Table 1. Crystallographic Data and Structure Refinement for 4, 6, and 7
Braddock-Wilking et al.
4
6
7
formula
fw
C74 H56 P2 Pt Si4
1314.58
C74 H56 Ge4 P2 Pt CD2Cl2
1577.50
C50 H42 Ge2 P2 Pt
1045.05
3
cryst size/mm
cryst syst
space group
0.19 ꢀ 0.14 ꢀ 0.11
orthorhombic
Pna21
23.4146(13)
10.3148(6)
24.4550(12)
90
5906.3(6)
1.478
4
2.556
1.93 to 26.47
173 667/12 023
[R(int) = 0.108]
semiempirical from equivalents
0.7663 and 0.6423
0.0442
0.35 ꢀ 0.09 ꢀ 0.05
monoclinic
P21/n
16.714(3)
19.448(3)
20.010(3)
102.905(7)
6340.2(17)
1.653
4
4.252
2.71 to 26.02
115 163/12 479
[R(int) = 0.11]
numerical
0.8155 and 0.3176
0.0434
0.17 ꢀ 0.13 ꢀ 0.08
tetragonal
I41/acd
17.9479(3)
17.9479(3)
52.441(3)
˚
a/A
˚
b/A
˚
c/A
β/deg
90
3
˚
V/A
16892.6(9)
1.644
16
Dcalcd/g cm-3
Z
abs coeff/mm-1
θ range/deg
reflns collected/indep reflns
4.829
2.83 to 25.07
134 807/3745
[R(int) = 0.109]
numerical
0.7777 and 0.6096
0.0234
abs correct
max. and min. transmn
final R indices [I > 2σ(I)]
R indices (all data)
0.0971
2.905 and -1.655
0.1052
2.238 and -2.312
0.0402
0.469 and -0.519
-3
˚
largest diff peak and hole/e A
(dppe)Pt(GeC12H8)4 (6). 1H NMR (500 MHz, CD2Cl2, 27 °C):
δ7.60-7.03 (overlapping resonances, ArH), 1.91 (m, CH2). 31P{1H}
NMR (202 MHz, CD2Cl2, 27 °C): δ 55.9 (s, 1JPtP = 2177 Hz).
Reaction of D2GeC12H8 (5-d2) with (dppe)PtMe2 (2). A solu-
tion of 5-d2 (0.050 g, 0.22 mmol) in 0.4 mL of C7H8 was added to
a solution of 2 (0.046 g, 0.73 mmol) in 0.4 mL of C7H8. A small
drop of C6D6 was added to the solution as a reference. The
progressed, some of the other resonances observed in the
6:1 germafluorene/(dppe)PtMe2 reaction were observed but in
a much smaller amount. After heating, the NMR tube contained
a clear yellow solution, a colorless solid, and a fine yellow solid.
The solution was decanted, and the solid mixture was washed
with a small amount of CD2Cl2 to give a clear crystalline solid
(7, 43 mg, 67% yield) that was suitable for X-ray crystallogra-
phy. A minor amount of 6 (<10%) was produced from the
reaction as an impure solid. Anal. Calcd for C50H42P2PtGe2: C,
57.46; H, 4.05. Found: C, 57.53; H, 4.05.
2
reaction was monitored by H NMR. The NMR spectra were
recorded approximately 40 min after addition at 27 °C. Then the
solution was heated in 5 °C increments every 10 min to 52 °C and
held at that temperature for 1 h.
(dppe)Pt(GeHC12H8)2 (7). 1H NMR (500 MHz, CD2Cl2,
27 °C): δ 7.8-6.8 (overlapping resonances, ArH), 6.52 (m, GeH),
1.55 (m, CH2). 31P{1H} NMR (202 MHz, CD2Cl2, 27 °C): δ 56.9
(s, 1JPtP=2139 Hz). Selected IR data (solid, cm-1): ν 1945 (Ge-H).
X-ray Structure Determination of 4, 6, and 7. Crystals of
appropriate dimension were obtained by room-temperature
crystallization in toluene-d8 (4 and 7) or methylene chloride-d2
(6). Crystals of appropriate dimensions were mounted on a
Mitgen loop in random orientations. Preliminary examination
and data collection were performed using a Bruker Kappa Apex
II charge coupled device (CCD) detector system single-crystal
X-ray diffractometer equipped with an Oxford Cryostream LT
device at 100(2) K. All data were collected using graphite-
2H NMR (76 MHz, C7H8 + C6D6, 37 °C, 1 h after addition):
δ 6.3 (br), 6.1 (br), 5.4 (s), 5.3 (s), 5.2 (s), 4.9 (s, 5-d2, major
component), 4.5 (s, D2), 4.3 (s), 4.16 (s), 2.1 (t, C7(H/D)8, 1.75
(br), 1.6 (br), 1.4 (br), 0.1 (q, CH3D), -9.1 (br). As the sample
was heated, the signals at δ 6.3 and -9.1 disappeared and most
of 5-d2 had been consumed. The other resonances listed above
were still present in the solution. After heating, complex 6
precipitated in the NMR tube and was isolated in a 41% yield.
Reaction of H2GeC12H8 (5) with (dppe)PtMe2 (2) in the
Presence of DMI. A solution of 5 (0.042g, 0.18 mmol) and
DMI (0.007 g, 0.06 mmol) in 0.4 mL of C7D8 was added to a
solution of 2 (0.038 g, 0.061 mmol) in 0.4 mL of C7D8. After
50 min at room temperature, the solution was then heated to
50 °C for approximately 3 h in the NMR probe. Complex 6
precipitated in the NMR tube after heating and was isolated in
30% yield (27 mg). Analysis of the reaction mixture during the
heating period by 1H and 31P{1H} NMR spectroscopy showed
essentially all of the same resonances observed in the 6:1
germafluorene/(dppe)PtMe2 reaction described above, but the
31P{1H} NMR spectrum for the reaction solution after heating
for 3 h showed that the major component was complex 2 along
with one new signal at 57.3 (s, 1JPtP = 2012 Hz, unassigned). No
Ge-H or Pt-H signals and only signals for uncoordinated
DMI were observed in the 1H spectrum after heating for 3 h.
Reaction of H2GeC12H8 (5) with (dppe)PtMe2 (2) in the
presence of CD3CN. Formation of (dppe)Pt(GeHC12H8)2 (7).
A solution of 5 (0.043 g, 0.19 mmol) and CD3CN (0.005 g,
0.12 mmol) in 0.4 mL of C7D8 was added to a solution of 2 (0.038
g, 0.061 mmol) in 0.4 mL of C7D8 in an NMR tube. The solution
˚
monochromated Mo KR radiation (λ= 0.71073 A) from a
fine-focus sealed tube X-ray source. Preliminary unit cell con-
stants were determined with a set of 36 narrow frame scans.
Typical data sets consist of combinations of ϖ and φ scan frames
with typical scan widths of 0.5° and counting times of 15-30 s/
frame at a crystal to detector distance of 4.0 cm. The collected
frames were integrated using an orientation matrix determined
from the narrow frame scans. Apex II and SAINT software
packages39 were used for data collection and data integration.
Analysis of the integrated data did not show any decay. Final
cell constants were determined by global refinement of reflec-
tions from the complete data set. Collected data were corrected
for systematic errors using SADABS40 based on the Laue
symmetry using equivalent reflections.
Crystal data and intensity data collection parameters are
listed in Table 1.
Structure solution and refinement were carried out using
was heated in the NMR probe starting at 27 °C, and 1H and 31
P
the SHELXTL- PLUS software package.41 The structures
{1H} NMR spectra were collected beginning 15 min after
addition. Fifty minutes after addition the solution was heated
to 50 °C for 6.5 h. The NMR spectra were recorded every 15 min
after heating was initiated. Analysis of the reaction mixture
during the initial heating period by 31P{1H} NMR spectro-
scopy showed signals for 2, 7, D, and E. As the reaction
(39) Apex II and SAINT; Bruker Analytical X-Ray: Madison, WI,
2008.
(40) Blessing, R. H. Acta Crystallogr. 1995, A51, 33–38.
(41) Sheldrick, G. M. (Bruker-SHELXTL) Acta Crystallogr. 2008,
A64, 112-122.

Article
Organometallics, Vol. 28, No. 14, 2009 4105
were solved by direct methods and refined successfully in the
space groups Pna21, P21/n, and I41/acd, respectively. Full
coefficients for the non-hydrogen atoms are in the Supporting
Information. A table of the calculated and observed structure
factors is available in electronic format.
matrix least-squares refinement was carried out by minimizing
P
w(F2o - F2c)2. All non-hydrogen atoms were refined anisotro-
pically to convergence except C1 and C2 in the case of 4. Some
twinning was observed in the case of 4. Twin refinement was
carried out with the use of BASF/TWIN (SHELXTL). All
hydrogen atoms were treated using an appropriate riding model
(AFIX m3). Disorder in a phenyl ring in the structure of 7 was
resolved with 50% occupancy atoms. The crystal data and
structure refinement parameters for 4, 6, and 7 are listed in
Table 1.
Acknowledgment. Funding from the National Science
Foundation is greatly appreciated (CHE-0719380 and
MRI, CHE-0420497 for the purchase of the Apex II
diffractometer).
Supporting Information Available: Crystallographic data for
complexes 4, 6, and 7 as a CIF file and VT NMR data for the
reaction of (dppe)PtMe2 (2) with H2GeAr2 (5). This material is
available free of charge via the Internet at http://pubs.acs.org.
Complete listings of geometrical parameters, positional and
isotropic displacement coefficients, and anisotropic displacement