Unusual reactivity of methylphosphaalkyne (P=CMe) toward digermenes and distannenes: Stepwise formations of bridged 2,3,5,6-tetraphospha-1,4- dimethylidenecyclohexanes

Article abstract of DOI:10.1021/ic700926u

Reactions of methylphosphaalkyne, P≡CMe, with a digermene, R″₂Ge≡GeR″₂ (R″ = -CH(SiMe ₃)₂), and two distannenes, R″₂Sn≡ SnR″₂ and Ar′₂Sn≡SnAr′₂ (Ar′ = C₆H₂Prⁱ₃-2,4,6), have given moderate to high yields of the first bridged 2,3,5,6-tetraphospha-1,4- dimethylidenecyclohexanes, [R₂E{C(Me)(H)PC(≡CH ₂)P}]₂ (R = R″ or Ar′, E = Sn or Ge), all of which have been structurally characterized. Their mechanisms of formation are thought to involve successive [2 + 1] and [2 + 2] phosphaalkyne cycloaddition, heterocycle rearrangement, phosphaalkene/vinylphosphine tautomerization, and intermolecular hydrophosphination reactions. In one reaction, two intermediates have been spectroscopically observed and one trapped by coordination to one or two W(CO)₅ fragments, yielding the first diphosphagermole complexes, {[W(CO)₅}_1or2{R″₂Ge[C(Me)PC(Me)P]}], which have been structurally characterized. Differences between the reactivities of P≡CMe and P≡CBu^t are highlighted.

Full text of DOI:10.1021/ic700926u

Inorg. Chem. 2008, 47, 1273-1278
Unusual Reactivity of Methylphosphaalkyne (Pt CMe) toward
Digermenes and Distannenes: Stepwise Formations of Bridged
2,3,5,6-Tetraphospha-1,4-dimethylidenecyclohexanes
Cameron Jones,*,† Christian Schulten,†,‡ and Andreas Stasch†,‡
School of Chemistry, Monash UniVersity, P.O. Box 23, Clayton, Victoria, 3800, Australia, and
School of Chemistry, Main Building, Cardiff UniVersity, Cardiff, CF10 3AT, U.K.
Received May 13, 2007
Reactions of methylphosphaalkyne, Pt CMe, with a digermene, R″2Get GeR″2 (R″ ) -CH(SiMe3)2), and two
distannenes, R″2Snt SnR″2 and Ar′2Snt SnAr′2 (Ar′ ) C6H2Pri3-2,4,6), have given moderate to high yields of the
first bridged 2,3,5,6-tetraphospha-1,4-dimethylidenecyclohexanes, [R2E{C(Me)(H)PC(t CH2)P}]2 (R ) R″ or Ar′, E
) Sn or Ge), all of which have been structurally characterized. Their mechanisms of formation are thought to
involve successive [2 + 1] and [2 + 2] phosphaalkyne cycloaddition, heterocycle rearrangement, phosphaalkene/
vinylphosphine tautomerization, and intermolecular hydrophosphination reactions. In one reaction, two intermediates
have been spectroscopically observed and one trapped by coordination to one or two W(CO)5 fragments, yielding
the first diphosphagermole complexes, {[W(CO)5}1or2{R″2Ge[C(Me)PC(Me)P]}], which have been structurally
characterized. Differences between the reactivities of Pt CMe and Pt CBut are highlighted.
Introduction
phaalkynes have proven to be much more alkyne than nitrile
like in their reactivity because of the polarization of their
δ+Pt Cδ- bonds, and the high energy of their π-bonding
HOMOs relative to that of their P lone pair.1
The low coordination chemistry of phosphorus has been
extensively developed over the past two decades. Compounds
containing P(III)–C multiple bonds are now readily prepared,
and their metal complexes have found a variety of applica-
tions.1 Generally, however, bulky substituents are required
to stabilize such unsaturated organophosphorus systems
toward oxidation, hydrolysis, and cycloaddition reactions.
In this area, phosphaalkynes, Pt CR, have been particularly
well investigated and over 450 papers describing their
chemistry have appeared.2 By far the most studied phos-
phaalkyne is Pt CBut, which has a diverse coordination
chemistry and has been utilized as a building block in the
synthesis of numerous organophosphorus cage, heterocyclic,
and acyclic compounds.1 Throughout this work phos-
Recent theoretical studies have suggested that the steric
(and electronic) properties of the substituents of phos-
phaalkynes (and other low coordination phosphorus com-
pounds) could have an important bearing on their chemistry.3
Accordingly, we have initiated a study of the previously
unexplored reactivity of the unhindered phosphaalkyne,
Pt CMe, to compare it to that of Pt CBut. This is also of
interest as Pt CMe is the phosphorus analogue of acetonitrile
and propyne. Our preliminary results suggest that the
chemistry of Pt CMe will not mirror that of Pt CBut, as
the two phosphaalkynes can yield different product types
from cyclodimerization, cycloaddition, and transition metal
coordination reactions.4 In general, the smaller phos-
phaalkyne appears to be significantly more reactive than its
bulkier counterpart.
* To whom correspondence should be addressed. E-mail: cameron.jones@
sci.monash.edu.au.
†
Monash University.
Cardiff University.
‡
(1) For example, see: (a) Dillon, K. B.; Mathey, F.; Nixon, J. F. In
Phosphorus: The Carbon Copy; Wiley: Chichester, 1998. (b) Phos-
phorus–Carbon Heterocyclic Chemistry: The Rise of a New Domain:
Mathey, F., Ed.; Pergamon: Amsterdam, 2001. (c) Ozawa, F.;
Yoshifuji, M. Dalton Trans. 2006, 4987. (d) Breit, B.; Winde, R.;
Mackewitz, T.; Paciello, R.; Harms, K. Chem. Eur. J. 2001, 7, 3106.
(e) Mathey, F. Angew. Chem., Int. Ed. 2003, 42, 1578 and references
therein.
(3) For example, see: (a) Nyulaszi, L. J. Organomet. Chem. 2005, 690,
2597. (b) Mo, O.; Yanez, M.; Guillemin, J.-C.; Riague, E. H.; Gal,
J.-F.; Maria, P.-C.; Poliart, C. D. Chem. Eur. J. 2002, 8, 4919. (c)
¨
Hltzl, T.; Szieberth, D.; Nguyen, M. T.; Veszpremi, T. Chem. Eur. J.
2006, 12, 8044 and references therein.
(4) (a) Jones, C.; Schulten, C.; Stasch, A. Dalton Trans. 2007, 1929. (b)
Jones, C.; Schulten, C.; Stasch, A. Dalton Trans. 2006, 3733.
(2) Results of a literature survey using SciFinder Scholar, May, 2007.
10.1021/ic700926u CCC: $40.75
Published on Web 07/14/2007
2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 4, 2008 1273

Jones et al.
Chart 1
reported. All other compounds have masses greater than 1000
Da, and as such, their accurate mass data are not considered
meaningful. IR spectra were recorded using a Nicolet 510 FT-
IR spectrometer as Nujol mulls between NaCl plates. Reproduc-
ible microanalyses could not be obtained for the complexes due
to solvent of crystallization (9) or their air- and/or moisture-
sensitive nature. Their NMR spectra, however, suggested purities
of >97% in each case. Pt CMe,11 [Ge{CH(SiMe3)2}2]2,12
13
[Sn{CH(SiMe3)2}2]2,12 and [Sn(Ar′)2]3 were synthesized by
literature procedures. All other reagents were used as received.
Preparation of [R″2Ge{C(Me)(H)PC(t CH2)P}]2 (7). Pt CMe
(1.2 mL of a 0.52 M solution in diethyl ether, 0.62 mmol) was
added to a solution of [Ge{CH(SiMe3)2}2]2 (100 mg, 0.13 mmol)
in toluene (20 mL) at -80 °C. The resultant solution was warmed
to 20 °C and stirred for 48 h, during which time 7 deposited as a
colorless crystalline solid. The solid was isolated by filtration and
dried under a stream of argon (110 mg, 85%). mp ) 197–199 °C.
1H NMR (400 MHz, CD2Cl2, 298 K): δ 0.14 (s, 2H, CHSiMe3),
0.15 (s, 2H, CHSiMe3), 0.19 (s, 18H, SiMe3), 0.21 (s, 18H, SiMe3),
As an extension of this preliminary work, we believed it
would be of interest to compare the reactivity of the two
phosphaalkynes toward the heavier Group 14 analogues of
carbenes and alkenes, viz. :ER2 and R2Et ER2 respectively
(E ) Si, Ge, and Sn), which normally exist in equilibrium
in solution. In this respect, Pt CBut has been shown to
undergo [2 + 1] cycloaddition reactions with silylene or
germylene fragments to give the three-membered hetero-
cycles, 1–3.5–7 A germadiphosphacyclobutene, 4, has also
been prepared and is thought to result from ring opening
and a subsequent dimerization reaction of a phosphager-
mirene similar to 3.8 In addition, the reaction of a distannene
with Pt CBut has given the phosphadistannacyclobutene, 5,9
via a [2 + 2] cycloaddition. Moreover, a silicon analogue
of this, 6, has been reported to be formed from the stepwise
addition of two silylene fragments to two other hindered
phosphaalkynes, Pt CR (R ) adamantyl or 2-methylcyclo-
hexyl).10 The very different reactivity of Pt CMe toward
germylene, stannylene, and related fragments is described
herein.
3
0.27 (s, 18H, SiMe3), 0.30 (s, 18H, SiMe3), 1.59 (dd, JHH ) 7.8
3
Hz, JPH ) 23.4 Hz, 6H, CH3), 2.99 (br. m, 2H, CH), 6.25 (dd,
2H, 3JPH ) 46 and 10 Hz, t CHH), 6.52 (dd, 2H, 3JPH ) 33 and 16
Hz, t CHH); 31P{1H} NMR (121.6 MHz, THF-d8, 298 K): δ –13.7
1
1
(br. d, JPP ) 303.1 Hz, PGe), 31.7 (br. d, JPP ) 303.1 Hz,
PPCCH2); IR ν/cm-1 (Nujol): 1570w, 1377m, 1307m, 1250s,
1169m, 1087m, 1056m, 1025m; (MS/EI) m/z (%): 1014 [M+, 55],
855 [M+ – CH(SiMe3)2, 25], 624 [M+ – Ge{CH(SiMe3)2}2, 56].
Preparation of [R″2Sn{C(Me)(H)PC(≡CH2)P}]2 (8). Pt CMe
(3.3 mL of a 0.25 M solution in diethyl ether, 0.82 mmol) was
added to a solution of [Sn{CH(SiMe3)2}2]2 (120 mg, 0.14 mmol)
in toluene (20 mL) at -80 °C. The resultant solution was warmed
to 20 °C and stirred for 48 h, during which time 8 deposited as a
colorless crystalline solid. The solid was isolated by filtration and
dried under a stream of argon (122 mg, 81%). mp ) 240–245 °C.
1H NMR (400 MHz, CD2Cl2, 298 K): δ 0.00 (s, 2H, CHSiMe3),
0.02 (s, 2H, CHSiMe3), 0.08 (s, 18H, SiMe3), 0.19 (s, 18H, SiMe3),
3
0.27 (s, 18H, SiMe3), 0.29 (s, 18H, SiMe3), 1.53 (dd, JHH ) 8.0
3
Hz, JPH ) 15.5 Hz, 6H, CH3), 2.76 (br. m, 2H, CH), 6.18 (dd,
2H, 3JPH ) 43 and 11 Hz, t CHH), 6.65 (dd, 2H, 3JPH ) 32 and 19
Hz, t CHH); 31P{1H} NMR (121.6 MHz, CD2Cl2, 298 K): δ –63.2
Experimental Section
1
1
1
(br. d, JPP ) 311.2 Hz, JSnP ) 621.2 Hz, PSn), 16.5 (br. d, JPP
) 311.2 Hz, PPCCH2); IR ν/cm-1 (Nujol): 1564w, 1376m, 1246m,
General Methods. All manipulations were carried out using
standard Schlenk and glovebox techniques under an atmosphere
of high-purity argon. Diethyl ether, hexane, and toluene were
1026m, 996m, 982m; (MS/EI) m/z (%): 1107[M+, 6], 948 [M+
CH(SiMe3)2, 28], 670 [M+ – Sn{CH(SiMe3)}2, 12].
–
1
distilled over Na/K alloy. H NMR spectra were recorded on a
Preparation of [Ar′2Sn{C(Me)(H)PC(t CH2)P}]2 (9). Pt CMe
(1.0 mL of a 0.51 M solution in diethyl ether, 0.51 mmol) was
added to a toluene solution (50 mL) of [Sn(Ar′)2]2 (120 mg, 0.13
mmol) at -80 °C (which had been generated in situ by UV
irradiation (λ ) 254 nm) of [Sn(Ar′)2]3 at -80 °C). The resultant
solution was warmed to 20 °C and stirred for 48 h, during which
time 9 deposited as a colorless crystalline solid. The solid was
isolated by filtration and dried under vacuum (50 mg, 31%). mp )
Bruker DPX400 spectrometer operating at 400.13 MHz and were
referenced to the residual 1H resonances of the solvent used.
31P{1H} NMR spectra were acquired using a Jeol Eclipse 300
spectrometer operating at 121.6 MHz and were referenced to
external 85% H3PO4. EI mass spectra and accurate mass spectra
were obtained from the EPSRC National Mass Spectrometric
Service at Swansea University. Although molecular ion peaks
displaying correct isotopic distribution patterns were observed
for all new complexes, only the accurate mass data for 14 are
1
210–215 °C (dec). H NMR (400 MHz, C6D6, 298 K): δ 0.83 (2
overlapping br., 24H, CH(CH3)2), 1.30 (br. overlapping m, 48H,
CH(CH3)2), 1.60 (br. m, 6H, CH3), 2.72, 2.93 (2 × br., 2 × 4H,
CH(CH3)2), 2.92 (br. m, 2H, PCH(CH3)), 3.25, 3.46 (2 × br., 2 ×
2H, CH(CH3)2), 5.80 (dd, 2H, 3JPH ) 35 and 18 Hz, t CHH), 6.19
(5) Scha¨fer, A.; Weidenbruch, M.; Saak, W.; Pohl, S. Angew. Chem., Int.
Ed. Engl. 1987, 26, 776.
(6) Tokitoh, N.; Suzuki, H.; Takeda, N.; Kajiwara, T.; Sasamori, T.;
Okazaki, R. Silicon Chem. 2002, 1, 313.
3
(dd, 2H, JPH ) 46 and 12 Hz, t CHH), 7.03 (br., 8H, ArH);
(7) Cowley, A. H.; Hall, S. W.; Nunn, C. M.; Power, J. M. J. Chem.
Soc., Chem. Commun. 1988, 753.
(8) Meiners, F.; Saak, W.; Weidenbruch, M. Chem. Commun. 2001, 215.
(9) Cowley, A. H.; Hall, S. W.; Nunn, C. M.; Power, J. M. Angew. Chem.,
Int. Ed. Engl. 1988, 27, 838.
(11) Guillemin, J.-C.; Janati, T.; Denis, J.-M. J. Org. Chem. 2001, 66, 7864.
(12) Fjeldberg, T.; Haaland, A.; Schilling, B. E. R.; Lappert, M. F.; Thorne,
A. J. J. Chem. Soc., Dalton Trans. 1986, 1551 and references therein.
(13) Weidenbruch, M.; Scha¨fer, A.; Kilian, H.; Pohl, S.; Saak, W.;
Marsmann, H. Chem. Ber 1992, 125, 563.
(10) Weidenbruch, M.; Olthoff, S.; Peters, K.; von Schnering, G. Chem.
Commun. 1997, 1433.
1274 Inorganic Chemistry, Vol. 47, No. 4, 2008

ReactiWity of Pt CMe toward Digermenes and Distannenes
Table 1. Summary of Crystallographic Data for Compounds 7–9, 14, and 15
7
8
9·(toluene)
14
15
empirical formula
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
C36H88Ge2P4Si8
1014.84
monoclinic
P21/c
13.580(3)
16.645(3)
11.978(2)
90
97.60(3)
90
2683.6(9)
2
1.256
1.442
1080
0.30 × 0.20 × 0.15
2.99–26.00
10 263
C36H88P4Si8Sn2
1107.04
monoclinic
P21/c
13.726(3)
16.959(3)
11.860(2)
90
96.38(3)
90
2743.5(9)
2
1.340
1.225
1152
0.08 × 0.05 × 0.02
2.96–25.00
8895
C75H112P4Sn2
1374.91
C23H44GeO5P2Si4W
831.32
C28H44GeO10P2Si4W2
1155.22
orthorhombic
P212121
11.323(2)
18.487(4)
20.297(4)
90
triclinic
triclinic
j
j
P1
P1
10.727(2)
12.633(3)
14.198(3)
71.70(3)
80.66(3)
83.61(3)
1798.7(6)
1
1.269
0.822
722
0.25 × 0.20 × 0.15
2.93–26.50
13 448
9.836(2)
11.780(2)
16.021(3)
99.46(3)
100.06(3)
100.66(3)
1758.9(6)
2
1.570
4.377
828
0.35 × 0.25 × 0.15
3.03–28.00
15 783
90
90
4284.7(15)
4
1.806
6.337
2232
0.25 × 0.25 × 0.22
2.91–27.00
34 743
Z
F(calcd) (g·cm-3
)
µ (mm-1
F(000)
)
cryst size (mm3)
θ range (deg)
reflns collected
Rint
0.0224
0.0610
0.0265
0.0224
0.0794
data/restraints/params
5273/0/239
1.032
0.0280
0.0690
0.305 and –0.334
4766/0/239
1.035
0.0506
0.0879
0.652 and –0.447
7362/6/375
1.034
0.0312
0.0723
0.708 and –0.422
8421/0/339
1.025
0.0233
0.0513
0.572 and –1.282
2 2
9211/0/438
1.048
0.0246
0.0538
0.784 and –1.406
GOF on F2
R1 indices [I > 2σ(I)]a
wR2 indices (all data)a
largest peak and hole (e·A-3
a
)
R1(F) ) {∑(|Fo| – |Fc|)/∑|Fo|} for reflections with Fo > 4(σ(Fo)). wR2(F2) ) {∑w(|Fo|2 – |Fc|2)2/∑w|Fo | }1/2 where w is the weight given for each
reflection.
31P{1H} NMR (121.6 MHz, C6D6, 298 K): δ –76.3 (d, 1JPP ) 320
on F2 by full matrix least-squares (SHELX97)14 using all unique
data. All non-hydrogen atoms are anisotropic (except the carbon
atoms of the toluene of crystallization in the structure of 9) with
H atoms included in calculated positions (riding model). The
Flack parameter for the structure of 15 is –0.004(5). Crystal data,
details of data collections, and refinement are given in Table 1.
Hz, 1JSnP ) 614 Hz, PSn), 15.8 (d, 1JPP ) 320 Hz, PP); IR ν/cm-1
(Nujol): 1594w, 1377m, 1260m, 1154m, 1096m, 1018m; (MS/EI)
m/z (%): 1283 [M+, 7], 1079 [M+ – Ar′, 10], 758 [M+ – Sn(Ar′)2,
20].
Preparation of [{W(CO)5}{R″2Ge[C(Me)PC(Me)P]}] (14)
and [{W(CO)5}2{R″2Ge[C(Me)PC(Me)P]}] (15). Pt CMe (1.2
mL of a 0.52 M solution in diethyl ether, 0.62 mmol) was added
to a solution of [Ge{CH(SiMe3)2}2]2 (100 mg, 0.13 mmol) in
toluene (20 mL) at 20 °C. After 5 min [W(CO)5(THF)] (198
mg, 0.501 mmol) in THF (50 mL) was added to the solution.
After stirring for 24 h, volatiles were removed in vacuo and the
residue extracted with hexane (5 mL). The extract was chro-
matographed (silica gel/hexane) and yellow and red bands
collected. Both bands were concentrated in vacuo, yielding
yellow 14 and red 15 as crystalline solids. 14: (38 mg, 13%)
Results and Discussion
Reactions of Pt CMe with examples of sources of the
heavier carbene analogues, :ER2 (E ) Si, Ge, Sn, or Pb),
were attempted. Treatment of the disilene, Mes2Sit SiMes2
(Mes ) mesityl), the diplumbene, Ar′2Pbt PbAr′2 (Ar′ )
C6H2Pri3-2,4,6), or the plumbylene, :Pb{CH(SiMe3)2}2
(which is monomeric in the solid state), with Pt CMe in
1:1, 1:2, and 1:4 stoichiometries all led to intractable
mixtures of phosphorus containing products. As the
disilene is known not to significantly dissociate to the
corresponding silylene in solution,15 UV irradiation (λ )
254 nm) of a 1:1 mixture of Pt CMe and Mes2Si(SiMe3)2
in THF at -80 °C was attempted. Although irradiation
of the trisilane is known to generate the silylene, :SiMes2,
in situ,16 many phosphorus containing products again
resulted from this reaction, none of which could be
isolated. It is of note that Pt CMe failed to react with
monomeric :Sn{N(SiMe3)2}2, which Cowley et al. have
shown to be the case when it is treated with Pt CBut.9
More success was had in the reactions of R″2Et ER″2
(E ) Ge or Sn, R″ ) –CH(SiMe3)2) with Pt CMe which,
under 1:4 stoichiometries of reactants, led to the deposition
of high yields of colorless crystals of 7 or 8 upon warming
the reaction mixtures from -80 °C to ambient temperature
and stirring for 18 h (Scheme 1). Similarly, reactions of
1
mp ) 83–85 °C; H NMR (400 MHz, C6D6, 298 K): δ 0.05 (br
s, 2H, CHSiMe3), 0.22 (br, 18H, SiMe3), 0.25 (br, 18H, SiMe3),
2.56 (d, 3JPH ) 31 Hz, 3H, GeC(CH3)P), 2.71 (v. tr, 3JPH ) 3JPH
) 20 Hz, 3H, P2C(CH3)); 31P{1H} NMR (121.6 MHz, C6D6,
2
1
298 K): δ 247.5 (d, JPP ) 53.8 Hz, JPW ) 257 Hz, PCMe),
342.0 (d, JPP ) 53.8 Hz, GePCMe); IR ν/cm-1 (Nujol): 2072s,
2
1977s, 1948s (CO str.); (MS/EI) m/z (%): 831 (M+, 16), 803
(M+ – CO, 12), 392 (R″2GeH+, 46); EI Acc. Mass. on M+: calcd
for C23H44O570Ge1P2Si4182W1: 826.0460, found 826.0462. 15: (32
1
mg, 15%) mp ) 55–58 °C; H NMR (400 MHz, C6D6, 298 K):
δ 0.05 (br, 2H, CHSiMe3), 0.28 (br, 18H, SiMe3), 0.33 (br, 18H,
3
4
SiMe3), 2.40 (dd, JPH ) 35 Hz, JPH ) 8 Hz, 3H, GeC(CH3)P),
2.68 (dd, 3JPH ) 29 Hz, 3JPH ) 20 Hz, P2C(CH3)); 31P{1H} NMR
(121.6 MHz, C6D6, 298 K): δ 251.0 (d, JPP ) 66 Hz, JPW
2
1
)
2
1
245 Hz, CPCMe), 287.5 (d, JPP ) 66 Hz, JPW ) 256 Hz,
GePCMe); IR ν/cm-1 (Nujol): 2068s, 1982sh, 1966s, 1955s (CO
str.); (MS/EI) m/z (%): 1155 [M+, 2], 392 [R″2GeH+, 86%].
X-ray Crystallography. Crystals of 7–9, 14, and 15 suitable
for X-ray structural determination were mounted in silicone oil.
Crystallographic measurements were made using a Nonius Kappa
CCD diffractometer using a graphite monochromator with Mo
KR radiation (λ ) 0.710 73 Å). The data were collected at 150
K, and the structures were solved by direct methods and refined
(14) Sheldrick, G. M. SHELX-97; University of Göttingen: Göttingen,
Germany, 1997.
(15) Okazaki, R.; West, R. AdV. Organomet. Chem. 1996, 39, 231.
(16) West, R.; Fink, M. J.; Michl, J. Science 1981, 214, 1343.
Inorganic Chemistry, Vol. 47, No. 4, 2008 1275

Jones et al.
Scheme 1
Scheme 2
Pt CMe to give intermediate, 12, which rapidly rearranges.
Once formed, 11 persists in solution at -80 °C but on
warming to ambient temperature it converts into 7, which
has low solubility and precipitates from the reaction
mixture over ca. 12 h. It should be noted that spectroscopic
monitoring of the reactions that gave 8 and 9 revealed
them to be more rapid than that which gave 7 and no long-
lived intermediates could be identified.
A plausible mechanism for the conversion of 11 to 7
involves the former being in equilibrium with 13 via a 1,3-
hydrogen migration. Two molecules of 13 then react via
hydrophosphination of the Pt C bonds of each other to give
7. This proposal seems reasonable, as a precedent exists for
phosphaalkene/vinylphosphine tautomerizations.20 The ab-
sence of any observable signals corresponding to 13 in the
31P{1H} NMR spectrum of the reaction mixture suggest that
11 is heavily favored in the equilibrium. Despite this, the
formation of 7 and its precipitation from solution both
conspire to fully consume 11 in the reaction.
Given that 10 and 11 are long-lived enough to be
spectroscopically observable, attempts were made to isolate
them and/or complexes of them from reactions of Pt CMe
with R″2Get GeR″2. When an excess of the digermene was
employed, the proposed phosphagermirene intermediate, 10,
persisted in solution for hours below –50 °C but on warming
to ambient temperature decomposed to unidentified products.
In order to trap a stable complex of 11, the reaction was
repeated with an excess of Pt CMe at 20 °C. After 5 min,
a THF solution of [W(CO)5(THF)] was added to the reaction
mixture. After chromatographic workup, low yields of the
1:1 and 1:2 adducts of the heterocycle with the W(CO)5
fragment, viz. 14 and 15, were obtained as crystalline solids
(Scheme 2). The isolation of these compounds gives strong
support to the proposed structure of 11. Both compounds
are indefinitely stable in solution, as they are presumably
prohibited from further intermolecular reactions to give
tungsten carbonyl complexes of 7 or related species.
The low solubility of 7–9 leads to them precipitating
from their toluene reaction solutions. It is difficult to
redissolve these compounds in most deuterated solvents,
but 6 and 7 have sufficient solubility in CD2Cl2 or THF-
d8 to obtain their 1H and 31P{1H} NMR spectra. Similarly,
these spectra can be acquired for weak saturated C6D6
the in-situ-generated distannene, Ar′2Snt SnAr′2, with Pt CMe
yielded the related bridged 2,3,5,6-tetraphospha-1,4-dimeth-
ylidenecyclohexane, 9, but in lower yield (31%). In contrast,
no reaction occurred with the digermene, Ar′2Get GeAr′2.
This difference probably results from the fact that
R″2Et ER″2 and Ar′2Snt SnAr′2 significantly dissociate into
germylene or stannylene fragments in solution, while
Ar′2Get GeAr′2 remains largely intact17 and is, therefore,
less reactive toward Pt CMe. It is also of interest that
R″2Get GeR″2 is known to react in a completely different
fashion with Nt CMe, in that upon dissociation of the
digermene, the germanium center of the monomeric ger-
mylene inserts into one C–H bond of the nitrile to give R″2-
Ge(H)CH2Ct N, which has been structurally characterized.18
It is clear from the products of the reactions reported
here that they proceed via different pathways than those
that gave 1–6. In order to shed light on their mechanisms,
the reaction that gave 7 (with Pt CMe in excess) was
monitored by 31P{1H} NMR spectroscopy. In toluene-d8
a reaction occurred immediately at -80 °C, as evidenced
by the appearance of a singlet resonance at δ 436.6 ppm.
This completely disappeared within 5 min, giving rise to
2
an AB spin system (δ PA 319.8, PB 308.5 ppm; JPAPB
)
29.8 Hz) with the concomitant consumption of the Pt CMe
reactant (δ –61.1 ppm). We attribute the low-field singlet
resonance to the [2 + 1] cycloaddition product, 10 (cf. 3:
δ 315 ppm7), which rapidly reacts with excess Pt CMe
to give the 2,4-diphosphagermole, 11, which gives rise
to the AB spin pattern (cf. the 2,4-diphosphatellurole, Te-
P2C2But2: δ 299, 302 ppm; JPP ) 50.8 Hz19). Although
2
there is no spectroscopic evidence, the formation of 11
from 10 could involve a [2 + 2] cycloaddition of 10 with
(17) Scha¨fer, H.; Saak, W.; Weidenbruch, M. Organometallics 1999, 18,
3159.
(18) Miller, K. A.; Watson, T. W.; Bender, J. E., IV; Banaszak, H.; Kampf,
J. W. J. Am. Chem. Soc. 2001, 123, 982.
(19) Francis, M. D.; Jones, C.; Morley, C. P. Tetrahedron Lett. 1999, 40,
3815.
(20) (a) Yam, M.; Tsang, C.-W.; Gates, D. P. Inorg. Chem. 2004, 43, 3719.
(b) Chuang, C.-H.; Lien, M.-H. J. Phys. Chem. A 2004, 108, 1790.
1276 Inorganic Chemistry, Vol. 47, No. 4, 2008

ReactiWity of Pt CMe toward Digermenes and Distannenes
solutions of 9, but meaningful 13C{1H} NMR spectra could
not be obtained for any complex and the NMR samples
of 8 and 9 were too dilute for signals to be observed in
1
their 119Sn{1H} NMR spectra. The H and 31P{1H} NMR
spectra of 7–9 show that they are formed completely
diastereoselectively. Four trimethylsilyl methyl singlets
1
were observed in the H NMR spectra of 7 and 8, while
the spectra of all three complexes display two inequivalent
alkenic proton signals, each split into a doublet of doublets
3
2
by two JPH couplings (N.B.: geminal JHH couplings for
these signals were not observable). The 31P{1H} NMR
spectra of 7–9 are similar, and each consists of two doublet
signals with characteristic 1JPP couplings. In addition, 1JSnP
satellites of typical magnitudes flank the high-field signals
of the tin complexes, 8 and 9. Moreover, the doublets in
each spectrum are broadened, presumably because of
unresolved second-order JPP couplings. Molecular ion
signals exhibiting the expected isotopic abundance patterns
are present in the EI mass spectra of 7–9.
Figure 1. Thermal ellipsoid plot (25% probability surface) of the
molecular structure of [R″2Ge{C(Me)(H)PC(t CH2)P}]2 (7) (hydrogen
atoms on the R″ substituents are omitted for clarity). Selected bond
lengths (Å) and angles (deg): Ge(1)–C(1) 2.020(2), Ge(1)–P(1) 2.3715(7),
P(1)–C(3) 1.832(2), P(1)–P(2)′ 2.2298(8), P(2)–C(3) 1.830(2), P(2)–C(1)
1.875(2), C(3)–C(4) 1.335(3), C(1)–Ge(1)–P(1) 98.30(6), C(3)–P(1)–P(2)′
100.81(7), C(3)–P(1)–Ge(1) 91.21(7), P(2)′–P(1)–Ge(1) 105.36(3),
C(3)–P(2)–C(1) 101.78(9), C(3)–P(2)–P(1)′ 105.21(7), C(1)–P(2)–P(1)′
97.76(7), P(2)–C(1)–Ge(1) 112.51(10), P(2)–C(3)–P(1) 121.22(11).
Symmetry operation: ′ –x + 2, –y, –z + 2. Selected bond lengths (Å)
and angles (deg) for [R″2Sn{C(Me)(H)PC(t CH2)P}]2 (8): Sn(1)–C(1)
2.198(5), Sn(1)–P(1) 2.5388(15), P(1)–C(3) 1.842(5), P(1)–P(2)′
2.2079(19), P(2)–C(3) 1.845(5), P(2)–C(1) 1.873(6), P(2)–P(1)′ 2.2079(19),
C(3)–C(4) 1.335(7), C(1)–Sn(1)–P(1) 95.07(14), C(3)–P(1)–P(2)′
102.29(17), C(3)–P(1)–Sn(1) 90.83(17), P(2)′–P(1)–Sn(1) 103.41(6),
C(3)–P(2)–C(1) 103.9(2), C(3)–P(2)–P(1)′ 105.73(16), C(1)–P(2)–P(1)′
97.69(18), P(2)–C(1)–Sn(1) 111.9(2), P(1)–C(3)–P(2) 123.4(3). Sym-
metry operation: ′ –x + 2, –y, –z + 2.
The spectroscopic data for the tungsten carbonyl
complexes, 14 and 15, are consistent with their structures.
Most informative are their 31P{1H} NMR spectra which
each display two low-field doublet signals related by
2
mutual JPP couplings. Both resonances in the spectrum
1
of 15 possess JWP satellites, while only the higher-field
signal in the spectrum of 14 does. It is of note that
although the phosphaalkenic resonances for 14 and 15 are
in the normal low-field range,1 those associated with the
tungsten-coordinated P centers are at significantly higher
field than seen in the spectrum of the uncoordinated
intermediate, 11. Similar upfield shifts for peaks in the
31P{1H} NMR spectra of phophaalkenes upon P-center
metal coordination are common.1
The X-ray crystal structures of 7–9, 14, and 15 were
determined. Complexes 7 and 8 are isomorphous, so only
the molecular structure of 7 is depicted in Figure 1, though
relevant geometrical parameters for 8 are included in the
figure caption. Compound 9 has a near identical core
structure to those of 7 and 8, and its molecular structure is
shown in Figure 2. As the heterocycle geometries of 14 and
15 are not significantly different, only the molecular structure
of 14 is highlighted in Figure 3. That for 15 can be found in
the Supporting Information.
The geometries of the heterocyclic cores of 7–9 are very
similar, and their structural characterizations represent the
first for tetraphospha-1,4-dimethylidenecyclohexanes. Each
contains a P4C2 six-membered ring adopting a chair
configuration with two fused P2C2E (E ) Ge or Sn) rings.
All of the interatomic distances within the polycyclic
systems are normal for single-bonded interactions,21 with
the exception of that between the methylidene carbon,
C(4), and C(3). Compounds 14 and 15 are the first
structurally elucidated diphosphagermole complexes. Each
has a near-planar heterocyclic core with two largely
localized P–C double bonds. Their intracyclic Ge-C bond
lengths are in the normal range for germole heterocycles
Figure 2. Thermal ellipsoid plot (25% probability surface) of the
molecular structure of [Ar′2Sn{C(Me)(H)PC(t CH2)P}]2 (9) (hydrogen
atoms on the Ar′ substituents are omitted for clarity). Selected bond
lengths (Å) and angles (deg): Sn(1)–C(1) 2.202(2), Sn(1)–P(1) 2.5565(9),
P(1)–C(3) 1.843(3), P(1)–P(2)′ 2.2097(12), P(2)–C(3) 1.833(3), P(2)–C(1)
1.863(2), P(2)–P(1)′ 2.2097(12), C(3)–C(4) 1.338(3), C(1)–Sn(1)–P(1)
94.78(7),C(3)–P(1)–P(2)′107.75(9),C(3)–P(1)–Sn(1)90.23(8),P(2)′–P(1)–
Sn(1) 98.91(3), C(3)–P(2)–C(1) 100.00(11), C(3)–P(2)–P(1)′ 106.71(8),
C(1)–P(2)–P(1)′ 103.52(8), P(2)–C(1)–Sn(1) 112.13(12), P(2)–C(3)–P(1)
123.11(13). Symmetry operation: ′ –x + 2, –y, –z + 1.
(1.92–2.02 Å21), and their Ge-P distances are unexcep-
tional. The fact that in 14 the W(CO)5 group is coordinated
by the P center in the 4 position of the heterocycle suggests
that the lone pair of this phosphorus is more sterically
accessible than the P center in the 2 position. Despite this,
the lone pair of the latter is available for bonding, as seen
in complex 15.
(21) As determined by a survey of the Cambridge Crystallographic
Database, May, 2007.
Inorganic Chemistry, Vol. 47, No. 4, 2008 1277

Jones et al.
1,4-dimethylidenecyclohexanes, all of which have been
structurally characterized. The mechanisms for the formation
of these products are thought to involve successive [2 + 1]
and [2 + 2] phosphaalkyne cycloaddition, heterocycle
rearrangement, phosphaalkene/vinylphosphine tautomeriza-
tion, and intermolecular hydrophosphination reactions. Two
intermediates in one reaction were spectroscopically ob-
served. One of these has been trapped by coordination to
one or two W(CO)5 fragments to give crystallographically
characterized diphosphagermole complexes. This work fur-
ther highlights significant differences in the reactivity of
Pt CMe compared to that of more sterically protected
phosphaalkynes, e.g., Pt CBut. We continue to explore these
differences which will be reported on in future publications.
Figure 3. Thermal ellipsoid plot (25% probability surface) of the molecular
structure of [{W(CO)5}{R″2Ge[C(Me)PC(Me)P]}] (14) (hydrogen atoms
omitted for clarity). Selected bond lengths (Å) and angles (deg): W(1)–P(2)
2.4848(12), Ge(1)–C(3) 1.975(3), Ge(1)–P(1) 2.3403(9), P(1)–C(1) 1.691(3),
P(2)–C(3) 1.674(2), P(2)–C(1) 1.813(2), C(1)–P(1)–Ge(1) 96.10(8),
C(3)–P(2)–C(1) 106.85(12), C(3)–P(2)–W(1) 128.08(9), C(1)–P(2)–W(1)
124.85(9), P(1)–C(1)–P(2) 124.09(14), P(2)–C(3)–Ge(1) 114.25(12).
Acknowledgment. We thank the Australian Research
Council (fellowships for C.J. and A.S.) and the EPSRC
(partial studentship for C.S.).
Supporting Information Available: Crystallographic data as
CIF files for 7–9, 14, and 15, and ORTEP diagrams of 8 and 15.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Conclusion
In summary, reactions of the unhindered phosphaalkyne,
Pt CMe, with a digermene and two distannenes have
afforded the first examples of bridged 2,3,5,6-tetraphospha-
IC700926U
1278 Inorganic Chemistry, Vol. 47, No. 4, 2008