Synthesis and properties of mercury bis(trifluoromethyl)phosphanides and their phosphane complexes

Article abstract of DOI:10.1021/ic001335k

The thermally unstable compounds Hg(CN)P(CF₃)₂ and Hg[P(CF₃)₂]₂ were obtained by reactions of mercury cyanide and bis(trifluoromethyl)phosphane in solution and characterized by multinuclear NMR spectr

Full text of DOI:10.1021/ic001335k

3084
Inorg. Chem. 2001, 40, 3084-3088
Synthesis and Properties of Mercury Bis(trifluoromethyl)phosphanides and Their
Phosphane Complexes
Berthold Hoge,* Christoph Tho1sen, and Ingo Pantenburg
Institut fu¨r Anorganische Chemie, Universita¨t zu Ko¨ln, Greinstrasse 6, D-50939 Ko¨ln, Germany
ReceiVed NoVember 28, 2000
The thermally unstable compounds Hg(CN)P(CF3)2 and Hg[P(CF3)2]2 were obtained by reactions of mercury
cyanide and bis(trifluoromethyl)phosphane in solution and characterized by multinuclear NMR spectroscopy. An
increase in thermal stability is observed when the products form 18 valence electron complexes. The compounds
[Hg{P(CF3)2}2(dppe)] (dppe ) 1,2-bis(diphenylphosphanyl)ethane) and [Hg{P(CF3)2}2(Me3P)2] have been isolated
in almost quantitative yield by reacting [Hg(CN)2(dppe)] or [Hg(CN)2(Me3P)2] with HP(CF3)2. [Hg{P(CF3)2}2-
(dppe)] crystallizes in the triclinic space group P1h. The mercury atom is coordinated in a distorted tetrahedral
fashion. The Hg-P(CF3)2 bonds, ca. 250 pm, are significantly longer than those of the mercury bis(phosphanides)
Hg(PR2)2 with R ) t-Bu, 245 pm, or SiMe3, 241 pm. These easily accessible compounds [Hg{P(CF3)2}2(dppe)]
and [Hg{P(CF3)2}2(Me3P)2] act as nucleophilic bis(trifluoromethyl)phosphane group transfer reagents.
Introduction
stability, e.g. bis(trifluoromethyl)mercury is a common reagent
in nucleophilic trifluoromethyl group transfer reactions.4
Metal compounds with covalently bonded, nonbridging bis-
Bidentate phosphane ligands play an important role in
asymmetric catalysis.1 The Lewis acid properties of metal
catalysts are influenced by ancillary ligand effects, so the study
of strongly electron-withdrawing phosphane ligands on poten-
tially catalytic metal centers is of interest. Strong electron-
withdrawing CF3 groups, attached to the coordinating phos-
phorus atoms, will have a strong impact on the ligand properties,
e.g. decreasing the σ donation ability while simultaneously
increasing the π acidity of the phosphorus atom.
Chiral bidentate phosphane ligands are usually prepared from
chiral tosylates and diarylphosphanides. For the synthesis of
chiral bidentate 1,2-bis[bis(trifluoromethyl)phosphanyl)ethanes
nucleophilic P(CF3)2 group transfer reagents are desirable. The
sodium and cesium bis(trifluoromethyl)phosphanides have been
characterized by NMR spectroscopy, but reaction with the
solvent prevented their isolation.2,3 In addition, these salts are
thermally quite unstable. They decompose into perfluoro-2-
phosphapropene and the corresponding metal fluoride.
-
(trifluoromethyl)phosphanido groups are potential P(CF3)2
synthons. While transition metal phosphanides with electron-
rich substituents on the phosphorus are converted by iodo-
methane to quaternary phosphonium salts,6 electron-poor bis-
(trifluoromethyl)phosphanido complexes such as Cp(CO)3CrP-
(CF3)2 react selectively with iodomethane by cleavage of the
metal phosphorus bond and formation of MeP(CF3)2 and
Cp(CO)3CrI.7 In principle, this nucleophilic displacement of
iodide by the phosphanide is well suited for the synthesis of
alkyl bis(trifluoromethyl)phosphanes. Because the hitherto
known nonbridged bis(trifluoromethyl)phosphanido complexes
Cp(CO)2FeP(CF3)28 and Cp(CO)3MP(CF3)2 (M ) Cr, Mo, W),9
as well as (CO)5M′P(CF3)2 (M′ ) Mn, Re),10 are tedious to
synthesize, these compounds appear to be hardly suitable for
preparative chemistry.
In 1972, Grobe and Demuth prepared mercury bis{bis-
(trifluoromethyl)phosphanide}, Hg[P(CF3)2]2, by treatment of
divinylmercury with bis(trifluoromethyl)phosphane, HP(CF3)2.11
The new mercury compound was characterized solely by its
19F NMR spectrum, and attempts to isolate the species were
not successful. In a footnote, the authors mentioned that the
reaction time decreased in the series HgMe2 > Hg(SMe)2 >
Hg(CHdCH2)2 > Hg(CN)2.11
Such elimination reactions are a well-known problem in the
chemistry of (trifluoromethyl)metal compounds. For example,
LiCF3 or M(CF3)2 (M ) Zn, Cd)5 decompose at low temper-
4
atures by elimination of difluorocarbene and formation of metal
fluorides. On the other hand, trifluoromethyl derivatives of less
electropositive metals such as mercury show enhanced thermal
On the basis of these results, we have reinvestigated the
reaction between Hg(CN)2 and HP(CF3)2 with the aim to prepare
Hg[P(CF3)2]2 on a larger scale and to explore its capabilities as
a P(CF3)2 synthon. Such synthons are not only desirable for
the synthesis of π-acidic bis(trifluoromethyl)phosphane ligands
-
* Corresponding author. Fax: 049-221-470-5196. E-mail: b.hoge@
uni-koeln.de.
but may also be useful in the selective synthesis of bis(tri-
(1) Cornils, B.; Herrmann, W. A. Applied Homogeneous Catalysis with
Organometallic Compounds, A ComprehensiVe Handbook in Two
Volumes; VCH Verlagsgesellschaft: Weinheim, Germany, 1996.
(2) Minkwitz, R.; Liedtke, A. Inorg. Chem. 1989, 28, 1627-1630.
(3) Burg, A. B. Inorg. Chem. 1981, 20, 2739-2741.
(4) Burton, D. J.; Yang, Z. Y. Tetrahedron 1992, 48, 189-275.
(5) Eujen, R.; Hoge, B. J. Organomet. Chem. 1995, 503, C51-C54.
Guerra, M. A.; Bierschenk, T. R.; Lagow, R. J. J. Am. Chem. Soc.
1986, 108, 4103-4105. Guerra, M. A.; Bierschenk, T. R.; Lagow, R.
J. J. Chem. Soc., Chem. Commun. 1985, 1550-1551. Lange, H.;
Naumann, D. J. Fluorine Chem. 1985, 27, 299-308.
(6) Malisch, W.; Maisch, R.; Colquhoun, I. J.; McFarlane, W. J.
Organomet. Chem. 1981, 220, C1-C6.
(7) Grobe, J.; Haubold, R. Z. Anorg. Allg. Chem. 1986, 534, 121-136.
(8) Dobbie, R. C.; Hopkinson, M. J.; Whittaker, D. J. Chem. Soc., Dalton
Trans. 1972, 1030-1034.
(9) Grobe, J.; Haubold, R. Z. Anorg. Allg. Chem. 1985, 522, 159-170.
(10) Grobe, J.; Rau, R. Z. Anorg. Allg. Chem. 1975, 414, 19-29. Grobe,
J.; Rau, R. J. Fluorine Chem. 1978, 11, 265-290.
(11) Grobe, J.; Demuth, R. Angew. Chem. 1972, 84, 1153.
10.1021/ic001335k CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/19/2001

Mercury Bis(trifluoromethyl)phosphanides
Inorganic Chemistry, Vol. 40, No. 13, 2001 3085
Table 1. Crystal Data and Details of Data Collection and Structure
Refinement for [Hg{P(CF3)2}2(dppe)]a
fluoromethyl)phosphanido transition metal complexes with
nonbridging P(CF3)2 groups. To our knowledge, Cp(CO)2FeP-
(CF3)2 is the only structurally characterized transition metal
complex of this type.12
compd
[Hg{P(CF3)2}2(dppe)]
fw
1873.92
cryst system
space group
lattice params
triclinic
P1h
Experimental Section
a ) 1003.4(2) pm, R ) 91.42(2)°
b ) 1029.9(2) pm, â ) 93.98(2)°
c ) 1819.2(4) pm, γ ) 105.89(2)°
1.8019(6) nm3
Materials and Apparatus. Chemicals were obtained from com-
mercial sources and used without further purification. Modified literature
methods were used for the synthesis of HP(CF3)2.13 Instead of Me3-
SnH the less volatile Bu3SnH was used for the reduction of (CF3)2-
PBr. This allows easily separation by fractional condensation after
reacting for 30 min at 0 °C. Bromobis(trifluoromethyl)phosphane was
synthesized treating neat (CF3)2PNEt214 with gaseous HBr at -78 °C.
Caution! The toxic compounds (CF3)2PBr as well as (CF3)2PH react
Violently with air. The known complex [Hg(CN)2(dppe)]15 was
synthesized reacting Hg(CN)2 in THF with the corresponding phosphane
ligand and fully characterized.
Solvents were purified by standard methods.16 Standard high-vacuum
techniques were employed throughout all preparative procedures;
nonvolatile compounds were handled in a dry N2 atmosphere by using
Schlenk techniques.
Differential thermal analysis was carried out on a Netzsch model
STA 409-Skimmer instrument. Infrared spectra were recorded on a
Nicolet-5PC FT-IR spectrometer as KBr pellets. Raman spectra were
obtained with a Bruker FRA-106/s spectrometer, with a Nd:YAG laser
operating at λ ) 1064 nm.
cell vol
formula units/unit cell
Z ) 1
Dcalc
1.727 Mg m-3
µ
calc(Mo KR)
4.530 mm-1
F(000)
904
cryst size
2θ range
0.1 × 0.12 × 0.2 mm
4.24 e 2θ e 48.34˚
3923
obsd reflcns (I0 > 2σ(I))
no. of params
goodness of fit
R1; wR2 (I0 > 2σ(I))
R1; wR2 (all data)
∆Fmin/max
425
1.090
0.0869; 0.2208
0.1106; 0.2372
(-4.861/9.190) × 10-6 pm-3
a Weighting w-1 ) σ2(|Fo| ) + (aP)2 + bP with P ) (|Fo| + 2|Fc| )/
2
2
2
3; extinction Fc* ) kFc[1 + 0.001|Fc| λ3/sin(2θ)]-1/4; R ) Σ| |Fo| -
2
|Fc| |/Σ|Fo|, wR ) [Σw(|Fo| - |Fc| )2/Σw(|Fo| )2]1/2, and S ) [Σw(|Fo|
2
2
2
2
2
- |Fc| )2/(n - p)]1/2
.
(CN)2(Me3P)2] as a white solid. DTA/TG analysis: exothermic
decomposition peak at 142-143 °C. Anal. Found (calcd for C8H18-
HgN2P2): Hg, 48.7 (49.5); N, 6.8 (6.9); C, 24.0 (23.7); H, 4.6 (4.5).
Infrared spectrum (cm-1) (KBr pellet): 2990 vw, 2974 vw, 2913 vw,
2133 vw, 1434 m, 1427 m, 1293 w, 965 vs, 863 vw, 852 vw, 753 m,
674 vw. Raman (cm-1): 2984 (50), 2911 (100), 2133 (40), 1417 (8),
750 (10), 681 (10), 259 (10), 155 (17), 84 (12). Mass spectrum (EI, 20
eV) {m/z (%) [assignment]}: 254 (10) [Hg(CN)2+]; 228 (2) [HgCN+];
202 (8) [Hg+]; 76 (71) [P(CH3)3+]; 61 (100) [P(CH3)2+]. NMR (CH2-
The NMR spectra were recorded on Bruker model AMX 300 (199Hg,
53.51 MHz; 13C, 75.47 MHz; 31P, 121.50 MHz; 19F, 282.35 MHz) and
Bruker AC200 spectrometers (31P, 81.01 MHz; 19F 188.31 MHz; 13C,
50.32 MHz; 1H, 200.13 MHz) with positive shifts being downfield from
the external standards HgMe2 (199Hg), 85% orthophosphoric acid (31P),
1
CCl3F (19F), and TMS (13C and H). High-order NMR spectra were
calculated with the program gNMR.17
1
Cl2; 213 K): δ(31P) -20.8 ppm; J(31P199Hg) 3195 Hz.
Preparation of (1,2-Bis(diphenylphosphanyl)ethane)bis(bis(tri-
fluoromethyl)phosphanido)mercury, [Hg{P(CF3)2}2(dppe)]. A 0.83
g (4.90 mmol) amount of HP(CF3)2 was condensed onto a solution of
1.30 g (2.00 mmol) of [Hg(CN)2(dppe)] in 10 mL of CH2Cl2 at -196
°C. After the mixture was warmed to room temperature and stirred for
10 min, the volatile compounds were removed in vacuo, giving 1.80 g
(1.92 mmol; 96% yield) of [Hg{P(CF3)2}2(dppe)] as a white solid. DTA/
TG analysis: exothermic decomposition peak at 142 °C. Anal. Found
(calcd for C30H24F12HgP4): Hg, 21.1 (21.4); P, 13.0 (13.2); F, 24.1
(24.3); C, 37.9 (38.5); H, 2.7 (2.6). Infrared spectrum (cm-1) (KBr
pellet): 3061 m, 2917 w, 2361 m, 2343 m, 1575 vw, 1485 m, 1438 s,
1417 w, 1334 vw, 1306 w, 1265 w, 1197 m, 1157 vs, 1117 vs, 1090
vs, 1027 m, 1000 m, 971 w, 866 w, 823 w, 742 s, 692 s, 669 m, 650
w, 617 vw, 563 vw, 520 m, 479 w, 456 m. Raman (cm-1): 3062 (100),
2975 (18), 2911 (25), 1585 (50), 1098 (20), 1027 (23), 1000 (70), 734
(13), 450 (7), 378 (8), 189 (35), 88 (90). Mass spectrum (EI, 20 eV)
{m/z (%) [assignment]}: 540 (8) [Hg[P(CF3)2]2+]; 398 (25) [Ph2PC2H4-
PPh2+]; 371 (19) [HgP(CF3)2+]; 289 (16) [Ph2PCPh(CH3)+]; 275 (6)
[Ph2PCPhH+]; 262 (15) [Ph3P+]; 202 (2) [Hg+]; 185 (18) [PPh2+]; 169
(51) [P(CF3)2+]; 108 (23) [PPh+]; 69 (100) [CF3+]; 28 (7) [C2H4+].
For NMR spectroscopic data, see Table 2.
Preparation of Bis[bis(trifluoromethyl)phosphanido]bis(trimeth-
ylphosphane)mercury, [Hg{P(CF3)2}2(Me3P)2]. A 0.71 g (1.75 mmol)
amount of [Hg(CN)2(Me3P)2] was dissolved in 5 mL of CH2Cl2. A
4.80 mmol amount of HP(CF3)2 was condensed onto the reaction
mixture and stirred for 10 min at room temperature. After removal of
all volatile materials in vacuo, 1.09 g (1.58 mmol) of [Hg{P(CF3)2}2-
(Me3P)2] (yield 90%) was obtained as a white powder. DTA/TG
analysis: exothermic decomposition peak at 157 °C. Anal. Found (calcd
for C10H18F12HgP4): Hg, 28.9 (29.0); P, 17.8 (17.9); F, 33.0 (33.0); C,
17.6 (17.4); H, 2.7 (2.7). Infrared spectrum (cm-1) (KBr pellet): 2983
w, 2918 w, 2816 w, 2161 w, 1425 s, 1297 s, 1214 s, 1151 vs, 1106 vs,
1081 vs, 952 vs, 865 vw, 803 vw, 744 m, 732 w, 671 vw, 583 vw, 559
w, 506 vw, 456 m. Raman (cm-1): 2985 (31), 2915 (100), 2809 (10),
1423 (12), 1145 (6), 1106 (6), 1085 (7), 952 (6), 745 (16), 733 (17),
673 (20), 454 (8), 373 (9), 328 (7), 289 (11), 261 (12), 176 (33), 149
(24), 81 (17). Mass spectrum (EI, 20 eV) {m/z (%) [assignment]}: 540
(32) [Hg[P(CF3)2]2+]; 371 (77) [HgP(CF3)2+]; 202 (2) [Hg+]; 169 (42)
[P(CF3)2+]; 119 (10) [FPCF3+]; 100 (19) [C2F4/PCF3+]; 76 (75)
[P(CH3)3+]; 69 (95) [CF3+]; 61 (100) [P(CH3)2+]; 45 (16) [PCH2+].
For NMR spectroscopic data, see Table 2.
Nucleophilic Displacement Reactions. Solutions of Hg[P(CF3)2]2,
[Hg{P(CF3)2}2(dppe)], and [Hg{P(CF3)2}2(Me3P)2] were treated at -30
°C with an excess of ethyl tosylate, iodoethane, and Ph2PCl. The
temperature was raised overnight to room temperature, and the products
Preparation of Dicyanobis(trimethylphosphane)mercury, [Hg-
(CN)2(Me3P)2]. A 16.00 mmol amount of PMe3 was condensed onto a
reaction mixture containing 2.00 g (7.92 mmol) of Hg(CN)2 in 10 mL
of THF. After the mixture was stirring at room temperature for 30 min,
all volatiles were removed in vacuo yielding 3.20 g (7.90 g) of [Hg-
18
EtP(CF3)2 and Ph2PP(CF3)2 were identified by multinuclear NMR
spectroscopy. NMR spectroscopic data for Ph2PP(CF3)2 (CH2Cl2;
RT): δ(31PPh2) -30.1 ppm; δ(31P(CF3)2) 4.7 ppm; δ(19F) -46.9 ppm;
(12) Barrow, M. J.; Sim, G. A. J. Chem. Soc., Dalton Trans. 1975, 291-
295.
2
3
1J(PP) 180.0 Hz; J(PF) 59.9 Hz; J(PF) 9.0 Hz.
Crystal Structure Determination. Crystals of [Hg{P(CF3)2}2(dppe)]
were grown by cooling a saturated toluene solution from room
temperature to -20 °C. A colorless small single crystal was selected
and sealed in a glass fiber (d ) 0.3 mm). Single-crystal X-ray data of
the compound were collected on an image plate diffractometer (STOE
(13) Ansari, S.; Grobe, J. Z. Naturforsch. 1975, 30b, 651-652.
(14) Kolomeitsev, A.; Go¨rg, M.; Dieckbreder, U.; Lork, E.; Ro¨schenthaler,
G.-V. Phosphorus, Sulfur, Silicon 1996, 109-110, 597-600.
(15) Camalli, M.; Caruso F.; Zambonelli, L. Acta Crystallogr. 1982, B38,
2468-2470.
(16) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals; Pergamon Press: Oxford, England, 1980.
(17) Budzelaar, P. H. M. gNMR Version 4.1; Cherwell Scientific: Oxford,
U.K., 1998.
(18) Fields, R.; Haszeldine, R. N.; Kirman, J. J. Chem. Soc. C 1970, 197-
200. Dyer, J.; Lee, J. J. Chem. Soc. B 1970, 409-412.

3086 Inorganic Chemistry, Vol. 40, No. 13, 2001
Hoge et al.
Table 2. NMR Spectroscopic Data for Mercury Bis(trifluoromethyl)phosphanide Derivatives
δ(199Hg)
δ(19F)
δ(31P)
δ(13CF3)
2J(PF)
3J(HgF)
1J(HgP)
1J(PCF3)
δ(31Plig)
1J(HgPlig)
b
Hg(CN)P(CF3)2
-1237
-1090
-293
-39. 7
-39. 8
-39. 4
-39. 0
-8.6
1.8
133.6
134.2
136.9
138.3
58.7
54.2
54
231.8
187.8
138
1682
822.6
623
37.5
42.3
50.4
55
c
Hg[P(CF3)2]2
[Hg{P(CF3)2}2(dppe)]d
[Hg{P(CF3)2}2(Me3P)2]e
-5.2
11.1
-21.9
115
1526
-192
-7.3
51
115
n.o.
b
a Chemical shifts in ppm; coupling constants in Hz; n.o. ) not observed or not resolved. In diglyme at 243 K; internal lock C6D6 and external
lock acetone-d6. cIn diglyme at 243 K; internal lock C6D6 and external lock acetone-d6; 2J(PP) 12; 4J(PF) 1.0; 1J(CF) 317.9; 4J(FF) 8.0; 3J(PC) 0.8
3
3
2
1
3
Hz. dIn CH2Cl2 at 220 K; internl lock C6D6 and external lock acetone-d6; J(CF) 317.8; J(CF) 7.0; J(PCF Pligand) 44; J(CF) 317.8; J(CF) 7.0 Hz.
3
Ligand data: δ(13Cdppe) 133.5; 132.3; 130.8; 130.2; 24.3 ppm; δ(1Hdppe) 8.4; 3.8 ppm. In CH2Cl2 at 210 K; internal lock C6D6 and external lock
e
acetone-d6; J(CF) 317; J(FF) 8.0; J(CF) 8 Hz. Ligand data: δ(13CPMe ) 14.9 ppm; J(PC) 19.5 Hz; δ(1HPMe ) 2.5 ppm; J(PH) 8.6 Hz.
1
4
3
1
2
3
3
Table 3. Characteristic Infrared and Raman Data of the HgP(CF3)2
Unit of the Complexes [Hg{P(CF3)2}2(Me3P)2] and
Table 4. Selected Bond Lengths (pm) and Angles (deg) for
[Hg{P(CF3)2}2(dppe)]
[Hg{P(CF3)2}2(dppe)] (cm-1
)
Hg1-P1
Hg1-P2
Hg1-P3
Hg1-P4
P1-C11
P1-C5
P2-C3
P2-C4
P3-C1
P3-C2
P4-C6
P4-C41
271.7(4)
250.3(4)
248.6(5)
257.1(4)
182(2)
183(2)
187(2)
187(2)
187(2)
189(2)
184(2)
183(2)
C1-F13
C1-F12
C1-F11
C2-F22
C2-F21
C2-F23
C3-F33
C3-F32
C3-F31
C4-F42
C4-F41
C4-F43
133(3)
135(3)
136(3)
131(3)
135(2)
136(2)
133(2)
133(3)
137(3)
132(3)
136(3)
136(2)
[Hg{P(CF3 )2}2(Me3P) 2] [Hg{P(CF3 )2}2(dppe)]
IR
Raman
IR
Raman
assgnt
1197 m
1157 vs
1117 vs
1090 vs
742 s
ν(CF)
1151 vs
1106 vs
1081 vs
732 w
583 vw
559 vw
456 m
1145(6)
1106(6)
1085(7)
733(17)
ν(CF)
ν(CF)
ν(CF)
734(13) δ(CF3)
δas(CF3)
563 vw
456 m
δa(CF3)
454(8)
373(9)
176(33)
450(7)
378(8)
189(35) ν(Hg-P)
ν(PC2)
δ(CPC)/F(CF3)
P3-Hg1-P2
P3-Hg1-P4
P2-Hg1-P4
C3-P2-C4
C3-P2-Hg1
C4-P2-Hg 1
122.88(15 )
118.03(15)
115.7(2)
P3-Hg1-P1
P2-Hg1-P1
P4-Hg1-P1
C1-P3-C2
C1-P3-Hg1
C2-P3-Hg1
108.5(2)
97.56(14)
80.74(13)
96.7(10)
101.7(7)
101.4(7)
IPDS) using graphite-monochromatized Mo KR radiation (λ ) 71.069
pm).19 The structure was solved by direct methods (SHELXS-86) and
Fourier synthesis.20 The refinement21 was done by full-matrix least-
squares procedures using anisotropic thermal parameters. The H atoms
were placed in idealized positions with one thermal parameter for all
H atoms of one molecule. Further details are given in Table 1. A
selection of bond distances and angles is given in Table 4.
98.6(11)
100.4(8)
103.4(7)
and Hg[P(CF3)2]2 by multinuclear NMR spectroscopy (see Table
2). The substitution of one cyanide group by a P(CF3)2 group
causes a low-field shift in the 199Hg NMR spectrum of about
260 ppm relative to Hg(CN)2 (δ(199Hg) -1495 ppm); substitu-
tion of the second cyanide is accompanied by an additional low-
field shift of approximately 150 ppm. The absolute value of
1J(HgP) of 1682 Hz for Hg(CN)P(CF3)2 is dramatically reduced
to 822 Hz by substitution of the cyanide by a second P(CF3)2
phosphanide group.
Results and Discussion
Treatment of HP(CF3)2 with Hg(CN)2, suspended in THF or
diglyme, gives HCN, Hg(CN)P(CF3)2, and Hg[P(CF3)2]2, the
relative amounts depending on the chosen stoichiometry:
-30 °C
Hg(CN)2 + HP(CF3)2
8
For Hg[P(CF3)2]2 the 2J(PF) and the long-range 4J(PF)
couplings with values of 54.2 and 1.0 Hz, respectively, give
rise to a magnetic nonequivalence of the two P(CF3)2 moieties,
resulting in a high-order [AX6]2M spin system with A ) P, X
-HCN
Hg(CN)P(CF3)2 -30 °C8 Hg[P(CF3)2]2 (2)
-HCN
) F, and M ) 199Hg. Both high-order 199Hg (Figure 1) and 31
P
With an excess of HP(CF3)2 complete conversion to Hg-
[P(CF3)2]2 is achieved. Upon being warmed to ambient tem-
perature, this compound decomposes slowly both in THF and
in diglyme solution to elemental mercury and tetrakis(trifluo-
romethyl)diphosphane, (CF3)2PP(CF3)2:
NMR spectra (Figure 2) are in excellent agreement with the
simulated spectra displayed in the respective bottom traces.
Hg[P(CF3)2]2 RT8 Hg + (CF3)2P-P(CF3)2
(3)
Similarly, all attempts to isolate Hg[P(CF3)2]2 by removing the
solvent, HCN, and excess of HP(CF3)2 in vacuo at low
temperatures failed due to decomposition (eq 3).
When the complex is dissolved in THF, neither 199Hg-19F
nor 199Hg-31P couplings are detectable in the NMR spectra due
to phosphanide exchange phenomena via solvated [Hg{P-
(CF3)2}3]- and [HgP(CF3)2]+. If diglyme is used as the solvent,
the 199Hg satellite spectra are clearly observed at -30 °C which
allows a full characterization of the products Hg(CN)P(CF3)2
(19) IPDS-Bedienungsanleitung, Stoe Darmstadt, Darmstadt, Germany,
1997.
(20) Sheldrick, G. M. SHELXS-86, Program for X-ray Structure Analysis;
University of Go¨ttingen: Go¨ttingen, Germany, 1986.
(21) Sheldrick, G. M. SHELXL-93, Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1993.
Figure 1. Experimental (A) and simulated (B) 199Hg NMR spectrum
of Hg[P(CF3)2]2. The spectrum was recorded at 220 K by means of
DEPT polarization transfer from 19F (1849 scans, 32 K data points,
spectral with 27 800 Hz, relaxation delay 2 s, variable pulse length
32E, no decoupling).

Mercury Bis(trifluoromethyl)phosphanides
Inorganic Chemistry, Vol. 40, No. 13, 2001 3087
Figure 2. Experimental (A) and calculated (B) 31P NMR spectrum of
Hg[P(CF3)2]2.
Figure 3. 19F-decoupled 199Hg NMR spectrum of [Hg{P(CF3)2}2-
(dppe)].
The rate of the thermal decomposition of Hg[P(CF3)2]2
decreases with increasing donor strength of the solvent; e.g.,
the compound is stable at room temperature in pyridine solution.
This indicates that Hg[P(CF3)2]2 is stabilized due to formation
of 18 valence electron complexes, [Hg{P(CF3)2}2D2]. Removal
of these donor molecules during the working up procedure
results in the decomposition to elemental mercury and (CF3)2-
PP(CF3)2. For this rather soft Lewis acid, phosphanes may be
regarded as suitable ligands. The intermediate formation of the
rather instable mercurial is avoided by reacting phosphane
adducts of Hg(CN)2 with excessive HP(CF3)2. Thus (1,2-bis-
(diphenylphosphanyl)ethane)dicyanomercury, [Hg(CN)2(dppe)],15
was reacted at room temperature in CH2Cl2 with a slight excess
of HP(CF3)2. After removal of the volatile compounds, the bis-
(trifluoromethyl)phosphanido complex [Hg{P(CF3)2}2(dppe)] is
obtained as a white powder in almost quantitative yield.
Figure 4. Perspective drawing of the complex [Hg{P(CF3)2}2(dppe)]
with 50% thermal ellipsoids.
The moderately air stable product shows no sign of decom-
position over a period of several months in an inert gas
atmosphere at room temperature. The exothermic decomposition
temperature of 142 °C was determined by DTA/TG measure-
ment. To study the stabilization by nonchelating phosphanes
we have prepared [Hg{P(CF3)2}2(Me3P)2] by reacting the novel
compound [Hg(CN)2(Me3P)2] with HP(CF3)2. The decomposi-
tion temperature of the trimethylphosphane complex which has
been fully characterized is increased by 15 °C as compared with
the dppe complex as a result of the higher donor strength of
Me3P.
As compared with a diglyme solution of Hg[P(CF3)2]2, the
199Hg NMR resonances of the phosphane complexes [Hg-
{P(CF3)2}2(dppe)] (Figure 3) and [Hg{P(CF3)2}2(Me3P)2] appear
at distinctive lower fields, -293 and -192 ppm, respectively
(see Table 2). A comparable low-field shift of about 1145 ppm
is observed of HgCl2 complexed by two triphenylphosphane
ligands.22 The coordination of the mercury atom by four
phosphorus atoms in the complex [Hg{P(CF3)2}2(dppe)] is
indicated by the triplet of triplet splitting of the 199Hg NMR
resonance as shown in Figure 3.
The analysis of the vibrational spectra, based on earlier
assignments,23 locates the symmetric ν(Hg-P(CF3)2) stretching
mode of the complex [Hg{P(CF3)2}2(dppe)] at 189 cm-1 (see
Table 3). The stronger donor Me3P in [Hg{P(CF3)2}2(Me3P)2]
causes the v(Hg-P(CF3)2) mode to decrease by 13 cm-1
.
However, these ν(Hg-PR2) frequencies are significantly lower
than the value of 370 cm-1 which has been reported for Hg-
[P(t-Bu)2]2.24
The crystal structure of [Hg{P(CF3)2}2(dppe)] has been
determined by X-ray diffraction (Figure 4). The strongly
distorted tetrahedral coordination of the mercury center is
apparent from the P-Hg-P bond angles for the (CF3)2P-Hg-
P(CF3)2 and Ph2P-Hg-PPh2 units of 122.9 and 80.7°, respec-
tively, the four Ph2P-Hg-P(CF3)2 angles being 118.0, 115.7,
108.5, and 97.6°. In an alternate description the complex may
be regarded as a distorted triangular, spanned by the phosphorus
atoms P2, P3, and P4, the fourth coordination by P1 being much
weaker. The Hg-P distances are of special interest (Table 4).
It is well-known that metal-P bond lengths for fluorinated
(23) Dehnert, P.; Demuth, R.; Grobe, J. Spectrochim. Acta 1980, 36A, 3-6.
Demuth, R.; Grobe, J.; Rau, R. Z. Naturforsch. 1975, 30b, 539-543.
(24) Baudler, M.; Zarkadas, A. Chem. Ber. 1972, 105, 3844-3849.
(22) Wrackmeyer, B.; Contreras, R. Annu. Rep. NMR Spectrosc. 1992, 24,
267-329.

3088 Inorganic Chemistry, Vol. 40, No. 13, 2001
Hoge et al.
Table 5. Hg-P Bond Distances Together with the Corresponding
1J(31P199Hg) Coupling Constants of Phosphane Mercury Complexes
[Hg(X)2(R3P)2]15,28
stable Hg[P(CF3)2]2 is stabilized by addition of donors and
formation of 18 valence electron donor acceptor adducts.
Structural data demonstrate, compared with binary Hg(PR2)2
compounds, a weakening of the Hg-PR2 bonds in the com-
plexes [Hg{P(CF3)2}2(R3P)2]. The destabilization of the Hg-
PR2 bond is compensated by the kinetic stabilization of the
complex.
Electronically unsaturated transition metal phosphanides such
as the complexes Cp2M(PR2)2 (M ) Zr, Hf; R ) Alkyl, Ph)30
have been shown to exhibit a phosphanido/phosphenium bond-
ing dualism.31 In the solid state they contain both a phosphanido
and a phosphenium ligand which interconvert rapidly on the
NMR time scale in solution:
phosphane (R3P)2
anion X
d(HgP) (pm)
1J(31P199Hg) (Hz)
(Ph3P)2
(Ph3P)2
(Ph3P)2
(Ph3P)2
dppe
NO3
SCN
I
245
5928
3726
3074
2617
1817a
115a
249
257
CN
259/243
261/253
272/257a
CN
P(CF3)2
dppe
a This work; in CH2Cl2 at 220 K; internal lock C6D6 and external
lock acetone-d6.
phosphanes are significantly shorter than corresponding alkyl-
phosphane M-P bond lengths.25 The opposite trend is observed
for phosphanide ligands. The Hg-P(CF3)2 bonds, 249 and 250
pm, are slightly longer than those in Hg[P(t-Bu)2]2, 244 and
245 pm,26 or Hg[P(SiMe3)2]2, 240 and 241 pm.27
With values of 272 and 257 pm the two Hg-P bonds of the
dppe ligand are significantly different. The Hg-P distance of
272 pm is longer than the sum of the covalent radii28 but clearly
lower than the sum of their van der Waals radii (335pm).29
Different Hg-P bond lengths have also been observed in
polymeric [Hg(CN)2(dppe)] with 261 and 253 pm15 as well as
in monomeric [Hg(CN)2(Ph3P)2] with 259 and 243 pm.28 An
interesting correlation exists between the 1J(199Hg31P) coupling
constant and the Hg-P bond length in the compounds [Hg-
(X)2(R3P)2] as shown in Table 5. For these compounds the
Hg-P bond lengths increases with a decreasing of the
1J(199Hg31P) coupling constant.
In a preliminary study we have investigated the synthetic
potential of the complexes [Hg{P(CF3)2}2(dppe)] and [Hg-
{P(CF3)2}2(Me3P)2] as well as that of the homoleptic compound
Hg[P(CF3)2]2 with respect to electrophilic substrates. While the
halides in iodoalkanes or chlorodiphenylphosphane are readily
replaced by the phosphanido group, no reaction with alkyl
tosylates was observed.
X-ray structural results indicate that the Hf-P bond length
for the planar phosphenium ligand of the R ) Et derivative is
248.8 pm, while the corresponding bond length for the pyramidal
phosphido ligand is about 20 pm longer. The pyramidal
phosphanido ligand, which may be described as a nucleophilic
PR2- unit, is in contrast to the planar electrophilic phosphenium
PR2+ cation, which is stabilized by pπ dπ bond contribution.
For a mercury bis(phosphanide) compound, Hg(PR2)2, the
following mesomeric structures consequently might be formu-
lated: The resonance structures B and C contain both nucleo-
philic and electrophilic phosphorus atoms. This approach
explains why two phosphorus atoms smoothly combine with
reductive elimination of elemental mercury. The formal opposite
charges of the two phosphorus atoms based on a phosphenium
bonding contribution may become real in a ligand exchange
process as is it observed by NMR experiments. However, also
a radical decay via elimination of two P(CF3)2 radicals cannot
be fully excluded. The stabilization of Hg[P(CF3)2]2 by donors
is ascribed to the electronic saturation of the mercury atom
which does not allow phosphenium bonding contributions as it
is proven by the pyramidality of the P(CF3)2 phosphanide ligands
in the complex [Hg{P(CF3)2}2(dppe)] by X-ray crystallography
(Figure 4).
Conclusion
In this paper a convenient synthesis for mercury bis-
(trifluoromethyl)phosphanides is described. The thermally un-
(25) For example: Manojlovic-Muir, L.; Millington, D.; Muir, K. W.;
Sharp, D. W. A.; Hill, W. E.; Quagliano, J. V.; Vallarino, L. M. J.
Chem. Soc., Chem. Commun. 1974, 999-1000. MacLeod, I.; Manojlo-
vic-Muir, L.; Millington, D.; Muir, K. W.; Sharp, D. W. A.; Walker,
R. J. Organomet. Chem. 1975, 97, C7-C10.
The easy to handle complexes are suitable tools for nucleo-
philic substitutions. Further investigations to synthesize chiral
bidentate bis(trifluoromethyl)phosphane containing ligands for
use in asymmetric catalysis are in progress.
(26) Benac, B. L.; Cowley, A. H.; Jones, R. A.; Nunn, C. M.; Wright, T.
C. J. Am. Chem. Soc. 1989, 111, 4986-4988.
Acknowledgment. We are grateful to Prof. Dr. D. Naumann
for his generous support. We thank Prof. Dr. R. Eujen and Dr.
W. Tyrra for helpful discussions.
(27) Goel, S. C.; Chiang, M. Y.; Rauscher, D. J.; Buhro, W. E. J. Am.
Chem. Soc. 1993, 115, 160-169.
(28) Buergi, H. B.; Fischer, E.; Kunz, R. W.; Parvez, M.; Pregosin, P. S.
Inorg. Chem. 1982, 21, 1246-1256.
(29) Bondi, A. J. Phys. Chem. 1964, 38, 441-451.
Supporting Information Available: A crystallographic file in CIF
format for the compound [Hg{P(CF3)2}2(dppe)]. This material is
available free of charge via the Internet at http://pubs.acs.org.
(30) Baker, R. T.; Whitney, J. F.; Wreford, S. S. Organometallics 1983, 2,
1049-1051.
(31) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Application of Organotransition Metal Chemistry; University
Science Books: Mill Valley, CA, 1987.
IC001335K