Syntheses and crystal structures of bi- and tri-metallic complexes containing a trioxoosmium(VIII) moiety

Article abstract of DOI:10.1039/a702404e

Interaction of cis-[Pt(dppm)₂(O₃SCF₃)₂] [dppm = bis(diphenylphosphino)methane], cis-[Pt(Bupy)(O₃SCF₃)₂] (Bupy = 4-tert-butylpyridine), [Ir(CO)(PPh₃)₂(O₃SCF₃)], and [Rh(cod)(OH₂)(OTs)] (cod = cycloocta-1,5-diene, OTs = tosylate) with [NBuⁿ₄][NOsO₃] afforded bimetallic nitrido-bridged complexes cis-[Pt(dppm)(NOsO₃)₂] 3, trans-[Pt(Bupy)₂(NOsO₃)₂] 4, [Ir(CO)(PPh₃)₂(NOsO₃)] 5 and [{Rh(cod)(NOsO₃)}₂] 6, respectively. Complex 4 crystallises in the P1 space group with a = 7.936(1), b = 10.758(2), c = 7.738(1) A, α = 100.02(1), β = 99.75(1), γ = 101.75(1)°, U = 622.5(2) A³ for Z = 1. The Pt-N (Os), Os-N and the mean Os-O distances are 1.958(7), 1.681(7) and 1.724 A, respectively. Complex 5 crystallises in the P2₁/n space group with a = 10.124(1), b = 15.564(2), c = 22.623(3) A, β = 100.08(2)°, U = 3509.7(7) A³ for Z = 4. The Ir-N, Os-N and the mean Os-O distances are 1.998(7), 1.710(7) and 1.718 A, respectively. Treatment of [Au(PPh₃)(NOsO₃)] 1 with Ph₃P=NPh gave the N-phosphinimine complex [Au(PPh₃){N(=PPh₃)Ph}][NOsO₃] 7. Complex 7 crystallises in the P2₁/n space group with a = 8.780(1), b = 20.781(2), c = 20.711(5) A, β = 91.23(1)°, U = 3788.0(9) A³ for Z = 4. The Au-N distance is 2.091(8) A and the C-N-P angle in the phosphinimine is 127.0(7)°. Reaction of 1 with Bupy led to substitution of Bupy for [NOsO₃] and formation of [Au(PPh₃)(Bupy)][NOsO₃] 8. Reaction of [Pt(dppf)(O₃SCF₃)Cl] [dppf = 1,1′-bis(diphenylphosphino)ferrocene] with [NBuⁿ₄][NOsO₃] afforded the trimetallic complex [Pt(dppf)(NOsO₃)Cl] 11. Complex 11 crystallizes in the P2₁/c space group with a = 20.058(2), b = 14.899(1), c = 23.949(2) A, β = 114.57(2)°, U = 6508(1) A³ for Z = 8. The mean Pt-N, Os-N and Os-O distances are 2.06, 1.66 and 1.67 A, respectively.

Full text of DOI:10.1039/a702404e

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Syntheses and crystal structures of bi- and tri-metallic complexes
containing a trioxoosmium(VIII) moiety†
Wa-Hung Leung,*,‡,a Joyce L. C. Chima and Wing-Tak Wongb
a
Department of Chemistry, The Hong Kong University of Science and Technology,
Clear Water Bay, Kowloon, Hong Kong
b Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
Interaction of cis-[Pt(dppm)2(O3SCF3)2] [dppm = bis(diphenylphosphino)methane], cis-[Pt(Bupy)(O3SCF3)2]
(Bupy = 4-tert-butylpyridine), [Ir(CO)(PPh3)2(O3SCF3)], and [Rh(cod)(OH2)(OTs)] (cod = cycloocta-1,5-diene,
OTs = tosylate) with [NBun ][NOsO3] afforded bimetallic nitrido-bridged complexes cis-[Pt(dppm)(NOsO3)2] 3,
4
trans-[Pt(Bupy)2(NOsO3)2] 4, [Ir(CO)(PPh3)2(NOsO3)] 5 and [{Rh(cod)(NOsO3)}2] 6, respectively. Complex 4
¯
crystallises in the P1 space group with a = 7.936(1), b = 10.758(2), c = 7.738(1) Å, α = 100.02(1), β = 99.75(1),
γ = 101.75(1)Њ, U = 622.5(2) Å3 for Z = 1. The Pt᎐N (Os), Os᎐N and the mean Os᎐O distances are 1.958(7),
1.681(7) and 1.724 Å, respectively. Complex 5 crystallises in the P21 /n space group with a = 10.124(1),
b = 15.564(2), c = 22.623(3) Å, β = 100.08(2)Њ, U = 3509.7(7) Å3 for Z = 4. The Ir᎐N, Os᎐N and the mean Os᎐O
distances are 1.998(7), 1.710(7) and 1.718 Å, respectively. Treatment of [Au(PPh )(NOsO )] 1 with Ph P᎐NPh
᎐
3
3
3
gave the N-phosphinimine complex [Au(PPh ){N(᎐PPh )Ph}][NOsO ] 7. Complex 7 crystallises in the
᎐
3
3
3
P21 /n space group with a = 8.780(1), b = 20.781(2), c = 20.711(5) Å, β = 91.23(1)Њ, U = 3788.0(9) Å3 for Z = 4. The
Au᎐N distance is 2.091(8) Å and the C᎐N᎐P angle in the phosphinimine is 127.0(7)Њ. Reaction of 1 with Bupy led
to substitution of Bupy for [NOsO3] and formation of [Au(PPh3)(Bupy)][NOsO3] 8. Reaction of
[Pt(dppf)(O3SCF3)Cl] [dppf = 1,1Ј-bis(diphenylphosphino)ferrocene] with [NBun ][NOsO3] afforded the
4
trimetallic complex [Pt(dppf)(NOsO3)Cl] 11. Complex 11 crystallizes in the P21/c space group with a = 20.058(2),
b = 14.899(1), c = 23.949(2) Å, β = 114.57(2)Њ, U = 6508(1) Å3 for Z = 8. The mean Pt᎐N, Os᎐N and Os᎐O
distances are 2.06, 1.66 and 1.67 Å, respectively.
Oxoosmium() complexes have attracted much attention
because of their applications to organic syntheses, particularly
dihydroxylation 1 and aminohydroxylation 2 of alkenes by
[OsO4] and [Os(NR)O3] (R = alkyl), respectively. The signifi-
cance of these reactions is highlighted by the seminal works of
Sharpless and co-workers, who have successfully developed
versatile syntheses of optically pure vicinal diols and amino
alcohols via enantioselective osmium-catalysed dihydroxyl-
ation 3 and aminohydroxylation 4 of alkenes, respectively. In an
effort to explore new reactivities of oxoosmium() complexes,
we set out to investigate the electronic influence of the substit-
uent on nitride (X) on the reactivity of the imidoosmium()
trometer. Cyclic voltammetry was performed with a Princeton
Applied Research (PAR) Model 273A potentiostat, the working
and reference electrodes were glassy carbon and Ag–AgNO3
(0.1 mol dmϪ3 in acetonitrile), respectively, potentials were
reported with reference to the ferrocenium–ferrocene couple.
Elemental analyses were performed by Medac Ltd., Brunel
University, UK.
Materials
The preparations of [Au(PPh3)(NOsO3)] 1, cis-[Pt-
(PMe ) (NOsO ) ] 2 and [Au(PPh ){N(᎐PPh )Ph}][NOsO ] 7
᎐
3
2
3
2
3
3
3
have been reported previously.5 The compounds [NBun ]-
4
complex [Os(NX)O3]. To this end, a series of bimetallic nitrido-
[NOsO3],6 cis-[Pt(Bupy)2Cl2] (Bupy = 4-tert-butylpyridine),7
᎐
bridged trioxoosmium() complexes of the type [L M᎐N᎐
᎐
[Pt(dppm)Cl2]
[dppm = bis(diphenylphosphino)methane],8
n
OsO3] (M = electrophilic metal; L = PR3, CO, etc.) are syn-
thesised. Of particular interest are the osmate() complexes
containing square planar platinum() and iridium() centres,
which may promote the reactivities of unsaturated organic
substrates with the trioxoosmium() moiety. We describe here
the syntheses and reactivities of some bi- and tri-metallic com-
plexes with a trioxoosmium() moiety. Preliminary results of
this work have been published in a communication.5
[Ir(CO)(PPh3)2Cl],9 [Rh(cod)(OH2)(OTs)] (cod = cycloocta-1,5-
diene, OTs = tosylate),10 and [Pt(dppf)Cl2] [dppf = 1,1Ј-bis-
(diphenylphosphino)ferrocene]11 were synthesised according to
the literature methods.
Preparations
cis-[Pt(dppm)(NOsO3)2] 3. To a suspension of [Pt(dppm)Cl2]
(0.1 g, 0.15 mmol) in thf (10 cm3) were added 2 equivalents of
AgO3SCF3 (79 mg, 0.31 mmol) and the resulting mixture
was stirred at room temperature overnight and filtered. To the
Experimental
filtrate was added a solution of [NBun ][NOsO3] (0.15 g, 0.3
All manipulations were carried out under nitrogen using stand-
ard Schlenk techniques. Solvents were purified and distilled
prior to use; NMR spectra were recorded on a Bruker ALX 300
spectrometer, chemical shifts (δ) were reported with reference to
SiMe4 (1H) and H3PO4 (31P). Infrared spectra (Nujol) were
recorded on a Perkin-Elmer 16 PC FT-IR spectrophotometer,
mass spectra were obtained on a Finnigan TSQ-7000 spec-
4
mmol) in CH2Cl2 (5 cm3) and the mixture was stirred for a
further hour. The yellow solid was collected and recrystallised
from dimethylformamide (dmf)–ether (yield: 0.08 g, 50%).
NMR (CDCl3): 1H, δ 5.61 (s, 2 H, CH2) and 7.67–7.99 (m, 20 H,
phenyl protons); 31P, δ Ϫ61.07 (d, 2JPt᎐P 1458 Hz). IR(cmϪ1): 890
᎐
[ν(Os᎐O)] and 1080 [ν(Os᎐N)] (Found: C, 28.2; H, 2.2; N, 2.0.
᎐
᎐
Calc. for C25H22N2O6Os2P2Pt: C, 27.7; H, 2.0; N, 2.6%).
trans-[Pt(Bupy)2(NOsO3)2] 4. To suspension of cis-
[Pt(Bupy)2Cl2] (87 mg, 0.16 mmol) in acetone–CH2Cl2 (20 cm3,
a
† Dedicated to the memory of Professor Sir Geoffrey Wilkinson.
‡ E-Mail: chleung@usthk.ust.hk
J. Chem. Soc., Dalton Trans., 1997, Pages 3277–3282
3277

View Article Online
Table 1 Crystallographic data and experimental details for trans-[Pt(Bupy)2(NOsO3)2] 4, [Ir(CO)(PPh3)2(NOsO3)] 5, [Au(PPh3){N(᎐PPh3)-
᎐
Ph}][NOsO3] 7 and [Pt(dppf)(NOsO3)Cl] 11
4
5
7
11
Empirical formula
M
C18H26N4O6Os2Pt
969.92
C37H30IrNO4OsP2
997.02
C42H35AuN2O3OsP2
1064.86
C34H28ClFeNO3OsP2Pt
1037.14
Crystal system
Space group
Colour, habit
Crystal dimensions/mm
a/Å
b/Å
c/Å
α/Њ
Triclinic
P1 (no. 2)
Monoclinic
P21 /n (no. 14)
Orange, block
0.18 × 0.20 × 0.25
10.124(1)
Monoclinic
P21 /n (no. 14)
Yellow, plate
0.12 × 0.24 × 0.28
8.780(1)
Monoclinic
P21 /c (no. 14)
Red, block
0.22 × 0.22 × 0.29
20.058(2)
¯
Yellow, block
0.14 × 0.18 × 0.19
7.936(1)
10.758(2)
7.738(1)
100.02(1)
99.75(1)
101.75(1)
622.5(2)
1
15.564(2)
22.623(3)
20.781(2)
20.711(5)
14.899(1)
23.949(2)
β/Њ
100.08(2)
91.23(1)
114.57(2)
γ/Њ
U/Å3
3509.7(7)
4
1.887
Enraf-Nonius CAD4
3778.0(9)
4
1.872
Rigaku AFC7R
25.0
6508(1)
8
2.117
MAR-research image plate
25.0
Z
Dc /g cmϪ3
Diffractometer
T/ЊC
2.587
Rigaku AFC7R
25.0
25.0
λ/Å
Scan type
0.710 73
ω–2θ
45.0
157.95
1770
0.710 73
ω–2θ
44.9
75.43
5094
0.710 73
ω–2θ
45.0
73.76
5507
0.710 73
2θmax /Њ
51.3
µ/cmϪ1
88.19
12 298
6682
No. of reflections
No. of reflections observed
[I > 3.00σ(I )]
Weighting scheme
R a
1205
3466
3114
1/[σ2(Fo) ϩ 0.005Fo /4]
2.3%
2.2%
440
1/σ2(Fo)
5.4%
3.90%
1896
1/[σ2(Fo) ϩ 0.007Fo /4]
1/σ2(Fo)
5.4%
7.2%
3920
2
2
3.0%
3.0%
2040
1.24
RЈb
F(000)
Goodness of fit c
1.34
2.46
2.24
¹
¹
a
R = (Σ|Fo| Ϫ |Fc|)/Σ|Fo|. b RЈ = [(Σw2|Fo| Ϫ |Fc|)2/Σw2|Fo|2]². c Goodness of fit = [(Σw|Fo| Ϫ |Fc|)2/(Nobserved Ϫ Nparameters)]².
1:1) was added to 2 equivalents of AgO3SCF3 (83 mg, 0.32
mmol). The mixture was stirred at room temperature overnight
was stirred at room temperature overnight. The solvent was
pumped off and the residue was recrystallised from CH2Cl2–
hexane to give pale yellow crystals (yield 63 mg, 75%). NMR
(CDCl3): 1H, δ 1.34 (s, 9 H, But), 7.55–7.62 (m, 17 H, aromatic
and filtered. To the filtrate was added a solution of [NBun ]-
4
[NOsO3] (0.16 g, 0.32 mmol) in CH2Cl2 (5 cm3) and the mixture
was stirred for 2 h. The solvent was pumped off and the residue
recrystallised from CH2Cl2–hexane to give X-ray quality yellow
crystals (yield 50 mg, 32%). NMR (CDCl3): 1H, δ 1.37 (s, 9 H,
But), 7.55 (d, 4 H, Hm) and 8.38 (d, 4 H, Ho). IR(cmϪ1): 888, 906
protons) and 8.59 (d, 2 H, Ho or Bupy); 31P, δ 28.5 (s). IR(cmϪ1):
᎐
868, 888 [ν(Os᎐O)] and 1016 [ν(Os᎐N)] (Found: C, 38.1; H, 3.3;
᎐
᎐
N 3.1. Calc. for C27H28AuN2O3OsP: C, 38.3; H, 3.3; N, 3.3%).
[Pt(dppf)(O3SCF3)2] 9 and [Pt(dppf)(O3SCF3)Cl] 10. To a
solution of [Pt(dppf)Cl2] (0.1 g, 0.12 mmol) in CH2Cl2 (10 cm3)
was added 2 equivalents of AgO3SCF3 (63 mg, 0.24 mmol) and
the solution was stirred at room temperature overnight. The
solvent was pumped off and the residue was recrystallised from
CH2Cl2–diethyl ether to give orange and red crystals, which can
be separated by inspection or fractional recrystallisation from
CH2Cl2–hexane (yield 70 mg). The orange product was identi-
3
᎐
[ν(Os᎐O)] and 1078 [ν(Os᎐N)]. UV/VIS (CH Cl ); λ/nm (ε/dm
᎐
᎐
2
2
molϪ1 cmϪ1) 352 (14 000), 421 (2890), 437 (2930) and 467 (1540)
(Found: C, 22.0; H, 2.7; N, 5.4. Calc. for C18H26N4O6Os2Pt: C,
22.3; H, 2.7; N, 5.8%).
[Ir(CO)(PPh3)2(NOsO3)] 5. To a suspension of [Ir(CO)-
(PPh3)2Cl] (0.13 g, 0.17 mmol) in CH2Cl2 (25 cm3) was added 1
equivalent of AgO3SCF3 (44 mg, 0.17 mmol) and the mixture
was stirred for 1 d and filtered. To the filtrate was added a
1
fied as the ditriflate [Pt(dppf)(O3SCF3)2]. NMR (CDCl3): H,
solution of [NBun ][NOsO3] (84 mg, 0.17 mmol) in CH2Cl2 (10
δ 4.49 (s br, 4 H, C5H5), 4.58 (s br, 4 H, C5H5) and 7.48–7.78
(m, 20 H, phenyl protons); 31P, δ 8.04 (t, 1JPt᎐P 2102 Hz) (Found:
C, 39.4; H, 3.1. Calc. for C36H28F6FeO6P2PtS2ؒ3H2O: C, 39.2;
H, 3.1%).
The red product was identified as the monotriflate [Pt(dppf)-
(O3SCF3)Cl], which can be synthesised in good yield by reac-
tion of [Pt(dppf)Cl2] with 1 equivalent of AgO3SCF3. NMR
(CDCl3): 1H, δ 4.40–4.63 (overlapping s, 8 H, C5H5) and 7.22–
7.74 (m, 20 H, phenyl protons); 31P, δ 17.53 (d, 1JPt᎐P 1993.5 Hz)
(Found: C, 44.2; H, 3.1. Calc. for C35H28ClF3FeO3P2PtS: C,
45.0; H, 3.0%).
4
cm3) and the mixture was stirred for a further hour. The solvent
was pumped off and the residue recrystallised from CH2Cl2–
hexane to give red crystals, which were suitable for an X-ray
diffraction study (yield 0.15 g, 90%). NMR (CDCl3): 1H,
δ 7.45–7.68 (m, phenyl protons); 31P, δ 27.92 (s). IR(cmϪ1): 886,
᎐
᎐
896, 908 [ν(Os᎐O)], 1098 [ν(Os᎐N)] and 1986 [ν(C᎐O)]. UV/VIS
᎐
᎐
᎐
(CH2Cl2): λmax /nm (ε/dm3 molϪ1 cmϪ1) 350 (5460) (Found: C,
44.6; H, 3.2; N, 1.4. Calc. for C37H30IrNO4OsP2: C, 44.6; H, 3.0;
N, 1.4%).
[{Rh(cod)(NOsO3)}2] 6. To a solution of [Rh(cod)(OH2)-
(OTs)] (0.1 g, 0.26 mmol) in acetone (10 cm3) was added 1
[Pt(dppf)(NOsO3)Cl] 11. To a solution of 9 (0.14 g, 0.15
equivalent of [NBun ][NOsO3] (0.13 g, 0.26 mmol) and the mix-
mmol) in CH2Cl2 (10 cm3) was added 1 equivalent of [NBun ]-
4
4
ture was stirred for 1 h. The brown precipitate was collected,
washed with acetone and recrystallised from dmf–diethyl ether
(yield 0.17 g, 70%). NMR [(CD3)2SO]: H, δ 2.32 (s br, 4 H,
[NOsO3] (74 mg, 0.15 mmol) and the mixture was stirred for 2
h. The solvent was pumped off and the residue recrystallised
from CH2Cl2–hexane to give orange crystals (yield 0.14 g,
1
1
CH2), 2.81 (s br, 4 H, CH2) and 4.67 (s br, 4 H, olefinic protons).
90%). NMR (CDCl3): H, δ 3.99 (s, 1 H, C5H5), 4.37 (s, 1 H,
IR(cmϪ1): 904 [ν(Os᎐O)] (Found: C, 21.7, H, 2.8; N, 3.1. Calc.
C5H5), 4.56 (s, 2 H, C5H5) and 7.38–7.92 (m, 20 H, phenyl pro-
᎐
for C16H24N2O6Os2Rh2: C, 20.7; H, 2.6; N, 3.0%).
tons); 31P, δ 14.90 (s) and 15.01 (s). IR(cmϪ1): 888, 908
᎐
[Au(PPh3)(Bupy)][NOsO3] 8. To a solution of [Au(PPh3)-
(NOsO3)] (71 mg, 0.1 mmol) in CH2Cl2 (10 cm3) was added
1 equivalent of Bupy (0.015 cm3, 0.1 mmol) and the mixture
[ν(Os᎐O)] and 1096 [ν(Os᎐N)]. UV/VIS (CH Cl ): λmax /nm
᎐
᎐
2
2
(ε/dm3 molϪ1 cmϪ1) 322 (7510) (Found: C, 39.3; H, 2.8; N, 1.4.
Calc. for C34H28ClFeNO3OsP2Pt: C, 39.4; H, 2.7; N, 1.4%).
3278
J. Chem. Soc., Dalton Trans., 1997, Pages 3277–3282

View Article Online
Fig. 1 Perspective view of trans-[Pt(Bupy)2(NOsO3)2] 4
Scheme 1 (i) [Au(PPh3)(O3SCF3)]; (ii) cis-[PtL2(O3SCF3)2]; (iii) cis-
[Pt(Bupy)2Cl2]; (iv) [Ir(CO)(PPh3)2(O3SCF3)]; (v) [Rh(cod)(OH2)(OTs)];
(vi) [Pt(dppf)(O3SCF3)Cl]
X-Ray crystallography
A summary of crystal data and experimental details for com-
plexes 4, 5, 7 and 11 are listed in Table 1. Intensity data were
made on a Rigaku AFC7R diffractometer (for 4 and 7), an
Enraf-Nonius CAD4 diffractometer (for 5), and a MAR
research image plate scanner (for 11) at ambient temperature
using graphite-monochromated Mo-Kα radiation (λ 0.710 73
Å). All intensity data were corrected for Lorentz and absorp-
tion effects. Semiempirical absorption corrections (ψ scan) were
applied for 4, 5 and 7. However, no absorption correction was
made for 11. The space group of the crystals was determined by
their systematic absences and Laue symmetry. It is noteworthy
that for 11 the reported cell data can be transformed into an
orthorhombic C-centre system. However, the required mmm
Laue symmetry is absent. The three structures were solved by
direct methods and refined on F by full-matrix least-squares
analysis. Some non-hydrogen atoms were refined anisotropic-
ally while the rest were refined isotropically.
Fig. 2 Perspective view of [Ir(CO)(PPh3)2(NOsO3)] 5
Table
2 Selected bond lengths (Å) and angles (Њ) for trans-
Atomic coordinates, thermal parameters, and bond lengths
and angles have been deposited at the Cambridge Crystallo-
graphic Data Centre (CCDC). See Instructions for Authors,
J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the
CCDC for this material should quote the full literature citation
and the reference number 186/568.
[Pt(Bupy)2(NOsO3)2] 4
Pt᎐N(1)
Os(1)᎐O(1)
Os(1)᎐O(3)
2.040(7)
1.716(7)
1.745(8)
Pt᎐N(2)
Os(1)᎐O(2)
Os(1)᎐N(2)
1.958(7)
1.711(8)
1.681(7)
N(1)᎐Pt᎐N(1*)
N(1)᎐Pt᎐N(2*)
N(1*)᎐Pt᎐N(2*)
O(1)᎐Os(1)᎐O(2)
O(1)᎐Os(1)᎐N(2)
O(2)᎐Os(1)᎐N(2)
Pt᎐N(2)᎐Os(1)
180.0
N(1)᎐Pt᎐N(2)
89.4(3)
90.6(3)
180.0
111.5(4)
109.2(4)
108.7(4)
90.6(3)
89.4(3)
109.9(4)
109.0(4)
108.5(4)
172.5(5)
N(1*)᎐Pt᎐N(2)
N(2)᎐Pt᎐N(2*)
O(1)᎐Os(1)᎐O(3)
O(2)᎐Os(1)᎐O(3)
O(3)᎐Os(1)᎐N(2)
Results and Discussion
Bimetallic nitrido-bridged osmate(VIII) complexes
᎐
Bimetallic nitrido-bridged vanadium() complexes V᎐N᎐M
᎐
(M = Rh or Ir) have been previously isolated by Doherty and
co-workers12 from the reaction of X V᎐NSiMe (X = halide)
᎐
3
3
with F᎐ML2(CO) (L = PR3) [equation (1)]. We found that
respectively, have been described previously.5 Interaction of cis-
[Pt(dppm)(O3SCF3)2] and cis-[Pt(Bupy)2(O3SCF3)2] with
X V᎐NSiMe ϩ [F᎐ML (CO)] →
᎐
3
3
2
[NOsO3]Ϫ afforded [Pt(dppm)(NOsO3)2]
3
and trans-
᎐
[X V᎐N᎐ML (CO)] ϩ SiFMe (1)
᎐
᎐
3
2
3
[Pt(Bupy) (NOsO ) ] 4, respectively. The Os᎐O and Os᎐N
᎐
᎐
2
3 2
stretching frequencies in the IR spectra of complexes 3 and 4
are similar to those found for complex 2.5 The structure of 4 has
been established by X-ray crystallography. A perspective view
of 4 is shown in Fig. 1; selected bond lengths and angles are
given in Table 2. The geometry around Pt is square planar with
the two [NOsO3] groups trans to each other. The Pt᎐N (Os)
distance of 1.958(7) Å is slightly shorter than those in com-
plexes 25 and 11 (see below) because the trans influence for
[NOsO3] is smaller than that for phosphine. The reason why 4
prefers trans geometry, which is in contrast to 2, is not clear.
The Os᎐N and the mean Os᎐O distances of 1.681(7) and 1.724
Å, respectively, are similar to those for 1 and 2.
bimetallic nitrido-bridged osmate() complexes could be pre-
pared conveniently by metathesis of [NOsO3]Ϫ with metal tri-
flates [LnM(O3SCF3)] (M = electrophilic metal) [equation (2)].
[NBun ][NOsO3] ϩ [LnM(O3SCF3)] →
4
n
᎐
[L M᎐N᎐OsO ] ϩ [NBu ][O SCF ] (2)
᎐
n
3
4
3
3
The syntheses of the nitrido-bridged osmate() complexes are
summarised in Scheme 1. The characterisation and crystal struc-
tures of [Au(PPh3)(NOsO3)] 1 and cis-[Pt(PMe3)2(NOsO3)2] 2,
which were synthesised by the reactions of [NBun ][NOsO3]
4
with [Au(PPh3)(O3SCF3)] and cis-[Pt(PMe3)2(O3SCF3)2],
The Vaska-type complex [Ir(CO)(PPh3)2(NOsO3)] 5 was syn-
J. Chem. Soc., Dalton Trans., 1997, Pages 3277–3282
3279

View Article Online
Table 3 Selected bond lengths (Å) and angles (Њ) for [Ir(CO)-
(PPh3)2(NOsO3)] 5
Table 4 Selected bond lengths (Å) and angles (Њ) for [Au(PPh3)-
{N(᎐PPh3)Ph}][NOsO3] 7
᎐
Ir᎐P(1)
2.321(3)
1.998(7)
1.715(8)
1.708(8)
1.14(1)
Ir᎐P(2)
2.327(3)
1.83(1)
1.730(9)
1.710(7)
Au᎐P(2)
Os᎐O(1)
Os᎐O(3)
P(1)᎐N(1)
2.240(3)
Au᎐N(1)
Os᎐O(2)
Os᎐N(2)
2.091(8)
1.699(8)
1.696(9)
Ir᎐N(1)
Os᎐O(2)
Os᎐O(4)
O(1)᎐C(1)
Ir᎐C(1)
Os᎐O(3)
Os᎐N(1)
1.706(9)
1.714(9)
1.607(9)
P(2)᎐Au(1)᎐N(1)
O(1)᎐Os(1)᎐O(3)
O(2)᎐Os(1)᎐O(3)
O(3)᎐Os(1)᎐N(2)
Au(1)᎐N(1)᎐P(1)
178.1(2)
108.9(5)
110.1(4)
108.9(5)
115.6(5)
O(1)᎐Os(1)᎐O(2)
O(1)᎐Os(1)᎐N(2)
O(2)᎐Os(1)᎐N(2)
Au(1)᎐N(1)᎐C(1)
P(1)᎐N(1)᎐C(1)
109.8(4)
109.1(6)
109.9(5)
115.7(6)
127.0(7)
P(1)᎐Ir᎐P(2)
P(1)᎐Ir᎐C(1)
P(2)᎐Ir᎐C(1)
O(2)᎐Os᎐O(3)
O(2)᎐Os᎐N(1)
O(3)᎐Os᎐N(1)
Ir᎐N(1)᎐Os
169.3(1)
92.5(3)
91.8(3)
109.9(4)
108.6(4)
109.2(4)
175.5(5)
P(1)᎐Ir᎐N(1)
P(2)᎐Ir᎐N(1)
N(1)᎐Ir᎐C(1)
O(2)᎐Os᎐O(4)
O(3)᎐Os᎐O(4)
O(4)᎐Os᎐N(1)
Ir᎐C(1)᎐O(1)
87.2(2)
88.8(2)
177.9(4)
109.3(5)
110.9(5)
108.9(4)
177(1)
thesised by the reaction of [Ir(CO)(PPh3)2(O3SCF3)] with
[NOsO3]Ϫ, isolated as air-stable red crystals. Fig. 2 shows a dia-
gram of the molecule; selected bond lengths and angles are
given in Table 3. As expected the geometry around Ir is square
planar with the [NOsO3] group trans to the carbonyl. The Ir᎐P,
Ir᎐C and Ir᎐N distances are normal by comparison with the
isostructural iridium()–amide complex [Ir(CO)(PPh3)2(3,5-
Me2C6H3NH)].13 The short Os᎐N distance [1.710(7) Å] and
long Ir᎐N bond [1.998(7) Å] is suggestive of the unsymmetric
᎐
Fig. 3 Perspective view of [Au(PPh3){N(᎐PPh3)Ph}][NOsO3] 7
bridging mode of the nitride, i.e. Ir᎐N᎐Os. The ν(C᎐O) for 5
᎐
᎐
᎐
was found at 1986 cmϪ1, which is lower than that for
[Ir(CO)(PPh3)2(3,5-Me2C6H3NH)] (1941 cmϪ1
)
and [Ir(CO)-
the phosphinimine is 127.0(7)Њ. The AuI᎐N distance is similar to
that in 1.4 There is no interaction of the Au centre with the
osmate, which is essentially a counter anion.
13
(PPh3)2(CO)] (1965 cmϪ1), indicating that [NOsO3]Ϫ is a weak
donor ligand. On the basis of the CO stretching frequency,
the donor strength of [NOsO3]Ϫ is considered comparable to
that of a nitrite (1987 cmϪ1).14
In contrast to the imido(trioxo)osmium() complexes, no
reactions of complexes 1–4 with alkenes were observed. In an
attempt to activate these osmate() complexes by Lewis base
complexation, or so-called ‘ligand accerelation’,15 we tried the
reactions of 1 with alkenes in the presence of pyridine. Treat-
ment of dimethylbut-2-ene with stoichiometric amounts of
complex 1 and 4-tert-butylpyridine (Bupy) led to isolation of an
adduct analysed as 1ؒBupy 8. No cycloaddition reaction of 1
Reaction of [Pt(cod)(O3SCF3)2] and ‘Ir(cod)(O3SCF3)’,
which were prepared in situ from [Pt(cod)Cl2] and [{Ir(cod)Cl}2],
respectively, with [NOsO3]Ϫ led to isolation of uncharacterised
insoluble brown solids. On the other hand, treatment of [Rh-
(cod)(OH2)(OTs)] with [NOsO3]Ϫ gave a well defined solid
analysed as [Rh(cod)(NOsO3)] 6. This solid is insoluble in
chlorinated solvents but readily dissolves in dmf and dimethyl
sulfoxide. The 1H NMR spectrum of 6 shows signals character-
istic of co-ordinated cod. In addition, the IR spectrum shows
1
with dimethylbut-2-ene occurred, as evidenced by H and 13C
NMR spectroscopy. Complex 8 was, however, incorrectly for-
mulated as the osmium–pyridine adduct [OsO3{NAu(PPh3)}-
Bupy] in the previous communication.5 The correct structure
᎐
that ν(Os᎐O) and ν(Os᎐N) are shifted to higher frequency,
᎐
᎐
indicating that the [NOsO3] moiety in 6 is co-ordinated rather
than a counter anion. Unfortunately, we were not able to obtain
X-ray quality crystals for 6 due to its poor solubilities in
common organic solvents. We tentatively formulate 6 as a
NOsO3-bridged dirhodium()complex[{Rh(cod)}2(µ-NOsO3)2],
which is the first example of a complex with a bridging [NOsO3]
ligand.
for 8 should be [Au(PPh )(Bupy)][NOsO ] because the Os᎐O
᎐
3 3
᎐
and Os᎐N stretching frequencies for 8 are close to the values
᎐
for 7, in which the [NOsO3] moiety is a counter anion. The
[NOsO3] group in 1 is quite labile and can be displaced easily
apparently because the Au᎐N bond is weak.
Similar to Vaska complexes, 5 was found to undergo oxid-
ative addition with MeI. The IR spectrum of the crude product,
᎐
presumably [Ir(CO)(PPh )(Me)(NOsO )I], shows a ν(C᎐O)
᎐
3
3
Reactivities of bimetallic nitrido-bridged complexes
stretch at 2010 cmϪ1, which is typical for IrIII complexes.14,16
However, the H and 31P-{1H} NMR spectra show that the
1
In an attempt to synthesise an imido(nitrido)osmium()
complex via oxo–imido exchange, we tried the reaction of com-
crude product consists of three isomers, which have yet to be
separated.
plex 1 with phosphinimine. Treatment of 1 with PhN᎐PPh
᎐
3
resulted in substitution of the phosphinimine for [NOsO3],
instead of the oxo–imido exchange. The product was character-
Trimetallic complexes
ised as [Au(PPh ){N(᎐PPh )Ph}][NOsO ] 7 by X-ray crystallo-
graphy. Fig. 3 shows a perspective view of the molecule;
selected bond lengths and angles are given in Table 4. The
In the hope of activating the [NOsO3] group by intramolecular
electron transfer, trioxoosmium() complexes containing the
redox-active dppf ligand were synthesised. Metathesis of
[Pt(dppf)Cl2] with 2 equivalents of AgO3SCF3 led to the
᎐
3
3
3
P᎐Au᎐N linkage is essentially linear while the C᎐N᎐P angle in
᎐
3280
J. Chem. Soc., Dalton Trans., 1997, Pages 3277–3282

View Article Online
Fig. 5 Cyclic voltammogram of [Pt(dppf)(NOsO3)Cl]. Supporting
electrolyte: 0.1 mol dmϪ3 NBun PF6 in CH2Cl2; working electrode
4
glassy carbon; scan rate 100 mV sϪ1
Fig. 4 Perspective view of one of the two independent molecules in
the unit cell for [Pt(dppf)(NOsO3)Cl] 11
Table 6 Formal electrode potentials (EЊ) for nitrido-bridged osmate-
() complexesa
EЊ/V vs. ferrocene–ferrocenium
Table 5 Selected bond lengths (Å) and angles (Њ) for [Pt(dppf)-
(NOsO3)Cl] 11
Compound
[NOsO3]Ϫ
Oxidation
Reduction
Ϫ1.45b
[Au(PPh3)(NOsO3)]
[Pt(Bupy)2Cl2]
trans-[Pt(Bupy)2(NOsO3)2]
[Pt(dppf)Cl2]
[Pt(dppf)(O3SCF3)2]
[Pt(dppf)(NOsO3)Cl]
[Ir(CO)(PPh3)2(NOsO3)]
[Os(NBut)O3]
Ϫ1.31b
Ϫ2.13b
Ϫ1.23b
Ϫ2.13b
Ϫ1.34b
Ϫ1.50b
Ϫ1.67b
0.92
Pt(1)᎐Cl
2.317(5)
2.265(5)
1.77(2)
1.69(2)
2.354(6)
2.287(5)
1.66(2)
1.53(2)
Pt(1)᎐P(1)
Pt(1)᎐N(1)
Os(1)᎐O(2)
Os(1)᎐N(1)
Pt(2)᎐P(3)
Pt(2)᎐N(2)
Os(2)᎐O(5)
Os(2)᎐N(2)
2.269(4)
2.05(1)
1.69(1)
1.66(1)
2.250(5)
2.06(2)
1.68(2)
1.65(2)
Pt(1)᎐P(2)
Os(1)᎐O(1)
Os(1)᎐O(3)
Pt(2)᎐Cl(1)
Pt(2)᎐P(4)
Os(2)᎐O(4)
Os(2)᎐O(6)
0.56
0.86
0.67
Supporting electrolyte: 0.1 mol dmϪ3 NBun PF6 in CH2Cl2; working
a
4
electrode glassy carbon; scan rate = 100 mV sϪ1 b Irreversible, Epc
.
Cl(1)᎐Pt(1)᎐P(1)
Cl(1)᎐Pt(1)᎐N(1)
P(1)᎐Pt(1)᎐N(1)
O(1)᎐Os(1)᎐O(2)
O(1)᎐Os(1)᎐N(1)
O(2)᎐Os(1)᎐N(1)
Pt(1)᎐N(1)᎐Os(1)
Cl(2)᎐Pt(2)᎐P(4)
P(3)᎐Pt(2)᎐N(2)
O(4)᎐Os(2)᎐O(5)
O(4)᎐Os(2)᎐N(2)
Os(5)᎐Os(2)᎐N(2)
Pt(2)᎐N(2)᎐Os(2)
85.0(2)
83.5(4)
168.1(4)
108.7(8)
108.1(9)
109.6(7)
160.4(9)
87.7(2)
90.4(5)
111(1)
Cl(1)᎐Pt(1)᎐P(2)
P(1)᎐Pt(1)᎐P(2)
P(2)᎐Pt(1)᎐N(1)
O(1)᎐Os(1)᎐O(3)
O(2)᎐Os(1)᎐O(3)
O(3)᎐Os(1)᎐N(1)
Cl(2)᎐Pt(2)᎐P(3)
P(3)᎐Pt(2)᎐P(4)
P(4)᎐Pt(2)᎐N(2)
O(4)᎐Os(2)᎐O(6)
O(5)᎐Os(2)᎐O(6)
O(6)᎐Os(2)᎐N(2)
175.4(2)
99.6(2)
91.9(4)
112(1)
111.3(9)
106.4(9)
174.6(2)
97.7(2)
171.8(5)
107.1
values.
vs. Cp2Feϩ/0 (Cp = η5-C5H5). This reduction wave is tentatively
attributed to the OsVIII–OsVII reduction because the Pt-centred
reduction for cis-[Pt(Bupy)2Cl2] was found at a more negative
potential (ca. Ϫ2.13 V). The reduction of OsVIII in 4 occurs at
a less negative potential than that in [NOsO3]Ϫ (ca. Ϫ1.45 V
under the same conditions), suggestive of delocalisation of
electrons from [NOsO3] to PtII in complex 5.
110.6(8)
107.1(8)
152(1)
116(1)
103(1)
The cyclic voltammogram of complex 11(Fig. 5) shows a
reversible couple at 0.67 V (∆Ep = 80 mV, ia/ic ≈ 1 and is scan rate
independent) along with an irreversible reduction wave at
Ϫ1.50 V vs. Cp2Feϩ/0. The oxidation couple is assigned as the
ferrocene-centred FeIII᎐FeII couple. However, it seems that this
oxidation couple might also have some PtIII᎐PtII character
because the oxidation potential for the [Pt(dppf)X2] complexes
shows a dependence on the nature of X. It decreases from
[Pt(dppf)(O3SCF3)2] (0.866 V), [Pt(dppf)(NOsO3)Cl] (0.67 V)
to [Pt(dppf)Cl2] (0.56 V). This order is consistent with the trend
of donor strength of X: Cl > NOsO3 > O3SCF3. The irrevers-
ible wave at Ϫ1.50 V in 11 is tentatively assigned as the osmium-
centred reduction because the reduction of PtII for [Pt(dppf)-
Cl2] was found at a very negative potential (ca. Ϫ2.13 V).
The cyclic voltammogram of complex 5 shows an irreversible
reduction wave at Ϫ1.67 V vs. Cp2Feϩ/0. This was tentatively
attributed to the reduction of OsVIII–OsVII because the iridium-
centred reductions for Vaska-type compounds are known to
occur at more negative potentials (<Ϫ2.00 V vs. Agϩ᎐Ag).14 On
the basis of the potential at which OsVIII in [LnM᎐NOsO3] is
reduced, the donor strength of the fragment LnM can be ranked
in the order {IrI(CO)(PPh3)2} > {AuI(PPh3)} > {PtII(Bupy)2}.
This trend is in agreement with the order of electron-
withdrawing power of the metal centre: IrI < AuI < PtII. It
might also be noted that the OsVIII᎐OsVII reduction potential
for [Os(NBut)O3] is found to be less negative than those for
isolation of a mixture of orange ditriflate [Pt(dppf)(O3SCF3)2]
9 and red monotriflate [Pt(dppf)(O3SCF3)Cl] 10, which can be
separated by inspection or fractional crystallisation. Reaction
of [Pt(dppf)Cl2] with 1 equivalent of AgO3SCF3, however,
gave the monotriflate as the major product. Treatment of
10 with [NOsO3]Ϫ resulted in the formation of the trimetallic
FeII᎐PtII᎐OsVIII complex [Pt(dppf)(NOsO3)Cl] 11, the structure
of which has been confirmed by X-ray diffraction. Fig. 4 shows
a perspective view of one of the two independent molecules in
the unit cell; selected bond lengths and angles are given in Table
5. As expected, the geometry around Pt is square planar. The
mean Pt᎐P and Pt᎐Cl bond distances in 11 are similar to those
for [Pt(dppf)Cl2].10 The mean Os᎐N and Os᎐O distances of
1.66 and 1.67 Å, respectively, are normal compared with other
᎐
osmate() complexes. Interestingly, the Pt᎐N᎐Os linkage in
᎐
11 is found to be slightly bent with an average angle of ca.
156.2Њ, this bending is attributed to the non-bonding repulsion
between the NOsO3 group and the phenyl ring of dppf.
Electrochemical studies
Table 6 summarises the electrochemical data for the nitrido-
bridged osmate() complexes. The cyclic voltammogram of
complex 4 shows an irreversible reduction wave at ca. Ϫ1.23 V
J. Chem. Soc., Dalton Trans., 1997, Pages 3277–3282
3281

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Table 7 Structural and IR spectral data for nitrido-bridged osmate() complexes
Ϫ1
᎐
᎐
Complex
d(Os᎐N)/Å
d(Os᎐O)/Å
ν(Os᎐N)/cm
ν(Os᎐O)/cmϪ1
᎐
᎐
᎐
᎐
[NOsO3]Ϫ a
1.67(2)
1.696(9)
1.69(2)
1.68(4)
1.681(7)
1.655(1)
1.710(7)
1.744(1)
1.706(9)
1.71
1.76
1.724
1.67
1073
1104
1088
1088
1078
1096
1098
891, 871
888
894
[NOsO3]Ϫ in 7
[Au(PPh3)(NOsO3)]b
cis-[Pt(PMe3)2(NOsO3)2]b
trans-[Pt(Bupy)2(NOsO3)2]
[Pt(dppf)(NOsO3)Cl]
[Ir(CO)(PPh3)2(NOsO3)]
[{Rh(cod)}2(µ-NOsO3)2]
[Os(NBut)O3]c
894
888, 906
888, 908
886, 896, 908
904
1.718
1.697
1.715
1184
912, 925
a
Structural data for Cs[NOsO3], Raman spectrum of aqueous K[NOsO3] (ref. 17). b Ref. 5. c Ref. 18.
᎐
[L M᎐N᎐OsO ], indicating that the donor strength of nitride is
᎐
References
n
3
significantly reduced upon formation of a C᎐N covalent bond.
1 R. Criegee, Justus Liebigs Ann. Chem., 1936, 522, 75; M. Schröder,
Chem. Rev., 1980, 80, 107 and refs. therein; W. B. Motherwell
and A. S. Williams, Angew. Chem., Int. Ed. Engl., 1995, 34,
2031.
2 K. B. Sharpless, D. W. Patrick, L. K. Truesdale and S. A. Biller,
J. Am. Chem. Soc., 1975, 97, 2305; K. B. Sharpless, A. O. Chong and
K. Oshima, J. Org. Chem., 1976, 41, 177.
Structural and IR spectral data for osmate(VIII) complexes
Table 7 summarises the structural and IR spectra data for the
᎐
nitrido-bridged osmate() complexes [L M᎐N᎐OsO ]. It
᎐
n
3
᎐
appears that neither the Os᎐N nor the Os᎐O distances for these
᎐
᎐
complexes are significantly changed upon co-ordination to the
3 H. C. Holb, M. S. VanNieuwenhze and K. B. Sharpless, Chem. Rev.,
1994, 94, 2483 and refs. therein.
metal (M) despite the large estimated standard deviation (e.s.d.)
4 G. Liu, H. T. Chang and K. B. Sharpless, Angew. Chem., Int. Ed.
Engl., 1996, 35, 45; J. Rudolph, P. C. Sennhenn, C. P. Vlaar and
K. B. Sharpless, Angew. Chem., Int. Ed. Engl., 1996, 35, 2810; G. Li,
H. H. Angert and K. B. Sharpless, Angew. Chem., Int. Ed. Engl.,
1996, 35, 2813.
5 W.-H. Leung, J. L. C. Chim and W.-T. Wong, J. Chem. Soc., Dalton
Trans., 1996, 3153.
6 A. F. Clifford and C. S. Kobayashi, Inorg. Synth., 1960, 6, 204.
7 G. B. Kauffamn, Inorg. Synth., 1963, 7, 249.
8 M. P. Brown, R. J. Puddephatt, M. Rashidi and K. R. Seddon,
J. Chem. Soc., Dalton Trans., 1977, 951.
9 J. P. Collman and M. Kubota, Inorg. Synth., 1990, 28, 92.
10 U. Kölle, R. Görissen and T. Wagner, Chem. Ber., 1995, 128,
911.
11 D. A. Clemente, G. Pilloni, B. Corain, B. Longato and
M. Tiripicchio-Camellini, Inorg. Chim. Acta, 1986, 115, L9.
12 N. W. Hoffman, N. Prokopuk, M. J. Robbins, C. M. Jones and
N. M. Doherty, Inorg. Chem., 1991, 30, 4177.
13 M. Rahim and K. J. Ahmed, Organometallics, 1994, 13, 1751.
14 G. J. Leigh and R. L. Richards, in Comprehensive Organometallic
Chemistry, eds. G. Wilkinson, F. G. A. Stone and E. W. Abel,
Pergamon, Oxford, vol. 5, p. 543.
᎐
values for these structural data. In all cases, the Os᎐N᎐M link-
᎐
᎐
age is linear with an Os᎐N triple bond and an M᎐N single
᎐
bond. This suggests that these bimetallic complexes are best
formulated as the unsymmetrically nitrido-bridged complexes
[L M᎐N᎐OsO ].19 Unlike imido(trioxo)osmium() complexes
᎐
᎐
n
3
᎐
[Os(NR)O ], the M᎐N bond in [L M᎐N᎐OsO ] is of donor–
᎐
3
n
3
acceptor type only and is rather weak. Accordingly, the [NOsO3]
group in these complexes is found to be substitution labile.
The IR stretching frequency is found to be more sensitive
than the bond length to the change in bond strength. In general,
᎐
ν(Os᎐N) for [NOsO ] increases upon co-ordination to metal. A
᎐
3
similar observation has been reported for the complexation of
Lewis acids with [Re(N)Br4]Ϫ.20 The strengthening of the Os᎐N
᎐
᎐
bond in [NOsO3]Ϫ upon metal complexation may be explained
by the fact that the lone pair on the nitride has anti-bonding
᎐
character. In addition, ν(Os᎐O) for [L M᎐N᎐OsO ] complexes
᎐
᎐
n
3
are found to be higher than those for [NOsO3]Ϫ, indicating
that the donor strength of the nitride is weakened upon co-
᎐
ordination to metal. For [L M᎐N᎐OsO ] ν(Os᎐O) is, however,
᎐
᎐
n
3
15 D. J. Berrisford, C. Bolm and K. B. Sharpless, Angew. Chem., Int.
Ed. Engl., 1995, 34, 1059.
16 C. A. Reed and W. R. Roper, J. Chem. Soc., Dalton Trans., 1973,
1370.
lower than that for [Os(NR)O3] (Table 7) because the donor–
acceptor type M᎐N bond is weaker than a C᎐N covalent bond.
On the basis of ν(Os᎐O) it can be concluded that the donor
᎐
strength for NX in [Os(NX)O3] decreases in the order
17 W. A. Nugent and J. M. Mayer, Metal-Ligand Multiple Bonds,
Wiley, New York, 1988, p. 126.
18 B. S. McGilligan, J. Arnold, G. Wilkinson, B. Hussain-Bates and
M. B. Hursthouse, J. Chem. Soc., Dalton Trans., 1990, 2465.
19 K. Dehnicke and J. Strähle, Angew. Chem., Int. Ed. Engl., 1992, 31,
955.
N3Ϫ > (LnMN)2Ϫ > RN2Ϫ, which is consistent with the electro-
᎐
chemical data (see above). The complexes [L M᎐N᎐OsO ] are
᎐
n
3
less reactive than [Os(NR)O3], e.g. in cycloaddition reactions
with alkenes,2 possibly because the former complexes are more
electron-rich and thus less electrophilic than the latter.
20 W. Kafitz, F. Weller and K. Dehnicke, Z. Anorg. Allg. Chem., 1982,
590, 175.
Acknowledgements
The financial support from the Hong Kong University of
Science and Technology and the Hong Kong Research Grants
Council is gratefully acknowledged.
Received 8th April 1997; Paper 7/02404E
3282
J. Chem. Soc., Dalton Trans., 1997, Pages 3277–3282