Reactivity of an N-mesityl bis(phosphinimino)methane with group 10 metals

Article abstract of DOI:10.1016/j.poly.2006.10.020

In an attempt to form a group 10 'carbenoid' derivative by double deprotonation of the N-mesityl substituted bis(phosphinimino)methane [CH₂(Ph₂P{double bond, long}N-2,4,6-Me₃C₆H₂)₂], reaction with [PdCl₂(MeCN)₂] yielded a singly metallated dichloropalladate(II) complex as the only product. This was completely characterised specroscopically and by single crystal crystal X-ray diffraction. In contrast, reaction of [CH₂(Ph₂P{double bond, long}N-2,4,6-Me₃C₆H₂)₂] with [PtMe₂(COD)] produced a bis(phosphinimino)methanide complex, which had also undergone ortho-metallation of two P-phenyl groups to effect a triple C-H activation reaction.

Full text of DOI:10.1016/j.poly.2006.10.020

Polyhedron 26 (2007) 1245–1250
www.elsevier.com/locate/poly
Reactivity of an N-mesityl bis(phosphinimino)methane with
group 10 metals
a,
b
Michael S. Hill *, Peter B. Hitchcock
a
Department of Chemistry, Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, UK
b
The Chemistry Laboratory, University of Sussex, Falmer, Brighton, East Sussex BN1 9QJ, UK
Received 6 September 2006; accepted 13 October 2006
Available online 19 October 2006
Abstract
In an attempt to form a group 10 ‘carbenoid’ derivative by double deprotonation of the N-mesityl substituted bis(phosphini-
mino)methane [CH2(Ph2P@N-2,4,6-Me3C6H2)2], reaction with [PdCl2(MeCN)2] yielded a singly metallated dichloropalladate(II) com-
plex as the only product. This was completely characterised specroscopically and by single crystal crystal X-ray diffraction. In
contrast, reaction of [CH2(Ph2P@N-2,4,6-Me3C6H2)2] with [PtMe2(COD)] produced a bis(phosphinimino)methanide complex, which
had also undergone ortho-metallation of two P-phenyl groups to effect a triple C–H activation reaction.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Platinum; Palladium; Phosphiniminomethanide
1. Introduction
with the dilithio bis(phosphinimino)methanediide, [Li2C-
(Ph2P@NSiMe3)2]2 IV. As the N-mesityl analogue of the
unusual dianion IV is not yet available, we report here
our attempts to develop alternative routes to similar ‘carb-
enoid’ compounds of the heavier group 10 metals, palla-
dium and platinum. Although this has not yet been
successful, we have uncovered some notable contrasts in
the outcome of reactions of M(II) centres toward the pro-
tonated version of II, the bis(phosphinimino)methane,
[CH2(Ph2P@N-2,4,6-Me3C6H2)2], V resulting in the forma-
tion and characterisation of the palladium(II) and plati-
num(II) organometallics, compounds 1 and 2 (Chart 1).
Great attention has recently been directed toward the
coordination chemistry of a variety of N,N-bidentate
monoanions such as those illustrated in Chart 1. Although
the b-diketiminato ligand structure, I [1] has been especially
prominent, a number of topologically related ligand systems
have also attracted attention. We, and others, have
employed the N-mesityl bis(phosphinimino)methanide, II
(and its N-SiMe3 substituted analogue) as a supporting
environment for explorations of low-coordinate main group
and mid (groups 7–9) transition metal reactivity [2–4].
While the use of I has enabled notable advances in under-
standing of the discrete molecular steps involved in alkane
activation chemistry by Pt(II) and Pt(IV) centres [5], the
researches of Cavell and co-workers have realised a fasci-
nating variety of unusual reactivities and structures derived
from the platinum-coordinated ‘carbenoid’ ligand complex,
II [6]. Compound II is derived by reaction of [PtCl2(COD)]
2. Results and discussion
Reaction of V with a single molecular equivalent of
[PdCl2(NCMe)2] in CH2Cl2 produced an immediate colour
change to dark orange at room temperature. Work up and
crystallisation from hexane produced dark red crystals of
an air stable compound, 1, which was characterised by
1
solution H, 13C and 31P NMR spectroscopies and (FAB)
*
mass spectrometry. This latter technique revealed a highest
mass fragment of 792 consistent with loss of HCl and
Corresponding author. Tel.: +44 207 594 5709; fax: +44 207 594 5804.
E-mail address: mike.hill@imperial.ac.uk (M.S. Hill).
0277-5387/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2006.10.020

1246
M.S. Hill, P.B. Hitchcock / Polyhedron 26 (2007) 1245–1250
H
nation of the ligand precursor had occurred under these
H
mild conditions, compound 1 also contained the HCl liber-
ated during the deprotonation process and may be best
described as a dichloropalladate(II). The molecular struc-
ture of 1 is illustrated in Fig. 1. Details of the X-ray anal-
ysis are provided in Table 1, while selected bond lengths
and angles are provided in Tables 2 and 3, respectively.
Coordination around the palladium centre is approxi-
mately square planar. Two of the coordination sites about
Pd are occupied by the three-membered chelate provided
by the methanide carbon (C1) centre and one of the phos-
phinimino substituents of the j-C,j-N bis(phosphin-
imo)methanide ligand. The chlorides occupy the two
remaining sites. Despite the restricted bite angle of the
three-membered N(1)–P(1)–C(1) chelate [N(1)–Pd–C(1),
Ph2P
N
PPh2
N
_
iPr
iPr
_
N
N
Pri
iPr
II
I
SiMe3
H
H
Ph2P
N
Ph2P
N
PPh2
N
Pt
Ph2P
N
V
Me3Si
III
Ph
NMes
Ph2P
P
MesN
Table 1
Pd
Cl
Cl
Pt
NCMe
Selected data collection parameters for compounds 1 and 2
Ph
1
2
Ph2P
P
H
H
N
Chemical formula
Formula weight
T (K)
C
828.06
173(2)
43H44Cl2N2P2Pd C45H42D3N3P2Pt(C2D3N)
N
Mes
Mes
931.9
173(2)
2
1
Crystal size (mm3)
Crystal system
Space group
0.30 · 0.25 · 0.20 0.25 · 0.20 · 0.10
monoclinic
P21/c (No. 14)
22.0530(3)
11.2115(1)
16.7783(2)
90
106.964(1)
90
4
3967.88(8)
1.38
0.72
3.72–27.49
0.036, 0.068
0.053, 0.073
monoclinic
P21/c (No. 14)
10.6441(1)
17.3375(2)
22.4742(3)
90
97.576(1)
90
4
4111.23(8)
1.51
3.53
3.75–25.70
0.032, 0.072
0.035, 0.073
Chart 1.
˚
a (A)
˚
formation of the singly metallated complex [Pd(II)Cl]. The
solution spectroscopic data were not however consistent
with this, likely, square planar and symmetrical configura-
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
Z
1
tion. The H NMR spectrum revealed two singlet reso-
nances for each of the ortho- and para-methyls as well as
the meta-methine centres of two inequivalent N-mesityl
substituents. The P-phenyl region of the spectrum was also
considerably more complex than anticipated. The 31P{1H}
NMR spectrum indicated an unsymmetrical disposition
of the bis(phosphinimino)methanide ligand and appeared
as an AX pair of doublet signals centred at 39.9 and
27.6 ppm [2JPP = 15.4 Hz].
3
˚
V (A )
dcalc (Mg mÀ3
)
l (mmÀ1
h Range (ꢁ)
)
R1; wR2 [I > 2r(I)]
R1; wR2 all data
Measured/independent
reflections/Rint
Reflections with
I > 2r(I)
49405/9050/0.055 65986/7674/0.053
7456 7092
This inference was confirmed by a single crystal X-ray
diffraction analysis, which revealed that, although deproto-
Fig. 1. ORTEP drawing (30% ellipsoids) of compound 1. Hydrogen atoms except those attached to C1 and N2 removed for clarity.

M.S. Hill, P.B. Hitchcock / Polyhedron 26 (2007) 1245–1250
1247
Table 2
chelated ligand. Any effect is probably offset by the relative
trans influences of the C(1) and N(1) donors.
˚
Selected bond lengths (A) for compounds 1 and 2
1
2
It did not prove possible to enforce any further deproto-
nation of the C(1) centre within compound 1, to produce
palladium carbenoid species analogous to III, either by
heating (100 ꢁC) or by addition of an external base
(DBU, Et3N). Monitoring of these reactions by 31P{1H}
NMRin d8-toluene indicated either decomposition to
complex mixtures of products or no apparent reaction
respectively.
Pd–N(1)
Pt–N(3)
M–C(1)
Pd–Cl(2)
Pd–Cl(1)
Pt–C(15)
Pt–C(3)
2.043(2)
2.003(4)
2.051(4)
2.103(2)
2.3177(6)
2.3257(6)
2.051(4)
2.074(4)
1.643(4)
1.789(4)
1.771(4)
1.805(5)
1.572(4)
1.804(4)
1.801(4)
1.829(5)
1.437(6)
1.407(6)
P(1)–N(1)
P(1)–C(1)
P(1)–C(2)
P(1)–C(8)
P(2)–N(2)
P(2)–C(1)
P(2)–C(14)
P(2)–C(20)
N(1)–C(26)
N(2)–C(35)
1.594(2)
1.784(2)
1.803(2)
1.807(2)
1.639(2)
1.768(2)
1.797(3)
1.801(2)
1.425(3)
1.441(3)
Although the directly analogous reaction of V and
[PtCl2(NCMe)2] has not yet yielded identifiable products,
reaction of [Pt(PPh2Me)Cl(l-Cl)]2 and a closely related
N-tolyl-substituted bis(phosphinimino)methane has been
reported by Elsevier and co-workers to produce the
similarly N,C-coordinated complex [PtCl(PPh2Me){CH-
(Ph2PNC6H4-4-Me)(Ph2P@N(H)C6H4-4-Me)}]+Cl
[7].
This cation was also formed irrespective of added base
and, for this reason, we attempted the alternative meth-
ane-elimination route to the platinum carbenoid species
illustrated in Scheme 1. Extended heating and NMR (1H,
31P{1H}) monitoring of an NMR-scale reaction of [PtMe2-
(COD)] and V in C6D6 indicated that no reaction had
occurred. In contrast, a similar reaction performed in d3-
MeCN resulted in the complete disappearance of Pt–Me
resonance at 0.63 ppm in the 1H NMR spectrum after
18 h at 100 ꢁC. These conditions also resulted in the loss
of the characteristic methylene triplet of V centred at
4.01 ppm and the appearance of a series of resonances con-
sistent with the formation of unligated COD. Attempted
31P NMR monitoring of this reaction at regular intervals
over a 7 day period was not informative and revealed only
the resonances due to the starting material and several
unidentifiable resonances, which, once apparent, did not
alter in relative intensity. Upon slow cooling, however,
colourless crystals of compound 2 deposited within the
NMR tube, and we assume that plausible intermediates
(vide infra) are either short-lived or present in too low
concentration as to be observable, while the ultimate prod-
uct, compound 2, deposits and is depleted from solution as
the reaction proceeds and is thus not observed. The crystal-
line material would not redissolve in d3-MeCN, but proved
to be highly soluble in CDCl3 enabling the full spectro-
scopic characterisation of compound 2. Although the
31P{1H} NMR spectrum consisted of a single resonance
at 46.0 ppm, indicative of symmetrical coordination of
the deprotonated ligand, it was apparent that the desired
Table 3
Selected bond angles (ꢁ) for compounds 1 and 2
1
2
N(1)–Pd–C(1)
N(3)–Pt–C(1)
75.74(8)
178.84(16)
93.19(16)
N(3)–Pt–C(15)
N(1)–Pd–Cl(2)
C(1)–Pd–Cl(2)
N(1)–Pd–Cl(1)
C(1)–Pd–Cl(1)
Cl(2)–Pd–Cl(1)
C(1)–Pt–C(15)
N(3)–Pt–C(3)
172.33(6)
96.62(6)
94.91(6)
169.38(7)
92.63(2)
85.83(16)
92.37(17)
88.59(17)
174.29(17)
111.5(2)
110.9(2)
104.9(2)
110.6(2)
107.7(2)
111.1(2)
108.1(2)
121.1(2)
99.3(2)
C(1)–Pt–C(3)
C(15)–Pt–C(3)
N(1)–P(1)–C(1)
N(1)–P(1)–C(2)
C(1)–P(1)–C(2)
N(1)–P(1)–C(8)
C(1)–P(1)–C(8)
C(2)–P(1)–C(8)
N(2)–P(2)–C(1)
N(2)–P(2)–C(14)
C(1)–P(2)–C(14)
N(2)–P(2)–C(20)
C(1)–P(2)–C(20)
C(14)–P(2)–C(20)
C(26)–N(1)–P(1)
C(26)–N(1)–Pd
P(1)–N(1)–Pd
C(35)–N(2)–P(2)
P(2)–C(1)–P(1)
P(2)–C(1)–M
97.62(10)
114.29(10)
118.32(11)
117.54(11)
106.27(11)
103.27(11)
107.42(11)
104.24(11)
112.19(12)
110.44(12)
111.31(11)
110.95(12)
136.76(17)
126.16(15)
94.14(9)
112.9(2)
109.7(2)
104.7(2)
119.9(3)
124.22(18)
125.87(13)
115.63(12)
86.78(10)
134.2(3)
119.4(2)
109.1(2)
108.3(2)
P(1)–C(1)–M
Mes
Ph2P
N
75.74(8)ꢁ], the remaining angles provided by the cis-dis-
posed ligands are close to 90ꢁ. The Pd–Cl bond distances
V
+
[PtMe2(COD)]
Pt
X
, C6D6 or d3 -MeCN
˚
Ph2P
[Pd–Cl(1) 2.3257(6), Pd–Cl(2) 2.3177(6) A] are similar
N
despite the increased coordination number of the Cl(2) cen-
tre which displays an additional hydrogen bonded interac-
tion to the N(2) proton of the ‘free’ P(2)–N(2) arm of the
Mes
Scheme 1.

1248
M.S. Hill, P.B. Hitchcock / Polyhedron 26 (2007) 1245–1250
synthesis of a carbenoid species had again been unsuccess-
ful. Compound 2 did not contain coordinated COD and it
was clear that the PCH2P methylene of V had not been
doubly deprotonated as evidenced by a triplet resonance
the X-ray analysis are provided in Table 1, while selected
bond lengths and angles are provided in Tables 2 and 3
respectively. Three coordination sites about the square pla-
nar platinum centre are provided by the deprotonated C(1)
methanide carbon and two bonds to sp2 carbon atoms
which have been formed by ortho-metallation of two of
the P-bound phenyl rings. A coordinated molecule of ace-
tonitrile, trans to the methanide carbon centre, occupies the
remaining coordination site. Charge balance is maintained
by protonation of one of the non-coordinated phosphini-
mine (N1) nitrogen atoms. The resulting chemical inequiv-
alence of the phosphorus nuclei was not, however,
apparent in the NMR spectra most likely due to rapid
exchange of the proton between the two phosphinimino
nitrogen centres and the development of apparent C2 sym-
metry. Although the bond lengths and angles within the
structure itself are entirely normal and consistent with pre-
viously reported Pt(II) alkyl and aryl derivatives [8], and
such intramolecular aromatic substitution by late transi-
tion metal complexes has been known to occur for over
40 years [9], a transformation of a neutral bis(phosphini-
mino)methane into a formally trianionic chelate is unique.
It is interesting to note that Cavell has reported that III
underwent thermally initiated ortho-metallation of a single
P-phenyl with concomitant protononation of the carbe-
noid C@Pt bond [6a]. This latter process occurred diastere-
oselectively to generate P and C stereocentres with fixed
relative absolute configurations and it was speculated that
metallation involved the intermediacy of an undetectable
platinum(IV) hydride intermediate. The formation of com-
pound 2 occurred with similar diastereoselectivity and,
although we have not yet definitively identified any inter-
mediates and a number of viable alternative pathways
may be envisaged, it is plausible that 2 results from a sim-
ilar mechanism (Scheme 2) and the intermediacy of a carb-
enoid species similar to that depicted in Scheme 1.
1
(1H by integration) at 3.26 ppm (2JPP = 9.2 Hz) in the H
NMR spectrum. Attempts to acquire 195Pt NMR data were
unsuccessful, most likely due to the anisotropic magnetic
environment of the metal centre.
The origin of these solution data was made clear by a
single crystal X-ray analysis performed on crystals of com-
pound 2. The results of this study, illustrated in Fig. 2, were
consistent with the solution data and revealed that V had
undergone a triple C–H activation reaction. Details of
Fig. 2. ORTEP drawing (30% ellipsoids) of compound 2. Hydrogen
atoms except those attached to C1 and N1 removed for clarity.
Mes
Mes
H
Mes
N
N
Ph2P
Ph2P
Ph2P
Ph2P
N
Ph2P
Ph2P
-CH4
-CH4
+ M
V
+
PtMe2(MeCN)2
Pt
N
CH3
Pt
N
Pt
N
NCMe
- 2MeCN
eC
N
CH3
Mes
Mes
Mes
ortho-activation
Ph
Ph
Ph
H+ transfer
PtIV→PtII
ortho-activation
MesN
P
P
P
MesN
H
MesN
Pt
NCMe
Ph
Pt NCMe
H+ transfer
Pt
N
NCMe
Mes
P
H
Ph2P
N
Ph2P
N
Mes
Mes
Scheme 2. Proposed ‘carbenoid’ pathway to compound 2.

M.S. Hill, P.B. Hitchcock / Polyhedron 26 (2007) 1245–1250
1249
1
We are continuing to investigate this hypothesis and will
report the outcome of these studies in a future publication.
Pt–Me signal (0.62 ppm) in the H spectrum and the 31P
NMR (À17 ppm) signal for V had completely disappeared.
Upon standing at room temperature overnight colourless
crystals of compound 2 deposited and were isolated by fil-
tration (0.07 g, 70%). A sample for analysis was prepared
by grinding and exposure to a dynamic vacuum. Anal.
Calc. for C43H43D3N3P2Pt: C 60.86, H 4.78, N 4.73.
3. Experimental section
All manipulations were carried out using standard
Schlenk and glovebox techniques under an inert atmo-
sphere of either nitrogen or argon. All solvents were dis-
tilled under nitrogen and dried with conventional drying
agents. NMR spectra were recorded at 270 or 500 (1H),
125.8 (13C) and 202.5 (31P) MHz from samples in either
C6D6 or d8-toluene or CDCl3; chemical shifts are given rel-
ative to SiMe4. Mass spectra were recorded under fast
atom bombardment (FAB) on samples in a matrix of
nitrobenzyl alcohol. In spectral assignments Mes = 2,4,6-
trimethylphenyl. The ligand precursor V was synthesised
by a literature procedure [4g].
1
Found: C 60.65, H 4.65, N 4.80. H NMR (CDCl3); d
2.11 (s, 6H, p-Me), 2.14 (s, 12H, o-Me), 3.26 (t, 1H,
2JHP = 9.2 Hz, JHPt = 54 Hz, PCHP), 6.60 (s, 4H, m-
2
CH,mes), 6.82 (4, 6H, o-CH,PhP), 7.16–7.51 (m, 18H,
Ph–P). 13C NMR (CDCl3): d 19.9 (p-Me), 20.9 (o-Me),
30.9 (CHP) 122.3 (Ar), 127.9 (Ar), 128.4 (Ar), 130.8 (Ar),
131.8 (Ar), 136.5. 31P{1H} NMR (CDCl3): d 46.0. MS
(FAB: m/z): 888 [30, M+], 844 [10, M+Àd3-MeCN], 650
[5], 277 [100], 57 [70].
5. Crystal structure determinations
3.1. Preparation of compound 1
Data for 1 and 2 were collected at 173 K on a Nonius
KappaCCD diffractomer, k(Mo-Ka) = 0.71073 A. An
A solution of V (0.25 g, 3.8 mmol), in CH2Cl2 (10 cm3)
was added at room temperature to a CH2Cl2 (10 cm3) solu-
tion of [PdCl2(NCMe)2] (0.1 g, 3.8 mmol), resulting in an
immediate colour change from yellow to orange/red. This
solution was stirred for 14 h before complete removal of
volatiles. The red solid was crystallised from hexane at
room temperature to yield 1 as dark red crystals (0.25 g,
79%). Anal. Calc. for C43H44Cl2N2P2Pd: C, 62.38; H,
5.31; N, 3.38. Found: C, 62.55; H, 5.50; N, 3.23%. 1H
NMR (CDCl3); d 1.39 (s, 3H, p-Me, mesN), 1.54 (s, 3H,
p-Me, mesN@P), 1.96 (s, 6H, o-Me, mesN), 1.99 (s, 6H,
˚
absorption correction (MULTISCAN) was applied. The struc-
tures were solved by direct methods (SHELXS-97) [10] and
refined by full matrix least squares (SHELXL-97) [11] with
non-H atoms anisotropic and H atoms included in riding
mode except for the H atoms on C1 and N1 of compound
1, and C1 and N1 of compound 2 which were refined.
Acknowledgement
We thank the Royal Society for a University Research
Fellowship (M.S.H.).
2
p-Me, mesN@P), 2.78 (dd, 1H, JPH = 14.8, 1.6 Hz,
PCHP), 5.25 (s, 1H, NH), 6.39 (s, 2H, m-CH, mesN),
6.39 (s, 2H, m-CH, mesN@P), 6.80–8.20 (m, 20H, Ph–P).
Appendix A. Supplementary material
1
13C NMR (CDCl3): d À15.5 (dd, JPP = 79.2, 75.5 Hz,
PCP), 20.4 (o-Me), 20.7 (o-Me), 20.8 (p-Me), 122.1 (d,
CCDC 285813 and 285814 contain the supplementary
crystallographic data for 1 and 2. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts.retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit
@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2006.10.020.
1
1JPP = 93.1 Hz, i–CP), 125.2 (Ar), 125.4 (d, JPP
=
106.9 Hz, i–CP), 127.9 (d, JPP = 12.5 Hz, PhP), 128.1
(Ar), 128.4 (d, JPP = 11.3 Hz, PhP), 128.4, 128,7, 128.8
(Ar), 129.5 (d, JPP = 11.3 Hz, PhP), 131.8 (d, JPP
=
23.9 Hz, PhP), 131.8 (Ar), 132.6 (Ar), 132.9 (d,
JPP = 12.0 Hz, PhP), 133.4 (d, JPP = 16.3 Hz), 133.8 (Ar),
134.4 (d, JPP = 11.0 Hz, PhP), 135.9 (Ar), 136.3, 136.4
(Ar), 136.7 (d, JPP = 8.9 Hz, PhP), 137.8 (Ar). 31P{1H}
2
NMR (CDCl3): d 27.6 (d, JPP = 15.4 Hz), 39.9 (d,
2JPP = 15.4 Hz). MS (FAB: m/z): 792 [2, M+ÀHCl], 756
[5, M+ÀHClÀCl], 651 [5], 440 [100], 330 [40], 183 [35],
147 [55].
References
[1] For a general review of b-diketiminate chemistry, see: L. Bourget-
Merle, M.F. Lappert, J.R. Severn, Chem. Rev. 102 (2002) 3031.
[2] (a) Examples of s-block bis(phosphinimino)methanide complexes:
M.T. Gamer, P.W. Roesky, Z. Anorg. Allg. Chem. 627 (2001) 877;
(b) R.P.K. Babu, A. Kasani, R. McDonald, R.G. Cavell, Inorg.
Chem. 39 (2000) 4981;
4. Preparation of compound 2
A mixture and [PtMe2(COD)] (0.035 g, 0.11 mmol) and
V (0.070 g, 0.11 mmol) were dissolved in d3-MeCN and
transferred to an NMR tube equipped with a Youngs
tap. Initial NMR analysis of the pale yellow solution indi-
cated that no reaction had occurred. The NMR tube was
then heated to 100 ꢁC for 18 hours, after which time the
(c) R.P.K. Babu, A. Kasani, R. McDonald, R.G. Cavell, Organo-
metallics 20 (2001) 1451;
(d) P. Wei, D. Stephan, Organometallics 22 (2003) 601;
(e) M.S. Hill, P.B. Hitchcock, Chem. Commun. (2003) 1758;
(f) T.K. Panda, A. Zulys, M.T. Gamer, P.W. Roesky, J. Organomet.
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M.S. Hill, P.B. Hitchcock / Polyhedron 26 (2007) 1245–1250
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`
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