Carbonyl complexes of platinum(0): Synthesis and structure of [(Cy 3P)2Pt(CO)] and [(Cy3P)2Pt(CO) 2]

Article abstract of DOI:10.1021/ic102200t

The platinum(0) monocarbonyl complex, [(Cy₃P) ₂Pt(CO)], was synthesized by reaction of [(Cy₃P) ₂Pt] with [(η⁵-C₅Me₅)Ir(CO) ₂] and subsequent irradiation. X-ray structu

Full text of DOI:10.1021/ic102200t

1816 Inorg. Chem. 2011, 50, 1816–1819
DOI: 10.1021/ic102200t
Carbonyl Complexes of Platinum(0): Synthesis and Structure of [(Cy3P)2Pt(CO)]
and [(Cy3P)2Pt(CO)2]
Stefanie Bertsch, Holger Braunschweig,* Melanie Forster, Katrin Gruss, and Krzysztof Radacki
€
€
€
Institut fu€r Anorganische Chemie, Julius-Maximilians-Universitat Wurzburg, Am Hubland, 97074 Wurzburg,
Germany
Received November 8, 2010
The platinum(0) monocarbonyl complex, [(Cy3P)2Pt(CO)], was synthesized by reaction of [(Cy3P)2Pt] with [(η5-
C5Me5)Ir(CO)2] and subsequent irradiation. X-ray structure analysis was performed and represents the first structural
evidence of a platinum(0) monocarbonyl complex bearing two free phosphine ligands. Its corresponding dicarbonyl
complex [(Cy3P)2Pt(CO)2] was synthesized by treatment of [(Cy3P)2Pt] with CO at -40 °C and confirmed by X-ray
structure analysis.
Scheme 1. Synthesis of the Triangular Cluster 2
Introduction
Early work on platinum carbonyl complexes dates back to
the late 1950s, when the search for well-defined carbonyl
complexes of platinum(0) led to the discovery of numerous
structural motifs.1 As far as platinum(0) carbonyl complexes
with phosphines as sole coligands are concerned, multinuclear
clusters as well as monocarbonyl and dicarbonyl compounds
are long known. A first outlook on phosphine derivatives of
platinum(0) carbonyl complexes was given by Malatesta and
Cariello2 and further investigated by Booth, Chatt, and
to -65 °C resulted in the conversion to the spectroscopically
Chini.3 Crystal structure determination of the clusters
[(Cy3P)3Pt3(CO)3]4 and [(Cy3P)4Pt3(CO)3]5 followed a few
years later. Numerous platinum carbonyl phosphine cluster
types with a variety of compositions have been prepared since
then.6 An interesting system is the dinuclear species [Pt2(μ-
PtBu2)2(H)2(PtBu2H)2] (1) which converts to [Pt3(μ-PtBu2)3-
H(CO)2] (2) under a CO atmosphere (Scheme 1). Treatment
of 1 in the presence of an excess of phosphines led to the
formation of the monocarbonyl derivatives [(R3P)3Pt(CO)]
(R3=Ph3, Et3, tBu2H).7
characterized [(Ph3P)2Pt(CO)2].8 To the best of our knowl-
edge, the only structural evidence for a dicarbonyl phos-
phine platinum complex was provided in the case [(EtPh2P)2-
Pt(CO)2] (4).9 A typical reaction pathway to obtain this species
is the reductive elimination of a suitable leaving group from a
platinum(II) center in the presence of CO.10 Thus, the afore-
mentioned dicarbonyl complex [(Ph3P)2Pt(CO)2] is also acces-
sible by reaction of [(Ph3P)2Pt(H)Cl] EtOH with CO.11
3
The known platinum monocarbonyl compounds incorpo-
rate either three phosphines or chelating bis(phosphine) li-
gands. [(Ph3P)3Pt(CO)] (3), reported by Bellon et al. in 1969,
represents the first structural characterization of this type of
compound.12
Low-temperature treatment of [(Ph3P)3Pt] with CO at -80 °C
also afforded [(Ph3P)3Pt(CO)] (3), and subsequent warming
*To whom correspondence should be addressed. E-mail: h.braunschweig@
mail.uni-wuerzburg.de. Fax: þ49-(0)931/31-84623. Tel: þ49-(0)931/31-85260.
(1) Tripathi, S. C.; Srivastava, S. C.; Mani, R. P.; Shrimal, A. K. Inorg.
Chim. Acta 1976, 17, 257.
Chelating phosphine ligands were important for the synth-
esis of platinum monocarbonyl complexes bearing only
two phosphine centers. The reaction of [(dfepe)Pt(μ-H)]2
(2) Malatesta, L.; Cariello, C. J. Chem. Soc. 1958, 2323.
(3) (a) Booth, G.; Chatt, J.; Chini, P. Chem. Commun. 1965, 639. (b) Booth,
G.; Chatt, J. J. Chem. Soc. A 1969, 14, 2131.
(8) Sen, A.; Halpern, J. Inorg. Chem. 1980, 19, 1073.
(9) (a) Chini, P.; Longoni, G. J. Chem. Soc. A 1970, 1542. (b) Albano, V. G.;
Bellon, P. L.; Manassero, M. J. Organomet. Chem. 1972, 35, 423.
(10) (a) Iverson, C. N.; Smith, M. R., III Organometallics 1996, 15, 5155.
(b) Willis, R. R.; Shuchart, C. E.; Wojcicki, A.; Rheingold, A. L.; Haggerty, B. S.
Organometallics 2000, 19, 3179.
(11) Grushin, V. V.; Akhrem, I. S.; Vol’pin, M. E. Metalloorg. Khim.
1988, 1, 474.
(12) Albano, V.; Bellon, P. L.; Sansoni, M. J. Chem. Soc. D 1969, 899.
(4) Albinati, A. Inorg. Chim. Acta 1977, 22, L31.
(5) Albinati, A.; Carturan, G.; Musco, A. Inorg. Chim. Acta 1976, 16, L3.
(6) (a) Dahmen, K. H.; Moor, A.; Naegeli, R.; Venanzi, L. M. Inorg.
Chem. 1991, 30, 4285. (b) Sterenberg, B. T.; Ramachandran, R.; Puddephatt, R. J.
J. Cluster Sci. 2001, 12, 49. (c) Beni, Z.; Ros, R.; Tassan, A.; Scopelliti, R.;
Roulet, R. Inorg. Chim. Acta 2005, 358, 497.
(7) Leoni, P.; Manetti, S.; Pasquali, M.; Albinati, A. Inorg. Chem. 1996,
35, 6045.
r
pubs.acs.org/IC
Published on Web 01/25/2011
2011 American Chemical Society

Article
Inorganic Chemistry, Vol. 50, No. 5, 2011 1817
Scheme 2. Reaction of 5 with CO
Scheme 3. Formation of the Platinum Monocarbonyl Complex 8
(dfepe = (C2F5)2PCH2CH2P(C2F5)2) (5) with CO gave access
to both the mono- and dicarbonyl products 6 and 7, though 7
could not be isolated due to the facile loss of CO (Scheme 2).
However, neither complex could be characterized in the crystal.13
The same group showed that, in addition to Pt(0) systems,
cationic (fluoroalkyl)phosphine Pt(II) mono- and dicarbonyl
complexes are also accessible.14
required treatment of [(Cy3P)2Pt] with [(η5-C5Me5)Ir(CO)2]
as a selective source for 1 equiv of CO under photolytic con-
ditions, whereupon one carbonyl ligand is transferred from
the iridium to the platinum center.
The synthesis of monocarbonyl platinum complexes was
motivated by our search for suitable precursors for borylene-
carbonyl exchange reactions, thus allowing for the synthesis
of platinum(0)borylene complexes. Despite the rather well-
developed chemistry of borylene complexes,15 corresponding
mononuclear species deriving from platinum are still re-
stricted to only two examples, which display platinum in
the formal oxidation state of þII.16
After workup, the monocarbonyl complex 8 is isolated as
an orange crystalline material in 31% yield. The 31P NMR
spectrum reveals a signal at 63.7 ppm similar to that of the
starting material [(Cy3P)2Pt] (62.3 ppm, 1JP-Pt = 4160 Hz),
with a marginally lower coupling constant of 1JP-Pt = 4101 Hz.
The crystal structure of 8 revealed a C2v symmetric molecule
displaying a trigonal-planar coordinated platinum center
Herein we present the synthesis and structural character-
ization of [(Cy3P)2Pt(CO)] (8), the first platinum monocar-
bonyl complex with two nonchelating phosphine ligands and
the platinum dicarbonyl complex [(Cy3P)2Pt(CO)2] (9).
17
˚
with a P1-Pt-P1_a angle of 124.0(9) A.
To the best of our knowledge, compound 8 represents the
first structurally characterized complex of the composition
[(R3P)2Pt(CO)]. In comparison to the four-coordinated tris-
(phosphine) carbonyl complex 3, which displays Pt-C dis-
Results and Discussion
The title compounds were synthesized via two different
reaction pathways. The synthesis of [(Cy3P)2Pt(CO)] (8)
˚
tances of 1.86(3) and 1.84(2) A, due to the presence of two
polymorphs, the three-coordinate bis(phosphine) complex
(13) Bennett, B. L.; Roddick, D. M. Inorg. Chem. 1996, 35, 4703.
(14) Houlis, J. F.; Roddick, D. M. J. Am. Chem. Soc. 1998, 120, 11020.
(15) (a) Braunschweig, H.; Wagner, T. Angew. Chem., Int. Ed. Engl. 1995,
34, 825. (b) Braunschweig, H.; Kollann, C.; Englert, U. Angew. Chem., Int. Ed.
1998, 37, 3179. (c) Cowley, A. H.; Lomeli, V.; Voigt, A. J. Am. Chem. Soc. 1998,
120, 6401. (d) Coombs, D. L.; Aldridge, S.; Jones, C.; Willock, D. J. J. Am.
Chem. Soc. 2003, 125, 6356. (e) Braunschweig, H.; Dewhurst, R. D.; Schneider,
A. Chem. Rev. 2010, 110, 3924. (f) Braunschweig, H.; Dewhurst, R. D. Chim.
Oggi 2009, 27, 40. (g) Vidovic, D.; Pierce, G. A.; Aldridge, S. Chem. Commun.
2009, 1157. (h) Anderson, C. E.; Braunschweig, H.; Dewhurst, R. D. Organo-
metallics 2008, 27, 6381. (i) Braunschweig, H.; Kollann, C.; Seeler, F. Struct.
Bonding (Berlin) 2008, 130, 1.
12,18
˚
8 exhibits a very similar Pt-C separation of 1.885(12) A.
Likewise, the C-O bond lengths are in the same range that is
˚
˚
1.139(7) and 1.12(4) A for 3 and 1.131(18) A for 8.
An effort to generate the corresponding platinum(0) dicar-
bonyl complex [(Cy3P)2Pt(CO)2] (9) was achieved via a dif-
ferent synthetic approach. A toluene solution of [(Cy3P)2Pt]
was briefly exposed to CO at temperatures below -20 °C to
afford a bright yellow solution. The product is formed as con-
firmed by a 31P NMR signal at 21.2 ppm with a coupling con-
stant of 1JP-Pt = 3138 Hz.
A similar synthetic route based on the treatment of
[(Cy3P)2PtH2] with CO at room temperature was reported
in 1979. A new resonance at 19.8 ppm was observed in the 31P
NMR spectra, but attempts to isolate the product only re-
sulted in the cluster [(Cy3P)3Pt3(CO)3].19 Later work of the
same group described the reaction of trans-[(Cy3P)2PtH2]
with CO at low temperature that succeeded in the formation
of 9, which was spectroscopically characterized.20 We were
able to isolate the dicarbonyl compound [(Cy3P)2Pt(CO)2] (9)
as a yellow solid in 71% yield upon concentration of the reac-
tion mixture at low temperatures. Colorless crystals suitable
for X-ray structure determination were obtained from toluene
solutions after 7 days at -30 °C. In the crystal, 9 displays a
(16) (a) Braunschweig, H.; Radacki, K.; Uttinger, K. Angew. Chem., Int.
Ed. 2007, 46, 3979. (b) Braunschweig, H.; Radacki, K.; Rais, D.; Schneider, A.;
Seeler, F. J. Am. Chem. Soc. 2007, 129, 10350.
(17) The crystal data of 8 were collected at a Bruker X8Apex diffractometer
with a CCD area detector and multilayer mirror monochromated Mo KR
radiation. The crystal data of 9 were collected at a Bruker D8 diffractometer
with an Apex CCD area detector and graphite monochromated Mo KR
radiation. The structures were solved using direct methods, refined with the
Shelx software package (Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112) and
expanded using Fourier techniques. All non-hydrogen atoms were refined aniso-
tropically. Hydrogen atoms were assigned idealized positions and were included in
structure factor calculations. Crystal data for 8: C37H66OP2Pt, Mr = 783.93, orange
plate, 0.27 ꢀ 0.17 ꢀ 0.07 mm3, monoclinic space group C2/c, a = 16.7337(12) Å,
b = 9.1857(7) Å, c = 24.2468(17) Å, β = 109.375(3)°, V = 3515.9(4) Å3, Z = 4,
F
calcd = 1.481 g cm-3, μ = 4.109 mm-1, F(000) = 1616, T = 100(2) K, R1 = 0.0314,
wR2 = 0.0725, 5214 independent reflections [2θ e 65.5°] and 187 parameters.
Crystal data for 9: C45H74O2P2Pt, Mr = 904.07, colorless block, 0.19 ꢀ 0.38 ꢀ 0.44
mm3, orthorhombic space group Pna21, a = 26.531(2) Å, b = 10.7170(9) Å, c =
15.0153(13) Å, V = 4269.3(6) Å3, Z = 4, Fcalcd = 1.407 g cm-3, μ = 3.396 mm-1
,
F(000) = 1872, T = 173(2) K, R1 = 0.0195, wR2 = 0.0397, 10 706 independent
reflections [2θ e 56.9°] and 452 parameters. Crystallographic data have been
deposited with the Cambridge Crystallographic Data Center as supplementary
publication no. CCDC-795251 (8) and CCDC-795252 (9). These data can be
obtained free of charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
(18) Albano, V.; Basso Ricci, G. M.; Bellon, P. L. Inorg. Chem. 1969, 8,
2109.
(19) Clark, H. C.; Goel, A. B.; Wong, C. S. Inorg. Chim. Acta 1979, 34,
159.
(20) Anderson, G. K.; Clark, H. C.; Davies, J. A. Organometallics 1982, 1,
550.

1818 Inorganic Chemistry, Vol. 50, No. 5, 2011
Bertsch et al.
Figure 2. Molecular structure of 9 (thermal ellipsoids at the 50%
probability level). One molecule of toluene and hydrogen atoms are
˚
omitted for clarity. Selected bond lengths [A] and angles [deg]: Pt-C1
Figure 1. Molecular structure of 8 (thermal ellipsoids at the 50%
probability level). Hydrogen atoms are omitted for clarity. Symmetry-
related positions (-x, y, -z þ 1/2) are denoted by the suffix _a. Selected
1.920(3), Pt-C2 1.897(3), C1-O1 1.139(4), C2-O2 1.143(4); P1-Pt-P2
116.62(2).
˚
of forming a stronger bond with transition metals.22 Based on
these bonding properties, various transition metal borylene
complexes have been prepared in our group in the past decade
by means of intermetallic borylene transfer reactions, by treating
transition metal carbonyl complexes with aminoborylene
complexes [(OC)5MdBN(SiMe3)2] (M = Cr, Mo, W).15b,23
Compound 8 has been examined for thermally and photo-
chemically induced borylene transfer by treatment with equi-
molar amounts of [(OC)5ModBN(SiMe3)2] and [(OC)5Crd
bond lengths [A] and angles [deg]: Pt-C 1.885(12), C-O 1.131(18);
P1-Pt-P1_a 124.0(9).
Scheme 4. Synthesis of the Platinum Dicarbonyl Complex 9
BN(SiMe3)2], respectively. However, the detected 11B and 31
P
NMR signals do not suggest the formation of a terminal pla-
tinum borylene complex [(Cy3P)2PtdBN(SiMe3)2]. Instead,
8 releases a PCy3 ligand under these conditions, which reacts
with [(OC)5ModBN(SiMe3)2] resulting in trans-[(Cy3P)(OC)4-
ModBN(SiMe3)2] (31P: δ = 51.2 ppm; 11B: δ = 92 ppm) and
with [(OC)5CrdBN(SiMe3)2] yielding trans-[(Cy3P)(OC)4Crd
BN(SiMe3)2] (31P: δ = 64.7 ppm; 11B: δ = 96 ppm).23a In the
former case, after heating for 2 h at 80 °C, additional 31P
NMR signals (31P: δ=71.1, 47.6 ppm) can be observed that
suggest the formation of a semibridging molybdenum bor-
ylene species due to similar NMR values.24
distorted tetrahedral geometry of the platinum center with a
P1-Pt-P2 angle of 116.62(2)°, which is somewhat more
acute than the corresponding angle in complex 8 (124.0(9)°).
However, in the only other structurally characterized bisphos-
pine dicarbonyl complex of platinum, that is [(EtPh2P)2-
Pt(CO)2] (4),9b the phosphine ligands include a much smaller
angle of only 97.9(2)°. Besides this difference, further important
˚
structural data such as the Pt-C (9: 1.920(3) and 1.897(3) A; 4:
˚
˚
1.92(2) A) and C-O distances (9: 1.139(4) and 1.143(4) A; 4:
˚
1.14(2) A) are comparable.
As reported earlier (vide supra), the dicarbonyl complex 9
proved to be stable, both in solution and in the solid state,
only at temperatures below -20 °C. Thus, a bright yellow
solution of 9 turns immediately red upon warming to room
temperature with formation of the trinuclear clusters
[(Cy3P)4Pt3(CO)3] and [(Cy3P)3Pt3(CO)3], as indicated by
31P NMR signals at 69.8 ppm for the latter and X-ray
structure analyses.21 Likewise, direct treatment of the plati-
num precursor [(Cy3P)2Pt] with CO at room temperature
afforded a red solution and the aforementioned platinum
clusters. This finding is quite surprising as it significantly
differs from that of other platinum phosphine carbonyls such
as 6 and 7 (vide supra). Moreover, it already indicates that
degradation of 9 to the trinuclear cluster species proceeds via
initial loss of a PCy3 ligand. In the case of liberation of CO
from 9 one would have to expect exclusive formation of the
aforementioned complex 8, which proved to be thermally
stable at room temperature.
Conclusion
In conclusion, we have reported the first structural character-
ization of a platinum(0) monocarbonyl complex with two non-
chelating phosphine ligands, [(Cy3P)2Pt(CO)] (8). The corre-
sponding dicarbonyl compound [(Cy3P)2Pt(CO)2] (9) has
provided a rare structural evidence for this class of compound.
Experimental Section
All manipulations were performed in an inert atmosphere
of argon using standard Schlenk and glovebox techniques.
(23) (a) Blank, B.; Colling-Hendelkens, M.; Kollann, C.; Radacki, K.;
Rais, D.; Uttinger, K.; Whittell, G. R.; Braunschweig, H. Chem.;Eur. J.
2007, 13, 4770. (b) Braunschweig, H.; Colling, M.; Hu, C.; Radacki, K. Angew.
Chem., Int. Ed. 2003, 42, 205. (c) Braunschweig, H.; Herbst, T.; Rais, D.; Seeler,
F. Angew. Chem., Int. Ed. 2005, 44, 7461. (d) Braunschweig, H.; Forster, M.;
Radacki, K. Angew. Chem., Int. Ed. 2006, 45, 2132. (e) Braunschweig, H.;
Fernandez, I.; Frenking, G.; Radacki, K.; Seeler, F. Angew. Chem., Int. Ed. 2007,
46, 5215. (f) Braunschweig, H.; Forster, M.; Radacki, K.; Seeler, F.; Whittell,
G. R. Angew. Chem., Int. Ed. 2007, 46, 5212. (g) Braunschweig, H.; Colling, M.;
Kollann, C.; Merz, K.; Radacki, K. Angew. Chem., Int. Ed. 2001, 40, 4198.
(24) (a) Braunschweig, H.; Radacki, K.; Uttinger, K. Eur. J. Inorg. Chem.
2007, 4350. (b) Braunschweig, H.; Rais, D.; Uttinger, K. Angew. Chem., Int. Ed.
2005, 44, 3763. (c) Braunschweig, H.; Radacki, K.; Rais, D.; Uttinger, K.
Organometallics 2006, 25, 5159.
According to former calculations, borylene ligands are
better sigma donors than CO ligands and therefore capable
(21) Moor, A.; Pregosin, P. S.; Venanzi, L. M. Inorg. Chim. Acta 1981, 48,
153.
(22) Ehlers, A. W.; Baerends, E. J.; Bickelhaupt, F. M.; Radius, U.
Chem.;Eur. J. 1998, 4, 210.

Article
Inorganic Chemistry, Vol. 50, No. 5, 2011 1819
Solvents were distilled over alkali metal, degassed, and
˚
stored over molecular sieves (4 A) under argon. Deuterated
solvents were degassed by three freeze-pump-thaw cycles
and stored under argon over molecular sieves. [(Cy3P)2Pt]25
and [(η5-C5Me5)Ir(CO)2]26 were prepared according to known
methods.
NMR experiments were performed on a Bruker Avance
500 (1H: 500.1 MHz; 31P: 202.5 MHz; 13C: 125.8 MHz) appa-
ratus. 1H NMR and 13C{1H} NMR spectra were calibrated
to TMS; in the case of 31P{1H} NMR spectra 85% H3PO4
was used as external standard. Elemental analyses were
performed on an Elementar Vario Micro Cube elemental
analyzer.
31%). 1H NMR (500.1 MHz, d8-tol): δ = 2.07-1.11 (m, 66H,
Cy) ppm. 13C{1H} NMR (125.8 MHz, d8-tol): δ = 38.61 (m, C1,
Cy), 30.93 (br s, C3, C5, Cy), 28.05 (m, C2, C6, Cy), 26.98 ppm (s,
C4, Cy). 31P{1H} NMR (202.5 MHz, d8-tol): δ = 63.7 (1JP-Pt
=
4101 Hz) ppm. IR: 1916 cm-1. Elemental analysis (%) calcu-
lated for C37H66OP2Pt (783.95): C 56.69, H 8.49; found: C 56.94,
H 8.40.
Synthesis of [(Cy3P)2Pt(CO)2] (9). A solution of [(Cy3P)2Pt]
(0.050 g, 0.066 mmol) in toluene (2.0 mL) was cooled to -40 °C.
The bright yellow solution was treated for 1 s with CO and
darkened. The reaction mixture turned red within 10 min above
0 °C and yielded the Pt3 cluster [(Cy3P)3Pt3(CO)3]. Isolation of
9 was possible if the solvent of the intensely yellow solution
was removed at -15 to -35 °C (0.038 g, 71%). As the resulting
yellow solid was unstable at room temperature, no further IR
data and elemental analysis could be obtained. Colorless crys-
tals suitable for X-ray structure analysis were obtained from the
toluene solution after 7 days at -30 °C. 1H NMR (500.1 MHz,
d8-tol): δ = 2.04-1.18 (m, 66H, Cy) ppm. 13C{1H} NMR (125.8
MHz, d8-tol): δ = 37.78 (virtual triplet, N27 = 24 Hz, C1, Cy),
31.61 (s, C3, C5, Cy), 28.00 (virtual triplet, N28 = 16 Hz, C2, C6,
Cy), 27.00 ppm (s, C4, Cy). 31P{1H} NMR (202.5 MHz, d8-tol):
δ = 21.2 (1JP-Pt = 3138 Hz) ppm.
Synthesis of [(Cy3P)2Pt(CO)] (8). [(Cy3P)2Pt] (0.022 g, 0.029
mmol) was added to a pale yellow solution of [(η5-C5Me5)Ir-
(CO)2] (0.011 g, 0.029 mmol) in benzene (1.0 mL). The intensely
yellow solution was kept at room temperature for 24 h and then
irradiated for 18 h. The resulting dark orange solution was
layered with hexane, and orange crystals were obtained after 3
days. The crystals were washed thoroughly with hexane (10 ꢀ
0.5 mL) until the washing solution remained colorless (0.007 g,
(25) Yoshida, T.; Otsuka, S. Inorg. Synth. 1990, 28, 113.
(26) (a) Ball, R. G.; Graham, W. A. G.; Heinekey, D. M.; Hoyano, J. K.;
McMaster, A. D.; Mattson, B. M.; Michel, S. T. Inorg. Chem. 1990, 29, 2023.
(b) Kang, J. W.; Moseley, K.; Maitlis, P. M. J. Am. Chem. Soc. 1969, 91, 5970.
Acknowledgment. We thank the DFG for financial support.
(27) N = |1JP-C
(28) N = |2JP-C
þ
3JP-C|.
þ
4JP-C|. For details on N see: Fackler, J. P., Jr.;
Supporting Information Available: CIF files giving X-ray
structural data of 8 and 9. This material is available free of
charge via the Internet at http://pubs.acs.org.
Fetchin, J. A.; Mayhew, J.; Seidel, W. C.; Swift, T. J.; Weeks, M. J. Am.
Chem. Soc. 1969, 91, 1941.