A Bidentate Bisphosphine Functioning in Intramolecular Aliphatic Metalation and as an NMR Spectroscopic Probe for the Metal Coordination Environment

Article abstract of DOI:10.1021/ic9700819

The multistep synthesis of the novel diphosphine reference ligand L₂, 6, Ph₂P(o-C₆C₆H₄C₆H ₄-o)PPh₂, has been streamlined and can be prepared on a ca. 20 g scale. It forms metallacycles with a variety of metal fragments. The resulting, and very rigid, boat-boat conformation forces a proton (H_endo) of the bridging methylene in close proximity to the metal, which in turn renders these protons (H_endo H_exo) diastereotopic. The NMR spectra of [L₂MCl₂] [M = Pd, 9; M = Pt, 10] and of the organometallic derived compounds [L₂Pd(PPh₃)], 11, and [L₂Pd-(Cl)(η₂-CH₂Ph)], 12, consist of a pair of doublets, with the H_endo coupled to the P of the metallacycle. The CH₂-metal close proximity drives the electrophilic metalation of the bridging methylene by RhCl₃ to form [L*₂Rh(Cl)₂(MeCN)], 13, [L*₂ = Ph₂P(o-C₆H₆CHC₆-o)PPh₂]. A significant example, which shows how the coordination number of the metal can affect the H_exo-H_endo resonance separation, is provided by the couple [L₂Ni(C₂H₄)], 14, and [L₂Ni(CO)₂], 15. In order to show that the metallacycle size is crucial for the bridging methylene to function as a spectroscopic probe, we complexed the same [Fe(CO)₃] fragment to L₂, 6, and L'₂, 17, [L'₂ = Ph₂PO(o-C₆H₂(4,6Bul2)CH2(4,6Bu₁ ²)C₆H₂(4,6Bu₂¹)OPPh ₂], to give [L'₂Fe(CO)₃], 19, and [L'₂Fe(CO)₃], 18. respectively. In complex 17 the diastereotopic nature of these protons and hence the spectroscopic information was lost because of the presence of a 10-membered metallacycle. Crystal data: 9 is triclinic, space group P1?, a = 11.987(1) A?, b= 15.990(2) A?. c = 10.872(1) A?, a = 91.42(1)°, β= 111.01(2)°, γ = 99.86(2)°, V= 1908.2(5) A?³, Z = 2, and R = 0.053; 11 is monoclinic, space group C2/c, a = 39.071(5) A?, b = 13.657(4) A?, c = 19.848(5) A?,β = 92.45(2)°, V= 10581(5) A?³ Z = 8. and R = 0.047; 12 is triclinic, space group P1?, a = 11.289(1) A?, b = 18.769(2) A?, c = 11.077(1) A?, a = 91.20(1)°, β= 111.27(1)°, γ = 105.26(1)°, V = 2107.7(4) A?3, Z = 2, and R = 0.039; 13 is orthorhombic, space group P2₁2₁2₁, a = 15.346(2) A?, b = 18.188(3) A?, c = 12.072(2) A?, V = 3369.5(9) A?³, Z = 4. and R = 0.042.

Full text of DOI:10.1021/ic9700819

3354
Inorg. Chem. 1997, 36, 3354-3362
A Bidentate Bisphosphine Functioning in Intramolecular Aliphatic Metalation and as an
NMR Spectroscopic Probe for the Metal Coordination Environment
William Lesueur, Euro Solari, and Carlo Floriani*
Institut de Chimie Mine´rale et Analytique, BCH, Universite´ de Lausanne,
CH-1015 Lausanne, Switzerland
Angiola Chiesi-Villa and Corrado Rizzoli
Dipartimento di Chimica, Universita` di Parma, I-43100 Parma, Italy
ReceiVed January 23, 1997X
The multistep synthesis of the novel diphosphine reference ligand L2, 6, Ph2P(o-C6H4CH2C6H4-o)PPh2, has been
streamlined and can be prepared on a ca. 20 g scale. It forms metallacycles with a variety of metal fragments.
The resulting, and very rigid, boat-boat conformation forces a proton (Hendo) of the bridging methylene in close
proximity to the metal, which in turn renders these protons (Hendo, Hexo) diastereotopic. The NMR spectra of
[L2MCl2] [M ) Pd, 9; M ) Pt, 10] and of the organometallic derived compounds [L2Pd(PPh3)], 11, and [L2Pd-
(Cl)(η2-CH2Ph)], 12, consist of a pair of doublets, with the Hendo coupled to the P of the metallacycle. The
CH2-metal close proximity drives the electrophilic metalation of the bridging methylene by RhCl3 to form
[L*2Rh(Cl)2(MeCN)], 13, [L*2 ) Ph2P(o-C6H4CHC6H4-o)PPh2]. A significant example, which shows how the
coordination number of the metal can affect the Hexo-Hendo resonance separation, is provided by the couple
[L2Ni(C2H4)], 14, and [L2Ni(CO)2], 15. In order to show that the metallacycle size is crucial for the bridging
methylene to function as a spectroscopic probe, we complexed the same [Fe(CO)3] fragment to L2, 6, and L′2, 17,
[L′2 ) Ph2PO(o-C6H2(4,6But2)CH2(4,6But2)C6H2-o)OPPh2], to give [L2Fe(CO)3], 19, and [L′2Fe(CO)3], 18,
respectively. In complex 17 the diastereotopic nature of these protons and hence the spectroscopic information
was lost because of the presence of a 10-membered metallacycle. Crystal data: 9 is triclinic, space group P1h, a
) 11.987(1) Å, b ) 15.990(2) Å, c ) 10.872(1) Å, R ) 91.42(1)°, â ) 111.01(2)°, γ ) 99.86(2)°, V ) 1908.2(5)
Å3, Z ) 2, and R ) 0.053; 11 is monoclinic, space group C2/c, a ) 39.071(5) Å, b ) 13.657(4) Å, c ) 19.848(5)
Å, â ) 92.45(2)°, V ) 10581(5) Å3, Z ) 8, and R ) 0.047; 12 is triclinic, space group P1h, a ) 11.289(1) Å, b
) 18.769(2) Å, c ) 11.077(1) Å, R ) 91.20(1)°, â ) 111.27(1)°, γ ) 105.26(1)°, V ) 2107.7(4) Å3, Z ) 2, and
R ) 0.039; 13 is orthorhombic, space group P212121, a ) 15.346(2) Å, b ) 18.188(3) Å, c ) 12.072(2) Å, V )
3369.5(9) Å3, Z ) 4, and R ) 0.042.
Introduction
oligomeric calix[n]arenes.3 (ii) The eight-membered derived
metallacycle has a very rigid conformation and, in spite of the
rather large ring size, a narrow P‚‚‚P bite. (iii) The rigid boat-
boat conformation, observed for all the complexes so far
identified, forces the endo hydrogen of the bridging methylene
to approach the metal and consequently can favor the observed
metalation of the methylene group. Further, this type of
intramolecular C-H activation in diphosphine complexes, as
elucidated by Shaw,4 Milstein,5 and others, can be promising
in driving the intermolecular hydrocarbon activation.5 (iv) The
metal complexation by the reference ligand affords a confor-
mationally rigid metallacycle which easily differentiates the
prochiral methylene protons (in the free ligand). The endo one
is affected by the proximity to the metal and by other electronic
The bidentate bisphosphine derivatives in their achiral and
chiral form are the ligands “par excellence” in coordination,
organometallic chemistry, and catalysis.1,2 They have been
proposed in a variety of forms. This report deals with a
diphosphine having the following particular skeleton:
There are a number of features associated with this type of
skeleton: (i) It is the monomeric fragment of the cyclic
(2) (a) For a comprehensive review on chiral phosphorus ligands see:
Brunner, H.; Zettlmaier, W. Handbook of EnantioselectiVe Catalysis;
VCH: Weinheim, Germany, 1993; Vols. I, II. (b) Pietrusiewicz, K.
M.; Zablocka, M. Chem. ReV. 1994, 94, 1375. (c) Herrmann, W.;
Kohlpaintner, C. W. Angew. Chem., Int. Ed. Engl. 1993, 32, 1524
and references therein.
(3) (a) Gutsche, C. D. Calixarenes; The Royal Society of Chemistry:
Cambridge, U.K., 1989. (b) Calixarenes, A Versatile Class of
Macrocyclic Compounds; Vicens, J., Bo¨hmer, V., Eds.; Kluwer:
Dordrecht, The Netherlands, 1991.
(4) Empsall, H. D.; Hyde, E. M.; Markham, R.; McDonald, W. S.; Norton,
M. C.; Shaw, B. L.; Weeks, B. J. Chem. Soc., Chem. Commun. 1977,
589. Crocker, C.; Errington, R. J.; Markham, R.; Moulton, C. J.; Shaw,
B. L. J. Chem. Soc., Dalton Trans. 1982, 387.
* To whom correspondence should be addressed.
X Abstract published in AdVance ACS Abstracts, July 1, 1997.
(1) (a) McAuliffe, C. A. Phosphorus, Arsenic, Antimony and Bismuth
Ligands. In ComprehensiVe Coordination Chemistry; Wilkinson, G.,
Gillard, R. D., McCleverty, J. A., Eds.; Pergamon: Oxford, U.K., 1987;
Vol. 2, p 989. (b) Homogeneous Catalysis with Metal Phosphine
Complexes; Pignolet, L. H., Ed.; Plenum: New York, 1983. (c)
Puddephatt, R. J. Chem Soc. ReV. 1983, 12, 99. (d) Levason, W. The
Chemistry of Organophosphorus Compounds; Hartley, F. R., Patai,
S., Eds.; Wiley: New York, 1990; Vol. 1; p 617. Stelzer, O.; Langhans,
K.-P. Ibid., p 191. (e) Cotton, F. A.; Hong, B. Progr. Inorg. Chem.
1992, 40, 179. (f) Mayer, H. A.; Kaska, W. C. Chem. ReV. 1994, 94,
1239.
S0020-1669(97)00081-5 CCC: $14.00 © 1997 American Chemical Society

A Bidentate Bisphosphine
Inorganic Chemistry, Vol. 36, No. 15, 1997 3355
(colorless when hot, red on cooling) (lit. bp: 110-111 °C/0.01 mmHg,
or 175-180 °C/14-17 mmHg, or 177 °C/12 mmHg) to give 2 (70%).
and magnetic field affects and thus functions as a very sensitive
NMR spectroscopic probe for the metal environment. In this
context we will show how enlargement to a 10-membered
metallacycle causes the loss in conformation control and,
consequently, loss of the ability of CH2 to act as a spectroscopic
probe in NMR analyses.
Herein we report an improved and scaled up synthesis of the
reference ligand along with its use in the complexation of a
variety of metal fragments. In particular we have focused on
the complexation of PdCl2 and its organometallic derivatization
and the electrophilic metalation of the bridging methylene by
RhCl3. Further we show how a change in the coordination
number of the metal can affect the chemical shift of the endo
proton, exemplified with some Ni0 derivatives, and how
enlarging the metallacycle to a 10-membered ring results in loss
of the spectroscopic probe ensured by the bridging methylene.
This has been shown using both L2 and L′2 derived species.
28
22.5
20
nD
:
1.637 (lit.: nD
1.6417 or nD 1.6406). 1H-NMR (CCl4,
TMS): δ 4.06 (s, 2H, CH2), 6.70-7.91 (m, 9H, Ar-H). Mass EI: m/z
294 (calcd: 294.13).
Preparation of 3.8 A solution of peracetic acid9 was prepared by
slowly adding 30% H2O2 (77 mL) to acetic anhydride (308 mL) at 0
°C. The mixture was kept cold in an ice-water bath until it became
homogeneous and then left to stand overnight at room temperature. A
solution of 2 (57.0 g, 100 mmol) dissolved in acetic acid (60 mL) was
added dropwise over 2 h to the peracetic acid solution at 10 °C. The
mixture slowly turned from orange to yellow and was allowed to stand
at room temperature for 4 days. The reaction mixture (which now
contains the iodoso compound) was cooled to 10 °C, and to this stirred
solution was added dropwise 96% H2SO4 (77 mL). The mixture
became dark and after standing for 12 h at room temperature was diluted
with of cold water (200 mL), extracted with toluene (200 mL), treated
with activated carbon until the solution was colorless, and then treated
with a large excess of NaCl. Filtration yielded 3 as a white powder
(73%). Mp: 245 °C (lit.: 244-245 °C). 1H NMR (DMSO-d6): δ
4.23 (s, 2H, CH2), 7.35 (d t, 2H, Ar-Hγ), 7.52 (dt, 2H, Ar-Hâ) 7.72
(dd, 2H, Ar-Hδ), 8.22 (dd, 2H, Ar-HR). Anal. Calcd for C13H10ClI:
C, 47.52; H, 3.07. Found: C, 48.01; H, 2.99.
Preparation of 4.8 A mixture of 3 (45.4 g, 138 mmol), water (200
mL), ethanol (200 mL), and KI (excess) was refluxed for 15 min. The
off-white precipitate was collected by filtration and dried in a desiccator
over CaCl2 for 2 days (99%). MP: 198-199 °C (lit.: 184.5-185.5
or 177-178 °C). 1H NMR (DMSO-d6): δ 4.23 (s, 2H, CH2), 7.35 (d
t, 2H, Ar-Hγ), 7.52 (d t, 2H, Ar-Hâ), 7.72 (d d, 2H, Ar-Hδ), 8.22 (d d,
2H, Ar-HR). Anal. Calcd for C13H10I2: C, 37.17; H, 2.40; I, 60.43.
Found: C, 36.89; H, 2.37; I, 59.30.
Preparation of 5.10 4 (49.2 g, 120 mmol) was heated under N2 at
210 °C for 15 min. After cooling, the resulting violet liquid was
dissolved in CH2Cl2 (150 mL) and washed with an aqueous solution
of Na2S2O3. The organic layer was then dried (MgSO4), the solvent
removed, and then the solid recrystallized in diethyl ether (69%).
Mp: 78 °C (lit.: 79 °C). 1H NMR (CD2Cl2): δ ) 4.13 (s, 2H, CH2),
6.95 (m, 4H, Ar-H), 7.27 (m, 2H, Ar-H), 7.85 (m, 2H, Ar-H). Anal.
Calcd for C13H10I2: C, 37.17; H, 2.40; I, 60.43. Found: C, 36.89; H,
2.28; I, 61.20. Mass EI: m/z 420 (calcd: 420.04).
In preliminary studies we showed how the bridging methylene
of the bis-phenolato anion precursor of L′2 can be used as an
NMR spectroscopic probe.6 In order to support the fundamental
assumption on the rigidity of the metallacycle conformation in
a variety of complexes derived from L2, X-ray analyses have
been carried out on the key complexes. This allowed, among
other things, the establishment of a structural solid state-
solution relationship.
Experimental Section
Preparation of Ph2P(o-C6H4CH2C6H4-o)PPh2, L2, 6. BunLi (1.6
M in hexane, 29.8 mL, 47.6 mmol) was added dropwise to a stirred
suspension of 5 (10.0 g, 23.8 mmol) in pentane (80 mL) at room
temperature. After 2 h, freshly distilled chlorodiphenylphosphine (10.50
g, 47.6 mmol) was added to the chilled (0 °C) yellow suspension. The
mixture turned orange. After 5 days at room temperature, the mixture
was hydrolyzed with an aqueous saturated solution of NH4Cl. The
aqueous layer was eliminated, and the pale yellow suspension in the
organic layer was collected by filtration and washed with a minimum
of cold methanol. The white solid was dried in Vacuo for 8 h (73%).
Mp: 128-129 °C. 1H NMR (CD3COCD3): δ ) 4.45 (brd t, 2 H, JPH
) 2.0 Hz, CH2), 6.87-7.36 (m, 28 H, Ar-H). 31P{1H} NMR (CD3-
COCD3): δ ) -11.5 (s). Anal. Calcd for C37H30P2: C, 82.82; H,
5.64. Found: C, 82.15; H, 5.63.
Preparation of L2NiCl2, 7.11 A mixture of NiCl2‚6H2O (0.81 g,
2.8 mmol) and L2, 6 (1.5 g, 2.8 mmol), in ethanol was refluxed for 3
h. The mixture was allowed to cool to room temperature and the khaki
microcrystalline powder collected by filtration and dried (75%). Anal.
Calcd for C37H30Cl2NiP2: C, 66.71; H, 4.54; Cl, 10.65. Found: C,
66.32; H, 4.32; Cl, 9.95. µeff: 3.30 µB (298 K).
General Procedure. All reactions were carried out under an
atmosphere of purified nitrogen. Solvents were dried and distilled
before use by standard methods. Infrared spectra were recorded with
a Perkin-Elmer 883 spectrophotometer; 1H, 31P, and 13C NMR spectra
were measured on a 200-AC Bruker instrument at 298 K, unless
specified. Compounds 1 and 16 are commercially available.
Preparation of 2.7 (2-aminophenyl)phenylmethane (50.4 g, 270
mmol) was dissolved of in a mixture of 32% HCl (109 mL) and water
(60 mL) and the mixture cooled at 0 °C. A solution of NaNO2 (20.5
g) in water (85 mL) was added in small volumes of 2-3 mL (the
temperature was not allowed to rise above 10 °C). After 30 min a
solution of KI (46.0 g) in water (50 mL) was added dropwise with the
concomitant evolution of N2 gas (again, the temperature was not allowed
to rise above 10 °C). The mixture was warmed to room temperature
and then to 60 °C until effervescence ceased. After cooling, the upper
aqueous layer was decanted and the organic layer washed with 10%
NaOH solution. A small amount of Na2S2O5 (ca. 0.5 g) was added
until the crude reaction mixture was a pale red color. This mixture
was steam distilled in order to eliminate final traces of unreacted amine.
The aqueous layer was eliminated, the organic residue distilled (Vigreux
8 cm), and the fraction (bp: 125-126 °C, ∼10-2 Torr) collected
(8) Collette, J.; McGreer, D.; Crawford, R.; Chubb, F.; Sandin, R. B. J.
Am. Chem. Soc. 1956, 78, 3819.
(9) For an excellent review wich contains valuable information on the
preparation of organic peracids and precautions necessary in their use,
see: Swern, D. Organic Reactions; Wiley: New York, 1953; Vol.
VII, p 378.
(10) (Bickelhaupt, F.; Jongsma, C.; de Koe, P.; Lourens, R.; Mast, N. R.;
van Mourik, G. L.; Vermeer, H.; Weustink, R. J. M. Tetrahedron 1976,
32, 1921.
(11) Following the procedure by: Colquhoum, H. M.; Holton, J.; Thomp-
son, D. J.; Twigg, M. V. New pathways for organic synthesis, practical
applications of transitions metals; Plenum: New York, 1984; Chapter
9.
(5) (a) Milstein, D. Frontiers in Bond Activation by Electron-Rich Metal
Complexes. In StereoselectiVe Reactions of Metal-ActiVated Molecules;
Werner, H., Sundermeyer, J., Eds.; Vieweg: Braunschweig/Wiesbaden,
Germany, 1995; pp 107-115. (b) Gozin, M.; Weisman, A.; Ben-David,
Y.; Milstein, D. Nature 1993, 364, 699. (c) Gozin, M.; Aizenberg,
M.; Liou, S.-Y.; Weisman, A.; Ben-David, Y.; Milstein, D. Nature
1994, 370, 42.
(6) Lesueur, W.; Corazza, F.; Floriani, C.; Chiesi-Villa, A.; Guastini, C.
Angew. Chem., Int. Ed. Engl. 1989, 28, 66.
(7) Seidel, F. Ber. 1928, 61, 2267.

3356 Inorganic Chemistry, Vol. 36, No. 15, 1997
Lesueur et al.
Preparation of L2NiBr2, 8. A mixture of NiBr2‚3H2O (0.762 g,
2.79 mmol) and L2, 6 (1.5 g, 2.8 mmol), in ethanol was refluxed for 3
h. The mixture was allowed to cool at room temperature and the deep
green microcrystalline powder collected by filtration and dried (70%).
Anal. Calcd for C37H30Br2NiP2: C, 58.85; H, 4.00. Found: C, 58.89;
H, 3.95. µeff: 3.40 µB (298 K).
Preparation of L2PdCl2, 9. An equimolar mixture of [PdCl2-
(PhCN)2]12 (2.00 g, 5.22 mmol) and L2, 6 (2.80 g, 5.20 mmol), was
refluxed for 3 h in benzene (100 mL) and then cooled to room
temperature. The pale yellow solid was filtered out, washed with
benzene and ether, and dried in Vacuo for 4 h (88%). 1H NMR
(C6D6): δ 3.49 (d, 1H, JHH ) 14.4 Hz, CH2), 6.60-7.47 (m, 33H,
Ar-H, C2H4, CH2). 31P{1H} NMR (C6D6): δ 22.7 (s). Anal. Calcd
for C39H34NiP2: C, 75.15; H, 5.50. Found: C, 74.87; H, 5.42. IR
(Nujol): ν(C2H4), 1520 cm-1
.
Preparation of [L2Ni(CO2)], 15. To a yellow suspension of
[L2Ni(C2H4)], 14, in degassed methanol (30 mL) at room temperature
was bubbled CO. The color quickly became colorless followed by
precipitation of a white solid. The solid was collected by filtration
and dried in Vacuo for 2 h to give 15 as a pale gray powder (45%).
1H-NMR (CD2Cl2): δ 3.42 (d, 1H, JHH ) 13.4 Hz, CH2), 5.91 (d, 1H,
JHH ) 13.4 Hz, CH2), 6.43 (brd t, 2H, Ar-H), 6.81 (brd t, 2H, Ar-H),
7.19 + 7.39 (brd s, 24H, Ar-H). 31P{1H} NMR (CD2Cl2): δ 24.8 (s).
Anal. Calcd for C39H30NiO2P2: C, 71.92; H, 4.64. Found: C, 71.46;
(CD2Cl2): δ 3.84 (d, 1H, JH-H ) 14 Hz, CH2), 6.56 (brd d, 1H, JHH
)
14 Hz, CH2), 6.70-7.68 (m, 28H, Ar-H). 31P{1H} NMR (CD2Cl2,
ppm): δ 23.4 (s). Anal. Calcd for C37H30Cl2P2Pd: C, 62.25; H, 4.24;
Cl, 9.93. Found: C, 61.93; H, 4.32; Cl, 9.72.
H, 4.70. IR (KBr/Nujol): ν(CO), 1991 (s), 1925 (s) cm-1
.
Preparation of Ph2PO(o-C6H2(4,6But2)CH2(4,6But2)C6H2-o)-
OPPh2, L′2, 17. To a n-hexane (70 mL) solution of 16 (3.40 g, 8.0
mmol) was added a solution of BunLi (1.6 M, 16 mmol) in n-hexane.
After 30 min, 2 equiv of freshly distilled ClPPh2 (3.0 mL, 16 mmol)
was added at room temperature. After 13 h, the solid was removed by
filtration and the filtrate evaporated to dryness. The resulting white
solid was dried in Vacuo (84%). 1H NMR (CD2Cl2): δ 1.08 (s, 18H,
p-But), 1.26 (s, 18H, o-But), 4.09 (brd t, 2H, CH2), 6.59 (2s, 2H, Ar-
H), 7.15 (2s, 2H, Ar-H), 7.29-7.46 (m, 20 H, P-Ar-H). 31P{1H} NMR
(CD2Cl2): δ 113.5 (s). Anal. Calcd for C53H62O2P2: C, 80.27; H,
7.88. Found: C, 79.91; H, 7.98.
Preparation of L2PtCl2, 10. A solution of K2PtCl4 (1.54 g, 3.72
mmol) in the minimum amount of water/ethanol (1:2) was added to a
solution of L2, 6 (2.00 g, 3.72 mmol), in CH2Cl2 (30 mL). The mixture
was refluxed for 12 h. After the mixture was cooled to room
temperature, the pale yellow solid was collected by filtration and dried
in Vacuo (78%). 1H NMR (CD2Cl2): δ 3.44 (d, 1H, JHH ) 14 Hz,
CH2), 6.46 (brd d, 1H, JHH ) 14 Hz, CH2), 6.52-6.61 (m, 2H, Ar-H),
6.79-6.86 (m, 2H, Ar-H), 7.18-7.62 (m, 24H, Ar-H). 31P{1H} NMR
(CD2Cl2): δ 3.55 (t, JPt-P ) 3.686 Hz). Anal. Calcd for C37H30Cl2P2-
Pt: C, 55.37; H, 3.77; Cl, 8.84. Found: C, 54.89; H, 3.84; Cl, 8.42.
Preparation of [L2Pd(PPh3)], 11. A mixture of L2PdCl2, 9 (0.53
g, 0.73 mmol), and PPh3 (0.50 g, 1.9 mmol) in DMSO (15 mL) was
heated until the solution became clear orange. To this was added
N2H4‚H2O (0.15 mL, 3.0 mmol). A vigorous evolution of gas was
observed, and the color turned yellow. The solution was immediately
cooled in an ice-water bath, resulting in yellow crystals. These crystals
were filtered out, washed with ethanol (O2 free), and then dried in Vacuo
for 4 h (64%). 1H NMR (C6D6): δ 3.08 (d, 1H, JHH ) 14 Hz, CH2),
6.15 (d, 1H, JHH ) 14 Hz, CH2), 6.37-7.48 (m, 39H, Ar-H), 7.92 (brd
s, 4H, Ar-H). 31P{1H} NMR (C6D6): δ 6.78 (s), 23.94 (s). Anal. Calcd
for C55H45P3Pd: C, 72.97; H, 5.01. Found: C, 72.58; H, 5.21.
Preparation of [L2Pd(Cl)(η2-CH2Ph)], 12. A mixture of [L2Pd-
(PPh3)], 11 (0.39 g, 0.43 mmol), and freshly distilled benzyl chloride
(0.05 mL, 0.43 mmol) in toluene (15 mL) was heated at 80 °C for 10
min. The color turned from yellow to orange red. Cooling to room
temperature and standing at 4 °C for 12 h yielded red crystals of 12
(80%). 1H NMR (CD2Cl2): δ 2.80 (brd s, 1H, CH2 benzyl), 3.25 (d,
1H, JHH ) 15 Hz, CH2), 4.00 (brd s, 1H, CH2 benzyl), 6.20-8.00 (m,
34H, Ar-H and CH2). 31P{1H} NMR (C6D6): δ 9.58 (s), 27.71 (s).
Anal. Calcd for 12‚C7H8, C51H45ClP2Pd: C, 71.08; H, 5.26; Cl, 4.11.
Found: C, 71.58; H, 5.37; Cl, 3.80.
Preparation of [L′2Fe(CO)3], 18. Ligand 17 (L′2) (2.4 g, 3.0 mmol)
was added at -30 °C to a yellow n-hexane (50 mL) solution of
[Fe(CO)3(C8H14)2]14 (1.08 g, 3.0 mmol) and cyclooctene (1 mL). The
solution was warmed to room temperature and then was kept in the
freezer for several days. A yellow crystalline solid (87%) was filtered
out and dried. 1H NMR (CD2Cl2): δ 1.07 (2s, 36H, But), 4.71 (brd s,
2H, CH2), 6.21 (2s, 2H, Ar-H), 7.17-7.36 (m, 14 H, Ar-H), 7.54-
7.58 (m, 8 H, Ar-H). 31P{1H} NMR: δ 172 (s). Anal. Calcd for
C56H62FeO5P2: C, 72.10; H, 6.70. Found: C, 72.53; H, 6.62. IR
(KBr/Nujol): ν(CO), 2008 (s), 1938 (vs), 1915 (vs) cm-1
.
Preparation of [L2Fe(CO)3], 19. To a suspension of L2, 6 (1.2 g,
2.2 mmol), in 60 mL hexane (+1 mL of cyclooctene) at -90 °C was
added cold [Fe(CO)3(C8H14)2]14 (0.80 g, 2.2 mmol), and the mixture
was allowed to warm slowly to room temperature (the color became
red-brown at ca. -30 °C). This mixture was refluxed at 80 °C for 3
h. The suspension was filtered at 50 °C and then washed with Et2O
(50 mL) and dried in Vacuo for 3 h. The crude mixture (0.79 g) was
passed down a column (25 cm, 2 cm diameter) of alumina (neutral,
standard grade), previously washed with benzene, eluting with a mixture
of benzene/diethyl ether (1:1). The yellow fraction was collected and
evaporated to dryness to give 19 as a bright yellow solid (45%). 1H
NMR (CD2Cl2): δ 3.28 (d, 1H, JHH ) 14 Hz, CH2), 5.83 (d, 1H, JHH
) 14 Hz, CH2), 6.31-6.40 (m, 2H, Ar-H), 6.68-6.76 (m, 2H, Ar-H),
6.98-7.38 (m, 24H, Ar-H). 31P{1H} NMR (CD3COCD3): δ 56.8 (s).
Anal. Calcd for C40H30FeP2O3: C, 71.02; H, 4.47. Found: C, 71.83;
Preparation of [L*2Rh(Cl)2(MeCN)], 13 [L*2
) Ph2P(o-
C6H4CHC6H4-o)PPh2]. A red ethanolic solution of RhCl3‚2H2O (0.23
g, 0.93 mmol) was added to a solution of L2, 6 (0.50 g, 0.93 mmol), in
ethanol/acetonitrile (1:1), which was then refluxed for 30 min. To this
hot mixture was added an aqueous solution of formaldehyde (36.5%,
2 mL). This mixture was refluxed for 4 h and then cooled slowly to
room temperature to give a murky yellow solution. The solution was
filtered and the filtrate kept at room temperature overnight. The deep
yellow crystals were collected and washed with Et2O (82.6%). IR
H, 4.67. IR (KBr/Nujol): ν(CO), 1984 (s), 1909 (s), 1890 (s) cm-1
as for C2v symmetry (2A1 + B2).
,
X-ray Crystallography for Complexes 9 and 11-13. Suitable
crystals were mounted in glass capillaries and sealed under nitrogen.
The reduced cells were obtained with the use of TRACER.15 Crystal
data and details associated with data collection are given in Tables 1
and S1. Data were collected at room temperature (295 K) on a single-
crystal diffractometer (Siemens AED for 9 and 12 and Rigaku for 11
and 13). For intensities and background individual reflection profiles
were analyzed.16 The structure amplitudes were obtained after the usual
Lorentz and polarization corrections,17 and the absolute scale was
established by the Wilson method.18 The crystal quality was tested by
(KBr/Nujol): ν(CN), 1969 cm-1 1H NMR (CD3OD): δ 6.5-6.8 (m,
.
5H), 7.1-7.8 (m, 20H), 7.9-8.1 (m, 4H). 31P{1H}NMR (CD3OD): δ
60.3 (d, JRh-P ) 145 Hz), 54.60 (d, JRh-P ) 143 Hz). Anal. Calcd for
C39H32Cl2NP2Rh: C, 62.42; H, 4.30; N, 1.87. Found: C, 63.14; H,
4.52; N, 1.67.
Preparation of [L2Ni(C2H4)], 14.13 To a green suspension of
anhydrous [Ni(C5H7O2)2] (1.10 g, 4.29 mmol) in toluene (80 mL) at
room temperature was added L2, 6 (2.30 g, 4.29 mmol, 1 equiv).
Ethylene was bubbled into this mixture for 5 min and then a hexane
solution of Al(Et)3 (2 equiv) carefully added. The solution became
first yellow-orange and then orange-red after 3 h. Methanol (150 mL,
O2 free) was added. The mixture was filtered and the filtrate kept at
4 °C for 12 h, to give green khaki microcrystalline 14 (67%). 1H NMR
(14) Fleckner, H.; Grevels, F.-W.; Hess, D. J. Am. Chem. Soc. 1984, 106,
2027.
(15) Lawton, S. L.; Jacobson, R. A. TRACER (a cell reduction program);
Ames Laboratory, Iowa State University of Science and Technology:
Ames, IA, 1965.
(16) Lehmann, M .S.; Larsen, F. K. Acta Crystallogr., Sect. A: Cryst. Phys.,
Diffr., Theor. Gen. Crystallogr. 1974, A30, 580-584.
(17) Data reduction was carried out on an IBM AT personal computer
equipped with an INMOS T800 transputer.
(12) Tsuji, J. Organic synthesis with palladium compounds; Springer:
Berlin, Germany; Vol. 10, pp 2-3.
(13) Wilke, G.; Hermann, G. Angew. Chem. 1962, 74, 693.
(18) Wilson, A. J. C. Nature 1942, 150, 151.

A Bidentate Bisphosphine
Inorganic Chemistry, Vol. 36, No. 15, 1997 3357
Table 1. Experimental Data for the X-ray Diffraction Studies on Crystalline Complexes 9 and 11-13
complex
9
11
12
13
chem formula
a (Å)
b (Å)
C37H30Cl2P2Pd‚2CH2Cl2
11.987(1)
15.990(2)
10.872(1)
91.42(1)
111.01(2)
99.86(2)
1908.2(5)
2
C55H45P3Pd‚1.5C6D6
39.071(5)
13.657(4)
19.848(5)
90
92.45(2)
90
C44H37ClP2Pd‚C7H8
11.289(1)
18.769(2)
11.077(1)
91.20(1)
110.27(1)
105.26(1)
2107.7(4)
2
C39H32Cl2NP2Rh
15.346(2)
18.188(3)
12.072(2)
90
90
90
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å)3
Z
10581(4)
8
3369.5(9)
4
fw
883.8
P1h (No. 2)
22
1022.5
C2/c (No. 15)
22
861.7
P1h (No. 2)
22
750.4
P212121 (No. 19)
22
space group
t (°C)
λ (Å)
1.541 78
1.538
90.18
0.744-1.000
0.053
0.143
1.034
0.710 69
1.284
4.72
0.957-1.000
0.047
0.127
0.828
1.541 78
1.358
52.10
0.590-1.000
0.039
0.103
1.021
0.710 69
1.479
7.80
0.745-1.000
0.042 [0.043]a
0.127 [0.130]
0.852
F
calcd (g cm-3
)
µ (cm-1
transmn coeff
R
wR2
GOF
)
2 2
a Values in brackets refer to the “inverted structure”. R ) ∑|∆F|/∑|Fo| based on the unique observed data. wR2 ) [∑w|∆F2|2/∑w|Fo | ]1/2 based
on the unique observed data for 9 and 12 and on the unique total data for 11 and 14. GOF ) [∑w|∆F2|2/(NO - NV)]1/2
.
ψ scans showing that crystal absorption effects could not be neglected.
The data were corrected for absorption using ABSORB19 for complexes
9 and 12 and a semiempirical method20 for complexes 11 and 13. The
function minimized during the least-squares refinement was ∑w(∆F2)2.
Weights were applied according to the scheme w ) 1/[σ2(Fo)2 + (aP)2]
(P ) (Fo2 + 2Fc2)/3) with a ) 0.1011, 0.0463, 0.0678, and 0.1041 for
complexes 9 and 11-13, respectively. Anomalous scattering correc-
tions were included in all structure factor calculations.21b Scattering
factors for neutral atoms were taken from ref 21a for nonhydrogen
atoms and from ref 22 for H. Among the low-angle reflections no
correction for secondary extinction was deemed necessary. All
calculations were carried out on an IBM PS2/80 personal computer
and on an ENCORE 91 computer. The structures were solved by the
heavy-atom method starting from three-dimensional Patterson maps
using the observed reflections. Structure refinements were carried out
using SHELX9223 and based on the unique total data for 11 and 13
and on the unique observed data for 9 and 12. Refinement was first
done isotropically and then anisotropically for all non-H atoms except
for the disordered atoms. Refinements of complexes 12 and 13 were
straightforward. In complex 9 one of the two CH2Cl2 solvent molecule
of crystallization was found to be affected by disorder which was solved
by splitting the carbon and chlorine atoms over three positions (A, B,
C) isotropically refined with site occupation factors of 0.5, 0.25, and
0.25, respectively. During the refinement the C-Cl bond distances
were constrained to be 1.75(1) Å. In complex 11 a C6D6 solvent
molecule of crystallization was found to be disordered over two
positions (A, B) rotated each other by about 30°. They were
isotropically refined with a site occupation factor of 0.5 constraining
the aromatic rings to be regular hexagons (C-C 1.39(1) Å). The X-ray
analysis revealed the presence of another C6D6 crystallization molecule
with its gravity center on a crystallographic center of symmetry. The
hydrogen atoms, except those related to the solvent molecules of
crystallization in 9 and 11, which were ignored, were located from
difference Fourier maps and introduced in the subsequent refinements
as fixed atom contribution with U’s fixed at 0.08 for 9, 11, and 13 and
0.10 Å2 for 12. The final difference maps showed no unusual feature,
with no significant peak above the general background. The crystal
Scheme 1
chirality of complex 13, which crystallizes in a polar space group, was
tested by inverting all the coordinates (x, y, z|-x, -y, -z) and refining
to convergence once again. The resulting R values quoted in Table 1
indicated that the original choice should be considered the correct one.
Final atomic coordinates are listed in Tables S2-S5 for non-H atoms
and in Tables S6-S9 for hydrogens. Thermal parameters are given in
Tables S10-S13, and bond distances and angles, in Tables S14-S17.24
Results and Discussion
The synthesis of our target chelating ligand L2, 6, is outlined
in Scheme 1. This stepwise synthesis starts from commercially
available 1 and involves classic methodologies for the prepara-
tion of the intermediates 2-5 leading to the diphosphine, 6.
Specific reference to the methods applied, along with a detailed
synthesis of each intermediate, has been reported in the
Experimental Section. The present strategy has the advantage
of being easily scaled to ca. 20 g of the target diphosphine. It
is worth noting that the last step (h) of the sequence (Scheme
1) should in principle allow the generation of a variety of
different substituted diphosphines depending on the dialkyl- or
diarylchlorophosphine used.
(19) Ugozzoli, F. ABSORB, a Program for Fo Absorption Correction.
Comput. Chem. 1987, 11, 109.
(20) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1968, A24, 351.
(21) (a) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, England, 1974; Vol. IV, p 99. (b) Ibid., p 149.
(22) Stewart, R. F.; Davidson, E. R.; Simpson, W. T. J. Chem. Phys. 1965,
42, 3175.
(23) Sheldrick, G. M. SHELXL92 Gamma Test: Program for Crystal
Structure Refinement; University of Go¨ttingen: Go¨ttingen, Germany,
1992.
(24) See paragraph at the end regarding Supporting Information.

3358 Inorganic Chemistry, Vol. 36, No. 15, 1997
Lesueur et al.
Scheme 2
Ligand 6 has been characterized as reported in the Experi-
mental Section. Its 31P{1H} NMR spectrum shows a singlet at
-11.5 ppm, while the bridging methylene appears as a triplet
at 4.45 ppm (JP-H, 2.0 Hz) in the 1H NMR. It has been engaged
in the complexation of some metal fragments which can be
considered as prototypes in organometallic chemistry. Their
syntheses are reported in Scheme 2.
Figure 1. ORTEP drawing of complex 9 (30% probability ellipsoids).
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Complex 9
Although complexes 7 and 8 are useful starting materials,
their paramagnetism did not allow an inspection of the ligand’s
NMR characteristics when bound a metal. The magnetic
moment suggests a typical tetrahedral coordination geometry.
The NMR spectra of 9 and 10 are, on the contrary, particularly
significant. Due to the rather narrow P‚‚‚P bite angle and the
constantly rigid conformation of the metallacycle, we assume
that our compounds are exclusively cis, not only in the solid
state (Vide infra) but also in solution.25 In the case of 9, the
31P{1H} NMR spectrum shows a singlet for the two phosphorus
atoms at 23.4 ppm, in agreement with a variety of [(PR3)2PdCl2]
complexes,26 while in the case of 10 the signal is a 1:4:1
multiplet at 3.55 ppm, with a JPt-P ) 3.686 Hz. Such values
should be compared with those of other PtCl2-diphosphine
metallacycles containing a bidentate phosphorus ligand in which
the two PPh2 fragments are bridged by an aliphatic chain of
variable length.27 Both values seem to be affected, without
showing a regular trend, by the size of the metallacycle, unlike
Pd1-Cl2
Pd1-P1
Pd1-P2
P1-C1
2.360(1)
2.271(1)
2.268(1)
1.823(5)
P1-C31
P2-C13
P2-C41
P2-C51
1.840(5)
1.828(5)
1.833(4)
1.814(5)
P1-Pd1-P2
Cl2-Pd1-P2
Cl2-Pd1-P1
Cl1-Pd1-P2
Cl1-Pd1-P1
Cl1-Pd1-Cl2
Pd1-P1-C31
Pd1-P1-C21
Pd1-P1-C1
96.4(1)
165.8(1)
84.6(1)
91.0(1)
170.7(1)
89.5(1)
111.6(2)
123.7(2)
107.0(1)
C21-P1-C31
C1-P1-C31
C1-P1-C21
Pd1-P2-C51
Pd1-P2-C41
Pd1-P2-C13
C41-P2-C51
C13-P2-C51
C13-P2-C41
97.9(2)
110.1(2)
105.8(2)
114.1(2)
116.1(2)
112.3(2)
101.4(2)
109.4(2)
102.6(2)
The distortion is mainly indicated by the Cl2-Pd-P2 bond
angle [165.8(1)°] (Table 2) and the tetrahedral displacements
of the atoms from the mean coordination plane: Pd1, 0.018(1);
Cl1, 0.145(2); Cl2, -0.271(2); P1, 0.149(2); P2, -0.265(2) Å.
The chelating behavior of the ligand results in an eight-
membered chelation ring which assumes a distorted boat-boat
conformation (Figure 5a), the P1, C1, C8, and C13 atoms
defining the basal plane (maximum displacement 0.007(5) Å
for C8). The angle formed by the almost parallel C8-C13 and
P1-C1 bonds is 8.7(3)°. This feature of the metallacycle could
be described, considering the C1-C6-C7-C8 [-67.1(6)°] and
P1-Pd1-P2-C13 [-30.2(2)°], by the torsion angles which
should be equal to zero in a nondistorted boat-boat conforma-
tion. It is worth noting that the value of the first torsion angle
is comparable with those in complexes 11 and 12 (Vide infra)
(-80.4(8) and -74.6(5)°, respectively), while the value of the
latter indicates a deformation larger than that in complexes 11
and 12 where the P1-Pd1-P2-C13 torsion angle is 2.7(2) and
-3.9(1)°, respectively. The conformation of the metallacycle
is such as to orient the H71 hydrogen atom almost perpendicular
to the coordination plane (Pd‚‚‚H71, 2.46 Å), the angle between
the Pd1‚‚‚H71 line and the normal to the plane being 19.1(3)°.
The P1‚‚‚P2 bite distance is 3.385(2) Å. The phenyl rings of
the ligand 6 adopt a conformation which results in a pair of
hydrogen atoms (H36, H52) of different rings capping the metal
(Pd1‚‚‚H36, 2.77; Pd1‚‚‚H52, 2.89 Å) on the opposite side with
respect to H71. The plane through Pd1, H36, and H52 forms
a dihedral angle of 82.9° with the coordination plane. In spite
of different coordination geometries in complexes 9, 11, and
12 the mutual orientation of the C1‚‚‚C6 (Ph1) and C8‚‚‚C13
(Ph2) aromatic rings does not vary remarkably, as indicated by
the values of the dihedral angle between Ph1 and Ph2 [81.4(2),
76.6(2), and 77.8(2)° for 9, 11, and 12, respectively] and the
1
previous observations for the smaller metallacycles.28 The H
NMR spectrum for both 9 and 10 shows clearly differentiated
exo and endo protons of the bridging methylene. The two
protons become, in fact, diastereotopic on complexation. The
endo proton (complex 9) gives rise to a doublet of triplets at
6.45 ppm, due both to the geminal and phosphorus coupling
(JHH, 14 Hz; JPH, 3.0 Hz), while in the case of 10 the endo
proton (6.46 ppm) appears as a broad doublet due to the barely
detectable P-H coupling. The exo proton is a doublet at 3.84
ppm (JH-H, 14 Hz, 9) and 3.44 (JH-H, 14 Hz, 10). The
difference in chemical shift between the pair of doublets arising
from the -CH2- moiety in the complexed form of the ligand
is particularly sensitive to the nature of the metal, its coordina-
tion number, or in general its chemical environment. One of
the explanations which can be invoked may be the geometrical
proximity, i.e., a long-range interaction between the endo proton
and the metal. The X-ray analysis of 9 is particularly informa-
tive in this sense. The metal has the distorted square planar
geometry shown in Figure 1.
(25) In all the metallacycles derived from the same skeleton, regardless of
the nature of the donor atom O,6 N,29 and P cis compounds have been
exclusively obtained.
(26) (a) Meek, D. W.; Nicpon, P. E.; Imhof Meek, V. J. Am. Chem. Soc.
1970, 92, 5351. b) Phosphorus-31 NMR Spectroscopy in Stereochem-
ical Analysis; Verkade, J. G., Quin, L. D., Eds.; VCH: Weinheim,
Germany, 1987.
(27) Lindner, E.; Fawzi, R.; Mayer, H. A.; Eichele, K.; Hiller, W.
Organometallics 1992, 10, 1033.
(28) Garrou, P. E.; Chem. ReV. 1981, 81, 229.

A Bidentate Bisphosphine
Inorganic Chemistry, Vol. 36, No. 15, 1997 3359
Table 3. Selected Bond Distances (Å) and Angles (deg) for
Complex 11
Pd1-P1
Pd1-P2
Pd1-P3
P1-C1
P1-C21
P1-C31
2.328(2)
2.324(2)
2.289(2)
1.854(6)
1.824(6)
1.828(7)
P2-C13
P2-C41
P2-C51
P3-C61
P3-C71
P3-C81
1.845(5)
1.838(5)
1.831(6)
1.819(8)
1.838(6)
1.845(6)
P2-Pd1-P3
P1-Pd1-P3
P1-Pd1-P2
Pd1-P1-C31
Pd1-P1-C21
Pd1-P1-C1
C21-P1-C31
C1-P1-C31
C1-P1-C21
Pd1-P2-C51
Pd1-P2-C41
122.6(1)
125.7(1)
111.6(1)
113.6(2)
114.8(2)
122.0(2)
101.5(3)
102.0(3)
100.0(3)
119.7(2)
114.5(2)
Pd1-P2-C13
C41-P2-C51
C13-P2-C51
C13-P2-C41
Pd1-P3-C81
Pd1-P3-C71
Pd1-P3-C61
C71-P3-C81
C61-P3-C81
C61-P3-C71
113.0(2)
101.2(3)
103.9(3)
102.4(2)
120.7(3)
118.6(2)
109.2(2)
100.0(3)
103.1(3)
102.9(3)
Scheme 4
Figure 2. ORTEP drawing of complex 11 (30% probability ellipsoids).
Scheme 3
Pd1‚‚‚H71 line with the normal to the co-ordination plane being
41.6°. No other intramolecular Pd‚‚‚H contacts shorter than
3.02 Å are observed. The P1‚‚‚P2 bite distance [3.847(2) Å]
is rather wide, due to the trigonal coordination of the metal. In
C5-C6-C8-C9 torsion angle [40.1(6), 45.4(7), and 40.8(4)°
for 9, 11, and 12, respectively] which reflects the bending and
the twisting of the two rings. Similar structural parameters have
been observed in the structure of 10.29
Complex 9 has been engaged in a number of transformations,
demonstrating its utility as a starting material. Reduction with
hydrazine in the presence of PPh3 gave the tricoordinated Pd0
derivative 11 (Scheme 3).30
The 31P{1H} NMR spectrum of 11 shows two singlets at 23.9
and 6.8 ppm for the phosphorus set, the first one belonging to
the bidentate phosphine. It may be that the hydrogens from
the bridging methylene play a particular role, protecting the
coordinative unsaturation of the metal, as suggested by the
structure of 11, shown in Figure 2.
1
the H NMR spectrum of 11, the resonances of endo and exo
protons (∆ ) 3.07 ppm) are clearly separated and give rise to
two distinct pairs of doublets (JH-H ) 14 Hz), though the
coupling of the endo one can be missed because of the rather
broad shape of the peaks. The C‚‚‚H‚‚‚M interaction mentioned
above is structurally or spectroscopically detectable only when
the C-H bond is kept in a fixed position close to the metal,
reflecting the rigid overall conformation of the molecule.33
Complex 11 can be a particularly useful source of Pd(0) for
making Pd-C bonds Via oxidative addition reactions.34 One
of them is reported in Scheme 4.
The reaction with benzyl chloride led to the synthesis of a
η2-monobenzyl derivative.35 The 31P{1H} NMR spectrum
1
displays two singlets at 9.6 and 27.7 ppm, while the H NMR
Palladium is trigonally coordinated to the phosphorus donor
atoms and the out-of-plane distance from the P3 plane is 0.046(1)
Å. The Pd-P1 [2.328(2) Å] and Pd-P2 [2.324(2) Å] bond
distances are in good agreement with the values reported in the
literature for Pd(0)-PPh3 bonds e.g. 2.316(5) Å in [Pd-
(PPh3)3].31,32 They are significantly longer than those observed
in the Pd(II) square planar complex 9. The eight-membered
chelate ring assumes a boat-boat conformation (Figure 5b);
the angle between the P1-C1 and C8-C13 bonds defining the
basal plane [26.4(4)°] is remarkably wider than that found in
9. The Pd‚‚‚H71 contact is 2.61 Å, the angle between the
spectrum of the bridging methylene shows a doublet for the
Hexo at 3.25 ppm, with the resonances of the Hendo overlapping
(33) (a) Crabtree, R. H.; Hamilton, D. G. AdV. Organomet. Chem. 1988,
28, 299. (b) Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1993, 32,
789 and references therein. (c) Brookhart, M.; Green, M. L. H. J.
Organomet. Chem. 1983, 250, 395. (d) Brookhart, M.; Green, M. L.
H.; Wong, L. L. Prog. Inorg. Chem. 1988, 36, 1. (e) Kretz, C. M.;
Gallo, E.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J. Am.
Chem. Soc. 1994, 116, 10775.
(34) (a) Canty, A. J. In ComprehensiVe Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, U.K.,
1995; Vol. 9, Chapter 5. (b) Stille, J. K. In The Chemistry of the Metal-
Carbon Bond; Hartley, F. R., Patai, S., Eds.; Wiley: New York, 1985;
Vol. 2, p 625.
(35) (a) Dryden, N. H.; Legzdins, P.; Trotter, J.; Yee, V. C. Organometallics
1991, 10, 2857. (b) Solan, G. A.; Cozzi, P. G.; Floriani, C.; Chiesi-
Villa, A.; Rizzoli, C. Organometallics 1994, 13, 2572. (c) Pellecchia,
C.; Grassi, A.; Immirzi, A. J. Am. Chem. Soc. 1993, 115, 1160. (d)
Kalinin, V. N.; Cherepanov, I. A.; Moiseev, S. K.; Batsanov, A. S.;
Struchkov, Yu. T. MendeleeV Commun. 1991, 77. (e) Jordan, R. F.;
LaPointe, R. E.; Baenziger, N.; Hinch, G. D. Organometallics 1990,
9, 1539. (f) Canty, A. J.; Traill, P. R.; Skelton, B. W.; White, A. H.
J. Organomet. Chem. 1992, 433, 213.
(29) Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Unpublished results.
(30) (a) Malatesta, L.; Angoletta, M. J. Chem. Soc. 1952, 1186. (b) Coulson,
D. R. Inorg. Synth. 1972, 13, 21. (c) Dobinson, G. C.; Mason, R.;
Robertson, G. B.; Ugo, R.; Conti, F.; Morelli, D.; Cenini, S.; Bonati,
F. J. Chem. Soc., Chem. Commun. 1967, 739. (d) Clemmit, A. F.;
Glockling, F. J. Chem. Soc. A 1969, 2163.
(31) Sergienko, V. S.; Porai-Koshits, M. A. Zh. Strukt. Khim. 1987, 28,
103.
(32) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1.

3360 Inorganic Chemistry, Vol. 36, No. 15, 1997
Lesueur et al.
Scheme 5
of the respective van der Waals radii. The conformation of the
chelation ring is close to that observed in 11 (Figure 5c). The
angle formed by the P1-C1 and C8-C13 bonds defining the
basal plane is 18.2(2)°. The value of the P1‚‚‚P2 bite distance
[3.638(2) Å] is intermediate between those observed in 9 and
11. The conformation of the metallacycle allows the H71
hydrogen to approach the palladium metal at a distance of 2.77
Å.
The question arising at this stage is the following: Can we
force the bridging methylene to play, besides its role as a
spectroscopic probe, a chemical role? It is well-known that
intramolecular C-H bond activation can be the intermediate
step in the intermolecular hydrocarbon activation.5 The reaction
to test this possibility concerns 6 with RhCl3 shown in Scheme
5. It reports an electrophilic attack37 by Rh(III) on the bridging
methylene.
This reaction was carried out in acetonitrile which functions
as a base in case of HCl formation. The electrophilic attack of
Rh(III) on the bridging methylene is assisted by the close
proximity, imposed by the rigid boat-boat conformation of the
metallacycle, between the metal and the Hendo. Complex 13
has been isolated in high yields as deep yellow crystals. The
acetonitrile molecule is only loosely bonded to the metal and
is lost under vacuum (see Experimental Section). NMR spectra
have been recorded on the desolvated form. The metalated
carbon appears as a doublet in the 13C NMR spectrum at 57.28
ppm, with a corresponding JRh-C coupling constant of 22.4 Hz.38
In the 31P{1H} NMR spectrum we observe two doublets at 60.3
ppm (JRh-P ) 145 Hz) and 54.6 (JRh-P ) 134 Hz). Such
coupling constants are in accordance with the presence of a five-
coordinate Rh in the desolvated form.39 The exo proton of the
bridging methylene is not particularly informative since it falls
in the crowded aromatic region, between 7.1 and 7.8 ppm. The
X-ray analysis of 13 has been carried out on its solvated form
(Figure 4, Table 5).
The metal shows a slightly distorted octahedral coordination
provided by the P1, P2, and C7 atoms from 6, two chlorine
atoms, and the nitrogen atom of an acetonitrile molecule. This
distortion is mainly due to the trischelating nature of the ligand
which displays a fac arrangement around the metal (P1-Rh-
P2, 97.7(1)°). The resulting two five-membered chelate rings
are nearly perpendicular to each other [dihedral angle between
their mean planes, 84.1(1)°], one (Rh1,P2,C13,C8,C7) which
is planar and the other (Rh1,P1,C1,C6,C7) folded by 35.0(2)°
along the P1‚‚‚C7 line. This folding is probably due to the sp3
character of the C7 carbon atom and the fac arrangement of
Figure 3. ORTEP drawing of complex 12 (30% probability ellipsoids).
Table 4. Selected Bond Distances (Å) and Angles (deg) for
Complex 12
Pd1-Cl1
Pd1-P1
Pd1-P2
Pd1-C61
Pd1-C67
P1-C1
2.541(2)
2.383(1)
2.259(1)
2.408(6)
2.113(6)
1.838(4)
P1-C21
P1-C31
P2-C13
P2-C41
P2-C51
1.833(5)
1.830(4)
1.830(4)
1.838(4)
1.822(3)
C61-Pd1-C67
P2-Pd1-C67
P2-Pd1-C61
P1-Pd1-C67
P1-Pd1-C61
P1-Pd1-P2
Cl1-Pd1-C67
Cl1-Pd1-C61
Cl1-Pd1-P2
Cl1-Pd1-P1
Pd1-P1-C31
36.4(2)
90.2(1)
109.1(1)
161.9(1)
126.0(1)
103.2(1)
89.9(1)
103.1(1)
124.1(1)
92.6(1)
Pd1-P1-C21
Pd1-P1-C1
C21-P1-C31
C1-P1-C31
C1-P1-C21
Pd1-P2-C51
Pd1-P2-C41
Pd1-P2-C13
C41-P2-C51
C13-P2-C51
C13-P2-C41
114.7(1)
120.2(1)
102.2(2)
102.3(2)
104.6(2)
115.7(1)
112.5(1)
115.4(1)
104.1(2)
105.6(2)
101.9(2)
110.7(1)
those of the aromatic protons. The η2-bonding mode of the
benzyl group has been revealed by the 1H NMR spectrum with
the presence of a pair of unresolved doublets for the two
heterotopic benzylic protons (see Experimental Section)35 and
confirmed by an X-ray analysis of 12 (Figure 3).
The structure consists of the packing of 12 and toluene solvent
molecules of crystallization in the molar ratio of 1/1. Selected
bond distances and angles are listed in Table 4. The range of
the palladium-carbon distances suggests a metal-benzyl η2-
bonding mode involving the C61 and C67 carbon atoms [Pd1-
C67, 2.113(6) Å; Pd1-C61, 2.408(6)], the Pd1-C62, 2.729(6),
and Pd-C66, 3.315(6) Å, being too long to be considered as
interactions. The presence of a η2-interaction instead of a
σ-bond is supported by the value of the Pd-C67 distance,
though significantly longer than those observed for Pd-C
σ-bonds [mean value 2.064(14) Å]36 and by the value of the
Pd1-C67-C61 angle [83.0(4)°] which differs remarkably from
the tetrahedral one. The Pd1-P2 [2.259(1) Å] bond distance
is close to those observed in complex 9, while the Pd1-P1
[2.383(1) Å] as well as the Pd1-Cl1 [2.541(2) Å] bond
distances are remarkably longer. This lengthening could be
attributed to intraligand steric hindrance rather than to electronic
effects, as indicated by the P1‚‚‚Cl1 [3.560(2) Å] and C67-
Cl1 [3.301(5) Å] contacts which nearly correspond to the sum
(37) (a) Shilov, A. E. The ActiVation of Saturated Hydrocarbons by
Transition Metal Complexes; Reidel: Dordrecht, The Netherlands.
1984. (b) Labinger, J. A.; Herring, A. M.; Bercaw, J. E. AdV. Chem.
Ser. 1992, No. 230, 221. Luinstra, G. A.; Labinger, J. A.; Bercaw, J.
E. J. Am. Chem. Soc. 1993, 115, 3004. (c) Periana, R. Science 1993,
259, 340.
(38) Mann, B. E.; Taylor, B. F. 13-C NMR Data of Organometallic
Compounds; Academic: New York, 1981; p 44.
(39) Pregosin, P. R.; Kunz, R. W. In NMR Basic Principles and Progress;
Springer: Berlin, 1979; Vol. 16.
(36) (a) Geib, S. J.; Rheingold, A. L. Acta Crystallogr. Sect. C 1987, 43,
1427. (b) Osakada, K.; Ozawa, Y.; Yamamoto, A. J. Chem. Soc.,
Dalton Trans. 1991, 759. (c) Osakada, K.; Ozawa, Y.; Yamamoto,
A. Bull. Chem. Soc. Jpn. 1991, 64, 2002. (d) Reger, D. L.; Garza, D.
G.; Lebioda, L. Organometallics 1991, 10, 902.

A Bidentate Bisphosphine
Inorganic Chemistry, Vol. 36, No. 15, 1997 3361
Figure 5. SCHAKAL drawing showing the conformation of the
chelation rings in complexes 9 (a), 11 (b), 12 (c), and 13 (d).
Scheme 6
Figure 4. ORTEP drawing of complex 13 (30% probability ellipsoids).
Table 5. Selected Bond Distances (Å) and Angles (deg) for
Complex 13
Rh1-Cl1
Rh1-Cl2
Rh1-P1
Rh1-P2
Rh1-N1
Rh1-C7
2.419(2)
2.473(3)
2.265(2)
2.252(2)
2.107(6)
2.108(7)
P1-C1
1.807(9)
1.827(8)
1.825(9)
1.828(9)
1.853(8)
1.831(9)
P1-C21
P1-C31
P2-C13
P2-C41
P2-C51
N1-Rh1-C7
P2-Rh1-C7
P2-Rh1-N1
P1-Rh1-C7
P1-Rh1-N1
P1-Rh1-P2
Cl2-Rh1-C7
Cl2-Rh1-N1
Cl2-Rh1-P2
Cl2-Rh1-P1
Cl1-Rh1-C7
Cl1-Rh1-N1
Cl1-Rh1-P2
Cl1-Rh1-P1
Cl1-Rh1-Cl2
90.5(3)
86.3(2)
87.3(2)
81.4(2)
170.1(2)
97.7(1)
176.8(2)
86.3(2)
94.3(1)
101.6(1)
88.5(2)
86.5(2)
171.9(1)
87.6(1)
90.5(1)
Rh1-P1-C31
Rh1-P1-C21
Rh1-P1-C1
C21-P1-C31
C1-P1-C31
C1-P1-C21
Rh1-P2-C51
Rh1-P2-C41
Rh1-P2-C13
C41-P2-C51
C13-P2-C51
C13-P2-C41
Rh1-N1-C61
N1-C61-C62
119.9(3)
121.2(3)
100.9(3)
100.8(4)
106.6(4)
106.2(4)
123.0(3)
113.7(3)
103.2(3)
99.4(4)
110.5(4)
106.1(4)
174.3(7)
175.6(10)
complex, 14. It has been obtained as a green-yellow crystalline
solid. Its relatively high stability depends on the steric
protection of the diphosphine ligand which provides a type of
protective cage. The easy displacement of C2H4 by carbon
monoxide led to the tetracoordinate Ni(0)-dicarbonyl derivative
15.42 Let us now compare the spectroscopic properties of the
ligand in the two cases. The 31P{1H} NMR spectrum shows
for 14 and 15 singlets at 22.7 (C6D6) and 24.8 (CD2Cl2) ppm,
1
respectively. The H NMR spectrum shows a doublet for the
Hexo in 14 at 3.49 ppm, while the Hendo overlaps with the
ethylene protons in the aromatic region (6.60-7.50 ppm). In
the case of 15, Hendo appears as a doublet at 5.91 ppm, while
the Hexo remains almost unchanged at 3.42 ppm. In the X-ray
analysis of 1543 we observed the usual structural feature of the
metal-bonded ligand 6, including the metallacycle conformation.
These results show how the methylene protons are sensitive to
the metal environment. In the meantime we found, however,
that they are only slightly sensitive to the solvent used for the
NMR spectrum. In all the cases so far reported, we assumed
that the eight-membered metallacycle conformation does not
change significantly because of the presence of the transition
metal and thanks to its size.25 In order to prove the consequence
of the ring size on the spectroscopic behavior of the bridging
the ligand (Figure 5d). Other peculiar features are the C1-
C6-C7-C8 torsion angle [-93.3(9)°], the P1‚‚‚P2 bite distance
[3.403(2) Å], and the dihedral angle between the aromatic rings
of the ligand [113.0(3)°]. The two Rh-P bond lengths [Rh-
P1, 2.265(2); Rh-P2, 2.252(2) Å], as well as the Rh-C7
[2.108(7) Å] bond distance are in agreement with the values
observed in the Milstein complex5a and metalated Rh(III)
species.40 The relatively high trans-influence of the methylenic
carbon is shown by the lengthening of Rh-Cl2 [2.473(3) Å]
with respect to Rh-Cl1 [2.419(2) Å].
In order to better define the spectroscopic and, eventually,
the steric properties of our novel chelating phosphine, we
explored its binding ability in some nickel and iron complexes.
The reaction in Scheme 6 shows the synthesis of two Ni0
derivatives with different coordination number at the metal.
(41) (a) Chatt, J.; Hart, F. A.; Watson, H. R. J. Chem. Soc. 1962, 2537.
(b) Aresta, M.; Nobile, C. F.; Sacco, A. Inorg. Chim. Acta 1975, 12,
167.
(42) Cenini, S.; Ratcliff, B.; Ugo, R. Gazz. Chim. Ital. 1974, 104, 1161.
(43) Crystal data for 15: C39H30NiO2P2‚CD2Cl2, M ) 738.3, triclinic, space
group P1h, a ) 13.157(5) Å, b ) 14.087(6) Å, c ) 11.123(4) Å, R )
112.00(3)°, â ) 106.59(4)°, γ ) 94.13(4)°, Z ) 2, R ) 0.045 (wR2
) 0.112).
The conventional reduction of [Ni(acac)2] in the presence of
13,41
C2H4
afforded the very reactive monoethylene-Ni(0)
(40) Sharp, P. R. In ComprehensiVe Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, U.K.,
1995; Vol. 8, Chapter 2.

3362 Inorganic Chemistry, Vol. 36, No. 15, 1997
Lesueur et al.
Scheme 7
the phosphorus at 56.8 (s) ppm. In both complexes the local
symmetry of iron is C2V, with the phosphorus occupying two
equatorial sites,44 which thus gives rise to CO IR-active
stretching bands 2A1 + B2 at 2008, 1938, 1915 cm-1 (complex
18) and 1984, 1909, 1890 cm-1 (complex 19).
Concluding Remarks
The use of the specifically designed ligand 6 with a variety
of organometallic fragments served to emphasize some of its
structural, chemical, and spectroscopic properties. Among them
we should mention the following: (1) The steric hindrance along
with the weak interaction of the metal with the endo hydrogen
of the bridging methylene provides a protective cavity for
reactive, that is coordinatively unsaturated, metal centers. (2)
The close geometrical proximity between the endo hydrogen
from the bridging methylene and the metal favors metalation,
which can play a very peculiar role in the σ-bond metathesis
reaction with hydrocarbons, thus promoting intermolecular
activation. (3) The rigid conformation of the eight-membered
metallacycle allowed the differentiation of the exo and endo
protons. The latter one is able to serve as a spectroscopic probe
for structural correlations, particularly considering the changes
in chemical shift and the magnitude of the JP-H coupling
constant.26 The first argument concerning this structural
spectroscopic relationship is based on geometrical constraints
and postulates a sort of weak interaction between the metal
center and the Hendo proton. However, this kind of interaction
was not further specified. An agostic type of interaction can
be excluded, because this would result in a high-field shift for
the proton which undergoes the agostic interaction.33c,d This is
clearly not the case. Instead, the opposite trend was observed,
a downfield shift of the signal assigned to Hendo, compared to
the free ligand. This phenomenon may be explained in terms
of an increased deshielding of the endo proton, because the
formation of a metallacycle results in an additional ring current
which opposes the external field.28,45 Additional electron density
increases the deshielding and leads to a further downfield shift,
compared to the electron-poor derivatives.
Scheme 8
methylene, we prepared the 10-membered metallacycle using
the phosphite-phosphine bidentate ligand 17 derived from the
same skeleton (Scheme 7).
Ligand 17 has been reacted with [Fe(CO)3(C8H14)2]14 to afford
18. Ligand 17 can display either a bridging or a chelating
bonding mode,4 the latter one being shown in the proposed
structure of 18. The chelate bonding mode of 17, however, is
supported by the X-ray structural determination on the closely
related [L′2Mo(CO)3].29 The 31P{1H} NMR spectrum shows a
singlet at 172.0 ppm, while that of 17 is at 113.5 ppm. The
bridging methylene is a poorly defined triplet at 4.09 ppm in
the free ligand 17, while the same triplet is displaced to 3.29
ppm in 18 [JP-H ) 11.8 Hz]. According to the geometrical
flexibility of the 10-membered metallacycle, the two methylene
protons are not differentiated; thus -CH2- cannot serve as a
spectroscopic probe for the metal environment. This is proved
by the comparison with complex 19, where the same [Fe(CO)3]
fragment is bonded to ligand 6 to form an eight-membered
metallacycle (Scheme 8).
Acknowledgment. We thank the “Fonds National Suisse de
la Recherche Scientifique” (Bern, Switzerland, Grant No. 20-
40268.94) and Ciba Specialty Chemicals (Basel, Switzerland)
for financial support.
Supporting Information Available: X-ray crystallographic files,
in CIF format, for complexes 9 and 11-13 are available on the Internet
only. Access information is given on any current masthead page.
IC9700819
(44) (a) Casey, C. P.; Whiteker, G. T.; Campana, C. F.; Powell, D. R. Inorg.
Chem. 1990, 29, 3376. (b) Ittel, S. D.; Tolman, C. A.; Krusic, P. J.;
English, A. D.; Jesson, J. P. Inorg. Chem. 1978, 17, 3432.
(45) Lindner, E. AdV. Heterocyclic Chem. 1986, 39, 239.
In the case of 19, the bridging methylene protons appear as
a pair of doublets at 3.28 and 5.83 ppm (JH-H ) 14 Hz) and