Diphosphines Possessing Electronically Different Donor Groups: Synthesis and Coordination Chemistry of the Unsymmetrical Di(N-pyrrolyl)phosphino-Functionalized dppm Analogue Ph2PCH 2P(NC4H4)2

Article abstract of DOI:10.1021/ic034487z

The unsymmetrical diphosphinomethane ligand Ph₂PCH ₂P(NC₄H₄)₂ L has been prepared from the reaction of Ph₂P-CH₂Li with PCl(NC₄H ₄)₂. The diphenyl

Full text of DOI:10.1021/ic034487z

Inorg. Chem. 2003, 42, 7227−7238
Diphosphines Possessing Electronically Different Donor Groups:
Synthesis and Coordination Chemistry of the Unsymmetrical
Di(N-pyrrolyl)phosphino-Functionalized dppm Analogue
Ph2PCH P(NC H )
2
4 4 2
,†
Andrew D. Burrows,* Mary F. Mahon,† Steven P. Nolan,‡ and Maurizio Varrone†
Department of Chemistry, UniVersity of Bath, ClaVerton Down, Bath BA2 7AY, U.K., and
Department of Chemistry, UniVersity of New Orleans, New Orleans, Louisiana 70148
Received May 9, 2003
The unsymmetrical diphosphinomethane ligand Ph PCH P(NC H ) L has been prepared from the reaction of Ph P-
2
2
4
4 2
2
CH Li with PCl(NC H ) . The diphenylphosphino group can be selectively oxidized with sulfur to give Ph2P(S)-
2
4 4 2
CH P(NC H ) 1. The reaction of L with [MCl2(cod)] (M ) Pd, Pt) gives the chelate complexes [MCl2(L-κ2P,P′)] (2,
2
4 4 2
M ) Pd; 3, M ) Pt) in which the M−P bond to the di(N-pyrrolyl)phosphino group is shorter than that to the
corresponding diphenylphosphino group. However, the shorter Pd−P bond is cleaved on reaction of 2 with an
additional 1 equiv of L to give [PdCl2(L-κ1P)2] 4. Complex 4 reacts with [PdCl2(cod)] to regenerate 2, and with
[Pd2(dba)3]‚CHCl3 to give the palladium(I) dimer [Pd2Cl2(µ-L)2] 5, which exists in solution and the solid state as a
1:1 mixture of head-to-head (HH) and head-to-tail (HT) isomers. The palladium(II) dimer [Pd2Cl2(CH ) (µ-L)2] 6,
3 2
formed by the reaction of [PdCl(CH )(cod)] with L, also exists in solution as a mixture of HH and HT isomers,
3
although in this case the HT isomer prevails at low temperature and crystallizes preferentially. Complex 6 reacts
with TlPF to give the A-frame complex [Pd2(CH ) (µ-Cl)(µ-L)2]PF 7. The reaction of L with [RuCp*(µ3-Cl)]4 leads
6
3 2
6
to the dimer [Ru2Cp*2(µ-Cl)2(µ-L)] 8, for which the enthalpy of reaction has been measured. The reaction of L with
[Rh(µ-Cl)(cod)]2 gives a mixture of compounds from which the dimer [Rh2(µ-Cl)(cod)2(µ-L)]PF 9 can be isolated.
6
The crystal structures of 2‚CHCl3, 3‚CH Cl2, 4, 5‚1/4CH Cl2, 6, 7‚2CH Cl2, 8, and 9‚CH Cl2 are reported.
2
2
2
2
Introduction
the copolymerization of CO and ethene, in contrast to
analogous complexes of dppm.4
Diphosphinomethanes such as bis(diphenylphosphino)-
methane (dppm) are well-established as flexible ligands, with
chelating, terminal, and bridging coordination modes all
possible.1,2 The small bite angle and inherent strain of the
chelating mode can lead to interesting chemistry, such as
the recent isolation of an alkylrhodium complex stabilized
by agostic interactions.3 The reactivities and catalytic proper-
ties of diphosphinomethane complexes are dependent on the
substituents on the phosphino groups. Thus, for example,
palladium(II) complexes of Ar2PCH2PAr2, in which Ar is
an ortho-substituted phenyl group, are efficient catalysts for
Unsymmetrical diphosphinomethanes of the general for-
mula R2PCH2PR′2 have attracted less attention than their
symmetrical analogues. Grim and Mitchell reported ligands
of the type Ph2PCH2PRR′ and studied their group 6 carbonyl
derivatives.5 More recently Werner et al. have reported the
synthesis of a series of unsymmetrical diphosphinomethanes
and arsino(phosphino)methanes and presented studies on their
coordination chemistry with rhodium6,7 and palladium.8
We have recently become interested in functionalized
N-pyrrolyl phosphine ligands, since the N-pyrrolyl group
(4) Dossett, S. J.; Gillon, A.; Orpen, A. G.; Fleming, J. S.; Pringle, P. G.;
Wass, D. F.; Jones, M. D. Chem. Commun. 2001, 699-700.
(5) Grim, S. O.; Mitchell, J. D. Inorg. Chem. 1977, 16, 1770-1776.
(6) Wolf, J.; Manger, M.; Schmidt, U.; Fries, G.; Barth, D.; Weberndo¨rfer,
B.; Vicic, D. A.; Jones, W. D.; Werner, H. J. Chem. Soc., Dalton
Trans. 1999, 1867-1875.
(7) Werner, H.; Manger, M.; Schmidt, U.; Laubender, M.; Weberndo¨rfer,
B. Organometallics 1998, 17, 2619-2627.
(8) Schmidt, U.; Ilg, K.; Brandt, C. D.; Werner, H. J. Chem. Soc., Dalton
Trans. 2002, 2815-2824.
* E-mail: a.d.burrows@bath.ac.uk. Tel: +44 1225 386529. Fax: +44
1225 386231.
† University of Bath.
‡ University of New Orleans.
(1) Puddephatt, R. J. Chem. Soc. ReV. 1983, 12, 99-127.
(2) Anderson, G. K. AdV. Organomet. Chem. 1993, 35, 1-39.
(3) Urtel, H.; Meier, C.; Eisentra¨ger, F.; Rominger, F.; Joschek, J. P.;
Hofmann, P. Angew. Chem., Int. Ed. 2001, 40, 781-784.
10.1021/ic034487z CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/02/2003
Inorganic Chemistry, Vol. 42, No. 22, 2003 7227

Burrows et al.
ensures that the phosphorus center is a strong π-acceptor.9
As part of this program we have developed the keto-
functionalized N-pyrrolyl phosphines Ph2P{NC4H3C(O)Me-
2}10 and (H4C4N)2P{NC4H3C(O)Me-2}11 and investigated
their properties, including their hemilabile character.12 In this
paper we report the synthesis and group 10 chemistry of the
unsymmetrical diphosphinomethane Ph2PCH2P(NC4H4)2, in
which the two phosphino groups are isosteric,13 but differ
strongly in their electronic characters. We also report
examples of reactions with ruthenium(II) and rhodium(I)
complexes.
colorless oil. This was kept under reduced pressure (0.2 mbar) at
ambient temperature until no more volatiles were present. Distil-
lation (2.0 mbar, 83-85 °C) gave the product as a colorless oil.
Yield: 22.6 g (79%). 31P{1H} NMR (161.8 MHz, C6D6): δ 105.3
(s). 1H NMR (399.8 MHz, CDCl3): δ 6.79 (ps quin, 4H, J 2.0 Hz,
HR), 6.18 (ps t, 4H, J 2.0 Hz, Hâ). 13C{1H} NMR (100.5 MHz,
2
3
C6D6): δ 122.5 (d, JCP 18 Hz, CR), 113.9 (d, JCP 5 Hz, Câ).
Synthesis of Ph2PCH2P(NC4H4)2 L. A THF solution of Ph2-
PCH2Li (3.46 g, 0.017 mol) was added dropwise with stirring to a
THF-hexane solution of PCl(NC4H4)2 (3.66 g, 0.018 mol) at -78
°C. The mixture was allowed to reach ambient temperature, stirred
for further 2 h, and filtered. Evaporation of the solvent produced a
colorless oil, which was triturated with hexane to give a white
powder. This was separated by filtration, washed with small
amounts of a 1:1 mixture of THF-hexane, and dried under reduced
pressure. Yield: 4.62 g (76%). Anal. Calcd for C21H20N2P2: C,
69.6; H, 5.56; N, 7.73. Found: C, 69.5; H, 5.58; N, 7.82. 31P{1H}
Experimental Section
General. Reactions were routinely carried out using Schlenk-
line techniques under pure dry dinitrogen or argon, using dry
dioxgen-free solvents unless noted otherwise. Microanalyses (C,
H, and N) were carried out by Mr. Alan Carver (University of Bath
Microanalytical Service). NMR spectra were recorded on JEOL
EX-270, Varian Mercury 400, and Bruker Avance 300 spectrom-
eters referenced to TMS or 85% H3PO4. 31P{1H} NMR simulations
were carried out using gNMR.14 IR spectra were recorded on a
Nicolet Nexus spectrometer as Nujol mulls between KBr disks.
The complexes [PdCl2(cod)],15 [PtCl2(cod)],16 [Pd2(dba)3]‚CHCl3,17
[PdCl(CH3)(cod)],18 [RuCp*(µ3-Cl)]419 and [Rh(cod)(µ-Cl)]220 were
prepared by standard literature methods. Ph2PCH2Li was prepared
according to the method reported by Peterson.21 Pyrrole was dried
over molecular sieves and distilled before used. Triethylamine was
distilled over potassium before use. Calorimetric measurements were
made as previously reported.22
Synthesis of PCl(NC4H4)2. A 2.0 M solution of PCl3 in
dichloromethane (72.0 cm3, 0.144 mol) was placed in a three-neck
flask equipped with a glass frit and a dropping funnel charged with
pyrrole (19.34 g, 0.288 mol). The flask was then charged with THF
(200 cm3) and NEt3 (50 cm3, 0.356 mol). The first equivalent of
pyrrole was added dropwise over 2 h with stirring, and a white
precipitate formed immediately. The reaction mixture was stirred
for a further 2 h, and the second equivalent of pyrrole was added
dropwise over 4 h. The mixture was stirred overnight and filtered
into a Schlenk tube through the frit. The remaining solid was washed
with THF, and the washings were combined with the filtrate. The
resulting solution was evaporated under reduced pressure to give a
2
NMR (161.8 MHz, CDCl3): δ 66.1 (d, JPP 147 Hz), -25.5 (d,
1
2JPP 147 Hz). H NMR (399.8 MHz, CDCl3): δ 7.23-7.40 (m,
4H, Hm), 7.37-7.34 (m, 6H, Ho, Hp), 7.00 (ps quin, 4H, HR), 6.29
2
2
(ps t, 4H, Hâ), 3.18 (dd, 2H, JHP 6.0 Hz, JHP 1.6 Hz, CH2). 13C-
{1H} NMR (75.5 MHz, CDCl3): δ 136.8 (dd, JCP 14 Hz, JCP
8
1
3
Hz, Ci), 132.4 (dd, 2JCP 20 Hz, 4JCP 2 Hz, Co), 128.8 (s, Cp), 128.5
3
2
3
(d JPC 7 Hz, Cm), 123.0 (d, JCP 15 Hz, CR), 112.3 (d, JCP 4 Hz,
1
1
Câ), 31.0 (dd, JCP 26 Hz, JCP 20 Hz, CH2).
Synthesis of Ph2P(S)CH2P(NC4H4)2 1. Sulfur (0.090 g, 2.81
mmol) was added to a dichloromethane solution of L (0.089 g,
0.25 mmol) and the mixture stirred for 4 h. The undissolved sulfur
was removed by filtration, and the solution was concentrated under
reduced pressure. On standing for 24 h at -20 °C a yellow
crystalline precipitate of sulfur formed which was separated by
filtration and discarded. Hexane was added to the filtrate, which
on further standing at -20 °C for 24 h gave a colorless solid, which
was separated by filtration and dried under reduced pressure.
Yield: 0.080 g (82%). Anal. Calcd for C21H20N2P2S‚CH2Cl2: C,
55.1; H, 4.63; N, 5.84. Found: C, 55.1; H, 4.54; N, 6.00. 31P{1H}
2
2
NMR (161.8 MHz, CDCl3): δ 56.8 (d, JPP 85 Hz), 36.6 (d, JPP
85 Hz). 1H NMR (399.8 MHz, CDCl3): δ 7.74-7.68 (m, 4H, Hm),
7.47-7.36 (m, 6H, Ho, Hp), 6.87 (ps quin, 4H, HR), 6.17 (ps t, 4H,
Hâ), 3.66 (dd, 2H, 2JHP 13.2 Hz, 2JHP 1.2 Hz, CH2). 13C{1H} NMR
(75.5 MHz, CDCl3): δ 131.7 (s), 131.5 (s), 130.7 (d, J 10 Hz),
128.5 (d, J 12 Hz), 123.4 (d, 2JCP 17 Hz, CR), 112.3 (d, 3JCP 3 Hz,
Câ), 37.4 (dd, 1JCP 50 Hz, 1JCP 26 Hz, CH2). IR: ν(PS) 625 cm-1
.
Synthesis of [PdCl2(L-K2P,P′)] 2. [PdCl2(cod)] (0.155 g, 0.54
mmol) was added to a dichloromethane solution of L (0.197 g,
0.54 mmol). The mixture was stirred for 4 h, and then hexane was
added to precipitate a yellow powder. The powder was separated
by filtration, washed with hexane, and dried under reduced pressure.
Crystallization from dichloromethane-hexane gave yellow crystals.
Yield: 0.284 g (97%). Anal. Calcd for C21H20Cl2N2P2Pd‚3/4CH2-
Cl2: C, 43.3; H, 3.59; N, 4.64. Found: C, 43.7; H, 3.60; N, 4.66.
31P{1H} NMR (161.8 MHz, CDCl3): δ 0.0 (d, 2JPP 84 Hz), -46.7
(d, 2JPP 84 Hz). 1H NMR (399.8 MHz, CD2Cl2): δ 7.85-7.80 (m,
4H), 7.62-7.57 (m, 2H), 7.51-7.46 (m, 4H), 7.41 (ps quin, 4H,
HR), 6.41-6.40 (m, 4H, Hâ), 4.54 (dd, 2H, 2JHP 12.3 Hz, 2JHP 10.9
Hz, CH2).
(9) Moloy, K. G.; Petersen, J. L. J. Am. Chem. Soc. 1995, 117, 7696-
7710.
(10) Andrews, C. D.; Burrows, A. D.; Lynam, J. M.; Mahon, M. F.; Palmer,
M. T. New J. Chem. 2001, 25, 824-826.
(11) Burrows, A. D.; Mahon, M. F.; Palmer, M. T.; Varrone, M. Inorg.
Chem. 2002, 41, 1695-1697.
(12) Andrews, C. D.; Burrows, A. D.; Jeffery, J. C.; Lynam, J. M.; Mahon,
M. F. J. Organomet. Chem. 2003, 665, 15-22.
(13) Burrows, A. D. CrystEngComm 2001, 3, 217-221.
(14) Budlezaar, P. H. M. gNMR 4.0; Cherwell Scientific Publishing:
Oxford, 1997.
(15) Chatt, J.; Vallarino, L. M.; Venanzi, L. M. J. Chem. Soc. 1957, 3413-
3416.
(16) Drew, D.; Doyle, J. R. Inorg. Synth. 1972, 13, 47-55.
(17) Ukai, T.; Kawazura, H.; Ishii, Y.; Bonnet, J. J.; Ibers, J. A. J.
Organomet. Chem. 1974, 65, 253-266.
(18) Ru¨lke, R. E.; Ernsting, J. M.; Spek, A. L.; Elsevier: C. J.; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769-
5778.
(19) Fagan, P. J.; Ward, M. D.; Calabrese, J. C. J. Am. Chem. Soc. 1989,
111, 1698-1719.
(20) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1990, 28, 88-90.
(21) Peterson, D. J. J. Organomet. Chem. 1967, 8, 199-208.
(22) Li, C. B.; Serron, S.; Nolan, S. P.; Petersen, J. L. Organometallics
1996, 15, 4020-4029.
Synthesis of [PtCl2(L-K2P,P′)] 3. The synthesis was carried out
as for compound 2 using [PtCl2(cod)] (0.228 g, 0.61 mmol) and L
(0.221 g, 0.61 mmol). Crystallization from dichloromethane-
hexane gave colorless crystals. Yield: 0.379 g (98%). Anal. Calcd
for C21H20Cl2N2P2Pt‚1/4CH2Cl2: C, 39.3; H, 3.18; N, 4.31. Found:
C, 39.5; H, 3.27; N, 4.49. 31P{1H} NMR (121.5 MHz, CD2Cl2): δ
2
1
2
1
-16.5 (d, JPP 75 Hz, JPPt 3932 Hz), -57.0 (d, JPP 75 Hz, JPPt
2951 Hz). 1H NMR (300.2 MHz, CD2Cl2): δ 7.86-7.78 (m, 4H),
7228 Inorganic Chemistry, Vol. 42, No. 22, 2003

Diphosphines Possessing Electronically Different Donor Groups
7.58-7.56 (m, 2H), 7.53-7.48 (m, 4H), 7.32 (ps quin, 4H, HR),
6.42-6.40 (m, 4H, Hâ), 4.60 (dd, 2H, 2JHP 13.7 Hz, 2JHP 11.3 Hz,
3JHPt 63.6 Hz, CH2).
24 h and hexane added to precipitate an orange powder. Crystal-
lization by slow evaporation of a dichloromethane-hexane solution
produced dark orange crystals. Yield: 0.331 g (90%). Anal. Calcd
for C41H50Cl2N2P2Ru2: C, 54.4; H, 5.56; N, 3.09. Found: C, 54.7;
H, 5.59; N, 3.23. 31P{1H} NMR (161.8 MHz, C6D6): δ 119.1 (d,
2JPP 24 Hz), 34.6 (d, 2JPP 24 Hz). 1H NMR (399.8 MHz C6D6): δ
7.60-7.55 (m, 4H, Ph), 7.06-7.01 (m, 6H, Ph), 6.77 (ps quin, 4H,
CR), 6.09-6.08 (m, 4H, Câ), 3.92 (ps t, 2H, CH2), 1.41 (d, 15H,
Synthesis of [PdCl2(L-K1P)2] 4. Two methods were used:
(a) L (0.023 g, 0.063 mmol) was added to a dichloromethane
solution of 2 (0.040 g, 0.074 mmol) and the mixture stirred for 30
min. Addition of hexane precipitated out a yellow powder, which
was isolated by filtration and dried under reduced pressure.
(b) A dichloromethane solution of [PdCl2(cod)] (0.102 g, 0.36
mmol) was added dropwise to a stirred dichloromethane solution
of L (0.259 g, 0.71 mmol) over 2 h. The stirring was continued for
an additional 1 h, after which all the solvent was eliminated under
reduced pressure. The resulting yellow powder was washed with
hexane and dried under reduced pressure. Crystallization from
dichloromethane-hexane gave yellow crystals. Yield: 0.313 g
(97%). Anal. Calcd for C42H40Cl2N4P4Pd: C, 55.9; H, 4.47; N, 6.21.
Found: C, 55.7; H, 4.48; N, 6.05. 31P{1H} NMR (161.8 MHz, CD2-
Cl2): δ 59.9 (ps t), 12.3 (AB pattern). 1H NMR (399.8 MHz, CD2-
Cl2): δ 7.58-7.55 (m, 4H), 7.44-7.41 (m, 2H), 7.33-7.30 (m,
4H), 6.79 (br s, 4H, HR), 6.11 (br s, 4H, Hâ), 4.69 (ps t, 2H, CH2).
Synthesis of [Pd2Cl2(µ-L)2] 5. [Pd2(dba)3]‚CHCl3 (0.162 g, 0.16
mmol) was added to a dichloromethane solution of 4 (0.286 g, 0.32
mmol) with stirring, giving a slow lightening of color to red.
Addition of hexane precipitated a red powder, which was washed
with small amounts of dichloromethane and dried under reduced
pressure. Crystallization from dichloromethane-hexane gave deep
red crystals. Yield: 0.298 g (93%). Anal. Calcd for C42H40Cl2N4P4-
Pd2: C, 50.0; H, 4.00; N, 5.56. Found: C, 50.1; H, 4.19; N, 5.20.
3
3JHP 2.0 Hz, CH3), 1.32 (d, 15H, JHP 2.0 Hz, CH3).
Isolation of [Rh2(cod)2(µ-Cl)(µ-L)]PF6 9. NH4PF6 (0.110 g,
0.67 mmol) was added to a dichloromethane solution of [Rh(cod)-
(µ-Cl)]2 (0.166 g, 0.34 mmol) and L (0.244 g, 0.67 mmol). The
mixture was stirred for 2 h and filtered to removed the white
precipitate of NH4Cl. The solvent was removed under reduced
pressure to give an orange powder, which was washed with diethyl
ether and dried under reduced pressure. Crystallization by slow
diffusion of hexane in a dichloromethane solution gave an orange
powder and small yellow crystals of 9, which were separated
manually. 31P{1H} NMR (109.4 MHz, CD2Cl2): δ 109.2 (dd, 1JPRh
2
1
2
218 Hz, JPP 72 Hz), 25.8 (dd, JPRh 145 Hz, JPP 72 Hz), -143.0
(sept, PF6, 1JPF 711 Hz). 1H NMR (270.2 MHz CD2Cl2): δ 7.80-
7.45 (m, 10H, Ho, Hp, Hm), 6.95 (ps quin, 4H, CR), 6.52-6.46 (m,
4H, Câ), 5.20-5.05 (m, 4H, cod), 3.72-3.64 (m, 2H, CH2), 3.28-
3.05 (m, 4H, cod), 2.36-1.75 (m, 4H, cod).
Crystallography. Crystallographic data for compounds 2‚CHCl3,
3‚CH2Cl2, 4, 5‚1/4CH2Cl2, 6, 7‚2CH2Cl2, 8 and 9‚CH2Cl2 are
summarized in Table 8. Data were collected on a Nonius Kap-
paCCD diffractometer throughout. Full matrix anisotropic refine-
ment was implemented in the final least-squares cycles for all
structures with the specific exceptions described below. All data
were corrected for Lorentz and polarization. Absorption corrections
(multiscan) were applied on merit to data for 2‚CHCl3, 4, 5‚1/4-
CH2Cl2, 6, 7‚2CH2Cl2, and 9‚CH2Cl2 (maximum, minimum trans-
mission factors were 1.00, 0.87; 1.00, 0.94; 0.80, 0.74; 0.89, 0.80;
0.84, 0.75; and 0.94, 0.88, respectively). Hydrogen atoms were
included at calculated positions throughout with the exceptions of
those specifically mentioned below.
1
31P{1H} NMR (161.8 MHz, CD2Cl2): see main text. H NMR
(399.8 MHz, CD2Cl2): δ 7.53-7.26 (m, 20H), 7.05 (m, 4H), 6.93
(m, 4H), 6.30 (m, 4H), 6.21 (m, 4H), 4.57-4.45 (m, 4H).
Synthesis of [Pd2Cl2(CH3)2(µ-L)2] 6. [PdCl(CH3)(cod)] (0.340
g, 1.28 mmol) was added to a dichloromethane solution of L (0.463
g, 1.28 mmol). The mixture was stirred for 4 h, and then hexane
was added to precipitate a colorless powder. After separation by
filtration, the powder was washed with hexane and dried under
reduced pressure. Crystallization from dichloromethane-hexane
gave colorless crystals. Yield: 0.630 g (95%). Anal. Calcd for
C44H46Cl2N4P4Pd2‚CH2Cl2: C, 48.1; H, 4.31; N, 4.99. Found: C,
48.4; H, 4.56; N, 4.92. 31P{1H} NMR (161.8 MHz, CDCl3): see
main text. 1H NMR (399.8 MHz, CDCl3): δ 7.59-7.56 (m), 7.37-
7.26 (m), 6.87 (br s), 6.33 (br s), 6.15 (br s), 4.62 (br m), 4.35 (br
m), 1.24 (ps t), 0.64 (ps t), 0.15 (ps t).
Synthesis of [Pd2(CH3)2(µ-Cl)(µ-L)2]PF6 7. TlPF6 (0.045 g, 0.13
mmol) was added to a dichloromethane solution of 6 (0.120 g, 0.12
mmol). The mixture was stirred for 2 h with the formation of a
colorless precipitate of TlCl. This was removed by filtration, and
the solvent was removed from the filtrate under reduced pressure
to give a yellow powder. The product was recrystallized from
dichloromethane-hexane. Yield: 0.123 g (93%). Anal. Calcd for
C44H46ClF6N4P5Pd2‚3/4CH2Cl2 C, 44.4; H, 3.95; N, 4.62. Found:
C, 44.4; H, 3.92; N, 4.60. 31P{1H} NMR (161.8 MHz, CD2Cl2): δ
83.8 (m, HH), 82.1 (dd, J 476 Hz, J 69 Hz, HT), 15.9 (dd, J 476
Hz, J 69 Hz, HT), 15.2 (m, HH), -143.0 (sept, PF6, 1JPF 711 Hz).
1H NMR (399.8 MHz, CD2Cl2): δ 7.87-7.76 (m), 7.64-7.51 (m),
7.50-7.42 (m), 7.36 (ps quin, CR), 7.31-7.25 (m), 7.19-7.14 (m),
7.11 (ps quin, CR), 6.62-6.61 (m, Câ), 6.58-6.57 (m, Câ), 6.55-
6.51 (m), 6.44-6.35 (m), 4.38-4.28 (br m, CH2), 4.24 (ps quin,
CH2), 4.13-4.03 (br m, CH2), 1.01 (ps t, CH3, HH), 0.86 (ps t,
CH3, HT), 0.71 (ps t, CH3, HH).
In 2‚CHCl3, the chloroform molecule was found to be disordered
over two sites in the occupancy ratio 3:2, with one common chlorine
atom [Cl(3)]. Efforts to model three-way disorder in this solvent
because of the proximity of the largest positive peak in the
difference Fourier electron density map to Cl(5) were abandoned
as they had a detrimental effect on convergence of the model. The
structure of 4, where the asymmetric unit contains two crystallo-
graphically independent molecule halves, refined routinely. In 5‚
1/4CH2Cl2, the pyrrolyl rings on P(3) exhibited disorder in a 1:1
ratio with the phenyl rings attached to P(4). Disordered rings were
treated as rigid groups in the latter stages of refinement. The
included solvent fragment, proximate to the inversion center, is
disordered, and consequently the hydrogens on this fragment were
not included in the model. The structure of 7‚2CH2Cl2 was
successfully refined using a twin law which involves a 180° rotation
about the 1 0 0 reciprocal lattice vector. This twin law was
determined using ROTAX,23 followed by use of WinGX24 to output
the data in SHELXL-97, HKLF 5 format.
Analysis of the data for structure 8 led to initial solution in space
group P21/n with severe disorder of the Cp* rings which could not
be successfully modeled in any sensible manner. However, while
reflection intensities in the data set suggesting the presence of an
Formation of [Ru2Cp*2(µ-Cl)2(µ-L)] 8. [RuCp*(µ3-Cl)]4 (0.220
g, 0.20 mmol) was added with stirring to a THF solution of L (0.147
g, 0.41 mmol). The resulting dark orange solution was stirred for
(23) Cooper, R. I.; Gould, R. O.; Parsons, S.; Watkin, D. J. J. Appl.
Crystallogr. 2002, 35, 168-174.
(24) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837-838.
Inorganic Chemistry, Vol. 42, No. 22, 2003 7229

Burrows et al.
Scheme 1
n glide perpendicular to b were weak, they were undeniably
observed. Thus, the structure as presented here converged optimally
as a racemic twin, in space group P21 with two molecules in the
asymmetric unit. The asymmetric unit in 9‚CH2Cl2 consists of half
a dimeric cation with C(19) and Cl(1) located on a 2-fold
-
crystallographic rotation axis, half of a PF6 anion with the
phosphorus located on an inversion center, and half of a molecule
of dichloromethane. The solvent chlorine was disordered over two
positions in a 1:1 ratio, with the carbon atom therein also located
on a 2-fold axis. Hence, the methylene hydrogens were not included
in the refinement. As in 5‚1/4CH2Cl2, the pyrrolyl and phenyl groups
in the cation were disordered in a 1:1 ratio between the phosphines.
These rings were treated as rigid groups in the latter stages of
refinement where atomic displacement parameters therein were also
restrained. Hydrogen atoms were included at calculated positions
except for H(19) and the cyclooctadiene alkenic hydrogens. These
exceptions were readily located in the penultimate difference Fourier
electron density map, and refined at a distance of 0.90 Å from the
relevant parent atoms.
2
with JPP 85 Hz. The doublet at δ 56.8 can be assigned to
the di(N-pyrrolyl)phosphino group and is shifted only slightly
with respect to L. In contrast, the signal at δ 36.6 is shifted
considerably downfield with respect to the PPh2 signal in
L, and is consistent with the selective oxidation of this
phosphorus atom. The NMR parameters observed for 1 are
comparable with those previously reported for Ph2P(S)CH2-
PPh2 for which doublets at δ 39.2 and δ -29.1 with 2JPP 74
Hz were observed.25 In the IR spectrum of 1 ν(PS) was
observed at 625 cm-1, in the anticipated region.26
Synthesis and Characterization of the Chelate Com-
plexes [MCl2(L-K2P,P′)] (M ) Pd, Pt). The reaction of 1
equiv of L with [MCl2(cod)] (M ) Pd, Pt) in dichlo-
romethane gave the complexes [PdCl2(L-κ2P,P′)] 2 and
[PtCl2(L-κ2P,P′)] 3, respectively, in good yields (Scheme 1).
Both complexes were isolated as air-stable crystalline materi-
als and fully characterized by multinuclear NMR spectro-
scopy, microanalysis, and single-crystal X-ray analyses.
The 31P{1H} NMR spectrum of 2 consisted of two
doublets, at δ 0.0 and δ -46.7, with 2JPP 84 Hz. The higher
field signal can be assigned to the diphenylphosphino group
on the basis of the chemical shift, which is similar to that
observed for [PdCl2(dppm-κ2P,P)] (δ -53.727). In addition,
the lower field signal is broader, which is consistent with
bonding to the quadrupolar nitrogen atoms.9 The upfield shift
of the signals with respect to the free ligand is typical of a
four-membered chelate ring.28 In the 1H NMR spectrum, the
methylene hydrogen atoms were observed as a doublet of
doublets at δ 4.54.
Results and Discussion
Synthesis and Reactivity of Ph2PCH2P(NC4H4)2 L. Ph2-
PCH2P(NC4H4)2 L was prepared in a two-step procedure
starting from PMePh2. The first step involved conversion of
PMePh2 into Ph2PCH2Li by reaction with BuLi in the
presence of TMEDA.21 Ph2PCH2Li was isolated as a colorless
powder, and a THF solution of this was added dropwise to
a THF-hexane solution containing 1 equiv of PCl-
(NC4H4)2,11 to give L as a colorless powder following
recrystallization from THF-hexane. The 31P{1H} NMR
spectrum of L consists of two doublets at δ 66.1 and δ
2
-25.5, with JPP 147 Hz. The lower field signal can be
assigned to the di(N-pyrrolyl)phosphino group on the basis
of its chemical shift, by comparison with PPh(NC4H4)2 (δ
70.6).9 The 1H NMR spectrum of L showed a characteristic
pseudo-quintet and pseudo-triplet for the protons of the
pyrrolyl rings and two multiplets for the protons of the phenyl
rings. The signal for the protons of the methylene bridge
The 31P{1H} NMR spectrum of 3 consisted of two doublets
2
appeared as a doublet of doublets at δ 3.18 with JHP 6.0
2
with 195Pt satellites, at δ -16.5 (1JPPt 3932 Hz, JPP 75 Hz)
and 1.6 Hz. In the 13C{1H} NMR spectrum the signal
and δ -57.0 (1JPPt 2951 Hz), respectively. As with 2 the
higher field signal can be assigned to the diphenylphosphino
group, and is close to the resonance observed for the dppm
assigned to the methylene carbon was observed as a doublet
of doublets at δ 31.0 with JCP 26 and 20 Hz.
The order of addition in the second step proved to be
important in optimizing the yield of L. Addition of PCl-
(NC4H4)2 to Ph2PCH2Li led to significant amounts of a
byproduct, whose 31P{1H} NMR spectrum consists of a
1
1
analogue [PtCl2(dppm-κ2P,P)] (δ -64.3, JPPt 3078 Hz).29
1
The larger JPPt coupling constant observed for the di(N-
pyrrolyl)phosphino group is consistent with this being a better
π-acceptor than the diphenylphosphino group. The methylene
hydrogen atoms were observed in the 1H NMR spectrum as
a doublet of doublets at δ 4.60 with 195Pt satellites.
Single crystals of 2 and 3 were grown by slow diffusion
of hexane into chloroform and dichloromethane solutions,
respectively. The X-ray crystal structures of 2‚CHCl3 and
3‚CH2Cl2 confirmed the chelating coordination mode of L.
2
triplet (δ 39.6) and a doublet (δ -23.4) with JPP 126 Hz
and in the intensity ratio 1:2. The spectrum is consistent with
this compound being (Ph2PCH2)2P(NC4H4), formed by reac-
tion of L with a second equivalent of Ph2PCH2Li.
L was found to be moderately air-stable, and the P-N
bonds are stable to methanolysis at ambient temperature in
contrast to those in (H4C4N)2P{NC4H3C(O)Me-2}.11 Al-
though L is not prone to aerial oxidation, the differential
reactivity of the two phosphino groups can be witnessed by
its reaction with sulfur. On stirring a dichloromethane
solution of L with excess sulfur for 4 h, full conversion to
Ph2P(S)CH2P(NC4H4)2 1 was achieved. The 31P{1H} NMR
spectrum for 1 contained two doublets at δ 56.8 and δ 36.6,
(25) Blagborough, T. C.; Davis, R.; Ivison, P. J. Organomet. Chem. 1994,
467, 85-94.
(26) Birdsall, D. J.; Slawin, A. M. Z.; Woollins, J. D. Polyhedron 2001,
20, 125-134.
(27) Oliver, D. L.; Anderson, G. K. Polyhedron 1992, 11, 2415-2420.
(28) Garrou, P. E. Chem. ReV. 1981, 81, 229-266.
(29) Appleton, T. G.; Bennett, M. A.; Tomkins, I. B. J. Chem. Soc., Dalton
Trans. 1976, 439.
7230 Inorganic Chemistry, Vol. 42, No. 22, 2003

Diphosphines Possessing Electronically Different Donor Groups
P(NC4H4)2 group. However, significant differences in the two
Pd-P bond lengths in [PdCl2(dppm-κ2P,P)] [2.234(1) and
2.250(1) Å]30 suggest that the electronic difference between
the phosphino groups in the structures of 2 and 3 may not
be the only factor involved in the M-P bond length
difference. Notably, though, the bond distances between the
methylene carbon and the two phosphorus atoms in 2 and 3
are also different. In both cases the bond to the phosphorus
atom of the diphenylphosphino group [P(2)-C(13) 1.850-
(5) Å in 2 and P(1)-C(21) 1.856(3) Å in 3] is longer than
that to the phosphorus atom of the di(N-pyrrolyl)phosphino
group [P(1)-C(13) 1.814(5) Å in 2, P(2)-C(21) 1.822(3)
Å in 3].
There is a difference in the orientation of the two aromatic
ring types in 2 and 3, with the pyrrolyl rings facing each
other and the phenyl rings twisted. In the supramolecular
structures, one of the phenyl rings from each molecule is
directed into the cleft between the pyrrolyl rings in a
neighboring molecule. Moreover, the disordered chloroform
solvate molecule in 2 forms C-H‚‚‚Cl hydrogen bonds with
the coordinated chlorides [C(24)‚‚‚Cl(2) 3.460 Å, H(24)-
Cl(2) 2.55 Å, C(24)-H(24)‚‚‚Cl(2) 151°; C(24)‚‚‚Cl(1) 3.446
Å, H(24)‚‚‚Cl(1) 2.57 Å, C(24)-H(24)‚‚‚Cl(1) 146°].
Reaction of L with [MCl2(L-K2P,P′)] (M ) Pd, Pt). The
addition of an additional 1 equiv of L to a dichloromethane
solution of 2 led to the disappearance of the pair of doublets
in the 31P{1H} NMR spectrum and the appearance of a more
complex pattern. This spectrum consisted of a broad pseudo-
triplet at δ 59.9 and an AB pattern at δ 12.3, and was
identified as arising from an [AX]2 spin system31,32 with the
broadness in the pseudo-triplet a consequence of the nitrogen
quadrupoles. The increase in chemical shift of both signals
from those observed for 2 suggested that the four-membered
ring was no longer present, whereas the proximity of the
lower field resonance to that for L suggested that the di(N-
pyrrolyl)phosphino groups were uncoordinated. Hence the
product from the reaction of 2 with L was identified as trans-
[PdCl2(L-P)2] 4 (Scheme 1), which could be isolated
following recrystallization from dichloromethane-hexane.
The large value of the trans 2JPP coupling constant between
the diphenylphosphino groups together with a small but
Figure 1. Molecular structure of [PdCl2(L-κ2P,P′)]‚CHCl3 (2‚CHCl3) with
the included solvent omitted for clarity and thermal ellipsoids shown at the
30% probability level.
Figure 2. Molecular structure of [PtCl2(L-κ2P,P′)]‚CH2Cl2 (3‚CH2Cl2)
with the included solvent omitted for clarity and thermal ellipsoids shown
at the 30% probability level.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for Complexes
2‚CHCl3 and 3‚CH2Cl2
2‚CHCl3
3‚CH2Cl2
Pd(1)-P(1)
Pd(1)-P(2)
Pd(1)-Cl(1)
Pd(1)-Cl(2)
P(1)-N(1)
P(1)-N(2)
P(1)-C(13)
P(2)-C(13)
2.2109(13)
2.2347(13)
2.3273(13)
2.3540(13)
1.673(4)
1.689(5)
1.814(5)
1.850(5)
Pt(1)-P(2)
Pt(1)-P(1)
Pt(1)-Cl(2)
Pt(1)-Cl(1)
P(2)-N(1)
P(2)-N(2)
P(2)-C(21)
P(1)-C(21)
2.1877(7)
2.2372(7)
2.3445(7)
2.3667(7)
1.681(2)
1.682(3)
1.822(3)
1.856(3)
4
nonzero JPP coupling between the diphenylphosphino and
di(N-pyrrolyl)phosphino phosphorus nuclei is the origin of
P(1)-Pd(1)-P(2)
P(1)-Pd(1)-Cl(2)
P(2)-Pd(1)-Cl(1)
Cl(1)-Pd(1)-Cl(2)
P(1)-Pd(1)-Cl(1)
P(2)-Pd(1)-Cl(2)
P(1)-C(13)-P(2)
73.36(5)
100.55(5)
91.77(5)
94.29(5)
164.97(5)
173.88(5)
92.9(2)
P(1)-Pt(1)-P(2)
P(1)-Pt(1)-Cl(2)
P(2)-Pt(1)-Cl(1)
Cl(1)-Pt(1)-Cl(2)
P(1)-Pt(1)-Cl(1)
P(2)-Pt(1)-Cl(2)
P(1)-C(21)-P(2)
73.32(3)
97.47(3)
98.51(3)
90.69(2)
171.80(3)
170.65(3)
91.85(13)
1
the appearance of the spectrum. The H NMR spectrum of
4 shows the signal for the methylene protons of L at δ 4.69
2
as a pseudo triplet due to the two JHP coupling constants
having very similar values. Variable temperature 31P{1H}
and 1H NMR spectra (room temperature to -70 °C) showed
no variation, suggesting that 4 is static on the NMR time
scale.
Selected bond lengths and angles are reported in Table 1,
and the structures are shown in Figures 1 and 2. In both 2
and 3 the metal adopts a distorted square planar coordination
geometry, with L assuming bite angles of 73.36(5)° and
73.32(3)°, respectively. In both cases the M-P bond to the
di(N-pyrrolyl)phosphino group is significantly shorter than
that to the diphenylphosphino group [Pd-P 2.2109(13),
2.2347(13) Å in 2; Pt-P 2.1877(7), 2.2372(7) Å in 3], which
is consistent with the stronger π-acceptor ability of the
Complex 4 can also be prepared directly from the reaction
of [PdCl2(cod)] and 2 equiv of L. In addition to the signals
above, crude reaction mixtures showed the presence of two
(30) Steffen, W. L.; Palenik, G. J. Inorg. Chem. 1976, 15, 2432-2439.
(31) Becker, E. D. High-resolution NMR spectroscopy; Academic Press:
New York, 1969.
(32) Akitt, J. W.; Mann, B. E. NMR and chemistry: an introduction to
modern NMR spectroscopy, 4th ed.; Stanley Thornes: Cheltenham,
U.K., 2000.
Inorganic Chemistry, Vol. 42, No. 22, 2003 7231

Burrows et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complex 4a
Scheme 2
Pd(1)-P(1)
Pd(1)-Cl(1)
P(1)-C(9)
P(2)-C(9)
P(2)-N(1)
P(2)-N(2)
2.3361(10)
2.3077(10)
1.842(4)
1.850(4)
1.731(4)
1.712(4)
Pd(2)-P(3)′
Pd(2)-Cl(2)
P(3)-C(30)
P(4)-C(30)
P(4)-N(3)
P(4)-N(4)
2.3196(10)
2.3000(12)
1.833(4)
1.839(4)
1.702(5)
1.729(4)
Cl(1)-Pd(1)-P(1)′
Cl(1)-Pd(1)-P(1)
Cl(2)-Pd(2)-P(3)
91.94(4)
88.06(4)
85.89(4)
Cl(2)-Pd(2)-P(3)′′
P(1)-C(9)-P(2)
P(3)-C(30)-P(4)
94.11(4)
115.1(2)
110.9(2)
a Primed atoms generated by the symmetry operation -x + 2, y + 2, z.
Double primed atoms generated by the symmetry operation -x + 1, y +
1, z + 1.
The generation of trans-[PdCl2(L-P)2] 4 from 2 involves
cleavage of the Pd-P(NC4H4)2 bond, so the reaction shows
selective cleavage of the shorter Pd-P bond. In contrast to
this reaction, the platinum analogue 3 does not react with
L. The reaction of 2 equiv of L with [PtCl2(cod)] produced
a number of products as evidenced by the 31P{1H} spectrum,
and it did not prove possible to isolate trans-[PtCl2(L-P)2]
or any other compound from this reaction mixture.
Reactions of [PdCl2(L-K1P)2]. The complex [PdCl2(L-
κ1P)2] 4 possesses two pendant di(N-pyrrolyl)phosphino
groups and, thus, has the potential to form homo- or
heterometallic dimers. The reaction of 4 with [PdCl2(cod)]
gave only complex 2, suggesting that dimeric palladium
complexes with bridging L and terminal chloride are less
stable than those with chelating L. This behavior resembles
that of dppm for which the face-to-face dimer [Pd2Cl4(µ-
dppm)2] isomerizes to the chelate complex [PdCl2(dppm-
κ2P,P)].33 Similarly, the reaction of 4 with [PtCl2(cod)] gave
a 1:1 mixture of complexes 2 and 3 rather than a mixed metal
dimer.
In contrast to these observations, the reaction of 4 with
[Pd2(dba)3]‚CHCl3 gave a red complex 5, the 31P{1H} NMR
spectrum of which consisted of two complex groups of
signals at δ 68.6 to 63.2 and δ -5.2 to -10.5, similar in
appearance, with each group containing 13 lines: too many
for the spectrum to be derived from a simple [AX]2 spin
system. In addition, the relative movement of some of the
lines within each group upon changes in concentration or
temperature suggested that they did not comprise one single
multiplet. The spectrum was interpreted as being composed
of two overlapping [AX]2 spin systems, from the product
[Pd2Cl2(µ-L)2] existing as both head-to-head (HH) and head-
to-tail (HT) isomers (Scheme 2). In the HH isomer the two
palladium centers are different, one being coordinated to two
PPh2 groups and the other to two P(NC4H4)2 groups, whereas
in the HT isomer both are identical, being coordinated to
one PPh2 group and one P(NC4H4)2 group.
Figure 3. Molecular structure of one of the independent molecules of
trans-[PdCl2(L-P)2] 4 with thermal ellipsoids shown at the 30% probability
level.
broad signals. These resonances were found to be temperature
dependent, and on cooling to -66 °C they were observed
2
as sharp doublets at δ 56.4 and δ 28.2, with JPP 100 Hz.
These values are consistent with this compound being cis-
[PdCl2(L-P)2]. The spectrum of cis-[PdCl2(L-P)2] is simpler
than that of the trans isomer 4 due to the negligible value of
4JPP. As a consequence of this the two diphenylphosphino
groups are magnetically equivalent and the spin system is
A2X2.
The identity of 4 as trans-[PdCl2(L-P)2] was confirmed
by a single-crystal X-ray analysis. Suitable crystals were
obtained following recrystallization from dichloromethane-
hexane, and two crystallographically independent half-
molecules were observed in the asymmetric unit. Each
molecule contains a crystallographically imposed center of
symmetry at the palladium atom, and, consistent with the
NMR data, the diphenylphosphino group is coordinated while
the di(N-pyrrolyl)phosphino group is pendant. The metal
geometry is distorted square planar, with bond lengths and
angles very similar for the two independent units, and cis
angles in the range 85.89(4)-94.11(4)°. Selected bond
lengths and angles for both independent molecules are given
in Table 2, and one of the molecules is depicted in Figure 3.
The major difference between the independent molecules lies
in the position of the uncoordinated di(N-pyrrolyl)phosphino
groups. The Pd‚‚‚P distances to the uncoordinated phospho-
rus atoms are 4.739 and 3.638 Å, and in the latter case the
phosphorus lone pair appears to be directed toward the metal
center.
Of the two 13-line patterns, that at lower field can be
assigned to the P(NC4H4)2 groups and that at higher field to
the PPh2 groups. The lower field pattern is shown in Figure
4 together with simulations for the HH and HT isomers.
(33) Hunt, C. T.; Balch, A. L. Inorg. Chem. 1981, 20, 2267-2270.
7232 Inorganic Chemistry, Vol. 42, No. 22, 2003

Diphosphines Possessing Electronically Different Donor Groups
Figure 5. Molecular structure of the HT isomer of [Pd2Cl2(µ-L)2]‚1/4-
CH2Cl2 (5‚1/4CH2Cl2) with the phenyl and pyrrolyl protons and included
solvent omitted for clarity and thermal ellipsoids shown at the 30%
probability level.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for Complex
5‚1/4CH2Cl2
Pd(1)-Pd(2)
Pd(1)-P(1)
Pd(1)-P(3)
Pd(2)-P(2)
Pd(2)-P(4)
Pd(1)-Cl(1)
2.6344(5)
Pd(2)-Cl(2)
P(1)-C(41)
P(2)-C(41)
P(2)-N(1)
P(2)-N(2)
2.4041(13)
1.844(4)
1.811(4)
1.707(4)
1.718(4)
2.3179(11)
2.2842(12)
2.2579(13)
2.2841(13)
2.3894(13)
Figure 4. Low-field part of the 31P{1H} NMR spectrum of [Pd2Cl2(µ-
L)2] 5 (c) together with simulations for the HH (a) and HT (b) isomers.
P(1)-Pd(1)-Cl(1)
Cl(1)-Pd(1)-P(3)
P(3)-Pd(1)-Pd(2)
Pd(2)-Pd(1)-P(1)
P(1)-Pd(1)-P(3)
Pd(2)-Pd(1)-Cl(1)
P(2)-Pd(2)-Cl(2)
90.06(4)
91.34(5)
90.10(4)
88.49(3)
176.77(4)
178.56(4)
93.09(4)
Cl(2)-Pd(2)-P(4)
P(4)-Pd(2)-Pd(1)
Pd(1)-Pd(2)-P(2)
P(4)-Pd(2)-P(2)
Pd(1)-Pd(2)-Cl(2)
P(1)-C(41)-P(2)
P(4)-C(42)-P(3)
96.58(5)
87.37(3)
83.63(3)
169.79(5)
169.85(3)
103.2(2)
106.0(3)
Although both isomers give rise to [AX]2 multiplets, their
appearances are very different due to the relative magnitudes
of the coupling constants. The central pseudo-triplet can be
2
2
assigned to the HH isomer in which J(AA′) and J(XX′)
[A ) P(NC4H4)2, X ) PPh2] are considerably larger than
all the other coupling constants. The observation of only these
three lines precludes a full spectral analysis. The remaining
10 lines result from the HT isomer, and in this case a full
formal electron count. Both palladium centers possess
distorted square planar coordination geometries with trans-
coordinated phosphorus atoms. The Cl-Pd-Pd-Cl unit is
approximately linear with a torsion angle Cl(1)-Pd(1)-Pd-
(2)-Cl(2) of 30.0° and angles Cl(2)-Pd(2)-Pd(1) of
169.85(3)° and Pd(2)-Pd(1)-Cl(1) of 178.56(4)°. The mean
coordination planes of the two palladium centers form an
angle of approximately 32°. The structural parameters are
similar to those reported for [Pd2Br2(µ-dppm)2], which also
contains a distorted geometry with a twist about the Pd-Pd
bond.35 The Pd-Pd bond distance in this complex is 2.699(5)
Å, and the distortion from planarity has been rationalized as
resulting from the conflicting requirements of interaxial d
orbital repulsion and accommodation of the bridging dppm
ligands with minimum strain. This explanation is likely to
be equally valid in the case of 5.
2
analysis is possible, giving J(AX) 60 Hz, 2J(AX′) 582 Hz,
3J(XX′) 23 Hz, and 3J(AA′) 53 Hz. The spectral parameters
obtained for the HT isomer are similar to those reported for
the complex [PdCl2(µ-dppm){µ-Ph2PCH(CH3)PPh2}], for
which 2JPP′ through the metal is 440 Hz.34 The 31P{1H} NMR
spectrum of 5 recorded at both high and low temperature in
C2D2Cl4 shows no significant changes, suggesting no inter-
conversion of the isomers in solution.
Orange single crystals of 5‚1/4CH2Cl2 were grown from
the slow diffusion of hexane into a dichloromethane solution
of 5. The compound crystallized as a 1:1 mixture of the HH
and HT isomers, together with a small amount of disordered
solvent. The co-crystallization of the isomers results in one
of the L ligands being disordered, with the phenyl and
N-pyrrolyl rings present on both ends with 50% occupancy.
Selected bond distances and angles are reported in Table 3,
and the structure of one of the isomers is shown in Figure
5. The Pd(1)-Pd(2) distance of 2.6344(5) Å indicates the
presence of a Pd-Pd bond, which is in agreement with the
Due to the disorder in 5, the bond distances Pd(1)-P(3)
[2.2842(12) Å] and Pd(2)-P(4) [2.2841(13) Å] are indis-
tinguishable. However, for the non-disordered ligand the Pd-
(1)-P(1) distance [2.3179(11) Å] to the diphenylphosphino
group is longer than the Pd(2)-P(2) distance [2.2579(13)
Å] to the di(N-pyrrolyl)phosphino group.
(34) Lee, C.-L.; Yang, Y.-P.; Rettig, S. J.; James, B. R.; Nelson, D. A.;
(35) Holloway, R. G.; Penfold, B. R.; Colton, R.; McCormick, M. J. J.
Chem. Soc., Chem. Commun. 1976, 485-486.
Lilga, M. A. Organometallics 1986, 5, 2220-2228.
Inorganic Chemistry, Vol. 42, No. 22, 2003 7233

Burrows et al.
Scheme 3
Table 4. Selected Bond Lengths (Å) and Angles (deg) for Complex 6a
Synthesis of [Pd2Cl2(CH3)2(µ-L)2]. The reaction of 1
Pd(1)-Cl(1)
Pd(1)-C(1)
2.4266(7)
2.064(3)
Pd(1)-P(1)
Pd(1)-P(2)′
2.2865(7)
2.3150(7)
equiv of L with [PdCl(CH3)(cod)] produced [Pd2Cl2(CH3)2-
(µ-L)2] 6, which was characterized by multinuclear NMR
spectroscopy, microanalysis and X-ray crystallography. As
with 5, complex 6 exists in solution as a mixture of HH and
HT isomers (Scheme 3). However, the HT isomer prevails
at low temperature and crystallizes preferentially.
C(1)-Pd(1)-P(2)′
P(1)-Pd(1)-C(1)
P(1)-Pd(1)-Cl(1)
Cl(1)-Pd(1)-P(2)′
90.61(8)
86.74(8)
98.00(2)
85.77(2)
P(1)-Pd(1)-P(2)′
C(1)-Pd(1)-Cl(1)
P(1)-C(10)-P(2)
172.37(2)
169.92(2)
118.74(14)
a Primed atoms generated by the symmetry operation -x, -y + 1, -z
+ 1.
The 31P{1H} NMR spectrum of 6 recorded at ambient
temperature showed a number of broad resonances, consistent
with the presence of both HH and HT isomers; however, at
-80 °C the spectrum consisted solely of two doublets of
doublets at δ 80.3 and δ 17.4, both with coupling constants
of 468 and 72 Hz. The low-temperature spectrum can be
interpreted by considering it a special case of the [AX]2 spin
system in which J(AA′) and J(XX′) are very small or equal
to zero. This suggests that the compound exists solely as
the HT isomer at this temperature, and that in this dimer
there is no bond between the two palladium atoms, which
was subsequently confirmed by the crystallographic analysis.
The NMR data indicates that the HT and HH isomers are
in equilibrium with the proportion of the HH isomer
increasing with the temperature. This was verified by
recording 31P{1H} NMR spectra at higher temperatures, and
at 80 °C the HH isomer was observed to be the major species,
though the spectrum also showed a significant amount of
complex 5. This is consistent with 6 being thermally unstable
and decomposing with the reductive elimination of ethane
to give the palladium(I) dimer 5 as a mixture of HH and HT
isomers. Related reactions involving the formation of com-
pounds such as [Pd2(µ-Cy2PCH2PCy2)2] from [Pd(CH3)2(Cy2-
PCH2PCy2-κ2P,P)] have recently been reported.36
Figure 6. Molecular structure of [Pd2Cl2(CH3)2(µ-L)2] 6 with the phenyl
and pyrrolyl protons omitted for clarity and thermal ellipsoids shown at
the 30% probability level.
The palladium atoms adopt distorted square-planar coor-
dination with mutually trans phosphorus atoms, and cis
angles ranging from 85.77(2)° to 98.00(2)°. The palladium
mean coordination planes form an angle of approximately
70° with the plane containing the four phosphorus atoms.
The Pd(1)‚‚‚Pd(1)′ distance of 3.371 Å indicates the absence
of any metal-metal bonding, as expected from the NMR
data and electron-counting rules. The Pd-P(NC4H4)2 bond
distance [Pd(1)-P(1) 2.2865(7) Å] is shorter than the Pd-
PPh2 distance [Pd(1)-P(2) 2.3150(7) Å] as observed for 2
and 3, indicating the greater π-acceptor character of the
N-pyrrolyl groups.
Single crystals of 6 were prepared by recrystallization from
dichloromethane-hexane, and the X-ray analysis of these
confirmed their identity as the HT isomer of [Pd2Cl2(CH3)2-
(µ-L)2]. Selected bond angles and distances for 6 are reported
in Table 4, and the complex is shown in Figure 6. The
asymmetric unit consists of one half-molecule of 6, with the
remainder generated through a crystallographically imposed
center of symmetry.
(36) Reid, S. M.; Mague, J. T.; Fink, M. J. J. Am. Chem. Soc. 2001, 123,
4081-4082.
7234 Inorganic Chemistry, Vol. 42, No. 22, 2003

Diphosphines Possessing Electronically Different Donor Groups
Table 5. Selected Bond Lengths (Å) and Angles (deg) for Complex
7‚2CH2Cl2
Pd(1)-P(1)
Pd(1)-P(4)
Pd(1)-C(1)
Pd(1)-Cl(1)
Pd(2)-P(2)
Pd(2)-P(3)
Pd(2)-C(2)
Pd(2)-Cl(1)
2.3127(8)
2.3143(8)
2.056(3)
2.4589(8)
2.3166(8)
2.3081(8)
2.053(3)
P(1)-N(1)
P(1)-N(2)
P(3)-N(3)
P(3)-N(4)
P(1)-C(3)
P(2)-C(3)
P(3)-C(32)
P(4)-C(32)
1.705(3)
1.696(3)
1.702(3)
1.709(3)
1.823(3)
1.847(3)
1.827(3)
1.852(3)
2.4644(8)
C(1)-Pd(1)-P(1)
C(1)-Pd(1)-P(4)
P(1)-Pd(1)-Cl(1)
P(4)-Pd(1)-Cl(1)
C(1)-Pd(1)-Cl(1)
P(1)-Pd(1)-P(4)
C(2)-Pd(2)-P(2)
C(2)-Pd(2)-P(3)
92.05(9)
90.33(9)
92.21(3)
85.31(3)
175.01(9)
176.70(3)
91.17(9)
91.80(9)
P(2)-Pd(2)-Cl(1)
P(3)-Pd(2)-Cl(1)
C(2)-Pd(2)-Cl(1)
P(3)-Pd(2)-P(2)
Pd(1)-Cl(1)-Pd(2)
P(1)-C(3)-P(2)
P(3)-C(32)-P(4)
84.09(3)
92.91(3)
175.24(9)
175.62(3)
73.59(2)
Figure 7. Molecular structure of [Pd2(CH3)2(µ-Cl)(µ-L)2]PF6‚2CH2Cl2
(7‚2CH2Cl2) with the phenyl, pyrrolyl, and methyl protons, anion, and
included solvent omitted for clarity and thermal ellipsoids shown at the
30% probability level.
114.52(16)
114.04(17)
Reaction of [Pd2Cl2(CH3)2(µ-L)2] with TlPF6. The reac-
tion of 6 with TlPF6 occurred with abstraction of one of
the chlorides and formation of the “A-frame” complex [Pd2-
(CH3)2(µ-Cl)(µ-L)2]PF6 7, with the 31P{1H} NMR spec-
trum showing a mixture of HH and HT isomers in the
approximate ratio 1:4 (Scheme 3). The signals assigned to
the HT isomer appeared as a pair of doublets of doublets
centered at δ 82.1 and δ 15.9 with coupling constants of
476 and 69 Hz. As for the HT isomer of 6, the appearance
of these signals can be interpreted as being derived from a
[AX]2 spin system in which the 4J coupling constants J(AA′)
and J(XX′) are close or equal to zero. The signals assigned
to the HH isomer appeared as two complex multiplets of
identical appearance centered at δ 83.8 and δ 15.2. These
multiplets can be interpreted as being derived from an [AX]2
plexes [Pd2HMe(µ-Cl)(µ-dppm)2]BPh4 [3.031(1) Å37], [Pd2-
Cl2(µ-Cl)(µ-dppm)2]OH [3.170 Å38], and [Pd2Bz2(µ-Br)(µ-
dppm)]PF6 [3.356 Å38] though the electron count suggests
the absence of a Pd-Pd bond. The P-Pd‚‚‚Pd-P torsion
angle of 20.9° reflects a significant degree of twisting around
the Pd‚‚‚Pd axis; a similar twist was observed in [Pd2Bz2-
(µ-Br)(µ-dppm)2]PF6,38 and as in the structure of 5 the likely
origin is in the reduction of steric interactions between
ligands on the two coordination centers.
Formation of the Ruthenium(II) Dimer [Ru2Cp*2(µ-
Cl)2(µ-L)]. The ruthenium tetramer [RuCp*(µ3-Cl)]4 gener-
ally reacts with phosphines to give either 16-electron com-
plexes [RuCp*ClL] or 18-electron complexes [RuCp*ClL2].
In order to determine whether L would coordinate in a
monodentate or bidentate mode, 4 equiv of L was added to
a solution of [RuCp*(µ3-Cl)]4. NMR spectra showed that only
2 equiv of L reacted, leading to formation of the dimer [Ru2-
Cp*2(µ-Cl)2(µ-L)] 8 instead of monomeric complexes.
The 31P{1H} NMR spectrum of 8 consists of two doublets
at δ 119.1 and δ 34.6 with a coupling constant of 24 Hz.
The lower field signal can be assigned to the phosphorus
atom with pyrrolyl substituents and the higher field signal
to the phosphorus atom with phenyl substituents. Both signals
are shifted downfield compared with the analogous signals
for L in agreement with a bridging coordination mode. The
1H NMR spectrum of 8 contains the expected signals for a
dimeric complex with one bridging molecule of L. The
signals for the protons of the two chemically inequivalent
Cp* rings are observed as doublets at δ 1.41 and δ 1.32,
2
spin system in which the J coupling constants J(AA′) and
J(XX′) are much larger than all the others. Variable tem-
perature NMR studies showed no changes in the appearance
or in the relative intensities of the signals for the HH and
HT isomers, indicating the absence of an equilibrium between
them.
The presence of the two isomers was also apparent from
1
the H NMR spectra, in particular from the appearance of
the signals from the methyl protons. These are observed as
a pseudo-triplet at δ 0.86 for the HT isomer and as a pair of
pseudo-triplets at δ 1.01 and δ 0.71 for the HH isomer, with
coupling constants of 2 Hz.
Recrystallization of 7 by slow diffusion of hexane in a
dichloromethane solution gave crystalline material that on
the basis of NMR data was enriched in the HT isomer (>95:
5). Further recrystallization gave crystals that, though
twinned, were suitable for X-ray crystallography. The
asymmetric unit contained one molecule of 7 and two
molecules of dichloromethane. Analysis of the structure
confirmed the presence of the HT isomer of 7, which is
shown in Figure 7. Selected bond lengths and angles are
given in Table 5. The two palladium centers are distorted
square planar in geometry, with cis angles in the range 84.09-
(3)-92.91(3)° and a Pd-Cl-Pd angle of 73.59(2)° around
the bridging chloride. The Pd‚‚‚Pd distance of 2.9488(3) Å
is somewhat shorter than those in the related dppm com-
4
both with JPH 2.0 Hz.
Crystals of 8 suitable for a single-crystal X-ray analysis
were obtained by slow evaporation of a THF-hexane
solution. The analysis confirmed the dimeric nature of 8,
with the molecular structure shown in Figure 8 and selected
bond lengths and angles given in Table 6. Each ruthenium
center is coordinated to a pentamethylcyclopentadienyl ring,
two bridging chlorides, and a bridging L ligand. The Ru-P
bond to the diphenylphosphino group is longer than that to
(37) Young, S. J.; Kellenberger, B.; Reibenspies, J. H.; Himmel, S. E.;
Manning, M.; Anderson, O. P.; Stille, J. K. J. Am. Chem. Soc. 1988,
110, 5744-5753.
(38) Stockland, R. A., Jr.; Janka, M.; Hoel, G. R.; Rath, N. P.; Anderson,
G. K. Organometallics 2001, 20, 5212-5219.
Inorganic Chemistry, Vol. 42, No. 22, 2003 7235

Burrows et al.
Figure 9. Molecular structure of [Rh2(µ-Cl)(cod)2(µ-L)]PF6‚CH2Cl2
(9‚CH2Cl2) with the phenyl, pyrrolyl, and cyclooctadiene protons, anion,
and included solvent omitted for clarity and thermal ellipsoids shown at
the 30% probability level.
Figure 8. Molecular structure of [Ru2Cp*2(µ-Cl)2(µ-L)] 8 with the phenyl,
pyrrolyl, and methyl protons omitted for clarity and thermal ellipsoids shown
at the 30% probability level.
Table 7. Selected Bond Lengths (Å) and Angles (deg) for Complex
a
9‚CH2Cl2
Table 6. Selected Bond Lengths (Å) and Angles (deg) for Complex 8
Rh(1)-P(1)
Rh(1)-Cl(1)
Rh(1)-C(11)
Rh(1)-C(14)
2.2618(9)
2.4074(7)
2.236(3)
2.120(4)
Rh(1)-C(15)
Rh(1)-C(18)
P(1)-N(1)
2.122(4)
2.231(4)
1.679(8)
1.755(5)
Ru(1)-P(1)
Ru(1)-Cl(1)
Ru(1)-Cl(2)
Ru(2)-P(2)
Ru(2)-Cl(1)
Ru(2)-Cl(2)
P(2)-N(1)
2.2888(19)
2.483(2)
2.4763(19)
2.2596(17)
2.4635(18)
2.465(2)
Ru(1A)-P(1A)
Ru(1A)-Cl(1A)
Ru(1A)-Cl(2A)
Ru(2A)-P(2A)
Ru(2A)-Cl(1A)
Ru(2A)-Cl(2A)
P(2A)-N(1A)
P(2A)-N(2A)
2.3070(19)
2.4754(18)
2.476(2)
2.2502(18)
2.476(2)
2.454(2)
1.736(7)
1.754(6)
P(1)-N(2)
P(1)-Rh(1)-Cl(1)
Rh(1)-Cl(1)-Rh(1)′
90.31(3)
120.78(5)
P(1)-C(19)-P(1)′
113.8(3)
1.737(7)
1.790(6)
a Primed atoms generated by the symmetry operation -x + 1, y, -z +
P(2)-N(2)
1/2.
P(1)-Ru(1)-Cl(1)
P(1)-Ru(1)-Cl(2)
P(2)-Ru(2)-Cl(1)
P(2)-Ru(2)-Cl(2)
Cl(2)-Ru(1)-Cl(1)
Cl(1)-Ru(2)-Cl(2)
Ru(2)-Cl(1)-Ru(1)
Ru(2)-Cl(2)-Ru(1)
C(1)-P(1)-Ru(1)
C(1)-P(2)-Ru(2)
P(2)-C(1)-P(1)
88.72(7) P(1A)-Ru(1A)-Cl(1A)
89.00(6) P(1A)-Ru(1A)-Cl(2A)
90.31(6) P(2A)-Ru(2A)-Cl(1A)
86.90(7) P(2A)-Ru(2A)-Cl(2A)
81.20(7) Cl(1A)-Ru(1A)-Cl(2A)
81.82(7) Cl(2A)-Ru(2A)-Cl(1A)
97.86(7) Ru(1A)-Cl(1A)-Ru(2A)
97.99(7) Ru(2A)-Cl(2A)-Ru(1A)
89.77(6)
87.70(7)
87.01(7)
91.05(6)
81.44(7)
81.88(7)
97.48(7)
98.06(7)
115.6(2)
119.3(2)
119.7(4)
Calorimetric studies indicated that ∆Hrxn for the reaction
[RuCp*(µ3-Cl)]4 + 2L f 2[Ru2Cp*2(µ-Cl)2(µ-L)]
is -74.1(2) kcal mol-1, whereas the value for the reaction
[RuCp*(µ3-Cl)]4 + 4dppm f 4[RuCp*Cl(dppm)]
117.1(2)
119.8(2)
119.7(4)
C(1A)-P(1A)-Ru(1A)
C(1A)-P(2A)-Ru(2A)
P(2A)-C(1A)-P(1A)
it is calculated to be -117.4(2) kcal mol-1.40 Although the
two values are not directly comparable, these initial results
suggest that substitution of two phenyl groups by two
N-pyrrolyl groups markedly decreases ∆Hrxn, which is
consistent with observations comparing PPh3 and P(NC4H4)3.22
Formation of the Rhodium(I) Dimer [Rh2(µ-Cl)(cod)2-
(µ-L)]PF6. The reaction of [Rh(µ-Cl)(cod)]2 with L was
expected to proceed with cleavage of the chloride bridges
to give either [RhCl(cod)(L-κ1P)] or [Rh(cod)(L-κ2P,P)]+.
However, the reaction resulted in a mixture from which no
product could be isolated. Similar mixtures resulted from
the reaction in the presence of NH4PF6, though in this case
crystallization by slow diffusion of hexane into a dichlo-
romethane solution gave an orange powder and a small
quantity of yellow crystals 9. Although the powder was
revealed to be a mixture, the yellow crystals gave a
reasonably simple 31P{1H} NMR spectrum. This was com-
posed of a doublet of doublets at δ 109.2 with coupling
constants of 218 and 72 Hz, and a doublet of doublets at δ
25.8 with coupling constants of 145 and 72 Hz, in addition
the di(N-pyrrolyl)phosphino group, as anticipated given the
electronic difference between the two phosphino groups. The
Ru‚‚‚Ru distance is 3.722 Å, consistent with the absence of
a metal-metal bond.
The synthesis of 8 is similar to the reaction of [RuCp*-
(µ3-Cl)]4 with dppm, which has been reported to give [Ru2-
Cp*2(µ-Cl)2(µ-dppm)].39 This is in contrast to the reaction
of [RuClCp*(cod)] with dppm which gives [RuCp*Cl-
(dppm)].40 Additional interest in these reactions derives from
the body of thermochemical data that has been reported for
ligands such as phosphines,22,41-43 phosphites,44 and N-
heterocyclic carbenes,45 which has enabled the relative
importance of electronic and steric factors to be assessed.
(39) Mauthner, K.; Kalt, D.; Slugovc, C.; Mereiter, K.; Schmid, R.;
Kirchner, K. Monatsh. Chem. 1997, 128, 533-540.
(40) Luo, L.; Zhu, N.; Zhu, N. J.; Stevens, E. D.; Nolan, S. P.; Fagan, P.
J. Organometallics 1994, 13, 669-675.
(41) Luo, L.; Nolan, S. P.; Fagan, P. J. Organometallics 1993, 12, 4305-
4311.
(42) Shen, J. Y.; Stevens, E. D.; Nolan, S. P. Organometallics 1998, 17,
3000-3005.
(43) Smith, D. C.; Haar, C. M.; Luo, L. B.; Li, C. B.; Cucullu, M. E.;
Mahler, C. H.; Nolan, S. P.; Marshall, W. J.; Jones, N. L.; Fagan, P.
J. Organometallics 1999, 18, 2357-2361.
-
to the characteristic septet for PF6 .
The identity of 9 as [Rh2(µ-Cl)(cod)2(µ-L)]PF6 was
confirmed by X-ray crystallography, with the compound
crystallizing as 9‚CH2Cl2. The structure of the cation in 9 is
shown in Figure 9, and selected bond distances and angle
are given in Table 7. The asymmetric unit consists of half a
(44) Serron, S. A.; Luo, L. B.; Stevens, E. D.; Nolan, S. P.; Jones, N. L.;
Fagan, P. J. Organometallics 1996, 15, 5209-5215.
(45) Huang, J.; Jafarpour, L.; Hillier, A. C.; Stevens, E. D.; Nolan, S. P.
Organometallics 2001, 20, 2878-2882.
7236 Inorganic Chemistry, Vol. 42, No. 22, 2003

Diphosphines Possessing Electronically Different Donor Groups
Table 8. Crystallographic Data for Complexes 2‚CHCl3, 3‚CH2Cl2, 4, 5‚/4CH2Cl2, 6, 7‚2CH2Cl2, 8 and 9‚CH2Cl2
2‚CHCl3
3‚CH2Cl2
4
5‚1/4CH2Cl2
6
7‚CH2Cl2
8
9‚CH2Cl2
empirical
formula
M
C22H21Cl5-
N2P2Pd
659.00
170(2)
C22H22Cl4-
N2P2Pt
713.25
C42H36Cl2-
N4P4Pd
897.93
C
42.25H40.50Cl2.50
N4O2P4Pd2
-
C44H46Cl2-
N4P4Pd2
1038.42
150(2)
C46H50Cl5-
F6N4P5Pd2
1317.80
150(2)
C41H50Cl2-
N2P2Ru2
905.81
C38H42Cl3-
F6N2P3Rh2
1045.82
150(2)
1061.59
293(2)
T/K
150(2)
150(2)
150(2)
λ/Å
0.71073
monoclinic
P21/c
10.6090(2)
17.0690(3)
14.5520(3)
90
96.6390(7)
90
2617.48(9)
4
1.672
1.356
0.0564,
0.1320
0.0594,
0.1334
0.71073
triclinic
P1h
0.71073
triclinic
P1h
0.71073
monoclinic
P21/c
13.2580(2)
15.8300(2)
21.0940(3)
90
107.7090(8)
90
4217.30(10)
4
1.671
1.205
0.0474,
0.1387
0.0720,
0.1653
0.71073
monoclinic
P21/c
10.1650(2)
17.1910(3)
12.4510(2)
90
102.2590(8)
90
2126.16(7)
2
1.622
1.160
0.0305,
0.0718
0.0423,
0.0782
0.71073
triclinic
P1h
0.71073
monoclinic
P21
17.3300(3)
12.0900(2)
20.7670(4)
90
114.132(1)
90
3970.83(12)
4
1.515
1.007
0.0508,
0.1028
0.0945,
0.1186
0.71073
monoclinic
C2/c
15.6150(4)
16.6400(4)
15.7910(4)
90
92.1460(10)
90
4100.16(18)
4
1.694
1.176
0.0407,
0.0938
0.0743,
0.1099
cryst syst
space group
a/Å
8.14100(10)
10.43800(10)
15.0570(2)
77.2310(6)
84.1030(6)
86.3170(6)
1240.10(3)
2
1.910
6.231
0.0238,
0.0583
0.0256,
0.0595
9.3820(2)
10.5300(2)
22.6890(4)
91.1460(10)
99.3950(10)
109.7990(8)
2073.85(7)
2
1.438
0.766
0.0448,
0.1248
0.0664,
0.1416
13.3250(3)
15.1020(3)
15.1540(3)
65.136(1)
83.041(1)
77.135(1)
2696.08(10)
2
1.623
1.121
0.0628,
0.1420
0.0882,
0.1598
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
Z
d
calc/g cm-3
µ/mm-1
R1, wR2
[I > 2σ(I)]
R indices
(all data)
-
dimeric cation, half a PF6 anion, and half a molecule of
dichloromethane. In a manner similar to the structure of 5,
the pyrrolyl and phenyl groups are disordered in a 1:1 ratio.
Each rhodium(I) center is in a square planar coordination
geometry with an angle of 62° between the two coordination
planes. The Rh(1)‚‚‚Rh(1)′ distance at 4.18 Å confirms the
absence of a metal-metal bond in agreement with the formal
electron count. Due to the disorder in the structure, the Rh-P
bond distances appear identical for both phosphorus atoms
of L, whereas the P-C-P angle of 113.8(3)° is comparable
with those observed in the other structures with bridging L.
[PdX2(dppm-κ1P)2].46-48 Such compounds exhibit fluxional
behavior in solution, in contrast to 4 for which the 31P{1H}
NMR spectra are temperature invariant.
Although the palladium dimers [Pd2Cl2(µ-L)2] 5, [Pd2Cl2-
(CH3)2(µ-L)2] 6, and [Pd2(CH3)2(µ-Cl)(µ-L)2]PF6 7 all have
dppm analogues, the presence of two unsymmetrical diphos-
phine ligands affords possibilities of isomerism, and an
opportunity to study interconversion between these isomers.
The palladium(I) dimer 5 exists both in solution and in the
solid state as a 1:1 mixture of HH and HT isomers. In
solution, the ratio of the isomers is neither temperature nor
concentration dependent, and interconversion of the isomers
was not observed on the NMR time scale. In contrast, the
HH and HT isomers of 6 do interconvert in solution, and
the position of equilibrium in this instance is temperature
dependent. At low temperatures the HT isomer is dominant
and is isolable by crystallization. The formation of both HH
and HT isomers of 6 is similar to previous observations on
the reaction of [PdCl(CH3)(cod)] with the arsino(phosphino)-
methane Pri2AsCH2PPri2, though reaction with the bulkier
ligand But2AsCH2PPri2 gave the chelate complex [PdCl-
(CH3)(But2AsCH2PPri2-κ2P,As)] rather than a dimer.8 The
A-frame dimer 7 exists as both HH and HT isomers in
solution, with the HT complex dominant in the original
reaction mixture. These isomers do not interconvert in
solution, and the HT isomer can be isolated by fractional
crystallization.
Discussion
The reactions described above demonstrate that L can act
as a monodentate, chelating, or bridging ligand in a manner
similar to dppm. However, there are both structural and
reactivity differences between the two ligands, which center
on the fact that the di(N-pyrrolyl)phosphino group is a poorer
σ-donor and better π-acceptor than the diphenylphosphino
group. Thus, in the complexes studied, the M-P bonds
involving the P(NC4H4)2 groups are shorter, typically by
∼0.03 Å, than those to the PPh2 groups due to the greater
π-character. However, the poorer σ-donor capability of the
di(N-pyrrolyl)phosphino groups means that these bonds are
also weaker than the M-PPh2 bonds, as witnessed by the
reaction of [PdCl2(L-κ2P,P′)] 2 with L to give exclusively
trans-[PdCl2(L-κ1P)2] 4. This relative weakness of the Pd-
P(NC4H4)2 bond leads to a marked difference in the chemistry
of L with respect to dppm, since [PdCl2(dppm-κ2P,P)] reacts
with dppm to give [Pd(dppm-κ2P,P)2]Cl2, following dis-
placement of chloride, rather than [PdCl2(dppm-κ1P)2] fol-
lowing displacement of the phosphino group.46,47 Moreover,
with dppm complexes, stronger field ligands such as cyanide
or acetylides are required to prepare compounds of the type
Formation of 9 from the reaction between [Rh(µ-Cl)(cod)]2
and L in the presence of NH4PF6, albeit in low yield, con-
trasts with similar reactions involving dppm or arsino(phos-
phino)methanes. The reaction of [Rh(µ-Cl)(nbd)]2 (nbd )
norbornadiene) with dppm gave a mixture of [Rh(dppm-
κ2P,P)2]+ and [Rh(nbd)(dppm-κ2P,P)]+,49 whereas the reac-
tion of [Rh(µ-Cl)(cod)]2 with a range of arsino(phosphino)-
methanes in the presence of KPF6 gave [Rh(cod)(PR2CH2-
(46) Pringle, P. G.; Shaw, B. L. J. Chem. Soc., Chem. Commun. 1982,
956.
(47) Hassan, F. S. M.; Markham, D. P.; Pringle, P. G.; Shaw, B. L. J.
Chem. Soc., Dalton Trans. 1985, 279.
(48) Langrick, C. R.; Pringle, P. G.; Shaw, B. L. Inorg. Chim. Acta 1983,
76, L263.
(49) Ernsting, J. M.; Elsevier: C. J.; de Lange, W. G.; Timmer, K. Magn.
Reson. Chem. 1991, 29, S118-S124.
Inorganic Chemistry, Vol. 42, No. 22, 2003 7237

Burrows et al.
AsR2-κ2P,As)]PF6. However, in the absence of KPF6 the
product depended on the steric bulk of the substituents.7
In addition to influencing the course of the reaction,
alteration of the steric demands within one of the phosphino
groups in L would be expected to reduce the potential for
the phenyl/pyrrolyl disorder that was observed in the crystal
structures of 5 and 9. Thus future work will focus on the
development of ligands in which the isostericity is lifted and,
in addition, the electronic difference between the two donor
groups is further exaggerated.
Acknowledgment. The authors would like to thank the
EPSRC for financial support, the Royal Society of Chemistry
for a journal grant for international authors (to A.D.B.) and
Johnson-Matthey plc for a generous loan of platinum metals.
Supporting Information Available: X-ray crystallographic data
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC034487Z
7238 Inorganic Chemistry, Vol. 42, No. 22, 2003