Various coordination modes of the bis(di(o-N,N-dimethylanilinyl)phosphino) methane ligand in mononuclear and binuclear complexes of group 8 and group 9 metals

Article abstract of DOI:10.1021/ic051639c

The synthesis and characterization of a series of compounds involving the bis(di(o-N,N-dimethylanilinyl)phosphino)-methane (dmapm) ligand are described. The mononuclear complexes [MCI(CO)(P,N-dmapm)] (M = Rh, Ir) have a square-planar geometry in which the dmapm ligand chelates via a phosphine functionality and an adjacent amino group. The carbonyl ligand lies opposite the amine, while the chloro ligand is trans to the phosphine. The related complex [RhI(CO)(P,A/-dmapm)] has also been prepared. All compounds are highly fluxional by at least three independent processes, as discussed for the rhodium-chloro species. A diiridium complex, [Ir₂Cl₂(CO) ₂(P,N,P′,N′-dmapm)], and the closely related rhodium/iridium analogue, [RhIrCl₂(CO)₂(P,N,P′, N′-dmapm)], have been prepared in which the metals are bridged by the diphosphine group while an amino group at each end of the diphosphine is also coordinating to each metal on opposite faces of the MIrP₂ plane (M = Ir or Rh). For the Ir₂ species, the carbonyl and chloro groups are again shown to be opposite the amine and phosphine functionalites, respectively. The mononuclear complex [Ru(CO)₃(P,P′-dmapm)] has also been prepared. In contrast to the mononuclear species of rhodium and iridium, the dmapm group chelates the ruthenium center through both phosphorus atoms, occupying one axial and one equatorial site of Ru in a distorted trigonal bipyramidal geometry. Reaction of this Ru species with 1/2 equiv of the complexes [RhCIL₂]₂ (L₂ = COD, (C ₂H₄)₂, (CO)₂) yields the unstable Rh/Ru product [RhRuCl-(CO)₃(P,N,P′,N′-dmapm)].

Full text of DOI:10.1021/ic051639c

Inorg. Chem. 2006, 45, 3705−3717
Various Coordination Modes of the
Bis(di(o-N,N-dimethylanilinyl)phosphino)methane Ligand in Mononuclear
and Binuclear Complexes of Group 8 and Group 9 Metals
James N. L. Dennett,† Matthias Bierenstiel,† Michael J. Ferguson,‡ Robert McDonald,‡ and
Martin Cowie*,†
Department of Chemistry, UniVersity of Alberta, Edmonton, Alberta, T6G 2G2, Canada, and
X-ray Crystallography Laboratory, UniVersity of Alberta, Edmonton, Alberta, T6G 2G2, Canada
Received September 22, 2005
The synthesis and characterization of a series of compounds involving the bis(di(o-N,N-dimethylanilinyl)phosphino)-
methane (dmapm) ligand are described. The mononuclear complexes [MCl(CO)(P,N-dmapm)] (M Rh, Ir) have
)
a square-planar geometry in which the dmapm ligand chelates via a phosphine functionality and an adjacent amino
group. The carbonyl ligand lies opposite the amine, while the chloro ligand is trans to the phosphine. The related
complex [RhI(CO)(P,N-dmapm)] has also been prepared. All compounds are highly fluxional by at least three
independent processes, as discussed for the rhodium
dmapm)], and the closely related rhodium/iridium analogue, [RhIrCl2(CO)2(P,N,P
in which the metals are bridged by the diphosphine group while an amino group at each end of the diphosphine
is also coordinating to each metal on opposite faces of the MIrP2 plane (M Ir or Rh). For the Ir2 species, the
carbonyl and chloro groups are again shown to be opposite the amine and phosphine functionalites, respectively.
The mononuclear complex [Ru(CO)3(P,P -dmapm)] has also been prepared. In contrast to the mononuclear species
−
chloro species. A diiridium complex, [Ir2Cl2(CO)2(P,N,P
′,N′-
′
,N′-dmapm)], have been prepared
)
′
of rhodium and iridium, the dmapm group chelates the ruthenium center through both phosphorus atoms, occupying
one axial and one equatorial site of Ru in a distorted trigonal bipyramidal geometry. Reaction of this Ru species
1
with /2 equiv of the complexes [RhClL2]2 (L2
)
COD, (C2H4)2, (CO)2) yields the unstable Rh/Ru product [RhRuCl-
(CO)3(P,N,P′,N′-dmapm)].
Introduction
NMR spectroscopy has also been especially useful in
characterization of its complexes.3
Studies of binuclear complexes, in which the adjacent
metals can function in a synergic manner in their interactions
with substrate molecules,1 have been possible owing in a
large part to the use of bridging ligands that hold the metals
in close proximity even upon cleavage of metal-metal
bonds. Arguably, the most frequently used family of bridging
ligands are the diphosphines, of which bis(diphenylphos-
phino)methane (dppm) is the most common.2 This ligand
has been particularly prominent in chemistry involving late
transition-metal complexes, to which it binds effectively. Not
only does this ligand have a flexible bite that allows it to
span a wide range in metal-metal separations, corresponding
to a range in metal-metal bond orders, but the use of 31P
(1) (a) Jones, N. D.; James, B. R. AdV. Synth. Catal. 2002, 344, 1. (b)
Tsukada, N.; Ohba, Y.; Inoue, Y. J. Organomet. Chem. 2003, 687,
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J. A.; Lahoz, F. J.; Werner, H.; Oro, L. A. Organometallics 1998, 17,
683. (d) Yuan, Y.; Jime´nez, M. V.; Sola, E.; Lahoz, F. J.; Oro, L. A.
J. Am. Chem. Soc. 2002, 124, 752. (e) Gauthier, S.; Scopelliti, R.;
Severin, K. Organometallics 2004, 23, 3769. (f) Braunstein, P.; Clerc,
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Chem. Eur. J. 2002, 8, 1514. (h) Le Gendre, P.; Comte, V.; Michelot,
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H.; Guo, N.; Li, L.; Stern, C. L.; Marks, T. J. Organometallics
2004, 23, 5112. (j) Man, M. L.; Zhou, Z. Y.; Ng, S. M.; Lau, C.
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Scopelliti, R.; Severin, K. Angew. Chem., Int. Ed. 2004, 43, 1520. (l)
Torkelson, J. R.; Antwi-Nsiah, F. H.; McDonald, R.; Cowie, M.; Prius,
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* To whom correspondence should be addressed. E-mail: martin.cowie@
ualberta.ca.
(2) See the following for examples: (a) Puddephatt, R. J. Chem. Soc.
ReV. 1983, 12, 99. (b) Chaudret, B.; Delavaux, B.; Poilblanc, R. Coord.
Chem. ReV. 1988, 86, 191.
† Department of Chemistry.
‡ X-ray Crystallography Laboratory.
10.1021/ic051639c CCC: $33.50
Published on Web 04/05/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 9, 2006 3705

Dennett et al.
groups involving phosphorus together with nitrogen,11 and
some of these systems have shown interesting catalytic
activity.10d,e,12
Chart 1
As noted above, our interest in dmapm is as a ligand that
can bridge pairs of adjacent metals. Binuclear complexes in
which the pairs of metals are either the same or different
are currently of interest as potential catalysts,5,6,13 owing to
the prospects of improved catalytic activity and/or selectivity
as a result of the adjacent metals acting in a cooperative
manner. In this regard, it has been proposed by Tsukada and
co-workers14 that a cis-chelating ligand configuration at the
adjacent metals, similar to those diagrammed in structures
B and C, might be important in promoting the cooperative
involvement of adjacent metals. In this paper we describe
our attempts to generate mononuclear dmapm-containing
precursors for use in synthesizing dmapm-bridged homo- and
heterobinuclear complexes and outline our initial success in
generating the targeted binuclear species.
Most of the late transition-metal complexes involving the
dppm ligand have two such groups in a mutually trans
arrangement at both metals as diagrammed in structure A in
Chart 1 (ancillary ligands and dppm phenyl groups omitted;
the dashed line indicates that a metal-metal bond may or
may not be present). In such a geometry, access of substrates
to the metals can be inhibited by the bulky dppm phenyl
substituents, which project above and below the plane of
the drawing. One approach to increasing accessibility to the
metals is to substitute the phenyl groups with smaller alkyl
groups.4 Another approach is to utilize diphosphines having
pendent groups that can also chelate to the metals giving a
cis arrangement at each metal as shown in structures B and
C. In these geometries (but particularly for C) the cis chelates
appear to allow better access to the metals at the sites
opposite the donor groups. Two such bridging groups that
have received recent attention are a series of tetraphosphines
in which the pendent chelating groups are CH2CH2PR2 (X
) PR2 in structure B), the chemistry of which has been
pioneered by Stanley and co-workers5 and also studied by
Su¨ss-Fink,6 and the bis(di(o-N,N-dimethylanilinyl)phosphi-
no)methane (dmapm) ligand, in which the pendent groups,
both chelated and dangling (R groups in structures B and
C), are dimethylanilinyl substituents (X ) NMe2, only ipso
and ortho carbons of phenyl groups are shown for the
chelated groups), recently reported by James and co-
workers.7-9 We were intrigued by the possibility that dmapm
could perform a dual role, in which the diphosphine moiety
could bridge a pair of late transition metals, while the
chelating amine groups might be labile, generating, in effect,
linked pairs of hemilabile10 P,N-bound ligands at each metal.
There has been significant recent interest in related hemilabile
Experimental Section
General Comments. All solvents were deoxygenated, dried
(using appropriate drying reagents), distilled before use, and stored
under nitrogen. The reactions were performed under an argon
atmosphere using standard Schlenk techniques. RhCl3‚3H2O and
Ru3(CO)12 were purchased from Strem Chemicals, and [NH4]2[IrCl6]
was obtained from Vancouver Island Precious Metals. 13C-enriched
CO (99.4% enrichment) was purchased from Isotec Inc. and
Cambridge Isotope Laboratories (99% enrichment). The compounds
[Rh2(µ-Cl)2(CO)4],15 [Rh2(µ-Cl)2(COD)2],16 [Rh2(µ-Cl)2(C2H4)4],17
and [Ir2(µ-Cl)2(COE)4]18 (COD ) 1,5-cycloctadiene; COE )
cyclooctene) were prepared by the literature routes. The diphosphine
ligand, bis(di(o-N,N-dimethylanilinyl)phosphino)methane (dmapm),
was prepared as previously reported.7
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Chem. Res. 2000, 33, 336. (b) Ittel, S. D.; Johnson, L. K.; Brookhart,
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(3) See the following for recent examples: (a) Trepanier, S. T.; Dennett,
J. N. L.; Sterenberg, B. T.; McDonald, R.; Cowie, M. J. Am. Chem.
Soc. 2004, 126, 8046. (b) Oldham, S. M.; Houlis, J. F.; Sleigh, C. J.;
Duckett, S. B.; Eisenberg, R. Organometallics 2000, 19, 2985. (c)
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Organomet. Chem. 2005, 690, 1600 and references therein.
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Chem. 1985, 24, 3589. (d) Pamplin, C. B.; Rettig, S. J.; Patrick, B.
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3706 Inorganic Chemistry, Vol. 45, No. 9, 2006

Group 8 and Group 9 Mononuclear and Binuclear Complexes
Table 1. Spectroscopic Data for the Compounds,
a
IR (cm-1
)
NMRb δ (31P{1H})c
NMRb δ (1H)d
NMRb δ (13C{1H})d
[RhCl(CO)(P,N-dmapm] (1)
NMe2: 3.29 (s, 3H), 2.99 (s, 3H),
2.79 (s, 6H), 2.65 (s, 3H),
1980 (s)
40.9 (dd,
NMe2: 50.0 (m, 1C), 49.5 (s, 1C),
47.1 (s, 1C), 45.0 (br/m, 2C),
44.2 (m, 2C), 42.9 (s, 1C)e
CH2: 29.6 (m)e
1JRhP ) 170 Hz,
2JPP ) 138 Hz),
2.26 (s, 6H), 1.54 (s, 3H)e
-41.8 (d, 2JPP ) 138 Hz)e
CH2: 3.15 (m, 1H)e,f
NMe2: 2.71 (s, 12H), 2.60 (s/br, 12H)g
CH2: 3.23 (s/br, 1H), 3.20 (s/br, 1H)g
CO: 187.8 (dd, 1JRhC
)
73 Hz, 2JPC ) 19 Hz)e
[IrCl(CO)(P,N-dmapm] (2)
NMe2: 3.28 (s, 3H), 3.00 (s, 3H),
2.71 (s, 6H), 2.55 (s, 3H),
2.23 (s, 6H), 1.54 (s, 3H)e
CH2: 3.45 (m, 2H)
1966 (s)
14.2 (d, 2JPP ) 126 Hz),
-41.8 (d, 2JPP ) 126 Hz)e
NMe2: 50.4 (1C), 49.9 (1C),
47.3 (1C), 45.0 (2C),
44.1 (2C), 42.5 (1C)e
CH2: 29.3 (m)e
NMe2: 3.30 (s/br, 3H), 3.14 (s/br, 3H),
2.73 (s/br, 6H), 2.22 (s/br, 6H),
2.53 (s/br, 6H)g
CO: 172.0 (d, 2JPC ) 12 Hz)e
CH2: 3.39 (s/br, 2H)g
[RhI(CO)(P,N-dmapm] (3)
NMe2: 2.78 (s/br, 12H), 2.60 (s, 12H)g
CH2: 3.23 (m, 2H)g
1978 (s)
1989 (s),
37.1 (dd, 1JRhP ) 74 Hz,
2JPP ) 128 Hz),
-41.3 (d, 2JPP ) 128 Hz)g
[RhIrCl2(CO)2(P,N,P′N′-dmapm] (4)
NMe2: 3.81 (s, 3H), 3.65 (s, 3H),
2.96 (s, 3H), 2.91 (s, 3H),
2.71 (s, 6H), 2.34 (s, 3H),
2.31 (s, 3H)i
41.6 (dd, 1JRhP ) 176 Hz,
2JPP ) 37 Hz, 1P),
NMe2: 52.5 (m, 1C), 51.6 (s, 1C),
47.6 (s, 2C), 47.4 (s, 2C),
1995 (sh)h
13.9 (br, d, 2JPP ) 37 Hz)g
45.2 (m, 1C), 43.6 (m, 1C)g
CH2: 25.8 (m)g
CH2: 4.85 (m, 1H), 4.78 (m, 1H)i
CO: 187.8 (dd, 1JRhC ) 75 Hz, 2JPC ) 13 Hz),
171.0 (d, 2JPC ) 16 Hz)g,j
[Ir2Cl2(CO)2(P,N,P′,N′-dmapm] (5)
NMe2: 3.73 (s, 6H), 2.89 (s, 6H),
2.68 (s, 6H), 2.35 (s, 6H)e
1988 (s),
1979 (s/sh)
13.9 (s, 2P)g
NMe2: 52.6 (2C), 50.9 (2C),
47.5 (2C), 47.15 (2C)e
CH2: 5.08 (t, 2JHP ) 3.2 Hz, 2H)e
NMe2: 3.80 (s, 6H), 3.02 (s, 6H),
2.66 (br, 6H), 2.54 (br, 6H)g
CH2: 22.4 (t, 1JPC ) 17 Hz)e
CO: 170.5 (d, 2JPC ) 8 Hz)e
CH2: 5.05 (t, 2JHP ) 13 Hz, 2H)g
[Ru(CO)3(P,P′-dmapm)] (6)
NMe2: 2.12 (s, 24H)
1989 (s),
1910 (m),
1883 (m)
-21.0 (s, 2P)g
NMe2: 46.0 (s)e
CH2: 4.57 (t, 2JHP ) 9 Hz 2H)
CH2: 34.4 (m)e
CO: 214.3 (t, 2JPC ) 15 Hz)e
RhRuCl(CO)3(P,N,P′,N′-dmapm)] (7)
NMe2: 3.74 (s, 3H), 3.03 (s, 3H),
2.76 (s, 6H), 2.55 (s, 3H),
2.54(s, 3H), 2.51 (s, 3H),
2.36 (s, 3H)e
2001(s),
1908(m),
1726 (w)
52.5 (dd, 1JRhP ) 77 Hz,
2JPP ) 102 Hz),
NMe2: 61.6 (s, 1C), 55.5 (m, 1C),
50.7 (s, 1C), 50.1 (s, 1C),
47.6 (s, 1C), 46.7 (s, 1C),
44.1 (s, 2C)e
33.6 (d, 2JPP ) 102 Hz),e
50.5 (dd, 1JRhP ) 179 Hz,
2JPP ) 107 Hz),
CH2: 4.48 (m, 1H), 3.78 (m, 1H)e
NMe2: 3.73 (s, 3H), 3.08 (s, 3H),
2.77 (s, 6H), 61 (s/br, 6H),
2.49 (s, 6H)g
CO: 250.1 (m), 202.9 (d, 2JPC ) 102 Hz),
34.2 (d, 2JPP ) 107 Hz)g
197.2 (m),e,k 246.3 (m, 1JRhC
42 Hz, 2JP(Rh)C ) 1 Hz,
2JP(Ru)C ) 7 Hz),
)
CH2: 4.56 (m, 2H)g
203.1 (d, 2JPC ) 102 Hz),
197.3 (d, 2JPC ) 15 Hz)g
a IR abbreviations: s ) strong, m ) medium, w ) weak, sh ) shoulder. Dichloromethane solution; in units of cm-1
.
b NMR abbreviations: s ) singlet,
d ) doublet, t ) triplet, m ) multiplet, br ) broad, dd ) doublet of doublets. NMR data in CD2Cl2 unless otherwise indicated. c 31P chemical shifts
referenced to external 85% H3PO4. d 1H and 13C chemical shifts referenced to tetramethylsilane. Chemical shifts for the phenyl groups not given. e NMR
data at -80 °C. f Signal of other CH2 obscured by other peaks. g 27 °C. h Acetone. i NMR data at -40 °C. j 13C{1H} NMR data obtained with 13CO
enrichment. k The dmapm CH2 not observed.
NMR spectra were recorded on either a Bruker AM-400 or a
Varian Inova-400 spectrometer operating at 400.0 or 399.8 MHz,
Preparation of Compounds. (a) [RhCl(CO)(P,N-dmapm)] (1).
A CH2Cl2 (20 mL) solution of [Rh2(µ-Cl)2(CO)4] (133.0 mg; 0.341
mmol) was added dropwise to a CH2Cl2 solution of dmapm (401
mg; 0.721 mmol) at -78 °C over a 50 min period. The solution
was allowed to warm slowly over 1 h and stirred for a further 3.5
h. The solvent was removed in vacuo to give a yellow residue.
Dichloromethane (ca. 2 mL) was added, to give an orange solution
which yielded a yellow precipitate of [RhCl(CO)(P,N-dmapm)] (1)
(450 mg; 91.0%) upon the addition of n-pentane (60 mL). Crystals
suitable for an X-ray crystallographic study were grown through
layering a saturated CH2Cl2 solution of 1 with n-pentane. Anal.
Calcd for C34H42ClN4OP2Rh: C, 56.50; H, 5.86; N, 7.75%.
1
respectively, for H, at 161.9 or 161.8 MHz, respectively, for 31P,
and at 100.6 MHz for 13C nuclei (Bruker AM-400). Infrared spectra
(KBr cell) were recorded on either a FTIR Bomem MB-100
spectrometer or a Nicolet Avator 370 DTGS spectrometer. Elemen-
tal analyses were performed by the Microanalytical Laboratory of
this department. Electrospray ionization mass spectra were run on
a Micromass Zabspec spectrometer in the department MS facility.
In all cases, the distribution of isotope peaks for the appropriate
parent ion matched very closely that calculated from the formulation
given. Spectroscopic data for the compounds are given in Table 1.
Inorganic Chemistry, Vol. 45, No. 9, 2006 3707

Dennett et al.
Found: C, 56.14; H, 5.86; N, 7.46%. MS (EI): m/z 723.2 (M+),
695.2 (M+ - CO), 687.2 (M+ - Cl), 659.2 (M+ - CO - Cl).
(b) [IrCl(CO)(P,N-dmapm)] (2). Dichloromethane (10 mL) was
added to a mixture of [Ir2(µ-Cl)2(COE)4] (224 mg; 0.250 mmol)
and dmapm (278 mg; 0.500 mmol). The solution was stirred for 5
min, purged with carbon monoxide for 5 min, and then was stirred
under a CO atmosphere for a further 1 h. The solution was
concentrated under vacuum to approximately 1 mL, and upon
addition of n-pentane (30 mL) a yellow solid precipitated which
was filtered yielding (2) (362 mg, 87%). Crystals suitable for an
X-ray crystallographic study were grown by layering a satu-
rated CH2Cl2 solution of 2 with n-pentane. Anal. Calcd for
C34H42ClN4OP2Ir: C, 50.27; H, 5.21; N, 6.90%. Found: C, 50.66;
H, 5.41; N, 6.51%. MS (EI): m/z 813.2 (M+).
(c) [RhI(CO)(P,N-dmapm)] (3). Compound 1 (80.0 mg; 0.110
mmol) was dissolved in a mixture of methanol (30 mL) and
dichloromethane (10 mL), to which solid KI (500 mg, 3.00 mmol)
was added, and the reaction mixture was stirred at ambient
temperature for 18 h. The solvent was completely removed under
high vacuum, and the remaining solids were extracted with 10 mL
of dichloromethane. The supernatant solution was carefully trans-
ferred to another flask via a cannula, and the solvent volume was
reduced to approximately 1 mL. Addition of 20 mL of n-pentane
produced a yellow-brown solid which was filtered and dried in
vacuo, producing [RhI(CO)(P,N-dmapm)] (3) (84.2 mg; 93.5%).
Anal. Calcd for C34H42IN4OP2Rh: C, 50.14; H, 5.20; N, 6.88%.
Found: C, 49.78; H, 5.35; N, 6.97%.
(d) [RhIrCl2(CO)2(P,N,P′,N′-dmapm)] (4). Method i. To a
solution of [IrCl(CO)(P,N-dmapm)] (2) (249 mg; 0.306 mmol)
dissolved in dichloromethane (10 mL) was added [RhCl(COD)]2
(75.0 mg, 0.153 mmol). Carbon monoxide was passed through the
reaction mixture for 10 min, and the solution was stirred at ambient
temperature for 18 h. The resulting yellow solution was concentrated
in vacuo to approximately 1 mL, and n-pentane (30 mL) was added,
yielding a yellow solid which was filtered and dried in vacuo (269.8
mg; 90.0%).
Method ii. In an NMR tube, [RhCl(CO)(P, N-dmapm)] (1) (8.0
mg; 0.011 mmol) and [Ir2(µ-Cl)2(COE)4] (5.0 mg; 0.0055
mmol) were dissolved in 0.6 mL of CD2Cl2. Carbon monoxide was
passed through the solution at ambient temperature for 5 min, and
an NMR spectrum was recorded after 1 h. The 31P{1H} spec-
trum of the resulting solution was identical to the product (4)
obtained in method i. Yellow crystals were grown by layering a
saturated CH2Cl2 solution of 4 with n-pentane. Anal. Calcd for
C35H42Cl2IrN4O2P2Rh: C, 42.95; H, 4.33; N, 5.72%. Found: C,
42.88; H, 4.54; N, 5.71%.
the NMR spectrum was recorded after 1 h. The 31P{1H} spectrum
was identical to the product described in method i, indicating
quantitative conversion to compound 5. Yellow/orange crystals
suitable for an X-ray crystallographic study were grown by layering
a saturated CH2Cl2 solution of 5 with n-pentane. Anal. Calcd for
C35H42Cl2Ir2N4O2P2: C, 39.39; H, 3.96; N, 5.25%. Found: C, 39.20;
H, 3.96; N, 4.85%. MS (EI): m/z 1069.1 (M+).
(f) [Ru(CO)3(P,P′-dmapm)] (6). An n-pentane solution (140
mL) of [Ru(CO)4(η2-C2H4)] was prepared photolytically with the
use of [Ru3(CO)12] (195.4 mg, 0.306 mmol) and an ethylene purge.19
The solution was then slowly added, in the dark, to a pentane (100
mL) suspension of dmapm (340.0 mg, 0.612 mmol), and the
suspension was stirred overnight, giving an orange suspension. The
solvent was removed in vacuo, and the orange residue was dis-
solved in Et2O (70 mL) and filtered through Celite to remove any
[Ru3(CO)12]. The solvent was removed, and pentane (20 mL) was
added. The orange suspension was cooled to -78 °C, the solvent
was removed by cannula, and the process was repeated, eventually
giving (after drying) [Ru(CO)3(P,P′-dmapm)] (6) as a yellow/orange
precipitate (340 mg, 75.1%). Yellow/orange crystals suitable for
an X-ray crystallographic study were grown by the slow evaporation
of a saturated CD2Cl2 solution. Anal. Calcd for C36H42N4O3P2Ru:
C, 58.29; H, 5.71; N, 7.55%. Found: C, 58.30; H, 5.65; N, 7.53%.
MS (EI): m/z 742.2 (M+).
(g) [RhRuCl(CO)3(P,N,P′,N′-dmapm)] (7). Method i. To a
CD2Cl2 solution (0.3 mL) of [Ru(CO)3(P,P′-dmapm)] (6) (39.0 mg;
0.0526 mmol) was added slowly, over 1 min, a CD2Cl2 solution
(0.4 mL) of [Rh2(µ-Cl)2(C2H4)4] (13.0 mg; 0.0334 mmol). An
instant color change was observed, darkening to burgundy within
1
minutes. Free ethylene could be removed (observed by H NMR)
by freeze-thaw-degassing the solution several times.
Method ii. To a CD2Cl2 solution (0.3 mL) of [Ru(CO)3(P,P′-
dmapm)] (6) (36.5 mg; 0.0493 mmol) was added slowly, over 1
min, a CD2Cl2 solution (0.4 mL) of [Rh2(µ-Cl)2(COD)2] (12.1 mg;
0.0245 mmol). An instant color change was observed, the mixture
darkening to a burgundy solution. To remove the liberated COD,
the solution was cooled to -78 °C and precooled n-pentane (20
mL) was added, giving a dark brown/black precipitate, which was
found (by 31P{1H} NMR spectroscopy) to consist of varying yields
(up to a maximum of 80%) of 7 together with several unidentified
decomposition products. Although this sample was stable for weeks
as a solid or in solution at -78 °C, it decomposed within hours at
ambient temperature. MS (EI), using precooled methanol as carrier
solvent: m/z 879.0 (M+
- H). Attempts to obtain high-resolution
mass spectroscopy data were unsuccessful.
(h) Attempted Reactions of Compounds 1-3 with Metal-
Carbonylate Anions. The reaction of compounds 1-3 with slight
excesses of the metal-carbonylate anions [PPN][HOs(CO)4] and
Na[FeCp(CO)2] were attempted in a number of solvents (CH2Cl2,
THF, acetone, nitromethane) between -80 and 20 °C. After several
days either no reaction was observed or small amounts of
unidentified species were observed together with mainly starting
materials. The 31P{1H} NMR spectra of these minor products were
inconsistent with the targeted “MM′(µ-dmapm)” geometry, so they
were not investigated further. A typical reaction is described as
follows: Compound 1 (31 mg; 0.043 mmol) was dissolved in 13
mL of THF giving a pale yellow solution, which was subsequently
cooled to -78 °C in a dry ice/acetone bath. A THF solution (5
mL) of [PPN][HOs(CO)4] (38 mg; 0.045 mmol) was slowly added
via cannula over a 10 min period. The solution was allowed to
warm slowly overnight. The solvent was removed in vacuo giving
(e) [Ir2Cl2(CO)2(P,N,P′,N′-dmapm)] (5). Method i. Dichlo-
romethane (50 mL) was added to a mixture of [Ir2(µ-Cl)2(COE)4]
(309 mg; 0.340 mmol) and dmapm (200 mg; 0.360 mmol), and
the orange solution was stirred for 15 min. Carbon monoxide was
passed over the solution which was heated to reflux for 1.25 h,
giving a dark red solution. (The reaction could also be carried out
at ambient temperature but required a longer reaction time.) The
heating was stopped, and carbon monoxide was passed through
the solution for a further 2 h. The solution was then filtered through
Celite, and the solvent was removed in vacuo, giving a red residue.
Dichloromethane (ca. 2 mL) was added, followed by n-pentane (50
mL), giving [Ir2Cl2(CO)2(P,N,P′,N′-dmapm)] (5) as an orange
precipitate (250.0 mg; 67.8%).
Method ii. In an NMR tube, [IrCl(CO)(P,N-dmapm)] (2) (20.0
mg; 0.0250 mmol) and [Ir2(µ-Cl)2(COE)4] (11.0 mg; 0.0125
mmol) were dissolved in 0.6 mL of CD2Cl2. Carbon monoxide was
passed through the solution at ambient temperature for 5 min, and
(19) Wuu, Y.-M.; Zou, C.; Wrighton, M. S. Inorg. Chem. 1988, 27, 3039.
3708 Inorganic Chemistry, Vol. 45, No. 9, 2006

Group 8 and Group 9 Mononuclear and Binuclear Complexes
Table 2. Crystallographic Data for Compounds
compd 1
compd 2
compd 5
compd 6
formula
fw
C34H42ClN4OP2Rh
723.02
C34H42ClIrN4OP2
812.31
C35H42Cl2Ir2N4O2P2
1067.97
C36H42N4O3P2Ru
741.75
cryst dimensions (mm)
0.55 × 0.49 × 0.33
0.53 × 0.42 × 0.36
0.35 × 0.28 × 0.25
0.29 × 0.26 × 0.18
cryst syst
space group
unit cell params
a (Å)
b (Å)
c (Å)
monoclinic
monoclinic
orthorhombic
monoclinic
P21/c (No. 14)
P21/c (No. 14)
P212121 (No. 19)
P21/c (No. 14)
15.667(2)a
14.431(2)
15.658(2)
104.966(2)
3420.1(6)
4
15.7236 (6)b
14.3785(5)
15.6551(6)
105.026(1)
3418.3(2)
4
17.3516(6)c
20.0932(7)
20.9362(7)
90
7299.4(4)
8
12.2902(7)d
16.4522(9)
19.015(1)
107.735(1)
3662.2(4)
4
â (deg)
V (Å3)
Z
F
calcd (g cm-3
)
1.404
0.704
1.578
4.110
1.944
7.557
1.345
0.554
µ (mm-1
)
diffractometer
Bruker PLATFORM/SMART 1000 CCD
radiation (λ [Å])
graphite-monochromated Mo KR (0.710 73)
temp (°C)
-80
-80
-80
-80
scan type
data collection 2θ limit (deg)
total data collected
ω scans (0.3°, 20 s)
52.78
ω scans (0.3°, 20 s)
52.78
ω scans (0.2°, 20 s)
52.76
ω scans (0.3°, 20 s)
52.76
25 535 (-19 e h e 19,
-18 e k e 18,
-19 e l e 19)
6971 (Rint ) 0.0301)
6182
25 961 (-19 e h e 19,
-17 e k e 17,
-19 e l e 19)
6980 (Rint ) 0.0192)
6416
50 608 (-21 e h e 19,
-25 e k e 25,
-26 e l e 26)
14 900 (Rint ) 0.0297)
14 049
27 899 (-15 e h e 15,
-20 e k e 20,
-23 e l e 23)
7492 (Rint ) 0.0330)
6547
no. of independent reflns
no. of observed reflns (NO)
2
[Fo2 g 2σ(Fo )]
abs correction method
multiscan
multiscan
multiscan
multiscan
(SADABS)
0.8010-0.6982
6971/0/396
(SADABS)
0.3192-0.2193
6980/2e/385
(SADABS)
0.2538-0.1773
14900/0/847
(SADABS)
0.9068-0.8558
7492/0/415
range of transm factors
data/restraints/params
2
[Fo2 g -3σ(Fo )]
Flack absolute structure paramf
-0.001(3)
1.042
GOF (S)g [Fo2 g -3σ(Fo )]
1.110
1.037
1.032
2
final R indicesh
2
R1 [Fo2 g 2σ(Fo )]
0.0357
0.1002
1.456 and -0.490
0.0215
0.0560
1.647 and -0.635
0.0210
0.0491
1.522 and -0.342
0.0264
0.0688
0.444 and -0.283
wR2 [Fo2 g -3σ(Fo )]
2
largest difference peak
and hole (e Å-3
)
a Obtained from least-squares refinement of 7288 reflections. b Obtained from least-squares refinement of 7781 centered reflections. c Obtained from
least-squares refinement of 6862 centered reflections. d Obtained from least-squares refinement of 8005 centered reflections. e The N31A-C32 and N31B-
C32 distances were restrained to be 1.44(1) Å. f Flack, H. D. Acta Crystallogr. 1983, A39, 876-881. Flack, H. D.; Bernardinelli, G. Acta Crystallogr. 1999,
A55, 908-915. Flack, H. D.; Bernardinelli, G. J. Appl. Crystallogr. 2000, 33, 1143-1148. The Flack parameter will refine to a value near 0 if the structure
2
2
is in the correct configuration and will refine to a value near 1 for the inverted configuration. g S ) [∑w(Fo - Fc )2/(n - p)]1/2 (n ) number of data; p )
2
2
2
number of parameters varied; w ) [σ2(Fo ) + (a0P)2 + a1P]-1 where P ) [max(Fo , 0) + 2Fc ]/3). For 1, a0 ) 0.0459, a1 ) 3.5716; for 2, a0 ) 0.0278,
a1 ) 4.3124; for 5, a0 ) 0.0191, a1 ) 0; for 6, a0 ) 0.0320, a1 ) 1.6202. h R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑w(Fo - Fc )2/∑w(Fo )]1/2
.
2
2
4
a yellow residue. Fresh THF (10 mL) was added, and the yellow
solution was filtered through Celite. The resulting yellow solution
was reduced to ca. 2 mL, and 20 mL of pentane was added, yielding
The final model for 1 was refined to values of R1(F) ) 0.0357
2
(for 6182 data with Fo2 g 2σ(Fo )) and wR2(F2) ) 0.1002 (for all
6971 independent data).
1
a yellow precipitate. NMR spectra (31P{1H} and H) showed that
(b) Yellow crystals of [IrCl(CO)(P,N-dmapm)] (2) were ob-
tained via slow diffusion of n-pentane into a dichloromethane
solution of the compound. Data were collected and corrected for
absorption as for 1 above (see Table 2). Unit cell parameters
were obtained from a least-squares refinement of the setting
angles of 7781 reflections from the data collection, and the
space group was determined to be P21/c (No. 14). The structure of
2 was solved, and refinement was completed in the same man-
ner as for 1, with the same hydrogen atom treatment. One of the
dimethylamino groups of 2 was disordered; the major and
minor conformers were assigned occupancy factors of 0.55 and
0.45, and the nitrogen-to-ring-carbon distances (N31A-C32 and
N31B-C32) were restrained to be 1.44(1) Å. The final model
for 2 was refined to values of R1(F) ) 0.0215 (for 6416 data with
the major species present were compound 1 and [PPN][OsH(CO)4]
with small amounts (<5% total) of several impurities detected in
the 31P{1H} NMR spectrum. The same reaction in acetone yielded
only starting material.
X-ray Data Collection and Structure Solution. (a) Yellow
crystals of [RhCl(CO)(P,N-dmapm)] (1) were obtained via slow
diffusion of n-pentane into a dichloromethane solution of the
compound. Data were collected on a Bruker PLATFORM/SMART
1000 CCD diffractometer20 using Mo KR radiation at -80 °C. Unit
cell parameters were obtained from a least-squares refinement of
the setting angles of 7288 reflections from the data collection. The
space group was determined to be P21/c (No. 14). The data were
corrected for absorption through use of the SADABS procedure.
See Table 2 for a summary of crystal data and X-ray data collection
information.
2
2
Fo g 2σ(Fo )) and wR2(F2) ) 0.0560 (for all 6980 independent
data).
The structure of 1 was solved using the direct-methods program
SHELXS-86.21 Refinement was completed using the program
SHELXL-93.22 Hydrogen atoms were assigned positions based on
the geometries of their attached carbon atoms and were given
thermal parameters 20% greater than those of the attached carbons.
(20) Programs for diffractometer operation, data collection, data reduction,
and absorption correction were those supplied by Bruker.
(21) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467-473.
(22) Sheldrick, G. M. SHELXL-93: Program for Crystal Structure Deter-
mination; University of Go¨ttingen: Go¨ttingen, Germany, 1993.
Inorganic Chemistry, Vol. 45, No. 9, 2006 3709

Dennett et al.
Scheme 1
(c) Yellow crystals of [Ir2Cl2(CO)2(P,N,P′,N′-dmapm)] (5) were
shown in this scheme at ambient temperature, the yields are
variable under these conditions, and the known binuclear
complex [Rh2Cl2(CO)2(µ-P,N,P′,N′-dmapm)]24 is invariably
present as a contaminant. We have found that carrying out
the reaction at -78 °C by slow addition of the Rh-carbonyl
dimer eliminates this impurity and gives rise to consistently
higher yields of the targeted product (1).
obtained via slow diffusion of n-pentane into a saturated dichlo-
romethane solution of the compound. Data were collected and
corrected for absorption as for 1 and 2 above (see Table 2). Unit
cell parameters were obtained from a least-squares refinement of
the setting angles of 6862 reflections from the data collection, and
the space group was determined to be P212121 (No. 19). The
structure of 5 was found to consist of two independent molecules
in the unit cell, one having an S,S and the other an R,R
configuration. Solution and refinement proceeded as for compounds
1 and 2. The final model for 5 was refined to values of R1(F) )
The 31P{1H} NMR spectrum of compound 1 displays a
doublet of doublets at δ 40.9, having 170 Hz coupling to
Rh and 138 Hz coupling to the other phosphorus nucleus,
which appears as a doublet at δ -41.8 (see Table 1). Whereas
the former resonance is typical of a Rh-bound diphosphine,25
the latter appears near the resonance observed for the free
dmapm ligand (δ -36.0).7 The 13C{1H} NMR spectrum
displays a single resonance for the carbonyl group at δ 187.8,
displaying 73 Hz coupling to Rh and 19 Hz coupling to the
adjacent 31P nucleus. The magnitude of this coupling (2JPC)
is typical for a mutually cis phosphine and carbonyl
arrangement26 and is much smaller than values typical of a
trans arrangement (ca. 120 Hz).26b In the IR spectrum, the
stretch at 1980 cm-1 is consistent with a terminal carbonyl
involving Rh(I).27 Taken together with the elemental analysis
and the mass spectral information, the above spectral data
suggest the formulation shown in Scheme 1. Coordination
of one of the anilinyl nitrogens is necessary to give Rh a
2
0.0210 (for 14 049 data with Fo2 g 2σ(Fo )) and wR2(F2) ) 0.0491
(for all 14 900 independent data).
(d) Yellow crystals of [Ru(CO)3(P,P′-dmapm)] (6) were obtained
upon cooling of a solution of the compound in diethyl ether to
-80 °C. Data were collected and corrected for absorption as for 1,
2, and 5 above (see Table 2). Unit cell parameters were obtained
from a least-squares refinement of the setting angles of 8005
reflections from the data collection, and the space group was
determined to be P21/c (No. 14). The structure of 6 was solved
using the direct-methods program SIR97;23 the refinement and
hydrogen atom treatment proceeded as for 1, 2, and 5. The final
model for 6 was refined to values of R1(F) ) 0.0264 (for 6547
2
2
data with Fo g 2σ(Fo )) and wR2(F2) ) 0.0688 (for all 7492
independent data).
Results and Compound Characterization
The targeted mononuclear complexes [MCl(CO)(P,N-
dmapm)] (M ) Rh (1), Ir (2)) containing the chelating
dmapm ligand are readily prepared as outlined in Scheme
1. Although complex 1 can be prepared from the reagents
(24) Jones, N. D. Ph.D. Thesis, University of British Columbia, British
Columbia, Canada, 2002.
(25) Carlton, L. Magn. Reson. Chem. 2004, 42, 760.
(26) (a) Mann, B. E. 13C NMR Data for Organometallic Compounds; Mann,
B. E., Taylor, B. F., Eds.; Academic Press: London, U.K., 1981; p
23. (b) Rotondo, E.; Battaglia, G.; Giordano, G.; Cusmano, F. P. J.
Organomet. Chem. 1993, 450, 245. (c) Partridge, M. G.; Messerle, B.
A.; Field, L. D. Organometallics 1995, 14, 3527.
(23) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115-119.
(27) Otto, S.; Roodt, A. Inorg. Chim. Acta 2004, 357, 1.
3710 Inorganic Chemistry, Vol. 45, No. 9, 2006

Group 8 and Group 9 Mononuclear and Binuclear Complexes
of 3.70 Å.22,29 Both contacts are potentially chemically
meaningful; the close Rh-N(2) contact has implications in
the fluxionality of compound 1, and the position of P(2)
seems ideal for generating a diphosphine-bridged complex
by displacement of the chloro ligand by a carbonylate anion,
a strategy that we have used successfully in the past for the
generation of dppm-bridged heterobinuclear species.30
The structure of 1 is reminiscent of that reported for PdCl2-
(P,N-dmapm),8 having a P,N-bound dmapm ligand and also
having pendent amine and phosphine moieties on either side
of the Pd square-plane, outside of the inner coordination
sphere. As was the case for the Pd(II) compound, the struc-
ture of 1 allows a comparison to be made of the structural
parameters within the coordinated and free phosphine and
amine groups. The P-C(aryl) distances (1.812(3), 1.823(2)
Å) and the P-CH2 distance (1.832(2) Å) for the coordinated
end of the diphosphine are significantly shorter than those
(1.858(3), 1.842(3), and 1.865(3) Å, respectively) of the
uncoordinated end. Furthermore, this is accompanied by
wider C-P-C angles (range 102.8(1)-105.1(1)°) for the
coordinated end than those (range 97.2(1)-102.9(1)°) of the
free end. Similar trends in the related Pd(II) system have
been interpreted,8 on the basis of previous arguments,31 as
indicating that the phosphine is functioning primarily as a
σ-donor.
Data for the coordinated amines show an N-C(aryl)
bond distance (1.479(4) Å) and N-C(methyl) distances
(1.504(4), 1.492(4) Å) that are generally longer than the
corresponding distances for the uncoordinated amines (range
1.422(4)-1.438(4) Å for the N-C(aryl) and 1.447(4)-
1.470(6) Å for N-C(methyl)). Also, the angles around the
coordinated nitrogen are somewhat more acute (range 108.1-
(2)-109.5(3)°) than those of the uncoordinated nitrogens
(range 111.0(3)-115.4(3)°). A similar pattern was noted in
[PdCl2(P,N-dmapm)].8
It is clear from 1H NMR spectroscopy, presented in Table
1, that there is a high degree of fluxionality within the P,N-
chelated complex 1. At low temperature (-80 °C), the
dimethylanilinyl protons exhibit six resonances, assigned to
the six different methyl group environments at δ 2.79 (6Ha),
2.26 (6Hb), 3.29 (3Hc), 2.99 (3Hd), 2.65 (3He), and 1.54 (3Hf)
(see Chart 2 for labeling of the H nuclei). These assignments
were established by HMQC, HMBC, spin-saturation-transfer
experiments, and 31P-decoupling experiments. According to
the solid-state structure shown in Figure 1, there should be
four separate resonances for the four inequivalent methyl
groups associated with the dangling end of the diphosphine
(C(37), C(38), C(47), and C(48)), but even at -80 °C only
two resonances (Ha and Hb) are observed. Either two pairs
Figure 1. Perspective view of [RhCl(CO)(P,N-dmapm)] (1) showing the
atom labeling scheme. Each carbon atom within an anilinyl group bears
the number of this group (e.g., C(n1)-C(n8)). Non-hydrogen atoms are
represented by Gaussian ellipsoids at the 20% probability level. Hydrogen
atoms are shown with arbitrarily small thermal parameters for the methylene
group of the dmapm ligand; all other hydrogen atoms are omitted.
favored 16-electron, square-planar configuration. At -80 °C,
1
the H NMR spectrum displays six different methyl reso-
nances for the anilinyl methyl groups in a 1:1:2:1:2:1
intensity ratio (see Table 1), consistent with the proposed
structure (a detailed interpretation of these data appears later
in this section). In contrast to what has been observed for
the related species [PdCl2(dmapm)], in which isomerism
between the P,N-bound and P,P′-bound forms of the ligand
was observed, and the Pt analogue [PtCl2(dmapm)], which
was only observed as the P,P′-bound isomer,8 we see no
evidence in the NMR spectra for an isomer in which the
dmapm is coordinated to Rh through both phosphorus atoms.
The structure proposed for 1 has been confirmed by an
X-ray determination, and a representation of the molecule
is shown in Figure 1 with selected bond lengths and angles
given in Table 3. The chelating dmapm ligand is shown to
bind via one phosphorus and an adjacent anilinyl group,
forming a planar five-membered metallacycle. Completing
the square-planar geometry of the metal, the carbonyl ligand
lies opposite the anilinyl group, with the chloro ligand
opposite the coordinated phosphine moiety. In this geom-
etry, the carbonyl and phosphine groups having the greatest
trans labilizing effect28 are mutually cis, while the σ-donor
amine functionality is opposite the strongest π acceptor.
Two pendent groups lie above and below the Rh coordi-
nation plane, outside of the immediate coordination sphere.
One anilinyl group lies below the square plane, having a
Rh-N(2) distance of 3.583(2) Å, while the other end of the
diphosphine lies above the plane with a Rh-P(2) distance
of 3.5859(7) Å. Although the Rh-N(2) contact is slightly
beyond the van der Waals separation of around 3.40 Å, the
Rh-P(2) distance is within a normal van der Waals contact
(29) (a) Bondi, A. J. Phys. Chem. 1964, 68, 441. (b) http://www.
webelements.com/webelements/elements/text/H/radii.html.
(30) (a) Hilts, R. W.; Franchuk, R. A.; Cowie, M. Organometallics 1991,
10, 304. (b) Dell’Anna, M. M.; Trepanier, S. T.; McDonald, R.; Cowie,
M. Organometallics 2001, 20, 88. (c) Antonelli, D. M.; Cowie, M.
Organometallics 1990, 9, 1818. (d) Hilts, R. W.; Franchuk, R. A.;
Cowie, M. Organometallics 1991, 10, 1297.
(28) (a) Basolo, F.; Pearson, R. G. Prog. Inorg. Chem. 1962, 4, 381. (b)
Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry
Principles of Structure and ReactiVity, 4th ed.; HarperCollins: New
York, 1993; Chapter 13.
(31) (a) Marynick, D. S. J. Am. Chem. Soc. 1984, 106, 4064. (b) Xiao,
S.-X.; Trogler, W. C.; Ellis, D. E.; Berkovitch-Yellin, Z. J. Am. Chem.
Soc. 1983, 105, 7033. (c) Orpen, A. G.; Connelly, N. G. Organome-
tallics 1990, 9, 1206.
Inorganic Chemistry, Vol. 45, No. 9, 2006 3711

Dennett et al.
Table 3. Selected Distances and Angles for Compounds 1 and 2
compd 1
(M ) Rh)
compd 2
(M ) Ir)
compd 1
compd 2
compd 1
compd 2
Bond Lengths (Å)
1.842(3)
M-Cl
2.3862(8)
2.1921(7)
2.209(2)
1.801(3)
1.832(2)
1.812(3)
1.823(2)
1.865(3)
1.858(3)
2.3794(8)
2.1934(6)
2.208(2)
1.804(3)
1.833(2)
1.811(3)
1.828(2)
1.866(2)
1.859(3)
P(2 )-C(41)
M-P(2)b
1.843(3)
3.5897(7)
1.154(3)
1.484(4)
1.499(4)
1.499(4)
1.442(4)
1.461(4)
N(2)-C(28)
N(3)-C(32)
N(3)-C(37)
N(3)-C(38)
N(4)-C(42)
N(4)-C(47)
N(4)-C(48)
M-N(2)b
1.464(4)
1.422(4)
1.470(6)
1.447(7)
1.427(4)
1.460(4)
1.451(4)
3.583(2)
1.460(4)
a
a
M-P(1)
3.5859(7)
1.147(3)
1.479(4)
1.504(4)
1.492(4)
M-N(1)
M-C(1)
P(1)-C(10)
P(1)-C(11)
P(1)-C(21)
P(2)-C(10)
P(2)-C(31)
O(1)-C(1)
N(1)-C(12)
N(1)-C(17)
N(1)-C(18)
N(2)-C(22)
N(2)-C(27)
a
1.425(4)
1.466(4)
1.449(5)
3.628(2)
1.438(4)
1.458(4)
Bond Angles (deg)
Cl-M-C(1)
90.21(9)
92.05(7)
93.31(9)
84.42(7)
102.8(1)
104.3(1)
105.1(1)
97.2(1)
91.67(9)
90.24(7)
93.68(9)
84.41(7)
102.7(1)
104.2(1)
104.9(1)
97.0(1)
C(10)-P(2)-C(41)
C(31)-P(2)-C(41)
C(12)-N(1)-C(17)
C(12)-N(1)-C(18)
C(17)-N(1)-C(18)
C(22)-N(2)-C(27)
C(22)-N(2)-C(28)
C(27)-N(2)-C(28)
102.9(1)
98.1(1)
102.9(1)
97.9(1)
C(32)-N(3)-C(37)
C(32)-N(3)-C(38)
C(37)-N(3)-C(38)
C(42)-N(4)-C(47)
C(42)-N(4)-C(48)
C(47)-N(4)-C(48)
P(1)-C(10)-P(2)
114.3(4)
113.9(3)
111.9(5)
115.4(3)
112.4(2)
111.0(3)
108.5(1)
a
a
a
Cl-M-N(1)
P(1)-M-C(1)
P(1)-M-N(1)
C(10)-P(1)-C(11)
C(10)-P(1)-C(21)
C(11)-P(1)-C(21)
C(10)-P(2)-C(31)
108.1(2)
109.6(3)
109.5(3)
112.4(2)
112.0(2)
111.3(2)
108.2(2)
108.6(3)
109.2(3)
112.3(2)
112.1(2)
111.4(2)
115.4(3)
112.7(2)
111.4(3)
108.4(1)
a This amine group in compound 2 was disordered over two positions. See the Supporting Information for a complete listing of the parameters. b Nonbonded
distance.
Chart 2
experiments. At 0 °C, Ha and Hb have coalesced to a broad
peak that has become sharp by 27 °C. The interconversion
of the four methyl groups at these intermediate temperatures
must involve a series of inversions at nitrogen and at
phosphorus (P(2)) combined with rotation about aryl-amine
and the C(1)-P(2) bonds. The third process occurs at
approximately 15 °C and involves coalescence of the signals
for protons Hc, Hd, He, and Hf. This behavior appears to result
from exchange of the coordinated and uncoordinated anilinyl
groups (associated with N(1) and N(2), respectively) that are
bound to the coordinated phosphorus atom. Certainly, the
close proximity of N(2) to Rh should facilitate such a process.
Again Figure 1 clearly shows how this exchange might be
possible. Surprisingly perhaps, no exchange between the
bound and unbound phosphorus nuclei is observed in the
31P{1H} NMR spectra, despite the relatively close positioning
of P(2) to Rh, shown in Figure 1. We suggest that such an
exchange is unfavorable since it would need to involve
simultaneous exchange of the coordinated anilinyl group with
one of those adjacent to P(2) to maintain the favored five-
membered Rh-P-C-C-N metallacyle. In any case, facile
exchange of the free and coordinated amine groups, while
no exchange of the phosphorus nuclei is observed, is in
keeping with the proposed hemilabile nature of the dmapm
ligand.
of resonances are accidentally degenerate or pairs of methyl
groups are exchanging at this low temperature. If the latter
is the case, it is not clear which pairs are exchanging. At
ambient temperature only two resonances are seen at δ 2.71
(12H; Ha and Hb) and 2.60 (12H; Hc, Hd, He, and Hf),
resulting from rapid exchange of the methyl resonances
shown in the respective parentheses. Through a variety of
1H NMR experiments at various temperatures, we were able
1
to detect three distinct fluxional processes. At -80 °C, H
NMR spin-saturation-transfer experiments demonstrate that
the anilinyl methyl protons He and Hf are exchanging slowly.
As the temperature rises, these two resonances broaden until
at -40 °C they are almost in the baseline; by -20 °C they
have presumably coalesced (although the presence of the
other signals makes this difficult to confirm). This process
exchanges one set of protons that are in the vicinity of Rh
(those on C(27) of Figure 1) with those on C(28) that are
aimed away from Rh. We suggest that the protons in the
vicinity of Rh are those that resonate at high field (δ 1.54),
although the distances of these protons from Rh (the closest
Rh-H contact is at 3.24 Å) are beyond the van der Waals
separation and appear to rule out an actual agostic interaction
involving the methyl group. The exchange of this pair of
methyl groups would occur by rotation around the aryl-
amine bond (C(22)-N(2)) accompanied by inversion at this
nitrogen.32 The second process begins to appear at -40 °C
and involves the interconversion of the methyl protons Ha
and Hb, as shown by 1H NMR spin-saturation-transfer
The iridium analogue of compound 1, namely, [IrCl(CO)-
(P,N-dmapm)] (2), has been synthesized in a similar manner
by the reaction of [IrCl(COE)2]2 and dmapm at ambient
temperature, under 1 atm of CO. Spectroscopic parameters
for this compound are closely comparable with those of 1
(Table 1). The most significant differences (aside from the
lack of Rh coupling) appear in the 31P{1H} NMR spectrum
in which the chemical shift for the coordinated end of the
diphosphine is at significantly higher field (δ 14.2 vs δ 40.9)
(32) Gu¨nther, H. In NMR Spectroscopy: Basic Principles, Concepts, and
Applications in Chemistry, 2nd ed.; Wiley & Sons: New York, 1995;
p 357.
3712 Inorganic Chemistry, Vol. 45, No. 9, 2006

Group 8 and Group 9 Mononuclear and Binuclear Complexes
than for the Rh analogue, as is commonly observed.33
Similarly, in the 13C{1H} NMR spectrum the carbonyl
resonance is at higher field and displays coupling to only
the cis-phosphine. An X-ray structural determination of
compound 2 shows that it is almost superimposable on that
of 1, so a representation of this compound is not shown but
is given in the Supporting Information. Selected bond lengths
and angles are given, together with those of compound 1, in
Table 3 (an identical numbering system was used for both
compounds). A comparison of these parameters confirms the
close similarity of the two species. Indeed, the same general
trends for the phosphine and amine bonding that are seen
for 1sshorter P-C and longer N-C bonds for the coordi-
nated ligandssare also seen for 2.
Similar fluxional processes to those occurring in 1 are
thought to be taking place in 2, albeit at slightly different
temperatures. The exchange process, corresponding to ex-
change of He and Hf protons of 1, is occurring at -80 °C
(by 1H NMR spin-saturation-transfer experiments), with
coalescence around -20 °C. The second process (exchange
of Ha and Hb protons) is occurring at 0 °C in CD2Cl2 (as
shown by 1H NMR spin-saturation-transfer experiments). In
this case coalescence has not yet been reached by 35 °C (the
temperature limit for CD2Cl2). In d8-toluene, the resonances
for Ha and Hb coalesce around 60 °C. The third process, the
exchange of uncoordinated and coordinated anilinyl ligands,
is occurring at 0 °C in CD2Cl2 but again requires higher
temperatures in an alternate solvent to reach coalescence (50
°C in d8-toluene).
perature and could also be obtained by the reverse reaction
of compound 1 with 1/2 equiv of [IrCl(COE)2]2 under carbon
monoxide. In the 31P{1H} spectrum at ambient temperature
compound 4 displays a sharp doublet of doublets, corre-
sponding to the Rh-bound end of the diphosphine, at δ 41.6
having 176 Hz coupling to Rh and 37 Hz coupling to the
other phosphorus nucleus, and it also displays a broad doublet
at δ 13.9, corresponding to the Ir-bound phosphorus nucleus.
Both chemical shifts are in good agreement with the
respective values for the coordinated ends of the diphosphines
in the Rh and Ir compounds 1 and 2. Upon the sample being
cooled to -40 °C, the broad high-field signal sharpens to a
line-width comparable to that of the Rh-bound end, sug-
gesting a fluxional process occurring at Ir. We have not
investigated this further. Selective homonuclear 31P-decou-
pling experiments confirm the mutual coupling between both
ends of the diphosphine. Two resonances are observed in
the 13C{1H} NMR spectrum of a 13CO-enriched sample,
corresponding to a Rh-bound (δ 187.8; 1JRhC ) 75 Hz) and
an Ir-bound carbonyl (δ 171.0). The two expected car-
bonyl stretches are not resolved in CH2Cl2 but can be
resolved into a band at 1989 cm-1 and a shoulder at 1995
cm-1 in acetone.
The diiridium analogue, [Ir2Cl2(CO)2(P,N,P′,N′-dmapm)]
(5), is readily obtained upon reacting an equimolar mixture
of [IrCl(COE)2]2 and dmapm, under an atmosphere of CO,
and could also be obtained quantitatively in an NMR-scale
reaction by combining the mononuclear [IrCl(CO)(P,N-
dmapm)] (2) with 1/2 equiv of [IrCl(COE)2]2 under 1 atm of
carbon monoxide. Spectral parameters for 5 show some
significant differences compared to those of the mononuclear
species 2. In particular, only one resonance is seen in the
31P{1H} NMR spectrum at a chemical shift (δ 13.9) in the
region expected for coordination of the phosphine moiety
to Ir (see compounds 2 and 4); this spectrum is also invariant
between ambient temperature and -80 °C. The absence of
a resonance corresponding to an uncoordinated end of the
diphosphine supports a structure in which two iridium cen-
ters are bridged by the diphosphine moiety. Although the
13C{1H} NMR spectrum shows only one carbonyl resonance,
consistent with a terminal carbonyl, the IR spectrum shows
two stretches at 1988 and 1979 cm-1. Mass spectral data
and elemental analyses support a binuclear formulation in
which the two Ir centers are bridged by a single dmapm
ligand, as shown in Scheme 1. This has been confirmed by
an X-ray structure determination, a representation of which
is shown in Figure 2, with selected bond lengths and angles
in Table 4. The structure shown for 5 is similar to that
proposed earlier for the heterobinuclear species [PtPdCl4(µ-
dmapm)].1a Several structures are possible for a binuclear
species, and the unit cell of 5 contains two independent
molecules consisting of a racemic mixture of both S,S and
R,R enantiomers; these are labeled molecule 1 and molecule
2, respectively, in Table 4, which gives selected bond lengths
and angles. A representation of molecule 1 is shown in Figure
2. These molecules have the targeted geometry in which the
metals are bridged by the diphosphine moiety while each is
simultaneously chelated in a cis arrangement by an anilinyl
Complex 1 reacts with an excess of potassium iodide to
yield the iodide analogue, [RhI(CO)(P,N-dmapm)] (3) (Scheme
1). The solvent combination used for this metathesis reaction
is a 3:1 methanol-dichloromethane mixture, since no
reaction was observed in pure dichloromethane at ambient
temperature even after 24 h and an unidentified species was
observed using methanol alone. The use of methanol-
dichloromethane yielded a pure sample of 3. All spectral
parameters for compound 3 (see Table 1) correspond very
closely to those of 1; the 31P resonance for the pendent
1
phosphine is almost identical in these species as are the H
resonances at ambient temperature. Only the 31P resonance
for the Rh-coordinated end of the diphosphine differs
significantly from that of 1, appearing at slightly higher field
in the iodo species (δ 37.1). Furthermore, the carbonyl stretch
for the two halide compounds is almost identical at 1980
and 1978 cm-1 for 1 and 3, respectively. All other spectro-
scopic data, including the fluxional data, are reminiscent of
compound 1.
The binuclear mixed-metal complex [RhIrCl2(CO)2-
(P,N,P′,N′-dmapm)] (4) was readily prepared by reaction of
1/2 equiv of [RhCl(COD)]2 with [IrCl(CO)(P,N-dmapm)] (2)
under an atmosphere of carbon monoxide at ambient tem-
(33) (a) Alvey, L. J.; Meier, R.; Soo´s, T.; Bernatis, P.; Gladysz, J. A. Eur.
J. Inorg. Chem. 2000, 1975. (b) Bushweller, C. H.; Rithner, C. D.;
Butcher, D. J. Inorg. Chem. 1984, 23, 1967. (c) Hilts, R. W.; Oke,
O.; Ferguson, M. J.; McDonald, R.; Cowie, M. Organometallics 2005,
24, 4393. (d) George, D. S. A.; Hilts, R. W.; McDonald, R.; Cowie,
M. Organometallics 1999, 18, 5330. (e) Oke, O.; McDonald, R.;
Cowie, M. Organometallics 1999, 18, 1629.
Inorganic Chemistry, Vol. 45, No. 9, 2006 3713

Dennett et al.
Scheme 2
Ir(2) torsion angle of 41.78(5)° and 46.84(4)° for the two
independent molecules; the effect of this twist is to thrust
Ir(1) out of the plane of Figure 2 while Ir(2) lies behind this
plane. All twists appear to result from the close contacts
between one methyl group on each coordinated anilinyl group
and the chloro ligand on the adjacent metal; these contacts
between Cl and the methyl hydrogens (2.9 Å) correspond to
van der Waals contacts.
Figure 2. Perspective view of one of the two crystallographically-
independent molecules of [Ir2Cl2(CO)2(P,N,P′,N′-dmapm] (5) (molecule 1)
showing the atom labeling scheme. Non-hydrogen atoms are represented
by Gaussian ellipsoids at the 20% probability level. Hydrogen atoms are
shown with arbitrarily small thermal parameters for the methylene group
of the dmapm ligand; all other hydrogen atoms are omitted.
At ambient temperature the 1H NMR spectrum of 5 shows
only four equal-intensity resonances for the anilinyl methyl
groups, reflecting a degree of symmetry in solution. In addi-
tion, two of these resonances are broad, and on heating
coalesce, suggesting the occurrence of a fluxional process.
The two broad peaks sharpen as the temperature is lowered,
and spin-saturation-transfer experiments show that exchange
is occurring at -20 °C. Two of these four resonances
presumably correspond to the coordinated anilinyl groups,
and we suggest that the fluxional process that exchanges the
other two occurs by lone pair inversion at the uncoordinated
anilinyl groups. We see no evidence of exchange between
the free and coordinated anilinyl groups indicating that their
lability is less than in the mononuclear precursor (2).
group at each end of the molecule. These anilinyl groups
are bound on opposite faces of the Ir2P2 plane. Coordination
of only one anilinyl group at each metal renders the
phosphorus atoms chiral, and the transoid arrangement of
the bound anilinyl groups, binding to opposite faces of the
complex, gives rise to the two observed enantiomers. As in
the mononuclear species, 1 and 2, the phosphines are opposite
the chloro ligands while the carbonyls are opposite the amine
groups. In fact, a glance at Figures 1 and 2 shows how 5
can result from 2 by coordination of an “IrCl(CO)” group at
the pendent phosphine in 2 with concomitant coordination
of an anilinyl group. The two square-planar Ir centers are
tilted away from each other by angles of 27.57(4)° (molecule
1) and 26.6(2)° (molecule 2), and this is clearly demonstrated
by the much larger Ir(1)-Ir(2) separation (4.1272(3), 4.3313-
(3) Å) than the P(1)-P(2) separation (3.156(2), 3.217(2) Å).
This opening up of the diphosphine bite is also seen in the
wide P(1)-C(3)-P(2) angles of 118.9(2)° and 121.9(3)° for
the two independent molecules; this angle is 10° wider than
those in compounds 1 and 2 in which there are no constraints
on the diphosphine bite. In addition to the tilt apart of the
square planes, they are staggered with regards to each other
by approximately 42-47°, with the carbonyl ligand on each
metal lying directly above the aryl group of the coordinated
anilinyl group on the other metal. Furthermore, the diphos-
phine moiety is twisted resulting in an Ir(1)-P(1)-P(2)-
In attempts to generate potential precursors for mixed-
metal group 8/group 9 complexes bridged by dmapm, we
chose to investigate mononuclear dmapm complexes of Ru.
Reaction of [Ru(CO)4(η2-C2H4)] with dmapm yielded the
targeted species [Ru(CO)3(P,P′-dmapm)] (6) in good yield,
as outlined in Scheme 2. As observed for the diiridium
complex (5), the 31P{1H} NMR spectrum of 6 displays only
one ligand resonance at δ -21.0, suggesting either a fluxional
process that exchanges coordinated and uncoordinated phos-
phine moieties or a structure in which both phosphorus atoms
are coordinated. The invariance of this spectrum over a wide
temperature range (down to -80 °C) suggests the latter.
Certainly, the relatively high-field chemical shift for this 31
P
Table 4. Selected Distances and Angles for Compound 5
molecule 1
molecule 2
molecule 1
molecule 2
molecule 1
molecule 2
Bond Lengths (Å)
1.814(5)
Ir(1)-Ir(2)
Ir(1)-Cl(1)
Ir(1)-P(1)
Ir(1)-N(1)
4.1272(3)a
2.388 (1)
2.187(1)
2.192(4)
4.3313(3)a
2.397(1)
2.186(1)
2.209(4)
Ir(1)-C(1)
Ir(2)-Cl(2)
Ir(2)-P(2)
1.813(5)
2.400(1)
2.192(1)
Ir(2)-N(3)
Ir(2)-C(2)
P(1)-P(2)
2.192(4)
1.818(5)
3.156(2)a
2.210(4)
1.828(5)
3.217(2)a
2.384(1)
2.191(1)
Bond Angles (deg)
Cl(1)-Ir(1)-N(1)
Cl(1)-Ir(1)-C(1)
P(1)-Ir(1)-N(1)
89.6(1)
90.6(2)
85.3(1)
90.7(1)
93.8(2)
84.6(1)
P(1)-Ir(1)-C(1)
P(1)-C(3)-P(2)
Cl(2)-Ir(2)-N(3)
94.5(2)
118.9(2)
89.4(1)
90.9(2)
121.9(3)
90.0(1)
Cl(2)-Ir(2)-C(2)
P(2)-Ir(2)-N(3)
P(2)-Ir(2)-C(2)
91.0(2)
85.6(1)
93.9(2)
90.8(2)
84.7(1)
94.4(2)
a Nonbonded distance.
3714 Inorganic Chemistry, Vol. 45, No. 9, 2006

Group 8 and Group 9 Mononuclear and Binuclear Complexes
resulting in a significant deviation of P(1) from the axial
site opposite C(1)-O(1), as demonstrated by the P(1)-Ru-
C(1) angle of 168.05(7)°. This strain also results in distortion
within the trigonal plane leading to widely different P(2)-
Ru-C(2) (102.19(6)°), P(2)-Ru-C(3) (137.69(6)°), and
C(2)-Ru-C(3) (118.32(9)°) angles.
Clearly, the X-ray structure indicates that both phosphorus
nuclei are inequivalent, one (P(1)) occupying an axial site
and one (P(2)) occupying an equatorial site. The observation
of only one resonance in the 31P{1H} NMR spectrum (even
down to -80 °C) suggests that these nuclei are exchanging
rapidly, presumably by a Berry pseudorotation process.35
Similar fluxionality was reported in a series of Ru(CO)3L2
complexes, in which L2 represents chelating diphosphines.36
This proposed fluxionality also explains the appearance of
only a single carbonyl resonance in the 13C{1H} NMR
spectrum.
Figure 3. Perspective view of the [Ru(CO)3(P,P′-dmapm)] (6) molecule
showing the atom labeling scheme. Non-hydrogen atoms are represented
by Gaussian ellipsoids at the 20% probability level. Hydrogen atoms are
shown with arbitrarily small thermal parameters for the methylene group
of the dmapm ligand; all other hydrogen atoms are omitted.
1
Compound 6 reacts with /2 equiv of either [Rh2(µ-Cl)2-
(COD)2] or [Rh2(µ-Cl)2(C2H4)4] to give the same mixed
rhodium/ruthenium-containing product [RhRuCl(CO)2(µ-
1
CO)(dmapm)] (7) in each case (by 31P{1H}, H NMR, and
IR spectroscopy), as outlined in Scheme 2. With [Rh2(µ-
Cl)2(CO)4], the same product, in 31% yield, is seen by
31P{1H} NMR spectroscopy but with a number of additional
unidentified species. In the 31P{1H} NMR spectrum, at
ambient temperature, this new compound shows two mutu-
ally coupled resonances at δ 50.5 (dd, 2JPP ) 107 Hz, 1JRhP
Table 5. Selected Distances and Angles for Compound 6
Bond Lengths Å
Ru-P(1)
Ru-P(2)
Ru-C(1)
2.3853(5)
2.3881(5)
1.891(2)
Ru-C(2)
Ru-C(3)
P(1)-P(2)a
1.909(2)
1.897(2)
2.7651(6)
Bond Angles (deg)
P(1)-Ru-P(2)
P(1)-Ru-C(1)
P(1)-Ru-C(2)
P(1)-Ru-C(3)
P(2)-Ru-C(1)
70.80(2)
168.05(7)
89.21(6)
96.76(6)
98.26(7)
P(2)-Ru-C(2)
P(2)-Ru-C(3)
P(1)-C10-P(2)
C(2)-Ru-C(3)
102.19(6)
137.69(6)
97.40(8)
2
) 179 Hz) and δ 34.2 (d, JPP ) 107 Hz). The low-field
chemical shift of both resonances, which differ substantially
from that observed for the free ligand (δ ) -36.0), as well
as the Rh-coupling observed in the former, indicates that
the dmapm ligand bridges rhodium and ruthenium centers
through its two phosphorus atoms. The 13C{1H} NMR
spectrum confirms the presence of three carbonyl ligands,
two of which are terminally bound to ruthenium at δ 203.1
and 197.3, while the third, at δ 246.3, is bridging. The former
Ru-bound carbonyl displays a large coupling (102 Hz) to
phosphorus that is typical for a trans arrangement of carbonyl
and phosphine groups,21b while the bridging carbonyl shows
42 Hz coupling to Rh and additional coupling to both 31P
nuclei. Additional support for the formulation shown in
Scheme 2 comes from the IR spectrum of 7, which shows
two terminal carbonyl stretches at 2001 (s) and 1908 (m)
and a bridging stretch at 1726 (w) cm-1. Our attempts to
isolate complex 7 for elemental analysis and X-ray crystal-
lography have been unsuccessful; although reaction solutions
of this species are stable at ambient temperature for short
periods of time, any attempt to isolate a pure species by
recrystallization resulted in its decomposition. Solutions of
7, prepared using [Rh2(µ-Cl)2(C2H4)4], were slightly more
stable (up to 1 day at ambient temperature), even upon
removal of the ethylene by freeze-thaw-degassing the
solution several times. However, again attempts to isolate
118.32(9)
a Nonbonded distance.
resonance is consistent with that of a strained four-mem-
bered ring.34 No evidence of a P,N-bound diphosphine unit
was observed over the temperature range investigated. In the
13C{1H} NMR spectrum, a single carbonyl resonance (δ
214.3) is observed, which broadens slightly at -80 °C,
suggesting a fluxional process. The IR spectrum shows three
stretches for the terminal carbonyls at 1883, 1910, and 1989
cm-1. The 1H NMR spectrum of 6 shows only one peak for
the anilinyl methyl groups at δ 2.12; this resonance broadens
on cooling the sample to -80 °C, also suggesting the onset
of a fluxional process.
An X-ray structural determination of 6 confirms the P,
P′-binding mode of the diphosphine, in which the phosphorus
atoms bind in one axial and one equatorial site of a distorted
trigonal bipyramid as shown in Figure 3. Selected bond
lengths and angles are given in Table 5. The strain inherent
in the four-membered ring formed by the chelating diphos-
phine is clear, with the P(1)-C(10)-P(2) angle (97.40(8)°)
being significantly compressed from the idealized value for
an sp3-hybridized carbon. In addition, the P(1)-Ru-P(2)
angle (70.80(2)°) is much less than the idealized 90°,
(34) See the following for examples: (a) Bickley, J. F.; La Pense´e, A. A.;
Higgins, S. J.; Stuart, C. A. J. Chem. Soc., Dalton Trans. 2003, 4663.
(b) Higgins, S. J.; La Pense´e, A. A.; Stuart, C. A.; Charnock, J. M. J.
Chem. Soc., Dalton Trans. 2001, 902. (c) Garrou, P. E. Chem. ReV.
1981, 81, 229.
(35) (a) Shriver, D. F.; Atkins, P. W. In Inorganic Chemistry, 3rd ed.; W.
H. Freeman and Co.: New York, 1999; Chapter 7. (b) Berry, R. S. J.
Chem. Phys. 1960, 32, 933.
(36) Bunten, K. A.; Farrar, D. H.; Poe¨, A. J.; Lough, A. J. Organometallics
2000, 19, 3674.
Inorganic Chemistry, Vol. 45, No. 9, 2006 3715

Dennett et al.
the solid led to decomposition. Our inability to isolate
compound 7 from solution initially suggested a possible
involvement of residual coordinated olefin, but this seems
unlikely on the basis that the spectroscopic parameters for
products prepared from COD, COE, and ethylene-containing
precursors were superimposable. In addition, the above
solutions could be obtained essentially free of the olefin
by degassing the solutions and could also be obtained in
the complete absence of olefins in the reaction of 6 with
[Rh2Cl2(CO)4]. Solvent also appeared not to influence sta-
bility, with similar behavior obtained in a number of solvents.
The structure proposed for 7 is reminiscent of a series of
dppm-bridged complexes [Rh2X2(µ-L)(dppm)2] (X ) Cl, Br;
L ) CO, SO2, CF3C2CF3),37-39 except in having an extra
ligand bound to Ru, giving this metal its favored 18e
configuration. In particular, compound 7 has a low-frequency
stretch for the bridging carbonyl that is reminiscent of those
in the dppm-bridged species, [Rh2X2(µ-CO)(dppm)2].37
has the chelating amine groups on opposite faces of the Ir2P2
plane as shown earlier for structure B, rather than on the
same face, as diagrammed in structure C. The observed
arrangement of the dmapm substituents is adopted in order
to minimize contacts between the methyl groups on the
coordinated amines, which would be very unfavorable in
structure C. A similar geometry was proposed involving the
group 10 metals Pd and Pt.1a
Our strategy of generating mixed-metal complexes, bridged
by the dmapm ligand, through chloride displacement from
[MCl(CO)(P,N-dmapm)] by the carbonylate anion, [OsH-
(CO)4]-, did not succeed. Similarly, use of a strong nucleo-
phile such as Na[FeCp(CO)2]40 also gave no reaction as did
attempts to displace the iodide ion from [RhI(CO)(P,N-
dmapm)] (3) by these anions. Certainly, the successful
replacement of the chloride anion in 1 by the iodide ion to
give 3 indicates that nucleophilic displacement by small
anions is possible.
One problem with our anion-displacement strategy for the
generation of dmapm-bridged heterobinuclear complexes
appears to be the geometry of the precursor (1), in which
the halide lies opposite the Rh-phosphorus bond. To
maintain the favored square-planar geometry at Rh, the
metal-carbonylate anion must bind opposite the Rh-P bond
at the site of the displaced halide (see Figure 1). In this site
the added metal is too far from the pendent phosphorus to
allow coordination of the latter. Although one can envision
a rearrangement at Rh that would bring the added metal to
a site cis to the Rh-bound end of the diphosphine in a position
appropriate for binding of the pendent end, this would place
two ligands (CO, phosphine) having a high trans effect
opposite each other, destabilizing this arrangement. Further-
more, as discussed for compound 5 and as shown in Figure
2, destabilizing interactions involving the methyl groups on
the coordinated amine and ligands on the adjacent metal
cannot be overlooked. In the previously structurally char-
acterized compounds in which a dmapm group bridges a
metal-metal bond,1a,8 both group 10 metals have a relatively
uncrowded square-planar geometry in which the remaining
three sites, besides the metal-metal bond, are occupied by
dmapm (P- and N-bound) and a chloro ligand. The incor-
poration of the group 8 metals, Ru and Os, into dmapm-
bridged complexes will give rise to additional nonbonding
repulsions between ligands and the dmapm substituents
owing to the tendencies of these earlier metals to be
coordinatively saturated and to consequently have higher
coordination numbers.
Discussion
In previous studies we have reported a convenient route
to binuclear mixed-metal complexes of groups 8 and 9 metals
through chloride displacement from the group 9 complexes
[MCl(dppm)2] (M ) Rh, Ir) by the metal-carbonylate anions
[M′H(CO)4]- (M′ ) Ru, Os), yielding the products [MM′H-
(CO)3(dppm)2].30 As noted in the Introduction, we sought
to extend this chemistry to the dmapm ligand, in which the
diphosphine moiety could bridge the metals while a pair of
anilinyl groups could chelate, one to each metal, via the
amine nitrogens. Such a binding mode would give a cis
arrangement of this multidentate ligand at each metal, in
contrast to the usual trans arrangement of the disphosphines
in the dppm-bridged complexes noted above (Chart 1). A
pair of obvious mononuclear precursors for employing such
a strategy are the complexes [MCl(CO)(P,N-dmapm)] (M
) Rh (1), Ir (2)). These species were readily prepared as
outlined earlier in Scheme 1 and have the expected square-
planar geometry, in which the dmapm ligand is bound to
the metal via one phosphorus and one of the adjacent anilinyl
nitrogens. The resulting five-membered M-P-C-C-N
metallacycle is relatively unstrained and is certainly much
less so than the four-membered M-P-C-P metallacycle
that would result had the ligand been bound to the metal via
both phosphorus atoms. The structures of both the rhodium
and the iridium species suggested that these complexes would
be promising precursors for the synthesis of heterobinuclear
species, owing to the positioning of the pendent phosphine,
immediately above the metal, seemingly in an ideal position
to coordinate a second metal.
An alternate strategy for generating a heterobinuclear
complex of Rh and Ru is to start with a diphosphine complex
of the latter and to react it with an appropriate Rh species.
The targeted complex [Ru(CO)3(P,P′-dmapm)] (6) was
synthesized by ethylene displacement from [Ru(C2H4)(CO)4].
Unlike the mononuclear analogues of the group 9 metals
(1-3), in which the dmapm ligands are bound through one
phosphine and one amine functionality, the Ru species is
coordinated to dmapm through both phosphorus atoms. The
The suitability of dmapm as a bridging group in group 9
metal chemistry is clearly demonstrated in the rhodium-
iridium (4) and diiridium species (5), as shown for the latter
in Figure 2. The geometry adopted for the diiridium product
(37) (a) Cowie, M.; Dwight, S. K. Inorg. Chem. 1980, 19, 2508. (b)
Gelmini, L.; Loeb, S. J.; Stephan, D. W. Inorg. Chim. Acta 1985, 98,
L3.
(38) Cowie, M.; Dwight, S. K. Inorg. Chem. 1980, 19, 209.
(39) Cowie, M.; Dickson, R. S. Inorg. Chem. 1981, 20, 2682.
(40) King, R. B. Acc. Chem. Res. 1970, 3, 417.
3716 Inorganic Chemistry, Vol. 45, No. 9, 2006

Group 8 and Group 9 Mononuclear and Binuclear Complexes
P,P′-binding mode is initially surprising, generating a highly
strained, four-membered Ru-P-C-P metallacycle instead
of a more favorable five-membered Ru-P-C-C-N met-
allacycle as observed in compounds 1 and 2. However, the
preference of the “Ru(CO)3” unit for the softer phosphine
than the harder amine group41 presumably overcomes the
unfavorable ring strain. In the case of compounds 1 and 2,
the “MCl(CO)” unit is slightly harder (M(+1) vs Ru(0)), so
its preference for the softer phosphine linkage is less,
allowing ring strain to dominate. In any case, the highly
strained Ru-P-C-P ring fits our strategy for generating
heterobinuclear complexes, a strategy that has previously
been exploited,30,42 in which the strained diphosphine readily
unwinds to adopt a relatively unstrained bridging arrange-
ment. In this case, the reaction of 6 with an appropriate
source of “RhCl” generates the dmapm-bridged product
[RhRuCl(CO)2(µ-CO)(P,N,P′,N′-dmapm)] (7), as shown in
Scheme 2. Unfortunately, this product is unstable, decom-
posing upon workup, so a full structural analysis was not
possible. As noted earlier, steric crowding involving the
o-N,N-dimethylanilinyl groups on one metal and ligands on
the adjacent metal will tend to destabilize a metal-metal
bonded species. This destabilization will clearly become more
problematic with earlier metals than Rh, owing to their higher
coordination numbers. In compound 7, the metal-metal
bonded species seems possible owing to the geometry at Rh,
in which we propose that the coordinated amine is opposite
the Rh-Ru bond as observed for the terminally bound groups
in related carbonyl-bridged dppm compounds.37 Such an
arrangement allows the coordinated dimethylanilinyl groups
to avoid each other. Nevertheless, the steric crowding that
results from the higher coordination number at Ru may
contribute to the instability of this compound.
either through adjacent phosphine and amine functionalities
or by both phosphine groups. Although the former binding
mode is favored by less strain within the resulting five-
membered metallacycle, the latter can be formed by soft
metal centers despite the resulting strained four-membered
metallacycle. This ligand can also bridge metals through the
diphosphine moiety in which a neighboring amino group on
each end of the diphosphine can also chelate to the adjacent
metal. Although we did not succeed in synthesizing the
targeted group 8/group 9 metal complexes by the anticipated
route, we did succeed in generating a diiridium species, a
mixed Rh/Ir analogue, and a Rh/Ru species by alternate
routes. The potential of dmapm to function as a bridging
ligand that is capable of enhancing metal-metal cooperat-
ivity in heterobinuclear complexes of group 8 and group 9
metals and the roles of the coordinated amines as labile
groups for the generation of coordinative unsaturated species
remain to be demonstrated. These topics will form the basis
of subsequent investigations.
Acknowledgment. We thank the Natural Sciences and
Engineering Research Council of Canada (NSERC) and the
University of Alberta for financial support of this research
and NSERC for funding the Bruker PLATFORM/SMART
1000 CCD diffractometer and the Nicolet Avator IR spec-
trometer. We also thank Dr. N. D. Jones for helpful
discussions.
Supporting Information Available: X-ray experimental details,
atomic coordinates, interatomic distances and angles, anisotropic
thermal parameters, hydrogen parameters for compounds 1, 2, 5
and 6 in a CIF file and a perspective view (ORTEP) of compound
2. This material is available free of charge via the Internet at
http://pubs.acs.org.
Conclusions
IC051639C
The dmapm ligand displays a versatile coordination
chemistry in which it can chelate to a single metal, binding
(42) See the following for examples: (a) Hutton, A. T.; Pringle, P. G.;
Shaw, B. L. Organometallics 1983, 2, 1889. (b) Iggo, J. A.; Markham,
D. P.; Shaw, B. L.; Thornton-Pett, M. J. Chem. Soc., Chem. Commun.
1985, 432. (c) Blagg, A.; Shaw, B. L. J. Chem. Soc., Dalton Trans.
1987, 221. (d) Blagg, A.; Pringle, P. G.; Shaw, B. L. J. Chem. Soc.,
Dalton Trans. 1987, 1495.
(41) (a) Pearson, R. G. J. Am. Chem. Soc. 1963, 85, 3533. (b) Huheey, J.
E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry Principles of
Structure and ReactiVity, 4th ed.; HarperCollins: New York, 1993;
Chapter 9.
Inorganic Chemistry, Vol. 45, No. 9, 2006 3717