Sterically tunable phosphenium cations: Synthesis and characterization of bis(arylamino)phosphenium ions, phosphinophosphenium adducts, and the first well-defined rhodium phosphenium complexes

Article abstract of DOI:10.1021/om0005351

A family of bis(arylamino)chlorophosphines of the general formula ClPN(Ar)CH2CH2N-(Ar) (Ar = 4-MeO-C6H4, 3a; Ar = 2,4,6-Me3-C6H2) 3b; Ar = 2,6-(CHMe2)2-C6H3, 3c) has been prepared from PCls and the appropriate diamine.

Full text of DOI:10.1021/om0005351

4944
Organometallics 2000, 19, 4944-4956
Articles
Ster ica lly Tu n a ble P h osp h en iu m Ca tion s: Syn th esis a n d
Ch a r a cter iza tion of Bis(a r yla m in o)p h osp h en iu m Ion s,
P h osp h in op h osp h en iu m Ad d u cts, a n d th e F ir st
Well-Defin ed Rh od iu m P h osp h en iu m Com p lexes
Michael B. Abrams, Brian L. Scott, and R. Thomas Baker*
Los Alamos Catalysis Initiative, Chemistry Division, Los Alamos National Laboratory,
Los Alamos, New Mexico 87545
Received J une 22, 2000
A family of bis(arylamino)chlorophosphines of the general formula ClPN(Ar)CH2CH2N-
(Ar) (Ar ) 4-MeO-C6H4, 3a ; Ar ) 2,4,6-Me3-C6H2, 3b; Ar ) 2,6-(CHMe2)2-C6H3, 3c) has been
prepared from PCl3 and the appropriate diamine. Steric interactions involving the 2,6-aryl
1
substituents in 3b,c result in hindered rotation about the N-CAr bond, as evidenced by H
NMR spectroscopy. Treatment of halophosphines 3a -c with AgOSO2CF3 (AgOTf) or Tl-
{B[3,5-(CF3)2-C6H3]4} (TlBArF) affords the cationic bis(arylamino)phosphenium compounds
[PN(Ar)CH2CH2N(Ar)](A), (4a -e; A ) OTf, BArF), in high yield. Phosphenium cations 4a -d
reversibly form adducts with trimethylphosphine. The structure of the phosphinophosphe-
nium adduct 5c (Ar ) 2,6-(CHMe2)2-C6H3) has been determined by single-crystal X-ray
diffraction techniques, revealing both the steric influences of the 2,6-Ar substituents and
the electronic nature of the bonding in 5. Treatment of Wilkinson’s catalyst, RhCl(PPh3)3,
with 1 equiv of 4a gives the first well-defined Rh phosphenium complex, {trans-RhCl(PPh3)2-
[PN(4-MeO-C6H4)CH2CH2N(4-MeO-C6H4)]}(OTf) (6), which is isolated in 80% yield. In
contrast, treatment of Wilkinson’s catalyst with 4c results in quantitative formation of [Rh-
(PPh3)3](OTf) and chlorophosphine 3c. The influence of the phosphenium N-Ar substituents
is further evidenced by the analogous reaction between RhCl(PPh3)3 and mesityl-substituted
4b, which affords products analogous to 4a ,c as well as the isomeric Rh phosphenium complex
7a , having cis PPh3 ligands. 31P NMR spectroscopic parameters for 6 and 7a ,b are consistent
with Rh-P multiple bonding.
In tr od u ction
ments for reactivity are generated by protonation of an
alkyl group or abstraction of a halide or alkyl group from
neutral LnMR2 or LnMX2 precursors and (2) control over
the steric environment at the metal center, through use
of the appropriate ligand ensemble, is invaluable for
obtaining high catalyst activity.
Significant advances in the use of electrophilic late-
metal complexes as homogeneous catalysts have been
realized in the last 5 years. In particular, cationic group
10 species of general formula [LnMR]+ have been
successfully employed for the selective functionalization
of alkanes1-3 and for polymerization,4 copolymeriza-
tion,4,5 and functionalization6 of unsaturated hydrocar-
bons. Common to many of the catalysts employed for
these reactions are two general features: (1) the transi-
tion-metal complexes that satisfy the electronic require-
It occurred to us that utilization of cationic phosphe-
nium ligands of the general formula [PN(Ar)CH2CH2N-
(Ar)](A) (Ar ) substituted aryl group, A ) weakly
coordinating/noncoordinating counterion) could offer
additional methods (i.e., addition or substitution) for
synthesizing late-metal electrophiles in which steric and
electronic environments could be easily controlled
(Scheme 1). In addition, the availability of multiple
metallophosphenium resonance structures may provide
additional means of stabilizing reactive organometallic
species (Scheme 2).
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The coordination chemistry of cationic phosphenium
ions, [PR2]+, has been developed extensively since the
10.1021/om0005351 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 10/28/2000

Sterically Tunable Phosphenium Cations
Organometallics, Vol. 19, No. 24, 2000 4945
Sch em e 1
R substituents and for adducts which do not contain
such a chelating tether.11,13-19 Shagvaleev and co-
workers investigated phosphinophosphenium com-
pounds of the general formula [RXP-PRXCl][A] (R, X
) -Cl, -C2H5, -C6H5, -4-Cl-C6H4, -4-CH3-C6H4; A )
AlCl4, Al2Cl7, AlClBr3, Al2Br6Cl) by variable-tempera-
ture 31P NMR spectroscopy.18 The ambient-temperature
spectra of some of these salts exhibited broad reso-
nances, indicative of rapid, reversible phosphine dis-
sociation; typical AB spin systems were observed at low
temperatures. These studies indicated that the lability
of the P-P bond depends on both the chlorophosphine
substituents and the aluminum counterion employed.
Examples of structurally characterized phosphenium-
donor complexes are rare in comparison to the number
of phosphenium-donor complexes that have been ob-
served spectroscopically. X-ray diffraction studies of
compounds in which neutral amines or phosphines are
tethered to the phosphenium center have been reported
by Schomburg,20 Schmutzler,21-23 Gololobov,24 Lap-
pert,25 and Burford;26 Reed and co-workers reported the
first example of a structurally characterized phosphe-
nium-donor complex in which the donor is not covalently
attached to one of the phosphenium R substituents:
namely, the DBU adduct of {[(Me2HC)2N]2P}(PF6) (I),10
Sch em e 2
initial report of a dicoordinate phosphorus cation over
35 years ago.7 Ligation of one or more heteroatoms to
the electrophilic phosphorus center has facilitated the
synthesis of a wide variety of stable phosphenium salts,
phosphenium-donor adducts, and metallophosphenium
complexes. Phosphenium cations may be both σ-donors
and π-acceptors, rendering them isoelectronic with
neutral carbene, silylene, and carbon monoxide frag-
ments.8,9 The free cationic phosphenium ligands, which
typically incorporate hydrocarbon, aryloxy, or alkyl-
amino groups covalently bound to phosphorus, form
adducts with a variety of neutral bases, permitting the
characterization of both amino-10-12 and phosphino-
phosphenium11,13-18 complexes.
in which the positive charge is delocalized over the two
DBU nitrogens (DBU ) (1,8-diazabicyclo[5.4.0]undec-
7-ene). Burford and co-workers subsequently reported
structures of two complexes in which amine moieties
are intermolecularly coordinated to zwitterionic alumi-
natophosphines, Cl2Al(µ-NSiMe3)2PNMe2CH2CH2NMe2-
P(µ-NSiMe3)2AlCl2 (II) and Cl2Al(µ-NSiMe3)2PN(CH2-
CH2)3CH (III),27 as well as disordered crystal structures
of the phosphine-phosphenium-gallium chloride com-
plex IV, [Me2ClPPMe2GaCl3][GaCl4].14,19 Although sev-
eral examples of intermolecular phosphine coordination
to low-coordinate cationic phosphorus centers (such as
R2CdP+ and ArPdP+ ions) have been reported,28,29
I-IV represent the only structurally characterized
intermolecular phosphenium-donor compounds to date.
For phosphenium-phosphine adducts, 31P NMR spec-
troscopy is invaluable for probing the extent of P-P
interaction; 1J P-P coupling constants typically fall in the
range of 240-385 Hz, both for compounds in which the
phosphine is covalently attached to one or both of the
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4946 Organometallics, Vol. 19, No. 24, 2000
Abrams et al.
The use of phosphenium ions as ligands for transition
metals has also been investigated, although primarily
with group 6 and 8 metals. A variety of η5-cyclopenta-
dienyl (Cp) molybdenum30-41 and tungsten41,42 piano-
stool complexes, as well as a Cp-free complex of man-
ganese,43 have been prepared by treatment of neutral
halophosphines with anionic transition-metal frag-
ments, as shown in eq 1. A cationic, trigonal-bipyram-
idal iron-phosphenium complex,44 cationic piano stool
complexes of molybdenum,45 tungsten,45-48 iron,49-53
and ruthenium,54 and cationic octahedral complexes of
chromium,55-57 molybdenum,55-58 and tungsten-55-57
were all readily obtained from hydride, halide, or
alkoxide abstraction from neutral M-phosphine or
-phosphinite precursors (eq 2).
metals. The only known group 10-phosphenium com-
plexes are the structurally characterized zwitterion Cl2-
Ga(µ-NSiMe3)2P;Ni(CO)3, reported by Niecke,59 and
the clusters {[(R2N)2P]Pd(µ-Cl)}3 (R ) CHMe2, C6H11),
recently observed by Dyer.60 Lang and co-workers
reported neutral Co-phosphenium compounds of the
general formula (R)(R′)P;Co(CO)3, which may be syn-
thesized by the route shown in eq 242,61,62 (R ) 2,4,6-
(CMe3)3-C6H2O, R′ ) CHdCHPh; R ) 2,4,6-(CMe3)3-
C6H2O, R′ ) C5Me5; R ) 2,4,6-(CMe3)3-C6H2O, R′ ) (η2-
CCPh)Co2(CO)6) or by reductive dehalogenation of
(R)(R′)PCl by Co2(CO)8 (R ) 2,6-(CMe3)2-4-Me-C6H2O,
R′ ) (η2-CCPh)Co2(CO)6; R ) 2,4,6-(CMe3)3-C6H2O, R′
) (η2-CCPh)Co2(CO)6).63,64 A recent report by Breit65
indicated that regioselectivity for internal aldehyde in
sytrene hydroformylation was increased by addition of
[LnM]- + X-PE2 f LnMsPE2 + X-
(1)
(2)
varying amounts of either [P(NEt2)2](OTf) or {PN[CH-
LnM-PE2R Lewis acid8 [LnMsPE2]+
(Me)Ph]CH2CH2N[CH(Me)Ph]}(OTf) to Rh(CO)2(acac).
Neither the organometallic complexes initially formed
nor the catalytically active species operating in these
systems could be identified.66
-R-
Comparatively few reports exist in the literature of
phosphenium compounds of group 9 or 10 transition
We report herein (1) the synthesis and characteriza-
tion of a family of bis(arylamino)phosphenium com-
pounds in which the aryl substituents may be varied in
order to influence the steric environment at the phos-
phorus center, (2) assessment of the barriers to N-Ar
rotation for bis(arylamino)chlorophosphines, (3) NMR
spectroscopic characterization of reversible phosphino-
phosphenium adduct formation, (4) the first structurally
characterized intermolecular phosphine adduct of a bis-
(amino)phosphenium ion, and (5) the first well-defined,
cationic group 9 phosphenium compounds, accessible in
high yield from the addition of isolable phosphenium
ions to a neutral Rh complex.
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Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of Ha lop h os-
p h in es a n d P h osp h en iu m Ion s. The synthetic route
to bis(arylamino)phosphenium compounds 4 is shown
in Figure 1. Treatment of glyoxal with 2 equiv of
primary aromatic amine afforded bis(imines) 1a -c67-69
as bright yellow crystalline solids in good yield (69-
84%). Sodium borohydride reduction of 1a -c, followed
by quenching with water, provided bis(amines) 2a -c70,71
in 77-87% yield; although 2a -c are known compounds,
the synthesis described above provides considerable
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Boese, R. Angew. Chem., Int. Ed. Engl. 1984, 23, 738.
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Chem., Int. Ed. Engl. 1986, 25, 92.
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1525.
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oshi, K. Organometallics 1995, 14, 4635.
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results.
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Sterically Tunable Phosphenium Cations
Organometallics, Vol. 19, No. 24, 2000 4947
Ta ble 1. 31P {1H} NMR Da ta for 3-5
δ(P(NRAr)2) δ(PMe3) 1J P-P
compd solvent temp (°C)
(ppm)
(ppm)
(Hz)
3a
3b
3c
4a
4b
4c
4d
4e
5a
5b
5c
5d
CDCl3
CDCl3
CDCl3
CDCl3
CDCl3
CDCl3
CDCl3
CDCl3
CD2Cl2
CD2Cl2
CD2Cl2
CD2Cl2
25
25
25
25
25
25
25
25
-90
-90
-90
-90
138.7
155
154
196.8
203.1
199.4
225
257
105.0
127.4
138.5
134.5
7.6
-4.2
-6.0
-9.2
442
493
504
507
coincidentally equivalent 31P NMR resonances is elimi-
nated on the basis of the observed 13C{1H} NMR
spectrum, which shows a single resonance for the
F igu r e 1. Syntheses of bis(arylamino)phosphenium com-
plexes. [M][A] ) AgOSO2CF3, TlB[3,5-(CF3)2-C6H3]4. 1a -
3a : Ar ) 4-MeO-C6H4. 1b-3b, Ar ) 2,4,6-Me3-C6H2. 1c-
3c, Ar ) 2,6-(CHMe2)2-C6H3. 4a , Ar ) 4-MeO-C6H4, [A] )
OSO2CF3. 4b: Ar ) 2,4,6-Me3-C6H2, [A] ) OSO2CF3. 4c:
Ar ) 2,6-(CHMe2)2-C6H3, [A] ) OSO2CF3. 4d : Ar ) 4-MeO-
C6H4, [A] ) B[3,5-(CF3)2-C6H3]4. 4e: Ar ) 2,4,6-Me3-C6H2,
[A] ) B[3,5-(CF3)2-C6H3]4.
2
heterocycle NCH2 carbons (54.76 ppm, J P-C ) 10 Hz).
Alternative dynamic processes which could account
for the observed chlorophosphine NMR spectra, includ-
ing ring flippage of the five-membered heterocycle,72
racemization of the configuration at a cationic P center
resulting from P-Cl heterolysis,10,73 inversion at N,74
or inversion at P, are inconsistent with the observed
combinations of spectral changes and associated kinetic
parameters.
Treatment of the appropriate chlorophosphine with
1 equiv of AgOSO2CF3 (AgOTf) gives stable cationic bis-
(arylamino)phosphenium ions 4, as evidenced by the
44-48 ppm downfield shifts of the 31P NMR resonances
for 4a -c, relative to those for 3a -c (Table 1). To probe
the nature of cation-anion interactions, compounds
4d ,e, containing the weakly coordinating anion {B[3,5-
(CF3)2-C6H3]4}- (BArF), have been prepared by treat-
ment of 3a ,b with 1 equiv of TlBArF. The fact that the
[BArF] compounds exhibit 31P NMR signals significantly
deshielded (29-54 ppm) relative to the corresponding
[OTf] compounds is indicative of a weakly coordinated
triflate anion in 4a -c, consistent with the solution
phosphenium-triflate interactions observed previously
by Kee and co-workers.13
improvement in isolated yield relative to previously
reported procedures. Chlorophosphines 3a -c were iso-
lated as moisture-sensitive Et2O- or THF-soluble solids
from the treatment of CH2Cl2/triethylamine solutions
of the appropriate diamine with 1 equiv of PCl3.
The steric effects of the N-Ar groups are evident upon
examination of the NMR spectra of 3a -c, as Ar‚‚‚Cl
interactions may inhibit rotation about the N-CAr bond.
Whereas complex 3a, with relatively uncongested 4-MeO-
C6H4 groups, exhibits unrestricted rotation about the
N-CAr bonds, even at temperatures as low as -58 °C,
mesityl-substituted chlorophosphine 3b exhibits tem-
perature-dependent NMR spectra. The two ortho methyl
1
resonances observed at δ 2.21 and 2.61 in the H NMR
at -69 °C give rise to a sharp singlet at δ 2.39 at 98 °C,
corresponding to a free energy of activation ∆Gq of 15.4-
(( 0.1) kcal/mol (Tc ) 50 °C, toluene-d8). The peak
separations for both the ortho methyls and meta hydro-
gens do not reach an invariant value at low tempera-
tures, thus precluding deconvolution of ∆Gq into en-
thalpic and entropic terms.
Assessing the ease of N-Ar rotation for cationic
phosphenium compounds 4a -c is more difficult than
for the corresponding halophosphines, due to the rapid,
reversible binding of the triflate counterion. Two-
coordinate cationic phosphenium compounds are gener-
ally considered to be planar (thus resulting in magneti-
cally equivalent aryl substituents for compounds 4a -
c);75 coordination of the triflate counterion to phosphorus
would produce a pyramidal phosphorus center and,
thus, inequivalent Ar substituents in the limit of slow
N-Ar rotation. Although the upfield 31P NMR chemical
shifts of the triflate compounds relative to the corre-
sponding borate compounds indicate some coordination
Incorporation of bulky isopropyl groups in the 2- and
6-aryl positions completely inhibits rotation about the
N-CAr bonds, as evidenced by two sets of observed
resonances for the pairwise-inequivalent CHMe2 groups
1
in the H NMR spectra of 3c. As shown in Figure 2a,
the resonances for the two magnetically inequivalent
isopropyl methine hydrogens are observed at δ 3.38 and
3.84. The corresponding isopropyl methyl resonances are
observed as a series of overlapping doublets (inset,
Figure 2a); selective decoupling experiments confirmed
that the six-line pattern centered at δ 1.32 is, in fact,
four overlapping doublets (δ 1.29, J ) 7.3 Hz; δ 1.31, J
) 7.3 Hz; δ 1.32, J ) 6.8 Hz; δ 1.35, J ) 6.4 Hz). No
coalescence or broadening of the observed NMR signals
is observed, even at 100 °C (toluene-d8). A lower limit
of 17.7 kcal/mol for the barrier to N-Ar rotation may
be inferred from the 138 Hz peak separation of the
CHMe2 resonances in 3c. The possibility of 3c existing
as a 1:1 mixture of two distinct geometric isomers with
1
of the triflate anion to the phosphorus center, both H
and 13C NMR spectroscopy show magnetically equiva-
lent aryl substituents for 4a -c (even at temperatures
1
as low as -35 °C); the H NMR spectrum of 4c at 25 °C
is shown in Figure 2b. In accounting for the observed
(72) Oki, M. Applications of Dynamic NMR Spectroscopy to Organic
Chemistry; VCH: Deerfield Beach, FL, 1985.
(73) Lamande, L.; Munoz, A. Tetrahedron Lett. 1991, 32, 75.
(74) Lehn, J . M.; Wagner, J . Tetrahedron 1970, 26, 4227.
(75) In the limit of slow N-CAr bond rotation, we also assume that
the N-aryl planes are eclipsed along the N-N axis (i.e. C2v symmetry).

4948 Organometallics, Vol. 19, No. 24, 2000
Abrams et al.
F igu r e 2. 300 MHz 1H NMR spectra (CDCl3) of (a, top) ClPN[2,6-(CHMe2)2-C6H3]CH2CH2N[2,6-(CHMe2)2-C6H3] (3c) (inset
shows detail of overlapping CHMe2 methyl resonances), (b, bottom) {PN[2,6(CHMe2)2-C6H3]CH2CH2N[2,6-(CHMe2)2-C6H3]}-
(OTf) (4c).

Sterically Tunable Phosphenium Cations
Organometallics, Vol. 19, No. 24, 2000 4949
F igu r e 3. Equilibria between phosphenium and phosphi-
nophosphenium complexes. 5a : Ar ) 4-MeO-C6H4, [A] )
OSO2CF3. 5b: Ar ) 2,4,6-Me3-C6H2, [A] ) OSO2CF3. 5c:
Ar ) 2,6-(CHMe2)2-C6H3, [A] ) OSO2CF3. 5d : Ar ) 2,4,6-
Me3-C6H2, [A] ) B[3,5-(CF3)2-C6H3]4.
high symmetry of 4b,c, we cannot differentiate between
rapid rotation about the N-CAr bond and a dynamic
equilibrium between covalently bound and discrete ionic
triflate counterions, with the equilibrium weighted
toward the planar, two-coordinate phosphenium com-
plex.
For comparison, a previous crystal structure of the
phosphenium-triflate complex V13 revealed P-O bond
distances of 2.841 and 2.755 Å, intermediate between
the van der Waals distance for P-O interactions (3.35
Å) and P-O covalent single bond length (1.63 Å);76
solution NMR studies (CDCl3) on V indicate dynamic
P-OTf interactions, with the “naked” phosphenium
cation predominating at high dilution.
F igu r e 4. Variable-temperature 31P NMR data (CD2Cl2)
for phosphinophosphenium complexes 5a -c: (a, top) phos-
phenium chemical shift versus temperature; (b) phosphine
chemical shift versus temperature. Legend: (2) 5a ; (9) 5b;
(b) 5c.
Syn th esis a n d Ch a r a cter iza tion of P h osp h in o-
p h osp h en iu m Com p ou n d s. The electrophilic phos-
phenium compounds 4 reversibly form adducts with
neutral bases, as exemplified by the formation of tri-
methylphosphine adducts 5a -d (Figure 3). Despite the
lability of the phosphine ligands at room temperature
(vide infra), 1:1 phosphenium-phosphine adducts may
be isolated by treatment of 4 with a slight excess of
PMe3 and then removal of volatiles in vacuo and/or
filtration from toluene. At room temperature, the 31P
NMR resonances of 5a -d are broad, indicating a rapid
equilibrium between the free and bound species. At low
temperatures, each of the phosphine and phosphenium
denced by the dramatic chemical shift changes toward
free PMe3 and phosphenium cation 4c at temperatures
above -20 °C. The observed rapid N-CAr rotation for
5c (25 °C) is consistent with a labile phosphine ligand,
as a bulky substituent ligated to the heterocycle phos-
phorus would be expected to result in slow N-CAr
rotation (vide supra).
Although a significant (7 ppm) downfield shift of the
phosphenium 31P NMR resonance was observed for 5d
(vs 5b), no change in phosphine lability was observed
upon switching from [OTf] to [BArF] counterions, in
contrast to previous studies on aluminum halide salts
of phosphinophosphenium adducts.18
1
peaks may be resolved into sharp doublets, with J P-P
in the range of 442-507 Hz (Table 1). Of phosphino-
phosphenium adducts reported in the literature, only
the chelating zwitterion11 {[2,4,6-(CMe3)3-C6H2](AlCl3)N}-
Cr ysta llogr a p h ic Ch a r a cter iza tion of 5c. Single
crystals of 5c suitable for X-ray diffraction studies
(Table 2) were grown at -15 °C from a 3:2 methylene
chloride/diethyl ether solution. Although crystal struc-
tures have previously been obtained for several intra-
molecular phosphinophosphenium compounds, and struc-
tures with severe disorder were reported for the
phosphinophosphenium-gallium trichloride complex IV,
5c is the first well-behaved example of a structurally
characterized intermolecular phosphinophosphenium
adduct. A view of the phosphenium cation is shown in
Figure 5, and selected bond lengths and angles are
provided in Table 3.
1
[2-(CH2PPh2)-C6H4]P exhibits a higher J P-P value (525
Hz).
Inspection of the 31P DNMR chemical shift data for
5a ,b (Figure 4) shows a gradual shift from the adduct
toward the free phosphine and phosphenium cation; the
loss of P-P coupling is observed above -30 °C. While
we made no attempts to obtain equilibrium and rate
constants, the most sterically congested phosphenium
ion, 5c, clearly forms the least stable adduct, as evi-
No cation-anion interactions are observed in the solid
state for 5c; the closest P-OTf distances are 3.432 Å
(76) Huheey, J . E. Inorganic Chemistry: Principles of Structure and
Reactivity, 3rd ed.; Harper: New York, 1983.

4950 Organometallics, Vol. 19, No. 24, 2000
Abrams et al.
Ta ble 2. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for ([P Me3]{P N[2,6-(CHMe2)2-C6H3]CH2CH2N-
[2,6(CHMe2)2-C6H3]})(OTf) (5c)
empirical formula
fw
C30H47F3N2O3P2S
634.70
temp
wavelength
cryst syst
203(2) K
0.71073 Å
triclinic
space group
unit cell dimens
P1h
a
10.4082(6)
b
10.7169(6)
c
16.1629(10)
R
99.956(1)
99.879(1)
â
γ
vol
104.199(1)
1677.69(17) Å3
2
Z
density (calcd)
abs coeff
abs cor
1.256 Mg/m3
0.241 mm-1
empirical (SADABS,
1996, Sheldrick)
0.98/0.98
T
min/Tmax
Figu r e 5. Molecular structure of (PMe3){PN[2,6-(CHMe2)2-
F(000)
crystal size
θ range for data collecn
index ranges
676
0.08 × 0.08 × 0.12 mm3
C6H3]CH2CH2N[2,6-(CHMe2)2-C6H3]}(OTF) (5c). Hydro-
gens and triflate counterion are omitted for clarity.
1.3-26.5°
-13 e h e 12, -13 e k e 13,
0 e l e 20
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
no. of rflns collected
no. of indep rflns
refinement method
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
8680
6198 (R(int) ) 0.019)
full-matrix least squares on F2
6198/0/370
(d eg) for ([P Me3]{P N[2,6-(CHMe2)2-C6H3]CH2CH2N-
[2,6(CHMe2)2-C6H3]})(OTf) (5c)
P(1)-N(1)
P(1)-N(2)
P(1)-P(2)
P(2)-C(15)
P(2)-C(17)
1.661(2)
1.696(2)
2.3065(9)
1.794(3)
1.798(3)
P(2)-C(16)
N(1)-C(1)
N(1)-C(13)
N(2)-C(7)
N(2)-C(14)
1.799(3)
1.449(3)
1.474(3)
1.440(3)
1.473(3)
1.393
R1 ) 0.0531, wR2 ) 0.1385
R1 ) 0.0712, wR2 ) 0.1520
0.515 and -0.410 e/Å3
largest diff peak and hole
for P(1)-F(3AA) and 4.071 Å for P(2)-O(1AA). The
markedly nonplanar geometry at P(1) (∑(angles) )
301.2°) indicates that the positive charge in 5c is
localized on P(2) and that the phosphonium-phosphine
resonance structure B is a more accurate description
of the bonding in 5c than is structure A. The transfer
N(1)-P(1)-N(2)
N(1)-P(1)-P(2)
N(2)-P(1)-P(2)
92.29(10) C(16)-P(2)-P(1) 122.96(10)
109.13(8)
99.74(8)
C(1)-N(1)-C(13) 121.89(19)
C(1)-N(1)-P(1) 124.74(17)
C(15)-P(2)-C(17) 106.12(15) C(13)-N(1)-P(1) 113.30(15)
C(15)-P(2)-C(16) 108.20(14) C(7)-N(2)-C(14) 120.9(2)
C(17)-P(2)-C(16) 108.85(14) C(7)-N(2)-P(1)
C(15)-P(2)-P(1)
C(17)-P(2)-P(1)
123.57(17)
108.91(11) C(14)-N(2)-P(1) 113.06(15)
100.51(10)
(Cl) (2.208 Å),25 and the zwitterion P[µ-N(SiMe3)]P[N-
(SiMe3)2]N(SiMe3)N(SiMe3)AlCl2N(SiMe3) (2.1051 Å),26
although this may be due to the fact that there is no
chelation of phosphine to phosphenium moieties in 5c.
More surprising, however, is that the P-P bond length
in 5c is also considerably longer than the 2.138(7) and
2.156(10) Å lengths reported for IV (crystals of IV were
disordered such that several atoms each occupy multiple
positions in the unit cell), confirming the sterically
congested coordination environment of the phosphenium
phosphorus center.
The long P(1)-N bonds (1.662(2) and 1.697(2) Å) are
also consistent with resonance structure B, while the
nearly planar N atoms (sum of angles: around N(1),
359.9°; around N(2), 357.5°) presumably reflect the
steric demands of the bulky aryl substituents (cf. also
the 53 and 76° dihedral angles between the Ar rings
and the N-P(1)-N plane). Similar features were ob-
served for the bis(N-methylamino)phosphenium cation
adduct of the 18e- [Cp*Fe(CO)2]- anion (P-N(av) )
1.701(6) Å).77
of positive charge from the phosphenium to the donor
molecule in 5c is analogous to the charge distribution
observed for I, where the two planar DBU nitrogens (∑-
(angles) ) 359.2, 359.9°) are diagnostic for the delocal-
ization of the positive charge.
The P-P bond length of 2.3065(9) Å in 5c is signifi-
cantly longer than those in previously reported struc-
turally characterized intramolecular phosphinophos-
phenium compounds {P[µ-N(Me)C(O)N(Me)]2P(NEt2)}-
(OTf) (2.191 Å),20 [MePN(Me)C(O)N(Me)P(NEt2)(Ph)]-
(Cl) (2.191 Å),22 [(Cl2HC)PN(Me)C(O)N(Me)P(CMe3)-
(Ph)](BPh4) (2.223 Å),23 [PhPN(H)C(CMe3)dC(H)PPh2]-
Ca tion ic Rh -P h osp h en iu m Com p ou n d s. With a
selection of phosphenium cations in hand, we were
(77) Hutchins, L. D.; Duesler, E. N.; Paine, R. T. Organometallics
1982, 1, 1254.

Sterically Tunable Phosphenium Cations
Organometallics, Vol. 19, No. 24, 2000 4951
F igu r e 6. 121 MHz 31P NMR spectra (CDCl3) of (a, top) {trans-RhCl(PPh3)2[PN(4-MeO-C6H4)CH2CH2N(4-MeO-C6H4)]}-
(OTf) (6) and (b, bottom) 4b/RhCl(PPh3)3 reaction products. Legend: (b) [Rh(PPh3)3](OTf); (2) {trans-RhCl(PPh3)2[PN-
(2,4,6-Me3-C6H2)CH2CH2N(2,4,6-Me3-C6H2)]}(OTf) (7b ); (9) {cis-RhCl(PPh3)2[PN(2,4,6-Me3-C6H2)CH2CH2N(2,4,6-Me3-
C6H2)]}(OTf) (7a ).
interested to see whether well-defined metallophosphe-
nium cations could be obtained from the direct addition
of 4 to neutral transition-metal-containing species.
Despite an early report by Montemayor et al.44 that the
results in the immediate formation of a clear, bright
yellow solution. 1H NMR spectroscopy revealed the
complete consumption of starting 4a and formation of
a single new heterocycle-containing complex, 6, as
evidenced by the single set of resonances at δ 3.75 (d, J
) 7.1 Hz, 4H, NCH2) and 3.86 (s, 6H, OCH3). The
presence of overlapping multiplets for the various aryl
cationic iron-phosphenium complex {Fe[PN(Me)CH2-
CH2N(Me)](CO)4}(PF6) could be obtained from addition
1
protons complicated further identification by H NMR.
of [PN(Me)CH2CH2N(Me)](PF6) to Fe(CO)5 or Fe2(CO)9,
this synthetic approach has found use only in a single
report of the in situ generation of Rh-phosphenium-
based hydroformylation catalysts.65 For our investiga-
tions, we chose to utilize phosphine-containing com-
pounds of rhodium for initial study, in part on the basis
of the profusion of Rh-phosphine compounds used for
homogeneous catalysis78 and on the potential for facile
product identification by 31P NMR spectroscopy.79
31P NMR, however, proved invaluable in determining
the course of this reaction, confirming that both 4a and
the Rh starting material had been consumed. A singlet
for free PPh3 and an AX2 spin system consisting of an
1
upfield doublet of doublets (24.91 ppm, J Rh-P ) 102,
2J P-P ) 51 Hz) and a downfield doublet of triplets
1
2
(240.18 ppm, J Rh-P ) 311, J P-P ) 51 Hz) (Figure 6a),
in a 1:2:1 ratio, were the only signals observed in the
crude reaction mixture. The coupling of the phosphe-
nium resonance to two equivalent phosphines indicates
that the phosphine trans to the halide in RhCl(PPh3)3
has been replaced by the phosphenium ligand. The large
downfield shift (∼100 ppm relative to 4a) of the deshield-
ed phosphenium resonance argues strongly against
formation of the isomeric Rh-chlorophosphine complex
Addition of 1 equiv of the methoxy-substituted 4a to
a CDCl3 solution of Wilkinson’s catalyst, RhCl(PPh3)3,
(78) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis: the
Applications and Chemistry of Catalysis by Soluble Transition Metal
Complexes; Wiley: New York, 1992.
(79) Pregosin, P. S.; Kunz, W. R. 31P and 13C NMR of Transition
Metal Phosphine Complexes; Springer-Verlag: New York, 1979.

4952 Organometallics, Vol. 19, No. 24, 2000
Abrams et al.
Sch em e 3
4 to form stable metallophosphenium compounds
(Scheme 3). In contrast to that observed for 4a , addition
of 1 equiv of the isopropyl-substituted 4c to a CDCl3
solution of Wilkinson’s catalyst results in quantitative
formation of [Rh(PPh3)3](OTf) and chlorophosphine 3c,
with no metallophosphenium species observed at any
time in the crude reaction mixture (31P NMR).
{Rh(PPh3)2[P(Cl)N(4-MeO-C6H4)CH2CH2N(4-MeO-C6-
H4)]}(OTf). The large J Rh-P of the downfield resonance
1
is also consistent with a phosphenium ligand residing
trans to a halide (rather than to a phosphine).79 Pre-
parative-scale reactions (CH2Cl2) afford 6 as an orange,
toluene-insoluble powder in 80% yield; 13C NMR spec-
troscopy and elemental analysis, as well as the fully
The analogous reaction using mesityl-substituted 4b
affords a mixture of products; 31P NMR spectroscopy on
the crude reaction mixture shows the complete con-
sumption of all starting materials and exhibits reso-
nances attributable to [Rh(PPh3)3](OTf)/3b (53%), free
PPh3, and two metallophosphenium compounds, 7a and
7b (Figure 6b). The minor metallophosphenium complex
(6%, 7b) exhibits a 31P spectrum with an AX2 splitting
pattern similar to that of 6: an upfield doublet of
1
resolved H NMR spectra (see Experimental Section) all
support the assignment of 6 as {trans-RhCl(PPh3)2[PN-
(4-MeO-C6H4)CH2CH2N(4-MeO-C6H4)]}(OTf).
In the absence of a crystal structure, it is difficult to
unambiguously establish details of the bonding within
the cation of 6, particularly to distinguish between
Rh(I)-phosphenium structures C and D, or to deter-
mine the extent of M-P multiple bonding. In C and D,
1
2
doublets (31.38 ppm, J Rh-P ) 106 Hz, J P-P ) 43 Hz),
and a downfield doublet of triplets (255.76 ppm) with a
large 1J Rh-P value (316 Hz) and a small 2J P-P value (not
completely resolved). Accordingly, 7b is assigned as
{trans-RhCl(PPh3)2[PN(2,4,6-Me3-C6H2)CH2CH2N(2,4,6-
Me3-C6H2)]}(OTf).
The major phosphenium-containing product (41%, 7a )
exhibits an AXY splitting pattern, with two upfield and
one downfield resonances. The upfield resonances con-
sist of a doublet of doublets of doublets (2J P-P ) 451
the positively charged phosphenium ion acts as a two-
electron σ-donor to the Rh center, with the vacant
π-symmetry orbital on the phosphenium ion (localized
on phosphorus) available for back-bonding from Rh.
Steric interactions between the phosphenium Ar sub-
stituents and the PPh3 ligands are minimized in struc-
ture C through rotation of the phosphenium heterocycle
out of the Cl-Rh-PPh3 plane; this orientation also
provides favorable overlap of the vacant phosphenium
π-symmetry orbital with a filled d orbital on Rh. For
these reasons we favor structure C as the most accurate
representation of the bonding in 6.80 Although sugges-
tive of M-P multiple bonding character, the large (311
Hz) 1J Rh-P value in 6 may result from factors other than
1
2
Hz, J Rh-P ) 158 Hz, J P-P ) 21 Hz) at 26.39 ppm, and
an apparent doublet of doublets (1J Rh-P ) 153 Hz,
smaller additional coupling not resolved) at 41.32 ppm;
the downfield signal (247.63 ppm) is a doublet of doublet
1
of doublets (2J P-P ) 448 Hz, J Rh-P ) 234 Hz, plus an
additional, unresolved, smaller coupling). Both the large
1
2J P-P value and the small J Rh-P value of 7a (relative
to 6 and 7b) are indicative of a trans phosphenium-
phosphine arrangement. The downfield chemical shift
of the most deshielded resonance argues against the
T-shaped Rh cation 8 or the corresponding square
1
π-donation from the Rh center; a similar J Rh-P value
(300 Hz) is observed for the neutral Rh-chlorophos-
phine complex trans-RhCl(PPh3)2[P(Cl)N(4-MeO-C6H4)-
CH2CH2N(4-MeO-C6H4)].81
The steric demands imparted by the phosphenium
aryl substituents dramatically influence the ability of
planar complex with a bound triflate. Accordingly, we
assign 7a as the square-planar Rh(I) complex {cis-RhCl-
(80) This phosphenium orientation is also supported by DFT
calculations: Abrams, M. B.; Martin, R. L.; J ohn, K. D.; Baker, R. T.
Manuscript in preparation.
(81) Abrams, M. B.; Baker, R. T. Unpublished results.
(PPh3)2[PN(2,4,6-Me3-C6H2)CH2CH2N(2,4,6-Me3-C6H2)]}-

Sterically Tunable Phosphenium Cations
Organometallics, Vol. 19, No. 24, 2000 4953
Pangborn et al.82 Triethylamine was purchased from Fluka,
dried over CaH2, and vacuum-distilled prior to use. Chloroform
was dried over P2O5 and vacuum-distilled prior to use. CDCl3
(Acros) was dried over P2O5, vacuum-distilled, and stored over
4 Å molecular sieves. CD2Cl2 (Acros) and toluene-d8 (Aldrich)
were stored over 4 Å sieves. Deuteriobenzene (Acros) was
distilled from Na or dried over sieves prior to use. Methanol,
ethanol, 2,6-diisopropylaniline (Fluka), glyoxal, p-anisidine,
2,4,6-trimethylaniline, sodium borohydride, silver triflate, and
trimethylphosphine (Aldrich) were used as received. Phospho-
rus trichloride (Acros) was transferred to a Schlenk flask and
(OTf) with the sterically more demanding mesityl
substituents enforcing a cis disposition of triphenylphos-
phine ligands.
Con clu sion s
The bis(arylamino)phosphenium cations 4a -e re-
ported herein have been shown to provide steric tun-
ability in the stability of their phosphine adducts and
in their variety of reactions with Wilkinson’s catalyst.
The chlorophosphines 3a-c also exhibit hindered N-CAr
bond rotation for bulky N-Ar substituents. The struc-
tural information provided by the first well-behaved,
single-crystal X-ray diffraction study on an intermo-
lecular phosphinophosphenium adduct reveals addi-
tional steric consequences, both in the long P-P bond
distance and in the structure and bonding within the
phosphenium ligand array.
The Rh complexes 6 and 7a ,b are the first well-
characterized, cationic group 9 complexes incorporating
phosphenium ligands. Of particular interest is the
bonding within 6 and 7. All available spectroscopic
evidence (31P chemical shifts and Rh-P and P-P
coupling constants, in particular) indicate that these
compounds contain square-planar, cationic, Rh(I) frag-
ments (with the phosphenium ligand acting as a two-
electron σ-donor), as opposed to Rh(III)-phosphido
species such as E. This is in contrast to the spectro-
83
84,85
stored under N2. TlB[3,5-(CF3)2-C6H3]4 and RhCl(PPh3)3
were prepared according to literature procedures. NMR spectra
were recorded on a Varian Unity Inova 300 spectrometer
(299.93 MHz for 1H, 75.42 MHz for 13C, 121.42 MHz for 31P).
Temperatures were calibrated using external methanol or
ethylene glycol standards. Elemental analysis was performed
using a Perkin-Elmer 2400 Series II CHNS/O analyzer.
Although hydrogen and nitrogen analyses were satisfactory,
carbon analysis often provided values slightly below the
expected numbers; abnormally low carbon values, in addition
to being internally consistent from run to run and from sample
to sample, were observed for nearly all of the compounds
analyzed.
(4-MeO-C6H4)NdCHCHdN(4-MeO-C6H4) (1a ). Anisidine
(48.90 g. 397 mmol, 2.00 equiv) and EtOH (750 mL) were
placed in a 1 L pear-shaped flask equipped with a magnetic
stir bar. Glyoxal (28.79 g, 40 wt % in H2O, 198 mmol, 1.00
equiv) was pipetted into the blackish solution, and the contents
of the flask were stirred at room temperature for 18 h; a bright
yellow solid began precipitating from the solution within
minutes of the glyoxal addition. The solution was filtered using
a medium-porosity filter frit, yielding a large amount of
flocculent yellow EtOH/H2O-insoluble solid. The solid was
washed once with 60 mL of toluene (0 °C), and was dried in
vacuo, yielding 35.67 g of yellow solid. A second crop was
obtained by concentrating the EtOH/H2O solution to a volume
of ∼40 mL on a rotavap (50 °C) and then cooling (0 °C) and
filtering the solution; the solid was then washed with 30 mL
of 0 °C EtOH and 60 mL of 0 °C toluene, yielding an additional
1.01 g of diimine after drying in vacuo. Total isolated yield:
36.68 g (137 mmol, 69% yield). 1H NMR (δ, in CDCl3): 3.85
(s, 6H, OCH3), 6.95 (d, J ) 9.0 Hz, 4H, C6H4), 7.34 (d, J ) 8.8
Hz, 4H, C6H4), 8.42 (s, 2H, NCH).
(2,4,6-Me3-C6H2)NdCHCHdN(2,4,6-Me3-C6H2) (1b). To a
500 mL round-bottom flask equipped with a magnetic stir bar
was added 250 mL of ethanol and 15.115 g (111.8 mmol, 2.00
equiv) of 2,4,6-Me3PhNH2. Glyoxal (8.106 g, 40 wt % solution,
55.86 mmol, 1.00 equiv) was added to the clear, faint yellow
solution, and the resulting bright yellow solution was stirred
at room temperature for 14 h. The solution was filtered,
affording 8.035 g of a bright yellow EtOH/H2O-insoluble solid
(after drying in vacuo). A second crop of 1.809 g of yellow
needles precipitated from the EtOH/H2O solution upon stand-
ing over the course of 3 weeks; additional crops of 1.487 and
2.335 g (after washing with small aliquots of 0 °C ethanol and
drying in vacuo) of yellow solid were obtained by concentrating
the EtOH/H2O solution on a rotavap (50 °C), cooling to 0 °C,
and isolating the resultant bright yellow solids by filtration.
Total isolated yield: 13.666 g, 46.7 mmol, 84%. 1H NMR (δ,
in CDCl3): 2.20 (s, 12 H, 2,6-(CH3)2-C6H2), 2.33 (s, 6H, 4-CH3-
C6H2), 6.95 (s, 4H, C6H2), 8.15 (s, 2H, NCH).
scopically and crystallographically characterized phos-
phine adducts 5, which are best described as phos-
phinophosphonium compounds, where the positive charge
from the phosphenium ion has been transferred to the
coordinated PMe3 ligand (structure B).
This behavior has been noted previously by Paine et
al. in comparing phosphenium complexes of the 16e-
[CpMo(CO)2]- and 18e- [CpFe(CO)2]- anions.31,77 The
short M-P bond and planar phosphorus center in the
former are consistent with both donor and acceptor
functions for the phosphenium ligand, while the long
Fe-P and P-N bonds and pyramidal phosphorus in the
latter are more in concert with an iron phosphido
complex with a stereochemically active lone pair at
phosphorus. While the bonding in Rh complexes 7a ,b
is also likely to involve both donor and acceptor func-
tions for the phosphenium ligand, it is difficult to predict
a priori how this balance will be affected by changing
from a trans chloride in 7b to a trans phosphine in 7a .
We are currently applying density functional theory to
address these questions and others that have arisen
from analogous coordinatively unsaturated group 10
complexes we have recently prepared.81 Further inves-
tigations also include the use of electron-withdrawing
N-aryl substituents to assess the effects of P-N π-bond-
ing in precious-metal phosphenium complexes.
[2,6-(CHMe2)2-C6H3]NdCHCHdN[2,6-(CHMe2)2-C6H3] (1c).
A 250 mL round-bottom flask equipped with a magnetic stir
(82) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J . Organometallics 1996, 15, 1518.
(83) Hughes, R. P.; Lindner, D. C.; Rheingold, A. L.; Yap, G. P. A.
Inorg. Chem. 1997, 36, 1726.
(84) Osborn, J . A.; J ardine, F. H.; Young, J . F.; Wilkinson, G. J .
Chem. Soc. A 1966, 1711.
Exp er im en ta l Section
All reactions were conducted under nitrogen using standard
Schlenk, cannula, and glovebox techniques. Toluene, diethyl
ether, and THF were purified using the system described by
(85) Osborn, J . A.; Wilkinson, G. Inorg. Synth. 1967, 10, 67.

4954 Organometallics, Vol. 19, No. 24, 2000
Abrams et al.
bar was charged with 10.043 g (56.65 mmol, 1.99 equiv) of 2,6-
diisopropylaniline and 130 mL of ethanol. Glyoxal (4.173 g,
40 wt % in H2O, 28.45 mmol, 1.00 equiv) was added dropwise
to the stirred solution, which acquired a bright yellow color
within minutes of the glyoxal addition; the solution was
refluxed for 12 h and then cooled to room temperature. The
volume of solvent was reduced to ∼100 mL on a rotavap (45
°C), and the yellow insoluble material was isolated by filtration
and was then washed with cold ethanol. A second crop was
obtained by further concentration of the mother liquor, filtra-
tion, and washing of the resultant solid with two 5 mL portions
of 0 °C ethanol. The combined yellow solids were crushed with
a mortar and pestle, washed twice with 20 mL aliquots of 0
°C ethanol, and dried in vacuo. Isolated yield: 8.313 g of yellow
powder, 22.10 mmol, 78% yield. 1H NMR (δ, in CDCl3, 25 °C):
1.24 (d, J ) 6.8 Hz, 24H, CH(CH3)2), 2.97 (septet, J ) 6.8 Hz,
4H, CH(CH3)2), 7.21 (m, 6H, overlapping C6H3), 8.13 (s, 2H,
NCH).
NMR (δ, in CDCl3): 2.28 (s, 6H, 4-CH3-C6H2), 2.33 (s, 12H,
2,6-(CH3)2-C6H2), 3.19 (s, 4H, NCH2), 3.32 (s, 2H, NH), 6.87
(s, 4H, C6H2). 13C{1H} NMR (δ, in CDCl3): 18.3 (4-CH3-C6H2),
20.5 (2,6-(CH3)2-C6H2), 49.3 (NCH2), 129.5 (C6H2), 129.8 (C6H2),
131.4 (C6H2), 143.3 (C6H2).
[2,6-(CHMe2)2-C6H3]N(H)CH2CH2N(H)[2,6-(CHMe2)2-C6-
H3] (2c). A 200 mL round-bottom flask, equipped with a
magnetic stir bar, was charged with 3.141 g (8.341 mmol, 1.00
equiv) of 1c and 125 mL of ethanol. The solution was cooled
to 0 °C, and 3.220 g (85.10 mmol, 10.2 equiv) of sodium
borohydride was added in small batches over the course of 20
min. The bright yellow solution with white precipitate was
stirred at 0 °C for 10 min and then refluxed for 105 min. The
solution was cooled to 50 °C, and 20 mL of a saturated NaCl/
H2O solution was added slowly to the pale orange solution and
white precipitate, maintaining a gentle reflux. After it was
stirred at room temperature for an additional 30 min, the
solution was diluted with 100 mL of water and 75 mL of
chloroform. The organic layer was separated and washed with
10 mL of water. Volatiles were removed on a rotavap from the
organic layer, and the resulting pale orange solid was dried
in vacuo, dissolved in 100 mL of THF, and dried over 4 Å
sieves. After filtering and removal of volatiles, 2.628 g of a
pale orange solid was isolated (6.90 mmol, 83% yield). 1H NMR
(δ, in CDCl3): 1.23 (d, J ) 6.8 Hz, 24H, CH(CH3)2), 3.14 (s,
4H, NCH2), 3.32 (s, 2H, NH), 3.34 (septet, J ) 6.8 Hz, 4H,
CH(CH3)2), 7.09 (overlapping multiplets, 6H, C6H3). 13C{1H}
NMR (δ, in CDCl3): 24.24 (CH(CH3)2), 27.78 (CH(CH3)2), 52.34
(NCH2), 123.59 (C6H3), 123.84 (C6H3), 142.50 (C6H3), 143.34
(C6H3).
(4-MeO-C6H4)N(H)CH2CH2N(H)(4-MeO-C6H4) (2a ). A 3
L three-necked round-bottom flask, equipped with a stir bar,
a solid addition funnel, a solution addition funnel, and a reflux
condenser, was charged with 36.62 g (136.5 mmol, 1.0 equiv)
of 1a and 1750 mL of EtOH. Sodium borohydride (51.61 g,
1364 mmol, 9.99 equiv) was added to the solution (via the
addition funnel) over the course of 135 min. The solution was
then heated with a heating mantle and was refluxed for 60
min. The colorless solution and white precipitate were cooled
to room temperature and were stirred at room temperature
overnight. A saturated NaCl (H2O) solution (350 mL) was
added to the solution via the solution addition funnel; the rate
of addition was adjusted to maintain a steady reflux. After
the solution was cooled to room temperature, the white solid
was removed from the light orange solution by filtration using
a medium porosity filter frit; the EtOH/H2O insolubles were
washed with 1500 mL of H2O and were dried in vacuo. The
white solid was then dissolved in THF (450 mL), and stirred
overnight over 4 Å molecular sieves; after filtration though a
medium-porosity filter frit, solvent was removed from the
colorless solution in vacuo, affording 26.2 g of white solid. An
additional 6.17 g of diamine (after drying over sieves in THF)
was obtained as a tan microcrystalline solid by extraction of
the combined EtOH/aqueous solutions with CHCl3; total
isolated yield of (4-CH3O-C6H4)N(H)CH2CH2N(H)(4-CH3O-
ClP N(4MeO-C6H4)CH2CH2N(4-MeO-C6H4) (3a ). A 100
mL Schlenk flask, equipped with a magnetic stir bar, was
charged with 801 mg (2.94 mmol, 1.02 equiv) of 2a , 45 mL of
CH2Cl2, and 7 mL (50 mmol, 17 equiv) of Et3N; the resulting
clear, colorless solution was cooled to 0 °C. Phosphorus
trichloride (0.25 mL, 2.87 mmol, 1.00 equiv) was syringed
dropwise into the cooled solution against a N2 counterflow,
accompanied by the precipitation of a white solid. The solution
was stirred at 0 °C for 30 min, was warmed to 25 °C, and was
stirred at room temperature for an additional 90 min. Volatiles
were removed from the light yellow solution, and the solids
were dried in vacuo. The resulting light yellow solid was
washed once with 20 mL and once with 10 mL of THF, and
Et3NHCl was removed by filtration using a medium-porosity
filter frit. Solvent was removed from the combined organics,
leaving a pale yellow solid (864 mg, 2.57 mmol, 89% yield).
Anal. Calcd for C16H18N2O2PCl: C, 57.06; H, 5.40; N, 8.32.
Found: C, 55.59, 56.30, 56.24; H, 5.69, 5.73, 5.88; N, 8.02, 8.15,
8.08. 31P{1H} NMR (δ, in CDCl3): 138.7. 1H NMR (δ, in
CDCl3): 3.81 (s, 6H, OCH3), 3.92 (br, 4H, NCH2), 6.91 (m, J )
7.6 Hz, 2H, C6H4), 7.13 (m, J ) 6.8 Hz, 2H, C6H4). 13C{1H}
NMR (δ, in CDCl3): 48.9 (d, J P-C ) 10 Hz, NCH2), 55.6 (s,
OCH3), 115.0 (s, C6H4), 119.0 (d, J P-C ) 13 Hz, C6H4), 135.8
(d, J P-C ) 14 Hz, C6H4), 155.5 (s, C6H4).
1
C6H4) 32.4 g (118.9 mmol, 87% yield). H NMR (δ, in CDCl3):
3.34 (s, 4H, NCH2), 3.68 (s, 2H, NH), 3.77 (s, 6H, OCH3), 6.63
(d, J ) 8.8 Hz, 4H, C6H4), 6.82 (d, J ) 9.0 Hz, 4H, C6H4).
(2,4,6-Me3-C6H2)N(H)CH2CH2N(H)(2,4,6-Me3-C6H2) (2b).
A 250 mL round-bottom flask, equipped with a magnetic stir
bar, a solid addition funnel, and a water-cooled reflux con-
denser, was charged with 2.455 g (8.39 mmol, 1.00 equiv) of
1b. Ethanol (125 mL) was added to the flask, and the bright
yellow solution cooled to 0 °C. Sodium borohydride (3.178 g,
84.0 mmol, 10.00 equiv) was added to the solution via the
addition funnel over the course of 55 min. The 0 °C bath was
removed and replaced with a heating mantle; the solution was
refluxed for 45 min, affording a colorless solution and a white
precipitate. The solution was cooled to 25 °C, and 20 mL of an
aqueous saturated NaCl solution was added slowly to the flask,
acquiring and then maintaining a gentle reflux. Upon cooling
to room temperature, the solution was filtered using a medium-
porosity filter frit, and the white insoluble material was
washed once with 50 mL of H2O. The combined ethanol and
aqueous solutions were diluted with 40 mL of additional water
and extracted with 60 mL of chloroform. The organic layer was
separated, and volatiles were removed on a rotavap, yielding
a small amount of yellow oil which crystallized upon standing
in air. The yellow solid was then dissolved in 40 mL of THF
and stirred over 4 Å sieves for 2 days. The solution was filtered,
and volatiles were removed in vacuo, leaving a clear yellow
oil which crystallized upon standing under N2, affording 1.905
g of a yellow microcrystalline solid (6.42 mmol, 77% yield). 1H
ClP N(2,4,6-Me3-C6H2)CH2CH2N(2,4,6-Me3-C6H2) (3b). A
100 mL Schlenk flask was charged with 1.872 g (6.31 mmol,
1.00 equiv) of 2b, 45 mL of CH2Cl2, and 16 mL (114.7 mmol,
18.2 equiv) of Et3N, and the clear, pale yellow solution was
cooled to 0 °C. PCl3 (0.55 mL, 6.30 mmol, 1.00 equiv) was
syringed dropwise into the cooled solution, and the resulting
light yellow solution with fine white precipitate was stirred
at 0 °C for 30 min. The 0 °C bath was removed, and the
solution was stirred for an additional 95 min at room temper-
ature. Volatiles were removed, and the remaining light yellow
solid was dried in vacuo. The solid was washed once with 40
mL of Et2O and once with 10 mL of Et2O. The Et2O-insoluble
solid was extracted once with 40 mL of THF; volatiles were
removed in vacuo from the THF solution, yielding 1.393 g of
white solid. Additional crops of 113 and 97 mg of white solid
were obtained from additional THF extractions of the Et2O-

Sterically Tunable Phosphenium Cations
Organometallics, Vol. 19, No. 24, 2000 4955
insoluble solid. Total isolated yield: 1.414 g, 3.92 mmol, 62%.
Anal. Calcd for C20H126N2PCl: C, 66.56; H, 7.28; N, 7.76.
Found: C, 61.45. 60.67, 60.17; H, 8.11, 8.01, 7.96; N, 7.10, 7.06,
6.93. H NMR (δ, in CDCl3, 25 °C): 2.31 (s, 6H, 2,4,6-(CH3)3-
C6H2), 2.45 (br, 12H, 2,4,6-(CH3)3-C6H2), 3.54 (br, 2H, NCH2),
3.99 (d, J ) 5.1 Hz, 4H, NCH2), 6.98 (s, 4H, C6H2). 13C{1H}
NMR (δ, in CDCl3): 18.47 (d, J P-C ) 2 Hz, (CH3)3-C6H2), 20.83
(s, (CH3)3-C6H2), 53.54 (d, J P-C ) 9 Hz, NCH2), 119.37 (quartet,
1
J C-F ) 319 Hz, OSO2CF3), 129.97 (s, C6H2), 132.35 (d, J P-C )
12 Hz, C6H2), 136.10 (d, J P-C ) 4 Hz, C6H2), 138.49 (s, C6H2).
4.13 (br, 2H, NCH2), 7.03 (s, 4H, C6H2).
{P N[2,6-(CHMe2)2-C6H3]CH2CH2N[2,6-(CHMe2)2-C6H3]}-
(OTf) (4c). A 100 mL round-bottom flask was wrapped in Al
foil and charged with 1.0043 g (2.36 mmol, 1.01 equiv) of 3c
and 45 mL of toluene. AgOTf (601 mg, 2.34 mmol, 1.00 equiv)
was added slowly to the stirred solution, and the resulting
solution was stirred at 25 °C for 4 h. The solution was filtered
through a medium-porosity filter frit, and volatiles were
removed from the clear, light yellow toluene solution, yielding
1.161 g of white solid after drying in vacuo (2.08 mmol, 89%
yield). Anal. Calcd for C27H38N2O3PSF3: C, 58.04; H, 6.87; N,
5.02. Found: C, 57.09, 57.67, 56.67; H, 7.34, 7.35, 7.21; N, 4.85,
ClP N[2,6-(CH Me 2)2-C6H 3]CH 2CH 2N[2,6-(CH Me 2)2-C6-
H3] (3c). A 200 mL Schlenk flask was charged with 2.016 g
(5.59 mmol,1.00 equiv) of 2c, 100 mL of CH2Cl2, and 12 mL
(86.0 mmol, 15.4 equiv) of Et3N, and the solution was cooled
to 0 °C. PCl3 (0.49 mL, 5.62 mmol, 1.01 equiv) was syringed
into the cooled solution dropwise against a N2 counterflow, and
the light yellow solution was stirred at 0 °C for 3.5 h. Volatiles
were removed, and the resultant light yellow solid was dried
in vacuo. Diethyl ether (35 mL) was added to the solid, and a
fine white solid was removed by filtration from the clear yellow
liquid; the white solid was washed twice with 20 mL portions
of Et2O. Volatiles were removed from the combined organics,
yielding 1.836 g of light yellow solid (4.32 mmol, 77% yield).
Anal. Calcd for C26H38N2PCl: C, 70.16; H, 8.62; N, 6.30.
Found: C, 69.49, 69.55, 69.48; H, 9.07, 9.24, 9.19; N, 7.05, 6.12,
6.18. 1H NMR (δ, in CDCl3): 1.29 (d, J ) 7.3 Hz, 6H, CH-
(CH3)2), 1.31 (d, J ) 7.3 Hz, 6H, CH(CH3)2), 1.32 (d, J ) 6.8
Hz, 6H, CH(CH3)2), 1.35 (d, J ) 6.4 Hz, 6H, CH(CH3)2), 3.38
(septet, J ) 6.6 Hz, 2H, CH(CH3)2), 3.60 (m, 2H, NCH2), 3.84
(septet, J ) 6.8 Hz, 2H, CH(CH3)2), 4.12 (m, 2H, NCH2), 7.28
(overlapping multiplets, 6H, C6H3). 13C{1H} NMR (δ, in
CDCl3): 24.36 (d, J P-C ) 3 Hz, CH(CH3)2), 24.56 (s, CH(CH3)2),
25.25 (s, CH(CH3)2) 25.42 (s, CH(CH3)2), 28.48 (s, CH(CH3)2),
28.98 (d, J P-C ) 6 Hz, CH(CH3)2), 54.76 (d, J P-C ) 10 Hz,
NCH2), 123.96 (s, C6H4), 124.94 (s, C6H4), 128.20 (s, C6H4),
134.90 (d, J P-C ) 13 Hz, C6H4), 147.55 (d, J P-C ) 3 Hz, C6H4),
149.90 (d, J P-C ) 4 Hz, C6H4).
1
5.33, 4.79. H NMR (δ, in CDCl3): 1.30 (d, J ) 6.8 Hz, 12H,
CH(CH3)2), 1.35 (d, J ) 6.8 Hz, 12H, CH(CH3)2), 3.34 (septet,
J ) 6.8 Hz, 4H, CH(CH3)2), 3.99 (d, J ) 5.9 Hz, 4H, NCH2),
7.25 (m, 4H, C6H3), 7.37 (m, 4H, C6H3). 13C{1H} NMR (δ, in
CDCl3): 24.35 (s, CH(CH3)2), 25.53 (s, CH(CH3)2), 28.99 (s, CH-
(CH3)2), 56.04 (d, J P-C ) 10.6 Hz, NCH2), 119.20 (quartet, J C-F
) 320 Hz, OSO2CF3), 124.76 (s, C6H3), 129.35 (s, C6H3), 132.46
(d, J P-C ) 12.1 Hz, C6H3), 147.35 (d, J P-C ) 3.5 Hz, C6H3).
[P N(4-CH3O-C6H4)CH2CH2N(4-CH3O-C6H4)](BAr F ) (4d ).
In the glovebox, a vial was charged with 53 mg (0.157 mmol,
1.14 equiv) of 3a and 1 mL of CH2Cl2. The solution was cooled
to -45 °C in a cold well, and 146 mg (0.137 mmol, 1.00 equiv)
of TlBArF was added to the pale yellow solution with white
precipitate. The mixture was shaken for several minutes at
-45 °C and was then warmed to room temperature and
allowed to sit overnight; the solution was then filtered through
a 2 mL medium-porosity frit, and solvent was removed from
the maroon solution, leaving a viscous red oil. 31P{1H} NMR
(δ, in CD2Cl2/C6D6, 25 °C): 225.7. 1H NMR (δ, in CD2Cl2/
C6D6): 3.81 (s, 6H, OCH3), 4.28 (d, J ) 4.7 Hz, NCH2), 6.93
(d, J ) 9.0 Hz, 4H, C6H4), 7.12 (d, J ) 8.6 Hz, 4H, C6H4), 7.56
(s, 4H, B[(3,5-CF3)2-C6H3]4), 7.76 (s, 8H, B[(3,5-CF3)2-C6H3]4).
[P N(4-MeO-C6H4)CH2CH2N(4-MeO-C6H4)](OTf) (4a ). A
250 mL round-bottom flask was wrapped in Al foil and charged
with 2.274 g (6.75 mmol, 1.00 equiv) of 3a and 80 mL of
toluene. Silver triflate (AgOSO2CF3, AgOTf, 1.732 g, 6.74
mmol, 1.00 equiv) was added slowly to the stirred solution,
and the solution was stirred at room temperature for 2.5 days.
The solution with yellow solid was filtered through a medium-
porosity filter frit; volatiles were removed from the bright
yellow toluene solution, affording 496 mg of bright yellow
powder. Additional crops of 870, 879, and 297 mg of bright
yellow powder were obtained by repeated (3-4×) washings of
the filter cake with toluene (50 mL aliquots) and removal of
volatiles from the combined organics. Total isolated yield:
2.542 g, 5.65 mmol, 84% yield. Anal. Calcd for C17H18N2O5-
PSF3: C, 45.33; H, 4.04; N, 6.22. Found: C, 45.46, 45.48, 45.38;
[P N(2,4,6-Me3-C6H 2)CH 2CH 2N(2,4,6-Me3-C6H 2)](BAr F )
(4e). A NMR tube was charged with 29 mg (0.081 mmol, 1.21
equiv) of 3b and 71 mg (0.067 mmol, 1.00 equiv) of TlBArF.
Deuteriochloroform (0.4 mL), previously cooled to -15 °C, was
added to the two solids, affording a bright yellow solution with
finely divided white solid. The mixture was then allowed to
sit at room temperature overnight; subsequent proton NMR
spectroscopy indicated the complete consumption of 3b. TlCl
could then be removed by filtration of the solution through a
medium-porosity filter frit. 31P{1H} NMR (δ, in CDCl3): 257.3.
1H NMR (δ, in CDCl3): 2.32 (s, 18H, coincidentally degenerate
2,4,6-(CH3)3), 4.27 (d, J ) 3.9 Hz, 4H, NCH2), 7.03 (s, 4H,
C6H2), 7.55 (s, 4H, B[(3,5-CF3)2-C6H3]4), 7.75 (s, 8H, B[(3,5-
CF3)2-C6H3]4).
1
H, 4.54, 4.57, 4.46; N, 6.05, 5.92, 6.01. H NMR (δ, in CDCl3):
3.82 (s, 6H, OCH3), 4.21 (d, J ) 5.4 Hz, 4H, NCH2), 6.94 (m,
J ) 9.0 Hz, 2H, C6H4), 7.30 (m, J ) 7.3 Hz, 2H, C6H4). 13C-
{1H} NMR (δ, in CDCl3): 52.2 (d, J P-C ) 9 Hz, NCH2), 55.6 (s,
OCH3), 115.1 (s, C6H4), 119.7 (quartet, J C-F ) 319 Hz,
OSO2CF3), 121.7 (d, J P-C ) 10 Hz, C6H4), 132.2 (d, J P-C ) 16
Hz, C6H4), 158.0 (s, C6H4).
{(P Me 3)[P N(4-Me O-C 6H 4)CH 2CH 2N(4-Me O-C 6H 4)]}-
(OTf) (5a ). In the glovebox, a NMR tube was charged with
29 mg (0.064 mmol, 1.00 equiv) of 4a and 0.4 mL of CDCl3.
Trimethylphosphine (1.0 M in toluene, 0.075 mL, 0.075 mmol,
1.18 equiv) was syringed into the clear, bright orange solution;
the orange color disappeared immediately upon addition of
PMe3, giving a clear, colorless solution upon mixing. 31P NMR
spectroscopy on the crude reaction mixture indicated that all
of the 4a had been consumed within 15 min at room temper-
ature. The tube was then brought back into the glovebox, the
volatiles were removed, and the resulting pale yellow solid was
dried in vacuo. 31P{1H} NMR (δ, in CD2Cl2, 25 °C): 2.57 (br,
[P N(2,4,6-Me3-C6H2)CH2CH2N(2,4,6-Me3-C6H2)](OTf) (4b).
A 200 mL round-bottom flask was charged with 1.334 g (3.70
mmol, 1.00 equiv) of 3b and 50 mL of toluene, giving a colorless
solution with a suspension of white solid. The flask was
wrapped in Al foil, and AgOTf (949 mg, 3.69 mmol, 1.00 equiv)
was slowly added to the stirred solution; the solution was
stirred at room temperature for 2 h and was then filtered
through a medium-porosity frit, affording a small amount of
white solid and a clear, colorless solution. Volatiles were
removed from the toluene solution, yielding 1.588 g (3.35
mmol, 91% yield) of white solid. Anal. Calcd for C21H26N2O3-
PSF3: C, 53.15; H, 5.53; N, 5.90. Found: C, 52.72, 52.81, 52.13;
P(CH3)3), 114.28 (br, PN(4-CH3O-C6H4)(CH2CH2N(4-CH3O-
1
C6H4)). H NMR (δ, in CD2Cl2): 1.62 (d, J P-H ) 12.5 Hz, 9 H,
1
H, 6.00, 6.56, 5.91; N, 5.82, 5.82, 5.68. H NMR (δ, in CDCl3):
P(CH3)3), 3.78 (s, 6H, OCH3), 3.97 (br, 4H, NCH2), 6.94 (br,
4H, C6H4), 7.14 (br, 4H, C6H4).
2.31 (s, 6H, 2,4,6-(CH3)3-C6H2), 2.43 (s, 12H, 2,4,6-(CH3)3-C6H2),

4956 Organometallics, Vol. 19, No. 24, 2000
Abrams et al.
(660 mg, 0.713 mmol) was cooled to -50 °C, to which solid 4a
(321 mg, 0.712 mmol, 1.00 equiv) was added slowly. The
solution was warmed to room temperature and was stirred
for an additional 60 min at 25 °C. After removal of volatiles,
the resulting solid was washed three times with 10 mL
portions of toluene and was dried in vacuo, yielding 635 mg of
a bright orange powder, 6 (0.571 mmol, 80% yield). Anal. Calcd
for C53H48N2O5P3SF3RhCl: C, 57.17; H, 4.35; N, 2.52. Found:
C, 56.54, 56.72, 56.27; H, 4.51, 4.50, 4.45; N, 2.42, 2.40, 2.41.
1H NMR (δ, in CDCl3): 3.75 (d, 7.1 Hz, 4H, NCH2), 3.86 (s,
6H, OCH3), 6.78 (d, 8.8 Hz, 4H, C6H4), 7.38, 7.40, 7.41
(overlapping multiplets, 28H, C6H4 and C6H5), 7.51 (m, J )
4.4 Hz, 6H, C6H5). 13C{1H} NMR (δ, in CDCl3): 50.15 (s,
NCH2), 55.73 (s, OCH3), 114.31 (s, C6H4), 119.96 (m, overlaps
with Ph resonances, 1J C-F ) 323 Hz, OSO2CF3), 121.93 (d, J P-C
) 7.6 Hz, C6H4), 128.72 (m, J ) 5.3 Hz, C6H5), 130.18 (d, J )
11.1 Hz, C6H4), 131.34 (s, C6H5), 131.99 (m, J ) 24.8, C6H5),
133.87 (m, J ) 6.0 Hz, C6H5), 158.88 (s, C6H4). 31P{1H} NMR
(δ, in CDCl3): 24.91 (dd, 1J Rh-P ) 102 Hz, 2J P-P ) 51 Hz, PPh3),
{(P Me3)[P N(2,4,6-Me3-C6H2)CH2CH2N(2,4,6-Me3-C6H2)]}-
(OTf) (5b). A screw-top NMR tube was charged with 28 mg
(0.058 mmol, 1.00 equiv) of 4b and 0.4 mL of CDCl3. Tri-
methylphosphine (1.0 M in toluene, 0.070 mL, 0.070 mmol,
1.20 equiv) was syringed into the pale yellow solution, afford-
ing immediately upon shaking a clear, colorless solution. 31P
NMR spectroscopy indicated that all of the starting materials
had been consumed within 15 min. Volatiles were removed in
vacuo, yielding a pale yellow solid. 31P{1H} NMR (δ, in CD2-
Cl2, 25 °C): -10.4 (br, P(CH3)3), 144.7 (br, PN[2,4,6-(CH3)3-
C6H2]CH2CH2N[2,4,6-(CH3)3-C6H2]).
((P Me3){P N[2,6-(CHMe2)2-C6H3]CH2CH2N[2,6-(CHMe2)2-
C6H3]})(OTf) (5c). A 50 mL round-bottom flask equipped with
a magnetic stir bar was charged with 306 mg (0.548 mmol,
1.00 equiv) of 4c and 10 mL of toluene. Trimethylphosphine
(1.0 M in toluene, 1.0 mL, 1.0 mmol, 1.82 equiv) was syringed
dropwise into the clear golden solution, and the resulting
colorless solution and white precipitate were stirred at room
temperature for 3 h. The precipitate was isolated by filtration
and dried in vacuo, yielding 257 mg of white solid (0.405 mmol,
74% yield). Anal. Calcd for C30H47N2O3P2SF3: C, 56.76; H, 7.48;
N, 4.41. Found: C, 52.50, 53.09, 53.06; H, 7.75, 7.78, 7.65; N,
3.96, 4.09, 3.96. 31P{1H} NMR (δ, in CD2Cl2, 25 °C): -17.1 (br,
1
2
240.18 (dt, J Rh-P ) 311 Hz, J P-P ) 51 Hz, N2P).
Rea ction of 4b,c w ith Rh Cl(P P h 3)3. An NMR tube was
charged with approximately 0.04 mmol of the appropriate
phosphenium (4) and 1.0 equiv of RhCl(PPh3)3, to which CDCl3
(0.4 mL) was added at room temperature. The crude reaction
mixtures were then analyzed by 1H and 31P NMR spectroscopy.
No attempts were made to isolate or further characterize either
the cis or trans isomers of 7 due to the mixture of products
resulting from 4b/RhCl(PPh3)3.
P(CH3)3), 153.1 (br, PN{2,6-[CH(CH3)2]2-C6H3}CH2CH2N{2,6-
1
[CH(CH3)2]2-C6H3}). H NMR (δ, in CD2Cl2, 25 °C): 1.32 (d, J
) 6.6 Hz, 12H, CH(CH3)2), 1.38 (d, J ) 6.8 Hz, 12H, CH(CH3)2),
1.54 (d, J P-H ) 10.0 Hz, 9H, P(CH3)3), 3.22 (sept, J ) 6.6 Hz,
4H, CH(CH3)2), 3.87 (s, 4H, NCH2), 7.28 (m, 4H, C6H3), 7.40
(m, 4H, C6H3).
Ack n ow led gm en t. This work was funded by a
Department of Energy Laboratory Directed Research
and Development Grant. We thank Professor Richard
D. Broene (Bowdoin College), Dr. Kristina A. Kreutzer
(DuPont), Professor Bernhard Breit (Universita¨t Mar-
burg), and Professor Philip W. Dyer (University of
Leicester) for helpful discussions, Trudi M. Foreman for
NMR maintenance, and Dr. Wayde V. Konze and Dr.
Gregory J . Kubas for a generous gift of TlBArF.
{(P Me3)[P N(2,4,6-Me3-C6H2)CH2CH2N(2,4,6-Me3-C6H2)]}-
(BAr F ) (5d ). A solution of 0.067 mmol of 4e in 0.4 mL of CDCl3
was placed in an NMR tube, and trimethylphosphine (0.07 mL,
1.0 M in toluene, 0.07 mmol, 1.05 equiv) was added dropwise
to the clear yellow solution. After the NMR tube was allowed
to stand overnight, volatiles were removed from the clear,
yellow solution in vacuo, affording a light yellow solid. 31P-
{1H} NMR (δ, in CD2Cl2, 25 °C): -15.0 (br, P(CH3)3), 151.8
(br, PN[2,4,6-(CH3)3-C6H2]CH2CH2N[2,4,6-(CH3)3-C6H2]). 1H
NMR (δ, in CD2Cl2, 25 °C): 1.55 (br, 9H, P(CH3)3), 2.30 (s,
6H, 2,4,6-(CH3)3-C6H2), 2.40 (s, 12H, 2,4,6-(CH3)3-C6H2), 3.84
(br, 4H, NCH2), 7.00 (s, 4H, 2,4,6-(CH3)3-C6H2), 7.61 (s, 4H,
B[(3,5-CF3)2-C6H3]4), 7.78 (s, 8H, B[(3,5-CF3)2-C6H3]4).
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra for
1a -c, 2a -c, 3a -c, and 4a -c, as well as tables of atomic
coordinates, anisotropic thermal parameters, and bond lengths
and angles for 5c. This material is available free of charge
via the Internet at http://pubs.acs.org.
{tr a n s-Rh Cl(P P h 3)2[P N(4-MeO-C6H4)CH2CH2N(4-MeO-
C6H4)]}(OTf) (6). A CH2Cl2 (20 mL) solution of RhCl(PPh3)3
OM0005351