Rhodium-Catalyzed Isomerization of a Bis(secondary phosphine) to an Unsymmetrical Diphosphine via P-C Cleavage and P-P and C-H Bond Formation

Article abstract of DOI:10.1021/acs.organomet.7b00515

To develop Rh-catalyzed dehydrocoupling for stereocontrolled synthesis of P-P bonds, we prepared potential intermediates, chiral rhodium phosphine-phosphido complexes, and investigated their stoichiometric and catalytic transformations. Treatment of [Rh(diphos)(COD)][X] with the bis(secondary phosphine) IsHPCH₂PHIs (1, Is = 2,4,6-(i-Pr)₃C₆H₂) gave the cations [Rh(diphos)(IsHPCH₂PHIs)][X] (diphos? = (R,R)-Me-DuPhos (2), (R,R)-i-Pr-DuPhos (3), or (R,R)-Me-BPE (4); X = BF₄ or OTf) with high diastereoselectivity as single C₂-symmetric diastereomers. Deprotonation of 2-4 with NaN(SiMe₃)₂ yielded phosphine-phosphido chelates Rh(diphos)(IsHPCH₂PIs) 5-7 with high diastereoselectivity. Thermolysis of 5-7 in toluene at 90 °C caused isomerization to give Rh(diphos)(IsMeP-PIs) (8-10) as mixtures of diastereomers. Under catalytic conditions, Rh-DuPhos precursors slowly converted 1 to a mixture of diastereomers of its isomer, the unsymmetrical diphosphine IsHP-PMeIs (12). We propose a possible mechanism for the isomerization and discuss its relationship to dehydrocoupling catalysis.

Full text of DOI:10.1021/acs.organomet.7b00515

Article
pubs.acs.org/Organometallics
Rhodium-Catalyzed Isomerization of a Bis(secondary phosphine) to
an Unsymmetrical Diphosphine via P−C Cleavage and P−P and C−H
Bond Formation
Perry M. Scheetz,† David S. Glueck,*,† and Arnold L. Rheingold‡
†Department of Chemistry, Dartmouth College, 6128 Burke Laboratory, Hanover, New Hampshire 03755, United States
‡Department of Chemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
S
* Supporting Information
ABSTRACT: To develop Rh-catalyzed dehydrocoupling for stereocontrolled synthesis of
P−P bonds, we prepared potential intermediates, chiral rhodium phosphine-phosphido
complexes, and investigated their stoichiometric and catalytic transformations. Treatment
of [Rh(diphos*)(COD)][X] with the bis(secondary phosphine) IsHPCH2PHIs (1, Is =
2,4,6-(i-Pr)3C6H2) gave the cations [Rh(diphos*)(IsHPCH2PHIs)][X] (diphos* = (R,R)-
Me-DuPhos (2), (R,R)-i-Pr-DuPhos (3), or (R,R)-Me-BPE (4); X = BF4 or OTf) with
high diastereoselectivity as single C2-symmetric diastereomers. Deprotonation of 2−4 with
NaN(SiMe3)2 yielded phosphine-phosphido chelates Rh(diphos*)(IsHPCH2PIs) 5−7
with high diastereoselectivity. Thermolysis of 5−7 in toluene at 90 °C caused isomerization
to give Rh(diphos*)(IsMeP-PIs) (8−10) as mixtures of diastereomers. Under catalytic conditions, Rh-DuPhos precursors slowly
converted 1 to a mixture of diastereomers of its isomer, the unsymmetrical diphosphine IsHP-PMeIs (12). We propose a
possible mechanism for the isomerization and discuss its relationship to dehydrocoupling catalysis.
Scheme 2. Proposed Mechanism of Rh-Catalyzed
Dehydrocoupling
INTRODUCTION
■
a
Metal-catalyzed dehydrocoupling of primary and secondary
phosphines yields H2 and forms P−P bonds in diphosphines.1
Because P-stereogenic diphosphines are building blocks for
chiral bis(phosphines) of value as ligands for metal complexes
in asymmetric catalysis,2 an asymmetric version of this reaction,
leading to enantiomerically enriched diphosphines,3 is poten-
tially useful. For example, a chiral metal catalyst might
selectively convert a mixture of diastereomers of bis(secondary
phosphine) A to enantiomerically enriched, C2-symmetric
diphosphine B (Scheme 1).4 Sequential treatment of B with
an electrophilic alkylating agent, such as MeOTf, and a
nucleophilic one, like a Grignard reagent, could then give C2-
or C1-symmetric chelate bis(phosphines) C.2
With a chiral rhodium catalyst, the proposed dehydrocou-
pling could proceed by the mechanism shown in Scheme 2.5,6
P−H oxidative addition in Rh(I) phosphine-phosphido
a
[Rh]* = Rh(diphos*).
Scheme 1. Metal-Catalyzed Asymmetric Dehydrocoupling of
a Bis(secondary phosphine) (A) as a Route to P-Stereogenic
Chelates C via Diphosphine B
complex D gives Rh(III)-bis(phosphido) hydride E, whose
P−P reductive elimination yields diphosphine B with retention
of configuration at P.7 Coordination of substrate A, P−H
activation in F to give G and loss of H2 would regenerate D.
The desired diastereoselectivity and enantioselectivity might
arise as shown in Scheme 3. Because metal-phosphido
complexes undergo rapid pyramidal inversion,8 the three
possible diastereomers of hydride intermediate E could
Received: July 10, 2017
© XXXX American Chemical Society
A
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diastereomers (Scheme 4). Notably, the initial reaction
mixtures contained mixtures of diastereomers, as observed by
Scheme 3. Proposed Origin of Selectivity in Rhodium-
Catalyzed Asymmetric Dehydrocoupling of Bis(secondary
phosphine) A
Scheme 4. Synthesis of Cations 2−4 and Their
Deprotonation to Yield Phosphine-Phosphido Complexes
a
5−7
interconvert rapidly, with their equilibrium speciation con-
trolled by steric interactions of the coordinated substrate with
the chiral ligand diphos*. Assuming that this isomerization is
faster than P−P reductive elimination, the product ratio would
be under Curtin-Hammett control, potentially leading to
selective formation of one enantiomer of the target cyclic
diphosphine.9
To investigate these possibilities, we planned to synthesize
phosphine-phosphido intermediate D and examine its stoichio-
metric and catalytic transformations. Because the bis-
(phosphido) complex Pt((R,R)-Me-DuPhos)(IsPCH2PIs) (Is
= 2,4,6-(i-Pr)3C6H2) was found to be a single enantiomer,10 we
chose the same substrate and similar chiral ligands, in hopes
that intermediates like Rh(Me-DuPhos)(IsPCH2PIs)(H) (E)
would also be formed selectively (Chart 1).
a
diphos* = Me-DuPhos (R = Me), i-Pr-DuPhos (R = i-Pr), or Me-
BPE.
Chart 1. Structure of a Platinum Bis(phosphido) Complex
and Its Proposed Rhodium Analog E (Is = 2,4,6-(i-
Pr)3C6H2)
31P{1H} NMR spectroscopy, but over several days, these
mixtures evolved to yield single products. Presumably this
process occurred by the known epimerization of P-stereogenic
secondary phosphines, which is promoted by weak acids or
bases,13 and has previously been used for similar resolution of
secondary phosphines.14
Complexes 2−4 showed characteristic AA′XX′M 31P{1H}
NMR spectra; simulation with gNMR yielded the coupling
constants shown in Table 1.15 As in similar square planar
complexes,16 large trans JPP and JPH couplings (both ca. 300
Hz) were observed, while the cis JPP values in the bis(secondary
phosphine) ligand were much smaller, around 60 Hz. Rotation
about the P−C(Is) bonds was slow on the NMR time scale,
1
making ortho-i-Pr groups inequivalent in the H and 13C{1H}
NMR spectra, consistent with the crowded environment of the
bulky isityl groups.10
The C2 symmetry indicated by the NMR spectra was
confirmed by X-ray crystallography for complexes 2-BF4 and 3-
OTf (Figures 1 and 2, Table 2, and the Supporting
Information). As in the structure of Pt(Me-DuPhos)-
(IsPCH2PIs) mentioned in the introduction,10 the bulky isityl
groups occupied empty quadrants, avoiding the DuPhos Me or
i-Pr substituents. Because (R,R)-Me-DuPhos and (R,R)-i-Pr-
DuPhos have different absolute configurations despite the same
(R,R) label,11 coordinated bis(phosphine) 1 had configurations
of (S,S) in 2-BF4 and (R,R) in 3-OTf. Rhodium in these
complexes was approximately square planar, with distortions
caused by the small bite angle (about 73°) of the bis(secondary
RESULTS AND DISCUSSION
■
Treatment of [Rh(diphos*)(COD)][X]11 with the bis-
(secondary phosphine) IsHPCH2PHIs (1, mixture of rac and
meso diastereomers)12 gave the cations [Rh(diphos*)-
(IsHPCH2PHIs)][X] (diphos* = (R,R)-Me-DuPhos (2),
(R,R)-i-Pr-DuPhos (3), or (R,R)-Me-BPE (4); X = BF4 or
OTf) with high diastereoselectivity as single C2-symmetric
B
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a
Table 1. 31P{1H} NMR Data for Rhodium Complexes 2−10 and 15
# (ligand)
δ1 (JRh−P
)
δ2 (JRh−P
)
δ3 (JRh−P
)
δ4 (JRh−P
)
J12
J13
J14
J23
J24
J34
JPH
2 (Me-DuPhos)
3 (i-Pr-DuPhos)
4 (Me-BPE)
84.6 (135)
75.0 (136)
84.4 (135)
78.1 (158)
69.8 (158)
76.9 (158)
84.6 (178)
84.1 (188)
82.0 (189)
76.1 (189)
77.2 (185)
87.3 (185)
83.1 (186)
84.6 (135)
75.0 (136)
84.4 (135)
77.8 (126)
69.0 (129)
76.4 (129)
84.6 (169)
81.7 (172)
75.1 (165)
66.5 (170)
79.2 (169)
83.4 (169)
89.3 (162)
−103.1 (105)
−97.9 (111)
−103.2 (106)
−116.7 (112)
−112.5 (117)
−117.3 (116)
−103.1 (105)
−97.9 (111)
−103.2 (106)
−111.6 (50)
−105.1 (55)
−111.6 (51)
−128.3 (31)
−137.1 (20)
−118.8 (24)
−126.8 (24)
−137.5 (19)
25
25
25
34
29
30
27
27
19
19
28
20
29
287
296
285
341
334
333
247
247
247
247
234
242
232
−31
−31
−31
−33
−36
−33
15
−31
−31
−31
−10
−11
−16
29
287
296
285
113
116
115
89
65
60
343
334
326
334
328
326
69
5 (Me-DuPhos)
6 (i-Pr-DuPhos)
7 (Me-BPE)
−8
−9
−9
469
460
482
467
477
477
448
b
c
8 (Me-DuPhos)
−62.0 (br)
−65.3 (121)
18
36
81
b
c
9 (i-Pr-DuPhos)
−65.3 (br)
21
36
94
−74.5 (118)
−60.0 (121)
20
37
84
b
10 (Me-BPE)
19
38
87
c
c
−61.7 (br)
−123.3 (br)
−149.5 (18)
16
38
87
d
15 (Me-DuPhos)
−50.0 (115)
9
34
87
360
a
The chemical shift standard was 85% H3PO4. Solvents: CDCl3 for 2 and 3, CD2Cl2 for 4, THF for 5 and 6, toluene-d8 for 7 and 10, and C6D6 for
15. Coupling constants are given in Hz. Negative values of coupling constants were obtained from spectral simulation and by analogy to related
complexes; coupling constants for 8−10 and 15 are absolute values. See ref 10 and ref 23 therein for comments on the signs of coupling constants in
b
c
related compounds. Two isomers (1:1 ratio for 8 and 10, 5:1 for 9; data for the major isomer is listed first). This signal was too broad to determine
d
JRh−P Ca. 9:1 ratio of isomers. Spectral overlap prevented assignment of signals for the minor isomer, except for a peak at δ −151.5 (br dd, J = 430,
91, PIs)
Figure 1. ORTEP diagram of the cation in [Rh((R,R)-Me-DuPhos)-
((S,S)-IsHPCH2PHIs)][BF4] (2-BF4). The P−H hydrogen atoms
were located and refined; other H atoms are not shown.
Figure 2. ORTEP diagram of the cation in [Rh((R,R)-i-Pr-
DuPhos)((R,R)-IsHPCH2PHIs)][OTf] (3-OTf). The P−H atoms
phosphine) in a four-membered ring. The i-Pr-DuPhos
were located and refined; other H atoms are not shown.
complex 3-OTf contained slightly longer Rh−P(DuPhos)
bonds than in Me-DuPhos analog 2-BF4, perhaps because of
increased steric repulsion.
in Chart 1. In agreement with this idea, in NMR spectra of 5 in
toluene-d8 the phosphido 31P{1H} NMR signal shifted upfield
on cooling to −80 °C until it overlapped the PHIs peak, but
only one set of signals was observed throughout. As previously
observed in Rh, Pt, and other phosphido complexes,16,17 the
change in phosphorus coordination number from four to three
on deprotonation of 2−4 to yield 5−7 resulted in decreased JPP
and JRh−P couplings, for example, from 287 (trans JPP) and 105
Hz in 2 to 113 and 50 Hz in 5 (Table 1). As with the cationic
Deprotonation of orange cations 2−4 with NaN(SiMe3)2
gave the red phosphine-phosphido complexes 5−7 (Scheme 4),
identified by their ABXYM 31P{1H} NMR spectra (Table 1).
Only one set of signals was observed for Me-DuPhos and Me-
BPE complexes 5 and 7, while i-Pr-DuPhos analog 6 was a 96:4
ratio of diastereomers. The simplest explanation of these
observations is that one diastereomer was favored sterically,
consistent with the behavior of 2−4 and the related Pt complex
C
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Table 2. Selected Bond Lengths (Å) and Angles (deg) for
[Rh((R,R)-Me-DuPhos)((S,S)-IsHPCH2PHIs)][BF4] (2-
BF4), [Rh((R,R)-i-Pr-DuPhos)((R,R)-
Scheme 5. Thermolysis of Phosphine-Phosphido Complexes
5−7 Gave Deprotonated Diphosphine Complexes 8−10
a
IsHPCH2PHIs)][OTf] (3-OTf), and Rh((R,R)-Me-
DuPhos)((S,S)-IsHPCH2PIs) (5)
complex
2-BF4
3-OTf
5
Rh−P (DuPhos)
2.2562(14),
2.2562(15)
2.2924(9),
2.2812(10)
2.2393(7)
Rh−P (Is)
2.2911(14),
2.3111(14)
2.3055(9),
2.3464(10)
2.3079(9)
P−Rh−P (DuPhos)
P−Rh−P (Is)
P−Rh−P (trans)
85.53(5)
72.95(5)
85.66(3)
72.93(3)
86.43(4)
72.98(5)
171.50(3)
174.63(6),
172.23(5)
166.74(4),
172.84(4)
a
diphos* = Me-DuPhos (5, 8), i-Pr-DuPhos (6, 9), or Me-BPE (7,
P−Rh−P (cis)
99.71(5),
101.76(5)
101.49(3),
100.01(3)
100.54(3)
10).
The ABXYM 31P{1H} NMR spectrum of 9 (toluene-d8,
Table 1) included two signals assigned to the IsMeP group (δ
−65.3 (very broad m) and −74.5 (dddd, JP−P = 37, 247, 467,
precursors 2−4, rotation about the P−C(Is) bonds was slow on
the NMR time scale in 5−7.
The crystal structure of 5 (Figure 3, Table 2) was consistent
with the NMR conclusions. Although the crystallographically
J
Rh−P = 118) and the PIs group (δ −118.8 (dddd, JP−P = 21, 94,
482, JRh−P = 24); −126.8 (dddd, JP−P = 20, 84, 467, JRh−P = 24))
for the major and minor isomers, respectively. The large JPP
values are similar to those in related chelate complexes of the
deprotonated diphosphine ligand (R2P−PR−) and are charac-
teristic of the presence of a P−P bond.20 The new P-Me group
in 9 was identified for the major diastereomer by 1H (δ 1.71, t, J
= 7 Hz) and 13C{1H} NMR (δ 22.0, d, J = 11 Hz) spectroscopy
in toluene-d8, while the PH and CH2 signals of precursor 6
disappeared. When 6 was prepared with a PD group, the
resulting P-CH2D in 9 was observed by 2H NMR spectroscopy.
The structure of 8 was confirmed by an independent
synthesis using unsymmetrical diphosphine 12, which was
prepared from PMe(Is)(Cl) and LiPHIs (Scheme 6). As in
Scheme 6. Synthesis of Unsymmetrical Diphosphine 12 as
the Major Component of a Mixture Containing Symmetrical
Diphosphines 13 and 14 and Independent Generation of 14
Figure 3. ORTEP diagram of Rh((R,R)-Me-DuPhos)((S,S)-
IsHPCH2PIs) (5). The PH atom, which was located and refined at
half occupancy (disordered between the two P1 positions) is not
shown.
required 2-fold symmetry and the resulting disorder of the PH
group limited the conclusions available from this structure,
removing the proton had little effect on the Rh−P bond lengths
and angles (Table 2).
Thermolysis of 5−7 (toluene, 90 °C) resulted in P−C
cleavage and P−P and C−H bond formation to give the new
complexes Rh(diphos*)(IsMeP-PIs) (8−10) as mixtures of
diastereomers (1:1 for 8 and 10, 5:1 for 9; Scheme 5). These
isomerizations also gave small amounts of the known
diphosphirane IsPCH2PIs (11),18 the secondary phosphine
PHMe(Is),19 and unidentified Rh complexes. For Me-BPE
complex 10, some of the new unsymmetrical diphosphine
IsMeP-PHIs (12, see below) was also formed. The rate and
selectivity of the thermolysis of 5 was unchanged in the
presence of 1 equiv of PPh3 or PCy3; similarly, heating 6 with
PMe3 (4 equiv) had little effect on the reaction.
The thermolysis was best behaved for i-Pr-DuPhos complex
6, and product 9 could be isolated as a 5:1 mixture of
diastereomers in ca. 95% purity. Similar results for 8 and 10 are
described in the Experimental Section, while details of the
characterization of 9 are summarized here.
related procedures,21 this gave a mixture of 12 (major product,
about 60% of the mixture) and two symmetrical diphosphines,
the known IsHP-PHIs (13)6,22 and the new IsMeP-PMeIs
(14), about 24 and 16%, respectively. This mixture was
1
characterized by H and 31P NMR spectroscopy, and by mass
spectrometry. Diphosphine 14 was generated independently as
a mixture of two diastereomers by treatment of LiPMe(Is) with
dibromoethane (Scheme 6).23
Treatment of Rh(Me-DuPhos)(η3-CH2Ph)24 with this
mixture of diphosphines gave a mixture of 8 (major product)
and PH analog 15 (minor product, prepared separately from
pure diphosphine 13; Scheme 7). Diphosphine 16 did not react
under these conditions. As shown in Table 1 and the
D
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Scheme 7. Generation of Deprotonated Diphosphine
Complexes 8 and 15 from the Diphosphine Mixture of
Scheme 6 and Independent Synthesis of 15
Figure 4. ORTEP diagram of {Rh((R,R)-Me-DuPhos)(Cl)}2(μ-
IsHPCH2PHIs) (16). The P−H hydrogens were located and refined;
other hydrogens are not shown. Selected bond lengths (Å) and angles
(deg): Rh(1)−P(2) 2.1935(16), Rh(1)−P(1) 2.2441(17), Rh(1)−
P(3) 2.3195(18), Rh(1)−Cl(1) 2.4168(15), P(2)−Rh(1)−P(1)
85.18(6), P(2)−Rh(1)−P(3) 90.85(6), P(1)−Rh(1)−P(3)
175.15(6), P(2)−Rh(1)−Cl(1) 170.58(6), P(1)−Rh(1)−Cl(1)
88.64(6), P(3)−Rh(1)−Cl(1) 95.64(6).
Experimental Section, the NMR spectra of IsHP−PIs complex
15 were very similar to those of IsMeP−PIs analog 8.
Scheme 9. Synthesis of Dinuclear μ-Phosphine Complex 16
([Rh] = Rh(Me-DuPhos))
Heating 5 with 1 equiv of bis(secondary phosphine) 1 at 90
°C in toluene resulted in isomerization to give unsymmetrical
diphosphine 12. Complex 5 was partially converted to its
isomer, 8, and a small amount of PHMe(Is) was formed. Under
catalytic conditions at 90 °C in toluene, Rh-DuPhos precursors
slowly catalyzed the isomerization of 1 to 12 (Scheme 8). For
Scheme 8. Rhodium-Catalyzed Isomerization of
Bis(secondary phosphine) 1 to Unsymmetrical Diphosphine
12
a
Scheme 10. Proposed Isomerization Mechanism
example, thermolysis of 5 gave a solution of 8, which was
treated with 4 equiv of 1. Further heating converted 1 to 12
over 4 days (about 1 turnover per day). In similar catalytic
reactions, small amounts of diphosphirane 11, PHMe(Is), and
unidentified Rh complexes were also formed.
An attempt to isolate rhodium complexes from such a
catalytic reaction by recrystallization from a solvent mixture
containing CH2Cl2 gave C2-symmetric bis(phosphine)-bridged
[Rh(Me-DuPhos)(Cl)]2(μ-IsHPCH2PHIs) (16), which was
identified by X-ray crystallography (Figure 4) and by
independent synthesis (Scheme 9). We presume that the
chloride ligand was formed from an unobserved rhodium
hydride; a similar transformation using CH2Cl2 has been
reported.25
a
[Rh] = Rh(diphos*).
addition of the strained diphosphirane P−C ring in 18 would
yield alkyl hydride 19, whose C−H reductive elimination forms
the methyl group in 8−10. Added phosphines PR3 (R = Ph, Cy,
and Me) did not slow the isomerization, suggesting that the
diphosphirane does not dissociate from the metal.26
Catalytic turnover could occur by coordination of substrate 1
to 8−10, followed by P−H oxidative addition to give 20, or a
related intermediate in which the PMe(Is) donor had
dissociated (Scheme 11). P−H reductive elimination would
then yield unsymmetrical diphosphine 12 and regenerate 5−7.
This mechanism could explain observation of the minor
byproduct diphosphirane 11, which might be formed by ligand
substitution on hydride complex 18; the resulting Rh(Me-
On the basis of these observations, we propose the
mechanism shown in Scheme 10 for the stoichiometric
isomerization of phosphine-phosphido complexes 5−7 to
deprotonated diphosphine complexes 8−10. P−H oxidative
addition in 5−7 gives five-coordinate bis(phosphido) hydride
17, called E in the Introduction. P−P reductive elimination
then yields diphosphirane hydride intermediate 18. Oxidative
E
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provided elemental analyses. Mass spectrometry was performed at the
University of Illinois. Reagents were from commercial suppliers.
These compounds were made by the literature procedures:
[Rh(Me-DuPhos)(COD)][X], [Rh(i-Pr-DuPhos)(COD)][X], [Rh-
(Me-BPE)(COD)][X],11 and [Rh(Me-DuPhos)(Cl)]2,28
IsHPCH2PHIs (1),12 IsPCH2PIs (11),18 PH2Is,29 and PHMe(Is).19
Rh(Me-DuPhos)(CH2Ph) (13) was prepared from Rh(COD)-
(CH2Ph) and Me-DuPhos, as in related procedures with achiral
bis(phosphines).24 Full details will be reported separately.
Scheme 11. Proposed Mechanism for Catalytic
Isomerization of 1 to 12
a
Compound purity was established by elemental analyses and NMR
spectroscopy (see the Supporting Information for NMR spectra). For
cations 2-BF4 and 3-OTf, crystals from the same batch of material
used for X-ray structure determination gave elemental analyses which
were close to the required 0.4% accuracy; we were not able to get
better results. The cation 4-OTf was characterized spectroscopically
and used directly for the next step. For the air-sensitive phosphido
complexes 5−7, we could not get satisfactory analyses; see specific
comments below for each one. As described above, complexes 8−10
could not be obtained in pure form, so elemental analyses were not
attempted. In some cases we could identify the impurities present by
NMR spectroscopy. Similarly, diphosphines 12−14 and Rh complex
15 were not obtained in pure form. The purity of Rh complex 16 was
established by NMR spectroscopy.
[Rh((R,R)-Me-DuPhos)(IsHPCH2PHIs)][BF4] (2-BF4). A solution
of [Rh((R,R)-Me-DuPhos)(COD)][BF4] (34 mg, 0.056 mmol) in 0.6
mL of CH2Cl2 was added to a clear solution of IsHPCH2PHIs (27 mg,
0.056 mmol) in 0.4 mL of CH2Cl2. The resulting orange solution was
stirred for 5 min. The reaction was monitored by 31P{1H} NMR
spectroscopy, which showed complete conversion of [Rh((R,R)-Me-
DuPhos)(COD)][BF4] (δ 76.3, JRh−P = 149) after 3 days. The solvent
was then removed under vacuum, and the orange solid was washed
with pentane (3 × 1 mL). The orange solid was dissolved in 0.5 mL of
CH2Cl2, and 1.5 mL of pentane was added to the solution, which was
then cooled to −20 °C for 2 days. The solution was warmed to room
temperature, and another 1 mL of pentane was added. The solution
separated into an orange oil and yellow liquid. After 4 h, bright orange
crystals had formed. The solvent was decanted, and the crystals were
dried under vacuum (35 mg). A second crop of crystals yielded 17 mg
(total 52 mg, 0.050 mmol, 89% yield). The crystals were used for X-ray
crystallography and elemental analysis. This reaction was also
successfully scaled up. Using the triflate [Rh((R,R)-Me-DuPhos)-
(COD)][OTf] (284 mg, 0.426 mmol) and IsHPCH2PHIs (206 mg,
0.426 mmol) gave 298 mg of the product (0.286 mmol, 67%).
Anal. Calcd for C49H78P4RhBF4: C, 60.01; H, 8.02. Found: C,
59.66; H, 8.48. HRMS: m/z calcd for C49H78P4Rh 893.4100, found m/
z 893.4109. 31P{1H} NMR (CDCl3): δ 84.6 (AA′XX′M, JP−P = 25,
−31, 287, JP−Rh = 135, DuPhos), −103.1 (AA′XX′M, JP−P = 65, −31,
a
[Rh] = Rh(diphos*); for 21, [Rh] = Rh(Me-DuPhos).
DuPhos)(H) fragment could be trapped by substrate 1 to yield
dinuclear hydride 21, the proposed precursor to chloride 16.
Control experiments showed that diphosphirane 11 is unstable
under catalytic conditions (90 °C, toluene), forming a mixture
of unidentified products. However, the secondary phosphine
PHMe(Is) was not observed, so its origin in the stoichiometric
or catalytic reaction mixtures is not clear.
CONCLUSIONS
■
These observations provide some encouragement for develop-
ing syntheses of P-stereogenic diphosphines via Rh-catalyzed
asymmetric dehydrocoupling of bis(secondary phosphines).
The highly selective formation of phosphine-phosphido
complexes 5−7 suggests that the hypothesis of Scheme 3 is
plausible. The desired P−P bond formation was also observed,
but target C2-symmetric diphosphirane 11 was only a minor
product. We propose that the novel title isomerization is driven
by strain in the diphosphirane, promoting P−C oxidative
addition. To avoid this problem, we plan to investigate related
reactions using bis(secondary phosphine) substrates with
longer linkers to prepare diphosphetanes, diphospholanes,
and related products.
1
287, JP−Rh = 105, Is-P). H NMR (CDCl3): δ 7.67−7.65 (m, 2H,
DuPhos CH), 7.63−7.61 (m, 2H, DuPhos CH), 7.18 (2H, Is CH),
7.16 (2H, Is CH), 6.55 (br dm, JP−H = 343, 2H, PH), 5.10−5.06 (m,
2H, o-i-Pr CH), 4.24−4.20 (m, 2H, P−CH2−P), 3.35−3.31 (m, 2H, p-
i-Pr CH), 2.95−2.90 (m, 2H, o-i-Pr CH), 2.77−2.72 (br m, 2H, CH),
2.34−2.24 (m, 2H, CH2), 2.05−2.00 (br m, 2H, CH), 1.90−1.83 (m,
2H, CH2), 1.70−1.63 (m, 2H, CH2), 1.54 (dd, J = 22, 8, 6H, Me), 1.47
(d, J = 8, 6H, o-i-Pr Me), 1.38 (d, J = 8, 6H, p-i-Pr Me), 1.26
(overlapping doublets, 24H, 4 i-Pr Me), 1.21−1.14 (m, 2H, CH2),
0.68 (dd, J = 17, 9, 6H, Me). 13C{1H} NMR (CDCl3): δ 153.2 (m,
quat, DuPhos), 153.0 (quat Is), 150.9 (quat Is), 142.2 (t, J = 34, quat
Is), 132.7 (m, DuPhos Ar CH), 131.5 (DuPhos Ar CH), 123.2 (m, Is
CH), 122.7 (m, Is CH), 43.5 (m, PCH2), 42.1 (m, DuPhos CH), 38.9
(m, DuPhos CH), 37.2 (CH2), 36.0 (CH2), 34.5 (m, o-i-Pr CH), 34.3
(o-i-Pr CH), 32.7 (p-i-Pr CH), 26.3 (o-i-Pr Me), 25.4 (o-i-Pr Me), 24.6
(o-i-Pr Me), 23.7 (p-i-Pr Me), 23.6 (p-i-Pr Me), 23.2 (o-i-Pr Me), 18.8
(DuPhos Me), 15.2 (DuPhos Me). One of the quaternary Is aryl
signals was not observed; it may overlap other peaks from 153.2 to
153.0 ppm.
EXPERIMENTAL SECTION
■
General Experimental Details. Unless otherwise noted, all
reactions and manipulations were performed in dry glassware under
a nitrogen atmosphere at ambient temperature in a glovebox or using
standard Schlenk techniques. Pentane, CH2Cl2, ether, THF, and
toluene were dried over alumina columns similar to those described by
Grubbs et al.27 NMR spectra were recorded with 500 or 600 MHz
spectrometers. H or 13C NMR chemical shifts are reported vs Me4Si
1
and were determined by reference to the residual H or 13C solvent
1
peaks. 31P NMR chemical shifts are reported vs H3PO4 (85%), used as
an external reference. Coupling constants are reported in Hz as
absolute values. Unless indicated, peaks in NMR spectra are singlets.
Quantitative Technologies Incorporated/Intertek Pharmaceutical
Services (Whitehouse, NJ) or Atlantic Microlab (Norcross, GA)
[Rh((R,R)-i-Pr-DuPhos)(IsHPCH2PHIs)][OTf] (3-OTf). A clear
solution of IsHPCH2PHIs (27 mg, 0.056 mmol) in 0.4 mL of
CH2Cl2 was added dropwise to a stirring orange solution of
[Rh((R,R)-i-Pr-DuPhos)(COD)][OTf] (43 mg, 0.055 mmol) in 0.7
F
DOI: 10.1021/acs.organomet.7b00515
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
mL of CH2Cl2. The solution darkened slightly upon addition. After 1
day, 31P{1H} NMR spectroscopy confirmed that [Rh((R,R)-i-Pr-
DuPhos)(COD)][OTf], δ 64.5 (JRh−P = 149), had been consumed.
The solvent was then removed under vacuum, and the resulting orange
solid was washed with pentane (3 × 1 mL). Slow evaporation of a
solution in THF/pentane (1:4 ratio) gave X-ray quality crystals. The
solvent was then decanted, and the crystals were dried under vacuum
(35 mg, 0.030 mmol, 55%). This reaction may be scaled up, where
[Rh((R,R)-i-Pr-DuPhos)(COD)][OTf] (350 mg, 0.449 mmol) and
IsHPCH2PHIs (218 mg, 0.450 mmol) gave crystals of [Rh((R,R)-i-Pr-
DuPhos)(IsHPCH2PHIs)][OTf] (486 mg, 0.421 mmol) in 94% yield.
The same crystals used for X-ray analysis were used to obtain
elemental analysis and mass spectrometry data.
−111.6 (JP−P = −8, −33, 113, JP−Rh = 50), −116.7 (JP−P = −8, −10.5,
1
341, JP−Rh = 112). H NMR (C6D6): δ 7.32 (m, 3H, Ar), 7.25 (1H,
Ar), 7.18 (1H, Ar), 7.10 (1H, Ar), 7.08−7.03 (m, 2H, Ar), 6.97 (d, J =
324, 1H, PH), 6.03 (m, 1H, i-Pr CH), 5.57 (m, 1H, i-Pr CH), 5.43 (m,
1H, i-Pr CH), 4.07−3.96 (m, 2H, P−CH2−P), 3.82−3.78 (m, 1H, i-Pr
CH), 2.89−2.85 (m, 1H, i-Pr CH), 2.73−2.69 (m, 1H, i-Pr CH),
2.41−2.37 (m, 2H, DuPhos CH), 2.36−2.28 (m, 1H, DuPhos CH),
2.13−2.08 (m, 1H, DuPhos CH), 2.05−2.01 (m, 2H, CH2), 2.00−1.95
(m, 2H, CH2), 1.90 (dd, J = 17, 7, 3H, DuPhos Me), 1.87−1.80 (m,
2H, CH2), 1.74 (d, J = 7, 3H, i-Pr Me), 1.65−1.62 (m, 2H, CH2),
1.62−1.58 (m, 3H DuPhos Me + 6H i-Pr Me), 1.50 (d, J = 7, 3H, i-Pr
Me), 1.47 (d, J = 7, 3H, i-Pr Me), 1.44 (d, J = 7, 6H, i-Pr Me), 1.27 (d,
J = 7, 6H, i-Pr Me), 1.25 (br d, J = 6, 3H), 1.14 (d, J = 7, 6H, i-Pr Me),
0.71 (dd, J = 13, 7, 3H, DuPhos Me), 0.64 (dd, J = 13, 7, 3H, DuPhos
Me). 13C{1H} NMR (C6D6): δ 155.2 (d, J = 22, quat Ar), 154.5 (d, J =
15, quat Ar), 153.0 (quat Ar), 149.9 (quat Ar), 149.5 (quat Ar), 147.9
(t, J = 20, quat Ar), 147.4 (t, J = 23, quat Ar), 147.3 (quat Ar), 144.2
(d, J = 7, quat Ar), 143.9 (d, J = 7, quat Ar), 132.6 (d, J = 15, DuPhos
Ar CH), 132.3 (d, J = 15, DuPhos Ar CH), 129.0 (DuPhos Ar CH),
128.7 (DuPhos Ar CH), 122.5 (d, J = 7, Is CH), 121.8 (Is CH), 121.1
(Is CH), 120.7 (Is CH), 43.7 (d, J = 24, DuPhos CH), 41.0 (dd, J =
20, 7, DuPhos CH), 39.1 (dd, J = 17, 6, DuPhos CH), 38.9 (apparent
t, J = 21, P−CH2), 37.6 (CH2), 37.4 (d, J = 17, DuPhos CH), 37.0
(CH2), 36.6 (i-Pr CH), 36.3 (d, J = 4, CH2), 35.9 (CH2), 34.7 (i-Pr
CH), 34.6 (i-Pr CH), 33.0 (d, J = 36, DuPhos CH), 32.4 (i-Pr CH),
32.0 (dd, J = 17, 6, DuPhos CH), 27.1 (i-Pr Me), 26.7 (i-Pr Me), 26.5
(i-Pr Me), 26.3 (i-Pr Me), 25.6 (i-Pr Me), 24.8 (i-Pr Me), 24.38 (i-Pr
Me), 24.37 (i-Pr Me), 24.0 (2 i-Pr Me), 23.4 (i-Pr Me), 19.6 (d, J = 14,
DuPhos Me), 19.0 (dd, J = 15, 11, DuPhos Me), 15.8 (DuPhos Me),
15.4 (DuPhos Me). Of the 12 expected i-Pr Me signals, 11 were
observed.
Rh((R,R)-i-Pr-DuPhos)(IsHPCH2PIs) (6). A pale brown solution of
NaN(SiMe3)2 (14 mg, 0.075 mmol, 2 equiv) in 0.5 mL of THF was
added to a stirring orange solution of [Rh((R,R)-i-Pr-DuPhos)-
(IsHPCH2PHIs)][OTf] (44 mg, 0.038 mmol) in 2 mL of THF; the
solution immediately became dark red. After 30 min, the solution was
filtered through Celite, and the solvent was removed under vacuum to
yield a dark red powder. After extraction with pentane and filtration
through Celite, the solvent was evaporated under vacuum to yield a
red solid (36 mg, 0.036 mmol, 94%). Larger scale reactions are also
effective; the cation (250 mg, 0.216 mmol) gave 207 mg of product
(0.206 mmol, 95% yield). This complex is highly soluble in pentane
and other organic solvents, and we were not able to purify it by
recrystallization or to obtain satisfactory elemental analyses.
Anal. Calcd for C58H94F3O3P4RhS: C, 60.30; H, 8.20. Found: C,
59.37; H, 8.10. HRMS: m/z calcd for C57H94P4Rh, 1005.5361; found
m/z 1005.5377. 31P{1H} NMR (CDCl3): δ 75.0 (AA′XX′M, JP−P = 25,
−31, 296, JP−Rh = 136), −97.9 (AA′XX′M, JP−P = 60, −31, 296, JP−Rh
=
1
111). H NMR (CDCl3): δ 7.67 (2H, DuPhos), 7.55 (2H, DuPhos),
7.11 (2H, Is), 7.09 (2H, Is), 6.52 (dt, J = 37, 344, 2H, PH), 4.40 (2H,
i-Pr CH), 4.31 (m, 2H, P−CH2−P), 3.30 (m, 2H, i-Pr CH), 2.90−2.80
(m, 4H, i-Pr CH), 2.38 (br, 2H, DuPhos CH), 2.29 (m, 2H, DuPhos
CH2), 2.27 (m, 2H, DuPhos CH2), 1.80 (2H, DuPhos CH), 1.68 (m,
2H, DuPhos CH2), 1.62 (m, 2H, DuPhos CH2), 1.53 (m, 2H, i-Pr
CH), 1.45 (d, J = 7, 6H, DuPhos CH3), 1.38 (d, J = 7, 6H, Is CH3),
1.35 (d, J = 7, 6H, DuPhos CH3), 1.24 (d, J = 7, 6H, DuPhos CH3),
1.20 (18H, overlapping Is CH3), 0.98 (d, J = 7, 6H, DuPhos CH3),
0.41 (d, J = 7, 6H, Is CH3), 0.06 (d, J = 7, 6H, Is CH3). 13C{1H} NMR
(CDCl3): δ 152.9 (quat, Is), 152.8 (m, quat, DuPhos), 150.8 (quat,
Is), 148.5 (quat, Is), 142.6 (t, J = 34, quat Is), 133.1 (m, DuPhos Ar
CH), 131.5 (DuPhos Ar CH), 123.2 (t, J = 4, Is CH), 122.5 (Is CH),
54.8 (m, DuPhos CH), 52.3 (d, J = 23, DuPhos CH), 42.3 (t, J = 23,
P−CH2), 34.2 (DuPhos i-Pr CH), 33.6 (m, DuPhos i-Pr CH), 32.8 (Is
CH), 32.0 (br, Is CH), 31.3 (CH2), 29.8 (CH2), 29.2 (Is CH), 26.6 (Is
CH3), 25.9 (DuPhos CH3), 25.7 (DuPhos CH3), 24.8 (DuPhos CH3),
24.0 (Is CH3), 23.6 (d, J = 25, DuPhos CH3), 23.1 (m, Is CH3), 22.5
(Is CH3), 21.3 (m, Is CH3), 20.2 (m, Is CH3). The triflate 13C NMR
signal was not observed.
[Rh((R,R)-Me-BPE)(IsHPCH2PHIs)][OTf] (4-OTf). A clear solution
of IsHPCH2PHIs (49 mg, 0.10 mmol) in 0.5 mL of CH2Cl2 was added
dropwise to a stirring red solution of [Rh((R,R)-Me-BPE)(COD)]-
[OTf] (66 mg, 0.10 mmol) in 0.5 mL of CH2Cl2. The solvent was
removed under vacuum to yield an orange powder that was washed
with pentane (3 × 1 mL). The yield was 98 mg (0.099 mmol, 97%).
This material was used directly in deprotonation to yield Rh((R,R)-
Me-BPE)(IsPCH2PHIs) (7). 31P{1H} NMR (CD2Cl2): δ 84.4
(AA′XX′M, JP−P = 25, −31, 285, JRh−P = 135), −103.2 (AA′XX′M,
JP−P = 69, −31, 285, JRh−P = 106).
Rh((R,R)-Me-DuPhos)(IsHPCH2PIs) (5). A pale brown solution of
NaN(SiMe3)2 (19 mg, 0.10 mmol, 2 equiv) in 0.5 mL of THF was
added to a stirring orange solution of [Rh((R,R)-Me-DuPhos)-
(IsHPCH2PHIs)][OTf] (50 mg, 0.048 mmol) in 0.5 mL of THF. The
solution immediately became dark red. After 30 min, the solvent was
removed under vacuum to give a red solid. A portion of the solid was
redissolved in THF; slow evaporation yielded red X-ray quality single
crystals. The remaining solid was extracted with pentane, and the
resulting solution was filtered through Celite. The solvent was
removed from the filtrate to yield a red powder (41 mg, 0.046 mmol,
96%). X-ray crystallography and NMR spectroscopy showed that the
red crystals and powder were both Rh((R,R)-Me-DuPhos)-
(IsHPCH2PIs). The reaction may also be scaled up; [Rh((R,R)-Me-
DuPhos)(IsHPCH2PHIs)][OTf] (158 mg, 0.151 mmol) gave 139 mg
of the crude product (0.156 mmol, 103%). Purification of this complex
by recrystallization was difficult because of its high solubility in
pentane, and we have not been able to get satisfactory elemental
analyses, similar to what we and others have observed previously for
air-sensitive metal phosphido complexes.30
Anal. Calcd for C57H93P4Rh: C, 68.11; H, 9.33. Found: C, 65.65; H,
8.96. 31P{1H} NMR (THF): ABXYM pattern. δ 69.8 (JP−P = 29, −36,
334, JP−Rh = 158), 69.0 (JP−P = −9, 29, 116, JP−Rh = 129), −105.1 (JP−P
= −11, −36, 116, JP−Rh = 55), −112.5 (JP−P = −9, −11, 334, JP−Rh
=
117, JP−H = 328). The 31P{1H} NMR spectrum also showed 4%, by
integration, of the minor isomer: δ 77.6 (m), 76.3 (m), −100.6 (m),
−116.1 (m). 1H NMR (C6D6): δ 7.43−7.42 (m, 2H, DuPhos Ar), 7.26
(br, 1H, Is), 7.23−7.22 (m, 1H, Is), 7.17 (1H, Is), 7.08 (1H, Is), 7.07−
7.02 (m, 2H, DuPhos Ar), 6.90 (d, J = 323, 1H, PH), 5.50 (br, 1H, i-Pr
CH), 5.42 (br, 1H, i-Pr CH), 5.36 (m, 1H, i-Pr CH), 4.27−4.12 (m,
2H, P−CH2−P), 3.79 (sep, J = 7, 1H, i-Pr CH), 3.49−3.47 (m, 1H, i-
Pr CH), 2.89 (sep, J = 7, 1H, i-Pr CH), 2.74 (sep, J = 7, 1H, i-Pr CH),
2.66 (sep, J = 7, 1H, i-Pr CH), 2.14 (m, 1H, DuPhos CH), 2.09−2.07
(m, 2H, DuPhos CH), 2.00−1.92 (m, 2H, DuPhos CH + CH2), 1.82−
1.78 (m, 1H, CH2), 1.71 (br, 3H, Me), 1.70−1.60 (br m, overlapping,
2H, CH2), 1.63 (br, 6H, 1Me + 1 i-Pr CH + 2CH2), 1.59 (d, J = 7, 3H,
Me), 1.56 (br, 6H, Me), 1.52 (d, J = 7, 3H, Me), 1.45 (d, J = 7, 3H,
Me), 1.42−1.39 (m, 1H, i-Pr CH), 1.39 (d, J = 7, 3H, Me), 1.32
(overlapping, 14H, 4 Me + 2H CH2), 1.22 (d, J = 7, 3H, Me), 1.18 (d,
J = 7, 6H, Me), 1.09 (d, J = 7, 3H, Me), 0.53 (d, J = 7, 3H, Me), 0.50
(d, J = 7, 3H, Me), 0.35 (d, J = 7, 3H, Me), 0.34 (d, J = 7, 3H, Me).
13C{1H} NMR (C6D6): δ 154.6 (quat Ar), 154.5 (quat Ar), 153.5 (m,
quat Ar), 149.9 (quat Ar), 149.6 (quat Ar), 148.4−148.0 (m, quat Ar),
147.4 (quat Ar), 132.9 (d, J = 10, CH, DuPhos Ar), 132.8 (d, J = 10,
CH, DuPhos Ar), 128.8 (CH, DuPhos Ar), 128.6 (CH, DuPhos Ar),
123.0 (d, J = 7, Is CH), 121.9 (d, J = 4, Is CH), 120.9 (d, J = 5, Is CH),
Anal. Calcd for C49H77P4Rh: C, 65.91; H, 8.69. Found: C, 62.65; H,
8.27. HRMS: m/z calcd for C49H78P4Rh (MH+) 893.4109, found m/z
893.4083. 31P{1H} NMR (THF): ABXYM pattern, δ 78.1 (JP−P = −33,
34, 341, JP−Rh = 158), 77.8 (JP−P = −10.5, 34, 113, JP−Rh = 126),
G
DOI: 10.1021/acs.organomet.7b00515
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Organometallics
Article
120.4 (br, Is CH), 55.5 (d, J = 22, DuPhos CH), 54.2 (dd, J = 20, 9,
DuPhos CH), 52.4 (dd, J = 4, 13, DuPhos CH), 51.3 (dd, J = 4, 15,
DuPhos CH), 37.8 (dd, J = 6, 21, P−CH2), 34.8 (i-Pr CH), 34.7 (i-Pr
CH), 34.7 (br shoulder, i-Pr CH), 33.2 (d, J = 39, i-Pr CH), 32.5 (i-Pr
CH), 32.0 (DuPhos CH2), 31.7 (DuPhos CH2), 31.6 (d, J = 11, i-Pr
CH), 31.4−31.2 (m, i-Pr CH), 30.4 (d, J = 9, DuPhos CH2 and
overlapping i-Pr CH), 30.0 (i-Pr CH), 29.9 (i-Pr CH), 29.5 (d, J = 7,
DuPhos CH2), 27.3 (br, Me), 26.8 (br, Me), 26.6 (Me), 26.4 (d, J = 5,
DuPhos Me), 26.1 (br, Me), 25.7 (Me), 25.5 (d, J = 5, DuPhos Me),
25.0 (Me), 24.2 (Me), 24.0 (Me), 23.8 (Me), 23.7 (Me), 23.5 (d, J =
5, DuPhos Me), 23.1 (d, J = 6, DuPhos Me), 22.8 (br, Me), 22.5 (Me),
22.0 (d, J = 6, DuPhos Me), 21.3 (d, J = 8, DuPhos Me), 20.7 (d, J = 5,
DuPhos Me), 20.5 (d, J = 5, DuPhos Me). Only 7 of the 10 expected
quaternary aryl signals were observed.
Information for additional coupling constants and 31P{1H} NMR
simulation results.
Rh((R,R)-i-Pr-DuPhos)(IsMeP-PIs) (9). A solution of Rh((R,R)-i-
Pr-DuPhos)(IsPCH2PHIs) (100 mg, 0.099 mmol) in toluene-d8 (1.0
mL) in an NMR tube with a seal-locked cap was heated to 90 °C. The
solution gradually darkened from bright red to deep maroon over the
course of the reaction, which was monitored by 31P NMR
spectroscopy. Full conversion to 9 (two isomers in 5:1 ratio) occurred
after 2 days; about 8% of the secondary phosphine PHMe(Is)19 and a
trace of the diphosphirane IsPCH2PIs was also formed.18 The solvent
was removed under vacuum to give a dark red oil, which we have not
been able to purify by recrystallization (94 mg, 0.094 mmol, 94%).
31P{1H} NMR (toluene-d8): data for major isomer A: δ 82.0 (br dd,
JP−P = 247, JRh−P = 189), 75.1 (dddd, JP−P = 19, 36, 94, JRh−P = 165),
−65.3 (very broad m), −118.8 (dddd, JP−P = 21, 94, 482, JRh−P = 24);
Rh((R,R)-Me-BPE)(IsPCH2PHIs) (7). A pale brown solution of
NaN(SiMe3)2 (18 mg, 0.098 mmol, 2 equiv) in 0.5 mL of THF was
added dropwise to a stirring orange solution of [Rh((R,R)-Me-
BPE)(IsHPCH2PHIs)][OTf] (50 mg, 0.049 mmol, 1 equiv) in 1 mL
of THF; the solution darkened to a deep red. The solvent was
evaporated under vacuum, and the resulting red solid was dissolved in
pentane and filtered through Celite. The solvent was removed again to
yield a bright red powder (40 mg, 0.046 mmol, 92%), which was
characterized by NMR spectroscopy.
data for minor isomer B: δ 76.1 (dddd, JP−P = 19, 20.5, 247, JRh−P
189), 66.5 (dddd, JP−P = 19, 37, 84, JRh−P = 170), −74.5 (dddd, JP−P
=
=
37, 247, 467.5, JRh−P = 118), −126.8 (dddd, JP−P = 20.5, 84, 467.5,
JRh−P = 24).
1
Data for major isomer A: H NMR (toluene-d8): δ 7.63−7.61 (m,
1H, DuPhos Ar CH), 7.51 (t, J = 6, 1H, DuPhos Ar CH), 7.13 (1H,
DuPhos Ar CH), 7.11 (1H, DuPhos Ar CH), 7.10 (1H, Is CH), 7.01
(1H, Is CH), 6.94 (1H, Is CH), 6.83 (1H, Is CH), 5.45 (2H,
overlapping DuPhos and Is CH), 3.33 (1H, DuPhos CH), 3.25 (1H,
DuPhos CH), 2.74−2.72 (m, 1H, DuPhos CH), 2.64−2.60 (m, 1H,
DuPhos CH), 2.39−2.35 (m, 2H, overlapping DuPhos CH), 2.28−
2.24 (m, 2H, DuPhos CH), 2.22−2.18 (m, 1H, DuPhos CH), 2.08
(2H, overlapping DuPhos and Is CH), 1.96−1.94 (m, 1H, DuPhos
CH), 1.79 (m, 1H, DuPhos CH), 1.76 (m, 2H, overlapping DuPhos
and Is CH), 1.71 (t, J = 7, 3H, P−Me), 1.60−1.58 (m, 1H, Is CH),
1.63 (d, J = 7, 6H, 2 Me), 1.23 (d, J = 7, Me), 1.21−1.17 (m, 21H, 7
Me), 1.15 (d, J = 7, Me), 1.11 (d, J = 7, Me), 1.07 (d, J = 7, Me), 1.00
(d, J = 7, Me), 0.68 (d, J = 7, Me), 0.62 (d, J = 7, Me), 0.61 (d, J = 7,
Me), 0.52 (d, J = 7, Me), 0.50 (d, J = 7, Me), 0.28 (d, J = 7, Me).
13C{1H} NMR (toluene-d8): δ 155.7 (m, quat, DuPhos), 153.5 (m,
quat, DuPhos), 153.1 (m, quat Is), 150.1 (quat Is), 147.0 (quat Is),
143.9 (m, quat Is), 137.8 (quat Is), 137.7 (quat Is), 137.5 (quat Is),
137.3 (quat Is), 133.2 (d, J = 15, DuPhos Ar CH), 132.4 (d, J = 17,
DuPhos Ar CH), 129.3 (DuPhos Ar CH), 128.5 (DuPhos Ar CH),
125.5 (Is CH), 122.4 (Is CH), 121.7 (Is CH), 121.0 (Is CH), 54.9 (d,
J = 7, DuPhos CH), 54.8 (d, J = 5, DuPhos CH), 53.1 (d, J = 14,
DuPhos CH), 52.7 (d, J = 17, DuPhos CH), 36.8 (d, J = 11, DuPhos i-
Pr CH), 34.7 (d, J = 8, DuPhos i-Pr CH), 33.7 (d, J = 15, DuPhos i-Pr
CH), 32.8 (d, J = 14, DuPhos i-Pr CH), 32.7 (i-Pr CH), 32.6 (CH2),
32.4 (Is CH), 31.3 (CH2), 30.6 (Is CH), 30.4 (CH2), 30.2 (d, J = 6,
CH2), 29.1 (Is CH), 28.1 (Is CH), 26.7 (d, J = 6, Is Me), 26.3 (d, J =
8, Is Me), 26.2 (Is Me), 25.9 (d, J = 4, Is Me), 25.4 (Is Me), 25.3 (d, J
= 7, Is Me), 24.5 (Is Me), 24.4 (Is Me), 24.3 (d, J = 8, Is Me), 24.1 (Is
Me), 23.9 (Is Me), 22.0 (d, J = 11, P-Me), 21.4 (DuPhos Me), 21.0
(DuPhos Me), 20.8 (DuPhos Me), 20.7 (DuPhos Me), 20.62
(DuPhos CH3), 20.54 (DuPhos Me), 20.5 (DuPhos Me).
31P{1H} NMR (toluene-d8): δ 76.9 (dddd, JP−P = 30, −33, 333,
JRh−P = 158), 76.4 (dddd, JP−P = −16, 30, 115, JRh−P = 129), −111.6
(dddd, JP−P = −9, −33, 115, JRh−P = 51), −117.3 (dddd, JP−P = −9,
1
−16, 333, JRh−P = 116). H NMR (toluene-d8): δ 7.23 (br, 1H, Is),
7.13 (br, 1H, Is), 7.09 (br, 1H, Is), 7.03 (br, 1H, Is), 6.65 (dm, JP−H
=
326, 1H, P−H), 5.93 (br, 1H, o-i-Pr CH), 5.42 (br, 1H, o-i-Pr CH),
5.23 (br, 1H, o-i-Pr CH), 3.94−3.88 (br m, 2H, P−CH2−P), 3.68 (br,
1H, o-i-Pr CH), 2.85 (m, 1H, p-i-Pr CH), 2.72 (m, 1H, p-i-Pr CH),
1.92 (m, 1H, BPE CH), 1.85−1.78 (m, 2H, CH2), 1.73 (dd, J = 7, 15,
3H, Me-BPE plus overlapping m, 1H, BPE CH), 1.66−1.63 (m, 5H,
overlapping 3H Me + 2H CH2), 1.57−1.49 (very br m, 5H, 3H Me +
1H CH2 + 1H BPE CH), 1.46−1.44 (m, 11H, overlapping 3H (Me-
BPE) + 6H (2 i-Pr Me) + 2H CH2), 1.40−1.32 (m, overlapping 2 i-Pr
Me, 6H), 1.29 (d, J = 7, 3H, i-Pr Me), 1.28 (d, J = 7, 3H, i-Pr Me),
1.26−1.22 (m, 6H, 2 i-Pr Me), 1.16 (d, J = 7, 3H, i-Pr Me), 1.15 (d, J =
7, 3H, i-Pr Me), 1.11−1.05 (m, 3H, 2H CH2 + 1H BPE CH), 0.98−
0.94 (m, 3H, CH2), 0.85 (dd, J = 7, 15, 3H, Me-BPE), 0.77 (dd, J = 7,
15, 3H, Me-BPE). 13C{1H} NMR (toluene-d8): δ 155.3 (very br, o-
quat Is), 154.5 (very br, o-quat Is), 153.0 (very br, 2 o-quat Is), 150.0
(p-quat Is), 147.3 (p-quat Is), 144.4 (d, J = 8, ipso quat Is), 144.0 (d, J
= 8, ipso quat Is), 122.8 (br, Is m-CH), 122.1 (br, Is m-CH), 121.2 (br,
Is m-CH), 120.8 (br, Is m-CH), 41.0 (d, J = 22, BPE CH), 39.6 (dd, J
= 8, 18, P−CH2, overlapping next two signals), 39.4 (d, J = 18, BPE
CH), 39.3 (d, J = 18, BPE CH), 36.8 (BPE CH2), 36.5 (br, o-i-Pr CH),
36.2 (BPE-CH2), 36.1 (BPE-CH2), 35.8 (br m, BPE-CH2), 35.1 (p-i-
Pr CH), 35.0 (p-i-Pr CH), 34.0 (br d, J = 16, BPE-CH), 33.2 (br d, J =
37, o-i-Pr CH), 32.4 (br, o-i-Pr CH), 32.1 (br, o-i-Pr CH), 27.1 (br, i-
Pr Me), 26.5 (very br, i-Pr Me), 25.5 (br, i-Pr Me), 25.4−25.1 (m,
overlapping i-Pr Me), 24.7 (i-Pr Me), 24.6−24.5 (m, i-Pr Me), 24.4 (2
i-Pr Me), 21.9 (BPE Me), 21.8 (i-Pr Me), 21.7 (BPE Me), 15.8 (BPE
Me), 15.7 (BPE Me).
Rh((R,R)-Me-BPE)(IsMeP-PIs) (10). A solution of Rh((R,R)-Me-
BPE)(IsPCH2PHIs) (7, 40 mg, 0.046 mmol) in toluene-d8 (1.0 mL)
in a seal-locked NMR tube was heated to 90 °C. The solution
darkened from bright red to deep maroon. Full conversion occurred
after 3 days, yielding two isomers of 10 (∼1:1 ratio), the
unsymmetrical diphosphine IsHP-PMeIs (10%), and the diphosphir-
ane IsPCH2PIs (6%), according to 31P{1H} NMR integration. Some
unidentified Rh(Me-BPE) complexes also formed.
Rh((R,R)-Me-DuPhos)(IsMeP-PIs) (8). A solution of Rh((R,R)-
Me-DuPhos)(IsPCH2PHIs) (68 mg, 0.076 mmol) in toluene-d8 (1.0
mL) was heated in a screw-cap NMR tube to 90 °C. The solution
gradually darkened from bright red to a deep maroon, and the reaction
was monitored by 31P NMR spectroscopy. Full conversion to a 1:1
mixture of isomers of the product (A and B) occurred after 4 days. We
were not able to purify this complex by recrystallization because of its
high solubility in nonpolar solvents. This thermolysis was carried out
several times using different batches of the rhodium complex. In some
cases, small amounts of the diphosphirane IsPCH2PIs and the
unsymmetrical diphosphine IsHP-PMeIs also formed; we have not
been able to discover the reasons for this variability.
31P{1H} NMR (toluene-d8): data for isomer A (ABXYM): δ 87.3
(dddd, JP−P = 16, 20, 242, JRh−P = 185), 83.4 (dddd, JP−P = 20, 38, 87,
JRh−P = 169), −61.7 (very broad m), −123.3 (br dd, J = 87, 477); data
for isomer B: δ 79.2 (dddd, JP−P = 28, 38, 87, JRh−P = 169), 77.2 (dddd,
JP−P = 28, 19, 234, JRh−P = 185), −60.0 (dddd, JP−P = 38, 234, 477,
JRh−P = 121), −137.5 (dddd, JP−P = 19, 87, 477, JRh−P = 19).
Thermolysis of 5 or 6 in the Presence of Phosphines. A
solution of PPh3 (15 mg, 0.057 mmol) in 0.5 mL of toluene was added
to a red solution of Rh((R,R)-Me-DuPhos)(IsHPCH2PIs) (5, 50 mg,
0.057 mmol) in 0.5 mL of toluene, and the resulting solution was
transferred to a seal-locked NMR tube. The mixture was heated at 90
31P{1H} NMR (toluene-d8); data for A: δ 85.6−83.7 (m, DuPhos),
−62.0 (broad), −128.4 (broad dd, JP−P = 89, 469); data for B: δ 85.6−
83.7 (m, DuPhos), −65.3 (dddd, J = 36, 121, 247, 460), −137.4
(dddd, J = 18, 27, 81, 460). See Table 1 and the Supporting
H
DOI: 10.1021/acs.organomet.7b00515
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Article
°C for 40 h. Isomerization of 5 to 8 proceeded, and PPh3 remained
unchanged. Similar results were observed for 5 (50 mg, 0.057 mmol)
and PCy3 (16 mg, 0.057 mmol), as well as for 6 (48 mg, 0.048 mmol,
1 equiv) and PMe3 (20 μL, 0.19 mmol, 4 equiv).
spectrum showed that this material was a mixture of the diphosphine
(1:1 mixture of diastereomers, 80%) and the primary phosphine
starting material (20%), along with unreacted dibromoethane.
31P NMR (C6D6): δ −112.5 (AA′XX′; JPP = −212, JPH = 13, 204,
1
Generation and Thermolysis of D-Labeled Rh((R,R)-i-Pr-
DuPhos)(IsDPCH2PIs) (6-D) to Give Rh((R,R)-i-Pr-DuPhos)(Is-
(CH2D)P-PIs) (9-D). An aliquot of D2O (0.3 mL) was added to an
orange solution of [Rh((R,R)-i-Pr-DuPhos)(IsHPCH2PHIs)][OTf]
(3, 100 mg, 0.087 mmol) in 1.0 mL of THF. A 31P{1H} NMR
spectrum of the resulting product, [Rh((R,R)-i-Pr-DuPhos)-
(IsDPCH2PDIs)][OTf] (3-D), showed a broad doublet in the
phosphine region, a significant difference from the AA′XX′M pattern
for 3. The solvent was removed to yield an orange powder (96 mg,
JHH = 7), −117.0 (AA′XX′; JPP = −186, JPH = 13, 204, JHH = 7). H
NMR (C6D6): δ 7.08 (2H, Is), 7.06 (2H, Is), 7.03 (2H, Is), 6.99 (2H,
Is), 4.88 (JPP = −212, AA′XX′, J = 204, 13, 2H, PH), 4.63 (AA′XX′, JPP
= −186, J = 204, 13, 2H, PH), 4.02 (m, 2H, i-Pr CH), 3.64 (m, 4H, i-
Pr CH), 2.81 (m, 2H, i-Pr CH), 2.77−2.67 (m, 4H, i-Pr CH), 1.24 (d,
J = 7, 12H, Me), 1.21 (d, J = 4, 6H, Me), 1.19 (d, J = 8, 6H, Me), 1.17
(d, J = 5, 6H, Me), 1.12 (d, J = 7, 6H, Me), 1.07 (d, J = 8, 6H, i-Pr
Me). 13C{1H} NMR (C6D6): δ 153.9 (t, J = 7, quat Ar), 153.4 (t, J = 6,
quat Ar), 153.1 (d, J = 11, quat Ar), 152.3 (d, J = 10, quat Ar), 150.0
(quat Ar), 149.8 (quat Ar), 149.2 (quat Ar), 149.1 (quat Ar), 122.4 (Is
CH), 121.9 (Is CH), 121.8 (Is CH), 121.3 (d, J = 3, Is CH), 34.8 (i-Pr
CH), 34.7 (i-Pr CH), 33.1 (t, J = 7, i-Pr CH), 33.0 (t, J = 7, i-Pr CH),
30.5 (d, J = 9, i-Pr CH), 30.3 (d, J = 8, i-Pr CH), 24.6 (Is Me), 24.4 (Is
Me), 24.2 (d, J = 2, Is Me), 24.2 (Is Me), 24.1 (Is Me), 23.8 (Is Me).
IsMeP-PMeIs (14). Titrated n-BuLi (80 μL, 2.5 M in hexanes, 0.20
mmol) was added via microliter syringe to a solution of PH(Me)(Is)
(50 mg, 0.20 mmol) in 1 mL of THF at −78 °C; the clear solution
became bright yellow. After 30 min, a solution of BrCH2CH2Br (8.6
μL, 18.8 mg, 0.10 mmol) in 0.5 mL of THF was added at −78 °C via a
syringe; the solution became clear again. The solvent was removed
under vacuum, and the residue was extracted with pentane. Removing
the pentane under vacuum gave a clear oil, 48 mg total. This material
contained the diphosphine as a ca. 2:1 mixture of diastereomers, plus
an unidentified impurity (31P{1H} NMR: δ −50.2, ca. 30%) and the
secondary phosphine starting material (ca. 15%). 31P{1H} NMR
(C6D6): δ −54.4, −57.9 (ca. 2:1).
1
0.83 mmol, 95%). H NMR (CD2Cl2): the P−H signal disappeared.
2H NMR (CD2Cl2): δ 6.60 (br d, J = 60).
A pale tan solution of NaN(SiMe3)2 (30 mg, 0.17 mol, 2 equiv) in
0.5 mL of THF was added dropwise to an orange solution of 3-D (96
mg, 0.083 mmol) in 1 mL of THF. The solution immediately
darkened to blood red. The 31P{1H} NMR spectrum of the resulting
product, 6-D, showed additional splitting on the original PHIs peak at
−112 ppm. The solvent was removed to yield a red powder that was
extracted with pentane and filtered through Celite. Removal of the
solvent again gave a red powder (78 mg, 0.078 mmol, 94%).
A solution of 6-D (78 mg, 0.078 mmol) in 1.0 mL of toluene was
transferred to a seal-locked NMR tube and heated for 72 h at 90 °C.
The 31P{1H} NMR spectrum showed formation of both isomers of 9-
D, with additional P−D coupling on the P(CH2D)Is peaks at −119
2
and −127 ppm. H NMR (C6D6): δ 1.72 (br, CH2D).
Synthesis of a Mixture of Diphosphines, IsHP-PMeIs (12),
IsHP-PHIs (13), and IsMeP-PMeIs (14). Titrated n-BuLi (76 μL, 2.5
M in hexanes, 0.19 mmol) was added via syringe to a solution of PH2Is
(45 mg, 0.19 mmol) in 1 mL of THF at −78 °C; the colorless solution
became bright yellow. Separately, IsMgBr (0.38 mL of a 0.5 M solution
in THF, 0.19 mmol) was added to a solution of MePCl2 (54 mg, 0.19
mmol) in THF at −78 °C to generate IsPMeCl.19 The mixture was
stirred at −78 °C for 20 min, then added to the yellow n-BuLi/PH2Is
solution at −78 °C via syringe; the solution became colorless. The
solvent was removed under vacuum, and the resulting white flaky
residue was extracted with pentane (10 mL) to give a colorless oil (78
mg).
Reaction of Rh((R,R)-Me-DuPhos)(η3-CH2Ph) with the Mix-
ture of Diphosphines IsHP-PMeIs (12), IsHP-PHIs (13), and
IsMeP-PMeIs (14): Formation of Rh((R,R)-Me-DuPhos)(IsHP-PIs)
(15) and Rh((R,R)-Me-DuPhos)(IsMeP-PIs) (8). A clear solution of
the diphosphine mixture (60:24:16; 24 mg, 0.050 mmol) in 0.5 mL of
THF was added dropwise to a red solution of Rh((R,R)-Me-
DuPhos)(CH2Ph) (25 mg, 0.050 mmol). The reaction was monitored
by 31P{1H} NMR spectroscopy. After 10 min, IsHP-PHIs (13) was
consumed, and peaks from Rh((R,R)-Me-DuPhos)(IsHP-PIs) (15, see
below) had appeared. After 1 day, half of the IsHP-PMeIs (12)
remained, and formation of Rh((R,R)-Me-DuPhos)(IsMeP-PIs) (8)
was evident. After 4 days, IsHP-PMeIs was consumed, and more of 8
had formed. Diphosphine 14 did not react even after 11 days. Note
that a substantial amount of [Rh(Me-DuPhos)(Cl)]2 also formed in
this reaction, apparently via decomposition of Rh(Me-DuPhos)-
(CH2Ph); the chloride source is unknown.
The 31P{1H} NMR spectrum of this material showed that it was a
mixture of three diphosphines, IsMeP-PHIs (12, 60%), IsHP-PHIs
(13, 24%), and IsMeP-PMeIs (14, 16%), each as a mixture of two
diastereomers. Symmetrical diphosphines 13 and 14 were prepared
independently (see below). The mass spectrum of the mixture
confirmed the identity of all three diphosphines, which oxidized in
handling before analysis. For 12, HRMS m/z calcd for C31H51O2P2
(MO2H)+ 517.3364, found m/z 517.3361. For 13, HRMS m/z calcd
for C30H49OP2 (MOH)+ 487.3259, found m/z 487.3259. For 14,
HRMS m/z calcd for C32H53O2P2 (MO2H)+ 531.3521, found m/z
531.3519. 31P{1H} NMR (C6D6): For 12, −56.7 (d, JP−P = 160),
−58.4 (d, JP−P = 210), −97.9 (d, JP−P = 210), −102.6 (d, JP−P = 160)
(1:1 ratio). For 13, δ −112.4, −116.9 (1:1 ratio). For 14, δ −54.6,
Rh((R,R)-Me-DuPhos)(IsHP-PIs) (15). A clear solution of IsHP-
PHIs (17 mg, 0.036 mmol) in 0.5 mL of pentane was added to a red
solution of Rh((R,R)-Me-DuPhos)(CH2Ph) (18 mg, 0.036 mmol) in
0.5 mL of pentane, causing a color change to brown-red. Because the
31P{1H} NMR spectrum showed incomplete reaction (excess
diphosphine remained), another equivalent of the Rh complex was
added, resulting in complete conversion of the starting materials into
the product. We were not able to purify this complex because of its
high solubility in nonpolar solvents, and NMR spectra showed it
contained impurities, including one with a 31P NMR singlet at 4 ppm
(d, JPH = 470 Hz).
1
−57.9 (ca. 2:1 ratio). Selected data for 12 in the mixture: H NMR
(C6D6): δ 4.88 (dd, J = 208, 10, 1H, PH), 4.63 (dd, J = 223, 13, 1H,
PH).
IsHP-PHIs (13). This diphosphine has been mentioned several
times in the literature, but with limited experimental details.6,22 Only
31P{1H} NMR data and the mass spectrum seem to have been
reported.6 We describe a new synthesis and additional characterization
data.31 Titrated n-BuLi (0.92 mL, 2.3 M solution in hexanes, 2.1
mmol) was delivered via a microliter syringe to a colorless solution of
PH2Is (500 mg, 2.12 mmol) in 10 mL of THF at −78 °C; the mixture
became bright yellow. After 30 min, a solution of BrCH2CH2Br (0.37
mL, 4.2 mmol, 2 equiv) in 0.5 mL of THF was added to the PH2Is/n-
BuLi mixture at −78 °C via a syringe. After stirring overnight at room
temperature, the solvent was removed under vacuum to yield an
opaque canary yellow oil. Extraction with pentane gave a pale yellow
solution, leaving a white solid behind. The pentane was removed
under vacuum to give a pale yellow oil (891 mg). The 31P NMR
31P{1H} NMR (C6D6): δ 89.3 (dddd, JP−P = 29, 34, 87, JRh−P
162), 83.1 (dddd, JP−P = 9, 29, 232, JRh−P = 186), −50.0 (dddd, JP−P
=
=
34, 232, 448, JRh−P = 115, JP−H = 362), −149.5 (dddd, JP−P = 9, 87,
448, JRh−P = 18). Signals due to a minor isomer (∼10%) were also
observed. Because of spectral overlap, only one could be assigned: δ −
151.5 (br dd, J = 430, 91, PIs). 1H NMR (C6D6): δ 7.46 (t, J = 6, 1H,
DuPhos Ar CH), 7.39 (t, J = 6, 1H, DuPhos Ar CH), 7.19 (2H, Ar
CH), 7.13 (1H, Ar CH), 7.12 (1H, Ar CH), 7.08 (1H, Ar CH), 6.99
(1H, Ar CH), 5.70 (d, JP−H = 362, 1H, PH), 5.02 (br, 2H, i-Pr CH),
4.15 (sep, J = 7, 2H, i-Pr CH), 2.91 (m, 1H, DuPhos CH), 2.79 (m,
2H, i-Pr CH), 2.63 (m, 1H, DuPhos CH), 2.47 (m, 1H, DuPhos CH),
2.25 (m, 1H, DuPhos CH), 2.09−1.80 (m, 8H, CH2), 1.76 (dd, J = 7,
18, 3H, DuPhos Me), 1.61 (dd, J = 7, 19, 3H, DuPhos Me), 1.57 (d, J
I
DOI: 10.1021/acs.organomet.7b00515
Organometallics XXXX, XXX, XXX−XXX

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Article
= 7, 3H, Is Me), 1.52 (d, J = 7, 3H, Is Me), 1.34 (d, J = 7, 3H, Is Me),
1.24 (d, J = 7, 3H, Is Me), 1.22−1.20 (m, 6H, 2 Is Me), 1.15 (d, J = 7,
6H, 2 Is Me), 1.13−1.10 (overlap, 9H, 3 Is Me), 1.11 (d, J = 7, 3H, Is
Me), 0.82 (dd, J = 7, 14, 3H, DuPhos Me), 0.53 (dd, J = 7, 14, DuPhos
Me). 13C{1H} NMR (C6D6): δ 154.6 (overlapping m, quat Ar), 153.0
(d, J = 11, quat Ar), 152.8 (d, J = 8, quat Ar), 149.1 (quat Ar), 148.9
(quat Ar), 148.3−147.8 (several poorly resolved peaks, including quat
Ar signals at 148.3, 148.1, and 147.8), 146.8 (quat Ar), 132.4 (d, J =
15, DuPhos Ar CH), 132.1 (d, J = 15, DuPhos Ar CH), 129.2 (d, J =
39, DuPhos Ar CH), 128.7 (d, J = 30, DuPhos Ar CH), 122.7 (d, J =
11, Is CH), 122.4 (Is CH), 121.6 (d, J = 7, Is CH), 121.4 (Is CH),
42.6 (d, J = 25, DuPhos CH), 41.9 (dd, J = 6, 22, DuPhos CH), 41.7
(d, J = 19, DuPhos CH), 40.3 (dd, J = 6, 20, DuPhos CH), 37.6
(DuPhos CH2), 37.3 (DuPhos CH2), 36.6 (d, J = 6, DuPhos CH2),
36.2 (d, J = 4, DuPhos CH2), 35.6 (br m, i-Pr CH), 34.8 (i-Pr CH),
34.7 (i-Pr CH), 34.5 (i-Pr CH), 32.1 (overlapping d, J = 6, i-Pr CH),
30.3−30.2 (m, i-Pr CH), 26.6 (Is Me), 25.6 (2 Is Me), 25.4 (Is Me),
24.7 (Is Me), 24.5 (Is Me), 24.4 (Is Me), 24.3 (Is Me), 24.0 (Is Me),
23.91 (Is Me), 23.87 (Is Me), 23.8 (Is Me), 20.8 (d, J = 16, DuPhos
Me), 19.2 (t, J = 13.5, DuPhos Me), 15.6 (DuPhos Me), 15.1 (DuPhos
Me).
Stoichiometric Reaction of Rh((R,R)-Me-DuPhos)-
(IsHPCH2PIs) (5) with IsHPCH2PHIs (1). The bis(phosphine)
IsHPCH2PHIs (clear oil, 43 mg, 0.089 mmol) was added dropwise
to a red solution of Rh((R,R)-Me-DuPhos)(IsHPCH2PIs) (5, 79 mg,
0.089 mmol) in 1.0 mL of toluene. The resulting solution was
transferred into a seal-locked NMR tube and heated at 90 °C for 24 h,
when 31P{1H} NMR spectroscopy showed full consumption of
IsHPCH2PHIs. The mixture contained 5, isomerized Rh complex 8,
the unsymmetrical diphosphine 12, and a small amount of PHMe(Is).
Catalytic Isomerization of IsHPCH2PHIs (1) to IsMeP-PHIs
(12). A solution of Rh(Me-DuPhos)(IsHPCH2PIs) (5, 19 mg, 0.021
mmol) in 1.0 mL of toluene in an NMR tube was heated to 90 °C in
toluene for 4 days to generate the isomer 8. A solution of
IsHPCH2PHIs (1, 40 mg, 0.084 mmol, 4 equiv) in 0.5 mL of toluene
was added, and the mixture was heated at 90 °C for 96 h. The 31P{1H}
NMR spectrum showed that 1 was converted to the unsymmetrical
diphosphine 12 and that Rh complex 8 was consumed. Signals due to
two Rh(Me-DuPhos) complexes were observed; one was dinuclear 16
(see below), for which the source of chloride is unknown. The second
had a spectrum similar to that of 16: δ 88.9 (apparent dt, J = 35, 182),
85.1 (ddd, J = 30, 145, 362), −62.8 (apparent ddd, J = 35, 126, 362).
The catalytic reaction was also carried out with Rh(DuPhos)(η3-
CH2Ph) (DuPhos = Me-DuPhos or i-Pr-DuPhos), resulting in the
isomerization of 1 to 12 as well as formation of diphosphirane 11, the
secondary phosphine PHMeIs, and unidentified Rh complexes. We
presume that the variability in formation of these catalytic byproducts
is related to that seen in generation of 8 from 5 (see above).
Thermolysis of the Diphosphirane IsPCH2PIs (11). A solution
of the diphosphirane (10 mg, 0.032 mmol) in toluene (1.0 mL) was
heated for 3 h at 90 °C. 31P{1H} NMR analysis showed that while
some of the diphosphirane remained intact (−171 ppm), significant
decomposition to unidentified products also occurred.
2H DuPhos CH2), 2.11−2.09 (m, 2H, DuPhos CH), 1.95−1.88 (m,
9H, 1H DuPhos CH + 8 H DuPhos CH2), 1.85−1.72 (m, 12H, 2
DuPhos Me), 1.60−1.50 (m, 2H, DuPhos CH2), 1.45−1.41 (m, 12H,
i-Pr Me), 1.35−1.33 (m, 12H, i-Pr Me), 1.35−1.25 (m, 2H, DuPhos
CH2), 1.20−1.05 (m, 2H, DuPhos CH2), 1.00−0.98 (m, 12H, i-Pr
Me), 0.70 (dd, J = 14, 7, 6H, DuPhos Me), 0.40 (dd, J = 14, 7, 6H,
DuPhos Me). 13C{1H} NMR (C6D6): δ 154.2 (d, J = 20, quat Is),
153.6 (quat Is), 150.1−149.5 (m, quat DuPhos Ar), 148.9 (quat Is),
144.0−143.6 (m, quat DuPhos Ar), 130.5 (d, J = 18, DuPhos Ar CH),
130.4 (d, J = 15, DuPhos Ar CH), 128.2 (DuPhos Ar CH), 128.0
(DuPhos Ar CH), 128.1−127.9 (overlapping m, quat Is), 121.7 (d, J =
4, Is CH), 121.1 (d, J = 8, Is CH), 42.1 (d, J = 30, DuPhos CH), 40.5
(d, J = 25, DuPhos CH), 37.8 (d, J = 25, DuPhos CH), 36.3 (DuPhos
CH2), 36.0 (d, J = 23, DuPhos CH), 35.9 (DuPhos CH2), 35.8
(DuPhos CH2), 35.7 (DuPhos CH2), 33.3 (i-Pr CH), 33.1 (d, J = 16,
i-Pr CH), 30.4 (i-Pr CH), 27.5 (i-Pr Me), 26.3 (i-Pr Me), 24.65 (i-Pr
Me), 24.63 (i-Pr Me), 22.8 (i-Pr Me), 22.7 (i-Pr Me), 20.4 (br, P−
CH2−P), 18.9 (d, J = 12, DuPhos Me), 17.4 (d, J = 12, DuPhos Me),
14.3 (DuPhos Me), 12.6 (DuPhos Me).
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00515.
Crystallographic details and NMR spectra (PDF)
Accession Codes
CCDC 1553941−1553944 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: glueck@dartmouth.edu.
ORCID
David S. Glueck: 0000-0002-8438-8166
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the National Science Foundation (CHE-1265758
and CHE-1562037) for support, and the Department of
Education for a GAANN fellowship for P.M.S.
{Rh((R,R)-Me-DuPhos)(Cl)}2(μ-IsHPCH2PHIs) (16). A solution of
IsHPCH2PHIs (5.3 mg, 0.011 mmol) in 0.5 mL of THF was added
dropwise to a bright yellow solution of [Rh((R,R)-Me-DuPhos)Cl]2
(10 mg, 0.011 mmol) in 2.5 mL of THF; the mixture immediately
turned bright orange. After 4 h, two sets of 31P{1H} NMR signals were
observed, presumably due to two diastereomers. After 1 week, only
one set of signals was evident. The solution was concentrated under
vacuum; after 1 day, two types of crystals, bright yellow and bright
orange, formed (14 mg, 0.010 mmol, 93%). On a larger scale, 60 mg of
the Rh precursor (0.067 mmol) gave 84 mg of product (90% yield).
31P{1H} NMR (C6D6): δ 90.7 (ddd, JP−P = 32, 36, JRh−P = 177),
82.5 (ddd, JP−P = 32, 367, JRh−P = 142), −50.6 (dddd, JP−P = 14, 36,
REFERENCES
■
(1) (a) Melen, R. L. Chem. Soc. Rev. 2016, 45, 775−788.
(b) Waterman, R. Chem. Soc. Rev. 2013, 42, 5629−5641. (c) Water-
man, R. Curr. Org. Chem. 2012, 16, 1313−1331. (d) King, A. K.;
Buchard, A.; Mahon, M. F.; Webster, R. L. Chem. - Eur. J. 2015, 21,
15960−15963. (e) Dobrovetsky, R.; Takeuchi, K.; Stephan, D. W.
Chem. Commun. 2015, 51, 2396−2398. (f) Greenberg, S.; Stephan, D.
W. Chem. Soc. Rev. 2008, 37, 1482−1489.
(2) (a) Reynolds, S. C.; Hughes, R. P.; Glueck, D. S.; Rheingold, A. L.
Org. Lett. 2012, 14, 4238−4241. (b) Buergler, J. F.; Togni, A. Chem.
Commun. 2011, 47, 1896−1898.
1
367, JRh−P = 123). H NMR (C6D6): δ 7.51 (dm, J = 345, 2H, PH),
(3) (a) Zhang, S. Y.; Yemul, S.; Kagan, H. B.; Stern, R.; Commereuc,
D.; Chauvin, Y. Tetrahedron Lett. 1981, 22, 3955−3958. (b) Leseurre,
7.12 (m, 2H, DuPhos Ar), 7.05 (6H, 2H DuPhos Ar + 4H Is), 6.85
(4H, DuPhos Ar), 6.01−5.98 (m, 2H, i-Pr CH), 5.07−5.05 (m, 2H, i-
Pr CH), 3.45−3.42 (m, 2H, DuPhos CH), 2.91 (br, 2H, P−CH2−P),
2.56−2.52 (m, 2H, i-Pr CH), 2.36−2.30 (br, 4H, 2H DuPhos CH +
L.; Le Boucher d’Herouville, F.; Puntener, K.; Scalone, M.; Genet, J.-
̈
P.; Michelet, V. Org. Lett. 2011, 13, 3250−3253.
(4) Glueck, D. S. Chem. - Eur. J. 2008, 14, 7108−7117.
J
DOI: 10.1021/acs.organomet.7b00515
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(5) (a) Bohm, V. P. W.; Brookhart, M. Angew. Chem., Int. Ed. 2001,
R.; Budnikova, Y.; Ganushevich, Y.; Sinyashin, O. Russ. Chem. Bull.
2007, 56, 935−942. (c) Masuda, J. D.; Hoskin, A. J.; Graham, T. W.;
Beddie, C.; Fermin, M. C.; Etkin, N.; Stephan, D. W. Chem. - Eur. J.
2006, 12, 8696−8707. (d) Felsberg, R.; Blaurock, S.; Junk, P. C.;
Kirmse, R.; Voigt, A.; Hey-Hawkins, E. Z. Anorg. Allg. Chem. 2004,
630, 806−816.
́
40, 4694−4696. (b) Geer, A. M.; Serrano, A. L.; de Bruin, B.; Ciriano,
M. A.; Tejel, C. Angew. Chem., Int. Ed. 2015, 54, 472−475.
(6) Han, L.-B.; Tilley, T. D. J. Am. Chem. Soc. 2006, 128, 13698−
13699.
(7) (a) Moncarz, J. R.; Brunker, T. J.; Glueck, D. S.; Sommer, R. D.;
Rheingold, A. L. J. Am. Chem. Soc. 2003, 125, 1180−1181.
(b) Moncarz, J. R.; Brunker, T. J.; Jewett, J. C.; Orchowski, M.;
Glueck, D. S.; Sommer, R. D.; Lam, K.-C.; Incarvito, C. D.; Concolino,
T. E.; Ceccarelli, C.; Zakharov, L. N.; Rheingold, A. L. Organometallics
2003, 22, 3205−3221.
(8) Rogers, J. R.; Wagner, T. P. S.; Marynick, D. S. Inorg. Chem. 1994,
33, 3104−3110.
(9) Glueck, D. S. Synlett 2007, 2007, 2627−2634.
(23) Kurz, S.; Oesen, H.; Sieler, J.; Hey-Hawkins, E. Phosphorus,
Sulfur Silicon Relat. Elem. 1996, 117, 189−196.
(24) For related achiral complexes Rh(diphos)(η3-CH2Ph), see
Fryzuk, M. D.; McConville, D. H.; Rettig, S. J. J. Organomet. Chem.
1993, 445, 245−256.
(25) Stradiotto, M.; Fujdala, K. L.; Tilley, T. D. Helv. Chim. Acta
2001, 84, 2958−2970.
(26) As suggested by a reviewer, in a mechanism related to olefin
metathesis ( Mathey, F. Acc. Chem. Res. 1992, 25, 90−96 ), retro-[2 +
2] cleavage of the diphosphametallacyclobutane in 17 could yield a
phosphinidene-phosphaalkene complex, Rh(diphos*)(H)PIs)
(IsPCH2). Migratory insertion involving the hydride and
phosphaalkene would yield the phosphinidene phosphido complex
Rh(diphos*)(PIs)(PMeIs); P−P bond formation would then give
8−10..
(27) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518−1520.
(28) Meissner, A.; Preetz, A.; Drexler, H.-J.; Baumann, W.;
Spannenberg, A.; Konig, A.; Heller, D. ChemPlusChem 2015, 80,
169−180.
(29) van den Winkel, Y.; Bastiaans, H. M. M.; Bickelhaupt, F. J.
Organomet. Chem. 1991, 405, 183−194.
(30) See Scriban, C.; Glueck, D. S.; DiPasquale, A. G.; Rheingold, A.
L. Organometallics 2006, 25, 5435−5448 and ref 11 therein..
(31) For a related diphosphine, see Mokhtabad Amrei, L.; Dibble, P.
(10) Chapp, T. W.; Schoenfeld, A. J.; Sanderson, M. D.; Chang, C.
L.; Glueck, D. S.; Golen, J. A.; Moore, C. E.; Rheingold, A. L.
Organometallics 2012, 31, 5573−5585.
(11) (a) Burk, M. J.; Feaster, J. E.; Nugent, W. A.; Harlow, R. L. J.
Am. Chem. Soc. 1993, 115, 10125−10138. (b) Burk, M. J.; Feaster, J.
E.; Harlow, R. L. Organometallics 1990, 9, 2653−2655.
(12) (a) Bitterer, F.; Kucken, S.; Langhans, K. P.; Stelzer, O.;
Sheldrick, W. S. Z. Naturforsch., B: J. Chem. Sci. 1994, 49, 1223−1238.
(b) Bitterer, F.; Brauer, D. J.; Dorrenbach, F.; Fischer, J.; Stelzer, O. Z.
Naturforsch., B: J. Chem. Sci. 1992, 47, 1529−1540.
(13) (a) Bader, A.; Pabel, M.; Willis, A. C.; Wild, S. B. Inorg. Chem.
1996, 35, 3874−3877. (b) Bader, A.; Pabel, M.; Wild, S. B. J. Chem.
Soc., Chem. Commun. 1994, 1405−1406.
(14) (a) Albert, J.; Cadena, J. M.; Granell, J.; Muller, G.; Panyella, D.;
Sanudo, C. Eur. J. Inorg. Chem. 2000, 2000, 1283−1286. (b) Crisp, G.
̃
T.; Salem, G.; Wild, S. B.; Stephens, F. S. Organometallics 1989, 8,
2360−2367. (c) Wicht, D. K.; Kovacik, I.; Glueck, D. S.; Liable-Sands,
L. M.; Incarvito, C. D.; Rheingold, A. L. Organometallics 1999, 18,
5141−5151. (d) Bader, A.; Salem, G.; Willis, A. C.; Wild, S. B.
Tetrahedron: Asymmetry 1992, 3, 1227−1230. (e) Bader, A.;
Nullmeyers, T.; Pabel, M.; Salem, G.; Willis, A. C.; Wild, S. B. Inorg.
Chem. 1995, 34, 384−389.
́
W.; Boere, R. T. Can. J. Chem. 2016, 94, 392−400.
(15) Budzelaar, P.H. M. gNMR. http://home.cc.umanitoba.ca/
~budzelaa/gNMR/gNMR.html (accessed October 2016).
(16) Glueck, D. S. Coord. Chem. Rev. 2008, 252, 2171−2179;
erratum: 2011, 255, 356.
(17) (a) Bauer, R. C.; Gloaguen, Y.; Lutz, M.; Reek, J. N. H.; de
Bruin, B.; van der Vlugt, J. I. Dalton Trans. 2011, 40, 8822−8829.
(b) Dahlenburg, L.; Hock, N.; Berke, H. Chem. Ber. 1988, 121, 2083−
2093. (c) Sasamori, T.; Matsumoto, T.; Tokitoh, N. Polyhedron 2010,
29, 425−433.
(18) Bitterer, F.; Brauer, D. J.; Doerrenbach, F.; Gol, F.; Knueppel, P.
C.; Stelzer, O.; Krueger, C.; Tsay, Y. H. Z. Naturforsch., B: J. Chem. Sci.
1991, 46, 1131−1144.
(19) Brauer, D. J.; Bitterer, F.; Dorrenbach, F.; Hessler, G.; Stelzer,
O.; Kruger, C.; Lutz, F. Z. Naturforsch., B: J. Chem. Sci. 1996, 51,
1183−1196.
(20) (a) Schmiedeskamp, B. K.; Reising, J. G.; Malisch, W.; Hindahl,
K.; Schemm, R.; Sheldrick, W. S. Organometallics 1995, 14, 4446−
4448. (b) Lindner, E.; Darmuth, M.; Mayer, H. A.; Fawzi, R.; Maichle,
C.; Steimann, M. Chem. Ber. 1993, 126, 23−29. (c) Lindner, E.;
Stangle, M.; Hiller, W.; Fawzi, R. Chem. Ber. 1989, 122, 823−827.
̈
(d) Lindner, E.; Ossig, E.; Darmuth, M. J. Organomet. Chem. 1989,
379, 107−118. (e) Lindner, E.; Heckmann, M.; Fawzi, R.; Hiller, W.
Chem. Ber. 1991, 124, 2171−2179. (f) Lindner, E.; Funk, T.; Hiller,
W.; Fawzi, R. J. Organomet. Chem. 1991, 411, 491−500. (g) Malisch,
W.; Hindahl, K.; Schemm, R. Chem. Ber. 1992, 125, 2027−2029.
(h) Weber, L.; Noveski, G.; Stammler, H.-G.; Neumann, B. Z. Anorg.
Allg. Chem. 2007, 633, 994−999.
(21) Dodds, D. L.; Haddow, M. F.; Orpen, A. G.; Pringle, P. G.;
Woodward, G. Organometallics 2006, 25, 5937−5945. Unfortunately,
using LiPHIs(BH3), generated by adding n-BuLi to a mixture of PH2Is
and BH3-THF, did not improve the selectivity of this reaction.
(22) (a) Zou, J.; Berg, D. J.; Oliver, A.; Twamley, B. Organometallics
2013, 32, 6532−6540. (b) Yakhvarov, D.; Hey-Hawkins, E.; Kagirov,
K
DOI: 10.1021/acs.organomet.7b00515
Organometallics XXXX, XXX, XXX−XXX