Mixed anhydride complexes of rhodium(i) and ruthenium(ii)-their synthesis and ligand rearrangements

Article abstract of DOI:10.1039/c3dt52552j

The coordination chemistry and solution behaviour of Rh(i) and Ru(ii) complexes derived from mixed anhydride ligands of carboxylic acids and phosphorus acids were explored. Similar to the free ligand systems, mixed anhydride complexes rearranged in solution via a number of pathways, with the pathway of choice dependent on the mixed anhydride employed, the auxiliary ligands present as well as the nature of the metal centre. Plausible mechanisms for some of the routes of rearrangement and by-product formation are proposed. Where stability allowed, new complexes were fully characterised, including solid state structures for four of the unrearranged mixed anhydride complexes and two of the interesting rearrangement products.

Full text of DOI:10.1039/c3dt52552j

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Mixed anhydride complexes of rhodium(I) and
ruthenium(II) – their synthesis and ligand
rearrangements†
Cite this: Dalton Trans., 2014, 43,
3479
Jacorien Coetzee,a Graham R. Eastham,b Alexandra M. Z. Slawina and
David J. Cole-Hamilton*a
The coordination chemistry and solution behaviour of Rh(I) and Ru(II) complexes derived from mixed
anhydride ligands of carboxylic acids and phosphorus acids were explored. Similar to the free ligand
systems, mixed anhydride complexes rearranged in solution via a number of pathways, with the pathway
of choice dependent on the mixed anhydride employed, the auxiliary ligands present as well as the nature
of the metal centre. Plausible mechanisms for some of the routes of rearrangement and by-product for-
mation are proposed. Where stability allowed, new complexes were fully characterised, including solid
state structures for four of the unrearranged mixed anhydride complexes and two of the interesting
rearrangement products.
Received 16th September 2013,
Accepted 24th December 2013
DOI: 10.1039/c3dt52552j
www.rsc.org/dalton
Introduction
The coordination chemistry of mixed anhydrides of the
general formula [R2POC(O)R′] and their application in catalysis
remain a rather uncharted area of chemistry with only a small
number of reports in the literature relating to this topic.1–9
Earlier, we reported that mixed anhydride ligands derived
from diphenylphosphinous acid and acrylic acids react readily
with [{RhCl(cyclooctene)2}2] to form complexes of the general
formula [{RhCl(Ph2PO2CCRvCR′R″}2], containing the allylic-
mixed anhydride bound in a chelating manner via the phos-
phorus atom and the CvC double bond.1,3 In a later study, we
showed that these ligands can be used for the regioselective
hydrogenation of the parent acrylic acid when reacted with
hydrogen in the presence of rhodium based precursors such
as Wilkinson’s catalyst.8 Within these catalytic systems the
substrate is initially fixed to the catalyst by a phosphorus ester
bond and then released, following hydrogenation, by a base
catalysed transesterification reaction at phosphorus involving
a fresh substrate molecule (Scheme 1). Based on the principle
of microscopic reversibility the reverse reaction, i.e. the
Scheme 1 Mechanism for the catalytic hydrogenation of 3-methylbut-
2-enoic acid using a Rh(I) mixed anhydride based catalyst (P = PPh3).
aEaStCHEM, School of Chemistry, Purdie Building, University of St. Andrews,
St. Andrews, Fife Scotland KY16 9ST, UK. E-mail: djc@st-andrews.ac.uk;
Fax: +44 (0)1334 463808; Tel: +44 (0)1334 463805
bLucite International Technology Centre, P.O. Box 90, Wilton, Middlesborough,
Cleveland, England TS6 8JE, UK. E-mail: graham.eastham@lucite.com;
dehydrogenation of saturated mixed anhydrides, should in
theory also be possible. This should proceed through catalytic
C–H activation and may provide a potential new route to the
functionalisation of otherwise inert C–H bonds.
Until recently, mixed anhydride ligands have perhaps been
best known for their propensity to undergo spontaneous and
Fax: +44 (0)1642 447119; Tel: +44 (0)1642 447109
†Electronic supplementary information (ESI) available: Additional figures, crys-
tallographic discussion and data tables. CCDC 960849–960853. For ESI and crys-
tallographic data in CIF or other electronic format see DOI: 10.1039/c3dt52552j
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irreversible condensation and rearrangement reactions in the
uncoordinated state; a characteristic that limits their appli-
Results and discussion
cation in catalysis.7,10–12 In addition, Rh(I) and Ru(II) com- All new species were identified and characterised using stan-
plexes of Ph2PO2CCHvCHR (R = H or Me), are also known to dard analytical techniques. The 31P{1H} NMR data collected
undergo metal promoted rearrangements to give complexes for compounds 9–26 are summarised in Table 1, with
containing Ph2POPPh2 (POP).7,9 Despite this, mixed anhy- additional analytical data listed in the Experimental section
drides have shown promise as ligands in catalysts for isomeris- and ESI.† In addition, the crystal and molecular structures of
ing13 and asymmetric hydroformylation,14 enantioselective complexes 16–18 and 23–25 were determined by single crystal
hydrogenation reactions15 and as precursors to complex diaryl X-ray-diffraction and are given in the text, but not described in
phosphonate esters for medicinal application.16
detail (for a discussion see the ESI†).
We have recently shown that mixed anhydrides derived
from propanoic acid, sodium propanoate or phenylacetic acid
can be stabilised by changing from chlorodiphenylphosphine
as the phosphorus containing precursor to chlorophosphites
Rh(I) complexes with class I mixed anhydride ligands
Rh(I) Complexes with PPh3 auxiliary ligands. Although
during their preparation.17 By this approach, a series of earlier studies with mixed anhydrides derived from acrylic acid
mixed anhydrides was prepared that can be divided into three and vinylacetic acid have indicated metal complexes of steri-
classes, namely (I) those devoid of electron withdrawing cally undemanding mixed anhydrides to be prone to
atoms (with the exception of the acyloxy group) and steric bulk rearrangement,7,9 the known simple mixed anhydride (propa-
in the vicinity of the phosphorus (1–2), (II) those with electron noyloxy)diphenylphosphine (1)18 was still evaluated as a ligand
withdrawing atoms, but little steric bulk at P (3–4) and (III) to Rh(I). Thus, 1 was reacted in a 1 : 1 ratio with [RhCl(PPh3)3]
those with both electron withdrawing atoms at P and nearby in thf at −10 °C for 80 min. Not surprisingly, NMR analysis of
tert-butyl groups which shelter the phosphorus from neigh- the crude product mixture revealed the presence of a signifi-
bouring molecules (5–8; Fig. 1). Within this series, ligands cant amount of the rearrangement product [RhCl(PPh3)(POP)]
belonging to the third category are superior in terms of (9) (where POP = Ph2POPPh2),4,7 at the complete expense of
stability.17
the desired complex, [RhCl(PPh3)2(Ph2POC(O)CH2CH3)] (10)
Herein, we wish to report on the coordination chemistry of [Scheme 2(i)]. Compound 9 was detected by the presence of
all three classes of these ligands in Rh(I) and Ru(II) complexes, three sets of doublets of doublets of doublets at δ 106.1, δ 80.9
with emphasis on their stability in solution and various path- and δ 24.7 in the 31P{1H} NMR spectrum; a spectral profile
ways of rearrangement.
which is in good agreement with the literature values reported
for 9.7 Compound 9 also represented the major by-product in
earlier studies involving [RhCl(PPh3)3] and mixed anhydrides
of vinylacetic or acrylic acid, with its formation suggested to be
metal promoted with disruption of the ligand following
coordination to the metal centre.4,7 Shorter reaction times
[40 min, Scheme 2(ii)] did not alter the products but changing
from thf to dichloromethane as reaction solvent resulted in
31P{1H} NMR spectra revealing, in addition to 9, a doublet of
triplets at δ 138.2 (JP–Rh = 213.4 Hz and JP–P = 37.5 Hz) and a
doublet of doublets at δ 32.6 (JP–Rh = 128.7 Hz and JP–P
=
37.5 Hz) that correspond well with trace amounts of trans-
[RhCl(PPh3)2{Ph2POC(O)CH2CH3}] (10a) [Scheme 2(iii)]. The
observed coupling behaviour is consistent with coordination
of 1 only through phosphorus, and is comparable with
data reported for the related complex [RhCl(PPh3)2-
(PO2CCH2CH2CH3)] [δ 131.0 (dt) and δ 33.0 (dd)].8
Reacting [RhCl(PPh3)3] with an excess of
1 (1 : 2 or
1 : 6 mole ratio) led to the isolation of a mixture of rearrange-
ment products which could not be separated. Species detected
in the 31P{1H} NMR spectra included [RhCl(PPh3)(POP)] (9)
and a considerable amount of the free ligand disproportiona-
tion product, Ph2PP(O)Ph2. Furthermore, strong evidence for
the presence of an additional new complex [RhCl{Ph2POC(O)-
CH2CH3}(POP)] (11), bearing 1 intact, was also observed in the
31P{1H} NMR spectrum [with a ratio 9 : 11 of 1 : 1.4 Scheme 2(iv)].
Resonances at δ 121.3 (dt), δ 107.6 (ddd) and δ 82.8 (dt) could
be assigned tentatively to 11.
Fig. 1 The three classes of mixed anhydride ligands 1–8.
3480 | Dalton Trans., 2014, 43, 3479–3491
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Table 1 31P{1H} NMR data for the Rh(I) complexes 9–26
Chemical shifts δ (ppm)b
PA PB
Coupling constants J (Hz)
Rh–PA Rh–PB Rh–PC PA–PB PA–PC PB–PC
Compounda
PC
9 [RhCl(PAPh3)(Ph2PBOPCPh2)]
24.7 (ddd)
32.6 (dd)
31.1 (ddd)
121.3 (ddd)
80.9 (ddd) 106.1 (ddd) 132.2 127.0
138.2 (dt) 128.7
129.7 (ddd) 133.2
107.6 (ddd) 158.9 124.7
167.8
213.4
175.9
163.3
380.9 121.8
37.5
40.9 383.6
450.0 28.9 124.7
29.7
—
17.3
10a trans-[RhCl(PAPh3)2{Ph2PCOC(O)CH2CH3}]
10b cis-[RhCl(PA\BPh3)2{Ph2PCOC(O)CH2CH3}]
11 [RhCl(Ph2PBOPCPh2){Ph2PAOC(O)CH2CH3}]
12 [RhCl(PA\BPh3)2(Ph2PCOPDPh2)][Cl]
—
—
—
c
c
82.8 (dt)
Accurate values can only be determined by simulation, for accurate assignments see
literature.7
13 [{RhCl(Ph2PAOC(O)CH2CH3)}2]
135.1
—
—
—
228.1
—
—
—
—
—
14 [RhCl(Ph2PA\BOC(O)CH2CH3)2] (P,O coordinated)d 139.5 (bm) 177.5 (bm)
Fluxional – not determined due to line
broadening
15 [{RhCl(Ph2PAOPAPh2)}2]
16 [{RhCl{(Ph2PAO)2H}(C(O)CH2CH3)}2]
17 [RuCl2(Ph2PAOC(O)CH2CH3)2]
18 [{RuCl2(Ph2PAOC(O)CH2CH3) (Ph2PBOH)}2]
19 [RhCl(PAPh3)2(3)]e
87.1 (d)
83.7 (d)
188.6 (s)
—
—
—
132.5 (d)
—
—
—
—
—
—
—
161.3
160.5
—
—
—
—
—
—
—
—
—
—
—
—
321.8
260.5
322.5
261.1
331.3
331.8
332.7
334.0
—
—
—
44.2
—
—
—
—
—
—
—
—
—
—
—
—
188.3 (d)
36.1 (dd)
21.7 (dd)
35.2 (dd)
20.6 (ddd)
34.4 (ddd)
33.8 (ddd)
34.9 (ddd)
33.8 (ddd)
—
134.5 (dt)
79.9 (dt)
133.9 (dt)
132.7
113.0
132.9
46.6
20 [{RhCl(PAPh3)2(PCOPC)}2]f
21 [RhCl(PAPh3)2(4)]e
—
—
19.0
46.2
17.2
44.3
48.3
46.3
46.3
22 [{RhCl(PA\BPh3)2(PCOPC)}2]g
23 [RhCl(PA\BPh3)2(5)]e
20.5 (ddd)
84.7 (ddd) 113.3 111.3
370.5
349.5
347.9
344.3
346.9
21.2
37.2 (ddd) 129.3 (ddd) 138.2 138.2
38.2 (ddd) 124.9 (ddd) 135.3 135.3
37.8 (ddd) 131.1 (ddd) 134.9 134.9
38.7 (ddd) 127.0 (ddd) 134.9 134.9
44.3
48.3
46.3
46.3
24 [RhCl(PA\BPh3)2(6)]e
25 [RhCl(PA\BPh3)2(7)]e
26 [RhCl(PA\BPh3)2(8)]e
a Note: identical labels given to different phosphorus atoms present within the same complex indicate magnetic equivalence. b Chemical shifts
relative to 85% H3PO4 (CD2Cl2, 25 °C) with multiplicity given in parenthesis. c Could not be measured owing to extensive overlap of resonances in
the relevant region. d Significant line broadening observed as a result of an unresolved dynamic process. e Phosphorus present in coordinated
(acyl)phosphites listed as PC. f PCOPC represents 4,4′-oxydinaphtho[2,1-d:1′,2′-f][1,3,2]dioxaphosphepine. g PCOPC represents 6,6′-oxydibenzo[d,f]-
[1,3,2]dioxaphosphepine.
Scheme 2 Reaction conditions: (i) 1 (1 : 1 ratio), thf, −10 °C, 80 min.; (ii)
1 (1 : 1 ratio), thf, −10 °C, 40 min.; (iii) 1 (1 : 1 ratio), CH2Cl2, −10 °C,
30 min.; (iv) 1 in excess (1 : 2 or 1 : 6 mole ratio), CH2Cl2, −10 °C, 1 h.
Scheme 3 Species observed in the 31P{1H} NMR spectra recorded (i)
during in situ NMR experiments, 1 (1 : 1.2 mole ratio),CDCl3, −10 °C; (ii)
for a sample taken of the same solution after standing for 2 h at −10 °C.
In order to determine whether [RhCl(PPh3)2{Ph2POC(O)–
CH2CH3}] (10) perhaps forms as the major product during the
early stages of the reaction but then rapidly decays to form 9,
low temperature in situ NMR studies were performed. A solu-
tion of 1 in deuterated chloroform was added immediately after addition, a set of resonances corresponding to the ionic
dissolution to solid [RhCl(PPh3)3] at −30 °C. Without delay, a
small volume of the resulting solution was transferred to an
NMR tube and analysed by low temperature (−10 °C) 31P{1H}
NMR spectroscopy at regular intervals (every 5 min for 50 min).
Although the measured spectra were very different from
complex, [Rh(PPh3)2(Ph2POPPh2)][Cl], (12) was also observed
[Scheme 3(i)].
In the 31P{1H} NMR spectrum of the cis-isomer 10b, co-
ordinated 1 gives rise to a doublet of doublets of doublets at
δ 129.7 (JP–Rh = 175.9 Hz, JP–Ptrans = 383.6 Hz and JP–Pcis
=
those from earlier attempts, surprisingly little variation was 40.9 Hz), slightly upfield from those of the trans analogue 10a.
observed between spectra within the series. Despite the pres-
ence of Ph2PP(O)Ph2, significant amounts of the desired
Unfortunately, owing to the presence of several resonances
from PPh3 containing products within the same 31P{1H} NMR
complex
trans-[RhCl(PPh3)2{Ph2POC(O)CH2CH3}]
(10a), spectrum, extensive overlap of resonances within the region
together with the related cis-isomer (10b), were observed. In
δ 24–δ 35 is observed. As a result, resonances corresponding to
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the PPh3 ligand cis to 1 in 10b could only be assigned the product mixture also contained a significant amount
tentatively. (∼71%) of the monomeric complex, [RhCl(Ph2PO2CCH2CH3)2]
The chemically equivalent, but magnetically inequivalent (14), where one of the (propanoyloxy)diphenylphosphine (1)
phosphorus atoms for the POP and PPh3 ligands in 12, represent ligands is coordinated in a chelating fashion via both the
an AA′XX′ spin system, giving rise to second-order spectral phosphorus atom and the carbonyl oxygen, while the second
effects in the 31P{1H} NMR spectrum. Complex resonances at δ is coordinated only via phosphorus. Bonding of this type,
98.0 and δ 26.4 could be assigned tentatively to the POP and although not favoured in the presence of superior donors, is
PPh3 ligands, respectively. Unfortunately, the signal to noise not uncommon for such complexes and has been reported for
ratios in all spectra recorded during in situ NMR experiments the cationic complex [Rh(PPh3)2(Ph2PO2CCHvCMe2)][SbF6].6
were too low to allow for a better interpretation of these signals.
However, a very similar spectral profile has been reported for determination of the relevant JRh–P and JP–P values, was compli-
[Rh(PPh3)2(Ph2POPPh2)][PF6] which contains the same cation.7
cated by substantial line broadening as a consequence of an
The unambiguous NMR assignments of 14, as well as the
Since no major product decay was observed during the unresolved dynamic process involving the free and co-
in situ NMR experiment, the original reaction mixture was ordinated carbonyl oxygens of ligands 1. However, the high
allowed to stand for a further 70 min at −10 °C, and again ana- field chemical shift of the broad multiplet observed at δ 177.5
lysed by 31P{1H} NMR spectroscopy. The spectrum obtained in the 13P{1H} NMR is consistent with the incorporation of 1 in
this time differed significantly from earlier spectra, with a five membered metallocycle by bonding through both phos-
signals from both isomers of 10 as well as compound 12 com- phorus and oxygen.19 Likewise, the chemical shift observed for
pletely absent, while signals corresponding to the familiar a broad multiplet at δ 139.5 is consistent with coordination of
rearrangement product 9 [Scheme 3(ii)] were now present. 1 to a Rh(I) centre only via phosphorus. Despite their apparent
These observations suggest that such rearrangements may be superior stability, complexes 13 and 14 still undergo rearrange-
heavily dependent on the reaction time, concentration and ment in solution to afford the POP dimer [{RhCl(POP)}2] (15,
temperature. Moreover, the detection of 10a and 10b as inter- ∼11%) and more interestingly, [{RhCl{(Ph2PO)2H}(C(O)-
mediates prior to the formation of 9 supports the premise that CH2CH3)}2] (16, ∼11%); a diphenylphosphinito dimer contain-
the rearrangement is metal promoted and not the result of a ing propanoyl moieties directly coordinated to the Rh(III)
direct reaction between Ph2PP(O)Ph2 and [RhCl(PPh3)3].
centres (yields based on NMR intensities; Scheme 4). Although
Rh(I) complexes devoid of PPh3 auxiliary ligands. In light of 15 could only be assigned tentatively using 31P{1H} NMR spec-
the difficulties experienced with the metal promoted troscopy [δ 87.1 (d)], the identity of 16 [δ 83.7 (d)] could be veri-
rearrangement of 1, the possibility that PPh3 may facilitate fied crystallographically (Fig. 2; for discussion see ESI†).
such rearrangements was considered. A Rh(I) precursor devoid
of any PPh3 ligands, such as the chloro-bridged rhodium
dimer [{RhCl(COE)2}2] (where COE = cyclooctene), was there-
fore employed. In earlier work, this complex had proved highly
successful in the preparation of Rh(I) complexes of higher sub-
stituted mixed anhydrides.3 Treatment of a solution of [{RhCl-
(COE)2}2] in dichloromethane with four equivalents of 1 at
−10 °C for 30 min, after work-up, gave a mixture which could
not be separated, containing minor amounts (∼7%) of the
desired unrearranged dimer [{RhCl(Ph2PO2CCH2CH3)2}2] (13;
Scheme 4); detected as a doublet at δ 135.1 in the 31P{1H}
NMR spectrum. This was a significant improvement on earlier
attempts, since the PPh3 containing Rh(I) analogue 10 was
only observed in situ and could not be isolated. Furthermore,
Fig. 2 Molecular structure of 16 with thermal ellipsoids set at 50%
probability. Hydrogen atoms (with the exception of O–H) and solvent
molecules are omitted for clarity. Selected bond lengths and angles:
Rh(1)–C(1) 1.991(2), Rh(1)–Cl 2.4522(10), Rh(1)–P(1) 2.2517(9), Rh(1)–P(2)
2.2508(8), O(1)–C(1) 1.186(3), P(1)–O(2) 1.5574(18), P(2)–O(3) 1.5354(17),
Rh(1)–C(1)–O(1) 125.98(19), Rh(1)–C(1)–C(2) 111.95(16), P(1)–Rh(1)–P(2)
88.24(3), Cl(1)–Rh(1)–Cl(1)’ 83.24(2), P(2)–Rh(1)–Cl(1) 92.85(2), P(1)–
Scheme 4 Product mixture obtained for reactions of [{RhCl(COE)2}2]
with 1. Conditions: (i) 1 (4 equivalents), CH2Cl2, −10 °C, 30 min.
Rh(1)–Cl(1)’ 93.56(2), P(1)–Rh(1)–Cl(1) 170.73(2), C(1)–Rh(1)–P(1)
89.94(7), C(1)–Rh(1)–P(2) 91.50(7), C(1)–Rh(1)–Cl(1) 99.23(7).
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Scheme 5 Proposed mechanism for the formation of rearrangement product 15 in the absence of water or alcohol ( left) and 16 in the presence
of water or alcohol ( right).
Numerous reports on transition metal complexes contain- magnetically equivalent phosphorus atoms give rise to a sharp
ing hydrogen bonded [{Ph2PO}2H] ligands, similar to 16, exist singlet at δ 188.6, very high field in comparison to the values
in the literature with several routes to their preparation observed for coordinated 1 in the related Rh(I) complexes [see
described.20–24 In the majority of cases, such complexes are ESI, Fig. S1(a)†]. This serves as further confirmation for the
prepared either by the reaction of metal complexes with diphe- coordination of 1 in a chelating fashion, as the resultant five
nylphosphinous acid or by the hydrolysis of metal complexes membered metallocycle would lead to a high field shift in the
of
chlorodiphenylphosphine
or
diphenylphosphinite. phosphorus resonances.19 Furthermore, in the IR-spectrum of
Although no formal mechanistic studies have been performed, 17 the CvO bonds vibrate at a much lower frequency [single
a plausible mechanism for the rearrangement of 13 to 15 in absorption at 1649 cm−1 ν(CvO)], than that typically observed
the absence of water or alcohol, and to 16 in the presence of for such bonds [∼1700 cm−1].6,25 This is consistent with
water or alcohol is proposed in Scheme 5. All reactions were reduced double bond character as a result of coordination to a
performed under dry and inert conditions, but a water– metal centre. In contrast to the Rh(I) complexes of 1, com-
propan-2-ol mixture is employed during the preparation of, pound 17 could be isolated in high purity and yield without
[{RhCl(COE)2}2], and this may thus be the source of such trace the interference of unwanted side-reactions. Furthermore, 17
contaminants.
could also be stored in the solid state for prolonged periods of
time, provided that an inert atmosphere was maintained.
The greater stability of 17 compared to the Rh(I) analogues
comes as no surprise, since one can expect the relatively more
electron poor Ru(II) centre to be less likely to participate in any
rearrangements that necessitate oxidation of the metal centre or
nucleophilic attack on the carbonyl carbon of 1 by the metal.
Despite the enhanced stability, 17 rearranges within hours
when left standing in solution to afford the chloro-bridged
Ru(II) dimer 18, where one of the two mixed anhydrides per
Ru(II) centre has been converted to diphenylphosphinous acid
[Scheme 6(ii)]. Although no significant change in the chemical
shift of coordinated 1 is observed when 17 rearranges to 18,
the 31P{1H} NMR spectrum of 18 displays a mutual P–P coup-
ling of 44.2 Hz between coordinated 1 [δ 188.3 (d)] and the
generated Ph2POH [δ 132.5 (d); see ESI, Fig. S1(b)†].
Ru(II) complexes with class I mixed anhydride ligands
The reaction of [RuCl2(PPh3)3] with 2 equivalents of 1 gave
[RuCl2(Ph2PO2CCH2CH3)2] (17), with 1 coordinated in a chelat-
ing fashion via both the phosphorus and carbonyl oxygen
atoms [Scheme 6(i)]. This has been shown before to be the pre-
ferential mode of bonding for mixed anhydride Ru(II) com-
plexes of the general form [RuCl2(Ph2PO2CCHvRR′)2].9
In contrast to known literature examples where the P-atoms
occupy mutually trans positions, spectroscopic evidence
suggests that the P-atoms in 17 occupy positions cis with
respect to one another. In the 31P{1H} NMR spectrum of 17 the
During all initial attempts to crystallise 17 by slow diffusion
of pentane into dichloromethane or chloroform solutions of
17, orange prisms of 18 crystallised from solution instead,
allowing for its structure determination by X-ray crystallogra-
phy (Fig. 3). Single crystals of 17 could eventually be obtained
by diffusion of diethyl ether into a toluene solution of 17 at
room temperature (Fig. 4).
Scheme 6 Preparation of 17 and subsequent rearrangement to form
18. Conditions: (i) 1, (2 mole equivalents), CH2Cl2, R.T., 2 h; (ii) standing
in solution overnight.
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Rh(I) complexes with stabilised class II and III mixed
anhydride ligands
In reactions of [RhCl(PPh3)3] with mixed anhydride ligands of
the second class (Fig. 1), the desired trans-[RhCl(PPh3)2(L)]
complexes 19 (L = 3) and 21 (L = 4) were obtained as the major
products. However, similar to Rh(I) complexes of 1, complexes
19 and 21 were prone to rearrangement and as a result product
mixtures were heavily contaminated with the POP type
rearrangement products 20 and 22 (Scheme 7), which could
not be separated successfully. In contrast to the previously
observed complex [RhCl(PPh3)(POP)] (9), the POP type ligands
in complexes 20 and 22 are coordinated in a bridging rather
than chelating manner between two neighbouring Rh(I)
centres. The more rigid bond angles at the phosphorus atoms,
which are already constrained in a ring system, together with
the increased steric demands of the biphenyl and binaphthyl
containing alkoxy groups may be the cause of this observed
preference. Furthermore, the concentrations of 20 and 22 are
found to increase over time at the expense of 19 and 21 when
product mixtures are left in solution, suggesting once again
that these rearrangements are metal mediated.
Fig. 3 Molecular structure of the rearrangement product 18 with
thermal ellipsoids set at 35% probability. Hydrogen atoms (except O–H)
and solvent molecules are omitted for clarity. Selected bond lengths
and angles: Ru(1)–Cl(1) 2.379(3), Ru(1)–Cl(2) 2.486(4), Ru(1)–P(1)
2.189(4), Ru(1)–P(2) 2.227(4), Ru(1)–O(2) 2.227(8), P(1)–O(1) 1.729(9),
O(1)–C(1) 1.311(16), O(2)–C(1) 1.215(14), P(2)–O(3) 1.637(8), Ru(1)–O(2)–
C(1) 115.7(8), Ru(1)–P(1)–O(1) 100.6(3), Ru(1)–P(2)–O(3) 114.6(3), P(1)–
Ru(1)–O(2) 81.1(3), P(1)–Ru(1)–P(2) 98.43(13), P(1)–Ru(1)–Cl(1) 91.85(11),
P(1)–Ru(1)–Cl(2) 164.45(11), P(2)–Ru(1)–O(2) 179.4(3), P(2)–Ru(1)–Cl(1)
91.44(10), P(2)–Ru(1)–Cl(2) 96.40(11), Cl(1)–Ru(1)–Cl(2) 92.41(10).
In the 31P{1H} NMR spectrum of 19, coordinated 3 gives
rise to a doublet of triplets at δ 134.5, owing to coupling to
rhodium and the magnetically equivalent PPh3 ligands (JP–Rh
=
321.8 Hz, JP–P = 46.2 Hz). The latter resonate as a doublet of
doublets at δ 36.1. The observed coupling pattern confirms the
identity of 19 as the trans-complex, while the chemical shift of
coordinated 3 is consistent with bonding only through phos-
phorus. Likewise, a doublet of triplets at δ 133.9 and a broad
doublet of doublets at δ 35.2 are detected for complex 21 and
are in agreement with the values reported for [Rh(COD){(R)-
acetyl-(1,1′-binaphthyl-2,2′-diyl)phosphite}][BF4].15
In the 31P{1H} NMR spectrum of partially rearranged 19,
the bridging POP type ligand of the rearrangement product,
20, resonates as a doublet of triplets at δ 79.9 (JP–Rh
=
260.5 Hz, JP–P = 19.0 Hz), while the magnetically equivalent
PPh3 ligands are detected as a doublet of doublets at δ 21.7
Fig. 4 Molecular structure of 17 with ellipsoids set at 35% probability
and hydrogen atoms and solvent molecules omitted for clarity. Selected
bond lengths and angles: Ru(1)–Cl(1) 2.379(3), Ru(1)–Cl(2) 2.388(3),
Ru(1)–P(1) 2.182(3), Ru(1)–P(2) 2.182(3), Ru(1)–O(1) 2.169(6), Ru(1)–O(3)
2.173(6), P(1)–O(2) 1.716(6), P(2)–O(4) 1.706(7), Ru(1)–O(1)–C(1) 117.3(5),
Ru(1)–O(3)–C(4) 117.2(6), Ru(1)–P(1)–O(2) 101.8 (2), Ru(1)–P(2)–O(4)
101.9(3), P(1)–Ru(1)–O(3) 172.94(18), P(2)–Ru(1)–O(1) 173.48(15), P(1)–
Ru(1)–O(1) 80.45(16), P(2)–Ru(1)–O(3) 81.04(19), P(1)–Ru(1)–P(2)
105.93(9), O(1)–Ru(1)–O(3) 92.6(3), Cl(1)–Ru(1)–Cl(2) 168.81(8), Cl(1)–
Ru(1)–O(1) 86.92(15), Cl(1)–Ru(1)–O(3) 83.49(16), Cl(2)–Ru(1)–O(1)
86.00(15), Cl(2)–Ru(1)–O(3) 88.19(16), Cl(1)–Ru(1)–P(1) 95.11(8), Cl(1)–
Ru(1)–P(2) 91.13(10), Cl(2)–Ru(1)–P(1) 92.24(8), Cl(2)–Ru(1)–P(2)
94.94(10).
Scheme 7 Products observed for reactions of [RhCl(PPh3)3] with the
(propanoyl)phosphite ligands 3 and 4. Conditions: (i) 3 (1 : 1), CH2Cl2,
R.T., 30 min; (ii) 4 (1 : 1), CH2Cl2, R.T., 1 h.
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Fig. 5 Resonances corresponding to 22 in the 31P{1H} NMR spectrum of partially rearranged 21. In 22 mutually trans PPh3 ligands are chemically
and magnetically inequivalent (indicated as PA and PB) resulting in the observed second order spectral effects, while the P-atoms in the POP ligand
are equivalent (represented by PC).
(JP–Rh = 113.0 Hz, JP–P = 19.0 Hz). In contrast, the PPh3 ligands
In addition, these complexes could be further purified by
of the rearrangement product 22 (present in the product recrystallisation and single crystals suitable for X-ray structure
mixture of 21) are magnetically inequivalent, owing to the chir- determinations could be obtained for complexes 23–25 (Fig. 6
ality of the bridging POP ligand. The chemical shifts of the and 7). In the asymmetric unit of 23, two molecules of 23 are
PPh3 are, however, very similar and 22 therefore represents an co-crystallised with at least eight dichloromethane molecules,
ABMX spin system (A and B = PPh3, M = POP and X = Rh) and as a result, the determined structure is heavily disordered.
which gives rise to the more complex second order spectrum Owing to the poor quality of this data set, the structure of 23 is
depicted in Fig. 5. For both 20 and 22, the observed chemical only given in the ESI (see Fig. S5†).
shifts, coupling patterns and coupling constants are consistent
with the assigned structures, where a POP type ligand is co-
ordinated in a bridging fashion between two trans-[RhCl-
(PPh3)2] entities.
For Rh(I) complexes of the more stable (propanoyl)phos-
phites 5–6, and (phenylacetyl)phosphites 7–8 (which have
sterically demanding tert-butyl groups in the vicinity of their
phosphorus atoms) rearrangements of this type were not
observed. The trans-[RhCl(PPh3)2(L)]complexes 23–26 could be
prepared in high yield by reacting solutions of ligands 5, 6, 7
or 8 in dichloromethane with [RhCl(PPh3)3] at room tempera-
ture for 1 h. In most cases, crude products could be success-
fully purified by washing with copious amounts of hexane
[Scheme 8(i) and (ii)].
Fig. 6 Molecular structure of 24 with thermal ellipsoids set at 50%
probability. Hydrogen atoms are omitted for clarity. Selected bond
lengths and angles: Rh(1)–P(1) 2.140(2), Rh(1)–P(2) 2.338(2), Rh(1)–P(3)
2.310(2), Rh(1)–Cl(1) 2.384(2), P(1)–O(1) 1.643(6), P(1)–O(3) 1.637(6),
P(1)–O(4) 1.597(6), P(1)–Rh(1)–P(2) 97.71(8), P(1)–Rh(1)–P(3) 98.41(8),
P(1)–Rh(1)–Cl(1) 161.18(9), P(2)–Rh(1)–Cl(1) 84.46(8), P(3)–Rh(1)–Cl(1)
84.13(8), P(2)–Rh(1)–P(3) 159.96(9), Rh(1)–P(1)–O(1) 113.8(2), Rh(1)–
Scheme 8 Reaction scheme for the preparation of complexes 23–26
and their subsequent rearrangement to complexes 27 and 28. Con-
ditions: (i) 5 or 7, CH2Cl2, R.T., 1 h; (ii) 6 or 8, CH2Cl2, R.T., 1 h; (iii) stand-
ing in solution at R.T. for 1–2 days.
P(1)–O(3) 111.7(2), Rh(1)–P(1)–O(4) 123.9(2), O(1)–P(1)–O(3) 99.4(3),
O(1)–P(1)–O(4) 102.1(3), O(3)–P(1)–O(4) 102.7(3), P(1)–O(1)–C(1)
133.0(5), O(1)–C(1)–O(2) 123.0(8), O(2)–C(1)–C(2) 127.1(8), O(1)–C(1)–
C(2) 109.9(7).
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phosphite and the PPh3 ligands are equal in magnitude and
the phosphorus resonance from the (acyl)phosphite ligand
(PC) is observed as an apparent doublet of triplets at δ 124.9
(JP–Rh = 331.3 Hz, JPC–PA = JPC–PB = 48.3 Hz). The PPh3 ligands
give rise to an ABMX pattern of doublets of doublets of doub-
lets at δ 33.8 and δ 38.2, respectively. In addition to mutual
trans coupling (JPA–PB = 347.9 Hz), these ligands display
equal coupling to both Rh (JPA–Rh = JPB–Rh = 135.3 Hz) and PC
(JPA–PC = JPB–PC = 48.3 Hz) and as a result the observed coup-
ling pattern is highly symmetrical with the close proximity of
their chemical shifts resulting in the pattern depicted in Fig. 8.
In solution, however, these complexes undergo complete
rearrangement within 1 to 2 days via a mechanism different
from those previously observed. Instead of POP type com-
plexes, a variety of highly symmetrical rearrangement products
is obtained with the known carbonyl complex trans-[RhCl(CO)-
(PPh3)2] (27)26 representing the major product of rearrange-
ment. Large quantities of the latter crystallised, as either
yellow prisms or yellow needles from solutions of 23–26 when
left standing for a period of 1 to 2 days. The structure of
known 27 could also be confirmed by X-ray crystallography. In
addition to 27, the known dimeric compound [{RhCl(PPh3)2}2]
(28)27 is also observed as a product of decay and often crystal-
lises as burgundy prisms from solutions of 23–26 following
rearrangement [Scheme 8(iii)].
Although no formal mechanistic studies were conducted, it
is plausible that the formation of 27 involves decarbonylation
of coordinated ligands 5–6 and 7–8 via a dimeric metal acyl
intermediate. In the initial stages of the rearrangement, com-
plexes 23–24 may dimerise to form mixtures of [{RhCl-
(PPh3)2}2] and [{RhCl(PPh3)(L)}2] (where L = 5–6). While the
former is very insoluble and as a consequence crystallises from
solution, the latter can undergo further rearrangement to
generate 27. Scheme 9 depicts the proposed mechanism of
rearrangement for (propanoyl)phosphite complexes 23 and 24
only, but it is possible that a similar mechanism exists for
complexes 25–26. Migratory deinsertion of CO is not uncom-
mon and similar decarbonylation pathways to the one postu-
lated here have been described in the literature.28–30 In
addition, the detection of phosphonates in the final product
Fig. 7 Molecular structure of 25 with thermal ellipsoids set at 50%
probability. Hydrogen atoms and solvent molecules are omitted for
clarity. Rh(1)–P(1) 2.1412(17), Rh(1)–P(2) 2.3274(18), Rh(1)–P(3)
2.3040(18), Rh(1)–Cl(1) 2.3898(17), P(1)–O(1) 1.643(5), P(1)–O(3) 1.620(5),
P(1)–O(4) 1.609(5), O(1)–C(1) 1.406(9), C(1)–O(2) 1.197(9), P(1)–Rh(1)–
P(2) 98.60(6), P(1)–Rh(1)–P(3) 96.29(7), P(1)–Rh(1)–Cl(1) 173.88(7), P(2)–
Rh(1)–Cl(1) 82.62(6), P(3)–Rh(1)–Cl(1) 82.30(6), P(2)–Rh(1)–P(3)
164.89(6), Rh(1)–P(1)–O(1) 113.12(17), Rh(1)–P(1)–O(3) 114.97(18), Rh(1)–
P(1)–O(4) 121.55(18), O(1)–P(1)–O(3) 100.6(3), O(1)–P(1)–O(4) 99.5(3),
O(3)–P(1)–O(4) 104.1(3), P(1)–O(1)–C(1) 133.2(5).
Complexes 23–25 all display very similar behaviour in solu-
tion and 31P{1H} NMR spectra recorded for these compounds
are almost identical with very little variation among the com-
plexes in terms of their chemical shifts and coupling constants.
Similar to complex 22, the PPh3 ligands in complexes 23–25 are
chemically inequivalent with chemical shifts very close in value,
once again leading to second order spectral effects.
Fig. 8 represents the 31P{1H} NMR spectrum of 25; an
example of the typical spectral profile associated with these
complexes. Coupling constants between the coordinated (acyl)-
Fig. 8 31P{1H} NMR spectrum of complex 25, representing an example
of the typical spectral profile observed for complexes of the form [RhCl-
(PPh3)2(L)] where L denotes ligands 5, 6, 7 or 8.
Scheme 9 Proposed mechanism for the formation of Rh(I) CO com-
plexes by the decarbonylation of (propanoyl)phosphite ligands 5–6.
3486 | Dalton Trans., 2014, 43, 3479–3491
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mixtures by 31P{1H} NMR spectroscopy are in support of the Spectrometry Service Centre at the University of St. Andrews
proposed mechanism.
using either of a Micromass GCT EI/CI or a Micromass LCT ES
instrument.
Single crystal X-ray structure determinations
Experimental
General materials, methods and instruments
A summary of the crystal data collection and refinement para-
meters of compounds 16–18 and 23–25 can be found in the
Reactions were carried out under dinitrogen gas (N2, passed ESI.† Data sets were collected on a Rigaku Mo MM007 (dual
through a column of CrII adsorbed on silica) using standard port) high brilliance diffractometer with graphite monochro-
Schlenk, vacuum-line and cannula techniques. All glassware mated MoKα radiation (λ = 0.71075 Å). The diffractometer is
was flame-dried under vacuum. Triethylamine (NEt3) and fitted with Saturn 70 and Mercury CCD detectors and two
chlorodiphenylphosphine (Ph2PCl) were purchased from XStream LT accessories. Data were collected and processed
Aldrich and distilled under N2 prior to use. Before distilling, using CrystalClear (Rigaku).34 Neutral atom scattering factors
the NEt3 was dried over potassium hydroxide (KOH) pellets. were taken from Cromer and Waber.35 Anomalous dispersion
Sodium propanoate was also purchased from Aldrich and effects were included in Fcalc;36 the values for Δf ′ and Δf ″
dried azeotropically with toluene before use. Cyclooctene, tri- were those of Creagh and McAuley.37 The values for the mass
phenylphosphine, paraformaldehyde, sodium tertiarybutoxide attenuation coefficients are those of Creagh and Hubbell.38 All
and isopropanol were purchased from Aldrich and used as calculations were performed using the CrystalStructure39 crys-
received. Propanoic acid, purchased from BDH laboratories, tallographic software package except for refinement, which
was dried over Na2CO3 and distilled under N2 prior to use. All was performed using SHELX-97.40 All the structures were
gases were purchased from BOC gases. [RhCl(PPh3)3] was pre- solved using direct, heavy-atom Patterson or conventional
pared from [RhCl3·3H2O] and PPh3, while [RuCl2(PPh3)3] was difference Fourier methods. All non-hydrogen atoms were
prepared from [RuCl3·3H2O] and PPh3, using standard litera- refined anisotropically by full-matrix least squares calculations
ture procedures.31,32 [RhCl3·3H2O] was purchased from either on F2 using SHELX-97. The hydrogen atoms were fixed in cal-
Engelhard or Alfa Aesar and [RuCl3·3H2O] from Strem Chemi- culated positions. Figures were generated with X-seed41,42 and
cals. [{RhCl(COE)2}2] (where COE = cyclooctene) was prepared POV Ray for Windows, with the displacement ellipsoids at 50%
from [RhCl3·3H2O] and cyclooctene using a literature pro- probability level unless stated otherwise. Further information
cedure.33 Ligands 1–8 were prepared using the previously is available on request from Prof. Alexandra M. Z. Slawin at the
described methods.17
School of Chemistry, University of St. Andrews.
Toluene, thf, diethyl ether and hexane, purchased from
Fisher Scientific, were dried using a Braun Solvent Purification
Synthetic procedures
System and degassed by additional freeze–pump–thaw cycles A description of all attempts to prepare and isolate compounds
when deemed necessary. Methanol and ethanol, purchase 10 and 13 can be found in the ESI,† together with details on
from Aldrich, were distilled under nitrogen from magnesium. the formation of the rearrangement product 16.
Deuterated dichloromethane and chloroform were purchased
[RuCl2(Ph2PO2CCH2CH3)2], 17. A solution of 1 (0.21 g,
from Aldrich and dried over phosphorus pentoxide (P2O5), 0.80 mmol) in dichloromethane (5 ml) was added to a solution
degassed via three freeze–pump–thaw cycles and trap-to-trap of [RuCl2(PPh3)3] (0.34 g, 0.35 mmol) in dichloromethane
distilled prior to use.
(10 ml) at room temperature. Upon addition the reaction
NMR spectra were recorded on Bruker Avance 300 FT or mixture colour immediately became lighter until finally a
Bruker Avance II 400 MHz spectrometers (1H NMR at bright orange solution was observed. The reaction mixture was
300/400 MHz, 13C{1H} NMR at 75/100 MHz and 31P{1H} NMR allowed to stir at room temperature for 2 h after which the
at 121/162 MHz) with chemical shifts δ reported relative to mixture was concentrated and the product precipitated by the
tetramethylsilane (TMS) (1H, 13C{1H}) or 85% H3PO4 (31P{1H}) addition of hexane (20 ml). The resulting light orange precipi-
1
as external reference. H and 13C{1H} NMR spectra were refer- tate was then isolated, washed with hexane (2 × 20 ml) and
enced internally to deuterated solvent resonances which were dried in vacuo to yield the analytically pure product as a bright
referenced relative to TMS.
light orange solid (yield: 0.21 g, 87%). Single crystals in the
Solid state IR spectra were recorded using pressed KBr form of orange platelets suitable for analysis by single crystal
pellets on a Perkin Elmer Spectrum GX IR spectrometer. X-ray diffraction could be obtained by slow diffusion of diethyl
Elemental analysis were performed by the University of ether into a toluene solution of 17 at room temperature. Anal.
St. Andrews microanalytical service using
CHNS/O microanalyser. Melting points were determined on a 51.9, H 4.0. H NMR (400 MHz, CDCl3): δH = 1.44 (t, 3H, J =
a Carlo Erba Calculated (%) for C30H30Cl2O4P2Ru: C 52.3, H 4.4; Found C
1
3
3
Gallenkamp apparatus and are uncorrected. Mass spectra were 7.4 Hz; CH3), 2.98 (q, 2H, J = 7.4 Hz; CH2), 7.20–7.42 (m, 20H;
recorded either by the EPSRC National Mass Spectrometry Ph). 13C{1H} NMR (100 MHz, CDCl3): δC = 9.6 (s; –CH3), 28.7 (s;
Service Centre, Swansea on a Thermofisher LTQ Orbitrap XL –CH2–), 127.8 (m, JC–P = 5.7 Hz; PPh–Cmeta), 131.7 (s; PPh–
high resolution instrument coupled to an Advion TriVersa Cpara), 133.0 (m, JC–P = 5.7 Hz; PPh–Cortho), 134.8 (d, JC–P
=
1
NanoMate electrospray infusion system or by the Mass 56.0 Hz; PPh–Cipso), 179.4 (s; CvO). 31P{1H} NMR (161 MHz,
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Dalton Transactions
CDCl3): δP = 188.6 (s; P). IR (KBr): ˜ν = 3054 [w, sp2 ν(C–H)], obtained as an orange solid which, despite representing the
2940 [w, sp3 ν(C–H)], 1649 [st, ν(CvO)], 1434–1364 [st, major product, was contaminated by the rearrangement
Ar ν(CvC)], 694 [m, ν(P–O)]. ES-MS: m/z (%) = 653 (100) product 22. This product could not be separated from 21,
[M − Cl]+.
using standard purification techniques, without effecting
1
[{RuCl2(Ph2PO2CCH2CH3)(Ph2POH}2], 18. Compound 17 further rearrangement. For complex 21 – H NMR (300 MHz,
3
although stable in the solid state, rearranges to the chloro- CD2Cl2): δH = 0.91 (t, 3H, J = 6.6 Hz; CH3), 1.40 (m, 1H; CH2),
bridged Ru(II) dimer 18 when left standing in solution. Single 1.61 (m, 1H; CH2), 7.16–8.11 (m, 42H, Ph). 13C{1H} NMR
crystals of 18 suitable for X-ray analysis were obtained as (75 MHz, CD2Cl2): δC = 8.8 (s; CH3), 28.4 (s; CH2), 120.7 (s),
orange prisms during initial attempts to crystallise 17 by 122.5 (s), 123.3 (s), 123.9 (s), 125.4 (s), 125.8 (s), 126.6 (s),
vapour diffusion of pentane into a chloroform-d1 solution of 127.1 (s), 127.5 (s), 127.7 (d, JC–P = 4.8 Hz; PPh–Cmeta), 128.8
3
1
the 17 at room temperature. H NMR (300 MHz, CDCl3): δH
=
=
(s), 129.1 (s), 129.6 (s; PPh–Cpara), 129.8 (s), 130.4 (s), 131.4 (s),
3
3
4
2
1.18 (t, 3H, J = 7.5 Hz; CH3), 2.43 (qd, 2H, J = 7.5 Hz, JH–P
132.5 (s), 133.1 (s), (d, JC–P
=
5.7 Hz; PPh–Cortho),
1.6 Hz; CH2), 6.51–8.09 (m, 40H; Ph). 31P{1H} NMR (161 MHz, 135.8 (d, JC–P = 22.7 Hz; PPh–Cipso), 147.6 (d, JC–P = 5.5 Hz),
1
2
2
2
2
2
CDCl3): δP = 132.5 (d, JPA–PB = 44.2; PA), 188.3 (d, JPB–PA
44.2; PB).
[RhCl(PPh3)2(propanoyl-(1,1′-biphenyl-2,2′-diyl)phosphite)], 132.9 Hz, JPA–PB = 46.2 Hz; PA), 133.9 (dt, JPB–Rh = 322.5 Hz,
19. A solution of ligand 3 (0.08 g, 0.27 mmol) in dichloro- 2JPB–PA = 46.2 Hz; PB). IR (KBr): ˜ν = 3049 [m, sp2 ν(C–H)],
methane (15 ml) was added to a solution of [RhCl(PPh3)3] 3000–2960 [w, sp3 ν(C–H)], 1751 [w, ν(CvO)], 1505–1432 [m, Ar
=
148.7 (d, JC–P = 12.9 Hz), 170.2 (d, JC–P = 3.0 Hz; CvO).
31P{1H} NMR (121 MHz, CD2Cl2): δP = 35.2 (bdd, JPA–Rh
=
1
2
1
(0.25 g, 0.27 mmol) in dichloromethane (10 ml) at room temp- ν(CvC)], 692 [st, ν(P–O)]. For complex 22 (ABMX spin system)
1
erature. Upon addition the reaction mixture colour changed
–
31P{1H} NMR (121 MHz, CD2Cl2): δP = 20.6 (ddd, JPA–Rh
=
2
2
from burgundy to light yellow. Following a 30 minute stirring 113.3 Hz, JPA–PB = 370.5 Hz, JPA–PC = 17.2 Hz; PA), 20.5 (ddd,
period, the reaction mixture was reduced to dryness, the 1JPB–Rh = 111.3 Hz, JPB–PA = 370.5 Hz, JPB–PC = 21.2 Hz; PB),
2
2
1
2
2
residue washed with hexane (4 × 20 ml) and then dried 84.7 (ddd, JPC–Rh = 261.1 Hz, JPC–PA = 17.2 Hz, JPC–PB = 21.2
in vacuo to furnish the product as a yellow solid. This major Hz; PC).
product was, however, contaminated with the ligand dispro-
[RhCl(PPh3)2{propanoyl-(5,5′,6,6′-tetramethyl-3,3′-di-tert-
portionation product as well as the rearrangement product 20. butyl-1,1′-biphenyl-2,2′-diyl)phosphite}], 23. Compound 23 was
The title product could not be separated from these by-pro- prepared using a similar methodology to that which was
ducts using standard separation techniques. For complex 19 – described for the preparation of 19. A solution of 5 (0.09 g,
3
1H NMR (300 MHz, CD2Cl2): δH = 0.87 (t, 3H, J = 7.5 Hz; H3), 0.20 mmol) in dichloromethane (15 ml) was added to a solu-
1.54 (q, 2H, 3J = 7.5 Hz; H2), 6.60–7.7 (m, 2H; Ph). 13C{1H} tion of [RhCl(PPh3)3] (0.19 g, 0.20 mmol) at room temperature.
NMR (75 MHz, CD2Cl2): δC = 8.8 (s; C3), 28.5 (s; C2), 122.3 (s; The reaction mixture was stirred at this temperature for 1 h
3
C5/C11), 125.7 (s; C7/C13), 127.8 (d, JC–P = 4.7 Hz; PPh–Cmeta), during which time the solution colour changed from burgundy
129.7 (s; PPh–Cpara), 130.0 (s; C6/C12), 131.0 (s; C8/C14), 135.5 to light yellow. The mixture was subsequently stripped of all
(d, 2JC–P = 6.0 Hz; PPh–Cortho), 135.9 (s; C9/C15), 137.7 (d, 1JC–P
=
volatiles under reduced pressure and the resulting residue
2
11.5 Hz; PPh–Cipso), 149.5 (d, JC–P = 10.6 Hz; C4/C10), 170.2 (d; washed with hexane (3 × 10 ml) to yield the product as a
2JC–P = 3.4 Hz; C1). 31P{1H} NMR (121 MHz, CD2Cl2): δP = 36.1 bright yellow solid (yield: 0.17 g, 77%). Crystals suitable for
1
2
(dd, JPA–Rh = 132.7 Hz, JPA–PB = 46.6 Hz; PA), 134.5 (dt, structure determination by X-ray diffraction were obtained as
1JPB–Rh = 321.8 Hz, JPB–PA = 46.6 Hz; PB). IR (KBr): ˜ν = 3054 yellow platelets by cooling a concentrated solution of 23 in
2
[w, sp2 ν(C–H)], 3009 [w, sp3 ν(C–H)], 1761 [w, ν(CvO)], dichloromethane to −22 °C. H NMR (300 MHz, CD2Cl2): δH
=
1
1498–1434 [st, Ar ν(CvC)], 694 [st, ν(P–O)]. For complex 20 – 0.20 (t, 3H, J = 7.0 Hz; H3), 0.84 (q, 2H, J = 7.5 Hz; H2), 1.37
3
3
31P{1H} NMR (121 MHz, CD2Cl2): δP = 21.7 (dd, JPA–Rh
=
(s, 9H; H11), 1.50 (s, 3H; H12), 1.55 (s, 3H; H22), 1.74 (s, 9H;
1
113.0 Hz, JPA–PC = 19.0 Hz; PA), 79.9 (dt, JPC–Rh = 260.5 Hz, H21), 2.09 (s, 3H; H13), 2.26 (s, 3H; H23), 6.91–8.31 (m, 32H;
2
1
2JPB–PA = 19.0 Hz; PC).
Ph). 13C{1H} NMR (75 MHz, CD2Cl2): δC = 7.6 (s; C3), 16.3 (s;
C13), 16.9 (s; C23), 20.1 (s; C12), 20.5 (s; C22), 27.6 (s; C2), 31.6
(s; C11), 31.9 (s; C21), 34.9 (s; C10), 35.1 (s; C20), 127.3 (d, 3JC–P
=
3
8.1 Hz; PPh–Cmeta), 128.0 (d, JC–P = 9.8 Hz; PPh–Cmeta), 129.1
(s; PPh–Cpara), 129.3 (s; PPh–Cpara), 131.5 (s; C7/C17), 132.2 (s;
2
C6), 132.4 (s; C16), 132.6 (s; C9/C19), 135.0 (d, JC–P = 8.9 Hz;
2
PPh–Cortho), 135.7 (d, JC–P = 8.9 Hz; PPh–Cortho), 136.2 (s;
1
C8/C18), 136.6 (s; C5/C15), 136.8 (d, JC–P = 51 Hz; PPh–Cipso),
[RhCl(PPh3)2{(R)-propanoyl-(1,1′-binaphthyl-2,2′-diyl)phos- 148.1 (s; C4), 149.4 (s; C14). 31P{1H} NMR (121 MHz, CD2Cl2): δP
phite}], 21. Compound 21 was prepared using a similar = 34.4 (ABMX pattern, ddd, JPA–Rh = 138.2 Hz, JPA–PC
1
2
=
2
method to that described for 19, by treating a solution of 44.3 Hz, JPA–PB = 349.5 Hz; PA), 37.2 (ABMX pattern, ddd,
[RhCl(PPh3)3] (0.22 g, 0.24 mmol) in dichloromethane (10 ml) 1JPB–Rh = 138.2 Hz, JPB–PC = 44.3 Hz, JPB–PA = 349.5 Hz; PB),
2
2
1
2
with a solution of 4 (0.09 g, 0.24 mmol) in dichloromethane 129.3 (dt, JPC–Rh = 331.3 Hz, JPC–PA
(15 ml) at room temperature for 1 h. The title product was IR (KBr): ˜ν = 3054 [w, sp2 ν(C–H)], 2958–2866 [m, sp3 ν(C–H)],
=
2JPC–PB = 44.3 Hz; PC).
3488 | Dalton Trans., 2014, 43, 3479–3491
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1780 [m, ν(CvO)], 1481–1393 [m, Ar ν(CvC)], 695 [m, ν(P–O)]. (20 ml) was added to a solution of [RhCl(PPh3)3] (0.32 g,
ES-MS: m/z (%) = 1083 (80) [M − Cl]+, 821 (100) [M − Cl – 0.35 mmol) in dichloromethane (20 ml) at room temperature.
PPh3]+, 627 (5) [Rh(PPh3)2]+.
The reaction mixture was stirred at this temperature for 1 h.
Removal of all volatiles under reduced pressure gave the crude
product as an orange solid which could be purified by washing
with hexane (3 × 20 ml) (yield: 0.32 g, 78%). Crystals suitable
for X-ray structure determination were grown as yellow prisms
by slowly cooling a concentrated solution of 25 in dichloro-
methane to −22 °C. Mp 199–204 °C (decomposed). 1H NMR
(300 MHz, CDCl3): δH = 1.38 (s, 9H; H11), 1.76 (s, 9H; H21),
1.49 (bs, 6H; H12/H22), 2.04 (s, 3H; H13), 2.22 (s, 3H; H23), 2.33
2
(d, 1H, 2J = 19.0 Hz; H2), 2.61 (d, 1H, J = 19 Hz; H2), 6.52–7.84
[RhCl(PPh3)2{propanoyl-(3,3′,5,5′-tetra-tert-butyl-1,1′-biphenyl-
2,2′-diyl)phosphite}], 24. Using the same procedure as was
described for the preparation of 19, [RhCl(PPh3)3] (0.44 g,
0.48 mmol) was reacted with an excess of ligand 6 (0.39 g,
0.76 mmol) at room temperature for 1 h. After the removal of
all volatiles, the orange residue was washed with copious
amounts of hexane (3 × 30 ml) to furnish the analytically pure
title product as a bright yellow solid (yield: 0.52 g, 92%). Crys-
tals in the form of yellow needles suitable for analysis by X-ray
diffraction were grown by slow diffusion of hexane into a con-
centrated solution of 24 in toluene at room temperature. Mp
220–222 °C (decomposed). Anal. Calculated (%) for
C67H75ClO4P3Rh: C 68.5, H 6.4; Found C 68.5, H 6.6. 1H
NMR (300 MHz, CD2Cl2): δδH = 0.21 (t, 3H, 3J = 7.4 Hz; H3),
0.88 (q, 2H, 3J = 7.4 Hz; H2), 1.32 (s, 18H; H11 / /H21), 1.53
(s, 18H; H13/H23), 6.96 (d, 2H, 4J = 2.1 Hz; H6/H16), 7.10 (m, 6H),
7.21 (m, 3H), 7.33 (m, 11H), 7.63 (m, 6H), 7.81 (bt, J = 8.2 Hz,
6H). 13C{1H} NMR (75 MHz, CD2Cl2): δC = 7.7 (s; C3), 27.1 (s;
C2), 31.6 (s; C11/C21), 31.6 (s; C13/C23), 34.8 (s; C10/C20), 35.8 (s;
(m, 37H, Ph). 13C{1H} NMR (75 MHz, CDCl3): δC = 16.5 (s; C13),
17.1 (s; C23), 20.4 (s; C12), 20.5 (s; C22), 31.7 (s; C11), 32.0 (s;
C21), 35.0 (s; C10/C20), 40.2 (s; C2), 127.3 (d, 3JC–P = 8.8 Hz; PPh–
Cmeta), 127.9 (s; Ph–Cpara), 128.1 (s; PPh–Cpara), 128.3 (s; PPh–
Cpara), 128.8 (s; Ph–Cmeta), 129.5 (s; Ph–Cortho), 130.0 (s; C6/C16),
131.5 (s; C9), 132.0 (s; Ph–Cipso), 132.4 (s; C19), 132.8 (s; C7),
2
133.4 (s; C17), 134.8 (d, JC–P = 9.4 Hz; PPh–Cortho), 135.9 (d,
2JC–P = 8.2 Hz; PPh–Cortho), 136.4 (d, 1JC–P = 28.9 Hz; PPh–Cipso),
not observed due to overlap (C8/C18), 137.2 (s; C5/C15), 147.4 (s;
C4/C14). 31P{1H} NMR (121 MHz, CD2Cl2): δP = 34.9 (ABMX
1
2
2
pattern, ddd, JPA–Rh = 134.9 Hz, JPA–PC = 46.3 Hz, JPA–PB
=
1
344.3 Hz; PA), 37.8 (ABMX pattern, ddd, JPB–Rh = 134.9 Hz,
2JPB–PC = 46.3 Hz, JPB–PA = 344.3 Hz; PB), 131.1 (dt, JPC–Rh
=
2
1
2
332.7 Hz, JPC–PA
=
2JPC–PB = 46.3 Hz; PC). IR (KBr): ˜ν = 3051
[m, sp2 ν(C–H)], 2955–2867 [m, sp3 ν(C–H)], 1764 [m, ν(CvO)],
1482–1392 [st, Ar ν(CvC)], 695 [m, ν(P–O)]. ES-MS: m/z (%) =
1145 (100) [M − Cl]+, 883 (43) [M − Cl – PPh3]+, 627 (8)
[Rh(PPh3)2]+.
3
C12/C22), 124.4 (s; C6/C16), 127.5 (d, JC–P = 8.8 Hz; PPh–Cmeta),
3
128.1 (d, JC–P = 9.2 Hz; PPh–Cmeta), 128.4 (s; C8/C18), 129.4 (s;
2
PPh–Cpara), 134.9 (d, JC–P = 10.0 Hz; PPh–Cortho), 136.4 (d,
2JC–P = 9.2 Hz; PPh–Cortho), 136.4 (d, 1JC–P = 41.2 Hz; PPh–Cipso),
139.2 (s; C5/C15), 146.7 (s; C4/C14), 145.7 (s; C7/C17). 31P{1H}
NMR (121 MHz, CD2Cl2): δP = 33.8 (ABMX pattern, ddd,
2
2
1JPA–Rh = 135.3 Hz, JPA–PC = 48.3 Hz, JPA–PB = 347.9 Hz; PA),
1
2
38.2 (ABMX pattern, ddd, JPB–Rh = 135.3 Hz, JPB–PC = 48.3 Hz,
2JPB–PA = 347.9 Hz; PB), 124.9 (dt, JPC–Rh = 331.8 Hz, JPC–PA
=
1
2
[RhCl(PPh3)2{phenylacetyl-(3,3′,5,5′-tetra-tert-butyl-1,1′-biphe-
nyl-2,2′-diyl)phosphite}], 26. Using the same procedure as was
described for the preparation of 19–25, [RhCl(PPh3)3] (0.35 g,
0.38 mmol) was reacted with ligand 8 (0.22 g, 0.38 mmol) at
room temperature for 1 h. After the removal of all volatiles, the
product was extracted from the orange residue with hexane
(30 ml). The hexane extract was reduced to dryness in vacuo to
furnish the product as a bright yellow solid (yield: 0.33 g,
70%). 1H NMR (300 MHz, CD2Cl2): δH = 1.29 (bs, 18H;
H11/H21), 1.54 (bs, 18H; H13/H23), 2.24 (bs, 2H; H2), 7.00 (d,
2H, 4J = 2.7 Hz; H6/H16), 7.10 (d, 2H, 4J = 2.7 Hz; H8/H18),
2JPC–PB = 48.3 Hz; PC). IR (KBr): ˜ν = 3052 [m, sp2 ν(C–H)],
2956–2869 [st, sp3 ν(C–H)], 1775 [st, ν(CvO)], 1477–1395 [m,
Ar ν(CvC)], 694 [m, ν(P–O)]. ES-MS: m/z (%) = 1139 (100)
[M − Cl]+, 877 (35) [M − Cl – PPh3]+.
6.51–7.88 (m, 35H, Ph). 13C{1H} NMR (75 MHz, CD2Cl2): δC
=
31.1 (s; C13/C23), 31.7 (s; C11/C21), 34.9 (s; C12/C22), 35.9 (s;
C10/C20), 40.0 (s; C2), 124.5 (s; C6/C16), 127.1 (s; C8/C18), 128.2
[RhCl(PPh3)2{phenylacetyl-(5,5′,6,6′-tetramethyl-3,3′-di-tert-butyl- (d, JC–P = 9.3 Hz; Ph–Cmeta), 128.6 (s; Ph–Cpara), 128.9 (d,
3
1,1′-biphenyl-2,2′-diyl)phosphite}], 25. Compound 25 was pre- 3JC–P = 7.5 Hz; Ph–Cmeta), 129.1 (s; Ph–Cpara), 129.4 (d, JC–P
=
3
pared using the same procedure described for the preparation 6.4 Hz; Ph–Cmeta), 130.0 (s; Ph–Cpara), 132.4 (d; JC–P = 10.0 Hz;
2
of 19. A solution of 7 (0.18 g, 0.35 mmol) in dichloromethane Ph–Cortho), 132.8 (s; Ph–Cipso), 134.8 (d, JC–P = 10.4 Hz; Ph–
2
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Cortho), 135.9 (d, 2JC–P = 9.8 Hz; Ph–Cortho), 136.3 (d, 1JC–P = 38.2
Hz; PPh–Cipso), 137.7 (s; C9), 137.8 (s; C19), 132.8 (s; Ph–Cipso),
139.6 (s; C5), 139.7 (s; C15), 146.7 (s; C4/C14), 147.9 (s; C7),
4 D. J. Irvine, D. J. Cole-Hamilton, J. C. Barnes and
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5 D. J. Irvine, A. F. Borowski and D. J. Cole-Hamilton,
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9 D. J. Irvine, S. A. Preston, D. J. Cole-Hamilton and
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2
148.1 (s; C17), 164.4 (d, JC–P = 19.7 Hz; C1). 31P{1H} NMR
1
(121 MHz, CD2Cl2): δP = 33.8 (ABMX pattern, ddd, JPA–Rh
=
134.9 Hz, 2JPA–PC = 46.3 Hz, 2JPA–PB = 346.9 Hz; PA), 38.7 (ABMX
1
2
2
pattern, ddd, JPB–Rh = 134.9 Hz, JPB–PC = 46.3 Hz, JPB–PC
=
=
1
2
2
346.9 Hz; PB), 127.0 (dt, JPC–Rh = 334.0 Hz, JPC–PA = JPC–PB
46.3 Hz; PC). IR (KBr): ˜ν = 3054 [m, sp2 ν(C–H)], 2960–2867 [st,
sp3 ν(C–H)], 1776 [m, ν(CvO)], 1496–1398 [st, Ar ν(CvC)], 694
[m, ν(P–O)]. ES-MS: m/z (%) = 1201 (100) [M − Cl]+, 939 (22)
[M − Cl – PPh3]+.
12 J. A. Miller and D. Stewart, J. Chem. Soc., Perkin Trans. 1,
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Conclusions
The coordination chemistry of a series of Rh(I) and Ru(II) com-
plexes derived from mixed anhydride ligands was studied. Com-
plexes with these ligands spontaneously rearrange in solution
via a number of pathways, with the pathway of choice depen-
dent on the mixed anhydride employed, the auxiliary ligands
present as well as the nature of the metal centre. Plausible
mechanisms for the formation of the observed rearrangement
products could be proposed, although more advanced mechan-
istic studies are required to give more conclusive evidence.
Although the propensity of these complexes to rearrange
hampers their use in catalysis, the behaviour of these complexes
are still of interest from a more fundamental point of view.
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Acknowledgements
We thank David Johnson for helpful discussions, Lucite Inter-
national for a studentship (J. C.) and the EPSRC National Spec-
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mass spectrometry data.
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