Reaction of rhenium alkynyl carbene complexes with tertiary phosphines produces dihydrophospholium rhenium complexes by a formal CH insertion process

Article abstract of DOI:10.1016/S0022-328X(00)00733-6

Addition of PPh₂CH₃ to the alkynyl carbene complex Cp(CO)₂Re=C(Tol)(CCPh) (1a) led to formation of the dihydrophospholium complex Cp(CO)₂Re[C=C(Ph)PPh₂CH₂CH(Tol)] (4). When the reaction was monitored by low temperature NMR spectroscopy, initial phosphine addition to the carbene carbon atom of 1a to give σ-propargyl complex Cp(CO)₂ReC(PPh₂CH₃)(Tol)CCPh (5) was observed at -78°C. Upon warming to -20°C, 5 rearranged to the σ-allenyl complex Cp(CO)₂Re(Tol)C=C=C(Ph)(PPh₂CH₃) (6) via phosphine dissociation and readdition. Upon further warming to room temperature, 6 rearranged to 4. A protonation-deprotonation mechanism for the conversion of 6 to 4 is supported by the observation that reaction of 6 with DOTf produces the cationic allene complex Cp(CO)₂Re[η²-2,3-(Tol)DC=C=C(Ph)(PPh ₂CH₃)]OTf (11-d), which is converted to 4-d upon treatment with KO-t-Bu. The reaction of 1a with Ph₂PCH=CH₂ led to the formation of the cyclopropane Cp(CO)₂Re[C=C(Ph)PPh₂CHCH₂C(Tol)] (8).

Full text of DOI:10.1016/S0022-328X(00)00733-6

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 617–618 (2001) 723–736
Reaction of rhenium alkynyl carbene complexes with tertiary
phosphines produces dihydrophospholium rhenium complexes by a
formal CH insertion process
Charles P. Casey *, Stefan Kraft, Douglas R. Powell, Michael Kavana
Department of Chemistry, Uni6ersity of Wisconsin-Madison, Madison, WI 53706, USA
Received 28 September 2000; accepted 3 October 2000
Abstract
Addition of PPh2CH3 to the alkynyl carbene complex Cp(CO)2ReꢀC(Tol)(CꢁCPh) (1a) led to formation of the dihydrophos-
pholium complex Cp(CO)2Re[CꢀC(Ph)PPh2CH2CH(Tol)] (4). When the reaction was monitored by low temperature NMR
spectroscopy, initial phosphine addition to the carbene carbon atom of 1a to give s-propargyl complex Cp(CO)2-
ReC(PPh2CH3)(Tol)CꢁCPh (5) was observed at −78°C. Upon warming to −20°C, 5 rearranged to the s-allenyl complex
Cp(CO)2Re(Tol)CꢀCꢀC(Ph)(PPh2CH3) (6) via phosphine dissociation and readdition. Upon further warming to room tempera-
ture, 6 rearranged to 4. A protonation-deprotonation mechanism for the conversion of 6 to 4 is supported by the observation that
reaction of 6 with DOTf produces the cationic allene complex Cp(CO)2Re[h2-2,3-(Tol)DCꢀCꢀC(Ph)(PPh2CH3)]OTf (11-d), which
is converted to 4-d upon treatment with KO-t-Bu. The reaction of 1a with Ph2PCHꢀCH2 led to the formation of the cyclopropane
Cp(CO)2Re[CꢀC(Ph)PPh2CHCH2C(Tol)] (8). © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Alkynyl carbene complexes; Rhenium; Dihydrophospholium; Allene; Allenyl; Ylide
1. Introduction
2. Results
Alkynyl carbene complexes have emerged as a new
class of synthetically useful compounds [1]. The addi-
tion of nucleophiles to (CO)5M alkynyl carbene com-
plexes (M=Cr, Mo, W) is often the initial step in these
reactions. Recently, we reported the synthesis of the
non-donor substituted alkynyl carbene complex
Cp(CO)2ReꢀC(Tol)(CꢁCPh) (1a) (TolꢀC6H4-p-CH3), its
isomerization to Cp(CO)2ReꢀC(Ph)(CꢁCTol) (1b) via a
1,3-rhenium shift and its dimerization to [Cp(CO)2Re]2-
[TolCꢁCC(Ph)ꢀC(Ph)CꢁCTol)] (2) by coupling of the
remote alkynyl carbons (Scheme 1) [2].
To explore electronic effects on the rates of dimeriza-
tion and 1,3-rhenium shift reactions, we sought to
replace the electron withdrawing CO ligands with elec-
tron-rich phosphine ligands. Here we report that the
reaction of phosphines with rhenium alkynyl carbene
complexes leads to the formation of novel cyclic zwitte-
rionic dihydrophospholium compounds.
2.1. {Cp(CO)2Re[CꢀC(Tol)PPh2CHCH(Tol)]}2 (3)
The addition of 1,2-bis(diphenylphosphino)ethane
(DIPHOS) to a black solution of Cp(CO)2ReꢀC(Tol)-
CꢁTol (1c) produced {Cp(CO)2Re[CꢀC(Tol)PPh2-
CHCH(Tol)]}2 (3) as an orange solid in 72% yield
(Scheme 2). No formation of products resulting from
replacement of CO by phosphine was seen. Mass spec-
trometry established the formula of 3 as a 2:1
1c:DIPHOS addition product (m/z=1449, M+−1).
1H-NMR spectroscopy showed a single product of high
symmetry: only a single Cp resonance (l 4.22) and only
two tolyl CH3 resonances were observed (l 2.17 and
2.49). 31P{1H}-NMR spectroscopy showed a single res-
onance at l 44.4. Two low frequency CO stretches at
1879 and 1802 cm−1 in the IR spectrum indicated an
electron rich rhenium center; the CO stretches of start-
ing material 1c are 1961 and 1888 cm−1
.
* Corresponding author.
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00733-6

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C.P. Casey et al. / Journal of Organometallic Chemistry 617–618 (2001) 723–736
Scheme 3.
Scheme 1.
Addition of Ph2PCH3 to 1a led to the clean forma-
tion of the dihydrophospholium compound Cp(CO)2-
Re[CꢀC(Ph)PPh2CH2CH(Tol)] (4) in 91% yield. In the
13C{1H}-NMR spectrum of 4-13C, derived from reac-
tion of PPh2CH3 with 1a-13C, the labeled carbon ap-
peared as a doublet at l 117 (1JCP=64 Hz). In the
31P{1H}-NMR spectrum, the phosphorus resonance ap-
peared as a doublet at l 34.0 with a 64 Hz coupling to
13C. These spectra are consistent with formation of a
bond between phosphorus and the remote alkynyl car-
bon.
The X-ray crystal structure of 4 unambiguously es-
tablished the regiochemistry of the addition of phos-
phine to 1a (Fig. 2). Conjugate addition of phosphine
occurred at the remote alkynyl carbon of the alkynyl
carbene complex.
Scheme 2.
X-ray crystallography showed that 3 contained two
symmetrically related 5-membered 3,4-dihydrophospho-
lium units (Fig. 1). The remarkable formation of 3
requires the addition of phosphorus to one terminus of
the alkynyl carbene ligand, insertion of the other termi-
nus of the alkynyl carbene ligand into a methylene CH
bond of DIPHOS, and a 1,2-migration of rhenium to
the central carbon of the alkynyl carbene ligand.
2.2. Cp(CO)2Re[CꢀC(Ph)PPh2CH2CH(Tol)] (4)
2.3. Low temperature obser6ation of intermediates from
Ph2PCH3 and 1a
To determine whether the formation of dihydrophos-
pholium products involved bond formation between
phosphorus and the carbene carbon or the remote
alkynyl carbon, the reaction of PPh2CH3 with the un-
symmetric alkynyl carbene complex Cp(CO)2ReꢀC-
(Tol)CꢁCPh (1a) was studied (Scheme 3).
The reactions of 1a and of 1a-13C with PPh2CH3
were studied by low temperature-NMR spectroscopy in
an effort to detect intermediates in the complex trans-
formation leading to 4. When Ph2PCH3 was added to
black solutions of 1a and 1a-13C in CD2Cl2 at −80°C,
,
,
Fig. 1. X-ray crystal structure of {Cp(CO)2Re[CꢀC(Tol)PPh2CHCH(Tol)]}2 (3). Re(1)ꢂC(2) 2.11(2) A, C(1)ꢂC(2) 1.37(3) A.

C.P. Casey et al. / Journal of Organometallic Chemistry 617–618 (2001) 723–736
725
phosphine addition to the carbene carbon produced
the s-propargyl complexes Cp(CO)2ReC(PPh2CH3)-
(Tol)CꢁCPh (5) and Cp(CO)2ReC(PPh2CH3)(Tol)-
Cꢁ13CPh (5-13C) (Scheme 4, Table 1). In the 13C-NMR
spectrum of 5 at −80°C, alkyne carbon resonances
appeared at l 91.7 (d, JCP=9.0 Hz) and 95.0 (d,
13C-NMR resonance of the s-propargyl carbon
bonded to rhenium in 5 appeared at characteristic high
field (l 1.4).
When the solutions 5 and 5-13C were warmed to
−40°C, dissociation of Ph2PCH3 and regeneration of
starting materials 1a and 1a-13C was observed. The Cp
resonance of alkynyl carbene complex 1a at l 5.89
J
CP=9.0 Hz) with long range couplings to phospho-
rus. The 13C-NMR spectrum of 5-13C showed a label
reappeared in the H-NMR spectrum. The yellow solu-
1
3
enhanced resonance at l 91.5 (d, JCP=9.5 Hz). The
tions of 5 turned black as 1a was reformed at −40°C.
,
,
Fig. 2. X-ray crystal structure of Cp(CO)2Re[CꢀC(Ph)PPh2CH2CH(Tol) (4). Re(1)ꢂC(2) 2.120(3) A, C(1)ꢂC(2) 1.383(4) A.
Scheme 4.
Table 1
Selected 1H-, 13C- and 31P-NMR shifts (ppm) and C-P coupling constants (Hz) of compounds 5, 6, and 7
Cp-1H
l Ca
1JCaP
l Cb
2JCbP
l Cg
3JCgP
l
31P
a
5
6
7
4.64
4.98
4.82
1.42
96.82
98.19
95.00
185.15
185.15
9.0
9.0
9.0
91.66
59.58
58.57
9.0
105.0
107.3
27.5
20.0
20.2
12.9
13.5
a Broad signal, ꢀ1/2=97 Hz.

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C.P. Casey et al. / Journal of Organometallic Chemistry 617–618 (2001) 723–736
Scheme 5.
Upon further warming to −20°C, the new s-allenyl
2.5. Reaction of 1a with Ph2PCHꢀCH2 produces
cyclopropane deri6ati6e
Cp(CO)2Re[CꢀC(Ph)PPh2CHCH2C(Tol)] (8)
complexes Cp(CO)2Re(Tol)CꢀCꢀC(Ph)(PPh2CH3) (6)
and Cp(CO)2Re(Tol)CꢀCꢀ13C(Ph)(PPh2CH3) (6-13C)
were formed via conjugate addition of phosphine to the
remote alkynyl carbon atom. In the 13C-NMR spectrum
of 6, allenyl resonances were observed at l 59.6 (d,
1JCP=105 Hz, Cg), 96.8 (d, 3JCP=13 Hz, Ca) and 185.2
A possible mechanism for the conversion of s-allenyl
complex 6 to cyclic phospholium compound 4 involves
a 1,2-migration of rhenium to give ‘free carbene’ inter-
mediate A which could then insert into a CH bond of the
PCH3 group (Scheme 5). The possibility that such a
2
(d, JCP=9 Hz, Cb). These assignments are based on
chemical shifts and 31P-13C coupling constants. The low
frequency shifts of the terminal allenyl carbons Ca and
Cg as well as the high frequency shift of the central
allenyl carbon have been observed for other transition
metal allenyl complexes [3]. These chemical shift assign-
ments are supported by the 13C-NMR spectra of the
carbene might cyclopropanate
a tethered alkene
prompted us to investigate the reaction of alkynyl
carbene complex 1a with PPh2CHꢀCH2 and
PPh2CH2CHꢀCH2.
The reaction of 1a with Ph2PCHꢀCH2 led to the
formation of the cyclopropane derivative Cp(CO)2Re-
[CꢀC(Ph)PPh2CHCH2C(Tol)] (8) in 90% yield (Scheme
6). Reactions of labeled derivatives 1a-13C and 1a-13C2
with Ph2PCHꢀCH2 aided in structural and chemical
shift assignments of 8.
labeled
analogs,
6-13C
and
doubly
labeled
Cp(CO)2Re(Tol)Cꢀ13Cꢀ13C(Ph)(PPh2CH3) (6-13C2) [4].
Compound 6-13C has a label enhanced resonance at l
59.4 (d, JCP=104 Hz, Cg) and 6-13C2 has two label
1
enhanced resonances at l 59.2 (Cg) and 185.4 (Cb) with
1
a
13C-13C coupling constant of JCC=94 Hz.
The 13C-NMR data strongly supports the presence of
a cyclopropyl unit in 8. The 13C-NMR resonances of the
tertiary bridgehead carbon (l 22.50) and the secondary
cyclopropyl carbon (l 26.11) are similar to those found
in 1-phenylbicyclo[3.1.0]hex-2-ene (l 24.3, 26.5) [5]. The
high CꢂH coupling constants of the carbons in the
cyclopropyl ring (1JCH=176 Hz for the CH-unit;
1JCH=176 Hz, 1JCH=162 Hz for the CH2-unit) are due
to the high s character of the CH hybrid orbitals and are
similar to those of other cyclopropanes [6a–c]. The two
vinylic centers in the dihydrophospholium ring have
resonances at l 114.65 (ꢀCꢂP) and 215.57 (ꢀCꢂRe)
similar to that in 4 (Table 1). 8-13C has a strong one
bond coupling (1JCP=68.5 Hz) between the 13C-labeled
carbon (l 114.50) and phosphorous indicating an attack
of the phosphine at the remote carbon in 1a-13C. The
1H-NMR resonances of the cyclopropyl CH2 group of 8
appear at l 1.71 and 1.83 their small geminal coupling
(2J=5.8 Hz) is characteristic of cyclopropanes [7].
When the solutions of 6 and 6-13C were warmed up to
room temperature (r.t.), 4 and 4-13C formed cleanly. No
additional intermediates were observed by 1H-NMR
spectroscopy.
2.4. Cp(CO)2ReC(Tol)ꢀCꢀC(Ph)PPh3 (7)
The addition of PPh3 to the alkynyl carbene complex
1a afforded the s-allenyl addition product
Cp(CO)2ReC(Tol)ꢀCꢀC(Ph)PPh3 (7) (Scheme 4). In the
presence of an excess PPh3, 7 is stable at r.t. and does
not produce CH insertion products similar to 6. The
13C-NMR chemical shifts of the allenyl carbons of 7 (l
98.2 for Ca 185.2 for Cb and 58.6 for Cg ) are very similar
to the values of 6 (Table 1). Reaction of 1a-13C and
1a-13C2 with PPh3 afforded the labeled analogs
Cp(CO)2ReC(Tol)ꢀCꢀ13C(Ph)PPh3 (7-13C) (label at l
59.4, 1JCP=107 Hz) and Cp(CO)2ReC(Tol)ꢀ13Cꢀ13C-
(Ph)PPh3 (7-13C2) (labels at l 58.8, 1JCC=95 Hz, 1JCP
=
1
2
107.3 Hz; l 187.0, JCC=95 Hz, JCP=10 Hz). This
labeling pattern establishes the regiochemistry of PPh3
addition to the remote alkynyl carbon of 1a. The low
frequency CO stretches at 1878 and 1802 cm−1 in the IR
spectrum of 7 provide evidence for negative charge on
rhenium. When 7 was isolated and redissolved, partial
reappearance (20%) of starting materials 1a and PPh3
was observed after several hours. This demonstrates that
the formation of 7 from 1a and PPh3 is reversible.
Scheme 6.

C.P. Casey et al. / Journal of Organometallic Chemistry 617–618 (2001) 723–736
727
,
,
Fig. 3. X-ray crystal structure of Cp(CO)2Re[CꢀC(Ph)PPh2CHCH2C(Tol)] (8). Re(1)ꢂC(2) 2.112(3) A, C(1)ꢂC(2) 1.387(5) A.
The X-ray crystal structure of 8 confirmed the struc-
tural assignment (Fig. 3). The presence of a PꢂCPh bond
indicates that 8 is formed by initial attack of phosphorus
at the remote alkynyl carbon of 1a.
rous in each case. These couplings provide definitive
evidence for conjugate addition of phosphine to the
remote alkynyl carbon of 1a.
Crystals of the bis-tolyl analog 9c-(anti) suitable for an
X-ray crystal structure analysis were obtained from
reaction of 1c with Ph2PCH2CHꢀCH2 (Fig. 4). The
dihydrophospholium unit of 9c-(anti) is very similar to
the core structures of 3, 4, and 8.
2.6. Reaction of 1a with Ph2PCH2CHꢀCH2 gi6es CH
insertion product
Cp(CO)2Re[CꢀC(Ph)PPh2CH(CHꢀCH2)CH(Tol)] (9a)
Reaction of Ph2PCH2CHꢀCH2 with 1a did not lead to
cyclopropane formation but instead gave products
derived from insertion into an allylic CH bond of the
phosphine. The dihydrophospholium compounds
Cp(CO)2Re[CꢀC(Ph)PPh2CH(CHꢀCH2)CH(Tol)] [9a-
(anti ) and 9a-(syn), 5:1 ratio] were formed in 98% yield
(Scheme 7). Both isomers 9a-(anti ) and 9a-(syn) display
Scheme 7.
1
an intact vinyl group in their H-NMR and 13C-NMR
spectra. The internal vinyl hydrogen of 9a-(anti ) has a
resonance at l 5.36 with typical cis and trans couplings
to the neighboring terminal hydrogens at l 5.00 (3J=16.7
Hz) and 5.03 (3J=10.0 Hz). Similarly, the internal vinyl
hydrogen resonance of 9a-(syn) at l 4.72 is coupled to
the terminal vinyl hydrogens at l 4.99 (3J=10.0 Hz) and
5.20 (3J=16.8 Hz). The internal and terminal vinyl
carbons of 9a-(anti) have 13C-NMR shifts at l 126.97 and
120.14. The chemical shifts of the ring carbons of both
isomers are similar to those of 3 and 4. The stereochem-
istry of 9a-(anti) and 9a-(syn) were assigned with the aid
of NOE difference experiments (see Section 4).
The addition of Ph2PCH2CHꢀCH2 to 1a-13C afforded
a 5:1 mixture of 9a-13C-(anti) and 9a-13C-(syn). In the
13C-NMR spectrum, label-enhanced resonances were
seen at l 117.15 [9a-13C-(anti)] and l 115.57 [9a-13C-(syn)]
Fig. 4. X-ray crystal structure of Cp(CO)2Re[CꢀC(Tol)PPh2CH-
,
(CHꢀCH2)CH(Tol)] (9c). Re(1)ꢂC(2) 2.125(5) A, C(1)ꢂC(2) 1.401(8)
1
with one bond couplings of JCP=64.1 Hz to phospho-
,
A.

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C.P. Casey et al. / Journal of Organometallic Chemistry 617–618 (2001) 723–736
CH3)]OTf (10-13C2) (ReH l −8.57) was observed
(Scheme 9, Table 2). In the 13C-NMR spectrum, the
resonance for the labeled terminal carbon Cg appeared
at l 72.6 (t, 1JCC=97 Hz, 1JCP=97 Hz) and the
resonance for the labeled central carbon Cb appeared at
2
l 201.4 (1JCC=97 Hz, JCP=7.6 Hz). Both 13C-NMR
chemical shifts of 10-13C2 and all the coupling constants
are very similar to those of its precursor 6-13C2.
Scheme 8.
The s-allenyl rhenium hydride 10-13C2 underwent
reductive elimination to form the h2-allenyl complex
Cp(CO)2Re[h2 - 2,3 - (Tol)HCꢀ13Cꢀ13C(Ph)(PPh2CH3)] -
OTf (11-13C2) with a half life of 30 min at −80°C. New
13C-NMR resonances were observed at l 111.35 (dd,
2.7. Deuterium incorporation in the reaction of 1a with
Ph2PCH3 in CH3OD
Alternative mechanisms for the conversion of the
s-allenyl intermediate 6 to the phospholium product 4
involve acid-base chemistry rather than CH insertion.
Both deprotonation of the acidic phosphonium methyl
group of 6 and protonation of 6 to give allene com-
plexes were investigated. To test deprotonation of the
PCH3 group, we looked for deuterium incorporation
into the product of the reaction of 1a with Ph2PCH3 in
the presence of a 100 fold excess of CH3OD at r.t.
Within our detection limits, complete (\95%) deu-
terium incorporation into all three ring positions 4-d3
occurred and no (B5%) ring protons were seen in the
1H-NMR spectrum (Scheme 8). The 2H-NMR spec-
trum showed broad resonances at l 2.95 (CDD), 3.18
(CDD), 5.39 (CTolD).
1
1JCC=86.1 Hz, JCP=74.1 Hz) for the labeled terminal
1
2
carbon Cg and l 182.66 (dd, JCC=86.1 Hz, JCP=8.7
Hz) for the labeled central carbon Cb. No additional
splitting due to CH coupling was observed in the
1H-coupled 13C-NMR spectrum, indicating that hydro-
gen was not bonded to either of the labeled carbons.
The allenyl hydrogen resonance appeared at l 4.4 in the
1H-NMR spectrum; this hydrogen is shifted to lower
frequency than seen for typical 1-phenylallenyl hydro-
gens (l 6.5–7.0) [8]) due to p-complexation to the
Cp(CO)2Re fragment. Compound 11-13C2 was stable in
solution at r.t.
Deuteration of 6 with TfOD at −78°C followed by
warming to r.t. produced {Cp(CO)2Re[h2-2,3-(Tol)DCꢀ
CꢀC(Ph)(PPh2CH3)}OTf, 11-d (Scheme 10). In the
2H-NMR spectrum, a single resonance was observed at
l 4.50 for the allenyl deuterium. Crystallization of 11-d
was accomplished by diffusing pentane into a CH2Cl2
solution.
2.8. Low temperature protonation of 6-13C2
When HOTf was added to 6-13C2 at −80°C and the
1
solution was immediately monitored by H-NMR spec-
troscopy at −80°C, the transient metal hydride
intermediate [Cp(CO)2(H)Re(Tol)Cꢀ13Cꢀ13C(Ph)(PPh2-
Scheme 9.
Table 2
Selected 1H-, 13C- and 31P-NMR shifts (ppm) and C-P coupling constants (Hz) of compounds 6-13C2, 10-13C2, and 11-13C2
13
l H
l
Cg
l
13Cb
1JCgCb
1JCgP
2JCbP
l
13P
6-13C2
59.2
72.6
111.35
185.4
201.4
182.6
93.8
97 Hz
86.1
104.7
97 Hz
74.1
7.0
7.6
8.7
19.5
22.0
17.5
10-13C2
11-13C2
−8.57
4.40
Scheme 10.

C.P. Casey et al. / Journal of Organometallic Chemistry 617–618 (2001) 723–736
729
2.9. Deprotonation of 11-d with KO-t-Bu
als at −40°C in an entropy driven process. Upon
warming to −20°C, conjugate addition of PPh2CH3 to
the remote alkynyl carbon of 1a occurred to give a
more stable s-allenyl rhenium complex 6. The greater
stability of 6 might be related to the loss of a relatively
weak p-bond of an alkyne upon addition. The conju-
gate addition of PPh3 to 1a produced s-allenyl rhenium
complex 7; at least in this case, conjugate phosphine
addition was reversible.
Fischer reported that the addition of dimethylamine
to the carbene carbon of (CO)5CrꢀC(OEt)(CꢁCPh) with
the subsequent elimination of EtOH is a kinetically
controlled process at −115°C [14]. At −20°C, the
amine undergoes a thermodynamically controlled con-
jugate addition to the remote alkynyl carbon. Nucleo-
philic addition of phosphines to carbene complexes is
often reversible [15]. Conjugate additions of Ph2PCH3
to chromium and tungsten alkynyl carbene complexes
were reported by Aumann [16]. Interestingly, these
s-allenyl adducts failed to undergo further transforma-
tions similar to the conversion of 6 to dihydrophospho-
lium complex 4 (see Scheme 12).
When KO-t-Bu was added to a colorless solution of
11-d at −78°C, the solution turned bright yellow in-
stantaneously. The 1H-NMR spectrum taken at −91°C
provided evidence for the immediate conversion to a
3:1 mixture of 4-d and undeuterated 6 (Scheme 10).
Resonances for the CH2 group of 4-d at l 3.13 and 3.35
displayed a strong geminal coupling (2J=16.6 Hz) but
no vicinal coupling due to the absence of a neighboring
proton [9]. A broad peak at l 5.40 assigned to C(Tol)D
of 4-d was observed in the 2H-NMR spectrum. The
1
formation of 6 was established by H, 13C, and 31P-
NMR spectroscopy.
3. Discussion
3.1. Structure and bonding of dihydrophospholium
complexes
There are two reasonable resonance structures for
rhenium dihydrophospholium complex 4: zwitterionic
structure I and rhenium carbene-phosphorane structure
II (Scheme 11). Spectroscopy and X-ray crystallogra-
phy indicate that I is the major contributor. The low
frequency IR bands of 4 at 1878 and 1802 cm−1 are
consistent with an anionic Re(CO)2 unit. The 2.120(3)
3.3. Mechanism of con6ersion of |-allenyl rhenium
intermediates to dihydrophospholium products
Two mechanisms can explain the overall transforma-
tion of s-allenyl rhenium complexes to the dihy-
drophospholium products. One involves a ‘free carbene’
intermediate formed by a 1,2-rhenium shift of the s-al-
lenyl rhenium complex (Scheme 5). The other involves
acid-base chemistry and carbon-carbon bond formation
via attack of a phosphorane on an allene complex
(Scheme 13). Nucleophilic attack on allene complexes is
well documented, including intramolecular examples
leading to 5-membered rings [17,18]. The mechanism in
Scheme 13 is strongly supported by the observations
that protonation of s-allenyl intermediate 6 produces
the allene complex 11 and that deprotonation of 11
produces the dihydrophospholium complex 4.
,
,
A ReꢂC distance in 4 is 0.116(6) A longer than the
ReꢀC double bond distance in alkynyl carbene complex
1c and is similar to the ReꢂC single bond length in
Gladysz’ s-vinyl complex Cp(NO)(PPh3)ReCHꢀ
,
,
CHCH2Ph [2.129(10) A] [10]. The 0.116(6) A difference
between the ReꢀC double bond and the ReꢂC single
bond in 1a and 4 is significantly less than the 0.180(11)
,
A
difference between that in Gladysz’ Cp(NO)-
(PPh3)ReꢀCHPh and his s-vinyl-complex; this supports
some contribution from resonance structure II. The
,
1.383(4) A carbon-carbon distance in 4 is longer than
,
most CꢀC bonds (1.32–1.33 A) [11] and provides addi-
tional evidence for some contribution from II. The
small 13Cꢀ13C coupling constant (1JCC=48.9 Hz) for
the ring CꢀC in 8-13C2 is outside the range of typical
13Cꢀ13C couplings (65–80 Hz) [12,13] and again sup-
ports some contribution from resonance structure II.
3.2. Regiochemistry of phosphine addition to alkynyl
carbene complexes
Scheme 11.
Kinetic addition of phosphines to the carbene carbon
and thermodynamic addition to the remote alkynyl
carbon of alkynyl carbene complexes were observed.
Addition of PPh2CH3 to the carbene carbon of alkynyl
carbene complex 1a occurred at −78°C to produce 5
(Scheme 4). The formation of 5 was reversible, and
interestingly, the equilibrium shifted to starting materi-
Scheme 12.

730
C.P. Casey et al. / Journal of Organometallic Chemistry 617–618 (2001) 723–736
isolated previously [25]. An intramolecular attack of the
ylide carbon on the p-complexed double bond would
then form cyclopropane 8. This mechanism explains
how cyclopropane formation is limited to vinyl phos-
phines, allyl phosphines cannot react by similar
pathways.
We have found experimental support for the acid
base chemistry leading to allenyl phosphonium complex
11 in Scheme 13. The complete deuteration of the ring
hydrogens of 4 when the reaction of 1a and Ph2PCH3
was run in a CH3OD solution (Scheme 8) is proposed
to occur via reversible deprotonation of the phospho-
nium methyl group of intermediate 6. Deuterium ex-
change via reversible deprotonation of methyl
phosphonium salts is well precedented. Ph3PCH+3 un-
dergoes rapid and complete H-D exchange of the
methyl hydrogens in the presence of excess D2O and
catalytic amounts of Na2CO3. (CH3)3PꢀCH2 undergoes
rapid exchange of methyl and methylene protons in the
presence of traces of water via reversible formation of
(CH3)4P+ [26].
Scheme 13.
The conversion of s-allenyl intermediate 6 to allene
complex 11 via intermediate rhenium hydride 10 pro-
vides support for the proposed intermediacy of an
allene complex in the formation of dihydrophospho-
lium compounds. Related protonations of s-vinyl metal
anions have been reported [27,28]. Reductive elimina-
tion from vinyl hydride complexes have been thor-
oughly investigated [29]; with a few exceptions [30],
vinyl hydride complexes are thermodynamically un-
stable relative to the resulting alkene complexes [31].
When allene complex 11 was treated with KO-t-Bu,
some deprotonation to regenerate s-allenyl rhenium
complex 6 was seen in addition to predominant conver-
sion to the dihydrophospholium complex 4. Similar
deprotonation of a vinylic hydrogen of Cp(NO)(PPh3)-
Re(h2-CH2ꢀCꢀCH2) produced a s-allenyl complex
[32,33] and deprotonation of Cp(NO)(PPh3)Re(h2-
CH2=CHPh) produced a s-vinyl complex [34]. Based
on the principle of microscopic reversibility, we postu-
late that the deprotonation of 11 occurs via initial CH
bond activation to give rhenium hydride intermediate
10, followed by deprotonation of the rhenium hydride.
A related CH activation mechanism in conjunction with
a deprotonation-reprotonation sequence was postulated
by Oro to account for deuterium incorporation into an
iridium ethylene complex [35,36].
Scheme 14.
For the ‘free carbene’ mechanism to be correct, we
need to postulate that deuterium incorporation occurs
via acid-base chemistry in a side reaction unrelated to
carbonꢂcarbon bond formation. Moreover, we need to
postulate that cyclopropanation would occur for the
vinyl phosphine but not for the allyl phosphine even
though both cyclopropane products would be expected
to have comparable stability. Metal catalyzed in-
tramolecular cyclopropanations to form bicyclo-
[4.1.0]heptanones from alkenyl diazo carbonyl precur-
sors have been reported [19]. In some cases, allylic CH
insertions were found to be a competitive side reaction
[20] or the exclusive reaction [21]. Since no cyclo-
propane formation was observed from the allyl phos-
phine, a ‘free carbene’ mechanism seems unlikely.
For the mechanism proceeding via attack of a phos-
phorane on an allene rhenium complex, we need to
explain why cyclopropane is formed only from the vinyl
phosphine. We believe that the unique electrophilic
nature of a vinyl phosphonium intermediate can ex-
plain this difference (Scheme 14). Addition of C, O, S,
and N nucleophiles to vinyl phosphonium salts are well
documented [22]. The ability of the metal center of
Cp(CO)2Re(s-vinyl) anions to act as a nucleophile has
also been observed [23]. Nucleophilic attack of rhenium
on the vinyl phosphonium unit would produce metalla-
cycle D [24], which could reductively eliminate to give
the strained cyclic allene complex E. Related h2-1,2-cy-
clohexadiene complexes of platinum and iron have been
4. Experimental
4.1. General considerations
All manipulations were performed either in a nitro-
gen atmosphere glovebox or by standard high vacuum
line techniques. Compounds 1a, 1a-13C, 1a-13C2 and 1c

C.P. Casey et al. / Journal of Organometallic Chemistry 617–618 (2001) 723–736
731
1
were synthesized as described earlier [2]. Hexane, pen-
tane, THF, THF-d8, C6H6, C6D6 and diethyl ether were
distilled from sodium and benzophenone. C6D5CD3
was distilled from Na–K. CH2Cl2 and CD2Cl2 were
distilled from CaH2. CHCl3 and CDCl3 were distilled
from Na2SO4. 1H-NMR spectra were obtained on a
Bruker AC 250, AC 300, AM 500 or a Varian Unity
500 spectrometer. 13C{1H}-NMR spectra were obtained
on a Bruker AM 500 or a Varian Unity 500 spectrome-
ter operating at 126 MHz. 31P{1H}-NMR spectra were
obtained on a Bruker AM 500 or a Varian Unity 500
spectrometer operating at 202.5 MHz. Infrared spectra
21.71(CH3), 34.92 (d, JCP=61.0 Hz, PCH2), 71.08 (d,
2JCP=14.7 Hz, CTol), 83.75 (C5H5), 117.08 (d, JCP
=
1
64.4 Hz, CꢀCP), 123.60 (d, 1JCP=73.4 Hz, Cipso),
126.06 (1JCP=75.5 Hz, Cipso), 126.86 (4JCP=2.6 Hz,
aromatic), 128.32 (aromatic), 128.80 (aromatic), 129.01
3
(aromatic), 129.70 (d, JCP=11.3 Hz, aromatic), 129.89
3
(d, JCP=12.0 Hz, aromatic), 132.67 (aromatic), 132.74
(aromatic), 132.75 (aromatic), 133.53 (d, JCP=2.9 Hz,
aromatic), 136.04 (aromatic), 140.37 (d, JCP=20.4 Hz,
aromatic), 144.42 (aromatic), 208.77 (CO), 209.16 (CO),
218.94 (d, 2JCP=6.4 Hz, ReCꢀC). 31P{1H}-NMR
(CD2Cl2, 202.5 MHz) l 34.0. IR (CH2Cl2) 1878, 1802
cm−1. HRMS(EI) m/z Calc. for C36H30O2PRe (M+)
712.1542, found 712.1549.
4
2
were recorded on
spectrometer.
a
Mattson Polaris FT IR
4.2. {Cp(CO)2Re[CꢀC(Tol)PPh2CHCH(Tol)]}2 (3)
4.4. Cp(CO)2Re[Cꢀ13C(Ph)PPh2CH2CH(Tol)] (4-13C)
Addition of bis(diphenylphosphino)ethane (DIPHOS)
(5.0 mg, 0.013 mmol) to a black solution of Cp(CO)2-
ReꢀC(Tol)(CꢁCTol) (1c) (15 mg, 0.029 mmol) in 0.4 ml
benzene produced an orange solution after 30 min.
After 48 h, orange crystals suitable for X-ray crystallog-
raphy had precipitated. The solid was washed with very
Compound 4-13C (13 mg, 80% yield) was prepared
from Cp(CO)2ReꢀC(Tol)(Cꢁ13CPh) (1a-13C) (12 mg,
1
0.023 mmol) and Ph2PCH3 (12 mg, 0.060 mmol). H-
NMR (CD2Cl2, 500 MHz) l 2.33 (s, CH3), 2.95 (dddd,
2J=16.2 Hz, 3J=2.8 Hz, 2JPH=8.4 Hz, 3JCH=8.4 Hz,
CHCHHtrans), 3.18 (dddd, 2J=15.1 Hz, 3J=8.8 Hz,
2JPH=11.7 Hz, 3JCH=0.4 Hz, CHCHcisH), 4.35 (s,
C5H5), 5.40 (dddd, 3J=9.0 Hz, 3J=2.8 Hz, 3JPH=12.0
Hz, 4JCH=1.9 Hz, CHTol), 7.0–7.7 (m, aromatic).
13C{1H}-NMR (CD2Cl2, 125 MHz) l 21.19 (CH3),
34.94 (dd, 1JCP=61.0 Hz, 2JCC=8.3 Hz, PCH2),),
1
little benzene to yield 3·(3.5 C6H6) (18 mg, 72%). H-
NMR (CD2Cl2, 300 MHz) l 2.17 (s, CH3), 2.49 (s,
2
CH3), 3.51 (d, JPH=10.1 Hz, CHP), 4.22 (s, C5H5),
3
5.91 (d, JPH=3.7 Hz, CHTol), 7.0–7.6 (m, aromatic).
13C{1H}-NMR (CD2Cl2, 125 MHz) l 21.16 (CH3),
1
2
21.32 (CH3), 45.07 (d, JCP=57.6 Hz, PCH), 75.31 [d,
71.08 (d, JCP=15.2 Hz, CTol), 83.75 (C5H5), 117.08
2JCP=11.8 Hz, C(Tol)CH], 83.44 (C5H5), 116.51 (d,
1JCP=67.8 Hz, CꢀCP), 120–144 (aromatic signals),
207.81 (CO), 208.27 (CO), 218.85 (broad, ReCꢀC).
31P{1H}-NMR (CD2Cl2, 202.5 MHz) l 44.4. IR
(CH2Cl2) 1879, 1802 cm−1. MS(FAB) m/z Calc. for
C74H62O4P2Re2 (M+−1) 1449, found 1449.
(d, JCP=64.4 Hz C=13CP), 123.60–144.42 (aromatic
1
2
signals), 208.75 (CO), 209.14 (CO), 218.12 (d, JCP
=
7.0 Hz, 1JCC=48.1 Hz, ReCꢀC). 31P{1H}-NMR
1
(CD2Cl2, 202.5 MHz) l 34.0 (d, JCP=64.6 Hz). IR
(CH2Cl2) 1878, 1802 cm−1. HRMS(EI) m/z Calc. for
35
C CH30O2PRe (M+) 713.1575, found 713.1545.
13
4.3. Cp(CO)2Re[CꢀC(Ph)PPh2CH2CH(Tol)] (4)
4.5. Cp(CO)2Re[CꢀC(Ph)PPh2CD2CD(Tol)] (4-d3)
Addition of Ph2PCH3 (45.5 mg, 0.227 mmol) to a
solution of 14.3 mg (0.0280 mmol) Cp(CO)2ReꢀC(Tol)-
(CꢁCꢂPh) (1a) in 1 ml CH2Cl2 produced an orange
color after 1 min. After 48 h, hexane was added to
precipitate a yellow solid which was redissolved in a few
drops of CH2Cl2. Slow addition of 1 ml diethyl ether led
to the formation of orange needles of 4 (18.1 mg, 91%
yield) suitable for X-ray crystallography. 1H-NMR
Compound 4-d3 (12 mg, 88% yield) was prepared
from Cp(CO)2ReꢀC(Tol)(CꢁCPh) (1a) (10 mg, 0.019
mmol) and Ph2PCD3 (5 mg, 0.03 mmol). 1H-NMR
(CD2Cl2, 500 MHz) l 2.33 (s, CH3), 4.36 (s, C5H5),
2
7.0–7.75 (m, aromatic). H-NMR (CH2Cl2, 77 MHz) l
2.95 (s, br, CDCDDtrans), 3.18 (s, br, CDCDcisD), 5.39
(s, br, CDCDD). IR (CH2Cl2) 1878, 1802 cm−1. HRM-
S(EI) m/z Calc. for C36H27D3O2PRe (M+) 715.1730,
found 715.1745.
2
(CD2Cl2, 500 MHz) l 2.33 (s, CH3), 2.95 (ddd, J=
16.0, 3J=2.8 Hz, 2JPH=8.3 Hz, CHCHHtrans), 3.19
(ddd, 2J=15.9 Hz, 3J=9.0 Hz, 2JPH=11.7 Hz,
CHCHcisH), 4.35 (s, C5H5), 5.41 (ddd, 3J=8.9 Hz,
4.6. Reaction of (1a) and Ph2PCH3 in CH3OD
3
3
3J=2.8 Hz, JPH=12.1 Hz, CHTol), 7.09 (d, J=8.2
Addition of Ph2PCH3 (8 mg, 0.04 mmol) to a solu-
tion of Cp(CO)2ReꢀC(Tol)(CꢁCPh) (1a) (12 mg, 0.023
mmol) in CH3OD (360 mg, 10.9 mmol) produced an
orange color after 1 min. After 24 h, hexane was added
to precipitate a yellow solid which was redissolved in a
few drops of CH2Cl2. Slow addition of 1ml diethyl
3
Hz, aromatic), 7.12 (d, J=8.2 Hz, aromatic), 7.19–
3
3
7.30 (m, aromatic), 7.44 (dd, J=8.0 Hz, JPH=11.6
Hz, aromatic), 7.50 (td, 3J=8.0 Hz, 3JPH=3.1 Hz,
aromatic), 7.52–7.57 (m, aromatic), 7.61–7.69 (m, aro-
matic). 13C{1H}-NMR (CD2Cl2, 125 MHz)
l

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C.P. Casey et al. / Journal of Organometallic Chemistry 617–618 (2001) 723–736
ether led to the formation of orange needles of 4-d3 (14
NMR (CD2Cl2, 500 MHz) l 2.28 (s, CH3), 2.41 (dd,
1
2
3
mg, 85% yield). H and H-NMR were identical with
those from an authentic sample of 4-d3 obtained in the
previous experiment. Residual 1H-NMR signals for
each ring hydrogen amounted to less than 5%.
2JPH=12.8, JCH=2.2 Hz, PCH3), 4.98 (C5H5), 6.93–
7.90 (m, aromatic). 13C{1H}-NMR (CD2Cl2, 125 MHz)
l 59.4 (d, 1JCP=104 Hz, C=13CP). 31P{1H}-NMR
1
(CD2Cl2, 202.5 MHz) l 20.0 (d, JCP=105 Hz).
The sample was warmed to 24°C and Cp(CO)2Re-
4.7. Reaction of Cp(CO)2ReꢀC(Tol)(CꢁCPh) with
Ph2PCH3 (6ariable temperature-NMR experiment)
[Cꢀ13C(Ph)PPh2CH2CH(Tol)] (4-13C) formed slowly. No
1
intermediates were detected by H-NMR.
Addition of Ph2PCH3 (19 mg, 0.095 mmol) to a black
solution of Cp(CO)2ReꢀC(Tol)(CꢁCPh) (1a) (7.5 mg,
0.015 mmol) in 0.4 ml CD2Cl2 at −78°C produced a
4.9. Reaction of Cp(CO)2ReꢀC(Tol)(13Cꢁ13CPh)
(1a-13C2) with Ph2PCH3 at −20°C to form
Cp(CO)2Re[C(Tol)ꢀ13Cꢀ13C(Ph)(PPh2CH3) (6-13C2)
yellow color after
3
h. Spectra of Cp(CO)2-
ReC(PPh2CH3)(Tol)[CCꢁCPh] (5) were recorded without
Addition of Ph2PCH3 (10 mg, 0.050 mmol) to a black
solution of Cp(CO)2ReꢀC(Tol)(13Cꢁ13CPh) (1a-13C2) (7.3
mg, 0.014 mmol) in 0.4 ml CD2Cl2 at −20°C produced
an orange color after 15 min. Spectra of 6-13C2 were
recorded without isolation. 1H-NMR (CD2Cl2, 500 MHz,
−80°C) l 2.28 (s, CH3), 2.41 (d, 2JPH=12.8 Hz, PCH3),
4.98 (C5H5), 7.0–7.8 (m, aromatic). 13C{1H}-NMR
1
isolation. H-NMR (CD2Cl2, 500 MHz, −80°C) l 2.25
2
(s, CH3), 2.70 (d, JPH=12.2 Hz, PCH3), 4.64 (C5H5),
6.93–7.90 (m, partly obscured by excess Ph2PCH3,
aromatic). 13C{1H}-NMR (CD2Cl2, 125 MHz) l 1.42
(broad signal, ꢀ1/2=97 Hz, ReCP), 15.75 d, 1JCP=74.5
Hz, PCH3), 20.36 (CH3), 85.76 (broad, ꢀ1/2=22 Hz,
C5H5), 91.66 (d, 3JCP=9.0 Hz, CꢁCPh), 95.00 (d, 2JCP
=
(CD2Cl2, 125 MHz, −80°C) label at l 59.2 (dd, 1JCC
=
9.0 Hz, CꢁCPh), 124-142 (aromatic, partly obscured by
signals from excess Ph2PCH3), 207.71 (broad, ꢀ1/2=58
Hz, CO), 211.77 (broad, ꢀ1/2=58 Hz, CO). 31P{1H}-
NMR (CD2Cl2, 202.5 MHz, −80°C) l 27.5.
93.7, 1JCP=104.7 Hz, P13Cꢀ13C), 185.4 (dd, 1JCC=93.8,
2JCP=7.0 Hz, Cꢀ3Cꢀ13C). 31P{1H}-NMR (CD2Cl2, 202.5
1
2
MHz, −80°C) l 19.5 (dd, JCP=105.3, JCP=6.1 Hz).
The sample was warmed to −20°C for 1 h to form
Cp(CO)2ReC(Tol)ꢀCꢀC(Ph)(PPh2CH3) (6). 1H-NMR
(CD2Cl2, 500 MHz, −20°C) l 2.28 (s, CH3), 2.41 (d, 3H,
2JPH=12.8, PCH3), 4.98 (C5H5), 7.0–7.8 (m, aromatic).
4.10. Cp(CO)2ReC(Tol)ꢀCꢀC(Ph)PPh3 (7)
Addition of PPh3 (31.5 mg, 0.120 mmol) to a solution
of CpRe(CO)2ꢀC(Tol)(CꢁCPh) (1a) (12.1 mg, 0.0237
mmol) in 0.4 ml CDCl3 in an NMR tube produced an
orange color after 15 min. Spectroscopic charcterization
was performed without isolation. 1H and 31P-NMR
spectra indicated clean formation of 7. 1H-NMR (CDCl3,
500 MHz) l 2.25 (s, CH3), 4.82 (s, C5H5), 7.09–7.75 (m
13C{1H}-NMR (CD2Cl2, 125 MHz, −20°C) l 12.47 (d,
1
1JCP=67.8 Hz, PCH3), 20.87 (CH3), 59.58 (d, JCP
=
105.0 Hz, CꢀCP), 86.83 (C5H5), 96.82 (d, 3JCP=12.9 Hz,
ReCꢀC), 124–140 (aromatic, partly obscured by signals
from excess Ph2PCH3), 185.15 (d, 2JCP=9.0 Hz, CꢀCꢀC),
208.85 (CO). 31P{1H}-NMR (CD2Cl2, 202.5 MHz,
−20°C) l 20.0.
aromatic). 13C{1H}-NMR (CDCl3, 125 MHz)
l
21.02(CH3), 58.57 (d, 1JCP=107.3 Hz, CꢀCP), 83.22
3
Upon warming to 24°C Cp(CO)2Re[CꢀC(Ph)PPh2-
CH2CH(Tol)] (4) formed slowly. No intermediates were
detected.
(C5H5), 98.19 (d, JCP=13.5 Hz, ReCꢀC), 119.30 (d,
1
1JCP=84.7 Hz, Cipso), 123.60 (d, JCP=73.4 Hz, Cipso),
128.17 (aromatic), 128.21 (aromatic), 128.87 (aromatic),
3
131.87 (aromatic), 132.06 (d, JCP=10.2 Hz, aromatic),
4.8. Reaction of Cp(CO)2ReꢀC(Tol)(Cꢁ13CPh) (1a-13C)
with Ph2PCH3 (6ariable temperature-NMR experiment)
133.49 (aromatic), 134.58 (d, JCP=9.0 Hz, aromatic),
3
2
137.14 (d, JCP=11.3 Hz, aromatic), 139.26 (aromatic),
2
140.96 (d, JCP=6.8 Hz, aromatic), 144.73 (aromatic),
Addition of Ph2PCH3 (12 mg, 0.060 mmol) to a black
solution of Cp(CO)2ReꢀC(Tol)(Cꢁ13CPh) (1a-13C) (12
mg, 0.023 mmol) in 0.4 ml CD2Cl2 at −78°C produced
a yellow solution after 3 h. Spectra of Cp(CO)2ReC-
(PPh2CH3)(Tol)[CCꢁ13CPh] (5-C13) were recorded with-
185.15 (d, 2JCP=9.0 Hz, CꢀCꢀC), 208.85 (CO). 31P{1H}-
NMR (CDCl3, 202.5 MHz) l 20.2. IR (CH2Cl2) 1878,
1802 cm−1
.
4.11. Cp(CO)2ReC(Tol)ꢀCꢀ13C(Ph)PPh3 (7-13C)
1
out isolation. H-NMR (CD2Cl2, 500 MHz, −80°C) l
2.29 (s, CH3), 2.74 (d, 2JPH=12.2 Hz, PCH3), 4.65 (C5H5),
Compound 7-13C was prepared from Cp(CO)2ReꢀC-
(Tol)(Cꢁ13CPh) (1a-13C) (10 mg, 0.020 mmol) and PPh3
(15 mg, 0.057 mmol) in 0.4 ml CD2Cl2. 1H-NMR (CD2Cl2,
500 MHz) l 2.25 (s, CH3), 4.82 (s, C5H5), 7.09–7.75 (m
aromatic). 13C{1H}-NMR (CD2Cl2, 125 MHz) label at
6.93–7.90 (m, aromatic). 13C{1H}-NMR (CD2Cl2, 125
MHz) label at l 91.5 (d, 3JCP=9.5 Hz, Cꢁ13CPh).
3
31P{1H}-NMR (CD2Cl2, 202.5 MHz) l 27.5 (d, JCP
=
10.0 Hz).
1
The sample was warmed to −20°C for 1 h to form
l 59.4 (d, JCP=106.9 Hz, C=13CP). 31P{1H}-NMR
Cp(CO)2ReC(Tol)ꢀCꢀ13C(Ph)(PPh2CH3) (6-13C). 1H-
(CD2Cl2, 202.5 MHz) l 20.2 (d, JCP=106.9 Hz).
1

C.P. Casey et al. / Journal of Organometallic Chemistry 617–618 (2001) 723–736
3 3%
733
2
4.12. Cp(CO)2ReC(Tol)ꢀ13Cꢀ13C(Ph)PPh3 (7-13C2)
aromatic), 139.23 (dt, , JCH=6.7 Hz, JCP=20.3 Hz,
aromatic), 140.51 (s, broad), 207.82 (s, CO), 207.94 (s,
CO), 215.57 (s, ReCꢀC). 31P{1H}-NMR (CD2Cl2, 202.5
Compound 7-13C2 was prepared from Cp(CO)2ReꢀC-
(Tol)(13Cꢁ13CPh) (1a-13C2) (7.6 mg, 0.015 mmol) and
PPh3 (28.4 mg, 0.108 mmol) in 0.4 ml CD2Cl2. 1H-
NMR (CD2Cl2, 500 MHz, −40°C) l 2.19 (s, CH3),
2.23 (s, CH3), 4.72 (s, C5H5), 7.09–7.75 (m aromatic).
13C{1H}-NMR (CD2Cl2, 125 MHz, −40°C) l 20.61
MHz) l 39.5. IR (CH2Cl2) 1878, 1806 cm−1
.
4.14. Cp(CO)2Re[Cꢀ13C(Ph)PPh2CHCH2C(Tol)]
(8-13C)
1
1
(CH3), 20.80 (CH3), 58.79 (dd, JCC=94.9 Hz, JCP
=
=
Compound 8-13C (12 mg, 94% yield) was obtained
from Cp(CO)2ReꢀC(Tol)(Cꢁ13CPh) (1a-13C) (9 mg, 0.02
mmol) and Ph2PCHꢀCH2 (15 mg, 0.070 mmol). 1H-
NMR (CD2Cl2, 500 MHz) l 1.71 (dt, 2,3J=5.4 Hz,
1
107.3 Hz, 13Cꢀ13CP), 83.17 (C5H5), 97.77 (ddd, JCC
93.8 Hz, 2JCC=4.7 Hz 3JCP=13.6 Hz, ReCꢀ13C),
123–145 (12 aromatic peaks), 187.04 (labeled, dd,
1JCC=94.9 Hz, 2JCP=10.2 Hz, Cꢀ13Cꢀ13C), 208.61
(CO), 209.69 (CO). 31P{1H}-NMR (CD2Cl2, 202.5
MHz) l 21.7 at −40°C, 20.2 at 24°C.
3JPH=11.5 Hz, CHHtransCH), 1.83 (dddd, J=8.6 Hz,
3
2J=5.8 Hz, 3JPH=15.6 Hz, 3JCH=3.5 Hz,
CHcisHCH), 2.36 (s, CH3), 2.71 (ddd, 3J=8.8 Hz,
2
3J=5.3 Hz, JPH=9.3 Hz, CHP), 4.49 (s, C5H5), 7.08–
4.13. Cp(CO)2Re[CꢀC(Ph)PPh2CHCH2C(Tol)] (8)
7.12 (m, aromatic), 7.16 (d, 3J=7.9 Hz, aromatic),
7.20–7.27 (m, aromatic), 7.30–7.51 (m, aromatic),
7.53–7.72 (m, aromatic). 13C-NMR (CD2Cl2, 125
Addition of Ph2PCHꢀCH2 (18 mg, 0.084 mmol) to a
solution of Cp(CO)2ReꢀC(Tol)(CꢁCPh) (1a) (22 mg,
0.043 mmol) in 1 ml CH2Cl2 produced a yellow orange
solution after 10 min. After 48 h, pentane was added to
precipitate a yellow solid. The crude product was redis-
solved in a few drops of CH2Cl2 and 1 ml hexane was
slowly added to give 8 (28 mg, 90%) as orange crystals
1
2
MHz) l 21.28 (CH3), 22.50 (dd, JCP=97.1 Hz, JCC
=
2
6.1 Hz, PCH), 26.18 (CH2), 61.72 (d, JCP=14.7 Hz,
CTol), 83.74 (C5H5), 114.50 (d, 1JCP=68.5 Hz,
Cꢀ13CP), 121.96 (d, 1JCP=82.9 Hz, Cipso), 126.53
(d1JCP=76.3 Hz, Cipso), 126.96 (aromatic), 128.22 (d,
4JCP=2.2 Hz, aromatic), 128.73 (aromatic), 129.57
1
3
suitable for X-ray crystallography. H-NMR (CD2Cl2,
(aromatic), 129.70 (d, JCP=50.4 Hz, aromatic), 129.99
500 MHz) l 1.71 (dt, 2,3J=5.4 Hz, 3JPH=11.5 Hz,
CHHtransCH), 1.83 (ddd, 3J=8.6 Hz, 2J=5.8 Hz,
3JPH=15.6 Hz, CHcisHCH), 2.36 (s, CH3), 2.71 (ddd,
(aromatic), 132.69 (d, JCP=10.1 Hz, aromatic), 133.10
3
3
(aromatic), 133.14 (d, JCP=12.4 Hz, aromatic), 133.54
(broad, aromatic), 133.73 (broad, aromatic), 136.31
3
2
1
2
3J=8.8 Hz, J=5.3 Hz, JPH=9.3 Hz, CHP), 4.49 (s,
(aromatic), 139.29 (dd, JCC=62.8 Hz, JCP=20.3 Hz,
aromatic), 140.56 (s, broad), 207.77 (s, CO), 207.89 (s,
CO), 215.71 (d, 1JCC=48.8 Hz, ReCꢀ13C). 31P{1H}-
3
3
C5H5), 7.11 (d, J=7.1 Hz, aromatic), 7.16 (d, J=7.9
3
Hz, aromatic), 7.20–7.27 (m, aromatic), 7.33 (d, J=
1
8.0 Hz, aromatic), 7.40–7.51 (m, aromatic), 7.53–7.72
NMR (CD2Cl2, 202.5 MHz) l 39.5 (d, JCP=68.7 Hz).
(m, aromatic). 13C-NMR (CD2Cl2, 125 MHz) l 21.24
IR (CH2Cl2) 1878, 1806 cm−1. HRMS(EI) m/z Calc.
36
1
1
(q, JCH=126.5 Hz, CH3), 22.50 (ddt, JCH=176.3 Hz,
2,2%JCH=3.3 Hz, 1JCP=97.1 Hz, PCH), 26.11 (dddd,
1JCH=176.4 Hz, 1JCH=162.2 Hz, 2JCH=5.9 Hz,
for C CH30O2PRe (M+) 725.1575, found 725.1564.
13
4.15. Cp(CO)2Re[13Cꢀ13C(Ph)PPh2CHCH2C(Tol)] (8-
13C2)
2
2JCP=5.6 Hz, CH2), 61.72 (d, JCP=14.7 Hz, CTol),
83.72 (dp, 1JCH=177.3 Hz, 2,3JCH=5.9 Hz, C5H5),
114.65 (dt, 3,3%JCH=3.5 Hz, 1JCP=68.9 Hz, CꢀCP),
121.96 (dt, 3,3%JCH=8.5 Hz, 1JCP=82.9 Hz, Cipso),
126.45 (dt, 3,3%JCH=7.9 Hz, 1JCP=76.3 Hz, Cipso),
Compound 8-13C2 (6 mg, 85% yield) was obtained
from Cp(CO)2ReꢀC(Tol)(13Cꢁ13CPh) (1a-13C2) (9 mg,
0.01 mmol) and Ph2PCHꢀCH2 (8 mg, 0.04 mmol).
13C{1H}-NMR (CD2Cl2, 125 MHz) l 114.58 (dd,
1JCC=48.9 Hz, 1JCP=68.1 Hz, 13Cꢀ13CP), 215.5 (d,
1JCC=48.9 Hz, Re13Cꢀ13C). 31P{1H}-NMR (CD2Cl2,
1
3 3%
4
126.97 (dtd, JCH=159.1 Hz , JCH=7.1 Hz, JCP
=
2.2 Hz, aromatic), 128.20 (dtd, 1JCH=160.0 Hz
3,3%JCH=6.2 Hz, JCP=2.2 Hz, aromatic), 128.71 (dt,
4
1JCH=155.7 Hz 3,3%JCH=5.7 Hz, aromatic), 129.57 (dd,
1JCH=155.6 Hz, 3JCH=4.8 Hz, aromatic), 129.69 (ddd,
202.5 MHz) l 39.5 (d, JCP=68.7 Hz).
1
1JCH=163.6 Hz, JCH=7.2 Hz, JCP=50.8 Hz, aro-
4.16. Cp(CO)2Re[CꢀC(Ph)PPh2CH(CHꢀCH2)CH(Tol)]
(9a)
3
3
matic), 129.99 (dd, 1JCH=163.5 Hz, 3JCH=7.1 Hz,
1
3
aromatic), 132.69 (ddt, JCH=162.2 Hz, JCH=8.5 Hz,
3JCP=10.1 Hz, aromatic), 133.08 (dt, JCH=162.7 Hz,
Reaction of Cp(CO)2Re=C(Tol)CꢁCPh (1a) (15 mg,
0.030 mmol) with Ph2PCH2CHꢀCH2 (22 mg, 0.097
mmol) gave a 5:1 mixture of 9a-(anti ): 9a-(syn) (21 mg,
97%). Pure 9a-(anti ) (14 mg, 60%) was isolated as
orange crystals by slow evaporation of a CH2Cl2/hex-
ane solution.
1
3,3%JCH=7.0 Hz, aromatic), 133.10 (dd, 1JCH=161.8
3
3
Hz, JCH=7.6 Hz, JCP=12.4 Hz, aromatic), 133.54
(dtd, 1JCH=162.8 Hz, 3JCH=5.6 Hz, 4JCP=3.4 Hz,
aromatic), 133.7 (dtd, JCH=162.4 Hz, JCH=7.1 Hz,
4JCP=3.4 Hz, aromatic), 136.29 (q, 2JCH=6.5 Hz,
1
3

734
C.P. Casey et al. / Journal of Organometallic Chemistry 617–618 (2001) 723–736
1
Compound 9a-(anti): H-NMR (CD2Cl2, 500 MHz)
enhancement (4.6%) of the vicinal allylic syn hydrogen
at l 4.37 and no NOE enhancement of the internal
vinyl hydrogen (CHCHꢀCH2, l 4.72).
3
3
l 2.36 (s, CH3), 3.84 (ddd, J=9.5 Hz, J=5.9 Hz,
2JPH=11.4 Hz, CHCH=), 4.36 (s, C5H5), 4.77 (d,
3J=5.8 Hz, CHTol), 5.00 (dd, J=16.7 Hz, JPH=4.0
3
4
3
4
Hz, CHꢀCHHtrans), 5.03 (dd, J=10.0 Hz, JPH=2.4
4.17. Cp(CO)2Re[Cꢀ13C(Ph)PPh2CH-
(CHꢀCH2)CH(Tol)] (9a-13C)
3
3 3%
Hz, CHꢀCHcisH), 5.36 (dtd, J=16.8 Hz, , J=10.0
Hz, 3JPH=5.8 Hz, CHꢀCH2), 7.11 (d, 3J=8.1 Hz, tolyl
CH), 7.15 (d, 3J=8.1 Hz, tolyl CH), 7.19–7.29 (m,
Reaction of Cp(CO)2ReꢀC(Tol)Cꢁ13CPh (1a-13C) (10
mg, 0.020 mmol) with Ph2PCH2CHꢀCH2 (14 mg, 0.062
3
3
aromatic CH), 7.44 (dd, J=8.2 Hz, JPH=11.2 Hz,
aromatic CH), 7.48 (td, 3J=7.8 Hz, 4JPH=3.2 Hz,
aromatic CH), 7.55–7.62 (m, aromatic CH). 13C{1H}-
NMR (CD2Cl2, 125 MHz) l 21.25 (CH3), 52.63 (d,
mmol) gave a 5:1 mixture of 9a-13C-(anti): 9a-13C-(syn)
13
37
(14 mg, 97%). HRMS(EI) m/z Calc. for C CH32O2PRe
(M+) 739.1732, found 738.1739.
1JCP=57.4 Hz, PCH), 77.01(d, JCP=19.0 Hz, CTol),
Compound 9a-13C-(anti): 13C{1H}-NMR (CD2Cl2,
2
1
83.73 (C5H5), 117.14 (d, JCP=63.2 Hz, CꢀCP), 120.14
125 MHz) l 117.15 (d, 1JCP=64.1 Hz, Cꢀ13CP).
3
1
1
(d, JCP=12.1 Hz, ꢀCH2), 122.38 (d, JCP=61.5 Hz,
Cipso), 122.95 (d, 1JCP=57.5 Hz, Cipso), 126.97 (d,
2JCP=2.3 Hz, CHꢀ), 128.33 (aromatic), 128.89 (aro-
matic), 129.45 (aromatic), 129.81 (d, 2JCP=11.4 Hz,
aromatic), 129.95 (d, 2JCP=12.35 Hz, aromatic), 131.90
31P{1H}-NMR (CD2Cl2, 202.5 MHz) l 35.9 (d, JCP
=
64.1 Hz).
Compound 9a-13C-(anti): 13C{1H}-NMR (CD2Cl2,
125 MHz) l 115.57 (d, 1JCP=64.1 Hz, Cꢀ13CP).
1
31P{1H}-NMR (CD2Cl2, 202.5 MHz) l 30.5 (d, JCP
=
3
3
(d, JCP=4.5 Hz, aromatic), 132.46 (d, JCP=4.6 Hz,
aromatic), 132.51 (aromatic), 133.69 (d, JCP=2.3 Hz,
aromatic), 133.86 (d, JCP=2.4 Hz, aromatic), 134.01
(d, JCP=10.1 Hz, aromatic), 136.05 (aromatic), 140.28
64.1 Hz).
4
4
4.18. Cp(CO)2Re[CꢀC(Tol)PPh2CH(CHꢀCH2)-
CH(Tol)] [9c-(anti)]
3
(d, 3JCP=18.2 Hz, Cipso-tolyl), 143.27 (d, 3JCP=6.7 Hz,
Cipso-phenyl), 208.38 (CO), 208.74 (CO), 216.55 (d,
2JCP=4.2 Hz, ReCꢀC). 31P{1H}-NMR (CD2Cl2, 202.5
MHz) l 35.9. IR (CH2Cl2) 1877, 1804 cm−1. HRM-
S(EI) m/z Calc. for C38H32O2PRe (M+) 738.1698,
found 738.1729.
Compound 9c-(anti) (22 mg, 63% yield) was synthe-
sized from Cp(CO)2ReꢀC(Tol)CꢁCTol (1c) (24 mg,
0.051 mmol) and Ph2PCH2CHꢀCH2 (27 mg, 0.12
mmol). Crystals suitable for X-ray crystallography were
obtained by slow evaporation of
a
10:10:1
1
1
Compound 9a-(syn): H-NMR (CD2Cl2, 500 MHz) l
CH2Cl2:hexane:THF solution. H-NMR (CD2Cl2, 500
3
3
2.28 (s, CH3), 4.37 (CHCHꢀCH2, overlap with Cp
signal of major isomer) [37],4.51 (s, C5H5), 4.72 (ddt,
3J=16.8 Hz, 3JPH=4.8 Hz, 3,3%J=10.0 Hz (triplet),
CHꢀCH2), 4.99 (ddd, CHꢀCHcisH, overlap with
[CHꢀCHHtrans]-signal of major compound) [38] 5.20
(ddd, 3J=16.8 Hz, 4J=1.3 Hz, 4JPH=4.0 Hz,
MHz) l 2.32 (s, CH3), 3.82 (ddddd, J=9.6 Hz, J=
5.8 Hz, 4J=0.5 Hz, 4J=0.5 Hz, 2JPH=11.3 Hz,
CHCHꢀCH2), 4.36 (s, C5H5), 4.75 (d, 3J=6.0 Hz,
3
2
4
CHTol), 4.99 (dddd, J=16.9 Hz, J=1.4 Hz, J=0.3
Hz, 4JPH=4.0 Hz, CHꢀCHHtrans), 5.02 (dddd, 3J=
10.1 Hz, 2J=1.1 Hz, 4J=0.6 Hz, 4JPH=2.4 Hz,
3
3
3
3
CHꢀCHHtrans), 5.65 (dd, J=8.6 Hz, JPH=21.4 Hz,
CHꢀCHcisH), 5.34 (dddd, J=16.0 Hz, J=10.0 Hz,
3 3
3
3
CHTol), 7.11 (d, J=8.1 Hz, tolyl CH), 7.15 (d, J=
8.1 Hz, tolyl CH), aromatic signals overlap with major
isomer. 13C{1H}-NMR (CD2Cl2, 125 MHz) l 21.25
3J=9.7 Hz, JPH=5.7 Hz, CHꢀCH2), 7.09 (d, J=8.2
3
Hz, tolyl CH), 7.14 (d, J=8.2 Hz, tolyl CH), 7.30–
3
3
7.75 (m, aromatic CH), 7.44 (dd, J=8.2 Hz, JPH
=
(CH3), 50.76 (d, 1JCP=59.7 Hz, PCH), 77.97 (d, 1JCP
=
11.2 Hz, aromatic CH), 7.48 (td, 3J=7.8 Hz, 4JPH=3.2
Hz, aromatic CH), 7.55–7.62 (m, aromatic CH). IR
(CH2Cl2) 1877, 1802 cm−1. HRMS(EI) m/z Calc. for
C39H34O2PRe (M+) 752.1855, found 752.1875.
17.5 Hz, CTol), 84.27 (C5H5), 115.62 (d, 1JCP=64.4
4
Hz, CꢀCP), 119.78 (d, JCP=11.8 Hz, CꢀCH2), aro-
matic signals and signal of CHꢀCH2 overlap with peaks
of major compound, 208.95 (CO), 209.18 (CO), 220.26
(d, 2JCP=7.1 Hz, ReCꢀC). 31P{1H}-NMR (CD2Cl2,
202.5 MHz) l 30.5.
4.19. Protonation of Cp(CO)2Re[C(Tol)ꢀ13Cꢀ13C(Ph)-
(PPh2CH3) (6-13C2) at −80°C
NOE studies of 9a-(anti) and 9a-(syn). The stereo-
chemical assignment of 9a-(anti) and 9a-(syn) was es-
tablished by NOE difference experiments. Irradiation of
the benzylic ring hydrogen TolCH (l 4.77) in 9a-(anti)
led to a 2.0% NOE enhancement of the vicinal allylic
hydrogen (CHCHꢀCH2, l 3.84) and a 3.0% enhance-
ment of the internal vinyl hydrogen (CHCHꢀCH2, l
5.36). By contrast, irradiation of the benzylic ring hy-
drogen in 9a-(syn) (l 5.65) resulted in a strong NOE
Compound CF3SO3H (1.5 mL, 0.017 mmol) was
added to the solution of (6-13C2) at −80°C. Spectra of
the resulting solution of [Cp(CO)2(H)Re(Tol)-
Cꢀ13Cꢀ13C(Ph)(PPh2CH3)]OTf (10-13C2) were recorded
1
at −80°C. H-NMR (CD2Cl2, 500 MHz, −80°C) l
2
−8.57 (s, ReH), 2.29 (s, CH3), 2.49 (d, JPH=12.8 Hz,
PCH3), 5.03 (C5H5), 7.0–7.8 (m, aromatic). 13C{1H}-
NMR (CD2Cl2, 125 MHz, −80°C) label at l 72.6 (dd,

C.P. Casey et al. / Journal of Organometallic Chemistry 617–618 (2001) 723–736
735
1JCC=97.0, 1JCP=97.0 Hz, P13Cꢀ13C), 201.4 (dd,
5. Supplementary material
2
1JCC=97.0, JCP=7.6 Hz, Cꢀ13Cꢀ13C). 31P{1H}-NMR
1
(CD2Cl2, 202.5 MHz, −80°C) l 22.0 (dd, JCP=97.6,
Crystallographic data (excluding structure factors)
for compounds 3, 4, 8, and 9c have been deposited with
the Cambridge Crystallographic Data Center, CCDC
150167 for compound 3, CCDC 150164 for compound
4, CCDC 150166 for compound 8, and CCDC 150165
for compound 9c. Copies of this information may be
obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or http://
www.ccdc.cam.ac.uk).
2JCP=6.1 Hz).
At −80°C, conversion of 10-13C2 to Cp(CO)2Re[h2-
2,3-(Tol)HCꢀ13Cꢀ13C(Ph)(PPh2CH3)]OTf (11-13C2) oc-
curred with a half-life of 30 min. 11-13C2 was stable at
1
r.t. H-NMR (CD2Cl2, 500 MHz) l 2.27 (s, CH3), 2.45
(d, 2JPH=13.0 Hz), 4.4 (br s, ꢀCH), 5.33 (C5H5),
7.0–7.8 (m, aromatic). 13C{1H}-NMR (CD2Cl2, 125
MHz) l 111.35 (dd, 1JCC=86.1, 1JCP=74.11 Hz,
13Cꢀ13CP), 182.6 (dd, 1JCC=86.1, 2JCP=8.7 Hz,
13Cꢀ13CP). 31P{1H}-NMR (CD2Cl2, 202.5 MHz) l 17.5
1
2
(dd, JCP=74.3, JCP=8.9 Hz).
4.20. Cp(CO)2Re[p2-2,3-(Tol)DCꢀCꢀC(Ph)-
(PPh2CH3)]OTf (11-d)
Acknowledgements
Financial support from the National Science Foun-
dation is gratefully acknowledged. Grants from NSF
(CHE-9629688) for the purchase of the NMR spec-
trometers and a diffractometer (CHE-9709005) are
acknowledged.
Addition of Ph2PCH3 (13 mg, 0.064 mmol) to a black
solution of Cp(CO)2ReꢀC(Tol)(CꢁCPh) (1a) (28 mg,
0.053 mmol) in 1 ml CH2Cl2 at −20°C produced an
orange solution after 15 min. The solution was cooled
to −78°C and CF3SO3D (5 ml, 0.6 mmol) was added
by syringe. Solvent was evaporated under vacuum at
r.t. and the resulting yellow-brown precipitate was
washed with diethyl ether and dissolved in a few drops
of CH2Cl2. Slow vapor diffusion of pentane into the
solution at −35°C gave fine white needles of 11-d (25
mg, 45%). 1H-NMR (THF-d8, 500 MHz) l 2.20 (s,
CH3), 2.61 (d, 2JPH=13.5 Hz, PCH3), 5.44 (C5H5), 6.90
(d, 3J=7.9 Hz, aromatic), 7.31–7.49 (m, aromatic),
References
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4
7.61–7.64 (m, aromatic), 7.72 (ddd, J=13.0, J=1.2,
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8-13C2
was
directly
obtained
from
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2
17.14. H-NMR (THF-d8, 76.8 MHz) l 4.50 (broad).
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KO-t-Bu at −78°C
[6] (a) M. Hesse, H. Meier, B. Zeeh, Spectroskopische Methoden in
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Addition KO-t-Bu (17 mL of a 0.50 M solution in
THF-d8, 0.0085 mmol) to a colorless solution of 11-d
(5.7 mg, 0.0056 mmol) in 0.4 ml CD2Cl2 at −78°C
immediately produced a bright yellow solution of a 3:1
1
mixture of 4-d:6 as shown by H-NMR.
Compound 4-d: 1H-NMR (THF-d8, 500 MHz,
2
2
−91°C) l 2.27 (s, CH3), 3.13 (dd, J=16.7, JPH=8.1
Hz, PCHH), 3.35 (dd, 2J=16.5, 2JPH=12.6 Hz,
PCHH), 4.10 (C5H5), 7.0–7.8 (aromatic). 2H-NMR
(THF, 76.8 MHz, −91°C) l 5.4 (CH2CD). 31P{1H}-
NMR (THF-d8, 202.5 MHz, −91°C) l 34.5.
Compound 6: 1H-NMR (THF-d8, 500 MHz,
−91°C) l 2.22 (s, CH3), 2.47 (d, 2JPH=13.0 Hz,
PCH3), 4.94 (C5H5), 7.0–7.8 (aromatic). 31P-NMR
(THF-d8, 202.5 MHz, −91°C) l 17.7.
3
[9] The expected vicinal H-D couplings JHC should be 1/7 of the
respective 3JHH coupling in 4 (2.8 and 8.8 Hz) which would amount
to 0.4 and 1.3 Hz. With a resolution of 1.5 Hz in this low
temperature experiment we were unable to observe these couplings.

736
C.P. Casey et al. / Journal of Organometallic Chemistry 617–618 (2001) 723–736
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1H{31P}-NMR spectrum.