Phosphaalkyne cyclodimerization at a rhodium(I) centre. Syntheses of a cationic η4-1,3-diphosphacyclobutadiene rhodium complex and of its platinum(II) or tungsten(0) adducts

Article abstract of DOI:10.1039/a903130h

Treatment of [RhCl(triphos)] [triphos = PPh(CH₂CH₂PPh₂)₂] in thf with PnCBu^t, in the presence of TlBF₄, gave the η⁴-1,3-diphosphacyclobutadiene complex [Rh(triphos){η⁴-(PCBu^t)₂}][BF₄] 1a which formed the diadducts [Rh(triphos){η⁴:η¹:η¹-[W(CO) ₅]₂(PCBut)2}][BF₄] 2 or [Rh(triphos){η⁴:η¹:η¹-[PtCl ₂(PEt₃)]₂(PCBu^t) ₂}][BF₄] 3 on reaction with [W(CO)₅(thf)] or [Pt₂Cl₄(PEt₃)₂], respectively. These adducts dissociated in solution, the former in the presence of Na[BPh₄] to give [Rh(triphos){η⁴-(PCBu^t)₂}][BPh₄] 1b, and the latter to the mono-η¹-adduct [Rh(triphos){η⁴:η¹-[PtCl₂(PEt ₃)](PCBu^t)₂}][BF₄] 4. Reactions of [RhCl(triphos)] in thf with the 1-alkynes HC≡CR (R = CO₂Me or CO₂Et) in the presence of Tl[BF₄] afforded the corresponding benzene derivative complexes [Rh(triphos){η⁴-(HCCR)₃}][BF₄] 5a or 5b.

Full text of DOI:10.1039/a903130h

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Phosphaalkyne cyclodimerization at a rhodium(I) centre. Syntheses
of a cationic ꢀ4-1,3-diphosphacyclobutadiene rhodium complex and
of its platinum(II) or tungsten(0) adducts
Mohamed F. Meidine,a Armando J. L. Pombeiro*a and John F. Nixonb
a Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Av. Rovisco Pais,
1049-001 Lisboa, Portugal. E-mail: pombeiro@alfa.ist.utl.pt
b School of Chemistry, Physics and Environmental Science, University of Sussex, Brighton,
UK BN1 9QJ. E-mail: J.Nixon@sussex.ac.uk
Received 20th April 1999, Accepted 2nd July 1999
t
᎐
Treatment of [RhCl(triphos)] [triphos = PPh(CH CH PPh ) ] in thf with P᎐CBu , in the presence of TlBF , gave
᎐
2
2
2
2
4
the η4-1,3-diphosphacyclobutadiene complex [Rh(triphos){η4-(PCBut)2}][BF4] 1a which formed the diadducts
[Rh(triphos){η4 :η1 :η1-[W(CO)5]2(PCBut)2}][BF4] 2 or [Rh(triphos){η4 :η1 :η1-[PtCl2(PEt3)]2(PCBut)2}][BF4] 3
on reaction with [W(CO)5(thf)] or [Pt2Cl4(PEt3)2], respectively. These adducts dissociated in solution, the former
in the presence of Na[BPh4] to give [Rh(triphos){η4-(PCBut)2}][BPh4] 1b, and the latter to the mono-η1-adduct
4
1
t
᎐
[Rh(triphos){η :η -[PtCl (PEt )](PCBu ) }][BF ] 4. Reactions of [RhCl(triphos)] in thf with the 1-alkynes HC᎐CR
᎐
2
3
2
4
(R = CO2Me or CO2Et) in the presence of Tl[BF4] afforded the corresponding benzene derivative complexes
[Rh(triphos){η4-(HCCR)3}][BF4] 5a or 5b.
(PCBut)2}] (M = Co5 or Rh6) occur via displacement of the two
Introduction
ethylene ligands from the corresponding diethylene parent
complexes, and, in the case of Rh, the yields are low and other
types of products are also formed,6 e.g. metallacycles, P–P rings
or bridging cyclobutadiene ligands in polynuclear assemblies.
Our synthesis is more selective towards a mononuclear η4-1,3-
diphosphacyclobutadiene complex and has a higher yield. The
different steric hindrance of triphos compared with the cyclo-
pentadienyl-type ligands, as well as its distinct electronic
properties, conceivably constitute favourable factors for the
above reaction.
Phosphaalkynes are known to undergo a variety of cycloaddi-
tion reactions at transition metal centres to generate novel
P-containing rings,1,2 and in particular η4-1,3-diphosphacyclo-
butadiene complexes of Group 9 metals3–12 have been prepared
in such a way. However, in contrast to Co, the yields of the η4-
1,3-diphosphacyclobutadiene compounds of Rh are commonly
low and a variety of other products can be formed involving e.g.
the co-ordination of the phosphorus lone pair to another metal
centre, the formation of a metallacycle or the occurrence of
P–P coupling, namely in the reactions of a phosphaalkyne with
η5-indenyl or η5-cyclopentadienyl complexes such as [Rh(η5-
In the 13C-{1H} NMR spectrum of complex 1a the P᎐CCMe
᎐
3
signal of the η4-diphosphacyclobutadiene ligand occurs as a
L)(η2-CH ᎐CH )] (L = C H , C H or C Me ).3–6
᎐
2
2
9
7
5
5
5
5
broad resonance at δ 101.0, whereas that of P᎐CCMe is
᎐
3
We have selected a rhodium centre, [RhCl(triphos)] [triphos-
= PPh(CH2CH2PPh2)2], presenting a tridentate ligand with dif-
ferent steric and electronic properties to those of η5-indenyl or
observed as a broad singlet at δ 33.30. These chemical shifts
are in agreement with those reported6 for the related (η4-
1,3-diphosphacyclobutadiene)(η6-indenyl)rhodium
complex
5
t
᎐
η -cyclopentadienyl and now report its reaction with P᎐CBu ,
[Rh(η5-C9H7){η4-(PCBut)2}] (δ 112.7 and 34.5), respectively,
although in 1a the broadness of the resonances precluded the
estimate of J(CP) and J(CRh).
᎐
which leads to the selective formation, in high yield, of the
η4-1,3-diphosphacyclobutadiene complex [Rh(triphos){η4-
t
᎐
(P᎐CBu ) }][BF ] 1a. Moreover in view of our interest in the
The 31P-{1H} NMR spectrum of complex 1a presents a
rather complicated pattern which was successfully analysed
(Fig. 1) as an AAЈMRRЈX spin system (A, AЈ = P1P2; M = P3;
R, RЈ = P4, P5; X = Rh, see Scheme 1). In particular, the reson-
ance of the 1,3-diphosphacyclobutadiene 31P nuclei (A, AЈ) is a
complex multiplet centred at δ 83.51 (relative to H3PO4) with
2J(P1P2) = 17.0 and J(P1Rh) = J(P2Rh) = 17.1 Hz. The latter
coupling constant is smaller than those observed [J(P3Rh) =
138.0, J(P4Rh) = J(P5Rh) = 129.5 Hz] between the metal and
the phosphine 31P nuclei, and is even lower than those reported,
ca. 30 Hz, for [Rh(η5-C5R5){η4-(PCBut)2}] (R = H or Me)3 and
[Rh(η5-C9H7){η4-(PCBut)2}],6 thus ruling out3 the phosphorus
᎐
2
4
comparison of the co-ordination chemistries of phos-
phaalkynes and alkynes,1,9,13–16 we have also investigated the
᎐
reactions of HC᎐CR (R = CO Me or CO Et) with the above
᎐
2
2
Rh–triphos starting material and noticed that, in contrast with
t
᎐
P᎐CBu , alkyne cyclodimerization is not the preferred reaction.
᎐
Results and discussion
t
᎐
The reaction of P᎐CBu with [RhCl(triphos)], in thf, in the
᎐
presence of TlBF4 as a chloride ligand abstractor, results in
cyclodimerization of the phosphaalkyne to form the η4-1,3-
diphosphacyclobutadiene complex [Rh(triphos){η4-(PCBut)2}]-
[BF4] 1a (reaction 1, Scheme 1) which was isolated in high yield
(80%) as a yellow solid and characterized (see Experimental
metallacycle ring RhP᎐C(But)C(But)᎐P or possible η1-P bind-
᎐
᎐
ing mode where a value of J(PRh) of 150–200 Hz would be
more typical.
1
section) by elemental analysis, IR, H, 31P-{1H} and 13C-{1H}
NMR spectroscopies and FAB-MS spectrometry.
In the FAB-MS spectrum of complex 1a the molecular ion
and the fragment derived from loss of the diphosphacyclobuta-
diene ring are observed at 839 (Mϩ) and 638 ([M Ϫ 2PCBut]ϩ).
Complex 1a, in thf, reacts with [W(CO)5(thf)], added in a
The reported syntheses of the related η5-cyclopentadienyl-
type complexes [M(η5-C5R5){η4-(PCBut)2}] (M = Co, Rh or Ir;
R = H or Me)3,4 and η5-indenyl compounds [M(η5-C9H7){η4-
J. Chem. Soc., Dalton Trans., 1999, 3041–3045
3041

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t
᎐
Scheme 1 Reactions of [RhCl(triphos)] with P᎐CBu [triphos = P4P3P5 = PPh(CH2CH2PPh2)2].
᎐
2.7:1 molar ratio, to form (reaction 2, Scheme 1) the bis-η1-
which could be assigned to ν(CO) was detected, and its 31P-{1H}
NMR spectrum was similar to that of 1a.
adduct [Rh(triphos){η4 :η1 :η1-[W(CO)5]2(PCBut)2}][BF4] 2,
resulting from ligation of each of the electron lone pairs of the
two phosphorus atoms of the diphosphacyclobutadiene ring to
a {W(CO)5} centre. The co-ordination of one such P atom to
another rhodium site has been recognized previously in other
complexes such as [Rh(η5-C5H5){η4-(PCBut)2}]7 or [Rh(η5-
C9H7){η4-(PCBut)2}],6 and in the present case the addition reac-
tion proceeded further towards a diadduct involving both P
atoms of the ring. Complex 2 was isolated (77% yield) as a
greenish orange powder and characterized (see Experimental
section) by elemental analysis, IR, 1H and 13P-{1H} NMR
spectroscopies and FAB-MS spectrometry.
The ability of the ring phosphorus atoms to act as donor sites
towards {PtCl2(PEt3)} was also tested and the diadduct
[Rh(triphos){η4 :η1 :η1-[PtCl2(PEt3)]2(PCBut)2}][BF4]
3
was
obtained as an orange solid (reaction 4, Scheme 1). This reac-
tion parallels that observed8 for [Co(η5-C5Me5){η4-(PCBut)2}]
which adds the same platinum centre to form [Co(η5-
C5Me5){η4-Pt2Cl4(PEt3)2(PCBut)2}] as well as the intermediate
mono-adduct.
The molecular ion of the diadduct 3 is observed in its FAB-
MS spectrum, as well as the expected fragments derived upon
sequential loss of the platinum sites and of the diphospha-
cyclobutadiene ring, i.e. [M Ϫ {PtCl2(PEt3)}]ϩ, [M Ϫ {PtCl2-
(PEt3)}2]ϩ and [M Ϫ {PtCl2(PEt3)2}-(PCBut)2]ϩ.
The ligation of the P atoms (P1 and P2) of the 1,3-diphospha-
cyclobutadiene ring to the {W(CO)5} centres does not result
in a drastic change of the 31P-{1H} NMR spectrum which still
exhibits an AAЈMRRЈX spin system with a slight shift of the
complex resonance of such phosphorus nuclei from δ 83.51 (1a)
to 77.76 (2), and a slight increase of J(P1Rh) = J(P2Rh) from 17
(1a) to 24 Hz, showing that the identity of the ring has been
preserved. The coupling of P1 or P2 to 183W could not be
assigned due to the rather complex pattern of the signal.
The adduct 2 undergoes dissociation in CH2Cl2–MeOH, in
the presence of Na[BPh4], to regenerate (reaction 3, Scheme 1)
the parent complex (isolated in 85% yield) although with
[BPh4]Ϫ as the counter ion (1b). For this product no IR band
Complex 3 in CH2Cl2 solution undergoes a partial discussion
to form the monoadduct [Rh(triphos){η4 :η1-[PtCl2(PEt3)]-
(PCBut)2}][BF4] 4 (reaction 5, Scheme 1) which was the product
detected by 31P-{1H} NMR. The resonance of the ring-P
nucleus (P2) ligated to the PtCl2(PEt3) centre is a doublet
[2J(P2P6) = 493 Hz, P6 = P nucleus at PEt3] of doublets
[2J(P2P1) = 70 Hz] of multiplets, with the expected 195Pt satellites
2
[J(P2Pt) = 1987 Hz]. The high J(P2P6) value is indicative of
a trans arrangement of the PEt3 and the diphosphacyclo-
butadiene ligating the Pt as observed8 for the adduct
[Co(η5-C5Me5){η4-PtCl2(PEt3)(PCBut)2}]. The 31P resonance
3042
J. Chem. Soc., Dalton Trans., 1999, 3041–3045

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Fig. 1 Experimental (a) and simulated (b) 31P-{1H} NMR spectra of complex 1a (CD2Cl2) analysed as an AAЈMRRЈX (A, AЈ = P1,P2; M = P3;
R,RЈ = P4,P5; X = Rh) spin system.
associated to the P(6)Et3 ligand is the expected doublet
[2J(P6P2) = 493 Hz] at δ 18.55 with 195Pt satellites [J(P6Pt) = 2901
Hz]. The starting material [Pt2Cl4(PEt3)2] formed in solution
upon dissociation of 3 was also detected by its characteristic
singlet at δ 12.08 with 195Pt satellites [J(PPt) = 3827 Hz].
groups, but not from the loss of two of them. Hence, an altern-
ative formulation with a η2-cyclobutadiene and a η2-alkyne
ligand would be less favoured, although it cannot be ruled out.
Other examples of the formation of η4-arene complexes by
cyclotrimerization of alkynes are known, namely in the reac-
5
᎐
For comparative purposes, we have also investigated the reac-
tions of [Rh(η -C R )(CO) ] (R = H or Me) with RЈC᎐CRЈ
᎐
5
5
2
17
tions of [RhCl(triphos)], in thf, with the alkynes HC᎐CR
(RЈ = CF3
or CO2Me18) to yield [Rh(η5-C5R5){η4-(RЈ-
᎐
᎐
(R = CO2Me or CO2Et) in the presence of TlBF4. They appear
to lead to the formation of mixtures of isomers of complexes
which we tentatively formulate as the products of alkyne cyclo-
trimerization [Rh(triphos){η4-(HCCR)3}][BF4] (R = CO2Me 5a
or CO2Et 5b) mainly on the basis of elemental analysis, FAB-
MS spectrometry and IR spectroscopy (in view of the presence
CCRЈ)3}]. Only the products derived from alkynes with strongly
electron-withdrawing substituents (RЈ) could be isolated.
There is no evidence that alkynes behave similarly to the
phosphaalkyne in our systems and in particular we have not
obtained the η4-ligated cyclobutadiene complexes analogous to
the η4-diphosphacyclobutadiene 1a. Other cases of preferential
formation of the η4-1,3-diphosphacyclobutadiene ring in com-
parison with cyclobutadiene are known for Mo13 or Co.9
1
of various isomers, their H and 31P-{1H} NMR signals could
not clearly be identified) which indicate e.g the presence of 3
HCCR groups in the molecule. Since the co-ordination of three
alkyne molecules would not be expected (one of the P atoms of
the strongly co-ordinated triphos should be displaced from the
metal co-ordination sphere), a coupling process should occur
conceivably involving the cyclotrimerization of the alkynes. In
agreement, the FAB-MS spectra of 5a and 5b clearly exhibit the
corresponding molecular ion signals, as well as those for the
fragments derived from the loss of one and three HCCR
Experimental
All the manipulations and reactions were carried out in the
absence of air using standard inert gas flow and vacuum tech-
niques. Solvents were purified by standard procedures. The
t 21
compounds [RhCl(triphos)],19 [Pt2Cl4(PEt3)2]20 and P᎐CBu
᎐
᎐
were prepared by published methods, whereas NaBPh4 and the
J. Chem. Soc., Dalton Trans., 1999, 3041–3045
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(BF4Ϫ). NMR (CD2Cl2, 25 ЊC): 1H, δ 0.007 (s, br, 9 H, But), 1.04
᎐
1-alkynes HC᎐CR (R = CO Me or CO Et) were commercially
᎐
2
2
available (Aldrich).
(s, br, 9 H, But), 2.15–3.04 (m, 8 H, CH2) and 6.90–7.94 (m, 25
H, Ph); 31P-{1H}, δ 77.76 [m, P1P2, J(P1P2) = 16, J(P1Rh) =
J(P2Rh) = 24], 75.69 [dtt, P3, J(P1P3) = J(P2P3) = 8, J(P3Rh) = 138,
J(P3P4) = J(P3P5) = 138] and 52.24 [dm, P4P5, J(P4Rh) =
J(P5Rh) = 129, J(P1P4) = J(P2P5) = 17, J(P4P5) = 25 Hz].
Infrared measurements (KBr pellets) were carried out on a
Perkin-Elmer 683 spectrophotometer, 1H, 31P and 13C NMR on
a Varian Unity 300 spectrometer; δ values are in ppm relative
to SiMe4 (1H and 13C) or to H3PO4 (31P). Abbreviations: s =
singlet, d = doublet, t = triplet, m = complex multiplet, dd =
doublet of doublets, dt = doublets of triplets, dm = doublet of
complex multiplets, ddm = doublet of doublets of complex
multiplets, dtt = doublet of triplet of triplets, ddt = doublet of
doublets of triplets, br = broad. The FAB mass spectrometric
measurements were performed on a Trio 2000 spectrometer at
the Centro de Química Estrutural. Positive-ion spectra were
obtained by bombarding 3-nitrobenzyl alcohol matrices of
the samples with 8 keV (ca. 1.28 × 1015 J) Xe atoms. Mass
calibration for data system acquisition was achieved using
CsI.
[Rh(triphos){ꢀ4 :ꢀ1 :ꢀ1-[PtCl2(PEt3)]2(PCBut)2}][BF4] 3 and
[Rh(triphos){ꢀ4 :ꢀ1-[PtCl2(PEt3)](PCBut)2}][BF4] 4. A solution
of [Rh(triphos){η4-(PCBut)2}][BF4] 1a (0.10 g, 0.10 mmol) in
CH2Cl2 (2 cm3) was treated with a solution of [Pt2Cl4(PEt3)]
(0.038 g, 0.050 mmol) in CH2Cl2 (2 cm3) and the mixture stirred
for 15 h. The solvent was pumped off and the orange residue
washed with Et2O (2 × 5 cm3) and dried in vacuo to form
an orange solid of complex 3. FAB-MS: m/z 1605 (Mϩ), 1221
([M Ϫ PtCl2(PEt3)]ϩ), 837 ([M Ϫ {PtCl2(PEt3)}2]ϩ) and 637
([M Ϫ {PtCl2(PEt3)}2 Ϫ (PCBut)2]ϩ). IR: ν
˜
/cmϪ1 1080s (br)
(BF4Ϫ).
Preparations
In solution, the diadduct 3 converts into the corresponding
monoadduct 4 identified by 31P-{1H} NMR of a CD2Cl2 solu-
tion of 3: δ 101.59 [ddm, P2, J(P2P6) = 493, J(P2P1) 70,
J(P2Pt) = 1987], 84.17 [dm, P3, J(P3Rh) = 141.5], 71.94 (dm, br,
P1), 63.73 (m, P4), 54.62 [dm, P5, J(P5Rh) = 146.5], 18.55 [d, P6
(PEt3), J(P6P2) = 493; J(P6Pt) = 2901] and 12.08 {s, liberated
[Pt2Cl4(PEt3)]; J(PPt) = 3827 Hz}.
[Rh(triphos){ꢀ4-(PCBut)2}][BF4] 1a. A solution of [RhCl(tri-
phos)] (0.150 g, 0.223 mmol) in thf (10 cm3) was treated with a
t
3
᎐
1:1 mixture of P᎐CBu ϩ (Me Si) O (0.15 cm , 1.0 mmol of
᎐
3
2
t
᎐
P᎐CBu ) followed by addition of solid TlBF (0.10 g, 0.34
᎐
4
mmol) and stirred for 15 h. The yellow-orange solution was
then filtered and the volatiles were removed in vacuo. The resi-
due was extracted in CH2Cl2 (10 cm3), the solution filtered and
reduced in volume to ca. 1 cm3. Addition of Et2O (10 cm3)
precipitated complex 1a as a yellow solid which was separated
by decantation, washed with Et2O (10 cm3) and dried in vacuo
(0.16 g, 80%) (Found: C, 56.8; H, 5.9. C44H51BF4P5Rh requires
C, 57.1; H, 5.6%). FAB-MS: m/z 839 (Mϩ for 103Rh) and 638
[Rh(triphos){ꢀ4-(HCCR)3}][BF4] (R ؍ CO2Me 5a or CO2Et
5b). A solution of [RhCl(triphos)] (0.20 g, 0.30 mmol) in thf (50
3
᎐
cm ) was treated with the appropriate HC᎐CR [1.2 mmol, i.e.
᎐
0.10 cm3 (R = CO2Me) or 0.12 cm3 (R = CO2Et)] followed by
TlBF4 (0.17 g, 0.58 mmol) and the mixture stirred for 2 d. The
solution was then filtered and taken to dryness in vacuo. Extrac-
tion with CH2Cl2 (10 cm3), filtration of the solution and
removal of the solvent in vacuo left a residue that was washed
with Et2O (30 cm3), dried in vacuo and recrystallised from
CH2Cl2–Et2O to give a dark red (5a) or orange (5b) solid which
was filtered off and dried in vacuo (ca. 80% yields). Complex 5a
(Found: C, 53.6; H, 4.5. C46H45BF4O6P3RhؒCH2Cl2 requires C,
53.2; H, 4.5%): FAB-MS m/z 888 (Mϩ), 805 ([M Ϫ HCCR]ϩ]
([M Ϫ 2PCBut]ϩ). IR: ν/cmϪ1 1050s (br) (BF4Ϫ). NMR (CD2Cl2,
˜
25 ЊC): 1H, δ 0.017 (s, 9 H, But), 1.06 (s, 9 H, But), 2.45–3.04 (m,
8 H, CH2) and 6.88–7.90 (m, 25 H, Ph); 31P-{1H}, [AAЈMR-
RЈX] spin system (A,AЈ = P1P2; M = P3; R,RЈ = P4,P5; X = Rh),
δ 83.51 [M, P1P2, J(P1P2) = 17.0, J(P1Rh) = J(P2Rh) = 17.1],
81.45 [dtt, P3, J(P1P3) = J(P2P3) = 8.1, J(P3P4) = J(P3P5) = 25.5,
J(P3Rh) = 138.0] and 58.06 [ddt, P4P5, J(P1P4) = J(P2P5) = 16.4,
J(P2P4) = J(P1P5) = 2.4, J(P4P5) = 25, J(P4Rh) = J(P5Rh) = 129.5
Hz); 13C-{1H}, δ 29.87 [dd, CH2, 2J(CP) = 11, 1J(CP) = 29],
31.36 [dt, CH2, 2J(CP) = 8, 1J(CP) = 28 Hz], 32.05 [s, br,
and 638 ([M Ϫ 3HCCR]ϩ); IR ν/cmϪ1 1730m and 1680s
˜
[ν(CO)], 1070vs (br) (BF4Ϫ). Complex 5b (Found: C, 55.6; H,
4.9. C49H51BF4O6P3Rhؒ¹CH2Cl2 requires C, 56.0; H, 4.9%):
C(CH ) ], 33.30 (s, br, CMe ) and 101.0 (m, br, P᎐C).
¯
²
᎐
3
3
3
FAB-MS m/z 931 (Mϩ), 833 ([M Ϫ HCCR]ϩ) and 637
([M Ϫ 3HCCR]ϩ); IR ν/cmϪ1 1690s [ν(CO)] and 1050vs (br)
˜
[Rh(triphos){ꢀ4-(PCBut)2}][BPh4] 1b. To NaBPh4 (0.025 g,
0.070 mmol) was added a solution of [Rh(triphos){η4 :η1 :η1-
[W(CO)5]2(PCBut)2}][BF4] 2 (see below) (0.046 g, 0.030 mmol)
in CH2Cl2 (2.0 cm3), methanol (15 cm3) was layered on top and
the reaction allowed to proceed without stirring. In 2 d a pre-
cipitate of complex 1b formed as fibrous, orange crystals. The
supernatant solution was decanted and the crystals dried in
vacuo (0.028 g, 85% yield) (Found: C, 70.2; H, 6.2. C68H71BP5Rh
requires C, 70.6; H, 6.2%). FAB-MS; m/z 837 (Mϩ) and 637
(BF4Ϫ).
Acknowledgements
This work has been partially supported by the PRAXIS XXI
programme, the Junta Nacional de Investigação Científica e
Tecnológica (JNICT) and the Foundation for Science and
Technology (FCT) (Portugal), as well as by the Treaty of
Windsor programme (The Portuguese Council of Rectors/The
British Council) and the EC Network ERBCHRXCT 940501.
([M Ϫ (PCBut)2]ϩ). H NMR (CD2Cl2, 25 ЊC): δ 0.013 (s, br,
1
9 H, But), 1.02 (s, br, 9 H, But), 1.96–2.80 (m, 8 H, CH2) and
6.69–7.78 (m, 45 H, Ph).
References
[Rh(triphos){ꢀ4 :ꢀ1 :ꢀ1-[W(CO)5]2(PCBut)2}][BF2] 2. A solu-
tion of [Rh(triphos){η4-(PCBut)2}][BF4] 1a (0.27 g, 0.30 mmol)
in thf (15 cm3) was treated with a solution of [W(CO)5(thf)]
(0.80 mmol) in thf (20 cm3), and stirred in the dark for 3 d to
form a clear, dark orange solution. The volatiles were removed
in vacuo and the residue was extracted in CH2Cl2 (30 cm3), the
solution filtered and taken to dryness in vacuo. The resulting
dark brown sticky solid was washed with Et2O (10 cm3) by the
freeze–thaw technique and dried in vacuo to give a green-orange
powder of complex 2 (0.35 g, 77% yield) (Found: C, 43.5; H,
3.7. C54H51BF4O10P5RhW2ؒ2thf requires C, 43.4; H, 3.9%).
FAB-MS: m/z 838 ([M Ϫ 2W(CO)5]ϩ) and 637 ([M Ϫ 2W(CO)5-
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˜
2PCBut]ϩ). IR: ν/cmϪ1 1940s (br) [ν(CO)] and 1080s (br)
3044 J. Chem. Soc., Dalton Trans., 1999, 3041–3045

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