- Email: [email protected]
Dicarboxylate rhodium complexes with diolefins and carbon monoxide
Polyhedron Vol. 4, No. 2. pp. Printed in Great Britain.
325-331,
1985
0277-5387185 Q 1985 Pergamon
S3.00 + .oO Pms Ltd.
DICARBOXYLATE RHODIUM COMPLEXES WITH DIOLEFINS AND CARBON MONOXIDE Departamento
L. A. ORO,* de Quimica
M. T. PINILLOS and M. P. JARAUTA InorgBnica, Universidad de%ragoza, Zaragoza,
Spain
(Received 2 March 1984; accepted 14 April 1984) Abstract-Dinuclear rhodium complexes of the type [Rhz(C20,)(diolefin),1 (diolefin = l,Scyclooctadiene,2,Snorbornadiene and tetrafluorohenzobarrelene) with bridging oxalate ligands have been obtained by reaction of [Rh(acac)(diolefin)] with oxalic acid (2 : 1 mol ratio). The use of a 1 : 1 molar ratio affords [Rh(HC,O,)(COD)], that reacts with [Ir(acac)(COD)] yielding Lhe heterodinuclear [(COD)Rh(C,O,)Ir(COD)] complex. Treatment of [Rh,(C,O,)(diolefin),] complexes with phenanthroline type ligands leads to ionic complexes of formula [Rh(diolefin)(phen)][Rh(C,O,)(diolefin)]. Bubbling of carbon monoxide through solutions of the diolefin complexes leads to the formation of carbonylrhodium species of formula [Rh,(C,O,)(CO),L,] (L = CO, PPh,, f-BuNC) or [Rh(CO),(phen)] - [Rh(C,O,)(CO),]. Other related malonate complexes are also described.
A number of organorhodium(1) compounds containing bidentate oxygen anions have been reported.’ In particular the /3-diketonate anions form a variety of complexes which have six-membered rings. Concerning rhodium(I) complexes which have five-membered rings, some tropolonate derivatives have been recently reported.2 We describe in this paper some organorhodium complexes with the oxalate group. This dicarboxylate anion forms well-defined complexes which have five-membered rings, and it is able to function as a bidentate ligand to two metals simultaneously. In contrast, monocarboxylate anions in rhodium(I) chemistry are usually bound in a symmetrical syn-syn bridging.3 RESULTS AND DISCUSSION Oxalate diolefin complexes
The reaction of [Rh(acac)(COD)] with a stoichiometric amount of oxalic acid leads to the formation of the yellow microcrystalline compound [Rh(HC,O,)(COD)] (I). The experimental molecular weight measurements suggest a self-association by hydrogen bonding (Scheme 1). The acidic hydrogen atom in complex I can be removed with ease; thus, addition of [M(acac)(diolefin)] derivatives gives dinuclear complexes of formula [(COD)Rh(C,O,)Rh(diolefin)] (diolefin = 1,5cyclooctadiene, COD (II) or tetrafluorobenzo*Author dressed.
to whom correspondence
should
be ad-
barrelene, TFB (III)) or the heterodinuclear cbmpound [(COD)Rh(C,O,)Ir(COD)] (IV). A direct method of preparing homodinuclear complexes involves the reaction of two moles of [Rh(acac)(diolefin)] with one mole of oxalic acid, according to eqn (1): 2[Rh(acac)(diolefin)]
+ H2CzOl - 2Hz0 -
[Rh2(C20,)(diolefin)2]
+ 2 Hacac + 2 Hz0
[diolefin = COD(II), TFB(V), NBD(VI)]. Molecular weight measurements con&m the dinuclear formulation. Scheme 1 shows the suggested structures (five-membered chelate rings). The [Rh2(C20,)(diolefin)2] complexes usually react readily with different ligands. Thus, addition of the bidentate nitrogen donor ligand l,lOphenanthroline leads to the formation of ionic derivatives of formula [Rh(diolefin)(phen)] [Rh(C,O,)(diolefin)] (diolefin = COD(VI1) or TFB(VII1)). Similarly, complex V reacts with 2,2’bipyridine to give the analogous [Rh(TFB)(bipy)] IRhGO,)(TFB)I derivative (IX). The electrical conductivities of complexes VIII-IX show them to be l/l electrolytes. In particular the constituent cations of these complexes are reported species4’ of high stability. The stepwise addition of triphenylphosphite to [Rh2(C20,)(COD)2] affords the dinuclear derivatives [(COD)Rh(C20,)Rh{P(OPh)3)2] (X) and Rh2(C20,){P(OPh)3}4] (XI), but no further reaction 325
L.
326
.\/\ ml
A. OR0
et al.
Dicarboxylate rhodium complexes with diolefins and carbon monoxide
was observed by adding excess of triphenylphosphite at room temperature. A similar reaction has been previously reported by Haines6 by stepwise addition of triphenylphosphite to the compound [Rh+&(COD),], but the chloride bridges of the [RW1d’W’h),~,l complex can be cleaved with formation of [RhCl{P(OPh),},]. On the other hand, the related complex [Rh2(C,04)(PPh,),] (XII) can be prepared by adding four moles of triphenylphosphine to one mole of complex II. Table 1 lists the analytical data for the isolated complexes. Oxalate carbonyl complexes
Bubbling carbon monoxide through a dichloromethane solution of complex II leads to the displacement of the coordinated diolefin, causing an instantaneous change in colour from yellow to violet, which is followed by the precipitation of violet microcrystals, which were identified as the complex [Rh,(C,O.,)(CO)J, (XIII). The usual planarity of the oxalate group’ probably favours the presence of an intermolecular rhodium-rhodium interaction”” in complex XIII as is suggested by the dark colour and dichroism of the compound, along with a complex IR spectrum in nujol mull (2100-1990 cm-’ region). Unfortunately, the low solubility of this complex prevents us from molecular weight measurements, but a tetranuclear formulation cannot be completely excluded. Thus, the related dinuclear [Rh,(Biim)(COD),J complex9 containing the planar biimidazolate dianion forming five-membered rings reacts with carbon monoxide with formation of the tetranuclear red compound [Rh4(Biim)2(C0)8]? Furthermore, we have observed that a dinuclear complex of formula [Rh,(Biim)(CO),(PPh,),] is obtained by addition of triphenylphosphine to [Rh,(Biim),(CO),](PPh,/ Rh: l/l). Addition of triphenylphosphine to solutions of the carbonyl derivative XIII leads to the formation of [Rh,(C,O,)(CO),(PPh,),] (XIV). This product has an IR spectrum exhibiting only one terminal metal carbonyl stretching frequency (1987 cm-‘, CH,ClJ suggesting a trans-configuration as observed for trans-[Rh,C12(C0)2(PPhJ2].‘o No further reaction was observed by adding excess of triphenylphosphine, although complex XII can be obtained by reaction of complex II with triphenylphosphine. The reaction of complex X with carbon monoxide leads to the displacement of the coordinated diolefin, yielding to complex [Rh,(C204)(C0)2 bYOW,~,l wh’ich was not isolated as a solid, but the presence of one v(C0) band (2005 cm-‘, CH,Cl,) suggests a trans-configuration as observed for complex XIV.
327
The reaction of one mole of complex XIII with two moles of tert-butylisocyanide leads to the formation of trans-[Rh&OJ(CO),(t-BuNC)J (XV) (vE0: 2OlOcm-‘, CH,Cl,) but an ionic compound analyzing as [Rh(CO)(t-BuNC),] [Rh(C,O,)(CO)(t-BuNC)] (XVI) was obtained when four moles of tert.-butylisocyanide were used. The [Rh(diolefin)(L-L)] [Rh(CzO,)(diolefin)] complexes (L-L=phen or bipy) react with carbon monoxide with formation of complexes of the type (L-L = phen [Rh(CO),(L-L)] [Rh(C,O,)(CO),] (XVII) or bipy (XVIII). The complex IR spectra in the carbonyl-stretching frequency region, along with the dichroism and intense colour of the complexes when solids, indicate an ionic chain-like structure involving metal-metal interactions, as reported for related [Rh(CO),(L-L)] [RhCl,(CO),] complexes. ‘*” In fact the observed IR absorptions are the result of the superimposed individual cisdicarbonyl bands of [Rh(CO),(L-L)]+ and [Rh(CO),ClJ-. The above mentioned ionic derivatives behave as 1 : 1 electrolytes in solution. In general low values of the molar conductivities are found (Table l), probably due to the low mobility of the relatively bulky ions. Finally, some oxidative addition reactions have been studied. Thus, complex XIV undergoes reactions with iodine or methyl iodide leading to the complexes of formation pf type [Rh2(C204)12Z2(C0)2(Phh3)21 (Z = I (XIX) or Me (XX)). The presence of only one terminal v(C0) band in the dinuclear rhodium(II1) complexes at 2095 and 2053 cm-’ (CH,Cl,) respectively, suggests that a single symmetrical derivative was formed. As expected the v(C0) vibration of the oxidation products is shifted towards higher energies relative to the parent compound (65-llOcm_I). Table 1 lists some relevant data for the carbonyl derivatives. In general, only a v(CO0) band from the anion, in the range coordinated oxalate 1610-1670 cm-’ was unequivocally assigned, due to the presence of several absorptions in the 1300-l 350 cm-’ range, masking the expected v (COO) bands. Malonate complexes
Some dinuclear complexes with the related malonate group have been prepared according to eqn (1), when malonic acid is added to acetone solutions of Rh(acac)(diolefin) complexes. These compounds of formula [Rh2{CHz(CO&}(diolefin),] (diolefin = COD (XXI), TFB (XXII), NBD (XXIII)) react with carbon monoxide with formation of [Rh2{CH2(C02)2}(C0)41, (XXIV). The latter complex reacts with a stoichiometric amount of
(VII)
(Z,
36.1 (37.11
(COD)Rh(C204)Ir(COD)
(VI)
Rh2(C204)(~80)2
I (VIII)
4.5 (5.0)
66.3 (65.1)
Rh2(C204)(PPh3)4
(XII)
3.9 (4.0)
57.9 (57.7)
Rh2(C204)(P(OPh)3)4 (XI)
(::&
(ES)
4.8 (5.1)
3.4 (3.2)
(4)::)
(Xf
47.9 (46.1)
49.3 (49.2)
50.8 (50.9)
40.1 (41.0)
(E)
(COO)Rh(C204)Rh(P(OPh)3~2
lRh(T~)(bi~) 11~(~20~)(T~) i (IX)
IRh(TFB)(phen) I IRh(C204)(V6)
IRh(COD)(phen)((Rh(C204)(COD)I*H20
(V)
Rh2(C204)(TF8)2 (44:::) (bf)
(:::)
42.1 (42,O)
(CtlD)Rh(C204)Rh(TF8) (III)
(IV)
4.7 (4.6)
42.4 (42.7)
Rh2(C204)(c~)2
(11)
4.4 (4.3)
(I)
40.0 (39.6)
Rh(HC204)(@0)
H
Found(calcd.)X C
Canplex N
746 (758)
82%
yellow
71% 70x 72%
paleyellow yellow
88%
89%
74%
paleyellow
orange
orange
red
yellow
1022 (917) 1536 (1466)
478 (466)
599 (601)
65%
yellow
64%
628 (711)
yellow
yellow 72%
(found(calcd.))
Mol.wt. (CHCl3)
510 (546)
62%
Yield
85%
yellow
Colour
Table 1. Analytical and other data for the compounds
m-w
m-m
7ga
rs”!
91f
___
hM otnn'bn2mol'1
(XIII)
cw
bNitrobentene.
'Methanoj.
(56.7) 55.7
Rh2~CH2-(C02)21(CO)2(PPh3)2
"Acetone.
20.0 (20.9)
~2{CH2-(C02)21(W)4(XXIV)
3.1 (3.7)
43.5 (43.7)
41.5 (41.2)
(22::)
34.8 (35.2)
(XXIII) Rh2tCH2-(W2),l(NBD),
(S)
33.1 (33.0)
(41.9) 42.6
(:::)
36.9 (36.6)
(33::)
0.5 (0.6)
3.7 (3.7)
(G)
(E)
$1:)
42.2 (43.0)
Rh2tCH2-(C02),HTF8), (XXII)
(XVIII)
3.5 (3.6)
3..3 (3.7)
-
32.6 (31.8)
54.9 (56.0)
43.5 (43.1)
(XXV)
(XX)
(XVII)
(XVI)
17.77
(17.9)
~21CH2-(C02)21(COD)2 (XXI)
.
Rh2(C204)I2Me2(CO)2(PPh3)2
(XIX)
I IRh(C2’Jq)(C0)21-H20
IRh(CO)2bM4
Rh2(Cp04)14(C0)2(PPh3)2
I lRhiC20,,)(C0)21
lRh(CO12(phen)
IRh(CO)(t-BuNC)3)I~h(CiO4)(tO)(t-BuNC)I
Rh2(C204)(CO)2(t-BuNc)2
Rh2(C204)(C0)2(PPh3)2 (XIV)
Rh2(C204)(C0)4
-
-
-
-
-
-
-
4 B (4:5)
(::t)
8.2 (8.6)
5.4 (5.6)
-
-
orange
yellow
red
orange
yellow
yellow
brown
black
%tr-
brown
green
yellow
violet
516 (554)
83%
1158 (1163)
96%
85%
73%
82%
60%
55%
1382 (1330)
79%
BOX
80%
87%
874 (797)
83%
82%
___
___
___
22c
26'
60'
_--
_--
L. A. OR0 et al.
330
triphenylphosphine yielding trans-[Rhl{CH2 (CO,),](CO),(PPh,),] (v(C0): 1970 cm-‘, CH,Cl,). In the above mentioned complexes, the malonate group is probably acting as bidentate to two rhodium atoms through symmetrical chelate carboxylate bonding (four-membered rings). EXPERIMENTAL C, H and N analyses were carried out with a Perkin-Elmer 240-B microanalyzer. IR spectra were recorded on a Perkin-Elmer 599 spectrophotometer over the range 4000-200 cm-‘, using Nujol mulls between polyethylene sheets or in dichloromethane solutions between sodium chloride windows, and calibrated with polystyrene. Molecular weights were measured with a Perkin-Elmer 115 osmometer. Conductivity measurements were carried out, with a Philips 9509 conductimeter. [RhCl(COD)],, [RBCl(NBD)],, [RhCl(TFB)],, (IrCl(COD)],, Rh(acac)(COD), [Rh(acac)(TFB)], [Rh(acac)(NBD)], [Ir(acac)(COD)], were prepared by published methods.“-” Other chemicals were grade reagents and were used without purification.
of[Rh(HC,O,)(COD)] (I) HzC204.2H20 (81.24 mg, 0.644 mmol) was added to a solution of Rh(acac)(COD) (200 mg, 0.644 mmol) in dichloromethane (30 cm3). The suspension was stirred for 30 min and filtered off. The yellow filtrate was vacuum-concentrated to cu. 2 cm3 and addition of ether gave rise to the formation of a yellow solid, which was filtered off, washed with ether and vacuum-dried. Yield: 120.1 mg (62%). Preparation
Preparation of [(COD)Rh(C,O,)Rh(TFB)]. General methodfor the synthesis of(II1) and (IV)
[Rh(acac)(TFB)] (75.453 mg, 0.176 mmol) was added to a solution of [Rh(HC,O,)(COD)] (52.9 mg, 0.176 mmol) in dichloromethane (20 cm3). This stirred for 3 hr. Vacuumsolution was concentration and addition of hexane led to the precipitation of the pale yellow complex which was filtered off washed with hexane and vacuum-dried. Yield: 80 mg (72%). Complex (IV) was obtained in a similar way by adding a calculated amount of [Ir(acac)(COD)] (39.9 mg, 0.099 mmol) to a solution of [Rh(HC,O,)(COD)] in dichloromethane (30 mg, 0.099 mmol) under nitrogen. Ether was uced for the precipitation of this complex. Preparation of [Rh,(C,O,)(COD),]. General methodfor the synthesis of(II), (V) and (VI)
To a solution of [Rh(acac)(COD)] (100 mg, 0.322mmol) in acetone (20cm’), was added the stoichiometric amount of HzCz0,.2Hz0 (20.3 mg,
0.161 mmol). A yellow precipitate was formed immediately. After stirring for 2 hr, it was filtered off, washed with acetone and vacuum-dried. Yield: 70 mg (85%). Complexes (V) and (VI) were similarly prepared by the route described above, starting from a calculated amount of [Rh(acac)(TFB)] or [Rh(acac)(NBD)]. The reaction to obtain complex (VI) was carried out under nitrogen with deoxygenated solvent. Preparation of [Rh(COD)(phen)] [Rh(C,OJ (COD)] - HzO. General methodfor the synthesis of (VII-IX)
Addition of 1, lo-phenanthroline (7.7 mg, 0.039 mmol) to a solution of [Rh,(C,O,)(COD),] (20 mg, 0.039 mmol) in 20 cm3 of dichloromethane caused a colour change from yellow to red. The solution was stirred for 30 min under nitrogen atmosphere, then the solvent was evaporated off under reduced presure, and addition of ether led to the complete precipitation of a red solid. This was filtered off, washed with ether and vacuum-dried. Yield: 20 mg (74%). This way, 1, lo-phenanthroline and 2,2’-bipyridine reacted with [Rh,(C,O,)(TFB),] to give the complexes (VIII) and (IX). of [(COD)Rh(C,0,)Rh{P(OPh)3}J (X) P(OPh), (41.2 ~1, 0.156 mmol) was added to a solution of [Rh2(C,04)(COD)J (40 mg, 0.78 mmol) in dichloromethane (30 cm3); the colour of the solution changed from yellow to pale yellow. After stirring for 2 hr under nitrogen atmosphere, the solvent was evaporated off under reduced pressure and ether was added to give a pale yellow solid. This was filtered off, washed with ether and vacuum-dried. Yield: 56.4 mg (71%). Preparation
Preparation of [Rh,(C,0.J{P(OPh)3],]. General methodfor the synthesis of(X1) and (XII)
To a stirred suspension of [Rh,(C,O,)(COD)J (30 mg, 0.058 mmol) in deoxygenated ether (20 cm’) was added P(OPh), (61.85 ~1, 0.235 mmol). The suspension immediately turned into a yellow solution, then a pale-yellow solid was observed. This was filtered off, washed with ether and vacuum-dried. Yield: 60 mg (70%). Preparation of [Rh,(C,O,)(CO),],. General method for the synthesis of (XIII), (XVII-XVIII) and (XXIV)
Bubbling of carbon monoxide through a solution of [Rhz(Cz04)(COD)J (55.4 mg, 0.108 mmol) in 20 cm3 of dichloromethane, for 30 min gave a violet solid. The suspension was vacuum-concentrated to
Dicarboxylate rhodium complexes with diolefins and carbon monoxide cu.. 4 cm’ and ether was added. The complex was
filtered off, washed with ether and vacuum-dried. Yield: 50 mg (82%). Methanol was used to precipitate complex (XXIV). Preparation of [Rh2(C204)(C0)2(PPh3)21. General method for synthesis of (XIV-XV) and (XXV)
A stoichiometric amount of PPh, (63.7 mg, 0.242 mmol) was added to a suspension of [Rh,(C,O,)(CO),] (49.3 mg, 0.121 mmol) in dichloromethane, and the resulting yellow solution was stirred for 2 hr. Addition of hexane to the concentrated solution (3 cm’) gave a yellow solid, which was filtered off, washed with hexane and vacuum-dried. Yield: 88 mg (83%). Complex (XV) was prepared under nitrogen atmosphere.
331
[Rh(acac)(COD)] (70 mg, 0.225 mmol) in 20 cm3 of acetone. The mixture was stirred for 2 hr, during which time the product precipitated as a yellow solid. This was filtered off, washed with acetone and vaccum-dried. Yield: 32 5 mg (55%). Complex (XXIII) is air-sensitive, so it was prepared under nitrogen atmosphere and ether was used as solvent.
Note added in prooJ We have been informed about an independent preparation of [Rh,(C,O,)(CO),] by P. B. Hitchcock, S. Morton and J. F. Nixon (Paper D26, 2nd International Conference on the Chemistry of the Platinum Group Metals, Edinburgh, July 1984). We thank Dr. J. F. Nixon for useful discussion.
Reaction of (XIII) with t-butylisocyanide
To a suspension of [Rh,(C,O,)(CO),] (35.6 mg, 0.087 mmol) in 20 cm3 of deoxygenated dichloromethane was added t-BuNC (38.58 ~1, 0.350 mmol) under nitrogen atmosphere. The suspension was stirred for 5 hr giving a yellow solution. The solvent was evaporated off to 2 cm3 under reduced pressure, and then ether was added to give a brown solid which was filtered off, washed with ether, and vacuum-dried. This complex analyzed as [Rh(CO)(t-BuNC),][Rh(C,O,)(CO)(t-BuNC)]. Preparation of [Rh2(C20,)14(CO),(PPh,),l (XIX) To a solution of [Rh,(Cz0,)(C0)2(PPh3),] (30 mg, 0.034 mmol) in 30 cm3 of dichloromethane was added the stoichiometric amount of iodine (17.25 mg, 0.068 mmol); the colour of the solution changed from yellow to brown. The progress of the reaction was followed by IR spectra. After 90 min stirring the solvent was evaporated off to 3 cm3 and hexane was added to give a dark brown solid. This was filtered off, washed with hexane and vacuumdried. Yield: 37 mg (79%). of [Rh,(C,04)12Me2(CO),(PPh,)21 (XX) A suspension of [Rh2(CI0,)(C0)2(PPh3)2] (22 mg, 0.025 mmol) in 30 cm3 of methyl iodide was stirred. After 5 min, the suspension turned into a yellow solution, then the complex precipitated as a yellow solid. This suspension was stirred for 2 hr, after which time the solvent was evaporated to small volume and the product was filtered off, washed with hexane and vacuum-dried. Yield: 28 mg (96%).
REFERENCES 1. R. P. Hughes, In Comprehensive Drganometallic Chemistry (Edited by G. Wilkinson, F. G. A. Stone
and E. W. ‘Abel), Vol. 5, p. 278. Pergamon Press, Oxford (1982). 2. (a) M. Valderrama and L. A. Oro, J. Organometal.
3. 4. 5. 6. 7. 8. 9.
Preparation
Preparation of [Rh,{CH,(CO,),)(COD)]. method for the synthesis of (XXI-XXIII)
General
A stoichiometric amount of CHz-(C0,H)2 (11.7 mg, 0.112 mmol) was added to a solution of
10. 11. 12. 13. 14. 15. 16. 17.
Chem. 1981, 218, 241. (b) M. Valderrama, H. Rafart and L. A. Oro, Transition Met. Chem. 1981 6, 221. (c) I. G. Leipoldt, L. D. Bok, S. S. Basson and H. Meyer, Znorg. Chim. Acta 1980, 42, 105. A. Dobson and S. D. Robinson, Platinum Met. Rev. 1976, 20, 56. C. Cocevar, G. Mestroni and A. Camus, J. Organometal. Chem. 1971, 16, 863. R. Uson, L. A. Oro, R. Sariego, M. Valderrama and C. Rebullida, J. Organometal. Chem. 1980, 197, 87. L. M. Haines, Znorg. Chem. 1970, 9, 1517. P. T. Cheng, B. R. Loescher and S. C. Nyburg, Znorg. Chem. 1971,10,1275. F. Pruchnik and K. Wajda, J. Organometal. Chem. 1979, 164, 71. S. W. Kaiser, R. B. Saillant, W. M. Butler and P. G. Rasmussen, Znorg. Chem. 1976, 15, 2681; 2688. D. F. Steele and T. A. Stephenson, J. Chem. Sot., Dalton Trans. 1972, 2161. R. D. Gillard, K. Harrison and I. H. Mather, J. Chem. Sot., Dalton Trans. 1975, 133. G. Giordano and R. H. Crabtree, Znorg. Synth. 1979, 19, 218. E. W. Abel, M. A. Bennett and G. Wilkinson, J. Chem. Sot. 1959, 3178. D. M. Roe and A. G. Massey, J. Organometal. Chem. 1971,28,273. R. H. Crabtree and G. E. Morris, J. Orgatwmetal. Chem. 1977,135,395. F. Bonati and G. Wilkinson, J. Chem. Sot. 1964, 3156. S. D. Robinson and B. L. Shaw, J. Chem. Sot. 1965, 4997.
325-331,
1985
0277-5387185 Q 1985 Pergamon
S3.00 + .oO Pms Ltd.
DICARBOXYLATE RHODIUM COMPLEXES WITH DIOLEFINS AND CARBON MONOXIDE Departamento
L. A. ORO,* de Quimica
M. T. PINILLOS and M. P. JARAUTA InorgBnica, Universidad de%ragoza, Zaragoza,
Spain
(Received 2 March 1984; accepted 14 April 1984) Abstract-Dinuclear rhodium complexes of the type [Rhz(C20,)(diolefin),1 (diolefin = l,Scyclooctadiene,2,Snorbornadiene and tetrafluorohenzobarrelene) with bridging oxalate ligands have been obtained by reaction of [Rh(acac)(diolefin)] with oxalic acid (2 : 1 mol ratio). The use of a 1 : 1 molar ratio affords [Rh(HC,O,)(COD)], that reacts with [Ir(acac)(COD)] yielding Lhe heterodinuclear [(COD)Rh(C,O,)Ir(COD)] complex. Treatment of [Rh,(C,O,)(diolefin),] complexes with phenanthroline type ligands leads to ionic complexes of formula [Rh(diolefin)(phen)][Rh(C,O,)(diolefin)]. Bubbling of carbon monoxide through solutions of the diolefin complexes leads to the formation of carbonylrhodium species of formula [Rh,(C,O,)(CO),L,] (L = CO, PPh,, f-BuNC) or [Rh(CO),(phen)] - [Rh(C,O,)(CO),]. Other related malonate complexes are also described.
A number of organorhodium(1) compounds containing bidentate oxygen anions have been reported.’ In particular the /3-diketonate anions form a variety of complexes which have six-membered rings. Concerning rhodium(I) complexes which have five-membered rings, some tropolonate derivatives have been recently reported.2 We describe in this paper some organorhodium complexes with the oxalate group. This dicarboxylate anion forms well-defined complexes which have five-membered rings, and it is able to function as a bidentate ligand to two metals simultaneously. In contrast, monocarboxylate anions in rhodium(I) chemistry are usually bound in a symmetrical syn-syn bridging.3 RESULTS AND DISCUSSION Oxalate diolefin complexes
The reaction of [Rh(acac)(COD)] with a stoichiometric amount of oxalic acid leads to the formation of the yellow microcrystalline compound [Rh(HC,O,)(COD)] (I). The experimental molecular weight measurements suggest a self-association by hydrogen bonding (Scheme 1). The acidic hydrogen atom in complex I can be removed with ease; thus, addition of [M(acac)(diolefin)] derivatives gives dinuclear complexes of formula [(COD)Rh(C,O,)Rh(diolefin)] (diolefin = 1,5cyclooctadiene, COD (II) or tetrafluorobenzo*Author dressed.
to whom correspondence
should
be ad-
barrelene, TFB (III)) or the heterodinuclear cbmpound [(COD)Rh(C,O,)Ir(COD)] (IV). A direct method of preparing homodinuclear complexes involves the reaction of two moles of [Rh(acac)(diolefin)] with one mole of oxalic acid, according to eqn (1): 2[Rh(acac)(diolefin)]
+ H2CzOl - 2Hz0 -
[Rh2(C20,)(diolefin)2]
+ 2 Hacac + 2 Hz0
[diolefin = COD(II), TFB(V), NBD(VI)]. Molecular weight measurements con&m the dinuclear formulation. Scheme 1 shows the suggested structures (five-membered chelate rings). The [Rh2(C20,)(diolefin)2] complexes usually react readily with different ligands. Thus, addition of the bidentate nitrogen donor ligand l,lOphenanthroline leads to the formation of ionic derivatives of formula [Rh(diolefin)(phen)] [Rh(C,O,)(diolefin)] (diolefin = COD(VI1) or TFB(VII1)). Similarly, complex V reacts with 2,2’bipyridine to give the analogous [Rh(TFB)(bipy)] IRhGO,)(TFB)I derivative (IX). The electrical conductivities of complexes VIII-IX show them to be l/l electrolytes. In particular the constituent cations of these complexes are reported species4’ of high stability. The stepwise addition of triphenylphosphite to [Rh2(C20,)(COD)2] affords the dinuclear derivatives [(COD)Rh(C20,)Rh{P(OPh)3)2] (X) and Rh2(C20,){P(OPh)3}4] (XI), but no further reaction 325
L.
326
.\/\ ml
A. OR0
et al.
Dicarboxylate rhodium complexes with diolefins and carbon monoxide
was observed by adding excess of triphenylphosphite at room temperature. A similar reaction has been previously reported by Haines6 by stepwise addition of triphenylphosphite to the compound [Rh+&(COD),], but the chloride bridges of the [RW1d’W’h),~,l complex can be cleaved with formation of [RhCl{P(OPh),},]. On the other hand, the related complex [Rh2(C,04)(PPh,),] (XII) can be prepared by adding four moles of triphenylphosphine to one mole of complex II. Table 1 lists the analytical data for the isolated complexes. Oxalate carbonyl complexes
Bubbling carbon monoxide through a dichloromethane solution of complex II leads to the displacement of the coordinated diolefin, causing an instantaneous change in colour from yellow to violet, which is followed by the precipitation of violet microcrystals, which were identified as the complex [Rh,(C,O.,)(CO)J, (XIII). The usual planarity of the oxalate group’ probably favours the presence of an intermolecular rhodium-rhodium interaction”” in complex XIII as is suggested by the dark colour and dichroism of the compound, along with a complex IR spectrum in nujol mull (2100-1990 cm-’ region). Unfortunately, the low solubility of this complex prevents us from molecular weight measurements, but a tetranuclear formulation cannot be completely excluded. Thus, the related dinuclear [Rh,(Biim)(COD),J complex9 containing the planar biimidazolate dianion forming five-membered rings reacts with carbon monoxide with formation of the tetranuclear red compound [Rh4(Biim)2(C0)8]? Furthermore, we have observed that a dinuclear complex of formula [Rh,(Biim)(CO),(PPh,),] is obtained by addition of triphenylphosphine to [Rh,(Biim),(CO),](PPh,/ Rh: l/l). Addition of triphenylphosphine to solutions of the carbonyl derivative XIII leads to the formation of [Rh,(C,O,)(CO),(PPh,),] (XIV). This product has an IR spectrum exhibiting only one terminal metal carbonyl stretching frequency (1987 cm-‘, CH,ClJ suggesting a trans-configuration as observed for trans-[Rh,C12(C0)2(PPhJ2].‘o No further reaction was observed by adding excess of triphenylphosphine, although complex XII can be obtained by reaction of complex II with triphenylphosphine. The reaction of complex X with carbon monoxide leads to the displacement of the coordinated diolefin, yielding to complex [Rh,(C204)(C0)2 bYOW,~,l wh’ich was not isolated as a solid, but the presence of one v(C0) band (2005 cm-‘, CH,Cl,) suggests a trans-configuration as observed for complex XIV.
327
The reaction of one mole of complex XIII with two moles of tert-butylisocyanide leads to the formation of trans-[Rh&OJ(CO),(t-BuNC)J (XV) (vE0: 2OlOcm-‘, CH,Cl,) but an ionic compound analyzing as [Rh(CO)(t-BuNC),] [Rh(C,O,)(CO)(t-BuNC)] (XVI) was obtained when four moles of tert.-butylisocyanide were used. The [Rh(diolefin)(L-L)] [Rh(CzO,)(diolefin)] complexes (L-L=phen or bipy) react with carbon monoxide with formation of complexes of the type (L-L = phen [Rh(CO),(L-L)] [Rh(C,O,)(CO),] (XVII) or bipy (XVIII). The complex IR spectra in the carbonyl-stretching frequency region, along with the dichroism and intense colour of the complexes when solids, indicate an ionic chain-like structure involving metal-metal interactions, as reported for related [Rh(CO),(L-L)] [RhCl,(CO),] complexes. ‘*” In fact the observed IR absorptions are the result of the superimposed individual cisdicarbonyl bands of [Rh(CO),(L-L)]+ and [Rh(CO),ClJ-. The above mentioned ionic derivatives behave as 1 : 1 electrolytes in solution. In general low values of the molar conductivities are found (Table l), probably due to the low mobility of the relatively bulky ions. Finally, some oxidative addition reactions have been studied. Thus, complex XIV undergoes reactions with iodine or methyl iodide leading to the complexes of formation pf type [Rh2(C204)12Z2(C0)2(Phh3)21 (Z = I (XIX) or Me (XX)). The presence of only one terminal v(C0) band in the dinuclear rhodium(II1) complexes at 2095 and 2053 cm-’ (CH,Cl,) respectively, suggests that a single symmetrical derivative was formed. As expected the v(C0) vibration of the oxidation products is shifted towards higher energies relative to the parent compound (65-llOcm_I). Table 1 lists some relevant data for the carbonyl derivatives. In general, only a v(CO0) band from the anion, in the range coordinated oxalate 1610-1670 cm-’ was unequivocally assigned, due to the presence of several absorptions in the 1300-l 350 cm-’ range, masking the expected v (COO) bands. Malonate complexes
Some dinuclear complexes with the related malonate group have been prepared according to eqn (1), when malonic acid is added to acetone solutions of Rh(acac)(diolefin) complexes. These compounds of formula [Rh2{CHz(CO&}(diolefin),] (diolefin = COD (XXI), TFB (XXII), NBD (XXIII)) react with carbon monoxide with formation of [Rh2{CH2(C02)2}(C0)41, (XXIV). The latter complex reacts with a stoichiometric amount of
(VII)
(Z,
36.1 (37.11
(COD)Rh(C204)Ir(COD)
(VI)
Rh2(C204)(~80)2
I (VIII)
4.5 (5.0)
66.3 (65.1)
Rh2(C204)(PPh3)4
(XII)
3.9 (4.0)
57.9 (57.7)
Rh2(C204)(P(OPh)3)4 (XI)
(::&
(ES)
4.8 (5.1)
3.4 (3.2)
(4)::)
(Xf
47.9 (46.1)
49.3 (49.2)
50.8 (50.9)
40.1 (41.0)
(E)
(COO)Rh(C204)Rh(P(OPh)3~2
lRh(T~)(bi~) 11~(~20~)(T~) i (IX)
IRh(TFB)(phen) I IRh(C204)(V6)
IRh(COD)(phen)((Rh(C204)(COD)I*H20
(V)
Rh2(C204)(TF8)2 (44:::) (bf)
(:::)
42.1 (42,O)
(CtlD)Rh(C204)Rh(TF8) (III)
(IV)
4.7 (4.6)
42.4 (42.7)
Rh2(C204)(c~)2
(11)
4.4 (4.3)
(I)
40.0 (39.6)
Rh(HC204)(@0)
H
Found(calcd.)X C
Canplex N
746 (758)
82%
yellow
71% 70x 72%
paleyellow yellow
88%
89%
74%
paleyellow
orange
orange
red
yellow
1022 (917) 1536 (1466)
478 (466)
599 (601)
65%
yellow
64%
628 (711)
yellow
yellow 72%
(found(calcd.))
Mol.wt. (CHCl3)
510 (546)
62%
Yield
85%
yellow
Colour
Table 1. Analytical and other data for the compounds
m-w
m-m
7ga
rs”!
91f
___
hM otnn'bn2mol'1
(XIII)
cw
bNitrobentene.
'Methanoj.
(56.7) 55.7
Rh2~CH2-(C02)21(CO)2(PPh3)2
"Acetone.
20.0 (20.9)
~2{CH2-(C02)21(W)4(XXIV)
3.1 (3.7)
43.5 (43.7)
41.5 (41.2)
(22::)
34.8 (35.2)
(XXIII) Rh2tCH2-(W2),l(NBD),
(S)
33.1 (33.0)
(41.9) 42.6
(:::)
36.9 (36.6)
(33::)
0.5 (0.6)
3.7 (3.7)
(G)
(E)
$1:)
42.2 (43.0)
Rh2tCH2-(C02),HTF8), (XXII)
(XVIII)
3.5 (3.6)
3..3 (3.7)
-
32.6 (31.8)
54.9 (56.0)
43.5 (43.1)
(XXV)
(XX)
(XVII)
(XVI)
17.77
(17.9)
~21CH2-(C02)21(COD)2 (XXI)
.
Rh2(C204)I2Me2(CO)2(PPh3)2
(XIX)
I IRh(C2’Jq)(C0)21-H20
IRh(CO)2bM4
Rh2(Cp04)14(C0)2(PPh3)2
I lRhiC20,,)(C0)21
lRh(CO12(phen)
IRh(CO)(t-BuNC)3)I~h(CiO4)(tO)(t-BuNC)I
Rh2(C204)(CO)2(t-BuNc)2
Rh2(C204)(C0)2(PPh3)2 (XIV)
Rh2(C204)(C0)4
-
-
-
-
-
-
-
4 B (4:5)
(::t)
8.2 (8.6)
5.4 (5.6)
-
-
orange
yellow
red
orange
yellow
yellow
brown
black
%tr-
brown
green
yellow
violet
516 (554)
83%
1158 (1163)
96%
85%
73%
82%
60%
55%
1382 (1330)
79%
BOX
80%
87%
874 (797)
83%
82%
___
___
___
22c
26'
60'
_--
_--
L. A. OR0 et al.
330
triphenylphosphine yielding trans-[Rhl{CH2 (CO,),](CO),(PPh,),] (v(C0): 1970 cm-‘, CH,Cl,). In the above mentioned complexes, the malonate group is probably acting as bidentate to two rhodium atoms through symmetrical chelate carboxylate bonding (four-membered rings). EXPERIMENTAL C, H and N analyses were carried out with a Perkin-Elmer 240-B microanalyzer. IR spectra were recorded on a Perkin-Elmer 599 spectrophotometer over the range 4000-200 cm-‘, using Nujol mulls between polyethylene sheets or in dichloromethane solutions between sodium chloride windows, and calibrated with polystyrene. Molecular weights were measured with a Perkin-Elmer 115 osmometer. Conductivity measurements were carried out, with a Philips 9509 conductimeter. [RhCl(COD)],, [RBCl(NBD)],, [RhCl(TFB)],, (IrCl(COD)],, Rh(acac)(COD), [Rh(acac)(TFB)], [Rh(acac)(NBD)], [Ir(acac)(COD)], were prepared by published methods.“-” Other chemicals were grade reagents and were used without purification.
of[Rh(HC,O,)(COD)] (I) HzC204.2H20 (81.24 mg, 0.644 mmol) was added to a solution of Rh(acac)(COD) (200 mg, 0.644 mmol) in dichloromethane (30 cm3). The suspension was stirred for 30 min and filtered off. The yellow filtrate was vacuum-concentrated to cu. 2 cm3 and addition of ether gave rise to the formation of a yellow solid, which was filtered off, washed with ether and vacuum-dried. Yield: 120.1 mg (62%). Preparation
Preparation of [(COD)Rh(C,O,)Rh(TFB)]. General methodfor the synthesis of(II1) and (IV)
[Rh(acac)(TFB)] (75.453 mg, 0.176 mmol) was added to a solution of [Rh(HC,O,)(COD)] (52.9 mg, 0.176 mmol) in dichloromethane (20 cm3). This stirred for 3 hr. Vacuumsolution was concentration and addition of hexane led to the precipitation of the pale yellow complex which was filtered off washed with hexane and vacuum-dried. Yield: 80 mg (72%). Complex (IV) was obtained in a similar way by adding a calculated amount of [Ir(acac)(COD)] (39.9 mg, 0.099 mmol) to a solution of [Rh(HC,O,)(COD)] in dichloromethane (30 mg, 0.099 mmol) under nitrogen. Ether was uced for the precipitation of this complex. Preparation of [Rh,(C,O,)(COD),]. General methodfor the synthesis of(II), (V) and (VI)
To a solution of [Rh(acac)(COD)] (100 mg, 0.322mmol) in acetone (20cm’), was added the stoichiometric amount of HzCz0,.2Hz0 (20.3 mg,
0.161 mmol). A yellow precipitate was formed immediately. After stirring for 2 hr, it was filtered off, washed with acetone and vacuum-dried. Yield: 70 mg (85%). Complexes (V) and (VI) were similarly prepared by the route described above, starting from a calculated amount of [Rh(acac)(TFB)] or [Rh(acac)(NBD)]. The reaction to obtain complex (VI) was carried out under nitrogen with deoxygenated solvent. Preparation of [Rh(COD)(phen)] [Rh(C,OJ (COD)] - HzO. General methodfor the synthesis of (VII-IX)
Addition of 1, lo-phenanthroline (7.7 mg, 0.039 mmol) to a solution of [Rh,(C,O,)(COD),] (20 mg, 0.039 mmol) in 20 cm3 of dichloromethane caused a colour change from yellow to red. The solution was stirred for 30 min under nitrogen atmosphere, then the solvent was evaporated off under reduced presure, and addition of ether led to the complete precipitation of a red solid. This was filtered off, washed with ether and vacuum-dried. Yield: 20 mg (74%). This way, 1, lo-phenanthroline and 2,2’-bipyridine reacted with [Rh,(C,O,)(TFB),] to give the complexes (VIII) and (IX). of [(COD)Rh(C,0,)Rh{P(OPh)3}J (X) P(OPh), (41.2 ~1, 0.156 mmol) was added to a solution of [Rh2(C,04)(COD)J (40 mg, 0.78 mmol) in dichloromethane (30 cm3); the colour of the solution changed from yellow to pale yellow. After stirring for 2 hr under nitrogen atmosphere, the solvent was evaporated off under reduced pressure and ether was added to give a pale yellow solid. This was filtered off, washed with ether and vacuum-dried. Yield: 56.4 mg (71%). Preparation
Preparation of [Rh,(C,0.J{P(OPh)3],]. General methodfor the synthesis of(X1) and (XII)
To a stirred suspension of [Rh,(C,O,)(COD)J (30 mg, 0.058 mmol) in deoxygenated ether (20 cm’) was added P(OPh), (61.85 ~1, 0.235 mmol). The suspension immediately turned into a yellow solution, then a pale-yellow solid was observed. This was filtered off, washed with ether and vacuum-dried. Yield: 60 mg (70%). Preparation of [Rh,(C,O,)(CO),],. General method for the synthesis of (XIII), (XVII-XVIII) and (XXIV)
Bubbling of carbon monoxide through a solution of [Rhz(Cz04)(COD)J (55.4 mg, 0.108 mmol) in 20 cm3 of dichloromethane, for 30 min gave a violet solid. The suspension was vacuum-concentrated to
Dicarboxylate rhodium complexes with diolefins and carbon monoxide cu.. 4 cm’ and ether was added. The complex was
filtered off, washed with ether and vacuum-dried. Yield: 50 mg (82%). Methanol was used to precipitate complex (XXIV). Preparation of [Rh2(C204)(C0)2(PPh3)21. General method for synthesis of (XIV-XV) and (XXV)
A stoichiometric amount of PPh, (63.7 mg, 0.242 mmol) was added to a suspension of [Rh,(C,O,)(CO),] (49.3 mg, 0.121 mmol) in dichloromethane, and the resulting yellow solution was stirred for 2 hr. Addition of hexane to the concentrated solution (3 cm’) gave a yellow solid, which was filtered off, washed with hexane and vacuum-dried. Yield: 88 mg (83%). Complex (XV) was prepared under nitrogen atmosphere.
331
[Rh(acac)(COD)] (70 mg, 0.225 mmol) in 20 cm3 of acetone. The mixture was stirred for 2 hr, during which time the product precipitated as a yellow solid. This was filtered off, washed with acetone and vaccum-dried. Yield: 32 5 mg (55%). Complex (XXIII) is air-sensitive, so it was prepared under nitrogen atmosphere and ether was used as solvent.
Note added in prooJ We have been informed about an independent preparation of [Rh,(C,O,)(CO),] by P. B. Hitchcock, S. Morton and J. F. Nixon (Paper D26, 2nd International Conference on the Chemistry of the Platinum Group Metals, Edinburgh, July 1984). We thank Dr. J. F. Nixon for useful discussion.
Reaction of (XIII) with t-butylisocyanide
To a suspension of [Rh,(C,O,)(CO),] (35.6 mg, 0.087 mmol) in 20 cm3 of deoxygenated dichloromethane was added t-BuNC (38.58 ~1, 0.350 mmol) under nitrogen atmosphere. The suspension was stirred for 5 hr giving a yellow solution. The solvent was evaporated off to 2 cm3 under reduced pressure, and then ether was added to give a brown solid which was filtered off, washed with ether, and vacuum-dried. This complex analyzed as [Rh(CO)(t-BuNC),][Rh(C,O,)(CO)(t-BuNC)]. Preparation of [Rh2(C20,)14(CO),(PPh,),l (XIX) To a solution of [Rh,(Cz0,)(C0)2(PPh3),] (30 mg, 0.034 mmol) in 30 cm3 of dichloromethane was added the stoichiometric amount of iodine (17.25 mg, 0.068 mmol); the colour of the solution changed from yellow to brown. The progress of the reaction was followed by IR spectra. After 90 min stirring the solvent was evaporated off to 3 cm3 and hexane was added to give a dark brown solid. This was filtered off, washed with hexane and vacuumdried. Yield: 37 mg (79%). of [Rh,(C,04)12Me2(CO),(PPh,)21 (XX) A suspension of [Rh2(CI0,)(C0)2(PPh3)2] (22 mg, 0.025 mmol) in 30 cm3 of methyl iodide was stirred. After 5 min, the suspension turned into a yellow solution, then the complex precipitated as a yellow solid. This suspension was stirred for 2 hr, after which time the solvent was evaporated to small volume and the product was filtered off, washed with hexane and vacuum-dried. Yield: 28 mg (96%).
REFERENCES 1. R. P. Hughes, In Comprehensive Drganometallic Chemistry (Edited by G. Wilkinson, F. G. A. Stone
and E. W. ‘Abel), Vol. 5, p. 278. Pergamon Press, Oxford (1982). 2. (a) M. Valderrama and L. A. Oro, J. Organometal.
3. 4. 5. 6. 7. 8. 9.
Preparation
Preparation of [Rh,{CH,(CO,),)(COD)]. method for the synthesis of (XXI-XXIII)
General
A stoichiometric amount of CHz-(C0,H)2 (11.7 mg, 0.112 mmol) was added to a solution of
10. 11. 12. 13. 14. 15. 16. 17.
Chem. 1981, 218, 241. (b) M. Valderrama, H. Rafart and L. A. Oro, Transition Met. Chem. 1981 6, 221. (c) I. G. Leipoldt, L. D. Bok, S. S. Basson and H. Meyer, Znorg. Chim. Acta 1980, 42, 105. A. Dobson and S. D. Robinson, Platinum Met. Rev. 1976, 20, 56. C. Cocevar, G. Mestroni and A. Camus, J. Organometal. Chem. 1971, 16, 863. R. Uson, L. A. Oro, R. Sariego, M. Valderrama and C. Rebullida, J. Organometal. Chem. 1980, 197, 87. L. M. Haines, Znorg. Chem. 1970, 9, 1517. P. T. Cheng, B. R. Loescher and S. C. Nyburg, Znorg. Chem. 1971,10,1275. F. Pruchnik and K. Wajda, J. Organometal. Chem. 1979, 164, 71. S. W. Kaiser, R. B. Saillant, W. M. Butler and P. G. Rasmussen, Znorg. Chem. 1976, 15, 2681; 2688. D. F. Steele and T. A. Stephenson, J. Chem. Sot., Dalton Trans. 1972, 2161. R. D. Gillard, K. Harrison and I. H. Mather, J. Chem. Sot., Dalton Trans. 1975, 133. G. Giordano and R. H. Crabtree, Znorg. Synth. 1979, 19, 218. E. W. Abel, M. A. Bennett and G. Wilkinson, J. Chem. Sot. 1959, 3178. D. M. Roe and A. G. Massey, J. Organometal. Chem. 1971,28,273. R. H. Crabtree and G. E. Morris, J. Orgatwmetal. Chem. 1977,135,395. F. Bonati and G. Wilkinson, J. Chem. Sot. 1964, 3156. S. D. Robinson and B. L. Shaw, J. Chem. Sot. 1965, 4997.