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phosphine ruthenium(II) compounds
Inorganica Chimica Acta 230 (1995) 193-197
ELSEVIER
Note
Reactivity of cationic carbonyl/phosphine ruthenium(II) compounds E. Wynne Evans a,*, Mohammed B.H. Howlader a, Mark T. Atlay a School of Applied Sciences, University of Glamorgan, Pontypridd, Mid. Glamorgan CF37 1DL, UK b Centre for Science Education, The Open University, Walton Hall Milton Keynes MK7 6A,4, UK
Received 12 May 1994; revised 28 June 1994
Abstract
C/s(or trans)-[RuCl2(CO)2(PPh3)2] react with two and one equivalents of AgBF4 to give the recently reported [Ru(CO)2(PPhB)2][BF4]2-CH2CI2 (1) and novel [RuCI(CO)2(PPh~)2][BF4]-½CH2CI2 (2), respectively. Cis-[RuCl2(CO)2(PVh3)2] also reacts with two equivalents of AgBF4 in the presence of CO to give [Ru(CO)a(PPha)2][BF4]2 (3). Reactions of I and 2 with NaOMe and CO at 1 atm produce the carbomethoxy species [Ru(COOMe)2(CO)2(PPha)2] (4) and [RuCI(COOMe)(CO)2(PPh3)2] (5), respectively. Complex 4 can also be formed from the reaction of 3 with NaOMe and CO. Alternatively, 4 is formed from c/s-[RuCI2(CO)2(PPh3)2 ] with NaOMe and CO at elevated pressure (10 arm); if these reactants are refluxed under 1 atm of CO, [Ru(CO)3(PPh3)2] is the product. The reaction of [RuCI(CO)a(PPha)~][AICI4] with NaOMe provides an alternative route to the preparation of 5, but the product is contaminated with [RuCI2(CO)2(PPh3)2]. Compounds 1, 2, 4 and 5 have been characterised by IR, 1H NMR and analysis, whilst the formulation of 3 is proposed from spectroscopic data only. This account also examines the reactivity of [Ru(CO)2(PPh3)2][BF4]2-CH2CI2with NaBH4, conc. HCI, KI and, finally, MeCOONa in the presence of CO. The products of these reactions, namely c/s-[RuH2(CO)2(PPh3)2], c/s-[RuCl2(CO)2(PPh3)2], cis-[RuI2(CO)2(PPh3)2] and [Ru(OOCMe)2(CO)2(PPh3)2], have been identified by comparison of their spectra with previous literature. Keywords: Ruthenium complexes; Carbonyl complexes; Phosphine complexes
1. Introduction The catalytic chemistry of Group VIII metal carboalkoxy derivatives has yet to be fully examined. Dicarboalkoxy complexes, in particular, have been shown to play a part in the generation of oxalic esters from synthesis gas; thus providing an attractive synthetic route to ethylene glycol, for example [1]. We have previously described [2] the preparation of dichloromethane-solvated [Rh(CO)(PPh3)2][BF4] and its reactions with nucleophiles in a CO atmosphere, resulting in the formation of carboalkoxy complexes [3]. This account describes the results of analogous experiments carried out with ruthenium-based compounds. In addition, the reactivity of [Ru(CO)E(PPh3)2] 2+- CH2CI2 towards NaBH4, conc. HC1, KI and * Corresponding author.
0020-1693/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSDI 0020-1693(94)04201-6
M e C O O N a is compared with that of its precursor, c/s[RuCI2(CO)2(PPh3)2].
2. Experimental Reactions and manipulations were carried out in a dry, nitrogen atmosphere (unless otherwise specified) using dried, degassed solvents as previously described [2]. ~H and 3~p N M R spectra were obtained at 298 K using a J E O L FX90Q 90MHz Fourier Transform spectrophotometer. IR spectra (4000-250 cm -~) were recorded on Perkin-Elmer 881 and 457 instruments from nujol mulls and CsI discs, respectively. Products were dried in vacuo. Analyses were carried out by M E D A C Ltd., Brunel University, Middlesex. The starting materials [RuCI(CO)3(PPha)2][A1C14] and trans- or
194
cis-[RuCl,(CO),(PPh,),] described [4,5].
E. W. Evans et al. I Inorganica
’ were prepared
as previously
2.1. Preparation of [Ru(CO),(PPh,)J[BF,l,.
CH,Cl,
(1)
Cis-[RuClz(C0)2(PPh3)2] (0.60 g, 0.80 mmol) was stirred with AgBF,, (0.31 g, 1.60 mmol) in CH,Cl, (40 cm3) for 10 h at room temperature. The white precipitate formed was removed by filtration of the mixture through kieselguhr. Concentration of the solvent afforded a white solid which was recrystallised from a mixture of CH,Cl, and CsH14. Yield 0.45 g (60%). Anal. Calc. for CZ,9H3,B,C1,F,0,P,Ru: C, 49.8; H, 3.4. Found: C, 50.1; H, 4.0%. The reaction could also be effected using trans-
[RuC1,P),(PPh,M 2.2. Preparation of [RuCl(CO),(PPhJJ[BFJ
*f CH&
(2)
This preparation was essentially the same as for 1 except that cb(or trans)-[RuCl,(CO),(PPh,),] (0.40 g, 0.53 mmol) was reacted with AgBF, in a 1:l molar ratio. After 7 h, the solid product obtained was recrystallised as for 1, whereupon white crystals were formed. Yield 0.28 g (62%). Anal. Calc. for C&.,H,,BCl,F,O,P,Ru: C, 54.6; H, 3.7. Found: C, 54.0; H, 3.9%. 2.3. Preparation of [Ru(CO),(PPhJJ[BF,]2
(3)
Ck-[RuCl,(CO),(PPh,)J (0.40 g, 0.53 mmol) was stirred for 6 h under CO with AgBF, (0.21 g, 1.06 mmol) in CH,Q (25 cm’). The white precipitate formed was removed by filtration as for 1, but under CO. Concentration of the solvent gave a white solid, which was recrystallised from a mixture of CH,Cl, and C,H,, in a CO atmosphere. Yield 0.28 g (60%). 2.4. Preparation of [Ru(COOMe),(CO),(PPh,),]]
(4)
(a) Compound 1 (0.40 g, 0.43 mmol) in MeOH (15 cm3) was reacted with excess NaOMe ( N 2.20 mm01 in 10 cm3 MeOH) under CO. After 1 h, the product was filtered off and recrystallised from a mixture of C,H, and CsH,4. White microcrystals were formed. Yield 0.20 g (60%). Anal. Calc. for C_,2H3606P2R~: C, 63.1; H, 4.5. Found: C, 63.0; H, 4.5%. (b) As in (a), except that 3 (0.15 g, 0.17 mmol) was used as the starting material. Yield 0.09 g (66%). The IR and NMR spectra of the product were identical with those for 4. ’ Throughout this account the preti refers to the configuration of the CO groups; PPh, groups are exclusively imns, in agreement with earlier reports [6].
Chimica Acta 230 (1995) 193497
(c) As in (a), except that cis-[RuC1,(C0)2(PPh3)J (0.25 g, 0.33 mmol) was reacted with NaOMe solution (2.20 mmol in 10 cm3 MeOH) in a high pressure apparatus. The apparatus was charged with 10 atm of CO for 64 h. Yield 0.18 g (68%). Spectra of the product were as for 4. 2.5. Preparation of [RuCl(COOMe) (CO),(PPh,)J
(5)
(a) This preparation was essentially the same as in Section 2.4 (a), except that 2 (0.40 g, 0.47 mmol) was reacted with NaOMe in a 1:l molar ratio in 20 cm3 MeOH at - 10 “C. White microcrystals, which formed after 15 min, were filtered off and washed with MeOH. Yield 0.18 g (50%). Anal. Calc. for C,H,,ClO,P,Ru: C, 61.9; H, 4.3. Found: C, 61.8; H, 4.4%. (b) [RuCl(CO),(PPh,),][AlCl,] (0.25 g, 0.27 mmol) was reacted with NaOMe (0.45 mmol) in MeOH (15 cm3) at - 10 “C. White microcrystals were formed. The product was characterised as a mixture of 5 and [RuCl,(CO),(PPh,),] from its IR spectrum. 2.6. Reaction of I with NaBH, to form cis-[RuH2(CO),(PPh,)J
Compound 1 (0.20 g, 0.21 mmol) was dissolved in EtOH (10 cm3) and NaBH, solution (0.10 g, 2.60 mmol in 10 cm3 EtOH) added. After 30 min stirring brown crystals formed which were washed with EtOH, then Yield 0.09 g (63%). The hydrido complex GIL was characterised by comparison of its IR and ‘H NMR spectra with previous preparations of cis- [RuH,(CO),(PPh,),] from the reactions of [Ru(N,Ar)(CO),(PPh,),][BF,,] with NaBH, [7] and [Ru(CO),(PPh,),] with Hz [8]. 2.7. Reaction of 1 with cone. HCI to form cis-[RuClz(CO),(PPh,)J
To a solution of 1 (0.10 g, 0.11 mmol) in MeOH (5 cm3), was added cont. HCl ( N 0.20 g) dropwise. Within 10 min the product was formed as a white precipitate which was washed with MeOH. Yield 0.06 g (73%). Again, the spectra of our product are consistent with reported values [5,9,10]. 2.8. Reaction of 1 with Kl to for cis-[RuIz(CO),(PPh,)J
Compound 1 (0.20 g, 0.21 mmol) was reacted with KI (0.10 g, 0.60 mmol) in 15 cm3 MeOH. Within 15 min yellow crystals formed, which were recrystallised from CH,Cl, and C,H,,. Yield 0.14 g (70%). The IR spectrum of the product is consistent with a previous report [ll].
195
E. IV.. Evans et al. / lnorganica Chimica Acta 230 (1995) 193-197
2.9. Reaction of 1 with MeCOONa to form [Ru(OOCMe) 2(CO)2(PPhA2] Compound 1 (0.20 g, 0.21 mmol) was reacted with CH3COONa (0.10 g, 1.22 mmol) in 15 cm 3 MeOH. The mixture was stirred under CO for 1 h. White crystals formed, which were washed with MeOH. Yield 0.11 g (65%). The IR and 1H NMR spectra agree with those from previous preparations [12,13] using [Ru(CO)a(PPh3)2] as precursor.
Table 1 tH and 31p NMR data for ruthenium compounds Compound
1H NMR (3)"
1c 2 3 4 Sc
7.40-7.80 (m, 30H) 5.23 (s, 2H) 7.30-7.80 (m, 30H) 5.28 (s, 1H) 7.30-7.80 (m, 30H) 2.80 (s, 6H) 7.30-7.80 (m, 30H) 2.88 (s, 3H)
3tp NMR (6)b
24.50(s) 22.50(s) 30.50(s)
"In CDCI3 relative to Si(Me)4. b in CDCI 3 relative to 85% H3PO4. ¢ 31p NMR not clear.
3. Results and discussion
3.1. Formation and stability of cationic species Ruthenium cationic carbonyl/phosphine complexes can undergo addition or substitution reactions initiated by nucleophilic attack at the metal centre [4,14,15]. Our main objective, however, has been to study the reactivity of coordinated CO in cationic species towards nucleophilic addition; the CO group appears to be activated by the cationic nature of the compound [4,15]. Ballester et al. [16] have briefly mentioned the use of [Ru(CO)2(PPh3)2(THF)2][BF4]2 as a synthon for the preparation of Ru(I) species. The solvated complex was prepared by the reaction of [RuC12(CO)2(PPh3)2] with AgBF4 in THF. We have already used this halide abstraction reaction, in CH2C12, to prepare rhodium complexes of formula [Rh(CO)(PPh3)2] ÷ or [Rh(CO)2(PPh3)2] ÷ [2], then described their reactions with nucleophiles of the type R O - and R C O O - [3]. We now report extension of this work to include the analogous ruthenium-based compounds. Beck and coworkers have recently reported [17] the preparation of [Ru(CO)2(PPh3)2][BF4]2.CH2CI2 (1), stabilised by FBF3- coordination. We independently duplicated this preparation and concluded the same formulation, although our IR spectra are not as well-resolved as those reported by Beck. It is very probable that FBF3coordination accounts for the stability of the Rh(I) species previously reported [2] and we hope to confirm this through 19F NMR studies. In this account, we report that [RuCI(CO)2(PPhs)2][BF4].½CH2C12 (2) has been prepared by the reaction of [RuC12(CO)2(PPh3)2] with only one equivalent of AgBF4. The reaction of two equivalents of AgBF4 with [RuCI2(CO)2(PPh3)2] in a CO atmosphere gave a species suggested as [Ru(CO)3(PPh3)2][BF4]2 (3). The main NMR features of the compounds prepared are shown in Table 1; 31p NMR spectra were difficult to interpret because of the tendency of the compounds, over the period of time involved, to decompose in solution. However some principle resonances, which diminished in intensity as time proceeded, are included.
The IR spectrum for 1 shows v ( C - O ) values which are slightly lower than those previously reported [17], but v(BF4-) is given only as a broad, unresolved peak centred at 1092 cm -1 (Table 2). Similarly, v ( C - O ) for 2 has values which compare with those reported for other cationic carbonyl Ru(II) species [4,7]; again v(BF4-) is around 1091 c m - k The far-IR spectrum (CsI disc) of 2 shows a band for v(Ru--Cl) at 310 cm -~. Preparation of 1 in Me2CO resulted in an Me2COcoordinated species with v ( C - O ) values at 2090 and 2030 cm -~ and v(BF4-) at 1091 cm-1; solvent coordination is primarily demonstrated by the low value for v(C = O) of Me2CO at 1660 cm- 1 [18-20]. Complete halide abstraction of [RuCI2(CO)2(PPh3)2] in the presence of CO, or treatment of a CH2C12 solution of 1 with CO, resulted in the formation of a white compound with values for v(C = O) (Table 2) very simliar to those previously reported for cationic tricarbonyl species of Ru(II) [4,21]; v(BF4-) is measured at 1092 cm -~. We therefore suggest the compound may be formulated as [Ru(CO)3(PPh3)2][BF4]2 (3); five-coordinate cationic Ru(II) complexes have been previously prepared by addition of CO to a solvent-coordinated precursor [15]. Although the reaction of 1 with CO produced 3, the reaction was not reversed by bubbling N2 through a solution of 3. The enhanced stability of 3, as compared with 1, presumably is a consequence of the metal in 3 having the more stable electronic configuration.
3.2. Formation of carboalkoxy compounds Reactions of 1 or 3 with NaOMe in the presence of CO resulted in the formation of [Ru(COOMe)2(CO)2(PPh3)2] (4). The reaction of 2 with 1 equivalent of NaOMe under CO produced [RuCI(COOMe)(CO)2(PPh3)2] (5); the presence of excess NaOMe again gave 4. The IR spectra of 4 and 5 (Table 2) contain bands around 1650 and 1030 cm-1, for v(C = O) and v(C--OMe) of the carbomethoxy group, in good agreement with similar species previously prepared from the reactions of nucleophiles with cationic Os(II) and Ru(II) complexes [4,21]. In the IR spectrum
196
E.W. Evans et al. / lnorganica Chimica Acta 230 (1995) 193-197
Table 2 IR data a for ruthenium species (cm -1) Compound
v(C -= O)
I 2 3 4 5b
2085, 2070, 2162, 2032, 2042,
v(C = O)
2033(s) 2006(s) 2089, 2032(s) 1977(s) 1986(S)
v(BF4 - )
v(C-OMe)
1092(s,br) 1091(s, br) 1092(s, br) 1653(m), 1637(s) 1655(m)
1027(m) 1028(m)
In nujol. b v(Ru-CI) br at 300 cm-1.
for 4, two bands for both v(C=O) and v(C=O), respectively, suggest c/s-carbonyl [11] and c/s-carbomethoxy groups; we therefore propose 4 has C2v symmetry (Fig. l(a)). IR data for 5, is in good agreement with that reported [4] for the closely-related [RuI(COOMe)(CO)2(PPh3)2], suggesting 5 has the same structure (Fig. l(b)). The transformation of 1 into 4 could also be effected by reacting 1 with excess NEt3 in MeOH under CO. Alternatively, 4 was obtained by the reaction of c/s-[RuC12(CO)2(PPh3)2] with excess NaOMe and CO at 10 atm pressure. A summary of reactions is shown in Scheme 1. The IR spectrum of the product of the reaction of previously reported [4] [RuCI(CO)3(PPh3)2][A1CI4] with NaOMe indicates that a mixture of 5 and [RuC12(CO)2(PPh3)2] had formed. This appears to be in accord with the reported tendency
PPh3 OC. I OC~l"l
PPh3 COOMe
OC.
COOMe
PPh3
I
.-COOMe
O C " in'c1
(4)
PPh3
(a)
(5)
(b)
~g. 1. Structures ~ Ru(II) ~ o m e t h o ~ [Ru (COOMe) 2 (CO) 2 (PPh3) 2 ]4--- e - -
,\
com~exes.
[Ru (CO) 3 (PPh3) 2 ] [BF4 ] 2
/c [RuC12 (CO) 2 (PPh3) 21
b
[Ru(CO) 2(PPh3)21[BF412"cH2C12
a
[RuCl(CO) 2(PPh3)21[BF41"~H2C12
(1)
[23]. Two possible mechanisms exist for the formation of the carboalkoxy groups from their cationic precursors; addition of M e O - to the metal then CO insertion, or direct attack of the nucleophile on coordinated CO [3]. The former mechanism would appear to be likely given the coordinative unsaturation of the metal atom in these cationic species, but no direct evidence for any intermediate Ru-OMe species was found. The same intermediate might be expected to initially form during the reaction of c/s-[RuC12(CO)2(PPh3)2] with M e O and CO, by metathesis. Attempts to prepare methoxo compounds by reacting 1 or 2 with NaOMe under N2 gave an unstable product with broad IR bands for v(C---O) at 1971, 1929 and 1900 cm-1; decomposition of the compound in solution precluded meaningful NMR spectra. It seems likely that this product is a mixture [20,24]; previous attempts to prepare methoxo complexes have resulted in mixtures which include reduction products such as [Ru(CO)2(PPb3)3] and [Ru(CO)3(PPh3)2] that both exhibit v ( C - O ) around 1900 cm -1. If methoxo intermediates are formed, it seems that immediate CO insertion [25] takes place in the Ru-OMe bonds, with the formation of the carbomethoxy species. 3.3. Other reactions of 1
(2)
I
e
[RuCI (CO) 3 (PPh3) 2 ] [AICI4] - -
of [RuCI(CO)3(PPh3)2][A1CL] to convert to [RuCl2(CO)2(PPh3)2] in basic conditions [4]. The compounds c/s- and trans-[RuCl2(CO)2(PPh3)2] gave the reduction product [Ru(CO)3(PPh3)2] when refluxed with excess NaOMe and in the presence of 1 atm CO. This has been previously prepared by the reactions of [RuC12(CO)2(PPh3)2]with a Zn/CO mixture [22], or reduction of [RuC12(PPh3)3] with NaOEt/CO
d ~
[RuCl (COOMe) (CO) 2 (PPh3) 2 ] (5)
Scheme I. Preparations of ruthenium cationic carbonyl/phosphine species and their reactions to form earboalkox'y species, a: AgBF4; b: 2AgBF4; e: 2AgBFJCO; d: NaOMe, [RuCI2(CO~(PPh3)2] also formed; e: NaOMe/CO; f: NaOMe/CO (10 atm); g: NEt3/CO/MeOH.
Compound 1 proved to react readily with a number of reagents (Scheme 2); the products were characterised by comparison of their IR and 1H NMR spectra with previously reported spectra (see Section 2). The reaction of 1 with MeCOONa under CO, gives [Ru(OOCMe)2(CO)2(PPh3)2]. When this reaction was carried out under N2, the IR of the product shows
E.W. Evans et al. / Inorganica Chimica Acta 230 (1995) 193-197 cis- [}~uCl 2 (CO) 2 (PPh3) 2 ]
v,.
a
\
cis- [RuH 2 (CO) ~ (PPh 3 ) 2 ]
/
b,e
[Ru(CO) 2(PPh3) 2] [BF412.CH2C12
c,e cis- [Eul 2 (CO) 2 (PPh3) 2 ]
d,e [Ru (OOCMe) 2 (CO) 2 (PPh3) 2 ]
Scheme 2. Reactions of [Ru(CO)2(PPh3)2][BF4]2-CH2C12 (1). a: conc. HCl; b: NaBH4; c: KI; d: MeCOONa/CO; e: c/s-[RuC12(CO)2(PPh3)2 ] does not react under the same conditions.
bands which could be attributed to the carbonyl groups in [Ru(OOCMe)2(CO)2(PPh3)2 and a very broad, strong band centred around 1941 cm -1. The product of this reaction may be a mixture of both [Ru(OOCMe)2(CO)2(PPh3)2] and [Ru(OOCMe)2(CO)(PPh3)2]; the latter has a reported value for v ( C - O ) [26] at 1960 cm-1 and may be produced by loss of CO in solution during the reaction. If a suspension of [Ru(OOCMe)2(CO)2(PPh3)2], in methanol, was reacted with conc. HC1, then c/s-[RuCl2(CO)2(PPh3)2] formed almost immediately. These reactions are shown in Scheme 2.
Acknowledgements We thank Johnson Matthey Materials Technology, UK, for a loan of ruthenium. M.B.H.H. was supported by an O.D.A.S.S.S. scholarship.
References [1] P.L. Burk, D. Van Engen and ICS. Campo, Organometallics, 3 (1984) 493, and refs. therein. [2] E.W. Evans, M.B.H. Howlader and M.T. Atlay, Transition Met. Chem., 19 (1994) 37.
197
[3] E.W. Evans, M.B.H. Howlader and M.T. Atlay, Transition Met. Chem., 19 (1994) 183. [4] W. Hieber, V. Frey and P. John, Chem. Bet., 100 (1967) 1961. [5] T.A. Stephenson and G. Wilkinson, J. Inorg. Nucl. Chem., 28 (1966) 945. [6] D.R. Fahey, J. Org. Chem., 38 (1973) 80, and refs. therein. [7] S. Cenini, F. Porta and M. Pizzotti, lnorg. Chin~ Acta, 20 (1976) 119. [8] F. L'Eplattenier and F. Calderazzo, lnorg. Chem., 7 (1968) 1290. [9] B.R. James, L.D. Markham, B.C. Hui and G.L. Rempel, J.. Chem. Soc., Dalton Trans., (1973) 2247. [10] S. Cenini, A. Fusi and G. Capparella, Inorg. Nucl. Chem. Lett., 8 (1972) 127. [11] C.F.J. Barnard, J.A. Daniels, J. Jeffery and R.J. Mawby, J. Chem. Soc., Dalton Trans., (1976) 953. [12] S.D. Robinson and M.F. Uttley, Z Chem. Soc., Dalton Trans., (1973) 1912. [13] B.F.G. Johnson, R.D. Johnston, J. Lewis and I.G. Williams, J. Chem. Soc. A, (1971) 689. [14] B.L. Haymore and J.A. Ibers, Inorg. Chem., 14 (1975) 2784. [15] B.F.G. Johnson and J.A. Segal, Z Chem. Soc., Dalton Trans., (1973) 478. [16] L. Ballester, M.C. Barral, A. Guti6rrez, R. Jim6nez-Aparicio, J.M. Martinez-Muyo, M.F. Perpifian, M.A. Monge and C. Ruiz-Valero, Z Chem. Soc., Chem Commun., (1991) 1396. [17] R. Kr~imer, E. Lippmann, K. Noistemig, M. Steimann, U. Nagel and W. Beck, Chem. Ber., 126 (1993) 927. [18] Y.W. Yared, S.L. Miles, R. B~'u and C.A. Reed, J. Am. Chem. Soc., 99 (1977) 7076. [19] R.R. Schrock and J.A. Osborn, Z Am. Chem. Soc., 93 (1971) 2397. [20] B.N. Chaudret, D.J. Cole-Hamilton, R.S. Nohr and G. Wilkinson, J. Chem. Soc., Dalton Trans., (1977) 1546. [21] A.E. Kruse and R.J. Angelici, J. Organomet. Chem., 24 (1970) 231. [22] J.P. Collman and W.R. Roper, J. Am. Chem. Soc., 87 (1965) 4008. [23] S. Cenini, A. Mantovani, A. Fusi and M. Keubler, Gaze. Chim. Ital., 105 (1975) 255. [24] B.E. Cavit, K.R. Grundy and W.R. Roper, J. Chem. Soc., Chem. Commun., (1972) 60. [25] H.E. Bryndza, S.A. Kretchmar and T.H. Tulip, J. Chem. Soc., (-?hem. Commun., (1985) 977. [26] A. Dobson and S.D. Robinson, Inorg. Chem., 16 (1977) 1321.
ELSEVIER
Note
Reactivity of cationic carbonyl/phosphine ruthenium(II) compounds E. Wynne Evans a,*, Mohammed B.H. Howlader a, Mark T. Atlay a School of Applied Sciences, University of Glamorgan, Pontypridd, Mid. Glamorgan CF37 1DL, UK b Centre for Science Education, The Open University, Walton Hall Milton Keynes MK7 6A,4, UK
Received 12 May 1994; revised 28 June 1994
Abstract
C/s(or trans)-[RuCl2(CO)2(PPh3)2] react with two and one equivalents of AgBF4 to give the recently reported [Ru(CO)2(PPhB)2][BF4]2-CH2CI2 (1) and novel [RuCI(CO)2(PPh~)2][BF4]-½CH2CI2 (2), respectively. Cis-[RuCl2(CO)2(PVh3)2] also reacts with two equivalents of AgBF4 in the presence of CO to give [Ru(CO)a(PPha)2][BF4]2 (3). Reactions of I and 2 with NaOMe and CO at 1 atm produce the carbomethoxy species [Ru(COOMe)2(CO)2(PPha)2] (4) and [RuCI(COOMe)(CO)2(PPh3)2] (5), respectively. Complex 4 can also be formed from the reaction of 3 with NaOMe and CO. Alternatively, 4 is formed from c/s-[RuCI2(CO)2(PPh3)2 ] with NaOMe and CO at elevated pressure (10 arm); if these reactants are refluxed under 1 atm of CO, [Ru(CO)3(PPh3)2] is the product. The reaction of [RuCI(CO)a(PPha)~][AICI4] with NaOMe provides an alternative route to the preparation of 5, but the product is contaminated with [RuCI2(CO)2(PPh3)2]. Compounds 1, 2, 4 and 5 have been characterised by IR, 1H NMR and analysis, whilst the formulation of 3 is proposed from spectroscopic data only. This account also examines the reactivity of [Ru(CO)2(PPh3)2][BF4]2-CH2CI2with NaBH4, conc. HCI, KI and, finally, MeCOONa in the presence of CO. The products of these reactions, namely c/s-[RuH2(CO)2(PPh3)2], c/s-[RuCl2(CO)2(PPh3)2], cis-[RuI2(CO)2(PPh3)2] and [Ru(OOCMe)2(CO)2(PPh3)2], have been identified by comparison of their spectra with previous literature. Keywords: Ruthenium complexes; Carbonyl complexes; Phosphine complexes
1. Introduction The catalytic chemistry of Group VIII metal carboalkoxy derivatives has yet to be fully examined. Dicarboalkoxy complexes, in particular, have been shown to play a part in the generation of oxalic esters from synthesis gas; thus providing an attractive synthetic route to ethylene glycol, for example [1]. We have previously described [2] the preparation of dichloromethane-solvated [Rh(CO)(PPh3)2][BF4] and its reactions with nucleophiles in a CO atmosphere, resulting in the formation of carboalkoxy complexes [3]. This account describes the results of analogous experiments carried out with ruthenium-based compounds. In addition, the reactivity of [Ru(CO)E(PPh3)2] 2+- CH2CI2 towards NaBH4, conc. HC1, KI and * Corresponding author.
0020-1693/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSDI 0020-1693(94)04201-6
M e C O O N a is compared with that of its precursor, c/s[RuCI2(CO)2(PPh3)2].
2. Experimental Reactions and manipulations were carried out in a dry, nitrogen atmosphere (unless otherwise specified) using dried, degassed solvents as previously described [2]. ~H and 3~p N M R spectra were obtained at 298 K using a J E O L FX90Q 90MHz Fourier Transform spectrophotometer. IR spectra (4000-250 cm -~) were recorded on Perkin-Elmer 881 and 457 instruments from nujol mulls and CsI discs, respectively. Products were dried in vacuo. Analyses were carried out by M E D A C Ltd., Brunel University, Middlesex. The starting materials [RuCI(CO)3(PPha)2][A1C14] and trans- or
194
cis-[RuCl,(CO),(PPh,),] described [4,5].
E. W. Evans et al. I Inorganica
’ were prepared
as previously
2.1. Preparation of [Ru(CO),(PPh,)J[BF,l,.
CH,Cl,
(1)
Cis-[RuClz(C0)2(PPh3)2] (0.60 g, 0.80 mmol) was stirred with AgBF,, (0.31 g, 1.60 mmol) in CH,Cl, (40 cm3) for 10 h at room temperature. The white precipitate formed was removed by filtration of the mixture through kieselguhr. Concentration of the solvent afforded a white solid which was recrystallised from a mixture of CH,Cl, and CsH14. Yield 0.45 g (60%). Anal. Calc. for CZ,9H3,B,C1,F,0,P,Ru: C, 49.8; H, 3.4. Found: C, 50.1; H, 4.0%. The reaction could also be effected using trans-
[RuC1,P),(PPh,M 2.2. Preparation of [RuCl(CO),(PPhJJ[BFJ
*f CH&
(2)
This preparation was essentially the same as for 1 except that cb(or trans)-[RuCl,(CO),(PPh,),] (0.40 g, 0.53 mmol) was reacted with AgBF, in a 1:l molar ratio. After 7 h, the solid product obtained was recrystallised as for 1, whereupon white crystals were formed. Yield 0.28 g (62%). Anal. Calc. for C&.,H,,BCl,F,O,P,Ru: C, 54.6; H, 3.7. Found: C, 54.0; H, 3.9%. 2.3. Preparation of [Ru(CO),(PPhJJ[BF,]2
(3)
Ck-[RuCl,(CO),(PPh,)J (0.40 g, 0.53 mmol) was stirred for 6 h under CO with AgBF, (0.21 g, 1.06 mmol) in CH,Q (25 cm’). The white precipitate formed was removed by filtration as for 1, but under CO. Concentration of the solvent gave a white solid, which was recrystallised from a mixture of CH,Cl, and C,H,, in a CO atmosphere. Yield 0.28 g (60%). 2.4. Preparation of [Ru(COOMe),(CO),(PPh,),]]
(4)
(a) Compound 1 (0.40 g, 0.43 mmol) in MeOH (15 cm3) was reacted with excess NaOMe ( N 2.20 mm01 in 10 cm3 MeOH) under CO. After 1 h, the product was filtered off and recrystallised from a mixture of C,H, and CsH,4. White microcrystals were formed. Yield 0.20 g (60%). Anal. Calc. for C_,2H3606P2R~: C, 63.1; H, 4.5. Found: C, 63.0; H, 4.5%. (b) As in (a), except that 3 (0.15 g, 0.17 mmol) was used as the starting material. Yield 0.09 g (66%). The IR and NMR spectra of the product were identical with those for 4. ’ Throughout this account the preti refers to the configuration of the CO groups; PPh, groups are exclusively imns, in agreement with earlier reports [6].
Chimica Acta 230 (1995) 193497
(c) As in (a), except that cis-[RuC1,(C0)2(PPh3)J (0.25 g, 0.33 mmol) was reacted with NaOMe solution (2.20 mmol in 10 cm3 MeOH) in a high pressure apparatus. The apparatus was charged with 10 atm of CO for 64 h. Yield 0.18 g (68%). Spectra of the product were as for 4. 2.5. Preparation of [RuCl(COOMe) (CO),(PPh,)J
(5)
(a) This preparation was essentially the same as in Section 2.4 (a), except that 2 (0.40 g, 0.47 mmol) was reacted with NaOMe in a 1:l molar ratio in 20 cm3 MeOH at - 10 “C. White microcrystals, which formed after 15 min, were filtered off and washed with MeOH. Yield 0.18 g (50%). Anal. Calc. for C,H,,ClO,P,Ru: C, 61.9; H, 4.3. Found: C, 61.8; H, 4.4%. (b) [RuCl(CO),(PPh,),][AlCl,] (0.25 g, 0.27 mmol) was reacted with NaOMe (0.45 mmol) in MeOH (15 cm3) at - 10 “C. White microcrystals were formed. The product was characterised as a mixture of 5 and [RuCl,(CO),(PPh,),] from its IR spectrum. 2.6. Reaction of I with NaBH, to form cis-[RuH2(CO),(PPh,)J
Compound 1 (0.20 g, 0.21 mmol) was dissolved in EtOH (10 cm3) and NaBH, solution (0.10 g, 2.60 mmol in 10 cm3 EtOH) added. After 30 min stirring brown crystals formed which were washed with EtOH, then Yield 0.09 g (63%). The hydrido complex GIL was characterised by comparison of its IR and ‘H NMR spectra with previous preparations of cis- [RuH,(CO),(PPh,),] from the reactions of [Ru(N,Ar)(CO),(PPh,),][BF,,] with NaBH, [7] and [Ru(CO),(PPh,),] with Hz [8]. 2.7. Reaction of 1 with cone. HCI to form cis-[RuClz(CO),(PPh,)J
To a solution of 1 (0.10 g, 0.11 mmol) in MeOH (5 cm3), was added cont. HCl ( N 0.20 g) dropwise. Within 10 min the product was formed as a white precipitate which was washed with MeOH. Yield 0.06 g (73%). Again, the spectra of our product are consistent with reported values [5,9,10]. 2.8. Reaction of 1 with Kl to for cis-[RuIz(CO),(PPh,)J
Compound 1 (0.20 g, 0.21 mmol) was reacted with KI (0.10 g, 0.60 mmol) in 15 cm3 MeOH. Within 15 min yellow crystals formed, which were recrystallised from CH,Cl, and C,H,,. Yield 0.14 g (70%). The IR spectrum of the product is consistent with a previous report [ll].
195
E. IV.. Evans et al. / lnorganica Chimica Acta 230 (1995) 193-197
2.9. Reaction of 1 with MeCOONa to form [Ru(OOCMe) 2(CO)2(PPhA2] Compound 1 (0.20 g, 0.21 mmol) was reacted with CH3COONa (0.10 g, 1.22 mmol) in 15 cm 3 MeOH. The mixture was stirred under CO for 1 h. White crystals formed, which were washed with MeOH. Yield 0.11 g (65%). The IR and 1H NMR spectra agree with those from previous preparations [12,13] using [Ru(CO)a(PPh3)2] as precursor.
Table 1 tH and 31p NMR data for ruthenium compounds Compound
1H NMR (3)"
1c 2 3 4 Sc
7.40-7.80 (m, 30H) 5.23 (s, 2H) 7.30-7.80 (m, 30H) 5.28 (s, 1H) 7.30-7.80 (m, 30H) 2.80 (s, 6H) 7.30-7.80 (m, 30H) 2.88 (s, 3H)
3tp NMR (6)b
24.50(s) 22.50(s) 30.50(s)
"In CDCI3 relative to Si(Me)4. b in CDCI 3 relative to 85% H3PO4. ¢ 31p NMR not clear.
3. Results and discussion
3.1. Formation and stability of cationic species Ruthenium cationic carbonyl/phosphine complexes can undergo addition or substitution reactions initiated by nucleophilic attack at the metal centre [4,14,15]. Our main objective, however, has been to study the reactivity of coordinated CO in cationic species towards nucleophilic addition; the CO group appears to be activated by the cationic nature of the compound [4,15]. Ballester et al. [16] have briefly mentioned the use of [Ru(CO)2(PPh3)2(THF)2][BF4]2 as a synthon for the preparation of Ru(I) species. The solvated complex was prepared by the reaction of [RuC12(CO)2(PPh3)2] with AgBF4 in THF. We have already used this halide abstraction reaction, in CH2C12, to prepare rhodium complexes of formula [Rh(CO)(PPh3)2] ÷ or [Rh(CO)2(PPh3)2] ÷ [2], then described their reactions with nucleophiles of the type R O - and R C O O - [3]. We now report extension of this work to include the analogous ruthenium-based compounds. Beck and coworkers have recently reported [17] the preparation of [Ru(CO)2(PPh3)2][BF4]2.CH2CI2 (1), stabilised by FBF3- coordination. We independently duplicated this preparation and concluded the same formulation, although our IR spectra are not as well-resolved as those reported by Beck. It is very probable that FBF3coordination accounts for the stability of the Rh(I) species previously reported [2] and we hope to confirm this through 19F NMR studies. In this account, we report that [RuCI(CO)2(PPhs)2][BF4].½CH2C12 (2) has been prepared by the reaction of [RuC12(CO)2(PPh3)2] with only one equivalent of AgBF4. The reaction of two equivalents of AgBF4 with [RuCI2(CO)2(PPh3)2] in a CO atmosphere gave a species suggested as [Ru(CO)3(PPh3)2][BF4]2 (3). The main NMR features of the compounds prepared are shown in Table 1; 31p NMR spectra were difficult to interpret because of the tendency of the compounds, over the period of time involved, to decompose in solution. However some principle resonances, which diminished in intensity as time proceeded, are included.
The IR spectrum for 1 shows v ( C - O ) values which are slightly lower than those previously reported [17], but v(BF4-) is given only as a broad, unresolved peak centred at 1092 cm -1 (Table 2). Similarly, v ( C - O ) for 2 has values which compare with those reported for other cationic carbonyl Ru(II) species [4,7]; again v(BF4-) is around 1091 c m - k The far-IR spectrum (CsI disc) of 2 shows a band for v(Ru--Cl) at 310 cm -~. Preparation of 1 in Me2CO resulted in an Me2COcoordinated species with v ( C - O ) values at 2090 and 2030 cm -~ and v(BF4-) at 1091 cm-1; solvent coordination is primarily demonstrated by the low value for v(C = O) of Me2CO at 1660 cm- 1 [18-20]. Complete halide abstraction of [RuCI2(CO)2(PPh3)2] in the presence of CO, or treatment of a CH2C12 solution of 1 with CO, resulted in the formation of a white compound with values for v(C = O) (Table 2) very simliar to those previously reported for cationic tricarbonyl species of Ru(II) [4,21]; v(BF4-) is measured at 1092 cm -~. We therefore suggest the compound may be formulated as [Ru(CO)3(PPh3)2][BF4]2 (3); five-coordinate cationic Ru(II) complexes have been previously prepared by addition of CO to a solvent-coordinated precursor [15]. Although the reaction of 1 with CO produced 3, the reaction was not reversed by bubbling N2 through a solution of 3. The enhanced stability of 3, as compared with 1, presumably is a consequence of the metal in 3 having the more stable electronic configuration.
3.2. Formation of carboalkoxy compounds Reactions of 1 or 3 with NaOMe in the presence of CO resulted in the formation of [Ru(COOMe)2(CO)2(PPh3)2] (4). The reaction of 2 with 1 equivalent of NaOMe under CO produced [RuCI(COOMe)(CO)2(PPh3)2] (5); the presence of excess NaOMe again gave 4. The IR spectra of 4 and 5 (Table 2) contain bands around 1650 and 1030 cm-1, for v(C = O) and v(C--OMe) of the carbomethoxy group, in good agreement with similar species previously prepared from the reactions of nucleophiles with cationic Os(II) and Ru(II) complexes [4,21]. In the IR spectrum
196
E.W. Evans et al. / lnorganica Chimica Acta 230 (1995) 193-197
Table 2 IR data a for ruthenium species (cm -1) Compound
v(C -= O)
I 2 3 4 5b
2085, 2070, 2162, 2032, 2042,
v(C = O)
2033(s) 2006(s) 2089, 2032(s) 1977(s) 1986(S)
v(BF4 - )
v(C-OMe)
1092(s,br) 1091(s, br) 1092(s, br) 1653(m), 1637(s) 1655(m)
1027(m) 1028(m)
In nujol. b v(Ru-CI) br at 300 cm-1.
for 4, two bands for both v(C=O) and v(C=O), respectively, suggest c/s-carbonyl [11] and c/s-carbomethoxy groups; we therefore propose 4 has C2v symmetry (Fig. l(a)). IR data for 5, is in good agreement with that reported [4] for the closely-related [RuI(COOMe)(CO)2(PPh3)2], suggesting 5 has the same structure (Fig. l(b)). The transformation of 1 into 4 could also be effected by reacting 1 with excess NEt3 in MeOH under CO. Alternatively, 4 was obtained by the reaction of c/s-[RuC12(CO)2(PPh3)2] with excess NaOMe and CO at 10 atm pressure. A summary of reactions is shown in Scheme 1. The IR spectrum of the product of the reaction of previously reported [4] [RuCI(CO)3(PPh3)2][A1CI4] with NaOMe indicates that a mixture of 5 and [RuC12(CO)2(PPh3)2] had formed. This appears to be in accord with the reported tendency
PPh3 OC. I OC~l"l
PPh3 COOMe
OC.
COOMe
PPh3
I
.-COOMe
O C " in'c1
(4)
PPh3
(a)
(5)
(b)
~g. 1. Structures ~ Ru(II) ~ o m e t h o ~ [Ru (COOMe) 2 (CO) 2 (PPh3) 2 ]4--- e - -
,\
com~exes.
[Ru (CO) 3 (PPh3) 2 ] [BF4 ] 2
/c [RuC12 (CO) 2 (PPh3) 21
b
[Ru(CO) 2(PPh3)21[BF412"cH2C12
a
[RuCl(CO) 2(PPh3)21[BF41"~H2C12
(1)
[23]. Two possible mechanisms exist for the formation of the carboalkoxy groups from their cationic precursors; addition of M e O - to the metal then CO insertion, or direct attack of the nucleophile on coordinated CO [3]. The former mechanism would appear to be likely given the coordinative unsaturation of the metal atom in these cationic species, but no direct evidence for any intermediate Ru-OMe species was found. The same intermediate might be expected to initially form during the reaction of c/s-[RuC12(CO)2(PPh3)2] with M e O and CO, by metathesis. Attempts to prepare methoxo compounds by reacting 1 or 2 with NaOMe under N2 gave an unstable product with broad IR bands for v(C---O) at 1971, 1929 and 1900 cm-1; decomposition of the compound in solution precluded meaningful NMR spectra. It seems likely that this product is a mixture [20,24]; previous attempts to prepare methoxo complexes have resulted in mixtures which include reduction products such as [Ru(CO)2(PPb3)3] and [Ru(CO)3(PPh3)2] that both exhibit v ( C - O ) around 1900 cm -1. If methoxo intermediates are formed, it seems that immediate CO insertion [25] takes place in the Ru-OMe bonds, with the formation of the carbomethoxy species. 3.3. Other reactions of 1
(2)
I
e
[RuCI (CO) 3 (PPh3) 2 ] [AICI4] - -
of [RuCI(CO)3(PPh3)2][A1CL] to convert to [RuCl2(CO)2(PPh3)2] in basic conditions [4]. The compounds c/s- and trans-[RuCl2(CO)2(PPh3)2] gave the reduction product [Ru(CO)3(PPh3)2] when refluxed with excess NaOMe and in the presence of 1 atm CO. This has been previously prepared by the reactions of [RuC12(CO)2(PPh3)2]with a Zn/CO mixture [22], or reduction of [RuC12(PPh3)3] with NaOEt/CO
d ~
[RuCl (COOMe) (CO) 2 (PPh3) 2 ] (5)
Scheme I. Preparations of ruthenium cationic carbonyl/phosphine species and their reactions to form earboalkox'y species, a: AgBF4; b: 2AgBF4; e: 2AgBFJCO; d: NaOMe, [RuCI2(CO~(PPh3)2] also formed; e: NaOMe/CO; f: NaOMe/CO (10 atm); g: NEt3/CO/MeOH.
Compound 1 proved to react readily with a number of reagents (Scheme 2); the products were characterised by comparison of their IR and 1H NMR spectra with previously reported spectra (see Section 2). The reaction of 1 with MeCOONa under CO, gives [Ru(OOCMe)2(CO)2(PPh3)2]. When this reaction was carried out under N2, the IR of the product shows
E.W. Evans et al. / Inorganica Chimica Acta 230 (1995) 193-197 cis- [}~uCl 2 (CO) 2 (PPh3) 2 ]
v,.
a
\
cis- [RuH 2 (CO) ~ (PPh 3 ) 2 ]
/
b,e
[Ru(CO) 2(PPh3) 2] [BF412.CH2C12
c,e cis- [Eul 2 (CO) 2 (PPh3) 2 ]
d,e [Ru (OOCMe) 2 (CO) 2 (PPh3) 2 ]
Scheme 2. Reactions of [Ru(CO)2(PPh3)2][BF4]2-CH2C12 (1). a: conc. HCl; b: NaBH4; c: KI; d: MeCOONa/CO; e: c/s-[RuC12(CO)2(PPh3)2 ] does not react under the same conditions.
bands which could be attributed to the carbonyl groups in [Ru(OOCMe)2(CO)2(PPh3)2 and a very broad, strong band centred around 1941 cm -1. The product of this reaction may be a mixture of both [Ru(OOCMe)2(CO)2(PPh3)2] and [Ru(OOCMe)2(CO)(PPh3)2]; the latter has a reported value for v ( C - O ) [26] at 1960 cm-1 and may be produced by loss of CO in solution during the reaction. If a suspension of [Ru(OOCMe)2(CO)2(PPh3)2], in methanol, was reacted with conc. HC1, then c/s-[RuCl2(CO)2(PPh3)2] formed almost immediately. These reactions are shown in Scheme 2.
Acknowledgements We thank Johnson Matthey Materials Technology, UK, for a loan of ruthenium. M.B.H.H. was supported by an O.D.A.S.S.S. scholarship.
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197
[3] E.W. Evans, M.B.H. Howlader and M.T. Atlay, Transition Met. Chem., 19 (1994) 183. [4] W. Hieber, V. Frey and P. John, Chem. Bet., 100 (1967) 1961. [5] T.A. Stephenson and G. Wilkinson, J. Inorg. Nucl. Chem., 28 (1966) 945. [6] D.R. Fahey, J. Org. Chem., 38 (1973) 80, and refs. therein. [7] S. Cenini, F. Porta and M. Pizzotti, lnorg. Chin~ Acta, 20 (1976) 119. [8] F. L'Eplattenier and F. Calderazzo, lnorg. Chem., 7 (1968) 1290. [9] B.R. James, L.D. Markham, B.C. Hui and G.L. Rempel, J.. Chem. Soc., Dalton Trans., (1973) 2247. [10] S. Cenini, A. Fusi and G. Capparella, Inorg. Nucl. Chem. Lett., 8 (1972) 127. [11] C.F.J. Barnard, J.A. Daniels, J. Jeffery and R.J. Mawby, J. Chem. Soc., Dalton Trans., (1976) 953. [12] S.D. Robinson and M.F. Uttley, Z Chem. Soc., Dalton Trans., (1973) 1912. [13] B.F.G. Johnson, R.D. Johnston, J. Lewis and I.G. Williams, J. Chem. Soc. A, (1971) 689. [14] B.L. Haymore and J.A. Ibers, Inorg. Chem., 14 (1975) 2784. [15] B.F.G. Johnson and J.A. Segal, Z Chem. Soc., Dalton Trans., (1973) 478. [16] L. Ballester, M.C. Barral, A. Guti6rrez, R. Jim6nez-Aparicio, J.M. Martinez-Muyo, M.F. Perpifian, M.A. Monge and C. Ruiz-Valero, Z Chem. Soc., Chem Commun., (1991) 1396. [17] R. Kr~imer, E. Lippmann, K. Noistemig, M. Steimann, U. Nagel and W. Beck, Chem. Ber., 126 (1993) 927. [18] Y.W. Yared, S.L. Miles, R. B~'u and C.A. Reed, J. Am. Chem. Soc., 99 (1977) 7076. [19] R.R. Schrock and J.A. Osborn, Z Am. Chem. Soc., 93 (1971) 2397. [20] B.N. Chaudret, D.J. Cole-Hamilton, R.S. Nohr and G. Wilkinson, J. Chem. Soc., Dalton Trans., (1977) 1546. [21] A.E. Kruse and R.J. Angelici, J. Organomet. Chem., 24 (1970) 231. [22] J.P. Collman and W.R. Roper, J. Am. Chem. Soc., 87 (1965) 4008. [23] S. Cenini, A. Mantovani, A. Fusi and M. Keubler, Gaze. Chim. Ital., 105 (1975) 255. [24] B.E. Cavit, K.R. Grundy and W.R. Roper, J. Chem. Soc., Chem. Commun., (1972) 60. [25] H.E. Bryndza, S.A. Kretchmar and T.H. Tulip, J. Chem. Soc., (-?hem. Commun., (1985) 977. [26] A. Dobson and S.D. Robinson, Inorg. Chem., 16 (1977) 1321.