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Organometallics 1999, 18, 564-572
Reactivity of Dinuclear Platina-β-diketones toward Phosphines and Pyridines: Formation of Mononuclear Platina-β-diketones and Acyl(chloro)platinum(II) Complexes† Michael Gerisch, Frank W. Heinemann,‡ Clemens Bruhn, Joachim Scholz, and Dirk Steinborn* Institut fu¨ r Anorganische Chemie der Martin-Luther-Universita¨ t Halle-Wittenberg, Kurt-Mothes-Strasse 2, D-06120 Halle (Saale), Germany Received September 22, 1998
Dinuclear platina-β-diketones [Pt2{(COR)2H}2(µ-Cl)2] (R ) Me (1a), Et (1b)) react with phosphines (PPh3, Ph2P(CH2)nPPh2, n ) 1-3) and triphenylarsine to form acylplatinum(II) complexes as well as acetaldehyde and propionaldehyde, respectively. Reaction of 1 with 4 equiv of PPh3 and AsPh3 leads to trans-[PtCl(COR)L2] (L ) PPh3 (4), AsPh3 (5); R ) Me (a), Et (b)). Reaction of 1a with PPh3 in a 1:2 molar ratio results in formation of carbonyl(methyl)platinum complexes [PtCl(Me)(CO)(PPh3)] (11). Cationic A-frame complexes [Pt2(COR)2(µCl)(µ-dppm)2]Cl (R ) Me (6a), Et (6b)) were formed in reactions of 1 with 2 equiv of Ph2PCH2PPh2 (dppm). Treatment of 1a with Ph2P(CH2)2PPh2 (dppe) and Ph2P(CH2)3PPh2 (dppp) yields complexes [PtCl(COMe){Ph2P(CH2)nPPh2}] (n ) 2 (7), 3 (8)). However, at low temperatures (-30 °C) reactions of 1a with dppe and dppp afford mononuclear cationic platina-β-diketones [Pt{(COMe)2H}(Ph2P(CH2)nPPh2)]Cl (n ) 2 (9a), 3 (10)). The reaction of [Pt2{(COMe)2H}2(µ-Cl)2] (1a) with pyridine (py) or quinoline (quin) results in cleavage of the Pt-Cl-Pt bridges, yielding mononuclear neutral platina-β-diketones [PtCl{(COMe)2H}L] (L ) py (13a), quin (13b)). In the solid state complex 13b reveals a nonplanar arrangement of the platina-β-diketone unit with a strong hydrogen bond (O‚‚‚O 2.419(8) Å). From all these findings the mechanism of the aldehyde formation in the reactions of platina-β-diketones 1 with L (PPh3, AsPh3) and LL (dppm, dppe, dppp) is deduced. Introduction
Scheme 1
Hydroxycarbene complexes are proposed as important intermediates in CO reduction reactions, including the Fischer-Tropsch process.1 Calculations suggest that they are also key intermediates in hydroformylation and aldehyde decarbonylation reactions.2 Since the synthesis of the first hydroxycarbene complex, [Re{)C(OH)Me}(η5-C5H5)(CO)2] (A),3 by Fischer, hydroxycarbene complexes of groups 6-8 have been synthesized.4 Fischer proposed that aldehyde formation by thermal decomposition of A starts with the cleavage of the RedC bond, producing free methylhydroxycarbene that is rearranged to acetaldehyde (Scheme 1).3 Only very recently, Casey et al. reported an equilibrium between the tautomeric hydroxycarbene complex B and the acyl(hydrido) complex C (Scheme 1) as a consequence of ring strain perturbation in a system very similar to those of †
Dedicated to Professor Helmut Werner on the occasion of his 65th birthday. ‡ Present address: Institut fu ¨ r Anorganische Chemie II der FriedrichAlexander Universita¨t Erlangen-Nu¨rnberg, Egerlandstr. 1, D-91058 Erlangen, Germany. (1) (a) Cornils, B., Herrmann, W. A., Eds. Applied Homogeneous Catalysis with Organometallic Compounds; VCH: Weinheim, 1996. (b) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis; Wiley: New York, 1992. (c) Milstein, D. Acc. Chem. Res. 1988, 21, 428. (d) Muetterties, E. L.; Stein, J. Chem. Rev. 1979, 79, 479. (e) Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1982, 21, 117. (2) Sola`, M.; Ziegler, T. Organometallics 1996, 15, 2611. (3) Fischer, E. O.; Riedel, A. Chem. Ber. 1968, 101, 156.
Fischer.5 It is suggested that aldehyde formation occurs via reductive elimination from an unseen cis-acyl(hydrido) intermediate C′, because by thermolysis of B in the presense of PPh3 a clean formation of the untethered aldehyde [Re(η5-C5H4CH2CH2CHO)(CO)2(PPh3)] (D) is observed (Scheme 1).5b Dinuclear platina-β-diketones [Pt2{(COR)2H}2(µ-Cl)2] (R ) Me (1a), R ) Et (1b)), prepared by reaction of hexachloroplatinic(IV) acid with silyl-substituted acetylenes in n-butanol, proved to be electronically unsatur-
10.1021/om980793m CCC: $18.00 © 1999 American Chemical Society Publication on Web 01/22/1999
Reactivity of Dinuclear Platina-β-diketones Scheme 2
ated complexes with a kinetically labile ligand sphere.6 Complexes 1 can be regarded as acyl(hydroxycarbene) complexes intramolecularly stabilized by hydrogen bonds and exhibit a fundamentally different reactivity than Lukehart’s mononuclear metalla-β-diketones [LxM{(COR)2H}]7 (L ) CO, Cp; M ) Mo, W, Mn, Re, Fe, Os), which are electronically saturated and kinetically stable complexes. Previously, we have found that 1a reacts with bipyridines (NN ) bpy, 4,4′-Me2bpy, 4,4′-t-Bu2bpy) via oxidative addition to yield acyl(hydrido)platinum(IV) complexes [PtCl(H)(COMe)2(NN)] (2) (Scheme 2).8 Complexes 2 decompose in the solid state (above 150 ˚C) nearly quantitatively via reductive elimination of acetaldehyde to form acylplatinum(II) complexes [PtCl(COMe)(NN)] (3) (Scheme 2). We here report reactions of platina-β-diketones 1 with phosphines (PPh3, dppm, dppe, dppp), with triphenylarsine, and with pyridine (py) and quinoline (quin) yielding acyl(chloro)platinum(II) complexes and mononuclear platina-β-diketones, respectively. The pathway of aldehyde formation in reactions of 1 with phosphines will be discussed. Results and Discussion Reactions of Platina-β-diketones with PPh3, AsPh3, and dppm. Platina-β-diketones 1 react in methylene chloride at ambient temperature with 4 equiv of PPh3 or AsPh3 to give acyl(chloro)platinum(II) complexes trans-[PtCl(COR)L2] (L ) PPh3 (4), AsPh3 (5), R ) Me (a), Et (b)) (Scheme 3). The reaction with 2 equiv of dppm (bis(diphenylphosphino)methane) affords the cationic A-frame complexes [Pt2(COR)2(µ-Cl)(µ-dppm)2](4) (a) Green, M. L. H.; Mitchard, L. C.; Swanwick, M. G. J. Chem. Soc. A 1971, 794. (b) Fischer, E. O.; Kreis, G.; Kreissl, F. R. J. Organomet. Chem. 1973, 56, C37. (c) Moss, J. R.; Green, M.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1973, 975. (d) Darst, K. P.; Lukehart, C. M. J. Organomet. Chem. 1979, 171, 65. (e) Wong, W.-K.; Tam, W.; Gladysz, J. A. J. Am. Chem. Soc. 1979, 101, 5440. (f) Chatt, J.; Leigh, G. J.; Pickett, C. J.; Stanley, D. R. J. Organomet. Chem. 1980, 184, C64. (g) Darst, K. P.; Lehnert, P. G.; Lukehart, C. M.; Warfield, L. T. J. Organomet. Chem. 1980, 195, 317. (h) Buhro, W. E.; Wong, A.; Merrifield, J. H.; Lin, G.-Y.; Constable, A. C.; Gladysz, J. A. Organometallics 1983, 2, 1852. (i) Asdar, A.; Lapinte, C. J. Organomet. Chem. 1987, 327, C33. (j) Gibson, D. H.; Mandal, S. K.; Owens, K.; Richardson, J. F. Organometallics 1990, 9, 1936. (k) Casey, C. P.; Sakaba, H.; Underiner, T. L. J. Am. Chem. Soc. 1991, 113, 6673. (l) Lukehart, C. M.; Zeile, J. V. J. Am. Chem. Soc. 1976, 98, 2365. (m) Klingler, R. J.; Huffman, J. C.; Kochi, J. K. Inorg. Chem. 1981, 20, 34. (n) Powell, J.; Farrar, D. H.; Smith, S. J. Inorg. Chim. Acta 1984, 85, L23. (o) Motz, P. L.; Ho, D. M.; Orchin, M. J. Organomet. Chem. 1991, 407, 259. (5) (a) Casey, C. P.; Czerwinski, C. J.; Hayashi, R. K. J. Am. Chem. Soc. 1995, 117, 4189. (b) Casey, C. P.; Czerwinski, C. J.; Fusie, K. A.; Hayashi, R. K. J. Am. Chem. Soc. 1997, 119, 3971. (6) (a) Steinborn, D.; Gerisch, M.; Merzweiler, K.; Schenzel, K.; Pelz, K.; Bo¨gel, H.; Magull, J. Organometallics 1996, 15, 2454. (b) Heinemann, F. W.; Gerisch, M.; Steinborn, D. Z. Kristallogr. 1997, 212, 181. (7) Lukehart, C. M. Adv. Organomet. Chem. 1986, 25, 45. (8) Gerisch, M.; Bruhn, C.; Vyater, A.; Davies, J. A.; Steinborn, D. Organometallics 1998, 17, 3101.
Organometallics, Vol. 18, No. 4, 1999 565 Scheme 3
Cl (R ) Me 6a, Et 6b) (Scheme 3). In all these reactions the formation of acetaldehyde or propionaldehyde is observed by NMR spectroscopy (δ(CHO) ) 9.75 ppm for MeCHO; δ(CHO) ) 9.77 ppm for EtCHO). All complexes 4-6 were obtained as off-white or pale yellow, air-stable crystals in good yields (68-85%) and identified by microanalyses and NMR and IR spectroscopy. The spectroscopic data of the triphenylphosphine complexes 4 agree with literature data.9 Only the chemical shift of the methyl protons in complex 4b (-0.13 ppm) shows a noticeable difference from the reported value (0.15 ppm).9c The resonances of the carbonyl carbon atoms in complexes 4-6 appear at 200.5-218.8 ppm. The 1J(PtC) coupling constants were found to be 844-962 Hz. The typical anisochronic behavior of the protons of the methylene bridges in A-frame complexes10 is well observed in complexes 6, too, whereas splitting of the resonances in 6a appears only at low temperatures (-20 °C). Due to the nonzero value of the 2J(PP) coupling and the superposition of three subspectra of the platinum isotopomers (195Pt: I ) 1/2, 33.8% abundance), the coupling constants 2J(HH), 3J(PtH), and 2J(PH) could not be calculated in complexes 6. The 31P NMR chemical shifts in both complexes (6a, 6b, 7.3 ppm) are very similar to those found in [Pt2(COPh)2(µ-Cl)(µ-dppm)2]Cl (δ ) 5.9 ppm11). The 31P NMR spectra result from superposition of A4 (43.8%), AA′BB′X (44.8%), and AA′A′′A′′′XX′ subspectra (11.4%) (A, B ) 31P; X ) 195Pt). Coupling constants 1J(PtP) (6a, 3447 Hz; 6b, 3442 Hz), 3J(PtP) (6a, 56 Hz; 6b, 58 Hz), 2J(PP) (6a, 30/48 Hz; 6b, 31/42 Hz), 2J(PtPt) (6a, 474 Hz), and 4J(PP) ( 2σ(I)) R, all data largest diff peak and hole, e Å-3
6a
7
13b
C54H50Cl2O2P4Pt2 1315.90 293(2) triclinic P1 (no. 2) 11.364(1) 12.781(2) 18.694(2) 72.51(1), 88.01(1), 89.18(1) 2588.1(5) 2 1.689 5.665 1280 2.29 < θ < 25.00 25 435 8579 (Rint ) 0.1123) 590 1.086 R1 ) 0.0453, wR2 ) 0.1232 R1 ) 0.0630, wR2 ) 0.1323 1.669 and -3.178
C28H27ClOP2Pt 671.98 293(2) monoclinic P21/n (no. 14) 9.289(1) 26.458(7) 12.018(2) 90, 103.51(1), 90 2871.9(9) 4 1.554 5.107 1312 1.91 < θ < 22.50 13 241 3674 (Rint ) 0.1252) 299 0.971 R1 ) 0.0450, wR2 ) 0.0751 R1 ) 0.0960, wR2 ) 0.0885 0.585 and -0.504
C13H14ClNO2Pt 446.79 293(2) monoclinic P21/n (no. 14) 12.899(3) 7.517(1) 14.751(4) 90, 106.49(3), 90 1371.5(5) 4 2.164 10.418 840 2.48 < θ < 25.00 9362 2318 (Rint ) 0.0501) 180 0.997 R1 ) 0.0292, wR2 ) 0.0657 R1 ) 0.0408, wR2 ) 0.0695 2.537 and -1.120
TlPF6 (112 mg, 0.32 mmol) was added. After stirring for 5 min, the precipitate of TlCl was filtered. The solution of [Pt{(COMe)2H}(dppe)]PF6 (9b) was characterized by NMR spectroscopy (degree of conversion of 9a 100%). 1H NMR (300 MHz, 243 K, CD2Cl2): δ 2.03 (s+d, 6H, 3J(PtH) ) 16.5 Hz, CH3), 2.35 (“d”, 4H, N ) 17.0 Hz, CH2), 7.49 (m, 12H, m-, p-CH), 7.76 (m, 8H, o-CH), 14.6 (s br, 1H, OHO). 31P NMR (81 MHz, CD2Cl2): δ 39.5 (s+d, 1J(PtP) ) 1725 Hz), -141.7 (sept, 1J(PF) ) 711 Hz). Reaction of [Pt2{(COMe)2H}2(µ-Cl)2] (1a) with dppp. To a pale yellow suspension of [Pt2{(COMe)2H}2(µ-Cl)2] (1a) (100 mg, 0.16 mmol) in CD2Cl2 (4 mL) was added bis(1,3-diphenylphosphino)propane (132 mg, 0.32 mmol) at -30 °C, affording a pale yellow solution that was investigated by 1H and 31P NMR spectroscopy at -30 °C (1H NMR: degree of conversion of 1a yielding [Pt{(COMe)2H}(dppp)]Cl (10) 100%). The solution was slowly warmed to ambient temperature for 30 min and investigated by NMR spectroscopy (ratio of [PtCl(COMe)(dppp)] (8):[PtCl2(dppp)] ca. 85-90:15-10 detected by 31P NMR). To isolate 8 (in mixture with about 10% [PtCl 2 (dppp)]), diethyl ether (10 mL) was added. After standing overnight the off-white crystals were filtered off and dried briefly in vacuo. 8: IR (CsBr): ν(CO) 1637, ν(PtCl) 292 cm-1. 1H NMR (200 MHz, CDCl ): δ 1.74 (d, 3H, 4J(PH) ) 1.0 Hz, 3 CH3), 1.86 (m, 2H, CH2), 2.32 (m, 2H, CH2), 2.63 (m, 2H CH2), 7.36 (m, 12H, m-, p-CH), 7.67 (m, 8H, o-CH). 13C NMR (126 MHz, CDCl3): δ 19.2 (PCH2CH2), 26.3 (dd, 1J(PC) ) 20 Hz, 3J(PC) ) 7 Hz, PCH ), 26.9 (dd, 1J(PC) ) 33 Hz, 3J(PC) ) 12 2 Hz, PCH2), 40.7 (dd, 3J(PaC) ) 27 Hz, 3J(PbC) ) 11 Hz, CH3), 128.4-133.4 (phenyl-C), 244.3 (dd, 2J(PaC) ) 126 Hz, 2J(PbC) ) 9 Hz, CO). 31P NMR (202 MHz, CDCl3): δ -4.5 (d+dd, 1J(PtP) ) 4416 Hz, 2J(P P ) ) 27.8 Hz), -4.7 (d+dd, 1J(PtP) a b ) 1326 Hz, 2J(PaPb) ) 27.8 Hz). 10: 1H NMR (300 MHz, 243 K, CD2Cl2): δ 1.89 (s, 6H, CH3), 2.82 (m, 6H, CH2), 7.33 (m, 12H, m-, p-CH), 7.73 (m, 8H, o-CH), resonance for OHO not observed. 31P NMR (81 MHz, CD2Cl2): δ -7.7 (s+d, 1J(PtP) ) 1696 Hz). [PtCl{(COMe)2H}L] (13). To a suspension of [Pt2{(COMe)2H}2(µ-Cl)2] (1a) (200 mg, 0.32 mmol) in methylene chloride (3 mL) was added pyridine (53 µL, 0.66 mmol) or quinoline (86 µL, 0.66 mmol) at room temperature. After 30 min, the resulting green-yellow solution was layered with pentane (10 mL). After standing overnight at -30 °C off-white (13a) or pale yellow (13b) crystals that precipitated were filtered off, washed with pentane (5 mL), and dried briefly in vacuo. 13a (L ) py): Yield: 230 mg, 92%. Mp: 79-80 °C (dec 92-94 °C). Anal. Calcd for C9H12ClNO2Pt (396.73): C 27.25; H 3.05; Cl 8.94; N 3.53. Found: C 26.91; H 2.82; Cl 9.01; N 3.37. IR (CsBr): ν-
(CO) 1542, 1536, ν(PtCl) 273 cm-1. 1H NMR (200 MHz, 253 K, CD2Cl2): δ 1.81 (s+d, 3H, 3J(PtH) ) 19.3 Hz, CH3), 2.62 (s+d, 3H, 3J(PtH) ) 17.2 Hz, CH3), 7.55 (m, 2H, m-CH), 7.94 (m, 1H, p-CH), 8.65 (m, 2H, o-CH), 18.9 (s br, 1H, OHO). 13C NMR (100 MHz, CD2Cl2): δ 39.4 (s+d, 2J(PtC) ) 174 Hz, CH3), 40.8 (s+d, 2J(PtC) ) 124 Hz, CH3), 126.5 (m-CH), 139.1 (pCH), 152.2 (o-CH), 236.9 (s+d, 1J(PtC) ) 1361 Hz, CO), 245.0 (s+d, 1J(PtC) ) 1295 Hz, CO). 13b (L ) quin): Yield: 220 mg, 78%. Mp (dec): 100-102 °C. Anal. Calcd for C13H14ClNO2Pt (446.79): C 34.95; H 3.16; Cl 7.93; N 3.13. Found: C 34.78; H 2.83; Cl 7.86; N 2.82. IR (CsBr): ν(CO) 1539, ν(PtN) 504, ν(PtCl) 273 cm-1. 1H NMR (300 MHz, CD2Cl2): δ 1.62 (s+d, 3H, 3J(PtH) ) 19.0 Hz, CH3), 2.72 (s+d, 3H, 3J(PtH) ) 17.9 Hz CH3), [7.65 (dd, 1H, 3J(HH) ) 8.4 Hz, 4J(HH) ) 2.9 Hz), 7.72 (t, 1H, 3J(HH) ) 7.3 Hz), 7.91 (“quin”, 1H, N ) 16.5 Hz), 8.02 (d, 1H, 3J(HH) ) 8.0 Hz), 8.48 (d, 1H, 3J(HH) ) 8.0 Hz), 8.89 (d, 1H, 3J(HH) ) 8.4 Hz), 9.10 (dd, 1H, 3J(HH) ) 4.9 Hz, 4J(HH) ) 1.1 Hz)], 18.8 (s br, 1H, OHO). 13C NMR (100 MHz, CD2Cl2): δ 38.8 (s+d, 2J(PtC) ) 166 Hz, CH3), 40.6 (s+d, 2J(PtC) ) 140 Hz, CH ), [121.9 (s+d, 2J(PtC) ) 25 Hz), 128.0 3 (s+d, 2J(PtC) ) 36 Hz), 128.2, 128.6, 129.9, 131.6, 139.3, 146.4, 152.8], 234.2 (s+d, 1J(PtC) ) 1353 Hz, CO), 243.8 (s+d, 1J(PtC) ) 1290 Hz, CO). Resonances of the quinoline ligand are given in square brackets.
Crystallographic Studies Intensity data for 6a, 7, and 13b were collected on a Stoe IPDS diffractometer with Mo KR radiation (0.710 73 Å, graphite monochromator). A summary of crystallographic data, data collection parameters, and refinement parameters is given in Table 4. 13b was corrected for absorption numerically (Tmin/Tmax 0.15/0.29). The structures were solved by direct methods with SHELXS8626 and refined using full-matrix least-squares routines against F2 with SHELXL-93.26 Non-hydrogen atoms were refined with anisotropic displacement parameters. The hydrogen atom positions of 6a, 7, and 13b were calculated and allowed to ride on their corresponding carbon atoms. The isotropic displacement parameters (25) Sheldrick, G. M. SHELXS-86, SHELXS-93, Programs for Crystal Structure Determination; University of Go¨ttingen, Go¨ttingen, 1986, 1993. (26) Burnett, M. N.; Johnson, C. K. ORTEP-III: Oak Ridge Thermal Ellipsoid Plot Program for Crystal Structure Illustrations; Oak Ridge National Laboratory Report ORNL-6895, 1996.
572 Organometallics, Vol. 18, No. 4, 1999
of 6a and 7 were tied to those of the adjacent carbon atoms by a factor of 1.5 (6a) and 1.2 (7), respectively; those of 13b were refined. The bridging H atom in 13b was found in the difference Fourier map. The chloride anion in 6a is disordered, lying on two positions with a major (Cl2, 83.8%) and a minor (Cl2a, 16.2%) site occupancy. Acknowledgment. Dr. A. Porzel and Dr. M. Plass are kindly acknowledged for HMBC NMR spectrum and IR spectroscopical investigations, respectively. This
Gerisch et al.
work is supported by the Deutsche Forschungsgemeinschaft and by the Fonds der Chemischen Industrie. Gifts of chemicals by the companies Degussa (Hanau) and Merck (Darmstadt) are gratefully acknowledged. Supporting Information Available: Complete tables of atomic coordinates, H atom parameters, bond distances, bond angles, and anisotropic displacement parameters for 6a, 7, and 13b (23 pages). Ordering information is given on any current masthead page. OM980793M
