摘要:
CHEMICAL COMMUNICATIONS, 1968 733 The Mechanism of the Reaction of Low-valent Metal Complexes with Electrophilic Olefins By M. COOKE, M. GREEN,* and D. C. WOOD (Department of Inorganic Chemistry, University of Bristol, Bristol, 8) THE isoelectronic compounds, tetrafluoroethyl- ene,l y 2 tetra~yanoethylene,~ 94 hexafluoroacetone,5 and carbon disulphide6 have been shown to form complexes with low-valent transition-metal com- plexes. If a valence-bond description is adopted, the bonding in these complexes may be depicted as involving the metal atom in a three-membered a-bonded ring framework. Recently, the stereo- ~hemistry~9~ >' of these complexes has received attention, but little is known about the related topic of the mechanism of formation of these complexes. The ruthenium(0) complex trans- {EtC[CH,O],- P},Ru(CO), reacts very rapidly a t room tempera- ture with l,l-dicyano-2,2-bis(trifluoromethyl)ethyl- ene to form (I). The i.r.spectrum of (I) showed a single terminal carbonyl band a t 2061 vs cm.-l (CH,Cl,) and the lH n.m.r. spectrum showed the (POCH,) protons as a doublet (JHp 44c./sec.) centred at T 5.70, which establishes the illustrated stereochemistry. The 19F n.m.r. spectrumt con- taining a doublet (JPF 5.8 c./sec.) a t 54.4 p.p.m. confirming the structural assignment. The crystal- line solid (I) isomerises in solution [tt 6 min. (MeCN), t+ 30 min. (C,H,)] to form (11) with i.r. bands 2041 vs and 1938 vs cm.-l (CH,Cl,) ; the lH and 19F n.m.r. spectra had bands a t 5.63 (d, POCH,, JHP 4.5 c./sec.) and 5.707 (d, POCH,, JHp 4.5 c./sec.); and a doublet (JPF 5.8 c./sec.) centred a t 54-4 p.p.m., respectively. Tetrafluoroethylene reacts with trans- [(C,H50) 3- P],Ru(CO), to afford (111) m.p.59". vco 2019 vs cm.-l (hexane) with IH n.m.r. bands at T 6.30 (quint., POCH,CH,, JHP 7.0 c./sec., JHH 7-0 c./sec.), 8-72 (t, POCH,CH,, JHH 7.0 c./sec.), and a 1 9 F n.m.r. band at 114.2 p.p.m. (typical X- resonance of an X,AA'X,' system) .1 The isolation of (I), (11), and (111) is of general interest in that these are the first examples of ruthenium fluoro-olefin complexes, moreover, the n.m.r. data provides support for the rigid a-bonded structures illustrated i .e. the compounds are formally Run complexes. However, the stereo- chemistry of (I), (11) and (111) is in striking t The solvent used for the 1@F n.m.r.spectral work was CFC1,.734 contrast with that observed in the formally related'; reaction of trans- (Ph,P) ,Ru(CO) ,* or trans- (Ph,PMe) 2Ru(CO) , * e9 with iodine, when cis- addition of iodine occurs and the phosphines retain their relative trans-configuration. CHEMICAL COMMUNICATIONS, 1968 n.m.r. spectrum showed two bands a t 53.8 p.p.m. (d, JPF 11.7) and 58-0p.p.m. (d, JPF 9.3 c./sec.). Since vicinal inequivalent CF, groups only showlo F-F coupling when in a relative cis-configuration, no change in configuration of the olefin occurs on R (I; R=EtCTCH,O],P) R [III; R=(EtO),P] t P (I1 ; R= E t C[CH,O],P) P [IV; R=(EtO),P] In order to accommodate this difference in stereochemistry it is suggested, that in the reaction of (CF,) ,C= C(CN) ,, C,F, and other electrophilic olefins with ruthenium(0) complexes, the olefin approaches the metal broadside-on as depicted (mechanism A), rather than end-on (mechanism B) where reaction involves nucleophilic attack by the metal on the electrophilic olefin.Further evidence for the reaction proceeding v i a direct co-ordination of the olefin to the metal was provided by studying the reaction of trans- (Ph,P) ,IrCOCl with trans-1 Z-dicyano- 1,2-bis(tri- fluoromethyl)ethylene.lO The reaction is stereo- specific leading to the formation of (IV) m.p. 267-268", vco 2041 vs cm.-l (Nujol). The 19F P R C v Mechanism A Mechanism B complexing to iridium. The stereospecificity of this reaction implies that ionic intermediates of the kind depicted in mechanism B are not involved.A study of the rate of reaction of trans-(Ph,P)- IrCO-C1 with trans-CF,(CN)C=C(CN)CF, in diff- erent solvents confirms this point. The reaction in nitromethane proceeds at a rate only twice as fast as in methylene chloride. If an ionic inter- mediate was involved a large rate difference would be expected.1° These experiments clearly suggest that in the reaction of low-valent metal species with electro- philic olefins, weak 0-donor interaction occurs followed by developing overlap between the metal &orbitals and the olefinic rr-antibonding orbitals . (Received, April 8th, 1968; Corn. 430.) $ The reaction of electrophilic olefins with P,Ru (CO), systems may be thought of as an oxidative-elimination reaction. 1 M. Green, R. B. L. Osborn, A. J. Rest, and F. G. A. Stone, Chem. Comm., 1966, 502; M. Green, R. B. L. Osborn, 2 G. W. Parshall and F. N. Jones, J . Amer. Chem. Soc., 1965,87, 5356. 3 W. H. Baddley, J . Amer. Chem. SOC., 1966, 88, 4545. 4 W. H. Baddley, C. Panattoni, G. Bombieri, and U. Belluco, J . Amer. Chem. SOC., 1968,90, 798. 6 B. Clarke, M. Green, R. B. L. Osborn, and F. G. A. Stone, J . Chem. SOC. ( A ) , 1968, 167. 6 M. Baird, G. Hartnell, R. Mason, A. I. M. Rae, and G. Wilkinson, Chem. Comm., 1967, 92. 7 J. A. McGinnety and J. A. Ibers, Chem. Comm., 1968, 235. 8 J. P. Collman and W. R. Roper, J . Amer. Chem. SOC., 1965,87, 4008. 8 R. Burt, M. Cooke, and M. Green, unpublished work. 10 S. Proskow, H. E. Simmons, and T. L. Cairns, J . Amer. Chem. SOC., 1966,88, 5254. A. J. Rest, and F. G. A. Stone, J . Chem. SOC. ( A ) , 1968, in the press.
ISSN:0009-241X
DOI:10.1039/C19680000733
出版商:RSC
年代:1968
数据来源: RSC