Vinylcyclopropan‐Komplexe und Vinylcyclopropane aus Carben‐Komplexen und 1,3‐Dienen

Abstract

Benzylidenepentacarbonyl complexes (CO),M[C(C,H,R-p)H](1) [M = W: R = H (a), OMe (b); M = Cr: R = H (c), OMe (d)], react with cyclopentadiene by stereospecific transfer of the benzylidene ligand to one C = C bond of the diene and coordination of the resulting endo-6-arylbicyclo[3.l.0]hex-2-ene (4) to the metal. The (CO),M fragment occupies the exo-position. Addition of bromide liberates 4 from the metal. The reaction of l a with 1,3-cyclohexadiene gives the corresponding (endo-7-phenylbicyclo[4.1.O]hept-2-ene)tungsten complex (6) and, after addition of Br-, the free bicyclic compound. The sequential reaction of 1 a with 1,2,3,4,5-pentamethylcyclopentadiene and Br-affords the endo-6-phenyl-exo-4-methyl isomer of pentamethylphenylbicyclo[3.l.0]hex-2-ene 9 with more than 85% stereoselectivity. The benzylidene transfer from 1 a to cis-and trans-pentadiene, isoprene, and Z-chloro-l,3-butadiene proceeds regiospecifically to the more electron-rich C = C bond to give (E)-and (3-phenylvinylcyclopropanes. The E / Z ratio ranges from 0.52 to 2.2. The structures of the complexes 3d and 6 were established by X-ray analyses.Elektrophile Carben-Komplexe erwiesen sich in den letzten Jahren als sehr nutzliche Synthone fur den Aufbau von Carbo-und Heterocyclen'). So lafit sich z. B. der Carbenligand auf olefinische Doppelbindungen unter Bildung von Cyclopropanen ubertragen2'. Die Reaktionen verlaufen stereoselektiv, bevorzugt entstehen im allgemeinen die thermodynamisch weniger stabilen cis-Cyclopropane. Die Untersuchungen beschrankten sich im wesentlichen auf die Cyclopropanierung von Monoolefinen". Wahrend die Reaktionen von a,P-ungesattigten Carben-Komplexen mit

Dihydropyridines in Organometallic Synthesis. Formation of Pyridine and Dihydropyridine-Stabilized Alkylidene Complexes of Tungsten(0) and Chromium(0) from Fischer Carbene Complexes: Structure and Reactivity

“…First, complete retention of the stereochemistry of the alkene precursor is observed in the case of complex 30d since 31d was isolated as a single isomer . This result is reminiscent of the reaction of complex 3 with ( E )- and ( Z )-olefins during which conservation of the stereochemistry was observed . Second, complexes 30b and 30c gave rise to a 1:1 mixture of isomers.…”

“…Since the pyridinium ylide complexes described herein can be considered as the result of the interaction of pyridine with W(0) and Cr(0) alkylidene complexes ( vide infra ), one might address the question of the reversibility of this reaction. In such an event, a general access to alkylidene complexes such as 3 transferable to olefins would be possible: it has indeed been shown that simple olefins react with complex 3 at low temperature to give phenylcyclopropanes. , However, at first glance, no transformation of complexes 7a and 17 was observed in solution by NMR spectroscopy. They appeared to be quite stable although slow oxidation to the corresponding aldehydes took place in the presence of oxygen.…”

“…A slightly modified method gave, later on, access to a series of diarylcarbene complexes of chromium and tungsten . Attempts to synthesize and isolate other simple metal(0) alkylidene complexes of this type either failed due to fast β-elimination reactions or led to unexpected dinuclear complexes (Scheme ). − However, a benzylidene complex, 3 , of W(0) (and later of Cr(0)) could be prepared in a two-step process by reacting successively (CO) 5 WC(OEt)Ph ( 1 ) with a complex hydride, KHB(OiPr) 3 , and an acid. − Due to its unstability, complex 3 could only be handled at low temperature (−80 to −20 °C). Its reaction with phosphines led however to stable phosphorus ylides 4a , b .…”

Molecular weight control in organochromium olefin polymerization catalysis by hemilabile ligand–metal interactions

“…According to calculations the distances of the two carbon atoms of the coordinating unit to the Cr centers in 5a + , 6a + and 7a + are approximately 2.5 Å (shortest of the two Cr–C distances). No X-ray data are available for olefin complexes of chromium in oxidation state +3 whereas solid state molecular structures of Cr 0 and Cr 1+ complexes have been reported with C–Cr distances of 2.1 Å–2.2 Å (Cr 1+ ) [ 68 – 69 ] and 2.3 Å–2.4 Å (Cr 0 ) [ 70 – 71 ], respectively.…”

Stereochemistry of Carbenic 1,2-Vinyl Shifts

“…Oxidation of 18 (peracetic acid−sodium acetate in CH 2 Cl 2 , 20 °C, 16 h) gave 65% of 2,2-dimethyl-3-ethenyl-3-phenyloxirane ( 20 ): 1 H NMR (CDCl 3 ) δ 1.0 (s, 3 H), 1.4 (s, 3 H), 5.2 (ddd, J = 17, 11, 2 Hz, 2 H), 6.15 (dd, J = 17, 11 Hz, 1 H), 7.2−7.4 (m, 5 H); 13 C NMR (CDCl 3 ) δ 20.1 (CH 3 ), 21.9 (CH 3 ), 65.5 (C), 69.7 (C), 118.3 (CH 2 ), 126.9 (CH), 127.1 (CH), 128.0 (CH), 136.5 (CH), 138.8 (C). 1-Ethenyl-1-methyl-2-phenylcyclopropane ( 19 , E , Z mixture) was obtained by benzylidene transfer to isoprene . Since separation of the isomers on a preparative scale failed, trans- (1-methyl-2-phenylcyclopropyl)methanol ( trans - 50 ) was oxidized (MnO 2 , benzene, 45 h reflux) to the analogous aldehyde 51 which was converted into trans - 19 by methylenation (Ph 3 PCH 3 Br, NaH, DMSO, 90 °C, 2 h).…”