Gangolf Kriechbaum

Übergangsmetall—methylen-komplexe : XXXI. Primärkomplexierung von diazoalkanen an metall—metall-mehrfachbindungen; ein weiterer koordinationstyp

Abstract An unexpected novel coordination mode of diazoalkanes has been verified via addition of 2-diazopropane to the metal—metal triple bond of bis[dicarbonyl(η5-pentamethylcyclopentadienyl)molybdenum] (MoMo). The dinuclear 1:1 addition product isolated in nearly quantitative yield is structurally characterized by a bent, 4-electron type η1:η2-diazoalkane ligand, with the terminal nitrogen atom symmetrically bridging the metal-metal “single bond” (d(MoMo) 305.0(2) pm; d(MoN(1)) 212.0(12) and 212.6(10) pm, respectively) and the second nitrogen atom being bonded to one molybdenum atom only (d(MoN(2)) 213.4(13) pm).

Komplexchemie reaktiver organischer verbindungen: XLVII. Synthese, strukturchemie und druckcarbonylierung von metallcarben-komplexen

Abstract The diazoalkane route has been used for the clean incorporation of diarylcarbene ligands into the organomanganese complexes of composition (η 5 -C 5 H 4 R)Mn(CO) 2− thf ( 1 , R = H; 2 , R = CH 3 ; thf = tetrahydrofuran), whose precursors are labile to substitution. The structure of the complex 4b derived from diazosuberon ( 3b ) and exhibiting a seven-membered carbocyclic carbene ligand has been established by virtue of a single-crystal X-ray diffraction study (monoclinic, space group C 2h 5 - P 2/n; a 1045.6(4), b 789.9(4), c 2153.6(4) pm; β 101.56(3)°; Z = 4; R = 0.075, R w = 0.059). Using the same synthetic approach, the dinuclear compound 4d containing an ω,ω′-biscarbene bridge is accessible in 52% yield starting from 1,4-bis(diazobenzyl)benzene ( 3d ). A methodologically simple procedure for the synthesis of η 2 -ketene complexes emerges from high-pressure carbonylation of the metal carbenes 4b and 5b . The geometry of the benzannelated cycloheptanylidenketene derivative 7b has also been elucidated by X-ray diffraction techniques (monoclinic, space group P 2 1 /n; a 998.9(3), b 1302.3(4), c 1466.6(4) pm; β 91.33(4)°; Z = 4; R = 0.057; R w = 0.062).

Übergangsmetall—methylen-komplexe: XLVIII. Addition und ringschluss bei reaktionen von α-ketodiazoalkanen mit metall—metall-doppelbindungen der metallcarbonyl-reihe: Aufbau metallacyclischer strukturen

Abstract The α-diazoketones 2a–h,k,l react with the dinuclear organorhodium complex 1 with elimination of dinitrogen and concomitant addition of their carbonyl-flanked carbene moieties upon the metal—metal double bond. The μ-alkylidene complexes 3f–h thus accessible, represent the final products; the trimethylsilyl derivative 3i was synthesized for comparison. By contrast, the derivatives 3a–e,l behave rather as IR-spectroscopically identified intermediates that, at room temperature, undergo rapid consecutive intramolecular cycloaddition reactions yielding the novel compounds 4a–e and 5l, respectively. Formation of 4a–e results from nucleophilic attack of the keto groups of the bridging ligands upon one of the metal carbonyl units. This type of cyclization process comprises the construction of a new oxygen—carbon bond. The metallacyclic structures thus obtained have been elucidated in the cases of 4c and 4e by means of single crystal X-ray diffraction techniques and no longer obey the structural criteria of type-3 μ-alkylidene complexes. An internal experiment concurrently carried out by use of the diazoalkane 2e furnished proof that the cyclization process occurred regiospecifically: only the more nucleophilic keto-oxygen atom is subject to ring closure, whereas the oxygen atom of the ester carbonyl group does not participate in this reaction. The bis(acyl)methylene derivatives 3f–h resist cyclization and retain their structures even at elevated temperatures (cf. boiling tetrahydrofuran). The carbocyclic diazo precursor 2k (diazodimedone) requires more drastic conditions (boiling benzene) for the reaction with compound 1 to occur; here, the cycloadduct 5k is formed following nitrogen elimination. According to a single crystal X-ray diffraction study, the ketocarbene fragment derived from 2k has been added across the dinuclear metalcarbonyl core, finally acting as a bridging structural unit. In contrast to the cycloadducts 4a–e, a new carbon—carbon bond is formed during the synthesis of 5k. The dimetallacycle 5l results from a two-step cyclo-elimination between the bisdiazoalkane 2l and the organorhodium compound 1.