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Heterocycles as Ligands, X1). — 2,2′,5,5′-Tetra-tert-butyl-1,1′-diazaferrocene – Stabilization of the Diheterometallocene Structure by Steric Shielding Stable 2,2′,5,5′-tetra-tert-butyl-1,1′-diazaferrocene (3) is obtained by the reaction of the corresponding lithiopyrrole with FeCl2. The X-ray analysis reveals a distorted sandwich structure influenced by repulsive interactions presumably both between the nitrogen atoms and the bulky tert-butyl substituents.

Hetero π-Systems, la. - Highly Substituted 2,4-Di-tert-butyl-l-boracyclohexadienes Boracyclohexadiees 14 and 16 with three bulky groups should be ideal starting materials for the preparation of kinetically stabilized borabenzene derivatives. They are formed by substitution reactions of anion 11, which itself is derived from 2,4-di-tert-1-methoxy-1-bora-2,5-cyclohexadiene (10) by lithiation. Reaction of lithium compound 11 with ferrous chloride provides the sandwich-type complex 12. As shown by X-ray structure analysis, 12 has C2 symmetry with the boron atoms in a syn arrangement in staggered conformation, an unusal feature for borabenzene complexes. Exchange of the methoxy group in the trimethylsilylated substance 16 leads to compounds 18a, 18b, 18c, 18d. Pyrolyses of the various precursors are described.

Die beiden 4,5-Diethyl-2,5-dihydro-2,2-dimethyl-3-organo-1,2,5-thiasilaborole [1a: R = CH3; 1b: R = C(CH3)CH2] sind aus den offenkettigen Verbindungen ClSi(CH3)2CRC(C2H5)B(C2H5)Cl [A: R = CH3; B: R = C-(CH3)CH2] mit Dialkalimetallsulfiden M2S (M = Li, Na) oder mit Hexamethyldisilthian [CH3)3Si]2S praparativ leicht zuganglich. 1a reagiert mit Aluminiumtrichlorid sowie mit Lewisbasen (γ-Pic, PNO, TMP, MTPP) unter Bildung von 1:1-Additions-verbindungen (1a-AlCl3; γ-pic-1a, TMP-1a, MTPP-1a). Mit Ligand-Ubergangsmetall-Verbindungen LML erhalt man aus 1a bzw. b η4-Komplexe, deren LM-Fragment vorwiegend an die CCBS-Gruppierung [(OC)4Cr (2a), (OC)3Fe (3a, b), (OC)3Ru (4a, b), C5H5Co (5a, b), ClRh (6a)], bei 1b bisweilen auch an die CCCC-Gruppierung [C5H5Co (5′b)] gebunden ist. Aus 2 mol 1a und b lassen sich mit (Cyclododecatrien)nickel die Sandwich-Komplexe 7a (Rontgenstrukturanalyse von meso-7a) bzw. 7b herstellen. Mit hydroxylhaltigen Verbindungen wie Methanol und Eisessig reagieren 1a und b leicht unter BS- und SiS-Protolyse zu offenkettigen Verbindungen (8a, 11a) wahrend mit Acetylaceton unter S/O-Austausch substituiertes 2,5-Dihydro-1,2,5-oxasilaborol 9a gebildet wird. — Die Massenspektren, 1H-sowie 13C- und Heteroatom-NMR-Daten der neuen Verbindungen 1–7 werden zusammen mit Ergebnissen vorangegangener Publikationen dieser Reihe diskutiert. 2,5-Dihydro-1,2,5-thiasilaboroles — Preparations and Complexations The two 4,5-diethyl-2,5-dihydro-2,2-dimethyl-3-organo-1,2,5-thiasilboroles [1a: R = CH3; 1b R = C(CH3)CH2] are easily prepared from the acyclic compounds ClSi(CH3)2CRC(C2H5)B(C2H5)Cl[A: R = CH3; B R = C(CH3)CH2] with dialkaline metal sulfides M2S (M = Li, Na) or with hexamethyldisilthiane [(CH3)3Si]2S. 1a reacts with aluminium trichloride and with Lewis bases (γ-Pic, PNO, TMP, MTPP) to form 1:1-addition compounds (1a-AlCl3, γ-Pic-1a, PNO-1a, TMP-1a, MTPP-1a). π Complexes LM-1a or -1b are obtained from 1a or b and ligand-transition metal compounds LML′. The LM-fragments are preferentially η4-complexed with the CCBS grouping [(OC)4Cr (2a), (OC)3Fe (3a, b), (OC)3Ru (4a, b), C5H5Co (5a, b), ClRh (6a)], but sometimes also with the CCCC grouping of 1b [C5H5Co (5′b)]. The sandwich complexes 7a (X-ray analysis of meso-7a) and 7b are prepared from 2 mol of 1a or b with 1 mol of (cyclododecatriene)nickel. — The BS and SiS bonds of 1a and b are easily protolyzed by hydroxy compounds such as methanol and glacial acid with formation of acyclic compounds (8a, 11a), while with acetylacetone S/O exchange is observed leading to the substituted 2,5-dihydro-1,2,5-oxasilaborol 9a. — The mass spectra, the 1H-, 13C-, and heteratom-NMR data of the new compounds 1 to 7 are discussed in connection with results in earlier contributions to this series.

Decamethylchromocen, (C5(CH3)5)2 Cr, bildet mit CO den 18-Elektronen-Komplex (C5(CH3)5)2Cr(CO). Unter hoheren CO-Drucken entsteht der Dicarbonyl-Komplex (C5(CH3)5)2Cr(CO)2, der auch in Abwesenheit von CO stabil ist. Eine Rontgenstrukturanalyse ergibt, das diese Verbindung einen η3- und einen η5-koordinierten Ringliganden enthalt und damit ebenfalls als 18-Elektronen-Teilchen vorliegt. Mono- and Dicarbonyl Complexes of Decamethylchromocene Decamethylchromocene, (C5(CH3)5)2Cr, reacts with CO at ambient pressure to form the 18-electron species (C5(CH3)5)2Cr(CO). At elevated CO pressures, the dicarbonyl complex (C5(CH3)5)2Cr(CO)2 is formed, which persists in the absence of CO. An X-ray structure determination of (C5(CH3)5)2Cr(CO)2 shows the presence of one η3- and one η5-coordinated ring ligand and hence an 18-electron configuration even for this compound.