Walter Meier

Neuartige Phosphor/Schwefel-Liganden in aus Cp★2 Mo2(CO) 4 (Cp★ = η5-C5Me5) und P4S3 erzeugten Cp★2Mo2PxSy- Komplexen (× = 2, 4; y = 5 - ×)

Abstract The reaction of Cp★ 2 Mo 2 (CO) 4 ( Mo  Mo ) (Cp★ = η 5 -C 5 Me 5 ) with P 4 S 3 in boiling toluene gives the complexes Cp★(CO) 2 MoP 3 (I), Cp★ 2 (CO) 4 Mo 2 P 2 (II), Cp★ 2 Mo 2 P 2 S 3 (III), and Cp★ 2 Mo 2 P 4 S (IV). The structures of III and IV follow from their 31 P NMR spectra as well as from an X-ray diffraction analysis of their corresponding Cr(CO) 5 monoadducts (VII and VIII). Characteristic features of the structure of VII are an η 2 -PS and an η 3 -P 3 ligand in a plane perpendicular to the MoMo axis, which is bisecting. A similar geometry is found for VIII, which, however, contains an η 2 -S 2 and an η 3 -P 2 S ligand. Coordination of the Cr(CO) 5 fragment to the P 2 S ligand in III may either occur at an S atom, which then acts as a μ 5 -bridge (VIII) or at a P atom as manifested by the presence of a PW coupling in the W(CO) 5 adduct (VI).

Untersuchung der eigenschaften eines ungewöhnlichen dischwefelliganden: Vergleichende betrachtung der chemie von (C5Me5)2Cr2{μ,η1-S2)(μ,η2-S2)(μ-S)} und (C5Me5)2Mo2(μ,η2-S2)(μ-S)2

Abstract The uncoordinated sulphur of the iso-μ(η 1 -S 2 ) ligand in (C 5 Me 5 ) 2 Cr 2 S 5 is easily abstracted by PPh 3 causing formation of (C 5 Me 5 )Cr 2 S 4 , isoelectronic with (C 5 Me 5 ) 2 Mo 2 (μ-S 2 )(μ-S) 2 . From the nature of the products [(C 5 Me 5 ) 2 Cr 2 S 5 H]PF 6 , [(C 5 Me 5 ) 2 Cr 2 S 5 CH 3 ]PF 6 , [(C 5 Me 5 ) 2 Cr 2 S 4 CH 3 ]PF 6 and [C 5 Me 5 ) 2 Mo 2 S 4 CH 3 ]PF 6 formed from these complexes by reaction with CF 3 CO 2 H and CH 3 I a decrease in nucleophilicity is deduced for μ(η 1 -S 2 ) > μ-S > μ(η 2 -S 2 ). The reaction of (C 5 Me 5 ) 2 Mo 2 S 4 with C 5 H 5 (CO) 2 Mn(THF) gives a complex of composition (C 5 Me 5 ) 2 Mo 2 (C 5 H 5 )Mn(CO) 2 S 4 , whereas (C 5 Me 5 ) 2 Cr 2 S 5 gives only the known complexes [C 5 H 5 (CO) 2 Mn] 2 S 2 and [C 5 H 5 (CO) 2 Mn] 2 S together with (C 5 Me 5 ) 2 Cr 2 S 4 . In the reaction with H 2 (150 bar/80°C) (C 5 Me 5 ) 2 Mo 2 S 4 forms (C 5 Me 5 ) 2 Mo 2 S 4 H 2 , in contrast to (C 5 Me 5 ) 2 Cr 2 S 4 and (C 5 Me 5 ) 2 Cr 2 S 5 which give the cubane type cluster (C 5 Me 5 ) 4 Cr 4 S 4 .

Reaktivität der Metall-Metall-Mehrfachbindung in übergangsmetall-Komplexen: XIII. Untersuchungen zum stufenweisen Aufbau chalkogenreicher Zweikernkomplexe durch Reaktion von [CpM(CO)]2 (M = Co, Rh; Cp = η5-C5Me5) mit elementarem Schwefel, Selen oder Tellur

Abstract Reaction of the complexes Cp* 2 M 2 (μ-CO) 2 ( M = M ; Cp* = η 5 -C 5 Me 5 ; M = Co, Rh) with elemental sulfur, selenium, or tellurium results in addition of one or two equivalents of the chalcogen to the MM double bond, the outcome is dependent on the reaction conditions and the stoichiometry. Complexes of the type Cp* 2 Rh 2 (CO) 2 E (E = S, Se) and Cp* 2 M 2 (CO) 2 E 2 ( M= Co, Rh; E = Se, Te) have been isolated and characterized spectroscopically. Reaction of excess chalcogen with Cp* 2 M 2 (CO) 2 gives the CO-free diamagnetic compounds Cp* 2 Co 2 S 4 , Cp* 2 Rh 2 S 8 , and Cp* 2 M 2 Se 5 (M = Co, Rh). X-ray diffraction studies have been carried out on Cp* 2 Co 2 Se 5 and Cp* 2 Rh 2 (CO) 2 Se. The latter compound exhibits a Rh 2 Se three-membered cycle with attached anti -oriented Cp* and CO ligands. In the cobalt compound a Se 2− and a Se 4 2− ligand form a nearly planar pseudo five-membered cycle, which bisects the Co–Co axis. All reactions can be interpreted in terms of stepwise addition of chalcogens to the MM double bond with subsequent replacement of carbon monoxide.

Präparative, 11B-, 93Nb-NMR-spektroskopische und strukturelle Untersuchungen an Cp2NbBH4- und [CpNb(B2H6)]2-Komplexen

Abstract NbCl 5 reacts with NaBH 4 and LiCp + (Cp + = EtMe 4 C 5 ) dependent on the stoichiometry and temperature to give Cp + 2 NbCl 2 ( 1 ), Cp + 2 Nb 2 Cl 2 (B 2 H 6 ) ( 2 ), Cp + 2 NbBH 4 ( 3a ) and Cp + 2 Nb 2 (B 2 H 6 ) 2 ( 4a ). With a large excess of NaBH 4 , Cp + 2 NbCl 2 gives 2 at 25°C, which reacts further with NaBH 4 to give 4a . The synthesis of the deep violet, very stable 4a can be generalised by using C 5 Me 5 Li and t BuC 5 H 4 Li, respectively. Compounds 1–4 are characterised by means of IR, 1 H, and heteroatom NMR spectra. An X-ray structure analysis was carried out with 4a . Whereas 1 and 3 are analogous to already known complexes, in 2 and 4a the B 2 H 6 dianion (which is not stable in the free state) is present as a bridging ligand, oriented perpendicularly with respect to the NbNb axis. So far, the highest nuclear magnetic 93 Nb shielding has been observed for compounds 4 , extending the range of Imown δ( 93 Nb) values by 2500 ppm. The temperature dependence of the linewidths of both the 11 B and the 93 Nb NMR signals of 4c allows evaluation of the magnitude of J ( 93 Nb 11 B) = 50 ± 10 Hz.

Methylierung eines schwefelreichen dimolybdänkomplexes: darstellung, trennung und charakterisierung von (C5Me5)2Mo2(μ-SCH3)2(μ-S)2 in zwei isomeren formen

Abstract The methylation reaction of (C 5 Me 5 ) 2 Mo 2 (μ-S 2 )(μ-S) 2 (Ia) leads to two isomers of composition (C 5 Me 5 ) 2 Mo 2 (SMe) 2 S 2 (IV and IVb) which were separated by column chromatography. As an intermediate product of this reaction the iodine-containing adduct (C 5 Me 5 ) 2 Mo 2 S 4 I 2 is formed. All compounds were investigated by means of 1 H and 95 Mo NMR spectroscopy as well as by an X-ray structure analysis in the case of IVa. Thus, the SCH 3 ligands in IV are found to be arranged in a trans position. As a further result a cleavage of the η 2 -disulfur bridge, originally present in Ia, has been found to occur in the second step of the reaction sequence.

Von Cp+2Nb(η2-S2)H zu CP+3Nb3S12: Reaktivitätsstudien an Niobocensulfiden☆

Abstract The reaction of Cp + 2 NbBH 4 with sulfur gives two isomers of composition Cp + 2 NbS 2 H ( 3 , 4 ) and Cp + 2 NbS 3 H ( 5 ). The structures of 3 – 5 have been investigated by IR and 1 H NMR spectroscopic means. X-Ray diffraction analyses have been performed on 3 and 4 . These investigations demonstrate that 3 and 4 are niobocene derivatives, in which either a η 2 -S 2 2− -ligand and a hydride ( 3 ) or a S 2− and a SH − ligand ( 4 ) are attached to the Nb center. Complex 3 can be transformed thermally into 4 by a SS bond rupture, followed by the insertion of sulfur into the NbH bond. The polynuclear compounds Cp + 3 Nb 3 S 7 ( 6 ) and Cp + 3 Nb 3 S 12 ( 7 ) can be formed by the reaction of 3 with S 8 . The role of polysulfide intermediates is discussed.

Investigation into the reactivity of oxoniobocene complexes [Cp*2Nb(O)R] (Cp*=η5-C5Me5; R=H, OH, OMe) towards heterocumulenes: formation of carbamato and thiocarbamato complexes and catalytic cyclization of PhNCO

Abstract The reaction of [Cp*2NbCl2] (Cp*=η5-C5Me5) with KOH or Ba(OH)2·8H2O in THF was investigated under slightly modified conditions. In addition to the known complex [Cp*2Nb(O)H] (1), the new compound [Cp*2Nb(O)OH] (2) was formed. The reaction of 2 with PhNCS gave yellow [Cp*2Nb(O){SC(O)NHPh}] (3), while PhNCO formed yellow [Cp*2Nb(O){OC(O)NHPh}] (4). Complexes 3 and 4 were analytically and spectroscopically characterized. X-ray diffraction analyses of both compounds show that they contain either η1-S-thiocarbamato (3) or η1-O-carbamato ligand (4) along with a terminal NbO group. The reaction of 1 with one equivalent of PhNCO mainly gave orange [Cp*2NbH{OC(O)NPh}] (5) along with some 4. The molecular structure of 5 contains a niobocene unit comprising η2-N,O-carbamato chelate, which formally is a [2+2] cycloaddition product of the NbO group and the heterocumulene. A hydride ligand completes the coordination sphere around Nb. Reaction of 1 with excess PhNCO gave a mixture of heterocycles (PhNCO)2 (6) and (PhNCO)3 (7) in the approximate ratio 3:2. By contrast, the reaction of [Cp*2Nb(O)OMe] with PhNCO in molar ratios from 1:3 to 1:100 gave nearly pure triphenylisocyanurate 7.

Neue Aspekte in der Chemie von Übergangsmetallpolysulfidkomplexen: Synthese und Kristallstrukturen von Cp′3Nb3S12 und Cp′3Nb3S10O (Cp′ = t-BuC5H4)

Zusammenfassung Thermolysis of a mixture of Cp′4Nb2Sn (Cp′ = t-BuC5H4; n = 8, 9) results in the formation of the new niobium polysulfide complexes: Cp′3Nb3S12 (2), Cp′3Nb3S10O (3), Cp′3Nb3S10O (4) and Cp′4Nb4S13 (5). The structures of 2 and 3 have been established by X-ray diffraction studies. The complexes are characterized by an unusual variety of different sulfur ligands (up to five in 2), which is responsible for the absence of any metal-metal interaction.

CO-induced, reversible insertion of a terminal imido ligand into an η1η2-isocyanide bridge in the dimolybdenum complex Cp(CO)2Mo(μ-CNPh)Mo(NPh)Cp (Cp = η5-C5H5)

Abstract High pressure carbonylation of Cp(CO)2Mo(CNPh)Mo(NPh)Cp-(Mo-Mo) gives a product that has been shown by an X-ray diffraction study to be a metalla-amidinato complex. This means that the originally present terminal phenylimido ligand inserts into an η2, (σ + π)-bonded isocyanide bridge to form a four-membered heterocycle in which a CP(CO)2Mo unit is coordinated by both N atoms, whereas a Cp(CO)3Mo unit is attached to the central carbon atom. In boiling toluene this process is reversed, with release of CO. A by-product in this reaction is a mononuclear Cp(CO)2Mo-amidinato complex bearing a cyclopentadiene group at the central C atom.

Syntheses and reactivity of oxo niobocene complexes Cp*2Nb(O)X (X=H, OCH3) and crystal structures of [Cp*2Nb(OH)F]BF4 and Cp*2Nb(O)OC(O)H (Cp*=η5-C5Me5)

Reaction of Cp* 2 NbCl 2 (Cp*= η 5 -C 5 Me 5 ) with KOH or Ba(OH) 2 ·8H 2 O in THF forms the complexes Cp* 2 Nb(O)X (X=Cl: 2 , H: 3 ). The ratio of 2 and 3 depends on the stoichiometry. If NaOMe is added or MeOH in solution Cp* 2 Nb(O)OMe 4 is formed in good yields. Reactivity studies with 3 and 4 show that the NbO as well as the Nb–X unit behave as chemically active sites. Protonation of 3 or 4 with HBF 4 is followed by an attack of fluoride (from BF 4 − anion) to give [Cp* 2 Nb(OH)F]BF 4 6 and [Cp* 2 NbF 2 ]BF 4 7 . In contrast the reaction of 3 or 4 with HCO 2 H results in an exchange of X − by formate to give Cp* 2 Nb(O)OC(O)H 8 . The crystal structures of 6 and 8 are reported. Electrochemical investigations of 2–4 and 7 , 8 reveal reaction pathways for the transformation of 1 into 3 .