Franz Hohmann

ESR metallorganischer radikale—IV1 : Sterische effekte bei 1,4-diazabutadienchelaten

Zusammenfassung 1,4-Diazabutadiene, zweizahnige Liganden des Typs R 2 NCR 1 CR 1 NR 2 (R 1 H; R 2 t.-C 4 H 9 , i-C 3 H 7 , i-C 4 H 9 ), bilden ebenso wie entsprechende Molybdantetracarbonylkomplexe (R 1 H, CH 3 ; R 2 CH 3 , CH 2 C 6 H 5 , i-C 3 H 7 , c-C 6 H 11 , c-C 3 H 5 ) mit Kalium stabile paramagnetische Monoanionen. Deren hochaufgeloste ESR-Spektren erlauben den Vergleich der Konformationen des Substituenten R 2 im freien und komplexgebundenen Liganden. Seine Beweglichkeit wird als Funktion von R 1 und der Metallcarbonylgruppen im Hinblick auf sterische Ligandenqualitaten diskutiert.

Elektronenreiche übergangsmetallkomplexe : I. Nitril-phosphin-molybdändicarbonyle: Synthese und schwingungsspektren

Abstract Acetonitrile (AN) is substituted under very mild conditions in (AN) 2 - [P(C 6 H 5 ) 3 ] 2 Mo(CO) 2 , (AN) 2 [P(n-C 4 H 9 ) 3 ] 2 Mo(CO) 2 and AN[P(n-C 4 H 9 ) 3 ] 3 - Mo(CO) 2 by aromatic and α,β-unsaturated nitriles. In more than 60 new, highly coloured compounds the nitriles show solvent dependent π-acceptor properties. The nitrile stretching frequencies are substantially lowered and are split in cis -dinitrile complexes by π-coupling. Band position and splitting are opposite to corresponding parameters in the cis -dicarbonyl group. Structural peculiarities are discussed for isonicotinonitrile, acrylonitrile and benzodinitriles.

Zur komplexchemie von vierzentren-π-systemen VII. 1-azabutadien-komplexe des molybdäns

Abstract 1-Azabutadienes, R 1 NCHCHCHR 2 , substitute the acetonitrile in (CH 3 CN) 2 Mo(PBu 3 ) 2 (CO) 2 under mild conditions and yield 1-azabutadiene π-complexes, which can be protonated reversibly. IR spectroscopic data of butadiene-, 1-heterobutadieneand 1,4-diheterobutadiene-molybdenum dicarbonyls as well as electron spectroscopic data on butadiene complexes and their aza analogues are compared. ab]1-Azabutadiene, R 1 NCHCHCHR 2 , substituieren das Acetonitril in (CH 3 CN) 2 Mo(PBu 3 ) 2 (CO) 2 unter milden Bedingungen und geben 1-Azabutadien-π-Komplexe, die reversibel protonierbar sind. IR-spektroskopische Daten von Butadien-, 1-Heterobutadien- und 1,4-Diheterobutadien-molybdan-dicarbonylen sowie elektronen-spektroskopische Daten von Butadienkomplexen und ihren Aza-analogen werden verglichen.

Elektronenreiche übergangsmetallkomplexe ☆: V. Molybdän(0)-Komplexe α,β-ungesättigter nitrile und die struktur von Mo2(CO)4(PBu3)4(μ-CH2CHCN)2

Abstract Bis(acetonitrile)dicarbonyldiphosphinemolybdenum(0) and a corresponding monoacetonitrile-triphosphine complex react with α,β-unsaturated nitriles to give substitution products. In the case of tributylphosphine complexes a rapid subsequent reaction gives dimers with π-olefin—σ-nitrile bridging functions. The crystal and molecular structure of the acrylonitrile complex was determined by X-ray diffraction.

Elektronenreiche übergangsmetallkomplexe : IV. Dien-bis(phosphin)-molybdändicarbonyle☆

Abstract Dienes can replace the acetonitrile in (CH3CN)2Mo(PBu3)2,(CO)2 or acetoni- trile and the one phosphine trans to the CO group in (CH3CN)Mo(PBu3)3(CO)2 under mild conditions. IR-, H NMR, 13C NMR and electronic spectra of the new (diene)Mo(PBu3)2(CO)2 complexes are discussed and compared with similar compounds of other transition metals.

Elektronenreiche übergangsmetallkomplexe : II. Nitril-phosphan-molybdändicarbonyle: Farbe und solvatochromie

Abstract Complexes of aromatic or α,β-unsaturated nitriles YCN of the type (YCN) 2 (PR 3 ) 2 Mo(CO) 2 and (YCN)(PR 3 ) 3 Mo(CO) 2 are new chromophores. Their intense electronic absorption band in the visible spectrum is strongly influenced by substituents and solvent polarity. Acceptor properties of nitriles are discussed on the basis of CNDO-calculations. CT-character and solvato-chromism can be interpreted in terms of the back-bonding ability of the nitriles in electron-rich metal complexes.