2-Azoniaallenyliden-Komplexe des Mangans - Synthese, Struktur und Reaktivität

Abstract

Cp(CO) 3Mn ( 1) reacts with [NC(R 1)R 2] − and [Et 3O]BF 4 to give alkylideneamino(ethoxy)carbene complexes, Cp(CO) 2MnC(OEt)NC(R 1)R 2 ( 3) [C(R 1)R 2  CPh 2 ( a), C(C 6H 4) 2O ( b), C(CMe 3) 2 ( c), C(CMe 3)Tol ( d), Tol = C 6H 4Me- p]. From 1, [NCPh 2] − and MeOSO 2F the complex Cp(CO) 2 MnC(OMe)NCPh 2 ( 4a) is obtained. The reaction of 1 with [NC( iPr)Ph] − and Me 3SiCl, however, yields an isocyanide complex, Cp(CO) 2MnC  NC(Ph)CMe 2 ( 7). Photolysis of 3a in THF in the presence of PTol 3 affords Cp(CO)(PTol 3)MnC(OEt)NCPh 2 ( 6a). According to the X-ray structure analysis of 4a the CNC fragment is strongly bent (CNC angle: 130.0(2)°) and both CN distances are significantly different. Alkoxide abstraction from 3a- c 4a and 6a by BF 3 gives 2-azoniaallenylidene complexes 13a- c and 14a, [Cp(CO)(R)Mn CNC(R 1)R 2]BF 4 [R  CO( 13), PTol 3 ( 14a)], respectively. The structure of 14a-BF 4 has also been determined by an X-ray diffraction analysis. The MnCNC fragment is almost linear and allows the formation of two orthogonal π-systems. Both CN distances differ significantly. The complexes are best described as hybrids of three resonance structures with that of the carbocationic structure beeing the main contributor. Accordingly, 13a-BF 4 adds a number of nucleophiles (OEt 2, PMe 3, H −, Me −, tBuSH, PHPh 2, PH 2Mes) at the terminal carbon of the MnCNC fragment to give, depending on the nucleophile, cationic or, after H + abstraction, neutral isocyanide complexes.