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

Abstract Cp(CO) 3 Mn ( 1 ) reacts with [NC(R 1 )R 2 ] − and [Et 3 O]BF 4 to give alkylideneamino(ethoxy)carbene complexes, Cp(CO) 2 MnC(OEt)NC(R 1 )R 2 ( 3 ) [C(R 1 )R 2  CPh 2 ( a ), C(C 6 H 4 ) 2 O ( b ), C(CMe 3 ) 2 ( c ), C(CMe 3 )Tol ( d ), Tol = C 6 H 4 Me- p ]. From 1 , [NCPh 2 ] − and MeOSO 2 F the complex Cp(CO) 2 MnC(OMe)NCPh 2 ( 4a ) is obtained. The reaction of 1 with [NC( i Pr)Ph] − and Me 3 SiCl, however, yields an isocyanide complex, Cp(CO) 2 Mn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 − , t BuSH, PHPh 2 , PH 2 Mes) 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.