Insertion reactions of alkynes and organic isocyanides into the palladium-carbon bond of dimetallic Fe-Pd alkoxysilyl complexes

摘要

Insertion of MeO2C - C C - CO2Me ( DMAD) into the Pd - C bond of the heterodimetallic complex [( OC)(3)Fe{mu- Si(OMe)(2)( OMe)}(mu- dppm) Pd( dmba- C)] ( 2) ( dppm = Ph2PCH2PPh2, dmba- C = metallated dimethylbenzylamine) and [(OC)(3){( MeO)(3)Si} Fe(mu- dppm) Pd(8- mq- C, N)] ( 3) ( 8- mq- C, N = cyclometallated 8- methylquinoline) yielded the sigma- alkenyl complexes [(OC)(3)Fe{mu- Si( OMe) (2)( OMe)}(mu- dppm) Pd{C(CO2Me) = C(CO2Me)(omicron-C6H4CH2NMe2)}] ( 7) and [(OC)(3)Fe{mu-Si(OMe)(2)(OMe)}(mu- dppm) Pd{C(CO2Me) = C(CO2Me)(CH2C9H6N)}] ( 8), respectively. The latter afforded the adduct [(OC)(3){(MeO)(3)Si} Fe(mu- dppm) Pd{C(CO2Me) = C( CO2Me) (CH2C9H6N)}( CNBut)] ( 9) upon reaction with 1 equiv. of (BuNC)-N-t. The heterodinuclear sigma- butadienyl complexes [(OC)(3)Fe{mu- Si(OMe)(2)(OMe)}( mu- dppm) Pd{C( Ph) = C( Ph) C( CO2Me) = (CO2Me)( o- C6H4CH2NMe2)}] ( 11) and [(OC)(3)Fe{mu- Si(OMe)(2)(OMe)}( mu- dppm) Pd{C( Ph) = C(CO2Et) C( Ph) = C( CO2Et)( CH2C9H6N)}] ( 13) have been obtained by reaction of the metallate K[ Fe{Si( OMe)(3)}( CO)(3)( dppm- P)] ( dppm = Ph2PCH2PPh2) with [ PdCl{C( Ph) = C( Ph) C(CO2Me) = C(CO2Me)( o- C6H4CH2NMe2)}] or [PdCl{C( Ph) = C(CO2Et) C( Ph) = (CO2Et)}(CH2C9H6N)], respectively. Monoinsertion of various organic isocyanides RNC into the Pd - C bond of 2 and 3 afforded the corresponding heterometallic iminoacyl complexes. In the case of complexes [(OC)(3){( MeO)(3)Si} Fe(mu- dppm) Pd{C( = NR)(CH2C9H6N)}] ( 15a R = Ph, 15b R = xylyl), a static six- membered C, N chelate is formed at the Pd centre, in contrast to the situation in [( OC) Fe-3{mu- Si( OMe) (2)( OMe)}(mu- dppm) Pd{C(= NR)( o- C6H4CH2NMe2)}] ( 14a R = o- anisyl, 14b R = 2,6- xylyl) where formation of a mu- eta(2)- Si - O bridge is preferred over NMe2 coordination. The outcome of the reaction of the dimetallic alkyl complex [(OC)(3)Fe{mu- Si(OMe)(2)(OMe)}( mu- dppm) PdMe] with RNC depends both on the stoichiometry and the electronic donor properties of the isocyanide employed for the migratory insertion process. In the case of o- anisylisocyanide, the iminoacyl complex [(OC)(3)Fe{mu- Si(OMe)(2)(OMe)}( mu- dppm) Pd{C( = N- o- anisyl) Me}] ( 16) results from the reaction in a 1 : 1 ratio. Addition of three equiv. of o- anisylisocyanide affords the tris( insertion) product [(OC)(3)Fe{mu- Si( OMe) 2( OMe)}(mu- dppm) Pd{[ C( = N- o- anisyl)](3)Me}] ( 18). After addition of a fourth equivalent of o- anisylNC, exclusive formation of the isocyanide adduct [(OC)(3){( MeO)(3)Si} Fe(mu- dppm) Pd{[ C(= N- o- anisyl)](3)Me}( CN- o- anisyl)] ( 19) was spectroscopically evidenced. In the complex [(OC)(3)Fe{mu- Si(OMe)()( OMe)}( mu- dppm) Pd{[C( = N-o-C6H4COCH2)] Me-2}] ( 20), the sigma- bound diazabutadienyl unit is part of a 12- membered organic macrocyle which results from bis( insertion) of 1,2- bis( 2- isocyanophenoxy) ethane into the Pd - Me bond of the precursor complex [( OC) Fe-3{mu- Si( OMe) 2( OMe)}(mu- dppm) PdMe]. In contrast, addition of two equivalents of tert- butylisocyanide to a solution of the latter afforded [( OC) (3){( MeO) (3) Si}Fe( mu- dppm) Pd{C( = NBut) Me}( CNBut)] ( 21) in which both a terminal and an inserted isocyanide ligand are coordinated to the Pd centre. In all cases, there was no evidence for competing CO substitution at the Fe( CO) 3 fragment by RNC. The molecular structures of the insertion products 8 . CH2Cl2 and 16 . CH2Cl2 have been determined by X- ray diffraction.