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

Insertion of MeO(2)C-Ctriple bond]C-CO(2)Me (DMAD) into the Pd-C bond of the heterodimetallic complex (OC)(3)Fupper bond 1 start]e{mu-Si(OMe)(2)(lower bond 1 start]OMe)}(mu-dppm)Plower bond 1 end]upper bond 1 end]d(dmba-C)] (2) (dppm = Ph(2)PCH(2)PPh(2), dmba-C = metallated dimethylbenzylamine) and (OC)(3){(MeO)(3)Si}Fupper bond 1 start]e(mu-dppm)Pupper bond 1 end]d(8-mq-C,N)] (3) (8-mq-C,N = cyclometallated 8-methylquinoline) yielded the sigma-alkenyl complexes (OC)(3)Fupper bond 1 start]e{mu-Si(OMe)(2)(lower bond 1 start]OMe)}(mu-dppm)Plower bond 1 end]upper bond 1 end]d{C(CO(2)Me)=C(CO(2)Me)(o-C(6)H(4)CH(2)NMe(2))}] (7) and (OC)(3)Fupper bond 1 start]e{mu-Si(OMe)(2)(lower bond 1 start]OMe)}(mu-dppm)Plower bond 1 end]upper bond 1 end]d{C(CO(2)Me)double bond, length as m-dash]C(CO(2)Me)(CH(2)C(9)H(6)N)}] (8), respectively. The latter afforded the adduct (OC)(3){(MeO)(3)Si}Fupper bond 1 start]e(mu-dppm)Pupper bond 1 end]d{C(CO(2)Me)=C(CO(2)Me)(CH(2)C(9)H(6)N)}(CNBu(t))] (9) upon reaction with 1 equiv. of Bu(t)NC. The heterodinuclear sigma-butadienyl complexes (OC)(3)Fupper bond 1 start]e{mu-Si(OMe)(2)(lower bond 1 start]OMe)}(mu-dppm)Plower bond 1 end]upper bond 1 end]d{C(Ph=C(Ph)C(CO(2)Me)=(CO(2)Me)(o-C(6)H(4)CH(2)NMe(2))}] (11) and (OC)(3)Fupper bond 1 start]e{mu-Si(OMe)(2)(lower bond 1 start]OMe)}(mu-dppm)Plower bond 1 end]upper bond 1 end]d{C(Ph)=C(CO(2)Et)C(Ph)=C(CO(2)Et)(CH(2)C(9)H(6)N)}] (13) have been obtained by reaction of the metallate KFe{Si(OMe)(3)}(CO)(3)(dppm-P)] (dppm = Ph(2)PCH(2)PPh(2)) with Pupper bond 1 start]dCl{C(Ph)=C(Ph)C(CO(2)Me)=C(CO(2)Me)(o-C(6)H(4)CH(2)Nupper bond 1 end]Me(2))}] or Pupper bond 1 start]dCl{C(Ph)=C(CO(2)Et)C(Ph)=(CO(2)Et)}(CH(2)C(9)H(6)Nupper bond 1 end])], 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}Fupper bond 1 start]e(mu-dppm)Pupper bond 1 end]upper bond 1 start]d{C=(NR)(CH(2)C(9)H(6)Nupper bond 1 end])}] (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)(3)Fupper bond 1 start]e{mu-Si(OMe)(2)(lower bond 1 start]OMe)}(mu-dppm)Plower bond 1 end]upper bond 1 end]d{C(=NR)(o-C(6)H(4)CH(2)NMe(2))}] (14a R = o-anisyl, 14b R = 2,6-xylyl) where formation of a mu-eta(2)-Si-O bridge is preferred over NMe(2) coordination. The outcome of the reaction of the dimetallic alkyl complex (OC)(3)Fupper bond 1 start]e{mu-Si(OMe)(2)(lower bond 1 start]OMe)}(mu-dppm)Plower bond 1 end]upper bond 1 end]dMe] 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)Fupper bond 1 start]e{mu-Si(OMe)(2)(lower bond 1 start]OMe)}(mu-dppm)Plower bond 1 end]upper bond 1 end]d{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)Fupper bond 1 start]e{mu-Si(OMe)(2)(lower bond 1 start]OMe)}(mu-dppm)Plower bond 1 end]upper bond 1 end]d{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}Fupper bond 1 start]e(mu-dppm)Pupper bond 1 end]d{C(=N-o-anisyl)](3)Me}(CN-o-anisyl)] (19) was spectroscopically evidenced. In the complex (OC)(3)Fupper bond 1 start]e{mu-Si(OMe)(2)(lower bond 1 start]OMe)}(mu-dppm)Plower bond 1 end]upper bond 1 end]d{C(=N-o-C(6)H(4)COCH(2))](2)Me}] (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)(3)Fupper bond 1 start]e{mu-Si(OMe)(2)(lower bond 1 start]OMe)}(mu-dppm)Plower bond 1 end]upper bond 1 end]dMe]. In contrast, addition of two equivalents of tert-butylisocyanide to a solution of the latter afforded (OC)(3){(MeO)(3)Si}Fupper bond 1 start]Fe(mu-dppm)Pupper bond 1 end]d{C(=NBu(t))Me}(CNBu(t))] (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 x CH(2)Cl(2) and 16 x CH(2)Cl(2) have been determined by X-ray diffraction.