The nature of the heteroatom X incorporated in the five-membered PXP-diphosphine bridging chain was found to play a primary unit role both in the overall stability and in the stereochemical arrangement of nitrido-containing [M(N)(PXP)]2+ metal fragments (M ) Tc, Re). Thus, by mixing PXP ligands with labile [Re(N)Cl4]- and Tc(N)Cl2- (PPh3)2 nitrido precursors in CH2Cl2/MeOH mixtures, a series of neutral M(N)Cl2(PXP) complexes (M ) Tc, 1-5; M ) Re, 8, 9) was collected. In the resulting distorted octahedrons, PXP adopted facial or meridional coordination, and combination with halide co-ligands produced three different stereochemical arrangements, that is, fac,cis, mer,cis, and mer,trans, depending primarily on the nature of the diphosphine heteroatom X. When X ) NH, mer,cis- Tc(N)Cl2(PNP1), 1, was the only isomer formed. Alternatively, when a tertiary amine nitrogen (X ) NR; R ) CH3, CH2CH2OCH3) was introduced in the bridging chain, fac,cis-M(N)Cl2(PN(R)P) complexes (M ) Tc, 2, 3; M ) Re, 8f) were obtained. Isomerization into the mer,cis-Re(N)Cl2(PN(R)P), 8m, species was observed only in the case of rhenium when the tertiary amine group carried the less encumbering methyl substituent. fac,cis-Tc(N)Cl2(PSP), 4f, was isolated in the solid state when X ) S, but a mixture of fac,cis-Tc(N)Cl2(PSP) and mer,trans-Tc(N)Cl2(PSP), 4m, isomers was found in equilibrium in the solution state. A similar equilibrium between fac,cis-M(N)Cl2(POP) (M ) Tc, 5f; M ) Re, 9f) and mer,trans-M(N)Cl2(POP) (M ) Tc, 5m; M ) Re, 9m) species was detected in POPcontaining complexes. The molecular structure of all of these complexes was assessed by means of conventional physicochemical techniques including multinuclear NMR spectroscopy and X-ray diffraction analysis of representative mer,cis-Tc(N)Cl2(PN(H)P), 1, fac,cis-Tc(N)Cl2(PSP), 4f, and mer,cis-Re(N)Cl2(PN(Me)P), 8m, compounds.
The crucial role of the diphosphine heteroatom X in the stereochemistry and stabilization of the substitution-inert [M(N)(PXP)](2+) metal fragments (M = Tc, Re; PXP = diphosphine ligand)
DUATTI, Adriano;BOSCHI, Alessandra;
2004
Abstract
The nature of the heteroatom X incorporated in the five-membered PXP-diphosphine bridging chain was found to play a primary unit role both in the overall stability and in the stereochemical arrangement of nitrido-containing [M(N)(PXP)]2+ metal fragments (M ) Tc, Re). Thus, by mixing PXP ligands with labile [Re(N)Cl4]- and Tc(N)Cl2- (PPh3)2 nitrido precursors in CH2Cl2/MeOH mixtures, a series of neutral M(N)Cl2(PXP) complexes (M ) Tc, 1-5; M ) Re, 8, 9) was collected. In the resulting distorted octahedrons, PXP adopted facial or meridional coordination, and combination with halide co-ligands produced three different stereochemical arrangements, that is, fac,cis, mer,cis, and mer,trans, depending primarily on the nature of the diphosphine heteroatom X. When X ) NH, mer,cis- Tc(N)Cl2(PNP1), 1, was the only isomer formed. Alternatively, when a tertiary amine nitrogen (X ) NR; R ) CH3, CH2CH2OCH3) was introduced in the bridging chain, fac,cis-M(N)Cl2(PN(R)P) complexes (M ) Tc, 2, 3; M ) Re, 8f) were obtained. Isomerization into the mer,cis-Re(N)Cl2(PN(R)P), 8m, species was observed only in the case of rhenium when the tertiary amine group carried the less encumbering methyl substituent. fac,cis-Tc(N)Cl2(PSP), 4f, was isolated in the solid state when X ) S, but a mixture of fac,cis-Tc(N)Cl2(PSP) and mer,trans-Tc(N)Cl2(PSP), 4m, isomers was found in equilibrium in the solution state. A similar equilibrium between fac,cis-M(N)Cl2(POP) (M ) Tc, 5f; M ) Re, 9f) and mer,trans-M(N)Cl2(POP) (M ) Tc, 5m; M ) Re, 9m) species was detected in POPcontaining complexes. The molecular structure of all of these complexes was assessed by means of conventional physicochemical techniques including multinuclear NMR spectroscopy and X-ray diffraction analysis of representative mer,cis-Tc(N)Cl2(PN(H)P), 1, fac,cis-Tc(N)Cl2(PSP), 4f, and mer,cis-Re(N)Cl2(PN(Me)P), 8m, compounds.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
