Metal Atoms between Different Ligand Sites

Migration of Metal Atoms between Different Ligand Sites 

Fluxionality in allyl complexes is a widespread phenomenon. The 77 -allyl complexes [Ni(i7 -allyl)(aryl)(diphos)] (10) are nonrigid 18-electron species which exhibit syn-anti proton exchange and, in the case of the complex (R = Me, R = H), rapid site exchange of the two allylic termini. The syn-anti exchange is thought to occur via a short-lived Ty -allyl intermediate (11).  

Cyclopentadiene ligands display many types of fluxionality. A particularly novel type has recently been discovered in bis(cyclopentadienyl)beryllium. X-ray data show the molecule to possess a slip sandwich structure and this structure persists in the solution and vapor phases. A recent NMR study based on partially 

The 17 -benzyl complexes [CpFe(CO) i7 -CH(R)Ph ] (R = H, OMe) undergo scrambling processes which are best explained in terms of cr, n interconversions together with inversion at the Fe center for the R = H complex and in terms of aryl rotation for R = The 77 -benzyl ligand of complex (12) is also involved 

5-cyclooctadiene (COD) complexes [M(COD)(HC(PPh2)3)] BF4 (R = Rh, Ir) undergo exchange between structures with the tripod ligand acting as a 

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The intensity of the dicarbonyl at 2116cm is considerably reduced as compared to the 90 K deposit, indicating that the amount of metal atoms trapped at point defects is reduced for growth at 60 K. The difference in the nucleation sites is also reflected by the lower thermal stability of the systems, which decompose between 80 and 150 K as compared to 200 to 250 K for the 90 K deposits. With isotope mixing experiments the peak at 2087 cm was assigned to a carbonyl with three or more CO ligands, while the peak at 1999 cm is associated to a monocarbonyl [32]. 

Hetero site reactivity The simplest difference between a cluster and a mononuclear complex is that the cluster can do two or more things where a mononuclear complex can do one. Simple as it is, this difference has hardly ever been verified other than in multiple ligand substitutions. One verification is hetero site reactivity, i.e., different modes of reaction at different sites on one and the same cluster. Two examples of this appear to exist. Different phosphine ligands substitute CO on different metal atoms in H2FeRu3(CO),3 depending on their size and basicity (210), and Ru2Co2 (CO), 3 reacts with H2 at the ruthenium atoms (cf. Section IV, A) and... 

The second copper center near the heme as iron, which is readily assignable as Cub, has three histidine imidazole groups as the ligands (Fig. 3). The copper atom in this site is located approximately at the center of the triangle formed by three imidazole nitrogen atoms coordinated to the copper atom. The position of the copper atom is about 1.0 A from the heme normal for heme as. The Cub—Feaj distance is 4.7 A. In the fully oxidized state, a peroxide is bridged between the two metal atoms (Fig. 3). The To—Td difference Fourier map of the oxidized... 

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