Cp2M + complexes, structures

Studies of CpLi solutions showed high conductivity, suggesting ionic particles in solution.91 Ionic particles could consist of the free ions, but anionic cyclopentadienides MCp2- particles isoelectronic to the well-known alkaline earth cyclopentadienides Cp2M (M = alkaline earth metal),103 could also be envisioned. Moreover, the structural motif of a sandwich complex where two Cp ligands bind to a metal center is well established throughout the periodic table. Indeed, the Cp2 Li anion was suggested based on NMR techniques,114-116 and... 

In the Cp2M(dithiolene) series, d° complexes were investigated essentially with Ti, and to a lesser extent with Zr and Hf, in their IV oxidation state. These complexes can be reversibly reduced to the d1, Tim anionic species but they were never isolated in the solid state. Attempts to oxidize these d° complexes were also unsuccessful, as electrochemical oxidation leads to their decomposition [23, 24]. The essential structural characteristic of these d° complexes is the strong folding of... 

Fig. 1 X-ray crystal structures of Cp2M(dithiolene) complexes (a)d° Cp2Ti(dmit) (b)d1 Cp2V (bdt) (c) d2 Cp2Mo(dmit), showing the evolution of the metallacycle folding angle...

We have seen above several examples where [Cp2M(dt)]+ (M = Mo, W) complexes organize in the solid state into low dimensional structures, leading to characteristic magnetic behaviors such as spin chains (eventually alternated) or spin ladders. The extensive use in later years of dithiolene ligands such as dmit or dddt was aimed at... 

The possible mechanism for the formation of C—C coupled (1) and decoupled (2) bimetallic complexes from Cp2M has been investigated [1 lb,c]. We followed a stepwise procedure to arrive at a model that was practical and at the same time realistic. In the first stage, the substituted cyclopentadienyls were replaced by Cp and the substituents on acetylides and butadiynes were replaced by H. The relative energies showed that, the C—C coupled structure 1 for M = Ti when L = Cp and R = H is more stable than 2 by 3 kcal/mol, while 2 is calculated to be 14.8 kcal/mol... 

Addition of Sc-R moieties to metal coordinated carbon monoxide was ascribed to the high Lewis acidity of the organometallic scandium complexes [281b]. R-Substituted scandoxycarbene complexes of type Cp2M=C(R)OScCpf (M = Mo, W R = H, Me) and CpM(CO)[=C(R)OScCpf] (M = Co,Rh, R = H, Me, CH2CH2Ph, NMe2) were obtained. The molecular structure of... 

Cyclopentadienyl complexes of Ge, Sn, and Pb exist in a wide variety of composition and structure, such as half-sandwiches CpM and CpMX, bent and parallel sandwiches Cp2M, and polymeric (Cp2M)x. 

Metallocene complexes of Ti, Zr, and Hf have attracted considerable attention in recent years because of their high activity and since their ligand framework can be tailored to a wide variety of polymerization requirements.102 The active species is the 14-electron cationic alkyl [Cp2M—R]+, with a pseudo-tetrahedral structure and a vacant site suitable for forming a weak complex with ethylene. Calculations show that the alkyl transfer to ethylene is stabilized by an a-agostic interaction with the metal, with a very low (ca. 2 kJ mol-1) activation barrier 103... 

A number of metallocene cyanate complexes have been reported for these metals. Samuel (648) and Coutts and Wailes (219) reported cp2M(CNO)2 (M = Ti, Zr) independently in 1966. Samuel made no definite assignments of the structure, but Coutts and Wailes suggested the compounds were JV-cyanato complexes. Later, Burmeister et al. (145, 146) reexamined the compounds in more detail and argued that they, and the hafnium analog, were 0-cyanato complexes. This was... 

A 16-electron, d° Cp2M(R)X species contains one low-lying metal-centered LUMO localized in the equatorial plane between the Cp ligands which is utilized for substrate coordination (Fig. 1) (11). Zr—X r-bonding (X = OR, halide, etc.) utilizes this orbital and generally results in decreased reactivity (5). The electronic structure of a Cp2Zr(R)(L) complex is similar to that of neutral analogs, but the LUMO is stabilized by the metal... 

Cationic Cp2M(R)(L)+ complexes exhibit a variety of interesting structural features which result from the high Lewis acidity of the cationic (P metal centers. The first simple alkyl complex of this type to be structurally characterized was [(CsH5)2Zr(CH3)(THF)][BPh4] (3, Fig. 2) (32). The... 

The reactions of bis(alkynyl)metallocenes Cp2M(C=CR)2 (M = Zr, Hf R = Me, Pr11, Bu11, Gy) with B(C6F5)3 afford the corresponding metallocene borate betaines of structure type 760.586 An assumed intramolecular alkyne insertion reaction leads to their less stable methylenecyclopropene-derived isomers, which are effectively trapped by the added / /7-butylisocyanide to yield complexes 764 which contain a methylenecyclopropene derived [Pg.906]

---