Rhodium complexes polynuclear

A moderate pressure (>5 atm.) of CO in the reaction system leads to the selective formation of 29, while alkynes undergo rhodium-catalyzed hydrosilylation with a hydrosilane to afford vinylsilanes in the absence of CO. The presence of the rhodium complex is crucial for the smooth progression of siiyiformyiation, regardless of the presence of mononuclear or polynuclear complexes. This generalization is supported by the studies of many others [15]. The most important feature of this reaction is the excellent regioselectivity, which favors the formylation of the internal sp-carbon of the acetylenic bond of terminal... 

We have already observed that simple antonlc, e.g., CRh(C0)4] , and neutral, e.g, HRh(C0)4 or Rh2(C0)s> rhodium complexes could be involved In the fragmentation and aggregation reactions of polynuclear species. In addition, the cationic moiety "Rh(C0)2+" has been found to formally coordinate to [Rh 4(C0)2534- +0 form [Rhi 5(C0)27]3 (equation 8), or to get detached from the latter cluster by halide ligands (equation 9) JJJ under ambient conditions. 

Rhodium carbonyl clusters with encapsulated heteroatoms, e.g., CRh6(C0)i5C]2 , [RhgPtCO l12 and [Rhi7S2(C0)32]3 , have been observed to be more resistant to fragmentation under 500-1000 atm of C0 H2 than homometal lie rhodium clusters. Polynuclear species account for 95-98 and 80-85 percent, respectively, of the total rhodium content of those systems, while the greatest catalyst activity has been noted with the latter complexes. CRh(C0>4l]— Is the only fragmentation product detected In both Instances. . ... 

Our Involvement In the study of the chemistry of polynuclear rhodium complexes under high pressures of C0 H2 induced us to look at the reactions of [Rh 5(00)27]- with CO or H2. 

Hydride Complexes of Ruthenium, Rhodium, and Iridium G. L. Geoffroy and J. R. Lehman Structures and Physical Properties of Polynuclear Carboxylates Janet Catterick and Peter Thornton... 

Ojima has reported that a number of mono- and polynuclear rhodium carbonyl complexes catalyze the cyclization/... 

The cleavage of polynuclear hydroxo-bridged rhodium(III) and iridium(III) complexes into the corresponding mononuclear fragments has been reported in only a few instances, but the well-established tendency of mononuclear complexes of these metal ions to undergo substitution reactions with retention of configuration indicates the possibility of analytical and synthetic applications such as described above for chromium (III). 

Structural, thermodynamic, and kinetic studies have shown that hydroxo-bridged polynuclear complexes of (diromium(III), cobalt(III), rhodium(III), and iridium(III) have many general features in common. Structurally, the four metal ions exhibit an almost identical pattern, and in particular the occurrence of many well-characterized oligomers... 

Polynuclear Rhodium Carbonyl Complexes and Their Relationships to Mononuclear and Binuclear Rhodium Carbonyl Complexes1... 

Another simple rhodium carbonyl complex that has been shown to be involved in the aggregation and fragmentation reactions of polynuclear rhodium species is "Rh(C0)2+ ". This moiety has been shown to be involved in such reactions under ambient conditions as reported by Chinl, et al. UJ (equations 21 and 22). 

Increasing the number of electrons reduces the activation of N2, because the electrons occupy the orbitals which are bonding with respect to the NN bond, and actually stabilize it. In agreement with this prediction dinitrogen is sufficiently activated to be reduced by protonation by dinuclear complexes of titanium(II), zirco-nium(Il), niobium(III), tantalum(III), molybdenum(IV), and tungsten(IV), whereas it is not reduced by protonation by certain d -d complexes, such as those of molybdenum(O), ruthenium(II), or rhodium(I). Apparently dinuclear complexes M-N=N-M in which M has the d electronic configuration can be intermediates in dinitrogen reduction in protic media, particularly if they represent part of polynuclear complexes (vide infra). 

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