Paddlewheel compounds

Recent developments in the chemistry of metal-metal multiply bonded paddlewheel compounds... 

This review will summarise some of the main developments in the chemistry of M2" + paddlewheel compounds of Cr, Mo, W, Re, Ru, Os and Rh, that have appeared more recently in the literature, between 2007 and 2008. 

One of the attractions of dirhodium paddelwheel complexes is their ability to catalyse a wide variety of organic transformations such as C-H insertions, cyclopropanations and ylide formation. A review on the application of high symmetry chiral Rh2(II,II) paddlewheel compounds highlights their application as catalysts for asymmetric metal carbenoid and nitrenoid reactions, and as Lewis acids.59 Their impressive performance as catalysts in C-H functionalisation reactions has been exploited in the synthesis of complex natural products and pharmaceutical agents. A recent review on catalytic C-H functionalisation by metal carbenoid and nitrenoid insertion demonstrates the important role of dirhodium species in this field.60... 

Quadruply bonded compounds tend to adopt one of two geometries square parallelpiped or paddlewheel (see Fig. l). For square parallel-pipped compounds, such as [RcaClg], the ligands adopt an eclipsed geometry to maximise overlap of the orbitals that form the 8-bond. Paddlewheel compounds typically employ monoanionic bridging ligands, such as carborylates, amidates or amidinates, to support the metal-metal bond, and are more commonly encountered than their square parallelpiped cousins. There are now hundreds of examples of these compounds. ... 

Oxidation of the quadruply bonded paddlewheel compounds by one electron generates a radical cation with a electronic configuration,... 

The majority of dimetal quadruply bonded group 6 compounds are either the square parallelepiped type (k = 0-4j L = neutral donor ligand) compounds or paddlewheel compounds of... 

The chemistry of ditungsten paddlewheel compounds is substantially less developed than the periodically related dichromium and dimolybdenum analogs. This is in part due to the increased susceptibility of the W2 core to reaction with Oj and in part to the increased difficulty in synthesizing the tetracarhoxylate analogs. One of the most commonly used methods is the reaction of WCl and the sodium carhoxylate with Na/Hg in THF (Eq. (6.2)) [12]. While this route works for a number of carboxylates, Wj(02CCH3)4 has to be prepared by metathesis of... 

The syntheses of the tetragonal paddlewheel compound, Co2(DAniF), ([DAniF]" =Al,A/ -di-p-anisylformamidinate), and the trigonal paddlewheel compound, Co2(DAniF)3 have been reported... 

Table 9.1 Selected Co-Co bond lengths for dicobalt paddlewheel compounds.

Two dinickel(ll) paddlewheel compounds with amidinate (77) or guanidinate (78) ligands were synthesized and their one-electron oxidation was studied (Scheme 10.36) [45]. In the Ni2 compounds 79 and 80, the Ni-Ni distance was found to be 0.lA shorter than the corresponding dinickel(ll) precursor (2.476(1) A [77] vs 2.3703(4) A [79] 2.4280(5) A [78] vs 2.3298(6)A [80]) (Entries 4 and 5, Table 10.5). Based on this observation, it was proposed that upon oxidation one electron was removed from a metal-based a orbital to give an overall Ni-Ni bond order of 1/2 in the Nij species. Furthermore, a single-point calculation with no simplified solid-state structure of 79 suggested that the unpaired electron in the Ni2 species is in a metal-based a orbital, and this was also verified by a solution EPR spectrum. 

A handful of diptJladium(II) paddlewheel compounds with bidentate ligands were synthesized in the last decade and representations of them are listed in Figure 10.10. [104,105] The Pd(II)-Pd(II) bond length interestingly varies from 2.72 to 2.95A in compounds 140-143 (Entries 12-15, Table 10.8). 

Figure 10.28 Pd-Pt heterobimetallic paddlewheel compounds (229, 230), and (b) the intermolecular Pt-Pt interaction.

Recent reviews cover homo-dinuclear <7-alkynyl complexes of the type described here and another discusses substituent effects in dinuclear paddlewheel compounds. ... 

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