Mononuclear 3+ complexes halides

From both sources, the rhodium(II) mononuclear complex has a variety of options open to it. In the absence of other reagents, for example, it simply dimerizes and forms the metal-metal bonded species. However, it is quite a reactive species, and, among other things, it abstracts halogen atoms, for example, from organic halides [Scheme III]. 

With a few exceptions, the chemistry of WIU is almost entirely that of dinuclear species containing a metal-metal bond of order three. There are only a few well-characterized examples of mononuclear complexes. This undoubtedly results from the tendency of Wm to form metal-metal bonds and the susceptibility of mononuclear complexes to oxidation. Of the halides of Wm, only WBr3 and WI3 are known.269 The thermally unstable WBr3 is prepared by the reaction of WBr2 with excess Br2 in a sealed tube. It is inert to H20 and concentrated HC1. WI3 is prepared from W(CO)6 and I2 at 120 °C. 

In 1959, the coordinated mercaptide ion in the gold(III) complex (4) was found to undergo rapid alkylation with methyl iodide and ethyl bromide (e.g. equation 3).9 The reaction has since been used to great effect particularly in nickel(II) (3-mercaptoamine complexes.10,11 It has been demonstrated by kinetic studies that alkylation occurs without dissociation of the sulfur atom from nickel. The binuclear nickel complex (5) underwent stepwise alkylation with methyl iodide, benzyl bromide and substituted benzyl chlorides in second order reactions (equation 4). Bridging sulfur atoms were unreactive, as would be expected. Relative rate data were consistent with SN2 attack of sulfur at the saturated carbon atoms of the alkyl halide. The mononuclear complex (6) yielded octahedral complexes on alkylation (equation 5), but the reaction was complicated by the independent reversible formation of the trinuclear complex (7). Further reactions of this type have been used to form new chelate rings (see Section 7.4.3.1). 

Thus, for group 10 palladium and platinum metals, a mixture of 1,2-bis(dialkylamino)-3-halocyclopropenylium halide and a slight excess of Pd or Pt black is refluxed in MeCN for 24h, affording the corresponding dimeric cyclopropenylidene //-complexes [(R2N)2C3 MX2 2 (R = Me, Et, i-Pr, M = Pd, Pt X = Cl, I) (equation 276)340 347-352. The dimers further react with Bu3P to give the planar mononuclear complex cis-[(R2N)2C3]MX2(PBu3). 

At higher temperature, the red mononuclear complex is converted to the orange halide-bridged species ... 

The Cu ion is classified as a soft acid (see Hard Soft Acids and Bases), which predicts reasonably well the types of ligands that will be most stabilizing and are, thus, commonly observed in Cu complexes. The preference of Cu for softer ligands is quite apparent in the homoleptic complexes, for instance the halides discussed above. Polynuclear compounds are quite commonly seen in the chemistry of Cn. Thus, the solid-state structure cannot be reliably predicted from the reaction stoichiometry or from the empirical formula of the resulting compound. The careful selection of ligands, for instance, an appropriate macrocyclic ligand can ensnre the formation of a mononuclear complex if one is desired. 

A simple possibility for a complex halide is that it adopts a structure of a halide (or oxide) A, X with A and B replacing, either statistically or regularly, the positions occupied by atoms of one kind in the binary halide (oxide) these form our class (a) in Table 10.1. Known examples are all fluorides, that is, they are ionic crystals, and the basic requirement is that the ions A and B are of similar size and carry charges appropriate to the structure, as in Na Y F4 or KaU Fg with structures of the fluorite type. Other complex halides are conveniently classified according to the type of grouping of the B and X atoms in the crystal. These atoms may form a finite group, in the simplest case a mononuclear group BX , or the B... 

The reaction of 3-halo-l,2-bis(dialkylamino)cyclopropenylium halides 5 with palladium black or platinum black in refluxing acetonitrile afforded binuclear complexes of the type 6. When the palladium complexes 6 (M = Pd) were treated with tributylphosphane in dichloromethane at — 60 "C and the mixture warmed to room temperature, a nucleophilic cleavage occurred to give the mononuclear complexes 7. The structure of complex 7 (X = Cl, R = Me) was determined by X-ray crystallography. ... 

---