Halide complexes dimeric

Rhenium Halides and Halide Complexes. Rhenium reacts with chlorine at ca 600°C to produce rheniumpentachloride [39368-69-9], Re2Cl2Q, a volatile species that is dimeric via bridging hahde groups. Rhenium reacts with elemental bromine in a similar fashion, but the metal is unreactive toward iodine. The compounds ReCl, ReBr [36753-03-4], and Rel [59301-47-2] can be prepared by careful evaporation of a solution of HReO and HX. Substantiation in a modem laboratory would be desirable. Lower oxidation state hahdes (Re X ) are also prepared from the pentavalent or tetravalent compounds by thermal decomposition or chemical reduction. 

Copper(II) complexes of 2,6-lutidylphenylketone thiosemicarbazone, 38, have been prepared from copper(II) chloride and copper(II) bromide [186]. Similar to 2-pyridyl thiosemicarbazones, 38-H coordinates via the ring nitrogen, the azomethine nitrogen and the thiol sulfur based on infrared spectral assignments. Magnetic susceptibilities and electron spin resonance spectra indicate dimeric complexes and both are formulated as [Cu(38-H)A]2 with bridging sulfur atoms. The electronic spectra of both halide complexes show band maxima at 14500-14200 cm with shoulders at 12100 cm S which is consistent with a square pyramidal stereochemistry for a dimeric copper(II) center. 

Methylenative dimerization takes place when terminal alkynes are treated with the tita-nocene/methylidene/zinc halide complex generated from titanocene dichloride and CH2(ZnI)2. The process is believed to involve the formation of a titanacyclobutene intermediate [75],... 

One can set up to do this using the competition between dimerization and halogen atom abstraction from RX to form the rhodium(III) halide complex. As a function of [RX], the product ratio is quite easily evaluated. From that, one can get the rate constant ratio but, knowing independently the rate constant for dimerization, it is possible to extract from those data rate constants for reactions of the rhodium(II) complex with these organic halides. The rate constants obtained are listed in Table I. 

The re-allyl complexes can be isolated as halide-bridged dimers. 

The dimeric organomagnesium halide complexes 187-189 (Figure 82) were obtained from the reaction of (2-Py)(SiMe3)2C-Sb=C(SiMe3)(2-Py) with Et2Mg in THF in the... 

A series of zinc and cadmium complexes of N-ethyl- and A-propyl-imidazole have been described the 1 1 complexes [ML2XJ (M = Zn or Cd L = JV-alkylimidazole X = halide) are monomeric tetrahedral species, whereas [(MLX2)2] (M = Zn or Cd L = A-alkylimidazole X = halide) are halide-bridged dimers.428... 

Finally, there are two examples of intramolecular C,P chelates, viz. LPd k2-C,P-2-CH2C6H4P(o-To1)2 (L = Tp 468, Bp 469), both prepared by cleavage of the halide bridged dimer with KL (Scheme 46). 43 These complexes were targeted to explore their potential in the guise of catalysts for organic synthesis, a role to which the cyclopalladated tris(o-tolyl) phosphane precursor had been previously applied. However, this preliminary study revealed these materials to be unreactive toward electrophiles (see also Section III.C.3.b), and no further investigations have been reported. 

The possibility of formation of dimeric structures should be taken into account in the syntheses of metal-halide complexes of other ligands. In this respect, the transformation (3.72) is interesting and representative, in which not only monomeric mononuclear 637, but also dinuclear 638 complexes were isolated and their structures determined by x-ray diffraction [89] ... 

Addition of a dimeric carbonylmetalate to a metal halide complex [Eq. (64) 43)1... 

There are selected examples of the use of additional nitrogen sources such as NSC1, N2, and NC13 (Eqs. (29,30)). The molybdenum nitride halide complexes were isolated from the reaction of a MoVI complex and NSC1 in the presence of Cl- or F [34]. Cummins reported the remarkable reaction of low-valent Mom triamide with N2 (1 atm) to afford the corresponding nitride 80 (Eq. (29)). The presence of bulky amide ligands is critical to the success of the reaction, for it prevents the formation of the stable dimer [(ArRN)3Mo]2. 

Pd[P(o-tolyl)3]2] underwent oxidative addition of aryl halides to provide the unusual dimeric aryl halide complexes [Pd[P(o-tolyl)3](Ar)(Br) 2 (Eq. (44)) [77,102]. It is unusual for phosphine-ligated aryl halide complexes formed by oxidative addition to be dimeric. These oxidative addition products were isolated and structurally characterized. They remain dimeric in solution, as determined by solution molecular weight measurements, but react as the monomers, as described below. 

In 1994, Paul, Patt, and Hartwig showed that the Pd(0) catalyst in Kosugi s process was Pd[P(o-C6H4Me)312 (3), which underwent oxidative addition of aryl halides to give dimeric aryl halide complexes (4) [91]. These aryl halide complexes reacted directly with tin amides to form arylamine products (Eq. (3)). Thus, this chemistry could formally be viewed as being roughly parallel to Stille coupling. 

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