Tris complexes, preparation

With sp bond angles calculated to be around 162°, macrocycle 131 would be highly strained and was therefore expected to be quite reactive [79]. The octa-cobalt complex 132, on the other hand, should be readily isolable. Indeed, 132 was prepared easily from 133 in five steps, and was isolated as stable, deep maroon crystals (Scheme 30). All spectroscopic data supported formation of the strain-free dimeric structure. Unfortunately, all attempts to liberate 132 from the cobalt units led only to insoluble materials. Diederich et al. observed similar problems when trying to prepare the cyclocarbons [5c]. Whether the failure to prepare these two classes of macrocycles is due to the extreme reactivity of the distorted polyyne moiety or to the lack of a viable synthetic route is not certain. Thus, isolation and characterization of smaller bent hexatriyne- and octatetrayne-containing systems is an important goal that should help answer these questions. 

The octahedral complexes, pale green [VmL], purple VlvL]PF6, and blue-black [VvL](C104)2, where L represents a l,4,7-tris(2-hydroxybenzyl)-l,4,7-triazacyclononane derivative, serve as an example where all one-electron redox processes are clearly metal centered as depicted in Eq. (6). Table III lists the complexes prepared (148b, 152, 153). 

The water-soluble palladium complex prepared from [Pd(MeCN)4](Bp4)2 and tetrasulfonated DPPP (34, n=3, m=0) catalyzed the copolymerization of CO and ethene in neutral aqueous solutions with much lower activity [21 g copolymer (g Pd) h ] [53] than the organosoluble analogue in methanol. Addition of strong Brpnsted acids with weakly coordinating anions substantially accelerated the reaction, and with a catalyst obtained from the same ligand and from [Pd(OTs)2(MeCN)2] but in the presence of p-toluenesulfonic acid (TsOH) 4 kg copolymer was produced per g Pd in one hour [54-56] (Scheme 7.16). Other tetrasulfonated diphosphines (34, n=2, 4 or 5, m=0) were also tried in place of the DPPP derivative, but only the sulfonated DPPB (n=4) gave a catalyst with considerably higher activity [56], Albeit with lower productivity, these Pd-complexes also catalyze the CO/ethene/propene terpolymerization. 

In the majority of pentatetraenylidene complexes prepared or generated so far, the pentatetraenylidene ligand is derived from suitable C5 precursors. Usually penta-1,3-diynyl derivatives like the alcohol HC = C—C = C—CPh20H, its trimethylsilyl ether, or the 5,5,5-tris(dimethylamino)-substituted penta-l,3-diyne are employed. 

The only known example of this type of compound is a i74-trichlorosi-lylcyclohexadienetricarbonyliron complex, prepared (89% yield) by the reaction of cyclohexadienyltricarbonyliron tetrafluoroborate with tri-chlorosilane-triethylamine adduct in acetonitrile at 40° (117) ... 

Attempts to prepare adducts directly from [VO(oxme)2] (138) were unsuccessful and a trigonal bipyramidal structure was suggested for this compound as for [VO(2-Me-oxine)2] (139).825 The [VO(oxine)2X] compounds were prepared by addition of V0S04 to an aqueous solution containing 8-hydroxyquinoline and the base X. For the adducts [VO(oxine)2X], a correlation was found between v(V=0) and the pK of the X ligand, except with bases with substituents where steric hindrance may be operating, and no evidence was obtained for the existence of both cis and trans isomers, unlike the case of [VO(acac)2] adducts (Section 33.5.5.4.ii). For the tris complexes [VO(oxine)3] , an octahedral structure in which one oxine ligand is unidentate and bonded to V was proposed.825... 

The tris and bis complexes of acetylacetone (2,4-pentanedione) (167) with chromium(III) have been known for many years (168,169).739 The tris compound is generally prepared by the reaction of an aqueous suspension of anhydrous chromium(III) chloride with acetylacetone, in the presence of urea.740 Recently a novel, efficient synthesis of tris(acetylacetonato)chromium-(III) from Cr03 in acetylacetone has been reported.741 The crystal structure of the tris complex has been determined.744 A large anisotropic motion was observed for one of the chelate rings, attributed to thermal motion, rather than a slight disorder in the molecular packing. 

The complex [Cr(THF)3Cl3] was first prepared in 1958.802 However pure bromide, iodide and thiocyanate complexes were reported only in 1983.803 The preparation of [Cr(THF)6]3+ by the reaction of [Cr(THF)3Cl3] with AgBF4 in THF was attempted only an impure brown/pink oil was obtained. The tris complexes are useful starting materials in both organometallic and coordination chemistry. 

In aqueous solution, the equilibrium between the cis- and franj-diaqua complexes lies almost completely toward the cis isomer881 (K 0.17, pH 3-4). The sparingly soluble potassium salt of the tram isomer may, however, be prepared by the slow evaporation of a saturated solution at room temperature,878,880 and the cis isomer by cooling a hot solution or by allowing potassium dichromate and oxalic acid to react in the presence of a minimal quantity of water.878,879,882 The tris complex was resolved by Werner in 1912,883 providing the first example of an anionic optically active coordination complex. 

Malonic acid CH2(C02H)2 (H2mal) (209) has a coordination chemistry with chrommm(III) closely resembling that of oxalate. Malonic acid is a slightly weaker acid than oxalic acid and slightly more labile complexes are formed. The tris complex is the most extensively studied, prepared by the reduction of chromate solutions or the reaction of chromium(III) hydroxide with malonate.917,918 919 The cis and trans diaqua complexes may be prepared by the reduction of chromate with malonate the isomers are separated by fractional crystallization. The electronic spectrum of the tris complex is similar to that of the tris oxalate and a detailed analysis of these spectra has appeared.889... 

Complexes of salicylate with chromium(III) have not been reported but the tris complexes of salicylaldehyde and chromium(III) may be prepared by refluxing [Cr(THF)3Cl3] with salicylal-dehyde and sodium acetate in ethanol.939 The acid hydrolysis of this complex was studied in detail, but the isomerism obviously possible for this complex was not apparently considered. Khan and Tyagi940 studied the formation of phthalate complexes of chromium(III). 

Interesting complexes have been prepared from the chiral ligands derived from 3,3 -dimethyl-2,2 -bipyridyl Af,JV -dioxide (216,217).955,956 A number of diastereomeric tris complexes were isolated. These could be interconverted photochemically. 

Transition metal complexes encapsulated in the channel of zeolites have received a lot of attention, due to their high catalytic activity, selectivity and stability in field of oxidation reactions. Generally, transition metal complex have only been immobilized in the classical large porous zeolites, such as X, Y[l-4], But the restricted sizes of the pores and cavities of the zeolites not only limit the maximum size of the complex which can be accommodated, but also impose resistance on the diffusion of substrates and products. Mesoporous molecular sieves, due to their high surface area and ordered pore structure, offer the potentiality as a good host for immobilizing transition complexes[5-7]. The previous reports are mainly about molecular sieves encapsulated mononuclear metal complex, whereas the reports about immobilization of heteronuclear metal complex in the host material are few. Here, we try to prepare MCM-41 loaded with binuclear Co(II)-La(III) complex with bis-salicylaldehyde ethylenediamine schiff base. 

The tris(triphenylphosphinegold) oxonium ion is a particularly significant oxo complex, prepared most conveniently by reaction (16)178,180 and which crystallizes in dimeric units.179... 

Few Fe(III) complexes have been reported with dithioaliphatic or dithio-aromatic ligands. The deeply colored tris-complexes with the FhDta" and BzDta- ligands have been reported to contain a pseudooctahedral Fe(III)S6 chromophore (111). They all are low spin as expected from the high field strength of the ligands. The M5ssbauer spectra of these compounds were recorded (111). Attempts to prepare the Fe(PhDta)2Cl complex by the reaction of the tris complex with HG failed. 

Butyllithium reagents, with chromium, 5, 382 Butyl(tri-2-pyridyl)stannane, preparation, 3, 827 ft-Butylvanadium(III) complex, preparation, 5, 19... 

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