Mononuclear complexes adducts

Dimethyl-1,2,4-triazolium iodide with palladium acetate yields the carbene adduct 182 (97JOM(530)259). Under water it undergoes cis-trans isomerization to 183. Some other derivatives were reported in 1981 (81BCSJ800). 1,1 -Methylenebis(4-alkyl-l,2,4-triazolium)diiodides (alkyl = /-Pr, n-Bu, octyl) with palladium(II) acetate give the mononuclear complexes [L Pdl ] (99EJIC1965), where L2= l,l -methylenebis(4-R-l,2,4-triazol-2-ylidene) (R = /-Pr, n-Bu, octyl). Thermolysis of the products in THF gives the rran -dinuclear complexes 184... 

Although suggested to operate by a mechanism analogous to Scheme 14, the case of the catalysis by the mononuclear complex Fe(CO)5 was proposed to be more limited.86,88 Relative to the Ru catalyst, the equilibrium constant for formation of the metallocarboxylic acid adduct, Fe(C0)4(C02H)-, was found to be several orders... 

The attachment and encapsulation of metals and metal complexes in the cavities of zeolites is an active area of research and provides a versatile method for the modification of these molecular sieves (39). Because of the enforced dispersion of the metal complexes in the zeolite, systems not readily observable in solution can be investigated in zeolites. For example, the mononuclear superoxo adduct of the cobalt(HI)-ammine system, [Co(NH3 )6(00-)]2+, which would be expected to dimerize in solution, could be observed entrapped in zeolite Y (40). 

Mononuclear complex formation was confirmed for the adduct of zinc(II) salt with 2-mercaptobenzothiazole and o-phenanthroline (253). The t/-S coordination is observed in the complexes of triphenylphos-phine gold with 2-mercapto-l-methylimidazole (254) (88JOM119), 8-mercaptotheophilline (255) (91IC3743), 2-mercaptobenzoxazole (256) [94AX(C)1420], and purine-6-thiol (257) (94AJC577). 

Ni(acac)2 reacts with a variety of monodentate donors giving mono and bis adducts Ni(acac)2B (n = 1,2 B = H20, primary and secondary amines, pyridine and substituted pyridines, pyridine iV-oxide, alcohols, dioxane, substituted benzaldehydes).1558,1563-1570 Details of the structures of some complexes are reported in Table 78. The chelate ring of the coordinated /3-diketones is nearly planar, and, in thl mononuclear complexes, the Ni—O bond distances (as well as the C—O and C—C bond distances within the chelate ring) are substantially similar. Two different dinuclear structures have been found in the two complexes Ni2(acac)4B [B = py (197),1540,1571,1530 Ph3AsO (198)1542,1572]. 

This type of complex is derived from the mononuclear superoxo species via a further one-electron reduction of the dioxygen moiety. Cobalt is the only metal to form these complexes by reaction with dioxygen in the absence of a ligating porphyrin ring. Molybdenum and zirconium form peroxo-bridged complexes on reaction with hydrogen peroxide. In most cases the mononuclear dioxygen adducts of cobalt will react further to form the binuclear species unless specific steps are taken to prevent this. 

Precisely the last condition explains the fact that mainly ICC have been obtained by the immediate interaction of ligands and zero-valent metals. Thus, a large series of metal p-diketonates was synthesized in the absence of a solvent [513,634-638], for example, iron bis- and tra-acetylacetonates [635]. It was shown that other ligands can serve as activators or promoters in these processes. In particular, the introduction of a,a or y,y -bipy into the reaction mixture gives the possibility of isolating copper acetylacetonates and adducts of similar complexes of cobalt and nickel [636], meanwhile the p-diketonates of the metals above are not formed under conditions similar to those reported in Ref. 635. Under dissolution of more active metallic barium in the mixture of another p-dikctone - dipivaloyl-methane (DPM) - with dyglime (DG) or tetraglime (TG) in absolute pentane, the mononuclear complex [Ba(DPM)2(TG)] and binuclear complex [Ba2(DPM)4 ( t-H20)(DG)] were isolated and structurally characterized [637]. 

The routes for controlling the synthesis of mono- (903) and dinuclear (904) structure is, evidently, related to the donor properties of additional ligands [Scheme (4.62) L and L1]. In case of highly basic N-donors (L = py, bipy, o-phen), the mononuclear complexes 903 are generally formed [11,229,232], while the weakly basic solvents (L = MeOH [233]) lead to binuclear chelates of type 904. At the same time, the only example for 805 (L = o-phen) of a stable dimeric adduct with sufficiently high-basic o-phenanthroline is known and was shown above (Sec. 3.4.2). 

Use of less basic triphenylsiloxide ligands also allowed the isolation of mononuclear complexes (Table 1) [46,47]. In addition to the silylamide route, anhydrous nitrates and isopropoxides were employed as synthetic precursors (Eqs. 1,2). The siloxide bridges in the solvent-free dimeric systems Ln2(OSiPh3)6 are readily disrupted by donor solvents like THF, OP Bu3 or DME. The m s-THF adducts of lanthanum, cerium (Fig. 5) and yttrium adopt an approximately /ac-octahedral geometry. 

The adducts MC fterpy) and M2Cl8(terpy) (M = Nb or Ta) have been described. The structures are not known with any certainty, although the mononuclear complexes are nonelectrolytes, whereas the bromo compounds are 1 1 electrolytes with extensive magnetic interactions between the paramagnetic centers (S8). 

Chloride abstraction of (alkylideneamido)zirconocene chlorides Cp2ZrCl(N=CHR) (R = Me,/>-tolyl), prepared by a hydrozirconation reaction, with lithium butylborate Li+[/z-BuB(C6F5)3] at ambient temperature gives the transient cation [Cp2Zr(N=CHR)]+, which readily dimerizes under the reaction conditions to form the cis/trans-isomers of the dimeric /x-alkylideneamido zirconocene dications 728563 (Scheme 179). Treatment of these dications with acetonitrile leads to the respective mononuclear monocationic adduct complexes. 

In the presence of donating ligands, the dimer collapses into two equivalents of the mononuclear complex. For example, addition of pyridine gave rise to the pyridine adduct (Fig. 5) in which pyridine occupies the fourth coordination site of copper. 

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