Palladium macrocyclic complexes

Larsen, J., Rasmussen, B.S., Hazell, R.G. and Skrydstrup, T, (2004) Preparation of a novel diphosphine-palladium macrocyclic complex possessing a molecular recognition site. Oxidative addition studies. Chem, Commun., 202-203 Braunstein, P., Clerc, G. and Morise, X. (2003) Cyclopropanation and Diels-Alder reactions catalyzed by the first heterobimetallic complexes with bridging phosphinooxazoline ligands. New J. Chem., 27,68-72 Braunstein, P., Clerc, G., Morise, X., Welter, R. and Mantovani, G. (2003) Phosphinooxazolines as assembling ligands in heterometallic complexes. Dalton Trans., 1601-1605. 

A conjugated homobimetallic palladium(II) complex (see Figure 40) was formed by one-pot oxidative complexation of 1,4-phenylenediamine with a palladium(II) complex bearing the tri-dentate ligand shown. In the absence of 1,4-phenylenediamine this palladium(II) complex undergoes controlled formation of a macrocyclic tetramer via removal of a labile solvent ligand, as shown in Figure 41.514... 

A mild aerobic palladium-catalyzed 1,4-diacetoxylation of conjugated dienes has been developed and is based on a multistep electron transfer46. The hydroquinone produced in each cycle of the palladium-catalyzed oxidation is reoxidized by air or molecular oxygen. The latter reoxidation requires a metal macrocycle as catalyst. In the aerobic process there are no side products formed except water, and the stoichiometry of the reaction is given in equation 19. Thus 1,3-cyclohexadiene is oxidized by molecular oxygen to diacetate 39 with the aid of the triple catalytic system Pd(II)—BQ—MLm where MLm is a metal macrocyclic complex such as cobalt tetraphenylporphyrin (Co(TPP)), cobalt salophen (Co(Salophen) or iron phthalocyanine (Fe(Pc)). The principle of this biomimetic aerobic oxidation is outlined in Scheme 8. 

The use of a lipophilic zinc(II) macrocycle complex, 1-hexadecyl-1,4,7,10-tetraazacyclododecane, to catalyze hydrolysis of lipophilic esters, both phosphate and carboxy (425), links this Section to the previous Section. Here, and in studies of the catalysis of hydrolysis of 4-nitrophenyl acetate by the Zn2+ and Co2+ complexes of tris(4,5-di-n-propyl-2 -imidazolyl)phosphine (426) and of a phosphate triester, a phos-phonate diester, and O-isopropyl methylfluorophosphonate (Sarin) by [Cu(A(A(A/,-trimethyl-A/,-tetradecylethylenediamine)l (427), various micellar effects have been brought into play. Catalysis of carboxylic ester hydrolysis is more effectively catalyzed by A"-methylimidazole-functionalized gold nanoparticles than by micellar catalysis (428). Other reports on mechanisms of metal-assisted carboxy ester hydrolyses deal with copper(II) (429), zinc(II) (430,431), and palladium(II) (432). 

An extensive series of neutral macrocyclic complexes, mainly of nickel(II), copper(II), platinum(II) and palladium(II), has been developed by Dziomko and coworkers. The cyclization step in the template reaction is a nucleophilic aromatic substitution of an arylamine on to a haloaryl azo compound. A variety of aryl and heteroaryl rings can be incorporated in different combinations. For instance, a diaminoazo compound can be combined with a dihaloazo compound (Scheme 58).246 247 Another synthetic strategy involves the dimerization of an aminohaloazo compound and leads to more symmetrical macrocyclic complexes (Scheme 59).248 249 Most recently, dihalodiazo compounds have been synthesized from dihydrazines and pyrazolinediones and undergo template reactions with simple 1,2-diamines (Scheme 60).249 250... 

Figure 5-52. The reaction of the palladium diphosphine complex with diacetyl gives a palladium complex of a macrocyclic P4 donor ligand.

The reaction of the palladium complex with diacetyl is rather more interesting and yields the palladium(n) complex of a novel tetraphospha macrocyclic ligand. Note that the phosphorus analogue of an aminol rather than an imine is once again obtained, representing the general instability of P=C bonds in the absence of sterically hindering substituents (Fig. 5-52). 

When Nd or Yb complexes of a similar macrocycle are covalently linked to a palladium porphyrin complex, this sensitizes near-IR emission from the lanthanide, enhanced in the absence of oxygen and in the presence of a nucleic acid7 Another application of luminescence accompanies the terbium complex shown in (39) whose luminescence is enhanced by binding to zinc, and can therefore signal for that metal. " ... 

Complexes of nickel(II), copper(II), cobalt(III), zinc(II), iron(II), palladium(II), plati-num(II) and vanadyl can be obtained. Although the reaction sequence is fairly general for metal ions, it is not easily extendable to substituted 2-aminobenzaldehydes. However, 2-amino-5-me-thylbenzaldehyde has recently been used successfully in the macrocyclization reaction. Although the macrocyclic complexes (67) are very stable to hydrolysis they are susceptible to attack by nucleophiles, as exemplified in equation (25). " The nickel(II) and copper(II) complexes (67) undergo hydrogenation at relatively low pressures. 

Metathesis of Si-Si bonds is promoted by palladium catalysts presumably through bis(organosilyl)palladium(II) complexes. Though metathesis reaction of linear disilanes results only in disproportionation of the disilanes [88],use of cyclic disilane provides a useful method for the synthesis of macrocyclic or polymeric organosilicon compounds having newly formed Si-Si bonds. 

In the palladium(II) macrocyclic complexes, the metal ions were proposed to be coordinated in a square planar geometry, with a disordered smectic mesophase being observed, even for the polycatenar complexes (i. e. those with more than one chain on each terminal ring). Preliminary X-ray diffraction measurements determined the smectic if-spacing to be 53 A which is comparable to the calculated molecular length of the ligand (50-52 A) in the fully extended conformation [83b]. 

However, more remarkable was the discovery that in alkane solvents, large, orrfiometallated macrocyclic complexes of palladium shown in Figure 92 would form lyotropic columnar phases [171], These remarkable materials have been shown to form columnar hexagonal phases and, in suitable solvents, lyotropic nematic phases derived from columnar organization. Further, in certain non-mesomorphic examples, mesophases can be induced by the addition of an electron acceptor such as trinitrofluorenone chiral phases are introduced when the acceptor is resolved 2 -(2,4,5,7-tetranitro-9-fluorenylideneaminoxy)propionic acid (know as TAPA). 

Palladium gives complexes with many macrocyclic ligands containing N, S, and 0 heteroatoms. Some have already been... 

Stang and Cao have reported the novel preparation and characterization of platinum- and palladium-based cationic, tetranuclear, macrocyclic complexes... 

The success of this triple catalytic system relies on a highly selective kinetic control. From a thermodynamic point of view, there are 10 possible redox reactions that could occur in this system. However, the energy barrier for six of these (O2 + diene, O2 + Pd(0), etc.) are too high, and only the kinetically favored redox reactions shown in Scheme 11.14 occur. A likely explanation for this kinetic control is that the barrier is significantly lowered by coordination. Thus, the diene coordinates to Pd(II), BQ coordinates to Pd(0), HQ coordinates to (ML,), and Oj coordinates to ML ,. In a related system for aerobic oxidation, a heteropolyacid was employed in place of the metal macrocyclic complex (ML ,) as oxygen activator and electron transfer mediator [72]. Recent immobilization of the macrocyclic complex in ZeoHte-Y, led to eflBcient reoxidation of the HQ in the palladium-catalyzed 1,4-diacetoxylation [73]. 

In a similar manner, the rhodium(III) complex of macrocycle 2, [RhCl2(H20)(2)][PF6], and the palladium(II) complex of the macrocycle 3, [Pd(3)(H20)][BF4], were found to have a molecule of water bound to the metal center,... 

Moreno-Manas, M.. Pleixats. R.. Sebastian, R.M., Vallribera, A., and Roglans, A, (2004) Organometallic chemistry of 15-membered tri-olefinic macrocycles catalysis by palladium(O) complexes in carbon-carbon bondforming reactions,... 

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