Platinum metallocyclization

Sulfur atoms extraneous to the heteropentalene system in (4 X = S) can be oxidized by MCPBA to SO and SO2 groups in 64-70% yields <85JCS(P2)833>. Arsenic pentafluoride coordinates to the thiadiazole ring of (59 R = Cl) as shown in (15) (x-ray analysis) <86ZN(B)162>, whereas (rj -ethene)bis(triphenyl-phosphane)platinum(0) inserts into the thiadiazole ring to give a new six-membered metallocycle <86CB366>. 

The insertion of platinum into a Sn—C bond, presumably relieves the strain of a ferro-cenophane and forms the metallocycle 97 (equation 124)479... 

Hexagonal macrocycle 50 is produced from a 120°-angle-tecton 33 and 120°-angle-linker 49 <19990L1921> (Scheme 8). Tecton 33 is prepared by double oxidative addition of 4,4 -diiodobenzenophenone 47 with tetrakis(triethylphosphine)platinum(ll) followed by treatment with AgOTf. Bis(4-pyridyl)ketone 49 combines spontaneously with 33 at room temperature to form metallocycle 50. 

It has been shown that electron-rich cyclopropanes are able to displace ethylene from dichloro(ethylene)platinum to yield four-membered metallocyclic complexes (cf. equation 37). On the other hand 1,1,2,2-tetracyanocyclopropane (171) reacts under mild conditions with zerovalent platinum and palladium complexes of the type Pt(PPh3)2 (C2H4) or ML (n = 3, 4 M = Pd or Pt L = phosphines or triphenylarsines) to give metallocyclobutane derivatives (172) (equation 118) . 

Yang and Younghave observed a novel Friedel-Crafts metallocyclization of halomethyl(arylphos-phine)platinum(II) complexes (30) in the presence of AgBF4 and a triarylphosphine to afford cationic metallacyclic species (32 equation 97). 

The mechanism proceeds by two steps. The first step is first-order in both platinum oxygen complex and alkyne, and the rate of the second step is independent of alkyne concentration (R = CF3, C02Me). The intermediate may be an adduct with the alkyne coordinated to platinum, or the reaction may proceed in the unsymmetrical metallocycle as is suggested for the SO2... 

A zerovalent platinum bimetallic complex Pt2(dppm)3 will also catalyze the oxidation of CO to CO2 using either O2 or NO as oxidant. " Again, no comment can be made regarding the reaction mechanism. Oxidation of CO on platinum metal surfaces involves the reaction of chemisorbed atomic oxygen, but it is unlikely that such species are formed under the mild conditions of temperature used in these examples. In the conversion of the coordinated carbonyl in IrCl(CO)PN (PN = o-(diphenylphosphino)-A,A-dimethylaniline) to CO2 though it has been tentatively suggested that a metallocyclic intermediate is formed (23) ... 

A convenient way of storing and purifying the strained olefin bicyclo[2,2,0]hex-l(4)-ene is by formation of a platinum complex (776), whose structure has been confirmed by 2f-ray analysis. The olefin is readily liberated from (776) by carbon disulphide and undergoes the expected Diels-Alder reaction with cyclopentadiene. Addition of ethanol to (776) is accompanied by opening of the strained internal bond to give the metallocycle (777). ... 

Isobe started with hexyl-functionalized dibromo crysene 76, and accessed the metallocycle 78 via the diboronate 77 using platinum chloride and cesium fluoride. Reductive elimination with triphenylphosphine offered the hydrocarbon 79 cleanly. 

Mixed phosphorus compounds, bearing at least two different tervalent phosphorus moieties have been developed and have found several applications in catalysis. Iri li described the synthesis of aminophosphine-phosphinite ligands 149 and 150, from the commercially available 3-piperidinemethanol and 3-(methylamino) pro-pan-l-ol. Their palladium and platinum complexes 151 and 152, containing metallocyclic rings, were obtained as air-stable compounds with high yields, and characterized by P, and NMR spectroscopy, FTIR spectroscopy and X-ray crystallography. The Pd complexes were effective catalysts on Suzuki-Miyaura cross-coupling reactions of various aryl chlorides and atyl bromides with phe-nylboronic acid. 

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