Cyclo-metallated compounds

Cyclo-palladated chemistry has undergone important advances mainly due to the potential uses of compounds as technologically relevant materials (e.g, liquid crystals), catalysts, and anti-tumour drugs. De Almeida and coworkers reported a study on the thermal properties of cyclo-metallated compounds of general formula [Pd2(dmba)2X2(bpe)j, where X = NO ", Cl , N , NCO, NCS , dmba = N,N-dimethylbenzylamine and bpe = trans-l,2-bis(4-pyridyl)ethylene [211]. 

On the other hand, with diphenylacetylene or phenylmethylacetylene, cyclo-metalated compounds form nine-memberedring compounds 7.28 with bis-insertion of the alkynes, as shown in Eq. (7.25). When the R s are dissymmetric (R, R =Me, R2, R =Ph R, R =Ph, R, R =Me), head-to-tail and tail-to-tail arrangement isomers 7.28a and 7.28P are isolated X-ray diffraction studies were made on a bromo-derivative 7.28a and chloro-derivative 7.28P [79]. 

P(CH2QH5)3, P(SC6Hs)3, PPh(allyl)2, P(allyl)3, PPh(l-Np)2, PMePh 1-Np. Cyclo-metalation is possible with PPh(CH2CH2Ph)2 and P(0-totyl)3, the former compound yielding a six-membered ring and the latter undergoing metalation at an sp carbon atom. However, drastic conditions are necessary (450 w lamp). The results obtained reveal that ... 

Higher 43-hydrocarbyl derivatives of transition metals can be obtained by partial protolysis of the bis(7i-allyl)metal compounds formed from cyclo-octa-1,5-diene metal complexes and 1,3-butadiene with one equivalent of the Bronsted acid in the presence of the proper ligand in a polar solvent at lowered temperature (e.g. — 40°C). For instance, Ni [43-(CxHn)l and Ni—[43-(Ci2Hig)] derivatives have been yielded by the reaction of Ni(CxH 2)2 [(Ni(Cod)2] with 1,3-butadiene (C4H6), followed by treatment with a Bronsted acid, according to scheme (1) [132] and scheme (2) [37] respectively ... 

Substitution is also observed when l-bromo-2,2-dimethyl-l-phenylcyclopropane was reacted with lithium metal followed by copper(II) ditriflate. The cyclopropyllithium compound formed in the first step underwent a copper-mediated dimerization, leading to a mixture of meso- and ( + )-2,2,2, 2 -tetramethyl-l,T-diphenylbicyclopropyl (13). ° Reactions involving other cyclo-propylcopper compounds are reported in ref760. 

A limited number of complexes with cyclopropcnethione derivatives have been prepared by reaction of the respective ligand with the usual transition-metal compounds. The reaction of diphenylcyclopropenethione (11) with diironnonacarbonyl in tetrahydrofuran at room temperature gives a 61% yield of diphenylcyclopropenethione complex 12, in which the cyclo-propenethione ligand is coordinated at the sulfur atom and occupies an axial coordination site, as determined by an X-ray crystallographic analysis. ... 

At the same time, as described above, an enormous number of articles on cyclo-metalation reactions have been published. Many reviews [1-20, 36-40] and three books [21-35] by researchers other than the author have also been published. The first review having cyclometalation as the title word, Some Studies of the CyclopaUadation Reaction [2], was published by Trofimenko in 1973. This was followed by a review entitled CyclometaUated Compounds by Dehand and Pfeffer [3] in 1976 and by a review entitled Cyclometallation Reactions by Bruce [4] in 1977. 

In 1994, about 30 years after direct reactions of halo-p-carbonyl compounds with tinfoil were first conducted, the author sought to show the reasons why cyclo-metalation reactions for the production of organometallic intramolecular-coordination five-membered ring compounds proceed extremely quickly. To verify the above, the five-membered ring structure was demonstrated to be the most stable as compared with four- and six-membered ring structures. 

Cyclopentadienyl—metal bonds may be synthesized by direct reaction of cyclopentadiene with certain metals and their compounds or by reaction of ionic metal cyclopentadienides with compounds of metals wherein cyclo-pentadienide anion displaces a ligand bonded to the metal. These bonds may also be formed in a limited number of instances by reaction of alkenes or alkynes with metal compounds. 

In the usual experimental procedure, an acidic salt is first complexed with base and then treated with cyclopentadiene which reacts to form the cyclo-pentadienyl metal compound. The by-product salt is separated from the cyclopentadienyl metal compound by extraction with water. 

With azobenzene, benzylideneamine, dimethylaminomethylbenzene, etc., cyclo-metalations proceed to form five-membered ring compounds as shown in eq. (16.31)-( 16.34) [81-90cj. Transmetalation is shown in eq. (16.34) [86]. As shown in eq. (16.35), ketimine reacts with ruthenium compounds at room temperatures for a short time to afford the cyclometalation intermediate, further reaction for a long time affords cyclometalation products [87]. The other cyclometalations, e.g., reaction shown in eqs. (16.36) and (16.37), have been reported [88—90]. 

Co (CO) 2, and (n -C5H5)(n -Ci4Phtj)Co. 35 As a consequence, alternate methods for the preparation of functionally substituted cyclo-pentadienyl metal compounds became an important goal of our research. Sodium cyclopentadienide containing aldehyde, ketone, and ester substituents can be made by the reactions of C5H5Na with ethyl formate, methyl acetate, methyl chloroformate, and dimethyl carbonate (Scheme l),36-39... 

The bis(iminophosphorane) ligand (25) was used to form complexes with Y(iii) (26) and Sm(iii) (27). While the former was resistant to cyclo-metalation the latter underwent orthometalation reaction involving one phosphinimine aryl substituent. This compound undergoes a further transformation in solution affording dinuclear species. ... 

The preparation and structure determination of ferrocene marked the beginning of metallocene chemistry Metallocenes are organometallic compounds that bear cyclo pentadiemde ligands A large number are known even some m which uranium is the metal Metallocenes are not only stucturally interesting but many of them have useful applications as catalysts for industrial processes Zirconium based metallocenes for example are the most widely used catalysts for Ziegler-Natta polymerization of alkenes We 11 have more to say about them m Section 14 15... 

Coordination-catalyzed ethylene oligomerization into n-a-olefins. The synthesis of homologous, even-numbered, linear a-olefins can also be performed by oligomerization of ethylene with the aid of homogeneous transition metal complex catalysts [26]. Such a soluble complex catalyst is formed by reaction of, say, a zero-valent nickel compound with a tertiary phosphine ligand. A typical Ni catalyst for the ethylene oligomerization is manufactured from cyclo-octadienyl nickel(O) and diphenylphosphinoacetic ester ... 

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