Coordination complexes: derivatives

Coordination complexes derived from 3,6-di(2-pyridyl)-l,4-dihydro-l,2,4,5-tetrazines (DPDHT) and trimethylgallium have been described <98CJC1800>. 

The reactions of [Ml2(CO)3(NCMe)2] with thiourea, A,A,A, /V -tetra-methylthiourea, and thioacetamide to give a number of seven-coordinate complexes have been described. A large series of 42 triphenylphos-phine oxide and triphenylphosphine sulfide complexes derived from [Ml2(CO)3(NCMe)2] have been prepared as shown in Scheme 5. Also, a series of tricyclohexylphosphinecarbondisulfide seven-coordinate complexes derived from the reactions of [MT(CO)3(NCMe)2], [MI,(CO)3(NC Me)L] L = PPhj, AsPhj, SbPhj, PCOPh),, and [Wl2(CO)3(PPh3)2] with PCy3CS2 have been reported. 

The preparation of natural rubber-gra/t-methyl methacrylic acid has been reported by Lenka and coworkers. The vanadium ion was used as an initiator, which initiated the creation of free radicals on the backbone of natural rubber and this increased the interaction between the natural rubber and the methyl methacrylate surfaces. The coordination complexes derived from the acetylacetonate of Mn(III) ions could also be used as an initiator to form the natural rubber-gra/t-methyl methacrylic acid. Under different conditions, silver ions could be used as a catalyst to produce natural rubber-gra/t-methyl methacrylic acid with different concentrations of methyl methacrylic acid monomers, and potassium peroxydisulfate as an initiator. Consequently, these methods were successful in the preparation of compatible blended natural rubber and methyl methacrylic acid by graft copolymerization. This compatibility was confirmed by nuclear magnetic resonance and infrared spectroscopy techniques. The interaction between natural rubber and methyl methacrylic acid was significantly increased and was useful for further blending with other polyacrylate molecules or different polymer types. 

The complex MnI(CO)5 shows three IR and four Raman bands in the CO stretching region of spectra. Assign the point group of the six-coordinate complex, derive... 

Divalent molybdenum compounds occur in mononuclear, dinuclear, and hexanuclear forms. Selected examples are shown in Figure 6. The mononuclear compounds are mostiy in the realm of organometaUic chemistry (30—32). Seven-coordinate complexes are common and include MoX2(CO)2(PR3)2, where X = Cl, Br, and I, and R = alkyl MoCl2(P(CH3)3)4, heptakis(isonitrile) complexes of the form Mo(CNR) 2 (Fig. 6d), and their chloro-substituted derivatives, eg, Mo(CNR)3CR. The latter undergo reductive coupling to form C—C bonds in the molybdenum coordination sphere (33). 

When a Br nsted base functions catalytically by sharing an electron pair with a proton, it is acting as a general base catalyst, but when it shares the electron with an atom other than the proton it is (by definition) acting as a nucleophile. This other atom (electrophilic site) is usually carbon, but in organic chemistry it might also be, for example, phosphorus or silicon, whereas in inorganic chemistry it could be the central metal ion in a coordination complex. Here we consider nucleophilic reactions at unsaturated carbon, primarily at carbonyl carbon. Nucleophilic reactions of carboxylic acid derivatives have been well studied. These acyl transfer reactions can be represented by... 

The reaction of 4-(phenylsulfonyl)azetidin-2-one (128) with nucleophiles such as dialkylcopper lithium and Grignard reagents gives 4-alkyl, 4-allyl, 4-vinyl or 4-ethynyl-azetidinon-2-one (129) in good yields (equation 99)83. The yields of several azetidin-2-ones obtained by this method are given in Table 10. The reaction apparently proceeds through an intermediate azetin-2-one 131 derived from the five-membered coordination complex (equation 100). 

The electrophilic carbene carbon atom of Fischer carbene complexes is usually stabilised through 7i-donation of an alkoxy or amino substituent. This type of electronic stabilisation renders carbene complexes thermostable nevertheless, they have to be stored and handled under inert gas in order to avoid oxidative decomposition. In a typical benzannulation protocol, the carbene complex is reacted with a 10% excess of the alkyne at a temperature between 45 and 60 °C in an ethereal solvent. On the other hand, the non-stabilised and highly electrophilic diphenylcarbene pentacarbonylchromium complex needs to be stored and handled at temperatures below -20 °C, which allows one to carry out benzannulation reactions at room temperature [34]. Recently, the first syntheses of tricyclic carbene complexes derived from diazo precursors have been performed and applied to benzannulation [35a,b]. The reaction of the non-planar dibenzocycloheptenylidene complex 28 with 1-hexyne afforded the Cr(CO)3-coordinated tetracyclic benzannulation product 29 in a completely regio- and diastereoselective way [35c] (Scheme 18). 

A bidirectional benzannulation of the axial-chiral biscarbene complex 47 affords a bis-Cr(CO)3-coordinated biphenanthrene derivative 48, which combines elements of axial and planar chirality [49] (Scheme 31). Four diastereomers are formed in moderate diastereoselectivity, two of which have been isolated as the major isomers. 

The reaction of alkenes with alkenes or alkynes does not always produce an aromatic ring. An important variation of this reaction reacts dienes, diynes, or en-ynes with transition metals to form organometallic coordination complexes. In the presence of carbon monoxide, cyclopentenone derivatives are formed in what is known as the Pauson-Khand reaction The reaction involves (1) formation of a hexacarbonyldicobalt-alkyne complex and (2) decomposition of the complex in the presence of an alkene. A typical example Rhodium and tungsten ... 

The first and third examples illustrate a nuance of the naming rules. Iron and silver in anionic complexes are named by their Latin roots,/err- and argent-, from which their symbols (Fe and Ag) are derived. Metals taking their Latin names in anionic coordination complexes are listed in Table 20-4. 

A cyclam derivative with an amine pendent donor attached at the bridgehead carbon atom was presynthesized from diethylaminomalonate and l,9-diamino-3,7-diazanonane in refluxing MeOH, followed by BH3-THF reduction.1507 It acts as a pentadentate ligand at pH 8.5 and forms a six-coordinate complex (592) with a water molecule sitting at the remaining axial site. 

The susceptibility of phosphites to hydrolysis limits their application as ligands for homogeneous catalysis. The fused tricyclic monophosphites derived from ca 1 i x[4]arenes260-262 form coordination complexes with palladium.263... 

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