Nickel complexes silyls

Quite a number of silylnickel and silylenenickel compounds have been reported, and only a few can be cited here2305-2309 Bis(silyl)nickel complexes have been implicated as important intermediates in Ni-catalyzed double silylation of various organic substrates. Using an o-bis(dimethylsilyl)carborane ligand, complex (930) could be isolated and structurally characterized 2310 Its unusual thermal stability is attributed to the advantageous steric and electronic properties of the carboranyl unit. (930) undergoes... 

Oxidative addition of the silyl species to nickel is followed by insertion of unsaturated substrates. Zero-valent nickel complexes, and complexes prepared by reducing nickel acetylacetonate with aluminum trialkyls or ethoxydialkyls, and in general Ziegler-Natta-type systems, are effective as catalysts (244, 260-262). Ni(CO)4 is specific for terminal attack of SiHCl3 on styrene (261). 

The cross-coupling route to allylsilanes is effective with either aromatic or aliphatic a-silylated Grignard reagents16, and palladium catalysts are more reactive and stereoselective than the corresponding nickel complexes. Unsubstituted or i+monosubstituted alkenyl bromides work well but the Z-substituted bromides give lower yields and an inferior enantiomeric excess. The enantiomeric excess increases quite markedly with decreasing temperature, and optimum results are obtained at 0 C or below. 

THF if CuBr is present.1393 The reaction takes place either with or without allylic rearrangement.1394 Propargylic ethers give allenes.1395 Vinylic ethers can also be cleaved by Grignard reagents in the presence of a catalyst, in this case, a nickel complex.1396 Silyl enol ethers R2G=CROSiMe3 behave similarly.1397... 

Disilanaphthalenes can be prepared by the thermolysis of a disilacyclopropane in deuteriated benzene the reaction may be monitored by NMR spectroscopy <83JA7776>. A mechanism of formation is proposed which involves Si—Si bond rupture followed by C—Si bond formation via a silyl radical. Thermolysis of 2-(mesityl)-2-(phenylethynyl)hexamethyltrisilane also results in two isomeric 1,3-disilanaphthalenes <860M1518> but better yields are achieved if the reaction (either thermally or photochemically) is catalyzed by a nickel complex <86JA7417, 890M2050>. Nickel-... 

Klabunde and Ittel reported the use of nickel complexes containing the phosphorus—oxygen chelating ligands to homo- and copolymerize ethylene with a variety of functional olefins.Negative results were obtained with both vinyl acetate and methyl methacrylate, but copolymers could be obtained if monomers with at least two methylene spacers between the olefin and polar group, lihe functionalities successfully tolerated include ester, trimethyl-silyl-protected acids, ketones, fluoro groups, and 2° amides. 

A review has appeared on the synthesis and reactivity of (sUylamino) and (silyl-anilino)phosphines. The S5mthesis, derivatisation and coordination behaviour of the morpholine (69) and piperazine (70) derivatives have been described. They are formed from the appropriate amine with diphenylchlorophosphine, and both react with sulfur or selenium to give the chalcogenide, whilst reaction of (69) with paraformaldehyde leads to insertion of methylene into the P N bond to give the phosphine oxide. The reaction between ethylenediamine and diphenylchlorophosphine can lead to the bis-, tris- and tetrakis(diphenylphosphino)ethylene-diamines, depending upon the stoichiometry. The first two are oxidised in situ whist the latter, (71), is stable. A nickel complex of (71) has been shown to be active as a catalyst for ethylene pol5nnerisation. ... 

Shimada S, Rao MLN, Hayashi T, Tanaka M (2001) Isolation of dinuclear (p-silylene)(silyl) nickel complexes and Si-Si bond formation on a dinuclear nickel framewwk. Angew Chem Int Ed 40 213... 

The readily accessible oxalamidine derivative PhN = C(NHBu )C(NHBu ) = NPh provides another useful entry into the coordination chemistry of oxalamidinato ligands. Scheme 195 summarizes the results of an initial study. Mono- and dinuclear complexes of Ti, Zr, and Ta have been isolated and fully characterized. Silylation of both N-H functions was achieved by subsequent treatment with 2 equivalents of n-butyllithium and MesSiCl. The preparation of a nickel(II) complex failed and gave a hydrobromide salt instead. ... 

The disilanickela complex 21 was also found to be a good catalyst for the dehydrogenative double silylation of aldehydes. The nickel-catalyzed reactions of 1,2-bis(dimethylsilyl)carborane 11 with aldehydes such as isobutyraldehyde, trimethylacetaldehyde, hexanal, and benzaldehyde afforded 5,6-carboranylene-2-oxa-l,4-disilacyclohexane.32 34 36 The dehydrogenative 1,4-double silylation of methacrolein and tram-4-phenyl-3-buten-2-one in the presence of a catalytic amount ofNi(PEt3)4 also took place under similar conditions. In contrast, the reaction of 11 with a-methyl-tran.s-cinnamaldehyde and irans-cinnamaldehyde under... 

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