Bridged phosphine complexes nickel

The reaction of [LSi(TMS)=P(TMS)] (3) with [NifCODlzl generates a novel phosphorus-bridged bis(silylene) nickel complex [ (LSi)2P(TMS) Ni(COD)] with a tricoordinate phosphine substituted with a IMS group (Scheme 8.2.1) (4). 

Reaction of 3 with 1 equivalent of a phosphine results in formation of "phosphine-modified catalysts (4). The complex formed from 7r-allyl-nickel chloride, tricyclohexylphosphine, and methylaluminum dichloride (4a) has been isolated and its structure determined crystallographically (see Fig. 1) (57) The phosphine is bonded to the nickel atom, and interaction with the Lewis acid takes place via a chlorine bridge. The bridging chlorine atom is almost symmetrically bound to both the nickel... 

When simple nickel(II) salts are treated with thiols, in most cases stable thiolate-bridged polymers are formed. In a number of cases, treating these polymers with either tertiary phosphines or isocyanides gave mononuclear mixed-ligand complexes (equation 204).1951 These mononuclear complexes, due to the presence of terminal thiolates which possess lone pairs, can further react with nickel(II) and give trinuclear complexes (equation 205).1952... 

A variety of nickel(O) complexes, when treated tvith allyhc electrophiles, afford jt-allyl complexes (see also Houben-Weyl, Vol. E18, pp 64 and 76).l In early studies, tetracarbon-ylnickel(O) was widely employed. However, otving to its extreme toxicity, it is now rarely used. Direct treatment of bis(T] -cycloocta-l,5-diene)nickel(0) (2) with allyl halides such as 20 is now the method of choice for the stoichiometric preparation of nickel-3t-allyl complexes. In the absence of strong donor ligands such as phosphines, halo-bridged dimers (e.g., 21) are t5T3ically obtained (Scheme 12). In the presence of phosphines, monomeric species such as 22 may be obtained. Other less-electrophilic allylic substrates such as allylic ethers and allylic alcohols also serve as precursors to nickel-Jt-allyl complexes in cataljdic procedures. However, these precursors are less widely used than allyl halides in the stoichiometric preparation of the Jt-allyl complexes. 

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