Grubbs nickel

Fig. 6 Grubbs nickel complex bearing sterically encumbered nucleophilic heterocyclic carbene ligand...

Most recently, Grubbs group demonstrated that some neutral salicylaldiminato nickel(II) complexes, whose skeleton structure appears as lb in Figure 1, show catalytic activities rivaling those of the bisimine complexes [9], This potentially opens the door to a new class of catalysts as the active sites derived from these nickel complexes are neutral, thus reducing the ion-pairing problems encountered in the current catalysts. 

The synthesis and reactivity of a series of nickelacyclopentane compounds with a range of tertiary phosphine ligands was reported by Grubbs et ol. Compounds of type 69 were prepared by the reaction of 1,4-dilithiobutane with the appropriate dichlorobis(tertiaryphosphine)nickel(II) complex, and isolated as yellow crystals in ca. 40% yield78 (dppe = bis(diphenyl) (phosphinoethane). 

Grubbs group [31, 32] developed another type of Ni-based catalyst. This neutral Ni-catalyst, based on salicylaldimine ligands, is active in ethene polymerisation without any co-activator and originated from the Shell higher olefin process (SHOP). Shortly thereafter another active neutral P,0-chelated nickel catalysts for polymerisation of ethene in emulsion was developed by Soula et al. [33, 34, 35]. The historical development of single site catalysts is represented in Fig. 1. 

Michalak A, Ziegler T, DFT Studies on the Copolymerization of a-Olefins with Polar Monomers Comonomer Binding by Nickel- and Palladium-Based Catalysts with Brookhart and Grubbs Ligands, Organometallics, 20, 1521-1532 (2001)... 

Poly(para-phenylene) (PPP, 64) is insoluble and infusible and so films of PPP must be made by precursor routes (Scheme 6.19) [105]. The first of these, which was developed at ICI [106, 107], utilizes a radical polymerization of the diacetate 82 to produce a precursor polymer 83 that is thermally converted to PPP. This method produces PPP containing about 15% 1,2-linkages. A totally para-polymer can be made by the method of Grubbs involving the stereoregular nickel-catalyzed living polymerization of the bis(silyl ether) 84 to 85, and then its conversion to 83 [108-110],... 

T. R, Youiikin, E F. Connor, J. I. Henderson, S. K. Friedrich, R. H. Grubbs, and D. A. Bansleben. Neutral, single-component nickel (11) polyolefin catalysts that tolerate heteroatoms. Science, 287 460 462, 2000. 

Recently, Grubbs and co-workers reported the use of neutral salicylaldimine nickel complexes (e.g., complex III) for ethylene polymerizations.A phosphine scavenger (e.g., Ni(COD)2) is used as an activa-... 

Totally stereoregular PPP (i.e. with all 1,4-linkages) has been prepared by Grubbs and coworkers (Scheme 4) by a stereospecific nickel-catalysed polymerisation of a cyclohexadienediol disilylether 9, followed by conversion of the resulting polymer 10 to 1 via the acetoxy-precursor 8 [45-48]. However,... 

Younkin, T.R., Connor, E.F., Henderson, J.I., Friedrich, S.K., Grubbs, R.H. and Bansleben, D.A. (2000) Neutral, single-component nickel (II) polyolefin catalysts that tolerate heteroatoms. Science 287,460-462. Wunderlich, B. (1980) Macromolecular Physics, vol. 3, Academic Press, New York, pp. 275-278. 

Grubbs has studied the analogous nickel complexes and has found that there are three decomposition pathways, one for each of the different intermediates, 14e, 16e, and 18e, that can be formed (Eq. 7.36). An understanding of the reasons for this diversity has only come with a detailed m.o. study. 

The neutral salicylaldimine nickel complexes described hy Grubbs and coworkers (195,196) show unprecedented fimctional group tolerance and are capable of incorporating substituted norbornenes, carbon monoxide, and a-co fimctional olefins into polyolefins with well-defined compositional distributions (eq. 7) (196). Furthermore, ethylene can be homopoljnnerized with these catalysts in the presence of various functional additives including acetone, water, ethyl alcohol, and triethyl amine. In the presence of 1500 equivalents of H2O, polyethylene was produced at a rate of 5.4 x 10 g PE/mol Ni/h. 

Table 2.1 lists some of the mechanistic studies of organic and organometallic reactions reported in the literature by ESI-MS. All sorts of reactions have been successfully explored in the gas phase, such as the Baylis-Hillman reaction [211-213], C-H or N-H activation [214—219], cydopropanation reaction [220], Diels-Alder reactions [221], displacement reactions [222], electrophilic fluorination [223, 224], Fischer indole synthesis [225], Gilman reaction [226, 227], Grubbs metathesis reaction [228-231], Heck reaction [194], methylenation [232], oxidation [233, 234], Petasis olefination reaction [235], Raney Nickel-catalyzed coupling [236], ruthenium... 

Related Reagents. (Diisopropoxymethylsilyl)methylmag-nesium chloride trimethylsilylmethylpotassium (trimethyl-stannylmethyl)lithium trimethylsilylmethyllithium Grubbs catalyst AD-mix or osmium(VIII) tetraoxide cerium(III) chloride nickel(II) acetylacetonate cobalt(II) chloride. 

Books have been published on cyclic polyolefin complexes and metal vapour synthesis, while a review on metal vapour cryochemistry also contains information relevant to the latter. Reviews have also been published on organometallic derivatives of alkenes and ketenes, cationic Rh diolefin complexes, and nucleophilic addition to cationic hydrocarbon complexes. More personalized reviews have appeared by Maitlis on Pd -acetylene chemistry, by Jonas and Kruger on alkali-metal-transition-metal w-complexes, and by Werner on bridged allyl and cyclopentadienyl complexes. Articles by Wilke on homogeneous catalysis, by Vollhardt on metal-mediated approaches to steroid synthesis, by Schrock > on organotantalum chemistry, and by Grubbs on nickel metallocycles also contain material of relevance to r-complexes. 

---