This report examines the replacement of the imine and pyridine functionalities of the ubiquitous bis(imino)pyridine ligand with various heterocycles. The synthesis of a new class of ligand based around thiazole is described; 2,4-bis [1-(arylimino)ethyl]thiazole (aryl = Ph, 1a; Dipp, 1b) and 2,5bis [1-(arylimino)ethyl]thiazole (aryl=Ph, 1c; Dipp, 1d) have been prepared in good yield and fully characterized. The coordination chemistry of these ligands with chromium, iron, and cobalt is explored, and the potential of these complexes as ethylene oligomerization initiators is assessed. The chromium complex 2a shows an extremely unusual alternating distribution of higher R-olefin products, which has been previously observed on only one occasion. Both series of products, C 4n and C 4nþ2 , show Schulz-Flory behavior but with distinctly different k values. The new ligand 2,5bis[1-(phenylimino)ethyl]-1-methylpyrrole (1e) is reported along with the attempted synthesis of some corresponding iron complexes. The complexation of chromium by 2,5-bis-(phenyliminomethyl)thiophene (1f) is also described, and this material was screened for ethylene oligomerization activity, detailed studies indicating that the ligand may be labile under catalytic conditions. A number of other known heterocyclic ligands incorporating pyrazolyl and benzimidazole functionalities have also been explored with iron, and for the first time their potential to facilitate ethylene oligomerization was assessed. All complexes have been tested via activation with MMAO-3A and AlEt 3 /[Ph 3 C][Al(O t Bu F ) 4 ].

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Reaction of 1 or 2 equiv of Ph2PCl with PhP(N(H)R)2 (R = n-propyl) yields Ph2PN(R)P(Ph)N(R)H (1) or Ph2PN(R)P(Ph)N(R)PPh2 (2), respectively. In contrast, reaction of 1 or 2 equiv of Ph2PCl with PhP(N(H)R)2 (R = isopropyl) yields exclusively Ph2PN(R)P(Ph)N(R)H (3), even under more forcing conditions. Low-temperature NMR spectroscopy and a conformational analysis of Ph2PN(iPr)P(Ph)N(iPr)H (3) reveal the lowest energy conformer to have a close N−H···P interaction of 2.95 Å, which we speculate may hinder further reactivity of this molecule. Reaction of 3 with [Cr(CO)6] yields [Cr(3)(CO)4] (5), which has been structurally characterized. Coordination of ligand 3 facilitates its conversion to Ph2PN(iPr)P(Ph)N(iPr)PPh2 (4) while bound to chromium, yielding the complex [Cr(4)(CO)4] (6), which has also been structurally characterized. Ligands 1 and 2, when reacted in situ with [Cr(acac)3] (acac = acetylacetonate) and modified methylalumoxane, and complexes 5 and 6, when activated with Ag[Al(OC4F9)4] and triethylaluminum, are moderately active and selective catalysts for the selective oligomerization of ethene to 1-hexene and 1-octene.

The use of AlEt 3 (TEA) in combination with [Ph 3 C][Al(O t Bu F ) 4 ] (TA) for the activation of a range of bis(imino)pyridine complexes of vanadium, chromium, iron, and cobalt is reported. It is shown that this activator combination successfully replaces MMAO, in some cases showing improvements in terms of activity and productivity. Furthermore, when activities and productivities are considered in terms of the aluminum center (MMAO vs TEA), the true cost driver in the commercialization of most catalyst systems, then in nearly all cases a significant improvement is seen.

[reaction: see text] Homochiral beta-fluorinated gamma,delta-unsaturated carboxylic acids with an allylic fluorinated stereogenic center are available from the corresponding enantiopure allylsilanes. The key step for introduction of the fluorine substituent is an electrophilic fluorodesilylation reaction carried out in the presence of Selectfluor. Reduction of the resulting beta-fluorinated pentenoic acid into the corresponding fluorinated alcohol was also performed leading to the formation of an enantiopure second-generation fluorinated building block.