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The reaction of 2‐[bis(2‐methoxy‐phenyl)phosphanyl]‐4‐methyl‐benzenesulfonic acid (a) and 2‐[bis(2′,6′‐dimethoxybiphenyl‐2‐yl)phosphanyl]benzenesulfonic acid (b) with dimethyl(N,N,N′,N′‐tetramethylethylenediamine)‐palladium(II) (PdMe2(TMEDA)) leads to the formation of TMEDA bridged palladium based polymerization catalysts (1a and 1b). Upon reaction with pyridine, two mononuclear catalysts are formed (2a and 2b). These catalysts are able to homopolymerize ethylene and also copolymerize ethylene with acrylates or with norbornenes. With ligand b, high molecular weight polymers are formed in high yields, but higher comonomer incorporations are obtained with ligand a.magnified image

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Since Kagan's seminal studies in 1977, 1 samarium diiodide has become a popular reducing agent in organic synthesis. 2,3 It is used under a variety of conditions to accomplish a wide range of transformations. In many cases, reactivity is enhanced by adding hexamethylphosphoramide (HMPA) to SmI 2 (THF) x . 4 Unfortunately, this most effective and popular additive is highly carcinogenic 5 and alternatives are highly desirable. 6 Several other methods for increasing SmI 2 reactivity have been reported and include the addition of transition metal salts 7 or samarium metal, 8 photolysis, 9 and the design of intramolecular reactions. 10 Recently, in collaboration with the Bochkarev group, we reported the synthesis and structure of the first molecular Tm(II) complex, TmI 2 (DME) 3 . 11 This complex was found to be structurally analogous to samarium diiodide in DME, 12 but it is much more reactive since 4f 13 Tm(II) has a much greater reduction potential than 4f 6 Sm(II). 13 Preliminary studies indicated that this compound was so reactive 12 that it was uncertain if it would be useful as a reagent like SmI 2 (THF) x in organic transformations.To determine if TmI 2 (DME) x 14 was viable as a reagent and if it had utility as an alternative for SmI 2 (THF) x /HMPA, we have examined its reactivity in the coupling of 4-tert-butylcyclohexanone with alkyl halides, Scheme 1. This reaction was used as an assay, since it has been thoroughly studied with samarium diiodide. 15,16 Reactions were carried out 17 in accordance with the samarium Grignard procedure introduced by Curran 16 in which 2 equiv of the lanthanide reagent are added to the alkyl halide and the ketone is added subsequently. Reactions using SmI 2 -(THF) x /HMPA were conducted to ensure that Sm/Tm comparisons could be made under one uniform set of conditions.As shown in Table 1, SmI 2 (THF) x /HMPA gives yields and selectivities for the reaction of phenethyl iodide with 4-tertbutylcyclohexanone under our conditions which are consistent with the literature (entry 1). TmI 2 (DME) x in DME matched these results (entry 2), but without any HMPA present. In contrast, SmI 2 -(THF) x without HMPA is reported to reduce iodides only after extended reaction times in refluxing THF. 2a After establishing that HMPA-free TmI 2 (DME) x was at least equivalent to SmI 2 (THF) x /HMPA, less reactive halides 3d were examined. In our control reactions with 2-phenethyl bromide (entry 3), SmI 2 (THF) x /HMPA required 15 min to change color from the deep purple of Sm(II) to an orange-yellow characteristic of Sm(III). After the addition of 4-tert-butylcyclohexanone, a 65% conversion to 1 and 2 in a 77:23 ratio was found. In contrast, when 2-phenethyl bromide was added to TmI 2 (DME) x (entry 4), the color changed immediately from the emerald green Tm(II) solution to bright yellow. A white/gray precipitate formed

DyI(2) and NdI(2), which may become useful reagents in organic synthesis, can be prepared in up to 50 g quantities in a few hours without using welded tantalum tubes or temperatures over 1000 degrees C by direct reaction of the metal and iodine.