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The exposure of CrCl 2 (THF) 2 to 1 equiv. of TEMPO and 1 equiv. [TEMPO]Na afforded (η 2 -O,N-TEMPO) 2 CrCl (1, 67%); addition of [TEMPO]Na to 1 yielded (η 2 -O,N-TEMPO) 2 Cr(TEMPO) (2). Both 1 and 2 exhibit pseudo-pentagonal planar (PPP) geometry, instead of myriad alternatives. Calculations and spectral studies suggest the solid-state geometry persists in solution. 

Metathetical syntheses of (silox)2M(THF)2 (1-M, Fe, Co), [(silox)3M]Na(THF)2 (2-M, Fe, Co), and (silox)3Fe(THF) (3) are presented, as are X-ray structural studies of 1-Co, 2-Fe, and 2-Co. Exposure of these complexes to 1.1.1- propellane (111P, C5H6) and 1,3-dehydroadamantane (AdP), which are known progenitors of ROMP-active alkylidenes with ruthenium, failed to elicit similar reactivity. A total of 28 complexes were subjected to 111P in attempts to make “Fe(IV)” alkylidenes capable of some form of olefin metathesis with no success. At best, catalytic ring-opening to 3-exo-methylene cyclobutylidene was evidenced. The addition of triphenylboron as a Lewis acid failed to aid in metal complex formation of the propellanes, but an unusual rearrangement of AdP was noted. In addition, 2-Fe catalyzed the conversion of 111P to 3-exo-methylene cyclobutylidene, which added twice to Ph3B, affording a structurally characterized product, Ph(κ-CH=CMeCH2BPh