The synthesis, molecular and electronic structure of cyanovinylidene complexes

Abstract

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Optimised Syntheses of the Half-Sandwich Complexes FeCl(dppe)Cp*, FeCl(dppe)Cp, RuCl(dppe)Cp*, and RuCl(dppe)Cp

“…A more convenient laboratory preparation of FeCl(dppe)Cp* would avoid the use of ultrasonic irradiation, and the isolation and manipulation of air sensitive lithium [52] or pyrophoric potassium [53] pentamethylcyclopentadienides, whilst taking advantage of the ready availability of [FeCl2(dppe)]n. Although [FeCl2(dppe)2]n is commonly prepared from reaction of anhydrous FeCl2 with 1,2-bis(diphenylphosphino)ethane [41,51] it has been recently shown that [FeCl2(dppe)]n can be conveniently synthesised in high yield (ca. 80%) by treatment of FeCl2•4H2O with 1,2-bis(diphenylphosphino)ethane in acetone / chloroform mixtures [44,54] thereby avoiding the tedious preparation, or considerably greater cost, of anhydrous FeCl2 (As of March 2016 FeCl2•4H2O costs ~A$65 per mole and FeCl2 ~A$390 per mole, prices from Sigma Aldrich).…”

“…Potassium pentamethylcyclopentadienide is produced in situ by reaction of pentamethylcyclopentadiene with potassium metal in refluxing toluene, [53] and precipitates from the reaction as a fine white powder. The potassium pentamethylcyclopentadienide so produced is not isolated, but rather the reaction mixture is allowed to cool, diluted with a further portion of toluene and treated with thoroughly dried [FeCl2(dppe)]n. [44,54]…”

“…More recently, several groups have reported syntheses of FeCl(dppe)Cp using methods closely related to that originally described by Mays, [41] and involve treatment of [FeCl2(dppe)]n with a metal cyclopentadienide (M = Li [43,51] or Tl [44] )…”

“…Two points are worth highlighting from these more modern investigations: as detailed in the discussion of FeCl(dppe)Cp* one report notes that conduction of the reaction initially at −78 °C suppresses the formation of ferrocene derivatives; [51] the use of a sub-stoichiometric amount of thallium cyclopentadienide also limits the formation of ferrocene, with the excess [FeCl2(dppe)2]n being readily removed by filtration together with thallium chloride from the reaction mixture during work-up. [44] In elegant recent studies, Bouwman [61] and Whiteley [62] Our efforts towards producing FeCl(dppe)Cp in a convenient laboratory setting have considered approaches from [FeCl(dppe)]n and metal cyclopentadienide sources. The use of thallium cyclopentadienide in the manner originally described by Mays and Sears [41] and later optimized [44] is highly effective, but the use of toxic thallium reagents is less than desirable.…”

“…However, despite the demonstrable utility of both FeCl(dppe)Cp* and RuCl(dppe)Cp* as valuable starting materials, the closely related cyclopentadienyl derivatives FeCl(dppe)Cp [41] and RuCl(dppe)Cp [42] which offer intermediate electron donor capacity and smaller steric bulk at the metal centre than the Cp* derivatives have been less thoroughly exploited. [43][44][45][46][47] In part the restricted use of these compounds might be attributed to the limitations in synthetic routes to them. Here we summarise the known synthetic routes to the family of complexes MCl(dppe)(η 5 -C5R5) (M = Fe, Ru; R = H (Cp), CH3 (Cp*)), and describe in detail multi-gram scale procedures which afford these compounds in two-pot processes from commercial FeCl2•4H2O or RuCl3•xH2O.…”