Synthesis, Spectroscopic Characterization, and Crystal Structure Determination of Cationic [(Cyclopentadienyl)dicarbonyliron](alkynyl)‐aminocarbene Complexes

Abstract

Iron (2-methoxyviny1)aminocarbene complexes (Alkynoy1)iron complexes 1, Cp(C0)2Fe(O=CC=CR) (R = plexes 3, [Cp(CO),Fe(C(NHR')C=CR)+][PF,1, or (2-meth-CH,, Ph, SiMe3), were synthesized by applying a mixed an-oxyviny1)aminocarbene complexes 5. The spectroscopic prohydride procedure and transformed into the cationic meth-perties of the new complexes are discussed. The (alkyny1)-oxycarbene complexes 2, [Cp(CO) Previously we have reported on a convenient access to new alkynyl-substituted acyliron complexes l['l]. The corresponding electrophilic alkynyl-substituted methoxycarbene complexes 2 were synthesized (Scheme l), and the aminolysis with primary amines was studied. Thus, substitution at C-1 was observed exclusively at ambient temperature. A series of aminocarbene complexes 3 were obtained (Table l), and (2-methoxyviny1)aminocarbene complexes 5a, b (Scheme 2) were isolated from aniline and 2a, c, owing to the addition of the released methoxy group to the alkynyl residue. Even though a few electrophilic iron aminocarbene complexes have been prepared in the past, only very few structural data are available about this class of carbene complexes, e.g. synlunti isomer formation and ratio'6-9]. For structure determination a selected set of previously unknown simple alkyl-and aryl-substituted aminocarbene complexes 4, prepared from primary amines, was synthesized for comparison. In addition, the structures of two (alkyny1)aminocarbene complexes were assigned by X-ray crystallography. In this paper we give a detailed description of the syntheses of these complexes, published before in a preliminary communication ["], and their characterization. Results and DiscussionThe preparation of acyliron complexes 1 from carboxylic acid chlorides and the ferrates (CSH,)(C0)2FeM (M = Na, K) is well documented[l21. However, any attempts to obtain side chain-functionalized complexes in higher yield or propargylic acid derivatives failed. Therefore, we developed an alternative strategy using isobutyl chloroformate-derived mixed anhydrides of the carboxylic acids. This one-pot procedure provides access to the acyl complexes 1 in high yield after chromatographic purification. Results are given in Scheme I (see also Experimental). The spectroscopic properties of the alkynyl-substituted derivatives 1 are similar to those of other except the 13C-NMR acyliron signal [Cp(CO)2Fe-C= 0 1 being shifted upfield to about 6 = 239. In the IR spectra the iron acyl v(C0) absorptions are shifted to 1587-1583 cm-' and are about 40-50 cm-' lower than for alkyl-, aryl-, or alkenyl-substituted acyl complexes [Cp(CO)2Fe(O=CR)][61.The acyl complexes 1 were further converted into cationic methoxycarbene complexes 2 (Scheme 1). Thus, [(Me-O),CH+][PF;] was generated in CH2C12 at room temperature from trimethyl orthoformate and (Ph,CHC][PF;][lll. Solid acyl complexes were added neat to the methylating reagent, whereas oils were dissolved in CH2ClZ prior to addition to the reaction mixture by means of a cannula. The

Regioselective Nucleophilic Additions to Diiron Carbonyl Complexes Containing a Bridging Aminocarbyne Ligand: A Synthetic, Crystallographic and DFT Study

“…The reactions of 5a with primary amines result in selective aminolysis, to afford the new aminocarbyne/aminocarbene complexes [Fe 2 (µ‐CNMe 2 )(µ‐CO)(CO){C(Me)NH(R)}(Cp) 2 ][SO 3 CF 3 ] (R = i Pr, 6a ; R = Et, 6b ) in good to high yields. [11a], Instead, NHEt 2 acts as a base towards 5a , and demethylation effectively occurs to regenerate the parent compound [Fe 2 {µ‐CN(Me) 2 }(µ‐CO)(CO){(C=O)Me}Cp 2 ] (Scheme ). When 6b is treated with NaBH 4 , the aminocarbene unit dissociates and the bridging hydride complex [Fe 2 (µ‐CNMe 2 )(µ‐H)(CO) 2 (Cp) 2 ] is obtained as the prevalent product …”

Recent chemistry of the η5-cyclopentadienyl dicarbonyl iron anion

“…(Scheme 71). Rück-Braun et al extended [46,131] their procedure to other mixed anhydrides (Scheme 72) and reacted them with primary amines affording [(2-aminoethenyl)carbene]iron complexes.…”

Electrophilic Half-Sandwich (Carbene)metal (Metal = Fe, Ru, Os) Complexes: Recent Developments in Synthesis and Applications

“…This is for example the case for the ethylidene complex [Fe(C 5 Me 5 )(dppe)(=CHMe)][CF 3 SO 3 ] ( 49 ) in which the hydrogen atom is directed towards the C 5 ring 13. The aminocarbene complex 14a was found to exist in an “upright” conformation, whereas the related derivative 14b shows an “orthogonal” conformation 10b. Moreover, it has been shown that 14a and 14b exist in the solid state as anti isomers with respect to the C−N bond.…”