Demetalation of Tricarbonyl(cyclopentadienone)iron Complexes Initiated by a Ligand Exchange Reaction with NaOH—X-Ray Analysis of a Complex with Nearly Square-Planar Coordinated Sodium

Abstract

The [221] cycloaddition of two alkynes and carbon monoxide in the presence of pentacarbonyliron represents a useful method for the construction of five-membered ring systems. [1, 2] Applications of the resulting tricarbonyl(h 4 -cyclopentadienone)iron complexes to organic synthesis are feasible by demetalation to the free cyclopentadienones. This transformation was achieved by oxidation with trimethylamine Noxide. [1,3] Recently we reported a novel method for the demetalation of tricarbonyl(diene)iron complexes by a photolytically induced exchange of the carbonyl ligands by acetonitrile. [4] Herein we describe an alternative procedure for the ligand exchange at tricarbonyl(h 4 -cyclopentadienone)iron complexes and the subsequent demetalation in the air.Tricarbonyl(h 4 -cyclopentadienone)iron complexes undergo a transformation similar to the Hieber reaction. [5] Thus, reaction of complex 1 a with aqueous NaOH in THF leads to an equilibrium of the corresponding hydrido complexes 2 a and 4 a in a ratio of about 13:1 (Scheme 1). Tricarbonyl(cyclohexa-1,3-diene)iron complexes are inert under these conditions. Addition of H 3 PO 4 affords 2 a in 94 % yield, while reaction with NaH shifts the equilibrium towards the salt 4 a Scheme 1. a) 1m NaOH/THF (1/2); b) C 5 H 11 I; c) H 3 PO 4 ; d) air, daylight, Et 2 O/THF, Na 2 S 2 O 3 , Celite, 3 h; e) NaH, Et 2 O/THF.(82 % yield). Reaction of the hydrido complex 2 a with 1-iodopentane provides the iodo complex 3 a in 98 % yield. A related transformation is reported for the hydrido complex [CpFe(CO) 2 H]. [6] The addition of 1-iodopentane after the reaction of 1 a with NaOH affords an equilibrium of the iodo complexes 3 a and 5 a that is shifted again by addition of H 3 PO 4 or NaH, respectively. Preparation of the iodo complex 3 a without isolation of the intermediate hydrido complex 2 a increases the yield (98 % based on complex 1 a).The 13 C NMR and the IR data of the hydrido complex 2 a and the iodo complex 3 a suggest an h 5 -coordinated hydroxycyclopentadienyl ligand for both compounds. [7] A characteristic structural feature of the hydrido complex 2 a is the unsymmetrical arrangement of the coligands, which is apparent from two CO signals in the 13 C NMR spectrum. This assignment was confirmed by an X-ray structure determination of complex 2 a (Figure 1), [8] which shows an h 5 -coordinated hydroxycyclopentadienyl ligand and a C1ÀO1 bond length of 1.366 . [9] A loss of C S symmetry was also found for the hydrido complex 4 a from the 13 C NMR spectrum, which exhibits the two signals for the carbonyl ligands and a peak at d 170.13 for C1. [7] Figure 1. Molecular structure of 2 a in the crystal. Selected bond lengths []: FeÀC1 2.

(Cyclopentadienone)iron Shvo Complexes: Synthesis and Applications to Hydrogen Transfer Reactions

“…C19H26NaOSi requires 321.1645); νmax 2953,2930,2856,1490,1463,1471,1443,1330,1251,1094,1068,990,836,824,810,775,754, 689 cm -1 ; 1 H NMR (300 MHz, CDCl3) δ 7. 2H,Ar),3H,Ar), 4.64 (q, J = 6.8 Hz, 1H, CCH(CH3)O), 4.41 (d,J = 15.8 Hz,1H,CCH2O),4.33 (d,J = 15.8 Hz,1H,CCH2O),1.55 (d,J = 6.8 Hz,3H,(CCH(CH3) 128.43, 128.23, 122.54, 101.95, 89.68, 88.18, 87.25, 85.89, 64.36, 56.58, 26.05, 22.02, -4.68; m/z (ESMS+) 321 [M + Na] + . -2-propyn-1-yloxy(3-(trimethylsilyl)prop-2-yne), 23b 13e.…”

A new class of PN3-pincer ligands for metal–ligand cooperative catalysis

“…ionic hydrogenation [36,37]. Analogous Fe catalysts were studied by Casey and Guan with the Knölker complex which offered excellent tolerance to functional groups such as halides, nitro groups, benzyl ethers, and cyclopropyl rings [38,39]. One unique type of metal-ligand cooperation via aromatization-dearomatization of the central pyridine on pyridine-based pincer complexes via deprotonation-reprotonation of one of the pyridylic CH 2 arms was recently demonstrated by Milstein and co-workers [40][41][42].…”

Asymmetric catalysis using iron complexes – ‘Ruthenium Lite’?

“…This 35 remains to be tested experimentally. Although a racemic process, a very significant breakthrough was reported in 2007 by Casey and Guan, 24,25,3 who found that the known 26,27 cyclopentadienyl iron hydride complex 11, itself prepared from the iron tricarbonyl cyclone complex 12, was effective at the catalysis of carbonyl and imine 45 hydrogenation under relatively mild conditions (Figure 4). There are analogies in the speculated mechanism of the catalytic cycle to that of the reactions catalysed by the ruthenium-based Shvo catalyst 13, which has also been extensively studied by complex.…”

“…There was however evidence of the formation of diiron bridging complexes in attempted reactions with 37 and 38, as evidenced by characteristic 1H 55 NMR shifts for the iron hydride (ca -22--23). In contrast, 11 exhibits an equivalent hydride shift at -13.05, 27 which is indicative of a stable monomeric species, presumed to be of higher reactivity in hydride transfers. The preference for monomer formation in the case of 11 is believed to be due to 60 the high steric demand of the trimethylsilyl groups.…”