J. CHEM. SOC., CHEM. COMMUN., 1995 463 z Heterolytic zyxwvuts C-0 Cleavage in Arylethers Activated by zyxw [ Fe(q5-C5H5)]+ Frangoise Moulines," Laurent Djakovitch,a Marie-Helene Delville-Desbois,a Frangis Robert,&Pierre Gouzerhb and Didier Astruc*a zyxwvutsrq a Laboratoire de Chimie Organique et Organometallique, URA CNRS No. 35, Universite Bordeaux zyxw I, 351 Cours de la Liberation, 33405 Talence Cedex, France zyxwvut b Laboratoire de Chimie des Metaux de Transition URA CNRS No. 419, Universite Pierre et Marie Curie, Place Jussieu, BBtiment 74, 75252 Paris Cedex 05, France The C-0 bond of Fe(q5-C5H5)+ complexes of aryl ethers is cleaved smoothly by reaction of ButOK in THF or KOH in DME, yielding n-phenate complexes; transetherification can also be achieved in situ at room temperature. zyx The activation of aromatics by the cationic moiety [M(75- CSHs)]+ (M = Fe or Ru) is well known for nucleophilic addition or and benzylic deprotonation reaction^.^ We now report a new type of aromatic reaction which is also activated by the [Fe(qS-C5H5)]+fragment : heterolytic C-0 cleavage of aryl ethers whose driving force is the formation of n-phenate In the course of our project to develop the chemistry of organometallic molecular trees with multiple redox centres, we have serendipitously found that this cleavage reaction12 is effected by ButOK or KOH (Scheme 1). When KOR3 reacts with any complex of type 1 in DME (R3 = H) or THF (R3 = But) from -50 to 25 "C in the presence of one equiv. KBr or, even better, [Bu4N]+[PF6]-(Scheme 1, path i, the zwitterion 2 is obtained as a monohydrate,? after work-up [as indicated by the elemental analyses of 2b (R5 = H)] featuring H bonding. The latter is also apparent in the ORTEP of the X-ray crystal structure of 2c (Fig. 1) which shows a flat phenoxide ligand with a C-0 distance of 1.25 A and an angle between the C(1)-0 vector and the ligand plane of 1.55O.8 The parent complex 2a was previously obtained by deproton- ation of [Fe(y5-CsH5)(C6H@H)]+and formulated as an oxo- cyclohexadienyl complex.§ The solution structure is oscillating between the two forms [two mesomeric forms or two tautomers interconvertingmore rapidly than the IR time scale (1013 s-1) as shown by the IR and NMR datal.1 The complexes 2 are stable except compound 2a which is partly decomplexed in the course of the cleavage reaction (only ca. 10% yield of 2a was obtained along with extensive formation of PhOK). We find that all the complexes 2 exhibit a strong infrared absorbtion at YCO 1545 cm-1 (film) inconsistent with a full double bond. Likewise, the 13C NMR 6c- chemical shift is located zyxwvutsrq ca. 150 (CD3CN-DZ0) whereas 6c=o would be expected at ca. 190. The addition of Na+PF6- to acetone solutions of complexes 2 before removal of solvent causes strong changes in the IR spectra (film). In particular, the intensity of the YC-0 bond at 1545 cm-l is R5 R5 I R5 2 '. ii zyxwvutsrqpon 3 b R2 = C(allyl)s, R5 = H c R2 = H, R5 = Me Scheme 1 R1 = alkyl or phenyl; R2 = H or alkyl; R3 = H or But; R4 = alkyl, allyl or benzyl; R5 = H or Me; counter ion = PF6-. Reagents and conditions: i, DME (R3 = H) or THF (R3 = But), -50 "C + +20 "C, ii, DME (R3 = H) or THF (R3 = But), room temp; iii, DMF, KzCO3 (1 equiv.), room temp. strongly diminished whereas the bond corresponding to Y ~ - ~ at 1265 cm-1 is strongly increased. This indicates the formation of the hexahapto phenate complex in which the phenate oxygen is coordinated to Na+. 1H NMR spectra of CD3CNor CD3COCD3 solutions of the complexes 2a-b (but not 2c) give very broad patterns, which progressively sharpen upon addition of D20 until the signals become sharp at CD3COCD3 :D20 1 : 1 (or CD3CN: D2O 1 : 1). We believe these effects are due to intermolecular ion pairing involving the negatively charged oxygen atom (cf. the dimeric interaction in Fig. 1) inhibiting rotation of the arene ring about the (y5-C5H5)-Fe-arene axis. Protonation of 2a to give the phenol complex is achieved using CF3C02D, the (75-C5H5) signal in 1H NMR being shifted from 6 4.5 to 5. In summary, the stereoelectronic features of the phenate ligand strongly depend on the presence of solvent molecules giving rise to dimeric interaction and on potential coordination of the phenate oxygen to a metal. Alkyl or phenyl groups can be cleaved from 1 by the nucleophile. For instance, a 61% (resp. 42%) yield of 2b is obtained from lb, 1 equiv. ButOK and 1 equiv. [Bu4N]+[PF6]- (resp. KBr) in THF. These mild cleavage conditions strongly contrast with the drastic conditions required (200 "C, 10% ,'. . A ," , ,%," Fig. 1 CAMERON drawing of part of the molecular structure of 2c showing the hydrogen bonds. Owing to 0H.a.O hydrogen bonds between the water solvent molecule and the phenoxide ligand, the latter is disordered over two positions with 76 and 24% occupancies. For clarity, only one position of the phenoxide ligand has been drawn. Selected interatomic distances (A): Fe- C( 1) 2.269(9), Fe-C(2) 2.14( l), Fe-C(3) 2.09(2), Fe-C(4) 1.96(5), Fe-C(5) 2.05(2), Fe-C(6) 2.07( l), mean Fe-C(7-11) 2.043(6), C(1)-0(1) 1.250(1). Table 1 Transetherification conditions (Scheme 1, path ii): 20 OC, 1-3 days; (3 mol of KOR3 and 3 mol of R4Br per mol of 1 (PF6- salt); reactions with R41 gave close yields. Reported yields of iron complexes were obtained after work-up and purification R' R4 R3 Yield 3 (%) Me allyl H 71 Me benzyl H 76 (CH2)3Ph benzyl H 71 Ph allyl H 79 Ph benzyl But 81 Published on 01 January 1995. Downloaded by University of Illinois at Chicago on 27/10/2014 05:26:51. View Article Online / Journal Homepage / Table of Contents for this issue