Reactivity of Molybdenum and Rhenium Hydroxo‐Carbonyl Complexes toward Organic Electrophiles

Abstract

The hydroxo compounds [Re(OH)(CO)(3)(N-N)] (N-N=bipy, 2 a; Me(2)-bipy, 2 b) were prepared in a biphasic H(2)O/CH(2)Cl(2) medium by reaction of [Re(OTf)(CO)(3)(N-N)] with KOH. In contrast, when anhydrous CH(2)Cl(2) was used, the binuclear hydroxo-bridged compound [[Re(CO)(3)(bipy)](2)(mu-OH)]OTf (3-OTf) was obtained. Compound [Re(OH)(CO)(3)(Me(2)-bipy)] (2 b) reacted with phenyl acetate or vinyl acetate to afford [Re(OAc)(CO)(3)(Me(2)-bipy)] (4) and phenol or acetaldehyde, respectively. The reactions of [Mo(OH)(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (1), 2 a, and 2 b toward several unsaturated organic electrophiles were studied. The reaction of 1 with (p-tolyl)isocyanate afforded an adduct of N,N'-di(p-tolyl)urea and the carbonato-bridged compound [[Mo(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)](2)(mu-eta(1)(O),eta(1)(O)-CO(3))] (5). In contrast, the reaction of 2 a with phenylisocyanate afforded [Re(OC(O)NHPh)(CO)(3)(bipy)] (6); this results from formal PhNCO insertion into the O-H bond. On the other hand, compounds [Mo[SC(O)NH(p-tolyl)](eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (7), [Re[SC(O)NH(p-tolyl)](CO)(3)(Me(2)-bipy)] (8 a), and [Re[SC(O)NHEt](CO)(3)(Me(2)-bipy)] (8 b) were obtained by reaction of 1 or 2 b with the corresponding alkyl or aryl isothiocyanates. In those cases, RNCS was inserted into the M-O bond. The reactions of 1, 2 a, and 2 b with dimethylacetylenedicarboxylate (DMAD) gave the complexes [Mo[C(OH)-C(CO(2)Me)C(CO(2)Me)-O](eta(3)-C(3)H(4)-Me-2)(CO)(phen)] (9) and [Re[C(OH)C(CO(2)Me)C(CO(2)Me)O](CO)(2)(N-N)] (N-N=bipy, 10 a; Me(2)-bipy, 10 b). The molecules of these compounds contain five-membered metallacycles that are the result of coupling between the hydroxo ligand, DMAD, and one of the CO ligands. The new compounds were characterized by a combination of IR and NMR spectroscopy, and for [[Re(CO)(3)(bipy)(2)(mu-OH)]BF(4) (3-BF(4)), 4, 5, 6, 7, 8 b, 9, and 10 b, also by means of single-crystal X-ray diffraction.

Dehydrogenative Addition of Aldehydes to a Mixed NHC-Osmium-Phosphine Hydroxide Complex: Formation of Carboxylate Derivatives

“…Complex 1 reacts with n-propanal, acrolein, cinnamaldehyde, and benzaldehyde to give the carboxylate-hydride-alkylidyne derivatives [OsH(κ 2 -O 2 CR)(CPh)(IPr)(P i Pr 3 )]OTf (R = Et (2), CHCH 2 (3), CHCHPh (4), Ph (5)) and H 2 . Complexes 2, 4, and 5 afford the alkylidenes [Os(κ 2 -O 2 CR)(CO)(CHPh)(IPr)(P i Pr 3 )]OTf (R = Et (6), CHCHPh (7), Ph (8)) under a CO atmosphere.…”

A Theoretical Study on the Reactivity of a Rhenium Hydroxo‐Carbonyl Complex Towards β‐Lactams

“…A relative permittivity of 8.93 was assumed in the calculations to simulate dichloromethane which was the solvent used experimentally in related reactions between [Re(OH)(CO) 3 (Me 2 -bipy)] and several organic electrophiles. [15][16][17] The computational scheme chosen in this work is similar to that used in a theoretical study on the reactivity of [Re(OH)(CO) 3 -(N 2 C 2 H 4 )] towards phenyl acetate, [45] wherein the validity of the B3LYP mechanistic predictions compared with X-ray experimental data and more sophisticated quantum-chemical computations was confirmed. Thus, a similar trend could be expected for the present investigation.…”

“…The computational investigation was performed with the simplified complex [Re(OH)(CO) 3 (N 2 C 2 H 4 )] (N 2 C 2 H 4 =HN=CH-CH=NH) which was chosen to mimic the one used experimentally in the reactions with esters and other organic electrophiles [15][16][17] and to minimise the computational time. Besides, several theoretical studies have demonstrated the adequacy of replacing bidentate ligands such as phenanthroline (phen) or bipyridine (bpy) by the diimine (HN=CH-CH=NH).…”

“…[4,[13][14][15][16][17][18][19][20][21][22][23] In particular, it has been reported that the hydroxo complex [Re(OH)(CO) 3 (Me 2 -bipy)] (Me 2 -bipy = 4,4Ј-dimethyl-2,2Ј-bipyridine) reacts with a variety of organic electrophiles such as carbon disulfide, esters, aryl isocyanates, alkyl/aryl isothiocyanates, dimethyl acetylenedicarboxylate, ketenes, maleic anhydride and rac-lactide. [15][16][17] Some of these processes evolve through the cleavage of a single C-O bond [15,16] to form metal-carboxylate products which are subsequently demetalated by reaction with triflic acid to afford the corresponding free carboxylic acids. [16] Although it is well-known that an amide is less reactive than an ester, it would be interesting to investigate the reactivity of the above-mentioned complex towards β-lactams, an important class of cyclic amides, given that the cleavage fonato group is crucial for the cleavage of the β-lactam N1-C2 bond by the Re complex thanks to the interaction of the sulfonato group with the hydroxy and bidentate ligands of the complex.…”

The Importance of a Conformational Equilibrium on the Reactivity of Molybdenum and Rhenium Hydroxo−Carbonyl Complexes toward Phenyl Acetate: A Theoretical Investigation

“…[26][27][28][29][30][31][32][33][34] Recent experimental studies have reported the synthesis of the [Mo(OH)(η 3 -C 3 H 4 -Me-2)(CO) 2 (phen)] and [Re-(OH)(CO) 3 (Me 2 -bpy)] complexes 27,28,32 and their reactivity toward esters and other organic electrophiles. 31,32,34 It is interesting to note that the reactivity of the molybdenum hydroxocarbonyl complex toward phenyl acetate is larger than that of the rhenium hydroxo-carbonyl complex. 32 The former reaction is complete in 8 h at room temperature in dichloromethane solution, while the latter one needs 20 h.…”