Reactivity of molybdenum and rhenium hydroxo-carbonyl complexes toward organic electrophiles

The hydroxo compounds [Re(OH)(CO)(3)(N-N)] (N-N = bipy, 2a; Me-2-bipy, 2b) were prepared in a biphasic H2O/CH2Cl2 medium by reaction of [Re(OTf)(CO)(3)(N-N)] with KOH. In contrast, when anhydrous CH2Cl2 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)] (2b) 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)- C3H4-Me-2)(CO)(2)(phen)] (1), 2a, and 2b 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)-C3H4-Me-2)(CO)(2)-(phen)}(2)(mu-eta(1)(O),eta(1)(O)-CO3)] (5). In contrast, the reaction of 2a 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)-C3H4-Me-2)(CO)(2)(phen)] (7), [Re[SC(O)NH(p-tolyl)](CO)(3)(Me-2-bipy)] (8a), and [Re[SC(O)NHEt](CO)(3)- (Me-2-bipy)] (8b) were obtained by reaction of I or 2b with the corresponding alkyl or aryl isothiocyanates. In those cases, RNCS was inserted into the M-O bond. The reactions of 1, 2a, and 2b with dimethyl acetylene dicarboxylate (DMAD) gave the complexes [Mo[C(OH)-C(CO2Me)C(CO2Me)-O]-(eta(3)-C3H4-Me-2)(CO)(phen)] (9) and [Re[C(OH)C(CO2Me)C(CO2Me)O](CO)(2)(N-N)] (N-N = bipy, 10 a; Me-2-bipy, 10b). 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 Dew compounds were characterized by a combination of IR and NMR spectroscopy, and for [(Re(CO)(3)(bipy)}(2)(mu-OH)]BF4 (3-BF4), 4, 5, 6, 7, 8b, 9, and 10b, also by means of single-crystal X-ray diffraction.