ANIONIC GROUP-6B METAL-CARBONYL HYDRIDES AND FORMATES - CHEMISTRY RELEVANT TO CATALYSIS OF THE WATER GAS SHIFT REACTION BY GROUP-6B METAL HEXACARBONYLS
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The reaction of cryptand (kryptofix-222) solubilized KOH with the group 6B metal hexacarbonyls in aprotic solvents to afford the M(CO)6H anions is described. Subsequent facile insertion reactions of these hydridic metal complexes with CO2, COS, and CS2 have provided routes to the corresponding metalloformate, -thioformate, and -dithioformate derivatives. Alternatively, the M(CO)5O2CH derivatives were synthesized from the M(CO)5Y (Y = Cl, I) anions and TlO2CH. These salts were all fully characterized by 13C and 1H NMR and infrared spectroscopy. The bonding mode in the thioformate species was shown to be through the sulfur atom as revealed by X-ray crystallography on the chromium analogue. Crystals of [PPN]-[Cr(CO)5SC(O)H] were found to belong to the triclinic space group [formula omitted] with a = 12.671 (5) , b = 12.880 (5) , c = 15.356 (6) , = 108.01 (3), = 119.61 (3), = 97.48 (3), Z = 2. R = 4.0% for 5811 reflections with I > 3(I). Decarboxylation of the M(CO)5O2CH derivatives to provide M(CO)5H and CO2 was observed, with the Cr(CO)6O2CH species undergoing CO2 extrusion much more readily than its tungsten counterpart. This decarboxylation process was shown to proceed via CO dissociation; i.e., it was inhibited in the presence of carbon monoxide. Unlike their formato analogues, the thioformate derivatives displayed no tendency to extrude COS or CS2 with concomitant HM(CO)5 formation. 13C-labeling experiments demonstrated that the intermediate afforded from OH addition to M(CO)6, M(CO)6COOH, and its structural isomer, M(CO)5O2CH, do not interconvert by an intramolecular process. A discussion of the roles of M(CO)5COOH and M(CO)5O2CH intermediates in the foremost mechanistic step in the catalysis of the water gas shift reaction by group 6B metal hexacarbonyls in alkaline media is included. 1982, American Chemical Society. All rights reserved.
