Anionic group 6B metal carbonyl hydrides and formates. Chemistry relevant to catalysis of the water gas shift reaction by group 6B metal hexacarbonyls

Article abstract of DOI:10.1021/om00072a026

The reaction of cryptand (kryptofix-222) solubilized KOH with the group 6B metal hexacarbonyls in aprotic solvents to afford the M(CO)₅H^- anions is described. Subsequent facile insertion reactions of these hydridic metal complexes with CO₂, COS, and CS₂ have provided routes to the corresponding metallofonnate, -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 P1? with a = 12.671 (5) ?, b = 12.880 (5) ?, c = 15.356 (6) ?, α = 108.01 (3), = 119.61 (3), 7 = 97.48 (3), Z = 2. R = 4.0% for 5811 reflections with / 3r(/). Decarboxylation of the M(CO)E02CH" derivatives to provide M(CO)6H and C02 was observed, with the Cr(CO)s02CH species undergoing C02 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 formate 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)5COOH", and its structural isomer, M(CO)502CH, do not interconvert by an intramolecular process. A discussion of the roles of M(CO)6COOH and M(CO)502CH 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.