METAL-CARBONYL SYNTHESES .22. LOW-PRESSURE CARBONYLATION OF [MOCL(4)](-) AND [MO(4)](-) - THE TECHNETIUM(I) AND RHENIUM(I) COMPLEXES [NET(4)](2)[MCL(3)(CO)(3)]

Law pressure carbonylation (1 atm) of [MOCl(4)](-) or [MO(4)](-) in the presence of BH3/THF and halides X(-) results in the clean formation of [NEt(4)](2)[MX(3)(CO)(3)] containing monovalent rhenium or technetium (M = Re, Tc, X = Cl, Br). In the case of the radioactive element technetium this low pressure synthesis is an important progress since the potential hazards of traditional high-pressure carbonylations are thus avoided. The complex [NEt(4)](2)[ReBr3(CO)(3)] crystallizes in the space group P-1 with a = 10.166(2), b = 16.393(4), c = 17.243(5) Angstrom, and alpha = 69.27(2), beta = 86.42(2), gamma = 88.61(2)degrees, Z = 4, and V = 2682(1) Angstrom(3). [NEt(4)](2)[MX(3)(CO)(3)] is a versatile precursor compound of other Re(I) and Tc(I) complexes: substitution of the halide ligands by a variety of sigma-donor ligands is facile even under mild conditions. Examples include reactions with CN-(t)Bu to yield quantitatively TcCl(CN-(t)Bu)(2)(CO)(3) and with a tetradentate phosphine ligand to yield the dinuclear complex [Re2Br2(CO)(6)(tetraphos)]. The X-ray structures of both compounds were determined. Dissolution of [NEt(4)](2)[MX(3)(CO)(3)] in water under aerobic conditions results in the unusual organometallic aqua cation [M(OH2)(3)(CO)(3)](+), which species is stable in water for days (IR spectroscopy).