Kinetics of the reduction of Co(o-phen)33+ by the metal carbonyl anions Re(CO)5-, Mn(CO)4L- (L = CO, PEt3, PBu3, PPh3), Co(CO)4-, CpMo(CO)3- and CpFe(CO)2- (Cp = .eta.5-C5H5, o-phen = o-phenanthroline). Structural determinations of [PPN+][Mn(CO)5-] and [PPN+][Mn(CO)4(PEt3)-].cntdot.THF