Treatment of Na4[M(CO)4 with 2 equiv of Ph3SnCl provides approximately 50% yields of [Et4N]2-[(Ph3Sn)2M(CO)4] for M = Cr and W and very low yields for M = Mo. The reaction of L2M(CO)4) where L2 = norbornadiene, cyclooctadiene, tetramethylethylenediamine, or ethylenediamine (M = Cr, Mo, W), with 2 equiv of Ph3SnLi is a more facile and often higher yield route (60-70% for M = Cr, Mo; 35% for M = W) to the same dianions. These materials react with Ph3SnCl to provide 30-40% yields of [Et4N][(Ph3Sn)3M(CO)4], in which Cr, Mo, and W are seven-coordinate. Reactions of [Et4N]2-[(Ph3Sn)2M(CO)4] (M = Cr, Mo) with acetic acid, [Me2NCCl2]Cl, and methyl iodide in acetonitrile provide 30-40% yields of [Et4N][H(Ph3Sn)2M(CO)4], containing seven-coordinate metals, trans-Ph3Sn(CO)4M蠁 CNMe2, and [Et4N][(Ph3Sn)M(CO)4(CH3CN)], respectively. The coordinated acetonitrile in the latter compounds is slowly displaced by PPh3 in acetonitrile at 25 C to give 35-50% yields of [Et4N]-[Ph3SnM(CO)4(PPh3)]. All of these new materials are characterized by elemental analyses and IR and 1H NMR spectra.