Redn. of the metal-metal-bonded complex FvW2(CO)6 (Fv = fulvalene) generated the dianion FvW2(CO)62-. An x-ray crystallog. anal. of [Et4N+]2[FvW2(CO)6]2- showed the dianion to contain a planar Fv ring system bonded to the 2 metal centers in an anti fashion. The dianion reacted with a no. of electrophiles to yield the neutral species FvW2(CO)6E2 (E = H, Me, Et, s-C3H5, CH2Ph). The pKa values for the 2 consecutive deprotonations of FvW2(CO)6H2 were detd. as 14.0 and 16.6 by equil. measurements in MeCN. Thermolysis and photolysis of FvW2(CO)6H2 yielded FvW2(CO)6 and H2. Unlike Cp2W2(CO)6, FvW2(CO)6 underwent protonation at the W-W bond by HBF4.Et2O in MeCN. Reactions of FvW2(CO)6 and FvMo2(CO)6 with PMe3 and Me2PCH2PMe2 (dmpm) gave the dinuclear zwitterions FvM2(CO)5(PMe3)2 and FvM2(CO)5(dmpm), resp. An x-ray crystallog. anal. of FvMo2(CO)5(dmpm) showed an anti coordination of the Mo(CO)3- and Mo(CO)2(dmpm)+ moieties at a planar Fv ligand. Electrophiles added to the anionic part of the zwitterions, whereas LiAlH4 effected redn. of coordinated CO to Me at the cationic center of FvMo2(CO)5(PMe3)2. Excess PMe3 caused the conversion of FvMo2(CO)5(PMe3)2 and FvMo2(CO)5(dmpm) to Mo(CO)3(PMe3)3 along with FvMo(CO)2(PMe3)2 and FvMo(CO)2(dmpm), resp. These reactions constitute the 1st ring-slippage reactions that were obsd. in fulvalene metal complexes. When treated with Mo(CO)3(NCMe)3, FvMo(CO)2(PMe3)2 cleanly regenerated FvMo2(CO)5(PMe3)2.