The preparation of the six-membered rhenacyclohexanes (1a, b) [R = CH3 (a), C6H5 (b)] is accomplished by heterolytic cleavage of the Re-Re bond in the binuclear anions [(OC)4ReP(R2)O]22- with strong electrophiles like the alkanediylbis(triflate) (CH3)2C(CH2Y)2 (Y = OSO2CF3). followed by an attack of the co-positioned carbenium-like C atom on the phosphinite oxygejn of the anion. 1 a, b insert SO2 under ring expansion yielding the seven-memberod heterocyeles (2a, b). 1b crystallizes triclinic in the space group P1̄ with Z = 2. Some characteristic IR and NMR data are discussed.