The reaction of the recently reported sterically encumbered terphenyl tin(II) halide species Sn(CI)C6H3-2,6-Trip(2) (Trip = C6H2-2,4,6-i-Pr-3), 1, with I equiv of MeLi or MeMgBr afforded 2,6-Trip(2)H(3)C(6)Sn-Sn(Me)(2)C6H3-2,6-Trip(2), 2, which is the first stable group 14 element methylmethylene (i.e., CH3CH) analogue of ethylene (H2CCH2). Reaction of 1 with 1.5 equiv of MeLi yielded the stannylstannate species 2,6-Trip(2)H(3)C(6)(Me)(2)Sn -Sn(Li)(Me)C6H3-2,6-Trip(2), 3, whereas reaction of 1 with 1 equiv of t-BuLi gave the heteroleptic stannanediyl monomer Sn(t-Bu)C6H3-2,6-Trip(2) (4). The compounds 2-4 were characterized by H-1, C-13 (Li-7, 3 only), and Sn-119 NMR spectroscopy in solution and by W-vis spectroscopy. The X-ray crystal structures of 2-4 were also determined. The formation of the stannylstannanediyl 2 instead of the expected symmetrical, valence isomer "distannene" form {Sn(Me)C6H3-2,6-Trip(2)}(2), 6, is explained through the ready formation of LiSn(Me)(2)C6H3-2,6-Trip(2), 5, which reacts rapidly with 1 to produce 2 which can then react with a further equivalent of MeLi to give 3. The stability of singly bonded 2 in relation to the formally doubly bonded 6 was rationalized on the basis of the difference in the strength of their tin-tin bonds. In contrast to the methyl derivatives, the reaction of 1 with t-BuLi proceeded smoothly to give the monomeric compound 4. Apparently, the formation of a t-Bu analogue of 5 was prevented by the more crowding t-Bu group. Compound 2 is also the first example of a stable molecule with bonding between a two-coordinate, bivalent tin and four-coordinate tetravalent tin. Both compounds 2 and 3 display large J(119)Sn-Sn-119 couplings between their tin nuclei and the tin-tin bond lengths in 2 (2.8909(2) Angstrom) and 3 (2.8508(4) Angstrom) are relatively normal despite the presence of the sterically crowding terphenyl substituent's.