Abstract The synthesis of the heterobimetallic hafnium(IV)-nickel(0) complexes {[Hf](μ-σ ,π- C≡CR)2}Ni(CO) (3a, [Hf] = (η5-C5H5)2Hf, R = Ph; 3b, [Hf] = (η5-C5H4SiMe3)2Hf, R = tBu) in which an early (Hf) and a late (Ni) transition metal atom are bridged by σ - and π-bound alkynyl groups succeeds by treatment of [Hf](C≡CR)2 (1a, [Hf] = (η5-C5H5)2Hf, R = Ph; 1b, [Hf] = (η5-C5H4SiMe3)2Hf, R = tBu) with equimolar amounts of Ni(CO)4 (2). The reaction chemistry of 1and 3towards different substrates is discussed. Treatment of 3bwith P(OMe)3 (4a) affords the mononuclear nickel monocarbonyl complex Ni(CO)[P(OMe)3]3 (5), while the reaction of 1aor 1bwith MCl2 (6a, M = Fe; 6b, M = Ni; 6c, M = Co) produces by an cyclopentadienyl transfer from hafnium to M the sandwich compounds (η5-C5H4R’)2M (M = Fe: 7a, R’ = H; 7b, R’ = SiMe3; M = Ni: 7c, R’ = H; 7d, R’ = SiMe3; M = Co: 7e, R’ = H). Addition of KOH to 1b or 3b, respectively, affords the homobimetallic hafnium complex {[Hf](C≡CR)}2O (8) in which two [Hf](C≡CR) fragments are bridged by an oxygen atom. Possible reaction mechanisms for the formation of 5, 7and 8by starting from 1or 3will be given. The result of the X-ray structure analysis of 8is reported. Complex 8crystallises in the monoclinic space group C2/c with the cell parameters a = 24.437(8), b = 14.655(5), c = 14.123(4) Å, β = 101.67(2)◦, V = 4953(3) Å3, Z = 4 and D = 1.454 g cm−3. Complex 8contains a linear Hf-O-Hf unit with pseudo-tetrahedral coordinated hafnium atoms.