Reaction of Ni(CO) in toluene at room temperature with one equivalent of GaAr′ (Ar′ = CH-2,6-(CH-2,6- iPr)) and GaL (L = HC[C(Me)N(CH-2,6- iPr)]) formed the mono-substituted Ni(CO)(GaAr′) ( 1) and Ni(CO)(GaL) ( 3), respectively. Compound 1 decomposed under reduced pressure or upon heating in toluene to give the new cluster species Ni(CO)(GaAr′) ( 2). Reaction of 3 with a second equivalent of GaL in toluene at 95 °C afforded the disubstituted complex Ni(CO)(GaL) ( 4). All the compounds were characterized by IR, H and C{H} NMR spectroscopy and X-ray crystallographic studies were undertaken to elucidate the structures of the complexes 2, 3 and 4. Graphical Abstract: The reaction of Ni(CO) with GaAr′ affords [Ni(CO)(GaAr′)] (Ar′ = CH-2,6-(CH-2,6- iPr)) which readily decomposes to the new nickel carbonyl cluster [Ni(CO)(GaAr′)].[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]