Kinetic and DFT computational studies reveal that the reaction of {(IPr)Ni(mu-S)}(2) (1, IPr = 1,3-bis(2,6-diisopropyl-phenyl)imidazolin-2-ylidene) with dihydrogen to produce {(IPr)Ni(mu-SH)}(2) (2) proceeds by rate-limiting heterolytic addition of H-2 across a Ni-S bond of intact dinuclear 1, followed by cis/trans isomerization at Ni and subsequent H migration from Ni to S, to produce the bis-hydrosulfide product 2. Complex 1 reacts in a similar manner with pinacolborane to produce {(IPr)Ni}(2)(mu-SH)(mu-SBPin) (3), showing that heterolytic activation by this nickel mu-sulfide complex can be generalized to other H-E bonds.