Systematic Heterodinuclear Complexes with MM′(μ-meppp) Centers That Tune the Properties of a Nesting Hydride (M = Ni, Pd, Pt; M′ = Rh, Ir; H₂meppp = <i>meso</i>-1,3-Bis[(mercaptoethyl)phenylphosphino]propane)

Mononuclear complexes with a P₂S₂ ligand, [M­(meppp)] (M = Ni (<b>1a</b>), Pd (<b>1b</b>), Pt (<b>1c</b>); H₂meppp = <i>meso</i>-1,3-bis­[(mercaptoethyl)­phenylphosphino]­propane), were treated with [M′Cp*Cl₂]₂ or [M′Cp*­(NO₃)₂] (Cp* = η⁵-pentamethylcyclopentadienyl) to afford a series of bisthiolate-bridged M^IIM′^III heterodinuclear complexes, [M­(μ-meppp)­M′Cp*X]­X′ (M = Ni, Pd, Pt; M′ = Rh, Ir; X = Cl, NO₃; X′ = Cl, PF₆, NO₃). The nitrate complexes [M­(μ-meppp)-M′Cp*­(NO₃)]­NO₃ (M′ = Rh ([<b>4a</b>–<b>c</b>]­NO₃), Ir ([<b>5a</b>–<b>c</b>]­NO₃); M = Ni (<b>a</b>), Pd (<b>b</b>), Pt (<b>c</b>)) further reacted with sodium formate in water or methanol to be transformed into bisthiolate- and hydride-bridged complexes, [M­(μ-meppp)­(μ-H)­M′Cp*]­NO₃ (M′ = Rh ([<b>6a</b>–<b>c</b>]­NO₃), Ir ([<b>8a</b>–<b>c</b>]­NO₃); M = Ni (<b>a</b>), Pd (<b>b</b>), Pt (<b>c</b>)). Complexes [<b>6a</b>]­NO₃ (M = Ni, M′ = Rh) and [<b>8a</b>]­NO₃ (M = Ni, M′ = Ir) were characterized by X-ray analyses to reveal that a hydride is stabilized in a semibridging mode on the heterometal centers. In the Pd^IIRh^III ([<b>6b</b>]­NO₃) and Pt^IIRh^III ([<b>6c</b>]­NO₃) complexes, the hydrides were extremely unstable and were likely to undergo an unusual metal-to-Cp* ring hydrogen transfer, resulting in η⁴-C₅Me₅H M^IIRh^I complexes, [M­(μ-meppp)­Rh­(η⁴-C₅Me₅H)]­NO₃ (M = Pd ([<b>7b</b>]­NO₃), Pt ([<b>7c</b>]­NO₃)). The property of the hydride was drastically switched by varying the anchoring metal ions of the M′ site (Rh, Ir); that of [<b>6a</b>]­NO₃ (M′ = Rh) is not protic and decomposes in water below pH 4, while those of [<b>8a</b>–<b>c</b>]­NO₃ (M′ = Ir) are protic, subject to H⁺/D⁺ exchange reactions, and stable below pH 4. [<b>6a</b>]­NO₃ reacted with phenylacetylene to give [Ni­(μ-meppp)­RhCp*­(CCPh)]­NO₃ ([<b>10a</b>]­NO₃), which is in contrast with the inertness of the Ni^IIIr^III hydride complex [<b>8a</b>]­NO₃. The reaction is assumed to involve an alkenyl complex, [Ni­(μ-meppp)­RhCp*­(CHCHPh)]­NO₃ (<b>9a</b>), formed through an insertion of phenylacetylene into the metal–hydride bond. Analogous M^IIRh^III alkynyl complexes, [M­(μ-meppp)­RhCp*­(CCPh)]­NO₃ (M = Pd ([<b>10b</b>]­NO₃), Pt ([<b>10c</b>]­NO₃)), were synthesized by treating [<b>4b</b>,<b>c</b>]­NO₃ with phenylacetylene in basic media, and the structural differences among [<b>10a</b>–<b>c</b>]­NO₃ were discussed. These results interestingly demonstrated that the structures, properties, and reactivities of the nesting hydride on the {MM′(μ-meppp)} cores were tuned by varying metal ions of the M and M′ sites