Terminal Acetylenes React to Increase Unsaturation in [(tBu2PCH2SiMe2)2N]Re(H)4

(PNPtBu)Re(H)4, where PNPtBu is (tBu2PCH2SiMe2)2N, reacts at 23 °C with RC⋮CH (R = tBu, SiMe3, Ph) to give first H2 and mirror-symmetric (PNPtBu)ReH3(CCR), then H2 and C2ν symmetric (PNPtBu)Re(CCR)2. The diacetylide compounds show temperature-independent paramagnetism and 13C and 31P chemical shifts far beyond their normal values for other (PNPtBu)ReXn compounds. Single-crystal X-ray diffraction shows very similar structures for the cases R = Ph and R = SiMe3, each having an approximately C2v geometry with equivalent acetylides with ∠C−Re−C approximately 108°. No hydride or H2 ligands are detected in final difference Fourier maps. DFT(B3PW91) calculations give minimum energy geometries of these species, of their products upon adding H2, and of mechanistically significant analogues [(H2PCH2SiH2)2N]ReHnR‘mH2-m, with n = 0, 2, m = 1, 2, and R‘ = H or Ph. These calculated geometries, when compared to those from X-ray diffraction, indicate that the isolated compounds have no hydride or H2 ligands and are thus (PNP)ReIII(CCR)2, making them more unsaturated than the reagent (PNP)ReV(H)4 by two electrons. Triplet state geometries of (PNP)ReXY are calculated and analyzed, as are their frontier orbitals.