Terminal acetylenes react to increase unsaturation in [((Bu2PCH2SiMe2)-Bu-t)(2)N]Re(H)(4)

Abstract

(PNPtBu)Re(H)(4), where PNPtBu is ((Bu2PCH2SiMe2)-Bu-t)(2)N, reacts at 23 degreesC with RCdropCH (R = Bu-t, SiMe3, Ph) to give first H-2 and mirror-symmetric (PNPtBu)ReH3(CCR), then H-2 and C-2v symmetric (PNPtBu)Re(CCR)(2). The diacetylide compounds show temperature-independent paramagnetism and C-13 and P-31 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 C-2v geometry with equivalent acetylides with angleC-Re-C approximately 108degrees. No hydride or H-2 ligands are detected in final difference Fourier maps. DFT(B3PW91) calculations give minimum energy geometries of these species, of their products upon adding H-2, and of mechanistically significant analogues [(H2PCH2SiH2)(2)N] ReHnR'(m),H2-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 H-2 ligands and are thus (PNP)Re-III(CCR)(2), making them more unsaturated than the reagent (PNP)Re-v(H)(4) by two electrons. Triplet state geometries of (PNP)ReXY are calculated and analyzed, as are their frontier orbitals.