Terminal acetylenes react to increase unsaturation in [((Bu2PCH2SiMe2)-Bu-t)(2)N]Re(H)(4)
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abstract
(PNP tBu)Re(H) 4, where PNP tBu is ( tBu 2PCH 2SiMe 2) 2N, reacts at 23 C with RCCH (R = tBu, SiMe 3, Ph) to give first H 2 and mirror-symmetric (PNP tBu)ReH 3(CCR), then H 2 and C 2v symmetric (PNP tBu)Re(CCR) 2. The diacetylide compounds show temperature-independent paramagnetism and 13C and 31P chemical shifts far beyond their normal values for other (PNP tBu)ReX n compounds. Single-crystal X-ray diffraction shows very similar structures for the cases R = Ph and R = SiMe 3, each having an approximately C 2v geometry with equivalent acetylides with C-Re-C approximately 108. 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 [(H 2PCH 2SiH 2) 2N]ReH nR mH 2-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.
