Anionic d⁸ Alkyl Hydrides – Selective Formation and Reactivity of Anionic cis‐Pt^II Methyl Hydride

Abstract

The pincer‐type complexes [(PCN)PtR] {R = H, 2; Me, 4; PCN = C6H4[CH2P(tBu)2](CH2)2N(CH3)2} react with MeLi or Et3BHNa, to give anionic cis‐Pt(Me)H complexes [(PCN*)Pt(H)(Me)]–Li+ (Me trans to P; PCN* denotes the PCN ligand in which the amine arm is not coordinated) and [(PCN*)Pt(Me)(H)]–Na+ (H trans to P). Only the isomer in which the incoming nucleophile is situated trans to the phosphane ligand is formed. These first d8 anionic alkyl hydride complexes were fully characterized spectroscopically. The hemilabile PCN ligand allows for reversible de‐coordination of the amine arm, thereby providing a desirable balance of stability vs. reactivity. Theoretical calculations on model systems indicate a concerted mechanism in which the nucleophilic attack and the amine dissociation occur concurrently. The (unobserved) methane reductive elimination from the stable anionic methyl hydride complex [(PCN*)Pt(Me)(H)]–Li+ (3) is thermodynamically and kinetically unfavorable, as indicated by DFT. This complex reacts with electrophiles, such as water and methyl iodide, to yield exclusively methane and the corresponding organometallic product (either 2 or 4). This reactivity was also further examined by DFT.

Synthesis and Characterization of Anionic, Neutral, and Cationic PNP Pincer PdII and PtII Hydrides

“…Virtual triplet signals were observed for the C 2 v symmetric t Bu protons (18 H) and pincer “arms” (2 H) at 1.22 and 2.65 ppm, respectively. The spectral evidence is consistent with assignment of the new species as K[(PNP**)PdH] ( 1 **), a rare example of a group 10 anionic hydride complex . The 31 P{ 1 H} NMR spectrum shows a singlet at 72.9 ppm and the 13 C{ 1 H} NMR spectral data are also consistent with a C 2 v symmetric structure for complex 1 **.…”

“…The spectral evidence is consistent with assignment of the new species as K[(PNP**)PdH] (1**), a rare example of a group 10 anionic hydride complex. 32 The 31 P{ 1 H} NMR spectrum shows a singlet at 72.9 ppm and the 13 C{ 1 H} NMR spectral data are also consistent with a C 2v symmetric structure for complex 1**. While it was possible to characterize 1** by 1 H, 13 C{ 1 H}, and 31 P{ 1 H} NMR spectroscopy as well as IR spectroscopy, all attempts to isolate the material from solution led to decomposition of the complex.…”

Implication of a σ-Methane Complex en Route to Elimination of Methane from a Ruthenium Complex: An Experimental and Theoretical Investigation

“…Several attempts have been made to understand the mechanism of intermolecular methane (or simple alkane) activation reactions using organometallic complexes under homogeneous conditions. − The intramolecular methane elimination reactions from transition metal–(H)­(CH 3 ) complexes also provide us useful insights of methane binding at the metal center before it gets eliminated from the coordination sphere. − From this perspective, these reactions provide possibilities to detect an intermediate at low temperature or to calculate a transition state computationally along their reaction coordinate. In this context, Gross and Girolami reported an osmium–hydride–methyl complex in which the hydrogen atoms of the alkyl and hydride ligands exchange at a rate sufficient to be observed on the NMR time scale .…”