Anionic d⁸ alkyl hydrides - Selective formation and reactivity of anionic cisPt^II methyl hydride

The pincer-type complexes [(PCN)PtR] [R = H, 2; Me, 4; PCN = C ₆H₄[CH₂P(tBu)₂](CH₂) ₂N(CH₃)₂} react with MeLi or Et ₃BHNa, to give anionic cis-Pt(Me).H complexes [(PCN*)Pt(H)(Me) J-Li+(Me irons 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.