Hydride complexes of platinum(II) containing unsymmetrical di(phosphine) ligands: synthesis, characterization and evidence for pairwise addition of hydrogen based on parahydrogen induced polarization

Mechanism of nuclear spin initiated para-H2 to ortho-H2 conversion

“…Following the original proposal of Weitekamp and Bowers, para-H 2 was successfully employed for various NMR studies of catalytic reactions in one- [17][18][19] and two-dimensional NMR spectroscopy. 20 These techniques are an important diagnostic tool for mechanistic studies of chemical reactions 17,18,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] It was even suggested to employ the pure singlet quantum state of para-H 2 as an initial state for NMR quantum computing. 39 Triggered by the importance for catalytic studies the spin a FSU Jena, Institut fu¨r Physikalische Chemie, Helmholtzweg 4;…”

On the Mechanism of Dihydrogen Addition to Tantalocene Complexes

“…If the transfer of the protons occurs fast relative to proton relaxation, non-Boltzmann populations in their spin states can result, leading to enhanced absorption and emission lines in the product NMR spectrum. For the observation of PHIP, dihydrogen addition must lead to a product in which the transferred protons are magnetically distinct and J coupled to each other. − To date, PHIP in metal complexes has only been observed in the oxidative addition of dihydrogen to late transition metal complexes including those of rhodium, ,− iridium, ,,− ruthenium, and platinum. , The reaction proceeds in a concerted manner via a 3-centered triangular transition state. Activation of dihydrogen by low valent early transition metal complexes is presumed to occur by an analogous mechanism, although few systems have been investigated 19-21 and none have been studied with PHIP.…”

Detection of platinum dihydride bisphosphine complexes and studies of their reactivity through para-hydrogen-enhanced NMR methods

“…PHIP enhancements have been seen in the related platinum system, Pt(Ph 2 PCH 2 CH(Me)OPPh 2 )(H) 2 , where the hydride ligand symmetry was broken by the substituents located on the phosphine bridge. [38,39] Interestingly, when the reaction temperature was raised above 313 K, two additional mutually coupled hydride signals were detected at δ −2.81 and δ −2.25, which appeared as doublets of doublets of antiphase doublets (J HH = 6 Hz) with platinum satellites of 1047 and 1006 Hz, respectively. The corresponding 31 indicative of J PtP = 2184 Hz) and at δ 180.3 as a multiplet.…”

“…[5] In contrast, reports on this and related platinum complexes reveal that now J HH is positive. [38,39] Based on the observation of two magnetically distinct hydride ligands which couple to two distinct 31 31 P INEPT spectrum was recorded, the resonance at δ 25.9 exhibited an extra splitting of 295 Hz that was attributed to a direct P-H coupling, and hence, this signal was assigned to a PHCy 2 ligand. The 195 Pt signal of 2 was detected as a doublet of doublets due to couplings to two 31 P nuclei in the corresponding 1 H-195 Pt HMQC spectrum at δ −5492.…”