Structural and reactivity comparison of analogous organometallic Pd(iii) and Pd(iv) complexes

Abstract

The tetradentate ligands (R)N4 ((R)N4 = N,N'-di-alkyl-2,11-diaza[3,3](2,6)pyridinophane, R = Me or iPr) were found to stabilize cationic ((R)N4)PdMe(2) and ((R)N4)PdMeCl complexes in both Pd(III) and Pd(IV) oxidation states. This allows for the first time a direct structural and reactivity comparison of the two Pd oxidation states in an identical ligand environment. The Pd(III) complexes exhibit a distorted octahedral geometry, as expected for a d(7) metal center, and display unselective C-C and C-Cl bond formation reactivity. By contrast, the Pd(IV) complexes have a pseudo-octahedral geometry and undergo selective non-radical C-C or C-Cl bond formation that is controlled by the ability of the complex to access a five-coordinate intermediate.

Ligand Substituent Effects in Manganese Pyridinophane Complexes: Implications for Oxygen-Evolving Catalysis

“…This second oxidative process is irreversible for 2 and 3 ( Figures S8 -S10). Fc/Fc + that has been assigned as a ligand-based reduction, 38 we have likewise assigned the quasireversible reductive processes to ligand-based reduction. The first oxidative wave is assigned to the Mn III /Mn II couple, which is confirmed through independent synthesis (see below) and the second quasi-reversible oxidation wave is tentatively assigned to the Mn IV /Mn III couple.…”

“…The compounds of 2,6-bis(bromomethyl)pyridine, 47 N, N'-di-methyl-2,11-diaza [3,3](2,6)pyridinophane (Py2NMe2), 2,11-diaza [3,3](2,6)-pyridinophane (Py2NH2), 48 1 and 5, 17 N, N'-diisopropyl-2,11-diaza [3,3](2,6)-pyridinophane (Py2N i Pr2) 38 , 1′, 10 4′, 9 and thianthrenyl cation (Th• + BF4 -) 49 were prepared according to literature procedures. All other compounds were obtained from commercial suppliers and used as received.…”

Aerobic C–C and C–O bond formation reactions mediated by high-valent nickel species

“…[10][11][12][13][14][15][16][17][18][19][20] By comparison, stoichiometric and catalytic Ni-mediated C-heteroatom bond formation reactions have been developed mostly in the past two decades. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] In the past several years we have employed tetradentate pyridinophane ligands to stabilize uncommon organometallic Pd III/IV and Ni III/IV complexes, [37][38][39][40][41][42][43][44] which can undergo C-C and C-heteroatom bond formation reactions. In addition, we have recently reported the use of the ligand 1,4,7-trimethyl-1,4,7triazacyclonane (Me 3 tacn) to stabilize high-valent Ni III/IV complexes that undergo C-C and C-heteroatom bond formation reactions.…”

“…50 The CV of 4 shows a rst oxidation potential at 200 mV vs. Fc + /Fc, which is higher than those observed for 2 and 3, likely due to the steric bulk of the t-butyl group, and as observed previously. 37,[39][40][41]44 Given their accessible oxidation potentials, complexes 1-4 can easily be oxidized with one equivalent of acetylferrocenium tetrauoroborate ( Ac FcBF 4 ) or silver hexauoroantimonate (AgSbF 6 ) in THF at À50 C to yield [( TsMe N4)Ni III (cycloneophyl)] + , 2 + , [( Ts N4)Ni III (cycloneophyl)] + , 3 + , and [( tBu N4)Ni III (cycloneophyl)] + , 4 + . The X-ray structures of both 2 + and 3 + reveal six-coordinate Ni III centers in distorted octahedral geometries ( Fig.…”

Synthesis and Reactivity of (N2P2)Ni Complexes Stabilized by a Novel Diphosphonite Pyridinophane Ligand

“…In the past several years we have reported the isolation and characterization of mononuclear organometallic Ni III complexes stabilized by tetradentate R N4 ligands ( R N4 = N,N'-dialkyl-2,11-diaza [3.3](2,6)pyridinophane, R = Me, i Pr, or t Bu) as well as its C-donor derivative R N3C -ligands (R = t Bu, tert-butyl or Np, neopentyl) that can undergo C-C and C-heteroatom bond formation reactions. [26][27][28][29][30][31][32][33][34][35][36] These results suggest that Ni III complexes are more common than previously anticipated, and thus it prompted us to now target the low-valent Ni I species using a slightly modified ligand system. Inspired by the many examples of PONOP-type pincer metal complexes, [37][38][39][40][41] we have developed the N-and P-donor tetradentate ligand N2P2 (N2P2 = P,P'ditertbutyl-2,11-diphosphonito [3.3](2,6)pyridinophane) and investigated the redox properties and reactivity of its Ni complexes.…”